Gondwana Research 25 (2014) 1045–1056

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The δ13C excursions spanning the Cambrian explosion to theCanglangpuian mass extinction in the Three Gorges area, South China

Tomoko Ishikawa a, Yuichiro Ueno a,b, Degan Shu c, Yong Li d, Jian Han c, Junfeng Guo d, Naohiro Yoshida b,e,Shigenori Maruyama a,b, Tsuyoshi Komiya b,f,⁎a Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japanb Research Center for the Evolving Earth and Planets, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japanc Department of Geology and Key Laboratory for Continental Dynamics, Northwest University, Xi'an 710069, Chinad School of Earth Sciences and Resources Management, Chang'an University, Xi'an 710054, Chinae Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuda Midori-ku, Yokohama 226-8502, Japanf Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan

⁎ Corresponding author at: Research Center for the EvoInstitute of Technology, 2-12-1 Ookayama, Meguro-ku, To354546609.

E-mail address: komiya@ea.c.u-tokyo.ac.jp (T. Komiy

1342-937X/$ – see front matter © 2013 International Ahttp://dx.doi.org/10.1016/j.gr.2013.03.010

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 September 2012Received in revised form 1 March 2013Accepted 17 March 2013Available online 27 March 2013

Keywords:Carbon isotope ratiosEarly CambrianBotomian–Toyonian crisisCambrian explosion

A remarkable increase of the animal genera and a subsequent mass extinction in the late Early Cambrian are wellknown as the “Cambrian explosion” and the “Botomian–Toyonian crisis.” A composite global curve of the carbonisotope ratios for inorganic carbon (δ13Ccarb) shows multiple fluctuations during the evolution events, and itindicates significant changes of the oceanic carbon cycle at that time. This study reveals a new continuous isotopicchemostratigraphy for inorganic carbon (δ13Ccarb) from the bottom of the Shipai to the base of the Shilongdongformations in Three Gorges area, South China. This section covers the Canglangpuian to the Longwangmiaoianstages in the Lower Cambrian. The δ13Ccarb variation exhibits three negative excursions: a remarkably negativeexcursion down to ca. −12‰ in the middle Canglangpuian stage, a negative excursion to ca. −1.0‰ in theupper Canglangpuian stage, and a negative excursion to ca. −1.0‰ in the Longwangmiaoian stage, respectively.The largest negative δ13Ccarb excursion and a positive excursion before the excursion are definitely consistent withthe δ13Ccarb negative shift (AECE) during the mass extinction and the δ13Ccarb positive values (MICE) during theincrease of animal genera, respectively. However, the minimum values of the negative shifts among SouthChina, Siberia, and Canada sections are different from each other. The positive δ13Ccarb excursion at the bottomof the Canglangpuian stage indicates that primary productivities and organic carbon burial were enhanced. Asea level rise in the Qiongzhusian to bottom of the Canglangpuian stages in South China corresponds to theSinsk transgression event in Siberia and Canada. A eutrophication due to higher continental weathering duringthe transgression after the long-term retrogression enhanced the high primary production and consequentlypromoted the significant increase of animal diversity.On the other hand, deposition of laminated black shales without bioturbation signatures and a decline of trilobitediversity are observed during the negative δ13Ccarb excursion in the Canglangpuian stage, indicating that theshallowwater environment became anoxic at that time. The negative δ13Ccarb shift indicates an influx of abundant12CO2 due to oxidation of organic carbons in seawater. The difference of the minimum values among sectionsimplies the local difference in size of the organic carbon reservoirs and extent of the degradation of the carbons.The largest δ13C anomaly in South China suggests the presence of the largest OCPs due to higher activity of pri-mary production and high degree of oxidation of the OCPs because of higher activity of animals. The coincidenceof the timing of the negative δ13C excursions in the Canglangpuian stage among the sections indicates a globalevent, and suggests that the onset was caused by increase of oxygen contents of seawater and atmosphere. Abun-dant oxygen yielded by the increased primary productivity in the Atdabanian and the Qiongzhusian stages causedonset of the oxidation of OCP, and possibly led to the shallow water anoxia and the mass extinction of benthicanimals in the Botomian and the Canglangpuian stage.

© 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

lving Earth and Planets, Tokyokyo 152-8551, Japan. Tel.: +81

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ssociation for Gondwana Research.

1. Introduction

Many paleontological studies show that animals drastically evolvedin the Early Cambrian, called as “Cambrian explosion” (e.g. ZhuravlevandWood, 1996; Li et al., 2007; Shu, 2008). Especially, themost remark-able diversity of genera occurred in the Atdabanian stage (Fig. 1). In

Published by Elsevier B.V. All rights reserved.

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Fig. 1. Diversity of animal genera, modified after Zhuravlev and Wood (1996) and Li et al. (2007), and a composite δ13Ccarb curve, modified after Zhu et al. (2006) through theCambrian. BACE: Basal Cambrian Carbon isotope Excursion, ZHUCE: Zhujiaqing Carbon isotope Excursion, SHICE: Shiyantou Carbon isotope Excursion, CARE: Cambrian ArthropodRadiation isotope Excursion, MICE: Mingxinsi Carbon Isotope Excursion, AECE: Archaeocyathids Extinction Carbon isotope Excursion, and ROECE: Redlichiid–Olenellid ExtinctionCarbon isotope Excursion, are defined by Zhu et al. (2006). Developing Global Standard Chronostratigraphic Scale for the Cambrian System is modified from Babcock and Peng(2007). The Early Cambrian δ13Ccarb curve is mainly derived from Siberian profiles in Brasier et al. (1994), and exhibits one positive (MICE) and one negative (AECE) excursionsduring the peak of the animal diversity and a subsequent mass extinction. In the Late Cambrian, pronounced positive and negative C-isotope excursions are globally recognized:(Steptoean positive C-isotope excursion (SPICE) and Sunwaptan negative isotope carbon excursion (SNICE), respectively (Saltzman et al., 1998; Sial et al., 2008). Especially, theBACE is common over the world (e.g. Morocco: Magaritz et al., 1991; Kirschvink et al., 1991; Canada: Narbonne et al., 1994; Siberia: Magaritz et al., 1986; Brasier et al., 1994;Kaufman et al., 1996; Pelechaty et al., 1996; Brasier and Sukhov, 1998; Mongolia: Brasier et al., 1996; Iran: Kimura et al., 1997; Oman: Amthor et al., 2003; China: Hsü et al.,1985; Lambert et al., 1987; Shen and Schidlowski, 2000; Shen, 2002; Ishikawa et al., 2008).

1046 T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

contrast, the generic diversity declined and animals were extinct in thelate Botomian to the early Toyonian stage, known as the Botomian–Toyonian crisis (Brasier et al., 1994; Zhuravlev and Wood, 1996;Zhuravlev and Naimark, 2005; Li et al., 2007). In order to understandthe oceanic environment during the animal evolutions, it is importantto obtain secular change of carbonate carbon isotope ratio (δ13Ccarb).However, continuous δ13Ccarb chemostratigraphies during the changesof the animal diversity have been only reported in a few sections, suchas Siberia (Brasier et al., 1994) and Canada (Dilliard et al., 2007), andthus, the oceanic environment at that time is still controversial. InSiberia, a remarkable decline of Archaeocyatha coincides with a de-crease of δ13Ccarb values, ca. −2‰, in the late Botomian stage (Brasieret al., 1994). In Canada, δ13Ccarb values decrease to ca. −5‰ in the lateBotomian stage. These declines of δ13Ccarb are named as “AECE” (Zhuet al., 2006), and are thought to result from (1) decrease of the oceanicprimary production (Brasier et al., 1994), (2) upwelling of anoxic bot-tom water onto epicontinental seas (Zhuravlev and Wood, 1996), and(3) increase in river-flux of the 12CO2-rich water because of theHawke Bay regression event (Palmer and James, 1980; Dilliard et al.,2007). The various interpretations are because the limited and fragmen-tary evidence of the δ13Ccarb variations leads to confusion of the globaland regional δ13Ccarb signals. In order to discriminate the global and re-gional δ13Ccarb changes, it is important to obtain continuous δ13Ccarb

chemostratigraphies in some areas and to correlate the records to eachother.

