Geology of the Pyrenees
Encyclopedia
The Pyrenees
form part of the huge alpine orogenic system
. This 430 kilometre long, roughly east-west striking
, intracontinental mountain chain divides France
, Spain
, and Andorra
. It has an extended, polycyclic geological evolution dating back to the Precambrian
. The chain's present configuration is due to the collision
between the microcontinent Iberia
and the southwestern promontory of the European Plate (i.e. Southern France). The two continents were approaching each other since the onset of the Upper Cretaceous (Albian
/Cenomanian
) about 100 million years ago and were consequently colliding during the Paleogene
(Eocene
/Oligocene
) 55 to 25 million years ago. After its uplift, the chain experienced intense erosion
and isostatic readjustments
. A cross-section through the chain shows an asymmetric flower-like structure with steeper dips on the French side. The Pyrenees are not solely the result of compressional forces
, but also show an important sinistral shearing.
in the west to the Golfe du Lion and the Golf de Roses in the east, their width across strike varying between 65 and 150 km. They are bounded in the north by the North Pyrenean Front (French:
Front nord-pyrénéen, also North Pyrenean frontal fault or NPFF), a major thrust fault
along which units from the North Pyrenean Zone have been transported over the Subpyrenean Zone, southernmost part of the Aquitaine Basin
, their northern foreland
. Their southern limit is the South Pyrenean Frontal Fault. Here, thrust slices from the Sierras Marginales and their lateral equivalents are displaced southward over the Ebro Basin.
Yet in a larger, geologically more meaningful sense the Pyrenees continue farther west into the Basque
and the Cantabrian mountains
(the Basque-Cantabrian chain). They finally disappear along the continental margin
of Asturias
. Likewise in the east, they do not just vanish in the Mediterranean but rather pursue their course via the nappe units of the Corbières
into Bas Languedoc and even into southern Provence
. At their far eastern end in Provence, typical pyrenean fold trends are superimposed by alpine structures to be finally cut off by the arc of the Western Alps. The pyrenean chain in the larger sense is nearly a 1000 km long.
The double-sided orogen can be divided into several tectonic zones, from north to south, that are bounded by east-west–trending major faults:
Along strike, the pyrenean orogen can be split into three distinct domains: an eastern domain reaching from the Mediterranean to the Segre River
, a central domain extending from the Segre River to the Pamplona Fault, and a western domain beyond the Pamplona Fault.
and overthrust en echelon by the North Pyrenean Zone along the North Pyrenean Front. These upthrusts change their character in the west and in the east of the orogen, where they become nappe-like
, examples being the Bas Adour Nappe in the west and the Corbières Nappe in the east. The latter continues farther east via fold
s and tectonic slices near Saint-Chinian
, via the fold near Montpellier
to join the South Provence Thrust near Sainte-Baume
, which gradually disappears south of Brignoles
.
Within the Pyrenees sensu stricto, the Subpyrenean Zone consists of Upper Cretaceous
and very thick Paleogene
sediments in surface outcrops. The sediments show simple folds following a WNW-ESE trend.
The subsurface, however, has a far more complicated structure due to Triassic
salt
diapir
s and north-vergent thrusts. Hidden below a more than 6000 metre thick Mesozoic cover are probably more than 6000 m of Paleozoic
basement rocks. The Mesozoic cover consists of up to 1500 m of Triassic, well over 500 m of Jurassic and more than 3000 m of Cretaceous sediments.
The up to 500 m thick layer of Lower Triassic (Buntsandstein
) comprises conglomerates
, breccia
, brown sandstone
s, argillite
s, shale
s, and siltstone
s. The Middle Triassic (Muschelkalk
) can attain a thickness of 400 m and shows silty shales, evaporite deposits
, and dolomitic
micrite
s. The up to 500 m thick Upper Triassic Keuper
deposits are made up of carbonate-rich sediments, salt
, siltstones, and intercalated ophitic diabase
s/olivine
dolerites. The lower Lias
is a transgressive sequence
with up to 200 m of non-marine sandstone, near-shore marine limestone
and evaporites. A pelagic fauna at the top suggests open marine conditions. The middle and upper Lias consist of 230 m of shallow marine platform sediments (bioclastic limestone, argillaceous limestone, and micritic limestone). During the Middle Jurassic
, an oolitic barrier
, made up mostly of argillaceous micrites, separates an outer shelf from an inner shelf. The Upper Jurassic (Malm
) deposits are mainly shales and carbonates. Near the end of the Jurassic, restricted environments were established with dolomicrites, banded limestones, and evaporites. The Lower Cretaceous layer starts with sandstones, shales, limestones, and calcareous breccia
in the Neocomian, followed by Barremian
marl
s and limestones. During the lower Aptian
, sandstones, shales, sandy marls, and limestones were laid down. The upper Aptian and the Albian
are mainly marls and limestones. The Upper Cretaceous includes a littoral Turonian
with sandstones and sandy limestones. By the beginning of the Senonian (Campanian
), a deep trough had formed (the Subpyrenean Basin) receiving a very thick flysch
sequence. The Campanian and Maastrichtian
flyschs comprise 2000 to 3000 m of periodically interlayered fines (marls, calcareous shales, and mudstone
s) and coarser sediments (conglomerates, sandstones, and greywacke
s). Near the K/T boundary, the Subpyrenean Basin was filled with continental red deposits
in Garumnian facies
even including dinosaur
eggs in a few places. At this point, the Subpyrenean Basin underwent folding accompanied by a weak metamorphism
.
Above the Albian and before the onset of the Campanian, volcanic rock
s occur including basalt
ic lava
s, spilite
, and diabase, but also pyroclastic rocks like tuff
, lapilli tuff, volcanic breccia, and agglomerate
. The volcanic rocks can be cross-cut by lamprophyre
dike
s.
In Paleocene
/Eocene
times, the sea transgressed from the Atlantic into the Subpyrenean Basin which behaved as a downwarp to the slowly rising Pyrenees immediately to the south. A very thick (2000 to 3000 m) succession of fine-grained detrital or calcareous sediments was deposited. The sedimentation stopped in the late Eocene due to major compression (Pyrenean Main Phase).
In the vicinity of the Muret Fault, a left-lateral strike-slip fault and a prolongation of the Toulouse Fault to the south, the Subpyrenean Zone can be divided into two unequal halves. The eastern half between the rivers Garonne
and Aude can be separated into three different zones (from north to south):
In the western half, only the northern foreland is present; it is made up of gently folded, but strongly jointed, epicontinental Mesozoic
sediments covered and hidden by Miocene
molasse
sediments. The east-west and northwest-southeast-striking fold sets interfere and are cut by northeast-trending faults. In the subsurface, Triassic salt diapirs are also present.
Within the northern foreland east of the river Aude, the Paleozoic
basement
uplift of the Mouthoumet
appears, a horst tilted to the south and covered by continental Eocene
strata.
The fold trains of the Subpyrenean Zone are disrupted in the Bas Languedoc by the Cevennes Fault, a major left-lateral strike-slip fault.
s. The rocks in the vicinity bear horizontal lineations underlining the importance of the fault as a major shear zone. Elsewhere in the North Pyrenean Zone, the strain gradient is also high but the stretching direction is generally vertical.
The more than 6000 m thick sedimentary package of the North Pyrenean Zone is formed by Mesozoic (Jurassic and Cretaceous) rocks that have been detached above Upper Triassic evaporites and subsequently slid to the north. In contrast with the Subpyrenean Zone, the North Pyrenean Zone contains hardly any Paleogene. Upper Triassic (Keuper) shale and evaporite deposits locally contain interbedded dolostones, tuffs, and diabase (ophites); these deposits behave plastically and commonly form a tectonic mélange
with contacts being expressed as decollement
surfaces. From the beginning of the Jurassic till the end of the Lower Cretaceous, a shallow-water carbonate platform developed during tectonic quiescence with mainly limestones being sedimented. The Middle Albian
witnessed a major facies change to deep marine conditions. This changeover marks the inception of the North Pyrenean Basin, a 400 km long trough of pull-apart
origin filled with unconformable, turbiditic
flysch sediments during the Upper Cretaceous. By Upper Albian times, this pull-apart basin had split into an internal trough next to the North Pyrenean fault which accommodated the Flysch ardoisier and an external trough farther north filled by the Flysch noir. Later, during the Turonian and the Coniacian, the external flysch trough received the so-called Flysch à fucoides, a very thick succession of interbedded calcareous mudstones/marlstones and sandy calcarenites. This flysch is followed by a regressive series in the Maastrichtian
—thick marls (Marnes de Plagne)—platform limestones (Calcaires nankins), as well as lagoonal and lacustrine deposits. Altogether the Coniacian-Maastrichtian series reaches a thickness of 3000 m.
The Paleozoic basement pierces the sedimentary cover in several almond-shaped, horst-like uplifts, their size ranging from 1 to 300 km2. Examples are the so-called massifs satellites nord-pyrénéens (north pyrenean basement uplifts) between Lourdes
and Perpignan
, amongst them the following uplifts: Agly
, Arize
, Barousse
, Bessède-de-Sault
, Castillon
, Milhas
, Plantach, Saint-Barthélémy, Salvezines
, and Rabat-les-Trois-Seigneurs
, plus several uplifts in the northern Basque country
. These uplifts have a left-lateral shearing origin and are tilted to the north; simultaneously they also exhibit a vertical shearing component. They probably formed in the Variscan orogeny
. In the basement uplifts, mainly Precambrian
gneiss
es and granulitic gneisses
(in the Agly massif), and Paleozoic igneous and metamorphic rocks are found.
A small, maximally 5 km wide strip just north of the North Pyrenean Fault experienced dynamic and thermal metamorphism
during the Albian
/Cenomanian
about 110 million years ago (high temperature/low pressure, "HT/LP"-type). Some domains north of the basement uplifts were also metamorphosed (e.g. in the Bigorre
and in the southern Corbières). The metamorphism was isochemical without introduction of extraneous elements and affected only the sedimentary cover rocks which were transformed into marble
and hornfels
. The Paleozoic basement was not affected, probably due to its already dehydrated state.
Scattered within the metamorphic strip are several occurrences of lherzolite
s (including their type locality
at Lers). They were extruded from the upper mantle along deep-reaching faults. The lherzolites are associated with amphibolite
s, pyroxenite
s, and amphibole
-bearing peridotite
s. All these mantle rocks are arranged in swarms, the biggest outcrop at Moncaup
reaching a mere 3 km2. They are widely distributed, being found from Béarn
all the way to Aude. Their emplacement mode has not been clarified yet, but the following factors are relevant:
Scattered within the North Pyrenean Zone are also some occurrences of volcanic rock
s. They are intercalated in sediments of the Lias
and the Upper Cretaceous (Aptian
till Campanian
) and are found mainly in the west (near Tarbes
, Orthez
, and in the Basque country). They consist of silica undersaturated spilite
s, picrites, and nepheline syenite
s. Associated dike rocks are lamprophyre
s (camptonites and monchiquites).
Other features of interest are several different post-metamorphic breccia
formations.
The North Pyrenean Zone can be subdivided into three subzones bounded by major faults:
The North Pyrenean Zone is traversed in the west by NNE-SSW-trending, left-lateral strike-slip faults and then changes into the fold-belt of the Basque country. In the east, it continues after a sharp bend in the Corbières right into southern Provence. At the far eastern end, northwest-southeast-striking Miocene
fold trains of the Western Alps start interfering and finally completely overwhelm the pyrenean structures.
s. All the highest peaks of the Pyrenees are in the Axial Zone, hence the name.
Amongst the Variscan granitoids are biotite granite
s (Canigou
, Quérigut Massif), two-mica granites (Caillaouas Massif) and granodiorite
s (Bassiès, Maladeta
). The granitoids are mainly shallow epizonal intrusives, but mesozonal and catazonal rocks are also represented.
The high elevations of the Axial Zone (generally above 3000 m) are compensated isostatically
by an increased thickness of the continental crust
. For instance below the Maladeta massif, a root zone formed so that the Mohorovicic discontinuity
is encountered there at a depth of 50 km. Likewise over most peaks of the Axial Zone, a negative gravity anomaly
can be detected which slowly disappears to the east.
The basement is traversed by major east-west-striking, late Variscan fracture zones that were reactivated during the alpine orogeny cycle. In the eastern part of the Axial Zone, the fractures are generally upright, a good example being the mylonitic Merens Fault at Pic del Port Vell
near Mérens-les-Vals
. In the western part, the fractures are more gently dipping to the north and behave as en echelon thrusts arranged in a northwest-southeasterly fashion; along these fractures, the basement of the Axial Zone overthrusts Mesozoic sedimentary units to the south. Good examples are the en echelon thrusts at Eaux Chaudes, Gavarnie
and Bénasque
—Las Nogueras (referring to the upper reaches of the rivers Noguera Ribagorzana and Noguera Pallaresa
). Concomitant with the thrusts, a schistosity developed that affected the basement as well as the sedimentary cover implying an alpine origin. All these fractures account for an overall compression of the Axial Zone by 20% which translates as roughly 10 to 20 km of crustal shortening. As a result, the Axial Zone was squeezed into a south-directed antiformal stack.
The Axial Zone disappears in the Haut Béarn as a pericline underneath the Upper Cretaceous sedimentary cover only to reappear in the basement uplifts of Aldudés
-Quinto Réal
, the southernmost of the Basque basement massifs. In the east the Axial Zone becomes downfaulted into Neogene
and Quaternary
graben
s of Northern Catalonia
and finally disappears underneath the Mediterranean.
The central and eastern section of the Axial Zone is bounded in the north by the North Pyrenean Fault, a system of N 110-striking, steeply dipping reverse-faults. The trace of the North Pyrenean Fault becomes more and more diffuse west of Lourdes
; near the Basque basement massifs, it seems to be displaced to the south by a wrench fault and then possibly continues into Spain south of the Basque Marble Nappe and south of the Basque Fold Belt. In Cantabria
, it finally reaches the Atlantic coast. The southern limit of the Axial Zone runs completely on Spanish territory. It is represented by an alpine reverse-fault along which the sediments of the South Pyrenean Zone are overthrust by the Axial Zone. In the east, the Axial Zone abuts directly against nappes of eastern representatives of the Sierras Marginales.
river (Mediano and Boltaña anticlines), and in the east by the northeast-southwest-trending en echelon wrench faults at the Segre river. At the latter, the thrust system forms a break-back (hindward-thrusting) imbricate emergent fan which developed during the latest Eocene and early Oligocene. Due to constriction, the sedimentary cover was forced into several internal overthrusts, examples being the nappe
of the Monte Perdido
and the nappe of the Cotiella in the northwest. More centrally placed is the Bóixols Thrust Sheet which continues farther east in the Pedraforca Thrust Sheet (upper unit). The Bóixols Thrust Sheet is hindward-thrusting but also overrides the Montsec Thrust Sheet to the south. Its sediments reach 5000 m in thickness and are mostly Lower Cretaceous in age. The Montsec Thrust Sheet correlates with the lower unit of the Pedraforca Thrust Sheet. It consists of a 2000 m thick layer of Upper Cretaceous limestone followed by Lower and Middle Eocene syntectonic conglomerate, sandstone and shale.
The internal thrusts naturally led to a substantial increase in thickness. The South Pyrenean Zone finally terminates along the South Pyrenean Thrust where the Montsec Thrust Sheet overrides the Sierras Marginales.
The thrusting motions that formed an imbricate thrust system with associated piggyback basins took place mainly during the Eocene. The distances travelled by the thrust sheets is still debated, estimates varying from relatively small to as much as 30 to 50 km.
