74
the estimates from ancient units incorporate significant intervals of a missing section of a type that are
not present in the modern successions used by
Bridge and Leeder (1979).
Groups 8 and 9 of this book include the Quaternary shelf-margin sequences of Suter et aL (1987)
and the minor and major cyclothems of Heckel
(1986), The sequences described from the Gulf Coast
by Suter et aL (1987) averaged 25000 years in duration and range in thickness fr om about 25 to 160 m,
indicating average accumulation rates of 1-6.4 m/ka.
Heckel (1986) documented the chronology of 55
cycles of Westphalian-Stephanian age in the US
midcontinent. Estimates of the length of this time
span range fr om 8 to 12 million years. The thickness
of the sucession varies from 260 m in Iowa to 550 m
in Kansas. These values indicate an average accumulation rate of between 0.02 and 0.07 m/ka. Many of
the cyles contain substantial fluvial-deltaic sandstone units and, according to Ramsbottom (1979),
who studied similar cyclothems in Europe, rates of
lateral deltaic growth must have been about as rapid
as that of the modern Mississippii yet, the average
sedimentation rate is two orders of magnitude less
than that of the Holocene Mississipi delta complex
and its Pleistocene shelf-margin precursors on the
Louisiana Gulf Coast. Part of the explanation for this
marked contrast is that the Carboniferous cyclothems that were the subject of Heckel's study are
located in a cratonic region, where subsidence rates
would be expected to be substantially lower than on
the continental margin of the Gulf Coast. In addition, many of the cycles are separated by erosion
surfaces. Rapid sedimentation rates of an order-ofmagnitude more were measured by Johnson et al.
(1985) and Friend et al. (1989) in their study of the
Siwalik sediments of Pakistan. Detailed documentation of a nearly 2-km-thick section spanning more
than 9 million years yielded constant long-term sedimentation rates that increase from 0.1 m/ka at the
base to 0.3 m/ka at the top. Individual channel-fill
cycles in this succession are estimated to have return
periods of 1-4 x105 years (group 8 deposits).
Bentham et aL (1993) used magnetostratigraphic
correlation to estimate accumulation rates of0.17 to
0.57 m/ka over a 4 million year time period, for a
braided fluvial system of Eocene age in Spain. Beer
(1990) recorded a maximum accumulation rate of
0.9 m/ka in a Miocene sheetflood deposit in Argentina.
The long-term sedimentation rates of groups 8 to
10 depend largely on rates of generation of sedimentary-accommodation space. This depends on both
Concepts of Scale
basin subsidence, which is controlled by tectonic
setting� and changes in base level, such as eustasy.
Miall (1978) showed that nonmarine basins, in various tectonic settings, have sedimentation rates averaged over millions of years of 0.03 to 1.5 m/ka. This
subject is reviewed at greater length by Miall (1990),
and in Chap. !! of this book.
3.5 Application of Scale Concepts
to Basin Analysis and Petroleum Geology
The discussion in this chapter is intended to provide
a framework for the analysis of clastic deposits at all
scales, from the individual core sample) through outcrop-scale analysis) to the mapping of reservoir heterogeneities, depositional systems, stratigraphic
sequences, and entire basin-fill complexes.
Research at each level of the hierarchy requires
different techniques. Depositional units in the rock
record up to group 7 and) in exceptional cases) group
8) may be studied using outcrop data, especially if
the lateral-profiling technique described by Miall
(1988a,b) is employed (Chap. 4). Mapping and classification of bounding surfaces between depositional
elements are a key to such analyses. Detailed subsur �
face studies may be successful) if supported by detailed core analyses.
In the case of modern environments, side-scan
sonar techniques coupled with high-resolution)
shallow seismic profiling provide many critical new
data regarding depositional patterns, especially in
the study of estuarine and shelf bedforms and larger
features of groups 6 to 8 (e.g., Berne et a!. 1988, 1991;
Harris 1988).
Units as small as group 6 may be detailed on
exceptionally high-quality petroleum exploration
seismic data, especially on three-dimensional seismic surveys (e.g., Brown 1985, 1991). Larger fe atures,
including stratigraphic sequences of groups 8 to 10
(the third- to fifth-order stratigraphic cycles of Vail
et aL 1977; Miali 1984a, 1990), are now analyzed
routinely on seismic records. Surface and subsurface
lithostratigraphic correlation, with the aid of
magnetostratigraphy, marker beds, and refined biostratigraphic indicators, is also employed (Miali
1984a, 1990). The application of these various methods to the study of fluvial stratigraphic architecture
is described in Sect. 9.5, and examples of various
scales of heterogeneity in fluvial reservoirs (Fig. 3.4)
are described in Chaps. 14 and 15.
the estimates from ancient units incorporate significant intervals of a missing section of a type that are
not present in the modern successions used by
Bridge and Leeder (1979).
