3.5.4. Climate controls on topography

As the topography and morphology of mountainous terranes result from the interaction of tectonic, climatic and erosional processes, it is necessary to study mountain-building through a system-oriented approach that takes fluvial and glacial processes explicitly in to account. The Scandinavian mountain range has been extensively glaciated during the Quaternary period (Shackleton et al., 1984; Mangerud et al., 1996) with possible onset of local and regional glaciations already during the Middle Miocene (Fronval and Jansen, 1996; O’Connel et al., 1996). From then on, the elevated terrain of the Scandes Mountains acted as nucleation centre for the North European glaciations. Glaciers resided in the Scandinavian mountains for at least 65% of Pleistocene time (Porter, 1989; Fredin, 2002). Hence, the glacial imprint on the Scandinavian topography and landscape is profound (Fig. 60).

uring interglacial periods, mass movements and fluvial processes are thought to have played a major role. In spite of extensive glaciations, the Scandinavian mountains also bear significant imprint from geomorphologic processes predating the Quaternary glaciations, such as weathering remnants, incised fluvial valleys and uplifted highland plateaus akin to a mature landscape. Moreover, the Quaternary glacially sculpted valleys often follow pre-existing fluvial drainage systems (Fig. 60).

Offshore Mid-Norway a thick and extensive sequence of Quaternary sediments (Naust Formation) was deposited during the last ca. 2.7 My (Eidvin et al., 1998; Fig. 61). This sequence has a formidable potential for constraining terrestrial Quaternary erosion both in time and space. The Naust Formation was mainly deposited west of the 'deltaic sands' of the Middle Miocene - Early Pliocene Molo Formation, which subcrops parallel to the coast. This subcrop appears to represent an important hinge line between subsidence to the west and uplift to the east. The timing of the Neogene uplift and subsidence phases is still uncertain. Instability of these prograding Pliocene and younger clastic wedges has given rise to the development of several, presumably earthquake-triggered large submarine slide during Late Pleistocene and Holocene times that partly were associated with major tsunamis (Fig. 61; Bondevik et al., 2005; Evans et al., 2005).

Evidence for Late Neogene exhumation of southern Norway is provided by the subcrop pattern of Cenozoic and Mesozoic sediments beneath Quaternary deposits in the marginal parts of the North Sea Basin (Fig. 18). The thickness of sediments removed at this base Quaternary unconformity can be estimated from Chalk sonic velocities and amounts to some 1000 m where the Chalk is truncated (Japsen, 1998; 2000; Fig. 62).

Fig. 62. Late Cenozoic vertical movements in the North Sea area along a cross-section extending from Edinburgh (Edb) to Copenhagen (Cph). The Late Cretaceous-Danian Chalk Group was deposited in an epicontinental sea that covered most of NW Europe (65 Ma). In the North Sea the Chalk was buried beneath thick Paleogene and early Neogene sediments that extended beyond their present erosional limit (15 Ma). In the course of the Late Neogene the western and eastern margins of the North Sea Basin were uplifted and exhumed whilst the basin centre continued to subside. Along the basin margins Neogene and older sediments (including the Chalk) are truncated by the base-Quaternary unconformity (0 Ma). Comparison of observed Chalk interval velocities with a normal Chalk velocity-depth trend permits to estimate the thickness of eroded sediments (modified after Japsen, 1998; Japsen and Bidstrup, 1999; Japsen, 2000).

During the last 0.4-0.5 Ma (deposition of Naust sequences S and T) several extensive ice sheets extended seaward to the shelf break (Rise et al., 2005), while for Naust U time 3D seismic data indicate that glaciers extended onto the shelf. The progradation of sedimentary wedges was considerable during Naust N and A times (oldest; Fig. 61), although depositional processes are poorly understood. Ice rafted debris are found in samples from exploration wells, and grooves from icebergs are observed on some 3D seismic surfaces. The age of Naust U, A and N sequences is uncertain, and the limited chronostratigraphic data available provide conflicting results. Therefore, there is a need for better constraints on the timing and depositional mode of these sequences to improve the understanding of terrestrial erosion and relief generation (c.f. Riis, 1996).