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You are browsing the archive for mesozoic.

11 October 2016

A virtual field trip to Portrush, Northern Ireland

One of my favorite places in Northern Ireland is the east side of the peninsula that hosts the tourist town of Portrush. There, two early schools of geological thought engaged in a battle. The opposing sides were: the Neptunists, who thought all stratified rocks, and in particular basalt, must form from precipitation from the sea, and the Plutonists, who thought some rocks, including basalt, formed through intrusion of molten rock …

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27 March 2016

Another trio of 3D models

Here are three more of my Photoscan-generated, Sketchfab-hosted 3D models of rock samples: Mud cracks in Tonoloway Formation tidal flat carbonates, Corridor H, West Virginia: Diorite from the eastern Sierra Nevada of California: Vein cross-cutting foliated & lineated gneiss, Blue Ridge basement complex, Virginia:

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19 December 2014

Friday Fold: Mist Mountain Formation in Canmore, Alberta

Let’s journey to the Cretaceous today, to see sandstones, shales, and even some coal strata that have been folded during the eastward thrusting that built the Canadian Rockies. Here’s the same fold, in context, shot in GigaPan on a different day, from a different angle. Can you match it up? link Ben Gadd showed me (and my field class) this site last summer. It’s a little west of Canmore. There’s …

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12 March 2013

Five new GigaPans from Thoroughfare Gap

Yesterday, I took five new GigaPans at Thoroughfare Gap, a water gap where Broad Run cuts through Bull Run Mountain, the eastern limb of the Blue Ridge Anticlinorium at my latitude. The rocks here are the Cambrian-aged Chilhowee Group, with bedding tilted moderately to the east during Alleghanian mountain-building in the late Paleozoic. To the west is the crystalline core of this massive regional fold, and to the east is …

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15 November 2012

Neoacadian Inner Piedmont trip, part III: Mesozoic cataclasite

Quartzite, shattered and healed and shattered again and again and again. It’s cataclasite, seen in the North Carolina Piedmont and inferred to be Mesozoic in age due to its brittle style of deformation.

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19 October 2011

Bookshelfed mullions from Norway

Elizabeth Eide of the National Academies shared this image with me a year or two ago, when she gave a talk on Norwegian geology for the Geological Society of Washington. Those are some bookshelfed gneiss layers sandwiched between upper-left and lower-right carbonates. The “bookshelfing” refers to the numerous parallel brittle fractures along which the gneiss slabs have slid down the face of their neighbors, like a set of encyclopedias tilted …

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25 March 2011

Friday fold: conference samples

At last weekend’s northeastern / north-central GSA meeting in Pittsburgh, David Saja of the Cleveland Museum of Natural History presented a talk entitled, “Geometric Analysis of Folded Greywacke Layers from Pacheco Pass, California.” [Abstract link] In addition to the standard PowerPoint presentation that 99% of GSA speakers use, David also brought in some hand-samples (what we in the business like to call pocket folds) to display. As his title implies, …

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24 December 2010

GoSF6: Graywacke turbidites

The geological tour of San Francisco continues with an examination of the graywacke deposits of the

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21 December 2010

GoSF3: Chert

Episode three in the multi-part series on the geology of San Francisco. This post focuses on the chert layers of the Marin Headlands

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20 December 2010

GoSF2: Basalt

Second in the on-going series about the geology of San Francisco: this post explores the pillow basalts of the Marin Headlands Terrane.

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