Marcellus Formation
Encyclopedia
The Marcellus Formation is a unit of marine sedimentary rock
found in eastern North America
. Named for a distinctive outcrop
near the village of Marcellus
, New York
in the United States
,
it extends throughout much of the Appalachian Basin.
The shale contains largely untapped natural gas
reserves, and its proximity to the high-demand markets along the East Coast of the United States
makes it an attractive target for energy development
.
Stratigraphically
, the Marcellus is the lowest unit of the Devonian
age Hamilton Group, and is divided into several sub-units. Although black shale
is the dominant lithology
, it also contains lighter shales and interbedded limestone
layers due to sea level variation during its deposition
almost . The black shale was deposited in relatively deep water devoid of oxygen
, and is only sparsely fossiliferous. Most fossils are contained in the limestone members, and the fossil record in these layers provides important paleontologal
insights on faunal turnovers
. The black shales also contain iron ore that was used in the early economic development of the region, and uranium
and pyrite
which are environmental hazards. The fissile
shales are also easily eroded
, presenting additional civil
and environmental engineering
challenges.
beds
and concentrations of iron pyrite
(Fe
S
2) and siderite
(FeCO3
).
Its sedimentary structure, or bedding, is moderately well developed. Like most shales, it tends to split easily along the bedding plane, a property known as fissility
.
Lighter colored shales in the upper portion of the formation tend to split into small thin-edged fragments after exposure.
These fragments may have rust
stains from exposure of pyrite to air, and tiny gypsum
(Ca
SO4
·2H2O
) crystals from the reaction between pyrite and limestone particles.
Fresh exposures of the pyriteiferous shale may develop the secondary mineralization
of orange limonite
(FeO
(OH
)·nH2O), and the pale yellow efflorescence
or bloom of sulfur
, associated with acid rock drainage.
Pyrite is especially abundant near the base,
and the upper contacts of limestones, but framboid
al microcrystals and euhedral
crystals of pyrite occur throughout the organic-rich deposits.
The Marcellus also contains uranium
,
and the radioactive decay
of the uranium-238
(238U) makes it a source rock
for radioactive radon
gas (222Rn).
Measured total organic content of the Marcellus Formation ranges from less than 1% in eastern New York, to over 11% in the central part of the state,
and the shale may contain enough carbon to support combustion
.
The more organic-rich black shales can be bituminous, but are too old to contain bituminous coal
formed from land plants.
In petroleum geology
, these black shales are an important source rock
that filled conventional petroleum reservoirs in overlying formations, are an unconventional shale gas
reservoir, and are an impermeable seal that traps underlying conventional natural gas
reservoirs.
To the west the formation may produce liquid petroleum
; further east heating during deeper burial more than 240 million years ago cracked
this oil into gas.
region of the northern Appalachian Basin of North America. In the United States, the Marcellus shale runs across the Southern Tier
and Finger Lakes
regions of New York
, in northern and western Pennsylvania
, eastern Ohio
, through western Maryland
, and throughout most of West Virginia
extending across the state line into extreme western Virginia
. The Marcellus bedrock in eastern Pennsylvania extends across the Delaware River
into extreme western New Jersey
. It also exists in the subsurface of a small portion of Kentucky
and Tennessee
. Below Lake Erie
, it can be found crossing the border into Canada
, where it stretches between Port Stanley
and Long Point to St. Thomas
in southern Ontario
.
The Marcellus appears in outcrops along the northern margin of the formation in central New York. There, the two joint planes in the Marcellus are nearly at right angles, each making cracks in the formation that run perpendicular to the bedding plane, which lies almost level.
These joints form smooth nearly vertical cliff
s, and the intersecting joint planes form projecting corners in the rock faces.
Once exposed, the weathered faces lose most of their organic carbon,
turning from black or dark gray to a lighter shade of gray.
Outcrops of the Marcellus can contain very small beds that resemble coal
. The New York outcrops, and others further south in Pennsylvania and New Jersey, were extensively excavated in the early 19th century, sometimes at great expense, in the false hope of finding minable coal seams.
In Perry County, Pennsylvania
along the Juniata River
the false coal beds become up to 0.3 m (0.984251968503937 ft) thick, but they did not produce a valuable fuel, despite the considerable effort expended to mine it from the surrounding hills.
Seaweed
and marine plants probably formed the false coal. True coal is formed from terrestrial plants, which only began to appear in Marcellus and later fossils.
Close proximity to the surface of Marcellus bedrock south of the New York outcrops makes an east-west band running through the city of Syracuse
a high-risk area for radon as an indoor air pollutant
. From the surface exposures along the northern and eastern margins, the formation descends to depths of over 2700 m (8,858.3 ft) below the surface in southern Pennsylvania.
Ridge-and-Valley Appalachians
, including exposures on the flanks and axis of the Broad Top Synclinorium in south central Pennsylvania. Exposed beds are nearly horizontal on the Allegheny Plateau, but upturned to form slightly overturned beds found along the Allegheny Front
.
From Wind Gap, Pennsylvania
heading south, the dip
of the beds steepens, becoming vertical at Bowmanstown
on the Lehigh River
. Nearby, in the Lehigh Gap area of Pennsylvania, the Marcellus is extensively faulted,
and the beds are steeply overturned, with a reverse dip
angle of up to 40° south.
The Marcellus Shale and the fine-grained shales near the middle of the Mahantango Formation are classified by geologists as slope-former
s.
Marcellus and Mahantango shale beds dipping at 60° to 75° to the west form the west facing slopes of Tonoloway Ridge
on the west flank of the Cacapon Mountain
anticline
in the Eastern Panhandle of West Virginia
.
On the eastern limb of this anticline, beds of these shales dipping to the east at a shallower angle also form the steep slopes on the east side of Warm Springs Ridge.
, and is also found underlying low areas between some Appalachian ridges, forming linear valleys of moderate relief. These bedrock surfaces are typically covered with colluvium
from erosion of stratigraphically higher and more erosion-resistant strata that form the surrounding higher ground. The soils formed from the Marcellus and the overlying Hamilton shales are deep, free of stones, and well suited for agriculture
.
Sampling of soil formed on the Marcellus bedrock showed the dominant mineralogy
consisted of quartz
, illite
, montmorillonite
, muscovite
, and biotite
, with phases of todorokite
and trona
appearing at depths closer to the bedrock.
Upturned beds of the soft shale also capture streams and rivers with relatively straight segments in strike valleys such as the Aquashicola Creek
and McMichael Creek
at the foot of The Poconos
,
and the long, straight section of the Lost River
in West Virginia.
Below Port Jervis, New York
, the Walpack Ridge deflects the Delaware River
into the Minisink Valley, where it follows the southwest strike
of the eroded Marcellus beds along the Pennsylvania – New Jersey state line for 40 km (25 mi) to the end of the ridge at Walpack Bend in the Delaware Water Gap National Recreation Area
.
The Minisink is a buried valley
where the Delaware flows in a bed of glacial
till
that buried the eroded Marcellus bedrock during the last glacial period. This buried valley continues along the strike of the Marcellus southwest from the bend through Stroudsburg, Pennsylvania
, and northeast from Port Jervis toward the Hudson River
,
along the route of the Delaware and Hudson Canal
.
, as the Acadian Mountains were rising up, the black and gray shales of the Hamilton Group began accumulating as erosion of the mountains deposited terrigenous
sediments from the land into the sea.
The Marcellus Shale was formed from the very first deposits in a relatively deep, sediment- and oxygen-starved (anoxic
), trough
that formed parallel to the mountain chain.
These clastic fragments of rock were carried in braided streams to the ancient Catskill Delta
, a river delta
probably similar to the present day Niger Delta
of Africa.
Smaller particles remained suspended
longer in this epeiric sea
, flowing offshore as turbidites in a slow but persistent underwater avalanche. They finally came to rest at the bottom of the Acadian foredeep in the Appalachian Basin, hundreds of meters from shore, at depths that may have been 150 m (492.1 ft) or more beneath the surface.
Alternatively, the basin may have been as shallow as 50 metres (164 ft) or less, if the warm water was sufficiently stratified
so that oxygen rich surface water did not mix with the anoxic bottom water.
The Marcellus deposition produced a transgressive black shale,
because it was deposited in deepening conditions when the basin floor dropped as the mountains rose up.
The dark shale facies
of the Marcellus were formed from flysch
, a fine mud deposited in the deep water; it buried the underlying Onondaga limestone beds,
as the deepening sea cut off the supply of carbonates that form limestone.
Organic matter, probably dominated by plankton
, also settled to the bottom, but the normal aerobic decay
process was inhibited in the anaerobic
environment thereby preserving the organic carbon.
Uranium was also incorporated in these organic muds syndepositionally,
meaning it was deposited at the same time, rather than being introduced to the formation later.
The organic matter scavenged trace elements from the seawater,
including the redox
-sensitive elements uranium, rhenium
, molybdenum
, osmium
, chromium
, and selenium
.
The Marcellus was deposited during a period of development of land plants
, when atmospheric oxygen was increasing, resulting in a reduction of carbon dioxide in the atmosphere, and the seawater where it was deposited.
Named members of the Marcellus reflect two composite depositional sequences,
with a general coarsening upward cycle that continues into the base of the overlying Mahantango Formation.
The interbedding of lighter shale and limestone members is attributed to relatively short-term oscillations in basin depth.
Later deep water depositional sequences formed the overlying Brallier Formation
and Harrell Formation
.
period, in the Paleozoic
era, of the Phanerozoic
eon. Radiometric dating of a Marcellus sample from Pennsylvania placed its age at 384 million years old, and a sample from the bentonite at the top of the Onondaga at 390 ± 0.5 million years old.
Relative age dating of the Marcellus places its formation in the Cazenovia subdivision of the Givetian faunal stage
, or 391.9 to 383.7 million years ago (Ma).
The Union Springs member, at the base of the Marcellus in New York, has been dated to the end of the Eifelian, the stage which immediately preceded the Givetian.
Anoxic dark shales in the formation mark the Kačák Event,
a late-Eifelian-stage
marine anoxic event
also associated with an extinction event
.
, begun in 1836, Henry Darwin Rogers
classified the Marcellus as the "Cadent Lower Black Slate" which he numbered "No. VIII b." In the first New York State Geological Survey, also begun that year, James Hall
established the term "Marcellus Shale" in his 1839 report titled "Marcellus Shales in Seneca County." Professor Hall also argued in 1839 against formulating geological names based on observed characteristics that may vary from place to place or need revision in the future, and in favor of location-based nomenclature where "the rock or group will receive its name from the place where it is best developed." His arguments proved persuasive, and the location-based name for this, and many of the other group names he published based on exposures in New York, were adopted in the second Pennsylvania survey, and are now widely accepted.
In current practice, the Marcellus Formation (abbr. Dm or Dms) is classified as the basal unit of the Hamilton Group
(Dh), lying beneath the Mahantango Formation
(Dmh) member of this group in Pennsylvania and Maryland. In New York, the Mahantango, also of Middle Devonian age, is further divided. There the Marcellus is separated from the overlying Skaneateles Formation, a more clastic and fossiliferous dark shale, by the thin Stafford or Mottville Limestone bed.
In West Virginia, the Marcellus may be separated from the brown shales of the Mahantango by occasional sandstone
beds and concretions,
or it may lie directly below the younger Late Devonian Harrel Formation (or its lateral equivalents) because of a disconformity, which represents a gap in the geological record due to a period of erosion or non-deposition.
In eastern Ohio the Hamilton Group also lies disconformably beneath the Rhinestreet Shale Member of the West Falls Formation, another transgressive black shale tongue with similar characteristics to the Marcellus.
, the Marcellus overlies the Dundee Formation, a lateral equivalent of the Onondaga.
In Pennsylvania, the Marcellus forms a sharp conformable
contact with the Onondaga's Selinsgrove Limestone member.
A thin pyrite-carbonate bed is also found at the base of the Marcellus black shale in the exposures of south central Pennsylvania, above a thin calcerous green shale bed, which lies upon the Onondaga limestone.
In eastern New York, the contact between the Marcellus and Onondoga (where present) is gradational.
In western New York, the Union Springs member of the Marcellus conformably overlies the Seneca member of the Onondaga Limestone,
or the stratigraphically higher Cherry Valley Limestone member may rest directly and unconformably upon the Onondaga in the absence of the Union Springs shale.
The local disappearance of units of the Onondaga suggests that its upper contact with the Marcellus can be erosional.
In Erie County
in western New York, both the upper and lower contact of the Marcellus are eroded away.
In eastern West Virginia the Marcellus overlies the Onesquethaw Group, consisting of the dark gray or green, calcitic, mostly nonfissil Needmore Shale, which grades westward into the Huntersville Chert.
