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Volume 32 Issue 3
Jun.  2021
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Zhongyang Chen, Peep Männik, Junxuan Fan, Chengyuan Wang, Qing Chen, Zongyuan Sun, Dongyang Chen, Chao Li. Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section. Journal of Earth Science, 2021, 32(3): 524-533. doi: 10.1007/s12583-020-1350-6
Citation: Zhongyang Chen, Peep Männik, Junxuan Fan, Chengyuan Wang, Qing Chen, Zongyuan Sun, Dongyang Chen, Chao Li. Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section. Journal of Earth Science, 2021, 32(3): 524-533. doi: 10.1007/s12583-020-1350-6

Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section

doi: 10.1007/s12583-020-1350-6
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  • The age of the Silurian Lower Red Beds in the Upper Yangtze region remains debatable. Twenty-four samples were collected for conodont biostratigraphical studies from the Paiyunan Formation in the Sanbaiti Section, Huaying, Sichuan Province. The conodont fauna from the Paiyunan Formation, together with the graptolites from the underlying Lungmachi Formation, indicates that the Lower Red Beds at Sanbaiti correspond to the lower Telychian. Comparative analysis indicates that most exposures of the Lower Red Beds in the Upper Yangtze region can be assigned, in general, to the Telychian Stage, except for several localities, where the Lower Red Beds can be roughly dated as an interval between the upper Aeronian and lower Telychian.
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Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section

doi: 10.1007/s12583-020-1350-6

Abstract: The age of the Silurian Lower Red Beds in the Upper Yangtze region remains debatable. Twenty-four samples were collected for conodont biostratigraphical studies from the Paiyunan Formation in the Sanbaiti Section, Huaying, Sichuan Province. The conodont fauna from the Paiyunan Formation, together with the graptolites from the underlying Lungmachi Formation, indicates that the Lower Red Beds at Sanbaiti correspond to the lower Telychian. Comparative analysis indicates that most exposures of the Lower Red Beds in the Upper Yangtze region can be assigned, in general, to the Telychian Stage, except for several localities, where the Lower Red Beds can be roughly dated as an interval between the upper Aeronian and lower Telychian.

Zhongyang Chen, Peep Männik, Junxuan Fan, Chengyuan Wang, Qing Chen, Zongyuan Sun, Dongyang Chen, Chao Li. Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section. Journal of Earth Science, 2021, 32(3): 524-533. doi: 10.1007/s12583-020-1350-6
Citation: Zhongyang Chen, Peep Männik, Junxuan Fan, Chengyuan Wang, Qing Chen, Zongyuan Sun, Dongyang Chen, Chao Li. Age of the Silurian Lower Red Beds in South China: Stratigraphical Evidence from the Sanbaiti Section. Journal of Earth Science, 2021, 32(3): 524-533. doi: 10.1007/s12583-020-1350-6
  • The Silurian marine red beds are widely distributed in China, e.g., South China (Zhang et al., 2018, 2014; Rong et al., 2012, 2003, 1990; Geng et al., 1999; Chen and Rong, 1996), Tarim (Zhou and Chen, 1990), Ningxia and the Qilian Mountains (Zhang, 1962; Yin et al., 1958). Two suites of shallow marine red beds, known as the Lower Red Beds (LRBs) and the Upper Red Beds (URBs), respectively, were well developed in the Upper Yangtze region of South China during the Llandovery (Zhang et al., 2018, 2014; Rong et al., 2012, 2003; Chen and Rong, 1996; Ge et al., 1979, 1977). The LRBs is an informal name widely used by regional geologists, indicating the marine red beds between the underlying Majiaochong Formation and the overlying Xiushan Formation, or their coeval strata in the middle Llandovery of the Upper Yangtze Platform (e.g., Chen and Rong, 1996; Ge et al., 1979; Wang, 1976; Nanjing Institute of Geology and Palaeontology, Academia Sinica, 1974). In general, the formation of the marine red beds is considered to be an indication of oxidizing conditions at the sea bottom (Song et al., 2019; Rong et al., 2012; Kiipli, 2004).

