10.3 Organic Matter Production
10.2.8 Summary (Sedimentation Rates)
- In fluvial and shallow aquatic systems, the potential sedimentation rates of terrigenous and
biogenic materials are often greater than the actual rates which are controlled by subsidence
and base-level change. Surplus sediment is bypassed downstream or into deeper water.
- In areas of sufficient accommodation space (e.g.
on prodelta slopes and in deeper basins), the
sedimentation rates of siliciclastics can be very
high (up to 100-1000 cm/ka), whereas biogenic
sedimentation rates of pelagic carbonates and
biosiliceous deposits are low in these areas
(mostly 0.1-2 cmlka).
10.3 Production of Organic Matter in
Various Environments
10.3.1 Introduction
This section summarizes the most important facts
about the production and preservation of organic
matter in various depositional environments. The
transformation of organic matter under increasing
sediment load and temperature is described in Section 14.2.
There is a large body of publications dealing with this
topic. This overview is largely based on articles and special
volumes by Durand (1980), Grant Gross (1980),
Romankevich (1984), Tissot and Weite (1984), Brooks and
Fleet (1987), Berger et al. (1989); Berger (1991), Stein
(1991), Hedges and Keil (1995), Tyson (1995), Schlünz
(1998). Some further references related to specific problems are mentioned in the following text.
All life on earth is based on photosynthesis, which
began two to three billion years ago (Sect. 6.5). In
this process carbon dioxide combines with water to
form carbohydrates, at the same time releasing oxygen. The energy necessary for this synthesis is provided by the sun via light-absorbing pigments such as
chlorophyll. This basic process can be accomplished
by all autotrophic organisms, including primitive
bacteria and blue-green algae, as weIl as by highly
evolved plants. All of these organisms are the primary producers of the organic matter, whereas
heterotrophic organisms (animals) feed on this organic matter.
Carbohydrates contain stored energy which can be
released when oxygen is taken up by animals and
plants which thereby gain energy for their li fe proces ses (called "respiration"). Through respiration, the
gross productivity of plants, which is defined as the
mass of carbon fixed by photosynthesis per unit area
463
- Mixed siliciclastic and biogenic sediments tend
to produce higher rates than purely biogenic
material.
- Extremely high rates (up to several m/ka) can
be attained by weIl soluble evaporites (e.g. halite).
- Linear sedimentation rates should be given for
pore-free material or converted to accumulation
rates.
- The siliciclastic sedimentation rates of certain
basins are closely linked to the mechanical denudation rates in their source areas.
and time, is reduced by 10 to 50%. The remaining
mass is the primary net production, which is discussed further below. Part of the energy gained by
respiration is used to build up other organic compounds, such as proteins, lipids, lignin and tannin. Of
these, the carbohydrates (including cellulose), which
consist of carbon, oxygen, and hydrogen, are the
most important organic matter constituent of plants,
whereas animals (e.g., oceanic zooplankton or
zoobenthos ) and bacteria contain particularly high
proportions of proteins. Some of the organic compounds incorporate small amounts of nitrogen, sulfur, and other elements. In the following discussion
all of these organic compounds, including the products of biological activity such as excretions and secretions, :ue included in the term organic matter.
The overall terrestrial biosphere productivity appears to be six times higher than that of the marine
biosphere. However, if the consumption of primary
production by heterotrophic organisms and the preservation of organic matter in sediments are considered, the situation on land is completely different
from that in aquatic environments. Under aerobic
conditions in soils, only the most resistant organic
compounds, such as chitine or the cuticles of pollen
and spores (sporopollenine), can be preserved over
long time periods. Therefore, little organic matter is
preserved in continental deposits with the exception
of coal-forming environments and lakes (Sects. 2.2.3
and 3.4.3).
In aquatic environments, such as lakes, swamps,
and marine basins, in particular in coastal areas and
anoxic basins, decomposition of organic matter is
slower. Aerobic organisms may cease to destruct organic matter if the oxygen supply of the water body
is used up and cannot be replaced rapidly enough.
Thus, most of the organic matter preserved from earlier geologic times occurs in marine and lake sediments. Here, the preservation of organic matter in the
marine realm is dealt with in some detail (Sect. 10.5).
