Bermuda meteoric diagenesis

Because the bulk of the limestone volume of Bermuda has spent most of its existence in the vadose zone, much of the limestone mass shows the imprint of vadose diagenesis, and progressive depletion in 13C with increasing age. However, limestones older than 125,000 years have spent more time in the phreatic meteoric zone. These limestones are more extensively altered by freshwater and freshwater-seawater mixtures. Their relatively light 813C values, however, imply alteration in a relatively open system in which soil carbon dioxide, depleted in 13C because of oxidation of organic matter, was an important source of carbon for replacement reactions. 

The chemistry of the groundwaters of Bermuda was investigated in detail by Plummer et al. (1976). To date this investigation still remains one of the few major integrative studies of phreatic meteoric water diagenesis in the literature (see also, e.g., Harris and Matthews, 1968, Barbados Back and Hanshaw, 1970, Florida and Yucatan Plummer, 1977, Florida Budd, 1984, 1988, Bahamas). A summary of the conclusions of this work is given here. 

Figure 7.33. Geochemistry of the Devonshire, Bermuda groundwater lens. (A) Log of partial pressure of CO2 (PCO2X (B) strontium concentration in ppm, (C) calcium and (D) magnesium derived from the rock because of diagenesis in the meteoric realm. (After Plummer et al., 1976.)...

---