Middle Ordovician cephalopod biofacies and palaeoenvironments of Baltoscandia

During the Middle Ordovician cephalopods became an important part of the macrofauna of the Baltoscandian carbonate platform. The earliest cephalopod abundance peak was reached during the early Darriwilian, within the Kunda Stage Yangtzeplacognathus crassus and Lenodus pseudoplanus conodont zones. In sediments of this time interval large orthoconic cephalopods often occur in masses with more than one specimen per square‐meter on bedding surfaces. The assemblages are characterized by the strong dominance of often large endocerids. In proximal depositional settings coiled tarphycerids and other cephalopod groups are an important additional component. In the most distal settings orthocerids are the most important secondary component. Correspondence Analysis of assemblages throughout Baltoscandia revealed three distinct biofacies, which here are termed Orthocerid, Proterovaginoceras and Anthoceras Biofacies, respectively. The biofacies reflect differences in depth and proximity to the shoreline and are consistent with the Baltoscandian Confacies Belts. Spatial changes in absolute abundance and taxonomic composition indicate increased original cephalopod population densities and habitat expansion within the Y. crassus and L. pseudoplanus conodont zones. A nearly coeval abundance peak in a similar facies in South China indicates supraregional causes of the mass occurrence, probably reflecting a globally increased nutrient availability in the water column during the Darriwilian.     

The earliest known strophomenoids (Brachiopoda) from early Middle Ordovician rocks Of South China

The upper Daguanshan Formation (middle Expansograptus hirundo graptolite biozone, Dapingian, early Middle Ordovician) of the Shuanghe area, Changning County, southern Sichuan Province, contains three new genera and species of strophomenoids: Ochyromena plana, Shuangheella elongata, and Primotimena globula, which are attributed to the Strophomenidae, Rafinesquinidae and Glyptomenidae respectively. These are the earliest known strophomenoids from the South China palaeoplate, and also the oldest rafinesquinid and glyptomenid brachiopods worldwide. Global review of the superfamily Strophomenoidea of Middle Ordovician age suggests that the first diversity peak at the species level occurred in late Darriwilian (Llanvirn) time, mainly as a result of the rapid diversification of the family Strophomenidae. The first appearance datum (FAD) of strophomenoids and their possible westward dispersal were from North China (latest Floian) and/or South China (early Dapingian), through the Chu‐Ili terrane of Kazakhstan, Iran, and Baltica (early Darriwilian), to Avalonia and Laurentia (late Darriwilian). This points to the existence of early diversification hotspots of the strophomenoid superfamily in the North and South China palaeoplates during the early Middle Ordovician in generally shallow water (corresponding to BA2) environments. The high degree of similarity in the external morphology and ventral interior of the three new genera indicates that the early diversification of strophomenoids began with differentiation of the cardinalia, especially in the configuration of the bilobed cardinal process, a key evolutionary novelty for the strophomenoids.     

Conodontophorid biodiversification during the Ordovician in South China

Wu, R., Stouge, S. & Wang, Z. 2012: Conodontophorid biodiversification during the Ordovician in South China. Lethaia, Vol. 45, pp. 432–442. Analysis of the Ordovician conodontophorid diversity pattern for South China using normalized and total diversity measures reveals that diversity peaks occurred in the mid‐Tremadocian, mid‐late Floian, early Dapingian and mid‐Darriwilian periods. The conodontophorids radiated during the Floian, maintaining relatively high diversity into the early part of the Middle Ordovician until a significant diversity decrease occurred in the late Dapingian. A relatively low diversity level prevailed in the Late Ordovician. Three diversification intervals based on origination, extinction and turnover rates have been identified i.e. (1) Tremadocian to mid‐late Floian, (2) early Dapingian and (3) late Dapingian to early Darriwilian. Diversity curves for conodontophorids, brachiopods, graptolites, acritarchs and trilobites from South China are comparable during the Early Ordovician, although differences are apparent in the Middle and Late Ordovician. In South China, conodontophorid diversity reacted primarily to sea‐level changes during the Early and Middle Ordovician, when the peak of this biodiversification generally coincided with a transgression. Climate changes – especially the global cooling that occurred during the Late Ordovician glaciation – and sea‐water chemistry were also important controlling factors. □Biodiversification, conodonts, Ordovician, South China.     

