The pre-Silurian Riachão basin: a new perspective on the basement of the Parnaíba basin, NE Brazil
Amanda Porto, Michael C. Daly, Emanuele La Terra, Sergio Fontes, 2018. "The pre-Silurian Riachão basin: a new perspective on the basement of the Parnaíba basin, NE Brazil", Cratonic Basin Formation: A Case Study of the Parnaíba Basin of Brazil, M. C. Daly, R. A. Fuck, J. Julià, D.I.M. MacDonald, A. B. Watts
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We present a new interpretation of the basement immediately below the pre-Silurian unconformity in the mid-western part of the Parnaíba cratonic basin. Regional seismic reflection data, constrained by well and gravity data, have revealed the remnants of a pre-Silurian basin named the Riachão basin. It has a north–south trend and is about 120 km wide with a minimum area of c. 35 000 km2 and a maximum thickness of 4 km. Seismic interpretation shows the Riachão basin is defined by erosional unconformities at its top (the pre-Silurian unconformity) and base (the top of the pre-Riachão basement). The basin fill is formed of three stratigraphic sequences – Riachão I, II and III – separated by seismic discontinuities and laterally bounded by monoclinal folds and basement uplifts related to thrust faults. Exploration wells show that the Riachão sediments are Ediacaran to Lower Cambrian, clastic and a minimum of 1 km thick, unconformably overlying a heterogeneous metamorphic basement. The mechanism of formation of the basin is unclear. However, our seismic stratigraphic interpretation suggests that Riachão II and III are remnants of marine, clastic, foreland basin sequences of opposed polarity, related to late Neoproterozoic tectonics. The banded, high-amplitude, Riachão I sequence is interpreted as a carbonate platform preceding the main subsidence and clastic input of the Riachão basin.
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Cratonic Basin Formation: A Case Study of the Parnaíba Basin of Brazil
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Cratonic basins are large, distinctive features of the continental crust. They are preferentially developed on thick continental lithosphere, are typically sub-circular in shape and subside over periods of hundreds of millions of years. They are also endowed with significant resources. However, in spite of their location in continental interiors and often well-known geology, the subsidence driving mechanism and tectonic setting of these basins remains controversial.
This volume presents both lithospheric and basin scale datasets acquired specifically to interrogate the tectonic process of cratonic basin formation. Focused on the Silurian to Triassic Parnaíba cratonic basin of Brazil, the papers discuss the results of a multidisciplinary basin analysis project comprising new geophysical, geological and geochemical data. This unique dataset enables the characterization of the lithospheric crust and mantle beneath the Parnaíba Basin, constrains the detailed evolution of the basin itself, and enables comparisons with cratonic basins globally. Several convergent themes emerge providing new and powerful constraints for models of the driving mechanisms of these enigmatic basins.