Groups 8 and 9 of this book include the Quaternary shelf-margin sequences of Suter et aL (1987)
and the minor and major cyclothems of Heckel
(1986), The sequences described from the Gulf Coast
by Suter et aL (1987) averaged 25000 years in duration and range in thickness fr om about 25 to 160 m,
indicating average accumulation rates of 1-6.4 m/ka.
Heckel (1986) documented the chronology of 55
cycles of Westphalian-Stephanian age in the US
midcontinent. Estimates of the length of this time
span range fr om 8 to 12 million years. The thickness
of the sucession varies from 260 m in Iowa to 550 m
in Kansas. These values indicate an average accumulation rate of between 0.02 and 0.07 m/ka. Many of
the cyles contain substantial fluvial-deltaic sandstone units and, according to Ramsbottom (1979),
who studied similar cyclothems in Europe, rates of
lateral deltaic growth must have been about as rapid
as that of the modern Mississippii yet, the average
sedimentation rate is two orders of magnitude less
than that of the Holocene Mississipi delta complex
and its Pleistocene shelf-margin precursors on the
Louisiana Gulf Coast. Part of the explanation for this
marked contrast is that the Carboniferous cyclothems that were the subject of Heckel's study are
located in a cratonic region, where subsidence rates
would be expected to be substantially lower than on
the continental margin of the Gulf Coast. In addition, many of the cycles are separated by erosion
surfaces. Rapid sedimentation rates of an order-ofmagnitude more were measured by Johnson et al.
(1985) and Friend et al. (1989) in their study of the
Siwalik sediments of Pakistan. Detailed documentation of a nearly 2-km-thick section spanning more
than 9 million years yielded constant long-term sedimentation rates that increase from 0.1 m/ka at the
base to 0.3 m/ka at the top. Individual channel-fill
cycles in this succession are estimated to have return
periods of 1-4 x105 years (group 8 deposits).
Bentham et aL (1993) used magnetostratigraphic
correlation to estimate accumulation rates of0.17 to
0.57 m/ka over a 4 million year time period, for a
braided fluvial system of Eocene age in Spain. Beer
(1990) recorded a maximum accumulation rate of
0.9 m/ka in a Miocene sheetflood deposit in Argentina.
The long-term sedimentation rates of groups 8 to
10 depend largely on rates of generation of sedimentary-accommodation space. This depends on both
Concepts of Scale
basin subsidence, which is controlled by tectonic
setting� and changes in base level, such as eustasy.
Miall (1978) showed that nonmarine basins, in various tectonic settings, have sedimentation rates averaged over millions of years of 0.03 to 1.5 m/ka. This
subject is reviewed at greater length by Miall (1990),
and in Chap. !! of this book.
3.5 Application of Scale Concepts
to Basin Analysis and Petroleum Geology
The discussion in this chapter is intended to provide
a framework for the analysis of clastic deposits at all
scales, from the individual core sample) through outcrop-scale analysis) to the mapping of reservoir heterogeneities, depositional systems, stratigraphic
sequences, and entire basin-fill complexes.
Research at each level of the hierarchy requires
different techniques. Depositional units in the rock
record up to group 7 and) in exceptional cases) group
8) may be studied using outcrop data, especially if
the lateral-profiling technique described by Miall
(1988a,b) is employed (Chap. 4). Mapping and classification of bounding surfaces between depositional
elements are a key to such analyses. Detailed subsur �
face studies may be successful) if supported by detailed core analyses.
In the case of modern environments, side-scan
sonar techniques coupled with high-resolution)
shallow seismic profiling provide many critical new
data regarding depositional patterns, especially in
the study of estuarine and shelf bedforms and larger
features of groups 6 to 8 (e.g., Berne et a!. 1988, 1991;
Harris 1988).
Units as small as group 6 may be detailed on
exceptionally high-quality petroleum exploration
seismic data, especially on three-dimensional seismic surveys (e.g., Brown 1985, 1991). Larger fe atures,
including stratigraphic sequences of groups 8 to 10
(the third- to fifth-order stratigraphic cycles of Vail
et aL 1977; Miali 1984a, 1990), are now analyzed
routinely on seismic records. Surface and subsurface
lithostratigraphic correlation, with the aid of
magnetostratigraphy, marker beds, and refined biostratigraphic indicators, is also employed (Miali
1984a, 1990). The application of these various methods to the study of fluvial stratigraphic architecture
is described in Sect. 9.5, and examples of various
scales of heterogeneity in fluvial reservoirs (Fig. 3.4)
are described in Chaps. 14 and 15.