摘要
西藏南部岗巴盆地位于位于特提斯构造域的东端,发育有完整的晚白垩世至古近纪地层,地层中化石丰富,前人根据化石研究准确地进行了地层时代的划分。认为该区白垩纪/古近纪界线位于宗山组和基堵拉组之间,以底栖大有孔虫Orbitoides-Omphalocyclus动物群的消亡和Rotalia-Smoutina-Lockhartia动物群的始现为标志。界线上下岩层为平行不整合接触,期间有一短暂的暴露面。古新世的砂砾岩直接覆于晚白垩世的陆棚碳酸岩盐沉积之上,沉积的重大转变代表一次区域构造运动。西藏南部晚白垩世的海平面从坎潘晚期到丹尼早期是逐渐降低的,生物消亡特点显示出与海平面变化的一致性,可能原因主要受海平面变化的影响。锶同位素曲线与全球温度变化和全球海平面变化有很好的对应关系。在第22层位上,锶同位素曲线出现一处明显的负偏波谷,~(87)Sr/~(86)Sr比值达到了0.707605,此时全球温度也出现下降,对应坎潘期印度洋脊南北向迅速扩张,全球海平面上升,大规模海泛导致盆地中陆地剥蚀物减少。其余各点均表现出明显的正偏升高趋势,全球温度也表现为一个小的升高波动,对应马斯特里赫特晚期和丹尼初期,印度洋脊扩张速度减慢,海平面下降,印度板块北缘的陆壳及洋壳向下俯冲抬升遭受风化剥蚀,大规模的造山运动导致陆壳物质的输入增多。磁化率受古代海平面变化的控制。特别当陆源物质供应低时,磁化率曲线变化和海平面变化相一致,磁化率主要由自生矿物的种类决定。如果陆源物质供应高时,平均磁化率的值也会相应增高,但是与海平面变化还是有关联。海平面下降会导致陆源物质含量的增加,并且磁化率也会升高。西藏岗巴盆地质量磁化率高的层位颜色较深,大都为铁质胶结,含石英和岩屑较多,颗粒较粗,多为砂岩。可以看出其生成条件是氧化环境,陆源输入多,搬运距离近,沉积在高能环境里。白垩纪/古近纪界线由下往上岩性变化从灰岩到砂岩,可以推测出海水是由深变浅的。当时印度板块北移碰撞,导致藏南岗巴盆地局部隆升,造成海退。根据岩石薄片鉴别出的生物组合及岩性特征,认为白垩纪/古近纪界线时期,岗巴盆地海洋环境是处于温暖的热带、亚热带浅海陆棚相-开放循环环境中,分为碳酸盐缓坡相和碳酸盐浅滩相。
The Gamba basin of southern Tibet, is located in the east of Tethys tectonic region, whereexposes complete strata from late Cretaceous to Paleogene. The strata yield abundantfossils, and accurate biostratigraphic works have been done by previous studies. TheCretaceous/Paleogene boundary was recognized by the extinction of larger benthicforaminifora Orbitoides-Omphalocyclus fauna and the first appearance ofRotalia-Smoutina-Lockhartia fauna. The boundary is between the Zongshan and Jibulaformations. Both formations are disconformity. There is a short time exposing facebetween them. At the contact, the Paleocene clastic rock of Zongshan Formation overliesdirectly on the latest Cretaceous shelf carbonate rock. It indicates a regional tectonicprocess. The boundary extinction is mainly influenced by sea level changes in southernTibet. The regression occurred from late Campanian of Cretaceous to early Danian ofPaleogene. Sr isotopic curve is well correlated with global temperature and sea levelchanges. An apparent negative excursion at bed 22 is correlated with the globaltemperature decline. The ~(87)Sr/~(86)Sr ratio of 0.707605 can be related to the tectonic processand sea level rising resulting from the rapid Indian Ocean ridge expansion in Campanian.Decrease of detrital weathering materials is resulted from ingression. Other horizonsshow apparent positive excursions, which are correlated with the global temperature shift,we relate to the sea level regression resulting from the Indian Ocean ridge expansion inlate Masstrichtian and early Danian stages. Continental crust and ocean crust at northmargin of Indian Plate subducted and caused continental