Marion County
Features Typically Associated with the Pre-Wisconsin Surface in Outcrops and Boreholes
Anthony H. Fleming and Robin F. Rupp

Adapted from Fleming and others (1993) and Brown and Laudick (2003)

  1. Evidence for a weathering profile, commonly manifested by: sharp color changes from grey or light-brown (unweathered) Wisconsin deposits to oxidized red, yellow, or gleyed olive-green materials whose colors are suggestive of weathering; by the absence of some or all carbonate minerals from these same materials; and (or) by the abundance of expandable clay minerals at a certain horizon.
  2. Abrupt changes in hardness, with the pre-Wisconsin materials (especially till units) commonly being substantially harder than the overlying Wisconsin deposits. In outcrop, pre-Wisconsin tills, especially the Illinoian ones, are heavily jointed within 20 to 30 ft (6 to 9 m) of the paleosurface.
  3. Stratigraphy of till units as determined by their gamma-ray log response, relative grain-size percentages, and other attributes.
  4. Presence of pervasive organic silt units, peat beds, wood, or other indicators of a non-glacial landscape along a particular horizon.
  5. Presence of extensive sand and gravel sheets interpreted to have been deposited as outwash in front of the advancing late Wisconsin ice sheet.


Brown, S. E., and Laudick, A. J., eds., 2003, Hydrogeologic framework of Marion County, Indiana — a digital atlas illustrating hydrogeologic terrain and sequence: Indiana Geological Survey Open-File Study 00-14, CD-ROM.

Fleming, A. H., Brown, S. E., and Ferguson, V. R., 1993, Hydrogeologic framework of Marion County, Indiana: Indiana Geological Survey Open-File Study 93-05, 67 p.

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