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A refined succession of Changhsingian and Griesbachian neogondolellid conodonts from the Meishan section, candidate of the global stratotype section and point of the Permian–Triassic boundary
ELSEVIER
Palaeogeography, Palaeoclimatology, Palaeoecology 143 (1998) 213–226
A refined succession of Changhsingian and Griesbachian neogondolellid conodonts from the Meishan section, candidate of the global stratotype section and point of the Permian–Triassic boundary Shilong Mei a,Ł , Kexin Zhang b , Bruce R. Wardlaw c a b
China University of Geosciences, Beijing 100083, China China University of Geosciences, Wuhan 430074, China c U.S. Geological Survey, Reston, VA 22092-0001, USA Received 1 February 1997; accepted 1 October 1997
Abstract A detailed study of new conodont collections from the Changxing Formation at the Meishan section has resulted in taxonomic refinement of several important neogondolellid species. Most of the previously erected species are much more strictly redefined, mainly based on the denticulation of the holotypes, and the stratigraphic ranges attributed to key conodont taxa are modified. Three new species and two new subspecies, all of which are form-species, are tentatively erected and described mainly for the purpose of taxonomic explanation. As a result of the taxonomic refinement, six neogondolellid conodont zones are recognized for the Changxing Formation and the Permian–Triassic boundary interval. 1998 Elsevier Science B.V. All rights reserved. Keywords: Changhsingian; Griesbachian; neogondolellid conodonts; conodont zones
1. Introduction The Changhsingian conodonts were first studied by Sweet (in Teichert et al., 1973) in northwestern Iran. Two conodont assemblage zones were erected by Wang and Wang (in Zhao et al., 1981) at the Meishan section, Changxing, Zhejiang. They are the N. subcarinata–N. elongata Zone (lower) and the N. deflecta–N. changxingensis Zone (upper). Tian (1993a) further subdivided the upper Zone into the N. postwangi–N. changxingensis Zone (lower) and the N. xiangxiensis–N. changxingensis Zone (upŁ Corresponding
author. Fax: C86 (10) 6231 0897; E-mail: [email protected]
per), based on conodonts from northwestern Hunan. However, most of the common neogondolellid species have been reported to occur throughout the Changhsingian. Through careful reading of available publications and detailed study of abundant material, the authors found that each author’s determination of the species definition has varied dramatically. This inconsistency in taxonomy as well as inadequate attention to conodont provincialism have caused serious confusion in correlation of the Changhsingian (Kozur, 1992). In the last two years, important discoveries and progress were made by Orchard et al. (1994, 1996); Wang (1994, 1995, 1996); Zhang et al. (1995, 1996) and Mei (1996) in the study of conodonts around the
c 1998 Elsevier Science B.V. All rights reserved. 0031-0182/98/$ – see front matter PII: S 0 0 3 1 - 0 1 8 2 ( 9 8 ) 0 0 1 1 2 - 6
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Permian–Triassic boundary. Among them it is noteworthy that the contention that Otoceras is associated with conodonts of Permian age and the resultant correlation of Otoceras with the Changhsingian and Dorashamian (Kozur, 1977; Sweet, 1979, 1992) are found to be untenable. The Permian neogondolellids are not highly diversified in morphology and therefore are difficult to classify. Rare individuals within a population may exhibit one or several characteristics that are thought to be diagnostic of another species. The analysis of large numbers of individuals is necessary to understand ontogeny and intra-species variation. The present authors find that the most consistent and reliable character in Lopingian neogondolellids is the general configuration of the denticles, which can be used to define a natural population or an apparatus species. Of secondary importance is the shape of the platform, which can be used only to identify a form species within a natural population, as did most previous authors, or a temporal subspecies. Study of new conodont collections from the Meishan section, the Nanjiang section in South China and the Hambast C section in central Iran and comparison with other sections have resulted in taxonomic refinement of several neogondolellid species based on features of both the denticulation and the platform shape (see below). Consequently, most of the previously erected species are much more strictly defined with emphasis on the denticulation of the original holotypes, and the stratigraphic ranges attributed to key conodont taxa are modified. The reports of Neogondolella carinata from the Changhsingian in South China (Wang and Wang, in Zhao et al., 1981; Tian, 1993a,b; Zhang et al., 1995) and the Dorashamian in Iran (Sweet, in Teichert et al., 1973) cannot be confirmed, supporting the conclusion reached by both Matsuda (1984) and Orchard et al. (1994). This paper presents a refined neogondolellid conodont zonation for the Changxing Formation and the Permian–Triassic boundary interval in the Meishan section, one of the most important potential stratotypes of the Permian–Triassic boundary.
2. Material studied Samples from the Changxing Formation and the lowest limestone bed of the Qinglong Formation in the Meishan section were collected by Shilong Mei and Bruce R. Wardlaw in 1992, with the help of Dr. Yugan Jin and Dr. Wei Wang at the site. The average sampling interval was 1 m (Fig. 1), and the bed descriptions of the section were based on Sheng et al. (1984). Each sample weighed at least 8 kg. Eighty percent of rock samples produced neogondolellid conodonts, with an average production rate of 910 identifiable individuals per sample. Neogondolellid conodonts from the Permian–Triassic interval were mainly supplied by Dr. Kexin Zhang.
3. Neogondolellid conodont zones in the Meishan section and their correlation Newly collected neogondolellid conodonts from Meishan are divisible into six assemblage zones (Fig. 1). They are in ascending order the C. prechangxingensis–C. subcarinata–C. wangi– C. predeflecta Assemblage Zone, the Transitional Assemblage Zone, the C. changxingensis changxingensis–C. parasubcarinata–C. postwangi– C. deflecta Assemblage Zone, the C. changxingensis yini–C. meishanensis zhangi Assemblage Zone, the C. meishanensis meishanensis Zone and the C. zhejiangensis Zone. The C. prechangxingensis–C. subcarinata–C. wangi–C. predeflecta Assemblage Zone is characterized by the co-existence of the namegiving species, which all possess a continuous carina, as was well demonstrated by Sweet (in Teichert et al., 1973). The C. changxingensis changxingensis– C. parasubcarinata–C. postwangi–C. deflecta Assemblage Zone is represented by the concurrence of the name-giving species, which are the successors of the form species in the C. prechangxingensis– C. subcarinata–C. wangi–C. predeflecta Assemblage Zone and are all characterized by a denticulation that has largely fused denticles decreasing in size and
Fig. 1. Gondolellid conodont distribution in the Changxing Formation and the lower Qinglong Formation at the Meishan section in Changxing County, Zhejiang Province, South China. Columnar section is from Sheng et al. (1984). The asterisk indicates the position of the GSSP of the Permian–Triassic Boundary recommended by Yin et al. (1988, 1994) and Wang (1994, 1995).
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height toward the posterior so that there is commonly little continuity between the carina and the cusp (sometimes the posterior-most denticle fused with the cusp), which is commonly reclined and largely fused with the upturned posterior margin of the platform. The Transitional Assemblage Zone is characterized by the co-existence of C. subcarinata, C. predeflecta sp. nov., C. changxingensis changxingensis, C. parasubcarinata sp. nov., C. postwangi and C. deflecta, among which both kinds of denticultion mentioned above exist. The C. changxingensis yini–C. meishanensis zhangi Assemblage Zone contains C. parasubcarinata sp. nov. and C. deflecta as well as the two name-giving species, both of which can be discriminated from their predecessors in the underlying zone mainly by the much flattened posterior platform and the platform outline. The C. meishanensis meishanensis Zone and the C. zhejiangensis Zone are respectively distinguished by the name-giving species. These zones can be regarded as phylogenetic zones. The lower three zones can be recognized also in the widely separated Nanjiang section and northwestern Hunan. In the new collection made by the Iranian–Chinese Research Group (1995) from the Hambast C section, conodonts from the middle and upper part of unit 7 may be correlated to only the lower two assemblage zones mentioned above. The C. changxingensis changxingensis–C. parasubcarinata– C. postwangi–C. deflecta Assemblage Zone and the C. changxingensis yini–C. meishanensis zhangi Assemblage Zone appear to be missing in central Iran. They may be also absent in the Ali Bashi Formation in Julfa, judging from available data (Sweet, 1979, 1992). This result appears to confirm the conclusion reached by Zhao et al. (1981) based on ammonoids, and Wang and Wang (in Zhao et al., 1981) based on conodonts that the Dorashamian in Transcaucasia and the Ali Bashi Formation in Iran correlate with only the lower and middle Changhsingian.
