Mystery Outcrop
I’m a bit too busy with work to put up a proper post at the moment but here is a mystery exposure I came across the other day.
Any ideas?
Update:
Fiddling with photoshop, here is a closer look …
The Solution(?):
The stratigraphy here is Upper Carboniferous coal overlain by Coal Measure mudstones. This may (or may not – cue future post…) be unconformably overlain by a Permian sandstone breccia and Triassic conglomerate (although the official BGS map sheet has the post-Carboniferous here as ‘Quaternary Drift’).
From the morphology of the land surface just up-slope from this exposure there would appear to be an old bell pit sunk into the coal seam and this is a section through the surrounding spoil heap.
This explains the angular fragments of ?Permian sandstone and rounded Triassic pebbles but it doesn’t really explain why, if it is spoil, it contains so much coal, or so little mudstone.
Boy, that’s some weird looking stuff. It looks saprolitic… is it? I’ll be very curious to hear someone explain what’s going on here.
Photos can be so frustrating. What I’d give to actually be able to handle some of the stuff. It definitely looks lke some kind of breccia, maybe deeply weathered, as Callan says. My first take on the lighter areas was that they were lichen splotches, but squinting at the photo, they look more mineral than vegetable (though I see lots of little tufts of moss). I’m somewhat red-green color blind, so I can’t trust my color perception (I tend to see the color I want to see), but some of the textures look like there might be some serpentine or glass in there. We get a fair amount of hyaloclastic breccia in the basalts around here, so that’s one possibility- but the light material doesn’t look right for that. Perhaps the light clasts are overlying sediment that were caught up and included with a submarine volcanic explosion? It might also be fault gouge in a mixed basaltic/ultramafic suite, but while I feel like I’m seeing some very crude bedding, I don’t see the kind of fabric I’d expect with fault gouge. Furthermore, I’d expect to see more distinct reds from weathering if that were the case. At first I was thinking some kind of coaly breccia, but that seems unlikely the more I look at it.
I guess the only thing I feel the least bit confident about is that it *looks* like a breccia. I really hope you have an answer eventually.
As a clue, the black stuff is coal, the pinkish stuff is a fine sandstone.
1. I’m not 100% sure what this is myself
2. I apologise for the photograph but the light levels at this time of year are not good and this slope is north facing with a lot of trees around.
That is indeed some gnarly looking stuff … but, if it’s coal and sandstone then I guess I’d concur w/ the above ideas about a breccia. It looks so jumbled and disorganized.
And if it’s a coal-sandstone breccia – how did it get that way?!
Oh I do love a puzzle… so we’re actually trying to figure this out, not just waiting for the answer. OK, where is it? What is its age? What else is in the neighborhood? North-facing slope… Could it be soil creep? Do you know if coal and SS crop out uphill from it? Is the first picture pretty much the whole exposure, or does this material have substantial extent? There’s a couple of rounded pebbles (one appears above the point of the large SS clast in the upper right of the enlargement/enhancement). Is there a conglomerate uphll? Is it loose or consolidated?
“Is it loose or consolidated?” The breccia, not the (hypothetical) conglomerate.
Where is it?: Cannock Chase, English Midlands
What is its age?: Upper Carboniferous (Moscovian) … or ?Permian/Triassic … or Recent!!
Stratified coal and a grey mudstone occur at about the same level ~10m left of the top image (which is pretty much the whole exposure here). There may be sandstones above (exposure is not good here) and there is a conglomerate at the top of the slope.
The unit is moderately consolidated.
I think He’s Got It! Having grown up in Coal Country (SE Ohio, Pennsyvanian cyclothems), I can tell you in the old days they’d leave surprising amounts of spoils behind, especially if it was little crumblies… and even more so if it was “dirty” with other material.
Your potential solution would also be consistent with the crude bedding, and that the larger sandstone clasts seem to preferentially have a flat side down.
If culm dust was not economic, it would be discarded with the waste rock, and if it were cemented in the ensuing decades/centuries you’d get a coaliferous diamictite.
That looks like a mining spoil to me. I have seen similar “outcrops” outside coal mines in Utah. The coal does not look banded or cleted enough to be in situ. It’s amazing how difficult it can be to distinguish these sorts of exposures from “real outcrops”.
I see no problem with there being large amounts of reasonable quality coal discarded outside a mine, that is pretty common.
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