ABSTRACT: Regional Mapping of Strata from the Lower Pope Group (Chesterian) in Illinois

WHITAKER, STEPHEN T., and HANNES E. LEETARU, Illinois State Geological Survey, Champaign, IL

Applications of modern stratigraphic principles are providing new insights about the stratigraphic relationships and areal distribution of strata within the lower Pope Group (Chesterian) in the Illinois basin. These strata have already proven to be some of the most prolific hydrocarbon reservoirs in the basin, yet significant new reserves may still remain in unrecognized traps.

A portion of the basin covering 1400 sq mi and centered in Jefferson County, Illinois was chosen as the pilot study and is the first part of a major effort to map Chesterian-aged units throughout Illinois. Cross sections defined correlatable units that were then mapped throughout the study area. The distribution of these units was apparently caused by sea level fluctuations combined with shifting of siliciclastic source areas. These two variables have generated complex facies relationships between the units in the Pope Group that are not adequately reflected in the current stratigraphic column. Several lithologically distinct units which are currently considered formations are more accurately described as members that are commonly in facies relationships with one another. This is the ase with the Joppa Member of the Ste. Genevieve Formation, the Aux Vases Formation, and the Renault Formation. A similar relationship exists for the Bethel, Ridenhower, and Cypress Formations. Once these stratigraphic relationships are identified and mapped, the prediction of stratigraphic traps can be improved and more efficient exploration and development strategies can be planned.

AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)