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.

New ammonite collections from fine-grained rocks of the Laberge Group in the Whitehorse area are assigned nine ammonite zones or assemblages using the recently established North American regional zonations. Guide ammonites of these zones are illustrated. Supplemented by other published and critically revised data, the Laberge Group in the southern Yukon is shown to contain nearly all zones of the Upper Sinemurian to Lower Bajocian stages. The presence of the Hettangian and Lower Sinemurian is not adequately confirmed. In an Upper Pliensbachian section in the Miners Range, the occurrences of Fontanelliceras cf. fontanellense and Canavaria? sp. extend the known range of these taxa in North America to the Carlottense Zone. The base of the Toarcian is marked by the first appearance of Dactylioceras ex gr. simplex, which may characterize the deepest faunal level within the Kanense Zone. Another section on Goat Mountain contains a Lower to Middle Toarcian succession. Deposition of the Laberge Group continued throughout Early and Middle Jurassic time. Conglomerates are confined to Upper Sinemurian to Upper Pliensbachian in the Takhini area and to Toarcian and older in the Fish Lake area. It is likely that Laberge Group conglomerate was not deposited in response to a single episode of relative sea level change, but to several such events during Early Jurassic time. Fine-grained clastics are Upper Sinemurian to lowermost Toarcian in the Takhini area whereas Lower Toarcian to Lower Bajocian in the Fish Lake area. Dacite tuff of the Nordenskiold formation is Late Pliensbachian in age.

The tectonic evolution of the Whitehorse trough in central Yukon is largely preserved by the Early to Middle Jurassic Laberge Group, an ~3000-m thick succession of synorogenic clastic strata that unconformably overlies arc and arc marginal rocks of the Lewes River Group. A two-year project was initiated to test a Sinemurian to Toarcian transgression of basal Laberge Group strata westward across the Whitehorse trough and examine the regional relationships between the timing of Jurassic exhumation, sedimentation, and terrane accretion in the northern Canadian Cordillera. Field studies in 2017 targeted basal Laberge Group strata at seven locations in central Yukon. At each field locality, basal Laberge Group strata are known or inferred to unconformably overlie the Povoas formation and multiple units of the Aksala formation. Pre-Early Jurassic unconformities may indicate variable basin topography due to the complex internal stratigraphy of the Lewes River Group, or that regional exhumation and erosion affected the Whitehorse trough prior to Laberge Group sedimentation.

During retreat of the Cassiar lobe of the Cordilleran ice sheet from the last glacial maximum there was a large stagnation or re-advance near what is now the north end of Lake Laberge (Lower Laberge) in the south central Yukon. This stagnation generated a large moraine that would come to act as a sediment dam for Glacial Lake Laberge. As the retreat of the ice front resumed a lake formed between the ice front to the south, and the sediment dam to the north. With the ice front continually drawing further south, combined with incision of an outlet flow into the sediment dam, the geomorphology of Glacial Lake Laberge constantly changed. Throughout the history of Glacial Lake Laberge there has been a gradual decline in the lake level largely controlled by incision into the sediment dam near Lower Laberge, as is indicated from sets of fluvial terraces above the current outlet river (the Yukon River). This gradual decline has produced several sets of preserved shorelines rising above the present lake level. By surveying the shape, location, and elevation of these shorelines and outwash terraces, in combination of all other applicable data sets, a detailed glacial retreat and alluvial history can be examined.

A copy of this thesis is available at the EMR library – QE681.C43 2000.

