Donganzhen Fm
Type Locality and Naming
NE Heilongjiang, border with Russia. It was named by Ma Wanchang, Fu Lei in 1982. The naming section is located in the vicinity of the mountain root of the Nanshan Mts, Dong'an Township, Raohe County, Heilongjiang Province.
Synonym: （东安镇组）, Dong'anzhen Fm.
Lithology and Thickness
The Dong'anzhen Formation is a fully marine deposit composed of siltstones with silty shales in the lower part, and siltstones, silty mudstones, and sandstones in the upper part. Lower subformation of it represents an alternating layer of grey-black, grey-green and yellow-green argillaceous fine-grained sandstones and siltstones with silty shale, with a thickness of about 19 m. Upper subformation represents grey-black, dark-grey and grey-green fine-grained sandstone, siltstone, argillaceous siltstone, with the top part containing greywacke-fine-grained quartz-sandstone, siltstone and epi-metamorphic greywacke-siltstone, with a thickness of over 405 m..
Relationships and Distribution
Lower contact
Not exposed.
Upper contact
Disconformably overlain by Cenozoic (Hulin Fm of Eocene).
Regional extent
Distribution of the particular formation is limited, and being exposed only in the area of Raohe River in Heilongjiang Province, and extending easterly into the territory of Russia.
GeoJSON
Fossils
Lowermost part of the Dong'anzhen Formation contains a middle Volgian (Zakharov, 1981) buchiid assemblage including B. russiensis and B. fischeriana. This assemblage is replaced upward by an assemblage including B. fischeriana and B. unschensis. The latter assemblage corresponds to the upper Volgian-lower Ryazanian (Zakharov, 1981, 1987; Zakharov and Rogov, 2020). The assemblage including B. volgensis, B. cf. subokensis, B. cf. okensis and B. unschensis is identified from the overlying strata. This assemblage characterizes the lower Ryazanian (Zakahrov, 1981, 1987; Zakharov and Rogov, 2020). Uppermost part of the section contains B. pacifica. Note that according to Zakharov and Rogov (2020), the figured B. pacifica from this formation (Sha and Fürsich, 1993, fig. 3k-m) should be ascribed to the upper Valanginian B. sublaevis. If this is correct, the upper part of the formation should be considered as upper Valanginian. However, the determination of bivalve species often is very subjective. We [Kosenko et al., 2021] support the point of view of Sha and Fürsich (1993), who studied the bivalve collections from this formation, and supposed that the samples from the upper part of the Dong'anzhen Formation belong to the species Buchia pacifica, considering it as a characteristic species of the lower Valanginian of Northern Pacific.
Age
Depositional setting
Fully marine epicontinental-sea or littoral shallow-sea deposits.
Additional Information