The Sierras Marginales (Spanish:
Border Ranges) are the Sierras Aragonesas and Serres Catalanes of the southern Pre-Pyrenees
. They are, much like the South Pyrenean Zone, formed from a Mesozoic-Eocene sedimentary succession, albeit with a much reduced thickness of about 900 m. The succession comprises Keuper
, Jurassic, unconformable lower Cretaceous bauxites, unconformable Upper Cretaceous, Paleocene in Garumnian facies, and lower Eocene. Units of the Sierras Marginales underthrust successions of the Ebro Basin. Later on these underthrusts were unconformably
covered by Oligocene
and Miocene
sequences from the Ebro Basin. To the west, the Sierras Marginales are relayed by the Jaca-Pamplona Thrust Sheet which consists of a younger Eocene–Oligocene sedimentary succession. In this thrust sheet west of the Gállego River, the structures simplify: in the Basque and in the Cantabrian
Pyrenees, the sedimentary cover is affected only by long and relatively open fold trains, which are occasionally pierced by doming Keuper salt. In the east, the Sierras Marginales are represented by the tectonically comparable Port del Comte Thrust Sheeet and by the Cadí Thrust Sheet, which are made up essentially of an Eocene succession.
The Sierras Marginales are overthrust in the north by the Montsec
Thrust Sheet of the South Pyrenean Zone.
The end of the soutward directed thrusting motions was diachronous and migrated from east to west. For instance in the Cadí
Thrust Sheet, motions stopped 34 million years ago (Eocene/Oligocene boundary), whereas in the Jaca-Pamplona Thrust Sheet they stopped as late as 23 million years ago (Oligocene/Miocene boundary).
The sedimentary succession in the Ebro Basin shows Paleozoic rocks at the base followed by uppermost Cretaceous/lowermost Paleocene red beds and Eocene limestones, marine marl
s, and Upper Eocene evaporites (Cardona evaporites). The lower Oligocene is conglomeratic and pro-grades southward into evaporite and lacustrine deposits. In the Southern Folded Foreland, the folded Paleogene series are unconformably overlain by flat-lying non-marine Miocene and Pliocene strata of the main Ebro Basin.
The Ebro Basin deepens towards the South Pyrenean Frontal Fault where it comprises 3000 m of sedimentary infill. This reduces to 1500 m near the thrust front of the Sierra Marginales. The deepest part of the basin with 5000 m of sediments is near Logroño
at its most northwestern end.
and petrological
studies in metamorphic rocks of the Axial Zone and of the North Pyrenean Zone were able to prove the existence of incorporated Precambrian remnants. For example in the basement of the Canigou
massif and in the basement uplift of the Agly, the remnants of a Precambrian basement were discovered (recognised by radiometric dating on granitoids and by certain structures of tectonic origin), which were later incorporated into the Variscan orogen by tectonic movements and the associated metamorphism.
The original radiometric results were, however, not confirmed by the SHRIMP-method (only Ordovician ages between 477 and 471 million years were found). The Cadomian origin of the basement is therefore uncertain.
The Precambrian rocks are mainly gneiss
es and meta-sediments of amphibolite and granulite facies intruded by charnockite
s.
s of upper amphibolite facies grade, mica schists with andalusite
, cordierite
and staurolite
of lower amphibolite facies grade, and phyllite
s of greenschist facies grade.
The epicontinental, psammitic sediments of the Neoproterozoic
and the Lower Paleozoic are a very thick detrital (mudstone
-sandstone
) succession essentially devoid of fossil
s. These sediments were in a large part later overprinted by the Variscan orogeny. Intercalated near the base of the detrital succession are carbonates.
The (meta)sedimentary succession starts with the 2000 to 3000 m thick Canaveilles Group
in the Ediacarian about 580 million years ago. Its sediments consist mainly of shales and greywackes with intercalated rhyolite
s and carbonates. Within the Cadí Thrust Sheet archeocyathid–bearing limestones developed during the Lower Cambrian
. At the onset of the Middle Cambrian, the Canaveilles Group is replaced by the Jujols Group, a 2000 m thick flyschoid series comprising schist
s, shales, and siltstone
s interlayered with carbonates and quartzites. The Jujols Group is less metamorphic than the mesozonal Canaveilles Group. Its sedimentation lasted probably into the lowermost Ordovician
.
After a longer hiatus, up to 100 m of Caradocian (Ordovician stage 5 and 6) conglomerate
follow unconformably upon the Jujols Group—the Rabassa Conglomerate. This is overlain by nearly 500 m of the Cava Formation, interlayered greywackes, and shales containing volcanic horizons. The 200 m thick Estana Formation is made up of limestone
s and calcareous shales. Its end–Ordovician limestones contain a benthic
fauna (brachiopod
s, bryozoans, cystoids) as well as conodont
s. The succession ends with the badly layered Ansobell Formation (20 to 300 m), dark schists that bear microconglomerates indicating a glaciomarine depositional environment. The Ansobell Formation can develop an unconformity and sometimes follows directly upon the Cava Formation.
The included volcanic rocks and the conglomerates hint at unsettled tectonic conditions, which are probably connected with an early stage of the Caledonian orogeny
(Taconian Phase).
During the Rhuddanian (Silurian
) initially 20 m of quartzitic rocks, the Bar Quartzite, were deposited followed by 50 to 250 m of dark, graphitic
, graptolite
-bearing shale
s. The thickness of the shales can increase in the West to 850 m. They take up nearly the entire Silurian (Aeronian until Pridoli), documented by the graptolites. In their upper section (Ludlow), the shales incorporate calcareous horizons and calcareous nodules (with conodonts, nautiloid
s, bivalves, crinoid
s, and ostracod
s). Close to the Basque massifs, the calcareous facies changes into a detritic facies of interlayered sand– and silt–stones. The graptolite-bearing shales were later metamorphosed into lower amphibolite facies slate
s. They form prominent décollement
surfaces.
The Devonian
is marine and rich in fossils (spiriferids
and trilobite
s like phacops
). It consists of six depositional areas (and a wealth of formations) differing considerably in their sedimentary evolution (especially in the Basque Pyrenees). Generally in the western Pyrenees, shallow marine facies prevail, whereas in the eastern Pyrenees, hemipelagic facies with occasional high grounds predominate. The Devonian has highly variable thicknesses, its 100–600 m—and in places 1400 —thick succession is made up of many different sedimentary facies like greywacke
s, reef
al limestones, and sandstones. Quite distinctive are banded pink to red, blue or green limestones and nodular limestones, the so-called griottes of the lower Famennian
. Calcareous shales and black shales also occur.
The Lochkovian consists of black shales and limestones and is very rich in conodonts. During the Pragian, a siliciclastic wedge formed, the San Silvestre Quartzite of the Basibé Formation. The period Upper Givetian till Frasnian
witnessed pronounced lithological differences and increased sedimentation rates. In the Lower Frasnian, reef complexes developed, yet at the same time siliciclastic material was being delivered into the western, central, and Basque domain. At the beginning of the Middle Famennian
, the sedimentation in the Pyrenees became more uniform again and until the end of the Devonian, monotonous, condensed cephalopod-bearing limestones were laid down (Griotte limestones and grey to pinkish, nodular Supragriotte limestones). Towards the end of the Famennian, first hiati started to appear leading to complete emersion of the western Pyrenees at the onset of the Mississippian. The corresponding unconformity, which exists only in the western Pyrenees, belongs to an early deformation phase of the Variscan orogeny (Breton Phase).
Only in the western Pyrenees is the Lower Carboniferous
(Mississippian) distinguished from the Devonian sediments by an unconformity, starting off marine with a transgressive quartz
–pebble bed. Anywhere else, the Supragriotte limestones are conformably overlain by pre-orogenic sediments that begin with the Lower Cherts of the Tournaisian
. The Lower Cherts comprise 50 m of black, phosphate nodule-bearing chert
s interlayered with black shales. After an interlude of grey, nodular, goniatite
-bearing limestones, the Upper Cherts were deposited during the Viséan
—grey or green cherts sometimes interlayered with pyroclastics and ending with grey nodular limestones.
The Mississippian later on changes into the nearly 1000 m thick detrital, syn-orogenic sediments of the Kulm
–facies. An exception are the western Pyrenees, where, during the Serpukhovian
, dark grey, laminated limestones precede the Kulm. The diachronous Kulm sediments are a flysch-like
(turbidite
s) interlayering of sandstones and dark shales—harbingers of the Variscan tectonic movements. They also contain layers of hemipelagic limestones, conglomerates, carbonaceous breccias as well as olistoliths. Sedimentation of the Kulm facies started in the East already at the Viséan/Serpukhovian boundary (Namurian
), but west of the Gallégo river, it started only at the beginning of the Pennsylvanian
(Upper Westphalian, Bashkirian
). In the Basque Pyrenees, the Kulm sedimentation perdured into the Moskovian. The Kulm sediments were deposited as canyon deposits on the continental slope or as submarine fans in a southwest migrating foredeep of the Variscan orogen.
) and below the Stephanian (Moscovian
), but sometimes already below the Upper Westphalian. The tectonic movements therefore happened about 310 million years ago, dated by fossil plants.
The Upper Westphalian shows an important unconformity at its base and is made up of conglomerate
s. The Moscovian is represented by blue-black shales, overlain by the so-called Grey Unit of the Kasimovian
(Stephanian B) and the Transitional Layers of the Gzhelian
(Stephanian C and Autunian). These sediments are non-metamorphic or only weakly metamorphosed, whereas the sediments below the unconformity fully experienced the Variscan metamorphism.
The far-reaching effects of the Variscan orogeny influenced the pyrenean domain in many ways. Of prime importance were the compressional stresses that folded
the Paleozoic sediments. Several fold generations developed, sometimes superimposing each other. Associated with the folds are schistosities. The Paleozoic sediments and its Precambrian basement were also metamorphosed under high-temperature and low-pressure conditions (HP/LT). In places anatexis
was reached, an example being the melting of some Precambrian gneiss
es of the Prevariscan basement together with their enveloping mica schists. Another important consequence of the orogeny was late-orogenic magmatism
emplacing granitoids (granodiorite
s and biotite granites
) of mainly acid but occasionally also of basic composition. Amongst these granitoids are deep-seated, rather diffuse, intrusive bodies associated with migmatite
s, yet also typical, well-defined pluton
s often rising into the cores of anticline
s within the Variscan fold-belt. The main magmatism perdured from 310-270 million years (late Pennsylvanian and early Permian cooling ages). A good example for the main magmatism is the 280 million years old Maladeta granodiorite.
Also of importance was late-stage fracturing
under brittle conditions. The developing fractures probably followed weak zones already initiated during the Paleozoic. The main direction of these fractures is WNW-ESE, the so-called Pyrenean direction, an excellent example being the North Pyrenean Fault. These fractures will play a decisive role during the further development of the orogen.
— Sedimentary evolution
The sediments deposited after the Asturian Phase in the Upper Westphalian (Moscovian) right through to the Upper Triassic can be regarded as molasse
of the Variscan orogen which underwent late-stage extension. In half-grabens 2500 of sediment accumulated at the close of the Carboniferous and throughout the Permian, mainly interbedded non-marine and basalt
ic-andesitic
rocks. Detrital formations of lacustrine affinity with coal
measures during the Stephanian (Kasimovian
and Gzhelian
) followed by red sandstones with plant remains during the Permian
are typical erosional products of a chain not having reached stability.
The Grey Unit of the Kasimovian is a sequence of decreasing grain-size, starting with breccias and conglomerates and changing into sandstones and coal-bearing shales (anthracite is mined near Campo de la Troya). Also included are andesitic layers that can attain significant thicknesses in places. The Transitional Layers are also a sequence of decreasing grain-size (conglomerates, sandstones, and coal-bearing shales), but, instead of andesites, they include tuffs and rhyodacitic
lavas. They close with lacustrine limestones containing stromatolite
s, charophytes, and ostracods.
The continental red beds of the Permian rest unconformably on the Transitional Layers. They show strong variations in their thicknesses and reach 800 m, sometimes even 1000 m. They occur mainly in the Basque Pyrenees and in the Axial Zone. Like the Stephanian sediments, they were deposited as alluvial (as fans and in ephemeral streams) and lacustrine sediments within transtensive basins of the Variscan orogen.
The aforementioned fractures were decisive in determining facies distributions during this interval. They also influenced the distribution of volcanic eruptions during the Permian such as the calcalkaline volcanism at Pic du Midi d'Ossau
and the basalt
s of the Basque country. The trigger for these volcanic eruptions probably was early wrenching motions of Iberia relative to the Eurasian Plate.
In the Axial Zone, the Permian can be subdivided into three sedimentary series (from top to bottom):
The detrital Lower Triassic (Buntsandstein
) is very similar to the Permian. It reaches 400 to 500 m in thickness and is made up of coarse conglomerates, sandstones, psammites with plant remains (Equisetites, Coniferomyelon) as well as green and red to purple claystones. At this time, the peneplanation of the Variscan orogen had reached an advanced stage and the sedimentary accommodation spaces started to widen.
During Muschelkalk
times, the sea advanced again, but reached only the North Pyrenean Zone and the Basque country. The resulting sediments left behind are 20 to 100 m of dolomitic cellular limestones, grey fossiliferous limestones, and wavy limestones. In the Upper Triassic (Keuper
), the sedimentation spread over the entire Pyrenean domain. About 220 m million years ago (during the Carnian
) evaporites settled out in lagoon
s and grabens—variegated, gypsum
–bearing, iron-rich clays, gypsum, anhydrite
, dolomitic marls, dolomites, rock salt as well as potassium and magnesium salts occur. The evaporites served later as major decollement horizons. At the limit, Upper Triassic/Hettangian
doleritic tholeiite
s (ophites
) formed in the Pyrenees and in the southern Aquitaine Basin, indicating further movements along the fracture zones (submarine fissure eruptions and sills in unsolidified Keuper sediments).
The sedimentation during the Jurassic is characterised by the growth of a carbonate platform. The sediments are mainly epicontinental deposits of lacustrine character, as well as limestones, marl
s and dolomite
s with marine or littoral faunas. The basin was under tension during this period and as a result long horsts and graben structures of different subsidence rates were created following more or less the trend of the Variscan fractures. Its northern side is rimmed by the relatively stable Aquitanian shelf. The basin probably is caused by crustal thinning infiltrating from the Atlantic domain.
The Lias
started with a transgression that is more important than the advances of the Muschelkalk and Keuper seas. Its total thickness varies between 150 and 400 m. The sea level kept rising during the Hettangian
and fossiliferous limestones were deposited; this trend reversed later on into a regression leaving evaporites (rock salt and anhydrite with some calcareous interlayers). At the edge of the basin and in the eastern Pyrenees, argillaceous limestones and banded dolomites with layers of anhydrite settled out; the dolomites transformed upon dissolution of the anhydrite into monogenic breccias. The regression continued during the Lower Sinemurian
, sedimenting intra– and supra–tidal banded limestones and dolomites. In the Upper Sinemurian (Lotharingian), more open-marine conditions established themselves due to a renewed sea-level rise; in deeper parts of the basin, fossiliferous limestones developed, whereas, on high ground, oolithic limestones accumulated. The Middle Lias (Pliensbachian
) started off transgressive as well with fine-grained detrital, limey to marly sediments (ferruginous oolites, fossiliferous limestones and marls) that change over to marls. In the eastern Pyrenees, pyrite
-bearing claystones formed due to a badly oxygenated environment; they contain a very diverse fauna of ammonites belonging to the French southeastern domain, whereas the ammonite population on the Atlantic side is rather monotonous. During the Upper Lias (Toarcian
), the sea reached a high stand, continuing with the fine-grained detrital sedimentation and depositing black pelagic marls (marnes noires and schistes esquilleux). Towards the end of the Lias, regressive tendencies again became noticeable.
Falling sea levels continued right into the Middle Jurassic
. Near Pau an oolite barrier started to grow that extends all the way north to Poitiers
. It divided the sedimentary basin now into two major facies domains: a deeper western domain open to the Atlantic and undergoing infratidal sedimentation (black to blueish argillaceous limestones rich in benthic organisms, microfilaments, and ammonites) and a shallow, enclosed, eastern domain with intertidal sedimentation (variable carbonate facies like pseudo-oolites and banded dolomites, but also anhydrite-bearing evaporites). These intertidal sediments experienced a strong contemporaneous dolomitization
. Towards the end of the Middle Jurassic, sea levels fell even further.
) and especially during the Lower Cretaceous, drastic changes occurred. Iberia started to rift off the Armorican Massif
in a southerly direction and in its wake the Bay of Biscay
slowly began to spread (with formation of oceanic crust from the Middle Albian till the end of the Coniacian
).
