| Research in the Organic
Geochemistry Laboratory at UIC follow two
major lines. The first one is the evolution of the carbon cycle through
Earth’s history and is currently centered on the processes of accumulation
of organic carbon in the geosphere. The second is centered on the development
of molecular proxies for microbial biodiversity and evolution for the past
3.5By. Both these lines of research are based on the elucidation of paleoenvironmental
and paleobiological information preserved in buried organic matter, through
structural and isotopic analysis of molecular fossils. Compound specific
isotope analysis (CSIA) permits the measurement of the stable carbon (d13C)
and hydrogen (dD) isotopic composition of isolated
molecules. The isotopic composition of molecular fossils can indicate the
isotopic composition of parent organisms and, in turn, indicate the isotopic
composition of the carbon and hydrogen source used by these organisms.
Because the isotopic composition of the carbon and hydrogen source depends
on environmental factors d13C
and dD values of biomarkers are sensitive paleoenvironmental
and/or paleobiological indicators.
1-Water column structure dynamism
in epeiric seas:
The oceanographic processes at the
origin of accumulation of organic carbon in epeiric seas are not understood.
My interest in that issue arose from the paradox that paleontological and
sedimentological data often indicate aerobic or dysaerobic bottom water
conditions when molecular fossil data indicate anoxia and the presence
of hydrogen sulfide. With the exception of rare unicellular organisms,
Eukaryotes can not co-exist with hydrogen sulfide or survive long periods
of anoxia. Thus, I proposed a model of high frequency change in water column
redox conditions during deposition of organic matter-rich shales. This
model was successfully tested using Jurassic and Cretaceous sediments.
It is currently being tested on Devonian shales of Laurentia. This model
implies that organic matter accumulates under a stratified water mass with
anoxic bottom waters and that most benthic fossils accumulate during interruptions
of water column stratification, with oxygen in bottom waters. In Callovian
sediments, the life mode and life span of benthic fossils can be used as
chronometers of oxygenated bottom water periods (annual to decadal). Determination
of the stratigraphic and geographic extent of these recurrent anoxic bottom
water events permitted to define a theoretical model of oceanographic circulation
in Mesozoic epicontinental sea joining the Tethys to the Boreal sea. This
model which requires a recurrent fresh water lid derived from high latitude
continental masses will be tested through analyses of molecular fossils
and benthic fossil assemblages of high-latitude Mesozoic shales.
2- Lipids as proxies for microbial
diversity in modern “extreme” and ancient environments:
The objective of this research is
to provide a predictive tool for microbial biodiversity and evolution using
the structure, carbon and hydrogen isotopic composition of lipids. In modern
environments, biodiversity in microbial ecosystems is essentially monitored
by genetic methods. However, such methods cannot be used with ancient sediments,
as genetic information is usually not preserved. Because of diversity in
carbon source, in assimilation pathway, and in biosynthetic pathways, microbial
lipids preserved in ancient sediments on Earth, and potentially on other
planetary bodies, record the diversity of microbial processes.
Another aspect of this research
is to test the hypothesis that there is a substantial microbial biosphere
living within the oceanic upper crustal rocks away from mid-ocean ridges
(MOR), hundreds of meters below the water-rock interface. This hypothesis
is tested by detecting specific metabolic products associated with microbial
communities in low flow hydrothermal systems. Preliminary results indicate
that oceanic crustal fluids, away from MOR, are conducive to life.
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