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Conodont Colour Alteration Index (CAI) values for the Carboniferous of Scotland

  • Mark T. Dean (a1) and Nicholas Turner (a2)

Abstract

Conodont elements from Scottish Carboniferous rocks have been reviewed for Colour Alteration Index(CAI) data, and most values range between 1 and 1·5. Assuming a local average geothermal gradient similar to that of today, the observed and predicted CAI values generally fit well. Only a few of the samples analysed were influenced by local igneous intrusives. The CAI range shown lies within the immature (early dry gas) to mature (perhapsmid-oil window) stages of hydrocarbon generation, and this suggests that burial maturation (where CAI values are 1-5) could account for locally generated oil, where this occurred away from igneous intrusions. Alkali-dolerite and tholeiitic intrusives are, however, widespread in the Midland Valley of Scotland, and an understanding of their thermal effects has implications for both coal and petroleum exploration. The insensitivity of conodonts to low temperatures is noted, and the relevance, application and potential of various other palaeothermometers is discussed. Locally, the qualitative study of spore colour (SCI) appears useful.

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