28
B. Fractionation Mechanisms of Selected Elements
Table 7. Isotopic fractionation factor of various carbonates. (After SHARMA and
CLAYTON, 1965, in GARLICK, 1969)
Mineral
Rhodochrosite
Calcite
Aragonite
Dolomite (ordered)
rJ.
1.0 lO 12
1.0lO25
1.0lO34
1.01109
10.07
10.20
lO.29
11.03
Water is usually analyzed by equilibration of a small amount of CO2 with a
surplus of water. The equilibrium fractionation factor between CO 2 and H 2 0 has
been determined to be 1.0407 at 25° C (COMPSTON and EpSTEIN, 1958; O'NEIL and
EPSTEIN, 1966a). It is not necessary to know the oxygen isotopic composition of
the CO2 before equilibration with the surplus water, since the amount of oxygen
in the CO 2 may be neglected.
2. Standards
The standard now used world-wide is Standard Mean Ocean Water
(SMOW). The original standard, at least for the paleotemperature determinations, was the CO2 liberated by H3P04 from POB, a Cretaceous
belemnite from the Pedee formation, which has been exhausted. The
total carbonate of POB has a b l8 0-value of + 30.4%0 on the SMOW
scale. (Note that the liberated CO2 has an isotopic composition of
+40.9%0. Note also that due to the different fractionation factors associated with the acid liberation of CO2 :
(b I8 0(dolomile)-b I8 0(calcile) SMOW) * (b I8 0(dOlomile)-b I8 0(CaICile)) POB) .
f% Meteoric water!l ~
D Ocean water
~ Sedimentary rocks
~ Metamorphic rocks
~ Granitic rocks
~ Basaltic rocks
~ Extraterrestrial materials
~ (meteorites and lunar rocks)
I
I
I
I
I
I
I
I
I
I
I
I
40 30 20 10
0 -10 -20 -30 -40 -SO -60 -70
b 18 0 in"loe
Fig.lO. 18 0/ 6 0 ratios of some important oxygen-containing compounds (c5-variations in %. relative to SMOW)
B. Fractionation Mechanisms of Selected Elements
Table 7. Isotopic fractionation factor of various carbonates. (After SHARMA and
CLAYTON, 1965, in GARLICK, 1969)
Mineral
Rhodochrosite
Calcite
Aragonite
Dolomite (ordered)
rJ.
1.0 lO 12
1.0lO25
1.0lO34
1.01109
10.07
10.20
lO.29
11.03
Water is usually analyzed by equilibration of a small amount of CO2 with a
surplus of water. The equilibrium fractionation factor between CO 2 and H 2 0 has
been determined to be 1.0407 at 25° C (COMPSTON and EpSTEIN, 1958; O'NEIL and
EPSTEIN, 1966a). It is not necessary to know the oxygen isotopic composition of
the CO2 before equilibration with the surplus water, since the amount of oxygen
in the CO 2 may be neglected.
2. Standards
The standard now used world-wide is Standard Mean Ocean Water
(SMOW). The original standard, at least for the paleotemperature determinations, was the CO2 liberated by H3P04 from POB, a Cretaceous
belemnite from the Pedee formation, which has been exhausted. The
total carbonate of POB has a b l8 0-value of + 30.4%0 on the SMOW
scale. (Note that the liberated CO2 has an isotopic composition of
+40.9%0. Note also that due to the different fractionation factors associated with the acid liberation of CO2 :
(b I8 0(dolomile)-b I8 0(calcile) SMOW) * (b I8 0(dOlomile)-b I8 0(CaICile)) POB) .
f% Meteoric water!l ~
D Ocean water
~ Sedimentary rocks
~ Metamorphic rocks
~ Granitic rocks
~ Basaltic rocks
~ Extraterrestrial materials
~ (meteorites and lunar rocks)
I
I
I
I
I
I
I
I
I
I
I
I
40 30 20 10
0 -10 -20 -30 -40 -SO -60 -70
b 18 0 in"loe
Fig.lO. 18 0/ 6 0 ratios of some important oxygen-containing compounds (c5-variations in %. relative to SMOW)