Changes

[[:File:M97Ch4FG2.jpg|Figure 2]] shows the regional stratigraphy of the Devonian shales and the Marcellus Shale Formation. The Middle Devonian Marcellus Shale Formation is located within the lower part of the Hamilton Group, which is bounded above by the Middle Devonian Tully Limestone and below by the Lower Devonian Onondaga Limestone (Onesquethaw Group). The Marcellus is divided into two members, the lower Marcellus/Union Springs Shale and the upper Marcellus/Oatka Creek Shale, which are separated by the Cherry Valley/Purcell Limestone. Lash<ref name=Lsh2008>Lash, G. G., 2008, Stratigraphy and fracture history of the Middle and Upper Devonian succession, western New York: Significance to basin evolution and hydrocarbon exploration: Pittsburgh Association of Petroleum Geologists spring field trip guidebook, 88 p.</ref> interprets the Cherry Valley and the Purcell limestones to be equivalent, although other authors, including de Witt et al.<ref>de Witt Jr., W., J. B. Roen, and L. G. Wallace, 1993, Stratigraphy of Devonian black shales and associated rocks in the Appalachian Basin, in J. B. Roen and R. C. Kepferle, 1993, Petroleum geology of the Devonian and Mississippian black shale of eastern North America: U.S. Geological Survey Bulletin, v. 1909, p. M1–M16.</ref> and Werne et al.,<ref name=Wrnetal>Werne, J. P., B. B. Sageman, T. W. Lyons, and D. J. Hollander, 2002, An integrated assessment of a “type euxinic” deposit: Evidence for multiple controls on black shale deposits in the Middle Devonian Oatka Creek Formation: American Journal of Science, v. 302, p. 110–143, doi:10.2475/ajs.302.2.110.</ref> show the Cherry Valley and Purcell as separate members.

[[:File:M97Ch4FG2.jpg|Figure 2]] shows the regional stratigraphy of the Devonian shales and the Marcellus Shale Formation. The Middle Devonian Marcellus Shale Formation is located within the lower part of the Hamilton Group, which is bounded above by the Middle Devonian Tully Limestone and below by the Lower Devonian Onondaga Limestone (Onesquethaw Group). The Marcellus is divided into two members, the lower Marcellus/Union Springs Shale and the upper Marcellus/Oatka Creek Shale, which are separated by the Cherry Valley/Purcell Limestone. Lash<ref name=Lsh2008>Lash, G. G., 2008, Stratigraphy and fracture history of the Middle and Upper Devonian succession, western New York: Significance to basin evolution and hydrocarbon exploration: Pittsburgh Association of Petroleum Geologists spring field trip guidebook, 88 p.</ref> interprets the Cherry Valley and the Purcell limestones to be equivalent, although other authors, including de Witt et al.<ref>de Witt Jr., W., J. B. Roen, and L. G. Wallace, 1993, Stratigraphy of Devonian black shales and associated rocks in the Appalachian Basin, in J. B. Roen and R. C. Kepferle, 1993, Petroleum geology of the Devonian and Mississippian black shale of eastern North America: U.S. Geological Survey Bulletin, v. 1909, p. M1–M16.</ref> and Werne et al.,<ref name=Wrnetal>Werne, J. P., B. B. Sageman, T. W. Lyons, and D. J. Hollander, 2002, An integrated assessment of a “type euxinic” deposit: Evidence for multiple controls on black shale deposits in the Middle Devonian Oatka Creek Formation: American Journal of Science, v. 302, p. 110–143, doi:10.2475/ajs.302.2.110.</ref> show the Cherry Valley and Purcell as separate members.

Several unconformities have been identified within the Marcellus Shale by Lash<ref name=Lsh2008 /> in distal areas of the Appalachian Basin in western New York and northwestern Pennsylvania. These include unconformities that are the upper sequence boundaries for Union Springs and Oatka Creek shales. Lash<ref>Lash, G. G., 2009a, [http://www.searchanddiscovery.com/abstracts/html/2009/annual/abstracts/lash.htm The Middle Devonian Marcellus Shale: A record of eustasy and basin dynamics]: AAPG Search and Discovery article 90090.</ref><ref>Lash, G. G., 2009b, Sequence-stratigraphic framework of the Middle Devonian Marcellus Shale (abs.): AAPG 2009 Eastern Section Meeting: http://karl.nrcce.wvu.edu/esaapg/ESAAPG_Meetings/2009/2009_Abstracts.pdf (accessed September 18, 2009).</ref> documents that the entire Union Spring Shale is removed by a regional disconformity in some of these areas. These unconformity surfaces below and above the Marcellus Shale are interpreted to become conformable to the southeast, into the deeper parts of the basin (Hamilton-Smith, 1993; <ref name=M&S2006>Milici, R. C., and C. S. Swezey, 2006, [http://pubs.usgs.gov/of/2006/1237/of2006-1237.pdf Assessment of Appalachian Basin oil and gas resources: Devonian shale–Middle and Upper Paleozoic total petroleum system]: U.S. Geological Survey Open-File Report Series 2006-1237.</ref>; Boyce, 2009). A major Middle Devonian unconformity above the Tully Limestone (Hamilton-Smith 1993) progressively removes stratigraphically older units from east to west. Moving west toward the Cincinnati arch, this unconformity truncates the entire Tully, Hamilton, and progressively older formations.

