Bakevelliidae bivalves from the Romualdo Formation (Alagoas Stage, Lower Cretaceous), Araripe Basin, NE Brazil: paleoenvironmental and paleogeographic significance

Author(s)

Mariza Gomes Rodrigues

• Document type: Master's Dissertation
• Press: Rio Claro. 2020-07-02.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Geociências e Ciências Exatas. Rio Claro
• Defense date: 2020-05-15
• Advisor: Marcello Guimarães Simões

Abstract

Bakevelliids (Bivalvia, Pterioidea) are extinct, marine, stationary epifaunal to semi-infaunal, suspension feeding bivalves with at least 20 described genera and numerous occurrences worldwide. They thrived from the Late Paleozoic to Eocene, reaching the maximum diversity during the Mesozoic (mainly Early and Middle Jurassic). They were also abundant and widespread in many Cretaceous sedimentary successions, as in the Araripe and Sergipe- Alagoas basins, also occurring occasionally in Pernambuco-Paraíba basin, in NE Brazil. In this document, new Aptian (Lower Cretaceous) bakevelliid bivalves are described for the Romualdo Formation, Santana Group, Araripe Basin, northeastern Brazil. Analysis is based on the detailed examination of 361 specimens all from the upper third interval of the Romualdo Formation, mainly from geological sections in the southwestern and southeastern borders of the basin, but they were recorded in all four corners of the Araripe Basin. Together with the other known members of the family Bakevelliidae, already record in the unit (i.e., Aguileria dissita), the new bivalves (Araripevellia musculosa gen. et sp. nov., Aguileria romualdoensis sp. nov., and Gen et sp. indet.) indicate that the Romualdo bakevelliid fauna was more diverse than previously realized. Bakevelliid-rich carbonates, some with in situ specimens, are restrict to the upper third of this unit, the same stratigraphic interval yielding echinoderm-, gastropod- and stromatolitebearing limestones. These pteriomorphian bivalves were widely distributed in the Romualdo Formation and are a testimony of the short-lived bakevelliid-sea that flooded the whole Araripe Basin, during the Aptian. Paleoautoecologic analysis indicate that Araripevellia musculosa gen. et sp. nov. was an epifaunal, byssate species, living in bioclastic, stable substrates, whereas Aguileria romualdoensis sp. nov. was a semi-infaunal, byssate form. Specimens of the three studied bakevelliid species can be recorded all together in a given fossil concentration, but only Araripevellia musculosa gen. et sp. nov. is found in situ. This species is found in primarily biogenic fossil concentrations forming thin obrution deposits. Notably, Aguileria romualdoensis sp. nov. close resembles A. renauxiana from the Cenomanian Woodbine Formation, Texas, US. In addition, Aguileria dissita is also recorded in the Late Aptian-Albian Riachuelo Formation of the Sergipe-Alagoas Basin. Together with other macroinvertebrates (i.e., gastropods, echinoderms, bivalves) the bakevelliid fauna of the Romualdo Formation can be biocorrelated tightly with that of the Riachuelo Formation, supporting a paleogeographic scenario with the marine waters flooding the Araripe Basin from the southeast, probably via Recôncavo-Tucano-Jatobá Basin system. Finally, sedimentologic, stratigraphic and paleontological information indicate that the fate of the bakevelliids in the Romualdo Formation, is bound up with the onset of continentalization of the Araripe Basin. (AU)

• FAPESP's process: 18/01750-7 - Bakevelliidae bivalves of the Romualdo Formation (Alagoas stage, Lower Cretaceous), Araripe Basin, Brazil: paleoenvironmental and paleogeographic significance
• Grantee: Mariza Gomes Rodrigues
• Support Opportunities: Scholarships in Brazil - Master