Tracking the ¹⁰Be–²⁶Al source-area signal in sediment-routing systems of arid central Australia

• Main Authors: M. Struck, J. D. Jansen, T. Fujioka, A. T. Codilean, D. Fink, R.-H. Fülöp, K. M. Wilcken, D. M. Price, S. Kotevski, L. K. Fifield, J. Chappell
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-05-01
• Series: Earth Surface Dynamics
• Online Access: https://www.earth-surf-dynam.net/6/329/2018/esurf-6-329-2018.pdf

Sediment-routing systems continuously transfer information and mass from eroding source areas to depositional sinks. Understanding how these systems alter environmental signals is critical when it comes to inferring source-area properties from the sedimentary record. We measure cosmogenic ¹⁰Be and ²⁶Al along three large sediment-routing systems ( ∼  100 000 km²) in central Australia with the aim of tracking downstream variations in ¹⁰Be–²⁶Al inventories and identifying the factors responsible for these variations. By comparing 56 new cosmogenic ¹⁰Be and ²⁶Al measurements in stream sediments with matching data (<i>n</i> =  55) from source areas, we show that ¹⁰Be–²⁶Al inventories in hillslope bedrock and soils set the benchmark for relative downstream modifications. Lithology is the primary determinant of erosion-rate variations in source areas and despite sediment mixing over hundreds of kilometres downstream, a distinct lithological signal is retained. Post-orogenic ranges yield catchment erosion rates of  ∼  6–11 m Myr⁻¹ and silcrete-dominant areas erode as slow as  ∼  0.2 m Myr⁻¹. ¹⁰Be–²⁶Al inventories in stream sediments indicate that cumulative-burial terms increase downstream to mostly  ∼  400–800 kyr and up to  ∼  1.1 Myr. The magnitude of the burial signal correlates with increasing sediment cover downstream and reflects assimilation from storages with long exposure histories, such as alluvial fans, desert pavements, alluvial plains, and aeolian dunes. We propose that the tendency for large alluvial rivers to mask their ¹⁰Be–²⁶Al source-area signal differs according to geomorphic setting. Signal preservation is favoured by (i) high sediment supply rates, (ii) high mean runoff, and (iii) a thick sedimentary basin pile. Conversely, signal masking prevails in landscapes of (i) low sediment supply and (ii) juxtaposition of sediment storages with notably different exposure histories.