Bulletin of the Kitakyushu Museum of Natural History and Human History, Series A (Natural History)
Online ISSN : 2435-7545
Print ISSN : 1348-2653
Papers derived from the Symposium of Early Cretaceous Terrestrial Biota
Depositional environments and taphonomy of the bone-bearing beds of the Lower Cretaceous Kuwajima Formation, Tetori Group, Japan
Shinji IsajiHiroko OkazakiRen HirayamaHiroshige MatsuokaPaul M. BarrettTakehisa TsubamotoMikiko YamaguchiIchio YamaguchiTatsuya Sakumoto
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2005 Volume 3 Pages 123-133

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Abstract

The bone-bearing beds of the Lower Cretaceous Kuwajima Formation (Tetori Group) are described. Three facies of bone-bearing beds (Facies I: carbonaceous sandstones; Facies II: dark grey fine-grained silty sandstones; Facies III: dark greenish-grey mudstones) are present in inter-channel deposits that originated on a floodplain. The grain size of the sediments, and plant and molluscan fossils occurring in each bone-bearing bed, indicate that Facies I was deposited in a peat marsh, Facies II in a shallow lake, and Facies III in a vegetated swamp.

Isolated small bones and teeth are the most abundant vertebrate fossils. Common elements in Facies II are aquatic vertebrates such as fishes and turtles. Facies III is characterized by the occurrence of terrestrial lizards, tritylodontid synapsids and mammals. Vertebrate fossil assemblages in Facies II and III are not mixed with each other even though they both represent parautochthonous assemblages. In contrast, Facies I is allochthonous, and is composed mostly of reworked sediments from Facies II.

Depositional environments of the bone-bearing beds are strongly correlated with the composition of their fossil assemblages, indicating that different facies preserve the original faunal differences that existed between the shallow lake and vegetated swamp environments.

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