Early to middle Cretaceous paleogeography of north-central British Columbia: stratigraphy and basin analysis of the Skeena Group

Abstract

The Lower–middle Cretaceous Skeena Group records the Early Cretaceous evolution of the southern margin of the Jura-Cretaceous Bowser basin in north-central British Columbia. We formalize Skeena Group nomenclature and present interpretations of three distinct paleogeographic and tectonic phases. During the first phase (Neocomian–Aptian), Skeena deposition was limited to a restricted tidal basin represented by Laventie Formation black-shale deposits, surrounded by coal-swamp deltas of the lower Bulkley Canyon Formation. The lower Skeena Group, correlated to the McEvoy Formation (Bowser Lake Group) in the northern basin, represents final filling of the Bowser foredeep produced by Jurassic accretion of the Intermontane Superterrane to North America. In the second phase (early Albian – Early Cenomanian), marine deposition transgressed eastward and southward accompanied by intrabasinal Rocky Ridge volcanism shedding volcanic detritus into the Kitsuns Creek Member of the Bulkley Canyon Formation. The Rocky Ridge Formation does not correlate northward to other Bowser basin fill but represents intrabasinal volcanism in a transtensional setting along the Omineca continental arc. During the final phase (early–middle Cenomanian), red-bed chert-pebble fluvial deposits of the Rocher Deboule Formation prograded westward, shifting the shoreline to tide-dominated deltas on the far western basin margin. The Rocher Deboule Formation correlates to the Devil's Claw Formation (Bowser Lake Group), the lower member of the Tango Creek Formation (Sustut Group), and, tentatively, to the lower conglomeratic Kasalka Group, all attributed to transpressional Omineca uplift and cannibalization of older Bowser basin fill. Thus the southern basin margin evolved from an Early Cretaceous flexural foredeep to a middle Cretaceous arc setting dominated by oblique convergence, first transtensional then transpressional.