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Volume 44 (2005)
- Issue 6 Pages 323-
- Issue 5 Pages 275-
- Issue 4 Pages 193-
- Issue 3 Pages 131-
- Issue 2 Pages 79-
- Issue 1 Pages 1-
Volume 44, Issue 2
Displaying 1-4 of 4 articles from this issue
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Naoya Iwamoto, Masami Kawaguchi, Yoshio Inouchi2005 Volume 44 Issue 2 Pages 79-92
Published: April 01, 2005
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe particle density of BDP 98 core sediments (total length 674m) drilled in Lake Baikal in 1998 is controlled by their diatom valve contents. Deposition of abundant diatom valves occurs during warm periods, and clay particles with few diatom valves deposit during cold periods. Paleoclimates around Lake Baikal are reconstructed based on these facts.
Climatic history recorded in the BDP 98 core during the last 6.5Ma can be roughly classified into three phases based on the variation of particle density: Phase 3 (6.5-3.2Ma) of constant lower density, Phase 2 (3.2-1.8Ma) of abrupt shift to higher density, and Phase 1 (1.8Ma-to present) of high amplitude density changes with overall higher density. Climatic changes shown in the particle density profile of Phases 3 to 1 show a rough similarity with the δ18O record of benthic foraminifers of marine sediment cores.
Particle density of the BDP 98 core of Quaternary, Phase 1, also has good similarity with the δ18O record in a scale of tens of thousands years. Therefore, sediment ages and sedimentation rates of this period can be estimated by comparing the particle density profile of the BDP 98 core with the oxygen isotope ratio curve. Further, the biogenic silica content in sediments can also be estimated by particle density of the BDP 98 core postulating some other factors. Diatom production (biogenic silica flux), calculated from both biogenic silica content in sediments and sedimentation rate, fluctuates periodically in concordance with the δ18O record. These results also reveal some local characteristics of the Lake Baikal region such as cold periods of 1.77-1.45Ma and 0.9-0.8Ma, distinct cold events in interglacial periods since MIS 9, and the presence of a clear 100-kyr-frequency since 1.5Ma.View full abstractDownload PDF (2766K) -
Miyuki Inagaki, Akio Omura, Hiroe Yagi, Michio Kato2005 Volume 44 Issue 2 Pages 93-106
Published: April 01, 2005
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSPleistocene marine terraces distributed in Kikai Island generally have three steps. They consist of mainly thick Middle Pleistocene and thin Upper Pleistocene sediments. The higher two terraces are composed of coral limestone and the lowest terrace, extensively developed southwest of this island, overlies carbonate sediments composed of well-preserved biogenic remains. We applied α-spectrometric Useries dating to three genera of solitary corals collected from the lowest terrace sediments. They provided reliable dates ranging from 96.6±2.8 to 56.7±2.2ky (2σ statistical error), corresponding to MIS 5b to 3. These can be divided into four age groups. The lithofacies and dates suggest that this sediment was deposited on the insular shelf during both relatively high and low sea stands. We can recognize the correlation between the age and elevation of samples; the oldest sample occurred at ca. 40m, the youngest at ca. 18m above present sea level (apsl). In addition, corals obtained from the proximal location of this terrace tend to show older ages, while corals from the distal site showed younger ones. Coral limestone is also sporadically distributed on this terrace. The youngest date obtained from them was 40.2± 1.2ky from a sample collected at the southwest end of the terrace, about 25m apsl. Dates of three other samples from the same site are comparable within the margin of error; the average was calculated to be 41.2±0.8ky. We infer that this terrace was formed in different depositional environments between MIS 5b and 3 with the fall of relative sea level: from the insular shelf where fore-reef sediments were deposited to the shallow water environment where coral reefs were formed. Thus, no Pleistocene carbonate sediments, younger than about 41ky (MIS 3), are exposed on the surface of Kikai Island.View full abstractDownload PDF (1903K) -
Nobuo Ooi, Naoko Kitada, Reiko Saito, Chihiro Miyagawa, Daihachi Okai2005 Volume 44 Issue 2 Pages 107-116
Published: April 01, 2005
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSPollen analysis was conducted for samples from the fine sediment parts of the Lower Sand and Gravel Layers under Naka-ikemi, Fukui Prefecture, Japan. Cluster analysis (Ward method) was performed for correlating the pollen assemblages distributed spatially in columnar sections. Six types of fossil pollen assemblage are recognized from the result of cluster analysis. Characteristics of pollen assemblage types are as follows:
type C: Cryptomeria pollen dominated with Alnus pollen.
type S: Cryptomeria pollen occupied about 90%.
type P: Pinaceae (Abies, Tsuga, Picea, Pinus subgen. Haploxylon) pollen dominated with Alnus pollen. Cryptomeria pollen was less than 2.2%.
type T: Tsuga and Cryptomeria pollen dominated with Pinaceae pollen.
type D: Pollen of deciduous broadleaf trees such as Quercus, Fagus, Ulmus/Zelkova dominated with Alnus pollen. Cryptomeria pollen was less than 7.9%.
type A: Alnus and Cryptomeria pollen dominated.
Types C, S, T and A are similar in the abundant occurrence of Cryptomeria pollen.
Four regional pollen assemblage zones, NKM-I to IV, were established based on the correlation of the pollen assemblages. NKM-I, which was dominated by Cryptomeria pollen (types C, S, T, A), and NKM-II, which was dominated by deciduous broadleaf tree pollen (type D), are correlated to MIS (marine isotope stage) 7. NKM-III, which was dominated by Pinaceae (Abies, Tsuga, Picea, Pinus subgen. Haploxylon) pollen (type P), is correlated to MIS 6. Dominance of Pinaceae pollen indicates a cold and dry climate. NKM-IV, which was dominated by Cryptomeria pollen (types C, A, D), again is correlated to MIS 5.View full abstractDownload PDF (2616K) -
Takanobu Sawagaki, Kazuomi Hirakawa, Shogo Iwasaki2005 Volume 44 Issue 2 Pages 117-125
Published: April 01, 2005
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSA buried wood piece was discovered in alluvial cone sediments in the Esaoman-Tottabetsu Valley, Hidaka Mountains, Hokkaido, Japan.The buried wood was identified as Pinus subgen. Haploxylon sp., and it should most probably be Pinus pumila. The AMS age of 12.3cal ka of the wood indicates that the alluvial cone might have been deposited during the Younger Dryas (YD), a globally recognized distinct cold climate phase of about 11-13cal ka during the last deglaciation. During the same period, distribution of cold flora was also recognized in the lowland area of Hokkaido, and this cold period is called the Kenbuchi Stadial. The sediments containing the wood are considered to be slope failure deposits which overlie a diamicton that might be subglacial till formed by the last glaciations. Thus, the identification and dating of the buried wood piece in the Esaoman-Tottabetsu Valley provide valuable and fundamental information to evaluate the alpine environments in Hokkaido, in relation to the significant rapid climate change of YD, in the course of global warming of the late-/postglacial periods.View full abstractDownload PDF (2773K)
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