Evidence for a Late Cretaceous or Palaeocene Arctic Seagrass Lagoon?

Lawrence M. Gill
PSEG, Leeds, United Kingdom

Banet, (1994) undertook a comparative study of oils from the North Slope, Beaufort Sea and Chukchi Shelf. This study revealed, but did not explain anomalous gas chromatographic characteristics for an otherwise marine oil from the Chukchi Burger #1 well including: 1) a predominant C₂₅ n-alkane peak in the saturate fraction of a crude oil; 2) a highly predominant 24-ethyldiacholestane peak in its m/z 217 mass fragmentogram; 3) elevated levels of C₃₅ homohopanes in its m/z 191 mass fragmentogram. Further research into these characteristics as part of a Circum-Arctic regional study conducted by GETECH, has revealed strong similarities between the biomarkers found in the Chukchi oil, and those exhibited by the seagrass Zostera marina. This has lead to the implication of a possible precursor-derivative relationship between the two. Furthermore, the elevated C₃₅ homohopanes and the predominant diacholestane are used to infer an enclosed and brackish nearshore environment at the time of source rock deposition. The distribution and setting of present day seagrass meadows has also been investigated with particular reference to water temperature tolerances. It is concluded that organic matter from Zostera marina, or similar species, could have contributed to source rocks at high, Arctic latitudes (in excess of 70ºN) in the Late Cretaceous-Palaeocene, the period in which, as angiosperms, the seagrasses are thought to have evolved. From the data in this investigation, the most plausible source rock horizons from which an oil with these characteristics could be derived are identified as being either the more likely nearshore Palaeocene Sagavanirktok Formation, or the more unlikely Campanian Colville Group. These findings could have implications for source rock identification across both North American and Russian Arctic basins.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece