411Lucas, S.G., et al. eds., 2013, The Carboniferous-Permian Transition. New Mexico Museum of Natural History and Science, Bulletin 60.

THE INTERNATIONAL PERMIAN TIMESCALE: MARCH 2013 UPDATE

SHU-ZHONG SHEN1, JOERG W. SCHNEIDER2, LUCIA ANGIOLINI3 AND CHARLES M. HENDERSON4

1 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing, Jiangsu,China 210008, email: szshen@nigpas.ac.cn; 2 Department of Palaeontology, Institute of Geology, Technical University Bergakademie Freiberg,Bernhard-von-Cotta-Str. 2 Freiberg, D-09596, Germany; 3 Dipartimento di Scienze Terra “A. Desio”, Via Mangiagalli 34, 20133, Milano, Italy;

4 Department of Geoscience, University of Calgary, Calgary, Alberta, Canada T2N 1N4

Abstract—The Subcommission on Permian Stratigraphy is concentrating its efforts to establish the remainingthree GSSPs in the Cisuralian as well as refining the Permian timescale for global correlation, including into theterrestrial realm. In this paper, we provide a brief overview on recent progress of Permian timescale developmentbased on new biostratigraphic, geochemical and geochronologic data. The Permian Period was from 298.9 Ma to252.17 Ma based on the latest U-Pb ages in the southern Urals and South China. The Cisuralian, Guadalupian andLopingian have durations of 26.6 Myr, 12.5 Myr and 7.63 Myr, respectively.

INTRODUCTION

The international Permian timescale has been significantly im-proved during the past five years although no new GSSPs have beenformally ratified since 2005. The Permian System is composed of threeseries (Cisuralian, Guadalupian and Lopingian in ascending order) andnine stages, among which significant progress has been made on theGSSPs and GSSP candidates. New data for several stages are now avail-able. Three GSSPs (base-Sakmarian, base-Artinskian and base-Kungurian)remain to be proposed and ratified. We present here a brief summary andan updated timescale (Fig. 1) to show recent advances on each stage ofthe Permian System. This timescale is updated from Henderson (2005).A more comprehensive paper on the Permian timescale is presented byHenderson et al. (2012a), but some important data have been updatedsince then. The current chart provides the latest high-precision geochro-nologic dates for each stage, high-resolution biostratigraphic data basedon multiple fossil groups including terrestrial tetrapods (Lucas, 2006),sea-level changes and paleomagnetic reversal zones. The Cisuralian Work-ing Group has formally published the proposal for the candidates for thebase-Kungurian GSSP (Henderson et al., 2012b; Chernykh et al., 2012),and the proposals for the base-Sakmarian and base-Artinskian are inpreparation. High-resolution conodonts are from Henderson and Mei(2003) and Chernykh (2006) for the Cisuralian; from Glenister et al.(1999), Wardlaw (2000) and Jin et al. (2006a) for the Guadalupian; andfrom Jin et al. (2006b), Mei and Henderson (2004) and Shen and Mei(2010) for the Lopingian.

CISURALIAN

The base of the Permian System (also the base of the AsselianStage) was defined by the First Appearance Datum (FAD) ofStreptognathodus isolatus Chernykh, Ritter and Wardlaw at AidaralashCreek, Aktöbe (formerly Aktyubinsk) region, northern Kazakstan(Davydov et al., 1998). Biostratigraphic data from this GSSP have beenrarely updated since it was defined. Geochemical and geochronologicdata are not available. However, some progress was made from the Usolkasection on the north bank of the Usolka River that was defined as anauxiliary section for the Carboniferous–Permian boundary (CPB)(Davydov et al., 1998; Schmitz and Davydov, 2012).The CPB is recog-nized in the Usolka section at the first occurrence of Streptognathodusisolatus associated with multiple ash beds, and the radiometric calibra-tion and biostratigraphy for this part of the section has been published(Ramezani et al., 2007). Those radiometric ages were recently confirmedby new dating of ash beds above and below those ash beds dated byRamezani et al. (2007). Thus, the CPB is interpolated as 298.9±0.15Ma(Schmitz and Davydov, 2012). In addition, high-resolution carbon isoto-

pic data were analyzed from the Usolka section. A gradually increasingtrend in 13Ccarb from -4.8‰ at the base of the Asselian upward to 4.2‰within Bed 22 in the Sweetognathus expansus Zone occurs at the Usolkasection based on whole rock samples, although the lower values mayhave some diagenetic influence. This is followed by an interval with highvalues around 4‰ from Beds 22 to 24 in the upper Asselian (Zeng et al.,2012).

