159
age in which bacteria may still be active – should be
stored deep-frozen (-18°C or lower) between sampling
and analysis. Grinding can be done by mortar and pestle
or in an electrical ball or disc mill, but excessive grinding
should be avoided due to the associated rise in
temperature in the sample.
4.5.2
Elemental and Bulk Isotope Analysis
The basic parameter determined in most organic
geochemical studies is the total organic carbon (TOC,
C org ) content. Most marine sediments and sedimentary
rocks contain carbon both as carbonates (C inorg , C carb ,
C min ) and as organic matter. There are numerous
methods for quantifying carbon, most of them are based
on heating solid samples in an oxygen atmosphere and
detection of the evolving CO 2 by coulometric or
spectrometric techniques or by a thermal conductivity
detector. Commonly used instruments are elemental
analyzers, which determine carbon, nitrogen, hydrogen
(only applicable to pure organic matter), and sulfur
(CHN, CNS, CS analyzers). Organic carbon is either
determined directly, after destruction of carbonate with
mineral acids before combustion in the elemental
analyzer, or as the difference between total carbon
(combustion) and mineral carbon (measurement of CO 2
released upon acid treatment).
For the determination of bulk stable carbon
isotope ratios (
13
C/
12
C) the organic matter is converted
to carbon dioxide by oxidation following digestion of
the sediment with mineral acid to remove carbonates.
Traditionally, oxidation of organic matter was performed off-line, CO 2 was separated from other gaseous
oxidation products, and the purified gas introduced
into an isotope ratio mass spectrometer. Modern
instruments provide on-line combustion isotope-ratio
measurement facilities. In this case, an elemental
analyzer is connected to an isotope ratio mass
spectrometer via a special interface that allows
removal of gases other than CO 2 . This configuration
can also be used to separate sulfur and nitrogen
oxides which, after on-line conversion to a suitable
single species (SO 2 and N 2 , respectively), can be used
to determine stable sulfur (
34
S/
32
S) and nitrogen (
15
N/
14
N) isotope ratios. A special technical configuration
of the mass spectrometer is required for hydrogen
isotope (
2
H/
1
H) ratio measurement. Isotope ratios are
not determined directly, but relative to an internationally accepted standard. The results are reported
in the delta notation (δ
13
C, δ
34
S, δ
15
N, δ
2
H [or
commonly δD for deuterium]) relative to this standard.
For details see, e.g., Fogel and Cifuentes (1993) and
references therein.
4.5.3
Rock-Eval Pyrolysis and
Pyrolysis Gas Chromatography
Rock-Eval pyrolysis (Espitalié et al. 1985) is conducted using bulk sediment samples to determine,
(1) the amount of hydrocarbon-type compounds
already present in the sample (S1 peak [mg hydrocarbons per g sediment]; compounds released at
low temperature and roughly equivalent to the
amount of organic matter extractable with organic
solvents), (2) the amount of hydrocarbon-type
compounds generated by pyrolytic degradation of
the macromolecular organic matter during heating
up to 550°C (S2 peak [mg hydrocarbons per g
sediment]), (3) the amount of carbon dioxide
released from the organic matter up to 390°C, i.e.
before carbonates decompose (S3 peak [mg CO 2
per gram sediment]), and (4) the temperature of
maximum pyrolysis yield (Tmax [°C]). The
Hydrogen Index (HI) and Oxygen Index (OI)
derived from the S2 and S3 values correspond to
the pyrolysis yield normalized to the content of
organic carbon (mg hydrocarbons and mg CO 2 per
g TOC, respectively). The results of Rock-Eval
pyrolysis are usually displayed in a van-Krevelentype diagram of HI versus OI values which
roughly corresponds to an H/C versus O/C atomic
ratio van Krevelen diagram (see Fig. 4.11; Tissot
and Welte 1984).
One of the methods of studying the composition
of macromolecular sedimentary organic matter in more
detail is the molecular analysis of pyrolysis products.
For this purpose, the pyrolysis products are transferred
to a gas chromatographic column and analyzed as
described for extractable organic matter in Sect. 4.5.5,
with or without the combination with a mass
spectrometer. Both flash pyrolysis (Curie-point
pyrolysis; samples are heated on a magnetic wire by
electrical induction almost instantaneously, e.g., to
610°C) or off-line pyrolysis at various heating rates
have been applied to geological samples (see Larter
and Horsfield 1993 for an overview of various pyrolysis
techniques).
4.5.4
Organic Petrography
Organic petrography is the study of the
macroscopically and, more importantly, microscopically recognizable organic matter components initially of coal, but meanwhile more generally in sediments and sedimentary rocks. Organicmatter-rich rocks and coal are usually studied as
4.5
Analytical Techniques
age in which bacteria may still be active – should be
stored deep-frozen (-18°C or lower) between sampling
and analysis. Grinding can be done by mortar and pestle
or in an electrical ball or disc mill, but excessive grinding
should be avoided due to the associated rise in
temperature in the sample.
