Discovery of microbial mounds of the Lower Permian Qixia Formation in northwestern Sichuan Basin and its geological significance
Quan Zi-Ting1,2,3, Tan Xiu-Cheng1,2,3, Zhang Ben-Jian4, Tang Hao1,2,3, Luo Bing4,5, Yang Xun6, Zhang Ya4, Xiao Di1,2,3, Tang Yan-Ling1,2,3
1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China; 2 Research Branch of Southwest Petroleum University,Key Laboratory of Carbonate Reservoirs,CNPC,Chengdu 610500,China; 3 Sichuan Natural Gas Geology Key Laboratories,Southwest Petroleum University,Chengdu 610500,China; 4 Exploration and Development Research Institute,PetroChina Southwest Oil & Gas Field Company,Chengdu 610041,China; 5 Chongqing Gas Field, PetroChina Southwest Oil & Gas Field Company, Chongqing 400021, China; 6 Northwest Sichuan Gas Mine of PetroChina Southwest Oil & Gas Field Company, Sichuan Jiangyou 621700, China
Abstract Through analysis of outcrops and drilling profile data in the field and laboratory,microbial mounds were found in the Lower Permian Qixia Formation in the northwestern Sichuan Basin. The microbial mound is mainly composed of thrombolites,stromatolites,and microbial bindstones. These microbial carbonates are characterized by development of typical clots,stromatolitic,fenestral,and microbial bonding fabrics. Microbial mounds of the Qixia Formation are typical mound-shaped with flat bottom and convex-up top,and various in size. They range from tens of centimeters to several meters in height and from several meters to tens of meters in width. The mounds are characterized by shallowing-upward sequences,which are generally composed of mound base,core and cap,and also may form a mound-bank complex with carbonate shoals. Analysis of regional paleogeographic background and the characteristics of microbial mounds suggests that the Qixia period in northwestern Sichuan was deposited in a semi-restricted platform,with shallow-water and the relatively low-energy conditions. The high-frequency sea-level change,lateral migration,and superposition of microbial mounds lead to the restricted environment on carbonate platform with ramp background,which results in penecontemporaneous dolomitization in earlier sediments. Microbial mound-bank complexes provide basis for development of the dolomite reservoirs in the Qixia Formation. The slope-break belt of platform margin,gentle slope break belt,and local highland inside carbonate platform are favorable zones for the development of the dolomite reservoirs in the Qixia Formation. This understanding plays an important guiding role in finding banded dolomite reservoirs with unstable scale horizons,and will greatly expand the exploration field of dolomite reservoirs in the Qixia Formation.
Fund:National Natural Science Foundation of China(No.41802147)and Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance
Corresponding Authors:
Tan Xiu-Cheng,born in 1970,professor and Ph.D. advisor,is mainly engaged in the research on sedimentology and reservoir geology. E-mail: tanxiucheng70@163.com.
About author: Quan Zi-Ting,born in 1994,is a master degree candidate of Southwest Petroleum University. She is mainly engaged in the reasearch on carbonate sedimentology. E-mail: qzt_0904@qq.com.
Cite this article:
Quan Zi-Ting,Tan Xiu-Cheng,Zhang Ben-Jian et al. Discovery of microbial mounds of the Lower Permian Qixia Formation in northwestern Sichuan Basin and its geological significance[J]. JOPC, 2021, 23(6): 1110-1124.
Quan Zi-Ting,Tan Xiu-Cheng,Zhang Ben-Jian et al. Discovery of microbial mounds of the Lower Permian Qixia Formation in northwestern Sichuan Basin and its geological significance[J]. JOPC, 2021, 23(6): 1110-1124.
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