Oceanic Anoxic Event (OAE) 1b (late Aptian - early Albian): evolutionary, palaeoecological, palaeoceanographic and palaeoclimatic implication

The late Aptian – early Albian interval (110 – 118 Ma) represents a crucial period of pronounced biotic and climate/ocean changes. It was characterized by enhanced volcanic activity linked to the progressive opening of the Indian Ocean, increased levels of atmospheric greenhouse gases, and high climate instability. The widespread deposition of multiple prominent black shale horizons in the Northern Tethyan and North Atlantic realms is the sedimentary expression of Oceanic Anoxic Event (OAE) 1b, a major perturbation of global carbon cycle. The late Aptian – early Albian OAE 1b is also the scenario of the first major turnover in the planktonic foraminifera evolutionary history, with an event of dramatic extinction of large-sized, heavy ornamented planktonic species, and subsequent diversification of small and thin-walled taxa. Investigation of the complex nature and dynamics of oceanographic changes in response to the OAE 1b are the goals of this thesis, along with a deep analysis of the ecological stressors affecting the evolutionary behaviour of the planktonic foraminiferal community. A high-resolution study of multiple paleontological, organic and inorganic geochemical proxies (microfaunal assemblage composition, morphometry of Pa. rohri, δ13Ccarb, TOC, CaCO3, trace elements, organic biomarkers) has been performed on the nearly continuous and undisturbed pelagic sedimentary succession of Poggio le Guaine (Umbria-Marche Basin, central Italy). The results clearly suggest the emplacement of the Southern Kerguelen Plateau as the external driver triggering global climatic/oceanographic changes. The consequent complex feedback mechanisms among ocean, land and atmosphere, strictly controlled by the regional features, led to intermittent episodes of water column anoxia/dysoxia, inducing enhanced burial and preservation of marine organic carbon. The high environmental variability destabilized the marine ecosystems, triggering ecological stress and forcing biotic crises. The planktonic foraminifera turnover has been therefore the result of an irreversible and drastic regime shift toward more mesotrophic – eutrophic ecosystem that promoted the blooming of opportunistic/disaster species and siliceous organism as Radiolaria, which dominated the microfaunal assemblages. The comparison of the planktonic foraminifera records from the Poggio le Guaine succession and the DSDP Site 511 section chosen as “control ocean section”, provided the evidence that widely separated marine ecosystems had similar response to global drivers, both experiencing relevant ecological system shift. The dwarfism of planktonic foraminifera prior the extinction turned out to be an ecological response to increasing environmental stresses rather an evolutive behaviour preceding the extinction.