Mechanisms of late Quaternary fault throw-rate variability along the north central Gulf of Mexico coast: implications for coastal subsidence

Quaternary sea-level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw-rate variability over 10(3) to 10(5)year time scales. Here we present 11 mean throw rates for the Tepetate-Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca.0.22mmyear(-1) during the late Holocene, ca. 0.03mmyear(-1) during the last glacial and at least 0.07mmyear(-1) during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea-level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land-surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.