The sedimentation in the Malm
(total thickness 600 to 750 m) did not increase until the Upper Oxfordian, the Lower Oxfordian rarely being present. The 100 to 150 m thick Upper Oxfordian is represented west of the oolite barrier by intratidal platform sediments (argillaceous to sandy, pyrite-bearing limestones), whereas, in the east, dolomitization continues. By Kimmeridgian
times, the facies differences attenuated due to shallowing of the western domain, resulting in massive, fine-grained, black, lithographic
limestones and fine-grained platy limestones. During the Tithonian, strong regressive tendencies set in that led to a complete withdrawal of the sea. In the Basque country, the sea had withdrawn already at the end of the Kimmeridgian. During times of falling sea levels, evaporitic, dolomitic, lagoonal, and lacustrine facies were left behind.
After a southeasterly re-advance of the sea in the Berriasian
via a small strait east of Pau, which deposited 100 m of inter– to sub–tidal limestones and a sandy to clayey detrital border facies, emersion set in during the Neocomian. During Valanginian
and Hauterivian
times, clayey marls on top of the emerged horsts were transformed under ferralitic climatic conditions into bauxite
s, which were fossilised by later transgressions. After another marine trangression from the east during the Barremian
, the elongated graben regions in the Pyrenean domain received 200 to 300 m of marine shelf sediments of the Urgonian facies, such as dolomites, algal
limestones, foraminiferous limestones, and rudist limestones. The Urgonian facies can perdure in the Corbières and in the South Pyrenean Zone into the Albian. With falling sea levels in the Upper Barremian, black, pyrite-bearing claystones and lagoonal limestones rich in ostracods and characeans were sedimented.
After the Barremian/Aptian
boundary, marked by another high stand of the sea, there were four more sea-level oscillations during the Aptian and the Albian, bringing about a very significant sediment accumulation (in some places up to 3000 m). Due to sinking grabens in the Atlantic domain, the water masses of the Atlantic and the Tethys mixed for the first time. The Aptian/Albian sediments are characterised by the competitive interplay between fine-grained terrigenic and organic material. The organic material is responsible for the formation of shallow platforms built by rudists, hexacorals, and algae. In the Upper Abian, the terrigenic material predominated, and several shallow marine, partially calcareous sandstone formations were deposited. The source region of the detrital material was the Aragon
/Pyrenees domain that was undergoing a first epirogenetic uplift. In the same context, the fluvial delta sediments of the Formation de Mixe were transported from the south, and the very heterogeneous, up to 1000 m thick conglomerates of the Poudingues de Mendibelza, interpreted as the topset of a delta-front.
into two very different sedimentary facies realms. On the northern edge of Iberia (in the South Pyrenean Zone and in the Axial Zone), shelf carbonates were then being deposited. Because of several emersions, they only show very reduced thicknesses. Due to transtension in the North Pyrenean Zone, a very strongly subsiding flysch basin (North Pyrenean Basin) developed, which follows essentially the east-west-trending Variscan fracture zones. The basin was deepening towards the Atlantic and shallowing towards the east, where it terminates before the Aude river. It is split by the basement massifs of the North Pyrenean Zone into two strands—a southerly strand called sillon aturien, which received up to 2500 m of flysch ardoisier and a northerly strand with the flysch noir. The flysch basin is rimmed to the north by the relatively stable Aquitanian Shelf. It was formed probably by extensive crustal thinning that penetrated from the Atlantic side.
Concurrent with the transtension, the Pyrenean Metamorphism took place characterised by high heat flow (peak temperatures were 500-600 °C) but relatively low pressure
s (HT/LP-metamorphism). Under these conditions, new mineral
s like biotite
, diopside
and scapolite
grew. The metamorphism is diachronous and has been dated radiometrically in the eastern North Pyrenean Zone as Albian, whereas in the Basque country in the west (for example in the Basque Marble Nappe) it has been dated only as Campanian
. It is possible that the metamorphism lasted in a milder form until the end of the Cretaceous or even the beginning of the Eocene.
Two major deformational phases with the development of schistosities (Upper Albian till Lower Cenomanian
and Santonian
till Maastrichtian
) affected the pyrenean domain during the Upper Cretaceous expressing themselves as unconformities in the sedimentary record. The flysch basin was shortened and at the northern edge of Iberia, an orogenic wedge formed that moved slowly into the northern foreland. As a consequence, the flysch basin receiving the erosional products from the wedge was forced to migrate to the north too (changeover during the Santonian of the centre of subsidence from the North Pyrenean Basin to the Subpyrenean Basin). The Subpyrenean Basin was consequently filled in by 1000 to 4000 m of flysch à fucoides.
The Variscan fracture zones were active during the entire Upper Cretaceous and decisively influenced the sedimentary facies distributions. This activity was further underlined by alkaline magmatism lasting from the Middle Albian until the end of the Coniacian; thus in the west of the North Pyrenean Zone, submarine basaltic lavas extruded, while farther east in the Béarn and in the Bigorre, different magmatic rock types intruded the Upper Cretaceous strata.
highlight the differences between the eastern and the western Pyrenees. In the west, the marine shelf facies continued and the flysch basin carried on subsiding. In the east, the continental red beds of the Garumnian facies (whose deposition started already at the close of the Cretaceous) were laid down, mainly alluvial and paludial facies. At the same time, the first tectonic shortenings and uplifts affected the eastern Pyrenees.
In the western Pyrenees, the marine sedimentation also carried on during the Eocene
. In two subsiding basins on both sides of today's chain, limestones, marls, foraminiferous sandstones, and sandstones with a benthic
fauna were sedimented. The Eocene sedimentary successions along the French northern edge of the Pyrenees (in the North Pyrenean Zone) are fairly thin and full of facies changes. There, short-lived transgressions and regressions can be followed into the Languedoc
. During the Ypresian
, the first conglomerates start being delivered.
This very thick conglomeratic formation, called the Poudingues de Palassou, is the indicator for the most important orogenic phase in the Pyrenean domain, the Pyrenean Main Phase, which was accompanied by very strong deformations and uplifts. The conglomerates are later unconformably
overlain by end–Eocene strata, therefore the orogenic phase can be assigned to the interval Ypresian/Lutetian
, i.e. roughly 50 to 40 million years ago.
On the southern side of the Pyrenees in Catalonia, folded conglomeratic formations have been dated as Upper Lutetian to Bartonian
, representing the interval 44 to 37 million years ago. They also are unconformably overlain by end–Eocene sediments bearing a continental fauna.
The Pyrenean Main Phase manifested itself on both sides of the axial zone as reverse faults and thrusts with fairly large displacements. The movements were directed on the French side to the north, and on the Spanish side to the south. But their spatial arrangement was not symmetrical; the Spanish side for instance has much lower dipping structures. The faulting and thrusting disrupted not only the Mesozoic and Paleogene sedimentary cover, but also large parts of the Variscan basement. The basement had failed not just rigidly at the Paleozoic fracture systems, but also underwent intensive alpine deformations around heterogeneities and anisotropies in its structural fabric.
Deformational phases of lesser importance followed the Pyrenean Main Phase, all contributing to the final appearance of the orogen. At the northern margin of the Ebro Basin close to the Sierras Marginales, for example, folded Oligocene
is covered unconformably by flat-lying, detrital Miocene
of continental origin. This points to another deformational phase at the end of the Oligocene about 25 million years ago.
After the beginning of the Miocene, the uplifted orogen underwent severe erosion, expressed by enormous molasses being shed into the foreland basins such as for example the Aquitaine Basin. In the Pliocene
, a renewed uplift started, leading to the formation of huge alluvial fan
s at the mountain front, a notable example being the Lannemezan
alluvial fan. Another important consequence of the uplifting was peneplanation. Several peneplanation levels have been found on very different heights (3000 to 2000 m in the Axial Zone, close to a 1000 m in the Pays de Sault, near 400 m in the Agly massif and at 100 m in the Corbières). They generally become lower in the east, with several uplifts towards the end of the Oligocene, towards the end of the Miocene (Pontian peneplanation), and towards the end of the Pliocene (Villafranchian peneplanation).
Neogene
sediments have been preserved in the Pyrenees mainly in small graben
s close to the Mediterranean (near Cerdagne). The grabens have also repeatedly been flooded by the Mediterranean, examples being the graben near Ampurdan and grabens in the Roussillon
containing a Pliocene fauna. These extensional structures most likely owe their existence to renewed movements on Variscan fractures. The very young volcanic area near Olot
probably has a similar cause.
During the Quaternary
, the Pyrenees experienced several glaciations, but of far less intensity than for example in the Alps. Large glacier
s advanced through the valleys of the Gave d'Ossau
, Gave de Pau
, Garonne, and Ariège on the French northern side. Today about 20 smaller true glaciers as well as cirques and glacier remnants subsist (examples are the Aneto glacier, the Ossoue glacier in the Vignemale
massif and glaciers on Maladeta and Monte Perdido). All these glaciers have undergone a large retreat since 1850 due to global warming
. The total glaciated surface area amounted to 45 km2 in 1870, whereas in 2005 a mere 5 km2 were left.
. Neoproterozoic
crustal remains (Canigou, Agly) hint at possible Cadomian
domains. Indications for Caledonian
movements are somewhat clearer (conglomerates and volcanic rocks in the Ordovician). During the Variscan orogeny in the Pennsylvanian, the Axial Zone and the South Pyrenean Zone became an integral part of what was to become the microcontinent Iberia. The Sierras Marginales were part of the Ebro Block, a northeastern section of Iberia. The appartenance of the North Pyrenean Zone is still uncertain, but the Subpyrenean Zone certainly formed part of the microcontinent Aquitania. Iberia and Aquitania were on the south side of the South Variscan Thrust and therefore constituted the foreland of the Variscan orogen. Both microcontinents had originated from Gondwana
's northern margin.
At the close of the Variscan orogeny, Iberia was still connected to northwestern France (the Armorican Massif
) and most likely was a northwestern prolongation of Aquitania. Its later movements were vital to the alpine cycle of the Pyrenean orogeny. This is accepted by most geologists, yet the details of Iberia's movements are still uncertain.
During the Upper Jurassic
, a rift
was propagating from the spreading Central Atlantic along the continental margin of northwestern France towards Aquitaine
. This happened probably as early as the Tithonian
. As a consequence, the rift wedged Iberia southward and separated it from the Armorican Massif. In the wake, the continental crust was thinned and eventually oceanic crust
was beginning to form in the Middle Aptian
—the opening of the Bay of Biscay
was under way. Final oceanisation of the Bay of Biscay was achieved by Santonian
/Campanian
times (about 84 million years ago as witnessed by the magnetic polarity chron C 34). Paleomagnetic
studies additionally show an anticlockwise 35° rotation of Iberia. The drifting motion of Iberia had taken up the entire Lower Cretaceous. Due to the rotational motion, the northeastern edge of Iberia started to interfere with Aquitania, first creating transtension
al pull-aparts along the North Pyrenean Zone in the Middle Albian
. The crustal thinning associated with the transtensional rifting process led to HT/LP metamorphism in the North Pyrenean Zone, its onset being dated at about 108 million years ago. At the same time, the lherzolites were finally emplaced. The transcurrent motion along the North Pyrenean pull-apart zone was also accompanied by alkaline magmatism that lasted from the Middle Albian to the end of the Coniacian
. The slow progression of the metamorphism into the west seems to imply a large sinistral shearing between Iberia and Aquitania, estimated as an offset of about 200 km (the metamorphism reached the Basque Country only about 80 million years ago in the Campanian
).
By the beginning of the Turonian
about 90 million years ago, the transtensional regime had finished and was replaced by compression
. The rifting in the Basquo-Cantabrian, North Pyrenean, and Subpyrenean Basin had stopped and basin inversion set in; tensional faults were then being used as thrusts. This first rather weak compressional phase with very low shortening rates (less than 0.5 mm/year) lasted till the end of the Thanetian
. On the Spanish side of the orogen, the first thrust sheets were emplaced (Upper Pedraforca, Bóixols, and Turbón thrust sheets).
In Ilerdian and Cuisian times (Paleocene
/Eocene
boundary, Thanetian/Ypresian
, about 55 million years ago), the Pyrenees underwent very strong compression in the upper crust, bringing about the orogen's actual zonation and structural organisation. The orogen was squeezed into an asymmetric fan-like structure due to the aborted subduction of Iberia underneath Aquitania. This is inferred from the behaviour of the Mohorovicic discontinuity, which at the North Pyrenean Fault abruptly jumps from 30 to 50 km depth. This Pyrenean Main Phase lasted till about 47 million years ago (beginning of the Lutetian
), showing high shortening rates of 4.0 to 4.4 mm/year and emplacing for example the Lower Pedraforca and the Montsec thrust sheets.
After the Pyrenean Main Phase, other compressional deformational phases followed during the Oligocene
and the Pliocene
. Since the Neogene
, the orogen exhibits post-kinematic collapse (graben structures at its eastern end, volcanism near Olot) associated with the extension of the Golfe de Lion and the opening of the Valencia Trough. The orogen still undergoes strong erosion (since the Eocene), isostatic movements, post-kinematic extension, and even renewed compression (in the western Pyrenees) that can cause medium-sized earthquake
s (a magnitude 5,1 earthquake near Arudy
in 1980 and a magnitude 5,0 earthquake in 2006 near Lourdes
and other historic earthquakes which even destroyed parts of villages, e.g. a magnitude ≥ 6,0 earthquake near Arette
in 1967, where 40% of the buildings were damaged and the church steeple collapsed).
Current opinions favour Iberia subducting beneath Aquitania; this interpretation seems to be supported by the results of deeep seismic (ECORS) and magnetotelluric profiling across the orogen.
Estimates of the overall shortening across the pyrenean orogen are mostly between 100 and 150 km. Using the ECORS-data Muñoz (1992) arrives at 147 km of shortening with the subduction of the Iberian middle and lower crust taking up around 110 km. Further interpretations of the ECORS-data led to the recognition of a 50 km thick Iberian crust that was subducting beneath the 30 km thick Aquitanian crust. As a consequence, a low-angle intracrustal detachment level formed at 15 km depth, above the subducting middle and lower Iberian crust. Along this detachment, the rocks now making up the Axial Zone, the South Pyrenean Zone, and the Sierras Marginales were gliding southward and gradually ramping up to the surface. With continuing constriction, the Axial Zone buckled up into a south-directed antiformal stack. Towards the end of the subduction, a backthrust initiated near the actual trace of the North Pyrenean Fault, which was cutting upward into the Aquitanian crust by utilising its previously thinned, faulted nature. When the subduction process was finally blocked, parts of the northern Axial Zone and the North Pyrenean Zone with lower crustal fragments and lherzolites sandwiched in between were pushed back northward over the Subpyrenean Zone.
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...
form part of the huge alpine orogenic system
Alpine orogeny
The Alpine orogeny is an orogenic phase in the Late Mesozoic and Tertiary that formed the mountain ranges of the Alpide belt...
. This 430 kilometre long, roughly east-west striking
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
, intracontinental mountain chain divides France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, and Andorra
Andorra
Andorra , officially the Principality of Andorra , also called the Principality of the Valleys of Andorra, , is a small landlocked country in southwestern Europe, located in the eastern Pyrenees mountains and bordered by Spain and France. It is the sixth smallest nation in Europe having an area of...
. It has an extended, polycyclic geological evolution dating back to the Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
. The chain's present configuration is due to the collision
Continental collision
Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...
between the microcontinent Iberia
Iberian plate
The microcontinent Iberia encompassed not only the Iberian Peninsula but also Corsica, Sardinia, the Balearic Islands, and the Briançonnais zone of the Penninic nappes of the Alps...
and the southwestern promontory of the European Plate (i.e. Southern France). The two continents were approaching each other since the onset of the Upper Cretaceous (Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
/Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
) about 100 million years ago and were consequently colliding during the Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
(Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
/Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
) 55 to 25 million years ago. After its uplift, the chain experienced intense erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and isostatic readjustments
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
. A cross-section through the chain shows an asymmetric flower-like structure with steeper dips on the French side. The Pyrenees are not solely the result of compressional forces
Compression (geology)
In geology the term compression refers to a set of stresses directed toward the center of a rock mass. Compressive strength refers to the maximum compressive stress that can be applied to a material before failure occurs. When the maximum compressive stress is in a horizontal orientation, thrust...
