Uplift, burial and fault reactivation across the Norwegian margin: A Viking Graben - Utsira High - Haugesund - Hardangervidda thermochronological transect

Much of Norway’s economic wealth lies offshore in the form of oil and gas deposits stored in the sediments of the North Sea and North Atlantic. Another important source of income, tourism, capitalizes on the spectacular landscape of western Norway’s mountains and fjords. These two very different natural resources formed side by side by the same geological processes that have been shaping Norway for a very long time. The story starts about 420 million years ago, when Norway collided with Greenland and North America, pushing up the Caledonian mountain range, which was similar in size to the Himalayas. When Norway and Greenland/North America started moving away from each other, the mountain range broke apart along large fracture zones (faults). Weathering and erosion added their destructive forces to help wear down the mountains, and the erosional products, sand and clay, were deposited in topographic lows (sedimentary basins). Eventually, the continents pulled apart far enough, that a new ocean, the North Atlantic, could open between them. The details of this development from a high mountain range to a new ocean are not yet fully understood. Our research project helps to provide a timeline of geological events, by measuring the age of rocks and by estimating when certain rocks came to the earth’s surface or when they were buried again under sediments. We have focused on two areas: the Utsira High in the northern North Sea and a transect from Haugesund to the Hardangervidda.

The Utsira High is especially interesting because it is also the location of the latest large oil discoveries of the Johan Sverdrup and Edward Grieg fields. Our data show that the Utsira High was a topographic high from late Carboniferous/Permian to Jurassic/Cretaceous times. During these ca. 150 million years, the rocks experienced deep weathering and erosion, acting as a sediment source for the surrounding sedimentary basins.

In the late Carboniferous/Permian, when the Utsira High first reached the earth’s surface, most rocks of onshore western Norway were still located deep in the earth’s crust. The coastal areas experienced rapid uplift and erosion during the Permian and Triassic when rifting between Norway and Greenland/North America created the sedimentary basins of the North Sea. Rocks of the inland were the last to reach the surface, with significant uplift and erosion of the inland during the Mesozoic and Cenozoic. The large faults that formed during the destruction of the Caledonian mountains played an important role during this later history. Dating of minerals that grow during fault movements shows that many faults were reactivated during North Sea rifting and possibly again when the North Atlantic opened. These faults allow large blocks of rock to move vertically against each other, changing the topography and creating potential for erosion. Some of these faults still seem to control the landscape of western Norway today.