Stratigraphic Cross Sections Through Niagaran Strata of the Central Appalachian Basin: A Regional Perspective of the Lower Silurian Oil and Gas Accumulation
R. D. Hettinger1 and R. T. Ryder2
1U.S. Geological Survey, Denver, CO
2U.S. Geological Survey, Reston, VA
Six new cross sections show facies transitions and gas-bearing intervals in the Lower Silurian regional oil and gas accumulation (LSRA) in New York, Ohio, Pennsylvania, and West Virginia. Featured are the “Clinton” sandstone in Ohio and the Medina Group in Pennsylvania and New York. Also shown is the equivalent and more proximal Tuscarora Sandstone of Pennsylvania and West Virginia. The cross sections provide excellent perspectives of depositional variability across the basin-center and conventional/hybrid parts of the LSRA.
In contrast to most investigations that associate deposition of the “Clinton”, Medina, and Tuscarora with a single transgressive-regressive marine cycle, we suggest two transgressive-regressive marine cycles (sequences 1 and 2) and the transgressive phase of a third cycle in sequence 3. We suggest three sea level lowstands existed during the Rhuddanian Stage, each followed by a sea level rise that culminated in a highstand. Unconformities associated with the lowstands include the Cherokee unconformity at the base of the Whirlpool Sandstone, and two unnamed unconformities in the middle and upper part of the “Clinton”/Medina interval. Paleovalleys were backfilled with fluvial or tidally-influenced sediment during the initial phase of each sea level rise, and thick deposits of estuarine strata overlie the uppermost unconformity.
Most sandstone in sequences 1–3 yield commercial quantities or shows of oil and/or natural gas. Wells with the highest initial yields do not consistently favor any particular facies or sequence. However, some wells have greater gas yields from fluvial and estuarine sandstone in sequences 1 and 3, perhaps caused by the dissolution of feldspar-grains derived from eastern highlands, and an accompanying increase in secondary porosity.
AAPG Search and Discovery Article #90900©2001 AAPG Eastern Section Meeting, Kalamazoo, Michigan