西藏南部聂拉木志留纪笔石新材料_陈旭.pdf

收稿日期:2021-10-09;改回日期:2022-11-03;录用日期:2022-11-06*第二次青藏高原科学考察研究(2019QZKK0706)、中国科学院战略性先导科技专项(B 类)(XDB26000000)、国家自然科学基金(42102013)和中国地质科学院地质调查项目(DD20221829)联合资助。*通讯作者:陈旭,研究员,e-mail: 古生物学报,61(4):525540(2022年12月)Acta Palaeontologica Sinica,61(4):525540(December 2022)亮点论文 DOI:10.19800/ki.aps.2021059 西藏南部聂拉木志留纪笔石新材料*陈 旭1,2*于深洋3 方 翔1 李文杰1 Lucy Muir 4 张元动1,5 1 现代古生物学和地层学国家重点实验室,中国科学院南京地质古生物研究所,南京 210008;2 浙江省核工业地质调查队院士工作站,浙江湖州 313000;3 曲阜师范大学地理与旅游学院,山东日照 276826;4 Department of Natural Sciences,Amgueddfa CymruNational Museum Wales,Cathays Park,Cardiff CF10 3NP,UK;5 中国科学院大学,北京 100049 提要 聂拉木是西藏南部志留纪含笔石地层(石器坡组)的主要产地。近期在该地亚来村新发现一批笔石标本,包括Normalograptus sp.、Glyptograptus sp.、Campograptus lobiferus、C.cf.lobiferus、C.cf.obtusus、C.?circularis、Lituigraptus cf.convolutus、Rastrites cf.perfectus、Stimulograptus sedgwickii、Streptograptus sp.和Torquigraptus decipiens。该组合面貌确定其属于志留系兰多维列统埃隆阶上部Lituigraptus convolutus带至Stimulograptus sedgwickii带。这一新材料的发现,使西藏南部的志留纪地层得以作全球对比。关键词 志留系 聂拉木 西藏 笔石 全球对比 中文引用 陈旭,于深洋,方翔,李文杰,Lucy Muir,张元动,2022.西藏南部聂拉木志留纪笔石新材料.古生物学报,61(4):525540.DOI:10.19800/ki.aps.2021059 英文引用 Chen Xu,Yu Shen-yang,Fang Xiang,Li Wen-jie,Lucy Muir,Zhang Yuan-dong,2022.New Silurian graptolite material from Nyalam,southern Xizang(Tibet),China.Acta Palaeontologica Sinica,61(4):525540.DOI:10.19800/ki.aps.2021059 New Silurian graptolite material from Nyalam,southern Xizang(Tibet),China CHEN Xu1,2,YU Shen-yang3,FANG Xiang1,LI Wen-jie1,Lucy Muir4,ZHANG Yuan-dong1,5 1 State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008,China;2 Academician Studio,Zhejiang Nuclear Industry Geological Survey Team,Huzhou 313000,Zhejiang,China;3 School of Geography and Tourism,Qufu Normal University,Rizhao 276826,Shandong,China;4 Department of Natural Sciences,Amgueddfa CymruNational Museum Wales,Cathays Park,Cardiff CF10 3NP,UK;5 University of Chinese Academy of Sciences,Beijing 100049,China Abstract Silurian graptolite-bearing strata in Nyalam County are one of the few known sources of Silurian grapto-lites in southern Xizang(Tibet).Recent graptolite collections from the Shiqipo Formation at Yalai Village,Nyalam County,contain Normalograptus sp.,Glyptograptus sp.,Campograptus lobiferus,C.cf.lobiferus,C.cf.obtusus,C.?circularis,Lituigraptus cf.convolutus,Rastrites cf.perfectus,Stimulograptus sedgwickii,Streptograptus sp.and Tor-quigraptus decipiens.This assemblage indicates a late Aeronian(Llandovery)age(Lituigraptus convolutus to Stimu-526 古 生 物 学 报 61 卷 lograptus sedgwickii biozones).This new finding provides the potential for the correlation of Silurian strata between Xizang(Tibet)and other parts of the world.Key words Silurian,Nyalam,Xizang(Tibet),graptolites,global correlation INTRODUCTION Nyalam is a county in the Himalayan Mountains,situated between Mount Qomolangma(Mount Everest)and Mount Shishapangma in southern Xizang(Tibet),China.The county borders Nepal,and the county town lies on the major passway(National Highway 318)from Lhasa to Kathmandu,the capital of Nepal(Fig.1).This is an high-altitude area,and has been difficult for scien-tists to access.Since the 1970s,geologists have been able to investigate and collect Ordovician and Silurian fossils in the area many times,and to establish the strat-igraphic sequence framework.From 1966 to 1968,a large-scale scientific expedi-tion to Xizang organized by the Chinese Academy of Sciences explored mostly the Mount Qomolangma area.As a result of the expedition,Mu et al.