分岐などの炭層の初成的堆積構造
新しい石炭地質学
1997 年 106 巻 3 号 p. 307-319
詳細
1997 年 106 巻 3 号 p. 307-319
Recent coal exploration introduces depositional modeling for interpretation and estimation of morphologic or qualitative changes of the coal beds. Depositional modeling is framed by sedimentary facies of the strata in the coal-bearing formations. Sedimentary facies can be determined from their lithofacies and sedimentary structures as explained previously (Muraoka, 1997). Sedimentary structures which should be studied by the geologists, in charge of exploration, are discussed in this paper. Sedimentary structures comprise primary and secondary ones. Splitting of the coal beds, a typical primary sedimentary structure, is discussed at first due to its importance in coal geology such as its sensitive reflection of subsidence of a basin and deposition of clastics in addition to its critical factor in mining. Furthermore the origin of the coal beds can be discussed based on various features of splitting, and the similarity to Recent peat deposits is concluded.
Splitting is attributed to the following origins : 1) Tilting of a coal basin in an orogenic belt, a) One directional tilting, b) Multi-directional tilting, 2) Migration of delta lobes, 3) The balance between subsidence and supply of clastics in an intermontane lacustrine basin, and 4) Splits that rejoin.
Other primary sedimentary structures such as thinning, rolling, fading-out and silicified wood are briefly discussed.
