James Hutton and the origin of salt rocks: implications for the catastrophic vs uniformitarian controversy in the Messinian salinity crisis debate

In 1970, when a thick layer of salt was discovered beneath the deep Mediterranean seafloor, the prophetic prediction of James Hutton about the origin of salt rocks became reality. The initial hypothesis that a salinity crisis affected the Mediterranean Sea between 5 and 6 million years ago then evolved into contrasting interpretations. However, these theories agree that the crisis was triggered by geodynamic and eustatic forcings causing the reduction of Atlantic connections at Gibraltar, as remarkably anticipated by Hutton in 1788. The scientific debate on the Messinian salinity crisis has been characterized by the opposition between catastrophic and gradualistic scenarios, renewing the geological controversies of the 18th and 19th centuries. The current catastrophic paradigm of the Messinian salinity crisis envisages a nearly complete Mediterranean desiccation and its almost instantaneous refilling following the collapse of the Gibraltar sill. Alternative, non-catastrophic scenarios, commonly indicated as “ gradualist ” or “ actualist ”, are considered inadequate to explain unlikely events, such as the formation of salt giants. The analysis of the different scenarios reveals an amazing paradox. While the catastrophic paradigm is based on actualist arguments, the “ gradualist ” scenarios imply processes and environmental settings which, albeit plausible on a physical basis, do not show present-day analogues.