Identification of carbonates with high positive carbon isotope excursion from the Liaohe Group in the northeastern North China Craton and implications for the Lomagundi-Jatuli Event

Abstract

The Great Oxidation Event (GOE) during the early Paleoproterozoic represents the first significant buildup in Earth’s atmospheric oxygen and resulted in a series of significant changes in the Earth’s surface environment. Among them is the 2.22 (or 2.33)–2.06 Ga Lomagundi-Jatuli Event (LJE), which is globally, the largest magnitude and longest duration, marine carbonate positive carbon isotope excursion (δ¹³C_V-PDB>10‰) known. This event has attracted the attention of scholars all over the world. However, except for a high positive carbon isotope excursion (δ¹³C_V-PDB>10‰) recently identified from marine carbonate rocks within the Daposhan Formation in the lower Fanhe Group (or the Sanchazi Group) in the Longgang Block in the northeast North China Craton (NCC), Paleoproterozoic carbonates in the NCC are characterized by a low-amplitude positive carbon isotope excursion (δ¹³C_V-PDB<5‰). This feature is significantly different from the high positive carbon isotope excursion characteristics of carbonates deposited during the LJE period in other cratons. To determine whether there are large-scale and reliable sedimentary records of the LJE in the NCC and the reasons for the low positive δ¹³C excursion of the Paleoproterozoic carbonates obtained by the previous studies, we conducted field investigations, carbon-oxygen isotopes, and whole-rock major and trace element geochemical analyses of Liaohe Group carbonate rocks from the Anshan area in the northwestern margin of the Jiao-Liao-Ji Belt in the northeast NCC. Our results show that the Gaojiayu Formation of the Liaohe Group in the Anshan area has high positive δ¹³C_V-PDB values from 8.6‰ to 12.4‰ and δ¹⁸O_V-SMOW values of 17.9‰–27.4‰ (δ¹⁸O_V-PDB values ranging from −12.6‰ to −3.4‰). This provides solid evidence for the preservation of reliable sedimentary records of the LJE in the northeastern NCC. Deposition of the high positive δ¹³C excursion (>10‰) of marine carbonate rocks occurred at about 2.15 Ga. Lithological comparisons of different sections and whole-rock geochemical results show that the high positive δ¹³C excursion is mainly controlled by the stratigraphic interval and depositional ages; the changes of sedimentary facies and diagenesis have no significant effects on reducing of the δ¹³C values. The intrusion of mafic sills into carbonates has resulted in synchronous decrease of C–O isotopes near the contact zones, but the decreasing amplitude of δ¹³C is less than 3‰. Therefore, our study firstly identified marine carbonates with high positive δ¹³C excursion (>10‰) from the Gaojiayu Formation, which provides robust evidence for global correlation of the LJE, which has implications for its genesis and global significance. Moreover, due to global near-synchronization of the LJE, the carbon-oxygen isotope chemical stratigraphy of carbonate rocks deposited during the LJE period, combined with geochronological data, can provide new constraints on the stratigraphic subdivision and correlations of Paleoproterozoic sedimentary successions in the NCC.