CONICET | Buscador de Institutos y Recursos Humanos

Lago Yehuin, a WNW-ESE elongated basin locatedin the outer fold-and-thrust belt of the Fuegian Andes, occupies a compartmented structural depression originated along a segment of theleft-lateral, strike slip Lago Deseado fault system. This paper describesthe first geophysical survey performed within the lake. New acquiredhigh-resolution single- channel seismic data, integrated with geological information in the surroundings of the Lago Yehuin, allowed to derive a complete bathymetric map, reconstruct the basement surface of the lake, and the geometry,distribution, and thickness of the sedimentary infill. Two sub-basins were recognized within LagoYehuin: A western sub-basin, of 7.5 kmlong with a maximum depth of 118 m; aneastern sub-basin, of 7.2 km length and a maximum depth of 80 m. Both sub-basins are limited bya setof normal faults which overprint NE- verging thrusts. Three seismo-stratigraphic units have been identified in the seismic records: (1) a lower unit with wedged geometry interpreted as mass flowdeposits; (2) a thickest (up to ∼ 120 m) intermediate unit of glacio-lacustrine nature and irregularly distributed in the Yehuin basin; (3) a thin (generally < 10m) upper lacustrine unit which drapes the entire basin. Lago Yehuin isconsidered a Neogene basin generated bystrike- slip motion that was later affected by glacial and glacio-lacustrine deposition.Interpreted submerged ridge moraines within Lago Yehuin are correlated with onland moraine arcs built by the complete recessional paths of Fuego and Ewan ice lobes. A significant structural control is proposed not only for the formation of LagoYehuin, but also for the general pathsof the northern arms of the Fagnano palaeo-glacier.

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