| 长江河口百米以浅土体含盐特征及其沉积环境演化 |
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| 引用本文： | 苟富刚,龚绪龙,杨露梅,张岩,刘明遥.长江河口百米以浅土体含盐特征及其沉积环境演化[J].现代地质,2022,36(2):462-473. |
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| 作者姓名： | 苟富刚 龚绪龙 杨露梅 张岩 刘明遥 |
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| 作者单位： | 1. 江苏省地质调查研究院,江苏 南京 2100492. 自然资源部地裂缝地质灾害重点实验室,江苏 南京 210049 |
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| 基金项目： | 中国地质调查局地质大调查项目(1212011220005)；;国家自然科学基金项目(41772327)； |
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| 摘 要： | 土体含盐特征是研究环境演化、工程地基基础设计和农业开发的重要参考指标。通过采集长江河口地区土样907件并对土体盐分进行测试,得到土体易溶盐8大离子含量和pH值。根据测试结果对研究区100 m以浅土层含盐特征进行系统分析。研究结果表明:各土层含盐量介于0.028%~1.226%之间。全新世土体随着深度的增加,土体含盐量呈增加趋势。含盐量最大值出现在如东组下段4-1层(埋深约26 m)淤泥质粉质黏土,盐分主要为NaCl。含盐量最小值出现在滆湖组下段的7~2砂层(埋深约81 m),其中HC03-离子含量最高,其次为Cl-与Na+。深部土层(滆湖组)含盐量有所降低,黏性土含盐量一般大于砂土。各土层ESR(交换性钠)值均大于当地地表淡水SAR(钠吸附比)值,ESR最大值为当地地表淡水SAR值的47.7倍,最低值也为当地地表淡水SAR值的2.7倍,说明土体中可交换Na含量高。100 m以浅地层含盐特征受晚更新世晚期海侵和全新世海侵控制,土体盐分主要为NaCl,其主要来源为海水浸渍或浸染。更新世土层为陆相沉积,但受晚更新世晚期海侵与全新世海侵浸染,土体含盐量较高。如东组下段和中段地层为三角洲相沉积,受长江和海侵共同作用,盐渍土广泛分布;如东组上段土层为陆相沉积,土体已普遍脱盐,HC03-离子含量最高。土体中Cl-含量对混凝土结构中的钢筋腐蚀性较大,特别是4-1淤泥质粉质黏土层,具有弱腐蚀性等级以上的土体占比高达99%,要做好基础防腐蚀工作。如东组上段的2-1和2-2土层(浅表土层)碱性较大,对农业和工程建设影响最大,需添加改良剂进行土体改良。
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| 关 键 词： | 沉积环境 含盐特征 易溶盐 软土 盐渍化 滨海盐渍土 |
| 收稿时间： | 2021-08-30 |
| 修稿时间： | 2021-12-05 |
Salt Content Features and Sedimentary Environmental Evolution in Shallow-Level (<100 m) Soils from the Yangtze River Estuary |
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| GOU Fugang,GONG Xulong,YANG Lumei,ZHANG Yan,LIU Mingyao.Salt Content Features and Sedimentary Environmental Evolution in Shallow-Level (<100 m) Soils from the Yangtze River Estuary[J].Geoscience——Journal of Graduate School,China University of Geosciences,2022,36(2):462-473. |
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| Authors: | GOU Fugang GONG Xulong YANG Lumei ZHANG Yan LIU Mingyao |
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| Institution: | 1. Geological Survey of Jiangsu Province, Nanjing, Jiangsu 210049, China2. Key Laboratory of Earth Fissures Geological Disaster, Ministry of Natural Resources, Nanjing, Jiangsu 210049, China |
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| Abstract: | Soil salinity is an important reference indicator for engineering foundation design and agricultural development. By collecting and analyzing the soil salinity of 907 soil samples from the Yangtze River estuary region, the content of eight ions and pH value of the soil soluble salts were obtained. Accordingly, the study area (<100 m depth) was systematically analyzed in a brine-bearing characteristics of the light soil. The results show that each layer contains 0.028%-1.226% salt. The Holocene land has higher soil salt content with depth, with the maximum and minimum salinity (NaCl) occurring in layer 4-1 soft soil (26 m depth) of the lower Rudong Formation and layer 7-2 sand (81 m depth) of the lower Gehu Formation, respectively. For the latter, the HC03- ion content is the highest, followed by the Cl- and Na+ contents. Deep soil layer (Gehu Formation) has lower salt content, and the amount of viscous soil is generally greater than sand. Earth layer ESR value is higher than local surface freshwater SAR. The ESR maximum is 27.7 times that of the freshwater SAR, whilst the minimum is 2.7 times that of local surface freshwater ESR, indicating that the exchangeable soil Na content is high. Soil salinity (<100 m depth) was largely controlled by the Late Pleistocene transgression and Holocene transgression. The soil salinity comprises mainly NaCl, and the most important salt source is seawater impregnation or soaking. The Pleistocene layers contain terrestrial sediments, and have high salinity due to the Pleistocene and Holocene transgression. The lower and middle members of Rudong Formation are of deltaic facies, which are affected by Yangtze River and transgression, and the soil salinity ranges widely. The Rudong Formation (upper member) comprises continental sediments, and the soil has been widely desalted, with the highest HC03- content. The Cl- content has high corrosiveness in concrete construction, especially for the 4-1 silty clay layer, where the proportion of soils with at least low corrosive grade account for up to 99%, and basic anti-corrosion treatment should be done. The 2-1 and 2-2 soil layers (exposed on the surface) of the upper Rudong Formation are more alkaline, which has high impact on agriculture and engineering construction. It is necessary to add improved agents for soil improvement. |
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| Keywords: | sedimentary environment salt characteristic soluble salt soft soil salinization coastal saline soil |
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