70
surfaces, pass upward into hummocky cross� stratification, and are capped by plane lamination and
ripples. This is the idealized storm sequence of Dott
and Bourgeois (1982). The first-order surfaces (their
terminology) that bound these sequences represent
the completion of single storm events or storm seasons, and therefore may be used to define deposits of
group 4 or 5 of the present work. At present, there are
no criteria for the distinction between the storm
sequences that might accumulate during individual
storms within an annual storm season, and those
that represent rarer, and perhaps more violent
events, such as hurricanes.
In the eolian environment, dune cross-stratification may include interbedded grain flow, grain fall,
and ripple cross-lamination. These can be separated
in the field by their distinctive facies characteristics,
but determining the temporal significance of each
unit may be extremely difficult (G. Kocurek, pers.
comm., 1988). In coastal environments, differential
heating and cooling of the sea and the land lead to
diurnal fluctuations in the strength and direction of
sea breezes, with a resultant distinctive bundling of
eolian wind-ripple cross-lamination (Hunter and
Richmond 1988). Such bundles are thought to have
low preservation potential, but yearly cycles have
been tentatively identified in ancient deposits
(Hunter and Rubin 1983). The eo1ian third-order
surfaces of Brookfield (1977) are dune reactivation
surfaces, but these could represent daily, seasonal,
or1onger term (e.g., 100-year wind storm) erosional
events (G. Kocurek, pers. comm., 1988). The depositional units enclosed by these surfaces may therefore
be of group 3, 4, or 5 of the present classification.
Some of the eolian stratification surfaces shown in
Fig. 3.SC may include third-order surfaces.
The architecture of estuarine and shelf sand
waves (Allen 1980; Dalrymple 1984), and sand ridges
(Houbolt 1968; Harris 1988), and that of downstream-accreted macroforms in fluvial and deltaic
deposits (Miall 1988a,b; Yang and Nio 1989), is superficially similar (cf. Figs. 3.5B and 3.7 A,B, although
these drawings are at different scales). In each case,
the deposit rests on a flat erosion surface and contains gently dipping ( < 10') accretion surfaces that
commonly truncate underlying bedding at a low
angle (the reactivation surfaces of Fig. 3.5). Bedding,
including cross-bedding, commonly downlaps onto
these accretion surfaces. The deposits typically are
lens-shaped, with a convex-up upper surface. In the
bounding-surface classification of Miall (1988a,b),
the internal accretion surfaces in fluvial macroforms
are classified as third-order surfaces. The C1 and C2
Concepts of Scale
surfaces in the ebb-tide deltas described by Yang and
Nio (1989, p. 187) are comparable. Houbolt (1968)
termed those that occur in sand ridges "master bedding surfaces", and this term has also been applied to
the large modern sand waves studied by Berne et al.
(1988, 1991). Berne et al. (1988) implied an analogy
between their master bedding surfaces and the E2
surfaces of Allen ( 1980). There may be a confusion in
bedform terminology here, because what Berne et al.
(1988) termed sand waves are large structures 3.5 to
7.5 m high, compared to an average height of0.81 m
for those described by Allen (1980) and Dalrymple
(1984; his height data).
These estuarine and fluvial macroforms vary
widely in physical scales and probably represent
sedimentary processes_ acting . over a wide range of
time scales, although data relating to the migration
and accumulation rates of sand ridges are sparse.
Because of this, it is premature to attempt to develop
a common architectural classification scheme for
these deposits. Fluvial third-order erosion surfaces
(e.g., the reactivation surfaces of Fig. 3.5A) are considered to be related to seasonal or longer term (e.g.,
"10-year") floods. They may represent the internal
sedimentary breaks between individual ridges in
point-bar ridge-and-swale topography. They therefore enclose packages of strata of group 5 rank. As
noted above, the E2 surfaces in sand waves enclose
packages of groups 3 and 4. Berne et al. (1988) suggested that the master bedding surfaces in their
bedforms may represent longer-term phenomena,
longer than neap-spring tidal cycles. Possibly, they
are related to storm scour on a yearly or longer-term
scale, in which case the sediment packages between
the surfaces are group 5 deposits of the present classification. Berne et al. ( 1991) carried out seismic and
coring investigations through fields of giant sand
waves, and illustrated a threefold hierarchy of
bounding surfaces . . Their ((second-order" surfaces
(equivalent to master bedding surfaces, labeled D2
surfaces in core; their Figs. lO, 11) probably equate to
E2 surfaces and are of group 5 rank. The internal
structure and migration dynamics of sand ridges are
very poorly known. Harris (1988) suggested that
they consist of superimposed assemblages of sand
waves, separated by master bedding surfaces. If this
is the case, the master bedding surfaces may represent major erosional events, such as the "100-year
event" of group 6, for example, the scour of rare
violent storms.
