Kobiwako Group Research Articles

Two New Species of the Diatom Genus Praestephanos from the Pliocene Ueno Formation, Kobiwako Group, Mie Prefecture, Japan

Two New Species of the Diatom Genus Praestephanos from the Pliocene Ueno Formation, Kobiwako Group, Mie Prefecture, Japan

Supercritical-flow sedimentary structures of fluvial deposits in the Plio-Pleistocene Katata Formation, Kobiwako Group, Japan

鮮新-更新統古琵琶湖層群，堅田層の河川性堆積物からアンティデューンやサイクリックステップやシュートアンドプールなどの高流砂階で形成されたと考えられる堆積構造をみいだした．それらの堆積構造の特徴は，（1）上流への堆積を示すバックセット葉理とバックステッピング構造，（2) S字状葉理，波状葉理，HCSもどきの葉理，（3）侵食基底面をもつ下に凸の弓状の充填層と礫·砂·泥の分離，（4）等間隔で非対称の侵食基底面，（5）粒径の異なる部分の混在，などである．これらの堆積物は高流砂階の高いエネルギーのもと，内部で流況が激しく変動した結果つくられたものである．高流砂階の堆積構造を含む氾濫層は堆積速度が大きく，流れに多量の浮遊泥が含まれていたため，多様な堆積構造が記録されたと考えられる．また，高流砂階の堆積構造が多くみられる地層での古流向の解析には，その堆積構造の認定が重要となる．今後，いろいろな堆積環境からさまざまな高流砂階の堆積構造をみいだすことが，その多様性の解明と形成過程を考える上で重要になる．

Fossil diatom flora from the uppermost part of the Gamo Formation of the Kobiwako Group in Central Japan

Fossil diatom flora from the uppermost part of the Gamo Formation of the Kobiwako Group in Central Japan

O-47 広域なテフラ層序からみた古琵琶湖層群下部の層序と年代(5.地域間層序対比と年代層序スケール,口頭およびポスター発表,一般講演)

O-47 広域なテフラ層序からみた古琵琶湖層群下部の層序と年代(5.地域間層序対比と年代層序スケール,口頭およびポスター発表,一般講演)

Fossil record of common carp, genus Cyprinus, from the Ayama Formation of the Kobiwako Group

Fossil record of common carp, genus Cyprinus, from the Ayama Formation of the Kobiwako Group

A new species of the fossil cyprinid fish, Cyprinus (Mesocyprinus) okuyamai, from the Pliocene Ueno Formation of the Kobiwako Group in the Ueno Basin, Mie Prefecture, Central Japan

A new species of the fossil cyprinid fish, Cyprinus (Mesocyprinus) okuyamai, from the Pliocene Ueno Formation of the Kobiwako Group in the Ueno Basin, Mie Prefecture, Central Japan

Modeling for a change in the outflow direction on depositional basin of the Kobiwako Group, central Japan

Modeling for a change in the outflow direction on depositional basin of the Kobiwako Group, central Japan

Composition and paleoenvironment of wetland forests dominated by Glyptostrobus and Metasequoia in the latest Pliocene (2.6 Ma) in central Japan

