If there is any proportion of carbon isotopes 13C or 14C in calcium carbonate, there will most likely be a fractionation/ separation of carbon isotopes within the carbon monoxide after reaction.
Can isotope fractionation occur in carbon when calcium carboante shell is leached in dilute HCl ?
The answer is yes. When calcium carbonate in shell reacts with dilute acid light carbon isotopes react first and the remaining carbon in shell will be rich in heavy isotopes. So, isotope fractionations occur in carbon.