Preface
IGCP Project 591 is dedicated to investigating the \"Early to Middle Paleozoic Revolution\". Indeed, the geological interval from Cambrian to Devonian was full of revolutionary events, both in the organic and inorganic realms, and their interactions triggering the macroevolution of Earth ecosystems as well as the solid Earth itself. The well known Cambrian Explosion, the first macroevolutionary radiation of ecosystem, comprises several episodes from its prologue (represented by the Ediacara Biota), through the first (the Small Shelly Fauna) and the main stages (the Chengjiang Biota) to the epilogue (the Burgess Shale Fauna, the Kaili Fauna etc.). The great Ordovician biodiversification event (GOBE), i.e. the Ordovician radiation, spanned tens of million years, highlighted by several diversity acmes, and established the basic framework of the Paleozoic Evolutionary Fauna that dominated the marine ecosystems for more than 290 Ma. The endOrdovician mass extinction was the first catastrophic event in life history. It is now known not to be ranked as one of the Big Five, and the marine ecosystem did not collapse at all during this mass extinction. None of these major biotic events are regional in scale, not to say local, although all of them were closely related with local, regional and global tectonic movements, paleogeographic and paleoclimatic changes and apparently some sedimentary innovations (e.g. the Substrate Revolution in Cambrian and Ordovician), as well as some other geological activities such as vocanic eruptions, comets collisions, Milankovich cycles, etc. To investigate these Early to Middle Paleozoic revolutionary events and their dynamics, geoscientists in the world need a common language, i.e. the GSSPs and the establishment of regional and global chronostratigraphic frameworks, which have been some of the major tasks of each Subcommission of ICS for several decades.
On behalf of the Organizing Committee, we would like to take this opportunity to thank all 151 experts who have coauthored the 66 abstracts, summaries and extended summaries in this Extended Summary volume for this meeting. The scope of these papers covers all the abovementioned topics dealing with the Early to Middle Paleozoic revolutionary events and their triggering factors. Among the 151 contributors, nearly half of them are graduate students or young researchers who brought great vitality to this meeting as well as the IGCP Project. We also want to thank the three keynote speakers, Michael Melchin (ISSS), David Harper (ISOS) and Loren Babcock (ISCS), who prepared both extended summaries and reviewed presentations for this meeting.
Many thanks to the following institutions for their financial support:the National Natural Science Foundation of China (NNSFC: 41221001, 41290260 and another special project); the Nanjing Institute of Geology and Palaeontology (NIGP) of CAS; the State Key Laboratory of Palaeobiology and Stratigraphy (LPS); and the Yunnan Key Laboratory of Paleobiology (YLP) attached to the Yunnan University.
Zhan Renbin and Huang Bing
On behalf of the Organizing CommitteeExtended SummaryIGCP Project 591 Field Workshop 2014Contents
Leho AINSAAR, Peep MNNIK, Andrei V. DRONOV, Olga P. IZOKH, Tnu MEIDLA and Oive TINN: Carbon isotope chemostratigraphy and conodonts of the MiddleUpper Ordovician succession in Tungus Basin, Siberian Craton1
