A new permian bivalve (Megadesmidae, Plesiocyprinellinae) from the Serrinha member, Rio do Rasto Formation, Paraná Basin, Brazil

During a recent inspection in the Paleontological Collection of the Institute of Geosciences, University of São Paulo, we have identifi ed some specimens of undescribed mollusk bivalves. These called our attention for the following reasons: a) all specimens are internal molds of conjugated and closed articulated valves, some of them presenting fragments of silicifi ed shells; b) all internal molds have similar general shape and internal characters, representing specimens of the same taxon; c) the internal molds and silicifi ed valves are well preserved, including fragile structures, which are hardly preserved, such as the internal mold of the external ligament and muscle scars; d) and equally important, according to the labels of all specimens, they were collected from rocks of the Passa Dois Group (Permian), Serrinha Member of the Rio do Rasto Formation. Although who collected the shells and the precise geographic location of the specimens are still unknown, the detailed study of these fossils brings us to the conclusion that they are morphologically distinct from any heretofore published genus of the endemic fauna of bivalves from Passa Dois Group. Based in its general shape, hinge structure and muscles scars, the new form can be classifi ed under the Family Megadesmidae Vokes, 1967, the most diverse group of Permian bivalves of the Paraná Basin. The specimens are referred as Beurlenella elongatella new gen. and sp. The shell shape and taphonomy indicate that this bivalve was a shallow, rapid, active burrower, suspension feeder, probably preserved in situ, in event deposits.

Ciclos e seqüências deposicionais das formações Rio da Batateira e Santana (Andar Alagoas), Bacia do Araripe, Brasil

The Rio da Batateira e Santana formations, the latter with Crato, Ipubi and Romualdo members (Alagoas Stage, Aptian), were studied in four cored and logged wells from the eastern portion of Araripe Basin, Northeastern Brazil. The investigated section is 230 m-thick, and PS-14 well is the most representative, because it is the only one which sampled the evaporites of Ipubi Member. Nine facies cycles were identified, being formed by siliciclastics (estuarine, deltaic and lacustrine), mixed lithologies (lacustrine), carbonates, black shales and marls (lacustrine), and gypsum-anhydrite (lacustrine evaporite). The ordering of facies cycles furnished six depositional sequences. They were formed by siliciclastic, regressive-transgressive R-T cycles (S1 and S4, corresponding to Rio da Batateira Formation and to Santana Formation/Romualdo Member), by siliciclastics and carbonates, R-T cycles (S2, S3.1 and S3.2, corresponding to Crato Member), and by siliciclastic-carbonate, R-T cycles followed by evaporitic cycles (S3.3, referred to Ipubi Member). The last cycles correspond to concentration-dilution, C-D cycles of marine brines, which precipitated gypsum in the restricted lacustrine basin.

Palinoestratigrafia na passagem do grupo Itararé ao Guatá (carbonífero-permiano) no sul do Estado do Paraná e norte do Estado de Santa Catarina, borda leste da Bacia do Paraná

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)