Chapter 4
Methods of Architedlll ra!-E!emernt Arnaly$is
4.1 Introduction
A wealth of information is contained in many outM
crops of fl uvial deposits, that is not captured by
conventional methods of facies analysis, such a� the
measurement of vertical-proflies. In this chapter, the
formal methods of field architectural-element analysis are described. Analysis and interpretation of the
results are the subjects oflater chapters.
Earlier work on the development of architectural
concepts for fluvial deposits is discussed in Sect. 2.4.
This chapter describes current techniques, including
the writer's contributions (Miall 1985, 1988a,b), together with the modifications, improvements, and
additional suggestions contributed by other researchers, notably those of Soegaard (1990, 1992),
S.A. Smith (1990), and DeCelles et a!. (1991), who
worked mainly with conglomerates.
Methods of conventional facies analysis are not
covered in this book. The reader is referred to Miall
(1990, Chaps. 2, 4) for a detailed discussion of the
methods of facies analysis, including the measurement and interpretation of vertical profiles.
4.2 Construction of Outcrop Profiles
Architectural methods are based on the two- and
three-dimensional mapping oflarge outcrops, using
outcrop profiles. These are essentially vertical geological maps, and are constructed in much the same
way. The geologist begins with a base map, and then
carries out traverses across the map, making observations and walking out key structures and contacts.
The base map may be either a line-drawing of the
outcrop, made with or without the aid of surveying
equipment, or it may be a photo mosaic. The latter is
the easiest to construct and to use in the field.
In the simplest case, an entire outcrop may be
encompassed in a single photographic frame, but the
largest and most interesting outcrops tend to be too
large to be viewed within one field of view, unless the
photographer is required to move so far back from
the outcrop that the scale of the photograph becomes
too small to be useful. The obvious alternative is to
construct a mosaic from overlapping fr ames. The
geologist moves several tens or hundreds of meters
back from the face, and carries out a traverse parallel
to it, taking a series of overlapping photographs.
Dipping beds may be viewed from an adjacent hilltop, or from a low-flying aircraft. It is important to
stay the same distance from the face, so that the
frames are all as nearly as possible the same scale.
Ideally, this may be accomplished with the use of
surveying equipment, but the high degree of precision obtainable in this way is not really necessary for
sedimentological purposes. It is also useful fot'the
line of sight towards the outcrop to be situated in the
plane of the bedding, in order to minimize vertical
distortions. For a road cut, which can be photographed from the other side of the road, these requirements may be a simple matter to satisfy. For
many hillside exposures and river cliffs, it may be
considerably more difficult to generate an adequate
suite of photographs, with variations in the terrain
and obscuring trees causing problems of position
and distance. In practice� the writer has found that
useful mosaics can almost always be constructed
with a little effort, although perspective problems,
and variations in the scale or orientation of different
parts of the profile may remain problematic.
Variations in scale from one frame to the next can
be accomodated by varying the enlargment size of
the prints. This is particularly easily accomplished if
each frame includes a scale, or some object whose
dimensions are known. Perspective problems are
less easily eliminated. They can be troublesome if the
outcrop is not flat� but includes projecting and receding regions, because such features will not overlap exactly when
·
adjacent frames are joined.
An almost inevitable element of vertical distortion will be present in most profiles, because the
camera cannot view all beds along the plane of their
bedding from a single viewpoint. For example, when
Methods of Architedlll ra!-E!emernt Arnaly$is
4.1 Introduction
A wealth of information is contained in many outM
crops of fl uvial deposits, that is not captured by
conventional methods of facies analysis, such a� the
measurement of vertical-proflies. In this chapter, the
formal methods of field architectural-element analysis are described. Analysis and interpretation of the
results are the subjects oflater chapters.
Earlier work on the development of architectural
concepts for fluvial deposits is discussed in Sect. 2.4.
This chapter describes current techniques, including
the writer's contributions (Miall 1985, 1988a,b), together with the modifications, improvements, and
additional suggestions contributed by other researchers, notably those of Soegaard (1990, 1992),
S.A. Smith (1990), and DeCelles et a!. (1991), who
worked mainly with conglomerates.
Methods of conventional facies analysis are not
covered in this book. The reader is referred to Miall
(1990, Chaps. 2, 4) for a detailed discussion of the
methods of facies analysis, including the measurement and interpretation of vertical profiles.
4.2 Construction of Outcrop Profiles
Architectural methods are based on the two- and
three-dimensional mapping oflarge outcrops, using
outcrop profiles. These are essentially vertical geological maps, and are constructed in much the same
way. The geologist begins with a base map, and then
carries out traverses across the map, making observations and walking out key structures and contacts.
The base map may be either a line-drawing of the
outcrop, made with or without the aid of surveying
equipment, or it may be a photo mosaic. The latter is
the easiest to construct and to use in the field.
In the simplest case, an entire outcrop may be
encompassed in a single photographic frame, but the
largest and most interesting outcrops tend to be too
large to be viewed within one field of view, unless the
photographer is required to move so far back from
the outcrop that the scale of the photograph becomes
too small to be useful. The obvious alternative is to
construct a mosaic from overlapping fr ames. The
geologist moves several tens or hundreds of meters
back from the face, and carries out a traverse parallel
to it, taking a series of overlapping photographs.
Dipping beds may be viewed from an adjacent hilltop, or from a low-flying aircraft. It is important to
stay the same distance from the face, so that the
frames are all as nearly as possible the same scale.
Ideally, this may be accomplished with the use of
surveying equipment, but the high degree of precision obtainable in this way is not really necessary for
sedimentological purposes. It is also useful fot'the
line of sight towards the outcrop to be situated in the
plane of the bedding, in order to minimize vertical
distortions. For a road cut, which can be photographed from the other side of the road, these requirements may be a simple matter to satisfy. For
many hillside exposures and river cliffs, it may be
considerably more difficult to generate an adequate
suite of photographs, with variations in the terrain
and obscuring trees causing problems of position
and distance. In practice� the writer has found that
useful mosaics can almost always be constructed
with a little effort, although perspective problems,
and variations in the scale or orientation of different
parts of the profile may remain problematic.
Variations in scale from one frame to the next can
be accomodated by varying the enlargment size of
the prints. This is particularly easily accomplished if
each frame includes a scale, or some object whose
dimensions are known. Perspective problems are
less easily eliminated. They can be troublesome if the
outcrop is not flat� but includes projecting and receding regions, because such features will not overlap exactly when
·
adjacent frames are joined.
An almost inevitable element of vertical distortion will be present in most profiles, because the
camera cannot view all beds along the plane of their
bedding from a single viewpoint. For example, when