    Debate on the age of the LRBs has lasted for nearly a half century (Rong et al., 2012, 1990; Wang C Y, 2011, 1998; Tang et al., 2010; Wang and Aldridge, 2010; Wang et al., 2010; Geng et al., 1999; Chen and Rong, 1996; Mu et al., 1986; Ge et al., 1979). Since the LRBs in most localities are unfossiliferous, the age of these beds are usually inferred by evidences of graptolites, conodonts and chitinozoans from the underlying or overlying strata (Rong et al., 2012; Chen and Rong, 1996).

    So far, conodonts within the interval of the LRBs have only been found at two localities. In the Yushitan Section, Ningqiang, Shaanxi Province, the Wangjiawan Formation, i.e., the LRBs yield conodont fauna of the upper Aeronian to lower Telychian Ozarkodina guizhouensis Conodont Biozone (CBZ) (Wang and Aldridge, 2010). In the Sanbaiti Section located in Huaying, Sichuan Province, the LRBs are represented by the lower member, and the lower part of the upper member of the Paiyunan (Baiyun'an) Formation. Conodonts from the Paiyunan Formation in this section were studied by Zhou and Yu (1984), who reported faunas of the Spathognathodus parahassi-Sp. guizhouensis and Sp. c elloni assemblage-biozones. Later, Wang and Aldridge (2010) revised the regional conodont biostratigraphy based on the generalized data from the Yangtze Platform and reidentified these assemblage- biozones as the Oz. guizhouensis CBZ and the Pterospathodus eopennatus Conodont Superbiozone (CSBZ), respectively.

    However, the data published by Zhou and Yu (1984) and their dating of the strata of the Paiyunan Formation are difficult to assess. All their identifications of conodonts listed in that publication are based on form taxonomy, but specimens were not illustrated. Also, no descriptions of taxa or information about location of collections were provided, making restudy of their material impossible. Their list of taxa allows the recognition of the M element of Oz. guizhouensis (Zhou, Zhai, and Xian) only: the form species Neoprioniodus magnus Zhou, Zhai, and Xian. Two other form species, Exochognathus luomianensis Zhou, Zhai, and Xian and Hibbardella trichonodelloides (Walliser), which were considered to be characteristic of the Sp. celloni assemblage-biozone (=Pt. eopennatus CSBZ) in Guizhou Province by Zhou and Yu (1984), are actually Sb element of Galerodus macroexcavatus (Zhou, Zhai, and Xian) and Sa element of Pseudolonchodina fluegeli (Walliser), respectively. Both species ranged from the Rhuddanian to Telychian (Wang and Aldridge, 2010). Thus, restudy of the conodont fauna from the Paiyunan Formation is necessary to date the unit reliably. This paper will concentrate on the age of this formation, mostly based on conodonts recovered in it, and also on occurrences of some graptolites in the Lungmachi (Longmaxi) Formation underlying the Paiyunan Formation in the succession. Considering data from other regions of the Upper Yangtze Platform, the age of the LRBs in this region will also be briefly discussed in general.

  • The Sanbaiti Section (also referred to as the Hongyan Coal Mine Section or the Yanwanggou Section in some publications) is located at the east wing of Huayingshan anticline, near the Hongyan Coal Mine of Xikou Town, Huaying, Sichuan Province (Fig. 1). In the section, the Silurian succession includes the Lungmachi, Hsiaohopa (Xiaoheba), and Paiyunan formations (Fig. 2; Wang et al., 2011; Lin et al., 1998). The lower part of the Lungmachi Formation consists of 133 m of black graptolitic shales, and the 90 m upper part of greenish grey mudstones with rare graptolites (Sun et al., 2019). The Hsiaohopa Formation is represented by 170 m grey sandstones and siltstones with rare graptolites, brachiopods, trilobites, cephalopods, and crinoids (Editorial Group of Regional Stratigraphic Chart of Sichuan Province, 1978). The Paiyunan Formation can be subdivided into two members: the lower member is dominated by 25 m of purplish red mudstones, and the upper member by 26 m of purplish red and greyish green calcareous mudstones and dolostones with abundant corals (Lin et al., 1998). Based on lithology, the upper member of the Paiyunan Formation can be further subdivided into two parts: the lower part dominated by purplish red and greyish green (calcareous) mudstones, and the upper part by yellowish dolostones with some interbeds of greyish green mudstones with an interval of grey mudstones at its top (Fig. 3; Wang G X, 2011). The ripple marks recognized from the lower member of the Paiyunan Formation at the nearby Liziya Section (Fig. 1) indicate a shallow-water marine environment, and the analysis of the succession of sedimentary facies of the Paiyunan Formation indicates a gradual deepening of seawater (Wang et al., 2013).