To the south and west, the Hamilton Group grades laterally into the Millboro Shale formation in southern West Virginia and Virginia,
which grades into the lower part of the Chattanooga Shale of Tennessee
.
The Milboro is gradational with the underlying Needmore Formation shale.
South of the Mason-Dixon line
, due to the difficulty in differentiating the Millboro and Needmore shales with the limited exposures available,
and initial uncertainty in correlation with the New York survey, they were mapped as the Romney Formation, a unit containing all the Middle Devonian strata,
named for an exposure at Romney, West Virginia
.
The correlations were established by 1916 through tracing the New York exposures across Pennsylvania and Maryland into West Virginia, so under the principle of scientific priority
,
the Romney classification is now obsolete; but its Marcellus and underlying Needmore shale members are still found grouped in an undifferentiated map unit (Dmn).
Tioga metabentonite or K-bentonite
–stratigraphic unit about 0.6 m (2 ft) thick that consists of several discrete, relatively thin volcanic ash
falls–is also included at the base of the Marcellus in eastern Pennsylvania.
In 1843 it was described without being named by Hall,
and more than 100 years passed before it was eventually named for the natural gas field
in Tioga County, Pennsylvania
,
where it was encountered when drilling
gas wells
. It is a regional stratigraphic marker,
used by geologists to identify the Marcellus,
and correlate laterally equivalent strata. Difficulty in correctly identifying the more than 80 different ash falls during the Devonian period, collected in 15 or more beds, has also led to many miscorrelations.
From Virginia to New York the Tioga is widely distributed, running across the central and northern parts of the Appalachian basin,
an areal extent exceeding 265000 km² (102,317.1 sq mi).
Explosive eruption
s associated with the Acadian orogeny
originating near present-day central Virginia released the ash into the atmosphere.
It was dispersed across the Appalachian, Michigan
, and Illinois
Basins by the southern trade winds, because this area was in the southern hemisphere during the Devonian period.
The volcanic origin of the ash is evidenced by its distinctive mineralogy
–the ash was deposited directly upon the water, so its angular quartz grains differ from the clastic sediments rounded through the erosion process that carries them to the sea. As the volcanic ash settled to the bottom, it was admixed
with these terrigenous components, producing a distinctive lithology in the sedimentary rock.
The Tioga may appear in the formation as a gray, brown, black, or olive bed, or parting,
consisting of coarse crystal tuff
or tuffaceous shale,
thinly laminated, with sand-sized mica flakes.
The Tioga ash bed zone consists of eight ash beds labeled according to their stratigraphic order from A (oldest) to H (youngest),
and another bed known as the Tioga middle coarse zone.
Its basal beds are found within the uppermost beds of the Onondaga Limestone or Needmore Shale, and the uppermost ash bed within the lowermost part of the Marcellus or Millboro Shale.
In western New York state, the Tioga Ash Bed B marks the boundary between the Moorehouse and Seneca Members of the Onondaga Formation,
but in the central part of the state, and the southern part of the basin, the ash beds are actually in the Marcellus.
This indicates that deposition of the Marcellus there began earlier,
since the ash beds represent a single epoch in geologic time.
In West Virginia, the Marcellus Formation is as much as 60 m (196.9 ft) thick.
In extreme eastern Pennsylvania, it is 240 m (787.4 ft) thick,
thinning to the west, becoming only 15 m (49 ft) thick along the Ohio River
, and only a few feet in Licking County, Ohio
.
The thinning, or stratigraphic
convergence, from east to west is caused by decreasing grain size in the clastic deposits, which entered the basin from the east.
The beds finally "pinch out" westward because deposition was limited by the Cincinnati Arch,
the bulge that formed the west shore of the basin. Where the formation is relatively thick, it is divided into several members, and as the formation continues to thicken to the east, these members are further divided. Some workers chose to classify the Marcellus as a subgroup, and classify some of the members as separate formations.
divides the Marcellus in eastern Pennsylvania.
The Purcell is stratigraphically equivalent to the Cherry Valley Limestone member in New York,
a bioclast
ic packstone, consisting of skeletal limestones, with shaly intervals between its lower massive limestone layer, thick nodular limestone/marlstone, and upper limestone layer.
Other named members include the Bakoven Shale, Cardiff Shale, Chittenango shale, Solsville sandstone, Union Springs shale and limestone, and Stony Hollow shale and limestone. The Union Springs, Cherry Valley, and Oatka Creek merge beneath Lake Erie, into the Bell Shale, Rockport Quarry Limestone, and Arkona Shale of Ontario.
The Union Springs is an organic-rich, pyritiferous, thinly bedded, blackish gray to black shale with mudstone concretionary layers, and thin silt bands at the bottom. To the east, it becomes the Bakoven Member, a darker, less organic shale with fewer limestone layers. To the west the Union Springs beds thin, with its upper limestones merging with the overlying calcareous
Cherry Valley Member. A regional unconformity appears in western New York, as the Union Springs lenses in and out, and then reappears in northwest Pennsylvania and northeast Ohio between the Onondaga and Cherry Valley.
In Western and central New York, the uppermost member is the dark grey to black organic-rich Oatka Creek shale. Unlike the other Devonian shales in this region, the gray shale at the top of the Oatka Creek thickens gradually to the west, as well as the east,
where it divides into the Cardiff member lying above the Chittenango member in central New York.
Organic-rich, fissile, sooty black shales make up the Chittenango Member.
At the base of the Chittenango,
above the Bierne Member shale,
lies the Halihan Hill Bed, a highly bioturbated
bioclastic limestone.
Further east, the homogeneous Cardiff divides into the Bridgewater, Solsville, and Pecksport shale members, from base to top. The Bridgewater is a fissile dark silty shale with relatively rare fossils. A thin concretionary zone lies above, then the Solsville grades from a gray calcareous shale, to sandy siltstones and fine sandstones at the top, with the gray shale of the Pecksport shale and siltsone overlying it.
In south central Pennsylvania, the Marcellus is mapped with three members, from top to base: The Mahanoy Member (Dmm), a dark gray to grayish black silty shale and siltstone; the Turkey Ridge Member (Dmt), an olive to dark-gray fine to medium grained sandstone; and the Shamokin Member (Dms), a dark gray to grayish black fissile carbonaceous shale that is calcareous in places near the base. The Turkey Ridge is commonly mapped in the Mahantango Formation, or included in the Montebello Formation (Dmot), and only the Shamokin correlates with the Marcellus on adjacent map sheets. In extreme eastern Pennsylvania, the Broadhead Creek member, a dark gray silty shale with dark gray shaly limestone concretions, appears above the Stony Hollow and Union Springs, in a layer up to 275 m (902 ft) thick.
found in the Marcellus, but these fossils are still important to paleontology. For example, the Marcellus contains the oldest known diverse collection of thin-shelled mollusks still having well preserved shell microstructure.
It is also where goniatites
, an extinct shelled swimmer similar to a squid, make their first appearance in the fossil record.
Life on land also enters the fossil record in the Marcellus, with the trunks of branchless conifer trees that floated out to sea to be preserved in the black shale.
Marcellus fossils include specimens of the large clam-like brachiopod
Spinocyrtia.
External molds of crinoid
s, plant-like animals related to starfish also known as "sea lilies,"
are found in the formation,
with the molds partially filled with limonite
; brachiopod and bivalve (clam) molds have also been found in the shale.
Small conical tentaculitid
s are commonly found in the Chittenango Member.
The Halihan Hill bed contains styliolinids and macrofauna including brachiopods, coral-like bryozoans, small bivalves and gastropods (snails),
incorporated after the faunal turnover
when Emsian and Eifelian Schoharie/Onondaga fauna were replaced by the Givetian Hamilton fauna.
The Solsville member contains well preserved bivalves, gastropods, and brachiopods. These shellfish lived in the benthic zone
at the bottom of marginal marine to open marine environments that existed west of the ancient Catskill Delta
.
The fossil record in this member shows the base was dominated by deposit feeders, while the upper layers were dominated by filter feeder
s. This can be correlated to the lithology: the finer sediments of the shales at the base of this member would contain abundant adherent organic matter for deposit feeders, but would tend to foul the gills of filter feeders when suspended; the coarser sediments of the sandstones at the top would have contained less organic matter to support deposit feeders.
Below the Solsville, at the base of the Otsego in eastern New York, a coral bed
is found; another coral bed can be seen at the top of the Marcellus near Berne, New York
.
A diverse, eel-like conodont
fauna occurs in the limestone of the Cherry Valley Member,
which is also known for its rich nautiloid
and goniatite cephalopod
fauna.
Originally named the Goniatite Limestone,
it produces their fossilized remains with shells that can be larger than 0.3 metre (0.984251968503937 ft) across.
It also contains the "Cephalopod Graveyard" in the Schoharie Valley
of eastern New York, an unusual accumulation of abundant coiled and straight shells of several types of large adult cephalopods. This bed lacks juvenile fossils, indicating that if their behavior was similar to modern squid, this may have been an area where these Devonian cephalopods reproduced and died.
This stratigraphic interval also provides an excellent example of incursion epiboles, which are sudden appearances and disappearances of fossil taxa
in relatively thin sections of the rock unit. In the Cherry Valley, the taxa do not reoccur; instead each thin concretionary limestone bed contains different species of goniatites.
The Cherry Valley and Union Springs also contain well-preserved anarcestida.
reserves in this formation.
The gas is produced by thermogenic decomposition
of organic materials in the sediments under the high temperature and pressure generated after the formation was buried deep below the surface of the earth. The rock holds most of the gas in the pore spaces of the shale, with vertical fractures or joints providing additional storage as well as pathways for the gas to flow; gas is also adsorbed on mineral grains,
and the carbon in the shale.
The United States Geological Survey
had estimated that the Marcellus contained only 54 km³ (1,906,991,975,483.7 cu ft) (where x1012 = trillion, and is referred to as 1.9 TCF) of technically recoverable natural gas in a 2002 publication. In April 2009, the United States Department of Energy
estimated the Marcellus to contain 262 TCF of recoverable gas.
State University of New York at Fredonia
geology
professor Gary Lash has calculated that more than 14000 km³ (494,405,326,977,258 cu ft) (490 TCF) of natural gas
may be contained in the Marcellus black shale beds that lie between New York state and West Virginia. At the present level of technology, he believes approximately 10% of this – 1400 km³ (49,440,532,697,725.8 cu ft) (49 TCF) – could be recovered. This is enough to satisfy approximately two years' of total U.S. consumption, or a total value of two hundred billion dollars at winter 2010 – spring 2011 wellhead prices. That figure is part of an increase of as much as approximately one trillion United States dollar
s in the value of all recoverable reserves in the US attributable to improved recovery through vertical drilling and fracking.
During the 2012 presidential campaign, GOP Primary Candidate Rick Perry
cited a study funded by the Marcellus Shale Coalition that fracking the Romney Formation is expected to create a quarter million jobs under the current policies of the Obama administration.
geosciences professor called his estimate of 4800 km³ (169,510,397,820,774 cu ft) (170 TCF) conservative. In November 2008, based on drilling results, Engelder increased his estimate of the amount of natural gas in the Marcellus to 363 TCF of recoverable resource, which would be enough to supply U.S. consumption for at least fourteen years. That estimate assumed some acreage in the Marcellus would not be gas bearing. If the entire formation did contain gas, Engelder said the formation could contain 4,359 TCF. Assuming a 30% recovery rate, this would lead to a 1,307 TCF.
Before 2000, low production gas wells were completed to the Marcellus, but these had a low rate of return
, requiring a relatively long capital recovery period, although they did have a very long productive life. There are wells in Tioga and Broome County, NY which are 50 years old or more.
Now, to extract the shale gas
at more commercially viable rates, directional drilling
is done to depths of 7000 to 10000 ft (2,133.6 to 3,048 m) underground to reach the formation, and then water and a mixture of chemicals is pumped into the rock under high pressure in a process known as hydraulic fracturing
to release the gas from the low permeability shale.
Although hydraulic fracturing has been used since the middle of the 20th century, its use in horizontal wells in laterally extensive shale formations was perfected around the turn of the 21st century outside Fort Worth, Texas
to tap the reserves in the Barnett Formation
shales of the Bend Arch-Fort Worth Basin
, that are now the most prolific source of unconventional gas in the continental United States. The Marcellus covers several times more area, stretching 600 miles (965.6 km), compared to a linear extent of only 170 miles (273.6 km) for the Barnett.
Several companies, many that have specialized in tapping the Barnett, are working to do the same in the Marcellus. As of 2008, only a few new hydro fractured wells tapping the Marcellus reserves were actually in operation, with at least one reported to be producing more than 3 million cubic feet (85 thousand m³) per day. Engelder, who has studied natural rock fractures in this area for more than 25 years, also suggested drilling horizontally through the Marcellus shale perpendicular to these vertical fractures, to exploit these natural features for increased production. Early results show that horizontal wells in this formation are producing gas at a rate more than double that of vertical wells, and at slightly lower cost overall, despite the much higher initial cost of drilling.
