Chapter 9
The Stratigraphic Archited11re llf Fi111 11ial Depllsitillnal Systems
9.1 Introduction
In the preceding chapters we have seen how to describe and interpret the various lithofacies components of a fluvial depositional system (Chap. 5) and
how these components may combine to form channel fills and floodplain blankets (Chaps. 6, 7). Studies
of lithofacies and channel geometry then permit the
recognition of fluvial style, of which 16 typical examples are described (Chap. 8). These earher chapters describe units comprising groups 1-7 of Miall's
(Miall 1991b) hierarchical classification (Table 3.1).
The next step is to reconstruct fluvial systems on a
basin scale, that is, at the level of groups 8-11. How
many separate fluvial systems were there in a given
basin? Which way did they flow, and how did they
interact? What is the nature of vertical and lateral
transitions into other nonmarine facies and into
marine deposits?
Table 9.1 provides a listing of examples of largescale. fluvial units and depositional processes orga�
nized in accordance with the hierarchical
classification of Chap. 3. Many terms, such as
cyclothem and megasequence, have been assigned a
variety of different meanings. Also, terms such as
firsh second�order, etc., have been employed in
many conflicting ways for processes and products,
with the numbering arranged in order from both
large- to small-scale features and long- to short-term
processes, and the reverse. The result has been that
the use of «order" classifications has become very
confused. It is hoped that the listing in Table 9.1 of
examples of processes and depositional products
according to the time scale they represent (recu �
rence interval) and the use of the nongenet1c
«group" classification will help to clarify terminology and provide insights into processes. Many more
examples could be cited in this table. A repr : sent �
tive selection of ancient examples has been g1ven, m
which constraints on timing and rates of sedimentation are available to enable the units to be classified
into the appropriate group.
The construction of a basin-scale stratigraphy is a
question of correlation and mapping, and it is the
practical details of this procedure that are addressed
later in this chapter. General discussions of stratigraphic correlation have been provided in several
recent textbooks (e.g., Miall 1990, Chap. 3). Conventional stratigraphic methods are concerned with correlation at the fo rmation or member level and are
not the main interest here. The focus of this chapter
is on methods whereby the stacking of individual
large-scale elements of a fluvial succession, such as
the meander belts and floodplains and alluvial fan
lobes can be reconstructed using techniques of outcrop and subsurface mapping. On the larger s : ale,
fluvial units combine -into sequences of vanous
types. Unless specific depositional elements can be
traced, and their scale, geometry, and lateral relations determined, it is not possible to address the
larger questions regarding the action of autogenic
and allogenic sedimentary controls. Several of the
examples of the various scales of stratigraphic unit
discussed in Sects. 9.2-9.4 are used to illustrate mapping methods in Sect. 9.5.
9.2 Channel Belts
The subject of this section is the deposits of groups 7
and 8 (Table 9.1), corresponding to depositional
units formed over time periods of 103-105 years.
Over this time scale channels and channel belts are
fo rmed, and alluvial fans may undergo a progradational-trenching cycle. Deposits of group 8 compare
in duration to the high-frequency (fifth-order)
Milankovitch cycles of Vail et al. (1977) and Miall
(1990).
Examples from studies of the Siwalik Group of
Pakistan are illustrated in Figs. 2.32 and 9.1 (see also
Fig. 7.13). The Siwalik sections were constructed
from the measurement and physical correlation of
numerous outcrops in areas of excellent exposure.
The isochron and time scales were derived from
The Stratigraphic Archited11re llf Fi111 11ial Depllsitillnal Systems
9.1 Introduction
In the preceding chapters we have seen how to describe and interpret the various lithofacies components of a fluvial depositional system (Chap. 5) and
how these components may combine to form channel fills and floodplain blankets (Chaps. 6, 7). Studies
of lithofacies and channel geometry then permit the
recognition of fluvial style, of which 16 typical examples are described (Chap. 8). These earher chapters describe units comprising groups 1-7 of Miall's
(Miall 1991b) hierarchical classification (Table 3.1).
The next step is to reconstruct fluvial systems on a
basin scale, that is, at the level of groups 8-11. How
many separate fluvial systems were there in a given
basin? Which way did they flow, and how did they
interact? What is the nature of vertical and lateral
transitions into other nonmarine facies and into
marine deposits?
Table 9.1 provides a listing of examples of largescale. fluvial units and depositional processes orga�
nized in accordance with the hierarchical
classification of Chap. 3. Many terms, such as
cyclothem and megasequence, have been assigned a
variety of different meanings. Also, terms such as
firsh second�order, etc., have been employed in
many conflicting ways for processes and products,
with the numbering arranged in order from both
large- to small-scale features and long- to short-term
processes, and the reverse. The result has been that
the use of «order" classifications has become very
confused. It is hoped that the listing in Table 9.1 of
examples of processes and depositional products
according to the time scale they represent (recu �
rence interval) and the use of the nongenet1c
«group" classification will help to clarify terminology and provide insights into processes. Many more
examples could be cited in this table. A repr : sent �
tive selection of ancient examples has been g1ven, m
which constraints on timing and rates of sedimentation are available to enable the units to be classified
into the appropriate group.
The construction of a basin-scale stratigraphy is a
question of correlation and mapping, and it is the
practical details of this procedure that are addressed
later in this chapter. General discussions of stratigraphic correlation have been provided in several
recent textbooks (e.g., Miall 1990, Chap. 3). Conventional stratigraphic methods are concerned with correlation at the fo rmation or member level and are
not the main interest here. The focus of this chapter
is on methods whereby the stacking of individual
large-scale elements of a fluvial succession, such as
the meander belts and floodplains and alluvial fan
lobes can be reconstructed using techniques of outcrop and subsurface mapping. On the larger s : ale,
fluvial units combine -into sequences of vanous
types. Unless specific depositional elements can be
traced, and their scale, geometry, and lateral relations determined, it is not possible to address the
larger questions regarding the action of autogenic
and allogenic sedimentary controls. Several of the
examples of the various scales of stratigraphic unit
discussed in Sects. 9.2-9.4 are used to illustrate mapping methods in Sect. 9.5.
9.2 Channel Belts
The subject of this section is the deposits of groups 7
and 8 (Table 9.1), corresponding to depositional
units formed over time periods of 103-105 years.
Over this time scale channels and channel belts are
fo rmed, and alluvial fans may undergo a progradational-trenching cycle. Deposits of group 8 compare
in duration to the high-frequency (fifth-order)
Milankovitch cycles of Vail et al. (1977) and Miall
(1990).
Examples from studies of the Siwalik Group of
Pakistan are illustrated in Figs. 2.32 and 9.1 (see also
Fig. 7.13). The Siwalik sections were constructed
from the measurement and physical correlation of
numerous outcrops in areas of excellent exposure.
The isochron and time scales were derived from