TECTONICS, BASIN AND CRUSTAL DEVELOPMENT, SEDIMENTOLOGY. M.J. Bickle, J. A. Jackson, D. McKenzie, N. Hovius, K. Priestley, N.J. White & N.H. Woodcock. This area involves groups of staff from diverse subject areas of the Department in the interpretation of the rock record in terms of plate-tectonic and lithospheric processes. Much current research is concentrated on the evolution of basins and involves geophysics, sedimentology, petrology and structural geology. Research in active tectonics includes studies of faulting and distributed deformation in many continental areas, and subduction zones, using seismological, geomorphological and conventional structural techniques. We also compare the results of these studies with direct measurements of the deformation by space-based geodetic techniques. Deformation processes evidenced in ancient fault zones are also a current research focus. In sedimentary geology we employ a combination of methods, usually starting with field definition of problems but leading onto petrographic, geochemical and isotopic probing of rocks to reveal palaeoenvironmental and post-depositional aspects of their origin. We are particularly interested in high temporal resolution and spectral analysis of precisely determined time-series containing palaeo-climatic and oceanographic information from the Palaeozoic and Mesozoic. We have active groups working on turbidite sedimentology and terrestrial sediment systems. We have a strong tradition of work on the diagenesis of shallow marine carbonate sequences, the effects of increasing T and P on diagenesis and the nature, movement and timing of subsurface fluids effecting precipitation of cements and creation of pores.
TECTONICS, BASIN AND CRUSTAL DEVELOPMENT, SEDIMENTOLOGY. T1
Earthquake seismology, lithosphere structure and tectonics. James Jackson & Keith Priestley.
T2
Compositional Variations in Continental Magmas. (Also see P15) Dan McKenzie.
T3
Temporal Evolution of the Iceland Plume and its Influence on the Arctic Realm. N. White, J. Maclennan, B. Lovell & J. Bujak.
T4
Seismic Oceanography: Resolving Three-Dimensional Thermohaline Structure of the Water Column. N. White & R. Jones (Schlumberger Cambridge Research).
T5
Dynamic Uplift and Drainage of North Africa. Nicky White, John Maclennan, Bryan Lovell & Mark Shand (BP).
T6
The impact of the erosion of continental biomass on the Earth's thermostat. (Also See C11) Albert Galy & Niels Hovius.
T7
Coupling of hillslopes and channels in erosional landscapes. Niels Hovius.
T1 Title: Earthquake seismology, lithosphere structure and tectonics. Supervisors: James Jackson & Keith Priestley. Importance of the research: An important recent advance is our ability to map lithosphere thickness on the continents using surface waves. It has also become clear that, within the continents, there are significant spatial variations in earthquake depths and mechanical properties that are related to lithosphere thermal structure, composition and geological history. The aim of this project is to connect these observations, and improve our understanding of their effects on the evolution of the continents. What the project involves: The main effort will be a close examination of the crustal and lithosphere structure, the earthquake focal mechanisms and depths, the geological history and the active geomorphology, in several key areas of the continents. In some of these areas there will be additional observations from GPS and petrological measurements, which will further constrain the present-day deformation and the deeper lithosphere structure. The project will range widely, seeking to find patterns that are recognisable in several different areas, rather than focus exclusively in one place. What the student will do: The student will use a wide range of seismological tools, particularly involving synthetic seismogram techniques, for earthquake source analysis. They will also use surface wave and receiver function analyses to investigate lithosphere and crustal structure. Much of the seismic data will be available through the Global Digital Seismic Network, but some will also be available from local networks of seismometers, run both by ourselves and by other people. At the same time, a range of remote-sensing and other techniques (including analysis of digital topography, satellite imagery, GPS measurements) will be used to relate the earthquakes and their distribution to active tectonic processes and geological structure. Training: The student will receive a thorough training in many aspects of modern earthquake seismology, and learn to manipulate and use digital topography and satellite imagery to investigate geomorphology, tectonics and geological structure. The student will become part of the NCEO/COMET group (http://comet.nerc.ac.uk), who collaborate in all these activities, and will become familiar with current controversies in continental tectonics. References: Emmerson, B., Jackson, J., McKenzie, D. & Priestley, K., 2006. Seismicity, structure, and rheology of the lithosphere in the lake Baikal region. Geophysical Journal International, vol. 167, pp. 1233-1272. Priestley, K., Jackson, J. & McKenzie, D., 2007. Lithospheric structure and deep earthquakes beneath India, the Himalaya and southern Tibet. Geophysical Journal International, vol. 172, 345-362. Jackson, J., McKenzie, D., Priestley, K. & Emmerson, B., 2008. New views on the structure and rheology of the lithosphere. J. Geol. Soc. London, vol. 165, 453--465.
