High-resolution C-isotope chemostratigraphy of the uppermost Cambrian stage (Stage 10) in South China: implications for defining the base of Stage 10 and palaeoenvironmental change

2017 ◽  
Vol 154 (6) ◽  
pp. 1232-1243 ◽  
Author(s):  
DANDAN LI ◽  
XIAOLIN ZHANG ◽  
KEFAN CHEN ◽  
GUIJIE ZHANG ◽  
XIAOYAN CHEN ◽  
...  
Keyword(s):  
High Resolution ◽  
Organic Carbon ◽  
Sea Level ◽  
South China ◽  
Palaeoenvironmental Change ◽  
Carbon Isotope Excursion ◽  
Conodont Zone ◽  
Lowermost Part ◽  
Stratotype Section ◽  
Cambrian System

AbstractThe Wa'ergang section in South China has been proposed as a potential Global Stratotype Section and Point (GSSP) for the base of Stage 10, the uppermost stage of the Cambrian System. In this study, high-resolution C-isotopic compositions are reported and we identified three large negative δ13C excursions, namely N1, N2 and N3, at Wa'ergang. The N1 is located just above the First Appearance Datum (FAD) of Lotagnostus americanus, corresponding to the possible base of the Proconodontus posterocostatus conodont Zone. The N2 was identified within the Micragnostus chuishuensis trilobite Zone and the Proconodontus muelleri conodont Zone. The N3 is located in the lowermost part of the Leiagnostus cf. bexelli – Archaeuloma taoyuanense trilobite Zone or Eoconodontus conodont Zone. The N1 and N2 can be correlated with the negative δ13C excursions preceding the Top of Cambrian Carbon Isotope Excursion (TOCE) observed globally. The N3 can be correlated with the TOCE or the HEllnmaria–Red Tops Boundary (HERB) Event. The inter-basinal correlation of N1 and L. americanus strongly supports that the base of Stage 10 may be best defined by the FAD of L. americanus. We also used a box model to quantitatively explore the genesis of the negative δ13C excursions from South China. Our numerical simulations suggest that weathering of the organic-rich sediments on the platform, probably driven by intermittent sea level fall and/or the oxygenation of the Dissolved Organic Carbon (DOC) reservoir in seawater, may have contributed to the generation of the negative δ13C excursions observed in the Stage 10 at Wa'ergang in South China.

scholarly journals Precise age for the Permian-Triassic boundary in South China from high precision U-Pb geochronology and Bayesian age-depth modelling

2016 ◽  
Author(s):  
Björn Baresel ◽  
Hugo Bucher ◽  
Morgane Brosse ◽  
Fabrice Cordey ◽  
Kuang Guodun ◽  
...  
Keyword(s):  
High Resolution ◽  
South China ◽  
Volcanic Ash ◽  
Proof Of Concept ◽  
Triassic Boundary ◽  
Quantitative Evidence ◽  
Age Model ◽  
Stratotype Section ◽  
Permian Triassic Boundary ◽  
Environmental Proxies

Abstract. This study is based on zircon U-Pb ages of 12 volcanic ash layers and volcanogenic sandstones from two marine sections with conformable formational Permian-Triassic boundaries (PTB) in the Nanpanjiang Basin (South China). Our dates of single, thermally annealed and chemically abraded zircons bracket the PTB in Dongpan and Penglaitan and provide the basis for a first proof-of-concept study utilizing a Bayesian chronology model comparing the three sections of Dongpan, Penglaitan and the Global Stratotype Section and Point (GSSP) Meishan. Our Bayesian modeling demonstrates that the formational boundaries in Dongpan (251.938 ± 0.029 Ma), Penglaitan (251.982 ± 0.031 Ma) and Meishan (251.956 ± 0.033 Ma) are synchronous within analytical uncertainty of ca. 30 ka. It also provides quantitative evidence that the ages of the paleontologically defined boundaries, based on conodont Unitary Associations zones in Meishan and on macrofaunas in Dongpan, are identical and coincide with the age of the formational boundaries. The age model also confirms the extreme condensation around the PTB in Meishan, which distorts the projection of any stratigraphic points or intervals onto other more expanded sections by means of Bayesian age-depth models. Dongpan and Penglaitan possess significantly higher sedimentation rates and thus offer a greater potential for high resolution studies of environmental proxies and correlations around the PTB than Meishan. This study highlights the power of high-resolution radio-isotopic ages that allow a robust intercalibration of patterns of biotic changes and fluctuating environmental proxies and will help recognizing their global, regional or local significance.

