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Gondwana Research 19 (2011) 831–849

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GR Focus Stratigraphy and paleogeography of the Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China

Ganqing Jiang a,⁎, Xiaoying Shi b, Shihong Zhang b, Yue Wang c, Shuhai Xiao d a Department of Geoscience, University of Nevada, Las Vegas, NV 89154-4010, USA b School of Earth Sciences and Resources, China University of Geosciences, Beijing, 100083, China c School of Resources and Environments, Guizhou University, Guiyang, 550003, China d Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA article info abstract

Article history: The Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China contains exceptionally well-preserved Received 1 November 2010 fossils of multicellular eukaryotes including early animals, and it is one of the most intensively investigated Received in revised form 15 January 2011 Ediacaran units in the world. Various stratigraphic methods including litho-, chemo-, bio-, and sequence- Accepted 18 January 2011 stratigraphy have been applied to establish a stratigraphic framework for the Doushantuo Formation, but so far Available online 26 January 2011 regional correlation across the basin relies heavily on two distinctive marker beds, the cap carbonate at the base Handling Editor: M. Santosh and the organic-rich black shale at the top of the Doushantuo Formation. The majority of the Doushantuo Formation in the Yangtze platform was deposited on a rimmed carbonate shelf, with a shelf margin shoal complex Keywords: that restricted the shelf lagoon from the open ocean. Large facies variations are observed in the shallow margins of Ediacaran the shelf lagoon and in the shelf margin-to-slope transition, where depositional environments were near the Doushantuo Formation chemocline of the stratified, anoxic/euxinic shelf lagoon and of the broader Nanhua basin, respectively. Paleogeography Chemocline instability in the shelf lagoon and in the Nanhua basin caused local geochemical cycling, resulting in Early animals significant variations in carbon and sulfur isotopes and in redox-sensitive elemental concentrations. Most benthic Yangtze platform eukaryotic fossils (including animal fossils) of the Doushantuo Formation have been found from the shallow South China margins of the shelf lagoon and from the shelf margin–slope transition, but rarely from deep-water environments that may have been below the chemocline for most of the Doushantuo time, implying the sensitivity of eukaryotes to paleogeographically controlled chemocline fluctuations. © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Contents

1. Introduction ...... 832 2. Development of the Ediacaran Yangtze Platform ...... 832 3. Stratigraphy of the Doushantuo Formation ...... 834 3.1. Notes on Some Representative Sections ...... 834 3.2. Lithostratigraphic Marker Beds ...... 836 3.2.1. The Doushantuo Cap Carbonate ...... 836 3.2.2. The Organic-Rich Black Shale at the Top of the Doushantuo Formation ...... 837 3.3. Sequence Stratigraphy ...... 838 3.4. Chemostratigraphy and Biostratigraphy ...... 838 4. Paleogeography of the Doushantuo Formation ...... 838 4.1. Facies Distribution Across the Shelf-to-Basin Transects ...... 838 4.2. Depositional Model and Paleogeographic Reconstruction ...... 840 5. Discussion ...... 842 5.1. Paleogeographic Influence on Geochemical Variations ...... 842 5.2. Basin Restriction and Phosphorite Deposition ...... 844 5.3. Paleogeographic Distribution of the Doushantuo Biotas ...... 845

⁎ Corresponding author. Tel.: +1 702 895 2708; fax: +1 702 895 4064. E-mail address: [email protected] (G. Jiang).

1342-937X/$ – see front matter © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2011.01.006 Author's personal copy

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6. Conclusion ...... 845 Acknowledgements ...... 847 References ...... 847

1. Introduction et al., 2010), or even by complete isolation of the sedimentary basin (Bristow et al., 2009). Thus a comprehensive sedimentological and The Doushantuo Formation (ca. 635–551 Ma) in South China is paleogeographic framework for the Doushantuo Formation becomes one of the most intensively investigated Ediacaran stratigraphic units critical for future geochemical and paleobiological studies. owing to its exceptionally well-preserved fossil record (Yuan et al., Attempts to establish a stratigraphic and sedimentological frame- 2002; Chen, 2005). A plethora of multicellular fossils including early work for the Doushantuo Formation have been made in numerous animals, exemplified by a few representative biotas (Fig. 1) such as publications (e.g., Wang, 1985; Cao et al., 1989; Liu et al., 1993; Wang the Miaohe biota (Zhu and Chen, 1984; Chen and Xiao, 1992; Xiao et et al., 1998; Jiang et al., 2003a, 2006a, 2006b; Wang and Li, 2003; Zhu al., 2002), Jiulongwan biota (Yin and Liu, 1988; Xiao, 2004; Yin et al., et al., 2003, 2007; Zhou and Xiao, 2007; Vernhet et al., 2006, 2007, 2004, 2007; Zhou et al., 2007; McFadden et al., 2008, 2009), Weng'an 2010), but large uncertainties still exist, especially in aspects related biota (Zhang, 1989; Li et al., 1998; Xiao et al., 1998), Wenghui biota to the degree of basin restriction and the exact paleogeographic (Zhao et al., 2005; Tang et al., 2008; Wang et al., 2008a, 2008b; Zhu location of particular sections. This is largely due to the poor exposure et al., 2008) and Lantian biota (Yan et al., 1992; Yuan et al., 1999, of the Doushantuo Formation and the tectonic complexity in South 2011), have been described from the Doushantuo Formation, China in general. The Doushantuo Formation varies in thickness from providing a rare window for understanding the evolutionary pattern 40 m to 300 m (Zhu et al., 2007) and in cases shows rapid facies of organisms at the dawn of animal life. For the purpose of changes among adjacent sections. Patchy outcrops of the Doushantuo stratigraphic correlation and understanding the causal link between Formation cover the entire Yangtze block for more than biogeochemical events and biotic evolution, intensive geochemical 1,620,000 km2, but complete sequences can only be observed along analyses have also been conducted for the Doushantuo Formation, fresh roadcuts and stream valleys. In addition to these limitations, including carbon, sulfur, and strontium isotopes (e.g., Yang et al., strong weathering and civilian construction can destroy some of the 1999; Shields et al., 2004; Guo et al., 2007; Jiang et al., 2007, 2008; classic sections in a few years so that measurements of the same Zhou and Xiao, 2007; Zhu et al., 2007; McFadden et al., 2008; Ader section by different groups often show large variations in thickness et al., 2009; Zhao et al., 2009; Zhao and Zheng, 2010; Li et al., 2010; and contents. Sawaki et al., 2010) and redox-sensitive elements (Bristow et al., In this paper, we review and summarize some of the representa- 2009; Huang et al., 2009; Li et al., 2010), but in comparison with the tive stratigraphic sections of the Doushantuo Formation and provide a paleontological studies, conclusions are much less definitive. For sedimentological interpretation and paleogeographic reconstruction example, carbon isotope analyses from different sections across the for this unit across the Ediacaran Yangtze platform. Because most of basin show large variations in both absolute δ13C values and the the research on the Doushantuo Formation and the best outcrops of number of negative excursions (Guo et al., 2007; Jiang et al., 2007, this unit are concentrated on the central part of the Yangtze platform 2008; Zhou and Xiao, 2007; Zhu et al., 2007; Ader et al., 2009; Wang in Hubei, Hunan, and Guizhou provinces (Fig. 1B), the discussion will and Shi, 2009). Sulfur isotopes from the inner and outer shelf sections focus on this region (Fig. 2). show up to 30‰ differences in both carbonate-associated sulfur 34 34 (δ SCAS) and pyrite sulfur (δ SPY) isotopes (Li et al., 1999a, 1999b; 2. Development of the Ediacaran Yangtze Platform Shields et al., 2004; McFadden et al., 2008; Li et al., 2010). Such geochemical variations have been suspected to be controlled by water The Neoproterozoic sedimentary history along the southeastern column stratification and restriction of particular depositional side of the Yangtze block is best demonstrated by two stratigraphic environments (e.g., Jiang et al., 2007, 2008; Ader et al., 2009; Li transects: the north–south transect from the Yangtze Gorges area in

Fig. 1. (A) Tectonic outline showing the location of the Yangtze and Cathaysia blocks in China. (B) A generalized paleogeographic reconstruction for the Yangtze platform during the Doushantuo deposition. The region marked by the rectangle corresponds to Fig. 2A. Circled numbers indicate the major biotas found from the Doushantuo Formation: 1—Miaohe biota; 2—Jiulongwan biota (informally named here referring to silicified fossils from the lower-middle Doushantuo Formation in the Yangtze Gorges area; see McFadden et al., 2009); 3—Weng'an biota; 4—Wenghui biota; 5—Lantian biota. Author's personal copy

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Fig. 2. (A) Simplified geological map showing exposures of Neoproterozoic strata in the central Yangtze platform of South China and position of the late Neoproterozoic platform margin (coarse dotted line). Numbers 1–23 indicate the location of stratigraphic sections used for paleogeographic reconstruction (for other sections, see Zhu et al., 2007). (B) Neoproterozoic shelf-to-basin transect from north to south in Hubei and Hunan provinces (transect 1). (C) Shelf-to-basin transect from west to east in Guizhou and Hunan provinces (transect 2). Section numbers match those in (A). (D) Summary of stratigraphic units with major age constraints and marker beds (thick lines) for shelf-to-basin correlations.

Hubei province to northern Guangxi province (Fig. 2B and southward) from an ash bed at the lower part of the interglacial Datangpo and the west–east transect from eastern Guizhou to western Hunan Formation (Zhou et al., 2004), (6) 654±3.8 Ma from an ash bed at the (Fig. 2C). Neoproterozoic strata in this region consist of three major top of the interglacial Xiangmeng (Datangpo equivalent) Formation parts (Fig. 2D): the pre-Cryogenian siliciclastic units in the lower part, (Zhang et al., 2008c), (7) 635.2±0.6 Ma and 632.5±0.5 Ma from ash the Cryogenian glacial and interglacial deposits in the middle, and the beds within and above the cap carbonate (Condon et al., 2005), (8) Ediacaran mixed carbonate-siliciclastic units at the top. Compared to 551.1±0.7 Ma from an ash bed near the Doushantuo/Dengying their global equivalents, these strata have some of the best age boundary (Condon et al., 2005; Zhang et al., 2005), and (9) 539.4± constraints. Important U–Pb zircon ages (Fig. 2D) include (1) 830– 2.9 Ma (Compston et al., 2008; but see Zhu et al., 2009; Jenkins et al., 820 Ma ages from numerous granitoids and mafic–ultramafic intru- 2002; for slightly different ages from the same bed), 536.3±5.5 Ma sive rocks that unconformably underlie the Neoproterozoic sedimen- (Chen et al., 2009), and 532.3±0.7 Ma (Jiang et al., 2009) from ash tary succession (Li et al., 1999b; Li et al., 2003), (2) 748±12 Ma beds of the earliest Cambrian units. These data constrain the age of the (Ma et al., 1984) from an ash bed of the upper Liantuo Formation, (3) pre-glacial siliciclastic units from ca. 820 Ma to 725 Ma, the 758±23 Ma (Yin et al., 2003) and 809±8.4 Ma (Zhang et al., 2008a) Cryogenian glacial deposits from ca. 725 Ma to 635 Ma, and the from ash beds of the upper Banxi Group, (4) 725±10 Ma from an ash Ediacaran strata from 635 Ma to ca. 542 Ma. It also provides age bed at the top of the Banxi Group (Zhang et al., 2008b), (5) 663±4 Ma constraints for the two Cryogenian glaciations recorded in the Yangtze Author's personal copy