In South China, animals highly evolved through the Qiongzhusianstages, and subsequently, two mass extinctions occurred at the begin-ning and end of the Canglangpuian stage (Li et al., 2007). TheQiongzhusian stage is defined by the first appearance of trilobites(Zhu et al., 2003). Therefore, the Qiongzhusian stage is thought to beequivalent to the Atdabanian stage, and the following Canglangpuianstage corresponds to the Botomian and Toyonian stages (Rozanov etal., 2008). Therefore, it seems that the increase and decrease of animaldiversity in the Qiongzhusian and the Canglangpuian stages corre-spond to the global “Cambrian explosion” and the “Botomian–Toyonian crisis”, respectively (Li et al., 2007). However, an exact corre-lation between the Chinese and Siberian subdivisions is still obscure(Rozanov et al., 2008). Hence, the changes of the oceanic environmentin South China and its influence on the animal diversity are still un-known. A continuous δ13Ccarb chemostratigraphy through the EarlyCambrian in South China is essential to solve those problems.

In this study, we performed scientific drilling and obtained twodrill core samples in the Three Gorges area, South China. They coverfrom the bottom of the Canglangpuian stage to the bottom of theLongwangmiaoian. We analyzed δ13Ccarb and δ18Ocarb values ofthose samples and found two positive and two negative δ13Ccarb

1047T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

excursions during the Canglangpuian stage. We combine the recordswith the δ13Ccarb chemostratigraphy from the terminal Ediacaran tothe early Qiongzhusian stages (Ishikawa et al., 2008, 2013), anddiscuss the oceanic environment through the Qiongzhusian toLongwangmiaoian stages.

2. Geological setting

Neoproterozoic to Cambrian strata are widely distributed in SouthChina. These sedimentary rocks were deposited in a basin related tothe rifting of the Yangtze and Cathaysia Blocks coincident with thebreakup of the Rodinia supercontinent (Li, 1998). The present-dayYangtze platform is located between the Gingfeng–Xiangfan–Guangji(Qin-Ling) orogen to the North and the Cathaysia suture to the South-east. From the Northwest Qin-Ling fault towards the Southeastmargin of the Yangtze Block, Cryogenian to Cambrian deposits ofcontinental shelf, continental slope, and basin types are distributedin sequence (Zhu et al., 2003; Jiang et al., 2011; Fig. 2a). The studysection, the Three Gorges area, is located 25 km to the northwest of

Beijing

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Fig. 2. (a) A map of South China with reconstructed sedimentary environment (Huang et alPlatform. (b) A simplified geological map of the Three Gorges area, South China. Box indica

Yichang city in central Hubei province (Fig. 2b). Cryogenian to Cam-brian strata that were deposited on a continental shelf (Zhu et al.,2003) or in an intra-shelf basin (Vernhet and Reijmer, 2010) cropout in the Three Gorges area.

Cryogenian to Cambrian sedimentary rocks in the Three Gorgesarea, South China crop out around the dome of a mid-Archean tolate Proterozoic granite–gneiss complex (Fig. 2a). These sedimentswere deposited on the Western Hubei platform. The Wuhe–Aijahesection (Fig. 2b) contains nine formations: Liantuo, Nantuo,Doushantuo, Dengying, Yanjiahe, Shuijingtuo, Shipai, Tianheban andShilongdong formations in ascending order (e.g. Zhang, 1981; Zhaoet al., 1985; Chen, 1987; Zhou and Xu, 1987; Zhao et al., 1988; Dinget al., 1996). The Liantuo Fm. is about 400 m thick, and is composedof red, 750 Ma sandstone (Ma et al., 1984). The Nantuo Fm. comprisesa 40 m-thick diamictite that formed at the time of the MarinoanSnowball Earth. The Doushantuo Fm. consists of four members in as-cending order: I) a 5 m-thick cap dolostone, II) a 150 m-thick alterna-tion of dolostone and black shale with abundant siliceous nodules, III)a ~80 m thick massive dolostone, and IV) a 20 m-thick black shale

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., 2011). The Three Gorges area is on the proximal side of the inner shelf in the Yangtzetes the study area.

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(Zhou and Xu, 1987). The ca. 275 m-thick Dengying Fm. is subdividedinto three members: the Hamajing, Shibantan, and Baimatuo mem-bers in ascending order, which are characterized by light graydolostone, black limestone, and white dolostone, respectively. Theca. 35 m-thick Yanjiahe Fm. consists of partly dolomitized muddylimestone, calcareous black shale, and minor sandstone and chert.The ca. 130 m-thick Shuijingtuo Fm. mainly consists of black shalewith many prominent carbonate nodules and limestone in theupper. The 158–301 m-thick Shipai Fm. comprises calcareous blackshale, limestone, and minor sandstone. The Tianheban Fm. is about90 m thick, and is composed of limestone, oolitic limestone, beddedblack limestone, and minor calcareous black shale. The ShilongdongFm. is about 120 m thick, and consists of gray and grayish-whitedolostone.

According to paleontological studies in this area (Chen, 1984; Ding etal., 1992; Qian, 1999; Guo et al., 2008),Micrhystridium regulare occurs atthe bottom of the Yanjiahe Fm. (Ding et al., 1992; Guo et al., 2008), andlater Protohertzina anabarica and Anabarites trisulcatus, key fossils of theNemakit–Daldynian stage, first appeared at a horizon 12 m above theDengying–Yanjiahe boundary (Chen, 1984; Qian, 1999; Guo et al.,2008). This occurrence corresponds to the lower boundary of theMeishcunian stage in South China. In the middle Yanjiahe Fm. at18.5 m above the Dengying–Yanjiahe boundary, abundant macrofossils(macroscopic algae, conotubular life forms and presumed metazoans)and diverse Small Shelly Fossils (SSFs) (A. trisulcatus, Protohertzina sp.,Lopworthella sp., Emeiconus antique) have been found in siliceous-phosphatic nodules in the shale (Guo et al., 2008). Also, Tommotian-type SSFs (e.g. Aldanella and Maidipingoconus) first appear at 3 m(Chen, 1984) below the Yanjiahe–Shuijingtuo boundary. Also, trilobites,Tsunyidiscus xiadongensis, appear at a horizon 6.98 m above theYanjiahe–Shuijingtuo boundary (Wang, 1987). The first appearance oftrilobites defines the lower boundary of the Atdabanian stage and alsothe Qiongzhusian stage in South China. Also, abundant eodiscids, othertrilobites, bradoriids, brachiopods, sponges, and hyolithes occur in theShuijingtuo Fm. (Zhou and Xu, 1987). The Shipai Fm. includes two trilo-bite zones: Redlichia meitanensis zone in the lower part and Palaeolenuslantenoisi zone in the upper part (Zhou and Xu, 1987). Also, trilobitesof Megapalaeolenus deprati zone and archaeocyathids of theArchaeocyathus–Retecyathus–Sanxiacyathus zone are present inthe Tianheban Fm. Those trilobite zones in the Shipai and TianhebanFm. define the Canglangpuian stage in South China (Wang and Chen,2005). The trilobite Redlichia murakamii appears in the Shilongdong Fm,and this occurrence defines the lower boundary of the Longwangmiaoianstage in South China (Wang and Chen, 2005).

3. Description of the drill core samples

In the Aijiahe, Three Gorges area, we obtained two drill cores. Oneis 219 m-long, which extends from the bottom of the Shipai tothe bottom of the Tianheban formations (Fig. 3). The other is68 m-long, which covers from the Tianheban Fm. to the bottom ofthe Shilongdong Fm. The Shipai Fm. is about 181 m-thick, and com-prises 59 m-thick calcareous black shale, finely alternating blackshale and limestone at the bottom, 16 m-thick limestone with wavyblack mud layers, 27 m-thick black shale with minor limestone,40 m-thick alternating black shale, muddy black limestone and silt-stone, and the upper 40 m-thick reddish-gray shale, black shale,sandy limestone and minor oolitic limestone in ascending order(Fig. 3). Also, we observed many trilobites and Hyoliths fossils inlimestone (Fig. 3). Bioturbation is frequently observed through theShipai Fm., but non-bioturbation zone of black shale and alternationof black shale, limestone, and siltstone are particularly observed inthe middle of the Shipai Fm. (Fig. 3). The Tianheban Fm. is about88 m thick, and mainly consists of alternation of limestone and cal-careous black shale, limestone with wavy thin black mud layers, andoolitic limestone minor with black shale and black mudstone with

bioturbation structures. Many trilobites and brachiopods bioclastsare included in ooids, and also many sponges and Archaeocyathaare found particularly in the middle of the Tianheban Fm. The upper-most 9-m part of the drill core is composed of the bottom part of theShilongdong Fm. that consists of gray dolostone with black mud layer(Fig. 3).

