The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Friday, January 24, 2014

January 24. Belt Basin 1.3-1.4 billion years ago

By Richard I. Gibson

Here’s the podcast:

St. Mary Lake, Glacier National Park. Photo by David Restivo, NPS
We’ve talked briefly about continental crustal fragments large and small drifting around the earth’s surface, a process which continues today. Inevitably, at some times a lot of the continents might come together to create what we’ve come to call a supercontinent. While we won’t encounter the best known supercontinent, Pangea, until August, supercontinent assemblies have happened repeatedly in the past.

The Sioux Quartzite was deposited in North America during the time that the supercontinent called Columbia is thought to have existed, around 1.7 to 1.5 billion years ago. We know something more about the break up of that possible supercontinent than its assembly, and there is abundant evidence for a break, separating what is now western North America and eastern Siberia, around 1.4 billion years ago.

That break created a huge basin in what is now the northwestern United States and nearby parts of Canada. It was filled with as much as 50,000 feet of mostly fine-grained sediments, mostly mud and silt that lithified into shale, mudstone, and a few sandstones and limestones. We call this thick package of rocks the Belt Supergroup, named for occurrences in the Big and Little Belt Mountains of Montana.

Armored mud balls in Grinnell Formation,
Glacier Park. Photo by Richard Gibson.
The Belt rocks are beautifully exposed in Glacier and Waterton National Parks, where they display red and green colors sculpted by glaciers that were vastly younger than the rocks themselves. The rocks contain details that give us lots of information about the early earth. For example, thin layers of coarse grains indicate that storms probably stirred up the sediment on the floor of a shallow lake or sea. It may seem obvious that rain fell on the ancient earth, but we KNOW it did because of raindrop impressions found in some of the Belt rocks.

One of the most remarkable things about the Belt rocks is the immense span of time that they represent – maybe as much as 250,000,000 years of relatively undisturbed deposition. Understanding the Belt is challenging, to say the least, and has been the life work of many geoscientists.

From Idaho State University
Lots of geologists try to figure out how the earth’s early continents were combined before they broke up – this has implications for resource exploration as well as pure science – and a lot of effort went into the question of what continent separated from western North America to create the Belt Basin. Antarctica, Australia, and Siberia were popular candidates. But thanks especially to the work of Jim Sears and his students at the University of Montana, and Paul Link at Idaho State, I think it’s pretty well settled now that it was Siberia that was once where western Washington and Oregon are today. UPDATE March 2014: maybe not ... some recent work suggests that it might NOT have been Siberia out there... stay tuned - I'll add information soon.


  1. Hi - reviewing from the start ( I finally realised that the illustrations are superb!) - on 24 Jan you indicated that perhaps the Siberian kraton and the N American may NOT have been together in the Columbian and promised an update. how do we get to that and other updates?
    the series is realy great - it would be nice to be able to listen to them straight through without the daily intro and closing thanks - any way to do that?
    I live in South Africa, in Cape town though I am listening to you this month while I am at my vacation home in the Bahamas - lots of interesting geology in both places.

    1. Afraid I haven't done that update - it's been all I can do to keep up with the daily episodes. The intro is pretty much in each one (iTunes preferred; not required) but I can imagine how it could be annoying when you are listening to multiple episodes in sequence. Sorry about that. After the year is done, I might combine episodes for each month into one longer recording. No time, for now, though. Thanks for the nice words.