Cambrian Miaolingian Research Articles

Cambrian mercury mineralization event in South China: Insights from U-Pb dating of hydrothermal dolomite in the large Chatian Hg district

The genesis of many giant mercury (Hg) deposits/belts is widely debated largely because of a lack of reliable ore-forming age constraints. The LA-ICP-MS/MS dolomite U-Pb were employed to date the large Chatian Hg district in Xiangxi-Qiandong Hg belt of South China. The mineralization of this district can be divided into three stages: an initial Pyrite-Quartz stage before mercury deposition, a main Cinnabar-Sphalerite-Dolomite (Dol I) stage, and a subsequent Dolomite vein (Dol II) stage after ore formation. Three Dol I samples from the Chashula and Touponao Hg deposits were chosen for U-Pb dating, yielding ages of 509.8 ± 7.4 Ma, 509.4 ± 4.7 Ma and 507.4 ± 4.0 Ma respectively, indicating the mineralization occurred in the Cambrian Miaolingian, concurrent with or shortly after the deposition of the host-rock. These ages correspond with the emplacement periods of two Large Igneous Provinces (LIP) (the Pinghe silicic SLIP and the Kalkarindji LIP) in northeastern Gondwana, as well as the mantle-derived rocks in the study region. Combined with previous mercury isotopic data, our study proposes that the large-scale Hg mineralization in the area most likely resulted from the mantle-derived fluids, which would have directly contributed a significant amount of Hg for ore formation. Furthermore, the close timeframe between the Cambrian Series 2-Miaolingian trilobite extinction events and Hg mineralization in South China, may suggests a potential direct connection between the widespread mercury release and mineralization and the Cambrian Series 2-Miaolingian trilobite crisis in the region.

Microbial-dominated dendrolites in the Zhangxia Formation of the Cambrian Miaolingian: A case study of the Dongping section, Shandong Province, eastern China

Nonlamellar dendrolites, a type of microbial carbonate, exhibit dendritic fabric on the macroscale, which is different from stromatolites, thrombolites, and leiolites. This work reports the sedimentary environment and sedimentary characteristics of dendrolites dominated by calcified microbes in the Zhangxia Formation in the Dongping section of Shandong Province, China. Thick oolitic limestone affected by the rise in sea level is developed in the middle section of the Zhangxia Formation in the Dongping section, and a set of thick massive dendrolites are developed above the oolitic limestone. It exhibits the special sedimentary phenomenon of microbes seeking stability in a high-energy environment. Microscopically, the dendrolites are characterized by the rich development of calcified cyanobacteria fossils, such as the epiphyton group and Girvanella, demonstrating the diversity and complexity of the microbes that dominate the dendrolite formation in the Dongping section. The epiphyton group can be classified by morphological characteristics, namely, Epiphyton, Korilophyton, and Hedstroemia. The latter can be further categorized into typical Hedstroemia and Cayeuxia. Therefore, this study enhances our understanding of dendrolite sedimentary environments and provides a reference example for exploring diverse fossil records in ancient strata.

A Case Study on the Co-Occurrence of Oncoids and Ooids in the Cambrian Miaolingian Series, North China Platform

A Case Study on the Co-Occurrence of Oncoids and Ooids in the Cambrian Miaolingian Series, North China Platform

Chuaria Walcott from the early Cambrian Qingjiang biota: a taxon persisted for billions of years

As a globally distributed genus, Chuaria has an extremely long temporal range from the late Paleoproterozoic to the Cambrian Miaolingian but it is still absent in the pre-Miaolingian Cambrian. Here, we describe new specimens of Chuaria from the Qingjiang biota (black shale of the Cambrian Stage 3 Shuijingtuo Formation, ca. 518 Ma) in Hubei Province, South China, and review its tempo-spatial distribution worldwide. Chuaria from the Qingjiang biota is preserved as carbonaceous compressions or impressions that are discoidal or subdiscoidal in outline and range from 1.40 mm to 5.60 mm in diameter, it is interpreted as a spheroidal and thick-walled eukaryote, and its presence fills the early Cambrian gap in the fossil record. Chuaria remained consistent in morphology and survived harsh environmental perturbations throughout its evolutionary history. Its earliest record was restricted in a small region of Columbia supercontinent; thereafter its records were across a range of continents and became worldwide during the time of Rodinia supercontinent.

