Table 11.

Table T11. Summary of diagenetic reactions occurring in sediments, Site 1109.

Process Effect of interstitial water geochemistry Remarks

Microbial oxidation of organic matter
SO₄^2-decreases; alkalinity and NH₄⁺increase
SO₄^2-depletion by 100 mbsf, strong alkalinity, and NH₄⁺ maximum at 100 mbsf; secondary maxima 400-500 mbsf

Carbonate reactions

Dissolution
Ca, Sr, and alkalinity increase
Occurs with recrystallization in Units I and II; within Unit VIII provides important Sr source

Precipitation
Ca and alkalinity decrease
Unit VII (calcite cementation)

Leaching and weathering of ash layers and dispersed volcanic minerals (feldspars and plagioclase)
K, Li, SiO₂ and NH₄⁺ increase; Mg decreases
0-150 mbsf (Units I and II), glass dissolution; Si release more important than from biogenic source; precipitation of Mg-rich smectite in Units VIII and IX

Extended weathering of volcanics, detrital clays, and silicate precipitation
Si, K, and alkalinity decrease; Li increases
Uptake of K by illitization; transformation of chlorite/smectite interlayer clays; Li excluded during precipitation of silicates below 400 mbsf

Process	Effect of interstitial water geochemistry	Remarks
Microbial oxidation of organic matter	SO₄^2-decreases; alkalinity and NH₄⁺increase	SO₄^2-depletion by 100 mbsf, strong alkalinity, and NH₄⁺ maximum at 100 mbsf; secondary maxima 400-500 mbsf
Carbonate reactions
Dissolution	Ca, Sr, and alkalinity increase	Occurs with recrystallization in Units I and II; within Unit VIII provides important Sr source
Precipitation	Ca and alkalinity decrease	Unit VII (calcite cementation)
Leaching and weathering of ash layers and dispersed volcanic minerals (feldspars and plagioclase)	K, Li, SiO₂ and NH₄⁺ increase; Mg decreases	0-150 mbsf (Units I and II), glass dissolution; Si release more important than from biogenic source; precipitation of Mg-rich smectite in Units VIII and IX
Extended weathering of volcanics, detrital clays, and silicate precipitation	Si, K, and alkalinity decrease; Li increases	Uptake of K by illitization; transformation of chlorite/smectite interlayer clays; Li excluded during precipitation of silicates below 400 mbsf