Paleoecology and Paleogeography of Mollusks and Echinoids from Romualdo Formation, Aptian-Albian of the Araripe Basin, Brazil

The marine influence in the Aptian-Albian of the Araripe Sedimentary Basin, has always been suggested from fossils of several different taxonomic groups. Although the Romualdo Formation presented fossil assemblages of these invertebrates, relevant for the indication of this marine influence during the Aptian-Albian, they spent many years without receiving appropriate studies. Only after the recent work done with both the equinoids and the molluscs represented there allowed the paleoecological analysis of these assemblies. These studies will make it possible to configure a possible route of this marine incursion that occurred at the beginning of the formation of the Atlantic Ocean. From this study were made paleoecological inferences, as well as the paleogeographic distribution of the fauna showing probable environments of marine, lagoon and estuarine sedimentation, showing the possible entrances of the sea in the basin. Common species were found with the Albian of the Sergipe basin and with the Codó Formation, in Maranhão. This association of marine invertebrates is predominantly composed of echinoderms Pygurus (Echinopygus) tinocoi and Bothryopneustes araripensis; the gastropods Tylostoma ranchariensis, Cerithium sergipensis, Paraglauconia (Diglauconia) araripensis and the bivalves Aguileria dissita and Brachidontes araripensis. In the lagoon association prevails the gastropods Paraglauconia (Diglauconia) araripensis, Gymnentome (Gymnentome) romualdoi, Gymnentome (Craginia) beurleni, Pseudomesalia (Pseudomesalia) santanensis, Pseudomesalia (Pseudomesalia) mennessieri and Cerithium sergipensis and absence of echinoids. In the estuarine association occurs Tylostoma ranchariensis and predominates bivalves Brachidontes araripensis and Corbula sp.