OXYGEN ISOTOPIC INDICATIONS OF THE MECHANISMS OF SILICA TRANSPORT ANDQUARTZ CEMENTATION IN DEEPLY BURIED SANDSTONES

The oxygen isotopic compositions and inferred precipitation temperatur es of quartz cements in a suite of deeply buried sandstones from the N orth Sea, Gulf Coast, and western Canada basins indicate that, in almo st every case, the quartz precipitated from O-18-rich basinal waters. O-18-rich waters are found in strictly limited volumes in sedimentary basins. Silica transport and quartz cementation could not therefore ha ve occurred as a result of large-scale advection of basinal or meteori c waters, because this would require very large fluid fluxes. Quartz c ementation was driven by processes operating on a local scale. The iso topic data do not uniquely indicate the mechanisms of silica transport but are consistent with both diffusion and local recycling of fluid.