Anna ANTOSHKINA: Oolitestromatolite association: A possible sedimentological marker of Silurian
bioevents, Timannorthern Ural region5
Loren E. BABCOCK, PENG Shanchi, Carlton E. BRETT, ZHU Maoyan, Per AHLBERG and Michael BEVIS: Evidence of global climatic and sea level cycles in the Cambrian9
Carlton E. BRETT, Thomas J. MALGIERI, James R. THOMKA, Christopher D. AUCOIN, Ben DATTILO and Cameron E. SCHWALBACH: Calibrating water depths of a Late Ordovician ramp, southern Ohio and northcentral Kentucky, USA12
Carlton E. BRETT, James R. THOMKA, Thomas J. MALGIERI, Cameron E. SCHWALBACH and Christopher D. AUCOIN: Faunal epiboles in the Upper Ordovician of northcentral Kentucky: Implications for highresolution sequence and event stratigraphy and recognition of a major unconformity
15
CHEN Qing and FAN Junxuan: Changes in the sedimentary facies during the OrdovicianSilurian transition
in South China18
CHEN Zhongyang, WANG Chengyuan and FAN Junxuan: Problems on the correlation of the Llandovery (Silurian) strata on the Upper Yangtze Platform, South China21
Bradley D. CRAMER, Thijs R.A. VANDENBROUCKE and Gregory A. LUDVIGSON: Asking old
rocks new questions: Highresolution event stratigraphy (HiRES) and the quantification of stratigraphic uncertainty24
Yulia E. DEMIDENKO and Pavel Yu. PARKHAEV: On the problem of recognition of the lower Tommotian boundary using the SSF26
DUAN Ye: Middle and Upper Cambrian strata, depositional environments and trilobite faunas of the FenghuangChenxi area, western Hunan, China32
Jorge ESTEVE: Morphological variation in paradoxid trilobites from Cambrian Series 3 of Spain37
Jorge ESTEVE and YUAN Jinliang: Enrolment of Guzhangian trilobites from Shandong Province, North China40
FANG Xiang, ZHANG Yunbai, CHEN Tingen and ZHANG Yuandong: Taxonomy of Ordovician cephalopods Sinoceras chinense (Foord): A quantitative approach42
Oldich FATKA, Petr BUDIL, Martin DAVID, Vladislav KOZK, Vclav MICKA and Michal SZABAD: Digestive structures in Cambrian and Ordovician trilobites from the Barrandian area (Czech Republic)49
David A.T. HARPER: The Great Ordovician Biodiversification Event: Reviewing two decades of research on diversity’s big bang52
HUANG Bing, ZHAN Renbin and WANG Guangxu: Brachiopod associations from late Rhuddanian in South China and their bathymetric significance57HOU Xudong and FAN Junxuan: CONOP—A quantitative stratigraphic software and an approach to its parallelization61
JING Xiuchun, ZHOU Hongrui and WANG Xunlian: Conodont biostratigraphy of the Darriwilian and the Sandbian from Wuhai area, Inner Mongolia, China64
Igor V. KOROVNIKOV: New data on the paleobiogeography of Cambrian trilobites from western and northern margins of the Siberian Platform67
Luk LAIBL, Oldich FATKA, Jorge ESTEVE and Petr BUDIL: Ontogeny and larval ecology of paradoxidid trilobites (Eccaparadoxides and Hydrocephalus) from the SkryjeTy＇rˇovice Basin (Czech Republic)71
LI Yujing, ZHAO Jun, CONG Peiyun and HOU Xianguang: New morphological specificity of vetulicolians and its implications74
LIANG Yan, TANG Peng and ZHAN Renbin: Preliminary report on the chitinozoans from the Lower Ordovician Tungtzu and Hunghuayuan formations of Tongzi, northern Guizhou, southwest China75
LUAN Xiaocong, LIU Jianbo and ZHAN Renbin: Microfacies of the Lower to Middle Ordovician Zitai Formation of southern Anhui and its implications80
MA Xiaoya, CONG Peiyun, HOU Xianguang, Gregory EDGECOMBE and Nicholas STRAUSFELD:
