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Structure, evolution, and petroleum potential of the Queen Charlotte Basin Lyatsky, Henry

Abstract

This study focuses on the structure and evolution of the Tertiary Queen Charlotte sedimentary basin and its petroleum potential. The study is based on integrated geological basin analysis, which involves compiling all relevant geological, geophysical, and geochemical data; interpreting them using a multidisciplinary approach; and creating a petroleum-exploration model for the basin. The Queen Charlotte Basin lies offshore, and its geologic structure was interpreted from gravity, magnetic, and seismic data. Potential-field trend patterns are similar to physiographic lineaments. Regional faults are the Kitkatla, Principe Laredo/Banks Island, and Sandspit. Their crosscutting relationships, lack of strike-slip displacements, and presence of through going Oligocene dikes, all preclude substantial strike-slip movements in the basin during the Neogene. The origin of the basin by large extension and strike-slip faulting is ruled out; a model based on block tectonics is offered instead. The similarity of orthogonal, Tertiary fault networks within the basin with Mesozoic or older networks on its flanks, suggests the inheritance of the main structural characteristics of the basin from pre-Tertiary time. Themosaic of fault-bounded blocks was formed no later than the Late Jurassic; since then, block faulting and structural inversion have occurred repeatedly. Tertiary extension was too small to obliterate the older fault pattern. Large plutons lie beneath eastern Queen Charlotte Sound, on trend with the Neogene Anahim volcanic belt on the mainland. These features reflect the passage of the region over a mantle hot spot in the Miocene, which may have also caused the renewal of tectonic activity. Igneous heating and hydrothermal-fluid circulation occurred locally, whereas burial-related conductive heating was regional in scale. Petroleum potential is associated chiefly with Mesozoic rocks beneath Queen Charlotte Sound. Source rocks occur in the Upper Triassic-Lower Jurassic interval, and reservoirs in the Cretaceous units. Tertiary rocks form a regional seal. The Hecate Strait area lacks thick Mesozoic rocks, but the Queen Charlotte Sound area contains Mesozoic source and reservoir rocks, overlain by a Tertiary seal. The Cretaceous stratigraphic interval, which may contain large block structures, should be the primary target for future petroleum activity.

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