2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 19
Presentation Time: 8:00 AM-4:45 PM

Neotectonic Investigation of the Southern Death Valley Fault Zone, San Bernardino County, California

LACKEY, Heather Green and CASKEY, S. John, Dept. of Geosciences, San Francisco State University, 1600 Holloway Ave, San Francisco, CA 94132, hglackey@yahoo.com

The Death Valley Fault System (DVFS) is a major tectonic structure in California. Two structural components of the DVFS (the Northern Death Valley fault zone and the Black Mountains fault zone) have been the focus of numerous studies. However, very few studies have focused on a third component, the right-lateral Southern Death Valley Fault Zone (SDVFZ). A new 1:12,000-scale strip map documents the alluvial and lacustrine stratigraphy in Southern Death Valley (SDV) and the tectonic geomorphology along the SDVFZ. The geology was mapped on aerial photographs and NAIP imagery from the USDA. Alluvial map units were delineated according to the chronostratigraphic framework developed by the USGS for 1:24,000-scale Quaternary geologic maps of the Mojave Desert region. The framework is based on a specific set of surface development criteria including degrees of desert varnish, desert pavement, and soil development, as well as surface micro-topography and inset relations. We developed a new chronostratigraphic framework for lacustrine map units based primarily on their degree of deformation and preservation characteristics. Age control was established for the lacustrine units using interbedded correlated tephra deposits. Four mapped lacustrine sequences record pluvial Lake Manly history, right-lateral offsets across the SDVFZ, and progressive contractional deformation across SDV. The lacustrine sequences indicate that pluvial Lake Manly occupied SDV ~3.4 mya, ~1.2 to ~0.6 mya (OIS 16+), ~200-140 kya (OIS 6), and ~27 kya (OIS 2). Headward-eroded channels incised into the ~27 ka lacustrine sequence are offset ~5 m right-laterally and ~1.2 Ma deposits are right-laterally offset ~50 m. These data yield average minimum slip rates of 0.2 to <0.1 mm/yr. Our mapping also identifies ~3.4 Ma deposits folded by an earlier north-directed shortening and subsequently refolded by northeast-directed shortening, which appears to be ongoing.