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The Marcellus Formation or the Marcellus Shale is a
Middle Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
age
unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (alb ...
of
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
found in eastern
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
. Named for a distinctive
outcrop An outcrop or rocky 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 ...
near the village of Marcellus,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
, in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, it extends throughout much of the
Appalachian Basin The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ...
. The unit name usage by the U.S. Geological Survey (USGS) includes ''Marcellus Shale'' and ''Marcellus Formation''.See unit names marked by an asterisk a
Geolex
/ref> The term "Marcellus Shale" is the preferred name throughout most of the Appalachian region, although the term "Marcellus Formation" is also acceptable within the State of Pennsylvania. The unit was first described and named as the "Marcellus shales" by J. Hall in 1839.


Description

The Marcellus consists predominantly of
black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
and a few
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
beds A bed is an item of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many be ...
and concentrations of iron
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
 ( Fe S2) and
siderite Siderite is a mineral composed of iron(II) 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. Zinc, magnesium and ...
 (Fe CO3). Like most shales, it tends to split easily along the bedding plane, a property known as
fissility In nuclear engineering, fissile material is material capable of sustaining a nuclear fission Nuclear chain reaction#Fission chain reaction, chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal ene ...
. 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 is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH ...
stains from exposure of pyrite to air, and tiny
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
 ( Ca SO4·2 H2O) crystals from the reaction between pyrite and limestone particles. Fresh exposures of the pyriteiferous shale may develop the secondary mineralization of orange
limonite Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxid ...
 (Fe O( OH)·nH2O), and the pale yellow
efflorescence In chemistry, efflorescence (which means "to flower out" in French) is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an internally held salt in water, or ...
or bloom of
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
, associated with
acid rock drainage In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
. Pyrite is especially abundant near the base, and the upper contacts of limestones, but
framboid A framboid is a micromorphological feature common to certain sedimentary minerals, particularly pyrite (FeS2). The first known use of the term is ascribed to Rust in 1935 and is derived from the French ‘la framboise’, meaning ‘raspberry’, re ...
al microcrystals and
euhedral Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as ''xenomorphic'' or ''allotriomorphic''): a rock with an anhedral ...
crystals of pyrite occur throughout the organic-rich deposits. The Marcellus also contains
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
, and the
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
of the
uranium-238 Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it ...
 (238U) makes it a
source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depos ...
for radioactive
radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains through ...
gas (222Rn). Measured total organic content of the Marcellus 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, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
. The more organic-rich black shales can be
bituminous Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
, but are too old to contain
bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It ...
formed from land plants. In
petroleum geology Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration). Sedime ...
, these black shales are an important
source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depos ...
that filled conventional
petroleum reservoir A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...
s in overlying formations, are an unconventional
shale gas Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some a ...
reservoir, and are an impermeable seal that traps underlying conventional
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
reservoirs. To the west the formation may produce liquid
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
; further north heating during deeper burial more than 240 million years ago
cracked Cracked may refer to: Television * ''Cracked'' (British TV series), a 2008 British comedy-drama television series that aired on STV * ''Cracked'' (Canadian TV series), a 2013 Canadian crime drama series that aired on CBC * "Cracked", a Season 8 ( ...
this oil into gas.


Geographic extent

The Marcellus is found throughout the
Allegheny Plateau The Allegheny Plateau , in the United States, is a large dissected plateau area of the Appalachian Mountains in western and central New York, northern and western Pennsylvania, northern and western West Virginia, and eastern Ohio. It is divide ...
region of the northern
Appalachian Basin The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ...
of North America. In the United States, the Marcellus Shale runs across the
Southern Tier The Southern Tier is a geographic subregion of the broader Upstate New York region of New York State, consisting of counties west of the Catskill Mountains in Delaware County and geographically situated along or very near the northern border ...
and
Finger Lakes The Finger Lakes are a group of eleven long, narrow, roughly north–south lakes located south of Lake Ontario in an area called the ''Finger Lakes region'' in New York, in the United States. This region straddles the northern and transitional ...
regions of
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
, in northern and western
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, eastern
Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
, through western
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
, and throughout most of
West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...
extending across the state line into extreme western
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
. The Marcellus bedrock in eastern Pennsylvania extends across the
Delaware River The Delaware River is a major river in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. From the meeting of its branches in Hancock (village), New York, Hancock, New York, the river flows for along the borders of N ...
into extreme western
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
. It also exists in the subsurface of a small portion of
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...
and
Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...
. Below
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has t ...
, it can be found crossing the border into
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, where it stretches between
Port Stanley Stanley (; also known as Port Stanley) is the capital city of the Falkland Islands. It is located on the island of East Falkland, on a north-facing slope in one of the wettest parts of the islands. At the 2016 census, the city had a populat ...
and Long Point to St. Thomas in southern
Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
.


