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The North Sea is a shallow epicontinental sea, located on the UK Continental Shelf, between the east coast of the UK and the west coasts of Norway, Denmark and the Netherlands. It is more than 970 km (600 mi) long, 580 km (360 mi) wide, and covers over 570,000 km sq (220,000 mi sq) with an average water depth of 90 m. 

It contains several basins with regional highs seperating them that are remnants of significant geological events. These events are where the Earth's crust was thinned and stretched, causing subsidence. Each basin across the North Sea has its own unique name and geological history. 


While oil, gas and coal can be found onshore, the majority of the sedimentary rocks rich in oil and gas have found to be offshore. These rocks can be found in thick stratigraphic intervals that filled the basins of the North Sea and underwent the ideal heat and pressure conditions to turn organic matter into hydrocarbons.

The North Sea is a majority oil and gas basin and has been since exploration began in the late 1960's, with first production in the 1970's. At the height of its success, the combined exports of the UK, Norway, Denmark and the Netherlands made the North Sea the world's fourth largest oil producer and third largest gas producer.

The North Sea is now at a mature stage with a significant number of the fields in decline. It continues to supply oil and gas as part of the fuel mix  in the energy transition, as well being a centre for decommisioning hydrocarbon wells and facilitating exploration of geothermal energy, carbon capture and  hydrogen storage as we work to use less fossil fuels to combate climate change.

Regional map of the North Sea basins. From Patruno et al., 2021

The North Sea


The geology of the UK is famous for being extremely diverse, as it records almost every period of geological time. This complex geological history has helped shaped the landscapes we know today. 

The series of basins offshore around the UK have helped preserve a record of rocks from the Devonian to the Eocene, over 380 million years. This is because during the Permian t0 Triassic, and then the Jurassic, the whole area was dominated by significant rift systems as supercontinents started to break up. Following this, the North Sea basins have been affect by post-rift subsidence, uplift and have been infilled by siliciclastic and carbonate sediments through the Cretaceous to the present day.

Want to learn more? This video presented by Henk Kombrink and Stuart Archer takes the viewer throught the geological history of the North Sea through a series of maps, core samples and onshore outcrops.

The Rock Record
Geological Time


The Paleocene-Eocene is a largely unfaulted, post-rift sequence, with deepest burial recorded in the central part of the basin. The strata consist of significant amounts of siliciclastic sediments, with minor coals, tuffs, volcaniclastics rocks and reworked carbonate sediments.


Tectonic activity during the Paleocene is thought to have been related to the development of Icelandic plume, which drove the rifting of the North East Atlantic and associated volcanism in the West of Shetland area. This caused regional uplift and erosion, the source of the siliciclastic deposits which dominate the Paleocene and Eocene interval. Paleocene and Eocene sediments are distributed extensively across the Central and Northern North Sea and contain many of the hydrocarbon fields and discoveries within the basin.


The Upper Cretaceous is dominated by carbonate sequences in the Central and Southern North Sea, with little to no siliciclastic sediments. In the Northern North Sea, the Upper Cretaceous becomes dominated by siliciclastic, clay-rich sediments during the largest transgression (flooding event) in the Earth's history. These successions were deposited in an extensive, relatively deep epicontinental sea during typical 'greenhouse' conditions, when the climate was warm to subtropical.


This was also a tectonically quiet period, punctuated by periods of compression and inversion related to early phases of the Alpine Orogeny. Upper Cretaceous carbonates or Chalk provide reservoir rocks for significant hydrocarbon accumulations mainly in Danish waters but some fields can also be found in the UK North Sea. 


During the Early Cretaceous, siliciclastic rocks were deposited in a string of epicontinental seaways formed as a consequence of earlier Jurassic rifting activity. The tectonic regime of the North Sea was affected by active plate margins along the Western parts of the European plate, changes in the intra-plate stresses and regional thermal subsidence.


This includes the shift of rifting in the North Sea northwestward to the proto-North Atlantic region, now known as the West of Shetlands. Hydrocarbon accumulations are largely found in deep water siliciclastic mass flow deposits in the Central North Sea.


The Late Jurassic is a time of overall transgression in the main rift system of the North Sea. Shallow marine and shoreface sands can be found along the margins of the basins and on the adjacent platforms, gradually being overlain by deeper marine muds.


It is the organic-rich mudstone deposited during this transgression (Kimmeridge Clay) that forms the key source rock for the majority of the Central and Northern North Sea hydrocarbon fields.


Due to uplift associated with the onset of rifting in the North Sea, Lower and Middle Jurassic rocks are thin to absent in the Central North Sea.


However, away from the area of uplift in the Northern North Sea, a wedge of Middle Jurassic deltaic sediments was deposited, shed from the area further south. These deltaic rocks are today known as the Brent succession and these are the host of many oil fields in the area.


Triassic deposition across the Northern and Central North Sea occurred in broad arid to semi-arid, intra-continental basins, resulting in thick red bed successions. Variations in base level are attributed to a cyclical alternation of coarse grained alluvial deposition with finer grained plays lake sediments.


South of the Mid North Sea High, the Triassic has a tripartite subdivision of mainly sandstones at the base, followed by marine carbonates, which were subsequently overlain by an interval of playa fines. Triassic rocks are widely distributed in the North Sea but contain relatively few hydrocarbon accumulations.


During the Latest Permian, rising sea levels caused the flooding of the Northern and Southern Permian Basins and the creation of the Zechstein sea. The basins were still located in a hyper-arid desert environment, meaning at least five cycles of sea water evaporation and marine flooding caused the deposition of carbonate and evaporite sequences, with local clastic and volcanic rocks. Only a small portion of produced hydrocarbons in the North Sea is from Zechstein reservoirs. 


The Early and Middle Permian in the North Sea represent a hiatus in most areas. During the Rotliegend of Late Permian two east-west aligned basins developed across northwest Europe, the Northern and Southern Permian Basins, with the Mid North Sea High between them. These basins contain aeolian and lacustrine/sabkha sediments deposited in a semi-desert climate, with local volcanic rocks. It is the aeolian rocks that form the most important reservoir in the Northern North Sea, the Rotliegend.


The Devonian-Carboniferous transition is mostly recorded as an interval of continental to fluvial, sandstone dominated redbeds. In the Southern North Sea, the Lower Carboniferous is characterised by the establishment of carbonate platforms and adjacent deep-water basins, while in the Central and Northern North Sea a major delta slowly prograded southwards.


The Upper Carboniferous sees further delta progradation in the Southern North Sea with the formation of numerous swamps which form the source of our gas today. The North Sea was located on a tropical latitude at Carboniferous times.


During the Silurian to Early Devonian, the Iapetus Ocean progressively closed in the Caledonian Orogeny. There were significant sinistral strike-slip movement along faults we still recognise today, including the Great Glen and Highland Boundary faults.


With the creation of the 'Old Red Sandstone Continent', continental redbeds were deposited in a warm to hot, arid to semi-arid environment. Changes in the compressional regime and the gravitational collapse of Caledonian structures during the Middle Devonian created local basins which record sequences of alluvial, fluvial, lacustrine and volcaniclastics rocks.


Precambrian to Ordovician rocks form the crystalline 'basement' on which the younger sediments were deposited. They are rarely documented in the North Sea, but where they have been sampled they are known to include low to high grade metamorphic rocks, igneous rocks and metasedimentary rocks.


These basement rocks can be highly fractured due to having undergone multiple phases of deformation. The rocks underlying the North Sea are thought to be remnants of the Baltica, Laurentia and Eastern Avalonia crustal blocks which were once part of the supercontinent Pangea. 

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