Since parts of this region have been producing gas from wells drilled to the deeper Oriskany Formation sandstone, older wells that are no longer viable can be reused, either by fracturing the Marcellus layer in the existing well bore, or by refinishing the bore using horizontal drilling into the Marcellus. Re-use of the existing infrastructure has both environmental as well as economic benefits, because in addition to avoiding development of new drilling sites and wells, existing transportation facilities can be reused.
Lower transportation costs to the high demand markets on the East Coast of the United States
generate a US$0.35 per thousand cubic feet price premium over the Henry Hub
price, compared to a discount of as much as $1.50 for gas produced in the Rocky Mountains
.
However, heavy trucks and tankers crack the pavement and cause potholes. Such road damage is expensive for municipalities to repair. Engineers in Pennsylvania Department of Transportation have documented damage caused by the heavy trucks and tankers. Damages include but are not limited to the crushing of drain pipes, potholes, rutting, and other such pavement fatigue failures. The cost of these repairs are often much higher than the Pennsylvania Department of Transportation is allowed to charge for use of the roads. In addition to causing road damage, when heavy trucks and tankers drive over farmland, they compact the subsoil, which increases runoff and decreases crop productivity for years. Ecologists also have concerns about the ecological impact on forests when trees are cut down to make way for access roads. Ornithologists have already documented declining populations of woodland birds.
Environmental concerns around the drilling and extraction processes have sparked opposition to development of this resource. One concern is the release to the environment of underground naturally occurring radioactive material
through the drilling fluids and equipment. The hydraulic fracturing process also uses large quantities of surface water.
A large portion of the formation underlies the environmentally sensitive Chesapeake Bay Watershed as well as the Delaware River Basin. The Delaware River Basin Commission
holds regulatory jurisdiction in this watershed that houses much of the Marcellus Shale formation of any operations which involve water usage, extraction, or potential contamination. They have recently made a "Determination" which requires that any component of a hydro-fracing operation that is to take place within the boundaries of their Special Protection Waters must be permitted by the DRBC, regardless of whether or not the operation was previously subject to permitting.
Chesapeake’s (The gas Company) countered with a No-Drilling Pledge for the NYC watershed area, and five miles around the watershed, however, opposes any legislation like that presented by Jim Brennan, D-Brooklyn (Brooklyn, NY), October 2009. The Susquehanna River Basin Commission
, which oversees this other portion of the watershed, and the Pennsylvania Department of Environmental Protection
, issued orders to suspend operations at several wells in May 2008 because surface water was being diverted by the drillers without the necessary permits, and precautions to protect streams from contaminated runoff were questioned. The practices of "land men" who acquire leases for drilling and extraction rights have also been widely questioned.
New York City under the New York City Gas Fuel Code made it illegal to drill within city limits. Pennsylvania is following this trend, Pittsburgh on November 16, 2010 became the first city in Pennsylvania to ban hydrofracking within city limits.
Researchers at the University of Pittsburgh recently released a study showing that "7 percent of Allegheny County’s land has been leased for drilling and extraction since 2003" and the number of properties in the county leased for oil and gas exploration has grown exponentially in recent years.
It is alleged that gas drilling in Northeast Pennsylvania caused methane to infiltrate up to 15 homes in Dimock Township, Susquehanna County, via groundwater contamination. This conclusion came from the Pennsylvania Department of Environmental Protection, though it is disputed by Cabot Oil & Gas Corp which was cited for causing the contamination. It is also disputed by other long-term area residents who have noted that high methane levels had been present for more than 60 years prior to hydrofracking in Dimock. Northeast Pennsylvania is not the only place to experience groundwater contamination following commencement of gas drilling operations.
-carbonate
bed between the carbonaceous black shale and a green calcareous shale bed, pyrite, carbonate, and groundwater reacted to form gossan
iron oxide
and gypsum
.
As far as the ground water necessary for the conversion could penetrate, the pyrite-carbonate was converted to a usable brown hematite
iron ore along the outcrops and near the bedrock surface.
The Marcellus iron ore was actively mined in south Central Pennsylvania from its discovery in the late 18th century, until it was supplanted by the rich ore beds of the Iron Range
of Minnesota
in the early 20th century.
The ore was easily located and worked from shallow pits and shafts, but once the usable upper deposits were removed, or if a mine shaft entered the bed too far below the surface, only unusable unconverted pyritic deposits were found.
Hematite ore was converted to pig iron
in charcoal
-fired stone blast furnace
s that were constructed throughout the Juniata River
region near the workable ore deposits from the Marcellus and other formations.
Iron products from this area, known as "Juniata Iron," were produced during the period between the American Revolution
and the American Civil War
. These blast furnaces were important to the economy of the region at the time,
but the cold blast
stone furnaces typically employed were inefficient, and consumed significant amounts of timber from the nearby hardwood forests, which ultimately led to their demise. A typical furnace used 2400 kg (5,291.1 lb) of hematite ore and 7.3 cubic metre of charcoal to produce 910 kg (2,006.2 lb) of pig iron, and could produce several thousand pounds per day, which required logging more than 4000 m² (0.988420652061104 acre) of forest daily.
The ore from the Marcellus varied in thickness, becoming unworkably thin, and even disappearing altogether in places between the workable beds. The quality of the ore also varied, and it was not always profitable to smelt
, as several furnaces built near iron ore mines in the Marcellus were abandoned before the ore and timber resources used to fuel them became scarce.
Ore found interbedded in the black slaty shale contained a relatively high proportion of carbon which was burned in the furnace, and sulfur
, which produced a usable but "red-short
" iron.
Red-short iron has the undesirable properties of oxidizing more easily, and a tendency to crack, especially when heated to a red-hot state.
In some locations in Pennsylvania the quality of the ore was quite good, with relatively deep veins containing 45% iron, and very low sulfur.
In Virginia, the Marcellus ore occasionally contained zinc
, which produced a characteristic green flame in the furnace as it was consumed, but deposited a hard mass of impure zinc oxide
known as cadmia
, which built up over time near the top of the flue, and had to be removed periodically to keep it unobstructed.
near several outcrops of the Marcellus. In the 19th century, iron ore from these deposits was used as a mineral paint pigment. After being heated in a kiln and finely ground, it was mixed with linseed oil
, and used to paint exterior wood on barns, covered bridges, and railroad cars. In addition to the bog iron, at several sloped locations in eastern Pennsylvania brown hematite was found lying on the Marcellus bedrock buried beneath the soil. These deposits were also excavated and used for mineral paint during that time. A bed of hematite paint ore is also found almost directly below the Marcellus, but it is actually part of the underlying Oriskany Formation.
springs near the base of the Marcellus in Bedford, Pennsylvania
were believed to have healing powers by Native Americans. The Bedford Springs Hotel
was a mineral spa
built in 1802 around a series of mineral springs, including one of these, its "iron spring". The Chalybeate Springs Hotel, built nearby in 1851 around three other mineral springs including another chalybeate spring, became a "resort for invalids". The iron-rich waters were prescribed for anemia
and related complications. Both of these mineral springs contain iron in the form of dissolved iron carbonate, which gives these waters a "slightly inky taste".
and common fill
, although the pyritic shales are not suitable for this purpose because of acid rock drainage and volumetric expansion.
In the 19th century, this shale was used for walkways and roadways,
and was considered superior "road metal" because the fine grained fragments packed together tightly, yet drained well after a rain.
The dark slaty shales may have the necessary cleavage
and hardness to be worked, and were quarried for low grade roofing slate
in eastern Pennsylvania during the 19th century. The slates from the Marcellus were inferior to the Martinsburg Formation
slate quarried further south, and most quarries were abandoned, with the last significant operation in Lancaster County. The Marcellus black slate was also quarried in Monroe County, Pennsylvania, for school slates
used by students in 19th-century rural schools.
Carbonaceous shales, such as the Marcellus, are a possible target for carbon capture and storage
for mitigation of global warming
. Because carbon adsorbs
carbon dioxide
(CO2) at a greater rate than methane
(CH4), carbon dioxide injected into the formation for geological sequestration
could also be used to recover additional natural gas
in a process analogous to enhanced coal bed methane recovery
, but the practical value of this theoretical technique is not yet known. Scientists believe that adsorption would allow sequestration at shallower depths than absorption in deep saline formations, which must be at least 800 m (2,624.7 ft) below the surface to maintain liquid CO2 in a supercritical state
.
road construction in Virginia and Pennsylvania have resulted in localized acid rock drainage due to oxidation of the pyrite inclusions.
The newly exposed shale on the cut face weathers rapidly, allowing air and water into the unexcavated rock, resulting in acidic surface runoff
after precipitation events.
Acidic runoff disrupts aquatic ecosystem
s, and highly acidic soil contaminated
by this runoff will not support vegetation, which is unsightly, and can lead to problems with soil erosion.
Natural decomposition of the shale into smaller fragments can affect slope stability
, necessitating shallower slopes that require more material be disturbed in cut and fill work, exacerbating the acid rock drainage problem. The cut material cannot be used as fill beneath roads and structures due to volumetric expansion, compounding the problem. The Tioga ash beds contain bentonite
clay
which presents a landslide
hazard in the unexcavated rock as well.
Damage to structures constructed on fill consisting of pyritic Marcellus shale has been caused by expansion from sulfuric acid
(H2SO4) runoff reacting with the calcite
(CaCO3) in the shale to produce gypsum
(CaSO4), which has double the molar volume
.
Other sulfate
minerals that can be produced by reactions with pyrite include anhydrite
, melanterite
, rozenite
, jarosite
and alunite
.
The reactions have generated a heave pressure on the order of 500 kPa (10,000 pounds per square foot), but may be able to generate four times this pressure enough to heave foundations in a 5-story building.
Limestone
, which is used to neutralize the acid drainage, can actually exacerbate the expansion problem by promoting sulfate–sulfate reactions that form the minerals thaumasite
and ettringite
, which have even higher molar volumes.
Drilling borehole
s through the Hamilton Group shales in the subsurface can be problematic. The Marcellus has a relatively low density
, and these shales may not be chemically compatible with some drilling fluid
s. The shale is relatively fragile, and may fracture under pressure, causing a problem in circulating the drilling fluid back up through the borehole known as lost circulation. The formation may also be under-pressurized, further complicating the drilling process.
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
found in eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Named for a distinctive outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
near the village of Marcellus
Marcellus (village), New York
Marcellus is a village located in the Town of Marcellus in Onondaga County, New York, USA. The population was 1,826 at the 2000 census. The Village of Marcellus is southwest of Syracuse and is in the southern part of the Town of Marcellus.-History:...
, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
,
it extends throughout much of the Appalachian Basin.
The shale contains largely untapped natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
reserves, and its proximity to the high-demand markets along the East Coast of the United States
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
makes it an attractive target for energy development
Energy development
Energy development is the effort to provide sufficient primary energy sources and secondary energy forms for supply, cost, impact on air pollution and water pollution, mitigation of climate change with renewable energy....
.
Stratigraphically
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
, the Marcellus is the lowest unit of 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...
age Hamilton Group, and is divided into several sub-units. Although black 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...
is the dominant lithology
Lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...
, it also contains lighter shales and interbedded 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....
layers due to sea level variation during its deposition
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...
almost . The black shale was deposited in relatively deep water devoid of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, and is only sparsely fossiliferous. Most fossils are contained in the limestone members, and the fossil record in these layers provides important paleontologal
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
insights on faunal turnovers
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
. The black shales also contain iron ore that was used in the early economic development of the region, and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and 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...
which are environmental hazards. The fissile
Fissility (geology)
Fissility refers to the property of rocks to split along planes of weakness into thin sheets. This is commonly observed in shales, which are sedimentary rocks, and in slates and phyllites, which are foliated metamorphic rocks. The fissility in these rocks is caused by the preferred alignment of...
shales are also easily eroded
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...
, presenting additional civil
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...
and environmental engineering
Environmental engineering
Environmental engineering is the application of science and engineering principles to improve the natural environment , to provide healthy water, air, and land for human habitation and for other organisms, and to remediate polluted sites...
challenges.
Description
The Marcellus Formation is a black shale that may contain limestoneLimestone
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....
beds
Bed (geology)
In geology a bed is the smallest division of a geologic formation or stratigraphic rock series marked by well-defined divisional planes separating it from layers above and below. A bed is the smallest lithostratigraphic unit, usually ranging in thickness from a centimeter to several meters and...
and concentrations of iron 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...