, but also show an important sinistral shearing.
Geographic arrangement
The Pyrenees sensu stricto stretch in a westnorthwest-eastsoutheast-direction (N 110) over 430 km from the Bay of BiscayBay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
in the west to the Golfe du Lion and the Golf de Roses in the east, their width across strike varying between 65 and 150 km. They are bounded in the north by the North Pyrenean Front (French:
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
Front nord-pyrénéen, also North Pyrenean frontal fault or NPFF), a major thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
along which units from the North Pyrenean Zone have been transported over the Subpyrenean Zone, southernmost part of the Aquitaine Basin
Aquitaine Basin (geology)
The Aquitaine Basin is after the Paris Basin the second largest Mesozoic and Cenozoic sedimentary basin in France, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on Variscan basement which was peneplained during the Permian...
, their northern foreland
Foreland
Foreland is the easternmost point of the Isle of Wight. It is located three miles east of the town of Brading, and due south of the city of Portsmouth on the British mainland. It is characterised by a pub called the Crab and Lobster and various beach huts plus a beach cafe and a coast guard...
. Their southern limit is the South Pyrenean Frontal Fault. Here, thrust slices from the Sierras Marginales and their lateral equivalents are displaced southward over the Ebro Basin.
Yet in a larger, geologically more meaningful sense the Pyrenees continue farther west into the Basque
Basque mountains
The Basque Mountains are a mountain range situated in the northern Iberian Peninsula. Geographically it is considered as the eastern section of the larger Cantabrian Range...
and the Cantabrian mountains
Cantabrian Mountains
The Cantabrian Mountains or Cantabrian Range are one of the main systems of mountain ranges in Spain.They extend for more than approximately 180 miles across northern Spain, from the western limit of the Pyrenees to the edges of the Galician Massif close to Galicia, along the coast of the...
(the Basque-Cantabrian chain). They finally disappear along the continental margin
Continental margin
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....
of Asturias
Asturias
The Principality of Asturias is an autonomous community of the Kingdom of Spain, coextensive with the former Kingdom of Asturias in the Middle Ages...
. Likewise in the east, they do not just vanish in the Mediterranean but rather pursue their course via the nappe units of the Corbières
Corbières
Corbières is a municipality in the district of Gruyère in the canton of Fribourg in Switzerland. On 1 January 2011 the former municipality of Villarvolard merged into the municipality of Corbières.-History:...
into Bas Languedoc and even into southern Provence
Provence
Provence ; Provençal: Provença in classical norm or Prouvènço in Mistralian norm) is a region of south eastern France on the Mediterranean adjacent to Italy. It is part of the administrative région of Provence-Alpes-Côte d'Azur...
. At their far eastern end in Provence, typical pyrenean fold trends are superimposed by alpine structures to be finally cut off by the arc of the Western Alps. The pyrenean chain in the larger sense is nearly a 1000 km long.
Structural organisation of the orogen
A profile through the Pyrenees sensu stricto shows a fan-like, flower-like arrangement. The structure is strongly asymmetric with a steeper and narrower French northern side and a much wider and more gently inclined Spanish southern side.The double-sided orogen can be divided into several tectonic zones, from north to south, that are bounded by east-west–trending major faults:
- Northern foreland — Aquitaine BasinAquitaine Basin (geology)The Aquitaine Basin is after the Paris Basin the second largest Mesozoic and Cenozoic sedimentary basin in France, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on Variscan basement which was peneplained during the Permian...
- Subpyrenean Zone or Subpyrenean Basin.
- North Pyrenean Zone.
- Axial Zone.
- South Pyrenean Zone.
- Sierras Marginales.
- Southern foreland — Ebro Basin
Along strike, the pyrenean orogen can be split into three distinct domains: an eastern domain reaching from the Mediterranean to the Segre River
Segre River
The Segre is a river tributary to the Ebro with a basin comprising territories across three states: France, Andorra and Spain....
, a central domain extending from the Segre River to the Pamplona Fault, and a western domain beyond the Pamplona Fault.
Subpyrenean Zone
The Subpyrenean Zone is geologically part of the Aquitaine Basin, the northern foreland of the Pyrenees, and was caught up in the Pyrenean orogeny. The zone was folded during the EoceneEocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
and overthrust en echelon by the North Pyrenean Zone along the North Pyrenean Front. These upthrusts change their character in the west and in the east of the orogen, where they become nappe-like
Nappe
In geology, a nappe is a large sheetlike body of rock that has been moved more than or 5 km from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a...
, examples being the Bas Adour Nappe in the west and the Corbières Nappe in the east. The latter continues farther east via fold
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
s and tectonic slices near Saint-Chinian
Saint-Chinian
Saint-Chinian is a commune in the Hérault department in Languedoc-Roussillon in southern France.-Saint-Chinian wine:Saint-Chinian has given its name to Saint-Chinian wine, which is classified as Appellation d'Origine Contrôlée and covers several communes around Saint-Chinian itself.-References:*...
, via the fold near Montpellier
Montpellier
-Neighbourhoods:Since 2001, Montpellier has been divided into seven official neighbourhoods, themselves divided into sub-neighbourhoods. Each of them possesses a neighbourhood council....
to join the South Provence Thrust near Sainte-Baume
Sainte-Baume
The Sainte-Baume is a mountain ridge spreading between the départements of Bouches-du-Rhône and Var in southern France...
, which gradually disappears south of Brignoles
Brignoles
Brignoles is a commune in the Var department in the Provence-Alpes-Côte d'Azur region in southern France. It is a sub-prefecture of the department.It was the summer residence of the counts of Provence...
.
Within the Pyrenees sensu stricto, the Subpyrenean Zone consists of Upper Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
and very thick Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
sediments in surface outcrops. The sediments show simple folds following a WNW-ESE trend.
The subsurface, however, has a far more complicated structure due to Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
diapir
Diapir
A diapir is a type of intrusion in which a more mobile and ductily-deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh-Taylor instability-type structures in regions with low tectonic stress...
s and north-vergent thrusts. Hidden below a more than 6000 metre thick Mesozoic cover are probably more than 6000 m of Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
basement rocks. The Mesozoic cover consists of up to 1500 m of Triassic, well over 500 m of Jurassic and more than 3000 m of Cretaceous sediments.
The up to 500 m thick layer of Lower Triassic (Buntsandstein
Buntsandstein
The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...
) comprises conglomerates
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
, breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
, brown sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s, argillite
Argillite
An argillite is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into shale when the fissile layering typical of shale is...
s, shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
s, and siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s. The Middle Triassic (Muschelkalk
Muschelkalk
The Muschelkalk is a sequence of sedimentary rock strata in the geology of central and western Europe. It has a Middle Triassic age and forms the middle part of the Germanic Trias, that further consists of the Buntsandstein and Keuper...
) can attain a thickness of 400 m and shows silty shales, evaporite deposits
Evaporite
Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...
, and dolomitic
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
micrite
Micrite
Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to 4 μm formed by the recrystallization of lime mud.The term was coined in 1959 by Robert Folk for his carbonate rock classification system...
s. The up to 500 m thick Upper Triassic Keuper
Keuper
The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolostone, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs...
deposits are made up of carbonate-rich sediments, salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
, siltstones, and intercalated ophitic diabase
Diabase
Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. In North American usage, the term diabase refers to the fresh rock, whilst elsewhere the term dolerite is used for the fresh rock and diabase refers to altered material...
s/olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
dolerites. The lower Lias
Lias Group
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...
is a transgressive sequence
Transgression (geology)
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water...
with up to 200 m of non-marine sandstone, near-shore marine limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and evaporites. A pelagic fauna at the top suggests open marine conditions. The middle and upper Lias consist of 230 m of shallow marine platform sediments (bioclastic limestone, argillaceous limestone, and micritic limestone). During the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
, an oolitic barrier
Oolite
Oolite is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Hellenic word òoion for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites...
, made up mostly of argillaceous micrites, separates an outer shelf from an inner shelf. The Upper Jurassic (Malm
Malm
is a former municipality, a village, and the administrative centre of the municipality of Verran in Nord-Trøndelag county, Norway. Malm is located along the Trondheimsfjord, about a drive west from the town of Steinkjer. The village of Malm has a population of 1,572. The population density of...
) deposits are mainly shales and carbonates. Near the end of the Jurassic, restricted environments were established with dolomicrites, banded limestones, and evaporites. The Lower Cretaceous layer starts with sandstones, shales, limestones, and calcareous breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
in the Neocomian, followed by Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
s and limestones. During the lower Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
, sandstones, shales, sandy marls, and limestones were laid down. The upper Aptian and the Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
are mainly marls and limestones. The Upper Cretaceous includes a littoral Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
with sandstones and sandy limestones. By the beginning of the Senonian (Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
), a deep trough had formed (the Subpyrenean Basin) receiving a very thick flysch
Flysch
Flysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...
sequence. The Campanian and Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
flyschs comprise 2000 to 3000 m of periodically interlayered fines (marls, calcareous shales, and mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s) and coarser sediments (conglomerates, sandstones, and greywacke
Greywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
s). Near the K/T boundary, the Subpyrenean Basin was filled with continental red deposits
Red beds
Red beds are sedimentary rocks, which typically consist of sandstone, siltstone, and shale that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of...
in Garumnian facies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
even including dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
eggs in a few places. At this point, the Subpyrenean Basin underwent folding accompanied by a weak metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
.
Above the Albian and before the onset of the Campanian, volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
s occur including basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
s, spilite
Spilite
Spilite is a fine-grained igneous rock, resulting particularly from alteration of oceanic basalt.The term was introduced into the geological literature by Alexandre Brongniart in 1827...
, and diabase, but also pyroclastic rocks like tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
, lapilli tuff, volcanic breccia, and agglomerate
Agglomerate
Agglomerates are coarse accumulations of large blocks of volcanic material that contain at least 75% bombs...
. The volcanic rocks can be cross-cut by lamprophyre
Lamprophyre
Lamprophyres are uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions...
dike
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
s.
In Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
/Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
times, the sea transgressed from the Atlantic into the Subpyrenean Basin which behaved as a downwarp to the slowly rising Pyrenees immediately to the south. A very thick (2000 to 3000 m) succession of fine-grained detrital or calcareous sediments was deposited. The sedimentation stopped in the late Eocene due to major compression (Pyrenean Main Phase).
In the vicinity of the Muret Fault, a left-lateral strike-slip fault and a prolongation of the Toulouse Fault to the south, the Subpyrenean Zone can be divided into two unequal halves. The eastern half between the rivers Garonne
Garonne
The Garonne is a river in southwest France and northern Spain, with a length of .-Source:The Garonne's headwaters are to be found in the Aran Valley in the Pyrenees, though three different locations have been proposed as the true source: the Uelh deth Garona at Plan de Beret , the Ratera-Saboredo...
and Aude can be separated into three different zones (from north to south):
- a northern foreland.
- a 10 km wide folded zone. Its northern boundary are the ranges of the Petits Pyrénées, which are above a blind thrust. This zone narrows to the east and disappears before reaching the Aude. The sediments comprise a gypsumGypsumGypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
–bearing Triassic at the bottom followed by an internally thrusted JurassicJurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
and a very thick cover sequence of Upper Cretaceous flyschFlyschFlysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...
sediments. - a narrow band of flysch in the south. This fairly thick flysch sequence was also deposited in the Upper Cretaceous. It was upturned into a nearly upright position by thrusting movements on the North Pyrenean Front and now forms the overturned southern flank of an asymmetric synclineSynclineIn structural geology, a syncline is a fold, with younger layers closer to the center of the structure. A synclinorium is a large syncline with superimposed smaller folds. Synclines are typically a downward fold, termed a synformal syncline In structural geology, a syncline is a fold, with younger...
.
In the western half, only the northern foreland is present; it is made up of gently folded, but strongly jointed, epicontinental Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
sediments covered and hidden by Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
molasse
Molasse
The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...
sediments. The east-west and northwest-southeast-striking fold sets interfere and are cut by northeast-trending faults. In the subsurface, Triassic salt diapirs are also present.
Within the northern foreland east of the river Aude, the Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
basement
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
uplift of the Mouthoumet
Mouthoumet
Mouthoumet is a commune in the Aude department in southern France.-Population:...
appears, a horst tilted to the south and covered by continental Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
strata.
The fold trains of the Subpyrenean Zone are disrupted in the Bas Languedoc by the Cevennes Fault, a major left-lateral strike-slip fault.
North Pyrenean Zone
The North Pyrenean Zone is quite narrow, usually only about 10 km wide, but can widen to 40 km. It is characterised by very strong folding. The zone is thrust to the north along the North Pyrenean Front—its northern limit—over the Subpyrenean Zone. This thrusting motion compressed the overthrust foreland and as a result induced folding in the Subpyrenean Zone. The North Pyrenean Zone is itself overthrust by the Axial Zone along the North Pyrenean Fault (NPF), a high-angle reverse-fault forming its southern boundary. The North Pyrenean Fault is marked by highly strained myloniteMylonite
Mylonite is a fine-grained, compact rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. It is classified as a metamorphic rock...
s. The rocks in the vicinity bear horizontal lineations underlining the importance of the fault as a major shear zone. Elsewhere in the North Pyrenean Zone, the strain gradient is also high but the stretching direction is generally vertical.
The more than 6000 m thick sedimentary package of the North Pyrenean Zone is formed by Mesozoic (Jurassic and Cretaceous) rocks that have been detached above Upper Triassic evaporites and subsequently slid to the north. In contrast with the Subpyrenean Zone, the North Pyrenean Zone contains hardly any Paleogene. Upper Triassic (Keuper) shale and evaporite deposits locally contain interbedded dolostones, tuffs, and diabase (ophites); these deposits behave plastically and commonly form a tectonic mélange
Mélange
In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically consists of a jumble of large blocks of varied lithologies...
with contacts being expressed as decollement
Decollement
Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...
surfaces. From the beginning of the Jurassic till the end of the Lower Cretaceous, a shallow-water carbonate platform developed during tectonic quiescence with mainly limestones being sedimented. The Middle Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
witnessed a major facies change to deep marine conditions. This changeover marks the inception of the North Pyrenean Basin, a 400 km long trough of pull-apart
Pull Apart Basin
250px|thumb|[[Cami Lake]] in [[Tierra del Fuego]] develops on a [[Patagonian Ice Sheet|glacially]] excavated pull apart basin along the [[Magallanes-Fagnano Fault]], hence its elongated form...
origin filled with unconformable, turbiditic
Turbidite
Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...
flysch sediments during the Upper Cretaceous. By Upper Albian times, this pull-apart basin had split into an internal trough next to the North Pyrenean fault which accommodated the Flysch ardoisier and an external trough farther north filled by the Flysch noir. Later, during the Turonian and the Coniacian, the external flysch trough received the so-called Flysch à fucoides, a very thick succession of interbedded calcareous mudstones/marlstones and sandy calcarenites. This flysch is followed by a regressive series in the Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
—thick marls (Marnes de Plagne)—platform limestones (Calcaires nankins), as well as lagoonal and lacustrine deposits. Altogether the Coniacian-Maastrichtian series reaches a thickness of 3000 m.
The Paleozoic basement pierces the sedimentary cover in several almond-shaped, horst-like uplifts, their size ranging from 1 to 300 km2. Examples are the so-called massifs satellites nord-pyrénéens (north pyrenean basement uplifts) between Lourdes
Lourdes
Lourdes is a commune in the Hautes-Pyrénées department in the Midi-Pyrénées region in south-western France.Lourdes is a small market town lying in the foothills of the Pyrenees, famous for the Marian apparitions of Our Lady of Lourdes occurred in 1858 to Bernadette Soubirous...
and Perpignan
Perpignan
-Sport:Perpignan is a rugby stronghold: their rugby union side, USA Perpignan, is a regular competitor in the Heineken Cup and seven times champion of the Top 14 , while their rugby league side plays in the engage Super League under the name Catalans Dragons.-Culture:Since 2004, every year in the...
