EP33E-06
Source-to-Sink Sediment-Budget Variability in Southern California
Wednesday, 16 December 2015: 14:55
2005 (Moscone West)
Jacob A Covault, Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, United States, Brian Romans, Virginia Polytechnic Institute and State University, Department of Geosciences, Blacksburg, VA, United States, George E Hilley, Stanford University, Geological and Environmental Sciences, Stanford, CA, United States, Bodo Bookhagen, University of Potsdam, Potsdam, Germany and Andrea Fildani, Statoil Gulf ASA, Houston, TX, United States
Abstract:
Source-to-sink sediment routing across the Earth’s surface controls the evolution of continental margins. We measure sediment budgets in two small, tectonically active sediment-routing systems of Southern California, including the geologic provinces of the Transverse (north) and Peninsular (south) ranges, using cosmogenic radionuclide-derived denudation rates (averaging over 10^3 years) and submarine-fan sediment accumulation rates (>10^4 years of measurement) since the last glacial maximum (~20 ka). The surface areas and headwater elevations of Transverse and Peninsular ranges catchments are similar; however, the orographic effect of the Transverse ranges on El Niño-Southern Oscillation storms likely resulted in increased rainfall. The catchments of the Transverse ranges are also composed of rapidly uplifting (<5.0 mm/yr), and easily eroded Plio-Pleistocene sedimentary rocks compared to the core of the Peninsular ranges. Accordingly, the mass denudation rates of the Transverse ranges and sediment accumulation rates in submarine fans are ~3 times greater than the rates of the Peninsular ranges and submarine fans to the south. In both sediment-routing systems, submarine-fan mass accumulation exceeds terrestrial denudation by a factor of ~1.5. This imbalance might result from the fact that cosmogenic radionuclide-derived denudation rates average over shorter timescales than submarine-fan sediment accumulation rates; therefore, they do not account for sediment production during periods of greater precipitation and/or lower sea level during the latest Pleistocene and early Holocene. Additional sediment supply to the submarine fans might be from unaccounted beach-cliff erosion. These results show sediment-budget variability in nearby geologic provinces owed to differences in climate, catchment lithology, and tectonic uplift. However, both the Transverse and Peninsular ranges catchments are measured to have less sediment production than offshore accumulation in submarine fans. These examples are representative of a globally significant class of small, tectonically active sediment-routing systems, in which sediment dispersal is sensitive to geologic variability, such as underlying lithology and dynamic topographic evolution.
