Re-Discussion on the Geological Age of “Nanhao Formation” in Nanhao Area, Hainan Island——With Comments on the Paper “Geological Characters and Age of Nanhao Formation, Nanhao Area, Hainan Province”
详细信息
- 责任者：Zhang Renjie (Wuhan Institute of Geology and Mineral Resources ; China Geological Survey ; Wuhan 430223 ; China) ; Tu Bing
- 刊名：Geology in China
- 出版年：2013
- 卷期：40(4)
- 页码：p.1180-1188
- issnNo：ISSN1000-3657
- isbnNo：CN11-1167/P
摘要
Fairly abundant fossils,such as brachiopods Xinanospirifer flabellum Rong,X.cf.sanduensis(Jing),the trilobite Latiproetus latilimbatus(Grabau),and the gastropod Homotoma sp.,were found in the "Nanhao Formation" of Nanhao area,Baoting County,Hainan Island.This fauna strongly supports the conclusion that the fossil bearing rocks are Late Telychian(Llandovery,Silurian) in age;previously,the rocks were thought to belong to the Aikuanian Stage which is Early Carboniferous in age.Years’ intensive study of the brachiopods from the "Nanhao Formation" of the study area shows that the fossil-lists of brachiopods,comprising Eochoristites sp.,Fusella sp.,Cyrtiopsis sp.,Cyrtospirifer sp.,Tenticospirifer cf.supervilis Tien,and T.sp.,which have been used as the major evidence indicating an Early Carboniferous age for the "Nanhao Formation" in Nanhao area,are the results of misidentification.Hence,those fossil-lists can no longer be treated as evidence for the stratigraphic subdivision and correlation of the "Nanhao Formation" in the study area.Unfortunately,Chen Zhe-pei and others(2012) concluded incorrectly that the "Nanhao Formation" was Early Carboniferous Aikuanian in age.In the paper "Geological characters and age of Nanhao Formation,Nanhao area,Hainan Province",they based their conclusions on those fossil-lists.Great efforts were made by the authors in Nanhao area,but no Early Carboniferous brachiopod taxa reported previously were collected again from the original localities.In contrast,a large number of Early Silurian Xinanospirifer were collected from those localities.The above-mentioned data indicate that there are no Lower Carboniferous rocks in the area,and that there is no unconformity between the so-called Lower Carboniferous "Nanhao Formation" and the Lower Silurian Zusailing Formation in Nanhao area,southern Hainan Island.In addition,the Nanbing-Nanhao road-cut section has very complex structures with many faults and folds,strong repetition of beds,disordered sequence,and confusing overlapping relationship of rocks as well as rock thickness.Hence,the road-cut section cannot be treated as the lectostratotype section of the "Nanhao Formation" as previously thought.In summary,both the "Nanhao Formation" as a lithostratigraphic term and the lectostratotype section of the "Nanhao Formation" have to be abandoned.