Paleocorrentes e paleogeografia na Bacia do Araripe, nordeste do Brasil

Abstract

The Araripe basin is composed of four unconformity-bounded sequences: 1) Lower sequence; 2) Jurassic-Neocomian sequence; 3) Aptian-Albian sequence, and 4) Albian-Cenomanian sequence. Each sequence shows different alluvial paleocurrent pattern and bears no relation to the geometry of their areas of occurrence, suggesting that these areas are fragments of distinct and originally larger basins. The main sedimentary flow direction N-NW in the Lower sequence (Cariri Formation) is similar to the flow directions in the Paleozoic units in the neighbouring Tucano-Jatoba and Parnaiba basins. The paleocurrent pattern in the Jurassic-Neocomian sequence (Missao Velha and Abaiara formations) indicates a southward paleoflow towards the Reconcavo-Tucano basin. In both sequences the paleocurrent pattern is constant regardless of the several faults, either cutting through them or running along their boundaries, suggesting that the horst-and-graben style is a basin-modifying tectonic product. The fluvial deposits present at the base of the Aptian-Albian sequence (Barbalha Formation) portray southeast paleoflows towards the Sergipe-Alagoas basin. An opposite direction is suggested for the Albian marine transgression in the Santana Formation. Although the sea level was in a global eustatic rising movement, the Albian-Cenomanian deposits of the Exu Formation record the return to continental conditions with rivers flowing westward in the direction of the Parnaiba basin. Such rearrangement in the continental paleodrainage was a consequence of the uplift of Northeast Brazil during the Albian time.