Petrology, palynology, coal facies, and depositional environments of an Upper Carboniferous coal seam, Minto Coalfield, New Brunswick, Canada

摘要

Coal petrology and palynology of the Minto coal seam enable depositional environments of the precursor mire to be established in terms of facies-critical maceral ratios, maceral assemblages, and spore and pollen assemblages. The overall petrographic composition indicates a vitrinite-rich coal (mean 67 percent), followed by inertinite (mean 27 percent) and liptinite (mean 7 percent). Pyrite is common to abundant (maximum 15 percent). Lithotype logs demonstrate a dominance of dull lithotypes (dull and banded dull). Petrographic composition at the lithotype and seam subsection level is highly variable. Vitrinite maceral assemblages are enriched in brighter lithotypes (banded bright and bright), whereas liptinite and inertinite maceral assemblages are enriched in dull and banded dull lithotypes. The duller lithotypes are enriched by mineral matter. Based on spores, the seam is assigned to the Vestispora Zone of Atlantic Canada, with the basal Torispora securis-Torispora laevigata (SL) Zone of western Europe and the lower Torispora securis-Vestispora fenestrata (SF) of the Illinois Basin. This indicates an early Bolsovian (Westphalian C) age. Based on the Tissue Preservation Index - Gelification Index facies concept, the seam was deposited in an upper delta plain. At the seam subsection level, facies-critical maceral ratios (Groundwater Influence Index, Vegetation Index) and maceral assemblages suggest both limnic (open moor) conditions and somewhat drier conditions. Relative low Vegetation Indices suggest mainly herbaceous source material, which is partly supported by the rare to common occurrence of small lycopsid spores and arboreous lycopods. The abundant sphenopsids, including Calamites, and rare gymnosperms may have grown outside the mire.