Oncolites of the Lower Permian Chuanshan Formation in South China and Their Geological and Economic Significance

Abstract: A large amount of oncolites popularly named “Chuanshan balls” occur universally in the Lower Permian Chuanshan Formation in South China. These kinds of oncolites have the following characteristics: wide distribution, huge quantities, large sedimentary thickness and similar characters, which constitute a specific “fashion facies” in geological history. The authors consider that these kinds of oncolites were due to the intense differentiation of the global climate at that time, which resulted in a universal descent of the sea level and breeding of a large amount of algae in sea water over low‐latitude areas. According to the distribution and characteristics of the oncolitic, relative relationships between different tectonic blocks may be inferred, diagenetic strength indicated and diagenetic history recovered, and more important, oncolites serve as a favourable reservoir rock, so their study is of great theoretical and economic significance.