Forty samples were selected from Late Jurassic to early Cretaceous black shales of IKU sites 6307/07-U-02 and 6814/04-U-02, located on the mid-Norwegian shelf, for a detailed maceral analysis. The penetrated rocks include the Spekk and Hekkingen formations, which represent major potential petroleum source rocks in the region. It was our first objective to reveal the type of organic material that has produced the source rock potential of these sediments. The results suggest that black shale formation has occurred in two different paleoceanographic settings, i.e. in a "high-productive" and an "anoxic/stagnant" environment, which was supported by inorganic and sedimentological data. In addition, new data for estimating sedimentation rates (SR) gave impulse for using accumulation rates to access the authentic organic carbon flux to the sediment.Organic carbon accumulation rates are relatively low but similar to mid-Cretaceous black shales from other ocean areas (average 10 -300 mg/cm 2 /ka). Supported by redox-sensitive Re/Mo ratios, SR/TOC relationships, and paleoproductivity estimates we suggest that black shale formation in the Spekk Formation has followed largely the conditions of the "stagnation model", whereas the Hekkingen Formation is likely an example for the "productivity model".4. Origin of marine petroleum source rocks ...
IntroductionThe geological understanding of the middle and upper Norwegian shelf (Fig. 4-1) has been improved largely by prospective and explorative operations during the 1980s and early 1990s and is summarized in drilling reports and subsequent papers, e.g. by Skarbø et al. (1988), Worsley et al. (1988), Hansen et al. (1991), Leith et al. (1990), Jongepier et al. (1996. Modern insights in plate tectonic evolution, structural properties, sedimentology, paleoceanography, and geochemistry of late Mesozoic strata along the Norwegian shelf, including sediments of commercial importance, are owing to these investigations (e.g. Brekke et al., 1999; Smelror et al., 2001; Swientek and Ricken, 2002; Lipinski et al., 2003; Langrock et al., in press; Mutterlose et al., 2003). Late Jurassic to Early Cretaceous fine-grained sediments crop up along the eastern margin of the Norwegian-Greenland-Seaway and adjacent marginal seas (Smelror et al., 1994; Leith et al., 1990; Worsley et al., 1988; Århus et al., 1991; Wagner and Hölemann, 1995; Doré, 1991; Doré et al., 1997; Bugge et al., 2002; Mutterlose et al., 2003; Langrock et al., 2003).Drilling also recovered sediments that are exceptionally rich in organic carbon and provide moderate to very good source rock potential for liquid and gaseous petroleum. We investigated sediments from the mid-Norwegian shelf (Fig. 4-1) that represent major potential petroleum source rocks in the region. The cores are characterized by two major lithological units, including the Spekk and Hekkingen formations (Fig. 4-2). A thick sequence of dark-colored, organic carbon-rich claystones (i.e. black shales) with subordinate silty or calcareous intercalation...