Junzihe Fm
Type Locality and Naming
Yang Zunyi et al. named this formation in 1962. The named section is located in Dagaliangou, Xiahuancang Township, Tianjun County, Qinghai Province, and Qieerma Valley, on the west bank of Junzi River, 16 km to the northwest of Xiahuancang Township. It was named as the "Junzihe System", originally representing the Triassic system in the southern Qilian Mountains of Qinghai Province, and divided into the lower, middle and upper part. In 1962, Zhao Jinke and others renamed it "Junzi River Group", which was also divided into three parts. In 1976, the Northwest Marine Triassic and Jurassic Stratigraphic Dating Conference disintegrated the "Junzihe Group", and the lower part represented the Lower Triassic and was named the Yangkang Gr. The upper part represents the Middle Triassic Anisian, known as Junzihe Fm. In 1983, Yang Zunyi et al. extended this meaning and divided the Junzihe Fm into Dajialian and Qieerma members.
Synonym:
Lithology and Thickness
Lower Dajialian member is dominated by carbonate rocks and the upper Qieerma member is dominated by clastic rocks. Dajialian member is composed of gray and light gray biotic limestone, oolitic limestone with breccia, tubaceous limestone and banded limestone, with a thickness of 84 m. The lower part of Qieerma member is composed of gray and light gray green calcareous siltstone interlaced with gray sandy limestone or limestone lens, while the upper part is composed of gray and dark gray silty shale, calcareous siltstone and feldspar fine sandstone with a thickness of 683 m. The above sectional features are limited to Junzi River and the middle reaches of Xiariha River.
Relationships and Distribution
Lower contact
At the bottom, the sandy nodular limestone is conformable contact with the underlying Lower Triassic Jianghe Fm
Upper contact
At the top, it is conformable contact with the overlying Mole Gr
Regional extent
They are mainly distributed in the southern Qilian Mountains of Qinghai Province. In Nianrihai, Duosuo Mountain and Wuge Mountain area, it is a set of clastic rocks, occasionally interbedded with limestone, difficult to segment, with a thickness of 220 to 588 m. In the south of Hala Lake, east ridge of Yeniu Mountain and Yangkangqu area, the lithology is mainly carbonate rock with thickness greater than 837 m are dominant.
GeoJSON
Fossils
There are ammonoids, bivalves, brachiopods, gastropods and palynology and other phyla fossils.
The Dajialian Member of some area is Leptochondria albertii plana-Neomorphotis spinosa assemblage zone. And it can be divided into Eoantiptychia-Hirsutella extrarug assemblage, Chlamys gastropods assemblage and transition, from bottom to top; Brachiopods Lepismatina-Costirhynchopsis assemblage and ammonoids Lenotropites assemblage.
In the Qieerma Member are bivalves, brachiopods Neomorphotis gigantean-Paraantiptychia robusta local assemblage zone, Tianjunites-Pseudoplococeras local ammonoids assemblage zone and Worthenia conic gastropod assemblage.
Age
Depositional setting
The formation represents the stable littoral to shallow sea deposits.
Additional Information