Dacaotan Gr
Type Locality and Naming
The type section is located at Dacaotan area between Wangjiadian and Jiudianzi, south of Dongzhakou, southwest of Longxixian (Zhangxian) County, Gansu Province. It was named by Huang Zhenhui in 1959.
Lithology and Thickness
Sandstone. The lithology of the Dacaotan Group is dominated by dark-gray, brownish-yellow, grayish-white, dark-purple, purplish-red and grayish-green feldspathic quartz sandstone, calcareous siltstone, clayey siltstone, and fine-grained sandstone. The total thickness is more than 3300 m.
Relationships and Distribution
Lower contact
Its base has a fault contact with the underlying strata.
Upper contact
The upper contact of the group with the overlying Wangjiadian Fm of the latest Devonian to Lower Carboniferous is probably conformable in nature, but still remains pending.
Regional extent
The Dacaotan Group is mainly intermittently exposed north of the northern Qinling, from Niangniangba at Liushui of Dacaotan to Dingtanzi of Liangdang in Zhangxian County. In the area of Dazhuang and Gangoutan in Zhangxian County, the thickness is more than 4737 m and contains plant and fish fossils. In Zishigou area of Zhangxian County, the thickness is more than 1245 m and contains plant L. rhombicum etc. (according to scale 1:200,000 Longxi Geological Map). In the area of Sigou of Wushan to Jigou of Tianshui, the outcrop thickness is more than 7900 m, and overlies unconformably on the Yushuping Fm of the Middle Devonian. The corresponding beds in Moyugou, Huayangyu of Tianshui yield plant fossil L. rhombicum, etc. (according to scale 1:200,000 Tianshui Geological Map). Near the Dingtanzi of Liangdang, the outcrop thickness is more than 5000 m, where the basal conglomerate overlies unconformably on the Caotangou Gr of the Ordovician and contains plant fossils in its lower part.
GeoJSON
Fossils
No fossils have been found so far in the very thick interval at the lower part of the Group. The middle and upper parts yield plant fossils: Leptophloeum rhombicum, sublepidodendrom wusihensis, Knoria etc. and Placodermi fish fragments. Except for Leptophloeum rhombicum, the plant fossils in the Dacaotan Group of Cyclostigma kiltornense, Sublepidodendron mirabile etc., are similar to those of the Wutong Gr (Wutong Fm) in Nanjing area.
Age
Depositional setting
Additional Information