Stable Isotope Geochemistry of Speleothems and Cave Waters from the Flint Ridge-Mammoth Cave System, Kentucky: Implications for Terrestrial Climate Change during the Period 230,000 to 100,000 Years B.P.

O, H, C, U, and Th isotopic variations have been measured along the growth axis of a calcite stalagmite from the Flint Ridge-Mammoth Cave System, Kentucky. Ages were determined by the ²³⁰Th/²³⁴U method and indicate continuous deposition over the time interval from 230,000-100,000 years B.P. ¹⁸O/¹⁶O ratios of the speleothem calcite and D/H ratios of entrapped fluid inclusions imply that (i) the calcite-water fractionation is the predominant factor determining the oxygen isotopic of speleothem calcite at this site, (ii) glacial precipitation was depleted in deuterium by approximately 20‰ relative to interglacial precipitation, (iii) the maximum interglacial/glacial temperature decrease at this site was about 12°C. A curve of the secular δ¹⁸O calcite variations for the stalagmite suggests warm climate conditions in central Kentucky similar to that at present at about 215,000, 195,000, 185,000-165,000, 125,000, and 105,000 years B.P. Major cold periods are observed from 215,000-195,000 and 160,000-130,000 years B.P.