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1 doi: /nature Depositional Environment The fossiliferous Lantian Member II is interpreted to have deposited in open marine slope-basinal facies. This interpretation is supported by several lines of evidence. First, regional mapping shows that the Yangtze Block is a ESE facing passive continental margin during the early Ediacaran Period, with sandstone-dominated facies to the west giving way to shale-dominated facies to the east 1 (Fig. 1). These two facies are separated by a transitional siltstone facies and carbonate shoals. The Lantian locality sits in the shale facies (Fig. 1) that is widely and continuously distributed on the Yangtze Block 1. This facies continuity suggests that the Lantian black shales were not deposited in an isolated lake 2 or restricted lagoon 3. Second, the lack of wave- or current-influenced sedimentary structures suggests that Lantian Member II black shales were deposited below the wave base. The shales are finely laminated (Supplementary Fig. 1a) and show no evidence of grading (Supplementary Fig. 1b), suggesting that they were deposits from suspension settling rather than distal turbidites. Further, transportation of soft-bodied macrofossils within turbidity current would result in fossil preservation within beds rather than between beds (or on bedding surface), because the fossils would be entrained within turbidity currents. However, the Lantian fossils are mostly preserved on the bedding surface, inconsistent with transportation by turbidity current. Additionally, transportation within turbidity current would typically result in folding and deformation of soft-bodied fossils, which are not common among the Lantian fossils. Third, the lower Lantian Formation contains no sandstone or carbonate interbeds that would indicate shallow-water facies. It is dominated by organic- and pyrite-rich black shales that typically weather to buff colors (Supplementary Fig. 1a) because of the oxidation of pyrite. The in-situ preservation of epibenthic macroalgae in the Lantian Formation suggests deposition within the photic zone. Thus, the lower Lantian Formation was not deposited in abyssal environment like the Conception Group in Newfoundland. Still, the weight of sedimentary and regional geological evidence suggests that it was deposited in a quiet marine environment below the wave base. This is consistent with the random orientation of exceptionally preserved and minimally fragmented macrofossils in the lower Lantian Formation (Supplementary Fig. 2). The random orientation of benthic marcoalgae also indicates that deposition of the lower Lantian Formation was not influenced by deep-water 1

processes such as turbidity current or contour current, which would have resulted in unimodal or bimodal orientation of tethered macrofossils, as is the case in the Mistaken Point fossils in

(b) Plane light photomicrograph of fossiliferous black shale in lower Lantian Formation. Note the lack of graded beds. Dark layers are organic- and pyrite-rich. Stratigraphic up direction on top.

2 processes such as turbidity current or contour current, which would have resulted in unimodal or bimodal orientation of tethered macrofossils, as is the case in the Mistaken Point fossils in Newfoundland 4,5. Supplementary Figure 1. (a) Field photograph of weathered black shales at excavation site near Lantian in southern Anhui Province. Rock hammer (30 cm long) for scale. (b) Plane light photomicrograph of fossiliferous black shale in lower Lantian Formation. Note the lack of graded beds. Dark layers are organic- and pyrite-rich. Stratigraphic up direction on top. Supplementary Figure 2. Slab showing multiple specimens with random orientations. Note that the two specimens in upper part of the photograph are oriented in opposite directions. Scale bar 10 mm. 2. Stratigraphic Correlation and Age Constraints We estimate that the fossiliferous lower Lantian Formation is of early Ediacaran age, somewhere between 635 Ma and 576 Ma. Our estimate is based on a robust correlation with the Doushantuo Formation in the Yangtze Gorges area, which is constrained by several 2

