Posted by: Rose | March 26, 2009

Broken Beds

And nothing to do with damaged sleeping apparatus.  If you visit the fossil forest, you only have to turn around to see these broken rocks.

Broken Beds, Lulworth Cove

Broken Beds, Lulworth Cove

The explanation board at the site blames the collapse of these once horizontal beds upon the dissolution of underlying salts. Rock Boy and I weren’t convinced by this explanation; the destruction just seemed too spectacular.

Further reading has since  informed me that this is an carbonate-evaporite breccia* formed by a hyper-saline lagoon** which contributed to the preservation of the trees. Gypsum (calcium sulphate) was deposited by evaporation of the lagoon but it has been altered chemically to calcium carbonate (what limestone is normally formed of). It is tectonic activity that has completely damaged these weak evaporite beds and folded some of the stronger limestone beds above.

Even the walls on the Isle of Purbeck are geologically themed.

Even the walls on the Isle of Purbeck are geologically themed.

* Breccia (pronounced brechia) means smashed up rock, of any type.

**Hyper-saline lagoons or seas are formed when a water body becomes enclosed and shallow. Evaporation of the water causes minerals to accumulate in the water and they eventually come out of solution as a solid. Think of the Dead Sea and salt pans.


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