uplift. Increase of detritalweathering materials is resulted from orogeny activity. Magnetic susceptibility variationis controlled by ancient sea level changes. It is particular if the supply of detrital materialwas low, when the magnetic susceptibility was mainly controlled by the content ofauthigenic minerals. If the supply of detrital materials was high, the average susceptibilityvalue would be higher, but there is still a correlation between susceptibility and sea levelcurves. A sea level depress would lead to an increase in the content of the detrital
materials, and therefore to an increase in the susceptibility values. Beds with highermagnetic susceptibility are darker in color in the Gamba basin of southern Tibet. Most ofthem are ferruginous cement, more quarts and rock fragments, fine grain sandstone. It isconcluded that they occurred in oxidation environment, more detrital materials, longdistance transport and deposited in high-energy environment. There are carbonate rocksbelow the Cretaceous/Paleogene boundary and sandstone above the boundary. It isconcluded that the sea level was dropping down. The Gamba basin uplifted partly andseawater withdraw were the result of continental collision when Indian plate moved tonorth. According to the fossil assemblages and lithology, it is suggested that, during theCretaceous/Paleogene boundary time, Gamba basin was in a warm tropical, subtropicalshallow shelf-circulating environment. It can be recognized as carbonate gentle slope andcarbonate shallow bank facies.
引文
[1] 万晓樵.西藏岗巴地区白垩纪底层及有孔虫动物群.见:李廷栋主编,青藏高原地质文集,北京:地质出版社,1985,16:203~228
[2] 万晓樵.西藏白垩纪浮游有孔虫化石带.见:李廷栋主编,青藏高原地质文集,北京:地质出版社,1987a,18:112~121
[3] 万晓樵.西藏第三纪有孔虫生物地层及地理环境.现代地质,1987b,1(1):15~47
[4] 万晓樵.西藏白垩纪—早第三纪有孔虫与特提斯喜马拉雅海的演化.微体古生物学报,1990,7(2):169~186
[5] 万晓樵.从有孔虫分析西藏南部白垩纪海平面升降.现代地质,1992,6(4):392~398
[6] 万晓樵,阴家润.西藏岗巴地区白垩纪中期微体生物群与古海洋事件.微体古生物学报,1996,13(1):43~56
[7] 万晓樵,赵文金,李国彪.对岗巴上白垩统的新认识,现代地质,2000,14(3):281~285
[8] 文世宣.青藏高原白垩纪双壳类生物地理.古生物学报,1999,38(1):1~30
[9] 马宗晋,李存悌,高祥林.全球洋底增生构造及其演化.中国科学(D 辑),1998,28(2):157~165
[10] 马宗晋,杜品仁,卢苗安.地球的多圈层相互作用.地学前缘,2001,8: 3~8
[11] 王鸿祯.试论西藏地质构造分区问题.武汉地质学院学报,1983,第一期
[12] 王乃文.青藏印度古陆及其与华夏古陆的合并.中国地质科学院与法国科学院研究中心编,中法喜马拉雅考察成果,1980,北京:地质出版社,1984,39~62
[13] 王世杰,董丽敏,林文祝,等.泥河湾组有孔虫化石群的锶同位素研究.科学通报,1995,40(22)
[14] 西藏自治区地质矿产局.西藏自治区区域地质志.北京:地质出版社,1993
[15] 西藏自治区测绘局.西藏自治区地图册.北京:中国地图出版社,1995
[16] 西藏地质矿产局.西藏自治区岩石地层.武汉:中国地质大学出版社,1997,183~184
[17] 西藏自治区地质局综合地质大队(孙亦因等).中华人民共和国区域地质调查报告(1:100万),日喀则幅.北京:地质出版社,1984
[18] 李祥辉,王成善.西藏特提斯喜马拉雅显生宇的超层序.特提斯地质,1997,21:8~30
[19] 刘增乾,徐宪,潘桂堂,等.青藏高原大地构造与形成演化,中华人民共和国地质矿产部地质专报 五 构造地质 地质力学 第 10 号.北京:地质出版社,1990
