world ocean during most of the Phanerozoic was 40–50%
in contrast to 35% today (Hay et al., 2006).
Large evaporite basins occur on all continents, except
Antarctica, and range in age from Late Precambrian to
Late Miocene (Warren, 2006, 2010). The most recent
saline giant occurred in the Latest Miocene (Messinian)
in basins of the Mediterranean region (the so-called
Messinian salinity crisis; Ryan et al., 1973; Hsü et al.,
1973, 1978). Today, there are many environments with
extreme net evaporation, but there are no connected large,
deep basins with restricted marine connection. One candidate would be the Red Sea with a little more restriction and
possibly a more arid climate. Leg 23 of the Deep Sea Drilling Project (DSDP) recovered bedded middle Miocene
evaporates from the Red Sea when the basin was more
restricted than today (Stoffers and Ross, 1974). Comprehensive reviews of evaporite deposits, marine and
nonmarine, are given by Warren (2006, 2010).
Marine evaporite minerals
The first mineral to crystallize from evaporation of seawater is calcium carbonate (CaCO 3 ), usually as calcite, but at
other times aragonite may form. Next is calcium sulfate
either as gypsum (CaSO 4 · 2H 2 O) or anhydrite (CaSO 4 ).
The next most abundant evaporite mineral is halite
(NaCl), commonly known as rock salt. These two minerals, gypsum/anhydrite and halite, constitute more than
95 % by volume of the world’s Phanerozoic evaporates
(Warren, 2010). Under conditions of extreme,
nearly complete evaporation potassium (K) and/or magnesium (Mg), minerals may form. These, often referred to as
bittern or potash salts, are much less common. They
include polyhalite (K 2 Ca 2 Mg(SO 4 ) 4 · 2H 2 O, sylvite
(KCl), carnallite (KCl 2 · MgCl 2 · 6H 2 O), langbeinite
(K 2 SO 4 · 2MgSO 4 ), kainite (MgSO 4 · KCl · 3H 2 O),
glauberite (Na 2 SO 4 · CaSO 4 ), kieserite (MgSO 4 · H 2 O),
bischofite (MgCl 2 · 6H 2 O), epsomite (MgSO 4 · 7 H 2 O),
hexahydrite (MgSO 4 · 6 H 2 O), loeweite (Na 4 Mg 2 (SO 4 ) 4 ·
5H 2 O), and vanthoffite (Na 6 Mg(SO 4 ) 4 ). Any one bed in
an evaporite deposit commonly is monomineral, especially those composed of gypsum, anhydrite, or halite.
Many more salts have been recorded from evaporite
deposits but the above are by far the most common. Paragenetic mineral pairs with sylvite are common enough that
they have been given mine-mineral names. Sylvite combined with halite is called “sylvanite,” and sylvite combined with anhydrite and/or kieserite and/or polyhalite is
called “hartsalz” by the Germans.
Permian Zechstein formation
The Upper Permian Zechstein Formation underlies most
of Poland, Germany, the Netherlands, Denmark, east central England, and the North Sea. It is the most extensively
studied evaporite sequence in the world. The Zechstein
consists of four depositional cycles. The second oldest
depositional cycle is the Stassfurt cycle or series named
for its type section at Stassfurt, Germany. The Stassfurt
is the most studied and most economically important of
the Zechstein series. At Stassfurt, the basal anhydrite is
only 50 m thick, overlain by 500 m of halite, topped off
by only 50 m of potash salts. Borings into the Zechstein
throughout Germany in the early nineteenth century determined the locations of subsurface bedded rock salt and
other evaporite minerals that formed a stratigraphic
sequence more than 2,300 m thick at Stassfurt. At that
time potassium and magnesium deposits (potash) associated with salt were considered contaminants and were
discarded. However, it was soon recognized that potassium was necessary for plant growth, and for the rest of
the nineteenth century, most of the potash of the world
was supplied from mines near Stassfurt. Bischoff, in his
book Elements of Chemical and Physical Geology
(1864), was perhaps the first to recognize that halite and
anhydrite (or gypsum) were precipitated from seawater
but did not propose an exact method.
