Influence of fluvial supply on the coastal eolian system of São Francisco mouth: searching for sedimentological signatures

Abstract

Coastal regions with continental sedimentary supply favored by the presence of large rivers and with propension to form eolian dune-fields are conducive to the investigation of the relationship between fall or increase of river inflow, promoted respectively by reduction or increase of precipitation, and formation or stabilization of eolian coastal dunes. The São Francisco River mouth plain is one of the most representative regions attending this condition on the Brazilian coast. The eolian deposits of this coastal plain present a change seawards in their morphological configuration, from linear to sinuous paleodune ridges and, finally, to the current dune-field. This change is suggestive of an increase in eolian supply over time, which may be related to the increase of dryness in the Northeast during the Holocene and the consequent drop in fluvial contribution and rate of coastal progradation. The study of this coastal eolian system therefore has great potential to contribute to the understanding of continental input rate and progradation influence on the generation or stabilization of dune-fields. Within this theme, the main goal of this project is to use the sediment granulometry and the quantification of heavy minerals to evaluate the influence of the São Francisco river input on the different eolian morphostratigraphic units (generations) of the coastal plain. In order to achieve this goal, the following objectives are proposed: 1) to analyze the variation of grain-size and composition and texture of the heavy mineral assemblage in the São Francisco River sediments and in the eolian geomorphological units; 2) to relate the sedimentological data of the different eolian units with the climate and sea level variation models existing for the deposition period of each unit; 3) interpret the variations of sedimentary source in terms of influence of continental input versus influence of continental shelf sedimentary reworking. (AU)