While out at the eastern section of NAGT’s annual meeting last weekend in West Virginia, I participated in a field trip to look at the stratigraphy of the Bolt Mountain section of Pottsville Group strata. One thing that was particularly eye-catching about the sandstones we saw was that many of them had been stained by … Read more
Here’s a nice example of spheroidal weathering in a sandstone, developed using orthogonal jointing and bedding: This is one of many sites I visited Saturday near Bolt, West Virginia, on a field trip with NAGT’s Eastern Section.
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
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.
Three images, working our way in from outcrop setting to hand sample: link link link These fine red sandstones are the Silurian-aged Bloomsburg Formation, as it crops out in Fort Valley, Virginia. What would we see if we kept zooming in? …Stay tuned…
When visiting Athens, Greece, you are drawn to the Parthenon’s grand architecture atop the hill called the Acropolis. But why is the Acropolis a hill?
Zoltán Sylvester has contributed today’s Friday fold, an anticline in the Ross Sandstone of Ireland: Click image to go to the source (full sized). Thanks Zoltán! Happy Friday everyone.
Here’s a fold I saw in Texas, in the Mesilla Valley shale, close to the contact with the Muleros Andesite at Cristo Rey: This is a pretty wild looking fold. Let’s zoom in on the most deformed portion: Annotation: white is top of the distinctive, blocky, buckled bed, and black is its bottom side. Red … 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
We have a guest Friday fold today, from reader Ben Mackay-Scollay of the Monash University School of Geosciences in Melbourne: Ben writes: Hey there Professor Bentley, been a fan of your blog for a while and I thought you might be able to use this for your Friday Fold series. It’s an upright fold at … Read more
The Wallbridge Unconformity is a surface of stratigraphic hiatus or erosion between the depositional influence of the Tippecanoe and Kaskaskia epeiric seas. After Alan Pitts and I located ourselves in the Oriskany Sandstone (terminal Tippecanoe stratum), we looked stratigraphically above the quartz sandstone for the overlying unit, which should be the Needmore Formation shale (beginning … Read more
Today, a few more photos from the field trip last month to Corridor H, the fine new superhighway with so little traffic out in eastern West Virginia. Our antepenultimate stop of the day was at an outcrop we inferred should hold the Oriskany Sandstone, a Devonian quartz arenite that lies stratigraphically above the Helderberg Group … Read more
I went out last Tuesday to Corridor H, the exemplary new highway cutting through the Valley and Ridge province of eastern West Virginia. Joining me was former student Alan Pitts, a devotee of Corridor H from way back in the early days when we just called it “New Route 55.” The boondoggle highway is now … Read more
This past week, there’s been a beautiful sight along the stretch of the Fort Valley Road that goes past the Blue Hole section of Passage Creek. Click to enlarge Ice has been forming beautiful forms as groundwater seeps out along bedding planes in the Massanutten Sandstone (a Silurian-aged quartz arenite, folded during late Paleozoic Alleghanian … Read more
Over the summer, I shot these two GigaPans of the “Great Unconformity” in Wind River Canyon (Owl Creek Mountains), Wyoming: link link This week, Team M.A.G.I.C. (by which I mean my student Robin Rohrback-Schiavone) finished up a series of three macro GigaPans of rock samples from the site (made with our one-of-nine-in-the-world GIGAmacro rig by … Read more
I have two new GigaPans of hand samples to share with you this morning… The Edinburg Formation graptolites from Mint Spring, Virginia, that I featured here back in May, can now be explored in GIGAmacro hand sample: link Students: are these colonial or solitary organisms? Benthic, nektonic, or planktonic? Does this relate to their usefulness … Read more
Have a look at this lovely (almost glowing) example of a disconformity between Coloradan limestone and overlying sandstone.
Today, let’s go back to the Pike Dam, where we spent some lovely moments last week, agog at the lovely graded beds and flame structures visible there. In contrast, today we want to examine the deformational structures seen elsewhere at this same outcrop. There are folds and faults and joints and more exotic fare: tension … Read more
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