Journal of Asian Earth Sciences 67–68 (2013) 51–62

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Journal of Asian Earth Sciences

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Middle–Upper Permian carbon isotope stratigraphy at Chaotian, South China:Pre-extinction multiple upwelling of oxygen-depleted water onto continental shelf

Masafumi Saitoh a,⇑,1, Yukio Isozaki a,b, Yuichiro Ueno c, Naohiro Yoshida d,e, Jianxin Yao f, Zhansheng Ji f

a Department of Earth Science and Astronomy, The University of Tokyo, Meguro, Tokyo 153-8902, Japanb Department of Université Lille1, Avenue Paul Langevin, F-59655 Villeneuve d’Ascq, Francec Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japand Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, Midori, Yokohama 226-8503, Japane Department of Environmental Science and Technology, Tokyo Institute of Technology, Midori, Yokohama 226-8503, Japanf Geology Institute, Chinese Academy of Geological Science, Beijing 100037, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 20 July 2012Received in revised form 1 February 2013Accepted 5 February 2013Available online 18 February 2013

Keywords:GuadalupianLopingianCarbon isotopic negative excursionsDisphotic oxygen-depletionMultiple upwellingExtinction

1367-9120/$ - see front matter � 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jseaes.2013.02.009

⇑ Corresponding author. Address: 3-8-1, KomabaJapan. Tel.: +81 3 5454 6622; fax: +81 3 5465 8244.

E-mail address: saitoh.m.ab@m.titech.ac.jp (M. Sai1 Present address: Department of Earth and Planetar

Technology, Meguro, Tokyo 152-8551, Japan.

In order to examine the causal relationships between the carbon cycle in a shallow euphotic zone and theenvironmental changes in a relatively deep disphotic zone at the end-Guadalupian (Middle Permian), iso-topic compositions of carbonate carbon (d13Ccarb) of the Guadalupian–Lopingian (Upper Permian) rockswere analyzed in the Chaotian section in northern Sichuan, South China. By analyzing exceptionally freshdrill core samples, a continuous chemostratigraphic record was newly obtained. The ca. 65 m-thick ana-lyzed carbonate rocks at Chaotian comprise three stratigraphic units, i.e., the Limestone Unit of the Guad-alupian Maokou Formation, the Mudstone Unit of the Maokou Formation, and the lower part of theWuchiapingian (Lower Lopingian) Wujiaping Formation, in ascending order. The Limestone Unit of theMaokou Formation is characterized by almost constant d13Ccarb values of ca. +4‰ followed by an abruptdrop for 7‰ to �3‰ in the topmost part of the unit. In the Mudstone Unit of the Maokou Formation, thed13Ccarb values are rather constant around +2‰, although distinct three isotopic negative excursions for3‰ from ca. +2 to �1‰ occurred in the upper part of the unit. In the lower part of the Wujiaping Forma-tion, the d13Ccarb values monotonously increase for 5‰ from ca. 0 to +5‰. The present data newly dem-onstrated four isotopic negative excursions in the topmost part of the Maokou Formation in theCapitanian (Late Guadalupian) at Chaotian. It is noteworthy that these negative excursions are in accor-dance with the emergence of an oxygen-depleted condition on the relatively deep disphotic slope/basinon the basis of litho- and bio-facies characteristics. They suggest multiple upwelling of oxygen-depletedwaters with dissolved inorganic carbon of relatively low carbon isotope values along the continental mar-gin, from the deeper disphotic slope/basin to the shallower euphotic shelf, slightly before the end-Guad-alupian extinction. Although the negative excursions at Chaotian are apparently correlated with thepreviously proposed large negative excursion in the middle Capitanian in South China, the age differenceaccording to the biostratigraphic constraints clearly exclude this interpretation. The isotopic negativeexcursions at Chaotian are unique and no similar isotopic signal in the same period has been reportedelsewhere. The multiple upwelling of oxygen-depleted waters onto the euphotic shelf may have repre-sented local phenomena that occurred solely around northwestern South China.

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1. Introduction

The Permian mass extinction was the largest biodiversity crisisin the Phanerozoic (e.g., Erwin, 2006; Alroy, 2010). Although thecatastrophe has been traditionally regarded as a single event, itcomprises two distinct extinctions; i.e., the first occurred at the

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toh).y Sciences, Tokyo Institute of

end-Guadalupian (Middle Permian), ca. 260 million years ago(Ma), and the second at the end-Changhsingian (Late Late Perm-ian), ca. 252 Ma. The end-Changhsingian extinction has been tradi-tionally well known; however, the older end-Guadalupianextinction has been later focused since Jin et al. (1994) and Stanleyand Yang (1994) first emphasized its great magnitude. During thelast decade, various unique geologic phenomena, in addition to theextinction, around the Guadalupian–Lopingian (Late Permian)boundary (G-LB) have been emphasized; i.e., the lowest sea-levelin the entire Phanerozoic (Jin et al., 1994; Haq and Schutter,2008), the eruption of the Emeishan flood basalt in South China

52 M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62

(Chung and Jahn, 1995; Zhou et al., 2002), the onset of prolongeddeep-sea oxygen-depletion (superanoxia; Isozaki, 1997), one ofthe lowest 87Sr/86Sr ratio in the Phanerozoic (Veizer et al., 1999),and the onset of frequent geomagnetic polarity changes (IllawarraReversal; Irving and Parry, 1963). See Isozaki (2009) for more de-tails of the uniqueness of the end-Guadalupian geologic phenom-ena. Nonetheless, the ultimate cause of the end-Guadalupianextinction is still in discussion (e.g., Isozaki, 2007, 2009; Bottjeret al., 2008; Clapham et al., 2009; Bond et al., 2010a,b).

Previous stratigraphic researches on the environmental changesaround the G-LB mainly analyzed fossiliferous shallow-marineshelf carbonates in South China (e.g., Jin et al., 1998) and paleo-atoll limestones on ancient seamounts (e.g., Isozaki and Ota,2001; Ota and Isozaki, 2006; Kasuya et al., 2012) and pelagicdeep-sea cherts (e.g., Isozaki, 1997; Nishikane et al., 2011) in accre-tionary complex in Southwest Japan. The Middle–Upper Permianstrata deposited in South China have exceptionally continuousstratigraphic records with diverse shallow-marine fossils (e.g.,Zhao et al., 1981; Yang et al., 1987; Jin et al., 1998). For example,the best continuous Penglaitan section in Guangxi is officially des-ignated as the Global Stratotype Section and Point (GSSP) for the G-LB (e.g., Jin et al., 1998, 2006; Shen et al., 2007).

