--> Abstract: Estuarine Sandstones in Lower Pennsylvanian Strata in the Indiana Portion of the Illinois Basin, by E. P. Kvale, D. A. Fishbaugh, and M. D. Ruark; #91004 (1991)

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Estuarine Sandstones in Lower Pennsylvanian Strata in the Indiana Portion of the Illinois Basin

KVALE, ERIK P., and DAVID A. FISHBAUGH, Indiana Geological Survey, Bloomington, IN, and MICHAEL D. RUARK, Consulting Geologist, Parke County, IN

A program to integrate subsurface and outcrop data of known aquifers in lower Pennsylvanian strata in west-central Indiana has concentrated on mapping the extent and characteristics of thick (> 10 m) sandstone bodies in the area. These sandstone bodies are narrow linear features that may rest erosively on coals but otherwise are encased in, and locally interfinger with, flaser- to lenticular-bedded sandstones and mudstones.

The interbedded sandstones and mudstones display abundant evidence of tidal influence during deposition. Locally, a thick sequence (20 m) of vertically stacked flaser and lenticular beds may record multiple neap-spring cycles, similar to modern features present in the mixed fluvial-tidal zones at the head of the Bay of Fundy. These beds are laterally adjacent to a thick (15 m) sandstone dominated by large-scale planar and trough cross-stratified sets. This suggests that these sandstone bodies were deposited as barforms within an upper estuarine environment concurrent with the deposition of muddy sediments.

Sandy barforms in such settings could be entirely encased in muds resulting in stratigraphically isolated sandstone bodies. In the shallow subsurface these sandstones serve as aquifers but are also potential hydrocarbon reservoirs in the deeper parts of the basin.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)