Marcellus Formation

Marcellus Formation Stratigraphic range: Middle Devonian PreЄ Є O S D C P T J K Pg N
Marcellus shale exposure above Marcellus, N.Y. The vertical joints create sheer cliff faces.
Type	Geological formation
Unit of	Hamilton Group
Sub-units	See: Named members
Underlies	Mahantango Formation
Overlies	Onondaga Formation
Thickness	up to 900 feet (270 m)[1]
Lithology
Primary	Shale
Other	Slate, Limestone, Sandstone
Location
Named for	Marcellus, New York
Named by	James Hall, 1839
Region	Appalachian Basin of eastern North America
Extent	600 miles (970 km)[2]

The Marcellus Formation (also classified as the Marcellus Subgroup of the Hamilton Group, Marcellus Member of the Romney Formation, or simply the Marcellus Shale) is a unit of marine sedimentary rock found in eastern North America. Named for a distinctive outcrop near the village of Marcellus, New York in the United States,^[3] it extends throughout much of the Appalachian Basin.^[4] The shale contains largely untapped natural gas reserves, and its proximity to the high-demand markets along the East Coast of the United States makes it an attractive target for energy development.^[5]

Stratigraphically, the Marcellus is the lowest unit of the Devonian age Hamilton Group, and is divided into several sub-units. Although black shale is the dominant lithology, it also contains lighter shales and interbedded limestone layers due to sea level variation during its deposition almost 400 million years ago.^[6] The black shale was deposited in relatively deep water devoid of oxygen, and is only sparsely fossiliferous. Most fossils are contained in the limestone members, and the fossil record in these layers provides important paleontologal insights on faunal turnovers. The black shales also contain iron ore that was used in the early economic development of the region, and uranium and pyrite which are environmental hazards. The fissile shales are also easily eroded, presenting additional civil and environmental engineering challenges.

Geology

Description

The Marcellus Formation is a black shale that may contain limestone beds and concentrations of iron pyrite (FeS₂) and siderite (FeCO₃).^[7] Its sedimentary structure, or bedding, is moderately well developed. Like most shales, it tends to split easily along the bedding plane, a property known as fissility.^[7] Lighter colored shales in the upper portion of the formation tend to split into small thin-edged fragments after exposure.^[8] These fragments may have rust stains from exposure of pyrite to air, and tiny gypsum (CaSO₄·2H₂O) crystals from the reaction between pyrite and limestone particles.^[8] Fresh exposures of the pyriteiferous shale may develop the secondary mineralization of orange limonite (FeO(OH)·nH₂O), and the pale yellow efflorescence or bloom of sulfur, associated with acid rock drainage.^[9]

Fragments below exposure of fissile Marcellus black shale at Marcellus, N.Y.

Pyrite is especially abundant near the base,^[10] and the upper contacts of limestones, but framboidal microcrystals and euhedral crystals of pyrite occur throughout the organic-rich deposits.^[11] The Marcellus also contains uranium,^[12][13] and the radioactive decay of the uranium-238 (²³⁸U) makes it a source rock for radioactive radon gas (²²²Rn).^[14]

Measured total organic content of the Marcellus Formation ranges from less than 1% in eastern New York, to over 11% in the central part of the state,^[15][16] and the shale may contain enough carbon to support combustion.^[17] The more organic-rich black shales can be bituminous, but are too old to contain bituminous coal formed from land plants.^[18] In petroleum geology, these black shales are an important source rock that filled conventional petroleum reservoirs in overlying formations, are an unconventional shale gas reservoir, and are an impermeable seal that traps underlying conventional natural gas reservoirs.^[19] To the west the formation may produce liquid petroleum; further east heating during deeper burial more than 240 million years ago cracked this oil into gas.^[15][20]

Extent

The Marcellus is found throughout the Allegheny Plateau region of the northern Appalachian Basin of North America. In the United States, the Marcellus shale runs across the Southern Tier and Finger Lakes regions of New York, in northern and western Pennsylvania, eastern Ohio, through western Maryland, and throughout most of West Virginia extending across the state line into extreme western Virginia.^[21] The Marcellus bedrock in eastern Pennsylvania^[22] extends across the Delaware River into extreme western New Jersey.^[1] It also exists in the subsurface of a small portion of Kentucky and Tennessee.^[23] Below Lake Erie, it can be found crossing the border into Canada, where it stretches between Port Stanley and Long Point to St. Thomas in southern Ontario. ^[24][25]

Outcrops

Delaware River above Walpack Bend, where it leaves the buried valley eroded from Marcellus Shale bedrock

The Marcellus appears in outcrops along the northern margin of the formation in central New York. There, the two joint planes in the Marcellus are nearly at right angles, each making cracks in the formation that run perpendicular to the bedding plane, which lies almost level.^[8] These joints form smooth nearly vertical cliffs, and the intersecting joint planes form projecting corners in the rock faces.^[8] Once exposed, the weathered faces lose most of their organic carbon,^[26] turning from black or dark gray to a lighter shade of gray.

Outcrops of the Marcellus can contain very small beds that resemble coal.^[27] The New York outcrops, and others further south in Pennsylvania and New Jersey, were extensively excavated in the early 19th century, sometimes at great expense, in the false hope of finding minable coal seams.^[27] In Perry County, Pennsylvania along the Juniata River the false coal beds become up to .3 m (1 ft) thick, but they did not produce a valuable fuel, despite the considerable effort expended to mine it from the surrounding hills.^[28] Seaweed and marine plants probably formed the false coal. True coal is formed from terrestrial plants, which only began to appear in Marcellus and later fossils.^[29][30]

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^[12] a high-risk area for radon as an indoor air pollutant.^[31] From the surface exposures along the northern and eastern margins, the formation descends to depths of over 2,700 m (8,900 ft) below the surface in southern Pennsylvania.^[23]

Structural geology

Upturned beds are exposed in sections of the folded Ridge-and-Valley Appalachians,^[21] including exposures on the flanks and axis of the Broad Top Synclinorium in south central Pennsylvania.^[10] Exposed beds are nearly horizontal on the Allegheny Plateau,^[32] but upturned to form slightly overturned beds found along the Allegheny Front.^[33] From Wind Gap, Pennsylvania heading south, the dip of the beds steepens, becoming vertical at Bowmanstown on the Lehigh River.^[28] Nearby, in the Lehigh Gap area of Pennsylvania, the Marcellus is extensively faulted,^[34] and the beds are steeply overturned, with a reverse dip angle of up to 40° south.^[28]

The Marcellus Shale and the fine-grained shales near the middle of the Mahantango Formation are classified by geologists as slope-formers.^[35] Marcellus and Mahantango shale beds dipping at 60° to 75° to the west form the west facing slopes of Tonoloway Ridge on the west flank of the Cacapon Mountain anticline in the Eastern Panhandle of West Virginia.^[36] 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.^[36]

Bedrock geologic map showing Marcellus bedrock in New York and Pennsylvania

Surficial geology

The Marcellus is easily eroded, and is also found underlying low areas between some Appalachian ridges, forming linear valleys of moderate relief. These bedrock surfaces are typically covered with colluvium from erosion of stratigraphically higher and more erosion-resistant strata that form the surrounding higher ground.^[10] The soils formed from the Marcellus and the overlying Hamilton shales are deep, free of stones, and well suited for agriculture.^[8] Sampling of soil formed on the Marcellus bedrock showed the dominant mineralogy consisted of quartz, illite, montmorillonite, muscovite, and biotite, with phases of todorokite and trona appearing at depths closer to the bedrock.^[37]

Upturned beds of the soft shale also capture streams and rivers with relatively straight segments in strike valleys such as the Aquashicola Creek and McMichael Creek at the foot of The Poconos,^[28] and the long, straight section of the Lost River in West Virginia.^[38] Below Port Jervis, New York, the Walpack Ridge deflects the Delaware River into the Minisink Valley, where it follows the southwest strike of the eroded Marcellus beds along the Pennsylvania – New Jersey state line for 40 km (25 mi) to the end of the ridge at Walpack Bend in the Delaware Water Gap National Recreation Area.^[1][39] The Minisink is a buried valley where the Delaware flows in a bed of glacial till that buried the eroded Marcellus bedrock during the last glacial period. This buried valley continues along the strike of the Marcellus southwest from the bend through Stroudsburg, Pennsylvania, and northeast from Port Jervis toward the Hudson River,^[39] along the route of the Delaware and Hudson Canal.^[28]

Paleogeographic reconstruction of the Appalachian Basin area during deposition of the Marcellus^[37]

Deposition

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 sediments from the land into the sea.^[15] The Marcellus Shale was formed from the very first deposits in a relatively deep, sediment- and oxygen-starved (anoxic), trough that formed parallel to the mountain chain.^[40] These clastic fragments of rock were carried in braided streams to the ancient Catskill Delta, a river delta probably similar to the present day Niger Delta of Africa.^[41]

Smaller particles remained suspended longer in this epeiric sea, flowing offshore as turbidites in a slow but persistent underwater avalanche. They finally came to rest at the bottom of the Acadian foredeep in the Appalachian Basin,^[42] hundreds of meters from shore, at depths that may have been 150 m (490 ft) or more beneath the surface.^[11] Alternatively, the basin may have been as shallow as 50 metres (160 ft) or less, if the warm water was sufficiently stratified so that oxygen rich surface water did not mix with the anoxic bottom water.^[43] The Marcellus deposition produced a transgressive black shale,^[44] because it was deposited in deepening conditions when the basin floor dropped as the mountains rose up.^[45]

The dark shale facies of the Marcellus were formed from flysch, a fine mud deposited in the deep water; it buried the underlying Onondaga limestone beds,^[46] as the deepening sea cut off the supply of carbonates that form limestone.^[47] Organic matter, probably dominated by plankton, also settled to the bottom, but the normal aerobic decay process was inhibited in the anaerobic environment thereby preserving the organic carbon.^{[48] [49]} Uranium was also incorporated in these organic muds syndepositionally,^[12] meaning it was deposited at the same time, rather than being introduced to the formation later.^[50] The organic matter scavenged trace elements from the seawater,^[26] including the redox-sensitive elements uranium, rhenium, molybdenum, osmium, chromium, and selenium.^[51]

The Marcellus was deposited during a period of development of land plants, when atmospheric oxygen was increasing, resulting in a reduction of carbon dioxide in the atmosphere, and the seawater where it was deposited.^[52] Named members of the Marcellus reflect two composite depositional sequences,^[53] with a general coarsening upward cycle that continues into the base of the overlying Mahantango Formation.^[35] The interbedding of lighter shale and limestone members is attributed to relatively short-term oscillations in basin depth.^[54] Later deep water depositional sequences formed the overlying Brallier Formation and Harrell Formation.^[42]

Generalized geologic cross section of Catskill Delta magnafacies across western Pennsylvania and eastern Ohio. Clastic deposits entered the Appalachian Basin from the east, where the resulting sedimentary rock is thickest.