Nonetheless, more information from a relatively deep disphoticzone (usually deeper than 150 m), below a euphotic zone, isneeded in order to identify the entire environmental changes inthe oceans relevant to the end-Guadalupian extinction, particularlyto understand the relationships between the shallow-sea extinc-tion and the deep-sea oxygen-anomaly. Few previous studies,however, have focused on the disphotic zone in the Permianoceans. In fact, the late Guadalupian to early Lopingian carbonatesof deep-water facies on the northwest margin of South China (e.g.,Li et al., 1989; Zhu et al., 1999; Wang and Jin, 2000) recorded thatan oxygen-depleted condition has emerged on the disphotic slope/basin in the Capitanian (Late Guadalupian) during a rapid sea-levelrise slightly before the end-Guadalupian extinction (Isozaki et al.,2008; Saitoh et al., 2013; Fig. 1). The causal relationships betweenthe oxygen-depletion in a deeper disphotic zone and the extinctionin a shallower euphotic zone are, however, still unknown.

For analyzing the end-Guadalupian environmental changes, sev-eral chemostratigraphic studies of carbon isotope values of carbon-ates (d13Ccarb) have been conducted. Wang et al. (2004) firstanalyzed C-isotope stratigraphy of the G-LB interval of the GSSP atPenglaitan in Guangxi, and reported a negative d13Ccarb shift acrossthe boundary. Isozaki et al. (2007a) confirmed the identical G-LBnegative shift in paleo-atoll limestone deposited on an ancient sea-mount in mid-Panthalassa at Kamura in Southwest Japan. On theother hand, on the basis of the analyses of several sections in wes-tern South China, Bond et al. (2010a) pointed out that a large (over5‰) negative excursion occurred not at the G-LB but in the earliermiddle Capitanian. They also postulated the ‘‘end-Guadalupianextinction’’ was associated with their middle Capitanian larged13Ccarb excursion. Their propositions were later criticized by Chenet al. (2011) and by Saitoh et al. (2013), independently.

Under the circumstances, causal relationships between fluctua-tion of global carbon cycle and environmental changes relevant tothe end-Guadalupian extinction are still controversial. We investi-gated the d13Ccarb values of the Guadalupian–Lopingian marine car-bonates (ca. 65 m thick) at Chaotian in northern Sichuan, in orderto examine the processes how the oxygen-depleted waters in adeeper disphotic zone previously recognized at Chaotian did affectthe carbon cycle in a shallower euphotic zone around the G-LB. Weanalyzed exceptionally fresh and continuous drill core samples atChaotian and clarified the unique and large carbon isotopic fluctu-ations across the G-LB in accordance with the emergence of disph-otic oxygen-depletion. This article reports the new C-isotopechemostratigraphy across the G-LB at Chaotian. On the basis of

the new isotopic results, we discuss its geological significance withrespect to the environmental changes around the G-LB in north-western South China.

2. Geologic setting and stratigraphy

During the Permian, the South China craton was located on theeast of the Pangea around the equator (e.g., Scotese and Langford,1995). Thick shallow-marine carbonates with diverse shallow-marine fossils were extensively deposited on continental shelvesof South China (e.g., Zhao et al., 1981; Jin et al., 1998). In northernSichuan, along the northwestern edge of South China, carbonatesof relatively deep-water facies accumulated (Wang and Jin,2000). We have analyzed one of such carbonates of deep-water fa-cies at Chaotian (32�370N, 105�510E), located 20 km to the north ofGuangyuan (Isozaki et al., 2004; Fig. 1). The Chaotian section dis-plays extensive exposures of continuous Middle Permian to LowerTriassic rocks along a gorge called Mingyuexia of the JialingjiangRiver. Zhao et al. (1978) and Yang et al. (1987) originally describedthe overall biostratigraphy at Chaotian on the basis of fusulines,conodonts, and ammonoids. Several studies on litho- (Isozakiet al., 2004, 2007c, 2008; Lai et al., 2008; Saitoh et al., 2013), bio-(Xu, 2006; Ji et al., 2007; Kuwahara et al., 2007, 2008; Isozakiet al., 2008; Lai et al., 2008), chemo- (Lai et al., 2008), andchrono-stratigraphy (He et al., 2007) were subsequently performedat Chaotian.

The Permo-Triassic rocks at Chaotian consist of the GuadalupianMaokou Formation, the Lopingian Wujiaping and Dalong forma-tions, and the lowermost Triassic Feixianguan Formation, inascending order (Yang et al., 1987; Isozaki et al., 2004, 2007c,2008; Ji et al., 2007; Saitoh et al., 2013; Fig. 1). This study analyzedin detail the upper Maokou and lower Wujiaping formations (ca.65 m thick) for chemostratigraphic study. The analyzed carbonaterocks comprise three distinct stratigraphic units (Fig. 1); i.e., theLimestone Unit of the Maokou Formation, the Mudstone Unit ofthe Maokou Formation, and the lower part of the Wujiaping For-mation, in ascending order. The Limestone Unit of the Maokou For-mation, ca. 35 m thick, is mainly composed of dark gray massivebioclastic limestone and contains shallow-marine fossils such asalgae and fusulines. This Unit was probably deposited on a eupho-tic shelf. This part largely corresponds to ‘the L3 subunit of theLimestone Unit’ of the Maokou Formation in Saitoh et al. (2013).The Mudstone Unit of the Maokou Formation, ca. 11 m thick, ismainly composed of thinly bedded black calcareous mudstone,black chert, and black siliceous mudstone and yields abundantradiolarians, conodonts, and ammonoids. This Mudstone Unitwas deposited on a relatively deep disphotic slope/basin underoxygen-depleted condition, on the basis of litho- and bio-faciescharacteristics (Saitoh et al., 2013). This Unit comprises the lowerM1 subunit (ca. 8 m thick) and the upper M2 subunit (ca. 3 mthick). The lower M1 subunit yields abundant brachiopods andconodonts, whereas the upper M2 subunit contains abundant radi-olarians and ammonoids (Saitoh et al., 2013). The lower part of theWujiaping Formation, ca. 20 m thick, is mainly composed of darkgray bioclastic limestone and contains calcareous algae and smallfusulines. At the base of the Wujiaping Formation, a unique ca.2 m thick volcaniclastic ‘Wangpo bed’ occurs. The lower WujiapingFormation was deposited on a euphotic shelf.

Previously reported index fossils such as fusulines, conodonts,and ammonoids constrained the ages of these three stratigraphicunits (Isozaki et al., 2008; Lai et al., 2008): The Limestone Unit ofthe Maokou Formation entirely belongs to the Jinogondolella post-serrata Zone of the early Capitanian (Upper Guadalupian). TheM1 subunit of the Mudstone Unit of the Maokou Formationbelongs to the Jinogondolella shannoni Zone of the early-middle

Dal

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uan

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sbac

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Age Fm

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50 mcarbonate

siliceous rocktuffchert nodule

black chertdark gray limestoneblack mudstonetuff

chert nodule

10 m

biostratigraphically-defined G-L boundary

estimated extinction horizon

sedimentary environmentstratigraphic unit

euphotic shelf

euphotic shelf

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lower part of the Wujiaping Fm

Limestone Unit of the Maokou Fm

Mudstone Unit of the Maokou Fm

Limestone Unit of the Maokou Fm

Wujiaping Fm

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B

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Changjiang River

Huanghe River

Beijing

Chengdu

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A

Fig. 1. Location (A), Outcrop photograph (B), and stratigraphy (C) of the Chaotian section. A rest station for scale (circled) on the photograph (B).

