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116-543: The unit name usage by the U.S. Geological Survey (USGS) includes Marcellus Shale and Marcellus Formation . 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. The Marcellus consists predominantly of black shale and

232-586: A transgressive black shale, because it was deposited in deepening conditions when the basin floor dropped as the mountains rose up. The dark shale facies of the Marcellus were formed from flysch , a fine mud deposited in deep water; the deepening sea that deposited the Marcellus cut off the supply of carbonates that form limestone and the fine-grained flysch sediments buried the Onondaga limestone beds. Organic matter, probably dominated by plankton , also settled to

348-474: A few limestone beds and concentrations of iron pyrite  ( Fe S 2 ) and siderite  (Fe CO 3 ). Like most shales, it tends to split easily along the bedding plane, a property known as fissility . Lighter colored shales in the upper portion of the formation tend to split into small thin-edged fragments after exposure. These fragments may have rust stains from exposure of pyrite to air, and tiny gypsum  ( Ca SO 4 ·2 H 2 O ) crystals from

464-533: A few centimeters to several metres. They are often oriented perpendicular to either the upper surface and base of lava flows and the contact of the tabular igneous bodies with the surrounding rock. This type of jointing is typical of thick lava flows and shallow dikes and sills. Columnar jointing is also known as either columnar structure , prismatic joints , or prismatic jointing . Rare cases of columnar jointing have also been reported from sedimentary strata. Joints can be classified according to their origin, under

580-414: A hard, fissile, metamorphic rock known as slate . With continued increase in metamorphic grade the sequence is phyllite , then schist and finally gneiss . Shale is the most common source rock for hydrocarbons ( natural gas and petroleum ). The lack of coarse sediments in most shale beds reflects the absence of strong currents in the waters of the depositional basin. These might have oxygenated

696-535: 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 2,700 m (8,900 ft) below the surface in southern Pennsylvania. Upturned beds are exposed in sections of the folded Ridge-and-Valley Appalachians , including exposures on the flanks and axis of the Broad Top Synclinorium in south central Pennsylvania. Exposed beds are nearly horizontal on

812-519: A lava lake or flood basalt flow or the sides of a tabular igneous intrusion into either lava of the lake or lava flow or magma of a dike or sill. Joint propagation can be studied through the techniques of fractography in which characteristic marks such as hackles and plumose structures are used to determine propagation directions and, in some cases, the principal stress orientations. Some fractures that look like joints are actually shear fractures, which in effect are microfaults. They do not form as

928-571: A lighter shade of gray. Outcrops of the Marcellus can contain very small beds that resemble coal . The New York outcrops, and others further south in Pennsylvania and New Jersey, were extensively excavated in the early 19th century, sometimes at great expense, in the false hope of finding minable coal seams . In Perry County, Pennsylvania along the Juniata River the false coal beds become up to .3 m (1 ft) thick, but they did not produce

1044-470: A relatively deep, sediment- and oxygen-starved ( anoxic ), trough that formed parallel to the mountain chain. These clastic fragments of rock were carried in braided streams to the ancient Catskill Delta , a river delta probably similar to the present day Niger Delta of Africa. Smaller particles remained suspended longer in this epeiric sea , flowing offshore as turbidites in a slow but persistent underwater avalanche. They finally came to rest at

1160-428: A relatively high proportion of carbon which was burned in the furnace, and sulfur , which produced a usable but " red-short " iron. Red-short iron has the undesirable properties of oxidizing more easily, and a tendency to crack, especially when heated to a red-hot state. In some locations in Pennsylvania the quality of the ore was quite good, with relatively deep veins containing 45% iron, and very low sulfur. In Virginia,

1276-432: A result of vertical gravitational loading. In simple terms, the accumulation of either sediments, volcanic, or other material causes an increase in the pore pressure of groundwater and other fluids in the underlying rock when they cannot move either laterally or vertically in response to this pressure. This also causes an increase in pore pressure in preexisting cracks that increases the tensile stress on them perpendicular to

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1392-478: A tectonic - hydraulic hybrid. Exfoliation joints are sets of flat-lying, curved, and large joints that are restricted to massively exposed rock faces in a deeply eroded landscape. Exfoliation jointing consists of fan-shaped fractures varying from a few meters to tens of meters in size that lie sub-parallel to the topography. The vertical, gravitational load of the mass of a mountain-size bedrock mass drives longitudinal splitting and causes outward buckling toward

1508-458: A valuable fuel, despite the considerable effort expended to mine it from the surrounding hills. Seaweed and marine plants probably formed the false coal. True coal is formed from terrestrial plants, which only began to appear in Marcellus and later fossils. Close proximity to the surface of Marcellus bedrock south of the New York outcrops makes an east–west band running through the city of Syracuse

