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composed of a single tidal channel succession, the
upper part of which is composed of tidal rhythmites
(Tessier
1993
; Billeaud et al.
2007
). On the sides of the
estuarine mouth, the highstand systems tract corre-
sponds either to an aggradational unit of tidal fl at
deposits or to retrograding/aggrading back-barrier facies.
A wave ravinement surface signals the retrogradation
of the present-day barrier (Fig.
6.4
). Seismic data
clearly show bottomset geometry at the seaward end of
the tidal estuarine sands that progradate therefore over
the transgressive systems tract.
unit, composed of muds supplied by the fl uvial source,
can be assigned to the highstand systems tract.
6.3.3
Modern Estuaries with High
River Sediment Supply
All of the aforementioned modern case studies
described estuaries with a low to insignifi cant river
sediment supply. Systems characterized by high to
very high fl uvial sediment input are mentioned here.
Most of these systems are tide-dominated deltas, such
as the Fly River delta (Dalrymple et al.
2003
) , but some
of them are described as tide-dominated estuaries dur-
ing the deposition of the transgressive systems tract.
The Yangtze delta illustrates this case. The Qiantang
River estuary located immediately south the Yangtze is
described for comparison.
6.3.2.6 Vilaine Estuary, Northern Bay
of Biscay, NW France
The Vilaine estuary, situated along a rocky coast, is a ria-
type estuary, characterized by a very low sand supply of
marine origin. As a consequence, it does not develop
sand bodies such as longitudinal tidal bars and sand fl ats
at the mouth (Fig.
6.3
). The Vilaine estuary belongs to the
category of rocky-coast estuaries defi ned in Chaumillon
et al. (
2008
). Maximum tidal range is about 4.5 m, and
wave and fl uvial dynamics are of low energy. Hence,
tidal currents control sediment processes. The estuary is
mud-dominated and composed of one main tidal channel
with fringing tidal mudfl ats and salt marshes.
The sediment infi ll, reconstructed with core and
very high-resolution seismic data, is simple and related
to the Holocene transgression. It consists of four main
depositional units above the sequence boundary (cf.
Figs.
6.2
and
6.4
). The basal unit has the highest vol-
ume and is an aggradational unit made of fi ne-grained
organic-rich facies interpreted as muds deposited in a
well-sheltered estuarine environment such as a ria.
This unit is sharply eroded by a channelized surface
overlain by sandy to muddy facies interpreted as estua-
rine tidal channels and tidal fl ats. The channelized sur-
face is the tidal ravinement surface and is dated at
about 6,500 years BP.
This unit is in turn sharply eroded by a fl at surface
covered by offshore muds. This fl at surface is the wave
ravinement surface and is dated around 5,500-
4,500 years BP. Ages of 3,000 years BP are found at the
top of the offshore mud unit, indicating that sedimenta-
tion rate has been extremely low during the last stages
of the Holocene. Hence, in this tide-dominated estuary,
characterized by very low sediment supply, the sedi-
mentary infi ll records a continuously retrograding bay-
line. The maximum fl ooding is placed in the uppermost
part of the infi ll. In the most internal zones only, a last
6.3.3.1 Early Holocene Yangtze Estuary,
East China Sea, China
The Yangtze River is among the largest rivers in the
world, ranking fourth in terms of sediment discharge.
Present-day maximum tidal range reaches 4.5 m, and
maximum wave height at the mouth is 6.5 m. The pres-
ent-day Yangtze River mouth is thus defi ned as a
mixed-energy environment. The stratigraphy of the
Yangtze incised-valley infi ll, reconstructed using enor-
mous numbers of cores and well logs, comprises two
main depositional stages related to the last post-glacial
sea-level rise that almost stopped at about 7,000 years
BP (Fig.
6.4
). The transgressive systems tract is
assumed to comprise a succession of units that typify a
transgressed tide-dominated estuary. The main differ-
ence with tide-dominated estuaries as defi ned by
Dalrymple et al. (
1992
) is that this succession is fi ning
upward because sediment is mainly supplied by the
Yangtze River. In this transgressive tide-dominated
estuary succession, longitudinal tidal bars and tidal
channel and shoal complexes do not exist. The whole
estuary is occupied by a tidal distributary channel com-
plex passing seaward to muddy fl ats and a mud-
dominated estuarine front. Tidal rhythmites of different
types are very well preserved in almost all facies, indi-
cating the tide-dominated character of the setting.
Finally, this succession resembles that of a mixed-
energy estuary such as the present-day Gironde estuary,
with a tide-dominated bay-head delta and central basin
fed by river supply, but without the high-energy