4. Methods

Carbonate mineralogy was determined bymicroscopic observationsof thin sections. Samples were screened according to the proceduresdescribed in detail in Kaufman and Knoll (1995).

In order to determine the carbon and oxygen isotope ratios, pow-dered samples were first prepared from freshly cut surfaces of thedrill core, using a drill of 6 mm diameter. The sampling points werecarefully selected to avoid late stage diagenetic carbonate and veins.Samples were analyzed by a Thermoquest GasBench II preparationdevice connected with helium flow to DELTA Plus XL at the Tokyo In-stitute of Technology (modified from Révész and Landwehr, 2002).The detailed analytical method was described elsewhere (Ishikawaet al., 2008; Tahata et al., 2013). Powdered samples of 0.5–2 mgwere reacted with >100% phosphoric acid at 72 °C for >12 h. Analyt-ical reproducibility of the δ13Ccarb and δ18Ocarb values, based on repli-cate analyses of the laboratory standard and NBS-19, is better than ±0.35‰ and ±0.51‰, respectively.

5. Results

Results of the carbon and oxygen isotope analyses are listed inTable 1. Figs. 4 and 5 show the δ13Ccarb and δ18Ocarb profiles of thedrill cores at Sites 5 and 6, respectively.

The δ13Ccarb values continuously decrease from 0.67‰ to−11.65‰ from the bottom to the middle of the Shipai Fm. This de-cline displays two-step decrease. First, the δ13Ccarb values decreasegradually from 0.67‰ to −3.12‰ in the lower part of the ShipaiFm. Second, the δ13Ccarb values decline to −11.65‰ more rapidly.Above the negative anomaly, the δ13Ccarb values continuously in-crease to +2.33‰ from the upper Shipai Fm. to the lower TianhebanFm. (Fig. 5). The δ13Ccarb values exhibit a slight decline from +2.33‰to +0.10‰ in the lower part of the Tianheban Fm. (Figs. 4 and 5) andthe δ13Ccarb values are almost steady around +1‰ above the smallnegative excursion (Fig. 4). The δ13Ccarb values decrease from+0.92‰ to −0.99‰ in the middle part of the Tianheban Fm. andthen continuously increase to +1.08‰ from the middle part of theTianheban to the bottom of the Shilongdong formations. In the lower-most part of the Shilongdong Fm., the δ13Ccarb values sharply drop to−1.10‰.

The δ13Ocarb values vary around −10‰ in lower part of the ShipaiFm. and are scattered around −7.5‰ in the Shipai, Tianheban, andShilongdong formations.

6. Discussion

6.1. Diagenesis

In addition to limestone and dolostone, we also analyzed calcareousblack shale samples, which have lower carbonate contents. The origin ofthe δ13Ccarb values of these calcareous shales should be carefully consid-ered, because samples with low carbonate contents are relatively sus-ceptible to secondary alteration (Kaufman and Knoll, 1995). However,all the samples of various lithologies with different carbonate contentsform a consistent δ13Ccarb profile, and the δ13Ccarb values are indepen-dent of their lithologies or carbonate content (Figs. 4 and 5). The fact in-dicates that the primary δ13Ccarb values of our drill core samples are stillpreserved. Therefore, we propose that the δ13Ccarb profile represents asecular trend of the seawater chemistry. This conclusion is also

Sandy limestone

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Fig. 3. Lithostratigraphy of drill-core samples. The drill core samples at drill site 6 cover from the bottom of the Shipai to the Lower Tianheban formations. The drill core samples atdrill site 5 cover from the Tianheban Formation to the lowermost part of the Shilongdong Formation. Representative fossils of trilobite, hyolith, Archaeocyatha, sponge, and brachio-pod are observed from the drill-core samples by microscopic observations. Bars represent the points of thin-sections for microscopic observations.

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supported by the fact that the δ13Ccarb profile is comparable to those inother sections, as discussed below.

Generally speaking, the carbon isotopic composition of carbonateis less susceptible to diagenetic overprint than the oxygen isotopiccomposition. A decrease in δ18Ocarb values often results from isotopicexchange with meteoric or hydrothermal fluids (Kaufman and Knoll,1995). As result, the negative excursions of both δ13Ccarb and δ18Ocarb

values doubt influence of post-depositional alteration even on theδ13C values. In this work, there are no covariations between δ13Cand δ18O values (Figs. 4, 5), also suggesting that primary δ13C valuesare still preserved.

6.2. Comparison of the δ13Ccarb profile with those in other sections

Fig. 7 shows a comparison between the obtained δ13Ccarb profileand those of other sections within and out of the Yangtze Platform,respectively. Here, we discuss several common and unique featuresof these δ13Ccarb profiles in order to distinguish global and localsignatures.

A composite δ13Ccarb curve in the Pangjiowan and Duoding sec-tions, South China, exhibits positive values of ca. +2‰ from the lateQiongzhusian to the early Canglangpuian stages (Fig. 7). This featureis well consistent with the positive δ13Ccarb values in Shuijingtuo andthe bottom of Shipai formations of Three Gorges section (Fig. 7). A de-crease of the δ13Ccarb values in the Canglangpuian stage of theWangjiaping section, South China corresponds to remarkably lowvalues in the middle part of the Shipai Formation in the Three Gorgessection (Fig. 7). Both the negative δ13Ccarb values in the Wangjiaping

and Three Gorges sections are observed in the P. lantenoisi zone in theCanglangpuian stage. The minimum value in the Three Gorges sectionreaches ca. −12‰, and is much lower than the minimum δ13Ccarbvalue (ca. −4‰) in the Wangjiaping section. However, since theδ13Ccarb chemostratigraphy in the Wangjiaping section is fragmen-tary, it is highly possible that the δ13C profile obtained in the ThreeGorges section records the real minimum value. The δ13Ccarb valuesrecover to ca. +2‰ above the negative excursion in both the sections.The δ13Ccarb profiles, with a small negative δ13C anomaly down to ca.−1 to −2‰ in the middle, slightly increase from 0 to 1‰ in theArchaeocyatha zone of the upper Canglangpuian stage. Around theboundary between the Canglangpuian and Longwangmiaoian stages,a negative anomaly down to ca. −1‰ is observed in both sections.Thus, the δ13Ccarb changes in the Canglangpuian stage in both sectionsare quite similar each other, supporting that the δ13C profiles reflectvariations of isotopic compositions of dissolved marine inorganic car-bon (DIC) within the Yangtze Platform through the Canglangpuianstage.

The obtained δ13Ccarb profile is also comparable with those of rep-resentative sections in Siberia (Brasier et al., 1994) and Canada(Dilliard et al., 2007) (Fig. 7). It is still ambiguous to compare theSiberian and Chinese subdivisions in the late Early Cambrian. Forthe δ13Ccarb correlation, we used the first appearance of trilobites asa lower boundary, and Botomian–Toyonian boundary as an upperboundary among those sections. The positive δ13Ccarb anomaly, ca.+2‰ from the late Atdabanian to early Botomian stages, is observedin Siberia and Canada (Fig. 7). The positive δ13Ccarb values in theAtdabanian stage are also reported in Morocco, ca. +3‰ (Maloof et

Table 1Results of carbon and oxygen isotope analyses.

