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Abstract
The Ruyang Group distributes in the southwestern margin of the North China Craton, mainly locating in the border of Henan-Shaanxi-Shanxi Province. The Group, covering on the Xiong'er Group with angular unconformity and being overlain consistently by the Luoyu Group, is mainly composed of unmetamorphosed clastic and carbonate strata. In this paper, the authors reports LA-ICP-MS U-Pb ages from four quartz sandstones of the Baicaoping Formation of the Ruyang Group. The youngest 207Pb/206Pb ages are1 817±22 Ma, 1838±23 Ma, 1924±17 Ma and 1829±28 Ma, respectively. Those ages combined with the high-precise dates 1611±8 Ma in the Luoyu Group overlying on the Ruyang Group indicate that the Ruyang Group should be early Mesoproterozoic. The207Pb/206Pb ages of the detrital zircon range from 3000 Ma to 1800 Ma, with 67% between 2600 Ma to 2400 Ma and the main peak of ages(2550~2500 Ma), meaning that sedimentary materials mainly sourced from Paleoproterozoic geologic bodies.
... The authors declared that there is no conflict of interest. (Zhou et al., 2008;Hu et al., 2009Hu et al., , 2012aHu et al., , 2012bHu et al., , 2014aHu et al., , 2014bGao et al., 2011;Ying et al., 2011;Zhu et al., 2011;Wan et al., 2011;Yang et al., 2012;Li et al., 2013;Lan et al., 2014;Liu et al., 2014Liu et al., , 2017aLiu et al., , 2017cMa et al., 2014;Zhong et al., 2015;Zhang et al., 2016;Dong et al., 2017;Li et al., 2018;Meng et al., 2018); (b) the Xuhuai Basin (Zhou et al., 2008;Gao et al., 2011;Hu et al., 2012a;Yang et al., 2012;He et al., 2016); (c) the Zhaertai-Bayan Obo-Huade Basin (Hu et al., 2009(Hu et al., , 2014aMa et al., 2014;Liu et al., 2014Liu et al., , 2017cZhong et al., 2015;Li et al., 2018); (d) the Yanliao Basin (Gao et al., 2011;Wan et al., 2011;Ying et al., 2011;Wang et al., 2017); (e) the Xiong'er Basin (Zhu et al., 2011;Hu et al., 2012bHu et al., , 2014bLi et al., 2013;Lan et al., 2014;Zhang et al., 2016;Dong et al., 2017;Liu et al., 2017a;Meng et al., 2018). and editorial guidance are greatly appreciated. ...
... The authors declared that there is no conflict of interest. (Zhou et al., 2008;Hu et al., 2009Hu et al., , 2012aHu et al., , 2012bHu et al., , 2014aHu et al., , 2014bGao et al., 2011;Ying et al., 2011;Zhu et al., 2011;Wan et al., 2011;Yang et al., 2012;Li et al., 2013;Lan et al., 2014;Liu et al., 2014Liu et al., , 2017aLiu et al., , 2017cMa et al., 2014;Zhong et al., 2015;Zhang et al., 2016;Dong et al., 2017;Li et al., 2018;Meng et al., 2018); (b) the Xuhuai Basin (Zhou et al., 2008;Gao et al., 2011;Hu et al., 2012a;Yang et al., 2012;He et al., 2016); (c) the Zhaertai-Bayan Obo-Huade Basin (Hu et al., 2009(Hu et al., , 2014aMa et al., 2014;Liu et al., 2014Liu et al., , 2017cZhong et al., 2015;Li et al., 2018); (d) the Yanliao Basin (Gao et al., 2011;Wan et al., 2011;Ying et al., 2011;Wang et al., 2017); (e) the Xiong'er Basin (Zhu et al., 2011;Hu et al., 2012bHu et al., , 2014bLi et al., 2013;Lan et al., 2014;Zhang et al., 2016;Dong et al., 2017;Liu et al., 2017a;Meng et al., 2018). and editorial guidance are greatly appreciated. ...
... The Baicaoping and Beidajian formations of the Ruyang Group are dominated by fine-grained rocks and lack effective detrital zircon ages. The youngest detrital zircon Pb-Pb concordant age of 1817 ± 22 Ma has been reported from the quartz sandstone of the Baicaoping Formation (Li et al., 2013b). A zircon U-Pb age of 1648.4 ± 6.5 Ma obtained from the tuffaceous layer in the lower part of Cuizhuang Formation of the Luoyu Group in the Yongji section, Shanxi Province , limited the minimum age of Ruyang Group to ca. 1.65 Ga. ...
