PERMIAN AMMONOIDS PROSTACHEOCERS AND PERRINITES FROM THE SOUTHERN KITAKAMI MASSIF, NORTHEAST JAPAN

Permian shallow marine strata are widely distributed in the Southern Kitakami Massif, Northeast Japan. They yield many marine fossils and have been well studied both stratigraphically and biostratigraphically. However, the geological age of the upper part of the Permian in the Tassobe district, located in the northern part of the Southern Kitakami Massif (Fig. 1), is still an unsettled question. The Permian is divided into the lower Tassobe and upper Sotokawame Formations (Okuyama, 1980; Yoshida et al., 1992). Early Permian (Sakmarian–Artinskian) fusulinoideans have been known from the middle to lower-upper part of the Tassobe Formation (Hirokawa and Yoshida, 1956; Saito, 1968; Yoshida et al., 1992), whereas no age-diagnostic fossils have been found from the overlying Sotokawame Formation. In the course of the geologic survey of the Permian, we collected two ammonoid fossils from the lower part of the Sotokawame Formation, which can provide us a basis for stratigraphic correlation. This paper describes these ammonoids and discusses their stratigraphic and biogeographic significance. Figure 1 —Location map of the study area The Carboniferous Okawame and Permian Tassobe and Sotokawame formations occupy the Tassobe district (Fig. 2). The Tassobe Formation, unconformably covering the Lower-Middle Carboniferous Okawame Formation, is divided into three lithologic units: the lower, middle, and upper parts. The lower part is 300– 350 m thick and consists of sandstone and mudstone, with minor amounts of conglomerate (Fig. 3). The middle part, 450–550 m in thickness, is composed mostly of limestone with intercalated mudstone. The upper part consists mainly of mudstone associated with lenticular limestones and its total thickness reaches 450 m. From the limestone of the middle part, fusulinoidean fossils such as Robustoschwagerina shellwieni (Hanzawa, 1938); Pseudofusulina kraffti (Shellwien and Dyhrenfurth, 1909); P. paramotohashii Morikawa, 1960; Charaloschwagerina vulgaris (Shellwien and Dyhrenfurth, 1909); and Parafusulina chihsiaensis (Lee, 1931 …