    Figure 1.  Sketch map showing (a) the location of the Sanbaiti Section and (b) geological map of the study area.

    Figure 2.  Succession of the Sanbaiti Section. Carb. Carboniferous; Fm. Formation; range of graptolite Spirograptus guerichi; conodont samples: filled rectangle. productive sample; hollow rectangle. barren sample; distribution of conodonts: solid line. continuous occurrence of a taxon; dotted line. sporadic occurrence of a taxon; filled circle. confident identification of a taxon; hollow circle. problematic identification of a taxon. Biozones identified in this study are marked and distinguished by grey shadings of different intensity.

    Figure 3.  Photographs showing the outcrop of the Sanbaiti Section. (a) The upper member of the Paiyunan Formation in the Sanbaiti Section. (b) Purplish red and greyish green mudstone in the lower part of the unit. (c) Yellowish dolostone with beds of greyish green mudstone in the upper part of the unit. Scale bar corresponds to 5 m (a) and 50 cm (b), (c).

  • Wang et al. (2013, 2011) found several conodont fragments while studying corals from the Sanbaiti Section. Later, in 2014 and 2016, some authors of these papers revisited the section and resampled for conodonts for this study. In total, 24 samples were collected from intervals of the greyish green calcareous mudstones and dolostones of the upper member of the Paiyunan Formation, and one sample from the base of the overlying Weining Formation (Fig. 2). No sample was collected from the purplish red mudstones. Nineteen of the processed samples were productive. Sample weight varied from four to six kilograms. Samples were dissolved in buffered 10% acetic acid. Fifteen of them were processed at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGP), and nine at the Hebei Geologic Surveying and Mapping Institute. Heavy liquid separation of residues was carried out in the laboratory at NIGP. A Leica M125 stereomicroscope and a LEO 1530 VP scanning electron microscope at NIGP were used for handpicking and photographing of specimens, respectively. The studied collection is deposited in NIGP (catalogue numbers 172747–172764). Conodont specimens are dark to blackish brown in color (CAI=2–3), indicating post-depositional burial temperatures of 60–200 ℃ (Rejebian et al., 1987; Epstein et al., 1977).

  • An abundant and diverse conodont association was recovered from the lower part of the upper member of the Paiyunan Formation (Fig. 2; samples AGH 1291 to 1704). The fauna includes Distomodus sp. (Figs. 4a and 4c), Galerodus macroexcavatus (Figs. 4k and 4l), Oulodus? sp. (Fig. 4i), Ozarkodina parahassi (Zhou, Zhai, and Xian) (Figs. 4m and 4n), Oz. cf. parainclinata (Zhou, Zhai, and Xian) sensu Wang and Aldridge (2010) (Figs. 4d and 4e), Oz. spp., Panderodus serratus Rexroad (Fig. 4r), Pand. spp., Pseudolonchodinafluegeli sensu Wang and Aldridge (2010) (Fig. 4g), and Walliserodus sp. (Fig. 4p). One questionable poorly preserved Pb element of Aulacognathus Mostler (identified as Aulacognathus? sp.) (Fig. 4o) was found in sample AGH 1292, and Pseudobelodella cf. spatha (Zhou, Zhai, and Xian) (Fig. 4q) in sample AGH 1295. Conodonts are rare in the upper part of the section (Fig. 2; samples AGH 1301 to 1310). G. macroexcavatus (Fig. 4j), Oul.? sp. (Fig. 4h), Oz. cf. parainclinata (Fig. 4f), and Pseudolonch. fluegeli were discovered from sample AGH 1303. Only a few conodonts were found in the uppermost part of the Paiyunan Formation: Oz. cf. parainclinata was identified from sample AGH 1307; Oz. sp. and D. sp. from sample AGH 1309 (Fig. 2). In sample AGH 1724 from the base of the overlying Weining Formation, some elements of the typical Carboniferous conodont genus Gnathodus Pander were recovered (Fig. 2).