Conodont biostratigraphy and carbon isotope chemostratigraphy of the Middle to Upper Ordovician on the western Yangtze Platform,South China

Middle and Late Ordovician strata in the nearshore area of the western Yangtze Platform are investigated. In total, 241 δ¹³C_carb samples and 108 conodont samples from the Songliang and Tuanjie sections in the northeastern Yunnan Province were collected for chemostratigraphic and biostratigraphic studies. Altogether, 21 species belonging to 16 conodont genera were recovered from the two sections, among which Ansella jemtlandica, Drepanoistodus basiovalis, Hamarodus brevirameus, and Microzarkodina hagetiana are important age indicators within the Dapingian to early Katian interval. Four carbon isotope shifts are recognized in the studied sections: a negative shift in the early Darriwilian, the middle Darriwilian carbon isotope excursion (MDICE), the early Katian Guttenberg carbon isotope excursion (GICE), and a further positive carbon isotope shift later in the early Katian which is a new record of this event in South China. Integrated carbon chemostratigraphy and conodont biostratigraphy indicate early Darriwilian and early Katian ages for the base and top, respectively, of the Huadan Formation at the Songliang section, and a Darriwilian to early Katian age for the Shihtzupu Formation at the Tuanjie section.     

Facies of a Lower Ordovician carbonate shelf (Mungok Formation: Taebaeksan Basin,Korea)

Summary The lithologic associations within the Lower Ordovician Mungok Formation in Korea define four depositional facies that formed across a continental margin fringing the Sino-Korean block: these facies represent lagoonal/restricted marine, shoal, inner shelf, and outer shelf environments. The stacking pattern of these facies reveals two systems tracts composed of five depositional sequences. The lower highstand systems tract consists of the lagoonal/restricted marine and shoal facies, whereas the upper lowstand systems tract comprises, in ascending order, inner shelf, outer shelf, and inner shelf facies. Three trilobite biofacies are recognized in the Mungok Formation: i.e.,Yosimuraspis, Kainella, andShumardia biofacies in ascending order. TheYosimuraspis Biofacies is dominated byYosimuraspis but also containsJujuyaspis andElkanaspis. The predominance of the endemic eponymous taxon suggests a lagoonal/restricted marine environment. The nearly monotaxicKainella Biofacies, which comprises pandemic genera such asKainella and occasionallyLeiostegium, may represent a less restricted environment than theYosimuraspis Biofacies. TheShumardia Biofacies occurs in the marlstone/shale lithofacies through relatively thick stratigraphic interval and is dominated by cosmopolitan trilobite taxa with some endemic species. The lithofacies and cosmopolitan trilobite assemblage of theShumardia Biofacies indicate that it occupied an outer shelf environment. The vertical succession of lithofacies and trilobite biofacies in the Mungok Formation records in general a shift from a restricted, shallow water environment to deeper-water environment.     

下扬子区奥陶纪牙形刺多样性演变初探

根据前人和作者现有资料,对下扬子地区,特别是宁镇地区奥陶纪已经报道的牙形刺属种进行厘定,并按牙形刺带逐带进行多样性统计分析,初步编制出该地区奥陶纪牙形刺属种的地层延限表.研究表明;下扬子区牙形刺在奥陶纪的宏演化经历了3次较明显的辐射事件,分别发生在特马豆克期晚期-弗洛期早期(Serratognathus diversua带)、大坪期早期(Baltoniodus triangularis带)、达瑞威尔期晚期(Eoplacognathus suecicus带);此外,还经历了2次快速增长期,分别发生在达瑞威尔期早期(Lenodus antivariabilis带)、桑比期晚期至凯迪期早期(Hamarodus europaeus带),后者可能与局部环境变化有关.研究表明:华南海平面升降对下扬子区牙形刺宏演化趋势有重要影响.     

Biogeographic associations of Silurian bryozoan genera in North America, Baltica and Siberia

Six distinct bryozoan paleobiogeographical provinces existed during the Silurian of North America, Baltica and Siberia. These provinces are based on parsimony analysis of endemicity (PAE), each supported by a number of endemic genera only present in that assemblage. The area cladogram displays a nested pattern, permitting the clustering of assemblages into larger units that might be indicative of their areas of origin. Paired-group cluster analysis supports the existence of provincial assemblages. Relationships indicate the action of both vicariance and geodispersal. Geographic boundaries between the provinces include land, deep sea, and climate zone boundaries, including barriers created by the Iapetus Ocean and the Tornquist Sea.     

