Characteristics of carbon and oxygen isotopes of the Ordovician carbonate rocks in Ordos and their implication
Chen Qiang1, Zhang Huiyuan2, Li Wenhou3, Hao Songli3, Liu Zhuo3
1 School of Earth Science and Resources，Chang′an University，Xi′an 710054，Shaanxi 2 Xi′an Center of Geological Survey，CGS，Xi′an 710054，Shaanxi 3 Department of Geology，Northwest University，Xi′an 710069，Shaanxi
Abstract The Ordos has gigantically thick Paleozoic marine strata.The carbon and oxygen isotopes of the Ordovician carbonate rocks in the Ordos are less modified by post-depositional diagenesis，and thus provide helpful insights into the original ocean.The δ13C values of the Ordovician carbonate rocks in the Ordos range from -7.30‰ to 2.26‰ with a mean value of -0.30‰ and the δ18O varies between -13.14‰ and -1.94‰，averaging at -6.38‰，which indicate the carbon and oxygen isotopes of the Ordovician in the Ordos are comparable to those of the global Ordovician.Spatially，the δ13C shows a decreasing trend，indicating shoaling in water-depth from the western margin of the Ordos，to the southern margin and then to the eastern margin.Temporally，the δ13C gradually increases，showing that sea level rose from the Early to the Late Ordovician，with a significant positive excursion between the Middle and Late Ordovician that is indicated by increase in mean δ13C value from -0.36‰ in the Majiagou Formation to 0.15‰ in the Pingliang Formation and then to 0.68‰ in the Beiguoshan Formation.Sea level change suggested by carbon isotope distribution is consistent with the evolution of sedimentary facies.The positive excursion of carbon isotopes in the Middle and Late Ordovician in the Ordos indicates relative high productivity and organic carbon burial，which is of important petroleum geological significance，reflecting the Pingliang Formation，Wulalike Formation and Beiguoshan Formation in the southwestern margin as the most important and efficient hydrocarbon source rocks of the Lower Paleozoic in the Ordos.
About author: Chen Qiang，born in 1980，graduated from Northwest University in 2011 with a Ph.D.degree.Now he is a lecturer in Chang′an University and is engaged in sedimentology.E-mail: qchen110@163.com.
Cite this article:
Chen Qiang,Zhang Huiyuan,Li Wenhou et al. Characteristics of carbon and oxygen isotopes of the Ordovician carbonate rocks in Ordos and their implication[J]. JOURNAL OF PALAEOGEOGRAPHY, 2012, 14(1): 117-124.
Chen Qiang,Zhang Huiyuan,Li Wenhou et al. Characteristics of carbon and oxygen isotopes of the Ordovician carbonate rocks in Ordos and their implication[J]. JOPC, 2012, 14(1): 117-124.
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