You are browsing the archive for archean Archives - AGU Blogosphere.
14 September 2018
A trip back to Archean sedimentary rocks in Barberton, South Africa, reveals a few folds on the roadside…
5 June 2018
Cross-bedding isn’t just for modern sedimentary deposits; you can find it in truly ancient ash deposits too! Let’s head to South Africa and take a look.
2 November 2017
This morning on Twitter I was reminded of komatiites, those “extinct” ultramafic lavas that were relatively common eruptions during the Archean. I’ve actually got a good number of komatiite photos to share from my time last year in South Africa’s Barberton Greenstone Belt. But since time is short this morning, I’ll start with a short photo set of three images, all showing different aspects of how these ultramafic rocks weather …
25 May 2017
Deep in the Archean, things suddenly got violent in the deep water of the Mapepe Formation’s oceanic setting. What was a quiet precipitation of chert suddenly was torn apart and tumbled downslope. Was an earthquake to blame? A bolide impact? This is the result.
1 May 2017
Volcanic “hailstones” called accretionary lapilli rained down on South Africa 3 billion years ago, and have survived to be seen in the present day, along the R40 road through Barberton Mountain Land, near the Bulembu border crossing into Swaziland.
21 February 2017
A reader asks about the use of zircons in isotopic dating, and the argument for submerged continental crust beneath Mauritius.
2 February 2017
Banded iron formation is an “extinct rock” that can be found in ancient marine strata such as those found in the Barberton Greenstone Belt. Visit an outcrop on the Barberton GeoTrail and contemplate the bizarre anoxic world that Earth used to be.
18 November 2016
I tried something new this morning, and polled Twitter for their choice of Friday fold: Quick poll – What do you want for the Friday fold? 30 minutes to respond. — Callan Bentley (@callanbentley) November 18, 2016 As of the time of this posting, the first choice, “Lewisian gneiss @ Tarbet” won out with 7 / 10 votes. The people have spoken, and this time I like the result of …
28 October 2016
Have a look at this week’s Friday fold – but be aware that it will be looking back!
26 October 2016
Archean meteorite impact evidence from the Fig Tree Group in Barite Valley, Barberton Greenstone Belt, South Africa
What does the sedimentary record of a giant meteorite impact look like? Turns out it is full of tsunami breccia, fine ash, hail-like spherules, and a barium-rich ocean’s crystal precipitates. Join us in the Barberton Greenstone Belt of South Africa to learn more.
24 October 2016
Erik Klemetti posted today at Eruptions about komatiite, which is apropos, considering I just finished imaging some samples of that ultramafic volcanic rock. Have a look at three samples from Barberton Greenstone Belt here, each from the 3.27 Ga Weltevreden Formation: [gigapan id=”192621″] Link GigaPan by Callan Bentley [gigapan id=”192599″] Link GigaPan by Callan Bentley [gigapan id=”192337″] Link GigaPan by Callan Bentley And, while we’re at it, here’s one from …
2 September 2016
A quick Friday fold – Ulundi Formation, basal Fig Tree Group of the Barberton Greenstone Belt, exposed in a creekbed etched into the trace of the Sheba Fault. This is one of the outcrops I visited one week ago today as part of the pre-IGC field trip to the Barberton. The rocks are iron-rich cherts and pelites that have enjoyed some serious strain, presumably due to movement along the Sheba …
1 September 2016
The news yesterday of 3.7 Ga stromatolites in Greenland prompts a closer look at 3.22 Ga microbially-induced sedimentary structures in the Barberton Greenstone Belt’s Moodies group sandstones.
16 August 2016
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.
29 July 2016
A quick Friday fold here from the North-West Highlands of Scotland: These are Lewisian gneisses exposed on a headland northwest of the little outpost of Tarbet (where the Handa Island ferry departs from). I was out there in search of shear zones, but I found plenty of nice folds, too. There are two main folds in the image – a synform in the foreground (yellow), and an antiform in the …
11 July 2016
I’m in the North-West Highlands of Scotland, enjoying spectacular geology and less-than-spectacular weather. I’ve been fairly productive on the GigaPan front, regardless, nipping outdoors when the weather permits to shoot outcrops and landscapes. One set I’m particularly pleased with is this suite of four images. They show the Archean-aged Lewisian gneiss, the oldest rock unit in the North-West Highlands, as exposed on a beachside outcrop east of Durness, Sutherland. The …
2 May 2016
More 3D models: digital facsimiles of real rock samples. Check them out and explore! Clinker from the Powder River Basin, Wyoming: [sketchfab id=”afb351be49f04c8eab1acc29a8a2bcfb” start=”0″ spin=”” controls=”0″] Ripple marks from the Rose Hill Formation, West Virginia: [sketchfab id=”6b56924ee2f84dd2821c4cb30e4869f9″ start=”0″ spin=”” controls=”0″] Meta-komatiite from the Red Lake Greenstone Belt, northern Ontario, Canada: [sketchfab id=”53dc4d161c974d7b86f70639062551e0″ start=”0″ spin=”” controls=”0″]
29 March 2016
Here are a few new images I’ve been working on with my home-based Magnify2 imaging system from GIGAmacro. Archean basement complex gneiss from the Gallatin Range of Montana: [gigapan id=”185543″] Link (If this looks familiar, that’s because one of the samples I imaged with the Photoscan 3D modeling technique and published on Sketchfab the week before last.) Banded iron formation from Minnesota with ooids and stromatolites: [gigapan id=”185076″] Link Intrusion …
24 March 2016
Pahoehoe “ropes” on a basalt, sample site unknown: [sketchfab id=”d846c69192804bcfbcb2a625fd807af1″ start=”0″ spin=”” controls=”0″] Archean gneiss from the Gallatin Range of Montana: [sketchfab id=”4abba639632945aa8bd93c0d4e996e6a” start=”0″ spin=”” controls=”0″] Tafoni in Malmesbury Group turbidites, South Africa: [sketchfab id=”ddb2ec0a22214192907886d56e17ad11″ start=”0″ spin=”” controls=”0″]
25 September 2015
I don’t think I’ve featured this sample here before… It’s a lovely gneiss from near the trailhead for the Spanish Peaks, near Ted Turner’s Ranch in the Gallatin/Madison Range in southern Montana, not too far from Big Sky. Have fun checking it out in this macro GigaPan: [gigapan id=”161099″] link Happy Friday to all.