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Overview |
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| The Marlstone Rock Bed forms the top formation
of the Middle Lias. It consists of light grey sandstones and sandy greenish-grey or
oolitic red-brown limestones, and is often conglomeritic. It is actually part of the rock
band known as the Junction Bed, forming the lower part of it.
Only 2m thick at Thorncombe Beacon, this formation is over 100m thick when examined on the Yorkshire coast at Whitby. It is also rich in ironstone, in many places the top 5-25cm of the formation has been weathered and altered, the original green iron minerals (such as glauconite, chamosite and vermiculite) having been oxidised to hydrous iron oxides (limonite). The formation also shows variations in the sand content. |
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Fossils |
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| The ammonite Pleuroceras salebrosum and the brachiopod Tetrarhynchia tetrahedra have been found fossilised in the Marlstone Rock Bed. | |||||||||
Zones and sub-zones |
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Beds and fossils |
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Bed photographs |
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Other Marlstone Rock Bed references |
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