Channel-Fill Sandstones in the Middle Pennsylvanian Rocks of Indiana

Abstract

Data from coal-test boreholes and outcrops show that channel-fill sandstones occur at 32 localities in western Indiana in the Brazil, Staunton, Linton, Petersburg, and Dugger Formations of middle Pennsylvanian age. These sandstones average 40 feet thick, 3 miles long, and a quarter of a mile wide at the top and commonly trend southwestward down the regional dip. At least nine different coal beds are cutout or replaced locally by these channel-fill sandstones. Four classes of channel-fill sandstones are recognized in Indiana. Channel-fill sandstones of class 1 form a dendritic pattern and trend and thicken downdip; those of class 2 also form a dendritic pattern and trend downdip without thickening; channel sandstones of class 3 do not form a dendritic pattern but also trend downdip; and those of class 4 do not trend downdip; instead, they are parallel to the regional strike, and they do not have a dendritic pattern. The channel-fill sandstones are light brown or red brown, thick bedded and crossbedded, medium grained to coarse grained, and micaceous. Their bases rest disconformably on underlying strata, and they represent the lowest stratigraphic unit in a cyclothem. Paleotopography, influenced by differential compaction of sandstone and shale, underlying structure, and a southwesterly regional slope determined the geographic distribution and orientation of the channel-fill sandstones. The periodic lowering of sea level during middle Pennsylvanian time probably exposed the Cincinnati Arch and thus permitted consequent subaerial streams to erode the channels and fill them mostly with sand on at least six different occasions. Possibly most of the channel-fill sandstones were derived from the Pottsville (lower and middle? Pennsylvanian) and the Chester rocks that were presumably on the arch. The Coxville Sandstone, first referred to by G. H. Ashley in 1899, is herein proposed as a member at or near the base of the Linton Formation of the Allegheny Series (middle Pennsylvanian) in Indiana. The Palzo Sandstone of Illinois probably is correlative with the Coxville Sandstone Member. The main objectives of this report are (1) to show the geographic and stratigraphic distribution of some of the channel-fill sandstones in the Allegheny Series (middle Pennsylvanian) in Indiana, (2) to show how these sandstones can be recognized by means of a working geometric classification, and (3) to discuss their tectonic relations, genesis, and economic significance. Except for some field descriptions, the petrography of the channel sandstones was not studied. The author collected data on channel sandstones from outcrops and coal-test boreholes while he worked on coal resources studies in parts of Parke, Vermillion, and Vigo Counties from 1953 to 1958 inclusive. Other geologists of the Coal Section provided data from Clay, Knox, Daviess, Pike, Spencer, and Warrick Counties. Although channel-fill sandstones occur in the other coal-bearing counties in Indiana, they have not been studied and thus are not included in this report.