- Review -
A case study on the relation between culture and building stones in Hokkaido, especially culture-geological investigations in the Otaru district [PDF for web-browsing 1.0 MB] [Hi-resolution PDF 13.0 MB]
Yoshiaki Matsuda
General Geology, Vol. 6, Page 1–12.
Abstract
There are four types of historical artifact and relic of different ages deeply related to stone in Hokkaido: stone tools made from obsidian in the Palaeolithic era, stone circles in the Late Jomon period, lithographs in the Sequel Jomon period, and buildings made of “Sapporo−Nanseki" and "Otaru−Nanseki" in modern age (from the Meiji period to the Early Showa period). Here, I focus on cultural significances of the following histrical artifacts related to stone: "Oshoro stone circle" in the Otaru district and "Nishizaki−yama stone circle” in the Yoichi district of the Late Jomon period, “Ancient lithographs of Temiya cave” and “Fugoppe cave” of the Sequel Jomon period , and welded tuff called “Sapporo−Nanseki" and subaqueous pyroclastic rocks, made of lappili tuff, pumice tuff, and tuffaceous sand stone called "Otaru−Nanseki" used as building stones in modern age. The investigations reveal that the culture related to stone in Hokkaido from the Palaeolithic era to the modern age was different considerably from that of the main island of Japan and there existed specific culture affected by local geology in Hokkaido.
- Article -
Exhumation of the high P/T Sanbagawa metamorphic rocks: Mechanism and process [PDF for web-browsing 1.4MB] [Hi-resolution PDF 3.7MB]
Kazuo Kiminami
General Geology, Vol. 6, Page 13–33.
Abstract
Exhumation of high P/T metamorphic rocks is a subject of ongoing debate. The Sanbagawa metamorphic belt is a typical high P/T metamorphic belt in Southwest Japan. Geodynamic cause(s) and process for the exhumation of the Sanbagawa metamorphic rocks are still debated, and yet to be resolved. Here, I examine depositional ages of the protoliths for the lowgrade (chlorite zone) metamorphic rocks in the Sanbagawa belt, eastern Shikoku, SW Japan, in addition to geologic structures of the Sanbagawa and Northern Chichibu belts, and propose a plausible scenario for the exhumation of the Sanbagawa metamorphic rocks described below.
1) The Sanbagawa belt represents underplated deeper facies of the Cretaceous Shimanto accretionary complex, but not the Jurassic Chichibu accretionary complex.
2) The depositional ages of the parent sediments of low-grade metamorphic rocks found in the Sanbagawa belt and the Jurassic Northern Chichibu belt, indicate a north younging polarity. In contrast, sedimentological evidence indicates younging to the south.
3) During a depositional stage of the main part (Campanian−Early Maastrichtian) of KS-II unit in the Northern Shimanto belt, a large volume of coarse-grained clastic sediments was deposited in the Shimanto trench, leading to active underplating, and consequently a wide forearc domain was uplifted as a domal structure, and dip and facing directions of beds in the Sanbagawa and Northern Chichibu belts have changed to the south.
4) Previously reported data on vitrinite reflectance and geologic structure indicate that the Northern Chichibu belt was part of the overburden formerly lying on the Sanbagawa metamorphic rocks.
5) The Sanbagawa belt, which was the domain of maximum exhumation, experienced extensional tectonics and subsequent normal faulting in the belt and at the both sides of the belt (Median Tectonic Line and the boundary fault between the Sanbagawa belt and Mikabu greenstones). The overburden above the Sanbagawa metamorphic rocks was removed by normal faulting and surface erosion during the latest Cretaceous and early Paleogene.
- Article -
Diatom assemblage and volcanic ash composition of the Karurusu Clay Bed in the Noboribetsu, Hokkaido, Japan [PDF for web-browsing 0.5MB] [Hi-resolution PDF 6.3MB]
Tsumoru Sagayama, Ikuo Izima and Masanobu Arakawa
General Geology, Vol. 6, Page 35-38.
Abstract
The Karurusu Clay Bed, lake sediments, spreads in the the Noboribetsu, central Hokkaido. It is said this bed deposited on dam up of paleo Chitose River by the Noboribetsu Pumice Flow Deposits. We analyses diatom fossils and intercalated volcanic materials in the bed. Result of diatom analysis shows the Pinnularia subcapitata (Ehr.) Greg. yields dominantly, and a lot of Pinnularia genus is also found. The volcanic materials is not correlated with other one for the present.
- Article -
Diatom biostratigraphy of the Isoya Formation, Neogene, in Isoya region, northern part of southwestern Hokkaido, Japan [PDF for web-browsing 0.9MB] [Hi-resolution PDF 1.3MB]
Makoto Sugawara and Tsumoru Sagayama
General Geology, Vol. 6, Page 39–46.
