Stable isotopes tell us a great deal about diagenetic processes. Early Meteoric processes produce carbon and oxygen isotopic signatures which differ greatly from the original values.

Oxygen isotopic composition of two end members of dolomites from the Arab-D (A&B) showing some of the problems of interpretation.  Diagonal lines show waters with different oxygen isotopic compositions.  More saline waters have more positive oxygen isotopic compositions.  Dolomites in field A have been interpreted as having been formed early from saline fluids.  However if they formed from isotopically positive fluids they would need to have formed at elevated temperatures.  There are no fluid inclusion data for these dolomites and the temperature estimates have been derived from what is considered to have been depositional temperature for the Jurassic.   Dolomites in field B are interpreted as forming from saline fluids and at high temperatures on the basis of fluid inclusions and stable isotope evidence (Swart et al., 2005).

Alternatives are need to determine salinity of porefluids, so-called non-conventional indicators S, Na. K. and Cl.

This study investigated the d18O of pore waters from Sites 1003-1007 collected during Leg 166 of the Ocean Drilling Program which drilled sites along the western margin of Great Bahama Bank. These data generally show a positive correlation between d18O and the concentration of chloride with the exception of Site 1006 which exhibits non-linear behavior with respect to chloride. However, the correlation between Cl- and d18O at most of the sites is a coincidence as the increase in Cl- is a result of diffusion of Cl- from an underlying Cl- rich source, while the increases in d18O result from recrystallization of metastable carbonates in the presence of a geothermal gradient.