A fully-funded PhD studentship is available for one of the following topics:

1. Controls and impacts of benthic communities and bioturbation in marginal marine environments: testing the application of trace fossils
2. Mass extinctions and the trace fossil record
3. Petrochronology and mineral chemistry of mid-crustal shear zones: new tools for tectonics and mineral exploration
4. Response of baddeleyite to shock metamorphism in large meteorite impacts: new opportunities in Solar System chronology

Full details of each project are provided overleaf together with the names of the supervisors. Applicants MUST be from the UK/EU only. Funding is for three years and will cover University tuition fees and provide an annual stipend at standard RCUK rates for postgraduate research students (£13,726 in autumn 2013). There will be a requirement to carry out c. 6 hrs per week of laboratory demonstrating duties to undergraduate classes.

The successful candidate will have a minimum of an Upper Second Class Honours degree and be available to start 1^st October 2013. Please contact the first-named supervisor with a covering letter that details your interest in the chosen project and a cv (including the contact details of two referees) by midday Friday 30^th August. Interviews will be held on either 12^th or 13^th September.

School of Earth & Environmental Sciences,
University of Portsmouth,
Burnaby Rd,
Portsmouth,
PO1 3QL,
UK

Controls and impacts of benthic communities and bioturbation in marginal marine environments: testing the application of trace fossils

Supervisors: Dr Nicholas Minter (nic.minter@port.ac.uk) and Dr Steve Mitchell

The activities of benthic organisms leave behind physical structures in sediments. These are readily preserved in both modern and ancient environments. When preserved in the geological record, these structures are known as trace fossils and are widely applied in palaeoenvironmental analysis. Recent research has proposed a number of models for the distributions of trace fossils in marginal marine environments through time [1]. However, comparatively little research has been undertaken on modern environments to analyse the governing factors on their distribution in order to validate such models [2].

The principal aim of this project is to investigate the distributions of modern bioturbating organisms and their traces in relation to physicochemical factors in the Thames Estuary and Langstone and Pagham Harbours. The Thames Estuary is a site of ongoing Environment Agency monitoring [3] with stations located along a downstream gradient of freshwater to saltwater conditions. The location of the freshwater-saltwater interface varies with freshwater flow and creates a zone of mixed salinity stress within the estuary. Data on the distribution of modern bioturbating communities and their traces with respect to such physicochemical gradients will be used to validate models on the distribution of trace fossils in marginal marine environments. There will also be scope for geological fieldwork. The outcomes will have broad implications for interpreting palaeoenvironmental and palaeoecological conditions. They will also contribute to debates regarding traces of early organisms colonising freshwater habitats or following salt wedges upstream into fluvial systems [4,5].

In addition, Langstone and Pagham Harbours are Special Protection Areas. Comparison with the Thames Estuary will enable assessment of differing degrees of anthropogenic impacts on benthic habitats and lead to refinement of indices for assessing ecosystem state [6] under the EU Water Framework Directive. Other data and complementary flume tank experiments will also be utilised to investigate the effects of different bioturbating communities on sediment stability and re-suspension. These will be fed into mathematical models of sediment flux based on understanding of rates of sediment deposition and erosion [7].

This project will provide the student with the triumvirate of observational field skills, experimental lab studies, and mathematical modelling. It would be suitable for candidates with strong backgrounds in either geology/palaeontology or aquatic biology/ecology.

References: [1] Buatois, LA. et al. (2005) Palaios 20, 321-347. [2] Dashtgard, SE. (2011) Sedimentology 58, 1303-1325. [3] Mitchell, S. et al. (2012) Water Environ. J. 26, 511-520. [4] Kennedy, MJ. & Droser, ML. (2011) Geology 39, 583-586. [5] McIlroy, D. (2012) Geology, e269. [6] Rosenberg, R. et al. (2004) Mar. Pollut. Bull. 49, 728-739. [7] Mitchell S. et al. (2008) Estuar. Coast. Shelf S. 78, 385-395.

Mass extinctions and the trace fossil record

Supervisor: Dr Nicholas Minter (nic.minter@port.ac.uk)

The spread of oxygen poor marine waters is a significant threat to productive shallow marine ecosystems and this risk will only increase with ongoing climate change [1,2]. By reworking sediments through bioturbation, benthic marine organisms help to regulate many important ecosystem functions, including carbon and nitrogen cycling, and facilitate biodiversity [3,4] but such ecosystems are particularly vulnerable to the effects of reduced oxygen. Data on short-term, small-scale responses to environmental change may be acquired from modern monitoring studies and experimentally induced manipulations but predicting how ecosystems will respond over longer timescales is not straightforward due to issues related to scale, complexity and the possibility of non-linear responses and threshold effects. The long-term evolution of life on Earth has been punctuated by five mass extinctions [5]. Global oceanic anoxic events (OAEs) are implicated as major causal factors in several of these and also occurred frequently during the Mesozoic era where they are linked with several smaller-scale extinctions during the early Toarcian, Aptian, and Cenomanian-Turonian [6]. These may be viewed as a series of 'natural experiments' detailing the effects and recovery of ecosystems to extinction events with various causal mechanisms [5].

