Santa Marta Formation
Encyclopedia
The Santa Marta Formation is a geologic formation
in Antarctica. It, along with the Mount Kirkpatrick Formation
and the Snow Hill Island Formation
, are the only formations yet known on the continent where dinosaur
fossils have been found. The formation outcrops on James Ross Island
off the coast of the northern tip of the Antarctic Peninsula
. In its entirety, the Santa Marta Formation is on average one kilometer thick.
and Campanian
ages of the Late Cretaceous
. It overlies the Gustav Group laid down during the Barremian
and Santonian ages and is succeeded by the Snow Hill Island Formation of late Campanian age. Together, the Santa Marta Formation, Snow Hill Island Formation, the overlying López de Bertodano Formation
(deposited from the late Campanian age of the Late Cretaceous to the early Paleocene
epoch of the early Paleogene
), and the Sobral Formation
(deposited during the early Paleocene
) form the Marambio Group.
Originally the formation was subdivided into three informal members termed the Alpha, Beta, and Gamma members. The names were later changed to the Lachman Crags, Herbert Sound, and Rabot members. The Lachman Crags and Herbert Sound members, named after the areas in which they outcrop, are found in the northern part of James Ross Island. Both members are late Campanian in age. The Lachman Crags Member, the older of the two, is around 500 meters thick. The lower section of the member consists of tuffaceous mudstone
while the upper section consists of tuffaceous turbidites formed by underwater avalanche
s. Bioturbation
is evident in tuff
beds throughout the member due to the disruption of sediments by benthic life
during the time of deposition. The Herbert Sound member is also around 500 meters thick and also can be divided into two distinct sections. Channeled debris flows
interbedded with turbides make up the lower portion of the member and are overlain by fine sandstone
s (followed by coarser sandstones and coquina
s) that make up the upper portion of the member.
The depositional environment
is thought to have been a system of abyssal fan
s radiating out from a large river delta
. The rapid aggradation
of sediments from the delta produced a steep delta slope, which may have resulted in occasional debris flows that formed the turbides. A high degree of tectonic activity in the region at the time may explain the intermittent tuff beds throughout the formation.
The Rabot Member of the Santa Marta Formation is confined to the southeastern part of James Ross Island and dates back to the early to late Campanian. Outcroppings of the member are separated from those of other members in the northern part of the island. Originally the member was regarded as its own formation, and now it is considered to be the lateral equivalent of both the Lachman Crags and Herbert Sound members. Like the Lachman Crags and Herbert Sound members, the Rabot member consists of mudstones and beds of tuff that are often highly bioturbated, and also consists of rare conglomerates
. Recently a fourth member has been assigned to the formation called the Hamilton Point Member. The beds of this member used to be considered part of the upper portion of the Rabot member, but now are considered to be their own distinct member.
s and dinoflagellate
s.
Invertebrates were also common. Fossils of ammonite
s can be found in the formation, often embedded vertically in the bedding plane. Originally it was thought that dead ammonites could only be oriented this way in sediment if they were in shallow waters below a certain pressure, but there is evidence to support that due to specific conditions during burial, it was possible for these ammonites to be vertically oriented at greater depths. Ammonite genera
present in the formation include Anagaudryceras
, Anapachydiscus
, Eupachydiscus
, Gaudryceras, Maorites, Natalites, Parasolenoceras, Yezoites
, and the heteromorph ammonites Ainoceras
, Eubostrychoceras
, Ryugasella and Baculites. Many bivalve fossils have been found such as Cucullaea, Panopea
, Pinna
, and Pterotrigonia. Polychaete
annelid
worms such as Rotularia and gastropods such as the cerithiid
sea snail
Cerithium
have also been discovered in beds within the formation.
Numerous ichnofossils
provide evidence of benthic activity, along with the bioturbated sediments previously mentioned. Vertical spreite trace fossils have been found as part of fodinichnia
dominated ichnocoenosis and were assigned to ichnogenre
such as Paradictyodora. Trackway
s thought to belong to decapods
have also been found.
