Paleogeographic Evolution of the Atlantic Coast of South America During Marine Isotope Stage 3 (MIS 3)

Abstract

The preparation of a digital model showing the rising and lowering of relative sea level, by means of using the Global Mapper 10 program, allowed an approximate reconstruction of the paleogeographic evolution of the Atlantic coast of South America during the Marine Isotopic Stage 3 (MIS 3). To elaborate this digital model, the curve of global sea level variations as proposed by Lambeckand Chappell (2001), for the last glacial cycle, was taken into consideration. The model shows the development of an extensive coastal plain, which extended almost continuously from Staten Island (Isla de los Estados; southeastern end of Argentina) until the Panama isthmus. The surface of this coastal plain varied from a maximum expansion of around 1,182,000 km2, when sea level achieved its minimum level of approximately −80 m below present sea level (b.p.s.l.) within the Marine Isotope Stage 3 , in between 40,000 and 30.000 cal. years B.P., and a minimum area of approximately 954,000 km2, when sea level was at its highest position of −60 m b.p.s.l. (in between 57,000 and 63,000 cal. years B.P.). These figures represent an overall surface variation in the order of only 20 % between both extreme paleogeographic configurations, proving that the coastal plain was a permanent, stable feature of the landscape of eastern South America, not only during the Late Pleistocene glacial stages MIS 4 and MIS 2, but even also during MIS 3. Its average width varied between 76 ± 73 km and 61 ± 71 km, showing significant latitudinal variations. Thus, South America increased its total surface by 6.6 and 5.3 % during MIS 3. This coastal plain had its maximum extent at the latitude of the eastern Argentina province of Buenos Aires (between approximately 35° and 40° South latitude), when the Rio de la Plata estuary did not exist. Its minimum amplitude occurred in central Brazil and in front of the Caribbean coast of Venezuela and Colombia. The information provided by the present model sustains the importance of the Atlantic coastal plain of South America as a distinctive feature of the South American landscape and proves its paleogeographic continuity even during the warmest periods of Marine Isotope Stage 3. These facts suggest that the coastal plain, most of it submerged today, has been a major element of the landscape during most of the Quaternary.