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

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This report includes a legend and schematic cross section, 3 maps straddling Whitehorse trough, and an appendix of geochronological and fossil data tables for each map sheet. This compilation presents an integrated structural interpretation of Whitehorse trough in southern Yukon.

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.

The Whitehorse Trough is a Mesozoic sedimentary basin in south-central Yukon that has been identified as an immature, gas-prone basin, based on a limited geoscience database. A total of 170 km of regional, multi-channel, multi-component Vibroseis seismic reflection data were acquired in 2004 across the northern Whitehorse Trough in order to improve understanding of its structural architecture. The shallow seismic images appear to depict broad antiformal and synformal structures, truncated by relatively steep faults. Strata interpreted as the Lewes River and Laberge groups seem to attain a maximum thickness of 6000-7000 m toward the west side of the Trough, with interpreted Laberge Group accounting for up to ~3000 m of this total. Maximum vertical relief of the structures is ~4000 m.

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

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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.

Previous studies based on regional geology, sediment type and stratigraphic thickness, concluded that the Bonnet Plume Basin in northeastern Yukon has gas potential, but insignificant oil potential. However, these studies were not based on samples collected from within the basin. For this study, in total, 226 rock samples collected from outcrop and drill core throughout the Bonnet Plume Basin were analyzed by Rock-Eval 6 programmed pyrolysis and combustion to assess the petroleum source-rock potential of the strata. The results indicate that the Road River Formation (Cambrian to Devonian) has no source rock potential, but the Bonnet Plume Formation (Cretaceous to Tertiary) has gas and perhaps oil potential. Potential oil generation in the Bonnet Plume Formation is attributed to the occurrence of liptinite-bearing coal and previously unrecognized, siliceous, oil shale. A hydrocarbon-rich tar associated with a naturally burning coal seam was also discovered in the Bonnet Plume Formation.