Sub-bottom facies of the Beagle Channel, Tierra del Fuego

Abstract

The Beagle Channel connects the Pacific and Atlantic oceans in the southernmost part of South America, and has a subantarctic environment. It is a deep basin (300 m depth) separated from the Atlantic Ocean by a shallow sill (30 m depth). The Beagle Channel is a tectonic valley that was completely covered by ice during the Last Glaciation. Later, it was occupied by a glacial lake from 12,000 to 8,000 years B.P. and then flooded by the sea, reaching a maximum sea level between 6,000 and 5,000 years B.P. A geophysical survey (side scan sonar and 3.5 kHz profiler) was carried out in the channel to analyze the sea-bed and sub-bottom sedimentary facies. Metamorphic Mesozoic basement rocks are overlain by glacial deposits (till) and fining upwards sequences. These sequences represent different stages of the glacial retreat, showing in their upper parts proglacial lacustrine facies. Holocene marine deposits overlie the glacigenic deposits. Palaeovalleys and submerged fluvial sequences transgressed by marine deposits were also observed.