Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Boucot, Rowell, Racheboeuf, Pereira, Gonçalves De Melo, De Siqueira

Position of the Malvinokaffric Realm's northern boundary (Early Devonian) based on newly discovered brachiopods from the Parecis Basin (Brazil)

Journal of the Czech Geological Society, volume 46 (2001), issue 3-4, 109 - 120

The northern biogeographic boundary between the earlier Devonian Malvinokaffric Realm and the adjacent Eastern Americas Realm has customarily been placed midway between the northern margin of the Paraná Basin and the southern margin of the Amazon Basin, which also permits it to pass through the Parnaíba Basin. The recent discovery of typical Early Devonian Malvinokaffric Realm brachiopods within the Parecis Basin, to the north of the Paraná Basin now permits one to move this boundary significantly to the north, placing it between the Parecis and Amazon basins, and still permitting it to pass through the Parnaíba Basin. Previously described trilobites from the Parecis basin are in agreement with the biogeographic conclusions based on the brachiopods.
The inarticulate brachiopods, identified by Rowell are Orbiculoidea falklandensis, Orbiculoidea sp. cf. Orbiculoidea collis, and Lingula sp. cf. Lingula lepta; the articulate brachiopods, chonetoids identified by Racheboeuf, include Australostrophia mesembria, Australostrophia clarkei, Pleurochonetes sorucoi, non-choetoids, identified by Boucot, include Australospirifer sp., Australocoelia palmata, Pleurothyrella cf. knodi, Derbyina sp., and an unidentified orthotetacid.
Among these brachiopods Orbiculoidea falklandensis, Australostrophia mesembria, Australocoelia palmata, and Pleurothyrella are typical Malvinokaffric Realm taxa. No typically Eastern Americas Realm brachiopods are present in this fauna. Paleoecologically this fauna is best placed near the boundary between Benthic Assemblages 2 and 3, i.e., shallow subtidal, photic zone. In terms of age it corresponds to the earlier Devonian of the Paraná Basin, of which it represents an outlier.