Print this pageEarly Permian Chronostratigraphic Correlation Between Paraná and Tasman Basins, Southern Gondwana
This history is supported initially by event stratigraphy, exactly between two latest sequences of Taciba Fm.\Itararé Group (a deglaciation and an interglacial sequence), where a 0,2m-thick core of marine limestone occurs. It is detrital, brachiopod-bearing wackestone, with a dropstone of basement pebble. The Tasman stratigraphy exhibits Late Carboniferous glacial Wynyard Fm. followed by “glaciomarine” Woody Island Fm. (Asselian) formed by glendonitic siltstones; one is tempted to correlate it with Itararé Group latest interglacial, marine sequence (fossiliferous sandstone, siltstone and shale); supporting the idea is the occurrence of a maximum flooding event in lower part of both units, represented in Woody Island Fm. by Tasmanite Oil Shale. History continues in Tasman Basin where two carbonate platforms developed in Sakmarian and Artinskian times, respectively Darlington and Berriedale limestones: both are fossiliferous, including brachiopods and pectens, and commonly display large dropstones. We tentatively correlate them with two limestone-bearing units in Paraná Basin, the Paraguaçu and Assistencia mbs. of Rio Bonito and Irati fms.; both have a non-marine fauna except Taió Beds in Paraguaçu lower portion, a transgressive sandstone containing pecten bivalves. Besides their approximate time equivalences, chronostratigraphy concepts corroborate: Facies Cycle Wedge (T-R cycle) and Siliciclastic-Carbonate Cycle. The first one is applied to Paraná Basin, where the transgressive half of the F.C.W. is formed by three 3rd order sequences, each one with predominant sandstones in lower part (lowstand tract) and shales in the upper part (highstand): they are in ascending order the Triunfo and Paraguaçu mbs. (Rio Bonito Fm.), the Siderópolis Mb. (R.B. Fm.) and Palermo Fm., and a local, nameless sandy unit and Taquaral Mb. shale of Irati Fm. These three sequences exhibit decreasing thickness and textures, and increasing marine imprints upwards. It follows the mid-part of the wedge, represented by the Assistencia Mb. limestones and black shales. The Triunfo and Siderópolis sandstones are potencial reservoirs for oil, supplied by Assistencia black shales. In Tasman Basin one recognizes two marine, siliciclastic-carbonate cycles: the lower is Bundella Fm. siltstones and limestones, and the upper one the Liffey Group sandstones, Nassau siltstones and Berriedale limestones; both carbonates are large events, despite tropical/temperate setting.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil