Reconstruction of Early Cretaceous Basin Configuration in the Methow and Tyaughton Basins, British Columbia

Jurassic to Early Cretaceous strata of the Methow and Tyaughton Basins were deposited on the accreted Cadwallader, Bridge River, and Methow terranes. An overlap assemblage referred to as the Methow-Tyaughton basin establishes a link between these disparate terranes by Late Cretaceous time. Our objective is to establish an Early Cretaceous link between these basins using detailed sedimentologic, petrographic, geochemical, and geochronological analyses of the Lower Cretaceous Jackass Mountain Group (JMG) and the Lower-Upper Cretaceous Taylor Creek Group (TCG) that were deposited within the Methow and Tyaughton Basins, respectively.

Near Chilko Lake in south-central British Columbia, the JMG and the TCG are exposed southwest of the dextral Yalakom Fault. The rocks of the JMG are exposed in a major northeast-trending synclinorium and unconformably overlie the middle Jurassic Nemaia Formation and mid- to late Jurassic Relay Mountain Group. The TCG is exposed as a south-dipping monocline 10 km southeast of the JMG syncline, across the Konni Lake Fault, and also unconformably overlies the Jurassic Relay Mountain Group.

The JMG in the northern limb of the syncline is dominated by shoreface deposits while the southern limb consists of a distal assemblage typified by a significant succession of classic turbidite deposits. The TCG is composed of a lower succession of chert-rich conglomerate and encasing marine sahle overlain by a series of sandstone, mudstone, and conglomerate beds that are interpreted to represent delta plain to delta front sedimentation. Petrographic analyses of the JMG and TCG are both characterized by volcanic-rich, immature sediment and varying amounts of chert detritus. Preliminary geochemical analyses of the JMG and TCG display similar trends suggesting that these units may have similar provenance throughout their histories. Sedimentologic, petrographic, and geochemical similarities, in addition to ongoing detrital zircon, palaeontologic, and palynologic analysis may establish an Early Cretaceous link within the Methow-Tyaughton Basin.