Steers, J. A., 1964. The Coastline of England and Wales, 2nd edn.
Cambridge: Cambridge University Press, p. 750.
Syvitski, J. P. M., and MacDonald, R., 1982. Sediment character
and provenance in a complex fjord; Howe Sound, British
Columbia. Sedimentary Geology, 36, 217–244.
Syvitski, J. P. M., Burrell, D. C., and Skei, J. M., 1987. Fjords: Processes and Products. New York: Springer, p. 279.
Zhao, J., Bianchi, T. S., Li, X., Allison, M. A., Yao, P., and Yu, Z.,
2012. Historical eutrophication in the Changjiang and Mississippi delta-front estuaries: stable sedimentary chloropigments
as biomarkers. Continental Shelf Research, 47, 133–144.
Cross-references
Coastal Bays
Coastal Lagoons
Fjord
Ria
Sediment Transport
Sandbanks
ESTUARINE SEDIMENTATION
Francisco José Lobo
Instituto Andaluz de Ciencias de la Tierra,
CSIC-Universidad de Granada, Armilla/Granada, Spain
Definition
An estuary was originally defined in geological terms as
the seaward portion of a drowned valley system that
receives sediments from both fluvial and marine sources
and which contains facies influenced by tide, wave, and
fluvial processes (Dalrymple et al., 1992). The estuary
itself is regarded as the middle reach (or segment 2) of
a complete incised-valley succession (Figure 1), being
bounded seaward by the shoreline position at the beginning of the highstand and landward by the limit of marine
influence (Dalrymple et al., 1994). A revised definition
considers an estuary as a transgressive coastal environment at the mouth of a river, which is not necessarily
linked to an incised valley. Instead, the two fundamental
criteria for estuarine system generation are the existence
of a relative sea-level rise leading to transgression and
the occurrence of net landward sediment transport
(Dalrymple, 2006).
Importance of estuaries
Modern drowned river valleys are generally populated
environments that constitute the site of numerous human
activities of economic importance. For example, they are
emplacement sites of industrial practices (harbors, wastedisposal sites); they also constitute fragile environments
of ecological significance, as they often support productive fisheries; and they also support recreational activities
mainly related to tourism (Dalrymple et al., 1994). In addition, they can host significant quantities of hydrocarbon
reserves produced by sand-dominated clastic reservoirs
(Boyd et al., 2006). Finally, they can be used to predict
future scenarios of environmental response to global
change, as they are sensitive to sea-level and climate
fluctuations (Tessier, 2012). In particular, they are good
candidates to apply sequence stratigraphy concepts at the
land-sea transition, allowing the precise identification of
sequence boundaries (Zaitlin et al., 1994; Chaumillon
et al., 2010). More recently, they have been investigated
as paleoclimatic and paleoceanographic sedimentary
archives (Troiani et al., 2011; Tessier, 2012).
Historical development
Historically, the study of estuarine deposits is logically
linked to incised-valley systems. The early studies focused
on the importance of erosional subaerial unconformities
for the subdivision of the stratigraphic record
(Dalrymple, 2006), with a fairly good documentation of
the plan-view geometry of the valleys (Dalrymple et al.,
1994). The initial research of estuarine deposits contained
in the incised valleys highlighted the circulation patterns
influenced by tides and the sediment dynamics, with distinctive upstream sediment transport (Boyd et al., 2006).
However, the estuarine depositional systems were poorly
documented (Dalrymple et al., 1994).
A significant step forward occurred between the
1960s and the 1980s, with the generation of models of
estuarine sedimentation based on static facies models that
emphasized the role of autocyclic processes (Figure 2), in
particular in wave-dominated estuarine environments
(Dalrymple et al., 1994; Boyd et al., 2006). The last mature
phase of estuarine research was driven by the establishment of a conceptual facies model for estuarine systems
(Dalrymple et al., 1992) and the subsequent development
of sequence stratigraphy concepts, with a major emphasis
on allocyclic factors leading to baselevel changes (studies
included in the SEPM Special Publication No. 51). From
these studies, a geological definition of an estuary was proposed, and a notable increase in the number of studies in
estuarine settings was observed (Dalrymple et al., 1994).
Facies model
In estuarine environments, fluvial and marine processes
interact, and as a consequence, a tripartite zonation is
observed in most estuaries (Figure 2), reflecting specific
energy levels and bedload transport patterns (Dalrymple
et al., 1992). These include: (1) an outer zone dominated
by marine processes; (2) a low-energy central basin; and
(3) an inner, river-dominated zone. The central basin
receives sediments both from the fluvial and marine systems and therefore is an area of net convergence.
There are two basic types of estuaries according to the
dominance of marine processes: wave-dominated and
tide-dominated systems (Figure 2). Wave-dominated estuaries exhibit the typical tripartite facies division, with an
energy minimum in the central basin. The outer marine
zone is occupied by a sandy body composed of several
sedimentary systems, such as beach-shoreface,
ESTUARINE SEDIMENTATION
289
Cambridge: Cambridge University Press, p. 750.
