Caracterização de fácies carbonáticas do sistema lacustre do intervalo Alagoas da Bacia do Araripe, nordeste do Brasil

Abstract

The Araripe Basin located in Northeastern Brazil contains a sequence of lacustrine carbonate rocks that represent an important record of the paleocontinent Gondwana during the separation of the tectonic plates and the opening of the South Atlantic Ocean during the Cretaceous. The Alagoas stage (~ Aptian) in Brazilian basins presents many problems concerning the geological, tectonic, stratigraphic, and mainly, paleoenvironmental environments, considering those raised by recent oil discoveries in the Santos Basin ("Pre-salt") in continental southeastern margin. The present study aims to characterize facies and microfacies of carbonate rocks, corresponding to the Rio da Batateira and Crato formations. In this context, the study of these rocks becomes important to understanding of the origin and evolution of this system and the possibility of correlation with other basins in the equatorial margins, continental and marine. Twenty two thin sections were prepared for petrographic analysis, collected in mines, outcrops and drill-cores from Araripe Basin. Carbonates are lacustrine in origin, autochthonous, including the balanced-fill and underfilled types, with possible marine influence, formed under conditions of fresh water to saline environments. They were classified into 4 types of facies: (1) laminated limestone (mudstone) (2) massive limestone (wackstone), (3) nodular microbial limestone (Bindstone), (4) microbial limestone with microcalcispheres (Bindstone). It was recognized nine types of microfacies ("A" through "I"), grouped into six facies associations deposited in marginal, transitional and central lake areas