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Correlation between the δ34S of pyritic and organic sulfur in coal and oil shale
Chemical Geology (Isotope Geoscience Section), 58 (1986) 333-337 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
333
CORRELATION BETWEEN THE d34S OF PYRITIC AND ORGANIC SULFUR IN COAL AND OIL SHALE FRED T. PRICE and Y.N. SHIEH Exxon Department
Production
of Geosciences,
(Received
February
Research Co., Houston, TX 77001 (U.S.A.) Purdue University, West Lafayette, IN 47907
15,1985;
revised and accepted
November
(U.S.A.)
29,1985)
Abstract Price, F.T. and Shieh, Y.N., 1986. Correlation between the 634S of pyritic shale. Chem. Geol. (Isot. Geosci. Sect.), 58: 333-337.
and organic
sulfur
in coal and oil
The 6”s of pyritic (Y) and organic (X) sulfur in high-sulfur Illinois Basin coals and the Saline Zone of the Piceance Creek Basin, Colorado, U.S.A., oil shale of the Green River Formation exhibit a linear relationship (Y = 1.16X - 4.8; R’ = 0.98). This relationship implies that a common mechanism resulted in the incorporation of sulfur in two different depositional settings. They were formed in an environment where bacterial sulfate reduction and plant assimilation were the two major pathways of sulfur incorporation and where dissolved sulfate concentration was high. Bacterial sulfate reduction has apparently produced large kinetic isotope fractionation effects in the high-sulfate-concentration environment. In contrast, low-sulfur coals from the Illinois Basin and the Leached and Mahogany Zones of the Piceance Creek were apparently formed in environments where the dissolved sulfate concentration was lower and where bacterial sulfate reduction, if it occurred, did not produce significant kinetic isotope fractionation.
1. Introduction
the Green River Formation,
In a study of the distribution and isotopic composition of sulfur in coals from the Illinois Basin, U.S.A., Price and Shieh (1979a) reported a linear relationship between the 634S of massive pyrite (Y) and organic sulfur (X) in high-sulfur coals (> 0.8 wt.% So%): Y = 1.1X-
4.8,
Y = 1.241X
R2 = 0.93
o 1986 Elsevier
U.S.A.:
R2 = 0.82
When both sets of data are plotted on the same diagram (Fig. l), an excellent common linear regression is observed:
Recently, Smith and Young (1983) reported a similar relationship between the S34S of pyritic sulfur (Y) and associated organic sulfur (X) for oil shales at 529-789-m depths in a core from the Parachute Creek Member of 0168-9622/86/$03.50
- 6.575,
Colorado,
Science Publishers
Y = 1.16X-
4.8,
R2 = 0.98
(1)
In both studies the organic and pyritic sulfurs were carefully prepared from the same specimens for isotopic analysis so that the correlation cannot be due to the mixing of pyfitic and organic sulfur during the measurement. Although Smith and Young (1983) found a
B.V.
334
25
Fig. 1. Linear relationship Creek Basin oil shales.
