26
B. Fractionation Mechanisms of Selected Elements
Sedimentary organic material,~
petroleum, coal
~
'"'I'/////////////"""""""'"""""''''''''~ Marine + non mar i ne
~
organisms
,#
~ ,/Freshwater carbonates
,
~ Marin:/{arbonates
~ "
' [ ] Air C02
~ Carbonatites, diamonds
~~~~~ Extr~t~~~~~tr.ipl 'iri~t.erJPi~,!rryi~79n\~~,.l.u.1pr r0f.k~, ~tS· l,;a
I
I
I
I
I
I
I
I
40
30
20
10
0
-10
-20
-30
b 13C in %.
-40
-so
Fig. 9. !3C/ l2 C ratios of some important carbon compounds (b-variations in %0
relative to PDB)
cracking reactions are extremely important for the isotopic composition
of light hydrocarbons, especially methane.
b) BOTTINGA (1969a) has calculated the fractionation factors for the
isotope-exchange systems involving pairings of calcite, carbon dioxide,
graphite, and methane. Second to the calcite-carbon dioxide system, the
carbon dioxide-methane system is of great geological importance (see
Fig. 8).
c) Other phenomena producing isotope fractionations are diffusion
processes, for instance, during the migration of methane and other light
hydrocarbons. In this connection adsorption-desorption phenomena
may also influence the carbon isotope ratios of methane and related
substances.
In Fig.9, b DC-variations of some important carbon compounds are
schematically demonstrated.
III. Oxygen
Oxygen is the most abundant element on earth. It occurs in gaseous,
liquid, and solid compounds, most of which are thermally stable over
large temperature ranges. These facts make oxygen one of the most
interesting elements in isotope geochemistry. A large amount of literature deals with the naturally occurring variations of oxygen isotopes.
There have been several review papers on this subject: SILVERMAN
B. Fractionation Mechanisms of Selected Elements
Sedimentary organic material,~
petroleum, coal
~
'"'I'/////////////"""""""'"""""''''''''~ Marine + non mar i ne
~
organisms
,#
~ ,/Freshwater carbonates
,
~ Marin:/{arbonates
~ "
' [ ] Air C02
~ Carbonatites, diamonds
~~~~~ Extr~t~~~~~tr.ipl 'iri~t.erJPi~,!rryi~79n\~~,.l.u.1pr r0f.k~, ~tS· l,;a
I
I
I
I
I
I
I
I
40
30
20
10
0
-10
-20
-30
b 13C in %.
-40
-so
Fig. 9. !3C/ l2 C ratios of some important carbon compounds (b-variations in %0
relative to PDB)
cracking reactions are extremely important for the isotopic composition
of light hydrocarbons, especially methane.
b) BOTTINGA (1969a) has calculated the fractionation factors for the
isotope-exchange systems involving pairings of calcite, carbon dioxide,
graphite, and methane. Second to the calcite-carbon dioxide system, the
carbon dioxide-methane system is of great geological importance (see
Fig. 8).
c) Other phenomena producing isotope fractionations are diffusion
processes, for instance, during the migration of methane and other light
hydrocarbons. In this connection adsorption-desorption phenomena
may also influence the carbon isotope ratios of methane and related
substances.
In Fig.9, b DC-variations of some important carbon compounds are
schematically demonstrated.
III. Oxygen
Oxygen is the most abundant element on earth. It occurs in gaseous,
liquid, and solid compounds, most of which are thermally stable over
large temperature ranges. These facts make oxygen one of the most
interesting elements in isotope geochemistry. A large amount of literature deals with the naturally occurring variations of oxygen isotopes.
There have been several review papers on this subject: SILVERMAN