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The depositional records of two coastal lakes in south-central Chile (Lago Lanalhue and Lago Lleu Lleu, 38°S): Active forearc tectonics and climate variability
Echtler, H. P. ; Stefer, S.; Moernaut, J.; Melnick, D.; Arz, H. W. ; Lamy, F.; Haug, G. H. (2008). The depositional records of two coastal lakes in south-central Chile (Lago Lanalhue and Lago Lleu Lleu, 38°S): Active forearc tectonics and climate variability. Eos, Trans. (Wash. D.C.) 89(53): H33C-1019
In: Eos, Transactions, American Geophysical Union. American Geophysical Union: Washington, etc.. ISSN 0096-3941, more
Peer reviewed article  

Available in Authors 
Document type: Summary

Keyword
    Marine
Author keywords
    Geomorphology: general; Modeling; Sedimentation; Sediment transport; Marine sediments: processes and transport

Authors  Top 
  • Echtler, H. P.
  • Stefer, S.
  • Moernaut, J., more
  • Melnick, D.
  • Arz, H. W.
  • Lamy, F.
  • Haug, G. H.

Abstract
    On millennial time scales, the southern Chilean active margin is not only characterized by active tectonics and subduction-related coastal deformation, but also influenced by pronounced variations in the prevailing climate conditions. Here we focus on the depositional records of two coastal lakes in the southern part of the Arauco Peninsula (38°S, Lago Lanalhue and Lago Lleu Lleu), an area very sensitive to changes in both climate and tectonics. For the present study, we used a multi-proxy approach including seismic reflection surveys, sedimentological, mineralogical, and geochemical analyses, supported by radiocarbon dating. Seismic reflection analyses reveal that Lago Lanalhue and Lago Lleu Lleu developed within former river valleys that once drained into the Pacific Ocean. During the early Holocene, the ancient rivers were dammed by rising sills due to inverse faulting and tectonic uplift, turning first into marginal-marine lagoonal systems and subsequently evolving into lakes. On the basis of sedimentological analyses and radiocarbon dating, the different stages of the lakes development have been reconstructed in consideration of the regional tectonic and climatic history. The comparison of the transitions between different stratigraphic units with contemporaneous variations in the global sea level, allowed the calculation of Holocene uplift rates. These are about twenty times higher for the upraised sills than for the lakes themselves. Therefor, we interpret the sills to be the surface expression of a blind thrust associated with a prominent inverse fault (Morguilla Fault) controlling uplift and folding of the Arauco Peninsula. Geochemical data from the lacustrine part of the sedimentary sequences reveal a continuous record of the middle to late Holocene regional climate history. The results indicate more arid conditions during the middle Holocene and more humid conditions during the late Holocene. An additional increase in climate variability is recorded during the last 2000 years. Our study demonstrates the use of lake sediments to decipher time-integrated landscape evolution by quantifying tectonic deformation and climate variability.

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