All issues
Volume 40, Issue 1
Displaying 1-7 of 7 articles from this issue
- |<
- <
- 1
- >
- >|
-
Chiho Sekiguchi2001 Volume 40 Issue 1 Pages 1-17
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThree peat cores were obtained by boring surveys for pollen analysis from the Kitadobu bog, the Chayaike bog, and the Numanohara bog to reveal the vegetational changes since the Last Glacial Period in the mountains around Iiyama basin, central Japan. Marker tephras AT, K-Ah, On-Kt, As-K, My-A, and My-Ot were recognized in the cores. It is clear that the deposits of the Chayaike bog were produced since the beginning of the Last Glacial Period.
Six regional pollen zones can be distinguished in this area. The ages, durations, and boundaries between the pollen zones were calculated from depositional rates on the basis of the marker tephras and 14C datings.
The vegetational changes reconstructed from these pollen zones are as follows. IB-I zone: temperate coniferous and deciduous forest in the first half of the Last Glacial Period (from ca. 93, 000 to ca. 74, 000yrs BP); IB-II zone: boreal coniferous and deciduous forest before AT was deposited (from ca. 26, 000 to ca. 25, 000yrs BP); IB-III zone: boreal forest dominated by conifer and Betula in the cold phase of the Last Glacial Period (from ca. 18, 000 to ca. 14, 000yrs BP); IB-TV zone: Betula-dominated forest in the Late Glacial (from ca. 14, 000 to ca. 10, 000yrs BP); IB-V zone: Fagus-dominated forest in the Holocene including the Climatic optimum (from ca. 10, 000 to ca. 4, 000yrs BP); IB-VI zone: Fagus-dominated forest with increased coniferous forest (from about 4, 000yrs BP).
The Fagus-dominated stage in the Post Glacial Period in this area suggests that Fagus crenata forest was formed and spread since about 10, 000yrs BP; the vegetation change reveals that this area has become a heavy snowfall area since the Post Glacial Period.View full abstractDownload PDF (2457K) -
Makiko Watanabe, Takayuki Kobayashi2001 Volume 40 Issue 1 Pages 19-28
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSPg fraction of humic acid is one of the components of humic substances extracted from soils and terrestrial sediments; it is characterized by the presence of green pigment. This green pigment derives from metabolites of many species of fungi and is widely distributed in world soils. In this paper, the vertical distribution of Pg absorption strength was obtained for the tephra soil sequence consisting of 6 representative tephras in southern Kyushu. The chronological sequence of Pg absorption strength, which covers ca. 100ka, shows good correspondence to the marine oxygen isotope curve up to stage 5a. From the analytical results of inorganic components, we clarified that Pg exists with iron oxides such as geothite and ferrihydrite. Strong fluctuation of Pg absorption was recognized in oxygen isotope stage 3, which was considered to correspond to the strength of past weathering and leaching process. This assumption was also supported by the distribution of silica/alumina ratio and alumina/mobile bases ratio in the profile. We confirm that Pg fraction of humic acid remains in tephra soil sequences as a signal of past environment, and indicates the strength of leaching controlled by the relative strength of precipitation and evaporation.View full abstractDownload PDF (1738K) -
Takehiko Suzuki2001 Volume 40 Issue 1 Pages 29-41
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe Iizuna-Kamitaru Tephra Group, which consists of three distinctive fallout tephras (Iz-KT a to Iz-KT c in descending order), erupted from the Iizuna volcano, a Quaternary stratovolcano of the Myoko Volcano Group in central Japan. The purpose of this paper is to describe the characteristic properties, distribution, and stratigraphic position in several areas of this group, to discuss its age, and to show the possibility of applicative studies. Iz-KT a (9.8km3), the most widespread tephra of the group, is a plinian deposit distributed in the boundary area between Nagano and Niigata prefectures, north part of Gunma and Tochigi prefectures. Iz-KT a is petrographically identified by min eral composition, characteristic shape of orthopyroxene, refractive indices of orthopyroxene (γ: 1.707-1.716) and hornblende (n2: 1.673-1.687), and chemical composition of titanomagnetite (FeO: 82.0-82.5%, TiO2: 5.9-6.0%). Stratigraphic positions of the Iizuna-Kamitaru Tephra Group in the tephra sequence of distal areas and radiometric ages by the K-Ar dating method carried out in proximal areas show that the deposition of the group occurred between 150ka and 125ka of the transition from the marine isotope stage 6 to 5. This group is useful for identification of climatic fluvial terraces formed in the glacial stage of marine isotope stage 6, and provides a datum plane for eruptive histories of several Quaternary volcanoes in this area.View full abstractDownload PDF (2651K) -
