Gênese e morfologias de microrrelevos gilgais no Seridó Potiguar

Abstract

Microreliefs are present in several terrestrial ecosystems, including on other planets, such as Mars. Microreliefs can be indicators of environments with greater presence of humidity (such as in semiarid regions), they can be indicators of the presence of expansive clays (2:1), bioturbation or the occurrence of permafrost (in periglacial environments). There is a large gap in the literature regarding the gilgal microreliefs of the Brazilian semiarid region, even more so when it refers to the Seridó Potiguar region. Thus, the objective of this study was to analyze the genesis and morphologies of gilgal microreliefs in the semiarid region of Seridó Potiguar from a pedogeomorphological approach. As a methodological procedure, soil collections and morphological, physical and chemical analyses were carried out. The soils were classified according to the Brazilian Soil Classification System and according to the main International Systems (U.S. Soil Taxonomy and IUSS Working Group WRB). Morphometric analyses of the silts were also performed, with in situ measurements and geomorphological mapping of the areas of occurrence and their morphologies. Satellite images (ALOS-PALSAR and Google Earth) and images collected by UAV (Unmanned Aerial Vehicle) were used. In all areas analyzed, the occurrence of silts is associated with accumulation models, predominantly fluvial-lacustrine. In these areas, the deposition of expansive clays is favored and there is also seasonal water accumulation essential for the expansion and contraction of clays. Based on the results of this study, it is suggested that the existence of excessive water does not favor the genesis of silts, which is why they are concentrated on the edges of the seasonal lakes analyzed. In all areas analyzed, silts are associated with Vertisols. The occurrence of cracking was widespread across the surface and along the soil profiles. In areas with microreliefs, soil turbation occurs in a generalized manner; in the case of clayey mounds, the main process is clay pedoturbation. In semi-arid tropical environments, the primary process for the genesis of clayey mounds is associated with the presence of expansive clays of high activity and accumulation patterns with a greater occurrence of wetting and drying cycles. Landscapes with microreliefs have in common a complexity of pedological and geomorphological processes, which, in order to be better understood, require interscale relationships, from macro to micro and vice versa.