A latest Pliocene (2.6Ma) wetland forest vegetation that was dominated by Glyptostrobus and Metasequoia was reconstructed from in situ woods, fruits and seeds, and pollen assemblages in deposits of the Kobiwako Group exposed in the Yasu River, Shiga Prefecture, central Japan. Based on species composition of stumps and autochthonous plant macrofossil assemblages in the fossil forest beds and their sedimentological assessments, habitat partitioning of Glyptostrobus and Metasequoia was clarified. The forest floor of Glyptostrobus dominant stands were covered by wetland plants, including Cyperaceae and submersed herbs. Size class distribution of stumps indicates that Glyptostrobus regenerated continuously and grew over a long period of time in a stable environment in a water-logged backmarsh. Metasequoia dominant stands were established in environments drier than those dominated by Glyptostrobus, and were accompanied by forest floor herbs and shrubs with mesic habit preferences. The upland forest vegetation reconstructed from allochthonous assemblages in sandy channel-fill deposits was mixed coniferous and deciduous broadleaved tree forest that was dominated by Picea, and included trees now extinct in Japan, such as Sequoia, Cunninghamia, Cyclocarya, and Fagus microcarpa. Sciadopitys and Cathaya, represented only by pollen, grew on mountain slopes and ridges away from the river. Their habitats did not extend to backmarshes in the lowlands during the Neogene and the Early Pleistocene in East Asia. Paleotemperature reconstructed from plant macrofossil assemblages indicates the temperature conditions typical of the lower boundary of the cool temperate deciduous broadleaved forest zone. The occurrence of Glyptostrobus and Metasequoia in another fossil forest in the Early Pleistocene (1.8–1.9Ma) in the same sedimentary basin demonstrates their tolerance to cool-temperate climates.

Stratigraphic reexamination for a lower part of the Kobiwako Group, central Japan

琵琶湖周辺に分布する古琵琶湖層群は日本の鮮新-更新統として代表的な陸水成層として研究対象とされてきたが，近年になってその最下部層序の間違いが指摘されている．その間違いを修正するために，33の火山灰層の調査が行われ，広域テフラやそれぞれの対比の検討を行った．その結果，6層の火山灰層が対比され，それによって，最下部層序が確立された．また，修正された層序によれば，古琵琶湖層群はおよそ4.4 Maにこの地域の東部で形成がはじまり，この時代の地形的制約によって西部は遅れて堆積が開始されたことが明らかにされた．

Correlation of Ogotooogi tephra from Kobiwako Group with Ks7.03 tephra from Kazusa Group

Correlation of Ogotooogi tephra from Kobiwako Group with Ks7.03 tephra from Kazusa Group

The old and newly defined Pliocene-Pleistocene boundary sites of the Kobiwako Group, central Japan

近年，第四紀が正式な地質年代区分の一つとしてその定義が国際地質学連合（IUGS）に承認された．第四紀の始まりは更新世の始まりでもあり，地層としての第四系の下限は，鮮新−更新統境界という意味でもある．鮮新−更新統境界の新定義は1980年代に決められた旧定義より下げられ，年代的には約80万年古くなった．本コースでは，近畿地方において旧定義と新定義における鮮新−更新統境界の両方が観察できる古琵琶湖層群において，両者を露頭観察するとともに，陸域における地層にとっての鮮新−更新統境界の意味を考える．

585 Palaeoecology of fossil forests dominated by Metasequoia and Glyptostrobus in the Plio-Pleistocene Kobiwako Group, Central Japan

585 Palaeoecology of fossil forests dominated by Metasequoia and Glyptostrobus in the Plio-Pleistocene Kobiwako Group, Central Japan

Development and Evaluation of Teaching Materials for Understanding the Debris Flow with Gravels in the Kobiwako Group : the Observation Lesson "Square-shaped Gravels and Round Gravels"

Development and Evaluation of Teaching Materials for Understanding the Debris Flow with Gravels in the Kobiwako Group : the Observation Lesson "Square-shaped Gravels and Round Gravels"

Paleovegetation reconstruction of fossil forests dominated by Metasequoia and Glyptostrobus from the late Pliocene Kobiwako Group, central Japan

ABSTRACT A late Pliocene (1.8–1.9 Ma) wetland fossil forest community that was dominated by Metasequoia and Glyptostrobus was reconstructed based on the species composition of the stumps and other plant macrofossil assemblages. The plant fossils were recovered from a fossil forest preserved in deposits of the Kobiwako Group that are exposed in the Echi River, Shiga Prefecture, central Japan. Fossil wood of Metasequoia and Glyptostrobus was distinguished based on anatomical characteristics. Apportionment of the wood from different horizons in the fossil forest indicates Metasequoia grew over a long period of time in a stable environment, while Glyptostrobus and Alnus grew in unstable environments characterized by shortinterval floods. The fossil forest as a whole represents a fluvial back-marsh environment. The upland forest was composed of mixed evergreen conifers and deciduous broad-leaved trees including Chamaecyparis pisifera, Tsuga, Magnolia, and Acer. Aquatic and wetland herbs such as Cyperus, Carex,...

