ABSTRACT: Regional Diagenetic Variations and Implications for Paleohydrology in a Structurally Simple Setting: the Mississippian Berea Sandstone, Ohio

Karen S. Taylor, Samuel M. Savin, Jean-Pierre Girard, Gerald Matisoff

The Mississippian Berea Formation in northeast Ohio consists of widely distributed and structurally undeformed, well-sorted deltaic sandstones and minor shales. The Berea is hydrologically discontinuous. It is a source of potable water in north Ohio and a hydrocarbon reservoir in south Ohio and West Virginia. Discontinuities are especially apparent in the zone between fresh water and hydrocarbon-associated brines. The initial stage of a petrographic study (preliminary to isotopic and hydrochemical analyses) shows that aquifer/reservoir quality varies mainly due to sedimentologic and diagenetic factors.

Diagenesis in core and quarry samples from a 25-km transect in the northwest part of the study area varies vertically and laterally. At the western end of the transect, the diagenetic sequence is relatively uniform vertically with quartz overgrowths first, followed by feldspar dissolution, illitic cement, and infiltrated clays. Porosities are between 15 and 25%. In the eastern and central parts of the transect, Berea is vertically divided by a relatively thin (about 1.25 m), low-porosity (< 1%) zone in the middle of the section. Carbonate cement replaces detrital grains and quartz overgrowths and is followed by hematite. Above that zone the Berea is characterized by early quartz overgrowths, as in the west, hematitic and illitic cement, and feldspar dissolution. There is no infiltr ted clay, and porosities are between 5 and 20%. Below the low-porosity zone, the same diagenetic phases are present but clay and hematite are less abundant than in the upper portion. There is no infiltrated clay, and porosity is strictly primary, ranging from 20 to 25%. No relationships were seen between sedimentology and the development of the low-porosity zone, which, once developed, must have affected vertical groundwater movement and subsequent diagenesis.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990