Geoscience Reference
In-Depth Information
Plan view
Seaward
flow of
sediment
laden river
water
Tides
Outflow &
dispersion
Wave
s
Currents
Estuarine/marine
processes active
Zone of flow expansion,
deceleration & dispersion
Active delta plain
Fluvial sediment in
put
Marginal salt marsh
(see Fig 7.5) or mangroves
(see Chapter 9)
Relic
channel
Waves and tide reworking
of delta front
Abandoned
delta lobe
MHWM
Colonization of emerging
land with vegetation
Cross-sectional view
Historic delta
front
Sedimentary
environment
Sediments and
sedimentary
structures
Exposed surface
- soil & vegetation
Delta platform
Topset - flat-lying
gravels/sands
Foreset - sands, typically inclined
10-25
o
seawards
Bottomset - silts, gently
inclined or flat
Delta front/slope
Prodelta
Fig. 7.4
Hypothetical delta section showing typical morphology, processes and grain size trends: MHWM, mean high-water mark.
stored and retained within the sedimentary sys-
tem. A sediment grain will settle once its fall
velocity exceeds the ability of the water to keep
it in suspension. Hence, it is easier for heavier
grains to settle than for lighter ones. Deltas, for
example, often develop a characteristic strati-
graphy with coarser sediments deposited close
in shore, grading to finer with increasing dis-
tance from the coast (Fig. 7.4), such as is shown
in the Mississippi delta (Scruton 1960). This
land to sea sediment gradation is also marked
by structural properties. The coarser delta
