Paleontologia e paleoecologia dos moluscos biválvios da localidade Pedro Gonçalves, formação Cotinguiba, Bacia de Sergipe

Abstract

The Sergipe-Alagoas Basin has one of the most complete and exposed stratigraphic sequences of all Brazilian sedimentary marginal basins. The Cotinguiba Formation (Upper Cretaceous) is characterized by the deposition of a set of carbonate rocks with genesis associated to the depositional environment of the ramp. The bivalves are abundant fossil groups in these rocks. Some taxa have specific characteristics that allow their use in paleoecological and paleoenvironmental reconstructions of Mesozoic sedimentary basins. This work had as main objective the study of the molluscs of the Bivalvia class and to interpret the paleoecology of the Pedro Gonçalves locality, Cotinguiba Formation, Upper Cretaceous of Sergipe Basin. The material studied here consists of 147 specimens of bivalve molluscs from the locality of Pedro Gonçalves. Twenty-two species are attributed to fifteen genera. Twelve families of bivalve molluscs were identified: Pinnidae, Inoceramidae, Plicatulidae, Pectinidae, Limidae, Ostreidae, Gryphaeidae, Cardiidae, Dicerocardiidae, Corbulidae, Pleuromyidae and Poromyidae. The abundance of infaunal bivalves dominated by suspension-feeders suggests a moderate energy environment living in an unconsolidated substratum. The increasing degree of shells disarticulation in the intermediate to upper part of the section, demonstrates that there was a short distance transport during a period of higher energy. The section is positioned in the middle Turonian range based on the fauna of inoceramids and ammonites. The faunal succession in the studied section is marked by the gradual substitution of taxa living in a deeper environment by others on a shallower environment, especially with the occurrence of plicatulids and ostreid banks. This fact suggests an episode of reassessment in the middle Turonian interval.