between
the 69
of organic
linear correlation between the 634S for pyrite and organic sulfur in the saline mineral section of their core (529-789 m), they found no such correlation for samples from the overlying leached zone (389-529 m) and Mahogany Zone (310-389 m). In contrast to highsulfur coals, Price and Shieh (1979a) found no linear correlation in coals from the Illinois Basin with low sulfur contents (< 0.8 wt.% S,,s). A general relationship between the 634S of organic sulfur and sulfur contents of coals had been observed by Smith and Batts (1974) for Australian coals. 2. Discussion The relationship between pyritic and organic sulfur shown in Fig. 1 could conceivably result from an isotopic equilibrium exchange reaction between the two forms of sulfur. However, there is no known reason to think that such an exchange reaction might operate only in the saline mineral section of the oil shale core and the high-sulfur coals in the Illinois Basin but not in the other sections of the oil shale core or the low-sulfur coals. Smith and Young (1983) explained the linear relationship for oil shales by suggesting
and pyritic
sulfur
from
Illinois
Basin coals and Piceance
that organic matter was the primary transporting and precipitating agent for pyritic sulfur. They proposed that the sulfide produced from organic sulfur was probably incorporated quantitatively in the pyrite. The enrichment in 32S of pyritic sulfur over organic sulfur was explained using a mechanism involving transportation of the sulfide formed from organic matter, followed by conversion to disulfides. Price and Shieh (1979a) explained the linear relationship for coals by suggesting that there were two isotopically distinct sulfur sources. One source responsible for a portion of the organic sulfur and all of the pyritic sulfur, while the other source contributed only to the organic sulfur. Kaplan et al. (1963) showed that one of the sources of sulfur in marine sediments is hydrogen sulfide produced by bacterial reduction of dissolved sulfate. Part of the hydrogen sulfide contributed to the organic sulfur content of the coal and part was incorporated in massive pyrite. The second sulfur source was thought to be sulfate assimilated by living plants which contributed only to the organic sulfur content of the coals. We believe that the conceptual model discussed in Price and Shieh
335 SOLUBLE
SULFATE
n
that if the dissolved sulfate concentration were very low such as in a freshwater environment, there would be little bacterial reduction and the major form of sulfur in the sediments would be organic. Where pyritic sulfur was found in the low-sulfur coals it was not isotopically related to the organic sulfur and did not exhibit a linear trend. The lack of a linear trend is also apparent in the data from the Leached and Mahogany Zones reported by Smith and Young (1983). In Fig. 3, those points which plot off the line may have formed in low dissolved-sulfate concentration environments. Where soluble-sulfate concentrations are high, bacterial reduction should flourish in organic-rich sediments which form coal and oil shale. High dissolved-sulfate concentrations may be due to the influx of marine water, or due to the concentration of sulfate in freshwater by evaporation or the dissolution of sulfate from evaporites. If dissolved sulfate is present in high concentrations, then bacteria will produce H2S enriched in 32S by 50%0 or greater (Goldhaber and Kaplan, 1974; Lisitsin et al., 1975). Based on the work of Price and Shieh (1979b) we believe
PLANT ASSIMILATION
SULFATE
MATTER
Fig. 2. A generalized flow-chart illustrating principal sources and methods of sulfur incorporation in terrestrial organic-rich sediments.
(1979a) can be used to explain the relationship presented in Fig. 1. The model is diagrammatically depicted in Fig. 2. Price and Shieh (1979a) explained the lack of a linear trend between pyritic and organic sulfur in low-sulfur coals (Fig. 3) using the model illustrated in Fig. 2. They suggested 45 _ 35 -
.
ILLINOIS BASIN COALS. LOWSULF”R
.
PlCEANCE CREEK BASIN OIL SHALE. LEACHED AND MAHOGANY ZONES (SMITH AND YOUNG. 19831
CONTENT IPRICE ANDSHIEH.
19791
-5 -
I .’ -15 -10
-5
0
5
10 6%
15
20
25
30
OF ORGANIC SULFVH
Fig. 3. Coal and oil shale data which show a poor fit with the linear relationship
of Fig. 1.