Deep thoughts from deep time—central nervous systems of Cambrian panarthropods85
Michael J. MELCHIN and KevinDane MACRAE: Insights into the RhuddanianAeronian and AeronianTelychian boundary intervals from eastern and Arctic Canada86
Michael J. MELCHIN, H. David SHEETS, Charles E. MITCHELL and FAN Junxuan: Global stratotype sections and points and quantitative stratigraphic correlation: A way forward for defining and correlating the Silurian System89
Lucy A. MUIR and Joseph P. BOTTING: Environmental distribution and diversity of Ordovician Porifera
in the Builth Inlier, Wales92
Martina NOHEJLOV and Oldich FATKA: Ontogenetic development of the genus Akadocrinus (Eocrinoidea, Echinodermata) from the Barrandian area, Czech Republic97
Natalya V. NOVOZHILOVA: Morphological and microstructural features of Early Cambrian Archiasterella (Chancelloriida) of the Siberian Platform99
Pavel Yu. PARKHAEV: On the stratigraphy of Aldanella attleborensis—potential indexspecies for defining
the base of Cambrian Stage 2102
PENG Jin, ZHAO Yuanlong, SUN Haijing, YAN Qiaojie, WEN Rongqin, SHEN Zhen and LIU Shuai: Biostratigraphic study on the Balang Formation (Series 2, Cambrian) of Guizhou, China106
Ian G. PERCIVAL and Peter D. KRUSE: Biostratigraphy and biogeographic affinities of middle to late Cambrian linguliformean brachiopods from Australasia109
Kairi PLDSAAR and Leho AINSAAR: Recognizing triggers for extensive liquefaction structures in two Early Paleozoic shallowmarine sandstones, NW Estonia: Earthquake shock vs. cyclic storm loading
117
RONG Jiayu, ZHAN Renbin and HUANG Bing: The preHirnantian Late Ordovician shallow water brachiopod biogeography of Tarim, Qaidam, North and South China： A preliminary report120
Jacky ROUSSELLE: A look at certainties and uncertainties relating to the Early Paleozoic climate (earliest Cambrianend of Silurian)126Sergey ROZHNOV: The history of tiering in Ordovician and Silurian crinoid communities and myelodactylid occurrences in Russia and China130
N.V. SENNIKOV, O.A. RODINA, N.G. IZOKH and O.T. OBUT: New data on Silurian vertebrates from Siberia and their stratigraphic ranges134
SONG Yanyan, ZHANG Yuandong, Daniel GOLDMAN, WANG Zhihao, FANG Xiang and MA Xuan: Latest Darriwilian to early Sandbian graptolite biostratigraphy in Chengkou, northern Chongqing, South China138
Colin SPROAT, Jisuo JIN, ZHAN Renbin and David RUDKIN: Morphological variability in the Late Ordovician Parastrophina from eastern Canada and the Tarim Basin, northwestern China and its paleoecological implications144
Petr TORCH, těpn MANDA and Zuzana TASRYOV: RhuddanianAeronian boundary strata in graptolitebearing black shale succession of the Barrandian area (Czech Republic)148
Svend STOUGE, Gabriella BAGNOLI, QI Yuping, WU Rongchang and LI Zhihong: DarriwilianSandbian (Ordovician) conodonts from the top Kuniutan, Datianba and Miaopo formations, central and south
China152
SUN Haijing, Loren E. BABCOCK, PENG Jin and ZHAO Yuanlong: New systematic and anatomical information about Cambrian hyoliths from Guizhou, China and Nevada, USA153
TANG Peng, WANG Jian, WANG Chengyuan, LIANG Yan and WANG Xin: Microfossils from the LlandoveryWenlock boundary sections in ZiyangLangao region, southern Shaanxi, central China155
Zuzana TASRYOV, Petr SCHNABL, Vojtěch JANOUEK, Petr PRUNER, Petr TORCH,