Sedimentary records of the North China Craton (NCC) between 1.8–0.8 Ga are indispensable for studying the evolution of the Earth’s surface ecosystem in the middle Proterozoic. Continuous late Paleoproterozoic successions (1.8–1.6 Ga) were found in the Xiong’er and Yanliao basins, which are located in the southern and northern margins of present NCC. The formation and evolution of these two basins were likely related to the breakup of Columbia supercontinent. With the deepening of research in recent years, the rifting and filling processes of these two basins are getting increasing attentions and controversies. Among them, a crucial controversy is the distribution of isochronous strata in these two basins, which is related to whether these two basins have ever been connected. In this study, we scrutinized the Paleoproterozoic successions in the Taihang Mountain area, which is located in the junction of the Xiong’er and Yanliao basins. The sedimentary distributions and overlaps indicated gradually transgression and northward extension of the Xiong’er Basin during 1.75–1.65 Ga, and demonstrated a temporary connection of the Xiong’er and Yanliao basins, at least during 1.67–1.64 Ga. We further estimated the maximum depositional ranges of the isochronous stratigraphic units and drew the evolutionary history of the Xiong’er and Yanliao basins in 1.8–1.6 Ga. These results will be helpful in further understanding the habitats of early life and predicting the distribution of mineral-containing sediments, such as iron ore and source rocks.
The occurrence of plate tectonic processes on Earth during the Paleoproterozoic is supported by ca. 2.2–1.8 Ga subduction-collision orogens associated with the assembly of the Columbia-Nuna supercontinent. Subsequent supercontinent breakup is evidence by global ca. 1.8–1.6 Ga large igneous provinces. The North China craton is notable for containing Paleoproterozoic orogens along its margins, herein named the Northern Margin orogen, yet the nature and timing of orogenic and extensional processes of these orogens and their role in the supercontinent cycle remain unclear. In this contribution, we present new field observations, U-Pb zircon and baddeleyite geochronology dates, and major/trace-element and isotope geochemical analyses from the northern margin of the North China craton that detail its Paleoproterozoic tectonic and magmatic history. Specifically, we record the occurrence of ca. 2.2–2.0 Ga magmatic arc rocks, ca. 1.9–1.88 Ga tectonic mélange and mylonitic shear zones, and folded lower Paleoproterozoic strata. These rocks were affected by ca. 1.9–1.8 Ga granulite-facies metamorphism and ca. 1.87–1.78 Ga post-collisional, extension-related magmatism along the cratonal northern margin. We interpret that the generation and emplacement of these rocks, and the coupled metamorphic and magmatic processes, were related to oceanic subduction and subsequent continent-continent collision during the Paleoproterozoic. The occurrence of ca. 1.77–1.73 Ga mafic dykes and ca. 1.75 Ga mylonitic shear zones along the northern margin of the North China craton may have been related to a regional mantle plume event. Our results are consistent with modern style plate tectonics, including oceanic subduction-related plate convergence and continent-continent collision, operating in the Paleoproterozoic.
The Meso- to Neoproterozoic Eras were characterized by environmental, evolutionary, and lithospheric stability in the North China Craton (NCC). It is controversial that huge uplift(s) occurred in the North China Craton during this period. The southern NCC developed early terrestrial deposition in the late-Paleoproterozoic and glacial sequence in the late Neoproterozoic record integrated geological history of the NCC in the intervening interval. Geochemistry compositions of mid-Mesoproterozoic carbonaceous slates (ca. 1330 Ma) show similar provenances to the underlying Mesoproterozoic sedimentary rocks in the southern NCC. Detrital zircons from the mid-Mesoproterozoic strata yield U–Pb ages from ca. 2450 to 1850 Ma with minor ages of 2950 and 2750 Ma. U–Pb ages of detrital zircons from the Neoproterozoic strata yield from ca. 1700 to 1000 Ma besides peak ages of 2600, 2400, and 1950 Ma. The early Paleozoic sedimentary rocks also display peak ages between ca. 1850 and 1000 Ma along with peaks at ca. 2500 and 2300 Ma. These detrital zircon ages are quite different from those of the Mesoproterozoic sedimentary rocks in the NCC. According to paleogeography study, the late-Paleoproterozoic to the early Mesoproterozoic clastic sequences are controlled by Xiong’er volcanic event in the southern NCC and carbonate platform developed later. The Mesoproterozoic sequences are overlain disconformably by the Neoproterozoic strata. In combination with compiled magmatic and detrital zircon ages, a sedimentary gap spanned at least 300 Ma from mid-Mesoproterozoic to Neoproterozoic in the southern NCC. Thus, the disconformity between the Mesoproterozoic and Neoproterozoic sedimentary sequences in the southern NCC should represent a huge sedimentary hiatus. Both the variable provenances and huge sedimentary hiatus between the Mesoproterozoic and Neoproterozoic sedimentary sequences support that the NCC might not split from relict landmass of Columbia Supercontinent before Neoproterozoic. The relict landmass was involved in aggregation of the Rodinia supercontinent.
