What is the maximum thickness of limestone layers on earth?
(Limestone or any other biochemical sedimentary rocks, for example chalk or coral reefs.)
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$\begingroup$ I'm a bit confused of the question. Can you specify what you are aiming for? $\endgroup$– user2821Aug 9, 2015 at 20:02
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1$\begingroup$ Limestone is not necessarily biochemical. Early limestone deposits were formed from the reaction of carbonic acid (H20 + CO2 = H2CO3) with lime and had no biological origin. $\endgroup$– BillDOeAug 9, 2015 at 20:25
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$\begingroup$ @BillOer ok, and this process still exists today but in a little proportion compared to biogenic limestone. $\endgroup$– reunsAug 9, 2015 at 21:27
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1$\begingroup$ I'm not sure about the exact maximum depth, but this can go for several kilometres deep of almost pure limestone. $\endgroup$– GimelistAug 9, 2015 at 21:54
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1$\begingroup$ As @BillOer points out, limestone doesn't need to be of biological origin. If you are interested in total storage of carbon, the porosity of the chalk would be an important factor and siliciclastic component can also be high in some cases. $\endgroup$– user2821Aug 9, 2015 at 22:19
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1 Answer
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Reading your comments I see that you're asking:
so could we find for example 1km high limestone layers on earth ?
The answer is definitely yes. Here's an example of a stratrigraphic geological section from Israel:
source: Chronostratigraphic table and subsidence curves of southern Israel, Gvirtzman 2004, Israel Journal of Earth Sciences, 53
You can see that in the north of the country there is an almost entirely continuous section of "platformal carbonates" which is just a fancy name for limestones. That's 5 kilometres of limestone. And I'm pretty sure that's not the deepest - that's only the one I personally know.
That's a sedimentary basin where you can drill and still find fossil-bearing limestones deep down. This gets even better if you start adding tectonics to this. Plate movements can do funny stuff to rocks, including burying them really deep. If you take limestones and do that to them, you actually transform them into marble. Basically marble (proper) is limestone buried deep and cooked. And by deep I mean really deep. Some marbles from the Alps are known to come from more than 100 kilometres deep! Note that I'm not saying it's limestone all the way down, but there are chucks of marble (formerly limestone) down there.
If you want to be really extreme, there is an article where the authors say:
...carbonate sediments were subducted into the upper mantle...
Upper mantle is 200-300 kilometres deep. And you know what? That's only the ones we know of. Who knows, there might be some limestones that were subducted all the way down to the core-mantle boundary, almost 3000 kilometres deep.
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3$\begingroup$ I think the best example of a carbonate platform is the Grand Bahama Banks. See en.wikipedia.org/wiki/Bahama_Banks $\endgroup$– staliAug 10, 2015 at 12:42
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1$\begingroup$ That's a great modern active example indeed. The thickness (4.5 km) is just below what I showed in my answer. $\endgroup$– GimelistAug 10, 2015 at 12:48