Stratigraphy and structure of upper paleozoic rocks, northeast Dease Lake map area, British Columbia

Upper Paleozoic rocks of the Cache Creek Group in northeastern Dease Lake map-area (104 J) consist of the basal Kedahda Formation, the French Range Formation and the uppermost Teslin Formation. The Kedahda Formation is at least 5, OOO feet thick and composed largely of chert and pelite, with minor interbedded volcanic sandstones and limestones towards the top. Its base is not exposed in the map-area, and it is conformably and diachronously overlain by the French Range Formation with mid-Permian (Leonardian and earliest Guadalupian) fossils at the contact. The French Range Formation consists of 3, OOO to less than 1, OOO feet of saussuritic, locally pillowed, basic flow rocks, intrusive equivalents, and pyroclastic rocks, and is conformably overlain by, and in part a facie s equivalent of, the Teslin Formation. The Teslin Formation, composed of carbonate with locally abundant algal structures and fusulinids, is about 1, 500 feet thick and ranges in age from Early Permian (Leonardian or possibly Wolfcampian) to Late Permian (late Guadalupian). The top of the formation is not recognizedinthe map-area, and lower Mesozoic volcanic rocks and sandstones are in faultcontact with the older rocks. Upper Paleozoic rocks appear to have undergone two phases of deformation; (1) an early phase of probably isoclinal recumbent folding accompanied by low-grade regional metamorphism of the glaucophanitic type, best dated as post-Late Permian - pre-Late Triassic, was followed by (2) a later phase that affected both late Paleozoic and Mesozoic rocks. The later phase was accompanied by little or no regional metamorphism and is largely responsible for the present map-pattern.