Outcrops in New York

The Marcellus appears in outcrops along the northern margin of the formation in central New York. There, the two
joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...
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 In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on co ...
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 is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
. 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 seam Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...
s. In
Perry County, Pennsylvania Perry County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 45,842. The county seat is New Bloomfield. The county was created on March 22, 1820, and was named for Oliver Hazard Perry, a hero of the ...
along the
Juniata River The Juniata River () is a tributary of the Susquehanna River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed August 8, 2011 in central Pennsylvania. The river is ...
the false coal beds become up to thick, but they did not produce a valuable fuel, despite the considerable effort expended to mine it from the surrounding hills.
Seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
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 may refer to: Places Italy *Syracuse, Sicily, or spelled as ''Siracusa'' *Province of Syracuse United States *Syracuse, New York **East Syracuse, New York **North Syracuse, New York *Syracuse, Indiana * Syracuse, Kansas *Syracuse, Miss ...
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 below the surface in southern Pennsylvania.


Geomorphological expression

Upturned beds are exposed in sections of the folded
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 ...
, 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 The Allegheny Front is the major southeast- or east-facing escarpment in the Allegheny Mountains in southern Pennsylvania, western Maryland, eastern West Virginia, and western Virginia, USA. The Allegheny Front forms the boundary between the Rid ...
. From
Wind Gap, Pennsylvania Wind Gap ( Pennsylvania Dutch: ''Gratdaal'') is a borough in Northampton County, Pennsylvania. The population of Wind Gap was 2,820 at the 2020 census. Wind Gap is part of the Lehigh Valley metropolitan area, which had a population of 861,899 a ...
heading south, the dip of the beds steepens, becoming vertical at Bowmanstown on the
Lehigh River The Lehigh River is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 1, 2011 tributary of the Delaware River in eastern Pennsylvania. The river flows in a generally southward pat ...
. Nearby, in the
Lehigh Gap The Lehigh Gap or Lehigh Water Gap is a water gap located in the townships of Lehigh, Washington, Lower Towamensing and East Penn in the Lehigh Valley region of eastern Pennsylvania. It was formed by the Lehigh River where it cuts through the ...
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-formers. 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 Cacapon Mountain ( ) runs northwest through Morgan and Hampshire counties in West Virginia's Eastern Panhandle, rising to its greatest elevation of above sea-level at High Point. Cacapon Mountain is a folded mountain ridge, belonging to the A ...
anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...
in the
Eastern Panhandle of West Virginia The Eastern Panhandle is the eastern of the two salient (geography), panhandles in the U.S. state of West Virginia; the other is the Northern Panhandle of West Virginia, Northern Panhandle. It is a small stretch of territory in the northeast of ...
. 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. The Marcellus is easily
eroded Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...
, 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 (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combinatio ...
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 or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
. Sampling of soil formed on the Marcellus bedrock showed the dominant
mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
consisted of
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
,
illite Illite is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandwich of silica tetrahedron (T) – alumina ...
,
montmorillonite Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite gro ...
,
muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage ...
, and
biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...
, with phases of
todorokite Todorokite is a rare complex hydrous manganese oxide mineral with the chemical formula . It was named in 1934 for the type locality, the Todoroki mine, Hokkaido, Japan. It belongs to the prismatic class 2/m of the monoclinic crystal system, but ...
and
trona Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3•2NaHCO3•3H2O) is a non- marine evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has replace ...
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 (pronounced Ahkwa-SHIK-ola), also known as Aquanchicola Creek, or Aquanshicola Creek, is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 1, 2011 tributary of the ...
and
McMichael Creek McMichael Creek is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 1, 2011 tributary of Pocono Creek in the Poconos of eastern Pennsylvania in the United States.Gertler, Edward. ' ...
at the foot of
The Poconos The Pocono Mountains, commonly referred to as the Poconos , are a geographical, geological, and cultural region in Northeastern Pennsylvania. They overlook the Delaware River and Delaware Water Gap to the east, Lake Wallenpaupack to the north, W ...
, and the long, straight section of the Lost River in West Virginia. Below
Port Jervis, New York Port Jervis is a city located at the confluence of the Neversink and Delaware rivers in western Orange County, New York, United States, north of the Delaware Water Gap. Its population was 8,775 at the 2020 census. The communities of Deerpark, ...
, the Walpack Ridge deflects the
Delaware River The Delaware River is a major river in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. From the meeting of its branches in Hancock (village), New York, Hancock, New York, the river flows for along the borders of N ...
into the Minisink Valley, where it follows the southwest
strike Strike may refer to: People * Strike (surname) Physical confrontation or removal *Strike (attack), attack with an inanimate object or a part of the human body intended to cause harm *Airstrike, military strike by air forces on either a suspected ...
of the eroded Marcellus beds along the Pennsylvania – New Jersey state line for to the end of the ridge at Walpack Bend in the
Delaware Water Gap National Recreation Area Delaware Water Gap National Recreation Area is a national recreation area administered by the National Park Service in northwest New Jersey and northeast Pennsylvania. It is centered around a stretch of the Delaware River designated the Middle ...
. The Minisink is a
buried valley A buried valley is an ancient river or stream valley that has been filled with glacial or unconsolidated sediment. This sediment is made up of predominantly gravel and sand, with some silt and clay. These types of sediments can often store and trans ...
where the Delaware flows in a bed of
glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
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 is a borough in Monroe County, Pennsylvania. It lies within the Poconos region, approximately five miles (8 km) from the Delaware Water Gap at the confluence of the Brodhead, McMichaels and Pocono Creeks in Northeastern Pennsyl ...
, and northeast from Port Jervis toward the
Hudson River The Hudson River is a river that flows from north to south primarily through eastern New York. It originates in the Adirondack Mountains of Upstate New York and flows southward through the Hudson Valley to the New York Harbor between N ...
, along the route of the
Delaware and Hudson Canal The Delaware and Hudson Canal was the first venture of the Delaware and Hudson Canal Company, which would later build the Delaware and Hudson Railway. Between 1828 and 1899, the canal's barges carried anthracite coal from the mines of northeaster ...
.


