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The 3 limestone of garden
TWhile walking through the garden of the plants you will discover 3 types of limestone of different age:
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The tufa; 90 million years ago, Mesozoic (secondary era), Cretaceous,
Oolitic limestone,; 170 million years Mesozoic, Jurassic, Pliensbachian stage
gray limestone; 370 million years, Paleozoic (primary era), Devonian .
tuffa
The tufa is a calcareous rock that was formed from a loose mud and waterlogged, which then gradually and slowly transform into rock, especially under the effect of pressure, forming benches up to 40 m thick. It is a sandy chalk with fine grain, white or sometimes yellowish cream color..
oolitic limestone
The oolitic limestone found here probably comes from the Durtal region. (near Angers) The rock is composed of small juxtaposed balls called oolites, Oolites are small, regular spherical mineral structures (ooid) formed, during a particular process of sedimentation, embedded in a limestone cement. It can come from:
- debris of biological origin
- small fragment of rock debris
- a solubilized carbonate grain
Oolitic l had been formed in a shallow but agitated marine environment
Gray limestone
Gray limestone is of Devonian age and of reef origin.
These limestones were constrained during the formation of the Hercynian chain (middle of the primary era). These stresses induce folds, faults and diaclases (fractures without displacement) in the rocks. These fractures are often underlined by calcite veins; a mineral recognizable by its clear crystals and hues.
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