HR: 0800h
AN: PP31A-1505    [Abstracts]
TI: Climate Change Over a Glacial-Interglacial Cycle From the Mid Pleistocene: A Lacustrine Record From the Valles Caldera, New Mexico
AU: * Fawcett, P J
EM: fawcett@unm.edu
AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Heikoop, J
PP31A-1505 AF: Earth and Environmental Sciences Division, EES-6, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Goff, F
PP31A-1505 AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Allen, C
PP31A-1505 AF: U.S. Geological Survey, Fort Collins Science Center, Jemez Mountains Field Station, Los Alamos, NM 87544 United States
AU: Anderson, S
PP31A-1505 AF: Center for Environmental Sciences and Education, Northern Arizona University, Flagstaff, AZ 86011 United States
AU: Donohoo-Hurley, L
PP31A-1505 AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Geissman, J
PP31A-1505 AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Johnson, C
PP31A-1505 AF: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: WoldeGabriel, G
PP31A-1505 AF: Earth and Environmental Sciences Division, EES-6, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Fessenden-Rahn, J
PP31A-1505 AF: Earth and Environmental Sciences Division, EES-6, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AB: The Valles Caldera in the Jemez Mountains of northern New Mexico contains a thick sequence of lacustrine and volcaniclastic sediments that date from the inception of the caldera (c.a. 1.25 Myr). Lakes formed in the caldera immediately after its formation and existed for some period of time before the caldera wall was breached. A major lake formed during the middle Pleistocene in the Valle Grande when a post-caldera eruption (c.a. 550 kyr) filled the drainage to San Diego Canyon. The deposits of this ancient lake were cored in May 2004 (GLAD 5 drilling project) and a total depth of 81 m of lacustrine mud and silts and gravels was recovered. The age of the core is partly defined by an Ar-Ar date of 552,000 +/- 3,000 yrs B.P. from a tephra near the base of the core at 75 m depth and a possible paleomagnetic excursion corresponding to the Calabrian Ridge 2 event (~520,000 yrs B.P.) at about 17 m depth. This lacustrine sequence from the mid Pleistocene offers a unique opportunity to gain insight into the climatic response to a middle Pleistocene glacial cycle in southwestern North America. Initial analyses show considerable down-core variability in sedimentary facies, magnetic susceptibility and rock magnetic properties, gamma-ray density, organic carbon isotopic ratios and other parameters. Sedimentary facies, pollen and carbon-isotopic ratios vary in a manner consistent with changes from a glacial to an interglacial climate. In particular, major facies changes associated with lake shallowing and/or drying appear to correlate with the major glacial-interglacial transition over this time interval (oxygen isotopic stages 14 to 13). The initial lake filling sequence is marked by pumice sands and gravels at the base of the core which grade up into variably laminated and bioturbated diatom-rich silty muds. The mm-scale laminations found in much of the lacustrine mud sequence possibly represent varves. The rapid vertical facies changes within the core and intervals with well-developed mudcracks indicate multiple water level changes over the lake history.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1513 Geomagnetic excursions
DE: 1637 Regional climate change
DE: 4914 Continental climate records
DE: 4942 Limnology (0458, 1845, 4239)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005