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Lithological column and the vertical distribution of graptolite and shelly fossils from Ludiping, Songtao, northeastern Guizhou (Loc. 27).
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Late Ordovician to earliest Silurian is an important geological period marked by large geological and biological events. However, the strata and fossils of this interval are not complete in many parts of the world. Based on studies of 43 sites in South China, in particular the continuous sections on the Yangtze platform, we recognize a complete suc...
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... the present systematic collections from these four sections, only four monospecific genera, Neurograptus, Nymphograptus, Orthoretiograptus and Sinoretiograptus described by Mu et al. (1993) have not yet been re-collected since they are all based on very rare specimens. The ranges of the graptolites and shelly fossil groups, mainly brachiopods, are demonstrated on four range charts (Figs 3-6). We also demonstrate some important forms of the related graptolite fauna in Figure 7 and the shelly fauna in Figure 8. Finally, we list the important species for which we differ significantly in our interpretations from those of Mu et al. (1993) ...
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... beds) is diachronous within the Yangtze region. The timing of the first appearance of the Hirnantia fauna differs markedly among the studied sections. At rela- tively shallow water sites such as Ludiping, Songtao County, northeastern Guizhou, the Hirnantia fauna (AFA414-416) occurs immediately above the Diceratograptus mirus Subzone (AFA413) (see Fig. 6), indicating that the Hirnantia fauna appears at the base of the N. extraordinarius-N. ojsuensis Zone. As far as we know, this is one of the earliest occurrences of the Hirnantia fauna in South China ( ...
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... specimens described by Williams (1982b) as Dicellograptus ornatus Elles & Wood from Band E dif- fer somewhat from one another and do not agree exactly with the form of D. ornatus sensu stricto. His specimens illustrated in plate 1, figure 6 and text-fig. 6f, 6g represent Dicellograptus mirabilis Mu & Chen, which occurs in the Tangyagraptus typicus Subzone and Diceratograptus mirus Subzone in the Yangtze region. Williams' (1982b) specimen illustrated in plate 1, figure 8 is a specimen of Dicellograptus turgidus Mu, which occurs commonly in the Tangyagraptus typicus Subzone of P. pacificus ...
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... North African biozonation after Massa (2003, 2006) and Legrand (2003a, b), biozonation of Canadian Arctic Islands after Melchin (1989), Lenz & Melchin (1991), Lenz (1995), Lenz & Kozłowska-Dawidziuk (2002 and Lenz et al. (2012). Biozonation of South China after Chen (1984), Chen et al. (2000Chen et al. ( , 2017, Mu et al. 1986, Fu et al. (2000, Maletz et al. (2021a, b), and biozonation of Central Asia after Koren & Suyarkova (1997. Black star indicates the base of the chronostratigraphical unit formally defined by a graptolite marker species, outlined star indicates a base under revision, effectively identified by means of a graptolite marker species. ...
... He et al. 2002) prior to the Hirnantian glacio-eustatic lowstand. Although the OST Yangtze Sea has been extensively studied with regard to its lithostratigraphy (Rong 1984), palaeobiology (Rong and Chen 1987;Wang 1989; X. Chen et al. 2001;Rong et al. 2006), sequence stratigraphy (Fan et al. 2009) and sedimentology (Wang 1989), the only analysis of its salinity characteristics to date has been that of Cao et al. (2023). ...
... This proxy is based on a reduction in aqueous Mo concentrations in restricted watermasses due to the sink flux to the sediment exceeding the Mo resupply via deep-water renewal . This process leads to a strong depletion of Mo in both the water column and the sediments of modern strongly restricted basins such as the Black Sea ( Chen et al. 2001;Zhan et al. 2010;L. Zhang et al. 2014) consists of a more restricted inner basin (herein termed the IYS; see ...
... o) Bed and the uppermost Ordovician-lower Silurian Longmaxi (or Lungmachi) Formation. The Wufeng and Longmaxi formations are composed mainly of organic-rich black shales containing few benthic, but abundant pelagic, fossils, especially well-preserved graptolite specimens that facilitate international biostratigraphic correlations (Wang et al. 1993;X. Chen et al. 2001;Y. Li et al. 2017). The abundance of organic-rich facies in the Ordovician-Silurian Yangtze Sea has been linked to upwelling and enhanced productivity (Zhou et al. 2015;Luo et al. 2016;Y. Liu et al. 2020;S. Yang et al. 2021) and the Wufeng and Longmaxi formations have yielded substantial hydrocarbon resources and represent important targ ...
