A comparative study of the Parnaíba, Michigan and Congo cratonic basins

Abstract

We used compilations of geological and geophysical data to compare the structure, subsidence history and evolution of the Parnaíba, Michigan and Congo cratonic basins. These basins consist of 3–6 km of Paleozoic to Recent sediments and are located on thick (>150 km) lithosphere, far from plate boundaries. Sediment-corrected Bouguer gravity anomalies show that the basins are associated with a central high of up to 40–60 mGal. The high could reflect crustal thinning, but seismic refraction data suggest that the Moho is either at a similar depth or deeper beneath the basins than beneath their flanks. The seismic reflection profiles show no evidence of extensional structures in the underlying basement. We propose that the central high reflects an extensive igneous intrusion, which, on solidification, loaded the crust and lithosphere, causing a surface flexure into which sediments accumulated. Viscoelastic plate modelling of the backstripped well data shows that a subsurface load can explain the tectonic subsidence of the basins as well as some details of their internal stratigraphy, including offlap. Offlap, a ubiquitous feature of cratonic basins, can therefore be explained by tectonics in the form of flexure and does not require other controlling factors such as long-term sea-level changes.

Cratonic basin formation: a case study of the Parnaíba Basin of Brazil

“…They also record an unexpected bulk conductivity increase in the crust beneath the central part of the Parnaíba Basin. This broadly corresponds to the observations of the sediment-corrected Bouger gravity anomaly high of + 40-60 mGal of Watts et al (2018), and the anomalously high, uppermantle (V p 8.2-8.4 km s −1 ) and lower-crust (V p 6.7-6.8 km s −1 ) P-wave velocities of Soares et al (2018) and lower-crustal S-wave velocities (V s 3.7-3.8 km s −1 ) of Coelho et al (2018). Solon et al (2018) suggest this zone may be related to Brasiliano orogenesis or to the igneous events of the Triassic and Cretaceous.…”

“…• There is good agreement on the high seismic velocity of the lower crust and upper mantle beneath the Parnaíba cratonic basin between the teleseismic receiver function data of Manenti et al (2018) and the WARR of Soares et al (2018). In line with these observations, Watts et al (2018) used gravity modelling to conclude that from the zone of mid-crustal reflectivity (MCR) downwards to the Moho and possibly into the upper mantle, there is a zone of relatively dense mafic material that underlies the basin centre. Further supporting these observations of anomalous crust, Solon et al (2018) define a central conductive zone beneath the centre of the basin extending down c. 100 km.…”

“…• The origin and age of the anomalous highvelocity, conductive and enriched lower crust and upper mantle appears key to understanding basin formation, whether it reflects a post-cratonic basin Mesozoic event, or something earlier and related to the cratonic basin initiation. If it is an Early Paleozoic event, a possibility raised by Padilha et al (2015) for the Paraná Basin, it may be indicative of the subsidence-driving mechanism of the basin as proposed, for example, by Watts et al (2018). The isotopic and traceelement analysis of mantle nodules from kimberlite pipes across the basin could greatly enlighten this issue.…”

“…Solon et al (2018) suggest this zone may be related to Brasiliano orogenesis or to the igneous events of the Triassic and Cretaceous. A further possibility is that the zone records the dense load required to generate the subsidence of the basin in the early Phanerozoic as postulated by Watts et al (2018).…”

“…Taking a comparative approach to the same question, Watts et al (2018) have compiled geophysical and geological data to compare the structure, subsidence history and evolution of the Parnaíba, Congo and Michigan cratonic basins. Of the many commonalities between the basins, they focus on the central gravity high evident in each of them.…”