Fish were present, including one of the first frilled sharks, Chlamydoselachus thomsoni. Other marine vertebrate
s included the small mosasaur
Taniwhasaurus antarcticus
, previously known as Lakumasaurus antarcticus. The close relation of T. antarcticus to other species of Taniwhasaurus found in New Zealand
and Patagonia
provides evidence for a Gondwana
n endemism.
Antarctopelta oliveroi
, an ankylosaur, was discovered in 1986 on the northern part of James Ross Island about 2 kilometers south of Santa Marta Cove in beds that were part of the Santa Marta Formation. It was the first dinosaur found in Antarctica. It may be a possible nodosaur
but there has been no formal phylogenic analysis
to prove its relationship with other ankylosaurs. Although the formation is made up of only marine deposits, the bodies of these animals along with other debris may have frequently been washed out to sea to later sink to the bottom and be buried by sediment.
Leaves and fragments of plants are commonly found as fossils throughout the formation as well as large tree trunks in the lower members. This is evidence of the forested environment that covered Antarctica during the Late Cretaceous due to the overall warmer global temperature and milder climate. At that time the river delta had much vegetation, and was able to support large herbivores such as Antarctopelta.
Geologic formation
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties...
in Antarctica. It, along with the Mount Kirkpatrick Formation
Mount Kirkpatrick Formation
The Mount Kirkpatrick Formation is one of only two major dinosaur-bearing rock formations yet found on the continent of Antarctica; the other is the Santa Marta Formation from the Late Cretaceous...
and the Snow Hill Island Formation
Snow Hill Island Formation
The Snow Hill Island Formation is a Late Cretaceous geologic formation. Dromaeosaur remains have been recovered from it.-External links:*...
, are the only formations yet known on the continent where 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...
fossils have been found. The formation outcrops on James Ross Island
James Ross Island
James Ross Island is a large island off the southeast side and near the northeastern extremity of Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north-south direction. It was charted in October 1903 by the Swedish...
off the coast of the northern tip of the Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
. In its entirety, the Santa Marta Formation is on average one kilometer thick.
Stratigraphy
The Santa Marta Formation was deposited during the SantonianSantonian
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...
and 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 ...
ages of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
. It overlies the Gustav Group laid down 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...
and Santonian ages and is succeeded by the Snow Hill Island Formation of late Campanian age. Together, the Santa Marta Formation, Snow Hill Island Formation, the overlying López de Bertodano Formation
Lopez de Bertodano Formation
The Lopez de Bertodano Formation is a geological formation in the James Ross archipelago of the Antarctic Peninsula. The strata date to the end of the Late Cretaceous , about 70-65 million years ago. Dinosaur remains are among the fossils that have been recovered from the formation....
(deposited from the late Campanian age of the Late Cretaceous to the early 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...
epoch of the early 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...
), and the Sobral Formation
Sobral Formation
The Sobral Formation is a palaeontological formation located in Antarctica. It dates to the Danian stage of the Lower Paleocene period.Spectacular fossils documenting the wildlife soon after the dinosaurs became extinct are found in this formation. One of the most significant sites is on Seymour...
(deposited during the early 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...
) form the Marambio Group.
Originally the formation was subdivided into three informal members termed the Alpha, Beta, and Gamma members. The names were later changed to the Lachman Crags, Herbert Sound, and Rabot members. The Lachman Crags and Herbert Sound members, named after the areas in which they outcrop, are found in the northern part of James Ross Island. Both members are late Campanian in age. The Lachman Crags Member, the older of the two, is around 500 meters thick. The lower section of the member consists of tuffaceous 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...
while the upper section consists of tuffaceous turbidites formed by underwater avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...
s. Bioturbation
Bioturbation
In oceanography, limnology, pedology, geology , and archaeology, bioturbation is the displacement and mixing of sediment particles and solutes by fauna or flora . The mediators of bioturbation are typically annelid worms , bivalves In oceanography, limnology, pedology, geology (especially...
is evident in 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...
