HR: 1400h
AN: PP43C-06    [Abstracts]
TI: Evidence of two glacial-interglacial climatic shifts from lacustrine records of TOC, δ¹³C and C/N ratios in the southwestern USA
AU: Heikoop, J
EM: jheikoop@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division Hydrology, Geochemistry and Geology Group EES-6, MS-D462 , Los Alamos, NM 87545, United States
AU: * Cisneros-Dozal, L
EM: cisnerosd@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division Hydrology, Geochemistry and Geology Group EES-6, MS-D462 , Los Alamos, NM 87545, United States
AU: Fessenden-Rahn, J
EM: julianna@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division Hydrology, Geochemistry and Geology Group EES-6, MS-D462 , Los Alamos, NM 87545, United States
AU: Fawcett, P
EM: fawcett@unm.edu
AF: University of New Mexico, Dept. Earth & Planetary Sciences University of New Mexico MSCO3-2040, Albuquerque, NM 87131, United States
AB: Valles Caldera, located in Northern New Mexico, contains lacustrine deposits dating back to the middle Pleistocene. An 82 m long core containing ~75 meters of lacustrine sediments was recovered from Valles Caldera in 2004. The age of the sediments was constrained by Ar-Ar dating of a primary tephra layer from the base of the core, in combination with correlation to the deep-sea marine isotope stage record along the length of the core. The lacustrine sediments span from ~350 k YBP to 552 k YBP covering two glacial-interglacial stages, from MIS 11 to MIS 14 and part of MIS 10. Total organic carbon (TOC) in the siderite free fraction (i.e. diagenetic siderite was chemically removed) ranged from <1% to 7% with the lowest values predominantly observed during glacial times and marked increases at the onset of interglacials. Particularly high TOC is observed during the long interglacial MIS 11. C/N ratios ranged from values of <2 to ~11 with lowest values in general observed during glacial times indicating increased input from aquatic sources and suggesting deepening of the lake as a result of wetter glacial climate. δ¹³C values measured in the siderite free fraction, ranged from - 28‰ to -20‰ and remained more negative overall during glacial times. Further isotopic analyses including δD values of n-alkanes will be performed to reconstruct the delivery of meteoric water to the region and thus contribute to understand the history of climate change.
DE: 1051 Sedimentary geochemistry
DE: 4926 Glacial
DE: 4936 Interglacial
DE: 4940 Isotopic stage
DE: 4942 Limnology (0458, 1845, 4239)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly