13.3 Chemical Diagenesis
677
a
SALINITY VS. OEPTH (TRENDS)
b
o
TDS (g/l)
100
I-SEA WATER
J (32·37 g/l )
J
Jr~~
200
mr, SOUTHERN
300
Mk.. NORTH SEA
~ 2 tJU~> .. (ABOVE EVAPORITES)
I
b: w
o 3
5
(NO EVAPORITES)
C SALINITY PROFILES
E 1
~
I
h: w
o
ON TOP OF EVAPORITES
o
100
200
300
\
\
EVAPORITES WITH HAllTE
Fig. 13.18. a,b Salinity of pore fluids vs. burial depth
depending (a) on the presence of evaporites in the
deep subsurface and (b) on the fluid pressure.
Overpressured systems prevent the injection of pore
fluids from other regions. c Salinity profiles of pore
fluids on top of evaporites caused either by pure molecular diffusion or a combination of diffusion and
upward directed fluid flow (advection). d,e Concentrations of major dissolved species in pore water as a
TDS (g/l)
o
100
200
300
2
3
:f[tt OVERPRESSURED FLUIDS
4 · ·r· (MUDSTONE.DOIMINATED)
MAJOR DISSOLVED SPECIES
AS A FUNCTION OF CHLORIDE
d 100 r------,-----..
2
K
o
-'
i=
'"
<{
0 .1
Ä. - - NORTH SEA
u
,/ Mg
SHELF
0 .01 ........ _ _ _ _ _ _ _ _ .....J
10
100
CI (g/kg)
1000
0 ... 100 e
I
Cl
-'t!
-- ~
10
"
/ , - Mg
~ 0 .1
-;; .... ~+-~
"
CALCULA TED
~ 0 .01toC---/ ...... _ ........ :-1.~ 0.001 " ~ - -
-~. "'<;.~C03
U
10
100
1000
CI (g/kg H 2 0)
function of chloride. Values of d are observed in
N orth Sea sediments, those of e are calculated for
waters in equilibrium with quartz, muscovite, albite,
K-feldspar, calcite and dolomite at a temperature of
100°C, apressure of 1 bar and a RC0 3 fugacity of
0.001 bar. (a,b After Bj0r1ykke and Gran 1994;
Hanor 1994, modified; c-e after Ranor 1994, modified)