Stratigraphic evolution of a Brazilian carbonate platform during the Cretaceous: the late Albian-early Turonian of the Sergipe-Alagoas Basin

摘要

The Cretaceous of Brazil is widely known for vast carbonate platforms that developed along the Brazilian east coast. An onshore well drilled and logged in Sergipe State on a structural low allowed the recovery and study of a continuous 439-m core section that records an interval aged from the late Albian to the early Turonian. The section is characterized by calcilutites, marls, and shales, with occasional carbonate breccias. Ten sedimentary microfacies were recognized that indicate deposition in a deep-marine paleoenvironment constantly affected by gravitational flows. These deposits were influenced by climatic variation, as suggested by the alternation of micritic and clayey layers. The analysis of the vertical microfacies pattern, supported by well logs and geochemistry analyses, led to the subdivision of the core into three third-order depositional sequences. A long-term sea-level rise trend in the studied interval, which records the evolution of a partially protected carbonate-siliciclastic mixed platform to a distally steepened carbonate ramp, is proposed herein. The conclusion obtained by this study is important to the understanding of carbonate platform evolution, with the integrated approach of microfacies, geochemistry, and well logs proving to be essential in obtaining precise information when working with deep-marine deposits.