The NSS Bulletin - ISSN 1090-6924
Volume 38 Number 4: 88-93 - October 1976

A publication of the National Speleological Society

Investigations of Sinkhole Stratigraphy and Hydrogeology, South-Central Indiana
Robert D. Hall


Bedrock basins dissolved in the St. Louis and Ste. Geneviève limestones of Middle Mississippian age in the Mitchell Plain of south-central Indiana are partly filled with surficial deposits whose thicknesses may total several tens of feet. These deposits consist of a variety of silty and clayey sediments, including, from oldest to youngest: 1) calcareous, laminated muds in the lower part of the basin; 2) red clay in the upper part of the basin, grading laterally to red silt above the calcareous mud in the lower part of the basin; 3) chert gravel over the red clays and silts; 4) loess in the upper part of the basin; and 5) yellowish-brown silts above the red silt in the lower part of the basin. All the deposits appear to be of sedimentary origin, including the red clays and silts often called terra rossa.

The water table in Sinkhole A does not respond with a change in elevation until the materials above the clay are saturated, under which conditions the water table normally responds with a lag time of about 2 weeks. In summer, heavy cloudbursts probably supply some intermittent runoff to the basin center which, in turn, results in some temporary downward flow through the basin silts to the water table. This type of flow can also occur in winter, but saturation of the loess during that season also flow at the top of the clay toward the basin center and probably downward flow through the clay along fractures.

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