scholarly journals Carbon isotope (δ13Ccarb) and facies variability at the Wenlock–Ludlow boundary (Silurian) of the Midland Platform, UK

2016 ◽  
Vol 53 (7) ◽  
pp. 725-730 ◽  
Author(s):  
John A. Blain ◽  
David C. Ray ◽  
James R. Wheeley
Keyword(s):  
High Resolution ◽  
Sea Level Rise ◽  
Sea Level ◽  
Carbon Isotope ◽  
Carbonate Platform ◽  
Temporal Variations ◽  
Spatial Variations ◽  
Sea Level Fluctuations ◽  
Depositional Settings ◽  
Carbon Isotope Excursion

The Wenlock–Ludlow series boundary (Silurian) has been recognized as a time of pronounced sea-level rise and the end of a globally recognized Late Homerian Stage (Mulde) positive carbon isotope excursion (CIE). However, the precise timing and synchronicity of the end of the excursion with respect to the Wenlock–Ludlow boundary is debated. Within the type Wenlock and Ludlow areas (UK), high-resolution δ13Ccarb isotope data are presented across the Wenlock–Ludlow boundary, and within a range of carbonate platform settings. Correlation between sections and depositional settings has been based upon the characteristics of high-order sea-level fluctuations (parasequences). Comparisons between parasequence-bounded δ13Ccarb values reveal clear spatial variations, with lighter values recorded from more distal settings and heavier values from shallower settings. Temporal variations in the δ13Ccarb values are also documented and appear to reflect local variations in carbonate provenance and productivity in response to sea-level rise. While δ13Ccarb values converge in all sections towards the Wenlock–Ludlow boundary, the apparent end of the Mulde CIE appears diachronous and is progressively older within more distal settings.

scholarly journals High-resolution correlation of the Homerian carbon isotope excursion (Silurian) across the interior of the Midland Platform (Avalonia), UK

2019 ◽  
Vol 157 (4) ◽  
pp. 603-620
Author(s):  
David C. Ray ◽  
Emilia Jarochowska ◽  
Philipp Röstel ◽  
Graham Worton ◽  
Axel Munnecke ◽  
...  
Keyword(s):  
High Resolution ◽  
Sea Level ◽  
Carbon Isotope ◽  
Depositional Environment ◽  
Sea Level Change ◽  
The West ◽  
Relative Sea Level ◽  
Level Change ◽  
Carbon Isotope Excursion ◽  
West Midlands

AbstractNew δ13Ccarb and microfacies data from Hereford–Worcestershire and the West Midlands allow for a detailed examination of variations in the Homerian carbon isotope excursion (Silurian) and depositional environment within the Much Wenlock Limestone Formation of the Midland Platform (Avalonia), UK. These comparisons have been aided by a detailed sequence-stratigraphic and bentonite correlation framework. Microfacies analysis has identified regional differences in relative sea-level change and indicates an overall shallowing of the carbonate platform interior from Hereford–Worcestershire to the West Midlands. Based upon the maximum δ13Ccarb values for the lower and upper peaks of the Homerian carbon isotope excursion (CIE), the shallower depositional setting of the West Midlands is associated with values that are 0.7 ‰ and 0.8 ‰ higher than in Hereford–Worcestershire. At the scale of parasequences the effect of depositional environment upon δ13Ccarb values can also be observed, with a conspicuous offset in the position of the trough in δ13Ccarb values between the peaks of the Homerian CIE. This offset can be accounted for by differences in relative sea-level change and carbonate production rates. While such differences complicate the use of CIEs as a means of high-resolution correlation, and caution against correlations based purely upon the isotopic signature, it is clear that a careful analysis of the depositional environment can account for such differences and thereby improve the use of carbon isotopic curves as a means of correlation.

