11 Structural Geology and Tectonics (Posters)
Sunday, 22 March 2026
8:00 AM - 12:00 PM
CCC, Ballroom C
Fluids in an Oriskany Sandstone Core from the Chestnut Ridge Anticline, Pennsylvania
Paper number: 11-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
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Mark EvansCentral Connecticut State University, New Britain, CT
Abstract
The Middle Devonian Oriskany Sandstone is a prolific producer of natural gas and extends from northern Pennsylvania to West Virginia. The gas is commonly found trapped in anticline fold structures like the North Summit field located in Fayette County, Pennsylvania. Mineralized fractures were sampled from the Devonian Oriskany sandstone from well 114 in this field. The well is in an intensely fractured and faulted region at the northeast extent of the Chestnut Ridge Anticline which formed during the Alleghanian orogeny ~300 million years ago. Veins are 2 to 5 mm thick and consist of twinned calcite and quartz.
Stable Isotopic Values for 𝛿18O and 𝛿13C from calcite vein samples were analyzed to constrain the history of how the fractures and fluids formed within the rock layers before and after large scale deformation. Vein calcite samples have isotopic values ranging from: -6.9 to -9.0 𝛿18O V-PDB and -0.5 to 1.1 𝛿13C V-PDB. These values are similar to those from the underlying Devonian Helderberg limestone in the Valley and Ridge to the east.
Preliminary fluid inclusion microthermometry of two-phase aqueous inclusions from veins in the Oriskany gives two populations of homogenization data. The first group gives Th values of 100℃ to 150℃ and the ice melting temperatures range from -23℃ to -30℃. The second group gives Th values of 170℃ to 198℃ and the ice melting temperatures range from -28℃ to -30.5℃. The extremely low ice melting temperatures indicate high salinity levels. Structural cross sections of the field show thrust fault splays ramping from the Silurian salina salt to form the anticline. The source of the extremely high salinity fluids is likely fluids from the salt that migrated along the fault splays.
The Th value for the first group of inclusions indicates trapping depths of about 5.04 to 6.48 km (20° to 25°/km geothermal gradient). The Th value for the second group indicates trapping depths of about 6.92 to 8.85 km (20° to 25°/km geothermal gradient). Post Mississippian syn-tectonic maximum sediment loads ranged from 4.12 to 6.05 km.
Geological Society of America Abstracts with Programs. Vol. 58, No. 2
doi: 10.1130/abs/2026NE-411300
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