Gongguan Fm
Type Locality and Naming
The type section is located at Xichaliangding—Xujiacao, Luohe Township, Xunyang County, Shaanxi Province. It was named by No 1 Shaanxi Geological Team in 1964 and was published by “Regional Stratigraphical Scale of Central-Southern China” in 1974.
Lithology and Thickness
Dolomite. It is dolomitic rocks. The total thickness is 549.8 m . Lower part composed of gray and dark-gray medium-bedded micritic limestone and fine-grained dolomite intercalated with dolomitic slate. Upper part composed of gray to light-gray medium-bedded sandy dolomite intercalated with clayey dolomite.
In Gongguan area, this formation is composed of algal dolomite and stromatolite-bearing dolomite, with trough and tabular cross-bedding in the Lower part, with climbing-ripple lamination, lenticular bedding and flaser bedding in the Middle part, and with exposure marks such as bird's-eyes, mutlion structures, drying cracks, etc. in the Upper part.
Relationships and Distribution
Lower contact
This formation overlies conformably on the Xichahe Fm.
Upper contact
Conformably overlain by the Shijiagou Fm.
Regional extent
The formation is distributed in the area of Xunyang and Shanyany counties, along the western margin of Wudang Old Land.
GeoJSON
Fossils
In the upper part, it yields ostracods Paramoelleritia subtrapezoidalis; gastropods Murchisonia cf. loxomemoides; and stromatopora Amphipora
Age
Depositional setting
It is interpreted as a tidal flat to lagoon facies deposit deposited within a marine transgression.
Additional Information
In Gongguan-Shuanghe area, it may reach up to 550~689 m in thickness, and belongs to the Lower Devonian. But was deposited within a marine transgression from south to north, therefore in Nankuanping--Shanyang, the thickness reduces down to 47~160 m and the age correspondingly goes up to Middle Devonian.