T2 Title: Compositional Variations in Continental Magmas. (Also see P15) Supervisor: Dan McKenzie. Importance of the research: Compositional variations in basalts from oceanic ridges are small, and most are associated with fractionation processes that generate the oceanic crust. In contrast, melts generated from the mantle beneath continents show very large variations in both elemental on centrations and in isotopic ratios. Though their classification has led to the definition of an enormous number of rock types, it is unclear what the relationship is between the processes by which these magmas are generated and the categories into which they have been divided. It has always seemed likely that a major control on the magma composition is the thickness of the underlying lithosphere. However, there is no accurate barometer that can be used to estimate the pressure at which spinel peridotite nodules equilibrated. Since most continental magmas do not contain garnet peridotite nodules, the absence of a suitable barometer for spinel peridotites has meant that the depth from which the magmas come is not known. In the last few years it has become possible to estimate lithospheric thickness from surface wave tomography (Priestley and McKenzie 2006). Where the thickness can also be estimated from the petrology of garnet peridotite nodules, the agreement between the two methods is good. However, unlike nodule studies, seismology allows us to make maps of the lithospheric thickness beneath most continental regions. It is therefore straight forward to study what effect such variations have on the composition of the magmas. What the project involves: The first step involves a literature survey, to collect and model the large number of existing analyses of alkaline basic rocks from continental environments. The programs required for this purpose have been extensively used and tested (Slater et al. 2001, Tainton and McKenzie 1994), as have those required to obtain the lithospheric thickness from surface wave tomography. One important aim of this part of the project is to select a suitable region to carry out a field project, which will involve sampling and analysis of a suite of magmas along a profile where the thickness of the lithosphere changes rapidly. The existing maps show several regions which may be suitable. What the student will do: The geochemists have made a major effort to archive magma compositions in machine-readable form, and I have written programs that can calculate the magma compositions generated by simple models of mantle melting. These will be compared with the seismological observations. The understanding that results from such comparisons will be used to select an area suitable for field work, which the student will then carry out, followed by analysis and modelling of the sample compositions. Training: The student will receive training in geochemical analysis, programming, and the use of simple physical models to understand complex processes. Previous students trained in geochemical modelling have been especially in demand as reservoir engineers, and several also now occupy univesity positions in the UK and US. They have also done well in research and management positions in oil and mining companies. References: Priestley and McKenzie D. 2006 The thermal structure of the lithosphere from shear wave velocities. Earth Planet. Sci. Lett. 244 285-301. Slater L. et al. 2001 Melt generation and movement beneath Theistareykir, NE Iceland J. Petrol. 42 321354. Tainton K.M. and McKenzie D. 1994 The generation of kimberlites, lamproites, and their source rocks. J. Petrol 35 787-817.
T3 Title: Temporal Evolution of the Iceland Plume and its Influence on the Arctic Realm. Supervisors: N. White, J. Maclennan, B. Lovell & J. Bujak. Importance of the research: Convincing evidence now exists which supports the notion that vertical motion of the Greenland-Iceland-Scotland Ridge (GISR) has modified overflow of North Atlantic Deep Water throughout the Neogene period. This motion has an amplitude of hundreds of metres and appears to be controlled by temperature changes which travel up the mantle plume conduit beneath Iceland and flow sideways beneath the fringing continental margins. Geophysical, geochemical, stratigraphic and palaeoceanographic datasets can now be combined to reconstruct the Icelandic plume’s temperature history over the last 60 million years. During Cenozoic times, it is likely that plume-controlled changes in deepwater overflow have had a significant effect upon the biogeographical evolution of the Arctic Ocean, which is largely an enclosed basin. For example, there is excellent evidence during Late Eocene times that the Arctic Ocean freshened sufficiently to permit blooms of Azolla, a fresh-water algae, to develop. This freshening event terminated suddenly when warmer saline water flooded in from the south. What the project involves A combined approach will be used to investigate the detailed temporal record of the Icelandic plume and to explore how plume fluctuations have moderated the stratigraphic evolution of sedimentary basins located north of the GISR (e.g. Norwegian Sea, Greenland Sea, Arctic Ocean). First, geochemical and petrological data from a region encompassing Iceland will be integrated with the history of the V-shaped ridges along the Reykjanes Ridge and used to develop a time-varying plume model of plume flux. Secondly, Neogene and Paleogene stratigraphic records from numerous sedimentary basins which fringe the plume (e.g. North Sea basin, Porcupine basin, West Greenland basin) will be analyzed in order to constrain the spatial and temporal pattern of transient vertical motions associated with the Icelandic plume. Three-dimensional seismic reflection surveys, calibrated by well-log information, will form the cornerstone of the analysis. Thirdly, this general attack will be extended into the Arctic Realm where possible links between palaeoceanographic events and mantle convective circulation will be explored. Training: A wide-ranging project will appeal to geology and/or geophysics graduates who are interested in understanding the unusual problem of how convective circulation deep within the Earth’s mantle is manifest by disparate surficial geological records. He/she will be trained in many aspects of seismic and well data manipulation, plume dynamics, numerical modelling and Arctic palaeogeography. Research will be carried out in close collaboration with our colleagues in the hydrocarbon industry who have considerable interest in the geological evolution of the Arctic Realm.
