| 长江河口地区全新世以来的弱透水层孔隙水地球化学特征及成因分析 |
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| 引用本文：苟富刚,龚绪龙.2023.长江河口地区全新世以来的弱透水层孔隙水地球化学特征及成因分析[J].地球学报,44(6):1063-1075. |
| DOI：10.3975/cagsb.2023.030602 |
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| 基金项目:中国地质调查局地质大调查项目(编号: 1212011220005);国家自然科学基金项目(编号: 42007402; 41772327);江苏省自然资源厅自然资源发展专项(编号: JSZRHYKJ202106) |
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| 中文摘要:弱透水层孔隙水反映了土体沉积时的原始溶液, 对于古气候重建具有重大作用。为了解析长江河口地区全新世以来弱透水层孔隙水的补给及其盐分来源, 采集易溶盐、土工、潜水、近岸海水等样品。采用易溶盐指标结合土工指标(含水率、湿密度、比重)获取了研究区弱透水层孔隙水的水化学特征。采用二端元法、Piper三线图、Gibbs图、离子比值法等解析了孔隙水的补给及其盐分来源。结果表明: 孔隙水矿化度介于1.16~32.79 g/L, 平均值为10.68 g/L, 盐水占比最高, 其次为咸水和微咸水。孔隙水类型以Cl-Na型(85.6%)为主, 其次从高到低依次为Cl-Ca·Mg、HCO3-Ca·Na、HCO3-Ca、Cl-Ca型。当地潜水类型为HCO3-Ca型, 深层孔隙类型为Cl-Na型, 说明深层孔隙水保留了土体沉积时的环境信息。中层与浅层孔隙水受到了大气降水补给、人类活动、蒸发作用等表层作用影响, 孔隙水水化学数据较为离散。孔隙水的δ18O与δD数据说明孔隙水样点受到了海水混合作用与蒸发作用的叠加影响, 蒸发作用较为强烈。孔隙水海水补给比例介于30.2%~87.0%, 大气降水补给比例介于13.0%~69.8%。土体中的盐分主要来自全新世海侵(海源)与蒸发盐岩溶解、长石风化溶解(地壳源)。海水补给深层孔隙水盐分的比例约为37%, 其余盐分主要来自地壳源。 |
| 中文关键词:弱透水层 易溶盐 孔隙水 盐分来源 水化学 同位素 |
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| Analysis of Geochemical Characteristics and Genesis of Aquitard in the Yangtze Estuary since the Holocene |
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| Abstract:The porewater of the aquitard reflects the original composition of the soil when it was deposited, and is of great importance for paleoclimate reconstruction. In order to analyze the recharge of aquitard porewater and its salt source since the Holocene in the Yangtze estuary, samples of labile salt, geotechnical, phreatic water, and nearshore seawater were collected. The hydrochemical characteristics of the porewater of the aquitard in the study area were determined using the soluble salt index combined with geotechnical parameters (water content, wet density, specific gravity). The recharge of porewater and its salt source were analyzed using the bipartite element method, Piper trilinear diagram, Gibbs diagram, and ion ratio method. The results showed that the mineralization of porewater ranged from 1.16 to 32.79 g/L, with an average value of 10.68 g/L. The percentage of haline water was the highest, followed by saline water and brackish water. The porewater type was dominated by Cl-Na type (85.6%), followed by Cl-Ca·Mg, HCO3-Ca-Na, HCO3-Ca, and Cl-Ca types in descending order. The local phreatic water type was HCO3-Ca and the deep porewater type was Cl-Na, indicating that the deep porewater sea retains the environmental information when the soil was deposited. The middle and shallow porewaters were affected by the surface effects such as atmospheric precipitation recharge, human activities and evaporation, and the porewater hydrochemical data were more discrete. The porewater δ18O and δD data indicated that the sample sites were influenced by both seawater mixing and evaporation, of which evaporation was stronger. The porewater seawater recharge ratio ranged from 30.2% to 87.0%, and the atmospheric precipitation recharge ratio ranged from 13.0% to 69.8%. The salt in the soil mainly originated from Holocene sea intrusion (sea source) with evaporative salt rock dissolution and feldspar weathering dissolution (crustal source). Taking deep porewater as an example, seawater recharge contributes 37% to porewater salinity, while the remainder was from crustal sources. |
| keywords:aquitard soluble salt porewater salt source water chemistry isotope |
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