M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62 53

Capitanian. Although precise age of the M2 subunit of the Mud-stone Unit is unknown without conodont, Saitoh et al. (2013) re-garded that the M2 subunit belongs to the middle-lateCapitanian. The lower Wujiaping Formation likely belongs to theearly Wuchiapingian (Lower Lopingian) on the basis of fusuline re-cords (Yang et al., 1987; Isozaki et al., 2008). Isozaki et al. (2008)tentatively assigned the biostratigraphically-defined G-LB at thebase of the bioclastic limestone of the Wujiaping Formation. Saitohet al. (2013) set the extinction horizon at Chaotian at the top of the

M2 subunit of the Mudstone Unit of the Maokou Formation on thebasis of regional correlations in western South China.

Significant litho- and bio-facies changes suggest that the sea-le-vel largely fluctuated across the G-LB at Chaotian (Saitoh et al.,2013); a two-stepped sea-level rise occurred in the Capitanianand the sedimentary environment changed from a shallow eupho-tic shelf to a relatively deep disphotic slope/basin. This deepeningevent was followed by a significant sea-level drop around the G-LBand the sedimentary environment returned to a euphotic shelf.

54 M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62

3. Materials and analytical methods

3.1. Materials

We collected samples for stable carbon isotope analysis from theoutcrop and from the drill core. Exceptionally fresh and continuousdrill core samples were mainly analyzed, particularly of the Mud-stone Unit of the Maokou Formation (Fig. 2D). On the outcrop, thesedimentary rocks of the Mudstone Unit of the Maokou Formationwere strongly weathered and are unsuitable for any geochemicalanalysis (Fig. 2B and C). Exceptionally fresh part in a rock sample

A

B

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F

Maokou Fm

Wujiaping FmDalong Fm

Feixianguan Fm

Outcrop

P-TBG-LB

E

2 mm 0.5 mm

H I

100 µm

Fig. 2. Photographs of the outcrop and sedimentary rocks at Chaotian. (A) The Chaotian soutcrop and of drilling, respectively. A car (circled) for scale. (B and C) Outcrop photoggenerally strongly weathered. (D) A photograph of exceptionally fresh drilling core samdark gray bioclastic limestone (E) in the Limestone Unit and of black calcareous mudstonimage of SEM photograph of black calcareous mudstone in the Mudstone Unit. Carbonatransported from the shallower shelf to the deeper slope/basin by gravity flow.

was carefully chosen on the basis of detailed observation of polishedslabs and thin sections under microscope. The rock samples contain-ing frequent dolomite crystals are removed before isotope analysis.We analyzed two types of carbonate rocks (Fig. 2E and F); i.e., darkgray bioclastic limestone (50 samples) in the Limestone Unit of theMaokou Formation and in the lower part of the Wujiaping Formationand black calcareous mudstone (36 samples) in the Mudstone Unitof the Maokou Formation. Only one sample from a bed in the Mud-stone Unit of the Maokou Formation is classified as dark gray bio-clastic limestone because the bed is regarded as a carbonate debrisflow deposit on the basis of its bioclastic texture under microscope.

Drilling site

1 cm

D

G

10 µm

J

1 mm

20 µm

ection viewed from the western side of the Jialingjiang River. Stars represent sites ofraphs of the Mudstone Unit of the Maokou Formation at Chaotian. The rocks are

ple from the Mudstone Unit of the Maokou Formation. (E–G) Photomicrographs ofe (F and G) in the Mudstone Unit of the Maokou Formation. (H–J) Secondary electrontes in black mudstone are exclusively fine fragmented bioclasts (arrows) probably

M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62 55

3.2. Analytical methods

Powdered sample of ca. 100–500 lg is prepared using micro-drills of 0.8–1.2 mm diameter. Samples were analyzed by a Ther-moquest GasBench II preparation device connected with heliumflow to DELTA Plus XL at the Tokyo Institute of Technology (mod-ified from Revesz and Landwehr, 2002). The standard acid diges-tion technique was used for extracting carbonate carbon(Wachter and Hayes, 1985). Powdered sample was reacted with>100% phosphoric acid at 80 �C for >12 h in order to release CO2.After the digestion, the extracted CO2 was separated from H2Oand other non-condensable gases in a chromatography line witha helium flow, and carbon and oxygen isotope ratios were mea-sured by DELTA Plus XL. The carbonate carbon and oxygen isotoperatios (d13C and d18O) are reported in ‰ relative to Vienna PeedeeBelemnite (VPDB) standard. Analytical reproducibility of the d13Cand d18O values determined by replicate analyses of the laboratorystandard is better than ±0.3‰ and ±0.5‰, respectively.

4. Results

Table 1 lists all the 86 measurements of d13Ccarb and d18Ocarb

values from the ca. 65 m thick study section. Figs. 3 and 4 showstratigraphic changes in d13Ccarb values plotted along the columnof the analyzed section. The d13Ccarb values of dark gray bioclasticlimestone range in �3.0 to +4.9‰. Most of them are within +2 to+4‰, and some have relatively low (<0‰) values. All d18Ocarb val-ues of dark gray bioclastic limestone are negative, and range in�12.4 to �3.5‰, although most of them are within �8 to �4‰.On the other hand, black calcareous mudstone occurs solely withinthe Mudstone Unit of the Maokou Formation. The d13Ccarb values ofblack calcareous mudstone range in �1.3 to +3.1‰. The d18Ocarb

values of black calcareous mudstone range in �12.6 to �5.6‰.No linear correlation is recognized between the d13Ccarb andd18Ocarb profiles regardless of rock type. Thus, we interpret thatthe all samples represent their original d13Ccarb values.

Stratigraphic changes of d13Ccarb values demonstrated four dis-tinct negative excursions in the topmost part of the Maokou For-mation at Chaotian (Fig. 3). The Limestone Unit of the MaokouFormation is mainly characterized by almost constant d13Ccarb val-ues of ca.+4‰ followed by an abrupt drop for 7‰ to �3‰ in thetopmost part of the unit. We named this excursion, N1. In theupper Mudstone Unit of the Maokou Formation, most of thed13Ccarb values of black calcareous mudstone are rather constant,around +2‰, throughout the unit although they are somewhatscattered. It is noteworthy, however, that three negative excur-sions for 3‰ from ca. +2 to �1‰ occur in the upper part of theMudstone Unit. We named these excursions, N2, N3, and N4, inascending order (Fig. 3). The N2 excursion occurs ca. 6 m abovefrom the base of the Mudstone Unit. The N3 excursion occursimmediately below the M1/M2 subunit boundary. The N4 excur-sion occurs in the upper part of the M2 subunit, ca. 2.4 m abovefrom the M1/M2 subunit boundary. In the lower part of the Wujia-ping Formation, the d13Ccarb values of bioclastic limestone monot-onously increase for 5‰ from ca. 0 to +5‰.

