The intrinsic relationship between geodynamic and biological evolution of the Earth is testified by the multiple mass extinctions connected to the extrinsic perturbations of the biosphere. Most of these extinctions were triggered by massive igneous activity. Direct CO2 volcanic plume emissions as well as indirect CO emissions produced severe change in the chemistry of atmosphere and oceans, influencing oceanographic currents and flows, as well as phytoplankton blooms, resulting in profound climate changes. The Cenozoic time interval is punctuated by many episodes of climate changes, some of which are phases of rapid global warming known as hyperthermals. The most important short-living intervals identified by a large C-cycle perturbation are recorded during the Palaeocene-Eocene Thermal Maximum (PETM ~55 Ma), the Middle Eocene Climatic Optimum (MECO ~40 Ma) and late Miocene (CM7; 7th Carbon Maximum ~11.8 Ma).
Carbonate sediments are particularly significant for climate research because the carbonate secreting biota (but also chemically induced abiotic sediments) are sensitive archives of climate, and because geochemical methods such as stable isotope measurements that yield information on climatic parameters are applicable to carbonate biota producing sediments of pelagic and carbonate platform successions.
One of the goal of this project is to understand the response of biota producing carbonate sediment in shallow water domain to the PETM, MECO and CM7 hyperthermals and to evaluate the changes of environmental conditions produced by these warming events in the photic zone.
The second goal of this project is to identify the effects of interaction of carbonate sedimentary rocks (limestones and marly limestones) with silicate magmas at shallow depth in magma chambers.
The petrological-volcanological approach, the investigation of anomalously SiO2-understaturated and ultrabasic volcanic compositions will give new constraints on the deep carbon cycle in specific areas
The changes in climate observed during the past decades have ignited intensive interest in climate evolution through Earth's history in order to gain a better understanding of current changes and to increase prediction power. In the last decades, the palaeoclimatology has become a central topic of carbonate sedimentology. Carbonate sediments are particularly significant for climate research because the carbonate secreting biota are sensitive archives of climate, and because geochemical methods such as stable isotope measurements that yield information on climatic parameters are applicable to carbonate biota of pelagic successions (benthic and planktonic forams) as well as biota of carbonate platform successions (pectinids, oysters, brachiopods, forams).
Understanding the ocean climate system during past climate modes is indispensable for more accurately perception of future climate evolution in a warming Earth. There is a general agreement in the scientific community that the anthropogenic carbon input, predominantly carbon dioxide (CO2), will have strong influence on climate evolution of the Earth (Zachos et al 2008). This anthropogenic carbon input would eventually return to the geosphere through the deposition of calcium carbonate and organic matter. The CO2 transferred into the oceans, where it reacts to form carbonic acid, will cause an increase of the pH and a decrease of the carbonate saturation of the ocean.
During the PETM hyperthermal, more than 2,000 Gt C as CO2 entered the atmosphere and ocean. The stratigraphic record for this carbon release includes a rapid and pronounced decrease in the 13C/12C ratio of carbonate and organic carbon across the globe and a prominent drop in the carbonate content of marine sediment deposited at several thousands of metres water depth, in other words a biocalcification crisis.
The main output of this project is to produce a isotope C curve and to individuate the changes of carbonate production and saturation along the Thanetian and Ypresian interval for the PETM, along the Bartonian interval for the MECO and between the Serravallian and Tortonian for the CM7 in a shallow water carbonate succession. Another important output is the reconstruction of the environmental conditions in the shallow-water seafloor during these events.
Successively, precise stratigraphic collocation of these events with the Sr stratigraphy will allow the stratigraphic correlation of different domains, contributing to fill a gap currently present in the Mediterranean Cenozoic stratigraphy offering a new perspective to understand the causes of the PETM, MECO and CM7 hyperthermals.
We will approach the study of Cenozoic hyperthermals starting from the classical stratigraphic analysis (facies analysis and biostratigraphy), followed by the quantitative microfacies analysis, stable isotope stratigraphy and detailed petrographic characterization of volcanic activity. The age constrains will be refined performing the strontium isotope stratigraphy, widely used to correlate and to integrate the biostratigraphy. The result of the integrated stratigraphic analyses will be correlated with the deep ocean global record. The innovative aspect of this project is represented by the integrated stratigraphic approach, and by the use of Ca isotopes which allow to reconstruct seawater carbonate chemistry, being this systematics particularly sensitive to ocean acidification. Indeed, the dissolution of deep-marine carbonate sediments coincides with a negative excursion in ¿44Ca.
As concerns the petrological-volcanological approach, the investigation of anomalously SiO2-understaturated and ultrabasic volcanic compositions (with SiO2 ranging from ~5 wt% to ~40 wt%) will give new constraints on the deep carbon cycle in specific areas. The investigated tectonic settings will range from active subduction (yet to be confirmed) in the Italian case, post-collisional stage in the Iranian case and the not-yet fully understood setting of the internal Betic case. Based on the first investigated results our model will lead to a complete confutation of the petrogenetic models proposed in literature, proposing a completely different origin for the carbonate component associated to the igneous rocks. The idea that will be tested in this research project will check the possibility that the carbonatitic rocks should better be defined pseudo-carbonatites, being related to digestion of limestones and marly limestones at shallow depths, as already demonstrated in Calatrava volcanic district (central Spain; Lustrino et al 2016) and Polino (central Italy; Lustrino et al 2019). Alternatively a 'normal' sedimentary origin (in the form of caliche or travertine pools) instead of mantle origin (in the form of Ca-carbonatitic melt) is to evaluate for the internal Betic case (Tallante, SE Spain).
References
Lustrino et al 2016 Geochim Cosmochim Acta, 185, 477-497
Lustrino et al 2019 Sci Rep 9:9212
Zachos et al 2008 Nature 451, 279-283