Organic petrology of an early Paleocene coal zone, Wabamun, Alberta: palynology, petrography and geochemistry

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An interdisciplinary investigation of a section through the early Paleocene Ardley coal zone at Wabamun, Alberta reveals that there are distinct vertical variations in the palynological, petrographical and geochemical properties reflecting changes in the original depositional environment. Palynological assemblages are dominated by Taxodiaceaepollenites hiatus revealing that the original coal-accumulating mires were inhabited by taxodiaceous vegetation. Subordinate palynomorphs include varied gymnosperm pollen other than T. hiatus, Laevigatosporites spp (fern spores of polypodiaceous affinity), Stereisporites spp (mosses including Sphagnum) and Osmundacidites sp. (Family Osmundaceae). Coal petrography reveals that these coals are inertinite-rich. Abundant fusinite (pyrofusinite), along with semi-fusinite and inertodetrinite comprise up to 65% of the maceral assemblages. Huminite macerals are predominantly eu-ulminite B with lesser eu-ulminite A, densinite and geli-huminite (gelified huminite lacking any remnant cell structure). Liptinite macerals include resinite, sporinite and cutinite. Thinner, stratigraphically lower seams at Wabamun (seams Nos 6-3) consist predominantly of bright coal with high huminite contents. Palynofloral assemblages are comprised of T. hiatus with few abundances of other palynomorphs, suggesting that the original depositional environment was low-lying, dominated by taxodiaceous vegetation, and frequently flooded as evidenced by numerous shale partings, high ash contents and relatively high sulphur percentages. The thick No. 2 seam displays a distinct dulling-up petrographic profile resulting from increasing inertinite contents. Coupled with increased abundances of Stereisporites spp, this may be evidence of localized ombrogeny within the original Wabamun mires, and may support a genetic relationship between Stereisporites sp. and inertodetrinite. The No. 1 seam consists of abundant fibrous (fusain-rich) coal. Modes of origin of this fibrous coal include extreme oxidation due to prolonged drought and possibly forest fires. Elevated ash contents within the Nos 1 and 2 seams may be a result of this oxidation of organic matter and concentration of the inorganics, as well as airborne volcanic ash as evidenced by numerous bentonite bands within these coals. Sulphur contents are extremely low, as low as 0.05% reflecting a terrestrial depositional environment. © 1993.

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Organic Geochemistry

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