High-Resolution Forward Stratigraphic Modeling of Ca2-Carbonate Platforms ...
319
ea, and less than 5 cm/ka for the periplatform realm (Fig. 3). Compared to the
northwest German setting, the main reasons for these lower production rates
seem to be unfavourable energy conditions (generally higher water energy,
which leads to reworking and resedimentation of unconsolidated sediments)
and the rate and spatial distribution of tectonic subsidence.
Evaporites occur commonly in Upper Permian sediments and a reasonable
simulation of Ca2 sediments cannot be done without taking into account the existence of anhydrites below and above Ca2 strata. Within PHIL 5.1 the sedimentation rate of evaporites is a function of water depth, which is determined from
the user-defined maximum evaporation rate, the duration of the simulated time
step and the water column thickness (Marco Polo Software 1994). In the program, the deposition of evaporites is restricted to areas deeper than the upper
tidal range. The evaporite options implemented in PHIL 5.1 are not tenable to
simulate pure evaporite formations like the Werra Anhydrite (AI). Furthermore,
the Al lacks data necessary for reasonable modeling. However, simulations of
the Ca2 show that the change from Ca2 carbonates to evaporites of the overlying
Basal Anhydrite (A2) and mixed carbonate-evaporite successions, mostly of
short-term durations, can be modeled. Using estimated evaporite production
rates between 15 cm/ka and 120 cm/ka during the simulated time span (early
TST of Zechstein sequence ZS3 to early HST of Zechstein sequence ZS4), simulation results do not show any sedimentation of evaporites until the TST of Zechstein sequence ZS4 (Figs. 19,27). This fits very well to Ca2 core observations in
both of the studied areas. Varying the model's input parameters suggests that the
amplitude and frequency of the relative sea-level fluctuations is an important
factor in the production and sedimentation of evaporites, especially during the
LST and TST of Zechstein sequence ZS4. Once deposited, even thin evaporite
layers often change inclination angles of mainly shallow-water areas due to their
rapid sedimentation.
In addition, to quantify the above-mentioned parameters, high-resolution
stratigraphic modeling requires a fixing of adequate time increments for carbonate production calculations (carbonate production time step). Because setting a large time step will not record short-term influences and their effects on
carbonate production, and is not able to explain the development of the geometry of a carbonate body sufficiently, a time step of 5 ka was chosen for calculation
of carbonate production during Ca2 time in both areas.
Sedimentation is commonly ruled by more parameters than those mentioned
above and PHIL 5.1 contains many additional options to define and quantify
sedimentary processes adequately. Variables like lithospheric flexure loading,
gradients of depositional profiles, gravity flow and erosion rates and evaporation rates were also quantified in the study, but it would go far beyond the scope
of this chapter to demonstrate their estimation and impact on Ca2 sedimentation.
319
ea, and less than 5 cm/ka for the periplatform realm (Fig. 3). Compared to the
northwest German setting, the main reasons for these lower production rates
seem to be unfavourable energy conditions (generally higher water energy,
which leads to reworking and resedimentation of unconsolidated sediments)
and the rate and spatial distribution of tectonic subsidence.
Evaporites occur commonly in Upper Permian sediments and a reasonable
simulation of Ca2 sediments cannot be done without taking into account the existence of anhydrites below and above Ca2 strata. Within PHIL 5.1 the sedimentation rate of evaporites is a function of water depth, which is determined from
the user-defined maximum evaporation rate, the duration of the simulated time
step and the water column thickness (Marco Polo Software 1994). In the program, the deposition of evaporites is restricted to areas deeper than the upper
tidal range. The evaporite options implemented in PHIL 5.1 are not tenable to
simulate pure evaporite formations like the Werra Anhydrite (AI). Furthermore,
the Al lacks data necessary for reasonable modeling. However, simulations of
the Ca2 show that the change from Ca2 carbonates to evaporites of the overlying
Basal Anhydrite (A2) and mixed carbonate-evaporite successions, mostly of
short-term durations, can be modeled. Using estimated evaporite production
rates between 15 cm/ka and 120 cm/ka during the simulated time span (early
TST of Zechstein sequence ZS3 to early HST of Zechstein sequence ZS4), simulation results do not show any sedimentation of evaporites until the TST of Zechstein sequence ZS4 (Figs. 19,27). This fits very well to Ca2 core observations in
both of the studied areas. Varying the model's input parameters suggests that the
amplitude and frequency of the relative sea-level fluctuations is an important
factor in the production and sedimentation of evaporites, especially during the
LST and TST of Zechstein sequence ZS4. Once deposited, even thin evaporite
layers often change inclination angles of mainly shallow-water areas due to their
rapid sedimentation.
In addition, to quantify the above-mentioned parameters, high-resolution
stratigraphic modeling requires a fixing of adequate time increments for carbonate production calculations (carbonate production time step). Because setting a large time step will not record short-term influences and their effects on
carbonate production, and is not able to explain the development of the geometry of a carbonate body sufficiently, a time step of 5 ka was chosen for calculation
of carbonate production during Ca2 time in both areas.
Sedimentation is commonly ruled by more parameters than those mentioned
above and PHIL 5.1 contains many additional options to define and quantify
sedimentary processes adequately. Variables like lithospheric flexure loading,
gradients of depositional profiles, gravity flow and erosion rates and evaporation rates were also quantified in the study, but it would go far beyond the scope
of this chapter to demonstrate their estimation and impact on Ca2 sedimentation.