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SUMMARY:Impacts of Depositional Environments on δ34S Records: Rethinking 
 Stratigraphic Trends and Geobiological Interpretations - Professor David F
 ike\, Washington University in St Louis
DTSTART:20161101T120000Z
DTEND:20161101T130000Z
UID:TALK67273@talks.cam.ac.uk
CONTACT:Alexandra Turchyn
DESCRIPTION:Stable isotopic data (e.g.\, 13C or 34S) provide a framework f
 or understanding microbial ecology today and for reconstructing both globa
 l redox budgets and microbial metabolic activity over Earth history. Howev
 er\, reports of coeval but divergent isotopic data in the stratigraphic re
 cord are becoming increasingly common\, which calls into question how thes
 e proxies are most commonly interpreted (i.e.\, as reflecting seawater che
 mistry).  Sulfur isotope records in particular are characterized not just 
 by disparate 34S values\, but also by differences in the spatial signature
  and magnitude of isotopic variability. Such discordant data suggest that 
 we do not fully understand how isotopic signatures are generated or subseq
 uently incorporated into and eventually preserved in the rock record. Here
  we examine the spatial signature and magnitude of isotopic variability in
  modern marine systems as a function of differential microbial metabolic a
 ctivity and the surrounding depositional environment. Varying depositional
  conditions\, particularly sedimentary reworking\, sedimentation rate\, an
 d organic loading\, are seen to play a major role in generating and modify
 ing the isotopic signatures of sulfur phases in modern environments.  Thes
 e observations can be extrapolated to investigate records of sulfur cyclin
 g preserved in marine sediment cores and in ancient strata.  The results s
 uggest that many apparent secular 34S trends may be related to changing de
 positional environment rather than changes in the global sulfur cycle.  Fu
 rther\, this environmental dependence can also help explain coeval but dis
 cordant 34S data from within and between sedimentary basins.  Together\, t
 hese observations enable us to refine our interpretations of 34S data that
  have the potential both to improve our understanding of modern deposition
 al processes and to better constrain the behavior of the sulfur biogeochem
 ical cycle over geological timescales.\n
LOCATION:Tilley Lecture Theatre\, Department of Earth Sciences
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