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Rhuddanian
First stage of the Silurian From Wikipedia, the free encyclopedia
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In the geologic timescale, the Rhuddanian is the first age of the Silurian Period and of the Llandovery Epoch. The Silurian is in the Paleozoic Era of the Phanerozoic Eon.[9] The Rhuddanian Age began 443.8 ± 1.5 Ma and ended 440.8 ± 1.2 Ma (million years ago). It succeeds the Hirnantian Age (the last age of the Ordovician Period) and precedes the Aeronian Age.[10]
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GSSP
The GSSP for the Silurian is located in a section at Dob's Linn, Scotland, in an artificial excavation created just north of the Linn Branch Stream. Two lithological units (formations) occur near the boundary.[9] The lower is the Hartfell Shale (48 metres (157 ft) thick), consisting chiefly of pale gray mudstone with subordinate black shales and several interbedded meta-bentonites.[9] Above this is the 43 metres (141 ft) thick Birkhill Shale, which consist predominantly of black graptolitic shale with subordinate gray mudstones and meta-bentonites.[11]
The name is given after Cefn-Rhuddan Farm, Llandovery in Carmarthenshire, Wales.
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References
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