Anomalous negative excursion of carbon isotope in organic carbon after the last Paleoproterozoic glaciation in North America

作者：Sekine Yasuhito^*; Tajika Eiichi; Ohkouchi Naohiko; Ogawa Nanako O; Goto Kazuhisa; Tada Ryuji; Yamamoto Shinji; Kirschvink Joseph L

来源：Geochemistry Geophysics Geosystems, 2010, 11: Q08019.

DOI：10.1029/2010GC003210

• Great Oxidation Event
• carbon isotope
• climate change
• glaciation
• Paleoproterozoic
• atmospheric evolution

Early Paleoproterozoic time (2.5-2.0 Ga) spanned a critical phase in Earth's history, characterized by repeated glaciations and an increase in atmospheric oxygen (the Great Oxidation Event (GOE)). Following the last and most intense glaciation of this period, marine carbonates record a large positive excursion of delta C-13 value (termed the "Lomagundi event") between about 2.2 and 2.1 Ga coinciding with the global appearances of red beds and sulfates, which suggest an accumulation of high levels of atmospheric oxygen. Here we report the discovery of large negative excursions of delta C-13 in organic matter (down to -55 parts per thousand) from quartzose sandstones (of the Marquette Range and the Huronian Supergroups, North America) intermediate in age between the last Paleoproterozoic glaciation and the possible onset of the Lomagundi event. The negative excursion is concomitant with the appearance of intensely weathered quartzose sandstones, which may represent hot and humid conditions. There are some interpretations that potentially explain the negative excursions: (1) redeposition of older C-13-depleted kerogen, (2) later post-depositional infiltration of oil, (3) active methane productions by methanogens in shallow-marine environments, or (4) dissociation of methane hydrate. If the latter two were the case, they would provide clues for understanding the environmental change connecting the intense glaciation and an increase in oxygen.

• 出版日期2010-8-21