Abstract: Fracture Patterns in Pennsylvanian Strata of Southeastern Ohio
SYROWSKI, KIMBERLY A., R. DAMIAN NANCE and GREG C. NADON
Department of Geological Sciences, 316 Clippinger Labs, Ohio University, Athens, Ohio 45701
Lithologic control on the orientation and density of fractures has been used in a wide variety of sediments and basin settings to determine stress patterns and to better predict permeabilities in the subsurface. In the Appalachian Basin of southeastern Ohio, regional fracture patterns based on LANDSAT lineament data are dominated by ENE trends. Ongoing field studies in the Pennsylvanian sediments of Athens County, however, show that lithology, bed thickness and heterogeneity all affect fracture orientation at outcrop scale. The Pennsylvanian strata are a complex assemblage of marine sandstones, siltstones and shales, marine and nonmarine limestones, and thick nonmarine to estuarine sandstones. AD were subjected to the compressive stress field associated with the Alleghanian Orogeny and may also have been affected by reactivation of listric normal faults associated with the Precambrian — Early Paleozoic Rome Trough.
Detailed studies designed to determine the effect of lithologic character on fracture pattern and density reveal a wide range of fracture orientation in three separate lithologies. Thin-bedded (<O. 1 m thick) fine-grained sandstones have a predominant fracture orientation similar to the regional LANDSAT pattern. Thicker (>3 m) sandstones have NW and NNW modes that are essentially perpendicular to the regional pattern. The Ames and Cambridge marine limestones (<0.8 m thick) show NW and NE modes, respectively. Fracture densities are lowest in thick competent sandstones and highest in thin sandstones.
AAPG Search and Discovery Article #90930©1998 AAPG Eastern Section, Columbus, Ohio