4. Taxonomy Three distinct morphotypes were recognized for neogondolellids from the Changxing Formation at the Meishan section by Mei (1996), based on the shape of the posterior end and the platform outline.
They were named as the round-morphotype, squaremorphotype and narrow-morphotype. The roundmorphotype, such as Clarkina changxingensis, has a symmetric and bluntly rounded posterior end and a lachrymiform platform outline. The square-morphotype, exemplified by Clarkina deflecta, has a squared and usually oblique posterior end. The narrow-morphotype, typified by Clarkina wangi, has a narrowly rounded to pointed posterior end and a lenticular platform outline. Transitional forms among these three morphotypes are likely common and were mostly referred to C. subcarinata by the previous authors. These three morphotypes clearly represent distinct variants of a single population as shown by Tian (1993b), who firstly treated C. changxingensis as a multi-element species. In addition to the shape of the platform, the present authors find that the general configuration of the denticles is the most consistent and reliable characteristic and can be used to subdivide the time continuum of populations into phyletic species, or temporal subspecies. Previously described species of the Changhsingian were mostly based on solely the platform shape and even rare and=or pathological features, with inadequate attention to the denticulation. Consequently, most of the species have been reported to occur throughout the Changhsingian. In order to detail the conodont succession and straighten out the taxonomic quagmire of neogondolellid species established for Chinese specimens from the Changhsingian, it is necessary to make taxonomic refinement to several known species and erect several new form species on the basis of taking both the denticulation and the platform shape into consideration. Only brief diagnostic and comparative notes are provided herein for these species because of limited space. A lengthy description with much more illustrations of conodonts from the Changxing Formation is in preparation by Wardlaw and Mei. The taxonomy of form species is tentatively followed here to avoid dramatic taxonomic change, although the present authors are ready to accept taxonomic adjustments to the multi-element species in the near future.
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Clarkina changxingensis changxingensis (Wang and Wang) (Plate I, B–D, F–H, K; Plate II, G)
Clarkina changxingensis yini Mei subsp. nov. (Plate IV, L–N)
1981 Neogondolella subcarinata changxingensis Wang and Wang, in Zhao et al., (part), p. 80, pl. V, figs. 6, 7, 10, 11. 1993a Neogondolella postwangi Tian, part, pl. II, figs. 2, 3; 1993b, pl. 5, figs. 3, 4, 11. 1993a Neogondolella xiangxiensis Tian, pl. II, figs. 4, 5; 1993b, pl. 5, figs. 6–10, 13. 1994 Neogondolella changxingensis Wang and Wang, Orchard et al., part, p. 833, 834, pl. 1, figs. 10, 13, 16. 1994 Neogondolella n. sp. A, Orchard et al., part, p. 833, pl. 1, figs. 11, 12; ? pl. 3, figs. 7–9.
Etymology. Named after Dr. Yin Hongfu, in tribute to his important contributions to the study of the Permian–Triassic boundary. Diagnosis. A Clarkina with an evenly arched platform of the round-morphotype, denticles decreasing gradually in size and height toward the posterior until the cusp, which is erect to slightly reclined and terminally located, and a much flattened posterior platform. Remarks. This new subspecies is distinguishable from C. changxingensis changxingensis mainly by the erect cusp, and the much flattened posterior platform. Occurrence. Uppermost Changhsingian.
Amended diagnosis. A Clarkina with an elongate platform of the round-morphotype, denticles decreasing distinctly in size and height toward the posterior so that there is usually little continuity between the carina and the small, erect to moderately reclined cusp, which is usually elevated by the upturned platform margin around it. Sometimes the discontinuity is replaced by a downwardly curved low ridge made of the reclined cusp fused with the posteriormost one or two denticles. Remarks. Tian (1993b) illustrated several specimens under the name of C. xiangxiensis to demonstrate its ontogeny. These specimens are all from a single sample, i.e., H11-1, which is from Bed 11 and about 12 m below the top of the Changxing Formation, which is less than 40 m thick, at the Hanglianyu section (Tian, 1993a,b, p. 141). They are indistinguishable from the holotype of C. changxingensis and its associates in both denticulation and platform outline. Therefore, C. xiangxiensis is here regarded as a junior synonym of C. changxingensis. This species is different from Clarkina taylorae, which is concurrent with Otoceras in peri-Gondwana and was once mostly misidentified as C. changxingensis or C. orientalis, in that the denticulation in C. taylorae is characterized by largely discrete denticles that slightly rise anteriorly to a low blade and terminate near the posterior end of the platform in a prominent and upright cusp. Occurrence. Upper Changhsingian.
Clarkina deflecta (Wang and Wang) (Plate III, A, H, I; Plate IV, J) 1981 Neogondolella deflecta Wang and Wang, in Zhao et al., p. 79, pl. VI, figs. 6–9. 1981 Neogondolella dicerocarinata Wang and Wang, in Zhao et al., p. 79, pl. V, figs. 19, 20. 1993a Neogondolella deflecta Wang and Wang, Tian, pl. I, fig. 13. 1993a Neogondolella dicerocarinata Wang and Wang, Tian, pl. I, figs. 19–21. 1994 Neogondolella deflecta Wang and Wang, Orchard et al., part, p. 834, pl. 1, fig. 17. Amended diagnosis. A Clarkina with a square-morphotype platform with subparallel posterior and middle platform margins and a gradually tapered and thus relatively broad anterior platform. Denticles are fused as a low carina except the posteriormost one (or sometimes two) which is the smallest and discrete from both the carina and the terminally located but often deflected cusp. When the cusp is not located at the end of the platform, one or two short accessory carinae are developed posterior to the cusp and deflect to the posterior–lateral corner of the platform. Remarks. Our study of ontogeny and intra-species variation of this species shows that Neogondolella diceocarinata Wang and Wang is simply the synonym of C. deflecta. This species is the successor of Clarkina predeflecta sp. nov., from which it can be distinguished by the denticulation. Occurrence. Upper Changhsingian.
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Clarkina meishanensis zhangi Mei subsp. nov. (Plate I, A; Plate IV, K) Etymology. Named after Dr. Zhang Kexin, in tribute to his important contributions to the study of the Permian–Triassic boundary. Diagnosis. A Clarkina with an evenly arched platform of the narrow-morphotype, denticles decreasing gradually in size and height toward the posterior until the cusp, which is prominent, reclined and terminally located, and a much flattened posterior platform. Remarks. This new subspecies can be distinguished from C. meishanensis meishanensis (Plate V) mainly by the fact that in the latter the cusp is larger relative to the posterior denticles, much more set off from the carina and less reclined. Occurrence. Uppermost Changhsingian.
Clarkina prechangxingensis sp. nov. (Plate I, I, J) Diagnosis. A Clarkina with an elongate platform of the round-morphotype; denticles and the cusp are largely fused as a continuous carina that usually keeps nearly the same height. In advanced forms the carina is less fused and decreases slowly in height until the slightly higher cusp. Remarks. This species is the predecessor of Clarkina changxingensis, from which it can be distinguished by the denticulation. Occurrence. Lower Changhsingian. Clarkina predeflecta sp. nov. (Plate II, E, J; Plate III, B, C) 1993a Neogondolella changxingensis Wang and Wang, Tian, pl. I, fig. 12.
