25th International Meeting on Organic Geochemistry IMOG 2011

P-506
Preservation of particulate organic carbon from an active
mountain belt in shallow marine sediments
Robert Sparkes, Niels Hovius, Albert Galy, Vasant Kumar
University of Cambridge, Cambridge, United Kingdom (corresponding author:rbs26@cam.ac.uk)
Particulate Organic Carbon (POC) export from active
mountain belts can be a more effective sink of CO2
than silicate weathering. Foreland basin deposits in
these environments are supplied by large amounts of
sediment, containing a mixture of organic carbon
particles. Woody debris, litter and soil carbon
removed by landsliding from mountain slopes is
mixed with petrogenic carbon sourced from bedrock.
Both forms of carbon can be exported by hyperpycnal
discharge from the fluvial and shallow-marine system,
and have the potential to be stored on a geological
timescale in foreland basins. Storage of fresh POC
and subsequent forest re-growth leads to a sink of
carbon from the hydrosphere-biosphere-atmosphere,
while efficient transport and burial of petrogenic
carbon prevents oxidation of this material and limits
the effects of this possible carbon source.
Using coupled carbon and nitrogen isotope
measurements and Raman Spectroscopy, we have
investigated the Miocene export of POC from the Alps
into the Marnoso Arenacea Formation, exposed in the
present-day Apennines. The Marnoso Arenacea
Formation is a 3500 m thick turbidite sequence in
which individual beds can be correlated over large
areas. This has allowed vertical profiling through
representative turbidite deposits in several places
along their 100 km length. Both petrogenic graphite
and disordered carbonaceous material were found in
the turbidites. Permeability of the lower, sandy units of
turbidites has permitted oxidation of disordered
carbonaceous material. These units tend to have a
relatively low Total Organic Carbon (TOC) content of
around 0.05 % with POC only as graphite, as this is
much more stable than the disordered forms. Muddy
parts of the turbidites contain similar amounts of
graphite, but also preserve disordered material, with
TOC up to 0.8 %.
Combining published volumetric estimates for the
turbidite sequences with our carbon profiles, we
estimate that a turbidites in the Marnoso Arenacea,
with volume 7 km 3 , contains 46 Mt of carbon. This is
~50 % of the annual global CO2 consumption by
silicate weathering.
627