north america

101 American fossil sites you’ve gotta see, by Albert B. Dickas

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Mountain Press has released a new volume by frequent author Bert Dickas: it’s a compilation of 101 places in the United States where fossils can be viewed. Some sites are collection sites on public land; others are museums or protected areas. The book is a useful collection of information in a concise, well-illustrated form. Each … Read more

“Making North America,” episode 3: Human

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The PBS series NOVA has a new three-part series called “Making North America” that premiered two weeks ago. Hosted by the director of the Smithsonian Institution’s National Museum of Natural History, Kirk Johnson, the series explores the tectonic assembly of terranes that resulted in the bedrock of the continent, the panoply of diverse creatures that … Read more

“Making North America,” episode 2: Life

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The PBS series NOVA has a new three-part series called “Making North America” that premiered last week. Hosted by the director of the Smithsonian Institution’s National Museum of Natural History, Kirk Johnson, the series will explore the tectonic assembly of terranes that resulted in the bedrock of the continent, the panoply of diverse creatures that … Read more

“Making North America,” episode 1: Origins

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The PBS series NOVA has a three-part series coming out next week called “Making North America.” Hosted by the director of the Smithsonian Institution’s National Museum of Natural History, Kirk Johnson, the series will explore the tectonic assembly of terranes that resulted in the bedrock of the continent, the panoply of diverse creatures that have … Read more

101 American Geo-Sites You’ve Gotta See, by Albert B. Dickas

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I just finished reading 101 American Geo-Sites You’ve Gotta See, one of the latest publications by geology-friendly (and Missoula-based) Mountain Press. I’m grateful to the the publishers for sending me a review copy. It’s a nicely written and produced book highlighting sites across the United States of America of geological interest. The book is organized … Read more

Roadside wonders of Route 287

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Northern Colorado’s route 287 connects Fort Collins, Colorado with Laramie, Wyoming. Along its length, it displays roadcuts into Archean-aged basement complex. Two of these outcrops are featured in this post: one metamorphic (mostly), and a second igneous (mostly), with some intriguing polka-dotted plutons.

Jointed Virgelle

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One of the stops my Rockies students and I made this summer was a dinosaur paleontology tour through the Two Medicine Dinosaur Center in Bynum, Montana. The folks there are very accommodating, and at my request gave the class a bit of stratigraphic context for the dinosaur fossils. For instance, we visited the geologic formation … Read more

Easter egg

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Searching through my photo archives this morning for something suitably “Eastery”… something in pastel colors, perhaps? … a petrified lagomorph? … how about an egg, or something egg-shaped? This is as close as I got: This is in the Owens Valley of eastern California, showing a boulder of the Mesozoic Sierra Nevada Batholith bearing a … Read more

Here, ptyggie ptyggie ptyggie!

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Yesterday, I took my GMU structural geology class to the Billy Goat Trail, my favorite local spot for intriguing geology. Unlike last year, we managed our time well enough that we got to clamber around on the rocks downstream of the amphibolite contact. Here’s Sarah, Lara, Kristen, and Alan, negotiating a steep section: Justin, Joe, … Read more

Sugarloaf

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Sunday morning, NOVA adjunct geology instructor Chris Khourey and I went out to Sugarloaf Mountain, near Comus, Maryland, to poke around and assess the geology. Sugarloaf is so named because it’s “held up” by erosion-resistant quartzite. It’s often dubbed “the only mountain in the Piedmont,” which refers to the Piedmont physiographic province. Here’s a map, … Read more

Transect debrief 8: late brittle deformation

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The final chapter in our Transect saga is now here. In some ways, it’s the least thrilling of the bunch. On the other hand, when I see a nice example of this structure, it makes me squeal like a little girl. I refer, of course, to plumose structure, the small-scale architecture of a joint surface. … Read more

Transect debrief 7: Brittle-ductile deformation

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On the transect trip, I also saw some nice meso-scale “minor” structures that probably formed during Alleghanian deformation. Prominent among the ones that really impressed me were these en echelon tension gash arrays, deforming the Antietam Formation quartz sandstone and well exposed in blocks used to construct the wall along Skyline Drive and the Sandy … Read more

Transect debrief 5: sedimentation continues

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We just looked at the Chilhowee Group, a package of sediments that records the transition for the North American mid-Atlantic from Iapetan rifting through to passive margin sedimentation associated with the Sauk Sea transgression. Well, if we journey a bit further west, we see the sedimentary stack isn’t done telling its story. The saga continues … Read more

Transect debrief 4: transgression, passive margin

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…So where were we? Ahh, yes: an orogeny, and then some rifting. What happened next to Virginia and West Virginia? Let’s consult the column… After the rifting event opened up the Iapetus Ocean, seafloor spreading took place and tacked fresh oceanic crust onto the margin of the ancestral North American continent. As North America (“Laurentia”) … Read more

Transect debrief 3: Rodinian rifting

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The Grenville Orogeny, responsible for Virginia’s basement complex, was one mountain-building event among many that helped put together a Mesoproterozoic supercontinent called Rodinia. But Rodinia didn’t last: it broke apart during the Neoproterozoic to form the Iapetus Ocean basin. This rifting event is recorded in Virginia’s Blue Ridge province in the Swift Run Formation and … Read more

Transect debrief 2: weathering the Grenvillian landscape

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From the basement complex, the next unit up in the Blue Ridge province’s stratigraphic sequence is the Swift Run Formation. It rests atop an erosional unconformity. After the Grenville Orogeny (~1.1 Ga) added a swath of new crust along the margin of the North American continent, the landscape began to weather and erode. Eventually, an … Read more