5. Discussion

5.1. Chemostratigraphy at Chaotian

5.1.1. Two types of carbonate rocksWe analyzed two types of carbonate rocks (Fig. 2E–G); i.e., dark

gray bioclastic limestone in the Limestone Unit of the Maokou For-mation and in the lower part of the Wujiaping Formation, andblack calcareous mudstone in the Mudstone Unit of the Maokou

Formation. Bioclastic limestone, deposited on the shallow euphoticshelf, is composed of sand-sized bioclasts of shallow-marine fossilssuch as corals, algae, and fusulines. Their d13Ccarb values probablyrecord the carbon isotope values of dissolved inorganic carbon(d13CDIC) values in a euphotic zone.

On the other hand, black calcareous mudstone in the MudstoneUnit of the Maokou Formation was deposited on the deeper disph-otic slope/basin (Saitoh et al., 2013). Black calcareous mudstonecontains abundant fragments of shallow-marine fossils, such asbrachiopods, gastropods, and bryozoan (Fig. 3G and H). It is note-worthy that, in addition to those recognizable large bioclasts, blackcalcareous mudstone contains two distinct types of small (lessthan 100 lm in diameter) carbonates; i.e., abundant calcite andminor dolomite crystals. Small calcite crystals in black mudstonetake various forms and their size is not uniform, recognized byscanning electron microscopy (SEM) and Energy Dispersion X-raySpectrometry (EDS) (Fig. 2I and J). Their various shape and sizesuggest that the calcite crystals are fine-grained bioclasts of shal-low-marine fossils as similar to large bioclasts frequently sur-rounding them (Fig. 2F–H). They were probably generated bybiomineralization in a shallower euphotic shelf and subsequentlyfragmented and transported to the deeper disphotic slope/basinsetting by gravity flow, although they are too finely fragmentedto specify their original taxa. In a remarkable contrast, minor dolo-mite crystals in black mudstone are constantly euhedral and ca.100 lm-sized. They were likely generated within sediments bydiagenesis. We removed all the black mudstone samples in whichdolomite crystals are frequently observed before isotope analysisto avoid possible diagenetic overprint, as mentioned in Section 3.1.

As carbonates in analyzed black calcareous mudstone are exclu-sively clay-sized fine-grained bioclasts, the d13Ccarb values of blackmudstone deposited on the deeper disphotic slope/basin probablyrecord the d13CDIC in a shallower euphotic zone, the same as thoseof bioclastic limestone. The d13Ccarb values of both of dark gray bio-clastic limestone and black calcareous mudstone probably recordd13CDIC of the Permian seawater in a shallow euphotic zone, regard-less of rock type. The composite d13Ccarb stratigraphic changes ofdark gray bioclastic limestone and of black calcareous mudstonelikely represent the secular changes of the d13CDIC values in theshallow euphotic zone across the G-LB in northwestern South Chi-na. In the next section, we examine how the d13CDIC changes in theshallow euphotic zone are correlated with the emergence of oxy-gen-depleted waters in the deep disphotic zone at Chaotian.

5.1.2. Four negative excursions in the CapitanianThe present new isotopic data demonstrate four negative excur-

sions in the topmost part of the Maokou Formation at Chaotian(Figs. 3 and 4). The N1 excursion occurred for 7‰ from +4 to�3‰ in the topmost Limestone Unit, whereas the N2, N3, and N4excursions occurred for 3‰ from ca. +2 to �1‰ in the upper Mud-stone Unit. These negative excursions (at least the N1, N2, and N3excursions) have occurred in the early-middle Capitanian (the J.postserrata–J. shannoni Zone) on the basis of conodont biostratigra-phy (Fig. 4).

Two possible mechanisms were proposed for the shift in thed13Ccarb values of shelf-carbonates toward a negative direction;i.e., (1) decline of primary productivity in the surface oceans to de-crease organic carbon burial, and (2) input of 13C-depleted carbon(e.g., fossilized organic carbon and volcanic CO2) into the surfaceocean reservoir. For the early-middle Capitanian, no evidence foran abrupt decline of primary productivity in the ocean has been re-ported anywhere in the world. Therefore, a decline of primary pro-ductivity in the surface oceans may not be a plausible candidate forthe cause of the isotopic negative excursions in the topmost Mao-kou Formation at Chaotian. On the other hand, previous studiessuggested that the initial eruption of the Emeishan basalts in

Table 1Analytical results of d13Ccarb and d18Ocarb normalized to the Vienna Pee Dee belemnite of the Guadalupian Maokou and Wuchiapingian Wujiaping formations at Chaotian, SouthChina. Errors were calculated by numerical propagation through the measurements.

Stratigraphic unit Sample ID Lithology Thickness (cm) d13C (‰) Error (‰) d18O (‰) Error (‰)

