evidence for strongstagnationstrong and upwelling - AWI.pdf

4. Origin of marine petroleum source rocks ... 63 CHAPTER 4 submitted to Marine and Petroleum Geology Origin of marine petroleum source rocks from the Late Jurassic/Early Cretaceous Norwegian Greenland Seaway – evidence for stagnation and upwelling U. Langrock and R. Stein Alfred Wegener Institute for Polar and Marine Research, Department of Geosciences, Columbusstrasse, 27568 Bremerhaven, Germany 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 2 from other ocean areas (average 10 – 300 mg/cm /ka). Supported by redox-sensitive Re/Mo ratios, SR/TOC relationships, and paleoproductivity estimates we suggest that black shale formation in the Spekk Formatio