Messinian Salinity Crisis

Messinian Salinity Crisis
Name	Messinian Salinity Crisis
Date	5.96–5.33 Ma
Location	Mediterranean Basin
Type	geological event

Messinian Salinity Crisis The Messinian Salinity Crisis was a geological episode in the late Miocene when extensive evaporite deposition and large-scale desiccation affected the Mediterranean Sea, producing dramatic changes in sea level, sedimentation, and biota across the Iberian Peninsula, North Africa, and surrounding Europe. Research integrates data from offshore drilling such as the Deep Sea Drilling Project, paleomagnetic stratigraphy linked to the Geologic time scale, seismic profiling tied to studies by institutions like the International Ocean Discovery Program, and isotopic analyses comparable to work on oxygen isotope stages, to reconstruct event dynamics and termination.

Background and Geological Setting

The Mediterranean Basin during the late Miocene lay between the African Plate and the Eurasian Plate following tectonic interactions including the closure of the Tethys Ocean and episodes related to the Alpine orogeny and the Atlas Mountains. Gateway configurations such as the connections at the Betic Corridor, Rifian Corridor, and the later Gibraltar Strait were controlled by regional uplift, subsidence, and strike-slip motions of the Iberian Plate and microplates like the Adriatic Plate. Basin physiography integrated margins like the Sicilian Channel, the Tyrrhenian Sea back-arc, and the Levant Basin, with sediment supply from systems comparable to the Rhône River, Ebro River, and Nile River influencing depositional patterns. Paleogeographic reconstructions employ chronostratigraphy, correlations with the Messinian Stage of the Neogene, and comparisons to global events such as the Pliocene transgressions.

Onset and Causes

The initiation has been attributed to progressive restriction of marine gateways—particularly closure or severe narrowing of the Betic Corridor and the Rifian Corridor—driven by tectonic uplift associated with the African Plate–Eurasian Plate convergence, regional volcanism like the Sardinia-Corsica block activity, and eustatic sea-level falls recorded in the Marine isotope stages. Paleoceanographic models drawing on work by researchers affiliated with the Scripps Institution of Oceanography and the National Oceanic and Atmospheric Administration simulate evaporation exceeding inflow, intensified by climatic aridification linked to patterns seen in the Messinian salinity chronology and teleconnections to the Monsoon system, North Atlantic Oscillation, and global cooling trends culminating in early Pleistocene shifts.

Evaporite Deposition and Sedimentary Evidence

Massive deposits of halite, gypsum, and anhydrite observed in onshore exposures of the Gulf of Cádiz, the Apennines, and the Balearic Islands and in seismic profiles across the Ionian Basin and the Alboran Sea document evaporitic accumulation. Borehole data from programs like the Ocean Drilling Program show stacked sequences of primary and diapiric salt, polygonal fault systems, and subaerial erosional surfaces analogous to features documented in the Dead Sea and Great Salt Lake. Mineralogical studies referencing the work of institutions such as the British Geological Survey and the Geological Survey of Spain report cyclic sequences of carbonate-evaporite alternations, chemostratigraphic signatures comparable to strontium isotope excursions, and micropaleontological turnovers in ostracod assemblages similar to records from the Mediterranean Paleogene.

Chronology and Phases

High-resolution chronostratigraphy integrates magnetostratigraphy, biostratigraphic markers from planktonic foraminifera, and astrochronology aligned with the Geologic time scale to subdivide the crisis into phases spanning roughly 5.96–5.33 million years ago. Proposed phase models—advanced in studies at venues such as the American Geophysical Union and the European Geosciences Union—include an initial restriction, peak evaporitic accumulation, and terminal reflooding. Correlation with regional records in the Maghreb, the Italian Peninsula, and the Aegean Sea reveals diachronous behavior, with evidence for multiple desiccation and partial refilling episodes similar to conceptions of stepwise events in other basins like the Atlantic gateways.

Paleoenvironmental and Climatic Impacts

Desiccation altered atmospheric moisture budgets over the Mediterranean Basin and adjacent regions including the Iberian Peninsula, Levant, and North Africa, influencing dust fluxes to the Sahara and modulating monsoonal circuits linked to the African Humid Period concept. Paleoclimatic reconstructions use proxies such as stable isotopes, pollen records from cores comparable to those analyzed by the Natural History Museum, London and CNRS teams, and sedimentological indicators paralleling research on the Pliocene warm period. Changes in regional albedo, reduced evaporative cooling, and altered regional runoff affected river systems like the Ebro and Nile with knock-on effects evident in coastal terraces and marine terraces surveyed by agencies such as the Instituto Geográfico Nacional.

Biological Consequences and Biogeography

Marine extinctions and faunal turnovers impacted nektonic and benthic assemblages across the Mediterranean Sea; planktonic foraminifera, benthic foraminifera, and calcareous nannoplankton show shifts comparable to extinction patterns recorded in the Paleogene–Neogene boundary intervals. Isolation and new dispersal pathways influenced vertebrate and invertebrate biogeography on the Iberian Peninsula, Sicily, Crete, and North Africa, with terrestrial corridors facilitating migrations similar to those documented for Pliocene mammals in the Fossil record of Greece and Spain. Studies by paleontologists at institutions like the Natural History Museum of Los Angeles County and the Museo Nacional de Ciencias Naturales document endemic radiations and extirpations, while genetic studies of extant Mediterranean taxa incorporate phylogeographic frameworks used in research on the Iberian refugia and Sicilian biogeography.

Termination and Reflooding (Zanclean Flood)

Termination is widely linked to catastrophic or gradual reflooding via the reopened Gibraltar Strait during the early Pliocene Zanclean stage, an event modeled with hydrodynamic scenarios by teams at the University of Oxford and ETH Zurich. Geological indicators for the Zanclean reflood include marine transgressive deposits, erosional canyons carved into the Gibraltar arc and continental shelves, and the reappearance of open-marine microfauna analogous to records from the Atlantic Ocean and Mediterranean Outflow. The reflooding shaped subsequent Mediterranean circulation patterns, contributed to modern configurations observed near the Strait of Gibraltar and the Alboran Sea, and reset biogeographic and sedimentary regimes leading into the Pliocene and Quaternary history examined by the Paleontological Society and other research bodies.

Category:Miocene events Category:Geology of the Mediterranean