beds throughout the member due to the disruption of sediments by benthic life
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...
during the time of deposition. The Herbert Sound member is also around 500 meters thick and also can be divided into two distinct sections. Channeled debris flows
Debris flow
A debris flow is a fast moving, liquefied landslide of unconsolidated, saturated debris that looks like flowing concrete. It is differentiated from a mudflow in terms of the viscosity and textural properties of the flow. Flows can carry material ranging in size from clay to boulders, and may...
interbedded with turbides make up the lower portion of the member and are overlain by fine 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 (followed by coarser sandstones and coquina
Coquina
Coquina is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of the shells of either molluscs, trilobites, brachiopods, or other invertebrates. For a sediment to be considered to be a coquina, the average size of the...
s) that make up the upper portion of the member.
The depositional environment
Sedimentary depositional environment
In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock...
is thought to have been a system of abyssal fan
Abyssal fan
Abyssal Fans, also known as deep-sea fans, underwater deltas, and submarine fans, are underwater structures that look like deltas formed at the end of many large rivers, such as the Nile or Mississippi Rivers. Abyssal fans are also thought of as an underwater version of alluvial fans.- Formation...
s radiating out from a large river delta
River delta
A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river...
. The rapid aggradation
Aggradation
Aggradation is the term used in geology for the increase in land elevation due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport...
of sediments from the delta produced a steep delta slope, which may have resulted in occasional debris flows that formed the turbides. A high degree of tectonic activity in the region at the time may explain the intermittent tuff beds throughout the formation.
The Rabot Member of the Santa Marta Formation is confined to the southeastern part of James Ross Island and dates back to the early to late Campanian. Outcroppings of the member are separated from those of other members in the northern part of the island. Originally the member was regarded as its own formation, and now it is considered to be the lateral equivalent of both the Lachman Crags and Herbert Sound members. Like the Lachman Crags and Herbert Sound members, the Rabot member consists of mudstones and beds of tuff that are often highly bioturbated, and also consists of rare 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...
. Recently a fourth member has been assigned to the formation called the Hamilton Point Member. The beds of this member used to be considered part of the upper portion of the Rabot member, but now are considered to be their own distinct member.
Flora and fauna
A wide variety of microorganisms inhabited the coastal waters at the time of the deposition of the Santa Marta Formation. Microfossils include ostracodOstracod
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 and dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...
s.
Invertebrates were also common. Fossils of ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
s can be found in the formation, often embedded vertically in the bedding plane. Originally it was thought that dead ammonites could only be oriented this way in sediment if they were in shallow waters below a certain pressure, but there is evidence to support that due to specific conditions during burial, it was possible for these ammonites to be vertically oriented at greater depths. Ammonite genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
present in the formation include Anagaudryceras
Anagaudryceras
Anagaudryceras is an extinct genus of cephalopod belonging to the Ammonite family Gaudryceratidae.-References:* Accessed on 9/24/07...
, Anapachydiscus
Anapachydiscus
Anapachydiscus is an extinct cephalopod genus from the Upper Cretaceous, Coniacian - Maastrichtian of Europe, Africa, Madagascar, S.India, N Z, Calif. Mexico, Argentina, and the antarctic belonging to the ammonoid family Pachydiscidae....
, Eupachydiscus
Eupachydiscus
Eupachydisus is a large, coarse-ribbed Pachydiscid ammonite genus from the Upper Cretaceous, found in Coniacian to Campanian age strata in Europe, Madagascar, Japan, and British Columbia....
, Gaudryceras, Maorites, Natalites, Parasolenoceras, Yezoites
Yezoites
Yezoites is an extinct genus of cephalopod belonging to the Ammonite subclass....
, and the heteromorph ammonites Ainoceras
Ainoceras
Ainoceras is a genus of extinct, aberrantly coiled ammonite cephalopod that live in the Pacific Ocean during the Campanian division of the Cretaceous, where Japan is today...
