湖北大洪山地区原“莲沱组”时代质疑

Doubt about the age of the original "Liantuo Formation"in the Dahongshan area,Hubei Province,Central China

根据野外观察,出露在襄樊-广济断裂带南侧大洪山地区绿林(厂河)镇一带主要由紫红色砂砾岩组成的原“震旦纪莲沱组”,呈向南缓倾斜、倾角40°左右的单斜岩层产出,顶部与震旦纪陡山沱组之间以一条向南倾斜的逆断层为界,底部与下伏花山群之间为高角度不整合而不是微角度不整合;下伏前震旦纪(?)花山群和构造上覆的震旦系—下三叠统共同卷入了与扬子地块盖层岩系构造变形类似的向南的叠瓦构造和向南的倒转褶皱。通过组成与构造变形方面的研究得出该套地层可能不是震旦系而是中生代红层一部分的结论。

Based on field investigations ,the original Sinian Liantuo Formation exposed near Lulin(Changhe)Township in the Dahong Mountains south of the Xiangfan-Guangji fault is the original'Sinian Liantuo Formation'composed mainly of purplish red sandstones and conglomerates.It occurs as a mono-cline dipping gently to the south at～40°.Its top is in contact with the Sinian Doushantuo Formation a-long a south-dipping thrust and its bottom is in contact with the underlying Huashan Group with a high-angle unconformity rather than with a low-angle unconformity.The Nantuo Formation which was previ-ously placed between the Doushantuo and Liantuo formations in the area does not exist.The underlying pre-Sinian(?)Huashan Group and the structurally overlying Sinian-Lowe Triassic strata are both in-volved in south-vergent imbricate structures and south-vergent overturned folds similar to the structural deformation of the cover sequences of the Yangtze block.These geological data about the organization and structural deformation leads the author to conclude that the Liantuo Formation was not deposited during the early Sinian but is probably part of the Mesozoic red beds.