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You are browsing the archive for mesoproterozoic.

22 July 2015

Oolitic soft sediment deformation in Helena Fm. limestone

Another gem from the Grinnell Glacier cirque: Zooming in on the contact, showing the concentrically-zoned ooids: Near the tip of the flame structure (?), I noted alignment of longer platy / flaky components within the oolitic layer: This looks like a loading structure – soft sediment deformation due to a density inversion – perhaps when some high-energy event (a storm?) dumped a bunch of relatively coarse ooids atop some squishy …

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9 January 2015

Friday fold: a surging rippled whale of Grinnell Formation

The Friday fold is asymmetric, overturned, and chock full of primary sedimentary features. Join us in Glacier National Park’s Mesoproterozoic Belt Supergroup.

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1 September 2014

Field work on the Grinnell Formation at Red Rock Canyon, Waterton Lakes National Park, Alberta

Callan’s Rockies field course students document faulting and jointing in Red Rock Canyon, Waterton Lakes National Park, Alberta.

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12 July 2014

Stromatolite from near Crypt Lake

Greetings from the field… here’s a scene I contemplated yesterday…

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16 June 2014

Weathering on Old Rag Mountain 1: feeder dikes

Old Rag Mountain is a distinctive mountain in the eastern Blue Ridge of Virginia, contained in a little lobe of Shenandoah National Park. It’s a great hike on several levels: (1) it’s got no trees on the summit, so you can actually get a decent view from on top, (2) it’s got a great section of full-body rock scrambling on the Ridge Trail, and (3)  it’s long (9.2 miles round …

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28 March 2014

Friday fauxld: the “Not a Box” at Confusion Hill

It’s Friday… that means it’s time for a fold. Let’s try this outcrop at “Confusion Hill” in the Franklin Mountains of West Texas: See it? Let’s zoom in… From the shadows to the left of the hammer, trace out the dark green layer… it may make you think of a box fold: …but it’s not. This is actually a completely planar sedimentary bed, tilted to more or less vertical, and …

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26 March 2014

The Great Unconformity in the Franklin Mountains

Good morning! Let’s take a walk up the east side of the Franklin Mountains, north of El Paso, Texas, to walk across the Great Unconformity. The basement rock exposed here is the Red Bluff Granite, a 1.1 Ga felsic magma that intruded the columnar basalts of the Mundy “Breccia” and the Castner Marble. (It is unknown what substrate the Castner Marble was deposited upon.) This is what the Red Bluff …

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2 March 2014

A chip off the ol’ charnockite

We visited the Philip Carter Winery this weekend with family. Baxter and I were pleased to see outcrops of charnockite scattered over the property (located in the middle of the Blue Ridge geologic province). As any 18-month-old will tell you, charnockite is a pyroxene-bearing granitoid. It’s a distinctive and common rock type in Virginia’s Proterozoic basement complex. Here’s a close-up: The dark green is pyroxene. The white is plagioclase feldspar. …

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12 December 2013

Some folds along the Crypt Lake trail

Hiking up to Crypt Lake in Waterton Lakes National Park, Alberta, Canada, you can see some sweet stromatolites, We’ve already taken a look at the falls, but today, let’s zoom into the folds exposed in that shadowy cliff near the center… These limestone layers are Mesoproterozoic in age – they’re part of the Purcell (Belt) Supergroup. The folding likely dates to the late Cretaceous into early Paleogene “Laramide” Orogeny (as …

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26 October 2012

Friday fold: South African gneiss

Another Friday, another fold. …By another Bentley!

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