Stratigraphy

Stratigraphically, the Marcellus is the lowest unit of the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
age Hamilton Group, and is divided into several sub-units. In the first
Pennsylvania Geological Survey The Pennsylvania Geological Survey or Bureau of Topographic and Geologic Survey (BTGS), is a geological survey enacted by the Pennsylvania General Assembly "to serve the citizens of Pennsylvania by collecting, preserving, and disseminating impartial ...
, begun in 1836,
Henry Darwin Rogers Henry Darwin Rogers FRS FRSE LLD (1 August 1808 – 26 May 1866) was an American geologist. His book, ''The Geology of Pennsylvania: A Government Survey'' (1858), was regarded as one of the most important publications on American geology issu ...
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.


Overlying units

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 Shale (abbr. Dm or Dms) is classified as the basal unit of the
Hamilton Group The Hamilton Group is a Devonian-age geological group in the Appalachian region of the United States. It is present in New York, Pennsylvania, Maryland, Ohio, West Virginia, northwestern Virginia and Ontario, Canada. It is mainly composed of mar ...
 (Dh), lying beneath the
Mahantango Formation The Devonian Mahantango Formation is a mapped bedrock unit in Pennsylvania, West Virginia, 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 Gro ...
 (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 is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
beds and
concretions A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...
, or it may lie directly below the younger
Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
Harrel Formation (or its lateral equivalents) because of a
disconformity An unconformity is a buried erosional or non-depositional 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 ...
, 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 units

