CRC 1211 “Earth – Evolution at the dry limit”, Project C2: Transport and deposition

  Dissection of the Coastal Cordillera in the hyperarid Atacama Desert Copyright: J. Walk

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Janek Walk

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+49 241 80 96049

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Phase 2 (2020/2 – 2024/1): Deciphering the late Neogene and Quaternary evolution of alluvial fans along the coastal ranges in the Atacama and Namib deserts

After a very successful first phase of the Collaborative Research Centre 1211, for short CRC 1211 (see below), our subproject C2 also entered the second phase in July 2020. Our research associate Dr. Janek Walk is working on this project with the support of Dr. Dominik Brill of the Institute of Geography at the University of Cologne, Dr. Tobias Ullmann of the Institute of Geography and Geology of the Julius-Maximilians-University of Würzburg, Anna Nguno of the Geological Survey of Namibia and Andrés Quezada of the Geological Survey of Chile on new interdisciplinary questions concerning the Quaternary to Neogene landscape development of the coastal deserts in northern Chile and northwestern Namibia as well as the interaction between fluvial, aeolian, and marine processes there.

 
Schematic landscape transects through the Atacama and Namib Copyright: J. Walk Landscape transects through (top) the Atacama Desert in North Chile and (bottom) the Skeleton Coast and its hinterlands in Northwest Namibia.

Research objectives

On the one hand, we will investigate the transport and sedimentation dynamics under hyperaridity from the coast of the Atacama into the interior Coastal Cordillera. On the other hand, an intercontinental comparison between the external control of alluvial fan morphodynamics at the active continental margin of northern Chile and the passive continental margin at the Skeleton Coast in northwestern Namibia will be made. In close cooperation with the other subprojects in the CRC, the influence of Loma vegetation on sediment supply in the Atacama Desert is also being investigated. A further research question deals with the function of surface texture and spectral signatures as well as weathering and soil formation intensity for morphostratigraphic characterizations.

Methods

Within the four years, several field campaigns are planned in the Coastal Cordillera of the Atacama as well as to the Skeleton Coast. In this project, Dr. Janek Walk will apply proven methods from the first phase together with a portfolio of new methods. The focus will remain on remote sensing in combination with geochronological analyses. Hydromorphometric, climatic, and geological spatial as well as trend analyses in Northwest Namibia will be compared with those from the Atacama Desert. In addition, a better understanding of heavy rainfall events on the fluvial morphodynamics in hyperarid deserts will be achieved by a combination of high-resolution remote sensing and in-situ measurements. Furthermore, the genesis of sedimentary landforms – mainly alluvial fans – will be studied chronologically by a combination of cosmogenic nuclide dating and luminescence dating. Finally, the composition of the individual results will provide new insights into the geomorphological processes and the landscape genesis of hyperarid regions.

 
Sampling for surface exposure dating Copyright: G. Stauch Sampling for dating the alluvial fan surface using cosmogenic nuclides.

Phase 1 (2016/2 – 2020/1): Deciphering the evolution of the alluvial fans between 21°S and 25°S – the interplay between climatic and tectonic control

Since the beginning of 2017, as part of the CRC 1211, "Earth – Evolution at the dry limit", we have been working together with the working group for Geoarchaeology, Coastal Morphology and Geochronology of the University of Cologne under the direction of Professor Helmut Brückner on the subproject "Transport and deposition", in which the development of alluvial fans along the coast of the hyperarid Atacama desert from about 21 to 25 degrees south are investigated. With the help of remote sensing analysis and detailed mapping, the alluvial fan surfaces as well as the drainage basins are to be geomorphologically characterized. In addition, stratigraphic investigations in combination with various numerical dating methods serve to assign absolute ages to the alluvial fan generations.

Methods

Within this project the PhD study of our scientific employee Janek Walk is settled. On the one hand his focus is on the remote sensing-based geomorphological analysis. On the other hand he is working on the exposure dating of the various alluvial fan surfaces using in-situ produced cosmogenic nuclides. Melanie Bartz, our colleague from the working group for Geoarchaeology, Coastal Morphology and Geochronology, specializes in the dating of alluvial fan sediments using optically stimulated luminescence, for short OSL, and electron spin resonance, for short ESR.

  Field work at an alluvial fan Copyright: J.-P. Francois Field work at the alluvial fan Guanillos.

Field works

Following an introductory workshop of the CRC 1211 at Hornitos, longer field work was carried out in March 2017 in the northern part of the study area, supported by two Chilean colleagues. In addition to the geomorphological mapping of several alluvial fans and the associated catchments, numerous sediment and rock samples were obtained for the various dating procedures. The samples are currently being processed.

In March and April as well as in September 2018, we conducted further field campaigns with a focus on the southern part of the study area between Antofagasta and Taltal. Several interesting and well-developed coastal alluvial fans were included into the research.

  Alluvial fan at Quebrada de Izcuña Copyright: J. Walk Coastal alluvial fan at Quebrada de Izcuña close to Caleta Botija.

The exciting impressions from the field work motivated us to offer a student excursion to northern Chile in the summer of 2018.

Conclusion

The first phase of the project expired in June 2020. During this phase, new insights into the morphology, primary processes, and Late Pleistocene evolution of the coastal alluvial fans of the Atacama Desert, the associated paleoenvironmental conditions along a latitudinal climate gradient, as well as methodological advances in pIR-IRSL and ESR dating were obtained and published internationally:

  • Bartz, M., Duval, M., Brill, D., Zander, A., King, G.E., Rhein, A., Walk, J., Stauch, G., Lehmkuhl, F., Brückner, H. (2020). Testing the potential of K-feldspar pIR-IRSL and quartz ESR for dating coastal alluvial fan complexes in arid environments. Quaternary International, in press. doi:10.1016/j.quaint.2020.03.037
  • Bartz, M., Walk, J., Binnie, S., Brill, D., Lehmkuhl, F., Hoffmeister, D., Brückner, H. (2020). Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile). Global and Planetary Change 190, 103091. doi:10.1016/j.gloplacha.2019.103091
  • Walk, J., Stauch, G., Bartz, M., Brückner, H., Lehmkuhl, F. (2019). Geomorphology of the coastal alluvial fan complex Guanillos, northern Chile. Journal of Maps 15, 436–447. doi:10.1080/17445647.2019.1611499
  • 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. doi:10.1016/j.gloplacha.2019.102994

Furthermore, the thematic results are also published in the cumulative dissertation by Janek Walk:

  • Walk, J. (2020). Alluvial fans along the coastal Atacama Desert – landforms, processes, and evolution. Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen. doi: 10.18154/RWTH-2020-06003
 
Duration 1st phase: 2016/2 - 2020/1
2nd phase: 2020/2 - 2024/1
Funding DFG SFB1211
Project partners

1st phase:
Dr. Melanie Bartz Insitute of Geography, University of Cologne
Prof. Dr. Helmut Brückner Insitute of Geography, University of Cologne

2nd phase:
Dr. Dominik Brill – Insitute of Geography, University of Cologne

Associated partners 2nd phase:
Dr. Tobias Ullmann – Institute of Geography and Geology, University Würzburg
Anna Nguno – Geological Survey of Namibia
Andrés Quezada – Servicio Nacional de Geología y Minería, Chile