Using 10Be and 26Al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin

Abstract

We measured 10 Be and 26 Al in 64 sediment and bedrock samples collected throughout the arid, 187 km 2 Yuma Wash drainage basin, southwestern Arizona. From the measurements, we determine long-term, time-integrated rates of upland sediment generation (81 F 5 g m À 2 year) and bedrock equivalent lowering (30 F 2 m Ma À 1 ) consistent with other estimates for regions of similar climate, lithology, and topography. In a small ( f 8 km 2 ), upland sub-basin, differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment (40 Â 10 4 kg year) than weathering of exposed bedrock surfaces (10 Â 10 4 kg year). Mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas. Hillslope colluvium is the dominant sediment source to the upper reaches of the sub-basin channel; channel cutting of alluvial terraces is the dominant source in the lower reaches. Similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times ( < 10 3 years). Nuclide concentrations, measured in channel sediment from tributaries of Yuma Wash and in samples collected along the length of the Wash, were used to construct mixing models and determine sediment sources to the main stem channel. We find an exponential decrease in the channel nuclide concentrations with distance downstream, suggesting that as much as 40% of sediment discharged from Yuma Wash has been recycled from storage within basin fill alluvium. Sediment generation and denudation rates determined from the main stem are greater (25%) than rates determined from upland sub-basins suggesting that, currently, sediment may be exported from the basin more quickly than it is being generated in the uplands. Independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material, suggesting that differences in transport times for different size materials are minimal. D

Erosion in northwest Tibet from in‐situ‐produced cosmogenic 10Be and 26Al in bedrock

“…Table II compares erosion rates obtained by the cosmogenic nuclide dating technique for extremely arid regions. While bedrock erosion rates in Antarctica, Australia and the Namib Desert are very low, at 0·1-1 mm ka −1 , the erosion rates in Yuma Wash, Arizona (Clapp et al, 2002) and Nahal Yael, Israel (Clapp et al, 2000) are much higher, c. 30 mm ka −1 . Obviously the low erosion rates in Antarctica, Australia and the Namib Desert cannot be solely attributed to the lack of water or low annual precipitation as previously suggested (Nishiizumi et al, 1991;Bierman and Turner, 1995;Bierman and Caffee, 2002).…”

Combining contemporary and long-term erosion rates to target erosion hot-spots in the Great Barrier Reef, Australia

“…To calculate the upstream integrated erosion rate at each site, the CRONUS calculator Version 2.2 (Balco et al, 2008) Brown et al, 1995), we consider the influence of grain size variation to be relatively low in this environment. Therefore, this study did not explicitly investigate the changes in 10 Be concentration with particle size, but instead relied on previous publications indicating that cosmogenic nuclide concentrations are not particularly sensitive to changes in grain size (Clapp et al, 2002;Lupker et al, 2012;Safran et al, 2005).…”

“…Therefore, in this study, we used in-situ 10 Be (herein referred to as 10 Be), which is found in very small concentrations within quartz based sediments. Its concentration does not vary significantly with particle size (Clapp et al, 2002). Due to its long half-life (1.4 Ma), 10 Be is a useful integrator of upstream erosion rates over large spatial scales (Binnie et al, 2006;Hippe et al, 2012;Ivy-Ochs and Schaller, 2010).…”

&lt;sup&gt;10&lt;/sup&gt;Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

“…Glacial erosion is not properly accounted for, as sediments eroded under a glacier are shielded from cosmic rays and, hence, supply sediment with very low TCN concentrations independent of glacial erosion rates (Godard et al, 2012;Delunel et al, 2014). Different erosion processes also affect the final grain size of fluvially exported sediment, which may in turn lead to a grain size dependence of TCN signals that needs to be taken into account in order to derive robust CWDRs (Clapp et al, 2002;Belmont et al, 2007;Aguilar et al, 2014;Puchol et al, 2014;Lukens et al, 2016). The assumption of quartz ubiquity or content within the eroded lithology of a studied catchment is also likely to be violated in a number of cases and is also a source of biases in CWDR (Carretier et al, 2015a).…”