The Marcellus Shale is typically found deposited on the limestone of the
Onondaga Formation The Onondaga Limestone is a group of hard limestones and dolomites of Devonian age that form an important geographic feature in some areas in which it outcrops; in others, especially its Southern Ontario portion, the formation can be less promine ...
 (Don), which extends down to the end of the
Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the P ...
period. The contact between them may be sharp, gradational, or erosional. In southwestern Ontario, Canada, north of
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has t ...
, the Marcellus overlies the Dundee Formation, a lateral equivalent of the Onondaga. In Pennsylvania, the Marcellus forms a sharp
conformable In mathematics, a matrix is conformable if its dimensions are suitable for defining some operation (''e.g.'' addition, multiplication, etc.). Examples * If two matrices have the same dimensions (number of rows and number of columns), they are ...
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 Onondaga (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 Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...
. 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 Romney is a town in and the county seat of Hampshire County, West Virginia, United States. The population was 1,722 at the 2020 census. History Established by consecutive acts of the Virginia House of Burgesses and approved by the governor on ...
. 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 In science, priority is the credit given to the individual or group of individuals who first made the discovery or propose the theory. Fame and honours usually go to the first person or group to publish a new finding, even if several researchers arr ...
, 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 () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...
–stratigraphic unit about thick that consists of several discrete, relatively thin
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
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 A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...
in
Tioga County, Pennsylvania Tioga County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 41,045. Its county seat is Wellsboro. The county was created on March 26, 1804, from part of Lycoming County and later organized in 1812. ...
, where it was encountered when
drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ra ...
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 .
Explosive eruption In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such ...
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 Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
, and
Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...
Basins by the southern
trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...
, 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 is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
–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 Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
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 in New Jersey, to in Canada. In West Virginia, the Marcellus Shale is as much as thick. In extreme eastern Pennsylvania, it is thick, thinning to the west, becoming only thick along the
Ohio River The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illino ...
, and only a few feet in
Licking County, Ohio Licking County is a county located in the central portion of the U.S. state of Ohio. At the 2020 census, the population was 178,519. Its county seat is Newark. The county was formed on January 30, 1808, from portions of Fairfield County. It is ...
. The thinning, or
stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...
convergence, from east to west is caused by decreasing grain size in the
clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
deposits, which entered the basin from the east. The beds finally "pinch out" westward because deposition was limited by the
Cincinnati Arch The Cincinnati Arch is a broad structural uplift between the Illinois Basin to the west, the Michigan Basin to the northwest and the Appalachian Basin and Black Warrior Basin to the east and southeast. It existed as a positive topographic area du ...
, 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.


Named members

A local Purcell limestone member, 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 Bioclasts are skeletal fossil fragments of once living marine or land organisms that are found in sedimentary rocks laid down in a marine environment—especially limestone varieties around the globe. some of which take on distinct textures and col ...
ic
packstone Under the Dunham classification (Dunham, 1962Dunham, R.J. (1962) Classification of carbonate rocks according to depositional texture. In: Classification of Carbonate Rocks (Ed. W.E. Ham), Am. Assoc. Pet. Geol. Mem., 1, 108–121.) system of limesto ...
, consisting of skeletal limestones, with shaly intervals between its lower massive limestone layer, thick nodular limestone/
marlstone Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part ...
, 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 () 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 ''Calcareous'' is used as an adje ...
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 thick.


Fossils

There are relatively sparse inclusions of fossilized marine
fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...
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 Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
still having well preserved shell microstructure. It is also where
goniatites ''Goniatites'' is a genus of extinct cephalopods belonging to the family Goniatitidae, included in the superfamily Goniatitaceae. '' Hibernicoceras'' and '' Hypergoniatites'' are among related genera. Species Description The shell is genera ...
, 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 Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
trees that floated out to sea to be preserved in the black shale. Marcellus fossils include specimens of the large clam-like
brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...
Spinocyrtia. External molds of
crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which 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 () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxid ...
; brachiopod and
bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
(clam) molds have also been found in the shale. Small conical
tentaculitid Tentaculita is an extinct class of uncertain placement ranging from the Early Ordovician to the Middle Jurassic. They were suspension feeders with a near worldwide distribution. For a more thorough discussion, see ''Tentaculites''. The presenc ...
s are commonly found in the Chittenango Member. The Halihan Hill bed contains styliolinids and macrofauna including brachiopods, coral-like bryozoans, small bivalves and
gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
s (snails), incorporated after the
faunal turnover An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rap ...
when
Emsian The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after the ...
and
Eifelian The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American s ...
Schoharie/Onondaga fauna were replaced by the
Givetian The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in Fra ...
Hamilton fauna. The Solsville member contains well preserved bivalves, gastropods, and brachiopods. These shellfish lived in the
benthic zone The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning " ...
at the bottom of marginal marine to open marine environments that existed west of the ancient
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 (up to ). It is equivalent to the Hampshire Form ...
. The fossil record in this member shows the base was dominated by
deposit feeder Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...
s, while the upper layers were dominated by
filter feeder Filter feeders are a sub-group of suspension feeding 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 feedin ...
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 Berne is a town in Albany County, New York, United States. The population was 2,689 at the 2020 census. The town is at the western border of Albany County. History The town of Berne was originally spelled "Bern", until the Berne Post Office wa ...
. A diverse, eel-like
conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...
fauna occurs in the limestone of the Cherry Valley Member, which is also known for its rich
nautiloid Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species ...
and goniatite
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
fauna. Originally named the ''Goniatite Limestone'', it produces their fossilized remains with shells that can be larger than 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 Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...
interval also provides an excellent example of incursion
epibole In biostratigraphy, an acme zone, abundance zone, or peak zone is the area of a teilzone where a particular fossil taxon reaches a higher level of abundance. See also *Biozone In biostratigraphy, biostratigraphic units or biozones are intervals of ...
s, which are sudden appearances and disappearances of fossil
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
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.