Age

On the geological timescale, the Marcellus occurs in the Middle Devonian epoch, of the Devonian period, in the Paleozoic era, of the Phanerozoic eon. Radiometric dating of a Marcellus sample from Pennsylvania placed its age at 384 million years old, and a sample from the bentonite at the top of the Onondaga at 390 ± 0.5 million years old.^[55]

Relative age dating of the Marcellus places its formation in the Cazenovia subdivision of the Givetian faunal stage, or 391.9 to 383.7 million years ago (Ma).^[56] The Union Springs member, at the base of the Marcellus in New York, has been dated to the end of the Eifelian, the stage which immediately preceded the Givetian.^[57] Anoxic dark shales in the formation mark the Kačák Event,^[58] a late-Eifelian-stage marine anoxic event also associated with an extinction event.^[59]

Generalized stratigraphic nomenclature for the Middle Devonian strata in the Appalachian Basin.^[60]

Stratigraphy

In the first Pennsylvania Geological Survey, begun in 1836, Henry Darwin Rogers classified the Marcellus as the "Cadent Lower Black Slate" which he numbered "No. VIII b."^[61] 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."^[62] 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."^[63] His arguments proved persuasive, and the location-based name for this, and many of the other group names he published based on exposures in New York, were adopted in the second Pennsylvania survey, and are now widely accepted.

Overlying

In the first New York survey, the Marcellus shale was placed below the Hamilton Group at the base of the Erie division of the New York system, but this taxonomy is obsolete.^[39]

In current practice, the Marcellus Formation (abbr. Dm or Dms) is classified as the basal unit of the Hamilton Group (Dh),^[15] lying beneath the Mahantango Formation (Dmh) member of this group in Pennsylvania^[64] 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.^[65][66]

In West Virginia, the Marcellus may be separated from the brown shales of the Mahantango by occasional sandstone beds and concretions,^[67] or it may lie directly below the younger Late Devonian Harrel Formation (or its lateral equivalents) because of a disconformity,^[68] 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.^[44]

Underlying

The Marcellus shale is typically found deposited on the limestone of the Onondaga Formation (Don), which extends down to the end of the Early Devonian period. The contact between them may be sharp, gradational, or erosional. In southwestern Ontario, Canada, north of Lake Erie, the Marcellus overlies the Dundee Formation, a lateral equivalent of the Onondaga.^[69][70] In Pennsylvania, the Marcellus forms a sharp conformable contact with the Onondaga's Selinsgrove Limestone member.^[71] 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.^[17]

In eastern New York, the contact between the Marcellus and Onondoga (where present) is gradational.^[72][73] In western New York, the Union Springs member of the Marcellus conformably overlies the Seneca member of the Onondaga Limestone,^[11] or the stratigraphically higher Cherry Valley Limestone member may rest directly and unconformably upon the Onondaga in the absence of the Union Springs shale.^[74][69] The local disappearance of units of the Onondaga suggests that its upper contact with the Marcellus can be erosional.^[74] In Erie County in western New York, both the upper and lower contact of the Marcellus are eroded away.^[75]

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.^[67] To the south and west, the Hamilton Group grades laterally into the Millboro Shale formation in southern West Virginia and Virginia,^[60] which grades into the lower part of the Chattanooga Shale of Tennessee.^[76]

The Milboro is gradational with the underlying Needmore Formation shale.^[76] South of the Mason-Dixon line, due to the difficulty in differentiating the Millboro and Needmore shales with the limited exposures available,^[77] 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,^[36] named for an exposure at Romney, West Virginia.^[3] 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,^[36] the Romney classification is now obsolete; but its Marcellus and underlying Needmore shale members are still found grouped in an undifferentiated map unit (Dmn).^[78]

Geologic cross section of upper to middle Devonian strata from Cherry Valley, New York southwest across the Allegheny Plateau and then along the Ridge-and-Valley Appalachians to Tennessee. Note the Marcellus grades up to the Milboro and Chattanooga black shales.^[67]

Tioga ash beds

Tioga metabentonite or K-bentonite–stratigraphic unit about .6 m (2 ft) thick that consists of several discrete, relatively thin volcanic ash falls–is also included at the base of the Marcellus in eastern Pennsylvania.^[64] In 1843 it was described without being named by Hall,^[79] and more than 100 years passed before it was eventually named for the natural gas field in Tioga County, Pennsylvania,^[80] where it was encountered when drilling gas wells. It is a regional stratigraphic marker,^[60] used by geologists to identify the Marcellus,^[81] and correlate laterally equivalent strata.^[69][82] Difficulty in correctly identifying the more than 80 different ash falls during the Devonian period, collected in 15 or more beds,^[83] has also led to many miscorrelations.^[84]

From Virginia to New York the Tioga is widely distributed, running across the central and northern parts of the Appalachian basin,^[85] an areal extent exceeding 265,000 km² (102,000 sq mi).^[86] Explosive eruptions associated with the Acadian orogeny^[6] originating near present-day central Virginia released the ash into the atmosphere.^[80] It was dispersed across the Appalachian, Michigan, and Illinois Basins by the southern trade winds, because this area was in the southern hemisphere during the Devonian period.^[86] The volcanic origin of the ash is evidenced by its distinctive mineralogy–the ash was deposited directly upon the water, so its angular quartz grains differ from the clastic sediments rounded through the erosion process that carries them to the sea.^[84] As the volcanic ash settled to the bottom, it was admixed with these terrigenous components, producing a distinctive lithology in the sedimentary rock.^[84]

Marcellus exposure along Interstate 80 in eastern Pennsylvania where the formation is thickest.

The Tioga may appear in the formation as a gray, brown, black, or olive bed, or parting,^[84] consisting of coarse crystal tuff or tuffaceous shale,^[80] thinly laminated, with sand-sized mica flakes.^[87] The Tioga ash bed zone consists of eight ash beds labeled according to their stratigraphic order from A (oldest) to H (youngest),^[85][88] and another bed known as the Tioga middle coarse zone.^[83][86] 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.^[60] In western New York state, the Tioga Ash Bed B marks the boundary between the Moorehouse and Seneca Members of the Onondaga Formation,^[89] but in the central part of the state, and the southern part of the basin, the ash beds are actually in the Marcellus.^[73][85][90] This indicates that deposition of the Marcellus there began earlier,^[73] since the ash beds represent a single epoch in geologic time.

Thickness

Maximum thickness of the Marcellus ranges from 270 m (890 ft) in New Jersey,^[1] to 12 m (40 ft) in Canada.^[25] In West Virginia, the Marcellus Formation is as much as 60 m (200 ft) thick.^[67] In extreme eastern Pennsylvania, it is 240 m (790 ft) thick,^[39] thinning to the west, becoming only 15 m (49 ft) thick along the Ohio River, and only a few feet in Licking County, Ohio.^[4] The thinning, or stratigraphic convergence, from east to west is caused by decreasing grain size in the clastic deposits, which entered the basin from the east.^[82] The beds finally "pinch out" westward because deposition was limited by the Cincinnati Arch,^[44][91] 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.

Members of the Marcellus Formation from West to East in New York Buffalo  Rochester   Syracuse  Utica Albany Oatka Creek shale Cardiff dark gray shale Pecksport shale (Mt. Marion Fm.) Solsville shale and sandstone Bridgewater shale Otsego Chittenango black shale Berne Cherry Valley limestone Stony Hollow shale & limestone (Seneca Mb.) (Onondaga Fm.) Union Springs shale and limestone (Onondaga Fm.) Union Springs shale and limestone Table showing approximate correlation between Marcellus Formation named members from west to east across central New York state.[16][65]

Named members

A local Purcell limestone member, 15 to 30 m (49 to 98 ft) of inter-bedded calcitic shale and limestone,^[82] divides the Marcellus in eastern Pennsylvania.^[64] The Purcell is stratigraphically equivalent to the Cherry Valley Limestone member in New York,^[92] a bioclastic packstone,^[11] consisting of skeletal limestones, with shaly intervals^[16] between its lower massive limestone layer, thick nodular limestone/marlstone, and upper limestone layer.^[93] Other named members include the Bakoven Shale, Cardiff Shale, Chittenango shale, Solsville sandstone, Union Springs shale and limestone,^[56] and Stony Hollow shale and limestone.^[94] The Union Springs, Cherry Valley, and Oatka Creek merge beneath Lake Erie, into the Bell Shale, Rockport Quarry Limestone, and Arkona Shale of Ontario.^[69]

The Union Springs is an organic-rich, pyritiferous, thinly bedded, blackish gray to black shale with mudstone concretionary layers,^[93] and thin silt bands at the bottom. To the east, it becomes the Bakoven Member, a darker, less organic shale with fewer limestone layers.^[16] To the west the Union Springs beds thin, with its upper limestones merging with the overlying calcareous Cherry Valley Member.^[16] A regional unconformity appears in western New York, as the Union Springs lenses in and out,^[16] and then reappears in northwest Pennsylvania and northeast Ohio between the Onondaga and Cherry Valley.^[69]

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,^[95] where it divides into the Cardiff member lying above the Chittenango member in central New York.^[16] Organic-rich, fissile, sooty black shales make up the Chittenango Member.^[93] At the base of the Chittenango,^[96] above the Bierne Member shale,^[97] lies the Halihan Hill Bed, a highly bioturbated bioclastic limestone.^[11]

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.^[98]

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.^[99] The Turkey Ridge is commonly mapped in the Mahantango Formation,^[100] or included in the Montebello Formation (Dmot),^[101] and only the Shamokin correlates with the Marcellus on adjacent map sheets.^[102] In extreme eastern Pennsylvania, the Broadhead Creek member, a dark gray silty shale with dark gray shaly limestone concretions, appears above the Stony Hollow and Union Springs, in a layer up to 275 m (902 ft) thick.^[103]

Illustration of a Cephalopod (Goniatites vanuxemi) fossil from the Marcellus Formation.^[104]