References: Poore, H. R., Samworth, R., White, N. J., Jones, S. M. & McCave, I. N., 2006. Neogene overflow of Northern Component Water at the Greenland-Scotland Ridge. G-Cubed, 7, doi:10.1029/2005GC001085. Shaw-Champion, M. E., White, N. J., Jones, S. M. & Lovell, J. P. B., 2007. Quantifying transient mantle plume uplift in the Faroe-Shetland basin. Tectonics, in press. Contact
[email protected] Rudge, J.F., Shaw-Champion, M.E., White, N., McKenzie, D. & Lovell, J.P.B., 2007. A plume model of transient diachronous uplift at the Earth’s surface. Earth Planet. Sci. Letts., in press. Contact
[email protected]
T4 Title: Seismic Oceanography: Resolving Three-Dimensional Thermohaline Structure of the Water Column. Supervisors: N. White & R. Jones (Schlumberger Cambridge Research) Importance of the research: Recently, it has been shown that seismic reflection profiling yields spectacular and well-resolved acoustic images of different water masses in the oceans. These images have already provided new and exciting insights into important oceanographic phenomena (e.g. structure and evolution of thermohaline fronts, internal eddy formation, diapycnal mixing). Just as satellite imagery revolutionized our understanding of the physical, chemical and biological evolution of the sea surface, the nascent discipline of ‘seismic oceanography’ is likely to have an equally profound impact upon our quantitative understanding of four-dimensional (4D) oceanic circulation which moderates climate in important ways. The Project: It is well known within the seismic industry that the acoustic velocity of the water column changes rapidly through time and space in certain locations (e.g. Faroe-Shetland Channel, Gulf of Mexico). The resultant static and amplitude shifts are often abrupt and they can have important and deleterious effects upon 3D and 4D seismic images. As exploration and production move into ultra-deep waters (≥ 1.5 km), these effects will be more dramatic for at least two reasons. First, significant internal tides break along the continental shelf in water depths of ≥ 1 km. Secondly, deep-water masses flow along, and interact in a complex manner at, continental shelves. Automatic methods for correcting water static shifts rely upon direct picking of acoustic velocity at the sea bed and little attempt has been to develop a general understanding of the changing acoustic velocity structure of the water column and the way in which it distorts both downgoing and upgoing wavefields. What will the student be doing: This PhD project will attack the general problem of 3D acoustic imaging of the water column and its implications for time-lapse imaging. It is divided into four stages. First, the student will generate acoustic images by developing and applying a novel processing strategy to 3D datasets from oceanographically significant deep-water locations where we already know that excellent images of the water column can be obtained. Secondly, these images will be interpreted and calibrated with the aid of extensive legacy hydrographic measurements, notably temperature and salinity. Thirdly, existing 1D and 2D seismic tomographic imaging algorithms will be adapted to generate accurate acoustic velocity models. Fourthly, when converted to temperature, these models will form the basis of a fluid dynamical understanding of important phenomena such as diapycnal mixing. They will also be used to develop strategies for correcting static and amplitude shifts along and across repeat sail lines. Training: This multidisciplinary project will be carried out by a PhD student who has a strong back ground in physics and applied mathematics. He/she will be trained in many aspects of data acquisition, processing, interpretation and modelling. The supervisors necessarily cover a broad spectrum of expertise from physical oceanography to signal processing. This project will be carried out in close collaboration with colleagues at Schlumberger Research, at the Universities of Durham and Wyoming, and at the National Oceanographic Centre, Southampton. References: Lonergan, L. & White, N., 1999, Three-dimensional seismic imaging of a dynamic Earth. Philosophical Transactions of the Royal Society, Series A, 357, 3359–3375. Holbrook, W.S. et al., 2003. Thermohaline fine structure in an oceanographic front from seismic reflection profiling. Science, 301, 821–824. Holbrook, W.S. & Fer, I., 2005. Ocean internal wave spectra inferred from seismic reflection transects. Geophys. Res. Letts., 32, doi:10.1029/2005GL023733.
