Newsletter of the Subcommission on Permian Stratigraphy Number ...

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fossils are frequently present in <strong>the</strong>se beds. Accordingly, <strong>the</strong> sequenceboundary or <strong>the</strong> maximum regression lies on <strong>the</strong> top <strong>of</strong> Bed5 at Tieqiao, and <strong>the</strong> top <strong>of</strong> Bed 3 at Penglaitan.The top <strong>of</strong> <strong>the</strong> uppermost shallowing-upward cycle <strong>of</strong><strong>the</strong> “lowstand” unit is <strong>the</strong> transgressive surface (VanWagnor et al., 1988, 1990). The early transgressive systemstract (Bed 5f to Bed 6h in Tieqiao, Bed 3c6 to Bed 6k inPenglaitan) with thick-bedded crinoid grainstone andlenticular packstone, reflects an overall deepening. Theserocks consist <strong>of</strong> high frequency cycles <strong>of</strong> fining upwarddeposition. Each cycle is dominated by <strong>the</strong> hummocky,cross-stratified crinoid grainstone in <strong>the</strong> lower portion,lenticular packstone in <strong>the</strong> upper, and <strong>of</strong>ten with verticalburrows or infilling structures at <strong>the</strong> top. The facies changeis interpreted to range from proximal slope deposition withplatform-derived sediments to fine-grained deposits <strong>of</strong>relative deeper below-wave-base facies to <strong>the</strong> intertidalenvironment. The conodonts <strong>of</strong> <strong>the</strong> Jinogondolella grantiand Clarkina postbitteri zones are associated with deposition<strong>of</strong> <strong>the</strong> earliest TST, and occur mostly in <strong>the</strong> lenticularpackstone. It is obvious that <strong>the</strong>re were depositionalhiatuses between all cycles, however, none <strong>of</strong> <strong>the</strong>m aresignificant in term <strong>of</strong> <strong>the</strong> resolution <strong>of</strong> conodontchronostratigraphy because most <strong>of</strong> <strong>the</strong>m occur within <strong>the</strong>same conodont zone.The last two cycles in <strong>the</strong> Penglaitan Section arerespectively composed <strong>of</strong> Bed 6h - 6i lower and Bed 6i upper-6k. The lower beds contain abundant mud-rich intraclasts(Bed 6i upper), numerous small solitary corals (Bed 6j), oro<strong>the</strong>r platform-derived sediments. Wavy bedding between<strong>the</strong> neighbouring couplets is distinct, but well developedburrows are only seen from <strong>the</strong> upper part <strong>of</strong> Bed 6k. Thecycle <strong>of</strong> Bed 6h - 6i lower indicates a much faster andwidespread transgression starting in <strong>the</strong> top part <strong>of</strong> <strong>the</strong>Laibin Limestone. The flooding event is delineated by <strong>the</strong>occurrence <strong>of</strong> <strong>the</strong> C. postbitteri conodont Zone extendingnorthward to <strong>the</strong> Chengzhou Basin <strong>of</strong> sou<strong>the</strong>rn Hunan, farbeyond <strong>the</strong> distribution <strong>of</strong> <strong>the</strong> underlying conodonts <strong>of</strong> <strong>the</strong>J. granti Zone.The subsequent transgressive unit (Bed 7) in Penglaitan iscomposed <strong>of</strong> deepening-upward cycles from lenticular mud limestonedeposited below storm-wave-base to chert <strong>of</strong> <strong>the</strong> shelf-basinfacies, with or without clay bed at <strong>the</strong> base. This transgressiveunit is a response to <strong>the</strong> most rapid sea-level rise at <strong>the</strong> time <strong>of</strong> <strong>the</strong>C. dukouensis Zone.Fossil successionsConodonts from <strong>the</strong> Laibin Limestone in both Tieqiao andPenglaitan sections are exclusively dominated byJinogondolella species in <strong>the</strong> basal part (Bed 2 at Tieqiao andBed 2 at Penglaitan) and Clarkina species in <strong>the</strong> upper part (<strong>the</strong>upper part <strong>of</strong> Bed 5 to Bed 8 at Tieqiao; <strong>the</strong> uppermost Bed 3 toBed 6). The lower part <strong>of</strong> <strong>the</strong> Laibin Limestone (Bed 3 to <strong>the</strong>middle <strong>of</strong> Bed 5 at Tieqiao; Bed 3 (except <strong>the</strong> uppermost part) atPenglaitan) is dominated by Hindeodus. Rare specimens <strong>of</strong>shallow water elements like Sweetognathus fenshanensis andIranognathus erwini were also recovered respectively within <strong>the</strong>lower Bed 3 