Messinian West Alboran Sea record in the proximity of Gibraltar: Early signs of Atlantic-Mediterranean gateway restriction

Abstract

Late Miocene sedimentary records in the Gibraltar arch region hold fundamental information on the Atlantic-Mediterranean connectivity before, during and after the Messinian Salinity Crisis (MSC; 5.96-5.33 Ma). In this work we tackle this still unresolved problem through a detailed foraminifer-based biostratigraphy, micropaleontological and geochemical analyses of four available records (ODP 976B and DSDP 121) and boreholes (Andalucia-G1 and Alboran A1) in the West Alboran Basin (WAB). The combined use of these different analytical techniques together with new seismic stratigraphy enabled us to create a new and revised Upper Tortonian-Lower Pliocene Alboran Sea chronostratigraphic framework and estimate the magnitude of the Zanclean erosion. At Site 976, the dominance of a peculiar cold planktonic foraminifer fauna in the late Tortonian-early Messinian could possibly imply the existence of a proto-Gibraltar Strait, while at ~7.2 Ma, changes towards warmer foraminifer assemblages, increasingly stratified water column and sharp increase in terrestrial input indicate the beginning of the restriction of the Mediterranean from the Atlantic Ocean. Cyclical changes visible both in the elemental composition and foraminifer assemblages from here onward highlight a strong precessional cyclicity, which can be correlated to the first signs of reduced ventilation and sapropel deposition in the Eastern Mediterranean. The integration of seismic profiles and core analyses finally revealed that the Messinian expression in the Alboran basin is limited to two units: one hemipelagic and one chaotic, most probably connected to the MSC final stages. The Messinian succession in the Alboran basin is topped by an unconformity, most likely related with the Zanclean reflooding, which eroded a sedimentary succession of ~1.67 Ma. An extremely rare phosphate (canaphite) and Mg rich minerals were recognized described and associated to interstitial fluids and diagenetic processes.