Refining Middle–Upper Ordovician Conodont Biostratigraphy in the Hatuke Creek Section, Western North China Craton: Evidence from Bedding Plane Assemblages and Implications for Shale Gas Exploration

Abstract

The 128.6-m-thick, shale-dominated Klimoli, Wulalike and Lashizhong formations exposed at the Hatuke Creek Section in the Zhuozishan area of Inner Monglia, North China, have been investigated for conodonts. Detailed stratigraphical collections of conodonts preserved on bedding planes from graptolitic shales, supplemented by additional discrete conodonts acid-leached from limestones, enable a refinement of the conodont biostratigraphic scheme at this section. Four successive conodont biozones, ranging in age from mid Darriwilian to late Sandbian (Stage slices Dw2–Sa2), are identified: the Dzikodus tablepointensis Biozone, the Eoplacognathus suecicus Biozone, the Pygodus serra Biozone, and the Pygodus anserinus Biozone, in ascending order. New sub-biozones, based on morphotypes of the biozonal index species, are proposed for the Pygodus serra and Pygodus anserinus biozones, providing alternatives when the traditional sub-biozones are unrecognizable. The biozonation is clearly correlated with the coeval Baltoscandian, South American and South China reference standard successions. The diverse preservation states of conodont bedding plane assemblages suggest that the alteration of conodonts in graptolitic shales represents a diagenetic process, challenging the prevailing hypothesis of pre-diagenetic dissolution. This study highlights the crucial role of previously overlooked conodont bedding plane assemblages in correlating Ordovician slope/basin facies shales, which holds great potential for marine shale gas exploration.

Keywords

conodont biostratigraphy / Darriwilian / Sandbian / graptolitic shales / shale gas / Zhuozishan area / geology

References

[1] Abaimova G P. New Early Ordovician Conodonts from the Southeastern Part of the Siberian Platform. Paleontological Journal, 1971, 5(4): 486-493

[2] Albanesi G L. Taxonomia de Conodontes de las Secuencias Ordovicicas Del Cerro Potrerillo, Precordillera Central De San Juan, R. Argentina. Academia Nacional de Ciencias, Córdoba, 1998, 12: 101-253

[3] Albanesi G L, Ortega G. La Biofacies Periodon-Pygodus (Conodonta) en las Secuencias Euxínicas del Ordovícico de la Precordillera Argentina. VII Congreso Argentino de Paleontología y Bioestratigrafía (Bahía Blanca), Octubre, 199879

[4] Albanesi G L, Barnes C R. Subspeciation within a Punctuated Equilibrium Evolutionary Event: Phylogenetic History of the Lower–Middle Ordovician Paroistodus originalis-P. horridus Complex (Conodonta). Journal of Paleontology, 2000, 74(3): 492-502

[5] Albanesi G L, Ortega GMontenari M. Conodont and Graptolite Biostratigraphy of the Ordovician System of Argentina. Stratigraphy & Timescales, 2016, Amsterdam. Elsevier61-121

[6] An T X. Early Palaeozoic Conodonts from South China, 1987, Beijing. Peking University Publishing House238(in Chinese)

[7] An T X, Zheng Z C. The Conodonts of the Marginal Areas around the Ordos Basin, North China, 1990, Beijing. Science Press201(in Chinese with English Summary)

[8] An T X. Conodonts and Conodont Biostratigraphy of the Middle and Upper Ordovician in North China, 1993, Tsukuba. University of Tsukuba

[9] Armstrong H A, Clarkson E N K, Owen A W. A New Lower Ordovician Conodont Faunule from the Northern Belt of the Southern Uplands. Scottish Journal of Geology, 1990, 26(1): 47-52.

[10] Bagnoli G, Stouge S. Lower Ordovician (Billingenian-Kunda) Conodont Zonation and Provinces Based on Sections from Horns Udde, North Öland, Sweden. Bollettino della Società Paleontologica Italiana, 1997, 35: 109-163

[11] Barnes C R, Williams S H. Conodonts from the Ordovician–Silurian Boundary Stratotype, Dob’s Linn, Scotland. Bulletin of the British Museum, Natural History Geology, 1988, 43: 31-39

[12] Bauer J A. Conodonts from the Bromide Formation (Middle Ordovician), South-Central Oklahoma. Journal of Paleontology, 1994, 68(2): 358-376.

[13] Bergström S M. Conodont biostratigraphy of the Middle and Upper Ordovician of Europe and Eastern North America. Geological Society of America Memoir, 1971, 127: 83-162.

[14] Bergström S M. Biogeography, Evolutionary Relationships, and Biostratigraphic Significance of Ordovician Platform Conodonts. Fossils and Strata, 1983, 15: 35-58.

[15] Bergström S M. Biostratigraphic Integration of Ordovician Graptolite and Conodont Zones—A Regional Review. Geological Society, London, Special Publications, 1986, 20(1): 61-78.

