Tracking the formation of iron-rich coated grains from the
Precambrian through the Phanerozoic: evolving oceans and
sedimentary environments.
Supervisors: Prof Kevin G. Taylor (Manchester), Prof Jim Marshall (Liverpool), Prof Peir Pufahl
(Univ. Acadia, Canada).
Contact: [email protected]
Introduction: Sedimentary ironstones are highly unusual deposits which offer a glimpse into
chemical and physical processes operating in ancient oceans. They commonly contain coated
grains (ooids, pisoids) that formed under unique sedimentary conditions and possess a
mineralogical composition (either iron oxides - goethite and haematite, or iron silicates
berthierine, chamosite and glaucony plus the iron carbonate siderite) that result from
biochemical processes operating near the sediment-water surface. The main aim of the project
will be to test the hypothesis that two contrasting biochemical pathways can take place within
ironstones; one leading to haematite composition and another leading to iron-rich clay
compositions. Furthermore, the prevalence of each pathway changed through geological time
due to changes in ocean chemistry, biological processes and organic matter reactivity.
Figure 1. (A and B). Oolitic ironstones containing coated grains from the Cambro-Ordovician of
Newfoundland and the Jurassic of the UK. (C) Thin section showing the characteristic iron-mineral
composition of ironstones (berthierine – B – and siderite)..
Fieldwork and sampling will be undertaken in Canada and the UK, and will integrate
mineralogical, geochemical and isotopic techniques to address this aim. There has been a
recent explosive growth in the understanding of ocean and sediment system evolution through
deep Earth time and this project will add a valuable insight into this evolution for ironstone
systems that have largely been ignored for 3 decades, yet that offer potentially unique insights.
Project Summary: Field observations will be used to interpret the sedimentary environment for
ironstones from a range of ironstones from the Precambrian to the Jurassic. Ironstones from
the Precambrian of NE Canada, the Cambro-Ordovician of Newfoundland and Novia Scotia, the
Ordovician of Wales, and the Jurassic of the UK will be studied and sampled. A range of
petrological, mineralogical and microanalytical techniques will used by the student, as well as
stable carbon and oxygen isotope analysis of carbonate cement phases. These analyses will be
used to characterise the nature and mineralogy of coated grains within these rocks, interpret the
diagenetic history of the ironstones; and generate models linking sedimentological and
biochemical evolution.
Work plan: Year 1: Literature review; sample preparation/characterisation of initial sample set
(petrographic, mineralogical, SEM and electron probe work); data evaluation and discussion;
first phase of fieldwork and sampling in UK and Canada. Year 2: Analysis of field samples,
Phase 2 of field work and sampling; sample preparation/characterisation of second sample set;
write first paper. Year 3: Analysis and data evaluation; present work at international conference;
write papers; thesis.
The student will join a vibrant research group at the University of Manchester, and will receive
training in a range of analytical techniques including x-ray fluorescence, electron microprobe,
secondary scanning electron microscopy. X-ray diffraction, stable isotope analysis. In addition
to specialist scientific training, the student will also receive training in generic transferrable and
professional skills. This PhD will provide experience and skills that will be ideal for either
pursuing a career in academia or in the oil and gas industry. The project spans the fields of
sedimentology, petrology, and geochemistry, and is suitable for a student with a background in
geology/geoscience. Previous laboratory and/or analytical experience is an asset but not
essential as full training will be given.
References and further reading:
Pufahl, P.K., Anderson, S.L., Hiatt, E.E., and Pirajno, F., 2014. Dynamic sedimentation of
Paleoproterozoic continental margin iron formation, Labrador Trough, Canada: paleoenvironments and
sequence stratigraphy. Sedimentary Geology, v. 309, 48-65.
Pufahl, P.K. and Hiatt, E.E., 2012. Oxygenation of the Earth’s ocean-atmosphere system: a review of
physical and chemical sedimentological responses. Marine and Petroleum Geology, v. 32, 1-20.
Taylor, K.G., Simo, A, Yocum, D. & Leckie, D. (2002) Stratigraphic significance of ooidal ironstones from
the Cretaceous Western Interior Seaway: the Peace River Formation, Alberta and the Castlegate
Sandstone, Utah Journal of Sedimentary Research, 72, 345-356.
Taylor, K.G. and Macquaker, JHS (2011). Iron in marine sediments: minerals as records of chemical
environments. Elements, 7, 83-88.
Taylor, K.G. & Curtis, C.D. (1995). The stability and facies association of early diagenetic mineral
assemblages: an example from a Jurassic ironstone - mudstone succession, U.K. Journal of
Sedimentary Research, A65, 358-36.