Xia’ertai Gr
Type Locality and Naming
The type section is at Xia'ertai in Changtu County, Liaoning. The Xia'ertai Gr was named by No.1 Liaoning Party of Regional Geological Survey in 1969, and was published by Jilin Compiling Group for Regional Stratigraphic Scale (1978). The Xia'ertai Gr was formerly divided into Panling Fm, Huangdingzi Fm, Shaoguotun Fm and Wangxiangtun Fm, in ascending order. In 1978, Jilin Compiling Group for Regional Stratigraphic Scale abandoned the top Wangxiangtun Fm according to the suggestion of Liaoning Party of Regional Geological Survey, and considered the Xia'ertai Gr to be Ordovician-Silurian in age. Therefore, the Xia'ertai Gr is divided into the Panling Fm, Huangdingzi Fm, and Shaoguotun Fm, in ascending order.
Synonym: (下二台群）
Lithology and Thickness
The Xia'ertai Gr is exposed in Siping area, and is composed of terrigenous clastic-carbonate rocks and minor volcanic rock. Its upper and lower boundaries are cut by fault, and the residual thickness is 4000 m. The Xia'ertai Gr is divided into the Panling Fm, Huangdingzi Fm, and Shaoguotun Fm, in ascending order. The Panling Fm recorded incomplete thickness of 927 m, and is dominated by hornblende-leptite, biotite leptite and two-mica quartz schist intercalated with a large number of marble lenses. ["Leptite" is "A near obsolete term for a fine-grained … metamorphic rock … variably interpreted as metamorphosed volcanics, pyroclastics, or sediments ..." – See Additional Information.]. At areas 4 km southeast of Yehe, the marble lenses yield sponge Eospongiidae? gen et sp. indet. (Jilin Compiling Group for Regional Stratigraphic Scale, 1978). The lower boundary of the Panling Fm is covered. The Huangdingzi Fm, 887.6 m thick, is composed of hornfels and quartz schist intercalated with local quartz albitophyre (a porphyritic rock containing phenocrysts of albite) in the Lower part, and of marble and slate intercalated with sandstone, schist and local metamorphosed volcanic rock and albitophyre in the Upper. The volcanic rock has a whole rock Rb-Sr isochron age of 456.36 Ma (Tang Kedong et al., 1992), indicating a Late Ashgill age. The Huangdingzi Fm rests conformably on the Panling Fm. The Shaoguotun Fm, 1437.5 m thick, is composed dominantly of schist and various leptites, and is in fault contact with the underlying Huangdingzi Fm, with a fault cutting at the upper boundary.
Relationships and Distribution
Lower contact
The lower boundary of the Panling Fm is covered.
Upper contact
The Shaoguotun Fm is in a fault cutting at its upper boundary.
Regional extent
GeoJSON
Fossils
Age
Depositional setting
Additional Information
Lithology-pattern: Volcanics
Relationships and Distribution:
Lower contact:
The lower boundary of the Panling Fm is covered.
Upper contact:
The Shaoguotun Fm is in a fault cutting at its upper boundary.
Regional extent:
GeoJSON:
Fossils:
Age:
Ordovician. In 1992, Tang Kedong followed the primary definition of the Xia'ertai Gr, and defined it to be Ordovician-Silurian in age on the sponges from the Panling Fm. At the same time, he suggested a Late Ordovician age for the Huangdingzi Fm, and a possible Early Silurian age for the Wangxiangtun Fm, on the whole rock Rb-Sr isochron age of 456±36 Ma gained on the volcanic rocks of the Huangdingzi Fm.
Age span:
Beginning stage: Tremadocian
Fraction up in beginning stage: 0.0
Beginning date (Ma):
Ending stage: Hirnantian
Fraction up in ending stage: 1.0
Ending date (Ma):
Depositional setting:
Depositional-pattern:
Additional Information
"Leptite" is "A near obsolete term for a fine-grained banded, gneissose to granulose or hornfelsic, feldspathic metamorphic rock of varied origin, mainly composed of feldspar and quartz with subordinate mafic minerals. They have been variably interpreted as metamorphosed volcanics, pyroclastics, or sediments, sometimes probably highly matasomatized." [Mindat entry at https://www.mindat.org/min-50043.html]