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Structure and development of upper Permian brachiopod shells from North Iran
No full textThe calcareous shell of several Rhynchonelliform brachiopods from the Nesen Formation (Late Permian) of North Iran was studied under scanning electron microscopy and cathodoluminescence to define their ultrastructure and their state of preservation versus diagenetic alteration. The Strophomenata shell succession is composed of a cross-bladed laminar secondary layer crossed by pseudopunctae; a prismatic tertiary layer has been observed in a few species only. The Rhynchonellata shell succession is composed of a fibrous secondary layer and a prismatic tertiary layer in all the studied species. Specimens were classified into six morphological types based on layer fabric and the morphology of its structural units (laminae, fibres and prisms). Subsequently these morphological types were analyzed through cathodoluminescence to assess their eventual diagenetic alteration. Relative frequencies were calculated for each morphological type and for the degree of luminescence based on the different lithology of the host rocks to evaluate the main factors that affect shell preservation. Results show that diagenetic alteration depends on shell fabric, taxonomy and lithology of the host rocks, but it appears that the first and the second features are the most important factors in determining the fate of the shell and its preservation
BIOMINERALIZATION AND GLOBAL CHANGES: BRACHIOPOD SHELLS AS ARCHIVES OF THE END PERMIAN EVENTS
Full text linkThe Permian has been the theatre of major global changes in the Earth’s geodynamics, climate, seawater and atmosphere geochemistry, and thus it represents an interesting case study to understand the response of organisms to environmental changes, a topic which is of increasing interest to the scientific community, who has to face the current global change. In fact, in the Permian the biotic response was dramatic, culminating at the end of the period with the greatest mass extinction of the Phanerozoic. Noteworthy, the end Permian mass extinction coincided with one of the largest known continental eruptions, the Siberian trap basalts, that are considered to have generated more than 100,000 Gt of CO2 as well as CH4, leading to ocean acidification and global warming. Brachiopods, which are low buffered organisms with a heavily calcified shell, can be the perfect candidates to record the trends related to changes in seawater chemistry during this critical interval. The aim of this research is thus to study the biomineralization of brachiopod shells to unravel the patterns of biotic changes caused by the extreme Late Permian events.
To reach this goal, I organized my research in three different phases, starting to investigate the main differences in the shell fabric of the brachiopod groups ruling the benthic communities in the Late Permian, that are the classes Rhynchonellata and Strophomenata (phase 1); then comparing the stratigraphic distribution of brachiopod genera during the Late Permian in a paleogeographic perspective (phase 2); finally, analyzing in great details, both qualitatively and quantitatively, the shell fabric of several taxa from Tethyan Permian-Triassic Boundary (PTB) successions, to unravel the biomineralization activity at generic level(phase 3).
To develop this research I investigated brachiopods belonging to different paleogeographic localities in the Tethyan realm. The specimens were in part collected by myself during field activity, in part already available from the collections of Dipartimento di Scienze della Terra “A. Desio” and also provided by external partners. The studied brachiopods come from:
1. Nesen Formation, Alborz Mountains, northern Iran;
2. Julfa Formation, Ali Bashi Formation and Boundary Clay, Ali Bashi Mountains, Northwestern Iran;
3. Selong Group, southern Tibet;
4. Gyanyima Formation, southwestern Tibet;
5. Bulla Member, Dolomites, Northern Italy;
6. Gomaniibrik Formation, Hazro, Turkey;
7. Changhsing Limestone and Dalong Formation, South China
These data were integrated with the analysis of the available published literature on Upper Permian brachiopods, in particular to develop step 1 and 2. The methods used to develop this research may be grouped in four main categories:
1. Microscopical analysis of the shell structure using SEM (phases 1 and 3)
2. Geochemical analysis of the calcitic shell contents for trace elements (Mg, Sr, Fe, Mn) and stable isotopes (C and O)(phase 1)
3. Image analysis to acquire quantitative parameters of the shell ultrastructure (phase 3)
4. Statistical analysis of the stratigraphic distribution of brachiopod taxa using the logistic regression in order to test association between environmental variable and taxonomic composition (phase 2).
