Rhuddanian

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]

Rhuddanian
443.8 ± 1.5 – 440.8 ± 1.2 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Chronology
−444 — – −442 — – −440 — – −438 — – −436 — – −434 — – −432 — – −430 — – −428 — – −426 — – −424 — – −422 — – −420 — – −418 — Paleozoic O Silurian D L Llandovery Wenlock Ludlow Přídolí E Hirnantian Rhuddanian Aeronian Telychian Sheinwoodian Homerian Gorstian Ludfordian Lochkovian             ← Lau event ← Mulde event[1] ← Ireviken event[2] Subdivision of the Silurian according to the ICS, as of 2023.[3] Vertical axis scale: Millions of years ago
Etymology
Name formality	Formal
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Age
Stratigraphic unit	Stage
Time span formality	Formal
Lower boundary definition	FAD of the graptolite Akidograptus ascensus
Lower boundary GSSP	Dob's Linn, Moffat, U.K. 55.4400°N 3.2700°W / 55.4400; -3.2700
Lower GSSP ratified	1984[4][5]
Upper boundary definition	FAD of the graptolite Demirastrites triangulatus
Upper boundary GSSP	Hlásná Třebaň section, Czech Republic 49.9230°N 14.2119°E / 49.9230; 14.2119[6]
Upper GSSP ratified	2024[7][8]

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.

See also

• Ordovician-Silurian extinction events
• Early Palaeozoic Icehouse