The Late Precambrian Wufoshan Group from the southern North China Craton (NCC) is significant for its contribution to our understanding of the Precambrian evolution of the NCC, which consists of the Lower Ma'anshan, Upper Ma'anshan, Puyu, Luotuopan, and Hejiazhai formations. Detrital zircon U–Pb ages and Lu–Hf isotopes from the Puyu, Luotuopan, and Hejiazhai formations are used in this study to constrain the depositional age and provenance of the Wufoshan Group and crustal evolution of the NCC. The Puyu Formation is characterized by detrital zircon U–Pb age populations of ~2.13 Ga and ~2.50 Ga, similar to the Lower–Upper Ma'anshan formations from the literature. The Luotuopan Formation exhibits age populations of 1.85–2.18 Ga and 2.28–2.98 Ga, with mainly negative εHf(t) values and scattered positive εHf(t) values clustering at two groups of 2.48–2.52 Ga and 2.64–2.97 Ga. The Hejiazhai Formation displays age populations of 0.98–2.00 Ga and 2.51–2.79 Ga with mainly positive εHf(t) values, whose depositional age is constrained as Neoproterozoic era by the youngest graphical detrital zircon age of 976 ± 20 Ma. Provenance studies indicate that the Mesoproterozoic Lower–Upper Ma'anshan and Puyu formations were sourced from the middle Trans-North China Orogen (TNCO), while the Neoproterozoic Luotuopan and Hejiazhai formations were derived from the southern TNCO and the North Qinling Terrane, respectively. The clastic rock series in the southern NCC is divided into Luotuopan type and Hejiazhai type by detrital zircon U–Pb age pattern and Hf isotopic characteristics, suggesting Late Mesoarchean to Early Palaeoproterozoic (2.47–2.97 Ga) crustal growth in the interior NCC, and Late Palaeoproterozoic to Early Neoproterozoic (0.98–2.08 Ga) crustal growth in the marginal NCC. The crustal evolution of the NCC can be classified into three stages, namely >3.0 Ga continental nuclei generation, the Meso-Neoarchean massive growth, and the Palaeo-Mesoproterozoic interior reworking and marginal growth.
Controversial issues on the Paleo-Mesoproterozoic tectonic setting of the southern margin of North China Craton (NCC) restricted our understanding of its role in breaking up the Columbia/Nuna Supercontinent. Existing models are still arguing on whether the southern margin was an intra-continental rift or active continental margin. Previous studies mainly focused on the magmatic records in the Paleoproterozoic Xiong’er Group, while the overlain sedimentary series and their depositional nature and the related tectonic environment were not yet well constrained. In this study, we scrutinized the comprehensive geochronological and geochemical dataset for the Mesoproterozoic sedimentary rocks along the southern margin of NCC. Our new results, together with the previous geochemical data show that the interior part of NCC southern margin (e.g. Wufoshan Group of the Song-Ji area) is dominated by the materials from the mature continental crust. Approaching the marginal area of southern NCC (e.g. Gaoshanhe and Guandaokou Groups of the Xiaoqinling-Luanchuan area), sediments are more enriched in magmatic arc fragments and unfractionated materials. Detrital zircon geochronological results revealed a progressive younging tendency from the northern Song-Ji to southern Xiaoqinling-Luanchuan areas. Together with the newly-reported zircon hafnium data, the synthesized dataset in this study favors the hypothesis that the southern NCC during the Paleo-Mesoproterozoic was in an active continental arc setting under a prolonged peripheral subduction regime, which was surrounding the marginal areas of the Columbia/Nuna Supercontinent.
