Footwall drainage evolution and scarp retreat in response to increasing fault displacement: Loreto fault, Baja California Sur, Mexico

Abstract

The displacement rate history of the Loreto fault, Gulf of California, is well documented; it is characterized by episodically accelerating displacement (10 k.y. frequency) superimposed upon a period of 200 k.y. of increasing fault displacement rate. A detailed conglomerate provenance analysis in the Loreto basin records the footwall unroofing history, which has been profoundly affected by increased fault displacement rate. Clast count data capture an immediate drainage response to a significant increase in slip rate, along with the occurrence and systematic increase in abundance of a new source rock type. Our data record an increase in the rate of incision and catchment expansion associated with this increase in displacement rate. A provenance signal from a shorter-term (100 k.y.) displacement rate increase has a 30–40 k.y. lag time. No change in provenance is recorded for high-frequency (10 k.y.) variations, which are filtered out by the system.