[20] 刘传联,成鑫荣.渤海湾盆地早第三纪非海相钙质超微化石的锶同位素证据.科学通报,1996, 41(10)
[21] 同济大学海洋地质系.古海洋学概论.上海:同济大学出版社,1989
[22] 齐文同.事件地层学.北京:地质出版社,1990
[23] 陈骏,仇钢,杨杰东.黄土碳酸盐 Sr 同位素组成与原生和次生碳酸盐识别.自然科学进展,1997,7(6)
[24] 陈智梁.特提斯地质一百年.特提斯地质,1994,18: 1~22
[25] 陈智梁.寻觅失踪的特提斯海.海洋世界,1996,1~3
[26] 余光明和王成善. 西藏特提斯沉积地质,地质专报(三,12) ,北京:地质出版社,1990,185
[27] 余素玉.化石碳酸盐岩微相.北京:地质出版社,1989
[28] 张世红,李海燕.地磁学、古地磁学和环境磁学的研究新发展-第 32 届国际地质大会学科总结和评述,现代地质,2004,18 卷,第 4 期,415~422
[29] 吴芮堂,张守信,等编著.现代地层学.武汉:中国地质大学出版社,1989
[30] 金性春,周祖翼,汪品先.大洋钻探与中国地球科学.上海:同济大学,1995,349
[31] 旺罗,万晓樵,李杰.西藏日喀则地区恰布林组地层及构造背景分析.现代地质,1999,13(3):281~286.
[32] 胡修棉,王成善.100 Ma 以来若干重大地质事件与全球气候变化.大自然探索,1999,18 (1): 53~58
[33] 胡修棉,王成善.古海洋溶解氧研究方法综述.地球科学进展,2001,16(1):65~71
[34] 赵文金.西藏岗巴晚白垩世有孔虫动物群与海平面变化.高校地质学报,2001,7(1):106~117
[35] 赵文金,万晓樵.西藏特提斯演化晚期生物古海洋事件,北京:地质出版社,2003,14~15
[36] 赵振华.微量元素地球化学原理.北京:科学出版社,1997,1~238
[37] 郝诒纯,万晓樵.西藏定日的海相白垩、第三系.青藏高原地质文集,1985,(17),227~232
[38] 郝诒纯,叶留生,郭宪璞等.新疆塔里木盆地西南地区海相白垩系—第三系界线.北京:地质出版社,2001
[39] 涂光炽.地球化学.上海:上海科技出版社,1995,190~266,326~375
[40] 徐钰林,万晓樵,苟宗海,等.西藏侏罗、白垩、第三纪生物地层.武汉:中国地质大学出版社,1989,1~147
[41] 徐钰林,茅绍智.西藏南部白垩纪-早第三纪钙质超微化石及其沉积环境.微体古生物学报,1992,9(4):331~348
[42] 殷勇,方念乔.云南中甸纳帕海湖泊沉积物的磁化率及环境意义.地理科学,2002,22 卷,4期
[43] 常承法.雅鲁藏布江缝合带地质构造特征及其演化.中国地质科学院与法国科学院研究中心编,中法喜马拉雅考察成果,1980,北京:地质出版社,1984,327~340
[44] 郭铁鹰,梁定益.青藏高原地区古生代—始新世的大陆“开”“合”演化.王鸿祯,杨森楠,刘本培等,中国及邻区构造古地理和生物古地理,湖北:中国地质大学出版社,1990,187~205
[45] 陶发祥.锶同位素对环境变化的指示意义.地质地球化学,1996,5 期,45~69
[46] 黄汲清,陈国铭,陈炳蔚.特提斯—喜马拉雅构造域初步分析.地质学报,1984,58(1)
[47] 黄汲清,陈炳蔚.中国及邻区特提斯海的演化.北京:地质出版社,1987
[48] 黄思静.川西北甘溪中、上泥盆统海相碳酸盐岩的碳、锶同位素组成及其地质意义.岩石学报(9 月增刊),1993
[49] 黄思静.上扬子地台区晚古生代海相碳酸盐岩的碳、锶同位素研究.地质学报,1997,71(1)
[50] 黄思静,石和,沈立成.锶同位素地质学研究进展.地球科学进展,2001,16(2)
[51] 蓝先洪.加利福尼亚圣弗朗西斯科湾河口古盐度的锶同位素.海洋地质动态,1994,03:7~9
[52] 蓝先洪.锶同位素的环境指示意义.海洋地质动态,1997,第 8 期:4~6
[53] 颜佳新.古海洋缺氧事件与地球历史中水圈的节律.地学前缘,1997,4(3~4):174
[54] 穆恩之,尹集祥,文世宣,等.中国西藏南部珠穆朗玛峰地区的地层.中国科学,1973,16(1):59~71
[55] Adams, A.E., MacKenzie W.S. and Guilford C. Atlas of sedimentary rocks under the microscope, Longman Group Limited. 1984
[56] Auden, J.B. Transverses in the Himalaya, Rec. Geol. Survey of India. 1935. XIX: 123~167
[57] Barrera, E., and Johnson C.C. Evolution of the Cretaceous Ocean-Climate System. Boulder, Colorado, Geological Society of America Special Paper, 1999. 332: 445
[58] Berger, W.H. Impact of deep-sea drilling on Paleoceanography. In: Talwani M., Hay W.,and Ryan W.B.F., eds. Deep drilling results in the Atlantic Ocean: continental margins and paleoenvironment. American Geophysical Union, 1979. 297~314
[59] Barron, E.J. A warm equable Cretaceous: the nature of the problem. Earth-Sci. Rev., 1983. 19: 305~338
