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Isotope evidence for multiple sources of B and Cl in Middle Miocene (Badenian) evaporites, Carpathian Mountains
Applied Geochemistry ( IF 3.1 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.apgeochem.2020.104819
Yao Zhao , Hai-Zhen Wei , Xi Liu , Yi-Jing Wang , Shao-Yong Jiang , Christopher J. Eastoe , Tadeusz M. Peryt

ABSTRACT Evaporites of Middle Miocene Badenian stage occur widely in basins from the Carpathian Mountain region (Poland, Slovakia and Ukraine), but their source and formation process are still debatable. A detailed boron isotope study in combination with previous chlorine isotope and chemistry data of the salt samples from three localities (Wieliczka mine, Trans-Carpathian Basin, East Slovakian Basin) reveal huge ranges of δ11B (-4.5 to +35.7‰) and δ37Cl (-0.2 to +0.8‰). Modelling calculation indicates that both Rayleigh fractionation and incorporation of fluid inclusion solutes cannot cause such a large shift on δ11B values in halite. Instead, the B and Cl isotope data imply multiple brine sources, including evaporite brine, dissolved diapiric halite and basin brine in addition to the predominant seawater source during the formation of these evaporites. At Wieliczka salt mine, a positive δ11B excursion (from -5‰ to +20 and +30‰) matches the negative δ37Cl variation (from +0.5 ± 0.1‰ to negative values) stratigraphically upwards, which indicate both terrestrial boron and non-marine chloride made significant contributions to the composition of the basin brine during the early development of the basin. In the upper column, the δ11B values are within the marine range, but show influence by the sorption of boron onto clay, whereas the δ37Cl values at +0.5‰ still indicate the presence of non-marine chloride, possibly from recrystallized, diapiric halite. In the Trans-Carpathian Basin, constant δ37Cl (+0.3 ‰) and δ11B (+15 ‰) in the middle of the profile are consistent with a dominant marine source, whereas the lower δ11B (+2.21‰) and higher δ37Cl (+0.8‰) in the lower column suggest terrestrial fresh water flowed into the basin during the formation of basal halite. Halites in the upper part of the profile show near 0‰ of δ37Cl, suggesting incorporation of Cl from a mixture of expelled basin brines. In the Slovakian Basin, the δ11B values (+18.12 to +19.14‰) at the base of the profile lie within the marine range, but high δ37Cl values (+0.7 to +0.8‰) require a non-marine chloride source. In the upper part of the profile, boron isotope data indicate a change from marine (+12.17 to +23.36‰) to non-marine (+5.43 to +6.09‰) derivation of B, but the sources of Cl remain marine (+0.0 to +0.5‰). Overall, both B and Cl isotopes show coupled variation in the Middle Miocene Badenian evaporites and suggest multiple sources of B and Cl.

中文翻译:

喀尔巴阡山脉中中新世(巴登阶)蒸发岩中 B 和 Cl 多种来源的同位素证据

摘要 中中新世巴登阶蒸发岩广泛存在于喀尔巴阡山脉地区(波兰、斯洛伐克和乌克兰)的盆地中,但其来源和形成过程仍有争议。一项详细的硼同位素研究结合先前来自三个地点(维利奇卡矿、跨喀尔巴阡盆地、东斯洛伐克盆地)的盐样品的氯同位素和化学数据揭示了 δ11B(-4.5 至 +35.7‰)和 δ37Cl( -0.2 至 +0.8‰)。建模计算表明,瑞利分馏和流体包裹体溶质的掺入都不会导致岩盐中 δ11B 值发生如此大的变化。相反,B 和 Cl 同位素数据意味着多种卤水来源,包括蒸发卤水、除了这些蒸发岩形成过程中的主要海水来源之外,溶解的底辟石岩盐和盆地盐水也是这些蒸发岩的主要来源。在维利奇卡盐矿,δ11B 的正偏移(从 -5‰ 到 +20 和 +30‰)在地层上与负的 δ37Cl 变化(从 +0.5 ± 0.1‰ 到负值)相匹配,这表明陆地硼和非海洋硼在盆地的早期开发过程中,氯化物对盆地卤水的组成做出了重大贡献。在上列中,δ11B 值在海洋范围内,但显示出受硼吸附在粘土上的影响,而 +0.5‰ 的 δ37Cl 值仍表明存在非海洋氯化物,可能来自重结晶的底辛石岩盐。在跨喀尔巴阡盆地,常数 δ37Cl (+0. 剖面中部的 3 ‰) 和 δ11B (+15 ‰) 与主要海洋源一致,而下部柱中较低的 δ11B (+2.21‰) 和较高的 δ37Cl (+0.8‰) 表明有陆地淡水流过在基底岩盐形成过程中进入盆地。剖面上部的岩盐显示 δ37Cl 接近 0‰,表明从盆地排出的盐水混合物中掺入了 Cl。在斯洛伐克盆地,剖面底部的 δ11B 值(+18.12 至 +19.14‰)位于海洋范围内,但高 δ37Cl 值(+0.7 至 +0.8‰)需要非海洋氯化物来源。在剖面的上部,硼同位素数据表明 B 的来源从海洋(+12.17 到 +23.36‰)变为非海洋(+5.43 到 +6.09‰),但 Cl 的来源仍然是海洋(+0.0到 +0.5‰)。全面的,
更新日期:2021-01-01
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