Holkerian

The Holkerian is a sub-stage of the Viséan stage of the International Commission on Stratigraphy (ICS) geological 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 subperiod. Rock formations laid down in this time were frequently different types of fossiliferous limestone. 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, scientists divided a part of Earth's history called the Viséan into smaller parts, or substages. One of these is the Holkerian. The start of the Holkerian was set at a specific place in Cumbria, between two rock layers: the Dalton Beds and the Park Limestone Formation at Barker Scar. The end of the Holkerian was set at another spot called Little Asby Scar, also in Cumbria. These boundaries help scientists understand and study very old rocks and the history of life on Earth.

Holkerian sub-stage rocks

The Park Limestone Formation in south Cumbria, England, is an example of rock from the Holkerian sub-stage. The name comes from Holker in Cumbria, where part of Holker Hall estates lie on this limestone.

East of Cumbria, the Yorkshire Dales contain large areas of Holkerian limestone, forming dramatic landscapes such as Scaleber Force and Gordale Scar. Further south, in south Wales, Holkerian limestone of the Hunts Bay Oolite Subgroup forms bedrock from the western Gower peninsula to the Wye valley. In Ireland, the Tubber Formation in the Burren limestone region of Co.Clare also consists of rocks from this time.