Conclusions
exception was comprised of those geologists con�
cerned with the stratigraphy and sedimentology of
coal (e.g., Horne et a\. 1978; Flores 1981, 1984; Fielding 1984; Rahmani and Flores 1984; McCabe 1984).
One of the most distinctive characteristics of the
anastomosed fluvial environment is the presence of
large, stable floodplain areas, typically wetlands with
large crevasse splays. Some of the early references to
this model are noted in Sect. 2.4.4.3, although most
of these studies are concerned with the composition
and geometry of the channel and crevasse�splay
units rather than th� fine-grained deposits of the
floodplain. Similarly, Bridge (1984), in a paper on
facies sequences in overbank environments of highsinuosity rivers, dealt exclusively with the types of
filling-upward and coarsening-upward sandstonedominated successions found in levee and crevassesplay deposits.
Several studies of coal-bearing successions subdivided fl oodplain deposits into a series of distinct
facies assemblages. For example, Ethridge et al.
(1981) recognized crevasse-splay, levee, abandonedchannel, well-drained swamp, poorly drained
swamp, and lacustrine assemblages. A similar range
of facies was described by Gersib and McCabe
(1984). Both of these studies focused on vertical
profJJ .es, and on the building of generalized fades
models, but did not deal in detail with floodplain
architecture. Wing (1984) subdivided plant-bearing
floodplain fines into two main facies assemblages,
and was able to construct a separate depositonal
model for each, based on lithofacies, plant assemblages, and unit geometry. Tabular units were interpreted as the deposits of gradually aggrading
swamps, whereas lenticular bodies represent the fJJ .l
of abandoned channels. This is one of the few studies
to have exploited the floodplain deposits themselves
for their potential to yield architectural information.
As discussed in Chap. 9, floodplain sequences may
hold the key for unlocking a vast amount of architectural detail, but few workers have made use of this
potential.
Coal is commonly interpreted as an integral part
of the floodplain succession in fluvial and deltaplain environments. McCabe (1984) pointed out,
however, that in an active clastic environment characterized by crevassing and avulsion, floodplains
receive so much detrital input that high-quality, lowash coals are unlikely to form. Raised peat swamps
may develop where rainfall permits an elevated water table to be maintained as rapid peat accumulation outpaces channelized clastic aggradation. The
relief of these swamps prevents detrital influx, and
55
constrains channel migration and avulsion (Flores
1984; McCabe 1984).
The use of floodplain deposits in reconstructing
fluvial architecture is discussed in Sect. 2.4.3.2. A
modern classification of floodplains by Nanson and
Croke (1993) is presented in Chap. 8 (Table 8.4) and
is discussed in Chaps. 7 and 8.
2.5 Conclusions
Although sedimentology and basin analysis have always been concerned with the geology of rocks in
three dimensions, during the 1970s the main focus
was on the elaboration of facies models, relying
heavily on the use of the vertical profile. The weaknesses in this method were apparent by the end of
that decade, and several unrelated attempts to systematize architectural methods were made during
the 1980s. It is only since the late 1980s that we have
had the tools to carry out systematic three-dimensional investigations of fluvial strata, using the architectural techniques described in later chapters of
this book.
Bersier, in 1948, attributed fluvial fining-upward
cycles to a tectonic cause. However, the 1960s and
1970s were a time when sedimentological studies
were dominated by a fascination with autogenic processes. Much of the fascination of the facies-model
revolution was the discovery that appeals to such
awkwar4 mechanisms as pulsating tectonism were
not necessary. In the case of fluvial sedimentology,
this led to the development of the point-bar model
and, later, an unraveling of the complexities of
braided and anastomosed rivers. To some exent,
however, we are coming full circle. The latest stratigraphic revolution - that of sequence stratigraphy
is returning us to some old ideas about allogenic
causes. The field of sequence stratigraphy, currently
one of the most exciting areas of research in strati�
graphy, evolved from new ideas about basin development that derived from developments in the
analysis of seismic�reflection data during the 1970s.
These burst onto the geological scene in 1977 with
the publication of AAPG Memoir 26 (Payton 1977),
but the implications of this research for fl uvial sedimentology only became apparent with the work of
Posamentier and Vail (1988) and Posamentier et a!.
