干旱区生态环境知识资源中心

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 Be-10 and Al-26 along three large sediment-routing systems (similar to 100000 km(2)) in central Australia with the aim of tracking downstream variations in Be-10-Al-26 inventories and identifying the factors responsible for these variations. By comparing 56 new cosmogenic Be-10 and Al-26 measurements in stream sediments with matching data (n = 55) from source areas, we show that Be-10-Al-26 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 similar to 6-11 mMyr(-1) and silcrete-dominant areas erode as slow as similar to 0.2 mMyr(-1). Be-10-Al-26 inventories in stream sediments indicate that cumulative-burial terms increase downstream to mostly similar to 400-800 kyr and up to similar 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 Be-10-Al-26 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.