During the Late Ordovician Hirnantian Ice Age, the South China Craton experienced large changes in climate, eustasy, and environmental conditions, but their impact on the watermass architecture of the Yangtze Sea has not been thoroughly evaluated to date. Here, we reconstruct the salinity-redox structure of the Yangtze Sea based on five Upper Ordovician-lower Silurian shale successions representing a lateral transect, from a deep-water area of the Inner Yangtze Sea (IYS; Shuanghe section) across the shallow Hunan-Hubei Arch (Pengye, Jiaoye, and Qiliao sections) to the relatively deep-water Outer Yangtze Sea (OYS; Wangjiawan section). Carbon-isotope ( δ ¹³ C org ) profiles show that the Guanyinqiao Bed (recording peak Hirnantian glaciation) thins and is less completely preserved at sites on the flanks of the Hunan-Hubei Arch than in deeper-water areas to the SW and NE, reflecting bathymetric influences. Watermass salinities were mainly marine at Shuanghe and brackish at the other four study sites, with little variation between Interval I (pre-glaciation), Interval II (Hirnantian glaciation), and Interval III (post-glaciation). Redox proxies document mainly euxinia at Shuanghe and Wangjiawan and suboxia at the other sites during Interval I, with shifts toward more reducing (mostly euxinic) conditions at most sites during Intervals II and III, which shows that all study sections were deep enough to remain below the redoxcline during the glacio-eustatic lowstand. Two features of the Shuanghe section mark it as being unusual: it alone exhibits fully marine salinities, implying greater proximity to the open ocean than for the other four sites, and it exhibits an especially large shift toward more reducing conditions during Interval III (i.e., the post-Hirnantian transgression), implying greater water depths. These features are difficult to reconcile with the standard palaeogeographic model for the Ordovician-Silurian South China Craton, which is characterized by a geographically enclosed and restricted IYS and a more-open OYS, arguing instead for the SW end of the IYS having been connected to the global ocean and the OYS having been a restricted oceanic cul-de-sac. A review of sedimentologic and facies data for the IYS region suggests that our re-interpretation of the Ordovician-Silurian palaeogeography of the South China Craton is viable, although further vetting of this hypothesis will be needed.
Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system
Supplementary material: https://doi.org/10.6084/m9.figshare.c.7170648
... The well-established graptolite biostratigraphy of the O-S succession provides standard criteria for stratigraphic correlation of the studied deposits. (Chen et al., 2000(Chen et al., , 2004. In this study, the existing graptolite biostratigraphic data of the Bailu and Mingtong sections are based on previous work (He, 2002;Wang et al., 2018). ...
Silica accumulation in the Yangtze Sea during the Ordovician‐–Silurian (O‐–S) transition appears to have coincided with global climatic fluctuations, widespread upwelling, and volcanism. There is a need to further evaluate their respective contributions to silica deposition and potential relationships among these factors. The current study selected siliceous deposits in the Wufeng and Longmaxi Formations from four sections spanning the inner to outer Yangtze Sea, South China, to gain a deeper understanding of the climatic and oceanographic evolution associated with silica enrichment. Al/(Al + Fe + Mn) values, the presence of radiolarians, and Si isotope values of samples recovered from the investigated shale successions offer compelling evidence that the silica is largely of biogenic origin with some terrigenous contributions. Further, various productivity and redox proxies suggest that biogenic silica (BSi) accumulated under conditions of enhanced marine productivity and anoxic bottom water conditions. Hg/TOC and Zr/Al2O3 profiles suggest intermittent volcanism during the BSi deposition in the Yangtze Sea. However, the lack of correlation between BSi and Hg/TOC values indicates that volcanic iron fertilization was not responsible for BSi accumulation. Instead, most BSi-rich samples are dominated by low MnEF × CoEF values (< 0.5), consistent with BSi deposited in modern upwelling settings. Hydrographic reconstruction based on Mo‐–U covariation indicates a more open water setting in the outer Yangtze Sea, while the coeval inner Yangtze Sea was relatively restricted. Therefore, Upwelling events appear to have been more vigorous in the outer Yangtze Sea. Published and new Chemical Index of Alteration (CIA), BSi, and MnEF × CoEF data for the Wufeng and Longmaxi Formations across the inner to outer Yangtze Sea demonstrates that temporal and spatial variations of BSi were controlled by climate-driven upwelling. In particular, cool-water upwelling contemporaneous with Hirnantian glaciation may have been responsible for the establishment of the cool-water fauna of the shallow-water Guanyinqiao Bed and enhanced silica deposition in deeper water. Moreover, a moderate negative relationship ofbetween compiled CIA and BSi contents suggests that enhanced upwelling driving BSi accumulation appears to have been favored during cooling events. Integrated analysis of BSi deposits of the Laurentia and Baltica continental margins further suggests that BSi accumulation on continental margins during the O‐–S transition was primarily influenced by global cooling. Therefore, we suggest that wind patterns or/and thermohaline circulation, influenced by climate fluctuations, induced widespread cold water upwelling events during the O‐–S transition. Moreover, elevated BSi production diluted accumulating OM resulting in the observed parabolic relationship of BSi and TOC.
