Lower Tertiary black shales near the North Pole: Organic-carbon sources, paleoenvironment and source-rock potential (IODP Expedition 302 – ACEX)

• Main Authors: Stein, Rüdiger, Backman, J.
• Format: Conference Object
• Language: unknown
• Published: 2011
• Subjects: Arctic; Arctic Ocean; Lomonosov Ridge; North Pole; Sea ice
• Online Access: https://epic.awi.de/id/eprint/25394/; https://hdl.handle.net/10013/epic.38626

In late summer 2004, the Integrated Ocean Drilling Program (IODP) conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling: the IODP Expedition 302 or „Arctic Coring Expedition (ACEX)“ (Backman, Moran et al., 2006; Backman and Moran, 2008). This technically challenging expedition to the Lomonosov Ridge near 88°N recovered the first long-term Cenozoic sediment record from the permantly ice-covered central Arctic Ocean–extending previous records from ~1.5 Ma to an unprecedented ~56 Ma. Some of the ACEX highlights include a Paleocene/Eocene Thermal Maximum (appr. 55 Ma) and Early Eocene Climate Optimum (EECO) substantially warmer than previously estimated; an episodic freshening of Arctic surface waters reflected in the major occurrence of the freshwater fern Azolla near 49 Ma; and ice-rafted debris and sea-ice diatoms having started to occur in the middle Eocene epoch (~46-47 Ma), i.e., some 35 myr earlier than previously thought. During ACEX, in total a 430 m thick sequence of upper Cretaceous to Quaternary sediments has been drilled. The lower 230 m of the ACEX sequence consist of unique, very dark gray biosiliceous oozes and mudstones (“black shales“ in a broader sense) of Campanian and Paleogene (late Paleocene to middle Eocene) age, which are distinctly enriched in organic carbon reaching values of about 1 to 14% (Stein et al., 2006). Significant amounts of the organic matter preserved in these sediments is of algae-type origin and accumulated under anoxic/euxinic conditions. Detailed data on the source-rock potential of these black shales indicate that most of the Eocene sediments have a (fair to) good source-rock potential, prone to generate a gas/oil mixture. The source-rock potential of the Campanian and upper Paleocene sediments, on the other hand, is rather low. The presence of oil or gas already generated in-situ from the Campanian and Paleogene ACEX sediments at this part of Lomonosov Ridge, however, can be ruled out due to the immaturity of the ...