834 G. Jiang et al. / Gondwana Research 19 (2011) 831–849 block: ca. 725–663 Ma for the older Chang'an glaciation and ca. 654– the shelf-to-basin transects (Figs. 3–5). Numerous sections (N50) 635 Ma for the younger Nantuo glaciation. have been reported in literature (see Zhu et al., 2007 for review of The pre-glacial siliciclastic units in the Yangtze block are sections), particularly from the Yangtze Gorges area, but most of them represented by the Liantuo Formation/Banxi Group (transect 1; are either strongly covered by vegetation or only portions of the Fig. 2B) and Qingshuijiang Formation/Xiajiang Group (transect 2; Doushantuo Formation were documented. Fig. 2C). The thickness of these units varies significantly, from b300 m The overall sequence of the Doushantuo Formation was estab- in the shelf to a few thousand meters towards the basin in the lished in the Yangtze Gorges area, which has been summarized in a southeast. The stratal pattern of these units, along with widespread few monographs (e.g., Zhao et al., 1985, 1988; Ding et al., 1996). In biomodal magmatism from 830 to 745 Ma in South China (Li et al., this area, the Doushantuo Formation was divided into four members, 2003), indicates that they were deposited in a rift basin (the Nanhua as marked in the Jiulongwan section (section 4 in Fig. 3). Member 1 basin; Wang and Li, 2003) that started at ca. 820 Ma between the refers to the ca. 5-m-thick cap carbonate at the base of the Yangtze and Cathaysian blocks. Doushantuo Formation. Member 2 consists of alternating organic- The Cryogenian succession includes two glacial diamictite inter- rich shale and carbonates with abundant pea-sized chert nodules. vals separated by interglacial manganese-bearing shale/siltstone. The Member 3 consists of predominately carbonates with bedded chert lower diamictite units represented by the Gucheng/Chang'an forma- layers and minor shale laminae. Member 4 refers to the ca. 10-m-thick tions in transect 1 (Fig. 2B) and Guiping/Tiesi'ao formations in black, organic-rich shale interval at the top of the Doushantuo transect 2 (Fig. 2C) vary in thickness from 0 to 10 m in the shelf to Formation. The first member represented by the cap carbonate and, to N2000 m in the basin. The interglacial manganese-bearing shale/ a lesser degree, the organic-rich black shale of member 4, are the siltstone represented by the Xiangmeng Formation in transect 1 regional stratigraphic marker beds for the Doushantuo Formation. (Fig. 2B) follows approximately the same thickness pattern, which is Members 2 and 3, however, are very difficult to identify and correlate very thin (b10 m) or entirely missing in the shelf but up to 400 m with sections in other areas (Figs. 3–5). For this reason, the thick in the basin. In general, the interglacial Datangpo Formation in stratigraphic location of the Doushantuo/Dengying boundary can be transect 2 (Fig. 2C) also thickens towards the basin, but shows greater slightly different among research groups if the organic-rich black thickness variation in some sections that may have been resulted from shale at the top of the Doushantuo Formation is missing (or covered) erosion by the overlying Nantuo glacial diamictite or topographic in that particular section (e.g., sections 1, 7B, and 9 in Fig. 3; variations inherited from the early Cryogenian glaciation. The upper sections 15 and 16 in Fig. 5). glacial diamictites of the Nantuo Formation thicken towards the basin with a maximum thickness of ~2000 m, but in comparison with the underlying units, the Nantuo Formation has a broader distribution 3.1. Notes on Some Representative Sections into the shelf. About 60–100 m thick glacial diamictites of the Nantuo Formation cover most of the shelf areas, except in the vicinity of Stratigraphic sections listed in Figs. 3–5 represent the best Weng'an and Duoding (loc. 15 and 16 in Fig. 2A and C) where the exposure of the Doushantuo Formation in each area and some of Nantuo diamictite is b10 m thick. Large variations in stratal thickness, the sections have been studied multiple times by different groups. plus the lack of significant Cryogenian volcanism, suggest that However, even these sections are partially covered and/or tectonically Cryogenian strata were deposited during the final rifting phase of offset so that the thickness and contents differ among authors. Such the Nanhua basin (Wang and Li, 2003). The rift–drift transition sections include the Xiaofenghe, Zhongling, and Yangjiaping sections. corresponds with a level at the base or within the lower glaciogenic Some other sections had the excellent exposure 10–15 years ago but unit (Jiang et al., 2003a). are now mostly destroyed by landslides and/or civilian activities. Such The Ediacaran Doushantuo and Dengying formations display a sections include the Fengtan, Yuanjia, and also Hefeng sections. Some different pattern of stratal thickness, which is thick (≤1000 m) in the notes about these sections are provided below. interior of the Yangtze block and thin (b250 m) in the basin (Fig. 2B The Xiaofenghe section (section 1 in Fig. 3) was measured from the and C). The thickness and spatial distribution, along with the lack of northern and southern hillsides of a stream valley about 6 km west of major tectonic events and igneous activity, suggest that the the Xiaofeng town. The thickness of the Xiaofenghe section varies from Doushantuo and Dengying formations were deposited in a passive- 100 m (Vernhet and Reijmer, 2010), to 185 m (McFadden et al., 2009), margin setting. In the eastern part of the region represented by shelf- and to 220 m (Yin et al., 2007; Zhu et al., 2007) in literature and our to-basin transect 1 (Fig. 2B), the Cryogenian shelf margin was located measurement is 165 m. These differences are mainly caused by the between Yuanling and Huaihua (between loc. 12 and 13; Fig. 2A and uncertain stratigraphic correlation between the northern and south- B), but the Ediacaran shelf margin stepped northwards to a new ern hillsides of the stream valley. We believe that the greater thickness location close to Zhangjiajie (loc. 8 in Fig. 2A and B). In contrast, the estimate was caused by some stratigraphic repetition due to the large Ediacaran shelf margin along shelf-to-basin transect 2 (Fig. 2C) landslide in the southern hillside but we are not sure about the origin remained at approximately the same location as the Cryogenian shelf of the smaller thickness estimate in Vernhet and Reijmer (2010). The margin. While the Cryogenian shelf margin is largely determined by top of the Doushantuo Formation in this section is characterized by 25- abrupt change in stratal thickness, the Ediacaran shelf margin is m-thick oolitic grainstone/packstone that distinguishes it from the defined by the abundance of shallow-water carbonates that thin and overlying cherty dolostone of the Dengying Formation. Yin et al. change facies both basinward and into the interior shelf (shelf (2007) and Zhu et al. (2007) reported a black shale unit (Member 4) in lagoon), and by the abundance of slump blocks, olistostrome breccias, the uppermost Doushantuo Formation at the southern hillside of the and turbidites in the basinward side of the margin (Jiang et al., 2003a, Xiaofenghe section, which was adopted as the upper Doushantuo 2006a; Vernhet et al., 2006, 2007; Zhu et al., 2007). The Ediacaran Formation in McFadden et al.'s (2009) stratocolumn. However, we Yangtze platform refers to this new paleogeographic configuration were not able to locate this black shale unit at Xiaofenghe. The absence that started approximately at the Cryogenian–Ediacaran transition of this marker bed at Xiaofenghe could be caused by a bedding-parallel and extended into the Cambrian. fault or by facies changes. We prefer the facies change interpretation because (1) the transition from oolitic grainstone/packstone to cherty 3. Stratigraphy of the Doushantuo Formation dolostone at the Doushantuo–Dengying boundary is stratigraphically concordant and (2) this black shale marker bed is missing towards the The Doushantuo Formation shows significant changes in facies and north in a number of other sections such as the Zhangcunping section thickness that can be exemplified by a dozen classic sections across (Zhu et al., 2007; McFadden et al., 2009). Author's personal copy

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Fig. 3. Representative stratigraphic sections of the Doushantuo Formation from shelf-to-basin transect 1 (Fig. 2B). Section numbers match those in Fig. 2A and B. The Zhongling (7A) and Yangjiaping (7B) sections are ~4 km apart and they are indicated as a single number in Fig. 2A and B. Notice that the Miaohe biota was found from the equivalent stratigraphic interval in the Miaohe section (loc. 3 in Fig. 2A). The Jiulongwan biota is informally named here, referring to silicified microfossils including acanthomorphic acritarchs in the lower- middle Doushantuo Formation of the Yangtze Gorges area (Xiao, 2004; Yin et al., 2007; McFadden et al., 2009). The Doushantuo Formation has been divided into 4 members in the Yangtze Gorges area, as exemplified in the Jiulongwan section (section 4), but only the cap carbonate (Member 1) and the black shale interval at the top (Member 4) have regional significance. Exposure/erosional surfaces and flooding surfaces expressed by abrupt facies change were found from the middle and upper Doushantuo Formation, but their regional correlation requires further confirmation by other independent geochronological or biostratigraphic data, which is not available at the current stage.

The Hefeng section (section 6 in Fig. 3) was measured in 1999 outcrop that consists of mainly gray to dark gray shales with along a small stream valley about 30 km east of the Hefeng County. subordinate shaly dolostone layers. The 8-m-thick black shale unit Only the upper part of the Doushantuo Formation has measurable at the Doushantuo–Dengying boundary contains phosphorite nodules Author's personal copy

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The Fengtan section (section 12 in Fig. 4) had excellent exposure a decade ago when the road to the Fengtan power station was built, but is now mostly destroyed by civilian construction and cultivation. Our recent check indicates that the overall lithology of the section is still identifiable, but obtaining fresh samples is now difficult. The Yuanjia section in Huaihua (section 13 in Fig. 4) also had excellent exposure when the roadcut was fresh, but is now mostly covered by a large landslide.

3.2. Lithostratigraphic Marker Beds

Stratigraphic correlation of the Doushantuo Formation relies heavily on two distinct marker beds, the 3–6 m thick cap carbonate at the base of the Doushantuo Formation and the organic-rich black shale at the top of the Doushantuo Formation. Sequence stratigraphic study could potentially divide the Doushantuo Formation into three sequences but the lateral extent and regional correlation of these physical surfaces needs further investigation. Carbon isotope anoma- lies from the Doushantuo Formation show large spatial variations across the shelf-basin transects, but serve as the only guide to correlate the Doushantuo Formation with other Ediacaran successions globally. Biostratigraphy, particularly the diversification and extinc- tion of acanthomorphic acritarchs, could potentially add values to the subdivision and global correlation of the Doushantuo Formation, but at the current stage its application in the Doushantuo stratigraphy is still limited due to taphonomic and environmental control of fossil preservation.

