sediment

What those geologists were looking at

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Yesterday, I showed you a scene of geologists (including me) clustered around some (presumably interesting) outcrop. I asked what you thought we might be looking at. Howard Allen, a denizen of this part of the globe, immediately identified the scene as that of the downstream end of the Athabasca Glacier. Several people guessed that we … Read more

Friday fold: Spray Mountain Group siltstone

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Today, we return to Banff National Park, to the outcrops next to the parking area for Bow River Falls… Zoomed-in closer to the thinner layers at left: These strata (shale and siltstone) were laid down in the quiet aftermath of the Permo-Triassic extinction, as terranes colliding with the edge of North America (far to the … Read more

Salt casts from Purcell (Belt) Supergroup rocks, Waterton National Park

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I’ve previously mentioned the lovely salt casts that can be found in Mesoproterozoic argillites of the Belt (“Purcell” in Canada) Supergroup of the Canadian Rockies (including the North American portion of the Canadian Rockies: Glacier National Park and the Sevier fold and thrust belt immediately south of it). When I led my Rockies field class … Read more

Friday fold: Bedford Canyon Fm., California

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Another guest submission for the Friday fold: Callan – Please find enclosed a collection of photos you could possibly use for a future Friday Fold blog post. The following photos were all taken by me on Sunday, April 29th, in the vicinity of Bedford Peak and the Maple Springs Trailhead (Silverado Canyon Road), Cleveland National … Read more

Veiled geology at Naked Creek

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As I mentioned, Monday had me out in the field, looking at the western Blue Ridge and eastern Valley & Ridge provinces in Virginia. This was a field review for the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox, and Grace Dawson. Immediately after lunch, we visited an … Read more

Friday fold: ball & pillow in volcanic ash

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Another guest Friday fold – this one supplied by Ander Sundell of the College of Western Idaho, and his student Katie Ursenbach, who took the shot and gave permission for me to re-post it here. You’re looking at cuspate-lobate folds due to primary sedimentary settling. the Snake River Canyon in southwestern Idaho. A pile of … Read more

Visiting the Swift Run

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I took my structural geology students to that fine outcrop of the Swift Run Formation in eastern Shenandoah National Park on Friday. There, we saw lovely primary structures with tectonic fabric overprinting (as I have showcased here previously). Consider this graded bed with subsequent (vertical) cleavage: And here’s the hinge of a nice passive fold, … Read more

Strained Antietam Formation sandstone

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I collected this sample the weekend before last on the Blue Ridge Thrust Fault field trip led by Alan Pitts. It’s a chunk of the Antietam Formation quartz sandstone, a Cambrian beach deposit. The face we photographed measures 15 cm by 12 cm. link It definitely looks best in full screen mode, so please feel … Read more

Tafoni weathering of Malmesbury Group turbidites

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Some tafoni (pattern of little weathering pits) expressed on Malmesbury Group (~700 Ma) turbidite sandstones at a little outcrop on the eastern shore of False Bay, South Africa: That last one seems to have some concentric layering to the tafoni pits – exfoliation? Spheroidal weathering? Hmm…

An edgy outcrop

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That’s a big pile of alluvial fan deposits (and colluvial debris?) on the eastern edge of the highway leading from Cape Town down to Rooiels. It’s not lithified, but it does seem to be at least partially cemented (perhaps by caliche?), because the outcrop face is essentially vertical, and there seems to be very little … Read more