The isotopic composition and diagenetic history of pleistocene carbonates, North Qatar

Abstract

Field, petrographic, and geochemical data for Pleistocene oolitic carbonates from North Qatar suggest that the ooids formed in a marine environment separating the open Gulf from the coastal sabkhas. Locally, the more homogeneous granulometry and abundant cross-bedding of these rocks reveal an aeolian depositional environment. Petrographic examination shows that theserrocks are ooid grainstones with low-Mg calcite cements. The sequence of petrographic features suggests a progression of diagenetic fluids from more marine to more meteoric. Early marine cementation was followed by partial dissolution of the ooids and cements. Dissolution and cementation processes redistributed the primary porosity. After mineralogical stabilization was completed, subsequent meteoric flow caused very localized cementation. The final diagenetic phase precipitated was a low-Mg calcite spar cement, representing diagenesis in a fresh-water zone. There is no indication for the presence of dolomites. This sequence of diagenetic features was the result of a fall in eustatic sea-level following deposition.