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Origin and development of maar Laguna Potrok Aike, Southern Patagonia, Argentina seismic data

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Citation:
Gebhardt, C. , De Batist, M. , Niessen, F. , Anselmetti, F. S. , Ariztegui, D. , Haberzettl, T. , Ohlendorf, C. and Zolitschka, B. (2010): Origin and development of maar Laguna Potrok Aike, Southern Patagonia, Argentina seismic data , IODP/ICDP Meeting, March 9-11, 2010, Frankfurt am Main, Germany. .
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Abstract:

Seismic reflection and refraction data provide insights into the sedimentary infill and the underlying volcanic structure of Laguna Potrok Aike, a maar lake situated in the Pali Aike Volcanic Field, Southern Patagonia. The lake has a diameter of ~3.5 km, a maximum water depth of ~100 m and a presumed age of ~770 ka. Its sedimentary regime is influenced by climatic and hydrologic conditions related to the Antarctic Circumpolar Current, the Southern Hemispheric Westerlies and sporadic outbreaks of Antarctic polar air masses. Multiproxy environmental reconstructions of the last 16 ka document, that this terminal lake reacts highly sensitive to climate change. Laguna Potrok Aike has recently become a major focus of the International Continental Scientific Drilling Program (ICDP) and was drilled down to 100 m below lake floor in late 2008 within the PASADO project.Seismic reflection data show relatively undisturbed, stratified lacustrine sediments at least in the upper ~100 m of the sedimentary infill but are obscured possibly by gas and/or coarser material in larger areas. A model calculated from seismic refraction data reveals a funnel-shaped structure embedded in the sandstone rocks of the surrounding Santa Cruz Formation. This funnel structure is filled by lacustrine sediments of up to 370 m in thickness. These can be separated into two distinct subunits with low acoustic velocities of 1500-1800 m s-1 in the upper subunit pointing at unconsolidated lacustrine muds, and enhanced velocities of 2000-2350 m s-1 in the lower subunit. Below these lacustrine sediments, a unit of probably volcanoclastic origin is observed (>2400 m s-1). This sedimentary succession is well comparable to other well-studied sequences (e.g. Messel and Baruth maars, Germany), confirming phreatomagmatic maar explosions as the origin of Laguna Potrok Aike.Seismic reflection data of the uppermost 100 m of the sediments reveal a rather dynamic development of the lake: on top of pelagic sediments a desiccation horizon is found, probably with sand dunes in the eastern part of the lake basin. These are overlain by a series of paleo shorelines documenting the history of lake level rise in this early stage of the newly formed lake. While this new lake formed in the central and eastern part of the maar depression, the western part probably was filled by stacked coarse-grained, delta-type sediments. The latter quite likely derive from the hinterland of the only inlet that is sporadically active at present. After this early lake stage, a stage of probably rapid lake level rise can be observed in the seismic reflection data.

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