and 6k at Penglaitan. Jinogondolella and ClarkinaPermophiles Issue #38 200132species also dominate conodonts from equivalent beds at <strong>the</strong>Fengshan Section, but contain more common to abundantnearshore shallow water elements Hindeodus, Sweetognathusfenshanensis, Iranognathus erwini, and Sweetina (in order <strong>of</strong>decreasing abundance). Based on <strong>the</strong> stratigraphic range andevolution <strong>of</strong> species <strong>of</strong> Jinogondolella and Clarkina, threeephylogenetic conodont zones are recognized around <strong>the</strong>Guadalupian and Wuchiapingian boundary in Tieqiao andPenglaitan sections: <strong>the</strong> Jinogondolella granti Zone rangesfrom upper part <strong>of</strong> Bed 5 through Bed 6h in <strong>the</strong> Tieqiao Section,and from <strong>the</strong> uppermost Bed 3 through 6i (4.8m thick) in <strong>the</strong>Penglaitan Section; <strong>the</strong> Clarkina postbitteri Zone ranges fromBed 6i through lower Bed 9 in <strong>the</strong> Tieqiao Section, and from 6jthrough 7d in <strong>the</strong> Penglaitan Section; <strong>the</strong> Clarkina postbitteriZone is overlain by <strong>the</strong> Clarkina dukouensis Zone that starts atBed 7e in <strong>the</strong> Penglaitan Section. Recently, <strong>the</strong> Clarkinapostbitteri Zone in <strong>the</strong> Penglaitan section has been subdividedinto two subzones: <strong>the</strong> lower Clarkina postbitterihongshuiensis subsp. nov. Subzone ranges through 6j, and <strong>the</strong>upper Clarkina postbitteri postbitteri Subzone ranges from 6kthrough 7d. Clarkina postbitteri hongshuiensis subsp. nov. istransitional between Jinogondolella granti or Jinogondolellacr<strong>of</strong>ti and Clarkina postbitteri postbitteri. It is close toJinogondolella granti in its denticulation with closely spaceddenticles and less reduced anterior platform and it is close toClarkina postbitteri postbitteri with a high anterior blade, ausually much more reduced anterior platform and lack <strong>of</strong> anteriorplatform serration.Fusulinaceans are rich in <strong>the</strong> Maokouan-Lopingian boundarysuccession <strong>of</strong> <strong>the</strong> Laibin section. The lower part <strong>of</strong> <strong>the</strong> LaibinLimestone comprises <strong>the</strong> fusulinaceans <strong>of</strong> <strong>the</strong> Metadoliolina Zone.The upper part <strong>of</strong> this Member is referred to an acme zone, <strong>the</strong>Lantschichites minima Zone. This zone is very thin, only 2 metresin thickness. The Codon<strong>of</strong>usiella kueichowensis Zone is recognizedin <strong>the</strong> beds with <strong>the</strong> conodont Clarkina postbitteri in <strong>the</strong>Tieqiao Section, which contains monotonous Codon<strong>of</strong>usiella andReichelina. The newly established Palae<strong>of</strong>usulina jiangxianaZone occurs in <strong>the</strong> lower part <strong>of</strong> <strong>the</strong> Heshan Formation, whichalso contain <strong>the</strong> Clarkina asymmetrica conodont Zone and rangeupward to <strong>the</strong> C. guangyuanensis conodont Zone.Ammonoids referred to Waagenoceras have been found in<strong>the</strong> topmost part <strong>of</strong> <strong>the</strong> Maokou Formation (Bed 6k) at <strong>the</strong>Penglaitan Section. This fact implies that Maokouan ammonoidsextend upward into <strong>the</strong> C. postbitteri Zone as do <strong>the</strong> ammonoidsfrom <strong>the</strong> same zone in sou<strong>the</strong>rn Hunan.Magnetostratigraphic investigation and isotopic datingFor magnetostratigraphic investigation, Menning collected640 oriented cylinders from <strong>the</strong> Chihsia, Maokou and basal part <strong>of</strong><strong>the</strong> Heshan formations at <strong>the</strong> Tieqiao Section and <strong>the</strong> Guadalupian-Lopingian boundary sequence at <strong>the</strong> Penglaitan Section (Menninget al., 1996). Partial or total remagnetization complicates <strong>the</strong>magnetostratigraphic research. Isotopic age <strong>of</strong> <strong>the</strong> tuff beds at <strong>the</strong>Penglaitan Section has been studied since 1995, and <strong>the</strong> tuff bed<strong>of</strong> <strong>the</strong> late Changhsingian was dated as 252.4 ± 0.2 Ma by Bowringet al. (1998). Samples from Bed 6a and 7c near <strong>the</strong> boundary in <strong>the</strong>Penglaitan Section are under analysis.
