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Miospore assemblages from Late Ordovician (Katian-Hirnantian), Ghelli Formation, Alborz Mountain Range North-eastern Iran: Palaeophytogeographic and palaeoclimatic implications
Get PDFWell-preserved miospore assemblages are recorded from the Late Ordovician (Katian-Hirnantian), Ghelli Formation in Pelmis-gorge at the north-eastern Alborz Mountain The palynomorphs were extracted from siliciclastic deposits which are well-dated by using of marine palynomorphs (acritarchs and chitinozoans). The encountered miospore assemblages consist of 14 genera (28 species: 26 cryptospores and 2 trilete spores). Six new cryptospore taxa are described: Rimosotetras punctata, Rimosotetras granulata, Dyadospora asymmetrica, Dyadospora verrucata, Segestrespora iranense and Imperfectotriletes persianense. The present findings contribute to improving knowledge of origin and onset of development of vegetative cover during the Late Ordovician. The recovery of diverse and abundant cryptospores in the Late Ordovician (Katian-Hirnantian) Ghelli Formation are probably related to increasing input of land-derived sediments during the global sea-level fall linked to the Late Ordovician glaciation, and tolerance of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by earliest primitive land plants which probably grew close to the shoreline and washed in from the adjacent areas and produced high amount of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts and graptolite remains which are not discussed in detail herein. The established chitinozoan biozones of this part of Palaeozoic sequences are Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata and Spinachitina oulebsiri, suggesting the Late Ordovician (Katian-Hirnantian). These chitinozoan biozones are well-known only in peri-Gondwanan Domain, indicating that the study area has been part of this palaeo-continent during the Late Ordovician
Biostratigraphy of Acritarchs and Chitinozoans in Ordovician Strata from the Fazel Abad Area, Southeastern Caspian Sea, Alborz Mountains, Northern Iran: Stratigraphic Implications
Get PDFSixty-four surface samples from the Lower Palaeozoic rock units (mainly Lalun,Abastu and Abarsaj formations) near Kholin-Darreh village in the Fazel Abad area,southeastern the Caspian Sea, Northern Iran, were analyzed to determine their agerelationships. The samples of Lalun Formation were barren, but those of Abastu andAbarsaj formations contained well-preserved and abundant palynomorph entities, whichare dominated by acritarchs (23 species belonging to 15 genera) and chitinozoans (29species distributing among 15 genera) with remains of scolecodonts, graptolite and afew cryptospores, although not determined in detail. Based on the restricted stratigraphicrange of acritarch species, an Early Ordovician (Tremadocian) age was assigned to theAbastu Formation; while based upon index chitinozoan and acritarch taxa, a LateOrdovician (Katian to Hirnantian) age was assigned to the Abarsaj Formation. Likewise,based on the presence of diagnostic chitinozoan taxa, the Abarsaj Formation can beassigned to the Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongataand Spinachitina oulebsiri chitinozoan Biozones. These chitinozoan assemblages reflecta clear palaeobiogeographic affinity with the so-called "North Gondwana Domain".Two major hiata are present within the studied Lower Palaeozoic succession in the FazelAbad area. The first hiatus appeared between the Lalun Formation (Early Cambrian) andthe Abastu Formation (Tremadocian) and includes the Middle-Upper Cambrian MilaFormation. The second hiatus occurs between the Abastu Formation (Tremadocian) andthe Abarsaj Formation (Katian-Hirnantian) and spans the interval of the Floian-Sandbian, which corresponds to uplift related to the initial stage of rifting of the Palaeo-Tethys Ocean
Chronostratigrahy of Acritarchs and Chitinozoans from upper Ordovician Strata from the Robat-e Gharabil Area, NE Alborz Mountains, Northern Khorassan Province: Stratigraphic and Paleogeographic Implications
Get PDFThe Palaeozoic rock units mainly, Ghelli, Niur, Padeha, Khoshyeilagh and Mobark formations are well-exposed in the north of Robat-e Gharabil village. 116 out of 157 surface samples were analyzed to determine aged relationships of Ghelli Formation. The samples of Ghelli Formation are dominated by acritarchs (42 species belonging to 23 genera) and chitinozoans (26 species distributing among 15 genera). Two new acritarch species are introduced, consisting of Goniosphaeridium iranense n.sp., and Goniosphaeridium persianense n. sp. Based on the restricted stratigraphic range of chitinozoan species, Late Ordovician (Ashgill) age is assigned to the Ghelli Formation. On the other hand, the presence of diagnostic chitinozoan taxa in the Ghelli Formation consisting of Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones, suggest a clear palaeobiogeographic affinity between NE Alborz Mountain and North Gondwana Domain. The presence of some chitinozoan and acritarch taxa from the Baltic and Laurentia in Gondwanan chitinozoan biozones of the Robat-e Gharabil area suggests the existence of counter-clockwise marine currents that resulted in bringing planktonic organisms (acritarchs and chitinozoans) from lower latitudes (Baltica) to higher latitudes (Northern Gondwanan Domain) settings
Palynostratigraphy, Palaeogeography and Source Rock Evaluation of the Nayband Formation at the Parvadeh area, Central Iran, Iran
Get PDFThe Nayband Formation was measured and sampled in Parvadeh area, southern Tabas city. In this area, this formation has a thickness of 1410 m, dividing into four members, namely Gelkan, Bidestan, Howz-e-sheikh and Howz-e-khan. A total 573 samples were treated for Palynological analysis, and only 120 samples were productive. A total of 57 miospore taxa and 11 plant macrofossil were encountered. Based on stratigraphic distribution of macrofossil and miospore taxa ten assemblage zones were established throughout the Nayband Formation. The encountered miospore taxa and plant macrofossil suggest Upper Triassic (Norian-Rhaetian) for the Nayband Formation.Rock-Eval data shows the presence of organic matter-rich shales with Type III kerogen. The Nayband Formation in the studied section has experienced high temperature which is confirmed by vitrinite reflectance measurements of 0.9-1.2 %VRr. At this thermal maturity stage, organic-rich shales in the formation have generated liquid hydrocarbons as evidenced by the occurrence of solid bitumen in the respective samples
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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