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

Abstract

The Ceará Basin, one of the sedimentary domains related to the Brazilian Equatorial Margin, was formed by extensional events responsible for the fragmentation of the supercontinent Pangea and consequently the generation of African and Sul-American continents. The tectono-structural evolution of this segment was marked by complex and multiphase transtrative and transpressive stages, posteriorly evolving into transcurrent. Thus, the previous researches are focused in the tectono-structural evolution of this area, with few studies regarding its Sequence Stratigraphy. Based on tectono-structural and stratigraphic divergences, the Ceará Basin was compartmented, from west to east, in Piauí-Camocin, Acaraú, Icaraí and Mundaú sub-basins. The last basin is the most studied due to its economic importance related to hydrocarbon exploration. With the support of well logging and 2D seismic lines, the Alagoas section, within the Atum Field, object of this study, was investigated using the concepts of Rift Sequence Stratigraphy. The main object of this report is to identify the depositional sequences, its internal unities and its chronostratigraphic limits. The product of this research is the delimitation of two composed sequences, denominated Mundaú and Paracuru. Those sequences were divided in internal sequences M1 to M4 and P1 to P2, respectively. The Mundaú Sequence is composed of lithofacies essentially siliciclastic, with interbedded shales, arenites and silstones. The Paracuru exhibits, besides those facies, carbonate beds marking the first marine ingression. The 1D analysis, with higher resolution, allowed the delimitation of transgressive and regressive depositional systems tracts, identified by typical retrogradational and progradational stacking patterns. The 2D analysis, with lower resolution, allowed the identification of sismofacies and the positioning of unities and chronostratigraphic surfaces. This study, based on rift basin models, highlighted moments with higher and lower tectonic activity, shaping the tectonic and depositional context of Alagoas section, within Atum Field, contributing to the understanding of the Brazilian Equatorial Margin.