cleavage

Friday fold: flexed turbidites

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Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday: These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia. Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back … Read more

Bedding / cleavage relations in the Stephen Formation, Yoho NP

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Good afternoon! Here are a few photos, both plain and annotated, showing the relationship between primary sedimentary bedding and tectonic cleavage in the “tectonised Stephen” Formation atop the Cathedral Escarpment (in Yoho National Park), just northeast of the Walcott Quarry where the (thicker, basinward) Stephen Formation hosts the Burgess Shale. Weathering exploits both these planes … Read more

Friday fold: Three more from the Chancellor Slate

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Remember our examination of buckle folding versus passive folding in the Chancellor Slate (cleaved limy mudrock) of eastern British Columbia? Well, here’s another example: There’s so much awesomeness going on in that image, it’s hard to know where to start. The prominent black thin layers are buckled in a very boxy, asymmetric way. In places, … Read more

Friday fold: Miette Group anticline in Banff National Park, Alberta

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Here’s an outcrop of Miette Group slate, seen at the intersection of the Icefields Parkway with the Trans-Canada Highway, just north of Lake Louise, Alberta: There’s a lovely anticline just to the right of Zack, who obligingly provided a sense of scale. Also note how cleavage which is subparallel to bedding on the far left … Read more

Bedding / cleavage relationships in the Edinburg Formation

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Here’s a little scene along Route 340 / 522, north of Front Royal and south of Double Tollgate, Virginia, in the Shenandoah Valley: The rock here is limestone and shale of the Edinburg Formation, a late Ordovician unit that records the transition from passive margin sedimentation to the increasingly ‘dirty’ clastic influence of the Taconian … Read more

Natural Bridge, Yoho National Park: Bedding/cleavage relationships

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Check out the scene at Natural Bridge in Yoho National Park, British Columbia, Canada: Don’t confuse this “Natural Bridge” with the one in Virginia. Here, in the western Canadian Rockies, the structural geology is much better. You may recall that I’ve previously featured outcrops from nearby this site as a Friday fold. It’s a great … Read more

Return to the Outdoor Lab

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Two years ago, I took a trip to the Phoebe Hall Knipling Outdoor Lab, which is Arlington, Virginia’s outdoor education facility in the Pond Mountains (southern continuation of the Bull Run Mountains), on the eastern edge of the Blue Ridge geologic province. I was invited back last week to look at some new exposures. I … Read more

Two new GigaPans of Rockfish Gap, Virginia

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I took a trip down to Charlottesville this week for a couple of meetings, and I made time along the way to capture two new GigaPans of the lovely exposures of Catoctin Formation greenstone at Rockfish Gap, where Interstate 64 traverses the Blue Ridge. This is very close to the southernmost tip of Shenandoah National … Read more

GigaPan suite from the South Page Valley Martinsburg Outcrop

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Are you into structure? Sedimentology? Stratigraphy? Well, I’ve got some good news for you – I’ve imaged several key outcrops on the newly-discovered (to me) roadcut on South Page Valley Road, showcasing the middle Martinsburg Formation turbidites (and their Alleghanian structural overprint). link link link link link link See if you can find: an anticline … Read more

Upper Martinsburg “Cub Sandstone” in GigaPan

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Today, two GigaPans shot of the uppermost Martinsburg Formation, informally known as the “Cub Sandstone” since it crops out along Cub Run in the southern part of the Massanutten range. 10 or 15 meters upsection (west) of these two outcrops is the base of the Silurian-aged Massanutten Sandstone, the ridge-forming unit. Lower in the section: … Read more

A closer look at the recumbent anticline from last Friday

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Last week, the Friday fold was presented in GigaPan format only, which led to a concerned reader lamenting that he couldn’t see it on his mobile device. (GigaPans are Flash-based images; they don’t work on Apple devices in the standard GigaPan format, though there is a perfectly suitable workaround with two extra clicks.) So, for … Read more

Friday fold: a recumbent anticline in an abandoned quarry

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Yesterday, I spent a pleasant day in the field with John Singleton, the new structural geology professor at George Mason University. I was showing John a couple of sites I’ve used as field trip locations for the GMU structural geology class, and John was showing a couple of new sites to me – places he … Read more