炭層と夾炭層の成因論の変遷 Genesis of coal beds and coal- bearing formations.
Exploration of mineral resources should be conducted taking their geneses into consideration. Although coal is historically one of the most mined and utilized mineral resources, it has often been explored without regard to its genesis, probably due to the abundant occurrence in the thin surface layer of the Earth's crust. Not only modern, improved and systematic coal exploration is required for a large field within a limited period, but also it is necessary to investigate the depositional environments which controlled the deposition of coal beds, by analyzing all available geologic data. Recent studies on the genesis of coal beds and coal-bearing formations have been concerned mainly with the following four themes.<BR>(1) Studies on modern peat deposits in tropical or temperate zones.<BR>(2) Studies on modern delta and fluvial deposits.<BR>(3) Basin analysis by means of depositional modeling.<BR>(4) Sedimentary structures in coal beds reflecting original materials of coal.<BR>It is concluded that peat deposits of geologic age were formed similar to modern peat deposits, contradicting the for-est-swamp concept. In the past, genesis of coal-bearing formations was explained by the cyclothem concept. The cyclic nature of both marine and non-marine deposits was observed in the Pennsylvanian coal-bearing formations that were deposited on a platform and was termed cyclothem. The origin of the cyclothem was interpreted to be predominantly a result of eustatic movement caused by change of sea water level, regional tectonics and climatic change. However, subsequent studies have revealed evidence against this interpretation so that the cyclicity of the cyclothem is not considered to have a stratigraphic significance because of poor correlation except for a few limestone beds. The development of most coal basins has been satisfactorily explained by delta and fluvial models, in particular the formation of the Appalachian Basin. Coal basins unrelated to deltaic depositional systems are some intermontane lacustrine coal basins in graben or orogenic belts.
資源地質 48(2), 105-113, 1998-10-01
The Society of Resource Geology