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

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

Cordoba

Congreso; III Congreso Argentino de Cuaternario y Geomorfología; 2006

Escuela de Geología. Fac. de Ciencias Exactas, Fisicas y Naturales. Universidad Nacional de Cordoba

A new drumlin field has been recognized at Lago Fagnano (54º 36´ S, 67º 36´ W). Other drumlin fields in this region had been found at Gable Island, Beagle Channel and Magellan Straits. A small number of these landforms have been preserved, due to meltwater and wave erosion. Orientation of landform 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. 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 large 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 has a varied mineralogical composition, with quartz, chlorite, illite, felspar and illite-smectite. Mineral crystallinity is high, with the exception of illite-smectite. These glacigenic deposits are mostly of the melt-out till type. 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 within a mountain environment, 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 Late Mesozoic and Tertiary marine sedimentary rocks.