Marine and transitional Holocene terraces in the eastern area of the Straits of Magellan, Chile

Along the coasts on the east Atlantic side of the Straits of Magellan there are at least three orders of terrace, prevalently marine. They lie either on a meso-Tertiary sedimentary basement or on glacial and glaciofluvial deposits linked to the last four Quaternary glacial stages. The most ancient terrace order (I) is mainly characterised by glaciolacustrine, transitional and marine deposits and/or erosion surfaces with a maximum height ranging from 18 to 25 m above sea level (a.s.l.). Radiometric ages on macrofossil samples date this order to be of 8000-9000 years B.P., although its base could be even older. The second terrace order (II) ranges from 6 to 11 m above msl and is formed by deposits and erosion surfaces mostly related to the marine and intertidal environments. Its age can be estimated at ca. 6000-7000 years B.P. The third terrace order (III) ranges from 3 to 5 m a.s.l. It also belongs to the marine intertidal environment and its age can be estimated at ca. 4000-5000 years B.P. Younger terraces are also present, dated 1200-2500 years B.P. Due to problems of horizontal scale, they are not examined and mapped in this work. The first-order terraces evolved in the environments of the first phase of the last deglaciation. The other two orders are connected to the subsequent stages of the last deglaciation. The influence of tectonics in their evolution cannot be excluded. In this paper, we have reproduced the cartography of the marine terraces mentioned above, with the aim of verifying their lateral continuity. The analysis of detailed lithostratigraphic examples contributes to a redifinition of the Holocene palaeogeographical evolution of the Straits of Magellan coasts