[16] Bergström S M, Finney S C, Chen X, et al. . A Proposed Global Boundary Stratotype for the Base of the Upper Series of the Ordovician System: The Fågelsång Section, Scania, Southern Sweden. Episodes, 2000, 23(2): 102-109.

[17] Bergström S M. Middle and Upper Ordovician Conodonts from the Fågelsång GSSP, Scania, Southern Sweden. GFF, 2007, 129(2): 77-82.

[18] Bergström S MEbbestad J O R, Wickström L M, Högström A E S. The Ordovician Conodont Biostratigraphy in the Siljan Region, South-Central Sweden: A Brief Review of an International Reference Standard. 9th Meeting of the Working Group on Ordovician Geology of Baltoscandia, Field Guide and Abstracts, 200726-41

[19] Bergström S M, Chen X, Gutiérrez-Marco J C, et al. . The New Chronostratigraphic Classification of the Ordovician System and Its Relations to Major Regional Series and Stages and to δ¹³C Chemostratigraphy. Lethaia, 2009, 42(1): 97-107.

[20] Bergström S M, Wang Z H, Goldman D, et al. Chen X, Zhang Y D, Goldman D, et al. . Relations between Darriwilian and Sandbian Conodont and Graptolite Biozones. Darriwilian to Sandbian (Ordovician) Graptolites from Northwest China, 2017, Amsterdam. Elsevier39-78.

[21] Chen J Y, Zhou Z Y, Lin Y K, et al. . Ordovician Biostratigraphy of Western Ordos. Memoirs of Nanjing Institute of Geology and Palaeontology, Academica Sinica, 1984, 20: 1-31(in Chinese with English Summary)

[22] Chen J Y, Zou X P. Ordovician Cephalopods from the Ordos Area, China. Memoirs of Nanjing Institute of Geology and Palaeontology, Academica Sinica, 1984, 20: 33-112(in Chinese with English Summary)

[23] Chen X, Fan J X, Zhang Y D, et al. . Subdivision and Delineation of the Wufeng and Lungmachi Black Shales in the Subsurface Areas of the Yangtze Platform. Journal of Stratigraphy, 2015, 39(4): 351-358(in Chinese with English Abstract)

[24] Chen X, Fan J X, Wang W H, et al. . Stage-Progressive Distribution Pattern of the Lungmachi Black Graptolitic Shales from Guizhou to Chongqing, Central China. Science China Earth Sciences, 2017, 60(6): 1133-1146.

[25] Chen X, Zhang Y D, Wang Z H, et al. . Biostratigraphy. Darriwilian to Sandbian (Ordovician) Graptolites from Northwest China, 2017, Amsterdam. Elsevier7-38.

[26] Chen X, Shen Y J, Mu Q Y, et al. . Why are the Qinling Mountains Significant to China?. Journal of Earth Science, 2025, 36(1): 357-363.

[27] Cho D L, Lee S R, Koh H J, et al. . Late Ordovician Volcanism in Korea Constrains the Timing for Breakup of Sino-Korean Craton from Gondwana. Journal of Asian Earth Sciences, 2014, 96: 279-286.

[28] Di L J, Xie G C. Queries about Helan Aulacogen. Lithologic Reservoirs, 2008, 20(2): 16-2136 (in Chinese with English Abstract)

[29] Ding L S, Chen M J, Zhang J H, et al. Wang C, et al. . Cambrian to Ordovician Conodonts. Conodonts of Lower Yangtze Valley—An Indexes to Biostratigraphy and Organic Metamorphic Maturity, 1993, Beijing. Science Press155-214(in Chinese with English Summary)

[30] Dong Y P, Li W, Zhang F F, et al. . Formation and Evolution of the Helan Mountain in the Northern Section of the North-South Tectonic Belt. Journal of Northwest University (Natural Science Edition), 2021, 51(6): 951-968(in Chinese with English Abstract)

[31] Du P D, Zhao Z X, Huang Z B, et al. . Discussion on Four Conodont Species of Histiodella from Tarim Basin and Their Stratigraphic Implication. Acta Micropalaeontologica Sinica, 2005, 22(4): 357-369(in Chinese with English Abstract)

[32] Dzik J. Remarks on the Evolution of Ordovician Conodonts. Acta Palaeontologica Polonica, 1976, 21(4): 395-455

[33] Dzik J. Relationships between Ordovician Baltic and North American Midcontinent Conodont Faunas. Fossils and Strata, 1983, 15: 59-85.