, amongst them the following uplifts: Agly
Agly
The Agly River is a river of southwestern France. Its source is in the Corbières hills, near Camps-sur-l'Agly. It flows through Saint-Paul-de-Fenouillet, Estagel, Rivesaltes and Saint-Laurent-de-la-Salanque before it flows into the Mediterranean Sea near Le...
, Arize
Arize
The Arize is a river of France, a right affluent of the Garonne. It arises at 1,355 in the massif of Arize, in the Pyrenees, in the department of Ariège. Its length is 67 km. It flows into the Garonne at Carbonne....
, Barousse
Barousse valley
The Barousse is a small region of southwestern France, including the valley of the Ourse, a left tributary of the Garonne, in the Hautes-Pyrénées, and the smaller valley of Siradan.The main towns are Loures-Barousse and Mauleon-Barousse.-Toponymy:...
, Bessède-de-Sault
Bessède-de-Sault
Bessède-de-Sault is a commune in the Aude department in southern France.-Population:-References:*...
, Castillon
Castillon
Castillon may refer to several communes in France:*Castillon, Alpes-Maritimes, in the Alpes-Maritimes département*Castillon, Calvados, in the Calvados département...
, Milhas
Milhas
Milhas is a commune in the Haute-Garonne department in southwestern France.-Population:-References:*...
, Plantach, Saint-Barthélémy, Salvezines
Salvezines
Salvezines is a commune in the Aude departement in southern France.-Population:...
, and Rabat-les-Trois-Seigneurs
Rabat-les-Trois-Seigneurs
Rabat-les-Trois-Seigneurs is a commune in the Ariège department in the Midi Pyrénées region in southwestern France.-Population:The inhabitants of Rabat are called "Rabatols" in Occitan or Rabatois.-Name:...
, plus several uplifts in the northern Basque country
Northern Basque Country
The French Basque Country or Northern Basque Country situated within the western part of the French department of the Pyrénées-Atlantiques constitutes the north-eastern part of the Basque Country....
. These uplifts have a left-lateral shearing origin and are tilted to the north; simultaneously they also exhibit a vertical shearing component. They probably formed in the Variscan orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
. In the basement uplifts, mainly Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es and granulitic gneisses
Granulite
Granulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...
(in the Agly massif), and Paleozoic igneous and metamorphic rocks are found.
A small, maximally 5 km wide strip just north of the North Pyrenean Fault experienced dynamic and thermal metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
during the Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
/Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
about 110 million years ago (high temperature/low pressure, "HT/LP"-type). Some domains north of the basement uplifts were also metamorphosed (e.g. in the Bigorre
Bigorre
Bigorre is region in southwest France, historically an independent county and later a French province, located in the upper watershed of the Adour, on the northern slopes of the Pyrenees, part of the larger region known as Gascony...
and in the southern Corbières). The metamorphism was isochemical without introduction of extraneous elements and affected only the sedimentary cover rocks which were transformed into marble
Marble
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...
and hornfels
Hornfels
Hornfels is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses and have been rendered...
. The Paleozoic basement was not affected, probably due to its already dehydrated state.
Scattered within the metamorphic strip are several occurrences of lherzolite
Lherzolite
Lherzolite is a type of ultramafic igneous rock. It is a coarse grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser calcic chromium rich clinopyroxene. Minor minerals include chromium and aluminium spinels and garnets. Plagioclase can occur in lherzolites...
s (including their type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
at Lers). They were extruded from the upper mantle along deep-reaching faults. The lherzolites are associated with amphibolite
Amphibolite
Amphibolite is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. The modern terminology for a holocrystalline plutonic igneous rocks composed primarily of hornblende amphibole is a hornblendite, which are...
s, pyroxenite
Pyroxenite
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite. They are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both pyroxenes...
s, and amphibole
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...
-bearing peridotite
Peridotite
A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron...
s. All these mantle rocks are arranged in swarms, the biggest outcrop at Moncaup
Moncaup, Pyrénées-Atlantiques
Moncaup is a commune in the Pyrénées-Atlantiques department in south-western France.-References:*...
reaching a mere 3 km2. They are widely distributed, being found from Béarn
Béarn
Béarn is one of the traditional provinces of France, located in the Pyrenees mountains and in the plain at their feet, in southwest France. Along with the three Basque provinces of Soule, Lower Navarre, and Labourd, the principality of Bidache, as well as small parts of Gascony, it forms in the...
all the way to Aude. Their emplacement mode has not been clarified yet, but the following factors are relevant:
- associated Jurassic and lower Cretaceous marbles of the metamorphic band.
- granulites of the basement uplifts in the vicinity.
- migmatiticMigmatiteMigmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
kinzigites. - the close spatial association with the North Pyrenean Fault a bit farther south.
- lherzolite sedimentary clasts occur in marbles of the metamorphic strip, so the lherzolites must be older than the metamorphism.
Scattered within the North Pyrenean Zone are also some occurrences of volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
s. They are intercalated in sediments of the Lias
Lias Group
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...
and the Upper Cretaceous (Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
till Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
) and are found mainly in the west (near Tarbes
Tarbes
Tarbes is a commune in the Hautes-Pyrénées department in south-western France.It is part of the historical region of Gascony. It is the second largest metropolitan area of Midi-Pyrénées, with 110,000 inhabitants....
, Orthez
Orthez
Orthez is a commune in the Pyrénées-Atlantiques department in south-western France.It lies 40 km NW of Pau on the Southern railway to Bayonne. The town also encompasses the small village of Sainte-Suzanne thus residents of the town are called either Orthéziens or Sainte-Suzannais...
, and in the Basque country). They consist of silica undersaturated spilite
Spilite
Spilite is a fine-grained igneous rock, resulting particularly from alteration of oceanic basalt.The term was introduced into the geological literature by Alexandre Brongniart in 1827...
s, picrites, and nepheline syenite
Nepheline syenite
Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varieties are also known...
s. Associated dike rocks are lamprophyre
Lamprophyre
Lamprophyres are uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions...
s (camptonites and monchiquites).
Other features of interest are several different post-metamorphic breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
formations.
The North Pyrenean Zone can be subdivided into three subzones bounded by major faults:
- a northern subzone. Its sedimentary cover has detached from the basement uplifts farther south. It contains flysch from the Upper Cretaceous.
- an intermediate subzone. Here the basement uplifts crop out.
- a southern subzone. It was affected by metamorphism and contains outcrops of ultramafic rocks.
The North Pyrenean Zone is traversed in the west by NNE-SSW-trending, left-lateral strike-slip faults and then changes into the fold-belt of the Basque country. In the east, it continues after a sharp bend in the Corbières right into southern Provence. At the far eastern end, northwest-southeast-striking Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
fold trains of the Western Alps start interfering and finally completely overwhelm the pyrenean structures.
Axial Zone
The Axial Zone, also called Primary Axial Zone, is a huge basement dome of Precambrian and Paleozoic (Primary) rocks folded and metamorphosed during the Variscan orogeny and intruded by late-stage Variscan granitoidGranitoid
A granitoid or granitic rock is a variety of coarse grained plutonic rock similar to granite which mineralogically are composed predominately of feldspar and quartz. Examples of granitoid rocks include granite, quartz monzonite, quartz diorite, syenite, granodiorite and trondhjemite. Many are...
s. All the highest peaks of the Pyrenees are in the Axial Zone, hence the name.
Amongst the Variscan granitoids are biotite granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
s (Canigou
Canigou
The Canigou is a mountain located in the Catalan Pyrenees of southern France.Due to its sharp flanks and its dramatic location close to the coast, until the 18th century the Canigou was believed to be the highest mountain in the Pyrenees.-Trekking and sightseeing:Spectacular jeep tracks on the...
, Quérigut Massif), two-mica granites (Caillaouas Massif) and granodiorite
Granodiorite
Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...
s (Bassiès, Maladeta
Maladeta
Maladeta is a mountain in the Pyrenees, close to the highest peak in the range, Aneto, Aragon, Spain. Its name comes from the Spanish montes malditos which means "Damned Mountains". According to some authorities the local name for the massif was Mala hita...
). The granitoids are mainly shallow epizonal intrusives, but mesozonal and catazonal rocks are also represented.
The high elevations of the Axial Zone (generally above 3000 m) are compensated isostatically
Isostasy
Isostasy is a term used in geology to refer to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. This concept is invoked to explain how different topographic...
by an increased thickness of the continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
. For instance below the Maladeta massif, a root zone formed so that the Mohorovicic discontinuity
Mohorovicic discontinuity
The Mohorovičić discontinuity , usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle...
is encountered there at a depth of 50 km. Likewise over most peaks of the Axial Zone, a negative gravity anomaly
Gravity anomaly
A gravity anomaly is the difference between the observed acceleration of Earth's gravity and a value predicted from a model.-Geodesy and geophysics:...
can be detected which slowly disappears to the east.
The basement is traversed by major east-west-striking, late Variscan fracture zones that were reactivated during the alpine orogeny cycle. In the eastern part of the Axial Zone, the fractures are generally upright, a good example being the mylonitic Merens Fault at Pic del Port Vell
Pic del Port Vell
Pic del Port Vell is a mountain in the Pyrenees on the border of Spain and northwest Andorra. The nearest town is Arinsal, La Massana....
near Mérens-les-Vals
Mérens-les-Vals
Mérens-les-Vals is a commune in the Ariège department in southwestern France. Its demonym is Mérengois.-Population:- Geography:Mérens-les-Vals, as its name implies, has several valleys. The village is at the confluence of three valleys: Ariège, Nabre and Morgoulliou.The village has a train...
. In the western part, the fractures are more gently dipping to the north and behave as en echelon thrusts arranged in a northwest-southeasterly fashion; along these fractures, the basement of the Axial Zone overthrusts Mesozoic sedimentary units to the south. Good examples are the en echelon thrusts at Eaux Chaudes, Gavarnie
Gavarnie
Gavarnie is a commune in the Hautes-Pyrénées department in south-western France.-See also:* Cirque de Gavarnie* Gavarnie Falls*Communes of the Hautes-Pyrénées department-References:*...
and Bénasque
Benasque
Benasque or Benasc is a town in the comarca of Ribagorza, province of Huesca, . It is the main town in the Benasque Valley, located in the heart of the Pyrenees and surrounded by the highest peaks in that range.-Language:...
—Las Nogueras (referring to the upper reaches of the rivers Noguera Ribagorzana and Noguera Pallaresa
Noguera Pallaresa
The Noguera Pallaresa is a river in Catalonia, Spain. Its source is at Era Font d'era Noguereta in the municipality of Naut Aran at an elevation of about 2000 m and barely a hundred meters from those of the Garonne...
). Concomitant with the thrusts, a schistosity developed that affected the basement as well as the sedimentary cover implying an alpine origin. All these fractures account for an overall compression of the Axial Zone by 20% which translates as roughly 10 to 20 km of crustal shortening. As a result, the Axial Zone was squeezed into a south-directed antiformal stack.
The Axial Zone disappears in the Haut Béarn as a pericline underneath the Upper Cretaceous sedimentary cover only to reappear in the basement uplifts of Aldudés
Aldudes
Aldudes is a commune in the Pyrénées-Atlantiques department in south-western France.-Population:The population has been steadily declining over the years.It is located in the former province of Lower Navarre.-References:* -External links:...
-Quinto Réal
Quinto Real
The Quinto Real or the Quinto del rey, the "King's fifth", was a 20% tax established in 1504 that Spain levied on the mining of precious metals. The tax was a major source of revenue for the Spanish monarchy. In 1723 the tax was reduced to 10%....
, the southernmost of the Basque basement massifs. In the east the Axial Zone becomes downfaulted into Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
and Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s of Northern Catalonia
Catalonia
Catalonia is an autonomous community in northeastern Spain, with the official status of a "nationality" of Spain. Catalonia comprises four provinces: Barcelona, Girona, Lleida, and Tarragona. Its capital and largest city is Barcelona. Catalonia covers an area of 32,114 km² and has an...
and finally disappears underneath the Mediterranean.
The central and eastern section of the Axial Zone is bounded in the north by the North Pyrenean Fault, a system of N 110-striking, steeply dipping reverse-faults. The trace of the North Pyrenean Fault becomes more and more diffuse west of Lourdes
Lourdes
Lourdes is a commune in the Hautes-Pyrénées department in the Midi-Pyrénées region in south-western France.Lourdes is a small market town lying in the foothills of the Pyrenees, famous for the Marian apparitions of Our Lady of Lourdes occurred in 1858 to Bernadette Soubirous...
; near the Basque basement massifs, it seems to be displaced to the south by a wrench fault and then possibly continues into Spain south of the Basque Marble Nappe and south of the Basque Fold Belt. In Cantabria
Cantabria
Cantabria is a Spanish historical region and autonomous community with Santander as its capital city. It is bordered on the east by the Basque Autonomous Community , on the south by Castile and León , on the west by the Principality of Asturias, and on the north by the Cantabrian Sea.Cantabria...
, it finally reaches the Atlantic coast. The southern limit of the Axial Zone runs completely on Spanish territory. It is represented by an alpine reverse-fault along which the sediments of the South Pyrenean Zone are overthrust by the Axial Zone. In the east, the Axial Zone abuts directly against nappes of eastern representatives of the Sierras Marginales.
South Pyrenean Zone
The South Pyrenean Zone consists of a Mesozoic-Eocene sedimentary sequence which has detached from the Axial Zone within evaporitic horizons of the Middle or Upper Triassic and consequently was transported southward. The basement of this sequence does not outcrop. The southward motion was "channelised" by two major conjugated faults, in the west by the more or less north-south-trending folds and thrusts near the CincaCinca (Spain)
The Cinca is a river in Aragon, Spain. Its source is in the Circo de Pineta, in the Ordesa y Monte Perdido National Park, in the Aragonese Pyrenees. It is a tributary to the Segre River, with its confluence at La Granja d'Escarp, not far from the point where the Segre flows into the Ebro River...
river (Mediano and Boltaña anticlines), and in the east by the northeast-southwest-trending en echelon wrench faults at the Segre river. At the latter, the thrust system forms a break-back (hindward-thrusting) imbricate emergent fan which developed during the latest Eocene and early Oligocene. Due to constriction, the sedimentary cover was forced into several internal overthrusts, examples being the nappe
Nappe
In geology, a nappe is a large sheetlike body of rock that has been moved more than or 5 km from its original position. Nappes form during continental plate collisions, when folds are sheared so much that they fold back over on themselves and break apart. The resulting structure is a...
of the Monte Perdido
Monte Perdido
Monte Perdido is the third highest mountain in the Pyrenees. The summit of Monte Perdido , located in Spain, lies hidden from France by the seemingly impenetrable peaks of the Cirques of Gavarnie and Estaubé. It is in the north of Huesca province...
and the nappe of the Cotiella in the northwest. More centrally placed is the Bóixols Thrust Sheet which continues farther east in the Pedraforca Thrust Sheet (upper unit). The Bóixols Thrust Sheet is hindward-thrusting but also overrides the Montsec Thrust Sheet to the south. Its sediments reach 5000 m in thickness and are mostly Lower Cretaceous in age. The Montsec Thrust Sheet correlates with the lower unit of the Pedraforca Thrust Sheet. It consists of a 2000 m thick layer of Upper Cretaceous limestone followed by Lower and Middle Eocene syntectonic conglomerate, sandstone and shale.
The internal thrusts naturally led to a substantial increase in thickness. The South Pyrenean Zone finally terminates along the South Pyrenean Thrust where the Montsec Thrust Sheet overrides the Sierras Marginales.
The thrusting motions that formed an imbricate thrust system with associated piggyback basins took place mainly during the Eocene. The distances travelled by the thrust sheets is still debated, estimates varying from relatively small to as much as 30 to 50 km.
Sierras Marginales
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...
Border Ranges) are the Sierras Aragonesas and Serres Catalanes of the southern Pre-Pyrenees
Pre-Pyrenees
The Pre-Pyrenees are the foothills of the Pyrenees.-Description:As a mountainous system the Pre-Pyrenees are part of the Pyrenees. They run parallel to the main mountain range in a west to east direction...
