Cortes Basin

Interplay between tectonics and submarine mass transport deposits in Cortes Basin: novel high-resolution geophysics in the Outer California Borderland

https://doi.org/10.7284/909885 

Abstract - Episodic submarine mass transport deposits (MTDs) have been identified through high-resolution sub-bottom data collected within the fault-bounded Cortes Basin in the Outer California Borderland (OCB). This study presents new high-resolution bathymetric and sub-bottom datasets that allow for detailed mapping and reconstruction of the depositional history of MTDs and slope failures in the basin. The Cortes Basin, extending ~3,600 km², is about 170 km offshore from San Diego, California. It is bounded by steep slopes and has a NW-SE orientation, with a central ridge that divides the basin into two asymmetric depocenters: East and West Cortes Basin. Our high-resolution bathymetric data reveal deformational features, including slide scarps and newly identified fault segments, some of which show evidence of Holocene activity. The sub-bottom profiles and the ODP Leg 167, Site 1012, allowed for the identification and dating of 10 MTDs in the East Cortes Basin (one slump-type and nine turbidity currents-type) and eight MTDs in the West Cortes Basin, that are likely records of significant ground motion that has occurred within the OCB. The estimated cumulative volume of the mass wasting events exceeds 5 km³, affecting an area of up to 737 km² (i.e., MTD IV), with a recurrence interval of approximately 75ka. Potential failure synchronicity across Cortes Basin suggests that the imaged mass wasting events are likely triggered by strong ground motion and/or glacio-eustatic fluctuations of the late Quaternary. The shallowest MTD observed in the West Cortes Basin, is a surficial, near-bottom slump that originated by flow transformation, possibly driven by local slope collapse of the gully drainage. The proximal slump is characterized by an erosional base and sediment waves at the seafloor, while the distal turbidity current is thinner and pinches out at the toe of the deposit. The proximity of stacked MTDs to active fault segments suggests that earthquake ground motion within the basin may trigger mass wasting events. Additionally, the upward termination of the fault at stratigraphic levels, often coinciding with MTD horizons, supports the idea that fault activity triggers MTDs. Although the MTDs identified in Cortes Basin are located relatively far from the densely populated Southern California coastline, still pose a potential tsunamigenic hazard that requires further investigation. Additionally, if related to earthquakes along strike-continuous faults, e.g., the Ferrelo fault, the MTDs could serve as valuable geological proxies for reconstructing the seismic and slope failure history of the relatively understudied OCB.