A nice wet day in Swildon's and some Geology question

[VWScully]

Hello everyone;
I had an introduction to Swildon's on Tuesday with @mrodoc and it was fab! However, I am an Ecologist and Geo-Environmental Scientist and have a question about how the folded rocks visible in the cave are described as my understanding has always been as follows:
I always understood it be caused by significant stress or compression; such as the movement of Pangea or intense pressure along faults.
However, I've also heard it said that it may be due to movement as it was being deposited; i.e. still being silt or soft material.
What is the understanding of the formation in Swildon's?
It is visible in my Video at about 7:25 minute mark.

Could it have been formed whilst still soft? I am not familiar with that explanation.
Any insight by more experienced Cave Geologists is appreciated .

 

[The Old Ruminator]

Lots on Goggle " Folding of sedimentary strata occurs when originally flat, layered rock formations are bent or curved due to intense tectonic stress, typically during mountain-building events (orogeny). These ductile deformations produce large-scale structural features like anticlines (arched upward) and synclines (U-shaped), or smaller, complex folds. These structures are common in tectonically active regions. " I would have thought Mr O'Doc would have explained it all. Glad you had a great visit.

 

[VWScully]

Thank you. Yes, that is how I understand it, but he also thought there may be some formation occurring when the Shale is being deposited.

 

[ChrisB]

I'm not a geologist, but apparently soft-sediment deformation is a thing. See https://en.wikipedia.org/wiki/Soft-sediment_deformation_structures

I don't know if it occurred on Mendip though. Also, if you search for other references, be careful to distinguish between geological research and arguments for creationism (claiming it as evidence that all rocks must formed since Noah's flood).

 

[martinr]

a question about how the folded rocks visible in the cave are described

If you mean the large fold in the streamway in Swildons -

.... the beds are metres thick, representing deposition over hundreds of thousands of years, so it's not down to movement as it was being deposited.

I understand this fold occurred during the Variscan orogeny at the end of the Carboniferous period, roughly 300 million years ago

 

[Brains]

IMO, the folds seen in Swildons are tectonic in origin, being seen consistently over a depth of many meters. Soft sediment deformation is usually seen in a single bed, sandwiched between smoother, unaffected beds. This image was stolen from Google...

 

[Andy Farrant]

The folds in Swildons Hole are tectonic, not syn-sedimentary, and formed when the Mendip periclines were created during the Variscan orogeny. The more mudstone-rich 'shaley' beds near the base of the Black Rock Limestone Formation (ie the rocks we see in Swildon's 1 streamway) are particularly prone to being folded as they are more ductile than the more massive purer limestones higher in the sequence. Similar folding and faulting can be seen in the Gorge in GB.