GIS-enabled geology maps of the McConnell Range and environs, Northwest Territories

Nine previously published 1:50,000 scale Geological Survey of Canada Open File maps are reproduced here in a GIS-enabled format. The distribution of Cretaceous strata has been upgraded by the subdivision of previously undivided Cretaceous units. The nine earlier NTS map products were: 96B/3, Blackwater Lake North (Open File 5334); 96B/4, Twin Peaks (OF5335); 96B/5, Twin Fish Lake (OF5336); 96C/1, Birch Island (OF 5470); 96C/7, Burnt Point (OF 5469); 96C/8, Saline River (OF5468); 96C/9, unnamed (OF5467); 96C/10, Old Fort Point (OF5472); 96C/15, St Charles Creek (OF5466). The McConnell Range north of 64o North latitude is divided along the Saline River valley into morphologically different northern and southern parts. A broad upland south of Saline River is replaced to the north by a number of individual hills or mountains. Mount Clark, the most prominent landmark in the region is 4798 ft. (1454 m) high, and towers above other mountains, which more typically are 2500- ft. (760- m) high. The south-to-north topographic change corresponds to an abrupt change in structural style. The southern part is a broad asymmetric anticlinal uplift bounded on the east by a steeply dipping thrust fault with subsidiary splays and an overturned footwall panel. The steeply dipping thrust is rooted in Proterozoic strata. The gently dipping west limb of the anticlinal uplift is separated from the plain of Mackenzie valley by Birch Island Anticline, a northwest trending narrow short wavelength fold, which appears to be detached on the Saline River Formation and having no obvious direct linkage to the main, deeply-rooted fault, underlying the McConnell Range. The isolated hills and mountains north of Saline River are characterized by smaller, doubly plunging anticlinal culminations cored by resistant sandstone of the Lower Cambrian Mount Clark Formation and mantled by recessive shale, siltstone, and sandstone of the Mount Cap Formation. The largest of these anticlines is Mount Clark, a complex dome, bounded to the east by a steeply dipping reverse fault, essentially the same fault that bounds the southern broad anticline. A component of right-lateral strike-slip apparently accompanied the northeast-southwest shortening. Mount Clark dome can be reasonably inferred to be cored by Proterozoic strata. Northwest of Mount Clark Paleozoic carbonates (Franklin Mountain Formation to Hume Formation) lie in a broad upland dissected by normal faults and related grabens. The normal faults may be a local collapse phenomenon related to dissolution of Saline River Formation salt. The normal faults are of uncertain age other than post-Middle Devonian (post-Hume Formation). Cretaceous strata are poorly exposed and their relationship to the extensional phase is unknown. McConnell Range plunges northward and essentially has no expression north of Big Smith Creek. Correspondingly, stratigraphic offset on the frontal fault decreases northward such that Paleozoic carbonates are faulted against carbonates of similar age. Forty-five km north of Big Smith Creek, a narrow range informally known as the St Charles range occurs essentially on trend with the McConnell Range frontal thrust. It appears to be detached on the Saline River Formation and cored by a pillow of Saline River Formation salt. It may be localized along an ancestral Cambrian normal fault. The interpretation of a salt-cored anticline, based on equivocal seismic data, is supported by the presence of a salt-cored anticline documented on seismic records from the subsurface to the west of the 'range'. Proterozoic strata outcrop at the mountain front in the southernmost part of the report area. They probably pertain to a 'Sequence B' equivalent to the Mackenzie Mountains Supergroup; although a single detrital zircon implies that these strata belong in 'Sequence C', equivalent to the Windermere Supergroup. Lower, Middle, and Upper Cambrian clastics and evaporites are thin (0-140 m) in the subsurface within the study area to the east but thicken to greater than 1000m in Mackenzie valley to the west. They appear to thicken abruptly across a hinge line coinciding with the McConnell range frontal thrust. Apparently a normal fault or fault zone bounding Mackenzie Trough was inverted during Laramide compression to form McConnell Range. The Paleozoic carbonate succession (Upper Cambrian Franklin Mountain Formation to Middle Devonian Hume Formation) is punctuated by unconformities at the base of the Upper Ordovician - Silurian Mount Kindle Formation, and at the base of the Silurian - Lower Devonian Tsetso or Bear Rock formations. Cretaceous strata are poorly exposed but were encountered in exploration drill holes. In general Cretaceous strata to the east of McConnell Range are Early Cretaceous in age, whereas to the west in Mackenzie River valley they are Late Cretaceous. An unconformity occurs at each of the Lower and Upper Cretaceous successions. Lower Cretaceous strata were removed from the Mackenzie valley area by pre-Late Cretaceous erosion along Keele Arch.

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