Carbon and sulfur isotopic compositions of Early Cambrian black shales, NW Hunan, China: Implications for the Paleoceanographic sedimentary environment

AbstractNitrogen is an essential element for biological activity, and nitrogen isotopic compositions of geological samples record information about both marine biological processes and environmental evolution. However, only a few studies of N isotopes in the early Cambrian have been published. In this study, we analysed nitrogen isotopic compositions, as well as trace elements and sulphur isotopic compositions of cherts, black shales, carbonaceous shales and argillaceous carbonates from the Daotuo drill core in Songtao County, NE Guizhou Province, China, to reconstruct the marine redox environment of both deep and surface seawater in the study area of the Yangtze shelf margin in the early Cambrian. The Mo–U covariation pattern of the studied samples indicates that the Yangtze shelf margin area was weakly restricted and connected to the open ocean through shallow water flows. Mo and U concentrations, δ15Nbulk and δ34Spy values of the studied samples from the Yangtze shelf margin area suggest ferruginous but not sulphidic seawater and low marine sulphate concentration (relatively deep chemocline) in the Cambrian Fortunian and early Stage 2; sulphidic conditions (shallow chemocline and anoxic photic zone) in the upper Cambrian Stage 2 and lower Stage 3; and the depression of sulphidic seawater in the middle and upper Cambrian Stage 3. Furthermore, the decreasing δ15N values indicate shrinking of the marine nitrate reservoir during the middle and upper Stage 3, which reflects a falling oxygenation level in this period. The environmental evolution was probably controlled by the changing biological activity through its feedback on the local marine environment.

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Mo isotope records from Lower Cambrian black shales, northwestern Tarim Basin (China): Implications for the early Cambrian ocean

Geological Society of America Bulletin ◽

10.1130/b35726.1 ◽

2021 ◽

Author(s):

Guangyou Zhu ◽

Tingting Li ◽

Kun Zhao ◽

Chao Li ◽

Meng Cheng ◽

...

Keyword(s):

Lower Cambrian ◽

Bottom Water ◽

Black Shales ◽

Early Cambrian ◽

Middle Portion ◽

Isotopic Compositions ◽

Tarim Block ◽

Time Period ◽

Fe Speciation ◽

Marine Areas

The widely developed black shales deposited during the early Cambrian recorded paleoenvironmental information about coeval seawater. Numerous studies have been conducted on these shales to reconstruct the paleomarine environment during this time period. However, most research has been conducted on stratigraphic sections in South China, and equivalent studies of sections from other cratons are relatively rare. Here, we report Mo isotopic compositions as well as redox-sensitive trace-element and iron (Fe) speciation data for black shales of the Lower Cambrian Yuertusi Formation from the Tarim block (i.e., a small craton). The Fe speciation data show high FeHR/FeT and Fepy/FeHR ratios, indicating roughly sustained euxinic bottom-water conditions during their deposition. Based on Mo isotopic compositions (δ98/95Mo), we further classified the euxinic black shales into two intervals: a lower interval (0−21.3 m) and an upper interval (21.3−32.3 m). The lower interval is characterized by variable Mo isotopic compositions (−2.12‰ to +0.57‰, mean = −0.52‰ ± 0.72‰), with an obvious negative excursion in its middle portion. The overlying upper interval has relatively heavy δ98/95Mo values up to +1.42‰ (mean = +0.62‰ ± 0.37‰). We ascribe δ98/95Mo differences in the lower and upper intervals to inadequate aqueous H2S concentrations for quantitative thiomolybdate formation under euxinic conditions. The most negative Mo isotope excursion may have been caused by upwelling hydrothermal inputs during a transgression, consistent with significantly elevated total organic carbon (TOC) contents, Mo and U enrichments, and Fe supply. Relatively positive δ98/95Mo values in the upper interval have roughly similar variations with other coeval sections, indicating such variations were common for early Cambrian euxinic deposits, and they were most likely caused by local differences in [H2S]aq. Compilation of Mo isotope data from the early Cambrian and earlier times further indicates relatively oxygenated seawater, especially the deep-marine areas during the early Cambrian before reaching a state like modern seawater.

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Elemental and isotopic compositions of trench-slope black shales, Bohemian Massif, with implications for oceanic and atmospheric oxygenation in early Cambrian

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2020.110195 ◽

2020 ◽

pp. 110195

Author(s):

Jan Pašava ◽

Lukáš Ackerman ◽

Jiří Žák ◽

František Veselovský ◽

Robert A. Creaser ◽

...

