482
and accumulation (e.g. Hennunrud 1993). It is evident that such models are becoming increasingly important in hydrocarbon exploration, i.e. in predicting
the occurrence and distribution of source rocks, reservoirs, and seals in limited areas. With the aid of
simulations, based on a limited number of data and
assumptions, gaps in the existing data set can be partially closed, although there is no guarantee that the
simulation is either correct or unique (e.g. Levell and
Leu 1993). On the other hand, such models also have
a high educational value. They help to better understand the theoretical background of basin evolution
and to find out the influence of certain parameters on
basin filling and its stratigraphical architecture.
The Elementary Approach in This Book
The approach in the following Sections is generally
more elementary than the above mentioned computer
models. It takes into account part of the variables
listed above with emphasis on empirically determined data and can be done with small pocket calculators. Whereas most ofthe published computer models deal, for example, with the dynamic evolution and
stratigraphic architecture of specific regions within a
basin, the generalized models described below are
not "dynamic" in the same sense. They actually represent entire basin systems, often including the
source area of terrigenous sediments. They may
therefore be regarded as models of denudation-sediment accumulation systems which differ in some aspects of the geometric and dynamic models mentioned above. I distinguish between:
- Steady-state systems. The areas of both the
terrigenous sediment source and the receiving basin
as weIl as the rates of denudation (sediment influx)
and subsidence (unifonn over the entire basin) are
kept constant. This type of model is useful for relatively short-period evaluations which are undertaken
to clarify, for example, the relationship between the
mean rates of denudation and sedimentation.
- Dynamic systems. One or several of the basin parameters vary with time. (a) The rates of denudation
(sediment influx) and subsidence change, while the
areas of both sediment source and basin remain constant throughout the time considered. (b) Either the
basin area or both the basin area and source area and
thus also the sediment influx and sedimentation rate
change with time. These models cover long time periods and describe various degrees ofbasin filling.
In all cases, only mean rates of denudation, subsidence and sedimentation for the entire drainage and
basin areas are considered (apart from Sect. 11.5).
The effects of sea-level or base-level changes are
neglected here (cf. Chap. 7). The data used in the
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
model calculations are adjusted to those found in
nature for regions of similar characteristics. Several
case studies supplement the results of the models.
Inspite of the various generalizations, this exercise
may serve as an introduction to more sophisticated
basin simulations with the aid of computer programs.
11.2 Denudation-Sediment
Accumulation (DA) Systems
11.2.1 General Concept
The method, evaluating denudation-sediment accumulation systems (in short: DA systems) as an interrelated unit, is based on the mass balance of
terrigenous sediment eroded in the source area and
accumulated in adjacent closed or semi-closed basins. In other words, the denudation area on land and
the depositional basin constitute a closed erosiondepositional system (e.g. Hay et al. 1989; Leeder
1991 and 1997; Einseie and Hinderer 1998). Denudation in the source area, although varying from 10cality to locality, can be expressed in terms of masses
of mechanical and chemical denudation, M me and M cb
(Fig. l1.1a). It is assumed that no sediment is intermittently stored or reworked along the way from the
source to the basin (delivery ratio = 1). M me provides
terrigenous material which can be entirely trapped in
the depositional area (trap efficiency· TE=100%,
sedimentologically closed basin). The situation is
different for M cb ' In hydrologically open systems part
of it (mainly MbJ is used to produce biogenic sediment, the remainder is lost to neighboring basins or
the open sea. In closed systems part of M cb can fonn
evaporites (Mev)'
The masses of solid and dissolved material can be
converted into specific yields (SY, mass per unit area
and time, e.g. in metric tonsIkm 2 /a, cf. Sect. 9.2 and
9.3) or rates of denudation, D~e and DR.,b' and rates
of mechanical, biogenic, and evaporitic sedimentation, S~e' SRbj, SR.v or SR.,b (m 3 /km 2 /a or mmIka or
mlMa). All these tenns describe mean values under
the assumption that the masses of mechanical and
chemical denudation and deposition are distributed
evenly over the total drainage and basin areas. In addition, mean rock densities and sediment densities
have to be known to detennine (linear) denudation
and sedimentation rates (for conversion factors see
Fig. 11.1 b). A method to detennine the volume of
compact (pore-free) sediment from isopach maps is
explained in Section 11.3.6 (Gulf of Califomia).