10.2.8 Summary (Sedimentation Rates)
- In fluvial and shallow aquatic systems, the potential sedimentation rates of terrigenous and
biogenic materials are often greater than the actual rates which are controlled by subsidence
and base-level change. Surplus sediment is bypassed downstream or into deeper water.
- In areas of sufficient accommodation space (e.g.
on prodelta slopes and in deeper basins), the
sedimentation rates of siliciclastics can be very
high (up to 100-1000 cm/ka), whereas biogenic
sedimentation rates of pelagic carbonates and
biosiliceous deposits are low in these areas
(mostly 0.1-2 cmlka).
10.3 Production of Organic Matter in
Various Environments
10.3.1 Introduction
This section summarizes the most important facts
about the production and preservation of organic
matter in various depositional environments. The
transformation of organic matter under increasing
sediment load and temperature is described in Section 14.2.
There is a large body of publications dealing with this
topic. This overview is largely based on articles and special
volumes by Durand (1980), Grant Gross (1980),
Romankevich (1984), Tissot and Weite (1984), Brooks and
Fleet (1987), Berger et al. (1989); Berger (1991), Stein
(1991), Hedges and Keil (1995), Tyson (1995), Schlünz
(1998). Some further references related to specific problems are mentioned in the following text.
All life on earth is based on photosynthesis, which
began two to three billion years ago (Sect. 6.5). In
this process carbon dioxide combines with water to
form carbohydrates, at the same time releasing oxygen. The energy necessary for this synthesis is provided by the sun via light-absorbing pigments such as
chlorophyll. This basic process can be accomplished
by all autotrophic organisms, including primitive
bacteria and blue-green algae, as weIl as by highly
evolved plants. All of these organisms are the primary producers of the organic matter, whereas
heterotrophic organisms (animals) feed on this organic matter.
Carbohydrates contain stored energy which can be
released when oxygen is taken up by animals and
plants which thereby gain energy for their li fe proces ses (called "respiration"). Through respiration, the
gross productivity of plants, which is defined as the
mass of carbon fixed by photosynthesis per unit area
463
- Mixed siliciclastic and biogenic sediments tend
to produce higher rates than purely biogenic
material.
- Extremely high rates (up to several m/ka) can
be attained by weIl soluble evaporites (e.g. halite).
- Linear sedimentation rates should be given for
pore-free material or converted to accumulation
rates.
- The siliciclastic sedimentation rates of certain
basins are closely linked to the mechanical denudation rates in their source areas.
and time, is reduced by 10 to 50%. The remaining
mass is the primary net production, which is discussed further below. Part of the energy gained by
respiration is used to build up other organic compounds, such as proteins, lipids, lignin and tannin. Of
these, the carbohydrates (including cellulose), which
consist of carbon, oxygen, and hydrogen, are the
most important organic matter constituent of plants,
whereas animals (e.g., oceanic zooplankton or
zoobenthos ) and bacteria contain particularly high
proportions of proteins. Some of the organic compounds incorporate small amounts of nitrogen, sulfur, and other elements. In the following discussion
all of these organic compounds, including the products of biological activity such as excretions and secretions, :ue included in the term organic matter.
The overall terrestrial biosphere productivity appears to be six times higher than that of the marine
biosphere. However, if the consumption of primary
production by heterotrophic organisms and the preservation of organic matter in sediments are considered, the situation on land is completely different
from that in aquatic environments. Under aerobic
conditions in soils, only the most resistant organic
compounds, such as chitine or the cuticles of pollen
and spores (sporopollenine), can be preserved over
long time periods. Therefore, little organic matter is
preserved in continental deposits with the exception
of coal-forming environments and lakes (Sects. 2.2.3
and 3.4.3).
In aquatic environments, such as lakes, swamps,
and marine basins, in particular in coastal areas and
anoxic basins, decomposition of organic matter is
slower. Aerobic organisms may cease to destruct organic matter if the oxygen supply of the water body
is used up and cannot be replaced rapidly enough.
Thus, most of the organic matter preserved from earlier geologic times occurs in marine and lake sediments. Here, the preservation of organic matter in the
marine realm is dealt with in some detail (Sect. 10.5).