Over how long is skeletal calcium essentially replaced by mineral depositation?
I don't know too much about bones, but with calcium carbonate in sea shells, it can be very variable. Mineral replacement will vary in speed and type with rock type, pore water movement pore water chemistry etc, so its hard to give a definate answer. I'll dig through my notes tomorrow to see if I can come up with any rough figures for you. It should be noted that as long as pore water is present, dissolution, deposition and replacement of minerals won't stop, so diagenesis and fossilisation could be viewed as continuous processes.
First of all, fosils are most broadly defined as remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth's crust.
Fossil do not need to be mineralized to be fossils. From what I have observed about fossils from the North sea when caught in fish trawlers net, there is little mineralization up to 30-40,000 years. However, Eemian (Sangamonian) remains >130,000 years are heavily mineralized.
The setback here is that those fossils can not be dated radiological because of that chemical alteration. So we assume something to be "Eemian" or "Sangamonian" from other clues. I've seen an "Eemian" vertebra of a Arctic whale that was not mineralized at all, the complete skeleton was found on a hill (!!) at one of the October revolution Islands, north of Siberia.
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