The Messinian Salinity Crisis Brendan Seely Ryan Shirilla
Outline: • What is the Messinian Salinity Crisis ? • What Caused It ? • What Evidence Do We Have to Prove the Crisis Happened ?
What is the Messinian Salinity Crisis ? • Messianian = geologic interval of time corresponding to dated fossils found in rock formation near Messina, Sicily • Crisis = complete drying up of Mediterranean basin • 5.5 Ma: Repeated flooding and dessication of the Mediterranean Sea basin over a 700,000 year span.
Two Periods of Evaporite Deposition: • 5.5 Ma – First deposition of evaporates • Atlantic cut off completely • Period of non-deposition and erosion • Marine transgression • Deep-H2O sedimentation • Cut off again – Evaporite deposition • Seawater refilled basin 4.8 Ma
Cause: • 20 Ma • Arabian plate impinged upon Eurasion plate blocking connection between Mediterranean and Indian ocean • Mediterranean totally landlocked with exception of small connection to Atlantic • Connection closed periodically as Africa moved closer to Europe • Led to drier climatic conditions in entire region
Cause: • 5-6 Ma • Connection of Red Sea and Mediterranean was broken (formed) • Deposition of evaporates ceased in Red Sea, but developed in Mediterranean • Thick salts were deposited over next 700,000 yrs. • Combined effects of uplift in west (African plate) and fall of sea levels • Flooding caused by sea level changes due to changes in glacier ice volumes in Miocene and early Pliocene • Time to dry up
Time to Dry: -Surface area of Mediterranean = 2.5 x 106 km2 -Depth 1.5 km -Volume 3.75 x 106 km3 -Present rate of evaporation = 4.7 x 103 km3 -Annual precipitation 1.2 x 103 km3 -River input 0.25 x 103 km3 -Loss = 3.25 x 103 km3/yr -Made up for by input from Atlantic *without Atlantic, Mediterranean would dry up in 1,153 yrs
Evidence: • Buried river gorges below sea level at base of Nile and Rhone deltas • Late Miocene salt deposits (>1km thick, from cores)
Evidence: • Salt domes (seen wherever evaporates are overlain by sediment)
Evidence: • DSDP Core “Pillar of Atlantis” • Anhydrite and stromatolite, which is usually only seen in arid coastal flats • Turned scientists on to idea of Mediterranean as a desert.
Problem: • No way present volume of 3.75 x 106 km3 could produce 1 km salt • Salts have volume of 6.5 x 104 km3 • Over 2 x 106 km2 (4/5 area of Mediterranean) = 32.5 m thick • Therefore, Mediterranean could not have been totally cut off from Atlantic • Huge volumes of water must have poured over (Gibraltar waterfall) for continuous deposition
Gibraltar Waterfall 100 times larger than the Victoria Falls on Zambezi River! Allowed for continuous deposition of salt water into the Mediterranean
More Evidence: • 18O • Changes in sea level from glacier volumes recorded by benthic foraminifera in sediment from Atlantic and Pacific and compared to evaporite ages
Back to “Normal”: • 4.8 Ma • Whole basin refilled, normal marine conditions ensued, mud and carbonate deposition, cold deep water from Atlantic had access. • 1 Ma sill uplifted and deep supply cut off
Review: • 5.5 Ma: Repeat dessication and flooding • 1.5 km: Average depth of salt deposit (3 km max) • 4.8 Ma: Seawater refills basin • Caused: Combination of tectonic activity and glacial/interglacial periods