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 head of that valley:


Zooming in further, you can see four people standing on the contact metamorphosed zone on the left side of this dike:


I went and searched for it in Google Maps, and found it quite easily emerging from that icy valley;


How this escaped my notice during my previous trips to this site, I’ll never know. I was glad to find something new there, though.

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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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10 July 2015

Friday fold: Lawson Syncline and Mount Inflexible

View of Lawson Syncline looking obliquely along strike (SSE) from an unnamed peak SW of Mount Inflexible, Kananaskis Range, Alberta. The axis of the syncline forms the bottom of the valley and plunges slightly toward the south. The syncline is in the hanging wall of the Sulphur Mountain Thrust sheet. On the right side of the photo, beds can be seen dipping to the right (west) in the ridge the photographer is standing on, evidence of the adjacent Kent Anticline, whose axis is eroded but would be above the right side of the valley. Rocks are Carboniferous to Permian Etherington Formation to Rocky Mountain Group carbonates and clastics on the flanks of the folds and recessive Triassic clastics of the Sulphur Mountain Formation forming the core of the syncline (now mostly eroded; remaining beds are most vegetated, down-valley).

Allen FF 3

Of course, that’s another gem from longtime reader and contributor Howard Allen. Thanks, Howard!

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3 July 2015

Friday fold: Opal Range, Alberta

Howard Allen is the Friday folder who keeps on giving… Here’s his latest:

Multiple folds at top of ridge, Opal Range, Alberta. Photographed from Kananaskis Highway 40, looking SE. Beds are Carboniferous carbonates, probably Mount Head and/or Etherington formations.

Allen FF 2 Allen FF 2zoom

There are lots of great folds to be seen along that road. The Kananaskis Trail is in the “tourist shadow” of the nearby Trans-Canada Highway, which means it’s well worth your time to drive it if you ever find yourself in the southern Canadian Rockies.

Happy Friday!

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26 June 2015

Friday fold: Subvertical carbonates

Another Friday, another Friday fold from Howard Allen:

Folds in near-vertical beds, north side of Grizzly Creek, Opal Range, Alberta. Beds are Carboniferous carbonates, Mount Head and Etherington formations.

Allen FF 1

Enjoy your day!

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19 June 2015

Friday fold: subglacial drag fold (Pleistocene) in Cretaceous sediments, Alberta

Howard Allen, a retired petroleum geologist from Calgary, and longtime reader of this blog, contributed this week’s Friday fold:

Subglacial drag fold (Pleistocene) in Upper Cretaceous Horseshoe Canyon Fm. bedrock (sandstone, shale).

The locality is SE of Drumheller, AB at UTM 12U 394247 5692469 (WGS84).

Glacial drag fold in bedrock, road cut, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta

Glacial drag fold in bedrock, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta

Did you hear that right? Yes, you did: This is Cretaceous aged sedimentary rock, folded by a Pleistocene glacier, tens of millions of years after it was deposited. And a massive tongue of ice did it!

Here’s another perspective on the same fold, looking roughly along (regional) strike to north, the direction from which the Laurentide ice sheet moved:

Glacial drag fold in bedrock, road cut, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta

Glacial drag fold in bedrock, Hwy 573, east of Willow Creek Hoodoos, SE of Rosedale, Alberta

A very happy Friday to you!

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12 June 2015

Friday fold: Flow banding in obsidian, Newberry Volcano National Monument, Oregon

Lockwood Dewitt is the purveyor of this week’s Friday fold ensemble:


All these folds are primary (not tectonic) in nature: they are flow banding of the viscous lava that oozed out to make the Big Obsidian Flow at Newberry.


And closer in:


One more:


Awesome stuff! Thanks for sharing, Lockwood!

Happy Friday, everyone!

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29 May 2015

Friday fold: Hayward neighbor

Reader Bill Mitchell contributed this week’s Friday fold, viewed here zooming in closer and closer over three photos:




Bill says:

Here we have a fold found along a trail in Strawberry Canyon just east of the University of California, Berkeley and the Hayward fault. It seems to be mapped (http://pubs.usgs.gov/mf/2000/2342/) as Cretaceous undivided (Great Valley sediments), but I wouldn’t be surprised if it were Claremont Chert (late to middle Miocene) or Claremont Shale (late Miocene). Superficially they are similar to the type section of the Claremont Shale, found just a canyon or two over, and perhaps too small to show on the geologic map.

Bill is on Twitter too: @i_rockhopper

Thanks for the contribution, Bill!

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22 May 2015

Friday fold: Welsh carbonates

Kate Littler sent in this Friday fold, via Twitter:

lovely parasitic folds in the Carb limestone,  West Angle Bay south Wales.

CEv4BtIWEAMounF.jpg large

Awesome. Looks like a great place. Thanks, Kate!

Happy Friday!

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21 May 2015

Soft sediment deformation in sandstone and shale, Bolt Mountain

Today, I’ll treat you to two examples of soft-sediment deformation from the Kanawha Formation on Bolt Mountain, West Virginia…









This cross section looks very much like the 3D “sled” shapes to the soft sediment deformation “ploudins” at Corridor H

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