. They are, much like the South Pyrenean Zone, formed from a Mesozoic-Eocene sedimentary succession, albeit with a much reduced thickness of about 900 m. The succession comprises Keuper
Keuper
The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolostone, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs...
, Jurassic, unconformable lower Cretaceous bauxites, unconformable Upper Cretaceous, Paleocene in Garumnian facies, and lower Eocene. Units of the Sierras Marginales underthrust successions of the Ebro Basin. Later on these underthrusts were unconformably
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
covered by Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
and Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
sequences from the Ebro Basin. To the west, the Sierras Marginales are relayed by the Jaca-Pamplona Thrust Sheet which consists of a younger Eocene–Oligocene sedimentary succession. In this thrust sheet west of the Gállego River, the structures simplify: in the Basque and in the Cantabrian
Cantabrian Mountains
The Cantabrian Mountains or Cantabrian Range are one of the main systems of mountain ranges in Spain.They extend for more than approximately 180 miles across northern Spain, from the western limit of the Pyrenees to the edges of the Galician Massif close to Galicia, along the coast of the...
Pyrenees, the sedimentary cover is affected only by long and relatively open fold trains, which are occasionally pierced by doming Keuper salt. In the east, the Sierras Marginales are represented by the tectonically comparable Port del Comte Thrust Sheeet and by the Cadí Thrust Sheet, which are made up essentially of an Eocene succession.
The Sierras Marginales are overthrust in the north by the Montsec
Serra del Montsec
The Serra del Montsec is a mountain system of the Pre-Pyrenees.-Description:The Serra del Montsec consists of a series of calcareous mountain ranges. Runs from east to west, it is about 40 km long and 186.96 square kilometres in area...
Thrust Sheet of the South Pyrenean Zone.
The end of the soutward directed thrusting motions was diachronous and migrated from east to west. For instance in the Cadí
Serra del Cadí
The Serra del Cadí is a mountain range running north of Catalonia, Spain, part of the Pre-Pyrenees. Its highest peak is the Vulturó, with an altitude of 2,648 metres....
Thrust Sheet, motions stopped 34 million years ago (Eocene/Oligocene boundary), whereas in the Jaca-Pamplona Thrust Sheet they stopped as late as 23 million years ago (Oligocene/Miocene boundary).
Southern foreland
The Southern foreland of the pyrenean orogen is the Ebro Basin or Ebro Foreland Basin. It can be divided into a Southern Folded Foreland section in the northeastern Catalonian sector and a basically undeformed flat-lying main section taking up the rest. Like the Subpyrenean Zone in the north, the Southern Folded Foreland was also affected by the thrusting motions of the Sierras Marginales and their easterly representatives. The induced folding intensity decreases the farther one moves away from the thrust fronts until one reaches the undeformed Ebro Basin. The fold trends follow more or less the pyrenean direction or parallel to the thrust fronts, but turn NE-SW near the Segre River (e.g. the Oliana Anticline).The sedimentary succession in the Ebro Basin shows Paleozoic rocks at the base followed by uppermost Cretaceous/lowermost Paleocene red beds and Eocene limestones, marine marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
s, and Upper Eocene evaporites (Cardona evaporites). The lower Oligocene is conglomeratic and pro-grades southward into evaporite and lacustrine deposits. In the Southern Folded Foreland, the folded Paleogene series are unconformably overlain by flat-lying non-marine Miocene and Pliocene strata of the main Ebro Basin.
The Ebro Basin deepens towards the South Pyrenean Frontal Fault where it comprises 3000 m of sedimentary infill. This reduces to 1500 m near the thrust front of the Sierra Marginales. The deepest part of the basin with 5000 m of sediments is near Logroño
Logroño
Logroño is a city in northern Spain, on the Ebro River. It is the capital of the autonomous community of La Rioja, formerly known as La Rioja Province.The population of Logroño in 2008 was 153,736 and a metropolitan population of nearly 197,000 inhabitants...
at its most northwestern end.
Evolution of the orogen
Due to its polycyclic geological evolution, the Pyrenees can be attributed to two major orogenic cycles:- a prealpine cycle.
- an alpine cycle.
Precambrian
StructuralStructural geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and...
and petrological
Petrology
Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....
studies in metamorphic rocks of the Axial Zone and of the North Pyrenean Zone were able to prove the existence of incorporated Precambrian remnants. For example in the basement of the Canigou
Canigou
The Canigou is a mountain located in the Catalan Pyrenees of southern France.Due to its sharp flanks and its dramatic location close to the coast, until the 18th century the Canigou was believed to be the highest mountain in the Pyrenees.-Trekking and sightseeing:Spectacular jeep tracks on the...
massif and in the basement uplift of the Agly, the remnants of a Precambrian basement were discovered (recognised by radiometric dating on granitoids and by certain structures of tectonic origin), which were later incorporated into the Variscan orogen by tectonic movements and the associated metamorphism.
The original radiometric results were, however, not confirmed by the SHRIMP-method (only Ordovician ages between 477 and 471 million years were found). The Cadomian origin of the basement is therefore uncertain.
The Precambrian rocks are mainly gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es and meta-sediments of amphibolite and granulite facies intruded by charnockite
Charnockite
Charnockite is applied to any orthopyroxene-bearing granite, composed mainly of quartz, perthite or antiperthite and orthopyroxene , as an end-member of the charnockite series.-Charnockite series:...
s.
Neoproterozoic and Paleozoic
The Cambro-Ordovician metamorphic rocks comprise migmatiteMigmatite
Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
s of upper amphibolite facies grade, mica schists with andalusite
Andalusite
Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.The variety chiastolite commonly contains dark inclusions of carbon or clay which form a checker-board pattern when shown in cross-section....
, cordierite
Cordierite
Cordierite or iolite is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: 2 to 2...
and staurolite
Staurolite
Staurolite is a red brown to black, mostly opaque, nesosilicate mineral with a white streak.-Properties:It crystallizes in the monoclinic crystal system, has a Mohs hardness of 7 to 7.5 and a rather complex chemical formula: 2Al94O204...
of lower amphibolite facies grade, and phyllite
Phyllite
Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the...
s of greenschist facies grade.
The epicontinental, psammitic sediments of the Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
and the Lower Paleozoic are a very thick detrital (mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
-sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
) succession essentially devoid of fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s. These sediments were in a large part later overprinted by the Variscan orogeny. Intercalated near the base of the detrital succession are carbonates.
The (meta)sedimentary succession starts with the 2000 to 3000 m thick Canaveilles Group
Canaveilles Group
The Canaveilles Group is the basal metasedimentary succession of late Neoproterozoic and Cambrian age outcropping in the Pyrenees.- Etymology :...
in the Ediacarian about 580 million years ago. Its sediments consist mainly of shales and greywackes with intercalated rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
s and carbonates. Within the Cadí Thrust Sheet archeocyathid–bearing limestones developed during the Lower Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
. At the onset of the Middle Cambrian, the Canaveilles Group is replaced by the Jujols Group, a 2000 m thick flyschoid series comprising schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
s, shales, and siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s interlayered with carbonates and quartzites. The Jujols Group is less metamorphic than the mesozonal Canaveilles Group. Its sedimentation lasted probably into the lowermost Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
.
After a longer hiatus, up to 100 m of Caradocian (Ordovician stage 5 and 6) conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
follow unconformably upon the Jujols Group—the Rabassa Conglomerate. This is overlain by nearly 500 m of the Cava Formation, interlayered greywackes, and shales containing volcanic horizons. The 200 m thick Estana Formation is made up of limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
s and calcareous shales. Its end–Ordovician limestones contain a benthic
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
fauna (brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
s, bryozoans, cystoids) as well as conodont
Conodont
Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
s. The succession ends with the badly layered Ansobell Formation (20 to 300 m), dark schists that bear microconglomerates indicating a glaciomarine depositional environment. The Ansobell Formation can develop an unconformity and sometimes follows directly upon the Cava Formation.
The included volcanic rocks and the conglomerates hint at unsettled tectonic conditions, which are probably connected with an early stage of the Caledonian orogeny
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
(Taconian Phase).
During the Rhuddanian (Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
) initially 20 m of quartzitic rocks, the Bar Quartzite, were deposited followed by 50 to 250 m of dark, graphitic
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, graptolite
Graptolite
Graptolithina is a class in the animal phylum Hemichordata, the members of which are known as Graptolites. Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous...
-bearing shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
s. The thickness of the shales can increase in the West to 850 m. They take up nearly the entire Silurian (Aeronian until Pridoli), documented by the graptolites. In their upper section (Ludlow), the shales incorporate calcareous horizons and calcareous nodules (with conodonts, nautiloid
Nautiloid
Nautiloids are a large and diverse group of marine cephalopods belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and...
s, bivalves, crinoid
Crinoid
Crinoids are marine animals that make up the class Crinoidea of the echinoderms . Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 6,000 meters. Sea lilies refer to the crinoids which, in their adult form, are...
s, and ostracod
Ostracod
Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
s). Close to the Basque massifs, the calcareous facies changes into a detritic facies of interlayered sand– and silt–stones. The graptolite-bearing shales were later metamorphosed into lower amphibolite facies slate
Slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...
s. They form prominent décollement
Decollement
Décollement is a gliding plane between two rock masses. In French, "décoller" means "to detach from" or "to rip off" and was first used by geologists studying the structure of the Swiss Jura Mountains, but is also known as a detachment zone. This is a structure of strata owing to deformation,...
surfaces.
The Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
is marine and rich in fossils (spiriferids
Spiriferida
Spiriferida is an order of extinct articulate brachiopod fossils which are known for their long hinge-line, which is often the widest part of the shell. In some genera it is greatly elongated, giving them a wing-like appearance. They often have a deep fold down the center of the shell...
and trilobite
Trilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
s like phacops
Phacops
Phacops is a genus of trilobite in the order Phacopida, family Phacopidae that lived in Europe and North American in the Silurian and Devonian periods. It was a rounded animal, with a globosa head and large eyes, and probably fed on detritus...
). It consists of six depositional areas (and a wealth of formations) differing considerably in their sedimentary evolution (especially in the Basque Pyrenees). Generally in the western Pyrenees, shallow marine facies prevail, whereas in the eastern Pyrenees, hemipelagic facies with occasional high grounds predominate. The Devonian has highly variable thicknesses, its 100–600 m—and in places 1400 —thick succession is made up of many different sedimentary facies like greywacke
Greywacke
Greywacke or Graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found...
s, reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
al limestones, and sandstones. Quite distinctive are banded pink to red, blue or green limestones and nodular limestones, the so-called griottes of the lower Famennian
Famennian
The Famennian is one of two faunal stages in the Late Devonian epoch. It lasted from 374.5 ± 2.6 million years ago to 359.2 ± 2.5 million years ago. It was preceded by the Frasnian stage and followed by the Tournaisian stage and is named after Famenne, a natural region in southern Belgium.It was...
. Calcareous shales and black shales also occur.
The Lochkovian consists of black shales and limestones and is very rich in conodonts. During the Pragian, a siliciclastic wedge formed, the San Silvestre Quartzite of the Basibé Formation. The period Upper Givetian till Frasnian
Frasnian
The Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
witnessed pronounced lithological differences and increased sedimentation rates. In the Lower Frasnian, reef complexes developed, yet at the same time siliciclastic material was being delivered into the western, central, and Basque domain. At the beginning of the Middle Famennian
Famennian
The Famennian is one of two faunal stages in the Late Devonian epoch. It lasted from 374.5 ± 2.6 million years ago to 359.2 ± 2.5 million years ago. It was preceded by the Frasnian stage and followed by the Tournaisian stage and is named after Famenne, a natural region in southern Belgium.It was...
, the sedimentation in the Pyrenees became more uniform again and until the end of the Devonian, monotonous, condensed cephalopod-bearing limestones were laid down (Griotte limestones and grey to pinkish, nodular Supragriotte limestones). Towards the end of the Famennian, first hiati started to appear leading to complete emersion of the western Pyrenees at the onset of the Mississippian. The corresponding unconformity, which exists only in the western Pyrenees, belongs to an early deformation phase of the Variscan orogeny (Breton Phase).
Only in the western Pyrenees is the Lower Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
(Mississippian) distinguished from the Devonian sediments by an unconformity, starting off marine with a transgressive quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
–pebble bed. Anywhere else, the Supragriotte limestones are conformably overlain by pre-orogenic sediments that begin with the Lower Cherts of the Tournaisian
Tournaisian
The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 359.2 ± 2.5 Ma to 345.3 ± 2.1 Ma...
. The Lower Cherts comprise 50 m of black, phosphate nodule-bearing chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
s interlayered with black shales. After an interlude of grey, nodular, goniatite
Goniatite
Goniatites are extinct ammonoids, shelled cephalopods related to squid, octopus, and belemnites, that form the order Goniatitida. The Gonatitida originated from within the more primitive anarcestine ammonoids in the Middle Devonian some 390 million years ago...
-bearing limestones, the Upper Cherts were deposited during the Viséan
Viséan
The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...
—grey or green cherts sometimes interlayered with pyroclastics and ending with grey nodular limestones.
The Mississippian later on changes into the nearly 1000 m thick detrital, syn-orogenic sediments of the Kulm
Kulm
The name Kulm is a German language toponym which is derived from the Latin culmen, meaning hill. It may be used as follows:-Places:Austria* Kulm bei Weiz, a municipality in Styria* Kulm am Zirbitz, a municipality in Styria...
–facies. An exception are the western Pyrenees, where, during the Serpukhovian
Serpukhovian
The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from 328.3 Ma tot 318.1 Ma...
, dark grey, laminated limestones precede the Kulm. The diachronous Kulm sediments are a flysch-like
Flysch
Flysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...
(turbidite
Turbidite
Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...
s) interlayering of sandstones and dark shales—harbingers of the Variscan tectonic movements. They also contain layers of hemipelagic limestones, conglomerates, carbonaceous breccias as well as olistoliths. Sedimentation of the Kulm facies started in the East already at the Viséan/Serpukhovian boundary (Namurian
Namurian
The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age...
), but west of the Gallégo river, it started only at the beginning of the Pennsylvanian
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
(Upper Westphalian, Bashkirian
Bashkirian
The Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous...
). In the Basque Pyrenees, the Kulm sedimentation perdured into the Moskovian. The Kulm sediments were deposited as canyon deposits on the continental slope or as submarine fans in a southwest migrating foredeep of the Variscan orogen.
Variscan orogeny
The Variscan orogeny is expressed as an important unconformity within the Paleozoic sedimentary succession, usually placed above the Lower Westphalian (BashkirianBashkirian
The Bashkirian is in the ICS geologic timescale the lowest stage or oldest age of the Pennsylvanian, the youngest subsystem of the Carboniferous...
) and below the Stephanian (Moscovian
Moscovian (Carboniferous)
The Moscovian is in the ICS geologic timescale a stage or age in the Pennsylvanian, the youngest subsystem of the Carboniferous. The Moscovian age lasted from 311.7 ± 1.1 to 306.5 ± 1.0 Ma, is preceded by the Bashkirian and is followed by the Kasimovian...
), but sometimes already below the Upper Westphalian. The tectonic movements therefore happened about 310 million years ago, dated by fossil plants.
The Upper Westphalian shows an important unconformity at its base and is made up of conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
s. The Moscovian is represented by blue-black shales, overlain by the so-called Grey Unit of the Kasimovian
Kasimovian
The Kasimovian is an geochronologic age or chronostratigraphic stage in the ICS geologic timescale. It is the third stage in the Pennsylvanian , lasting from 306.5 ± 1.0 to 303.9 ± 0.9 Ma. The Kasimovian stage follows the Moscovian and is followed by the Gzhelian.-Name and definition:The Kasimovian...
(Stephanian B) and the Transitional Layers of the Gzhelian
Gzhelian
The Gzhelian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the youngest stage of the Pennsylvanian, the youngest subsystem of the Carboniferous. The Gzhelian lasted from 303.9 ± 0.9 to 299.0 ± 0.8 Ma...
