Biospheric oxygenation and atmospheric evolution across Earth's earliest glacial episodes

地球最早冰期的成因尚不清楚，但与太阳亮度变化和温室气体丰度（主要是甲烷和二氧化碳）相关的模型表明，大气氧化状态的变化可能驱动了早古元古代（约2.2至2.4 Ga）冰期的振荡周期。海洋和大气的氧化还原状态反映在古代沉积物中保存的硫酸盐和硫化物矿物的多重硫同位素数据（32S, 33S， 34S和36S）中。在最新的太古宙沉积物中，硫同位素分异表明大气氧低于10-5 PAL。然而，在南非最早的古元古代冰河时期，硫同位素记录表明pO2显著上升，可能达到几个百分点或更高。这项研究建议通过对小硫同位素变化的高分辨率研究来调查南非下一个最年轻的冰河期，包括有机结合硫，这是一种尚未在任何以前的小同位素研究中研究过的代用物——在大约2.3 Ga的Timeball Hill组的深时间钻探岩芯中，该岩芯位于广泛的冰川二晶岩之下。研究结果为大气氧化还原状态的变化驱动最早的冰期旋回提供了经验约束。

The cause(s) of Earth s earliest glaciations are poorly understood, but models that relate changes in solar luminosity and greenhouse gas abundance (primarily methane and carbon dioxide) suggest that variations in the oxidation state of the atmosphere may have driven the oscillatory cycle of early Paleoproterozoic (ca. 2.2 to 2.4 Ga) ice ages. The redox state of the oceans and atmosphere is reflected in multiple sulphur isotope data (32S, 33S, 34S, and 36S) of sulphate and sulphide minerals preserved in ancient sediments. In the latest Archean sediments reveal mass-independent sulphur isotope fractionation, suggesting that atmospheric oxygen was less than 10-5 PAL. However, by the time of the earliest Paleoproterozoic ice age in South Africa, the sulphur isotopic record suggests a significant rise in pO2, to perhaps a few percent or higher. This study proposes to investigate the run up to the next youngest ice age in South Africa, through a high resolution study of minor sulphur isotope variations - including organic-bound sulphur, a proxy that has not yet been investigated in any previous minor isotope study - in deep time drill cores through the ca. 2.3 Ga Timeball Hill Formation, which lies immediately beneath a widespread glacial diamictite. Results should provide empirical constraints that changes in the atmospheric redox state drove the earliest glacial cycles.