The composition of Earth’s atmosphere and oceans have varied over the Phanerozoic and is tightly coupled with the planet’s climate and the extinction and evolution of life. Central to Earth’s climate and habitability is the concentration of CO2 in the atmosphere-ocean system, where rapid perturbations of CO2 correspond with hyperthermal and mass extinction events. These intervals of environmental catastrophes coincide with several periods of large-scale volcanic eruptions (million km3 of lava) called Large Igneous Provinces (LIPs), capable of releasing massive quantities of CO2. Among these events, the end-Triassic extinction (ETE; 201.564 Ma) represents one of the most severe biotic crises of the Phanerozoic and is temporally associated with the emplacement of the Central Atlantic Magmatic Province (CAMP). As one of the most voluminous large igneous provinces, CAMP is characterized by repeated disruptions to the global carbon cycle and intense ocean acidification events. However, understanding the relationship between the massive release of CO2, ocean chemistry, and extinction dynamics requires robust constraints on ancient CO2 concentrations. For time intervals prior to the ice core record, CO2 reconstructions rely on geochemical proxies derived from fossils and minerals. While these proxies often reproduce similar long-term trends, they commonly diverge in absolute CO2 estimates, limiting confidence in quantitative reconstructions of ancient atmospheric and oceanic carbon reservoirs. Direct constraints on CO2 in deep time can overcome this limitation, which can be achieved by using fluid inclusions hosted in minerals that precipitated in equilibrium with the environment. These fluid inclusions trap and preserve aliquots of ancient air and brine at the time of mineral formation in which the bulk gas compositions can be directly quantified using mass spectrometry and Raman spectroscopy. Fluid inclusions have increasingly been recognized to be excellent archives of past environmental conditions, including temperature, salinity, and atmospheric composition, though uncertainties remain about carbon speciation, the fidelity of preserved gas and brine compositions, and the broader applicability of using fluid inclusions to reconstruct major carbon cycle perturbations. This dissertation applies direct and quantitative methods to extract CO2 concentrations from fluid inclusions trapped in sedimentary minerals. Confocal Raman spectroscopy is used to quantify carbonate system parameters using fluid inclusions hosted in calcite, enabling reconstruction of pH and pCO2 conditions during mineral formation. Subsequently, fluid inclusions in halite are assessed for their reliability to trap gases during mineral precipitation and validate their use for ancient CO2 reconstructions. Fluid inclusion analyses were applied to deep ocean bedded cherts, showing repeated pulses of elevated CO2 and associated decreases in ocean pH and aragonite saturation state across the ETE and the Triassic-Jurassic transition. Integration of these records with carbon cycle modeling constrains the magnitude and pacing of the carbon release associated with CAMP volcanism and shows that large, repeated CO2 injections are sufficient to reproduce observed perturbations in ocean chemistry. By combining fluid inclusion analyses with carbon cycle modeling and independent geological and paleontological constraints, link large igneous province volcanism, repeated disruptions to the global carbon cycle, mass extinctions, and widespread ocean acidification during the end-Triassic.
Hudgins M. N., 2026. Ocean acidification and mass extinctions: reconstructing CO2 from fluid inclusions. PhD thesis, Rensselaer Polytechnic Institute. Thesis (restricted access).
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