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GeneralUnusual geological formations. Any ideas how they were formed?

13th Feb 2019 11:14 UTCLarry Maltby Expert

These photos were taken in the North Dakota Badlands. The shape of these geological formations seems unusual to me. Does anyone have an idea how they were formed?

The four similar formations appear to have formed in a straight line.

13th Feb 2019 14:27 UTCBob Harman

HI LARRY, I have a few morning moments before I start my day's wanderings in Tucson so I will take a stab at answering your question.

Most importantly, I think all the formations are entirely natural, nothing man created here. You are in the Badlands of North Dakota on a dry sloped area which is regularly windswept and experiences infrequent, but regular heavy rains. The barren slope is covered by fine mud/sand/grit etc with evidence of the rains with its numerous rivulets flowing down the slope. The mud, sand, and rock is of slightly varying resistance to all the natural elements so there are all local manner of natural weird shapes. There is a thin horizontal seam of resistant rock running along near the bottom of the photo. There are several small "domes", upslope, near the left side of the photo and then there are the odd circular shapes in the photo. All are naturally slightly more resistant areas of the surface than the surrounding surface areas.

For a comparison on a grand scale, look at all the fabulous formations in the sandstone in the Arches National Park. After a long time of exposure to the elements, weird localized surface shapes, both grand and small, are the final result. CHEERS.....BOB

13th Feb 2019 14:42 UTCPaul Brandes 🌟 Manager

Bob is correct.

It's the same processes that create the hoodoos (I had to include that word ;-) in Bryce Canyon and Goblin Valley. It all has to do with differential weathering and the difference in the hardness of materials in those formations. A modern day example of this can be seen at Sleeping Bear Dunes and Grand Sable Dunes where sand is blown around a more resistant layer of sand or roots/small trees, creating strange shapes and such.

13th Feb 2019 15:18 UTCBill Cordua 🌟 Manager

I wonder if these aren't a layer of concretions whose interiors are variable cemented, so that once breached, an inner less consolidate zones were preferentially worn away.

13th Feb 2019 15:47 UTCEd Clopton 🌟 Expert

These may be related in a very general way to the "reduction spheroids" discussed recently (https://www.mindat.org/forum.php?read,11,455048,455113#msg-455113)--not necessarily the same chemistry, but something having to do with a 3D zone of chemical alteration around a foreign object that resulted in the differently resistant concretions Bill suggests.

13th Feb 2019 15:53 UTCAlfredo Petrov Manager

I agree with Bill that these are broken concretions. The outer shell and the central core consist of slightly more indurated material, so they stand out on weathering.

14th Feb 2019 04:15 UTCGregg Little 🌟

I agree as well with differential weathering of what are likely nodules. In the first photo even the ovoid shape of the nodule is apparent with the bowl shaped appearance of its outer wall. The nodules also are seen to occur in one horizon which likely favored their formation.

14th Feb 2019 20:16 UTCRalph S Bottrill 🌟 Manager

Yes to concretionary structures. These can form due to groundwater moving through permeable sands and remobilising some minerals into spherical to ellipsoidal bodies of cemented sand. The minerals can include quartz, calcite, baryte, etc.

14th Feb 2019 23:20 UTCKevin Conroy Manager

The hill has eyes!

15th Feb 2019 00:11 UTCPaul Brandes 🌟 Manager

Kevin Conroy Wrote:

-------------------------------------------------------

> The hill has eyes!

But, are they alive with the sound of music?

15th Feb 2019 07:25 UTCDale Foster Manager

Most likely the sound of duelling banjos.

15th Feb 2019 20:20 UTCLarry Maltby Expert

Thanks everyone for the comments.

It looks like we have a consensus on the mode of formation. This is the result of weathering on concretions with variable hardness and porosity. There are many variations of concretions and hoodoos (I also like that word, Paul) in the North Dakota Badlands. More to follow in the data base.

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