... Previous studies of Wufeng shales mainly focus on its organic petrology (Luo et al., 2017;Luo et al., 2018;Luo et al., 2020), paleogeographic environment (Chen et al., 2004), paleontology (Chen et al., 2000), and petroleum geochemistry (Liang et al., 2008;Chen et al., 2011;Liu et al., 2011;Zou et al., 2012;Guo and Zhang, 2014;Gao et al., 2022), but until now the study on its provenance and the variations of weathering and paleoclimate is still insufficient. Chen et al. (2004) proposed that the palaeoclimate changed from Greenhouse effect to icehouse effect at Ashgillian (Figure 1(b)). ...
... During the Late Ordovician, there was a global transgression in Yangtze Block, which led to the development of Wufeng Formation (Mu et al., 2011). The Wufeng Formation mainly comprises black graptolitic shales including Dicellograptus complanatus-Paraorthograptus pacificus graptolite zones (Chen et al., 2000;2005), indicating the transgressive systems tracts (TST) in a typical sea-level sequence. The Guanyinqiao Formation, which includes typical Hirnantia Fauna (Rong et al., 2002) and is primarily composed of argillaceous limestones (Figure 1(b)), lie conformably on the Wufeng Formation, indicating a shelf-margin systems tract (SMST) at the margin of Yangtze Platform. ...
Wufeng Formation shale is an important source rock of unconventional hydrocarbons in the Lower Paleozoic shales of Sichuan Basin. However, the study on its provenance and paleoclimate is still relatively limited. In this study, mineralogical and geochemical data of the shales from the Upper Ordovician Wufeng Formation in southwestern China has been used to interpret the provenance and conditions of weathering and paleoclimate. The Wufeng shales have intermediate to high SiO 2 (57.72–82.38 wt. %, av. = 68.84 wt. %) and Al 2 O 3 (5.26–16.17 wt. %, av. = 10.62 wt. %), are rich in transition metal elements (i.e. V, Ni, Cu, Co and Cr) and Y as well as moderate depletion in Na 2 O and Sr, relative to the concentrations of the upper continental crust (UCC). In the chondrite-normalized (CN) rare earth elements (REE) distributions, these rocks display light REE (LREE) enrichment (La/Yb CN = 6.69–12.63, av. = 9.28), flat heavy REE (HREE) (Gd/Yb CN = 1.35–2.41, av. = 1.70), and clearly negative Eu anomalies (Eu an = 0.50–0.66, av. = 0.58), showing similar characteristics with the CN post-Archean Australian Average Shales (PAAS). Wufeng Formation shales are immature composition without evident recycling sediments, and they are originated from an intermediate-felsic igneous source composed of tonalite–trondhjemite–granodiorite (TTG), granitic and andesitic igneous rocks. The chemical weathering conditions of studied shales decreased from moderate to low in the provenance region, suggesting a gradual cooling trend of the climate at Late Ordovician Thus, this article will be helpful to discern the provenance and variations of chemical weathering conditions and paleoclimate of Wufeng Formation shales.
... The Late Katian to early Hirnantian in the Late Ordovician was the depositional interval of the Wufeng Formation, which was equivalent to the D. complexus-M. extraordinarius biozones (Chen et al., 2000). ...
