USING KENTUCKY'S DIGITAL GEOLOGICAL QUADRANGLES FOR UNRAVELING MISSISSIPPIAN-PENNSYLVANIAN STRATIGRAPHIC PROBLEMS

Stratigraphic complications associated with the Mississippian-Pennsylvanian Unconformity of the Illinois Basin in western and south central Kentucky remains a challenging problem. Mapping by the Kentucky Geological Survey (KGS) and the U. S. Geological Survey during the 1960s and 1970s revealed these complications as is evident by workers’ use of various names for Upper Chester Series strata. Since the geologic mapping of decades ago, several questions have been raised about the systemic boundary in the region, in particular in cases where marker beds are lacking or where sandstone facies of Pennsylvanian age are juxtaposed on lithologically similar Mississippian-aged strata. Discerning the systemic boundary may also be complicated because of facies changes in Chesterian strata and because of differences in stratal accommodation space from the basin center toward the basin edge.

This study is but one example of an attempt to identify and correlate various Mississippian (Chester Series) rocks and show their relationship to overlying basal Pennsylvanian strata in an effort to better understand the relationship of the systemic boundary at the southeastern edge of the Illinois Basin. Subsurface and outcrop investigation was aided by KGS’s newly available digital geological quadrangles (available in CD-ROM format), KGS’s online geophysical well logs, and the incorporation of these data into a basic Geographic Information System (GIS). Revisions of the geological quadrangles through a study such as ours will provide new data for identifying Pennsylvanian paleochannel systems that have proven to be economically important.