    Figure 4.  Photomicrographs showing the selected conodonts from the Paiyunan Formation of the Sanbaiti Section. (a)–(c) Distomodus sp.; (a) 172747, Sa element, AGH 1300; (b) 172748, Sa element, AGH 1309; (c) 172749, fragment of S (?) element, AGH 1292. (d)–(f) Ozarkodina cf. parainclinata (Zhou, Zhai, and Xian, 1981) sensu Wang and Aldridge (2010); (d) 172750, Pa element, AGH 1299; (e) 172751, Pa element, AGH 1292; (f) 172752, Pb element, AGH 1303. (g) Pseudolonchodina fluegeli (Walliser, 1964) sensu Wang and Aldridge (2010), 172753, Pb element, AGH 1299. (h), (i) Oulodus? sp.; (h) 172754, Sa element, AGH 1303; (i) 172755, Pb element, AGH 1700. (j)–(l) Galerodus macroexcavatus (Zhou, Zhai, and Xian, 1981); (j) 172756, Sc element, AGH 1303; (k) 172757, Sb element, AGH 1704; (l) 172758, Pc? element, AGH 1292. (m), (n) Ozarkodina parahassi (Zhou, Zhai, and Xian, 1981); (m) 172759, Pa element, AGH 1701; (n) 172760, Pa element, AGH 1298. (o) Aulacognathus? sp., 172761, Pb? element, AGH 1292. (p) Walliserodus sp., 172762, AGH 1701. (q) Pseudobelodella cf. spatha (Zhou, Zhai, and Xian, 1981), 172763, AGH 1295. (r) Panderodus serratus Rexroad, 1967, 172764, AGH 1702. Scale bar corresponds to 200 μm (a)–(h) and 100 μm (i)–(r).

  • Zhou and Yu (1984) assigned the Paiyunan Formation to their Sp. parahassi-Sp. guizhouensis and Sp. celloni assemblage- biozones (=Oz. guizhouensis CBZ and Pt. eopennatus CSBZ according to Wang and Aldridge (2010), and in this paper). Such correlation, later adopted by Wang et al. (2011), dated the Paiyunan Formation as the upper Aeronian–lower Telychian. Our data indicate that the conodont fauna of the upper member of the Paiyunan Formation is dominated by long-ranging species, which are known to appear in China at least in the Rhuddanian, e.g., G. macroexcavatus (Figs. 4j4l) and Pseudolonch. fluegeli (Fig. 4g), or in the Aeronian, e.g., Oz. cf. parainclinata (Figs. 4d4f) and Oz. parahassi (Figs. 4m and 4n) (Wang and Aldridge, 2010; and references therein). Based on the data of Wang and Aldridge (2010), occurrences of the last two taxa are limited within the Aeronian. However, it was lately found that the known last occurrence of Oz. cf. parainclinata and Oz. parahassi in the Yangtze region is in the Pt. eopennatus CSBZ (Wang, 2013). Also, occurrence of Aulacognathus? sp. (Fig. 4o) in sample AGH 1292 might indicate that this sample, and also the lowermost horizon of the upper member of the Paiyunan Formation are of the Telychian, although Aulacognathus-lineage might have already appeared in the late Aeronian (Männik et al., 2016; Bischoff, 1986). However, the wide platform-like base of our specimens suggests that, most probably, it is a younger, Telychian form. Hence, the conodont evidence indicates that the upper member of the Paiyunan Formation (at least the interval between samples AGH 1291 and 1307, but probably also higher, up to AGH 1309; Fig. 2) is Telychian in age but, considering occurrence of Oz. cf.parainclinata and Oz. parahassi, not younger than the Pt.eopennatus CSBZ.

