THE CONUNDRUM OF COAL BED THICKNESS - A THEORY FOR STACKED MIRE SEQUENCES

Maximum thicknesses for modern peats have been documented only up to a bout 20 m, whereas coal beds can often be as much as 90 m thick. Since peat is expected to compact appreciably during burial, there appears to be no modern analogue for the processes which formed thick coal bed s, and this seems to challenge the Law of Uniformitarianism. However, the conundrum of coal bed thickness can be resolved by identification of discontinuities in coal beds. Coal beds are generally treated as si ngle entities, created by a continuous process of peat deposition. It is more likely, however, that most thick coal beds are composed of mul tiple paleo-peat bodies, stacked one upon another, rather than a singl e paleo-peat body. It is suggested that there are three types of bound ing surfaces seen in modern peat bodies that can be used to distinguis h individual paleo-peats in coal beds; these bounding surfaces can be recognized both in the field and microscopically. Each of these surfac es represents cessation, or at least extreme slowing, of peat depositi on. The presence of these surfaces, and thus stacked mire sequences, i n modern and ancient equivalents shows that processes in peat bodies h ave been similar through time and therefore do not challenge the Law o f Uniformitarianism.