Baikouquan Fm
Type Locality and Naming
Junggar Basin, Mahu Sag. Type locality is Baikouquan in Urho area, 80 km NE of Karamay, NW Junggar Basin, Xinjiang Uygur Autonomous region. Named (as Beds) by Compiling Group for Xinjiang Regional Stratigraphic Scale, 1981, Regional Stratigraphic Scale of Northwest China, Beijing Geological Publishing House.
Synonym: Baikouquan Beds. Formerly a component subdivision within a Wu'erhe Fm
Lithology and Thickness
Reddish brown fan-delta fining-upward deposits of conglomerate to siltstone. Borehole succession in Figure 1: "The thickness of the Lower Triassic Baikouquan Formation (T1b), is 120-250 m. From bottom to top, it is divided into three members, marked as T1b1, T1b2 and T1b3. The lithologis of T1b1, with thickness of 30-50 m, are mainly gray, grayish-green and brown conglomerate imbedded thin brown mudstone. The lithologies of T1b2, with thickness of 60-100 m, are composed of thick interbeds of grayish-green conglomerate and brown mudstone. The major lithologies of T1b3, with thickness of 40- 90 m, are gray sandstone and gray-brown mudstone."
[Figure: (a) Map of China, the Junggar Basin locates in northwestern China. (b) Location of the Mahu Depression in the Junggar Basin. (c) Plain figure of sedimentary facies of the Baikouquan Formation, the Mahu Depression. (d) Well logging and testing synthetic graph of the Baikouquan Formation, well M134. (from: Yuan, Rui, et al., 2017. Utilizing borehole electrical images to interpret lithofacies of fan-delta: A case study of Lower Triassic Baikouquan Formation in Mahu Depression, Junggar Basin, China. Open Geoscience, 9: 539-553.)]
Relationships and Distribution
Lower contact
Unconformable on the Shangwurhe Fm of upper Permian, but it is hard to differentiate between them, therefore these used to be called by a joint name known as the Shangzonghongse Fm. But judging from the seismic stratigraphic section, it is clear that there is a distinct unconformity between them. [From Permian Lexicon entry for Shangwurhe Fm].
Upper contact
Regional extent
"The Mahu Depression is one of the largest hydrocarbon depressions in the Junggar Basin, northwestern China. At the slope of the depression, the formation has been described as a succession of proximal coarse fan-delta deposits with complicated conglomerates in shallow water."
GeoJSON
Fossils
Age
Depositional setting
"Large-scale conglomerate fan-delta aprons were typical deposits on the slope of Mahu Depression during the Early Triassic." Suite of fan deltas coming from west and north. "As a result of collision and subduction between the Junggar-Turpan and Kazakhstan Plates in the Late Paleozoic, the foreland depression of Mahu formed at northwestern margin of the basin (see figure). On the hanging wall of thrust fault, Zaire and Hala’alat mountainswere denuded and supplied sufficient sediments for the Mahu Depression during the Early Triassic. One part of these coarse sediments accumulated at the margin of depression formed alluvial fans, while others moved further to the gentle slope by the interaction of gravity and water, resulting in a series of proximal fandelta aprons in shallow water (see figure). They are respectively called Zhongguai, Karamay, Huangyangquan, Xiazijie, Xiayan and Dabasong Fan-delta." (Yuan, Rui, et al., 2017. Utilizing borehole electrical images to interpret lithofacies of fan-delta: A case study of Lower Triassic Baikouquan Formation in Mahu Depression, Junggar Basin, China. Open Geoscience, 9: 539-553.)
Additional Information
"Major hydrocarbon reservoir in conglomerates."