178
J. W.Morse
Table 7.4. Possible reactions for the incorporation of metals into FeS and FeS2 phases. FeS2 reactions
are given for those where the kinetics are well-described (Rickard 1975; Luther 1991; Rickard 1997; Rickard
and Luther 1997; from Morse and Luther 1999)
Eq.
FeS
7.33
Fe 2 + + HS- ~ FeS + H+
(FeS formation)
7.34
FeS + Me 2 + ~ Fe-S-Me 2 +
(Metal adsorption onto FeS)
7.35
Fe-S-Me 2 + ~ Fe(Me)S + Fe 2 +
(Metal inclusion into FeS)
7.36
FeS + Me 2 + ~ MeS + Fe 2 +
(Metathesis or metal exchange reaction)
FeS 2
7.37
FeS or [Fe(Me)S] + S(O) ~ Fe(Me)S2
(Pyrite formation and metal inclusion)
7.38
FeS or [Fe(Me)S] + H 2 S ~ Fe(Me)S2 + H2
7.39
FeS 2 + Me 2 + ~ Fe-S-S-Me
(Metal adsorption onto pyrite)
7.40
Fe-S-S-Me ~ Fe(Me)S2
(Metal inclusion into pyrite)
l4C is mostly used for two purposes. The first is for age dating and obtaining sediment accumulation rates. The second is incubation of 14C-Iabelled organic compounds
in sediments in order make rate measurements on their decomposition. The primary
use of 35S is to make measurements of the rates of sulphate reduction using radiolabelled sulphate (e.g. Jorgensen 1978). It is additionally widely used to investigate the
biogeochemical cycling of sulphur (see review of Fossing 1995).
7.3
Sedimentary Geochemistry of Carbonate and Sulphide Systems
7.3.1
"Normal" Marine Sediments
7.3.1.1
Relationship Between Organic-C and pyrite-S Burial
The term "normal marine" is often used to describe fairly common coastal and even
to some degree estuarine sediments as a depositional environment for sedimentary
sulphides and carbon. Normal marine alone refers to sediments overlain by oxic sea
water of typical oceanic salinity. The type of sediment of interest is typically a finegrained siliciclastic sediment. Excluded from the larger definition are coarse, sandy
sediments, CaCOrrich sediments (hence the adjective "siliciclastic"), and sediments
overlain by freshwater and anoxic marine waters (e.g. Berner 1982; Berner and Raiswell
1984). Because of the virtual absence of sulphur, also excluded are sediments that do
not become sufficiently anoxic for sulphate reduction to become a major process near
the sediment-water interface (e.g. many deep-sea sediments and sediments containing very low concentrations of organic-C).
Fine-grained, normal marine siliciclastic sediments have a relatively narrow range
of CIS ratios. Consequently, organic-C and pyrite-S must covary in a close to linear
J. W.Morse
Table 7.4. Possible reactions for the incorporation of metals into FeS and FeS2 phases. FeS2 reactions
are given for those where the kinetics are well-described (Rickard 1975; Luther 1991; Rickard 1997; Rickard
and Luther 1997; from Morse and Luther 1999)
Eq.
FeS
7.33
Fe 2 + + HS- ~ FeS + H+
(FeS formation)
7.34
FeS + Me 2 + ~ Fe-S-Me 2 +
(Metal adsorption onto FeS)
7.35
Fe-S-Me 2 + ~ Fe(Me)S + Fe 2 +
(Metal inclusion into FeS)
7.36
FeS + Me 2 + ~ MeS + Fe 2 +
(Metathesis or metal exchange reaction)
FeS 2
7.37
FeS or [Fe(Me)S] + S(O) ~ Fe(Me)S2
(Pyrite formation and metal inclusion)
7.38
FeS or [Fe(Me)S] + H 2 S ~ Fe(Me)S2 + H2
7.39
FeS 2 + Me 2 + ~ Fe-S-S-Me
(Metal adsorption onto pyrite)
7.40
Fe-S-S-Me ~ Fe(Me)S2
(Metal inclusion into pyrite)
l4C is mostly used for two purposes. The first is for age dating and obtaining sediment accumulation rates. The second is incubation of 14C-Iabelled organic compounds
in sediments in order make rate measurements on their decomposition. The primary
use of 35S is to make measurements of the rates of sulphate reduction using radiolabelled sulphate (e.g. Jorgensen 1978). It is additionally widely used to investigate the
biogeochemical cycling of sulphur (see review of Fossing 1995).
7.3
Sedimentary Geochemistry of Carbonate and Sulphide Systems
7.3.1
"Normal" Marine Sediments
7.3.1.1
Relationship Between Organic-C and pyrite-S Burial
The term "normal marine" is often used to describe fairly common coastal and even
to some degree estuarine sediments as a depositional environment for sedimentary
sulphides and carbon. Normal marine alone refers to sediments overlain by oxic sea
water of typical oceanic salinity. The type of sediment of interest is typically a finegrained siliciclastic sediment. Excluded from the larger definition are coarse, sandy
sediments, CaCOrrich sediments (hence the adjective "siliciclastic"), and sediments
overlain by freshwater and anoxic marine waters (e.g. Berner 1982; Berner and Raiswell
1984). Because of the virtual absence of sulphur, also excluded are sediments that do
not become sufficiently anoxic for sulphate reduction to become a major process near
the sediment-water interface (e.g. many deep-sea sediments and sediments containing very low concentrations of organic-C).
Fine-grained, normal marine siliciclastic sediments have a relatively narrow range
of CIS ratios. Consequently, organic-C and pyrite-S must covary in a close to linear