ChatterBank0 min ago
geology
what is a sharp bend in a geological formation
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Seen in certain conditions the deposited rocks from a meander could explain the question Mrs Jo, however it is probably quite unlikely. But it would be easy to tell the difference.
Usually 'geological formation' would denote a horizontally extensive unit of rock that was widespread over an area. It would be bound above and below by other formations. A river deposit would be a much smaller & narrower and would pervade other rocks.
First of all, you need to establish the relationship the bent formation has to the other formations, to which it is adjacent. If they are bent in the same pattern, then they have been affected by the same thing. This is probably folding: as the rocks have been deformed at some point after they were formed (for sedimentary rocks this is usually in horizontal layers).
If it were a preserved meander, the shape of the river has been retained and is what you are actually looking at. A meander would be contained within other rocks. So, we could expect to see a narrow channel that is meandering through and enclosed by other rocks (below, to either side & above), so the bend can be seen in the rocks of the meander but not these enclosing rocks.
The folds we were talking about are seen by their expression within the 'bedding' of the rock; these are the horizontal surfaces formed when the original sediments were lain down. Whereas a river is a channel moving across a horizontal surface, so for you to see this in a cliff-face, the rocks must have been rotated, so the original horizontal surface is now vertical (or thereabouts) and for this to happen would conditions under which folding of the rocks would normally occur....just to mix matters up.
There are a host of other explanations, but these are even more unlikely: folding is much more widespread than any other explanation.
Usually 'geological formation' would denote a horizontally extensive unit of rock that was widespread over an area. It would be bound above and below by other formations. A river deposit would be a much smaller & narrower and would pervade other rocks.
First of all, you need to establish the relationship the bent formation has to the other formations, to which it is adjacent. If they are bent in the same pattern, then they have been affected by the same thing. This is probably folding: as the rocks have been deformed at some point after they were formed (for sedimentary rocks this is usually in horizontal layers).
If it were a preserved meander, the shape of the river has been retained and is what you are actually looking at. A meander would be contained within other rocks. So, we could expect to see a narrow channel that is meandering through and enclosed by other rocks (below, to either side & above), so the bend can be seen in the rocks of the meander but not these enclosing rocks.
The folds we were talking about are seen by their expression within the 'bedding' of the rock; these are the horizontal surfaces formed when the original sediments were lain down. Whereas a river is a channel moving across a horizontal surface, so for you to see this in a cliff-face, the rocks must have been rotated, so the original horizontal surface is now vertical (or thereabouts) and for this to happen would conditions under which folding of the rocks would normally occur....just to mix matters up.
There are a host of other explanations, but these are even more unlikely: folding is much more widespread than any other explanation.
Answer was submitted before I saw your reply - I was referring to the post before.
Taking a meander as being a fluvial feature, hence geomorphological. Meanders are dynamic, ephemeral (in geological time) features, forming in alluvial, submarine or tidal environments - so any preservation in a geological sense, would merely be a series of cross-cutting relationships, cross-bedding, minor unconformities and channel infills.
Agreed brachiopod, that in a pre-diagenetic environment, meandering river systems are geomorphological features and it would be obvious if you were looking at a meandering channel deposit and not a fold.
But at the same time you seem to discount deposits from these systems as 'geological features'. Meandering rivers are a sedimentary facies, experiencing specific patters of deposition. The telltale features you go on to describe ("so any preservation in a geological sense, would merely be a series of cross-cutting relationships, cross-bedding, minor unconformities and channel infills") can be used to describe most sedimentary systems and channel deposits can be an extremely valuable econmoic resource. Channel deposits can contain highly lucrative oil reserves (e.g. Canada & Algeria), not to mention their vital role in coal formation.
Anyways, sorry for hijacking your thread kads, the answer is almost certainly a fold, related to the tectonics of the area, as they are one of the most prevelent geological features
http://en.wikipedia.org/wiki/Fold_%28geology%29
But its been ages since i've had a geology debate and couldn't resist (sorry brachiopod ;-) ).
But at the same time you seem to discount deposits from these systems as 'geological features'. Meandering rivers are a sedimentary facies, experiencing specific patters of deposition. The telltale features you go on to describe ("so any preservation in a geological sense, would merely be a series of cross-cutting relationships, cross-bedding, minor unconformities and channel infills") can be used to describe most sedimentary systems and channel deposits can be an extremely valuable econmoic resource. Channel deposits can contain highly lucrative oil reserves (e.g. Canada & Algeria), not to mention their vital role in coal formation.
Anyways, sorry for hijacking your thread kads, the answer is almost certainly a fold, related to the tectonics of the area, as they are one of the most prevelent geological features
http://en.wikipedia.org/wiki/Fold_%28geology%29
But its been ages since i've had a geology debate and couldn't resist (sorry brachiopod ;-) ).
Hehe, believe it or not, but I haven't heard that one before actually gen2. I wish I did live in Hawaii sometimes; especially cold Monday mornings, but I'm English as it happens.
I just always thought it was such a cool word it was a shame not to use it: although the spelling isn't as good as the pronunciation (Pa-hoey-hoey, for those of you who didn't know)!
I just always thought it was such a cool word it was a shame not to use it: although the spelling isn't as good as the pronunciation (Pa-hoey-hoey, for those of you who didn't know)!
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