Depth (m) Microsampling ID Lithology δ13CvsVPDB (‰) Δ18OvsVPDB (‰) Carbonate content (wt.%)

Shilongdong Formation_Drill Core 50.05 500501 Gray dolostone 0.19 −7.40 113.10.65 500504 Ooids bearing gray dolostone −1.08 −8.05 98.81.90 500604 Bioturbated muddy dolostone −1.10 −7.53 96.02.65 500703 Weakly laminated gray dolostone 0.34 −7.64 82.93.77 500802 Dolostone 0.91 −7.28 97.25.46 500903 Dolostone 1.08 −7.58 99.4

Tianheban Formation_Drill Core 58.20 501102 Siliceous limestone 0.87 −7.46 94.79.83 501203 Siliceous black limestone 0.80 −6.83 105.510.90 501213 Black limestone 0.82 −7.85 98.511.49 501304 Black limestone 0.59 −8.20 94.613.60 501401 Black limestone 0.70 −8.12 101.014.79 501407 Black limestone 0.68 −8.00 110.215.83 501413 Limestone 0.66 −7.87 103.516.76 501504 Limestone 0.69 −8.18 102.317.90 501509 Limestone 0.61 −7.73 101.219.50 501604 Limestone 0.62 −7.96 100.620.64 501609 Limestone 0.45 −7.69 99.021.35 501613 Ooids bearing limestone 0.40 −7.41 100.622.49 501703 Ooids bearing limestone 0.27 −7.33 96.224.25 501802 Limestone 0.34 −7.27 91.226.51 501812 Black limestone 0.26 −7.17 93.627.93 501902A Black limestone 0.32 −7.11 101.429.44 501905 Limestone 0.16 −7.17 93.530.79 502004 Dark gray limestone 0.01 −7.19 95.232.57 502010 Black limestone 0.53 −7.63 51.534.11 502107B Limestone 0.06 −7.30 98.235.08 502111 Limestone −0.15 −7.24 93.336.58 502203 Limestone −0.31 −7.49 85.037.29 502205 Limestone −0.24 −7.53 89.437.73 502207 Black limestone −0.41 −7.57 86.939.15 502302 Limestone −0.99 −7.63 74.140.66 502310 Black limestone −0.82 −8.33 67.541.95 502316 Calcareous black shale −0.75 −7.16 15.542.14 502401-01 Ooids bearing limestone −0.85 −7.63 100.342.32 502401-02 Limestone −0.62 −8.00 96.243.12 502405 Black limestone −0.76 −7.33 64.343.93 502409 Black limestone −0.73 −7.99 74.544.84 502413 Limestone −0.32 −7.58 79.445.88 502504 Limestone −0.52 −7.70 100.446.20 502505-01 Limestone −0.24 −7.65 77.846.40 502505-02 Limestone −0.38 −7.47 62.547.52 502508 Dark gray limestone −0.49 −7.57 84.248.45 502513 Limestone −0.41 −7.89 67.249.33 502606 Black limestone 0.14 −7.47 92.450.58 502609 Black limestone 0.11 −6.89 95.751.80 502701 Black limestone 0.92 −7.23 111.953.62 502801 Limestone 0.92 −7.23 109.054.92 502808 Black limestone 0.81 −7.53 110.056.90 502904 Black limestone 0.70 −7.54 101.858.28 502910 Black limestone 0.89 −7.67 107.959.29 503004 Black limestone 1.00 −7.87 101.460.15 503008 Black limestone 1.02 −6.64 97.961.24 503012 Black limestone 0.87 -7.48 102.863.36 503106-01 Black limestone 0.61 −7.03 95.563.68 503106-02 Black limestone 0.48 −6.43 111.064.49 503108 Black limestone 0.61 −6.81 100.164.79 503201 Black limestone 0.10 −6.32 100.665.35 503202B Black limestone 0.61 −6.93 93.8

Tianheban Formation_Drill Core 67.11 600703 Limestone 0.95 −8.88 66.29.57 600802 Limestone 2.33 −8.66 65.612.59 600902 Limestone 1.86 55.714.76 600914 Laminated limestone 1.05 −8.68 60.616.34 601007 Laminated limestone 1.64 53.319.69 601104 Laminated limestone with thin black mud layer 0.80 −7.69 111.221.55 601113 Limestone 0.98 −11.30 56.423.85 601213 Laminated limestone with thin black mud layer 0.72 −9.14 58.525.71 601314 Laminated limestone with thin black mud layer 1.69 53.528.25 601403C Laminated limestone 1.21 −9.23 55.530.65 601501C Limestone 0.90 −9.55 60.733.64 601602A Limestone 0.87 −9.50 56.037.15 601702D Laminated black limestone 0.89 −8.12 18.8

1050 T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

Table 1 (continued)

Depth (m) Microsampling ID Lithology δ13CvsVPDB (‰) Δ18OvsVPDB (‰) Carbonate content (wt.%)

Shipai Formation_Drill Core 638.27 601707 Reddish-gray shale 0.57 −7.41 4.240.84 601812 Dark gray shale −0.17 −7.89 2.443.60 601912 Calcareous black shale −1.21 −8.52 1.446.45 602014 Reddish black shale −1.23 −5.55 0.250.01 602110 Ooids bearing black limestone 0.97 −10.77 62.751.91 602204 Ooids bearing limestone 0.14 −10.98 61.154.28 602303A2 Reddish dark gray shale −1.86 −9.23 0.857.17 602407_01 Reddish dark gray shale −2.69 −12.04 2.359.69 602512 Calcareous black shale −3.59 −11.94 7.261.36 602605 Calcareous black shale (slightly reddish) −2.17 −4.72 0.264.06 602702 Calcareous black shale −1.97 −4.09 0.466.33 602710B Black shale −3.71 −8.10 0.667.91 602804 Calcareous black shale −5.42 −11.61 1.871.75 602902 Calcareous black shale −4.64 −7.33 0.474.78 602925 Calcareous dark gray shale −2.17 −7.51 0.777.66 603102 Calcareous dark gray shale −3.76 −7.93 0.379.42 603111 Finely alternation of black shale and dark gray shale −3.24 −4.21 0.381.61 603122 Calcareous black shale −7.57 −11.43 1.883.46 603207 Muddy black limestone −7.28 −11.08 2.285.34 603216 Reddish black shale −4.88 −7.58 0.591.03 603404A1 Calcareous black shale −7.36 −5.92 0.493.23 603412A Calcareous black shale −7.73 −8.46 0.696.32 603514 Calcareous black shale −7.87 −7.15 0.3101.63 603702 Finely alternation of black shale and black limestone −8.87 −6.62 0.2106.42 603804B Finely alternation of black shale and muddy black limestone −10.69 −6.60 0.3111.29 603908 Finely alternation of black shale and muddy black limestone −10.44 −6.24 0.2113.73 603931 Finely alternation of black shale and muddy black limestone −11.65 −7.48 0.3116.41 604023 Calcareous black shale −9.94 −6.90 0.3119.71 604112 Calcareous black shale −11.15 −5.85 0.3124.27 604211 Calcareous black shale −8.97 −6.41 0.4126.36 604222 Calcareous black shale −8.77 −8.63 0.3128.01 604308 Finely alternation of black shale and muddy black limestone −9.19 −7.35 0.4131.25 604407 Calcareous black shale −8.31 −5.82 0.9134.89 604503 Calcareous black shale −7.77 −6.63 0.3136.40 604512 Calcareous black shale −4.31 −5.44 0.2138.63 604601A Calcareous black shale −6.51 −5.80 0.2140.67 604608B1 Calcareous black shale −6.10 −4.16 0.2143.94 604706B Calcareous black shale −4.97 −3.81 0.2147.34 604805 Laminated black limestone −3.12 −9.28 1.8149.15 604813A Muddy black limestone −3.39 −6.94 1.0151.61 604904 Laminated muddy black limestone −3.78 −10.90 0.8154.71 604916 Laminated muddy black limestone −2.83 −13.54 1.6156.32 605007 Muddy black limestone −2.89 −5.16 0.9158.18 605016A Muddy black limestone −5.06 −8.14 1.0160.50 605106B Calcareous black shale −3.63 −9.09 1.8162.65 605114A Calcareous black shale −3.85 −13.58 3.0166.49 605209 Muddy black limestone −2.70 −12.79 1.3168.46 605301C Finely alternation of black limestone and black shale −2.87 −6.73 0.3171.51 605310B Muddy black limestone −1.56 −6.89 0.9174.34 605412 Calcareous black shale −2.33 −11.36 2.4176.86 605501 Black limestone −2.32 −11.64 12.7178.91 605508 Muddy black limestone −0.85 −13.44 2.6181.10 605601 Wavy laminated muddy black limestone −1.71 −13.09 3.7184.22 605612A Wavy laminated muddy black limestone −1.32 −9.82 3.4185.37 605616 Muddy black limestone 0.14 −8.38 1.1187.90 605709A Muddy black limestone −1.64 −11.35 3.7190.60 605803C Muddy black limestone −0.88 −10.02 1.1194.75 605813 Finely alternation of black shale and black limestone −0.84 −10.67 3.6195.39 605904A calcareous black shale −1.42 −8.93 0.5200.70 606008B Finely alternation of black shale and black limestone −0.03 −9.80 0.6203.14 606105 Finely alternation of black shale and black limestone 0.92 −7.64 1.6205.78 606114A Finely alternation of black shale and black limestone 0.00 −14.36 7.2208.71 606211 Finely alternation of black shale and black limestone 0.15 −12.58 6.6211.12 606219 Finely alternation of black shale and black limestone 0.30 −12.30 1.8213.67 606308 Finely alternation of black shale and black limestone 0.80 −8.00 0.9216.37 606404B Finely alternation of black shale and black limestone 0.66 −10.92 2.1217.87 606412 Finely alternation of black shale and black limestone 0.67 −10.81 1.4

