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.
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.
安太庠，郑昭昌.1990.鄂尔多斯盆地周缘的牙形石［M］.北京：科学出版社，1-201. 包洪平，杨承运.2000.鄂尔多斯东部奥陶系马家沟组微相分析［J］.古地理学报，2（1）:33-42. 鲍志东，李儒峰，冯增昭.1999.鄂尔多斯盆地东西部奥陶系对比再研究［J］.地质论评，45（4）:375-382. 陈孟晋，宁宁，胡国艺，等.2007.鄂尔多斯盆地西部平凉组烃源岩特征及其影响因素［J］.科学通报，52(S1):78-85. 陈孟晋，汪泽成，孙粉锦.2006.鄂尔多斯西缘前陆盆地油气地质［M］.北京：石油工业出版社，1-229. 冯增昭，鲍志东，康祺发，等.1999a.鄂尔多斯早古生代古构造［J］.古地理学报，1（2）:84-91. 冯增昭，鲍志东，康祺发，等.1999b.鄂尔多斯奥陶纪古构造［J］.古地理学报，1（3）:83-94. 冯增昭，鲍志东，张永生，等.1998.鄂尔多斯奥陶纪地层岩石岩相古地理［M］.北京：地质出版社，1-144. 冯增昭，陈继新，张吉森.1991.鄂尔多斯地区早古生代岩相古地理［M］.北京：地质出版社，1-190. 付金华，郑聪斌.2001.鄂尔多斯盆地奥陶纪华北海和祁连海演变及岩相古地理特征［J］.古地理学报，3（4）:25-34. 彭冰霞，王岳军，范蔚茗，等.2006.贵州乐康剖面茅口阶—吴家坪阶碳同位素组成变化及峨眉山大火成岩省的响应［J］.地球化学，35(2):126-132. 腾格尔，刘文汇，徐永昌，等.2004.海相沉积有机质的碳同位素记录及其环境意义——以鄂尔多斯盆地为例［J］.石油勘探与开发，31(5):11-16. 腾格尔，刘文汇，徐永昌，等.2005.海相地层无机参数与烃源岩发育环境的相关研究——以鄂尔多斯盆地为例［J］.石油与天然气地质，26(4):411-421. 腾格尔，刘文汇，徐永昌，等.2006.高演化海相碳酸盐烃源岩地球化学综合判识——以鄂尔多斯盆地为例［J］.中国科学（D辑），36(2):167-176. 王大锐，冯晓杰.2002.渤海湾地区下古生界碳、氧同位素地球化学研究［J］.地质学报，76(3):400-408. 王大锐，白玉雷，贾承造.1998.塔里木中、上奥陶统碳同位素组成正向偏移的石油地质学意义［J］.石油勘探与开发，25(4):15-16. 夏新宇，洪峰，赵林，等.1999.鄂尔多斯盆地下奥陶统碳酸盐岩有机相类型及生烃潜力［J］.沉积学报，17（4）:638-643. 张水昌， Wang R L，金之钧，等.2006.塔里木盆地寒武纪—奥陶纪优质烃源岩沉积与古环境变化的关系：碳氧同位素新证据［J］.地质学报，80（3）:459-466. 张水昌，张宝民，边立曾，等.2005.中国海相烃源岩发育控制因素［J］.地学前缘，12（3）:39-48. 左景勋，童金南，邱海鸥，等.2006.下扬子地区早三叠世碳酸盐岩碳同位素组成的演化特征［J］.中国科学（D辑），36(2):109-122. Bergstrom S M，Chen X，Schmitz B， et al.2009.First documentation of the Ordovician Guttenberg δ13C excursion（GICE）in Asia: Chemostratigraphy of the Pagoda and Yanwashan formations in southeastern China［J］.Geological Magazine，146: 1-11. Bergstrom S M，Young S，Schmitz B.2010.Katian（Upper Ordovician）δ13C chemostratigraphy and sequence stratigraphy in the United States and Baltoscandia: A regional comparison［J］.Palaeogeography，Palaeoclimatology，Palaeoecology，296(3-4): 217-234. Derry L A，Brasier M D，Corfield R M， et al.1994.Sr and C isotopes in Lower Cambrian carbonates from the Siberian craton: A paleoenvironmental record during the ‘Cambrian explosion［J］.Earth and Planetary Science Letters，128(3-4): 671-681. Hatch J R，Jacobson S R，Witzke B J， et al.1987.Possible late Middle Ordovician organic carbon isotope excursion: Evidence from Ordovician oils and hydrocarbon source rocks，Mid-Continent and east-central United States［J］.AAPG Bulletin，71(11):1342-1354. Kaljo D，Martma T，Saadre T.2007.Post-Hunnebergian Ordovician carbon isotope trend in Baltoscandia，its environmental implications and some similarities with that of Nevada［J］.Palaeogeography，Palaeoclimatology，Palaeoecology，245(1-2): 138-155. Kaufman A J，Jacobsen S B，Knoll A H.1993.The vendian record of Sr and C-isotopic variations in seawater: Implications for tectonic and paleoclimate［J］.Earth and Planetary Science Letters，120(3-4): 409-430. Kaufman A J，Knoll A H.1995.Neoproterozoic variations in the C-isotopic composition of seawater: Stratigraphic and biogeochemical implications［J］.Precambrian Research，73(1-4): 27-49. Qing H，Veizer J.1994.Oxygen and Carbon isotopic composition of Ordovician brachiopods: Implications for coeval seawater［J］.Geochimica et Cosmochimica Acta，58(20):4429-4442. Saltzman M R，Young S A.2005.Long-lived glaciation in the Late Ordovician？Isotopic and sequence-stratigraphic evidence from western Laurentia［J］.Geology，33（2）: 109-112. Shields G A，Carden G A F，Veizer J， et al.2003.Sr，C，and O isotope geochemistry of Ordovician brachiopods: A major isotopic event around the Middle-Late Ordovician transition［J］.Geochimica et Cosmochimica Acta，67(11):2005-2025. Veizer J，Ala D，Azmy K， et al.1999. 87Sr/86Sr，δ13C and δ18O evolution of Phanerozoic seawater［J］.Chemical Geology，161(1-3): 59-88. Wang K，Chatterton B D E，Wang Y.1997.An organic carbon isotope record of Late Ordovician to Early Silurian marine sedimentary rocks，Yangtze Sea，South China: Implications for CO2 changes during the Hirnantian glaciation［J］.Palaeogeography，Palaeoclimatology，Palaeoecology，132(2):147-158. Young S A，Saltzman M R，Bergstrom S M.2005.Upper Ordovician（Mohawkian）carbon isotope（δ13C）stratigraphy in eastern and central North America: Regional expression of a perturbation of the global carbon cycle［J］.Palaeogeography，Palaeoclimatology，Palaeoecology，222（1-2）: 53-76. Young S A，Saltzman M R，Bergstrom S M， et al.2008.Paired δ13Ccarb and δ13Corg records of Upper Ordovician（Sandbian-Katian）carbonates in North America and China: Implications for paleoceanographic change［J］.Palaeogeography，Palaeoclimatology，Palaeoecology，270(1-2): 166-178.
