Geomorphology, stratigraphy, and radiocarbon chronology of Llanquihue drift in the area of the southern Lake District, Seno Reloncavi, and Isla Grande de Chiloe, Chile

Glacial geomorphologic features composed of (or cut into) Llanquihue drift delineate former Andean piedmont glaciers in the region of the southern Chilean Lake District, Seno Reloncavi, Golfo de Ancud, and northern Golfo Corcovado during the last glaciation. These landforms include extensive moraine belts, main and subsidiary outwash plains, kame terraces, and meltwater spillways. Numerous radiocarbon dates document Andean ice advances into the moraine belts during the last glacial maximum (LGM) at 29,363-29,385 C-14 yr sp, 26,797 C-14 yr sp, 22,295-22,570 C-14 yr sp, and 14,805-14,869 C-14 yr sp. Advances may also have culminated gt close to 21,000 C-14 yr sp,shortly before 17,800 C-14 yr sp, and shortly before 15,730 C-14 yr sp. The maximum at 22,295-22,567 C-14 yr sp was probably the most extensive of the LGM in the northern part of the field area, whereas that at 14,805-14,869 C-14 yr sp was the most extensive in the southern part. Snowline depression during these maxima was about 1000 m. Andean piedmont glaciers did nor advance into the outer Llanquihue moraine belts during the portion of middle Llanquihue time between 29,385 C-14 yr sp and more than 39,660 C-14 yr BP. In the southern part of the field area, the Golfo de Ancud lobe, as well as the Golfo Corcovado lobe, achieved a maximum at the outermost Llanquihue moraine prior to 49,892 C-14 yr sp. Pollen analysis of the Taiquemo mire, which is located on this moraine, suggests that the old Llanquihue advance probably corresponds to the time of marine isotope stage 4. The implication is that the Andean snowline was then depressed as much as during the LGM. A Llanquihue-age glacier expansion into the outer moraine belts also occurred more than about 40,000 C-14 yr sp for the Lago Llanquihue piedmont glacier.