Geochemical and petrologic characterization of the Glamorgan coal seam and implications for paleoenvironment reconstruction in southeastern Pike County, Kentucky

The Lower Pennsylvanian Glamorgan Coal of the Lee and Breathitt Formation (undifferentiated) in southeastern Pike County, Kentucky, is a high-volatile type-A bituminous coal. A low-sulfur (x= 0.96%, std. x= 0.47%, raw coal basis), relatively high-BTU (x= 13,360, std. x= 1757, raw coal basis) coal, the Glamorgan is of economic interest but exhibits peculiar thinning and splitting characteristics, making assessment of mineable areas difficult. This study was undertaken within an approximately 440 sq. km. area of southeastern Pike County, Kentucky, to characterize the seam and explain its occurrence in light of its depositional setting.

Utilizing the Surface II Computer Mapping Program, core, outcrop and chemical data were used to generate a series of computer maps, including isopach, structure contour and chemical isopleth maps. Proximate analyses were enhanced by X-ray fluorescence analysis of coal samples to determine weight percent of major oxides (Na₂O, MgO, AI₂O₃, SiO₂, P₂O₅, K₂O, CaO, TiO₂, Fe₂O₃) and sulfur. Raw coal samples were described petrographically.

Elemental content of the Glamorgan seam is directly related to depositional subenvironments within the study area. To the east, where peat accumulation was relatively uninterrupted, AI₂O₃ is enriched in the 1.5 specific gravity float separate, i.e., the coal portion of samples, and is interpreted to be due to slow settling of suspended clays in a low energy backswamp environment. Na₂O, MgO, AI₂O₃, SiO₂, TiO₂, Fe₂O₃ are enriched in the 1.5 specific gravity sink separate, i.e., the sediment enriched portion of samples. Na₂O is enriched in the float separate, but is probably not present in a mineral matrix. The low amount of total sulfur within the seam as a whole (x= 0.96%, std. x= 0.47%) is indicative of little marine influence on the swamp during peat accumulation. Marine lithologies above the seam in the northwestern portion of the study area are interpreted to be the source of higher sulfur values in the upper split of the Glamorgan.

The Glamorgan is split into an upper and lower seam by a major intra-seam parting (Middleman), and each split contains numerous minor partings in the western portion of the study area, reflecting its river-dominated setting. Thickness variations (from approximately 0.5 - 1.5 m) of the Glamorgan are likely due to a buttressing effect of the underlying Gladeville Sandstone during compaction.

Petrographic data indicate uniformity of maceral content across the study area (vitrinite x= 75.9%, std. x= 16.4%, exinite x= 13.8%, std. x= 4.7% and inertinite x= 7.2%, std. x= 2.2%). A possible trend of exinite enrichment may be due to marine influence, although the limited number of data points makes statistical evaluation uncertain.

Comparison of all data indicates the Glamorgan coal seam formed on a lower delta plain. Two distinct subenvironments are present in the study area: 1) a river-dominated setting in the western portion of the study area, and 2) a protected backswamp setting to the east.