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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 8. (August)

First Page: 1172

Last Page: 1172

Title: Lithofacies of Subsurface "Packer Shell" (Brassfield Limestone-Rochester Shale) Interval in Eastern Ohio: ABSTRACT

Author(s): Bradford E. Nelson, Alan H. Coogan

Article Type: Meeting abstract

Abstract:

The interval between the subsurface "Clinton" (Medina) sandstone in Ohio and the base of the Niagaran dolomite was mapped using geophysical logs and samples over an area of 37 counties in eastern Ohio. The density of control approximated 1 well per 5 mi2 (13 km2) over the 23,640 mi2 (61,228 km2) studied. Between the "Clinton" sandstone and the Niagaran dolomite, the limestones and dolomites of the "Packer Shell," "Casing Shell," and other carbonate rock units are interbedded with shales called the Rochester in Ohio. On logs, the differentiation between the limestone or dolomite and shale was based on greater than 50% gamma-ray deflection and the density log readings.

Lithologically, the "Packer Shell" is a gray to dark gray, dense crystalline bioclastic limestone and/or dolomite. The Brassfield Limestone on the outcrop includes glauconitic oolitic grainstones, glauconitic molluscan crinoidal packstones with chert, and glauconitic bioturbated mudstones to wackestones. The "Casing Shell" and other carbonate units in the Rochester are gray to dark gray and contain bioclasts. At the base of the "Packer Shell" is a distinctive red, hematitic shale which is present over 65% of the area.

Regional cross sections show the three to four main carbonate units interbedded with shale in eastern Ohio. These carbonate rocks maintain their approximate individual thicknesses as the interbedded shales thin west and southwestward until the "Casing Shell" merges with the "Packer Shell" to form the unbroken stratigraphic unit recognizable on the outcrop as the Brassfield Limestone in southwestern Ohio.

The shale interbeds are thickest in east-central and southeast Ohio where they average 110 and 170 ft (33 and 52 m) thick, respectively, indicating the possible source direction for the shale influx from the east and southeast.

Correlations indicate a transgression of the Brassfield-"Packer Shell"-"Casing Shell" units so that the carbonate rocks appear to climb eastward in the section with respect to a datum at the base of the "Packer Shell." In Ohio, on the outcrop, the Brassfield Limestone is dated as Silurian, Albion, although part of its lithostratigraphic equivalents--the "Casing Shell" and other Rochester Shale carbonate beds--are Niagaran.

The "Packer Shell" is a useful unit on which to base a structural map, if care is taken at the critical locations of facies changes. The "Packer Shell" is porous locally and is reported to produce gas from some wells in Ohio. The production appears to be related to the occurrence of small structural noses, possibly associated with fracturing above the "Clinton" sandstone reservoir.

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Copyright 1997 American Association of Petroleum Geologists