Jiezha Gr

Synonym: Gyiza Gr; upper coal-bearing clastics were called the Tumengela Fm (Rhaetian)

Lithology and Thickness:

The Gyiza Gr originally refers to a set of marine carbonate and clastic rocks in the Late Triassic in the Tanggula Mountain area, as well as marine-terrestrial interfacies coal-bearing clastic rock deposits. From bottom to top, it is divided into purple-red Clastic rock group and lower Limestone group, gray Clastic rock group and upper Limestone group. In 1984, Ma Fubao, Wang Xiulin, Che Yi, et al. named the strata roughly equivalent to the purple-red Clastic rock group, the Carbonate rock group and the Coal-bearing Clastic rock group as the Dongmaolong Fm, the Xiaoqiacuo Fm and the Jiadengda Fm, respectively – see those Fm entries for details; and Additional Information below for history.

Lithology-pattern: Sandy limestone

Relationships and Distribution:

Lower contact:

The yellowish-brown conglomerate at the bottom is unconformably lying on the Upper Permian feldspar quartz siltstone. Regionally, next older unit is the Benpulong Fm of Middle Triassic.

Upper contact:

Initial entry said "conformable with Batang Gr of Jurassic", but Batang Gr entry implies it is largely coeval Late Triassic (TJ32 column). Therefore, the next younger regional unit is the Middle Jurassic base of the Qoimaco Fm (Yanshiping Gr); with apparent absence of Lower Jurassic?

Regional extent:

The Gyiza Gr (now Jiezha Gr) originally refers to a set of marine carbonate and clastic rocks in the Late Triassic in the Tanggula Mountain area.

GeoJSON:

Fossils:

See component Fm entries for details

Age:

Schematic stratigraphic section indicates Carnian through Norian.

Age span:

Beginning stage: Carnian

Fraction up in beginning stage: 0.0

Beginning date (Ma):

Ending stage: Norian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

Depositional-pattern:

Additional Information

In 1972, the Qinghai area survey team believed that the upper and lower limestone formations belonged to the same layer, so the Jiezha Gr was divided into the purple red clastic rock formation and the carbonate formation from bottom to top, and the age was determined as the Carnian to Norian, Late Triassic. In 1982, Chen Guolong et al. followed this division plan, but they determined the age as Ladinian (Middle Triassic) to Norian (Late Triassic). In the same year, Zhao Jinke et al. narrowed the lithostratigraphic range of the Jiezha Gr and classified the upper coal-bearing clastic rock group into the Tumengela Fm (Rhaetian), and set the age to the Late Triassic Carnian to Norian period. In 1984, Ma Fubao, Wang Xiulin, Che Yi, et al. named the strata roughly equivalent to the purple-red clastic rock group, the carbonate rock group and the coal-bearing clastic rock group as the Dongmaolong Fm, the Xiaoqiacuo Fm and the Jiadengda Fm, respectively. And the age was determined to be the Late Ladinian in middle Triassic to the Norian in late Triassic. The Bureau of Geology and Mineral Resources of Qinghai Province divided the group into the Jiapila Fm, Bolila Fm and the Bagong Fm. This lexicon follows the division scheme of Ma Fubao et al.