Proterozoic strata have become a new target for hydrocarbon exploration worldwide. They exhibit the potential to become a resource replacement target. To provide a reference for hydrocarbon source rock evaluation, the sedimentary environment and mechanism of organic matter enrichment of dark shales in the Mesoproterozoic Cuizhuang Fm. were investigated for the first time by combining organic and inorganic research concepts. Although the total organic carbon (TOC) content in the Cuizhuang Fm. is relatively low (mean value of 0.59%), it still can be considered as a potential source rock. Thin-section observations, main and trace element contents, and biomarker compounds revealed the following: (1) the Cuizhuang Fm. was deposited in a neritic shelf sedimentary environment at a passive continental margin, and the climate was warm and humid. The hydrocarbon-generating organisms mainly comprised prokaryotes such as cyanobacteria and other bacteria. All these characteristics meet the conditions of source rock formation. (2) The low oxygen level, felsic source provenance, and absence of submarine hydrothermal activity led to low productivity, and the low productivity and low-grade hydrocarbon-generating organisms led to low TOC content in the Cuizhuang Fm. (3) The enrichment of V in the Cuizhuang Fm. is apparent, but does not reach the hyper-enrichment threshold of 500 ppm associated with euxinic conditions, revealing anoxic ferruginous conditions. Moreover, the V content is positively correlated with TOC content, indicating that organic matter enrichment was mainly controlled by the redox conditions of the bottom water. Therefore, the sedimentary areas with high productivity were related to basic source provenance and submarine hydrothermal activity, and anoxic bottom water may have promoted the development of better source rocks. This findings may represent the main direction for identifying effective source rocks in subsequent work.
Early Precambrian geological events in the Zhongtiao Mountain of China provide important clues for understanding Neoarchean to Paleoproterozoic crustal evolution in the southern segment of North China Craton (NCC). Based on analysis and compare of the component features, spatial and temporal distribution and geochemical features of the crystalline basements in the Zhongtiao Mountain with its surroundings, we identify five distinct episodes of the early Precambrian geological events in the Zhongtiao Mountain as: ca. 2.72–2.61 Ga, ca. 2.56–2.44 Ga, ca. 2.35–2.20 Ga, ca. 2.20–2.0 Ga and ca. 1.97–1.85 Ga. The ca. 2.72–2.61 Ga magmatism mainly involved a significant period of crustal growth with some crustal reworking. These ca. 2.72–2.70 Ga TTG gneisses were produced by partial melting of a subducted oceanic slab, and the ca. 2.62–2.61 Ga granitic rocks were originated from the partial melting of a protolith of juvenile origin (such as the pre-existing ca. 2.72–2.70 Ga TTG suite) together with its intermixing with mantle material. Together with other ca. 2.90–2.61 Ga old rocks in the southern segment of NCC, they made up the ‘Southern Ancient Terrane’. The ca. 2.56–2.44 Ga magmatism represented a major crustal reworking (melting) event with some juvenile addition in the Zhongtiao Mountain, and the formation of TTGs and K-rich granitic rocks during ca. 2.56–2.44 Ga marked a tectono-magmatic event resulting in stabilization of the NCC. The ca. 2.35–2.20 Ga magmatic activities reflected another stage of crustal extension and reworking of the basement rocks. The ca. 2.20–2.0 Ga volcanic-sedimentary rocks, A-type granites, and metamorphic basic volcanic rocks indicated that the stabilized blocks in the NCC still experienced the stage of extension. The ca. 1.97–1.85 Ga magmatic and metamorphic events formed in a phase of compressional deformation and led to the reworking of pre-existed old rocks.
The widespread Mesoproterozoic successions around the world have recorded the breakup of the ancient supercontinent Columbia. In the North China Craton (NCC), the Mesoproterozoic basins in the Yan-Liao and southern NCC are the important evidence to study the nature and evolution of the Mesoproterozoic basins. In this study, we scrutinized the stratigraphic pattern and detrital zircon U–Pb geochronology in the southern Yan-Liao and Mianchi-Queshan areas in the southern NCC, to investigate the evolutionary relationship between the Mesoproterozoic basins in the north and south of NCC. Detrital zircons from the Mesoproterozoic sequence in the southern Yan-Liao areas showed monotonous source with age peak at ca. 2500 Ma, corresponding well with the ages of the Neoarchean complex in the central NCC. However, the Mesoproterozoic sequence in the Mianchi-Queshan areas, which is represented by the Ruyang Group, exhibited significantly different characteristics with influx of much younger zircons. The southern Yan-Liao and Mianchi-Queshan areas showed distinct similarity in the stratigraphic pattern, reflected by the Mesoproterozoic successions in these two areas being both bracketed by two sequence boundaries and further divided into two sequences under a uniform sea-level change. The Mesoproterozoic strata in these two areas probably possessed a correlative relationship in the stratigraphic patterns and basin evolutionary history.
