Print this pageNew radiocarbon ages from diamictons and associated sediments in Indiana and Ohio average about 40,000 RCYBP. These deposits may reflect climatic warming that lasted only a few millennia but triggered melting of permafrost that induced extensive viscous flows. These diamictons were originally assumed to be glacial (i.e. till) and commonly assigned to a middle Wisconsinan glaciation, in some cases on the basis of radiocarbon dating. However, as advocacy of middle Wisconsinan glaciation became climatically problematic, the diamictons were commonly reassigned to either the Illinoian or the late Wisconsinan glaciations. However, reassignment requires rejection of middle Wisconsinan radiocarbon ages. A nonglacial viscous-flow origin fits better with growing global evidence for middle Wisconsinan climatic warming.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana