The Ordovician of the Middle East (Iran, Afghanistan, Pakistan)
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Abstract Ordovician studies in Iran have shown significant progress since the beginning of the century. A number of individual faunas have been documented and a biostratigraphical framework based on conodonts, chitinozoans, acritarchs and trilobites developed. Correlation of Ordovician successions with the International Chronostratigraphic Chart has been significantly improved, and the position of the series and stage boundaries can be recognized with greater precision. While geographical proximity to temperate latitude Gondwana is apparent for most Iranian terranes, biogeographical links of Alborz and Kopet-Dagh with South China prevailed through the Early–Middle Ordovician. In Pakistan, Ordovician deposits have a restricted distribution in the Karakorum block (Chitral). Here they are represented by the Yarkhun and Vidiakot formations with Floian–Darriwilian acritarchs, chitinozoans and early Darriwilian conodonts. In Peshawar District of the North-West Frontier Province, an Early–Middle Ordovician age is likely for the Misri Banda Quartzite with Cruziana rugosa trace fossils. It is overlain conformably by carbonates of the Panjpir Formation, which has an inferred Middle Ordovician–Silurian age. Presently available information on the Ordovician of Afghanistan is mostly based on reconnaissance studies performed almost half a century ago, and a few monographed Early and Late Ordovician faunas.Keywords:
Conodont
Acritarch
Ordovician conodont collections from several Argentinian basins including the Eastern Cordillera, Famatina and Precordillera allow recognition of a group of conodonts that comprise a new genus here named Condorodus n. gen. Species of this genus have an apparatus composed of six elements recovered so far: Pa, Pb, Sb1, Sb2, Sc and Sd. The differences mainly between the P elements support recognizing three species, from the older to younger: C. diablensis n. gen., n. sp., C. gracielae n. gen., n. sp. and C. chilcaensis n. gen., n. sp., that appeared in the upper Floian (Lower Ordovician) and vanished in middle Darriwilian time (Middle Ordovician). The Eastern Cordillera is here assumed as the place of origin of the Condorodus n. gen. lineage during the late Floian, and then this genus dispersed through the western margin of Gondwana, reaching the Precordillera in the early Darriwilian, from there it could have dispersed to different regions of Gondwana, Perigondwana and Laurentia during the late Darriwilian, and probably give rise to conodont apparatuses of similar morphology in the Late Ordovician.
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Upper Cambrian (Furongian) and lowermost Ordovician conodonts are reported for the first time from the Kulumbe River section, northwest Siberian Platform. This section consists of a remarkably monotonous section of Cambrian and Ordovician shallow-water marine carbonates assigned to the Uyigur and Il'tyk Formations of the Mansian, Loparian and Nyaian regional stages. The 70 samples collected along the section produced 2870 identifiable conodont elements assigned to 23 species. The new data demonstrate that the upper Cambrian and lower Ordovician conodont faunas of the Siberian Platform are very similar to those reported elsewhere. The faunas are endemic at species level, but include genera that are widely distributed on other continents. Five new species are described including Hirsutodontus galerus sp. nov., Hirsutodontus limus sp. nov., Hispidodontus kulumbense sp. nov., Semiacontiodus asianus sp. nov. and Teridontus? angustus sp. nov. Based upon conodont evidence the Cambrian-Ordovician boundary is located within an unexposed 5 m thick interval in the upper part the Nyaian regional stage.
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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.
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A new study on conodont biostratigraphy of Cambrian-Ordovician boundary in Yaowangshan Section, Qingzhou area, Shandong Province is first reported in this paper. 9 conodont zones have been recognized in the Chaomidian limestone formation, among which 3 are from the Lower Ordovician and 6 from the Fengshanian Stage of upper Upper Cambrian. The first discovery of the Cambrian-Ordovician Boundary species Iapetognathus fluctivagus in this section is of great significance. It will provide a new rule for Cambrian-Ordovician Boundary study in the Shandong area as well as in the whole North China. Additionally, through the further detailed study, the well-developed Yaowangshan Section will probably become the stratotype section in China, which will deeply affect the establishment of Cambrian stages, a still uncompleted work so far.
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This first study on chitinozoans from Greenland has revealed representatives of twenty-two chitinozoan species recovered from Ordovician and Silurian beds in North Greenland. The Ordovician faunas are sirnilar to those described from North Arnerica, while the Silurian faunas are more sirnilar to those of Baltoscandia. Four distinct assemblages can be separated between Maysvillian - early Garnachian and Ludlow. The chitinozoan biostratigraphy is in agreement with that of the graptolites but differs from the conodont biostratigraphy.
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The last two decades have seen the publication of a large number of papers dealing with Palaeozoic acritarchs including many devoted to the description of Ordovician assemblages. It has become clear that, these microfossils have considerable potential for correlation and that they are frequently recovered From sequences otherwise devoid of fossil material. In Britain, acritarchs have been described in detail from the Cambrian (Potter 1974 M. S.); Tremadoc (Rasul 1971 M. S., 1974, 1977a, l977b) and from the Silurian (Lister 1966 M. S., 1970; Hill 1974 M. S.) Until the recent work of Booth (l979 M. S.) dealing with Arenig-Llanvirn assemblages, no detailed systematic investigation of British Ordovician acritarchs had been attempted. The primary objective of the present study is to provide a comprehensive description of acritarchs from the Middle and Upper Ordovician of Britain, with particular emphasis on the type-areas of the Llandeilo and Caradoc. In conjunction with the work of Booth it is hoped that this account will go some way towards providing a biostratigraphical framework which will facilitate the use of these microfossils for the purposes of correlation in the Ordovician.
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