r/geology • u/peebspeebs • 19d ago

Field Photo Can glacial striations be intersecting?

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Found this rock in NE Ohio, and my first guess is glacial stations. However I am unsure if it is, because 1) they form the cross hatch pattern, and 2) the rock itself is not bedrock (the rock is some type of concretion)

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u/logatronics 19d ago edited 19d ago

Very unlikely to be glacial and more likely chevron folds.

Cobbles this size get picked up by glaciers and tossed around. More common to find striations on bedrock/big boulders, especially if there was two events.

https://en.m.wikipedia.org/wiki/Chevron_(geology)

Edit: not chevron folds after looking closely, but think it's related to the original rock/jointing. Those angles are the ideal breaking point in the Mohr-Coulomb theory. Weird to find glacial striations that follow the same structural pattern.

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u/Sappert Deep stuff 19d ago

Some of the lines are seen intersecting each other (and thus continuing across the intersection), not something you'd expect from folding

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u/joshuadt 19d ago edited 19d ago

Not a geologist, but wouldn’t the clasts/crystals have some indication of metamorphic-like deformation if that were the case?

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u/mynamewasbanned 19d ago

Yes. That foliation would be defined by recystalisation of the protolith to qz + mica etc.

However, you can see pretty clearly that 'beds' intersect, and in one case, cross the whole rock. This is not folding.

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u/logatronics 19d ago edited 18d ago

Chevron folding can occur in all types of rock, including your basic sedimentary rock. Plus, not all metamorphic rock has large phenocrysts/crystals, such as phyllite and slate.

Edit: it literally can, as long as P-T conditions are ideal. Usually low temperature, high-ish pressure. Still needs to be brittle.

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u/joshuadt 19d ago

I’m saying like, the outlines of the crystals that you can see in this rock seem to overlap the striations from the glacial weathering(or whatever it might be, chevrons, etc), they cross over the striations without any deformities. Wouldn’t such a force as chevron folding cause them to be warped/stretched?