Giant ooids of microbial origin from the Zhangxia Formation (Cambrian Miaolingian Series) in North China

The role of microorganisms in the formation of giant ooids is one of the areas of long-term controversy in ooidal research, but it has not been confirmed conclusively. Abundant giant ooids developed in the Zhangxia Formation of the Cambrian Miaolingian Series in North China. Giant ooids in the study area were examined by using Polarized Light Microscopy and Field Emission Environmental Scanning Electron Microscopy. The nuclei of the ooids consist of micritic pellets or radial ooids with diameters less than 2 mm and are formed in a weak-agitating seawater environment. Their cortices are concentric, and are characterized by the alternations of the dark laminae of micritic calcite or Girvanella filaments and light laminae of microsparry calcite. In the environments of inter-bank sea with the alternating development of medium and low energy and chiefly weak-agitating conditions, giant ooids were formed under the joint action of Girvanella filamentous growth, biologically-induced calcification and/or biologically-influenced calcification and inorganic calcium carbonate precipitation. The microfossils of Girvanella are distributed in inner and outer cortices of giant ooids, especially dense in the latter. This distinctly indicates that microbes play a significant role in the formation of giant ooids, and also provides a vital example for discussing the microbial origin of giant ooids.

First Report of Small Shelly Fossils from the Cambrian Miaolingian Limestones (Zhangxia and Hsuzhuang Formations) in Yiyang County, Henan Province of North China

Small Shelly Fossils (SSFs) from the Cambrian are widely distributed and well known across different paleocontinents of the world. However, middle Cambrian SSFs from North China Platform have only rarely been documented until now. In this paper, we presented the first report on SSFs from bioclastic and oolitic limestones of the Zhangxia and Hsuzhuang formations of Henan province, North China. The carbonate-hosted fauna includes brachiopods (Micromitra sp., M. modesta, Eoobolus sp., and Schizopholis sp.), helcionellids (Oelandiellaaccordionata and O. aliciae), hyolithids, Hyolithellus sp., Chancelloriaeros, sponge spicules, echinoderm ossicles, and chancelloriid sclerites. In terms of preservation, the brachiopod shell valves of M. modesta appeared to be homogeneous, consisting of tightly packed phosphate grains. Eoobolus sp. is composed of primary layer and secondary baculate, both of which consist of tightly compacted phosphate grains. Schizopholis sp. has multiple-lamellar phosphatized microstructures that distinctly differ from the other brachiopods recovered from the Longwanggou section. A similar multiple-lamellar microstructure was also revealed in conchs of Hyolithellus, with tightly compacted phosphate grains. The argillaceous shell of Oelandiellaaccordionata and O. aliciae, and the calcitic inner molds of hyolith did not preserve any shell structure. The helcionellids O. accordionata and O. aliciae and the brachiopod M. modesta were reported for the first time from North China. The fauna is most similar to the middle Cambrian faunas of Australia, in the brachiopod and mollusk components; it is also similar in composition of brachiopods and mollusks to coeval faunas from South China. The new fauna of SSFs in the Yiyang Longwanggou Section indicated that the Hsuzhuang and Zhangxia formations are late Drumian to middle Guzhuangian in age, most likely correlating with the Murrawong Creek Formation of Australia.

Microbiogenic thrombolites from the Cambrian Miaolingian Series of southern North China Craton

Microbiogenic thrombolites from the Cambrian Miaolingian Series of southern North China Craton

Cambrian marine radial cerebroid ooids: Participatory products of microbial processes

