New Constraints on Maar Geometry and Sedimentary Fill of Laguna Potrok Aike, Southern Patagonia

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Gebhardt, C. , Niessen, F. , Anselmetti, F. , Ariztegui, D. , De Batist, M. , Haberzettl, T. , Ohlendorf, C. and Zolitschka, B. (2007): New Constraints on Maar Geometry and Sedimentary Fill of Laguna Potrok Aike, Southern Patagonia , Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract U31B-0302. .
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Laguna Potrok Aike is located in Southern Patagonia, Argentina, at 52°S and 70°W. The maar lake has a diameter of 3.5 km and is almost circular and bowl-shaped with a deep, flat plain (100 m water depth) in its central part. Steep flanks separate the lake shoulders at 15 to 35 m water depth from the central plain. The lake is situated in the Pali Aike Volcanic Field at the present boundary between the Southern Hemispheric Westerlies and the Antarctic Polar Front. Its lake level is highly susceptible to changes in the Antarctic Circumpolar Current that controls the regional precipitation patterns. Its sedimentary infill possibly contains a long and continuous record of several glacial and interglacial cycles, which is unique in the southern South American realm. Two major stratigraphic units (I and II) were distinguished in the seismic sections. Unit I consists of the lacustrine infill and was further subdivided into Sub-units I-a and I-b on the lake shoulders and I-ab, I-c, and I-d in the central basin. Sub-units I-a and I-b on the lake shoulders are separated by a major unconformity and contain several paleoshoreline structures formed during a step-wise transgression after a lake level lowstand of approx. 35 m below the present lake level. In the central basin, Sub-units I-a and I-b are merged into Sub-unit I-ab, not being separated by any unconformity. Pelagic sedimentation dominates in the northern and central parts, whereas mass movement deposits were found in the southern, western and eastern parts close to the steep diatreme flanks. The boundary between I-ab and I-c is non-erosive with I-ab forming downlaps onto I-c from the eastern and western parts of the lake, pointing at a significantly lower lake level during its accumulation. Sub-unit I-d shows similar characteristics as I-ab. The bedrock (Unit II) that forms the steep diatreme flanks consists of the well-layered sandstones found in the lake surroundings.

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