黔东南华纪铁丝坳期-大塘坡期古气候的演变:来自CIA的证据
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摘要
新元古代晚期是全球气候急剧变化的时期,目前可区分出至少2个全球性冰期事件。黔东地区南华纪地层中存在上下2个具有明显冰碛岩特征的地层:下部的两界河组-铁丝坳组与上部的南沱组,可分别与720 Ma的Sturtian冰期、650 Ma的Marinoan冰期事件相对应,而铁丝坳组与南沱组之间的大塘坡组则代表了间冰期的沉积。通过对铜仁松桃2口钻孔岩心铁丝坳组-大塘坡组样品主量元素的研究,探讨了Sturtian冰期晚期至其冰后期的古气候演变过程,结合化学地层学与岩石学证据,发现Sturtian冰期结束后,气候的回暖并非是突然出现,而是在主冰期结束之后尚存在短暂的小冰期。由下至上,钻孔样品的化学蚀变指数(CIA)平均值从Sturtian冰期末铁丝坳组顶部的51升至大塘坡组底部的60。大塘坡组底部CIA值波动较大,在52~68之间呈锯齿状震荡上升,代表古气候环境所发生的动荡变化,结合在大塘坡组底部所发现的组内冰碛岩层位,指示存在着短暂的寒冷事件。大塘坡组一段黑色炭质页岩的CIA值稳定在66左右,反映气候稳定在相对温暖的状态;大塘坡组二、三段粉砂质页岩CIA指数平均值为67,向上CIA值表现出逐渐下降的趋势,可能与Marinoan冰期启动所导致的气候转冷有关。通过A-CN-K三角图解判断沉积气候环境的稳定性与源岩成分,进一步证明了Sturtian冰期结束后气候的不稳定,以及间冰期稳定的温暖气候。冰期-间冰期波动的古气候演化可能与"大塘坡"型锰矿的成矿作用相关。
Presently two episodes of global glacial events could be distinguished in Neoproterozoic,when dramatic changes in climate happened globally.Two formations of strata distributed in Nanhua System(Cryogenian)around eastern Guizhou Province with typical characteristics of glacial sediments.The lower named Tiesi'ao Formation and the upper named Nantuo Formation correspond with Sturtian glaciation in720 Ma and Marinoan glaciation in 650 Ma respectively,and the strata between the two formations are of Datangpo Formation representing deposition during the interglaciation.This paper discusses paleoclimate evolution during the late Sturtian glacial period to interglacial period with the main elements dated from samples in Tiesi′ao Formation-Datangpo Formation,Songtao county and Tongren city,combined with evidence from chemistry and petrology.This illustrates that transient glacial events occurred following the end of Sturtian age.From bottom to top,the chemical index of alteration(CIA)raises from 51 in late Tiesi'ao period to 60 in early Datangpo period.However,the shape of curve drawn with date from 52 to 68is not linear but a serrated upward trend,showing the occurrence of ephemeral glacial event.The average value of CIA from Carbonaceous shales in upper Datangpo Formation and silty shales in middle,lower Datangpo Formation are 66 and 67,both supporting a stable warm condition.However,the mean of CIA decreases suddenly at the top of the latter which may due to the beginning of the Marinoan glaciation.On the other hand,it is further confirmed with evaluations on stability of sedimentary condition and composition of source rocks by A-CN-K triangle graph that the instability of climate follows the Sturtian glaciation and the stability of warm climate during the interglaciation.Thus,the fluctuations of glaciation-interglaciation paleoclimate evolution may be related to "Datangpo" type manganese mineralization.
