Climate variability and past environmental changes: lessons from the Messinian record of the Tertiary Piemonte Basin

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Up to 6 million years ago, the hilly area of the central Piedmont region was a gulf of the Mediterranean Sea. During the Messinian (between 5.9 and 5.3 million years ago) the entire basin experienced an environmental and climate change that occurred very fast (compared to the scale of geological time): it was caused by the hydrographic isolation of the Mediterranean Sea from the Atlantic Ocean.

This event caused profound changes that affected the geosphere, the biosphere and the microclimate. In a short time span (less than a million years) deep sea sediments are replaced by shallow sea deposits, continental deposits, lacustrine sediments and eventually deep sea sediments; the rocks and the fossils contained in these deposits also record cyclical climatic oscillations from arid to more humid climates.

Messinian age rocks deposited in the Tertiary Piedmont Basin and currently cropping out in the Langhe and Monferrato areas describe the chronologic succession of these events and represent a small scale model of the vast Mediterranean Sea.

What you can see:

  • Marl and mudstones. Rocks derived from deep sea sediments; the richness of life is evidenced by fish and planktonic microorganisms (foraminifera and coccolithophorids) fossils. These rocks record the alternation between a warm and humid climate and a cooler and less humid climate. Microfossil assemblages recorded in the rocks also indicate the precise moment when the Mediterranean was cut off from the Atlantic Ocean, the beginning of the salinity crisis.
  • Gypsum selenite and laminate. These minerals were formed in water with high salinity and point to an increased evaporation, linked to the isolation of the Mediterranean Sea. Despite this current interpretation, in these minerals it is possible to observe microscopic marine organisms (algae and bacteria) that tolerate extreme environmental conditions.
  • Sandstones and mudstones. Sediments deposited on the continent in low salinity waters, rich in fossil vertebrate remains and shells of lacustrine molluscs. These remains testify to a savanna environment with temporary pools of fresh water.
  • Calcareous marl. These rocks tell the re-established full connection between the Atlantic Ocean and the Mediterranean Sea, and are rich in marine planktonic microfossils recording a deep (around 800m deep) marine basin.
  • Erosion surface. This surface describes an event of rapid dismantling of sediments caused by compressive tectonic forces (seen in Moncucco).

Image gallery (click to enlarge)

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