ORGANIC MATURATION OF SEDIMENTARY CLASTS FROM VOLCANIC NECKS IN THE EASTERN MIDLAND VALLEY OF SCOTLAND

Reflectances have been measured on vitrinites in coals and argillite clasts contained in tuffs and agglomerates of Carboniferous and early Permian volcanic necks along a ca. 6.5 km shore section in East Fife (Midland Valley of Scotland). The vitrinite reflectances extended from R(oil) (average) almost-equal-to 0.4% to greater than 5.0%. The lower part of this range overlaps with the reflectance distribution of vitrinites of shales in the country rocks which are principally at the stratigraphic level of the Pathhead Beds, low in the Carboniferous succession. The lowest vitrinite reflectances of both distributions are probably due to absorption by the vitrinites of hydrocarbons expelled from associated liptinitic macerals. The higher modal-class interval for the reflectance distribution of vitrinites from the volcanic clasts, compared with that for the vitrinite reflectances of the country rocks, suggests that the vitrinites in the tuffs and agglomerates reached their reflectance levels most probably in two ways: (a) through temperature rise in the hot ash steams associated with phreatomagmatic eruptions; and (b) through other thermal episodes elsewhere and then incorporation in the vents from lower or higher stratigraphic levels. Comparisons are made with the diatremes of the Sydney Basin, Australia which have a similar origin to the volcanic necks of East Fife.