fluctuations, the most significant of them related to the
8.2 ka abrupt climatic event (Rodriguez et al., 2010), or
to recent climatic changes such as transitions to more
humid conditions (Simms et al., 2008) or to changes in
wind strengths (Troiani et al., 2011).
2. The transgressive parasequences are mainly composed
of bayhead deltas, evolving upward to central basin
facies (Figure 4); the development of barrier systems
has taken place only in the most recent estuarine filling
stages and is generally restricted to the outermost parts
of the estuaries (Anderson et al., 2008; Maddox et al.,
2008; Milliken et al., 2008).
In contrast to the primary model that favored estuarine
deposition during the transgression stage, a different
scheme has been documented in numerous southeastern
Australian wave-dominated estuarine systems, which is
mainly applicable to the infilling of narrow incised valleys.
In the case of low sediment supplies, these estuaries act as
open coastal embayments during inundation of the incised
valley. There, the main characteristic is the deposition of
a basinwide transgressive sand sheet composed of
washover and tidal channel sands and sand flats that extends
much farther landward than the barrier of models described
above (Sloss et al., 2005, 2006). The low fluvial supply
does not favor bayhead delta construction during estuarine
flooding (Heap and Nichol, 1997). The major development
of estuarine infilling takes place during the highstand stage,
due to continued growth of the sandy barrier, infilling of the
tidal inlet, and development of a flood tidal delta. These all
favor the development of estuarine infilling back-barrier
facies. This process also triggers the progradation of
bayhead deltas (with delta mouth bar sands and prodelta
deposits) at the landward margins, induced by a relative
sea-level fall (Sloss et al., 2005, 2006).
In the case of shallow incised valleys, but with conditions of high sedimentation rates, the main stratigraphic
consequence would be the absence of fine-grained central
basins due to enhanced fluvial sediment flux and/or low
wave energy retarding the construction of subaerial barriers (Heap and Nichol, 1997). Instead, the occurrence of
sediment bars would indicate localized tide dominance
(Abrahim et al., 2008).
Tide-dominated estuaries
The stratigraphic patterns of tide-dominated estuaries are
much less studied than the wave-dominated systems. The
most significant examples of tide-dominated estuarine
stratigraphy are provided by the Cobequid Bay-Salmon
River Estuary (Dalrymple and Zaitlin, 1994) and several
estuaries along the French coast of the English Channel
and the northern Bay of Biscay (Tessier, 2012).
The sequence boundary of tide-dominated estuaries is
a fluvial valley related to a sea-level fall, conforming to
the generic definition (Figure 5). This is possibly due to
the fact that narrow-valley features are necessary to cause
an increase of tidal influence and by extension to generate
a tide-dominated estuary. The LST deposited at the bottom
of the fluvial valley is generally strongly reduced due to
very strong tidal transgressive ravinement (Tessier, 2012).
The main stratigraphic component of tide-dominated
estuaries is the marine sand body composed by tidal sandbars (Figure 5). Landward, the tidal sandbars may evolve
to point-bar deposits sandwiched by straight tidal-fluvial
deposits (Dalrymple et al., 1992), but bayhead deltas are
not present (Dalrymple and Zaitlin, 1994). According to
local hydrodynamic and sediment supply conditions, the
bulk of the infill may be related either to the TST or to
the HST.
Stratigraphic patterns of tide-dominated estuaries
derived soon after the development of the estuarine facies
model, and stratigraphy depicted the main development of
estuarine facies as preferentially taking place during the
transgressive interval (Dalrymple and Zaitlin, 1994). The
dominance of transgressive over highstand deposition
was linked to the development of extensive sediment
facies during the estuarine flooding (Figure 5), from significant fluvial transgressive deposition to tidal ridge systems related to the transport of sediments into the estuary
due to tidal current amplification (Zhang and Li, 1996;
Lin et al., 2005). In these cases, the estuarine HST is composed of the most recent (thin) infilling stages that tend to
bury the transgressive infilling (Figure 5).
However, more recent case studies have shown that the
bulk of the infill may have occurred under highstand conditions (Figure 6), and the TST is an aggradational unit of
reduced volume. This pattern is usually related to strong
tidal ravinement and deep occurrence of the TRS, which
cause the erosion of the TST, and the development of thick
highstand tidal sand bodies, resulting in the dominance of
the HST, particularly at the estuarine mouth (Tessier,
2012; Tessier et al., 2012).
The TRS is the most important stratigraphic surface in
the sediment record of tide-dominated estuaries, as it
extends through the entire estuarine section (Figure 6),
although the TRS may not incise as deeply as in wavedominated or mixed estuaries due to the absence of channel constriction at the estuary mouth (Dalrymple and
Zaitlin, 1994). Depending on the major development of
estuarine facies, the TRS may be amalgamated with other
estuarine surfaces. For example, in the case of major estuarine infill during transgression, the TRS is amalgamated
with the TS, whereas during major estuarine development
during the highstand, the TRS is amalgamated with the
MFS (Figure 6). In contrast, the WRS tends to be absent
or poorly developed, as a wave-dominated shoreface is
not present (Dalrymple and Zaitlin, 1994).
Another significant stratigraphic feature of tidedominated estuaries is the fact that most of them contain
wave-dominated facies, which may exhibit temporal or
spatial variability. For example, several tide-dominated
estuaries have wave-dominated environments, such as
coastal barriers or central muddy basins during the transgressive stage, indicating that most tide-dominated estuaries undergo a significant change during their
development, most possibly due to tidal amplification
294
ESTUARINE SEDIMENTATION
8.2 ka abrupt climatic event (Rodriguez et al., 2010), or
to recent climatic changes such as transitions to more
humid conditions (Simms et al., 2008) or to changes in
wind strengths (Troiani et al., 2011).
