Extensive, large-scale pervasive cementation in the form of cement bodies within fluvial strata has rarely been documented although fluvial strata commonly act as important hydrocarbon reservoirs, as well as groundwater aquifers. Here, we present outcrop, petrographic and geochemical data for pervasive ferroan dolomite cement bodies up to 250 m in size from Upper Cretaceous Desert Member and Castlegate Sandstone fluvial strata exposed in the Book Cliffs in Utah. These cement bodies are present with coastal plain fluvial strata within both the Desert and Castlegate lowstand sandstones and are most abundant in the thin, distal fluvial strata. Cement bodies are almost entirely absent in updip, thicker, fluvial strata. Petrographic observations suggest a predominantly early diagenetic timing to the mildly ferroan dolomite, with a component of later burial origin. δ 13C values for the cement (+4.8 to −5.7‰ V-PDB) suggest a marine-derived source for the earliest phase with a burial organic matter source for later cement. δ 18O data (−6.3 to −11.8‰ V-PDB) suggest precipitation from freshwater dominated fluids. It is proposed here that dolomite was derived from leaching of detrital dolomite under lowstand coals and cementation took place in coastal aquifers experiencing mixed meteoric-marine fluids as a result of base-level fluctuations. This data presented here shows that large cement bodies can be an important component within fluvial sandstones with a potentially significant impact upon both reservoir quality and fluid flow within reservoirs, especially at the marine-non-marine interface. ► Upper Cretaceous fluvial strata exposed in the Book Cliffs, Utah. Studied here. ► Dolomite cement bodies up to 250 m in size abundant in distal fluvial strata. ► Petrographic observations indicate an early diagenetic origin. ► Mixed meteoric-marine coastal aquifer resulted from base-level shifts. ► Carbonate cementation potentially has significant impact upon reservoir quality.