  • Graptolites are common in the Lungmachi Formation in the Sanbaiti Section, and are also reported from the Hsiaohopa Formation underlying the LRBs (Editorial Group of Regional Stratigraphic Chart of Sichuan Province, 1978). Unfortunately, no further researches on graptolites from the Hsiaohopa Formation have been carried out since they were found. In the characterization of the formation they were reported just as 'graptolites' (Editorial Group of Regional Stratigraphic Chart of Sichuan Province, 1978). Spirograptus guerichi Loydell, Štorch, and Melchin (Fig. 5) was identified from the upper part of the Lungmachi Formation. In older Chinese publications this graptolite was usually recorded as Sp. turriculatus (Barrande) (e.g., Chen and Rong, 1996; Chen, 1984; Jin et al., 1982). Sp. guerichi is the index species of the lowermost graptolite biozone (GBZ) in the Telychian (Loydell, 1992). Recently, it was also recovered from the Huaying drill core located not far from the studied section (Sun et al., 2019). Occurrence of Sp. guerichi suggests that the upper Lungmachi Formation in the Sanbaiti Section corresponds to the lowermost Telychian Sp. guerichi GBZ. Hence, the strata above, the Hsiaohopa and Paiyunan formations are surely of the Telychian but, considering the conodont information above, probably not younger than the early Telychian Pt. eopennatus CSBZ.

    Figure 5.  Graptolite Spirograptus guerichi Loydell, Štorch, and Melchin, 1993 from the Lungmachi Formation of the Sanbaiti Section (red arrows). Scale bar corresponds to 20 mm.

  • The LRBs are widely distributed on the Upper Yangtze Platform. Rong et al. (2012, 2003) subdivided their distribution area into four regions (Fig. 6). They also found that the strata of the LRBs in different localities are composed of material derived from different oldland regions, and their boundaries are diachronous (Rong et al., 2012). Below, the biostratigraphical evidences on the ages of the LRBs provided by Rong et al. (2012) are briefly summarized.

    Figure 6.  Paleogeographical distribution of the LRBs in the Upper Yangtze Region. Modified from Rong et al. (2012). A. Area on the north of the Cathaysian- Dianqian Oldland; B. area on the north of the Dianqian Oldland; C. four sites (C1–C4) in the vicinity of the Chuanzhong Oldland; D. area on the south of the Eyu Oldland. Numbered localities: 1. Wuxi, Chongqing Municipality; 2. Yichang, Hubei Province; 3. Qianjiang, Chongqing Municipality; 4. Daozhen, Guizhou Province; 5. Xiushan, Chongqing Municipality; 6. Shiqian, Guizhou Province; 7. Tongzi, Guizhou Province; 8. Kaili, Guizhou Province; 9. Daguan, Yunnan Province; 10. Butuo, Sichuan Province; 11. Erlangshan, Sichuan Province; 12. Weiyuan, Sichuan Province; 13. Huaying, Sichuan Province.

