The Darriwilian is the upper stage of the Middle Ordovician. It is preceded by the

Dapingian The Dapingian is the third stage of the Ordovician period and the first stage of the Middle Ordovician series. It is preceded by the Floian and succeeded by the Darriwilian. The top of the Floian is defined as the first appearance of the conodont s ...

and succeeded by the Upper Ordovician

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million yea ...

Stage. The lower boundary of the Darriwilian is defined as the first appearance of the graptolite species ''Undulograptus austrodentatus'' around million years ago. It lasted for about 8.9 million years until the beginning of the

around million years ago. This stage of the Ordovician was marked by the beginning of the Andean-Saharan glaciation.

Naming

The

name A name is a term used for identification by an external observer. They can identify a class or category of things, or a single thing, either uniquely, or within a given context. The entity identified by a name is called its referent. A personal ...

Darriwilian is derived from Darriwil, a parish in County of Grant,

Victoria (Australia) Victoria is a state in southeastern Australia. It is the second-smallest state with a land area of , the second most populated state (after New South Wales) with a population of over 6.5 million, and the most densely populated state in ...

. The name was proposed in 1899 by

Thomas Sergeant Hall Thomas Sergeant Hall (23 December 1858 – 21 December 1915) was an Australian geologist and biologist, recipient of The Murchison Fund in 1901. Early life Hall was born in Geelong, the son of Thomas March Hall, a business man originally from L ...

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GSSP

The GSSP of the Darriwilian is the Huangnitang Section () near the village Huangnitang, 3.5 km southwest of Changshan County Town (

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by Jiang ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

). It is an outcrop of the Ningkuo Formation, consisting of mainly black shale. The lower boundary of the Darriwilian is defined as the

first appearance datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a particu ...

of the graptolite species ''Undulograptus austrodentatus'' in that section. A secondary

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

marker is the graptolite ''Arienigraptus zhejiangensis''.

Biostratigraphy

The base of the Darriwilian is also the base of the ''Undulograptus austrodentatus'' graptolite zone. This zone lies just above the North Atlantic ''Microzarkodina parva''

conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...

zone. The base also lies in the upper part of the North American ''Histiodella altifrons'' conodont zone. The ''Undulograptus austrodentatus'' graptolite zone is known from outcrops around the world, making the base of the Darriwilian easily correlatable.

Regional stages

The Darriwilian overlaps with the upper Arenig and the

Llanvirn The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

. The base of the Darriwilian can be correlated with a level in the Fennian stage of the Arenig.

References

{{Geological history, p, p, state=collapsed Middle Ordovician Ordovician geochronology