KristnaCˇY＇KOV, těpn MANDA and Jií FRY＇DA: Paleomagnetism and geochemistry of middle Silurian volcanic rocks of the Prague Basin158
Oive TINN, Viirika MASTIK, Leho AINSAAR and Tnu MEIDLA: Exceptionally wellpreserved noncalcified algal fossils from the lower Silurian (Llandovery, Aeronian) of Estonia160
Tatiana Yu. TOLMACHEVA and K.E. DEGTYAREV: Conodonts of the OpenSea Realm and their diversity in the Early and Middle Ordovician163
Petra TONAROV and Olle HINTS: Silurian scolecodonts and extinction events168
Valéria VAKANINOV: Preliminary report on the occurrence of vertebrate remains in the Silurian of the Prague Basin170
WANG Chuanshang, CHEN Xiaohong, WANG Xiaofeng and LI Xubing: The Sedimentary Evolution of
the late Caledonian foreland basin in the Upper Yangtze Region173
WANG Guangxu and ZHAN Renbin: A new species of Paramplexoides (rugosans) from the Hirnantian Kuanyinchiao Formation of northern Guizhou, South China178
WANG Jian, WANG Xin, Petr TORCH, ZHANG Ju, MENG Yong, FU Lipu and LI Rongshe: Graptolite fauna from the LlandoveryWenlock boundary section, southern Shaanxi Province, central
China182
WANG Pingli, SUN Zhixin and YUAN Jinliang: Preliminary study on an exceptionally wellpreserved preserved fauna from the Mantou Formation, Cambrian Series 3, Weifang City, Shandong185
WANG Yi, ZHANG Xiaole and JIANG Qing: The Pridoli palynological assemblage of the Sibumasu Block from Baoshan, western Yunnan, SW China189
WEN Rongqin, PENG Jin and ZHAO Yuanlong: The morphology and ontogeny of Tuzoia bispinosa from the Cambrian in eastern Guizhou, South China193
Anthony J. WRIGHT: Evolution and biogeography of Silurian and Devonian operculate corals197
WU Rongchang, ZHAN Renbin, LIU Jianbo, Michael JOACHIMSKI, CHEN Jun and Axel MUNNECKE: Carbon and conodont apatite oxygen isotope records from the Floian to lower Darriwilian (upper Lower and Middle Ordovician) in South China, and their paleoenvironmental implications201
YAN Kui and LI Jun: Acritarch and prasinophyte assemblage from the Qiaojia Formation in Luquan, Yunnan Province, South China206
ZHANG Linna, FAN Junxuan and ZHANG Yuandong: Insights into the lithofacies paleogeography and paleobiogeography in South China during the Darriwilian (Middle Ordovician)210
ZHANG Xiaole and LIU Jianbo: Red beds of the Laojianshan Formation in western Yunnan: Sedimentary evolution of tidal dominated deposits213
ZHANG Yuanyuan, LI Yue and WANG Jianpo: Lithofacies of the Yijianfang Formation (Darriwilian, Middle Ordovician) in the Lunnan Oil Field, Tarim, northwest China216
ZHAO Wenjin and ZHU Min: Silurian fishes from Yunnan, China and related biostratigraphy221
ZHAO Xiuli, LI Shoujun, REN Xiangbin, WANG Lili, CHEN Yuhui, MA Wenzhao and WANG Xiujing: Sporopollen assemblage characteristics and significance of the Forth Member of Shahejie Formation in Qingdong Sag226
ZHAO Yuanlong, CHENG Xin, ZHU Maoyan, YANG Xinglian, PENG Jin, WANG Pingli and WANG Mingkun: Preliminary study on the Medusiform fossils Pararotadiscus (Zhao and Zhu, 1994) coexistence with other fossils from the Kaili Biota231
ZHEN Yongyi and Ian G. PERCIVAL: Floian (Early Ordovician) conodont biogeography, biofacies, and biostratigraphic correlation between Australia and South China234
ZHEN Yongyi and ZHANG Yuandong: Early Ordovician conodont biostratigraphy of the Jiangnan Slope, South China238
ZHU Xuejian and PENG Shanchi: A new Burgess Shaletype biota from the later Cambrian rocks of China.
