10.5 Organic Matter Preservation in Marine Sediments
479
10.5.7 Summary (Production and Preservation of Organic Matter)
- Presently, <0.5% (mean value) of the primary
marine production of organic matter is exported
to the sea floor and preserved in marine sediments. Land-derived organic carbon (oC) significantly contributes to marine oe burial.
- High oe preservation factors can be expected in
fine-grained deltaic and shaHow-water sediments, in particular in front of tropical river deltas, below zones of high fertility (nutrient supply) and oxygen minimum zones. oe preservation in shaHow waters can be high even under
oxic conditions, if productivity is sufficiently
developed.
- In deep waters, most of the new production escaping the productive surface waters is
remineralized. The benthic degradation loss by
epifauna and infauna on the sea floor is reduced
by high inorganic accumulation rates, but considerable amounts of oe may also be consumed
by aerobic and anaerobic bacteria (dissolution
of carbonate, sulfate reduction). High accumulation rates of oe in deep water only occur if
productivity is high and the water anoxic.
- Thus, high oe concentrations in sediments do
not always reflect high primary productivity,
and low oe values can also occur in basins of
high primary productivity when they are weH
oxygenated and have low sedimentation rates.
- According to these roles, black shales (commonly Oe=1-4%) can form in a variety of
depositional environments.
- In the geological past, the environmental conditions for the production and preservation of
organic matter often were quite different from
the present situation and repeatedly changed at
different time scales.
479
10.5.7 Summary (Production and Preservation of Organic Matter)
- Presently, <0.5% (mean value) of the primary
marine production of organic matter is exported
to the sea floor and preserved in marine sediments. Land-derived organic carbon (oC) significantly contributes to marine oe burial.
- High oe preservation factors can be expected in
fine-grained deltaic and shaHow-water sediments, in particular in front of tropical river deltas, below zones of high fertility (nutrient supply) and oxygen minimum zones. oe preservation in shaHow waters can be high even under
oxic conditions, if productivity is sufficiently
developed.
- In deep waters, most of the new production escaping the productive surface waters is
remineralized. The benthic degradation loss by
epifauna and infauna on the sea floor is reduced
by high inorganic accumulation rates, but considerable amounts of oe may also be consumed
by aerobic and anaerobic bacteria (dissolution
of carbonate, sulfate reduction). High accumulation rates of oe in deep water only occur if
productivity is high and the water anoxic.
- Thus, high oe concentrations in sediments do
not always reflect high primary productivity,
and low oe values can also occur in basins of
high primary productivity when they are weH
oxygenated and have low sedimentation rates.
- According to these roles, black shales (commonly Oe=1-4%) can form in a variety of
depositional environments.
- In the geological past, the environmental conditions for the production and preservation of
organic matter often were quite different from
the present situation and repeatedly changed at
different time scales.