A 250,000-Year Climatic Record from Great Basin Vein Calcite: Implications for Milankovitch Theory

Abstract

A continuous record of oxygen-18 (δ¹⁸O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole—an open fault zone at Ash Meadows, Nevada—between 50 and 310 ka (thousand years ago). The configuration of the δ¹⁸O versus time curve closely resembles the marine and Antarctic ice core (Vostok) δ¹⁸O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 ± 3 ka, at least 17,000 years earlier than indicated by the marine δ¹⁸O record and 7,000 years earlier than indicated by the less well dated Antarctic δ¹⁸O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine δ¹⁸O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.