Paleogeographical and Paleoenvironmental studies across the Ordovician–Silurian transition in the Yangtze region are based on the GBDB database and isopach maps. Sedimentary processes during the Late Ordovician to early Silurian of the Yangtze Platform are reviewed. Microfacies analyses on the shale gas drill cores in Weiyuan and Luzhou are provided as additional data.
... Graptolites, the globally recognised dominant palaeontological fossils for this period, live at different depths and evolved rapidly. They are used as the ''golden rulers" for stratigraphic division and provide the basis for the fine isochronous division of the Wufeng and Longmaxi formation shales (Chen et al., 2000). For example, the first appearance of the graptolite species Normalograptus extraordinarius (Sobolevskaya) was defined 0.39 m below the base of the Guanyinqiao Member (or the Kuanyinchiao Bed (Chen et al., 2004) as the Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian. ...
... Graptolite biozones are helpful for accurately characterising black shale over time (Zou et al., 2019). Chen et al. (2000) established the biostratigraphic sequences of the Wufeng Formation, the Guanyyinqiao Member and the bottom of the Longmaxi Formation based on more than 30 stratigraphic sections in the Yangtze Platform. These sequences have gradually been recognised as the international standard for contemporaneous stratigraphic division and comparison (Chen et al., 2006;Rong et al., 2008;Gradstein et al., 2012). ...
... The Wufeng Formation includes the Dicellograptus complanatus, the Dicellograptus complexus and Paraorthograptus pacificus biozones in the Katian and the Metabolograptus extraordinarius Biozone in the Hirnantian. According to Chen et al. (2000) and Fan et al. (2011), the Dicellograptus complanatus Biozone is undeveloped in the Sichuan Basin. The Dicellograptus complexus Biozone is directly overlaid on the limestone of the Linxiang Formation. ...
... They have a rather homogeneous, detrital-sourced, and coarser-grained component vertically (Zhao et al., 2016b). The tectonic movements and transgressions also led to thin layers of siliceous shale being deposited in the late Ordovician (Chen et al., 2000). This siliceous shale is widely distributed at a thickness ranging from a few to tens of meters with rich radiolarian (Fig. 2) (Su et al., 2007;Zhao et al., 2016b). ...
... This article focuses on the Lower Member, which is currently the primary interval for commercial shale gas production. The Longmaxi Formation is widely distributed on the Yangtze Platform [37,[42][43][44]. Below the Longmaxi Formation lies the Wufeng Formation, separated from the underlying black shale of the Longmaxi Formation by a thin layer of interbedded shelly limestone [16]. ...
... The stratigraphic sequence model was based on traditional stratigraphic sequence principles and terminology [9,18,56], and the approach mainly relied upon Rider (1986) [57] and Van Wagoner et al. (1990) [22]. The isochronous framework of twelve wells was identified to constrain the boundary of the sequence stratigraphy based on the standard graptolite zones established by Chen et al. (2015) [1,42,45]. The location of the first appearance of characteristic graptolites served as a representative indicator of the sedimentary age of the corresponding stratigraphic layer. ...
In contrast to the widely used sequence stratigraphic models for passive continental margins, the stacking patterns of strata within epeiric seas, which are influenced by regional tectonic activity, may display opposing characteristics during the same geological period. These variations serve as a record of basin evolution and also affect the accumulation of hydrocarbons within the strata. Our study investigated the development potential of the deep Longmaxi Shale in the southern Sichuan Basin by examining the sequence stratigraphy and sedimentary fill patterns. Using a combination of core observation, well-logging data analysis, and 3D seismic profile interpretation, we aimed to gain an understanding of the sedimentary fill history of the Longmaxi Shale during the Early Silurian. Our analysis revealed that deglaciation and regional tectonic events affected the sequence stratigraphy, resulting in unconformities that were identifiable using seismic data and wireline logs. Through an analysis of thirty wireline logs and two seismic profiles, we identified two third-order sequences suggested in the Lower Longmaxi Formation. Within the two third-order sequences were five systems tracts, with the first exhibiting a complete cycle of sea-level change and the second cycle being incomplete due to regional tectonic events. The graptolite succession on the upper Yangtze Platform provided a temporal view of the sequence stratigraphy and sedimentation rates of the Longmaxi Shale. The thickness trends of the systems tracts reflected the interplay of short-term eustasy fluctuations, subsidence, and uplift. Our analysis suggests that regional subsidence played a significant role in the deposition of the second transgressive systems tract (TST) in the Weiyuan and Luzhou areas, which represents a promising target for shale gas exploration, in addition to the first TST. However, the Changning area experienced a relative sea-level decrease due to the intense uplift of the Qianzhogn Paleo-uplift and the increased supply of sediment and is interpreted as a highstand systems tract (HST); it is not considered to have shale gas exploration potential.
