| 太湖地区早全新世沉积物中富铁质棍状结核体成因研究 |
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| 引用本文： | 左书豪,谢志东.太湖地区早全新世沉积物中富铁质棍状结核体成因研究[J].高校地质学报,2021,27(2):172-182. |
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| 作者姓名： | 左书豪 谢志东 |
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| 作者单位： | 南京大学 地球科学与工程学院,内生金属矿床成矿机制研究国家重点实验室,南京 210023 |
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| 基金项目： | 国家自然科学基金项目(40972031)资助。 |
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| 摘 要： | 文章主要介绍太湖地区富铁质棍状结核体的原始直立产状、分布特征、外形特征,内部胶体结构及其矿物学组合特征,进而讨论棍状结核体的成因模式.棍状结核体横向上广泛分布于太湖及其周边地区,产于一层标志性泥质层中;纵向上,棍状结核体在不同高度,从湖底到山边的田地,山麓下的沟槽里都有发现.原始层位可见新鲜棍状结核体,外表颜色为钢灰色...
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| 关 键 词： | 太湖 菱铁矿 棍状结核体 冲击 空中爆炸 |
Mineralogical Study of Iron-rich Elongated Concretions in Holence Silt Layer in Taihu Lake Region |
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| ZUO Shuhao,XIE Zhidong.Mineralogical Study of Iron-rich Elongated Concretions in Holence Silt Layer in Taihu Lake Region[J].Geological Journal of China Universities,2021,27(2):172-182. |
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| Authors: | ZUO Shuhao XIE Zhidong |
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| Institution: | State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China; |
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| Abstract: | The paper mainly focuses on the original upright occurrence of the elongated(rod-shaped)concretions in one specific silt layer,distribution,morphology,internal colloidal structure and mineral assemblages of the iron-rich elongated concretions in Taihu Lake area.The main purpose of the paper is to discuss the formation mechanisms of the iron-rich elongated concretions.In horizontal,the rod-shaped concretions are widely distributed in one specific silty layer in Taihu Lake.Vertically,the rod-shaped concretions are found at different heights,from the bottom of Tai lake to the farm fields on the hillside,and in the grooves near the foothills.Fresh rodshaped concretions only can be seen in the landmark silty layer with a rigid gray for the outer surface and the color of the natural broken surface is gray.The original occurrence of the rod-shaped concretions is upright inserted in the landmark silty layer,with the head down and the tail upward,and the heads of elongated concretions have hemispherical shape and curved threads lines.While,another kind of concretions found in the disturbed layer have short columns with smooth outer surface due to moving wearing,and the color appears grayish brown or yellowish brown due to weathering.The length of the rod-shaped concretions range from 1 to 80 cm,some is short and some is long.Most of short ones are broken sections of the long one.The diameters of the elongated concretions range from half cm to 2 cm.Most of rod-shaped concretions have weathering crusts with a thickness about 1 to 2 mm.The outer surface of the rod-shaped concretions has unique spiral patterns.Major inclusions in the concretions are angular sharp-edged quartz grains with poor roundness and poor separation surrounding by fine matrix of cement of the concretions.Minors inclusions are rock debris or dusts aggregates.The main cements are siderite euhedral crystals with size of several micrometers.In addition,many iron-rich spherulites adhere to outer surface of the concretions,and part of elongated concretions consisting with iron-rich spherules.The porosity of the elongated concretions is less than 20%,and they are much denser than most concretions formed in surface depth.The original upright occurrence of the rod-shaped concretions indicate that it is not the residue product after leaching the underlying hard loess layer.Also,the upright occurrence infers that the age of the elongated concretions are not older than the age of the specific silty layer which is dated as~7 ka B.P.There are two possible origins of iron-rich concretions.One is lake deposition hypothesis,that concretions grow and form in the porous space of mudlayer in lake bottom;the other is airburst fallout hypothesis,that elongated concretions form in airburst plume and fall down and insert into lake mud layer.We think airburst fallout hypothesis is more reasonable,because the fallout materials of airburst plume can explain the unique morphology and internal characteristics of the elongated concretions. |
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| Keywords: | Taihu Lake siderite elongated concretions impact airburst |
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