The Quaternary Research (Daiyonki-Kenkyu)

Phytolith Records from Tephra-soil Sequence since the Last Interglacial in the Southern Ishikari Lowland, Hokkaido, Japan

With Special Reference to the Fluctuation of the Sasa Group (Dwarf Bamboo) in Paleo-vegetation

Takashi Sase, Kotaro Yamagata, Mamoru Hosono, Jun Kimura

2004 Volume 43 Issue 6 Pages 389-400
Published: December 01, 2004
Released on J-STAGE: August 21, 2009

DOIhttps://doi.org/10.4116/jaqua.43.389

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We carried out phytolith analysis of the tephra-soil sequence since the Last Interglacial period in the southern Ishikari Lowland, Hokkaido. The Sasa group of so-called dwarf bamboo, one of the representative modern taxa, was a main component of the vegetation from Marine Oxygen Isotope Stage (MIS) 5e to the early half of MIS 5b. However, the Sasa group declined from the horizon of Aso-4 tephra (the late half of MIS 5b) to that of Kuttara-6 tephra (MIS 5b/5a), and then almost disappeared during the Last Glacial period when Pooideae was the most dominant of the Gramineae flora. Meanwhile the sub-boreal coniferous forests were estimated to have occurred at MIS 5b and MIS 3. The former was accompanied by the Sasa group like the present sub-boreal coniferous forest in Hokkaido, but the latter was not. It was after the early Holocene period that the Sasa group became a main component of the vegetation again.

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Last Interglacial Sea Level Changes Deduced from Coral Reef Terraces in Southwest Bohol, Central Philippines

Cherry L. Ringor, Akio Omura, Yasuo Maeda

2004 Volume 43 Issue 6 Pages 401-416
Published: December 01, 2004
Released on J-STAGE: August 21, 2009

DOIhttps://doi.org/10.4116/jaqua.43.401

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High precision α-spectrometric U-series dates for fossil corals from raised marine terraces in Pamilacan Island and from the neighboring Panglao Island and Punta Cruz in southwest Bohol were combined with previous data to re-examine the sea level history during the Last Interglacial and its implications to the tectonic setting of the area. Hermatypic corals were collected at elevations between 3-6m, 9-13m, and 20-27m apmsl (above present mean sea level) from three successive terraces in Pamilacan which have maximum elevations of 6m, 13m, and 27m apmsl. The dates of these corals cluster within 79-83ky, 101-108ky, and 122-131ky (from lowest to highest terrace) which correspond respectively to the marine isotope stages (MIS) 5a, 5c, and 5e. A constant rate of tectonic uplift ranging from 0.18-0.21m/ky in the past 125ky was estimated based on the published mean sea level data of 3-6m apmsl during MIS 5e. Using these local uplift rates, the respective paleo-sea levels during 5c (105ky) and 5a (82ky) are calculated to be 9-11m and 6-9m below present, which are consistent with uplift-corrected reef data estimates from Haiti, Barbados, and Huon Peninsula. The 5a paleo-sea level also coincides closely with the results from the submerged reefs of the tectonically stable Florida margin. The substantial agreement between the Pamilacan paleo-sea levels with those from different localities worldwide support the assumption of a constant uplift rate in the past 125ky. In contrast, the altitude of the sea level indicators correlated to the MIS 5e in Panglao and Punta Cruz are much lower, ≥12m apmsl, while that of 5c are ca. 5-6m apmsl. Minimum local uplift rates since MIS 5e ranges from 0.06-0.09m/ky, three times lower than that of Pamilacan. The estimated mean sea level during 5c is only a few meters (ca. 3m) below present indicating that uplift is not constant. Significant variation in the elevations of contemporaneous terraces at the three neighboring islands may have been greatly influenced by localized tectonic activity which puts the reported relative vertical stability of the region into question.

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Reconstruction of the Southern Channel of the Japan Sea at 3.9-1.0Ma