... During the Late Ordovician to Early Silurian, oceanic anoxia, global glaciation, and mass extinction events frequently occurred, accompanied by the deposition of a black shale sequence on a global scale, which has drawn significant attention from the scientific community [1,2]. Black shales in the Wufeng Formation-Longmaxi Formation are the primary shale gas reservoirs in the Sichuan Basin in China and are also the key boundary layers for the first mass extinction during the Late Ordovician to Early Silurian. ...
... Extensive research has been conducted worldwide regarding the paleontology, paleoclimate, and redox conditions of the seawater body and has achieved fruitful results. Chen et al. [1] separated the Wufeng Formation-Longmaxi Formation into various biozones and compared them internationally. According to sedimentary and geochemical studies undertaken by Su et al. [2] on the Wangjiawan region of Hubei, there may be a link between the extinction of biological species and changes in the ancient marine environment. ...
... The data on the content of shale oxidants in the Wufeng Formation-Longmaxi Formation, of the Youc Well 2 are presented in Table A1. The total organic carbon (TOC) content of the Wufeng Formation shale ranges from 1.050% to 3.17%, with an average value of 2.14%; the shale content (TOC) of the Guanyinqiao member is 2.568%, and the Longmaxi Formation shale content (TOC) ranges from 0.181% to 2.980%, with an average value of 1 ...
The relationship between the Late Ordovician–Early Silurian sedimentary system, weathering, paleoclimate, and primary productivity in the Yangzi region is not well understood. In this study, by analyzing the sedimentation cycle and major trace elements of the Youc well 2 in the southeast Sichuan Basin, the coupling relationships of weathering indicators, terrigenous debris input indicators, paleoclimate, redox condition indicators, U-Mo covariance model, Mo/TOC relationship, and paleoproductivity indicators are investigated. The results show that single-well logs delineate four third-order sedimentary sequences (SS1, SS2, SS3, and SS4), two sedimentary subfacies, and four sedimentary microfacies in the Wufeng Formation–Longmaxi Formation. The weathering degree is stronger at the bottom where the climate shifts from warm–wet to cold–dry, and the seawater is in an oxidic–anoxic–oxidic–anoxic environment. While the primary productivity and material source input decreases gradually in the middle and upper part, the climate becomes dry and cold, and the seawater is in an anoxic–oxidic environment. Thus, a rock enrichment model for the organic matter shale of the Wufeng Formation–Longmaxi Formation in southeast Sichuan has been established. This provides more information on the control factors concerning organic matter enrichment and their interactions.
... (3) The paleoecological and biostratigraphical evolution in the Cathaysia and Yangtze blocks are related and continuous [111]. (4) The age spectra of detrital zircon from lower Paleozoic sandstones of the Cathaysia and Yangtze blocks have similar characteristics [109,112]. ...
Controversy over the geodynamic interpretation of the early Paleozoic granites in the South China Block constrains understanding of tectonic–magmatic evolution. In this paper, we present zircon U-Pb age, Hf isotope, and major and trace element data of the early Paleozoic granites in the Jilongjie region, south-central Hunan Province. A sample that yielded a weighted average 206Pb/238U age of 425 ± 3 Ma falls into the post-collisional granite field in the classification discriminant of magmatic rocks. Geochemical features indicate that the Jilongjie pluton is a shoshonitic metaluminous rock. The Jilongjie pluton’s chondrite-normalized rare earth element patterns exhibit a slight enrichment of light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs) with (La/Yb)N ratios of 15.1–23.7 and weak Eu anomalies (Eu/Eu* = 0.68–0.78). Zircon Hf isotope results show εHf(t) ranging from −9.94 to −0.69. Jilongjie granite’s parent magma originated from a mixing of crust-derived felsic and mantle-derived mafic magmas, which then underwent fractional crystallization during its ascent. Jilongjie granite was generated through a post-collisional extensional setting associated with delamination of the thickened lithosphere.
