BIOMINERALIZATION AND GLOBAL CHANGES: BRACHIOPOD SHELLS AS ARCHIVES OF THE END PERMIAN EVENTS
Tesi di Dottorato
Data di Pubblicazione:
2015
Citazione:
BIOMINERALIZATION AND GLOBAL CHANGES: BRACHIOPOD SHELLS AS ARCHIVES OF THE END PERMIAN EVENTS / C. Garbelli ; tutor: A. Tintori, L. Angiolini ; coordinator: N. Saino. DIPARTIMENTO DI SCIENZE DELLA TERRA "ARDITO DESIO", 2015 Mar 16. 27. ciclo, Anno Accademico 2014. [10.13130/garbelli-claudio_phd2015-03-16].
Abstract:
The 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
Tipologia IRIS:
Tesi di dottorato
Keywords:
Brachiopod shell; biomineralization; end Permian event; ocean acidification; shell geochemistry; shell ultrastructure; shell fabric; stable isotopes
Elenco autori:
C. Garbelli
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