Chalk rocks 1: Chalk
Автор: OneMinuteGeology
Загружено: 2021-10-02
Просмотров: 14248
Описание:
Chalk is a young (Cretaceous), shallow-water, limestone composed mainly of the microscopic carbonate shells of plankton. While it looks very homogeneous, with little evidence of bedding we believe it could not have simply been laid down by a slow continual rain of dead microfossils. This is because we quite often find intact fossils of quite fragile sea-floor-dwelling echinoids which would have disaggregated very rapidly after death. The mean rate of sedimentation of around 100 years for one millimetre of chalk deposited. So, while it might have built up by a slow, gradual rain of microfossils we thing the top layers were re-worked, or churned up, by occasional large storms. This would have killed and simultaneously buried the surface creatures allowing them to survive intact as fossils.
See also:
Chalk rocks 2: Flint
• Chalk rocks 2: Flint
Chalk rocks 3: Marcasite
• Chalk rocks 3: Marcasite
More old fossils in Benidorm:
• More old Fossils in Benidorm - Urchins and...
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