Seismic stratigraphy of the northern area of Punta Bandera (Lago Argentino, southern Patagonia)

Abstract

Lago Argentino is one of the largest lakes in Patagonia. Some of its arms host calving glaciers that flow from the southern Patagonian Ice Field. The best known of these is the Perito Moreno glacier. Although recent studies have reconstructed part of glacier dynamics in the southern arms of Lago Argentino, there are no studies yet for the northern arms. A high-resolution seismic survey was carried out in the northern area of Punta Bandera, i.e., in the sector between the Brazo Norte and the Canal de los T´ empanos to characterize the stratigraphy of the sedimentary fill of the lake and identify the main unconformities related to glacial dynamics. Eight seismic facies grouped into two seismic units were mapped, and ten unconformities were recognized. Based on the acquireddata, a bathymetric grid was created for the first time to obtain a morphological representation of the lake floor and access to a previously unmapped area of Lago Argentino. The analysis of the geometries and acoustic properties of the different seismic facies identified, correlated with the available information on land moraines, has allowed us to partially reconstruct the advance and retreat phases of the glacial lobes that formerly were present in the two arms of the lake, although the temporal assignments are still speculative due to the lack of calibrations with boreholes. Nevertheless, this study provides important information for deciphering the glaciation history of a key sector of the southern Patagonian Ice Field during the late Pleistocene/Holocene. The datashow that the northern and southern areas have different lake floor morphologies, with the southern, shallower area of the Canal de los T´empanos being glaciated first than the northern, more overdeepened area of the Brazo Norte.