As I mentioned, Monday had me out in the field, looking at the western Blue Ridge and eastern Valley & Ridge provinces in Virginia. This was a field review for the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox, and Grace Dawson. Immediately after lunch, we visited an … Read more
On Monday, I was out in the field at the Blue Ridge / Valley & Ridge transition (“boundary”?) in the Elkton East quadrangle, where Chuck Bailey and students (from the College of William & Mary) were leading a field review of their new geologic map. A field review is a form of field-based peer review, … Read more
Another guest Friday fold – this one supplied by Ander Sundell of the College of Western Idaho, and his student Katie Ursenbach, who took the shot and gave permission for me to re-post it here. You’re looking at cuspate-lobate folds due to primary sedimentary settling. the Snake River Canyon in southwestern Idaho. A pile of … Read more
Today, for your viewing pleasure, I offer you: A series of big honkin’ gas pockets in a 615 ka basaltic lava flow in the Owens Valley of California. This same lava flow has been featured here before, since it imparted a lovely contact metamorphism to the alluvial fan over which it erupted. These things are … Read more
Have you ever seen Archean pillow basalts? How about Archean pillow basalts that have grown much taller through vertical extrusion along a ductile shear zone? Come to the southern Superior Craton to see more!
Last Saturday, before the rains moved in…
I got this note via email last week. Hi Callan, First of all, congratulations to your blog. It is just great. I would like to contribute to your “Friday fold” section. A few words about myself. I am born in Austria and did my BSc and MSc at the Montanuniversitaet Leoben. In September 2011 I started … Read more
One of Callan’s former students leads a field trip to examine the western edge of the Blue Ridge geologic province, attempting to answer the question of whether the Blue Ridge / Valley & Ridge contact is indeed the trace of a thrust fault. Breccias and S-C fabrics tell part of the story…
The Castner Marble is an extraordinary Mesoproterozoic limestone (later re-crystallized and metamorphosed) that exhibits some primary structures (both explicit and ambiguous) and some secondary (tectonic) overprints. It’s exposed in the Franklin Mountains of west Texas.
In December, Callan found an outcrop of Neoproterozoic-aged turbidites in South Africa, on the eastern shore of False Bay.
Hand sample of folded limestone strata in West Virginia (presumably Devonian in age). Note the rip-up clasts and large grain size at the base of the sample (to the right in the photo). Note the fine-grained, thin-bedded shale laminations towards the top (left) of the sample, too. Together, they tell a story of decreasing energy … Read more
After a roadside explanation just an hour and a half earlier on how the relationship between bedding and cleavage can reveal whether bedding is likely right-side-up or up-side-down, my students and I were walking up the road to the Ancient Bristlecone Pine Forest in the White Mountains of California, and I saw this outcrop that … Read more
Today, two examples of outcrops that reveal an overprinting relationship between metamorphic cleavage and sedimentary bedding. Both are Devonian in depositional age, from the new stretch of New Route 55 in West Virginia, west of Moorefield. The first is from limestones of the Helderberg Group, and the second is from shale of the Brallier Formation. … Read more
More evidence of currents in the Devonian deep… Primary structures that give us clues, preserved in a place where preservation over 360 million years isn’t necessarily guaranteed. As you might expect, this turbidity currents roared in from the east, where the mountains were rising, and generating a fair bit of sand and mud, during the … Read more
Callan and his wife journey to Africa’s southernmost point, and find a geological mystery there.
After our safari, Lily and I were taken up onto the Great Escarpment in northern South Africa. The escarpment is supported by sedimentary strata of the Transvaal Supergroup that overlie the Archean basement rock of the Kaapvaal Craton. The Transvaal strata are Paleoproterozoic in age, somewhere between 2.5 and 2.0 billion years old. They are … Read more
Here’s a look at what you see if you go to the Three Rondawels viewpoint above the Blyde River Nature Reserve in northern South Africa: A lovely scene. The three mega-hoodoos on the left are the eponymous “rondawels” (pronounced ron-da-vulz), which is the Afrikaans word for a round hut. These erosional remnants are more or … Read more
Here’s two nice examples of mudcracks I saw used as paving stones in South Africa:
Yesterday, I showed you this picture and asked what you saw there: Today I’ll give you my impressions. This is an outcrop of sandstone of the Table Mountain Supergroup, seen on the beach in the idyllic village of Rooiels, on the eastern side of False Bay, north of Cape Hangklip, in South Africa.The field of … Read more
At the Three Rondavels overlook in the northern Drakensburg Mountains of South Africa, I saw this chunk of quartzite with a peculiar variety of Liesegang banding (iron oxide staining of the rock by groundwater): A short distance away, I found another example: In one key way, I liked this second example better, even though the … Read more