Eruptive Rates and Volatile Emissions of the Deccan Large Igneous Province and Environmental Consequences

Author(s): Fendley, Isabel | Advisor(s): Renne, Paul R | Abstract: The end-Cretaceous mass extinction resulted in the demise of the dinosaurs and many other plant and animal species, irrevocably changing Earth’s ecosystems. The environmental changes which influenced the mass extinction and recovery were most likely caused by a combination of the Chicxulub impact and Deccan Traps Large Igneous Province volcanism. The climate and ecological effects of the Deccan Traps remain ambiguous, due in part to a paucity of constraints on eruption rates and frequency. I have addressed this by using mercury concentration as an indicator of eruptions and combining these chemostratigraphic records with mercury box models to estimate eruptive rate and emissions rate of climate-altering gases. Additionally, the timing of the largest known Deccan eruptions, the Rajahmundry Traps, was unclear with respect to the extinction event. As the largest eruptions have been hypothesized to have the most significant climate impact, knowing the timing of these eruptions allows for direct comparison with climate records. Using a combination of geochronological techniques, I found that all three subaerially exposed Rajahmundry Traps lava flows erupted after the Cretaceous-Paleogene boundary. I then used scalings from the LOSCAR carbon cycle model along with paleoclimate records and found that these eruptions most likely did not cause multi-degree warming. However, they could have contributed to ongoing carbon cycle perturbations during the recovery interval. I then investigated the nature of these carbon cycle perturbations by creating a new high-resolution carbon isotope record from terrestrial organic material. I specifically addressed the discrepancy between terrestrial carbon isotope records, which have been interpreted as containing short (l10 ka) excursions, and marine records, which contain a much longer (∼ 1.5 Ma) excursion linked to decreased export productivity in the surface ocean. My new record shows that, contrary to previously thought, terrestrial records also show a long duration excursion during this time interval. However, while the duration of the excursions is now known to be similar between terrestrial and marine realms, the shape of the excursion is different. The different trends indicate that the open ocean DIC pool and marine CO2 were possibly in disequilibrium during parts of the recovery interval.