Chawan Fm
Type Locality and Naming
Eastern Zhejiang. The Chawan Formation was erected by the Zhejiang Bureau of Geology and Mineral Resource in 1989. The section for the designation is at Jiuliping of the Tiantai County, Zhejiang. The formation is the fourth formation upward in the Moshishan Gr between the Xishantou Fm and the Jiuliping Fm, consisting of tuffaceous sandy conglomerate, sandstone, silty mudstone, sediment tuff and breccia tuff.
Lithology and Thickness
The formation is mainly represented by a suite of tuffaceous sedimentary rocks dominated by dark purple and gray black moderately thick - thick-bedded breccia tuff intercalated by massive sediment tuff, siltstone and marl. It is 265.30 m thick and contains flora Sphenopteris sp.
Relationships and Distribution
Lower contact
Its base is separated from the gray black massive basalt of the underlying Xishantou Fm by the appearance of dark purple massive tuffaceous conglomerate, showing conformable contact between the two.
Upper contact
Its top is bounded by the gray white rhyolitic tuff breccia of the overlying Jiuliping Fm, showing unconformable contact with the latter.
Regional extent
The formation is distributed in the small areas of Longquan-Shangyu and Wencheng-Fenghua, which varies considerably both in lithology and thickness. In the Longquan-Shangyu, Lishui-Laozu and Dongyang-Yangyanjian depressions, normal sedimentary rocks were deposited, which yield abundant fossils. In the small area of Wencheng-Fenghua, sedimentary rocks at Shuikou of Jinyun are intercalated with small amounts of moderately acidic pyroclastic rocks. In Xiaoling of Linhai, the middle and upper parts of the formation are intercalated with black mudstone, coal streaks, acidic pyroclastic rocks and vitric ignimbrite of which the whole rock gives the K/Ar date of 107.0 Ma. In Shipu of Xiangshan, sedimentary rocks are intercalated with a lot of algae limestone. The Chawan Formation is generally 300-700 m thick and only 177.3 m in Longtanshan of Fenghua, and up to 1589 m in Shawan of Zhenhai. The formation is generally 300-700 m thick, only 177.3 m thick in Fenghua and up to 1589 m thick at maximum in Shawan of Zhenhai.
GeoJSON
Fossils
In Laozu of Lishui, Huaqian and Huazuling of Wencheng, Shangyutou of Longyou and Xiaoling of Linhai, it yields bivalves Ferganoconcha shouchangensis, F.ovalis, F.elongata; gastropods Probaicalia tricarmata, Viviparus onogoensis, Reesidella concentrica; Estherias Yanjiesthria kyongsangensis, Orthestheria intermedia; Fish Ikechaoamia meridionalis, Paraclupea chetungensis, Mesoclupea showchangensis, Huashia gracilis, Fuchunkiangia sp., F.chesiensis; shrimps Cathaysergesis Zhejiangensis; insects Ephemeropsis trisetalis; floras Onychiopsis elongata, Coniopteris cf. burejensis, Sagenopteris yunganensis, etc.
Age
Depositional setting
It is mainly built up by sediments deposited in the volcanic depression.
Additional Information