--> ABSTRACT: Palynologic, Petrographic, and Coal-Quality Characteristics of Middle and Upper Pennsylvanian Coal Beds: a Comparison, by Cortland F. Eble and William C. Grady; #91031 (2010)

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Palynologic, Petrographic, and Coal-Quality Characteristics of Middle and Upper Pennsylvanian Coal Beds: a Comparison

Cortland F. Eble, William C. Grady

Comparative palynologic, petrographic, and coal-quality data from the Hernshaw coal bed (Kanawha Formation, Middle Pennsylvanian Series) and the Redstone coal bed (Monongahela Group, Upper Pennsylvanian Series) suggest that compositional differences between the two beds may be related to paleoenvironmental conditions under which the peat accumulated. Full-bed thickness channel samples and vertically continuous increment samples show the Hernshaw coal to be dominated by miospores assignable to arborescent (Lycospora) and herbaceous (Densosporites) lycopods, tree ferns (Punctatisporites minutus and Punctatosporites minutus) and herbs (Granulatisporites). Petrographically, the Hernshaw coal contains a low vitrinite content (50-70% mmf [mineral matter-free] vol. %), high exin te (7-9% mmf) and inertinite (15-30% mmf) abundances, and low ash yield (5-10%) and sulfur content (0.5-1.5%). Typically, the Hernshaw coal exhibits vertical palynologic and petrographic stratification. Basal increments are commonly high in Lycospora and vitrinite content, passing upward into more tree-fern miospore- and Densosporites-rich layers, which also contain very high amounts (>40% mmf) of inertinite macerals. In contrast, the Redstone coal is dominated by miospores assignable to tree ferns (Punctatisporites minutus and Punctatosporites minutus) and calamites (Calamospora and large Laevigatosporites). Petrographically, the Redstone coal contains a very high vitrinite content (80-95% mmf) with low exinite (2-3% mmf) and inertinite (8-10% mmf) maceral abundances, and moderate bu highly variable ash yield (5-30%) and sulfur content (1-5%). Unlike the Hernshaw coal, the Redstone coal does not exhibit distinct vertical palynologic and petrographic stratification.

The vertical change in miospore composition, increased amount of inertinite macerals, and low ash yield and sulfur content suggest that the ancient Hernshaw swamp was a domed, ombrogenous peat system, resulting from a climate with abundant rainfall. The more homogeneous miospore and maceral distribution, overall high vitrinite content, and higher and more variable ash yield and sulfur content of the Redstone coal suggest that the ancient Redstone swamp was more planar in profile, and was soligenous to topogenous, the result of a less wet climate.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.