structure

Deformation associated with the intrusion of the Muleros Andesite

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Yesterday, I showed off a few views of the contact between the Cretaceous aged Mesilla Valley Formation shale and the hypabyssal Muleros Andesite which intruded into it during the Eocene at Mt. Cristo Rey (on the US/Mexico border where Texas meets New Mexico). Today, I’d like to look at some of the structure associated with … Read more

Structural geology of Mount Evan-Thomas

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Longtime reader and frequent contributor Howard Allen has three images to share with us today. Let’s see what he’s got… Oh my. What is that? West ridge of Mount Evan-Thomas, Opal Range, Peter Lougheed Provincial Park, Alberta. View looking south across Grizzly Creek at structural features (yellow boxes outline detail images to highlight key features, … Read more

Friday fold: limestones of the Silurian, Corridor H

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For the Friday fold, let’s journey back to the Silurian, as exposed in the limestones of that age that were deformed during Alleghanian mountain-building (Pennsylvanian and Permian), and exposed along Corridor H in eastern West Virginia. Some buckling (cuspate-lobate form) seen in that one… A little pop-up with hinge collapse: And, finally, as a digestif, … Read more

Carbonate mudcracks in cross-section (Tonoloway Formation)

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While on Corridor H 2 weeks ago with Alan Pitts, we stopped astride the Patterson Creek Mountain Anticline, with extensive road cuts displaying Tonoloway Formation overlying Wills Creek Formation. We love this spot for its lovely folds and halite casts. See what I mean? link link This time, however, my eye was drawn to the … Read more

Stylolite from the Helderberg Group, exposed on Corridor H

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While out on the Corridor H field trip last week before the heavy snow, I found this squeal-inducingly-lovely example of a stylolite in Helderberg Group limestones (Devonian passive margin carbonates): The stylolite is a pressure-solution surface, made especially apparent in this example because of the starkly different grain sizes and colors on either side of … Read more

Friday fold: Okanagan gneiss

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Todd Redding is our genorous sponsor for this week’s Friday fold. Todd reports that this boulder is derived from the Okanagan Metamorphic Complex near Penticton, British Columbia, Canada. He gives its lat/long as 49°28’14.10″N, 119°30’23.14″W. Did you spot the small fault in there, too? Thanks for sharing, Todd!

Antietam Formation breccia with Fe/Mn oxide cement: 2 GigaPans

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One of the intriguing rocks you find in Virginia, at the interface between the Valley and Ridge province and the Blue Ridge province, is distinctive brecciated Antietam Formation. The Antietam (sometimes known as the “Erwin,” especially in Shenandoah National Park), is a quartz arenite (quartz sandstone) that has been variably fused to quartzite in some … Read more

Friday fold: anticline in Belgium

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Reader Eric Fulmer contributed this week’s Friday fold. It’s a beauty! Eric writes that this outcrop is from “the Belgian Ardennes near Durbuy. There’s a well-exposed anticline along the Ourthe River. The stone is late-Devonian limestone typical of the immediate area that was later deformed regionally due to the Variscan orogeny. The Ardennes are classic … Read more

Samples from Austin: another stretched-pebble conglomerate

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While at the University of Texas at Austin, where the Jackson School of Geosciences was hosting the Summit on the Future of Geoscience Education this past weekend, I was impressed to see a well-developed rock garden outside the student center. Here’s an example of a stretched-pebble conglomerate from that garden: Note the nice epidote boudins … Read more

Samples from Austin: Stretched pebble conglomerate

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While at the University of Texas at Austin, where the Jackson School of Geosciences was hosting the Summit on the Future of Geoscience Education this past weekend, my friend and colleague Pete Berquist snapped this image of a stretched pebble conglomerate in the structure teaching lab: Some nice examples of pressure solution evidence in there … Read more

Some folds along the Crypt Lake trail

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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) … Read more

Friday fold: Ventura Avenue Anticline

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A guest post today for the Friday fold from my former student Naseem Naghdi, who’s now in southern California: The Ventura Avenue anticline is a fault-propogated fold and is located in the core of (Conoco’s) San Miguelito oil field, which is on the Ventura-Rincon anticlinorium. Carbon dating of seashells have indicated that the terraces range … Read more

Friday fold: below the Dorado Thrust

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Here’s a scene from last summer’s Regional Field Geology of the Northern Rockies course… students examining and sketching some tight folds in Cretaceous strata of the Western Interior Seaway, crumpled beneath the Dorado Thrust (a more southerly equivalent of the infamous Lewis Thrust to the north)… I’ve featured this site before, in a previous Friday … Read more

Friday fold: recumbent fold at Two Medicine Lake, Montana

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Here’s a photo from Tom Biggs (University of Virginia), taken on the NOVA Rockies field course last summer. It shows a recumbent fold along the Front Range of Glacier National Park, in Montana, just north of Two Medicine Lake. I hope you get some ‘recumbent’ time this weekend… I know I could use some rest. … Read more