A comparison of temperate and boreal peats from Ontario, Canada: possible modem analogues for Permian coals

Peat profiles were sampled from a raised bog and an interior fen located in the boreal James Bay Lowlands, Northern Ontario, and a cold-temperate swam p and a cold-temperate bog in the Great Lakes-St. Lawrence Lowlands, southe rn Ontario. An examination of the micromorphology and maceral compositions of the peats indicates that considerable differences exist between environm ents. The boreal bog and fen both consist predominantly of relatively unalt ered textinite (commonly Sphagnum-derived), with higher liptinite contents in the fen profile attributable to the more diverse vegetation. Both the co ld-temperate swamp and bog show high levels of humification at the surface, possibly partially attributable to recent climatic warming trends causing a decline in water table elevation. In all profiles, funginite was persiste nt, ranging from 2 to 10% of the total maceral content, indicating that aer obic conditions generally prevailed at the surface at the time of depositio n. The influence of depositional environment and vegetation type on the res ulting peat was born out in plots of Tissue Preservation Index vs. Gelifica tion Index. The petrographic study also demonstrated that none of the profi les contained high ineaodetrinite/semifusinite contents comparable to those within cold-climate cratonic Permian Gondwana coals. Since the oxidation p rocesses leading to the formation of inertinite are considered to take plac e at the peat stage, if the peats studied were to contain a similar maceral assemblage upon coalification, inertinite precursors may be present in the peat. The lack of petrographic similarity between the Holocene peats and t he Permian coals may be related to a number of factors. The decrease in wat er table elevation possibly responsible for the inertinization of the Permi an coals may have occurred following the cessation of peat formation, not c oncurrently with accumulation, and is potentially attributable to long-term factors such as climatic warming. The change in the peat-forming vegetatio n (from Permian Glossopteris- and Gangamopteris-dominated communities to Ho locene Sphagnum and coniferous vegetation) alters the characteristics of th e initial botanical starting materials, and some aspects of the ecology, pa rticularly trophic and pH conditions, which control the post-depositional a lteration of the plant materials and the resulting maceral assemblages. (C) 1999 Elsevier Science B.V. All rights reserved.