High-Resolution Forward Stratigraphic Modeling of Ca2-Carbonate Platforms ...
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taining reworked intraclasts (Fig. SB). This erosive contact at the base of the
LSW also can be recognized in cores, and is even more obvious in a more platformward position because facies change from upper slope mudstones to intertidal sediments (tidal flat or algal tidal flat; Fig. SA).
As suggested by Strohmenger et al. (l996a), the slow sea-level rise during the
late LST also causes a gradual but important diagenetic change in previously unaffected landward sediments on the Ca2 platform (Fig. 9). Due to an inferred
change in water chemistry during the late LST, the uppermost layers of the Ca2highstand carbonates are nearly completely altered to anhydrites of sabkha type
(alterations of anhydrite and dolomite). This suggests that the sabkha-type anhydrites and the upper parts of the Ca2-LSW carbonates are synchronously generated, and their formation mainly depends on their paleotopographic position.
4.4
Parasequence Ca2/A2-3 (Figs. 19,27)
The rise in sea level continues through the third parasequence of Zechstein sequence ZS4. This parasequence belongs to the second Ca2/ A2-cycle and generates the uppermost part of the Ca2 lowstand wedge, which is bound by the Ca2
transgressive surface (TS) of Zechstein sequence ZS4. This marine-flooding surface marks the end of Ca2 time and is overlain by the first sedimentary anhydrites (salina-type anhydrites) of the A2 (Basal Anhydrite, Fig. 9). The simulation ends in the late stages of parasequence Ca2/ A2-3 and shows only the first
70 ka of A2 sedimentation.
In both Northwest Germany and eastern Germany, the transgressive surface
TS of Zechstein sequence ZS4 (Figs. IS, 26) marks the change from carbonate to
evaporitic sedimentation (salina-type anhydrites; Fig. 9). A main reason for this
change in mineralogy is thought to be a change in water chemistry. Given the
reconstructed sea level, the formation of main parts of the A2 and the entire overlying Na2 salt takes place during the regressive stage of a third-order sea level cycle superimposed on the regressive trend of the second-order cycle. Consequently, this leads to a general lack of freshwater input into the Southern Permian Basin
and favors the deposition of evaporites. In addition, a very slow, but long-term,
sea level rise might also support evaporitic sedimentation. This is reflected in the
simulation, because the initial formation of anhydrites at the beginning of A2
time relates to a very slow sea-level rise during the first stages of Ca2/ A2 cycle IIa.
In Northwest Germany, the basinward parts of the Ca2 platform affected by
LST sedimentation experienced no diagenetic changes during the late LST, and
therefore show a transition from mostly intertidal Ca2 carbonates to anhydrites
of salina type (pure anhydrites). In contrast, those parts of the Ca2 platform affected by diagenetic changes during the late LST show a transition from Ca2 sabkha-type anhydrites to salina-type anhydrites of early A2 (Fig. 9). The eastern
German high-relief off-platform highs, which are generally affected by higher
subsidence rates, do not show excessive alterations of Ca2 strata during the sealevel rise at the end of the LST of Zechstein sequence ZS4. The transition in these
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taining reworked intraclasts (Fig. SB). This erosive contact at the base of the
LSW also can be recognized in cores, and is even more obvious in a more platformward position because facies change from upper slope mudstones to intertidal sediments (tidal flat or algal tidal flat; Fig. SA).
As suggested by Strohmenger et al. (l996a), the slow sea-level rise during the
late LST also causes a gradual but important diagenetic change in previously unaffected landward sediments on the Ca2 platform (Fig. 9). Due to an inferred
change in water chemistry during the late LST, the uppermost layers of the Ca2highstand carbonates are nearly completely altered to anhydrites of sabkha type
(alterations of anhydrite and dolomite). This suggests that the sabkha-type anhydrites and the upper parts of the Ca2-LSW carbonates are synchronously generated, and their formation mainly depends on their paleotopographic position.
4.4
Parasequence Ca2/A2-3 (Figs. 19,27)
The rise in sea level continues through the third parasequence of Zechstein sequence ZS4. This parasequence belongs to the second Ca2/ A2-cycle and generates the uppermost part of the Ca2 lowstand wedge, which is bound by the Ca2
transgressive surface (TS) of Zechstein sequence ZS4. This marine-flooding surface marks the end of Ca2 time and is overlain by the first sedimentary anhydrites (salina-type anhydrites) of the A2 (Basal Anhydrite, Fig. 9). The simulation ends in the late stages of parasequence Ca2/ A2-3 and shows only the first
70 ka of A2 sedimentation.
In both Northwest Germany and eastern Germany, the transgressive surface
TS of Zechstein sequence ZS4 (Figs. IS, 26) marks the change from carbonate to
evaporitic sedimentation (salina-type anhydrites; Fig. 9). A main reason for this
change in mineralogy is thought to be a change in water chemistry. Given the
reconstructed sea level, the formation of main parts of the A2 and the entire overlying Na2 salt takes place during the regressive stage of a third-order sea level cycle superimposed on the regressive trend of the second-order cycle. Consequently, this leads to a general lack of freshwater input into the Southern Permian Basin
and favors the deposition of evaporites. In addition, a very slow, but long-term,
sea level rise might also support evaporitic sedimentation. This is reflected in the
simulation, because the initial formation of anhydrites at the beginning of A2
time relates to a very slow sea-level rise during the first stages of Ca2/ A2 cycle IIa.
In Northwest Germany, the basinward parts of the Ca2 platform affected by
LST sedimentation experienced no diagenetic changes during the late LST, and
therefore show a transition from mostly intertidal Ca2 carbonates to anhydrites
of salina type (pure anhydrites). In contrast, those parts of the Ca2 platform affected by diagenetic changes during the late LST show a transition from Ca2 sabkha-type anhydrites to salina-type anhydrites of early A2 (Fig. 9). The eastern
German high-relief off-platform highs, which are generally affected by higher
subsidence rates, do not show excessive alterations of Ca2 strata during the sealevel rise at the end of the LST of Zechstein sequence ZS4. The transition in these