Along with the breakup of the supercontinent Nuna and Rodinia during the Mesoproterozoic and Neoproterozoic, a series of sedimentary basins formed within or at the periphery of the ancient cratons. Under the regime of breakup of the supercontinent, these basins underwent different evolutionary history hence formed different geological elements constituting the petroleum systems. In this contribution, the distribution and the stratigraphic successions of the Meso-Neoproterozoic basins in the North China Craton (NCC) were examined, as well as the retrospective review for the mechanisms of the basin formation. The synthesized geological and geochronological data support a long-term extensional environment for the basins in the northern NCC. The Mesoproterozoic basins in the Yanshan, western Liaoning (Yan-Liao) and the Zhaertai areas formed at the intracratonic position later than that in the Bayan Obo, which possibly deposited in the continental margin. The further efforts still need to be devoted to decipher the huge controversial around the tectonic nature of the basins in the southern NCC, as well as their stratigraphic correlations with the basins in the north and central. The distribution and organic geochemical characteristics of the Mesoproterozoic source rock were also summarized. Three sets of source rock in the central NCC, namely the Chuanlinggou, Hongshuizhuang and Xiamaling Formations developed favorable geological and geochemical conditions for the generation of the hydrocarbon. While in the south, the Cuizhuang Formation was the only interval feasible for potential source rock. The progress in seismic geophysics and borehole drilling suggested the existence of the Mesoproterozoic beneath deep Ordos Basin. This open a new window for the reconstruction of the Mesoproterozoic paleogeography as well as the evaluation of the source potential of the Mesoproterozoic basins in the North China Craton.
A large number of primary oil and gas reservoirs have been discovered in Proterozoic strata all over the globe. Proterozoic sequences are widely distributed in China, and the discovery of large Sinian-aged gas reservoirs in the Sichuan Basin and Mesoproterozoic liquid oil seepages in North China shows that attention should be paid to the exploration potential of Proterozoic strata. In this paper, the main controlling factors of Proterozoic source rocks are discussed. Principally, active atmospheric circulation and astronomical cycles may have driven intense upwelling and runoff to provide nutrients; oxygenated oceanic surface waters could have provided suitable environments for the organisms to thrive; volcanic activity and terrestrial weathering caused by continental break-up would have injected large amounts of nutrients into the ocean, leading to persistent blooms of marine organisms; and extensive anoxic deep waters may have created ideal conditions for the preservation of organic matter. Additionally, the appearance of eukaryotes resulted in diversified hydrocarbon parent material, which effectively improved the generation potential for oil and gas. Through the comparison of Formations across different cratons, seven sets of Proterozoic organic-rich source rocks have been recognized in China, which mainly developed during interglacial periods and are also comparable worldwide. The Hongshuizhuang and Xiamaling Formations in North China have already been identified previously as Mesoproterozoic source rocks. The early Proterozoic Changchengian System is highly promising as a potential source rock in the Ordos Basin. In the Upper Yangtze area, the Neoproterozoic Datangpo and Doushantuo Formations are extensively distributed, and represent the major source rocks for Sinian gas reservoirs in the Sichuan Basin. Moreover, the Nanhuan System may contain abundant shales with high organic matter contents in the Tarim Basin, although this possibility still needs to be verified. Indeed, all three cratons may contain source rocks of Proterozoic strata; thus, these strata represent major exploration targets worthy of great attention.
