Minor structures to predict larger folds

[@Geology_clips]

Thanks, excellent presentation, and I will recommend it to my students. But please check: the red arrows appearing at 5 min 16 sec seem to indicate the wrong shear sense. It should be top-left, shouldn't it?

[@robbutler2095]

Arghhhh - yes - well-spotted - they're correct on the theoretical image but not on the real fold - a good discussion point for tutorials!!

[@argendarne8204]

Thanks for the nice lecture! I have a small question about minor folds. are they usually paracitic folds of larger folds? Is there any other mechanism that makes small folds?

[@robbutler2095]

There are various ideas on the formation of folds of different size (amplitude/wavelength) in different layers. I cover some of these in the "how do rocks fold?" video
ruclips.net/video/PY2AOWML8qo/видео.html
But of course folds can also form in different, distinct "episodes" ... check out the refolded folds video and the deformation in fine-grained strata one too! Thanks for the question

[@argendarne8204]

@@robbutler2095 OK I'll check other videos, too. Thank you for kind answer!

[@张宏远-z8t]

So much nice pictures. Why cleavages are always confined in layer boundary planes? Can the duplex-like structure initiated layer cooling structure (a kind of columnar jointing)?

[@robbutler2095]

In turbidite units ("greywackes") like this, where the tops of beds are finer grained - these parts tend to develop slatey cleavage better than the coarse grained parts. So these parts show vergence most clearly. These features can resemble duplex structures - but they're not faults...