A climate change from icehouse to greenhouse following Huronian glaciation: Evidence from long-term storm deposits of the Paleoproterozoic Hutuo Group in the North China Craton

The Hutuo Group was deposited from 2.14 to 2.0 Ga in Wutai Mountain, North China Craton. This group is composed of the Doucun and Dongye subgroups, which are likely contemporaneous heterotopic facies. The Hutuo Group displays well-known positive to negative drifts of inorganic carbon isotopes, large-scale stromatolitic carbonates, and red beds in epigenetic environments. Twelve storm-deposited lithofacies were identified in the Dongye Subgroup, which changes from sandstones, siltstones, and mudstones of the Qingshicun and lower Wenshan formations to carbonates of the upper Wenshan, Hebiancun, Jian’ancun, Daguanshan, Huaiyincun, Beidaxing, and Tianpengnao formations from bottom to top. The above sedimentary sequence transformation indicates a gradual transformation from terrigenous storm deposits in the Qingshicun and Wenshan formations to endogenous or mixed-source storm deposits in the Hebiancun, Jian’ancun, Daguanshan, and Huaiyincun formations. Additionally, coastal and shallow-marine storm deposits are revealed from sedimentary structures, including hummocky cross-stratification, intraclasts or boulder clays exhibiting radial or chrysanthemum-shaped stacking, and sinuous or torn stromatolites. These storm deposits, occurring with oolitic and stromatolitic carbonates of mid-low latitudes or tropical-subtropical zones, are characterized as tropical storm deposits. Based on reported ages, we propose that such tropical storms started from ca. 2.1 Ga and lasted for over 40 Myr. The long-term storm deposits indicate high temperatures and intense water circulation during the greenhouse climate. A climate change from icehouse to greenhouse is also evident by the extensive distribution of carbonates, evaporates, and organic-rich shales above the glacial diamictites in multi-cratons, and was probably driven by the transformative evolution of the atmosphere.