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The differences between the depositional settings of the Smith and Anderson subbituminous coal beds (Paleocene, central Powder River Basin, U.S.A.) are interpreted on the basis of their petrographic composition and palynologic assemblages. The Smith coal bed is relatively thin (< 5 m) and has a high degree of thickness variation (0-5 m) over short distances (< 8 km), the result of deposition in an anastomosed fluvial environment where numerous lakes and small channels limited the extent of peat deposits. Although plants related to the living genus Glyptostrobus dominated the swamp, peat-forming plant communities contained mixes of ancestral species of Platanus and Ulmus as well as vegetation of lower stature such as Spagnum. Some intervals within the coal bed contain anomalously high concentrations of cell walls (humotelinite) and cell fillings (corpohuminite), some of which came from locally abundant, decay-resistant Pinaceae (or pinaceous) vegetation. Raised areas of the peat swamp characterized by Sphagnum were also favorable for the accumulation of carbonized plant components (inertinites). Because the peat of the Anderson coal bed formed on top of thick (> 50 m) sandstone bodies of an abandoned meander-belt complex, the coal bed is generally thicker (> 7 m) and more widespread (> 15 km) in extent than the Smith coal bed. The sands provided a relatively stable, poorly compactable platform that was favorable to the growth of large, arborescent vegetation, such as the dominant ancestral Glyptostrobus, as well as ancestral Nyssa, Carya, and Betulaceae in a well-drained but moist swamp environment. The stability of the peat-forming environment resulted in a raised peat deposit of relatively uniform paleoflora and peat composition. In the thicker areas of the Anderson coal bed, the upward increase in carbonized plant components indicates a progressively drier or better-drained swamp environment. Intervals within the coal bed that overlie or are lateral to crevasse-splay deposits contain a high concentration of pollen attributable to Pterocarya and an absence of carbonized plant remains, an indication that ancestral Pterocarya preferred a water-saturated environment close to the edge of the swamp where detrial influx occurred. ?? 1990.
Additional Publication Details
Maceral and palynomorph facies from two tertiary peat-forming environments in the Powder River Basin, U.S.A.