PLATE I Specimens with the depository code MGL96 are housed in Department of Geology and Mineral Resources, China University of Geosciences, Beijing, P. R. China. Specimens from samples marked with the prefix CB are housed in China University of Geosciences, Wuhan, P.R. China. All illustrations are ð80 and from Changhxing Formation in the Meishan section, except B–D, which are ð60 and from the Changhsingian beds in the Nanjiang section. Aa, Ab: Clarkina meishanensis zhangi Mei subsp. nov., upper and oblique lateral view of a young specimen; Mc-40=MGL96001. B–D, F–H, K: Clarkina changxingensis changxingensis (Wang and Wang, 1981), all are upper views, except Fb, Gb and Hb, which are respectively the oblique lateral views of Fa, Ga and Ha; B and D are from Qt-9=MGL96002, MGL96004, C is from Qt-5=MGL96003, F is from Mc-23=MGL96005, G, H and K are from Mc-17=MGL96006, MGL9607, MGL96008. Ea, Eb: Clarkin subcarinata (Sweet, 1973), upper and lateral views of a middle-sized specimen; Mc-1=MGL96009. I, J: Clarkina prechangxingensis sp. nov.; Ia and Jb are respectively the oblique lateral views of Ib and Ja, which are upper views; I is the Holotype and from Mc-3=MGL96010; J is from Mc-10= MGL96011. PLATE II (see p. 220) All illustrations are ð80 and from the Changxing Formation at the Meishan section, except J, which is ð60 and from the Nanjiang section. A–C: Clarkina postwangi Tian, 1993a; all are upper views, except Bb and Cb, which are respectively the oblique upper view of Ba and Ca; B is the Holotype; A is from Mc-18=MGL96012 and B, C are from Mc-23= MGL96013, MGL96014. D, F, H: Clarkina parasubcarinata sp. nov., all are upper views, except Hb, which is the oblique upper view of Ha; D is the Holotype; D and F are from Mc-42=MGL96015, MGL96016 and H is from Mc-14=MGL96017. E, J: Clarkina predeflecta sp. nov., all are upper views, except Eb, which is the oblique lateral view of Ea; E is from Mc-4= MGL96018 and J is from Qt-12=MGL96019. G: Clarkina changxingensis changxingensis (Wang and Wang, 1981) upper view, from Mc-13=MGL96020. I, K: Clarkina subcarinata (Sweet, 1973), Ib and Ka are respectively the lateral views of Ia and Kb, which are upper views; I is from Mc-7=MGL96021 and K is from Mc-14=MGL96022. PLATE III (see p. 221) All specimens are from the Changxing Formation at the Meishan section and all illustrations are ð80, except those specially marked. A, H, I: Clarkina deflecta (Wang and Wang, 1981), all are upper views, except Aa, which is the oblique upper view of Ab; A and H are from Mc-42=MGL96023, MGL96024, and I is from Mc-17=MGL96025. B, C: Clarkina predeflecta sp. nov., all are upper views, except Bb, which is the oblique lateral view of Ba; B is the Holotype and from Mc-10=MGL96026, C is ð73 and from Mc-3=MGL96027. D: Hindeodus parvus (Kozur and Pjatakova, 1977), lateral view, ð120, from Wang (1994, 1995) who reported occurrence in the uppermost of Boundary Bed 2 (equivalent to Bed 24 in Fig. 1). E: Iranognathus tarazi Kozur, Mostler and Rahimi-Yazd, 1975, upper view, from Mc-1=MGL96028. F: Clarkina orientalis (Barskov and Koroleva, 1970), upper view, from Mc-1=MGL96029. G: Hindeodus latidentatus (Kozur et al., 1975) (sensu Kozur, 1995, amended), lateral view, ð90, from Zhang et al. (1995) who reported occurrence in Bed 25 (equivalent to Bed 22 in Fig. 1). J, K: Clarkina wangi Zhang (1984), both are upper views, J is ð73 and from Mc-17=MGL96030, and K is from Mc-3=MGL96031.
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PLATE I
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PLATE II
For description see p. 218.
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PLATE III
For description see p. 218.
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PLATE IV
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Diagnosis. A Clarkina with an elongate platform of the square-morphotype, with subparallel posterior and middle platform margins and a gradually tapered and thus relatively broad anterior platform. Denticles and the cusp are largely fused as a continuous carina that keeps nearly the same height and often extends postero-laterally. In advanced forms the posterior denticles are less fused. Remarks. This species can be differentiated from C. subcarinata by a more squared posterior end, less tapered anterior platform and a longer unit. Occurrence. Lower Changhsingian. Clarkina parasubcarinata sp. nov. (Plate II, D, F, H; Plate IV, I) 1981 Neogondolella subcarina changxiensis Wang and Wang, in Zhao et al., part, p. 80, pl. VII, figs. 7, 8. 1994 Neogondolella subcarinata Sweet, morphotype 1, Orchard et al., part, p. 835, pl. 1, fig. 5. 1994 Neogondolella changxingensis Wang and Wang, Orchard et al., part, p. 833, 834, pl. 1, figs. 7, 8, 14, 15?, 18, 19. 1994 Neogondolella deflecta Wang and Wang, Orchard et al., part, p. 834, pl. 1, fig. 22. Diagnosis. A Clarkina with a relatively wide platform that narrows abruptly near both the anterior and posterior ends of the element, posterior end of the platform usually asymmetric, denticles decreasing distinctly in size and height toward the posterior so that there is usually little continuity between the carina and the reclined cusp, which is deflected and terminally located and gives the posterior platform end a projecting outline. Remarks. This species can be differentiated from
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C. changxingensis by the asymmetric and projecting posterior end, much more reclined cusp, and more reduced and deflected anterior platform, although transitional forms are common. Occurrence. Upper Changhsingian. Clarkina postwangi (Tian) (Plate II, A, B, C) 1993b Neogondolella postwangi Tian, part, pl. 5, fig. 12. 1981 Neogondolella carinata Wang and Wang, in Zhao et al., part, p. 80, pl. VII, figs. 9, 10. Amended diagnosis. A Clarkina with a platform of the narrow-type, which is widest at the midlength where the platform tapers evenly towards both the anterior and posterior and is thus lenticular in outline; platform end narrowly rounded, and sometimes one or occasionally two shallow indentations present on the posterior-lateral margins, denticles decreasing in size and height and becoming progressively discrete toward the posterior so that there is usually little continuity between the carina and the reclined cusp. Remarks. Tian (1993b) erected this species without assigning the holotype and giving detailed description of the denticulation. Among his illustrated specimens, which are all from a single sample, i.e., HJ18-5 from Bed 18 and about 5m below the top of the Dalong Formation in the Jiangya section (Tian, 1993a,b, p. 139), only the specimen illustrated as pl. 5, figs. 12a, 12b (Tian, 1993b) is diagnostic, the other specimens are indistinguishable from specimens of C. changxingensis (ibid, pl. 5, figs. 3, 4, 11) and juvenile specimens of C. deflecta (ibid. figs. 1, 2). The holotype of this species is herein assigned and illustrated as Plate II, B. The specimens with one
PLATE IV All from the Permian–Triassic boundary interval at the Meishan section. Samples marked as CB*-25 are from Bed 25 of Zhang et al. (1995, 1996), which correlates with Bed 22 in Fig. 1. A, B: Clarkina aff.deflecta (Wang and Wang, 1981), A is upper view, ð70, CBIV-25=946129, B is oblique upper view, ð73, CBII-25=946185. C–G, H?: Clarkina meishanensis meishanensis Zhang et al., 1995, C–E upper views, ð80, from Wang (1995), F upper view, ð73, from CBIII-25=946184, G oblique upper view, ð66, from CBV-25=946181, H upper view, ð60, from CBII-25=946186. Ia, Ib: Clarkina parasubcarinata sp. nov., oblique upper view and upper view of a middle sized specimen, ð80, from Mc-42=MGL96032. Ja, Jb: Clarkina deflcta (Wang and Wang, 1981), oblique upper view and upper view of a middle-sized specimen, ð80, from Mc-43=MGL96033. Ka, Kb: Clarkina meishanensis zhangi subsp. nov., oblique upper view and upper view of a middle-sized specimen, the Holotype, ð80, from Mc-42=MGL96034. L–N: Clarkina changxingensis yini subsp. nov., all ð80; La, Mb and Na are respctively oblique lateral views of Lb, Ma and Nb, which are all upper views; L is the Holotype and from Mc-43=MGL96035, M and N are from MC-40=MGL96036, MGL96037.
