IDENTIFICATION OF REMNANTS OF EARLY PLEISTOCENE TILLS

A 2007 GSA abstract calls attention to increasing evidence that there have been multiple advances of continental ice sheets across North America accompanied by noteworthy repetitions of both global and regional geomorphic cycles. If there indeed were at least 10 major ice sheet advances and retreats, as field evidence indicates is a realistic number, it may be assumed that each glaciation had associated widespread erosional (perhaps concentrated in the advancing hemicycle) and depositional (mainly in the retreating hemicycle) events. It is certainly true that records of earlier glaciations are, in general, poorer and more limited than subsequent, younger records. And it is much more difficult to decipher those incomplete older sequences. Attempted correlations may turn out to be wildly in error. Scattered small exposures or drill-hole penetrations of highly restricted remnants of the earlier records, both depositional and erosional, may appear to be coeval, though actually separated by hundreds of millenia. Attempts to explain apparent synchroneity may employ illogical contortions of hypothetical lobate advances and sedimentary facies. Tills in glaciated northeastern Kansas can be grouped into at least 10 categories based on grain size, lithology, and weathering. All have previously been included in a single "Kansan Glaciation", but it has now been shown that at least two of those deposits markedly predate that event. The increase in number of recognizable glacial advances results in easier interpretation of certain specific deposits, so some previous interpretations should now be reexamined in terms of more-numerous early Pleistocene glaciations.