(Fe
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
S
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
2) and siderite
Siderite
Siderite is a mineral composed of iron carbonate FeCO3. It takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus...
(FeCO3
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
).
Its sedimentary structure, or bedding, is moderately well developed. Like most shales, it tends to split easily along the bedding plane, a property known as fissility
Fissility (geology)
Fissility refers to the property of rocks to split along planes of weakness into thin sheets. This is commonly observed in shales, which are sedimentary rocks, and in slates and phyllites, which are foliated metamorphic rocks. The fissility in these rocks is caused by the preferred alignment of...
.
Lighter colored shales in the upper portion of the formation tend to split into small thin-edged fragments after exposure.
These fragments may have rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
stains from exposure of pyrite to air, and tiny 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...
(Ca
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
SO4
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
·2H2O
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
) crystals from the reaction between pyrite and limestone particles.
Fresh exposures of the pyriteiferous shale may develop the secondary mineralization
Mineralization (geology)
In geology, mineralization is the hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".The first scientific studies of this process took place in Cornwall, United Kingdom by J.W.Henwood FRS and later by R.W...
of orange limonite
Limonite
Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...
(FeO
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(OH
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
)·nH2O), and the pale yellow efflorescence
Efflorescence
In chemistry, efflorescence is the loss of water of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.-Examples:...
or bloom of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, associated with acid rock drainage.
and the upper contacts of limestones, but framboid
Framboid
The term framboid describes a micromorphological feature common to certain sedimentary minerals, particularly pyrite . The first known use of the term is ascribed to Rust in 1935 and is derived from the French ‘la framboise’, meaning ‘raspberry’, reflecting the appearance of the structure under...
al microcrystals and euhedral
Euhedral
Euhedral crystals are those that are well-formed with sharp, easily recognised faces. Normally, crystals do not form smooth faces or sharp crystal outlines. Many crystals grow from cooling liquid magma...
crystals of pyrite occur throughout the organic-rich deposits.
The Marcellus also contains uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
,
and the radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
of the uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
(238U) makes it a source rock
Source rock
In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...
for radioactive radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
gas (222Rn).
Measured total organic content of the Marcellus Formation ranges from less than 1% in eastern New York, to over 11% in the central part of the state,
and the shale may contain enough carbon to support combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
.
The more organic-rich black shales can be bituminous, but are too old to contain bituminous coal
Bituminous coal
Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite...
formed from land plants.
In petroleum geology
Petroleum geology
Petroleum geology refers to the specific set of geological disciplines that are applied to the search for hydrocarbons .-Sedimentary basin analysis:...
, these black shales are an important source rock
Source rock
In petroleum geology, source rock refers to rocks from which hydrocarbons have been generated or are capable of being generated. They form one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including...
that filled conventional petroleum reservoirs in overlying formations, are an unconventional shale gas
Shale gas
Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...
reservoir, and are an impermeable seal that traps underlying conventional natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
reservoirs.
To the west the formation may produce liquid petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
; further east heating during deeper burial more than 240 million years ago cracked
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...
this oil into gas.
Extent
The Marcellus is found throughout the Allegheny PlateauAllegheny Plateau
The Allegheny Plateau is a large dissected plateau area in western and central New York, northern and western Pennsylvania, northern and western West Virginia, and eastern Ohio...
region of the northern Appalachian Basin of North America. In the United States, the Marcellus shale runs across the Southern Tier
Southern Tier
The Southern Tier is a geographical term that refers to the counties of New York State west of the Catskill Mountains along the northern border of Pennsylvania. It is a loosely defined term that generally includes the counties that border Pennsylvania west of Delaware County inclusive...
and Finger Lakes
Finger Lakes
The Finger Lakes are a pattern of lakes in the west-central section of Upstate New York in the United States. They are a popular tourist destination. The lakes are long and thin , each oriented roughly on a north-south axis. The two longest, Cayuga Lake and Seneca Lake, are among the deepest in...
regions of New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, in northern and western Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, eastern Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, through western Maryland
Maryland
Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...
, and throughout most of West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
extending across the state line into extreme western Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
. The Marcellus bedrock in eastern Pennsylvania extends across the Delaware River
Delaware River
The Delaware River is a major river on the Atlantic coast of the United States.A Dutch expedition led by Henry Hudson in 1609 first mapped the river. The river was christened the South River in the New Netherland colony that followed, in contrast to the North River, as the Hudson River was then...
into extreme western New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
. It also exists in the subsurface of a small portion of Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
and Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
. Below Lake Erie
Lake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
, it can be found crossing the border into Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, where it stretches between Port Stanley
Port Stanley, Ontario
Port Stanley is a community in the Municipality of Central Elgin, Ontario, Elgin County, located on the north shore of Lake Erie at the mouth of Kettle Creek.-History:...
and Long Point to St. Thomas
St. Thomas, Ontario
St. Thomas is a city in southern , Ontario, Canada. It is the seat for Elgin County and gained its city charter on March 4, 1881.-History:...
in southern Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
.
Outcrops
These joints form smooth nearly vertical cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s, and the intersecting joint planes form projecting corners in the rock faces.
Once exposed, the weathered faces lose most of their organic carbon,
turning from black or dark gray to a lighter shade of gray.
Outcrops of the Marcellus can contain very small beds that resemble 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...
. The New York outcrops, and others further south in Pennsylvania and New Jersey, were extensively excavated in the early 19th century, sometimes at great expense, in the false hope of finding minable coal seams.
In Perry County, Pennsylvania
Perry County, Pennsylvania
As of the census of 2000, there were 43,602 people, 16,695 households, and 12,320 families residing in the county. The population density was 79 people per square mile . There were 18,941 housing units at an average density of 34 per square mile...
along the Juniata River
Juniata River
The Juniata River is a tributary of the Susquehanna River, approximately long, in central Pennsylvania in the United States. The river is considered scenic along much of its route, having a broad and shallow course passing through several mountain ridges and steeply-lined water gaps...
the false coal beds become up to 0.3 m (0.984251968503937 ft) thick, but they did not produce a valuable fuel, despite the considerable effort expended to mine it from the surrounding hills.
Seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
and marine plants probably formed the false coal. True coal is formed from terrestrial plants, which only began to appear in Marcellus and later fossils.
Close proximity to the surface of Marcellus bedrock south of the New York outcrops makes an east-west band running through the city of Syracuse
Syracuse, New York
Syracuse is a city in and the county seat of Onondaga County, New York, United States, the largest U.S. city with the name "Syracuse", and the fifth most populous city in the state. At the 2010 census, the city population was 145,170, and its metropolitan area had a population of 742,603...
a high-risk area for radon as an indoor air pollutant
Indoor air quality
Indoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....
. From the surface exposures along the northern and eastern margins, the formation descends to depths of over 2700 m (8,858.3 ft) below the surface in southern Pennsylvania.
Structural geology
Upturned beds are exposed in sections of the foldedFold (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...
Ridge-and-Valley Appalachians
Ridge-and-valley Appalachians
The Ridge-and-Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian division and are also a belt within the Appalachian Mountains extending from southeastern New York through northwestern New...
, including exposures on the flanks and axis of the Broad Top Synclinorium in south central Pennsylvania. Exposed beds are nearly horizontal on the Allegheny Plateau, but upturned to form slightly overturned beds found along the Allegheny Front
Allegheny Front
The Allegheny Front is the major southeast- or east-facing escarpment in the Allegheny Mountains in southern Pennsylvania, western Maryland, and eastern West Virginia, USA. The Allegheny Front delineates the Ridge-and-Valley Appalachians to its east from the Appalachian Plateau to its west...
.
From Wind Gap, Pennsylvania
Wind Gap, Pennsylvania
Wind Gap is a borough in Northampton County, Pennsylvania, United States. Wind Gap is located in the Lehigh Valley region of the state. It is part of Pennsylvania's Slate Belt .The population of Wind Gap was 2,720 at the 2010 census.-Geography:...
heading south, the dip
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...
of the beds steepens, becoming vertical at Bowmanstown
Bowmanstown, Pennsylvania
Bowmanstown is a borough in Carbon County, Pennsylvania, United States. The population was 895 at the 2000 census. Bowmanstown is at an elevation of and is located west of Palmerton and south of Lehighton off of Route 248.-Geography:...
on the Lehigh River
Lehigh River
The Lehigh River, a tributary of the Delaware River, is a river located in eastern Pennsylvania, in the United States. Part of the Lehigh, along with a number of its tributaries, is designated a Pennsylvania Scenic River by the state's Department of Conservation and Natural Resources...
. Nearby, in the Lehigh Gap area of Pennsylvania, the Marcellus is extensively faulted,
and the beds are steeply overturned, with a reverse dip
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...
angle of up to 40° south.
The Marcellus Shale and the fine-grained shales near the middle of the Mahantango Formation are classified by geologists as slope-former
Slope-former
The term slope-former is a geologic term indicating that a unit of bedrock is less resistant to erosion than overlying or underlying units and consequently outcrops have low slope angles. It may be contrasted with cliff-former. Typical slope formers include shales, and limestones in humid...
s.
Marcellus and Mahantango shale beds dipping at 60° to 75° to the west form the west facing slopes of Tonoloway Ridge
Tonoloway Ridge
Tonoloway Ridge is a stratigraphic ridge that runs southwest northeast through the U.S. states of Pennsylvania, Maryland, and West Virginia. It reaches its highest elevation above mean sea level of 1,292 feet at a knob on its southern end in Morgan County, West Virginia...
on the west flank of the Cacapon Mountain
Cacapon Mountain
Cacapon Mountain runs northwest through Morgan and Hampshire counties in West Virginia's Eastern Panhandle, rising to its greatest elevation of 2,618 feet above sea-level at High Point. Cacapon Mountain is a folded mountain ridge, belonging to the Appalachian Ridge and Valley Province. Cacapon...
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...
in the Eastern Panhandle of West Virginia
Eastern Panhandle of West Virginia
The Eastern Panhandle of West Virginia is a narrow stretch of territory in the northeast of the state, bordering Maryland and Virginia, United States. The Eastern Panhandle Board of Realtors and other local civic organizations consider only the three Easternmost counties, Jefferson, Berkeley and...
.
On the eastern limb of this anticline, beds of these shales dipping to the east at a shallower angle also form the steep slopes on the east side of Warm Springs Ridge.
Surficial geology
The Marcellus is easily erodedErosion
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 is also found underlying low areas between some Appalachian ridges, forming linear valleys of moderate relief. These bedrock surfaces are typically covered with colluvium
Colluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
from erosion of stratigraphically higher and more erosion-resistant strata that form the surrounding higher ground. The soils formed from the Marcellus and the overlying Hamilton shales are deep, free of stones, and well suited for agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
.
Sampling of soil formed on the Marcellus bedrock showed the dominant mineralogy
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...
consisted of 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,...
, illite
Illite
Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations...
, montmorillonite
Montmorillonite
Montmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central...
, muscovite
Muscovite
Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...
, and 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...
, with phases of todorokite
Todorokite
Todorokite is a rare complex hydrous manganese oxide mineral with formula 2Mn3O12·3H2O. It is a brown to black monoclinic mineral which occurs in massive or tuberose forms. It is quite soft with a Mohs hardness of 1.5, and has a specific gravity of 3.49 - 3.82.It was discovered in 1934 in...
and trona
Trona
Trona ; Na3•2H2O is an evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has replaced the Solvay process used in most of the rest of the world for sodium carbonate production.- Etymology :The word "trona" comes to English by way of either...
appearing at depths closer to the bedrock.
Upturned beds of the soft shale also capture streams and rivers with relatively straight segments in strike valleys such as the Aquashicola Creek
Aquashicola Creek
Aquashicola Creek, also known as Aquanchicola Creek, or Aquanshicola Creek, is a tributary of the Lehigh River in the Poconos of eastern Pennsylvania in the United States....
and McMichael Creek
McMichael Creek
McMichael Creek is a tributary of Pocono Creek in the Poconos of eastern Pennsylvania in the United States.McMichael Creek drops off the Pocono Plateau and joins Pocono Creek in Stroudsburg.-References:...
at the foot of The Poconos
The Poconos
The Pocono Mountains is a region located in northeastern Pennsylvania, United States. The Poconos, located chiefly in Monroe and Pike counties , are an upland of the larger Allegheny Plateau...
,
and the long, straight section of the Lost River
Lost River (Cacapon River)
The Lost River is a river in the Appalachian Mountains of Hardy County in West Virginia's Eastern Panhandle region. The Lost River is geologically the same river as the Cacapon River: it flows into an underground channel northeast of Baker along West Virginia Route 259 at "the Sinks" and reappears...
in West Virginia.
