Coupled Cr and Mo isotope investigations of post-GOE Paleoproterozoic sediments: Testing the hypothesis of an oxygen overshoot in atmospheric O2 levels

通过对俄罗斯佩琴加绿岩带（PGB）和奥涅加盆地（OB）2.5 - 2.0 Gyr沉积物中氧化还原敏感元素Cr和Mo的同位素研究，重建了大氧化事件（GOE）后大气和海洋的氧化还原演化。GOE标志着大气氧含量的首次显著增加，并定义了从缺氧到好氧环境条件的转变。GOE的后果的特点是在2.22 - 2.05 Gyr-old Lomagundi和随后的Shunga事件期间氧，碳和硫循环的重大扰动-可能是全球性的。虽然后GOE沉积物存档的证据，大量的有机碳的埋葬，海水硫酸盐水库的膨胀和收缩，一个建议的氧气超负荷和有效的大陆风化的开始，时间和大气和海洋之间的氧化反应是不受约束。此外，更令人费解的是，即使GOE标志着富氧大气条件的开始，可能是随后的氧超负荷，铬同位素，建议作为示踪剂的自由氧未能确定富氧条件下的古元古代。该项目旨在对Kuetsjärvi、Kolosjoki（PGB）和Zaonezhskaya（OB）地层的各种近岸沉积环境进行详细的Cr和Mo同位素研究。该项目的第一部分将通过主要和微量元素以及碳同位素来描述古环境条件，而第二部分则侧重于Cr和Mo同位素的综合调查。将对来自2.2 - 2.1-Gyr-old比勒陀利亚群（博茨瓦纳）的近岸沉积物进行补充地球化学调查，因为这些沉积物也记录了Lomagundi事件，并将有助于对古元古代大气-海洋系统提供更详细的、可能是全球性的了解。

Coupled isotope investigations of the redox-sensitive elements Cr and Mo in 2.5 – 2.0-Gyr-old sediments of the Pechenga Greenstone Belt (PGB) and the Onega Basin (OB) in Russia will be used to reconstruct the redox evolution of the atmosphere and oceans postdating the Great Oxidation Event (GOE). The GOE marks the first significant increase in atmospheric oxygen levels and defines the transitions from anoxic to oxic environmental conditions. The aftermath of the GOE is characterized by major perturbations of the oxygen, carbon, and sulfur cycle - probably global - during the 2.22 – 2.05-Gyr-old Lomagundi and the following Shunga events. While the post-GOE sediments archive evidence for the burial of vast amounts of organic carbon, the expansion and contraction of the seawater sulfate reservoir, a proposed oxygen overshoot and the onset of effective continental weathering, the timing and response between the oxygenation of the atmosphere and oceans is poorly constrained. Moreover and more puzzling, even though the GOE marks the onset of oxygen-rich atmospheric conditions that was probably followed by an oxygen overshoot, Cr isotopes that are suggested as a tracer for free oxygen fail to identify oxygen-rich conditions in the Paleoproterozoic. This project seeks to perform detailed coupled Cr and Mo isotope investigations on various near-shore sedimentary environments from the Kuetsjärvi, Kolosjoki (PGB) and Zaonezhskaya (OB) formations. The first part of the project will characterize the paleoenvironmental conditions by major and trace elements and carbon isotopes, whereas the second part focuses on the combined Cr and Mo isotope investigations. Complementary geochemical investigations will be carried out on near-shore sediments from the 2.2 – 2.1-Gyr-old Pretoria Group (Botswana), because these sediments also capture the Lomagundi Event and will help to provide a more detailed, and probably global, understanding of the Paleoproterozoic atmosphere-ocean system.