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 used in the Viséan stage.

As part of the Viséan, Holkerian rocks formed about 339 to 335 million years ago, in the Early Carboniferous subperiod. These rocks were often types of fossiliferous limestone. They formed in warm, sub-tropical marine conditions when north-western Europe was close to the equator.

Definition

In 1976, scientists split a part of Earth's history called the Viséan into smaller pieces. One of these pieces is the Holkerian. The start of the Holkerian was set at a spot 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 points help scientists study very old rocks and Earth's history.

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. This creates 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.