PhD: Fossilization at the dawn of animal life

Summary
This project seeks to understand the exceptional preservation of Earth’s earliest macroscopic animals and the microbial communities in which they lived, using novel analytical and experimental methods.

Project background
The fossil record suggests that macroscopic organisms did not become diverse or widespread on Earth until ~574 Ma with the arrival of the impressive, diverse “Ediacaran biota”, which almost certainly included multicellular animals. Soft-bodied benthic Ediacaran macro-organisms are found as exceptionally well-preserved fossils in siliciclastic sedimentary rocks around the world, commonly associated with microbial mats that carpeted the seafloor and may have mediated fossilization processes.

This project, based in Edinburgh with co-supervisors in Cambridge, aims to combine taphonomic experiments with the study of important fossil specimens to advance debates surrounding the role of microbial activity and early diagenetic cementation in the preservation of Ediacaran macro-organisms and microbial mats. The results will have important implications for the affinities of these organisms, their tissue composition, mode of life, and their distribution across space and time. The doctoral student will have the opportunity to study outstanding Ediacaran fossils both in collections in Cambridge and Edinburgh, and in the field in Russia, Canada, Namibia and/or Australia. The student will develop a broad understanding of Ediacaran palaeobiology, sediment geochemistry, and “experimental taphonomy”, as well as cutting-edge analytical methods.

Research questions
1. What was the biogeochemical activity of microbial mats associated with Ediacaran macro-organisms, and what was their role in fossil preservation?
2. How viable are the “early silicification”, “rheological”, and “pyrite death mask” models for the preservation of Ediacaran soft-bodied organisms and matgrounds in relief on bedding planes within different facies represented at global fossil localities?
3. Can rapid cementation of sediment grains by pyrite, clay and/or silica be induced experimentally under realistic Ediacaran burial conditions?
4. Does early cementation lead to the formation of sediment moulds around soft tissues and microbial mats on experimental timescales?

Methodology
This project will involve (a) experiments to test hypotheses about soft tissue and microbial mat preservation in Ediacaran sediments, (b) petrological and geochemical analysis of important Ediacaran fossil and sedimentological material from South Australia, Russia, Brazil, Namibia and Canada (in collections in Cambridge), and comparison with experimental products. Work in years 1–2 will concentrate on petrographic observations of fossil material coupled with preliminary experiments to refine methods for (a) simulating the Ediacaran seafloor with appropriate seawater compositions, mineral assemblages, and microbial communities, and (b) tracking the decay and mineralisation of invertebrate tissue and biofilms under these conditions using microanalytical techniques. In years 2–3+, these methods will be put to work in long-duration experiments (up to ~100 days) addressing the extent of pyrite, silica and clay mineral precipitation, the affinity of these minerals for buried microbial mats and animal tissues, and implications for the interpretation of Ediacaran fossils.

Training
A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Practical training will be provided in geomicrobiological laboratory methods, experimental taphonomy, petrographic and microbiological microscopy, ICP-OES, Raman spectroscopic microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and advanced methods of mineralogical analysis.

Requirements
This project would suit a geoscience graduate with knowledge of palaeobiology and geochemistry. Experience in laboratory-based practical work is not necessarily required but would be an advantage.