Dashalong Fm

Synonym: Pingdashalong Fm. Strata that were definitive to the Dashalong Fm have been named by Yazhi Fm by Rongbiao Rao et al. (1987) and have been cited by Chuanrong Tian (1982) and Xian Xu et al. (1982) before officially published. Therefore, the “Yazhi formation” is synonym to the Dashalong Fm.

Lithology and Thickness:

This formation is characterized by interbedded grey medium bioclastic limestone, sandy limestone and calcareous siltstone, sandy shale.

Lithology-pattern: Limestone

Relationships and Distribution:

Lower contact:

Siltstone and sandstone in the bottom of the Dashalong Fm is conformity onto the underlying Zamure Fm (Zhamure Fm)

Upper contact:

Conformable with the overlying Qulonggongba Fm

Regional extent:

Thickness is about 179 m. This formation is mainly distributed in Southern part of Qomolangma (Mount Everest).

GeoJSON:

Fossils:

Ammonoid zone: Nedotibetites nodosus zone, Griesbachites-Gonionotites zone; Conodont zone: Epigondolella abneptis zone and diverse brachiopods, nautilus, ostracods, foraminifers, spore and pollen, acritarchs

Age:

Tong et al. (2019, Triassic integrated stratigraphy and timescale in China, Science China: Earth Sciences, v. 62, no. 1) assign it as spanning the early Norian.

Age span:

Beginning stage: Norian

Fraction up in beginning stage: 0.0

Beginning date (Ma):

Ending stage: Norian

Fraction up in ending stage: 0.5

Ending date (Ma):

Depositional setting:

Shallow marine facies

Depositional-pattern:

Additional Information

In 1974, Yin Jixiang et al. took the Tulong section in Nyalam County as the stratigraphic type and collectively referred to the Early Triassic Indian to Late Triassic Early Norian strata as the Tulong Gr, which was divided into three subgroups: Upper, Middle and Lower. In 1980, Wang Yigang et al. took the Tulong profile as the stratigraphic type, further divided the Tulong Gr, and named the lower strata of the upper and lower strata of the original Tulong Gr as the Zamure Fm, which was in the Carnian stage. This Lexicon follows this usage (see Kangsha Gr [= Kangshare Fm] for details). Strata located between the Qulongbagong Fm of Late Triassic and Selong Gr of Permian in south Qomolangma was once designed to Tulong Gr by Jixiang Yi in 1974, and was divided into lower, middle and upper formations. The Selong Gr was later divided in detail by Yigang Wang et al. (1980). In the meantime, Pingdashalong Fm was established based on the designed stratotype within upper part of upper formation of Tulong Gr, and interpreted early Norian of Late Triassic.