(1973)first pub-lished a brief stratigraphic report that included the Silu-rian strata of the Shiqipo Group in the area.This group was formally described by Wang(1974),and was di-vided into a Lower Formation of silty shale,sandstone and limestone,and an Upper Formation of limestone,argillaceous limestone and sandstone,with a list of Llandovery graptolites(identified by Mu)from the silty shale and a list of Wenlock graptolites from the argilla-ceous limestone.The Llandovery strata have been given different lithostratigraphic names with lists of different graptolite species(Yang,1985);among them,the name“Lower Formation of the Shiqipo Group”in the Nyalam area was mostly accepted(Lin et al.,1984).The Lower Formation was later redefined as the Shiqipo Formation,while the Upper Formation was named the Pulu For-mation(Mu and Chen,1984).The graptolites of the Shiqipo Formation were first systematically described by Mu and Ni(1985),with additional material described by Mu and Chen(1984).Unfortunately,the description of the graptolites from the Shiqipo Formation was rather too simple,with poor illustrations,likely owing to the poor preservation of the specimens.In the summer of 2016,four of the authors(Yu,Fang,Li and Zhang)re-collected some graptolites from the Shiqipo For-mation on the slope of the hill in the Yalai section(Fig-ure 1B).All these graptolites were examined and identi-fied by Chen Xu.Although most of these graptolites from the Shiqipo Formation were not well-preserved due to severe weathering,some identifiable specimens of biostratigraphic significance were obtained,which are studied and illustrated in the present paper.The present study also includes a few identifiable specimens pub-lished by Mu and Ni(1985).The graptolite genera and species of the Shiqipo Formation are listed in Table 1.The graptolite fauna suggests a Lituigraptus con-volutus to Stimulograptus sedgwickii Biozone(Aeroni-an,Llandovery)age.The majority of the graptolites are from these two biozones,and include both the epony-mous species.Most species are common constituents of contemporary graptolite faunas in other parts of the world,particularly in Europe and North America,al-lowing correlation of the Shiqipo Formation with coeval strata elsewhere.Normalograptus sp.and Streptograptus sp.might have been obtained from loose rocks that be-came mixed with collection AGQ-35 near the outcrop.The Shiqipo Formation may represent a temporal range longer than that of the L.convolutus Biozone to S.sedgwickii Biozone.SYSTEMATIC PALEONTOLOGY All figured specimens are deposited in the type and figured collection of the Nanjing Institute of Geology and Palaeontology(NIGP),Chinese Academy of Sciences.Infraorder Neograptina torch et al.,2011 Family Normalograptidae torch and Serpagli,1993 Genus Normalograptus Legrand,1987,emend Melchin et al.,2011 Type species Climacograptus scalaris normalis Lapworth,1877 Normalograptus sp.(Figs.2-J,3-D)Material Specimens NIGP175440 and 175447.Description The tubarium is 24 mm long with a proximal width of 0.75 mm across the first thecal pair.A short virgella(1.16 mm long)projects downwards.The tubarium increases gradually to a maximum width of 1.5 mm at the tenth thecal pair,and this width is retained to the end of the tubarium;thus,the tubarium looks uni-form in width.The thecae are of typical climacograptid type with parallel supragenicular walls and very narrow apertures.There are thirteen thecae per 10 mm.Remarks This graptolite is similar to Nor-malograptus rectangularis(MCoy,1850)in general aspects,but differs in having more closely spaced thecae.However,most normalograptids are from the Rhudda-nian Stage.4期 陈旭等:西藏聂拉木志留纪笔石新材料;Chen et al.:New Silurian graptolite material from Nyalam,Tibet 527 Horizon and locality Shiqipo Formation at Yalai,Nyalam,southern Xizang.Family Retiolitidae Lapworth,1873,emend.Genus Glyptograptus Lapworth,1873,emend.Melchin et al.,2011 Type species Diplograpsus tamariscus Nichol-son,1868 Glyptograptus sp.