Revised stratigraphy of the Xiazhen Formation (Upper Ordovician) at Zhuzhai, South China, based on palaeontological and lithological data

초록

Three exposures of the Upper Ordovician Xiazhen Formation at Zhuzhai, Yushan, Jiangxi Province, China are re-measured and described in detail. Comparison of palaeontological and lithological data from the exposures (designated sub-sections ZU1, ZU2 and ZU3) reveals that the sub-sections overlap stratigraphically. Nearly identical assemblages of trilobites and brachiopods occur in mudstones of ZU1 and ZU3, whereas a different assemblage occurs in those of ZU2. Identical coral species occur in the overlapped intervals of ZU1 and ZU2, and ZU1 and ZU3, respectively. In addition, a distinctive identical lithological succession consisting of brachiopod-bearing nodular limestone at the base to coral floatstone at the top is evident in the overlapped interval of ZU1 and ZU2; prism-cracked algal laminites are found in the same interval; and bioclastic limestone beds, which represent bioherms consisting mainly of corals and stromatoporoids, occur in both ZU1 and ZU3. A thrust fault system appears to be responsible for the repetition in the subsections, and the faulting was probably due to the major post-Ordovician structural movements exerted on the Zhe-Gan Platform of the Jiangnan Region of the South China Block.

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