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determined for the Ganges-Brahmaputra river delta,
where both modern and Holocene budgets show
that ~40% of the annual load is trapped within the pro-
grading subaerial and subaqueous clinothems of the
tide-dominated portion of the delta. The remaining
60% is distributed about evenly to the fl uvial deltaplain
through overbank sedimentation and to the Swatch of
No Ground canyon that feeds the deep-sea Bengal Fan
(Goodbred and Kuehl
1999
) .
Liu et al. (
2009
) recently developed budget approx-
imations for several tide-dominated or tide-infl uenced
deltas, showing that 30-40% of the sediment load for
the Huanghe (Yellow), Mekong, and Changjiang rivers
escape the deltaic depocenters located in the vicinity
of the river mouth, similar to the portion observed for
the Fly and Ganges-Brahmaputra dispersal systems. In
the case of these East Asian examples, though, sedi-
ments are advected distances of up to 500-800 km
before being deposited as an alongshelf clinothem at
inner- to mid-shelf water depths. Prior to these recent
studies, it was thought that only the Amazon dispersal
system supported such long-distance alongshelf-export
of sediment from its river delta (Allison et al.
2000
) .
Aside from their distance, though, these remote cli-
nothems share nearly all characteristics of a prodelta
mud wedge, raising the question of whether they
should be considered part of the delta system.
Regardless of their classifi cation, these fi ndings
emphasize that tide-dominated deltas are only part
of a larger source-to-sink continuum of interacting
continental-margin components (e.g., Goodbred
2003
) .
(Fig.
7.3a
). In river-dominated delta systems the
subaerial delta, together with the delta-front platform,
comprises the topsets of a single deltaic clinoform,
with wave-dominated systems often having a defi nable
but closely spaced double clinoform. In the case of
most tide-dominated deltas though, these environ-
ments are separated by a broad high-shear zone of
limited sediment accumulation that separates the pro-
grading subaerial and subaqueous clinoforms of the
compound delta system (Nittrouer et al.
1986
; Swenson
et al.
2005
). Beyond the rollover point (i.e. topset-
foreset transition) the 'foreset' and 'bottomset' regions
of the clinoform correspond to the delta-front slope
and prodelta, respectively. Another feature of tide-
dominated deltas is that this zonation is irregular along
the coast with multiple, wide distributary channels and
islands occurring within a funnel-shaped embayment
(Fig.
7.5
), as compared with wave-dominated deltas
where environmental zonation is roughly parallel to
the shoreline.
7.4.1
Subaerial Delta
As noted by Middleton (
1991
) many of the largest riv-
ers discharging to tide-dominated coasts have a princi-
pally fi ne-grained sediment load that forms a
mud-dominated delta system. The shoreline of such
deltas is often fringed by expansive tidal fl ats, marshes,
and/or mangroves threaded by tidal channels (see
Chaps. 8 - 10 ). These tidally-dominated environments
are characteristic of the intertidal to shallow subtidal
zone, particularly at the rivermouth and along adjacent
coasts, and may include salt marshes, mangroves,
muddy tidal fl ats, tidal channels, and channel-mouth
bars. In tropical to subtropical tide-dominated deltas
the subaerial deltaplain comprises broad mangrove-
colonized plains that extend from the limits of salt
intrusion downward to the upper half of the intertidal
zone, where they merge with wide intertidal mud and
sand fl ats in the lower intertidal zone.
This transition between subtidal and supratidal
environments is the principal zone of subaerial delta
progradation and is largely defi ned by the develop-
ment of channel-mouth bars within and just seaward
of the active river mouth (Allison
1998
) . These bars
are generally large (10
2
-10
4
m) elongate features that
extend from shallow subtidal to supratidal elevations,
7.4
Sedimentary Environments
The sedimentary environments of tide-dominated delta
systems can be largely divided into those associated
with the 'subaerial' and 'subaqueous' portions of the
compound clinoform (Figs.
7.3
and
7.5
). The subaerial
delta can be further subdivided into a 'lower delta
plain' that is infl uenced by tides and other marine pro-
cesses and an 'upper delta plain' that is above the tidal
infl uence and dominated by fl uvial processes. Offshore
the subaqueous delta has often been subdivided into the
'delta front' and 'prodelta', but here we subdivide
the clinothem into the 'delta-front platform' (or sub-
tidal delta plain), the 'delta-front slope', and 'prodelta'
based on both morphology and sediment facies