    The LRBs exposed in the area located on the north of the Cathaysian-Dianqian Oldland (Figs. 6 and 7, Region A), are represented mostly by the Rongxi Formation but also by parts of the Hanchiatien Formation, the Shamao Formation, and the Wengxiang Group (Rong et al., 2012, figs. 3A and 5). In several localities of the region, the characteristic early Telychian fossils were recognized, especially from the underlying strata of the LRBs. For example, in the Wuxi drill core in Chongqing Municipality (Fig. 6, Locality 1), where the LRBs are represented by the base of the Hanchiatien Formation (purplish red silty mudstones), the graptolite Sp. guerichi was recovered from its underlying Lungmachi Formation (Wang et al., 2017), and the conodont Pt. eopennatus Männik was recognized from its overlying strata (the uppermost Hanchiatien Formation). In Yichang of Hubei Province (Fig. 6, Locality 2), where the LRBs are represented by the lowermost part of the second member of the Shamao Formation (purplish red calcareous sandstones), the conodont Pt. eopennatus was identified from both of its underlying Lojoping Formation and overlying middle to upper part of the second member of the Shamao Formation (Wang et al., 1987). The graptolite Pristiograptus xiushanensis Mu, occurring within an interval from the latest Aeronian Stim. halli to early Telychian Sp. guerichi GBZs (Loydell et al., 2015), was identified from the Hsiaohopa Formation underlying the Rongxi Formation (LRBs; purplish red and greyish green silty mudstones and argillaceous siltstones) in Xiushan (Chongqing Municipality; Fig. 6, Locality 5; Ge et al., 1979), and, as indicated by conodonts, the Xiushan Formation overlying the LRBs is not older than the early Telychian Pt. eopennatus CSBZ (Chen et al., 2016; Wang et al., 2010). Thus, the Rongxi Formation (LRBs) in Xiushan can be assigned to the early Telychian, based on the known biostratigraphical evidences. The graptolite Streptograptus plumosus (Baily), chitinozoans Eisenackitina daozhenensis Geng and Ancyrochitina brevicollis Geng were discovered together from the lower and middle parts of the Hanchiatien Formation underlying the LRBs (the upper part of this formation, dominated by purplish red silty mudstones, is regarded as the LRBs) in Dao- zhen, Guizhou Province (Fig. 6, Locality 4; Geng, 1986). Str. plumosus is common in the Sp. guerichi to Sp. turriculatus GBZs (e.g., Worsley et al., 2011; Štorch and Kraft, 2009; Loydell, 1990; Chen, 1986; Baily, 1871). E. daozhenensis and A. brevicollis are regarded as the index species of the eponymous chitinozoan biozones (ChBZs), which were correlated with the Sp. guerichi to M. crenulata GBZs (Tang et al., 2010). These two chitinozoan species were also discovered in the Hanchiatien Formation (underlying and overlying the LRBs) in Tongzi (Fig. 6, Locality 7; Geng et al., 1997), in the Rongxi Formation (in the LRBs) in Shiqian (Fig. 6, Locality 6; Geng et al., 1997), and in the Wengxiang Group (in and overlying the LRBs) in Kaili (Fig. 6, Locality 8; Tang et al., 2010) of Guizhou Province.

    The LRBs recognized in four separated areas in the vicinity of the Chuanzhong Oldland (Figs. 6 and 7, Region C), i.e., the four sub-regions in sense of Rong et al. (2012, fig. 3C), can also be assigned to the Telychian based on the fauna from the strata underlying or overlying the LRBs. In the Erlangshan area of Sichuan Province (Fig. 6, Region C1, Locality 11), the LRBs correspond to the middle part of the Changyanzi Formation (purplish red and greyish green calcareous mudstones), which can be assigned to the Telychian based on discovery of the conodont Aulacognathus bashanensis Ding and Li (recorded as Aulacognathus bullatus) in the overlying upper part of the Changyanzi Formation, and the graptolite Sp. turriculatus in the underlying Luoquanwan Formation (Wang and Aldridge, 2010; Ye, 1991; Jin et al., 1989). Recognition of the graptolite Sp. guerichi from the middle part of the Lungmachi Formation in the drill cores of Weiyuan, Sichuan Province (Fig. 6, Region C2, Locality 12; Wang et al., 2015) indicates that the overlying uppermost Lungmachi Formation (LRBs; purplish red and greyish green mudstones; Editorial Group of Regional Stratigraphic Chart of Sichuan Province, 1978) cannot be older than the Sp. guerichi GBZ. Our data presented in this study indicate that the Paiyunan Formation in the Huayingshan area (Fig. 6, Region C3, Locality 13) is also of the early Telychian in age. Although Rong et al. (2012) did not include Ningqiang in the southern Shaanxi Province in their paleogeographical map, it in fact belongs to Region C4 (Zhang, X. L., personal communication, 2020). The Wangjiawan Formation (LRBs; purple and grey-yellowish silty shales and siltstones) in Ningqiang corresponds to the late Aeronian to early Telychian Oz. guizhouensis CBZ (Wang and Aldridge, 2010) based on the conodonts. However, considering the recognition of the chitinozoan E. daozhenensis and graptolite Sp. guerichi from its underlying Cuijiagou Formation (Geng et al., 1997; Chen, 1984), the Wangjiawan Formation evidently corresponds to the lower Telychian.

