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 … Read more
Lockwood Dewitt is the purveyor of this week’s Friday fold ensemble: All these folds are primary (not tectonic) in nature: they are flow banding of the viscous lava that oozed out to make the Big Obsidian Flow at Newberry. And closer in: One more: Awesome stuff! Thanks for sharing, Lockwood! Happy Friday, everyone!
Two nice new examples of soft sediment deformation structures in Pennsylvanian-aged clastic sedimentary rocks from West Virginia.
I was in Tucson this past weekend for a book project meeting, and my editor and coauthor and I took a hike on Sunday morning in the Tucson Mountains to Wasson Peak. Not far from the summit, we saw an epidotized tuff, where the fiamme and pumice blobs had undergone reactions to produce pods of … Read more
Recently, I posted about an excellent road cut in Fort Valley showing well-developed 10 cm+ Zoophycos trace fossils. Presented here are three new GigaPan images (two outcrop; one macro) of Zoophycos from the Devonian-aged Mahantango Formation: [gigapan id=”170978″] link [gigapan id=”170977″] link [gigapan id=”170875″] link These images are part of a new “virtual field trip” … Read more
A report from the field: new outcrops of Ordovician-aged turbidites featuring geopetal indicators, fossil content, and a structural overprint imparted during Pangaea’s assembly.
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
Pisolites are large primary concretions that develop in backreef or lagoonal settings such as the Permian Tansil Formation of New Mexico, into which is cut the enormous hole called Carlsbad Caverns.
The coarser strata of the Neoproterozoic Miette Group in the Canadian Rockies of Alberta record changing water current strength over time, and maybe an iceberg or two.
The Friday fold is asymmetric, overturned, and chock full of primary sedimentary features. Join us in Glacier National Park’s Mesoproterozoic Belt Supergroup.