3 radiometric ages. The correlation between the lower Lantian Formation and the lower Doushantuo Formation is supported by regional mapping, lithostratigraphy, and chemostratigraphy. The lithostratigraphic sequence of the Lantian Formation (in southern Anhui) and Doushantuo Formation (in the Yangtze Gorges area) is similar, including three depositional sequences. The first sequence consists of a cap dolostone (Member I) followed by a shale-rich member (Member II). The second depositional sequence is a carbonate rich member (approximately equivalent to Member III: a dolostone unit overlain by a ribbon rock unit, Supplementary Fig. 3). The third depositional sequence is represented by another black shale unit (Member IV) and the lower part of the Dengying Formation. As discussed above, black shales of early Ediacaran age (Member II) can be traced throughout much of the Yangtze Block. In the Yangtze Gorges area, which was situated in the inner platform in early Ediacaran Period, the lower Doushantuo Formation contains some argillaceous dolostone beds, but black shale represents the dominant facies. The lithostratigraphic correlation between the lower Lantian Formation and lower Doushantuo Formation is further supported by δ 13 C chemostratigraphic data. Despite the abundance of shale, the Lantian Formation does contain two carbonate units. The basal Lantian cap dolostone has sedimentary features (e.g., sheet cracks) and δ 13 C values (around 5 ) 6,7 similar to the 635 Ma basal Doushantuo cap dolostone (with the negative δ 13 C excursion EN1) 8,9. The upper Lantian carbonate (Member III) is characterized with a strongly negative δ 13 C excursion 7 that is remarkably similar to the negative δ 13 C excursion EN3 in the upper Doushantuo Formation (Member III) of the Yangtze Gorges area 8 ; importantly, both excursions occur in similar facies (thick-bedded dolostone overlain by ribbon rock; Supplementary Fig. 3). In the Yangtze Gorges area, a zircon U-Pb TIMS age of 635.2±0.6 Ma is reported from within the cap dolostone (Member I) 10, a zircon U-Pb TIMS age of 632.5±0.5 Ma from the lower Member II black shale 10, a Re-Os age of 593±17 Ma from the lower Member IV black shale 11, and a zircon U-Pb TIMS age of 551.1±0.7 Ma from the uppermost Member IV 10. In addition, Kendall et al. reported a Re-Os age of 598±16 Ma from Doushantuo Member IV black shale in the Yangtze Gorges area 12, which is consistent with the 593±17 Ma Re-Os age 11, although Kendall et al. cautioned the interpretation of the Re-Os ages because of possible heterogeneity of the black shale samples 12. Considering their analytical uncertainty, these radiometric dates constrain the minimum age range of Member IV between 576 Ma and Ma. Thus, the maximum age range of Member II is between Ma and 576 Ma. In 3

4 other words, Doushantuo Member II (and by extension the fossiliferous Lantian Member II) is likely than 576 Ma. Additionally, Liu et al. 13 reported a zircon U-Pb SHRIMP age of 614±7.6 Ma from an ash bed in the Doushantuo Formation at the Zhangcunping section (Supplementary Fig. 4), about 60 km to the NE of the Yangtze Gorges area. This ash bed was collected from a dolostone unit that overlies the lower Doushantuo black shale but underlies an exposure surface representing a mid-doushantuo sequence boundary. A traditional correlation 14 using the mid-doushantuo sequence boundary, biostratigraphic data, and δ 13 C chemostratigraphic data would correlate this ash bed to a horizon within the upper part of Doushantuo Member II in the Yangtze Gorges. Adopting this correlation, the 614±7.6 Ma age gives a direct age constraint on Doushantuo Member II and Lantian Member II. Similarly, a Pb-Pb age of 599±4 Ma 15 has been reported from the upper Doushantuo phosphorite at Weng an, above the mid-doushantuo exposure surface (Supplementary Fig. 4). Again, adopting the traditional correlation between upper Doushantuo phosphorite/dolostone at Weng an and Doushantuo Member III/IV in the Yangtze Gorges 8, the 599±4 Ma age provides a minimum age constraint on Doushantuo Member II. Together, these two ages constrain the mid-doushantuo sequence boundary between 614±7.6 Ma and 599±4 Ma, and provide further support for a 576 Ma minimum age of Doushantuo Member II which lies below the sequence boundary. An alternative correlation has been proposed that the upper Doushantuo dolostone above the mid-doushantuo exposure surface at Zhangcunping and Weng an be correlated with the lower Doushantuo Member II in the Yangtze Gorges area 16. This alternative correlation was motivated by the presumed correlation of EN2 and the associated mid-doushantuo flooding surface or sequence boundary (see Supplementary Fig. 4) with the 582 Ma Gaskiers glaciation 10,16. Not only is this alternative correlation inconsistent with lithostratigraphy and sequence stratigraphy, it is also in disagreement with available biostratigraphic data: the lower Doushantuo Member II in the Yangtze Gorges hosts an acritarch assemblage that is distinct from acritarchs from the upper Doushantuo dolostone at Zhangcunping and upper Doushantuo phosphorite/dolostone at Weng an 13,14,17. Finally, this alternative correlation is inconsistent with chemostratigraphic data (Fig. 1; Supplementary Fig. 4) which show the presence of EP2 in the upper Doushantuo dolostone at Zhangcunping, Weng an, and Yangtze Gorges area 8. We would like to emphasize that the minimum age of 576 Ma for the Lantian biota is derived from the correlation between Lantian and Yangtze Gorges areas; it is corroborated by, but not dependent on, the validity of the traditional correlation between Weng an, Zhangcunping, and Yangtze Gorges areas. Taken at face value, 4

