68
Turning to the alluvial environment, paleosols
require several thousand years to develop, and may
take at least tens of thousands of years to reach
"maturity'' (Leeder 1975; Retallack 1984; Wright
1990; see Sects. 9.2, 10.3.1 for additional discussion).
Most river valleys aggraded with fl uvial and estuarine deposits immediately following the postglacial
sea-level rise. Following this, many rivers have had
6000 to 8000 years to build major delta complexes.
The modern (postglacial) Mississippi delta complex
is one example (Kolb and Van Lopil< 1966; Frazier
1967). The Rh6ne delta is another. Both are illustrated in Fig. 3.8.
Fluvial deposits of groups 8 to I! are described
at length in Chap. 9. The sequence stratigraphy of
these deposits is discussed in Chap. 13. The following
are some brief notes on marine and nonmarine deposits.
Group 8 sedimentary bodies represent time periods of tens to hundreds of thousands of years. Examples include major fluvial channel-belt deposits,
such as the "third-order" cycles of the Siwalik Group
in Pakistan (as demonstrated by detailed studies of
the magnetostratigraphy by johnson et a!. 1985). The
nine eolian "complexes" bounded by supersurfaces
described by Kocurek et a!. (1991) each represent an
average of about 700000 years. Other examples include such major depositional elements as delta
complexes and alluvial fans, shelf sand-ridge fi elds
(group III "regional lentils" of Shurr 1984), and major lobes of submarine fans (third-order «turbidite
stages" of Mutti and Normark 1987). The distribution in time and space of such elements is commonly
controlled by regional tectonism or by regional sealevel change which itself is commonly caused, in
turn, by tectonism, astronomical (Milankovitch)
forcing, such as glacioeustasy, or other eustatic
causes.
Many stratigraphic sequences are of group 8, such
as the "minor" cyclothems of Heckel (1986), the
''punctuated aggradational cycles" of Goodwin and
Anderson (1985), and the Cardium Sandstone cycles
of Plint et a!. (1986). These have been termed "fifthorder cycles)> in earlier syntheses (Vail et al. 1977;
Miall 1984a, 1990). The Cardium sequences may
record tectonic thrust-loading events, as suggested
by Swift and Rice (1984), who pointed out the common occurrence of repeated coarsening-upward
cycles in shelf sandstone bodies of the Cretaceous
Western Interior. This model has now been developed by many workers, as discussed in Sect. 13.4.
Other fifth -order cycles (group 8 deposits of this
classification) m�y be caused by glacioeustatic seaConcepts of Scale
level change. For example, Suter et a!. (1987) described six sequences that have formed on the Louisiana continental shelf since about 150 ka, with an
average duration of25000 years. There is increasing
evidence of astronomical forcing in t h e development
of cycles of this duration - the so-called
Milankovitch cycles (Fischer 1986). For example,
Olsen (1990, 1994) postulated a Milankovitch
cyclicity to explain variations in fluvial cycle thickness and calculated stream discharge in some Devonian deposits of East Greenland (Sects. 9.2, 12.13).
Major bounding surfaces within group 8 deposits
may not be caused by autogenic mechanisms, such
as channel migration, but may be regional in extent
and allogenic in nature. Such are the ravinement
surfaces and other types of diastem described by
Nummedal and Swift (1987), and the sequence
boundaries of Van Wagoner et a!. (1990; see Chap.
13).
Group 9 deposits represent major depositional
systems, accumulating over hundreds of thousands
to a few millions of years. Some stratigraphic sequences, including many cyclothems (the ''major"
cycles of Heckel 1986), are of this group. These have
been termed ''fourth-order cycles'' in earlier syntheses (Vail et al. 1977; Miall 1984a, 1990), in a numbering system that uses lower "order" numbers for
cycles of increasing duration (the reverse of the
''group" numbering used here).
Group 10 deposits are basin-fill complexes (depositional systems tracts), representing time spans of
millions to tens of millions of years. They correspond to "third-order cycles" in earlier syntheses.
There is ample evidence for such cycles in the stratigraphic record, including Cambrian grand cycles
(Aitken 1966, 1978; Chow and james 1987), Carboniferous megacyclothems (Heckel 1986) and mesothems (Ramsbottom 1979), and the Cretaceous
mesothems of the Western Interior (Weimer 1960;
Kauffman 1969, 1984). Regional or global sea-level
changes caused by regional tectonism, or by global
changes in seafloor spreading rates, may be the main
mechanism leading to the development of this type
of cyclicity. Another promising idea regarding the
origin of third-order cycles is that of plate-margin
tilting as a result of in-plane stress transmitted
across plate interiors from extensional or compressional plate margins (Cloetingh 1988). Miall (1990,
1991c) provided reviews of this topic, and the ideas
are discussed further in Sects. 11.3.5 and 13.4.
Second- and first-order cycles, in the terminology
of Vail et a!. (1977) and Mia!! (1990), may be designated stratigraphic groupS 11 and 12, if required.