ChemostratigraphyValues for δ 13 C drop from + 2.0 per mil in <strong>the</strong> Laibin Limestoneto -0.7 per mil at <strong>the</strong> base <strong>of</strong> <strong>the</strong> Heshan Formation (Bed 8a to Bed8c, <strong>the</strong> upper par <strong>of</strong> <strong>the</strong> C. postbitteri Zone), return to an averagevalue in Bed 9, and jump to <strong>the</strong> highest value 5%δ 13 C in <strong>the</strong> reefcarbonate <strong>of</strong> <strong>the</strong> Heshan Formation. Change <strong>of</strong> isotope strontiumvalue is consistent with isotope carbon with a dramatic drop in Bed8a to Bed 8c. (Wang et al., in press ).In summary, <strong>the</strong> Penglaitan and <strong>the</strong> Tieqiao sections are excellentsections in which to establish a finely resolved chronologyand meet with <strong>the</strong> requirements for serving as GSSP. However, <strong>the</strong>Penglaitan Section is preferred as <strong>the</strong> GSSP for <strong>the</strong> Guadalupian-Lopingian boundary because <strong>of</strong> excellent outcrops <strong>of</strong> bothWuchiapingian and Changhsingian beds.Potential stratotype pointsTwo levels are presented here for selection. The proposal for<strong>the</strong> FAD <strong>of</strong> Clarkina dukouensis at bed 6k is not regarded as anacceptable choice for selection because <strong>the</strong> basal boundary <strong>of</strong> <strong>the</strong>C. dukouensis Zone, after fur<strong>the</strong>r study by conodont experts, is atbed 114-7d <strong>of</strong> <strong>the</strong> Penglaitan Section, which is just above a claybed (114-7c) that may indicate considerable environmental change(Jin, 2000). A detailed study proved that specimens <strong>of</strong> Clarkinafrom bed 6k belong to Clarkina postbitteri ra<strong>the</strong>r than to earlyforms <strong>of</strong> Clarkina dukouensis (Henderson et al., 2000; Henderson,2001) and herein, bed 6k (Figure 1) is reported to contain <strong>the</strong> firstappearance <strong>of</strong> Clarkina postbitteri postbitteri (Henderson et al.,this issue).Option A:This option is a point defined by <strong>the</strong> FAD <strong>of</strong> Clarkinapostbitteri hongshuiensis subsp. nov. (Henderson and Mei, inpress) that occurs within an evolutionary lineage fromJinogondolella granti to Clarkina postbitteri postbitteri.Henderson et al. provide <strong>the</strong> informal descriptions <strong>of</strong> <strong>the</strong>se taxaelsewhere in this issue <strong>of</strong> Permophiles.The FAD <strong>of</strong> C. postbitteri hongshuiensis is close to <strong>the</strong> boundarysurface between <strong>the</strong> Middle and <strong>the</strong> Upper AbsarokaMegasequences. This horizon can be traced in different lith<strong>of</strong>aciesby <strong>the</strong> recognition <strong>of</strong> ei<strong>the</strong>r <strong>the</strong> major sequence boundary or aremarkable changeover from conodont faunas dominated byJinogondolella below in <strong>the</strong> Maokouan to those dominated byClarkina above with total absence <strong>of</strong> Jinogondolella in <strong>the</strong>Wuchiapingian. The conodont succession around <strong>the</strong> Guadalupian– Lopingian boundary is marked by a rapid change fromJinogondolella into Clarkina. Consequently, it would be easy tolocate <strong>the</strong> Guadalupian-Lopingian boundary close to <strong>the</strong> sequenceboundary by <strong>the</strong> level <strong>of</strong> lowest occurrence <strong>of</strong> Clarkina and o<strong>the</strong>rcorresponding stratigraphic markers.Permophiles Issue #38 2001Two questions are raised by this option. The first is that <strong>the</strong>occurrence <strong>of</strong> Clarkina postbitteri in Texas is in dispute. Hendersonand Mei are convinced that <strong>the</strong> illustrated highest conodonts inWest Texas are Jinogondolella xuanhanensis cr<strong>of</strong>ti, which appearedprior <strong>the</strong> global maximum regression. Wardlaw suggeststhat Clarkina postbitteri is present in West Texas. A model <strong>of</strong>convergent evolution may accommodate a new subspecies <strong>of</strong>Clarkina postbitteri evolving from Jinogondolella cr<strong>of</strong>ti in Texas,which subsequently became extinct as <strong>the</strong> S.W. USA Delaware33Basin was drained. A second lineage developed within a continousmarine environment from Jinogondolella granti or from ano<strong>the</strong>rsubspecies derived from a Panthalassan refuge to Clarkinapostbitteri hongshuiensis.The second question is that a depositional