Climate-driven unsteady denudation and sediment flux in a high-relief unglaciated catchment-fan using Al-26 and Be-10: Panamint Valley, California

摘要

Environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics. However, empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi-millennial timescales. Tectonic boundary conditions and climate history in the Panamint Range, California, are relatively well-constrained by existing low-temperature thermochronology and regional multi-proxy paleoclimate studies, respectively. Catchment-fan systems present there minimize sediment storage and recycling, offering an excellent natural laboratory to test models of climate-sedimentary dynamics. We used stratigraphic characterization and cosmogenic radionuclides (CRNs; Al-26 and Be-10) in the Pleasant Canyon complex (PCC), a linked catchment-fan system, to examine the effects of Pleistocene high-magnitude, high-frequency climate change on CRN-derived denudation rates and sediment flux in a high-relief, unglaciated catchment-fan system. Calculated Al-26/Be-10 burial ages from 13 samples collected in an similar to 180 m thick outcropping stratigraphic succession range from ca. 1.55 +/- 0.22 Ma in basal strata, to ca. 0.36 +/- 0.18-0.52 +/- 0.20 Ma within the uppermost part of the succession. The mean long-term CRN-derived paleodenudation rate, 36 +/- 8 mm/kyr (1 sigma), is higher than the modern rate of 24 +/- 0.6 mm/kyr from Pleasant Canyon, and paleodenudation rates during the middle Pleistocene display some high-frequency variability in the high end (up to 54 +/- 10 mm/kyr). The highest CRN-derived denudation rates are associated with stratigraphic evidence for increased precipitation during glacial-pluvial events after the middle Pleistocene transition (post ca. 0.75 Ma), suggesting 100 kyr Milankovitch periodicity could drive the observed variability. We investigated the potential for non-equilibrium sedimentary processes, i.e. increased landslides or sediment storage/recycling, to influence apparent pal