Below Port Jervis, New York
Port Jervis, New York
Port Jervis is a city on the Delaware River in western Orange County, New York, with a population of 8,860 at the 2000 census. The communities of Deerpark, Huguenot, Sparrowbush, and Greenville are adjacent to Port Jervis, and the towns of Montague, New Jersey and Matamoras, Pennsylvania face the...
, the Walpack Ridge deflects the Delaware River
Delaware River
The Delaware River is a major river on the Atlantic coast of the United States.A Dutch expedition led by Henry Hudson in 1609 first mapped the river. The river was christened the South River in the New Netherland colony that followed, in contrast to the North River, as the Hudson River was then...
into the Minisink Valley, where it follows the southwest strike
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...
of the eroded Marcellus beds along the Pennsylvania – New Jersey state line for 40 km (25 mi) to the end of the ridge at Walpack Bend in the Delaware Water Gap National Recreation Area
Delaware Water Gap National Recreation Area
Delaware Water Gap National Recreation Area, administered by the National Park Service, preserves almost of land along the Delaware River's New Jersey and Pennsylvania shores, stretching from the Delaware Water Gap northward almost to the New York state line...
.
The Minisink is a buried valley
Buried valley
A buried valley is an ancient river or stream valley that since has been filled with glacial or unconsolidated sediment. This sediment is made up of gravel, sand, silt, and clay. These types of sediment can often store and transmit large amounts of ground water....
where the Delaware flows in a bed of glacial
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...
till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
that buried the eroded Marcellus bedrock during the last glacial period. This buried valley continues along the strike of the Marcellus southwest from the bend through Stroudsburg, Pennsylvania
Stroudsburg, Pennsylvania
Stroudsburg is a borough in Monroe County, Pennsylvania, United States. It is located in the Poconos region of the state, approximately five miles from the Delaware Water Gap, at the confluence of the Brodhead and Pocono Creeks. It is the county seat of Monroe County. Stroudsburg is part of the...
, and northeast from Port Jervis toward the Hudson River
Hudson River
The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...
,
along the route of the Delaware and Hudson Canal
Delaware and Hudson Canal
The Delaware and Hudson Canal was the first venture of the Delaware and Hudson Canal Company, which later developed the Delaware and Hudson Railway...
.
Deposition
Early in the Acadian orogenyAcadian orogeny
The Taconic, Acadian and Alleghenian orogenies are the three tectonic phases responsible for the formation of the present Appalachian Mountains. The Acadian orogeny is a middle Paleozoic mountain building episode dating back 325-400 million years which should not be regarded as a single event but...
, as the Acadian Mountains were rising up, the black and gray shales of the Hamilton Group began accumulating as erosion of the mountains deposited terrigenous
Terrigenous
In oceanography, terrigenous sediments are those derived from the erosion of rocks on land; that is, that are derived from terrestrial environments. Consisting of sand, mud, and silt carried to sea by rivers, their composition is usually related to their source rocks; deposition of these sediments...
sediments from the land into the sea.
The Marcellus Shale was formed from the very first deposits in a relatively deep, sediment- and oxygen-starved (anoxic
Anoxic sea water
Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen. This condition is generally found in areas that have restricted water exchange....
), trough
Trough (geology)
In geology, a trough generally refers to a linear structural depression that extends laterally over a distance, while being less steep than a trench.A trough can be a narrow basin or a geologic rift....
that formed parallel to the mountain chain.
These clastic fragments of rock were carried in braided streams to the ancient Catskill Delta
Catskill Delta
The Devonian Catskill Formation or the Catskill clastic wedge is a unit of mostly terrestrial sedimentary rock found in Pennsylvania and New York. Minor marine layers exist in this thick rock unit...
, a 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...
probably similar to the present day Niger Delta
Niger Delta
The Niger Delta, the delta of the Niger River in Nigeria, is a densely populated region sometimes called the Oil Rivers because it was once a major producer of palm oil...
of Africa.
Smaller particles remained suspended
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
longer in this epeiric sea
Epeiric Sea
An epeiric sea is a shallow sea that extends over part of a continent.Epeiric seas are usually associated with the marine transgressions of the geologic past, which have variously been due to either global eustatic sea level changes, local tectonic deformation, or both, and are occasionally...
, flowing offshore as turbidites in a slow but persistent underwater avalanche. They finally came to rest at the bottom of the Acadian foredeep in the Appalachian Basin, hundreds of meters from shore, at depths that may have been 150 m (492.1 ft) or more beneath the surface.
Alternatively, the basin may have been as shallow as 50 metres (164 ft) or less, if the warm water was sufficiently stratified
Stratification (water)
Water stratification occurs when water masses with different properties - salinity , oxygenation , density , temperature - form layers that act as barriers to water mixing...
so that oxygen rich surface water did not mix with the anoxic bottom water.
The Marcellus deposition produced a transgressive black shale,
because it was deposited in deepening conditions when the basin floor dropped as the mountains rose up.
The dark shale 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....
of the Marcellus were formed from 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...
, a fine mud deposited in the deep water; it buried the underlying Onondaga limestone beds,
as the deepening sea cut off the supply of carbonates that form limestone.
Organic matter, probably dominated by plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, also settled to the bottom, but the normal aerobic decay
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
process was inhibited in the anaerobic
Hypoxia (environmental)
Hypoxia, or oxygen depletion, is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system...
environment thereby preserving the organic carbon.
Uranium was also incorporated in these organic muds syndepositionally,
meaning it was deposited at the same time, rather than being introduced to the formation later.
The organic matter scavenged trace elements from the seawater,
including the redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
-sensitive elements uranium, rhenium
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
, molybdenum
Molybdenum
Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...
, osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
, chromium
Chromium
Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...
, and selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
.
The Marcellus was deposited during a period of development of land plants
Evolutionary history of plants
The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today...
, when atmospheric oxygen was increasing, resulting in a reduction of carbon dioxide in the atmosphere, and the seawater where it was deposited.
Named members of the Marcellus reflect two composite depositional sequences,
with a general coarsening upward cycle that continues into the base of the overlying Mahantango Formation.
The interbedding of lighter shale and limestone members is attributed to relatively short-term oscillations in basin depth.
Later deep water depositional sequences formed the overlying Brallier Formation
Brallier Formation
The Devonian Brallier Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Brallier Formation was described by Charles Butts in 1918 as a fine-grained, siliceous shale with few fine-grained sandstone layers, from outcrops in central Pennsylvania...
and Harrell Formation
Harrell Formation
The Devonian Harrell Formation is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia.-Description:The Harrell Formation was first described by Charles Butts in 1918...
.
Age
On the geological timescale, the Marcellus occurs in the Middle Devonian epoch, of the DevonianDevonian
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...
period, in the Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
era, of the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
eon. Radiometric dating of a Marcellus sample from Pennsylvania placed its age at 384 million years old, and a sample from the bentonite at the top of the Onondaga at 390 ± 0.5 million years old.
Relative age dating of the Marcellus places its formation in the Cazenovia subdivision of the Givetian faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
, or 391.9 to 383.7 million years ago (Ma).
The Union Springs member, at the base of the Marcellus in New York, has been dated to the end of the Eifelian, the stage which immediately preceded the Givetian.
Anoxic dark shales in the formation mark the Kačák Event,
a late-Eifelian-stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
marine anoxic event
Anoxic event
Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused...
also associated with an extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
.
Stratigraphy
In the first Pennsylvania Geological SurveyPennsylvania Geological Survey
The Pennsylvania Geological Survey or Bureau of Topographic and Geologic Survey , is a geological survey enacted by the Pennsylvania General Assembly "to serve the citizens of Pennsylvania by collecting, preserving, and disseminating impartial information on the Commonwealth's geology, geologic...
, begun in 1836, Henry Darwin Rogers
Henry Darwin Rogers
Henry Darwin Rogers FRS FRSE was an American geologist.-Biography:Rogers was born at Philadelphia. His middle name was given him in honor of Erasmus Darwin, of whose poem “The Botanic Garden” his father was a great admirer...
classified the Marcellus as the "Cadent Lower Black Slate" which he numbered "No. VIII b." In the first New York State Geological Survey, also begun that year, James Hall
James Hall (paleontologist)
James Hall was an American geologist and paleontologist. He was a noted authority on stratigraphy and had an influential role in the development of American paleontology.-Early life:...
established the term "Marcellus Shale" in his 1839 report titled "Marcellus Shales in Seneca County." Professor Hall also argued in 1839 against formulating geological names based on observed characteristics that may vary from place to place or need revision in the future, and in favor of location-based nomenclature where "the rock or group will receive its name from the place where it is best developed." His arguments proved persuasive, and the location-based name for this, and many of the other group names he published based on exposures in New York, were adopted in the second Pennsylvania survey, and are now widely accepted.
Overlying
In the first New York survey, the Marcellus shale was placed below the Hamilton Group at the base of the Erie division of the New York system, but this taxonomy is obsolete.In current practice, the Marcellus Formation (abbr. Dm or Dms) is classified as the basal unit of the Hamilton Group
Hamilton Group
The Devonian Hamilton Group is a mapped bedrock unit in New York, Pennsylvania, Maryland, and West Virginia. In Virginia, it is known as the laterally equivalent Millboro Shale.The group is named for the village of Hamilton, New York...
(Dh), lying beneath the Mahantango Formation
Mahantango Formation
The Devonian Mahantango Formation is a mapped bedrock "unit" in Pennsylvania, New Jersey, New York and Maryland. It is named for the North branch of the Mahantango Creek in Perry and Juniata counties in Pennsylvania. It is a member of the Hamilton Group, along with the underlying the Marcellus...
(Dmh) member of this group in Pennsylvania and Maryland. In New York, the Mahantango, also of Middle Devonian age, is further divided. There the Marcellus is separated from the overlying Skaneateles Formation, a more clastic and fossiliferous dark shale, by the thin Stafford or Mottville Limestone bed.
In West Virginia, the Marcellus may be separated from the brown shales of the Mahantango by occasional 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,...
beds and concretions,
or it may lie directly below the younger Late Devonian Harrel Formation (or its lateral equivalents) because of a disconformity, which represents a gap in the geological record due to a period of erosion or non-deposition.
In eastern Ohio the Hamilton Group also lies disconformably beneath the Rhinestreet Shale Member of the West Falls Formation, another transgressive black shale tongue with similar characteristics to the Marcellus.
Underlying
The Marcellus shale is typically found deposited on the limestone of the Onondaga Formation (Don), which extends down to the end of the Early Devonian period. The contact between them may be sharp, gradational, or erosional. In southwestern Ontario, Canada, north of Lake ErieLake Erie
Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...
, the Marcellus overlies the Dundee Formation, a lateral equivalent of the Onondaga.
In Pennsylvania, the Marcellus forms a sharp conformable
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...
contact with the Onondaga's Selinsgrove Limestone member.
A thin pyrite-carbonate bed is also found at the base of the Marcellus black shale in the exposures of south central Pennsylvania, above a thin calcerous green shale bed, which lies upon the Onondaga limestone.
In eastern New York, the contact between the Marcellus and Onondoga (where present) is gradational.
In western New York, the Union Springs member of the Marcellus conformably overlies the Seneca member of the Onondaga Limestone,
or the stratigraphically higher Cherry Valley Limestone member may rest directly and unconformably upon the Onondaga in the absence of the Union Springs shale.
The local disappearance of units of the Onondaga suggests that its upper contact with the Marcellus can be erosional.
In Erie County
Erie County, New York
Erie County is a county located in the U.S. state of New York. As of the 2010 census, the population was 919,040. The county seat is Buffalo. The county's name comes from Lake Erie, which in turn comes from the Erie tribe of American Indians who lived south and east of the lake before 1654.Erie...
in western New York, both the upper and lower contact of the Marcellus are eroded away.
In eastern West Virginia the Marcellus overlies the Onesquethaw Group, consisting of the dark gray or green, calcitic, mostly nonfissil Needmore Shale, which grades westward into the Huntersville Chert.
To the south and west, the Hamilton Group grades laterally into the Millboro Shale formation in southern West Virginia and Virginia,
which grades into the lower part of the Chattanooga Shale of Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
.
The Milboro is gradational with the underlying Needmore Formation shale.
South of the Mason-Dixon line
Mason-Dixon line
The Mason–Dixon Line was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute between British colonies in Colonial America. It forms a demarcation line among four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and...
, due to the difficulty in differentiating the Millboro and Needmore shales with the limited exposures available,
and initial uncertainty in correlation with the New York survey, they were mapped as the Romney Formation, a unit containing all the Middle Devonian strata,
named for an exposure at Romney, West Virginia
Romney, West Virginia
Romney is a city in and the county seat of Hampshire County, West Virginia, United States. The population was 1,940 at the 2000 census, while the area covered by the city's ZIP code had a population of 5,873. It is a city with a very historic background dating back to the 18th century...
.
