New results from IODP Expedition 401 and their implications for the next phase of IMMAGE Land-2-Sea drilling

IMMAGE is a Land-2-Sea drilling project designed to recover a complete record of Atlantic-Mediterranean exchange from around 8 million years ago, to its current configuration with a gateway through the Gibraltar Strait. The aim of the project is to evaluate the influence of Mediterranean-Atlantic exchange on local, regional and global climate before, during and after the formation of a salt giant – the Messinian Salinity Crisis (MSC). This is being achieved by targeting Miocene offshore sediments on either side of the Gibraltar Strait with IODP Expedition 401 and recovering Miocene successions from the two precursor connections now exposed on land in southern Spain and northern Morocco with ICDP.

Expedition 401 (December 2023-February 2024) drilled three Atlantic sites (U1385, U1609 and U1610) and one in the Alborán Sea (U1611). The Atlantic sites record strong precessional cyclicity in NGR and XRF data. These records have been astronomically tuned and correlated with Mediterranean Late Miocene-Pliocene sequences that include the MSC. Changes in the character of the Atlantic signals correlate with Mediterranean-Atlantic gateway changes associated with progressive restriction of exchange that led to evaporite precipitation in the Mediterranean and the abrupt termination of the MSC with the Zanclean deluge.

The influence of gateway changes in the Alborán Basin are less obvious. The Messinian sequence recovered from the Site U1611 includes 150 m of near continuous subaqueous sediments through the MSC. Initial sedimentological, faunal and geochemical results suggest during the Miocene the basin was mostly highly stratified with anomalous but not extreme salinity even during the MSC. Sediments deposited by bottom currents which are commonly associated with gateway exchange only occur in the Pliocene. This suggests that the Gibraltar Strait only started functioning as the Mediterranean-Atlantic gateway from 5.33 Ma and that during the Messinian the Mediterranean-Atlantic connection must have been elsewhere. Future ICDP drilling of the fossil gateways through Morocco and Spain are required to identify and characterise this enigmatic gateway.