摘要
海相沉积物的化学特征是分析古环境变化的重要指标。本研究以连云港滨海地区浅部海相沉积物为研究对象,开展易溶盐、粒度、AMS 14C年龄及微体古生物测试,分析海相沉积物的化学特征及沉积环境。结果表明,连云港滨海地区浅部海相沉积物Cl^(−)含量最高,Na^(+)含量次之;5 m以浅土体含盐量变化较大,绝大数土体含盐量为0.3%~3.0%;至埋深20 m时,土体含盐量稳定在1.0%。沉积物中Cl^(−)含量与含盐量相关性最高,以直线型和多项式型拟合效果最佳;与Ca^(2+)、Mg^(2+)、K^(+)、SO_(4)^(2−)含量拟合效果好,以多项式型拟合效果最佳;与Na^(+)含量以幂型拟合效果最佳。沉积物含盐量与pH值呈负相关关系,说明碱性环境不利于土体盐分的增加。沉积物交换性钠(ESR)值高,说明研究土体含盐特征保留了海水特征。推测连云港滨海地区海相沉积物受到了海平面变化、东亚冬季风及黄河夺淮事件的影响。以ZK1孔为例,中全新世以来海相沉积物经历了滨海–浅海陆架环境、滨海陆架环境、近岸滨海环境、滨海潮间带环境4个阶段。阶段Ⅰ(6.3~4.2 ka):土体平均含盐量为1.2%,呈碱性,平均海水混合比为55.2%,未出现窄盐性浮游孔虫,说明土体沉积时有淡水与海水混合,水体盐度变化明显,土体颗粒组成以粉粒和黏粒为主,底栖有孔虫以玻璃质属种为主,最高占比达70%,基本未见到胶结类有孔虫,Ammonia beccari平均含量为11.80%,Ammonia compressiuscula平均含量为28.70%,为滨海–浅海陆架环境。阶段Ⅱ(4.2~0.6 ka):土体平均含盐量为1.3%,含盐量增加,海水混合比增加,土体颗粒组成与阶段Ⅰ相似,底栖有孔虫以Ammonia beccarii为主,平均含量为48.40%,Ammonia compressiuscula含量减少,为滨海陆架环境。阶段Ⅲ(0.6~0.3 ka):海平面与现今海面位置相当,受黄河夺淮后物源补给影响,沉积速率显著增加,达1.22 cm/a,与阶段Ⅱ相比,本阶段含盐量升高,pH值稍有下降,土体颗粒稍有变细,底栖有孔虫丰度显著增加,海水混合比进一步提高,Ammonia beccarii平均含量为44.30%,为近岸滨海环境。阶段Ⅳ(0.3 ka以来):土体含盐量显著增加,pH值下降,土体颗粒组成、底栖有孔虫丰度及沉积速率与阶段Ⅲ基本持平,海水混合比最高达163.3%,主要与现代积盐过程有关,Ammonia beccarii含量为47.20%,为滨海潮间带环境。
The salt content of soft soil is an important indicator of foundation design and soil improvement in engineering construction.This study focused on the shallow marine sediments in the coastal area of Lianyungang.Multiple sets of samples were collected for soluble salt,particle size,AMS 14C,and micropaleontological testing and analysis,and the chemical characteristics of the marine sediments and sedimentary environments were analyzed.The results show that soft soil salt has a high concentration of chloride ions(Cl^(−)),with sodium ions(Na^(+))ranking second in concentration.The salt content of most soils is between 0.3%and 3.0%,with shallow soils varying greatly within a depth of 5 m.Up to a depth of 20 m,the soil salt content stabilizes at 1.0%.The salt content exhibits the strongest correlation with the Cl−content.The relationship between Cl−content and salt content has a good fitting effect,with both linear and polynomial fitting effects providing the most accurate representation.In addition,the Cl−content in soils shows a robust relationship with Na^(+),Ca^(2+),Mg^(2+),and K^(+)content and is best represented using polynomial fitting.Similarly,the correlation between soluble salt Cl−and SO_(4)^(2−)content in soil is significant,and logarithmic fitting provides the best representation.The salt content was negatively correlated with the pH value,indicating that an alkaline environment was not conducive to increased soluble salt content in the soil.The high ESR value of exchangeable Na in the sediments indicated that the salt characteristics of the studied soil layers retained the characteristics of seawater.Sediment deposits are affected by factors such as changes in sea level,the East Asian winter monsoon,and the diversion of the Huanghe River into the Huaihe River.Considering hole ZK1 as an example,the research area has undergone four stages since the Holocene:Coastal-shallow shelf,coastal shelf,coastal,and coastal intertidal environments.StageⅠ(6.3 ka to 4.2 ka):In this stage,the salt content of the soil is 1.2%,and the soil is alkaline.The average seawater mixing ratio was 55.2%,indicating that fresh water and seawater were mixed during soil deposition.Salinity fluctuated significantly within the sedimentary environment of the waterbody.The soil particles are predominantly silt and clay.Benthic foraminifera assemblages were dominated by vitreous species,constituting 70%of the population.No foraminiferal cementation was observed.The average content of Ammonia beccarii is 11.80%,and Ammonia compressiuscula averages 28.70%.Multiple indicators strongly suggest a shallow coastal shelf environment.StageⅡ(4.2 ka to 0.6 ka):During this stage,the average salt content of the soil increased to 1.3%from StageⅠ.The seawater mixing ratio increased,indicating unstable salinity levels in the waterbody.The composition of the soil particles was similar to that in StageⅠ.The average content of Ammonia beccarii increased significantly to 48.40%,and the content of Ammonia compressiuscula decreased.Multiple indicators suggestive of a coastal shelf environment are available.StageⅢ(0.6 ka to 0.3 ka):The sea level at this stage was equivalent to the current level.After the Yellow River captured the Huaihe River,the sedimentation rate reached 1.22 cm/a.Compared to StageⅡ,the salt content increased,and the pH decreased slightly.Soil particles became finer,and the abundance of benthic foraminifera increased significantly.The seawater mixing ratio further increased.The average content of Ammonia beccarii was 44.30%.Multiple indicators are suggestive of a coastal environment.StageⅣ(0.3 ka to 0 ka):In this stage,the salt content of the soil increased significantly,and the pH decreased.The particle composition of the soil,abundance of benthic foraminifera,and sedimentation rate were the same as those during StageⅢ.The mixing ratio of seawater was as high as 163.3%,which is primarily related to the modern salt accumulation process.The Ammonia beccarii content was 47.20%.Several indicators pointed to a coastal intertidal environment.
作者
苟富刚
龚绪龙
宋玉明
沈辰
蔡田露
GOU Fugang;GONG Xulong;SONG Yuming;SHEN Chen;CAI Tianlu(Geological Survey of Jiangsu Province,Key Laboratory of Earth Fissures Geological Disaster,Ministry of Natural Resources,Nanjing 210049,Jiangsu,China;The Sixth Geological Party,Jiangsu Geological Bureau,Lianyungang 222002,Jiangsu,China)
出处
《地球化学》
CAS
CSCD
北大核心
2023年第5期649-662,共14页
Geochimica
基金
连云港城市地质调查项目(20170821)
中国地质调查局项目(1212011220005)
国家自然科学基金项目(41772327)联合资助。
关键词
沉积环境
含盐特征
易溶盐
海相沉积物
有孔虫
sedimentary environment
salt characteristics
soluble salt
marine sediments
foraminifera
