A paleoictiofauna da Formação Marizal (Bacia de Tucano, Cretáceo Inferior do Nordeste do Brasil): nova interpretação paleoambiental e reavaliação das bacias marginais brasileiras

Abstract

The present work aimed to review the validity of Actinopterygii species found in the Lower Cretaceous of the Marizal Formation, Tucano Basin, presenting an amended diagnosis for each species and a new paleoenvironmental interpretation, comparing the analyzed ichthyofauna with other ichthyofaunas in western Gondwana. The first Cretaceous fossil deposits found in the Marizal Formation were discovered in the 1950s and 1960s. In the associated fauna predominate the Teleostei Clupavus brasiliensis and Britoichthys marizalensis, being also present: Vinctifer longirostris, Placidichthys tucanensis, Nanaichthys longipinnus and Ogunichthys triangularis, in addition to a Vidalamiinae. Here, for the first time, scales and a vertebra attributed to Vidalamiinae were described. This amid fish is, to date, the largest fish in the Marizal Formation biota, reaching approximately 1400 mm. Such faunal composition suggests an Aptian age for the formation. The specific difference of the fauna of the Marizal Formation compared to other basins in North-East Brazil and western Gondwana shows a pattern of endemism, demonstrating that, most likely, this fauna originated from an epicontinental sea prior to the one that is represented in other Aptian formations, such as the Santana Formation, regarding the stratigraphic arrangement of such formations. Although the presence of a Vidalamiinae, V. longirostris and a Cladocyclidae are indicative of a probable marine environment, so far no conclusive evidence proves a marine environment in the Marizal Formation, and it can only be stated that part of the fauna of the Amargosa Bed has tethyan affinity. The presence of known marine specimens in the Amargosa Bed can be explained by their entry into the Lagoa Amargosa during one of the marine transgressions of Tethyan origin through the sedimentary basins north of the Tucano Basin. The Santos-Benguela segment seems to have acted as a barrier, preventing the circulation and mixing of marine waters between the South Atlantic and the Central-Equatorial Atlantic. The presence of fossil levels with a high concentration of conchostraceans, associated with plant remains, as well as the predominance of fingerling and juvenile fish at different intervals within the Amargosa Bed, suggest a predominantly freshwater lacustrine environment