a minimum age of 576 Ma still allows a marginal temporal overlap between the Lantian biota and the 579 565 Ma Avalon biota 18-20.

5 a minimum age of 576 Ma still allows a marginal temporal overlap between the Lantian biota and the Ma Avalon biota However, fossiliferous Lantian Member II is separated from Lantian Member IV (= Doushantuo Member IV, from which the 593±17 Ma age came) by a complete depositional sequence, and the fossiliferous horizon is ~20 m below Lantian Member III. Thus, we consider the Lantian biota is likely older than the Avalon biota Beyond South China, the correlation becomes more tenuous, particularly the correlation with the exceptionally dated 582 Ma Gaskiers glaciation in Newfoundland 21. It is widely accepted that EN3 in the Yangtze Gorges area is correlated with the Shuram negative δ 13 C excursion 22-26, but the temporal relationship between the Shuram and the Gaskiers is controversial. Condon et al. 10 and Sawaki et al. 16, partly driven by the assumption that the Shuram event could not have lasted >10 myr, correlated the mid-doushantuo sequence boundary and the associated δ 13 C feature EN2 (=Shuram) with the Gaskiers glaciation. However, this correlation is in direct conflict with the 599±4 Ma Pb-Pb age from Weng an and the 593±17 Ma Re-Os age from the Yangtze Gorges, both from levels above EN2 and above the mid-doushantuo flooding surface 15. Thus, we accept the alternative correlation that EN3 (or Shuram) started Ma and may have lasted more than 10 myr. Supplementary Figure 3. Ribbon rocks (limestone and dolostone intercalations) in the upper Doushantuo Formation in the Yangtze Gorges area (a) and the upper Lantian Formation in southern Anhui (b). Both are characterized by strongly negative δ 13 C values down to 10. Limestone is light grey in color, whereas dolostone is dark grey [buff color in (a) due to weathering]. Coin in (a) is 21 mm in diameter. 5

