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Discovery and significance of erect fossil stumps from the Upper Triassic Momonoki Formation of the Mine Group, SW Japan

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Yukawa, Hirokazu | Oyama, Nozomu | Shinoda, Kenji | Takahashi, Humio

Edité par CCSD -

National audience. Five erect fossil stumps (ES-1 to -5) were discovered in the Upper Triassic Momonoki Formation, Mine Group, Yamaguchi, Japan. The outcrop at the Mine fossil collection facility where the erect fossil stumps were discovered is located in the upper part of the Momonoki Formation, between the Upper Coal Bed and about 50 m above this bed. Each specimen was carbonized, and although none were identified as species, some had roots extending laterally and along the strata. The largest erect stump was up to 30 em wide and 60 em tall (ES-2), and some roots extending laterally from the primary root were about 40 em wide (ES-1). There were also traces of fine roots with diameters of 0.2 em or less, indicating that there was a lot of vegetation other than those identified as erect stumps. Fossilized erect stumps and root traces, when found in sedimentary rocks, are important evidence to identify them as paleosols. It is also direct evidence that vegetation grew in the area, indicating that the strata in which erect stumps and roots are found were once exposed to the surface of the earth. This means that both Bar-top and Over bank sediments in the study area have paleosols and have been exposed to the earth' s surface for a period of time. These erect stumps reported from the Momonoki Formation are the oldest record including those of unidentified species.

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