The correlations were established by 1916 through tracing the New York exposures across Pennsylvania and Maryland into West Virginia, so under the principle of scientific priority
Scientific priority
In science, priority is the claim and recognition of first discovery or theory. Fame and honors usually go to the first person or group to publish a new finding, even if several researchers arrived at the same conclusion independently and at the same time....
,
the Romney classification is now obsolete; but its Marcellus and underlying Needmore shale members are still found grouped in an undifferentiated map unit (Dmn).
Tioga ash beds
Tioga metabentonite or K-bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
–stratigraphic unit about 0.6 m (2 ft) thick that consists of several discrete, relatively thin volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
falls–is also included at the base of the Marcellus in eastern Pennsylvania.
In 1843 it was described without being named by Hall,
and more than 100 years passed before it was eventually named for the natural gas field
Natural gas field
Oil and natural gas are produced by the same geological process according fossil fuel suggestion: anaerobic decay of organic matter deep under the Earth's surface. As a consequence, oil and natural gas are often found together...
in Tioga County, Pennsylvania
Tioga County, Pennsylvania
Tioga County is a county located in the U.S. state of Pennsylvania. As of the 2010 census, the population was 41,981. Tioga County was created on March 26, 1804, from part of Lycoming County and named for the Tioga River. Its county seat is Wellsboro....
,
where it was encountered when drilling
Borehole
A borehole is the generalized term for any narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation, environmental site...
gas wells
Oil well
An oil well is a general term for any boring through the earth's surface that is designed to find and acquire petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well that is designed to produce mainly or only gas may be termed a gas well.-History:The earliest...
. It is a regional stratigraphic marker,
used by geologists to identify the Marcellus,
and correlate laterally equivalent strata. Difficulty in correctly identifying the more than 80 different ash falls during the Devonian period, collected in 15 or more beds, has also led to many miscorrelations.
From Virginia to New York the Tioga is widely distributed, running across the central and northern parts of the Appalachian basin,
an areal extent exceeding 265000 km² (102,317.1 sq mi).
Explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s associated with the Acadian orogeny
Acadian orogeny
The Taconic, Acadian and Alleghenian orogenies are the three tectonic phases responsible for the formation of the present Appalachian Mountains. The Acadian orogeny is a middle Paleozoic mountain building episode dating back 325-400 million years which should not be regarded as a single event but...
originating near present-day central Virginia released the ash into the atmosphere.
It was dispersed across the Appalachian, Michigan
Michigan Basin
The Michigan Basin is a geologic basin centered on the Lower Peninsula of the US state of Michigan. The feature is represented by a nearly circular pattern of geologic sedimentary strata in the area with a nearly uniform structural dip toward the center of the peninsula.The basin is centered in...
, and Illinois
Illinois Basin
The Illinois Basin is a Paleozoic depositional and structural basin in the United States, centered in and underlying most of the state of Illinois, and extending into southwestern Indiana and western Kentucky...
Basins by the southern trade winds, because this area was in the southern hemisphere during the Devonian period.
The volcanic origin of the ash is evidenced by its distinctive mineralogy
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...
–the ash was deposited directly upon the water, so its angular quartz grains differ from the clastic sediments rounded through the erosion process that carries them to the sea. As the volcanic ash settled to the bottom, it was admixed
Mixture
In chemistry, a mixture is a material system made up by two or more different substances which are mixed together but are not combined chemically...
with these terrigenous components, producing a distinctive lithology in the sedimentary rock.
consisting of coarse crystal 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...
or tuffaceous shale,
thinly laminated, with sand-sized mica flakes.
The Tioga ash bed zone consists of eight ash beds labeled according to their stratigraphic order from A (oldest) to H (youngest),
and another bed known as the Tioga middle coarse zone.
Its basal beds are found within the uppermost beds of the Onondaga Limestone or Needmore Shale, and the uppermost ash bed within the lowermost part of the Marcellus or Millboro Shale.
In western New York state, the Tioga Ash Bed B marks the boundary between the Moorehouse and Seneca Members of the Onondaga Formation,
but in the central part of the state, and the southern part of the basin, the ash beds are actually in the Marcellus.
This indicates that deposition of the Marcellus there began earlier,
since the ash beds represent a single epoch in geologic time.
Thickness
Maximum thickness of the Marcellus ranges from 270 m (885.8 ft) in New Jersey, to 12 m (39.4 ft) in Canada.In West Virginia, the Marcellus Formation is as much as 60 m (196.9 ft) thick.
In extreme eastern Pennsylvania, it is 240 m (787.4 ft) thick,
thinning to the west, becoming only 15 m (49 ft) thick along the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
, and only a few feet in Licking County, Ohio
Licking County, Ohio
Licking County is a county located in the state of Ohio, United States. As of the 2010 census, the population was 166,492. Its county seat is Newark and is named for the salt licks that were in the area....
.
The thinning, or stratigraphic
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
convergence, from east to west is caused by decreasing grain size in the clastic deposits, which entered the basin from the east.
The beds finally "pinch out" westward because deposition was limited by the Cincinnati Arch,
the bulge that formed the west shore of the basin. Where the formation is relatively thick, it is divided into several members, and as the formation continues to thicken to the east, these members are further divided. Some workers chose to classify the Marcellus as a subgroup, and classify some of the members as separate formations.
EWLINE
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Named members
A local Purcell limestone member, 15 to 30 m (49.2 to 98.4 ft) of inter-bedded calcitic shale and limestone,divides the Marcellus in eastern Pennsylvania.
The Purcell is stratigraphically equivalent to the Cherry Valley Limestone member in New York,
a bioclast
Bioclast
Bioclasts are skeletal fragments of marine or land organisms that are found in sedimentary rocks laid down in a marine environment—especially limestone varieties, some of which take on distinct textures and coloration from their predominate bioclasts—that geologists, archaeologists and...
ic packstone, consisting of skeletal limestones, with shaly intervals between its lower massive limestone layer, thick nodular limestone/marlstone, and upper limestone layer.
Other named members include the Bakoven Shale, Cardiff Shale, Chittenango shale, Solsville sandstone, Union Springs shale and limestone, and Stony Hollow shale and limestone. The Union Springs, Cherry Valley, and Oatka Creek merge beneath Lake Erie, into the Bell Shale, Rockport Quarry Limestone, and Arkona Shale of Ontario.
The Union Springs is an organic-rich, pyritiferous, thinly bedded, blackish gray to black shale with mudstone concretionary layers, and thin silt bands at the bottom. To the east, it becomes the Bakoven Member, a darker, less organic shale with fewer limestone layers. To the west the Union Springs beds thin, with its upper limestones merging with the overlying calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
Cherry Valley Member. A regional unconformity appears in western New York, as the Union Springs lenses in and out, and then reappears in northwest Pennsylvania and northeast Ohio between the Onondaga and Cherry Valley.
In Western and central New York, the uppermost member is the dark grey to black organic-rich Oatka Creek shale. Unlike the other Devonian shales in this region, the gray shale at the top of the Oatka Creek thickens gradually to the west, as well as the east,
where it divides into the Cardiff member lying above the Chittenango member in central New York.
Organic-rich, fissile, sooty black shales make up the Chittenango Member.
At the base of the Chittenango,
above the Bierne Member shale,
lies the Halihan Hill Bed, a highly bioturbated
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...
bioclastic limestone.
Further east, the homogeneous Cardiff divides into the Bridgewater, Solsville, and Pecksport shale members, from base to top. The Bridgewater is a fissile dark silty shale with relatively rare fossils. A thin concretionary zone lies above, then the Solsville grades from a gray calcareous shale, to sandy siltstones and fine sandstones at the top, with the gray shale of the Pecksport shale and siltsone overlying it.
In south central Pennsylvania, the Marcellus is mapped with three members, from top to base: The Mahanoy Member (Dmm), a dark gray to grayish black silty shale and siltstone; the Turkey Ridge Member (Dmt), an olive to dark-gray fine to medium grained sandstone; and the Shamokin Member (Dms), a dark gray to grayish black fissile carbonaceous shale that is calcareous in places near the base. The Turkey Ridge is commonly mapped in the Mahantango Formation, or included in the Montebello Formation (Dmot), and only the Shamokin correlates with the Marcellus on adjacent map sheets. In extreme eastern Pennsylvania, the Broadhead Creek member, a dark gray silty shale with dark gray shaly limestone concretions, appears above the Stony Hollow and Union Springs, in a layer up to 275 m (902 ft) thick.
Fossils
There are relatively sparse inclusions of fossilized marine faunaFauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
found in the Marcellus, but these fossils are still important to paleontology. For example, the Marcellus contains the oldest known diverse collection of thin-shelled mollusks still having well preserved shell microstructure.
It is also where goniatites
Goniatites
Goniatites is genus of the Goniatitaceae superfamily. They are an extinct group of ammonoid, which are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids.-References:* accessed on 10/01/07...
, an extinct shelled swimmer similar to a squid, make their first appearance in the fossil record.
Life on land also enters the fossil record in the Marcellus, with the trunks of branchless conifer trees that floated out to sea to be preserved in the black shale.
Marcellus fossils include specimens of the large clam-like 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...
Spinocyrtia.
External molds of 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, plant-like animals related to starfish also known as "sea lilies,"
are found in the formation,
with the molds partially filled with limonite
Limonite
Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...
; brachiopod and bivalve (clam) molds have also been found in the shale.
Small conical tentaculitid
Tentaculite
Tentaculites is an extinct genus of molluscs known from Devonian age fossils, ranging from 360-410 million years ago. The taxonomic classification of tentaculitids is uncertain, but some group them with pteropods. They may also be related to other conical shells of uncertain affinity including...
s are commonly found in the Chittenango Member.
The Halihan Hill bed contains styliolinids and macrofauna including brachiopods, coral-like bryozoans, small bivalves and gastropods (snails),
incorporated after the faunal turnover
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
when Emsian and Eifelian Schoharie/Onondaga fauna were replaced by the Givetian Hamilton fauna.
The Solsville member contains well preserved bivalves, gastropods, and brachiopods. These shellfish lived in the benthic zone
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...
at the bottom of marginal marine to open marine environments that existed west of the ancient Catskill Delta
Catskill Delta
The Devonian Catskill Formation or the Catskill clastic wedge is a unit of mostly terrestrial sedimentary rock found in Pennsylvania and New York. Minor marine layers exist in this thick rock unit...
.
The fossil record in this member shows the base was dominated by deposit feeders, while the upper layers were dominated by filter feeder
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
s. This can be correlated to the lithology: the finer sediments of the shales at the base of this member would contain abundant adherent organic matter for deposit feeders, but would tend to foul the gills of filter feeders when suspended; the coarser sediments of the sandstones at the top would have contained less organic matter to support deposit feeders.
Below the Solsville, at the base of the Otsego in eastern New York, a coral bed
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
is found; another coral bed can be seen at the top of the Marcellus near Berne, New York
Berne, New York
Berne is a town in Albany County, New York, United States. The population was 2,794 at the 2010 census. The town is at the west border of Albany County.- History :...
.
A diverse, eel-like 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...
fauna occurs in the limestone of the Cherry Valley Member,
which is also known for its rich 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...
and goniatite cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
fauna.
Originally named the Goniatite Limestone,
it produces their fossilized remains with shells that can be larger than 0.3 metre (0.984251968503937 ft) across.
It also contains the "Cephalopod Graveyard" in the Schoharie Valley
Schoharie Valley
The Schoharie Valley is a corridor that runs through Schoharie County from Schoharie, New York until Gilboa, New York.-Geography:The Schoharie Valley is made up of plains surrounding the Schoharie Creek. Within the Schoharie Valley are the locations of Middleburgh, Schoharie, Fultonham, Breakabeen...
of eastern New York, an unusual accumulation of abundant coiled and straight shells of several types of large adult cephalopods. This bed lacks juvenile fossils, indicating that if their behavior was similar to modern squid, this may have been an area where these Devonian cephalopods reproduced and died.
This stratigraphic interval also provides an excellent example of incursion epiboles, which are sudden appearances and disappearances of fossil taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
in relatively thin sections of the rock unit. In the Cherry Valley, the taxa do not reoccur; instead each thin concretionary limestone bed contains different species of goniatites.
The Cherry Valley and Union Springs also contain well-preserved anarcestida.
Fossil fuel
The impervious limestone layers of the Onondaga directly below the Marcellus, and the Tully Limestone at the top of the Hamilton Group, have trapped valuable natural gasNatural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
reserves in this formation.
The gas is produced by thermogenic decomposition
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
of organic materials in the sediments under the high temperature and pressure generated after the formation was buried deep below the surface of the earth. The rock holds most of the gas in the pore spaces of the shale, with vertical fractures or joints providing additional storage as well as pathways for the gas to flow; gas is also adsorbed on mineral grains,
and the carbon in the shale.
