Late Pleistocene drumlin field in the southern coast of Lago Fagnano, Tierra del Fuego, Argentina.

CORONATO, A., SEPPÄLÄ, M, RABASSA, J., PONCE, J.

Córdoba

Congreso; IV Congreso Argentino de Geomorfología y Cuaternario; 2006

Fac. Cs. Exactas, Físicas y Naturales, Univ. Nac. de Córdoba

A new drumlin field has been recognized at Lago Fagnano (54º 36´ S, 67º 36´ W). Only a small number of these landforms have been preserved, due to meltwater and wave action. Orientation of long axes is N 107°-N 117°, their mean length is 80 m and their altitude varies between 63 and 91 m a.s.l. The heights range from 20 to 30 m. Fabric analyses show an inconsistent orientation of clast long axes, being not parallel with landform orientation. These drumlins are composed of basal till, with abundant rock clasts in a silty-clayey matrix. Clasts are often rounded to sub-rounded, with a dominant fraction <4 cm. Matrix makes up between 30-54 % of the total weight. The clayey fraction is composed by quartz, chlorite, illite, felspar and illite-smectite. Drumlins were formed by the Fagnano paleoglacier where it merged with lateral tributary glaciers. These landforms are of high palaeoenvironmental significance, since they allow the recognition of warm-based, active ice conditions that reveal features normally characteristic of continental glaciation, as a result of size and thickness of the Fuegian Pleistocene glaciers, very gentle slope of pre-glacial valleys and great availability of silty and clayey bed-load sediments, eroded from the local marine sedimentary rocks.