High-Resolution Forward Stratigraphic Modeling of Ca2-Carbonate Platforms ...
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relief types (Zl/ AI-thickness about 300 m) and low-relief types (Zl! Al thickness about 200 m, Strohmenger et al. 1993c, 1996b). As core investigations and
simulation results show, the low-relief off-platform highs were flooded during
Ca2 transgressive systems tract (TST), and subsequently drowned during Ca2
maximum flooding (condensed section representing Ca2 highstand systems
tract deposits). In contrast, the high-relief off-platform highs and the platform
in the Southeast Brandenburg area, like the Northwest German platform, were
flooded only during Ca2 maximum flooding, and record sedimentation
throughout Ca2 highstand systems tract (HST). This allows a comparison of
sedimentary processes and developments of both areas.
Core studies show that Ca2 facies development is driven by the thickness distribution of the underlying AI. The Ca2 platform facies is restricted to the Al
platform area and simulation shows that a progradation of Ca2 facies (Ca2 highstand systems tract) first happened after 400 ka of Ca2 time (Ca2 maxium flooding surface, Figs. 15,23). This point in Ca2 time marks when the slope sediment
accumulation rate exceeds that of the platform. One of the main reasons for this
relatively long timespan with nearly no progradation (Ca2 transgressive systems
tract) seems to be the slope of the Al platform, which ranges from 2° to probably
more than 10°. As simulation results show, these slopes may have prevented autochthonous deposition of Ca2 transgressive systems tract deposits along the
upper AI-slope, but resulted in the redeposition of these sediments at deeper
slope positions. Additionally, the water chemistry in this restricted Southern
Zechstein Basin was characterized by a high content of sulfate ions, at least at the
end of A 1 time and the beginning of Ca2 time. Therefore, carbonate production
rates may have been low during early Ca2 time. Furthermore, the water body
likely was stratified at the transition time between Al and Ca2. This would allow
different mineralogies and production rates depending on the depth of the water
column. Decreased sediment production in basinal position (starved basin) may
also lead to decreasing progradation (Harris,1989).
2.2
Ca2 depositional model (Figs. 4,7)
Detailed examination of vertical platform facies successions shows, that these
sediments are generally comprised of two major shallowing upward cycles (Ca2cycle II and III, Fig. 4) and four sub cycles or parasequences (PS 4-7). The higher-order cycles represent the Ca2 highstand systems tract and are characterized
by a transition from high-energy (representing coated-grain facies or ooid
facies) at the base of the subcycle to low-energy algal-laminated facies and tidal
flat facies at the uppermost parts of the subcycle. These four sub cycles are
thought to be the result of higher-order sea-level fluctuations and therefore are
called parasequences (Strohmenger et al.1996a; Strohmenger and Strauss 1996).
The preservation of four parasequences on the Ca2-platform gives valuable information about eustatic sea-level fluctuations, their amplitudes, and impacts
on sedimentation_ Because these parasequences are short-term phenomena,
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relief types (Zl/ AI-thickness about 300 m) and low-relief types (Zl! Al thickness about 200 m, Strohmenger et al. 1993c, 1996b). As core investigations and
simulation results show, the low-relief off-platform highs were flooded during
Ca2 transgressive systems tract (TST), and subsequently drowned during Ca2
maximum flooding (condensed section representing Ca2 highstand systems
tract deposits). In contrast, the high-relief off-platform highs and the platform
in the Southeast Brandenburg area, like the Northwest German platform, were
flooded only during Ca2 maximum flooding, and record sedimentation
throughout Ca2 highstand systems tract (HST). This allows a comparison of
sedimentary processes and developments of both areas.
Core studies show that Ca2 facies development is driven by the thickness distribution of the underlying AI. The Ca2 platform facies is restricted to the Al
platform area and simulation shows that a progradation of Ca2 facies (Ca2 highstand systems tract) first happened after 400 ka of Ca2 time (Ca2 maxium flooding surface, Figs. 15,23). This point in Ca2 time marks when the slope sediment
accumulation rate exceeds that of the platform. One of the main reasons for this
relatively long timespan with nearly no progradation (Ca2 transgressive systems
tract) seems to be the slope of the Al platform, which ranges from 2° to probably
more than 10°. As simulation results show, these slopes may have prevented autochthonous deposition of Ca2 transgressive systems tract deposits along the
upper AI-slope, but resulted in the redeposition of these sediments at deeper
slope positions. Additionally, the water chemistry in this restricted Southern
Zechstein Basin was characterized by a high content of sulfate ions, at least at the
end of A 1 time and the beginning of Ca2 time. Therefore, carbonate production
rates may have been low during early Ca2 time. Furthermore, the water body
likely was stratified at the transition time between Al and Ca2. This would allow
different mineralogies and production rates depending on the depth of the water
column. Decreased sediment production in basinal position (starved basin) may
also lead to decreasing progradation (Harris,1989).
2.2
Ca2 depositional model (Figs. 4,7)
Detailed examination of vertical platform facies successions shows, that these
sediments are generally comprised of two major shallowing upward cycles (Ca2cycle II and III, Fig. 4) and four sub cycles or parasequences (PS 4-7). The higher-order cycles represent the Ca2 highstand systems tract and are characterized
by a transition from high-energy (representing coated-grain facies or ooid
facies) at the base of the subcycle to low-energy algal-laminated facies and tidal
flat facies at the uppermost parts of the subcycle. These four sub cycles are
thought to be the result of higher-order sea-level fluctuations and therefore are
called parasequences (Strohmenger et al.1996a; Strohmenger and Strauss 1996).
The preservation of four parasequences on the Ca2-platform gives valuable information about eustatic sea-level fluctuations, their amplitudes, and impacts
on sedimentation_ Because these parasequences are short-term phenomena,