11.1 Introduction
more or less independent factors (cf. Chaps. 7 and 9),
including:
- Size and denudation characteristics (specific sediment yield) of land areas delivering terrigenous sediments.
- Areal extent and geometry of the corresponding
basin receiving sediment.
- Biogenic sediment production in the basin itself.
- Tectonic and total subsidence ofbasin floor as well
as compaction of sediments.
- Distribution of sediments in relation to the hydraulic regime ofthe water-filled basin or, on land, ofthe
river system crossing and feeding the basin with sediment.
- Relative sea-level or base-level changes and their
frequencies and amplitudes.
U sing these parameters and taking into account their
interrelationships, other, dependent variables may be
derived, such as:
- Grain size distribution and lateral and vertical sedimentary facies successions within the basin, dependent, e.g., on water depth.
- Sedimentation rates at different locations within the
basin (e.g. exponentially declining seaward).
- Occurrence and extent of carbonate buildups, etc.
These and other points have been intensely discussed
recently in numerous articles and some special volumes dealing with computer simulations of sedimentary basins and their application in different fields of
earth science, mainly in the oil industry. A thorough
treatment of this complex topic is beyond the intention of this book, but it rnay be useful to discuss
briefly some general principles related to basin modeling. After that, some simple basin-filling models
are presented in which variations in terrestrial sediment supply are emphasized.
General Remarks to Basin-Filling Models
Basin-filling models or "quantitative dynamic stratigraphy" (Cross 1990) are a means of generalizing
complex systems and of exploring the effects of
varying parameters (Angevine et al. 1990). Basinfilling models can be subdivided into two groups:
(1) Geometric models characterize basins which have
a constant surface geometry, for example a fluvial
basin which subsides but is filled with sediments all
the time. In this case, sedimentation rate and subsidence are in balance and rnaintain an equilibrium.
Similarly, a coastal plain and the adjacent foreshore
zone rnay maintain a fixed slope which is restored all
the time, regardless of sea level fluctuations andlor
481
differential subsidence. Such models are relatively
simple to construct. These models are not identical
with the steady-state models introduced below in
which sediment supply is kept constant.
(2) Dynarnic models take into account sediment
transport and the rate of deposition. Both tend to
change laterally, i.e., downstream along rivers, or
from the coastline toward the center of a basin. As a
result, the geometry of the sedimentary surface rnay
undergo significant modification with time. The basic concept of this approach is founded on the fact
that the factors mentioned above and additional relevant processes can be subdivided into two groups
(Lawrence et al. 1990; cf. also Sect. 7.2):
- Processes controlling the creation and destruction
of space in a basin.
- Processes controlling the introduction and removal
of sediment.
For a given rate of space creation, the volume of sediment introduced into the basin controls how far the
sediments pro grade seaward. If clastic sediment
sources can be neglected, in situ biogenic sediment
production is the principal factor interacting with
space-creating processes (cf. Sect. 7.5). Most of the
factors mentioned above are subjected to changes not
only spatially (landward-seaward) but also during the
evolution of a basin. The characteristics of the source
area on land, the size and geometry of the basin, and
processes within the basin may vary substantially
with time. Such an evolution is referred to as "basin
dynamics".
Forward numerical simulation of carbonate buildups, for
example, is only possible under the assumption that empirical growth rates at different locations within a basin can be
used (e.g. Aigner et al. 1989). In addition, lateral
prograding of these buildups and their reactions to minor
fluctuations of sea level have to be taken into account.
Various working groups are trying to simulate the evolution of sedimentary basins with the aid of computers
(e.g., Strobel et al. 1989; Cross 1990; Lawrence et al.
1990; Hermanrud 1993; Weite et al. 1997; and others).
This forward modeling is commonly carried out in two dimensions along transects and requires both a large data set
and special training.
So far, most of the published computer models have
been devised to produce two-dimensional cross-sections.
Common examples are cross-sections of rift basins and
passive continental margins. These models are normally
based on both theoretical and empirical algorithms for the
creating and filling of accommodation space within the
basin.
The most important objectives ofthe models are simulations of (1) the stratigraphic architecture including
the influence of relative sea-level changes, (2) the
thermal history of the basin fill, and (3) fluid flow
within the basin including hydrocarbon generation
more or less independent factors (cf. Chaps. 7 and 9),
including:
- Size and denudation characteristics (specific sediment yield) of land areas delivering terrigenous sediments.