The Cambrian Miaolingian Series strata at the Kouquan section, North China, are primarily divided into the Xuzhuang, Zhangxia, and Gushan formations. This particular series comprises oolitic limestone in the middle to upper intervals. Thin section observations of carbonate rock samples from the Zhangxia Formation show that the well‐preserved and most remarkable grains among them are cerebroid ooids. Although these ooids have characteristic serrated margins, they are distinct from ooids reported in previous publications due to inconspicuous concentric laminae and radial structures composed of micrite and microspar. To understand the origin of these ooids, we employed petrographic examination, X‐ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and isotope analyses to explore their compositions and conditions of development. In addition, the occurrence of these cerebroid ooids is closely related to that of dark‐coloured micrite: most cerebroid ooids and quasi‐cerebroid ooids float inside dark micrite; dark micrite appears in the interior of cerebroid ooids as a radial micrite structure. EPMA and energy‐dispersive X‐ray (EDX) spectroscopy analyses of micrite reveal that the dark micrite consists of lithomicrobial mats. Fine‐scale characterization of the dark micrite inside these cerebroid ooids shows the presence of filamentous and bowl‐shaped calcified microbial fossils and extracellular polymeric substance (EPS) calcified remnants. Isotopic data indicate a variation of δ13C isotopic values between −4.92‰ and −0.11‰ (VPDB) and −9.89‰ and −4.93‰ for δ18O values (VPDB). The negative values of δ13C in the studied ooid suggest the genesis of carbon from the high organic‐rich zone such as the microbial zone. Also, the 13C‐depleted carbon values in the ooids advocate that the carbon is mainly derived from organic sources associated with the sulphate reduction bacterial activity. Thus, isotopic data of this study also provide consistent clues in favour of microbial participation during the genesis of cerebroid ooids. In conclusion, our new findings strongly confirm that the cerebroid ooids of the North China Platform are genetically related to microbial processes.

Late Neoproterozoic – early Paleozoic basin evolution in the Coal Creek inlier of Yukon, Canada: implications for the tectonic evolution of northwestern Laurentia

The age and nature of the Neoproterozoic – early Paleozoic rift–drift transition has been interpreted differently along the length of the North American Cordillera. The Ediacaran “upper” group (herein elevated to the Rackla Group) of the Coal Creek inlier, Yukon, Canada, represents a key succession to reconstruct the sedimentation history of northwestern Laurentia across the Precambrian–Cambrian boundary and elucidate the timing of active tectonism during the protracted breakup of the supercontinent Rodinia. These previously undifferentiated late Neoproterozoic – early Paleozoic map units in the Coal Creek inlier are herein formally defined as the Lone, Cliff Creek, Mount Ina, Last Chance, Shade, and Shell Creek formations. New sedimentological and stratigraphic data from these units is used to reconstruct the depositional setting. In the Last Chance Formation, chemostratigraphic observations indicate a ca. 5‰ δ13Ccarbgradient coincident with the globally recognized ca. 574–567 Ma Shuram carbon isotope excursion. Map and stratigraphic relationships in the overlying Shell Creek Formation provide evidence for latest Ediacaran – middle Cambrian tilting and rift-related sedimentation. This provides evidence for active extension through the Cambrian Miaolingian Series in northwestern Canada, supporting arguments for a multiphase and protracted breakup of Rodinia.

Sequence stratigraphic and petrological analyses of the Cambrian oncoids exposed in the Liaoning Province, North China Platform

The Cambrian Miaolingian Series strata are continuously exposed in the North China Platform and contain diverse sedimentary phenomena, including substantial with oncoid-rich units. Limestone samples from the Zhangxia Formation in the Sandaogou section were collected to characterise unique macroscale to microscale sedimentary characteristics of the marine carbonate oncoids. In the oncolitic beds (∼4.5 m thick), the individual size of oncoids gradually increases from bottom to top. The oncoid morphology and the presence of a nucleus and laminae in thin-sections are used to classify these oncoids into three types (concentric laminar, lateral growth and multicore oncoids). As evidenced by scanning electron microscopy and energy-dispersive X-ray observations, Girvanella are abundant inside these oncoids and are associated with nanospheres, framboidal pyrite, and spherical and filamentous microbial fossils, confirming the biogenicity of the studied oncoids. These results suggest that the oncolitic–oolitic limestone formed in an upward-shallowing marine environment caused by a forced regression process that resulted in a decrease in accommodation space in a fourth-order sequence. Thus, the conditions became increasingly suitable for the development of cyanobacteria-dominated microbial mats and large oncoids. The late stage of the depositional setting and elevated solar radiation resulted in the formation of the growth termination surface. KEY POINTS Evidence of microbial origin from the oncoids of the Cambrian Miaolingian Series in the North China Platform. Vertical variation in oncoid size and distribution coincide with geochemical data. A shallowing depositional environment is interpreted as the reason for variation in oncoid size and formation of oncoid growth termination surfaces.