(Fig.2-D)Material One specimen,NIGP175439.Description Only one poorly preserved specimen with a tubarium length of about 18 mm and a tubarium width of 2.4 mm.A short virgella extends downwards.The thecae are of glyptograptid type,which is observa-ble only in the middle part of the tubarium.There are five thecae per 5 mm in the middle of the tubarium.Remarks The single,incomplete specimen is similar to Glyptograptus incertus Elles and Wood,1907 in general aspects.The latter species was originally rec-orded from the Stimulograptus sedgwickii Biozone in southern Scotland and the Lake District,England(Elles and Wood,1907),and has subsequently been reported from the Lituigraptus convolutus Biozone to S.sedg-wickii Biozone of southern Scotland(Packham,1962)and the Lake District(Hutt,1975).Horizon and locality Shiqipo Formation at Yalai,Nyalam,southern Xizang.Superfamily Monograptoidea Lapworth,1873 Family Monograptidae Lapworth,1873 Genus Campograptus Obut,1949,emend.torch,1998 Type species Monograptus convolutus com-munis Lapworth,1876 Campograptus lobiferus(MCoy,1850)(Figs.2-B,2-E,2-F,2-H,2-I,2-O,2-U,3-C,3-F,3-H,3-I)1850 Graptolites lobiferus MCoy,p.270.1855 Graptolites lobiferus MCoy;MCoy,p.4,pl.1B,fig.3.1868 Graptolites lobiferus MCoy;Nicholson,p.532,pl.19,fig.30,non figs.27 and 28.1876a Monograptus lobiferus(MCoy);Lapworth,p.499,pl.20,fig.1a,b and d,non fig.1c.1876b Monograptus lobiferus(MCoy);Lapworth,p.5,pl.1,fig.25.1892 Monograptus lobiferus(MCoy);Trnquist,p.18,pl.1,fig.37,(non fig.36),pl.2,figs.13,non fig.4,non fig.5.1897 Monograptus lobiferus(MCoy);Perner,pp.1617,plate 10,fig.20,plate 11,figs.13,text-fig.16.1913 Monograptus lobiferus(MCoy);Elles and Wood,p.448,pl.45,fig.1 af,text-fig.308ae.1945 Monograptus lobiferus(MCoy);Waterlot,p.83,pl.38,fig.384.1955 Monograptus lobiferus(MCoy);Bulman,p.V49,text-fig.32,fig.2a and b.1967 Monograptus lobiferus(MCoy);Obut et al.,p.93,pl.10,figs.3,4.1968 Monograptus lobiferus(MCoy);Obut et al.,p.98,pl.24,fig.7.1970 Monograptus lobiferus(MCoy);Churkin and Carter,p.42,pl.3,figs.12,21.1970 Monograptus lobiferus(MCoy);Rickards,text-fig.16.5.1971 Monograptus(Monogra.)lobiferus,(MCoy);Schauer,p.58,pl.36,figs.6 and 7.1975 Monograptus lobiferus(MCoy);Hutt,p.94,pl.18,figs.1,3,pl.19,fig.6,text-fig.24,fig.4a,b(see for further references).1975 Monograptus lobiferus harpago Trnquist;Bjerreskov,p.67,fig.20A,non pl.10E.1981 Monograptus lobiferus lobiferus(MCoy);Bjerreskov,p.41,pl.4,fig.1.1986 Streptograptus?lobiferus(MCoy);Wang and Xue,p.42,pl.1,fig.8,pl.2,fig.9.1988 Monograptus lobiferus(MCoy);torch,pp.37,38,pl.12,figs.1,2,6,text-figs.4E,M.1991 Monograptus lobiferus(MCoy);Loydell,text-fig.2.1993 Monograptus lobiferus(MCoy,1850);torch and Serpagli,p.38,pl.7,fig.6,text-fig.B and J.1998 Monograptus lobiferus(MCoy);Gutirrez-Marco and torch,fig.7a.1998 Monograptus lobiferus(MCoy);torch,p.244,pl.12,figs.7,8,text-fig.10,fig.6AC.2001 Campograptus lobiferus cf.harpago(Trnquist);torch,p.65,pl.4,fig.1,text-fig.9,fig.2.2003 Campograptus lobiferus(MCoy);Chopey-Jones et al.,p.78,figs.2,3JL,4AC,F.2009 Campograptus lobiferus(MCoy);Loydell and Maletz,pp.286288,pl.8,text-figs.1D,4.Material Specimens NIGP175431175435,175437,175438.Description The studied material includes eight long,straight tubarium fragments,the longest being ap-proximately 96 mm.The proximal ends of the tubaria are not preserved,unfortunately.The tubaria exhibit uniform widths of 1.55 to 2.0 mm in different portions.However,the width of a scalariform specimen(NIGP175436;Fig.2K,3J)is up to 2.77 mm,indicating that the tubaria may be wider laterally.The thecae possess broad prothecal bases,simply hooked metathecae and rounded apertures;in other words,the metathecae are initially broader and become more