Fossils

There are relatively sparse inclusions of fossilized marine fauna found in the Marcellus,^[64] but these fossils are still important to paleontology. For example, the Marcellus contains the oldest known diverse collection of thin-shelled mollusks still having well preserved shell microstructure.^[105] It is also where goniatites, an extinct shelled swimmer similar to a squid, make their first appearance in the fossil record.^[106] Life on land also enters the fossil record in the Marcellus, with the trunks of branchless conifer trees that floated out to sea to be preserved in the black shale.^[29][30]

Marcellus fossils include specimens of the large clam-like brachiopod Spinocyrtia.^[107] External molds of crinoids, plant-like animals related to starfish also known as "sea lilies,"^[108] are found in the formation,^[109] with the molds partially filled with limonite; brachiopod and bivalve (clam) molds have also been found in the shale.^[110] Small conical tentaculitids are commonly found in the Chittenango Member.^[93] The Halihan Hill bed contains styliolinids and macrofauna including brachiopods, coral-like bryozoans, small bivalves and gastropods (snails),^[11] incorporated after the faunal turnover when Emsian and Eifelian Schoharie/Onondaga fauna were replaced by the Givetian Hamilton fauna.^[96]

The Solsville member contains well preserved bivalves, gastropods, and brachiopods.^[98] These shellfish lived in the benthic zone at the bottom of marginal marine to open marine environments that existed west of the ancient Catskill Delta.^[111] The fossil record in this member shows the base was dominated by deposit feeders, while the upper layers were dominated by filter feeders.^[111] 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.^[111] 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.^[112]

A diverse, eel-like conodont fauna occurs in the limestone of the Cherry Valley Member,^[113] which is also known for its rich nautiloid and goniatite cephalopod fauna.^[93] Originally named the Goniatite Limestone,^[114] it produces their fossilized remains with shells that can be larger than .3 metres (1 ft) across.^[61] 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.^[115] This stratigraphic interval also provides an excellent example of incursion epiboles, which are sudden appearances and disappearances of fossil taxa in relatively thin sections of the rock unit.^[116] In the Cherry Valley, the taxa do not reoccur; instead each thin concretionary limestone bed contains different species of goniatites.^[116] The Cherry Valley and Union Springs also contain well-preserved anarcestida.^[117]

Economic impact

Marcellus Shale
Country	United States
Region	Allegheny Plateau
Offshore/onshore	Onshore
Operator(s)	Chesapeake Energy Chief Oil and Gas Range Resources Rex Energy
Field history
Start of production	2000s
Production
Estimated gas in place	168,000 billion cubic feet (4,800×10^9 m3)
Producing formations	Marcellus Formation

Fossil fuel

The impervious limestone layers of the Onondaga directly below the Marcellus, and the Tully Limestone at the top of the Hamilton Group, have trapped valuable natural gas reserves in this formation.^[118] The gas is produced by thermogenic decomposition of organic materials in the sediments under the high temperature and pressure generated after the formation was buried deep below the surface of the earth. The rock holds most of the gas in the pore spaces of the shale, with vertical fractures or joints providing additional storage as well as pathways for the gas to flow; gas is also adsorbed on mineral grains,^[23] and the carbon in the shale.^[19]

The United States Geological Survey had estimated that the Marcellus contained only 54 km³ (1.9×10¹² cu ft) (where x10¹² = trillion, and is referred to as 1.9 TCF) of technically recoverable natural gas in a 2002 publication.^[119] In April 2009, the United States Department of Energy estimated the Marcellus to contain 262 TCF of recoverable gas.^[120]

State University of New York at Fredonia geology professor Gary Lash has calculated that more than 14,000 km³ (4.9×10¹⁴ cu ft) (490 TCF) of natural gas may be contained in the Marcellus black shale beds that lie between New York state and West Virginia.^[121] At the present level of technology, he believes approximately 10% of this – 1,400 km³ (4.9×10¹³ cu ft) (49 TCF) – could be recovered.^[121] This is enough to satisfy approximately two years' of total U.S. consumption,^[119] or a total value of two hundred billion dollars at winter 2010 – spring 2011 wellhead prices. That figure is part of an increase of as much as approximately one trillion United States dollars in the value of all recoverable reserves in the US attributable to improved recovery through vertical drilling and fracking.^[21]

During the 2012 presidential campaign, GOP Primary Candidate Rick Perry cited a study funded by the Marcellus Shale Coalition that fracking the Romney Formation is expected to create a quarter million jobs under the current policies of the Obama administration.^[122]

Drilling and environmental issues

In 2008, Terry Engelder, a Pennsylvania State University geosciences professor called his estimate of 4,800 km³ (1.7×10¹⁴ cu ft) (170 TCF) conservative.^[119] In November 2008, based on drilling results, Engelder increased his estimate of the amount of natural gas in the Marcellus to 363 TCF of recoverable resource, which would be enough to supply U.S. consumption for at least fourteen years.^[123] That estimate assumed some acreage in the Marcellus would not be gas bearing. If the entire formation did contain gas, Engelder said the formation could contain 4,359 TCF. Assuming a 30% recovery rate, this would lead to a 1,307 TCF.^[124]

Before 2000, low production gas wells were completed to the Marcellus, but these had a low rate of return, requiring a relatively long capital recovery period, although they did have a very long productive life.^[23] There are wells in Tioga and Broome County, NY which are 50 years old or more. Now, to extract the shale gas at more commercially viable rates,^[21] directional drilling is done to depths of 7,000 to 10,000 ft (2,100 to 3,000 m) underground to reach the formation, and then water and a mixture of chemicals is pumped into the rock under high pressure in a process known as hydraulic fracturing to release the gas from the low permeability shale.^[125] Although hydraulic fracturing has been used since the middle of the 20th century, its use in horizontal wells in laterally extensive shale formations was perfected around the turn of the 21st century outside Fort Worth, Texas to tap the reserves in the Barnett Formation shales of the Bend Arch-Fort Worth Basin, that are now the most prolific source of unconventional gas in the continental United States.^[119] The Marcellus covers several times more area,^[126] stretching 600 miles (970 km), compared to a linear extent of only 170 miles (270 km) for the Barnett.^[2]

Several companies, many that have specialized in tapping the Barnett, are working to do the same in the Marcellus.^[127] As of 2008, only a few new hydro fractured wells tapping the Marcellus reserves were actually in operation, with at least one reported to be producing more than 3 million cubic feet (85 thousand m³) per day.^[119] Engelder, who has studied natural rock fractures in this area for more than 25 years, also suggested drilling horizontally through the Marcellus shale perpendicular to these vertical fractures, to exploit these natural features for increased production.^[21] Early results show that horizontal wells in this formation are producing gas at a rate more than double that of vertical wells, and at slightly lower cost overall,^[126] despite the much higher initial cost of drilling.^[21]

Since parts of this region have been producing gas from wells drilled to the deeper Oriskany Formation sandstone, older wells that are no longer viable can be reused, either by fracturing the Marcellus layer in the existing well bore, or by refinishing the bore using horizontal drilling into the Marcellus.^[119] Re-use of the existing infrastructure has both environmental as well as economic benefits,^[21] because in addition to avoiding development of new drilling sites and wells, existing transportation facilities can be reused.^[126] Lower transportation costs to the high demand markets on the East Coast of the United States generate a US$0.35 per thousand cubic feet price premium over the Henry Hub price, compared to a discount of as much as $1.50 for gas produced in the Rocky Mountains.^[128]

However, heavy trucks and tankers crack the pavement and cause potholes. Such road damage is expensive for municipalities to repair.^[129] Engineers in Pennsylvania Department of Transportation have documented damage caused by the heavy trucks and tankers. Damages include but are not limited to the crushing of drain pipes, potholes, rutting, and other such pavement fatigue failures. The cost of these repairs are often much higher than the Pennsylvania Department of Transportation is allowed to charge for use of the roads. In addition to causing road damage, when heavy trucks and tankers drive over farmland, they compact the subsoil, which increases runoff and decreases crop productivity for years. Ecologists also have concerns about the ecological impact on forests when trees are cut down to make way for access roads. Ornithologists have already documented declining populations of woodland birds.^[129]

Environmental concerns around the drilling and extraction processes have sparked opposition to development of this resource. One concern is the release to the environment of underground naturally occurring radioactive material through the drilling fluids and equipment.^[130] The hydraulic fracturing process also uses large quantities of surface water.^[130]

A large portion of the formation underlies the environmentally sensitive Chesapeake Bay Watershed as well as the Delaware River Basin. The Delaware River Basin Commission holds regulatory jurisdiction in this watershed that houses much of the Marcellus Shale formation of any operations which involve water usage, extraction, or potential contamination. They have recently made a "Determination" which requires that any component of a hydro-fracing operation that is to take place within the boundaries of their Special Protection Waters must be permitted by the DRBC, regardless of whether or not the operation was previously subject to permitting.^[131]

Chesapeake’s (The gas Company) countered with a No-Drilling Pledge for the NYC watershed area, and five miles around the watershed, however, opposes any legislation like that presented by Jim Brennan, D-Brooklyn (Brooklyn, NY), October 2009.^[132] The Susquehanna River Basin Commission, which oversees this other portion of the watershed, and the Pennsylvania Department of Environmental Protection, issued orders to suspend operations at several wells in May 2008 because surface water was being diverted by the drillers without the necessary permits, and precautions to protect streams from contaminated runoff were questioned.^[133] The practices of "land men" who acquire leases for drilling and extraction rights have also been widely questioned.^[134]

New York City under the New York City Gas Fuel Code made it illegal to drill within city limits. Pennsylvania is following this trend, Pittsburgh on November 16, 2010 became the first city in Pennsylvania to ban hydrofracking within city limits.

Researchers at the University of Pittsburgh recently released a study showing that "7 percent of Allegheny County’s land has been leased for drilling and extraction since 2003" and the number of properties in the county leased for oil and gas exploration has grown exponentially in recent years.

