Paper No. 14
Presentation Time: 11:15 AM
CORE VC-3: A WINDOW INTO THE MIDDLE PLEISTOCENE CLIMATIC AND GEOLOGIC EVOLUTION OF THE VALLES CALDERA, NEW MEXICO
FAWCETT, Peter J., Earth and Planetary Sciences, University of New Mexico, 220 Northrop Hall, Albuquerque, NM 87131, WERNE, Josef P., Department of Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260, ANDERSON, R. Scott, Environmental Programs, School of Earth Sciences & Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, HEIKOOP, Jeff, Earth and Environmental Sciences Division, Los Alamos National Lab, Los Alamos, NM 87545, BROWN, Erik, University of Minnesota Duluth, Large Lakes Observatory, Duluth, MN 55812, GOFF, Fraser, Earth and Planetary Sciences Dept, University of New Mexico, Albuquerque, NM 87131, HURLEY, Linda, Earth and Planetary Sciences, University of New Mexico, 1 University of New Mexico, MSCO3-2040, Albuquerque, NM 87131-0001, WOLDEGABRIEL, Giday, Earth and Environmental Sciences Division, Los Alamos National Laboratory, EES-16/MS D462, Los Alamos, NM 87545, GEISSMAN, John W., Earth and Planetary Sciences, University of New Mexico, Albuqueruqe, NM 87131 and ALLEN, Craig D., Fort Collins Science Center, Jemez Mountains Field Station, USGS, Los Alamos, NM 87544, fawcett@unm.edu
An 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico contains a high-resolution record of climate change over two mid-Pleistocene glacial cycles. Core VC-3 was taken from the Valle Grande and sampled sediments from a long-lived lake which formed following the eruption of the South Mountain Rhyolite. A basal Ar-Ar date of 552 ka from a tephra associated with the eruption of the South Mountain rhyolite constrains the core to the middle Pleistocene. A variety of proxies including core sedimentology, organic carbon and carbon isotopic ratios, pollen, scanning XRF analysis and a novel molecular paleotemperature proxy, MBT/CBT, reveal two major warm periods above the basal tephra which we correlate with interglacials MIS 13 and MIS 11. This chronology is supported by the identification of two geomagnetic field events which are correlated with globally recognized events (14α and 11α). The lacustrine record terminates at ~363 ka when the lake filled its available accommodation space.
Within this long paleoclimatic record, we find that periods of aridity lasting centuries to millennia occurred during the warmest parts of the interglacial periods when MATs were comparable to or higher than the modern, and may be an analog to projected future southwestern aridity. A collapse of interglacial C4 plant communities during these warm, dry intervals indicates significantly lower summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three cycles of ~2oC MAT amplitude occur within Marine Isotope Stage (MIS) 11, an analog for Holocene and future climate, and appear to correspond to the muted precessional cycles within this interglacial. A significant portion of MIS 13 was warmer than MIS 11 and larger MAT variations (4 to 6oC) during MIS 13 when precessional cycle amplitudes were larger suggests that local insolation variations were important to southwestern interglacial climate variability. During the glacial periods, millennial-scale D-O-like variability dominated with MAT amplitudes of up to 6oC and correspondingly large shifts in Spruce and Fir pollen percentages.
