Abstract
Upper Triassic (Karnian-Norian) limestones of the Quatsino Formation, Vancouver Island, and the Kunga Formation, Queen Charlotte Island, were deposited within a complex rifted island arc system, which was accreted to the western margin of North America as Wrangellia during the mid-Cretaceous. Carbonates sedimentation began after a transgressive event submerged the subaerially exposed Karmutsen volcanics. In both Vancouver and Queen Charlotte Islands, the lower part of the carbonate sequence records the widespread development of a shallow, subtidal platform composed mainly of two facies: open-platform deposits (bioturbated fossiliferous wackestones) and platform sand-shoal deposits (oolitic-bioclastic grainstones). This early depositional stage evolved gradually into a second stage characterized by the fragmentation of the platform and development of a carbonate bank/basin topography controlled by extensional tectonics within Wrangellia. The interior facies of these carbonate banks consist of cyclic subtidal lagoonal and tidal-flat limestones, each cycle commonly capped by a vadose diagenetic layer. The bank margin facies comprises exclusively high-energy, oolitic sandshoal deposits. The adjacent basin facies include (1) pelagic/hemipelagic limestones, (2) platform-derived and slope-derived carbonate breccia, and (3) proximal to distal carbonate turbidites. In both island systems, carbonate sedimentation ended abruptly when the isolated carbonate banks were drowned and covered by basinal clastics in responsemore » to rapid subsidence probably caused by tectonic activity within Wrangellia.« less
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