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The Bonnet Plume Basin, Yukon, Canada: a Previously Unrecognized Oil Play

Lowey, Grant W.1
1 Yukon Geological Survey, Government of Yukon, Whitehorse, YT, Canada.

The Bonnet Plume Basin is a physiographic and structural depression near the eastern margin of the Frontal Belt of the Cordilleran Orogen in northeastern Yukon, Canada. It formed in early Late Cretaceous time by down-dropping Paleozoic strata along regional faults, and contains up to 7,500 m of clastic and carbonate sediments ranging from Precambrian to Tertiary in age. The oldest strata are Precambrian metasediments, which are unconformably overlain by a thick Paleozoic succession of marine mudstone and limestone. The Paleozoic sediments are unconformably overlain by the Bonnet Plume Formation, which is informally subdivided into a lower and upper unit. The lower Bonnet Plume Formation (Albian) consists of interbedded conglomerate, sandstone, mudstone and bituminous coal deposited in a marginal marine to fluvial environment, and the upper Bonnet Plume Formation (Maastrichtian to Paleocene) consists of fluvial sandstone, mudstone and lignite. Previous studies, based on regional geology, sediment type and stratigraphic thickness, concluded that the Bonnet Plume Basin has gas potential, but insignificant oil potential. However, these studies were not based on samples collected from within the basin. Two-hundred-twenty-eight 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 the Bonnet Plume Formation is gas-prone and possibly oil-prone. Potential oil generation in the Bonnet Plume Formation is attributed to the occurrence of liptinite-bearing coal (i.e., S1 up to 0.65 mg HC/g rock, S2 up to 20.93 mg HC/g rock, and HI up to 414 mg HC/g TOC) and previously unrecognized siliceous 'oil shale' (i.e., S1 up to 7.19 mg HC/g rock, S2 up to 116.66 mg HC/g rock, and HI up to 229 mg HC/g TOC). A hydrocarbon-rich tar associated with a naturally burning coal seam was also discovered in the upper Bonnet Plume Formation. Further work is planned to determine quantity, thickness and geographic extent of oil-prone coal seams and oil shale beds throughout the basin.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009