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| Titel |
100-kyr fluvial fill terrace cycles since the Middle Pleistocene in the
southern Central Andes, Toro Basin, NW Argentina |
| VerfasserIn |
Stefanie Tofelde, Taylor F. Schildgen, Bodo Bookhagen, Sara Savi, Heiko Pingel, Andrew D. Wickert, Hella Wittmann, Ricardo N. Alonso, Manfred R. Strecker |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144630
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| Publikation (Nr.) |
 EGU/EGU2017-8480.pdf |
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| Zusammenfassung |
| Fluvial fill terraces in intermontane basins are valuable sedimentary and geomorphic archives
that record tectonic and/or climate- driven changes of river networks and their adjacent
hillslopes. However, the rarely complete preservation of such geomorphic features, often
combined with large distances from sediment source areas, complicates the identification of
causal links between tectonic/climatic forcing mechanisms and landscape response,
especially over timescales of 105 to 106 years.
The intermontane Quebrada del Toro Basin in the Eastern Cordillera of NW Argentina
contains at least five fluvial terrace-surface remnants that have been sculpted into a
succession of several-hundred-meter-thick Quaternary gravel conglomerate. These terraces
can be followed over several tens of kilometers and are located in the higher part of the basin,
close to the sediment source areas. In this study, we determined the onset of multiple river
incision phases by dating the abandonment of the three most extensive and best
preserved terrace surfaces with nine cosmogenic 10Be-depth profiles. The timing of
terrace-gravel deposition is based on four cosmogenic 26Al/10Be burial ages and
U-Pb zircon age estimates of three intercalated volcanic ashes in the conglomeratic
fill.
The 10Be depth profile ages suggest a successive abandonment of these terrace surfaces
with a 100-kyr-cyclicity between 487 ± 34 ka and 75 ± 7 ka. Depositional ages
of the conglomerates, determined by 26Al/10Be burial samples and U-Pb zircon
ages, range from 936 ± 170 ka to 18 ± 141ka. They show a clear overlap with the
terrace-surface abandonment ages and thus indicate the existence of multiple cut-and-fill
cycles.
Although the initial onset of aggradation of the Quaternary gravel conglomerate at ∼1 Ma
and the overall net fluvial incision since ∼0.5 Ma can be linked to tectonic processes
affecting the narrow basin outlet, the superimposed 100-kyr-cycles of aggradation and
incision are best explained by eccentricity-driven climate change. Within these cycles, the
onset of river incision can be correlated with global cold periods that are linked with regional
humid phases recorded on the Bolivian Altiplano, 1000 km north of the Toro Basin.
Deposition, on the other hand, occurs mainly during more arid conditions on the Altiplano
(regional) and global interglacial periods.
We suggest that enhanced runoff during global cold phases – due to increased
regional precipitation, reduced evapotranspiration, or both – resulted in increased
sediment-transport capacity in the Toro Basin, which outweighed any possible increases in
upstream sediment supply and thus triggered incision. On the other hand during arid
phases, the river runoff decreases and the still high sediment supply rates result in
overall aggradation. Although located far from major ice-sheets, our study shows
that global eccentricity-driven glacial-interglacial cycles also result in significant
variations in the sediment-transport system in high mountains of the sub-tropics. |
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