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Tesi Redatta Con Il Contributo Finanziario Dell'università Degli Studi Di Padova

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Tesi Redatta Con Il Contributo Finanziario Dell'università Degli Studi Di Padova Sede Amministrativa: Università degli Studi di Padova Dipartimento di Geoscienze Via G. Gradenigo n.6 - 35131- Padova CORSO DI DOTTORATO DI RICERCA IN SCIENZE DELLA TERRA CICLO XXIX LATE NORIAN-RHAETIAN CARBON CYCLE PERTURBATIONS: FROM A TETHYAN TO A GLOBAL PERSPECTIVE Tesi redatta con il contributo finanziario dell’Università degli Studi di Padova Coordinatore: Ch.mo Prof. Fabrizio Nestola Supervisore: Ch.mo Dott. Manuel Rigo Co-Supervisore: Ch.mo Prof. Claudia Agnini Dottorando: Mariachiara Zaffani 1 2 Ai miei Grandi Giganti Gentili: Giulio, Giordano e Giancarlo, modelli ed esempi di professionalità ed umanità, sempre. 3 4 CONTENTS General Introduction 7 Synopsis 11 Methods 25 δ13Corg and TOC sample preparation methods: which one? 25 Protocol for δ13Corg analyses sample preparation 26 Protocol for TOC analyses sample preparation 27 Focus on: why coeval shift could show different δ13Corg amplitude? 28 13 Chapter 1: The Norian “chaotic carbon interval”: new clues from the δ Corg record of the Lagonegro Basin (southern Italy) 31 Abstract 31 Introduction 32 Geological setting 33 Pignola-Abriola section 35 Mt Volturino section 36 Madonna del Sirino section 37 Methods 40 Results 41 Discussion 43 Correlation with published record 43 Causes of carbon cycle perturbations 44 Conclusions 52 Acknowledgements 52 Chapter 2: Through a complete Rhaetian δ13Corg record: carbon cycle disturbances, volcanism, end-Triassic mass extinction. A composite succession from the Lombardy Basin (N Italy) 69 Abstract 69 Introduction 69 Geological setting 71 Methods 76 Results 77 Discussion 78 Option 1 824 Option 2 86 Conclusions 90 Chapter 3: Unpublished data and minor works 99 Mt. S. Enoc section (Lagonegro Basin, southern Italy) 99 Lithostratigraphy 99 Biostratigraphy 100 Chemostratigraphy 102 5 Kastelli section (Pindos Zone, Peloponnese, Greece) 103 Lithostratigraphy 103 Biostratigraphy 103 Geochemical analyses 104 δ15N of the Pignola-Abriola section (Lagonegro Basin, southern Italy) 106 Methods 107 Results 107 Discussion 107 ODP Site 761C from the Wombat Basin (northwestern Australia 108 Lithostratigraphy and biostratigraphy 108 Geochemical analyses 111 Chapter 4: Strontium isotopes: δ88/86Sr and 87Sr/86Sr from Triassic conodonts 113 Introduction 113 Methods: test and evaluation of a protocol for sample preparation procedure prior to δ88/86Sr analyses 115 Preliminary results 118 Discussion of the preliminary results 120 87/86Sr record 120 δ88/86Sr record 121 Concluding remarks 129 Acknowledgements 131 Appendix A: The Pignola-Abriola section (southern Apennines, Italy): a new GSSP candidate for the base of the Rhaetian Stage 133 13 Appendix B: The Norian “chaotic carbon interval”: new clues from the δ Corg record of the Lagonegro Basin (southern Italy) - Supplementary Material 167 Appendix C: Through a complete Rhaetian δ13Corg record: carbon cycle disturbances, volcanism, end-Triassic mass extinction. A composite succession from the Lombardy Basin (N Italy) - Supplementary material 173 References 183 6 GENERAL INTRODUCTION We are facing global climate changes driven by increasing concentrations of greenhouse gases in the atmosphere, which are responsible for global warming and possibly detrimental for the biosphere. Earth’s climate has significantly and repeatedly changed throughout the geological past, but the recent rate of global warming appears to far exceed any previous episode of extreme climate occurred since now. The Intergovernmental Panel on Climate Change (IPCC) estimates that the present atmospheric concentrations of greenhouse gases, related to human activities, are at unprecedented levels since at least 800,000 years (IPCC, 2014). In particular, carbon dioxide has been increased at the fastest observed rate of change in the last two decades (2.0±0.1 ppm/yr for the 2002–2011 decade; IPCC, 2014), trigging a detectable lowering of the pH values of the ocean surface waters (ocean acidification) and, consequently, a reduction of the CaCO3 saturation state and the shoaling of the CCD. These changes will lead to unpredictable impacts on calcifying organisms, such the aragonitic corals and the calcareous microplankton (e.g., Caldeira and Wickett, 2003; Kleypas et al., 2006; Allen et al., 2009; IPCC, 2014). Observational data on current climate change and models predicting the future evolution of Earth’s climate should be integrated with geologic data, which could serve to unveil analogous patterns providing clues onto the future scenarios (Raven et al., 2005; Ruhl; 2009; Hönisch et al., 2012).The study of geological time intervals characterized by carbon emissions comparable to the present-day conditions is crucial for describing their effects on the past carbon cycle and consequently on the ocean geochemistry and marine ecosystem(e.g., Sala et al., 2000). During the Mesozoic (ca. 252 Ma – 66 Ma), our planet was affected by recurrent carbon cycle perturbations, marked by episodes of climate change and biodiversity loss (e.g., Rampino & Stothers, 1988; Wignall, 2001, Jones and