Pacific Section AAPG Convention

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Holocene Relative Sea Level In Southern California: Implications For Estimates Of Recent Tectonic Rates On The Coast

Abstract

Estimates of recent vertical tectonic rates in coastal areas based on elevations of paleo-shoreline features rely on the ability to remove the effects of Holocene eustatic and isostatic contributions to sea-level change, which at the present is poorly constrained for southern California. Here we present the first regional, uplift-corrected Holocene relative sea-level (RSL) curve for southern California derived from a compilation of ∼80 radiocarbon dates from nearshore, estuarine, marsh, and freshwater deposits in sediment cores. We correct for long-term uplift using Marine Isotope Stage 5e (MIS 5e) terrace elevations, assuming an age of 120ka and interglacial RSL of 12+/-3m above modern. Our resulting compilation shows rapid sea-level rise decelerating to present between 6 and 8ka, with 0.8¬± .21mm/yr average late Holocene (<4ka) rates of rise. We demonstrate the utility of our compilation by comparing it to RSL data from regions thought to be experiencing recent, localized vertical tectonic motion, additional to long-term motion indicating by uplifted 5e terraces, such as Carpinteria Marsh, Elkhorn Slough and an exposed Holocene terrace in Santa Barbara. We show magnitude of Holocene vertical tectonic motion on the coast is quantifiable when comparing the deviations of site-specific RSL data to the regional curve.