1624-515: Is 240 m (790 ft) thick, thinning to the west, becoming only 15 m (49 ft) thick along the Ohio River , and only a few feet in Licking County, Ohio . The thinning, or stratigraphic convergence, from east to west is caused by decreasing grain size in the clastic deposits, which entered the basin from the east. The beds finally "pinch out" westward because deposition was limited by

1740-435: Is a significant part of understanding the geology and geomorphology of an area. Joints often impart a well-develop fracture-induced permeability to bedrock. As a result, joints strongly influence, even control, the natural circulation ( hydrogeology ) of fluids, e.g. groundwater and pollutants within aquifers , petroleum in reservoirs , and hydrothermal circulation at depth, within bedrock. Thus, joints are important to

1856-1201: Is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the shale, such as dissolution of some of the cement to produce secondary porosity . Pyrite may be oxidized to produce gypsum . Black shales are dark, as a result of being especially rich in unoxidized carbon . Common in some Paleozoic and Mesozoic strata , black shales were deposited in anoxic , reducing environments, such as in stagnant water columns. Some black shales contain abundant heavy metals such as molybdenum , uranium , vanadium , and zinc . The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils , animal tracks or burrows and even raindrop impressions are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite , or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into

1972-675: Is attributed to relatively short-term oscillations in basin depth. Later deep water depositional sequences formed the overlying Brallier Formation and Harrell Formation . 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 and export . 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,

2088-420: Is characterized by its tendency to split into thin layers ( laminae ) less than one centimeter in thickness. This property is called fissility . Shale is the most common sedimentary rock. The term shale is sometimes applied more broadly, as essentially a synonym for mudrock , rather than in the narrower sense of clay-rich fissile mudrock. Shale typically exhibits varying degrees of fissility. Because of

2204-658: Is classified as the basal unit of the Hamilton Group  (Dh), lying beneath the Mahantango Formation  (Dmh) member of this group in Pennsylvania and Maryland. In New York, the Mahantango, also of Middle Devonian age, is further divided. There the Marcellus is separated from the overlying Skaneateles Formation, a more clastic and fossiliferous dark shale, by the thin Stafford or Mottville Limestone bed. In West Virginia,

2320-638: Is composed of about 58% clay minerals, 28% quartz, 6% feldspar , 5% carbonate minerals, and 2% iron oxides . Most of the quartz is detrital (part of the original sediments that formed the shale) rather than authigenic (crystallized within the shale after deposition). Shales and other mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron (Fe ) and sulfur (S ). Amorphous iron sulfide , along with carbon, produce

2436-430: Is evidence that shale acts as a semipermeable medium, allowing water to pass through while retaining dissolved salts. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. As a result, shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas , on floodplains and offshore below

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2552-455: Is more likely to form nonfissile mudstone than shale. On the other hand, black shales often have very pronounced fissility ( paper shales ) due to binding of hydrocarbon molecules to the faces of the clay particles, which weakens the binding between particles. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as

2668-452: Is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. It is during compaction that shale develops its fissility, likely through mechanical compaction of

2784-579: 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 , natural gas trapped in low-permeability shale, and requires the well completion method of hydraulic fracturing 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. The black shales also contain iron ore that

2900-744: The Aquashicola Creek and McMichael Creek at the foot of The Poconos , and the long, straight section of the Lost River in West Virginia. Below Port Jervis, New York , the Walpack Ridge deflects the Delaware River into the Minisink Valley, where it follows the southwest strike of the eroded Marcellus beds along the Pennsylvania – New Jersey state line for 40 km (25 mi) to the end of

3016-589: The Cincinnati Arch , the bulge that formed the west shore of the basin. Where the formation is relatively thick, it is divided into several members, and as the formation continues to thicken to the east, these members are further divided. Some workers chose to classify the Marcellus as a subgroup, and classify some of the members as separate formations. Oatka Creek shale Cardiff dark gray shale A local Purcell limestone member, 15 to 30 m (49 to 98 ft) of inter-bedded calcitic shale and limestone, divides

3132-679: The Hudson River , along the route of the Delaware and Hudson Canal . Stratigraphically , the Marcellus is the lowest unit of the Devonian age Hamilton Group, and is divided into several sub-units. 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." In the first New York State Geological Survey , also begun that year, James Hall established

3248-399: The U.S. Gulf Coast . As sediments continue to accumulate, the older, more deeply buried sediments begin to undergo diagenesis . This mostly consists of compaction and lithification of the clay and silt particles. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in

