Advertisement

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

24 June 2022

Friday fold: Kinked Lynchburg metasediments near a soapstone body

Happy Friday! Here are some kink-folded metasediments from Virginia’s Lynchburg Group to help usher in the weekend.

Read More >>


25 June 2021

Friday fold: The Blue Ridge Tunnel

Inside the Blue Ridge (in an 1850s-era railroad tunnel), Callan finds folds and boudinage that formed during Appalachian mountain-building.

Read More >>


22 November 2019

Friday fold: Noonday Dolomite in Mosaic Canyon

Because I’m putting together a field course for spring break 2020 to Death Valley California, I was looking through old Death Valley photos this week, from the last time I went to that special place. It was seven years ago! How time flies… This one is in Mosaic Canyon, and was taken by my student Marcelo Arispe, a talented photographer as well as a talented geologist: By the standards of …

Read More >>


11 October 2019

Friday fold: Watern Cove

A moderate mesoscale monocline at Watern Cove, Newfoundland, shows off multicellular animal fossils of the Ediacaran Mistaken Point Formation.

Read More >>


18 October 2017

VGFC 2017: Limbs of arkose

The 2017 Virginia Geological Field Conference had a heavy arkose infusion. Meet some of these feldspar-rich Neoproterozoic sediments of the Lynchburg Group.

Read More >>


15 April 2017

Basement xenoliths in Catoctin Formation, Compton Pass

My son and I hiked Compton Peak in Shenandoah National Park this morning, and saw these two lovely examples of xenoliths. The example above is small, but it shows clearly the difference between the coarse, felsic basement rock (Mesoproterozoic granitoid, comprising the xenolith) and the surrounding fine-grained dark green metabasalt of the Catoctin Formation (Neoproterozoic). Here’s another, bigger example: These two Blue Ridge examples both illustrate the principle of relative …

Read More >>


21 December 2016

Stromatolites of Bunnahabhain

Remember the diamictite I featured here a few weeks ago, from Islay? It was the one that might be a Snowball Earth diamictite. Well, if you follow Snowball Earth science at all, you’ll doubtless be aware that the glaciogenic sediments are characteristically overlain by “cap” carbonates. There’s a stratigraphic successor to the Port Askaig Tillite, too – it’s called the Bonahaven Dolomite. Unlike what you might expect for a cap …

Read More >>


9 December 2016

Friday fold: Machir Bay I

It’s Friday! Today’s fold comes to you from Neoproterozoic metasediments on the west side of Islay, at Machir Bay.

Read More >>


30 November 2016

“Drumsticks” of Islay tillite

One fun thing about examining the Port Askaig Tillite in the field is to find odd-shaped exemplars of the unit lying on Islay’s beaches. My favorites were shaped like wands, or antennae, or perhaps the drumsticks freshly detached from a Thanksgiving turkey… a big clast at one end and then a thin septum of the finer-grained matrix to hang on to: Here’s an example: The shape results from differential weathering …

Read More >>


29 November 2016

Islay’s Port Askaig tillite

The Port Askaig Tillite is a Neoproterozoic diamictite on the eastern shore of Islay (Scotland) that may record a “Snowball Earth” glaciation.

Read More >>


29 October 2016

New digital media of Shenandoah National Park feeder dikes

In Shenandoah National Park, astride Virginia’s Blue Ridge, feeder dikes of Catoctin Formation (meta-)basalt cut across the Grenvillian-aged granitoid basement. Due to their mafic composition and columnar jointing, these feeder dikes generally weather more rapidly than their host rocks. I led a field trip in the park on Thursday for my son’s school, and my student Marissa was there the weekend prior, checking out the autumn leaves and geology with …

Read More >>


22 July 2016

Friday fold: The walls of Scalloway Castle

When in Shetland, one of my first stops was the museum in Scalloway, and one of the ancillary benefits of visiting there is the castle next door: Scalloway Castle includes building stones derived from the local limestone – a Neoproterozoic unit that has recently been chemostratigraphically correlated with Snowball Earth cap carbonates elsewhere in the world. But that need not concern us today. Today we are here for the folds! …

Read More >>


6 June 2016

Cleavage refraction in Konnarock Fm. rhythmites – a virtual sample

Here’s 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 cleavage refraction going from meta-clay-shale (now ‘slate’) through a graded bed of fine sand and silt. [gigapan id=”187755″] Link GIGAmacro by Callan Bentley [sketchfab id=”fb3eb77f46524d15b3a23649c63cd863″ start=”0″ spin=”” controls=”0″] Photoscan model by Marissa Dudek …

Read More >>


24 May 2016

Nine new GigaPans from Team M.A.G.I.C.

Alethopteris fern fossil: [gigapan id=”187190″] Link GIGAmacro by Robin Rohrback Rapid River Canyon, Idaho: [gigapan id=”187535″] Link GigaPan by Callan Bentley River cobble of brecciated Columbia River Basalt, Hammer Creek (Salmon River), Idaho: [gigapan id=”187524″] Link GIGAmacro by Callan Bentley Petersburg Granite exposed at Belle Isle, Richmond, Virginia: [gigapan id=”187523″] Link GigaPan by Jeffrey Rollins Ammonite: [gigapan id=”187221″] Link GIGAmacro by Callan Bentley Slickensides in ultramafic rocks of the Wallowa …

Read More >>


20 April 2016

Cooling columns of the Catoctin Formation, Indian Run Overlook, Shenandoah National Park

An inaugural visit to an outcrop in Shenandoah National Park reveals the signature of lava flows ~600 million years old.

Read More >>


27 January 2015

Miette Group gritstone showing scours, mudchip rip-ups, cross-bedding, and dropstones

The coarser strata of the Neoproterozoic Miette Group in the Canadian Rockies of Alberta record changing water current strength over time, and maybe an iceberg or two.

Read More >>


12 December 2014

Friday fold: Miette slate, Alberta

The Friday fold returns to Canada, looking at Neoproterozoic slate and quartzite at the southern terminus of the Icefields Parkway. Bonus features include ripple marks, graded beds, cross-bedding, cleavage, and boudinage.

Read More >>


24 April 2013

Native copper from the Catoctin Formation

Another new insight from last week’s visit to the Outdoor Lab was that they have several fine examples of native copper found in float of the Catoctin Formation on their property. Here are a few examples: Classic examples – a bit of malachite in there too, it looks like. I wasn’t totally shocked when I saw these items, since just a month or two ago, I was shown a similar …

Read More >>


17 April 2013

Four new GigaPans from an intriguing contact

Callan and his colleague Jay Kaufman (University of Maryland) go to extraordinary lengths to document an intriguing block of rock in northern Virginia’s Blue Ridge province. Great images and a lot of fun result – but what do these rocks tell us?

Read More >>


5 April 2013

Two new GigaPans of Rockfish Gap, Virginia

I took a trip down to Charlottesville this week for a couple of meetings, and I made time along the way to capture two new GigaPans of the lovely exposures of Catoctin Formation greenstone at Rockfish Gap, where Interstate 64 traverses the Blue Ridge. This is very close to the southernmost tip of Shenandoah National Park, and at the northern terminus of the Blue Ridge Parkway. The Catoctin is an …

Read More >>