New palynological and floral information from the Potí Formation (late Viséan), Riacho do Roncador creek, Parnaíba Basin, northern Brazil

IANNUZZI, R.; DI PASQUO, M.M.

Lisboa

Congreso; 1st International Congress on Stratigraphy (STRATI 2013); 2013

Department of Earth Sciences and the Research Centre in Geological Science and Engineering, of the Faculty of Science and Technology, Universidade Nova de Lisboa (New University of Lisbon).

The aim of this contribution is to present the first palynological assemblage recovered from surface deposits of the Poti Formation cropping out in the Riacho do Roncador, northeastern Brazil. The lower Pennsylvanian Piaui Formation unconformably overlies this unit, and unconformably is underlain by the Longá Formation. The Potí Formation consists mainly of sandstones with minor proportions of carbonaceous shales and other siliciclastic lithologies in part fossiliferous, containing plant remains, bivalves, and palynomorphs of early late Visean age. The formation accumulated in fluvial to marine environmental settings. From an outcrop of 5 m thick, five carbonaceous shales and siltstones (3m thick) yielded diverse and abundant well-preserved palynomorphs. The assemblage is composed of 62 indigenous species, of which 57 are spores and 5 are algae, and 32 are reworked species (9 spores and 23 microplankton). First records for the Mississippian of Brazil and South America are also recorded. Stratigraphically significant species, some of them not previously recorded in subsurface investigations, include: Anapiculatisporites concinnus, Tricidarisporites phippsae, Punctatisporites subvaricosus, Foveosporites pellucidus, Grandispora maculosa, Knoxisporites ruhlandi, Verrucosisporites morulatus, Retusotriletes mirabilis, Waltzispora polita, which confirm the late Visean age of the Mag Zone Melo and Loboziak. Worldwide comparison of the Brazilian association indicates greater affinity with coeval palynofloras from Gondwana region (South America and North Africa) and North America. The degree of similarity is likely to be determined by paleolatitude. Sedimentologic features along this section clearly reflect depositional environments between brackish deltaic to estuarine facies. The dominance of Botryococcus with varied morphologies throughout this section, the presence of reworking restricted to the uppermost level and the plant remains found into the basal part, support this interpretation.