process and to the transformation from a wave- to a
tide-dominated estuary (Dalrymple and Zaitlin, 1994).
4. Sediment supply. In general terms, the amount of sediment supply will control the nature of sedimentation in
estuarine environments. The most extreme case would
be a give-up estuary, where conditions of very reduced
sediment supply would be insufficient to generate an
incised-valley fill (Cooper et al., 2012). Low-supplied
systems are mainly filled with marine sediments,
such as the case of French estuarine environments
(Chaumillon et al., 2010). In general, those lowsupplied estuaries show reduced and absent TSTs.
The variability of sediment supply is particularly important during estuarine transgression, as high-sediment
supply may account for significant development of estuarine mouth barriers under wave dominance, or high
fluvial supply may favor anomalously thick TSTs.
In contrast, highstand conditions are generally characterized by increases of sediment supply, as the decrease
in the rate of sea-level rise favors the influence of
fluvial sedimentation, accounting for the generation of
bayhead deltas that may develop seaward into prodeltaic
environments and ultimately leading to significant finegrained sediment delivery to the shelf. In addition, carbonate production may also be enhanced by highstand
conditions, thus increasing the volume of the HST
(Tessier, 2012).
5. Climate change. The impact of recent climatic variability
on estuarine sediment infillings has been addressed in
several recent studies, mainly in northwestern Europe
and the Gulf of Mexico estuaries. For example, periods
of increased storminess at millennial timescales are
mainly recorded in marginal estuarine highstand facies,
where the destruction of coastal barriers adjacent to estuarine settings and tidal incisions has been documented
(Tessier et al., 2012). The activity of intense storms
may also be imprinted in the estuary mouth through
the formation of wave-dominated sandy facies (Tessier,
2012). In the Gulf of Mexico, several recent transitions
from dry to humid conditions appear to be responsible
of sediment supply reductions to estuarine settings
(Anderson et al., 2008; Simms et al., 2008).
6. Human influences. The exploitation of drainage basins
for human activities in the last few centuries is argued
to have caused significant modifications of estuarine
sediment rates. In particular, a recent period (i.e., the last
1,000 years) of increased fine-grained deposition
documented in several French estuaries has been related
to increased soil erosion by deforestation and agricultural
practices (Tessier, 2012). The intensification of agricultural practices as triggering mechanism for bayhead delta
growth has also been documented in some estuaries
along the Gulf of Mexico coast (Anderson et al., 2008).
Recent and future trends
Future research on sediment infill of present-day estuarine
systems should be directed at improving the definition of
estuarine systems by using different techniques and/or
approaches such as the following (Boyd et al., 2006):
1. Numeric models that can provide a quantitative
approach to the major operating processes (sediment
flux versus relative sea-level changes) and can be used
to predict the future estuarine behavior.
2. 3D seismic data and seabed imagery can enhance our
visualization of the complexity of estuarine sedimentary environments.
3. Other geological approaches such as brackish
ichnology and petrological and chemostratigraphical
studies, among others, may be helpful for the recognition of estuarine facies and for the subdivision of the
estuarine record into different sequences.
4. Improved knowledge of the longitudinal variability of
the estuarine infill, as most of the present knowledge
involves lateral variability (Tessier, 2012).
5. Better understanding of the influence of anthropic
activities in the development of estuarine stratigraphy,
which is thus far poorly documented (Tessier, 2012).
Summary
The sedimentary infill of present-day estuaries has been
mostly generated during the course of the postglacial
sea-level rise (simple infill), although in some cases older
sequences may be preserved in deep incised valleys
(compound infill). The base of the infill is generally
represented by a Last Glacial Maximum incised valley,
which may be covered by lowstand (to early transgressive) fluvial deposits. The record of subsequent transgressive to highstand sediments and surfaces will be
mostly determined by the hydrodynamic conditions, with
two end-member cases (wave- versus tide-dominated
estuaries).
Most wave-dominated estuaries show a major development of transgressive deposits, either with preferential
occurrence of the outer marine sand body, in cases of moderate tidal ravinement, or with major generation and/or
preservation of bayhead deltas and central basin facies,
under conditions of very high sediment supply.
A different picture has been provided in narrow incisedvalley estuaries, where the transgressive interval is
recorded by a widespread sand sheet, and the major development of the estuarine stratigraphy takes place during
highstand conditions.
In the case of tide-dominated estuaries, two distinct
stratigraphies may be observed. A major development of
transgressive deposits is linked to tidal activity (and widespread occurrence of the tidal ravinement surface) that
favor the generation of tidal sand ridges. Alternatively,
a very strong tidal ravinement would cause the erosion
of most of the transgressive deposits and major deposition
of estuarine facies (tidal sand ridges and fluvial point bars)
during the subsequent highstand.
Other estuary systems show peculiar stratigraphic features. For example, rias and rocky-bound estuaries tend
to preserve older sequences in the deep estuarine sections.
