SEDIMENTOLOGICAL ANALYSES OF THE STEMSEAS SITE 1 CORE (TANNER BASIN, CALIFORNIA BORDERLANDS) SHOWING CHANGES IN SEDIMENT TRANSPORT AND PALEOENVIRONMENTAL CONDITIONS FROM THE YOUNGER DRYAS THROUGH THE HOLOCENE

In May 2016 the STEMSEAS educational transit cruise OC1605-tranA traveled from San Diego to Honolulu on the R/V Oceanus and collected a core from the Tanner Basin in the California Borderland. While the purpose of the expedition was to provide students with onboard hands-on research experience, a subsequent benefit was being able to have students continue to conduct research on the core post-cruise.

This research serves as the first sedimentological analysis conducted on the 1.6 m core, which spans the Younger Dryas and Holocene. It builds on shipboard XRF results that suggested a lithologic boundary at ~115-120 cmbsf, and on a paleontological study by Stone et al (2018) which showed foraminiferal evidence for millennial-scale variability of SST and nutrient supply. Here we examine a suite of characteristics that could indicate changes in sediment transport and paleoenvironmental conditions at Site 1 from the Younger Dryas through the Holocene. Data are being collected at James Madison University using x-ray fluorescence (XRF), x-ray diffraction (XRD), and grain size analyses. In addition, magnetic susceptibility (MS) and color reflectance (L*) were measured at the USGS in Reston, VA. Results show a distinct decrease in MS values above ~115 cmbsf, marking the boundary between the Younger Dryas and Holocene and consistent in timing with decrease in linear sedimentation rates. In addition, increases in mean and standard deviation of grain size can be seen in the upper Holocene. The shift to coarser and more poorly sorted grains suggests greater terrigenous input. These sedimentological changes generally correlate with lower abundances of G. Bulloides, which is an indicator of reduced nutrient supply, possibility related to changes in upwelling (Fisler & Hendy, 2008). This suggests that the STEMSEAS Site 1 record may document changes in the strength and frequency of ENSO events that could impact both terrestrial runoff and upwelling in the region. The results from ongoing analyses of stratigraphic changes in major elements and changes in clay mineralogy will also be presented.