Druidston Haven: Cliff Section 6

Druidston Haven geology: Cliff Section 6

Photo No.6 of a series of six photos and interpretations to illustrate the geology of Druidston Haven, Pembrokeshire.

The cliffs of Druidston Haven mostly consist of Ordovician (Caradocian) age shales with some thin sandstones. During the Caledonian orgogeny at the end of the Silurian period, these were deformed into a series of mostly upright open folds. These were then re-folded by Variscan movements at the end of Carboniferous, to become largely recumbent (near horizontal) or partly inverted, facing down towards the south.

The Ordovician rocks form a horst - a ridge or block of strata faulted against younger rocks on either side. The Druidston Horst is bounded by the South Druidston Boundary Fault at the south end of the Haven, and the North Druidston Boundary Fault at the north end. This photo shows the southern end of the horst, terminated by the Southern Boundary Fault; a significant structure with a throw (displacement) of at least 1500 metres to the south, bringing Namurian 'Millstone Grit Series' (upper Carboniferous) rocks into contact with the Ordovician shales.