Morphologic and sedimentologic patterns of active aeolian dune-fields on the east coast of MaranhAo, northeast Brazil

摘要

The eastern portion of the MaranhAo coast is characterized by large active dune-fields located in a tropical setting. This article combines the analysis of dune-field morphologic patterns with the classical analysis of grain size and heavy minerals to study the sedimentary dynamics of the active aeolian system in this region. Based on the heavy mineral analysis, the main sedimentary suppliers feeding the system are the westward alongshore drift bringing sand from the coast east of the Parnaiba River mouth and the river itself. The absence of well-defined variation patterns of the two morphometric parameters studied, dune spacing and crest length, reflects complex sedimentary dynamics and transport pathways, inside the aeolian system, despite the unidirectional wind. During the wet season, the interdune plains are flooded and the system is intensely reworked by intermittent drainages. During the dry season, the deposits formed by the drainages and interdune lakes become temporary internal sedimentary sources for the system. Due to this combined aeolian-fluvial transport, the sediment source area has a planar geometry, with contributions from the beach and interdune plains, and not linear as expected in a typical case of source only in the beach. The areal limits of the dune-fields is the main boundary condition controlling the dune-field patterns, as dune spacing and crest length, by changing the sedimentary inflow-outflow balance and interactions between migration dunes. Copyright (c) 2015 John Wiley & Sons, Ltd.