A new Middle Ordovician conodont from central Kazakhstan, nothern Kyrgyzstan, and Altai

Naimanodus degtyarevi gen. et sp. nov., a new conodont genus and species from the Lower Darriwilian (Middle Ordovician) limestones of the Naiman Formation in central Kazakhstan is described. Three types of coniform nongeniculate elements are identified in the apparatus of this species. The new species was widespread in the Asian Paleobasin and recorded in three localities in Kazakhstan, eastern Kyrgyzstan, and Altai.     

First report of craniide brachiopods in the Palaeozoic of Iran (Pseudocrania,Ordovician), and Early to Mid‐Ordovician biogeography of the Craniida

Abstract: Lower Ordovician faunas of Bohemia (Perunica), Baltica and North China include the oldest known representatives of the Order Craniida, but otherwise in Gondwana and associated terranes, the record of craniides is sparse. Pseudocrania insperata sp. nov. from the Lashkarak Formation of the Eastern Alborz Mountains is the first and as yet only record of the occurrence of craniides in the Middle Ordovician (Darriwilian) of Iran and temperate to high latitude peri‐Gondwana. Pseudocrania was known hitherto only from the Middle Ordovician of Baltoscandia and the Chu‐Ili terrane of Kazakhstan.     

Stratigraphical distribution of the Ordovician graptolite Azygograptus Nicholson & Lapworth in the Central Andean Basin (northwestern Argentina and southern Bolivia)

We analyzed new occurrences of Azygograptus lapworthi from the Cordillera Oriental, Argentina. The bearer sandstones levels, corresponding to the Acoite Formation, are overlying the deposits, in which the Didymograptellus bifidus Biozone (Lower Ordovician, upper Floian, Fl3) was previously recognized, and are overlain by younger pelitic levels yielding Xiphograptus lofuensis (Middle Ordovician, early Dapingian, Dp2). Previous records from the Central Andean Basin are also reviewed in detail and accurately correlated, allowing us to conclude that the Azygograptus lapworthi Biozone corresponds to the Middle Ordovician (lower Dapingian, Dp1). This biostratigraphic framework documents that the transition between the Lower and Middle Ordovician deposits occurs in the uppermost levels of the Acoite Formation in the Argentine Cordillera Oriental. It is additionally integrated with up to date conodont records to establish a high-resolution regional correlation, with equivalent deposits from the Puna of northwestern Argentina and Cordillera Oriental of Bolivia, and to discuss new insights for global correlation.     

AnOistodus venustus-like conodont species from the Middle Ordovician of Baltoscandia

Ordovician conodont specimens resemblingOistodus venustus Stauffer, 1935 have been reported from many areas. There is increasing evidence, however, that several lineages with homeomorphic conodont elements have erroneously been referred to one and the same species. I have investigated Baltoscandian conodont elements of this kind in order to find out about their origins and phylogenetic relationships with morphologically comparable elements from other areas. A natural grouping of finds from the Middle and lower Upper Ordovician of Baltoscandia is here described as belonging to a new species of a new genus,Venoistodus balticus n. gen., n. sp. The new species probably evolved paedomorphically fromDrepanoistodus forceps (Lindström, 1955) in the Early Ordovician.     

Ostracodes from the Tuloi and Karasu formations (Ordovician) of northeastern Gorny Altai

Ostracodes from the Tuloi (Floian, Dapingian and the lower Darriwilian) and Karasu (Darriwilian and Sandbian) formations of the northeastern Gorny Altai are discussed and several ostracode localities are briefly described. Two new species Soanella tuloica sp. nov. and Maraphonia caliginosa sp. nov. are described and figured. The previously described forms are only illustrated.     

Did hard substrate taxa diversify prior to the Great Ordovician Biodiversification Event?

The Great Ordovician Biodiversification Event (GOBE) refers to one of the greatest increases in biodiversity during the Phanerozoic. Recent studies have shown that this taxonomic increase can be attributed to elevated origination rates around the Dapingian–Darriwilian boundary in the Middle Ordovician, while extinction rates stayed relatively constant throughout the Ordovician. Even though this global pattern of origination and extinction appears similar across diverse groups and geographical areas, earlier studies suggested that hard substrate taxa may have diversified prior to the GOBE, during the Early Ordovician. Here, we quantify Ordovician diversification dynamics of hard substrate taxa while simultaneously accounting for temporally varying sampling probabilities. Diversification rates of hard substrate taxa, both as a whole and when analysed as separate groups, appear to be very similar to those of free-living benthic taxa. The observation that the diversification dynamics of many different taxonomic and ecological groups show the same temporal pattern, suggests a common cause of Ordovician diversification dynamics.     

