454
although the limitations imposed on the models by
this fact were not clearly acknowledged by Vail and
his colleagues until recently (Posamentier and
Weimer 1993; Posamentier and Allen 1993). In the
meantime, working on the Mesa Verde Group of the
Western Interior foreland basin of Utah, Swift et a!.
(1987) proposed a quite different type of sequence
model. In foreland basins the relationship between
subsidence and sediment supply is reversed from
that prevailing in extensional continental-margin
basins. In the latter, sediment enters the basin near
the tectonic hinge and is transported toward the
more rapidly subsiding side of the basin. Sequences
in foreland basins are '�clastic wedgesn, as defined by
Sloss (1962). "They are sediment prisms poured into
the deeper side of a linear half-basin undergoing
subsidence along its landward margin. Hence it is
the proximal (landward) end of the wedge that is
most completely preserved" (Swift et a!. 1987, p.
449). Accommodation space is generated more
slowly in the deeper part of the basin because of
slower subsidence there) and so stratigraphic units
tend to thin and pinch out toward the center of the
foreland basin, whereas many units thicken toward
the basin center in the case of extensional continental margins. The major architectural differences between the two types of basin setting are illustrated in
Fig. 13.1.
Nonmarine deposits are much better preserved in
foreland basins than in extensional basins because of
the relationship between subsidence and sediment
supply, and many of the recent studies of nonmarine
sequences have been carried out in deposits formed
in this tectonic setting (Aubry 1989; Hanneman
and Wideman 1991; Holbrook and Dunbar 1992;
Shanley and McCabe 1991, 1993; Martinesen et a!.
1993; Miall !993; Aitken and Flint 1995; Olsen et a!.,
in press; Yoshida et al., in press). These studies effectively answered the question that had been raised
by Posamentier and Weimer (1993) regarding the
applicability of sequence concepts to nonmarine deposits. Posamentier and Allen (1993) provided a useful discussion of the particular characteristics of
sequences formed in foreland basins and made several predictions regarding the architecture of nonmarine deposits in such basins that are discussed
later in this chapter.
The purpose of the present chapter is to review
recent work on sequence models. Does the response
of fluvial systems to allogenic controls, including
source-area uplift (tectonic control) and base-level
change (tectonic or eustatic control), lead to predicSequence Stratigraphy
table facies successions and architectures? To turn
this question around, what can be deduced regarding allogenic controls from the detailed documentation of such fades and architectures? The research
that has taken place since the late 1970s on the effects
of base-level change on fluvial systems is discussed
at length in Sect. 11.2.2. The most important such
research, because of the attention it received, was
that by Posamentier et a!. (1988), which was based on
extensive computer modeling and observations on
small modern rivers. As argued by Mia!! (1991c), this
research was seriously flawed. In Sect. 11.2.2 the
work of later researchers, particularly that of
Schumm (1993) and Wescott (1993), is reviewed, and
it is demonstrated how rivers respond to base-level
change by incision or aggradation and by changes in
sinuosity. The most recent work by Posamentier and
Allen (in press) is touched on in this section. The
effects of tectonism on the middle and upper reaches
of river courses are also discussed at length in Chap.
II. The purpose of the present chapter is to review
current attempts to put these data and ideas into a
sequence framework, that is to say, a predictive
model.
Modern sequence· models for fluvial deposits
have been proposed by Shanley and McCabe (1991,
1993, 1994), Wright and Marriott (1993), and
Posamentier and Allen (in press). Very few modern
sequence studies of fluvial deposits have been published. Those by Legarreta and Gulisano (1989),
Shanley and McCabe (1991, 1993), Van Wagoner et
a!. (1990, 1991), Hanneman and Wideman (1991),
Miall (1993), Gibling and Bird (1994), Gibling
and Wightman (1994), Olsen et a!. (1995), and
Yoshida et a!. (in press) are the most important.
This chapter builds mainly on the work of these
researchers.
It is important to note that, unless otherwise
stated, no particular time connotation is placed
upon the sequence models discussed in this chapter.
The examples of alluvial stratigraphy described in
Sects. 9.2 to 9.4 (summarized in Table 9.1) include
sequences of third to fifth order (groups 8 to !0, in
the classification of this book: Tables 3.2, 4.2, 9.1).
These range in duration from a few thousand years
to a few million years. These sequences all display a
certain degree of ('self-similarity'), indicating that
the dynamic balance between the various allogenic
controls can be achieved and maintained over a wide
range of time scales. The various temporal scales of
nonmarine sequences, and their causes, are reviewed in Sect. 13.4.
although the limitations imposed on the models by
this fact were not clearly acknowledged by Vail and
his colleagues until recently (Posamentier and
Weimer 1993; Posamentier and Allen 1993). In the
meantime, working on the Mesa Verde Group of the
Western Interior foreland basin of Utah, Swift et a!.