The bounding surfaces that enclose entire fluvial
macroforms, sand waves, and sand ridges typically
have convex-up shapes. This reflects accretionary
surfaces, pass upward into hummocky cross� stratification, and are capped by plane lamination and
ripples. This is the idealized storm sequence of Dott
and Bourgeois (1982). The first-order surfaces (their
terminology) that bound these sequences represent
the completion of single storm events or storm seasons, and therefore may be used to define deposits of
group 4 or 5 of the present work. At present, there are
no criteria for the distinction between the storm
sequences that might accumulate during individual
storms within an annual storm season, and those
that represent rarer, and perhaps more violent
events, such as hurricanes.
In the eolian environment, dune cross-stratification may include interbedded grain flow, grain fall,
and ripple cross-lamination. These can be separated
in the field by their distinctive facies characteristics,
but determining the temporal significance of each
unit may be extremely difficult (G. Kocurek, pers.
comm., 1988). In coastal environments, differential
heating and cooling of the sea and the land lead to
diurnal fluctuations in the strength and direction of
sea breezes, with a resultant distinctive bundling of
eolian wind-ripple cross-lamination (Hunter and
Richmond 1988). Such bundles are thought to have
low preservation potential, but yearly cycles have
been tentatively identified in ancient deposits
(Hunter and Rubin 1983). The eo1ian third-order
surfaces of Brookfield (1977) are dune reactivation
surfaces, but these could represent daily, seasonal,
or1onger term (e.g., 100-year wind storm) erosional
events (G. Kocurek, pers. comm., 1988). The depositional units enclosed by these surfaces may therefore
be of group 3, 4, or 5 of the present classification.
Some of the eolian stratification surfaces shown in
Fig. 3.SC may include third-order surfaces.
The architecture of estuarine and shelf sand
waves (Allen 1980; Dalrymple 1984), and sand ridges
(Houbolt 1968; Harris 1988), and that of downstream-accreted macroforms in fluvial and deltaic
deposits (Miall 1988a,b; Yang and Nio 1989), is superficially similar (cf. Figs. 3.5B and 3.7 A,B, although
these drawings are at different scales). In each case,
the deposit rests on a flat erosion surface and contains gently dipping ( < 10') accretion surfaces that
commonly truncate underlying bedding at a low
angle (the reactivation surfaces of Fig. 3.5). Bedding,
including cross-bedding, commonly downlaps onto
these accretion surfaces. The deposits typically are
lens-shaped, with a convex-up upper surface. In the
bounding-surface classification of Miall (1988a,b),
the internal accretion surfaces in fluvial macroforms
are classified as third-order surfaces. The C1 and C2
Concepts of Scale
surfaces in the ebb-tide deltas described by Yang and
Nio (1989, p. 187) are comparable. Houbolt (1968)
termed those that occur in sand ridges "master bedding surfaces", and this term has also been applied to
the large modern sand waves studied by Berne et al.
(1988, 1991). Berne et al. (1988) implied an analogy
between their master bedding surfaces and the E2
surfaces of Allen ( 1980). There may be a confusion in
bedform terminology here, because what Berne et al.
(1988) termed sand waves are large structures 3.5 to
7.5 m high, compared to an average height of0.81 m
for those described by Allen (1980) and Dalrymple
(1984; his height data).
These estuarine and fluvial macroforms vary
widely in physical scales and probably represent
sedimentary processes_ acting . over a wide range of
time scales, although data relating to the migration
and accumulation rates of sand ridges are sparse.
Because of this, it is premature to attempt to develop
a common architectural classification scheme for
these deposits. Fluvial third-order erosion surfaces
(e.g., the reactivation surfaces of Fig. 3.5A) are considered to be related to seasonal or longer term (e.g.,
"10-year") floods. They may represent the internal
sedimentary breaks between individual ridges in
point-bar ridge-and-swale topography. They therefore enclose packages of strata of group 5 rank. As
noted above, the E2 surfaces in sand waves enclose
packages of groups 3 and 4. Berne et al. (1988) suggested that the master bedding surfaces in their
bedforms may represent longer-term phenomena,
longer than neap-spring tidal cycles. Possibly, they
are related to storm scour on a yearly or longer-term
scale, in which case the sediment packages between
the surfaces are group 5 deposits of the present classification. Berne et al. ( 1991) carried out seismic and
coring investigations through fields of giant sand
waves, and illustrated a threefold hierarchy of
bounding surfaces . . Their ((second-order" surfaces
(equivalent to master bedding surfaces, labeled D2
surfaces in core; their Figs. lO, 11) probably equate to
E2 surfaces and are of group 5 rank. The internal
structure and migration dynamics of sand ridges are
very poorly known. Harris (1988) suggested that
they consist of superimposed assemblages of sand
waves, separated by master bedding surfaces. If this
is the case, the master bedding surfaces may represent major erosional events, such as the "100-year
event" of group 6, for example, the scour of rare
violent storms.
The bounding surfaces that enclose entire fluvial
macroforms, sand waves, and sand ridges typically
have convex-up shapes. This reflects accretionary