江北砾岩沉积环境研究
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摘要
全球变化势必对人类产生有利或不利影响，人类必须认识全球变化才能采取相应的对策。因此，全球变化已成为当前的研究热点。第四纪(又称为人类纪)尤其是晚第四纪离人类产生、发展最近，是研究过去全球变化最有价值的信息库，对其环境演变的研究对人类的意义非常大。随着三峡大坝的兴建和库区的开发，加强对长江中上游环境演变的研究就显得非常重要。广泛分布在四川盆地河流一级阶地基座上的江北砾岩能反映其成岩时的古洪水、古气候、古植被等古环境信息，是研究本地区晚更新世末至全新世初古环境演变的不可多得的载体。
江北砾岩是指广泛分布于四川盆地及其邻近地区河流沿岸一级阶地第四系晚近阶段的一种次生表生胶结岩类，包括砾岩、砂岩。因此，又被称为江北期砂砾岩。江北砾岩具有与其它河流沉积物不同的特点，即在地表胶结成岩，且只分布在一级阶地中上部。学者们对其成因产生了浓厚的兴趣，推测其可能是特殊气候条件的产物，但在形成砾岩的具体气候条件方面存在争议。刘兴诗认为是全新世干热气候的产物，而杨达源认为是晚更新世干冷气候下形成的。由于江北砾岩填隙物成分复杂，选取准确定年和古环境分析的载体比较困难。因此，其成因至今未搞清楚。本文在前人研究的基础上运用近年古环境研究的新技术新方法对其成岩时代及其成岩环境进行研究。
江北砾石层堆积年代表明其堆积时代应为1-4万年，在长江分布的江北砾岩其中上部堆积时期属于晚更新世晚期(40000a BP)，顶部堆积时期应属于全新世(7500—10000 a BP)；嘉陵江下游分布的江北砾岩其底部堆积于28000 a BP，顶部河漫滩堆积物堆积于7500 a BP。江北砾岩填隙物、砂岩的~(14)C以及部分剖面方解石胶结物的U系时代分析表明，江北砾岩的胶结年代应大致为1-2.43万年。其顶部砂砾胶结年代为10000年左右，下部砾岩的胶结年代为24300年。
江北砾岩堆积期气候为在亚热带暖湿气候背景下受末次冰期全球气候变冷的影响转干冷。其填隙物孢粉组合表明植被类型为森林或者森林—草原，这说明晚更新世末晚期即末次冰期时位于亚热带湿热区的本区气候转向干冷转化，降水和气温均有所降低；江北砾岩填隙物总有机碳TOC含量从剖面底部往上逐渐升高的变化特征也表明随着晚更新世晚期气候的逐渐干冷，气温和降水减少，植被森林向森林—草原演化，堆积物中有机碳分解减弱。同时，河流搬运能力减弱，含有机质较多的细砾石和泥沙堆积。因此，逾往剖面上部总有机碳TOC增加；江北砾岩重矿含量及矿物组合以稳定矿物及其组合为主的特征说明其堆积时以气候暖热为主，符合本区亚热带气候背景和河流沉积物重矿特征，但大量褐铁矿、少量角闪石、绿帘石的存在以及黄角客运码头HJK4、江北寸滩砂岩CT以不稳定矿物和次稳定矿物为主的重矿组合也反映了其堆积期转干冷气候特
Global changes will bring advantageous or disadvantageous to influence human beings. Man must understand global changes and we can take proper countermeasures. Studying global changes is a hot spot now . Quaternary ( also named Human Period ) especially late Quaternary was close to human beings origin and development .It is the most valuable information base to study bypast global changes and studying its environment evolvement is very important for human beings . Along with building Three Gorges Dam and exploiting the reservoir area, It is very important to strengthen studying environment evolvement of middle and upper reaches of Yangtse River. Jiangbei conglomerate which wide-spreads in lower terrace of Quaternary sediment along the river in Sichuan Basin can reflect paleoenvironment information including paleoflood, paleoclimate, paleovegetation, etc, and is an un-come-at-able carrier of studying paleoenvironment evolvement of local area during last stage of late Pleistocene and Holocene.
