386
I. Gustavs
8.2
Effects on Pore Water Movement
On interpreting the pore-water movements predicted by the model, one should
consider that all diffusion effects within the sedimentary column and between
sediment and overlying water have been ignored. The reduction of the water-filled pore space induced by compaction causes an upward movement of
pore water in which older pore water rises into younger sedimentary layers and
displaces the younger pore fluids. This process leads to different burial velocities
of solid and liquid sediment components and to increasing distances of pore fluids to their source layers with burial. Assuming a complete water displacement,
finally, at the end of the process there will be complete separation of solids and
liquids.
Figure 8 outlines the extent of this effect for the sedimentary sequence of interest. The shade of the numbers marks the age of pore water (gray) and sedimentary layers (black). According to this scenario, one can expect differences of
up to 3000 years between the age of pore water and that of sediment particles.
Expressed in length units, this is equivalent to distances up to 2 m between pore
water and its source layer. One should keep this fact in mind when interpreting
pore-water analysis with respect to the accumulation environment of the apparent source layer.
9
Summary and Conclusions
It is our experience that the classical exponential compaction curve is not a good
model for the description of porosity decrease in near-surface muds. We have
been able to find that, for the Arkona Basin, integration of sedimentological factors into a pressure-based exponential model produces a satisfactory account of
measured porosity variations.
This new model was used for the reconstruction of initial porosities from sedimentological proxy data. The good coincidence of modeled and measured data
confirmed the high quality of the model and facilitated the generation of a dense
mesh of data points to be laid over the Arkona Basin. On this basis the lateral distribution of initial porosities could be approximated by a second-order trend
surface. Modeling a scenario of compaction effects on an idealized, homogeneous mud sequence showed significant differences between the rate of burial of
solids and pore fluid, caused by the compaction-driven, upward-directed movement of pore water.
Although the age boundaries of pore water are not sharp due to diffusion
processes, the estimated difference in age and distance between pore water and
source layer should be kept in mind when interpreting results of pore-water
analysis and relating them to the environmental conditions of sediment accumulation of the apparent source layer.
I. Gustavs
8.2
Effects on Pore Water Movement
On interpreting the pore-water movements predicted by the model, one should
consider that all diffusion effects within the sedimentary column and between
sediment and overlying water have been ignored. The reduction of the water-filled pore space induced by compaction causes an upward movement of
pore water in which older pore water rises into younger sedimentary layers and
displaces the younger pore fluids. This process leads to different burial velocities
of solid and liquid sediment components and to increasing distances of pore fluids to their source layers with burial. Assuming a complete water displacement,
finally, at the end of the process there will be complete separation of solids and
liquids.
Figure 8 outlines the extent of this effect for the sedimentary sequence of interest. The shade of the numbers marks the age of pore water (gray) and sedimentary layers (black). According to this scenario, one can expect differences of
up to 3000 years between the age of pore water and that of sediment particles.
Expressed in length units, this is equivalent to distances up to 2 m between pore
water and its source layer. One should keep this fact in mind when interpreting
pore-water analysis with respect to the accumulation environment of the apparent source layer.
9
Summary and Conclusions
It is our experience that the classical exponential compaction curve is not a good
model for the description of porosity decrease in near-surface muds. We have
been able to find that, for the Arkona Basin, integration of sedimentological factors into a pressure-based exponential model produces a satisfactory account of
measured porosity variations.
This new model was used for the reconstruction of initial porosities from sedimentological proxy data. The good coincidence of modeled and measured data
confirmed the high quality of the model and facilitated the generation of a dense
mesh of data points to be laid over the Arkona Basin. On this basis the lateral distribution of initial porosities could be approximated by a second-order trend
surface. Modeling a scenario of compaction effects on an idealized, homogeneous mud sequence showed significant differences between the rate of burial of
solids and pore fluid, caused by the compaction-driven, upward-directed movement of pore water.
Although the age boundaries of pore water are not sharp due to diffusion
processes, the estimated difference in age and distance between pore water and
source layer should be kept in mind when interpreting results of pore-water
analysis and relating them to the environmental conditions of sediment accumulation of the apparent source layer.