Several unconformities have been identified within the Marcellus Shale by Lash<ref name=Lsh2008 /> in distal areas of the Appalachian Basin in western New York and northwestern Pennsylvania. These include unconformities that are the upper sequence boundaries for Union Springs and Oatka Creek shales. Lash<ref>Lash, G. G., 2009a, [http://www.searchanddiscovery.com/abstracts/html/2009/annual/abstracts/lash.htm The Middle Devonian Marcellus Shale: A record of eustasy and basin dynamics]: AAPG Search and Discovery article 90090.</ref><ref>Lash, G. G., 2009b, [http://karl.nrcce.wvu.edu/esaapg/ESAAPG_Meetings/2009/2009_Abstracts.pdf Sequence-stratigraphic framework of the Middle Devonian Marcellus Shale (abs.): AAPG 2009 Eastern Section Meeting</ref> documents that the entire Union Spring Shale is removed by a regional disconformity in some of these areas. These unconformity surfaces below and above the Marcellus Shale are interpreted to become conformable to the southeast, into the deeper parts of the basin.<ref name=H-S>Hamilton-Smith, T., 1993, Stratigraphic effects of the Acadian orogeny in the autochthonous Appalachian Basin, in D. C. Roy and J. W. Skehan, eds., The Acadian orogeny: Recent studies in New England, Maritime Canada, and the authochthonous foreland: Geological Society of America Special Paper 275, p. 153–164.</ref><ref name=M&S2006>Milici, R. C., and C. S. Swezey, 2006, [http://pubs.usgs.gov/of/2006/1237/of2006-1237.pdf Assessment of Appalachian Basin oil and gas resources: Devonian shale–Middle and Upper Paleozoic total petroleum system]: U.S. Geological Survey Open-File Report Series 2006-1237.</ref><ref name=Byc>Boyce, M. L., 2009, [http://karl.nrcce.wvu.edu/esaapg/ESAAPG_Meetings/2009/2009_Abstracts.pdf Lithostratigraphy and petrophysics of the Marcellus interval in West Virginia and southwestern Pennsylvania (abs.)]: AAPG 2009 Eastern Section Meeting, p. 34–35.</ref> A major Middle Devonian unconformity above the Tully Limestone<ref name=H-S /> progressively removes stratigraphically older units from east to west. Moving west toward the Cincinnati arch, this unconformity truncates the entire Tully, Hamilton, and progressively older formations.

==Regional depositional setting==

==Regional depositional setting==

Like other organic-rich shales, the creation, deposition, and preservation of the organic Marcellus sediments was controlled by three factors: (1) primary photosynthetic production, (2) bacterial decomposition, and (3) bulk sedimentation rate (Sageman et al., 2003). The traditional interpretation of deposition of the organic-rich members of the Marcellus Shale is a preservation model of organic enrichment, where a permanently stratified water column with anoxic or euxinic (anoxic-sulfidic) bottom water conditions allowed for the preservation of organic material (Demaison and Moore, 1980). This preservation model is best reflected in the proposed model of a nearly permanent pycnocline by Ettensohn (1992).

Like other organic-rich shales, the creation, deposition, and preservation of the organic Marcellus sediments was controlled by three factors: (1) primary photosynthetic production, (2) bacterial decomposition, and (3) bulk sedimentation rate (Sageman et al., 2003). The traditional interpretation of deposition of the organic-rich members of the Marcellus Shale is a preservation model of organic enrichment, where a permanently stratified water column with anoxic or euxinic (anoxic-sulfidic) bottom water conditions allowed for the preservation of organic material (Demaison and Moore, 1980). This preservation model is best reflected in the proposed model of a nearly permanent pycnocline by Ettensohn (1992).

