Distribution of elements and minerals between a coal and its overlying sedimentary rocks in a limnic environment

Previous studies have shown that the Pewee coal, which outcrops in the Wartburg Basin in northeast Tennessee (U.S.A.), formed in an upper delta-plain (limnic) environment and had not been subject to marine conditions. Most elemental concentrations decrease upwards, from the base to the top of the coal; however in some locations, several elements show significant increases in concentration at the very top of the coal. Correlation coefficients for elements within the coal and to a lesser degree, the sediments, reflect typical clay minerals. The major mineral phases identified were kaolinite, illite, chlorite, siderite and quartz.Although minor lateral variations in chemical and maceral composition occur, the Pewee coal is relatively homogeneous within the study area. Elements which tend to be soluble in low-pH solutions (especially Ca) may have reacted with fluids coming from the peat and have been transported away from the coal-sediment contact. Chlorite is absent in the coal, perhaps due to its solubility in an acid environment. With these few exceptions, there is little direct evidence that diagenetic processes influenced the movement of elements from the coal into the sediment, or vice versa.The decrease in elemental concentrations upward in the Pewee coal is thought to result from a gradual decrease in the amount of detritus being brought into the Pewee swamp. The increase in abundance of detritus at the top of the coal in some locations suggests a sudden change in environmental conditions, perhaps as the result of the establishment of a new distributary system.