Presently two episodes of global glacial events could be distinguished in Neoproterozoic,when dramatic changes in climate happened globally.Two formations of strata distributed in Nanhua System(Cryogenian)around eastern Guizhou Province with typical characteristics of glacial sediments.The lower named Tiesi'ao Formation and the upper named Nantuo Formation correspond with Sturtian glaciation in720 Ma and Marinoan glaciation in 650 Ma respectively,and the strata between the two formations are of Datangpo Formation representing deposition during the interglaciation.This paper discusses paleoclimate evolution during the late Sturtian glacial period to interglacial period with the main elements dated from samples in Tiesi′ao Formation-Datangpo Formation,Songtao county and Tongren city,combined with evidence from chemistry and petrology.This illustrates that transient glacial events occurred following the end of Sturtian age.From bottom to top,the chemical index of alteration(CIA)raises from 51 in late Tiesi'ao period to 60 in early Datangpo period.However,the shape of curve drawn with date from 52 to 68is not linear but a serrated upward trend,showing the occurrence of ephemeral glacial event.The average value of CIA from Carbonaceous shales in upper Datangpo Formation and silty shales in middle,lower Datangpo Formation are 66 and 67,both supporting a stable warm condition.However,the mean of CIA decreases suddenly at the top of the latter which may due to the beginning of the Marinoan glaciation.On the other hand,it is further confirmed with evaluations on stability of sedimentary condition and composition of source rocks by A-CN-K triangle graph that the instability of climate follows the Sturtian glaciation and the stability of warm climate during the interglaciation.Thus,the fluctuations of glaciation-interglaciation paleoclimate evolution may be related to "Datangpo" type manganese mineralization.
引文
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[23]何明华.黔东北及邻区早震旦世成锰期岩相古地理及菱锰矿矿床[J].沉积与特提斯地质,2001,21(3):39-47.
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[25]Zhou Chuanming,Tucker R,Xiao Shuhai,et al.New constraints on the ages of Neoproterozoic glaciations in South China[J].The Journal of Geology,2004,32(5):437-440.
[26]尹崇玉,刘敦一,高林志,等.南华系底界与古城冰期的年龄:SHRIMP定年证据[J].科学通报,2003,48(16):1721-1725.
[27]尹崇玉,王砚耕,唐烽,等.贵州松桃南华系大塘坡组凝灰岩锆石SHRIMPⅡU-Pb年龄[J].地质学报,2006,80(2):273-278.
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[32]赵小明,刘圣德,张权绪,等.鄂西长阳南华系地球化学特征的气候指示意义及地层对比[J].地质学报,2011,85(4):576-585.
[33]王自强,尹崇玉,高林志,等.宜昌三斗坪地区南华系化学蚀变指数特征及南华系划分、对比的讨论[J].地质论评,2006,52(5):577-585.
[34]王自强,尹崇玉,高林志,等.黔南-桂北地区南华系化学地层特征[J].地球学报,2009,30(4):465-474.
[35]刘兵,徐备,孟祥英,等.塔里木板块新元古代地层化学蚀变指数研究及其意义[J].岩石学报,2007,23(7):1164-1170.
[36]潘桂棠,肖庆辉,陆松年,等.中国大地构造单元划分[J].中国地质,2009,36(1):1-28.
[37]Nesbitt H W,Young G M.Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations[J].Geochimica et Cosmochimica Acta,1984,48(7):1523-1534.
[38]Harnois L.The CIW index:A new chemical index of weathering[J].Sedimentary Geology,1988,55(3):319-322.
[39]McLennan S M.Relationships between the trace element composition of sedimentary rocks and upper continental crust[J].Geochemistry,Geophysics,Geosystems,2001,2(4):1021-1024.
[40]Gao S,Luo T C,Zhang B R,et al.Chemical composition of the continental crust as revealed by studies in East China[J].Geochimica et Cosmochimica Acta,1998,62:1959-1975.
[41]Taylor S R,McLennan S M.The continental crust:Its composition and evolution[M].Blackwell,Oxford,States[J].Geochimica et Cosmochimica Acta,1985,59:2919-2940.
