Sulphate isotopic composition

Taylor, B.E., M. C. Wheeler and D.K. Nordstrom, 1984, Isotope composition of sulphate in acid mine drainage as measure of bacterial oxidation. Nature 308, 538-541. 

Fritz P, Basharmel GM, Drimmie RJ, Ibsen J, Qureshi RM (1989) Oxygen isotope exchange between sulphate and water during bacterial reduction of sulphate. Chem Geol 79 99-105 Fry B (1988) Food web structure on Georges Bank from stable C, N and S isotopic compositions. Limnol Oceanogr 3 1182-1190... 

Rees CE, Jenkins WJ, Monster J (1978) The sulphur isotopic composition of ocean water sulphate. Geochim Cosmochim Acta 42 377-381... 

Changes in the isotope composition of marine sulphates during geological time is another exiting topic of S isotope geochemistry (Holser and Kaplan,... 

Mizutani Y. and Rafter T. A. (1969) Oxygen isotopic composition of sulphates Part 4. Bacterial fractionation of oxygen isotopes in the reduction of sulphate and in the oxidation of sulphur. NZ J. Sci. 12, 60—67. 

Kampschulte A. and Strauss H. (1998) The isotopic composition of trace sulphates in Paleozoic biogenic carbonates implications for coeval seawater and geochemical cycles. Min. Mag. 62A, 744-745. 

Palmer, M.R., Helvad, C. Fallick, A.E. (2004) Sulphur, sulphate oxygen and strontium isotope composition of Cenozoic Turkish evaporites. Chemical Geology 209, 341-356. 

Figure 12.22 Percent contributions to overall pyrite oxidation, of FeS2 oxidation by O2 (Eq. [12,39a)), and by (Eq. 112,39b]), plotted against 1ASO4" - H20(%o)], the expected oxygen isotope fractionation between sulphate and water. End-member points (open circles) are plotted for extreme fractionations measured in the following conditions anaerobic, sterile, and aerobic with T. ferrooxidans present. Bars denote the ranges of values measured in laboratory experiments. From Nature 308 539-41, E. B. Taylor et al.. Isotope composition of sulphate in acid mine drainage as measure of bacterial oxidation, copyright 1984 by Macmillan Magazines, Ltd. Used by permission.

The early marine cements on both basin margins have relatively wide variations in carbon isotopic composition compared with the basin centre (Fig. 10). Carbon isotopes in the basin centre have S CpDB values between +5%o and -10%o, whereas basin margin cements commonly have values between +10%o and -20%o values as low as -30%o and as high as +20%o also occur. Presumably, the overall shallower depositional conditions at the basin margin and/or greater fluid mobility compared with the basin centre have resulted in different reactions, producing dissolved carbon within tens of metres of the sediment-water interface. Negative S Cp B values presumably represent bacterial oxidation or sulphate reduction, and positive values are from bacterial fermentation (Irwin et ai, 1977). 

Buick R, Des Marais DJ, Knoll AH (1995) Stable isotope compositions of carbonates from the Mesoproterozoic Bangemall Group, Northwestern Australia. Chem Geol 123 153-171 Cameron EM (1982) Sulphate and sulphate reduction in early Precambrian oceans. Nature 296 145-148 Canfield DE (1998) A new model for Proterozoic ocean chemistry. Nature 396 450-453 Canfield DE, Raiswell R (1999) The evolution of the sulfur cycle. Am J Sci 299 697-723 Deines P (1980) The isotopic composition of reduced organic carbon. In Fritz P, Fontes JC (eds) HEIG, Elsevier, Amsterdam, p 329-406... 

Naturally occurring sulphur-bearing species include native sulphur, the sulphate and sulphide minerals, gaseous H S and SO2 and a range of oxidized and reduced suphur ions in solution. A summary of the isotopic compositions of some major rock types is given in Figure 7.21. 

Figure 7.22 Age curves for and 5 0 in sulphate in equilibrium with seawater. Note the change in scale is relative to CDT and 5 0 relative to SMOW. The curves are based upon the isotopic composition of sulphate in evaporite deposits and the error bars show the uncertainty in the curves at different rime intervals. The oxygen curve is less well constrained than the sulphur curve. The fractionation of between dissolved sulphate in seawater and evaporite sulphate is +1.65 Vm and therefore, strictly, this value should be subtracted from the values given. However, the relatively small difference is within the errors on the plotted curve and is usually ignored. On the other hand, the fractionation of 5 0 between seawater and evaporite sulphate is +3,5 /oa and so to obtain the isotopic composition of in sulphate in seawater at a given time, 3.5 Vm should be subtracted from the plotted values (after Qaypool et a/., 1980).

Sulphide mineral-pairs and sulphide-sulphate mineral-pairs are not always in equilibrium. This can arise when (1) the mineral-pair formed at low temperatures (7 < 200 °C) (2) the isotopic composition of a mineralizing fluid is variable (3) there was continued isotopic exchange following the formation of the mineral... 

Sulphur has relatively great atomic weight and minimum isotopic fractionating. That is why its isotopic composition is st noticeably worseless. The source of isotopically heavy sulphur is sulphate ion whose sulphur in oceanic water has 8 S of 20.1 0.8%. The main cause of sulphur... 

S-sulphate seawater curve and the 5 0-sulphate seawater curve (Figure 7.22) although the two isotopic systems are not closely coupled. in modern marine sediments has an extensive range from values around +20 V , reflecting the composition of seawater down to 56"/(n, the product of bacterial sulphate reduction (Section 7.5.2). Some metasediments have values as high as +40Voii CDT. 

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