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Tessellated Pavememt

Ancient cracks create a modern phenomenon

sunny 22 °C

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The Tessellated Pavement is an inter-tidal rock platform - a common enough sight on the coast. But here an unusual set of geological circumstances has resulted in a rare landform.
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From before 290 million to 265 million years ago a depression in the Earth's surface was located in central-eastern Tasmani. high country to the East and West had streams which transported silt into the basin. Muddy sediment built up, sea ice or iceburgs transported rocks into the basin, and shellfish died and were preserved in the siltstone. The surface of the Tessellated Pavement tells some of this story. You can see rocks of different types derived from distant places.
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From 160 million to 60 million years ago the silt was later covered by sediments, compacted and became siltstone. The flat-lying siltstone was cracked by stresses in the Earth's crust. This jointing, exaggerated by processes of erosion, has created the tiled appreance.
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Away from the seashore the pavements dries out for longer periods at low tide and this allows greater development of sea crystals. The salt forms on the surface and erodes the pavement's surface more quickly than the joints.
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The surface of the pavement is lowered while the joints which are eroding more slowly become rims.

These 'pans' contrast with the 'loaves' where the joints are eroding much more quickly that the surface, because of the abrasion by sand and other particles carried by the water.
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These loaf feature are close to the sea so they spend more time under water. As the drying period is shorter, salt crystalisation is less significant. The joints tend to channel the water and the abrasive sand.
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Posted by charlystyles 08:00 Archived in Australia

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