336
that further reaction of H2S with Fe to form pyrite produces little or no additional sulfur isotope fractionation. In Fig. 2, therefore, pyrite produced by bacterial sulfate reduction in an environment with a high dissolved-sulfate concentration will be isotopically more negative than the sulfate. Plant assimilation of sulfate produces little isotopic fractionation (Mektiyeva et al., 1976) so that the portion of the organic sulfur produced by plant assimilation will be isotopically equivalent to the sulfate. Casagrande et al. (1979) has shown, using 35S labeling, that HzS reacts with organic matter (peat) to form organic sulfur. Therefore the HzS produced by bacterial sulfate reduction may have reacted with organic matter in the sediments to produce part of the organic sulfur. Assuming no significant isotopic fractionation during the reaction of H# with organic matter, the isotope ratio of the total organic sulfur will be heavier than that of the coexisting pyrite as is the case for data plotted in Fig. 1. Where the soluble-sulfate concentrations are not great enough to continually replenish the sulfate reduced to H2S by anaerobic bacteria the kinetic fractionation factor, OL, for bacterial sulfate reduction may become smaller. The term (Yis defined as: a=
(34S/32S)product (34s/32%*&ant
(2)
and ranges from 1.020 for seawater (Nakai and Jensen, 1964) to 1.015 and as low as 1.001 for freshwater systems (Chambers and Trudinger, 1979). Laboratory experiments together with observation from natural systems suggest that OLmay respond to the dissolvedsulfate concentration (Harrison and Thode, 1958; Matrosov et al., 1975). Generally, as the sulfate concentration decreases, fractionation decreases. We suggest that the lacustrine oil shale environment may have contained dissolved sulfate in concentrations too low to produce significant isotopic fractionation but high enough to provide a source of sulfate for the sulfate-reducing bacteria. In such a case the
H2S might be only slightly lighter than the soluble-sulfate source. The organic sulfur and pyritic sulfur would have similar isotope ratios with the value both dependent on the magnitude of the kinetic fractionation factor and indirectly on the concentration of dissolved sulfate. Acknowledgements The authors would like to thank Drs. D.J. Casagrande, N.R. Gray, A.T. James, W.A. Young and two anonymous reviewers for their helpful comments regarding this manuscript. The authors gratefully acknowledge Exxon Production Research Co. for persmission to publish this manuscript. References Casagrande, D.J., Idowo, G., Friedman, A., Rickert, P. and Schlenz, D., 1979. H,S incorporation in coal precursors: Origins of organic sulfur in coal. Nature (London), 282 (5739): 599-600. Chambers, L.A. and Trudinger, P.A., 1979. Microbial fractionation of stable sulfur isotopes: A review and critique. Geomicrobiol. J., 1: 249-293. Goldhaber, M.B. and Kaplan, I.R.. 1974. The sulfur cycle. In: E. Goldberg (Editor), The Sea, 5. Marine Chemistry. Wiley, New York, N.Y., pp. 569-655. Harrison, A.G. and Thode, H.G., 1958. Mechanism of the bacterial reduction of sulphate from isotope fractionation studies. Faraday Sot. Trans., 54: 84-92. Kaplan, I.R., Emery, K.O. and Rittenberg, S.C., 1963. The distribution and isotopic abundance of sulphur in recent marine sediments off southern California. Geochim. Cosmochim. Acta, 27: 297331. Lisitsin, A.K., Kondrateva, I.A. and Nosik, L.P., 1975. Zonation of sulfur isotope compositions in sulfides at the pinch-out of zones of stratified limonitization in coal-bearing rocks. Lithol. Miner. Resour., 10: 496-504. Matrosov, A-G., Chebotarev, E.N., Kudryavtseva, A.J., Zyakun, A.M. and Ivanov, M.B., 1975. Sulfur isotope composition in freshwater lakes containing H,S. Geochem. Int., 12 (3): 217-221. Mektiyeva, V.L., Gavrilov, E.Ya. and Pankina, R.G., 1976. Sulfur isotopic composition in land plants. Geochem. Int., 13 (6): 85-88. Nakai, N. and Jensen, M.L., 1964. The kinetic isotope
337 effect in the bacterial reduction and oxidation of sulfur. Geochim. Cosmochim. Acta, 28: 18931912. Price, F.T. and Shieh, Y.N., 1979a. The distribution and isotopic composition of sulfur in coals from the Illinois Basin. Econ. Geol., 74: 1446-1461. Price, F.T. and Shieh, Y.N., 197913. Fractionation of sulfur isotopes during laboratory synthesis of pyrite at low temperatures. Chem. Geol., 27: 245-253.
Smith, J.W. and Batts, B.D., 1974. The distribution and isotopic composition of sulfur in coal. Geochim. Cosmochim. Acta, 38: 121-123. Smith, J.W. and Young, N.B., 1983. Stratigraphic variation of sulfur isotopes in Colorado corehole number 1. In: J.H. Gary (Editor), 16th Oil Shale Symposium Proceedings. Colorado School of Mines Press, Golden, Colo., pp. 176-188.