[42]严旺生,高海亮.世界锰矿资源及锰矿业发展[J].中国锰业,2009,27(3):6-11
[43]何志威,杨瑞东,高军波,等.贵州省松桃杨家湾锰矿含锰岩系地质地球化学特征[J].现代地质,2013,27(3):593-602.
[44]何志威,杨瑞东,高军波,等.贵州松桃西溪堡锰矿沉积地球化学特征[J].地球化学,2013,42(4):576-588.
[45]黄道光,牟军.贵州印江-松桃地区含锰岩系及南华系早期沉积环境演化[J].贵州地质,2010,27(1):13-21.
[2]Hoffman P F,Kaufman A J,Halverson G P,et al.A Neoproterozoic snowball Earth[J].Science,1998,281:1342-1346.
[3]Hoffman P F,Halverson G P,Domack E W,et al.Are basal Ediacaran(635 Ma)postglacial“cap dolostones”diachronous?[J].Earth and Planetary Science Letters,2007,258:114-131.
[4]Hoffman P F,Schrag D P.The snowball Earth hypothesis:Testing the limits of globle change[J].Terra Nova,2002,14:129-155.
[5]Williams G E.Late Precambrian glaciation and the Earth′s obliquity[J].Geology Magazine,1975,112:441-465.
[6]王叶,延晓东.新元古代地球气候研究进展[J].气候与环境研究,2011,16(3):399-406.
[7]赵彦彦,郑永飞.全球新元古代冰期的记录和时限[J].岩石学报,2011,27(2):545-563.
[8]陆松年.关于中国新元古界划分几个问题的讨论[J].地质论评,2002,48(3):242-248.
[9]王剑.华南新元古代裂谷盆地沉积演化:兼论与Rodinia解体的关系[M].北京:地质出版社,2000:78-99.
[10]黄晶,储雪蕾,张启锐,等.新元古代冰期及其年代[J].地学前缘,2007,14(2):249-256.
[11]张飞飞,闫斌,郭跃玲,等.湖北古城锰矿的沉淀形式及其古环境意义[J].地质学报,2013,87(2):245-258.
[12]张启锐,储雪蕾.扬子地区江口冰期地层的划分对比与南华系层型剖面[J].地层学杂志,2006,30(4):306-314.
[13]夏文杰.贵州松桃地区早震旦世大塘坡期沉积环境及锰矿成因[J].成都地质学院学报,1989,16(1):67-78.
[14]周琦,杜远生,颜佳新,等.贵州松桃大塘坡地区南华及早期冷泉碳酸盐岩地质地球化学特征[J].地球科学:中国地质大学学报,2007,32(6):845-852.
[15]冯连君,储雪蕾,张启锐,等.化学蚀变指数(CIA)及其在新元古代碎屑岩中的应用[J].地学前缘,2003,10(4):539-543.
[16]冯连君,储雪蕾,张启锐,等.湘西北南华系渫水河组寒冷气候成因的新证据[J].科学通报,2004,48(12):1171-1178.
[17]冯连君,储雪蕾,张同钢,等.莲沱砂岩:南华大冰期前气候转冷的沉积记录[J].岩石学报,2006,22(9):2287-2393.
[18]Nesbitt H W,Young G M.Early Proterozoic climates and plate motions inferred from major element chemistry of lutites[J].Nature,1982,199:715-717.
[19]Nesbitt H W,Markovics G.Weathering of granodioritic crust,long-term storage of elements in weathering profiles,and petrogenesis of siliciclastic sediments[J].Geochimica et Cosmochimica Acta,1997,61(8):1653-1670.
[20]Young G M,Nesbitt H W.Paleoclimatology and provenance of the glaciogenic Gowganda Formation(Paleoproterozoic),Ontario,Canda:A chemostratigraphic approach[J].GSA Bullenin,1999,111:264-274.
[21]Harnois L.The CIW index:A new chemical index of weathering[J].Sedimentary Geology,1988,55(3):319-322.
[22]何明华.松桃及邻区早震旦世大塘坡早期岩相古地理及成锰条件[J].贵州地质,1993,10(1):62-67.