2. The transgressive parasequences are mainly composed
of bayhead deltas, evolving upward to central basin
facies (Figure 4); the development of barrier systems
has taken place only in the most recent estuarine filling
stages and is generally restricted to the outermost parts
of the estuaries (Anderson et al., 2008; Maddox et al.,
2008; Milliken et al., 2008).
In contrast to the primary model that favored estuarine
deposition during the transgression stage, a different
scheme has been documented in numerous southeastern
Australian wave-dominated estuarine systems, which is
mainly applicable to the infilling of narrow incised valleys.
In the case of low sediment supplies, these estuaries act as
open coastal embayments during inundation of the incised
valley. There, the main characteristic is the deposition of
a basinwide transgressive sand sheet composed of
washover and tidal channel sands and sand flats that extends
much farther landward than the barrier of models described
above (Sloss et al., 2005, 2006). The low fluvial supply
does not favor bayhead delta construction during estuarine
flooding (Heap and Nichol, 1997). The major development
of estuarine infilling takes place during the highstand stage,
due to continued growth of the sandy barrier, infilling of the
tidal inlet, and development of a flood tidal delta. These all
favor the development of estuarine infilling back-barrier
facies. This process also triggers the progradation of
bayhead deltas (with delta mouth bar sands and prodelta
deposits) at the landward margins, induced by a relative
sea-level fall (Sloss et al., 2005, 2006).
In the case of shallow incised valleys, but with conditions of high sedimentation rates, the main stratigraphic
consequence would be the absence of fine-grained central
basins due to enhanced fluvial sediment flux and/or low
wave energy retarding the construction of subaerial barriers (Heap and Nichol, 1997). Instead, the occurrence of
sediment bars would indicate localized tide dominance
(Abrahim et al., 2008).
Tide-dominated estuaries
The stratigraphic patterns of tide-dominated estuaries are
much less studied than the wave-dominated systems. The
most significant examples of tide-dominated estuarine
stratigraphy are provided by the Cobequid Bay-Salmon
River Estuary (Dalrymple and Zaitlin, 1994) and several
estuaries along the French coast of the English Channel
and the northern Bay of Biscay (Tessier, 2012).
The sequence boundary of tide-dominated estuaries is
a fluvial valley related to a sea-level fall, conforming to
the generic definition (Figure 5). This is possibly due to
the fact that narrow-valley features are necessary to cause
an increase of tidal influence and by extension to generate
a tide-dominated estuary. The LST deposited at the bottom
of the fluvial valley is generally strongly reduced due to
very strong tidal transgressive ravinement (Tessier, 2012).
The main stratigraphic component of tide-dominated
estuaries is the marine sand body composed by tidal sandbars (Figure 5). Landward, the tidal sandbars may evolve
to point-bar deposits sandwiched by straight tidal-fluvial
deposits (Dalrymple et al., 1992), but bayhead deltas are
not present (Dalrymple and Zaitlin, 1994). According to
local hydrodynamic and sediment supply conditions, the
bulk of the infill may be related either to the TST or to
the HST.
Stratigraphic patterns of tide-dominated estuaries
derived soon after the development of the estuarine facies
model, and stratigraphy depicted the main development of
estuarine facies as preferentially taking place during the
transgressive interval (Dalrymple and Zaitlin, 1994). The
dominance of transgressive over highstand deposition
was linked to the development of extensive sediment
facies during the estuarine flooding (Figure 5), from significant fluvial transgressive deposition to tidal ridge systems related to the transport of sediments into the estuary
due to tidal current amplification (Zhang and Li, 1996;
Lin et al., 2005). In these cases, the estuarine HST is composed of the most recent (thin) infilling stages that tend to
bury the transgressive infilling (Figure 5).
However, more recent case studies have shown that the
bulk of the infill may have occurred under highstand conditions (Figure 6), and the TST is an aggradational unit of
reduced volume. This pattern is usually related to strong
tidal ravinement and deep occurrence of the TRS, which
cause the erosion of the TST, and the development of thick
highstand tidal sand bodies, resulting in the dominance of
the HST, particularly at the estuarine mouth (Tessier,
2012; Tessier et al., 2012).
The TRS is the most important stratigraphic surface in
the sediment record of tide-dominated estuaries, as it
extends through the entire estuarine section (Figure 6),
although the TRS may not incise as deeply as in wavedominated or mixed estuaries due to the absence of channel constriction at the estuary mouth (Dalrymple and
Zaitlin, 1994). Depending on the major development of
estuarine facies, the TRS may be amalgamated with other
estuarine surfaces. For example, in the case of major estuarine infill during transgression, the TRS is amalgamated
with the TS, whereas during major estuarine development
during the highstand, the TRS is amalgamated with the
MFS (Figure 6). In contrast, the WRS tends to be absent
or poorly developed, as a wave-dominated shoreface is
not present (Dalrymple and Zaitlin, 1994).
Another significant stratigraphic feature of tidedominated estuaries is the fact that most of them contain
wave-dominated facies, which may exhibit temporal or
spatial variability. For example, several tide-dominated
estuaries have wave-dominated environments, such as
coastal barriers or central muddy basins during the transgressive stage, indicating that most tide-dominated estuaries undergo a significant change during their
development, most possibly due to tidal amplification
294
ESTUARINE SEDIMENTATION