333
CORRELATION BETWEEN THE d34S OF PYRITIC AND ORGANIC SULFUR IN COAL AND OIL SHALE FRED T. PRICE and Y.N. SHIEH Exxon Department
Production
of Geosciences,
(Received
February
Research Co., Houston, TX 77001 (U.S.A.) Purdue University, West Lafayette, IN 47907
15,1985;
revised and accepted
November
(U.S.A.)
29,1985)
Abstract Price, F.T. and Shieh, Y.N., 1986. Correlation between the 634S of pyritic shale. Chem. Geol. (Isot. Geosci. Sect.), 58: 333-337.
and organic
sulfur
in coal and oil
The 6”s of pyritic (Y) and organic (X) sulfur in high-sulfur Illinois Basin coals and the Saline Zone of the Piceance Creek Basin, Colorado, U.S.A., oil shale of the Green River Formation exhibit a linear relationship (Y = 1.16X - 4.8; R’ = 0.98). This relationship implies that a common mechanism resulted in the incorporation of sulfur in two different depositional settings. They were formed in an environment where bacterial sulfate reduction and plant assimilation were the two major pathways of sulfur incorporation and where dissolved sulfate concentration was high. Bacterial sulfate reduction has apparently produced large kinetic isotope fractionation effects in the high-sulfate-concentration environment. In contrast, low-sulfur coals from the Illinois Basin and the Leached and Mahogany Zones of the Piceance Creek were apparently formed in environments where the dissolved sulfate concentration was lower and where bacterial sulfate reduction, if it occurred, did not produce significant kinetic isotope fractionation.
1. Introduction
the Green River Formation,
In a study of the distribution and isotopic composition of sulfur in coals from the Illinois Basin, U.S.A., Price and Shieh (1979a) reported a linear relationship between the 634S of massive pyrite (Y) and organic sulfur (X) in high-sulfur coals (> 0.8 wt.% So%): Y = 1.1X-
4.8,
Y = 1.241X
R2 = 0.93
o 1986 Elsevier
U.S.A.:
R2 = 0.82
When both sets of data are plotted on the same diagram (Fig. l), an excellent common linear regression is observed:
Recently, Smith and Young (1983) reported a similar relationship between the S34S of pyritic sulfur (Y) and associated organic sulfur (X) for oil shales at 529-789-m depths in a core from the Parachute Creek Member of 0168-9622/86/$03.50
- 6.575,
Colorado,
Science Publishers
Y = 1.16X-
4.8,
R2 = 0.98
(1)
In both studies the organic and pyritic sulfurs were carefully prepared from the same specimens for isotopic analysis so that the correlation cannot be due to the mixing of pyfitic and organic sulfur during the measurement. Although Smith and Young (1983) found a
B.V.
334
25
Fig. 1. Linear relationship Creek Basin oil shales.
