Abstract The processes that govern formation and development of cratonic basins are poorly understood, both individually and as a class. The cratonic Silurian–Jurassic Parnaíba Basin in NE Brazil is less well-studied than North American examples such as Williston, Illinois and Michigan but offers an opportunity to study stratal architecture both in outcrop and the subsurface. Published stratigraphic compilations emphasize basin-wide unconformities separating layer-cake, basin-wide packages; analysis of geological maps indicates this interpretation is over-simplified, with at least 12 local unconformities, concentrated along the SW basin margin. Comparison of basin-margin and intrabasinal well-correlation panels shows that unconformities are more common in marginal areas, so the current exposure margins may have some validity as near-original margins. Palaeocurrents suggest a consistent SW–NE transport direction for the Serra Grande and lower Canindé groups. Supporting heavy mineral analysis from Silurian–Carboniferous strata on the SW and NE basin margins show that assemblages are dominated by ultra-stable zircon, tourmaline and rutile with minor amounts of staurolite, especially in the SW and older units. Tourmaline varietal results are remarkably consistent across the basin. U–Pb age spectra from detrital zircons are dominated by Neoproterozoic grains, with subsidiary Meso-Paleoproterozoic provenance. We infer that the source terrane was a medium-grade regionally metamorphosed mica schist, probably the Araguaia Fold Belt. These results are indicative of a large sediment routing system feeding material across an evolving crustal sag, analogous to observations from North American cratonic basins; this suggests that cratonic basins may not have strongly shaped or controlled the routing system. Supplementary material: High-resolution geological map of the Parnaíba Basin as a PDF. This shows all of the basement units and small details of the stratigraphic relationships between different basin-fill formations. This map is derived from the ArcGIS files of CPRM (2004) . Supplementary material available at https://doi.org/10.6084/m9.figshare.c.4183472

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.

Abstract Only Several wells drilled during the 70s and 80s in shallow waters of Pará-Maranhão offshore basin, Brazilian Equatorial Atlantic Margin, discovered Albian to Cenomanian source rocks, good Cenomanian to Santonian reservoirs, and, most importantly, recovered oil. Petrophysical reassessment of those wells using new techniques and knowledge combined with new 3D seismic acquisition methods and interpretation models guided by new theories on the breakup of continental margins, has shed light and improved understanding of the tectono-stratigraphic evolution of the Pará-Maranhão offshore basin and its petroleum system. The breakup of the Brazilian Equatorial Atlantic Margin at the Pará-Maranhão offshore basin occurred during the late Albian (102 Ma). The immediate post-breakup marine transgression over ancient continental areas coupled with the irregular paleotopography inherited from the rift phase created localized ponds and conditions for the source rock deposition. In the same period, the global geological record registers two anoxic global events, OAE1d (Breistroffer) and OAE2 (Bonarelli). Those two events enhanced the potential for source rock deposition during the early drifting phase in the Pará-Maranhão offshore basin. The new 3D seismic data show features suggesting that after the initial transgressive phase, when the source rock was deposited, recurrent deltaic progradation occurred and delivered sandy deposits on the continental shelf. Seismic imaging (geometry and three-dimensional distribution of the depositional bodies), well data (logs, lithology, biostratigraphy), and paleoecologic interpretation strongly suggest that the sandy bodies deposited on the shelf are turbidities likely fed by the same fluvial system ascribed for the deltaic building. The subsequent overburden of the drift succession pushed the source rocks into the oil window. The close proximity of source rock to the reservoirs, helped by faults active just after the breakup, represent an exceptional condition for migration and focalization of the hydrocarbon into the reservoirs. Some wells drilled in the analyzed area had oil shows and even have produced oil. However, all of them were classified as noncommercial. The posteriori assessment led to two conclusions: (1) the 2D seismic data available at that time precluded good imaging and hence compromised the interpretation of the tectono-sedimentary evolution of the basin and its petroleum system; and (2) the drilling and resource assessment at that time also precluded a conclusive result on the potential of those wells. Nevertheless, new data, techniques, and knowledge available nowadays have enhanced the confidence considering this area as a potential oil province.

The Phanerozoic Parnaíba sedimentary basin in the north-northeastern region of Brazil covers an area of ~400,000 km 2 and contains a number of circular structures, four of which are of possible impact origin: Serra da Cangalha, Santa Marta, Riachão, and São Miguel do Tapuio. All four exhibit a central morphological feature resembling a central uplift, characteristic of complex impact structures. A recently acquired regional aerogeophysical survey provided magnetic and gravity data for the entire basin. The magnetic and gravity characteristics of the four possible impact structures of the Parnaíba Basin were analyzed in comparison with impact structures elsewhere in the world. The analysis shows that, except for the São Miguel do Tapuio structure, three of the structures exhibit geophysical characteristics similar to the signatures found in some known impact structures of comparable sizes that have formed in clastic sedimentary rocks. Serra da Cangalha structure exhibits magnetic highs and gravimetric lows, Santa Marta structure exhibits magnetic lows and gravimetric highs, Riachão structure depicts subdued gravimetric and magnetic highs, and the São Miguel do Tapuio structure shows a magnetic high and a complex gravimetric signature. Based on the observed geophysical signatures presented here, Serra da Cangalha, Santa Marta, and Riachão could be regarded as potential impact structures, whereas São Miguel do Tapuio is the least likely of these four structures to have been formed by an impact event.