242
Index for Authors245
Extended Summary
IGCP Project 591 Field Workshop 2014
Carbon isotope chemostratigraphy and conodonts of the MiddleUpper Ordovician succession in Tungus Basin, Siberian Craton
Leho AINSAAR1, Peep MNNIK2, Andrei V. DRONOV3, Olga P. IZOKH4, To~nu MEIDLA1 and Oive TINN1
1Department of Geology, University of Tartu, Ravila 14a, Tartu 50411, Estonia
2Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, Estonia
3Institute of Geology, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow 119017, Russia
4Sobolev Institute of Geology and Mineralogy, Siberian Branch of RAS, Acad. Koptyug av., 3, Novosibirsk 630090, Russia
Secular variations of δ13C in marine carbonates have become an important tool in regional and global correlation of sedimentary successions. The stable carbon isotope chemostratigraphy is especially useful in correlation of separated marine basins and continents with different faunas and depositional environments. Numerous publications are dealing with Ordovician δ13C chemostatigraphy in Baltoscandia (e.g. Kaljo et al., 2007; Ainsaar et al., 2010), North America (e.g. Saltzman and Young, 2005; Bergstrm et al., 2010), China (e.g. Zhang et al., 2010), and elsewhere. These data are summarized in the Ordovician δ13C chemostratigraphic zonation of Baltoscandia (Ainsaar et al., 2010) and in the generalised global δ13C curve (Bergstrm et al., 2009). Although the δ13C chemostratigraphy has proved to be a useful tool in geological studies it has not been applied in the Ordovician succession of the Siberian Craton. In this paper we present the results of the first δ13C studies from the Middle and Upper Ordovician sections located in the Kulyumbe River and Podkamennaya Tungusta River areas in the Tungus Basin, and compare them with the data from Baltoscandia. To test the chemostratigraphic correlations, conodont faunas were studied from selected interval in these sections.
Geological setting
In early Paleozoic, the Siberia Paleocontinent was located in low latitudes and was slowly moving from the southern hemisphere (CambrianEarly Ordovician) to the northern hemisphere (Late OrdovicianSilurian) (Cocks and Torsvik, 2007). Central part of the continent was occupied by an extensive intracratonic Tungus Basin (Kanygin et al., 2010a, b). Sedimentation of warmwater tropical carbonates in the Early Ordovician was replaced by deposition of cool or temperatewater carbonate deposition in Darriwilian, although the palaeocontinent was still located in low latitudes (Dronov, 2013). The upper Darriwilian and lower Katian intervals (Volginian to Dolborian stages) were studied in the Kulyumbe and Podkamennaya Tunguska sections. Both areas, located about 700 km from each other, expose coolwater carbonates dominated by bioclastic wackestones and packstones intercalating with finegrained carbonate siliciclastics. The carbonates are almost not affected by tectonics and deep burial, although some intervals are altered in the Kulyumbe River sections due to the Late PaleozoicTriassic folding and sill intrusions (see Kouchinsky et al., 2008).
Stable isotopes in the Tungus Basin
Altogether 117 wholerock samples from two localities in the Kulyumbe area were analysed for stable isotope composition in the Institute of Geology and Mineralogy, Russian Academy of Sciences Siberian Branch, Novosibirsk, and 140 samples from two localities in the Podkamennaya Tunguska area were analysed in the Department of Geology, University of Tartu. In all localities, the δ13C values vary mainly (with few exceptions) between -5 and 0‰. This is in general 2—5‰ lower than carbonates in the same interval in Baltoscandia (Ainsaar at al., 2010) and in North America (Saltzman and Young, 2005). However, numerous studies have demonstrated that characteristic secular changes in the carbon isotope composition can be correlated globally despite the different δ13C baseline values (e.g. Bergstrm et al., 2010).
The δ13C curves of Kulyumbe and Podkamennaya Tunguska sections share several similarities (Fig. 1). Both curves start with relatively high δ13C values in the Volginian Stage, followed by gradual drop of 4—7‰ in the KirenskoKudrinian Stage. The Chertovskian Stage shows some rise in the δ13C curve in both areas. There is a negative peak in the lower part of the Baksian Stage followed by increase of δ13C values about 4‰, again in both studied areas. The slight decrease of δ13C values in the Dolborian Stage in the Podkamennaya Tunguska area is followed by a clear rise in the upper part of this unit in both areas (Fig. 1).