[60] Berner, R.A. Sulphate reduction, organic matter decomposition and pyrite formation. Phil. Trans. R. Soc. Lond. 1985. A315, 25~38
[61] Berner, R.A. "GEOCARB Ⅱ: A revised model of atmospheric CO over Phanerozoic time". Am. J. Sci., 1994. 294: 56~91
[62] Borman, F.H. and G.E. Likens. The watershed-ecosystem concept and studies of nutrientcycles. In: ecosystem concept in natural resource management, G.M. Van Dyne (ed.). 1969
[63] Broecker, W.S. Will our ride into the greenhouse future be a smooth one? GSA Today, 1997. 7: 1~6
[64] Canfield, D.E., R.A. Berner. Dissolution and pytitization of magnetite in anixic marine sediments. Geochinica and Cosmochimica Acta. 1987. Vol.51: 645~659
[65] Colemsan, M.L. Geochemistry of diagenetic non-silicate minerals: Kinetic conetic considerations. Phil. Trans. R. Soc. Lond. 1985. A315, 39~56
[66] Dourille, H. Le Cretace et I'Eocene du Tibet central. Palaenol, Indica, N.S., 1916. S: 1~52 Calcutia
[67] Fisher, A.G. The two Phanerozoic supercycles. In: Berggren W.A. and van Couvering J.A., Catastrophes and earth history. Princeton University Press. 1984. 129~149
[68] Fisher, A.G. Climatic rhythms recorded in strata Ann. Rev. Earth Planet. Sci., 1986. 14: 351~376
[69] Frakes, L.A. Climates throughout geologic time. Elsevier, 1979. 322
[70] Fuchs, G. Zurn Ban des Himalaya: Osterreichische Akademic der Wissenschaften, Mathematisch Naturwissenschaftliche Klasse, Denkschriften, 1967. 113: 1~211
[71] Gansser, A. Geology of the Himalayas, Interscience Publication John Wiley and Sons, New York. 1964
[72] Garzanti, E. Sedimentary evolution and drowning of a passive margin shelf (Giumal Group: Zanskar Tethys Himalaya, India): palaeoenvironmental changes during final break-up of Gondwanaland. In Himalayan Tectonices, (Edited by Treloar P.J., and Searle M.P.), Geological Society of London Special Publication, 1993a. 74, 277~298
[73] Garzanti, E. Himalayan ironstones, "superplumes," and the breakup of Gondwana. Geology, 1993b. 21:105~108
[74] Hayden, H.H. The geology of the provinces Tsang and U in Tibet. Mem. Geological Survey of India, 1907. 36: 122~201
[75] Hayden, H.H. The geology of Spiti. Mem. Geol. Surv. India, 1912. 36:1~144
[76] Haq, B.U., Hardenbol, J. and Vail, P.R. Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change. 71~108 in Wilgus, C.K., Hastings, B.S., Kendall, C.G.ST.C. Posamentier, H.W., Ross, C.A. and Van Wagoner, J.C. (eds). Sea-level changes: an integrated approach. Society of Economic Paleontologists and Mineralogists Special Publ., 1988. 42
[77] Heron, A.M. Geological results of the Mount Everest reconnaissance expedition. Records of the Geological Survey of India, 1922. 54: 215~234
