Northern England as a desert and tropical seas. Permian and Triassic times. 296 to 208 Ma.
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
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
(carnallite KMgCl3.6H2O). Some of these minerals are mined at Boulby
and also at Kirkby Thore near Penrith.
Towards the end
of the Triassic, high rates of evaporation returned and low lying
areas such as Cheshire and north east Yorkshire became sabkha
environments. (A sabka is a wide area of coastal flats bordering the sea;
name comes from such an area on certain parts of the coast of Arabia).
Periodic flooding caused by spring tides and strong on-shore winds
followed by intense evaporation results in the precipitation of
carbonate-sulphate and halite deposits. It was in this type of
environment that the Mercia Mudstone Group (formerly Keuper Marl) was deposited.
sands containing large scale cross-bedding are well displayed in
Field House Farm
Quarry, Durham, where the Yellow Sands underlie the "Marl
Slate" famous for its fossil fish as well as on the coast
around Cullercoats harbour and below Tynemouth Priory. Between
Frenchman's Bay (where there is a geological information board) and
Marsden Bay (on the coast near South Shields) Permian rocks viz. the
Yellow Sands, Marl Slate and overlying Magnesian Limestone are well
displayed. The cliffs on the coast between Hartlepool and Tynemouth
consist mainly of Magnesian Limestone. Reef limestone is exposed on
the coast at Black Halls rocks and on the Tunstall Hills (SSSI) south
Exposures of Triassic rocks are sparse. Some can be seen by the River Leven west of Hutton Rudby and also on the beach at Seaton Carew.