Stratigraphic and Tectonic Evolution of the Jurassic Hazelton Trough-Bowser Basin, Northwest British Columbia, Canada

The Hazelton trough--Bowser basin is a large sedimentary basin that developed on volcanic arc rocks of the Stikine terrane in northern British Columbia, Canada. Its fill mostly consists of the Lower to Middle Jurassic Hazelton Group and the Middle Jurassic to Lower Cretaceous Bowser Lake Group. Regional correlations indicate that the Hazelton Group can be divided in two distinct lithostratigraphic intervals separated in most places by an unconformity. The lower Hazelton Group (LHG) is dominated by arc-related volcanic rocks, whereas the upper Hazelton Group (UHG) contains mainly fine-grained clastic rocks and lesser bimodal rift-related volcanic rocks. Lowermost coarse-grained strata of the UHG, including the bioturbated and fossiliferous units of the Smithers Formation and the Spatisizi River Formation, record a transgressive trend consistent with thermal subsidence and relative sea-level rise. Transgression of the Stikine arc culminated with the establishment of deep-water conditions in the Late Toarcian-Early Aalenian, and deposition of the Quock Formation. Interbedded siliceous mudstone and rusty-weathered tuff of the Quock Formation are correlated throughout most of the basin, except in the Iskut River area on the northwestern margin of the basin, where contemporaneous strata of the Iskut River Formation are dominated by rift-related volcanic rocks and conglomerates. Inception of rifting in the Iskut River area constitutes an independent extensional event on Stikinia, and could be related to reorganization of tectonic plates during a protracted period of terrane accretion in the Middle Jurassic. Obduction of the Cache Creek terrane over Stikinia in early Middle Jurassic provided a new source of sediment, which led to accumulation of the Bowser Lake Group. The second pulse of subsidence observed at Todagin Mountain can be explained by sediment loading of the accommodation previously generated during extension of the Hazelton trough in Early Jurassic time.