Rocks of the Quesnel Lake area belong to three terranes. These are, from east to west, the Barkerville terrane (a continental prism sequence), the Slide Mountain terrane (an ocean-floor sequence), and the Quesnel terrane (an island-arc-marginal basin sequence). The major deformation of these rocks occurred during the Jurassic. There has been renewed discussion recently as to whether the Barkerville terrane was deformed prior to the Jurassic. Two conglomerate localities within the Quesnel terrane contain clasts we identify as being derived from deformed rocks of the Barkerville and Slide Mountain terranes. These include gneiss, orthoquartzite, graphitic phyllite, and grit from the Barkerville, and serpentine-talc and chromite fragments from the Slide Mountain terrane. Some clasts inferred to be from the Barkerville terrane show two predeposition foliations, implying two phases of deformation prior to the deposition of the conglomerate (Middle Jurassic at the latest). One of these events may be deformation associated with the intrusion of Devonian granitoid bodies. Deformation must also have accompanied the emplacement of the Slide Mountain terrane some time between its deposition (Mississippian-Permian) and its erosion (Triassic-Jurassic).

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