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Pyrite Textures, Trace Elements and Sulfur Isotope Chemistry of Bijaigarh Shales, Vindhyan Basin, India and Their Implications
Minerals ( IF 2.5 ) Pub Date : 2020-06-29 , DOI: 10.3390/min10070588
Indrani Mukherjee , Mihir Deb , Ross R. Large , Jacqueline Halpin , Sebastien Meffre , Janaína Ávila , Ivan Belousov

The Vindhyan Basin in central India preserves a thick (~5 km) sequence of sedimentary and lesser volcanic rocks that provide a valuable archive of a part of the Proterozoic (~1800–900 Ma) in India. Here, we present an analysis of key sedimentary pyrite textures and their trace element and sulfur isotope compositions in the Bijaigarh Shale (1210 ± 52 Ma) in the Vindhyan Supergroup, using reflected light microscopy, LA-ICP-MS and SHRIMP-SI, respectively. A variety of sedimentary pyrite textures (fine-grained disseminated to aggregates, framboids, lags, and possibly microbial pyrite textures) are observed reflecting quiet and strongly anoxic water column conditions punctuated by occasional high-energy events (storm incursions). Key redox sensitive or sensitive to oxidative weathering trace elements (Co, Ni, Zn, Mo, Se) and ratios of (Se/Co, Mo/Co, Zn/Co) measured in sedimentary pyrites from the Bijaigarh Shale are used to infer atmospheric redox conditions during its deposition. Most trace elements are depleted relative to Proterozoic mean values. Sulfur isotope compositions of pyrite, measured using SHRIMP-SI, show an increase in ծ34S as we move up stratigraphy with positive ծ34S values ranging from 5.9‰ (lower) to 26.08‰ (upper). We propose limited sulphate supply caused the pyrites to incorporate the heavier isotope. Overall, we interpret these low trace element signatures and heavy sulfur isotope compositions to indicate relatively suppressed oxidative weathering on land during the deposition of the Bijaigarh Shale.

中文翻译:

印度Vindhyan盆地Bijaigarh页岩的黄铁矿质地,微量元素和硫同位素化学及其意义

印度中部的Vindhyan盆地保留着厚厚的(约5 km)沉积和少量火山岩序列,为印度部分元古代(〜1800-900 Ma)的一部分提供了宝贵的档案。在这里,我们分别使用反射光显微镜,LA-ICP-MS和SHRIMP-SI分析了Vindhyan超群Bijaigarh页岩(1210±52 Ma)中的关键沉积黄铁矿质地及其微量元素和硫同位素组成。 。观察到各种沉积的黄铁矿质地(细粒状散布到聚集体,黄粉,矿渣和可能的微生物黄铁矿质地),反映出安静且强烈缺氧的水柱状况,偶尔会出现高能事件(暴风雨入侵)。对氧化风化痕量元素(Co,Ni,Zn,Mo,Se)和(Se / Co,Mo / Co,在比贾加尔页岩的沉积黄铁矿中测得的Zn / Co)可用于推断沉积过程中的大气氧化还原条件。相对于元古代平均值,大多数痕量元素都被消耗掉了。使用SHRIMP-SI测量的黄铁矿的硫同位素组成显示出ծ的增加34个S作为我们具有正ծ向上移动地层34的价值观范围从5.9‰(低级)到26.08‰(上部)。我们建议有限的硫酸盐供应导致黄铁矿结合较重的同位素。总的来说,我们解释这些低痕量元素特征和重硫同位素组成,以表明在比贾加尔页岩沉积过程中陆地上的氧化风化受到相对抑制。
更新日期:2020-06-29
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