Stratigraphic analysis of rift basins: application of genetic concepts in Camamu-Almada and Jequitinhonha basins

Abstract

The stratigraphic succession of Camamu-Almada and Jequitinhonha rift basins have been analyzed based on a data set formed by 73 wells and 832 2D seismic lines. Based upon revised concepts of sequence stratigraphy as a tool for genetic analysis, five second-order sequences were recognized: a basal Paleozoic sequence (SEQ-Plz), formed by sandstones and mudstones of the Afligidos Formation; sequence A (SEQ-A) encompassing Aliança, Sergi and Itaípe formations; the sin-rift sequence SEQ-B (encompassing four third-order sequences), Sequence C (SEQ-C) formed by the Algodões (in Camamu-Almada basin) and the São Mateus and Regência formations (in Jequitinhonha basin) and sequence D (SEQ-D) represented by the Urucutuca, Caravelas, Rio Doce and Barreiras formations, forming the passive margin succession of both basins. The regional unconformities that delimit the rift phase of Camamu-Almada and Jequitinhonha basins are sequence boundaries LS-B and LS-C; which envelope a rock succession formed in a time span of 30 million of years. Using the concept of tectonic systems tracts to understand the evolution of the Camamu-Almada and Jequitinhonha rift basins, the following interpretation can be provided: sequences SEQ-Plz and SEQ-A are pre-rift successions; SEQ-B1 forms the rift initiation systems tract, SEQ-b2 and SEQ-B3 represent the rift climax systems tract, SEQ-B4 forms the rift fill systems tract, while SEQ-C and SEQ-D form the late post-rift systems tract. The process-oriented focus of the stratigraphic analysis is an important step forward in order to understand the geologic evolution of Camamu-Almada and Jequitinhonha basins because it helps to characterize petroleum systems and provides better predictions of source rock and reservoirs within the studied section.