Characteristics of carbon and oxygen isotopes and their significance of the Cambrian Xixiangchi Group carbonate rocks in eastern Sichuan Basin
Jia Peng1, Li Wei1, Li Ming1, Deng Shenghui1, Lu Yuanzheng1, Li Xin1, Fan Ru1, Liu Xin2
1 Research Institute of Petroleum Exploration & Development,PetroChina,Beijing 100083; 2 Southwest Oil & Gas Field Company,PetroChina,Chengdu 610000,Sichuan
Abstract：The carbon and oxygen isotopes of the Cambrian Xixiangchi Group carbonate rocks in eastern Sichuan Basin are less affected by post-depositional diagenesis,and thus provide helpful insights into the original ocean. Based on the C and O isotopic profile of 111 analytic results obtained by the standard method of phosphorolysis,we have discussed the composition and evolution of δ13C and δ18O recorded in the Middle-Upper Cambrian carbonate rocks in eastern Sichuan Basin,as well as their geological implication. The research shows the values of δ13C range from-3.36‰ to 2.65‰ with mean value of-1.027‰,most of which are in the range of-2‰~2‰;and the values of δ18O range from-11.1‰ to-6.01‰, most range in of-10‰~-6‰, with average value of-7.991‰. Carbon and oxygen isotope analysis illustrates that the Xixiangchi Group was formed in a warm to hot onshore marine sedimentary environment with a high salinity. The δ13C analysis suggests there were a slow regression after a rapid and short transgression at the early-middle depositional stage,as well as a rapid regression after a slow transgression at the late depositienal stage of Xixiangchi Group. Sea level changes reflected by carbon isotope distribution are consistent with the evolution of sedimentary facies.The positive excursion of carbon isotopes in the Middle Xixiangchi Group in Sichuan Basin indicates relative high productivity and burial rate of organic carbon,which is of great petroleum geological significances.
Jia Peng,Li Wei,Li Ming et al. Characteristics of carbon and oxygen isotopes and their significance of the Cambrian Xixiangchi Group carbonate rocks in eastern Sichuan Basin[J]. JOPC, 2017, 19(3): 503-512.
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