6 Supplementary Figure 4. Locality maps and stratigraphic columns, with biostratigraphic, chemostratigraphic, and geochronological data. (a) Yangtze Block (YB) in relation to North China Block (NCB) and Tarim Block (TB). (b) Early Ediacaran facies distribution on Yangtze Block (simplified from Zhu et al. 1 ), showing the localities of Yangtze Gorges (YG), Lantian (LT), Zhangcunping (ZCP), and Weng an (WA). (c) Lantian section. Carbonate δ 13 C data for basal Lantian cap dolostone (EN1) from Zhou et al. 6, and those for upper Lantian Formation from this study (Supplementary Table 1). (d) Jiulongwan (Yangtze Gorges) section. δ 13 C and radiometric dates from previously published data 10,11,27,28. Stratigraphic thickness scale bar applies to the Doushantuo Formation only. DY, Dengying Formation. (e) Weng an section. δ 13 C and radiometric dates from previously published data 15,17,29. Cryo: Cryogenian. (f) Zhangcunping section. Radiometric date from Liu et al. 13. δ 13 C data from this study (Supplementary Table 2). The two acritarch biozones are recognized by McFadden et al

7 3. Estimate of Taxonomic Diversity Yan et al. 30 described 11 taxa of macroscopic carbonaceous compression fossils from the lower Lantian Formation. Later, Chen et al. 31 reported 13 additional species from the same horizon. Yuan et al. 3 carried out a systematic revision of the Lantian fossils. After synonymizing some taxa described by Yan et al. 30 and Chen et al. 31, Yuan et al. 3 estimated that there are 12 forms of macroscopic algal fossils in the Lantian biota, including 10 named taxa and 2 unnamed forms. Our new excavation revealed at least 6 new forms, bringing the total number of morphotaxa to be 18. We realize that the taxonomy of the Lantian fossils is complicated by ontogenetic and preservational issues. For example, as mentioned in the main text, there may be possible ontogenetic relationship between Type A, Type B, and Flabellophyton despite the lack of transitional forms. Also, the same taxon may appear very different depending on how it is compressed, a complication that has been long appreciated by paleontologists working on the Burgess Shale and Chengjiang biotas 32,33. Indeed, a case may be made that some specimens described as Anhuiphyton lineatum in Yuan et al. 3 could represent a species of Flabellophyton compressed top-down (as opposed to sideway or lateral compression typically seen in Flabellophyton species). Realizing these ontogenetic and preservational issues, we estimate that there are ~15 distinct morphotaxa in the Lantian biota. 4. δ 13 C and δ 18 O Data δ 13 C and δ 18 O analysis followed standard procedures described in the literature 34. Fresh carbonate samples were cut into chips. Carbonate powders were made from fresh chips for isotope analysis. CO 2 was extracted using standard offline technique, with powder reacting with concentrated H 3 PO 4 at 25 C for 12 h. Isotope ratios were measured using a Finnigan MAT 253 mass spectrometer at Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. δ 13 C and δ 18 O are reported as deviation from VPDB. Analytical precision is better than 0.1 for δ 13 C and 0.3 for δ 18 O. No effort was made to distinguish dolomite and calcite mineral facies as Zhao and Zheng did 7. δ 18 O values were not corrected for dolomite. 7

8 Supplementary Table 1. Carbonate δ 13 C and δ 18 O values (, VPDB) of the Lantian Formation near Lantian Village in southern Anhui Province. Note that stratigraphic height measurements use a datum at the base of the third member of the upper Lantian Formation, rather than the base of the Lantian Formation. Zhao and Zheng 7 reported similar δ 13 C data (around 10 ) from equivalent strata at a nearby section, but their δ 18 O values (around 20 ) are much lower. They interpreted the extremely low δ 18 O values as evidence for isotope exchange with glacial meltwater. Alternatively, such low δ 18 O values could indicate diagenetic alteration. Regardless, the similar δ 13 C values between the two measured sections suggest that the δ 13 C values were buffered against isotopic re-equilibration despite oxygen isotope exchange. sample # lithology Height (m) δ 13 C VPDB δ 18 O VPDB 10LJL-01 limestone LJL-02 limestone LJL-03 dolostone LJL-04 dolostone LJL-05 dolostone LJL-06 dolostone LJL-07 dolostone LJL-09 limestone LJL-11 limestone LJL-12 limestone LJL-13 dolostone LJL-14 dolostone LJL-15 limestone LJL-15A dolostone LJL-16 dolostone LJL-17 dolostone LJL-18 dolostone LJL-19 dolostone LJL-20 dolostone LJL-21 limestone LJL-22 dolostone LJL-23 dolostone