Age

On the
geological timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...
, the Marcellus occurs in the
Middle Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
epoch, of the
Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...
, in the
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
era An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth. Comp ...
, of the
Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...
eon Eon or Eons may refer to: Time * Aeon, an indefinite long period of time * Eon (geology), a division of the geologic time scale Arts and entertainment Fictional characters * Eon, in the 2007 film ''Ben 10: Race Against Time'' * Eon, in the ...
. 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 The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in Fra ...
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 convent ...
, 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 Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American s ...
, the stage which immediately preceded the Givetian. Anoxic dark shales in the formation mark the
Kačák Event The Kačák Event (), also known as the Kačák-''otomari'' Event, is a widely recognised bioevent or series of events that occurred close to the end of the Eifelian Age (geology), Age of the Middle Devonian Epoch. It involved a global eustatic ris ...
, a late-
Eifelian The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American s ...
-
stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...
marine
anoxic event Oceanic anoxic events or anoxic events ( anoxia conditions) describe periods wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulfidic) waters. Although anoxic events have not ...
also associated with an
extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...
. In 2012, Read and Erikson also depicted the formation as Eifelian.


Interpretation of depositional environment

Although black
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
is the dominant
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. Physical characteristics include colour, texture, grain size, and composition. Lit ...
, it also contains lighter shales and
interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedim ...
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
layers due to sea level variation during its deposition almost . The black shale was deposited in relatively deep water devoid of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, and is only sparsely
fossiliferous A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
. Most fossils are contained in the limestone members, and the fossil record in these layers provides important
paleontological Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes t ...
insights on faunal turnovers. Early in the Acadian orogeny, 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 In oceanography, terrigenous sediments are those derived from the erosion of rocks on land; that is, they are derived from ''terrestrial'' (as opposed to marine) environments. Consisting of sand, mud, and silt carried to sea by rivers, their ...
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 The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
),
trough Trough may refer to: In science * Trough (geology), a long depression less steep than a trench * Trough (meteorology), an elongated region of low atmospheric pressure * Trough (physics), the lowest point on a wave * Trough level (medicine), the l ...
that formed parallel to the mountain chain. These
clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...
fragments of rock were carried in
braided stream A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment lo ...
s to the ancient
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 (up to ). It is equivalent to the Hampshire Form ...
, a
river delta A river delta is a landform shaped like a triangle, created by deposition (geology), deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, res ...
probably similar to the present day
Niger Delta The Niger Delta is the delta of the Niger River sitting directly on the Gulf of Guinea on the Atlantic Ocean in Nigeria. It is located within nine coastal southern Nigerian states, which include: all six states from the South South geopolitical ...
of Africa. Smaller particles remained suspended longer in this
epeiric sea An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...
, flowing offshore as
turbidites A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...
in a slow but persistent underwater avalanche. They finally came to rest at the bottom of the Acadian
foredeep A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere ...
in the
Appalachian Basin The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ...
, hundreds of meters from shore, at depths that may have been or more beneath the surface. Alternatively, the basin may have been as shallow as or less, if the warm water was sufficiently
stratified Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...
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 In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...
of the Marcellus were formed from
flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building ep ...
, a fine mud deposited in deep water; the deepening sea that deposited the Marcellus cut off the supply of
carbonates A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
that form limestone and the fine-grained flysch sediments buried the Onondaga limestone beds. Organic matter, probably dominated by
plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
, also settled to the bottom, but the normal aerobic decay process was inhibited in the
anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
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 (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...
-sensitive elements uranium,
rhenium Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...
,
molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...
,
osmium Osmium (from Greek grc, ὀσμή, osme, smell, label=none) is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mos ...
,
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
, and
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
. The Marcellus was deposited during the 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 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 s ...
and
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. Hasson and Dennison (1978) state "The Harrell Shale ...
.


