Geochemical and petrographical characteristics of a domed bog, Nova Scotia: a modern analogue for temperate coal deposits

A freshwater domed bog in Nova Scotia, Canada, was investigated for its petrographic, mineralogical and geochemical characteristics. Three cores were taken from the lagg zone, margin and centre, to examine different stages of evolution in a fen to domed bog sequence. Based on this study, a model was developed, which shows the relationship between factors controlling peat geochemistry and petrography, all of them being dependent on trophic conditions. The bog may represent a modern analogue for temperate coal deposits, and thus can be used to help understand spatial variability within coal beds. Rheotrophic conditions in the early stages of mire development result in the formation of high-ash, highly humified Carex-dominated peat, while the evolution toward ombrotrophic conditions is reflected in a progressive replacement by low-ash and well-preserved Sphagnum-dominated peat. The associated decrease in pH reflects a decrease of groundwater influence, which is also supported by the mineralogical assemblage and petrographic data (decrease in reflectance and change in maceral composition). Except for Cl, Br, I and Se, which are associated with the organic fraction, variations in elemental composition can be explained in terms of mineral matter abundance, i.e. decrease upward and with increasing distance from the margin. Sea spray is the most probable origin for halogen enrichment in the peat.