Keyword(s):

Bohemian Massif ◽

Black Shales ◽

Early Cambrian ◽

Isotopic Compositions ◽

Trench Slope

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Geochemistry of the black rock series of lower Cambrian Qiongzhusi Formation, SW Yangtze Block, China: Reconstruction of sedimentary and tectonic environments

Open Geosciences ◽

10.1515/geo-2020-0228 ◽

2021 ◽

Vol 13 (1) ◽

pp. 166-187

Author(s):

Hao Liu ◽

Chan Wang ◽

Yong Li ◽

Jianghong Deng ◽

Bin Deng ◽

...

Keyword(s):

Environmental Changes ◽

Sedimentary Environment ◽

Hydrothermal Fluids ◽

Early Cambrian ◽

Rock Series ◽

Yangtze Block ◽

Tectonic Environment ◽

Weathering Intensity ◽

Black Rock Series ◽

Tectonic System

Abstract The black rock series in the Qiongzhusi Formation contains important geochemical information about the early Cambrian tectonic and ecological environment of the southwestern Yangtze Block. In this paper, major, trace, and rare earth element data are presented in an attempt to reveal the sediment source during the deposition of the early Cambrian Qiongzhusi Formation and to reconstruct the sedimentary tectonic environment and weathering intensity during that time. The basin primarily received continental clastic material with neutral-acidic igneous rocks from a stable source and with a moderate level of maturity during the depositional period of the Qiongzhusi Formation. Furthermore, the strata were weakly influenced by submarine hydrothermal fluids during diagenesis. The reconstruction of the sedimentary environment and weathering intensity shows that P2O5 enrichment and water body stratification occurred due to the effects of upwelling ocean currents during the depositional period of the Qiongzhusi Formation. The combination of upwelling and bottom-water hydrothermal fluids led to environmental changes in the study area, from dry and hot to moist and warm. Last, the reconstruction of the tectonic environment of the Qiongzhusi Formation indicates that deposition occurred in continental slope and marginal marine environments associated with a continental arc tectonic system. These findings provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary environment of the Yangtze Block.

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Brachiopod-dominated communities and depositional environment of the Guanshan Konservat-Lagerstätte, eastern Yunnan, China

Journal of the Geological Society ◽

10.1144/jgs2020-043 ◽

2020 ◽

Vol 178 (1) ◽

pp. jgs2020-043 ◽

Cited By ~ 1

Author(s):

Feiyang Chen ◽

Glenn A. Brock ◽

Zhiliang Zhang ◽

Brittany Laing ◽

Xinyi Ren ◽

...

Keyword(s):

Depositional Environment ◽

Sedimentary Environment ◽

Low Energy ◽

Cambrian Explosion ◽

Early Cambrian ◽

Tissue Preservation ◽

Content Type ◽

Guanshan Biota ◽

Supplementary Material ◽

Later Phase

The Guanshan Biota is an unusual early Cambrian Konservat-Lagerstätte from China and is distinguished from all other exceptionally preserved Cambrian biotas by the dominance of brachiopods and a relatively shallow depositional environment. However, the faunal composition, overturn and sedimentology associated with the Guanshan Biota are poorly understood. This study, based on collections through the best-exposed succession of the basal Wulongqing Formation at the Shijiangjun section, Wuding County, eastern Yunnan, China recovered six major animal groups with soft tissue preservation; brachiopods vastly outnumbered all other groups. Brachiopods quickly replace arthropods as the dominant fauna following a transgression at the base of the Wulongqing Formation. A transition from a botsfordiid-, eoobolid- and acrotretid- to an acrotheloid-dominated brachiopod assemblage occurs up-section. Four episodically repeated lithofacies reveal a relatively low-energy, offshore to lower shoreface sedimentary environment at the Shijiangjun section, which is very different from the Wulongqing Formation in the Malong and Kunming areas. Multiple event flows and rapid obrution are responsible for faunal overturn and fluctuation through the section. A detailed lithofacies and palaeontological investigation of this section provides a better understanding of the processes and drivers of faunal overturn during the later phase of the Cambrian Explosion.Supplementary material: Composition and comparison of the Malong Fauna and the Guanshan Biota is are available at: https://doi.org/10.6084/m9.figshare.c.5080799

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Copper, zinc, chromium and osmium isotopic compositions of the Teplá-Barrandian unit black shales and implications for the composition and oxygenation of the Neoproterozoic-Cambrian ocean

Chemical Geology ◽

10.1016/j.chemgeo.2019.05.013 ◽

2019 ◽

Vol 521 ◽

pp. 59-75 ◽

Cited By ~ 5

Author(s):

Lukáš Ackerman ◽

Jan Pašava ◽

Adéla Šípková ◽

Eva Martínková ◽

Eva Haluzová ◽

...