Economic resources


Natural gas

The shale contains largely untapped
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
reserves, and its proximity to the high-demand markets along the
East Coast of the United States The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The eastern seaboard contains the coa ...
makes it an attractive target for
energy development Energy development is the field of activities focused on obtaining sources of energy from natural resources. These activities include production of renewable, nuclear, and fossil fuel derived sources of energy, and for the recovery and reuse ...
and
export An export in international trade is a good produced in one country that is sold into another country or a service provided in one country for a national or resident of another country. The seller of such goods or the service provider is an ...
. The Marcellus natural gas trend, which encompasses 104,000 square miles and stretches across Pennsylvania and West Virginia, and into southeast Ohio and upstate New York, is the largest source of natural gas in the United States, and production was still growing rapidly in 2013. The Marcellus is an example of
shale gas Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some a ...
, natural gas trapped in low-permeability shale, and requires the well completion method of
hydraulic fracturing Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
to allow the gas to flow to the well bore. The surge in drilling activity in the Marcellus Shale since 2008 has generated both economic benefits and environmental concerns—and thus, considerable controversy.


Iron

The black shales also contain
iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...
that was used in the early economic development of the region, and
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
which are environmental hazards. At the base of the Marcellus, in the
pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), lust ...
-
carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
bed between the carbonaceous black shale and a green calcareous shale bed, pyrite, carbonate, and groundwater reacted to form
gossan Gossan (eiserner hut or eisenhut) 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 i ...
iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
and
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
. As far as the ground water necessary for the conversion could penetrate, the pyrite-carbonate was converted to a usable brown
hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...
iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the fo ...
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 The term Iron Range refers collectively or individually to a number of elongated iron-ore mining districts around Lake Superior in the United States and Canada. Much of the ore-bearing region lies alongside the range of granite hills formed by ...
of
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
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, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with silic ...
in
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...
-fired stone
blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being "forced" or supplied above atmospheric ...
s that were constructed throughout the
Juniata River The Juniata River () is a tributary of the Susquehanna River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed August 8, 2011 in central Pennsylvania. The river is ...
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 The American Revolution was an ideological and political revolution that occurred in British America between 1765 and 1791. The Americans in the Thirteen Colonies formed independent states that defeated the British in the American Revolut ...
and the
American Civil War The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...
. These blast furnaces were important to the economy of the region at the time, but the
cold blast Cold blast, in ironmaking, refers to a metallurgical furnace where air is not preheated before being blown into the furnace. This represents the earliest stage in the development of ironmaking. Until the 1820s, the use of cold air was thought to b ...
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 of hematite ore and of charcoal to produce of pig iron, and could produce several thousand pounds per day, which required logging more than 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 Smelt may refer to: * Smelting, chemical process * The common name of various fish: ** Smelt (fish), a family of small fish, Osmeridae ** Australian smelt in the family Retropinnidae and species ''Retropinna semoni'' ** Big-scale sand smelt ''At ...
, 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 (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
, which produced a usable but "
red-short Red-short, hot-short refers to brittleness of steels at red-hot temperatures. It is often caused by high sulfur levels, in which case it is also known as sulfur embrittlement. Description Iron or steel, when heated to above 900 °F (460  ...
" 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 is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, which produced a characteristic green flame in the furnace as it was consumed, but deposited a hard mass of impure
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
known as
cadmia In alchemy, cadmia (Latin for cadmium) is an oxide of zinc (tutty; from ar, توتيا ''tutiya'', via Persian, from Sanskrit तुत्थ ''tuttha'') 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.


