Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Paul Repstock on 07/12/2016 03:21:10
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We have an odd one here: A group of snail shells (1/2" to 2" diameter) Not completely infilled (no sediment?) The shell and body of the animal have been replaced with crystaline matter (carbonate?) This was found at about 300M elevation 20 miles from the ocean, on Northern Vancouver Island, Canada.
The area has an annual rainfall of about 150"/year. I am wondering why the fossil did not disolve like the surrounding limestone does. So far, we have not discovered the deposit this sample came from and can only say that it was found adjacent to a bedded deposit of compressed mudstone.
My interpretation is that this gray limestone was deposited by an undersea vent, and then rapidly uplifted at some point in the recent past. There are no reports that I've found, suggesting a major uplift of this area in the past few thousand years?
Paul
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Close up
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... The shell and body of the animal have been replaced with crystaline matter (carbonate?) ... I am wondering why the fossil did not disolve like the surrounding limestone does.
The contents of the shell could be a replacement-fossil (https://www.google.com/search?q="replacement+fossil) where the flesh has been replaced by silica, (silicification (https://en.wikipedia.org/wiki/Petrifaction#Silicification)), which would not weather-away as readily as limestone.
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Thank you RD. It sounds right? I guess the silica would also be consistent with vent. This was a lucky, chance find. The shell knob standing up to catch my eye.
Are these fossils datable?
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...Are these fossils datable?...
I think you'll need a specialist-forum for that, e.g. ...
http://www.thefossilforum.com/index.php?/forum/14-fossil-id/
They'll need a close-up photo of intact shells, (include an object, like a coin, for scale).
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Could it be a sea shell, washed far inland by a massive tsunami?
The Juan de Fuca plate boundary is offshore from Vancouver. Unlike the fault lines in California, it appears to be "stuck", remaining quiescent for many centuries, and then generating some enormous earthquakes and tsunamis.
Some of these tsunamis were documented as far away as Japan, where the occurence of a tsunami without an accompanying local earthquake was noted as an anomaly.
See: https://en.wikipedia.org/wiki/Juan_de_Fuca_Plate
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Thanks Evan. I have some knowlege of the activities of the Jaun Da Fuca Plate. Because of the threat in the Cascadia Fault many papers have been written on it. The topography of the Northern part of Vancouver Island is crumpled like the front end of a head-on crash. There are large outcrops of strata standing with the visible statifications in the vertical orientation. This Island seems to be a loose collection of boulders moving together.
There are many places on the island showing fossile evidence of uplift.
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Could it be a sea shell, washed far inland by a massive tsunami?
Looks like there are trace fossil (https://en.wikipedia.org/wiki/Trace_fossil) trails across the rock which are converging on the shell, (nom nom nom (http://www.urbandictionary.com/define.php?term=nom%20nom%20nom)) ...
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D69245.0%3Battach%3D22739%3Bimage&hash=13ba39db49b8cbd9adebdd6bcb491ff8)
If so, what you've got is fossilized sea-floor, (that rules-out tsunami).