Native Sulfur Deposits
101
4. Sedimentary Sulfides
Due to the activity of sulfate-reducing bacteria (producing
light sulfide and heavy residual sulfate) most of the sulfur
isotope fractionation takes place in the uppermost layers of the
muds of shallow sea basins and of tidal flats. THODE et al. (1954), FEELY
and KULP (1957), THODE et al. (1960), VINOGRADOV et al. (1962), KAPLAN et al. (1963), NAKAI and JENSEN (1964), HARTMANN and NIELSEN
(1969), and others found that in various natural environments enrichments occurred in 32S from 15 to 62%0 for sulfides relative to associated
sulfates.
Sedimentary sulfides should normally have a <5 34 S-value somewhere
between -10 and - 30%0, although numerous examples exist where the
sedimentary sulfides show rather heavy (i-values.
Sulfur isotope ratios in sediments are sensitive indicators of certain
variable conditions in the microenvironment of a given sedimentation
region. VINOGRADOV et al. (1962) found in Recent Black Sea sediments
(i34S-values between - 20 and - 36%0 for the various sulfur compounds
(pyrite, H 2S, elemental sulfur) in the H2S-containing region. More positive values between - 6 and - 21%0 have been found in sediments from
the oxygen-containing zone. KAPLAN et al. (1963) report (i34S-values between -16.6 and 3.1%0. The organic sulfur from decaying organic matter
apparently plays only a small role in the sulfur economy. HARTMANN
and NIELSEN (1969) demonstrated that as sediment depth increases, the
pore water sulfate shows increasing (i34S-values and that the 34Sj32S ratios
of the pore water sulfide increases parallel to the sulfate sulfur, with a
nearly constant (i-difference. These examples should make it clear that
even under similar sedimentation conditions, the 34S-contents of sediments can vary considerably.
The isotopic composition of sedimentary sulfates (evaporites) is discussed under the isotopic composition of ocean water.
5. Native Sulfur Deposits
The large native sulfur deposits found on earth, e.g., Sicily, Louisiana,
and Texas, are always associated with gypsum and anhydrite and are
usually encountered within the cap rock of salt domes. THODE et al.
(1954), FEELY and KULP (1957), DESSAU et al. (1962), SCHNEIDER and
NIELSEN (1965), and DAVIS and KIRKLAND (1970) analyzed sulfur isotope
ratios of native sulfur of this type. The isotope measurements have provided overwhelming evidence that the native sulfur is formed by the reduction of sulfate by sulfate-reducing bacteria (the normally associated
petroleum provides a source of carbon and the energy for metabolism).
101
4. Sedimentary Sulfides
Due to the activity of sulfate-reducing bacteria (producing
light sulfide and heavy residual sulfate) most of the sulfur
isotope fractionation takes place in the uppermost layers of the
muds of shallow sea basins and of tidal flats. THODE et al. (1954), FEELY
and KULP (1957), THODE et al. (1960), VINOGRADOV et al. (1962), KAPLAN et al. (1963), NAKAI and JENSEN (1964), HARTMANN and NIELSEN
(1969), and others found that in various natural environments enrichments occurred in 32S from 15 to 62%0 for sulfides relative to associated
sulfates.
Sedimentary sulfides should normally have a <5 34 S-value somewhere
between -10 and - 30%0, although numerous examples exist where the
sedimentary sulfides show rather heavy (i-values.
Sulfur isotope ratios in sediments are sensitive indicators of certain
variable conditions in the microenvironment of a given sedimentation
region. VINOGRADOV et al. (1962) found in Recent Black Sea sediments
(i34S-values between - 20 and - 36%0 for the various sulfur compounds
(pyrite, H 2S, elemental sulfur) in the H2S-containing region. More positive values between - 6 and - 21%0 have been found in sediments from
the oxygen-containing zone. KAPLAN et al. (1963) report (i34S-values between -16.6 and 3.1%0. The organic sulfur from decaying organic matter
apparently plays only a small role in the sulfur economy. HARTMANN
and NIELSEN (1969) demonstrated that as sediment depth increases, the
pore water sulfate shows increasing (i34S-values and that the 34Sj32S ratios
of the pore water sulfide increases parallel to the sulfate sulfur, with a
nearly constant (i-difference. These examples should make it clear that
even under similar sedimentation conditions, the 34S-contents of sediments can vary considerably.
The isotopic composition of sedimentary sulfates (evaporites) is discussed under the isotopic composition of ocean water.
5. Native Sulfur Deposits
The large native sulfur deposits found on earth, e.g., Sicily, Louisiana,
and Texas, are always associated with gypsum and anhydrite and are
usually encountered within the cap rock of salt domes. THODE et al.
(1954), FEELY and KULP (1957), DESSAU et al. (1962), SCHNEIDER and
NIELSEN (1965), and DAVIS and KIRKLAND (1970) analyzed sulfur isotope
ratios of native sulfur of this type. The isotope measurements have provided overwhelming evidence that the native sulfur is formed by the reduction of sulfate by sulfate-reducing bacteria (the normally associated
petroleum provides a source of carbon and the energy for metabolism).