Bittencourt, A.C.S.P.

Dominguez, J.M.L.

Flexor, J.M.

Martin, Louis

Suguio, K.

Horizon / Pleins textes

3 
Quaternary Emergent and Submergent Coasts : Comparison of the Holocene 
Sedimentation in Brazil and Southeastern United States" 
(Quateniary sea level chdnges\Holocene coastal sedimentation\@aternary oceanic deltas) 
KEM'ITRO SUGUIO, LOUIS MARTIN, ABhIO CARLOS DA SILVA PINTO BI"COURT, Jose MARIA 
LANDIM D0MLNC;UEZ and JEAN-MARIE FLEXOR 
Instituto de Geociências, Universidade de São Paulo, SLo Paulo, SP; Departamento de Geofisica, Observatório Nacional, 
Rio de Janeiro, RJ and Instituto de Geociências, Universidade Federal da Bahia, Salvador, BA 
(With 3 text-figures) 
INTRODUC rlON 
Relative sea level fluctuations during the 
past 7,000 years and coastal sedimentation 
processes active over more than 2,000 km of the 
central Brazilian coastline (Fig. 1) are now well 
known through research carrried out during the 
last few years (Bittencourt et al., 1979 and 
1982, Dominguez et al., 1981 and 1982; Martin 
and Suguio, 1975 and 1978; Martin et al., 
1979a, 1979/1980 and 1980; Suguio and Martin, 
1976, 1978, 1981 and 1982; Suguio et al., 
1982). Sea level fluctuation curves have been 
delineated for many homogeneous sectors of 
the coastlines of the States of São Paulo, Rio 
de Janeiro and Bahia (Martin et al., 1979b 
and Suguio et d., 1980). Comparison of these 
curves shows great similarity in their 
configuration, although some small differences 
in amplitude are observed. The present zero 
level was crossed between 6,500 and 7,000 years 
B.P. and the Holocene maximum, about 4-5 
m above present sea level, occurred 5,100 
years B.P. After this date relative sea levei 
returned more-or-less gradually and regularly 
toward the present level, with the exception 
of two short periods of sea levels higher than 
today's between 3,800-3,600 and 2,700-2,500 
.years B.P. 
A great number of ancient sea level 
reconstruction curves for the past 7,000 years 
have been made for the coast of the south- 
eastern United States. Newman et al. (1980) 
present a table with curves for 14 different 
sectors of this coastline. Discounting second 
order variations, a constant feature of these 
curves is that not one shows a sea level higher 
than the present one. Similarly, curves 
representing several coastal sectors of the Gulf 
of Mexico (Curray, 1960; Coleman and Smith, 
1964; Shepard and Curray, 1967; Scholl et 
al., 1969 and Nelson and Bray, 1970) also 
loo 
e 
20° 
* Accepted for publication November 29, 1983; 
presented by A. C. ROCHA-CAMPOS. 
Fig. 1 - Index map of the central Brazilian coastline 
showing the sectors where the main relative sea level fluo 
tuation curves have been obtained. 
brasil. Ciênc., (1984) 56 (2). A bd?bM Fonds Documentaire 
164 K .  SUGUIO ct dii 
exhibit a sea level lower than present during 
the past 7,000 years. 
COhlPARlSON OF BRALILIAN AND 
SOUTHEASTERN UNITED SKATES AVERAtiE SEA 
LEVEL CURVES 
In spite of minor local differences between 
sea level curves for these areas, an astonishing 
resemblance exists between them. It is possible 
to consti-uct schematic average curves by 
eliminating second order variations and 
representing only the most important variations 
(Fig. 2). Along the Brazilian coast the relative 
sea level rose until about 5,100 years B.P., 
when sea level was 4 to 5m above the present 
level. After that, relative sea level dropped 
more-or-less regularly until reaching its present 
level. In order to simplify the Brazilian curves, 
two short periods of higher sea levels between 
3,800-3,600 and 2,700-2,500 years B.P. have 
been neglected because of the general tendency 
for emergence since 5,100 years B.P. until 
the present. It is evident, however, that these 
short submergent periods have played an 
important role in coastal sedimentation 
(Suguio et al., 1982). The schematic average 
curve for the coastline of the southeastern 
United States shows that the Quaternary sea 
level has risen continuously toward its present 
position and has never been above its present 
level. 
It is obvious that both the present coastal 
morphology and depmitional patterns in Brazil 
and southeastern United States have heen 
Fig. 2 - Schematic average cunes of relative sea Ic~el 
fluctuitions along the central Br;iailian and bouttieastem 
United States coabtlines during the past 7.OilO years. 
influenced by distinctive relative sea level 
fluctuations. Prior to 5.100 years B.P. the 
Brazilian coast was probably quite similar 
to that of the present southeastern United 
States. 
GENERAL FEATURES OF THE CENTRAL 
BRAZILIAN AMD SOUTHEASTERN UNITED STATES 
The Gulf coast of the United States is 
characteïizec! by barrieï islaiids and lagoons h i  
have spread over extensive pre-Holocene 
lowlands. 
On the other hand, the central Brazilian 
coastline is characterized by extensive 
Quaternary sedimentary plains partly made up 
of Pleistocene and Holocene marine terraces. 
Holocene terraces may be widespread and their 
surfaces, which slope gently oceanward, are 
characterized by numerous aligned beach ridges. 
,ln the swampy lowlands that comprise the 
contact zone between Pleistocene and Holocene 
terraces there are many paleolagoons filled 
by organic-rich muddy sediments containing 
abundant mollusk shells. 
COMP.4RISON BETWEEN KHE CAPL HA ITERAS 
AREA (UNITED STATES) AND THE DOCE RIVER 
COASPAL PLAIN (BRALIL) 
The Cape Hatteras region is characterized 
by an extensive lagoon (Palmico Sound) sepa- 