, Eubostrychoceras
Eubostrychoceras
Eubostrychoceras is a genus of helically wound, corkscew form, heteromorph ammonite which lived during the Upper Cretaceous . The genus is included in the ancycleratid family Nostoceratidae....
, Ryugasella and Baculites. Many bivalve fossils have been found such as Cucullaea, Panopea
Panopea
In Greek mythology, Panopea and Panope were two of the Nereids.Asteroid 70 Panopaea is named after one of them.Panope is also the name of one of the daughters of Thespius and Megamede. She bore Heracles a son, Threpsippas....
, Pinna
Pinna (genus)
Pinna is a genus of pen shells. It is a cosmopolitan genus of bivalve molluscs characterized by elongated, wedge-shaped shells which most commonly stand point-first in the sea bottom in which they live, anchored by a net of byssus threads....
, and Pterotrigonia. Polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
worms such as Rotularia and gastropods such as the cerithiid
Cerithiidae
Cerithiidae, common name the cerithiids or ceriths, is a large family of medium-sized marine gastropods in the clade Sorbeoconcha.- Distribution :...
sea snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
Cerithium
Cerithium
Cerithium is a genus of small to medium-sized sea snails, marine gastropod mollusks in the family Cerithiidae, the ceriths. The genus is known from the Cretaceous to the Recent periods.- Species :Species within this genus include:...
have also been discovered in beds within the formation.
Numerous ichnofossils
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
provide evidence of benthic activity, along with the bioturbated sediments previously mentioned. Vertical spreite trace fossils have been found as part of fodinichnia
Fodinichnia
Fodinichnia are trace fossils formed by deposit feeders as they excavate the sediment in search of food. They tend to have repeated patterns or spreites , the shape reflecting the systematic feeding strategy used by the organism as it scours the sediment...
dominated ichnocoenosis and were assigned to ichnogenre
Ichnotaxon
An ichnotaxon is defined by the International Code of Zoological Nomenclature as "a taxon based on the fossilized work of an organism", that is, the non-human equivalent of an artifact. Ichnotaxa are names used to identify and distinguish morphologically distinctive ichnofossils, more commonly...
such as Paradictyodora. Trackway
Fossil trackway
A fossil trackway is a type of trace fossil, a trackway made by an organism. Many fossil trackways were made by dinosaurs, early tetrapods, and other quadrupeds and bipeds on land...
s thought to belong to decapods
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
have also been found.
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s included the small mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
Taniwhasaurus antarcticus
Taniwhasaurus
Taniwhasaurus is an extinct genus of mosasaur, a carnivorous, marine reptile which inhabited New Zealand, Japan and Antarctica. The genus was a close relative of the genera Tylosaurus and Hainosaurus.-Species:-T...
, previously known as Lakumasaurus antarcticus. The close relation of T. antarcticus to other species of Taniwhasaurus found in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
provides evidence for a 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,...
n endemism.
Antarctopelta oliveroi
Antarctopelta
Antarctopelta was a genus of ankylosaurian dinosaur with one known species, A. oliveroi, which lived in Antarctica during the Late Cretaceous Period. It was a medium-sized ankylosaur, reaching no more than 4 meters in length, and showed characteristics of two different families, making more...
, an ankylosaur, was discovered in 1986 on the northern part of James Ross Island about 2 kilometers south of Santa Marta Cove in beds that were part of the Santa Marta Formation. It was the first dinosaur found in Antarctica. It may be a possible nodosaur
Nodosauridae
Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous Period of what are now North America, Asia, Antarctica and Europe.-Characteristics:...
but there has been no formal phylogenic analysis
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
to prove its relationship with other ankylosaurs. Although the formation is made up of only marine deposits, the bodies of these animals along with other debris may have frequently been washed out to sea to later sink to the bottom and be buried by sediment.
Leaves and fragments of plants are commonly found as fossils throughout the formation as well as large tree trunks in the lower members. This is evidence of the forested environment that covered Antarctica during the Late Cretaceous due to the overall warmer global temperature and milder climate. At that time the river delta had much vegetation, and was able to support large herbivores such as Antarctopelta.