Cheniers were originally defined as shallow-based, sandy
beach ridges resting on clay along a marshy or swampy,
seaward facing, tidal shore, with other beach ridges
stranded in a marsh behind, forming a belted marsh-andridge plain (Price, 1954, 1955), and usually enriched in
up to pebble-size shelly material (Otvos, 2000). In other
words, beach-ridge plains have local names in Louisiana
(cheniers) and Suriname (ritsen). The term chenier was
given to the ridges with oaks growing on them, which
are called “chênes” in Southwest Louisiana. The chenier
plain comprised of the vegetated marshes, water bodies
(including lakes, streams, and tidal inlets), and beach
ridges (Byrne et al., 1959). However, these ridges possess
certain characteristics. They are less than 3 m high,
30–50 m wide, and no more than 5 m thick. The growth
of these cheniers was clearly related to the mud delivered
by the Atchafalaya River (Wells and Kemp, 1981).
The link between cheniers and fluvial input has been
applied to other deltas or river estuaries. Since the origin
of the term, they have been reported at the deltas of the
Mississippi, Amazon, Orinoco, Po, and Rhone Rivers
(Price, 1954). Wells and Coleman (1977) extended their
studies of the suspended sediment transported from the
Amazon and Orinoco deltas to the chenier plains of Suriname (Wells and Coleman, 1981). Their model related
chenier growth to the number of days when the tide
exceeded a certain level, the increase in sediment concentration, the decrease in sediment compaction, and the root
density of mangroves at the coastline (Wells and Coleman,
1981).
In recent times, beach ridges are being used as
a common term for coastal features originating from several processes: (1) swash action, (2) settling lag, (3) eolian
action, (4) and storm surges (Tanner, 1995). They are also
related to the episodic input of sediment, either of fluvial
(Anthony, 1995) or volcanic origin (Nieuwenhuyse and
Kroonenberg, 1994). They can be composed of sand,
gravel, or shells (Reineck and Singh, 1980).
Sea-level trend
Although they were originally defined for low-lying
deltaic plains affected by rising sea levels, as along the
Mississippi River, cheniers are more abundant on plains
of regressive coasts subject to periodic or episodic highenergy levels. The mid-Holocene was the time when the
alluvial plains became stable (Xiqing, 1996). This
occurred around the same time as the mid-Holocene
sea-level maximum, which varied from less than 1 m to
around 4 m above the current level in the Southern Hemisphere (Isla, 1989). However, this highstand was not uniform or stable. In the Northern Hemisphere, sea level is
still rising, while in the Southern Hemisphere, it has been
dropping slightly. The differences of 2–3 m in the last
5,000 years have produced significant changes in
bedforms developing in estuaries. Morphodynamic
models are mostly biased toward transgressive
coasts (Tanner, 1995; Hesp and Short, 1999).
Although progradational barriers are assumed to have
a higher potential of preservation on regressive (falling
sea level) coasts, not many models have been proposed
for these coasts (Roy et al., 1995). Sediment availability
controls the facial relationships either in transgressive or
regressive sequences (Davis and Clifton, 1987; Isla, 1998).
Location
Cheniers have been observed in every estuary subject to
episodic processes or where the availability of coarse
material is episodic. They have been found in every continent, with the exception of Antarctica, from low to high
latitudes (Figure 1). Therefore, climate only affects its
composition and the type of plant communities (e.g., mangroves or salt marshes, in low or mid-high latitudes,
respectively).
Origin and composition
As their origin implies high energy, cheniers are composed
of different materials. Sandy cheniers are quite common,
although they can also be composed of shells and gravel.
Cheniers have been divided in medium- to coarse-sandy
cheniers and fine-sandy cheniers, each one with different
accumulation processes, depending on the mode of sandy
supply.
Chenier ridges are formed by the interplay between
washover and beach drift processes. Sand in low- to
medium-energy coasts is effectively transported by constructive wave action. The grains are suspended by the turbulence of the breaking waves and transported by beach
drift. During the rising tide, the sediment is stirred at the
seaside of a developing chenier by approaching breakers.
If the crest is low, sand will be washed over it and deposited on the lee side, causing the chenier to migrate gradually landward. Once the crest is high enough, beach drift
becomes the dominant process, and the chenier begins to
extend laterally, depending on the direction of the current
(Augustinus, 1980).
Another mechanism of chenier formation is the
switching of delta lobes (Otvos and Price, 1979; Penland
and Suter, 1989). This is particularly evident in the variations of the Huang He (Yellow) River outlet to the North
Jiangsu of Bohai Bay (Xitao, 1989; Yan et al., 1989).
Medium- to coarse-sandy cheniers are built up by sand
delivered by longshore currents, beach drift, and washover
processes. Thus, they form at or just above high-tide level.