[34] Epstein A G, Epstein J B, Harris L D. Conodont Color Alteration—An Index to Organic Metamorphism. U.S. Geological Survey Professional Paper, 1977, 995: 1-27

[35] Ethington R L. Conodonts of the Ordovician Galena Formation. Journal of Paleontology, 1959, 33(2): 257-292

[36] Fåhræus L E. Lower Viruan (Middle Ordovician) Conodonts from the Gullhögen Quarry, Southern Central Sweden. Sveriges Geologiska Undersökning C, 1966, 601: 1-40

[37] Fan J J, Jing X C, Ma Z R, et al. . On the Evolution and Biostratigraphic Significance of the Middle – Late Ordovician Conodont Pygodus Lamont et Lindström and Periodon Hadding. Acta Micropalaeontologica Sinica, 2024, 41(1): 28-44(in Chinese with English Abstract)

[38] Fan R Y, Zong R W, Gong Y M. Behavioural Imprint of the Ordovician Radiation: Evidence from Middle–Upper Ordovician Deep-Sea Trace Fossils in Western Inner Mongolia, North China. Palaeogeography, Palaeoclimatology, Palaeoecology, 2021, 563: 110174.

[39] Fei A W. Trace Fossil Assemblages and Palaeoenvironment of Middle Ordovician Gongwusu Formation, Zhuozishan, Inner Mongolia. Geoscience, 2000, 14(3): 366-372(in Chinese with English Abstract)

[40] Fei A W. Study of Trace Fossil Assemblage and Paleoenvironment of Middle Ordovician Lashizhong Formation, Ordos Basin. Geological Journal of China Universities, 2001, 7(3): 278-287(in Chinese with English Abstract)

[41] Fei A W, Liu C L, Gan J, et al. . Bioturbation Structures and Paleogeography of Mixed Deposits of the Lower Ordovician Sandaokan Formation, Ordos Basin. Geology in China, 2004, 31(4): 347-355(in Chinese with English Abstract)

[42] Feltes N A, Albanesi G L, Bergström S M. Conodont Biostratigraphy and Global Correlation of the Middle Darriwilian–Lower Sandbian (Ordovician) Las Aguaditas Formation, Precordillera of San Juan, Argentina. Andean Geology, 2016, 43(1): 60-85.

[43] Feng Z Z, Peng Y M, Jin Z K, et al. . Lithofacies Paleogeography of the Cambrian and Ordovician in China, 2004, Beijing. Petroleum Industry Press233(in Chinese with English Summary)

[44] Ferretti A, Bergström S M. Middle–Upper Ordovician Conodonts from the Ffairfach and Golden Grove Groups in South Wales, United Kingdom. Historical Biology, 2022, 34(3): 462-485.

[45] Fu L P, Hu Y X, Zhang Z F, et al. . The Mark of the Ecology of Sedimentarial Environment in Middle and Upper Ordovician at Ordos Basin. Northwest Geoscience, 1993, 14(2): 1-88(in Chinese with English Abstract)

[46] Fu S T, Fu J H, Xi S L, et al. . Geological Characteristics of Ordovician Marine Shale Gas in the Ordos Basin and Its Prospects. China Petroleum Exploration, 2021, 26(2): 33-44(in Chinese with English Abstract)

[47] Gao Z Z, Luo S S, He Y B, et al. . Middle Ordovician Isobathic Deposits in the Western Margin of Ordos Area. Acta Sedimentologica Sinica, 1995, 13(4): 16-26(in Chinese with English Abstract)

[48] Golding M L, McMillan R. The Impacts of Diagenesis on the Geochemical Characteristics and Color Alteration Index of Conodonts. Palaeobiodiversity and Palaeoenvironments, 2021, 101(3): 803-821.

[49] Goldman D, Leslie S A, Nõlvak J, et al. . The Global Stratotype Section and Point (GSSP) for the Base of the Katian Stage of the Upper Ordovician Series at Black Knob Ridge, Southeastern Oklahoma, USA. Episodes, 2007, 30(4): 258-270.

[50] Goldman D, Mitchell C E, Maletz J, et al. . Ordovician Graptolites and Conodonts of the Phi Kappa Formation in the Trail Creek Region of Central Idaho: A Revised, Integrated Biostratigraphy. Acta Palaeontologica Sinica, 2007, 46: 155-162Suppl.

[51] Goldman D, Sadler P M, Leslie S A, et al. . The Ordovician Period. Geologic Time Scale 2020, 2020, Amsterdam. Elsevier631-694.

[52] Goldman D, Leslie S A, Liang Y, et al. . Ordovician Biostratigraphy: Index Fossils, Biozones and Correlation. Geological Society, London, Special Publications, 2023, 532(1): 31-62.

[53] Graves R W, Ellison S P. Ordovician conodonts of the Marathon basin, Texas. University of Missouri, School of Mines and Metallurgy, Bulletin of the Technical Series, 1941, 14: 1-26

[54] Guan S C, Che S Z. Stratigraphic System of the Zhuozhishan Mountains Area in Ih Ju League, Inner Mongolia. Acta Geologica Sinica, 1955, 35(2): 95-108(in Chinese)

[55] Hadding A R. Undre Dicellograptusskiffern i Skåne jämte Några Dågra Därmed Ekvivalenta Bildningar. Lunds Universitets Årsskrift, Ny Följd, Afdelning, 1913, 9(15): 1-902

[56] Hamar G. Preliminary Report on Conodonts from the Oslo-Asker and Ringerike Districts. Norsk Geologisk Tidsskrift, 1966, 46: 27-83

[57] Hao R L, Huang W H, Bo J, et al. . Fractal Characteristics and Main Controlling Factors of High-Quality Tight Sandstone Reservoirs in the Southeastern Ordos Basin. Journal of Earth Science, 2024, 35(2): 631-641.

