Influence of exinitic macerals on the reflectance of vitrinite in Carboniferous sediments of the Midland Valley of Scotland

Vitrinite reflectances are reported for coals and argillaceous sediments from nine borehole successions in the eastern and central Midland Valley of Scotland. Suppression of reflectances of vitrinite clasts in argillaceous sediments is significant in samples with exinite contents greater than 20 vol%. There is also a correlation between the amount of exinite present, irrespective of type, and the degree of suppression of the reflectances, but the correlation is not particularly strong. Weight of current evidence, although still not absolutely unequivocal, now suggests that the reflectance suppression is principally due to absorption by vitrinite clasts of aliphatic-rich fluids, emanating from different exinitic macerals, at different stages during coalification. Estimations of maturity of organic-rich sediments, particularly sapropelic, that are based on vitrinite reflectance should be accompanied by a statement of the amount and type of exinite present.