Lower part of the Wujiaping Fm 99W017 Dark gray bioclastic limestone 3024 4.9 0.4 �3.7 0.6Lower part of the Wujiaping Fm 99W013 Dark gray bioclastic limestone 2579 4.6 0.3 �6.9 0.6Lower part of the Wujiaping Fm 99W0104 Dark gray bioclastic limestone 2392 4.8 0.3 �6.4 0.7Lower part of the Wujiaping Fm 99W06 Dark gray bioclastic limestone 2075.5 3.5 0.3 �4.1 0.6Lower part of the Wujiaping Fm 99W13 Dark gray bioclastic limestone 1683 1.5 0.3 �9.0 0.5Lower part of the Wujiaping Fm 99W5 Dark gray bioclastic limestone 1568 0.4 0.4 �7.3 0.2Lower part of the Wujiaping Fm 99W3 Dark gray bioclastic limestone 1538 �0.4 0.4 �5.6 0.6Mudstone Unit of the Maokou Fm E99 Black calcareous mudstone 1088.5 0.0 0.7 �5.8 1.6Mudstone Unit of the Maokou Fm 5N4-6 Black calcareous mudstone 1055 �0.9 0.7 �10.4 1.5Mudstone Unit of the Maokou Fm E82 Black calcareous mudstone 1045.5 2.3 0.4 �12.6 1.0Mudstone Unit of the Maokou Fm E72 Black calcareous mudstone 1025 1.3 0.3 �6.8 0.7Mudstone Unit of the Maokou Fm 8-3-10L Black calcareous mudstone 1011.25 1.4 0.5 �6.4 1.1Mudstone Unit of the Maokou Fm E48-1 Black calcareous mudstone 947.25 2.6 0.3 �5.8 0.5Mudstone Unit of the Maokou Fm E48-2 Black calcareous mudstone 947.25 2.8 0.4 �6.5 0.5Mudstone Unit of the Maokou Fm 18-7-1 Black calcareous mudstone 893.5 1.5 0.4 �6.2 1.1Mudstone Unit of the Maokou Fm E26U Black calcareous mudstone 879 3.1 0.4 �12.2 1.1Mudstone Unit of the Maokou Fm E26L Black calcareous mudstone 876.5 2.0 0.4 �7.6 0.6Mudstone Unit of the Maokou Fm E22U Black calcareous mudstone 870.5 1.4 0.4 �8.5 1.1Mudstone Unit of the Maokou Fm E22L Black calcareous mudstone 869.5 2.5 0.3 �10.8 0.5Mudstone Unit of the Maokou Fm E13 Black calcareous mudstone 855.25 1.0 0.3 �6.7 0.8Mudstone Unit of the Maokou Fm E2U Black calcareous mudstone 835 0.3 0.4 �6.8 1.1Mudstone Unit of the Maokou Fm E2M Black calcareous mudstone 834 1.3 0.3 �5.7 0.7Mudstone Unit of the Maokou Fm E2L Black calcareous mudstone 833 2.2 0.4 �8.7 1.1Mudstone Unit of the Maokou Fm D125 Dark gray bioclastic limestone 825.5 �0.3 0.4 �6.9 1.0Mudstone Unit of the Maokou Fm D118 Black calcareous mudstone 814 �1.0 0.4 �6.5 0.5Mudstone Unit of the Maokou Fm D105 Black calcareous mudstone 756.5 1.0 0.4 �9.4 1.1Mudstone Unit of the Maokou Fm D85 Black calcareous mudstone 694.75 0.9 0.3 �8.1 0.6Mudstone Unit of the Maokou Fm D71-1 Black calcareous mudstone 640 0.5 0.3 �5.6 0.6Mudstone Unit of the Maokou Fm D71-2 Black calcareous mudstone 640 0.3 0.3 �9.6 0.6Mudstone Unit of the Maokou Fm D61 Black calcareous mudstone 614.5 1.3 0.3 �6.8 0.5Mudstone Unit of the Maokou Fm D59-1 Black calcareous mudstone 609.5 �1.3 0.3 �6.8 0.5Mudstone Unit of the Maokou Fm D59-2 Black calcareous mudstone 609.5 �0.1 0.3 �9.6 0.5Mudstone Unit of the Maokou Fm D24 Black calcareous mudstone 457.25 2.6 0.3 �7.9 0.5Mudstone Unit of the Maokou Fm D12 Black calcareous mudstone 429.25 1.4 0.4 �5.6 1.0Mudstone Unit of the Maokou Fm C62 Black calcareous mudstone 333 1.5 0.4 �5.5 0.8Mudstone Unit of the Maokou Fm C55 Black calcareous mudstone 295 1.5 0.3 �6.6 0.5Mudstone Unit of the Maokou Fm C53 Black calcareous mudstone 293.5 2.6 0.3 �6.8 0.5Mudstone Unit of the Maokou Fm D37 Black calcareous mudstone 229.5 0.9 0.4 �6.8 0.6Mudstone Unit of the Maokou Fm C27 Black calcareous mudstone 208.5 1.7 0.3 �7.2 0.5Mudstone Unit of the Maokou Fm 23-1-3 Black calcareous mudstone 160.5 1.9 0.4 �8.4 1.1Mudstone Unit of the Maokou Fm B24 Black calcareous mudstone 120.5 3.0 0.4 �5.0 0.8Mudstone Unit of the Maokou Fm B19 Black calcareous mudstone 107 2.7 0.5 �9.6 1.0Mudstone Unit of the Maokou Fm 3-3LL Black calcareous mudstone 107 2.5 0.4 �9.3 1.1Mudstone Unit of the Maokou Fm 3-3LR Black calcareous mudstone 107 2.9 0.4 �10.4 1.1Limestone Unit of the Maokou Fm 13-1-3 Dark gray bioclastic limestone 0 �2.3 0.4 �4.7 1.0Limestone Unit of the Maokou Fm 13-1-2 Dark gray bioclastic limestone 0 �3.0 0.4 �4.0 1.1Limestone Unit of the Maokou Fm 13-1-1 Dark gray bioclastic limestone �1 �3.0 0.4 �3.5 1.1Limestone Unit of the Maokou Fm 07MaoU32 Dark gray bioclastic limestone �1.875 �2.2 0.3 �6.6 0.6Limestone Unit of the Maokou Fm 14-1 Dark gray bioclastic limestone �7.5 �1.3 0.3 �4.8 0.6Limestone Unit of the Maokou Fm 07MaoU31 Dark gray bioclastic limestone �10 1.5 0.4 �5.2 0.6Limestone Unit of the Maokou Fm 03Mao30 Dark gray bioclastic limestone �23.75 1.8 0.5 �6.0 0.6Limestone Unit of the Maokou Fm 16-1 Dark gray bioclastic limestone �24.5 0.7 0.3 �5.3 0.6Limestone Unit of the Maokou Fm 07MaoU29.5 Dark gray bioclastic limestone �38.75 2.0 0.3 �8.3 0.6Limestone Unit of the Maokou Fm 18L-1 Dark gray bioclastic limestone �52.75 2.0 0.3 �6.6 0.6Limestone Unit of the Maokou Fm 07MaoU29 Dark gray bioclastic limestone �53.75 1.4 0.4 �8.7 0.6Limestone Unit of the Maokou Fm 07MaoU28 Dark gray bioclastic limestone �70 1.5 0.4 �5.5 0.7Limestone Unit of the Maokou Fm 07MaoU27 Dark gray bioclastic limestone �86.25 2.4 0.4 �7.3 0.5Limestone Unit of the Maokou Fm 07MaoU26 Dark gray bioclastic limestone �101.25 2.1 0.4 �4.3 0.6Limestone Unit of the Maokou Fm 07MaoU25 Dark gray bioclastic limestone �116.25 1.9 0.4 �7.4 0.5Limestone Unit of the Maokou Fm 07MaoU23.5 Dark gray bioclastic limestone �167.5 2.2 0.3 �4.8 0.5Limestone Unit of the Maokou Fm 07MaoU23 Dark gray bioclastic limestone �186.25 2.2 0.4 �6.1 0.5Limestone Unit of the Maokou Fm 07MaoU22 Dark gray bioclastic limestone �211.25 1.8 0.3 �4.3 0.6Limestone Unit of the Maokou Fm 07MaoU21.5 Dark gray bioclastic limestone �211.25 1.6 0.3 �4.8 0.6Limestone Unit of the Maokou Fm 07MaoU21 Dark gray bioclastic limestone �246.25 2.9 0.3 �4.0 0.5Limestone Unit of the Maokou Fm 07MaoU19 Dark gray bioclastic limestone �318.75 2.5 0.3 �4.8 0.6Limestone Unit of the Maokou Fm 07MaoU17 Dark gray bioclastic limestone �387.5 3.0 0.4 �6.1 0.3Limestone Unit of the Maokou Fm 07MaoU16 Dark gray bioclastic limestone �420 3.5 0.3 �12.3 0.5Limestone Unit of the Maokou Fm 07MaoU13 Dark gray bioclastic limestone �502.5 3.3 0.3 �7.2 0.3Limestone Unit of the Maokou Fm 07MaoU12 Dark gray bioclastic limestone �532.5 3.1 0.3 �7.1 0.6Limestone Unit of the Maokou Fm 07MaoUll Dark gray bioclastic limestone �565 4.0 0.4 �7.3 0.5Limestone Unit of the Maokou Fm 07MaoU10 Dark gray bioclastic limestone �597.5 3.6 0.3 �7.3 0.2Limestone Unit of the Maokou Fm 07MaoU9 Dark gray bioclastic limestone �628.75 3.7 0.4 �6.4 0.2Limestone Unit of the Maokou Fm 07MaoU8 Dark gray bioclastic limestone �657.5 3.2 0.3 �5.8 0.3

