Might help if you state your definition of "crust" for this question, and that for carbon dioxide. Including ground water and gases in solution, or not? Including hydrocarbon reservoirs and associated gases, or not? Including gases in soil pore volume, or not?
Physically, the distinction between carbon dioxide in limestone as a distinct chemical species from carbon dioxide dissolved in crustal rock (with a hell of a large heat of solution) doesn't exist.
You're going to be limited to making distinctions among oxidation states of carbon, reduced, elemental, sub-, mon-, or di-oxide --- "free" carbon dioxide in solution in this, that, or the other rock type? Parts per million --- try degassing anything completely, and you'll see. You want to do an assay and MAKE the distinctions among carbon dioxide that is chemically (salts, adsorbed), or physically (whatever that means in this context --- trapped in inclusions) present in rock samples?