YES-27-D-18. The Lifeless Edge: Contourites in the Closing Iapetus Ocean

Year
2027
Primary Supervisor
Jeffrey Peakall <[email protected]>
Institution
Possibility of becoming a CASE project
No
Collaborative Project
No
Academic Supervisors
David Hodgson <[email protected]> (University of Leeds, School of Earth and Environment), Paul Wignall <[email protected]> (University of Leeds, Earth Environment and Sustainability)
Research Themes
,
Project Partners
None
Research Keywords
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Relevant Degree Courses
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Summary: Contour currents are long lived flows that traverse ocean floors. They drive thermohaline circulation thus regulating global climate, and erode, transport, and deposit sediment and pollutants across huge distances. Their deposits, contourites, are a primary archive of palaeoceanographic circulation, showing where flows were present and how these changed in strength over time. Despite their importance as records of palaeoceanographic change, there is an absence of process-based sedimentological models to support identification of contourites in sedimentary successions. Existing contourite facies models are characterised by heavily bioturbated silt beds that show repeated bi-gradational sequences that first coarsen-upward before subsequently fining-upward. The bioturbation is pervasive because accumulation rates in contourites are very low, and in oxygenated oceans organisms thrive and have plentiful time to thoroughly rework the sediments. This bioturbation therefore removes almost all the primary sedimentological evidence for the formative conditions of these deposits. Consequently, the detailed dynamics of contourites as archived in the original sediments, and the process understanding that can be derived from these deposits, are largely unknown.

Life is thus paradoxically the agent of death for the sedimentological record. Here we will study contourites on the lifeless edge of the Iapetus Ocean, where oxygen restriction was sufficient to minimise bioturbation and therefore preserve the primary sedimentary record in exquisite detail. The project thus enables a high-resolution look at contourites, and analysis of their sedimentary sequences, their sedimentary structures, and their associated grain-size changes. This detailed analysis will enable an examination into the spatial and temporal changes within contourite successions at an unprecedented level, and in turn enable process-based sedimentary models to be developed for the first time.

This project will examine Ordovician rocks across Ireland, the Welsh basin and the Isle of Man that were positioned on the northern edge of the great Iapetus Ocean as it closed. Here contour currents were active for long periods, but under restricted oxygen conditions. There may also be an opportunity to compare these Ordovician rocks to modern contourite cores.

Aims and Objectives:

This project’s primary aim is to generate a new process-based model(s) of contourites, that will enable a deeper understanding of the underlying spatio-temporal variation in contour currents and how this record is preserved in non-bioturbated sediments.

Key objectives are to:

  • Record the detailed sedimentology of a range of different contourite deposits from across the northern margin of the Iapetus Ocean.
  • Examine the sedimentary structures and grain size variations in detail both in the field, in slabbed sections, and in thin-sections.
  • Understand how the processes are recorded in the sedimentary structures and sedimentary sequences.
  • Erect new facies sequences – are repeated bi-gradational sequences the only sedimentary motif?
  • Construct a new process-based model(s) of contourites.

Eligibility: Applicants should have a BSc degree (or equivalent) in geology, geoscience, earth sciences, or a similar discipline. An MSc in an earth science field would also be advantageous.

Training: The successful applicant will join the vibrant Sedimentology and Earth Surface Processes group within the School of Earth, Environment & Sustainability. You will be provided with field training through direct supervision in the field, alongside the ability to access training in process sedimentology and sedimentary environments. Additionally, the Faculty provides access to a wide range of training workshops covering all aspects of the PhD process from managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk). There are big opportunities here for publishing high-impact science, and you will be strongly encouraged and supported in writing up your work for publication in leading international journals. There will also be opportunity to attend and present at international conferences, where you will also be able to meet workers from across the field.

Further Information: For more information about this project contact:

Professor Jeff Peakall, [email protected]