scholarly journals Spatiotemporal Evolution and Genesis of the Late Ordovician—Early Silurian Marine Euxinia in Northeastern Upper Yangtze Basin, South China

2021 ◽  
Vol 9 ◽  
Author(s):  
Chaoyong Wang ◽  
Zaitian Dong ◽  
Xuehai Fu ◽  
Qing Chen ◽  
Xiaofan Liu ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Sea Level ◽  
South China ◽  
Accumulation Rate ◽  
Water Area ◽  
Late Ordovician ◽  
Redox Conditions ◽  
Water Columns ◽  
Yangtze Basin ◽  
Upper Yangtze Basin

Marine redox conditions and their dynamic changes were a major factor that controlled the formation of black shale and caused the late Ordovician marine extinction in the Upper Yangtze Basin (South China). However, the spatiotemporal variation and potential controlling factors of marine redox conditions in this area remain unclear. We analyzed whole-rock geochemistry and pyrite sulfur isotopes (δ34Spy) of 47 shale samples from the Late Katian to Rhuddanian in a shelf-to-slope (Qianjiang Shaba section and Wc-1 well) region of northeastern Upper Yangtze Basin, and reconstructed water column redox conditions during the Late Ordovician–Early Silurian Transition. The geochemical characteristics of shale, including the ratio of elements, discriminant function and ternary diagram location in the study area suggest a passive continental margin sedimentary environment, wherein the terrigenous detritus is mainly derived from felsic igneous rocks in the upper crust, showing characteristics of near-source deposition. The redox indices (Fe speciation, Corg/P, UEF, and MoEF) showed that the development of anoxic water, especially euxinia, has obvious spatiotemporal heterogeneity. Under conditions of high availability of active organic carbon and limited sulfate supply, high active Fe input and strong biological irrigation in the shallow water area may effectively remove H2S produced by microbial sulfate reduction, conducive to the prevalence of ferruginous water columns. However, for this deep water area, the rapid accumulation rate of organic matter, decrease in dissolved Fe (caused by upwelling in the open sea), and seawater stratification (caused by the rising of sea level) promoted the development of a euxinic water column. This inference is supported by the covariant relationship between organic carbon accumulation rate, chemical index of alteration, Co × Mn, and δ34Spy. Our study highlights the potential control effects of sea level change, continental weathering and upwelling on the development of euxinic water columns.

scholarly journals Precise age for the Permian–Triassic boundary in South China from high-precision U-Pb geochronology and Bayesian age–depth modeling

Solid Earth ◽  
2017 ◽  
Vol 8 (2) ◽  
pp. 361-378 ◽  
Author(s):  
Björn Baresel ◽  
Hugo Bucher ◽  
Morgane Brosse ◽  
Fabrice Cordey ◽  
Kuang Guodun ◽  
...  
Keyword(s):  
High Resolution ◽  
South China ◽  
Sediment Accumulation ◽  
Proof Of Concept ◽  
Triassic Boundary ◽  
Quantitative Evidence ◽  
Age Model ◽  
Stratotype Section ◽  
Permian Triassic Boundary ◽  
Environmental Proxies

