New Mexico Geological Society Annual Spring Meeting — Abstracts

The Valle Grande lacustrine system, Jemez Mountain, New Mexico, formed after the collapse of the Valles Caldera (VC), 1.25 Ma, and eventually drained via San Diego Canyon. One of the youngest lake systems in the caldera formed after the South Mountain rhyolite eruption at c.a. 530 ka, which dammed the East Fork Jemez River. Unlike other lake basins in the American Southwest, termination of the sediment deposition in the Valle Grande was not due specifically to the drier climate. Theretofore the most recent low lake stand was no due to the morphology of the basin and not climatically controlled conditions. Approximately 80 m of lacustrine sediments were recovered from the Valle Grande during a drilling experiment conducted in mid-May, 2004. Initial paleomagnetic date (typical NRM intensity of 4.0mA/m) and rock magnetic results (mean destructive field of 35 mT in alternating field demagnetization) indicate that fine-grained (single-domain and pseudo-single domain) magnetite is the primary contributor to the overall magnetization and that well-defined magnetizations are readily obtainable from these materials. Because the source are for these sediments remain constant over time (primarily rhyolitic rocks of VC), down hole variations on magnetic properties and changes in texture and lithology will be used to help resolve the nature of interactions between surficial, hydrological, and volcanic processes. Eventually the results of this study will be integrated with those of other workers to compile a regional climate model for northern New Mexico over the late Quaternary time interval sampled by the VC-3 hole.