Jiangbei conglomerate is a kind of allothigenic supergene cemented rock that wide-spreads in lower terrace of Quaternary sediment along the river in Sichuan Basin and it's adjacent area, and consists of conglomerate and sandstone. Hence, it is also named Jiangbei conglomerate and sandstone rock. Jiangbei conglomerate has its own characteristic different from other river sediment, namely it cemented to solid rock on earth's surface and only spread on the lower terrace. Scholars are interested in its diagenetic reason and speculate that it might diagenism in special climate . But there are many different opinions about the diagenesis climate. Liu Xingshi thought that it diagenismed in dry-hot climate in Holocene Epoch .But Yang Dayuan thought it diagenismed in dry-cold climate in late Pleistocene. Because the matrix of Jiangbei conglomerate is very complex, it is very difficult to choose the carrier of dating exactly and paleoenvironment analysis . The diagensis reason isn't clear now. The author bases on the past investigation and uses new technology and new method which are used in studying paleoenvironment to study diagentic age and diagentic environment.
We draw a conclusion that the sedimental chron of Jiangbei conglomerate is between 10000 and 40000 years . The upper of Jiangbei conglomerate along Yangts River was
江北砾岩是指广泛分布于四川盆地及其邻近地区河流沿岸一级阶地第四系晚近阶段的一种次生表生胶结岩类，包括砾岩、砂岩。因此，又被称为江北期砂砾岩。江北砾岩具有与其它河流沉积物不同的特点，即在地表胶结成岩，且只分布在一级阶地中上部。学者们对其成因产生了浓厚的兴趣，推测其可能是特殊气候条件的产物，但在形成砾岩的具体气候条件方面存在争议。刘兴诗认为是全新世干热气候的产物，而杨达源认为是晚更新世干冷气候下形成的。由于江北砾岩填隙物成分复杂，选取准确定年和古环境分析的载体比较困难。因此，其成因至今未搞清楚。本文在前人研究的基础上运用近年古环境研究的新技术新方法对其成岩时代及其成岩环境进行研究。
江北砾石层堆积年代表明其堆积时代应为1-4万年，在长江分布的江北砾岩其中上部堆积时期属于晚更新世晚期(40000a BP)，顶部堆积时期应属于全新世(7500—10000 a BP)；嘉陵江下游分布的江北砾岩其底部堆积于28000 a BP，顶部河漫滩堆积物堆积于7500 a BP。江北砾岩填隙物、砂岩的~(14)C以及部分剖面方解石胶结物的U系时代分析表明，江北砾岩的胶结年代应大致为1-2.43万年。其顶部砂砾胶结年代为10000年左右，下部砾岩的胶结年代为24300年。
江北砾岩堆积期气候为在亚热带暖湿气候背景下受末次冰期全球气候变冷的影响转干冷。其填隙物孢粉组合表明植被类型为森林或者森林—草原，这说明晚更新世末晚期即末次冰期时位于亚热带湿热区的本区气候转向干冷转化，降水和气温均有所降低；江北砾岩填隙物总有机碳TOC含量从剖面底部往上逐渐升高的变化特征也表明随着晚更新世晚期气候的逐渐干冷，气温和降水减少，植被森林向森林—草原演化，堆积物中有机碳分解减弱。同时，河流搬运能力减弱，含有机质较多的细砾石和泥沙堆积。因此，逾往剖面上部总有机碳TOC增加；江北砾岩重矿含量及矿物组合以稳定矿物及其组合为主的特征说明其堆积时以气候暖热为主，符合本区亚热带气候背景和河流沉积物重矿特征，但大量褐铁矿、少量角闪石、绿帘石的存在以及黄角客运码头HJK4、江北寸滩砂岩CT以不稳定矿物和次稳定矿物为主的重矿组合也反映了其堆积期转干冷气候特
Global changes will bring advantageous or disadvantageous to influence human beings. Man must understand global changes and we can take proper countermeasures. Studying global changes is a hot spot now . Quaternary ( also named Human Period ) especially late Quaternary was close to human beings origin and development .It is the most valuable information base to study bypast global changes and studying its environment evolvement is very important for human beings . Along with building Three Gorges Dam and exploiting the reservoir area, It is very important to strengthen studying environment evolvement of middle and upper reaches of Yangtse River. Jiangbei conglomerate which wide-spreads in lower terrace of Quaternary sediment along the river in Sichuan Basin can reflect paleoenvironment information including paleoflood, paleoclimate, paleovegetation, etc, and is an un-come-at-able carrier of studying paleoenvironment evolvement of local area during last stage of late Pleistocene and Holocene.