Jenkyns, 2001; Ward et al., 2004; Richoz et al., 2007; Van de Schootbrugge et al., 2008; Jenkyns, 2010; Tanner, 2010; Palfy et al., 2014, Trotter et al., 2015). On this perspective, the Triassic is paradigmatic and it is the System bounded by 2 mass extinctions. The Triassic (ca. 252-201 Ma) is in fact a key period of the Earth’s history, characterized by a supercontinent in which all the land were merged together named Pangaea and later by its the break- up, a variable climate regime (e.g., Preto et al., 2010; Rigo et al., 2012a; Trotter et al., 2015) interrupted by several global geological events, such as humid (e.g., Carnian Pluvial Event-CPE, Late Triassic, Simms and Ruffell, 1989, 1990; Simms et al., 1995) and warm episodes (W1, W2, W3 by Trotter et al., 2015) deeply affecting the Earth biota or extreme volcanic activity likely triggering profound biotic crises (e.g., Raup & Sepkoski, 1982; McElwain et al., 1999; Hallam, 2002; Marzoli 7 et al., 2004; McRoberts et al., 2008; Lucas, 2010; Ogg et al., 2012; Dal Corso et al., 2013, 2014; Trotter et al., 2015). This System is constrained by two of the biggest mass extinctions of the Phanerozoic, the end-Permian mass extinction - the most extensive biotic decimation of the Phanerozoic (e.g., Lucas, 1999; Benton & Twitchett, 2003; Lucas & Orchard, 2004; Erwin, 2006) and the end-Triassic mass extinction, culminating at the Triassic/Jurassic boundary (e.g., Hallam, 2002; Tanner et al., 2004; Richoz et al., 2007). An important proxy to give essential clues on the evolution of ocean water chemistry, oxygenation, and productivity of past marine environments are represented by the changes in the isotopic composition documented in the sediments. In particular, perturbations observed in δ13C values are widely applied and interpreted in terms of palaeoclimate and palaeoenvironmental changes (e.g., Hayes et al., 1999; Veizer et al., 1999; Payne et al., 2004; Korte et al., 2005; Lucas, 2010; Muttoni et al., 2004, 2014; Galli et al., 2005, 2007; Mazza et al., 2010; Preto et al., 2012). Indeed, the stable carbon isotope record available for the Triassic gives a general overview of the δ13C evolution, but its paleoclimatic/paleoocenographic interpretation is somewhat uncertain due to the multiple ecological and geochemical controls driving changes on the carbon isotope system. In a long-term perspective the Triassic δ13C profile starts with a, pronounced negative excursion coinciding with the Permian-Triassic boundary, this deep perturbation of the global carbon cycle is followed by a strong isotopic instability during the earliest Triassic (e.g., Payne et al., 2004; Lucas, 2010) that eventually lead to a more stable period spanning the Middle-Late Triassic (Julian, early Carnian) (Payne et al., 2004; Tanner, 2010) . This interval is characterized by steadily rising values in δ13C, which is likely related to biotic reassessment in the aftermath of the end-Permian mass extinction and the consequentially enhanced storage of organic carbon in terrestrial environments (e.g., Lucas, 2010). The Late Triassic (ca. 237 Ma - 201.3 Ma) is bracketed by two significant negative carbon isotope shifts, both linked to the emplacement of Large Igneous Provinces (LIPs). The first δ13C excursion occurred in the middle Carnian is referred to as the Carnian Pluvial Event and it is associated to the emplacement of the Wrangellia igneous province (e.g., Furin et al., 2006; Dal Corso et al., 2014, 2015). The second δ13C perturbation, recorded at the Triassic-Jurassic transition, is associated with the end-Triassic mass extinction and the emplacement of the Central Atlantic Magmatic Province (CAMP; e.g., Marzoli et al., 2004; Whiteside et al., 2010; Schaller et al., 2012; Dal Corso et al., 2013). The causes of the Triassic carbon isotope excursions remain a topic of much debate, with the most likely trigger mechanisms being related to the greenhouse gases emissions produced by the volcanic activity, with a total estimated amount of CO2 input in the atmosphere comparable to nowadays anthropogenic carbon dioxide feed in. Alternatively, other processes that can explain the occurrence and magnitude of observed carbon cycle perturbation would be changes in biotic 8 productivity, global ocean anoxia or seafloor methane release (e.g., Richoz et al., 2007; Lucas, 2010). In principle, all these processes are able to perturb the global carbon cycle and cause episodes of biotic crises (e.g., Rampino & Stothers, 1988; Wignall, 2001; Jones and Jenkyns, 2001; Ward et al., 2004; Richoz et al., 2007; van de Schootbrugge et al., 2008; Jenkyns, 2010; Tanner, 2010; Palfy et al., 2014, Trotter et al., 2015). Therefore, a global composite carbon isotope curve for the Triassic would have the potential for global correlations and would provide new insights on how the Earth’s dynamics respond to carbon dioxide emissions similar to the ongoing anthropogenic input, hopefully providing useful insight for climate modeling. Muttoni et al. (2014) provide a new almost continuous 13 million-year scale composite δ Ccarb record from the Ladinian (ca. 242 Ma) to Rhaetian (ca. 205.7 Ma), but the construction of an analogous Triassic organic carbon isotope record is not available to 13 date.
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