[58] Heredia S, Mestre A, Soria T, et al. . The Ordovician Genus Pygodus (Conodont) in the Cuyania Terrane, Argentina. Geological Magazine, 2017, 154(5): 1105-1116.

[59] Heredia S, Mestre A, Gallardo M, et al. . Middle–Upper Ordovician Conodont Biostratigraphy of the Eastern Precordillera, San Juan, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina, 2024, 24(1): 217-232

[60] Jin H J, Li Y C, Fang G Q. Paleo-Abysmal Deposits and Ichnocoenoses in China, 2003, Beijing. Science Press231(in Chinese with English Summary)

[61] Jing X C, Zhou H R, Wang X L. Ordovician (Middle Darriwilian–Earliest Sandbian) Conodonts from the Wuhai Area of Inner Mongolia, North China. Journal of Paleontology, 2015, 89(5): 768-790. 898

[62] Jing X C, Zhou H R, Wang X L. Biostratigraphy and Biofacies of the Middle Darriwilian (Ordovician) Conodonts from the Laoshidan Section in the Western Margin of the North China Craton. Marine Micropaleontology, 2016, 125: 51-65.

[63] Jing X C, Zhou H R, Wang X L. Conodont Biostratigraphy of the Gongwusu Formation (Upper Ordovician) in the Wuhai Area of Inner Mongolia, North China. Paleontological Research, 2017, 21(2): 183-194.

[64] Jing X C, Zhou H R, Wang X L, et al. . A Review on Ordovician Conodont Biostratigraphy of the North China Plate and New Research Advances on Its Northwestern Margin. Earth Science Frontiers, 2020, 27(6): 199-212(in Chinese with English Abstract)

[65] Lamont A, Lindström M. Arenigian and Llandeilian Cherts Identified in the Southern Uplands of Scotland by Means of Conodonts, etc. Transactions of the Edinburgh Geological Society, 1957, 17(1): 60-70.

[66] Lee B S, Cho S H, Choh S J, et al. . Reassessment of the Serratognathus Bilobatus Conodont Biozone (Early Ordovician) of the Taebaek Group, Korea. Journal of Earth Science, 2025, 36(2): 373-381.

[67] Lee H Y. Conodonten aus dem Unteren und Mittleren Ordovizium von Nordkorea. Palaeontographica Abteilung A, 1975, 150(4–6): 161-186(in German with English Summary)

[68] Li R H. Trace Fossils and Ichnofacies of Middle Ordovician Gongwusu Formation, Zhuozishan, Inner Mongolia. Acta Palaeontologica Sinica, 1993, 32(1): 88-104145–148

[69] Li X D, Que Y, Huan Y Q. Deep-Water Channel Deposits of Contour Current in the Lower Part of Middle Ordovician Kelimoli Formation of Shixiagu Section in Zhuozishan Area, Western Margin of Ordos Basin. Journal of Palaeogeography (Chinese Edition), 2019, 21(2): 321-338. DOI: (in Chinese with English Abstract)

[70] Li X D, Chen H Y. Analysis of Paleocurrent Direction and Identification of Ponded Turbidity Current Deposits in Deep Water Environment: A Case Study of the Upper Ordovician Lashenzhong Formation in Zhuozishan Area, Ordos Basin. Acta Petrolei Sinica, 2020, 41(11): 1348-1365(in Chinese with English Abstract)

[71] Li X D, Chen H D, Chen H Y, et al. . Genesis Mechanism Analysis of Convolute Laminations of the Upper Ordovician Lashenzhong Formation in Western Margin of Ordos Basin. Journal of Palaeogeography (Chinese Edition), 2022, 24(6): 1130-1148(in Chinese with English Abstract)

[72] Li Z Y, Xie F, Hu T B, et al. . Gas Accumulation Model of Ordovician in the North Section of the Western Margin of the Ordos Basin. Petrochemical Industry Application, 2024, 43(1): 73-78(in Chinese with English Abstract)

[73] Lin C S, Yang Q, Li S T, et al. . Sedimentary Characters of the Early Paleozoic Deep Water Gravity Flow Systems and Basin Filling Style in the Helan Aulacogen, Northwest China. Geosciences, 1991, 5: 252-263

[74] Lin C S, Yang Q, Li S T. Sedimentary Filling Evolution of the Helan Aulacogen, Northwest China, 1995, Beijing. Geological Publishing House143(in Chinese with English Summary)

[75] Lin Y K. Ordosograptus—A New Graptolite Genus and Its Affinites. Acta Palaeontologica Sinica, 1980, 19(6): 475-481(in Chinese with English Summary)

[76] Lindström M. Conodonts from the Lowermost Ordovician Strata of South-Central Sweden. Geologiska Föreningen i Stockholm Förhandlingar, 1955, 76(4): 517-604.

