PRELIMINARY RESULTS OF THE ENVIRONMENTAL MAGNETIC RECORD OF PLEISTOCENE VALLES CALDERA LACUSTRINE SEDIMENTS, NEW MEXICO

Environmental magnetic techniques have been used as a proxy for small-scale lithologic variation, assumed to result from changes in climate or environment. A young lake system in the Valles Caldera, northern New Mexico, formed ca. 550 ka and may record a mid-Pleistocene glacial-interglacial cycle. Lacustrine core VC-3, about 80 m deep, was recovered from the Valles Caldera in May, 2004. A first-pass sampling interval of 20 cm was subject to comprehensive paleomagnetic and rock magnetic experiments. Those intervals of the Valles Caldera core characterized by abrupt or large variations in magnetic properties with depth are subject to further more robust sampling efforts. Initial paleomagnetic data (typical NRM intensities of 4.0 mA/m) indicate that well-defined magnetizations are readily isolated in progressive alternating field demagnetization. Rock magnetic results (mean destructive fields of 35 mT, anhysteretic remanent magnetization intensities of 30 mA/m, saturation of isothermal remanent magnetization intensities of 100 mA/m, coercivity of remanence of 0.07 mT) suggest that fine-grained (single-domain and pseudo-single-domain) magnetite is the primary contributor to the overall magnetization in most materials. Because the source area for these sediments remained constant over time (primarily rhyolitic rocks of the caldera), down core variations in magnetic properties, along with changes in texture and lithology, may be used to help resolve the nature of interactions between glacial and inter-glacial, surficial, hydrological, and volcanic processes. In time the results of this study will be integrated with those of other workers on the VC-3 core to compile a regional climate model for northern New Mexico for this interval of the late Pleistocene.