The Holkerian is a sub-stage of the

Viséan The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Ma. It follow ...

stage of the

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...

(ICS)

geological Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other E ...

timescale. It is one of five sub-stages commonly used in the Viséan stage within stratigraphy by British, Irish and other geologists outside the US and Asia. As part of the Viséan, Holkerian rocks were formed about 339 to 335 million years ago, in the

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * ...

subperiod. Rock formations laid down in this time were frequently different types of

fossiliferous limestone Fossiliferous limestone is any type of limestone, made mostly of calcium carbonate (CaCO3) in the form of the minerals calcite or aragonite, that contains an abundance of fossils or fossil traces. The fossils in these rocks may be of macroscopic ...

. The material for all these rocks was laid down in warm, sub-tropical marine conditions of the time when north-western Europe was close to the equator.

Definition

In 1976, the Viséan and

Tournaisian The Tournaisian is in the ICS geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy ...

were divided into six stages (now substages) by George et al. (the substages underwent some redefinition by Waters et al. in 2011). The Holkerian base was defined at the boundary between the

Dalton Dalton may refer to: Science * Dalton (crater), a lunar crater * Dalton (program), chemistry software * Dalton (unit) (Da), the atomic mass unit * John Dalton, chemist, physicist and meteorologist Entertainment * Dalton (Buffyverse), minor ch ...

Beds and the Park

Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

Formation at Barker Scar,

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. C ...

. The boundary was supposed to be below the appearance of certain sea organisms, including ''Pojarkovella nibelis''; this organism is found elsewhere below this lithological boundary definition. The upper limit of the Holkerian (at the Asbian) was defined at

Little Asby Little Asby is a small village in Cumbria, England. Historically part of Westmorland, its name is said to be derived from the Norse words ''askr'', meaning "ash", and ''by'', meaning "farm".

Scar, Cumbria. This boundary was supposed to be below the appearance of three organisms, ''Dibunophyllum bourtonense'', ''Siphonodendron pauciradiale'' and ''S. junceum''. Similar organisms are found elsewhere in Holkerian rocks.

Holkerian sub-stage rocks

The Park Limestone Formation of south Cumbria, in the north west of England, is an example of rock from the Holkerian. The name of the sub-stage actually comes from Holker in Cumbria where part of

Holker Hall Holker Hall (pronounced Hooker by some) is a privately owned country house located about 2 km to the southwest of the village of Cartmel in the ceremonial county of Cumbria and historic county of Lancashire, England. It is "the grandest ...

estates lie on the limestone. East of Cumbria lie the

Yorkshire Dales The Yorkshire Dales is an upland area of the Pennines in the historic county of Yorkshire, England, most of it in the Yorkshire Dales National Park created in 1954. The Dales comprise river valleys and the hills rising from the Vale of York w ...

which contain large areas of Holkerian limestone, sometimes forming dramatic landscapes such as Scaleber Force and Gordale Scar, some of which are quarried commercially. Further south, another area associated with the sub-stage is south

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

, where Holkerian limestone of the Hunts Bay Oolite Subgroup forms bedrock ranging from the western

Gower Gower ( cy, Gŵyr) or the Gower Peninsula () in southwest Wales, projects towards the Bristol Channel. It is the most westerly part of the historic county of Glamorgan. In 1956, the majority of Gower became the first area in the United Kingdom ...

peninsula to the

Wye valley The Wye Valley Area of Outstanding Natural Beauty (AONB; cy, Dyffryn Gwy) is an internationally important protected landscape straddling the border between England and Wales. The River Wye ( cy, Afon Gwy) is the fourth-longest river in th ...

and quarried at locations such as

Creigiau Creigiau is a dormitory settlement in the north-west of Cardiff, the capital of Wales. The village currently has about 1,500 houses and a population of approximately 5,000 people. The Cardiff electoral ward is called Creigiau/St. Fagans. The ...

, north-west of

Cardiff Cardiff (; cy, Caerdydd ) is the capital and largest city of Wales. It forms a principal area, officially known as the City and County of Cardiff ( cy, Dinas a Sir Caerdydd, links=no), and the city is the eleventh-largest in the United Kingd ...

. The Tubber Formation of the extensive and substantial Burren limestone region of Co.Clare,

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

, consists of rocks that were deposited in a time beginning in the Arundian and finishing in the Holkerian substages.

Gallery

References

{{Reflist Viséan Geology of Great Britain Geology of Ireland