56 M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62

Table 1 (continued)

Stratigraphic unit Sample ID Lithology Thickness (cm) d13C (‰) Error (‰) d18O (‰) Error (‰)

Limestone Unit of the Maokou Fm 07MaoU7 Dark gray bioclastic limestone �686.25 3.6 0.3 �6.4 0.1Limestone Unit of the Maokou Fm 07MaoU6 Dark gray bioclastic limestone �717.5 3.7 0.4 �6.7 0.3Limestone Unit of the Maokou Fm 07MaoU6-2 Dark gray bioclastic limestone �717.5 3.4 0.3 �6.8 0.3Limestone Unit of the Maokou Fm 07MaoU5 Dark gray bioclastic limestone �750 3.8 0.4 �6.9 0.2Limestone Unit of the Maokou Fm 07MaoU5-2 Dark gray bioclastic limestone �750 3.7 0.3 �7.1 0.2Limestone Unit of the Maokou Fm 07MaoU4 Dark gray bioclastic limestone �788.75 3.5 0.4 �7.5 0.2Limestone Unit of the Maokou Fm 07MaoU3 Dark gray bioclastic limestone �841.25 3.7 0.3 �7.9 0.3Limestone Unit of the Maokou Fm 07MaoU2 Dark gray bioclastic limestone �925 3.7 0.4 �6.3 0.3Limestone Unit of the Maokou Fm 03Maol7 Dark gray bioclastic limestone �1153.75 3.9 0.3 �6.7 0.2Limestone Unit of the Maokou Fm 03Maol5 Dark gray bioclastic limestone �1446.25 3.9 0.4 �5.8 0.2Limestone Unit of the Maokou Fm 03Mao9 Dark gray bioclastic limestone �2546.25 4.3 0.4 �6.0 0.3Limestone Unit of the Maokou Fm 03Mao6 Dark gray bioclastic limestone �3164.25 4.4 0.3 �6.4 0.2Limestone Unit of the Maokou Fm 03Mao5 Dark gray bioclastic limestone �3286.75 4.3 0.4 �6.8 0.2

black chertdark gray limestoneblack mudstonetuff

chert nodule

Mao

kou

Form

atio

n

Lim

esto

ne U

nit

Mud

ston

e U

nit

low

er p

art o

f the

Wuj

iapi

ng F

m

Wuj

iapi

ng F

orm

atio

n

Cap

itani

anW

uchi

apin

gian

-3 -2 -1 0 1 2 3 4 5 (‰)

N1

N2N3N4

10 m

Fig. 3. Stable carbon isotope stratigraphy of the Guadalupian–Lopingian (Middle–Upper Permian) carbonates at Chaotian. Samples of dark gray bioclastic limestone and ofblack calcareous mudstone are shown by light blue circle and green square, respectively. (For interpretation of the references to color in this figure legend, the reader isreferred to the web version of this article.)

M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62 57

southern Sichuan occurred in the Jinogondolella altudaensis Zone ofthe middle Capitanian (e.g., Sun et al., 2010), clearly younger thanthe timing of the negative d13Ccarb excursions at Chaotian in the J.postserrata–J. shannoni Zone. Hence, the possibility that the nega-

tive excursions at Chaotian were caused by input of volcanic CO2

gas associated with the Emeishan eruptions is also excluded.Rather, we emphasize that the four negative excursions at Chao-

tian are in accordance with the emergence of oxygen-depleted

Capitanian (Late Guadalupian)Wuchiapingian

Jino

gond

olel

la g

rant

i

J. p

osts

erra

ta

J. s

hann

oni

J. a

ltuda

ensi

s

J. p

rexu

anha

nens

is

J. x

uanh

anen

sis

C. p

ostb

itter

i hon

gshu

iens

is

C. p

ostb

itter

i pos

tbitt

eri

Cla

rkin

a du

koen

sis

Maokou Formation

Limestone UnitMudstone Unit

‘the L3 subunit’M1 subunitM2

Wujiaping Formation

lower part of the Wujiaping Fm

?

blac

k ch

ert

dark

gra

y lim

esto

nebl

ack

mud

ston

etu

ff

cher

t nod

ule

poss

ible

upw

ellin

g

Cla

rkin

a as

ymm

etric

a

Jino

gond

olel

la g

rant

i

J. a

ltuda

ensi

s

J. p

rexu

anha

nens

is

J . x

uanh

anen

s is

C. p

ostb

itter

i hon

gshu

iens

is

C. p

ostb

itter

i pos

tbitt

eri

Cla

rkin

a du

koen

sis

Cla

rkin

a as

ymm

etric

a

N1 -4

-

3

-2

-1

0

1

2

3

4

5 (‰

)-4

-

3

-2

-1

0

1

2

3

4

5 (‰

)

This

stu

dyLa

i et a

l. (2

008)

10 m

N2N3N4

Fig. 4. Comparison of carbon isotope stratigraphy across the Guadalupian–Lopingian boundary at Chaotian of this study and of Lai et al. (2008). The conodont zones shown inwhite are those directly recognized at Chaotian and those in gray are inferred. Four isotopic negative excursions (N1–N4) in the topmost Maokou Formation are newlyclarified by this study.

58 M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62

waters on the relatively deep disphotic slope/basin. The oxygen-de-pleted waters in the deep disphotic zone were likely enriched bybicarbonate ions of low d13C values generated by the anoxic oxida-tion of organic matters, such as sulfate reduction and denitrification

in the water column. It is likely that the d13CDIC values of the oxy-gen-depleted waters on the disphotic slope/basin at Chaotian wererelatively low compared to those in the shallower euphotic zonedue to a biological pump and anaerobic decomposition of organic

euphotic zone

disphotic zone

East

multiple upwellingsend-Guadalupian

extinction

West

Tethys

oxygen-depleted waterof low 13C values

shelf

depositional site of the M.U. of the Maokou Fm

slope/basinnorthwest margin ofSouth China craton

Fig. 5. Schematic diagram of environmental changes in northwestern South China at the end-Guadalupian. Multiple local upwelling of oxygen-depleted waters along acontinental margin from a deeper disphotic slope/basin to a shallower euphotic shelf may have occurred prior to the extinction. M.U.: Mudstone Unit.