Jiangbei conglomerate is a kind of allothigenic supergene cemented rock that wide-spreads in lower terrace of Quaternary sediment along the river in Sichuan Basin and it's adjacent area, and consists of conglomerate and sandstone. Hence, it is also named Jiangbei conglomerate and sandstone rock. Jiangbei conglomerate has its own characteristic different from other river sediment, namely it cemented to solid rock on earth's surface and only spread on the lower terrace. Scholars are interested in its diagenetic reason and speculate that it might diagenism in special climate . But there are many different opinions about the diagenesis climate. Liu Xingshi thought that it diagenismed in dry-hot climate in Holocene Epoch .But Yang Dayuan thought it diagenismed in dry-cold climate in late Pleistocene. Because the matrix of Jiangbei conglomerate is very complex, it is very difficult to choose the carrier of dating exactly and paleoenvironment analysis . The diagensis reason isn't clear now. The author bases on the past investigation and uses new technology and new method which are used in studying paleoenvironment to study diagentic age and diagentic environment.
We draw a conclusion that the sedimental chron of Jiangbei conglomerate is between 10000 and 40000 years . The upper of Jiangbei conglomerate along Yangts River was
引文
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2.M.A.HAYWARD,P.R.BLACKE, Signicance of Middle Devonian granitoid-bearing conglomerates in the MT Morgan region,central Queenslang,Australian Journal of Earth Science (1999)46,487-492
3.J.W.Riesterter,J.Brian Maloney ,and Paul kart Link.The conglomerat of Churn Creek:Late Cretaceous basin evolution along the Insular-Intermontane superterrane boundary,southern Britsh Columbia,Published on the NRC Research Press web site on December 18,2000.
4.Davis Aileen M,Aitchison Jonathan C.Palleocene Island Arc collision-Related conglomerates,Yarlung-Tsangpo suture zone,Tibet.Sedimentary Geology,Jul2002,Vol150 Issue3/4,p247,27p
5.Colombo.F,Nomal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive. Geology, Mar 94, Vol 22 Issue 3, P235,4P,2charts.
6.Robinson Ruth A.J and slingerl Ruoly L. Grain-sice trends, basin subsidence and sediment supply in the Canpanian castlegate sandstone and equivalent conglomerates of central Utah, Basin research; Mar98, Vol 10 Issue 1,P109.19P.
7.Noda Atsushi, Takenchi Makoto. Sedimentary Geology; Feb2004, Vol,164 Issue 3/4, P203,20P.
8.Bluck, Brian J. Sedimentology; 1965, Vol, 4 Issue 3, P225, 21P.
9.Todd, Simonp. Sedimentology, Aug 89, Vol, 36 Issue 4, P513, 18P.
10..Depoll, H.W.Van and Patel I.M. Sedimentology, Feb89, Vol,36 Issuel, P137, 9P.
11.Nemec, W and Pore bski. S. J. Sedimentology. Oct 80. Vol 27 Issue 5, P519, 20P.
12..Winn Jr, R,D and Dott Jr, R.D. Sedimentology; Apr 79, Vol 26, Issue 2, P203, 26P.
13. Higgs. Roger, Sedimentology; Feb 90, Vol 37. Issue 1. P83, 21P.
14.Fielding, C.R. and Webb J.A. Geological Magazine, Jan 95, Vol 132 Issue 1, P51, 13P.
15.Noll. C.A. and Hall. M. Stratigraphic architcture and depositional setting of coarse-grained Upper Cambrian Owen Conglomerate, West Coast Range, western Tasmania. Australian Journal of Earth Science; Dec 2003, Vol 50 Issue 6, P835, 18P.
16.Reddy V and Germs. G J. B. Stratigraphy and Facies of the Venterpost conglomerate formation at western areas gold mine. South African Journal of Geology, Sep 94, Vol 97 Issue 3. P288, 9P.
17.Cox, Ronadh and Gutmann, Ethan D. Geology, Apr 2002, Vol 30 Issue 4, P323, 4P.
18.Lowey, GW. White channel Gravel alteration revisited. Yokon Exploration and Geology 2001, P147-162, D. S. Emond, L. H. Weston and L. L. Lewis eds.
19. M. J. WOLFE. An electron microscope study of the Surface Texture of Sand Grains from Basal conglomerate. Sedimentology-Elsevier Publishing company. Amsterdam-Printed in the Netherlands
20. E. ASGHARI, D. G. Toll and S. M. HAERI. Geotechnical and Geological Engneering 21: 1-28, 2003 (?) 2003 Kluwer Academic publishers. Printed in the Netherlands.
21. Peter R. Wilcock. Two-fraction Model of Initial sediment. Motion in Gravel-Bed Rivers. Science. Apr17, 1998; 280, 5362; ProQuest Education Journals.
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