You are browsing the archive for concretions.
25 February 2017
Some enormous concretions are encountered in a shale quarry in the central Fort Valley. Concretions like these are typical of the Devonian-aged Millboro Formation.
7 June 2016
Here’s another example of a visualization combination that leverages the advantages of the GIGAmacro system with the 3D ‘virtual sample’ perspective of the Sketchfab-hosted model: the same sample presented in both formats. In this case, it’s a lovely example of a conglomerate that I found in our lab at NOVA, showing variations in the level of cementation around a central ‘nucleus’. Link GIGAmacro by Callan Bentley Photoscan model by Marissa …
31 March 2016
Anorthosite with lovely garnet reaction rims, a spherical hematite concretion, and some sweet breccia. Check them out and explore!
28 July 2015
Another site from the GMU sedimentology field trip in April: An outcrop on Route 33 in Brandywine, West Virginia, showing the Millboro Formation. It’s mostly shale, with some intriguing sandstones, too. There are fossils and diagenetic carbonate nodules (concretions). Here’s the outcrop, the largest GigaPan I’ve taken so far (7.9 billion pixels): link The shale itself looks… like shale. It’s fine-grained, and dark (high carbon content, suggesting low oxygen levels …
23 December 2014
Two years ago, I posted on some interesting structures my students and I saw at Consolation Lakes, near Moraine Lake in Banff National Park. They were little concretions, “oncoids” roughly speaking, and may have indicated (thanks Howard!) that the boulders were sourced to the Peyto Formation, a Cambrian carbonate within the Gog group: The purpose of today’s post is to confirm that these structures are still there two years later, …
20 August 2012
Royal Tyrrell Museum geologist Dave Eberth donates time and expertise to help Callan’s students understand the Cretaceous-aged Horseshoe Canyon Formation in central Alberta.
9 August 2012
Callan presents a mystery rock found in blocks of sedimentary rock on a talus slope near the Consolation Lakes in Banff National Park, Alberta. Are they orange oncolites? Or alien embryos? 🙂
22 September 2011
More moki marbles: little concretions in sandstone, kind of like the ones I showed you Tuesday from Illinois. But these ones are from the Navajo Sandstone, a late Triassic or early Jurassic erg deposit from the Colorado Plateau. These photos were taken in Zion National Park, near Springdale, Utah (real close to the cross-beds I featured a month ago). They are tougher than the sandstone in which they formed, and …
20 September 2011
Giant City State Park is a patch of protected forest south of Carbondale, Illinois, where there are some pretty cool exposures of Pennsylvanian-aged Makanda Sandstone. Here’s a typical look at one: Notice the deep chasm on the right. This leads, maze-like, to other flat-bottomed and vertically-walled canyons: The orthogonal joint sets produces some nice tall, cliff-like vertical exposures that reveal the history of these rocks in several stages: deposition by …
15 August 2011
Concentrically-zoned ironstone concretion in sandstone of the Morrison Formation, eastern flank of the Bighorn Mountains / western edge of the Powder River Basin, Wyoming, at the Sheridan College dinosaur fossil quarry, last week. The white stuff is caliche. A quick post to celebrate the fact that as of three hours ago, Lily & I are back home in our condo in D.C. It’s been a great summer, and I have …