| Rhuddanian | |
| Color: | Rhuddanian |
| Time Start: | 443.8 |
| Time Start Uncertainty: | 1.5 |
| Time End: | 440.8 |
| Time End Uncertainty: | 1.2 |
| Timeline: | Silurian |
| Name Formality: | Formal |
| Celestial Body: | earth |
| Usage: | Global (ICS) |
| Timescales Used: | ICS Time Scale |
| Chrono Unit: | Age |
| Strat Unit: | Stage |
| Timespan Formality: | Formal |
| Lower Boundary Def: | FAD of the graptolite Akidograptus ascensus |
| Lower Gssp Location: | Dob's Linn, Moffat, U.K. |
| Lower Gssp Accept Date: | 1984[1] [2] |
| Upper Boundary Def: | FAD of the graptolite Demirastrites triangulatus |
| Upper Gssp Location: | Hlásná Třebaň section, Czech Republic |
| Upper Gssp Coords: | [3] |
| Upper Gssp Accept Date: | 2024[4] [5] |
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.[6] 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.[7]
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.[8] The lower is the Hartfell Shale (48m (157feet) thick), consisting chiefly of pale gray mudstone with subordinate black shales and several interbedded meta-bentonites.[9] Above this is the 43m (141feet) thick Birkhill Shale, which consist predominantly of black graptolitic shale with subordinate gray mudstones and meta-bentonites.[10]
The name is given after Cefn-Rhuddan Farm, Llandovery in Carmarthenshire, Wales.