New Middle Devonian conodont data from the Dong Van area,NE Vietnam (South China Terrane)

Middle Devonian conodonts from the Si Phai section in NE Vietnam are described. The section ranges from the Middle Devonian ensensis to timorensis conodont zones to the Late Devonian rhomboidea conodont Zone. A rich overall assemblage is described, including 27 taxa of species or subspecies rank and 11 taxa described in an open nomenclature. Among the dominant Polygnathus forms, four new taxa are described: Polygnathus linguiformis saharicus subsp. nov., Polygnathus linguiformis vietnamicus subsp. nov., Polygnathus rhenanus siphai subsp. nov., and Polygnathus xylus bacbo subsp. nov. Conodont assemblages are attributed to polygnathid, polygnathid-klapperinid, and klapperinid conodont biofacies representing hemipelagic to pelagic environments. The klapperinid biofacies, unreported in the previous literature, are here attributed to offshore areas of the external shelf. The taxonomic compositions of the studied conodont assemblages, as well as their CAI characteristics (CAI 4–5), suggest a palaeogeographic affinity of the studied strata to the Chinese Devonian Guangxi Basin, and the South China Terrane in general. Furthermore, the conodont biofacies and the palaeogeographic distribution of the fauna are discussed.     

Middle–Late Ordovician chitinozoans from Songliang of Qiaojia,western South China,and their biostratigraphic implications

Ordovician chitinozoans are as yet inadequately documented from the western Yangtze Platform, South China. Here we present a systematic study on chitinozoans from a Middle–Upper Ordovician succession at Songliang of Qiaojia, northestern Yunnan, southwestern China. Altogether 34 species of 12 genera are identified from the upper Hungshihyen and the Huadan formations. The top of the Hungshihyen Formation yields typical Early and Middle Ordovician forms, for instance, Lagenochitina obeligis and Belonechitina chenjiawuensis, with the latter only known from the lower Darriwilian in South China, thus suggesting an early Darriwilian age for this interval. The chitinozoans recovered from the Huadan Formation include Lagenochitina prussica and Spinachitina fossensis, both are mainly confined in Katian and sometimes ranging into younger strata. This indicates an age younger than the middle to late Darriwilian previously determined for the Huadan Formation. However, conflicts exist in age assignment of the Huadan Formation based on chitinozoan and other evidence, and further work is required.     

Billingen (Lower Arenig/Lower Ordovician) acritarchs from the East European Platform and their palaeobiogeographic significance

Billingen (Lower Arenig/Lower Ordovician) sediments of the St. Petersburg region, northwest Russia and the Leba area, northern Poland of the East European Craton yield acritarch assemblages, which are largely homogenous though displaying minor compositional differences that probably reflect a gradient from inner to outer shelf environments. Comparison with coeval acritarch microflora from the Yangtze Platform, South China, shows an overall similarity between Baltoscandian and South Chinese phytoplankton. The widespread uniformity in the fossil microphytoplankton may be related to the extensive global 'evae' sea-level transgression, which characterized the Billingen time. This suggests that during the Tremadoc through early Arenig times, acritarch assemblages displayed essentially an undifferentiated cold-water and oceanic character along the whole margin of Perigondwana in the South, as well as on the South Chinese and Baltic platforms, at middle latitudes (Mediterranean oceanic Realm). Despite this overall similarity, however, some typical taxa of the high-latitude Mediterranean Province (Arbusculidium, Coryphidium and Striatotheca) occur in South China, but are absent in Baltica. This discrepancy is explained as caused by differences in climatic and physiographic conditions that prevailed at the two palaeocontinents at this time. The inferred pattern of oceanic circulation during the Lower Ordovician is consistent with the palynological evidence of a prevailing warmer climate in Baltica than in South China, although the two palaeocontinents occupied the same palaeolatitudinal position.     

