“…In contrast to the Yundong area (Guizhou Province), the Three Gorges area was likely situated more proximal to paleocoastline and landmass, which was influenced by higher influx of radiogenic riverine-delivered Os from the weathering of continental crust. In addition, the initial 187 Os/ 188 Os value (0.902 ± 0.048) of the top part of the Liuchapo Formation is comparable with those of contemporaneous polymetallic Ni-Mo layers (0.87 ± 0.07, Xu et al, 2011;0.90 ± 0.09, Fu et al, 2016) and black shale (0.83 ± 0.02; Wei et al, 2018). All 187 Os/ 188 Os values are below the initial 187 Os/ 188 Os value (~1.0; Levasseur et al, 1998) of modern normal seawater (Fig.…”
Section: Implications For Os Isotopic Composition Of Ediacaran-cambri...supporting
The Ediacaran-Cambrian (E-C) succession in South China records remarkable oceanic, biological and geochemical variations, but it was not well defined geochronologically, which hinders the interpretation of the spatio-temporal seawater chemical architecture during the time E-C interval. This study presents two Re-Os isochron ages of 520.2 ± 6.1 and 561.7 ± 8.5 Ma for the barite-rich black shales from the top Liuchapo and Doushantuo formations respectively in Tianzhu County, Guizhou Province. In combination with existing age data, the two new Re-Os isochron ages suggest that the Liuchapo Formation was deposited between 550 and 520 Ma. Moreover, like the polymetallic Ni-Mo-PGE layers of shelf margin (or platform) facies and V-rich horizons of transitional (or shelf slope) to deep-water facies, the barite deposits were likely formed due to differential mineralization. The timing offset likely resulted from differential elemental concentration related to certain local factors (i.e., hydrothermal fluids, seawater redox and biological activity). The isochron-derived initial 187Os/188Os ratios of the top Liuchapo Formation (0.902 ± 0.048) and the Doushantuo Formation (0.740 ± 0.042) fall within the range of continental weathering flux (1.54) and oceanic crust (0.126), implying the involvement of marine hydrothermal fluids. Moreover, their difference of initial 187Os/188Os ratios may reflect variations of continental weathering intensity and uplift magnitude.
“…In contrast to the Yundong area (Guizhou Province), the Three Gorges area was likely situated more proximal to paleocoastline and landmass, which was influenced by higher influx of radiogenic riverine-delivered Os from the weathering of continental crust. In addition, the initial 187 Os/ 188 Os value (0.902 ± 0.048) of the top part of the Liuchapo Formation is comparable with those of contemporaneous polymetallic Ni-Mo layers (0.87 ± 0.07, Xu et al, 2011;0.90 ± 0.09, Fu et al, 2016) and black shale (0.83 ± 0.02; Wei et al, 2018). All 187 Os/ 188 Os values are below the initial 187 Os/ 188 Os value (~1.0; Levasseur et al, 1998) of modern normal seawater (Fig.…”
Section: Implications For Os Isotopic Composition Of Ediacaran-cambri...supporting
The Ediacaran-Cambrian (E-C) succession in South China records remarkable oceanic, biological and geochemical variations, but it was not well defined geochronologically, which hinders the interpretation of the spatio-temporal seawater chemical architecture during the time E-C interval. This study presents two Re-Os isochron ages of 520.2 ± 6.1 and 561.7 ± 8.5 Ma for the barite-rich black shales from the top Liuchapo and Doushantuo formations respectively in Tianzhu County, Guizhou Province. In combination with existing age data, the two new Re-Os isochron ages suggest that the Liuchapo Formation was deposited between 550 and 520 Ma. Moreover, like the polymetallic Ni-Mo-PGE layers of shelf margin (or platform) facies and V-rich horizons of transitional (or shelf slope) to deep-water facies, the barite deposits were likely formed due to differential mineralization. The timing offset likely resulted from differential elemental concentration related to certain local factors (i.e., hydrothermal fluids, seawater redox and biological activity). The isochron-derived initial 187Os/188Os ratios of the top Liuchapo Formation (0.902 ± 0.048) and the Doushantuo Formation (0.740 ± 0.042) fall within the range of continental weathering flux (1.54) and oceanic crust (0.126), implying the involvement of marine hydrothermal fluids. Moreover, their difference of initial 187Os/188Os ratios may reflect variations of continental weathering intensity and uplift magnitude.