T5 Title: Dynamic Uplift and Drainage of North Africa. Supervisors: Nicky White, John Maclennan, Bryan Lovell & Mark Shand (BP) Importance of the research: It is now accepted that the topography of Africa is largely supported by upwellings and down-wellings within convecting mantle. In North Africa, regions of predicted convective upwelling such as Ahaggar, Tibesti and Jebel Marra, are associated with recently active volcanism and elevated topography. In contrast, predicted convective down wellings coincide with sedimentary depressions such as the Chad and Sudd basins. In sub-equatorial Africa, analysis of drainage patterns and erosion indicates that the pattern of uplift and subsidence changes with time. These changes are also reflected in the temporal variation of solid sedimentary flux at deltas. Thus geomorphological and sedimentological datasets can be used to gain important insights into spatial and temporal variations of mantle convection. The Project: These ideas will be tested by investigating the relationship between topography, gravity, drainage and magmatism in North Africa which straddles the northern boundary of the African Superswell. A key element in this study is determining the development of the River Nile catchment whose Neogene solid sedimentary flux will be analyzed using regional seismic reflection data and well-log information provided by BP. Results will be integrated with ongoing provenance and magmatic studies and with our understanding of the Cenozoic evolution of sub-equatorial Africa. What will the student be doing: This multidisciplinary and ambitious project will be carried out in close collaboration with BP Cairo where the student will spend study periods. It will suit a geologist or geophysicist who is interested in exploring the relationship between drainage/sedimentation and dynamic uplift. He/she will be trained in many aspects of basin and topographic analysis. This studentship will cover all university fees and maintenance (£12,300 and industrial top up of £1,000 totals £13,300 per annum). Please send CV and email addresses of two referees as soon as possible to
[email protected] (Dr N.J. White, Bullard Laboratories, Department of Earth Sciences, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ, UK). References: Walford, H. L. & White, N. J., 2005, Constraining uplift and denudation of West African continental margin by inversion of stacking velocity data. Journal of Geophysical Research, 110, doi:org/10.1029/2003JB002893 Walford, H. L., White, N. J. & Sydow, J. C., 2005, Solid sediment load history of the Zambezi delta. Earth and Planetary Science Letters, 238, 49-63. Jones, S.M. & White, N.J., 2003. Shape and size of the starting Iceland Plume swell. Earth Planet. Sci. letts., 216, 271–282.
