Subsidence dynamics of the Montney Formation (Early Triassic, Western Canada Sedimentary Basin): insights for its geodynamic setting and wider implications

Sébastien Rohais 1 Vincent Crombez 1 Tristan Euzen 2 John-Paul Zonneveld 3
1 IFPEN - IFP Energies nouvelles
2 IFP Technologies
3 Ichnology Research Group
Abstract : This study presents the first published subsidence analysis during the deposition of the Montney Formation. It was deposited during the Early Triassic (ca. 252.2–245 Ma) in the Western Canadian Sedimentary Basin (WCSB) located along the western margin of the North American craton. Subsidence analyses of six representative wells and two outcrop sections along a proximal to distal transect are presented using a backstripping method integrating recent high-resolution stratigraphic correlations for the Montney Formation. The entire Paleozoic to Cenozoic sedimentary column of the WCSB was backstripped to put the deposition of the Montney Formation into a broader context and provide results regarding the type of subsidence and geodynamic setting for the Montney Formation. The spatial and temporal evolution of the subsidence during the deposition of the Montney Formation indicates that the most likely basin setting is a foreland. The tectonic subsidence during the Triassic is herein interpreted as a combination of the topographic loading of the orogenic wedge (flexure) and the sublithospheric “loading” caused by slab load-driven subsidence (dynamic subsidence). This suggests that the retro-foreland basin setting was associated with an eastward dipping subduction during the deposition of the Montney Fm. Three foreland stages are thus recorded in the whole WCSB, with evidence for: 1) a Late Permian (fore-arc) pro-foreland setting; then 2) a Triassic collisional retro-foreland basin prior to the well-known; 3) Jurassic-Cenozoic collisional retro-foreland.
Keywords : slabs Slide Mountain Terrane subduction subsidence lithosphere Lower Triassic high-resolution methods Alberta backstripping basins British Columbia Canada Canadian Cordillera clastic rocks correlation deformation deposition flexure fold and thrust belts foreland basins geodynamics geosynclines Mesozoic miogeosynclines Montney Formation North America North American Cordillera North American Craton oceanic lithosphere Omineca Belt outcrops Pacific Plate plate collision plate tectonics sandstone sediment supply sedimentary rocks shale siltstone tectonic wedges terranes thickness Triassic Western Canada Western Canada Sedimentary Basin Yukon-Tanana Terrane
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Sébastien Rohais, Vincent Crombez, Tristan Euzen, John-Paul Zonneveld. Subsidence dynamics of the Montney Formation (Early Triassic, Western Canada Sedimentary Basin): insights for its geodynamic setting and wider implications. Bulletin of Canadian Petroleum Geology, Canadian Society of Petroleum Geologists, 2018, 66 (1), pp.128-160. ⟨hal-02196726⟩

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