3364-466: The benthic zone at the bottom of marginal marine to open marine environments that existed west of the ancient Catskill Delta . The fossil record in this member shows the base was dominated by deposit feeders , while the upper layers were dominated by filter feeders . 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

3480-628: 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. Relative age dating of the Marcellus places its formation in

3596-651: The wave base . Thick deposits of shale are found near ancient continental margins and foreland basins . Some of the most widespread shale formations were deposited by epicontinental seas . Black shales are common in Cretaceous strata on the margins of the Atlantic Ocean , where they were deposited in fault -bounded silled basins associated with the opening of the Atlantic during the breakup of Pangaea . These basins were anoxic, in part because of restricted circulation in

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3712-661: The Allegheny Plateau, but upturned to form slightly overturned beds found along the Allegheny Front . From Wind Gap, Pennsylvania heading south, the dip of the beds steepens, becoming vertical at Bowmanstown on the Lehigh River . Nearby, in the Lehigh Gap area of Pennsylvania, the Marcellus is extensively faulted , and the beds are steeply overturned, with a reverse dip angle of up to 40° south. The Marcellus Shale and

3828-588: 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

3944-720: The Cazenovia subdivision of the Givetian faunal stage , or 391.9 to 383.7 million years ago ( Ma ). The Union Springs member, at the base of the Marcellus in New York, has been dated to the end of the Eifelian , the stage which immediately preceded the Givetian. Anoxic dark shales in the formation mark the Kačák Event , a late- Eifelian - stage marine anoxic event also associated with an extinction event . In 2012, Read and Erikson also depicted

4060-699: The Cherry Valley Member, which is also known for its rich nautiloid and goniatite cephalopod fauna. Originally named the Goniatite Limestone , it produces their fossilized remains with shells that can be larger than .3 m (1 ft) across. It also contains the "Cephalopod Graveyard" in the Schoharie Valley of eastern New York, an unusual accumulation of abundant coiled and straight shells of several types of large adult cephalopods. This bed lacks juvenile fossils, indicating that if their behavior

4176-725: The Hamilton Group grades laterally into the Millboro Shale formation in southern West Virginia and Virginia, which grades into the lower part of the Chattanooga Shale of Tennessee . The Milboro is gradational with the underlying Needmore Formation shale. South of the Mason-Dixon line , due to the difficulty in differentiating the Millboro and Needmore shales with the limited exposures available, and initial uncertainty in correlation with

4292-756: The Mahantango Formation, or included in the Montebello Formation ;(Dmot), and only the Shamokin correlates with the Marcellus on adjacent map sheets. In extreme eastern Pennsylvania, the Broadhead Creek member, a dark gray silty shale with dark gray shaly limestone concretions, appears above the Stony Hollow and Union Springs, in a layer up to 275 m (902 ft) thick. There are relatively sparse inclusions of fossilized marine fauna found in

4408-479: The Marcellus and the overlying Hamilton shales are deep, free of stones, and well suited for agriculture . Sampling of soil formed on the Marcellus bedrock showed the dominant mineralogy consisted of quartz , illite , montmorillonite , muscovite , and biotite , with phases of todorokite and trona appearing at depths closer to the bedrock. Upturned beds of the soft shale also capture streams and rivers with relatively straight segments in strike valleys such as

4524-701: The Marcellus in eastern Pennsylvania. The Purcell is stratigraphically equivalent to the Cherry Valley Limestone member in New York, a bioclastic packstone , consisting of skeletal limestones, with shaly intervals between its lower massive limestone layer, thick nodular limestone/ marlstone , and upper limestone layer. Other named members include the Bakoven Shale, Cardiff Shale, Chittenango shale, Solsville sandstone, Union Springs shale and limestone, and Stony Hollow shale and limestone. The Union Springs, Cherry Valley, and Oatka Creek merge beneath Lake Erie, into

4640-545: 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

4756-418: The Marcellus may be separated from the brown shales of the Mahantango by occasional sandstone beds and concretions , or it may lie directly below the younger Late Devonian Harrel Formation (or its lateral equivalents) because of a disconformity , which represents a gap in the geological record due to a period of erosion or non-deposition. In eastern Ohio the Hamilton Group also lies disconformably beneath

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4872-418: 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. Drainage that reacted with the pyrite inclusions also deposited a form of bog iron near several outcrops of

4988-494: The Marcellus overlies the Dundee Formation, a lateral equivalent of the Onondaga. In Pennsylvania, the Marcellus forms a sharp conformable contact with the Onondaga's Selinsgrove Limestone member. A thin pyrite-carbonate bed is also found at the base of the Marcellus black shale in the exposures of south central Pennsylvania, above a thin calcerous green shale bed, which lies upon the Onondaga limestone. In eastern New York,