The following six zones represent a complete progressive evaporite cycle within the Stassfurt from youngest
to oldest:
Hartsalz – sylvite plus anhydrite and/or kieserite,
polyhalite, and halite
Carnallite – 55–60 % carnallite, 25 % halite, 17 %
kieserite
Kieserite and carnallite – with approximately 65 % halite
Polyhalite – with approximately 93 % halite
Anhydrite plus halite – approximately 96 % anhydritelaminated halite
Basal anhydrite – with dolomite laminae and some halite
Probably the most significant experiment in understanding the origin of evaporite minerals was the classic
work of an Italian chemist named Usiglio (1849). He
determined the sequence of precipitation of evaporite minerals from seawater by simply evaporating an aliquot of
Mediterranean seawater and noting the sequence and
quantities of precipitates with progressive evaporation.
The results of Usiglio’s experimental evaporation of
seawater (1849; reproduced in Clarke, 1924) show that
calcium carbonate begins to precipitate inorganically
when seawater has been evaporated to about half of its
original volume. The most common carbonate mineral to
form from seawater at normal-marine temperatures and
pressures is low-Mg calcite, although aragonite, highMg calcite, and dolomite may also form if conditions are
right, usually at higher salinities and/or in association with
biogenic controls. Aragonite is unstable and with time and
burial aragonite will recrystallize to form low-Mg calcite.
When the original water volume has been reduced to
about 20 %, calcium sulfate begins to precipitate. Under
salinity and temperature conditions of most evaporite
deposits, anhydrite should theoretically be the most stable
calcium sulfate mineral. However, in experimental and
observed modern evaporite systems, gypsum is the almost
universal calcium sulfate mineral to form. This may or
may not have been true in the past. Primary anhydrite
has been found in a few Holocene evaporite deposits such
428
MARINE EVAPORITES
in contrast to 35% today (Hay et al., 2006).
Large evaporite basins occur on all continents, except
Antarctica, and range in age from Late Precambrian to
Late Miocene (Warren, 2006, 2010). The most recent
saline giant occurred in the Latest Miocene (Messinian)
in basins of the Mediterranean region (the so-called
Messinian salinity crisis; Ryan et al., 1973; Hsü et al.,
1973, 1978). Today, there are many environments with
extreme net evaporation, but there are no connected large,
deep basins with restricted marine connection. One candidate would be the Red Sea with a little more restriction and
possibly a more arid climate. Leg 23 of the Deep Sea Drilling Project (DSDP) recovered bedded middle Miocene
evaporates from the Red Sea when the basin was more
restricted than today (Stoffers and Ross, 1974). Comprehensive reviews of evaporite deposits, marine and
nonmarine, are given by Warren (2006, 2010).
Marine evaporite minerals
The first mineral to crystallize from evaporation of seawater is calcium carbonate (CaCO 3 ), usually as calcite, but at
other times aragonite may form. Next is calcium sulfate
either as gypsum (CaSO 4 · 2H 2 O) or anhydrite (CaSO 4 ).
The next most abundant evaporite mineral is halite
(NaCl), commonly known as rock salt. These two minerals, gypsum/anhydrite and halite, constitute more than
95 % by volume of the world’s Phanerozoic evaporates
(Warren, 2010). Under conditions of extreme,
nearly complete evaporation potassium (K) and/or magnesium (Mg), minerals may form. These, often referred to as
bittern or potash salts, are much less common. They
include polyhalite (K 2 Ca 2 Mg(SO 4 ) 4 · 2H 2 O, sylvite
(KCl), carnallite (KCl 2 · MgCl 2 · 6H 2 O), langbeinite
(K 2 SO 4 · 2MgSO 4 ), kainite (MgSO 4 · KCl · 3H 2 O),
glauberite (Na 2 SO 4 · CaSO 4 ), kieserite (MgSO 4 · H 2 O),
bischofite (MgCl 2 · 6H 2 O), epsomite (MgSO 4 · 7 H 2 O),
hexahydrite (MgSO 4 · 6 H 2 O), loeweite (Na 4 Mg 2 (SO 4 ) 4 ·
5H 2 O), and vanthoffite (Na 6 Mg(SO 4 ) 4 ). Any one bed in
an evaporite deposit commonly is monomineral, especially those composed of gypsum, anhydrite, or halite.