Performing phase 1, I discovered important differences in the structural and chemical composition of the shell in the two main Upper Permian brachiopod classes: the Strophomenata and the Rhynchonellata. These taxa bear a different calcitic shell fabric: the former possesses a double or triple layer shell consisting of a primary layer, a secondary layer with cross-bladed laminae and a prismatic tertiary layer; the latter have a shell succession similar to extant ones, which is composed of a primary layer of crystallites, a secondary layer of discrete fibers and, eventually, a tertiary layer of prisms. Their different fabric corresponds to differences in the chemical composition. In particular the Strophomenata, which have a laminar fabric enriched in organic compounds, have higher Sr and Mg contents and a lower δ13C in their shells than co-occurring Rhynchonellata. In phase 2, the logistic regression analysis has shown that important changes in terms of taxonomic composition took place from the Wuchiapingian to the Changhsingian, with the Strophomenata being the dominant group in terms of abundance, but the Rhynchonellata being more prone to high rank diversification. In phase 3, the detailed study of the shell structure at the SEM, has revealed that Upper Permian genera can produce different type of shells, especially regarding the ratio between the organic and inorganic content. In particular, the taxa occurring during the first part of the Late Permian (Wuchiapingian and early Changhsingian) biomineralized thick shells with a relatively high inorganic content. Instead, in the late Changhsingian, brachiopod taxa produced shells with a higher organic content. In addition, the quantitative analysis of the fabric, based on the measured size of its structural units, revealed different trends in the two classes. Rhynchonellata reduced the size of the structural units (fibers) of their shell as approaching the PTB. On the other hand, the Strophomenata show a more complex response, either continuing in their normal biomineralization activity or increasing the size of their structural units (laminae).
Through this research, two important conclusions were reached: the first concerns the paleobiological implications of the different biomineralization processes performed by brachiopods, and the second is related to the brachiopod response to the end Permian global environmental changes. It is now clear that the brachiopod classes of Strophomenata and Rhynchonellata have profound differences in terms of the structural and elemental composition of their shell. These differences are likely related to the biomineralization process responsible for the formation of their shell, a collective process where arrays of mantle cells secrete the biocomposite in the Strophomenata, versus a discrete, single cell driven process in the Rhynchonellata . The observed changes in brachiopod shell biomineralization in the latest Permian are compatible with a change in the carbonate saturation state of seawater and thus with ocean acidification, related to Siberian Traps flood basalt volcanism. In fact, a general trend toward production of calcitic shells with higher organic content is recorded up to the PTB in most brachiopod groups. This may have been likely the result of changes in the physical and chemical composition of seawater that produced an increase in the energetic cost for carbonate precipitation in low buffered organisms such as brachiopods
The spermatozoon of a “living fossil”, Tubiluchus troglodytes (Priapulida)
No full textThe spermatozoon of Tubiluchus troglodytes, the first priapulid formally described from the Mediterranean Sea has a head composed
of an acrosome and a nucleus. The acrosome is divided in two branches coiled around the nucleus. The nucleus is basally columnar, but
apically generates two rods helically coiled one around the other. The midpiece is formed by an axoneme with 27 accessory microtubules,
surrounded by three mitochondria. An annulus separates the midpiece from the tail that contains a 9 + 2 axoneme surrounded by nine accessory microtubules. The spermatozoon of T. troglodytes is similar to that of the other two species known from the genus, and completely different from the ‘primitive’ one of the other priapulids. Since Tubiluchus is considered the most basal of the extant priapulids, and the only genus with an internal fertilization, it may be that in priapulids the external fertilization is a derived character
Brachiopod fabric, classes and biogeochemistry: implications for the reconstruction and interpretation of seawater carbon-isotope curves and records