3.2.1. The Doushantuo Cap Carbonate The Doushantuo cap carbonate rests directly on glacial diamictites of the Nantuo Formation, but in many places, there is an 8–20 cm thick, fine-grained siltstone/claystone at the top of the diamictite (Jiang et al., 2006b; Zhang et al., 2008c). No interbedded cap carbonate and glacial diamictite are found anywhere across the Fig. 4. Representative stratigraphic sections of the Doushantuo Formation from the basin (see Fig. 2A for location of sections). Note that the cap carbonate at the base and shelf-to-basin transects, although sporadic pebble-sized conglomer- organic-rich black shale at the top of the Doushantuo Formation commonly serve as the ates have been seen in the basal 0.5 m of the cap carbonate in a only markers for regional correlation in the basin. Both sections had the excellent few shelf sections of the Yangtze Gorges area and in eastern Guizhou exposure a decade ago when the roads was freshly cut, but are now mostly destroyed (e.g., sections 1–4 and 14–16 in Fig. 2). The Doushantuo cap carbonate by civilian cultivation (Fengtan) and by landside (Yuanjia). is widespread across the basin, even in the Sanjiang area of Guangxi province where the thickest glacial and preglacial strata indicate the depocenter of the Nanhua rift basin. All these features indicate and shows a gradual transition to the overlying dark-gray dolostone of that the Doushantuo cap carbonate was deposited during the late the Dengying Formation. Because we have not examined this section stage of postglacial transgression when continental ice sheets have since 1999, we are not sure about the current outcrop condition of this largely disappeared from the Yangtze block (Jiang et al., 2003b, 2006a, section. 2006b; Zhang et al., 2008c). The Doushantuo cap carbonate The Zhongling section (section 7A in Fig. 3) has been measured mainly consists of micritic and/or microcrystalline dolostone and along a road 4 km west of the Yangjiaping village, but the thickness of subordinate limestone. The general lack of coarse-grained lithology the Doushantuo Formation varies from ~140 m (Vernhet and Reijmer, and cross-stratifications and the presence of parallel lamination 2010) to 300 m (Zhu et al., 2007; Li et al., 2010). This discrepancy suggest deposition mostly below fair-weather wave base (Jiang et al., may be caused by the miscalculation of thickness for covered intervals 2006a). and the uncorrected offset of two faults in the middle part of the The basal part of the Doushantuo cap carbonate contains localized section. Our observations concur with Zhu et al. (2007) on the general bedding disruption, brecciation, and cementation that are strongly lithological sequences but the thickness of the middle Doushantuo is silicified. These features were interpreted as formed by methane gas less (the thickness of the entire section is 210 m in our measurement). and fluids from gas hydrate destabilization (Jiang et al. 2003a, 2006a, The Yangjiaping section (section 7B in Fig. 3) has been measured 2006b; Wang et al., 2008a). Recent interpretation ascribed these numerous times by different groups with varying thickness from features to karstification immediately after cap carbonate precipita- ~200 m (Vernhet and Reijmer, 2010)toN400 m (e.g., Macouin et al., tion in respond to deglacial isostatic rebound (Zhu et al., 2007; Zhou et 2004). This is mainly due to the poor exposure along the roadcut al., 2010). Evidence for karstification at the top of the Doushantuo cap section. In this study we traced the cap carbonate and the carbonate, however, is rather weak. Localized bedding disruption and Doushantuo–Dengying boundary along the river valleys/hillsides in brecciation in the Doushantuo cap carbonate are widespread across adjacent areas. Our best estimation on the thickness of the the shelf-to-basin transects. These features decrease rather than Doushantuo Formation is 190 m. The lower part of the Doushantuo increase upward towards the inferred karstic surface. Dissolution Formation in the Yangjiaping area is dominated by black shale and the features at the top of the cap carbonate are rare and if ever present, are upper part is mainly oolitic/intraclastic grainstone/packstone. Two associated with massive barite indicative of high sulfate concentration exposure/erosional surfaces with reworked, poorly sorted intraclasts that could cause local carbonate dissolution through sulfur recycling can be observed from the river valleys away from the road section. (e.g., Ku et al., 1999). Thus dissolution features associated with barites Author's personal copy

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Fig. 5. Representative stratigraphic sections of the Doushantuo Formation from shelf-to-basin transect 2 (Fig. 2B). Note that the Duoding section was measured by tracing the roadcut section at Duoding to the northern valleys. The Dengying +Liuchapo Formation in Wuhe section should be time equivalent to the Dengying or Liuchapo Formations in other sections. Two exposure/karst surfaces can be identified at the Weng'an and Duoding sections, but their correlation to other sections is tentative. do not require involvement of meteoric water. In most sections that underlying strata and makes it the second most important marker have been studied, the Doushantuo cap carbonate shows a transi- with which to correlate the Doushantuo Formation, particularly in the tional change to the overlying black shales and interbedded carbonate deep-water slope and basinal facies where the partially chertified (Jiang et al., 2006a, 2010). Regardless of debates on the origin of the Doushantuo Formation may be similar to its overlying Liuchapo Doushantuo cap carbonate, its associated carbon isotope anomaly and Formation. unique sedimentary features, the distinctive lithology and widespread The black shale unit at the top of the Doushantuo Formation is distribution of the Doushantuo cap carbonate make it the most traditionally interpreted as transgressive deposits formed during sea- important stratigraphic marker for the identification and correlation level rise (e.g., Wang et al., 1998; Jiang et al., 2003a, 2007; Zhu et al., of the Doushantuo Formation in South China. 2007). Vernhet and Reijmer (2010), however, pointed out that the lack of retrogradation of the Ediacaran Yangtze platform does not 3.2.2. The Organic-Rich Black Shale at the Top of the Doushantuo support sea-level rise at the end of the Doushantuo Formation. Thus Formation deposition of the organic-rich black shale may have been restricted to In comparison with the Doushantuo cap carbonate, the black shale protected environments of the shelf. It is true that the shelf margin of unit at the top of the Doushantuo Formation is regionally less the Ediacaran Yangtze platform did not show obvious landward shift consistent. It appears in most shelf sections and in slope and basinal during the Doushantuo deposition, but the spatial distribution of the sections, but is absent in more proximal areas of the shelf and in the black shale at the top of the Doushantuo Formation is much broader shelf margin where time-equivalent strata are composed of carbo- than inferred by Vernhet and Reijmer (2010). In the shelf margin nates or phosphorite-rich facies (Figs. 3–5). The high-TOC contents represented by the Yangjiaping and Duoding sections, base-level fall (N5%) of this black shale unit (e.g., Dong et al., 2008; McFadden et al., indicated by exposure surfaces and subsequent carbonate/phoshorite 2008; Li et al., 2010) distinguish itself from the overlying and deposition (Figs. 3 and 5) do suggest transgression at the end of the Author's personal copy

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Doushantuo Formation, although the magnitude of sea-level change is Recent studies, however, challenge the validity of the Ediacaran difficult to quantify. In Phanerozoic carbonate platforms, retrograda- carbon isotope chemostratigraphy due to large uncertainties in (1) 13 tion of shelf margins associated with sea-level rise is best expressed the synchrony of the negative δ Ccarb anomalies in the absence of by marginal reefs and/or by the highly productive carbonate factory precise radiometric age data (Derry, 2010a), (2) co-variation of 13 that tracks sea-level changes (Sarg, 1988). In cases when sea-level rise carbon and oxygen isotopes temporally across negative δ Ccarb resulted in water-column anoxia and/or high organic production, anomalies indicative of burial diagenesis (Knauth and Kennedy, drowning carbonate platforms would not show obvious backstepping 2009; Derry, 2010a), (3) decoupled carbonate and organic carbon (Schlager, 1999; Mallarino et al., 2002). The regional discontinuity at isotopes from Ediacaran successions indicative of diagenetic alter- 13 the base of the black shale unit in the uppermost Doushantuo ation on δ Ccarb (Derry, 2010b), and (4) the lack of a reasonable 13 Formation may well represent a “drowning unconformity” (cf., mechanism to explain the unusually large negative δ Ccarb anomalies Schlager, 1999) that resulted from transgression and high organic as a global seawater signature (Bristow and Kennedy, 2008). 13 production. These challenges, along with the large spatial variations in δ Ccarb across the shelf-to-basin transects of the Doushantuo Formation, 3.3. Sequence Stratigraphy require more detailed diagenetic study on the Doushantuo Formation. Nonetheless, at the current status, carbon isotope stratigraphy Enormous efforts have been made to promote the subdivision and remains critical to establish the correlation between the Doushantuo correlation of the Doushantuo Formation using physical surfaces (e.g., Formation and other time-equivalent strata globally. Wang et al., 1998; Wang et al., 2001; Jiang et al., 2003a, 2007; Zhu et al., Biostratigraphic data, particularly the diversification and extinc- 2003, 2007; Mei et al., 2006; Zhou and Xiao, 2007; Vernhet and tion of acanthomorphic acritarchs (Zhou et al., 2007; McFadden et al., Reijmer, 2010), but due to the limitation of outcrop exposure and large 2008, 2009), have become increasingly important in correlating the facies variations of the Doushantuo Formation, establishing a reliable Doushantuo Formation with other Ediacaran strata globally. However, sequence stratigraphic framework has been difficult. In general, two due to taphonomic and environmental biases, biostratigraphic regional stratigraphic discontinuities have been recognized in the correlation across different facies of the Doushantuo Formation will Doushantuo Formation, one at the middle of the formation and the be difficult. Therefore the validity of global biostratigraphic correla- other near the top of the formation (Figs. 3 and 5). Both surfaces are tion of the Doushantuo Formation relies heavily on the availability of a characterized by exposure/erosional features such as karst breccias stratigraphic framework established from integrated stratigraphic and reworked intraclasts in the shelf margin (e.g., section 7B in Fig. 3; methods. sections 15 and 16 in Fig. 5) and by abrupt facies change that has been interpreted as flooding surfaces in the shelf lagoon and slope. 4. Paleogeography of the Doushantuo Formation Identification of these surfaces is mainly based on vertical facies change in individual stratigraphic sections, but the lateral extension 4.1. Facies Distribution Across the Shelf-to-Basin Transects and the amount of base-level fall recorded by these surfaces have not been well-documented. Therefore, whether these surfaces record local The sedimentary facies and depositional environments of the vs. regional/global sea-level changes is still uncertain and their global Doushantuo Formation across the shelf-to-basin transects are sum- correlation, although attempted in literature (e.g., Jiang et al., 2003a; marized in Figs. 6 and 7. In transect 1, the Doushantuo Formation in Pyle et al., 2004; Zhu et al., 2007), requires further confirmation with the Yangtze Gorges area represents deposition mostly from the reliable radiometric age, or high-resolution chemo/biostratigraphic proximal side of an intrashelf lagoon. Except the lowermost 30 m, the constraints. majority of facies recorded in the Xiaofenghe section was deposited from shallow subtidal to intertidal environments (cf. Vernhet and 3.4. Chemostratigraphy and Biostratigraphy Reijmer, 2010). Facies represented by the Jiulongwan section may have been deposited from relatively deeper and more restricted 13 Carbonate carbon isotope (δ Ccarb) chemostratigraphy of the environments, with the lower part from deep subtidal shelf lagoon Doushantuo Formation has been intensively reviewed in Jiang et al. below fair-weather wave base and the upper part from low-energy, (2007, 2008), Zhou and Xiao (2007), Zhu et al. (2007), and Ader et al. shallow subtidal environments. Deep shelf-lagoon environments are 13 (2009). Although large variations in δ Ccarb values have been inferred to have been located between the Yangtze Gorges area and observed in the Doushantuo Formation, it has been proposed that Yangjiaping. Whether the central part of the shelf lagoon shoaled up the isotope record from shallow-water, carbonate-rich sections in the above fair-weather wave base in the middle Doushantuo Formation Yangtze Gorges area have the best chance to record a global isotope (represented by the erosional/exposure surface in Xiaofenghe 13 signature. In the Yangtze Gorge area, three negative δ Ccarb section) is uncertain and requires testing with sections between anomalies have been documented from the cap carbonate, the middle Jiulongwan and Hefeng. Facies of the Doushantuo Formation in and upper Doushantuo Formation, respectively (Fig. 8A). However, Zhongling and Yangjiaping areas represent deposition in the distal 13 the magnitude of the negative δ Ccarb anomaly at the middle side of the shelf lagoon, close to the shelf margin. The lower part of the Doushantuo Formation (N2 in Fig. 8A) varies among sections in the Doushantuo Formation in these sections was likely deposited in a Yangtze Gorges area and its significance remains uncertain. In deep shelf lagoon with the marginal barrier located between 13 contrast, the δ Ccarb anomalies at the base and the top of the Yangjiaping and Tianping (likely close to Sancha). The upper part of Doushantuo Formation have been considered as time-equivalent to the Doushantuo Formation in Yangjiaping section is dominated by those documented from India (Jiang et al., 2002; Kaufman et al., grainstones and packstones that are interpreted to have been 2006), Oman (Fike et al., 2006; Le Guerroué et al., 2006; Le Guerroué deposited in a shelf margin shoal complex above fair-weather wave and Cozzi, 2010), Australia (Calver, 2000; Walter et al., 2000)(Fig. 8), base. In contrast, the upper part of the Doushantuo Formation in and less certainly to those from Namibia (Saylor et al., 1998; Zhongling and Hefeng sections is dominated by shale and shaly Halverson et al., 2005) and western United States (Kaufman et al., carbonates that were likely deposited in back-barrier shelf lagoon 2007). Strontium isotopes from the Yangtze Gorges area also seem to environments. Zhongling and Yangjiaping sections are only 4 km support an overall increase in 87Sr/86Sr values throughout the apart; the contrasting facies (Fig. 4) indicate that the shelf lagoon may Doushantuo Formation (Jiang et al., 2007; Sawaki et al., 2010), have been asymmetric, with the depocenter close to the shelf margin. consistent with the overall Ediacaran 87Sr/86Sr record (Halverson et The inferred shelf margin during the early Doushantuo time is al., 2010). based on the contrasting facies between Yangjiaping and Tianping. Author's personal copy

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Fig. 6. Sedimentological interpretation of shelf-to-basin transect 1. Abundant slump blocks and olistostrome breccias in the lower part of Tianping and Siduping sections contrast with the shale-dominated facies in Yangjiaping and Zhongling sections. A shallow-water carbonate factory (shelf margin) must have existed between Yangjiaping and Tianping, most likely located close to Sancha (loc. 8 in Fig. 2A and B). Carbonate-rich facies with slump blocks and olistostrome breccias appear ~7 m and 11 m above the cap carbonate in Tianping and Siduping, respectively, indicating that the shelf margin barrier existed very early during the Doushantuo deposition, separating the shelf lagoon from the open ocean.

The cap carbonate and its overlying black shale interval cover the cap carbonate deposition in the vicinity of Weng'an and Duoding entire region including the Yangtze Gorges area. However, subse- areas. This marginal shoal complex separated the shelf lagoon in the quent carbonate-dominated facies with abundant slump blocks and west, represented by the Songlin section, from the open ocean in the olistostrome carbonate breccias in Tianping and Siduping sections east. The thickness distribution of the Doushantuo Formation across contrast with the shale-dominated facies in Yangjiaping and Zhon- this transect mimics that of the underlying Nantuo Formation, which gling (Fig. 3). A shallow-water carbonate factory (shelf margin) must is about 60 m in Songlin, 0–8 m in Weng'an and Duoding, and 200 m have existed between Yangjiaping and Tianping, most likely located in Wuhe, indicating that the shelf margin shoal complex was close to Sancha (loc. 8 in Fig. 2A and B). The poor exposure at Sacha developed from a topographic high inherited from the Nantuo prevents a detailed stratigraphic/sedimentological log, but sparse glaciation. Facies in Songlin section show a deepening at the middle outcrops available in this area do contain coarse-grained carbonate part, whereas in Weng'an and Duoding, shallow-water facies remain lithologies including oolitic, oncolitic, or intraclastic grainstone and until the end of the Doushantuo Formation. This phenomenon implies packstone that are consistent with a shelf-margin interpretation. either sediment starvation or syndepositional faulting along the Carbonate-rich facies with slump blocks and olistostrome breccias lagoonal side of the shelf margin during the middle Doushantuo time. appear 7 m and 11 m above the cap carbonate in Tianping and In the open-shelf side of the margin, carbonate factory may have Siduping, respectively, indicating that a shelf margin barrier existed prograded basinward during the upper Doushantuo deposition, as very early during the Doushantuo deposition, shortly after cap indicated by the increase of carbonate facies in slope sections carbonate deposition. Thus for most of the Doushantuo time, (section 17, 19, and 21; Fig. 7). The absence of the black shale unit depositional environments north of the Yangjiaping area (including at the top of the Doushantuo Formation in Weng'an and Duoding the Yangtze Gorges region) were restricted from the open ocean. implies that the shelf margin in these areas continued during Whether the shelf-margin barrier inherited a topographic high from deposition of the overlying Dengying Formation. the Nantuo glaciation or was formed after cap carbonate deposition Facies overlying the Doushantuo Formation in Rongxi and Taoying through syndepositional faulting is uncertain and requires additional (sections 17 and 19) are bedded cherts with minor siliceous shale stratigraphic and sedimentological work along the shelf margin. beds, but in Wuhe section, a 12-m-thick carbonate unit (lithologically In comparison with transect 1, facies distribution across the shelf- named as the Dengying Formation) overlies the Doushantuo to-basin transect 2 is relatively simple (Fig. 7). A shelf margin shoal Formation, followed by bedded cherts and siliceous shales of the complex characterized by shallow-water grainstone/packstone and Liuchapo Formation (Fig. 5). In the Wuhe section, a 5-m-thick, phosphorites with subaerial exposure features developed shortly after organic-rich black shale unit in the uppermost Doushantuo Formation Author's personal copy

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Fig. 7. Sedimentological interpretation of shelf-to-basin transect 2. A peritidal shoal complex served as a shelf margin barrier of the shelf lagoon. The stratigraphic pattern suggests that the shoal complex may have developed on topographic highs inherited from the Cryogenian glaciation. underlies a carbonate unit (Dengying Formation) and is identical to of the lower Dengying Formation until a platform-wide karstic the black shale marker bed just below the Doushantuo–Dengying unconformity (Cao et al., 1989; Jiang et al., 2003a; Zhu et al., 2007) boundary elsewhere. This correlation is also confirmed by the positive developed when the shelf lagoon was infilled with shallow-water δ13C values in the carbonate unit (Jiang et al., 2007). Thus in the Wuhe carbonates. section, the Dengying and Liuchapo formations together are time Previous paleogeographic reconstruction suggested that the equivalent to the Dengying Formation or Liuchapo Formation in other Doushantuo Formation could have been deposited from a few isolated sections, respectively. The presence of carbonate layers above the carbonate platforms surrounded by deep-water, siliciclastic-domi- Doushantuo Formation in Wuhe section may indicate that the nated basinal facies (Cao et al., 1989; Zhou and Xiao, 2007), mainly carbonate factory was close to this location after the Doushantuo because of the lack of shallow-water carbonate sections between deposition. Note that Rongxi (section 17) and Taoying (section 19) Weng'an and Yangjiaping. The overall scarcity of exposure in this sections are projected to the shelf-to-basin profile in Fig. 7 according region (northwest of the shelf-margin from section 14 in Zunyi to to their distance to the inferred shelf margin, but paleogeographically section 7 in Hunan, Fig. 2A) indeed makes a continuous shelf margin they are located 180 km and 80 km north of the Wuhe section, reconstruction debatable. However, the presence of carbonate-rich respectively (Figs. 9 and 10). facies and olistostrome carbonates in sections between Weng'an and Yangjiaping, exemplified by Rongxi and Taoying sections (loc. 17 and 4.2. Depositional Model and Paleogeographic Reconstruction 19 in Figs. 1A, 7, 9, and 10), indicates a shallow-water carbonate factory close to those areas. Thus a continuous shelf-margin connect- Based on the facies analyses of representative sections (Figs. 6 ing eastern Guizhou and northwestern Hunan provinces (Fig. 10)is and 7) and observations of the Doushantuo Formation in other areas more likely. Whether this shelf margin extends southwestwards to (e.g., locations in Fig. 1A and in Zhu et al., 2007), a general depositional eastern Yunnan is uncertain (Fig. 1B) and requires additional work in model for the Doushantuo Formation is summarized in Fig. 9 and its that region. Another area with uncertain paleogeographic affinity is paleogeographic reconstruction is provided in Fig. 10. The uniform the southern Anhui province where the Doushantuo equivalent thickness and similar facies of the Doushantuo cap carbonate and its Lantian Formation contains abundant fossils of multicellular eukar- immediately overlying black shale across the basin suggest an open yotes (Fig. 1B; Yan et al., 1992; Yuan et al., 1999, 2011). Exposure in shelf setting at the beginning of the Doushantuo deposition (Fig. 9A). this area is close to an “oldland” (Fig. 1B) from which no late The open shelf evolved into a rimmed shelf (Fig. 9B) shortly after the Neoproterozoic strata has been documented. It is uncertain whether Doushantuo cap carbonate deposition, from a topographic high the “oldland” represent an uplifted region without deposition during inherited from the Nantuo glaciation and/or through syndepositional the Neoproterozoic (Wang, 1985) or Neoproterozoic strata have been faulting. Most of the Doushantuo Formation west of the Weng'an/ eroded during the early Paleozoic Caledonian orogeny and afterwards. Duoding areas and north of the Yangjiaping/Zhongling area was The spatial distribution of the Lanitan Formation needs further deposited from restricted, intrashelf lagoon environments. The investigation but it was more likely deposited from a slope to basin depth of the shelf lagoon may have reached the maximum at the environment of an isolated platform with or without connection to lower to middle part of the Doushantuo Formation but may have been the Yangtze platform (Fig. 1B). Additional areas that require further shallowed during the late stage of the Doushantuo deposition. Such a investigation include the northwestern margin of the Yangtze paleogeographic configuration may have extended to the deposition platform. In a few sections of the Chengkou County in northeastern Author's personal copy

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Fig. 8. Composite litho-, chemo- and bio-stratigraphic comparisons between South China (A), Lesser Himalaya of northern India (B), Oman (C), and the Adelaide rift complex of 13 South Australia (D). Data source: South China (Jiang et al., 2007; Zhou and Xiao, 2007; Zhou et al., 2007; Ishikawa et al., 2008), but see Zhu et al. (2007) for more δ Ccarb and Sawaki et al. (2010) for more 87Sr/86Sr data; India (Jiang et al., 2002, 2003c; Kaufman et al., 2006); Oman (Fike et al., 2006; Le Guerroué et al., 2006; Le Guerroué and Cozzi, 2010); Australia (Calver, 2000; Walter et al., 2000; Grey et al., 2003).

