approaching the nearshore and the settling out of muddy
deposits. Bayhead chenier plains in turn are formed on
bayheads of smaller dimensions than those on bight
coasts. Classic bayhead chenier plains include Broad
Sound and Burdekin River, Queensland (Cook and
Polach, 1973), the Colorado Delta, California Gulf
(Otvos and Price, 1979), Firth of Thames, New Zealand
(Woodroffe et al., 1983), or at the headlands of the Rio
de la Plata (Cavalotto et al., 2005). Other examples are
San Sebastian (Vilas et al., 1999) and Samborombon
Bays (Bértola, 1994) on the coast of Argentina. Recently,
Spanish authors distinguished a third setting for chenier
formation: estuarine coasts protected from the open sea
by a coastal barrier (Rodríguez-Ramírez and YáñezCamacho, 2008). Tentatively, the ridges along the Mar
Chiquita lagoon coast fall into this category.
Age
Radiocarbon dates from shells collected from cheniers do
not relate directly to ridge accumulation but to the time of
the organism’s death before ridge formation (Woodroffe,
2002). As the maximum limit of the Holocene transgression occurred $6,000 years ago, there are differences in
the ages of the shells composing beach deposits. Shells
sampled in living position from estuarine facies are better
indicators of the maximum highstand (Isla, 1989;
Cavalotto et al., 2005).
Schofield was the first to relate a chenier plain to the
sea-level fall of $2.6 m in 2,000 years at the North Island
of New Zealand. The Miranda plain is composed of
cheniers and regressive spits dated between 3,900 and
980 years BP (Schofield, 1960). Recently, the sequence
of regressive spits was reanalyzed based on GPR records.
Significant differences were recognized based on the
architecture of the older ridges (13-6), related to mudflats,
and the modern ridges (5-1) deposited on embayed tidal
flats (Dougherty and Dickson, 2009).
After the maximum highstand of 5,800–5,500 years
BP, a chenier plain developed as sea level dropped at the
mesotidal Gulf of Carpentaria, Australia (Rhodes, 1982).
At the eastern side of Queensland, another chenier plain
developed in Princess Charlotte Bay. From a maximum
highstand of $6,000 years BP, beach ridges and cheniers
composed of shells are interfingered (Chappell and
Grindrod, 1984). Mangroves colonized cheniers in
a prograding shoreline. Managing different chenier plains,
significant changes in the progradation were detected over
the last 6,000 years at Princess Charlotte Bay, Karumba,
and South Alligator River (Woodroffe, 2002). At Southern
Australia, another chenier plain composed of shells
increased in size due to organic-rich mangrove facies
(Short, 1988). This plain expanded to a highstand of
2–3 m above today’s sea level $6,400 years ago. The
plain’s growth was recorded using organic remains from
the transition between Posidonia sea grass and sand flats
and from these flats to ridges dominated by Avicennia
mangroves (Belperio et al., 2002).
Cheniers can be used as reliable markers of
paleocoastlines, since they only form on stable or slightly
retreating coasts. When there is a steady sediment supply
along with a gradually falling sea level, the result is an
increased rate of mudflat progradation (Chappell and
Grindrod, 1984), which prevents chenier formation or
lowers their frequency of appearance. Moreover, an
increased deposition of muds causes a reduction in shellfish communities, which in turn diminishes shell production and the quantity of the material available to form
cheniers. On the northern outer shelf of the East China
Sea, submerged chenier ridges were used to map
a Pleistocene paleocoastline, with ages between 24,000
and 15,000 years BP. They were found at depths between
150 and 110 m (Xitao, 1989), which reflect the lowstand at
the last glacial maximum. The Lelydorp member of the
Coropina Formation (Suriname) consists of the deposits
of an early Pleistocene chenier plain (Wong et al., 2009).
Beach ridges and delta development
Beach-ridge sequences have also been linked to delta
development. The so-called wave-dominated deltas of
northeastern Brazil grew in relation to beach ridges. During the maximum highstand, coastal lagoons developed
and were progressively infilled by intralagoonal deltas
(Figure 4; Martin and Dominguez 1994). This regressive
model differs from the original view of coastal lagoon
development at a coast dominated by longshore drift with
a stable sea level (Lucke, 1934; Kumar and Sanders, 1974;
Borrego et al., 1993).
Several deltas were significantly affected in recent
years by the construction of river dams or jetty improvements in coastal areas. These changes altered the sediment
dynamics of their beach-ridge plains. The Volcán Dam
reduced sediment transported to the Orinoco Delta
(Warne et al., 2002).
The coast of Nayarit, Western Mexico, provides
another good example of a regressive area where coastal
lagoons and deltas interact. The region also has a good
succession of beach ridges spanning in time from
4,500 years BP to present (Curray et al., 1969). Based on
these progradation-aggradation examples, Curray
et al. (1969) call attention to non-transgressive models.
On transgressive coasts, a barrier is a single ridge
transporting onshore. However, other barrier models do
exist: (1) a single barrier composed of several ridges that
characterize progradation in stable conditions, (2) multiple
barrier systems composed of a single ridge each, and
(3) multiple barriers composed of several ridges, where
each characterizes a regressive coast, related to sea-level
fluctuations, climate-triggered net drift changes, or variations in sediment input (deltaic variations).
