A succession of biotic and geochemical changes that occurred during the Cyrtograptus lundgreni Event (Late Wenlock) have been recorded from the ‘pelagic’ black-shales in the Goni section, eastern mid-Sardinia, Italy. The studied interval encompasses the Cyrtograptus rigidus to Pristiograptus dubius-Gothograptus nassa zones. The fossil association includes graptolites, chitinozoans and microplankton i.e. probable linings of agglutinated foraminifera and radiolaria capsular membranes. Analysis of the chitinozoan distribution revealed a succession of several chitinozoan associations with low species diversity and dominated by opportunistic species. Three chitinozoan faunal turnovers and three extinction events have been recorded. Two of them coincide with graptolite extinctions whereas one probably is of local significance. Disappearance of the chitinozoan and microplankton associations occurred during four consecutive graptolite zones. Geochemical data (trace elements analysis) showed significantly higher (up to c . 100%) values for Co and Cd in the sedimentary organic matter (SOM) than in the whole rock samples. Possible relationships between peaks of metal enrichment, the major faunal changes among chitinozoans, extinction events among chitinozoans and graptolites and, to a certain extent, oceanic events may be inferred. The first extinction datum is older that those occurring in Gotland, Sweden and Thu¨ringen, Germany and is so far considered to be of local significance. The second extinction datum of Sardinia can be matched with Datum 1 of Gotland and Thu¨ringen. A close correlation between the third extinction datum of Sardinia and Datum 2 of Thu¨ringen and Gotland reinforces the importance of these events at global scale. I Biogeochemistry, chitinozoans, extinction event, graptolites, sedimentary organic matter, Silurian, trace elements.

Palaeontological and biogeochemical characterization of the Cyrtograptus lundgreni Event in the black shales of Eastern Sardinia

PITTAU, PAOLA;
2006-01-01

Abstract

A succession of biotic and geochemical changes that occurred during the Cyrtograptus lundgreni Event (Late Wenlock) have been recorded from the ‘pelagic’ black-shales in the Goni section, eastern mid-Sardinia, Italy. The studied interval encompasses the Cyrtograptus rigidus to Pristiograptus dubius-Gothograptus nassa zones. The fossil association includes graptolites, chitinozoans and microplankton i.e. probable linings of agglutinated foraminifera and radiolaria capsular membranes. Analysis of the chitinozoan distribution revealed a succession of several chitinozoan associations with low species diversity and dominated by opportunistic species. Three chitinozoan faunal turnovers and three extinction events have been recorded. Two of them coincide with graptolite extinctions whereas one probably is of local significance. Disappearance of the chitinozoan and microplankton associations occurred during four consecutive graptolite zones. Geochemical data (trace elements analysis) showed significantly higher (up to c . 100%) values for Co and Cd in the sedimentary organic matter (SOM) than in the whole rock samples. Possible relationships between peaks of metal enrichment, the major faunal changes among chitinozoans, extinction events among chitinozoans and graptolites and, to a certain extent, oceanic events may be inferred. The first extinction datum is older that those occurring in Gotland, Sweden and Thu¨ringen, Germany and is so far considered to be of local significance. The second extinction datum of Sardinia can be matched with Datum 1 of Gotland and Thu¨ringen. A close correlation between the third extinction datum of Sardinia and Datum 2 of Thu¨ringen and Gotland reinforces the importance of these events at global scale. I Biogeochemistry, chitinozoans, extinction event, graptolites, sedimentary organic matter, Silurian, trace elements.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11584/17561
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