There’s something about conglomerates that just draws me in. Here’s a lovely example — you might even say it’s an exemplar — from Sandy Hollow in Montana: That’s the basal conglomerate of the Cretaceous Kootenai Formation, one of the mappable units in this mappable region. Feast your eyes on those well-rounded pebbles!
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
Two nice new examples of soft sediment deformation structures in Pennsylvanian-aged clastic sedimentary rocks from West Virginia.
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
A quick virtual field trip to the Neoproterozoic glaciogenic sedimentary rocks from the central Virginia Blue Ridge province: Can you feel the chill of Snowball Earth?
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.
My family and I went to the Strasburg Museum in Strasburg, Virginia, last fall, because (1) we’ve lived out here for two and a half years now without stopping in, and we felt “overdue” for checking it out, and (2) a big train is prominently featured out front, and my son is really keen on … Read more
Some boulders seen on the trail to Helen Lake sported lovely sets of Skolithos trace fossils. Here are two boulders, with the perspective on the tubular paleo-vertical Skolithos burrows being “map view”: Another boulder, in the middle of the trail, showed them in a fine cross-sectional view: (click to enlarge substantially) It also included some … Read more
Look at this! A whole boulder made of trace fossils. Three photos, each more progressively zoomed in than the last. Update: The @ichnologist identifies these as perhaps Thalassinoides.
Let’s journey to the Cretaceous today, to see sandstones, shales, and even some coal strata that have been folded during the eastward thrusting that built the Canadian Rockies. Here’s the same fold, in context, shot in GigaPan on a different day, from a different angle. Can you match it up? link Ben Gadd showed me … Read more
Silurian aged mud cracks feature small lensoidal features: are they casts of ancient gypsum crystals?
Today, I thought I would share some images of lovely “textbook” glacial striations from rocks I saw in the Canadian Rockies this summer…
What are these Border to Beltway students up to?… Clearly, they are all immersed in their field notebooks, sketching away. This was in March, in west Texas. There must be something worth drawing at this road cut… A clue can be seen on the wall of rock behind them. There, you can find features such … Read more
Howard Allen is the documentarian of this week’s fold: Howard writes that this is: Middle Cambrian Chancellor Formation rock with recessive weathering intraclasts(?). Hamilton Lake trail, Yoho National Park, British Columbia. My interpretation of this one is a little shaky–it was raining when I took the photo (in 1982) and I was hiking with a … Read more
My favorite rocks are those that tell multiple stories – rocks that are “palimpsest” with subsequent “chapters” of their biography capable of being teased out, based on different features to be observed in the rock. Click to enlarge What can we see in this small sample of the Silurian-aged Tonoloway limestone, from Corridor H, West … Read more
While on Corridor H last week with Team “Border to Beltway” (and USGS research geologist Dan Doctor), we stopped at the putative mass transport deposit. We still haven’t figured out which unit this is (It’s not the Foreknobs), but as we approached it, Dan wondered aloud, “I wonder where the top of the Devonian is. … Read more
Remember this past winter when Alan Pitts and I found what we interpreted to be a mass transport deposit (a submarine landslide/slump) along the new section of Corridor H leading up the Allegheny front? Well, I was back out there yesterday, with Dan Doctor (USGS Reston) and Jay Kaufman (University of Maryland). One new thing … Read more
As noted previously, I live in a regional scale fold: the differential erosion of the Massanutten Synclinorium has produced the ridge of Massanutten Mountain, which separates the Fort Valley from the Shenandoah and Page valleys on either side. The Fort is “fort” like because the strata which underlie it are relatively friable, soluble, or otherwise … Read more
Check out the immense climbing ripples preserved in surge deposits at Hunt’s Hole (a maar volcanic crater in southern New Mexico) and imagine the strong currents couples with an extraordinary amount of entrained pyroclastic material.