Iron pigments

Drainage that reacted with the pyrite inclusions also deposited a form of
bog iron Bog iron is a form of impure iron deposit that develops in bogs or swamps by the chemical or biochemical oxidation of iron carried in solution. In general, bog ores consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)). Iron-bea ...
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, also known as flaxseed oil or flax oil (in its edible form), is a colourless to yellowish oil obtained from the dried, ripened seeds of the flax plant (''Linum usitatissimum''). The oil is obtained by pressing, sometimes followed by ...
, 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
chalybeate 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, , which follows from the Greek word . is the singular form of ...
springs near the base of the Marcellus in
Bedford, Pennsylvania Bedford is a borough and spa town in and the county seat of Bedford County in the U.S. state of Pennsylvania. It is located west of Harrisburg, the state capital, and east of Pittsburgh. Bedford's population was 2,861 at the 2020 census. His ...
were believed to have healing powers by Native Americans. The
Bedford Springs Hotel Omni Bedford Springs Resort is a resort hotel outside of Bedford, Pennsylvania. Established in 1806, it is one of last and best-preserved of 19th-century resort hotels based around mineral springs. The hotel was documented in 2005 by the Histor ...
was a
mineral spa Mineral spas are destination spa, spa resorts developed around naturally occurring mineral springs. Like seaside resorts, they are mainly used recreationally although they also figured prominently in traditional medicine, prescientific medicine. ...
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 or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
and related complications. Both of these mineral springs contain iron in the form of dissolved
iron carbonate Iron(II) carbonate, or ferrous carbonate, is a chemical compound with formula , that occurs naturally as the mineral siderite. At ordinary ambient temperatures, it is a green-brown ionic solid consisting of iron(II) cations and carbonate anions ...
, which gives these waters a "slightly inky taste".


Other uses

The Marcellus has also been used locally for shale aggregate 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 A road surface (British English), or pavement (American English), is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, hoggin, cobbles ...
" 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 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. It is the finest grained foliated metamorphic rock. ...
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 Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
for
mitigation of global warming Climate change mitigation is action to limit climate change by reducing emissions of greenhouse gases or removing those gases from the atmosphere. The recent rise in global average temperature is mostly caused by emissions from fossil fuels bur ...
. Because carbon
adsorbs Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a Surface science, surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorpti ...
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
 (CO2) at a greater rate than
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
 (CH4), carbon dioxide injected into the formation for geological sequestration could also be used to recover additional
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
in a process analogous to
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 (CO2) injected into a bituminous coal bed would occupy pore space ...
, but the practical value of this theoretical technique is not yet known. Scientists believe that adsorption would allow sequestration at shallower depths than
absorption Absorption may refer to: Chemistry and biology * Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which ...
in deep saline formations, which must be at least below the surface to maintain liquid CO2 in a supercritical state.


