Litoestratigrafia e paleogeografia do carbonífero na bacia de Sergipe-Alagoas

Abstract

Despite the increasing recognition of glaciations in Carboniferous Gondwana in recent years, there is a lack of detailed paleoclimatic, faciological, and paleogeographical studies in the central region of this paleocontinent. The Carboniferous section of the Sergipe-Alagoas basin, Northeast Brazil, represented by the Batinga Formation, presents geological features that are significant for understanding the sedimentary processes that occurred during this period. Based on integrated analysis of lithostratigraphic data from boreholes and outcrops from this and coeval sections in adjacent basins, this study provides a paleogeographic interpretation for the Carboniferous of central Gondwana. The deposition of the Batinga Formation was related to six glacial and interglacial paleoclimatic stages, reflecting the advance and retreat of glaciers. The first stage represented a glacial event, with extensive diamictite deposition, while the following four stages were represented by an intercalation of interglacial and glacial events associated with a probably glaciolacustrine system, with the influence of rivers, deltas, and debris flows deposits. The final stage represented the end of glaciation and the reworking of glacial deposits. The paleogeographic reconstruction proposed for the region consists of glacial valleys controlled by Brazilian age mountain chains, with a preferential NW-SE direction, which acted as basin boundaries. Glacial valleys, between these mountains, were delimited by records of the Mulungu Member of the Batinga Formation found in boreholes and outcrops. In glacial periods, these valleys accommodated glaciers, while in interglacial periods, they were partly filled with water and became lakes. Both would have drained into a main valley with a NE-SW direction, defined by the action of previous river systems of probable Siluro-Devonian age. In the central portion of Gondwana, glaciation began around 337 Ma, extending to the central-east until approximately 320 Ma. After this, the continents moved away from the South Pole, and the ice began to melt and, by 290 Ma, glaciation decreased considerably in this region. This resulted in hot and arid conditions already prevailing in the Sergipe-Alagoas basin, which led to the deposition of sediments from the Aracaré Formation at the beginning of the Permian. The age indicated by palynomorphs for the rocks of the Batinga Formation, in the Sergipe Alagoas basin, suggests that the last glacial events in this portion of Gondwana occurred in the Westphalian.