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    再论海南岛南好地区“南好组”的地质时代——兼评“海南省南好地区南好组地质特征及时代”一文

    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”

    • 摘要: 提要:海南岛保亭县南好地区“南好组”所产腕足类Xinanospirifer flabellum Rong, Xu et Yang, X. cf. sanduensis (Jing), 三叶虫 Latiproetus cf. latilimbatus (Grabau)和腹足类Homotoma sp.等化石证明,该组的地质时代为早志留世特里奇期晚期。对腕足类化石的深入研究结果表明,早先划分该地区下石炭统岩关阶“南好组”所依据的主要化石Eochoristites sp., Fusella sp., Cyrtiopsis sp., Tenticospirifer cf. supervilis, Cyrtospirifer sp.等是误定的结果,不能用作地层划分对比的证据。因此,陈哲培等(2012)根据早已废弃的化石名单得出南好地区“南好组”属下石炭统岩关阶的结论明显有误。对南兵—南好公路剖面、南好矿区锌山等早先采获早石炭世腕足类化石产地的反复多次采集,都没有重复采到原先报道的化石种类、而全部为早志留世属种,以及南好地区迄今没有发现可靠的早石炭世化石等事实表明,该地区既不存在下石炭统,也不存在下石炭统与下志留统之间的不整合接触关系。“南好组”原选层型剖面的地质构造极其复杂、地层多次重复、叠覆关系不明、层序混乱、厚度不清,不能充当岩石地层单位的选层型,应连同“南好组”一名一并废弃。

       

      Abstract: Abstract: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.

       

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