End of a modern geological myth: there are no rudists in Brazil! Paleobiogeographic implications

Abstract

Abstract:Out of the few records of rudists from the Cretaceous strata of the South Atlantic coastal basins only two refer to Brazilian localities. However, petrographic analyses demonstrate that these shells should be assigned to Ostreids or to Pycnodontids rather than to Rudistids. More specifically, the domain considered herein, north of the Río Grande Rise -Walvis Ridge barrier, was part of the warmwater "tropical" realm, but it was not part of the Mesogean domain because both Rudistids and Orbitolinas are missing. In addition, the scarcity of corals leads us to ascribe the taphonomic assemblage to the Chloralgal facies. Neither generalized hypersalinity or extreme sea-water temperatures seem to account for these biotic peculiarities. Instead, our alternative hypothesis favors the driving role played by oceanic circulation in the dispersal of the benthic organisms.Key Words: Rudists; Ostreids; Pycnodontids; corals; Orbitolinids; calcareous algae; Cretaceous; Albian; Cenomanian; South Atlantic; Tethys; Mesogea; Chloralgal; paleobiogeography. Résumé : Fin d'un mythe géologique moderne : il n'y a pas de rudistes au Brésil ! et ses implications paléobiogéographiques.-Parmi les quelques signalements de rudistes dans les séries crétacées des bassins côtiers de l'Océan Atlantique Sud, deux seulement correspondent à des sites brésiliens. Toutefois, les analyses pétrographiques montrent que ces coquilles ne sauraient être attribuées à des rudistes mais plutôt à des Ostréidés ou à des Pycnodontidés. Plus spécifiquement, les régions situées au N de la barrière Rio Grande Rise-Walvis appartenaient au domaine à eaux "tropicales" chaudes, mais pas au domaine mésogéen parce que rudistes et orbitolines y font défaut. De plus, la rareté des coraux nous a conduit à attribuer l'association taphonomique au faciès Chloralgal. Ni une hypersalinité généralisée, ni des températures particulièrement élevées de l'eau de mer ne semblent rendre compte de ces particularités biotiques. Au lieu de cela, notre hypothèse alternative favorise le rôle moteur joué par la circulation océanique dans la dispersion des organismes benthiques.

There are rudists in Brazil! Derived examples of cf. Amphitriscoelus Harris and Hodson, 1922, in the Araripe Basin, north-east Brazil: Implications for dating of the fossil Lagerstätten of the Santana and Crato formations

“…[See Masse et al, 2015bSha et al, 2020]) has been recorded from Barremianlower Aptian strata at Paita, Pan de Azucar, Estancia el Muerto (Gerth, 1928), and Paraarrettia peruviana (Gerth, 1928) (see Skelton, 1993, p. 21), was described from the Campanian -Maastrichtian of Cerro la Silla de Paita (Gerth, 1928), while Philip and Jaillard (2004) also reported on Upper Cretaceous rudist from Peru. The occurrence of Amphitriscoelus described here is the first record of rudists in Brazil (see Granier and Dias-Brito, 2015, for refutation of claims for Brazilian rudists) and provides evidence of a link between the Araripe Basin and the central Atlantic Caribbean province. The Araripe locality is some 3200 km from the Venezuelan localities and between 500 to 600 km from the present coastline of northeastern Brazil, where Atlantic marginal basins contain marine Cretaceous deposits (for example, the Ceará/Potiguar basins to the north and Sergipe/Alagoas basin to the east).…”

“…Although rudist bivalves were previously reported to occur in Brazil (Falkenheim et al, 1981;Granier et al, 1991), Granier and Dias Brito (2015) have demonstrated that none of those accounts are reliable. It is probable that all so-called rudist bivalves reported from Brazil hitherto are, in fact, misidentified ostreids, shells of the grypheid Pycnodonte and possibly even large serpulid worm tubes (Granier and Dias Brito, 2015). These authors were resolute that there are no rudist bivlaves in Brazil and made a well-reasoned argument for their absence in the Brazilian marginal basins of the South Atlantic.…”