The base of the Sakmarian was previously considered as the FADof Sweetognathus merrilli Kozur at the Kondurovsky section in thesouthern Urals (Chuvashov et al., 2002b). However, subsequent studiesindicate that the conodont lineage to define the base-Sakmarian GSSP atthe Kondurovsky section proposed by the Cisuralian Working Group(Chuvashov et al., 2002b) was rare or absent in samples processed bydifferent labs. Thus, the Kondurovsky section is no longer being consid-ered, and the Usolka section is now under consideration as the candidatefor the base-Sakmarian GSSP. Two alternative possibilities for definingthe base of the Sakmarian Stage are under consideration. One is the FADat 54.3 mab of Sweetognathus merrilli Kozur within thechronomorphocline Sweetognathus expansus–S. merrilli (Chernykh,2005). However, results from the Apillapampa section in Bolivia, whichyields abundant conodonts, interbedded with zircon-rich ash beds, dem-onstrates that forms comparable to Sweetognathus merrilli were presentalready in the mid-Asselian (Henderson and Kotlyar, 2009).The secondoption is the FAD at 51.6 mab of Mesogondolella uralensis Chernykhwithin the chronomorphocline of M. pseudostriata–M. arcuata–M.uralensis (Chernykh, 2006). The latter lineage is considered acceptableby the Cisuralian Working Group because a similar lineage has beenfound from Nevada, SE Alaska and possibly in Arctic Canada (Hendersonand Kotlyar, 2009). This lineage has not been confirmed yet in SouthChina, which is an important area for global correlation. The estimatedage of the base of the Sakmarian Stage is 295.0 Ma (Schmitz and Davydov,2012). An excursion with double negative shifts in 13Ccarb value is docu-mented around the Asselian/Sakmarian boundary in both the Usolka andKondurovsky sections, which may have potential to serve aschemostratigraphic markers for intercontinental correlation (Zeng et al.,2012). However, more work in different areas is necessary to confirmthis pattern.

The base of the Artinskian Stage is best represented in the DalnyTulkas section, which was proposed as the GSSP for the base of theArtinskian (Chuvashov et al., 2002a). The base is proposed to be definedby the FAD in Bed 4 of Sweetognathus “whitei” (Rhodes sensu Chernykh)within the chronomorphocline S. binodosus–S. anceps–S. “whitei”. Threeash beds in the Dalny Tulkas section closely constrain the age of the baseof the Artinskian to 290.1 Ma (Schmitz and Davydov, 2012). The 13Cand 18O curves in the DalnyTulkas section are characterized by a rapid

412

FIGURE 1. Updated Permian timescale. Geochronologic ages are combined from Shen et al. (2011) for the Lopingian; Schmitz and Davydov (2012) forthe Cisuralian, Henderson et al. (2012a) for the GLB and Henderson et al. (2012b) for the base of Kungurian. Tetrapod biochronology is after Lucas (2006).Biostratigraphic columns are a work in progress and comments are invited.

413and sharp drop around the Sakmarian/Artinskian boundary and a long-term deep depletion stage in the following Artinskian interval, which wasinterpreted as a diagenetic signature or a result of enhanced organic car-bon burial and subsequent isotopic refractionation by microbial chemo-synthetic processes (Zeng et al., 2012). The strontium isotopic compo-sition of seawater at the base of the Artinskian Stage is 87Sr/86Sr = 0.70767(Chernykh et al., 2012).

The base of the Kungurian Stage was proposed for the Mechetlinosection exposed along the right bank of the Yuryuzan River downstream(Chuvashov et al., 2002a). However, subsequent studies indicated thatsamples collected to test reproducibility of the index conodont speciesNeostreptognathodus pnevi FAD did not produce any conodonts; thesection is also too heavily weathered to carry out any chemostratigraphicanalysis. Therefore, the Rockland section in the Pequop Mountains ofNevada, USA, with the same chronomorphocline from Neostrepto-gnathodus pequopensis to N. pnevi was proposed as a potential newcandidate for the base-Kungurian GSSP by SPS (Henderson et al., 2012b).Meanwhile, a new section called the Mechetlino Quarry section, whichis about 600 m east of the previous Mechetlino section, was also pro-posed as a new candidate for the base-Kungurian GSSP (Chernykh et al.,2012). This section contains fusulinaceans, ammonoids, conodonts, andpresumably some layers of volcanic ash beds. Unfortunately, there areno U-Pb ages for late Artinskian to Kungurian strata at both the Mechetlinoand Rockland sections. However, strontium isotopic analysis of con-odonts yielded reproducible values of 87Sr/86Sr = 0.70743 to 0.70739.Projecting these compositions onto the interpolated seawater curve yieldsan apparent age for the boundary of 283.5 ± 0.5 Ma (Chernykh et al.,2012). This is much older than the age of 279.3 Ma for the base ofKungurian in GTS 2012 (Henderson et al., 2012a).