5104-417: The Marcellus varied in thickness, becoming unworkably thin, and even disappearing altogether in places between the workable beds. The quality of the ore also varied, and it was not always profitable to smelt , as several furnaces built near iron ore mines in the Marcellus were abandoned before the ore and timber resources used to fuel them became scarce. Ore found interbedded in the black slaty shale contained

5220-412: The Marcellus, but these fossils are still important to paleontology. For example, the Marcellus contains the oldest known diverse collection of thin-shelled mollusks still having well preserved shell microstructure. It is also where goniatites , an extinct shelled swimmer similar to a squid, make their first appearance in the fossil record. Life on land also enters the fossil record in the Marcellus, with

5336-413: The Marcellus. In the 19th century, iron ore from these deposits was used as a mineral paint pigment. After being heated in a kiln and finely ground, it was mixed with linseed oil , and used to paint exterior wood on barns, covered bridges, and railroad cars. In addition to the bog iron, at several sloped locations in eastern Pennsylvania brown hematite was found lying on the Marcellus bedrock buried beneath

5452-862: The New York survey, they were mapped as the Romney Formation, a unit containing all the Middle Devonian strata, named for an exposure at Romney, West Virginia . The correlations were established by 1916 through tracing the New York exposures across Pennsylvania and Maryland into West Virginia, so under the principle of scientific priority , the Romney classification is now obsolete; but its Marcellus and underlying Needmore shale members are still found grouped in an undifferentiated map unit (Dmn). Tioga metabentonite or K- bentonite –stratigraphic unit about .6 m (2 ft) thick that consists of several discrete, relatively thin volcanic ash falls–is also included at

5568-535: 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,

5684-683: The Rhinestreet Shale Member of the West Falls Formation , another transgressive black shale tongue with similar characteristics to the Marcellus. 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 ,

5800-690: 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

5916-411: The angle at which joint sets of systematic joints intersect to form a joint system, systematic joints can be subdivided into conjugate and orthogonal joint sets. The angles at which joint sets within a joint system commonly intersect are called dihedral angles by structural geologists. When the dihedral angles are nearly 90° within a joint system, the joint sets are known as orthogonal joint sets . When

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6032-519: The ash into the atmosphere. It was dispersed across the Appalachian , Michigan , and Illinois Basins by the southern trade winds , because this area was in the southern hemisphere during the Devonian period. The volcanic origin of the ash is evidenced by its distinctive mineralogy –the ash was deposited directly upon the water, so its angular quartz grains differ from the clastic sediments rounded through

6148-499: The base of the Marcellus in eastern Pennsylvania. In 1843 it was described without being named by Hall, and more than 100 years passed before it was eventually named for the natural gas field in Tioga County, Pennsylvania , where it was encountered when drilling gas wells . It is a regional stratigraphic marker, used by geologists to identify the Marcellus, and correlate laterally equivalent strata. Difficulty in correctly identifying

6264-533: 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. Maximum thickness of the Marcellus ranges from 270 m (890 ft) in New Jersey, to 12 m (40 ft) in Canada. In West Virginia, the Marcellus Shale is as much as 60 m (200 ft) thick. In extreme eastern Pennsylvania, it

6380-421: The black coloration. Because amorphous iron sulfide gradually converts to pyrite , which is not an important pigment, young shales may be quite dark from their iron sulfide content, in spite of a modest carbon content (less than 1%), while a black color in an ancient shale indicates a high carbon content. Most shales are marine in origin, and the groundwater in shale formations is often highly saline . There

6496-531: The bottom of the Acadian foredeep in the Appalachian Basin , hundreds of meters from shore, at depths that may have been 150 m (490 ft) or more beneath the surface. Alternatively, the basin may have been as shallow as 50 m (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. The Marcellus deposition produced

6612-493: The bottom, but the normal aerobic decay process was inhibited in the anaerobic environment thereby preserving the organic carbon. Uranium was also incorporated in these organic muds syndepositionally, meaning it was deposited at the same time, rather than being introduced to the formation later. The organic matter scavenged trace elements from the seawater, including the redox -sensitive elements uranium, rhenium , molybdenum , osmium , chromium , and selenium . The Marcellus

6728-506: The clumps of clay particles produced by flocculation vary in size from a few tens of microns to over 700 microns in diameter. The floccules start out water-rich, but much of the water is expelled from the floccules as the clay minerals bind more tightly together over time (a process called syneresis ). Clay pelletization by organisms that filter feed is important where flocculation is inhibited. Filter feeders produce an estimated 12 metric tons of clay pellets per square kilometer per year along