Keyword(s):

Black Shales ◽

Isotopic Compositions ◽

Copper Zinc

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Surface water oxygenation and bioproductivity – A link provided by combined chromium and cadmium isotopes in Early Cambrian metalliferous black shales (Nanhua Basin, South China)

Chemical Geology ◽

10.1016/j.chemgeo.2020.119785 ◽

2020 ◽

Vol 552 ◽

pp. 119785

Author(s):

Robert Frei ◽

Bernd Lehmann ◽

Lingang Xu ◽

Jesper Allan Frederiksen

Keyword(s):

Surface Water ◽

South China ◽

Black Shales ◽

Early Cambrian

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Accumulation Conditions and Gas Content Characteristics of the Lower Silurian in Northwestern Hunan, China

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.868.192 ◽

2013 ◽

Vol 868 ◽

pp. 192-195

Author(s):

Tuo Lin ◽

Jin Chuan Zhang ◽

Bo Li ◽

Wei He ◽

Xuan Tang

Keyword(s):

Black Shale ◽

Sedimentary Environment ◽

Sedimentary Facies ◽

Black Shales ◽

Gas Content ◽

Burial Depth ◽

Reservoir Properties ◽

Isothermal Adsorption ◽

Lower Silurian ◽

Deposition Conditions

The Lower Silurian marine shale is widely distributed in Northwestern Hunan and features in a large thickness of dark shale showed at outcrops. However, the accumulation conditions and gas content is unknown. The sedimentary facies, thickness and distribution, organic matter types and content, maturity, reservoir properties and gas content of the Lower Silurian black shale in Northwestern Hunan were investigated by field observation, sampling and experimental analysis. The results show that the black shales sedimentary environment is deep water continental shelf, with featured in abundant fossil. The burial depth of the Lower Silurian black shale is 0-3000 m, and its thickness is 10-40m while the average TOC is 1.0% and average Ro is 2.9%. For the disadvantaged sedimentary facies and shallow depth, the maximum gas content of the Lower Silurian black shale from well site desorption test is 0.59m3/t only, but the result of isothermal adsorption simulate test show that the Lower Silurian black shale have a good adsorption capacity, and can generate a large number of shale gas in Northwestern Hunan where better deposition conditions and suitable depth exist in.

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Cuticular reticulation replicates the pattern of epidermal cells in lowermost Cambrian scalidophoran worms

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.0470 ◽

2020 ◽

Vol 287 (1926) ◽

pp. 20200470

Author(s):

Deng Wang ◽

Jean Vannier ◽

Xiao-guang Yang ◽

Jie Sun ◽

Yi-fei Sun ◽

...

Keyword(s):

Epidermal Cell ◽

Mechanical Response ◽

Sedimentary Environment ◽

Epidermal Cells ◽

Early Cambrian ◽

Extracellular Material ◽

Cuticle Formation ◽

Stem Group ◽

The Relationship

The cuticle of ecdysozoans (Panarthropoda, Scalidophora, Nematoida) is secreted by underlying epidermal cells and renewed via ecdysis. We explore here the relationship between epidermis and external cuticular ornament in stem-group scalidophorans from the early Cambrian of China (Kuanchuanpu Formation; ca 535 Ma) that had two types of microscopic polygonal cuticular networks with either straight or microfolded boundaries. Detailed comparisons with modern scalidophorans (priapulids) indicate that these networks faithfully replicate the cell boundaries of the epidermis. This suggests that the cuticle of early scalidophorans formed through the fusion between patches of extracellular material secreted by epidermal cells, as observed in various groups of present-day ecdysozoans, including arthropods. Key genetic, biochemical and mechanical processes associated with ecdysis and cuticle formation seem to have appeared very early (at least not later than 535 Ma) in the evolution of ecdysozoans. Microfolded reticulation is likely to be a mechanical response to absorbing contraction exerted by underlying muscles. The polygonal reticulation in early and extant ecdysozoans is clearly a by-product of the epidermal cell pavement and interacted with the sedimentary environment.

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