6.4 Marine Evaporites
261
CLOSED MARINE SAL T BASIN AND SAL T LAGOON
b
CROSS
SECTION
a
PLAN VIEW :
BULL'S EYE
FACIES
PATTERN
0.3
PROPORTION OF
SAlTS PRECIPITATED
(TOTAL SALT
CONTENT = 100)
ClOSED BASIN,
STATIC CONCENTRATION OF
SEA WATER
CARBONATE
HAllTE
GYPSUM & ANHYDRITE
EVAPORATION
INCREASING CONCENTRATION OF BRINE
llDEAl EVAPORITE SEQUENCE
OF ClOSED MARINE BASIN
WIND-BLOWN SANDS AND SILTS
POTASH SALTS (+HALlTE)
c:II=-- HAUTE
~ANHYDRITE (pERIODS
OF BRINE DILUTION)
OPEN SYSTEM
SAlT lAGOON WITH FREE
C REFLUX OF BRINE
(BAR MODEL)
PLAN VIEW: TEAR'DROP PATTERN
SEEPAGE MODEL
(PERMEABLE BAR)
d
f
n. EVAPORITE SEQUENCE OF lAGOON,
VARYING INFlUX AND REFLUX
I-'!+'r.!"cI"'" BIOGENIC
UMEST.
1INLE T WIDENING
DECREASING BRINE
DOLOMITE
CO~CENTRATION
-------------r --------..... """'_ A
INLET NARROWING
G
INCREASING BRINE
(G) & ANHYDRITE (A)
O::::::Z::::;;t- DOLOMITE
CONCENTRATION
CARBONATE --------g:;2i~ UMESTONE,
I
OLDER ROCKS
NORMAL MARINE
Fig. 6.4. Models of evaporite deposition. a Closed
basin with "static" concentration of sea water and
"bull's eye" facies pattern. b Proportions of different
evaporites precipitated under conditions of a. c Silled
salt lagoon, open system with brine reflux ("dynamic" system of evaporite deposition), frequently
causing a "tear drop" facies pattern. d Lagoon separated from the open sea by permeable bar (sand
dunes, reef etc.) allowing slow influx of sea water
and reflux of brine. Situation similar to c with tendency to high brine concentration and therefore predominance of halite. e Idealized evaporite sequence
of closed basin (a). f Idealized example of evaporite
sequence of silled lagoon (c) with reversed development (prograding dilution) in upper half. For further
explanations see text