(Stephanian C and Autunian). These sediments are non-metamorphic or only weakly metamorphosed, whereas the sediments below the unconformity fully experienced the Variscan metamorphism.
The far-reaching effects of the Variscan orogeny influenced the pyrenean domain in many ways. Of prime importance were the compressional stresses that folded
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
the Paleozoic sediments. Several fold generations developed, sometimes superimposing each other. Associated with the folds are schistosities. The Paleozoic sediments and its Precambrian basement were also metamorphosed under high-temperature and low-pressure conditions (HP/LT). In places anatexis
Anatexis
Anatexis in geology, refers to the differential, or partial, melting of rocks, especially in the forming of metamorphic rocks such as migmatites.-Optimum Temperature Conditions for Crustal Melting:...
was reached, an example being the melting of some Precambrian gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
es of the Prevariscan basement together with their enveloping mica schists. Another important consequence of the orogeny was late-orogenic magmatism
Magmatism
The formation of igneous rocks from magma is known as Magmatism.Magmatism is a process responsible for mountain formation. The process of magmatism produces an additional mass and volume to the Earth’s surface. For example the formation of volcanoes or island arcs at convergent plate boundaries...
emplacing granitoids (granodiorite
Granodiorite
Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...
s and biotite granites
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
) of mainly acid but occasionally also of basic composition. Amongst these granitoids are deep-seated, rather diffuse, intrusive bodies associated with migmatite
Migmatite
Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
s, yet also typical, well-defined pluton
Pluton
A pluton in geology is a body of intrusive igneous rock that crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies...
s often rising into the cores of anticline
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
s within the Variscan fold-belt. The main magmatism perdured from 310-270 million years (late Pennsylvanian and early Permian cooling ages). A good example for the main magmatism is the 280 million years old Maladeta granodiorite.
Also of importance was late-stage fracturing
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
under brittle conditions. The developing fractures probably followed weak zones already initiated during the Paleozoic. The main direction of these fractures is WNW-ESE, the so-called Pyrenean direction, an excellent example being the North Pyrenean Fault. These fractures will play a decisive role during the further development of the orogen.
Alpine orogenic cycle
Also compare with: Aquitaine BasinAquitaine Basin (geology)
The Aquitaine Basin is after the Paris Basin the second largest Mesozoic and Cenozoic sedimentary basin in France, occupying a large part of the country's southwestern quadrant. Its surface area covers 66,000 km2 onshore. It formed on Variscan basement which was peneplained during the Permian...
— Sedimentary evolution
Pennsylvanian, Permian and Lower Triassic
Molasse
The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...
of the Variscan orogen which underwent late-stage extension. In half-grabens 2500 of sediment accumulated at the close of the Carboniferous and throughout the Permian, mainly interbedded non-marine and basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic-andesitic
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
rocks. Detrital formations of lacustrine affinity with coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
measures during the Stephanian (Kasimovian
Kasimovian
The Kasimovian is an geochronologic age or chronostratigraphic stage in the ICS geologic timescale. It is the third stage in the Pennsylvanian , lasting from 306.5 ± 1.0 to 303.9 ± 0.9 Ma. The Kasimovian stage follows the Moscovian and is followed by the Gzhelian.-Name and definition:The Kasimovian...
and Gzhelian
Gzhelian
The Gzhelian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the youngest stage of the Pennsylvanian, the youngest subsystem of the Carboniferous. The Gzhelian lasted from 303.9 ± 0.9 to 299.0 ± 0.8 Ma...
) followed by red sandstones with plant remains during the Permian
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
are typical erosional products of a chain not having reached stability.
The Grey Unit of the Kasimovian is a sequence of decreasing grain-size, starting with breccias and conglomerates and changing into sandstones and coal-bearing shales (anthracite is mined near Campo de la Troya). Also included are andesitic layers that can attain significant thicknesses in places. The Transitional Layers are also a sequence of decreasing grain-size (conglomerates, sandstones, and coal-bearing shales), but, instead of andesites, they include tuffs and rhyodacitic
Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate...
lavas. They close with lacustrine limestones containing stromatolite
Stromatolite
Stromatolites or stromatoliths are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria ....
s, charophytes, and ostracods.
The continental red beds of the Permian rest unconformably on the Transitional Layers. They show strong variations in their thicknesses and reach 800 m, sometimes even 1000 m. They occur mainly in the Basque Pyrenees and in the Axial Zone. Like the Stephanian sediments, they were deposited as alluvial (as fans and in ephemeral streams) and lacustrine sediments within transtensive basins of the Variscan orogen.
The aforementioned fractures were decisive in determining facies distributions during this interval. They also influenced the distribution of volcanic eruptions during the Permian such as the calcalkaline volcanism at Pic du Midi d'Ossau
Pic du Midi d'Ossau
The Pic du Midi d'Ossau is a mountain rising above the Ossau Valley in the French Pyrenees. Despite possessing neither a glacier nor, in the context of the range, a particularly high summit, its distinctive shape makes it a symbol of the French side of the Pyrenees...
and the basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
s of the Basque country. The trigger for these volcanic eruptions probably was early wrenching motions of Iberia relative to the Eurasian Plate.
In the Axial Zone, the Permian can be subdivided into three sedimentary series (from top to bottom):
- La Peña de Marcanton series. It reaches a thickness of 500 m and is mainly fine-grained.
- Pic Baralet series. Up to 300 m thick. It is composed of polygenic conglomerates with Paleozoic limestone fragments embedded in red sandstone. The series rests partially unconformable on the Somport series.
- Somport series. A generally fine-grained series that can attain 300 m in thickness and is composed of red to purple claystones. It rests unconformably on the Transitional Layers.
The detrital Lower Triassic (Buntsandstein
Buntsandstein
The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...
) is very similar to the Permian. It reaches 400 to 500 m in thickness and is made up of coarse conglomerates, sandstones, psammites with plant remains (Equisetites, Coniferomyelon) as well as green and red to purple claystones. At this time, the peneplanation of the Variscan orogen had reached an advanced stage and the sedimentary accommodation spaces started to widen.
Middle Triassic till Upper Jurassic
The sedimentary successions from the Middle Triassic to the Upper Jurassic are very similar on both sides of the Pyrenees.During Muschelkalk
Muschelkalk
The Muschelkalk is a sequence of sedimentary rock strata in the geology of central and western Europe. It has a Middle Triassic age and forms the middle part of the Germanic Trias, that further consists of the Buntsandstein and Keuper...
times, the sea advanced again, but reached only the North Pyrenean Zone and the Basque country. The resulting sediments left behind are 20 to 100 m of dolomitic cellular limestones, grey fossiliferous limestones, and wavy limestones. In the Upper Triassic (Keuper
Keuper
The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolostone, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs...
), the sedimentation spread over the entire Pyrenean domain. About 220 m million years ago (during the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
) evaporites settled out in lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s and grabens—variegated, gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
–bearing, iron-rich clays, gypsum, anhydrite
Anhydrite
Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...
, dolomitic marls, dolomites, rock salt as well as potassium and magnesium salts occur. The evaporites served later as major decollement horizons. At the limit, Upper Triassic/Hettangian
Hettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
doleritic tholeiite
Tholeiite
The tholeiitic magma series is one of two main magma series in igneous rocks, the other magma series being the calc–alkaline. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
s (ophites
Verd antique
Verd antique , or verde antique, is a serpentinite breccia popular since ancient times as a decorative facing stone. It is a dark, dull green, white-mottled serpentine, mixed with calcite, dolomite, or magnesite, which takes a high polish...
) formed in the Pyrenees and in the southern Aquitaine Basin, indicating further movements along the fracture zones (submarine fissure eruptions and sills in unsolidified Keuper sediments).
The sedimentation during the Jurassic is characterised by the growth of a carbonate platform. The sediments are mainly epicontinental deposits of lacustrine character, as well as limestones, marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
s and dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
s with marine or littoral faunas. The basin was under tension during this period and as a result long horsts and graben structures of different subsidence rates were created following more or less the trend of the Variscan fractures. Its northern side is rimmed by the relatively stable Aquitanian shelf. The basin probably is caused by crustal thinning infiltrating from the Atlantic domain.
The Lias
Lias Group
The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...
started with a transgression that is more important than the advances of the Muschelkalk and Keuper seas. Its total thickness varies between 150 and 400 m. The sea level kept rising during the Hettangian
Hettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
and fossiliferous limestones were deposited; this trend reversed later on into a regression leaving evaporites (rock salt and anhydrite with some calcareous interlayers). At the edge of the basin and in the eastern Pyrenees, argillaceous limestones and banded dolomites with layers of anhydrite settled out; the dolomites transformed upon dissolution of the anhydrite into monogenic breccias. The regression continued during the Lower Sinemurian
Sinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
, sedimenting intra– and supra–tidal banded limestones and dolomites. In the Upper Sinemurian (Lotharingian), more open-marine conditions established themselves due to a renewed sea-level rise; in deeper parts of the basin, fossiliferous limestones developed, whereas, on high ground, oolithic limestones accumulated. The Middle Lias (Pliensbachian
Pliensbachian
The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...
) started off transgressive as well with fine-grained detrital, limey to marly sediments (ferruginous oolites, fossiliferous limestones and marls) that change over to marls. In the eastern Pyrenees, pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
-bearing claystones formed due to a badly oxygenated environment; they contain a very diverse fauna of ammonites belonging to the French southeastern domain, whereas the ammonite population on the Atlantic side is rather monotonous. During the Upper Lias (Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
), the sea reached a high stand, continuing with the fine-grained detrital sedimentation and depositing black pelagic marls (marnes noires and schistes esquilleux). Towards the end of the Lias, regressive tendencies again became noticeable.
Falling sea levels continued right into the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
. Near Pau an oolite barrier started to grow that extends all the way north to Poitiers
Poitiers
Poitiers is a city on the Clain river in west central France. It is a commune and the capital of the Vienne department and of the Poitou-Charentes region. The centre is picturesque and its streets are interesting for predominant remains of historical architecture, especially from the Romanesque...
. It divided the sedimentary basin now into two major facies domains: a deeper western domain open to the Atlantic and undergoing infratidal sedimentation (black to blueish argillaceous limestones rich in benthic organisms, microfilaments, and ammonites) and a shallow, enclosed, eastern domain with intertidal sedimentation (variable carbonate facies like pseudo-oolites and banded dolomites, but also anhydrite-bearing evaporites). These intertidal sediments experienced a strong contemporaneous dolomitization
Dolomitization
Dolomitization is a process by which dolomite is formed when magnesium ions replace calcium ions in calcite. It is common for this alteration into dolomite to take place due to evaporation of water in the sabkha area. Dolomitization involves substantial amount of recrystallization...
. Towards the end of the Middle Jurassic, sea levels fell even further.
Upper Jurassic and Lower Cretaceous
During the Upper Jurassic (TithonianTithonian
In the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
) and especially during the Lower Cretaceous, drastic changes occurred. Iberia started to rift off the Armorican Massif
Armorican Massif
The Armorican Massif is a geologic massif that covers a large area in the northwest of France, including Brittany, the western part of Normandy and the Pays de la Loire. Its name comes from the old Armorica, a Gaul area between the Loire and the Seine rivers...
in a southerly direction and in its wake the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
slowly began to spread (with formation of oceanic crust from the Middle Albian till the end of the Coniacian
Coniacian
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...
).
The sedimentation in the Malm
Malm
is a former municipality, a village, and the administrative centre of the municipality of Verran in Nord-Trøndelag county, Norway. Malm is located along the Trondheimsfjord, about a drive west from the town of Steinkjer. The village of Malm has a population of 1,572. The population density of...
(total thickness 600 to 750 m) did not increase until the Upper Oxfordian, the Lower Oxfordian rarely being present. The 100 to 150 m thick Upper Oxfordian is represented west of the oolite barrier by intratidal platform sediments (argillaceous to sandy, pyrite-bearing limestones), whereas, in the east, dolomitization continues. By Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
times, the facies differences attenuated due to shallowing of the western domain, resulting in massive, fine-grained, black, lithographic
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
limestones and fine-grained platy limestones. During the Tithonian, strong regressive tendencies set in that led to a complete withdrawal of the sea. In the Basque country, the sea had withdrawn already at the end of the Kimmeridgian. During times of falling sea levels, evaporitic, dolomitic, lagoonal, and lacustrine facies were left behind.
After a southeasterly re-advance of the sea in the Berriasian
Berriasian
In the geological timescale, the Berriasian is an age or stage of the Early or Lower Creteceous. It is the oldest or lowest subdivision in the entire Cretaceous. It spanned between 145.5 ± 4.0 Ma and 140.2 ± 3.0 Ma...
via a small strait east of Pau, which deposited 100 m of inter– to sub–tidal limestones and a sandy to clayey detrital border facies, emersion set in during the Neocomian. During Valanginian
Valanginian
In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 140.2 ± 3.0 Ma and 136.4 ± 2.0 Ma...
and Hauterivian
Hauterivian
The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous epoch or a stage in the Lower Cretaceous series. It spans the time between 136.4 ± 2 Ma and 130 ± 1.5 Ma...
times, clayey marls on top of the emerged horsts were transformed under ferralitic climatic conditions into bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
s, which were fossilised by later transgressions. After another marine trangression from the east during the Barremian
Barremian
The Barremian is an age in the geologic timescale between 130.0 ± 1.5 Ma and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch...
, the elongated graben regions in the Pyrenean domain received 200 to 300 m of marine shelf sediments of the Urgonian facies, such as dolomites, algal
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
limestones, foraminiferous limestones, and rudist limestones. The Urgonian facies can perdure in the Corbières and in the South Pyrenean Zone into the Albian. With falling sea levels in the Upper Barremian, black, pyrite-bearing claystones and lagoonal limestones rich in ostracods and characeans were sedimented.
After the Barremian/Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
boundary, marked by another high stand of the sea, there were four more sea-level oscillations during the Aptian and the Albian, bringing about a very significant sediment accumulation (in some places up to 3000 m). Due to sinking grabens in the Atlantic domain, the water masses of the Atlantic and the Tethys mixed for the first time. The Aptian/Albian sediments are characterised by the competitive interplay between fine-grained terrigenic and organic material. The organic material is responsible for the formation of shallow platforms built by rudists, hexacorals, and algae. In the Upper Abian, the terrigenic material predominated, and several shallow marine, partially calcareous sandstone formations were deposited. The source region of the detrital material was the Aragon
Aragon
Aragon is a modern autonomous community in Spain, coextensive with the medieval Kingdom of Aragon. Located in northeastern Spain, the Aragonese autonomous community comprises three provinces : Huesca, Zaragoza, and Teruel. Its capital is Zaragoza...
/Pyrenees domain that was undergoing a first epirogenetic uplift. In the same context, the fluvial delta sediments of the Formation de Mixe were transported from the south, and the very heterogeneous, up to 1000 m thick conglomerates of the Poudingues de Mendibelza, interpreted as the topset of a delta-front.
Upper Cretaceous
Just before the onset of the Upper Cretaceous, the pyrenean domain had separated in the AlbianAlbian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
into two very different sedimentary facies realms. On the northern edge of Iberia (in the South Pyrenean Zone and in the Axial Zone), shelf carbonates were then being deposited. Because of several emersions, they only show very reduced thicknesses. Due to transtension in the North Pyrenean Zone, a very strongly subsiding flysch basin (North Pyrenean Basin) developed, which follows essentially the east-west-trending Variscan fracture zones. The basin was deepening towards the Atlantic and shallowing towards the east, where it terminates before the Aude river. It is split by the basement massifs of the North Pyrenean Zone into two strands—a southerly strand called sillon aturien, which received up to 2500 m of flysch ardoisier and a northerly strand with the flysch noir. The flysch basin is rimmed to the north by the relatively stable Aquitanian Shelf. It was formed probably by extensive crustal thinning that penetrated from the Atlantic side.
Concurrent with the transtension, the Pyrenean Metamorphism took place characterised by high heat flow (peak temperatures were 500-600 °C) but relatively low pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
s (HT/LP-metamorphism). Under these conditions, new mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s like biotite
Biotite
Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...