The principal premise of this approach is that the
mass of terrigenous sediment accumulating in the
basin per time unit is equal to the mass of material
eroded mechanically in the drainage basin. This
premise also applies to open basins with sills at their
outflow or to deep-sea fans of known extent. Then
theofollowing calculations can be carried out:
and accumulation (e.g. Hennunrud 1993). It is evident that such models are becoming increasingly important in hydrocarbon exploration, i.e. in predicting
the occurrence and distribution of source rocks, reservoirs, and seals in limited areas. With the aid of
simulations, based on a limited number of data and
assumptions, gaps in the existing data set can be partially closed, although there is no guarantee that the
simulation is either correct or unique (e.g. Levell and
Leu 1993). On the other hand, such models also have
a high educational value. They help to better understand the theoretical background of basin evolution
and to find out the influence of certain parameters on
basin filling and its stratigraphical architecture.
The Elementary Approach in This Book
The approach in the following Sections is generally
more elementary than the above mentioned computer
models. It takes into account part of the variables
listed above with emphasis on empirically determined data and can be done with small pocket calculators. Whereas most ofthe published computer models deal, for example, with the dynamic evolution and
stratigraphic architecture of specific regions within a
basin, the generalized models described below are
not "dynamic" in the same sense. They actually represent entire basin systems, often including the
source area of terrigenous sediments. They may
therefore be regarded as models of denudation-sediment accumulation systems which differ in some aspects of the geometric and dynamic models mentioned above. I distinguish between:
- Steady-state systems. The areas of both the
terrigenous sediment source and the receiving basin
as weIl as the rates of denudation (sediment influx)
and subsidence (unifonn over the entire basin) are
kept constant. This type of model is useful for relatively short-period evaluations which are undertaken
to clarify, for example, the relationship between the
mean rates of denudation and sedimentation.
- Dynamic systems. One or several of the basin parameters vary with time. (a) The rates of denudation
(sediment influx) and subsidence change, while the
areas of both sediment source and basin remain constant throughout the time considered. (b) Either the
basin area or both the basin area and source area and
thus also the sediment influx and sedimentation rate
change with time. These models cover long time periods and describe various degrees ofbasin filling.
In all cases, only mean rates of denudation, subsidence and sedimentation for the entire drainage and
basin areas are considered (apart from Sect. 11.5).
The effects of sea-level or base-level changes are
neglected here (cf. Chap. 7). The data used in the
Chapter 11 Sediment Supply, Subsidence, and Basin Fill
model calculations are adjusted to those found in
nature for regions of similar characteristics. Several
case studies supplement the results of the models.
Inspite of the various generalizations, this exercise
may serve as an introduction to more sophisticated
basin simulations with the aid of computer programs.
11.2 Denudation-Sediment
Accumulation (DA) Systems
11.2.1 General Concept
The method, evaluating denudation-sediment accumulation systems (in short: DA systems) as an interrelated unit, is based on the mass balance of
terrigenous sediment eroded in the source area and
accumulated in adjacent closed or semi-closed basins. In other words, the denudation area on land and
the depositional basin constitute a closed erosiondepositional system (e.g. Hay et al. 1989; Leeder
1991 and 1997; Einseie and Hinderer 1998). Denudation in the source area, although varying from 10cality to locality, can be expressed in terms of masses
of mechanical and chemical denudation, M me and M cb
(Fig. l1.1a). It is assumed that no sediment is intermittently stored or reworked along the way from the
source to the basin (delivery ratio = 1). M me provides
terrigenous material which can be entirely trapped in
the depositional area (trap efficiency· TE=100%,
sedimentologically closed basin). The situation is
different for M cb ' In hydrologically open systems part
of it (mainly MbJ is used to produce biogenic sediment, the remainder is lost to neighboring basins or
the open sea. In closed systems part of M cb can fonn
evaporites (Mev)'
The masses of solid and dissolved material can be
converted into specific yields (SY, mass per unit area
and time, e.g. in metric tonsIkm 2 /a, cf. Sect. 9.2 and
9.3) or rates of denudation, D~e and DR.,b' and rates
of mechanical, biogenic, and evaporitic sedimentation, S~e' SRbj, SR.v or SR.,b (m 3 /km 2 /a or mmIka or
mlMa). All these tenns describe mean values under
the assumption that the masses of mechanical and
chemical denudation and deposition are distributed
evenly over the total drainage and basin areas. In addition, mean rock densities and sediment densities
have to be known to detennine (linear) denudation
and sedimentation rates (for conversion factors see
Fig. 11.1 b). A method to detennine the volume of
compact (pore-free) sediment from isopach maps is
explained in Section 11.3.6 (Gulf of Califomia).
The principal premise of this approach is that the
mass of terrigenous sediment accumulating in the
basin per time unit is equal to the mass of material
eroded mechanically in the drainage basin. This
premise also applies to open basins with sills at their
outflow or to deep-sea fans of known extent. Then
theofollowing calculations can be carried out: