Coastal geomorphology and evolution of Tierra del Fuego (Southern Argentina)

摘要

The northeastern Atlantic coast and the Beagle Channel are significant geomorphological areas of Tierra del Fuego (Southern Argentina). The northeastern Atlantic coast is located at the extra Andean lowlands (South- American Plate Domain). This coast line undergoes a macrotidal regime and is exposed to high energy waves and intense westerly winds. Extensive and wide beaches and littoral forms are composed of gravel and coarse sand. This zone was a free-ice area since 1,8 Ma B.P. Glacigenic deposits were re-worked by litoral processes that formed gravel beaches during sea level highstands of the. During the Holocene (i.e. approximately 5,000 years B.P.) gravel barriers plugged the inner estuaries of the palaeoembayments These barriers suggest a relative sea level fall of 0.214 m each 1,000 years, but a portion of this gradient could be due to wave dynamics since greater set-up of the storm waves enters the embayments. The growth of the northern gravel beach ridge plains and spits at the seaward flank of the embayments took place under limited sediment supply. The elongation of these littoral forms was triggered by erosion and sediment recycling at the seaward side (cannibalism), resulting in a significant landward retreat. Southward the gravel beach ridge plains underwent a regressive trend during the Holocene. They do not reveal either erosion, or sediment recycling, or significant landward retreat. The Beagle Channel connects the Pacific and Atlantic oceans. It is a 300 m depth basin separated from the Atlantic Ocean by a 30 m depth shallow sill. The Beagle Channel is located at the active seismotectonic setting of the Fuegian Andes (Scotia Plate Domain). It is a 5 km wide tectonic valley that was completely covered by ice during the Last Glaciation. After this period, glaciofluvial and glaciolacustrine environments developed in the basin. The Beagle valley was rapidly flooded by the sea immediately after the Younger Dryas, 11,000 year B.P. It undergoes a micro tidal range regime and shows a rugged, rocky shoreline where pocket gravel beaches develop in the embayments. Holocene raised beaches can be recognized in many places along the channel and their elevations vary considerably, reaching maximum elevations of 10 m above the present counterpart at ages of 6,000 years B.P. The estimated average tectonic uplift for this period is 1.5 to 2.0 mm/year.