Methods of Correlation and Mapping
1993; Gawthorpe et al. 1993; Alexander et al. 1994).
Core or outcrop data are desirable to ((ground�truth''
the radar facies.
several applications have demonstrated the abi�
lity of the tool to map architectural details in fluvial
deposits down to depths of as much as 30 m, with
resolution as high as 10 em, although where the
section consists of saturated fine-grained deposits,
as in the case of modern floodplains, penetration
may be only a few meters. Both modern (Moorman
et al. 1991; Huggenberger 1993; Gawthorpe et al.
1993) and ancient (Stephens 1994) fluvial deposits
have been examined.
There are two main potential applications of the
technique.
1. For the the evaluation of sand-body architecture
as an aid to the study of reservoir heterogeneity. A
particularly powerful approach is to examine an
ancient unit in outcrop, using two�dimensional
lateral profiling techniques (Chap. 4), and to run a
GPR survey over the top of the outcrop, in order
to calibrate the radar data and to extend the architectural analysis back into the third dimension.
Pratt and Miall (1993) reported a preliminary
study of a Silurian carbonate shoal deposit carried out this way. Gawthorpe et al. (1993) reconstructed lateral-accretion bedding in a modern
point-bar deposit. Stephens (1994) examined an
ancient fluvial system and was able to document a
history of complex braid-bar development.
2. The evaluation of the flow of groundwater and
toxic wastes through shallow aquifers, including
ancient sediments and modern surficial deposits
(Huggenberger 1993; Knoll et al. 1994).
A single example of a radar line and its interpretation are illustrated in Figs. 9.53 and 9.54. This survey
was carried out by Stephens (1994) over the top of a
large outcrop of the Kayenta Formation, a Lower
Jurassic ephemeral fluvial system in southwest Colorado. Most of the reflections are interpreted to represent bounding surfaces, probably of third-order
rank, that record the lateral to oblique accretion of
DA units in a broad sandy�braided river channel.
9.5.6 Magnetostratigraphy
The record of magnetic reversals preserved in sedimentary rocks has, in recent years, become a powerful tool for intrabasin and global correlation.
Carefully sampled stratigraphic sections can lead to
the erection of a local chronostratigraphy (examples
293
are shown in Figs. 9.55 and 9.56), and with the assistance of biostratigraphic data or information from
radiometric dating of interbedded tuffs, the local
record may be correlated with the global time scale
(Fig. 9.57). The procedure is summarized in Miall
(1990, Sect. 3.7.5).
Not all fluvial deposits lend themselves to paleomagnetic study. The quality of the results decreases
sharply with increasing age, because of diagenetic
complications, and, because the magnetic signature
is best obtained from fine-grained units, reliable
results depend on the presence of such facies at least
every few meters through the succession. The work
on the Siwalik Group, which is the Late Cenozoic fill
of the Himalayan foredeep basin in Pakistan
(Behrensmeyer and Tauxe 1982; Behrensmeyer 1987;
johnson et al. 1985; Burbank and Raynolds 1988;
Burbank et al. 1986; Mulder and Burbank 1993) is of
the highest quality and has been widely quoted because of the insights the work has provided on stratigraphic architecture (this chapter) and tectonic
controls (Chap. 11). The data permit the subdivision
and regional correlation of fluvial successions down
to the group 8 or 7 level, as discussed in Sect. 9.2.
Under ideal conditions, this is comparable to the
subdivisions that can be erected based on interbedded tuffs, coals, and paleosols, as described in
Sect. 9.5.1.
9.5.7 Paleocurrent Analysis
Methods of outcrop paleocurrent measurement and
documentation are discussed in Sect. 4.4, in which it
is shown how orientation data relating to cross�bedding and macroform accretion directions may be
used to reconstruct channel and bar configurations
(Fig. 4.1). Elsewhere, the concept of the hierarchy of
depositional units is introduced, and it is shown how
the directional properties vary at each level of the
hierarchy (Fig. 2.10). Reconstruction of macroforms
using paleocurrent and facies data is discussed in
Chap. 6 (e.g., see Fig. 6.24c).
Paleocurrent analysis may be used as a supplementary mapping tool to investigate the following
kinds of information:
1. Changes in channel and bar orientation and directional variability through a stratigraphic unit,
as one of several indicators of vertical or lateral
changes in fluvial style
2. Reconstruction of tributary or distributary patterns, e.g., determination of radial alluvial-fan
1993; Gawthorpe et al. 1993; Alexander et al. 1994).