Abstract. This study is based on zircon U-Pb ages of 12 volcanic ash layers and volcanogenic sandstones from two deep water sections with conformable and continuous formational Permian–Triassic boundaries (PTBs) in the Nanpanjiang Basin (South China). Our dates of single, thermally annealed and chemically abraded zircons bracket the PTB in Dongpan and Penglaitan and provide the basis for a first proof-of-concept study utilizing a Bayesian chronology model comparing the three sections of Dongpan, Penglaitan and the Global Stratotype Section and Point (GSSP) at Meishan. Our Bayesian modeling demonstrates that the formational boundaries in Dongpan (251.939 ± 0.030 Ma), Penglaitan (251.984 ± 0.031 Ma) and Meishan (251.956 ± 0.035 Ma) are synchronous within analytical uncertainty of  ∼  40 ka. It also provides quantitative evidence that the ages of the paleontologically defined boundaries, based on conodont unitary association zones in Meishan and on macrofaunas in Dongpan, are identical and coincide with the age of the formational boundaries. The age model also confirms the extreme condensation around the PTB in Meishan, which distorts the projection of any stratigraphic points or intervals onto other more expanded sections by means of Bayesian age–depth models. Dongpan and Penglaitan possess significantly higher sediment accumulation rates and thus offer a greater potential for high-resolution studies of environmental proxies and correlations around the PTB than Meishan. This study highlights the power of high-resolution radio-isotopic ages that allow a robust intercalibration of patterns of biotic changes and fluctuating environmental proxies and will help recognizing their global, regional or local significance.

scholarly journals Multiple Controls on the Accumulation of Organic-Rich Sediments in the Besa River Formation of Liard Basin, British Columbia, Canada

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Jiyoung Choi ◽  
Hyun Suk Lee ◽  
Yuri Kim ◽  
Omid H. Ardakani ◽  
Sung Kyung Hong
Keyword(s):  
British Columbia ◽  
Organic Matter ◽  
High Resolution ◽  
Organic Carbon ◽  
Sea Level ◽  
Shale Gas ◽  
Biogenic Silica ◽  
Gas Production ◽  
Geochemical Data ◽  
Geographic Variations

The Late Devonian Besa River Formation is an organic-rich shale sequence in Liard Basin, northeastern British Columbia, Canada, with significant natural gas reserves. High-resolution elemental geochemistry of three long continuous cored intervals of the Besa River Formation was used to better understand the paleodepositional environment of organic-rich intervals in this thick marine shale. The studied core intervals were divided into five chemostratigraphic units based on organic and inorganic geochemical proxies. The highest total organic carbon (TOC) content (up to 13 wt.%) was identified in the upper part of the Patry member (Unit III) within the Liard Basin. During the deposition of Unit III, low clastic influx and euxinic bottom conditions mostly contributed to the high accumulation of organic carbon. Moreover, a high productivity and organic influx may have increased organic-rich basinal sediments, which further depleted the seawater column oxygen content in the presence of a large amount of organic matter. This took place within the oxygen-deficient bottom water from the Patry–Exshaw stratigraphic units. This high TOC interval was most likely deposited through abundant biogenic silica production by radiolarians, thereby utilizing the supply of nutrients from the upwelling. Sea level change was also an important factor that controlled organic matter accumulation in the Besa River Formation. The transgression in sea level changed the residence time of the organic matter in oxic zones within the water column, which limited its supply in deeper water; this decreased the TOC content in Unit IV. Before the deposition, silica production collapsed and was replaced by terrestrial sedimentation of clay minerals in the upper part of the Exshaw member, which caused organic matter dilutions in Unit V (under 5 wt.%). These results provide new insights into the effects of relative sea level changes on redox conditions, productivity, and detrital flux, which are related to organic matter enrichment patterns and their geographic variations. Unit III is characterized by an organic-rich interval as well as an abundance of biogenic silica that is closely related to fracturing. Thus, Unit III is expected to have the highest shale gas potential in the Devonian Besa River Formation. The high-resolution geochemical data integrated with well log and/or seismic data can be used to determine the distribution of the perspective interval for shale gas production in the Liard Basin.

Carbon-Isotope Excursions Recorded in the Cambrian System, South China: Implications for Mass Extinctions and Sea-Level Fluctuations

2018 ◽  
Vol 29 (3) ◽  
pp. 479-491 ◽  
Author(s):  
Jingxun Zuo ◽  
Shanchi Peng ◽  
Yuping Qi ◽  
Xuejian Zhu ◽  
Gabriella Bagnoli ◽  
...  
Keyword(s):  
Sea Level ◽  
Carbon Isotope ◽  
South China ◽  
Mass Extinctions ◽  
Sea Level Fluctuations ◽  
Cambrian System ◽  
And Sea Level
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