Sedimentary structures within coarse-textured cheniers
include lamination in two different directions – foreslopeand backslope-parallel laminations. The foreslope-parallel
lamination occupies a narrow strip on top of the chenier,
with the rest of the chenier’s body composed of the
landward-parallel lamination. Cross-stratification sets
may appear intercalated with the parallel laminate
depending on the water level landward of the chenier
(e.g., in mangroves or salt pans). If the chenier is sufficiently high, small washover deltas develop due to the
sudden slowing down of the running water containing
114
CHENIERS AND REGRESSIVE BEDFORMS
beach ridges resting on clay along a marshy or swampy,
seaward facing, tidal shore, with other beach ridges
stranded in a marsh behind, forming a belted marsh-andridge plain (Price, 1954, 1955), and usually enriched in
up to pebble-size shelly material (Otvos, 2000). In other
words, beach-ridge plains have local names in Louisiana
(cheniers) and Suriname (ritsen). The term chenier was
given to the ridges with oaks growing on them, which
are called “chênes” in Southwest Louisiana. The chenier
plain comprised of the vegetated marshes, water bodies
(including lakes, streams, and tidal inlets), and beach
ridges (Byrne et al., 1959). However, these ridges possess
certain characteristics. They are less than 3 m high,
30–50 m wide, and no more than 5 m thick. The growth
of these cheniers was clearly related to the mud delivered
by the Atchafalaya River (Wells and Kemp, 1981).
The link between cheniers and fluvial input has been
applied to other deltas or river estuaries. Since the origin
of the term, they have been reported at the deltas of the
Mississippi, Amazon, Orinoco, Po, and Rhone Rivers
(Price, 1954). Wells and Coleman (1977) extended their
studies of the suspended sediment transported from the
Amazon and Orinoco deltas to the chenier plains of Suriname (Wells and Coleman, 1981). Their model related
chenier growth to the number of days when the tide
exceeded a certain level, the increase in sediment concentration, the decrease in sediment compaction, and the root
density of mangroves at the coastline (Wells and Coleman,
1981).
In recent times, beach ridges are being used as
a common term for coastal features originating from several processes: (1) swash action, (2) settling lag, (3) eolian
action, (4) and storm surges (Tanner, 1995). They are also
related to the episodic input of sediment, either of fluvial
(Anthony, 1995) or volcanic origin (Nieuwenhuyse and
Kroonenberg, 1994). They can be composed of sand,
gravel, or shells (Reineck and Singh, 1980).
Sea-level trend
Although they were originally defined for low-lying
deltaic plains affected by rising sea levels, as along the
Mississippi River, cheniers are more abundant on plains
of regressive coasts subject to periodic or episodic highenergy levels. The mid-Holocene was the time when the
alluvial plains became stable (Xiqing, 1996). This
occurred around the same time as the mid-Holocene
sea-level maximum, which varied from less than 1 m to
around 4 m above the current level in the Southern Hemisphere (Isla, 1989). However, this highstand was not uniform or stable. In the Northern Hemisphere, sea level is
still rising, while in the Southern Hemisphere, it has been
dropping slightly. The differences of 2–3 m in the last
5,000 years have produced significant changes in
bedforms developing in estuaries. Morphodynamic
models are mostly biased toward transgressive
coasts (Tanner, 1995; Hesp and Short, 1999).
Although progradational barriers are assumed to have
a higher potential of preservation on regressive (falling
sea level) coasts, not many models have been proposed
for these coasts (Roy et al., 1995). Sediment availability
controls the facial relationships either in transgressive or
regressive sequences (Davis and Clifton, 1987; Isla, 1998).
Location
Cheniers have been observed in every estuary subject to
episodic processes or where the availability of coarse
material is episodic. They have been found in every continent, with the exception of Antarctica, from low to high
latitudes (Figure 1). Therefore, climate only affects its
composition and the type of plant communities (e.g., mangroves or salt marshes, in low or mid-high latitudes,
respectively).
Origin and composition
As their origin implies high energy, cheniers are composed
of different materials. Sandy cheniers are quite common,
although they can also be composed of shells and gravel.
Cheniers have been divided in medium- to coarse-sandy
cheniers and fine-sandy cheniers, each one with different
accumulation processes, depending on the mode of sandy
supply.
Chenier ridges are formed by the interplay between
washover and beach drift processes. Sand in low- to
medium-energy coasts is effectively transported by constructive wave action. The grains are suspended by the turbulence of the breaking waves and transported by beach
drift. During the rising tide, the sediment is stirred at the
seaside of a developing chenier by approaching breakers.
If the crest is low, sand will be washed over it and deposited on the lee side, causing the chenier to migrate gradually landward. Once the crest is high enough, beach drift
becomes the dominant process, and the chenier begins to
extend laterally, depending on the direction of the current
(Augustinus, 1980).
Another mechanism of chenier formation is the
switching of delta lobes (Otvos and Price, 1979; Penland
and Suter, 1989). This is particularly evident in the variations of the Huang He (Yellow) River outlet to the North
Jiangsu of Bohai Bay (Xitao, 1989; Yan et al., 1989).
Medium- to coarse-sandy cheniers are built up by sand
delivered by longshore currents, beach drift, and washover
processes. Thus, they form at or just above high-tide level.
Sedimentary structures within coarse-textured cheniers
include lamination in two different directions – foreslopeand backslope-parallel laminations. The foreslope-parallel
lamination occupies a narrow strip on top of the chenier,
with the rest of the chenier’s body composed of the
landward-parallel lamination. Cross-stratification sets
may appear intercalated with the parallel laminate
depending on the water level landward of the chenier
(e.g., in mangroves or salt pans). If the chenier is sufficiently high, small washover deltas develop due to the
sudden slowing down of the running water containing
114
CHENIERS AND REGRESSIVE BEDFORMS