Chongqing (Fig. 1B), the Doushantuo Formation is composed of black It is expected that a laterally continuous shelf shoal complex more shale and thinly bedded limestone and overlain by thinly bedded than 50 km wide (Fig. 9B) would have created strongly restricted cherts of the Liuchapo Formation (C.M. Zhou, personal communica- environments in the shelf lagoon. Open-ocean seawater may have tion, 2011). The lithology and sequence of the Doushantuo Formation prevailed in the entire Yangtze platform during cap carbonate in this area are similar to those of the slope-to-basin sections in deposition and the immediate aftermath, but may have been western Hunan and eastern Guizhou. It is uncertain whether the restricted by the marginal barrier shortly after the a-few-meter- Doushantuo Formation in this area records deposition in the thick black shale deposition following the cap carbonate. Exchange northwestern margin of the Yangtze platform that may have faced between the shelf lagoon and the open ocean could have been limited towards the north or northwest. during some periods of the Doushantuo deposition. Particularly, Author's personal copy

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Fig. 9. Generalized depositional model for the Doushantuo Formation. (A) Open shelf during deposition of the cap carbonate and its immediately overlying black shales. (B) Rimmed shelf during subsequent Doushantuo time. Red numbers represent the same sections as in Figs. 1–7. Note that the orientation of transect 1 sections has been rotated counterclockwise about 45°.

during times when the shelf margin was exposed, as indicated by the 5. Discussion presence of subaerial exposure and karst features in Yangjiaping and Weng'an, the shelf lagoon may have been strongly restricted, a 5.1. Paleogeographic Influence on Geochemical Variations scenario perhaps comparable to the modern Black Sea although in a much shallower fashion. Large geochemical variations have been reported from the Large facies variations would be expected in the proximal side of Doushantuo Formation. However, except for the carbon isotope the shelf lagoon as tidal flat facies prograded towards the shelf lagoon analyses (Figs. 11 and 12), most of the other geochemical analyses and retrograded towards land (Figs. 9B and 10). This may explain were focused on the Yangtze Gorges areas, the proximal side of the abrupt facies changes among sections in the Yangtze Gorges area. Also shelf lagoon, or to less extent, the distal side of the lagoon close to the expected is the facies heterogeneity within the shelf shoal complex, as shelf margin (Fig. 13). 13 the shallow-water carbonate platform partially exposed and facies Three negative δ Ccarb anomalies have been documented from the migrated towards the shelf lagoon and the upper slope. Large Doushantuo Formation in the Yangtze Gorges area (section 4 in variations in facies and thickness in the vicinity of Weng'an (cf., Fig. 11). However, the magnitude of the middle Doushantuo negative Zhou et al., 2007; Zhu et al., 2007; Jiang et al., 2008) agree well with excursion varies from section to section even in the Yangtze Gorges such expectations. Due to the slope instability and progradation/ area (Jiang et al., 2007; Zhou and Xiao, 2007; Zhu et al., 2007). This retrogradation of the shelf margin, facies variation in slope environ- phenomenon may be caused by different sampling resolution among ments is also expected, as has been seen in the vicinity of Rongxi and research groups or, the isotope anomaly at the middle Doushantuo 13 Taoying areas. Formation represents a local or diagenetic signature. The δ Ccarb Author's personal copy

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Fig. 10. Paleogeographic reconstruction of the Doushantuo Formation. This configuration may have existed shortly after the Doushantuo cap carbonate deposition and extended into the lower Dengying deposition. anomaly associated with the cap carbonate at the base of the reflect water column stratification and recycling of carbon through Doushantuo Formation is regionally consistent across the shelf-to- sulfate reduction (Jiang et al., 2007, 2008) and/or methanogenesis 13 basin transect, but the δ Ccarb anomaly near the top of the (Ader et al., 2009). In the strongly stratified shelf lagoon and the open 13 Doushantuo Formation varies from a single, continuous anomaly in ocean basin, recycling of C-depleted CO2 and CH4 at and below the the proximal side of the shelf lagoon (section 4 in Fig. 11) to multiple chemocline may have created a large δ13C gradient. Carbonates negative-positive shifts in the distal side of the shelf lagoon produced in the surface ocean could have isotopic exchange with 13C- 13 (section 7A and 7B in Fig. 11). The absence of the δ Ccarb anomaly depleted DIC in the deep-water column and/or during early in the top of the Doushantuo Formation at Tianping (section 9 in diagenesis on the seafloor (Fig. 14A). In depositional environments Fig. 11) is likely due to the covered interval that was not sampled by above the chemocline, carbonate deposits were from the surface Zhu et al. (2007). In the basinal section (section 12 in Fig. 11), the ocean production and may have positive or near zero δ13C values, 13 entire Doushantuo Formation has negative δ Ccarb values, but the while carbonate deposits below the chemocline may have signifi- stratigraphic resolution is limited by the available carbonate beds cantly negative δ13Cvalues(Fig. 14A). Chemocline fluctuations 13 amenable for δ Ccarb analysis. resulted from enhanced weathering sulfate input or increased Carbonate carbon isotope variations across the shelf-to-basin atmospheric oxygen may have resulted in the transfer of 13C-depleted transect 2 (Fig. 12) are even larger than those in transect 1. In the carbon from organic matter or methane to carbonate carbon, forming shelf lagoon section (section 14 in Fig. 12) and in the lower slope negative δ13C shifts in shallow-water environments above the section (section 21 in Fig. 12), the entire Doushantuo Formation has chemocline (Fig. 14B). 13 negative δ Ccarb values. Both sections, however, have limited data Both the diagenetic interpretation (Derry, 2010a, 2010b) and the points due to the lack of continuous carbonates for isotope analyses. In stratified basin interpretation (Jiang et al., 2007; 2008; Ader et al., 13 the distal side of the shelf lagoon represented by the Weng'an section 2009) for the δ Ccarb variability of the Doushantuo Formation imply 13 13 (section 15 in Fig. 12), multiple negative δ Ccarb shifts are found that the δ Ccarb values may not be representative of global seawater throughout the Doushantuo Formation. In the shelf margin repre- signatures. Much more detailed work needs to be done to clarify the sented by the Duoding section (section 16 in Fig. 12), negative degree of diagenetic alteration and local environmental control on the anomalies are found at the base and the upper part of the Doushantuo carbon isotopes of the Doushantuo Formation, particularly in Formation, respectively, but the magnitude of the later is smaller than consideration of the potential influence of basin restriction and 13 those found in other sections. chemocline fluctuation on δ Ccarb variation. The carbon isotope variability across the shelf-to-basin transects Sulfur isotopes, redox sensitive elemental concentrations and iron led to contrasting interpretations. In one interpretation, carbon speciation data from the Doushantuo Formation are rather perplexing. isotope anomalies from the Doushantuo Formation (and in other Iron speciation data from the Yangtze Gorges area (section 4 in Fig. 13) time-equivalent sections globally) record a diagenetic signal during indicated alternating euxinic and ferruginous conditions throughout burial (Derry 2010a). In another interpretation (Fig. 14), spatial the Doushantuo deposition (Li et al., 2010), but the pyrite sulfur variations in carbon isotope values of the Doushantuo Formation isotopes and sulfur isotope fractionation do not show fluctuations Author's personal copy

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Fig. 11. Carbonate carbon isotope profiles of the Doushantuo Formation across the shelf-to-basin transect 1. Data of sections 4 and 12 are from Jiang et al. (2007) and other sections 13 are from Zhu et al. (2007). Note that at the Yangjiaping section, δ Ccarb fluctuations continue upward to the lower Dengying Formation (Zhu et al., 2007). Most data points reported in Macouin et al. (2004) and Ader et al. (2009) are actually from the Dengying Formation and their relationship with the upper Doushantuo δ13C anomaly needs further clarification. corresponding to variations in iron chemistry (McFadden et al., 2008; distal sides of the shelf lagoon but are much less common in the slope Li et al., 2010). Iron speciation data from the Zhongling section and basin. (section 7A in Fig. 13) indicated mostly ferruginous conditions during Phanerozoic phosphorite deposits are commonly associated with the Doushantuo deposition, but the moderate sulfur isotope fraction- upwelling of nutrient-rich oceanic waters along coastal regions and ation (Δ34S=10–25‰) suggests a local sulfate supply close to the shelf their formation could be widespread across shelf environments (e.g., margin (Li et al., 2010). A local source of sulfate, along with the oxic Glenn et al., 1994; Hiatt and Budd, 2001; Nelson et al., 2010). In environments indicated by iron speciation at the lower part of the general, phosphate formation involves the release of elemental Zhongling section (section 7A in Fig. 13), can be better explained as a phosphorus through organic matter degradation, followed by precip- local phenomenon near the shallow margin of the shelf lagoon. Much itation of carbonate-fluoroapatite as the mineral francolite (Krajewski needs to be done to distinguish local geochemical signature recorded et al., 1994; Hiatt and Budd, 2001). Phosphate may precipitate with in the restricted shelf lagoon from open-ocean signal that may have organic-rich sediments, but its concentration is normally enhanced by broader implications for the Ediacaran ocean chemistry. winnowing and reworking to form economically significant phos- phorite (Hiatt and Budd, 2001; Pufahl et al., 2003). Because organic matter degradation through bacterial sulfate reduction is the most 5.2. Basin Restriction and Phosphorite Deposition efficient process to promote phosphogenesis (Arning et al., 2009), Precambrian environments are commonly considered as unfavorable An interesting phenomenon emerging from the paleogeographic for phosphorite formation due to the overall low sulfate concentration reconstruction is the distribution of phosphorite of the Doushantuo in seawater (Nelson et al., 2010). The enrichment of the Doushantuo and lower Dengying formations. Most of the enriched phosphorite ore (and lower Dengying) phosphorites at the margins of the shelf lagoon deposits are either distributed in the proximal side of the shelf lagoon may have been controlled by (1) high productivity fertilized by (e.g., Baokang and Yuan'an, north of Yichang in Hubei province) or in nutrient supply from weathering input, (2) sulfate availability along the distal side of the shelf lagoon within the shelf shoal complex (e.g., margins of the shelf lagoon promoting phosphogenesis through Weng'an and Kaiyang in Guizhou province). In contrast, phosphorite organic matter degradation, and (3) enrichment of phosphorite ore deposits are rare in the open-ocean side of the shelf margin through Fe-redox pumping (Fe-oxyhydroxides liberating absorbed 3− towards the slope and basin. Phosphorite nodules and clasts are also PO4 to pore water beneath the Fe-redox interface; Nelson et al., more common in the Doushantuo Formation along the proximal and 2010), winnowing and reworking above fair-weather wave base in Author's personal copy

