Abstract: Biohermal Facies and Asphalt in the Silurian Lilley and Bisher Formations (Clinton-Lockport) of Adams County, Ohio

HERRING, DONNA M.
Petroglyph Consulting, P.O. Box 100, Alexandria OH 43001-0100 ([email protected])

Large biohermal buildups in the Silurian Lilley Formation (Niagaran, Clinton-Lockport, Wenlockian) along the outcrop belt in Adams County, Ohio, occur over carbonate-sand thicks of the underlying Bisher Formation (Niagaran, Clinton, Llandoverian-Wenlockian), which includes small bioherms. These bioherms and buildups do not appear to be framework reefs, but are characterized by a disorganized core and inclined flanking beds. The largest exposed buildups are 10-12 in thick and perhaps as extensive as 60 km². Previously-reported outcropping Lockport bioherms north of Adams County are smaller, though subsurface workers southeast of Adams County reported bioherms of similar thickness and greater extent.

Asphaltic and bitumenous vug fillings are common countywide in the lowermost Bisher, which immediately overlies the Silurian Estill Shale (Clinton, Llandoverian). Minor asphalt seeps occur in the Bisher along bedding contacts and stylolites. Asphaltic vug fillings and petroliferous odor are common in the Lilley, especially in biohermal facies. In the Bisher, some roadcuts weep asphalt, and some old quarry walls have accumulated surface droplets of asphalt.

The combined outcrop evidence of biohermal facies and a petroliferous system suggests that nearby subsurface facies are likely to have reservoired hydrocarbons. There is presently a geographic gap in the map pattern of Lockport oil and gas fields, which includes all of southern Ohio. This gap appears likely to be an artifact of geologic interpretation rather than actual lack of accumulation; application of biohermal facies models based on outcrop should improve subsurface prediction in the gap area.

AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio