The High Plains of Southern Norway: Result of Late Mesozoic – Cenozoic Episodic Tectonics

The origin of the mountains of Norway (the Scandes) is controversial. Here we show that the high-level landscape of the Southern Scandes consists mostly of three extensive, low-relief surfaces separated by escarpments. The surfaces extend across 90,000 km² and cut across rocks of different lithologies and post-date the Jurassic surface on the slopes of the Southern Scandes. The surfaces are peneplains graded by river erosion to a base level of sea level during the Late Cretaceous, Paleocene and Miocene. They were all subsequently slightly folded, tilted and uplifted to their present elevations of 1000–1400, 1300–1700 and 1600–1900 m, forming a landscape with distinct steps. The final uplift began in the early Pliocene and caused incision of fluvial valleys and exhumation of the Jurassic surface stripped from its protective cover of Jurassic and younger sediments. Many fluvial valleys were reshaped into glacial valleys and fjords during the Quaternary, while the stepped peneplains kept much of their pre-glacial appearance. The Scandes have not remained high since the Caledonian Orogeny, they are not shaped by footwall uplift and the plateau surfaces are not the result of glacial erosion. The repeated episodes of subsidence and uplift, burial and exhumation that shaped the high-level landscape of the Southern Scandes were driven by sub-lithospheric forces and intra-plate stress. This landscape resembles the elevated passive continental margins (EPCMs) that occur globally in all climate zones. The observations reported here provide important constraints on studies of the tectonic development of western Scandinavia and other EPCMs.