268
(3) Onset of sea level fall. The salt concentration of the
inland sea begins to increase and first leads to stagnant, slightly hypersaline bottom waters in parts ofthe
basin (Fig. 6.9b). During such aperiod, black, bituminous shales or marls may be deposited. The accumulation of carbonate and gypsum in shallow waters continues. Due to continued falling sea level, the connection ofthe salt basin to the open seais interrupted (Fig.
6.9b).
(4) The water level in the closed basin is drawn down
by evaporation. Entering rivers start to incise valleys
into the emerging shelf and slope areas. Earlier formed
marginal carbonates and lagoonal and sabkha
evaporites are partially leached and their salts transported into the shrinking inland sea. During this phase,
i.e. still in rather deep water, the major part ofhalite is
rapidly precipitated from highly concentrated brine. It
may alternate with thin layers of anhydrite indicating
minor climatic variations including annual varves. In
marginal areas of the inland sea deposition of carbonates, lagoonal and sabkha evaporites continues at a
lower level or is replaced by continental beds (Fig.
6.9c). The main basin may become subdivided into
several subbasins (Fig. 6.9b) with differing salt concentrations and salt deposition.
(5) Finally, the basin may fall dry except for some
playa lakes containing highly concentrated brine including potash salts. Then the dry, huge salt flats are
more or less covered by thin continental beds and
some playas. Increased subsidence, driven by the additional salt load, tends to restore the situation to the one
at the beginning of this development. Dessication and
subsidence will persist until a further pronounced sealevel high again causes flooding of the inland depression and initiates a new cycle of evaporite deposition.
6.4.3 Examples of Giant Salt Deposits
The European Zechstein Basin. This basin experienced up to eight large depositional cycles including
some smaller ones at the end of its existence. Their
total thickness varies considerably from some tens of
meters in the marginal zones to more than 2000 m
(maximum thickness 3500 m, including Rotliegend
Fig. 6.9. Model of complex large evaporite basin on
continental or transitional crnst (Zechstein-type basin), demonstrating one major depositional cycle in
two stages of development. a Stage I (low to intermediate sea level). Inland drainage basin has subsided up to several hundred meters below mean sea
level. Stage 2. Particularly high sea level causes basin flooding and accumulation of sediments with normal marine fauna, basin-wide correlatable. Then salinity increases and evaporite deposition can begin.
b Stage 3. Lowering sea level restores land barrier
toward the open sea and creates large hypersaline
inland sea; evaporative drawdown of water level
Chapter 6 Special Depositional Environments
evaporites) in special troughs. The thicknesses of the
salt deposits of a single large cycle often reach several
hundred meters, but they also vary considerably from
marginal to central parts of the basin (Fig. 6.10). The
marginal facies zones include coastal sabkhas, tidal
flats with microbial mats, lagoons, progradational carbonate buildups (including ooid shoals, dolomite) with
their slope sediments. The wide carbonate slopes
formed mainly during lowstand and transgressive systems tracts, followed by sulfate deposition on the
slopes and platforms during the highstand systems
tract. Halite was precipitated in the central parts ofthe
basin when the margins were exposed and karstified.
Stromatolitic reefs grew on topographic highs. The
central basin may have been 100-300 m deep during
transgressions.
In the classical concept for the German Zechstein Basin, only
four large evaporite cycles were distinguished (e.g. RichterBernburg 1985). The famous "Kupferschiefer", a laminated
marI rich in trace metals, particularly copper, lead and zinc,
formed at the beginning of the first Zechstein evaporite cycle. It accumulated very slowly (5 mmlka) and is interpreted
as a condensed section (cf. Sect. 7.2).
The differences in the evaporite thicknesses result from
synsedimentary subsidence (horst and graben structures in
combination with some strike-slip) as weIl as variations in
the sedimentation rates. The large depositional cycles are
superimposed by minor, sea-Ievel or tectonically controlled
cycles. Emerging platforms experienced karstification and
rapid meteoric diagenesis: Displaced shaIlow-water sediments (e.g. coated grains and packstones) formed locally
slope fans. In detail, the facies architecture of this basin is
very complicate and changes from location to location (see,
e.g., Füchtbauer and Peryt 1980; Smith 1980; Langbein
1987; Paul 1982, 1987; Peryt 1987a; Ziegler 1989;
Kiersnowski et al. 1995; Strohmenger et al. 1996a and b).
The Messinian evaporites below the Mediterranean. These late Miocene salt deposits were detected
and explored by deep-sea drilling and compared with
uplifted Messinian sections on land. The salts below
the Mediterranean represent two evaporite cycles and
generally reach thicknesses of several hundred meters,
in places 1000 to 2000 m. They cover an area of about
2.5 x 10 6 km 2 and lie on top of hemipelagic deepwater sediments which in turn accumulated, at least
(Stage 4) leads to rapid "deep-water" salt precipitation (mainly halite). Finally, large areas fall dry and
potash salts may accumulate in residual playa lakes
(Stage 5), before continental deposits take over. Note
that during all stages of development shelf carbonates and marginallagoonal and sabkha evaporites can
form. For further explanations see text. c Schematic
cross section of western Mediterranean Sea and
southern Spain displaying heterochronous evaporite
deposition in shallow coastal basins as compared to
the mid-Messinian deep-basin evaporites. 1,2,3
Stages of evolution. See text for further explanation.