GUADALUPIAN

The Cisuralian/Guadalupian boundary (CGB) is defined by theFAD of Jinogondolella nankingensis within the conodontchronomorphocline from Mesogondolella idahoensis lamberti toJinogondolella nankingensis that can be readily distinguished by theappearance of the distinctly characteristic serration on the anterior partof the Jinogondolella platform. However, the correlation between thefusulinacean-based Tethyan and the conodont-based internationaltimescales of the Permian System has become one of the most disputedissues among the Permian community during the past two decades; thisuncertainty is reflected in Figure 1. The main problem was derived fromthe appearance of Murgabian fusulinids including Neoschwagerina sim-plex in a horizon about 150 m below the first appearance of the serratedconodont Jinogondolella nankingensis at the Luodian section in Guizhou,South China. This point may actually be close to the base of the Roadianif the first occurrence of serrated conodonts is diachronous at the section.The co-occurrence of Neoschwagerina simplex with some Kungurianconodonts has been confirmed recently based on the collection fromHatahoku, Japan (Shen et al., in press). However, preliminary resultsfrom SE Pamir suggest that in the Tethyan stratotypes, N. simplex co-occurs with conodonts that straddle the Kungurian-Roadian boundaryand range up into the Roadian. Geochronologic constraints for the CGBare interpolated as 272.3 Ma in GTS 2012 (Henderson et al., 2012a).Recently, U-Pb ages from two volcanic ash beds around the CGB atChaohu, South China were dated as 272.0±5.5 Ma (MSWD=2.6) and271.5±3.3 Ma (MSWD=1.7) (Zhu et al., in press).

The three Guadalupian GSSPs were defined more than 10 yearsago (Glenister et al., 1999), but little has been updated since then. Al-though they are the earliest GSSPs defined in the Permian, the GSSPpapers have not yet been published, and conodonts from the actualGSSP levels have yet to be figured. Furthermore, high-resolutionchemostratigraphy for the whole Guadalupian Series is not available.Only one numerical age, of 265.3 Ma from an ash bed, which lies 2 mabove the top of the Hegler Member, 20 m below the base of Capitanian

Stage, is available (Bowring et al., 1998). The interpolated ages are 265.1Ma for the base Capitanian Stage and 268.8 Ma for the base of theWordian (Henderson et al., 2012), but many more control points areneeded. The Illawarra Reversal during the late Wordian (ca 266 Ma) is amark for time correlation among different regions. This reversal repre-sents a remarkable change in geomagnetism following the long-term stableKiaman Reverse Superchron (throughout the Late Carboniferous andEarly-Middle Permian) and marks the beginning of the Permian–TriassicMixed Superchron with frequent polarity changes during the Late Per-mian and Triassic (Embleton et al., 1996; Isozaki, 2009; Jin et al., 1999;Vozarova and Tunyi, 2003). This reversal has not yet been found inSouth China due to a serious Mesozoic magnetic overprint. Anotheruseful marker in chemostratigraphic correlation of the Late Guadalupianis the late Capitanian minimum of 87Sr/86Sr ratio (ca. 0.7068–0.7069;~260.4 Ma), which represents one of the most significant features inPhanerozoic seawater 87Sr/86Sr history (Kani et al., 2013; Liu et al., 2013;McArthur et al., 2012; Veizer et al., 1999).

Carbon isotope chemostratigraphy around the GLB has been ex-tensively studied in different sections, but the results are controversial. Alarge negative shift was reported from the late Capitanian Jinogondolellaxuanhanensis/J. prexuanhanensis zones in Guizhou, South China (Wignallet al., 2009), but this negative excursion is not confirmed at the PenglaitanGSSP section (Chen et al., 2011). A negative excursion with minor mag-nitude at GLB was reported by Wang et al. (2004) and Jin et al. (2006a),but may have little significance. A significant positive excursion of car-bon isotopic values during the late Capitanian was documented as theKamura event by Isozaki (2007), but the precise horizon with this eventbased on conodonts is still unclear.

LOPINGIAN

The Guadalupian/Lopingian boundary (GLB) is defined by thechronomorphocline from Clarkina postbitteri hongshuiensis to C.postbitteri postbitteri at the Penglaitan section in Laibin, Guangxi Prov-ince of South China. Conodonts reported from other sections (Lambertet al., 2002, 2010; Nishikane et al., 2011; Xia et al., 2006; Zhang et al.,2007) as representing this chronomorphocline are mostly questionablein terms of taxonomy. This boundary was associated with the Emeishanvolcanism and the largest regression during the Phanerozoic. A wide-spread distinct disconformity is present in most areas around the world.Only a few areas, such as South China, Iran, and SE Pamir possesscontinuous deposits around the GLB. The age of the GLB is muchdiscussed and still uncertain. Although widespread volcanism was presentaround the GLB and numerous dating of the Emeishan basalt has beencarried out, high-precision ages are still not available. Some new zirconCA–TIMS U–Pb ages were obtained from intrusive rocks of the Panxiregion (Inner Zone) of the Emeishan Large Igneous Province, whichyielded a wide range of ages between >257 Ma and ~260 Ma (Shellnuttet al., 2012). An age of about 259 Ma is suggested by Shenet al. (2010)and 259.8 Ma is provided in GTS 2012 (Henderson et al., 2012a). Acombined study of mineralogy, geochemistry and geochronology on sixlayers of claystone around the GLB at the Penglaitan GSSP sectionindicate that the Penglaitan claystones are not suitable for age determina-tion of the GLB (Zhong et al., 2013).