1051T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

al., 2005). The δ13C changes, defined as the “MICE” (Zhu et al., 2006),are consistent with the δ13Ccarb positive excursion from theQiongzhusian to the Canglangpuian stages in South China (Fig. 7). Inthe late Botomian stage above the excursion, the δ13Ccarb valuesexhibit negative values: ca. −2‰ in Siberia (Brasier et al., 1994), ca.−5‰ in Canada (Dilliard et al., 2007) and ca. −6‰ in Morocco

(Maloof et al., 2005), respectively. The negative values correspondto the negative excursion in the Canglangpuian stage in South China(Fig. 7), but the minimum values in Siberia, Canada and Moroccoare remarkably different from those in South China. This indicatestwo possibilities: (1) the negative δ13C values in South China reflecta local signal around the Yangtze platform, and (2) the negative

δ Ocarb [‰]18

-8.5 -6.0-7.5 -7.0 -6.5-8.0

δ C carb [‰]13

-1.5 -1.0 1.51.00.50-0.5

LimestoneCalcareous black shale

Dolostone

0

Dep

th (

m)

Form

atio

nT

ianh

eban

Shilo

ngdo

ng

Can

glan

gpui

anE

arly

Cam

bria

n

10

20

30

40

50

60

70

Stag

eL

ongw

ang-

mia

oian

Limestone

Alternation of limestone and black mud layers

Black limestone with wavy thin black mud layers

Black shale

Ooids-bearing limestone

Dolostone with black mud layers

Alternation of black shale and limestone with ooids

Black mud layer and limestone with bioturbation structures

Alteration of limestone and black limestone

Trilobite

Pellet

Archaeocyatha

BrachiopodSponge

Fig. 4. Carbon and oxygen isotope profiles (δ13Ccarb and δ18Ocarb) of the drill site 5. Biological subdivisions are from a literature (Wang, 1987).

1052 T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

δ13C changes in Siberia, Canada, and South China represent the globalchanges of the isotopic compositions of the oceanic dissolved inor-ganic carbons, but the difference of δ13Ccarb values is because of sam-pling bias, and stratified or spatial heterogeneous ocean in δ13CDICvalues due to high activity of degradation and remineralization of or-ganic matters in the Cambrian ocean. The former simply accounts forthe difference in δ13C values among the sections, but coincidence ofthe timing of the negative δ13Ccarb changes among the sections sug-gests a global cause, as the details shown in the following sections.After the negative δ13Ccarb change, the δ13Ccarb values increase to ca.0 to +1‰ at the boundary between Botomian and Toyonian stages,and the δ13Ccarb values show slightly negative values of ca. −1‰ inthe lower Toyonian in Siberia, Canada, and South China (Fig. 7).

6.3. Origin of the carbon isotope excursions

6.3.1. Environmental changes during the positive excursion in theAtdabanian and the Qiongzhusian stages

The similarity of the δ13C variations in the later Early Cambrian inSiberia (Brasier et al., 1994), Canada (Dilliard et al., 2007) and SouthChina sections (this work) suggests a global control of oceanic carbonisotope compositions. In addition, the δ13Ccarb changes are correlatedto biological activities, including diversity and extinction events.Especially in Siberia, the increase of the Archaeocyatha diversity, cor-responding to the Cambrian explosion, occurred during the positiveδ13Ccarb excursion from the late Atdabanian to the early Botomianstages (Brasier et al., 1994). The positive δ13Ccarb values are thoughtto result from increase of primary productivity (Brasier et al., 1994).Also, the peak in the animal diversity in South China occurs in theQiongzhusian stage (Li et al., 2007), and the δ13Ccarb profile exhibitsalso positive values through the Qiongzhusian stage (Fig. 6).

The positive excursion indicates increase in primary productivityand/or organic carbon burial. Their enhancement resulted in increaseof oxygen content of seawater through active oxygenic photosynthe-sis and burial of the organic materials. The increase in oxygen content

of seawater favors activity of animals. Fecal pellets, produced by ani-mals, were efficiently removed because they sank more quicklythrough the seawater (Logan et al., 1995). Namely, higher activity ofanimals resulted in enhancement of organic burial, and consequentincrease of oxygen contents. On the other hand, there is an unconfor-mity between the Shuijingtuo and Yanjiahe formations in the ThreeGorges area (Fig. 6), and the ubiquitous occurrence of unconformitiesin the world around the beginning of the Tommotian indicatingeustatic sea level falling (Ripperdan, 1994). The long-term sea levelfalling led to widespread continental denudation for a long time. Ex-pansion in the area of shallow epicontinental seas after the sea levelfalling resulted in enhanced continental weathering, and consequenthigher continental influxes (Peters and Gaines, 2012). The high conti-nental influxes increased nutrient contents of seawater, and conse-quently primary productivity. In a summary, increase in continentalinfluxes due to sea level changes promoted primary productivity.The enhancement of primary productivity increased oxygen contentsof seawater, and resulted in higher activity of animals. Higher activityof animals promoted burial of organic materials through formation offecal pellets, and consequently sustained increase of oxygen contentsof seawater. Increase of subaerial oxygen content accompanied withthe increase of oxygen content of seawater promoted continentalweathering through oxidation of sulfide and dissolutions of feldsparsand phosphate, and sustained high nutrient contents. The positivefeedback resulted in animal diversification in the early Cambrian.

6.3.2. Environmental changes during the negative excursion in theBotomian–Toyonian and the Canglangpuian stages

A decrease of the Archaeocyatha diversity started from the lateBotomian stage, so called “Botomian–Toyonian crisis” (Brasier et al.,1994; Zhuravlev and Wood, 1996). A prolonged negative δ13Ccarb ex-cursion has been observed during this crisis in Siberia. It was previ-ously suggested that the significant decrease of the biologicaldiversity in the Botomian stage was derived from (1) the decreaseof the primary productivity, and (2) the influx of anoxic bottom

-18 -16 -12 -8 -4 0 -14 -12 -10 -8 -6 -4 -2 0 2 4

Limestone

Calcareous black shale

Muddy black limestone

Finely alternated black shale and limestone

δ C carb [‰]13δ Ocarb [‰]

18

0

20

40

60

80

100

120

140

160

180

200

220

Dep

th (

m)

Form

atio

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ly C

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ian

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age

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Limestone with wavy thin black mud layers

Black shale

Ooids-bearing limestone

Reddish-black shale

Alternation of reddish siltstoneand black limestone

Alternation of black shale and muddy black limestone

Finely-alternated black shale and limestone

Fig. 5. Carbon and oxygen isotope profiles (δ13Ccarb and δ18Ocarb) of the drill site 6. Biological subdivisions are from a literature (Wang, 1987). Gray shaded area shows a zone withnon-bioturbated sediments.

1053T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

water to shallow platform, associated with the Sinsk transgressionevent (Zhuravlev and Wood, 1996).

