The Norwegian Continental Margin: Tectonic, Volcanic, and Paleoenvironmental Framework

A major goal of both the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) has been to elucidate the temporal and spatial geologic history of the birth of an ocean. This fundamental objective can only be seriously ad dressed by sampling the sedimentary and underlying basement rocks at the passive continental margin. Rock samples shed light and place constraints on models of the geodynamic pro cesses acting during the important phase of transition from con tinental rifting to continental drifting. However, most of the world's passive margins are Mesozoic in age and covered by thick sedimentary sequences requiring deep drilling to reach basement. Drilling of this kind has generally been unattainable with the technology available during DSDP and the initial phase of ODP. During the last 20 yr the Norwegian-Greenland Sea (Fig. 1) has been surveyed extensively; in particular, a large number of high-quality seismic profiles cover the eastern continental mar gin. The investigations have proven that the ocean is an excellent laboratory to study a number geological events associated with the creation and evolution of an ocean basin. Because it is a rel atively young ocean, about 57 Ma, the sediment thickness at the outer margin is locally quite small. Thus, basement drilling is achievable using a vessel like JOIDES Resolution. This was dem onstrated on ODP Leg 104 when we drilled a characteristic seg ment of the Norwegian continental margin at the Wring Pla teau in the summer of 1985. A particularly important observation in the seismic records is the existence of buried structural highs along regions of the outer margins in the Norwegian-Greenland Sea (Fig. 1). These features are often locally underlain by sequences of seawarddipping reflectors also described along many other passive mar gins (Hinz, 1981). It is generally accepted that the marginal highs are related to the initial formation of the NorwegianGreenland Sea during the early Eocene; however, a number of diverging models have been proposed for the high's evolution and the relationship with the continent/ocean boundary. Throughout most of the Cenozoic period the NorwegianGreenland Sea has acted as a major pathway for the influx of cold polar water into the North Atlantic Ocean as well as the advection of warm water from the North Atlantic to the polar deep-sea basin (Fig. 2). The temporal and spatial evolution of this water exchange has had profound paleoenvironmental ef fects on the world's ocean as a whole. During this period both the surfaceand bottom-water circulations were governed by