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PLATE V
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or two shallow posterior-lateral indentations were previously misidentified as Neogondolella carinata, from which it can be easily distinguished by the denticulation. Occurrence. Upper Changhsingian. Clarkina subcarinata (Sweet) (Plate I, E; Plate II, I, K) 1973 Neogondolella carinata subcaranata Sweet, in Teichert et al., pp. 436–437, text-figure 16E–H, pl. 13, figs. 1–3, 12–17. 1981 Neogondolella subcarinata subcaranata Sweet, Wang and Wang, in Zhao et al., pl. V, figs. 1–5, 8, 9, 15, 16. 1994 Neogondolella subcarinata Sweet, morphotype 2, Orchard et al., part, p. 835, pl. 1, fig. 3, 4, 9. 1993b Neogondolella subcarinata Sweet, Tian, figs. 6–8. 1993b Neogondolella wangi Dai and Zhang, Tian, pl. 4, figs. 21, 22, 24a, 24b. Amended diagnosis. A Clarkina with a relatively wide and short platform that narrows abruptly near both the anterior and posterior ends of the element; denticles and the reclined cusp are largely fused as a continuous carina that keeps nearly the same height and often extends slightly beyond the posterior platform margin. In advanced forms the carina is less fused and decreases slowly in height until the higher and reclined cusp. Remarks. This species is the predecessor of Clarkina parasubcarinata sp. nov., from which it can be distinguished by the denticulation. Occurrence. Lower Changhsingian.
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Clarkina wangi (Zhang) (Plate III, J, K) 1987 Gondolella wangi Zhang, pl. 1, fig. 4. 1981 Neogondolella subcarinata elongata Wang and Wang, in Zhao et al., p. 80, pl. VI, figs. 1–5. 1993b Neogondolella wangi Dai, Tian and Zhang, Tian, pl. 4, figs. 23a, 23b. Amended diagnosis. A Clarkina with a platform of the narrow-type, widest at the midlength of the posterior and middle platform where the platform tapers to both the anterior and posterior and is thus lenticular in outline; denticles and the reclined cusp are largely fused as a continuous carina that keeps nearly the same height, extends beyond the posterior platform margin and thus makes the platform end projectively pointed. In advanced forms, the carina is less fused and decreases slowly in height until the reclined cusp. Remarks. This species is the predecessor of Clarkina postwangi, from which it can be easily distinguished by the denticulation. Occurrence. Lower Changhsingian.
Acknowledgements The authors acknowledge the support from the Chinese Academy of Science (Grant K2951-B1409) and the National Nature Science Foundation of China (Grant 49672092 and 49632070). The authors thank Dr. Jin Yugang for kind encouragement and the possibility to study the collection from Iran, Dr. Spencer G. Lucas and Dr. Yin Hongfu for kind encouragement and critical reading of the manuscript. Mr. Mao Yongqiang is thanked for the SEM photography.
PLATE V All are from the Permian–Triassic boundary interval at the Meishan section. Samples marked as CB*-26 and CB*-29 are respectively from Bed 25 and Bed 29 of Zhang et al. (1995, 1996), which correlate respectively with Bed 23 and the bed overlying Bed 24 in Fig. 1. A, D, G, N: Clarkina zhejiangensis Mei, 1996; A ð100; D ð80; G ð60; N ð80; all upper views, from Wang (1995), who reported N occurring in the upper part of Boundary Bed 1 (equivalent to Bed 23 in Fig. 1), and A, D, G occurring in the Boundary Bed 2 (equivalent to Bed 24 in Fig. 1). B, E, L, M?, O: Clarkina aff.deflecta (Wang and Wang, 1981); B ð80; E ð80; L ð60; M ð80; O ð50; all are upper views and from Wang (1995), who reported B occurring in the Boundary Bed 2 (equivalent to Bed 24 in Fig. 1), and E, L and M occurring in the upper part of Boundary Bed 1 (equivalent to Bed 23 in Fig. 1). C: Clarkina aff.meishanensis meishanensis Zhang et al., 1995, ð121, oblique upper view, from CBIII-29=946142. F, H–K, P?: Clarkina meishanensis meishanensis Zhang et al., 1995; F ð80; H the Holotype, ð120; I ð100; J ð87; K ð120; P ð80; F, H–K are oblique upper views, P is upper view; F and P are from CBV-26=946168, 946174; H–K are from CBIII-26=946146, 946145, 946176, 946175.
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References Barskov, I.S., Koroleva, N.V., 1970. Pervaya nakhodka verkhnepermskikh Konodontovna territorii SSSR. Dokl. Akad. Nauk SSSR 194, 933–934. Iranian–Chinese Research Group, 1995. Field work on the Lopingian stratigraphy in Iran. Permophiles 27, 5–8. ¨ nKozur, H., 1977. Die Lage der Perm=Trias-Grenze und die A derung der Faunen und Floren im Perm=Trias-Grenzbereich, Teil 1. Freibeiger Forschungscheft, C326, Leipizig. Kozur, H., 1992. Dzhulfian and Early Changxingian (Late Permian) Tethyan conodonts from the Glass Mountains, West Texas. Neues Jahrb. Geol. Pala¨ontol., Abh. 187 (1), 99–114. Kozur, H., 1995. Some remarks to the conodonts Hindeodus and Isarcicella in the latest Permian and earliest Triassic. Palaeoworld 6, 64–77. Kozur, H., Pjatakova, M., 1976. Die Conodontenart Anchignathodus parvis n. sp. eine wichtige Leitform der basalen Trias. Proc. Kon. Ned. Akad. Wetenschap. B 79 (2), 123–128. Kozur, H., Mostler, H., Rahimi-Yazd, A., 1975. Beitrage zur Mikropalaontologie permotnadischer Schichtfolgen. Teil II: Neue Conodonten aus dem Oberperm und der basalen Trias von Nord- und Zentral Iran. Geol.-Palaontol. Mittl. 5 (3), 1–23. Matsuda, T., 1984. Early Triassic conodonts from Kashmir, India, Part 4. Gondolella and Platyvillosus. J. Geosci., Osaka City Univ. 27 (4), 119–141. Mei, S., 1996. Restudy of conodonts from the Permian–Triassic boundary beds at Selong and Meishan and the natural Permian–Triassic boundary. In: Wang, H., Wang, X. (Eds.), Centennial Memorial Volume of Professor Sun Yunzhu (Y.C. Sun): Stratigraphy and Palaeontology. China University of Geosciences Press, Wuhan, pp. 141–148. Orchard, M.J., 1996. Conodont fauna from the Permian–Triassic boundary: observations and reservations. Permophiles 28, 36– 39. Orchard, M.J., Nassichuk, W.W., Rui, L., 1994. Conodonts from the lower Griesbachian Otoceras latilobatum bed of Selong, Tibet and the position of the Permian–Triassic boundary. Can. Soc. Pet. Geol., Mem. 17, 823–843. Sheng, J., Chen, C., Wang, Y., Rui, L., Liao, Z., Bando, Y., Ishii, K., Nakazawa, K., Nakamura, K., 1984. Permian–Triassic boundary in middle and eastern Tethys. J. Fac. Sci., Hokkaido Univ., Ser. IV 21 (1), 133–181. Sweet, W.C., 1973. Contodontophorida Eichenberg, 1930. In: Teichert, C., Kummel, B., Sweet, W.C. (Eds.), Permian– Triassic Strata, Kuh-e-Ali Bashi, Northwest Iran. Bull. Mus. Compar. Zool. 145 (8), 423–472. Sweet, W.C., 1979. Graphic correlation of Permian–Triassic rocks in Kashmir, Pakistan and Iran. Geol. Paleontol. 13, 239–248. Sweet, W.C., 1992. A conodont-based high- resolution biostratigraphy for the Permo–Triassic boundary interval. In: Sweet,
