78
not just those of braided type, but also demonstrated
that it was incomplete. In a later paper, Mia!! (1978c)
expanded the classification with the definition of a
number of additional minor but significant litho�
facies types. Subsequently) the classification has
been used by dozens of researchers and has become
a standard field methodology for the examination of
fluvial deposits.
Not all professionals agree with the use of prede�
termined lithofacies schemes, such as that described
here. Bridge (1993a) remains amongst the most sceptical of their value. He is particularly concerned that
the use of such schemes by the inexperienced will
lead to their uncritical application, with a possible
loss of important detail where new observations
might have been made of deposits and structures
that differ fr om the "standard". This is an important
warning that should be borne in mind by all researchers.
The scheme is presented in Table 4.1, and is used
throughout this book. Modifications have been
made to the scheme originally presented in Miall
(1978c) in an attempt to eliminate some superfluous
categories and to better discriminate between others. The capital letter in the facies code indicates
dominant grain size (G = gravel, S = sand, F fine�
grained facies, including very fm e sand, silt, and
mud). The lowercase letter serves as a mnemonic for
the characteristic texture or structure of the litho�
facies (e.g., p = planar cross-bedding, ms = matrix�
supported). The lithofacies are described in detail,
with illustrations, in Chap. 5.
It is recommended that the researcher use Table
4.1 as a basis for field research, while remaining alive
to the possibility that refinements are always pos�
sible, based on detailed observations of new units.
For example, Leblanc Smith (1980) incorporated
details on grain size into the coding scheme.
Haszeldine (1983a,b), who did not, in fact, use the.
lithofacies scheme of Table 4.1, subdivided trough
cros$·bedding (lithofacies St) into two types based
on trough thickeness, and was able to demonstrate
the utility of this refmement in interpreting the accretionary development oflarge bar fo rms. A similar
subdivision was used by Eberth and Miall (1991),
who employed the codes Sti and Stii for large- and
small-scale trough cross-bed sets, respectively.
Some of the lithofacies classes are gradational
with others. For example, there may be no clear
distinction in the field between lithofacies Sh and Sl;
lithofacies Fl may contain minor coal streaks or carbonate nodules, leading to quesdons about a work�
able definition of lithofacies C and P for logging
Methods of Architectural-Element Analysis
purposes; how thick should a sand bed be before it is
separated out from Fl? Bed thickness cutoffs, and
accessory percentage limits should be established at
the outset of a project exercise in order to facilitate
consistent logging practices.
The reader should be aware of the recent review of
bedform classifications undertaken by the Bedforms
and Bedding Structures Research Group of the Society for Sedimentary Geology (SEPM)(Ashley 1990).
A synthesis of modern work on bedforms of all types,
in fl uvial, tidal, and other environments, resulted in
a uniform approach to classification and a better
understanding of the causes of morphological varia�
tion. This is discussed in Chap. 5.
4.4 Principles of Paleocurrent Analysis
Paleocurrent data are essential for the purpose of
architectural-element analysis. For the typical, relatively flat, two-dimensional cliff outcrop, these data
provide the essential third dimension. Orientation
information on hydrodynamic sedimentary structures reflects the internal geometry of bar complexes, channels, and sand sheets. The dip and strike
of bounding surfaces reveal the orientation of accretionary bar growth and meander migration (Fig.
4.1). Overall, the data will show the orientation of
the outcrop relative to channel and bar trends, which
is important to know when carrying out visual examination of the architecture in order to assess bar
and channel evolution. For such purposes, even very
limited data can be extremely useful.
The tradition in basin-analysis practice has been
to collect very large numbers of readings without
necessarily recording very precise data regarding
the location of the measurements or, at best, keying
· such measurements to verti<;'al profiles. While such
methods provide good estimates of local and regional paleocurrent trends and of vertical changes in
these trends, they do not help much in the elucidation of the internal architecture of the sand bodies.
This approach also does not address the concerns
regarding the architectural scale of depositional
units (Chap. 3), and its effects on paleocurrent variability (Sect. 2.3.5; Fig. 2.10).
The method recommended here is to use the preliminary interpretations of the bounding surfaces
drawn up prior to detailed field examination of the
outcrop as a guide to the architectural subdivision of
the rocks. Attempts should then be made to collect a
suite of readings from each of the major elements
not just those of braided type, but also demonstrated
that it was incomplete. In a later paper, Mia!! (1978c)
expanded the classification with the definition of a
number of additional minor but significant litho�
facies types. Subsequently) the classification has
been used by dozens of researchers and has become
a standard field methodology for the examination of
fluvial deposits.
Not all professionals agree with the use of prede�
termined lithofacies schemes, such as that described
here. Bridge (1993a) remains amongst the most sceptical of their value. He is particularly concerned that
the use of such schemes by the inexperienced will
lead to their uncritical application, with a possible
loss of important detail where new observations
might have been made of deposits and structures
that differ fr om the "standard". This is an important
warning that should be borne in mind by all researchers.
The scheme is presented in Table 4.1, and is used
throughout this book. Modifications have been
made to the scheme originally presented in Miall
(1978c) in an attempt to eliminate some superfluous
categories and to better discriminate between others. The capital letter in the facies code indicates
dominant grain size (G = gravel, S = sand, F fine�
grained facies, including very fm e sand, silt, and
mud). The lowercase letter serves as a mnemonic for
the characteristic texture or structure of the litho�
facies (e.g., p = planar cross-bedding, ms = matrix�
supported). The lithofacies are described in detail,
with illustrations, in Chap. 5.
It is recommended that the researcher use Table
4.1 as a basis for field research, while remaining alive
to the possibility that refinements are always pos�
sible, based on detailed observations of new units.
For example, Leblanc Smith (1980) incorporated
details on grain size into the coding scheme.
Haszeldine (1983a,b), who did not, in fact, use the.
lithofacies scheme of Table 4.1, subdivided trough
cros$·bedding (lithofacies St) into two types based
on trough thickeness, and was able to demonstrate
the utility of this refmement in interpreting the accretionary development oflarge bar fo rms. A similar
subdivision was used by Eberth and Miall (1991),
who employed the codes Sti and Stii for large- and
small-scale trough cross-bed sets, respectively.
Some of the lithofacies classes are gradational
with others. For example, there may be no clear
distinction in the field between lithofacies Sh and Sl;
lithofacies Fl may contain minor coal streaks or carbonate nodules, leading to quesdons about a work�
able definition of lithofacies C and P for logging
Methods of Architectural-Element Analysis
purposes; how thick should a sand bed be before it is
separated out from Fl? Bed thickness cutoffs, and
accessory percentage limits should be established at
the outset of a project exercise in order to facilitate
consistent logging practices.
The reader should be aware of the recent review of
bedform classifications undertaken by the Bedforms
and Bedding Structures Research Group of the Society for Sedimentary Geology (SEPM)(Ashley 1990).
A synthesis of modern work on bedforms of all types,
in fl uvial, tidal, and other environments, resulted in
a uniform approach to classification and a better
understanding of the causes of morphological varia�
tion. This is discussed in Chap. 5.
4.4 Principles of Paleocurrent Analysis
Paleocurrent data are essential for the purpose of
architectural-element analysis. For the typical, relatively flat, two-dimensional cliff outcrop, these data
provide the essential third dimension. Orientation
information on hydrodynamic sedimentary structures reflects the internal geometry of bar complexes, channels, and sand sheets. The dip and strike
of bounding surfaces reveal the orientation of accretionary bar growth and meander migration (Fig.
4.1). Overall, the data will show the orientation of
the outcrop relative to channel and bar trends, which
is important to know when carrying out visual examination of the architecture in order to assess bar
and channel evolution. For such purposes, even very
limited data can be extremely useful.
The tradition in basin-analysis practice has been
to collect very large numbers of readings without
necessarily recording very precise data regarding
the location of the measurements or, at best, keying
· such measurements to verti<;'al profiles. While such
methods provide good estimates of local and regional paleocurrent trends and of vertical changes in
these trends, they do not help much in the elucidation of the internal architecture of the sand bodies.
This approach also does not address the concerns
regarding the architectural scale of depositional
units (Chap. 3), and its effects on paleocurrent variability (Sect. 2.3.5; Fig. 2.10).
The method recommended here is to use the preliminary interpretations of the bounding surfaces
drawn up prior to detailed field examination of the
outcrop as a guide to the architectural subdivision of
the rocks. Attempts should then be made to collect a
suite of readings from each of the major elements