Daluzhai Fm

Lithology and Thickness:

It is dominated by mudstone and siltstone and comprises many layers of argillaceous limestone and marl.

Lithology-pattern: Pelagic marl

Relationships and Distribution:

Lower contact:

It is conformable with the underlying Sifengya Fm

Upper contact:

It is conformable/coeval with the Huixingshao Fm; but next younger regional unit is the early Devonian Cuifengshan Gr.

Regional extent:

The Daluzhai Fm is mainly distributed in Ludian, Qiaojia, Daguan, Zhengxiong and Zhaotong areas of northeastern Yunnan province. It is 70-379 m in thickness, dominated by calcareous argillaceous siltstone interbedded with shale to the east of Niujie and Laojie of Yiliang; it is 50-368 m in thickness, calcareous argillaceous siltstone, shale interbedded with argillaceous lenticulated limestone to the west of Niujie and Laojie, and to the north of Niulanjiangkou; it is mainly shale interbedded with lenticulated limestone to the south of Niulanjiangkou and more limestone southward with thickness of 81-273 m.

GeoJSON:

Fossils:

It yields fossils include graptolites Stomatograptus sinensis, Monoclimacis guizhouensis, M. shiqianensis; trilobites Coronocephalus rex, Encrinuroides, Kailia; brachiopod Nikiforovaena flabellum, etc.

Age:

The age of the formation is from the latest Llandovery to earliest Wenlock according to the fossil assemblages.

Age span:

Beginning stage: Telychian

Fraction up in beginning stage: 0.8

Beginning date (Ma):

Ending stage: Telychian

Fraction up in ending stage: 1.0

Ending date (Ma):

Depositional setting:

Depositional-pattern:

Additional Information

The Xiaohuatian Fm was proposed by Zhou Tieming (1982). The type section is located at the roadside from Xiaotianhua, Doushaguan of Yanjin County to Laotiancheng Village of Daguan County, about 22 km south of the Yanjin County in northeastern Yunnan Province. It consists of light grey, grey green calcareous mudstone and argillaceous siltstone, intercalated with limestone lenses; the top is composed of light grey medium-to-thin-bedded argillaceous limestone of 22 m in thickness; the lower part is intercalated with dark grey massive micritic marl of 16 m in thickness. All the fossils yielded in the Xiaotianhua Fm are common elements found in the upper part of the Daluzhai Fm in the area of Daguan and also those in the upper part of the Xiushan Fm exposed in southwestern Sichuan and northeastern Guizhou. Therefore, the Xiaotianhua Fm is roughly equivalent to the upper part of the Daluzhai Fm.

The strata of about 60 m in thickness under the Xiaotianhua Fm, which used to be called by Zhou Tieming (1982) the Majiaochong Fm, consist of grey green calcareous shale and silty shale intercalated with crystalline limestone and siltstone, bear fossils brachiopod Nucleospira, Nalivkinia,“Leptostrophia”, Striispirifer etc., and are higher than the Majiaochong Fm at the original type section locality in sequence and roughly equivalent to the lower part of the Daluzhai Fm (or the lower part of the Xiushan Fm). Therefore, the Majiachong Fm by Zhou Tieming (1982), and the Xiaotianhua Fm together, are equivalent to the Daluzhai Fm according to Rong (1998).