T6 Title: The impact of the erosion of continental biomass on the Earth's thermostat. (Also see C11) Supervisors: Albert Galy & Niels Hovius. Importance of the area of research: The erosion of the terrestrial biosphere and transfer of particulate organic carbon (POC) by rivers to the oceans is an important component of the global carbon cycle. It is now clear that storm-driven mass wasting in active mountain belts yields globally significant amounts of POC, but the contribution of densely forested area outside the tropics remains poorly constrained. What are the mechanisms responsible for the mobilization and transport of POC in eroding uplands outside the intertropical convergence zone (ITCZ)? What is the source of this POC: fossil carbon in the rock mass, or life biomass? How much POC is transferred from uplands outside the ITCZ? What is the potential impact of this transfer on global climate? What the project will involve: This project will involve discussions with local organisations to identify catchment targets (contacts in Norway and Canada are in place) and visits to Southern Norway and British Columbia to set up sampling, validate choice of field sites, initiate sampling, and establish a geomorphological framework. The core of the project will involve the measurement of the elemental and isotopic composition of organic carbon and their interpretation within a larger geomorphological and hydrological framework. This work will form part of a larger study aimed at understanding the multiple controls on erosion rate, temperature, rainfall, storm, earthquake, vegetation and comparison with ongoing research in active mountain belts will be promoted. What the student will be doing: In the field, the student will be trained to interact with local scientific communities in charge of river monitoring and to sample river material for environmental sciences study. The student will also be trained in the recognition and quantification of geomorphic processes. In the lab, the student will learn the methodologies involved in 1) state of the art mass spectrometry, 2) the treatment of geological samples, and 3) topographic analysis and geographic information systems (GIS). The data collected by the student will form the basis for the modelling of hydrological and chemical processes in environmental sciences. Therefore, the student will gain experience of modern geochemistry laboratory and instrumental techniques, and modelling techniques used in environmental sciences. Training that will be provided: The student will be trained in field sedimentology and geomorphology, ArcGIS, and in several organic geochemical techniques (from the acquisition to the modelling) including organic extractions and analysis by GC-MS and LC-MS, and isotope organic chemistry. The student will be familiar with several topical aspects of research in climate change. The project will receive additional funding for fieldwork and analytical costs from BUFI, the University Funding Initiative of the British Geological Survey (BGS). The student will have access to BGS analytical facilities. References: Leithold, E. L., Blair, N. E. & Perkey, D. W. Geomorphologic controls on the age of particulate organic carbon from small mountainous and upland rivers. Glob. Biogeochem. Cycles 20, GB3022 (2006). Hilton, R. G., Galy, A. & Hovius, N. Riverine particulate organic carbon from an active mountain belt: The importance of landslides. Glob. Biogeochem. Cycles 22, GB1017 (2008). Prahl, F.G., Ertel, J.R., Goni, M.A., Sparrow, M.A. & Eversmeyer, B. 1994. Terrestrial organic-carbon contributions to sediments on the Washington margin Geochim. Cosmochim. Acta 58, 3035-3048.
T7 Title: Coupling of hillslopes and channels in erosional landscapes. Supervisons: Niels Hovius. Importance of the area of research concerned: Erosional landscape evolution is driven by fluvial incision of uplifting rock mass, but most sediment originates on hillslopes. A double coupling exists between the two domains. Rivers undercut valley sides and drive hillslope erosion. This provides sediment to the channel, where it acts as tool for river cutting. Too much sediment in the channel results in aggradation instead of erosion. The dynamics of erosional landscapes can not be understood without knowledge of the coupling of hillslopes and channels. The project: The aim of this project is to constrain the nature of the coupling of hillslopes and channels in erosional landscapes. This will be done by a combination of observation of natural systems, analogue modelling of coupled landscapes, and consideration of the physics of the principal geomorphic processes involved. Questions may include: • How is river cutting transmitted to hillslopes? • What is the time scale on which hillslopes and rivers are connected? • Are headwater dynamics different from valley side dynamics? What the student will do: Field observations of channel and slope processes and their interactions will help constrain the nature and dynamics of their coupling. Mass transfer from hillslopes and removal of sediment by rivers will be documented; channel and valley cross sections will be analysed; local erosion rates in channels and slopes will be measured (using cosmogenic isotopes and real time observations) and compared. Field observations and theoretical considerations will drive a series of analogue experiments. Coupled hillslope and channel models will be used to study the longer-term interaction between the two domains, and to evaluate the propagation of known perturbations through the landscape. Training: • Terrain analysis using digital elevation models • Geomorphic analysis of remote sensed images • Field observation and measurement • Familiarisation with cosmogenic isotope analysis • Scaled, analogue modeling of landscapes Fieldwork will be in an active mountain belt, e.g., Taiwan, Alps. Experimental work will be located, in part, in the laboratory for experimental geomorphology of the University of Rennes, France. References: Hartshorn, K., Hovius, N., Dade, W. B., and Slingerland, R. L.2002. Climate-driven bedrock incision in an active mountain belt. Science, vol. 297, pp. 2036-2038. Lague, D., Crave, A., and Davy, P. 2003. Laboratory experiments simulating the geomorphic response to tectonic uplift. Journal of Geophysical Research, vol. 108, doi: 10.1029/2002JB001785. Turowski, J.M., Lague, D., and Hovius, N.: The cover effect in bedrock abrasion: A new derivation and its implications for fluvial modeling. Journal of Geophysical Research, Earth Surface, doi:10.1029/2006JF000697. Turowski, J.M., Hovius, N., Hsieh, M.L., Lague, D., and Chen, M.C.: Distribution of erosion across bedrock channels. Earth Surface Processes and Landforms, doi:10.1002/esp.1559.
