An ~2-km-thick stratigraphic section measured through three consecutive shale-carbonate sequences documents the previously undescribed upper Fifteenmile Group in the Coal Creek inlier. These descriptions provide the basis for correlation with Proterozoic strata of adjacent inliers in eastern Alaska, as well as in the eastern Ogilvie Mountains. The lowest unit contains interbedded limestone and mudstone with distinctive maroon-weathering layers. Similar strata are present in unit D of the Pinguicula Group exposed in the Hart River inlier. In that area however, the middle sequence containing massive dolostone, that is the most prominent unit of the upper Fifteenmile Group, is missing beneath an angular unconformity. The Callison Lake dolostone is above this surface and is lithologically indistinguishable from the uppermost, stromatolitic carbonate of the upper Fifteenmile Group. Both the middle and upper dolostone units are preceded by black shale, indicating abrupt transgressions. In contrast, the carbonate units contain abundant evidence of shallow water and periodic emergence. We interpret the upper Fifteenmile Group to comprise three shallowing-upward cycles in this area.

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.

Paleozoic rocks of the Pelly Mountains, central Yukon, preserve greater than 150 m.y. of sedimentation, magmatism and base-metal mineralization. To identify secular trends in regional tectonics and metallogeny, a multi-year project on the stratigraphy of the Pelly Mountains in the Quiet Lake (105F) and Finlayson Lake (105G) map areas was initiated. Field studies during summer 2015 focused on two stratigraphic intervals: (1) mafic volcanic, volcaniclastic and clastic rock successions assigned to the Cambrian-Ordovician Cloutier and Groundhog formations (Kechika group); and (2) felsic volcanic, volcaniclastic and clastic rock successions assigned to the Devonian-Mississippian Black Slate and Felsic Volcanic formations (Seagull group). Cambrian-Ordovician strata were deposited in a marine environment characterized by episodic mafic volcanism and extensional tectonism. Devonian-Mississippian strata record the transition from an extensional turbidite basin to a metalliferous volcanic rift basin, and resemble key rock assemblages of the Selwyn basin (Earn Group) and Yukon-Tanana terrane (Grass Lakes and Wolverine Lake groups).

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

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.

Stratigraphic and structural relationships within Stikinia, and overlap assemblages of the Whitehorse trough, are investigated in the Teslin Mountain area, southern Yukon. The Middle Triassic Joe Mountain Formation is dominated by a thick sequence of aphyric basalt produced by subaqueous volcanism. The Upper Triassic Lewes River Group displays complex lateral and vertical lithological and facies changes. It illustrates synvolcanic terrane exhumation, with erosion of the volcanic upland leading to deposition of thick volcaniclastic sequences, in parallel with ongoing clastic and carbonate sedimentation in marginal basins. Unravelling the Lewes River Group stratigraphy is critical in understanding the latest stages of Stikinia arc volcanism and the onset of Whitehorse trough marine sedimentation in the Early-Middle Jurassic. Further mapping and analytical work will focus at characterizing the Joe Mountain Formation and Lewes River Group, to determine how Stikinia evolved prior to final amalgamation of the Intermontane terranes with North America.

A lithologic succession is recognized in tectonites of the eastern Teslin suture zone in south-central Yukon. Metagraywacke and quartzite, marble, mafic metavolcanics, and interbedded metagraywacke and argillite outcrop on both limbs of an upright northwest-trending syncline at Little Salmon Lake. A body of equigranular granodiorite intrudes the basal stratigraphic units. The granodiorite and its host sediments were penetratively deformed during top-to-the-SW shearing and greenschist facies metamorphism. The granodiorite gives a Devono-Mississippian U-Pb zircon age (353 +1.3/-1.4 Ma) which is interpreted as the minimum age of crystallization. This provides a minimum depositional age for these suture zone protoliths. Based on the sedimentary succession and the age constraints, the eastern suture zone protoliths show a clear genetic link to other pericratonic terranes in the northern Cordillera.

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.

End-on arc collision and onset of the northern Cordilleran orogen is recorded in Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon, and in development of the synorogenic Whitehorse trough (WT). A synthesis of the extensive data set for these plutons supports interpretation of the magmatic and tectonic evolution of the northern Intermontane terranes. Late Triassic juvenile plutons that locally intrude the Yukon-Tanana terrane represent the northern extension of arc magmatism within Stikinia. Early Jurassic plutons that intrude Stikinia and Yukon-Tanana terranes were emplaced during crustal thickening (200–195 Ma) and subsequent exhumation (190–178 Ma). The syn-collisional magmatism migrated to the south and shows increasing crustal contributions with time. This style of magmatism in Yukon contrasts with coeval, juvenile arc magmatism in British Columbia (Hazelton Group), that records southward arc migration in the Early Jurassic. Exhumation and subsidence of the WT in the north were probably linked to the retreating Hazelton arc by a sinistral transform. East of WT, Early Jurassic plutons intruded into Yukon-Tanana record continued arc magmatism in Quesnellia. Middle Jurassic plutons were intruded after final enclosure of the Cache Creek terrane and imbrication of the Intermontane terranes. The post-collisional plutons have juvenile isotopic compositions that, together with stratigraphic evidence of surface uplift, are interpreted to record asthenospheric upwelling and lithospheric delamination. A revised tectonic model proposes that entrapment of the Cache Creek terrane was the result of Hazelton slab rollback and development of a sinistral transform fault system linked to the collision zone to the north.