Recent workers have disputed the original theory of deep-water deposition with consistent anoxia. Werne et al.<ref name=Wrnetal /> and Sageman et al. (2003) proposed that deposition of the Marcellus organic-rich members did not appear to have been beneath a permanently stratified water column. Instead, they proposed that the Marcellus organic-rich units were deposited without a permanent pycnocline and with possible seasonal fluctuations. Macquaker et al. (2009) investigated the Marcellus Shale at bed-scale levels and found a variety of sedimentary structures inconsistent with a continuous deep-water anoxic model, including rip-up clasts and ripple lamina. Based on this work, Macquaker et al. (2009) proposed that the organic-rich mudstones were not deposited in waters that were persistently anoxic, but that instead, the sea floor was occasionally reworked, which would have led to a destruction of a part of the organics. Boyce and Carr (2010) proposed that possible small local microanoxic environments were factors in the deposition of the organic-rich members based on local variations in the black shale units and thin limestones.

Recent workers have disputed the original theory of deep-water deposition with consistent anoxia. Werne et al.<ref name=Wrnetal /> and Sageman et al. (2003) proposed that deposition of the Marcellus organic-rich members did not appear to have been beneath a permanently stratified water column. Instead, they proposed that the Marcellus organic-rich units were deposited without a permanent pycnocline and with possible seasonal fluctuations. Macquaker et al. (2009) investigated the Marcellus Shale at bed-scale levels and found a variety of sedimentary structures inconsistent with a continuous deep-water anoxic model, including rip-up clasts and ripple lamina. Based on this work, Macquaker et al. (2009) proposed that the organic-rich mudstones were not deposited in waters that were persistently anoxic, but that instead, the sea floor was occasionally reworked, which would have led to a destruction of a part of the organics. Boyce and Carr<ref>Boyce, M., and T. Carr, 2010, [http://www.searchanddiscovery.com/abstracts/pdf/2010/annual/abstracts/ndx_boyce.pdf Stratigraphy and petrophysics of the Middle Devonian black shale interval in West Virginia and southwest Pennsylvania]: Poster presented at AAPG Denver ACE 2010.</ref> proposed that possible small local microanoxic environments were factors in the deposition of the organic-rich members based on local variations in the black shale units and thin limestones.

The paleogeographic reconstruction by Ettensohn (1985b), Woodrow and Sevon (1985), and Blakey (2005) shows that the organic-rich deposition occurred in a large, nearly enclosed, three-sided embayment that likely would have served to enhance oceanic organic productivity. [[:File:M97Ch4FG3.jpg|Figure 3]] shows the paleogeographic reconstruction by Blakey (2005) of the Appalachian area about 385 Ma. The arid conditions that were likely present during deposition of the organic-rich facies led to a probable sediment starvation, as evidenced by the decrease in noneolian siliciclastic deposition in the organic-rich facies, preventing dilution of the accumulating organic material.

The paleogeographic reconstruction by Ettensohn (1985b), Woodrow and Sevon (1985), and Blakey (2005) shows that the organic-rich deposition occurred in a large, nearly enclosed, three-sided embayment that likely would have served to enhance oceanic organic productivity. [[:File:M97Ch4FG3.jpg|Figure 3]] shows the paleogeographic reconstruction by Blakey (2005) of the Appalachian area about 385 Ma. The arid conditions that were likely present during deposition of the organic-rich facies led to a probable sediment starvation, as evidenced by the decrease in noneolian siliciclastic deposition in the organic-rich facies, preventing dilution of the accumulating organic material.

Several older studies from the EGSP provide good regional overviews of the general thickness trends of the Marcellus Shale across the Appalachian Basin. In general, the most current industry drilling activity is associated with areas having greater than 15 m (gt50 ft) of gross Marcellus Shale thickness. These earlier studies all show a general eastward thickening of the Marcellus Shale within, or near, the Rome trough.

Several older studies from the EGSP provide good regional overviews of the general thickness trends of the Marcellus Shale across the Appalachian Basin. In general, the most current industry drilling activity is associated with areas having greater than 15 m (gt50 ft) of gross Marcellus Shale thickness. These earlier studies all show a general eastward thickening of the Marcellus Shale within, or near, the Rome trough.

[[:File:M97Ch4FG10.jpg|Figure 10]] is a map of the gross thickness of the Marcellus Shale across the Appalachian Basin, as well as major mapped basement fault trends. The gross thickness of the Marcellus Shale as mapped is defined by the top of the first occurrence of organic shale near the base of the Mahantango Formation to the top of the Onondaga Limestone. The gross thickness of the Marcellus Shale increases generally eastward from the zero isopach in eastern Ohio and western West Virginia to a maximum thickness of more than 107 m (gt350 ft) in northeastern Pennsylvania. The trend of thickening generally parallels the Appalachian structural front, as shown in [[:File:M97Ch4FG10.jpg|Figure 10]]. The gross thickness map has not been corrected for potentially repeated sections or areas that encounter significant bed dips. The gross depositional patterns of the Marcellus Shale appear likely to be influenced by basement fault patterns showing both a general strike-parallel thickening within the Rome trough and related strike-parallel basement faults. In addition, abrupt depositional terminations may exist at, or near, the cross-striking basement faults. Excellent reviews of the thickness trends of the Marcellus Shale and related intervals have been recently addressed by Lash and Engelder<ref name=L&E2008 /> and Boyce (2009).