Whether the North Qinling Terrane (NQT) was accreted to the North China Craton (NCC) in the Proterozoic is still a matter of debate. We report the first detrital zircon study from the Baishugou Formation, which forms the uppermost part of the Mesoproterozoic Guandaokou Group, at the southernmost NCC margin. Detrital zircons from carbonaceous silty phyllite in the lower part of the Baishugou Formation yield U–Pb ages peaking at ca. 2500 Ma, with minor peaks at ca. 2300–2000, 1800, and 1600 Ma, and εHf(t) values ranging from −10.8 to +9.1. These zircons are considered to have been sourced from the NCC. In contrast, the middle-to-upper part of the formation contains detrital zircons which yield an age group ranging from 1800 to 1000 Ma, with peaks at 1800, 1500, 1300, and 1100 Ma; the zircons with ages of 1500–1300 Ma dominantly have εHf(t) values greater than +5 and the majority plot along the depleted mantle evolution curve. The striking difference between the U–Pb ages of the detrital zircons from the upper and lower parts of the formation suggests a shift in provenance. Magmatism at 1500–1300 Ma has not been reported from the southern margin of the NCC but has been discovered in the NQT. Hence, we deduce that the zircons from the upper part of the formation were primarily derived from the NQT, where an episode of crustal growth and magmatism is recorded between 1500 and 1100 million years. The variable sediment provenances imply that the NCC and NQT could be connected during the late Mesoproterozoic to early Neoproterozoic. The pattern of detrital zircon ages in the new sediments from the Baishugou Formation is distinct from those in the Kuanping Group and the Palaeozoic Erlangping Complex, which are at present sandwiched between the NCC and the NQT. The detrital zircons from these two groups are dominated by an age peak at ca. 1000 Ma, which is formed as the result of amalgamation of the NQT and the Rodinia Supercontinent during the Grenville orogeny. It is possible that the new sediments of the Baishugou Formation were deposited before Grenville orogeny.
The Zoige Depression is an important depocenter zone within the northeast of the Songpan–Ganzi Flysch Basin, which is bounded by the South China, North China, and Qiangtang blocks, and also forms the northeastern margin of Tibetan Plateau. This paper discusses the provenance of Middle to Late Triassic sedimentary rocks in the Zoige Depression using petrography, heavy mineral assemblages, and zircon U–Pb geochronology. The results demonstrate that the detritus is derived from multiple source regions. Four distinct parent rocks can be distinguished based on the heavy mineral assemblages and lithic fragments: Provenance 1 predominantly comprises intermediate–acidic volcanic rocks; Provenance 2 includes high-grade metamorphic rocks; Provenance 3 contains a mixture of various detrital components; and Provenance 4 primarily consists of mafic volcanic rocks. The different U–Pb ages of the zircons from the Middle to Late Triassic ranging from 260 to 280, 429–480, 792–974, and 1,800–2,500 Ma represent distinct source regions, which are comparable to the 4 provenances mentioned above: Provenance 1 (260–280 Ma), Eastern Kunlun Orogen; Provenance 2 (429–480 and/or 1,800–2,500 Ma), Qinling orogeny (mainly in North Qinling); Provenance 3 (1,800–2,500 Ma), the North China Block; and Provenance 4 (792–974 Ma), the Yangtze Block. Overall, the detritus in the Middle Triassic (Ladinian, T2zg) primarily originates from the Eastern Kunlun Orogen and North Qinling. During the Late Triassic (Early Carnian, T3z), the southern margin of the North China Block was likely transported westward to the basin by a river network between the North China and South China blocks flowing through the Qinling region, because of the predominance of the detrital zircon age ranging from 1,800 to 2,500 Ma and the occurrence of quartz sandstone with visible enlargement texture. Since the Late Triassic (Middle Carnian, T3zh), great changes have occurred in the source terrains, such as the absence of sources of the Eastern Kunlun Orogen and North China Block and the predominance of Yangtze Block. This drastic change can be explained by the Triassic collision between the South China and North China blocks, and the clockwise rotation of the South China Block progressively closed the basin and uplifted the Qinling orogeny.
Organic-walled microfossils described in this paper have been obtained from the Beidajian Formation of the Mesoproterozoic Ruyang Group (ca. 1300Ma) in southern Shanxi Province, China. They are characterized by many eukaryotic organisms, such as acanthomorphic acritarchs, sphaeromorphic acritarchs with a distinct circular excystment, acritarchs with multilayered walls and ornamentation, and multicellular filaments and algal thallose. Recently, more eukaryotic microfossils have been found and the triaromatic dinosteroid biomarker was extracted from the whole rock sample containing abundant acritarch specimens of Dictyosphaera delicata and Shuiyousphaeridium. One acritarch form, Spiromorpha segmentata, shows morphological similarities to the extant green alga Spirotaenia. It means that sexual reproduction by conjugation probably arose in the late Mesoproterozoic.A new genus Spiromorpha is proposed here. In combination with known Mesoproterozoic microfossil assemblages from the Roper Group of Australia and the Bahraich Group of Ganga Basin, India, we infer that marine protests had a rapid development during the Mesoproterozoic Era.
