Middle Devonian-Tournaisian miospore biostratigraphy in the southwestern outcrop belt of the Parnaíba Basin, North-Central Brazil

Abstract

This contribution presents the first detailed account of miospore assemblages from outcrop samples of Devonian and Lower Carboniferous rock units exposed along the Tocantins River valley, on the southwestern border of the Parnaíba Basin, Brazil. The miospore assemblages are discussed in the light of zonal schemes currently in use for Euramerican as well as western Gondwanan areas. Eight miospore assemblages are distinguished based on the recognition of selected index species. The six older assemblages are from the Pimenteira Formation and range in age from early Givetian to late early Frasnian. The seventh miospore assemblage concerns the Cabeças Formation and indicates a latest Famennian age. The eighth and youngest miospore assemblage is restricted to the Longá Formation and points out to an early middle Tournaisian age. The miospore results in this paper are compared to previous biostratigraphic works in correlative Devonian and Lower Carboniferous sections of the Parnaíba Basin. They contribute to a better understanding of complex field relationships of regional rock units, particularly as concerns the latest Famennian diamictites and the underlying glacio-eustatic unconformity.