Abstract

Patterns of Pennsylvanian sandstone deposition in the Illinois Basin are delineated by a series of local and regional maps. Pennsylvanian sand bodies in the basin are classified into sheet and several elongate types. These sand bodies occur throughout the basin. Regional patterns of sandstone deposition are displayed by basin-wide maps of 2 intervals: from the base of the Pennsylvanian system to the Illinois No. 2 coal and its equivalents and from the No. 2 coal to the Shoal Creek Limestone and its equivalents in the basin. Number of sand bodies, sand thickness, and sand-shale ratios were mapped. All 3 maps have broadly similar basin-wide patterns. They differentiate the more rapidly subsiding basin from more stable western and northern shelf areas and, in conjunction with 2 isopach maps and a basin-wide compilation of 1887 cross-bedding directions, reveal the dispersal patterns of clastics into and across the basin. Clastics came from the E., N., and NW. The salient features of Pennsylvanian sedimentation in the basin are summarized in terms of basin geometry, lithic fill, arrangement or distribution of lithic fill within the basin, and tectonic setting.

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