dug up while quahogging in the pond - not sure how many years go by to turn an oyster into a fossil!
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oyster fossil from point judith pond - narragansett ri
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There’s an example of a palm tree stump from underneath an old hotel in Tampa Florida, it was in saltwater for a hundred fifty or so years and it’s agatized...So it would seem it depends on the sediment, minerals, etc.it comes in contact with..Floridaboy.
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Hey Hal Here on Long Island there are a few known sites where ancient white cedar stumps can be seen at extreme low tides or after storm erosion. Rising sea levels drowned them some 4 to 6 thousand years ago and they remain relatively unchanged.
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So unless an object is organic it can’t be dated, Right?
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I always read that fossils were at least 10,000 yrs old, but apparently that doesn’t mean it takes 10,000 yrs to make them:
“To become fossilized, organisms must be rapidly buried, preferably in a fine sediment with geochemical conditions that favor the exchange of minerals between the sediment and organic components of the organism, and that exchange of minerals is possible because of dissolved minerals in flowing water. If those conditions occur, fossilization must necessarily be a rapid process of a few hours to a few months if it is to occur before decay destroys any record of the organism. Fossilization does not take thousands or millions of years, but is most likely to occur in catastrophic conditions …”
Raúl Esperante
Geoscience Research Institute
Last edited by Cecilia; 01-27-2022, 01:33 AM.Digging in GA, ‘bout a mile from the Savannah River
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From the appearance alone, I would be sure that’s a fossil in the millions of years and not a recent or subfossil shell. Charlie will likely have a better handle on the stratigraphy of that area, but I believe the marine deposits are largely Cretaceous, so that’s a strong possibility.
I don’t want to hijack your thread, but fossilisation processes are a strong interest of mine and I don’t completely agree with all that has been said above.
That quote from Raúl Esperante, although correct, is misleading in that it’s incomplete. He’s only talking about replacement fossils (which yours appears to be)… ie where the organic materials of the original organism have been replaced by mineralisation. That’s not the only way in which fossils arise though.
The generally accepted definition for a fossil is that it’s the “preserved remains, impression, or trace of any once-living thing from a past geological age.”
Some prefer to narrow down that definition to exclude traces that aren’t themselves biological in origin. So for example: acceptance of things like poo and secretions as fossils; putting moulds or casts of organisms in special categories such as “steikern”; differentiating things like footprints or burrowing and feeding traces as “ichnofossils”; and not regarding things like gastroliths from the digestive tract as fossils at all.
We’re currently in the geological period known as the “Holocene”, which began around 11,650 years ago, and so we have (somewhat arbitrarily) defined a fossil as being more than 10,000 years old. The distinction between fossil and non-fossil status did not switch over at midnight 10,000 years ago, but that’s the general rule and it isn’t a moving target. The Holocene began at a fixed point in time and – under our current definition – something from the Holocene not regarded as a fossil today wouldn’t suddenly become one in a few thousand years’ time just because it had then achieved an age beyond 10,000 years.
When Esperante says “to become fossilized, organisms must be rapidly buried, preferably in a fine sediment with geochemical conditions that favor the exchange of minerals” he is specifically referring to replacement fossils. Complete organisms or organic material from them can also be preserved in other ways such as mineral encrustation, coating or enrobement; dehydration/mummification; freezing; and other mechanisms. Sometimes the preservation can be purely a consequence of the material being protected from the elements and/or from placement where it wasn’t discovered by scavengers… in a cave for example.
Most usually, when we talk about fossils, there has been at least some degree of mineralisation, even if only on the surface) but it doesn’t have to be the case. Even when there is mineralisation, that doesn’t qualify the material as “fossil” unless it also meets the 10,000 year rule because mineralisation can be a very rapid process if the conditions are right.
Here’s a lobster and one of John Wayne’s hats, preserved by carbonate deposition and encrustation at a tourist attraction I visited a while ago in Yorkshire. It’s one of the few worldwide “petrifying wells” where the water is rich enough in limestone minerals to encrust things in a matter of a few months, preserving them by excluding oxygen and protecting them from the decomposition effects of micro-organisms:
These are completely mineralised wooden fence posts from Australia but, again, not to be regarded as fossils since they’re estimated to be only around 120 years old at most:
I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.
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A few more items from my collection, which underline those principles.
This is a piece of copal from Madagascar containing a preserved spider, some small midge-like insects and some plant fragments. Copal is essentially “young amber” – tree resin that hasn’t (yet) undergone the polymerisation and chemical reactions to convert it to amber. But it doesn’t qualify as a fossil because it’s no more than about 200 years old.
This is mammoth hair (Mammuthus primigenius). It meets the criteria for a fossil since it’s about 22,000 years old but, apart from a bit of iron-staining, there’s no mineralisation. This is the actual hair recovered from the Lena River region of Siberia, preserved only by being trapped in permafrost until a thaw released it:
This is a cave bear tooth (Ursus spelaeus) which went extinct around 24,000 years ago, so certainly qualifies as a fossil. But there’s virtually no mineralisation and it has remained preserved by virtue of the durability of its enamel and the fact it was found in a dry cave environment in Romania.
Finally, this a gastrolith from a large herbivorous Sauropod dinaosaur. It’s from the Late Jurassic, but not a fossil since it wasn’t an organic part of the animal. Just a rock that got swallowed and has only been superficially altered by its functional use.
PS: It’s also not the case that “unless an object is organic it can’t be dated”. When people think of radiometric dating, they’re generally thinking of radiocarbon dating and organic materials, but carbon-14 isn’t the only isotope that can be used as marker via its radioactive decay. There are plenty of others to chose from which can be (and are) used as markers for the age of rocks, in the complete absence of anything organic. Unfortunately these techniques aren’t helpful for lithic artefact dating since they tell you the age of the rock, not the age of the artefact.
I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.
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To the best of my knowledge, the only Cretaceous Period fossils exposed in Rhode Island are found in clays of the Raratan Formation on Block Island. I am aware of no Cretaceous deposits on the mainland. Years ago, I did hear of Pleistocene age beaver teeth being found along Point Judith Pond. Besides the Cretaceous Age clays on Block Island, Rhode Island has Cambrian Period phyllites containing trilobite fossils on Conanicut Island, in Narragansett Bay, and flora and faunal fossils in the Upper Carboniferous formations of the Narragansett Basin in RI and Ma.Rhode Island
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