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Famennian (Late Devonian) conodonts from the Pizzul West section (Carnic Alps, Italy)
No full textConodonts from the Pizzul West section are presented. e section is located in the Cason di Lanza/Mt. Zermula area
of the central Carnic Alps and it exposes about twenty-four metres of Upper Devonian limestone. e forty-one taxa documented
allow the discrimination of seven biozones of Frasnian and Famennian: Upper rhenana, Upper crepida, Uppermost crepida,
Lower rhomboidea, Upper rhomboidea, Lower marginifera and Lower expansa
The Devonian/Carboniferous boundary in Sardinia (Italy)
No full textIn Sardinia (Italy) two sections, located in the southeastern part of the island, expose the Devonian/Carboniferous Boundary: the Monte Taccu Section and the Bruncu Bullai section. Both expose limestones from the middle Famennian to the lower Tournaisian Siphonodella jii Zone. The limestone sequence is interrupted by a thin level of shales representing the Hangenberg Event. Data on conodont biostratigraphy and magnetic susceptibility across the Devonian/Carboniferous
Boundary are here summarised and reviewed
Conodonts across the Devonian/Carboniferous boundary in SE Sardinia (Italy)
Full text linkThe Bruncu Bullai section, located in SE Sardinia, exposes limestones from the styriacus Zone (upper Famennian) to the Upper duplicata Zone (Tournaisian), but the Upper praesulcata Zone is not documented; at the Devonian/Carboniferous boundary a black shales level, equivalent to the Hangenberg Shales, is present. Fifty-six conodont taxa were recovered, three of which are here described as new species: Polygnathus bicristatus, Po. nuragicus, Pseudopolygnathus granulobatus; two more species, probably new, are described, but left in open nomenclature because of the low number of specimens collected. The relative high abundance of Protognathodus and low abundance of Siphonodella in some levels and the opposite in others is discussed, and a new hypothesis on the occurrences of protognathodids as influenced by ecological factors is suggested. The early phase of the Hangenberg crisis is testified by a faunal turnover in an impoverished fauna within the deposition of limestones of the Lower praesulcata Zone
Conodonts across the Devonian/Carboniferous boundary: a review and implication for the redefinition of the boundary and a proposal for an updated conodont zonation
Full text linkThis paper is a contribution to the redefinition of the base of Carboniferous system. At present the criterion for the definition of the Devonian–Carboniferous boundary is the first occurrence of a conodont species. In order to evaluate the stratigraphic potential for new criteria for the definition of the Devonian–Carboniferous boundary, the distribution of conodont species of Bispathodus, Branmehla, Palmatolepis, Polygnathus, Protognathodus, Pseudopolygnathus and Siphonodella across the boundary is presented and discussed. An updated biozonation scheme across the boundary based on the First Appearance of Bispathodus ac. aculeatus, Bispathodus costatus, Bispathodus ultimus, Protognathodus kockeli, Siphonodella bransoni and Siphonodella duplicata is proposed, and it is suggested that the new criterion for the definition of the base of the Carboniferous system be the First Appearance Datum of Pr. kockeli or Si. bransoni
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
Selected Famennian (Late Devonian) events (Condroz, Annulata, Hangenberg) in Sardinia and in the Carnic Alps: conodont biostratigraphy, magnetic susceptibility and geochemistry.
Full text linkThe Condroz, the Annulata and the Hangenberg are three events occurred in the Famennian. Causes and consequences are different for each one. The Condroz event is related to a sharp regression associated with an extinction of few ammonoid groups. The Annulata event to a transgression associated with a global spread of the ammonoid Platyclymeniae annulata. The Hangenberg event is a major event, that took place in a complex phase of eustatic variations that affected severely the fauna, and it is considered as one of the biggest extinction in the history of the earth.
A multidisciplinary approach is here provided to investigate the selected events. A biostratigraphic study based on conodonts was carried out to individuate the precise biostratigraphic position when the events occurred. The evolution of the low field magnetic susceptibility and the major elements geochemistry (Al, Si, K and Ti) have been investigated to study the evolution of the detrital input across the events.
Six different section were studied in two different areas of North Gondwana where the Famennian rocks are well exposed. Two sections bearing the Condroz and the Annulata events were studied in the Carnic Alps, four sections containing the three events were studied in the South East of Sardinia.
A detailed biostratigraphic study is here provided from both areas. More than 28 000 conodonts have been collected and discriminated into 101 taxa. Each taxon is described and illustrated. Ten conodont Zones, from the Upper rhenana Zone (Frasnian) to the Lower expansa Zone (Famennian) have been recognized in the Carnic Alps. Nineteen conodont Zones, from the Lower crepida Zone (Famennian) to the Upper duplicata Zone (Tournaisian) have been discriminated in the Sardinian sections.
The three events have been recognized in both areas. As for the Condroz and for the Annulata events, even if there is no change in lithology, the curves obtained by the MS and the major elements tends to show distinctive peaks time-equivalent to the events. In addition, a stratum rich in ammonoids marks the Annulata event in the field.
As for the Hangenberg event, marked in the field by a thin level of black shales, while the curves of the magnetic susceptibility and the major elements show a constant trend immediately before the main event (Hangenberg equivalent shales), in the earliest Carboniferous the magnetic curve shows distinctive fluctuations. These fluctuations are here explained by a phase of oceanic instability after the event. Despite there are no changes in the MS and in the major element data, the fauna is impoverished and seems to be affected by an earlier phase of the main event already in the Lower praesulcata Zone.
The major detrital input in the Carnic Alps sections may indicate a closer distance to the source for the latter respect to the Sardinia-Corsica microplate, therefore a new palaeogeographic interpretation for the two areas investigated in the Upper Devonian is here hypothesize
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