The present study used a multitool approach to characterize fractures of several orders of magnitude in large fracture corridors, caves, and canyons to investigate their impact on fluid flow in carbonate units. The study area is the Brejões carbonate karst system that is located in the Neoproterozoic Salitre Formation in the Irecê Basin, São Francisco Craton, Brazil. The approach included satellite imagery, used for interpreting the regional structural context, Unmanned Aerial Vehicle (UAV) and ground-based Light Detection And Ranging (LiDAR) imagery, used for detailed structural interpretation. Regional interpretation revealed that fracture corridors, caves and canyons occur along a N–S-oriented anticline hinge. An advanced stage of karstification caused fracture enlargement and intrabed dissolution, and the formation of caves and canyons. A river captured by the highly fractured zone along the anticline hinge played an important role as an erosive agent. Detailed characterization of fracture corridors comprised structural analysis, topological studies, persistence estimations, power-law fitting of fracture trace length distributions, and identification of network backbones. Our results indicate that fracture corridors comprise four subvertical fracture sets: N–S and E-W and a conjugate pair, NNE-SSW and NW-SE. Fractures observed in the caves show the same dominant directions. Fracture directions are consistent with a common origin associated with the anticline folding. Fracture traces range from 1.0 m to 300 m, comprising both subseismic (<50 m) and seismic scale fractures (>50 m). Networks have dominance of node terminations Y and X (notably Y), CB values higher than 1.8, high P20 and P21 persistence values, and highly interconnected backbones. Fracture network connectivity is associated with power-law exponents greater than 2.5 for the fracture trace distributions, indicating large influence of subseismic-scale fractures on fluid flow. As the final result of folding and karstification, large volumes of secondary macroporosity were created, particularly in the zone of maximum fracture intensity around the hinge zone of the anticline. This scenario can be used to understand better oil reservoirs formed in similar structural controls in near-surface conditions.@en

The Potiguar Basin, located in the Brazilian Equatorial Margin, evolved from a complex rifting process implemented during the Atlantic Ocean opening in the Jurassic/Cretaceous. Different driving mechanisms were responsible for the onset of an aborted onshore rift and an offshore rift that initiated crustal rupture and the formation of a continental transform margin. Therefore, we applied the backstripping method to quantify the tectonic subsidence during the rift and post-rift phases of Potiguar Basin formation and to analyze the spatial variation of subsidence during the two successive and distinct tectonic events responsible for the basin evolution. The parameters required to apply this methodology were extracted from 2D seismic lines and exploratory well data. The tectonic subsidence curves present periods with moderate subsidence rates (up to 300 m/My), which correspond to the evolution of the onshore Potiguar Rift (∼141 to 128 Ma). From 128–118 Ma, the tectonic subsidence curves show no subsidence in the onshore Potiguar Basin, whereas subsidence occurred at high rates (over 300 m/My) in the offshore rift. The post-rift phase began ca. 118 Ma (Aptian), when the tectonic subsidence drastically slowed to less than 35 m/My, probably related to thermal relaxation. The tectonic subsidence rates in the various sectors of the Potiguar Rift, during the different rift phases, indicate that more intense faulting occurred in the southern portion of the onshore rift, along the main border faults, and in the southeastern portion of the offshore rift. During the post-rift phase, the tectonic subsidence rates increased from the onshore portion towards the offshore portion until the continental slope. The highest rates of post-rift subsidence (up to 35 m/My) are concentrated in the central region of the offshore portion and may be related to lithospheric processes related to the continental crust rupture and oceanic seafloor spreading. The variation in subsidence rates and the pattern of tectonic subsidence curves allowed us to interpret the tectonic signature recorded by the sedimentary sequences of the Potiguar Basin during its evolution. In the onshore rift area, the tectonic subsidence curves presented subsidence rates up to 300 m/My during a long-term rift phase (13 Ma), which confirmed that this portion had an extensional tectonic regime. In the offshore rift, the curves presented high subsidence rates of over 300 m/My in a shorter period (5–10 My), typical of basins formed in a transtensional tectonic regime.@en