GEOCHEMICAL AND ISOTOPIC CONSTRAINTS ON THE DIAGENETIC HISTORY OF A MASSIVE STRATAL, LATE CAMBRIAN (ROYER) DOLOMITE, LOWER ARBUCKLE GROUP, SLICK HILLS, SW OKLAHOMA, USA

The diagenetic history of the late Cambrian massive Royer dolomite from the lower Arbuckle Group, Slick Hills, SW Oklahoma, USA, has been evaluated through comprehensive geochemical analyses. The dolomite probably formed during early diagenesis from contemporaneous late Cambrian seawater, evidenced by similar 87Sr 86Sr ratios (from 0.70891 to 0.70913) of most (70%) dolomite samples, to coeval late Cambrian seawater (from 0.7089 to 0.7092). Very light δ18O values (-10.2 to -12.9‰, PDB), however, indicate that the dolomite was significantly modified during burial. Correlation of various geochemical parameters (Sr, Fe, δ18O, and 87Sr 86Sr) demonstrates that dolomite samples with increased modification are characterized by lower Sr and higher Fe concentrations, lighter δ18O values, and less radiogenic 87Sr 86Sr ratios. This correlation, coupled with the light δ18O values of the dolomite, demonstrates that meteoric water, recharged into overlying carbonates, was responsible for burial modification of the dolomite. Geochemical comparison of the dolomite with associated limestone and quantitative modelling of δ18O, Sr, and 87Sr 86Sr variation during water-rock interaction suggest that the dolomite underwent long-lasting modification. The timing of meteoric modification was coincident with the development of regional overlying unconformities corresponding to emergence of the carbonate platform. Similar diagenetic modification has probably been responsible for 18O depletion and trace element modification of ancient dolomites in many other areas, although many of these dolomites have been interpreted to have formed either in mixing-zone environments or in subsurface environments. © 1990.