Zhuravlevka Fm

Koppi-Luzhki zone of Eastern Sikhote-Alin Basin

The formation mainly comprises silty mudstones with subordinate interbeds of sandstones, siliceous rocks and tuffs and lava with a total thickness of up to 2000 m (Turbin, 1994; Markevich et al., 2000). The formation is subdivided into three members.

Lower member contains Buchia cf. volgensis and B. cf. uncitoides. Both species are characteristic of the Berriasian (Zakharov, 1981, 1987; Zakharov et al., 1997; Zakharov and Rogov, 2020). The member is considered as Berriasian. Middle member contains Buchia fischeriana, B. volgensis and B. cf. uncitoides in the lower part and B. uncitoides, B. ex gr. keyserlingi, B. cf. volgensis, B. cf. uncitoides, B. ex gr. sibirica, B. cf. visingensis (B. sibirica and B. visingensis are synonymized as B. keyserlingi by Zakharov, 1981), B. cf. pacifica in the middle part (Markevich et al., 2000). This latter assemblage is characterized by the presence of B. volgensis and B. uncitoides transited from the Berriasian and typically Valanginian B. keyserlingi, B. pacifica. This combination of species suggests lower Valanginian for the middle and upper parts of the middle member (Zakharov, 1981, 1987; Zakharov and Rogov, 2020). Upper member yields abundant B. keyserlingi, B. inflata, B. wollossowitschi, B. visingensis, B. sibirica (these three species are regarded as B. keyserlingi by Zakharov, 1981) and B. pacifica and rare B. uncitoides and B. volgensis (Markevich et al., 2000). This assemblage of Buchia is typical for the lower Valanginian (Zakharov, 1981, 1987; Zakharov and Rogov, 2020). The Valanginian range is also suggested by finds of ammonites Olcostephanus sp., Neohoploceras sp., Thurmanniceras ex gr. jenkinsi, Phyllopachyceras ex gr. trinitense in the upper member (Markevich et al., 2000). Also, fossil plants Coniopteris bureyensis, Onychiopsis cf. psilotoides, Cladophlebis sp. and Nilssonia ex gr. schaumburgensis have been reported from the upper member (Markevich et al., 2000).