The δ13Ccarb profile on the Yangtze platform in South China alsoshows remarkably negative values for a long time, over 3 million years(Fig. 7) in the Canglangpuian stage. The timing of the negative excursioncoincides with those of Siberia and Canada, but the minimum values aredifferent among those areas: ca. −12‰ in South China (this work), ca.−2‰ in Siberia (Brasier et al., 1994) and ca. −5‰ in Canada (Dilliardet al., 2007). Since the C-isotopic composition of the incoming carbonto the ocean is averaged ca. −5‰ (Holser et al., 1988), the extremelynegative excursion in South China likely resulted frommovement of iso-topically light inorganic carbons into the shallowwater, due to degrada-tion and remineralization of organic matters. Possible processes are(1) upwelling of bottom water with abundant 12CO2 contents due tosulfate reduction and/or oxidation of organic carbons onto the epiconti-nental sea during the transgression, (2) increase in recycling oforganic-rich deposits on continental shelf during sea level falling,(3) decrease in biomass related to mass extinction, and (4) methane re-lease due to decomposition of gas hydrate. Generally speaking, the pro-cess (4) is a short event, inconsistent with the long-term negativeδ13Ccarb excursion in South China. The sedimentary stratigraphy on theYangtze platform during that negative δ13Ccarb excursion containsshale, siltstone, and alternation of black shale and black limestone, andindicates relatively deep depositional environment. As a result, theprocess (2) is also inconsistent with the lithostratigraphy.

The negative δ13Ccarb excursion in South China possibly resultedfrom the processes (1) and/or (3). But, a short-term event such as over-turn of stratified ocean cannot explain the long-term negative δ13C ex-cursion. A long-lived supply of CO2 and HCO3

− with low δ13C values by

an oxidation of a large organic carbon pool (OCP) onto shallow marineenvironment accounts for the large-scale negative δ13Ccarb excursion inSouth China. Presence of the quite large δ13C negative anomaly, b−6‰,suggests that the large OCP existed locally or temporarily even inthe Early Cambrian, analogues to a significantly long-lived and largedissolved organic carbon pool in the Neoproterozoic ocean (Rothmanet al., 2003; Fike et al., 2006; McFadden et al., 2008). If so, the differencein the minimum of δ13Ccarb values among sections can be explained bydifference in the size of the local OCPs and extent of oxidation of theOCPs. The largest δ13C anomaly in South China suggests the presenceof the largest OCPs due to higher activity of primary production andhigh degree of oxidation of the OCPs because of higher activity of ani-mals. The coincidence of the timing among the sections suggests thatthe onset was caused by a global event such as increase of oxygen con-tents of seawater and atmosphere.

Globally, trilobite and Archaeocyatha diversity decreased in theBotomian stage (Brasier et al., 1994; Zhuravlev and Wood, 1996;Zhuravlev and Naimark, 2005) and animal diversity also decreased inthe Canglangpuian stage in South China (Li et al., 2007). In the ThreeGorges areas, trilobite diversity declined in the middle Canglangpuianstage (Fig. 6), and especially, only trilobite Redlichia lived during theδ13Ccarb negative excursion (Fig. 6). In addition, remarkably bioturbat-ed mud layers are often observed from the upper Shuijingtuo to theTianheban formations but the occurrence of bioturbation is minor inthemiddle of the Shipai Formation (Figs. 3 and 6). The lines of evidenceindicate that the shallowmarine environment became anoxic and hab-itats of benthic animals were reduced at that time.

In the Atdabanian stage, enhancement of nutrient supply throughhigher continental weathering due to the sea level rise led to

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1054 T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

phytoplankton blooming and organic carbon burial, and consequenthigher oxygen content of seawater as mentioned in the above section.The oxygen was consumed by oxidation of the organic carbons aswell as aerobic respiration of animals and anaerobic remineralizationso that large amount of CO2 and HCO3

− with low δ13C values wasstored in deep seawater. The continuous upwelling of the deep sea-water was brought into the shallow water environment so that theshallow water environment became anoxic and mass extinction oc-curred in the Botomian to Toyonian stages.

The occurrence of sandy and oolitic limestones and the appear-ance of abundant Archaeocyatha and sponge fossils in the TianhebanFormation indicate the prosperity of poriferans on an epicontinentalreef in the Yangtze platform (Figs. 3 and 4). The δ13Ccarb values recov-er from−10‰ to +2‰ from the upper Shipai to the lower Tianhebanformations, indicating an increase of the primary productivity. Theoccurrence of trilobite and Archaeocyatha fossils also increases inthis interval (Fig. 6). On the other hand, the shallow water sedimentin the Tianheban Fm. broadly corresponds to a diachronous and re-gional sea level falling “Hawk Bay event” in the latest Early Cambrian(Palmer and James, 1980; Dilliard et al., 2007). Previous works sug-gested the δ13Ccarb values fluctuate around 0‰ during this regressionevent (Brasier et al., 1994; Dilliard et al., 2007). The South China

sections also have δ13C values around 0‰ with small negative anom-alies, consistent with the δ13C profiles in Siberian and Canada (Fig. 7).The negative δ13Ccarb values possibly resulted from increase inrecycling of organic-rich deposits during the sea level falling.

7. Conclusion

We obtained a new high-resolution δ13C curve of drill-core samplesfrom the bottom of the Shipai to Shilongdong formations in the EarlyCambrian in the Three Gorges section, South China. We identifiedtwo positive and two negative isotope excursions within this interval.The similarity of the δ13C variation among some sections in Siberia,Canada, and Morocco indicates that the profile records global signa-tures. In the Qiongzhusian stage, the δ13Ccarb values increase from−2‰ to +2‰, corresponding to the positive δ13C excursion MICE(Zhu et al., 2006) in the Atdabanian stage. The deposition of blackshale in the earliest Qiongzhusian stage corresponds to the globally ob-served sediments of black shale during the Sinsk transgression event(Zhuravlev andWood, 1996). This sea level rise brought eutrophicationto the shallow water environment, and the positive δ13Ccarb values in-dicate the resultant increase of the primary productivity and organiccarbon burial. Increase in diet and oxygen through the enhanced

0 42-2-4-6

0 42-2-4-6

Tom

.B

otom

.Toy

.

δ C13carb(‰ vs.PDB )

Canada(Dilliard et al., 2007)

0 42-2-4-6

0 42-2-4-6

Nem

akit-

Dal

dyni

anT

omm

otia

nA

tdab

.B

otom

.Toy

.E

diac

aran

δ C13carb(‰ vs.PDB )

Siberia(Brasier and Sukhov, 1998)

~528

~521

~512

542.3

Three Gorges section,South China (This study)

Nem

akit-

Dal

dyni

anT

omm

otia

nA

tdab

ania

n to

Toy

onia

nE

diac

aran

Edi

acar

an

-12 -8 -4 0 4

-12 -8 -4 0 4 δ C13

carb(‰ vs.PDB )

?

Ma

-4 0 4

-4 0 4

δ C13carb(‰ vs.PDB )

Atd

aban

ian

to T

oyon

ian

Some sections,South China

(Rozanov etal., 2008)

Den

gyin

gY

anjia

he

Atd

ab.

Shui

jingt

uoSh

ipai

TS

Mei

shuc

unia

nC

angl

an.

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ng.

L

Fuch

eng

(Sha

anxi

)X

inch

ao(S

ichu

an)

Pang

jiow

anA

nhui

Duo

ding

, G

uizh

ouW

anjia

ping

H

ubei

Fig. 7. A correlation of the δ13Ccarb profiles among representative sections within the Yangtze Platform and in the world in the Early Cambrian.

1055T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

primary productivity contributed to the animal diversification andtheir increase in the Qiongzhusian stage.

The δ13Ccarb continuously decreases from +2‰ to −12‰ fromthe late Qiongzhusian stage to the early Canglangpuian stage. Thenegative δ13Ccarb excursion corresponds to the negative δ13C excur-sion of AECE (Zhu et al., 2006). However, the minimum values ofthe negative δ13Ccarb excursions in the Botomian stage are differentamong sections. The difference is because difference in the size ofthe organic carbon pools and extent of degradation of the organic car-bons among the sections resulted in variation of 12CO2 supply to theshallowwater environment. The coincidence of the timing of the neg-ative δ13C excursion in the world requires a global event as a triggerof the excursion such as increases in oxygen contents of surface envi-ronment through high primary production and organic carbon burialthrough formation of fecal pellets by more animals in the Atdabanianstage. The large negative δ13C anomaly is accompanied with non-bioturbated black shales in the Shipai Formation, indicating that shal-low water anoxia caused the decrease of benthic animals in theBotomian and the Canglangpuian stages.