W.C., Yang, Z., Dickens, J.M., Yin, H. (Eds.), Permo–Triassic events in the Eastern Tethys. Cambridge University Press, Cambridge, pp. 120–133. Teichert, C., Kummel, B., Sweet, W.C., 1973. Permian–Triassic strata, Kuh-e-Ali Bashi, northwest Iran. Bull. Mus. Comp. Zool. 145 (8), 359–472. Tian, S., 1993a. The Permo–Triassic boundary and conodont zones in northwestern Hunan Province (in Chinese with English abstract). Bull. Chin. Acad. Geol. Sci. 26, 133–150. Tian, S., 1993b. Evolutions of conodont genera Neogondolella, Hindeodus and Isarcicella in northwestern Hunan, China. Stratigr. Paleontol. Chin. 2, 173–191. Wang, C., 1994. A conodont-based high-resolution eventostratigraphy and biostratigraphy for the Permian–Triassic boundaries in South China. Palaeoworld 4, 234–248. Wang, C., 1995. Conodonts of Permian–Triassic boundary beds and biostratigraphic boundary (in Chinese with English abstract). Acta Palaeontol. Sin. 34 (2), 129–151. Wang, C., 1996. Conodont evolutionary lineage and zonation for the Latest Permian and the Earliest Triassic. Permophiles 29, 30–37. Wang, C., Wang, Z., 1981. Conodonts. In: Zhao, J., Sheng, I., Yao, Z., Liang, X., Chen, C., Rui, I., Liao, Z. (Eds.), The Changhsingian and the Permian–Triassic boundary of South China (in Chinese with English summary). Nanjing Inst. Geol. Palaeontol. Acad. Sin 2, 79–81. Yin, H., Yang, F., Zhang, K., Yang, W., 1988. A proposal to the biostratigraphic criterion of Permian=Triassic boundary. Soc. Geol. Ital., Mem. 34 (1986), 329–344. Yin, H., Wu, S., Din, M., Zhang, K., Tong, J., Yang, F., 1994. The Meishan section: candidate of the Global Stratotype Section and Point of the Permian–Triassic boundary. Albertiana 14, 15–30. Zhang, K., 1984. New data on the conodont fauna from the Otoceras bed in the Baoqing section of Changxing, Zhejiang (in Chinese with English abstract). Earth Sci. J. Wuhan College Geol. 26 (3), 38, 104. Zhang, K., Lai, X., Ding, M., Wu, S., Liu, J., 1995. Conodont sequence and its global correlation of Permian–Triassic boundary in the Meishan section, Changxing, Zhejiang Province (in Chinese with English abstract). Earth Sci. J. Chin. Univ. Geosci. 20 (6), 669–676. Zhang, K., Ding, M., Lai, X., Liu, J., 1996. Conodont sequence of the Permian–Triassic boundary strata at Meishan section, South China. In: Yin, H. (Ed.), The Palaeozoic–Mesozoic Boundary Candidates of Global Stratotype Section and Point of the Permian–Triassic Boundary. China University of Geosciences Press, Wuhan, pp. 57–64. Zhao, J., Sheng, J., Yao, Z., Liang, X., Chen, C., Rui, L., Liao, Z., 1981. The Changhsingian and Permian–Triassic boundary of South China (in Chinese with English summary). Bull. Nanjing Inst. Geol. Palaeontol., Acad. Sin. 2, 58–128.
Palaeogeography, Palaeoclimatology, Palaeoecology 143 (1998) 213–226
A refined succession of Changhsingian and Griesbachian neogondolellid conodonts from the Meishan section, candidate of the global stratotype section and point of the Permian–Triassic boundary Shilong Mei a,Ł , Kexin Zhang b , Bruce R. Wardlaw c a b
China University of Geosciences, Beijing 100083, China China University of Geosciences, Wuhan 430074, China c U.S. Geological Survey, Reston, VA 22092-0001, USA Received 1 February 1997; accepted 1 October 1997
Abstract A detailed study of new conodont collections from the Changxing Formation at the Meishan section has resulted in taxonomic refinement of several important neogondolellid species. Most of the previously erected species are much more strictly redefined, mainly based on the denticulation of the holotypes, and the stratigraphic ranges attributed to key conodont taxa are modified. Three new species and two new subspecies, all of which are form-species, are tentatively erected and described mainly for the purpose of taxonomic explanation. As a result of the taxonomic refinement, six neogondolellid conodont zones are recognized for the Changxing Formation and the Permian–Triassic boundary interval. 1998 Elsevier Science B.V. All rights reserved. Keywords: Changhsingian; Griesbachian; neogondolellid conodonts; conodont zones
1. Introduction The Changhsingian conodonts were first studied by Sweet (in Teichert et al., 1973) in northwestern Iran. Two conodont assemblage zones were erected by Wang and Wang (in Zhao et al., 1981) at the Meishan section, Changxing, Zhejiang. They are the N. subcarinata–N. elongata Zone (lower) and the N. deflecta–N. changxingensis Zone (upper). Tian (1993a) further subdivided the upper Zone into the N. postwangi–N. changxingensis Zone (lower) and the N. xiangxiensis–N. changxingensis Zone (upŁ Corresponding
author. Fax: C86 (10) 6231 0897; E-mail: [email protected]
per), based on conodonts from northwestern Hunan. However, most of the common neogondolellid species have been reported to occur throughout the Changhsingian. Through careful reading of available publications and detailed study of abundant material, the authors found that each author’s determination of the species definition has varied dramatically. This inconsistency in taxonomy as well as inadequate attention to conodont provincialism have caused serious confusion in correlation of the Changhsingian (Kozur, 1992). In the last two years, important discoveries and progress were made by Orchard et al. (1994, 1996); Wang (1994, 1995, 1996); Zhang et al. (1995, 1996) and Mei (1996) in the study of conodonts around the
c 1998 Elsevier Science B.V. All rights reserved. 0031-0182/98/$ – see front matter PII: S 0 0 3 1 - 0 1 8 2 ( 9 8 ) 0 0 1 1 2 - 6
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Permian–Triassic boundary. Among them it is noteworthy that the contention that Otoceras is associated with conodonts of Permian age and the resultant correlation of Otoceras with the Changhsingian and Dorashamian (Kozur, 1977; Sweet, 1979, 1992) are found to be untenable. The Permian neogondolellids are not highly diversified in morphology and therefore are difficult to classify. Rare individuals within a population may exhibit one or several characteristics that are thought to be diagnostic of another species. The analysis of large numbers of individuals is necessary to understand ontogeny and intra-species variation. The present authors find that the most consistent and reliable character in Lopingian neogondolellids is the general configuration of the denticles, which can be used to define a natural population or an apparatus species. Of secondary importance is the shape of the platform, which can be used only to identify a form species within a natural population, as did most previous authors, or a temporal subspecies. Study of new conodont collections from the Meishan section, the Nanjiang section in South China and the Hambast C section in central Iran and comparison with other sections have resulted in taxonomic refinement of several neogondolellid species based on features of both the denticulation and the platform shape (see below). Consequently, most of the previously erected species are much more strictly defined with emphasis on the denticulation of the original holotypes, and the stratigraphic ranges attributed to key conodont taxa are modified. The reports of Neogondolella carinata from the Changhsingian in South China (Wang and Wang, in Zhao et al., 1981; Tian, 1993a,b; Zhang et al., 1995) and the Dorashamian in Iran (Sweet, in Teichert et al., 1973) cannot be confirmed, supporting the conclusion reached by both Matsuda (1984) and Orchard et al. (1994). This paper presents a refined neogondolellid conodont zonation for the Changxing Formation and the Permian–Triassic boundary interval in the Meishan section, one of the most important potential stratotypes of the Permian–Triassic boundary.