Core or outcrop data are desirable to ((ground�truth''
the radar facies.
several applications have demonstrated the abi�
lity of the tool to map architectural details in fluvial
deposits down to depths of as much as 30 m, with
resolution as high as 10 em, although where the
section consists of saturated fine-grained deposits,
as in the case of modern floodplains, penetration
may be only a few meters. Both modern (Moorman
et al. 1991; Huggenberger 1993; Gawthorpe et al.
1993) and ancient (Stephens 1994) fluvial deposits
have been examined.
There are two main potential applications of the
technique.
1. For the the evaluation of sand-body architecture
as an aid to the study of reservoir heterogeneity. A
particularly powerful approach is to examine an
ancient unit in outcrop, using two�dimensional
lateral profiling techniques (Chap. 4), and to run a
GPR survey over the top of the outcrop, in order
to calibrate the radar data and to extend the architectural analysis back into the third dimension.
Pratt and Miall (1993) reported a preliminary
study of a Silurian carbonate shoal deposit carried out this way. Gawthorpe et al. (1993) reconstructed lateral-accretion bedding in a modern
point-bar deposit. Stephens (1994) examined an
ancient fluvial system and was able to document a
history of complex braid-bar development.
2. The evaluation of the flow of groundwater and
toxic wastes through shallow aquifers, including
ancient sediments and modern surficial deposits
(Huggenberger 1993; Knoll et al. 1994).
A single example of a radar line and its interpretation are illustrated in Figs. 9.53 and 9.54. This survey
was carried out by Stephens (1994) over the top of a
large outcrop of the Kayenta Formation, a Lower
Jurassic ephemeral fluvial system in southwest Colorado. Most of the reflections are interpreted to represent bounding surfaces, probably of third-order
rank, that record the lateral to oblique accretion of
DA units in a broad sandy�braided river channel.
9.5.6 Magnetostratigraphy
The record of magnetic reversals preserved in sedimentary rocks has, in recent years, become a powerful tool for intrabasin and global correlation.
Carefully sampled stratigraphic sections can lead to
the erection of a local chronostratigraphy (examples
293
are shown in Figs. 9.55 and 9.56), and with the assistance of biostratigraphic data or information from
radiometric dating of interbedded tuffs, the local
record may be correlated with the global time scale
(Fig. 9.57). The procedure is summarized in Miall
(1990, Sect. 3.7.5).
Not all fluvial deposits lend themselves to paleomagnetic study. The quality of the results decreases
sharply with increasing age, because of diagenetic
complications, and, because the magnetic signature
is best obtained from fine-grained units, reliable
results depend on the presence of such facies at least
every few meters through the succession. The work
on the Siwalik Group, which is the Late Cenozoic fill
of the Himalayan foredeep basin in Pakistan
(Behrensmeyer and Tauxe 1982; Behrensmeyer 1987;
johnson et al. 1985; Burbank and Raynolds 1988;
Burbank et al. 1986; Mulder and Burbank 1993) is of
the highest quality and has been widely quoted because of the insights the work has provided on stratigraphic architecture (this chapter) and tectonic
controls (Chap. 11). The data permit the subdivision
and regional correlation of fluvial successions down
to the group 8 or 7 level, as discussed in Sect. 9.2.
Under ideal conditions, this is comparable to the
subdivisions that can be erected based on interbedded tuffs, coals, and paleosols, as described in
Sect. 9.5.1.
9.5.7 Paleocurrent Analysis
Methods of outcrop paleocurrent measurement and
documentation are discussed in Sect. 4.4, in which it
is shown how orientation data relating to cross�bedding and macroform accretion directions may be
used to reconstruct channel and bar configurations
(Fig. 4.1). Elsewhere, the concept of the hierarchy of
depositional units is introduced, and it is shown how
the directional properties vary at each level of the
hierarchy (Fig. 2.10). Reconstruction of macroforms
using paleocurrent and facies data is discussed in
Chap. 6 (e.g., see Fig. 6.24c).
Paleocurrent analysis may be used as a supplementary mapping tool to investigate the following
kinds of information:
1. Changes in channel and bar orientation and directional variability through a stratigraphic unit,
as one of several indicators of vertical or lateral
changes in fluvial style
2. Reconstruction of tributary or distributary patterns, e.g., determination of radial alluvial-fan