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Purposes The Hutuo Group belongs to the Early Proterozoic strata. As one of the most typical Paleoproterozoic strata in North China, the timing redefinition of the Hutuo Group is of great significance to the establishment of the early Precambrian stratigraphic chronology framework, the discussion of the early Precambrian geological evolution process in North China and the study of plate assembly. Methods This article conducts a detailed study of the Dongye Subgroup strata of the Hutuo Group, collecting 24 detrital zircon samples from the Jian'ancun Formation of the Hutuo Group. From 23 similar age detrital zircons, we define the weighted average age of the bottom boundary of the Hutuo Group is 2 469 Ma, and regional tectonic movements occurred in the Wutai area around 1 855 Ma. According to the 1 109 zircon ages in Hutuo Group from previous studies, we considered that the ages of >2.5 Ga are from underlying Gaofan subgroup and the maximum depositional age of Hutuo Group was early Paleoproterozoic. Findings The results show that the crust of the Wutai area was unstable at 2 376, 2 170, 2 066, 1 988, and 1 825 Ma, resulting in multiple magmatic events. The 1 825 Ma zircon age can further indicate the occurrence of the Lyuliang movement, and provide a basis for the early Proterozoic North China Craton integration.

• There are 2.1 Ga tropical storm deposits of coastal to shallow-marine environments in the Hutuo Group in North China Craton. • The storm deposits lasted for over 40 Myr, indicating a high-temperature greenhouse climate after Huronian glaciation. • Greenhouse climate is evident by extensive carbonate, evaporite, and black shale above glacial diamictite in multi-cratons. 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. [ABSTRACT FROM AUTHOR]

The Lomagundi-Jatuli Event (LJE) is one of the largest and earliest positive carbon isotope excursions preserving δC values between +5 and +16‰ in Paleoproterozoic carbonates worldwide. However, the duration, amplitude and patterns of these excursions remain poorly constrained. The 2.14-1.83 Ga Hutuo Group in the North China Craton is a >10 km thick volcano- sedimentary sequence, including >5 km thick well-preserved carbonates that were deposited in supra- tidal to sub-tidal environments. C-O isotopic and elemental analyses of 152 least altered samples of the carbonates revealed a three-stage δ13C evolution. It began with an exclusively positive δC (+1.3 to + 3.4‰) stage in the ~2.1 Ga carbonate in the Dashiling and Qingshicun Formations, followed by a transition from positive values to oscillating positive and negative values in ~3 000 m thick carbonates of the Wenshan, Hebiancun, Jianancun, and Daguandong Formations, and end with exclusively negative δC values preserved in > 500 m thick dolostones of the Huaiyincun and Beidaxing Formations. It appears that much of the LJE, particularly those extremely positive δC signals, was not recorded in the Hutuo carbonates. The exclusively positive δC values (+1.3 to + 3.4‰) preserved in the lower formations likely correspond to the end of the LJE, whereas the subsequent two stages reflect the aftermath of the LJE and the onset of Shunga-Francevillian event (SFE). The present data point to an increased influence of oxygen on the carbon cycle from the Doucun to the Dongye Subgroups and demonstrate that the termination of the LJE in the North China Craton is nearly simultaneous with those in Fennoscandia and South Africa. [ABSTRACT FROM AUTHOR]

The analysis of folds within pebbles in conglomerates has been used to infer deformation events before deposition of the conglomerate. However, it is not clear whether folds can develop within pebbles during subsequent conglomerate deformation. We use numerical modelling to investigate folding within internally layered pebbles in a ductile deformation regime and simple shear deformation. We vary the initial orientation and rheology of the layers within pebbles, as well as the relative rheology of the conglomerate matrix, for single isolated pebbles and multiple interacting pebbles. We use a power-law viscous rheology for both the pebbles and their matrix. Folding within pebbles can indeed occur, but only within a narrow range of initial layer orientations, strength or viscosity ratio between the internal layers and that of the matrix relative to the pebble layers. Results are used to interpret the strongly deformed conglomerates from the Proterozoic Hutuo Group in the Wutai Mountains, North China Craton, that contain a small percentage of pebbles with internal folds. Based on field observations and numerical modelling results, we suggest that these formed during deformation of the conglomerate and do not represent inclusion of previously folded lithologies into the unit. • The development of folds within layered pebbles of conglomerates is simulated in simple shear with ELLE + VPFFT code. • Initial orientation and rheology of layers within pebbles control the formation of internal folds. • Folding within pebbles can indeed occur, but only within a narrow range of initial layer orientations and rheology. • Folds within the BIF pebbles of conglomerates at the base of the Hutuo Group formed after the conglomerate deposition. [ABSTRACT FROM AUTHOR]