6844-408: The color of the rock. Red, brown and green colors are indicative of ferric oxide ( hematite – reds), iron hydroxide ( goethite – browns and limonite – yellow), or micaceous minerals ( chlorite , biotite and illite – greens). The color shifts from reddish to greenish as iron in the oxidized ( ferric ) state is converted to iron in the reduced ( ferrous ) state. Black shale results from

6960-452: 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

7076-402: The context of underground coal mining , shale was frequently referred to as slate well into the 20th century. Black shale associated with coal seams is called black metal. [REDACTED] Media related to Shale at Wikimedia Commons Joint (geology) A joint is a break ( fracture ) of natural origin in a layer or body of rock that lacks visible or measurable movement parallel to

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7192-412: The dihedral angles are from 30 to 60° within a joint system, the joint sets are known as conjugate joint sets . Within regions that have experienced tectonic deformation, systematic joints are typically associated with either layered or bedded strata that have been folded into anticlines and synclines . Such joints can be classified according to their orientation in respect to the axial planes of

7308-449: The east at a shallower angle also form the steep slopes on the east side of Warm Springs Ridge . 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. The soils formed from

7424-462: The economic and safe development of petroleum, hydrothermal, and groundwater resources and the subject of intensive research relative to these resources. Regional and local joint systems exert a strong control on how ore-forming hydrothermal fluids (consisting largely of H 2 O , CO 2 , and NaCl — which formed most of Earth's ore deposits ) circulated within its crust. As a result, understanding their genesis, structure, chronology, and distribution

7540-553: The erosion process that carries them to the sea. As the volcanic ash settled to the bottom, it was admixed with these terrigenous components, producing a distinctive lithology in the sedimentary rock. The Tioga may appear in the formation as a gray, brown, black, or olive bed, or parting, consisting of coarse crystal tuff or tuffaceous shale, thinly laminated, with sand-sized mica flakes. The Tioga ash bed zone consists of eight ash beds labeled according to their stratigraphic order from A (oldest) to H (youngest), and another bed known as

7656-525: 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 anticline in the Eastern Panhandle of West Virginia . On the eastern limb of this anticline, beds of these shales dipping to

7772-559: The folds as they often commonly form in a predictable pattern with respect to the hinge trends of folded strata. Based upon their orientation to the axial planes and axes of folds, the types of systematic joints are: Columnar jointing is a distinctive type of joints that join together at triple junctions either at or about 120° angles. These joints split a rock body into long, prisms or columns. Typically, such columns are hexagonal, although 3-, 4-, 5- and 7-sided columns are relatively common. The diameter of these prismatic columns ranges from

7888-409: The formation as Eifelian. 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 . 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

8004-507: The fossil record in these layers provides important paleontological 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 sediments from the land into the sea. The Marcellus Shale was formed from the very first deposits in

8120-460: The free air. In addition, paleostress sealed in the granite before the granite was exhumed by erosion and released by exhumation and canyon cutting is also a driving force for the actual spalling. Unloading joints or release joints arise near the surface when bedded sedimentary rocks are brought closer to the surface during uplift and erosion; when they cool, they contract and become relaxed elastically. A stress builds up which eventually exceeds

8236-504: The gills of filter feeders when suspended; the coarser sediments of the sandstones at the top would have contained less organic matter to support deposit feeders. Below the Solsville, at the base of the Otsego in eastern New York, a coral bed is found; another coral bed can be seen at the top of the Marcellus near Berne, New York . A diverse, eel-like conodont fauna occurs in the limestone of

8352-753: 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,

8468-543: 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 siltstone overlying it. In south central Pennsylvania,

8584-542: The labels of tectonics, hydraulics, exfoliation, unloading (release), and cooling. Different authors have proposed contradictory hypotheses for the same joint sets and types. And, joints in the same outcrop may form at different times under varied circumstances. Tectonic joints are joints formed when the relative displacement of the joint walls is normal to its plane as the result of brittle deformation of bedrock in response to regional or local tectonic deformation of bedrock. Such joints form when directed tectonic stress causes

8700-419: The local and regional geology and geomorphology but also in developing natural resources, in the safe design of structures, and in environmental protection. Joints have a profound control on weathering and erosion of bedrock. As a result, they exert a strong control on how topography and morphology of landscapes develop. Understanding the local and regional distribution, physical character, and origin of joints

8816-541: The location-based name for this, and many of the other group names he published based on exposures in New York, were adopted in the second Pennsylvania survey, and are now widely accepted. In 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)

