North-Central Section - 42nd Annual Meeting (24–25 April 2008)

Paper No. 8
Presentation Time: 4:00 PM


HECKEL, Philip H., Department of Geoscience, University of Iowa, Iowa City, IA 52242,

Conodont-based biostratigraphic correlation of Middle to Late Pennsylvanian Midcontinent cyclothems with those elsewhere in North America has been extended to the cyclothems now recognized in Russia and Ukraine in eastern Europe. This correlation of biostratigraphic zonation with major sea-level fluctuation events in the Pennsylvanian pantropical belt provides a framework for incorporating radiometric dates from volcanic-bearing marine successions into the named units of the Pennsylvanian time scale. It also provides a framework for tying the fluctuation events into the glaciation events that are becoming identified in Gondwana, where the cold-water marine faunas are too provincial to be correlated, and the subpolar spore assemblages have not yet allowed detailed correlation. However, the primary evidence developed so far for multiple glaciations in the Gondwana succession on a scale sufficient to have caused major fluctuations in sea level delineates only a few longer times of major glaciation during the entire late Paleozoic, in contrast to the large number of major and intermediate cyclothems recognized in the Pennsylvanian pantropical zone. This discrepancy results from several factors, including lack of data, both from parts of Gondwana where Pennsylvanian strata are absent and from the immense ice-covered part of Antarctica. More importantly, the most conspicuous evidence of glacio-eustatic fluctuation in the pantropical zone, the major and intermediate cyclothems, represent the highest stands of sea level when there was the least ice coverage on Gondwana. When marine withdrawals between the highest stands extended only to the lower Midcontinent shelf (Kansas), they indicate only regional ice buildup in Gondwana. Hence these longer periods of time that include several major and intermediate cyclothems with lesser regressions between them would appear only as longer interglacial episodes over most of Gondwana. In contrast, only the greatest sea-level withdrawals in the Midcontinent (into the basin margin of central Oklahoma) would be represented by glacial deposits over much more of Gondwana, and these times are only about one-fifth as frequent as the short intense highstands that are represented so conspicuously by the major and intermediate cyclothems on the Midcontinent shelf.