Depositional dip-oriented cross-section through the Lower Silurian "Clinton" sands and Medina Group in northeastern Ohio and western Pennsylvania
KEIGHIN, C.W., and HETTINGER, R.D., U.S. Geological Survey, Denver, CO.
A subsurface cross-section was constructed through the lower and middle
Silurian Niagaran Provincial Series in Ohio and Pennsylvania to: a) illustrate
the geometry of hydrocarbon-bearing sandstone reservoirs, and b) determine
if stratigraphic controls affect hydrocarbon accumulation. The 70-mile
long cross-section utilized geophysical logs from 62 wells, and was constructed
along a northwest-southeast depositional dip-oriented transect.
The study interval thins northwestward from about 380 feet in western
Pennsylvania (Mercer County) to 235 feet in central Ohio (Lake County).
The base of the interval overlies the Upper Ordovician Queenston Shale,
and is defined by the 4- to 14-foot thick Whirlpool Sandstone/Medina sand
which is interpreted as a fluvial dominated deposit. The overlying Cabot
Head Shale is interpreted as a lower shoreface mudrock containing irregularly
distributed upper shoreface sandstones. The Cabot Head is overlain by the
Grimsby Formation (in Pennsylvania) and coeval deposits in the "Clinton"
sands and upper Cabot Head Shale (in Ohio); this interval contains laterally
discontinuous sandstone and mudrock that we interpret as deposits of fluvial
and tidally influenced environments. The top of the study interval contains
several offshore carbonates, such as the Dayton and Reynales limestones,
separated by inner shelf mudrocks. The carbonate units coalesce to the
northwest, and form a 15- to 20-foot thick unnamed limestone in Lake County,
Ohio.
Facies dislocation interpreted along the transect may provide sequence
stratigraphic interpretations for the "Clinton"/Medina interval in western
Pennsylvania and northeastern Ohio. Perforated zones and initial production
data are available from the wells, but additional work is necessary to
relate stratigraphic relationships to production characteristics.
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