Seismic interpretation (2D and new 3D surveys) has been used to investigate sedimentary fills and timing of tectonic activity offshore Mid Norway. This study was focused on upper Permian and Lower Triassic sedimentary basin fills, but a longer stratigraphic interval (Devonian-Upper Triassic) was analysed in order to get a broad understanding of what happened prior to, during and after deposition of the upper Permian-Lower Triassic successions. The ages of the sedimentary fills were partly constrained by well ties. Seismic reflectors and sedimentary successions below the upper Permian interval are of Late Devonianmid Permian age. Six sedimentary fill geometries (fill type A -F) were identified. These are (A) fault-ward thickening packages with internal strata thickening towards bounding faults, (B) wedge-shaped packages whose internal strata have more or less uniform thickness, (C) sedimentary fills containing fill type A overlain by sedimentary strata with more or less uniform thickness, (D) gently dipping packages that thicken towards deeper areas of the basin, and downlap onto pre-existing topography, (E) gently dipping strata filling depressions, and (F) sedimentary wedge with rotated internal strata and folded top. These fill types were used to determine phases of active tectonics and quiescent phases. Based on temporal changes of the fill types, five late Palaeozoic-Triassic unconformities have been mapped: a nonconformity where the Palaeozoic strata onlap onto the basement, a mid-Permian unconformity, two Early Triassic unconformities and a Middle Triassic angular unconformity. Results show that Devonian-Permian, mid-Permian, late-
In this study, the available 2D seismic lines have been interpreted to understand the basin development and petroleum potential of the Late Cretaceous–Quaternary stratigraphy of the Tanga offshore Basin in Tanzania. Conventional seismic interpretation has delineated eight sedimentary fill geometries, fault properties, stratal termination patterns and unconformities characterizing the studied stratigraphy. The Late Cretaceous was found to be characterized by tectonic quiescence and uniform subsidence where slope induced gravity flows that resulted during the Miocene block movements was the major mechanism of sediment supply into the basin. The Quaternary was dominated by extensional regime that created deep N-S to NNE-SSW trending graben. The graben accommodated thick Pleistocene and Holocene successions deposited when the rate of tectonic uplift surpasses the rate of sea level rise. Thus, the deposition of lowstand system tracts characterized by debris flow deposits, slope fan turbidites, channel fill turbidites and overbank wedge deposits, known for their excellent petroleum reservoir qualities, especially where charged by Karoo Black Shales. Subsequent tectonic quiescence and transgression lead to the emplacement of deep marine deposits with characteristic seismic reflection patterns that indicate the occurrence of Quaternary shale sealing rocks in the study area. The occurrence of all the necessary petroleum play systems confirms the hydrocarbon generation, accumulations and preservation potential in the Tanga Basin.
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