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

A continuous record of oxygen-18 (δ ¹⁸O) 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 δ ¹⁸O versus time curve closely resembles the marine and Antarctic ice core (Vostok) δ ¹⁸O 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 δ ¹⁸O record and 7,000 years earlier than indicated by the less well dated Antarctic δ ¹⁸O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine δ ¹⁸O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.