Plant macrofossil assemblage from the Hata Formation, Kobiwako Group, in the late early Pleistocene, Japan

Plant macrofossil assemblage from the Hata Formation, Kobiwako Group, in the late early Pleistocene, Japan

Vivianite and siderite from the Kobiwako Group, Takashima, Shiga Prefecture, Japan(Photo)

Vivianite and siderite from the Kobiwako Group, Takashima, Shiga Prefecture, Japan(Photo)

Vivianite and siderite from the Kobiwako Group, Takashima, Shiga Prefecture, Japan

Vivianite and siderite from the Kobiwako Group, Takashima, Shiga Prefecture, Japan

古琵琶湖層群甲賀累層（鮮新統）よりＣａｔｈａｙａ（Ｐｉｎａｃｅａｅ）花粉の発見

Cathaya (Pinaceae) pollen was discovered from the Pliocene Koka Formation of the Kobiwako Group, Shiga Prefecture, Japan. The pollen morphology was examined with the light and scanning electron microscopes. The characteristics indicate that the bisaccate pollen is Cathaya. This discovery suggests that further study on the pollen flora of the Plio-Pleistocene Kobiwako Group will clarifythe disappearance process and horizon of Cathaya in the area with relation to the climate change.

Fossil Ginkgo biloba leaves from the Plio-Pleistocene Kobiwako Group in Shiga Prefecture, southwestern Japan

Fossil Ginkgo biloba leaves from the Plio-Pleistocene Kobiwako Group in Shiga Prefecture, southwestern Japan

Fossil bagrid catfishes from Japan and their zoogeography, with description of a new species,Pseudobagrus ikiensis

Morphological characteristics of fossil bagrid catfishes from six Miocene to Pleistocene localities in Japan are described. A new species of the Middle Miocene bagrid,Pseudobagrus ikiensis, is described, based on five nearly complete specimens (ca. 19 cm SL) and one half-body specimen from the Chojabaru Formation (15 Ma) of the Iki Group in Nagasaki Prefecture. The species is diagnosed by a unique combination of characters: 14–16 anal fin rays, 44–47 vertebrae, deeply forked caudal fin, pectoral spines with serrations on the anterior edge and supraoccipital process extending to the first pterygiophore of the dorsal fin.Pseudobagrus ikiensis is morphologically close to the extantP. fulvidraco, which is widely distributed in China, Siberia and the Korean Peninsula, suggesting that both lineages had appeared by the Middle Miocene. All other fossil specimens are from the Pliocene (3–4 Ma) Ueno Formation (lowest Kobiwako Group, Ohyamada, Mie Pref.) and Tokai Group (Tsu, Mie Pref.), and Pleistocene cave deposits (Inasa, Shizuoka Pref., Mine, Yamaguchi Pref. and Kanogawa, Ehime Pref.). These are incomplete, comprising mainly dorsal and pectoral spines. Being indistinguishable from the extantP. nudiceps, they are thus considered to be included in that lineage. Although the geological distribution of these Plio-Pleistocene fossils nearly overlaps that of the extantP. nudiceps (west of the Suzuka Mountains), fossil specimens have also been found in the Ise Bay area (Tsu), whereP. ichikawai is the only extant bagrid, and further east (Inasa). Based on evidence that the latter is not a sister species ofP. nudiceps, the distribution of the fossils indicates that the range ofP. nudiceps was restricted to west of the Suzuka Mts. during the Pleistocene or Holocene.