8932-592: The mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. The clay minerals may be altered as well. For example, smectite is altered to illite at temperatures of about 55 to 200 °C (130 to 390 °F), releasing water in the process. Other alteration reactions include the alteration of smectite to chlorite and of kaolinite to illite at temperatures between 120 and 150 °C (250 and 300 °F). Because of these reactions, illite composes 80% of Precambrian shales, versus about 25% of young shales. Unroofing of buried shale

9048-426: The minimum principal stress (the direction in which the rock is being stretched). If the tensile stress exceeds the magnitude of the least principal compressive stress the rock will fail in a brittle manner and these cracks propagate in a process called hydraulic fracturing . Hydraulic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets. In some cases, joint sets can be

9164-457: The minimum principal stress (the direction in which the rock is being stretched). This leads to the development of a single sub-parallel joint set. Continued deformation may lead to development of one or more additional joint sets. The presence of the first set strongly affects the stress orientation in the rock layer, often causing subsequent sets to form at a high angle, often 90°, to the first set. Joints are classified by their geometry or by

9280-449: 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 265,000 km (102,000 sq mi). Explosive eruptions associated with the Acadian orogeny originating near present-day central Virginia released

9396-455: The most well-consolidated, lithified, and highly competent rocks, such as sandstone , limestone , quartzite , and granite . Joints may be open fractures or filled by various materials. Joints infilled by precipitated minerals are called veins and joints filled by solidified magma are called dikes . Joints arise from brittle fracture of a rock or layer due to tensile stress . This stress may be imposed from outside; for example, by

9512-433: The narrow Atlantic, and in part because the very warm Cretaceous seas lacked the circulation of cold bottom water that oxygenates the deep oceans today. Most clay must be deposited as aggregates and floccules, since the settling rate of individual clay particles is extremely slow. Flocculation is very rapid once the clay encounters highly saline sea water. Whereas individual clay particles are less than 4 microns in size,

9628-470: The northern margin of the formation in central New York. There, the two joint planes in the Marcellus are nearly at right angles, each making cracks in the formation that run perpendicular to the bedding plane, which lies almost level. These joints form smooth nearly vertical cliffs , 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

9744-418: The order of centimeters, meters, tens of meters, or even hundreds of meters. As a result, they occur as families of joints that form recognizable joint sets. Typically, exposures or outcrops within a given area or region of study contains two or more sets of systematic joints, each with its own distinctive properties such as orientation and spacing, that intersect to form well-defined joint systems. Based upon

9860-806: The organic-rich deposits. The Marcellus also contains uranium , and the radioactive decay of the uranium-238  (U) makes it a source rock for radioactive radon gas (Rn). 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 . The more organic-rich black shales can be bituminous , but are too old to contain bituminous coal formed from land plants. In petroleum geology , these black shales are an important source rock that filled conventional petroleum reservoirs in overlying formations, are an unconventional shale gas reservoir, and are an impermeable seal that traps underlying conventional natural gas reservoirs. To

9976-415: The original open framework of clay particles. The particles become strongly oriented into parallel layers that give the shale its distinctive fabric. Fissility likely develops early in the compaction process, at relatively shallow depth, since fissility does not seem to vary with depth in thick formations. Kaolinite flakes have less tendency to align in parallel layers than other clays, so kaolinite-rich clay

10092-409: The overlying calcareous Cherry Valley Member. A regional unconformity appears in western New York, as the Union Springs lenses in and out, and then reappears in northwest Pennsylvania and northeast Ohio between the Onondaga and Cherry Valley. In Western and central New York, the uppermost member is the dark grey to black organic-rich Oatka Creek shale. Unlike the other Devonian shales in this region,

10208-631: The parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to the otherwise indistinguishable bedding planes . Non-fissile rocks of similar composition and particle size (less than 0.0625 mm) are described as mudstones (1/3 to 2/3 silt particles) or claystones (less than 1/3 silt). Rocks with similar particle sizes but with less clay (greater than 2/3 silt) and therefore grittier are siltstones . Shales are typically gray in color and are composed of clay minerals and quartz grains. The addition of variable amounts of minor constituents alters

10324-770: The period between the American Revolution and the American Civil War . These blast furnaces were important to the economy of the region at the time, but the cold blast stone furnaces typically employed were inefficient, and consumed significant amounts of timber from the nearby hardwood forests, which ultimately led to their demise. A typical furnace used 2,400 kg (5,300 lb) of hematite ore and 7.3 m (200 imp bu) of charcoal to produce 910 kg (2,010 lb) of pig iron, and could produce several thousand pounds per day, which required logging more than 4,000 m (1 acre) of forest daily. The ore from

