About the Project
Rivers draining catchments largely within the tropics occupy ~ 20% of the modern land surface (Syvitski et al., 2014) but transport a disproportionately large share of the world’s particulate and dissolved inorganic and organic matter to the ocean (Milliman and Farnsworth, 2011). This is because tropical catchments are characterised by high temperatures and intense rainfall, which promote rapid biogeochemical weathering and the liberation of sediment and solutes (Syvitski and Milliman, 2007). The export of weathered silicates and organic carbon is likely to have played a significant but unquantified role in driving global climate change during major greenhouse intervals of the Phanerozoic (Dahl and Arens, 2020). Addressing this question requires quantifying particulate carbon and sediment fluxes from ancient tropical catchments through reconstructions of catchment morphometrics and the morphodynamic and palaeohydraulic behaviour of their river systems (e.g. Duller et al., 2012; Colombera et al, 2023). River morphodynamics in tropical settings are influenced by a range of interrelated factors. Dense vegetation cover, extensive peatland development, and high concentrations of organic acids in runoff can strengthen banks, increase the frequency of log jams, and promote grain flocculation, among other effects. However, the distinct morphodynamic signature of tropical rivers in the depositional record, particularly over timescales longer than those captured by modern monitoring, remains poorly quantified. The extent to which sediment and organic matter are stored on floodplains or ultimately transferred to the ocean depends on the hydrological regime of the river system and the nature of coupling between channels and their densely vegetated floodplains (Straub et al., 2023). Upper Carboniferous stratigraphy provides an exceptional opportunity to study the geological record and impact of these ancient tropical rivers. In this project the student will reconstruct the morphodynamic signature of several fossilised tropical rivers from the Early-Mid Pennsylvanian Breathitt Group of the Central Appalachian foreland Basin (USA). An outstanding in-place coal-seam correlation framework and excellent exposure permits individual rivers to be tracked for >50 km from their emergence into the basin on its orogenic margin as they transverse the basin orthogonally across its axis towards the NW (Horne et al., 1978; Jerrett et al., 2017). The Breathitt Group is remarkable in that the succession also includes the deposits of a major continent-scale river which flowed down the axis of the basin to the SW, and whose catchment was largely the extra-tropical Canadian shield to the north (Archer and Greb 1995; Eriksson et al., 2004). This latter river formed the trunk distributary into which the smaller, fully tropical rivers were tributaries. This would permit side-by-side comparison of the dynamics of entirely tropical and largely extratropical rivers of equivalent age and in the same basin. The student will combine sedimentological and architectural field observations of fluvial deposits of key sedimentary transects in space and time, and apply state-of-the-art techniques for reconstructing the palaeohydrology of rivers (e.g. Lyster et al., 2020; McLeod et al., 2023). Quantitative reconstructions from bedform, bar-form and grain size measurements will include channel depths, slopes, and water discharge estimates. Based on this, channel planform and sediment transport capacities will be estimated, and run-off regimes reconstructed. These results will enable the morphodynamics of these rivers to be resolved quantitatively for the first time, will provide important new insights into the behaviour and impact of tropical rivers in the past, and will deliver quantitative constraints on sediment loads and nutrient fluxes at continental scale from an Upper Carboniferous mountain belt.
We encourage applicants with a 2:1 or equivalent degree in an Earth or Environmental Sciences discipline.
The student will be based at the School of Earth and Environmental Sciences, University of St Andrews, integrated into a rich postgraduate research community and have access to workshops on research methods and transferrable skills through the St Leonard’s College.
Short research stays at Imperial College and the University of Liverpool are likely. The student will receive practical training in novel methods for the collection and analysis of fluvial palaeohydrological data, basin and source-tosink analysis. The student should be prepared to undertake substantial fieldwork in the USA, and possibly elsewhere as required. The training will provide the basis for a future career in Earth and Environmental science, in the industrial, government or academic sectors, in a rapidly expanding research area of international societal importance.
Supervisors
- Dr Rhodri Jerrett (St Andrews) rmj9@st-andrews.ac.uk
- Alex Whittaker (Imperial College)
- Catherine Rose (University of St Andrews)
- Rob Duller (University of Liverpool)
Funding Notes
Funded by the School of Earth and Environmental Sciences, University of St Andrews.
References
References (copies can be provided by contacting Rhodri Jerrett
Archer, and Greb, 1995, An Amazon-Scale Drainage System in the Early Pennsylvanian of Central North America. Journal of Geology, 103, 611-627. Colombera, L., Reesink, AJ.H., Duller, R.A., Jeavons, V.A., Mountney, N.P., 2024, The thickness variability of fluvial cross-strata as a record of dune disequilibrium and palaeohydrology proxy: A test against channel deposits. Sedimentology, 71, 590–618. Dahl, T.W and Arens, S.K.M, 2020, The impacts of land plant evolution on Earth’s climate and oxygenation state – An interdisciplinary review. Chemical Geology, 547, 119665 Duller, R.A., Whittaker, A.C., Swinehart, J.B., Armitage, J.J., Sinclair, H.D., Bair, A., Allen, P.A., 2012, Abrupt landscape change post–6 Ma on the central Great Plains, USA. Geology, 40, 871–874. Eriksson, K.A., Campbell, I.H., Palin, J.M., Allen, C.M., and Bock, B., 2004, Evidence for multiple recycling in Neoproterozoic through Pennsylvanian sedimentary rocks of the central Appalachian basin: The Journal of Geology, v. 112, p. 261–276. Horne, J.C, Ferm, J.C., Caruccio, F.T, Baganz, B.P., 1978, Depositional models in coal exploration and mine planning in Appalachian region. AAPG Bulletin, 62, 2379-2411. Jerrett, R.M., Flint, S.S., Brunt, R.L., 2017, Palaeovalleys in foreland ramp settings: what happens as accommodation decreases down dip? Basin Research, 29, 747-774. Lyster, S.J., Whittaker, A.C., Allison, P.A., Lunt, D.J., Farnsworth, A. 2020, Predicting sediment discharges and erosion rates in deep time—examples from the late Cretaceous North American continent Basin Research, 32, 1547–1573. McLeod, J.S., Wood, J., Lyster, S.J., Valenza, J.M., Spencer A.R.T, Whittaker, A.C., 2023, Quantitative constraints on flood variability in the rock record. Nature Communications, 14, 3362. Milliman, J.D., and Farnsworth, K.L, 2011, River Discharge to the Coastal Ocean: A Global Synthesis, Cambridge University Press, 392 p. Straub, K.M., Dutt, R., Duller, R.A., 2023, Coupled channel–floodplain dynamics and resulting stratigraphic architecture viewed through a mass-balance lens. Journal of Sedimentary Research, 93, 595-616. Syvitski, J.P.M., Cohen, S., Kettner, A.J., Brakenridge, G.R., 2014, How important and different are tropical rivers? — An overview. Geomorphology, 227, 5-17 Syvitski, J.P.M., and Milliman, J.D., 2007, Geology, Geography, and Humans Battle for Dominance over the Delivery of Fluvial Sediment to the Coastal Ocean. Journal of Geology, 115, 1-19
