Ludfordian
425.6 ± 0.9 – 423.0 ± 2.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Paleogeography of the Ludfordian, 425 Ma
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
Name ratified	1980[4]
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	Imprecise. Near FAD of the graptolite Saetograptus leintwardinensis
Lower boundary definition candidates	None
Lower boundary GSSP candidate section(s)	None
Lower boundary GSSP	Sunnyhill, Ludlow, England 52°21′33″N 2°46′38″W / 52.3592°N 2.7772°W / 52.3592; -2.7772
Lower GSSP ratified	1980[4]
Upper boundary definition	FAD of the graptolite Monograptus parultimus
Upper boundary GSSP	Požáry Section, Prague-Řeporyje, Czech Republic 50°01′40″N 14°19′30″E / 50.0277°N 14.3249°E / 50.0277; 14.3249
Upper GSSP ratified	1984[5][6]

In the geologic timescale, the Ludfordian is the upper of two chronostratigraphic stages within the Ludlow Series. Its age is the late Silurian Period, and within both the Palaeozoic Era and Phanerozoic Eon. The rocks assigned to the Ludfordian date to between 425.6 ± 0.9 Ma and 423.0 ± 2.3 Ma (million years ago). The Ludfordian Stage succeeds the Gorstian Stage and precedes the Pridoli Epoch. It is named for the village of Ludford in Shropshire, England. The GSSP for the Ludfordian is represented as a thin shale seam, coincident with the base of the Leintwardine Formation, overlying the Bringewood Formation in England.

The Lau event is a rapid pulse of cooling during the Ludfordian, about 424 million years ago; it is identified by a pulse of extinctions and oceanic changes. It is one of the series of fast sea-level and excursions in oxygen isotope ratios that signal fast switches between warm and cold climate states, characteristic of the Silurian climatic instability. The Lau Event occurred during an extended period of elevated seawater saturation state, explained by reservoirs of the planet's fresh water being locked up in massive polar ice caps. The sudden reappearance in normally saline marine environments of stromatolites and a mass occurrence of oncoids during the event suggested that minor extinction events like the Lau Event also resulted in periods of reduced grazing pressures on surviving "disaster biota", which can be compared to the aftermath of the more catastrophic end-Ordovician and end-Permian mass extinctions.^[7]