We revisit the S‐isotope systematics of sedimentary pyrite in a shaly limestone from the ca. 2.52 Ga Gamohaan Formation, Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed rock is interpreted to have been deposited in a water depth of ca. 50–100 m, in a restricted sub‐basin on a drowning platform. A previous study discovered that the pyrites define a nonzero intercept δ³⁴S_V‐CDT–Δ³³S data array. The present study carried out further quadruple S‐isotope analyses of pyrite, confirming and expanding the linear δ³⁴S_V‐CDT–Δ³³S array with an δ³⁴S zero intercept at ∆³³S ca. +5. This was previously interpreted to indicate mixing of unrelated S‐sources in the sediment environment, involving a combination of recycled sulphur from sulphides that had originally formed by sulphate‐reducing bacteria, along with elemental sulphur. Here, we advance an alternative explanation based on the recognition that the Archaean seawater sulphate concentration was likely very low, implying that the Archaean ocean could have been poorly mixed with respect to sulphur. Thus, modern oceanic sulphur systematics provide limited insight into the Archaean sulphur cycle. Instead, we propose that the 20th‐century atmospheric lead event may be a useful analogue. Similar to industrial lead, the main oceanic input of Archaean sulphur was through atmospheric raindown, with individual giant point sources capable of temporally dominating atmospheric input. Local atmospheric S‐isotope signals, of no global significance, could thus have been transmitted into the localised sediment record. Thus, the nonzero intercept δ³⁴S_V‐CDT–Δ³³S data array may alternatively represent a very localised S‐isotope signature in the Neoarchaean surface environment. Fallout from local volcanic eruptions could imprint recycled MIF‐S signals into pyrite of restricted depositional environments, thereby avoiding attenuation of the signal in the subdued, averaged global open ocean sulphur pool. Thus, the superposition of extreme local S‐isotope signals offers an alternative explanation for the large Neoarchaean MIF‐S excursions and asymmetry of the Δ³³S rock record.

中文翻译：

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新古生界的表面硫循环：一种基于与20世纪大气铅相似的假说。

我们重新审视了加利福尼亚州页岩灰岩中沉积黄铁矿的S同位素系统。2.52南非特兰斯瓦尔的上坎贝尔朗德小组Ga Gamohaan组。被分析的岩石被解释为已经沉积在大约水深中。50–100 m，在溺水平台上的受限子盆地中。先前的研究发现，黄铁矿限定非零截距δ ³⁴小号_{V - CDT} -Δ ³³ S个数据数组。本研究中进行的黄铁矿进一步四倍S-同位素分析，证实并扩展线性δ ³⁴小号_{V - CDT} -Δ ³³与δ■数组³⁴在Δš零截距³³约 +5。先前曾解释说，这表明沉积物环境中无关的S源混合在一起，涉及从最初由还原硫酸盐的细菌形成的硫化物中回收的硫与元素硫的混合物。在此，我们基于对古细菌海水硫酸盐浓度可能很低的认识，提出了另一种解释，这意味着古细菌海洋与硫的混合可能很差。因此，现代海洋硫系统学对古生硫循环的了解有限。相反，我们建议20世纪的大气铅事件可能是一个有用的类比。与工业铅相似，古生硫的主要海洋输入是通过大气降雨，个别的巨型点源能够暂时控制大气输入。因此，没有全球意义的本地大气S同位素信号可能已经传输到了局部沉积物记录中。因此，非零截距δ³⁴ S _{V - CDT} –Δ ³³ S数据阵列可以替代地表示新古生界表面环境中非常局限的S同位素特征。局部火山喷发的尘埃可将回收的MIF-S信号压印在沉积环境受限的黄铁矿中，从而避免在平均水平低的全球开放性海洋硫磺池中衰减信号。因此，极端的局部S-同位素信号提供的叠加为Δ的大新太古代MIF-S游览和不对称的另一种解释³³的摇滚记录。