Multiple sulfur isotopes of sulfides from sediments in the aftermath of Paleoproterozoic glaciations
Multiple sulfur isotopes of sulfides from sediments in the aftermath of Paleoproterozoic glaciations
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DOI：
10.1016/j.gca.2005.07.005
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发表时间：
2005-11
影响因子：
5
通讯作者：
D. Papineau;S. Mojzsis;C. Coath;J. Karhu;K. McKeegan
中科院分区：
文献类型：
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作者：
D. Papineau;S. Mojzsis;C. Coath;J. Karhu;K. McKeegan
古元古代沉积物报告的地球化学证据长期以来一直被用来评估从缺氧太古宙大气到含氧大气的转变。沉积硫化物和硫酸盐中的硫同位素（32S、33S、34S 和 36S）是监测这一转变的特别敏感的方法，因此可以使用表示为 Δ33S 的质量无关分馏（MIF）硫同位素系统学来研究古元古代“大氧化事件”的时间。在此，我们报告了对来自芬兰、南非、怀俄明州和安大略省的 30 个不同样品进行的 83 项单独分析的数据，这些样品来自芬兰、南非、怀俄明州和安大略省，跨度约 600 My，并跟踪古元古代的一个或多个“雪球地球”事件。使用高分辨率二次离子质谱技术在多重收集模式下测量样品，该技术可研究单个硫化物颗粒内微域（<30 μm）中的多种硫同位素，同时保留岩相背景。我们重点关注古元古代冰川作用（1.9 至 2.2 Ga 之间）后沉积的沉积物，以追踪大气中氧气浓度的波动，这些波动可能受到大气、上层海洋和大陆地壳中氧气汇的相互作用以及需氧生物的出现和多样化的影响。我们的结果表明，古元古代全球长期变冷之后沉积的沉积物中不存在 MIF 硫同位素，并独立证实了 MIF 在此期间停止的观察结果。我们通过整合硫化物中的 Δ33S 和 δ34S 数据、碳酸盐中的 δ13C 数据以及古元古代冰川事件的估计时间来解释我们的结果。数据强烈暗示，在冰川作用之后，存在微生物硫酸盐减少以及溶解海水硫酸盐和/或δ34S硫酸盐浓度的波动，并且可能受到侵蚀率变化和向海洋输送营养物的影响。这些变化调节了初级生产者的数量，尤其是含氧光合作用者的数量，并导致大气中氧气、二氧化碳和甲烷丰度的波动。我们的结果支持这样的解释：在 ~2.25 和 2.05 Ga 之间观察到的全球 δ13C 碳偏移（Karhu 和 Holland，1996）是大气中 O2 显着积累的时期。
Geochemical evidence reported from Paleoproterozoic sediments has long been used to evaluate the transition from the anoxic Archean atmosphere to an oxygenated atmosphere. Sulfur isotopes (32S,33S,34S and36S) in sedimentary sulfides and sulfates are an especially sensitive means to monitor this transition, such that the timing of the Paleoproterozoic “Great Oxidation Event” can be investigated using mass-independently fractionated (MIF) sulfur isotope systematics expressed as Δ33S. Here we report data from 83 individual analyses of pyrite, pyrrhotite and chalcopyrite on a new suite of 30 different samples from Finland, South Africa, Wyoming and Ontario that span ∼600 My and follow one or several “Snowball Earth” events in the Paleoproterozoic. The samples were measured using a high-resolution secondary ion mass spectrometry technique in multicollection mode that investigates multiple sulfur isotopes in microdomains (<30 μm) within individual sulfide grains while preserving petrographic context. We focused on sediments deposited in the aftermath of the Paleoproterozoic glaciations (between 1.9 and 2.2 Ga) to trace fluctuations in atmospheric O2concentrations that were likely affected by an interplay of O2sinks in the atmosphere and the upper ocean and continental crust, and by the emergence and diversification of aerobic organisms. Our results demonstrate that MIF sulfur isotopes are absent in sediments deposited after the period of protracted global cooling in the Paleoproterozoic and independently confirm observations that MIF ceased during this time. We interpret our results by integrating Δ33S and δ34S data in sulfides, δ13C data in carbonates and the estimated timing of glaciation events in the Paleoproterozoic. Data strongly hint at the presence of microbial sulfate reduction and fluctuations in the concentration of dissolved seawater sulfate and/or in δ34Ssulfatein the aftermath of glaciations and likely were affected by changing erosion rates and nutrient delivery to the oceans. These changes modulated the population of primary producers, especially oxygenic photosynthesizers, and led to fluctuations in the abundance of atmospheric O2, CO2and CH4. Our results support the interpretation that the world-wide δ13Ccarbexcursion observed between ∼2.25 and 2.05 Ga (Karhu and Holland, 1996) was a period of significant accumulation of O2in the atmosphere.