Thermal effect of the Tertiary Cuillins Intrusive Complex in the Jurassic of the Hebrides: an organic geochemical study

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Abstract
The Tertiary Cuillins Intrusive Complex is partially located within the Mesozoic depositional basins of the Minch and intrudes a Jurassic sequence including a number of moderately organic-rich horizons. The thermal effect of the central intrusive activity, and related minor intrusions, on the Jurassic sediments has been assessed using organic geochemical molecular maturity parameters. Analysis of more than 60 samples, mainly from the Middle Jurassic Dun Caan and Cullaidh Shales, shows that the thermal effect of the igneous complex is very localized and that Jurassic sediments more than 15 km from the complex margin are extremely immature, except in the immediate vicinity of minor intrusions. Igneous activity similar to the Tertiary of western Britain should therefore not be invoked as an alternative maturation route for shallow-buried sediments.