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Biostratigraphic, Sedimentologic, and Chemostratigraphic Study of the La Luna Formation (Late Turonian–Campanian) in the San Miguel and Las Hernández Sections, Western Venezuela

Abstract Depositional paleoenvironments of the La Luna Formation were established based on investigation of sedimentology, foraminiferal assemblages, and stable isotope composition of two sections in the Venezuelan Andes. Planktonic foraminiferal biostratigraphy indicates that the age of the San Miguel section spans from the late Turonian to the early Campanian and the Las Hernández section ranges from the early Coniacian to the early Campanian. The base of the La Luna Formation becomes progressively younger towards the south. Early-diagenetic processes have altered stable isotopic composition of carbonates, however stratigraphic changes in carbon isotope values can be used to correlate between the sections. The environment of deposition of the La Luna Formation changed during the Late Cretaceous. Interval I, from the early Coniacian to mid-Santonian, was characterized by anoxic conditions. Alternating anoxic-dysoxic environments in Interval II lasted from the mid-Santonian to the base of the Campanian. Interval III, in the early Campanian, was marked by more oxygenated conditions. These trends can be partially observed in other ocean basins.