M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62 59

matters in the water column. We interpret that each of the N1–N4excursions in the topmost Maokou Formation at Chaotian may indi-cate the input of inorganic carbon of low d13C values by upwellingof the oxygen-depleted waters along the continental margin, fromthe deeper disphotic slope/basin to the shallower euphotic shelf(Fig. 5). The four negative excursions (N1–N4) imply that the sug-gested upwelling might have occurred repeatedly at least fourtimes in the Capitanian.

In contrast to the upper N2, N3, and N4 excursions, the N1excursion occurs within the topmost part of the Limestone Unitof the Maokou Formation apparently prior to the emergence ofthe oxygen-depleted condition in the upper Mudstone Unit. Itshould be noted that the Limestone Unit itself was deposited ona euphotic shelf, and did not necessarily record the redox conditionof the deeper disphotic slope/basin directly. The occurrence of theN1 excursion before the deposition of the Mudstone Unit impliesthat an oxygen-depleted condition in the deeper disphotic zonemight have appeared already in the early Capitanian (the J. postser-rata Zone).

On the other hand, a small positive d13C excursion (up to +3‰)is recognized in the M2 subunit of the Mudstone Unit of the Mao-kou Formation (Fig. 4). In general, high positive d13C values of car-bonates indicate high primary productivity in the surface oceanand enhanced burial of 13C-depleted organic carbon into sedi-ments (e.g., Kump and Arthur, 1999). The small positive d13Cexcursion in the Mudstone Unit at Chaotian may suggest a relativeincrease of primary productivity in the surface ocean. In the lowerWujiaping Formation, the d13C values of bioclastic limestonesmoothly rise for 5‰ from ca. 0 to +5‰ (Figs. 3 and 4). In contrastto the Maokou Formation, no isotopic negative excursion is ob-served in the lower Wujiaping Formation. It implies a terminationof multiple upwelling events. Moreover, a distinct isotopic increasein the lower Wujiaping Formation could be attributed to the recov-ery of primary productivity in the ocean and the following en-hanced burial of 13C-depleted organic carbon in the aftermath ofthe end-Guadalupian extinction.

5.1.3. Comparison with the previous study at ChaotianLai et al. (2008) first reported the secular change of d13Ccarb

values across the G-LB at Chaotian (Fig. 4). They continuously ana-lyzed the Limestone Unit of the Maokou Formation. In their results,the d13Ccarb values in the Limestone Unit are basically constant

around +4‰, followed by a sharp drop to ca. �2.5‰ in the topmostpart of the unit (lower black arrow in Fig. 4). We regard that thenegative excursion (reported by Lai et al.) corresponds to the N1excursion in the present study. The present results confirmed thoseof Lai et al. (2008) for the Limestone Unit.

In contrast, the results of Lai et al. (2008) for the upper Mud-stone Unit and the lower Wujiaping Formation are remarkably dis-tinct from those of this study (Fig. 4). Lai et al. (2008) reported onlyten measurements for the Mudstone Unit, probably owing to theintense weathering and discontinuous exposures of the outcrop(Figs. 2 and 4). Although the apparent negative excursion in theMudstone Unit in Lai et al. (2008) (upper black arrow in Fig. 4)may correspond to the N3 excursion recognized in this study, de-tails are uncertain. For the lower Wujiaping Formation, Lai et al.’sprofile is not consistent with that of the present study that showsa monotonous increase from ca. 0 to +5‰. We interpret theincreasing trend in this study is the common d13Ccarb signature inthe lower Wujiaping Formation in northwestern South China onthe basis of regional chemostratigraphic correlations, as discussedin the Section 5.2.2.

5.2. Chemostratigraphical correlation

5.2.1. Correlation with the GSSP for the G-LBWang et al. (2004) first analyzed d13Ccarb records across the G-

LB in the GSSP at Penglaitan in Guangxi, and recognized a negativeisotopic shift immediately above the boundary. Chen et al. (2011)recently expanded the d13Ccarb stratigraphy at Penglaitan on thebasis of the refined analysis of the Capitanian carbonates. They re-ported rather constant d13Ccarb values of ca. +4‰ during the Capit-anian at Penglaitan. It is noteworthy that Chen et al.’s resultsclearly demonstrated that no negative excursion has occurred dur-ing the early-middle Capitanian. The negative d13Ccarb excursionsrecognized at Chaotian by the present study is, therefore, appar-ently contradict to the isotopic records at Penglaitan. It impliesthat the upwelling of oxygen-depleted waters of low d13CDIC valueswas restricted solely within northwestern South China aroundChaotian.

5.2.2. Regional correlations in South ChinaBond et al. (2010a) examined several sections in southwestern

South China and reported a large (over 5‰) negative excursion in

60 M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62

the middle Capitanian, significantly before the G-LB. On the otherhand, at Chaotian, the present data clarified that four negativeexcursions occur in the topmost Maokou Formation in the early-middle Capitanian. At the first glance, the negative excursions atChaotian, as a whole, appear comparable with the putative ‘‘MiddleCapitanian excursion’’ by Bond et al. (2010a); however, these twoare completely different in age. Bond et al. (2010a) reported thatthe so-called ‘‘Middle Capitanian excursion’’ occurred at the topof the J. altudaensis Zone. In a remarkable contrast, the N1 andN2 and N3 excursions at Chaotian occurred at the top of the J. post-serrata and within the J. shannoni zones, respectively, clearly beforethe J. altudaensis Zone. Hence the N1, N2 and N3 excursions atChaotian cannot be correlated with the ‘‘Middle Capitanian excur-sion’’ in Bond et al. (2010a). No negative excursion is reported inthe J. postserrata and J. shannoni zones by Bond et al. (2010a). Itis noteworthy that no previous chemostratigraphic study in SouthChina (including that in the GSSP) has reported a negative excur-sion in the early-middle Capitanian (the J. postserrata and J. shan-noni zones) similar to the new isotope records at Chaotian. Thenewly recognized negative excursions (at least N1, N2, and N3)and upwelling of oxygen-depleted waters in the early-middleCapitanian at Chaotian might be local phenomena solely restrictedto northwestern South China around Chaotian, rather than regionalone all over South China.

