 |
| Titel |
A modern analog of past climatic impacts on sedimentary processes and landscape evolution in an intermontane basin: The Del Medio fan, NW Argentina |
| VerfasserIn |
Sara Savi, Taylor F. Schildgen, Stefanie Tofelde, Hella Wittmann, Manfred Strecker |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091772
|
| Publikation (Nr.) |
 EGU/EGU2014-6081.pdf |
|
|
|
|
|
| Zusammenfassung |
| The combined effects of tectonic and climatic forcing govern the evolution of landscapes,
setting the scale of topographic relief and the pace of landscape changes over time. Tectonic
uplift or changes in precipitation regimes can fundamentally modify erosional processes
and sediment flux from hillslopes, change river profiles, and ultimately impact
depositional systems downstream. The complexity of the response, however, often
means that we cannot predict a priori how a given landscape will react to future
changes in climate, or how it responded in the past to multiple episodes of climate
change.
The Del Medio catchment is located in the southern part of the Humahuaca Basin, an
intermontane valley within the Eastern Cordillera in transition to the Puna Plateau. This area
coincides with a climatic and vegetation divide between a sub-humid environment
downstream and the semi-arid upper Humahuaca Basin. An extensive fan sourced in the Del
Medio catchment covers ca. 18.6 km2 of the basin outlet. The fan stratigraphy and surface
morphology suggest that the fan dynamics are dominated by debris-flow processes. The
surface comprises abandoned channels, levees and lobes, while exposed sections in channel
cuts reveal unsorted, matrix-dominated deposits, with individual boulders reaching a diameter
of 5 m. To investigate rates and timing of the Del Medio fan evolution, we analyzed
cosmogenic 10Be concentrations on the surfaces of large boulders from the fan surface, river
sands in active channels, a depth profile, and bedrock exposed atop the drainage basin
margins. Our preliminary CRN results illustrate the rapid rate at which the active
fan surface is subject to change, with each of the 11 analyzed boulder samples
providing ages of < 200 years. In addition, river sands record very high denudation rates
that range from several mm/yr to tens of mm/yr, despite bedrock denudation rates
from the basin margins of only 0.04 mm/yr. These contrasting denudation rates
likely result from frequent landsliding and debris flows along the steep slopes of
the catchment area, which generates sediment of near-zero cosmogenic nuclide
concentrations.
Farther upstream in the more arid Humahuaca Basin, abandoned fluvial terrace sequences
that exceed 100 m in thickness have been linked to wetter episodes during the late
Quaternary. Within those fills, preliminary paleo-denudation rates reach values similar to
those currently observed in the Del Medio catchment, while modern denudation rates from
river sands are similar to the low rates observed from bedrock samples. Taken together, these
observations indicate that the Del Medio fan could be a modern analog of those older fill
sequences, providing a unique opportunity to link present-day processes in the Del Medio
catchment to those that were likely active in the past during wetter climate episodes in the
Humahuaca Basin. |
|
|
|
|
|
|