Most previously reported Mesoproterozoic (1600-1000 Ma) fossils are from silicified carbonates, and they are commonly small
in size (15–20 μm), ranging from coccoids to filaments in morphology. Many of them can be interpreted as cyanobacteria. Carbonaceous
shales represent another source of palaeontological information of the Mesoproterozoic biosphere. Sphaeromorphic and acanthomorphic
acritarchs, as well as filamentous fossils, are common in many Mesoproterozoic shales. Here we report an unusual assemblage
of tubular fossils from the Meosproterozoic Ruyang Group in Shanxi, North China. Some of these tubes are branched. Others
bear annular-helical thickening that might be represented by one extinct algae to adapt to a desiccating environment.
Abundant and well-preserved organic-walled microfossils including acanthomorphic acritarchs have been found in Mesoproterozoic
Beidajian Formation in the Yongji area of Shanxi Province, North China. The morphological and ultrastructural features of
these acanthomorphic acritarchs resemble living dinoflagellates (e.g. double-walled and polygonal structures), which leads
to the interpretation of these fossils as probably the oldest dinoflagellates. The detection of dinosterane, a dinoflagellate
biomarker, from pyrolytic product of these fossils further supports the morphological inference. This finding is consistent
with molecular clock estimate that dinoflagellates may have diverged 700 to 900 million years (Ma) before previously known
fossil record.
KeywordsMesoproterozoic-Beidajian Formation-acanthomorphic acritarch-dinoflagellate-dinosterane
According to the isotopic age data of inherited zircons in igneous and metamorphic rocks which occur at the surface and are derived from deep crust of the North China, Yangtze blocks and Qinling - Dabie orogenic belt, the paper is mainly reports some new information of Archean rocks (basement) and briefly discusses its geological significance. The deep crust of 6 areas on the northeastern, southeastern, northern and northwestern margin of the North China Block all show new information of Neoarchean, Mesoarchean and Paleoarchean magmatic events, and the deep crust of the southern margin demonstrates the existence of Paleoarchean magmatic event. In the histogram of isotopic data of early Precambrian of the North China Block, the highest peak is between 2.45 Ga and 2.6 Ga, where the 2.5-2.55 Ga culmination is most striking, suggesting that the magmatic event is strongest at the time span and the there was a possible important continent collision event then. While the other minor peaks at 2.7 Ga, 2.8-2.85 Ga, 2.95-3.0 Ga, 3.1-3.15 Ga, 3.3-3.4 Ga, 3.45-3.5 Ga, 3.6 Ga and 3.8 Ga may reflect the different stages of the evolving magmatic activity. Information of Archean materials similar to that of the North China Block can be found on the surface and in the deep crust of the northern margin of the Yangtze Block. New data of Neoarchean and/or Paleoarchean from inherited magmatic zircons can be obtained from rocks derived from the deep crust in the middle - lower reaches of the Yangtze River, southeastern margin of the Yangtze block (corresponding to the former Jiangnan paleocontinent) and region of the southwestern margin of the Yangtze block. In the Qinling - Dabie orogenic belt, the rocks which are mainly out of the deep crust at many localities from east to west have given Neo-Mesoarchean evidence by the inherited magmatic zircons.
Recently, the geological events and their significance during period of ca 2.1 - 1.7 Ga are attracted as an interesting study focus. Our study shows that a series of geological events occurred in the North China craton at that time do not belong to a simple orogenic or rifting tectonic process. These events could be divided into two event-subgroups, i. e. 2.1 - 1.9 Ga orogenic event-subgroup and 1.85 - 1.7 Ga rift event-subgroup. The major indications of the 2.1 - 1.9 Ga event-subgroup are listed below: (1) several mobile belts developed within the Neoarchean craton; (2) strong folded deformation and metamorphism of greenschist-epidote amphibolite facies; (3) magmatic intrusion of K-granite sills and Mafic dyke swarm. This event-subgroup is represented by the Jinyü and Liaohe mobile belts, and was possibly related to the Pre-Rodinia (Columbia) orogeny. This event-subgroup ended at ca 1.93 Ga. The 1.85 - 1.7 Ga event-subgroup is a rifting event. Its major indications are: (1) mantle upwelling and lower crust uplifting to the surface at whole, accompanied by strong migmatization and ductile deformation; (2) high-pressure granulites underwent moderate-pressure granulite-amphibolite facies overprint with 1820 - 1800 Ma and 1790 - 1760 Ma metamorphic ages and decompressional P-T path; (3) rifting event closely followed the basement uplifting, and the Xiong'er-Angou-Zhongtiao rift and Yanshan rift are of a same rift regime; (4) old mantle rapidly became richer at ca 1900 - 1760 Ma from a depleted composition. Therefore, we suggest that the ∼ 1.8 Ga event-subgroup represents a continental geological process within craton: an upwelling mantle caused the craton basement uplifting at whole and closely followed by an aulacogen system. Our new study shows that mafic dykes can be divided into two types: metamorphosed and unmetamorphosed. The former has 2150 Ma forming age and 1970 - 1930 Ma (high-pressure granulite facies) and 1830 Ma (granulite facies) metamorphic ages. The later has 1780 - 1750 Ma forming age which is similar to that of amphibolit facies overprint of the metamorphosed dykes. The unmetamorphosed dykes obviously intruded after the craton basement uplifting.
