Dr David Hodgson
No more applications being accepted
Competition Funded PhD Project (European/UK Students Only)
The interval across the Permo-Triassic boundary contains the largest mass extinction in Earth history, with around 90% of marine species becoming extinct. A broader swath of time beginning in the Late Permian is characterised by massive changes in both the carbon cycle and ocean oxygenation, which lasted well beyond the main extinction event and only subsided at the beginning of the middle Triassic. These perturbations are likely to have been set in motion by the eruption of the Siberian Traps large igneous province that occurred during a period of severe global warming, but the exact causal relationships are still the topic of much debate.
The deep-water Karoo Basin of South Africa contains thick, widespread sequences of fine-grained mud and silt. There has been some debate as to the palaeoenvironmental setting of these sediments: they may represent a lacustrine or brackish water body, an inland sea fed by the open ocean, or some intermediate setting where salinity fluctuated between fully marine and brackish. These rocks potentially contain expanded continuous records of changes in biogeochemical cycling across the broad period from the late Permian to the mid-Triassic, providing a prime opportunity for detailed paleoenvironmental reconstruction across this critical juncture in Earth history. However, despite its significance, the Karoo Basin succession has been the focus of very little geochemical research. A major research programme, aimed at exploring the sedimentary architecture of the basin, has produced large amounts of well-preserved core material (>2 km), which is available for this study. In particular, one fully cored well that is 950m long and cost £150k to collect largely comprises claystone and siltstone, which are ideal lithologies for the proposed geochemical techniques.
In a pilot study of a small sample set of core housed in Leeds, the C/S ratios from organic carbon-sulphur analyses suggest that the main Karoo Basin was freshwater close to the Permo-Triassic boundary event. Chemo-stratigraphic ?13C analyses conducted on the same sediments show an average drop of approximately 0.75‰ occurring over 40m, followed by an abrupt drop from -23‰ to almost -28‰.
Aims and Objectives
This aim of this research studentship will be to address fundamental questions about environmental evolution during the late Permian and the Permo-Triassic transition in the deep water Karoo basin:
a) Where is it? The student will analyse samples for organic-carbon stable isotope composition to establish the position of the Permo-Triassic transition. The later Permian to mid-Triassic is characterised by a series of large and easily recognisable carbon isotope fluctuations, which can be used to pinpoint the Permo-Triassic boundary interval.
b) How did salinity fluctuate in the basin? The student will analyse the sediments for their C/S ratio to estimate changes in the salinity of the basin during the mid-to-late Permian, and use the regional core database to investigate the spatial extent of salinity changes.
c) How did the oxygenation of the basin waters vary through time and what were the controls on this? During the Permo-Triassic boundary the oceans are known to have become extremely oxygen-depleted, but the temporal persistence and precise chemical nature of water column anoxia at different localities remains unknown. The student will produce detailed records of water column oxygenation in the Karoo Basin using novel iron speciation and trace metal techniques, some of which were developed by the supervisory team. In addition, P speciation techniques will be applied to evaluate the role of nutrient cycling in the development and persistence of anoxia in the region.
März, C., Poulton, S.W., Beckmann, B., Küster, K., Wagner, T., Kasten, S., 2008, Redox sensitivity of P cycling during marine black shale formation: Dynamics of sulfidic and anoxic, non-sulfidic bottom waters. Geochim. Cosmochim. Acta 72: 3703-3717.
McKay MP; Weislogel AL; Fildani A; Brunt RL; Hodgson DM; Flint SS (2015) U-PB zircon tuff geochronology from the Karoo Basin, South Africa: Implications of zircon recycling on stratigraphic age controls, International Geology Review, 57, pp.393-410.
Newton RJ; Pevitt EL; Wignall PB; Bottrell SH (2004) Large shifts in the isotopic composition of seawater sulphate across the Permo-Triassic boundary in northern Italy, EARTH PLANET SC LETT, 218, pp.331-345.
Poulton SW; Canfield DE (2005) Development of a sequential extraction procedure for iron: Implications for iron partitioning in continentally derived particulates, Chemical Geology, 214, pp.209-221.
Song H; Wignall PB; Chu D; Tong J; Sun Y; Song H; He W; Tian L (2014) Anoxia/high temperature double whammy during the Permian-Triassic marine crisis and its aftermath, Scientific Reports, 4, . doi: 10.1038/srep04132.
Song H; Wignall PB; Tong J; Yin H (2013) Two pulses of extinction during the Permian-Triassic crisis, Nature Geoscience, 6, pp.52-56.
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FTE Category A staff submitted: 79.20
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