Sodium in carbonate sediments and rocks; a possible index to the salinity of diagenetic solutions

ABSTRACT Sodium is present in the Recent marine carbonate minerals aragonite, calcite, Mg-calcite and dolomite greatly in excess of equimolar chloride concentration. The bulk sodium content of Recent carbonate sediments is greater than 1,000 ppm and decreases along with Sr, Mg, 18O, and 13C as meteoric diagenesis takes place. The low sodium content of most ancient dolomites suggests they are either primary products of solutions containing little sodium or they have re-equilibrated with a solution low in sodium.