10440-817: The presence of greater than one percent carbonaceous material and indicates a reducing environment. Pale blue to blue-green shales typically are rich in carbonate minerals . Clays are the major constituent of shales and other mudrocks. The clay minerals represented are largely kaolinite , montmorillonite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites , whereas in older rocks (especially in mid-to early Paleozoic shales) illites predominate. The transformation of smectite to illite produces silica , sodium , calcium , magnesium , iron and water. These released elements form authigenic quartz , chert , calcite , dolomite , ankerite , hematite and albite , all trace to minor (except quartz) minerals found in shales and other mudrocks. A typical shale

10556-628: The processes that formed them. The geometry of joints refers to the orientation of joints as either plotted on stereonets and rose-diagrams or observed in rock exposures. In terms of geometry, three major types of joints, nonsystematic joints, systematic joints, and columnar jointing are recognized. Nonsystematic joints are joints that are so irregular in form, spacing, and orientation that they cannot be readily grouped into distinctive, through-going joint sets. Systematic joints are planar, parallel, joints that can be traced for some distance, and occur at regularly, evenly spaced distances on

10672-476: The pyrite-carbonate was converted to a usable brown hematite iron ore along the outcrops and near the bedrock surface. The Marcellus iron ore was actively mined in south Central Pennsylvania from its discovery in the late 18th century, until it was supplanted by the rich ore beds of the Iron Range of Minnesota in the early 20th century. The ore was easily located and worked from shallow pits and shafts, but once

10788-451: The reaction between pyrite and limestone particles. Fresh exposures of the pyriteiferous shale may develop the secondary mineralization of orange limonite  (Fe O ( OH )·nH 2 O), and the pale yellow efflorescence or bloom of sulfur , associated with acid rock drainage . Pyrite is especially abundant near the base, and the upper contacts of limestones, but framboidal microcrystals and euhedral crystals of pyrite occur throughout

10904-528: The result of the perpendicular opening of a fracture due to tensile stress, but through the shearing of fractures that causes lateral movement of the faces. Shear fractures can be confused with joints because the lateral offset of the fracture faces is not visible in the outcrop or in a specimen. Because of the absence of diagnostic ornamentation or the lack of any discernible movement or offset, they can be indistinguishable from joints. Such fractures occur in planar parallel sets at an angle of 60 degrees and can be of

11020-444: The richest source rocks may contain as much as 40% organic matter. The organic matter in shale is converted over time from the original proteins, polysaccharides , lipids , and other organic molecules to kerogen , which at the higher temperatures found at greater depths of burial is further converted to graphite and petroleum. Before the mid-19th century, the terms slate , shale and schist were not sharply distinguished. In

11136-540: The ridge at Walpack Bend in the Delaware Water Gap National Recreation Area . The Minisink is a buried valley where the Delaware flows in a bed of glacial till that buried the eroded Marcellus bedrock during the last glacial period . This buried valley continues along the strike of the Marcellus southwest from the bend through Stroudsburg, Pennsylvania , and northeast from Port Jervis toward

11252-415: The same size and scale as joints. As a result, some "conjugate joint sets" might actually be shear fractures. Shear fractures are distinguished from joints by the presence of slickensides , the products of shearing movement parallel to the fracture surface. The slickensides are fine-scale, delicate ridge-in-groove lineations on the surface of fracture surfaces. Joints are important not only in understanding

11368-433: The sediments, with only slight compaction. Pyrite may be formed in anoxic mud at this stage of diagenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. As the sediments come under increasing pressure from overlying sediments, sediment grains move into more compact arrangements, ductile grains (such as clay mineral grains) are deformed, and pore space

11484-548: The shale. Small conical tentaculitids are commonly found in the Chittenango Member. The Halihan Hill bed contains styliolinids and macrofauna including brachiopods, coral-like bryozoans , small bivalves and gastropods (snails), incorporated after the faunal turnover when Emsian and Eifelian Schoharie/Onondaga fauna were replaced by the Givetian Hamilton fauna. The Solsville member contains well preserved bivalves, gastropods, and brachiopods. These shellfish lived in

11600-412: The sides of a tabular igneous, typically basaltic, intrusion. They exhibit a pattern of joints that join together at triple junctions either at or about 120° angles. They split a rock body into long, prisms or columns that are typically hexagonal, although 3-, 4-, 5- and 7-sided columns are relatively common. They form as a result of a cooling front that moves from some surface, either the exposed surface of

