Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, quantified using cosmogenic isotopes and topographic analyses

Alex Hughes, Dylan H. Rood, Duane E. DeVecchio, Alexander C. Whittaker, Rebecca E. Bell, Klaus M. Wilcken, Lee B. Corbett, Paul R. Bierman, Brian J. Swanson, & Thomas K. Rockwell

Accepted August 16, 2021, SCEC Contribution #11502

The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/-0.22 Ma to 1.06 +0.23/-0.26 Ma and our burial ages near the base of shallow marine or brackish sands, which underlie the Saugus Formation, increase eastwards from 0.55 +0.08/-0.07 Ma to 3.30 +0.30/-0.42 Ma. Our geochronology is used the calculate a rapid long-term fault throw rate of 4.7–6.3 mm yr-1 since ~1.5 Ma for the San Cayetano fault and a slip rate of 1.3–3.0 mm yr-1 since ~1.5 Ma for the Oak Ridge fault, both of which agree with contemporary reverse slip rates derived from GPS data. We also calculate terrestrial cosmogenic nuclide (TCN)-derived catchment-averaged erosion rates that range from 0.18–2.21mm yr-1 and discuss the applicability of TCN-derived catchment-averaged erosion rates in rapidly uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly uplifting, mountain belts, catchments may attain a quasi-steady state on timescales <10^5 years, even if catchment-averaged erosion rates are still adjusting to tectonic forcing.

Citation
Hughes, A., Rood, D. H., DeVecchio, D. E., Whittaker, A. C., Bell, R. E., Wilcken, K. M., Corbett, L. B., Bierman, P. R., Swanson, B. J., & Rockwell, T. K. (2021). Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, quantified using cosmogenic isotopes and topographic analyses . Geological Society of America Bulletin, (accepted).