IN SITU STABLE ISOTOPIC EVIDENCE FOR PROTRACTED AND COMPLEX CARBONATE CEMENTATION IN A PETROLEUM RESERVOIR, NORTH COLES LEVEE, SAN JOAQUIN BASIN,

ABSTRACT: Knowledge of the evolution of carbonate cementation in hydrocarbon reservoirs is key to understanding the history of fluid flow during petroleum accumulation. The Stevens sands is a sequence of marine shales and deep-sea fan sands that was deposited within the Miocene Monterey Formation in the south-central part of the San Joa-quin basin, California, during the upper Miocene (10–6 Ma). Rapid, high-precision in situ oxygen and carbon isotopic analyses of carbonate phases using the ion microprobe operated in multi-collection mode, in conjunction with electron microprobe analyses, indicate that carbonate cement zones within the Stevens sands at North Coles Levee (NCL) have had a complex and protracted fluid history. Three main genera-tions of carbonate cement were identified. The relative timing of carbonate cement precipitation within the Ste-vens sands at NCL was estimated using the thermal and burial history of the San Joaquin basin, in situ oxygen isotope data, and cementatio