--> On the source-to-sink relationships of the Capistrano Formation, onshore and offshore Orange County, California

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On the source-to-sink relationships of the Capistrano Formation, onshore and offshore Orange County, California

Abstract

Previous studies of the source-to-sink system of the Capistrano Formation focused on the provenance of clasts and sedimentology within the San Juan Creek catchment area, analysis of clasts and sedimentary fill sequences in the catchment and in outcrops at Dana Point Harbor, and log interpretations from onshore wells. Recent analysis of 1960’s vintage 2D reflection seismic from offshore Dana Point and San Clemente further supports a connection between the modern-San Juan Creek Watershed in Orange County, California which provided sediments that are now exposed in Mio-Pliocene Capistrano Formation at Dana Point Harbor; and seismically and well-log-data constrained submarine fan lobe deposits in the Capistrano Embayment of the Southern California Borderlands. The Dana Point Harbor section of the Capistrano is a channelized gorge-fill deposit fed by traction and debris flows sourced from the 456 square kilometer proto-San Juan Creek catchment. These deposits are envisioned to feed a partially seismically characterized channelized submarine fan which ranges in size from 215 sq. km. to in excess of 745 sq. km. A likely size for the fan is ~366 sq. km. area extent. The fan has a maximum thickness of ~3500m (~1.0 second two way travel time) and pinches out northward and westward as it onlaps the structurally complex floor of a rifted and faulted forearc basin. Based on the seismic, the furthest extent of the fan does not exceed the modern bathymetric transition from toe-of-slope to basin floor. The Capistrano source-to-sink system fits the global source to sink relationship of Somme et al., 2009, plotting catchment area versus fan area. The Capistrano varies from the Romans and Graham, 2013 source to sink model as there is no evidence for deltaic sedimentation up-channel from the Dana Point sections, the Mio-Pliocene shelf is quite narrow, the slope is steep, and the canyon is fault bounded.