Dinoflagellate cysts and palaeoenvironmental change during Cretaceous oceanic anoxic events: a study of OAE1a

This project will study Cretaceous dinoflagellate cysts. It seeks to understand relationships between dinocysts, a proxy for marine nutrient availability and organic zooplankton fertility, and episodes of black shale (petroleum source rock) deposition during Oceanic Anoxic Events (OAEs) in the mid-Cretaceous. Successions in geographically widely separated areas will be studied to isolate local biogeographic, climatic, preservational, and tectonic influences. While focussing on the mid-Cretaceous OAE1a, it is anticipated that results will have implications for understanding palaeoenvironmental controls on the deposition of organic-rich sediments in Mesozoic, Tertiary and Quaternary sequences.

OAEs are believed to have been driven by an abrupt rise in temperature, induced by rapid influx of CO2 into the atmosphere from volcanogenic and/or methanogenic sources. Global warming was accompanied by an accelerated hydrological cycle, increased continental weathering, enhanced nutrient discharge to oceans and lakes, intensified upwelling, and an increase in organic productivity transmitted to the sedimentary record as black shales. The high organic matter flux led to intense oxygen demand in the water column, and increased rates of carbon burial. Density-driven water stratification was favoured by palaeogeography and by significant fluvial input in restricted oceans and seaways, where conditions evolved from poorly oxygenated to anoxic and even euxinic (sulphidic). Ultimately, sequestration of CO2 in organic-rich black shales and by reaction with carbonate and silicate rocks exposed on the continents restored climatic equilibrium, but only after massive and catastrophic chemical change in the oceans and atmosphere over timescales of tens to hundreds of thousands of years. Could this be the future of the World oceans?

The student will study high-resolution (decimetre) samples across selected OAE1a intervals in sections from subtropical (north Tethyan) to high-latitude (Boreal) sites. Appropriate sections in southern (France, Spain, Italy) and northern Europe (England, Germany, North Sea) will be selected. Sections will be logged and sampled. Samples will be returned to the laboratory where optimised palynological methods (Lignum et al. 2008) will be employed to separate the dinocyst assemblages for analysis. Species identification using light and scanning electron microscopy (SEM) will be used to obtain quantitative data on assemblage compositions. Selected samples will be analysed for oxygen and carbon stable-isotopes and elemental composition to augment literature data on the study intervals. Results will be compared with complementary biotic (macrofossils, calcareous nannofossils, foraminifera, radiolaria) records. Geochemical data will provide stratigraphic (chemostratigraphy and sequence analysis) and palaeoenvironmental (δ18O palaeotemperature, δ13C palaeoproductivity proxies) constraints to aid interpretation of the dinocyst data (cf. Pearce et al. 2009; Olde et al., 2015).

The dinocyst records will provide new information on changing nutrient availability, surface-water temperatures, and water-mass changes accompanying OAEs. Outcomes will include: (1) testing and refinement of existing models of OAE models by characterising varying regional responses to individual OAEs and the similarities and differences between different OAEs; (2) identification of indicator species for the characterisation of different OAEs will assist in the refinement of regional palaeoceanographic models to enable the prediction of occurrences of organic-rich sediments in basins; (3) improved biostratigraphic models for dating and correlating strata will be obtained by studying geographically and stratigraphically dispersed sections. These will provide new information on the first and last occurrences and acmes of dinocyst species that will be tightly constrained by other biostratigraphic (microfossil, macrofossil) and chemostratigraphic (stable-isotope) data.

The student will receive training in field sampling and logging, palynological and geochemical sample preparation and analysis, dinocyst identification and taxonomy, chemostratigraphic methods, interpretation of palaeoenvironmental proxies, research methodologies and data analysis. They will participate in the University’s post-graduate training programme. The project is offered in collaboration with Evolution Applied Ltd, and will be co-supervised by Dr Martin Pearce, Company Director. On successful completion of the PhD, the combination of academic and industrial experience should provide the student with the experience necessary to pursue a career in the petroleum industry, consultancy, teaching or research.