Trace and rare earth elements geochemistry of sedimentary rocks in the Ediacaran-Cambrian transition from the Tarim Basin, Northwest China: Constraints for redox environments

Spatiotemporal variations in the redox conditions during the Ediacaran-Cambrian (E-C) transition are closely related to the extinction of Ediacaran biota and the Cambrian explosion. However, the detailed variations in the ocean redox gradients remain a controversial issue. In this study, a large dataset of major and trace elements was obtained from the leachates of carbonate rocks sampled from three sections of the E-C transition in the Tarim Basin, northwest China. The Ce anomaly in the late Ediacaran Qigebulage Formation exhibited a regular gradient from anoxic conditions at its base to oxic conditions at its top, suggesting a gradually oxidizing environment. This could have been a beneficial factor that led to the diversification of late Ediacaran fauna. In addition, significantly negative carbon isotope excursions within the E-C boundary of the three sections studied were identified at the base of the Yuertusi Formation. This is coincident with the extinction of Ediacaran biota due to an anoxic sedimentary environment. The base of the Yuertusi Formation was deposited under anoxic or/and euxinic conditions and intense hydrothermal activity during the early Cambrian. The upper layers of this formation exhibited significant Ce anomalies following a general increase in the oxidation level, which reflected an environment transitioning from anoxic/euxinic to oxic following the early Cambrian transgression. A significantly negative δ13Ccarb excursion was evidence of the Redlichiid-Olenellid Extinction Carbon isotopic Excursion event recorded at the boundary of the Cambrian Series 2 and Cambrian Miaolingian. From the Cambrian Series 2 Xiaoerbulak Formation to the Cambrian Miaolingian Awatage Formation, carbonate rocks were deposited in deep water conditions and an anoxic environment. Redox fluctuations could be ascribed to widespread early Cambrian transgressions and tectonic activity, such as the formation of the Tianshan Ocean during the early Cambrian, and the accompanying volcanic activity in the Tarim Basin. Marine redox fluctuations coupled with the paleontological records indicate that the increased concentration of oxygen in the water promoted evolutionary transitions and accelerated the diversification of species during the E-C transition.

Development of Middle Cambrian leiolitic bioherms dominated by calcified microbes: A case study of the Xinji Section (North China Platform)

Among the varieties of microbial carbonate rocks, leiolites are rare in ancient rock records and have only few examples in the modern environment, which makes them difficult to study. This study documents the sedimentary environment, characteristics and composition of microbial carbonates, dominated by calcified microbes, which developed in the Cambrian Miaolingian Xuzhuang Formation on the North China Platform. The upper part of the formation in the Xinji section of Lushan City, Henan Province is bounded by a drowning-unconformity surface of a third-order depositional sequence. Beside the development of an ooid shoal in response to sea-level fall, a bioherm dominated by leiolite also developed in the upper part of the Xuzhuang Formation. These leiolites represent special sedimentary phenomena due to their occurrence with high-energy ooid shoals. Microscopically, they are characterized by abundant calcified cyanobacteria fossils, such as dichotomous-branching Epiphyton and filamentous cyanobacteria, thus showing the diversity and complexity of the cyanobacterial microbial mats that predominate the leolitic bioherm. Four groups are confirmed for Epiphyton based on the morphological characteristics of calcified filaments. The filamentous cyanobacteria can be divided into Girvanella and Subtifloria , and their possible forming mechanisms are discussed. The macroscopic and microscopic characteristics of the current leiolites provide important research clues and typical examples for understanding the origin of the Miaolingian leiolitic bioherm and its paleoenvironmental significance. • The Cambrian leiolitic bioherm developed in a high-energy environment during a drop in sea-level on the North China Platform. • The present study delineates the chambered, shrub-like Epiphyton and filamentous cyanobacteria (Girvanella and Subtifloria) • The microbial calcification occurred prior to early diagenesis, thus opposing the possibility of Epiphyton as a “diagenetic fossil”.