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Fig. 12. Carbonate carbon isotope profiles of the Doushantuo Formation across the shelf-to-basin transect 2 (Jiang et al., 2008). In the Weng'an area, isotope data reported from other 13 sections (Zhu et al., 2007; Zhou et al., 2007) show similar temporal δ Ccarb fluctuations. shallow subtidal to intertidal environments. The lack of phosphorite shelf lagoon in Songlin (loc. 14 in Fig. 10). The upper Doushantuo enrichment in the open-ocean side of the shelf margin implies that Wenghui biota (which is taxonomically similar to the Miaohe biota) is phosphorites of the Doushantuo and lower Dengying formations may paleogeographically located in the upper slope environment at not have been sourced from upwelling of nutrient-rich oceanic Wenghui and Rongxi (loc. 17 and 19 in Fig. 10). Equivalent fossils waters. have not been found in the lower slope Wuhe section (loc. 21 in Fig. 10). 5.3. Paleogeographic Distribution of the Doushantuo Biotas We suspect that benthic multicellular organisms in the Doush- antuo Formation may have tracked paleogeographically controlled Except the Lantian biota (Fig. 1B) that may have lived and been chemocline. They may have lived in oxic/suboxic environments preserved in deep water characterized by anoxia but punctuated by mostly above the chemocline, although preservation may be episodes of oxic conditions (Shen et al., 2008; Yuan et al., 2011), other facilitated by redox conditions near the chemocline. Well-preserved Doushantuo biotas show a paleogeographic distribution either at the macroalgae holdfasts in the Miaohe biota (Xiao et al., 2002) and shallow-water margins of the shelf lagoon or at the shelf margin-to- Wenghui biota (Wang and Wang, 2006) indicate that at least some of slope transition. The Jiulongwan biota in the Yangtze Gorges area these organisms were preserved in situ, although geochemical data (section 4 in Figs. 3 and 10) is located in the proximal side of the shelf indicated that back shales at the top of the Doushantuo Formation lagoon and similar acritarch fossils have been found in more proximal were deposited in euxinic water column (Li et al., 2010). This seemly sections at Xiaofenghe (section 1 in Figs. 4 and 10; Yin et al., 2007) and perplexing phenomenon is best explained by chemocline fluctuations Zhangcunping (McFadden et al., 2009). The Miaohe biota is only at scales much finer than available geochemical data. Integrated present in the black shale unit at the top of the Doushantuo Formation geochemical and paleontological analyses at much higher resolution in Miaohe (loc. 2 in Fig. 10). The absence of Miaohe-like fossils at would lend insights into the preservation of the Doushantuo fossils. Xiaofenghe (section 1 Fig. 10) and further north section is possibly a taphonomic bias: coarse-grained carbonates and siliciclastics at those 6. Conclusion sections are not conducive to the preservation of macroscopic carbonaceous compressions even if similar organisms may have The majority of the Ediacaran Doushantuo Formation (ca. 635– lived in those environments. Further south towards the deeper 551 Ma) in the Ediacaran Yangtze platform in South China was lagoon, the Miaohe biota has not been found so far. The Weng'an biota deposited on a rimmed carbonate shelf with a shelf-margin barrier is located in the distal side of the shelf lagoon within the shelf margin separating the shelf lagoon from the open ocean. Such a paleogeo- shoal complex (loc. 15 in Fig. 10), and similar biotas have been known graphic configuration may have developed shortly after the deposi- from shallow facies in inner shelf (e.g., Chadian in southern Shaanxi tion of the Doushantuo cap carbonate (ca. 635 Ma) and its immediate Province; Xiao et al., 1999) or proximal margin of the shelf lagoon overlying black shales (ca. 632 Ma) and lasted until deposition of the (e.g., Baokang in Hubei Province; Zhou et al., 2001) or possibly lower Dengying Formation (b551 Ma), when a shelf-wide karstic isolated carbonate shoal facies (e.g., Chaoyang in Jiangxi Province; unconformity marked the infill and subaerial exposure of the shelf Zhou et al., 2002). Equivalent fossils have not been found towards the lagoon. Author's personal copy

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Fig. 13. Iron speciation and sulfur isotope data from the Jiulongwan (section 4) and Zhongling sections (section 7A). At the Jiulongwan section, three intervals with FePY/FeHR≥0.8 were interpreted as euxinic (anoxic+sulfidic) while the other intervals were considered as anoxic and ferruginous (Li et al., 2010). The pyrite sulfur isotopes and sulfur isotope fractionation data (McFadden et al., 2009; Li et al., 2010), however, do not show obvious changes at the anoxic–euxinic transitions. This is possibly due to the lower stratigraphic resolution of Fe speciation data. At the Zhongling section, the lower part of the section shows evidence for oxic conditions (with FeHR/FeTb0.38). For some stratigraphic intervals, the pyrite sulfur isotopes and sulfur isotope fractionation data show up to 30‰ difference from those of the Jiulongwan section. These geochemical variations may reflect differences between the margins of the shelf lagoon.

The particular paleogeographic configuration during the Doush- Most geochemical studies of the Doushantuo Formation, however, antuo deposition may have resulted in large variations in sedimentary have been focused on the proximal and distal sides of the shelf lagoon. facies and geochemistry between the shelf lagoon and the open ocean. Therefore the degree to which the existing geochemical record from

Fig. 14. Schematic diagram to explain the carbon isotope variations across the shelf-to-basin transects. (A) In a strongly stratified shelf lagoon and ocean, recycling of 13C-depleted 13 13 CO2 from organic degradation or CH4 from methanogenesis may result in a large δ C gradient. Carbonates precipitated from the surface ocean may have positive δ C values, but carbonates falling out from the surface ocean may have had isotopic exchange with 13C-depleted DIC in the deep-water column or during early diagenesis, generating negative δ13C values. (B) During times of increased supply of oxidants (such as sulfate and oxygen), chemocline fluctuations resulted in the transfer of 13C-depleted carbon to shallow-water regions, leading to negative δ13C shifts. The magnitude of δ13C excursions may vary, depending on the proportional contribution of carbon from surface ocean production in a particular depositional environment. Benthic eukaryotes may have also tracked the chemocline fluctuations. Author's personal copy

G. Jiang et al. / Gondwana Research 19 (2011) 831–849 847 the Doushantuo Formation is representative of open-ocean seawater Guo, Q., Strauss, H., Liu, C., Goldberg, T., Zhu, M., Pi, D., Heubeck, C., Vernhet, E., Yang, X., fi Fu, P., 2007. Carbon isotopic evolution of the terminal Neoproterozoic and early signature requires further con rmation in paleogeographic localities Cambrian: evidence from the Yangtze Platform, South China. Palaeogeography, towards the open-ocean side of the shelf margin. Palaeoclimatology, Palaeoecology 254, 140–157. The paleogeographic configuration during the Doushantuo depo- Halverson, G.P., Hoffman, P.F., Schrag, D.P., Maloof, A.C., Rice, A.H.N., 2005. Toward a Neoproterozoic composite carbon-isotope record. Geological Society of America sition may have also controlled the distribution and preservation of Bulletin 117, 1181–1207. multicellular organisms. Most biotas reported from the Doushantuo Halverson, G.P., Wade, B.P., Hurtgen, M.T., Barovich, K.M., 2010. Neoproterozoic Formation are either located in the shallow margins of the shelf lagoon chemostratigraphy. Precambrian Research 182, 337–350. or in the shelf margin-to-slope transition, although frequent fluctua- Hiatt, E.E., Budd, D.A., 2001. Sedimentary phosphate formation in warm shallow waters: new insights into the palaeoceanography of the Permian Phosphoria Sea tions of the chemocline may have allowed some of these organisms to from analysis of phosphate oxygen isotopes. Sedimentary Geology 145, 119–133. invade deeper water environments. The spatial distribution of the Huang, J., Chu, X.L., Chang, H.J., Feng, L.J., 2009. Trace element and rare earth element of Doushantuo biotas suggests that benthic multicellular eukaryotes cap carbonate in Ediacaran Doushantuo Formation in Yangtze Gorges. Chinese Science Bulletin 54, 3295–3302. (including early animals) may have tracked paleogeographically Ishikawa, T., Ueno, Y., Komiya, T., Sawaki, Y., Han, J., Shu, D., Li, Y., Maruyama, S., Yoshida, N., controlled chemoclines. Preservation of the Doushantuo biotas may 2008. Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary have been enhanced by frequent chemocline fluctuations that aided to section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion. Gondwana Research 14, 193–208. the mineralization and carbonization of fossils. Jenkins, R.J.F., Cooper, J.A., Compston, W., 2002. Age and biostratigraphy of Early Cambrian tuffs from SE Australia and southern China. Journal of the Geological Society of London 159, 645–658. Acknowledgements Jiang, G., Christie-Blick, N., Kaufman, A.J., Banerjee, D.M., Rai, V., 2002. Sequence stratigraphy of the Neoproterozoic Infra Krol Formation and Krol Group, Lesser – This research was supported by the National Science Foundation Himalaya, India. Journal of Sedimentary Research 72, 524 542. Jiang, G., Sohl, L.E., Christie-Blick, N., 2003a. Neoproterozoic stratigraphic comparison of (EAR-0745825 and EAR-0745827) and the National Natural Science the Lesser Himalaya (India) and Yangtze Block (South China); paleogeographic Foundation of China (40621002). Jiang gratefully acknowledges UNLV implications. Geology 31, 917–920. Sabbatical Leave support. We are grateful to Profs. M. Santosh Jiang, G., Kennedy, M.J., Christie-Blick, N., 2003b. Stable isotopic evidence for methane seeps in Neoproterozoic postglacial cap carbonates. Nature 426, 822–826. (Editor), Chuanming Zhou, and Nigel Hughes for their constructive Jiang, G., Christie-Blick, N., Kaufman, A.J., Banerjee, D.M., Rai, V., 2003c. Carbonate comments and corrections that helped improve the paper. platform growth and cyclicity at a terminal Proterozoic passive margin, Infra Krol Formation and Krol Group, Lesser Himalaya, India. Sedimentology 50, 921–952. Jiang, G., Kennedy, M.J., Christie-Blick, N., Wu, H., Zhang, S., 2006a. Stratigraphy, References sedimentary structures, and textures of the late Neoproterozoic Doushantuo cap carbonate in South China. Journal of Sedimentary Research 76, 978–995. Ader, M., Macouin, M., Trindade, R.I.F., Hadrien, M.H., Yang, Z., Sun, Z., Besse, J., 2009. A Jiang, G., Shi, X., Zhang, S., 2006b. Methane seeps, methane hydrate destabilization, and the multilayered water column in the Ediacaran Yangtze platform? Insights from late Neoproterozoic postglacial cap carbonates. Chinese Science Bulletin 51, 1152–1173. carbonate and organic matter paired δ13C. Earth and Planetary Science Letters 288, Jiang, G., Kaufman, A.J., Christie-Blick, N., Zhang, S., Wu, H., 2007. Carbon isotope variability 213–227. across the Ediacaran Yangtze platform in South China: implications for a large surface- Arning, E.T., Birgel, D., Brunner, B., Peckmann, J., 2009. Bacterial formation of phosphatic to-deep ocean δ13C gradient. Earth and Planetary Science Letters 261, 303–320. laminites off Peru. Geobiology 7, 295–307. Jiang, G.Q., Zhang, S.H., Shi, X.Y., Wang, X.Q., 2008. Chemocline instability and isotope Bristow, T.F., Kennedy, M.J., 2008. Carbon isotope excursions and the oxidant budget of variations of the Ediacaran Doushantuo basin in South China. Science in China. the Ediacaran atmosphere and ocean. Geology 36, 863–866. Series D: Earth Sciences 51, 1560–1569. Bristow, T.F., Kennedy, M.J., Derkowski, A., Droser, M., Jiang, G., Creaser, R.A., 2009. Jiang, G., Wang, X., Shi, X., Zhang, S., Xiao, S., Dong, J., 2010. Organic carbon isotope Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo constraints on the dissolved organic carbon (DOC) reservoir at the Cryogenian– Formation. Proceedings of the National Academy of Sciences of the United States of Ediacaran transition. Earth and Planetary Science Letters 299, 159–168. America 106, 13190–13195. Jiang, S.-Y., Pi, D.-H., Heubeck, C., Frimmel, H., Liu, Y.-P., Deng, H.-L., Ling, H.-F., Yang, J.-H., Calver, C.R., 2000. Isotope stratigraphy of the Ediacarian (Neoproterozoic III) of the 2009. Early Cambrian ocean anoxia in South China. Nature 459, E5–E6. Adelaide rift complex, Australia, and the overprint of water column stratification. Kaufman, A.J., Jiang, G., Christie-Blick, N., Banerjee, D.M., Rai, V., 2006. Stable isotope Precambrian Research 100, 121–150. record of the terminal Neoproterozoic Krol platform in the Lesser Himalayas of Cao, R., Tang, T., Xue, Y., Yu, C., Yin, L., Zhao, W., 1989. Research on Sinian strata with ore northern India. Precambrian Research 147, 156–185. deposits in the Yangtze region, China. In: Institute of Geology and Palaeontology Kaufman, A.J., Corsetti, F.A., Varni, M.A., 2007. The effect of rising atmospheric oxygen (Ed.), Upper Precambrian of the Yangzi (Yangtze) Region, China. Nanjing on carbon and sulfur isotope anomalies in the Neoproterozoic Johnnie Formation, University Press, Nanjing, pp. 1–94. Death Valley, USA. Chemical Geology 237, 47–63. Chen, D., Wang, J., Qing, H., Yan, D., Li, R., 2009. Hydrothermal venting activities in the Knauth, L.P., Kennedy, M.J., 2009. The late Precambrian greening of the Earth. Nature Early Cambrian, South China: petrological, geochronological and stable isotopic 460, 728–732. constraints. Chemical Geology 258, 168–181. Krajewski, K.P., Van Cappellen, P., Trichet, J., Kuhn, O., Lucas, J., Martin-Algarra, A., Chen, J., 2005. The Dawn of Animal World. Jiangsu Science and Technology Press, Prevot, L., Tewari, V.C., Gaspar, L., Knight, R.I., Lamboy, M., 1994. Biological Nanjing, pp. 1–366. processes and apatite formation in sedimentary environments. Eclogae Geologicae Chen, M., Xiao, Z., 1992. Macrofossil biota from upper Doushantuo Formation in eastern Helvetiae 87, 701–745. Yangtze Gorges, China. Acta Palaeontologica Sinica 31, 513–529. Ku, T.C.W., Walter, L.M., Coleman, M.L., Blake, R.E., Martini, A.M., 1999. Coupling Compston, W., Zhang, Z., Cooper, J.A., Ma, G., Jenkins, R.J.F., 2008. Further SHRIMP between sulfur recycling and syndepositional carbonate dissolution: evidence from geochronology on the early Cambrian of South China. American Journal of Science oxygen and sulfur isotope composition of pore water sulfate, South Florida 308, 399–420. Platform, U.S.A. Geochimica et Cosmochimica Acta 63, 2529–2546. Condon, D., Zhu, M., Bowring, S., Wang, W., Yang, A., Jin, Y., 2005. U–Pb ages from the Le Guerroué, E., Allen, P.A., Cozzi, A., Etienne, J.L., Fanning, M., 2006. 50 Myr recovery from Neoproterozoic Doushantuo Formation, China. Science 308, 95–98. the largest negative δ13C excursion in the Ediacaran ocean. Terra Nova 18, 147–153. Derry, L.A., 2010a. A burial diagenesis origin for the Ediacaran Shuram-Wonoka carbon Le Guerroué, E., Cozzi, A., 2010. Veracity of Neoproterozoic negative C-isotope values: the isotope anomaly. Earth and Planetary Science Letters 294, 152–162. termination of the Shuram negative excursion. Gondwana Research 17, 653–661. Derry, L.A., 2010b. On the significance of δ13C correlations in ancient sediments. Earth Li, C., Love, G.D., Lyons, T.W., Fike, D.A., Sessions, A.L., Chu, X., 2010. A stratified redox and Planetary Science Letters 296, 497–501. model for the Ediacaran Ocean. Science 328, 80–83. Ding, L., Li, Y., Hu, X., Xiao, Y., Su, C., Huang, J., 1996. Sinian Miaohe Biota. Geological Li, C.W., Chen, J.Y., Hua, T.E., 1998. Precambrian sponges with cellular structures. Publishing House, Beijing, pp. 1–221. Science 279, 879–882. Dong, J., Zhang, S.H., Jiang, G.Q., Zhao, Q.L., Li, H.Y., Shi, X.Y., Liu, J.L., 2008. Early Li, R., Chen, J., Zhang, S., Lei, J., Shen, Y., Chen, X., 1999a. Spatial and temporal variations diagenetic growth of carbonate concretions in the upper Doushantuo Formation in in carbon and sulfur isotopic compositions of Sinian sedimentary rocks in the South China and their significance for the assessment of hydrocarbon source rock. Yangtze platform, South China. Precambrian Research 97, 59–75. Science in China. Series D: Earth Sciences 51, 1330–1339. Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., 1999b. The breakup of Rodinia; did it start with a Fike, D.A., Grotzinger, J.P., Pratt, L.M., Summons, R.E., 2006. Oxidation of the Ediacaran mantle plume beneath South China? Earth and Planetary Science Letters 173, 171–181. Ocean. Nature 444, 744–747. Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., Zhang, S., Zhou, H., 2003. Geochronology of Glenn, C.R., Föllmi, K.B., Riggs, S.R., Baturin, G.N., Grimm, K.A., Trappe, J., Abed, A.M., Neoproterozoic syn-rift magmatism in the Yangtze Craton, South China and Galli-Oliver, C., Garrison, R.E., Ilyin, A.V., Jehl, C., Rohrlich, V., Sadaqah, R.M.Y., correlations with other continents: evidence for a mantle superplume that broke Schidlowski, M., Sheldon, R.E., Siegmund, H., 1994. P and phosphorites: up Rodinia. Precambrian Research 122, 85–109. sedimentology and environments of formation. Eclogae Geologicae Helveticae 87, Liu, B., Xu, X., Pan, X., Huang, H., Xu, Q., 1993. Paleocontinental Sediments, Crust 747–788. Evolution and Ore Deposits of South China. Science Press, Beijing, pp. 1–236. Grey, K., Walter, M.R., Calver, C.R., 2003. Neoproterozoic biotic diversification; snowball Ma, G., Lee, H., Zhang, Z., 1984. An investigation of the age limits of the Sinian System in Earth or aftermath of the Acraman impact? Geology 31, 459–462. south China. Bulletin of Yichang Institute of Geology and Mineral Resources 8, 1–29. Author's personal copy

