Carbonates as keys to the Messinian Salinity Crisis’s Puzzle: Insights into spatial variability and sedimentary processes on opposite Mediterranean margins

Late Miocene carbonate systems represent key archives of paleoenvironmental evolution related to the processes leading to the Messinian Salinity Crisis (MSC), culminating in Earth’s most recent saline giant. During the pre-MSC stage (7.1-5.97 Ma), the Mediterranean was affected by the superimposition of major global climatic and regional geodynamic forcing mechanisms, promoting overall restriction that disrupted marine circulation, amplified the effect of astronomically driven climatic oscillations on sedimentation, and impacted marine biodiversity. Within this framework, major structural and ecological changes occurred across the circum-Mediterranean region, including pronounced tectonic activity at gateway areas, shifts in terrestrial vegetation, and modifications in runoff regimes from African rivers. The spatial variability and interplay of these processes left a sedimentological expression in marine environments of different sectors of the Mediterranean. Carbonates and associated deposits represent excellent records of key parameters such as water column stratification, marine ecosystem evolution under rapid environmental change, the interaction between biotic and abiotic processes and tectonic activity.

We present two continuous bio- and magnetostratigraphically calibrated onshore pre-evaporitic successions, more than 100 m thick, from opposite Mediterranean margins (Tabernas Basin in Spain and Mesaoria Basin in northern Cyprus), focusing on exceptionally well-preserved carbonate deposits. Their integrated study through sedimentological, stratigraphic, petrological, quantitative micropaleontological, and geochemical analyses reveals the dynamic responses of these margins to progressive restriction, tectonic activity, climate forcing, and freshwater input. In the Tabernas Basin, pronounced tectonic activity in the Betic Cordillera, combined with increasing restriction, controlled the evolution of a mixed carbonate–siliciclastic platform and associated planktonic and benthic communities. Dysoxia-tolerant benthic foraminifera, deformed tests, and paragenetic relationships between pyrite and calcareous tests indicate stressed conditions and highlight the role of early diagenesis in preserving or biasing the micropaleontological record. Microbial mats developed in an inner-shelf setting, marking the climax of restriction before evaporite deposition.

In the Mesaoria Basin, early isolation and enhanced continental runoff promoted eutrophication in the upper water column, favoring algal blooms and water-column stratification, which in turn catalyzed microbial sulfate reduction at an anoxic seafloor of a bathyal setting. Ecological competition between bloom diatoms (Thalassionema nitzschioides) and opportunistic coccolithophore taxa (Reticulofenestra spp.) reveals the complex interaction between primary producers across different photic zones of a stratified basin. Precession-related cyclicity exerted a major control on pelagic sedimentation, driving the alternating deposition of carbonates and laminated marls with remarkably well-preserved calcareous nannofossils. These conditions favored the formation of “marine snow,” which is preserved in peloidal microbialites. In addition, the occurrence of Trichichnus, a trace fossil formed by giant sulfide-oxidizing bacteria, further reveals complex biotic–abiotic interactions in deep-water carbonate settings.

Our results improve the understanding of spatial and depositional variability of carbonate systems under rapidly changing paleoenvironmental conditions during a key interval of the Late Miocene. This study provides new insights for an integrated paleoceanographic reconstruction of the Mediterranean, emphasizing carbonate deposits as archives of forcing mechanisms and sedimentary processes prior to the onset of MSC.