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24 March 2016

Three new 3D rock sample models

Pahoehoe “ropes” on a basalt, sample site unknown: Archean gneiss from the Gallatin Range of Montana: Tafoni in Malmesbury Group turbidites, South Africa:

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25 September 2015

Friday fold: Macro GigaPan of Archean gneiss, Spanish Peaks, Montana

I don’t think I’ve featured this sample here before… It’s a lovely gneiss from near the trailhead for the Spanish Peaks, near Ted Turner’s Ranch in the Gallatin/Madison Range in southern Montana, not too far from Big Sky. Have fun checking it out in this macro GigaPan: link Happy Friday to all.

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12 August 2015

Student guest post: the Belt Supergroup in Glacier National Park

As longtime readers know, late summer is when my Rockies students submit their final projects – web-based explanations of key geologic sites they examined during the trip. Today, I offer you a guest blog post by student John Leaming. You’ll notice that I’m not *completely* absent from the post, however – I make a couple of cameos as “sense of scale.” Enjoy, -CB ______________________________________________________________ Glacier National Park, Belt Supergroup I …

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7 August 2015

Friday fold: Yin-Yang at Swift Dam

What is Matt looking at here? Matt was one of my Rockies students this summer, a geology major at the University of Virginia. Together with another UVA student and students from Mary Washington University and George Mason University, Matt embarked on a mountain-climbing hike during our evening camping at Swift Dam, near Depuyer, Montana. The hikers were treated to an extraordinary sight when they attained the summit: Click to embiggen; …

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31 July 2015

Friday fold: a return to the duplex structure in the Gastropod Limestone

Some time ago, I featured as Friday fold the extraordinarily complex duplex structure to be seen in the Cretaceous “gastropod limestone” member of the Kootenai Formation at Sandy Hollow, Montana. Today, let’s take a deeper look through a couple of hand-shot GigaPan images: Here’s the bigger of the two: link Here’s one with students for scale: link

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30 July 2015

Stromatolites of the Helena Formation, Grinnell Glacier Cirque, Montana

My favorite place to have lunch in Montana is at the Grinnell Glacier cirque in Glacier National Park. This is the dining room table: You’re looking at a bedding-plane-parallel exposure of Mesoproterozoic stromatolites here. Every few years, I’m lucky enough to hike up there with motivated students and share food atop this unparalleled view into the shallow seas of more than a billion years ago. Stromatolites are sedimentary structures that …

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27 July 2015

Conglomeratic ne plus ultra

There’s something about conglomerates that just draws me in. Here’s a lovely example — you might even say it’s an exemplar — from Sandy Hollow in Montana: That’s the basal conglomerate of the Cretaceous Kootenai Formation, one of the mappable units in this mappable region. Feast your eyes on those well-rounded pebbles!

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23 July 2015

Purcell Sill, layer-jumping

After reading the post last weekend about the discordant offshoot of the Purcell Sill, Rich Gashnig (post-doc at Georgia Tech) sent me a few photos he shot at Piegan Pass (at the head of a side-canyon adjacent to the one containing Grinnell Glacier). They show the Purcell Sill leaving one stratigraphic horizon and jumping to another, with the intermediate zone of Helena Formation limestone bending to accommodate the different positions: …

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18 July 2015

Purcell Sill → Dike, Grinnell Glacier Cirque, Montana

The Neoproterozoic Purcell Sill is a stark, obvious black stripe in the strata of Glacier National Park. Here it is emerging from behind “The Salamander” glacier, above Grinnell Glacier Cirque: Zooming in, you can see the “baked” (bleached) zones above and below this concordant intrusion. But this time, during my visit to this special place, I noticed a discordant offshoot from the main sill: See it? Up there at the …

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16 July 2015

Faulted sulfide vein, Golden Sunlight Mine, Montana

Here’s a really cool hand sample my student Xiuming found when were were exploring the waste rock piles at the Golden Sunlight Mine near Whitehall, Montana, the week before last: That’s a vein of pyrite and chalcopyrite, offset along a series of three small fault zones: Pocket faults! Three for the price of one.

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