Episodic coastal progradation of the coastal Oxnard Plain, southern California

Julie M. Zurbuchen, Alexander R. Simms, & Sebastien Huot

Published 2020, SCEC Contribution #10844

As droughts are projected to intensify over the next century, determining the coastal response is pivotal for hazard mitigation in the future. Ground-penetrating radar (GPR), in combination with radiocarbon and OSL dating methods, provide insight into the coastal response of the Oxnard Plain, southern California, to past droughts and storms through the imaging of sedimentary stratigraphy. GPR profiles contain three radar facies and two surfaces, which show both cut and fill structures as the beach accreted and eroded, and aeolian deposits. For the first time, beach cusps are recognized in shore-parallel profiles as concave up surfaces. Progradation rates at the 150- to 200-year timescale along the coastal Oxnard Plain have remained relatively constant, prograding at rates between 0.3 to 1.4 m a-1. However, on decadal timescales progradation has been episodic through time, with episodes of progradation after large floods along the nearby Santa Clara River, while periods of non-progradation during prolonged droughts result in the erosion of up to 90 m of the shoreline, equivalent to 5 to 120 years of the sediment record. Erosional surfaces often used to reconstruct past storms and tsunamis are more likely to be preserved in locations marked by higher rates of progradation, such as closer to the Santa Clara River delta.

Key Words
Ventura Fault

Citation
Zurbuchen, J. M., Simms, A. R., & Huot, S. (2020). Episodic coastal progradation of the coastal Oxnard Plain, southern California. Journal of Coastal Research, 36, 1130-1144. doi: https://doi.org/10.2112/JCOASTRES-D-19-00125.1.