Didao Fm
Type Locality and Naming
E. Heilongjiang – Sanjiang. The Didao Formation was established by G. Morita in 1943. The section for the designation is at a locality 1.5 km north of Kuangquan of Didao of the Jixi City, Heilongjiang. Lower formation in Jixi Gr.
The Didao Formation is equivalent to the lower part of the Didao Group erected by G. Morita, consisting of tuffaceous sandstone, andesite and coal beds. Ren Ji (1950) renamed it the Jixi series and named the coal-bearing strata in the lower part of the series as the Jixi carbonaceous bed. In 1959 Chen Guangya called the lower part of the Jixi carboniferous bed as the Didao pyroclastic rock and assigned it to Middle Jurassic. In 1960 Shi Tiemin erected the Didao coal-bearing formation in place of the Didao pyroclastic rock. Gu Zhiwei (1962) erected the Didao formation in place of the Didao coal-bearing formation. Zhang Qingbo (1986) assigned the Didao Formation to Early Cretaceous based on the sporopollen assemblage.
Lithology and Thickness
The Didao Formation is represented by a set of continental volcanic-sedimentary coal-bearing strata, which is divided into three parts. Lower part ("Effusive Member") is dominated by conglomerate and gravel-bearing sandstone with carbonaceous shale and tuff. Middle part ("Didao Member") is sandstone and shale with thin coal beds and carbonaceous shale. Upper part is andesite, tuffaceous sandstone and shale. The Didao Formation is 375.5 m thick.
Relationships and Distribution
Lower contact
The basal part is characterized by the appearance of conglomerate and lies unconformably on the granite gneiss of the Archean Mashan Gr. Regionally, the next older unit is the late Carboniferous Yangmugang Fm.
Upper contact
The top part of the formation is separated from the quartzose conglomerate of the overlying Chengzihe Fm by volcanic rocks and there is a disconformity between the two.
Regional extent
The present formation extends westward from the warm spring of Didao to Erlu, and eastward to Erlongshan where it becomes thinner rapidly. It also crops out on the southern side of the Boli basin and to the east of Taoshan.
GeoJSON
Fossils
The formation yields floras Coniopteris hymenophylloides, Onychiopsis elongata, Ruffordia geopperti, Adiantites sewardii, Cladophlebis cf. triangularis; in Daweizi of Qiezihe it yields Gleichenites sp., Acanthopetris sp., A. gothani; and in the Chengzihe area of Jixi sporopollen represented by the Cicaticosisporites-Gleicheniites- Pinuspollenites assemblage.
Age
Depositional setting
It is fluvial and lake bog in facies.
Additional Information