The Baffling Buildup Reef of Honghuayuanian Age, Ordovician in Zhangzhai of Yuping County, Guizhou

Abstract: The reef of the Honghuayuanian Age in Zhangzhai of Yuping County. Guizhou Province is a baffling buildup reef, which scatters in marginal platform facies. The association of fossils is characterized by sponge such as "calathium" sp., Anchaoscyphia chiliense, A. sp. and algae. The o'thers are Crinoil. Trilobite, Braichiopodaetc. The sedimentary rocks, th refore. are divided mainly into four types as algal limestone, sponge limestone, bioclastic limestone, oncolites and clotted limestone. In the reef core facies. there are algal limestone (A), sponge limestone (B). bioclastic limestone (C). and oncelites and clotted limestone (D). These types of rocks make up a practical sequence of stratum that consists of 41 layers: Top-DCDCDCDABADCDCBDBCDABABDC ABACBABDBDCBDCBD-bottom In which there are 7 As. 11 Bs. 11Cs and 12 Ds. In term of the Markov chain analysis, it was found that the depositional sequence of each cycle is composed of: →B→A→B→D→C→D→C→ Fore reef facies is characterized by micrite. pelmicrite and bioclastic limestone. These rocks are dolomitized locally. Joints are very developed, bitumens contaminated and stuffed in the joints as leticulars. There are much collapse breccia. This facies belong to the quiet environment which is much deep lower than the wave base. The buildup of reef core is washed by wave and collapsed, the breccia then is formed. The association of fossils and rocks in back reef facies. are similar to that of the reef core, but different in their thickness. This facies. actually, belongs to the carbonate platform biostrom facies. The base of reef are stratum of Tongzian Age which is composed of sparry pellet limstone and oncolites - clotted limestone, this stratum belongs to the carbonate platform marginal allochcm bank facies. The algal and other crust organisms arc very develeped. Similar to the strata of the same ages, this stratum form a buildup too. The depositional materials of this platform marginal facies formed a solid sedimentary base where is favour for reef forming.