The Geology and Formation of the North Sea

Today the North Sea is located northwest of central Europe and is touched by the shores of Great Britain, Norway, Denmark, Germany, the Netherlands, Belgium and the northern tip of France. The geological formation of the North Sea happened millions of years ago during four major tectonic events: the Caledonian phase, the Variscan phase, the Kimmerian phase and the Alpine phase.

The Caledonian phase

The Caledonian phase was active about 510 to 390 millions of years ago. Caledonian mountain building consisted of mostly metamorphic and igneous rocks. The Caledonians were a mountain chain from north to south where the current North Sea is located.

The Variscan phase

The Variscan phase occurred between 380 to 250 millions of years ago and was a giant mountain range that produced an important tectonic phase for the North Sea’s hydrocarbon potential. A series of smaller collisions and smaller continental plates began moving northward. In this phase the Ural mountain range was created.

During this phase the area of the North Sea began moving to the North, where a tropical climate was experienced. Also, the Caledonian mountain range began to experience heavy erosion, while most of the North Sea formed a flat, low-lying coastal plain. To the south, erosion from the Variscan mountain range supplied sediment into the newly formed North Sea basin.

This phase was associated with the Carboniferous period some 359.2 to 299 million years ago during the late Paleozoic era. This Carboniferous period marked a period of ideal conditions for the formation of coal.

The Variscan mountain range was quite extensive and similar to the Himalayas. These mountains formed just east of the Caledonian mountains. The Caledonian gradually phased into the Variscan mountains and, by the end of the Variscan phase, two basins had developed.

Kimmerian phase

The  continental configuration of the North Sea as it exists today occurred during the Kimmerian phase. It was a phase of much rifting and the production of “small confined oceanic basins.” This phase was ideal for the accumulation of hydrocarbon and its organic rich deposits, especially in the North Sea, were very important. This phase existed 240 to 120 million years ago.

The Rocccal-Faerde Rift developed along the Greenland Coast, and the Biscay rift developed west of Europe and France. There was minor rifting in the North Sea.

During the Jurassic period rifting reached its peak and North America moved away from Eurasia. During the Cretaceous period the southern part of the newly formed Atlantic Ocean opened up between Africa and South America. At the end of the Mesozoic era, the North Sea had almost reached its current position.

During the Triassic period, rifting started in the east, close to the Norwegian coastline. The rifting moved westward and became more narrow and, at the same time, small faults began to occur. Other depressions developed and over 3,000 miles of Triassic redbeds were deposited.

At the end of the Triassic period a 1,000-kilometer-long system began to develop in the north, with increased rift elements.

During the Cretaceous period, rifting slowly halted and “the rift of the North Sea became a failed rift.”  With the halt of this last rifting stage began the rifting of the North Atlantic.

This phase roughly occurred during the Mesozoic era and included the Triassic (251 to 199.6 million years ago), Jurassic (199.6 to 145.5 million years ago) and Cretaceous (145.5 to 65.5 million years ago) time periods.

The Alpine phase

The Alpine phase began during the late Cretaceous period, about 100 million years ago. Today this tectonic phase is still active and “has formed Europe as we currently know it.” The North Sea’s current configuration happened during this phase.

During this phase, rifting has all but stopped, and North America is continually moving westward as the Atlantic Ocean becomes broader. “Toward the South, South America is moving away from Africa.” “In the North Sea area tectonic activity was low, but several Alpine phases left their footprint in the structures in and around the North Sea area.”

Reactivation of pre-existing faults and structures occurred during this phase, and many rifts began to fill in.

During the late Cretaceous most of the North Sea was covered “by a shallow warm sea and thick chalk deposits.” Salt tectonics remained active as tertiary sediments.

The geological formation of the North Sea happened millions of years ago and still continues, since this is still the Alpine phase, the last phase of the four main tectonic phases: the Caledonian, the Variscan, the Kimmerian and the Alpine.