Análise estratigráfica da seção Alagoas na região do Campo de Xaréu, Sub-Bacia de Mundaú, Bacia do Ceará, Margem Equatorial Brasileira

Abstract

The Ceara Basin is located at the east portion of the Brazilian Equatorial Margin, and it covers, geographically, the states of Ceará, Piauí and part of Maranhão. Three tectono-sedimentary stages are recognized in that basin: Rift, post-Rift and Drift. There is a lack of tectonic and stratigraphic studies in the Alagoas section, which includes the Rift and post-Rift stages, that may provide further information about which were the conditions in a transitional environment between the Rift and Drift stages. The area of this study focuses on the Xaréu Field, located in the Mundaú Sub-Basin. In that area, the analysis interval is lithostratigraphically represented by the Mundaú and Paracuru formations, which were stratigraphically analyzed through well (composite profile, well files and general archives of wells) and seismic data (2D lines). For this study, lithological and gamma ray profile information from six exploration wells were integrated, which helped in the interpretation of two seismic lines. Thus, based on concepts of sequence stratigraphy in rift basins, seismic stratigraphy, and analysis of gamma ray profiles, it was possible to characterize, in detail, the Alagoas section in the basin. The analysis of the wells allowed the characterization of lithofacies, depositional systems and depositional sequences. In the seismic lines, reflectors terminations patterns, seismic facies and boundary surfaces were recognized, that, combined with the one-dimensional analysis, culminated in the individualization of four tectonic systems tract: Rift-Initiation tectonic systems tract (TIR), Half-Graben Development tectonic systems tract (TDMG), Rift-Climax tectonic systems tract (TCR), and Rift-Termination tectonic systems tract (TFR). The integration of all those analyses resulted in a proposition of a model about the tectonostratigraphic evolution in the Alagoas section, Xaréu field area, and, in addition, in a contribution with discussions about the formation of the Brazilian Equatorial Margin.