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The Origin and MgCl 2 –NaCl Variations in an Athalassic Sag Pond: Insights from Chemical and Isotopic Data
Aquatic Geochemistry ( IF 1.6 ) Pub Date : 2018-04-26 , DOI: 10.1007/s10498-018-9337-y
Tiziano Boschetti , Salih Muhammad Awadh , Emma Salvioli-Mariani

The examination of past and new chemical–isotopic data (2H/1H–18O/16O, 11B/10B and 87Sr/86Sr ratios) shows the meteoric origin of the Sawa Lake (Muthanna Governorate, Iraq) and its connection with the local aquifers, which feed the lake via the groundwater emerging from its floor through fault systems. The chemical and isotopic evaporation models are traced by geochemical computer codes by using a different composition of some potential inflows to the lake (e.g., the Euphrates River and Dammam aquifer). The main product of the chemical evaporation models is gypsum, as confirmed by the mineralogical examination of the sediment and the surrounding outcrops. A strong 18O–2H enrichment is a consequence of the evaporation effect in arid regions; δ18O–Cl models and δ11B = + 23.4‰ exclude the contribution of any seawater-derived fluids. This latter value along with 87Sr/86Sr = 0.707989 suggests a mixed origin from the Eocene–Miocene aquifers. The isotope and chemical evaporation paths from the meteorically recharged sources match the lake composition. However, compositional switches from NaCl toward MgCl2 occurred in the last decade and are related to post-drought periods, showing that the interaction of the recharging waters with the local soils (Na–Mg exchange and/or the leaching of the top layer salts) have a role in the chemical composition. This demonstrates that the lake is significantly influenced by climatic variations.

中文翻译:

卤水凹陷池塘的起源和MgCl 2 -NaCl变化:化学和同位素数据的见解

检查过去和新的化学同位素数据(2 H / 1 H– 18 O / 16 O,11 B / 10 B和87 Sr / 86Sr比率)显示了萨瓦湖(伊拉克穆塔纳省)的陨石起源及其与当地含水层的联系,这些含水层通过从地底流出的地下水通过断层系统为湖泊供水。化学和同位素蒸发模型由地球化学计算机代码通过使用一些潜在的入湖流量(例如幼发拉底河和达曼蓄水层)的不同组成来追踪。化学沉积模型的主要产品是石膏,通过沉积物和周围露头的矿物学检查证实。干旱地区蒸发作用的结果是18 O- 2 H的强烈富集。δ 18 O型氯模型和δ 11B = + 23.4‰,不包括任何海水衍生流体的贡献。后一个值与87 Sr / 86 Sr = 0.707989一起表明始新世-中新世含水层的混合来源。来自气象补给源的同位素和化学蒸发路径与湖泊组成相匹配。然而,从NaCl到MgCl 2的成分转换发生在最近十年中,并且与干旱后时期有关,这表明补给水与当地土壤的相互作用(Na-Mg交换和/或顶层盐的浸出) )在化学成分中起作用。这表明该湖受到气候变化的显着影响。
更新日期:2018-04-26
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