Bivalvos del Pérmico Inferior de la Formación Bonete, Sierras Australes (provincia de Buenos Aires, Argentina)

PAGANI, MARÍA ALEJANDRA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Año: 2000 vol. 37 p. 301 - 320

0002-7014

A bivalve fauna from the Pillahuinco Group in Sauce Grande Basin (Buenos Airesprovince, Argentina), first discovered and described by Harrington, is here revised and illustrated. A reassessment of the taxonomy, provincial affinities and age of the fauna reinforces its Gondwanic character. This feature denotes its probable correlation with Early Permian faunas of Brazil, Australia and SouthAfrica. Eight species of Bivalvia are described and illustrated. Two of them: Heteropecten sp. and Myonia sp. are described for the first time for the Bonete Formation. Other six species are revised: Leptodesma (Leiopteria) bonaerensis (Harrington), Leptodesma (Leiopteria) dutoiti (Harrington), Atomodesma (Aphanaia)? orbirugata (Harrington), Promytilus acinaciformis Harrington, Stutchburia argentinensis Harrington, Allorisma inflectovelltris Harrington. The association also contains brachiopods, gastropods and plant remains. Comparisons with genera registered from Brazil, Australia, New Zealand and United States are established. The recorded bivalve assemblage from the Bonete Formation suggests a possible faunal connection with similar assemblages from the Rio do Sui and Rio Bonito Formations in the Parana Basin (Brazil). This possible paleobiogeographic relationship between the two basins, would be favored by similar environJ1lentconditions. The record of Eurydesma, Deltopecten and Atomodesna in the Bonete Formation indicates a Late Asselian-Artinskian age for the bivalve fauna. The occurrence of the brachiopod Tivertonia in this formation, the faunal affinities with Australian and Brazilian faunas, and the paleofloristic assemblage, are additional evidences which support this age.