ORIGIN TO ACCRETION; CONSTRAINTS ON THE TECTONOSTRATIGRAPHIC EVOLUTION OF THE QUESNEL TERRANE BASED ON A REFINED BIOSTRATIGRAPHIC RECORD
The lower part of the Harper Ranch Group comprises the Tkemlups Formation and the conformably overlying South Thompson Formation. The main part of this succession was deposited between the Lower Tournaisian (duplicata Zone) and Serpukhovian (bilineatus Zone, sensu lato) although locally it may be as old as Early Famennian (triangularis Zone) based on conodonts recovered from conglomerate. This succession is interpreted to represent the development and subsequent infill of an island-arc marginal basin. The McGregor Creek Formation comprises the upper part of the Harper Ranch Group and records carbonate deposition on a slowly subsiding platform during Asselian to Wordian. These successions are separated by an unconformity in which the Pennsylvanian is missing.
Conodont and ammonite collections from the overlying Mesozoic successions provide evidence for the duration of the Nicola Group and aid the identification of an unconformity between Triassic and Jurassic strata in the area. This unconformity can be traced north and south within the Quesnel Terrane and is coincident with an eastward migration of the axis of arc magmatism.
Comparison of the tectonostratigraphic record of the Quesnel Terrane with those of other Cordilleran terranes, such as the Yukon-Tanana, Stikine, Chilliwack, and eastern Klamath terranes, demonstrates broad trends in the timing of major unconformities and suggests their development in a common tectonic regime.