Zircon U-Pb ages (SHRIMP and LA-ICPMS) and Lu-Hf isotope data (LA-ICPMS) are presented for two granite and two quartzite pebbles from the basal conglomerates of the Sijizhuang Formation in the Hutuo Group from the Wutai Mountains area in the North China Craton. These two granite pebbles give zircon Pb/Pb ages of 2513±8 Ma and 2527±8 Ma respectively, which are consistent with the emplacement ages of the Wangjiahui grey granite and Guangmingsi or Shifo granite in the Wutai Mountains. Detrital zircons from those two quartzite pebbles are mostly 2550-2490 Ma old with lesser number of 2800-2550 Ma grains, which is similar to the ages of detrital zircons from quartzites in the Gaofan Subgroup of the Neoarchean Wutai Group. Thus, the pebbles in the Hutuo Group basal conglomerates were derived locally from Wutai Mountains Neoarchean sources. Zircons from the Sijizhuang Formation conglomerate granite and quartzite pebbles mostly have positive ɛ( t) values, a minority with ɛ( t) values like model depleted mantle (DM) of the same age, but with most showing DM model ages 200-100 Ma. This indicates that most of the source materials were derived from the mantle within the previous 200 million years, whereas some are derived from 2550-2510 Ma juvenile crustal additions. This additional evidence suggests that in the North China Craton there was important initial polycyclic crustal formation and cratonization in the late Neoarchaean, prior to superimposed Palaeoproterozoic orogenic cycles. [ABSTRACT FROM AUTHOR]

Palaeoproterozoic global glaciation (∼2.3 Ga) may have been the first 'snowball' Earth event in Earth history. North China has well-exposed sedimentary deposits of this time period with minimal postdepositional alteration. Sedimentary evidence of a glaciation event has been lacking, however. Here we analyzed carbon isotope composition of the Paleoproterozoic Hutuo Group (2.5-2.2 Ga) in the Wutai Mountain area, Shanxi Province, North China. Our data show, in an older to younger chronostratigraphic order, (1) positive δC values in the Dashiling Formation of the Doucun Subgroup (3.2‰ to 1.0‰, VPDB); (2) a decrease in δC values from the Wenshan Formation to the middle Daguandong Formation (from 2.0‰ to-1.2‰), during which time the occurrence of stromatolites declined; (3) a pronounced negative excursion in the upper Daguandong Formation, at the boundary of the Daguandong and Huaiyincun formations (from 1.4‰ to −3.3‰), where stromatolites disappeared; and (4) a gradual increase of δC values in the Beidaxing and Tianpengnao formations (from −1.2‰ to 1.4‰), during which time stromatolites returned. We argue that the negative carbon isotope excursion recorded from the Jian'ancun Formation to the middle Daguandong Formation of the Hutuo Group may have been North China's response to the Palaeoproterozoic global glaciation. [ABSTRACT FROM AUTHOR]

Abstract: There is a broad consensus that the North China Craton formed by the amalgamation of the Western and Eastern Blocks along the nearly N-S trending Trans-North China Orogen. However, it still remains controversial whether the Western and Eastern Blocks collided at ~2.5Ga or ~1.85Ga. U-Pb ages and Hf isotopic data of detrital zircons from foreland basins in the Trans-North China Orogen can place rigorous constraints on this controversial issue. One of such foreland basins is represented by the Hutuo Group in the Wutai Complex in the middle sector of the Trans-North China Orogen. The sequences of the Hutuo Group range from lower basal conglomerates and sandstones (Doucun Subgroup), through clastic sediments, dolomites and meta-basalts (Lower Dongye Subgroup), phyllites and dolomites (Upper Dongye Subgroup), to coarse-grained sandstones and conglomerates at the top (Guojiazhai Subgroup), most of which contain large amounts of detrital zircons. The detrital zircons from the Doucun, Lower Dongye, Upper Dongye and Guojiazhai Subgroups yield concordant 207Pb/206Pb ages of 2.11–3.88Ga, 2.01–2.84Ga, 1.88–2.72Ga and 1.92–2.65Ga respectively, the majority with Neoarchean to Paleoproterozoic ages. The presence of ~1.88Ga detrital zircons in the Upper Dongye and Guojiazhai Subgroups indicates that they deposited at some time after ~1.88Ga. This is in accordance with collision between the Eastern and Western Blocks along the Trans-North China Orogen to form the North China Craton at ~1.85Ga. [Copyright &y& Elsevier]

