STRATIGRAPHY, MAGNETIC SUSCEPTIBILITY, AND OSTRACODE PALEONTOLOGY FROM PLEISTOCENE FOSSIL LAKE, OREGON

A total of five stratigraphic cores were recently taken throughout the Pleistocene Fossil Lake basin in south central Oregon. A 350 cm core from the northeastern section of the basin was intensively subsampled and studied to produce high-resolution stratigraphic, magnetic susceptibility, and ostracode paleontological data. Using previously dated tephras, the age of the core is constrained from 610 kya near the base to 23.2 kya at the top. A major unconformity is present at 282 cm from the top of the core and lasts from approximately 600 to 100 kya. The core contains seven packages each consisting of an upward fining sequence of gravel and sand grading into silt and clay. Paleosols are common throughout the core and occur at the top of five packages. There is major change in magnetic susceptibility in the core below the unconformity with values ranging from 28 to 126 below the unconformity and from 89 to 720 above the unconformity. In the lake sediments, the silt and clay unit within a package shows a lower magnetic susceptibility than the gravel and sand unit. Blocky ped paleosol units also show a lower magnetic susceptibility than the lacustrine units in their package. Magnetic clay particles concentration increases at the top and base of the core. Highest susceptibility is present in recognized ash layers. In general, the magnetic susceptibility of the core sediments above the unconformity correlate with ice core isotope record and indicate first order control by climate. Ostracode specimens are present throughout most of the core and generally are only absent in the paleosols units. Adult ostracodes are rare throughout the core. Faunal assemblage and the frequency and abundance of ostracodes is independent of lithology. While ostracode distribution and assemblages are uncorrelated with lithology and climate, ostracode oxygen isotopes may provide insights into climate change and lake hydrology.