4.5.2
Elemental and Bulk Isotope Analysis
The basic parameter determined in most organic
geochemical studies is the total organic carbon (TOC,
C org ) content. Most marine sediments and sedimentary
rocks contain carbon both as carbonates (C inorg , C carb ,
C min ) and as organic matter. There are numerous
methods for quantifying carbon, most of them are based
on heating solid samples in an oxygen atmosphere and
detection of the evolving CO 2 by coulometric or
spectrometric techniques or by a thermal conductivity
detector. Commonly used instruments are elemental
analyzers, which determine carbon, nitrogen, hydrogen
(only applicable to pure organic matter), and sulfur
(CHN, CNS, CS analyzers). Organic carbon is either
determined directly, after destruction of carbonate with
mineral acids before combustion in the elemental
analyzer, or as the difference between total carbon
(combustion) and mineral carbon (measurement of CO 2
released upon acid treatment).
For the determination of bulk stable carbon
isotope ratios (
13
C/
12
C) the organic matter is converted
to carbon dioxide by oxidation following digestion of
the sediment with mineral acid to remove carbonates.
Traditionally, oxidation of organic matter was performed off-line, CO 2 was separated from other gaseous
oxidation products, and the purified gas introduced
into an isotope ratio mass spectrometer. Modern
instruments provide on-line combustion isotope-ratio
measurement facilities. In this case, an elemental
analyzer is connected to an isotope ratio mass
spectrometer via a special interface that allows
removal of gases other than CO 2 . This configuration
can also be used to separate sulfur and nitrogen
oxides which, after on-line conversion to a suitable
single species (SO 2 and N 2 , respectively), can be used
to determine stable sulfur (
34
S/
32
S) and nitrogen (
15
N/
14
N) isotope ratios. A special technical configuration
of the mass spectrometer is required for hydrogen
isotope (
2
H/
1
H) ratio measurement. Isotope ratios are
not determined directly, but relative to an internationally accepted standard. The results are reported
in the delta notation (δ
13
C, δ
34
S, δ
15
N, δ
2
H [or
commonly δD for deuterium]) relative to this standard.
For details see, e.g., Fogel and Cifuentes (1993) and
references therein.
4.5.3
Rock-Eval Pyrolysis and
Pyrolysis Gas Chromatography
Rock-Eval pyrolysis (Espitalié et al. 1985) is conducted using bulk sediment samples to determine,
(1) the amount of hydrocarbon-type compounds
already present in the sample (S1 peak [mg hydrocarbons per g sediment]; compounds released at
low temperature and roughly equivalent to the
amount of organic matter extractable with organic
solvents), (2) the amount of hydrocarbon-type
compounds generated by pyrolytic degradation of
the macromolecular organic matter during heating
up to 550°C (S2 peak [mg hydrocarbons per g
sediment]), (3) the amount of carbon dioxide
released from the organic matter up to 390°C, i.e.
before carbonates decompose (S3 peak [mg CO 2
per gram sediment]), and (4) the temperature of
maximum pyrolysis yield (Tmax [°C]). The
Hydrogen Index (HI) and Oxygen Index (OI)
derived from the S2 and S3 values correspond to
the pyrolysis yield normalized to the content of
organic carbon (mg hydrocarbons and mg CO 2 per
g TOC, respectively). The results of Rock-Eval
pyrolysis are usually displayed in a van-Krevelentype diagram of HI versus OI values which
roughly corresponds to an H/C versus O/C atomic
ratio van Krevelen diagram (see Fig. 4.11; Tissot
and Welte 1984).
One of the methods of studying the composition
of macromolecular sedimentary organic matter in more
detail is the molecular analysis of pyrolysis products.
For this purpose, the pyrolysis products are transferred
to a gas chromatographic column and analyzed as
described for extractable organic matter in Sect. 4.5.5,
with or without the combination with a mass
spectrometer. Both flash pyrolysis (Curie-point
pyrolysis; samples are heated on a magnetic wire by
electrical induction almost instantaneously, e.g., to
610°C) or off-line pyrolysis at various heating rates
have been applied to geological samples (see Larter
and Horsfield 1993 for an overview of various pyrolysis
techniques).
4.5.4
Organic Petrography
Organic petrography is the study of the
macroscopically and, more importantly, microscopically recognizable organic matter components initially of coal, but meanwhile more generally in sediments and sedimentary rocks. Organicmatter-rich rocks and coal are usually studied as
4.5
Analytical Techniques