The beach-ridge plains attached to the progradation of
the Doce and Paraiba do Sul developed in response to
a steady sea-level fall since the mid-Holocene (Martin
et al., 1997). In the evolution of these intralagoonal deltas,
the net littoral drift toward the north and the episodic
CHENIERS AND REGRESSIVE BEDFORMS
117
deposits. Bayhead chenier plains in turn are formed on
bayheads of smaller dimensions than those on bight
coasts. Classic bayhead chenier plains include Broad
Sound and Burdekin River, Queensland (Cook and
Polach, 1973), the Colorado Delta, California Gulf
(Otvos and Price, 1979), Firth of Thames, New Zealand
(Woodroffe et al., 1983), or at the headlands of the Rio
de la Plata (Cavalotto et al., 2005). Other examples are
San Sebastian (Vilas et al., 1999) and Samborombon
Bays (Bértola, 1994) on the coast of Argentina. Recently,
Spanish authors distinguished a third setting for chenier
formation: estuarine coasts protected from the open sea
by a coastal barrier (Rodríguez-Ramírez and YáñezCamacho, 2008). Tentatively, the ridges along the Mar
Chiquita lagoon coast fall into this category.
Age
Radiocarbon dates from shells collected from cheniers do
not relate directly to ridge accumulation but to the time of
the organism’s death before ridge formation (Woodroffe,
2002). As the maximum limit of the Holocene transgression occurred $6,000 years ago, there are differences in
the ages of the shells composing beach deposits. Shells
sampled in living position from estuarine facies are better
indicators of the maximum highstand (Isla, 1989;
Cavalotto et al., 2005).
Schofield was the first to relate a chenier plain to the
sea-level fall of $2.6 m in 2,000 years at the North Island
of New Zealand. The Miranda plain is composed of
cheniers and regressive spits dated between 3,900 and
980 years BP (Schofield, 1960). Recently, the sequence
of regressive spits was reanalyzed based on GPR records.
Significant differences were recognized based on the
architecture of the older ridges (13-6), related to mudflats,
and the modern ridges (5-1) deposited on embayed tidal
flats (Dougherty and Dickson, 2009).
After the maximum highstand of 5,800–5,500 years
BP, a chenier plain developed as sea level dropped at the
mesotidal Gulf of Carpentaria, Australia (Rhodes, 1982).
At the eastern side of Queensland, another chenier plain
developed in Princess Charlotte Bay. From a maximum
highstand of $6,000 years BP, beach ridges and cheniers
composed of shells are interfingered (Chappell and
Grindrod, 1984). Mangroves colonized cheniers in
a prograding shoreline. Managing different chenier plains,
significant changes in the progradation were detected over
the last 6,000 years at Princess Charlotte Bay, Karumba,
and South Alligator River (Woodroffe, 2002). At Southern
Australia, another chenier plain composed of shells
increased in size due to organic-rich mangrove facies
(Short, 1988). This plain expanded to a highstand of
2–3 m above today’s sea level $6,400 years ago. The
plain’s growth was recorded using organic remains from
the transition between Posidonia sea grass and sand flats
and from these flats to ridges dominated by Avicennia
mangroves (Belperio et al., 2002).
Cheniers can be used as reliable markers of
paleocoastlines, since they only form on stable or slightly
retreating coasts. When there is a steady sediment supply
along with a gradually falling sea level, the result is an
increased rate of mudflat progradation (Chappell and
Grindrod, 1984), which prevents chenier formation or
lowers their frequency of appearance. Moreover, an
increased deposition of muds causes a reduction in shellfish communities, which in turn diminishes shell production and the quantity of the material available to form
cheniers. On the northern outer shelf of the East China
Sea, submerged chenier ridges were used to map
a Pleistocene paleocoastline, with ages between 24,000
and 15,000 years BP. They were found at depths between
150 and 110 m (Xitao, 1989), which reflect the lowstand at
the last glacial maximum. The Lelydorp member of the
Coropina Formation (Suriname) consists of the deposits
of an early Pleistocene chenier plain (Wong et al., 2009).
Beach ridges and delta development
Beach-ridge sequences have also been linked to delta
development. The so-called wave-dominated deltas of
northeastern Brazil grew in relation to beach ridges. During the maximum highstand, coastal lagoons developed
and were progressively infilled by intralagoonal deltas
(Figure 4; Martin and Dominguez 1994). This regressive
model differs from the original view of coastal lagoon
development at a coast dominated by longshore drift with
a stable sea level (Lucke, 1934; Kumar and Sanders, 1974;
Borrego et al., 1993).
Several deltas were significantly affected in recent
years by the construction of river dams or jetty improvements in coastal areas. These changes altered the sediment
dynamics of their beach-ridge plains. The Volcán Dam
reduced sediment transported to the Orinoco Delta
(Warne et al., 2002).
The coast of Nayarit, Western Mexico, provides
another good example of a regressive area where coastal
lagoons and deltas interact. The region also has a good
succession of beach ridges spanning in time from
4,500 years BP to present (Curray et al., 1969). Based on
these progradation-aggradation examples, Curray
et al. (1969) call attention to non-transgressive models.
On transgressive coasts, a barrier is a single ridge
transporting onshore. However, other barrier models do
exist: (1) a single barrier composed of several ridges that
characterize progradation in stable conditions, (2) multiple
barrier systems composed of a single ridge each, and
(3) multiple barriers composed of several ridges, where
each characterizes a regressive coast, related to sea-level
fluctuations, climate-triggered net drift changes, or variations in sediment input (deltaic variations).
The beach-ridge plains attached to the progradation of
the Doce and Paraiba do Sul developed in response to
a steady sea-level fall since the mid-Holocene (Martin
et al., 1997). In the evolution of these intralagoonal deltas,
the net littoral drift toward the north and the episodic
CHENIERS AND REGRESSIVE BEDFORMS
117