MESOZOIC EPISODES OF C-CYCLE AND CLIMATE PERTURBATIONS: GEOCHEMICAL SIGNATURES OF THE OCEANIC ECOSYSTEM DYNAMICS ACROSS THE TOARCIAN OCEANIC ANOXIC EVENT AND THE VALANGINIAN WEISSERT EVENT.
Tesi di Dottorato
Data di Pubblicazione:
2022
Citazione:
MESOZOIC EPISODES OF C-CYCLE AND CLIMATE PERTURBATIONS: GEOCHEMICAL SIGNATURES OF THE OCEANIC ECOSYSTEM DYNAMICS ACROSS THE TOARCIAN OCEANIC ANOXIC EVENT AND THE VALANGINIAN WEISSERT EVENT / L. Cavalheiro ; tutor: E. Erba ; co-supervisor: T. Wagner ; coordinatore del dottorato: F. Camara Artigas. Dipartimento di Scienze della Terra Ardito Desio, 2022 May 06. 34. ciclo, Anno Accademico 2021.
Abstract:
This Ph.D. research project investigated two paleo-environmental dynamics under extreme
Mesozoic carbon cycle and climate perturbations evidenced by major anomalies in the carbon isotope
record (δ13C) of the Early Jurassic and Early Cretaceous, namely the Toarcian Ocean Anoxic Event (TOAE) and the Valanginian Weissert Event, respectively. The material selected for the study of the T-OAE
is from two new cores (Sogno and Gajum), which represent pelagic deepest records (1000-1500 paleowater depth) of the Lombardy Basin (Southern Alps, Italy). Both cores record an expanded black shale
interval (the Fish Level) of 5 m and 16 m at Sogno and Gajum, respectively, representing the
lithostratigraphic expression of the T-OAE sensu Jenkyns (1985, 1988). The Fish Level correlates with the
early Toarcian negative δ13C anomaly named ‘Jenkyns Event’. The Weissert Event was studied in a unique
southern polar location, where a 40 m thick Lower Cretaceous black shale section was recovered at Ocean
Drilling Program (ODP) Site 692, in the Weddell Sea, nearshore Antarctica. The two case studies were
selected in distinct and very different paleo-settings and latitudes, in order to explore how global climate
perturbations translate into local paleo-environmental responses in the sedimentary record, documenting
potentially different pathways in the bio-geochemical cycles. A detailed characterization of δ
13C
stratigraphy, calibrated with nannofossil biostratigraphy, was the basis for a univocal identification of the
T-OAE (including the Jenkyns Event) and the Valanginian Weissert Event anomalies. Multi-proxy based
organic and inorganic geochemical analyses were used to reconstruct OC burial and preservation rates, the
nature and sources of organic matter, carbonate chemistry, the evolution of paleo-temperatures, the paleodepositional environment and redox conditions. Both case studies confirm that local sedimentary records of
strongly restricted and/or deep marine basins register the δ
13C signals of global perturbations and associated
environmental variables. This has been demonstrated at both locations by reconstructing proxy variations in
ocean temperatures, drastic changes in carbonate chemistry and the biologic response, linked to the T-OAE
and the Weissert Event. In contrast, both case studies emphasize that basin physiography and local climatic
and environmental conditions play a major role in controlling OC rates even across such extreme carboncycle perturbations. Notably, the aim of this Ph.D. research was to design and apply an integrated approach
combining modelling and multi-proxy data to demonstrate an innovative way forward to decouple
uncertainties and limitations of individual proxy results and locations from regional to global scale
interpretations. New temperature/pCO2 relationships based on multi-proxy data and modelling were
reconstructed for the Weissert Event case study. The analytical approach was not identical for the two case
studies. Modelling and part of the geochemical analyses were not applied to the T-OAE section due to
pandemic restrictions that prevented laboratory work and subsequent elaborations. The outcome suggests
that the established strategy for the Weddell Sea case study may now serve as a conceptual framework to
advance research on the Italian Jurassic sections, and other OAE examples. This research points out that
more emphasis should be made in understanding temperature/pCO2 relationships to evaluate processes,
rates, and dimensions of climate and environmental change back in time, setting boundaries either for the
study of past carbon-cycle/climate perturbations and for projecting future climate and environmental
response.
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
L. Cavalheiro
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