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You are browsing the archive for unconformities Archives - AGU Blogosphere.

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.

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31 May 2019

Friday fold: Point Arena, California

It’s Friday, and I’m grateful that Bret Leslie of the NRC has stepped up with a Friday fold contribution from coastal California: Bret says this outcrop is: from my trip last month to the Sonoma and Mendocino coast. The first is the cliff below the Pt. Arena lighthouse. The marine deposits (now a marine terrace) are unconformably on top of the folded Miocene sedimentary rocks in the second photo. Here …

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25 June 2018

Mafic volcanics atop felsic instrusives: Sonora Pass, California

Sonora Pass, California, is a lovely place to examine a volcanic-on-plutonic nonconformity that spans about 80 million years of missing time. Let’s check it out on a photo-rich virtual field trip!

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6 October 2016

Oddball Icelandic rocks, part I: A green ignimbrite

Iceland does basalt really, really well. But there are a few non-basaltic igneous rocks to be found there, too. One of them is a green ignimbrite (pyroclastic conglomerate) that crops out in coastal Berufjörður, eastern Iceland. Check it out!

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30 August 2016

Northwest Highlands unconformities (3 of 3): Sub-Ardvreck

It’s time to cover the third and final unconformity I observed this summer in the North-West Highlands of Scotland: the unconformity between the Neoproterozoic Torridonian Group below and the Cambrian Ardvreck Group above. Where I saw it, south of Loch Assynt on the mountain called Beinn Garbh (north of Canisp), it actually is displayed alongside the sub-Torridonian unconformity. The mountain hosts a “double unconformity”! Here is a view, looking south: …

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22 August 2016

Northwest Highlands unconformities (2 of 3): Sub-Torridonian Group

Let’s now profile the next unconformity in the sequence of pulses of erosion and deposition recorded in the North-West Highlands of Scotland. For a reminder, here’s a cartoon cross-section through the four relevant units: Today, we’ll look at the contact between the Lewisian Gneiss and the Torridonian Group (Diabeg Formation), marked with a “2” on the cartoon above, where it is exposed along the shore of Loch Assynt. There are …

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16 August 2016

Northwest Highlands unconformities (1 of 3): Sub-Stoer Group

First in a series profiling the three unconformities to be found in the North-West Highlands of Scotland. Today: the sub-Stoer unconformity as exposed at Clachtoll. Explore a Proterozoic buried topography topped with coarse, angular breccia.

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26 February 2016

Friday fold: Siccar Point video from BGS

The British Geological Survey just came out with a new video on Siccar Point, featuring some excellent drone video of the site (in very good weather!). In addition to the unconformity, one of the things you will appreciate about the video is an excellent end-on view of a plunging synform exposed just above waterline: You’ll get a much better sense of its shape by enjoying the motion of the drone’s …

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7 October 2015

The New Market / Lincolnshire contact

Yesterday, I put a photo up here on the blog, and asked you to figure out where the formational contact was in that image. Here’s the image I showed you: It turns out that my plan to have readers upload their copies of the image didn’t work as well as I had planned – apparently you all don’t have as complete a suite of control options as I do. Shocker! …

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24 October 2013

Exploring Wind River Canyon’s Great Unconformity in outcrop and hand sample (via GigaPan)

Over the summer, I shot these two GigaPans of the “Great Unconformity” in Wind River Canyon (Owl Creek Mountains), Wyoming: [gigapan id=”136109″] link [gigapan id=”136122″] link This week, Team M.A.G.I.C. (by which I mean my student Robin Rohrback-Schiavone) finished up a series of three macro GigaPans of rock samples from the site (made with our one-of-nine-in-the-world GIGAmacro rig by Four Chambers Studio): [gigapan id=”141715″] link [gigapan id=”143006″] link [gigapan id=”143007″] …

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1 December 2010

The Konnarock Formation

A detailed description of one of the Virginia Blue Ridge’s most intriguing geologic formations: a maroon sedimentary sequence showing the advance of “Snowball Earth” glaciers in the Neoproterozoic.

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