Abstract: Sequence Stratigraphic Model for Simpson Group of the Southern Mid-Continent: The Key to A New Stratigraphic Play

Magell P. Candelaria, C. Robertson Handford, Christy L. Reed

Middle Ordovician Simpson Group in southern Oklahoma has significant reservoir potential, which can be predicted and exploited through sequence stratigraphic analysis. Historically, exploration for Simpson reservoirs has been structurally driven, consequently there has been little exploratory drilling for stratigraphic traps.

The Simpson Group consists of several third-order depositional sequences. The major Simpson sandstones (Oil Creek, McLish, and Bromide) represent local lowstand to widespread transgressive deposits. Siliciclastics transported across the exposed shelf during relative lowstand were deposited as discontinuous shoreface complexes, or as for the thick basal Oil Creek sandstone, as lowstand systems tract deposits within the southern Oklahoma

aulacogen. During transgression, shoreline retreat resulted in deposition of retrogradational, shoreface complexes that overlie the third-order sequence boundary. Thinner sandstones along the more slowly subsiding cratonic margin represent widespread transgressive systems tract deposition. Upward gradation of basal sandstone to open marine shale represents continued transgression to a maximum flooding surface. Shelfal carbonates overlying the shales represent the highstand systems tract. Highstand deposition concluded with relative fall of sea level and development of a subaerial surface (sequence boundary) across which siliciclastics of the subsequent third-order sequence were transported basinward.

This regional model supports renewed Simpson Group exploration for laterally discontinuous retrogradational shoreface complexes. Incorporated into a well-log based exploration strategy, this stratigraphic architecture would aid definition of subtle stratigraphic traps that typically escape seismic detection.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994