Abstract We investigated the crustal architecture of the Parnaíba basin of NE Brazil by analysing receiver functions along a c . 600 km long transect crossing the central portion of the basin. The transect consisted of nine broadband stations interspaced at c . 70 km distance recording continuously for a period of 15 months, with the goal of improving our understanding of the origin and evolution of this large cratonic basin. Our results show that crustal thickness varies between 39 and 45 km along the transect, gradually thickening towards the depocentre, and that bulk V p / V s ratios vary between 1.70 and 1.78. The crust can be divided into a 2.0–3.5 km thick layer of low-velocity sediments, a 15–20 km thick upper crust (3.5 < V s < 3.6 km s −1 ) and a 18–22 km thick lower crust (3.7 < V s < 3.8 km s −1 ). Near the depocentre, where the crust is thickest, the bottom 10–12 km of the crust are characterized by fast S-velocities (4.0–4.2 km s −1 ). Our findings confirm that stretching of the lithosphere is minimal and compatible with flexural subsidence. However, loading from a thick, high-density layer of mafic intrusive rocks pervading the lower crust – as recently proposed for the basin – is found to be inconsistent with our bulk V p / V s ratios and lower crustal S-velocities. Flexural bending by a deeper load, perhaps related to deep mantle convection, seems more plausible.

Abstract Cratonic sedimentary basins are underlain by thick lithosphere and subside over hundreds of millions of years. The driving mechanism for these basins remains enigmatic due to the paucity of crustal-scale constraints. To address this shortcoming, an integrative study of the Parnaíba cratonic basin of NE Brazil is underway. We summarize field observations, well-log information, seismic reflection profiles and subsidence analyses with the objective of shedding light on possible basin-forming mechanisms. Lithological descriptions and borehole logs reveal a stratigraphic succession that consists of interbedded shallow marine and continental deposits. On seismic reflection profiles, this succession is divided into packages of relatively undisturbed reflections bounded by basin-wide disconformities. These disconformities are manifest as bright, rugose reflections that probably represent buried palaeo-landscapes. Backstripped and water-loaded subsidence curves calculated from boreholes distributed throughout the basin show that tectonic subsidence decreases exponentially over c . 350 Ma. A simple model suggests that this subsidence pattern agrees with a thermal time constant of 70–100 Ma, placing a significant constraint on the likely basin-forming mechanism. This background trend is punctuated by minor increases in subsidence that follow basin-wide erosional disconformities. These departures could be indicative of transient epeirogenic uplift events caused by changing patterns of dynamic topography.