- Areal extent and geometry of the corresponding
basin receiving sediment.
- Biogenic sediment production in the basin itself.
- Tectonic and total subsidence ofbasin floor as well
as compaction of sediments.
- Distribution of sediments in relation to the hydraulic regime ofthe water-filled basin or, on land, ofthe
river system crossing and feeding the basin with sediment.
- Relative sea-level or base-level changes and their
frequencies and amplitudes.
U sing these parameters and taking into account their
interrelationships, other, dependent variables may be
derived, such as:
- Grain size distribution and lateral and vertical sedimentary facies successions within the basin, dependent, e.g., on water depth.
- Sedimentation rates at different locations within the
basin (e.g. exponentially declining seaward).
- Occurrence and extent of carbonate buildups, etc.
These and other points have been intensely discussed
recently in numerous articles and some special volumes dealing with computer simulations of sedimentary basins and their application in different fields of
earth science, mainly in the oil industry. A thorough
treatment of this complex topic is beyond the intention of this book, but it rnay be useful to discuss
briefly some general principles related to basin modeling. After that, some simple basin-filling models
are presented in which variations in terrestrial sediment supply are emphasized.
General Remarks to Basin-Filling Models
Basin-filling models or "quantitative dynamic stratigraphy" (Cross 1990) are a means of generalizing
complex systems and of exploring the effects of
varying parameters (Angevine et al. 1990). Basinfilling models can be subdivided into two groups:
(1) Geometric models characterize basins which have
a constant surface geometry, for example a fluvial
basin which subsides but is filled with sediments all
the time. In this case, sedimentation rate and subsidence are in balance and rnaintain an equilibrium.
Similarly, a coastal plain and the adjacent foreshore
zone rnay maintain a fixed slope which is restored all
the time, regardless of sea level fluctuations andlor
481
differential subsidence. Such models are relatively
simple to construct. These models are not identical
with the steady-state models introduced below in
which sediment supply is kept constant.
(2) Dynarnic models take into account sediment
transport and the rate of deposition. Both tend to
change laterally, i.e., downstream along rivers, or
from the coastline toward the center of a basin. As a
result, the geometry of the sedimentary surface rnay
undergo significant modification with time. The basic concept of this approach is founded on the fact
that the factors mentioned above and additional relevant processes can be subdivided into two groups
(Lawrence et al. 1990; cf. also Sect. 7.2):
- Processes controlling the creation and destruction
of space in a basin.
- Processes controlling the introduction and removal
of sediment.
For a given rate of space creation, the volume of sediment introduced into the basin controls how far the
sediments pro grade seaward. If clastic sediment
sources can be neglected, in situ biogenic sediment
production is the principal factor interacting with
space-creating processes (cf. Sect. 7.5). Most of the
factors mentioned above are subjected to changes not
only spatially (landward-seaward) but also during the
evolution of a basin. The characteristics of the source
area on land, the size and geometry of the basin, and
processes within the basin may vary substantially
with time. Such an evolution is referred to as "basin
dynamics".
Forward numerical simulation of carbonate buildups, for
example, is only possible under the assumption that empirical growth rates at different locations within a basin can be
used (e.g. Aigner et al. 1989). In addition, lateral
prograding of these buildups and their reactions to minor
fluctuations of sea level have to be taken into account.
Various working groups are trying to simulate the evolution of sedimentary basins with the aid of computers
(e.g., Strobel et al. 1989; Cross 1990; Lawrence et al.
1990; Hermanrud 1993; Weite et al. 1997; and others).
This forward modeling is commonly carried out in two dimensions along transects and requires both a large data set
and special training.
So far, most of the published computer models have
been devised to produce two-dimensional cross-sections.
Common examples are cross-sections of rift basins and
passive continental margins. These models are normally
based on both theoretical and empirical algorithms for the
creating and filling of accommodation space within the
basin.
The most important objectives ofthe models are simulations of (1) the stratigraphic architecture including
the influence of relative sea-level changes, (2) the
thermal history of the basin fill, and (3) fluid flow
within the basin including hydrocarbon generation