Abstract

Backstripping calculations performed on a stratigraphic section near Todagin Mountain, north-central British Columbia, indicate that the northern edge of the Hazelton Trough–Bowser Basin was characterized by two phases of enhanced subsidence. An initial episode of rapid subsidence occurred in the Pliensbachian, during which bimodal volcanic flows and associated sedimentary rocks were deposited in a shallow-marine environment. This episode corresponds to the end of a rifting event in the Stikine arc when most of the accommodation space was generated by extensional faulting of the predominantly igneous basement. Slower subsidence took place in Toarcian to Bajocian time along with deposition of a condensed section in a deep-water basin. This part of the history is consistent with thermal subsidence following the end of volcanism. An increase of subsidence rates in the Bathonian–Callovian interval was accompanied by increased sediment supply, marking the start of deposition of the Bowser Lake Group. This second pulse of rapid subsidence can be explained by sediment loading alone but the subsidence history does not rule out tectonic loading of the basin floor. The Jurassic subsidence history observed at Todagin Mountain is consistent with a simple extensional model defined by a rifting episode followed by thermal contraction and sediment loading. Tectonic loading might also have played a role in the second episode but is not required by the subsidence model.