Petrographical, palynological and geochemical analyses of the Hub and Harbour seams, Sydney Coalfield, Nova Scotia, Canada—implications for facies development

Abstract

Benched channel samples and continuous block samples of the Hub and Harbour seams from the Sydney Basin, Nova Scotia were studied to define the variations in petrography, geochemistry and palynology of the seams and to interpret the depositional environments of the precursor mires. Petrographic compositions of the seams are very similar with high vitrinite content, low inertinite, moderate liptinite and negligible clastic mineral content. Pyrite content is moderate. There is little variation in petrographic composition between benches in either seam. There are marked variations in petrographic compositions at the lithotype scale. Petrographic facies parameters indicate deposition of the bulk of both seams under fairly uniform conditions in relatively wet mires. Unusually wet or dry periods were rare. The palynological assemblages of both seams indicate a middle to late Westphalian D age. The common to abundant palynomorphs are derived from “arborescent” and “herbaceous” lycopsids, tree ferns and other ferns(?), and sphenopsids. The palynological assemblages support the petrographic interpretation of relatively wet mires. Cordaites pollen ( Florinites) is rare, suggesting that there was little contribution from plants growing in dry or upland areas. The absence of the Densospore miospore phase, and the petrographic data, indicate there were no periods in which domed mires occurred. The distinctive dull bands occurring in the Hub and Harbour seams are characterised by low vitrinite contents, high inertinite content, high liptinite and common detrital minerals. Sporinite, showing varying degrees of degradation, is commonly highly concentrated in thin bands. The geochemistry is marked by much higher hi values than normally reported for coals but other indices are typical for coals of this rank. The palynological assemblages of the dull bands are dominated by tree fern spores and other ferns(?) with only a minor contribution by sphenopsid spores. The dull bands were deposited during periods of inundation of mires. Relatively low mineral content indicates that the distributary channels which flooded the mires were quite distant from the depositional sites of the samples.