Quaternary Stratigraphy and Geomorphic History of the Flatwoods Region of Owen and Monroe Counties, Indiana

Abstract

The Flatwoods region of Owen and Monroe Counties, Indiana is an archetype of late Quaternary history of the southern Midwest. We compile decades of field observations and sampling, including soil cores, a deep test hole, and hundreds of water well, seismic, and other data sources, to construct a detailed Quaternary stratigraphy and geomorphic history of the region, including a model of the preglacial bedrock topography. Optically stimulated luminescence (OSL) techniques provide the first numerical ages of the sediments and reveal the Illinois Episode glacier advanced into the region between 111-175 ka. Gray, calcareous Illinois Episode sediments dominate the valley fill, but highly weathered red glaciogenic sediments in the eastern part of the region may be related to a pre-Illinois Episode glacial event. Fine-grained stratified lake sediments indicate the southwestward draining bedrock valley was flooded as glacial ice entered the drainage basin. Sandy outwash covers the lake sediment marking the advance of glacier ice that ultimately crossed the basin and deposited till. Till is found in several ice-marginal ridges interpreted to be moraines marking the glacial limit. The Flatwoods valley routed water to the east end of the region where it spilled over one or more cols into Raccoon Creek, then continued toward the Ohio River in a glacial drainage system developed along the glacier margin. The Sangamon Geosol is a pervasive soil stratigraphic unit developed into Illinois Episode sediments, eroded only in modern stream valleys. The Geosol is well expressed morphologically, noted mostly by deep leaching of carbonates, red colors, and weathered mineralogy. Wisconsin Episode glaciation is represented by eolian sediments, including a thin increment of silty sediment incorporated into the upper solum of the Sangamon Geosol. Windblown Peoria Loess, deposited between ~27-16 ka, blankets the entire Flatwoods region, with greatest thicknesses preserved on flat lake or outwash plain landforms. Supplemental DataGeodatabase: The geodatabase includes locations of water-well records, borehole and outcrop sites, geophysical (gamma-ray) logs, refraction seismic surveys, passive seismic (horizontal-to-vertical spectral ratio [HVSR]) surveys, and data from the geological literature.Metadata: FGDC-compliant metadata for geodatabase.Data: Analytical data and other geological information include: a downhole geophysical (gamma-ray); data from the 2019 test hole, including clay mineralogy, core photographs, a downhole gamma-ray log, and particle size analysis; Indiana Geological and Water Survey (IGWS) archive data, which is comprised of borehole descriptions; a copy of Jacobs' (1994) Ph.D. dissertation; scanned profile description sheets and core stratigraphy from Jacobs (1994); and supplementary optically stimulated luminescence (OSL) data.ReadMe: Detailed file directory explaination of items within each of the supplemental data item ZIP files.