    The LRBs exposed in the localities above can be dated reliably as the early Telychian. However, based on the biostratigraphical information available, the LRBs recognized in several other localities can only be dated as the late Aeronian to early Telychian so far, especially in some localities of Region A (Figs. 6, 7). For example, conodonts of the Oz. guizhouensis CBZ were recovered only from the Xiushan Formation overlying the Rongxi Formation (LRBs; purplish red and greyish green silty mudstones and argillaceous siltstones) in the succession in Qianjiang (Chongqing Municipality; Fig. 6, Locality 3), indicating that the LRBs here were not younger than the Oz. guizhouensis CBZ (Wang et al., 2010). As the Oz. guizhouensis CBZ corresponds to an interval from the upper Aeronian to lower Telychian (Wang and Aldridge, 2010), it is not possible to tell whether the LRBs in these localities are of the Aeronian or Telychian in age. Similarly, in the area located on the north of the Dianqian Oldland (Figs. 6, 7, Region B), the LRBs are mostly dated as the late Aeronian to early Telychian. In Daguan (Yunnan Province; Fig. 6, Locality 9), the upper part of the Sifengya Formation (LRBs; purplish red shales with interbeds of thin-bedded argillaceous limestones) can be assigned to an interval between the Oz. guizhouensis CBZ and Pt. eopennatus CSBZ based on conodonts from its underlying and overlying strata (Wang, 2013). Although Wang et al. (2014) correlated the Wuke Formation (LRBs; purplish red and greyish green siltstones and silty mudstones) in Butuo of Sichuan Province (Fig. 6, Locality 10) with the Telychian based on brachiopods and corals from the underlying Shimenkan Formation, studies of conodonts from the limestone interbeds of both the underlying Shimenkan and overlying Daluzhai formations are still necessary to date the Wuke Formation more reliably. Also, the comprehensive biostratigraphical analysis of LRBs should be taken to date these strata in the area located on the south of the Eyu Oldland (Fig. 6, Region D).

    In summary, the LRBs in most localities of the Upper Yangtze region can surely be dated as the early Telychian (Fig. 7). However, in several localities, such as Qianjiang and Daguan, the LRBs can only be roughly dated as an interval from the late Aeronian to early Telychian. Further integrated and detailed biostratigraphical studies are required to date the LRBs in such localities more reliably.

    Figure 7.  Diagrams showing the dating of the LRBs based on the current data (indicated in red colors). The orange line shows the boundary between the Aeronian and Telychian stages. The numbers indicated the localities listed in Fig. 6. The two sections on the right are those with possible Aeronian-Telychian LRBs. The biozonations in China are from the following sources: graptolite, Ogg et al. (2016); conodont, Wang and Aldridge (2010); chitinozoan, Tang et al. (2010) and Geng et al. (1997). Fm. Formation; HGX Mbr. Huanggexi Member. The abbreviations in blue color indicate faunas of different biozones useful fbr dating and stratigraphic correlation: Ab.Ancyrochitina brevicollis ChBZ; Al. Angochitina longicollis ChBZ; Ed. Eisenackitina daozhenensis ChBZ; Og. Ozarkodina guizhouensis CBZ; Pe. Pterospathodus eopennatus CSBZ; Sg. Spirograptus guerichi GBZ; St. Spirograptus turriculatus GBZ.

    The early Telychian marine red beds are also known outside China, e.g., in Baltica and Laurentia paleocontinents. In the Baltoscandian Paleobasin, well-dated early Telychian red beds are recorded in the Jūrmala Formation (in Latvia) and the Velise Formation (in Estonia). In both regions the red beds were assigned to the Pt. eopennatus CSBZ (Männik, 2010; Loydell et al., 2003). McLaughlin et al. (2012) discussed the Telychian marine red beds and their probable origin occurring in the Appalachian Basin, USA. The lowermost Telychian red beds in that region also come from the Pt. eopennatus CSBZ. However, the mechanism of the formation of these marine red beds from in the early Telychian might be different. The lower Telychian LRBs in the Upper Yangtze Platform of South China were interpreted to be formed during a regressive stage of the evolution of the basin (Rong et al., 2012), whereas those in the Baltoscandian region probably during the trangression (Kiipli, 2004).

  • Based on conodonts from the Paiyunan Formation and graptolites from its underlying Lungmachi Formation, the Paiyunan Formation can be assigned to an interval from the Sp. guerichi GBZ to Pt. eopennatus CSBZ. The LRBs occurring on the Upper Yangtze Platform are of the early Telychian in age in most localities, but in several localities roughly correspond to the upper Aeronian to lower Telychian.

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