The United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
had estimated that the Marcellus contained only 54 km³ (1,906,991,975,483.7 cu ft) (where x1012 = trillion, and is referred to as 1.9 TCF) of technically recoverable natural gas in a 2002 publication. In April 2009, the United States Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
estimated the Marcellus to contain 262 TCF of recoverable gas.
State University of New York at Fredonia
State University of New York at Fredonia
The State University of New York at Fredonia is a four-year liberal arts college located in Fredonia, New York, United States; it is a constituent college of the State University of New York...
geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
professor Gary Lash has calculated that more than 14000 km³ (494,405,326,977,258 cu ft) (490 TCF) of natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
may be contained in the Marcellus black shale beds that lie between New York state and West Virginia. At the present level of technology, he believes approximately 10% of this – 1400 km³ (49,440,532,697,725.8 cu ft) (49 TCF) – could be recovered. This is enough to satisfy approximately two years' of total U.S. consumption, or a total value of two hundred billion dollars at winter 2010 – spring 2011 wellhead prices. That figure is part of an increase of as much as approximately one trillion United States dollar
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
s in the value of all recoverable reserves in the US attributable to improved recovery through vertical drilling and fracking.
During the 2012 presidential campaign, GOP Primary Candidate Rick Perry
Rick Perry
James Richard "Rick" Perry is the 47th and current Governor of Texas. A Republican, Perry was elected Lieutenant Governor of Texas in 1998 and assumed the governorship in December 2000 when then-governor George W. Bush resigned to become President of the United States. Perry was elected to full...
cited a study funded by the Marcellus Shale Coalition that fracking the Romney Formation is expected to create a quarter million jobs under the current policies of the Obama administration.
Drilling and environmental issues
In 2008, Terry Engelder, a Pennsylvania State UniversityPennsylvania State University
The Pennsylvania State University, commonly referred to as Penn State or PSU, is a public research university with campuses and facilities throughout the state of Pennsylvania, United States. Founded in 1855, the university has a threefold mission of teaching, research, and public service...
geosciences professor called his estimate of 4800 km³ (169,510,397,820,774 cu ft) (170 TCF) conservative. In November 2008, based on drilling results, Engelder increased his estimate of the amount of natural gas in the Marcellus to 363 TCF of recoverable resource, which would be enough to supply U.S. consumption for at least fourteen years. That estimate assumed some acreage in the Marcellus would not be gas bearing. If the entire formation did contain gas, Engelder said the formation could contain 4,359 TCF. Assuming a 30% recovery rate, this would lead to a 1,307 TCF.
Before 2000, low production gas wells were completed to the Marcellus, but these had a low rate of return
Rate of return
In finance, rate of return , also known as return on investment , rate of profit or sometimes just return, is the ratio of money gained or lost on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or...
, requiring a relatively long capital recovery period, although they did have a very long productive life. There are wells in Tioga and Broome County, NY which are 50 years old or more.
Now, to extract the shale gas
Shale gas
Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...
at more commercially viable rates, directional drilling
Directional drilling
Directional drilling is the practice of drilling non-vertical wells. It can be broken down into three main groups: Oilfield Directional Drilling, Utility Installation Directional Drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical wells. It can be broken down...
is done to depths of 7000 to 10000 ft (2,133.6 to 3,048 m) underground to reach the formation, and then water and a mixture of chemicals is pumped into the rock under high pressure in a process known as hydraulic fracturing
Hydraulic fracturing
Considerable controversy surrounds the current implementation of hydraulic fracturing technology in the United States. Hydraulic fracturing, or fracking, is the process of utilizing pressurized water, or some other liquid, to fracture rock layers and release petroleum, natural gas, or other...
to release the gas from the low permeability shale.
Although hydraulic fracturing has been used since the middle of the 20th century, its use in horizontal wells in laterally extensive shale formations was perfected around the turn of the 21st century outside Fort Worth, Texas
Fort Worth, Texas
Fort Worth is the 16th-largest city in the United States of America and the fifth-largest city in the state of Texas. Located in North Central Texas, just southeast of the Texas Panhandle, the city is a cultural gateway into the American West and covers nearly in Tarrant, Parker, Denton, and...
to tap the reserves in the Barnett Formation
Barnett Shale
The Barnett Shale is a geological formation located in the Bend Arch-Fort Worth Basin. It consists of sedimentary rocks of Mississippian age in Texas...
shales of the Bend Arch-Fort Worth Basin
Bend Arch-Fort Worth Basin
The Bend Arch–Fort Worth Basin Province is a major petroleum producing geological system which is primarily located in north central Texas and southwestern Oklahoma...
, that are now the most prolific source of unconventional gas in the continental United States. The Marcellus covers several times more area, stretching 600 miles (965.6 km), compared to a linear extent of only 170 miles (273.6 km) for the Barnett.
Several companies, many that have specialized in tapping the Barnett, are working to do the same in the Marcellus. As of 2008, only a few new hydro fractured wells tapping the Marcellus reserves were actually in operation, with at least one reported to be producing more than 3 million cubic feet (85 thousand m³) per day. Engelder, who has studied natural rock fractures in this area for more than 25 years, also suggested drilling horizontally through the Marcellus shale perpendicular to these vertical fractures, to exploit these natural features for increased production. Early results show that horizontal wells in this formation are producing gas at a rate more than double that of vertical wells, and at slightly lower cost overall, despite the much higher initial cost of drilling.
Since parts of this region have been producing gas from wells drilled to the deeper Oriskany Formation sandstone, older wells that are no longer viable can be reused, either by fracturing the Marcellus layer in the existing well bore, or by refinishing the bore using horizontal drilling into the Marcellus. Re-use of the existing infrastructure has both environmental as well as economic benefits, because in addition to avoiding development of new drilling sites and wells, existing transportation facilities can be reused.
Lower transportation costs to the high demand markets on the East Coast of the United States
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
generate a US$0.35 per thousand cubic feet price premium over the Henry Hub
Henry Hub
]The Henry hub is the pricing point for natural gas futures contracts traded on the New York Mercantile Exchange . It is a point on the natural gas pipeline system in Erath, Louisiana...
price, compared to a discount of as much as $1.50 for gas produced in the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
.
However, heavy trucks and tankers crack the pavement and cause potholes. Such road damage is expensive for municipalities to repair. Engineers in Pennsylvania Department of Transportation have documented damage caused by the heavy trucks and tankers. Damages include but are not limited to the crushing of drain pipes, potholes, rutting, and other such pavement fatigue failures. The cost of these repairs are often much higher than the Pennsylvania Department of Transportation is allowed to charge for use of the roads. In addition to causing road damage, when heavy trucks and tankers drive over farmland, they compact the subsoil, which increases runoff and decreases crop productivity for years. Ecologists also have concerns about the ecological impact on forests when trees are cut down to make way for access roads. Ornithologists have already documented declining populations of woodland birds.
Environmental concerns around the drilling and extraction processes have sparked opposition to development of this resource. One concern is the release to the environment of underground naturally occurring radioactive material
Naturally occurring radioactive material
Naturally Occurring Radioactive Materials and Technologically Enhanced Naturally Occurring Radioactive Materials consist of materials, usually industrial wastes or by-products enriched with radioactive elements found in the environment, such as uranium, thorium and potassium and any of their...
through the drilling fluids and equipment. The hydraulic fracturing process also uses large quantities of surface water.
A large portion of the formation underlies the environmentally sensitive Chesapeake Bay Watershed as well as the Delaware River Basin. The Delaware River Basin Commission
Delaware River Basin Commission
The Delaware River Basin Commission is a United States government agency created in 1961 by an interstate compact, signed into law by President John F...
holds regulatory jurisdiction in this watershed that houses much of the Marcellus Shale formation of any operations which involve water usage, extraction, or potential contamination. They have recently made a "Determination" which requires that any component of a hydro-fracing operation that is to take place within the boundaries of their Special Protection Waters must be permitted by the DRBC, regardless of whether or not the operation was previously subject to permitting.
Chesapeake’s (The gas Company) countered with a No-Drilling Pledge for the NYC watershed area, and five miles around the watershed, however, opposes any legislation like that presented by Jim Brennan, D-Brooklyn (Brooklyn, NY), October 2009. The Susquehanna River Basin Commission
Susquehanna River Basin Commission
The Susquehanna River Basin Commission is federal-interstate compact commission created by the Susquehanna River Basin Compact between three U.S states: , and the federal government, and signed into law by President Richard Nixon on Christmas Eve 1970 to be effective 30 days later on January 23,...
, which oversees this other portion of the watershed, and the Pennsylvania Department of Environmental Protection
Pennsylvania Department of Environmental Protection
The Pennsylvania Department of Environmental Protection was established on July 1, 1995, is the agency in the U.S. State of Pennsylvania responsible for protecting and preserving the land, air, water, and energy resources through enforcement of the State's environmental laws...
, issued orders to suspend operations at several wells in May 2008 because surface water was being diverted by the drillers without the necessary permits, and precautions to protect streams from contaminated runoff were questioned. The practices of "land men" who acquire leases for drilling and extraction rights have also been widely questioned.
New York City under the New York City Gas Fuel Code made it illegal to drill within city limits. Pennsylvania is following this trend, Pittsburgh on November 16, 2010 became the first city in Pennsylvania to ban hydrofracking within city limits.
Researchers at the University of Pittsburgh recently released a study showing that "7 percent of Allegheny County’s land has been leased for drilling and extraction since 2003" and the number of properties in the county leased for oil and gas exploration has grown exponentially in recent years.
It is alleged that gas drilling in Northeast Pennsylvania caused methane to infiltrate up to 15 homes in Dimock Township, Susquehanna County, via groundwater contamination. This conclusion came from the Pennsylvania Department of Environmental Protection, though it is disputed by Cabot Oil & Gas Corp which was cited for causing the contamination. It is also disputed by other long-term area residents who have noted that high methane levels had been present for more than 60 years prior to hydrofracking in Dimock. Northeast Pennsylvania is not the only place to experience groundwater contamination following commencement of gas drilling operations.
Iron
At the base of the Marcellus, in the pyritePyrite
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...
-carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
bed between the carbonaceous black shale and a green calcareous shale bed, pyrite, carbonate, and groundwater reacted to form gossan
Gossan
Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of boxworks, quartz lined cavities retaining the shape of the dissolved...
iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
and 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...
.
As far as the ground water necessary for the conversion could penetrate, the pyrite-carbonate was converted to a usable brown hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
iron ore along the outcrops and near the bedrock surface.
The Marcellus iron ore was actively mined in south Central Pennsylvania from its discovery in the late 18th century, until it was supplanted by the rich ore beds of the Iron Range
Iron Range
The Iron Range is a region that makes up the northeastern section of Minnesota in the United States. "The Range", as it is known by locals, is a region with multiple distinct bands of iron ore...
of Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
in the early 20th century.
The ore was easily located and worked from shallow pits and shafts, but once the usable upper deposits were removed, or if a mine shaft entered the bed too far below the surface, only unusable unconverted pyritic deposits were found.
Hematite ore was converted to pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...
in charcoal
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
-fired stone blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...
s that were constructed throughout the Juniata River
Juniata River
The Juniata River is a tributary of the Susquehanna River, approximately long, in central Pennsylvania in the United States. The river is considered scenic along much of its route, having a broad and shallow course passing through several mountain ridges and steeply-lined water gaps...
region near the workable ore deposits from the Marcellus and other formations.
Iron products from this area, known as "Juniata Iron," were produced during the period between the American Revolution
American Revolution
The American Revolution was the political upheaval during the last half of the 18th century in which thirteen colonies in North America joined together to break free from the British Empire, combining to become the United States of America...
and the American Civil War
American Civil War
The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...
. These blast furnaces were important to the economy of the region at the time,
but the cold blast
Cold blast
Cold blast, in ironmaking, refers to a furnace where air is not preheated before being blown into the furnace. This represents the earliest stage in the development of ironmaking...
stone furnaces typically employed were inefficient, and consumed significant amounts of timber from the nearby hardwood forests, which ultimately led to their demise. A typical furnace used 2400 kg (5,291.1 lb) of hematite ore and 7.3 cubic metre of charcoal to produce 910 kg (2,006.2 lb) of pig iron, and could produce several thousand pounds per day, which required logging more than 4000 m² (0.988420652061104 acre) of forest daily.
The ore from the Marcellus varied in thickness, becoming unworkably thin, and even disappearing altogether in places between the workable beds. The quality of the ore also varied, and it was not always profitable to smelt
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
, as several furnaces built near iron ore mines in the Marcellus were abandoned before the ore and timber resources used to fuel them became scarce.
