Dating Historical Sediments in Estuaries: A Multi-Proxy Approach

Abstract:

Interpretation of recent estuarine stratigraphy, especially differentiation between events with similar sedimentological features such as storm and tsunami deposits, requires a high resolution geochronology in order to accurately identify and differentiate between historically documented events. Dating sediments deposited in the last few centuries is difficult due to the uncertainty range of radiocarbon ages, bioturbation, and anthropogenic disturbance of systems. Here we show a variety of proxy records throughout the top 2 m of sediment in Carpinteria Marsh, southern California including charcoal, grain size, pollen, scanning XRF, and spheroidal carbon particle stratigraphies. We use the combination of these records to correlate stratigraphy and identify sedimentological evidence of documented historical storm occurrences, tsunami impacts, land use changes, and fire events. We show the sedimentation rate of the historical period varies from ~1 mm/yr to 5 mm/yr throughout the marsh, while long term rates of sedimentation are ~2 mm/yr. Sedimentation rates are also not consistent temporally, since the record is punctuated by periods of rapid or absent deposition. Multi-proxy comparisons can aid attempts to identify evidence of historical coastal hazards and correlate deposits despite variability in sedimentary processes throughout an estuary.