A 9000-year flood history for Southern California: A revised stratigraphy of varved sediments in Santa Barbara Basin

The center of Santa Barbara Basin (SBB) preserves annual laminations through most of the Holocene providing an important locality for high-resolution late Quaternary paleoclimate and paleoceanography reconstructions. An accurate chronology is necessary for these sediment-based records and enables comparisons with more distal data time-series of similar quality. Here we present an improved high-resolution radiocarbon chronology for the last 9000 yrs. based on 89 accelerator mass spectrometric (AMS) 14C dates of mixed planktonic foraminiferal carbonate from three sediment cores collected in SBB (MV0811-14JC, SPR0901-06KC and ODP Hole 893A). Accurate core-to-core correlation is demonstrated using prominent gray flood and olive turbidite layers identified in SBB and dated in multiple cores. Gray layer deposits were found more frequently in wetter intervals as determined by multi-proxy hydroclimate records in Southern California (e.g., lake deposits and tree rings). Mass accumulation rates (MARs) calculated for the SBB depocenter using the improved radiocarbon age model indicate high MARs are associated with these gray layers that have been associated with floods. Thus sediment accumulation in SBB is largely controlled by sediment delivery via river runoff following precipitation events although MARs may also be influenced by other factors that enhance erosion in river catchments. Folded sediment is observed within the basal core section of MV0811-14JC which stratigraphically correlates with 14C age reversals in ODP Hole 893A. We associate this sediment slump feature with the large Goleta submarine slide complex in Santa Barbara Channel and estimate the submarine slide event occurred at ~ 9000 ± 200 yrs. BP. Furthermore, small olive turbidite layers identified and dated in SBB can be temporally linked with large earthquakes along San Andreas Fault and can therefore potentially reconstruct earthquake history in Southern California.