 |
| Titel |
Constraints on sediment transfer from the Andes to the coast of northern Chile |
| VerfasserIn |
Steven Binnie, Ariane Liermann, Tibor Dunai, Alfred Dewald, Stefan Heinze |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077202
|
|
|
|
|
|
| Zusammenfassung |
| While rates of denudation have been suggested as having the potential to link tectonic
processes with climate in many settings, the roles that sediment transport must also
play have been largely neglected. It is the transport, or not, of eroded material, not
necessarily the rate at which that material is produced which is the critical factor in
many models of tectonic-climatic interactions. The notable lack of sediment in
sections of the Peru-Chile trench has been implicated as a key control of subduction
zone processes and consequently Andean mountain building, but little empirical
data on sediment transport in the region exists. Here, we present the initial results
of a study aiming to constrain the westward transfer of sediment from the Andes
Mountains to the Pacific Coast of northern Chile by using in situ-produced cosmogenic
nuclides. Fluvial sediments were collected at the mouths of several large catchments
between 19Ë S and 26Ë S, where they drain into the Pacific, and also from upstream
locations within each catchment. Sample sites were selected in order to investigate the
cosmogenic nuclide derived basin-averaged denudation rates of the western flank
of the Andes, and to compare this with the cosmogenic nuclide concentrations
of fluvial sediments further downstream where the catchments exit to the coast.
A simplistic interpretation of the cosmogenic 10Be concentrations as denudation
rates gives results varying between ~10 and 300 m/Myr. We would expect the
most rapid erosion to occur on the steeper, wetter western Andean flank and for
slower erosion to be recorded from the more gentle sloping, hyperarid/arid regions
between the foothills of the Andes and the Pacific coast. This pattern is observed
in some basins but in others the nuclide concentrations imply the opposite, with
several-fold higher erosion rates measured for the large catchments sampled at the coast in
comparison to their mountainous Andean headwaters. One explanation for this
unusual pattern of rates is that during travel downstream the modern alluvium is
being amalgamated with previously stored sediments that have lost 10Be by decay,
thus lowering the average nuclide concentration and artificially inflating apparent
erosion rates. The partner cosmogenic 26Al concentrations for the above 10Be results
are pending and will also be presented. The differential decay between these two
radionuclides after burial allows us to test the above explanation and constrain the potential
mixing ratios of stored and non-stored sediments. In turn these results can be used to
identify sources for the sediments currently being transported offshore. Potential
lag-times between sediment generation and offshore deposition after transport across,
or storage in, the hyperarid desert regions could complicate the cause and effect
relationships proposed to exist between climate, erosion and mountain building in
this region. Mechanisms controlling sediment routing thus become a key variable. |
|
|
|
|
|
|