PhD in Geographical and Earth Sciences – The shocking role of alkali feldspars in the death of the dinosaurs

Start date: October 2025

Aims: The impact of a ~12 km diameter asteroid sixty-six million years ago caused one of the most devastating mass extinctions in Earth history. Many groups of plants and animals including the non-avian dinosaurs succumbed to a cascade of environmental changes following the event (Morgan et al. 2022). The ‘smoking gun’ of this impact is the 200 km diameter Chicxulub structure in Mexico, and detailed analysis of its rocks has revealed a wealth of information on the impact event and its effects on the Earth system. One important new suggestion is that shock-damaged mineral grains were ejected into the Earth’s atmosphere where they played an important role in post-impact climate change (Pankhurst et al. 2022). This project seeks to test this hypothesis through characterisation of feldspar minerals in Chicxulub and other meteorite impact structures.

Background: In 2016 the Chicxulub structure was drilled by IODP-ICDP Expedition 364 and showed that the target rock comprises carbonates and evaporites overlying a granitoid basement (Feignon et al. 2021; Morgan et al. 2017). The basement lithologies experienced pressures of ~16–18 GPa during the impact event, with most minerals showing evidence for shock deformation. Alkali feldspar is abundant in the granite, but its response to the impact has received less attention than other common rock-forming minerals (e.g., quartz). Given that the impact structure has been so intensively studied, Chicxulub offers an excellent opportunity to characterise shock deformation of alkali feldspar including the microstructures produced, and associated chemical and isotopic alteration. Another very important reason for focusing on alkali feldspar is that the mineral is highly effective in nucleating clouds (Harrison et al. 2016) and so could have played a major role in the environmental aftereffects of the impact event (Coldwell et al. 2019; Pankhurst et al. 2022). However, key to understanding the atmospheric  Aims: The impact of a ~12 km diameter asteroid sixty-six million years ago caused one of the most devastating mass extinctions in Earth history. Many groups of plants and animals including the non-avian dinosaurs succumbed to a cascade of environmental changes following the event (Morgan et al. 2022). The ‘smoking gun’ of this impact is the 200 km diameter Chicxulub structure in Mexico, and detailed analysis of its rocks has revealed a wealth of information on the impact event and its effects on the Earth system. One important new suggestion is that shock-damaged mineral grains were ejected into the Earth’s atmosphere where they played an important role in post-impact climate change (Pankhurst et al. 2022). This project seeks to test this hypothesis through characterisation of feldspar minerals in Chicxulub and other meteorite impact structures.

Background: In 2016 the Chicxulub structure was drilled by IODP-ICDP Expedition 364 and showed that the target rock comprises carbonates and evaporites overlying a granitoid basement (Feignon et al. 2021; Morgan et al. 2017). The basement lithologies experienced pressures of ~16–18 GPa during the impact event, with most minerals showing evidence for shock deformation. Alkali feldspar is abundant in the granite, but its response to the impact has received less attention than other common rock-forming minerals (e.g., quartz). Given that the impact structure has been so intensively studied, Chicxulub offers an excellent opportunity to characterise shock deformation of alkali feldspar including the microstructures produced, and associated chemical and isotopic alteration. Another very important reason for focusing on alkali feldspar is that the mineral is highly effective in nucleating clouds (Harrison et al. 2016) and so could have played a major role in the environmental aftereffects of the impact event (Coldwell et al. 2019; Pankhurst et al. 2022). However, key to understanding the atmospheric properties of feldspars is knowing how they respond to the very high pressures of hypervelocity impacts.

Objectives: This project will characterise the mineralogy, microstructure and chemical/isotopic composition of alkali feldspars from the Chicxulub granite together with samples from other impact structures (e.g., Ries in Germany and Rochechouart in France). Work will use conventional imaging and microanalysis techniques (e.g., scanning electron microscopy, electron probe microanalysis) together with specialist tools for characterising microstructures over length scales from millimetres (electron backscatter diffraction) to nanometres (transmission Kikuchi diffraction, transmission electron microscopy, atom probe tomography). The outcome of that work will be a comprehensive understanding of how alkali feldspars respond to hypervelocity impacts, and the role of shock deformed minerals in environmental change.

Dissemination and skills: The student will be part of a lively team of planetary scientists in Glasgow, collaborate with partners in Europe and the USA, and present results at UK and international conferences. Upon completion they will be equipped with skills that could lead to employment in areas such as space exploration, materials technology, or environmental management.

References

Coldwell B.C. and Pankhurst M.J. (2019) Evaluating the influence of meteorite impact events on global potassium feldspar availability to the atmosphere since 600 Ma. Journal of the Geological Society 176, 209–224.

Feignon J.-G., de Graaff S. J., Ferrière L., Kaskes P., Déhais T., Goderis S., Claeys P. and Koeberl C. (2021) Chicxulub impact structure, IODP-ICDP Expedition 364 drill core: Geochemistry of the granite basement. Meteoritics and Planetary Science 56: 1243–1273.

Harrison A.D., Whale T.F., Carpenter M.A., Holden M., Neve L., O’Sullivan D., Vergara Temprado J. and Murray B.J. (2016) Not all feldspar is equal: a survey of ice nucleating properties across the feldspar group of minerals. Atmospheric Chemistry and Physics Discussions, 1–26.

Morgan J.V., Bralower T.J., Brugger J. et al. (2022) The Chicxulub impact and its environmental consequences. Nature Reviews Earth and Environment 3, 338–354.

Morgan J., Gulick S., Mellet C.L., Green S. L., and Expedition 364 Scientists. (2017) Chicxulub: Drilling the K-Pg impact crater. Proceedings of the International Ocean Discovery Program, 364. College Station, Texas: International Ocean Discovery Program. 164 p.

Pankhurst M.J., Stevenson C J. and Coldwell B.C. (2022) Meteorites that produce K-feldspar-rich ejecta blankets correspond to mass extinctions. Journal of the Geological Society 179.