Glacial Stratigraphy of the Rio Tecka upper Valley (43°30' S.L.), Patagonian Cordillera

LAPIDO OR; BELTRAMONE CA; HALLER MJ

Ushuaia

Taller; Reunión Final del Proyecto IGCP N° 201 "Cuaternario de América del Sur".; 1987

Proyecto IGCP N° 201

Deposits of glacial events were recognized in the area of the upper Rio Tecka, a stream of the Atlantic drainage basin of the Patagonian Andes. Te oldest one, which ground moraines are located at altitudes of 1300-1500 m are actually hanging on the later glacial valleys, may correspond to a mountain ice sheet. On the eastern slope of Cordon Caquel a sharp erosion surf ace covered by pediment gravels developed from elevation 1000 to 750 m on the old glacial deposits and the underlying Tertiary sediments. At the Rio Tecka valley, behind an external terminal moraine of high 850 m that correlates with the Pichileufu Glaciation, four recessional moraines are developed at elevation 750-830 m and less eroded than the external one, and are assigned to the El Condor Glaciation. The glacial stratigraphy of the Rio Tecka area allows establishing the alternating Quaternary climatic changes and the consequent morphogenesis of the Andean segment at 34º South Latitude: during the Early Pleistocene a very cold regime which leads to a widespread ice sheet was followed by a long interglacial with arid to semi-arid climate which allowed the development of pediments. A valley glaciation took place during the late Pleistocene as a result of new cooling conditions.