Laibuxi Fm

Synonym: In 1987, Rao Rongbiao et al. named Yin Jixiang et al. (1974) "Tulong Group Zhong Group" as "Qudeng Gongba Gr", which had been publicly quoted by Tian Chuanrong (1982) and Xu Xian et al. (1982) before publication. "Qudenggongba Fm" is the late emergence of the Laibuxi Fm of the same name.

Lithology and Thickness:

The formation is a combination of carbonate rocks and clastic rocks. Lower member is interbedded with yellowish shale and yellow sandy and tuffaceous limestone, interbedded with tuffaceous sandstone. Upper member is dark gray middle limestone, argillaceous limestone and gray argillaceous shale. The thickness is 259 m.

Lithology-pattern: Clayey limestone

Relationships and Distribution:

Lower contact:

At the bottom, the gray gravel sandstone banded limestone is in conformable contact with the underlying Fukangshare Fm [= Kangshare Fm in this Lexicon usage]

Upper contact:

At the top is conformable contact with the overlying Zhamure Fm

Regional extent:

The group outcrops well at Nyalam, Dingri, Dingjie and Jilong in the southern region of Mount Qomolangma in Tibet.

GeoJSON:

Fossils:

Four ammonoid zones can be divided from bottom to top: (1) Japonites magnus assemblage zone, (2) Anacrochordiceras nodosum assemblage zone, (3) Ptychites rugifer assemblage zone, (4) Protrachyceras-Joannites assemblage zone.

Three conodont zones: (1) Neogondolella regale assemblage zone, (2) Neogondolella constricta assemblage zone, (3) Paragondolella excelsa assemblage zone.

Three bivalve zones: (1) Plagiostoma beyrichi-Pleuronectites laevigatus assemblage zone, (2) Posidonia ussuria-P. bosniaca assemblage zone, (3) Daonella lommeli-D. indica assemblage zone.

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 Anisian through Ladinian.

Age span:

Beginning stage: Anisian

Fraction up in beginning stage: 0.0

Beginning date (Ma):

Ending stage: Ladinian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

This group is shallow marine facies.

Depositional-pattern:

Additional Information

In 1974, Yin Jixiang et al. took the Nyalamutulong section as the stratigraphic type and collectively called the marine sedimentary strata from the Early Triassic Induan to the Late Triassic Norian in the south of Mount Qomolangma as the Tulong Gr. Tulong Gr was divided into three groups: lower, middle and upper part. In 1980, Wang Yigang et al. further studied the Tulong section and named the middle formation of the Tulong Gr as the Laibuxi Fm, which was from the Middle Triassic Anisian to Ladinian. This lexicon follows that usage (see Kangshare Fm for details).