More than 1200 years ago, from 793 onwards, Vikings from Norway and Denmark started attacking northern Britain, and in 866 York was captured by a Viking army. Eric Bloodaxe, the last Viking King of York, was not thrown out until 954.
York – or Jorvik – prospered under Viking rule, taking advantage of the Vikings’ abilities as seamen and traders with connections from Newfoundland in the west to Uzbekistan in the east, and from Greenland in the north to the Mediterranean in the south. The population increased from a couple of thousand when the Vikings arrived to possibly fifteen thousand inhabitants 200 years later.
In 1066, when Jorvik had developed into the richest and second largest and city in England, King Harald Hardraade of Norway invaded England and recaptured York, but was subsequently defeated and killed in the Battle of Stamford Bridge just outside York. This failed invasion marked the end of the Viking Age.
Start in the museum
Nowadays, geologists from Norway are again invading Yorkshire, not to fight and conquer, but to learn about North Sea sedimentary rocks, because along this stretch of coast we find time and facies equivalents to several North Sea reservoir formations, particularly those of Middle Jurassic age.
The Yorkshire coast is also visited by other geologists from many countries, as some of the exposures are world-class. Moreover, amateur geologists run to the cliffs and the beaches below to look for another specimen of a treasured fossil (possibly a dinosaur footprint, if in the right place). With the help of a field-guide easily accessible online from several universities, or one of the guide books that can be purchased in local shops, you can go there by yourself and enjoy the culture, the scenery and the sedimentary rocks.
If so, the starting place is the Rotunda Museum in the Middle of Scarborough (GEO ExPro 08/2009, pp. 58-62).
William Smith, who published the first ever geological map in 1815, became the designer and then foreman of works of the Scarborough Museum, which was opened in 1829. The museum later became known as 'The Rotunda', because of its distinctive cylindrical shape.
The Heather Moorland
The Yorkshire Coast, best exposed between Staithes (Lower Jurassic shales) in the north and Flamborough Head (Upper Cretaceous chalk) in the south, is said to be one of the most beautiful landscapes in England. Cliffs, coves, headlands and bays are enjoyed by tourists all year long.
Inland from the coast, we find the high moors and forested hills, while in between the landscape is enriched by dales (valleys), gorges and escarpments.
The North Yorkshire Moors, one of the largest expanses of heather moorland in the UK, is a national park that is clearly defined to the east by the coastal cliffs. The northern and western boundaries are delineated by the steep scarp slopes caused by rivers eroding into the soft Lower Jurassic shales, while the moors themselves rest on Middle Jurassic sandstones, which erode slowly and form soils deficient in nutrients. They are also less permeable to water, impeding drainage and encouraging the formation of bogs.
Altogether, this makes a splendid framework for researching the rocks that make up this coastal stretch. From north to south we find an almost complete sequence of Jurassic and Cretaceous rocks along the cliffs. Access may be difficult in places (watch for avalanches and loose stones) and it is necessary to keep an eye on the tide table.
The Dinosaur Coast
The Cleveland Basin is so named because the Vikings called the land they raided Cleveland, meaning the land of cliffs, a name that is still very appropriate today, as the cliffs are an important resource for studying North Sea rocks.
“Along the Yorkshire coastline, there is an almost continuous exposure of sedimentary rocks ranging in age from Lower Jurassic to Upper Cretaceous. They have long lateral continuity, but accessibility is in some places restricted due to the almost vertical cliffs,“ says Sverre Ola Johnsen, professor at the Norwegian University of Science and Technology, who has been bringing students here for more than 30 years.
“The reason we go here are the similarities with the age-equivalent succession in the North Sea. The Middle Jurassic deltaic coastal and deltaic succession in Yorkshire serves as an approximate analogue to the Brent Group in the Viking Graben,” he explains.
At the beginning of the Jurassic, some 200 million years ago, this region was covered by sea, as was the whole of Europe. The Lower Jurassic succession thus consists predominantly of shales.
In the Middle Jurassic, about 30 million years later, the ocean receded from this area, leaving a series of coastal deltas. The rocks of this period are therefore predominantly sandstones, but as the sea level fluctuated we also find intermittent shales. These sandstones are analogues for the Brent Group, which is the reservoir in many fields in both the UK and the Norwegian sector, including Statfjord and – of course – Brent.
At the onset of the Late Jurassic, the sea once again invaded the area, now dominated by friendly ammonites and scary plesiosaurs. The rocks from this period are dominated by shales and are known as the Kimmeridge Clay Formation, which has sourced most, if not all, of the oil in the North Sea.
In the Late Cretaceous, the sea level rose considerably, flooding the continents. In the warm climate lived countless billions and trillions of minute plants and animals, of which the coccoliths are most famous. Chalk is made up of the remains of these animals, which consist of pure calcium carbonate. Several fields in the North Sea Central Graben, including Ekofisk, have chalk as reservoir.
Dinosaurs lived on the Middle Jurassic deltas and sandbars that are now exposed along the Yorkshire coast. They thrived on the abundant plants that grew here, and left their three-toed footprints, some of which are half a metre in size, on the sand and silt and mud of the beaches and deltas. Few fossil remains have been found, but this coastal stretch is still nicknamed the ‘Dinosaur Coast’.