11716-571: 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. 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 , Al 2 Si 2 O 5 ( OH ) 4 ) and tiny fragments ( silt -sized particles) of other minerals, especially quartz and calcite . Shale

11832-458: The state line into extreme western Virginia . The Marcellus bedrock in eastern Pennsylvania extends across the Delaware River into extreme western New Jersey . It also exists in the subsurface of a small portion of Kentucky and Tennessee . Below Lake Erie , it can be found crossing the border into Canada , where it stretches between Port Stanley and Long Point to St. Thomas in southern Ontario . The Marcellus appears in outcrops along

11948-402: The stretching of layers, the rise of pore fluid pressure , or shrinkage caused by the cooling or desiccation of a rock body or layer whose outside boundaries remained fixed. When tensional stresses stretch a body or layer of rock such that its tensile strength is exceeded, it breaks. When this happens the rock fractures in a plane parallel to the maximum principal stress and perpendicular to

12064-439: The surface (plane) of the fracture ("Mode 1" Fracture). Although joints can occur singly, they most frequently appear as joint sets and systems. A joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of their orientations, spacing, and physical properties. A joint system consists of two or more intersecting joint sets. The distinction between joints and faults hinges on

12180-501: The surface (plane) of the fracture that remains "invisible" at the scale of observation. Joints are among the most universal geologic structures, found in almost every exposure of rock. They vary greatly in appearance, dimensions, and arrangement, and occur in quite different tectonic environments. Often, the specific origin of the stresses that created certain joints and associated joint sets can be quite ambiguous, unclear, and sometimes controversial. The most prominent joints occur in

12296-465: The tensile strength of bedrock to be exceeded as the result of the stretching of rock layers under conditions of elevated pore fluid pressure and directed tectonic stress. Tectonic joints often reflect local tectonic stresses associated with local folding and faulting. Tectonic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets. Hydraulic joints are formed when pore fluid pressure becomes elevated as

12412-404: The tensile strength of the bedrock and results in jointing. In the case of unloading joints, compressive stress is released either along preexisting structural elements (such as cleavage) or perpendicular to the former direction of tectonic compression. Cooling joints are columnar joints that result from the cooling of either lava from the exposed surface of a lava lake or flood basalt flow or

12528-491: 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

12644-424: The terms visible or measurable, a difference that depends on the scale of observation. Faults differ from joints in that they exhibit visible or measurable lateral movement between the opposite surfaces of the fracture ("Mode 2" and "Mode 3" Fractures). Thus a joint may be created by either strict movement of a rock layer or body perpendicular to the fracture or by varying degrees of lateral displacement parallel to

12760-423: The trunks of branchless conifer trees that floated out to sea to be preserved in the black shale. Marcellus fossils include specimens of the large clam-like brachiopod Spinocyrtia. External molds of crinoids , plant-like animals related to starfish also known as "sea lilies," are found in the formation, with the molds partially filled with limonite ; brachiopod and bivalve (clam) molds have also been found in

12876-450: The usable upper deposits were removed, or if a mine shaft entered the bed too far below the surface, only unusable unconverted pyritic deposits were found. Hematite ore was converted to pig iron in charcoal -fired stone blast furnaces that were constructed throughout the Juniata River region near the workable ore deposits from the Marcellus and other formations. Iron products from this area, known as "Juniata Iron," were produced during

12992-414: The waters and destroyed organic matter before it could accumulate. The absence of carbonate rock in shale beds reflects the absence of organisms that might have secreted carbonate skeletons, also likely due to an anoxic environment. As a result, about 95% of organic matter in sedimentary rocks is found in shales and other mudrocks. Individual shale beds typically have an organic matter content of about 1%, but

13108-650: The west the formation may produce liquid petroleum ; further north heating during deeper burial more than 240 million years ago cracked this oil into gas. 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

13224-437: 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

13340-585: Was similar to modern squid, this may have been an area where these Devonian cephalopods reproduced and died. This stratigraphic interval also provides an excellent example of incursion epiboles , which are sudden appearances and disappearances of fossil taxa in relatively thin sections of the rock unit. In the Cherry Valley, the taxa do not reoccur; instead each thin concretionary limestone bed contains different species of goniatites. The Cherry Valley and Union Springs also contain well-preserved anarcestida . On

13456-410: Was used in the early economic development of the region, and uranium and pyrite which are environmental hazards. At the base of the Marcellus, in the pyrite - carbonate bed between the carbonaceous black shale and a green calcareous shale bed, pyrite, carbonate, and groundwater reacted to form gossan iron oxide and gypsum . As far as the ground water necessary for the conversion could penetrate,

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