Subsequent increase of the δ13Ccarb −12‰ to +2‰ in lateCanglangpuian stage indicates enhanced primary productivity,consistent with the recover of trilobite diversity and increase ofArchaeocyatha fossils. From the late Canglangpuian to the bottom ofthe Longwangmiaoian, the δ13C values are fluctuated around 0 to1‰ with some small negative anomalies. Abundant Archaeocyathaand sponge fossils, and the deposits of sandy and oolitic limestone

in the middle of the Tianheban Formation (Fig. 6) indicate the exis-tence of reef on the Yangtze platform, and broadly correspond to adiachronous and regional sea level falling “Hawk Bay event” in thelatest Early Cambrian. Small negative δ13C shifts from +2‰ to−1‰ suggest increase in recycling of organic-rich deposits duringthe regression.

Acknowledgments

We thank Dr. Keita Yamada at the Tokyo Institute of Technologyfor help with isotope analysis. This work was partly supported bygrants for “Coevolution of surface environment and solid earth fromthe Neoproterozoic Snowball Earth to Cambrian explosion events(no. 18740318)” and by the 21st Century COE Program “How tobuild habitable planets” at the Tokyo Institute of Technology fromthe Ministry of Education, Culture, Sports, Science and Technology,Japan, and by the Mitsubishi Foundation (T.K.). Y.U. is supported bythe MEXT's program “Promotion of Environmental Improvement forIndependence of Young Researchers” under the Special CoordinationFunds for Promoting Science and Technology.

References

Amthor, J.E., Grotzinger, J.P., Schröder, S., Bowring, S.A., Ramezani, J., Martin, M.W.,Matter, A., 2003. Extinction of Cloudina and Namacalathus at the Precambrian–Cambrian boundary in Oman. Geology 31, 431–434.

1056 T. Ishikawa et al. / Gondwana Research 25 (2014) 1045–1056

Babcock, L.E., Peng, S., 2007. Cambrian chronostratigraphy: current state and futureplans. Palaeogeography, Palaeoclimatology, Palaeoecology 254, 62–66.

Brasier, M.D., Sukhov, S.S., 1998. The falling amplitude of carbon isotopic oscillationsthrough the lower to middle Cambrian: Northern Siberia data. Canadian Journalof Earth Sciences 35, 353–373.

Brasier, M.D., Corfield, R.M., Derry, L.A., Rozanov, A.Y., Zhuravlev, A.Y., 1994. Multipleδ13C excursions spanning the Cambrian explosion to the Botomian crisis in Siberia.Geology 22, 455–458.

Brasier, M.D., Shields, G., Kuleshov, V.N., Zhegallo, E.A., 1996. Integrated chemo- andbiostratigraphic calibration of early animal evolution: Neoproterozoic–earlyCambrian of southwest Mongolia. Geological Magazine 133, 445–485.

Chen, P., 1984. Discovery of Lower Cambrian small shelly fossils from Jijiapo, YichangWest Hubei and its significance (in Chinese with English abstract). ProfessionalPapers of Stratigraphy and Palaeontology 13, 49–66.

Chen, P., 1987. The Sinian System. In: Wang, X. (Ed.), Stratigraphic Excursion Guidebookin the Yangtze Gorge Area. Yichang Institute of Geology and Mineral Resources,Chinese Academy of Geological Sciences, Geological Publishing House, Beijing,China, pp. 2–7.

Dilliard, K.A., Pope, M.C., Coniglio, M., Hasiotis, S.T., Lieberman, B.S., 2007. Stable iso-tope geochemistry of the lower Cambrian Sekwi Formation, Northwest Territories,Canada: implications for ocean chemistry and secular curve generation.Palaeogeography, Palaeoclimatology, Palaeoecology 256, 174–194.

Ding, L., Li, Y., Chen, H., 1992. Discovery of Micrhystridium regulare from Sinian–Cambrian boundary strata in Yichang, Hubei, and its stratigraphic significance.(in Chinese with English abstract) Acta Palaeontologica Sinica 9, 303–309.

Ding, L., Li, Y., Hu, X., Xiao, Y., Su, C., Huang, J., 1996. Sinian Miaohe Biota of China.Geological Publishing House, Beijing (261 pp.).

Fike, D.A., Grotzinger, J.P., Pratt, L.M., Summons, R.E., 2006. Oxidation of the EdiacaranOcean. Nature 444, 744–747.

Guo, J.F., Li, Y., Han, J., Zhang, X.L., Zhang, Z.F., Ou, Q., Liu, J.N., Shu, D.G., Maruyama, S.,Komiya, T., 2008. Fossil association from the Lower Cambrian Yanjiahe Formationin the Yangtze Gorges Area, Hubei, South China. Acta Geologica Sinica-EnglishEdition 82, 1124–1132.

Holser, W.T., Schidlowski, M., Mackenzie, F.T., Maynard, J.B., 1988. Biogeochemical cy-cles of carbon and sulfur. In: Gregor, C.B., Garrels, R.M., Mackenzie, F.T., Maynard,J.B. (Eds.), Chemical Cycles in the Evolution of the Earth. John Wiley & Sons, NewYork, pp. 105–173.

Hsü, K.J., Hedi, O., Y., G. J., Sun, S., Chen, H., Krahenbuhl, U., 1985. “Strangelove Ocean”before the Cambrian explosion. Nature 316, 809–811.

Huang, J., Chu, X., Jiang, G., Feng, L., Chang, H., 2011. Hydrothermal origin of elevatediron, manganese and redox-sensitive trace elements in the c. 635 Ma Doushantuocap carbonate. Journal of the Geological Society 168, 805–816.

Ishikawa, T., Ueno, Y., Komiya, T., Sawaki, Y., Han, J., Shu, D., Li, Y., Maruyama, S.,Yoshida, N., 2008. Carbon isotope chemostratigraphy of a Precambrian/Cambrianboundary section in the Three Gorge area, South China: prominent global-scaleisotope excursions just before the Cambrian explosion. Gondwana Research 14,193–208.

Ishikawa, T., Ueno, Y., Shu, D., Li, Y., Han, J., Guo, J., Yoshida, N., Komiya, T., 2013. Irrevers-ible change of the oceanic carbon cycle in the earliest Cambrian: high-resolution or-ganic and inorganic carbon chemostratigraphy in the Three Gorges area, South China.Precambrian Research 225, 190–208.

Jiang, G., Shi, X., Zhang, S., Wang, Y., Xiao, S., 2011. Stratigraphy and paleogeography ofthe Ediacaran Doushantuo Formation (ca. 635–551 Ma) in South China. GondwanaResearch 19, 831–849.

Kaufman, A.J., Knoll, A.H., 1995. Neoproterozoic variations in the C-isotopic composi-tion of seawater: stratigraphic and biogeochemical implications. PrecambrianResearch 73, 27–49.

Kaufman, A.J., Knoll, A.H., Semikhatov, M.A., Grotzinger, J.P., Jacobsen, S.B., Adams,W., 1996. Integrated chronostratigraphy of Proterozoic–Cambrian boundarybeds in the western Anabar region, northern Siberia. Geological Magazine 133,509–533.

Kimura, H., Matsumoto, R., Kakuwa, Y., Hamdi, B., Zibaseresht, H., 1997. The Vendian–Cambrian δ13C record, North Iran: evidence for overturning of the ocean before theCambrian explosion. Earth and Planetary Science Letters 147, E1–E7.

Kirschvink, J.L., Margaritz, M., Ripperdan, R.L., Zhuravlev, A.Y., Rozanov, A.Y., 1991. ThePrecambrian–Cambrian boundary: magnetostratigraphy and carbon isotopesresolve correlation problems between Siberia, Morocco, and South China. GSAToday 1, 69–91.

Lambert, I.B., Walter, M.R., Zhang, W., Lu, S., Ma, G., 1987. Palaeoenvironment and car-bon isotope stratigraphy of Upper Proterozoic carbonates of the Yangtze Platform.Nature 325, 140–142.

