2.5 Lake Sediments
Ww
~Cl.
IDIz
>-9
IDIz«
og:
f=z
«W I-U
-z 9=0
~u
O:(:J
Cl.z
...J«CI)
0:«
WW
zO:
_U
~~
Na - Mg - K - CI - (S04)
Mg SALTS, HAllTE,
AND OTHER SALTS
r
GYPSUM
1
/
/'
MAGNESITE 1 ,
DOLOMITE 1,
ARAGONITE,
/'
HIGH-Mg CALCITE
•
CARBONj TE LAKES
HAllTE
AND OTHER SAL TS
t
GLAUBERITE 1
(CaS0,jNa 2 S04)
Na - CI - HC0 3
ALKALI NE, RICH IN Si0 2
HAllTE
AND OTHER SALTS
THENARDITE (Na2S04)
-"
/
MIRABILITE
"SODA LAKES"
(Na2S04'10 H20)
WITH GAYLUSSITE
f ~............ (Na2COa' CaC03' 5H20~
"
AND TRONA
(NaHC03' Na2C03' 2H 2 0)
+
SODA (NATRON) LAKES
GYPSUM
t
SULFATE LAKES
LOW-Mg CALCITE
REGRADATION OF CLAY MINERALS, NEW CLAY MINERALS
t
t
t
(:J
HC
HC 2 (Ca + Mg)
Z
3:0:
OW
NORMAL HYDROGEN
SULFATE AND
HYDROGEN CARBONATE
...JICARBONATE WATERS
CHLORIDE WATERS
WATERS RICH.IN Na
u.«
~3:
(HUMID CLiMATE)
(AND K), PARTLY CAUSED
BY ION EXCHANGE
W
(:J
SEDIMENTARY ROCKS
DISSOLUTION OF
MAINL Y VOLCANIC
«
~«
AND OTHER ROCK TYPE S
OLDER EVAPORITES
AND PLUTONIC ROCKS
«w 0:0:
0«
') DIAGENETIC MINERALS
83
Fig. 2.31. Simplified scheme of salt precipitation in
lakes due to mcreasing evaporative concentration.
The principal lines of evolution are controlled by the
composition of inflowing water which in turn reflects
the rock types in the drainage areas. Minor deviations
from these trends are omitted. (Primarily based on
Eugster and Hardie 1978, modified)
dolomite, glauberite, and gaylussite). In addition, some
authigenic silicate minerals may form in conjunction with
salt deposits (e.g. zeolites).
Closed lake systems have in common that their fluctuating water levels cause exposure and considerable
reworking of nearshore sediments. They exhibit
widely shifting facies belts, and their deltas move
basinward during lowstands (cf. Sect. 7.6). Sheet
floods may repeatedly inundate large areas and leave
behind thin, graded beds.
Carbonate Lakes
As a result of calcite (CaC0 3 ) and gypsum
(CaS0 4 2H 2 0) precipitation, the Mg/Ca ratio in the
lake water increases. This, in conjunction with a high
pH (about 9) and high alkali ion concentrations, favors the formation of Mg-rich carbonates such as
high-Mg calcite and, in extreme cases, proto-dolomite and hydro-magnesite. During early diagenesis,
dolomitE- (CaC0 3 MgC0 3 ) and sometimes even
magnesite (MgC0 3 ) are generated (Müller et al.
Ww
~Cl.
IDIz
>-9
IDIz«
og:
f=z
«W I-U
-z 9=0
~u
O:(:J
Cl.z
...J«CI)
0:«
WW
zO:
_U
~~
Na - Mg - K - CI - (S04)
Mg SALTS, HAllTE,
AND OTHER SALTS
r
GYPSUM
1
/
/'
MAGNESITE 1 ,
DOLOMITE 1,
ARAGONITE,
/'
HIGH-Mg CALCITE
•
CARBONj TE LAKES
HAllTE
AND OTHER SAL TS
t
GLAUBERITE 1
(CaS0,jNa 2 S04)
Na - CI - HC0 3
ALKALI NE, RICH IN Si0 2
HAllTE
AND OTHER SALTS
THENARDITE (Na2S04)
-"
/
MIRABILITE
"SODA LAKES"
(Na2S04'10 H20)
WITH GAYLUSSITE
f ~............ (Na2COa' CaC03' 5H20~
"
AND TRONA
(NaHC03' Na2C03' 2H 2 0)
+
SODA (NATRON) LAKES
GYPSUM
t
SULFATE LAKES
LOW-Mg CALCITE
REGRADATION OF CLAY MINERALS, NEW CLAY MINERALS
t
t
t
(:J
HC
HC
Z
3:0:
OW
NORMAL HYDROGEN
SULFATE AND
HYDROGEN CARBONATE
...JICARBONATE WATERS
CHLORIDE WATERS
WATERS RICH.IN Na
u.«
~3:
(HUMID CLiMATE)
(AND K), PARTLY CAUSED
BY ION EXCHANGE
W
(:J
SEDIMENTARY ROCKS
DISSOLUTION OF
MAINL Y VOLCANIC
«
~«
AND OTHER ROCK TYPE S
OLDER EVAPORITES
AND PLUTONIC ROCKS
«w 0:0:
0«
') DIAGENETIC MINERALS
83
Fig. 2.31. Simplified scheme of salt precipitation in
lakes due to mcreasing evaporative concentration.
The principal lines of evolution are controlled by the
composition of inflowing water which in turn reflects
the rock types in the drainage areas. Minor deviations
from these trends are omitted. (Primarily based on
Eugster and Hardie 1978, modified)
dolomite, glauberite, and gaylussite). In addition, some
authigenic silicate minerals may form in conjunction with
salt deposits (e.g. zeolites).
Closed lake systems have in common that their fluctuating water levels cause exposure and considerable
reworking of nearshore sediments. They exhibit
widely shifting facies belts, and their deltas move
basinward during lowstands (cf. Sect. 7.6). Sheet
floods may repeatedly inundate large areas and leave
behind thin, graded beds.
Carbonate Lakes
As a result of calcite (CaC0 3 ) and gypsum
(CaS0 4 2H 2 0) precipitation, the Mg/Ca ratio in the
lake water increases. This, in conjunction with a high
pH (about 9) and high alkali ion concentrations, favors the formation of Mg-rich carbonates such as
high-Mg calcite and, in extreme cases, proto-dolomite and hydro-magnesite. During early diagenesis,
dolomitE- (CaC0 3 MgC0 3 ) and sometimes even
magnesite (MgC0 3 ) are generated (Müller et al.