Geological controls on the sulphur distribution in British Carboniferous coals: a review and reappraisal

Abstract

The very extensive literature on sulphur in peats and coals is reviewed and four case histories from British coalfields are considered. In the Parkgate seam (Langsettian) from the Nottinghamshire coalfield, the variation in the total sulphur content is attributed to pyritic sulphur, with organic sulphur also significant but showing a smaller variation. Sulphate sulphur is negligible. There is a spatial variation in the sulphur concentrations in individual sections (plies) of the Parkgate seam, but this is unrelated to other sections of the seam and to identifiable post-depositional controls, thereby providing indirect evidence of a depositional control on sulphur incorporation. In the Main Bright (Duckmantian, North Derbyshire coalfield) and Threequarters seams (Langsettian, North Derbyshire–Nottinghamshire coalfields), the depositional control is shown to be related to contemporaneous channels. There is a hierarchy of channels and it is concluded that these provided access of more saline waters into the peat mire. Coals associated with marine bands often show high sulphur contents, but there are exceptions, particularly in the Scottish Namurian as exemplified by the Upper Hirst seam where it is thought that there was no contemporary ingress of saline waters. Three Westphalian depositional provinces are recognised on the basis of channel sandstone loci and there is the possibility that different source areas influenced the salinity/sulphate content in the mires. There is some evidence of regional differences in the sulphur content of British coals, which is consistent with the distribution of the three provinces. On the other hand, there is irrefutable evidence that access of seawater leads to high sulphur coals and possibly the marine influence was more pervasive than is generally recognised. There is supporting geochemical evidence of enrichment of trace elements in coals which is indicative of a seawater source.