Fig. 1. Correlation of composite δ13C curves from Kulyumbe and Podkamennaya Tunguska sections with the Baltoscandian composite, and distribution of selected conodont taxa based on Moskalenko (1982; Kulyumbe section) and this study (Podkamennaya Tunguska). Left from the Kulyumbe and Podkamennaya Tunguska δ13C curves—regional stages (if not stated otherwise). Solid horizontal lines—sequence boundaries after Dronov et al. (2009) and Kanygin et al. (2010b). Dashed horizontal lines with arrows—probable correlation of isotope events with the Baltoscandian composite δ13C curve.
Correlations
Based on earlier biostratigraphic studies the VolginianDolborian interval has been correlated with the upper Darriwilianlower Katian interval on global scale (Kanygin et al., 2010a).The sequence stratigraphic subdivision of the Ordovician succession of Tungus Basin and correlation of sedimentary sequences with the Baltoscandian succession has been proposed by Dronov et al. (2009) and Kanygin et al. (2010b) (Fig. 1).
Carbon isotopes
Comparison of the δ13C curves of both continents does not contradict with these previous correlations. There are three possible chemostratigraphic markers, which could be correlated from Tungus Basin to the Baltoscandian Basin (Fig. 1): 1) relatively high δ13C values in the Volginian Stage could be correlated with the MidDarriwilian positive excursion (MDICE) in Baltoscandia and elsewhere (Ainsaar et al., 2010); 2) negative peak in the upper part of the KirenskoKudrinian Stage seems to fit with the Upper Kukruse Low in Baltoscandia (Kaljo et al., 2007); and 3) the rise of δ13C values in the middle of the Baksian Stage may indicate the start of the Guttenberg Excursion (GICE; Ainsaar et al., 2010). The latest dating of Kbentonites from the uppermost Baksian Stage in Podkamennaya Tunguska region provided age of 450.58±0.27 Ma (Huff et al., 2014). Differently from previous interpretations, this suggests a correlation of the base of Dolborian Stage with the base of Vormsi Stage in Baltoscandia. If this is correct, the upper Baksian interval with elevated δ13C values probably correlates with the GICE, Rakvere, and Saunja positive excursions in Baltoscandia.
Conodonts
Conodont faunas in the upper Sandbianlower Katian in Siberia are quite specific and almost completely different from those in Baltoscandia. However, occurrences of some taxa characteristic of Siberia in Baltoscandian sections do not contradict the correlations suggested by sequence stratigraphic analysis and δ13C data. Rare specimens of the genus Belodina represented by several taxa in the Baksian and Dolborian stages in Siberia occur sporadically in the Rakvereuppermost Pirgu interval in Estonia (identified as Belodina confluens Sweet; Mnnik and Viira, 2012). Few specimens of Phragmodus? tunguskaensis Moskalenko, a taxon appearing in the lower Baksian and reaching the lower Dolborian Stage, have been reported from the Rakvere and Nabala stages in Baltoscandia (Bergstrm et al., 2011; Mnnik and Viira, 2012). Specimens of Phragmodus characteristic of the upper Darriwilian to Katian in Siberia (Moskalenko, 1982) occur sporadically in the KukrusePirgu interval in Estonia. Pseudooneotodus mitratus (Moskalenko), described from Siberia (occurs in the Chertovskian to Dolborian stages) is quite common in the Lasnamgi to Porkuni stages in Estonia.
Most characteristic of the Baltoscandian faunas are the occurrence of Eoplacognathus, Yangtzeplacognathus, Baltoplacognathus and Baltoniodus in the Middle and lowermost Upper Ordovician, and Baltoniodus and Amorphognathus in the Upper Ordovician. All these genera are missing, or extremely rare, in Siberia. Rare specimens of Pseudobelodina dispansa (Glenister) known from the Rakvere to the upper Pirgu stages in Estonia occur in the upper part of the Baksian Stage.
Conclusions
1. Carbon stable isotope curves of the MiddleUpper Ordovician succession in the Kulyumbe and Podkamennaya Tunguska regions of the Tungus Basin are similar, but show more negative δ13C values compared to the other continents.
