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SUMMARY:The cycle of petrogenic organic carbon during orogeny: from metamo
 rphism to erosion - Olivier Beyssac\, CNRS\, Institut de Minéralogie et d
 e Physique des Milieux Condensés\, Paris\, France
DTSTART:20091201T170000Z
DTEND:20091201T180000Z
UID:TALK19436@talks.cam.ac.uk
CONTACT:Alex Piotrowski
DESCRIPTION:Organic C (OC) exported by rivers is a mix of biospheric OC an
 d petrogenic OC derived from erosion of rocks (e.g. Galy et al. 2007\, Hil
 ton et al. 2008). Burial of petrogenic OC is a simple recycling of reduced
  C and has no effect on atmospheric CO2 and O2 levels. Conversely\, its ox
 idation consumes O2 from and returns CO2 to the atmosphere. Addressing the
  role of continental erosion on the global C cycle thus requires assessing
  the fate of petrogenic OC during erosion. A structural characterization o
 f petrogenic OC contained in source rocks\, river and marine sediments fro
 m the Himalaya and Amazon erosionnal systems has been performed using Rama
 n Microspectrometry and High-Resolution Transmitted Electron Microscopy. D
 ating of bulk OC by radiocarbon allows for quantifying the proportion of p
 etrogenic and recent OC in river sediments. Altogether\, it is shown that 
 30 to 50% of the OC contained in the Himalayan rocks appears to be preserv
 ed and recycled in the Bengal fan during the erosion cycle (Galy et al. 20
 08)\, whereas only ~10% of the petrogenic OC is preserved between Andean r
 ivers and the Amazon floodplain (Bouchez et al.\, accepted). Structural in
 vestigations reveal that graphitic phases are the most resistant to oxidat
 ion. The thermal factory during orogeny thus plays a key role by transform
 ing sedimentary OC into graphite (e.g. Beyssac et al. 2002a\, 2002b) and s
 ubtracts C from the external cycle (atmosphere-biosphere-ocean) and locks 
 it into the geological cycle (crust-mantle). At geological timescales\, gr
 aphitization thus maintains an imbalance between photosynthesis and respir
 ation by locking reduced C into the crust.\n\nSome related papers (+ refer
 ences therein!):\n\nBeyssac O.\, Goffé B.\, Chopin\, C. and Rouzaud J.N. 
 (2002a) Raman spectra of carbonaceous material from metasediments: a new g
 eothermometer. Journal of Metamorphic Geology\, 20\, 859-871.\n\nBeyssac O
 .\, Rouzaud J.N.\, Goffé B.\, Brunet F. and Chopin C. (2002b) Graphitizat
 ion in high-pressure\, low-temperature metamorphic gradient: a HRTEM and R
 aman microspectroscopy study. Contributions to Mineralogy and Petrology\, 
 143\, 19-31.\n\nBouchez J.\, Beyssac O.\, Galy V.\, Gaillardet J. & France
 -Lanord C. Oxidation of fossil organic carbon in the Amazon floodplain as 
 a source of atmospheric CO2. Geology\, accepted pending minor revisions. [
 PDF available on request]\n\nGaly V.\, Beyssac O.\, France-Lanord C. & Egl
 inton T. (2008) Selective recycling of graphite during Himalayan erosion: 
 a geological stabilisation of C in the crust. Science\, 322\, 943-945.\n\n
 Galy V.\, France-Lanord C.\, Beyssac O.\, Kudrass H.\, Faure P. & Pailhol 
 F.\, (2007) Efficient organic carbon burial in the Bengal Fan sustained by
  the Himalayan erosional system. Nature\, 450\, 407-410.\n\nHilton RG.\, G
 aly A.\, Hovius N.\, Chen MC.\, Horng J. & Chen H. (2008) Tropical-cyclone
 -driven erosion of the terrestrial biosphere from mountains. Nature Geosci
 ences\, doi 10.1038/ngeo333.\n
LOCATION:Tilley Lecture Theater\, Department of Earth Sciences
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