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Located on the Brazilian Equatorial Margin, the Mundaú Sub-Basin is the only offshore hydrocarbon-producing region of the Ceará Basin. The origin and evolution of the Mundaú Sub-basin are a consequence of the rupture of the Pangea supercontinent during the Early Cretaceous, which led to the opening and development of the Equatorial Atlantic Ocean. This area has been considered a new exploration frontier, promoting research to be developed in recent years. However, the interactions between transtensive events and spatial-temporal distributions of tectonic subsidence have been poorly studied. To cover this gap, fifty-seven wells and approximately 5800 km of 2D seismic lines were analyzed to understand these events. From these data, stratigraphic and structural interpretations were performed throughout the sub-basin, enabling the construction of 43 pseudo-wells. Using descompactation of the wells and pseudo-wells using the backstripping method, it was possible to reconstruct seven tectonic phases for the Sub-Basin, which correspond to the rift sequence (RP01, RP02, and RP03), the transition sequence (BP01), and the drift sequence (DP01, DP02, and DP03). Four sets of faults of three zones of the three zones (WZ, CZ and EZ) proposed for the Mundaú Sub-Basin were also analyzed. The faults are distributed in two orthogonal families, formed in two distinct events. Older R and P faults, respectively trending NWW-SEE and NNESSW, formed during RP01 (first event). Younger R and P faults, respectively trending NNW-SSE and NEE-SWW, formed during RP02 (second event). Tectonic reconstruction revealed the diachronic formation of two depocenters, one in the West Zone (WZ) during RP01, and the other in the Central Zone (CZ) during RP02. Despite the intense tectonic activity in WZ and CZ, the East Zone (EZ) showed low subsidence rates and little development during the entire rift phase. In turn, BP01 showed faster subsidence rates when compared to RP03, indicating tectonic influence even during the breakup phase. Finally, the drift phase showed the lowest subsidence rates, spatially distributed in an opposite pattern to the rift phase. From these results, a rotation of the Principal Displacement Zone (PDZ) was identified, with initial parallel motion vectors, forming the WZ depocenter and generating the first fault family during RP01; after RP02, motion vectors were oblique, forming the second depocenter in CZ and generating the second fault family. Significant thermal control associated with magmatic events was identified during the drift phase. This study also describes the main structures formed along with the overlap of parallel and oblique PDZ displacement. [Display omitted] • This study provides new insights into the Mundaú Sub-Basin geodynamic evolution. • Tectonic stress and subsidence patterns from Early Aptian to Holocene. • Strike-slip features from seismic and subsidence rates obtained from decompression of well and pseudo-well data. • Evidence of the superposition of parallel and oblique Principal Displacement Zone. • Tectonic, thermal, and basement inheritance controls acting during rift, breakup and drift phases. [ABSTRACT FROM AUTHOR]

An organic geochemical investigation combined with sequence stratigraphy was performed in the Ceará Basin, an offshore basin located in Northeastern Brazil. The information available from 30 well logs (gamma-ray, resistivity, density), besides geochemical (TOC, and pyrolysis indexes) and isotopic (δ13C) data, aided the preparation of a dataset for this study. The application of sequence-stratigraphic methods helped classify and correlate seismic and organic facies. Four key petroleum source-rock units were identified, from the oldest to the youngest: (1) Mundaú Formation – top of the Rift Sequence (Berriasian-Aptian); (2) Paracuru Formation – Breakup Sequence (Aptian-Albian); (3) Itapajé Member of the Ubarana Formation – Continental Drift Sequence (Albian-Turonian), and (4) Uruburetama Member of the Ubarana Formation – Continental Drift Sequence (Turonian-Maastrichtian). The geochemical characteristics of the Mundaú Formation (high total organic carbon (TOC), hydrogen index (HI), relative hydrocarbon potential (RHP = (S1 + S2)/TOC)) point to a typical transgressive sequence. Six transgressive-regressive (T-R) cycles were recognized in the entire Paracuru Formation. The best geochemical marker is related to the top of the Paracuru Formation. This stratigraphic unit can be correlated to a major anoxic event and is the best source rock of this basin. Evaporitic facies found in this top section, maximum RHP values (anoxic conditions), and maximum flooding surfaces related to transgressive events characterize this interval. Moreover, the wide spatial cover of organic-rich rocks, carbon isotopic data, and the recognition of favorable characteristics for anoxia in other basins of the Equatorial Margin are suggestive of the Aptian-Albian Oceanic Anoxic Event (OAE-1b) occurring in the Ceará Basin. The Ubarana Formation represented by the Uruburetama Member and the Itapajé Member yields the least promising source rocks. However, high TOC values suggest the occurrence of the late Cenomanian–early Turonian Oceanic Anoxic Event (OAE-2), when organic-rich strata started to deposit in deep-water regions. The predominance of a regressive interval in the Uruburetama Member points to oxic or sub-oxic conditions. Additionally, the correlations between the Brazilian Equatorial Margin and its African counterpart, and the organic geochemical characterization allied to the definition of depositional systems for these regions proved to be useful for oil exploration. Flowchart representing the steps of this research. A) Database components. B) Data interpretation. C) Relative hidrocarbom potential (RHP) variations revealing changes in oxic conditions at depth and correlations with gamma-ray (GR) and lithofacies (Facies) stacking patterns. D) Sections showing the results obtained from data interpretation. E) A simplified model for the Paracuru Formation. [Display omitted] • Stratigraphic evolution, organic geochemistry, and Cretaceous Anoxic Events (CAE) were investigated. • Well-log correlations, redox conditions, and modeling to investigate anoxic events occurring in the Ceará Basin. • Relative sea-level fluctuations in 3rd- and 4th-order sequence-stratigraphic contexts are presented. • Relative hydrocarbon potential (RHP) as a geochemical index that reflects oxygenation conditions. • Anoxic markers were defined in the organic-rich, transgressive systems tracts (TST) and condensed section (CS) strata. [ABSTRACT FROM AUTHOR]