Baldassare F.J.,Echelon |
McCaffrey M.A.,Weatherford |
Harper J.A.,Pennsylvania Geological Survey
AAPG Bulletin | Year: 2014
As the pace of drilling activity in the Marcellus Formation in the northern Appalachian Basin has increased, so has the number of alleged incidents of stray natural gas migration to shallow aquifer systems. For this study, more than 2300 gas and water samples were analyzed for molecular composition and stable isotope compositions of methane and ethane. The sampies are from Neogene- to Middle Devonian-age strata in a five-county study area in northeastern Pennsylvania. Samples were collected from the vertical and lateral sections of 234 gas wells during mud gas logging MGL programs and 67 private groundwater-supply wells during baseline groundwaterquality testing programs. Evaluation of this geochemical database reveals that microbial, mixed microbial and thermogenic, and thermogenic gases of different thermal maturities occur in some shallow aquifer systems and throughout the stratigraphy above the Marcellus Formation. The gas occurrences predate Marcellus Formation drilling activity. Isotope data reveal that thermogenic gases are predominant in the regional Neogene and Upper Devonian rocks that comprise the potable aquifer system in the upper 305 m (1000 ft) (average δ13C1 = -43.53%0; average δ13C2 = -40.95%0; average δDC 1 = -232.50%o) and typically are distinct from gases in the Middle Devonian Marcellus Formation (average δ13C1 = -32.37%0; average δ13C2 = -38.48%0; average δDC1 = -162.34%0 ). Additionally, isotope geochemistry at the site-specific level reveals a complex thermal and migration history with gas mixtures and partial isotope reversals (δ13C1 > δ13C2) in the units overlying the Marcellus Formation. Identifying a source for stray natural gas requires the synthesis of multiple data types at the site-specific level. Molecular and isotope geochemistry provide evidence of gas origin and secondary processes that may have affected the gases during migration. Such data provide focus for investigations where the potential sources for stray gas include multiple, naturally occurring, and anthropogenic gases. ©2014. The American Association of Petroleum Geologists. All rights reserved.
Tibert N.E.,University of Mary Washington |
Dewey C.P.,Mississippi State University |
Skema V.,Pennsylvania Geological Survey
Micropaleontology | Year: 2011
Late Carboniferous and early PermianOstracoda from the Appalachian Basin include nonmarine genera that reveal taxonomically valuable information. Coal and mudrock beds from Pennsylvania and West Virginia yielded well preserved specimens of Paleodarwinula hollandi (Scott 1944), Whipplella cuneiformis Holland 1934, Gutschickia deltoidea (Holland 1934), G. ninevehensis (Holland 1934), and Hildboldtina magnitata (Holland 1934). Previously undocumented adductor muscle scars, anterior spines, and external patterns of reticulation confirm that these nonmarine genera are distinct and suggest potential connections to theDarwinulocopina andMetacopina.Additionally, the stratigraphic range of the nonmarine assemblage highlights the potential biostratigraphic zonation for Carboniferous and Permian deposits in North America.