2. Three carbon isotope events characteristic of the Baltoscandian composite isotope curve cantentatively be recognised in Tungus Basin: MDICE in the Volginian Stage, midSandbian Upper Kukruse Low in the KirenskoKudrinian Stage, and lower rise of the GICE in the Baksian Stage. These chemostratigraphic correlations support the sequence stratigraphic comparisons of two basins.
3. Conodont faunas in the upper Sandbianlower Katian in Siberia are specific and different from those in Baltoscandia. However, occurrences of few common taxa in Siberia and Baltoscandia do not contradict to the correlation suggested by sequence stratigraphic analysis and δ13C data.
Acknowledgements
The study was supported by the Estonian Research Council grants IUT2034 (LA, TM, OT) and PUT 378 (PM). This paper is also a contribution to the IGCP project 591 “Early to Middle Paleozoic Revolution”.
References
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Oolitestromatolite association: A possible sedimentological marker of Silurian bioevents, Timannorthern Ural region
Anna ANTOSHKINA
Institute of Geology, Komi Science Centre, Ural Branch RAS, Syktyvkar
Terms “oolite”, “stromatolith”, and “ooid” have been entered into the geological literature through the study of the Lower Triassic in northern Germany. The concomitant decline of skeletal carbonate production reduced a major agent for seawater carbonate (Paul et al., 2011). Such facies has been discussed from major crises such as endPermian (Pruss et al., 2004), Silurian Mulde and Lau events (Calner, 2005). The wellpreserved, abundant stromatolitic\/microbial carbonates in the Paleozoic Timannorthern Ural sea basin represent a wide range of depositional environments from subtidal to supratidal platform.
Why has it interest arisen to Lower Paleozoic oolites though it is enough lengthy and large carbonate bodies of such originations are more widely developed in Upper Paleozoic sections? Our studies of last years have shown that oolitic limestones in the Upper Paleozoic successions associate with only bioclastic limestones and their formation was appointed by an active hydrodynamics in the shallowwater seas. In contrast, oolites\/ooids in the Lower Paleozoic deposits are characterised mainly by their association with stromatolites or stromatolitelike microbial carbonates and their peculiarity (Antoshkina, 2011). Such associations have been established in the SilurianDevonian boundary units on the Kozhym River of the Subpolar Urals and on the Izyayu River of the Chernyshev Swell (Fig. 1), besides in the Wenlock and Ludlow on the Sharyu and Izyayu rivers of the Chernyshev Swell (Antoshkina and Beznosova, 1987; Antoshkina, 2007; Antoshkina and Shebolkin, 2014).
Fig. 1. Lithology and petrographic character and location of the Izyayu and Kozhym sections (1), facies and basin reconstruction near the SilurianDevonian boundary (2). 1a microbial limestone with clusters of very small ooids, cavities with ferrousclay material and dolomitization; 1b conglobreccia with ooids in a recrystallized calcite cement, and fragments of primary mudmicrobial matter; 2 environments of stromatoliteooid limestone beds formation: awithin the preboundary interval; bwithin the boundary interval.
In the Silurian section on the Padimejtyvis River of the Chernov Swell are situated at two levels (within the Gorstian and at the GorstianLudfordian boundary) with development limestones contained stromatoliteoolite\/ooid associations. Such beds range from 0.55 to 1.80 m in thickness. There are very interesting stromatoliteoolite\/ooid limestones of 0.2 to 2 m in thickness in the middle part of the Wenlock before the Mulde Event level revealed in the section on the Izyayu River of the Chenyshev Swell (Shebolkin and Mnnik, 2014).