The Whitehorse Trough, south-central Yukon, originated as a Mesozoic fore-arc basin separating the allochthonous Stikine Terrane to the west from the North American craton. Late Triassic erosion of a volcanic arc supplied detritus to the basin. Subsequent cessation of volcanism, unroofing and deep erosion of the arc into the Middle Jurassic resulted in a progressive increase in granodioritic sediment. Late Triassic-Jurassic Laberge conglomerate within the Whitehorse Trough are coarse, polymictic and typically massive. Inverse or normal grading, planar stratification and cross-bedding are less common. Conglomerates are debris flow, sheet-flood and bar deposits of braided alluvial fan-deltas. These conglomerates usually overlie and grade basinward into feldspathic graywacke or arkosic sandstone. Crystal tuffs grade laterally into sandstone and occur as interbeds as well. Sandstones commonly display trough cross-bedding or planar stratification. Hummocky cross-stratification rarely occurs in sandstones interbedded with bioturbated silty mudstone. Other facies include graded sandstone-mudstone with Bouma BC(E) sequences; float-stone/micritic limestone and rare calcarenite/rudite. Sandstone-conglomerate facies transitions indicate a vertical progression from shallow marine and shoreface sedimentary strata of Late Triassic age to coarse alluvial fan conglomerates of Jurassic age, reflecting progradation of fan-delta systems with progressive infilling of the basin. The Stikine Terrane accreted to North America in the Late Jurassic with basin shallowing and closure reflected by changes in the sedimentary sequences.

The Whitehorse Trough, a Mesozoic sedimentary basin in south-central Yukon that has potential for gas and oil, consists of the Lewes River Group (Triassic), the Laberge Group (Jurassic), and the Tantalus Formation (Jura-Cretaceous). The Laberge Group in the Carmacks (115I) and Laberge (105E) map areas is subdivided into four informal lithostratigraphic units: the Richthofen, Tanglefoot, Conglomerate and Nordenskiold formations. The Richthofen formation, distinguished by siltstone to very fine sandstone and mudstone couplets, is exposed in the southern part of the Laberge map area where it rests unconformably to conformably on the Lewes River Group and is unconformably and/or conformably overlain by the Tanglefoot formation. The Tanglefoot formation, distinguished by coalbearing, interbedded sandstone and mudstone, is exposed in the northern part of the Laberge map area and the southern part of the Carmacks map area where it rests unconformably on the Lewes River Group, and is overlain by the Tantalus Formation. The Conglomerate (conglomerate) and Nordenskiold (dacite tuff) formations occur as minor units within the Tanglefoot formation. The Richthofen-Tanglefoot formation unconformity and/or conformity is a potential petroleum play in the central Whitehorse Trough, whereas the Lewes River Group-Tanglefoot formation unconformity is a potential petroleum play in the northern Whitehorse Trough.

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The Middle Proterozoic Bear River dykes (ca.1.27 Ga) are mafic intrusions that crosscut the Gillespie Lake Group of the Wernecke Supergroup in the Slats Creek and Fairchild Lake map areas (106 D/16, 106 C/13). The dykes are fine-to medium-grained gabbros and basalts with tholeiitic affinities.The most northwesterly dyke was examined in detail. It was emplaced into mainly dolostone, and crosscuts an older fault. A white-weathering aureole along the margins of the dyke consists of calcite-magnetite-serpentine skarn. Within the dyke, hydrothermal effects are dominated by Fe (hematite and magnetite), with local enrichments of Cu (chalcopyrite) and U, a signature characteristic of earlier-formed zones of Wernecke Breccia (1.6 Ga). Alteration of the dyke indicates that a later pulse of hydrothermal fluids was channelled along the dyke or the fault.The Bear River dykes may belong to the coeval, giant radiating Mackenzie dyke swarm of the northern Canadian Shield.

Most chert-pebble conglomerate units within the Late Jurassic to mid-Cretaceous Tantalus Formation were deposited in shallow, deep and meandering gravel-bed rivers. However, the presence of largescale angle of repose foresets of large- to small-pebble conglomerate, with distinct down-slope termination in laminated mudrocks, indicates that at least some >5 m foresets were formed by episodic flood-controlled progradation of a small river-dominated lobate delta. Architectural analysis of exposures at the Whitehorse Coal deposit, 26 km south-southwest of Whitehorse, indicates periodic rapid progradation into a small lake that was at least 6 m deep. Thinning and downlap of some foreset units indicate shifting location of topset distributary channels. Down-slope transition of gravel foresets into thin sub-horizontal beds of massive and graded sandstone and pebbly sandstone suggests that the foresets were inertia-dominated. Deformation of bottomset beds is directly related to foreset progradation over under-compacted lacustrine clays.