RomaWiFi
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#1
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Hey guys, I don't study geology but I love learning reading about it and a week ago I was reading a sample book about an unnamed island in the middle of the Indian ocean and edge of a continent quoting
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RomaWiFi
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Hey guys, I don't study geology but I love learning reading about it and a week ago I was reading a sample book about an unnamed island in the middle of the Indian ocean and edge of a continent quoting "interesting section from the eastern most part of an island slightly tilted old pre-Cambrian surface towards the west under cretaceous and Eocene cover with the same dip!" the professor seemed really shocked I don't seem to understand is this something very rare , unusual phenomena?
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Plagioclase
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(Original post by RomaWiFi)
Hey guys, I don't study geology but I love learning reading about it and a week ago I was reading a sample book about an unnamed island in the middle of the Indian ocean and edge of a continent quoting "interesting section from the eastern most part of an island slightly tilted old pre-Cambrian surface towards the west under cretaceous and Eocene cover with the same dip!" the professor seemed really shocked I don't seem to understand is this something very rare , unusual phenomena?
Pretty hard to say without more context, what you're describing is an unconfirmity, specifically a disconformity or paraconformity, but there's nothing fundamentally unusual about that, unconformities are very common. Perhaps there's something about the regional context that makes this surprising.
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RomaWiFi
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(Original post by Plagioclase)
Pretty hard to say without more context, what you're describing is an unconfirmity, specifically a disconformity or paraconformity, but there's nothing fundamentally unusual about that, unconformities are very common. Perhaps there's something about the regional context that makes this surprising.
Well there's quite a long time between the pre-Cambrian and Cretaceous/Eocene, so the fact that tectonics HAVEN'T moved the older rocks at all, and the newer ones lie perfectly on top with the same dip is very very unusual!Normally the lower rocks will have been folded or tilted in some form to make an unconformity this is the reason it is a phenomena today I asked a friend from Cambridge university and the studied this so I was correct
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Plagioclase
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(Original post by RomaWiFi)
Well there's quite a long time between the pre-Cambrian and Cretaceous/Eocene, so the fact that tectonics HAVEN'T moved the older rocks at all, and the newer ones lie perfectly on top with the same dip is very very unusual!Normally the lower rocks will have been folded or tilted in some form to make an unconformity this is the reason it is a phenomena today I asked a friend from Cambridge university and the studied this so I was correct
A paraconformity or disconformity spanning such a long span of time isn't something you see every day and it's certainly cool but it's not that rare, unless there is context that you're omitting. In fact I saw a very similar disconformity in southern France with cretaceous and eocene limestones over ordovician schists which locally had the same bedding orientation.

It is very unlikely that tectonics have not moved the older rocks at all, particularly if this is an ocean island. The fact that this gap in time exists means that episodes of significant erosion occured between the precambrian and cretaceous, very likely driven/facilitated by tectonic uplift (just without rotation, or with components of rotation that cancelled each other out along that time-span). You don't just get a surface that sits, passively, without erosion or deposition at the Earth's surface for >400 million years, that's not geologically possible, particularly not for an ocean island.

That's all there is to be said on this - there is nothing else that we can say without knowing where this is.
Last edited by Plagioclase; 2 years ago
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RomaWiFi
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#6
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(Original post by Plagioclase)
A paraconformity or disconformity spanning such a long span of time isn't something you see every day and it's certainly cool but it's not that rare, unless there is context that you're omitting. In fact I saw a very similar disconformity in southern France with cretaceous and eocene limestones over ordovician schists which locally had the same bedding orientation.

It is very unlikely that tectonics have not moved the older rocks at all, particularly if this is an ocean island. The fact that this gap in time exists means that episodes of significant erosion occured between the precambrian and cretaceous, very likely driven/facilitated by tectonic uplift (just without rotation, or with components of rotation that cancelled each other out along that time-span). You don't just get a surface that sits, passively, without erosion or deposition at the Earth's surface for >400 million years, that's not geologically possible, particularly not for an ocean island.

That's all there is to be said on this - there is nothing else that we can say without knowing where this is.
Yes the thing that is shocking me till now is this is really in an ocean island it is something cool I need to find out where this island is when I find out do you want me to tell you ?
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