[1] The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceous are of special interest because this was a time when large amounts of marine organic matter were deposited in sediments that have subsequently become petroleum source rocks. However, because of the lack of outcrops, most studies have concentrated on low latitudes, in particular the Tethys and the ''Boreal Realm,'' where information has been based largely on material from northwest Germany, the North Sea, and England. These areas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. We have studied sediment samples of Kimmeridgian ($154 Ma) to Barremian ($121 Ma) age from cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrow seaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-Early Cretaceous these sites had paleolatitudes of 42-67°N. The Late Jurassic-Early Cretaceous sequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian and a climatic shift from warm humid conditions in Volgian times to arid cold climates in the early Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuations in the clastic influx and variations in carbonate and organic matter production. Trace element concentrations in the Volgian-Berriasian sediments suggest that the central part of the Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxic water column. Both marine and terrigenous organic matter are present in the seaway sediments. The Volgian-Berriasian strata have unusually high contents of organic carbon and are the source rocks for petroleum and gas fields in the region. The accumulation of organic carbon is attributed to restricted conditions in the seaway during this time of low sea level. It might be that the Greenland-Norwegian segment was the deepest part of the transcontinental seaway, bounded at both ends by relatively shallow swells. The decline in organic matter content of the sediments in the Valanginian-Hauterivian indicates greater ventilation and more active flow through the seaway as the sea level rose. The same benthic foraminifera assemblages are encountered throughout the seaway. Endemic assemblages of arenaceous foraminifera in the Volgian-Berriasian give way to more diverse and cosmopolitan ValanginianHauterivian benthic communities that include calcareous species. The foraminiferal assemblages also suggest low oxygen content bottom waters during the earlier Cretaceous, changing to more fully oxygenated conditions later. The calcareous nannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes and abundant in high latitudes, reflect the meridional thermal gradient. They indicate that the Greenland-Norwegian segment of the seaway was north of a subtropical frontal zone that acted as a barrier between the Tethyan and Boreal Realms. This implies the existence of stable climatic belts during the early Valanginian and Hauterivian, signif...

[1] The Late Jurassic to Early Cretaceous (Volgian-Ryazanian) was a period of a second-order sea-level low stand, and it provided excellent conditions for the formation of shallow marine black shales in the NorwegianGreenland Seaway (NGS). IKU Petroleum Research drilling cores taken offshore along the Norwegian shelf were investigated with geochemical and microscopic approaches to (1) determine the composition of the organic matter, (2) characterize the depositional environments, and (3) discuss the mechanisms which may have controlled production, accumulation, and preservation of the organic matter. The black shale sequences show a wide range of organic carbon contents (0.5-7.0 wt %) and consist of thermally immature organic matter of type II to II/III kerogen. Rock-Eval pyrolysis revealed fair to very good petroleum source rock potential, suggesting a deposition in restricted shallow marine basins. Well-developed lamination and the formation of autochthonous pyrite framboids further indicate suboxic to anoxic bottom water conditions. In combination with very low sedimentation rates it seems likely that preservation was the principal control on organic matter accumulation. However, a decrease of organic carbon preservation and an increase of refractory organic matter from the Volgian to the Hauterivian are superimposed on short-term variations (probably reflecting Milankovitch cycles). Various parameters indicate that black shale formation in the NGS was gradually terminated by increased oxidative conditions in the course of a sea-level rise.

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...

The late Volgian (early ''Boreal'' Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottomwater conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by wellpreserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.

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