A STALAGMITE RECORD OF THE PENULTIMATE DEGLACIATION FROM NORTHWESTERN ARKANSAS

We present stable isotopic data from CS-04-5, a 54 cm-high, cylindrical calcite stalagmite from Cosmic Cavern, northwest Arkansas, which grew during the penultimate deglaciation (Termination 2). The chronology for CS-04-5 is based on six U-Th mass spectrometry dates, all of which fall in correct stratigraphic order (140.6±1.9, 138.5±2.6, 137.4±2.1, 136.0±2.5, 134.2±2.0, and 128.7±2.4 ka). Petrographic examination finds five growth hiatuses, none of which were of sufficient duration to fall outside the uncertainties on the radiometric dates. The stalagmite has been analyzed for oxygen and carbon isotope ratios from 139-136 and 133-128 ka. δ¹⁸O values exhibit a range of approximately ~0.5‰, with a mean value of –5.4 ‰ (PDB). The mean δ¹³C value is –10.0 ‰ (PDB) from 139-136 ka and 133-132 ka at which time there was an interruption in calcite deposition. When growth resumed at ~130 ka, δ¹³C values were –7‰. The 3‰ increase in δ¹³C values at 130 ka can be attributed to a decrease in forest density over Cosmic Cavern or a change in water-rock interaction associated with an interglacial climate.