Damao Fm
Type Locality and Naming
The type section of Damao Formation is the Damaodong section. It is located at Damao Village, Sanya, Hainan Province, about 15 km northeast of the seat of Sanya City (109°37’47”E, 18°21’01”N). In the type section, the formation is over 309.9 m thick with its basal part and base are not exposed. The Damao Formation was firstly published by Guangdong Regional Geological Survey Team (1964) as Damao Group. The name is derived from Damao Mountain in Damao Village, Jiyang District, Sanya City, southern Hainan Province. Originally it was called Damao Group, appeared in a 1962 manuscript by Wang Shucai and Jin Bangquan from Guangdong Regional Geological Survey Team. Mu Enzhi and others from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences lowered the group in rank as Damao Formation in a 1977 manuscript, and the formation name was used subsequently in some regional surveying reports and was finally accepted by Chen (1997).
Synonym: （大茅组）
Lithology and Thickness
The Damao Formation is a sequence with alternation of clastic and carbonate rocks. Lower part of exposed interval consists of greyish white quartzose sandstone and dark grey silty shale, alternated with dolomite, dolomitic limestone and argillaceous limestone. Upper part consists of thick-bedded dolomite, dolomitic limestone, and chert with interbeds of siliceous shale, 2 to 5 layers of phosphorite, and brownish black manganese ore bed and manganese concretion.
Relationships and Distribution
Lower contact
The lower contact of the Damao Formation is not known in the type section as the basal part is not exposed, but in an auxiliary section nearby, the Cunzi-Luoyuxiacun section, the formation is in conformable contact with the underlying Mengyueling Fm. In that section, the lower boundary of the Damao Formation is marked by lithological change from the silty claysone of the Mengyueling Fm to the medium-grained quartzose sandstone of the Damao Fm.
Upper contact
The Damao Formation is in disconformable contact with overlying Ordovician Dakui Fm
Regional extent
The Damao Formation is exposed in the Sanya Area of Hainan Region, restricted to the Jiyan District, Sanya City. Geographically it outcrops in Tiandu Township and at An’you, Damao, and Honghua villages. Thickness of the formation varies between 309 and 794 m.
GeoJSON
Fossils
The Damao Formation yields rich fossils of multiple groups, including trilobites Galahetes hainanensis, Kootenia sp., Pagetia sp., Xystridura hainanensis, X. orientalis, and X. yaxianensis; brachiopods Acrotreta kutorgai, Bortsfordia yaxianensis, and Lingulella sp.; bradoriids Damaoella tricarinata, Guangdongella obesa, Houlongdongella disulcata, Indota acuta, Mannocosmia torquata, Ophiosema strumatum, O. (Sinophiosema) chinense, Plesidielymella convexolimbata,and Yaxianella sulcata; bivalve Cycloconcha subovata; and micro-paleoplant fossils Brocholaminaria sp., Leiomarginata sp., Leiominuscula sp., Lignum sp., Protoleiosperidium sp., Retinarites sp. and Trachysphaeridium sp., etc.
Age
Depositional setting
The formation represents shallow-water manganiferous, phosphoric and siliceous carbonate setting.
Additional Information