hiatus was suggestedbelow Bed 6i upper. As described in <strong>the</strong> paragraph ondepositional succession, <strong>the</strong> upper part <strong>of</strong> <strong>the</strong> Laibin Limestoneconsists <strong>of</strong> high frequency cycles. Both Bed 6i lower and Bed 6kform <strong>the</strong> upper parts <strong>of</strong> <strong>the</strong> uppermost two cycles and are fairlycontinuous with <strong>the</strong> lower parts. Though depositional gaps mightoccur between cycles, <strong>the</strong>y seem no more than those at normalbedding planes; that is, <strong>the</strong>y are insignificant in terms <strong>of</strong> <strong>the</strong> resolution<strong>of</strong> conodont chronostratigraphy. A conodont zone usuallycomprises many cycles.Some colleagues consider that only such rapid change <strong>of</strong>fossils and rocks permits worldwide correlation and recognition<strong>of</strong> beds <strong>of</strong> a defined age. Regarding <strong>the</strong> rapid faunal and sedimentologicalchanges as reflecting an incomplete geological record,would lead to a boundary definition based on subtle stratigraphicchanges that are not useful for subsequent correlation.Option B.A point defined by <strong>the</strong> FAD at <strong>the</strong> base <strong>of</strong> Bed 6k <strong>of</strong> Clarkinapostbitteri postbitteri within an evolutionary lineage from C.postbitteri hongshuiensis subsp. nov. to C. dukouensis. The FAD<strong>of</strong> C. postbitteri sensu lato could also be used to approximate thisboundary as it is only 20 cm below <strong>the</strong> defining point at <strong>the</strong> base<strong>of</strong> Bed 6i upper at <strong>the</strong> Penglaitan Section. The reason for taking<strong>the</strong> name Clarkina postbitteri postbitteri is that <strong>the</strong> holotype <strong>of</strong>C. postbitteri postbitteri is from Bed 6k, <strong>of</strong> which <strong>the</strong> main partwas originally marked as Bed 115 and <strong>the</strong> topmost part, as Bed114.6.Clarkina postbitteri postbitteri is a transitional form betweenC. postbitteri hongshuiensis and C. dukouensis. Therefore, <strong>the</strong>FAD <strong>of</strong> C. postbitteri postbitteri is defined within a gradationallineage in which deposition is continuous.The main questions regarding this option are as follows. First,it is hardly possible to consistently demonstrate <strong>the</strong> exact point atwhich Clarkina postbitteri hongshuiensis becomes C. postbitteripostbitteri. An arbitrary point in a morphologic transition is exactlythat, arbitrary, and almost certainly inconsistent.Second, alternative GSSP positions at <strong>the</strong> base <strong>of</strong> <strong>the</strong>Jinogondolella altudaensis and C. dukouensis zones are at leasttwo zones away from <strong>the</strong> geologically important boundary definedby sequence stratigraphy and extinction. It has been realizedthat <strong>the</strong>se two levels do not correspond to any major event inglobal biological or environmental change, and thus, <strong>the</strong>se fossilzones alone are not sufficient for inter-regional correlation <strong>of</strong> <strong>the</strong>Guadalupian-Lopingian boundary sequences.Lopingian Boundary Working Group PreferenceThere is general agreement that <strong>the</strong> boundary-stratotype <strong>of</strong> a stageshould be located within a sequence <strong>of</strong> continuous marine depositionand should be associated with distinct marker horizons thatcan be readily recognized and widely traced as an isochronoushorizon and <strong>the</strong>refore, it should be selected at or near <strong>the</strong> markerhorizons. Unfortunately, <strong>the</strong>re is rarely an ideal point that can
Page 1 and 2: PermophilesInternational Commission
Page 3 and 4: Notes from the SPS
Page 5 and 6: key species occur close to
Page 7 and 8: is under investigation (coordinated
Page 9: Some Problems and New Achievements
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Page 18 and 19: ably because the w
Page 20 and 21: serrated as clearly seen in <strong
Page 22 and 23: southwestern North America.The Word
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Page 26 and 27: Permophiles Issue #38 200124nated b
Page 28 and 29: laterally equivalent to the
Page 30 and 31: following.1. It is not clear what m
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Page 38 and 39: Permophiles Issue #38 2001fused tha
Page 40 and 41: Permophiles Issue #38 2001The Proce
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