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的休伦超群进行了地质调查，以调查古元古代（主要是约1000年）的环境变化。2450-2200万年前）。我们还对南非德兰士瓦超群和美国雪道超群进行了地质调查，以供比较。我们从庄稼和钻孔取了许多岩石样品，分析了它们的颜色、粒度、化学成分和同位素组成的变化，发现在戈瓦甘达组科尔曼段最上部的杂岩之上有锰的富集。我们还发现，有集中的赤铁矿之前的锰异常。这些证据表明，在戈瓦甘达冰川作用后不久，大气和海洋表面的氧含量应该很高。考虑到相似的年龄（CA。2222 Ma）、单位面积锰沉积量相当、沉积序列（冰川杂屑岩-锰、铁富集-红层）等，推测这两个地区可能记录了相同的全球性事件，即约2222 Ma的雪球冰川作用和氧含量上升。2222 Ma。我们还研究了碳酸盐和有机碳的碳同位素组成的变化，黄铁矿的硫同位素的质量独立分馏，和古地磁，基于采取的样品从休伦超群和雪道超群。利用数值模式研究了雪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.