Geology Reference
In-Depth Information
and dating of the infi lling are available, remain rare
(cf. next section). The Cobequid Bay-Salmon River
estuary (Bay of Fundy, Canada, cf. Fig.
6.3
) is undoubt-
edly the best-known example, as this tide-dominated
estuary is the basis of the morphosedimentary model
of Dalrymple et al. (
1992
). Almost no data are avail-
able for instance on the infi ll stratigraphy of the Thames
or Severn tide-dominated estuaries (Harris
1988
) . The
aim of this present section is thus to briefl y describe
the sedimentary infi lling of the few main examples of
tide-dominated estuaries that have been published. The
list includes mostly modern (Holocene) estuaries (the
Cobequid Bay-Salmon River; the Seine and Mont St
Michel, the Vilaine, France; the South Alligator,
Australia; the Yangtze and Qiantang, China) but also
some ancient cases (Pleistocene, Eocene, Cretaceous).
The tide-dominated estuary examples are compared to
the mixed-energy Gironde estuary.
Fig. 6.1
A tide-dominated estuary: ideal distribution of sedi-
mentary bodies and facies both in plan view and section.
BCZ
bedload convergence zone,
UFR
upper fl ow regime,
SB
sequence
boundary,
TS
transgressive surface,
TRS
tidal ravinement sur-
face (After Zaitlin et al. 1994, Emery and Myers
1999
)
6.3.1
Progress in the Assessment
of Estuary Stratigraphy: The Use
of Very High-Resolution Seismic Data
illustrate a single transgressive-regressive infi lling
cycle, with landward and then seaward shift of facies
and sedimentary bodies (see Fig.
6.1
for the tide-
dominated estuary model). The model for wave-dominated
estuaries, because of its distinct tripartite character,
appears to be more easily applicable. Independent to
the fact that wave-dominated estuaries are more abun-
dant around the world, this explains why many exam-
ples of estuarine infi llings have been described using
the wave-dominated estuaries model.
The lack of data and reconstruction studies on the sedi-
mentary infi ll of tide-dominated estuaries partly results
from the diffi culties to investigate such shallow water,
and sometimes dangerous (because of powerful tidal
currents) coastal settings. Most studies performed in
tide-dominated estuaries as well as wave-dominated
estuaries are based on sediment vibracores that are
relatively easy to collect, at least on the estuary rims at
low tide, but which provide only a partial knowledge
of the whole infi ll. In the 1990s and 2000s, the devel-
opment of very high-resolution seismic devices, more
adapted for coastal studies, allows the collection of
new data on coastal sediment wedge architecture. In
particular, boomer sources, the vertical resolution of
which (<0.5 m) is convenient to image modern sedi-
mentary bodies, were designed to be used on small
boats. As an example, along the coasts of France, char-
acterized by numerous estuaries and lagoons, a huge
amount of very high-resolution seismic data have been
collected since the beginning of the 2000s, providing
new advances in our understanding of incised-valley
infi ll in different geomorphological and hydrodynami-
cal contexts (Chaumillon et al.
2010
) . Over the last
10 years, a considerable effort has been made in carry-
ing out integrative studies combining seismic, core and
6.3
Stratigraphy of Tide-Dominated
Estuary Infi ll: Case Studies
As previously introduced, only a few examples of
stratigraphic studies describing the sedimentary infi ll
of tide-dominated estuaries are available compared
with wave-dominated estuaries. Surprisingly, one of
the most commonly cited examples is the Gironde
estuary, although the latter is defi ned as a mixed wave-
and tide-dominated estuary. The Gironde estuary is
macrotidal, but according to Dalrymple et al. (
1992
), it
is not a tide-dominated estuary, as powerful oceanic
swells largely control the morphodynamic behaviour
of the mouth. Published cases of tide-dominated
estuaries, as defi ned by Dalrymple et al. (
1992
), and
for which data including sedimentology, architecture