Akihisa Kitamura, Katsunori Kimoto

2004 Volume 43 Issue 6 Pages 417-434
Published: December 01, 2004
Released on J-STAGE: August 21, 2009

DOIhttps://doi.org/10.4116/jaqua.43.417

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Warm-water molluscs and planktonic foraminifers entered the Japan Sea from the East China Sea via the Tsushima Current. Their stratigraphic distribution in late Pliocene to early Pleistocene (3.9-1.0Ma) sediments provides a precise history of this southern channel into the Japan Sea. This study shows no direct evidence of inflow of the Tsushima Current from 3.9 to 3.1-3.0Ma. The current flowed into the Japan Sea rarely between 3.1-3.0 and 2.0Ma. Fossil records are incomplete for the 2.0 to 1.72Ma period (marine isotope stage 60), but there are no known occurrences of warm-water molluscs and planktonic foraminifers, except for MIS 69. At 1.72-0.98Ma (MIS 60-26), this warm current flowed into the Japan Sea during every interglacial highstand. Large numbers of the planktonic foraminifer Globorotalia inflata, a species which indicates that the southern channel had a water depth greater than at present (>200m), occur in MIS 57, 47, 45, 43, 41, and 29 with warm-water planktonic foraminifers. These results, combined with the global sea-level curve and the fossil record of land mammals in Honshu-Shikoku-Kyushu, imply that the minimum depth of the seaway between the East China Sea and the Japan Sea at 3.1-2.4Ma was about -10 to 35m relative to the modern sea level. The altitude of the seaway from 2.4 to 1.72Ma may have been the same as modern sea level, after which the southern channel deepened rapidly, by more than 200m, from MIS 59 to 57. This was probably related to rifting in the northern Okinawa Trough, which was associated with the onset of arc-normal subduction of the Philippine Sea plate at about 2.0Ma. This southern channel of the Japan Sea existed during all interglacial stages between MIS 59 and 27. It is possible that this channel persisted from MIS 47 to 41 (1.46-1.34Ma) and thereby severed the land connection between Asia and Honshu-Shikoku-Kyushu.

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Correlation among the Tephra Layers in the Lowest Daisen Volcanic Ash Formation, Western Japan, on the Basis of Their Petrographic Properties

Shigehiro Katoh, Tohru Yamashita, Tohru Danhara

2004 Volume 43 Issue 6 Pages 435-445
Published: December 01, 2004
Released on J-STAGE: August 21, 2009

DOIhttps://doi.org/10.4116/jaqua.43.435

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We determined the detailed petrographic properties (grain composition, heavy mineral composition, morphology and refractive indexes of volcanic glass shards, and refractive indexes of orthopyroxene, hornblende and cummingtonite phenocrysts) for the following nine tephra layers of the Daisen Volcanic Ash Formation in the Chugoku District: the Daisen Okutsu Pumice (DOP), hpm1 Pumice (hpm1), hpm2 Pumice (hpm2), Daisen Beshyo Pumice (DBP), and Daisen Hiruzenbara Pumice (DHP) Beds of middle Pleistocene age, and the Shitano-hoki (Sh), Odori Volcanic Sand (Od), Ueno-hoki (Uh), and Misen Pumice (MsP) Beds immediately above the Aira-Tanzawa tephra. The tephra layers are distinguishable by ratios of heavy mineral crystals to light ones and contents of cummingtonite and brown hornblende phenocrysts, and by refractive indexes of glass shards, hornblende, and cummingtonite crystals in spite of their similarity of heavy mineral composition, morphology of glass shards, and refractive indexes of orthopyroxene phenocrysts. In these tephra layers, it is possible that DOP is correlated with hpm1, because they have very similar petrographic properties and occur at the same relative stratigraphic and chronostratigraphic horizon with fission-track ages. A 50-cm thick tephra layer found in the northern part of Hyogo Prefecture, about 100km east of Daisen Volcano, is newly correlated with a DBP, indicating wide spread at least in the northern Kinki District.

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Holocene Sedimentary Environments and Relative Sea Levels at a Site along the Coast of Lake Tofutsu in the Eastern Part of Hokkaido, Japan

Hiroshi Sato, Isao Matsuda, Shigehiro Katoh, Takashi Matsubara

2004 Volume 43 Issue 6 Pages 447-455
Published: December 01, 2004
Released on J-STAGE: August 21, 2009

DOIhttps://doi.org/10.4116/jaqua.43.447

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We obtained the core sediment containing abundant molluscan shells at a site along the coast of Lake Tofutsu in the eastern part of Hokkaido, Japan. In order to clarify changes in sedimentary environments at this site, we analysed molluscan and diatom assemblages, and carried out sulfur analysis of sediments. These were then used along with three radiocarbon dates for molluscan shells to determine the marine limit (ML), which provides a relative sea-level (RSL) record approximating the height of the high water levels.
Intertidal molluscan shells are abundant in the sediments with the altitude below -0.23m. Crassostrea gigas is dominant accompanied by a warm-water species Trapezium (Neotrapezium) liratum below -1.33m, while Littorina (Neritrema) sitkana and Batillaria cumingii predominantly occurred between -1.33m and -0.23m. A shell of T. (N.) liratum at -1.40m showed the ¹⁴C age of 3, 320±60yrs BP, yielding an additional Holocene record of a warmwater species that lived in the coastal region along the Okhotsk Sea at that time. Diatom assembalges and sedimentary sulfur content more than 0.3% indicate marine influence for the range below+0.30m. The ML at +0.30m altitude identified by diatom and sulfur analyses is higher than that at -0.23m by the mollusca analysis. An intertidal diatom Pseudopodosira kosugii occurred between -0.23m and +0.02m, and Terpsinoe americana also occurred chracteristically between -2.08m and -1.33m, yielding reasonable RSLs for identifying the paleo-mean sea level (PMSL). These PMSL records with altitudes of -0.23m (1, 290±60yrs BP) and -1.40m (3, 320±60yrs BP) suggest relative subsidence during the late Holocene at the coast of Lake Tofutsu.

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