Bosbyshell H.,West Chester University |
Srogi L.,West Chester University |
Blackmer G.C.,Pennsylvania Geological Survey
American Mineralogist | Year: 2016
The central Appalachian Piedmont lies in the critical juncture between the northern and southern Appalachians, portions of the orogen with distinct middle to late Paleozoic accretionary histories. Orogen-scale compilation maps link the central and southern Appalachians, but until recently, limited geochronological data prevented robust tectonic comparisons between high-grade metamorphic rocks in different parts of the orogen. We report the results of in situ U-Th-total Pb monazite geochronology that date significant deformation and metamorphism as middle Silurian (∼425 Ma) through middle Devonian (∼385 Ma) and demonstrate the diachronous nature of orogen development. The Rosemont Shear Zone is identified as a major tectonic boundary in southeastern Pennsylvania and northern Delaware separating the rifted Laurentian margin from younger rock units that formed in a magmatic arc setting. The Laurentian margin rocks occur in a series of nappes in which the metamorphic grade decreases from the structurally highest nappe to the lowest. The in situ monazite ages show that maximum temperature in the lowest nappe may have been attained some 15 million years after maximum temperature in the highest nappe. We interpret this to be the result of successive nappe emplacement, with the warmer overriding sheets contributing heat to lower levels. Combining geochronologic and thermobarometric results with the geometry of deformation results in a new picture of the tectonic development of the central Appalachian Piedmont that further links the evolution of the southern and northern Appalachians. For the Laurentian margin rocks, tectonism resulted from the approach and collision of peri-Gondwanan terranes during the Silurian to early Devonian in a dominantly sinistral, transpressive tectonic regime. This portion of the Pennsylvania-Delaware Piedmont inboard of the Rosemont Shear Zone is contiguous with comparable rocks in the southern Appalachians. In contrast, arc-related rock units outboard of the Rosemont Shear Zone experienced primarily thermal metamorphism in the Silurian, while crustal thickening and associated regional metamorphism is middle Devonian in age and likely the result of the accretion of Avalonia during the Acadian orogeny. These arc-related and younger rocks probably originated to the north of their present location as part of the northern Appalachians. They were ultimately emplaced in a right-lateral transcurrent regime sometime after the middle Devonian. Thus, it is in this portion of the central Appalachian Piedmont that the northern and southern Appalachians are joined. © 2016 by Walter de Gruyter Berlin/Boston 2016.
Jones W.T.,Kent State University |
Feldmann R.M.,Kent State University |
Schweitzer C.E.,Kent State University |
Schram F.R.,University of Washington |
And 2 more authors.
Journal of Paleontology | Year: 2014
A single specimen of a shrimp-like crustacean, Devonostenopus pennsylvaniensis, new genus and species is described from the Huntley Mountain Formation, which is Devonian-Carboniferous (Mississippian) in age. The specimen was collected in north-central Pennsylvania. Devonostenopus pennsylvaniensis is attributed to Stenopodidae. Co-occurrence of the specimen with pinnules of Archaeopteris halliana Goeppert, 1852, suggests that it is Devonian in age. Occurrence of a stenopodidean in the Devonian of North America is significant, as only three definitive decapods have been previously described from the Paleozoic and only two have been described from the Devonian. The earliest stenopodideans described to date are Cretaceous (Cenomanian and Santonian) in age. As such, Devonostenopus pennsylvaniensis extends the geologic range of Stenopodidea from Cretaceous to Late Devonian. Occurrence of a stenopodidean in the Devonian of North America, as well as the occurrence of the only two other known Devonian decapods in North America, suggests that Laurentia might have been a major area of endemism for Devonian decapods. Copyright © 2014, The Paleontological Society.
Fedorko N.,West Virginia Geological and Economic Survey |
Skema V.,Pennsylvania Geological Survey
International Journal of Coal Geology | Year: 2013
Dunkard Group strata, the youngest Paleozoic rocks in the Appalachian Basin, extend from the base or top of the Waynesburg coal (varying among neighboring state geological surveys) to the highest exposures. Geologic investigation and mapping of the Dunkard Group began with the First Pennsylvania Geological Survey in the 1830s, but poor exposure, exposure of only limited stratigraphic intervals, and lack of significant economic commodities have hampered stratigraphic studies. Maximum thicknesses in excess of 335. m (1100. ft) are found beneath the highest ridges along the synclinorium axis near Wileyville, West Virginia and Windy Gap, Pennsylvania and the stratigraphic correlation of these sites is shown with composite sections constructed from core records and measured sections. Distinct facies provinces are documented in the Dunkard Group, from south to north interpreted as (1) upper fluvial plain, (2) lower fluvial plain, and (3) fluvial-lacustrine deltaic plain. This spatial array of facies provinces is illustrated by a cross section through Dunkard Group and underlying Monongahela Group strata based on drillers' and geologists' core logs. Strata in the upper fluvial plain are cyclic sequences of red, green, and gray, nonfissile mudstone and claystone paleosols exhibiting vertic features, red, green and gray fissile shale, and gray and green sandstone. Coal and limestone are rare, although abundant calcareous material is present as nodules and cement. In contrast, the fluvial-lacustrine deltaic plain cycles are comprised of coal and nonmarine limestone, fewer fluvial shale and sandstone units, and only rare redbeds. The lower fluvial plain cycles exhibit a transition between the other two provinces, containing coal and nonmarine limestone, as well as significant fluvial units and redbeds. Coal beds in the Dunkard Group are best developed in the fluvial-lacustrine deltaic plain but are generally thin and low in quality. Stratigraphically extensive, laterally continuous road cuts and numerous subsurface exploration records, particularly long continuous cores targeting coal beds beneath the Dunkard Group, now aid in better understanding the stratigraphy of the Dunkard Group and will aid in future investigations of these rocks. © 2013 Elsevier B.V.
