美濃帯古生層のsole markingsと古流系について

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The Paleozoic group in the Mino terrain, chiefly Permian in age, is composed of sandstone, shale, chert, Schalatein, limestone, and conglomerate deposited under the eugeosynclinal condition. Turbidite sequences, showing various primary sedimentary structures are developed in a large part of the Paleozoic clastic sedimentaries. Little has been reported, however, on the sole markings and related in formation in this terrain. The present authors carried out a field investigation in three separate areas (Fig. 1), aiming at a systematic study of paleocurrent system. The result obtained by field observation and structural analysis can be summarized as follows: 1) It became evident that various primary sedimentary structures, such as sole markings (groove cast, flute cast, load cast, bounce cast and others), graded bedding, flame structure, and convolute bedding, are commonly observed in turbidite sequences of the Paleozoic group in the Mino terrain. Over 60 percent of the measured sole markings is groove cast (Plate 1, 2), followed by flute cast (Plate 3) and load cast. The typical bounce cast has rarely been found. 2) Two major trends of paleocurrent have been recognized in the Paleozoic Mino terrain. In the Nomugi (Fig. 2) and the Mugi-Shichiso area (Figs. 3-6), situated in the northern and the middle part of the terrain respectively, the paleocurrent direction estimated from sole markings indicates current flowed from north to south with some variation. On the other hand, in the Inuyama area (Fig. 7) at the southern margin of the Mino terrain, the paleocurrent trend is predominantly E-W. As Dzulynski et al. (1959) pointed out, this fact may show the currents shifted from a lateral direction to a longitudinal one. In other words, the lateral supply in the Nomugi and the Mugi-Shichiso area may have shifted to the longitudinal supply in the Inuyama area. 3) The paleocurrent direction in the Mugi-Shichiso area is approximately from north to south, and it coincides well with the dispersal system inferred by one of the present authors (S.M.) from the isopach map and granulometry of the Wadano conglomeratic facies in this area. 4) On a basis of observation on sole markings in the Mugi-Shichiso area, the following attributes are recognized: a) Generally, the difference in orientations of sole markings on undersurface of the same single sandstone bed is quite small, and the paleocurrents estimated from the sole markings have very high constancy in direction. Some sole markings, however, have originally more than one trend (Plate 2). Similarly, the difference in orientation between groove cast and flute cast on the same bed is usually less than 20 degrees. b) By evaluating the paleocurrent direction from sole markings of every single sandstone in a turbidite succession, it is found that a paleocurrent direction of a bed sometimes deviates more than 90 degrees from the direction just above and below as well as from the average direction of the succession (Fig. 4). c) Development of sole markings is closely related to grain size and composition of sandstone, bed thickness and stratigraphic position. Sandstones in which the solemarkings are well developed are poorly sorted, medium- to coarse-grained graywacke sandstone, and 0.5〜1 m or so in thickness. d) Some of sole markings are found abundantly on the bottom of a sandstone bed of a certain specific stratigraphic position, which occurs within a turbidite sequence overlain or underlain by thick, generally hundreds of meters, chert formation. The stratigraphic position is characterized by several sandstone beds resting on a clastic formation a few to tens of meters in thickness made up of thick shale and/or alternation of shale and lesser amount of sandstone.
日本地質学会の論文
1971-07-31

美濃帯古生層のsole markingsと古流系について

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