It is alleged that gas drilling in Northeast Pennsylvania caused methane to infiltrate up to 15 homes in Dimock Township, Susquehanna County, via groundwater contamination. This conclusion came from the Pennsylvania Department of Environmental Protection, though it is disputed by Cabot Oil & Gas Corp which was cited for causing the contamination. It is also disputed by other long-term area residents who have noted that high methane levels had been present for more than 60 years prior to hydrofracking in Dimock. ^[135] Northeast Pennsylvania is not the only place to experience groundwater contamination following commencement of gas drilling operations.^[136]

Iron

At the base of the Marcellus, in the pyrite-carbonate bed between the carbonaceous black shale and a green calcareous shale bed,^[17] pyrite, carbonate, and groundwater reacted to form gossan iron oxide and gypsum.^[137] As far as the ground water necessary for the conversion could penetrate, the pyrite-carbonate was converted to a usable brown hematite iron ore along the outcrops and near the bedrock surface.^[28] The Marcellus iron ore was actively mined in south Central Pennsylvania from its discovery in the late 18th century, until it was supplanted by the rich ore beds of the Iron Range of Minnesota in the early 20th century.^[138] 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.^[17]

Hematite ore was converted to pig iron in charcoal-fired stone blast furnaces that were constructed throughout the Juniata River region near the workable ore deposits from the Marcellus and other formations.^[138] Iron products from this area, known as "Juniata Iron," were produced during the period between the American Revolution and the American Civil War. These blast furnaces were important to the economy of the region at the time,^[139] but the cold blast stone furnaces typically employed were inefficient, and consumed significant amounts of timber from the nearby hardwood forests, which ultimately led to their demise.^[140] A typical furnace used 2,400 kg (5,300 lb) of hematite ore and 7.3 m³ (200 imp bu) of charcoal to produce 910 kg (2,000 lb) of pig iron,^[17] and could produce several thousand pounds per day, which required logging more than 4,000 m² (1 acre) of forest daily.^[141]

The ore from the Marcellus varied in thickness, becoming unworkably thin, and even disappearing altogether in places between the workable beds.^[17][142] The quality of the ore also varied,^[17] and it was not always profitable to smelt, as several furnaces built near iron ore mines in the Marcellus were abandoned before the ore and timber resources used to fuel them became scarce.^[142]

Ore found interbedded in the black slaty shale contained a relatively high proportion of carbon which was burned in the furnace, and sulfur, which produced a usable but "red-short" iron.^[143] Red-short iron has the undesirable properties of oxidizing more easily, and a tendency to crack, especially when heated to a red-hot state.^[144] In some locations in Pennsylvania the quality of the ore was quite good, with relatively deep veins containing 45% iron, and very low sulfur.^[17] In Virginia, the Marcellus ore occasionally contained zinc, which produced a characteristic green flame in the furnace as it was consumed, but deposited a hard mass of impure zinc oxide known as cadmia, which built up over time near the top of the flue, and had to be removed periodically to keep it unobstructed.^[145]

Paint

Drainage that reacted with the pyrite inclusions also deposited a form of bog iron near several outcrops of the Marcellus. In the 19th century, iron ore from these deposits was used as a mineral paint pigment. After being heated in a kiln and finely ground, it was mixed with linseed oil, and used to paint exterior wood on barns, covered bridges, and railroad cars.^[28] 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.^[39] A bed of hematite paint ore is also found almost directly below the Marcellus, but it is actually part of the underlying Oriskany Formation.^[28]

Chalybeate

Iron rich "ferruginous waters" emanating from chalybeate springs near the base of the Marcellus in Bedford, Pennsylvania were believed to have healing powers by Native Americans. The Bedford Springs Hotel was a mineral spa built in 1802 around a series of mineral springs, including one of these, its "iron spring". The Chalybeate Springs Hotel, built nearby in 1851 around three other mineral springs including another chalybeate spring,^[146] became a "resort for invalids".^[147] The iron-rich waters were prescribed for anemia and related complications.^[148] Both of these mineral springs contain iron in the form of dissolved iron carbonate,^[147] which gives these waters a "slightly inky taste".^[148]

Other uses

The Marcellus has also been used locally for shale aggregate and common fill,^[10] although the pyritic shales are not suitable for this purpose because of acid rock drainage and volumetric expansion.^[149] In the 19th century, this shale was used for walkways and roadways,^[18] and was considered superior "road metal" because the fine grained fragments packed together tightly, yet drained well after a rain.^[28]

The dark slaty shales may have the necessary cleavage and hardness to be worked, and were quarried for low grade roofing slate in eastern Pennsylvania during the 19th century. The slates from the Marcellus were inferior to the Martinsburg Formation slate quarried further south, and most quarries were abandoned, with the last significant operation in Lancaster County.^[28] The Marcellus black slate was also quarried in Monroe County, Pennsylvania, for school slates used by students in 19th-century rural schools.^[28]

Carbonaceous shales, such as the Marcellus, are a possible target for carbon capture and storage for mitigation of global warming. Because carbon adsorbs carbon dioxide (CO₂) at a greater rate than methane (CH₄), carbon dioxide injected into the formation for geological sequestration could also be used to recover additional natural gas in a process analogous to enhanced coal bed methane recovery, but the practical value of this theoretical technique is not yet known.^[44] Scientists believe that adsorption would allow sequestration at shallower depths than absorption in deep saline formations, which must be at least 800 m (2,600 ft) below the surface to maintain liquid CO₂ in a supercritical state.^[19]

Engineering issues

Horizontal drilling rig for natural gas in the Marcellus formation in eastern Lycoming County, Pennsylvania.

Exposures from cut and fill road construction in Virginia and Pennsylvania have resulted in localized acid rock drainage due to oxidation of the pyrite inclusions.^[150] The newly exposed shale on the cut face weathers rapidly, allowing air and water into the unexcavated rock, resulting in acidic surface runoff after precipitation events.^[151] Acidic runoff disrupts aquatic ecosystems, and highly acidic soil contaminated by this runoff will not support vegetation, which is unsightly, and can lead to problems with soil erosion.^[150]

Natural decomposition of the shale into smaller fragments can affect slope stability, necessitating shallower slopes that require more material be disturbed in cut and fill work, exacerbating the acid rock drainage problem. The cut material cannot be used as fill beneath roads and structures due to volumetric expansion, compounding the problem.^[81] The Tioga ash beds contain bentonite clay which presents a landslide hazard in the unexcavated rock as well.^[81]

Damage to structures constructed on fill consisting of pyritic Marcellus shale has been caused by expansion from sulfuric acid (H₂SO₄) runoff reacting with the calcite (CaCO₃) in the shale to produce gypsum (CaSO₄), which has double the molar volume.^[152] Other sulfate minerals that can be produced by reactions with pyrite include anhydrite, melanterite, rozenite, jarosite and alunite.^[149] The reactions have generated a heave pressure on the order of 500 kPa (10,000 pounds per square foot), but may be able to generate four times this pressure   enough to heave foundations in a 5-story building.^[149] Limestone, which is used to neutralize the acid drainage, can actually exacerbate the expansion problem by promoting sulfate–sulfate reactions that form the minerals thaumasite and ettringite, which have even higher molar volumes.^[149]

Drilling boreholes through the Hamilton Group shales in the subsurface can be problematic. The Marcellus has a relatively low density, and these shales may not be chemically compatible with some drilling fluids. 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.^[44]

See also

• FracTracker: Blog and Shale Gas Data and Mapping System
• FrackTrack: Pennsylvania Marcellus Shale Mapping Application
• Geology of New Jersey
• Geology of Pennsylvania
  • List of mapped rock formations in Pennsylvania
• Geology of West Virginia
• Pittsburgh Association of Petroleum Geologists
• Shale gas
• Shale gas in the United States

