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Volume 39 (2000)
- Issue 6 Pages 489-
- Issue 5 Pages 411-
- Issue 4 Pages 283-
- Issue 3 Pages 189-
- Issue 2 Pages 107-
- Issue 1 Pages 1-
Volume 39, Issue 2
Displaying 1-5 of 5 articles from this issue
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Kaori Aoki, Fusao Arai2000 Volume 39 Issue 2 Pages 107-120
Published: April 01, 2000
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSA piston core (KH94-3, LM-8) was collected from the continental slope off the Sanriku district, east coast of northeast Japan. This core contains 14 tephra layers, the lowest of which is Aso-4. Identification of these tephras, based on the chemical compositions of the volcanic glass and the reflective indices of glass shards and minerals, indicate that there are widespread tephra from distal volcanoes in the Kyushu, Chugoku, and Hokkaido areas, as well as from the several volcanoes in the Tohoku district adjacent to the Sanriku.
There are some drift pumices (diameters are about 3-5mm) which accompanied two tephra layers in the LM-8 core- the Shikotsu-Daiichi and Towada-Hachinohe tephras. This is the first finding of drift pumice in the Shikotsu-Daiichi tephra.
The oxygen isotopic curve of the core LM-8 is so similar to the standard oxygen isotopic curve in the open ocean that the eruption ages of each of 14 tephras can be determined by the oxygen isotopic stratigraphy. We compared these ages with the calendar years converted from 14C ages on land of 4 tephra layers-Towada-Chyuseri, Towada-Hachinohe, Towada-Ofudo, and Shikotsu-Daiichi. There was close agreements between oxygen isotopic ages and converted 14C ages.View full abstractDownload PDF (1776K) -
Reconstruction from Wood and Pollen FossilsYayoi Kawamura, Norio Kito2000 Volume 39 Issue 2 Pages 121-138
Published: April 01, 2000
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe latest stage of the Last Glacial vegetation was reconstructed from wood and pollen fossils buried under Nigorikawa tephra (about 12, 000yrs BP), southwestern Hokkaido. Obtained wood fossil assemblages (including carbonized woods) were composed of Abies, Picea, Betula, Larix, and Rosa. Abies could be assigned to Abies sachalinensis and Larix could be Larix gmelinii, based on previous plant macrofossil studies. Arboreal pollen assemblages composed of Abies, Picea, Pinus, Betula, Alnus, Carpumus, and Ulmus were concordant with wood fossil composition. Non-arboreal pollen and spore assemblages are abundant in ferns associated with Artemisia, Gramineae, and Cyperaceae. Reconstructed forests are dominated with Abies, accompanied by Picea, Betula, Alnus, and Rosa, and herbaceous layers are composed mainly of ferns and small amounts of Artemisia, Gramineae, and Cyperaceae. Abies sachalinensis-dominated forests at the latest Last Glacial in the region are considered to reflect a milder climate than that of the Last Glacial Maximum.View full abstractDownload PDF (7515K) -
Nao Miyake, Kunito Nehira, Nobukazu Nakagoshi, Takahisa Hirayama2000 Volume 39 Issue 2 Pages 139-150
Published: April 01, 2000
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSVegetation changes were investigated by pollen analysis of forest soils under a temperate mixed forest in the southwestern part of the Tsurugi Mountains, Shikoku, Japan. The two soil profiles recorded vegetation changes that were caused by cutting practices on a large scale in the early Meiji period (the late 19th century). The previous vegetation type appears to have been an Abies firma-Tsuga sieboldii forest containing various broad-leaved trees, although Abies firma and Betula grossa are dominant in the present-day vegetation. The distribution patterns of several pollen types between the two soil profiles differed. These results may provide information about vegetation changes on a fine spatial scale.View full abstractDownload PDF (1517K) -
Shigeru Shimada2000 Volume 39 Issue 2 Pages 151-164
Published: April 01, 2000
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSKawagodaira volcano is a monogenetic volcano which is located on the northwest slope of Amagi volcano in the Izu Peninsula. Because the airborne pumice of Kawagodaira volcano (KGP) is distributed to the west, it is the most important Holocene marker tephra for dating archaeological remains in the Tokai region.
The study reported here shows the characteristics of the eruption of Kawagodaira volcano. The eruptive activity is divided into four continuous stages: I: pyroclastic surge eruption, II: Plinian eruption, III: pyroclastic flow eruption, IV: lava extrusion. In stage II, KGP was mostly blown by easterly winds; however, some KGP was distributed to the north, east, and south. In this way KGP reached the Tokai region, the southern Kanto region, some parts of the Chubu mountainous area, and the Kinki region. Because KGP was rarely affected by westerlies, it seems likely that Kawagodaira volcano erupted in summer. In stage III, co-ignimbrite ash fell at the north foot of Amagi volcano and to the west of it.
The time of eruption of Kawagodaira volcano was estimated at 3, 060-3, 190yrs BP based on the 14C ages of charcoals in the pyroclastic deposits, by tephrochronological study, and by the stratigraphic relationships between KGP and archaeological remains around the Izu Peninsula. However, it is necessary to determine the eruption age more precisely using dendrochronology in the future.
At the time when Kawagodaira volcano erupted, back swamps had been forming in the alluvial plains around the Izu Peninsula and Suruga Bay. Especially in the Seishin (Shizuoka-Shimizu) lowland, KGP was found in the peat layer of the upper alluvial deposits at many archaeological sites, suggesting that there were widespread shallow swamps at that time.View full abstractDownload PDF (2054K) -
Tabito Matsu'ura2000 Volume 39 Issue 2 Pages 165-170
Published: April 01, 2000
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSDokusawa tephra (Dks) is distributed in the northern part of Yamagata Prefecture, Northeast Japan. This study clarifies its petrographic properties, stratigraphic position, and distribution. It also discusses the locations of source vents and the eruptive age of Dks, and suggests a tentative correlation of Dks with specific tephra distributed in neighboring regions. The conclusions are as follows.
1. Dks is distinguished by its phenocristic biotite and cummingtonite.
2. The refractive index of volcanic glass (n) is 1.495-1.498, and that of cummingtonite (n2) is 1.665-1.671.
3. The mg-value of cummingtonite is 0.571-0.568.
4. The eruptive age of Dks is estimated as a bit later than 100ka because Dks is just above the Sanbe Kisuki tephra (100ka).
5. A source vent of Dks is presumably situated in the Hijiori caldera-Mt. Gassan-Mt. Hayama triangle or to its southwest, based on the Dks isopach.
6. Dks may correlate with Kitahara tephra (Kth) in the northern part of Miyagi Prefecture, because properties of Dks are quite similar to those of Kth.View full abstractDownload PDF (657K)
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