High‐resolution conodont biostratigraphy from the Darriwilian Stage (Middle Ordovician) of the Argentine Precordillera and biodiversity analyses: a CONOP9 approach

Ordovician conodonts have been extensively documented in the Argentine Precordillera, providing a robust database for a diverse set of palaeontological studies. Despite the numerous studies, the published taxonomy and stratigraphical ranges, data remain contradictory for particular time intervals. Data from a new conodont collection from the Gualcamayo Formation exposed at the Cerro La Chilca section, and new information on the occurrence and ranges of species from the Las Chacritas and Las Aguaditas sections are presented herein. We used a computer‐assisted numerical sequencing program (CONOP9) to construct a composite stratigraphical range chart from data of 57 conodont species in four sections from the Argentine Precordillera. The identified zones of Lenodus variabilis, Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus and Eoplacognathus suecicus allowed us to verify and adjust the biostratigraphical scheme for the Darriwilian of the Central Precordillera. Additionally, species of the genera Histiodella, namely Histiodella sinuosa, Histiodella holodentata, Histiodella kristinae and Histiodella bellburnenisis, enable a reasonable correlation between the Histiodella‐based zonation and the Baltoscandian zonation. Conodont diversity is evaluated using conventional measures (total diversity and normalized diversity) and an interval‐free approach with CONOP9 software. Our data show a positive pattern in conodont diversification, increasing rapidly through the L. variabilis to the Y. crassus zones and reaching a peak in the E. pseudoplanus Zone. When analysing diversity fluctuations with respect to the environmental changes within the depositional basin, migrations in and out of the basin related to local sea level fluctuations appear to be an important process driving the conodont diversity pattern in the Precordillera.     

湖北宜昌地区下-中奥陶统界线疑源类生物地层学意义

根据牙形类Baltoniodus? triangularis的首现,中奥陶统和大坪阶底界已界定于湖北宜昌黄花场剖面大湾组底界之上10.57m.对黄花场剖面以及邻近的大坪剖面大湾组疑源类研究表明,某些疑源类属种具有生物地层学意义,其首现可用于识别奥陶系下/中统界线.     

Volkhov graptolites from the lower-middle Ordovician boundary beds of the St. Petersburg region,Russia

The lower and lowermost Middle Ordovician strata of the Volkhov Stage exposed in the vicinity of St. Petersburg, Russia, yield a graptolite fauna at several stratigraphic levels, being more often confined to the mud-mound clays than to the normally stratified, Condensed carbonates. Overall taxonomic diversity of the Volkhov graptolites is relatively low and associations include no more than seven species in ail localities. TheTetragraptus, Didymograptus andXiphograptus species found are pandemic and have quite extensive stratigraphie ranges within the mid-Arenig Series. Based on the graptolite zonation, the Volkhov Stage can be correlated to thePseudophyllograptus angustifolius elongatus andDidymograptus (Expansograptus) hirundo graptolite biozones of Baltoscandia and to the upperDidymograptus simulans toDidymograptus (Expansograptus) hirundo biozones of the British graptolite succession. TheIsograptus victoriae lunatus lower zonal boundary probably falls within the graptolite-bearing interval of the lower Volkhov Stage. As the result of indirect biostratigraphic and interpretative lithological correlations, the first appearance ofUndulograptus austrodentatus at the base of the Darriwilian Stage is deemed to be close to the boundary of theMegistaspis simon andM. limbata trilobite biozones and the lowerBaltionodus norrlandicus conodont Biozone of the upper Volkhov Stage. Seven dichograptid species belonging to four genera are described, one of them,Azygograptus volkhovensis n. sp., new.      

Conodonts from the upper Ordovician siliceous rocks of Central Kazakhstan

Several conodont localities of the upper Sandbian Stage are known in siliceous deposits of Central Kazakhstan. All of them produced similar assemblages overwhelmingly dominated by Periodon grandis with insignificant admixture of Scabbardella altipes, Hamarodus europaeus, Pygodus anserinus, Protopanderodus sp., and Drepanodus sp. The main feature of this fauna is in the co-occurrence of H. europaeus and P. grandis, forms characteristic for deep-water facies at shelf or microcontinents margins of temperate and warm-water paleobiogeographic provinces. The Ordovician paleo-oceanic basin of Kazakhstan and southern Urals were parts of the uniform biogeographic area as indicated by similarity of Ordovician conodont assemblages in siliceous deposits of these regions.