Orbital Forcing and Climatostratigraphic Evolution during the Messinian Salinity Crisis: An Atlantic Perspective

The Messinian Salinity Crisis (MSC) represents a major stratigraphic and paleoceanographic perturbation of the Neogene, marked by complex interactions between tectonic, oceanographic, and climatic processes. Establishing a robust chronostratigraphic framework for this interval remains critical for improving correlations between the Mediterranean and the Atlantic domains. In this study, we investigate calcareous nannofossil assemblages from a continuous sedimentary succession spanning the upper Messinian to the lower Pliocene (from about 5.6 to 5.2 Ma), recovered at Integrated Ocean Drilling Program (IODP) Expedition 401, Site U1385, off the Iberian margin. The study combines grain size and clay mineral analysis. The aim is to obtain a high-resolution dataset for this time interval, which is currently missing on an Atlantic site and to understand the timing and mode of Atlantic Ocean response to MSC. The succession was deposited in a hemipelagic setting and is characterized by a continuous record with lithologies ranging from calcareous clay to clayey calcareous ooze. This relatively homogeneous depositional context provides an optimal archive for high resolution cyclostratigraphic and biostratigraphic analyses in an open ocean setting. Coccolith assemblages are dominated by reticulofenestrids, primarily Reticulofenestra minuta. Although conventional markers offer only limited biostratigraphic resolution, the abundance patterns of total coccoliths and selected key taxa provide further constraints on the timing of climatostratigraphic evolution during the late Messinian-early Pliocene transition. The spectral analysis performed on cyclic variations in total coccolith concentration, Coccolithus pelagicus (a cold-water taxon) and grain size suggests the presence of a precessional signal and points to a possible orbital control. Within this framework, the observed cyclicity tentatively supports the recognition of Messinian glacial (TG14, TG12, TG10, and TG8) and interglacial (TG11, TG9, and TG7) stages, which are respectively associated with decreases and increases in coccolith productivity. The transition from the Miocene to the Pliocene is marked by a distinct increase in productivity, likely reflecting the re-establishment of Atlantic-Mediterranean connections and providing an additional stratigraphic constrain within the succession. Ongoing clay mineral analyses are expected to better define the intensity and provenance of terrigenous input and to refine the timing of paleoenvironmental changes in the studied record. Overall, the integration of calcareous nannofossil biostratigraphy and cyclostratigraphic signals at Site 401-U1385 provides new data that delineate the expression of the MSC-related events in the Atlantic domain and improve correlations with Mediterranean successions.