848 G. Jiang et al. / Gondwana Research 19 (2011) 831–849

Macouin, M., Besse, J., Ader, M., Gilder, S., Yang, Z., Sun, Z., Agrinier, P., 2004. Combined Xiao, S., Yuan, X., Steiner, M., Knoll, A.H., 2002. Macroscopic carbonaceous compressions paleomagnetic and isotopic data from the Doushantuo carbonates, South China: in a terminal Proterozoic shale: a systematic reassessment of the Miaohe biota, implications for the ‘snowball Earth’ hypothesis. Earth and Planetary Science South China. Journal of Paleontology 76, 347–376. Letters 224, 387–398. Xiao, S., Zhang, Y., Knoll, A.H., 1998. Three-dimensional preservation of algae and Mallarino, G., Goldstein, R.H., Di Stefano, P., 2002. New approach for quantifying water animal embryos in a Neoproterozoic phosphorite. Nature 391, 553–558. depth applied to the enigma of drowning of carbonate platforms. Geology 30, Yan, Y., Jiang, C., Zhang, S., Du, S., Bi, Z., 1992. Research of the Sinian System in the region 783–786. of western Zhejiang, northern Jiangxi, and southern Anhui provinces. Bulletin of McFadden, K.A., Huang, J., Chu, X., Jiang, G., Kaufman, A.J., Zhou, C., Yuan, X., Xiao, S., the Nanjing Institute of Geology and Mineral Resources, Chinese Academy of 2008. Pulsed oxidation and biological evolution in the Ediacaran Doushantuo Geological Sciences 12, 1–105. Formation. Proceedings of the National Academy of Sciences of the United States of Yang, J., Sun, W., Wang, Z., Xue, Y., Tao, X., 1999. Variations in Sr and C isotopes and Ce America 105, 3197–3202. anomalies in successions from China; evidence for the oxygenation of Neoproter- McFadden, K.A., Xiao, S., Zhou, C., Kowalewski, M., 2009. Quantitative evaluation of the ozoic seawater? Precambrian Research 93, 215–233. biostratigraphic distribution of acanthomorphic acritarchs in the Ediacaran Yin, C., Liu, G., 1988. Micropaleofloras. In: Zhao, Z., Xing, Y., Ding, Q., Liu, G., Zhao, Y., Doushantuo Formation in the Yangtze Gorges area, South China. Precambrian Zhang, S., Meng, X., Yin, C., Ning, B., Han, P. (Eds.), The Sinian System of Hubei. China Research 173, 170–190. University of Geosciences Press, Wuhan, pp. 170–180. Mei, M.X., Nie, R.Z., Zhang, H., Chen, Y.H., Meng, X.Q., 2006. Sequence-stratigraphic Yin, C., Bengtson, S., Yue, Z., 2004. Silicified and phosphatized Tianzhushanian, division for the Sinian system of the upper-Yangtze region. Geoscience 20, 49–60. spheroidal microfossils of possible animal origin from the Neoproterozoic of Nelson, G.J., Pufahl, P.K., Hiatt, E.E., 2010. Paleoceanographic constraints on Precam- South China. Acta Palaeontologica Polonica 49, 1–12. brian phosphorite accumulation, Baraga Group, Michigan, USA. Sedimentary Yin, C., Liu, D., Gao, L., Wang, Z., Xing, Y., Jian, P., Shi, Y., 2003. Lower boundary age of the Geology 226, 9–21. Nanhua System and the Gucheng glacial stage; evidence from SHRIMP II dating. Pufahl, P.K., Grimm, K.A., Abed, A.M., Sadaqah, R.M.Y., 2003. Upper Cretaceous Chinese Science Bulletin 48, 1657–1662. (Campanian) phosphorites in Jordan: implications for the formation of a south Yin, L., Zhu, M., Knoll, A.H., Yuan, X., Zhang, J., Hu, J., 2007. Doushantuo embryos Tethyan phosphorite giant. Sedimentary Geology 161, 175–205. preserved inside diapause egg cysts. Nature 446, 661–663. Pyle, L.J., Narbonne, G.M., James, N.P., Dalrymple, R.W., Kaufman, A.J., 2004. Integrated Yuan, X., Li, J., Cao, R., 1999. A diverse metaphyte assemblage from the Neoproterozoic Ediacaran chronostratigraphy, Wernecke Mountains, northwestern Canada. Pre- black shales of South China. Lethaia 32, 143–155. cambrian Research 132, 1–27. Yuan, X., Chen, Z., Xiao, S., Zhou, S., Hua, H., 2011. An early Ediacaran assemblage of Sarg, J.F., 1988. Carbonate sequence stratigraphy. In: Wilgus, C.K., Hastings, B.S., macroscopic and morphologically differentiated eukaryotes. Nature 470, 390–393. Kendall, C.G.S.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. (Eds.), Sea-Level Yuan, X., Xiao, S., Yin, L., Knoll, A.H., Zhou, C., Mu, X., 2002. Doushantuo Fossils: Life on Changes: An Integrated Approach: Society of Economic Paleontologists and the Eve of Animal Radiation. China University of Science and Technology Press, Mineralogists Special Publication, 42, pp. 155–181. Hefei, China, pp. 1–71. Sawaki, Y., Ohno, T., Tahata, M., Komiya, T., Hirata, T., Maruyama, S., Windley, B.F., Han, Zhang, S., Jiang, G., Zhang, J., Song, B., Kennedy, M.J., Christie-Blick, N., 2005. U–Pb J., Shu, D., Li, Y., 2010. The Ediacaran radiogenic Sr isotope excursion in the sensitive high-resolution ion microprobe ages from the Doushantuo Formation in Doushantuo Formation in the Three Gorges area, South China. Precambrian south China: constraints on late Neoproterozoic glaciations. Geology 33, 473–476. Research 176, 46–64. Zhang, S., Jiang, G., Dong, J., Han, Y., Wu, H., 2008a. New SHRIMP U–Pb age from the Saylor, B.Z., Kaufman, A.J., Grotzinger, J.P., Urban, F., 1998. A composite reference Wuqiangxi Formation of Banxi Group: implications for rifting and stratigraphic section for terminal Proterozoic strata of southern Namibia. Journal of Sedimentary erosion associated with the early Cryogenian (Sturtian) glaciation in South China. Research 68, 1223–1235. Science in China. Series D: Earth Sciences 51, 1537–1544. Schlager, W., 1999. Type 3 sequence boundaries. In: Harris, P.M., Saller, A., Simo, J.A. (Eds.), Zhang, Q.-R., Li, X.-H., Feng, L.-J., Huang, J., Song, B., 2008b. A new age constraint on the Advances in Carbonate Sequence Stratigraphy: Application to Reservoirs, Outcrops, onset of the Neoproterozoic glaciations in the Yangtze platform, South China. and Models: Society for Sedimentary Geology Special Publication, 62, pp. 35–45. Journal of Geology 116, 423–429. Shen, Y., Zhang, T., Hoffman, P.F., 2008. On the co-evolution of Ediacaran oceans and Zhang, S., Jiang, G., Han, Y., 2008c. The age of the Nantuo Formation and Nantuo animals. Proceedings of the National Academy of Sciences of the United States of glaciation in South China. Terra Nova 20, 289–294. America 105, 7376–7381. Zhang, Y., 1989. Multicellular thallophytes with differentiated tissues from late Shields, G., Kimura, H., Yang, J., Gammon, P., 2004. Sulphur isotopic evolution of Proterozoic phosphate rocks of South China. Lethaia 22, 113–132. Neoproterozoic–Cambrian seawater: new francolite-bound sulphate δ34S data and Zhao, Z., Xing, Y., Ma, G., Chen, Y., 1985. Biostratigraphy of the Yangtze Gorge Area, (1) a critical appraisal of the existing record. Chemical Geology 204, 163–182. Sinian. Geological Publishing House, Beijing, pp. 1–143. Tang, F., Yin, C., Bengtson, S., Liu, P., Wang, Z., Gao, L., 2008. Octoradiate spiral organisms Zhao, Z., Xing, Y., Ding, Q., Liu, G., Zhao, Y., Zhang, S., Meng, X., Yin, C., Ning, B., Han, P., 1988. The in the Ediacaran of South China. Acta Geologica Sinica 82, 27–34. Sinian System of Hubei. China University of Geosciences Press, Wuhan, China, pp. 1–205. Vernhet, E., Heubeck, C., Zhu, M.-Y., Zhang, J.-M., 2006. Large-scale slope instability at Zhao, Y., He, M., Chen, M.E., Peng, J., Yu, M., Wang, Y., Yang, R., Wang, P., Zhang, Z., 2005. the southern margin of the Ediacaran Yangtze platform (Hunan province, central The discovery of a Miaohe-type biota from the Neoproterozoic Doushantuo China). Precambrian Research 148, 32–44. Formation in Jiangkou County, Guizhou Province, China. Chinese Science Bulletin Vernhet, E., Heubeck, C., Zhu, M.Y., Zhang, J.M., 2007. Stratigraphic reconstruction of the 49, 1916–1918. Ediacaran Yangtze platform margin (Hunan province, China) using a large Zhao, Y.Y., Zheng, Y.F., Chen, F.K., 2009. Trace element and strontium isotope olistolith. Palaeogeography, Palaeoclimatology, Palaeoecology 254, 123–139. constraints on sedimentary environment of Ediacaran carbonates in southern Vernhet, E., Reijmer, J.J.G., 2010. Sedimentary evolution of the Ediacaran Yangtze Anhui, South China. Chemical Geology 265, 345–362. platform shelf (Hubei and Hunan provinces, Central China). Sedimentary Geology Zhao, Y.Y., Zheng, Y.F., 2010. Stable isotope evidence for involvement of deglacial 225, 99–115. meltwater in Ediacaran carbonates in South China. Chemical Geology 271, 86–100. Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P., Hill, A.C., 2000. Dating the 840–544 Ma Zhou, C., Brasier, M.D., Xue, Y., 2001. Three-dimensional phosphatic preservation of Neoproterozoic interval by isotopes of strontium, carbon, sulfur in seawater, and giant acritarchs from the terminal Proterozoic Doushantuo Formation in Guizhou some interpretative models. Precambrian Research 100, 371–433. and Hubei provinces, South China. Palaeontology 44, 1157–1178. Wang, H.Z., 1985. Atlas of the Paleogeography of China. Cartographic Publishing House, Zhou, C., Chen, Z., Xue, Y., 2002. New microfossils from the late Neoproterozoic Beijing, pp. 1–143. Doushantuo Formation at Chaoyang phosphorite deposit in Jiangxi Province, South Wang, J., Jiang, G., Xiao, S., Li, Q., Wei, Q., 2008a. Carbon isotope evidence for widespread China. Acta Palaeontologica Sinica 41, 178–192. methane seeps in the ca. 635 Ma Doushantuo cap carbonate in south China. Zhou, C., Tucker, R., Xiao, S., Peng, Z., Yuan, X., Chen, Z., 2004. New constraints on the Geology 36, 347–350. ages of Neoproterozoic glaciations in south China. Geology 32, 437–440. Wang, J., Li, Z.-X., 2003. History of Neoproterozoic rift basins in South China: Zhou, C., Xie, G., Mcfadden, K., Xiao, S., Yuan, X., 2007. The diversification and extinction implications for Rodinia break-up. Precambrian Research 122, 141–158. of Doushantuo-Pertatataka acritarchs in South China: causes and biostratigraphic Wang, X., Erdtmann, B.D., Chen, X., Mao, X., 1998. Integrated sequence-, bio- and significance. Geological Journal 42, 229–262. chemo-stratigraphy of the terminal Proterozoic to lowermost Cambrian “black rock Zhou, C., Xiao, S., 2007. Ediacaran δ13C chemostratigraphy of South China. Chemical series” from central South China. Episodes 21, 178–189. Geology 237, 89–108. Wang, X.Q., Shi, X.Y., 2009. Spatio-temporal carbon isotope variation during the Zhou, C., Bao, H., Peng, Y., Yuan, X., 2010. Timing the deposition of 17O-depleted barite at Ediacaran period in South China and its impact on bio-evolution. Science in China. the aftermath of Nantuo glacial meltdown in South China. Geology 38, 903–906. Series D: Earth Sciences 52, 1520–1528. Zhu, M., Zhang, J., Steiner, M., Yang, A., Li, G., Erdtmann, B.D., 2003. Sinian–Cambrian Wang, Y., Wang, X., 2006. The holdfasts of macroalage in the Neoproterozoic stratigraphic framework for shallow- to deep-water environments of the Yangtze Doushantuo Formation in northeastern Guizhou province and their environmental platform: an integrated approach. Progress in Natural Science 13, 951–960. significance. Acta Micropalaeontologia Sinica 23, 154–164. Zhu, M., Zhang, J., Yang, A., 2007. Integrated Ediacaran (Sinian) chronostratigraphy of Wang, Y., Wang, X., Huang, Y., 2008b. Megascopic symmetrical metazoans from the South China. Palaeogeography, Palaeoclimatology, Palaeoecology 254, 7–61. Ediacaran Doushantuo Formation in the northeastern Guizhou, South China. Zhu, M., Gehling, J.G., Xiao, S., Zhao, Y.L., Droser, M., 2008. Eight-armed Ediacara fossil Journal of the China University of Geosciences 19, 200–206. preserved in contrasting taphonomic windows from China and Australia. Geology 36, Wang, Z.Q., Gao, L.Z., Yin, C.Y., 2001. Ascertainment and stratigraphic division of the 867–870. Sinian stratotype section. Geological Review 47, 450–458. Zhu, R.X., Li, X.H., Hou, X.G., Pan, Y.X., Wang, F., Deng, C.L., He, H.Y., 2009. SIMS U–Pb Xiao, S., 2004. New multicellular algal fossils and acritarchs in Doushantuo chert nodules zircon age of a tuff layer in the Meishucun section, Yunnan, southwest China: (Neoproterozoic, Yangtze Gorges, South China). Journal of Paleontology 78, 393–401. constraint on the age of the Precambrian–Cambrian boundary. Science in China. Xiao, S., Knoll, A.H., Zhang, L., Hua, H., 1999. The discovery of Wengania globosa in Series D: Earth Sciences 52, 1385–1392. Doushantuo phosphorites in Chadian, Shaanxi Province. Acta Micropalaeontologica Zhu, W., Chen, M., 1984. On the discovery of macrofossil algae from the late Sinian in Sinica 16, 259–266. the eastern Yangtze Gorges, south China. Acta Botanica Sinica 26, 558–560. Author's personal copy

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Ganqing Jiang is an Associate Professor at the Department Yue Wang is a Professor at the School of Resources and of Geoscience, University of Nevada Las Vegas (UNLV). He Environments, Guizhou University, China, where he has received his B.Sc. degree from Xiangtan Mining Institute been since 2007. He received his B.Sc. degree from China (Hunan, China, 1988), M.Sc. degree from China University University of Geosciences (Wuhan) in 1984 and Ph.D. of Geosciences (Beijing, China, 1991) and Ph.D. degree degree from China University of Geosciences (Beijing). His from Columbia University (New York City, USA, 2002). main research interests are in stratigraphy and paleontol- Prior to joining UNLV, he worked as a postdoctoral ogy of the Precambrian and Paleozoic successions in South researcher at the University of California, Riverside China. Recent projects also involve stratigraphy, paleoen- – (2002 2004). His research interests include carbonate vironments and paleontology of the Mesoproterozoic – sedimentology stratigraphy, stable isotope geochemistry, succession in north China. and their implications for deep-time paleoclimatologic and paleoceanographic change.

Xiaoying Shi is a Professor at the School of Earth Sciences and Resources, China University of Geosciences (Beijing). Shuhai Xiao is a Professor of Geobiology at the Depart- He received his B.Sc. from China University of Geosciences ment of Geosciences, Virginia Polytechnic Institute and (Wuhan) in 1979 and Ph.D. from China University of State University (also known as Virginia Tech). He Geosciences (Beijing) in 1986. He worked as a Postdoctor- received his B.Sc. and M.Sc. degrees from Beijing Uni- al Fellow in the Smithsonian Institution, Washington DC versity (Beijing, China, 1988) and Ph.D. degree from and the British Museum of Natural History, London in Harvard University (Cambridge, Massachusetts, USA, 1987 and 1988. His research focuses on the biological 1998). Prior to joining Virginia Tech, he was an Assistant evolution patterns, integrated stratigraphy, and the inter- Professor of Geology at the Department of Earth and actions between environmental changes and biotic crisis, Environmental Sciences at Tulane University, Louisiana, particularly the roles of microbial activities played in USA. His research is focused on the interaction of changing Precambrian paleoceanographic conditions. biological and environmental evolution in Earth's early history.

Shihong Zhang is a professor at the School of Earth Sciences and Resources, China University of Geosciences (Beijing). He received his B.Sc. (1985) and M.Sc. (1988) from Changchun University of Earth Sciences (now part of the Jinlin University), and Ph.D. (1992) from Nanjing University. His research interests include paleomagnetism, magnetostratigraphy, paleocontinental reconstruction and tectonics. His early research projects focused on the paleogeographic position of the north and south China blocks in the supercontinent “Rodina”. More recent research expands into Paleozoic and Paleo–Mesoproter- ozoic supercontinental reconstruction.