TILL IN KANSAS - PATCHY DEPOSITION OR EROSIONAL REMNANTS?

North American Pleistocene ice sheets attained their greatest southwesterly extent during the Kansan Glaciation,a chronological term now in disrepute but still without an adequate replacement.

Striated bedrock is restricted to scarce quarry surfaces. Evidence of glaciation is generally limited to northern erratics and limited exposures, mainly artificial, of till. Many occurrences are of cobbles and boulders resting directly on Pennsylvanian bedrock. This relationship has led to continuing debate regarding interpretation. Is the till distribution now observed the original depositional pattern, or has postglacial erosion removed most of the original deposits, leaving only scattered remnants?

Prominent in the till are clasts ranging up to 3m of Sioux Quartzite, a highly resistant lithology that shows little to no evidence of weathering or disintegration. Limestone boulders still bearing striations attest to similarly impotent postglacial change. Erosional removal of major thicknesses of till would have resulted in concentration of resistant clasts in topographic lows,especially valley troughs. No such clogging of drainageways is present. Furthermore, the southernmost limit of erratics forms a continuous line that is unaffected by topography. Patchy deposition of relatively clean ice satisfies field evidence.