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＜departmental bulletin paper＞
Correlation of the Lower Cretaceous formations in Japan
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| Abstract | Figure 1 shows the distribution of the Cretaceous outcrops with indication of the areas (1-7), where the Lower Cretaceous formations are known. In this report results of the recent biostratigraphic in...vestigations in these areas are outlined, with a concise summary of our present knowledge. In the list of references papers in press, as well as the recently published ones, are indicated. Correlation with the reference sequences in Europe and other regions as well as within Japan is attempted as far as possible on the basis of ammonite genera and speciesgroups that commonly occur in the regions concerned. A tentative result of the approximate correlation of the main formations in Japan is presented in Fig. 2. As a conclusion the following approximate correlation can be made between the Japanese and international scales. Japanese scale International scale Kl (Kochian) Berriasian plus Valanginia K2 (Aridan) H autenv1an plus Barremian K3 (Miyakoan) Aptian plus Albia Recent acquisitions have enabled us to correlate more precisely than in previous knowledge (e. g. MATSUMOTO, 1954, 67, 69) the Japanese scale with the international one. Selected indices of the Japanese Lower Cretaceous are shown in Fig. 3. The Barremian to Albian indices are subdivided into three major groups, i. e. Desmocerataceae, Hoplitaceae plus Acanthocerataceae, and Lytoceratina. They seem to roughly represent dwellers of off-shore sea, shallow sea and intermediate sea respectively. In our present knowledge several questions remain, especially about the Valanginian, Hauterivian and Lower Aptian ammonite species, and the position of the boundaries between successive stages. However, the Japanese sequence of the species will contribute to the Lower Cretaceous interregional correlation.show more |
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| Created Date | 2021.11.01 |
| Modified Date | 2023.11.22 |