Syvitski, J. P. M., and MacDonald, R., 1982. Sediment character
and provenance in a complex fjord; Howe Sound, British
Columbia. Sedimentary Geology, 36, 217–244.
Syvitski, J. P. M., Burrell, D. C., and Skei, J. M., 1987. Fjords: Processes and Products. New York: Springer, p. 279.
Zhao, J., Bianchi, T. S., Li, X., Allison, M. A., Yao, P., and Yu, Z.,
2012. Historical eutrophication in the Changjiang and Mississippi delta-front estuaries: stable sedimentary chloropigments
as biomarkers. Continental Shelf Research, 47, 133–144.
Cross-references
Coastal Bays
Coastal Lagoons
Fjord
Ria
Sediment Transport
Sandbanks
ESTUARINE SEDIMENTATION
Francisco José Lobo
Instituto Andaluz de Ciencias de la Tierra,
CSIC-Universidad de Granada, Armilla/Granada, Spain
Definition
An estuary was originally defined in geological terms as
the seaward portion of a drowned valley system that
receives sediments from both fluvial and marine sources
and which contains facies influenced by tide, wave, and
fluvial processes (Dalrymple et al., 1992). The estuary
itself is regarded as the middle reach (or segment 2) of
a complete incised-valley succession (Figure 1), being
bounded seaward by the shoreline position at the beginning of the highstand and landward by the limit of marine
influence (Dalrymple et al., 1994). A revised definition
considers an estuary as a transgressive coastal environment at the mouth of a river, which is not necessarily
linked to an incised valley. Instead, the two fundamental
criteria for estuarine system generation are the existence
of a relative sea-level rise leading to transgression and
the occurrence of net landward sediment transport
(Dalrymple, 2006).
Importance of estuaries
Modern drowned river valleys are generally populated
environments that constitute the site of numerous human
activities of economic importance. For example, they are
emplacement sites of industrial practices (harbors, wastedisposal sites); they also constitute fragile environments
of ecological significance, as they often support productive fisheries; and they also support recreational activities
mainly related to tourism (Dalrymple et al., 1994). In addition, they can host significant quantities of hydrocarbon
reserves produced by sand-dominated clastic reservoirs
(Boyd et al., 2006). Finally, they can be used to predict
future scenarios of environmental response to global
change, as they are sensitive to sea-level and climate
fluctuations (Tessier, 2012). In particular, they are good
candidates to apply sequence stratigraphy concepts at the
land-sea transition, allowing the precise identification of
sequence boundaries (Zaitlin et al., 1994; Chaumillon
et al., 2010). More recently, they have been investigated
as paleoclimatic and paleoceanographic sedimentary
archives (Troiani et al., 2011; Tessier, 2012).
Historical development
Historically, the study of estuarine deposits is logically
linked to incised-valley systems. The early studies focused
on the importance of erosional subaerial unconformities
for the subdivision of the stratigraphic record
(Dalrymple, 2006), with a fairly good documentation of
the plan-view geometry of the valleys (Dalrymple et al.,
1994). The initial research of estuarine deposits contained
in the incised valleys highlighted the circulation patterns
influenced by tides and the sediment dynamics, with distinctive upstream sediment transport (Boyd et al., 2006).
However, the estuarine depositional systems were poorly
documented (Dalrymple et al., 1994).
A significant step forward occurred between the
1960s and the 1980s, with the generation of models of
estuarine sedimentation based on static facies models that
emphasized the role of autocyclic processes (Figure 2), in
particular in wave-dominated estuarine environments
(Dalrymple et al., 1994; Boyd et al., 2006). The last mature
phase of estuarine research was driven by the establishment of a conceptual facies model for estuarine systems
(Dalrymple et al., 1992) and the subsequent development
of sequence stratigraphy concepts, with a major emphasis
on allocyclic factors leading to baselevel changes (studies
included in the SEPM Special Publication No. 51). From
these studies, a geological definition of an estuary was proposed, and a notable increase in the number of studies in
estuarine settings was observed (Dalrymple et al., 1994).
Facies model
In estuarine environments, fluvial and marine processes
interact, and as a consequence, a tripartite zonation is
observed in most estuaries (Figure 2), reflecting specific
energy levels and bedload transport patterns (Dalrymple
et al., 1992). These include: (1) an outer zone dominated
by marine processes; (2) a low-energy central basin; and
(3) an inner, river-dominated zone. The central basin
receives sediments both from the fluvial and marine systems and therefore is an area of net convergence.
There are two basic types of estuaries according to the
dominance of marine processes: wave-dominated and
tide-dominated systems (Figure 2). Wave-dominated estuaries exhibit the typical tripartite facies division, with an
energy minimum in the central basin. The outer marine
zone is occupied by a sandy body composed of several
sedimentary systems, such as beach-shoreface,
ESTUARINE SEDIMENTATION
289