Coastal Cartography of the quaternary deposits between Punta Arenas and Rio Quema Angusta – Peninsula Brunswick. Tierra del Fuego – Strait of Magellan – Chile

The 6th map of the Coastal Atlas of the Strait of Magellan is presented (1:50,000 scale). The map refers to sheets 84 and 101 of the Chilean I.G.M., and was made using the peliminary cartography by E.NA.P. (Empresa Nacional de Petroleo) and the Chilean I.G.M., aerial photos by S.A.F. (Servicio Aerofotogrammetrico Fuerza Aerea de Chile) and T.M. and M.S.S. Landsat satellite images. It is aimed mainly at locating and mapping the marine and transitional terraces in Tierra del Fuego, along the eastern coasts of the Strait of Magellan, between Punta Arenas and Cabo Froward. From a methodological point of view, we followed both the criteria of several more recent cartographic works produced by Programma Nazionale Ricerche in Antartide (Magellan Project), as well as the general criteria internationally adopted in coastal geological cartography. The coastal cartography of Quaternary deposits in the area south of Punta arenas (Tierra del Fuego-Strait of Magellan-Chile) is part of a wider ongoing research programmeon the recent evolution of the Strait of Magellan that started in 1991. To this purpose, within the Programma Nazionale di Ricerche in Antartide (P.N.R.A.) (National Research Programme in Antarctica), 3 campaigns were carried out on land. The first was in 1991 and dealt with the sedimentology and geology of coastal Pleisto-Holocene deposits, while the second and the third, in 1994 and 2002 that is after the cartographic and geomorphological data had been processed, was intended as a check of the cartography of the old coastlines and postglacial, Quaternary, prevalently marine deposits. Moreover, the study also involves the the project P RAS-PVS (Regione Autonoma Sardegna - Paesi in Via di Sviluppo - Cartografia delle Coste dello Stretto di Magellano). Among the objectives that developed during the research is the publication of an Atlas of the coasts of the Strait of Magellan on geological and geomorphological elements, prevalently Holocenic, that can be useful to formulate an evolutionary hypothesis of the Strait in very recent times. The Atlas is at present being refined while its publication depends exclusively on the retrieval of funds to print the maps in colour. The Atlas, that includes the attached colour map presented here (n. 6/12) and five other published maps (DE MURO el Al., 2000), will be made up of 12 sections at the 1:50,000 scale and will deal with the east coast of the Strait of Magellan. It is configured not only as a theme cartography of the evoluti (onary characteristics of the Late Pleistocene-Holocene sea, but also as a cartographic document of geomorphologic and evolutionary elements of the continental and transitional deposits underlying the marine deposits. Three thematic general maps at the 1:200,000 scale on the eastern region of the Strait of Magellan have already been published (BRAMBATI et Al., 1995a; DE MURO et Al, 1995; DI GRANDE et Al., 1995). On the whole the preparation of these documents, at least as regards the cartographic basis, has not been easy; at best we could refer to the 1:50,000 scale cartography by the Chilean I.G.M., which, besides the drawback of not covering the whole area, had a contour interval of 50 metres. This created even further difficulties in the evaluation of much smaller height differe Gnces, which was not infrequent. For areas not covered by the 1:50,000 scale sections, we resorted to the 1:100,000 preliminary cartography maps by the Chilean E.Na.P. (Ente Nacional de Petroleo), the 1:250,000 cartographic maps by the Chilean I.G.M. and at times also to other more general scales by the I.G.M.. At times, in solving objective difficulties it was necessary to use different scales at the same time, besides the various scale nautical charts for near coastal regions. Approximate 1:60,000 scale aerial photos of the Servicio Aerofotogrammetrico Fuerza Aerea de Cile (S.A.F.) and Landsat TM and MSS satellite images acquired with funds of the Programma Nazionale Ricerche in Antartide (P.N.R.A.) and processed at the University of Cagliari, with funds of the Programme "RAS-PVS – “Progetto per la cartografia delle Coste dello Stretto di Magellano” have also been used. The forms, processes and deposits that were most attended to during surveying, are those associated with the action of the Holo-Pleistocene sea, and, for a better regional view of the problems, with zonation regarding old glaciation. Moreover, the extremely intense coastal and eolian dynamics in progress today have been taken into account. For completion general elements concerning the surface water runoff, and lacustrine forms and deposits have been mapped.