(After Riding et al. 1998, modified)
(3) Onset of sea level fall. The salt concentration of the
inland sea begins to increase and first leads to stagnant, slightly hypersaline bottom waters in parts ofthe
basin (Fig. 6.9b). During such aperiod, black, bituminous shales or marls may be deposited. The accumulation of carbonate and gypsum in shallow waters continues. Due to continued falling sea level, the connection ofthe salt basin to the open seais interrupted (Fig.
6.9b).
(4) The water level in the closed basin is drawn down
by evaporation. Entering rivers start to incise valleys
into the emerging shelf and slope areas. Earlier formed
marginal carbonates and lagoonal and sabkha
evaporites are partially leached and their salts transported into the shrinking inland sea. During this phase,
i.e. still in rather deep water, the major part ofhalite is
rapidly precipitated from highly concentrated brine. It
may alternate with thin layers of anhydrite indicating
minor climatic variations including annual varves. In
marginal areas of the inland sea deposition of carbonates, lagoonal and sabkha evaporites continues at a
lower level or is replaced by continental beds (Fig.
6.9c). The main basin may become subdivided into
several subbasins (Fig. 6.9b) with differing salt concentrations and salt deposition.
(5) Finally, the basin may fall dry except for some
playa lakes containing highly concentrated brine including potash salts. Then the dry, huge salt flats are
more or less covered by thin continental beds and
some playas. Increased subsidence, driven by the additional salt load, tends to restore the situation to the one
at the beginning of this development. Dessication and
subsidence will persist until a further pronounced sealevel high again causes flooding of the inland depression and initiates a new cycle of evaporite deposition.
6.4.3 Examples of Giant Salt Deposits
The European Zechstein Basin. This basin experienced up to eight large depositional cycles including
some smaller ones at the end of its existence. Their
total thickness varies considerably from some tens of
meters in the marginal zones to more than 2000 m
(maximum thickness 3500 m, including Rotliegend
Fig. 6.9. Model of complex large evaporite basin on
continental or transitional crnst (Zechstein-type basin), demonstrating one major depositional cycle in
two stages of development. a Stage I (low to intermediate sea level). Inland drainage basin has subsided up to several hundred meters below mean sea
level. Stage 2. Particularly high sea level causes basin flooding and accumulation of sediments with normal marine fauna, basin-wide correlatable. Then salinity increases and evaporite deposition can begin.
b Stage 3. Lowering sea level restores land barrier
toward the open sea and creates large hypersaline
inland sea; evaporative drawdown of water level
Chapter 6 Special Depositional Environments
evaporites) in special troughs. The thicknesses of the
salt deposits of a single large cycle often reach several
hundred meters, but they also vary considerably from
marginal to central parts of the basin (Fig. 6.10). The
marginal facies zones include coastal sabkhas, tidal
flats with microbial mats, lagoons, progradational carbonate buildups (including ooid shoals, dolomite) with
their slope sediments. The wide carbonate slopes
formed mainly during lowstand and transgressive systems tracts, followed by sulfate deposition on the
slopes and platforms during the highstand systems
tract. Halite was precipitated in the central parts ofthe
basin when the margins were exposed and karstified.
Stromatolitic reefs grew on topographic highs. The
central basin may have been 100-300 m deep during
transgressions.
In the classical concept for the German Zechstein Basin, only
four large evaporite cycles were distinguished (e.g. RichterBernburg 1985). The famous "Kupferschiefer", a laminated
marI rich in trace metals, particularly copper, lead and zinc,
formed at the beginning of the first Zechstein evaporite cycle. It accumulated very slowly (5 mmlka) and is interpreted
as a condensed section (cf. Sect. 7.2).
The differences in the evaporite thicknesses result from
synsedimentary subsidence (horst and graben structures in
combination with some strike-slip) as weIl as variations in
the sedimentation rates. The large depositional cycles are
superimposed by minor, sea-Ievel or tectonically controlled
cycles. Emerging platforms experienced karstification and
rapid meteoric diagenesis: Displaced shaIlow-water sediments (e.g. coated grains and packstones) formed locally
slope fans. In detail, the facies architecture of this basin is
very complicate and changes from location to location (see,
e.g., Füchtbauer and Peryt 1980; Smith 1980; Langbein
1987; Paul 1982, 1987; Peryt 1987a; Ziegler 1989;
Kiersnowski et al. 1995; Strohmenger et al. 1996a and b).
The Messinian evaporites below the Mediterranean. These late Miocene salt deposits were detected
and explored by deep-sea drilling and compared with
uplifted Messinian sections on land. The salts below
the Mediterranean represent two evaporite cycles and
generally reach thicknesses of several hundred meters,
in places 1000 to 2000 m. They cover an area of about
2.5 x 10 6 km 2 and lie on top of hemipelagic deepwater sediments which in turn accumulated, at least
(Stage 4) leads to rapid "deep-water" salt precipitation (mainly halite). Finally, large areas fall dry and
potash salts may accumulate in residual playa lakes
(Stage 5), before continental deposits take over. Note
that during all stages of development shelf carbonates and marginallagoonal and sabkha evaporites can
form. For further explanations see text. c Schematic
cross section of western Mediterranean Sea and
southern Spain displaying heterochronous evaporite
deposition in shallow coastal basins as compared to
the mid-Messinian deep-basin evaporites. 1,2,3
Stages of evolution. See text for further explanation.
(After Riding et al. 1998, modified)