References

1. ^ ^{a b c d} White, Ron W.; Monteverde, Donald H. (2006-02-01). "Karst in the Delaware Water Gap National Recreation Area" (pdf). Unearthing New Jersey Vol. 2, No. 1. New Jersey Geological Survey. http://www.njgeology.org/enviroed/newsletter/v2n1.pdf. Retrieved 2008-06-07. 
2. ^ ^{a b} Durham, Louise S. (2008-03). "Appalachian Basin’s Marcellus – the new target : Another Shale Making Seismic Waves". AAPG Explorer. American Association of Petroleum Geologists. http://www.aapg.org/explorer/2008/03mar/marcellus.cfm. Retrieved 2008-04-06. 
3. ^ ^{a b} Clark, W. B. (1918.). The geography of Maryland. Maryland Geological Survey. vol. 10. Baltimore: Johns Hopkins Press. 
4. ^ ^{a b} Mayhood, Kevin (2008-03-11). "Low down, rich and stingy". The Columbus Dispatch. http://www.dispatch.com/live/content/science/stories/2008/03/11/Sci_shale.ART_ART_03-11-08_B4_A99I7HO.html?print=yes. Retrieved 2008-04-04. 
5. ^ Alan Bailey. "Appalachia to the rescue: Could Devonian shales deep under the Appalachians supply trillions of cubic feet of much needed natural gas for the U.S.?". Petroleum News. http://www.petroleumnews.com/pntruncate/246893563.shtml. Retrieved 2008-04-05. 
6. ^ ^{a b} Harper, John A.; Christopher D. Laughrey, Jaime Kostelnik, David P. Gold, Arnold G. Doden (2004-05-26). "Trenton and Black River Carbonates in the Union Furnace Area of Blair and Huntingdon Counties, Pennsylvania : Introduction". Field Trip Guidebook for the Eastern Section AAPG Annual Meeting, September 10, 2003 and the PAPG Spring Field Trip, May 26, 2004. Pennsylvania Geological Survey. http://www.dcnr.state.pa.us/topogeo/tbr/tbrintro.aspx. Retrieved 2008-06-14. 
7. ^ ^{a b} "HRS Documentation Record, Safety Light Corporation, EPA ID No. PAD987295276" (pdf). Hazard Ranking System. United States Environmental Protection Agency. http://www.epa.gov/superfund/sites/docrec/pdoc1724.pdf. Retrieved 2008-04-02. 
8. ^ ^{a b c d e} MacFarlane, James R. (1890) [1878]. An American Geological Railway Guide : Giving the Geological Formation at Every Railway Station,... (2nd ed.). New York: D. Appleton. pp. 30–31, 33. LCCN tmp96-004299. http://books.google.com/?id=AV8PAAAAYAAJ&pg=PA30. 
9. ^ McDowell, Ronald ; Katharine Lee Avary, Eric Lewis, James Britton, Paula Hunt; Paula Waggy, Megan Ganak (2006). "Milam and Cow Knob Quadrangles". WVGES STATEMAP Projects. West Virginia Geological & Economic Survey. http://www.wvgs.wvnet.edu/www/statemap/statemap06.htm. Retrieved 2008-07-13. 
10. ^ ^{a b c d} McElroy, Thomas A.; Hoskins, Donald M.. "Bedrock Geologic Map of the Allensville Quadrangle, Huntingdon and Mifflin Counties, Pennsylvania" (pdf). Open File Report OFBM 07-02.0. Pennsylvania Geological Survey. pp. 12. http://www.dcnr.state.pa.us/topogeo/openfile/allensville.pdf. 
11. ^ ^{a b c d e f} Sageman, B.B.; Murphy, A.E.; Werne, J.P.; Ver Straeten, C.A.; Hollander, D.J.; Lyons, T.W. (2003). "A tale of shales: The relative roles of production, decomposition, and dilution in the accumulation of organic-rich strata, Middle-Upper Devonian, Appalachian basin" (PDF). Chemical Geology 195: 229–273. doi:10.1016/S0009-2541(02)00397-2. http://www.earth.northwestern.edu/research/sageman/PDF/03.Sageman_etal.pdf. 
12. ^ ^{a b c} Hand, B.M.; Banikowski, J.E. (1988). "Radon in Onondaga County, New York; paleohydrogeology and redistribution of uranium in Paleozoic sedimentary rocks". Geology 16 (9): 775–778. Bibcode 1988Geo....16..775H. doi:10.1130/0091-7613(1988)016<0775:RIOCNY>2.3.CO;2. http://geology.geoscienceworld.org/cgi/content/abstract/16/9/775. Retrieved 2008-05-03. 
13. ^ Harrell, J.A.; Belsito, M.E.; Kumar, A. (1991). "Radon hazards associated with outcrops of Ohio Shale in Ohio" (PDF). Environmental Geology 18 (1): 17–26. Bibcode 1991EnGeo..18...17H. doi:10.1007/BF01704574. http://www.springerlink.com/index/U60V51862RJ08843.pdf. Retrieved 2008-05-03. 
14. ^ Wanty, Richard B. (1993). Field studies of radon in rocks, soils, and water. Chelsea, Michigan: C.K. Smoley. pp. 216. ISBN 0-87371-955-7. 
15. ^ ^{a b c d} Martin, John P.. "The Middle Devonian Hamilton Group Shales in the Northern Appalachian Basin: Production and Potential". New York State Energy Research and Development Authority. http://www.searchanddiscovery.net/documents/2006/06091eastern/abstracts/martin01.htm. Retrieved 2008-04-02. ^{[dead link]}
16. ^ ^{a b c d e f g} Nyahay, Richard; James Leone, Langhorne Smith, John Martin, and Daniel Jarvie (2007-09). "Update on the Regional Assessment of Gas Potential in the Devonian Marcellus and Ordovician Utica Shales in New York" (pdf). 2007 AAPG Eastern Section Meeting, September 16–18, Lexington, Kentucky. American Association of Petroleum Geologists. Search and Discovery Article #10136 (2007). http://www.searchanddiscovery.net/documents/2007/07101nyahay/index.htm. Retrieved 2008-05-25. 
17. ^ ^{a b c d e f g h} Dewees, John H.; Ashburner, Charles A. (1878). Report of Progress in the Juniata District on the Fossil Iron Ore Beds of Middle Pennsylvania. Harrisburg: Board of commissioners for the Second geological survey. LCCN gs07-714. 
18. ^ ^{a b} Underwood, L.M. (1879). The Geological Formations Crossed by the Syracuse and Chenango Valley Railroad: Together with a Sketch of the Hydrography and Valley Fomations of Madison and Onondaga Counties. Ph. D. Thesis, Syracuse University. Syracuse, N.Y.: Standard Pub. Co.. pp. 8. 
19. ^ ^{a b c} (pdf) Assessment of Geological Sequestration Potential in Pennsylvania. Pennsylvania Department of Conservation and Natural Resources. 2006-09-18. http://www.dcnr.state.pa.us/info/carbon/documents/geological_assessment_rev_091806.pdf. Retrieved 2008-07-07. 
20. ^ Laughrey, C.D.; Billman, D.A.; Canich, M.R. (2004). "Petroleum geology and geochemistry of the Council Run gas field, north central Pennsylvania". AAPG Bulletin 88 (2): 213–239. doi:10.1306/10060301104. 
21. ^ ^{a b c d e f g} "Unconventional natural gas reservoir could boost U.S. supply". Penn State Live. Pennsylvania State University. 2008-01-17. http://live.psu.edu/story/28116. Retrieved 2008-04-04. 
22. ^ "Pennsylvania Marcellus Shale Mapping Application". http://www.fracktrack.org/index.php. Retrieved 2011-03-17. 
23. ^ ^{a b c d} "Marcellus Shale Gas: New Research Results Surprise Geologists!". geology.com. Dr. Hobart M. King. http://geology.com/articles/marcellus-shale.shtml. Retrieved 2008-05-03. 
24. ^ Stop Fracking Ontario: Shale in Ontario
25. ^ ^{a b} Singer, S.N.; Cheng, C.K.; Scafe, M.G. (2003). "The Hydrology of Southern Ontario: Second Edition" (pdf). Hydrology of Ontario Series. Ontario Ministry of the Environment. http://www.ontario.ca/drinkingwater/stel01_049392.pdf. Retrieved 2008-04-06. 
26. ^ ^{a b} Peucker-ehrenbrink, B. (2001). "Dating Weathering of Organic-rich Shales with U-Series Disequilibrium". Eleventh Annual V. M. Goldschmidt Conference. 1. http://adsabs.harvard.edu/abs/2001eag..conf.3781P. 
27. ^ ^{a b} Vanuxem, L. (1842). Geology of New York, Pt. 3, Comprising the Survey of the Third Geological District. Natural History of New York.. Albany, New York: Carroll and Cook. LCCN gs07-386. 
28. ^ ^{a b c d e f g h i j k} Lesley, J.P. (1892). A summary description of the Geology of Pennsylvania. Vol. II. Pennsylvania Geol. Survey, 2d, Final Rept.. http://books.google.com/?id=TEA4AAAAMAAJ&pg=PA1233&lpg=PA1233. 
29. ^ ^{a b} MacFarlane, J. (1875). The Coal-regions of America: Their Topography, Geology, and Development. (3rd ed.). D. Appleton and Company. pp. 612. LCCN 03-433. 
30. ^ ^{a b} Ripley, G.; Dana, C.A. (1861). The New American Cyclopaedia: A Popular Dictionary of General Knowledge. New York: D. Appleton and Company. LCCN 07-446. 
31. ^ "New York State Studies (published)". Radon – The State of Radon in New York. NYS Department of Health Wadsworth Center. http://www.nyradon.org/abstracts.htm#1a. Retrieved 2008-05-03. 
32. ^ Engelder, T.. "Outcrops of the Marcellus Formation". The Pennsylvania State University. http://www.geosc.psu.edu/~engelder/marcellus/marcellus.html. Retrieved 2008-05-03. 
33. ^ Engelder, T.;Lash, G. (2008) (pdf). Systematic joints in Devonian black shale: A target for horizontal drilling in the Appalachian Basin (draft). Pittsburgh Association of Petroleum Geologists. http://www.papgrocks.org/engelder%20lash.pdf. Retrieved 2008-05-03. 
34. ^ Epstein, J.B. (2006). "Geology of the Delaware Water Gap National Recreation Area, New Jersey-Pennsylvania". Excursions in Geology and History: Field Trips in the Middle Atlantic States (Geological Society of America) 8: 52. doi:10.1130/2006.fld008(04). ISBN 9780813700083. http://books.google.com/?id=vQdHRNitfOoC&pg=PA47&dq=Geology+Delaware+Water+Gap+Pennsylvania+Epstein. Retrieved 2008-07-07. 
35. ^ ^{a b} Altamura, R.J. (1999). "Geologic Mapping UsingcRadar Imagery in the Ridge and Valley Province" (PDF). Pennsylvania Geology (Pennsylvania Bureau of Topographic and Geologic Survey) 30 (3/4): 9. http://www.dcnr.state.pa.us/topogeo/pub/pageolmag/pdfs/v30n3_4.pdf. Retrieved 2008-07-13. 
36. ^ ^{a b c d} Grimsley, G.P.; White, I. C. (1916). Jefferson, Berkley, and Morgan counties. County Reports. Morgantown, WV: West Virginia Geological Survey. pp. 123, 167, 210, 326. LCCN gs17-132. 
