收稿日期: 2001-08-08
修回日期: 2001-11-18
网络出版日期: 2002-06-01
基金资助
国家自然科学基金项目“西藏白垩纪海洋集群绝灭后的生物复苏”(编号:49872003)资助.
MID-CRETACEOUS GEOCHEMICAL ANOMALY AND THEIR RESPONSES TO SEA-LEVEL CHANGES IN TINGRI OF TIBET
Received date: 2001-08-08
Revised date: 2001-11-18
Online published: 2002-06-01
西藏南部定日地区在白垩纪中期为一套浅灰色-深灰色的陆源碎屑岩(钙质页岩)及碳酸盐岩(泥灰岩及微晶灰岩)的混积型沉积物,其中的地球化学特征变化反映了古海洋发生的重大变革。δ13 C的同位素曲线变化具有明显的低-高-低旋回变化,δ13 C正偏与有机碳大量埋藏、海平面上升及缺氧事件密切相关。铀、钍、钾的含量变化及Th/U比值的变化特征表明由海平面上升所形成的全球大洋缺氧的重要时期,由于有机物质及粘土矿物的增多,它们的含量均比标准平均值偏高。而87Sr/ 86Sr比值在该时期偏低,这也与当时的构造背景及海平面发生重大变化相一致。
赵文金 , 万晓樵 . 藏南定日地区白垩纪中期地球化学异常对海平面上升的响应[J]. 地球科学进展, 2002 , 17(3) : 331 -338 . DOI: 10.11867/j.issn.1001-8166.2002.03.0331
A series of light-dark gray marine clastic and carbonate rocks of middle Cretaceous (late Cenomanian to early Turonian) are well exposed in the Gongzha Section of Tingri in southern Tibet. The strata near the Cenomanian-Turonian boundary can be subdivided into the Lengqingre and Gangbacunkou formations in ascending order, and the Cenomanian-Turonian boundary located in the upper part of Lengqingre formation. The characteristics of microfauna and geochemistry from the strata show that tremendous changes took place in marine middle Cretaceous. In this paper, we mainly study the middle Cretaceous geochemical characteristics and their response to sea level changes in southern Tibet of China.
The carbon, strontium and Uranium (U), Thorium (Th), Kalium (K) isotope composition of marine rocks are mainly controlled by global events that are related to the changes of sea level, such as relative amount of organic accumulation, changes in seafloor spreading rate and palaeoclimate variation etc.The δ13C curve of Tingri in middle Cretaceous is characterized by low-high-low cycle change, and the positive excursion of δ13C values happens near the Cenomanian-Turonian boundary. Those characteristics coincide with sea level changes, accumulation of organic carbon and oceanic anoxic event during this period. The changes of U, Th and K abundance values near Cenomanian-Turonian boundary in Tingri indicate that their compositions are higher during oceanic anoxic period because of increase of organic materials and clay minerals, which are the results from the changes of sea level. In southern Tibet, the 87Sr/ 86Sr ratio in middle Cretaceous is 0.7076. It is obvious that the value is rather low. We suspect that it should be related to the tectonic activity and big change of sea level in this time.
In southern Tibet of China, middle Cretaceous is a period of short time expansion of the Tethyan ocean, which brings about sea level rises, accumulation of large amount of organic carbon and oceanic anoxic event. Some geochemical anomaly changes during this period, such as the positive excursion of δ13C values and U, Th and K abundance values, the relatively low 87 Sr/ 86 Sr ratio and so on, correspond to the sea level rises. There is no doubt that those geochemical anomaly changes are sensitive indicators of the sea level changes in middle Cretaceous.
[1] Wan Xiaoqiao, Yin Jiarun. Mid-Cretaceous microfossil assemblages and paleoceanographic event in Gamba, Tibet [J]. Acta Micropalaeontologica Sinica, 1996, 13(1): 43-56. [万晓樵, 阴家润. 西藏岗巴白垩纪中期微体生物群与古海洋事件[J]. 微体古生物学报, 1996,13(1):43-56.]
[2] Ken Caldeira, Michael R Rampino. The mid-Cretaceous super plume, carbon dioxide, and global warming [J]. Geophysical Research Letters, 1991, 18(6): 987-990.
[3] Yoshiyuki Tatsumi, Hironao Shinjoe, Hideo Ishizuka, et al. Geochemical evidence for a mid-Cretaceous superplume [J]. Geology, 1998, 26(2): 151-154.
[4] Hart M B, Kim C B. Late Cretaceous anoxic events, sea-level changes and the evolution of the planktonic foraminifera [A]. In: Summerhayes C P, Shackleton N J, eds. North Atlantic Palaeoceanography[C]. Geological Society Special Publication, 1986. 67-78.