9 Supplementary Table 2. Carbonate δ 13 C and δ 18 O values (, VPDB) of the Doushantuo and lower Dengying Formations at the Zhangcunping section, Hubei Province. Contact between the Doushantuo Formation and the underlying Nantuo Formation is not well exposed. Stratigraphic height measurements were made using a datum at the base of the exposed Nantuo Formation. sample # Height (m) δ 13 C VPDB δ 18 O VPDB 05WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG WJG ZCP ZCP ZCP

10 ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP ZCP

11 References 1. Zhu, M., Zhang, J. & Yang, A. Integrated Ediacaran (Sinian) chronostratigraphy of South China. Palaeogeogr. Palaeoclimatol. Palaeoecol. 254, 7-61 (2007). 2. Bristow, T. F. et al. Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation. Proc. Natl. Acad. Sci. USA 106, (2009). 3. Yuan, X., Li, J. & Cao, R. A diverse metaphyte assemblage from the Neoproterozoic black shales of South China. Lethaia 32, (1999). 4. Seilacher, A. Vendobionta and Psammocorallia: lost constructions of Precambrian evolution. Journal of the Geological Society, London 149, (1992). 5. Wood, D. A., Dalrymple, R. W. & Narbonne, G. M. Paleoenviromental analysis of the late Neoproterozoic Mistaken Point and Trepassey formations, Southeastern Newfoundland. Can. J. Earth Sci. 40, (2003). 6. Zhou, C. et al. The Neoproterozoic tillites at Lantian, Xiuning County, Anhui Province. J. Stratigr. 25, (2001). 7. Zhao, Y.-Y. & Zheng, Y.-F. Stable isotope evidence for involvement of deglacial meltwater in Ediacaran carbonates in South China. Chem. Geol. 271, (2010). 8. Zhou, C. & Xiao, S. Ediacaran δ 13 C chemostratigraphy of South China. Chem. Geol. 237, (2007). 9. Jiang, G., Kennedy, M., Christie-Blick, N., Wu, H. & Zhang, S. Stratigraphy, sedimentary structures, and textures of the late Neoproterozoic Doushantuo cap carbonate in South China. J. Sediment. Res. 76, (2006). 10. Condon, D. et al. U-Pb ages from the Neoproterozoic Doushantuo Formation, China. Science 308, (2005). 11. Zhu, B., Becker, H., Jiang, S.-Y., Pi, D.-H. & Fischer-Gödde, M. Re-Os geochronology of black shales from the Doushantuo Formation, Yangtze Platform, South China. Geol. Soc. Am. Programs Abstracts 42(5), 463 (2010). 12. Kendall, B., Creaser, R. A. & Selby, D. 187 Re 187 Os geochronology of Precambrian organic-rich sedimentary rocks. Geological Society of London Special Publications 326, (2009). 13. Liu, P., Yin, C., Gao, L., Tang, F. & Chen, S. New material of microfossils from the Ediacaran Doushantuo Formation in the Zhangcunping area, Yichang, Hubei Province and its zircon SHRIMP U-Pb age. Chin. Sci. Bull. 54, (2009). 14. McFadden, K. A., Xiao, S., Zhou, C. & Kowalewski, M. Quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the Ediacaran Doushantuo Formation in the Yangtze Gorges area, South China. Precambrian Res. 173, (2009). 15. Barfod, G. H. et al. New Lu-Hf and Pb-Pb age constraints on the earliest animal fossils. Earth Planet. Sci. Lett. 201, (2002). 16. Sawaki, Y. et al. The Ediacaran radiogenic Sr isotope excursion in the Doushantuo Formation in the Three Gorges area, South China. Precambrian Res. 176, (2010). 17. Zhou, C., Xie, G., McFadden, K., Xiao, S. & Yuan, X. The diversification and extinction of Doushantuo-Pertatataka acritarchs in South China: Causes and biostratigraphic significance. Geol. J. 42, (2007). 18. Narbonne, G. M. The Ediacara Biota: Neoproterozoic origin of animals and their ecosystems. Ann. Rev. Earth Planet. Sci. 33, (2005). 11

