丹波地帯の中・古生界(その4)

京都市西北山地の中・古生界の岩相と地質構造

抄録

Since 1967, many Triassic conodont fossils were discovered from many localities in Japan, where had been supposed to be composed of the Paleozoic formations. As to the Tamba Belt, the Tamba Group had been recognized as a whole to be the Carboniferous to Permian age (SAKAGUCHI 1962; TAMA BELT RES. GROUP, 1971). On the otherhand, sporadic occurrences of the Triassic fossils had been noticed (Halobia and Triassic conodonts by NAKAZAWA and NOGAMI, 1967, and Monotis by SHIMIZU et al., 1967). In the Ashimidani valley of the northwestern hills of Kyoto City, many Upper Triassic conodont fossils were found by YOSHIDA and WAKITA(1975), and this locality is apparently in lower horizon than the one of Permian fusuline fossil occurring. Our Group intended to clarify the stratigraphic relation between the two formations of the fossils in this area. In this report, geology of this region is treated. Lithologic nature of clastic rocks, bedded cherts and carbonate rocks are described. So-called "Schaistein" formation are described in detail their lithofacies, occurrences and petrographic natures, and also differences of petrographic natures between the horizons (Permian and Triassic) are suggested. The Permian conodont fossils are found near the occurrence of fusuline. The Permian and the Triassic beds are noticed to be in conformable relation. Many faults develop extending in the direction of WNW-ESE, and the Triassic formations are repeated by these faults. Occurrences and horizons of conodont fossils will be described in the next report.