ENVIRONMENTAL MAGNETIC IMPLICATIONS OF GREIGITE (FE3S4) FORMATION IN A 3 MY LAKE SEDIMENT RECORD FROM BUTTE VALLEY, NORTHERN CALIFORNIA

Authigenic greigite (Fe3S4) has been identified in several horizons of lake beds in a 102-m core from Butte Valley, northern California, usi ng mineral magnetic methods and x-ray diffraction analysis. The presen ce of greigite has several implications for the paleoenvironmental rec ord from Butte Valley. First, its occurrence in 2.5 - 3.0 Ma strata co nfirms that greigite can persist in the geological record for long per iods of time. Second, the detrital mineral magnetic record may be part ially obscured by the presence of authigenic greigite and care must be taken in interpreting magnetic variations in the greigite-bearing zon es as paleoclimate proxies. Third, differences in the timing of remane nce acquisition for authigenic and detrital phases may compromise stud ies of high-frequency geomagnetic field variations. Fourth, greigite m ay also be significant as a paleoenvironmental indicator of lake and s ediment chemistry, The magnetic detection of greigite may therefore pr ovide important information about paleolimnological conditions.