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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 

Lead Supervisor: Neil Davies, Earth Sciences

Co-Supervisor: Sasha Turchyn, Earth Sciences

Brief summary: 
Sedimentary strata do not provide a complete or continuous record of geological time, with implications for any studies that seek to utilise signatures within them: this project will assess where time is lost on entry into the geological record with the use of modern active sedimentary environments which witness sediment accrual on timescales of seconds through to centuries.
Importance of the area of research concerned: 
There is an increasing recognition that the sedimentary stratigraphic record is permeated with gaps representing intervals of non-deposition, sediment bypass and erosion: a phenomenon that has sometimes been used to question the veracity of the historical geological record. Gaps occur on a hierarchy of scales, from minutes or less (e.g., ripple migration) to hundreds of millions of years (e.g., cratonic cycling). Whilst statistical modelling and stratigraphic analyses have been applied to good effect to understand thesignificance of these gaps from the ‘bottom-up’ perspective of the geological record, there have been fewer attempts to monitor ‘active’ gaps in modern sedimentary environments. Using the Norfolk coast as a natural laboratory, this proposal seeks to monitor active geochemical processes, sedimentation, stasis, sediment bypass and erosion at selected staked points at timescales ranging from the instantaneous to annual. This will be augmented with secondary data to translate these observations onto a decadal to thousands-year timescale, in order to offer a general ‘top-down’ understanding of gaps in the sedimentary record.
Project summary : 
Our understanding of gaps in the sedimentary record – and the implications of these gaps for our interpretation of the record of ancient physical, chemical and biological signatures – has largely been approached from a theoretical stastical analysis of the stratigraphic record. This project aims to improve our understanding by employing a fieldwork-based ‘present-to-past’ approach, identifying the levels of permanence or transience of various sedimentological and geochemical signatures of the Norfolk coast on temporal scales ranging from minutes to tens of thousands of years. Through comparison with Quaternary, and older, sediment piles from similar environments, the project will generate a high resolution conceptual model for the 'preservation of time' in strata deposited in nearshore environments.
What will the student do?: 
The student will closely monitor the duration of permanence of, and the diurnal to seasonal variation in, different sedimentary signatures in the tidal environment, and attempt to understand any bias in their ‘preservation potential’. These will include physical sedimentary and geomorphic elements, geochemical signatures (e.g., seasonal production of sedimentary pyrite with different sulphur isotope compositions) and the intensity and type of bioturbation. For at least one year of the project, the student will make regular visits to north Norfolk in order to take measurements and samples over the course of full tidal and seasonal cycles (measurements on Sedimentation Rate Scales (SRS) 1-4 [Miall, 2015]). The collection of this data over a calendar year will permit the observation of annual changes on SRS 5. This original data will then be compared with secondary records (aerial photos, historic maps, core logs) available at Cambridge extending the study into timescales representing SRS 6-7. Sections of Pleistocene and Carboniferous tidal strata from around the UK will be visited to assess the extent to which the present is the key to the past, in terms of time preservation.
References - references should provide further reading about the project: 
Davies, N.S., Shillito, A.P. and McMahon, W.J., 2019. Where does the time go? Assessing the chronostratigraphic fidelity of sedimentary geological outcrops in the Pliocene–Pleistocene Red Crag Formation, eastern England. Journal of the Geological Society, 176(6), pp.1154-1168.
Miall, A.D., 2015, Updating uniformitarianism: stratigraphy as just a set of ‘frozen accidents’. In: Smith, D.G., Bailey, R.J., Burgess, P.M., Fraser, A.J., (eds.), Strata and Time: Probing the Gaps in Our Understanding. Geological Society, London, Special Publications, 404, http://dx.doi.org/10.1144/SP404.4
Lazarus, E., Harley, M.D., Blenkinsopp, C.E. and Turner, I.L., 2019. Environmental signal shredding on sandy coastlines. Earth Surface Dynamics, 7, pp.77-86.
Applying
You can find out about applying for this project on the Department of Earth Sciences page.
Dr Alexandra (Sasha) Turchyn
Department of Earth Sciences Graduate Administrator
Dr Neil Davies