CORRECTING MIS5E SEA-LEVEL ESTIMATES FOR TECTONIC UPLIFT, AN EXAMPLE FROM SOUTHERN CALIFORNIA (Invited Presentation)

One of the most widely used sea-level indicators along active margins are uplifted marine terraces. However, in such settings differentiating the relative influence of tectonic uplift versus higher than present former sea levels remains problematic. The most common approach to differentiating the relative influence of these two processes has been to use glacial-isostatic adjustment (GIA) models to predict former sea levels and thus isolate the tectonic component of the marine terrace elevations. However, GIA models require tectonically-corrected relative sea-level (RSL) data for their calibration. In this study we outline a strategy by which a much older marine terrace is used to isolate the tectonic contribution to marine isotope stage (MIS) 5e and 5a marine terrace elevations for the Southern California coast. New cosmogenic radionuclide burial ages of the middle Pleistocene Clairemont Terrace in San Diego suggest an age of 1.48±0.17 Ma. Using this older terrace as a datum for calculating tectonic uplift rate provides a much longer time period to average out uncertainties in past RSLs that arise from ambiguities in GIA parameters and global meltwater volumes. The assumption of constant uplift rates is warranted for this portion of the California coast given its relatively simple tectonic setting on the rift flank of the Salton Trough. From this approach, we determine an average uplift rate of 0.066 ± 0.020 mm/yr or 0.055± 0.013 mm/yr, depending on the RSL model for the time of the Clairemont Terrace formation, for much of the San Diego coastline. Correcting for this tectonic uplift rate leaves an estimate of 15.1 +2.6/-3.1 m (16.4 +1.9/-2.6 m) and 4.8 ± 1.9 m (5.6 ± 1.5 m) for RSL during MIS5e and MIS5a, respectively. These new estimates of MIS5e and MIS5a sea levels along the southern California coast provide important constraints on GIA parameters and former ocean and ice volumes.