(1987) proposed a quite different type of sequence
model. In foreland basins the relationship between
subsidence and sediment supply is reversed from
that prevailing in extensional continental-margin
basins. In the latter, sediment enters the basin near
the tectonic hinge and is transported toward the
more rapidly subsiding side of the basin. Sequences
in foreland basins are '�clastic wedgesn, as defined by
Sloss (1962). "They are sediment prisms poured into
the deeper side of a linear half-basin undergoing
subsidence along its landward margin. Hence it is
the proximal (landward) end of the wedge that is
most completely preserved" (Swift et a!. 1987, p.
449). Accommodation space is generated more
slowly in the deeper part of the basin because of
slower subsidence there) and so stratigraphic units
tend to thin and pinch out toward the center of the
foreland basin, whereas many units thicken toward
the basin center in the case of extensional continental margins. The major architectural differences between the two types of basin setting are illustrated in
Fig. 13.1.
Nonmarine deposits are much better preserved in
foreland basins than in extensional basins because of
the relationship between subsidence and sediment
supply, and many of the recent studies of nonmarine
sequences have been carried out in deposits formed
in this tectonic setting (Aubry 1989; Hanneman
and Wideman 1991; Holbrook and Dunbar 1992;
Shanley and McCabe 1991, 1993; Martinesen et a!.
1993; Miall !993; Aitken and Flint 1995; Olsen et a!.,
in press; Yoshida et al., in press). These studies effectively answered the question that had been raised
by Posamentier and Weimer (1993) regarding the
applicability of sequence concepts to nonmarine deposits. Posamentier and Allen (1993) provided a useful discussion of the particular characteristics of
sequences formed in foreland basins and made several predictions regarding the architecture of nonmarine deposits in such basins that are discussed
later in this chapter.
The purpose of the present chapter is to review
recent work on sequence models. Does the response
of fluvial systems to allogenic controls, including
source-area uplift (tectonic control) and base-level
change (tectonic or eustatic control), lead to predicSequence Stratigraphy
table facies successions and architectures? To turn
this question around, what can be deduced regarding allogenic controls from the detailed documentation of such fades and architectures? The research
that has taken place since the late 1970s on the effects
of base-level change on fluvial systems is discussed
at length in Sect. 11.2.2. The most important such
research, because of the attention it received, was
that by Posamentier et a!. (1988), which was based on
extensive computer modeling and observations on
small modern rivers. As argued by Mia!! (1991c), this
research was seriously flawed. In Sect. 11.2.2 the
work of later researchers, particularly that of
Schumm (1993) and Wescott (1993), is reviewed, and
it is demonstrated how rivers respond to base-level
change by incision or aggradation and by changes in
sinuosity. The most recent work by Posamentier and
Allen (in press) is touched on in this section. The
effects of tectonism on the middle and upper reaches
of river courses are also discussed at length in Chap.
II. The purpose of the present chapter is to review
current attempts to put these data and ideas into a
sequence framework, that is to say, a predictive
model.
Modern sequence· models for fluvial deposits
have been proposed by Shanley and McCabe (1991,
1993, 1994), Wright and Marriott (1993), and
Posamentier and Allen (in press). Very few modern
sequence studies of fluvial deposits have been published. Those by Legarreta and Gulisano (1989),
Shanley and McCabe (1991, 1993), Van Wagoner et
a!. (1990, 1991), Hanneman and Wideman (1991),
Miall (1993), Gibling and Bird (1994), Gibling
and Wightman (1994), Olsen et a!. (1995), and
Yoshida et a!. (in press) are the most important.
This chapter builds mainly on the work of these
researchers.
It is important to note that, unless otherwise
stated, no particular time connotation is placed
upon the sequence models discussed in this chapter.
The examples of alluvial stratigraphy described in
Sects. 9.2 to 9.4 (summarized in Table 9.1) include
sequences of third to fifth order (groups 8 to !0, in
the classification of this book: Tables 3.2, 4.2, 9.1).
These range in duration from a few thousand years
to a few million years. These sequences all display a
certain degree of ('self-similarity'), indicating that
the dynamic balance between the various allogenic
controls can be achieved and maintained over a wide
range of time scales. The various temporal scales of
nonmarine sequences, and their causes, are reviewed in Sect. 13.4.