O'Connell, Brennan

Earth’s marine environments and ecosystems have changed through geological time. I am a field-based sedimentologist and stratigrapher who works on environmental changes in Earth's past and present. My research combines sedimentology and stratigraphy with geobiology, palaeontology, petrography, and metal geochemistry. I have worked extensively on tide-influenced depositional systems through Earth history. Current projects focus on tidal sedimentology and coastal carbon storage, Precambrian reefs, and changes in ocean oxygen levels. I also examine the environments inhabited by the Ediacaran macrobiota (the oldest record of complex animal life), and the evolution of coastal wetland plant ecosystems.

• Marine sedimentology and tidal sedimentology 
• Sedimentary systems and environments through geological time 
• Earth history and environmental change 
• Tidal flats, salt marshes, and reefs 
• The evolution of coastal plants and mangroves 
• Ocean geochemical change 
• Precambrian geology and early life

• 2009–2013 BA in Geology, Colorado College (USA)
• 2014–2016 MSc. in Earth Science, University of Oregon (USA)
• 2016–2018 Research Scientist, Yale Metal Geochemistry Center, Yale University (USA)
• 2018–2023 PhD in Earth Science, University of Melbourne (Australia)
• 2022–2025 Post Doctoral Research Associate, University of Cambridge (UK)
• 2025–2026 Leverhulme Early Career Post Doctoral Fellow, University of Cambridge (UK)
• since September 2026 tenure track professorship for Earth System Sciences, University of Vienna