Dr Mark Tarplee, BSc, PGCE, PhD
Visiting Research Fellow
Tel: (+44) (0)20 7882 2777
School of Geography
Queen Mary, University of London
Mile End Road, London E1 4NS
Research interests:Subglacial Till – The ‘Upwardly Mobile’ Sediment?
My primary research interests are sediment dispersal dynamics and processes within the subglacial environment, particularly associated with the deformation of soft-sediment (till) proximal to the ice-bed interface. The nature and extent of subglacial till deformation is the subject of much conjecture and debate, its role in controlling ice-mass dynamics (with the consequent effects on global climate) still ambiguous. Palaeoglaciated landscapes (areas from which formally much more extensive ice-masses have retreated) offer an insight into what is a largely inaccessible contemporary environment.
Glacial erratic material is sediment of any size that has been transported and deposited beyond the margins of its source sub/outcrop, often forming definable three-dimensional lenses within till, referred to as erratic or dispersal plumes. The two-dimensional surface expressions of these sediment assemblages are termed erratic/dispersal trains/fans. Subglacial erratic plumes can be viewed as lithologically, mineralogically and/or geochemically distinct tracers (similar to chemical/dye tracers used in hydrological studies) providing a unique insight into the sedimentological processes that occur within this environment. Additionally material eroded and dispersed from mineral deposits located in palaeoglaciated areas produces a much larger target than the orebody itself, thereby increasing the chances of detecting the presence and exact location of the source which is often obscured by overlying glacigenic sediments
My PhD research involved three-dimensional, multi-scale geomorphological, geochemical, sedimentological, and micromorphological analyses of a 93 km2 area around the Tynagh mineral deposit, south-east County Galway, Ireland (Figs. 1-3). The surface expression of the associated erratic assemblage has a ‘ribbon-type’ form (a common shape), but within the sediment package its morphology diverges significantly from that of other three-dimensionally mapped erratic plumes. The findings of this research, including an updated idealised model of an erratic plume, are being prepared for publication in collaboration with Professor Jaap J.M. van der Meer and others, one paper published in 2010. The research is part of a wider project on subglacial sedimentary processes and glacial geomorphology being undertaken by fellow members of the Earth Surface Science Research Group.
The Geological Survey of Ireland generously provided equipment, field and technical support for the research as well as permitting use of the Open File Databank for the Tynagh area. Aurum Exploration Ltd. also provided materials and invaluable advice. Innov-X UK generously loaned me an Innov-X Systems Alpha Analyzer Field Portable X-Ray Fluorescence analyser for the geochemical analyses.
X-ray microtomography – a new perspective on some old issues:
X-ray computed tomography (CT scanning) has revolutionised the medical and materials sciences, providing insights into the composition and structure of objects, most notably humans, without the need for invasive/destructive analytical techniques. I used a SkyScan 1072 microtomograph (µCT), part of the Centre for Micromorphology, to analyse a variety of undisturbed subglacial sediment specimens in order to better understand how they responded to the shear stresses applied by the overriding ice. By creating volumetric three-dimensional visualisations of some of the ‘type’ examples of subglacial sediment microstructures, which could then be virtually dissected in a wide variety of ways, my colleagues and I were able to gain significant insights into their strain history, this research published in 2011 (Fig. 4).
Geological materials, especially (glacial) diamictons which are often composed of a highly variable variety of rock types, present specific challenges in the application of µCT. I have compiled information regarding how these problems may be mitigated and combined it with a set of protocols detailing how optimal quality scans and visualisations can be acquired using the Skyscan 1072, in collaboration with Mr Nick Corps, SkyScan Engineer, e2v scientific instruments. In 2011 the SkyScan 1072 was replaced by a Nikon Metrology XT H 225, which is capable of scanning much larger samples. As a consequence, and in collaboration with a number of researchers, I have now applied the technique in the analysis of a variety of (geo)materials/specimens including; glacier debris-rich basal ice, estuarine sediments, diamictites and ostracods, the results being prepared for publication currently.
Other research projects:
I have participated in a collaborative project between the Geological Survey of Canada and Alberta Geological Survey, mapping the surficial (glacial) deposits of northern Alberta. Micromorphological sampling of sediments located within the Bistcho Lake area (NTS 84M map sheet), northwest of Zama City was conducted (Figs.5-6). Thin-section and µCT analyses are being used to complement the macroscopic (field) analyses and assess the level of till microfabric development, in order to assist in reconstructing the direction and nature of ice flow across the area during the Last Glacial Maximum. The findings of this research are being prepared for publication in collaboration with members of the surveys.
I have also collaborated with Professor Ólafur Ingólfsson and Dr Anders Schomacker, among others, in a study of the recent flow dynamics of Múlajökull, a piedmont outlet glacier of the Hofsjökull ice cap, Iceland (Figs.7-8). My research is focussed on µCT analysis of samples acquired from five till units exposed in a river cut series of longitudinal sections through one drumlin, recently exposed through active retreat of the glacier margin. It is anticipated that the work will provide significant additional insights into the nature of sediment emplacement associated with glacier surging activity.
I have attended course AG-321 - Arctic Terrestrial and Marine Quaternary Stratigraphy – Excursion, at the University of Norway in Svalbard, in order to gain an insight into processes occurring within a high arctic glacial environment (Figs. 9-10). During the field excursion I acquired micromorphological samples from a variety of sedimentary environments, the results of the analyses in preparation for publication.
Examples of research funding:
Financial support for the PhD research and conference attendance has been provided in the form of grants from:
• Queen Mary, University of London Research Studentship
• Quaternary Research Association
• The International Association of Sedimentologists
• British Society for Geomorphology
• The Royal Society 20th International Geographical Congress Fund
Peer-reviewed journal articles:
- Tarplee, M.F.V., van der Meer, J.J.M., Davis, G.R., 2011. The 3D microscopic ‘signature’ of strain within glacial sediments revealed using X-ray computed microtomography. Quaternary Science Reviews. 30, 3501–3532
- Tarplee, M.F.V., van der Meer, J.J.M., 2010. Irish Ice Sheet sector dynamics as indicated by the Tynagh mineral deposit erratic assemblages. Proceedings of the Geologists’ Association. 121, 32–42.
- Tarplee, M.F.V., 2012. Irish Ice Sheet sector dynamics as indicated by the Tynagh mineral deposit erratic assemblages. In: XVIII INQUA Congress, 21st–27th July, 2011, Bern, Switzerland: Abstracts. Quaternary International. 279–280, 485
- Tarplee, M.F.V., 2012. The 3D microscopic ‘signature’ of strain within glacial sediments revealed using X-ray computed microtomography (µCT). In: XVIII INQUA Congress, 21st–27th July, 2011, Bern, Switzerland: Abstracts. Quaternary International. 279–280, 485
- Tarplee, M., Corps, N., 2008. Skyscan 1072 desktop X-ray microtomograph: sample scanning, reconstruction and visualisation (2D and 3D) protocols. Guidelines, notes, selected references and F.A.Q’s. Centre for Micromorphology, Department of Geography, Queen Mary, University of London. pp. 26
- Tarplee, M.F.V., 2006. Subglacial till – the ‘upwardly mobile’ sediment? Ph.D. Thesis, Queen Mary, University of London. pp. 318
- Tarplee, M., Sheehy, M., 2004. Report on the drilling project carried out in the vicinity of the Tynagh mineral deposit, southeast County Galway, 4th–14th May 2004. Geological Survey of Ireland Open-File report, Dublin, pp. 31