12 19. van Kranendonk, M. J. in The Concise Geological Time Scale eds J. G. Ogg, G. Ogg, & F. M. Goldstein) (Cambridge University Press, 2008). 20. Narbonne, G. M. Modular construction of early Ediacaran complex life forms. Science 305, (2004). 21. Hoffman, P. F. & Li, Z.-X. A palaeogeographic context for Neoproterozoic glaciation. Palaeogeogr. Palaeoclimatol. Palaeoecol. 277, (2009). 22. Le Guerroue, E., Allen, P. A., Cozzi, A., Etienne, J. L. & Fanning, M. 50 Myr recovery from the largest negative δ 13 C excursion in the Ediacaran ocean. Terra Nova 18, (2006). 23. Fike, D. A., Grotzinger, J. P., Pratt, L. M. & Summons, R. E. Oxidation of the Ediacaran ocean. Nature 444, (2006). 24. Halverson, G. P., Hoffman, P. F., Schrag, D. P., Maloof, A. C. & Rice, A. H. N. Toward a Neoproterozoic composite carbon-isotope record. GSA Bulletin 117, ; doi: /B (2005). 25. Xiao, S. in From Evolution to Geobiology: Research Questions Driving Paleontology at the Start of a New Century eds P. H. Kelly & R.K. Bambach) (The Paleontological Society, 2008). 26. Le Guerroue, E. & Cozzi, A. Veracity of Neoproterozoic negative C-isotope values: The termination of the Shuram negative excursion. Gondwana Res. 17, (2010). 27. McFadden, K. A. et al. Pulsed oxygenation and biological evolution in the Ediacaran Doushantuo Formation. Proc. Natl. Acad. Sci. USA 105, (2008). 28. Jiang, G., Kaufman, A. J., Christie-Blick, N., Zhang, S. & Wu, H. Carbon isotope variability across the Ediacaran Yangtze platform in South China: Implications for a large surface-to-deep ocean δ 13 C gradient. Earth Planet. Sci. Lett. 261, (2007). 29. Chen, D., Dong, W., Zhu, B. & Chen, X. P. Pb-Pb ages of Neoproterozoic Doushantuo phosphorites in South China: Constraints on early metazoan evolution and glaciation events. Precambrian Res. 132, (2004). 30. Yan, Y., Jiang, C., Zhang, S., Du, S. & Bi, Z. Research of the Sinian System in the region of western Zhejiang, northern Jiangxi, and southern Anhui provinces. Bull. Nanjing Inst. Geol. Mineral Resources (Chin. Acad. Geol. Sci.) 12, (1992). 31. Chen, M., Lu, G. & Xiao, Z. Preliminary study on the algal macrofossils -- Lantian Flora from the Lantian Formation of Upper Sinian in southern Anhui. Bulletin Institute of Geology, Academia Sinica No.7, (1994). 32. Whittington, H. B. The Burgess Shale. (Yale University Press, 1985). 33. Hou, X. et al. The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life. (Blackwell Science, 2004). 34. Kaufman, A. J. & Knoll, A. H. Neoproterozoic variations in the C-isotope composition of sea water: Stratigraphic and biogeochemical implications. Precambrian Res. 73, (1995). 12

Supporting Information

Supporting Information Yin et al. 10.1073/pnas.1414577112 SI Text Geological Setting The Doushantuo Formation in the Weng an phosphorite mining area, Guizhou Province, South China (Fig. S1A), crops out