A Significant Pleistocene Exposure in South-Central Indiana

Abstract

Unconsolidated deposits of the Pleistocene Series are exposed in a 50-ft railroad cut at the glacial boundary in northwestern Brown County, Indiana. The section exhibits a more complete sequence of Pleistocene sediments than do other exposures in south-central Indiana, it confirms an earlier interpretation that Kansan ice advanced somewhat beyond the Illinoian in this area, and it indicates the presence of both Peoria and pre-Peoria (Love-land?) loess deposits. Siltstone of the Borden Group (Mississippian System) at the base of the cut is overlain unconformably by 3.5 ft of unoxidized and oxidized till interpreted as Kansan. The till is overlain by about 30 ft of pebbly sand and fine gravel, much of which is strongly oxidized. In its upper part this deposit is altered to a sticky reddish sandy material that clearly represents a significant period of weathering. The sand and gravel is regarded as Illinoian outwash, and the weathering profile is interpreted as having formed during the interglacial Sangamonian Age. The section is capped by about 6 ft of silt, which is probably of eolian rather than lacustrine origin. In its lower part the loess is clayey and similar in color to the underlying weathered outwash but grades upward into more typical noncalcareous brown loess. The red silt is tentatively considered to be Illinoian and possibly early Sangamonian and the brown silt Wisconsinan in age.