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24 March 2015

Martinsburg Formation outcrops in Edinburg Gap

Martinsburg Formation outcrops in Edinburg Gap

A report from the field: new outcrops of Ordovician-aged turbidites featuring geopetal indicators, fossil content, and a structural overprint imparted during Pangaea’s assembly.

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20 March 2015

Friday fold: flexed turbidites

Friday fold: flexed turbidites

Spring is almost here! As you get ready for the equinox, enjoy this gentle fold on a Friday: These are turbidites (graywacke and shale) of the late Ordovician Martinsburg Formation, seen in Edinburg Gap, western Massanutten Range, greater Shenandoah Valley, Virginia. Bedding is flexed very slightly here, from moderately-dipping to more steep, and then back to moderate again. Slickensides on the top of some exposed layers indicate the beds shifted …

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27 January 2015

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

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.

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21 January 2015

Bloomsburg Formation in GigaPan

Three images, working our way in from outcrop setting to hand sample: link link link These fine red sandstones are the Silurian-aged Bloomsburg Formation, as it crops out in Fort Valley, Virginia. What would we see if we kept zooming in? …Stay tuned…

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17 January 2015

Geology of the Acropolis (Athens, Greece)

Geology of the Acropolis (Athens, Greece)

When visiting Athens, Greece, you are drawn to the Parthenon’s grand architecture atop the hill called the Acropolis. But why is the Acropolis a hill?

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16 January 2015

Friday fold: the Ross Sandstone, Ireland

Friday fold: the Ross Sandstone, Ireland

Zoltán Sylvester has contributed today’s Friday fold, an anticline in the Ross Sandstone of Ireland: Click image to go to the source (full sized). Thanks Zoltán! Happy Friday everyone.

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9 May 2014

Friday fold: knuckling under in the Mesilla Valley shale

Friday fold: knuckling under in the Mesilla Valley shale

Here’s a fold I saw in Texas, in the Mesilla Valley shale, close to the contact with the Muleros Andesite at Cristo Rey: This is a pretty wild looking fold. Let’s zoom in on the most deformed portion: Annotation: white is top of the distinctive, blocky, buckled bed, and black is its bottom side. Red shows brittle fractures in that same bed: Looks as if it rolled over on itself …

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29 April 2014

A second look at the mass transport deposit on Corridor H

A second look at the mass transport deposit on Corridor H

Remember this past winter when Alan Pitts and I found what we interpreted to be a mass transport deposit (a submarine landslide/slump) along the new section of Corridor H leading up the Allegheny front? Well, I was back out there yesterday, with Dan Doctor (USGS Reston) and Jay Kaufman (University of Maryland). One new thing we found was lots of weathered-out “ploudins” (pillows/boudins), many of which had a “sleigh” shape …

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4 April 2014

Friday fold: ‘Ben Folds One’

Friday fold: 'Ben Folds One'

We have a guest Friday fold today, from reader Ben Mackay-Scollay of the Monash University School of Geosciences in Melbourne: Ben writes: Hey there Professor Bentley, been a fan of your blog for a while and I thought you might be able to use this for your Friday Fold series. It’s an upright fold at Bermagui in New South Wales, where I visited recently as part of my post-grad coursework …

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6 March 2014

Puzzling over the Wallbridge Unconformity along Corridor H

Puzzling over the Wallbridge Unconformity along Corridor H

The Wallbridge Unconformity is a surface of stratigraphic hiatus or erosion between the depositional influence of the Tippecanoe and Kaskaskia epeiric seas. After Alan Pitts and I located ourselves in the Oriskany Sandstone (terminal Tippecanoe stratum), we looked stratigraphically above the quartz sandstone for the overlying unit, which should be the Needmore Formation shale (beginning of the Kaskaskia sequence). Indeed, the quartz sandstone was overlain by a black shale at …

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