Shin'ichi Sato2001 Volume 40 Issue 1 Pages 43-51
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSSpatial distributions of bivalves and gastropods on the mud flat of Isahaya Bay, western Kyushu, were studied. In Isahaya Bay, a vast expanse of mud flat (3, 550ha) was closed off from the Ariake Sea on April 14, 1997, by the construction of a dike for reclamation. Since that time, it has been possible to walk on the dried mud flat and see the numerous dead shells exposed by the reduction of the mud surface. The spatial distribution of each species is as follows. 1) Tegillarca granosa was very dense (>30 ind./m2) at the lower part of the dried mud flat, ca. 1 to 2km from the former mean high water point of the spring tide (MHWS). 2) Cerithideopsilla djadjariensis, Tellina (Moerella) iridescens and Estellacar olivacea were distributed at the middle part of the dried mud flat, ca. 0.5 to 1km from the former MHWS. 3) Glauconome chinensis was especially dense at the uppermost part of the dried mud flat near the former MHWS and ranged as far as the former mean high water of neap tide (MHWN). These facts suggest that there were three separate zones of mollusks arranged parallel to the water level on the tidal mud flat of Isahaya Bay.View full abstractDownload PDF (2647K) -
Masayuki Toyoshima, Tsutomu Soda, Shigeru Kitamura, Fusao Arai2001 Volume 40 Issue 1 Pages 53-59
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe geomorphic chronology of the Late Pleistocene age in the Sendai area remains unclear, although the Dainohara terrace was assigned to the last interglacial stage on the basis of topographic, geologic, and palynologic features. This paper reviews tephrochronological and paleopedological data and discusses the chronology of the Late Pleistocene terraces, with special reference to the Dainohara terrace.
A fine ash layer, which is called Aob in this paper, has been discovered above the Medeshima Pumice deposited after the completion of the Dainohara terrace. Mineral assemblage, refractive indices, and chemical compositions (major elements) of glass shards indicate that the Aob ash is correlative with the Onk 1-3 ash occurring in northern Miyagi Prefecture, which is between the Toya (103-123ka) and the Aso-4 (84-89ka). Red paleosol, which was dated to stage 5e (120-130ka) by δ18O, has not been found on the Dainohara terrace, although it covers the Aobayama-III terrace that precedes the Dainohara terrace. Moreover, recent palynological discoveries suggest that the fossil pollen assemblage seen with temperate forests and observed in Dainohara terrace deposits appears not only in interglacial stages but also in the interstadial stages. These data indicate that the formation of the Dainohara terrace should be assigned to stage 5c and is subsequent to stage 5e.View full abstractDownload PDF (935K) -
Hideaki Nagamori, Masakazu Hayashi2001 Volume 40 Issue 1 Pages 61-66
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSSeveral proboscidean footprints were recovered from the Lower Pleistocene Uonuma Formation at the Tagawa River in Tokamachi City, Niigata Prefecture. The stratigraphic horizon containing the trace fossils was between the SK110 and SK050 tephra beds (ca. 1.6-1.2Ma). The trackmaker was most likely Stegodon aurorae (Matsumoto), based on the proboscidean biostratigraphy of Japan. These trace fossils compensate for the otherwise poor record of land mammals in the Uonuma Formation. The paleoenvironment of the bed containing the traces was interpreted, on the basis of associated fossils, to have been a marsh associated with marshy woods and areas of standing water. It is likely that additional fossil footprints are present in the swamp deposits of the Uonuma Formation.View full abstractDownload PDF (1429K) -
Daisuke Hirouchi, Ken-ichi Yasue2001 Volume 40 Issue 1 Pages 67-74
Published: February 01, 2001
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe newly found Kentoyama fault runs through the northeastern part of Fukui plain, and its trend is nearly N-S. Based on the observation of its fault outcrop, Kentoyama fault is composed of a set of three faults, and it deforms marine terrace deposits and sand dune deposits. The strike and dip of the fault surface are N7°-15°and 62°E-90°, respectively.
The vertical slip rate of the Kentoyama fault is at least 0.04-0.12m/ky. We cannot estimate the fault scarp on the terrace surface, due to the thick sand dune deposits.
As the trend of the Kentoyama fault, which extends N-S direction, corresponds with that of the eastern marginal faults of the Fukui plain, the fault is considered to be an extension of the eastern marginal faults of the Fukui plain.View full abstractDownload PDF (1336K)
- |<
- <
- 1
- >
- >|