Abstract
Diatom fossils are obtained from the Siltstone Member of Isoya Formation, which is distributed in the Isoya coast in northern part of southwestern Hokkaido. The Isoya Formation has been regarded mainly as a Miocene stratum, but diatom analysis results of this paper show the geologic age of the formation is late Miocene to early Pliocene. The Shiribetsugawa Formation is widely distributed in the Rankoshi area to the east of the Isoya coast, covers the Isoya formation and has conventionally been considered to be the Pliocene stratum. However, the result of this paper indicates the possibility that the age of Shiribetsugawa Formation is early Pleistocene. The diatom analysis data is important for investigation of stratigraphy in the surrounding area. In the area south of the Kuromatsunai Lowland, the south of this area, microfossil strata have been investigated in detail by many studies. The Siltstone Member of Isoya Formation is compared with the Sumiyoshi siltstone Member of the Kuromatsunai Formation in the Imakane area.
- Article -
Appearance of the Paleo-Lake Kutchan deposits on the slope of Takasago, Kutchan-cho, Hokkaido, Japan [PDF for web-browsing 1.8MB] [Hi-resolutionPDF 14.8MB]
Takashi Inoue, Tatsuo Sekine, Satoshi Okamura, Ryo Odagiri and Tsumoru Sagayama
General Geology, Vol. 6, Page 47–56.
Abstract
We sketched the strata of the excavated slope on the west side of the Self-Defense Forces camp at Takasago, Kutchan-cho, and described the stratigraphy, sedimentary facies, and deformation structure. The strata of excavated slope is divided I, II and III units in ascending order, Unit I is eroded by Unit II, and Unit III unconformably overlying others. Unit I is mainly consist of “varved clay”, Unit II is consist of reworked Shikotsu Pumice Flow deposits, Unit III is consist of debris avalanche deposits. Unit I and Unit II are considered to sediments in the Paleo-Lake Kutchan. The upper part of the "varved clay" shows deformation structures such as folding and faults, which are considered to be caused by sediment sliding phenomena such as slumping.
It is clear that the depositional field and the depositional environment were not always stable throughout the depositional period of the "varved clay" and that the "varved clay" underwent some kind of movement in the later stages of deposition. Thrust fault, which displaces both the "varved clay" and the reworked Shikotsu Pumice Flow deposits, is observed near the southern end of the excavated slope. The formation of these geological structures occurred twice, before and after the deposition of reworked Shikotsu Pumice Flow deposits.
- Article -
Late Pleistocene to Holocene lacustrine deposits and ash fall (Ds-Oh) derived from the Daisetsu-Ohachidaira Caldera around the lower Yanbetsu River, northern coastal area of Lake Shikaribetsu in the eastern Hokkaido [PDF for web-browsing 2.1MB] [Hi-resolution PDF 21.9MB]
Takao Oka and Jun Ohnishi
General Geology, Vol. 6, Page 57–80.
Abstract
The Yanbetsu Formation cropped out around the lower Yanbetsu River, which flows into northern part of the Lake Shikaribetsu, was deposited in lacustrine environments. The formation was previously suggested to be Pleistocene (perhaps Middle Pleistocene) in age. The authors of this paper studied the Yanbetsu Formation by field work and geological analysis (AMS14C-dating, volcanic ashes analysis, pollen analysis). These analyses revealed that the Yanbetsu Formation is composed of middle terrace deposits (Tm; late of last glacial period) and lower terrace deposits (Tl; Holocene), which are parts of full deposits of Lake Shikaribetsu. The lake began with the damming of a river by the formation of new Shikaribetsu volcano group at about 4 to 5 ka. The age of 4 to 5 ka is derived from the observation that the tephra, Shikaribetsu purmice fall 2 (Sipfa-2), is laid below 1 m from the Shikotsu purmice fall 1 (Spfa-1), which has 4.6 ka of age, in the terrace deposit of Kamishihoro town. Furthermore, the authors found the Daisetsu-Ohachidaira ash fall (Ds-Oh), which is derived from the formation of Ohachidaira Caldera in Daisetsu volcano area, in the uppermost part of middle terrace deposits.
- Report -
Recent seismic activity in and around Hokkaido, Japan (2018-2021) [PDF for web-browsing 0.4MB] [Hi-resolution PDF 2.1MB]
Tetsuo Takanami
General Geology, Vol. 6, Page 81–84.
- Note -
History of the floods on the southern shore of Lake Shikotsu [PDF for web-browsing 0.8MB] [Hi-resolution PDF 7.6MB]
Seigo Miyasaka
General Geology, Vol. 6, Page 85–91.
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