LATE PLEISTOCENE ICE FLUCTUATIONS AND GLACIAL GEOMORPHOLOGY OF THE ARCHIPIELAGO DE CHILOE, SOUTHERN CHILE

Abstract

Most of the last glacial maximum (LGM) glacier record west of the southern Andes (40-55 degrees S) is today submerged under the Pacific Ocean and therefore the Archipielago de Chiloe (42-43 degrees S) provides an unusual opportunity to study local sediment and landform associations to help understand paleoglacial features of the former Patagonian ice sheet (PIS). In this context, this work presents the first comprehensive glacial geomorphologic mapping of the central region of the Archipielago de Chiloe, which is located in a transitional geomorphic region between the Chilean Lake District (CLD, 39-41 degrees S, 73 degrees W) and northwest Patagonia ( 43-48 degrees S, 74 degrees W).

The Chilotan glacial geomorphology and sediment associations resulted from a warm-based glacier that characterizes a typical active glacial temperate landsystem, which in central Chiloe combines deposits and landform units originated in subglacial and subaerial environments. Paleoglacial features that occur in central Chiloe are characteristic of an ice-sheet style of glaciation, which differentiates it from a typical Alpine glacial style defined previously for the CLD. Therefore, the Archipielago de Chiloe represents a geographical break point where the PIS became the large ice mass that occupied the Patagonian Andes during the last glacial period (Llanquihue Glaciation).

A double ice-contact slope on the east face of the Cordillera de La Costa provides evidence for the most extensive Early Llanquihue glacial advance on Isla Grande de Chiloe. The most prominent LGM advance in the area occurred at 26 000 cal yr BP, coincident with regional stadial conditions, and is defined by a big moraine along the east coast of the island.