37. ^ ^{a b} Fornadel, Andrew P.; Ryan D. Mathur, Susan L. Brantley. "Dirty work: Soil formation and isotope fractionation behind Brumbaugh Academic Center" (pdf). Juniata College Geology Department, and the Center for Environmental Kinetics Analysis, Pennsylvania State University. http://www.juniata.edu/faculty/mathur/Fornadel_Marcellus_LAS.pdf. Retrieved 2008-07-13. 
38. ^ Rich, J.L. (1939). "A Bird's-Eye Cross Section of the Central Appalachian Mountains and Plateau: Washington to Cincinnati". Geographical Review (Geographical Review, Vol. 29, No. 4) 29 (4): 561–586. doi:10.2307/209829. JSTOR 209829. 
39. ^ ^{a b c d e} White, I.C.; Chance, H.M. (1882). The geology of Pike and Monroe counties. Second Geol. Surv. of Penna.,. Rept. of Progress, G6. Harrisburg. pp. 17, 73–80, 114–115. 
40. ^ Barrett, Ramsay. "The Depositional Setting of The Marcellus Black Shale" (pdf). Appalachian Producers Issues Seminar. Independent Oil and Gas Association of West Virginia. http://www.iogawv.com/RamsayBarrett-Shale.pdf. Retrieved 2008-04-02. 
41. ^ Mazzullo, S.J. (1973). "Deltaic depositional environments in the Hamilton Group (middle Devonian, southeastern New York State)". Journal of Sedimentary Research 43 (4): 1061–1071. doi:10.1306/74D728F1-2B21-11D7-8648000102C1865D. 
42. ^ ^{a b} VanDiver, Bradford B. (1990). Roadside geology of Pennsylvania. Roadside Geology Series. Missoula, Mont: Mountain Press Pub. Co. pp. 86, 193. ISBN 0-87842-227-7. 
43. ^ Shultz, Charles H. (1999). The geology of Pennsylvania. Harrisburg, Pa: Pennsylvania Geological Survey. pp. 125–126. ISBN 0-8182-0227-0. 
44. ^ ^{a b c d e} Wickstrom, Lawrence H.; Ernie R. Slucher, Mark T. Baranoski, and Douglas J. Mullett (2008). "Geologic Assessment of the Burger Power Plant and Surrounding Vicinity for Potential Injection of Carbon Dioxide" (PDF). Columbus, Ohio: Ohio Geological Survey. Open-File Report 2008-1. http://www.dnr.state.oh.us/Portals/10/pdf/BurgerReport.pdf. Retrieved 2008-06-21. 
45. ^ Ettensohn, F.R. (1998). "Compressional tectonic controls on Epicontinental black-shale deposition: Devonian-Mississippian examples from North America". Shales and mudstones. Stuttgart: E. Schweizerbart. pp. 109–128,. ISBN 3-510-65181-2. http://cat.inist.fr/?aModele=afficheN&cpsidt=1809612. Retrieved 2008-06-12. 
46. ^ Patrick, K.J. (2004). Pennsylvania Caves and Other Rocky Roadside Wonders. Stackpole Books. pp. 18. ISBN 0-8117-2632-0. 
47. ^ Werne, J.P.; Sageman, B.B.; Lyons, T.W.; Hollander, D.J. (2002). "An integrated assessment of a" type euxinic" deposit: Evidence for multiple controls on black shale deposition in the middle Devonian Oatka Creek formation". American Journal of Science 302 (2): 110. doi:10.2475/ajs.302.2.110. http://www.ajsonline.org/cgi/content/abstract/302/2/110. Retrieved 2008-05-27. 
48. ^ McBride, P. (2004) (PDF). Facies Analysis of the Devonian Gordon Stray Sandstone in West Virginia, M.S. Thesis. West Virginia University, Morgantown, West Virginia. pp. 21. https://eidr.wvu.edu/files/3403/McBride_Patrick_thesis.pdf. 
49. ^ Lash, G.G. (2008). "Pyrite Laminae In Black Shale-An Additional Source of Permeability In Unconventional Reservoirs". 2008 Joint Meeting of the Geological Society of America, et al.. http://gsa.confex.com/gsa/2008AM/finalprogram/abstract_147721.htm. Retrieved 2008-07-14. 
50. ^ Smol, J. P.; Last, William M. (2001). Tracking environmental change using lake sediments. Vol. 2: Physical and Geochemical Methods. Kluwer Academic. pp. 191. ISBN 1-4020-0628-4. 
51. ^ "Black shale weathering". Bernhard Peucker-Ehrenbrink : Projects. Woods Hole Oceanographic Institution. http://www.whoi.edu/hpb/viewPage.do?id=1375&cl=8. Retrieved 2008-07-13. 
52. ^ Wilde, Pat; Quinby-Hunt, Mary S.; Lyons, Timothy W. (2005-10-13). "Sulfur Proxies in Type III Black Shales: Fe, Mn, Co, Cu, Ni, Zn, Sc" (ppt). 2005 Annual Meeting. Salt Lake City, Utah: Geological Society of America. Paper No. 76-7. http://www.marscigrp.org/gsa05whl.ppt. Retrieved 2008-06-21. 
53. ^ Desantis, M.K. (2003–09). "Eifelian (early Middle Devonian) Depositional Sequences And Bioevents In Eastern Laurentia: Appalachian Basin-wabash Platform Comparisons". 2003 Seattle Annual Meeting (Geological Society of America) 35 (6). http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65945.htm. Retrieved 2008-05-26. 
54. ^ Arthur, M.A.; Sageman, B.B. (2005). "Sea level control on source rock development: Perspectives from the Holocene Black Sea, the mid-Cretaceous Western Interior Basin of North America, and the Late Devonian Appalachian Basin". The Deposition of Organic Carbon-Rich Sediments: Models, Mechanisms and Consequences. SEPM Society for Sedimentary Geology. pp. 35–59. ISBN 1-56576-110-3. https://www.sepm.org/publishing/toc/sp82toc.htm. 
55. ^ Anstey, Robert L.; Erwin, Douglas H. (1995). New approaches to speciation in the fossil record. New York: Columbia University Press. ISBN 0-231-08248-7. 
56. ^ ^{a b} "Marcellus Formation, Group". The Paleobiology Database. http://paleodb.org/cgi-bin/bridge.pl?action=displayStrata&group_formation_member=Marcellus. Retrieved 2008-04-03. 
57. ^ Koutsoukos, Eduardo (2005). Applied Stratigraphy (Topics in Geobiology). Berlin: Springer. pp. 70. ISBN 1-4020-2632-3. 
58. ^ Menning, M.; Alekseev, A.S.; Chuvashov, B.I.; Davydov, V.I.; Devuyst, F.X.; Forke, H.C.; Grunt, T.A.; Hance, L.; Heckel, P.H.; Izokh, N.G.; Others, (2006). "Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian—Carboniferous—Permian Correlation Chart 2003 (DCP 2003)". Palaeogeography, Palaeoclimatology, Palaeoecology 240 (1–2): 318–372. doi:10.1016/j.palaeo.2006.03.058. 
59. ^ W. T. Kirchgasser (2007). "Recognising the Kacak Event in the Devonian terrestrial environment and its implications for understanding land-sea interactions". Devonian Events and Correlations : Special Publication no 278. (Geological Society Special Publication). London: Geological Society of London. pp. 133–155. ISBN 1-86239-222-6. 
60. ^ ^{a b c d} Milici, Robert C.; Swezey, Christopher S. (2006). "Assessment of Appalachian Basin Oil and Gas Resources: Devonian Shale–Middle and Upper Paleozoic Total Petroleum System" (PDF). Open-File Report Series 2006-1237. United States Geological Survey. http://pubs.usgs.gov/of/2006/1237/of2006-1237.pdf. Retrieved 2008-04-05. 
61. ^ ^{a b} Dana, J.D. (1895). "Historical Geology". Manual of Geology: Treating of the Principles of the Science with Special Reference to American Geological History (4th ed.\ ed.). New York: American book company. pp. 728. LCCN 04-705. http://www.geology.19thcenturyscience.org/books/1896-Dana-ManGeol/htm/doc728.html. 
62. ^ Ellis, Mary (1903). "Index to Publications of the New York State Natural History Survey and New York State Museum 1837–1902". New York State Museum Bulletin (Albany: University of the State of New York) (66): 429. LCCN 03-299. 
63. ^ white, Charles (1891). The Texan Permian and Its Mesozoic Types of Fossils. Washington D.C.: United States Geological Survey. pp. 401. 
64. ^ ^{a b c d} "Explanation of Geologic Units" (PDF). Pennsylvania Geological Survey. http://www.dcnr.state.pa.us/topogeo/map1/explanation.pdf. Retrieved 2008-01-26. 
65. ^ ^{a b} Grasso, T.X. (1968). "A new coral bed in the Hamilton Group (Middle Devonian) of central New York". Journal of Paleontology 42 (1): 84–87. JSTOR 1302130. 
66. ^ Martin, J.P.; Hill, D.G.; Lombardi, T.E. (2004). "Fractured Shale Gas Potential In New York". Northeastern Geology and Environmental Sciences 26 (1/2): 57–78. 
67. ^ ^{a b c d} Boughton, Carol J.; McCoy, Kurt J. (2006). Hydrogeology, Aquifer Geochemistry, and Ground-Water Quality in Morgan County, West Virginia. U.S. Geological Survey. Scientific Investigations Report 2006-5198. 
68. ^ Repetski, J.E.; Ryder, R.T.; Harper, J.A.; Trippi, M.H. (2002). "Thermal maturity patterns (CAI and% Ro) in the Ordovician and Devonian rocks of the Appalachian basin in Pennsylvania". US Geological Survey Open-File Report: 10. 
69. ^ ^{a b c d e} Rickard, L.V. (1984). "Correlation of the subsurface Lower and Middle Devonian of the Lake Erie region". Bulletin of the Geological Society of America 95 (7): 814–828. doi:10.1130/0016-7606(1984)95<814:COTSLA>2.0.CO;2. http://bulletin.geoscienceworld.org/cgi/content/abstract/95/7/814. Retrieved 2008-04-03. 
70. ^ "Geology of the Southwestern District". Resident Geologist Program. Ministry of Northern Development and Mines, Government of Ontario. 2004-05-21. http://www.mndm.gov.on.ca/mndm/mines/resgeol/southern/southwestern/geo_e.asp. Retrieved 2008-04-02. 
71. ^ Jackson, Margaret S.; Hanley, Peter M.; and Sak, Peter B. (2007). "Preliminary Bedrock Geologic Map of the Middle Portion of the Susquehanna River Valley, Cumberland, Dauphin, And Perry Counties, Pennsylvania" (pdf). Open File Report OFBM-07-05.0. Pennsylvania Geological Survey. http://www.dcnr.state.pa.us/topogeo/openfile/midsusque.pdf. Retrieved 2008-01-26. 
72. ^ Oliver Jr, W.A. (1976). "Noncystimorph colonial rugose corals of the Onesquethaw and Lower Cazenovia Stages (Lower and Middle Devonian) in New York and adjacent areas". Geological Survey Professional Paper 869: 1–156. 
73. ^ ^{a b c} Martin, R.L. (2002) (PDF). Taxonomic Revision and Paleoecology of Middle Devonian (Eifelian) Fishes of the Onondaga, Columbus and Delaware Limestones of the eastern United States.. West Virginia University. http://kitkat.wvu.edu:8080/files/2728/Martin_Robert_dissertation.pdf. Retrieved 2008-07-07. 
