著者

渡辺 和衞

出版者

公益社団法人 東京地学協会

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.64, no.3, pp.71-86, 1955

---

1) All geological phenomena in research works reveal its substance according to the sharp conceptions concerning its stratigraphical position and structural aspect. Especially, younger sediments, Neogene Tertiary, have more intricated forming process and interbed highly evoluted flora & fauna, therefore its stratigraphical subdivision meets accelerated difficulties along with the advance of geologic times. On this account, the geochemical criteria, i. e. -pleochroic halos or radioactivity, and the keybed probation have considerably been available to explain the geologic system. Above all the age determination method of C<SUP>14</SUP> ratio is the epoch-making discovery, in this century, but its applicable scope is about 30, 000 years. And its accuracy has often given rise to discussion from the stratigraphical view point. Recently Ernst Antevs discusses this problem in the report. (Jour. of Geology, Vol. 61, No. 3, 1953, p. 195-230) Another excellent works were published by W. D. Urry in 1949 by the tool of the &ldquo;percentage of equilibrium method&rdquo; for uranium, ionium, and radium. (ibid.p.252-262) But this method has its applicable scope of 300, 000 years. Setting aside this scope problem, these contributions have surely been valid to make the rigid progress of the earth science.<BR>2) The author has recently established the age determination method, that is, as stated above, &ldquo;the percentage equilibrium method&rdquo; for organic carbon. (K. Watanabe : The chronological significance of coal, Bull. Geol. Surv. Japan., Vol. 2, No. 8, 1951) In 1953, this device was reasonably appreciated by Dr. D. W. Van Krevelen, Director of the Central Research Laboratory in Holland. Thereafter this method has greatly been improved by making a comparative study with C14 method (three Japanese specimens, No. 629, 548, 603, determined by Libby were used.). These are considerably satisfactory results to the effect that they are not absolute but relative, Needless to say, this organic carbon method has a chronological index -&theta; (0&deg;-180&deg;), ranging from the present time to Carboniferous period or so on. Accordingly he applied this method to 76 specimens from Kuwana district. (Table 2, Fig. 3). These specimens have various indices ranging from 0.2&deg; to 5.9&deg; (3, 000 years-12, 600, 000 years; recent?upper Miocene). Synthesizing these data, he has drawn the new map, -Isogeochronological map of Kuwana. (Fig. 4) Of course these indices have performed a r&ocirc;le of the correlative tool and manifested several new geologic phenomena which had not been found before. He can show them as follows ;<BR>(1) Synchronous bed with the Chigusa member (marine sediments) exclusively depositing on the side of the Suzuka mountains has been detected on the other side of the Yoro mountains as a member of the terrigenous deposits.<BR>(2) The tentative boundary between Tertiary and Quaternary has quantitatively been determined.<BR>(3) A presumptive fault or folding A-B has been found out by recognizing the uncontinuous zone of &theta;-Isohypsen.<BR>(4) Both structural basins (Machiya system and Asaka system) have contracted drainage areas downwards by upwarping movement at the coastal plain.<BR>(5) Collectively all geologic displacements and fluctuations can quantitatively be measured.<BR>3) Applied geology of this region.<BR>(1) Porcelain clay or other lower class clay.<BR>By organic carbon method of age determination, synchronous strata with ones interbedding good porcelain clay (kaolinite-rich) at Seto, Tajimi, have been detected in this region, -Minami-Nakatsuhara, Tado, Oharaisshiki etc, but its quality is not so good as those porcelain clay. On the contrary, the Chigusa marine bed is rich in montmorillonite or illite minerals. All other lower class clay can be traced their origins and occurrences by Fig. 4 chart from the environmental or genetic point of view. (cf. Fig. 5)