Thorium-230 ages of corals and duration of the last interglacial sea-level high stand on oahu, hawaii.

Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from approximately 114,000 to approximately 131,000 years, indicating a duration for the last interglacial sea-level high stand of approximately 17,000 years, in contrast to a duration of approximately 8000 years inferred from the orbitally tuned marine oxygen isotope record. Sea level on Oahu rose to >/=1 to 2 meters higher than present by 131,000 years ago or approximately 6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at approximately 119,000 years ago, the Oahu coral ages indicate a near present sea level until approximately 114,000 years ago.

Continuous 500,000-year climate record from vein calcite in devils hole, nevada.

Oxygen-18 (delta(18)O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine delta(18)O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.

Mass-Spectrometric 230Th-234U-238U Dating of the Devils Hole Calcite Vein.

The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded (230)Th ages with precisions ranging from less than 1,000 years (2sigma) for samples younger than approximately 140 ka (thousands of years ago) to less than 50,000 years for the oldest samples ( approximately 566 ka). The (234)U/(238)U ages could be determined to a precision of approximately 20,000 years for all ages. Calcite accumulated continuously from 566 ka until approximately 60 ka at an average rate of 0.7 millimeter per 10(3) years. The precise agreement between replicte analyses and the concordance of the (230)Th/(238)U (234)U/(238)U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.

Uranium-series dated authigenic carbonates and acheulian sites in southern egypt.

Field investigations in southern Egypt have yielded Acheulian artifacts in situ in authigenic carbonate deposits (CaCO(3)-cemented alluvium) along the edges of nowaggraded paleovalleys (Wadi Arid and Wadi Safsaf). Uranium-series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45, 141 and 212 ka (thousand years ago). Most of the carbonate appears to have been precipitated from groundwater, which suggests that these three episodes of deposition may be related to late Pleistocene humid climates that facilitated human settlement in this now hyperarid region. Carbonate cements from sediments containing Acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys.

A 250,000-year climatic record from great basin vein calcite: implications for milankovitch theory.

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

Two-million-year record of deuterium depletion in great basin ground waters.

Fluid inclusions in uranium series-dated calcitic veins from the southern Great Basin record a reduction of 40 per mil in the deuterium content of ground-water recharge during the Pleistocene. This variation is tentatively attributed to major uplift of the Sierra Nevada Range and the Transverse Ranges during this epoch with attendant increasing orographic depletion of deuterium from inland-bound Pacific storms.

Quaternary climates and sea levels of the u.s. Atlantic coastal plain.

Uranium-series dating of corals from marine deposits of the U.S. Atlantic Coastal Plain coupled with paleoclimatic reconstructions based on ostracode (marine) and pollen (continent) data document at least five relatively warm intervals during the last 500,000 years. On the basis of multiple paleoenvironmental criteria, we determined relative sea level positions during the warm intervals, relative to present mean sea level, were 7 +/- 5 meters at 188,000 years ago, 7.5 +/- 1.5 meters at 120,000 years ago, 6.5 +/- 3.5 meters at 94,000 years ago, and 7 +/- 3 meters at 72,000 years ago. The composite sea level chronology for the Atlantic Coastal Plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200,000 years. Hydroisostatic adjustment from glacial-interglacial sea level fluctuations, lithospheric flexure, and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies. Alternatively, current eustatic sea level estimates for the middle and late Quaternary may require revision.