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High Resolution Seismic Study of the Holocene Infill of the Elkhorn Slough, Central California
Citation:
Garcia Garcia, A., M. Levey, AND E. Watson. High Resolution Seismic Study of the Holocene Infill of the Elkhorn Slough, Central California. Continental Shelf Research. Elsevier BV, AMSTERDAM, Netherlands, 55:108-118, (2013).
Impact/Purpose:
We conducted accoustic profiling of an estuary in California in order to evaluate the impacts of tidal erosion on salt marsh sustainability. We found that accoustic blanking by gaseous salt marsh deposits generally prevented visualization of stratigraphy beneath salt marsh, but we found erosion mapping of depositional units was possible using this technique. Furthermore, we discovered broader applications for this technique with respect to benthic mapping.
Description:
The seismic analysis of the sedimentary infill of the Elkhorn Slough, central California, reveals a succession of three main seismic units: U1, U2, U3, with their correspondent discontinuities d2, d3. These units are deposited over a paleorelief representing the channel location at least 8k years ago. The location of that paleochannel has not changed with time, but the geometry of the infilling sedimentary packages has done so through the years. Discontinuities d2 and d3 show a relic island or relative high in the center of the Slough that separated the sedimentation into two main small basins at least 3k years ago. There is evidence of erosion in the last two sedimentary units showing that the present erosive pattern started decades ago at minimum. We have correlated radiocarbon data of selected cores with the high resolution chirp profiles and reconstructed the infill for the Elkhorn Slough. In the most recent unit, the occurrence of numerous lateral accretion surfaces on both bends of the main channel is discussed within their environmental setting, tidal currents and the net ebb flux of the area. We have interpreted the presence of gas in the sediments of the slough, with a gas front located at the tops of units 2 and 3, which are discontinuities that reflect an effective seal for the gas. No obvious seepage evidence has been found on our data although the shallow presence of some of the fronts points out the fragility of the environment in the present erosive conditions.
