Depositional Environments and Regional Sedimentological Control of Caseyville Formation, Southern Illinois Basin

W. John Nelson, C. Pius Weibel

During the Morrowan Epoch (earliest Pennsylvanian), the Eastern Interior basins of the United States were characterized by a fluviatile system draining generally southwestward from central Pennsylvania to the Arkoma basin of northern Arkansas. In the southern Illinois basin, the system deposited the Caseyville Formation, consisting of two prominent cliff-forming quartzose sandstones with common quartz gravel, separated and succeeded by finer-grained, clastic intervals. Outcrop mapping in southernmost Illinois indicates that these cliff formers, the Battery Rock and Pounds Sandstone Members, are laterally widespread and generally continuous, but variable in thickness. The underlying Wayside Sandstone Member, the intervening Drury Shale Member, and strata immediately succee ing the Caseyville consist of variable sequences of shales, siltstones, thin-bedded sandstones, and local ledge-forming sandstones. Rare lenticular coals are scattered through the Caseyville.

We interpret the sandstone members to be dominantly of fluviatile-deltaic origin and the intervening, finer-grained intervals to be of deltaic and, at least in part, marginal-marine origin. Marine strata within the Drury Shale Member and the strata immediately overlying the Caseyville Formation contain scattered body fossils and trace fossils suggesting marine deposition.

The Wayside/Battery Rock and Drury/Pounds cycles are tentatively correlated with similar cycles in the Appalachian and Arkoma basins. This correlation suggests regional sedimentological control.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.