rated from the open ocean by a series of barrier 
islands. The Doce River mouth coastal plain, 
comparable in size to the Cape Hatteras region. 
forms an extensive oceanwardly convex crescent 
38 hm wide and iihout 150 kni long in a N-S 
direction. Detailed geological mapping, 
augmented by several hundred radiometric dates 
(Suguio and Martin, 1Y81 and Suguio ci al., 
1Y82). has allowed us to delineate the following 
sequence of events: 
a) Pleistocene marine terrace sedi- 
mentation: 
b) Formation of the first generation of 
Holocene beach ridges ; 
c) Formation of  the msiln paleohgoon, 
partially filled by the intralagoonsl Doce River 
QUATERNARY EMERGENT AND SUBMERGENT COASTS 165 
delta, located between the residual Pleistocene 
terraces and the first generation Holocene 
beach ridges ; 
d) Deposition of the second generation of 
Holocene beach ridges ; 
e) Formation of a new paleolagoon, 
situated between the two generations of 
Holocene beach ridges. 
Submergent episodes are recorded by a 
barrier island/lagoonal system, whereas emer- 
gent episodes promoted the desiccation of the 
lagoon and the development of a new generation 
of beach ridges seaward of the barrier islands. 
Radiocarbon dates on mollusk shells from the 
main paleolagoonal deposits indicate that the 
lagoon was formed 5,100 years B.P. (Fig. 3). 
Almost certainly this paleolagoon was prote'cted 
from the open ocean by a series of aligned 
barrier islands, which are presently 
incorporated within the first generation of 
Holocene beach ridges. Before about 5,100 years 
B.P., the Doce River mouth area was very 
similar to the present day Cape Hatteras area 
(Fig. 3). From the viewpoint of relative sea 
level evolution, before 5,100 years B.P. the 
Doce River mouth area was in submergence, 
just as the Cape Hatteras area is today. It 
is simple to imagine what will happen with 
a drop in relative sea level in the Cape Hatteras 
area. The Palmico Sound will dry up and a 
new generation of sand ridges will be added 
to the outer margin of the barrier island system 
giving rise to a coastal plain analogous to 
that of the Doce River mouth. Probably the 
only difference would be the absence of an 
intralagoonal delta since there are no important 
rivers flowing into Palmico Sound. 
CONCLUSIONS 
Very distinctive relative sea level 
fluctuations along the southeastern Atlantic 
and Gulf coasts of the United States and along 
the central Brazilian coast have occurred over 
the last 7,000 years. The southeastern coast 
of the United States has been subjected to 
continuous submergence during this period 
while the Brazilian coast was submerged prior 
to about 5,100 years ago and emergent since 
then. 
Paleogeographic reconstruction of the Doce 
River mouth area provides a picture of the 
morphological features of this area before 
5,100 years ago, which is very similar to the 
Cape Hatteras (USA) 
Present situation 
Doce River mouth (Brasil) 
About 6,590 to 5.500 y. B.P 
Comparison between present-day Cape Hatteras (USA) and the Doce River 
mouth (Brazil) coastal plains during the interval 6.500-5.500 years BP. (Radiocarbon 
ages obtained on samples from the paleolagoon within the Doce River mouth 
area). 
An. Acad. brasil. Ciénc., (1984) 56 (2). 
166 K. SUGUIO E I  ulii 
present-day Cape Hatteras area. Obviously, 
depositional histories of these two areas have 
been different during the past 7,000 years. 
The same depositional models can not be 
applied to these areas for the period from 
5,100 years B.P. to the present. Unfortunately, 
the drop of 4-5 m in relative sea level during 
the past 5,100 years along the Brazilian coast 
has rarely been considered by previous Brazilian 
authors. Moreover, the concept of wave- 
dominateci aeitas must be revised í ï ï  the light 
of recent knowledge about Brazilian river 
mouth areas, in whose construction a quickly 
prograding shoreline along an emergent coast 
was a major factor (Suguio and Martin, 1981). 
Along the Brazilian coastline, the relative sea 
level drop, together with longshore currents, 
played an essential role in coastal sedimentation. 
In most cases, rivers flowing into the ocean 
act above all like an obstacle, much as a jetty 
does, to the free longshore drift of the sediments. 
ACKNOWLEDGEMENTS 
Dr. Thomas R. Fairchild made the careful 
revision of the English text. 
SUNlNlARl’ 
Very distinctive relative sea level fluctuatiiin~ during 
the past 7.001) years occurred along the coasts of Brazil 
and the southeastern United States. The Brazilian coast 
was subjected to submergence until about S.ICI0 years 
B.P.. followed by emergence. The Atlantic and Gulf coastb 
of the United States, on the other hand. have been in 
submergence continuously. Consequently. great differences 
are evident in the respective patterns of coastal deposition 
during the Holocene. Before 5.100 yars B.P. th;’ ßrazilian 
coast was pmbablj quite simular to that of the present 
southeastern United States. 
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Quaternary emergent and submergent coast : comparison of the holocene sedimentation in Brazil and southeastern United States (quaternary sea level changes/holocene coastal sedimentation/quaternary oceanic deltas)

Quaternary emergent and submergent coast : comparison of the holocene sedimentation in Brazil and southeastern United States (quaternary sea level changes/holocene coastal sedimentation/quaternary oceanic deltas)

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