On the other hand, in the lower Wujiaping Formation, the pres-ent results show that the d13Ccarb values monotonously increasefrom ca. 0 to +5‰ at Chaotian. This increasing trend is not detectedby Lai et al. (2008), even though they studied exactly at the samesection. Although the number of isotope measurements in the low-er Wujiaping Formation in the present study is not sufficient tocompare in detail with the scattering data by Lai et al. (2008), itis noteworthy that the monotonous increasing d13Ccarb trend rec-ognized in this study is much clearer than those by Lai et al. (2008).Moreover, an isotopic increasing trend totally identical to the pres-ent results is recognized in the lowermost Wujiaping Formation atShangsi near Chaotian (Lai et al., 2008) and also in southern Sha-anxi (Wake et al., in prep.). Therefore, the remarkable d13Ccarb in-crease (up to 5‰) in the early Wuchiapingian is probably acommon isotopic signature at least in northwestern South China,on the basis of regional correlations.

5.2.3. Correlation with Japan and CroatiaIsozaki et al. (2007a,b) clarified the d13Ccarb stratigraphy across

the G-LB from the mid-Panthalassan paleo-atoll limestones accu-mulated on ancient seamounts in Japan. Isozaki et al. (2011) alsoreported the d13Ccarb profile of the Capitanian Velebit Formationin Croatia in western Paleo-Tethys. Their results showed no signif-icant d13Ccarb negative excursion in the early-middle Capitanian,supporting the interpretation that the negative excursions in theearly-middle Capitanian recognized at Chaotian were solely localphenomena rather than global isotopic perturbations. Korte et al.(2005) reconstructed the secular trend of d13CDIC values of the sea-water during the Permian on the basis of analyses of well-pre-served brachiopod shells, and confirmed that no d13Ccarb negativeexcursion has occurred in the early-middle Capitanian.

On the other hand, Isozaki et al. (2007a,b) pointed out a uniqueepisode of a high positive (over +5‰) plateau interval of d13Ccarb

values during the Capitanian in the mid-Panthalassan paleo-atolllimestones in Japan, and named it the ‘‘Kamura event’’. Isozakiet al. (2011) found an identical signal of the Kamura event in Croa-tia located in western Tethys and suggested this Capitanian isoto-pic anomaly was a global phenomenon. Isozaki et al. (2011)predicted that the Kamura event would be detected in the Capita-nian carbonates also in South China located at the eastern end ofPaleo-Tethys. In fact, Wang et al. (2004) reported such high posi-

tive d13Ccarb values in the latest Capitanian at Penglaitan, and Chenet al. (2011) confirmed those high positive values in the sameinterval. At Chaotian, Lai et al. (2008) claimed that a small positiveexcursion within the topmost part of the Limestone Unit of theMaokou Formation is a signal of the Kamura event (Fig. 4). Thepresent study, however, detected no such positive excursion inthe same interval in the Limestone Unit at Chaotian. The presentnew data did not detect the Capitanian Kamura event at Chaotianin eastern side of Tethys. It may suggest that a signal of the Kamuraevent was lost at Chaotian possibly because the late Capitanianrocks are missing (Saitoh et al., 2013).

5.3. Capitanian upwelling in northwestern South China?

The four distinct d13Ccarb negative excursions in the Capitanianat Chaotian may suggest the multiple upwelling of oxygen-depleted waters along the continental margin, from the deeperdisphotic slope/basin to the shallower euphotic shelf, slightly be-fore the end-Guadalupian extinction. The isotopic records atChaotian, however, are unique and no similar d13Ccarb negativeexcursion in the early-middle Capitanian (the J. postserrata–J.shannoni Zone) has been reported elsewhere around the world.The d13Ccarb negative excursions in the early-middle Capitanianshould be checked by further research. At present, we regard thatthe suggested multiple upwelling in the early-middle Capitanianmight be local phenomena solely around northwestern South Chi-na. The Chaotian section was located at the northwest edge ofSouth China and probably faced on the eastern Tethys. The Chao-tian on the western margin of South China around the equatormay have been suitable for upwelling possibly owing to sweepingof the surface waters by the trade winds, similar to those in themodern oceans. The putative upwelling of oxygen-depletedwaters from the deeper disphotic zone at Chaotian may havecaused the extinction in the shallow euphotic zone at theend-Guadalupian. However, local upwelling solely restricted innorthwestern South China cannot explain the global nature ofthe end-Guadalupian extinction. The model of the Capitanianupwelling in low latitude ocean caused by the trade wind-drivensweeping of surface waters should be checked by further researchparticularly focusing on the sections in the western margins of thesupercontinent Pangea. Moreover, in order to clarify the relation-ships between the environmental changes in the deep disphoticzone and the global extinction in the euphotic surface oceans atthe end- Guadalupian, further research is needed particularlyfocusing on a sequence deposited on a previously overlooked dis-photic zone in various sections around the world.

6. Conclusions

In order to examine how the oxygen-depleted waters in a dee-per disphotic zone affected the carbon cycle in a shallower eupho-tic zone with respect to the end-Guadalupian extinction, stablecarbon isotope ratios of marine carbonates (d13Ccarb) across theGuadalupian–Lopingian (Middle–Late Permian) boundary (G-LB)were analyzed in the Chaotian section, northern Sichuan, SouthChina. The following new results were obtained:

1. A continuous carbon isotope stratigraphy across the G-LB wasclarified by analyzing exceptionally fresh drill core samples.

2. The four distinct negative d13Ccarb excursions (N1–N4) in theCapitanian (Late Guadalupian) were detected at Chaotian. TheN1 excursion occurred for 7‰ from +4 to �3‰ in the topmostpart of the Limestone Unit of the Guadalupian Maokou Forma-tion, whereas the N2–N4 occurred for 3‰ from ca. +2 to �1‰ inthe upper Mudstone Unit of the Maokou Formation.

M. Saitoh et al. / Journal of Asian Earth Sciences 67–68 (2013) 51–62 61

3. The four isotopic negative excursions suggest multiple upwell-ing of oxygen-depleted waters of relatively low carbon isotopevalues along the continental margin, from the deep disphoticslope/basin to the shallow euphotic shelf, slightly before theextinction. The upwelling might be a local phenomenon solelyaround northwestern South China on the basis of chemostrati-graphic correlations with other areas around the world.

Acknowledgments

Masaki Ogawa, Tsuyoshi Komiya, Motoyuki Matsuo, and Yoshi-taka Kakuwa gave us helpful instructions. Tetsuo Matsuda, Haru-taka Sakai, Noriei Shimizu, Noritada Kobayashi, Teruhisa Kasuya,Tomohiko Sato and Takumi Futamori helped fieldwork. MiyukiTahata and Tomoko Ishikawa helped isotope analysis. Two anony-mous reviewers gave us constructive comments to improve themanuscript. This study was supported by grant-in-aid from JapanSociety for the Promotion of Science (Project Nos. 16204040 and20224012) and National Nature Science Foundation of China (Pro-ject Nos. 1212011120116 and 1212011120143). M.S. thanks theResearch Fellowships of The University of Tokyo and of the GlobalCOE program ‘‘Earth to Earths,’’ Tokyo Institute of Technology andThe University of Tokyo.

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