[[:File:M97Ch4FG10.jpg|Figure 10]] is a map of the gross thickness of the Marcellus Shale across the Appalachian Basin, as well as major mapped basement fault trends. The gross thickness of the Marcellus Shale as mapped is defined by the top of the first occurrence of organic shale near the base of the Mahantango Formation to the top of the Onondaga Limestone. The gross thickness of the Marcellus Shale increases generally eastward from the zero isopach in eastern Ohio and western West Virginia to a maximum thickness of more than 107 m (gt350 ft) in northeastern Pennsylvania. The trend of thickening generally parallels the Appalachian structural front, as shown in [[:File:M97Ch4FG10.jpg|Figure 10]]. The gross thickness map has not been corrected for potentially repeated sections or areas that encounter significant bed dips. The gross depositional patterns of the Marcellus Shale appear likely to be influenced by basement fault patterns showing both a general strike-parallel thickening within the Rome trough and related strike-parallel basement faults. In addition, abrupt depositional terminations may exist at, or near, the cross-striking basement faults. Excellent reviews of the thickness trends of the Marcellus Shale and related intervals have been recently addressed by Lash and Engelder<ref name=L&E2008 /> and Boyce.<ref name=Byc />

===Core Analysis: Porosity and Permeability===

===Core Analysis: Porosity and Permeability===

* Blakey, R., 2005, Global paleogeography: http://jan.ucc.nau.edu/~rcb7/globaltext2.html (accessed September 24, 2009).

* Blakey, R., 2005, Global paleogeography: http://jan.ucc.nau.edu/~rcb7/globaltext2.html (accessed September 24, 2009).

* Boswell, R., 1985, Stratigraphy and sedimentation of the Acadian clastic wedge in northern West Virginia: Master's thesis, West Virginia University, Morgantown, West Virginia, 179 p.

* Boswell, R., 1985, Stratigraphy and sedimentation of the Acadian clastic wedge in northern West Virginia: Master's thesis, West Virginia University, Morgantown, West Virginia, 179 p.

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* Canich, M. R., and D. P. Gold, 1977, A study of the Tyrone-Mt. Union lineament by remote sensing techniques and field methods: State College, Pennsylvania, The Pennsylvania State University Office of Remote Sensing and Earth Resources (ORSER) Technical Report 120-137, 59 p.

* Canich, M. R., and D. P. Gold, 1977, A study of the Tyrone-Mt. Union lineament by remote sensing techniques and field methods: State College, Pennsylvania, The Pennsylvania State University Office of Remote Sensing and Earth Resources (ORSER) Technical Report 120-137, 59 p.

* Frey, M. G., 1973, Influence of Salina Salt on structures in New York-Pennsylvania part of the Appalachian Plateau: AAPG Bulletin, v. 57, p. 1027–1037.

* Frey, M. G., 1973, Influence of Salina Salt on structures in New York-Pennsylvania part of the Appalachian Plateau: AAPG Bulletin, v. 57, p. 1027–1037.

* Gwinn, V. E., 1964, Thin-skinned tectonics in the Plateau and northwestern Valley and Ridge provinces of the central Appalachians: Geological Society of America Bulletin, v. 75, no. 9, p. 863–900, doi:10.1130/0016-7606(1964)75[863:TTITPA]2.0.CO;2.

* Gwinn, V. E., 1964, Thin-skinned tectonics in the Plateau and northwestern Valley and Ridge provinces of the central Appalachians: Geological Society of America Bulletin, v. 75, no. 9, p. 863–900, doi:10.1130/0016-7606(1964)75[863:TTITPA]2.0.CO;2.

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* Heidbach, O., M. Tingay, A. Barth, J. Reinecker, D. Kurfebeta, and B. Muller, 2008, The world stress map based on the database release 2008, equitorial scale 1:46,000,000: Paris, Commission for the Geological Map of the World, doi:10.1594/GFZ.WSM.Map2009, 2009.

* Heidbach, O., M. Tingay, A. Barth, J. Reinecker, D. Kurfebeta, and B. Muller, 2008, The world stress map based on the database release 2008, equitorial scale 1:46,000,000: Paris, Commission for the Geological Map of the World, doi:10.1594/GFZ.WSM.Map2009, 2009.