between
the 69
of organic
linear correlation between the 634S for pyrite and organic sulfur in the saline mineral section of their core (529-789 m), they found no such correlation for samples from the overlying leached zone (389-529 m) and Mahogany Zone (310-389 m). In contrast to highsulfur coals, Price and Shieh (1979a) found no linear correlation in coals from the Illinois Basin with low sulfur contents (< 0.8 wt.% S,,s). A general relationship between the 634S of organic sulfur and sulfur contents of coals had been observed by Smith and Batts (1974) for Australian coals. 2. Discussion The relationship between pyritic and organic sulfur shown in Fig. 1 could conceivably result from an isotopic equilibrium exchange reaction between the two forms of sulfur. However, there is no known reason to think that such an exchange reaction might operate only in the saline mineral section of the oil shale core and the high-sulfur coals in the Illinois Basin but not in the other sections of the oil shale core or the low-sulfur coals. Smith and Young (1983) explained the linear relationship for oil shales by suggesting
and pyritic
sulfur
from
Illinois
Basin coals and Piceance
that organic matter was the primary transporting and precipitating agent for pyritic sulfur. They proposed that the sulfide produced from organic sulfur was probably incorporated quantitatively in the pyrite. The enrichment in 32S of pyritic sulfur over organic sulfur was explained using a mechanism involving transportation of the sulfide formed from organic matter, followed by conversion to disulfides. Price and Shieh (1979a) explained the linear relationship for coals by suggesting that there were two isotopically distinct sulfur sources. One source responsible for a portion of the organic sulfur and all of the pyritic sulfur, while the other source contributed only to the organic sulfur. Kaplan et al. (1963) showed that one of the sources of sulfur in marine sediments is hydrogen sulfide produced by bacterial reduction of dissolved sulfate. Part of the hydrogen sulfide contributed to the organic sulfur content of the coal and part was incorporated in massive pyrite. The second sulfur source was thought to be sulfate assimilated by living plants which contributed only to the organic sulfur content of the coals. We believe that the conceptual model discussed in Price and Shieh
335 SOLUBLE
SULFATE
n
that if the dissolved sulfate concentration were very low such as in a freshwater environment, there would be little bacterial reduction and the major form of sulfur in the sediments would be organic. Where pyritic sulfur was found in the low-sulfur coals it was not isotopically related to the organic sulfur and did not exhibit a linear trend. The lack of a linear trend is also apparent in the data from the Leached and Mahogany Zones reported by Smith and Young (1983). In Fig. 3, those points which plot off the line may have formed in low dissolved-sulfate concentration environments. Where soluble-sulfate concentrations are high, bacterial reduction should flourish in organic-rich sediments which form coal and oil shale. High dissolved-sulfate concentrations may be due to the influx of marine water, or due to the concentration of sulfate in freshwater by evaporation or the dissolution of sulfate from evaporites. If dissolved sulfate is present in high concentrations, then bacteria will produce H2S enriched in 32S by 50%0 or greater (Goldhaber and Kaplan, 1974; Lisitsin et al., 1975). Based on the work of Price and Shieh (1979b) we believe
PLANT ASSIMILATION
SULFATE
MATTER
Fig. 2. A generalized flow-chart illustrating principal sources and methods of sulfur incorporation in terrestrial organic-rich sediments.
(1979a) can be used to explain the relationship presented in Fig. 1. The model is diagrammatically depicted in Fig. 2. Price and Shieh (1979a) explained the lack of a linear trend between pyritic and organic sulfur in low-sulfur coals (Fig. 3) using the model illustrated in Fig. 2. They suggested 45 _ 35 -
.
ILLINOIS BASIN COALS. LOWSULF”R
.
PlCEANCE CREEK BASIN OIL SHALE. LEACHED AND MAHOGANY ZONES (SMITH AND YOUNG. 19831
CONTENT IPRICE ANDSHIEH.
19791
-5 -
I .’ -15 -10
-5
0
5
10 6%
15
20
25
30
OF ORGANIC SULFVH
Fig. 3. Coal and oil shale data which show a poor fit with the linear relationship
of Fig. 1.