Long-term changes in bioturbating communities across extinction events during the Mesozoic will be analyzed by compiling a global database of shallow marine trace fossil assemblages. Information will be collected on an assemblage-by-assemblage basis with data on the palaeogeographic location, age, constituent trace fossils and specific sedimentological conditions. In addition, each trace fossil taxon will be categorized on the basis of its mode of life (tiering, motility, and feeding mode) and environmental modification (tiering, burrowing technique, and sediment modification mode). The quality of the database will be assessed by comparison with null models; after which, it will be used to investigate: (i) what were the baseline bioturbating community compositions and activity levels before extinction events in the Mesozoic; (ii) do communities ever fully recover to pre-event baseline states; (iii) are there any 'keystone' types of activities performed by bioturbating organisms whose loss precipitates community collapse, and that facilitate recovery; and (iv) what are the timescales for recovery and how does this relate to extinction intensity, duration and spacing?

Today, as in the past, different organisms performing the same activities leave behind similar physical bioturbation structures and these are readily preserved in the fossil record, even when the organisms themselves are not. Thus, they provide a unit of measurement and framework for comparison across time and space. Understanding the general rules by which the activities and composition of shallow marine bioturbating communities are affected by reduced oxygen is a key scientific challenge because it will help us to predict how these communities will change with ongoing climate change. In turn, this will help forecast the impacts on ecosystem functions and services provided by benthic marine communities and the knock-on consequences for the environment and economy.

This project would suit a numerate candidate with a strong background in geology, palaeontology or evolutionary biology. Depending on the background of the student, there would be possibilities for geological fieldwork on Mesozoic localities in Europe or laboratory experiments examining the impacts of the composition of bioturbating communities upon sediments and biodiversity.

References: [1] Díaz, RJ. & Rosenberg, R. (2008) Science 321, 926-929. [2] Stramma, L. et al. (2008) Science 320, 655-658. [3] Lohrer, AM. et al. (2004) Nature 431, 1092-1095. [4] Solan, M. et al. (2004) Science 306, 1177-1180. [5] Jablonski, D. (2004) Nature 427, 589. [6] Jenkyns, H.C. (2003) Phil. Trans. R. Soc. A 361, 1885-1916.

Petrochronology and mineral chemistry of mid-crustal shear zones: new tools for tectonics and mineral exploration

Supervisors: Dr. James Darling (james.darling@port.ac.uk), Dr. Craig Storey, Dr. Peter Lightfoot (Vale S.A.)

Resolving the timing and rates of crustal deformation is fundamental to the understanding of tectonic, orogenic and ore-forming processes. The direct dating of deformation in greenschist to amphibolite facies shear zones is of particular interest, as these structures can accommodate vast lateral and vertical crustal motions, control the development of tectonic features, and provide important pathways for orogenic and ore-forming fluids. Major advances are being made in this field, via the identification and isotopic analysis of synkinematic mineral phases that belong to the metamorphic assemblages associated with deformation. Certain U-Th bearing accessory minerals (e.g. allanite, monazite, titanite) have great potential in this regard, as they (1) can be linked to specific stages of deformation and physico-chemical conditions (e.g., pressure, temperature and fluid), based upon petrological observations (e.g. Janots et al., 2009; Cenki-Tok et al., 2013); (2) can be dated in-situ, preserving petrographic context (e.g. Storey et al., 2006; Darling et al., 2012); (3) are resilient to retrogression and low-grade alteration.

This industry-focused project will entail a detailed study of accessory mineral growth across well-constrained shear zones within the Sudbury structure, Ontario: one of the world's largest Ni-Cu-PGE sulphide ore deposits. The student will investigate how these phases can be better linked to deformation, metamorphism and ore-formation by combining petrological analysis, mineral chemistry and isotope geochemistry with surface and underground mapping of shear zones that are key to the late stage development of Sudbury's ore deposits. Pilot studies of these shear zones have revealed mineral chemistry trends that have great potential as exploration vectors towards highly valuable ore deposits. Accordingly, the student will work closely with Vale, a leading multinational metals and mining corporation, to develop understanding of the tectonic history (via geochronology), and test the use of mineral chemistry as a guide for future exploration.

