The step-by-step restriction of the Mediterranean (start, amplification, and consolidation phases) preceding the Messinian Salinity Crisis (climax phase) in the Bajo Segura basin

Abstract

This research explores the Messinian record in a western Mediterranean basin at the eastern end of the Betic Cordillera (the Garruchal section, southern sector of the Bajo Segura basin). Sedimentary facies development and foraminiferal assemblages were used as palaeoenvironmental proxies to characterize the palaeoceanographic evolution of the basin’s progressive restriction. Therefore, a succession of palaeoenvironmental phases can be established as follows. The “start phase” (until ~ 6.72 Ma) records the first ecological evidence of the restriction, evidenced by the sudden appearance of common benthic stress markers. The “amplification phase” of the restriction (up to ~ 6.35 Ma) marks a progressive increase in low bottom oxygen levels related to water-mass stratification in the evolution from upper epibathyal to outer shelf environments. The “consolidation phase” (until the intra-Messinian discontinuity ~ shortly after 6.03 Ma) records basin shallowing (from outer to inner shelf environments) in a context of a restricted basin. And lastly, the “climax phase” (until the end-Messinian discontinuity) records coastal sedimentation (marine coastal lagoon and sandy beaches). The findings of this research reveal that the Garruchal section is a good illustration of the sedimentary and palaeoenvironmental response of the peripheral basins to the progressive restriction of the Mediterranean before the Messinian Salinity Crisis. Finally, since it is widely accepted that the Mediterranean marine restriction has been developed in a stepwise mode, we here propose to establish the following terms for implementation at Mediterranean regional level: “start,” “amplification,” and “consolidation” phases, which finally led to the “climax” phase, that is, the Messinian Salinity Crisis stricto sensu.