117
3.7
Signals in the Sediment Solid Phase
and is, therefore, compared to molecular
diffusion, not of great importance. However, advection as a model concept in itself
may be quite easily included into computer
models by the employment of the Darcy
Equation 3.30. The advection of the sediment’s solid phase results from the formal
logic that the zero-point of the system of
coordinates is always defined at the sediment surface, and that the sediment particles stream downward relative to the coordination system. This process is of great
importance for balancing the diagenetical
effects in the sediment.
3.7
Signals in the Sediment
Solid Phase
As already described in the introductory
section to this Chapter, the ‘classic geological’
approach to the processes of diagenesis was
distinguished by the examination of the sediment’s solid phase. And whenever a reconstruction of diagenetic processes in previous
sediments - which nowadays consist of rock
and have lost their original pore water content a
long time ago -, is attempted, one will have to
resort to an investigation of the solid phase.
Analyzing the solid phase element profiles is
much more reliable than is the case with pore
water concentration profiles. However, the interpretation of such element profiles proves to be
much more difficult, since the signals of the
entire consecutive diagenetic processes interfere with those of sedimentation. Some of the
element profiles measured in sediments can only
be interpreted on account of the new understanding of diagenetic processes which was
gained, in particular, after many pore water
analyses had been carried out during the last
two decades. The ratios of the sedimentary
contents primarily originating from sedimentation compared to those originating from
diagenetic processes might differ greatly from
each other, depending on the element, the
sedimentation area, and the type of diagenesis.
In such case, it is always advisable to initially
perform an estimative, rough calculation of the
contents measured in the sediment in relation to
the contents potentially altered in the sediment
by the processes of diagenesis.
3.7.1
Analysis of the Sediment’s
Solid Phase
A variety of different analytical approaches lead
to the profiles of sedimentary element contents.
The two essential and most commonly used
methods are nowadays the following:
• Laborious, yet very reliable, is the complete
extraction of the dried, mortared and
homogenized sediment sample using appropriate acids. Usually a microwave pressure extraction in a closed system composed
of PTFE or a similarly inert and resistant
material is applied for this purpose nowadays. With this method, all the sedimentary
constituents are dissolved without exception by applying various mixtures of HF,
HCl and HNO 3 (HCLO 4 can be avoided in
most cases) at temperatures between 250
and 260 °C and a pressure ranging from 30 to
50 bars. In the ultimately received, slight
nitric solution - hydrofluoric acid is left to
evaporate in the course of the procedure -
practically all elements (including the rare
earth elements) can then be analyzed markedly above their limit of detection by atom
absorption spectrometry (AAS), optical
plasma emission spectrometry (ICP-OES)
and/or plasma mass spectrometry (ICP-MS).
• X-ray fluorescence spectroscopy (XRF) is
much easier in its performance but by no
means as reliable particularly in case of low
element contents. Here, the dried, mortared
and homogenized samples can be used
directly as powder, or better in this shape of
pressed tablets, or even better still, as molten
tablets. With this method, good detection
limits are obtained for most of the quantitatively relevant elements, the access to trace
metals, however, is not feasible to the same
extent as in complete extraction and subsequent analysis of the extract solution.
The following comparison illustrates the
greatly differing time and work effort associated
with these two methods:
In order to analyze the quantitative element
profiles, consisting of approximately 250 samples
derived from one single core which was extracted
with the gravity corer, several weeks are required
for drying, mortaring, homogenization, weighing,
3.7
Signals in the Sediment Solid Phase
and is, therefore, compared to molecular
diffusion, not of great importance. However, advection as a model concept in itself
may be quite easily included into computer
models by the employment of the Darcy
Equation 3.30. The advection of the sediment’s solid phase results from the formal
logic that the zero-point of the system of
coordinates is always defined at the sediment surface, and that the sediment particles stream downward relative to the coordination system. This process is of great
importance for balancing the diagenetical
effects in the sediment.
3.7
Signals in the Sediment
Solid Phase
As already described in the introductory
section to this Chapter, the ‘classic geological’
approach to the processes of diagenesis was
distinguished by the examination of the sediment’s solid phase. And whenever a reconstruction of diagenetic processes in previous
sediments - which nowadays consist of rock
and have lost their original pore water content a
long time ago -, is attempted, one will have to
resort to an investigation of the solid phase.
Analyzing the solid phase element profiles is
much more reliable than is the case with pore
water concentration profiles. However, the interpretation of such element profiles proves to be
much more difficult, since the signals of the
entire consecutive diagenetic processes interfere with those of sedimentation. Some of the
element profiles measured in sediments can only
be interpreted on account of the new understanding of diagenetic processes which was
gained, in particular, after many pore water
analyses had been carried out during the last
two decades. The ratios of the sedimentary
contents primarily originating from sedimentation compared to those originating from
diagenetic processes might differ greatly from
each other, depending on the element, the
sedimentation area, and the type of diagenesis.
In such case, it is always advisable to initially
perform an estimative, rough calculation of the
contents measured in the sediment in relation to
the contents potentially altered in the sediment
by the processes of diagenesis.
3.7.1
Analysis of the Sediment’s
Solid Phase
A variety of different analytical approaches lead
to the profiles of sedimentary element contents.
The two essential and most commonly used
methods are nowadays the following:
• Laborious, yet very reliable, is the complete
extraction of the dried, mortared and
homogenized sediment sample using appropriate acids. Usually a microwave pressure extraction in a closed system composed
of PTFE or a similarly inert and resistant
material is applied for this purpose nowadays. With this method, all the sedimentary
constituents are dissolved without exception by applying various mixtures of HF,
HCl and HNO 3 (HCLO 4 can be avoided in
most cases) at temperatures between 250
and 260 °C and a pressure ranging from 30 to
50 bars. In the ultimately received, slight
nitric solution - hydrofluoric acid is left to
evaporate in the course of the procedure -
practically all elements (including the rare
earth elements) can then be analyzed markedly above their limit of detection by atom
absorption spectrometry (AAS), optical
plasma emission spectrometry (ICP-OES)
and/or plasma mass spectrometry (ICP-MS).
• X-ray fluorescence spectroscopy (XRF) is
much easier in its performance but by no
means as reliable particularly in case of low
element contents. Here, the dried, mortared
and homogenized samples can be used
directly as powder, or better in this shape of
pressed tablets, or even better still, as molten
tablets. With this method, good detection
limits are obtained for most of the quantitatively relevant elements, the access to trace
metals, however, is not feasible to the same
extent as in complete extraction and subsequent analysis of the extract solution.
The following comparison illustrates the
greatly differing time and work effort associated
with these two methods:
In order to analyze the quantitative element
profiles, consisting of approximately 250 samples
derived from one single core which was extracted
with the gravity corer, several weeks are required
for drying, mortaring, homogenization, weighing,