Seismic Stratigraphy and Tectonic Evolution of the Forearc Georgia Basin (Upper Cretaceous–Miocene), Canada and USA , With Implications for CO 2 Sequestration

ABSTRACT The Georgia Basin in southwest Canada and northwest USA is a Late Cretaceous to Cenozoic forearc basin that transitioned into a forearc depression in the Eocene following uplift of the forearc high (Vancouver Island). Both the tectonostratigraphic transition of the Georgia Basin from a conventional forearc basin to a forearc depression and the CO 2 sequestration potential in the basin overall remain poorly understood due to limited subsurface data and complex tectonic histories. This study uses 2D seismic and well data to reconstruct the subsurface architecture of the Whatcom Sub‐Basin, which is the southeastern depocenter of the Georgia Basin. The Whatcom Sub‐Basin exhibits a wedge‐shaped geometry and thickens to the south and west; the thickest strata exceed 7000 m and are located east of the Outer Island Fault and below the Strait of Georgia. Basin architecture is shaped by NE‐SW and NW‐SE normal faults, including the Outer Island Fault which exhibits 5.9 km of vertical displacement. Four key tectono‐stratigraphic units are identified: the lower and upper Nanaimo Group, Huntingdon Formation, and Boundary Bay Formation. These units document episodes of erosion and tectonic reorganization and are separated by basin‐margin disconformities that transition to correlative conformities with localized erosion toward the basin center. The Upper Cretaceous Nanaimo Group (both lower and upper) records the initial phase of deposition within a forearc basin and its thickness is controlled by faults and underlying structural highs and lows of the Coast Plutonic Complex. In contrast, the overlying Huntingdon and Boundary Bay formations display more tabular geometries that were deposited in a forearc depression. Both fault density and throw decrease upsection and record the shift to relative tectonic quiescence in the Cenozoic. An eastward reduction in deformation demonstrates asymmetric strain distribution. The evolutionary pathway of the Georgia Basin makes it an exceptional example of forearc depression development, and the architecture of strata therein suggests there is significant potential for CO 2 storage. Specifically, the broad extents, consistent thickness and limited faulting of the Huntingdon and Boundary Bay formations suggest both intervals are favourable targets for CO 2 storage. Future high‐magnitude earthquakes may reactivate faults that crosscut the sedimentary fill; however, CO 2 leakage risk may be reduced through mineral trapping and by injecting CO 2 ‐water solutions in areas where faulting is minimal. By linking tectonic events to stratigraphic architecture, this study not only provides new insights into the multi‐phase evolution of the convergent‐margin Georgia Basin, from forearc basin to forearc depression, but also demonstrates how such systems can provide favourable geological conditions for carbon sequestration.