“… Figure 1 Early Cambrian time scale for the Siberian Platform, Russia, with key radiometric dates (numbered; Siberian radiometric dates are in bold), international chronostratigraphy (ICS), and stages and zones accepted for the Siberian Platform. Radiometric dates from 1 27 , 93 ; 2 94 ; 3 95 , 4 96 ; 5 97 ; 6 98 – 100 ; 7 30 ; 8 101 . Right column shows numbered temporal units, each c. 2.5 Myr in duration.…”
The dynamics of how metazoan phyla appeared and evolved – known as the Cambrian Explosion – remains elusive. We present a quantitative analysis of the temporal distribution (based on occurrence data of fossil species sampled in each time interval) of lophotrochozoan skeletal species (n = 430) from the terminal Ediacaran to Cambrian Stage 5 (~545 – ~505 Million years ago (Ma)) of the Siberian Platform, Russia. We use morphological traits to distinguish between stem and crown groups. Possible skeletal stem group lophophorates, brachiopods, and molluscs (n = 354) appear in the terminal Ediacaran (~542 Ma) and diversify during the early Cambrian Terreneuvian and again in Stage 2, but were devastated during the early Cambrian Stage 4 Sinsk extinction event (~513 Ma) never to recover previous diversity. Inferred crown group brachiopod and mollusc species (n = 76) do not appear until the Fortunian, ~537 Ma, radiate in the early Cambrian Stage 3 (~522 Ma), and with minimal loss of diversity at the Sinsk Event, continued to diversify into the Ordovician. The Sinsk Event also removed other probable stem groups, such as archaeocyath sponges. Notably, this diversification starts before, and extends across the Ediacaran/Cambrian boundary and the Basal Cambrian Carbon Isotope Excursion (BACE) interval (~541 to ~540 Ma), ascribed to a possible global perturbation of the carbon cycle. We therefore propose two phases of the Cambrian Explosion separated by the Sinsk extinction event, the first dominated by stem groups of phyla from the late Ediacaran, ~542 Ma, to early Cambrian stage 4, ~513 Ma, and the second marked by radiating bilaterian crown group species of phyla from ~513 Ma and extending to the Ordovician Radiation.
“…2a). The Re-Os isotopic age of the black shale of the Niutitang Formation is 522.9 ± 8.6 Ma (Wei et al, 2018).…”
Section: Profile Of Gezhongwumentioning
confidence: 99%
“…Trace element composition of pyrite from the Gezhongwu profile and Haishan V deposits. Wei et al, 2018;Wu et al, 2021), enabling it to be used as a marker layer. The distribution of in situ sulfur isotopes and trace elements of pyrite in polymetallic layers are inconsistent across regions, indicating that there are differences in the sedimentary environment (Ye et al, 2017).…”
Section: Sedimentary Environment In a Shelf Marginmentioning
A polymetallic layer is usually developed at the bottom of the Early Cambrian black shale in Guizhou province. The mineral that makes up the polymetallic layer is related to the sedimentary facies. To analyze the differentiation mechanism between polymetallic deposits (Ni‐Mo and V), the Zhijin Gezhongwu profile located in the outer shelf and the Sansui Haishan V deposit located in the lower slope are selected to study the in‐situ sulfur isotope and trace elements of pyrite. The results show that δ34S values of pyrite vary widely from −7.8 ‰ to 28 ‰ in the Gezhongwu profile, while the δ34S values are relatively uniform (from 27.8 ‰ to 38.4 ‰) in the Haishan profile. The isotopic S composition is consistent with the transition that occurs in the sedimentary phase from the shelf to the deep sea on the transgressive Yangtze platform; this indicates that the δ34 values in seawater must be differently distributed in depositional environments. The sulfur in the Ni‐Mo layer is produced after the mixing of seawater and hydrothermal fluid, while the V layer mainly originates from seawater. Overall, the Ni‐Mo and V deposits have been differentiated mainly on the basis of the combined effect of continental weathering and hydrothermal fluid.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
