PhD: The impact of meiofauna on sediment structure and chemistry across Earth history

Importance of the area of research concerned:
The burrowing activity of macroscopic benthic organisms has had a profound impact on the fabric, porosity and geochemistry of sediments throughout the Phanerozoic geological record. However, the physical and geochemical impact of meiofaunal burrowers — organisms typically between 50–1000 µm in size — on sediments is critically overlooked. The meiofauna include diverse groups such as metazoans, bacteria, and protists (e.g. foraminifera and amoebae), and in modern settings they are abundant in many depositional environments, particularly under low oxygen conditions where larger metazoans are excluded. Reports of fossil meiofaunal activity include the presence of discrete burrows, and cryptobioturbation (the total reworking of sediments with no distinct traces). However, the extent to which meiofaunal organisms engineered ecosystems in deep time remains poorly known. Also unknown is their environmental tolerance, their substrate preference, their impact on fluid flow through sediments, and their response to major environmental perturbations through Earth history.

Project summary :
This project will assess how meiofaunal communities impacted the physical and chemical properties of sediments in deep time, and address the question of whether their activity was necessary to condition substrates ready for macro-faunal habitation. Investigation of the extent and distribution of meiofaunal burrows in Triassic and Jurassic mudrocks of the UK will constrain how burrowing intensity varies as a function of fluctuating redox conditions and sediment composition, as well as relative to changes in macroscopic ichnofossil diversity and ichnofabric intensity. The project will then expand to explore sections through mass extinction intervals, documenting the meiofaunal response to a variety of environmental perturbations. Laboratory aquarium experiments investigating changes to physical and chemical sediment properties imparted by meiofaunal activity will provide necessary context.

What will the student do?:
The project will involve fieldwork on the Jurassic Coast of the UK, where reference sections will be logged and hand samples collected. These, and existing core material at the National Geological Repository, British Geological Survey, will be analysed with x-ray CT scanning and SEM microanalysis. Digital reconstruction of CT data, combined with geochemical (XRF) and microfacies analysis, will enable investigation of relationships between meiofaunal burrowing, substrate, redox geochemistry and resulting sedimentary fabric. Measurement of variables including total organic carbon, porosity, microfabric and clay mineral content in beds exhibiting a full spectrum of meiofaunal activity will enable comparison of burrowed versus non-burrowed substrates. Experimental work will be undertaken using aquaria in Supervisor Liu’s laboratory at the Department of Earth Sciences, Cambridge. The student will lead the design of experimental set-ups to determine the impact of modern meiofaunal organisms on physical and chemical sediment properties.