[77] Lindström M. The Conodonts Described by A. R. Hadding, 1913. Journal of Paleontology, 1955, 29(1): 105-111

[78] Liu G C, Zi J W, Nie X M, et al. . Late Cambrian Magmatic Events in SW Yunnan and Implications for the Tectonic Reconstruction of Northern Gondwana. Journal of Earth Science, 2024, 35(5): 1407-1425.

[79] Liu H P, Bergström S M, Witzke B J, et al. . Exceptionally Preserved Conodont Apparatuses with Giant Elements from the Middle Ordovician Winneshiek Konservat-Lagerstätte, Iowa, USA. Journal of Paleontology, 2017, 91(3): 493-511.

[80] Liu Z M, Fu S Y, Wei L B, et al. . Sedimentary Evolution Characteristics and Paleoenvironmental Analysis of the Ordovician in the Western Margin of the Ordos Basin. Mineralogy and Petrology, 2024, 44(2): 177-193. DOI: (in Chinese with English Abstract)

[81] Löfgren A. Arenigian and Llanvirnian Conodonts from Jämtland, Northern Sweden. Fossils and Strata, 1978, 13: 1-129.

[82] Löfgren A. The Conodont Fauna in the Middle Ordovician Eoplacognathus pseudoplanus Zone of Baltoscandia. Geological Magazine, 2004, 141(4): 505-524.

[83] Lu Y H. Strata Issues of the Cambrian and Ordovician from Northwest China. Acta Geologica Sinica, 1954, 34(3): 311-318(in Chinese)

[84] Lyons P, Percival I G. Middle to Late Ordovician Age for the Jindalee Group of the Lachlan Fold Belt, New South Wales: Conodont Evidence and Some Tectonic Implications. Australian Journal of Earth Sciences, 2002, 49(5): 801-808.

[85] Mango M J, Ortega G, Albanesi G L. Conodont and Graptolite Biostratigraphy of the Lower–Middle Darriwilian (Middle Ordovician), Cerro Viejo of Huaco, Argentine Precordillera. Geological Journal, 2019, 54(6): 3349-3361.

[86] McMillan R, Golding M. Thermal Maturity of Carbonaceous Material in Conodonts and the Color Alteration Index: Independently Identifying Maximum Temperature with Raman Spectroscopy. Palaeogeography, Palaeoclimatology, Palaeoecology, 2019, 534: 109290.

[87] Meng X H, Ge M, Tucker M E. Sequence Sequence Stratigraphy, Sea-Level Changes and Depositional Systems in the Cambro-Ordovician of the North China Carbonate Platform. Sedimentary Geology, 1997, 114(1/2/3/4): 189-222.

[88] Mestre A. Conodont Biostratigraphy of the Uppermost San Juan Formation and the Lower Member of Los Azules Formation at Cerro La Chilca, San Juan Precordillera. Ameghiniana, 2012, 49(2): 185-197.

[89] Mestre A, Heredia S. Darriwilian Species of Histiodella (Conodonta) in the Argentine Precordillera. Alcheringa, 2012, 36(2): 141-150.

[90] Metcalfe I. Gondwana Dispersion and Asian Accretion: Tectonic and Palaeogeographic Evolution of Eastern Tethys. Journal of Asian Earth Sciences, 2013, 66: 1-33.

[91] Miller J F, Dattilo B F, Ethington R L, et al. . Polyfocal Photography of Conodonts and Other Microfossils Using Petrographic Microscopes. Annales de Paléontologie, 2015, 101(3): 179-184.

[92] Mu E Z. Strata Containing Graptolites of China, 1959, Beijing. Geological Publishing House75(in Chinese)

[93] Murphy J B, Nance R D, Johnston S T, et al. . Speculations on the Paleozoic Legacy of Gondwana Amalgamation. Gondwana Research, 2024, 129: 107-131.

[94] Murray S I, Stewart I R. Palaeogeographic Significance of Ordovician Conodonts from the Lachlan Fold Belt, Southeastern Australia. Historical Biology, 2001, 15(1/2): 145-170.

[95] Myrow P M, Chen J T, Snyder Z, et al. . Depositional History, Tectonics, and Provenance of the Cambrian-Ordovician Boundary Interval in the Western Margin of the North China Block. Geological Society of America Bulletin, 2015, 127(9/10): 1174-1193.

[96] Ortega G, Albanesi G L, Frigerio S E. Graptolite-Conodont Biostratigraphy and Biofacies of the Middle Ordovician Cerro Viejo Succession, San Juan Precordillera, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology, 2007, 245(1/2): 245-263.

