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You are browsing the archive for 2014 March.

31 March 2014

Hunt’s Hole: Climbing ripples in volcanic surge deposits

Check out the immense climbing ripples preserved in surge deposits at Hunt’s Hole (a maar volcanic crater in southern New Mexico) and imagine the strong currents couples with an extraordinary amount of entrained pyroclastic material.

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28 March 2014

Friday fauxld: the “Not a Box” at Confusion Hill

It’s Friday… that means it’s time for a fold. Let’s try this outcrop at “Confusion Hill” in the Franklin Mountains of West Texas: See it? Let’s zoom in… From the shadows to the left of the hammer, trace out the dark green layer… it may make you think of a box fold: …but it’s not. This is actually a completely planar sedimentary bed, tilted to more or less vertical, and …

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27 March 2014

Aden Crater

That’s Aden Crater, a Pleistocene shield volcano in southern New Mexico. Here’s what it looks like from above (Google Maps view): I also noted the position of two nearby maar craters: Kilbourne and Hunt Holes. When you climb up to the edge of Aden and look in, you see the congealed and fractured remnants of a lava lake that once filled this to the brim (and indeed, spilled over the …

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26 March 2014

The Great Unconformity in the Franklin Mountains

Good morning! Let’s take a walk up the east side of the Franklin Mountains, north of El Paso, Texas, to walk across the Great Unconformity. The basement rock exposed here is the Red Bluff Granite, a 1.1 Ga felsic magma that intruded the columnar basalts of the Mundy “Breccia” and the Castner Marble. (It is unknown what substrate the Castner Marble was deposited upon.) This is what the Red Bluff …

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25 March 2014

Root wedging: examples from Maryland and Texas

While I’m showing photos from last week’s Billy Goat Trail field trips (3 in total), let me share a striking example of root wedging from Olmstead Island, on the walkway out to see Great Falls: And, since I meant to get back to blogging about west Texas this week, here’s another example of the same process, seen with a different kind of tree in different sorts of rocks, in the …

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24 March 2014

Monday migmatite

Here’s a sweet little sample of migmatite (~470 Ma late Ordovician Taconian Orogeny, U/Pb date from zircon), that my students and I spotted last week on the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province: Note the white translucent quartz, the orangey (partially kaolinitized and rusty stained) opaque potassium feldspar, and the shreds of biotite torn and tangled between them: I love the fact that I …

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21 March 2014

Friday fold: a random sample from the campus of UTEP

I know nothing about this sample, other than the fact that it was a thrown-away sample found in the rock pile next to the old geology building at the University of Texas at El Paso. Happy Friday!

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20 March 2014

Montoya Group fossils and faults on the Crazy Cat landslide

Today, I initiate a series of posts based on some of the geology I saw over spring break, in west Texas and southern New Mexico, on the field exchange between Northern Virginia Community College and El Paso Community College that I helped facilitate. We spent our first morning in the field in the Franklin Mountains, due north of El Paso (and, for that matter, Ciudad Juarez). It was unseasonably cold …

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18 March 2014

On ignorance, bias, data, and the tentative nature of (scientific) interpretations

A young-Earth creationist reinterprets one of Callan’s blog posts in light of a Biblical flood. Callan responds with a demonstration of how new information can change a true scientist’s mind, but no amount of data can convince someone whose conclusions are based on faith rather than empirical data.

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17 March 2014

Angle of repose in Devonian shale, Corridor H

Where the Needmore Formation is falling apart on Corridor H, sloughed-off shale is piling up in a tiny talus slope: You could slap a protractor on that photo and get a pretty good measurement of the angle of repose of this chippy, flaky granular material. Eyeballing it, that looks like about 45° to me.

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