, diopside
Diopside
Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class...
and scapolite
Scapolite
Scapolite , is a group of rock-forming silicate minerals composed of aluminium, calcium, and sodium silicate with chlorine, carbonate and sulfate.-Properties:...
grew. The metamorphism is diachronous and has been dated radiometrically in the eastern North Pyrenean Zone as Albian, whereas in the Basque country in the west (for example in the Basque Marble Nappe) it has been dated only as Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
. It is possible that the metamorphism lasted in a milder form until the end of the Cretaceous or even the beginning of the Eocene.
Two major deformational phases with the development of schistosities (Upper Albian till Lower Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
and Santonian
Santonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
till Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
) affected the pyrenean domain during the Upper Cretaceous expressing themselves as unconformities in the sedimentary record. The flysch basin was shortened and at the northern edge of Iberia, an orogenic wedge formed that moved slowly into the northern foreland. As a consequence, the flysch basin receiving the erosional products from the wedge was forced to migrate to the north too (changeover during the Santonian of the centre of subsidence from the North Pyrenean Basin to the Subpyrenean Basin). The Subpyrenean Basin was consequently filled in by 1000 to 4000 m of flysch à fucoides.
The Variscan fracture zones were active during the entire Upper Cretaceous and decisively influenced the sedimentary facies distributions. This activity was further underlined by alkaline magmatism lasting from the Middle Albian until the end of the Coniacian; thus in the west of the North Pyrenean Zone, submarine basaltic lavas extruded, while farther east in the Béarn and in the Bigorre, different magmatic rock types intruded the Upper Cretaceous strata.
Cenozoic
The sedimentary sequences of the PaleocenePaleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
highlight the differences between the eastern and the western Pyrenees. In the west, the marine shelf facies continued and the flysch basin carried on subsiding. In the east, the continental red beds of the Garumnian facies (whose deposition started already at the close of the Cretaceous) were laid down, mainly alluvial and paludial facies. At the same time, the first tectonic shortenings and uplifts affected the eastern Pyrenees.
In the western Pyrenees, the marine sedimentation also carried on during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
. In two subsiding basins on both sides of today's chain, limestones, marls, foraminiferous sandstones, and sandstones with a benthic
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
fauna were sedimented. The Eocene sedimentary successions along the French northern edge of the Pyrenees (in the North Pyrenean Zone) are fairly thin and full of facies changes. There, short-lived transgressions and regressions can be followed into the Languedoc
Languedoc
Languedoc is a former province of France, now continued in the modern-day régions of Languedoc-Roussillon and Midi-Pyrénées in the south of France, and whose capital city was Toulouse, now in Midi-Pyrénées. It had an area of approximately 42,700 km² .-Geographical Extent:The traditional...
. During the Ypresian
Ypresian
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between and , is preceded by the Thanetian age and is followed by the Eocene Lutetian age....
, the first conglomerates start being delivered.
This very thick conglomeratic formation, called the Poudingues de Palassou, is the indicator for the most important orogenic phase in the Pyrenean domain, the Pyrenean Main Phase, which was accompanied by very strong deformations and uplifts. The conglomerates are later unconformably
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
overlain by end–Eocene strata, therefore the orogenic phase can be assigned to the interval Ypresian/Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
, i.e. roughly 50 to 40 million years ago.
On the southern side of the Pyrenees in Catalonia, folded conglomeratic formations have been dated as Upper Lutetian to Bartonian
Bartonian
The Bartonian is, in the ICS's geological timescale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between and . It is preceded by the Lutetian and is followed by the Priabonian age.-Stratigraphic definition:...
, representing the interval 44 to 37 million years ago. They also are unconformably overlain by end–Eocene sediments bearing a continental fauna.
The Pyrenean Main Phase manifested itself on both sides of the axial zone as reverse faults and thrusts with fairly large displacements. The movements were directed on the French side to the north, and on the Spanish side to the south. But their spatial arrangement was not symmetrical; the Spanish side for instance has much lower dipping structures. The faulting and thrusting disrupted not only the Mesozoic and Paleogene sedimentary cover, but also large parts of the Variscan basement. The basement had failed not just rigidly at the Paleozoic fracture systems, but also underwent intensive alpine deformations around heterogeneities and anisotropies in its structural fabric.
Deformational phases of lesser importance followed the Pyrenean Main Phase, all contributing to the final appearance of the orogen. At the northern margin of the Ebro Basin close to the Sierras Marginales, for example, folded Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
is covered unconformably by flat-lying, detrital Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
of continental origin. This points to another deformational phase at the end of the Oligocene about 25 million years ago.
After the beginning of the Miocene, the uplifted orogen underwent severe erosion, expressed by enormous molasses being shed into the foreland basins such as for example the Aquitaine Basin. In the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
, a renewed uplift started, leading to the formation of huge alluvial fan
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
s at the mountain front, a notable example being the Lannemezan
Lannemezan
Lannemezan is a commune in the Hautes-Pyrénées department in south-western France.-Geography:The Petite Baïse has its source in the commune.Lannemezan is around 30 km east of Tarbes, and around 100 km south-west of Toulouse.-References:*...
alluvial fan. Another important consequence of the uplifting was peneplanation. Several peneplanation levels have been found on very different heights (3000 to 2000 m in the Axial Zone, close to a 1000 m in the Pays de Sault, near 400 m in the Agly massif and at 100 m in the Corbières). They generally become lower in the east, with several uplifts towards the end of the Oligocene, towards the end of the Miocene (Pontian peneplanation), and towards the end of the Pliocene (Villafranchian peneplanation).
Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
sediments have been preserved in the Pyrenees mainly in small graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s close to the Mediterranean (near Cerdagne). The grabens have also repeatedly been flooded by the Mediterranean, examples being the graben near Ampurdan and grabens in the Roussillon
Roussillon
Roussillon is one of the historical counties of the former Principality of Catalonia, corresponding roughly to the present-day southern French département of Pyrénées-Orientales...
containing a Pliocene fauna. These extensional structures most likely owe their existence to renewed movements on Variscan fractures. The very young volcanic area near Olot
Olot
Olot is the capital of the comarca of the Garrotxa, in the province of Girona, Catalonia, Spain.- Etymology :The etymology of Olot is not clear and there are several hypotheses...
probably has a similar cause.
During the Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
, the Pyrenees experienced several glaciations, but of far less intensity than for example in the Alps. Large glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s advanced through the valleys of the Gave d'Ossau
Gave d'Ossau
The Gave d'Ossau is the torrential river flowing through the Ossau Valley, one of the three main valleys of the High-Béarn , in the Southwest of France....
, Gave de Pau
Gave de Pau
The Gave de Pau is a river of south-western France and a left tributary of the Adour. It takes its name from the city Pau, through which it flows. The river is in length, and its source is at the Cirque de Gavarnie in the Pyrenees mountains....
, Garonne, and Ariège on the French northern side. Today about 20 smaller true glaciers as well as cirques and glacier remnants subsist (examples are the Aneto glacier, the Ossoue glacier in the Vignemale
Vignemale
The Vignemale , at 3298 metres, is the highest of the French Pyrenean summits, in the border with Spain ....
massif and glaciers on Maladeta and Monte Perdido). All these glaciers have undergone a large retreat since 1850 due to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
. The total glaciated surface area amounted to 45 km2 in 1870, whereas in 2005 a mere 5 km2 were left.
Geodynamic evolution
The Pyrenees have experienced a very long geological evolution with multiple orogeniesOrogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
. Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
crustal remains (Canigou, Agly) hint at possible Cadomian
Cadomian Orogeny
The Cadomian Orogeny was a tectonic event or series of events in the late Neoproterozoic, about 650-550 Ma, which probably included the formation of mountains. This occurred on the margin of the Gondwana continent, involving one or more collisions of island arcs and accretion of other material at a...
domains. Indications for Caledonian
Caledonian orogeny
The Caledonian orogeny is a mountain building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly...
movements are somewhat clearer (conglomerates and volcanic rocks in the Ordovician). During the Variscan orogeny in the Pennsylvanian, the Axial Zone and the South Pyrenean Zone became an integral part of what was to become the microcontinent Iberia. The Sierras Marginales were part of the Ebro Block, a northeastern section of Iberia. The appartenance of the North Pyrenean Zone is still uncertain, but the Subpyrenean Zone certainly formed part of the microcontinent Aquitania. Iberia and Aquitania were on the south side of the South Variscan Thrust and therefore constituted the foreland of the Variscan orogen. Both microcontinents had originated from Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
's northern margin.
At the close of the Variscan orogeny, Iberia was still connected to northwestern France (the Armorican Massif
Armorican Massif
The Armorican Massif is a geologic massif that covers a large area in the northwest of France, including Brittany, the western part of Normandy and the Pays de la Loire. Its name comes from the old Armorica, a Gaul area between the Loire and the Seine rivers...
) and most likely was a northwestern prolongation of Aquitania. Its later movements were vital to the alpine cycle of the Pyrenean orogeny. This is accepted by most geologists, yet the details of Iberia's movements are still uncertain.
During the Upper Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, a rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
was propagating from the spreading Central Atlantic along the continental margin of northwestern France towards Aquitaine
Aquitaine
Aquitaine , archaic Guyenne/Guienne , is one of the 27 regions of France, in the south-western part of metropolitan France, along the Atlantic Ocean and the Pyrenees mountain range on the border with Spain. It comprises the 5 departments of Dordogne, :Lot et Garonne, :Pyrénées-Atlantiques, Landes...
. This happened probably as early as the Tithonian
Tithonian
In the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
. As a consequence, the rift wedged Iberia southward and separated it from the Armorican Massif. In the wake, the continental crust was thinned and eventually oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
was beginning to form in the Middle Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
—the opening of the Bay of Biscay
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
was under way. Final oceanisation of the Bay of Biscay was achieved by Santonian
Santonian
The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
/Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
times (about 84 million years ago as witnessed by the magnetic polarity chron C 34). Paleomagnetic
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...
studies additionally show an anticlockwise 35° rotation of Iberia. The drifting motion of Iberia had taken up the entire Lower Cretaceous. Due to the rotational motion, the northeastern edge of Iberia started to interfere with Aquitania, first creating transtension
Transtension
Transtension is the term used to describe a rock mass or area of the Earth's crust that experiences both extensive and transtensive shear. As such, transtensional regions are characterised by both extensional structures and wrench structures ....
al pull-aparts along the North Pyrenean Zone in the Middle Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
. The crustal thinning associated with the transtensional rifting process led to HT/LP metamorphism in the North Pyrenean Zone, its onset being dated at about 108 million years ago. At the same time, the lherzolites were finally emplaced. The transcurrent motion along the North Pyrenean pull-apart zone was also accompanied by alkaline magmatism that lasted from the Middle Albian to the end of the Coniacian
Coniacian
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...
. The slow progression of the metamorphism into the west seems to imply a large sinistral shearing between Iberia and Aquitania, estimated as an offset of about 200 km (the metamorphism reached the Basque Country only about 80 million years ago in the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
).
By the beginning of the Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
about 90 million years ago, the transtensional regime had finished and was replaced by compression
Compression (geology)
In geology the term compression refers to a set of stresses directed toward the center of a rock mass. Compressive strength refers to the maximum compressive stress that can be applied to a material before failure occurs. When the maximum compressive stress is in a horizontal orientation, thrust...
. The rifting in the Basquo-Cantabrian, North Pyrenean, and Subpyrenean Basin had stopped and basin inversion set in; tensional faults were then being used as thrusts. This first rather weak compressional phase with very low shortening rates (less than 0.5 mm/year) lasted till the end of the Thanetian
Thanetian
The Thanetian is, in the ICS' Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between and . The Thanetian is preceded by the Selandian age and followed by the Ypresian age...
. On the Spanish side of the orogen, the first thrust sheets were emplaced (Upper Pedraforca, Bóixols, and Turbón thrust sheets).
In Ilerdian and Cuisian times (Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
/Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
boundary, Thanetian/Ypresian
Ypresian
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between and , is preceded by the Thanetian age and is followed by the Eocene Lutetian age....
, about 55 million years ago), the Pyrenees underwent very strong compression in the upper crust, bringing about the orogen's actual zonation and structural organisation. The orogen was squeezed into an asymmetric fan-like structure due to the aborted subduction of Iberia underneath Aquitania. This is inferred from the behaviour of the Mohorovicic discontinuity, which at the North Pyrenean Fault abruptly jumps from 30 to 50 km depth. This Pyrenean Main Phase lasted till about 47 million years ago (beginning of the Lutetian
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between and . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene subepoch...
), showing high shortening rates of 4.0 to 4.4 mm/year and emplacing for example the Lower Pedraforca and the Montsec thrust sheets.
After the Pyrenean Main Phase, other compressional deformational phases followed during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
and the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. Since the Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
, the orogen exhibits post-kinematic collapse (graben structures at its eastern end, volcanism near Olot) associated with the extension of the Golfe de Lion and the opening of the Valencia Trough. The orogen still undergoes strong erosion (since the Eocene), isostatic movements, post-kinematic extension, and even renewed compression (in the western Pyrenees) that can cause medium-sized earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s (a magnitude 5,1 earthquake near Arudy
Arudy
Arudy is a commune in the Pyrénées-Atlantiques department in south-western France.-References:*...
in 1980 and a magnitude 5,0 earthquake in 2006 near Lourdes
Lourdes
Lourdes is a commune in the Hautes-Pyrénées department in the Midi-Pyrénées region in south-western France.Lourdes is a small market town lying in the foothills of the Pyrenees, famous for the Marian apparitions of Our Lady of Lourdes occurred in 1858 to Bernadette Soubirous...
and other historic earthquakes which even destroyed parts of villages, e.g. a magnitude ≥ 6,0 earthquake near Arette
Arette
Arette is a commune in the Pyrénées-Atlantiques department in south-western France.-Geography:Arette is located in the arrondissement of Oloron-Sainte-Marie. It is one of the six communes of the canton of Aramits; the other five are Ance, Aramits , Féas, Issor et Lanne-en-Barétous...
in 1967, where 40% of the buildings were damaged and the church steeple collapsed).
Structural interpretations
The aforementioned asymmetric fan-like, flower-like structural organisation of the Pyrenean orogen has so far been interpreted as follows:- as a near-vertical collisional structure with the thrust-faults rooted in vertical faults.
- as an allochthonous orogen, with Iberia thrust over the Eurasian plate, i.e. Aquitania.
- as an allochthonous orogen, with Aquitania having overridden Iberia. The vertical faults are presumed to flatten at depth.
Current opinions favour Iberia subducting beneath Aquitania; this interpretation seems to be supported by the results of deeep seismic (ECORS) and magnetotelluric profiling across the orogen.
Estimates of the overall shortening across the pyrenean orogen are mostly between 100 and 150 km. Using the ECORS-data Muñoz (1992) arrives at 147 km of shortening with the subduction of the Iberian middle and lower crust taking up around 110 km. Further interpretations of the ECORS-data led to the recognition of a 50 km thick Iberian crust that was subducting beneath the 30 km thick Aquitanian crust. As a consequence, a low-angle intracrustal detachment level formed at 15 km depth, above the subducting middle and lower Iberian crust. Along this detachment, the rocks now making up the Axial Zone, the South Pyrenean Zone, and the Sierras Marginales were gliding southward and gradually ramping up to the surface. With continuing constriction, the Axial Zone buckled up into a south-directed antiformal stack. Towards the end of the subduction, a backthrust initiated near the actual trace of the North Pyrenean Fault, which was cutting upward into the Aquitanian crust by utilising its previously thinned, faulted nature. When the subduction process was finally blocked, parts of the northern Axial Zone and the North Pyrenean Zone with lower crustal fragments and lherzolites sandwiched in between were pushed back northward over the Subpyrenean Zone.
Sources
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- Chantraine J, Autran A, Cavelier C, et al. (1996): Carte géologique de la France au millionième. Éditions BRGM. Service Géologique National. ISBN 2-7159-2128-4.
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- Vergés J: Estudi geològic del vessant sud del Pirineu oriental i central. Evolució cinemàtica en 3D. (1999). Servei Geològic, Monografia Tècnica, no. 7, 192pp.