Continued investigations of sedimentary units in the Tatonduk and Coal Creek inliers of the western Ogilvie Mountains have resulted in a refinement of the regional Neoproterozoic and early Paleozoic stratigraphy. The proposed correlations simplify Yukon stratigraphic nomenclature and promote synthesis of geological data. Strata of the Fifteenmile, Rapitan and Hay Creek groups, as well as the upper WindermereSupergroup are present in both inliers. Prominent unconformities within the Fifteenmile Group, and between the Windermere Supergroup and the variable overlying Paleozoic stratigraphy, represent at least three distinct tectonic events and basin-forming episodes. We propose redefinition of the Fifteenmile Group, abandonment of the Tindir Group, and recognition of strata equivalent to the Coates Lake Group and Mackenzie Mountains supergroup. This refined nomenclature across the Ogilvie, Wernecke and Mackenzie mountains is a step toward enhanced regional correlation of exposures in the northern Cordillera and Proterozoic inliers of the western Arctic.

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Studies of biogeochemical and evolutionary change in the Neoproterozoic require a detailed understanding of stratigraphic successions and their intrabasinal correlation to integrate those records into regional and global frameworks. The early Neoproterozoic Fifteenmile Group in the Ogilvie Mountains has previously been shown to archive important information on the evolution of the biosphere, including ocean redox and early evolution of eukaryotes. Here, we formally define the Chandindu Formation, a 150 to 420-m-thick siltstone-dominated mixed carbonate-siliciclastic succession of the lower Fifteenmile Group in the Coal Creek and Hart River inliers. We present ten sections of the Chandindu Formation and propose a type section and formalization to promote the development of a consistent stratigraphic framework for Proterozoic successions in northwest Canada.The Chandindu Formation begins with muddy tidal flat facies, which are succeeded by shale-siltstone-sandstone coarsening-upward cycles deposited in a predominantly subtidal environment. However, carbonate occurrences throughout the entire unit suggest localized carbonate buildups, likely nucleated on fault-bound paleohighs where siliciclastic background sedimentation was low. These paleohighs originated from rift-inherited complex basin topography and syn-depositional faulting during deposition of the upper Chandindu Formation.

The Division Mountain area is underlain primarily by Jurassic to Cretaceous(?) sedimentary rocks of the Laberge Group and Tantalus Formation. The Laberge Group is divisible into the following informal units: the Richthofen, Nordenskiöld, Conglomerate, and Tanglefoot formations. The Tanglefoot, which comprises a large portion of the exposed strata at Division Mountain, is here subdivided into the lower and upper members. The lower member consists of quartz-rich sandstone, grit, polymicitic conglomerate and laminated siltstone. The upper member is coal-bearing and typified by white grit, sandstone, and carbonaceous shale. The overlying Tantalus Formation is characterized by thick packages of resistant chert pebble conglomerate with intercalated sandstone beds, which form local highlands at Cub, Corduroy, Division, and Vowel mountains. The strata at Division Mountain are folded into several upright, tight northwest-trending anticlines and synclines with amplitudes of 2 to 7 km. The folded strata are intruded by feldspar-hornblende andesite sills and dykes. Organic matter identified within coal and siltstone of the Tanglefoot and Tantalus formations consists of Type III and subordinate Type I kerogen, suggesting the material is largely gas-prone. A combination of thermal maturation indicators (vitrinite reflectance and Tmax ) suggests that the coal and related strata are in the early to late stages of thermal diagenesis. Samples of the underlying Richthofen formation contain Type III kerogen matured beyond the oil window. Local folding and thickening of the Tanglefoot and Tantalus strata, as well as local intrusions in the Tanglefoot, may play a key role in the determination of hydrocarbon potential of the Division Mountain area.

