silurian

Bookshelfed mullions from Norway

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Elizabeth Eide of the National Academies shared this image with me a year or two ago, when she gave a talk on Norwegian geology for the Geological Society of Washington. Those are some bookshelfed gneiss layers sandwiched between upper-left and lower-right carbonates. The “bookshelfing” refers to the numerous parallel brittle fractures along which the gneiss … Read more

Fault in Massanutten Sandstone

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Here’s a gigapan I shot last yesterday, looking west from “Blue Hole” towards a cliff of Massanutten Formation sandstone, south of Waterlick, Virginia. A prominent fault zone can be seen in the center of the image. Unfortunately, the auto-stitch deformed my face. I look like Quasimodo. Oh well. As usual, you can see it full … Read more

Friday fold: Siccar Point, Scotland

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As with last week, I’m going to show you someone else’s fold today. This one should have strong resonance with most geologists, because it’s a fold in the tilted (and contorted) older strata exposed below the famous unconformity at Siccar Point, Scotland: I found this image on the British Geological Survey’s online repository of images, … Read more

Transect debrief 6: folding and faulting

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Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the … Read more

Transect debrief 5: sedimentation continues

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We just looked at the Chilhowee Group, a package of sediments that records the transition for the North American mid-Atlantic from Iapetan rifting through to passive margin sedimentation associated with the Sauk Sea transgression. Well, if we journey a bit further west, we see the sedimentary stack isn’t done telling its story. The saga continues … Read more