Geochemistry-anic-rich-Cretaceous-and-Jurassic-mudstones-in-the-West-Lewis-and-West-Flannan-basins,-Offshore-north-west-Scotland-Implications-for-source-rock-presence-in-the-north-east-Rockall-Trough_20.pdf

Marine and Petroleum Geology 17 (2000) 27±42
Geochemistry anic-rich Cretaceous and Jurassic mudstones
in the West Lewis and West Flannan basins, O€shore north-west
Scotland: Implications for source rock presence in the north-east
Rockall Trough
Gary H. Isaksen a,*, David R. Wilkinson b, h Hitchen c
aExxon Production pany, Houston, Texas, USA
bEsso Exploration and Production UK Ltd, Leatherhead, Surrey, UK
cPetroleum and Marine Geology Group, British Geological Survey, Edinburgh, UK
Received 8 January 1999; received in revised form 27 January 1999; accepted 4 August 1999
Abstract
The West Lewis and West Flannan basins serve as important calibration sites for understanding the source rock distribution
and quality in the north-eastern part of the Rockall Trough. In the West Lewis Basin, two shallow boreholes rated
organic-rich, oil-prone Bathonian mudstones which were deposited in a fresh to brackish water environment. These mudstones
will generate oils rich in parans upon maturation. Organic-rich, oil-prone Ryazanian mudstones were discovered in both the
West Lewis and West Flannan basins. They are o€shore marine mudstones with a predominance of anic matter, akin
to the Kimmeridge Clay in the North Sea and basins west of Shetland. The Bathonian mudstones will generate their
hydrocarbon products at higher temperatures than the Ryazanian mudstones. The presence of lower Cretaceous and middle
Jurassic oil-prone mudstones in basins on the Hebrides Shelf is intriguing and suggests that similar source rocks may be present
along the north-eastern margin of the Rockall Trough. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: West Lewis Basin; West Flannan Basin; Rockall Trough; Source rocks; Yield-timing; Biomarkers
1. Introduction and study objectives Hebrides. Several targeted potential Mesozoic sections
in the West Lewis Basin (WLB) and the West Flannan
The basins on the Hebrides Shelf, to the north and Basin (WFB).
west of t