Xiongencuo Fm

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Upper contact:

Uncertain relationship to the other strata – See Additional Information.

Regional extent:

In the Guzala area, Kangyu Region, Bomi County the grey-black medium- and thick-bedded limestones with an exposed thickness only of 300 m yield Fusulinids and corals, with the latter comprising Waagenophyllum sp., whose stratigraphic horizon is corresponding to that of the Xion’ercuo Fm.

GeoJSON:

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Fossils:

The middle and lower parts of the Xiong’encuo Fm yield abundant fossils, including brachiopods, corals, bryozoan, Fusulinida, Foraminifera, Gastropoda, Nautilus and crinoid stems, with the first four kinds of fossils being predominant. The Fusulinida is represented by the Nankinella, Chusenella and Reichelina; the brachiopods comprises 19 genera and 22 species of which the more important member is the Tyloplecta cf. richthofeni; the bryozoan comprises 6 genera and 15 species of which the Hinganotrypa sichuanensis, Polypora cf. qinghaiensi and P. qinghaiensis are found to occur commonly in the upper part of the Qixia Fm and in the Maokou Fm in Sichuan Province. The coral fossils comprise 5 genera and 8 species of which the Multithecopora haydeni and Praewentzelella tibetica are all found to occur within the Permian System in the central part of Tibet.

Age:

The fossils imply that the Xion’encuo Fm can be correlated with the upper Qixia'an (Qixia Fm) and Maokou'an (Maokou Fm) of South China = Guadalupian Epoch (Middle Permian)

Age Span:

Beginning stage: Roadian

Fraction up in beginning stage: 0.0

Beginning date (Ma):

Ending stage: Capitanian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

Depositional-pattern:

Additional Information

The structure of the Permian System in the area from the Lagu to the Yinga Pastureland is fairly complicated, so there are different views on whether the whole stratigraphic sequence represents a great reversed stratigraphic sequence (?), or whether the subdivision of the particular sequence concerned into the upper, middle and the lower parts (namely into the Zadongcuo Fm, the Xiong’encuo Fm and the Yinga Fm) is tenable, that is to say whether the horizons containing pebbled slates in the upper and lower parts of the formation represent a repetition of one and the same stratigraphic unit? Yin Jixiang would think that the Permian strata in the Lagu area represent a reversed stratigraphic sequence, which includes in ascending order the Yinga Fm, the Xiong’encuo Fm and the Zhadongcuo Fm.

In addition, a different view has been put forth whether the pebbled slate in the lower part contains a part or the whole stratum be designated to the upper Carboniferous Series. Jin Yugan et al. (1977) would think that in accordance with the common plan of subdivision of the Permian System in the Gondwana, the Permian System here is composed of three lithological formations, namely in ascending order the Pebbled slate-bearing (glacio-marine), the Sandstone-and-slate-bearing, and the essentially Limestone-bearing formations.

From Dong-Li Sun, 1993 " On the Permian biogeographic boundary between Gondwana and Eurasia in Tibet, China as the eastern section of the Tethys", Palaeo-3, 100:59-77: " The Zhadongco Fm is overlying the Xiongenco Fm carbonate unit and consists of pebbly slate of 1000 m thick. A fault can be observed between them. Therefore, this pebbly slate sequence was interpreted as reappearance of the underlying Yinga Fm."