Some devonian Chonetoidea (Brachiopoda) from the Amazon and Parnaíba Basins, Brazil, and their stratigraphic and paleogeographic implications

SOME DEVONIAN CHONETOIDEA (BRACHIOPODA) FROM THE AMAZON AND PARNAÍBA BASINS, BRAZIL, AND THEIR STRATIGRAPHIC AND PALEOGEOGRAPHIC IMPLICATIONS

VERA M.M. FONSECA ^1* AND DEUSANA M.C. MACHADO ^2**

¹ Departamento de Geologia e Paleontologia, Museu Nacional / UFRJ, Quinta da Boa Vista s/n, São Cristóvão, Rio de Janeiro, RJ.

² Laboratório de Estudos de Comunidades Paleozóicas, Departamento de Ciências Naturais, ECB, CCBS, UNI-RIO, Av Pasteur, 428, Urca, Rio de Janeiro, RJ.

Presented by DIOGENES DE ALMEIDA CAMPOS

Montsenetes Rachebouef and Pleurochonetes Isaacson were identified in the Amazon and Parnaíba basins. The first genus, represented by a new species, occurs in the Maecuru Formation (Lontra Member), at the Maecuru river (Pará State) and in the Pimenteira Formation, at Picos (Piauí State), represented by the species Montsenetes cf. M. boliviensis Rachebouef. The second taxon is represented by Pleurochonetes comstocki Rathbun in the Ererê Formation, at the Monte Alegre dome (Pará State) as well as in the Cabeças Formation at Picos and Oiti (Piauí State). Although benthonic organisms are not suitable for accurate dating, the presence of these genera agrees with subsurface palynological datings that suggest an eifelian age for the macrofossiliferous horizons of the Maecuru and Ererê formations (Amazon Basin). The Montsenetes species of the Maecuru Formation (similar to the Venezuelan M. notius) and the Pleurochonetes species of the Ererê Formation (similar to the Bolivian P. anteloi) display compatible morphotypes with mesodevonian species of these genera. In the Parnaíba Basin the species Montsenetes cf. M. boliviensis (Pimenteiras Formation) does not provide any specific age due to the controversy about its stratigraphical position in Bolivia. However, the presence of Pleurochonetes comstocki in the Cabeças Formation suggests an eifelian age for the fossiliferous horizons of the outcrops situated at the eastern border of the Parnaíba Basin, where an age cannot be obtained by palynomorphs. The paleogeographic distribution of Montsenetes and Pleurochonetes shows changes in the connections between the Amazon and Parnaíba Basins during the Eifelian. The presence of one species of Montsenetes similar to Venezuelan M. notius in the Amazon Basin, suggests that, during the lower Eifelian, the two areas had some connection, while in the Parnaíba Basin the presence of Montsenetes cf. M. boliviensis indicated a connection between this area and Bolivia. At the upper Eifelian, the Ererê Formation (Amazon Basin) and the Cabeças Formation (Parnaíba Basin) shared a significant part of their benthonic invertebrate fauna, showing a direct connection between them. One of the taxa shared is Pleurochonetes comstocki, which is related to the Bolivian form P. anteloi Isaacson, suggesting a link to the Bolivia area. — ( December 20, 2001 ).

**E-mail: [e-mail]

Publication Dates

• Publication in this collection
  17 July 2002
• Date of issue
  June 2002