Many more salts have been recorded from evaporite
deposits but the above are by far the most common. Paragenetic mineral pairs with sylvite are common enough that
they have been given mine-mineral names. Sylvite combined with halite is called “sylvanite,” and sylvite combined with anhydrite and/or kieserite and/or polyhalite is
called “hartsalz” by the Germans.
Permian Zechstein formation
The Upper Permian Zechstein Formation underlies most
of Poland, Germany, the Netherlands, Denmark, east central England, and the North Sea. It is the most extensively
studied evaporite sequence in the world. The Zechstein
consists of four depositional cycles. The second oldest
depositional cycle is the Stassfurt cycle or series named
for its type section at Stassfurt, Germany. The Stassfurt
is the most studied and most economically important of
the Zechstein series. At Stassfurt, the basal anhydrite is
only 50 m thick, overlain by 500 m of halite, topped off
by only 50 m of potash salts. Borings into the Zechstein
throughout Germany in the early nineteenth century determined the locations of subsurface bedded rock salt and
other evaporite minerals that formed a stratigraphic
sequence more than 2,300 m thick at Stassfurt. At that
time potassium and magnesium deposits (potash) associated with salt were considered contaminants and were
discarded. However, it was soon recognized that potassium was necessary for plant growth, and for the rest of
the nineteenth century, most of the potash of the world
was supplied from mines near Stassfurt. Bischoff, in his
book Elements of Chemical and Physical Geology
(1864), was perhaps the first to recognize that halite and
anhydrite (or gypsum) were precipitated from seawater
but did not propose an exact method.
The following six zones represent a complete progressive evaporite cycle within the Stassfurt from youngest
to oldest:
Hartsalz – sylvite plus anhydrite and/or kieserite,
polyhalite, and halite
Carnallite – 55–60 % carnallite, 25 % halite, 17 %
kieserite
Kieserite and carnallite – with approximately 65 % halite
Polyhalite – with approximately 93 % halite
Anhydrite plus halite – approximately 96 % anhydritelaminated halite
Basal anhydrite – with dolomite laminae and some halite
Probably the most significant experiment in understanding the origin of evaporite minerals was the classic
work of an Italian chemist named Usiglio (1849). He
determined the sequence of precipitation of evaporite minerals from seawater by simply evaporating an aliquot of
Mediterranean seawater and noting the sequence and
quantities of precipitates with progressive evaporation.
The results of Usiglio’s experimental evaporation of
seawater (1849; reproduced in Clarke, 1924) show that
calcium carbonate begins to precipitate inorganically
when seawater has been evaporated to about half of its
original volume. The most common carbonate mineral to
form from seawater at normal-marine temperatures and
pressures is low-Mg calcite, although aragonite, highMg calcite, and dolomite may also form if conditions are
right, usually at higher salinities and/or in association with
biogenic controls. Aragonite is unstable and with time and
burial aragonite will recrystallize to form low-Mg calcite.
When the original water volume has been reduced to
about 20 %, calcium sulfate begins to precipitate. Under
salinity and temperature conditions of most evaporite
deposits, anhydrite should theoretically be the most stable
calcium sulfate mineral. However, in experimental and
observed modern evaporite systems, gypsum is the almost
universal calcium sulfate mineral to form. This may or
may not have been true in the past. Primary anhydrite
has been found in a few Holocene evaporite deposits such
428
MARINE EVAPORITES