Ore found interbedded in the black slaty shale contained a relatively high proportion of carbon which was burned in the furnace, and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, which produced a usable but "red-short
Red-short
Red-short, hot-short or Sulfur embrittlement is the quality possessed by carbon steel that suffers from having too much sulfur as an impurity.Iron or steel, when heated to above 900 °F , glows with a red color...
" iron.
Red-short iron has the undesirable properties of oxidizing more easily, and a tendency to crack, especially when heated to a red-hot state.
In some locations in Pennsylvania the quality of the ore was quite good, with relatively deep veins containing 45% iron, and very low sulfur.
In Virginia, the Marcellus ore occasionally contained zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, which produced a characteristic green flame in the furnace as it was consumed, but deposited a hard mass of impure zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
known as cadmia
Cadmia
In alchemy, cadmia , is an oxide of zinc which collects on the sides of furnaces where copper or brass was smelted, and zinc sublimed...
, which built up over time near the top of the flue, and had to be removed periodically to keep it unobstructed.
Paint
Drainage that reacted with the pyrite inclusions also deposited a form of bog ironBog iron
Bog iron refers to impure iron deposits that develop in bogs or swamps by the chemical or biochemical oxidation of iron carried in the solutions. In general, bog ores consist primarily of iron oxyhydroxides, commonly goethite...
near several outcrops of the Marcellus. In the 19th century, iron ore from these deposits was used as a mineral paint pigment. After being heated in a kiln and finely ground, it was mixed with linseed oil
Linseed oil
Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...
, and used to paint exterior wood on barns, covered bridges, and railroad cars. In addition to the bog iron, at several sloped locations in eastern Pennsylvania brown hematite was found lying on the Marcellus bedrock buried beneath the soil. These deposits were also excavated and used for mineral paint during that time. A bed of hematite paint ore is also found almost directly below the Marcellus, but it is actually part of the underlying Oriskany Formation.
Chalybeate
Iron rich "ferruginous waters" emanating from chalybeateChalybeate
Chalybeate waters, also known as ferruginous waters, are mineral spring waters containing salts of iron.-Name:The word "chalybeate" is derived from the Latin word for steel, "chalybs", which follows from the Greek word "khalups"...
springs near the base of the Marcellus in Bedford, Pennsylvania
Bedford, Pennsylvania
Bedford is a borough in Bedford County, Pennsylvania, west of the State Capital, Harrisburg. It is the county seat of Bedford County. Bedford was established in the mid-18th century. Population counts follow: 1890, 2,242; 1900, 2,167; 1910, 2,385. The population was 3,141 at the 2000...
were believed to have healing powers by Native Americans. The Bedford Springs Hotel
Bedford Springs Hotel
The Bedford Springs Hotel is a resort hotel outside of Bedford, Pennsylvania. It is a contributing property to the Bedford Springs Hotel Historic District, a designated National Historic Landmark...
was a mineral spa
Mineral spa
Mineral spas are resorts developed around naturally occurring mineral spring locales.- Origins :Spas grew in reputation in the nineteenth century on into the late middle-twentieth century for their purported healing or healthful benefits to those wealthy enough to partake of their waters...
built in 1802 around a series of mineral springs, including one of these, its "iron spring". The Chalybeate Springs Hotel, built nearby in 1851 around three other mineral springs including another chalybeate spring, became a "resort for invalids". The iron-rich waters were prescribed for anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
and related complications. Both of these mineral springs contain iron in the form of dissolved iron carbonate, which gives these waters a "slightly inky taste".
Other uses
The Marcellus has also been used locally for shale aggregateConstruction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
and common fill
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....
, although the pyritic shales are not suitable for this purpose because of acid rock drainage and volumetric expansion.
In the 19th century, this shale was used for walkways and roadways,
and was considered superior "road metal" because the fine grained fragments packed together tightly, yet drained well after a rain.
The dark slaty shales may have the necessary cleavage
Cleavage (geology)
This article is about rock cleavage, for cleavage in minerals see Cleavage Cleavage, in structural geology and petrology, describes a type of planar rock feature that develops as a result of deformation and metamorphism. The degree of deformation and metamorphism along with rock type determines the...
and hardness to be worked, and were quarried for low grade roofing 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...
in eastern Pennsylvania during the 19th century. The slates from the Marcellus were inferior to the Martinsburg Formation
Martinsburg Formation
The Ordovician Martinsburg Formation is a mapped bedrock unit in Pennsylvania, New Jersey, Maryland, Virginia, and West Virginia. It is named for the town of Martinsburg, West Virginia for which it was first described...
slate quarried further south, and most quarries were abandoned, with the last significant operation in Lancaster County. The Marcellus black slate was also quarried in Monroe County, Pennsylvania, for school slates
Chalkboard
A chalkboard or blackboard is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate or calcium carbonate, known, when used for this purpose, as chalk. Chalkboards were originally made of smooth, thin sheets of black or dark grey slate stone...
used by students in 19th-century rural schools.
Carbonaceous shales, such as the Marcellus, are a possible target for carbon capture and storage
Carbon capture and storage
Carbon capture and storage , alternatively referred to as carbon capture and sequestration, is a technology to prevent large quantities of from being released into the atmosphere from the use of fossil fuel in power generation and other industries. It is often regarded as a means of mitigating...
for mitigation of global warming
Mitigation of global warming
Climate change mitigation is action to decrease the intensity of radiative forcing in order to reduce the potential effects of global warming. Mitigation is distinguished from adaptation to global warming, which involves acting to tolerate the effects of global warming...
. Because carbon adsorbs
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) at a greater rate than methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
(CH4), carbon dioxide injected into the formation for geological sequestration
CO2 sequestration
Carbon sequestration is the capture of carbon dioxide and may refer specifically to:* "The process of removing carbon from the atmosphere and depositing it in a reservoir." When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering.*...
could also be used to recover additional natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
in a process analogous to enhanced coal bed methane recovery
Enhanced coal bed methane recovery
Enhanced coal bed methane recovery is a method of producing additional coalbed methane from a source rock, similar to enhanced oil recovery applied to oil fields. Carbon dioxide injected into a bituminous coal bed would occupy pore space and also adsorb onto the carbon in the coal at...
, but the practical value of this theoretical technique is not yet known. Scientists believe that adsorption would allow sequestration at shallower depths than absorption in deep saline formations, which must be at least 800 m (2,624.7 ft) below the surface to maintain liquid CO2 in a supercritical state
Supercritical fluid
A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid...
.
Engineering issues
Exposures from cut and fillCut and fill
In earthmoving, cut and fill is the process of constructing a railway, road or canal whereby the amount of material from cuts roughly matches the amount of fill needed to make nearby embankments, so minimizing the amount of construction labor...
road construction in Virginia and Pennsylvania have resulted in localized acid rock drainage due to oxidation of the pyrite inclusions.
The newly exposed shale on the cut face weathers rapidly, allowing air and water into the unexcavated rock, resulting in acidic surface runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
after precipitation events.
Acidic runoff disrupts aquatic ecosystem
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
s, and highly acidic soil contaminated
Soil contamination
Soil contamination or soil pollution is caused by the presence of xenobiotic chemicals or other alteration in the natural soil environment....
by this runoff will not support vegetation, which is unsightly, and can lead to problems with soil erosion.
Natural decomposition of the shale into smaller fragments can affect slope stability
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
, necessitating shallower slopes that require more material be disturbed in cut and fill work, exacerbating the acid rock drainage problem. The cut material cannot be used as fill beneath roads and structures due to volumetric expansion, compounding the problem. The Tioga ash beds contain bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
which presents a landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
hazard in the unexcavated rock as well.
Damage to structures constructed on fill consisting of pyritic Marcellus shale has been caused by expansion from sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
(H2SO4) runoff reacting with the calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
(CaCO3) in the shale to produce 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...
(CaSO4), which has double the molar volume
Molar volume
The molar volume, symbol Vm, is the volume occupied by one mole of a substance at a given temperature and pressure. It is equal to the molar mass divided by the mass density...
.
Other sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
minerals that can be produced by reactions with pyrite include 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...
, melanterite
Melanterite
Melanterite is a mineral form of hydrous iron sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by loss of water. It is a secondary sulfate mineral which forms from the oxidation of primary sulfide minerals such as pyrite and marcasite in the...
, rozenite
Rozenite
Rozenite is an uncommon hydrous iron sulfate mineral, Fe2+SO4•4.It occurs as a secondary mineral, formed under low humidity at less than 21 °C as an alteration of copper-free melanterite which is a post mine alteration product of pyrite or marcasite. It also occurs in lacustrine sediments and coal...
, jarosite
Jarosite
Jarosite is a basic hydrous sulfate of potassium and iron with a chemical formula of KFe3+362. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides...
and alunite
Alunite
Alunite is a sulfate mineral that was first observed in the 15th century in Monti della Tolfa, north of Rome, where it was mined for the manufacture of alum. First called aluminilite by J.C. Delamétherie in 1797, this name was contracted by François Beudant in 1824 to alunite.Distinct crystals of...
.
The reactions have generated a heave pressure on the order of 500 kPa (10,000 pounds per square foot), but may be able to generate four times this pressure enough to heave foundations in a 5-story building.
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....
, which is used to neutralize the acid drainage, can actually exacerbate the expansion problem by promoting sulfate–sulfate reactions that form the minerals thaumasite
Thaumasite
-External links:*...
and ettringite
Ettringite
Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2312·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system...
, which have even higher molar volumes.
Drilling borehole
Borehole
A borehole is the generalized term for any narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid or gases , as part of a geotechnical investigation, environmental site...
s through the Hamilton Group shales in the subsurface can be problematic. The Marcellus has a relatively low density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, and these shales may not be chemically compatible with some drilling fluid
Drilling fluid
In geotechnical engineering, drilling fluid is a fluid used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. Liquid drilling fluid...
s. The shale is relatively fragile, and may fracture under pressure, causing a problem in circulating the drilling fluid back up through the borehole known as lost circulation. The formation may also be under-pressurized, further complicating the drilling process.
See also
- FracTracker: Blog and Shale Gas Data and Mapping System
- FrackTrack: Pennsylvania Marcellus Shale Mapping Application
- Geology of New JerseyGeology of New JerseyThe Geology of New Jersey consists of four distinct physiographic provinces. They are: the Atlantic Coastal Plain Province, the Piedmont Province, the Highlands Province, and the Ridge and Valley Province.-Coastal Plain:...
- Geology of PennsylvaniaGeology of PennsylvaniaThe Geology of Pennsylvania consists of six distinct physiographic provinces, three of which are subdivided into different sections. Each province has its own economic advantages and geologic hazards and play an important role in shaping everyday life in the state...
- Geology of West VirginiaGeology of West VirginiaPrior to one billion years ago, the geologic history of West Virginia is obscure. The oldest evidences of life found in West Virginia occur in rocks about 600 million years old, in the Antietam Formation of Lower Cambrian age. The oldest exposed rock, the Catoctin greenstone, began to form between...
- Pittsburgh Association of Petroleum GeologistsPittsburgh Association of Petroleum Geologists]The Pittsburgh Association of Petroleum Geologists is a non-profit organization founded in 1984 to provide a forum for petroleum geologists in the Pittsburgh area to meet socially and discuss technical topics relative to the exploration and development of reserves in the Northern and Central...
- Shale gasShale gasShale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...
- Shale gas in the United StatesShale gas in the United StatesShale gas in the United States is rapidly increasing as a source of natural gas. Led by new applications of hydraulic fracturing technology and horizontal drilling, development of new sources of shale gas has offset declines in production from conventional gas reservoirs, and has led to major...
External links
- http://energy.wilkes.edu/pages/1.aspA Marcellus Shale Clearinghouse – The Institute for Energy and Environmental Research for Northeastern Pennsylvania Wilkes UniversityWilkes UniversityWilkes University is a private, non-denominational American university located in Wilkes-Barre, Pennsylvania. It has over 2,200 undergraduates and over 2,200 graduate students...
- Outcrops of the Marcellus Formation images with captions hosted at Pennsylvania State UniversityPennsylvania State UniversityThe Pennsylvania State University, commonly referred to as Penn State or PSU, is a public research university with campuses and facilities throughout the state of Pennsylvania, United States. Founded in 1855, the university has a threefold mission of teaching, research, and public service...
- Susquehanna River Basin Marcellus Shale Occurrence map
- Pittsburgh Association of Petroleum Geologists PAPG publications including the Marcellus Shale
- Marcellus Shale Links Maps and Links to Governmental and Non Governmental sites about the Marcellus Shale
- Natural Gas Changes the Energy Map MIT's Technology Review article about the gas potential of Marcellus Shale (only a brief synopsis is free)
- Citizens Campaign for the Environment: CAMPAIGNS: Natural Gas Hydro-Fracking in Shale