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Laba Limestone: Recognition of Origin of Deep-water Carbonate Deposits and it's Significance

ZHOU Zhi-cheng, FANG Zong jie, GUO Zhen yu, WANG Yu jing, (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing , 210008) and XIAO Yin wen (Regional Surveying Team of Geological Bureau of Yunnan, Yuxi, 653100)  
The interpretation of the origin of the Laba Limestone in the Permian Laba Formation in western Yunnan has been controversial for a long time. One viewpoint regards it as allodapic melanges body and the other considers it as normal autochthonous limestone . Abundant shallow water bioclasts including echinoderms, foraminifers, fusulinids, brachiopods, bryozoans, gastropods, calcareous algae (blue green algae and green algae) in the Laba Limestone are predominating over other grain types (ooids, intraclasts etc.). The diagenetic characters of the Laba Limestone also show that it was originally deposited in a shallow water environment. The isolated Laba Limestone occurs in the red mudstone, silicilith and muddy siltstone deposited in deep or semi deep water environments. The occurrence and features of structures of the Laba Limestone indicate that it was transported to deep or semi deep water environments by collapsing or slumping along the submarine channels. The Laba Limestone containing Triticites in the Haibang section of Ali of Lancang County was probably produced in the Qixia time of early Permian age but the Laba Limestone containing Newschwagerina around Nanpan of Laba of Lancang County was seemingly formed in the Maokou time of Middle Permian age. The origin of Laba Limestone can be used to infer the occurrence of the abrupt edge between the Changning-Menglian ocean and the adjacent shelf.
【Fund】: 国家自然科学基金项目!(No.49672 14 7)研究成果之一
【CateGory Index】: P534.46
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