Well preserved molluscan fossils of Olenekian age (Early Triassic) were obtained from the upper part of the Bac Thuy Formation in Lang Son City, northern Vietnam. We report here an ammonoid, Xenoceltites variocostatus Brayard and Bucher, and describe two bivalve species, Crittendenia australasiatica (Krumbeck) and Crittendenia langsonensis sp. nov. Xenoceltites variocostatus is a characteristic species of the uppermost Smithian Anasibirites ammonoid zone and the earliest Spathian Tirolites ammonoid zone. Crittendenia australasiatica and C. langsonensis may thus be significant diagnostic species suggesting a middle Olenekian age. In addition, these occurrences demonstrate a probable faunal exchange between the eastern Tethys and eastern Panthalassa during the Olenekian, because many species of Crittendenia have been reported from Asia and from Panthalassic basins in the United States.
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1 April 2013
Crittendenia (Bivalvia) from the Lower Triassic (Olenekian) Bac Thuy Formation, an Chau Basin, Northern Vietnam
Toshifumi Komatsu,
Yasunari Shigeta,
Dang Tran Huyen,
Dinh Cong Tien,
Takumi Maekawa,
Gengo Tanaka
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Paleontological Research
Vol. 17 • No. 1
April 2013
Vol. 17 • No. 1
April 2013
Bac Thuy Formation
biostratigraphy
Crittendenia
Lower Triassic
northern Vietnam