Whitehorse Trough is a frontier basin in south-central Yukon that is thought to contain gas and possibly oil. Over 400 samples from the Whitehorse Trough have been analysed by programmed pyrolysis and combustion, which together with coal rank, vitrinite reflectance, and the colour of microfossils indicate the following: the Povoas formation has no source rock potential; the Aksala formation is a poor source rock, probably gas-prone and postmature; the Richthofen formation is a poor to fair source rock, gas-prone and postmature; the Nordenskiold formation has no source rock potential; and the Tanglefoot and Tantalus formations are potentially good to very good source rocks, mainly gas-prone with a possibility of oil and mature. The Aksala and Richthofen formations are interpreted as spent source rocks, whereas the Tanglefoot and Tantalus formations are interpreted as potential source rocks and possibly effective source rocks. The most prospective areas for hydrocarbon exploration are Division Mountain, Tantalus Butte and Five Finger Rapids.

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

Map presents an interpretation of the bedrock geology of the northern Whitehorse trough as extrapolated from field observations and a reflection seismic survey.

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

Whitehorse Trough is a frontier basin in south-central Yukon that is thought to contain gas and possibly oil. It formed in the early Triassic as an arc-marginal basin between the ancient North American margin to the east and the volcano-plutonic Stikine Terrane to the west. Three stratigraphic units, termed the Lewes River Group (Upper Triassic), the Laberge Group (Lower-Middle Jurassic) and the Tantalus Formation (Upper Jurassic-Lower Cretaceous), are recognized in the Whitehorse Trough. The Laberge Group is informally subdivided into four units, which, from the base upwards includes the Richthofen, Conglomerate, Nordenskiold and Tanglefoot formations. The Richthofen formation in the Laberge map area (NTS 105E) is characterized by thin- to mediumbedded turbidites, massive sandstone, matrix- and clast-supported conglomerate, scarce ammonites and belemnites, and abundant trace fossils, particularly Chondrites. No comprehensive stratigraphic section exists for the Richthofen formation, but it is estimated to be at least 500 m thick and appears to consist of a lower clast-supported conglomerate unit, a middle unit dominated by thin- to-medium bedded turbidites with minor amounts of massive sandstone and clast- and matrix-supported conglomerate, and an upper clast-supported conglomerate unit. The Richthofen formation unconformably overlies the Lewes River Group and was deposited by a southeast-prograding submarine fan (or fans) during the Early Jurassic. It is correlative with the Inklin Formation in northwestern British Columbia. Programmed pyrolysis using Rock-Eval 6 analysis of 63 samples from the Richthofen formation indicates that it is a poor to fair source rock and is gas-prone.

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.

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