SPELEOTHEM-BASED d13C AND d18O RECORDS OF LATE QUATERNARY CLIMATES IN KENTUCKY

Stable isotopic results are presented for three speleothem samples recovered from caves in Rockcastle County (RC-1; ~400mm-long stalagmite), Lee County (LC-1; ~300mm-long stalagmite), and Edmonson County (EC-1; ~25mm-thick flowstone), KY.  Preliminary isotopic results from the upper 100mm of RC-1 indicate a dynamic range in d¹³C of 4‰ (-10.5‰ to -6.5‰ vs. VPDB), and a ~1.2‰ range in d¹⁸O (-6.0‰ to -4.8‰ vs. VPDB).  d¹³C and d¹⁸O values for the flowstone, EC-1, average –6.0‰ and –4.2‰, respectively.  Isotopic results for LC-1 are pending at the time of abstract submission.

The preliminary dataset of U-Th ages for the three formations indicates that they were deposited during the late Quaternary.  A sample taken at 200mm below the tip of RC-1 yields an alpha-counter age of 21 +/- 2  ka, indicating that the isotopic record spans across the last glacial maximum.  A sample taken from 150mm  below the tip of LC-1 yields an age of 111 +/- 8 ka, and a sample of the EC-1 flowstone yields an age of 112 +/- 11 ka, indicating that both records represent growth during Marine Isotope Stage (MIS) 5d.

Together, the three speleothem-based isotopic records provide unique natural (pre-anthropogenic change) compositional/formational endmembers that represent extremes in the climate system (glacial vs. interglacial).  In addition, the records may also provide insight into regional variability in isotopic signatures, potentially defining important differences in drainage basin flow (the samples represent the Kentucky, Green and Cumberland drainage basins, all of which flow into the Ohio River).  Continuing isotopic and geochronological research on the speleothem samples discussed above and travertine samples collected from Fayette County (Lexington) and Hart County, KY, will provide a regionally-extensive framework for defining paleoclimatic, paleohydrological, and geomorphic changes during and since MIS 5.