Table 1. Expected concentration changes in pore-fluid constituents due to carbonate diagenesis.
| Carbonate reaction | Ca | Mg | Sr | Mg/Ca | Sr/Ca |
|---|---|---|---|---|---|
Calcite precipitation: |
 |
-- | |
 |
|
Ca2+ + CO32-  CaCO3 |
|||||
Calcite dissolution: |
|
|
|
|
|
CaCO3 + H+ Ca2+ +
HCO3- |
|||||
| Calcite reprecipitation: | -- | |
|
|
|
*Dolomite precipitation: |
-- | |
|
|
|
CaCO3 + Mg2+ + 2HCO3-
CaMg(CO3) 2 + CO2 + H2O |
|||||
Dolomite precipitation: |
|
|
|
|
|
2CaCO3 + Mg2+ CaMg(CO3)2
+ Ca2+ |
|||||
*Dolomite precipitation: |
|
|
|
|
|
Ca2+ + Mg2+ + 4HCO3-
CaMg(CO3) 2 + 2CO2 + 2H2O |
|||||
*Impure siderite precipitation: |
|
|
|
|
|
2Fe2+ + Mg2+ + 2HCO3-
2(Ca,Mg,Fe)CO3- + H2 |
|||||
Impure siderite precipitation: |
|
|
|
|
|
CaCO3 + Fe2+ + Mg2+
(Ca,Mg,Fe)CO3 + Ca2+ |
|||||
Siderite precipitation: |
|
|
|
|
|
CaMg(CO3)2 + 2Fe2+
2FeCO3 + Ca2+ + Mg2+ |
|||||
= increases in
concentration, =
decreases in concentration,
= considerable increases or decreases, -- = no change. * = favored reaction for
carbonate mineral precipitation at Sites 994, 995, and 997. Modified from
Kastner et al. (1990).