Geochemical and Petrographic Analyses of the Cambrian Oncoids of the North China Platform: Implications for Their Paleogeography and Paleoenvironment

After the global extinction event at the end of the Cambrian Epoch 2, widely spread oolitic bank dominated the North China Carbonate Platform during the Cambrian Miaolingian Epoch. To better understand the influence of paleogeographic and paleoenvironmental factors on microbial carbonate particles during this period, carbonate oncoids of the Cambrian Miaolingian Series were selected to reconstruct the paleogeography and paleoenvironment. The study samples were collected from four different sections: Wuhai, Diaoquan, Xiawidian and Sandaogou (from west to east in the North China Platform). Stratigraphic, sedimentological, petrological and geochemical studies including analysis of trace and rare earth elements were carried out to define the stratigraphic location, and morphological and geochemical characteristics of oncoids. Geochemical analysis of oncoids reveals that Er/Nd and Y/Ho values are relatively low, signifying that the formation of oncoids was influenced by terrestrial inputs. Meanwhile, Sr/Cu, Sr/Ba, V/Sc and V/Cr values indicate that the oncoids were developed in a shallow marine environment under oxidizing conditions. The low content of total rare earth elements, low LREE/HREE ratios and LREEs, negative anomalies of Ce/Ce* and Eu/Eu* as well as (La/Sm)N suggest that the oncoids were less influenced by late diagenetic processes. More importantly, morphological differentiations of oncoids in the study area coincide with the changing trend of Y/Ho and Sr/Ba. The results of this study show that oncoids with regular morphology mainly formed at offshore area, while those with irregular shape and preserving rough laminae mostly occurred at nearshore area. From the comparison made between the paleogeographic locations of the study sections, it is proposed that the paleosalinity of marine depositional environment and the transportation distance are the prime controls for morphological differentiation of oncoids.

First occurrence of the Cambrian arthropodSidneyiaWalcott, 1911 outside of Laurentia

AbstractThe arthropodSidneyiaWalcott, 1911 is a remarkable animal of the Burgess Shale biota (Cambrian Miaolingian, Wuliuan; British Columbia, Canada), which has not been confidently reported from other Cambrian Konservat-Lagerstätten. Here we report the discovery ofSidneyiacf.inexpectansfrom the Wuliuan Mantou Formation of North China, which substantially expands the known palaeogeographical distribution of this genus. Our discovery suggests thatSidneyiahad much greater dispersal ability than hitherto thought. It also confirms the presence of exceptionally preserved fossils in the Wuliuan Mantou Formation, one of the rare Burgess Shale-type deposits of North China.

Calcified coccoid from Cambrian Miaolingian: Revealing the potential cellular structure of Epiphyton.

Epiphyton, Renalcis, and Girvanella are ubiquitous genera of calcified cyanobacteria/algae from Early Paleozoic shallow-marine limestones. One genus, Epiphyton, is characterized by a particular dendritic outline, and extensive research has revealed the morphology of calcified remains although little information on cellular structure is known. The mass occurrence of calcified Epiphyton in microbialites from Cambrian Miaolingian, the Mianchi area of North China is preserved as black clots within thrombolites and have dendritic and spherical outlines when viewed with a petrographic microscope. These remains, visible under scanning electron microscope (SEM), also comprise spherical or rectangle capsules. These capsules are made up from external envelopes and internal calcite with numerous pits, which closely resemble modern benthic coccoid cyanobacteria. These pits are between 2 μm and 4 μm in diameter and are interpreted here to represent the remnants of degraded coccoid cells, while the calcite that surrounds these pits is interpreted as calcified thin extracellular polymeric substances (EPS). In contrast, associated capsular envelopes represent thick EPS mineralized by calcium carbonate with an admixture of Al-Mg-Fe silicates. Dendritic ‘thalli’ are typically stacked apically because of the repeated growth and calcification of these capsules. Carbon and oxygen isotope results are interpreted to indicate that both photosynthesis and heterotrophic bacterial metabolism (especially sulfate reducing bacteria) contributed to carbonate precipitation by elevated alkalinity. Epiphyton are therefore here interpreted as colonies of calcified coccoid cyanobacteria, and the carbonate-oversaturated seawater during the Cambrian was conducive to their mineralization.