2. Material studied Samples from the Changxing Formation and the lowest limestone bed of the Qinglong Formation in the Meishan section were collected by Shilong Mei and Bruce R. Wardlaw in 1992, with the help of Dr. Yugan Jin and Dr. Wei Wang at the site. The average sampling interval was 1 m (Fig. 1), and the bed descriptions of the section were based on Sheng et al. (1984). Each sample weighed at least 8 kg. Eighty percent of rock samples produced neogondolellid conodonts, with an average production rate of 910 identifiable individuals per sample. Neogondolellid conodonts from the Permian–Triassic interval were mainly supplied by Dr. Kexin Zhang.
3. Neogondolellid conodont zones in the Meishan section and their correlation Newly collected neogondolellid conodonts from Meishan are divisible into six assemblage zones (Fig. 1). They are in ascending order the C. prechangxingensis–C. subcarinata–C. wangi– C. predeflecta Assemblage Zone, the Transitional Assemblage Zone, the C. changxingensis changxingensis–C. parasubcarinata–C. postwangi– C. deflecta Assemblage Zone, the C. changxingensis yini–C. meishanensis zhangi Assemblage Zone, the C. meishanensis meishanensis Zone and the C. zhejiangensis Zone. The C. prechangxingensis–C. subcarinata–C. wangi–C. predeflecta Assemblage Zone is characterized by the co-existence of the namegiving species, which all possess a continuous carina, as was well demonstrated by Sweet (in Teichert et al., 1973). The C. changxingensis changxingensis– C. parasubcarinata–C. postwangi–C. deflecta Assemblage Zone is represented by the concurrence of the name-giving species, which are the successors of the form species in the C. prechangxingensis– C. subcarinata–C. wangi–C. predeflecta Assemblage Zone and are all characterized by a denticulation that has largely fused denticles decreasing in size and
Fig. 1. Gondolellid conodont distribution in the Changxing Formation and the lower Qinglong Formation at the Meishan section in Changxing County, Zhejiang Province, South China. Columnar section is from Sheng et al. (1984). The asterisk indicates the position of the GSSP of the Permian–Triassic Boundary recommended by Yin et al. (1988, 1994) and Wang (1994, 1995).
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height toward the posterior so that there is commonly little continuity between the carina and the cusp (sometimes the posterior-most denticle fused with the cusp), which is commonly reclined and largely fused with the upturned posterior margin of the platform. The Transitional Assemblage Zone is characterized by the co-existence of C. subcarinata, C. predeflecta sp. nov., C. changxingensis changxingensis, C. parasubcarinata sp. nov., C. postwangi and C. deflecta, among which both kinds of denticultion mentioned above exist. The C. changxingensis yini–C. meishanensis zhangi Assemblage Zone contains C. parasubcarinata sp. nov. and C. deflecta as well as the two name-giving species, both of which can be discriminated from their predecessors in the underlying zone mainly by the much flattened posterior platform and the platform outline. The C. meishanensis meishanensis Zone and the C. zhejiangensis Zone are respectively distinguished by the name-giving species. These zones can be regarded as phylogenetic zones. The lower three zones can be recognized also in the widely separated Nanjiang section and northwestern Hunan. In the new collection made by the Iranian–Chinese Research Group (1995) from the Hambast C section, conodonts from the middle and upper part of unit 7 may be correlated to only the lower two assemblage zones mentioned above. The C. changxingensis changxingensis–C. parasubcarinata– C. postwangi–C. deflecta Assemblage Zone and the C. changxingensis yini–C. meishanensis zhangi Assemblage Zone appear to be missing in central Iran. They may be also absent in the Ali Bashi Formation in Julfa, judging from available data (Sweet, 1979, 1992). This result appears to confirm the conclusion reached by Zhao et al. (1981) based on ammonoids, and Wang and Wang (in Zhao et al., 1981) based on conodonts that the Dorashamian in Transcaucasia and the Ali Bashi Formation in Iran correlate with only the lower and middle Changhsingian.
4. Taxonomy Three distinct morphotypes were recognized for neogondolellids from the Changxing Formation at the Meishan section by Mei (1996), based on the shape of the posterior end and the platform outline.
They were named as the round-morphotype, squaremorphotype and narrow-morphotype. The roundmorphotype, such as Clarkina changxingensis, has a symmetric and bluntly rounded posterior end and a lachrymiform platform outline. The square-morphotype, exemplified by Clarkina deflecta, has a squared and usually oblique posterior end. The narrow-morphotype, typified by Clarkina wangi, has a narrowly rounded to pointed posterior end and a lenticular platform outline. Transitional forms among these three morphotypes are likely common and were mostly referred to C. subcarinata by the previous authors. These three morphotypes clearly represent distinct variants of a single population as shown by Tian (1993b), who firstly treated C. changxingensis as a multi-element species. In addition to the shape of the platform, the present authors find that the general configuration of the denticles is the most consistent and reliable characteristic and can be used to subdivide the time continuum of populations into phyletic species, or temporal subspecies. Previously described species of the Changhsingian were mostly based on solely the platform shape and even rare and=or pathological features, with inadequate attention to the denticulation. Consequently, most of the species have been reported to occur throughout the Changhsingian. In order to detail the conodont succession and straighten out the taxonomic quagmire of neogondolellid species established for Chinese specimens from the Changhsingian, it is necessary to make taxonomic refinement to several known species and erect several new form species on the basis of taking both the denticulation and the platform shape into consideration. Only brief diagnostic and comparative notes are provided herein for these species because of limited space. A lengthy description with much more illustrations of conodonts from the Changxing Formation is in preparation by Wardlaw and Mei. The taxonomy of form species is tentatively followed here to avoid dramatic taxonomic change, although the present authors are ready to accept taxonomic adjustments to the multi-element species in the near future.
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217
Clarkina changxingensis changxingensis (Wang and Wang) (Plate I, B–D, F–H, K; Plate II, G)
Clarkina changxingensis yini Mei subsp. nov. (Plate IV, L–N)
1981 Neogondolella subcarinata changxingensis Wang and Wang, in Zhao et al., (part), p. 80, pl. V, figs. 6, 7, 10, 11. 1993a Neogondolella postwangi Tian, part, pl. II, figs. 2, 3; 1993b, pl. 5, figs. 3, 4, 11. 1993a Neogondolella xiangxiensis Tian, pl. II, figs. 4, 5; 1993b, pl. 5, figs. 6–10, 13. 1994 Neogondolella changxingensis Wang and Wang, Orchard et al., part, p. 833, 834, pl. 1, figs. 10, 13, 16. 1994 Neogondolella n. sp. A, Orchard et al., part, p. 833, pl. 1, figs. 11, 12; ? pl. 3, figs. 7–9.
Etymology. Named after Dr. Yin Hongfu, in tribute to his important contributions to the study of the Permian–Triassic boundary. Diagnosis. A Clarkina with an evenly arched platform of the round-morphotype, denticles decreasing gradually in size and height toward the posterior until the cusp, which is erect to slightly reclined and terminally located, and a much flattened posterior platform. Remarks. This new subspecies is distinguishable from C. changxingensis changxingensis mainly by the erect cusp, and the much flattened posterior platform. Occurrence. Uppermost Changhsingian.
Amended diagnosis. A Clarkina with an elongate platform of the round-morphotype, denticles decreasing distinctly in size and height toward the posterior so that there is usually little continuity between the carina and the small, erect to moderately reclined cusp, which is usually elevated by the upturned platform margin around it. Sometimes the discontinuity is replaced by a downwardly curved low ridge made of the reclined cusp fused with the posteriormost one or two denticles. Remarks. Tian (1993b) illustrated several specimens under the name of C. xiangxiensis to demonstrate its ontogeny. These specimens are all from a single sample, i.e., H11-1, which is from Bed 11 and about 12 m below the top of the Changxing Formation, which is less than 40 m thick, at the Hanglianyu section (Tian, 1993a,b, p. 141). They are indistinguishable from the holotype of C. changxingensis and its associates in both denticulation and platform outline. Therefore, C. xiangxiensis is here regarded as a junior synonym of C. changxingensis. This species is different from Clarkina taylorae, which is concurrent with Otoceras in peri-Gondwana and was once mostly misidentified as C. changxingensis or C. orientalis, in that the denticulation in C. taylorae is characterized by largely discrete denticles that slightly rise anteriorly to a low blade and terminate near the posterior end of the platform in a prominent and upright cusp. Occurrence. Upper Changhsingian.
