burning coal and shale illuminate the ancient yukon

Shortly before the Klondike Gold Rush, a French explorer trekked through the Peel Watershed. Among the wonders Count Edouard V. de Sainville encountered on his Yukon journey was a deposit of burning coal.

By Erling Friis-Baastad

Shortly before the Klondike Gold Rush, a French explorer trekked through the Peel Watershed. Among the wonders Count Edouard V. de Sainville encountered on his Yukon journey was a deposit of burning coal. His account of that intriguing conflagration in Canada’s Far North subsequently appeared in the Bulletin de la Societe de Geographie in Paris. It is the first-known written record of the phenomenon in the northeast Yukon.

Over the past three field seasons, sedimentologist Grant Lowey of the Yukon Geological Survey found himself retracing some of de Sainville’s steps and paddle strokes in an effort to learn more about coal seams and black shale deposits in the Bonnet Plume Basin.

Research conducted there during the late 1970s and early 1980s had already revealed that the formation contained the Yukon’s largest coal deposit. However, there is far more to the basin geology than that. As Lowey has written in A summary of Rock-Eval data for the Bonnet Plume Basin, Yukon: Implications for a previously unrecognized oil play (Yukon Exploration and Geology, 2008): “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.”

Before 2007, “the only data they had was from around the basin rather than from in the basin itself,” says Lowey. “So I thought it would be a good project to go in there and sample the rocks and get a better idea of what the oil and gas potential is.”

What the potential is for the future remains anyone’s guess. Lowey refers to the Bonnet Plume Basin as a “stranded basin.” It’s far from established transportation routes. No one knows if it will ever be financially feasible to extract gas and oil from the deposits. And many experts, including First Nation people, warn of potential environmental costs associated with industrial activity in such a wildlife-rich landscape. However, an immediate, less-controversial, benefit concerns the distant past, and what we can learn about it by studying coal and shale deposits.

The Bonnet Plume Formation is located in a fascinating geologic region near the confluence of the Peel, Wind and Bonnet Plume rivers. The basin itself was probably a sort of bay in a great inland waterway, a primeval sea that once lapped against the east side of the Rocky Mountains, says Lowey. Bituminous coal, the oldest and highest-quality coal in the formation, was likely associated with sediment in that seaway. Further to the north a less-hydrocarbon-rich, more recent, lignite coal is associated with fluvial floodplain material.

The basin lies on the boundary of the Cretaceous and Tertiary periods, about 65 million years BP, when mammals were taking over from dinosaurs. It’s an intriguing period for paleontologists who hope to date the boundary more precisely.

Volcanic ash associated with coal contains tiny grains of zirconian silicate. With uranium/lead dating it is possible to determine the age of the grains and learn the age of fossils found at the level of those grains. Specific fossils are associated with different biozones. Like fish and finches, plant species have evolved through time. “Once you have an actual age you can calibrate the biozones a little better on the geologic time scale,” says the sedimentologist.

So what set the coal alight? It was obviously burning when de Sainville was greeted by smoke plumes and a stench one would now encounter downwind of a refinery. “It is the oldest burning coal in the Yukon that we have record of,” Lowey says. Over time, one of a number of processes could have ignited it. Spontaneous combustion, urged on by dampness and pyrite in the deposit, might account for the burning. Once you expose a coal seam to the air, it starts to oxidize.

Or perhaps a lightening strike or forest fire supplied the heat. At any rate, the basin is slumped and as old burnt material falls away new coal it exposed to air and the process continues.

Bits of sand and gravel will form a nucleus around which vapours can coagulate. As they percolate up through glacial-fluvial material above the coal, they precipitate as tar or creosote. “We came across tar pits; we were amazed by them. They hadn’t been described before,” says the geologist.

Meanwhile, just to the northeast of the Bonnet Plume Basin, black marine shales are also burning. That shale tar has not yet been analyzed for its oil potential and composition, but the shale is known to be about 400 million years old, dating to the Devonian Period, “the age of fishes.” Temperatures of 1,000 degrees Celsius cause the shale to bubble and flow: a substance called “paralava.”

Another intriguing aspect of burning shale is that it leaves behind red ochre deposits. Lowey and territorial archeologists are curious about how these deposits have been utilized by First Nations: a topic for a future Your Yukon.

For more information: ygsftp.gov.yk.ca/publications//yeg/yeg08/17-lowey.pdf

This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon

College. The articles are archived at www.taiga.net/yourYukon/archives.html

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