[23]何明华.黔东北及邻区早震旦世成锰期岩相古地理及菱锰矿矿床[J].沉积与特提斯地质,2001,21(3):39-47.
[24]Zhou C M,Tucker R,Peng Z X,et al.New constraints on the ages of Neoproterozoic glaciations in South China[J].Geology,2004,32:437-440.
[25]Zhou Chuanming,Tucker R,Xiao Shuhai,et al.New constraints on the ages of Neoproterozoic glaciations in South China[J].The Journal of Geology,2004,32(5):437-440.
[26]尹崇玉,刘敦一,高林志,等.南华系底界与古城冰期的年龄:SHRIMP定年证据[J].科学通报,2003,48(16):1721-1725.
[27]尹崇玉,王砚耕,唐烽,等.贵州松桃南华系大塘坡组凝灰岩锆石SHRIMPⅡU-Pb年龄[J].地质学报,2006,80(2):273-278.
[28]Zhang S H,Jiang G Q,Han Y G.The age of the Nantuo Formation and Nantuo glaciation in South China[J].Terra Nova,2008,20:289-294.
[29]贵州省地质矿产局.贵州省区域地质志[M].北京:地质出版社,1987.
[30]McLennan S M.Weathering and global denudation[J].The Journal of Geology,1993,101(2):295-303.
[31]Fedo C M,Nesbitt H W,Young G M.Unraveling the effects of potassium metasomatism in sedimentary rocks and paleosols,with implications for paleowearhering conditions and provenance[J].The Journal of Geology,1995,23(10):921-924.
[32]赵小明,刘圣德,张权绪,等.鄂西长阳南华系地球化学特征的气候指示意义及地层对比[J].地质学报,2011,85(4):576-585.
[33]王自强,尹崇玉,高林志,等.宜昌三斗坪地区南华系化学蚀变指数特征及南华系划分、对比的讨论[J].地质论评,2006,52(5):577-585.
[34]王自强,尹崇玉,高林志,等.黔南-桂北地区南华系化学地层特征[J].地球学报,2009,30(4):465-474.
[35]刘兵,徐备,孟祥英,等.塔里木板块新元古代地层化学蚀变指数研究及其意义[J].岩石学报,2007,23(7):1164-1170.
[36]潘桂棠,肖庆辉,陆松年,等.中国大地构造单元划分[J].中国地质,2009,36(1):1-28.
[37]Nesbitt H W,Young G M.Prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations[J].Geochimica et Cosmochimica Acta,1984,48(7):1523-1534.
[38]Harnois L.The CIW index:A new chemical index of weathering[J].Sedimentary Geology,1988,55(3):319-322.
[39]McLennan S M.Relationships between the trace element composition of sedimentary rocks and upper continental crust[J].Geochemistry,Geophysics,Geosystems,2001,2(4):1021-1024.
[40]Gao S,Luo T C,Zhang B R,et al.Chemical composition of the continental crust as revealed by studies in East China[J].Geochimica et Cosmochimica Acta,1998,62:1959-1975.
[41]Taylor S R,McLennan S M.The continental crust:Its composition and evolution[M].Blackwell,Oxford,States[J].Geochimica et Cosmochimica Acta,1985,59:2919-2940.
[42]严旺生,高海亮.世界锰矿资源及锰矿业发展[J].中国锰业,2009,27(3):6-11
[43]何志威,杨瑞东,高军波,等.贵州省松桃杨家湾锰矿含锰岩系地质地球化学特征[J].现代地质,2013,27(3):593-602.
[44]何志威,杨瑞东,高军波,等.贵州松桃西溪堡锰矿沉积地球化学特征[J].地球化学,2013,42(4):576-588.
[45]黄道光,牟军.贵州印江-松桃地区含锰岩系及南华系早期沉积环境演化[J].贵州地质,2010,27(1):13-21.