The Wuchiapingian/Changhsingian boundary (WCB) has been wellconstrained within the conodont chronomorphocline from Clarkinalongicuspidata to C. wangi at the Meishan GSSP section (Jin et al.,2006b). This same conodont succession was also confirmed at the Shangsisection in Sichuan province, South China. High-precision CA–TIMS U–Pb ages are available from both the Meishan and Shangsi sections. TheWCB is bracketed by two ash beds at Shangsi and constrained by a fewages above the WCB at the Meishan GSSP section; it is estimated as254.14 Ma (Shen et al., 2011) and 254.2 Ma (Henderson et al., 2012a).

The Permian-Triassic boundary (PTB) is very well dated becauseof a concentrated effort to understand the largest mass extinction in Earth

414history that occurred immediately below the PTB (Shen et al., 2011).This boundary, defined by the FAD of Hindeodus parvus, has been welldated by two ash beds at the Meishan GSSP section. Bed 25 is252.28±0.08 Ma and Bed 28 is 252.10±0.06 Ma. An interpolated age forthe PTB of 252.17±0.06 Ma is suggested from Meishan section data(Shen et al., 2011). The high-precision CA–TIMS U–Pb ages offer fargreater resolution at this level than that based on conodont zones.

MARINE-TERRESTRIAL CORRELATION

The Permian time scale is based on the marine record, and, al-though a few problems and issues are outstanding, it is essentially estab-lished. The next major direction for SPS research is to build a rich recordof terrestrial correlation proxies including insects, fresh water inverte-brates, vertebrates, palynology, paleobotany, magnetostratigraphy,chemostratigraphy and especially geochronology. Figure 1 provides apreliminary assessment of appearances of key vertebrate taxa during thePermian (Lucas, 2006). The latter gives a very rough time frame for thecontinental Permian and its correlation to the marine global scale. Besidesthe vertebrate zonation of continental deposits, several other tools havebeen developed for detailed stratigraphic subdivisions and correlationsof continental deposits in the different Euramerican non-marine basins.Most detailed and reliable are the insect (spiloblattinid) and amphibian(branchiosaurid) zonations (Schneider, 1982; Werneburg, 1989; Schneiderand Werneburg, 2006; Werneburg and Schneider, 2006). But, neitherepoch nor stage boundaries are really directly correlated by co-occurringmarine and nonmarine zone fossils or reliable isotopic ages thus far (e.g.,

Menning et al., 2006; Roscher and Schneider, 2005; Lützner et al., 2007).Recently, most promising for direct marine–non-marine correla-

tions are ongoing investigations in mixed marine-continental Late Penn-sylvanian/Early Permian deposits in New Mexico and brand new discov-eries of insect zone species in similar deposits of the Donets Basin,which provide for the first time direct links between conodont and fora-minifer zones as well as insect zones for the Late Pennsylvanian andearliest Permian (Schneider et al., 2004; Lerner et al., 2009; Lucas et al.,2011, 2013). An updated version of the current state for the Carbonifer-ous/Permian transition is given by Schneider et al. (2013, this volume).The focus of future work on marine–non-marine correlations should beset for the Cisuralian and Guadalupian mainly on mixed marine-terres-trial deposits on the East European platform and in the North AmericanMidcontinent basins and the East European platform (Sennikov andGolubev, 2006, 2012; Sherbakov, 2008). Most importantly, there needsto be more intensified cooperation by SPS with stratigraphers working inthe huge nonmarine basins of Gondwana. The correlation of the LopingianSeries based on marine-terrestrial transitional deposits in South China(Shen et al., 2011) and the vertebrate assemblages in the Middle and LatePermian in the Karoo Basin, South Africa, which is precisely calibratedby a set of new CA-TIMS U-Pb ages (Rubidge et al., 2013), are bothexcellent examples of how to develop an integrated marine and non-marine time scale.

ACKNOWLEDGMENTS

Shu-zhong Shen’s work is supported by NSFC (41290260) andCharles Henderson by a NSERC Discovery Grant.

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