The Messinian Salinity Crisis

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The Messinian Salinity Crisis

• Brendan Seely
• Ryan Shirilla

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Outline

• What is the Messinian Salinity Crisis ?
• What Caused It ?
• What Evidence Do We Have to Prove the Crisis
  Happened ?

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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.

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Present Day Mediterranean Sea
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Two Periods of Evaporite Deposition

1. 5.5 Ma First deposition of evaporates
2. Atlantic cut off completely
3. Period of non-deposition and erosion
4. Marine transgression
5. Deep-H2O sedimentation
6. Cut off again Evaporite deposition
7. Seawater refilled basin 4.8 Ma

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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

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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

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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

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Evidence

• Buried river gorges below sea level at base of
  Nile and Rhone deltas
• Late Miocene salt deposits (gt1km thick, from
  cores)

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Evidence

• Salt domes (seen wherever evaporates are overlain
  by sediment)

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Pillar of Atlantis
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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.

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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

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Gibraltar Waterfall 100 times larger than the
Victoria Falls on Zambezi River!
Allowed for continuous deposition of salt water
into the Mediterranean
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Victoria Waterfall, Zimbabwe
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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

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?18O Data From Foraminifera
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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

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History of Events
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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

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THE END
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