Purpose

To understand the impact of geochemical sedimentation history for arsenic (As) distribution in the sediment profiles of the Hetao Basin, we (1) evaluated sediments provenance and variations of weathering intensities, (2) attempted to reconstruct the depositional environments, and (3) explored the As and Fe speciation in the sediments. Combining the information above, different sedimentation facies were distinguished in the vertical profiles.

Methods

Two sediments cores were drilled up to 80 m depth. Major and trace element compositions, including rare earth elements (REE), were analyzed. Carbon isotope ratios (δ¹³C_org) of embedded organic matter in the sediments were analyzed by isotope ratio mass spectrometry (IR-MS). Arsenic and Fe speciation of the sediments were determined by sequential extractions.

Results and discussion

The similar REE geochemistry of rocks from the Lang Mountains and sediments in the Hetao Basin indicated that the sediments originated from the Lang Mountains. The C/N ratio (~ 4 to ~ 10) in combination with δ¹³C_org (− 27‰ to −2 4‰) suggested that sediments were mainly deposited in aquatic environments. The unconfined aquifer equaled the lacustrine deposit with less intensive weathering during last glacial maximum (LGM). Here, the As content (average, 5.4 mg kg⁻¹) was higher than in the aquifer sediments below (average, 3.6 mg kg⁻¹).

Conclusion

Higher content of releasable As in combination with paleolake-derived organic matter aquifer sediments probably contributes to higher groundwater As concentration in the unconfined aquifer. This study provides the first insight into the impact of sedimentation history on As distributions in sediment profiles in the Hetao Basin.

中文翻译：

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沉积历史对河套盆地晚更新世-全新世沉积物中As分布的影响

目的

为了了解地球化学沉积历史对河套盆地沉积物中砷（As）分布的影响，我们（1）评估了沉积物来源和风化强度的变化，（2）试图重建沉积环境，以及（3）探索了沉积物中的砷和铁形态。结合以上信息，在垂直剖面上可以区分出不同的沉积相。

方法

钻了两个沉积岩芯，深度达80 m。分析了主要和微量元素组成，包括稀土元素（REE）。碳同位素比率（δ ¹³ Ç_有机沉积物中的嵌入式有机物）通过同位素比质谱法（IR-MS）进行分析。沉积物中砷和铁的形态通过连续提取来确定。

结果和讨论

郎山岩石和河套盆地沉积物的相似稀土元素地球化学表明，这些沉积物起源于郎山。的C / N比（约4至〜10）结合δ ¹³ Ç_有机（ - 27‰至-2 4‰）建议，沉积物主要沉积在水生环境。在最后一次冰期最大值（LGM）期间，无侧限含水层等于湖相沉积，且风化强度较小。在此，As含量（平均5.4 mg kg ^-1）高于下面的含水层沉积物中（平均3.6 mg kg ^-1）。

结论

较高的可释放砷含量与源自古湖的有机质含水层沉积物相结合，可能有助于增加无限制含水层中地下水的砷浓度。该研究为河套盆地沉积历史对沉积物剖面中砷分布的影响提供了首次见解。