triangulate towards the apertures.The apertures face proximally or proximo-dorsally.There are eight to seven thecae per 10 mm.Remarks This species has been recorded from the Lituigraptus convolutus Biozone of Scotland,Wales,northern England and Ireland(Elles and Wood,1913;Chopey-Jones et al.,2003);the Pribylograptus lepto-theca Biozone of Bohemia(torch,1998);and the Litu-igraptus convolutus Biozone of Scania(Chopey-Jones et al.,2003)and Bornholm,Denmark(Bjerreskov,1975).It also occurs in the L.convolutus Biozone of Alaska(Churkin and Carter,1970),Greenland(Bjerreskov,1975),Kirghizia(now called Kyrgyzstan;Obut,1949),North Africa(Willefert,1963),Portugal(Romariz,1962),and Norilsk,Russia(Obut et al.,1968).The pre-528 古 生 物 学 报 61 卷 sent form occurs in the Stimulograptus sedgwickii Bi-ozone of Spain(Haberfelner,1931)and the same bi-ozone at Hskov,Czech Republic(Chopey-Jones et al.,2003).In Hunan Province,China,this species was re-ported in the interval from the Coronograptus leei Bi-ozone to the Stimulograptus sedgwickii Biozone(Wang and Xue,1986).Horizon and locality Shiqipo Formation at Ya-lai,Nyalam,southern Xizang.Campograptus cf.obtusus(Rickards,1970)(Figs.2-G,3-E)cf.1970 Monograptus communis obtusus Rickards,pp.8586,pl.8,fig.4,text-fig.18,fig.12.cf.1998 Campograptus obtusus(Rickards);torch,p.242,pl.10,figs.3,4,text-fig.10,fig.3A,B.Material Specimen illustrated by Mu and Ni(1985,pl.2,fig.7,NIGP64210).Description The distal fragment is 27 mm long and 1.51.7 mm wide.The tubarium is slightly curved dorsally.The metathecae are hooked and triangular in profile.The ventral metathecal walls are inclined at a very low angle to the tubarium axis.The coiled aper-tures occupy one-third of the tubarium width,and face dorsal-proximally to the tubarium.No apertural spines are visible.There are eight to seven thecae per 10 mm.Remarks The specimen in the collection of Mu and Ni(1985,pl.2,fig.7,NIGP64210)resembling this taxon was reported to be on the same slab as“Pristi-ograptus gregarius(Lapworth)”,but was not described.We checked the specimens stored in NIGPAS;unfortu-nately,the identification of“Pristiograptus gregarius(Lapworth)”was based on poorly preserved specimens,and we do not include that material in the present study.Campograptus obtusus occurs in the Stimulograptus sedgwickii Biozone in Britain(Rickards,1970)and the Lituigraptus convolutus Biozone at Tma,Czech Re-public(torch,1998).Horizon and locality Shiqipo Formation at Ya-lai,Nyalam,southern Xizang.Campograptus?circularis(Elles and Wood,1913)(Figs.2-R,3-M)1913 Monograptus circularis Elles and Wood,pp.479480,pl.48,fig.9a,b.1944 Spirograptus circularis(Elles and Wood);Pibyl,pp.2122,pl.7,figs.6,7.1982 Monograptus circularis Elles and Wood;Lenz,p.65,fig.21i.Material Specimen NIGP175451.Description The slender,convolute tubarium forms a low-relief spiral,usually of two to three whorls.The diameter of the coiled tubarium may reach 27 mm.The proximal end of the tubarium is only 0.86 mm wide,increasing gradually to the maximum width of 1.4 mm after seven thecae.The width then remains constant to the end of the tubarium.The thecae are of monograptid type with hooked apertures in the proximal portion,with more rounded apertures distally.There are approximately ten thecae in 10 mm.Remarks The thecae of the present species are slightly different from those of typical campograptids,which are characterized by round apertures and paired apertural spines.The present species occurs in the Stimulograptus sedgwickii Biozone in Scotland(Elles and Wood,1913),Bohemia(Pibyl,1944),and the Yukon of Canada(Lenz,1982).Horizon and locality Shiqipo Formation at Ya-lai,Nyalam,southern Xizang.Genus Lituigraptus Ni,1978,emend.torch,1998 Type speci