[78] Hagen, T. Report on the geological survey of Nepal. Vol. 2 Geology of the Thakkhola Zurich, Memoires de la sec. Helvetique des sci. naturelles, 1968. 185
[79] Hodell, D.A. et al. Variation in the strontium isotopic composition of seawater (8 Ma to present): Implications for chemical weathering rates and dissolved fluxes to the oceans. Chemical Geology (Isotope Geoscience Section), 1990. 80: 291~307
[80] Hsü, K.J. Paleoceanography of the Mesozoic Alpine Tethys. Geol. Soc. Am. 1976. Special Paper 170
[81] Irving, E., North, F.K., Couilland, R. Oil, climate and tectonics. Can. I. Earth Sci., 1974. 11: 1~17
[82] IOPD Initial Scientific Plan 2003-2013. Earth, Ocean, and life. 2001. download from www.iodp.org
[83] Jenkyns, H.C. Tethys: past and present. Proc. Geol. Ass. 1980b. 91: 107~118
[84] Kelts, K. Reading pages from limnogeological archives. In Special Proceedings for Symposia of The XIII INQUA, China, 1991. 10~19
[85] Klemme, H.D., Ulmishek G.F. Effect petroleum rocks of the world: stratigraphic distribution and controlling depositional factors. AAPG Bull., 1991. 75: 667~689
[86] Kunio Kaiho. A low extinction rate of intermediate-water benthic foraminifera at the Cretaceous/Tertiary boundary. In: Marine Micropaleontology, 1992. 18: 229~259
[87] Kunio Kaiho. Planktonic and benthic foraminiferal extinction events during the last 100 M. y. In: Palaeogeography, Palaeoclimatology, Palaeoecology, 1994a. 111: 45~71
[88] Kunio Kaiho. Benthic foraminiferal dissolved-Oxygen index and dissolved-oxygen levels in the modern ocean. Geology, 1994b. Vol. 22: 719~722
[89] Kunio Kaiho, Takashi Hasegawa. End-Cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the north-western Pacific Ocean. In: Palaeogeography, Palaeoclimatology, Palaeoecology, 1994. 111: 29~43
[90] Kukla, G. et al. Pleistocene climates in China dated by magnetic susceptibility. Geology, 1988. Vol. 16: 811~814
[91] Maher, B.A. and R. Thompson. Mineral magnetic record of the China loess and paleosols. Geology, 1991. Vol.19: 3~6
[92] Neumayr, M. Erdgeschichte, 2. Verlag des bibliographischen Instituts, Leipzig, 1887. 880
[93] Oldfield, F. Lakes and their drainage basins as unitsof sediment-based ecological study. Prog.Phys.Geog., 1977. 3, 460~504
[94] Oldfield, F. Man's impact on environment. Geography, 1983. Vol.68: 246~256
[95] O'Sullivan, P.E. The ecosystem-watershed concept in the environmental sciences – a review, J. Envirron. Sci., 1979. 13, 273~281
[96] Peter W. Skelton, Robert A. Spicer, Simon P. Kelley, et al. The Cretaceous World. Cambridge University Press, 2003. 35
