A basin analysis of the Lower to mid-Cretaceous Skeena Group, west-central British Columbia: Implications for regional tectonics and terrane accretion

The Lower to mid-Cretaceous Skeena Group was deposited in the Jura-Cretaceous Bowser basin on the Intermontane Superterrane in central British Columbia, now between cratonic North America and the Insular Superterrane. The thesis formalizes nomenclature, interprets depositional environments, paleogeography, provenance and basalt geochemistry based on measured profiles, paleocurrent measurements, facies relations, modal analyses, trace-element geochemistry, and {dollar}sp{lcub}40{rcub}{dollar}Ar/{dollar}sp{lcub}39{rcub}{dollar}Ar dating, and develops a regional tectonic interpretation.; The earliest phase (Neocomian-Aptian) contains tidally dominated, shallow marine deposits surrounded by coal-swamp deltas, based on marine fossils, paired mud drapes, and graded beds fining to coal, suggesting a period of low sedimentation and subsidence rates in the final stages of the transpressional(?) Bowser foredeep basin formed in response to Jurassic accretion of the Intermontane Superterrane to North America. The second phase contains a marine transgression, based on the expansion of marine facies and fossils, accompanied by alkali-basalt volcanism. Trace-element signatures vary with volcanic center from enrichment of light-rare-earth (LREE) and large-ion-lithophile elements (LILE) with strong Nb-Ta anomalies to depletion to slight enrichment of LREE, enrichment of select LILE with minimal Nb-Ta anomalies. Fossils and hornblende {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating indicate Early Albian onset to Early to Mid-Cenomanian waning of volcanism in an interpreted transtensional intra-arc basin within the Omineca continental arc. The final phase (Early to Mid-Cenomanian) contains a meandering fluvial system, based on channels within overbank deposits, terminating in a tidally-dominated delta to the west in an interpreted transpressional forearc basin.; Provenance analyses, including paleocurrent indicators, pebble and sandstone compositions, REE analyses of shales, and detrital muscovite {dollar}rmsp{lcub}40{rcub}Ar/sp{lcub}39{rcub}Ar{dollar} dating, indicate the eastern Omineca Belt, evolving from metamorphic belt to continental arc, as the primary source. Permian muscovite ages indicate a minor northern Intermontane Superterrane source with detrital muscovite transported 1,000 km south similar to modern Amazon sediment transport. No evidence exists for a western source, thus accretion models that place the Insular Superterrane west of the Intermontane Superterrane in the Early Cretaceous are not compatible with the provenance data from the Skeena Group.