Revised calcareous nannofossil biozonation of the Cretaceous at low and middle latitudes

We present a comprehensive revision of the calcareous nannofossil biozonation for Cretaceous marine sequences from both on-land and oceanic sites at low to middle paleolatitudes. A detailed re-evaluation of the literature and new data has led to the refinement of existing biostratigraphic frameworks. The revised biozonation incorporates cross-calibration with magnetostratigraphy and chemostratigraphy and includes an assessment of the repro ducibility of key nannofossil events. Ages of individual biohorizons are re-estimated based on recent advances in defining Cretaceous stage boundaries. The new zonation defines 27 CNC (Calcareous Nannofossils Cretaceous) zones spanning the Berriasian to Maastrichtian. For the Early Cretaceous, eleven zones and twenty-four subzones are proposed, supported by magnetostratigraphically calibrated events in the Berriasian–lower Aptian interval. It largely follows the zona tion of Bralower et al. (1995), with revisions to the CNC3, CNC5, CNC6, CNC8, and CNC10 zones. For the Late Cretaceous, seventeen zones and twenty-nine subzones are defined; the Albian–early Turonian interval adheres to Bralower et al. (1995), while the Turonian–Maastrichtian follows Sissingh (1977) as modified by Perch- Nielsen (1985), with updates to the CNC13, CNC14, CNC15, CNC18, and CNC20 zones reflecting revised tax onomy and event reliability. The new zonal scheme improves the biostratigraphic resolution for key paleoceanographic intervals, including the late Valanginian Weissert Event, early Aptian OAE1a, latest Albian OAE1d, latest Cenomanian-earliest Turonian OAE2, and Coniacian-Santonian OAE3. Secondary biostratigraphic markers and fluctuations in taxon abundance further enhance effectiveness, making it a robust framework for global correlation and paleoenvir onmental interpretation during the Cretaceous.