Abstract The Sr/Ba ratio is a geochemical indicator that distinguishes between terrestrial and marine sedimentary environments in terrigenous clastic sediments. However, conclusions drawn from the Sr/Ba ratio is often inconsistent with those drawn from other sedimentary environment indicators during practical application; therefore, the usability of this indicator is not widely acknowledged. First, to verify this theory and accurately determine the differences between the sedimentary geochemical behaviours of Sr and Ba under different salinity conditions, 14 artificial deltaic sediments were prepared by mixing clean seawater and muddy river water in varying proportions to produce different constant salinities, ranging from 0.0 to 31.2 psu. The Sr and Ba concentrations in the different fractions were then examined via sequential extraction. The experimental results show that, on average, 87% of the total Ba and 65% of the total Sr in the 14 artificial deltaic sediments existed in the residual fraction that is independent of the geochemical conditions of the depositional environment. The experiment also revealed that the decrease in Ba in the sediments was caused by the desorption of adsorbed Ba, owing to the addition of seawater with increasing salinity. Furthermore, the Sr/Ba ratio in the exchangeable fraction yielded a strong linear correlation with salinity, and the Sr/Ba ratio in the carbonate-bound fraction tended to increase slightly with increasing salinity, the Sr/Ba ratios in the Fe Mn oxide-bound, organic and reductive, and residual fractions, and the total Sr/Ba ratio were not significantly correlated with salinity. Therefore, the Sr/Ba ratio (Sr/Ba-HAc) of exchangeable and carbonate-bound Sr and Ba extracted using dilute acetic acid (HAc) and the Sr/Ba ratio (Sr/Ba-NH4Ac) of exchangeable Sr and Ba extracted using ammonium acetate (NH4Ac) can be used to distinguish between marine and terrestrial sedimentary environments. If the Sr/Ba-HAc or Sr/Ba-NH4Ac ratio in the sediment is >1.0, it can be considered to have been deposited in a sedimentary environment affected by seawater with a salinity >5.0 psu. Second, to verify the aforementioned conclusions, the Sr and Ba in 24 field samples from the Yangtze River Delta were extracted using 10% HAc or 1.0 M NH4Ac. The results indicate that the increase in the amount of Sr in the estuarine terrigenous clastic sediments from the river to the marine environments is caused by the addition of Sr-rich, Ba-poor, marine carbonate shells. The extracted Sr/Ba-HAc ratios were 8.0 in normal seawater (neritic environments and relict sand); however, in the traditional bulk analysis, total Sr/Ba ratio did not change significantly with increasing salinity. Therefore, it is suggested that the selective extraction of sedimentogenic Sr and Ba is the only effective means of using the Sr/Ba ratio to discriminate between marine and terrestrial sedimentary environments in terrigenous clastic sediments, while the traditional method of using the total Sr/Ba ratio of whole samples is unsuitable.

中文翻译：

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长三角碎屑沉积物中Sr/Ba比值对盐度的响应

摘要 Sr/Ba 比值是区分陆源碎屑沉积物中陆相和海相沉积环境的地球化学指标。然而，在实际应用中，Sr/Ba比值得出的结论往往与其他沉积环境指标得出的结论不一致；因此，该指标的可用性并未得到广泛认可。首先，为验证该理论并准确确定不同盐度条件下Sr和Ba的沉积地球化学行为的差异，通过将清洁海水和浑浊河水按不同比例混合以产生不同的恒定盐度，制备了14个人工三角洲沉积物。 0.0 至 31.2 psu。然后通过顺序提取检查不同馏分中的 Sr 和 Ba 浓度。实验结果表明，平均而言，14 种人工三角洲沉积物中 87% 的总 Ba 和 65% 的总 Sr 存在于与沉积环境地球化学条件无关的残余部分中。实验还表明，沉积物中 Ba 的减少是由于添加了盐度增加的海水，吸附的 Ba 解吸引起的。此外，可交换馏分中的 Sr/Ba 比与盐度呈强线性相关性，碳酸盐结合馏分中的 Sr/Ba 比随着盐度的增加而略有增加，Fe Mn 氧化物中的 Sr/Ba 比随盐度的增加而略有增加。结合的、有机的和还原的、残留的分数以及总 Sr/Ba 比与盐度没有显着相关性。所以，使用稀乙酸 (HAc) 提取的可交换和碳酸盐结合的 Sr 和 Ba 的 Sr/Ba 比 (Sr/Ba-HAc) 和使用铵提取的可交换 Sr 和 Ba 的 Sr/Ba 比 (Sr/Ba-NH4Ac)醋酸盐 (NH4Ac) 可用于区分海洋和陆地沉积环境。如果沉积物中的 Sr/Ba-HAc 或 Sr/Ba-NH4Ac 比值 >1.0，则可以认为沉积在盐度 >5.0 psu 的受海水影响的沉积环境中。其次，为验证上述结论，使用10% HAc或1.0 M NH4Ac提取长三角地区24个野外样品中的Sr和Ba。结果表明，从河流到海洋环境的河口陆源碎屑沉积物中Sr含量的增加是由于添加了富Sr、贫Ba、海洋碳酸盐壳。在正常海水（浅海环境和残砂）中提取的 Sr/Ba-HAc 比值为 8.0；然而，在传统的整体分析中，总 Sr/Ba 比没有随着盐度的增加而显着变化。因此，建议选择性提取沉积源Sr和Ba是利用Sr/Ba比值区分陆源碎屑沉积物中海陆沉积环境的唯一有效手段，而传统的使用总Sr/Ba的方法整个样本的比例不合适。