The origins and implications of paleochannels in hyperarid, tectonically active regions: the northern Atacama Desert, Chile

Binnie, S.A. et al. (2020) The origins and implications of paleochannels in hyperarid, tectonically active regions: the northern Atacama Desert, Chile. Global and Planetary Change, 185, 103083. (doi: 10.1016/j.gloplacha.2019.103083)

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Preserved remnants of fluvial activity in deserts constitute evidence for changing boundary conditions. The Atacama Desert of northern Chile is the global end-member for aridity, so the history of relict stream networks in this region is a record of how landscapes develop under extreme conditions. On Pampa de Tana in northern Chile (19.4°S), a series of channel forms that are presently inactive but in the past flowed westward are incised into the surface of a fault bounded, topographically elevated portion of the El Diablo Formation, a regionally extensive, relict pediment. We measure cosmic-ray produced 10Be, 26Al and 21Ne in fluvial deposits to date the timing of abandonment of three channels and couple this with topographic profile information from a SPOT-6 derived, 2 m resolution digital elevation model. We find two of the channels were abandoned approximately >5.6 Myr and 2.0 Myr ago. One channel is still capable of flow and has ages suggesting it was fluvially active within the last few hundred thousand years. Using the paleochannel ages measured here and published ages for the end of aggradation of the El Diablo Formation we estimate the rates of fluvial channel incision before channel abandonment, and uplift rates on the faults after channel abandonment. Maximum uplift rates of ~12 m/Myr over the last 2 Myr are found. In general, while rates of uplift are relatively low they are several-fold more rapid than the rates of fluvial incision prior to channel abandonment. This implies that westward channel flow was interrupted by uplift of topography above a blind NW-SE striking reverse fault that affects the Central Depression, an alluvial forearc basin. We consider also that shrinkage of the upstream catchment area by stream capture, promoted via headward erosion and lateral expansion of adjacent canyons (quebradas) could be a factor in the abandonment of the channels on Pampa de Tana. Our results highlight the polygenetic nature of this landscape and show that relatively minor amounts of fault displacement in hyperarid regions can have implications for stream network evolution. Even subtle topographic uplift upstream should be taken into account when fluvial deposits are used as proxies for long-term environmental conditions.

Item Type:Articles
Additional Information:This work was funded in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 268236062 – SFB 1211.
Glasgow Author(s) Enlighten ID:Freeman, Professor Stewart and Stuart, Professor Fin
Authors: Binnie, S.A., Reicherter, K.R., Victor, P., Gonzalez, G., Binnie, A., Niemann, K., Stuart, F.M., Lenting, C., Heinze, S., Freeman, S.P.H.T., and Dunai, T.J.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Global and Planetary Change
ISSN (Online):1872-6364
Published Online:18 November 2019
Copyright Holders:Copyright © 2019 Elsevier B.V.
First Published:First published in Global and Planetary Change 185: 103083
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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