ESTUARINE SEDIMENTATION
297
tide-dominated estuary (Dalrymple and Zaitlin, 1994).
4. Sediment supply. In general terms, the amount of sediment supply will control the nature of sedimentation in
estuarine environments. The most extreme case would
be a give-up estuary, where conditions of very reduced
sediment supply would be insufficient to generate an
incised-valley fill (Cooper et al., 2012). Low-supplied
systems are mainly filled with marine sediments,
such as the case of French estuarine environments
(Chaumillon et al., 2010). In general, those lowsupplied estuaries show reduced and absent TSTs.
The variability of sediment supply is particularly important during estuarine transgression, as high-sediment
supply may account for significant development of estuarine mouth barriers under wave dominance, or high
fluvial supply may favor anomalously thick TSTs.
In contrast, highstand conditions are generally characterized by increases of sediment supply, as the decrease
in the rate of sea-level rise favors the influence of
fluvial sedimentation, accounting for the generation of
bayhead deltas that may develop seaward into prodeltaic
environments and ultimately leading to significant finegrained sediment delivery to the shelf. In addition, carbonate production may also be enhanced by highstand
conditions, thus increasing the volume of the HST
(Tessier, 2012).
5. Climate change. The impact of recent climatic variability
on estuarine sediment infillings has been addressed in
several recent studies, mainly in northwestern Europe
and the Gulf of Mexico estuaries. For example, periods
of increased storminess at millennial timescales are
mainly recorded in marginal estuarine highstand facies,
where the destruction of coastal barriers adjacent to estuarine settings and tidal incisions has been documented
(Tessier et al., 2012). The activity of intense storms
may also be imprinted in the estuary mouth through
the formation of wave-dominated sandy facies (Tessier,
2012). In the Gulf of Mexico, several recent transitions
from dry to humid conditions appear to be responsible
of sediment supply reductions to estuarine settings
(Anderson et al., 2008; Simms et al., 2008).
6. Human influences. The exploitation of drainage basins
for human activities in the last few centuries is argued
to have caused significant modifications of estuarine
sediment rates. In particular, a recent period (i.e., the last
1,000 years) of increased fine-grained deposition
documented in several French estuaries has been related
to increased soil erosion by deforestation and agricultural
practices (Tessier, 2012). The intensification of agricultural practices as triggering mechanism for bayhead delta
growth has also been documented in some estuaries
along the Gulf of Mexico coast (Anderson et al., 2008).
Recent and future trends
Future research on sediment infill of present-day estuarine
systems should be directed at improving the definition of
estuarine systems by using different techniques and/or
approaches such as the following (Boyd et al., 2006):
1. Numeric models that can provide a quantitative
approach to the major operating processes (sediment
flux versus relative sea-level changes) and can be used
to predict the future estuarine behavior.
2. 3D seismic data and seabed imagery can enhance our
visualization of the complexity of estuarine sedimentary environments.
3. Other geological approaches such as brackish
ichnology and petrological and chemostratigraphical
studies, among others, may be helpful for the recognition of estuarine facies and for the subdivision of the
estuarine record into different sequences.
4. Improved knowledge of the longitudinal variability of
the estuarine infill, as most of the present knowledge
involves lateral variability (Tessier, 2012).
5. Better understanding of the influence of anthropic
activities in the development of estuarine stratigraphy,
which is thus far poorly documented (Tessier, 2012).
Summary
The sedimentary infill of present-day estuaries has been
mostly generated during the course of the postglacial
sea-level rise (simple infill), although in some cases older
sequences may be preserved in deep incised valleys
(compound infill). The base of the infill is generally
represented by a Last Glacial Maximum incised valley,
which may be covered by lowstand (to early transgressive) fluvial deposits. The record of subsequent transgressive to highstand sediments and surfaces will be
mostly determined by the hydrodynamic conditions, with
two end-member cases (wave- versus tide-dominated
estuaries).
Most wave-dominated estuaries show a major development of transgressive deposits, either with preferential
occurrence of the outer marine sand body, in cases of moderate tidal ravinement, or with major generation and/or
preservation of bayhead deltas and central basin facies,
under conditions of very high sediment supply.
A different picture has been provided in narrow incisedvalley estuaries, where the transgressive interval is
recorded by a widespread sand sheet, and the major development of the estuarine stratigraphy takes place during
highstand conditions.
In the case of tide-dominated estuaries, two distinct
stratigraphies may be observed. A major development of
transgressive deposits is linked to tidal activity (and widespread occurrence of the tidal ravinement surface) that
favor the generation of tidal sand ridges. Alternatively,
a very strong tidal ravinement would cause the erosion
of most of the transgressive deposits and major deposition
of estuarine facies (tidal sand ridges and fluvial point bars)
during the subsequent highstand.
Other estuary systems show peculiar stratigraphic features. For example, rias and rocky-bound estuaries tend
to preserve older sequences in the deep estuarine sections.
ESTUARINE SEDIMENTATION
297