HR: 1340h
AN: T43C-1346    [Abstracts]
TI: Deep Coring in the Valles Caldera, Northern New Mexico to Obtain a Long-Term Paleoclimatic Record
AU: * Fawcett, P J
EM: fawcett@unm.edu
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Goff, F
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Heikoop, J
AF: Earth and Environmental Sciences, MS D462 Los Alamos National Lab, Los Alamos, NM 87545 United States
AU: Allen, C D
EM: craig_allen@usgs.gov
AF: U.S. Geological Survey, Fort Collins Science Center Jemez Mountains Field Station, Los Alamos, NM 87554 United States
AU: Donohoo, L
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Wawrzyniec, T
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Geissman, J W
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Johnson, C
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AU: Fessenden-Rahn, J
AF: Earth and Environmental Sciences, MS D462 Los Alamos National Lab, Los Alamos, NM 87545 United States
AU: Woldegabriel, G
AF: Earth and Environmental Sciences, MS D462 Los Alamos National Lab, Los Alamos, NM 87545 United States
AU: Schnurrenberger, D
AF: Limnological Research Center, University of Minnesota, Minneapolis, MN 55455 United States
AB: The 22-km diameter Valles caldera in the Jemez Mountains of northern New Mexico contains a thick sequence of lacustrine sediments and hydromagmatic deposits that date from the inception of the caldera (c.a. 1.25 Myr). Geologic mapping shows that lakes formed in the caldera immediately after its formation and existed for some period of time before the caldera wall was breached and the lake drained to the SW through San Diego canyon. Another substantial lake formed during the mid-Pleistocene in the SE caldera moat (Valle Grande) when a post-caldera eruption (c.a. 520 kyr) filled the drainage to S.D. canyon. To determine their paleoclimatic significance, the deposits of this ancient lake were cored in May, 2004 (GLAD 5). Hole VC-3 achieved a total depth of 81 m recovering a complete section of ~75 m of lacustrine mud and silts and gravels. Recovery of lacustrine mud/silt was close to 100 percent while the recovery of gravels encountered at the top and bottom of the sequence was considerably less. The core is currently archived at the National Lacustrine Core Facility (LacCore) at the University of Minnesota. Preliminary analyses show considerable down-core variability in parameters including magnetic susceptibility, gamma-ray density and sedimentary facies. The base of the core consists of pumiceous-rhyolitic sands and gravels intercalated with indurated muds, which grades up into variably laminated and bioturbated lacustrine mud and silty mud. In the lower lacustrine sequence, several turbidites interrupt the laminated mud sequences and in some sections, thick diatomites (up to 5 cm) occur and are indicative of surface eutrophication in the lake. Higher in the core, thin sand lenses indicate periods of enhanced runoff into the lake, and occasional rhyolitic dropstones are observed. Much of the laminated silty clay is rich in diatoms, although both the density and diversity of diatoms are highly variable. In the middle of the core, a brecciated, diatom poor facies correlates with high magnetic susceptibility. Rapid facies changes and intervals with well-developed mudcracks indicate multiple lake level changes over the lake history that probably spans tens of thousands of years over the mid-Pleistocene. Future work on the core will include pollen, diatom, stable isotope and other geochemical and geophysical analyses.
DE: 3344 Paleoclimatology
DE: 1845 Limnology
DE: 1045 Low-temperature geochemistry
DE: 1512 Environmental magnetism
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting