- Environments in ‘deep time’, especially the Precambrian to early Palaeozoic
- Limestones formed in soils, springs, streams and lakes
- Processes of microbe fossilisation
- Indicators of biogenicity in ancient and extra-terrestrial rocks
- Carbon cycle in ‘deep time’
Astrobiology and geobiology, including processes of microbe fossilisation and identification of ancient microbial fossils. This is linked to the related topic of studying the deposition and diagenesis of non-marine carbonates (microbial tufas, hot-spring travertines, soil calcretes and cave speleothems), including the impact of the arrival and diversification of vascular plants on non-marine carbonates. I do this using a combination of field techniques, petrography and (isotope and elemental) geochemistry. Recent fieldwork has included Palaeozoic rocks of Newfoundland and modern lakes of California and Western Australia, as well as several sites in the UK.