Along a stretch of coastline, quarries and hills of the region bear witness to when part of what is now the North East was once a desert that was the flooded by a vast inland sea.
The legacy of the desert from the Permian era, from 298 million to 290 million years ago, can be seen layered into the coast from Cullercoats and Tynemouth into County Durham.
When the Earth’s ice caps melted as the climate warmed, the dune landscape of the Permian desert was rapidly flooded, with what is known as the Zechstein sea extending from the North East to Germany and Poland.
The sea led to the depositing of marl slate on top of the desert sand, with layers of magnesian limestone following, which has created the coastal scenery from Marsden to Seaham.
The limestone, like the Permian sand, has been exploited by quarrying.
A barrier reef also formed between the deep water of the sea and shallow lagoons, with outcrops visible at Tunstall Hills in Sunderland, Claxheugh Rock on the River Wear and Blackhall in County Durham. The radically-different world was described to the Natural History Society of Northumbria at the Great North Museum in Newcastle by Tim Pettigrew, now retired, but who was in charge of geological collections at Sunderland Museum from 1975-1991.
“The catastrophic flooding of the Northumbrian Permian desert by the Zechstein Sea formed the habitat for an amazing diversity of marine plants and animals, together with terrestrial flora and fauna in the adjacent coastal vegetation,” says Tim. The marl slate contains a wealth of fossils of fish, reptiles and plants.
One fossil is of the earliest known example of a lizard-like reptile which was adapted for gliding flight and was washed into the sea after it died.
The fossil was found in 1978 in Eppleton Quarry near Hetton-le-Hole and the specimen, the only one known in the UK, is in Sunderland Museum.
It is thought that the marl slate was formed over a period of 17,000 years by seasonal algal blooms.
The bottom of the sea was devoid of life, and when animals from the upper water layers and land died, they sank and the stagnant condition prevented scavengers and bacteria from disturbing the remains. “Some of the fossils are quite amazing and diverse,” says Tim.
The most abundant fossil fish was Palaeoniscum, which was probably similar to the modern mackerel. It was preyed on by another fossil, Pygopterus, a large powerful toothed fish. The most common fossil plants are conifers, with leaves which suggest harsh, semi-arid conditions.
The end of the Permian 250 million years ago saw the biggest life extinction event on Earth, when more than 90% of marine life and 70% of land life was exterminated.
It is thought that volcanic eruptions injected huge amounts of carbon dioxide into the atmosphere and melting frozen methane in marine sediments contributed to global warming on a massive scale.
“The last fossils in Northumbria were preserved in the rocks around Seaham Harbour before the worldwide mass extinction,” says Tim.
A large leftover from the Zechstein sea has proved a winner for hobby photographer Jonathan Barlow.
His early-morning picture of the magnesian limestone stack on Seaham beach in County came top in a photography competition run by the Limestone Landscapes Project.
The project, which is hosted by Durham County Council, is a three-year programme backed by the Heritage Lottery Fund.
The magnesian limestone plateau stretches almost from Tyne to Tees and from the coast to central Durham, and the Limestone Landscapes Partnership is working to conserve the landscapes, wildlife and heritage of the area. Jonathan, who lives in Peterlee and is a member of the East Durham Photographic Society, said: “I had gone to the beach at Seaham to get a picture of the sunrise.”