Biostratigraphy of the Akiyoshi Limestone Group,

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18 Yasuhiro Ota he correlated the base of Pseudoschwagerina Zone (including Triticites simplex Subzone) with the base of Sakmarian in Russia, Wolfcampian in North America and Sakamotozawan in Japan (Fig. 8). Hasegawa (1958, 1963) divided the Akiyoshi limestone Group into eight zones. Of them, Profusulinella, Fusulina-Fusulinella and Yabeina-Lepidolina Zones were almost the same as those by Toriyama (1954a, b, 1958), but he subdivided Pseudoschwagerina Zone into an upper, the Pseudoschwagerina muongthensis Subzone and a lower, the Triticites simplex Subzone. At that time, he did not clearly indicate the Carbonifer ous-Permian boundary. However, he noticed the Mg-rich and oolitic limestones in the lower part of Pseudoschwagerina Zone. Murata (1961) divided the Akiyoshi Limestone Group into eight foraminiferal zones. He put the Carboniferous-Permian boundary below the base of the Pseudo schwagerina Zone, where the subfamily, Schwagerininae first appeared, and the genera, Fusulinella, Fusulina and Beedeina disappeared. M. Ota (1968, 1977) established 21 fossil zones (Table 4). He considered the Carboniferous-Permian boundary below the Triticites simplex Zone. Minato, Kato, Nakamura, Niikawa and Hasegawa (1984) gave a review on studies of the Carboniferous-Permian boundary in Japan and mentioned that the Table 4. Biostratigraphic zones of the Akiyoshi Limestone Group (after M. Ota, 1977). Geologic age Name ofthe fossil zone Symbol Thickness C CO E Q_ Late Lepldollna multiseptata shlraiwensis Zone Puo +25m Middle Early Colania douvillei Zone Verbeekina verbeekl Zone Neoschwagerina craticullfera Zone Afghanellaschenckl Zone Parafusulina kaerimlzensis Zone Misellina daudiae Zone Pseudofusulina ambigua Zone Pseudofusulina vulgaris Zone Pseudoschwagerina (P.) muongthensis Zone Triticites simplex Zone PmS Pm y PmjS Pma2 Pma1 PIS Ply PI/5 Pla2 Plal 40m 20m 25m 15m 25m 20m 40m 50m 20m ±50m Late Triticites (s. 1.) matsumotoi Zone Cua 20m CO 2 *^ 'c o .a I— CO O Middle Early Beedeina akiyoshiensis Zone Fusulinella biconica Zone Akiyoshiella ozawalZone Profusulinella beppensis Zone Pseudostaftella antiqua Zone Millerellayowarensts Zone Nagatophyllum satol Zone Zahrentoldes sp. Zone Marginalia toriyama! Zone Cmy Cm 3 Cm a 3 Cm a 2 Cma1 CIS Cly CI0 CI a ±30m -80m 20m 20m 20m 60m 70m 40m 80m
Fusulinacean Biostratigraphy of the Akiyoshi Limestone Group, Part I 19 relationship between the Lower Permian and Carboniferous deposits in Japan is variable from place to place (Fig. 9). Ozawa and Kobayashi (1990) reexamined the fusulinacean zones of the Akiyoshi Limestone Group, and drew the Carboniferous-Permian boundary between the Daixina robusta-"Pseudoschwagerina" minatoi Zone and the "Sphaeroschwagerina" fusiformis Zone. Ozawa, Kobayashi and Watanabe (1990) established the new genus "Carbonoschwagerina" with Pseudoschwagerina morikawai Igo as the type species. They remarked that this genus represents Carboniferous age. They placed the Carbonif erous-Permian boundary at the same horizon as Ozawa and Kobayashi (1990). Watanabe (1991) emphasized the same opinion that the Carboniferous-Permian boundary should be placed under the Sphaeroschwagerina fusiformis Zone. Fig. 9. Correlation of the Upper Carboniferous and the Lower Permian in Japan (after Minato et al., 1984). Biostratigraphy of the Akiyoshi Limestone Group near the Carboniferous- Permian boundary in the three different areas -1-1. Biostratigraphy of the Jigoku-dani area The first area investigated, Jigoku-dani, is located in the northwestern of the Akiyoshi Plateau(s. s.). This area topographically consists ofa deep valley with NE-
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Biostratigraphy of the Akiyoshi Limestone Group,

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