Permian (296 - 245 million years ago)
By the early Permian, all the world's continents had converged, becoming one huge landmass called Pangaea. During late Carboniferous-early Permian times uplift coupled with a worldwide fall in sea-level led to erosion of up to 1.300 km. of Carboniferous sediments. Early Permian deposits in Northern England, therefore, rest unconformably on Carboniferous rocks.
As the British Isles drifted northwards from the equator the climate became hot and arid. During the early Permian higher ground, located in the present day North Sea and the Pennines, underwent continued erosion while low lying areas became deserts of wind-blown dune sands and conglomerates deposited by flash floods.
Later, parts of Britain were periodically invaded by a sea known as the Zechstein which extended to Germany. The Zechstein Sea flooded in and evaporated in four major cycles. It was this sea which laid down the Marl Slate, famous for its fossil fish, followed by beds of Magnesian Limestone (dolomite) which are quarried in many parts of Durham. High rates of evaporation at various levels of the upper Permian resulted in deposits of gypsum, halite (salt) and potash. These minerals are mined at Boulby, near Staithes.
The left image shows the Ninety Fathom Fault which separates rocks of Carboniferous and Permian age. The right hand image shows barite veins in Permian sandstone.