336
that further reaction of H2S with Fe to form pyrite produces little or no additional sulfur isotope fractionation. In Fig. 2, therefore, pyrite produced by bacterial sulfate reduction in an environment with a high dissolved-sulfate concentration will be isotopically more negative than the sulfate. Plant assimilation of sulfate produces little isotopic fractionation (Mektiyeva et al., 1976) so that the portion of the organic sulfur produced by plant assimilation will be isotopically equivalent to the sulfate. Casagrande et al. (1979) has shown, using 35S labeling, that HzS reacts with organic matter (peat) to form organic sulfur. Therefore the HzS produced by bacterial sulfate reduction may have reacted with organic matter in the sediments to produce part of the organic sulfur. Assuming no significant isotopic fractionation during the reaction of H# with organic matter, the isotope ratio of the total organic sulfur will be heavier than that of the coexisting pyrite as is the case for data plotted in Fig. 1. Where the soluble-sulfate concentrations are not great enough to continually replenish the sulfate reduced to H2S by anaerobic bacteria the kinetic fractionation factor, OL, for bacterial sulfate reduction may become smaller. The term (Yis defined as: a=
(34S/32S)product (34s/32%*&ant
(2)
and ranges from 1.020 for seawater (Nakai and Jensen, 1964) to 1.015 and as low as 1.001 for freshwater systems (Chambers and Trudinger, 1979). Laboratory experiments together with observation from natural systems suggest that OLmay respond to the dissolvedsulfate concentration (Harrison and Thode, 1958; Matrosov et al., 1975). Generally, as the sulfate concentration decreases, fractionation decreases. We suggest that the lacustrine oil shale environment may have contained dissolved sulfate in concentrations too low to produce significant isotopic fractionation but high enough to provide a source of sulfate for the sulfate-reducing bacteria. In such a case the
H2S might be only slightly lighter than the soluble-sulfate source. The organic sulfur and pyritic sulfur would have similar isotope ratios with the value both dependent on the magnitude of the kinetic fractionation factor and indirectly on the concentration of dissolved sulfate. Acknowledgements The authors would like to thank Drs. D.J. Casagrande, N.R. Gray, A.T. James, W.A. Young and two anonymous reviewers for their helpful comments regarding this manuscript. The authors gratefully acknowledge Exxon Production Research Co. for persmission to publish this manuscript. References Casagrande, D.J., Idowo, G., Friedman, A., Rickert, P. and Schlenz, D., 1979. H,S incorporation in coal precursors: Origins of organic sulfur in coal. Nature (London), 282 (5739): 599-600. Chambers, L.A. and Trudinger, P.A., 1979. Microbial fractionation of stable sulfur isotopes: A review and critique. Geomicrobiol. J., 1: 249-293. Goldhaber, M.B. and Kaplan, I.R.. 1974. The sulfur cycle. In: E. Goldberg (Editor), The Sea, 5. Marine Chemistry. Wiley, New York, N.Y., pp. 569-655. Harrison, A.G. and Thode, H.G., 1958. Mechanism of the bacterial reduction of sulphate from isotope fractionation studies. Faraday Sot. Trans., 54: 84-92. Kaplan, I.R., Emery, K.O. and Rittenberg, S.C., 1963. The distribution and isotopic abundance of sulphur in recent marine sediments off southern California. Geochim. Cosmochim. Acta, 27: 297331. Lisitsin, A.K., Kondrateva, I.A. and Nosik, L.P., 1975. Zonation of sulfur isotope compositions in sulfides at the pinch-out of zones of stratified limonitization in coal-bearing rocks. Lithol. Miner. Resour., 10: 496-504. Matrosov, A-G., Chebotarev, E.N., Kudryavtseva, A.J., Zyakun, A.M. and Ivanov, M.B., 1975. Sulfur isotope composition in freshwater lakes containing H,S. Geochem. Int., 12 (3): 217-221. Mektiyeva, V.L., Gavrilov, E.Ya. and Pankina, R.G., 1976. Sulfur isotopic composition in land plants. Geochem. Int., 13 (6): 85-88. Nakai, N. and Jensen, M.L., 1964. The kinetic isotope
337 effect in the bacterial reduction and oxidation of sulfur. Geochim. Cosmochim. Acta, 28: 18931912. Price, F.T. and Shieh, Y.N., 1979a. The distribution and isotopic composition of sulfur in coals from the Illinois Basin. Econ. Geol., 74: 1446-1461. Price, F.T. and Shieh, Y.N., 197913. Fractionation of sulfur isotopes during laboratory synthesis of pyrite at low temperatures. Chem. Geol., 27: 245-253.
Smith, J.W. and Batts, B.D., 1974. The distribution and isotopic composition of sulfur in coal. Geochim. Cosmochim. Acta, 38: 121-123. Smith, J.W. and Young, N.B., 1983. Stratigraphic variation of sulfur isotopes in Colorado corehole number 1. In: J.H. Gary (Editor), 16th Oil Shale Symposium Proceedings. Colorado School of Mines Press, Golden, Colo., pp. 176-188.