[97] Ortega G, Albanesi G L, Banchig A L, et al. . High Resolution Conodont-Graptolite Biostratigraphy in the Middle – Upper Ordovician of the Sierra de la Invernada Formation (Central Precordillera, Argentina). Geologica Acta, 2008, 6(2): 161-180

[98] Ottone E G, Albanesi G L, Ortega G, et al. . Palynomorphs, Conodonts and Associated Graptolites from the Ordovician Los Azules Formation, Central Precordillera, Argentina. Micropaleontology, 1999, 45(3): 225-250.

[99] Pålsson C, Månsson K, Bergström S M. Biostratigraphical and Palaeoecological Significance of Graptolites, Trilobites and Conodonts in the Middle–Upper Ordovician Andersö Shale: An Unusual ‘Mixed Facies’ Deposit in Jämtland, Central Sweden. Transactions of the Royal Society of Edinburgh: Earth Sciences, 2002, 93(1): 35-57.

[100] Pander C H. Monographie der Fossilen Fische des Silurischen Systems der Russisch-Baltischen Gouvernements, 1856, St. Petersburg. Buchdruckerei der Kaiserlichen Akademie der Wissenschaften91(in German)

[101] Rasmussen J A, Stouge S. Baltoscandian Conodont Biofacies Fluctuations and Their Link to Middle Ordovician (Darriwilian) Global Cooling. Palaeontology, 2018, 61(3): 391-416.

[102] Repetski J E. Conodont Age Constraints on the Middle Ordovician Black Shale Within the Ames Structure, Major County, Oklahoma. Oklahoma Geological Survaey Circular, 1997, 100: 363-369

[103] Rong J Y, Zhan R B, Xu H K. The Oldest Known Strophomenoid from the Sandaokan Formation (Late Arenig, Ordovician) of Inner Mongolia, North China. Acta Palaeontologica Sinica, 1999, 38(1): 31-45

[104] Sergeeva S P. Conodonts from the Lower Ordovician of the Leningrad Region. Paleontologicheskiy Zhurnal, Akademiya Nauk SSSR, 1963, 2: 93-108

[105] Serra F, Albanesi G L, Ortega G, et al. . Biostratigraphy and Palaeoecology of Middle–Late Ordovician Conodont and Graptolite Faunas of the Las Chacritas River Section, Precordillera of San Juan, Argentina. Geological Magazine, 2015, 152(5): 813-829.

[106] Serra F, Feltes N A, Albanesi G L, et al. . High-Resolution Conodont Biostratigraphy from the Darriwilian Stage (Middle Ordovician) of the Argentine Precordillera and Biodiversity Analyses: A CONOP9 Approach. Lethaia, 2019, 52(2): 188-203.

[107] Stewart I, Nicoll R S. Fifteen Element Septimembrate Apparatus Structure of the Early Ordovician Conodont Oepikodus evae Lindström from Australia and Sweden. Courier Forschungsinstitut Senckenberg, 2003, 245: 361-387

[108] Stouge S S. Conodonts of the Middle Ordovician Table Head Formation, Western Newfoundland. Fossils and Strata, 1984, 16: 1-145.

[109] Stouge S. Middle Ordovician (Late Dapingian – Darriwilian) Conodonts from the Cow Head Group and Lower Head Formation, Western Newfoundland, Canada. Canadian Journal of Earth Sciences, 2012, 49(1): 59-90.

[110] Sun G F, Liu J P. Helan Aulacogen and Front Basin and Their Evolution. Oil and Gas Geology, 1983, 4(3): 236-245(in Chinese with English Abstract)

[111] Sun X, Liu C H, Duan R H. The Age and Geological Significance of Early Neoproterozoic Mafic Sills on the Eastern Margin of the North China Craton: Evidence from Zirconology. Earth Science, 2024, 49(9): 3122-3139. DOI: (in Chinese with English Abstract)

[112] Sweet W C, Bergström S M. Conodonts from the Pratt Ferry Formation (Middle Ordovician) of Alabama. Journal of Paleontology, 1962, 36(6): 1214-1252

[113] Sweet W C, Bergstrom S M. Ordovician Conodonts from Penobscot County, Maine. Journal of Paleontology, 1966, 40(1): 151-154

[114] Tian G, Yang M H, Song L J, et al. . New Understanding of Basement Structural Characteristics and Its Evolution Process in Ordos Basin. Earth Science, 2024, 49(1): 123-139. DOI: (in Chinese with English Abstract)

[115] Tolmacheva T, Holmer L, Popov L, et al. . Conodont Biostratigraphy and Faunal Assemblages in Radiolarian Ribbon-Banded Cherts of the Burubaital Formation, West Balkhash Region, Kazakhstan. Geological Magazine, 2004, 141(6): 699-715.

[116] Tolmacheva T J, Danelian T, Popov L E. Evidence for 15 M.y. of Continuous Deep-Sea Biogenic Siliceous Sedimentation in Early Paleozoic Oceans. Geology, 2001, 29(8): 755-758.

[117] Tolmacheva T Y, Degtyarev K E, Ryazantsev A V, et al. . Conodonts from the Upper Ordovician Siliceous Rocks of Central Kazakhstan. Paleontological Journal, 2009, 43(11): 1498-1512.

