Quantitative study of bioclastic grains in carbonate rocks: Theoretical analysis and application of point-counting method
Wen Junjun1, Liu Jianbo1,2,3
1 School of Earth and Space Sciences， Peking University， Beijing 100871 2 Key Laboratory of Orogenic Belts and Crustal Evolution， Ministry of Education，Peking University, Beijing 100871 3 State Key Laboratory of Palaeobiology and Stratigraphy， Nanjing Institute of Geology and Palaeontology， Chinese Academy of Sciences， Nanjing 210008，Jiangsu
Abstract：The abundance of bioclastic grains in carbonate rocks is of great value in researches of fossil diversity and reconstruction of paleoecological environment. It can be easily valued with point-counting method， which is more suitable for carbonate rock than the other two quantitative approaches-visual estimation and image analysis. However， few studies have been attempted to determine how many points should be counted to yield adequate and precise results， which made the point-counting procedure time-consuming. By comparative analysis of the comparison charts for visual percentage estimation and microphotographs of the Ordovician carbonate rocks， this study focuses on how these attributes influence the precision of point-counting method， and discusses a moderate number of points which facilitates the method. As a result， a number of 500 points or so is appropriately enough for precise measure of the abundance of the referred component in most of carbonate thin sections with an error of ±2.5％， and should be adjusted with abundance， grain size， sorting as well as biodiversity of bioclasts in thin sections.
Wen Junjun,Liu Jianbo. Quantitative study of bioclastic grains in carbonate rocks: Theoretical analysis and application of point-counting method[J]. JOPC, 2009, 11(5): 581-592.
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