PRELIMINARY PALEOMAGNETIC DATA BEARING ON THE EVOLUTION OF TERRESTRIAL CLIMATE AND VEGETATION THROUGH THE MID-PLEISTOCENE TRANSITION: A 1.5 MA RECORD FROM STONEMAN LAKE, ARIZONA

Numerous studies have projected increasing climate aridity in southwestern North America over the next century and beyond. In terrestrial environments, continuous lake sediment cores of great antiquity provide enormous potential for interpreting paleoenvironmental histories to aid with interpreting 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 drought due to future climate changes. Here we report preliminary paleomagnetic data from the ~73m sediment record obtained from the Stoneman Lake, Arizona drill cores obtained in 2014. Portions of the core segments that had high relative magnetic susceptibility were sampled as ~1.5 cm³ cube samples to construct a rudimentary magnetostratigraphy record. 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. These samples were treated with alternating field demagnetization techniques as well as various rock magnetic experiments. The initial set of samples yielded promising results of four behaviors: 1) normal polarity of relatively steep inclination, 2) reverse polarity of steep inclination, 3) shallow inclination of normal and reverse polarity, and 4) unstable demagnetization behavior. From this first data set, a skeletal magnetostratigraphy was constructed that suggests that the record may extend back at least 1.5 Ma. The data indicates that the core likely spans the Brunhes - Matuyama polarity chron (781 ± 3 ka). Within these chrons, several short reversals (Jaramillo (988 ± 3 ka), Cobb Mountain (~1185 ± 5 ka), Olduval (1945 ± 4 ka), and Reunion (2133 ± 5 ka) and several failed reversals have occurred that will allow us to further constrain the age of the core sediments and paleoclimate conditions.