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11 avril 2017

Entree dans le Geopark du Nord West de l'Ecosse, Loch Assynt, Sutherland

geopark

Le Geopark se situe dans la region de la pointe nord ouest de l'Ecosse. Le pays et la region travaillent avec UNESCO pour developper cette region peu hospitaliere, en encourageant l'artisanat et metiers traditionnels et soutenant l'economie, tout en protegeant le patrimoine geologique, ecologique et naturel. 

La geologie de cette region est unique, avec les 2/3 de l'histoire geologique de la terre inscrite dans ces roches locales. Les roches les plus anciennes sont les gneiss Lewisien, qui sont vieilles de 3000 millions d'annees. Le sable blanc des plages date de 500 millions d'annees. La sequence se continue ainsi (sequence complete ci-dessous extraite de la classification officielle de l'histoire geologique de la region), se terminant evidemment par le developpement de la tourbe et la periode glaciere entre 10 000 ans et nos jours: 

10,000 years ago up to present time

  • the land recovers from the Ice Age
  • peat develops during wet periods
  • trees, animals and people inhabit the area

2 million years up to 10,000 years ago

  • the Ice Age affects the whole planet
  • periods of glacial conditions alternate with short warmer periods

65 to 2 million years ago

  • volcanoes erupt off the west coast as the North Atlantic Ocean continues to widen
  • most of chalk limestone removed by erosion as sea level falls
  • climate cools

140 to 65 million years ago

  • climate warm and humid
  • sea level much higher than today
  • thick layers of chalk limestone laid down on seabed over much of what is now Scotland

200 to 140 million years ago

  • climate warm and humid
  • opening of North Atlantic Ocean begins
  • sea levels much higher than today

400 to 200 million years ago

  • no rocks of this age in NW Highlands
  • evidence elsewhere in Scotland of inland deserts with tropical swamps on the coast and reefs
  • offshore widespread volcanic activity in rest of Scotland

500 to 400 million years ago

  • Durness Limestone (carbonates) deposition ends about 490 million years ago as land is pushed up and sea retreats
  • major mountain chain created where Highlands are now
  • rapid erosion of uplifted land
  • Moine Thrust formed as rocks from the east (Moine Schists) were pushed westwards, sliding over the top of NW Highlands rocks

550 to 500 million years ago

  • beach sands laid down on coastal fringes of large continent (to create Basal Quartzite, Pipe Rock and Salterella Grit formations)
  • mudstones (Fucoid Beds), and carbonates (Durness Limestone) laid down when sea level rose and water was deeper
  • worms burrowing in beach sands leave first evidence of life in this area

3500 to 550 million years ago

  • Lewisian Gneisses represent ancient rocks formed up to 3000 million years ago
  • much later, around 800 to 1000 million years ago, the rocks that are now the Moine Schists were laid down away to the east as layer upon layer of sand and silt; they were then pushed down into the Earth’s crust and changed into their present form
  • at about the same time, Torridonian Sandstones were laid down to the west as river sands and gravels in a desert environment; unlike the Moine Schists, they escaped being altered

 

 Premiere zone du Geopark traversee dans ce periple est le Loch Assynt, avec sur ses bords les ruines du chateau Ardwreck :

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Posté par burdigala ecosse à 11:21 - Ecosse - Commentaires [1] - Permalien [#]

Commentaires

    Super! On y va la semaine prochaine et tes explications vont nous être très utiles! Merci x

    Posté par Andrea, 29 mars 2018 à 16:14

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