[118] Tolmacheva T Y, Degtyarev K, Popov L, et al. Gutiérrez-Marco J C, Rábano I, García-Bellido D, et al. . The Lower to Middle Ordovician Conodont Biostratigraphy of Northern Tian Shan (Western Part of the Kirgyz Range), Kyrgyzstan. Ordovician of the World, 2011, Madrid. Instituto Geológico y Minero de España589-596

[119] Tolmacheva T Y. Biostratigraphy and Biogeography of the Ordovician Conodonts from the Western Part of Central Asian Fold Belt, 2014, Saint Peterburg. VSEGEI Publishing House263(in Russian)

[120] Wan T F. An Outline of Chinese Geotectonics, 2004, Beijing. Geological Publishing House387(in Chinese)

[121] Wang H Q. Graptolites and Stratigraphy of the Ordovician Wulalik Formation in the Western Margin of North China, 2024, Nanjing. University of Chinese Academy of Sciences(in Chinese with English Abstract)

[122] Wang Z H, Luo K Q. Late Cambrian and Ordovician Conodonts from the Marginal Areas of the Ordos Platform, China. Bulletin of Nanjing Institute of Geology and Palaeontology, Academica Sinica, 1984, 8: 239-304(in Chinese with English Summary)

[123] Wang Z H, Qi Y P. Ordovician Conodonts from Drillings in the Taklimakan Desert, Xinjiang, NW China. Acta Micropalaeontologica Sinica, 2001, 18(2): 133-148. DOI: (in Chinese with English Abstract)

[124] Wang Z H, Bergström S M, Zhen Y Y, et al. . On the Integration of Ordovician Conodont and Graptolite Biostratigraphy: New Examples from Gansu and Inner Mongolia in China. Alcheringa: An Australasian Journal of Palaeontology, 2013, 37(4): 510-528.

[125] Wang Z H, Bergström S M, Zhen Y Y, et al. . Ordovician Conodonts from Dashimen, Wuhai in Inner Mongolia and the Significance of the Discovery of the Histiodella fauna. Acta Micropalaeontologica Sinica, 2013, 30(4): 323-343(in Chinese with English Abstract)

[126] Wang Z H, Wu R C, Bergström S M. Ordovician Conodonts from the Lunnan Area of Northwestern Taklimakan Desert, Xinjiang, China, with Remarks on the Evolution of Pygodus. Acta Palaeontologica Sinica, 2013, 52(4): 408-423. DOI: (in Chinese with English Summary)

[127] Wang Z H, Zhen Y Y, Bergström S M, et al. . A New Conodont Biozone Classification of the Ordovician System in South China. Palaeoworld, 2019, 28(1/2): 173-186.

[128] Wei J Y, Zhang L, Wang H W, et al. . Geological Characteristics and Their Coupling Relationship between Structural Evolution and Reservoir Formation of Paleozoic Oil Reservoirs in the Southern Section of the Western Edge of the Ordos Basin. Earth Science, 2025, 50(5): 1933-1952. DOI: (in Chinese with English Abstract)

[129] Wu R C, Stouge S, Zhang Y D, et al. . Biostratigraphy and Palaeoecology of Middle and Late Ordovician Conodonts from the Hulo and Yenwashan Formations, Western Zhejiang, South-Eastern China. Geological Journal, 2020, 55(4): 2995-3009.

[130] Xi S L, Wei J Y, Zhang C L, et al. . Discovery and Significance of Marine Shale Oil Exploration in Ordos Basin. Acta Petrolei Sinica, 2022, 44(2): 253-269(in Chinese with English Abstract)

[131] Xi S L, Liu X S, Huang Z L, et al. . Enrichment Characteristics and Exploration Direction of Shale Oil and Gas in Wulalike Formation of Middle Ordovician in the Ordos Basin. Natural Gas Industry, 2023, 43(3): 12-22. DOI: (in Chinese with English Abstract)

[132] Xi S L, Yan W, Liu X S, et al. . New Fields, New Types and Resource Potentials of Natural Gas Exploration in Ordos Basin. Acta Petrolei Sinica, 2024, 45(1): 33-51. DOI: (in Chinese with English Abstract)

[133] Yang H, Fu J H, Yuan X Q. Atlas of Geological Sections in the Western Margin and Peripheral Basins of Ordos, 2011, Beijing. Petroleum Industry Press541(in Chinese)

[134] Yang S F. Palaeoichnology, 1990, Beijing. Geological Publishing House194(in Chinese)

[135] Zhang J H. Llanvirnian Conodonts from the Upper Ningguo Formation of Wuning, Jiangxi, with Discussion on Sedimentary Environment of Black Shales and Conodont Ecology. Acta Micropalaeontologica Sinica, 1993, 10(2): 191-200248–250 (in Chinese with English Summary)

