Diagenetic carbonate cements occur throughout Eocene turbidite lithic arkose in Niuzhuang sag, eastern China, displaying as sporadical siderite, dolomite, calcite 1, and massive ankerite and calcite 2. Petrographic and geochemical investigations suggest that the nonferroan calcite 1 (δ13Ccarbonate (carb) +3.1‰ to +4.7‰ Vienna Peedee belemnite [VPDB]; δ18Ocarb −12.5‰ to −10.5‰ VPDB) was the earliest carbonate cement that was followed by Ak (δ13Ccarb +0.2‰ to +5.1‰ VPDB; δ18Ocarb −12.8‰ to −10‰ VPDB) and ferroan calcite 2 (δ13Ccarb +2‰ to +3.1‰ VPDB; δ18Ocarb −12.6‰ to −15.8‰ VPDB). The homogenization temperatures (74.3°C–105.8°C, 105.6°C–130.4°C, and 119.7°C–144.6°C, respectively) reflect the pattern of increasing temperature with progressive burial. The δ13Ccarb values suggest that calcite 1 and calcite 2 were mainly derived from dissolution of carbonates in calcareous shales (δ13Ccarb +3.5‰ to +6.3‰VPDB), with minor contributions from organic matter. The δ13Ccarb values of ankerite documented some contributions from magmatic carbon.
Ankerite and calcite 2 were restricted under the top seal (geochemical barrier) of the overpressure compartment, and the highly cemented zones occur mainly along faults. Carbonate cementation seems to negatively impact the reservoir quality when it exceeds 10%.