The project will combine fieldwork, petrology, electron microscopy and in-situ trace element and isotopic analysis by laser ablation ICP-MS and MC-ICP-MS at the University of Portsmouth. The student will benefit from extensive training in these state-of-the-art techniques, as well as from working closely with exploration geologists from Vale.

References: Cenki-Tok, B., Darling, J.R., Rolland, Y., Dhuime, B. and Storey, C.D. (2013) Direct dating of mid-crustal shear zones with synkinematic allanite: New in-situ U-Th-Pb geochronological approaches applied to the Mont Blanc massif. Terra Nova
Darling J. R., Storey C. D. and Engi M. (2012) Allanite U-Th-Pb geochronology by laser ablation ICP-MS. Chem. Geol. 292-293, 103-115.
Janots, E., Engi, M., Rubatto, D., Berger, A., Gregory, C. and Rahn, M. (2009) Metamorphic rates in collisional orogeny from in situ allanite and monazite dating. Geology, 37, 11-14.
Storey, C.D., Jeffries, T., Smith, M., 2006. Common lead-corrected laser ablation ICP-MS U-Pb systematics and geochronology of titanite. Chemical Geology 227, 37-52.

Response of baddeleyite to shock metamorphism in large meteorite impacts: new opportunities in Solar System chronology

Supervisors: Dr. James Darling (james.darling@port.ac.uk), Dr. Desmond Moser (Western University)

Meteorites from the Moon, Mars and the asteroid belt offer tremendous insights into the evolution of our Solar System. They bear witness to the formation and differentiation of planets, as well as intensive bombardment of planetary surfaces. In order to fully understand the record that these precious rocks provide, it is critical to be able to distinguish the effects of extreme compression and heating that occur during planetary collisions from the original characteristics of the sample. Such "shock metamorphism" affects all meteorites during their ejection from planetary surfaces, and can produce recrystallization, deformation and pathways for chemical exchange amongst their constituent mineral phases. For example, the crystallization ages of basaltic Martian meteorites have been interpreted to vary by as much as 4 billion years (e.g. Nyquist et al., 2001; Bouvier et al., 2008; Moser et al., 2013): a reflection of our inability to resolve, by geochemical methods alone, the severity of mineral age disturbance by earthward-launching impact events.

Building upon recent advances by the group (Moser et al., 2013; Darling et al., 2013), this investigation will focus upon the effects of shock metamorphism on baddeleyite (ZrO2), a uranium-bearing mineral that is an important chronometer in meteorites from across the Solar System. Outstanding opportunities in this field are provided by terrestrial impact structures, allowing for the study of samples within a well understood geological and shock-metamorphic framework, and comparison of baddeleyite isotope systematics to other phases and dating systems (e.g. zircon U-Pb, whole-rock and mineral Sm-Nd isochrons, Pb isotopes). This project will focus upon target rocks in the 1.85 Ga Sudbury impact structure in Canada and the 2.02 Ga Vredefort impact structure in South Africa: the two largest, oldest and best-preserved meteorite impact structures on Earth.

The student will receive training in a wide-range of state-of-the-art microanalysis techniques at the University of Portsmouth and Western University, Ontario. These will include electron microscopy, X-ray spectroscopy, electron backscattered diffraction (HR-EBSD) and mass spectrometry (LA-ICP-MS, MC-ICP-MS, SIMS). There are also exciting opportunities to explore atomic-scale views of planetary chronology by TEM, STEM, transmitted kikuchi diffraction (TKD) and Atom Probe tomography (LEAP). The project will suit a student with a keen interest in planetary geology, petrology and geochronology, and lead to exciting future opportunities in impact studies, meteoritics and nanoscale to atomic-scale analysis of geological materials.

References: Bouvier, A., Blichert-Toft, J., Vervoort, J.D., Gillet, P., Albarède, F., 2008. The case for old basaltic shergottites. Earth and Planetary Science Letters, 266, 105-124.
Darling, J.R., Moser, D., Barker, I., Tait, K., Chamberlain, K., Schmitt, A. (2013) The shocking state of baddeleyite in basaltic shergottite NWA 5298. Mineralogical Magazine, 77(5) 946
Moser, D., Chamberlain, K., Tait, K., Schmitt, A., Darling, J.R., Barker, I. and Hyde, B. (2013) Solving the Martian meteorite age conundrum using micro-baddeleyite and launch-generated zircon. Nature, 499 (7459). pp. 454-457.
Nyquist, L.E., Bogard, D.D., Shih, C., Greshake, A., Stöffler, D., Eugster, O., 2001. Ages and geologic histories of martian meteorites. Space Science Reviews, 96, 105-164.