Clarkina deflecta (Wang and Wang) (Plate III, A, H, I; Plate IV, J) 1981 Neogondolella deflecta Wang and Wang, in Zhao et al., p. 79, pl. VI, figs. 6–9. 1981 Neogondolella dicerocarinata Wang and Wang, in Zhao et al., p. 79, pl. V, figs. 19, 20. 1993a Neogondolella deflecta Wang and Wang, Tian, pl. I, fig. 13. 1993a Neogondolella dicerocarinata Wang and Wang, Tian, pl. I, figs. 19–21. 1994 Neogondolella deflecta Wang and Wang, Orchard et al., part, p. 834, pl. 1, fig. 17. Amended diagnosis. A Clarkina with a square-morphotype platform with subparallel posterior and middle platform margins and a gradually tapered and thus relatively broad anterior platform. Denticles are fused as a low carina except the posteriormost one (or sometimes two) which is the smallest and discrete from both the carina and the terminally located but often deflected cusp. When the cusp is not located at the end of the platform, one or two short accessory carinae are developed posterior to the cusp and deflect to the posterior–lateral corner of the platform. Remarks. Our study of ontogeny and intra-species variation of this species shows that Neogondolella diceocarinata Wang and Wang is simply the synonym of C. deflecta. This species is the successor of Clarkina predeflecta sp. nov., from which it can be distinguished by the denticulation. Occurrence. Upper Changhsingian.
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Clarkina meishanensis zhangi Mei subsp. nov. (Plate I, A; Plate IV, K) Etymology. Named after Dr. Zhang Kexin, in tribute to his important contributions to the study of the Permian–Triassic boundary. Diagnosis. A Clarkina with an evenly arched platform of the narrow-morphotype, denticles decreasing gradually in size and height toward the posterior until the cusp, which is prominent, reclined and terminally located, and a much flattened posterior platform. Remarks. This new subspecies can be distinguished from C. meishanensis meishanensis (Plate V) mainly by the fact that in the latter the cusp is larger relative to the posterior denticles, much more set off from the carina and less reclined. Occurrence. Uppermost Changhsingian.
Clarkina prechangxingensis sp. nov. (Plate I, I, J) Diagnosis. A Clarkina with an elongate platform of the round-morphotype; denticles and the cusp are largely fused as a continuous carina that usually keeps nearly the same height. In advanced forms the carina is less fused and decreases slowly in height until the slightly higher cusp. Remarks. This species is the predecessor of Clarkina changxingensis, from which it can be distinguished by the denticulation. Occurrence. Lower Changhsingian. Clarkina predeflecta sp. nov. (Plate II, E, J; Plate III, B, C) 1993a Neogondolella changxingensis Wang and Wang, Tian, pl. I, fig. 12.
PLATE I Specimens with the depository code MGL96 are housed in Department of Geology and Mineral Resources, China University of Geosciences, Beijing, P. R. China. Specimens from samples marked with the prefix CB are housed in China University of Geosciences, Wuhan, P.R. China. All illustrations are ð80 and from Changhxing Formation in the Meishan section, except B–D, which are ð60 and from the Changhsingian beds in the Nanjiang section. Aa, Ab: Clarkina meishanensis zhangi Mei subsp. nov., upper and oblique lateral view of a young specimen; Mc-40=MGL96001. B–D, F–H, K: Clarkina changxingensis changxingensis (Wang and Wang, 1981), all are upper views, except Fb, Gb and Hb, which are respectively the oblique lateral views of Fa, Ga and Ha; B and D are from Qt-9=MGL96002, MGL96004, C is from Qt-5=MGL96003, F is from Mc-23=MGL96005, G, H and K are from Mc-17=MGL96006, MGL9607, MGL96008. Ea, Eb: Clarkin subcarinata (Sweet, 1973), upper and lateral views of a middle-sized specimen; Mc-1=MGL96009. I, J: Clarkina prechangxingensis sp. nov.; Ia and Jb are respectively the oblique lateral views of Ib and Ja, which are upper views; I is the Holotype and from Mc-3=MGL96010; J is from Mc-10= MGL96011. PLATE II (see p. 220) All illustrations are ð80 and from the Changxing Formation at the Meishan section, except J, which is ð60 and from the Nanjiang section. A–C: Clarkina postwangi Tian, 1993a; all are upper views, except Bb and Cb, which are respectively the oblique upper view of Ba and Ca; B is the Holotype; A is from Mc-18=MGL96012 and B, C are from Mc-23= MGL96013, MGL96014. D, F, H: Clarkina parasubcarinata sp. nov., all are upper views, except Hb, which is the oblique upper view of Ha; D is the Holotype; D and F are from Mc-42=MGL96015, MGL96016 and H is from Mc-14=MGL96017. E, J: Clarkina predeflecta sp. nov., all are upper views, except Eb, which is the oblique lateral view of Ea; E is from Mc-4= MGL96018 and J is from Qt-12=MGL96019. G: Clarkina changxingensis changxingensis (Wang and Wang, 1981) upper view, from Mc-13=MGL96020. I, K: Clarkina subcarinata (Sweet, 1973), Ib and Ka are respectively the lateral views of Ia and Kb, which are upper views; I is from Mc-7=MGL96021 and K is from Mc-14=MGL96022. PLATE III (see p. 221) All specimens are from the Changxing Formation at the Meishan section and all illustrations are ð80, except those specially marked. A, H, I: Clarkina deflecta (Wang and Wang, 1981), all are upper views, except Aa, which is the oblique upper view of Ab; A and H are from Mc-42=MGL96023, MGL96024, and I is from Mc-17=MGL96025. B, C: Clarkina predeflecta sp. nov., all are upper views, except Bb, which is the oblique lateral view of Ba; B is the Holotype and from Mc-10=MGL96026, C is ð73 and from Mc-3=MGL96027. D: Hindeodus parvus (Kozur and Pjatakova, 1977), lateral view, ð120, from Wang (1994, 1995) who reported occurrence in the uppermost of Boundary Bed 2 (equivalent to Bed 24 in Fig. 1). E: Iranognathus tarazi Kozur, Mostler and Rahimi-Yazd, 1975, upper view, from Mc-1=MGL96028. F: Clarkina orientalis (Barskov and Koroleva, 1970), upper view, from Mc-1=MGL96029. G: Hindeodus latidentatus (Kozur et al., 1975) (sensu Kozur, 1995, amended), lateral view, ð90, from Zhang et al. (1995) who reported occurrence in Bed 25 (equivalent to Bed 22 in Fig. 1). J, K: Clarkina wangi Zhang (1984), both are upper views, J is ð73 and from Mc-17=MGL96030, and K is from Mc-3=MGL96031.
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PLATE I
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PLATE II
For description see p. 218.
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PLATE III
For description see p. 218.
