How's this for a classic fault plane? We have two fault walls separated by three metres of fault breccia. The one on the left can only be seen in the bottom left of the photograph. The one on the right is reet well polished. Knowing where it is, I suspect that it is a thrust fault with the hanging wall on the right, but I am happy to be corrected.

This ain't a wezzit, but I know that quite a few of you will have passed this feature.

Lovely. The roof/wall of the passage ahead in our current dig looks just like that - can't quite reach it yet though

Excellent photo Langcliffe. You sure it's a thrust fault though, at that high angle?
Any slickensides to indicate direction of movement?

Are you going to tell us where it is?  :doubt:

It's the Salle d'Escalade near the entrance of the Guiers Mort. The exit into the short wind tunnel that leads into the entrance chambers is behind the caver,

It is a good photograph, but I won't claim it as mine. It was taken in June 2018 by Chris Blakeley when he, Colin Boothroyd and I did a big circuit going in via the upper series, and returning along the stream passage.

I am not sure it's a thrust fault, which is why I said that I suspect that it is. The slickenside is vertical, which isn't very useful.

Many of the thrust faults in that area are very steep - there was an awful lot of pressure being exerted when the pre-Alps were formed, but I do agree that this is exceptionally so.

Thanks Langcliffe - if it's in that area then your suggestion does seem likely.

To be peNdantic, in a shortening tectonic environment a thrust fault would be parallel to bedding up to about 45deg, from 45deg to 90deg it would be termed a reverse fault...
Slickensides will only record the last phase of movement on a slippage plane, and to grow mineral slickensides there would need to be an extensional phase to allow room for growth. Scouring and polishing of course can be in compression.
Lovely capture of the feature, very impressive 

Brains said:

To be peNdantic, in a shortening tectonic environment a thrust fault would be parallel to bedding up to about 45deg, from 45deg to 90deg it would be termed a reverse fault...

Click to expand...

Quite right - I should have said reverse fault. Thank you.

langcliffe said:

Brains said:

To be peNdantic, in a shortening tectonic environment a thrust fault would be parallel to bedding up to about 45deg, from 45deg to 90deg it would be termed a reverse fault...

Click to expand...

Quite right - I should have said reverse fault. Thank you.

Click to expand...

Ah, thank you, that's what I was thinking when I posted above.

Theres an excellent fault plane in Old Gells.

Plenty of nice fault planes on Mendip, although possibly not as photogenic. Swing Pitch and the climb below in Longwood is on a fault plane, the gouge is clearly visible as you descend the pitch. GB has a couple of nice faults exposed in the Gorge, with some nice folding, and Rift Chamber is on a fault. The passage downstream of the GB inlet in Charterhouse is on minor fault. Mny of the caves in Fairy Cave Quarry are close to or on a fault which forms the quarry face just north of Shatter Cave (see https://ukcaving.com/board/index.php?topic=20595.0). Brimble Pit Swallet is developed on a major thrust fault. But perhaps the best examples are seen in Reservoir Hole which is formed on a suite of strike slip faults with numerous riedal shears between them.

Is this one of the faults (with folding) in GB  that you mentioned?

droid said:

Theres an excellent fault plane in Old Gells.

Click to expand...

The fault plane in Gells, with some evidence of slickensides

There's a lovely fault plane on Alderley in West Mine, with great big recrystallised quartz slickensides.