Sediments in rivers record the dynamics of erosion processes. While bulk sediment fluxes are easily and routinely obtained, sediment caliber remains underexplored when inferring erosion mechanisms. Yet sediment grain size distributions may be the key to discriminating their origin. We have studied grain size‐specific suspended sediment fluxes in the Kali Gandaki, a major trans‐Himalayan river. Two strategically located gauging stations enable tracing of sediment caliber on either side of the Himalayan orographic barrier. The data show that fine sediment input into the northern headwaters is persistent, while coarse sediment comes from the High Himalayas during the summer monsoon. A temporally matching landslide inventory similarly indicates the prominence of monsoon‐driven hillslope mass wasting. Thus, mechanisms of sediment supply can leave strong traces in the fluvial caliber, which could project well beyond the mountain front and add to the variability of the sedimentary record of orogen erosion.
Abstract. 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 (n= 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.
Anmerkungen zu einigen Neuerscheinungen der letzten JahreMaigrit Jüsten-Hedtrich (Red.): Kölner Kirchen und ihre Ausstattung in Renaissance und Barock 1550 bis 1800 (= Colonia Romanica 16-
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