High-Resolution Forward Stratigraphic Modeling of Ca2-Carbonate Platforms ...
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types. In platform position, typical facies successions in cores of both study areas show transitions from karstified Al anhydrites to high-energy carbonates,
indicating transgressive deposits with carbonate and anhydrite clasts overlain
by shallow-subtidal or intertidal facies.
In contrast to the eastern German setting, the northwest German sea level
shows a rapid and more significant rise at the beginning of PS3. The shallow-water
carbonates of the preceding parasequence are reworked during this initial transgression. Due to moderate subsidence rates, the following sea-level fall is of small
magnitude and initiates the reworking of main parts of the PS3 shallow-water carbonates. At the end of PS3 sea level rises again and, with flooding of the karstified
top of the Al platform, the mfs of Zechstein sequence ZS3 is established.
4.2
Parasequences 4-7 (PS4-PS7; Figs. 16, 17, 24,25)
According to simulation results, parasequences 4-7 are generated during a time
period of about 600 ka. They represent the highstand systems tract (HST) of
Zechstein sequence ZS3 and their platform sediments form the main reservoir
rocks within the Ca2. The impact of two fourth-order cycles causes two main
shallowing-upward trends (Ca2 cycle II and Ca2 cycle III). The first two parasequences preserved in platform position are PS4 (Ca2 cycle IIa) and PS5 (Ca2 cycle lIb). The simulation of the East German high-relief off-platform highs shows
that the first notable aggradation on top of the affected off-platform highs occurs
during PS4, after the establishment of the mfs. The regressive phase of sea level
during PS4 is characterized by a smooth shape and quite short duration, which
leads to the generation of only thin intertidal successions on top of PS4. Although the fifth parasequence (PS5) during Ca2 high-stand systems tract begins
with a short-term and smooth transgressive stage, the following sea level fall has
a considerable impact on sedimentation and results in an erosional surface at the
end of PS5. The main reason for this drop in sea level is the coincidence of regression phases of both fourth and fifth order. Starting with PS6 (Ca2 cycle lIla)
the fourth and fifth orders coincide in their transgressive stages, leading to a
long-term sea level rise during which the briefly exposed platform sediments are
flooded again. Due to this sea level rise, PS6 consists mostly of thick, grain-dominated shallow-subtidal sediments generated during a catchup phase of sedimentation. Although accumulation accelerates in this situation and results in
aggradation of several meters up to several tens of meters, the progradation rate
remains low, mainly because of unfavorable current conditions. This process
continues for the remainder of Zechstein sequence ZS3-time (upper part of PS6
and the entire PS7). Therefore, in most areas on top of the high-relief off-platform highs, sedimentation no longer outpaces sea level during the highstand
systems tract of Zechstein sequence ZS3. The occurrence of a type-l sequence
boundary (Zechstein sequence boundary ZSB4) on top of PS7 marks the end of
the highstand systems tract of Zechstein sequence ZS3 and introduces Zechstein
sequence ZS4 with a major drop in sea level (Figs.lO, 11).
327
types. In platform position, typical facies successions in cores of both study areas show transitions from karstified Al anhydrites to high-energy carbonates,
indicating transgressive deposits with carbonate and anhydrite clasts overlain
by shallow-subtidal or intertidal facies.
In contrast to the eastern German setting, the northwest German sea level
shows a rapid and more significant rise at the beginning of PS3. The shallow-water
carbonates of the preceding parasequence are reworked during this initial transgression. Due to moderate subsidence rates, the following sea-level fall is of small
magnitude and initiates the reworking of main parts of the PS3 shallow-water carbonates. At the end of PS3 sea level rises again and, with flooding of the karstified
top of the Al platform, the mfs of Zechstein sequence ZS3 is established.
4.2
Parasequences 4-7 (PS4-PS7; Figs. 16, 17, 24,25)
According to simulation results, parasequences 4-7 are generated during a time
period of about 600 ka. They represent the highstand systems tract (HST) of
Zechstein sequence ZS3 and their platform sediments form the main reservoir
rocks within the Ca2. The impact of two fourth-order cycles causes two main
shallowing-upward trends (Ca2 cycle II and Ca2 cycle III). The first two parasequences preserved in platform position are PS4 (Ca2 cycle IIa) and PS5 (Ca2 cycle lIb). The simulation of the East German high-relief off-platform highs shows
that the first notable aggradation on top of the affected off-platform highs occurs
during PS4, after the establishment of the mfs. The regressive phase of sea level
during PS4 is characterized by a smooth shape and quite short duration, which
leads to the generation of only thin intertidal successions on top of PS4. Although the fifth parasequence (PS5) during Ca2 high-stand systems tract begins
with a short-term and smooth transgressive stage, the following sea level fall has
a considerable impact on sedimentation and results in an erosional surface at the
end of PS5. The main reason for this drop in sea level is the coincidence of regression phases of both fourth and fifth order. Starting with PS6 (Ca2 cycle lIla)
the fourth and fifth orders coincide in their transgressive stages, leading to a
long-term sea level rise during which the briefly exposed platform sediments are
flooded again. Due to this sea level rise, PS6 consists mostly of thick, grain-dominated shallow-subtidal sediments generated during a catchup phase of sedimentation. Although accumulation accelerates in this situation and results in
aggradation of several meters up to several tens of meters, the progradation rate
remains low, mainly because of unfavorable current conditions. This process
continues for the remainder of Zechstein sequence ZS3-time (upper part of PS6
and the entire PS7). Therefore, in most areas on top of the high-relief off-platform highs, sedimentation no longer outpaces sea level during the highstand
systems tract of Zechstein sequence ZS3. The occurrence of a type-l sequence
boundary (Zechstein sequence boundary ZSB4) on top of PS7 marks the end of
the highstand systems tract of Zechstein sequence ZS3 and introduces Zechstein
sequence ZS4 with a major drop in sea level (Figs.lO, 11).