2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 2:50 PM

Continuous ~30,000 Year Climate Record from An Early Permian Speleothem, Central Oklahoma, USA

HARMS, Brian S., ELMORE, R. Douglas and ENGEL, Michael H., School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019, bharms@ou.edu

Speleothem recordshave provided numerous insights into recentclimatic fluctuations, including the intensity of monsoonal rainfall, the composition of overlying plant communities and glacial/interglacial transitions. An additional advantage of speleothems is that they can grow continuously for millennia, and depending upon the rate of growth, may yield temporal resolutions ranging from weeks to decades. However, to date, studies have been largely restricted toQuaternary specimens, perhaps due to the limitation of the U-Th disequilibrium method, as well as a paucity of well-preserved ancient specimens. Here we present carbon and oxygen stable isotope recordsfrom an Early Permian speleothem, the age of which is constrained by paleomagnetic and fossil evidence. The speleothem was extracted from one of many small paleocaves in the Slick Hills of central Oklahoma, which are thought to represent an exhumed Early Permian terrain. Sedimentological and fossil evidence indicates that the caves were backfilled shortly after they were decorated. While the level of preservation appears to be variable from one cave to the next, several specimens – including the one in this study – seem to be exceptionally well preserved. The aforementioned speleothem exhibits alternating light and dark growth bands that range in thickness from 5-15 microns per light/dark couplet. On the presumption that these bands are annual, thisspecimen represents ~30,000 years of continuous growth. This interpretation is reasonable given independent evidence that the region was influenced by a strongly seasonal, tropical monsoonal climate. Carbon and oxygen isotope trends are consistent with decreasing rainfall and a decline in C3 vegetation density. However, the timing of several major carbon isotope excursions – which precede oxygen isotope excursions – suggest that rising atmospheric CO2 may have also contributed to these trends. Given its age, this high-resolution record may fall within the broader context of the deglaciaton of Gondwana.