Abstract

The Eocene Poway Conglomerate on San Miguel and San Nicolas Islands and age-equivalent turbidite sands on Santa Rosa Island appear to be parts of a bathyal fan deposit with an apex and source lying east of the halfway point between Santa Rosa and San Nicolas Islands. Palinspastic reconstruction along a proposed East Santa Cruz Basin fault system with 120 to 160 km of right slip aligns this bathyal point source with the compositionally equivalent Eocene river and shallow marine gravels of the type Poway Conglomerate in the San Diego area. Paleocurrent indicators in the Miocene San Onofre Breccia on Santa Cruz Island and the geometry of schist-bearing strata in the subsurface of the Santa Barbara Channel can be explained by right slip of the southern part of Santa Cruz Island from the southeast along the same fault system. Basement rock types in the borderland place no constraints on the proposed reconstruction, although they do constrain models involving large-scale westerly drift. The ridge and basin bathymetry of the central borderland is consistent with a strike-slip tectonic regime.

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