Basalt and basaltic andesite metamorphosed at greenschist facies occurs with conglomerate layers at the bottom of the Paleoproterozoic Hutuo Group in the Wutai Mountains area, North China Craton. Detailed geological surveying confirms that these volcanic rocks are conformable within the neighboring sedimentary rocks. The SHRIMP results on basaltic andesite are divided into two groups. In one group the 207Pb/206Pb ages are from 2433 to 2558 Ma, which is consistent with the basement crustal age in Fuping and Wutai areas. In the other group, 13 grains yielded a weighted mean 207Pb/206Pb age of 2140±14 Ma. The latter is interpreted as the eruption age of the basaltic andesite, and gives the age of the base of the Hutuo Group. This result further suggests that the Hutuo Group formed in the middle Paleoproterozoic, not the early Palaeoproterozoic or late Archaean, as thought before, and is related to a 2.22.1 Ga rifting event in the Central North China Craton. [ABSTRACT FROM AUTHOR]

This paper reports detrital zircon age distributions of meta-sedimentary rocks of the Gaofan, Hutuo and Dongjiao groups in the Wutai and Dongjiao areas of the North China Craton. Detrital zircons of a quartzite from the Gaofan Group are mainly ~2.5 Ga in age, with some ~2.7 Ga and older. A quartzite pebble from the basal conglomerate of the Hutuo Group is similar in detrital zircon age distribution to the quartzite of the Gaofan Group. For a meta-feldspar-quartz sandstone from the Dongjiao Group, the age of detrital zircons is mainly concentrated at ~2.5 Ga. No zircons older than 2.6 Ga have been identified, but with some being 1.84 Ga and 2.2-2.0 Ga in age. Combined with earlier studies, the following conclusions can be drawn: (1) The Gaofan Group is early Palaeoproterozoic in age and is much younger and unrelated to the late Neoarchaean Wutai granite-greenstone terrane, which it unconformably overlies. As such, the Gaofan Group is one of the oldest Palaeoproterozoic meta-sedimentary units in the North China Craton. (2) The Hutuo Group was deposited in the middle Palaeoproterozoic (2.14-2.09 Ga) on a continental basement, after the early Palaeoproterozoic Gaofan Group. (3) The Dongjiao Group was formed after 1.84 Ga, and probably belongs to the lower portion of the Changcheng System. (4) The detrital zircons from all the three groups show an obvious age peak of ~2.5 Ga, being sourced from the igneous rocks formed in the intense tectono-magma-thermal events at the end of Archaean in the North China Craton. [ABSTRACT FROM AUTHOR]

A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP 207Pb/206Pb weighted mean ages of 2180 ± S Ma and 2087 ± 9 Ma, respectively. The older date is within error of the age of the Dawaliang Granite in Wutaishan and is considered to be derived from a similar crustal magmatic source. The younger date is within error of reported ages from metasediments and meta-volcanics of the Wanzi supracrustal rocks and the Nanying granitic gneisses in the adjacent Fuping Complex and is interpreted to be the age of volcanism in the Hutuo Group. These data establish that: (1) the Hutuo Group is Paleoproterozoic and not Archean in age and (2) the volcanism and sedimentation were coeval in the Wutai and Fuping complexes. Sedimentation was therefore widespread at this time and possibly reflects deposition along an evolving continental margin, most likely the western margin of the Eastern Block of the North China Craton. The age of 2087 ± 9 Ma for volcanism in the Hutuo Group means that it must have been deformed and metamorphosed after this time. This further supports the evidence, obtained from other recent studies, that the main tectonism in the Wutaishan area occurred at ∼1.8 Ga during the Lüliang orogeny. This orogeny resulted in the collision of the Eastern and Western blocks of the North China Craton and formed part of a global supercontinental amalgamation event [ABSTRACT FROM AUTHOR]

• Well-persevered Paleoproterozoic microfossils described and illustrated. • A new genus of Acritarch, Dongyesphaera , is established. • Morphological diversity of microfossils increased through the Paleoproterozoic. • Evidence for the earlier occurrence of metabolic activity in eukaryotic protists. The Paleoproterozoic Hutuo Group is well-developed and distributed in the Wutai Mountains in the Xinzhou area of Shanxi Province, North China. Its middle part - the Dongye Subgroup is more suitable for obtaining microfossils in deposited sediments characterized with sandstone or slate in the lower part, and upward into interbedded sandstone, carbonate with stromatolites and phyllite. Based on recent zircon dating, the Hutuo Group was deposited around 2150–1950 Ma. In this study, eight morphological genera of microfossils, including the spheroid and filamentous cyanobacteria Eoentophysalis , Sphaerophycus , Siphonophycus , Pseudodendron , and the acritarchs Dictyosphaera , Dongyesphaera gen. nov., Leiosphaeridia , Satka were identified from the Wenshan, Hebiancun and Tianpengnao Formations of the Dongye Subgroup. The identified microfossils reveal that eukaryotic protists exercised metabolic activities rarely observed to have occurred in what are thought to have been suitable environments. [ABSTRACT FROM AUTHOR]