443.8 ± 1.5 – 440.8 ± 1.2 Ma
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitAge
Stratigraphic unitStage
Time span formalityFormal
Lower boundary definitionFAD of the graptolite Akidograptus ascensus
Lower boundary GSSPDob's Linn, Moffat, U.K.
55°26′24″N 3°16′12″W / 55.4400°N 3.2700°W / 55.4400; -3.2700
Lower GSSP ratified1984
Upper boundary definitionFAD of the graptolite Monograptus austerus sequens
Upper boundary GSSPTrefawr Track Section, Llandovery, Wales, U.K.
52°01′48″N 3°42′00″W / 52.0300°N 3.7000°W / 52.0300; -3.7000
Upper GSSP ratified1984

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. The Rhuddanian Age began 443.8 ± 1.5 Ma and ended 440.8 ± 1.2 Ma (million years ago). It succeeds the Himantian Age (the last age of the Ordovician Period) and precedes the Aeronian Age.


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. 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. 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.

See also

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