Turning to the alluvial environment, paleosols
require several thousand years to develop, and may
take at least tens of thousands of years to reach
"maturity'' (Leeder 1975; Retallack 1984; Wright
1990; see Sects. 9.2, 10.3.1 for additional discussion).
Most river valleys aggraded with fl uvial and estuarine deposits immediately following the postglacial
sea-level rise. Following this, many rivers have had
6000 to 8000 years to build major delta complexes.
The modern (postglacial) Mississippi delta complex
is one example (Kolb and Van Lopil< 1966; Frazier
1967). The Rh6ne delta is another. Both are illustrated in Fig. 3.8.
Fluvial deposits of groups 8 to I! are described
at length in Chap. 9. The sequence stratigraphy of
these deposits is discussed in Chap. 13. The following
are some brief notes on marine and nonmarine deposits.
Group 8 sedimentary bodies represent time periods of tens to hundreds of thousands of years. Examples include major fluvial channel-belt deposits,
such as the "third-order" cycles of the Siwalik Group
in Pakistan (as demonstrated by detailed studies of
the magnetostratigraphy by johnson et a!. 1985). The
nine eolian "complexes" bounded by supersurfaces
described by Kocurek et a!. (1991) each represent an
average of about 700000 years. Other examples include such major depositional elements as delta
complexes and alluvial fans, shelf sand-ridge fi elds
(group III "regional lentils" of Shurr 1984), and major lobes of submarine fans (third-order «turbidite
stages" of Mutti and Normark 1987). The distribution in time and space of such elements is commonly
controlled by regional tectonism or by regional sealevel change which itself is commonly caused, in
turn, by tectonism, astronomical (Milankovitch)
forcing, such as glacioeustasy, or other eustatic
causes.
Many stratigraphic sequences are of group 8, such
as the "minor" cyclothems of Heckel (1986), the
''punctuated aggradational cycles" of Goodwin and
Anderson (1985), and the Cardium Sandstone cycles
of Plint et a!. (1986). These have been termed "fifthorder cycles)> in earlier syntheses (Vail et al. 1977;
Miall 1984a, 1990). The Cardium sequences may
record tectonic thrust-loading events, as suggested
by Swift and Rice (1984), who pointed out the common occurrence of repeated coarsening-upward
cycles in shelf sandstone bodies of the Cretaceous
Western Interior. This model has now been developed by many workers, as discussed in Sect. 13.4.
Other fifth -order cycles (group 8 deposits of this
classification) m�y be caused by glacioeustatic seaConcepts of Scale
level change. For example, Suter et a!. (1987) described six sequences that have formed on the Louisiana continental shelf since about 150 ka, with an
average duration of25000 years. There is increasing
evidence of astronomical forcing in t h e development
of cycles of this duration - the so-called
Milankovitch cycles (Fischer 1986). For example,
Olsen (1990, 1994) postulated a Milankovitch
cyclicity to explain variations in fluvial cycle thickness and calculated stream discharge in some Devonian deposits of East Greenland (Sects. 9.2, 12.13).
Major bounding surfaces within group 8 deposits
may not be caused by autogenic mechanisms, such
as channel migration, but may be regional in extent
and allogenic in nature. Such are the ravinement
surfaces and other types of diastem described by
Nummedal and Swift (1987), and the sequence
boundaries of Van Wagoner et a!. (1990; see Chap.
13).
Group 9 deposits represent major depositional
systems, accumulating over hundreds of thousands
to a few millions of years. Some stratigraphic sequences, including many cyclothems (the ''major"
cycles of Heckel 1986), are of this group. These have
been termed ''fourth-order cycles'' in earlier syntheses (Vail et al. 1977; Miall 1984a, 1990), in a numbering system that uses lower "order" numbers for
cycles of increasing duration (the reverse of the
''group" numbering used here).
Group 10 deposits are basin-fill complexes (depositional systems tracts), representing time spans of
millions to tens of millions of years. They correspond to "third-order cycles" in earlier syntheses.
There is ample evidence for such cycles in the stratigraphic record, including Cambrian grand cycles
(Aitken 1966, 1978; Chow and james 1987), Carboniferous megacyclothems (Heckel 1986) and mesothems (Ramsbottom 1979), and the Cretaceous
mesothems of the Western Interior (Weimer 1960;
Kauffman 1969, 1984). Regional or global sea-level
changes caused by regional tectonism, or by global
changes in seafloor spreading rates, may be the main
mechanism leading to the development of this type
of cyclicity. Another promising idea regarding the
origin of third-order cycles is that of plate-margin
tilting as a result of in-plane stress transmitted
across plate interiors from extensional or compressional plate margins (Cloetingh 1988). Miall (1990,
1991c) provided reviews of this topic, and the ideas
are discussed further in Sects. 11.3.5 and 13.4.
Second- and first-order cycles, in the terminology
of Vail et a!. (1977) and Mia!! (1990), may be designated stratigraphic groupS 11 and 12, if required.