74. ^ ^{a b} Lash, Gary. "Influence of Basin Dynamics on Upper Devonian Black Shale Deposition, Western New York State and Northwest Pennsylvania" (pdf). American Association of Petroleum Geologists. http://www.searchanddiscovery.net/documents/2007/07022lash/images/Lash_AAPG_pg1_red.pdf. Retrieved 2008-05-27. 
75. ^ TVGA Consultants (2007-08-29) (PDF). Draft Environmental Impact Statement, Modification of Permit to Mine, Buffalo Crushed Stone Quarry. New York State Department of Environmental Conservation. p. 16. http://www.buffalocrushedstone.com/uploads/uploads5400/BCSDEISAsAccepted.pdf. 
76. ^ ^{a b} "Map Unit Descriptions" (pdf). Virginia Department of Mines, Minerals and Energy. 2007-09-28. http://www.dmme.virginia.gov/DMR3/dmrpdfs/Giles_Geologic_Descriptions.pdf. 
77. ^ Maryland Geological Survey (1913). "Adoption of the Romney Formation". Middle and Upper Devonian, text.. Reports Dealing with the Systematic Geology and Paleontology of Maryland. Baltimore: Johns Hopkins Press. pp. 40–48. LCCN gs13-808. http://books.google.com/books?id=169LAAAAMAAJ&pg=PA46. 
78. ^ Donovan, Joseph J.; Eberhard Werner; Dorothy J. Vesper; Lacoa Corder (2006-05) (PDF). Springs, source water areas, and potential for high-yield aquifers along the Cacapon Mountain anticline, Morgan County, WV. West Virginia University. HRC-3. http://www.hrc.nrcce.wvu.edu/HRC3/HRC3-MorganCounty-Final%20Report2006.pdf. Retrieved 2008-05-26. 
79. ^ Collins, H.R. (1979). "Devonian Bentonites in Eastern Ohio: GEOLOGIC NOTES". AAPG Bulletin 63. doi:10.1306/2F9181AD-16CE-11D7-8645000102C1865D. 
80. ^ ^{a b c} Dennison, J.M.; Textoris, D.A. (1970). "Devonian tioga tuff in Northeastern United States". Bulletin Volcanologique, 34 (1): 289–294. Bibcode 1970BVol...34..289D. doi:10.1007/BF02597791. 
81. ^ ^{a b c} Scheetz, B.E.; Ellsworth, C.J. (2007-07-31) (PDF). Preliminary Assessment of Acid Producing Rock on Future PENNDOT Construction, Final Report. National Technical Information Service (U.S.). pp. 41–42. FHWA-PA-2007-022-510401-05; PTI 2007–53. http://www.mautc.psu.edu/docs/PSU-2005-05.pdf. Retrieved 2008-06-14. 
82. ^ ^{a b c} Dennison, J.M.; Hasson, K.O. (1976). "Stratigraphic cross section of Hamilton Group (Devonian) and adjacent strata along south border of Pennsylvania". AAPG Bulletin 60 (2): 278–287. doi:10.1306/83D922BC-16C7-11D7-8645000102C1865D. http://search.datapages.com/data/doi/10.1306/83D922BC-16C7-11D7-8645000102C1865D. Retrieved 2008-05-03. 
83. ^ ^{a b} Ver Straeten, C.A. (2004). "K-bentonites, volcanic ash preservation, and implications for Early to Middle Devonian volcanism in the Acadian orogen, eastern North America". Bulletin of the Geological Society of America 116 (3–4): 474–489. doi:10.1130/B25244.1. 
84. ^ ^{a b c d} Droste, John B.; Robert H. Shaver (1997). "Tioga Bentonite Bed". Compendium of Paleozoic Rock-Unit Stratigraphy in Indiana — A Revision. http://igs.indiana.edu/geology/structure/compendium/html/comp1lb8.cfm. Retrieved 2008-06-12. 
85. ^ ^{a b c} Kaufmann, B. (2006). "Calibrating the Devonian Time Scale: A synthesis of U—Pb ID—TIMS ages and conodont stratigraphy". Earth-Science Reviews 76: 175–190. Bibcode 2006ESRv...76..175K. doi:10.1016/j.earscirev.2006.01.001. 
86. ^ ^{a b c} Dennison, J.M. (1986). Tioga Bentonite in the Appalachian Basin: Final report. U.S. Department of Energy. DOE/ET/12139-T2. 
87. ^ "Geologic Map Legends : Allegheny Plateau and Valley and Ridge". Geologic Map of Maryland. Maryland Geological Survey. 1968. http://www.mgs.md.gov/esic/geo/lgdalleg.html. Retrieved 2008-06-12. 
88. ^ Way, J.H.; Smith, R.C.; Roden, M. (1986). "Detailed correlations across 175 miles of the Valley and Ridge of Pennsylvania using 7 ash beds in the Tioga Zone". Selected geology of Bedford and Huntington Counties. 51st Annual Field Conference of Pennsylvania Geologists. U.S. Geological Survey. pp. 55–72. 
89. ^ New York State Museum (1990). New York State Geological Highway Map (Map). Educational Leaflet No. 33. http://geology.about.com/library/bl/maps/n_statemap_NYexplan.htm. 
90. ^ Koch Ii, W.F. (1981). "Brachiopod community paleoecology, paleobiogeography, and depositional topography of the Devonian Onondaga Limestone and correlative strata in eastern North America". Lethaia 14 (2): 83–103. doi:10.1111/j.1502-3931.1981.tb01909.x. 
91. ^ Roen, J.; Walker, B. (1996). The Atlas of Major Appalachian Gas Plays. West Virginia Geological and Economic Survey. Publication V-25. 
92. ^ Stein Jr, W.E. (1982). "Iridopteris eriensis from the Middle Devonian of North America, with Systematics of Apparently Related Taxa". Botanical Gazette 143 (3): 401. doi:10.1086/337316. JSTOR 2474838. 
93. ^ ^{a b c d e} Wilson, Karl A. (2006-09-27). "Lower Marcellus Formation – the Chestnut Street Road Cut". New York Paleontology. State University of New York at Binghamton. http://bingweb.binghamton.edu/~kwilson/Devonian/DevSites/Chestnut_Street/Chestnut_Street.htm. Retrieved 2008-05-23. 
94. ^ "Stony Hollow Member". The Paleobiology Database. http://paleodb.org/cgi-bin/bridge.pl?action=displayStrata&group_hint=Hamilton&formation_hint=Marcellus%20Shale&group_formation_member=Stony%20Hollow. Retrieved 2008-05-23. 
95. ^ Lash, Gary. "Influence of Basin Dynamics on Upper Devonian Black Shale Deposition, Western New York State and Northwest Pennsylvania, Page 2" (pdf). American Association of Petroleum Geologists. http://www.searchanddiscovery.net/documents/2007/07022lash/images/Lash_AAPG_pg2_red.pdf. Retrieved 2008-05-27. 
96. ^ ^{a b} Kasprak, A.H. (2008). Nowakia (dacryoconarida) In The Halihan Hill Bed (oatka Creek Formation, New York). Geological Society of America. http://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134728.htm. Retrieved 2008-05-26. 
97. ^ Bartholomew, A.; Schramm, T. (2007). "Faunal Turnover Between Two Ee Subunits: Investigating The Timing Of Large-scale Faunal Turnover In The Latest Eifelian Of Eastern North America". 2007 GSA Denver Annual Meeting. http://gsa.confex.com/gsa/2007AM/finalprogram/abstract_132498.htm. Retrieved 2008-05-26. 
98. ^ ^{a b} Wilson, Karl A. (2007-03-31). "The Marcellus Formation — The Swamp Road Roadcut". New York Paleontology. State University of New York at Binghamton. http://bingweb.binghamton.edu/~kwilson/Devonian/DevSites/SwampRd/swamprd.htm. Retrieved 2008-05-23. 
99. ^ Pennsylvania Geological Survey, Fourth Series. Geologic Map of the Mifflintown Qd., PA (Map). 1:24,000. Cartography by United States Geological Survey. A126. http://www.libraries.psu.edu/emsl/guides/pageomaps/A126_1.html. 
100. ^ Pennsylvania Geological Survey, Fourth Series (1995) (PDF). Bedrock Geology of the Freeburg 7.5 minute Quadrangle, Snyder County, Pennsylvania (Map). Open-File Reports. Cartography by United States Geological Survey. ORF 95-04. http://www.dcnr.state.pa.us/topogeo/pub/openfile/pdfs/of95_04_freeburg.pdf. 
101. ^ Pennsylvania Geological Survey, Fourth Series. Geologic Map of the Loysville Qd., PA (Map). 1:24,000. Cartography by United States Geological Survey. A127. http://www.libraries.psu.edu/emsl/guides/pageomaps/A127_1.html. 
102. ^ Pennsylvania Geological Survey, Fourth Series (1976). Geologic Map of the Millerstown 15 Minute Quadrangle, PA (Map). 1:24,000. Cartography by United States Geological Survey. A136. http://www.libraries.psu.edu/emsl/guides/pageomaps/A136_5.html. 
103. ^ Pennsylvania Geological Survey, Fourth Series (1973). Geologic Map of the Stroudsburg Qd., PA, NJ (Map). 1:24,000. Cartography by United States Geological Survey. GQ1047. http://www.libraries.psu.edu/emsl/guides/pageomaps/GQ1047.html. 
104. ^ Dana, J.D. (1896). Manual of Geology: Treating of the Principles of the Science with Special Reference to American Geological History (4rh ed.). American Book Company. pp. 599. 
105. ^ Carter, J.G.; Tevesz, M.J.S. (1978). "Shell microstructure of a Middle Devonian (Hamilton Group) bivalve fauna from central New York". Journal of Paleontology 52 (4): 859–880. JSTOR 1303906. 
106. ^ Schneider, Philip F. (1894). Notes on the Geology of Onondaga County, NY : Embracing a Short Description of the Various Eras, Periods and Groups. Syracuse, NY. pp. 37. 
107. ^ "Devonian Seas of Central New York : Syracuse Area, New York". New York Paleontological Society Field Trips. http://www.nyps.org/field.htm. Retrieved 2008-05-25. 
108. ^ "Flood of 1993 Uncovers Devonian Sea Floor". Iowa Geology. Iowa Department of Natural Resources. 1994. http://www.igsb.uiowa.edu/Browse/flood93/flood93.htm. Retrieved 2008-06-14. 
109. ^ Burns, Jasper (1991). Fossil Collecting in the Mid-Atlantic States: With Localities, Collecting Tips, and Illustrations of More Than 450 Fossil Specimens. Baltimore: Johns Hopkins University Press. pp. 96. ISBN 0-8018-4145-3. 
110. ^ Pabian, R.K.; Strimple, H.L. (1976). "Middle Devonian crinoids from western Maryland". Journal of Paleontology 50 (4): 759–762. JSTOR 1303668. 
111. ^ ^{a b c} Hill, Heidi. "Chapter 3 Fossils and Geologic Time". The Big Dig. North Carolina State University, Kenan Fellows Program. Archived from the original on October 25, 2007. http://web.archive.org/web/20071025085454/http://www.ncsu.edu/kenanfellows/2002/hhill/chapt3/chapt3.html. Retrieved 2008-05-25. 
