Geomorfhological dynamics of colluvial deposits in the Borborema Plateau (Northeast Brazil) through the use of scanning electron microscopy on the 200-250 µm fraction

Abstract

In the Borborema Highlands, Northeast Brazil, the definition of the types of surface processes involved in the deposition of colluvial and alluvial-colluvial sediments remains elusive. Most interpretations rely on field-based and macrofabric observation along stratigraphic sections. The present study proposes an evaluation of the surfaces of quartz and microcline sand grains in the 200-250mm fraction, originating from gravel matrices dating from the last glacial maximum to the historical period, through the use of micromorphological analysis, assisted by an environmental scanning electron microscope, to evaluate the subaerial processes to which they were subjected. The surface textures found in the sand grains were visually grouped and quantified based on the methodology adopted for Quaternary deposits with known erosion/depositional trajectories. The history indicated by the surface textures points to the presence of climatic controls (mechanical and weathering), in addition to burial time, on the aspect of the grains, with a greater incidence of mechanical features in those originating from recent deposition and topographically lower areas in the surroundings of Highland's escarpments under semi-arid climates.