The Pre - mesozoic stratigraphy and structure of Tuktoyaktuk Peninsula

Abstract

On the Tuktoyaktuk Peninsula northeast of the Mackenzie Delta, Northwest Territories, Mesozoic and younger strata are underlain by a succession of pre-Mesozoic formations that form a complex system of horsts and grabens. These formations are penetrated to varying depths by about 50 wells, and substantial amounts of core and drill cuttings are available. Pre-Mesozoic subcrop lithotype patterns allow an accurate definition of the elements of the ancestral Eskimo Lakes Arch. The Tuk Horst forms the backbone of this Arch, and trends to the northeast, obliquely across the Peninsula and into the Beaufort Sea. Based on lithology, conodonts, and other fossils, none of its lithotype units correlates with formations in the Northern lnterior Plains. The Tuk Horst contains, from older to younger, dolomite, clastic sequences, dolomite, volcanic rocks, quartzite, and dolomite. The clastic rocks, overlain and underlain by dolomite, are considered to be Precambrian. Hydrothermal alteration prevented absolute dating of the volcanic rocks; a latest Precambrian or earliest Cambrian age is suggested. The quartzite is Early Cambrian in age, and the dolomite at the northern end of the Tuk Horst is · Middle Ordovician. The latter may overlie the quartzite unconformably or, more probably, by fault contact. he Campbell Uplift is related in structural style and history to the Tuk Horst, and includes strata as young as the Middle Devonian Hume Formation. Large amounts of sand throughout the Ronning carbonate in the nearby Inuvik D-54 well may indicate an emergence of the uplift during early Paleozoic time. The lithotype of the Lower Cambrian rocks on the Tuk Horst indicates that the area was underlain by a Cambrian basin; the westward pinchout of the Lower Cambrian sandstone in the Northern Interior Plains basin shows that the basins were separated by a threshold or high, which later could have been the clastics source during Ronning carbonate deposition (lnuvik D-54). The Tuk Horst is bound on the southeast side by a regular succession in the homocline of the Northern Interior Plains, with the Upper Devonian Imperia! Formation as the youngest pre-Cretaceous rocks. The succession can be correlated through the Kilannak A-77 well to formations present on Banks Island. Of note is conglomerate in the upper part of the Imperia! Formation adjacent to Tuk Horst. This lithotype is rare outside the study area and indicates an emergent area nearby; this demarcates the initial phase of tectonic activity of the ancestral Eskimo Lakes Arch. To the northwest, the Tuk Horst is flanked by the "Tuk Flank," which consists of step-faulted blocks from southwest to northeast with alternating subcrop of carbonate of Early Ordovician to Early Devonian age. Part of the carbonate is Middle Ordovician; this age interval is represented by a lacuna in the Northern Interior Plains, but is present in the Mackenzie, Richardson, and Ogilvie mountains. In the Parsons area, Ronning carbonate changes facies to basinal shales. The carbonate farther to the southwest is overlain, probably unconformably, by rocks tentatively considered Permian. Structurally, the alternating subcrop pattern in the Tuk Flank indicates the presence of pre-Permian and post-Devonian or "Ellesmerian" deformation, which appears to link the study area to the Richardson and Ogilvie mountains. It is unclear if the carbonate formations butt against the Tuk Horst or if they swing around to parallel the Horst, as appears to be indicated by dip measurements.