Most marine limestones have about the same δC13 as marine carbonate sediments, about 0 per mil versus the PDB isotopic standard. Because the limestones are half cement, the cement too must have δC13 of about 0 per mil. In contrast, limestones lithified by contact with vadose or phreatic meteoric waters, as in Bermuda, have strongly negative δC13. This suggests that most limestones in the geologic record are cemented, at least mainly, by a different process that takes place during burial diagenesis. Pressure solution is important in transferring CaCO3 from “donor” sites along stylolites and microstylolites to “receptor” sites in pores. Shales may also be important donors for limestone cements.

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