The wide-spread non-metamorphic shales of the Ruyang Group (1150-950 Ma) in southern Shanxi, China contain abundant and well-preserved acritarchs and filamentous microfossils, suggesting a shallow-marine depositional environment. Acanthomorphic acritarchs obtained from both the Baicaoping Formation and the Beidajian Formation of the Ruyang Group include Shuiyousphaeridium Yan, emend. and a new genus Tappania Yin Lei-ming, gen. nov. In addition, Shuiyousphaeridium macroreticulatum (Du) Yan is emended and two new species Tappania plana Yin Lei-ming, sp. nov. and T. tubata Yin Lei-ming, sp. nov. are described.
Abstract On the basis of a study of the acanthomorphic acritarchs discovered in the Late Proterozoic to Early Cambrian Meishucunian Stage in different regions of China, especially in southern Shaanxi and the Yangtze Platform, coupled with a study of the assemblages, morphological correlation, microstructure, and evolutional relations of the acanthorphic acritarchs, as well as a wide correlation with those found in different regions of the world, the authors discuss the early evolutionary stages of the acanthomorphs, features of their assemblages in various stages, their biostratigraphical significance, and their evolutionary trend in China.
The northern slope of the Eastern Qinling Ranges is situated in a transitional region between the Qinling Fold Belt and the North China Platform. The Neoproterozoic Dongjia Formation of the northern slope of the East Qinling Ranges sits immediately beneath the glaciogenic Luoquan Formation. Abundant and moderately diverse organic-walled microfossils have been obtained by palynological preparation from grey–green sandy shale and grey carbonaceous shale with intercalated sandstone in the lower part of the Dongjia Formation. By considering known stratigraphic distributions of acritarchs, and abundant radial fibrous fabrics in microdigitate stromatolites and a narrow range of δ13C values (ca. 0±1‰ vs. PDB) from the underlying carbonate successions, the age of the Dongjia Formation is estimated to be early Neoproterozoic. In addition, many specimens of small Micrhystridium-like spinose acritarchs have been found in the glaciogenic Luoquan Formation. This supports the presence of a `Luoquan Glacial Period' after the Varangian glaciation. Nine previously described acritarch species have been identified, and one new combined species, three uncertain species, one undetermined form and fragment of an algal colony are described.
Marine protists can be affected by and reflect changes in the ecological environment. Based on available microfossil evidence from late Mesoproterozoic–Early Cambrian rocks of China, radiations of protists and related changes in ecological environments are discussed in the paper. Remarkable development of protists had occurred by as early as the Mesoproterozoic. Protist diversity significantly decreased in the middle Neoproterozoic due to disruption of the ecological environment that may have been caused by global glaciations. The Doushantuo microfossil assemblage records high diversity and radiation of protists during the early to middle Ediacaran. An acritarch assemblage of Asteridium–Comasphaeridium–Heliosphaeridium–Megathrix, which is contemporaneous with the lowermost Meishucunian small shelly fossil assemblage — Anabarites trisulcatus–Protohertzina anabarica, is widely distributed in the lowermost Cambrian strata of South China and the Tarim Basin and is useful for biostratigraphic correlation with Baltica and other areas.
This paper investigates a learning system based on growing radial basis function (RBF) networks for acquiring reactive behaviours in mobile robotics. The learning algorithm integrates unsupervised and su- pervised learning, directly mapping the sensor information to the required motor action. The learning system is evaluated through a number of exper- iments on a real robot. The experimental results show that our learning system can learn a wide range of robot behaviours from simple tasks to complex tasks, and demonstrate that the task need not be known at the programming time. This means that that many difierent behaviours could potentially be acquired by the same learning architecture, thus dramati- cally reducing the development cost of autonomous robotic systems.