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7 December 2022
The coastal section at Esterillos Oeste, Costa Rica
Callan documents a geological stroll along the coast of Esterillos Oeste, in central southern Costa Rica, investigating the sequence of sediment in the Punta Judas Formation (Mid-Miocene) exposed there. Fossils, sedimentary structure, diagenetic features, structural deformation, and modern weathering all make prominent appearances.
30 November 2022
Ichnoanalogue
Another glimpse of sand on the beach at Esterillos Oeste, Costa Rica… This time, I offer you a trace of an organism moving through the wet sediment: Note the two parallel lines of tracks laid down by little feet, and the central groove that overprints them. It reminded me very much of this similar arrangement, from near St. Andrews in Scotland, but: (1) this is the underside of a bed …
27 November 2022
Book report
Callan offers reviews of a suite of good reads – some old and some new, some geology and some general science, and some social justice/history.
21 June 2022
Another example of overturned bedding
One of my favorite tricks is using bedding / cleavage intersections to identify tectonically inverted strata. On a field trip yesterday to check out soapstone quarries in the Albemarle/Nelson border region, I got to see this lovely example of Lynchburg Group metasediments that showcased a textbook example of the phenomenon: Bedding was initially horizontal, or close to it, and cleavage (formed under tectonic compression) initially vertical. Subsequent deformation rotated the …
29 May 2022
Accretionary wedge turbidites from the Lost Coast
The Lost Coast of northern California shows geological evidence of deep sea turbidity current sedimentation, tectonic accretion during Mesozoic subduction, and then isostatic uplift interacting with shoreline erosion. Check out a few photographs taken by Callan’s wife on a recent backpacking trip through the region.
12 November 2021
Friday fold: Raven’s Ridge
Happy Friday, all! Two shots today from my friend Joe up in Vermont. He sends these from the Champlain Valley, at a place called Raven’s Ridge. It looks like an alternating series of sandstones and shales, arched into an anticline, perhaps during the Acadian Orogeny (??). According to the Nature Conservancy’s website, porcupines live in this anticline, which is called “The Oven.” Looks like most of the strata around there …
18 September 2020
Friday fan: Death Valley, California
Working up some new images for my free, online Historical Geology textbook, I annotated a photograph I took in March of this alluvial fan in southern Death Valley. The development of desert varnish on older parts of the fan shows their age visually in a quick and easy way of determining fan deposit sequence: I’ve been making a lot of these animated annotations as a way of conserving space in …
5 June 2020
Friday fold: Harbledown Island
Reader Christian Gronau writes with this Friday fold contribution: Greetings from Cortes Island, BC – at the opposite end of the Strait vis-a-vis Lopez Island. Your Mountain Beltway blog is always of interest, and I have been following it for several years by now. Thank you for putting the effort into this worthwhile website. Quite regularly your posts elicit “echoes” and make me go back to some of my own …
22 May 2020
Friday fold: Anticline in Glacier National Park
Some web research led to a serendipitous discovery and further exploration. Wherever you’re sheltering in place, you don’t have a view that’s this grand. Slip away for a few moments to the high country of Montana’s Glacier National Park, where an anticline may be seen in the towering cliffs…
8 May 2020
Friday fold: Wills Mountain Anticline
Eric Fulmer (who pitched in with last week’s Friday fold) returns this week with another treasure. He writes, I was in Hopeville, WV a couple of years ago. The entire area between Cabins and Hopeville is a real joy (geologically and recreationally) as some of the most resistant rocks of the Mid-Atlantic Appalachians are folded and exposed in quick succession and with great relief. I am particularly fond of seeing …
3 April 2020
Friday Fold: Saudi Arabia
The Friday fold is a guest post from Wadi Fatima, in Saudi Arabia.
6 March 2020
Friday fold: an Extreme(adura) geological history question
The Friday folds are revealed in an elegant cross-section through fantastic rocks in the Extremadura region of Spain.
14 February 2020
Friday fold: Miocene slump in Anza-Borrego
Today’s Friday Fold comes from Edith Carolina Rojas, the dynamic geology professor at The College of The Desert in Palm Desert, California. She’s an awesome person, and also the sense of scale in this amazing image: Edith shares that this gorgeous structure is an anticline is located in Split Mountain Gorge in Fish Creek Canyon. It’s a gigantic gravity-slide fold due to soft sediment deformation in the Latrania Formation. Wow …
3 September 2019
An unconformity at Bacon Cove, Newfoundland
At Bacon Cove in eastern Newfoundland, there is a nice example of an angular unconformity between Ediacaran and Cambrian sedimentary rocks.
30 August 2019
Friday fold: Calafia State Beach
The Friday fold is a guest contribution to “Mountain Beltway” from the manager of the AGU Blogosphere, Larry O’Hanlon. It shows apparent crumpling of a few sedimentary layers at the toe of a soft sediment slump at Calafia State Beach in southern California.
11 July 2019
A submarine slump complex at Sandy Cove, Newfoundland
Traveling in Newfoundland, Callan visits a seaside outcrop showing a Proterozoic submarine slump complex, overprinted by tectonic cleavage and weathered by the sea.
5 April 2019
Friday fold: Angel Island “I”
The Friday fold is on the north shore of Angel Island, San Francisco Bay, showing blueschist-facies high-contrast metalliferous cherts with folds on many scales.
18 March 2019
New discoveries in the Martinsburg Formation
A virtual field trip to examine some deepwater clastic sediments shed off the first phase of Appalachian mountain building, and deformed in the third phase. It’s a lovely day for a field trip to the late Ordovician!
19 October 2018
Friday fold: the Brooks Range, Alaska
It’s Friday, thank goodness. Today our “Friday fold” feature heads north, way north, to the Brooks Range of Alaska. There we find a trio of mountainsides exposing folds photographed in the 1990s.