The limestones with oolite\/ooids at the Izyayu479 section were analysed in detail (Antoshkina and Shebolkin, 2014). It is very interesting that lithological and geochemical studies on these limestones are shown that they have been generated in lagoon environments with a changeable salinity, abundance pelitic components in matrix and presence an ungraded bioclastic material, such as fragments of ostracods, gastropods, bivalves, and rare bryozoans. Whole ostracods shells are less than 2 mm in size. Ooids show wellpreserved cortical fabrics and little endolithic boring and\/or micritization of laminae. The important feature of ooids is such a fact that under an electronic microscope it is visible, that crystals have the distinct traces of dissolution formed at dissolution by organic acids of inlaying microorganisms. A honey comblike pattern of subpolygonal to subspherical pits and walls are supposed as calcified extracellular polymeric substance (EPS) matrix. The stable isotope composition of carbonates can be used to elucidate their precipitation mechanism(s). Bulk carbonate values from the Wenlock limestones with ooids average -5.4...-6.4 ‰, 22.9...24.6 ‰ for Δ13C PDB and for Δ18O SNOW, respectively. These data have significant implications for paleoenvironmental studies since photosynthetic microbes now provide an alternative to turbulent hydrodynamic conditions in the formation of freshwater ooids. Low content of boron 1130г\/т in these limestones also speak about the lowered salinity of waters. Similar conditions existed and in the Early Triassic basin, where by E. L. Kalkovsky have been described the stromatoliteooids associations, defined as lake conditions alkaline with lowered salinity of waters (Voigt et al., 2011).
Occurrence of mentioned above stromatoliteooids associations was defined by a sea level fall is connected of regional regressions in the marine basin common caused by regional tectonic processes. Shift of openmarine by lagoon\/lake environments with lower active hydrodynamics was occasioned by this situation. Periodically, some terrigenous material and lithoclasts were added in a microbialcarbonate mud. A thin radial cover also started to form around the clasts. Besides, it is possible to observe vadose cements around some skeletal fragments and lithoclasts. Change of hydrodynamics was accurately reflected on stromatolite bodies. Well expressed colonies, sometimes with “headlike” surfaces, were gradually replaced by microbial floormats with the layered crusts having laminarfenestral structure. The concomitant decline of skeletal carbonate production reduced a major agent for seawater carbonate. This is an important consideration as it is known that ooids occurrences are exceptionally rare in environments where pH and total alkalinity are significantly below values that allow facile carbonate precipitation (Summons et al., 2013).
Studies on the Silurian strata of the region have recently demonstrated that at least four levels with ooid\/oolitestromatolite associations are associated with changing landscape of sedimentary basins (carbonate platforms). Data of Silurian stable isotopes have revealed both positive and negative carbon excursions across the levels (Modzalevskaya and Wenzel, 1999; Shebolkin and Mnnik, 2014). It should be noted that during these intervals (inside the Gorstian and at the GorstianLudfordian boundary) are marked shorttime extinction events and decreasing of carbonateproducing biota (Subpolar Urals..., 2000). The specific facies for each episode are similar in that they: a) are associated with stromatoliteoolite\/ooid facies; b) are associated with influx of siliciclastic material to deposits; c) correlated in time with changing in faunas of brachiopods, tabulate corals, ostracods, and conodonts; d) are associated with regression phases in sea basins. Siliciclastic material is transported to basins during relative sea lowstand when microbial activity increases and benthic ecosystems are disturbed. The microbial activity decreases when its flux is intensive, and it is continued in time. During these intervals we do not observe the stromatoliteoolite\/ooid associations, at the WenlockLudlow boundary in the Subpolar Urals (the Shyuger River), and LudlowPidoli boundary in the Chernov Swell (the SizimTselebejshor River). As have shown our researches, stromatoliteoolite\/ooids associations appear dated for turningpoints in the Silurian basin of the region under study, that can be used as a sign of important levels reflecting certain phases of sedimental and biotic events, and also for correlation of these events for reconstructing the evolution of the sedimentary basin.
Acknowledgements
This summary is a contribution to IGCP Project 591 “Early to Middle Paleozoic Revolution”.
References
Antoshkina, A.I. 2007. Silurian sealevel and biotic events in the Timannorthern Ural region: sedimentological aspects. Acta Palaeontologica Sinica, 46, 2327.