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PLATE IV
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Diagnosis. A Clarkina with an elongate platform of the square-morphotype, with subparallel posterior and middle platform margins and a gradually tapered and thus relatively broad anterior platform. Denticles and the cusp are largely fused as a continuous carina that keeps nearly the same height and often extends postero-laterally. In advanced forms the posterior denticles are less fused. Remarks. This species can be differentiated from C. subcarinata by a more squared posterior end, less tapered anterior platform and a longer unit. Occurrence. Lower Changhsingian. Clarkina parasubcarinata sp. nov. (Plate II, D, F, H; Plate IV, I) 1981 Neogondolella subcarina changxiensis Wang and Wang, in Zhao et al., part, p. 80, pl. VII, figs. 7, 8. 1994 Neogondolella subcarinata Sweet, morphotype 1, Orchard et al., part, p. 835, pl. 1, fig. 5. 1994 Neogondolella changxingensis Wang and Wang, Orchard et al., part, p. 833, 834, pl. 1, figs. 7, 8, 14, 15?, 18, 19. 1994 Neogondolella deflecta Wang and Wang, Orchard et al., part, p. 834, pl. 1, fig. 22. Diagnosis. A Clarkina with a relatively wide platform that narrows abruptly near both the anterior and posterior ends of the element, posterior end of the platform usually asymmetric, denticles decreasing distinctly in size and height toward the posterior so that there is usually little continuity between the carina and the reclined cusp, which is deflected and terminally located and gives the posterior platform end a projecting outline. Remarks. This species can be differentiated from
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C. changxingensis by the asymmetric and projecting posterior end, much more reclined cusp, and more reduced and deflected anterior platform, although transitional forms are common. Occurrence. Upper Changhsingian. Clarkina postwangi (Tian) (Plate II, A, B, C) 1993b Neogondolella postwangi Tian, part, pl. 5, fig. 12. 1981 Neogondolella carinata Wang and Wang, in Zhao et al., part, p. 80, pl. VII, figs. 9, 10. Amended diagnosis. A Clarkina with a platform of the narrow-type, which is widest at the midlength where the platform tapers evenly towards both the anterior and posterior and is thus lenticular in outline; platform end narrowly rounded, and sometimes one or occasionally two shallow indentations present on the posterior-lateral margins, denticles decreasing in size and height and becoming progressively discrete toward the posterior so that there is usually little continuity between the carina and the reclined cusp. Remarks. Tian (1993b) erected this species without assigning the holotype and giving detailed description of the denticulation. Among his illustrated specimens, which are all from a single sample, i.e., HJ18-5 from Bed 18 and about 5m below the top of the Dalong Formation in the Jiangya section (Tian, 1993a,b, p. 139), only the specimen illustrated as pl. 5, figs. 12a, 12b (Tian, 1993b) is diagnostic, the other specimens are indistinguishable from specimens of C. changxingensis (ibid, pl. 5, figs. 3, 4, 11) and juvenile specimens of C. deflecta (ibid. figs. 1, 2). The holotype of this species is herein assigned and illustrated as Plate II, B. The specimens with one
PLATE IV All from the Permian–Triassic boundary interval at the Meishan section. Samples marked as CB*-25 are from Bed 25 of Zhang et al. (1995, 1996), which correlates with Bed 22 in Fig. 1. A, B: Clarkina aff.deflecta (Wang and Wang, 1981), A is upper view, ð70, CBIV-25=946129, B is oblique upper view, ð73, CBII-25=946185. C–G, H?: Clarkina meishanensis meishanensis Zhang et al., 1995, C–E upper views, ð80, from Wang (1995), F upper view, ð73, from CBIII-25=946184, G oblique upper view, ð66, from CBV-25=946181, H upper view, ð60, from CBII-25=946186. Ia, Ib: Clarkina parasubcarinata sp. nov., oblique upper view and upper view of a middle sized specimen, ð80, from Mc-42=MGL96032. Ja, Jb: Clarkina deflcta (Wang and Wang, 1981), oblique upper view and upper view of a middle-sized specimen, ð80, from Mc-43=MGL96033. Ka, Kb: Clarkina meishanensis zhangi subsp. nov., oblique upper view and upper view of a middle-sized specimen, the Holotype, ð80, from Mc-42=MGL96034. L–N: Clarkina changxingensis yini subsp. nov., all ð80; La, Mb and Na are respctively oblique lateral views of Lb, Ma and Nb, which are all upper views; L is the Holotype and from Mc-43=MGL96035, M and N are from MC-40=MGL96036, MGL96037.
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PLATE V
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or two shallow posterior-lateral indentations were previously misidentified as Neogondolella carinata, from which it can be easily distinguished by the denticulation. Occurrence. Upper Changhsingian. Clarkina subcarinata (Sweet) (Plate I, E; Plate II, I, K) 1973 Neogondolella carinata subcaranata Sweet, in Teichert et al., pp. 436–437, text-figure 16E–H, pl. 13, figs. 1–3, 12–17. 1981 Neogondolella subcarinata subcaranata Sweet, Wang and Wang, in Zhao et al., pl. V, figs. 1–5, 8, 9, 15, 16. 1994 Neogondolella subcarinata Sweet, morphotype 2, Orchard et al., part, p. 835, pl. 1, fig. 3, 4, 9. 1993b Neogondolella subcarinata Sweet, Tian, figs. 6–8. 1993b Neogondolella wangi Dai and Zhang, Tian, pl. 4, figs. 21, 22, 24a, 24b. Amended diagnosis. A Clarkina with a relatively wide and short platform that narrows abruptly near both the anterior and posterior ends of the element; denticles and the reclined cusp are largely fused as a continuous carina that keeps nearly the same height and often extends slightly beyond the posterior platform margin. In advanced forms the carina is less fused and decreases slowly in height until the higher and reclined cusp. Remarks. This species is the predecessor of Clarkina parasubcarinata sp. nov., from which it can be distinguished by the denticulation. Occurrence. Lower Changhsingian.
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Clarkina wangi (Zhang) (Plate III, J, K) 1987 Gondolella wangi Zhang, pl. 1, fig. 4. 1981 Neogondolella subcarinata elongata Wang and Wang, in Zhao et al., p. 80, pl. VI, figs. 1–5. 1993b Neogondolella wangi Dai, Tian and Zhang, Tian, pl. 4, figs. 23a, 23b. Amended diagnosis. A Clarkina with a platform of the narrow-type, widest at the midlength of the posterior and middle platform where the platform tapers to both the anterior and posterior and is thus lenticular in outline; denticles and the reclined cusp are largely fused as a continuous carina that keeps nearly the same height, extends beyond the posterior platform margin and thus makes the platform end projectively pointed. In advanced forms, the carina is less fused and decreases slowly in height until the reclined cusp. Remarks. This species is the predecessor of Clarkina postwangi, from which it can be easily distinguished by the denticulation. Occurrence. Lower Changhsingian.
Acknowledgements The authors acknowledge the support from the Chinese Academy of Science (Grant K2951-B1409) and the National Nature Science Foundation of China (Grant 49672092 and 49632070). The authors thank Dr. Jin Yugang for kind encouragement and the possibility to study the collection from Iran, Dr. Spencer G. Lucas and Dr. Yin Hongfu for kind encouragement and critical reading of the manuscript. Mr. Mao Yongqiang is thanked for the SEM photography.
PLATE V All are from the Permian–Triassic boundary interval at the Meishan section. Samples marked as CB*-26 and CB*-29 are respectively from Bed 25 and Bed 29 of Zhang et al. (1995, 1996), which correlate respectively with Bed 23 and the bed overlying Bed 24 in Fig. 1. A, D, G, N: Clarkina zhejiangensis Mei, 1996; A ð100; D ð80; G ð60; N ð80; all upper views, from Wang (1995), who reported N occurring in the upper part of Boundary Bed 1 (equivalent to Bed 23 in Fig. 1), and A, D, G occurring in the Boundary Bed 2 (equivalent to Bed 24 in Fig. 1). B, E, L, M?, O: Clarkina aff.deflecta (Wang and Wang, 1981); B ð80; E ð80; L ð60; M ð80; O ð50; all are upper views and from Wang (1995), who reported B occurring in the Boundary Bed 2 (equivalent to Bed 24 in Fig. 1), and E, L and M occurring in the upper part of Boundary Bed 1 (equivalent to Bed 23 in Fig. 1). C: Clarkina aff.meishanensis meishanensis Zhang et al., 1995, ð121, oblique upper view, from CBIII-29=946142. F, H–K, P?: Clarkina meishanensis meishanensis Zhang et al., 1995; F ð80; H the Holotype, ð120; I ð100; J ð87; K ð120; P ð80; F, H–K are oblique upper views, P is upper view; F and P are from CBV-26=946168, 946174; H–K are from CBIII-26=946146, 946145, 946176, 946175.
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