PALEOMAGNETIC DATA FROM STONEMAN LAKE, ARIZONA PLACING CONSTRAINTS ON THE EVOLUTION OF TERRESTRIAL CLIMATE AND VEGETATION THROUGH THE MID PLEISTOCENE TRANSITION

Numerous studies project increasing climate aridity in southwestern North America over the next century. In terrestrial environments, continuous lake sediment cores of great antiquity provide enormous potential for interpreting paleoenvironmental histories and current climate change directions. The Stoneman Lake record is uniquely posed to address two overarching questions: 1) the nature of terrestrial interglacial climates spanning the Mid Pleistocene Transition under different orbital and CO₂ forcings, and 2) the impact of large droughts in the American Southwest in the past and their potential for interpreting impacts of future. Unfortunately, materials for absolute age determinations are often lacking limiting our ability to interpret the rates of climate variability. Magnetostratigraphy provides the means to document polarity reversals and transitional field behavior preserved in the stratigraphic record that can serve to further resolve absolute dating techniques while associated rock magnetic data provides an environmental climate proxy. Here we report preliminary paleomagnetic data from the ~73m sediment record obtained from the Stoneman Lake drill cores obtained in 2014. We sampled the portions of the core segments that had high bulk magnetic susceptibility as ~1.5 cm³ cube samples to construct a magnetostratigraphy record. To date, 77 samples reveal four behaviors: 1) normal polarity of steep inclination, 2) reverse polarity of steep inclination, 3) very shallow inclination (<10°) of normal/reverse polarity, and 4) unstable demagnetization behavior. From these data, a magnetostratigraphy is constructed that indicates that the record may extend back at least 1.5 Ma to possibly 2.0 Ma. In the upper part of the core (~6 m depth), data reveal very shallow (<10°) normal/reverse polarity inclinations. We tentatively interpret this direction as the Laschamp Excursion in the Brunhes normal polarity Chron. The data from the middle part of the core (~38.5 m depth) likely captures the Brunhes-Matuyama reversal and the Jaramillo excursion (~41.5 m depth) in the Matuyama reverse polarity Chron. Initial results from the deepest part of the core (~62 m-72 m depth) yield very shallow (<10°) normal/reverse polarity inclinations and may reflect the Olduvai excursion (~1849 Ma). The paleomagnetic data provide critical constraints on assisting with placing absolute age estimates on the Stoneman Lake sediments to aid with interpreting paleoclimatic changes in the Southwest.