Autogenic process change in modern deltas: lessons for the ancient - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 154

50 km

Baton Rouge

Pre-delta deposits
Fluvial-dominated delta
Wave reworked delta
Old delta distributaries
Area of old deltas (fluvial
turned into wave)

New Orleans

Mississippi River

30 °

ST. BERNARD
(3ka-1.5ka)

29 °

LAFOURCHE (1ka-recent)

SALE-CYPREMORT (6ka-4ka)

BALIZE (0.5ka-modern)

92 ° 91 ° Gulf of Mexico 90 °

89 °

Fig. 3. Fluvial-dominated to wave-dominated autogenic process change, Mississippi Delta example (data from Coleman &
Gagliano, 1964; Frazier, 1967; Coleman et al ., 1998). Note that the oldest abandoned lobe (Sale-Cypremort) underwent the
most significant transgression and contains the most widespread wave reworked sediments when compared with younger
abandoned lobes.

and shore-parallel sandy spits were forming
between the distributaries, suggesting the tran-
sition to a wave-influenced morphology.
The southern Danube lobe (Sf. Gheorghe),
which is coeval with the northern lobe (Fig. 4)
has always been wave-dominated (Panin, 1989;
Giosan et al ., 2006). The southern lobe is wave-
dominated because it was shown that the south-
ern distributary has less than half the water
discharge (and presumably sediment flux) com-
pared to the northern distributary (Panin & Jipa,
2002). The wave regime is also different, as the
dominant wave front approaches the shoreline
of the southern lobe from the north-east at a high
angle with a resulting strong effect on sediment
transport (Giosan et al ., 1999; Dan et al ., 2009).

their locations are controlled by deeper faults
(Nguyen et al ., 2000). The modern delta is mesotidal
with a maximum tidal range of 3 m to 4 m (Ta et al .,
2002). During the interval 6 Ka to 3 Ka, the delta
had a tide-dominated morphology characterised
by radial distributary channels without shore-paral-
lel sandy ridges (Ta et al ., 2005). From 3 ka the
development of sandy ridges that are spaced
closer and closer together (Fig. 5) indicate the
increased influence of the waves on the shoreline.
Presently the delta is transitional between tide-
dominated and wave-dominated (Tamura et al .,
2012). The transition between the entirely tidal
and the tidal-wave part of the delta is delineated
by its plan-view shoreline trajectory (Helland-
Hansen & Hampson, 2009, fig. 12). The location
of the boundary between their tide-dominated
and wave-dominated segments suggests that the
autogenic process change was caused by prograda-
tion of the delta from a protected setting into a
higher energy, wave regime (Fig. 5). Another tidal to
wave process change has been described during the
last 5.4 ka evolution of Baram Delta in South China
Sea (Caline & Huong, 1992; Sandal, 1996).

Tide-dominated to wave-dominated process
change: modern example

The Mekong Delta in the South China Sea (Fig. 5)
has prograded more than 250 km during the last
6 ka (Ta et al ., 2002, 2005). The main distributary
channels have maintained the same position and