Study of snowball Earth events and rise of the atmospheric oxygen based on geologicalg survey of glacial sediments of the Paleoproterozoic

在这个项目中，我们对加拿大安大略省的胡伦超群进行了地质调查，以研究古元古代(主要是大约2450-2200万年前)的环境变化。我们还对南非的德兰士瓦超级群和美国的斯诺帕斯超级群进行了地质调查，以进行比较。我们从农作物和钻探岩芯中采集了大量的岩石样品，并对其进行了分析，研究了岩石的颜色、粒度、化学成分和同位素组成的变化。我们发现，高甘达组科尔曼段最上面的斜长岩层以上的锰含量很高。我们还发现，在锰异常之前有赤铁矿的聚集。这些证据表明，刚过Gowganda冰期，大气和表层海洋中的氧含量就应该很高。考虑到加拿大胡伦超群和南非德兰斯瓦尔超群之间相似的年龄(约2222 Ma)、相当的单位面积锰沉积量和沉积序列(冰川斜长石-锰和铁的浓缩-红化)，我们推测这两个地区可能记录了相同的全球事件，即约2222 Ma的雪球冰川和氧气上升。我们还研究了碳酸盐和有机碳的碳同位素组成的变化，黄铁矿硫同位素的质量无关分馏和古地磁。我们还利用数值模式研究了雪球地球事件期间的碳循环和古气候变化。

In this project, we conducted geological surveys of the Huronian Supergroup, Ontario, in Canada to investigate environmental changes during the Paleoproterozoic (mainly, ca. 2450-2200 million years ago). We also conducted geological surveys of the Transvaal Supergroup in South Africa and the Snowy Pass Supergroup in USA for comparison. We took many rock samples from out crops and boring core samples, and analyzed them to investigate variations of color, grain size, chemical composition, and isotopic composition.We found that concentration of manganese above the uppermost diamictite of the Coleman Member in the Gowganda Formation. We also found that there is concentration of hematite which precedes the manganese anomaly. These evidences suggest that oxygen contents in the atmosphere and the surface ocean should have been high just after the Gowganda glaciation. Considering similar ages (ca. 2222 Ma), comparable amounts of manganese deposited per unit area, and sedimentary sequence (glacial diamictite -manganese and iron concentration -redbed) between the Huronian Supergroup in Canada and the Transvaal Supergroup in South Africa, we infer that these two areas may have recorded the same global events, namely, the snowball glaciation and the oxygen rise at ca. 2222 Ma.We also investigate variations of carbon isotopic composition of carbonates and organic carbon, mass independent fractionation of sulfur isotopes of pyrites, and paleomagnetism, based on the samples taken from the Huronian Supergroup and Snowy Pass Supergroup. We also study carbon cycle and paleoclimate change during the snowball Earth events using numerical models.