Palaeontologic and biogeochemical characterization of the Cyrtograptus lundgreni event in the black shales of eastern Mid‐Sardinia, Italy

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 Thüringen, 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 Thüringen. A close correlation between the third extinction datum of Sardinia and Datum 2 of Thüringen and Gotland reinforces the importance of these events at global scale.

Chitinozoan biostratigraphy of the Silurian Wenlock–Ludlow boundary succession of the Long Mountain, Powys, Wales

“…In Sardinia, Pittau et al . (2006) marked a similar series of chitinozoan extinctions in the upper part of the lundgreni Biozone with the disappearance of C. subcyatha and a few regional taxa.…”

First evidence for the Homerian (late Wenlock, Silurian) positive carbon isotope excursion from peri-Gondwana: new data from the Barrandian (Perunica)

“…1), in contrast to the series of mid-Homerian extinction events (i.e, the Mulde conodont and the end lundgreni graptolite bioevents) which were already reported from the latter area (Štorch 1995, Gutiérrez-Marco et al 1996, Pittau et al 2006. Special attention is also paid to an improvement of the internal stratigraphy of the Homerian Kozel Limestone Member (new member) and dating of its very diverse fauna in respect to the mid-Homerian extinction events.…”