Xietan Fm
Type Locality and Naming
It was named by Zhang Zhenlai, Meng Fansong in 1987. The naming section is located by the bank of the Xiaoxi Stream, Xietan area, Zigui County.
Synonym: （泄滩组）
Lithology and Thickness
Lower part of its Lower member is composed of grey and dark-grey mudstone, siltstone and quartz-sandstone, intercalated occasionally with carbonaceous mudstone or coal seams, with the upper part of its lower member consisting of grey and yellow-green calcareous siltstone and mudstone, intercalated occasionally with thin-bedded shelly limestone or limestone lenses. Lower part of its Upper member is composed of purple and yellow-green mudstone, siltstone and fine-grained quartz-sandstone, with the upper part of its upper member consisting of blue-grey and dark-grey mudstone and siltstone, intercalated occasionally with shelly limestone. Its total thickness is about 352 m
Relationships and Distribution
Lower contact
The basal part of the formation is possessed of a layer pebble-bearing quartz-sandstone with the pebbles in it being always concentrated to form thin-bedded conglomerate, and is in a conformable contact with the underlying Tongzhuyuan Fm
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Chenjiawan Fm
Regional extent
It is distributed extensively, with a thickness varying from place to place. In the Niudouping area of Badong County the maximum thickness of the formation is of 550 m, while in the Pingyikou area of Xingshan County the formation has the smallest thickness which is of about 305 m; and in the Jingmen-Dangyang Basin the thickness of the formation varies in a range from 216 m to 350 m owing to the difficulty in differentiating these two lithological members.
GeoJSON
Fossils
It yields bivalve fossils as represented by the Lamprotula (Eolamprotula) cremeri-Pseudocardinia kweichouensis assemblage; Ostracod fossils as represented by Darwinula genus whose important members comprise D. sarytimenensis, D. impudica, D. incurva, D. henanensis and D. dubia; plant fossils as represented mainly by Clathropteris obovata, Otozamites bengalensis, Ptilophyllum contiguum, P. hsingshanense, Nilssonia parabrevis, Baiera furcata and Sphenobaiera huangi; and spore-pollen fossils as represented by the Cyathidites-Classopollis assemblage.
Age
Depositional setting
The formation belongs to lacustrine deposits formed under the conditions of a climate transition from a damp and hot weather into a dry and hot weather.
Additional Information