--> Abstract: Pennsylvanian Cyclothems and Sea Level Change: How Much Tectonic? How Much Eustatic? How Much Long-Term Climatic Change? Does it Matter?, by G. D. Klein; #90987 (1993).

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KLEIN, G. D., University of Illinois at Urbana-Champaign, Urbana, IL

ABSTRACT: Pennsylvanian Cyclothems and Sea Level Change: How Much Tectonic? How Much Eustatic? How Much Long-Term Climatic Change? Does it Matter?

Recalibrated sedimentological determinations of the magnitude of sea level changes associated with deposition of North American Pennsylvanian cyclotherms show that they accumulated in water depths ranging from 40 to 160 m in the mid-continent, 12 to 30 m in the Illinois basin, and 20 to 31 m in the Appalachian basin. Average sea level change for mid-continent cyclothems is 96 and 86 m for proposed sea level curves of Heckel and Gerhard, respectively.

Determination of per-cycle tectonic subsidence establishes the tectonic contribution to sea level change. In the mid-continent, tectonic subsidence accounts for approximately 5 to 20% of sea level change, whereas in the Illinois basin it accounts for 11 to 92% of sea level change. In the Appalachian basin, 9 to 100% of sea level change is tectonic.

Paleoclimate modeling suggests that 70% of sea level change is controlled by glacio-eustasy in the mid-continent. In the Illinois and Appalachian basins, glacio-eustasy accounts for a range of sea level change from 8 to 89% and 0 to 91% respectively.

In the Illinois and Appalachian basins, concurrent tectonic and glacio-eustasic forcing appears to be in balance to account for Pennsylvanian sea level change. In the mid-continent, up to an additional 15% of sea level change is required to balance the total magnitude of sea level change. Long-term climate change, perhaps controlled by paleotectonic shifts of North America from the tropical belt into the Hadley zone may account for these additional changes in sea level.

These findings suggest that away from orogenic belts, the sedimentary record indicates a stronger preservation of climate-forced deposition, whereas in orogenic belts, climate influences become subordinate, even though indicators of climate change appear to be preserved.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.