Abstract
Denmark is a key region for studies of the Cenozoic development of Scandinavia because Paleocene to Upper Miocene sediments crop out across the country and because it is possible to correlate these occurrences with the up to 3 km thick Cenozoic succession of the North Sea Basin. However, the reason why the Cenozoic deposits occur close to the surface of the Earth in Denmark is that the sediments have been exhumed from their cover of younger rocks. This implies that a reconstruction of the Cenozoic development across Denmark – involving both burial and exhumation – must rely on sedimentological and seismic studies of preserved sediments as well as on physical parameters that may yield evidence of the postdepositional history of the sediments now at the surface. Only if the burial and exhumation history of the basins can be deciphered is it possible to infer the geological development in the Scandinavian hinterland where Cenozoic sediments are rarely preserved. We have identified four Mesozoic–Cenozoic palaeothermal phases related to burial and subsequent exhumation, and one phase reflecting climate change during the Eocene. This is based on new apatite fission-track analyses (AFTA) and vitrinite reflectance data from eight Danish wells (Japsen et al. 2007a). The study combined thermal history reconstruction with exhumation studies based on palaeoburial (sonic velo city), stratigraphic and seismic data (cf. Japsen & Bidstrup 1999; Green et al. 2002; Nielsen 2003; Rasmussen 2004; Japsen et al. 2007b). Two of the exhumation phases occurred during the mid-Jurassic and the mid-Cretaceous. In this study we focus on the Cenozoic development and on the early and late Neogene exhumation phases during which up to 1 km of sediments were removed across most of the Danish region (Fig. 1).
Highlights
Early and late Neogene exhumationA major phase of exhumation of the parts of the eastern North Sea Basin adjacent to the presently exposed basement areas in Norway and Sweden began between 30 and 20 Ma ago according to the AFTA data (Fig. 1)
Rasmussen, E.S. 2005: The geology of the upper Middle – Upper Miocene Gram Formation in the Danish area
(2) A phase that began at the Oligocene–Miocene transition at c. 24 Ma, as indicated by early Neogene exhumation of the areas adjacent to the presently exposed basement areas and by early Miocene coarse-grained braided fluvial systems south of Scandinavia
Summary
A major phase of exhumation of the parts of the eastern North Sea Basin adjacent to the presently exposed basement areas in Norway and Sweden began between 30 and 20 Ma ago according to the AFTA data (Fig. 1). We suggest that this phase corresponds to the Oligocene–Miocene unconformity Prior to this early Neogene exhumation phase, the Mesozoic sediments in the Felicia-1 well were at maximum burial. Late Neogene exhumation began between 10 and 5 Ma ago according to the AFTA data from e.g. the Års-1 and Felicia-1 wells. The exhumation affected extensive regions where Neogene strata are truncated, and in southern Norway and Sweden a sub-Cretaceous etched surface was reexposed along the coasts (Lidmar-Bergström et al 2000)
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