Centennial- to millennial-scale hard rock erosion rates deduced from luminescence-depth profiles

Abstract

The measurement of erosion and weathering rates in different geomorphic settings and over diverse temporal and spatial scales is fundamental to the quantification of rates and patterns of earth surface processes. A knowledge of the rates of these surface processes helps one to decipher their relative contribution to landscape evolutioninformation that is crucial to understanding the interaction between climate, tectonics and landscape. Consequently, a wide range of techniques has been *Manuscript Click here to view linked References 2 developed to determine short-(<10 2 a) and long-term (> 4 a) erosion rates. However, no method is available to quantify hard rock erosion rates at centennial to millennial timescales. Here we propose a novel technique, based on the solar bleaching of luminescence signals with depth into rock surfaces, to bridge this analytical gap. We apply our technique to glacial and landslide boulders in the Eastern Pamirs, China. The calculated erosion rates from the smooth varnished surfaces of 7 out of the 8 boulders sampled in this study vary between < 0.038±0.002 and 1.72±0.04 mm ka-1 (the eighth boulder gave an anomalously high erosion rate, possibly due to a recent chipping/cracking loss of surface). Given this preferential sampling of smooth surfaces, assumed to arise from grain-by-grain surface loss, we consider these rates as minimum estimates of rock surface denudation rates in the Eastern Pamirs, China.

Luminescence as a Sediment Tracer and Provenance Tool

“…In general, the relationship between light and heat is complex and it is well known from the laboratory experiments that ambient temperature governs the optical depletion rate (Bøtter‐Jensen et al, ; Jain & Ankjærgaard, ; Wintle & Murray, ). The model equations describing the growth and depletion of a certain luminescence signal set the basis for techniques such as thermochronology and/or thermometry (e.g., Brown et al, ; Rengers et al, ; Spencer & Sanderson, ), exposure and erosion (Sohbati et al, ), and sediment transport (McGuire & Rhodes, ).…”

“…The use of luminescence to directly quantify geomorphic processes is an important research frontier (Heimsath & Ehlers, ). The potential applications of luminescence are rapidly expanding to provide new quantitative insights into geomorphic processes such as exhumation using OSL (Herman et al, ) and TL (Biswas et al, ; Brown et al, ), soil mixing and transport (Furbish, Schumer, et al, ; Reimann et al, ), surface exposure (Sohbati et al, ) and surface erosion (Sohbati et al, ; Guralnik & Sohbati, ), source area weathering and erosion (Haddadchi et al, ; Sawakuchi et al, ), fluvial sediment transport (Gray et al, ; McGuire & Rhodes, ), and coastal sediment transport (Ahmed et al, ; Reimann et al, ). Luminescence can provide quantitative sediment transport data from source to sink (Figure ) including the identification of provenance (Figure ).…”

Evaluating post-glacial bedrock erosion and surface exposure duration by coupling in-situ OSL and &lt;sup&gt;10&lt;/sup&gt;Be dating

“…(1) describes the electron-trapping rate in response to ambient radiation with ̇( ) the environmental dose rate [Gy a -1 ] at depth [m] and 0 the characteristic dose [Gy]. In the context of bedrock surface exposure dating, the dose rate can be approximated as a depth-independent constant in the case of homogeneous lithology i.e., ̇( ) = (e.g., Sohbati et al, 2018). 25…”

“…Recently, Sohbati et al (2018) showed that surface erosion has to be taken into consideration when OSL surface exposure dating is applied to natural bedrock surfaces. Indeed, removal of material would bring the bleaching front towards the surface, which may lead to a considerable underestimation of the OSL surface exposure age if not accounted for.…”

“…In practice, when erosion is 25 maintained long enough, an equilibrium between trapping, bleaching (i.e., detrapping) and erosion is reached, consequently the bleaching profile reaches steady state. Sohbati et al (2018) explained that the sensitivity difference to erosion between TCN and OSL surface exposure dating can be exploited to calculate erosion rate experienced by rock surfaces. Indeed, TCN dating is mainly sensitive to cosmic rays over the top ~50-60 cm below the exposed bedrock surface (depending on rock density; Lal et al, 1991) while OSL surface exposure dating is sensitive to light penetration of only millimeters to centimeters 30 (Sohbati et al, 2011(Sohbati et al, , 2012a(Sohbati et al, , 2012b.…”