Consequencias hidroclimáticas das glaciações quaternárias no relevo costeiro a leste da Baía de Guanabara

Abstract

After the mid-Tertiary rupture of the Sul-Americana surface through block faulting. responsible for the origin of the coastal range and also of the Serra do Mar escarpment, the evolution of the coastal relief below altitudes of 100 m in southern Rio de Janeiro State was driven mainly by alternation between morphoclimatic processes of pedimentation - associated with the deposition of thick colluvial deposits - and valley incision. The occurrence of such intense morphogenetic processes is mostly attributed to Pleistocene climatic changes, with alternating moist and dry periods. More recently some researchers expressed disagreement about the development of dry climates during the Pleistocene epoch. In the study area the application of van Wambecke's silt-clay ratio, for the dating of soils, indicated an ante-Pleistocene age for the colluvium and a Pleistocene age for the basal layers (including stone beds) of some of the colluvial deposits. Because the top material can not be older than the underlaying material, the explanation is that at least part of the ante-Pleistocene (Tertiary) sediments have been reworked in Pleistocene time. Micropaleontological analysis of cores collected from the continental slope, adjacent to the study area, indicated a change in the water temperature from cold to warm, suggesting the advance of the Falkland current to lower latitudes than at present during the glacial period with probable decrease in precipitation. The evidence supports the hypothesis that dry climates were associated with Pleistocene glaciations and agree with the Pleistocene age postulated for part of the topographic forms between the altitudes of 90 and 25 m.