Environmental influence on maturity parameters in carboniferous coals of The Netherlands

Abstract

An Upper Carboniferous coal sequence has been analysed by means of organic petrological, sedimentological and statistical methods in order to test the hypothesis of environmental influence on vitrinite reflectance values. Differences between the linear regression value and the vitrinite reflectance value along the depth profile have been taken as a measure of reflectance variation. Detailed maceral analyses have been carried out on forty-seven coal seams. Factor analyses of selected variables resulted in the recognition of common factors accounting for approximately 50% of the variation of the data matrix. Two factor analyses were performed including either maturity parameters ( T max and % R r), or variation in vitrinite reflectance. In both analyses, two factors were considered sufficient to represent the data. The factors have been attributed to coalification, degree of humification and oxidation. Clustering on the basis of detailed maceral analyses resulted in a two-fold subdivision of the coal seams. The two clusters are differentiated on the basis of the ratio of the vitrinite macerals telocollinite and desmocollinite, significant differences in hydrogen index, and marked differences in mean vitrinite reflectance values. The subdivision is related to differences in depositional environment. One cluster, interpreted to represent peat formation in a fluviatile influenced environment, accommodates samples with significantly lowered reflectance values. The other cluster is characterized by a deltaic setting of the coal seams. Petrographic and chemical differences are interpreted to be related to different levels of biochemical degradation in these two palaeo-environments. The fluviatile influenced coals have a marked lower maturity trend compared to those formed under deltaic conditions.