EGU2020-7461
https://doi.org/10.5194/egusphere-egu2020-7461
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Coupled controls of climate, geology, and biota on late Pleistocene alluvial fan morphodynamics along the coast of the hyperarid Atacama Desert

Janek Walk1, Melanie Bartz2, Georg Stauch1, Mark Reyers3, Steven A. Binnie4, Dominik Brill2, Paulina Vásquez5, Fernando A. Sepúlveda5, Dirk Hoffmeister2, Helmut Brückner2, and Frank Lehmkuhl1
Janek Walk et al.
  • 1Department of Geography, RWTH Aachen University, Aachen, Germany
  • 2Institute of Geography, University of Cologne, Cologne, Germany
  • 3Institute of Geophysics and Meteorology, University of Cologne, Cologne, Germany
  • 4Institute of Geology, University of Cologne, Cologne, Germany
  • 5Servicio Nacional de Geología y Minería, Santiago, Chile

In the hyperarid environment of the Atacama Desert, alluvial fans are the principle fluvial geo-archive reflecting variations in climate and tectonics in their architecture. While they have been studied in the core of the desert to reconstruct long-term palaeoenvironmental changes from the Oligocene to the Quaternary and, in particular, to constrain the onset of hyperaridity, alluvial fans along the coast (20.5°S – 25.5°S) are younger and show a much higher activity; thus, they can serve as archives during the Pleistocene to Holocene evolution. However, past and recent morphodynamics of the coastal alluvial fans (CAF) are yet poorly reconstructed so that the understanding of an interplay between climatic, geologic, and biotic controls is still challenging.

We related climatic, lithologic, and tectonic source-area characteristics to geomorphometric parameters of the CAF and their catchments. Geomorphometric analyses were conducted based on the 12.5 m TanDEM‑X WorldDEM™, lithological and tectonic data were extracted from regional geological maps, and the frequency of heavy rainfall events derived from a regional Weather Research and Forecasting (WRF) model was used as a climate parameter. We further combined luminescence dating, cosmogenic nuclide exposure dating, and existing chronological data to constrain the timing of Pleistocene alluvial fan deposition as well as the ages of interbedded marine terraces.

Results indicate a primary climatic control on CAF dynamics shown in the functional relationships with catchment hydromorphometrics that mirror a high susceptibility to debris-flows as well as in the temporal pattern of CAF activity. Distinct phases of CAF activity occurred during the late Pleistocene (95–80 ka, 60–45 ka, and 35-20 ka) and the Holocene – driven by atmospheric changes from the Pacific Ocean. The primary source of precipitation is reflected along the latitudinal gradient: frontal systems and cut-off lows mainly originating from the extratropics. Towards the south, an increasing density of Loma vegetation can be observed so that also possible feedback mechanisms of biota on sediment supply need to be considered. While source-area lithology is of negligible relevance for CAF morphodynamics, an important long-term influence of tectonics can be seen in the regional uplift, which in turn controls the catchment shape and relief. From the numerical dating of the marine terraces, uplift rates ranging between ~0.06 and ~0.57 m/ka were derived for the late Pleistocene period.

Acknowledgement: TanDEM-X WorldDEM™ data is provided by a DLR Science grant, 2017.

References:
Bartz, M., Walk, J., Binnie, S.A., Brill, D., Stauch, G., Lehmkuhl, F., Hoffmeister, D., Brückner, H., in press. Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile). Global and Planetary Change, 103091. https://doi.org/10.1016/j.gloplacha.2019.103091

Walk, J., Stauch, G., Reyers, M., Vásquez, P., Sepúlveda, F.A., Bartz, M., Hoffmeister, D., Brückner, H., Lehmkuhl, F., 2020. Gradients in climate, geology, and topography affecting coastal alluvial fan morphodynamics in hyperarid regions – The Atacama perspective. Global and Planetary Change 185, 102994. https://doi.org/10.1016/j.gloplacha.2019.102994

How to cite: Walk, J., Bartz, M., Stauch, G., Reyers, M., Binnie, S. A., Brill, D., Vásquez, P., Sepúlveda, F. A., Hoffmeister, D., Brückner, H., and Lehmkuhl, F.: Coupled controls of climate, geology, and biota on late Pleistocene alluvial fan morphodynamics along the coast of the hyperarid Atacama Desert, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7461, https://doi.org/10.5194/egusphere-egu2020-7461, 2020

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