No full textShell calcite of modern and ancient brachiopods is an important proxy in reconstructing oceanographic conditions of seawater. Our investigation reveals significant magnesium and carbon isotope relationships between two classes of ancient brachiopods. Brachiopods of the extinct Class Strophomenata constructed two- or three-layer shells with a primary layer of randomized granular calcite, a secondary layer of cross-bladed laminar calcite and, at times, a tertiary layer of large prismatic calcite. Contemporaneous, but extant, Rhynchonellata also have two- or three-layer shells, but their secondary layer consists of calcite fibers instead of cross-bladed laminar calcite. Furthermore, inter-crystalline space is limited in between the fibers of the secondary layer of the Rhynchonellata but higher in the laminar secondary layer of Strophomenata. δ18O values of the two classes of brachiopods from the same stratigraphic interval of the Lopingian Nesen Formation of North Iran show a considerable overlap with no significant difference (p=0.263). In contrast, carbon isotope values are significantly different (p=0.001) between contemporaneous Strophomenata (mean: +2.18‰) and Rhynchonellata (mean: +4.13‰). An evaluation of literature data of Permian (Asselian) and Carboniferous (Visean and Serpukhovian) Strophomenata (mean: +2.32‰, N=59) and Rhynchonellata (mean: +4.94‰, N=105) confirms a similar differentiation in their carbon isotope values.Its higher magnesium contents suggest that the Strophomenata probably secreted shell calcite at a faster rate than their coeval Rhynchonellata. This process may account for the δ13C differentiation observed between specimens of these two brachiopod classes. However, the different amount and composition of the organic matter of the Strophomenata may also play a role in shaping their more negative carbon isotope signature. Thus, the class of brachiopod and their associated different fabric must be adjusted for in their δ13C results and taken into consideration during the reconstruction of Paleozoic global δ13C carbonate-based seawater curves. Invariably, in some earlier studies undetected impacts imposed by the class-fabric on δ13C may account for some of the variation or trends documented in Deep-Time seawater-13C curves reconstructed with brachiopod populations from North America, Europe and Russia
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Micromorphology and differential preservation of Upper Permian brachiopod low-Mg calcite
No full textCalcareous shells of Rhynchonelliform brachiopods fromthe Nesen Formation (Late Permian) of Iran were studied
by scanning electron microscope, cathodoluminescence and trace element chemistry to define their microstructure
and state of preservation. In the Strophomenata shell succession, the secondary layer consists of
cross-bladed, laminar calcite, and in a few species there is a tertiary layer of prisms. In the Rhynchonellata
shell succession, the secondary layer consists of elongated fibers and the tertiary layer of prisms. All specimens
were classified into six micromorphological types based on the fabric of the layer and the morphology of their
microstructural units (laminae, fibres and prisms).
Shell micromorphology and enclosing whole rock were further analyzed by cathodoluminescence and trace
chemistry to assess preservation of brachiopod low-Mg calcite and specifically of their layers and microstructural
units. Relative color frequencies were determined for each morphological type and degree of luminescence
based on the lithology of the host rocks to evaluate the main factors that affect shell preservation. Results
suggest that diagenetic alteration may depend on shell fabric and taxonomy as well as lithology of the host
rock, but it appears that the first and the second features are the most important factors in determining the degree
of brachiopod low-Mg calcite preservation. In general, the fibrous secondary layer is likely more often and
better preserved than its laminar counterpart irrespective of host rock lithology. Furthermore, tertiary layers
tend to be better preserved than secondary ones in Rhynchonellata low-Mg calcite shells, whereas no preferential
preservation of either layer over the other was observed in the shells of Strophomenata. This information is
important when selecting fossil brachiopod low-Mg calcite shells as geochemical proxies for paleoclimatic,
paleoecologic, paleoenvironmental and other studies
Logiche e modelli organizzativi per le reti ospedaliere : analisi di due casi aziendali
No full textNel panorama della sanità ospedaliera moderna appare sempre più rilevante che le aziende sanitarie si dotino delle metodologie e degli strumenti necessari per analizzare la propria rete ospedaliera e per riprogettarla in modo da definire modelli di funzionamento che promuovano sinergie, integrazione, economie di know how e di scopo.
L’obiettivo di questo capitolo è quello di applicare a due diversi casi aziendali un modello metodologico finalizzato ad analizzare
le logiche di fondo e i fattori critici di contesto che ispirano le diverse soluzioni per la riorganizzazione delle reti ospedaliere.
I casi sono stati selezionati secondo il principio per il quale risultano massime le differenze in termini di fattori di contesto per osservare eventuali difformità/convergenze sulle proposte di riprogettazione organizzativa. Implicazioni per il management delle aziende sanitarie sono derivate nelle conclusioni
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