Dalazi Fm
Type Locality and Naming
Yanji Basin. K. Uetoko erected the Dalazi series in 1993. The type locality for the designation is in Yanbian of Jilin. The reference section is at the Dalong-Jingu Village of Zhixin about 12 km from the Yanji town, Jilin. K. Uetoko named the Fish-bearing oil shale as the Dalazi series in the Yanbian area, originated from the original name of the Yanji town. The Pisces contained were examined as Manchurichthys uwatokoii by H. Saito, which was assigned to Cretaceous. S. Nisida (1940) called the lower part of the Dalazi series the Longjing series and the upper part the Dalazi series. In 1953 the No.303 Coalfield Geological Team redesignated the series as the formation. In 1957 the No.102 Coalfield Geological Team collectively called the two formations the Longjing series. In 1959 Yang Xuelin renamed the Longjing series the Yanji series of which the lower part was called the Longjing Fm and the upper part the Dalazi Fm. In 1964 the Jilin Regional Geological Survey Team proposed for the first time that the Dalazi Formation was located under the Longjing Fm, then, the stratigraphic sequence was corrected.
Lithology and Thickness
The Dalazi Formation is represented by a set of continental clastic rocks with oil shales, which is divided in the ascending order into two members. Lower member is the sandy conglomerate rock member, built up mainly by yellow and yellow brown conglomerate and sandy conglomerate, intercalated with sandstone and sandy shale. Upper member is the oil shale member, built up by gray black claystone, gray paper-like shale and yellow sandstone, intercalated with clayey siltstone, brown oil shale and marly lumps. It is 1615.8 m thick.
[Figure: Luozigou section of Dalazi Formation in Wangqing, Yanbian of Jilin Province]
Relationships and Distribution
Lower contact
The basal part of the formation consisting of conglomerate lies unconformably over and is separated from the underlying gneissic biotite plagioclase granite in the type section, lies unconformably on the Changcai Fm, or rests unconformably or disconformably on the Quanshuicun Fm in other areas (see Regional extent). In the Yanqi column of Jingeng Sha in Kosenko et al., 2021, the underlying regional unit is the Tongfosi Fm of conglomerates and sandstones, of which the volcanic Quanshuicun Fm is the local basal portion.
Upper contact
The formation contacts conformably with the overlying Longjing Fm.
Regional extent
The present formation occurs in the Yanji, Helong, Antu, Songjiang, Tuntianying and Tumen basins. In the Songjiang basin the lower part of the formation is mostly represented by yellow brown and gray green conglomerate, with sandstone and siltstone thin beds, while the upper part oil shale, black shale and sandstone. It is 2849.5 m thick and lies unconformably on the Changcai Fm. In the Helong basin, the lower part of the formation is dominated by yellow brown conglomerate, sandstone and purple siltstone with black shale; while the upper part sandstone and siltstone interbedded with shale; being 177 m thick and resting unconformably or disconformably on the Quanshuicun Fm. In the Fudong basin, only the lower part of the formation is developed and the upper part is absent, with a total thickness of 470 m. In the Luozigou basin, the formation varies considerably in lithology, dominated by macroclastic sediments in the northern part of the basin, and marked by alternating macroclastic and microclastic sediments in the southern part. In the Wenhe basin, the strata that are equivalent to the present formation are called the Baojiatun Fm, dominated by conglomerate with siltstone in the lower part and composed of sandstone, shale and oil shale in the upper part, with a total thickness of 937 m.
GeoJSON
Fossils
It yields abundant fossils, including plant mega- and microfossils, charophytes, dinocysts, chlorophyte algae, acritarchs, conchostracans, ostracods, insects, gastropods, bivalves and fish. The formation contains Pisces Manchurichthys sp.; bivalves Trigonioides kodairai, Sphaerium chientaoense; gastropods Tulutomoides talazensis; Estherias Bairdestheria cf. posidonom yoides, Estherites mitsushii; ostracods Cypridea (Pseudocypridina) magna, C. (P.) aff. globra; floras Pagiophyllum sp., Elatocladus sp.; in the upper member around Badaohe of Yanji yielding floras Onychiopsis elongata, Ruffordia goeperti, Brachyphyllum crassum, Populus sp.; in Tongfosh of Laotougou yielding Estherias Yanjiestheria dalaziensis, Liograpta streptoformis. Ostracods are Cypridea rostata, Ziziphocypris costata, Ilyocyprimorpha netchaevae, Mongolocypris yanjiensis, Cypridea concinaformis, Cyprois sp., Lycopterocypris sp., Yumenella toorojensis; and spinicaudans Yanjiestheria bellula and Neodiestheria dalaziensis.
Floras are Gleichenites nipponensis, Cornus sp.; in the upper member of the Dalazi area yielding the Cicatricosisporites- Appendicisporites- Tricolpites sporopollen assemblage. The Dalazi Formation is characterized by the Pseudofrenelopsis - angiosperms flora assemblage also identified in the Hoshigou Fm, Denglouku Fm and Quantou Fm. This flora assemblage contains early angiosperms such as Sapindopsis, Sassafras and Araliaephyllum which also present in the Late Alchan floristic assemblage. Therefore, the Dalazi Formation roughly corresponds to the middle-upper Albian Alchan Fm. Moreover, the genus Sapindopsis is characterized by narrow stratigraphic range in Asia covering middle and upper Albian. Thus, the Dalazi Formation is probably Middle-upper Albian.
Bivalves include the non-marine Trigonioides (T.) heilongjiangensis [=Trigonioides kodairai] and Sphaerium (Sphaerium) cf. chientaoense [=S. cf. yanbianense] indicating Albian.
The palynoflora mainly consists of the dinocysts Vesperopsis sp. and Bosedinia sp., the acritarchs Filisphaeridium sp., Granodiscus sp. and Leiosphaeridia sp., and the chlorophyte Pediastrum sp. Like Nyktericysta, Vesperopsis is a Lower Cretaceous indicator; there is no record of it from the Albian in China, and outside China it is usually found in strata that are not younger than Albian, therefore indicating that the Dalazi Formation is no younger than this.
Age
Depositional setting
Additional Information
Enhanced with Igor N. Kosenko, Jingeng Sha and Boris N. Shurygin (2021). Upper Mesozoic stratigraphy of Sikhote-Alin (Russian Far East) and northeastern China: Non-marine and marine correlations. Part 1: Upper Jurassic-Hauterivian AND 2. Barremian-Aptian. Cretaceous Research, 124: articles 104811 (https://doi.org/10.1016/j.cretres.2021.104811) AND 104812 (https://doi.org/10.1016/j.cretres.2021.104812)