From fieldwork to lab work: Understanding the origin of
lacustrine dolomite in saline lakes of Canada
Dr. Veerle Vandeginste & Dr. Cédric John
INTRODUCTION
Dolomite is a common carbonate mineral, but its formation is still poorly understood. The two main
aspects of the “dolomite problem” are (i) that dolomite is much more abundant in ancient rocks than in
Holocene environments and that (ii) none of the laboratory experiments succeeded in growing
dolomite inorganically at near-surface conditions of 20-30ºC and 1 atm pressure (Machel, 2004).
Lacustrine dolomite has been reported to be abundant in multiple saline or hypersaline lakes (Last,
1990), but this phenomenon is still very sparsely studied. Current lacustrine environments thus provide
excellent opportunities to study the precipitation of dolomite at low temperature, where recent dolomite
formation can be assessed and both the dolomitizing fluid and resulting mineral can be sampled and
examined. Besides the scientific value of the project, lacustrine carbonates are also important for their
associated resources, since these rocks can be both source and reservoir rocks of petroleum and they
may host coal and oil shales or contain industrial minerals (Herrero and Escavy, 2010). A better
knowledge on how dolomite forms in these lacustrine settings will thus also have an economic impact
as it will help predictions on ancient lacustrine environments.
View on the Manitou Lake, Saskatchewan, Canada, where also dolomite was reported. Source:
Wikipedia
KEY OBJECTIVES
The purpose of this research project is to gain insight in the formation process of dolomite in lacustrine
environments. The project aims at evaluating which factors control the formation of dolomite in these
low temperature environments and how important microbial mediation is in this process, and by
extension what controls dolomite crystallinity and its chemical composition. An important parameter
will be to understand the sedimentology and hydrography of the selected lakes. Finally, another goal is
to relate dolomite characteristics to the chemical signature of the lake water and the biological activity
in the lakes as well as the location (depth, temperature, etc) within the lakes where dolomite is formed
and how this relates to potential seasonal variability in the lake water and biologic activity.
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METHODS
Lake water, sediments (box coring) and microbialites from a series of lakes will be sampled, including
the Redberry, Patience and Muskiki Lakes in Saskatchewan. Both Patience and Muskiki Lakes are
hypersaline lakes with a maximum depth of 1 to 2 m; these lakes contain salt crystals and the dominant
cation is Na+. In contrast, Redberry Lake is a large mesosaline lake with a maximum lake depth of 17
m; the lake is particular because Mg2+ is the dominant cation (Bowman and Sachs, 2008). In the lab,
the sediments will be described in the split cores, sieved and separated into different grain sizes.
Mineralogy will be determined by X-ray diffraction measurements and the sediments will be studied
using microscopy (including scanning electron microscopy). The lake waters and sediments will be
geochemically (major and minor elements) analysed. Separated dolomite minerals will be used for
stable carbon and oxygen isotope analysis. In addition, clumped isotope analysis will be performed on
the dolomite to assess the temperature at which it was formed, which might be useful to test whether
seasonality plays a role in dolomite precipitation. There is also scope for a microbiological analysis of
the lake waters and potential lab precipitation experiments.
OUTCOMES
A better characterization of lacustrine dolomite and the lacustrine environment in which the dolomite
precipitates or replaces calcite or aragonite will help to better understand the dolomite formation
process at low temperature. The study will bring more insight in both the importance and the
mechanism of sulphate reducing bacteria, cyanobacteria and microbial mats interacting with the
inorganic components to form authigenic minerals.
STUDENT PROFILE
We are looking for a highly motivated, hard-working Geology graduate with a strong interest in
geochemistry, sedimentology and geobiology who wishes to carry out a fundamental PhD in carbonate
geology/geochemistry. Excellence in geochemistry and sedimentary geology is essential; experience
with microscopy and analytical techniques is a must.
TRAINING
The successful candidate will join the Carbonate Research Group at the Royal School of Mines of
Imperial College London. The research Group has brand new labs with polarization and cold
cathodoluminescence facilities, in addition to the stable isotope lab, where conventional carbon and
oxygen isotopes can be measured and where the cutting edge technique of clumped isotopes is
established. The wet geochemistry lab is shared with other research groups at Imperial College and
several facilities, such as X-ray diffraction, scanning electron microscopy and elemental analysis using
ICP-AES are available at the Natural History Museum.
In addition to training of analytical skills, the student will also present his/her research during multiple
presentations, both at Imperial College and national and international conferences. The postgraduate
program at Imperial College also offers a wide range of opportunities to attend workshops, courses and
develop skills.
FURTHER INFORMATION
If you are interested in this project and would like to have further details please contact Veerle
Vandeginste at v.vandeginste@imperial.ac.uk or Cédric John at cedric.john@imperial.ac.uk.
www.carbonateresearch.com/vvandeginste
www.carbonateresearch.com/cjohn
REFERENCES
Bowman, J.S., Sachs, J.P., 2008. Chemical and physical properties of some saline lakes in Alberta and
Saskatchewan. Saline Systems, 4:3 doi:10.1186/1746-1448-4-3
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Herrero, M.J., Escavy, J.I., 2010. Chapter 6. Economic aspects of continental carbonates and
carbonates transformed under continental conditions. In: Alonson-Zarza, A.M., Tanner, L.H. (eds)
Carbonates in continental settings: Geochemistry, diagenesis and applications. Developments in
Sedimentology, 62, 275-296.
Last, W.M., 1990. Lacustrine dolomite – an overview of modern, Holocene, and Pleistocene
occurrences. Earth-Science Reviews, 27, 221-263.
Machel, H.G., 2004. Concepts and models of dolomitization: a critical reappraisal. In: Braithwaite,
C.J.R., Rizzi, G. Darke, G. (eds) The geometry and petrogenesis of dolomite hydrocarbon reservoirs.
Geological Society, London, Special Publications, 235, 7-63.