Geopuzzle #11 : Highly Allochthonous

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Chris Rowan is a geologist specialising in the dark arts of paleomagnetism, and getting people to pay him to travel to exotic destinations for fieldwork. Having drilled up New Zealand during his PhD, and South Africa in his first post-doc, he now works at the University of Edinburgh.

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Geopuzzle #11

Category: geopuzzling
Posted on: May 9, 2008 10:48 AM, by Chris Rowan

Spot (and explain, if you can) the differences.

It's not much of a hint to say that the last one is quite difficult - but the last one is quite difficult.

Update: Click through for the answer.

Find more posts in: Physical Science

Comments

I'm going to take a wild guess. The top one has asymmetric ripples formed in a stream dominated environment, the centre one symmetrical ripples caused by shallow water waves and the down one is ripples deposited by wind blown sand/silt.

Posted by: Lost Geologist | May 9, 2008 11:54 AM

I agree w/ Lost Geologist that the upper and middle look like asymmetric and more symmetric, respectively. Additionally, the crests on the upper one are straighter relative to middle, which are getting towards lingoid.

The bottom photo has two layers of slightly different directions superimposed on the outcrop. But, in terms of general characteristics, the ripple marks look more like the upper photo than the middle. But, I'm probably missing something obvious.

Posted by: BrianR | May 9, 2008 12:59 PM

I agree. In the lower photo the crests of the ripples seem much longer than the top two photos (laterally uniform current), it's also lighter in color with a red hue (oxidizing environment, less clay), and there is a ~45 degree change in current direction in a small vertical distance (short duration current direction changes). Without seeing inverse grading on the ripples, I'd say the bottom photo is eolian in origin as well. I can't wait to hear the answer!

Posted by: Mel | May 9, 2008 4:36 PM

The last one looks like my kitchen floor...

Posted by: Transient Reporter | May 10, 2008 9:55 PM

The bottom photo ripples are also much more laterally continuous, which makes me think wind. Are all of these in a close proximity? If so, you could have a stream entering an ocean with a beach. I had a field trip to a site like that once, and it was really cool to see all of the ripple forms close together. Also, any ripples in the sand in the background in photo 1?

Posted by: ScienceWoman | May 12, 2008 1:00 PM

so ... are ya just gonna leave us hangin'?

Posted by: BrianR | May 13, 2008 7:05 PM