[136] Zhang J H. Conodonts from the Guniutan Formation (Llanvirnian) in Hubei and Hunan Provinces, South-Central China. Stockholm Contributions in Geology, 1998, 46: 1-161

[137] Zhang J H. Four Evolutionary Lineages of the Middle Ordovician Conodont Family Polyplacognathidae. Meddelanden frän Stockholms Universitets Institution för Geologi och Geokemi, 1998, 298(5): 1-35

[138] Zhang J H. The Ordovician Conodont Genus Pygodus. Palaeontologica Polonica, 1998, 58: 87-105

[139] Zhang J X, Gong J H. Revisiting the Nature and Affinity of the Alxa Block. Acta Petrologica Sinica, 2018, 34(4): 940-962(in Chinese with English Abstract)

[140] Zhang R D. The Cephalopod Fossils of Lower Ordovician from Zhuozishan Area, Yikezhao Prefecture, Inner Mongolia, China. Acta Palaeontologica Sinica, 1959, 7(4): 259-271(in Chinese with Russian Abstract)

[141] Zhang Y D, Zhan R B, Zhen Y Y, et al. . Ordovician Integrative Stratigraphy and Timescale of China. Science China Earth Sciences, 2019, 62(1): 61-88.

[142] Zhao J, He Y B, Xiao B, et al. . Sedimentary Characteristics and Sedimentary Model of Calcirudite in the Wulalike Formation of Middle Ordovician in Zhuozishan Area of Inner Mongolia. Journal of Yangtze University (Natural Science Editition), 2014, 11(10): 6-8(in Chinese with English Abstract)

[143] Zhao J X, Li F J, Zhu G S, et al. . The Basic Characteristics, Spatial-Temporal Distribution, and Building Model of Reefs in the Western Margin of the Ordos Basin of Ordovician. Acta Petrologica Sinica, 2014, 30(3): 747-756. DOI: (in Chinese with English Abstract)

[144] Zhao Z X, Zhang G Z, Xiao J N. Palaeozoic Strata and Conodonts in Xinjiang, 2000, Beijing. Petroleum Industry Press340(in Chinese with English Summary)

[145] Zhen Y Y, Nicoll R S, Percival I G, et al. . Ordovician Rhipidognathid Conodonts from Australia and Iran. Journal of Paleontology, 2001, 75(1): 186-207.

[146] Zhen Y Y, Zhang Y D, Percival I G. Early Sandbian (Late Ordovician) Conodonts from the Yenwashan Formation, Western Zhejiang, South China. Alcheringa, 2009, 33(2): 133-161.

[147] Zhen Y Y, Wang Z H, Zhang Y D, et al. . Middle to Late Ordovician (Darriwilian-Sandbian) Conodonts from the Dawangou Section, Kalpin Area of the Tarim Basin, Northwestern China. Records of the Australian Museum, 2011, 63(3): 203-266.

[148] Zhen Y Y, Zhang Y D, Wang Z H, et al. . Huaiyuan Epeirogeny—Shaping Ordovician Stratigraphy and Sedimentation on the North China Platform. Palaeogeography, Palaeoclimatology, Palaeoecology, 2016, 448: 363-370.

[149] Zhen Y Y, Rutledge J. Conodont Biostratigraphy of the Ordovician Turbiditic Successions in New South Wales. Geological Survey of New South Wales Report, 2020, GS2020/0459: 1-53

[150] Zhen Y Y, Zhang Y D, Percival I G, et al. . Basal Darriwilian Graptolites and Associated Conodonts from New South Wales and Their Biostratigraphic Implications. Geological Survey of New South Wales Quarterly Notes, 2020, 153: 1-17

[151] Zhen Y Y. Middle Ordovician Conodont Biostratigraphy of Australasia. Journal of Earth Science, 2021, 32(3): 474-485.

[152] Zhen Y Y, Percival I G, Gilmore P, et al. . Conodont Biostratigraphy of Ordovician Deep-Water Turbiditic Sequences in Eastern Australia—A New Biozonal Scheme for the Open-Sea Realm. Journal of Earth Science, 2021, 32(3): 486-500.

[153] Zheng H P, Jiang Y Q, Yu W M, et al. . Petrogenesis and Tectonic Implications of ~2.33 Ga Luobuqigou Diabase-Gabbro in Northern End of Trans-North China Orogen of North China Craton. Earth Science, 2025, 50(7): 2735-2758. DOI: (in Chinese with English Abstract)

[154] Zheng Y F, Xiao W J, Zhao G C. Introduction to Tectonics of China. Gondwana Research, 2013, 23(4): 1189-1206.

[155] Zhu R X, Yang J H, Wu F Y. Timing of Destruction of the North China Craton. Lithos, 2012, 149: 51-60.

[156] Zou C N, Gong J M, Wang H Y, et al. . Importance of Graptolite Evolution and Biostratigraphic Calibration on Shale Gas Exploration. China Petroleum Exploration, 2019, 24(1): 1-6. DOI: (in Chinese with English Abstract)

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