[97] Richard J. Howarth & John M. McArthur. Statistics for strontium isotope stratigraphy: a robust LOWESS fit to marine Sr-isotope curve for 0 to 206 Ma, with look-up table for derivation of numeric age. Journal of Geology, 1997. 105:441~456
[98] Smit, J. A catastrophic event at the Cretaceous-Tertiary boundary. Thesis. Univ of Amsterdam, 1981. 1~138
[99] Sharpton, V.L. et al. New links between the Chicxulub impact structure and Cretaceous-Tertiary boundary. Nature, 1992. Vol. 359, No. 6398, 819~821
[100] Stolz, J.F., Shih-Bin R. Chang, Kirschvink, J.L. magnetotactic bacteria and single-domain magnetite in hemipelagic sediments. Nature, 1986. 321,349~351
[101] Suess, E. Are great ocean depths permanent? Natural Science, 1893. 2: 180~187
[102] Tissot, B. Effects on prolific petroleum source rocks and major coal deposits caused by sea-level changes. Nature, 1979. 277: 463~465
[103] Wan Xiaoqiao. The Cretaceous/Tertiary Boundary Event in Tibet. Revista Espanola DE Paleontologia, 1988. no. Extraordinario, 113~118
[104] Wan Xiaoqiao. Albian-Campanian (Cretaceous) planktic foraminiferal stratigraphy in southern Xizang (Tibet). In: Yang Zunyi (Editor-in-chief), Stratigraphy and Paleontology of China, Beijing: Geological Publishing House, 1991. vol. 1: 165~181
[105] Wang Chengshan, Xia Daixiang et al. T121-T387 Field Trip Guide: Geology between the Indus-Yarlung Zangbo suture zone and the himalaya Mt., Xizang (Tibet), China. Contrib. 30th IGC, Beijing, 1996. Geol. Pub. House, 1~72
[106] Willems H. Sedimentary history of the Tibetan Tethys Himalaya continental shelf in south Tibet (Gamba, Tingni) during Upper Cretaceous and Lower Tertiary (Xizang Autonomous Region, P. R. China). Berichte, Fachhereich Geowissenschaften, University Bremen, 1993. 38: 49~183
[107] Willems, H., 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. Berchte, Fachbereich Geowissenschaften, University Bremen, 1995. No. 64
[108] Wilson, L. Carbonate facies in geologic History, 1975. 93~151
[109] Wickman, F.E. Isotoperations: a clue to the age of certain marine sediments. Geol, 1948. 56: 61~66
[110] Yu Lüzhong, F. Oldfield, Wu Yushu, et al., Paleoenvironmental implications of magnetic measurements on sediment core from Kunming Basin, Southwest China. Journal of paleolimnology, 1990. Vol.3: 95~111
[111] ZHANG Shihong(张世红),WANG Xunlian(王训练)& ZHU Hong(朱鸿). Magnetic susceptibility variations of carbonates controlled by sea-level changes—Examples in Devonian to Carboniferous strata in southern Guizhou Province, China. Science in China (Series D), 2000. 43 (3): 266~276