FLOODS, STORMS, AND THE IDENTIFICATION OF WAVE-DOMINATED DELTAS: INSIGHTS FROM GROUND-PENETRATING RADAR PROFILES OF THE VENTURA-OXNARD COASTAL PLAIN

Distinguishing wave-dominated deltas from prograding clastic shorelines is a difficult task in ancient rock settings due to their lithological similarities. However, it is an important distinction in reconstructing past paleogeography essential in interpreting the rock record. Here we present ground-penetrating radar (GPR) profiles collected through the wave-dominated Santa Clara River Delta and other locations along the Ventura-Oxnard coastal plain of the southern California Coast. The GPR profiles reveal repeated packages of landward dipping reflections bordered on their seaward edge by an unconformable seaward dipping reflector. We interpret these landward dipping packages as the infilling of paleo-lagoons that formed after large flood-events on the Santa Clara River. After the flooding of January 2005 a small lagoon formed between a fluvially-derived offshore bar and the mainland and infilled slowly over the next several years. The packages of landward dipping reflections in our GPR profiles may represent the preserved sedimentary record of the infilling of these paleo-lagoons. Their documentation may provide a key criteria for identifying wave-dominated deltas in the ancient rock record. In addition, the GPR profiles from the Ventura-Oxnard coastal plain also contain several high-amplitude paleo-erosional scarps that likely represent coastal erosion of the delta front during past storms or potentially tsunamis.