Responses of a hybrid carbonate shelf to progressive basin restriction: Pre- and Messinian Salinity Crisis environmental shifts in the Western Mediterranean (Tabernas Basin)

Abstract

Before and during Stage 1 of the Messinian Salinity Crisis (MSC), carbonate platforms developed in marginal basins of the Western Mediterranean, recording some of the last manifestation of fully tropical climatic conditions in the region. In the Tabernas Basin (SE Spain), a mixed carbonate-siliciclastic succession was deposited between 6.080 and 5.971 Ma, recording a detailed archive of the environmental, ecological, and sedimentological changes that occurred during an advanced phase of Mediterranean restriction preceding the Messinian Salinity Crisis. Systematic semiquantitative micropaleontological analysis reveals five different benthic foraminiferal assemblages, which respond to a progressive shallowing-upward trend and shifting environmental conditions at the seafloor. In the upper epibathyal environment, the coexistence of planktonic foraminifera with dysoxia-tolerant benthic taxa suggests pronounced stratification within the water column. Enhanced primary productivity in the upper waters fuelled organic matter flux to the bottom waters, driving pyrite precipitation and conditioning benthic ecosystems. The transition to a shelf setting was recorded by an increased diversity of shallower-water benthic fauna and the deposition of bioclastic limestones. Further environmental stress produced by progressive restriction drove a general decline in the marine fauna, culminating in the deposition of barren limestones. The flourishing of microbial mats in the inner-shelf marked the climax phase of restriction preceding evaporite deposition at the onset of the Messinian Salinity Crisis.