HOLOCENE EVOLUTION OF THE PRIMERA ANGOSTURA BASED ON MAP 5/12 OF THE GEOMORPHOLOGICAL ATLAS OF THE STRAIT OF MAGELLAN (SOUTHERN CHILE). (+1:50.000 SCALE MAP)

Mapping of coastal Quaternary deposits in the Primera Angostura area forms part of an ongoing comprehensive research programme, started in 1991, concerning the recent evolution of the Strait of Magellan. Two field campaigns were carried out on land within the framework of the Italian Programma Nazionale di Ricerche in Antartid e (PNRA). The first , in 1991 concerned the sedimentology and geology of coastal Pleisto-Holocene deposits, while the second, carried out in 1994 once the cartographic and geomorphological data had been processed, was to check the maps of the old coastlines and postglacial, Quaternary and chiefly marine, deposits. The research also embraces two other projects , "International Geological Correlation Programme" TGCP 367 "Late Quaternary Coastal Records of Rapid Change" and "Coastal Geomorphology Laboratory at the Centro Austral Antartico" (RAS-PYS project) funded by the Autonomous Region of Sardinia within its "Developing Countries" programme. One of the objectives of the research is the publication of an Atlas of the mainly Holocene geological and geomorphological features of the Strait of Magellan coasts, which will be useful for formulating evolutionary hypothesis of the Strait in very recent times. The Atlas is currently being completed but its publication will depend on the retrieval of funds to print the maps in colour. The Atlas, that includes the colour map presented here (n. 5112) and three other published maps (De Muro el AI., 1996a; Di Grande et al., 1996; DeMuro et al., 1996b), will consist of 12 sections at the 1:50.000 scale of the east coast of the Strait of Magellan. It will not only contain thematic maps of the evolutionary characteristics of the Late Pleistocene-Holocene sea, but is also intended as a cartographic document of the geomorphologic and evolutionary features of the continental and transitional deposits underlying the marine deposits. Three general thematic maps 1:200.000 in scale of the eastern region of the Strait of Magellan have already been published (Brambati et al., 1995a; DeMuro et al., 1995; Di Grande et al., 1995). In the main the preparation of these maps, at least as regards the cartographic basis, has been far from easy. At best we could refer to the 1:50.000 scale maps compiled by the Chilean l.G.M., which, besides the drawback of not covering the whole area, had a contour spacing of 50 metres. This created even greater difficulties in evaluating minor height differences, which was not infrequent. For areas not covered by the 1:50.000 scale sections, we resorted to the 1:100.000 preliminary maps drawn up by the Chilean E.Na.P. (Empresa Nacional de Petroleo), the 1:250.000 maps of the Chilean l.G.M. and at times also to other l.G.M maps in smaller scales. In some instances, in solving objective difficulties it was necessary to use different scales at the same time, in addition to the various scale nautical charts for near coastal regions. We also used approximately 1:60.000 scale aerial photos provided by the Servicio Aerofotogrammetrico Fuerza Aerea de Cile (S.A.F.) as well as Landsat TM and MSS satellite images acquired with funds of the Italian Programma Nazionale di Ricerche in Antarticle (PNRA) and processed at Cagliari University's Photogeology and Remote Sensing Laboratory, using funds from the RAS-PVS Project for setting up a Remote Sensing Laboratory at the Centro Austral Antartico" (see satellite images on attached map). During surveying the attention was focused on those forms, processes and deposits associated with the action of the Holo-Pleistocene sea, and, for a better regional perspective of the problems, with zonation of old glaciation. Moreover, the extremely intense coastal and eolian dynamics in progress today have also been taken into account. For completenss the general features of the fluvial and lacustrine landforms and deposits have also been mapped. The mapping criterion follows the example of recent works by the National Group (Italy) of Physical Geography and Geomorphology for various themes (coastal, submarine, continental). Moreover, for certain graphic and explanatory aspects, the cartography of the Atlas of the Coasts of the Strait of Magellan is innovative and represents a new and modern contribution to thematic mapping.