No abstract

Sediment fingerprinting methods aim to determine the relative contribution of different source areas in detrital sediments based on natural properties – fingerprints – of the source areas. Here, we use U/Th–Pb age signatures as fingerprints, assuming that the age signal is not altered during erosion–transportation–deposition events, and given that recent technological advances enable precise dating of large amounts of grains. We introduce a formal inversion method that allows to disentangle the amalgamation of source contributions in detrital zircon data and enables to convert this information into an erosion rate map starting from the spatial distribution of zircon age signatures. Relying on the least‐squares method and using prior and covariance information to deal with non‐uniqueness, we show, using synthetic and natural examples, that we are able to retrieve erosion rate patterns of a catchment when the age distribution and zircon fertility for each source area are well known. Moreover, we show that not only zircon age fingerprints but also other tracers such as mineral content can be used. Furthermore, we found that adding data from samples taken at the outlet of tributaries improves the estimation of erosion rate patterns. We conclude that the least squares inverse model applied to detrital data has great potential for investigating erosion rates. © 2020 John Wiley & Sons, Ltd.

<p>Glacial erosion processes shape the Earth’s surface. Nevertheless, the processes that drive glacial erosion and the subsequent export of sediments are poorly understood and quantified. These processes include ice sliding, which controls erosion by abrasion and quarrying, and meltwater availability, which is essential to flush out sediment stocks that form a protective layer of sediments impeding bedrock erosion. Mapping glacial erosion rates can help understand the role of these different processes through the spatial relationships between the subprocesses and erosion rates. Here we report timeseries of glacial erosion rate maps inferred from the inversion of suspended sediment loads and their provenance. Geographically, we focus on the Gornergletscher complex (VS, Switzerland) where we collected data for the summer of 2017. The erosion rate timeseries are then compared to records of temperature, precipitation and estimates of discharge and turbidity of the meltwater river. Erosional activity seems to increase with rising temperatures and meltwater discharge, leading to an increased proportion of suspended sediments coming from the north-eastern (and occasionally western) side of the glacier. Interestingly, the peak in sediments from the north-eastern side is always preceded by a peak in sediments from the western side of the glacier. Sediments of these two zones are predominant in the suspended load signal when the maximal temperature at the Equilibrium Line Altitude (ELA) is above 10°C and on the rising limb of the hydrograph. Furthermore, the obtained erosion rate maps suggest that sliding velocities are not the only explanatory factor of the erosion rate patterns. We therefore postulate from these preliminary results that the present-day sediment output of the Gornergletscher complex is largely influenced by short term variations in temperature and meltwater availability.</p>

<p>Landscapes evolve through surface processes that are often transient in space and time. To understand the underlying geomorphic processes, one must assess how erosion rates vary spatially. This can be done using provenance analysis. Here, we introduce a formal inversion method to derive erosion patterns using detrital zircon age data as fingerprints. Zircons are omnipresent in Earth’s crust and contain information about the time since (re)crystallization in their U/Th-Pb ratio. For each geological unit having undergone a specific tectonic or magmatic history, one can find a unique age-frequency signature. Hence, erosion and sedimentation of grains originating from diverse source areas lead to a mix of the varying age-frequency signatures in sediments found at the outlet of a catchment. Considering that the age signal is not altered during erosion-transportation-deposition events, and given that recent technological advances enable precise dating of large amounts of grains, U/Th-Pb zircon ages provide an appropriate fingerprinting tool. Our inversion approach relies on the least-squares method with a priori information and model covariance to deal with non-uniqueness. We show with synthetic and natural examples that we are able to retrieve erosion rate patterns of a catchment when the age distribution for each geological unit is well known. Furthermore, relying on the nested form of catchments and their subcatchments, we demonstrate that adding samples taken at the outlet of subcatchments improves the estimation of erosion rate patterns. We conclude that the least squares inverse model applied on detrital zircon data has great potential for investigating erosion rates.</p>