Origin of marine petroleum source rocks from the Late Jurassic to Early Cretaceous Norwegian Greenland Seaway—evidence for stagnation and upwelling

Abstract

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...

Modelling Source‐Rock Distribution and Quality Variations: The Organic Facies Modelling Approach

“…Table 5) represents a general PP estimate for the Late Jurassic organicrich sediments of the Norwegian Shelf at least for near-shore environments. This is in contrast to the results from Langrock and Stein (2004) who estimated productivities from the same well, 6307/02, ranging between 20-30 g C m −2 yr −1 . Reasons for this difference remain unclear since their conclusions are not justified by more detailed data.…”

Orbital pacing and secular evolution of the Early Jurassic carbon cycle

“…The marine origin of the degraded particles is further supported by its fluorescence. The fluorescence of terrestrial organic matter should decrease with greater biodegradation (47) but in the studied samples appears higher compared to intact terrestrial liptinite. The HI values recorded in Mochras are likely highly compromised as a result of aerobic bacterial degradation of initially hydrogen-rich marine organic matter and are therefore not indicative for the primary source of the organic matter.…”

Upper Cretaceous/lower Tertiary black shales near the North Pole: Organic-carbon origin and source-rock potential

“…The hydrocarbons known from these circum Arctic basins probably derived from organic-carbon (OC)-rich mudrocks (''black shales''), which were deposited during Mesozoic and early Cenozoic times (Dixon et al, 1992;Leith et al, 1992;Bakke et al, 1998;Littke et al, 1999;Vyssotski et al, 2006). In the Barents Sea and northern North Atlantic off Norway, for example, organic-geochemical data from petroleum exploration drill holes representing Jurassic/ Cretaceous time intervals indicate that these black shales are characterized by very high OC contents (typically 15-25% with peak values of 430%) of a mixed marine/ terrigenous origin, probably related to anoxia and/or increased primary production (Leith et al, 1992;Langrock et al, 2003;Langrock and Stein, 2004). For the central Arctic Ocean, however, in only four short cores (FL533, FL437, FL422, and CESAR-6; Fig.…”