古地理学报 ›› 2012, Vol. 14 ›› Issue (1): 117-124. doi: 10.7605/gdlxb.2012.01.010

• 地球化学及沉积环境 • 上一篇    下一篇

鄂尔多斯奥陶系碳酸盐岩碳氧同位素特征及其意义*

陈强1 张慧元2 李文厚3 郝松立3 刘卓3   

  1. 1 长安大学地球科学与资源学院,陕西西安 710054
    2 中国地质调查局西安地质调查中心,陕西西安 710054
    3 西北大学地质学系,陕西西安 710069
  • 收稿日期:2011-06-13 修回日期:2011-07-26 出版日期:2012-02-01 发布日期:2012-02-01
  • 作者简介:陈强,男,1980年生,2011年毕业于西北大学,获博士学位,现为长安大学讲师,主要研究方向为沉积学。E-mail: qchen110@163.com。
  • 基金资助:
    国家科技重大专题(编号:2008ZX05005-004-007HZ)资助

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. 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
  • Received:2011-06-13 Revised:2011-07-26 Online:2012-02-01 Published:2012-02-01
  • 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.

摘要: 鄂尔多斯古生代海相地层沉积厚度巨大。鄂尔多斯奥陶系碳酸盐岩的碳氧同位素组成受后期成岩作用影响较小,基本保留了原始海洋的同位素组成: δ13C值分布于-7.30‰~2.26‰之间,均值-0.30‰;δ18O值分布于-13.14‰~-1.94‰之间,均值-6.38‰,碳氧同位素组成与全球基本一致。区域上,鄂尔多斯西缘具有相对较高的δ13C值,南缘次之,而东缘最低。纵向上,碳同位素组成逐渐增重,并在中晚奥陶世发生明显的正向偏移,δ13C均值由马家沟组的-0.36‰增加到平凉组的0.15‰,至背锅山组增加至0.68‰。碳同位素的区域分布差异表明鄂尔多斯西缘水体相对较深,南缘次之,东缘相对较浅,由早奥陶世至晚奥陶世水体逐渐加深,碳同位素组成反映的海平面变化趋势与沉积相演化一致。鄂尔多斯西南缘中晚奥陶世碳同位素组成的正向偏移,标志着较高的生产力和有机碳埋藏率,具有重要的石油地质学意义,西南缘的平凉组/乌拉力克组和背锅山组是下古生界最重要和有效的烃源岩层。

关键词: 碳氧同位素, 古环境, 石油地质, 奥陶系, 鄂尔多斯

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.

Key words: carbon and oxygen isotopes, paleoenvironment, petroleum geology, Ordovician, Ordos

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