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| 江汉盆地ZL钻孔微量元素含量的粒度效应与环境意义 | |
| 引用本文： | 袁胜元,李长安,邵磊.江汉盆地ZL钻孔微量元素含量的粒度效应与环境意义[J].沉积学报,2012,30(2):366-374. |
| 作者姓名： | 袁胜元 李长安 邵磊 |
| 作者单位： | 1. 中国地质大学地球科学学院,武汉430074／中国地质大学生物地质与环境地质教育部重点实验室,武汉430074／中国地质大学地质过程与矿产资源国家重点实验室,武汉430074／许昌学院城市与环境学院,河南许昌461000 2. 中国地质大学地球科学学院,武汉,430074 3. 中国地质大学地球科学学院,武汉430074／中国地质大学地质过程与矿产资源国家重点实验室,武汉430074 |
| 基金项目： | 国家自然科学基金项目，黄土与第四纪地质国家重点实验室开放基金项目，地质过程与矿产资源国家重点实验室开放基金项目，生物地质与环境地质教育部重点实验室开放基金项目 |
| 摘 要： | 江汉盆地是长江出三峡后第一个大型卸载区，近2.77 Ma以来堆积了近300m的碎屑沉积物,主要由河流相和湖沼相组成，形成了多个沉积旋回。选择江汉盆地中心位置的ZL钻孔,利用ICP-MS方法展开微量元素组成分析，细粒组分中微量元素含量与各粒组含量相关性并不明显，主要是5~7粒级组分表现出微弱的相关性.可见，粒度并非ZL钻孔微量元素丰度的主控因素。钻孔岩心中大部分亲石元素、亲硫元素相对上部陆壳均出现明显富集，亲铁元素总体低于上部陆壳，可能与江汉盆地总体上更多地接受了来自上游而非扬子古陆本地深源物质风化碎屑沉积有关。Sr、V/Ni和Sr/Ba值的变化则表明江汉盆地在2.6~2.43 Ma B.P.时可能有咸化湖的发育，而在2.1 Ma B.P.左右存在过一段大湖发育期。 |
| 关 键 词： | ,江汉盆地,微量元素,粒度效应,古湖泊 |
Grain-size Dependence and Environment Significance of Trace Elements from ZL Core in the Jianghan Basin |
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| YUAN Sheng-yuan,LI Chang-an,SHAO Lei.Grain-size Dependence and Environment Significance of Trace Elements from ZL Core in the Jianghan Basin[J].Acta Sedimentologica Sinica,2012,30(2):366-374. | |
| Authors: | YUAN Sheng-yuan LI Chang-an SHAO Lei |
| Institution: | 1,3(1.Faculty of Sciences,China University of Geosciences,Wuhan 430074; 2.Key Lab of Biogeology and Environmental Geology of Ministry of Education,China University of Geosciences,Wuhan 430074; 3.Stake Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430074; 4.College of Urban Planning & Environment Science,Xuchang University,Xuchang,Henan 461000) |
| Abstract: | Element content can be affected by the grain size of sediments.Previous studies revealed that elements,content of which can be easily affected the grain size distribution are usually concentrated in fine-grain fractions.The grain size effect makes it more complicated to decipher useful information on provenance via the elemental compositions of sediments.Provenance of the late Cenozoic sediments in the Jianghan Basin has been highlighted for a long time.Many provenance indictors have been taken to decipher information on the provenance of the sediments of the Jianghan Basin.Provenance study of the sediments in the Jianghan Basin plays an important role in reconstructing the evolutionary history of the Yangtze River and has been highlighted for a long time.Among these researches,geochemical methods have been largely adopted,e.g.the elemental compositions of the sediments.Unfortunately,it is still controversial that how the grain size affect the elemental compositions of the sediments.In this study,we presented the elemental compositions of the late Cenozoic sediments of the Jianghan Basin and tried to decipher some information on the correlation between the elemental compositions and the grain-size effect and the sedimentary environment of the Jianghan Basin. The correlation between the 23 elements and the grain-size effect revealed that only 6% of the 23 elements show correlation higher than 0.3,while 13%,35% and 46% of the 23 elements show correlation of 0.2~0.3,0.1~0.2 and <0.1,respectively.The elements of V,Sc,Cr,Zr,Co,Sr,Ba,Nb,Hf,Ta,Hf,Th,U are relatively concentrated in the grain size fraction of 5~7,in contrast the elements of Li,Rb,Cu,Cs are concentrated in the grain size fraction of 10~12.The content of Be,Y and Pb are not obviously affected by the grain-size effect.It means that the grain-size effect is not the main factor that affects the elemental compositions of the late Cenozoic sediments of the Jianghan Basin.Based on that,we conclude that the elemental compositions can be effective provenance indicators.The grain-size effect can be ignored when the elemental compositions are used to trace the source of the late Cenozoic sediments of the Jianghan Basin. The average variation coefficient of the 23 elements is 0.23,of which the Sr,Zr,Ba and Hf are the most fluctuant elements while the Y has the lowest variation coefficient.Curiously,the elements with higher variation coefficients are also enriched compared with the UCC. The lacustrine sediments with lowest Sr content in the core sediments around the depth of 287 m indicate the weak chemical weathering conditions.The lowest V/Ni ratio indicates the weak oxidizing or reduction conditions.Meanwhile content of the lithophile elements are low throughout the core sediments,indicating less terrigenous input.Besides the color of these sediments is steel gray,which accords well with the elemental characteristics.We propose that around 2.6~2.43 Ma BP,the Jianghan Basin was controlled by arid climate.Rivers around the basin were with small water discharge inducing the development of salt lake.All of these factors could result in less terrigenous input.Sediments around the depth of 214 m are characterized by highest Sr content.The Sr/Ba ratios are relatively low while the V/Ni ratios are generally high and fluctuant.Most lithophile elements are with peak values of content.All of the evidence indicates that during this period the Jianghan Basin was controlled by humid climate.The water discharge of the rivers was sufficient especially the upper reaches.Under this condition the basin received large amounts of terrigenous input.As a result of this weather condition and the river hydrodynamic conditions,the lake in the Jianghan Basin was under oxidizing environment.Based on those evidence,we made a reasonable assumption that large lake developed under the control of the Yangtze River during this period. Trace elemental compositions of the sediments revealed that most of the lithophile and chalcophile elements are relatively enriched compared to the Upper Continental Crust(UCC).The siderophile elements are depleted compared with the UCC.It probably indicates that the most of the sediments of the Jianghan Basin derived from the upper Yangtze rather than the materials from the deep earth in the Yangtze block.The lacustrine sediments of the Core Zhoulao around 287m show low-Sr,and V/Ni ratios and high Zr/Sr and Rb/Sr ratios,which indicate that salt lake largely developed in the Jianghan Basin under the cold and dry weather between 2.6 ~ 2.43 Ma B.P..In contrast,freshwater lake developed around 2.1 Ma B.P..It is consistent with the late Cenozoic pollen assemblages in the Jianghan Basin,and the sedimentary records in the Subei Basin and Yangtze delta.We conclude that the elemental compositions in the Jianghan Basin might record the global cooling around 2.5 Ma B.P.and the intense uplift of the Tibetan Plateau around 1.4~1.2 Ma B.P. |
| Keywords: | the Jianghan Basin trace element grain-size dependence palaeolake |
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