Late Paleozoic marine fauna succession in the Itararé Group, Brazil: towards an integrated brachiopod and bivalve biocorrelation scheme.

NEVES JACQUELINE; TABOADA, ARTURO CÉSAR; WEINSCHÜTZ LUIS; PAGANI MARÍA A; SIMOES MARCELLO

Madrid

Congreso; Gondwana 15; 2014

During the Late Paleozoic, the Paraná Basin was a huge intracratonic basin mainly filled by continental, marine and fluvial deposits. In this context, the basal portion of the Carboniferous?Permian sequence corresponds to the Itararé Group. This records one of the most continuous and thickest glacio-marine succession in South American Gondwana, including glacial diamictites, sandstones and shales. The succession is capped by coal-bearing sandstones of the Sakmarian?Artinskian Rio Bonito Formation. Marine invertebrates are rare and sparsely distributed in the Itararé succession. However, in the eastern border of the basin, at least nine marine assemblages were recorded in the Mafra and Rio do Sul (=Taciba) formations. Ongoing taxonomic analyses indicate that 10 brachiopod and 19 bivalve species can be recognized. Low diverse, linguliform-dominated brachiopod assemblages are recorded in the mid portion of the Mafra Formation (late Carboniferous) and in the basal portion of the Rio do Sul Formation (Lontras shale, Carboniferous-Permian boundary), and are associated to marine intercalations generated under transgressive events. At the top of the Rio do Sul/Taciba Formation, above the last diamictite beds, at least seven bivalve-dominated assemblages were recorded. The unique exception is the Butiá assemblage, Mafra county, Santa Catarina state, that is dominated by productid brachiopods. The older fauna, the Heteropecten paranaensis-Pleurophorella sp. assemblage, is recorded in sandstones deposited in shallow water conditions. This is stratigraphically succeeded by the following assemblages: Praeundolomya cf. subelongata-H. paranaensis; Exochorhynchus itararensis-Cosmomya (Paleocosmomya) baitaquensis-H. paranaensis (plus Tomiopsis cf. harringtoni and Streptorhynchus? sp.); Atomodesma (Aphanaia) orbirugata-H. paranaensis (plus Sulciplica? sp.); and Myonia argentinensis-H. paranaensis assemblages, which were found in siltstones deposited in shelfal conditions. The youngest fauna is represented by the Phestia aff. sabattiniae-Palaeoneilo sp. (plus Chonetes? rionegrensis, Crurithyris roxoi, Langella? imbituvensis and Orbiculoidea guaraunensis) assemblage and is recorded in massive or well-laminated shales, deposited under anoxic to dysaerobic offshore conditions. Within the studied assemblages key bivalve species for biocorrelations are: A. (Aphanaia) orbirugata, H. paranaensis and M. argentinensis, which indicate correlations with the Eurydesma Fauna, Bonete Formation, Sauce Grande-Colorado Basin, Argentina. The probable occurrences of Tomiopsis cf. harringtoni in the E. itararensis-C. (Paleocosmomya) baitaquensis-H. paranaensis assemblage would also support this correlation. The presence of the productid brachiopod Lyonia and pectinid bivalves (=Heteropecten) in the Butiá assemblage, Taciba Formation, is also noteworthy, suggesting a possible late Asselian?early Sakmarian age, and biocorrelation with Gondwanan deposits of the Carnarvon and Perth basins, Western Australia. In summary, the taxonomic composition of the faunal succession of the Itararé Group, mainly of the Rio do Sul/Taciba Formation, suggests the presence of endemic species in association with marine, cosmopolitan and gondwanic brachiopod and bivalve species. Such character offers valuable clues to better constrain these faunas to the late Asselian?early Sakmarian lapse, linking them to faunas of eastern Argentina and, to a lesser extent Western Australia.