O sistema eólico das bacias costeiras de São Luís e Barreirinhas, NE do Brasil: implicações climáticas e tectônicas durante o Quaternário

Abstract

Active and stabilized dune fields, built by NE trade winds in a wave- and tide-dominated coastal system characterizes the region between São Marcos Bay, Maranhão State, and the Parnaíba River Delta, Piauí State, northeastern coast of Brazil. In this context, Lençóis Maranhenses is the largest active dune field in South America with approximately 1,026 km2, adjacent to the largest stabilized eolian deposits with about 19,000 km2 covering basement rocks. These deposits mainly fill the onshore portion of the Barreirinhas Basin, and the NE-SW Pirapemas Lineament represents the main structure of the basement. Previous gravimetry and seismic data show that the NW portion of this lineament is a subsided block that controls the Holocene deposition. The main factors for the origin and preservation of this sedimentation were variations in humidity, wind speed, vegetation cover, and relative sea-level changes since the Pleistocene. Furthermore, the neotectonics events are confirmed and linked to the Pirapemas Lineament reactivation. The mapping of active and inactive morphologies of this eolian system, based mainly on remote sensing products, previous geochronological and field data, allowed us to infer evolutionary stages that culminated in the current relief configuration of the region. The interpretation of medium to high spatial resolution optical satellite images (SENTINEL-2 and CBERS-4a) and digital elevation model (ALOS) were suitable for the compilation of age data (LOE, C14, and thermoluminescence) to provide a spatial- that supported the proposed geological evolution. The eolian deposits are typical of the transgressive dune field, comprising about 20,000 km2, of active (12 %) and inactive (88 %) morphologies. The active deposits are close to the coast and consist of barchans, barchanoid and transverse ridges. Inactive deposits migrate inland for up to 150 km and are formed by parabolic dune morphologies, stabilized transverse ridges, and deflation plains. Although the older ages are unrepresentative, it suggests that these dune fields may have started 240,000 BP. The published age concentrations of the Late Pleistocene punctuate successive pulses of migration and preservation influenced by relative sea-level changes triggered from Quaternary glacial and interglacial cycles. Under more arid conditions, the coastal-eolian system had its most landward remarkable expansion during the Last Glacial Maximum (~22,000 BP). At the same time, the most significant preservation occurred between 19,000 and 14,000 BP, under a humid climate reflecting the Henrich event (HS1). In the Holocene, the normal reactivation to the NW of the Pirapemas Lineament increased the accommodation space with extensive development of coastal systems. The SE region from this lineament was uplifted, causing progressive dune field abandonment and reworked by deflation. These two distinct compartments form the current configuration of the coastal wind deposits in the onshore Barreirinhas Basin.