In the Ogilvie Mountains, west-central Yukon, the upper Proterozoic to Lower Cambrian Mount Harper Group (informal name) contains strata equivalent to both basal Windermere Supergroup and Lower Cambrian rocks in other areas of the North American Cordillera. Strata of the Mount Harper group are directly time constrained: the basal Windermere equivalents by a ca. 750 Ma U-Pb age from a volcanic complex which both conformably overlies and intertongues with the sedimentary rocks; the disconformably overlying units by the presence of Lower Cambrian trace fossils. The lower Mount Harper Group (LMHG) unconformably overlies a thick succession of dolostones informally named the Fifteenmile Group. A breccia layer is discontinuously preserved on the unconformity surface. This breccia contains silcretes and calcretes that record several episodes of subaerial exposure. Rare interbedded debris flows suggest that the most recent of these episodes was coincident with initial deposition of the LMHG conglomerates. Silcretes and calcretes in this succession suggest that, at the onset of Windermere deposition in this area, a temperate to equatorial, probably semi-arid to arid climate regime prevailed. Elsewhere, basal breccias in Windermere-equivalent strata generally have been interpreted as fault-related, but some contain features compatible with a karstic origin. A synsedimentary normal fault forms the southern margin of an asymmetric, east-trending half- graben basin which contains the lower Mount Harper Group. Basin fill appears to have been derived exclusively from source areas to the south. Proximal facies consist of fault-talus breccia and up to 1100 m of debris-flow conglomerates that were deposited in coalescing alluvial fans. Intermediate and distal facies include mid-to-lower fan conglomerates and sandstones deposited by sheetfloods, distal debris flows and braided channel streamflows. A basin-fill coarsening-upward megasequence in the eastern part of thc study area records a change from lacustrine redbeds to lower alluvial fan sandstones and conglomerates. The LMHG half-graben basin was formed, and sedimentation was controlled, by normal faulting along the southern margin. Synsedimentary faulting and minor back-stepping of the fault controlled development of the internal sequences. Volcanism conformably postdates this sedimentation, but northerly derived coarse clastic rocks of the upper Mount Harper group (UMHG) .

This interim report has reviewed stratigraphic characteristics of the lowermost succession of Proterozoic rocks exposed in the northern Wernecke Mountains. This sequence of rocks, which is in excess of 13 km thick, is named the Wernecke Supergroup. The Wernecke Supergroup is composed of three groups which from oldest to youngest are given the informal names Fairchild Lake Group, Quartet Group and Gillespie Lake Group. Several tentative subdivisions of formational status have been described in each of these groups. The Fairchild Lake Group is composed of at least 4 km of generally light grey weathering siltstones, slates and argillites. It is divided into four formations, two of which contain carbonate members:: one formation near the middle of the group, contains ribbed weathering, thinly bedded, siltstone-limestone rhythmites; the other formation at the top of the group consists of interbedded shaly siltstone and dolostone with a distinctive white weathering limestone marker horizon. The Quartet Group, which conformably overlies the Fairchild Lake Group, consists of up to 5 km of monotonous dark grey weathering siltstone, argillite and slate with minor sandstone. The Quartet Group is transitional into the overlying Gillespie Lake Group which is compposed of at least 4 km buff to orange to locally grey weathering dolostone with minor siltstone and sandstone. Metamorphism, faulting, complex folds, the monotonous and cyclical nature of stratigraphy, the lack of distinctive marker horizons and the possibility of facies changes have greatly hindered attempts at stratigraphic reconstruction in rocks of the Wernecke Supergroup. Thus much of the stratigraphic detail within the groups must be considered tentative in nature. Field investigations to be undertaken during the summer of 1978 will help further refine the stratigraphic relationships outlined above. An Appendix to this report contains 19 representative stratigraphic sections which illustrate the main features of these rocks and a 1::250 000 location map showing where the sections are from.

Volcanic rocks in the Dawson map-area occur as isolated lenses within the early Paleozoic Selwyn Basin assemblage and as sets of flows and complexes within Proterozoic carbonate rocks near the edge of the Mackenzie Platform. Mount Harper complex, an example of the latter group, has been studied in greater detail than the others because it is more completely exposed, and contains two mafic to felsic volcanic cycles. Unlike the sedimentary rocks, whose correlation with established units in the Wernecke Mountains and Alaska is now well advanced, understanding of the stratigraphic position and internal relations of the volcanic piles is less definite. This report, based on two field mapping seasons, has two parts. Characteristics of the two volcanic groups and correlative occurrences are discussed in the first part; the second presents interpretations from the stratigraphy of the Mount Harper complex as an illustration of the style of volcanism in the region.