(1988), at the end of the period dealt with in this
chapter. The ideas in these latter papers are still in
the category of current research, and are discussed in
Chaps. 11 and 13. It is being shown that many clastic
exception was comprised of those geologists con�
cerned with the stratigraphy and sedimentology of
coal (e.g., Horne et a\. 1978; Flores 1981, 1984; Fielding 1984; Rahmani and Flores 1984; McCabe 1984).
One of the most distinctive characteristics of the
anastomosed fluvial environment is the presence of
large, stable floodplain areas, typically wetlands with
large crevasse splays. Some of the early references to
this model are noted in Sect. 2.4.4.3, although most
of these studies are concerned with the composition
and geometry of the channel and crevasse�splay
units rather than th� fine-grained deposits of the
floodplain. Similarly, Bridge (1984), in a paper on
facies sequences in overbank environments of highsinuosity rivers, dealt exclusively with the types of
filling-upward and coarsening-upward sandstonedominated successions found in levee and crevassesplay deposits.
Several studies of coal-bearing successions subdivided fl oodplain deposits into a series of distinct
facies assemblages. For example, Ethridge et al.
(1981) recognized crevasse-splay, levee, abandonedchannel, well-drained swamp, poorly drained
swamp, and lacustrine assemblages. A similar range
of facies was described by Gersib and McCabe
(1984). Both of these studies focused on vertical
profJJ .es, and on the building of generalized fades
models, but did not deal in detail with floodplain
architecture. Wing (1984) subdivided plant-bearing
floodplain fines into two main facies assemblages,
and was able to construct a separate depositonal
model for each, based on lithofacies, plant assemblages, and unit geometry. Tabular units were interpreted as the deposits of gradually aggrading
swamps, whereas lenticular bodies represent the fJJ .l
of abandoned channels. This is one of the few studies
to have exploited the floodplain deposits themselves
for their potential to yield architectural information.
As discussed in Chap. 9, floodplain sequences may
hold the key for unlocking a vast amount of architectural detail, but few workers have made use of this
potential.
Coal is commonly interpreted as an integral part
of the floodplain succession in fluvial and deltaplain environments. McCabe (1984) pointed out,
however, that in an active clastic environment characterized by crevassing and avulsion, floodplains
receive so much detrital input that high-quality, lowash coals are unlikely to form. Raised peat swamps
may develop where rainfall permits an elevated water table to be maintained as rapid peat accumulation outpaces channelized clastic aggradation. The
relief of these swamps prevents detrital influx, and
55
constrains channel migration and avulsion (Flores
1984; McCabe 1984).
The use of floodplain deposits in reconstructing
fluvial architecture is discussed in Sect. 2.4.3.2. A
modern classification of floodplains by Nanson and
Croke (1993) is presented in Chap. 8 (Table 8.4) and
is discussed in Chaps. 7 and 8.
2.5 Conclusions
Although sedimentology and basin analysis have always been concerned with the geology of rocks in
three dimensions, during the 1970s the main focus
was on the elaboration of facies models, relying
heavily on the use of the vertical profile. The weaknesses in this method were apparent by the end of
that decade, and several unrelated attempts to systematize architectural methods were made during
the 1980s. It is only since the late 1980s that we have
had the tools to carry out systematic three-dimensional investigations of fluvial strata, using the architectural techniques described in later chapters of
this book.
Bersier, in 1948, attributed fluvial fining-upward
cycles to a tectonic cause. However, the 1960s and
1970s were a time when sedimentological studies
were dominated by a fascination with autogenic processes. Much of the fascination of the facies-model
revolution was the discovery that appeals to such
awkwar4 mechanisms as pulsating tectonism were
not necessary. In the case of fluvial sedimentology,
this led to the development of the point-bar model
and, later, an unraveling of the complexities of
braided and anastomosed rivers. To some exent,
however, we are coming full circle. The latest stratigraphic revolution - that of sequence stratigraphy
is returning us to some old ideas about allogenic
causes. The field of sequence stratigraphy, currently
one of the most exciting areas of research in strati�
graphy, evolved from new ideas about basin development that derived from developments in the
analysis of seismic�reflection data during the 1970s.
These burst onto the geological scene in 1977 with
the publication of AAPG Memoir 26 (Payton 1977),
but the implications of this research for fl uvial sedimentology only became apparent with the work of
Posamentier and Vail (1988) and Posamentier et a!.
(1988), at the end of the period dealt with in this
chapter. The ideas in these latter papers are still in
the category of current research, and are discussed in
Chaps. 11 and 13. It is being shown that many clastic