Engineering issues

The
fissile In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be typ ...
shales are also easily
eroded Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...
, presenting additional
civil Civil may refer to: *Civic virtue, or civility *Civil action, or lawsuit * Civil affairs *Civil and political rights *Civil disobedience *Civil engineering *Civil (journalism), a platform for independent journalism *Civilian, someone not a membe ...
and
environmental engineering Environmental engineering is a professional engineering discipline that encompasses broad scientific topics like chemistry, biology, ecology, geology, hydraulics, hydrology, microbiology, and mathematics to create solutions that will protect and a ...
challenges. Exposures from
cut 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 to minimize the amount of construction labor. ...
road construction in Virginia and Pennsylvania have resulted in localized
acid rock drainage In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
due to
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
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 (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...
after precipitation events. Acidic runoff disrupts
aquatic ecosystem An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
s, and highly
acidic soil Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. Soil pH is a key characteristic that can be used to make informative analysis both qualitative and quantitatively regarding soil characteristics. pH is defined as the neg ...
contaminated Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...
by this runoff will not support vegetation, which is unsightly, and can lead to problems with
soil erosion Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and ...
. Natural decomposition of the shale into smaller fragments can affect
slope stability Slope stability analysis is a static or dynamic, analytical or empirical method to evaluate the stability of earth and rock-fill dams, embankments, excavated slopes, and natural slopes in soil and rock. Slope stability refers to the condition of i ...
, 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 () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
which presents a
landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...
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 (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
 (H2SO4) runoff reacting with the
calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
 (CaCO3) in the shale to produce
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
 (CaSO4), which has double the
molar volume In chemistry and related fields, the molar volume, symbol ''V''m, or \tilde V of a substance is the ratio of the volume occupied by a substance to the amount of substance, usually given at a given temperature and pressure. It is equal to the molar ...
. Other
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ar ...
minerals that can be produced by reactions with pyrite include
anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula 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 ...
,
melanterite Melanterite is a mineral form of hydrous iron(II) 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 prima ...
,
rozenite Rozenite is a hydrous iron sulfate mineral, Fe2+SO4•4(H2O). It occurs as a secondary mineral, formed under low humidity at less than as an alteration of copper-free melanterite, which is a post mine alteration product of pyrite or marcasite. It ...
,
jarosite Jarosite is a basic hydrous sulfate of potassium and ferric iron (Fe-III) with a chemical formula of KFe3(SO4)2(OH)6. This sulfate mineral is formed in ore deposits by the oxidation of iron sulfides. Jarosite is often produced as a byproduct duri ...
, and
alunite Alunite is a hydroxylated aluminium potassium sulfate mineral, formula K Al3( S O4)2(O H)6. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. First called ''aluminilite'' by J.C. Del ...
. 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 Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...
in a 5-story building.
Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
, 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 is a calcium silicate mineral, containing Si atoms in unusual octahedron, octahedral configuration, with chemical formula calcium, Ca3silicon, Si(Ohydrogen, H)6(carbon, Coxygen, O3)(sulfur, SO4)·12water, H2O, also sometimes more simply ...
and
ettringite Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of ...
, which have even higher molar volumes. Drilling
borehole A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petro ...
s through the Hamilton Group shales in the subsurface can be problematic. The Marcellus has a relatively low
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
, and these shales may not be chemically compatible with some
drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is 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 us ...
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

*
Geology of New Jersey New Jersey is a very geologically and geographically diverse region in the United States' Middle Atlantic region, offering variety from the Appalachian Mountains and the Highlands in the state's northwest, to the Atlantic Coastal Plain region that ...
*
Geology of Pennsylvania The 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 plays an important role in shaping everyd ...
** List of mapped rock formations in Pennsylvania * Geology of West Virginia
Interactive timeline of gas production from the Marcellus Formation
* Pittsburgh Association of Petroleum Geologists *
Shale gas Shale gas is an unconventional natural gas that is found trapped within shale formations. Since the 1990s a combination of horizontal drilling and hydraulic fracturing has made large volumes of shale gas more economical to produce, and some a ...
*
Shale gas in the United States Shale gas in the United States is an available source of unconventional 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 fro ...


References


External links


A creative exploration of natural gas drilling and development in the Marcellus ShaleA_Marcellus_Shale_Clearinghouse_–_The_Institute_for_Energy_and_Environmental_Research_for_Northeastern_Pennsylvania_Wilkes_University
.html" ;"title="Wilkes University">A Marcellus Shale Clearinghouse – The Institute for Energy and Environmental Research for Northeastern Pennsylvania Wilkes University
">Wilkes University">A Marcellus Shale Clearinghouse – The Institute for Energy and Environmental Research for Northeastern Pennsylvania Wilkes University
br>Outcrops of the Marcellus Formation
images with captions hosted at Pennsylvania State University
Susquehanna River Basin Marcellus Shale Occurrence
map

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
FracTracker: Blog and Shale Gas Data and Mapping SystemFrackTrack: Pennsylvania Marcellus Shale Mapping ApplicationEconomist on Marcellus Region

Bucknell University Marcellus Shale Initiative Publications Database
{{Pittsburgh Metro Area Shale formations of the United States Oil-bearing shales in Canada Oil-bearing shales in the United States Oil shale formations Oil shale in Canada Oil shale in the United States Devonian Canada Devonian United States Middle Devonian Series Devonian Maryland Devonian geology of New Jersey Devonian geology of New York (state) Devonian Ohio Devonian Ontario Devonian geology of Pennsylvania Devonian geology of Virginia Devonian West Virginia Shale formations Sandstone formations of the United States Tuff formations Devonian System of North America Devonian southern paleotemperate deposits