Carbonate-clastic sedimentation in the Parnaiba Basin, northern Brazil: Record of carboniferous epeiric sea in the Western Gondwana

Abstract

The transgressive-regressive events due to changes in the eustatic sea level represent the occurrence of an epeiric sea in Western Gondwana. This event is recorded in the carbonate-siliciclastic succession exposed in the central portion of the Parnaiba Basin, Northern Brazil, mainly represented by densely fossiliferous deposits, with mollusks, brachiopods, corals and microfossils, related to the upper member of the Piauí Formation. Outcrop-based facies/microfacies and stratigraphic analysis of this succession allowed the individualization of two facies associations (FA), representative of a shallow carbonate platform system adjacent to a coastal dune field. The FA1– dune field/interdune, comprises well sorted, intensely biortubated, fine to medium-grained sandstone with even parallel and tabular cross stratification, as well as translatent climbing ripple cross-lamination. FA2-shallow sea deposits consist of fossiliferous pelletal carbonate and microspar carbonate layers, laterally continuous for hundreds of meters, interbedded with centimetric beds and lenses of organic shale with small pyrite crystals. Covariant values of positive δ18Ocarb and negative δ13Ccarb for the carbonate profiles, together with intense substitution of primary constituents by dolomite and an abundance of associated organic matter contributed towards determining an organogenic dolomitization model. Although the Pennsylvanian records a long icehouse event, glacioeustatic fluctuations were common during the Moscovian and Kasimovian. The icehouse periods contributed to the semi-arid to desert conditions that shaped the aeolic environments of the Piauí Formation. Later greenhouse events favored a rise in the sea level and development of an extensive epicontinental Pennsylvanian sea that extended throughout Western Gondwana called the Itaituba-Piauí sea in this paper, which connected the Andean, Solimões, Amazonas and Parnaíba basins.