Nutrient cycling and oxygenation of shallow seas during the Triassic-Jurassic mass extinction and the early Jurassic

Supervisor(s)

Dr Robert Newton, Professor Simon Poulton, Dr Clemens Ullmann (University of Exeter), Dr Cris Little and Professor Paul Wignall. Contact Dr Robert Newton to discuss the project informally.

Project description

Nutrient availability in the oceans is strongly dependent on the oxygenation state of the water column (e.g. März et al., 2008) and together these provide an overriding control on primary productivity and carbon cycling, but there is little information on how these interact during many of the major Earth system perturbations.

This project will examine changes in nutrient and oxygen availability across an extended period of Earth history from just before the Triassic-Jurassic (T-J) boundary extinction, through its recovery interval and into the environmental changes that characterised the early Jurassic. This time period contains major shifts in climate and the carbon cycle (Hesselbo et al., 2000; Korte and Hesselbo, 2011; Korte et al., 2015) but little is known about the interacting cycles of nutrients such as phosphorus and carbon, and their relationship to water column oxygenation during these time periods.

The T-J extinction is one of the ‘big five’ extinction events of the Phanerozoic, but perhaps one of the most enigmatic, whilst the early Jurassic contains the well-known early Toarcian anoxic event, transitions in and out of an icehouse climate in the Pliensbachian, and less well understood environmental changes such as those at the Sinemurian-Pliensbachian boundary and the late Pliensbachian.

Multiple cores from Sirius Minerals operations in Yorkshire, coupled with pre-existing cores stored at the British Geological Survey and coastal outcrops, represent a transect of the shallow sea that covered much of Europe at this time and offers a unique opportunity to evaluate how the events of this time interval unfolded.

The successful candidate will apply a range of techniques to understand the cycling of nutrients and their interaction with the oxygenation state of the water column:

  1. Sediment phosphorus speciation: This technique has recently been revised at Leeds for application to ancient sediments. It analyses the phosphorus present in different associations in the sediment (e.g. organic matter, apatite etc) to develop an understanding of phosphorus cycling in the water column at the time of sediment deposition.
  2. Various approaches to quantify oxygenation as appropriate. E.g. Oxygen restricted biofacies scheme (bivalve ecology, Savrda and Bottjer, 1991), iron speciation (Poulton and Canfield, 2005), framboid size measurements (Wignall and Newton, 1998; Wilkin et al., 1996).
  3. Belemnite phosphate. Some recent pilot work indicates that the amount of phosphate in the belemnite carbonate is substantial and varies in a systematic way across the early Toarcian event. Its behaviour is consistent with an increased flux of phosphate during the event which is intriguing.

The range of possible samples is extensive, too large in fact to produce a full record of the whole time period for multiple sites, so we would expect the exact focus of the project to evolve as data is produced focusing on particular strands from the palette of possibilities laid out above. Key starting points might be records across the T-J extinction, and work to validate and understand the belemnite phosphorus record.

The project is funded by the North York Moors National Park (NYMNP) and their ‘Section 106’ planning agreement with Sirius Minerals (SM). The successful candidate would be expected to liaise effectively with NYMNP and SM, and be involved in disseminating the results of the work via public engagement events in the region.

References:

  • Hesselbo, S.P. et al., 2000. Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event. Nature, 406: 392-395.
  • Korte, C., Hesselbo, S.P., 2011. Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic. Paleoceanography, 26(4).
  • Korte, C. et al., 2015. Jurassic climate mode governed by ocean gateway. Nature Communications, 6: 10015.
  • März, C. et al., 2008. Redox sensitivity of P cycling during marine black shale formation: Dynamics of sulfidic and anoxic, non-sulfidic bottom waters. Geochimica et Cosmochimica Acta, 72(15): 3703-3717.
  • Poulton, S.W., Canfield, D.E., 2005. Development of a sequential extraction procedure for iron: implications for iron partitioning in continentally derived particulates. Chemical Geology, 214(3-4): 209-221.
  • Savrda, C.E., Bottjer, D.J., 1991. Oxygen related biofacies in marine strata: An overview and update. In: R.V. Tyson, T.H. Pearson (Eds.), Modern and Ancient Continental Shelf Anoxia. The Geological Society Special Publication No. 58, London, pp. 201-219.
  • Wignall, P.B., Newton, R., 1998. Pyrite framboid diameter as a measure of oxygen deficiency in ancient mudrocks. American Journal of Science, 298(7): 537-552.
  • Wilkin, R.T., Barnes, H.L., Brantley, S.L., 1996. The size distribution of framboidal pyrite in modern sediments: An indicator of redox conditions. Geochimica et Cosmochimica Acta, 60(20): 3897-3912.

Key benefits

The successful candidate will be fully trained in a wide range of geochemical techniques providing a high level of specialist expertise. Completing a PhD also develops a broad array of transferable skills such as written communication, public speaking, project management, leadership, collaboration and perhaps most importantly, critical thinking. All of the analytical techniques are available in the School’s excellent laboratory suite.

The student will also benefit from being part of the Earth Surface Science Institute, the Cohen Geochemistry and Palaeo@Leeds research groups. This organisational framework provides a broader supportive environment which allows the cross fertilisation of ideas and expertise.

In addition, the project partners extremely well with the ongoing Jurassic Earth System and Timescale project at Leeds, Exeter and also incorporates ICDP funded drilling. These activities provide a ready-made wider community of national and international researchers working on the same time period for the student to engage with.

The kinds of combined analyses proposed for this project are likely to produce highly novel interpretations with excellent potential for high impact publication.

Entry requirements

Applications are invited from candidates with or expecting a minimum of a UK upper second class honours degree (2:1) and/ or a Master’s degree in Geological or Environmental Sciences, and an interest in Geochemistry, Earth history and the relationships between environmental and biological change.

If English is not your first language, you must provide evidence that you meet the University’s minimum English Language requirements.

How to apply

Formal applications for research degree study should be made online through the university's website. Please state clearly in the research information section that the PhD you wish to be considered for is the ‘Nutrient cycling and oxygenation of shallow seas during the Triassic-Jurassic mass extinction and the early Jurassic' as well as Dr Robert Newton as your proposed supervisor.

We welcome scholarship applications from all suitably-qualified candidates, but UK black and minority ethnic (BME) researchers are currently under-represented in our Postgraduate Research community, and we would therefore particularly encourage applications from UK BME candidates. All scholarships will be awarded on the basis of merit.

If you require any further information, please contact the Graduate School Office e: apply-phd@see.leeds.ac.uk, or t: +44 (0)113 343 1634.