The study of the late Dr. H. Kuno has been accepted as an established theory of the geological history of Towada Volcano (Caldera). His study was based upon only the geological data of the volcanic body of around the Lake Towada. The authors believed, however, that a correlative research of the tephra-stratigraphy of the foot-hills with the geology of the volcanic body would clarify a true geological history of Towada Volcano (Caldera). First of all this monograph is to clarify the geological and petrological character of the younger volcano which has not been made clear till now, and then to pursue the above-mentioned theme including the previous results. As an outcome of this study, a tentative conclusion was formed on the geological history of Towada Volcano (Caldera), which is shown Fig. 6. The main points are summarized as follows; [table]

View full abstract

In this article, the authors dealt with some proboscidean fossils occurred from the lower part of the Osaka Group (Early Pleistocene) at eastern part of the Habikino Hills in Tondabayashi City, Osaka Prefecture. Those fossils are composed of one broken molar, four complete and incomplete incisors (tusks of elephants) and other bone fragments. Those materials were found together in a restricted small spot in the area, and were confirmed to be yielded from the same bed, pebbly silt, which is probably about 30 m below the First Marine Clay bed (Ma 1) of the Osaka Group. The fossil molar was identified as a molar of Stegodon cf. akashiensis (TAKAI) from its characteristic features. On the other hand, it is not sure whether all of the present incisors belong exclusively to S. cf. akashiensis or not, but it may be possible to assume from consideration to form of incisors that there were another species. Therefore, it is necessory to examine the coexistence of S. cf. akashiensis with Mammuthus paramammonteus shigensis (MATSUMOTO et OSAKI) in this stratigraphic level. Among them, the latter species is known as a zone species designated for the stratigraphic level of the present fossil bed in the Osaka Group.

View full abstract

A mass of granite, which is covered unconformably by the Silurian-Devonian Yokokurayama Formation, is discovered in the Yokokurayama Lenticular Body of the Kurosegawa Tectonic Zone of Mt. Yokokura, Kochi Prefecture, and is named the Yokokurayama Granite. It is composed generally of medium-grained, hornblende-biotite granodiorite with some coarse-grained, pegmatitic varieties. It is characterized by 1) reddish potassium feldspar, 2) low grade of or almost devoid of mylonitization, and 3) zoned plagioclase. It is distinguished clearly from granites of the Mitaki Igneous Rocks. Many of the pebbles, grains and fragments of granite found in the Silurian sequence are identified with the granites of the Yokokurayama Granite.

View full abstract

In this paper the relationships between the total benthic foraminiferal assemblages and the sediment characters, especially those of the fine grained part of sediment, were studied by using 17 dradge samples taken from the surrounding sea area of Kamae Bay, southern part of Oita Prefecture. As for the clustering, both MORISITA'S Similarity Index (1957) and SPEARMAN'S sum of variable formula (1963) were applied to benthic foraminiferal assemblages which 17 dradge samples contained. Consequently four groups were formed. Furthermore, 17 dradge samples were divided into five groups by the topographical features of sampling points. Such two kinds of groups resulted from the fact that the bottom sediment was formed under the influences of water movements, such as bottom current and wave turbulance, judging from the characters of fine grained part of sediment. Clay content, mud content and mean grain size of sediment probably represented the water movements mentioned above and clay content was the the most significant parameter tested.

View full abstract

In Tarama Island, an emerged shoreline at about 1.5m above MSL (mean sea level) is clearly indicated by emerged notches, benches and beachrocks, and by fossil barnacles and corals in a growing position. This shoreline, which represents the uppermost level reached by the sea during the Holocene, was left by a sea stand lasting a few thousand years. The consecutive sea-level fall from 1.5m to the present situation was probably a gradual and recent phenomenon (Fig. 2).

View full abstract

Some geological problems on the upheaval of the northern part of the Hidaka Belt, cased on the studies of the Miocene strata, Kitami-Takinoue region, are described. The Miocene strata can be divided into the following two units in ascending order; i. e., the Kamishiyubetsu Formation (early middle Miocene) and the Oshiraneppu-gawa Formation (middle Miocene). The coarse clastic materials in the lower part of the Kamishiyubetsu Formation have been derived from the Hidaka Supergroup, during early middle Miocene. After the deposition of the muddy facies in the upper part of the Kamishiyubetsu Formation, coarse clastic materials among the Oshirneppu-gawa Formation, i. e., sandstone, slate, phyllite, hornfels, granite, and other rocks, are supplied from N-S trending Uenshiri Horst Zone (NAKAMURA et al. 1980). The Uenshiri Horst Zone, at the Central part of the Hidaka Belt, became the mountain range during the early middle Miocene. This zone provides a large amount of coarse clastic materials to the sorrounding strongly subsiding the Ishikari-Teshio Belt and Okoppe-Shikaribetsu Belt area.

View full abstract