Ogilvie Mountains breccia (OMB) is in Early (?) to Late Proterozoic rocks of the Coal Creek Inlier, southern Ogilvie Mountains, Yukon. Host rocks are the Wernecke Supergroup (Fairchild Lake, Quartet and Gillespie Lake groups) and lower Fifteenmile group. Ogilvie Mountains breccia crops out discontinuously along two east-trending belts called the Northern Breccia Belt (NBB) and the Southern Breccia Belt (SBB). Individual bodies of OMB vary from dike and sill-like to pod-like. The NBB coincides with a north side down reverse fault—an inferred ruptured anticline—called the Monster fault. The SBB coincides with a north side down fault called the Fifteenmile fault. The age of OMB is constrained by field relationships and galena lead isotope data. The age of OMB formation is between 1.45 and 0.90 Ga. Hydrothermal alteration has locally overprinted OMB and introduced silica, hematite and sulphide minerals. Rare earth element chemistry reflects a lack of mantle or deep-seated igneous process in the formation of OMB. However, this may be only an apparent lack because flooding by a large volume of sedimentary material could obscure a REE pattern indicative of another source. This thesis is available online at https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0052352. This thesis is available at the EMR library – QE446.Y8 L36.

The study area is underlain by four stratigraphic successions ranging in age from Middle Proterozoic to Early Paleozoic. From oldest to youngest, they are: Middle Proterozoic Wernecke Supergroup; Middle to Upper Proterozoic Pinguicula Group; Upper Proterozoic Windermere Supergroup; and Uppermost Proterozoic to Lower Paleozoic sandstone and carbonate. Together, they represent about a billion years of intermittent sedimentation punctuated by processes such as deformation, uplift, erosion, magmatism and mineralization. Rocks in the study area record eight phases of contractional and extensional deformation, some of which may be related to strike-slip faulting. Two phases of southwest-verging folds and thrust faults may be related to dextral transpression on the Snake River Fault. Mineral enrichments occur in two general forms:: breccia-related (Middle Proterozoic), and veins (Mesozoic to Tertiary). The breccia-related occurrences have enrichments of Cu ± U, Co, Au and Ag, as dissemminations and veinlets in and near intrusive breccia zones (Wernecke breccia). The vein occurrences comprise Zn-Pb-Ag ± Cu and Au, in veins and related lenses and irregular replacements of carbonate.

Whitehorse trough is a northwestward-tapering belt of Upper Triassic to Lower Cretaceous volcanic and sedimentary rocks extending ~650 km from the British Columbia–Yukon border, north to the vicinity of Carmacks in south-central Yukon. It consists of three main stratigraphic units (i.e., the Lewes River Group, Laberge Group and Tantalus Formation) representing three sedimentary basins, partially overlapping in space and time. The Laberge Group (Lower-Middle Jurassic), informally subdivided into the Richthofen, Tanglefoot and Nordenskiold formations, was deposited in the Laberge basin, a collapsing fore-arc basin in which the arc was undergoing uplift and erosion. The Richthofen formation consists of conglomerate, massive sandstone, sandstone-mudstone couplets, volcaniclastic rocks and minor limestone interpreted as submarine fan systems. The Tanglefoot formation consists of coal-bearing sandstone, mudstone, conglomerate, volcaniclastic rocks and minor limestone interpreted as delta systems and shallow marine deposits. The Richthofen and Tanglefoot formations are the same age (i.e., Sinemurian to Bajocian), but the Richthofen formation is restricted to the southern half of the basin, whereas the Tanglefoot formation occurs in the northern half. The Nordenskiold formation consists of subaerially erupted, resedimented volcaniclastics deposited mainly during Pliensbachian time. The Richthofen formation is interpreted as a spent source rock and the Nordenskiold formation is not a source rock. The Tanglefoot formation is interpreted as a potential source rock and possibly an effective source rock. It contains petroleum fluid inclusions (mainly 23°- 32° and 40°- 44° API gravity) indicating a minimum trapping temperature of 110-115°C. The Tanglefoot formation is also a potential reservoir rock.