Li, Z.-X., 1998. Tectonic history of the Major East Asian lithospheric blocks since theMid-Proterozoic — a synthesis. In: Martin, F.J., Chung, S.-L., Lo, C.-H., Lee, C.F.(Eds.), Mantle dynamics and plate interactions in East Asia. : Geodynamics Series,27. AGU, Washington DC, pp. 221–243.

Li, G., Steiner, M., Zhu, X., Yang, A., Wang, H., Erdtmann, B.D., 2007. Early Cambrianmetazoan fossil record of South China: generic diversity and radiation patterns.Palaeogeography, Palaeoclimatology, Palaeoecology 254, 229–249.

Logan, G.A., Hayes, J.M., Hieshima, G.B., Summons, R.E., 1995. Terminal Proterozoicreorganization of biogeochemical cycles. Nature 376, 53–56.

Ma, G., Li, H., Zhang, Z., 1984. An investigation of the age limits of the Sinian System inSouth China. Bulletin of the Yichang Institute of Geology and Mineral Resources 8,1–29 (in Chinese with English abstract).

Magaritz, M., Holser, W.T., Kirschvink, J.L., 1986. Carbon-isotope events acrossthe Precambrian/Cambrian boundary on the Siberian Platform. Nature 320,258–259.

Magaritz, M., Kirschvink, J.L., Latham, A.J., Zhuravlev, A.Y., Rozanov, A.Y., 1991. Precam-brian/Cambrian boundary problem: carbon isotope correlations for Vendian andTommotian time between Siberia and Morocco. Geology 19, 847–850.

Maloof, A.C., Schrag, D.P., Crowley, J.L., Bowring, S.A., 2005. An expanded record of EarlyCambrian carbon cycling from the Anti-Atlas Margin, Morocco. Canadian Journal ofEarth Sciences 42, 2195–2216.

McFadden, K.A., Huang, J., Chu, X., Jiang, G., Kaufman, A.J., Zhou, C., Yuan, X., Xiao, S.,2008. Pulsed oxidation and biological evolution in the Ediacaran DoushantuoFormation. Proceedings of the National Academy of Sciences 105, 3197–3202.

Narbonne, G.M., Kaufman, A.J., Knoll, A.H., 1994. Integrated chemostratigraphy andbiostratigraphy of the Windermere Supergroup, northwestern Canada: implica-tions for Neoproterozoic correlations and the early evolution of animals. GeologicalSociety of America Bulletin 106, 1281–1292.

Palmer, A.R., James, N.P., 1980. The Hawke Bay event: a circum-Iapetus regression nearthe lower Middle Cambrian boundary. In: Wones, D.R. (Ed.), Proceedings “TheCaledonides in the USA”: I.G.C.P. Project 27: Caledonide Orogen, 1979 Meeting,Blackberg, Virginia. Department of Geological Sciences, Virginia Polytechnic Insti-tute and State University, Blackburg, Virginia, pp. 15–18.

Pelechaty, S.M., Kaufman, A.J., Grotzinger, J.P., 1996. Evaluation of δ13C chemostratigraphyfor intrabasinal correlation: Vendian strata of northeast Siberia. Geological Society ofAmerica Bulletin 108, 992–1003.

Peters, S.E., Gaines, R.R., 2012. Formation of the ʻgreat unconformityʼ as a trigger for theCambrian explosion. Nature 484, 363–366.

Qian, Y., 1999. Taxonomy and Biostratigraphy of Small Shelly Fossils in China (inChinese with English Abstract). Scientific Publishing House, Beijing (247 pp.).

Révész, K.M., Landwehr, J.M., 2002. δ13C and δ18O isotopic composition of CaCO3 mea-sured by continuous flow isotope ratio mass spectrometry: statistical evaluationand verification by application to Devils Hole core DH-11 calcite. Rapid Communi-cations in Mass Spectrometry 16, 2102–2114.

Ripperdan, R.L., 1994. Global variations in carbon isotope composition during the LatestNeoproterozoic and Earliest Cambrian. Annual Review of Earth and PlanetarySciences 22, 385–417.

Rothman, D.H., Hayes, J.M., Summons, R.E., 2003. Dynamics of the Neoproterozoiccarbon cycle. Proceedings of the National Academy of Sciences 100, 8124–8129.

Rozanov, A., Zhu, M., Pak, K., Parkhaev, P., 2008. The 2nd Sino-Russian Symposium onthe Lower Cambrian Subdivision. Paleontological Journal 42, 441–446.

Saltzman,M.R., Runnegar, B., Lohmann, K.C., 1998. Carbon isotope stratigraphy of UpperCambrian (Steptoean Stage) sequences of the eastern Great Basin: record of a globaloceanographic event. Geological Society of America Bulletin 110, 285–297.

Shen, Y., 2002. C-isotope variations and paleoceanographic changes during the lateNeoproterozoic on the Yangtze Platform, China. Precambrian Research 113,121–133.

Shen, Y., Schidlowski, M., 2000. New C isotope stratigraphy from southwest China:implications for the placement of the Precambrian–Cambrian boundary on theYangtze Platform and global correlations. Geology 28, 623–626.

Shu, D., 2008. Cambrian explosion: birth of tree of animals. Gondwana Research 14,219–240.

Sial, A.N., Peralta, S., Ferreira, V.P., Toselli, A.J., Aceñolaza, F.G., Parada, M.A., Gaucher, C.,Alonso, R.N., Pimentel, M.M., 2008. Upper Cambrian carbonate sequences of the Ar-gentine Precordillera and the Steptoean C-Isotope positive excursion (SPICE).Gondwana Research 13, 437–452.

Tahata, M., Ueno, Y., Ishikawa, T., Sawaki, Y., Murakami, K., Han, J., Shu, D., Li, Y., Guo, J.,Yoshida, N., Komiya, T., 2013. Carbon and oxygen isotope chemostratigraphies ofthe Yangtze platform, South China: decoding temperature and environmentalchanges through the Ediacaran. Gondwana Research 23, 333–353.

Vernhet, E., Reijmer, J.J.G., 2010. Sedimentary evolution of the Ediacaran Yangtze plat-form shelf (Hubei and Hunan provinces, Central China). Sedimentary Geology 225,99–115.

Wang, X., 1987. Biostratigraphy of the Yangtze Gorges Area Geological. PublishingHouse, Beijing, China 4–42.

Wang, X., Chen, X. (Eds.), 2005. Stratigraphic Division and Correlation of China. GeologicalPublishing House, Beijing (596 pp.).

Zhang, Z., 1981. Precambrian microfossils from the Sinian of South China. Nature 289,792–793.

Zhao, Z., Xing, Y., Ma, G., Chen, Y., 1985. Biostratigraphy of the Yangtze Gorge Area (1)Sinian (in Chinese with English Abstract). Geological Publishing House, Beijing(164 pp.).

Zhao, Z., Xing, Y., Ding, Q., Liu, G., Zhao, Y., Zhang, S., Meng, X., Yin, C., Ning, B., Han, P.,1988. The Sinian System of Hubei. China University of Geosciences Press, Wuhan(205 pp.).

Zhou, T., Xu, G., 1987. The Cambrian system. In: Wang, X. (Ed.), Stratigraphic ExcursionGuidebook in the Yangtze Gorge Area. Yichang Institute of Geology and MineralResources, Chinese Academy of Geological Sciences, Geological Publishing House,Beijing, China, pp. 8–13.

Zhu, M.Y., Zhang, J.M., Steiner, M., Yang, A.H., Li, G.X., Erdtmann, B.D., 2003. Sinian–Cam-brian stratigraphic framework for shallow- to deep-water environments of theYangtze Platform: an integrated approach. Progress in Natural Science 13, 951–960.

Zhu, M.-Y., Babcock, L.E., Peng, S.-C., 2006. Advances in Cambrian stratigraphy andpaleontology: integrating correlation techniques, paleobiology, taphonomy andpaleoenvironmental reconstruction. Palaeoworld 15, 217–222.

Zhuravlev, A.Y., Naimark, E.B., 2005. Alpha, beta, or gamma: numerical view on theEarly Cambrian world. Palaeogeography, Palaeoclimatology, Palaeoecology 220,207–225.

Zhuravlev, A.Y., Wood, R.A., 1996. Anoxia as the cause of the mid-Early Cambrian(Botomian) extinction event. Geology 24, 311–314.