DiMichele W.A.,Smithsonian Institution |
Kerp H.,University of Munster |
Sirmons R.,Smithsonian Institution |
Fedorko N.,Cove Geological Services |
And 3 more authors.
International Journal of Coal Geology | Year: 2013
The Dunkard Group is the youngest late Paleozoic rock unit in the Central Appalachian Basin. Its age, however, remains controversial. In its southern and western two-thirds the Dunkard is comprised largely of red beds, sandstone and siltstone channel deposits and paleosols. In its thickest, most northerly exposures, in southwestern Pennsylvania, northern West Virginia, and east-central Ohio, much of the lower part of the unit is composed of coals, non-marine limestones and gray, often calcareous, paleosols. Age dating is confounded by the non-marine nature of the deposit and by the lack of dateable volcanic ash beds. Dunkard fossils include plants, vertebrates, and both aquatic and terrestrial invertebrates. Most of the fossil groups point to an age very close to, if not including, the Pennsylvanian-Permian boundary, though the exact position of that boundary is uncertain. Callipterids make their first appearance in the Dunkard flora in the middle of the Washington Formation and continue into the Greene Formation, but in different beds from those containing wetland floral elements. Publication of these plants in the "Permian Flora" of Fontaine and White (1880) created an immediate controversy about the age of the unit because Callipteris conferta (now Autunia conferta) was, at the time, considered to be an index fossil for the base of the Permian. Subsequent collecting has revealed these callipterds to comprise four species: A. conferta, Autunia naumannii, Lodevia oxydata and Rhachiphyllum schenkii. Callipterids - and the conifers with which they are sometimes associated - are typically found in seasonally dry equatorial environments and most likely constitute an environmentally controlled biofacies. This biofacies is not well known, resulting in limited biostratigraphic utility. © 2013.
Carter K.M.,Pennsylvania Geological Survey |
Harper J.A.,Pennsylvania Geological Survey |
Schmid K.W.,Pennsylvania Geological Survey |
Environmental Geosciences | Year: 2011
Pennsylvania is not only the birthplace of the modern petroleum industry but also the focus of the modern Marcellus Shale gas play. For more than 150 yr, Pennsylvania has experienced a rich history of oil and gas exploration and production, witnessed the advent of modern petroleum regulations, and now sits deep in the heart of the largest domestic shale gas play the United States has ever seen. Although a known source rock for decades, the Marcellus Shale was not considered a viable gas reservoir until Range Resources Corporation (Range) discovered the play with its completion of the Renz No. 1 well in Washington County in October 2004. Using horizontal drilling and hydraulic fracturing techniques used by operators working the Barnett Shale gas play, Range has gone on to complete hundreds of horizontal shale gas wells in Washington County alone. Other operators have followed suit in counties from one corner of the state to the other, and as of June 2011, the Commonwealth has issued nearly 6500 Marcellus Shale gas well permits. Based on publicly reported well completion and production data, an average Marcellus Shale gas well requires 2.9 million gal of water during the hydraulic fracturing process and produces 1.3mmcf gas/day. Furthermore, theU.S. Energy Information Administration has estimated that as of mid- 2011, daily Marcellus Shale gas production in Pennsylvania exceeds 2.8 bcf. Because of the level of drilling activity and production associated with the Marcellus play, Pennsylvania has become the nexus of shale gas production and water management issues. Copyright ©2011. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved.