Steady 10Be-derived paleoerosion rates across the Plio-Pleistocene climate transition, Fish Creek-Vallecito basin, California

Rates of erosion over time provide a valuable tool for gauging tectonic and climatic drivers of landscape evolution. Here we measure Be-10 archived in quartz sediment from the Fish Creek-Vallecito basin to resolve a time series of catchment-averaged erosion rates and to test the hypothesis that aridity and increased climate variation after approximately 3Ma led to an increase in erosion rates in this semiarid, ice-free setting. The Fish Creek-Vallecito basin, located east of the Peninsular Ranges in Southern California, is an ideal setting to derive a Plio-Pleistocene paleoerosion rate record. The basin has a rapid sediment accumulation rate, a detailed magnetostratigraphic age record, and its stratigraphy has been exposed through recent, rapid uplift and erosion. A well-defined source region of uniform lithology and low erosion rate provides a high, reproducible Be-10 signal. We find that paleoerosion rates were remarkably consistent between 1 and 4Ma, averaging 3824m/Myr (2 sigma). Modern catchment-averaged erosion rates are similar to the paleoerosion rates. The uniformity of erosion over the past 4Myr indicates that the landscape was not significantly affected by late Pliocene global climate change, nor was it affected by a local long-term increase in aridity.