The Pacific entrance of the Magellan Strait: Preliminary Result of a seismic and sampling survey

During Spring 1995, in the frame of the Italian Programma Nazionale di Ricerche in Antartide (PNRA) 290 km of intermediate-resolution multichannel reflection profiles have been acquired in the Pacific entrance of the Magellan Strait with the RN OGS Explora. The survey was carried out with two principal aims: a) to verify the occurrence and effects of the Magellan Fault along the western part of the South America-Scotia plate boundary, and b) to investigate the sedimentary architecture of the sequences of this sector of the Strait, with particular interest to those concerning the Pleistocene glacial events. The survey herein described has been carried out in a marine enlargement of the Strait north of Isla Desolaciòn, between Cabo Pilar and Isla Tamar. Seismicenergy was provided by two G.I. Guns of 210 cubic inches each, with shot interval of 25m. The cable was a 48 channels -600 m streamer which furnished a 1200% coverage. Record length was kept at 8 seconds and sampling interval at 1 ms. Three gravity cores were also collected from the bottom sediments. These data are integrated b a high-resolution seismic line longitudinal to the Strait recorded in 1991 and other three cores collected during different surveys in 1991 and 1995. This work describes the preliminary results of the survey in terms of both tectonic and palaeoenvironmental frame. Its original aspect consists in documenting for the first time the location and characterization of the Magellan Fault along the westernmost arm of the Strait. This result fills the gap with the central-eastern tract of the fault for which a number of works have been issued in the last years. Another aspect concerns the sedimentological data from core analyses that constrain the environmental evolution of the Pacific mouth of the Strait about the last 21 000 years.