Abstract The intracratonic Paleozoic Parnaíba Basin, NE Brazil covers c . 600 000 km 2 . Lithostratigraphic, mineralogical and geochemical approaches were used to deduce the changing environments of deposition of the Parnaíba Basin based on 150, mostly argillite, samples (Silurian–earliest Triassic). The results indicate that brackish conditions and mixed kerogen sources were important and that the palaeowater depth and sources of meteoric water varied from west to east. The chemical index of alteration results, together with other elemental and mineralogical data, indicate that the western margin was humid until the end of the Carboniferous and then became arid, whereas the eastern margin showed the reverse pattern. This supports observations of major stratigraphic differences between the two margins. There were also major variations in the palaeoredox and palaeosalinity conditions (oxic and fresh to brackish water systems in the east v. suboxic to dysoxic and saline water systems in the west). The clay mineral assemblages are characteristically dominated by kaolinite, which is considered to be inherited from weathering horizons developed in silicic granitic terranes. Regional palaeoclimate reconstructions were carried out in the Parnaíba Basin by linking GPlates software with the South America plate motion model (northwards drift during the Paleozoic coupled with a latest Paleozoic rotation phase) and with the regional database of information on the location, formation name and original references for each locality. Supplementary material: Chemical composition data and geographical coordinates from the 177 outcrops investigated as part of this study: a detailed description of the geochemical and mineralogical analyses with calculation of the CIA value and the GPlates Markup Language File (Animation 1). Supplementary material available online at https://doi.org/10.6084/m9.figshare.c.4100348

Abstract Although Permian fossils have been known from the Parnaíba Basin for two centuries, and some faunal and flora elements are well known worldwide, research on the fossil assemblages from this basin has lagged relative to other, more accessible basins. In the last decade, however, there has been a significant increase in the study of fossils from the two Permian units of the basin: the Pedra de Fogo and Motuca formations. The goal of this contribution is to synthesize and update the existing data on the Permian macrofossils from these formations, and to use them to address biostratigraphic, palaeoenvironmental and palaeogeographical questions. The Pedra de Fogo and Motuca formations are likely to be Cisuralian in age. Contrary to previous reports, there is more than one stratigraphic interval that preserves petrified fossil plants. The possible marine influence proposed for the Pedra de Fogo Formation must be reassessed based on the strongly terrestrial character of its fossil assemblages. Palaeoenvironmental and palaeoclimatic conditions are inferred to be wetter than is typically predicted for this region of the globe based on climatic modelling. Despite sharing some taxa with the Euramerican and Gondwanan biogeographical provinces, the Parnaíba Basin was likely to have been part of a distinct biogeographical province, as indicated by the high degree of endemism displayed by its Permian floras and faunas.