Triassic stratigraphy of northern Yukon Territory

This report presents a general outline of the Triassic stratigraphy based on field work carried out on a reconnaissance geologic study of the northern part of Yukon Territory. Triassic strata occur in three widely separated localities: the British and Barn Mountains, Richardson Mountains and northwestern Ogilvie Mountains. Triassic strata are most abundant in the British Mountains where representatives of the Lower Triassic Sadlerochit Formation and Upper Triassic Shublik Formation are present. The lvishak member of the Sadlerochit Formation consists of marine, fine-grained sandstones and siltstones with shale interbeds. The Shublik consists of thin-bedded shales and sandstones which grade laterally into carbonates and reflect deposition in relatively shallow waters close to shore on a stable shelf. The Richardson Mountain Triassic consists of marine limestones except for non-marine sediments near Rat River. A thicker sequence of black shales with thin lime - stone interbeds occurs in the Ogilvie Mountains. During Triassic time most of the region appears to have been moderately positive with some relief except for areas of the British and Barn Mountains and the northwestern Ogilvie Mountains. Early Triassic seas encroached from the west (?) onto the ·extreme western British Mountains. Middle Triassic sediments are only known at present to occur in Tombstone area of Ogilvie Mountains. Late Triassic seas inundated the region from the northwest and west along a shallow depression developed along the axis of the Brooks and British Mountains. The eastern edge of the Late Triassic shoreline appears to have extended from eastern Barn Mountains southeast across northern Richardson Mountains and thus was separated from the Sverdrup basin of the Arctic islands. These Triassic strata do not appear to be favourable for the accumulation of petroleum.