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Department of Earth Sciences

Planetary Geology


2010-2014: MSci. Geology., Imperial College London

2014-2018: Ph.D., University of Cambridge (Pre-vegetation alluvium: Geological evidence for river behaviour in the absence of vegetation)

2018-2020: Postdoctoral researcher., Utrecht University

2020-2021: Postdoctoral researcher., University of Hull

2021-        : Postdoctoral researcher., University of Cambridge

2021-        : Research Fellow., Clare Hall, University of Cambridge




My research currently integrates techniques in sedimentology, geochemistry and petrology to study some of Earth’s most fundamental transitions, such as the initial emergence of metazoans and subsequent terrestrialization of the continents. I also enjoy working in planetary geology and have focused projects aiming to demonstrate how, through biological evolution, Earth’s sedimentary-stratigraphic record has become differentiated from those on other planets.

The Paleozoic terrestrialization of the continents: Throughout Earth history there have been intervals where sedimentary environments have existed which have no modern analogue. Arguably the most profound of these is the “pre-vegetation Earth”. Numerous observations attest to the fundamental mechanical role played by vegetation in active sedimentary environments, yet sedimentary systems operated in the complete absence of land plants for the first 90% of Earth history. So far my research has given particular attention to unvegetated river and coastal environments, though I am now additionally exploring the marine impacts of an unvegetated landscape and, following the identification of an upsurge in continental mud volume coeval with expanding plant cover (McMahon and Davies, 2018, Science), am extending the breadth of this research to include mudstone petrology and geochemistry.

Ediacaran macrobiota: Earth's oldest credible macroscopic animal fossils are found in the late Ediacaran period and I am actively studying the environments they evolved within, ecosystems they formed, and rock record biases which may alter the perceived record of their origin and demise. Correct inferences of paleoenvironmental settings are essential to resolve outstanding questions in early animal evolution, such as the evidential basis for a late Ediacaran extinction event and the relationship between the Ediacaran biota with more familiar Cambrian-age fauna (McMahon et al., 2020, Journal of Sedimentary Research).

Martian sedimentary geology: It has become apparent that unvegetated sedimentary environments were not just the long-term norm on Earth: preserved sedimentary strata on Mars demonstrate that substantial volumes of sediment have been generated throughout the planet's history and the null hypothesis is that Martian sedimentary processes operated entirely in the absence of life. Previous and ongoing projectes have used the more accessible Precambrian terrestrial rock record as a partial analogue for understanding "abiotic" Martian stratigraphy (Salese et al., 2020, Nature Communications). 

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Key publications: 

18) Brückner, M.Z.M., McMahon, W.J., Kleinhans, M.G. (in press) Muddying the waters: Modelling the effects of early land plants in Paleozoic estuaries. Palaios

17) Davies, N.S., McMahon, W.J. (2021) Land plant evolution and global erosion rates. Chemical Geology, 120128

16) McMahon, W.J., Liu, A.G., Tindal, B., Kleinhans, M.G. (2020) Ediacaran life close to land: Coastal and shoreface habitats of the Ediacaran macrobiota, the central Ikara-Flinders Ranges, South Australia. Journal of Sedimentary Research, 90, 1463-1499

15) Terwisscha van Scheltinga, R.C., McMahon. W.J., van Dijk. W.M., Eggenhuisen, J.T., Kleinhans. M.G. (2020) Experimental distributive fluvial systems: Bridging the gap between river and rock record. The Depositional Record, 6, 670-684

14) Salese, F*., McMahon, W.J*., Balme, M., Ansan, V., Davis, J., Kleinhans, M. (2020) Sustained fluvial deposition recorded in Mars’ Noachian stratigraphic record. Nature Communications, 11, 1-8 (*contributed equally)

13) Salese, F., Kleinhans, M.G., Mangold, N., Ansan, V., McMahon, W.J., Haas, T., Dromart, G. (2020) Estimated minimum lifespan of the Jezero Fluvial delta (Mars). Astrobiology, 20, 977-993

12) McMahon, W.J., Davies, N.S. (2020) Physical and biological functioning in Proterozoic rivers: evidence from the archetypal pre-vegetation alluvium of the Torridon Group, NW Scotland. Scottish Journal of Geology, 56, 1-29

11) Davies, N.S., Slater, B.J., Shillito, A.P., Liu, A.G., McMahon, W.J. (2020) Evolutionary synchrony of Earth’s biosphere and sedimentary-stratigraphic record. Earth-Science Reviews 102979 2019

10) Davies, N.S., Shillito, A.P., McMahon, W.J. (2019) Where does the time go? Assessing the chronostratigraphic fidelity of sedimentary rock outcrops. Journal of the Geological Society 176, 1154-1168

9) Balme, M.R., Curtis-Rouse, M.C., McMahon, W.J., (53 authors). (2019) The UK Space Agency Mars Utah Rover Field Investigation (MURFI). Planetary and Space Science, 165, 31-56 2018

8) McMahon, W.J., Davies, N.S. (2018) The shortage of geological evidence for pre-vegetation meandering rivers. In: Ghinnasi, M. et al. (eds.) ‘Fluvial meanders and their sedimentary products in the rock record’ IAS Special Publication 48, 119-148

7) McMahon, W.J., Davies, N.S. (2018) Evolution of alluvial mudrock forced by early land plants. Science, 359, 1022-1024

6) McMahon, W.J., Davies, N.S. (2018) High-energy flood events recorded in the Mesoproterozoic Meall Dearg Formation, NW Scotland; their recognition and implications for the study of pre-vegetation alluvium. Journal of the Geological Society175, 13-32

5) Went, D.J., McMahon, W.J. (2018) Fluvial products and processes before the evolution of land plants: evidence from the Lower Cambrian Series Rouge, English Channel Region. Sedimentology65, 2559-2594

4) Davies, N.S., McMahon, W.J., Shilito, A.P. (2018) A graphic method for depicting horizontal direction data on vertical outcrop photographs. Journal of Sedimentary Research, 88, 516-521 2017

3) Davies, N.S., Shilito, A.P., McMahon, W.J. (2017) Short-term evolution of primary sedimentary surface textures (microbial, abiotic, ichnological) on a dry stream bed: modern observations and ancient implications. Palaios, 32, 125-134

2) Davies, N.S., Gibling, M.R., McMahon, W.J., Slater, B.J., Long, D.G.F., Bashforth, A.R., Berry, C.M., Falcon-Lang, H.J., Gupta, S., Rygel, M.C., Wellman, C.H. (2017) Discussion on ‘Tectonic and environmental controls on Palaeozoic fluvial environments: reassessing the impacts of early land plants on sedimentation’. Journal of the Geological Society, 174, 947-950

1) McMahon, W.J., Davies, N.S., Went, D.J. (2017) Negligible microbial matground influence on pre-vegetation river functioning: Evidence from the Ediacaran-Lower Cambrian Series Rouge, France. Precambrian Research, 292, 13-34.

Postdoctoral Research Associate
Research Fellow, Clare Hall

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