Abstract
The Mirandiba Basin has a well-defined stratigraphic sequence and its sedimentation may be directly correlated with the Jatoba Basin and some other interior basins. The sedimentation began in intracratonic conditions with a Paleozoic sequence (Tacaratu/Inaja Formations), which acted as a substrate without any genetic relationship with the basin. The fluvial Tacaratu Formation emerges beyond the limits of this basin, where a remnant core named here as Poco do Ico was found wrapped around the basement to the west of the basin. Subsequently, there was a deposition in a shallow marine environment of the Inaja Formation (Devonian) formed by the intercalation of clay/siltstones and sandstones with ichnofossils. Pre-rift sedimentation occurs over the Paleozoic sequence, characterized in the basin by the lacustrine sediments of the Alianca Formation, represented by the intercalation of shales and calcarenites with desiccation cracks and fossil fragments. In spite of depositional gap described between the local Aratu and Alagoas Stages, the presence of Salvador Formation close to the north border fault may represent a rare rift phase record in the interior basins. The post-rift sequence is represented by the Marizal Formation, deposited during the Aptian. This formation is distinguished by the intercalation of fine sandstone, siltstone and conglomerate deposited in an alluvial fan environment. The pre-rift, rift and post-rift sedimentation are embedded in the depocenter of the basin, where the main NE-SWgraben stands out. A gravity survey was carried out, which obtained a negative, asymmetric Bouguer anomaly, with gradients added to the northwest, suggesting the existence of a half-graben. The result of the gravity 3D model indicates the existence of a main depocenter in the NE-SW direction with depths of up to 400 meters. These geophysical results support the tubular well location drilled 410 m in depth that was used in this work to better characterize the basin. The joint interpretation of gravity, aeromagnetic and structural data suggest that the half-graben framework of the basin developed by the evolution of a pull-apart extension system. The structural system that gave rise to the Mirandiba Basin has the maximum compression tensioner oriented to NE-SW and the distention to NW-SE. It has a depth of around 400 meters and the depressions formed by tectonic events were filled by Post-Tacaratu sedimentation.
Highlights
The central-western portion of the Borborema Province concentrates the majority of the Cretaceous intracontinental basins at the northern end of the Recôncavo-Tucano-Jatobá rift (Milani and Davison, 1988) formed in the Brazilian territory (e.g. Araripe, Cedro, Mirandiba, Betânia, Fátima basins, among others).The deformation that controlled the development of these basins has a clear connection with previous structures of the crystalline basement that constitute discontinuous areas of weakness that act as concentrators of the associated deformation
This paper presents the integrated results of a terrestrial gravity survey, the interpretation of 405m of geophysical logs of gamma-ray (GR), spontaneous potential (SP), resistivity (SN) and sonic log (DT) parameters obtained from the Sítio Ervanso borehole and the systematic geological mapping, using fieldwork, petrographic, structural and paleontological aspects including stratigraphical sections surveyed along the basin units
The readings of radiation levels were made in the ferruginous sandstones, the concentrations of the radioisotopes are measured in percentage (%) for Potassium (K), part per million for equivalent Uranium and equivalent Thorium
Summary
The central-western portion of the Borborema Province concentrates the majority of the Cretaceous intracontinental basins at the northern end of the Recôncavo-Tucano-Jatobá rift (Milani and Davison, 1988) formed in the Brazilian territory (e.g. Araripe, Cedro, Mirandiba, Betânia, Fátima basins, among others). The deformation that controlled the development of these basins has a clear connection with previous structures of the crystalline basement that constitute discontinuous areas of weakness that act as concentrators of the associated deformation Some discontinuities such as Patos and Pernambuco lineaments were partially derived from the Transbrasiliano Lineament and may have played an important role in the lateral escape of masses (Ganade et al 2013) and were effectively reactivated in the Cretaceous times (Destro et al 1994; Lopes et al 2019; Vasconcelos 2018). The tectonic rearrangement resulting from these reactivations and which favored the installation of the interior basins suggests a set of distensional systems dominated by strike-slip deformation (Heine et al 2013) In this context, the Mirandiba Basin has dimensions of approximately 120 km. This paper presents the integrated results of a terrestrial gravity survey, the interpretation of 405m of geophysical logs of gamma-ray (GR), spontaneous potential (SP), resistivity (SN) and sonic log (DT) parameters obtained from the Sítio Ervanso borehole and the systematic geological mapping (scale 1:100.000), using fieldwork, petrographic, structural and paleontological aspects including stratigraphical sections surveyed along the basin units
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