<国立科博専報>赤石山地白亜系戸台層の時代

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This paper is to report the results of our biostratigraphic investigations of the type area of the Lower Cretaceous Todai Formation exposed in the northern part of Akaishi Mountains, Central Japan (Figs. 1,2). The Todai Formation is subdivided into three members, i.e., the lower, the middle, and the upper. Fig. 3 is a geological map of the surveyed area, in which the locations of molluscan fossils are indicated. Selected columnar sections are newly illustrated in Fig. 4,in which the stratigraphic positions of cephalopod species are indicated. The predominant ammonite species and some other invertebrate fossils are listed in Table l, in which their occurrences are also shown. A schematic stratigraphic profile (Fig. 5) is drawn to demonstrate lithological changes in the sedimentary basin. The fossils tend to occur more frequently in the upper part of the formation. Based on the litho- and the bio-facies of the Todai Formation, littoral to neritic sedimentary environments are suggested. The succession of ammonite species in the Upper Member of Todai Formation closely resembles that in the Hiraiga Formation of Miyako Group (HANAI et al., 1968), i.e., the Hypacanthoplites subcornuerianus fauna followed by the Diadochoceras nodosocostatiforme fauna (Table 1 ; Fig. 5). This enables us to correlate the upper member of the Todai Formation most probably with the upper to the upper-most part of the Upper Aptian in terms of the international scale. Another interesting fact is that the early Middle Permian fusulinid, Misellina claudiae (DEPRAT), is newly identified in several pebbles of limestone from the Lower Member of Todai Formation. It is safely concluded that the lower Middle Permian strata were exposed when the late Aptian transgression began in this area of Central Japan.
国立科学博物館の論文
1979-12-01

<国立科博専報>赤石山地白亜系戸台層の時代

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