Lin Zhiyong, Sun Xiaoming, Peckmann Jörn, Lu Yang, Strauss Harald, Xu Li, Lu Hongfeng, Teichert Barbara M A
School of Earth Sciences and Engineering, Sun Yat-sen University; Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering.
School of Earth Sciences and Engineering, Sun Yat-sen University; School of Marine Sciences, Sun Yat-sen University; Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center;
J Vis Exp. 2017 Aug 31(126):55970. doi: 10.3791/55970.
Different sulfur isotope compositions of authigenic pyrite typically result from the sulfate-driven anaerobic oxidation of methane (SO4-AOM) and organiclastic sulfate reduction (OSR) in marine sediments. However, unravelling the complex pyritization sequence is a challenge because of the coexistence of different sequentially formed pyrite phases. This manuscript describes a sample preparation procedure that enables the use of secondary ion mass spectroscopy (SIMS) to obtain in situ δS values of various pyrite generations. This allows researchers to constrain how SO4-AOM affects pyritization in methane-bearing sediments. SIMS analysis revealed an extreme range in δS values, spanning from -41.6 to +114.8‰, which is much wider than the range of δS values obtained by the traditional bulk sulfur isotope analysis of the same samples. Pyrite in the shallow sediment mainly consists of S-depleted framboids, suggesting early diagenetic formation by OSR. Deeper in the sediment, more pyrite occurs as overgrowths and euhedral crystals, which display much higher SIMS δS values than the framboids. Such S-enriched pyrite is related to enhanced SO4-AOM at the sulfate-methane transition zone, postdating OSR. High-resolution in situ SIMS sulfur isotope analyses allow for the reconstruction of the pyritization processes, which cannot be resolved by bulk sulfur isotope analysis.
自生黄铁矿不同的硫同位素组成通常源于海洋沉积物中由硫酸盐驱动的甲烷厌氧氧化（SO4-AOM）和有机碎屑硫酸盐还原（OSR）。然而，由于不同顺序形成的黄铁矿相共存，解析复杂的黄铁矿化序列具有挑战性。本手稿描述了一种样品制备程序，该程序能够利用二次离子质谱（SIMS）获得不同世代黄铁矿的原位δS值。这使研究人员能够确定SO4-AOM如何影响含甲烷沉积物中的黄铁矿化。SIMS分析揭示了δS值的极端范围，从-41.6到+114.8‰，这比通过对相同样品进行传统的全硫同位素分析获得的δS值范围要宽得多。浅层沉积物中的黄铁矿主要由贫硫莓球组成，表明是由OSR在早期成岩作用下形成的。在沉积物更深的地方，更多的黄铁矿以增生体和自形晶体的形式出现，其SIMS δS值比莓球高得多。这种富硫黄铁矿与硫酸盐-甲烷过渡带增强的SO4-AOM有关，晚于OSR。高分辨率原位SIMS硫同位素分析能够重建黄铁矿化过程，而这是全硫同位素分析无法解析的。
