Depositional history of the Fire Clay coal bed (Late Duckmantian), Eastern Kentucky, USA

On the fundamental difference between coal rank and coal type

“…Generally, preclusion or great reduction of sediment from the peatland has been attributed to mechanisms such as displacement of sediment deposition inland of coastal mires by rising sea level (e.g., Diessel, 1992;Flint et al, 1995); doming of the peat body, thus raising the surface above the sedimentary system (e.g., Ferm and Cavaroc, 1968;Greb et al, 1999); or baffling of sediment by vegetation growing at the margin of the peatland (e.g., Eble and Hower, 1995;Kravits and Crelling, 1981;Moore, 1991). These models implicitly or explicitly assume that peat formation takes place syndepositionally with local siliciclastic deposition.…”

“…Several of these are discussed herein. We will not consider clastic partings that can be identified unequivocally as resulting from volcanic ash falls (Spears, 1987), such as the parting in the Fire Clay coal bed of the Appalachian Basin (Greb et al, 1999), multiple ash layers in the Maning Formation Somerville Lignite (Raymond et al, 1997), or the Great Northern seam (Zhao et al, 2012).…”

“…Such partings are generally associated with the marginal parts of some coal beds (e.g., Greb et al, 1999). However, many published examples of such deposits need to be re-examined in light of newer interpretations that bring climate into consideration as a significant variable in the peat accumulation equation.…”

“…A recently emerging model reinterprets widespread clastic partings not as "splits," formed when siliciclastics were introduced into mires during flooding from nearby rivers and streams, but as "merges," formed when peat accumulation became interrupted over a widespread area. The different coal benches separated by merges are viewed as representing genetically distinct periods of peat formation Greb et al, 1999. Examples are widespread clastic partings such as the socalled 'blue band' in the Herrin coal of the Illinois Basin (Nelson, 1983), or the so-called binder beds of the Pittsburgh coal of the central Appalachian Basin (Gresley, 1894).…”

“…However, the subsequent planar peats have low amounts of fine-grained siliciclastics, suggesting limited clastic material in the background. Coals, or even benches within an apparently single coal bed, in their final phases of formation, may show changes in petrographic and palynological composition associated with the influx of fine-grained sediments (Greb et al, 1999;Jerrett et al, 2011), but without the introduction of a coarser siliciclastic fraction, again suggesting that such sediments either were not present in the depositional basin, or the flood intensities were too low to carry them out of the main drainage channels running through the mires. These interpretations are consistent with studies in modern tropical environments where streams draining humid to perhumid regions are virtually devoid of coarse siliciclastic sediment loads (Cecil et al, 2003a;Harris et al, 2008).…”