化石
Online ISSN : 2424-2632
Print ISSN : 0022-9202
ISSN-L : 0022-9202
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特集：西部上総層群のたまりはじめの頃（東京西部にたまった上総層群）2
  • 多摩川水系中・上流域に分布する上総層群から産出した浅海性硬骨魚類化石の概要
    宮田 真也, 尾﨑 薫, 福嶋 徹, 樽 創
    2024 年 115 巻 p. 5-17
    発行日: 2024/03/31
    公開日: 2024/03/31
    DOIhttps://doi.org/10.14825/kaseki.115.0_5
    ジャーナル フリー
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    The Plio-Pleistocene Kazusa Group, situated in the middle and upper basin of the Tama River in Northwestern Tokyo, Japan is known to have yielded various vertebrates, including both terrestrial and marine mammals as well as chondrichthyan fishes. Recently, osteichthyan fish fossils have been discovered from this stratum. Notably, marine fish fossils have been discovered in the Oyabe, Hirayama, Komiya, Oyamada, and Renkoji formations of Kazusa Group. Of these formations, the Oyabe Formation has revealed Clupeiformes and the first East Asian fossils of the Plotosidae, while the Renkoji Formation has yielded Clupeiformes, Clupeidae, Engraulidae, and the second recorded occurrence of the Mugilidae in Japan. These recent discoveries suggest that the Kazusa Group in Northwestern Tokyo has the potential to be a significant stratum for the study of Quaternary marine fossil osteichthyan fishes.
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  • 関東地方西部の上総層群狭山層に含まれる約130万年前の大型植物化石群集とその植物層序学的意義
    福嶋 徹, 鈴木 毅彦, 百原 新
    2024 年 115 巻 p. 19-32
    発行日: 2024/03/31
    公開日: 2024/03/31
    DOIhttps://doi.org/10.14825/kaseki.115.0_19
    ジャーナル フリー
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    We reinvestigated the composition and stratigraphical position of a plant macrofossil assemblage including Metasequoia glyptostroboides and Davidia involucrata, which has been reported from the upper part of the Sayama Formation, Kazusa Group in the Sayama Hills, west Kanto region. This fossil assemblage is composed of 24 taxa, including warm temperate plants such as Paliurus sp., Triadica sebifera var. pleistoceaca, and Vernicia sp., which indicate their deposition during an interglacial stage. Cool temperate taxa in the assemblage such as Picea sp. (sect. Picea) and Styrax obassia were possibly transported from mountains surrounding the sedimentary basin. We determined petrographic properties of tephra at the horizon immediately above the plant fossil layer. This shows that this tephra can be correlated to the Zoshiki tephra (ZSK) deposited in ca. 1.3 Ma. Stratigraphic occurrence of exotic taxa between the late Pliocene and Early Pleistocene in southwest Kanto region is similar with that in central Kinki region, which was influenced by warm and oceanic climate in this region facing the Pacific Ocean.Whereas, the ages of appearance of cold-loving plants as Picea maximowiczii in southwest Kanto region were earlier than those in Kinki region, which is possibly caused by distribution of mountains with high altitude areas where cold-loving plants have invaded much earlier.
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  • 京都市岩倉川の三畳紀放散虫年代と微小球体
    石田 昂汰朗, 鈴木 寿志, 小木曽 哲
    2024 年 115 巻 p. 43-52
    発行日: 2024/03/31
    公開日: 2024/03/31
    DOIhttps://doi.org/10.14825/kaseki.115.0_43
    ジャーナル フリー
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    The present authors conducted biostratigraphic research using fossil radiolarians on a continuous bedded chert sequence exposed on the riverbed of Iwakura River, Sakyo Ward, Kyoto City. The indicated geological ages of the chert sequence are as follows: (1) The lower to middle horizons: Anisian of the Middle Triassic, (2) the upper horizons: Anisian to Ladinian of the Middle Triassic, and (3) the uppermost horizon: Ladinian of the Middle Triassic to Carnian of the Late Triassic. Furthermore, glass and iron-rich microspherules were obtained from the chert beds. The chemical composition of the glass spherule is close to the spherules found in tephra deposits from the southern Payenia province of Argentina. However, further investigations are needed to clarify their origins.
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  • 長野県松本市の中部中新統別所層より産出したチューブワーム化石
    延原 尊美, 小池 伯一, 井尻 暁
    2024 年 115 巻 p. 53-64
    発行日: 2024/03/31
    公開日: 2024/03/31
    DOIhttps://doi.org/10.14825/kaseki.115.0_53
    ジャーナル フリー
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    The fossil record of tubeworms is scarce compared to that of chemosynthetic bivalves although tubeworms are one of the dominant inhabitants among seep and vent faunas at present. This study reports tubeworm fossils observed on a float of muddy dolomite concretion from the Middle Miocene Bessho Formation, central Japan. Vesicomyid bivalve fossils with seep carbonates have been reported from many localities of the Bessho Formation. The concretion float contains abundant tubes, 1 to 4 mm in diameter, with no surface ornamentation and their inner space filled by chalcedony. In microscopic view, the tubes consist of flexible multi-layered organic sheets, over 100 µm thick, which were deformed and delaminated. The tubes gently curve and are unbranched, elongating in an almost same direction; they form aggregation patches, separated from each other in matrix-supported condition. The tube aggregate matrices are more calcareous than the muddy surroundings. The tube size, wall structure and aggregation in calcareous patches are similar to posterior ‘root’ tubes of vestimentiferans in present seep sites such as the Gulf of Mexico and Congo deep-sea fan. Our study represents the first fossil record of tubeworms from a dolomite concretion, suggesting that silicification could be an important factor for fossil preservation of flexible tubes against sub-bottom fluidization, deformation, and dissolution of initial calcium carbonates.
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