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

点击翻译按钮获取中文摘要

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.