The Lewis Overthrust
A radical concept
Life in the USA is not normal. It feels pointless and trivial to be talking about small looks at the fascinating natural world when the country is being dismantled. But these posts will continue, as a statement of resistance. I hope you continue to enjoy and learn from them. Stand Up For Science!
In the fall of 1984, I was unemployed, between quitting Gulf Oil in May and starting with Everest Geotech in November. It was a perfectly good time to take in the Montana Geological Society conference in northwest Montana.
Arco had just finished drilling a very wild wildcat well in the hinterlands west of Kalispell, Montana, to test a radical tectonic concept: the idea was that the sedimentary rocks that are east of the Rocky Mountain Front, and beneath the Lewis Overthrust in Glacier National Park, MIGHT actually be present at great depth beneath thrust faults that had pushed ancient Precambrian rocks over them, much further to the west.
The well took nearly a year to drill, in 1983-84, and while I don’t think the cost is public, rumor at the time suggested it cost a million dollars (or two) or more – huge in 1984. The curved seismic reflectors there MIGHT have represented a huge oil or gas trap, which if present would have justified the cost.
It wasn’t present. They drilled almost 18,000 feet of Precambrian Prichard Formation, the age and type of rock that is extremely unlikely to hold oil or gas fields. The seismic reflectors turned out to be about 3,500 feet of igneous sills. The well effectively ended what was for a time almost an “oil rush” in northwest Montana, making plenty of people happy and some explorationists sad. But it did add to our understanding of the tectonic fabric of the region.
Richard, do you know where the drill site was? I grew up in whitefish and kinda know the area. In 83/84 I worked for Anaconda Minerals in Alaska. We didn’t get invited to any ARCO talks, as far as I can remember. ;)
I'm amazed at how deep those Belt formations are. Sometime in the 1980s when we lived in Billings, we heard a petroleum geologist talk about the innovation of directional drilling, and that there would be oil under Yellowstone Park. Given that there is oil in the Bighorn Basin just east of the Park, and several oil-seeping springs in the northwest quadrant of YNP.