112. ^ Oliver, W.A. (October 1, 1951). "Middle Devonian coral beds of central New York". American Journal of Science 249 (10): 705. doi:10.2475/ajs.249.10.705. http://ajsonline.org/cgi/content/abstract/249/10/705. Retrieved 2008-06-15. 
113. ^ Over, D.J.; Klapper, G.; Murphy, M.A.; Talent, J.A. (1997). Paleozoic Sequence Stratigraphy, Biostratigraphy, and Biogeography: Studies in Honor of J. Granville ('Jess') Johnson. Geological Society of America. pp. 152. ISBN 0-8137-2321-3. 
114. ^ Yochelson, E.L.; Hlavin, W.J. (1985). "Coleolus curvatus Kindle (" Vermes") from the Cleveland Member of the Ohio Shale, Late Devonian (Famennian) of Ohio". Journal of Paleontology 59 (5): 1298–1304. JSTOR 1305019. 
115. ^ "Ancient Life of New York : A Billion Years of Earth History". New York State Museum. 2003-09. http://www.nysm.nysed.gov/education/teacher/ancient_life_text.html. Retrieved 2008-05-26. 
116. ^ ^{a b} Brett, C.E.; Baird, G.C. (1997). Paleontological Events: Stratigraphic, Ecological, and Evolutionary Implications. Columbia University Press. pp. 269. ISBN 0-2310-8250-9\. 
117. ^ Davis, R. Michael; Landman, Neil H.; Tanabe, Kazushige (1996). Ammonoid paleobiology. New York: Plenum Press. pp. 644. ISBN 0-306-45222-7. 
118. ^ Wynne, Peter (2008-03-20). "Gas-drilling misinformation causing unnecessary anxiety in Wayne County". The Weekly Almanac (Wayne County, PA). 
119. ^ ^{a b c d e f} Gold, Russell (2008-04-02). "Gas Producers Rush to Pennsylvania : Promising Results There Spur Investment". The Wall Street Journal: p. A2. 
120. ^ US Department of Energy (April 2009): Modern shale gas development in the United States: a primer, p.17, PDF file, downladed 11 June 2009.
121. ^ ^{a b} Bertola, David (2008-02-08). "Researchers: Shale holds vast supply of natural gas". Business First of Buffalo. http://buffalo.bizjournals.com/buffalo/stories/2008/02/11/story2.html?b=1202706000%5E1587557. Retrieved 2008-04-02. 
122. ^ Farley, Robert. "Just the Fracking Facts." FactCheck.org, 14 October 2011.
123. ^ Esch, Mary (2008-11-04). "Estimated gas yield from Marcellus shale goes up". Philly.com. http://www.philly.com/philly/hp/news_update/20081104_Estimated_gas_yield_from_Marcellus_shale_goes_up.html. 
124. ^ "Got gas, lots". Pittsburgh Tribune-Review. 2008-11-05. http://www.pittsburghlive.com/x/pittsburghtrib/opinion/archive/s_596812.html. 
125. ^ Gebhart, Rob (2001-08-12). "Texas company to search for gas in Somerset County". Daily American. http://www.dailyamerican.com/articles/2008/01/12/news/news340.txt. Retrieved 2008-04-02. 
126. ^ ^{a b c} Chernoff, Harry (2008-03-17). "Investing in the Marcellus Shale". Seeking Alpha. http://seekingalpha.com/article/68716-investing-in-the-marcellus-shale. Retrieved 2008-04-06. 
127. ^ Faraj, Basim and James Duggan (2007). "Devonian Aged Shale Gas Potential of the Southern Tier of New York". 2007 AAPG Annual Meeting, Long Beach California (American Association of Petroleum Geologists). http://aapg.confex.com/aapg/2007am/preliminaryprogram/abstract_111956.htm. Retrieved 2008-04-28. ^{[dead link]}
128. ^ Brown, David (2007-04). "If It’s Shale, It’s Probably in Play". AAPG Explorer. American Association of Petroleum Geologists. http://www.aapg.org/explorer/2007/04apr/beyond_barnett.cfm. Retrieved 2008-07-13. 
129. ^ ^{a b} "Marcellus Shale Natural Gas: Environmental Impact". The League of Women Voters of Pennsylvania. http://palwv.org/issues/MarcellusShale/Marcellus%20Shale%20Study%20Guide%20II%20-%20Environmental%20Impact.pdf. 
130. ^ ^{a b} "Marcellus Shale". Catskill Mountainkeeper. http://catskillmountainkeeper.org/node/290. Retrieved 2008-06-09. 
131. ^ http://www.swarthmore.edu/marcellusshale
132. ^ http://www.propublica.org/article/does-chesapeakes-no-drilling-pledge-do-enough-to-protect-nycs-watershed-110
133. ^ Thompson, David (2008-05-31). "Gas Drilling : Companies told to stop operations". Williamsport SunGazette. http://www.sungazette.com/page/content.detail/id/511100.html. Retrieved 2008-06-09. 
134. ^ Engelder, Terry (2008-03-30). "Sunday Forum: Full of gas". Post Gazette. http://www.post-gazette.com/pg/08090/868880-109.stm. Retrieved 2008-06-09. 
135. ^ {{Cite document |url=http://www.cabotog.com/pdfs/Tab1.pdf |title=Resident affidavits regarding methane in Dimock wells|date=2010-07-20 |publisher=[[Cabot Oil & Gas}} |postscript=}}
136. ^ Consequences of gas drilling still unknown. The Times Leader. 2009-03-16. http://www.timesleader.com/news/hottopics/shale/Consequences_of_gas_drilling_still_unknown_03-16-2009.html 
137. ^ Feldmann, R.M.; Schweitzer, C.E.; Redman, C.M.; Morris, N.J.; Ward, D.J. (2007). "New Late Cretaceous Lobsters From The Kyzylkum Desert Of Uzbekistan". Journal of Paleontology 81 (4): 701–713. doi:10.1666/pleo0022-3360(2007)081[0701:NLCLFT]2.0.CO;2. http://findarticles.com/p/articles/mi_qa3790/is_200707/ai_n19434226/pg_10. 
138. ^ ^{a b} Swank, J.H. (1892). History of the Manufacture of Iron in All Ages, and Particularly in the United States From Colonial Times to 1891.. Philadelphia: Ayer Publishing. 
139. ^ Ashburner, Charles A. (1876). "A measured section of the Paleozoic Bucks of Central Pennsylvania, from the top of the Allegheny River Coal Series, down to the Trenton Limestone or the Lower or Cambro-Silurian System". Proceedings of the American Philosophical Society Held at Philadelphia for Promoting Useful Knowledge. Vol. XV, No. 96. American Philosophical Society. 
140. ^ Schallenberg, R.H.; Ault, D.A. (1977). "Raw Materials Supply and Technological Change in the American Charcoal Iron Industry". Technology and Culture (Technology and Culture, Vol. 18, No. 3) 18 (3): 436–466. doi:10.2307/3103901. JSTOR 3103901. 
141. ^ "Little Buffalo State Park: Park History". Pennsylvania State Parks. Pennsylvania Department of Conservation and Natural Resources. http://www.dcnr.state.pa.us/stateparks/parks/littlebuffalo/littlebuffalo_history.aspx. Retrieved 2008-06-21. 
142. ^ ^{a b} Lesley, J. P. (1859). The Iron Manufacturer's Guide to the Furnaces, Forges and Rolling Mills of the United States. New York: J. Wiley. pp. 651. LCCN 06-022651. http://books.google.com/?id=NSJDAAAAIAAJ&pg=PA651. 
143. ^ Platt, Franklin. (1881). The Geology of Blair County. Report of Progress. Harrisburg: Board of commissioners for the Second geological survey. LCCN gs07-757. 
144. ^ Crookes, W.; Röhrig, E. (1869). A practical treatise on Metallurgy. Vol. II. London: Longmans Green. pp. 695. 
145. ^ Firmstone, H. (1879). "On a Deposit of Cadmia in a Coke Blast Furnace". Transactions of the American Institute of Mining Engineers (American Institute of Mining Engineers) VII: 93–94. 
146. ^ "Chalybeate Springs Hotel — U.S. National Register of Historic Places". Waymarking.com. http://www.waymarking.com/waymarks/WM1054. Retrieved 2008-10-09. 
147. ^ ^{a b} Stevenson, John James (1882). The Geology of Bedford and Fulton Counties. Harrisburg: The board of Commissioners for the 2d. Geological Survey (of Pennsylvania). pp. 342–343. LCCN gs-07. 
148. ^ ^{a b} Hemmeter, John Conrad (1902). Diseases of the stomach. Blakiston. pp. 327. 
149. ^ ^{a b c d} Doden, A.G.; Gold, D.P.; Hoover, S.E.; Scheetz, B.E.; Ellsworth, C.J. (2008). Road Bed And Building Heave From Alteration Of Sulfide And Sulfate Minerals. Geological Society of America. http://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134913.htm. Retrieved 2008-05-04. 
150. ^ ^{a b} Orndorff, Z.W.; Lee Daniels, W. (2004). "Evaluation of acid-producing sulfidic materials in Virginia highway corridors" (PDF). Environmental Geology 46 (2): 209–216. doi:10.1007/s00254-004-1027-y. http://www.springerlink.com/index/8C50W05J4CR2JY2Y.pdf. Retrieved 2008-05-03. 
151. ^ Smith, M.W.; Varner, J.P.; Mital Jr, J.P.; Sokoloski, D.J. (2006). "Remediation Of Acid Rock Drainage From Highway Construction In The Marcellus Shale, Mifflin County, Pennsylvania". Geological Society of America Abstracts with Programs, 38 (2): 33. http://gsa.confex.com/gsa/2006NE/finalprogram/abstract_100515.htm. Retrieved 2008-05-04. 
152. ^ Hoover, S.E.; Wang, M.C.; Dempsey, B. (2004). "Structural damage induced by pyritic shale". Fifth International Conference on Case Histories in Geotechnical Engineering, April 13–17, 2004, New York, N. Y.Proceedings[electronic resource]. pp. 7. http://www.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=2004112611434CE&recid=20049978EQ. 

External links

• [http://energy.wilkes.edu/pages/1.asp A Marcellus Shale Clearinghouse – The Institute for Energy and Environmental Research for Northeastern Pennsylvania Wilkes University
• Outcrops of the Marcellus Formation images with captions hosted at Pennsylvania State University
• Susquehanna River Basin Marcellus Shale Occurrence map
• Pittsburgh Association of Petroleum Geologists PAPG publications including the Marcellus Shale
• Marcellus Shale Links Maps and Links to Governmental and Non Governmental sites about the Marcellus Shale
• Natural Gas Changes the Energy Map MIT's Technology Review article about the gas potential of Marcellus Shale (only a brief synopsis is free)
• Citizens Campaign for the Environment: CAMPAIGNS: Natural Gas Hydro-Fracking in Shale
• Drilling Updates: List of Company Operational Drilling Updates