[5] Leary P N, Carson G A, Cooper M K E, et al. The biotic response to the late Cenomanian oceanic anoxic event, integrated evidence from Dover, SE England [J]. Journal of the Geological Society, 1989,146: 311-317.
[6] Wan Xiaoqiao. Cretaceous foraminifera from southern Xizang (Tibet): A study on eustatic change [J]. Geoscience, 1992, 6(4): 392-398. [万晓樵. 从有孔虫分析西藏南部白垩纪海平面升降[J]. 现代地质,1992, 6(4):392-398.]
[7] Schlanger S O, Arthur M A, Jenkyns H C, et al. The Cenomanian-Turonian oceanic anoxic event, I. Stratigraphy and distribution of organic carbon-rich beds and the marine δ13C excursion [A]. In: Brooks J, Fleet A J, eds. Marine Petroleum Source Rocks [C]. Geol Soc Spec Pub, 1987. 371-399.
[8] Wapies D W, Cunningham R. Shipboard organic geochemistry, Leg 80, DSDP [A]. In: Poag W de Graciausky P C, et al, eds. Initial Reports Deep Sea Drilling Project [C]. 1985,80: 949-968.
[9] Scholle P A, Arthur M A. Carbon isotope fluctuations in Cretaceous pelagic limestones: potential stratigraphic and petroleum exploration tool [J]. Bull Am Ass Petrol Geol, 1980, 64: 67-87.
[10]Kunio Kaiho, Takashi Hasegawa. End-Cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern Pacific Ocean [J]. Palaeography, Palaeoclimatology, Palaeoecology, 1994, 111: 29-43.
[11]Raup D M, Sepkoski J J. Periodic extinctions of families and genera [J]. Science, 1984, 231: 833-836.
[12] Helmut Willems, Wan Xiaoqiao, Yin Jiarun, et al. The Mesozoic Development of the N-Indian Passive Margin and of the Xigaze Forearc Basin in Southern Tibet, China [M]. Berchte, Fachbereich Geowissenschaften, Universitt Bremen, 1995.
[13] Wang Jianfeng. Geochemistry of Uranium [M]. Beijing: Atomic Energy Publishing House, 1986. [王剑锋. 铀地球化学教程[M]. 北京:原子能出版社, 1986.]
[14] Zhao Qiyuan, et al, eds. Geochemistry of Ocean [M]. Beijing: Geological Publishing House, 1995. [赵其渊等编. 海洋地球化学[M]. 北京:地质出版社, 1995.]
[15] Yu Guangming, Wang Chengshan. Sedimentary Geology of the Xizang (Tibet) Tethys [M]. Beijing: Geological Publishing House, 1990. [余光明,王成善. 西藏特提斯沉积地质[M]. 北京:地质出版社, 1990.]
[16] Bureau of Geology and Mineral Resources of Xizang Autonomous Region. Regional Geology of Xizang (Tibet) Autonomous Region [M]. Beijing: Geological Publishing House, 1993. [西藏自治区地质矿产局. 西藏自治区区域地质志[M]. 北京:地质出版社, 1993.]
[17] William T Holser, Mordeckai Magaritz, Robert L. Ripperdan. Global isotopic events [A]. In: Otto H Walliser, ed. Global Events and Event Stratigraphy in the Phanerozoic[C]. Berlin: Springer-verlag Heidelberg, 1996. 63-80.
[18] Ján Veizer, Dieter Buhl, Andreas Dieuer, et al. Strontium isotope stratigraphy: potential resolution and event correlation [J]. Palaeography, Palaeoclimatology, Palaeoecology, 1997, 132: 65-77.
[19] Smalley P C, Higgins A C, Howarth R J, et al. Seawater Sr isotope variations through time: A procedure for constructing a reference curve to date and correlate marine sedimentary rocks [J]. Geology, 1994, 22: 431-434.
[20] Burke W H, Denison R E, Hetherington E A, et al. Variation of seawater 87Sr/ 86Sr through phanerozoic time [J]. Geology, 1982, 10: 516-519.
[21] Huang Sijing, Chen Jianming, Leng Dexun. The strontium isotopes of deep-sea siliceous rocks from earlier Carboniferous to earlier Permian, Qinzhou, Guangxi [J]. Acta Sedimentologica Sinica, 1999, 17(4): 542-546.[黄思静,陈建明,冷德勋. 广西钦州石炭—二叠纪深海硅质岩的锶同位素组成及其地质意义[J]. 沉积学报,1999,17(4):542-546.]
/
〈 |
|
〉 |