Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 64 Number 3: 165-174 - December 2002

A publication of the National Speleological Society

A late Pleistocene ceiling collapse in Bogus Cave, Jones County, Iowa: A potential relationship to coeval accelerated mass wasting events across the central Midwest
Richard L. Josephs

Abstract

A thick accumulation of boulder-size dolostone blocks, the result of one or more episodes of ceiling collapse, was encountered during geoarchaeological excavations in the front room of Bogus Cave, east-central Iowa. The rockfall layer was buried by a veneer of Holocene sediments that contained prehistoric artifacts dating to the Woodland Period (2500 - 1000 yr BP). An AMS 14C age of 17,260 ±120 yr BP, obtained from a caribou (Rangifer tarandus) mandible found wedged among the boulders, dates the collapse near the close of the last glacial maximum, a time when the projected mean annual temperature for this area was at least 14°C lower than at present. Paleoenvironmental evidence based on ä13C values from select vertebrate remains and their encompassing sediment, together with a uranium series age of 16,900 ±4800 yr BP from a stalagmite formed atop one of the boulders, strongly support a late Wisconsinan age for the collapse. The episode (or episodes) of collapse appears to be the result of cryoclastic processes associated with late glacial conditions and the onset of accelerated mass wasting that has been previously documented across the central Midwest.

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