BRAZILIAN COASTLINE QUATERNARY FORIVIATIONS - THE STATES OF SÃ0 PAULO AND BAHIA LIWORAL ZONE EVOLUTIVE SCHEMES
7 KENITIRO SUGUIO Instituto de Geociências - Universidade de São Paulo Caixa Postal np 20.899 - São Paulo - Brasil
9 LOUIS l+”N O.R.S.T.O.M. (Office de la Récherche Sciéntifique et Téchnique Outre-Mer) - France
ABSTRACT Sta.te of São Paulo’s littoral, are located in zones where the present day sedimentation rate is The State of São Paulo coastline and part insignificant. These plains were formed through of the State of Bahia, the Salvador area, may several transgressive cycles by successive re- be compared as Brazilian littoral evolutive working of the previous formations. scheme models during the Quaternary. The Recent Quaternary marine deposits of The Salvador coastal area, being a natural other areas were influenced particularly by the lengthening of the Recôncavo Sedimentary sediments transported by the rivers, like the Basin, shows directly the tectonic behaviour of Paraiba do Sul River, the Doce River, the São this <
DIFFERENT ZONES OF BRAZILIAN UTILIZATION OF THE ANCIENT MARINE QUATERNARY GEOLOGY STRANDLINES AS INDEX OF EVENTUAL TECTONIC ACTMTP Stretched out for 9,000 Km the Brazilian littoral shows several different characteristics. Some transgressions and regressions occurred The differences in the continental structures are during the Quaternary. These sea level changes reflected in the Quaternary coastal deposit dis- were a consequence of eustatic phenomena re- tribution (Fig. 1). In many places the Precam- lated to the glaciation events, tectonic activities brian basement rocks touch the sea. Frequently, and coastal dynamics. The eustatic changes had high relief is found near the coastline as a con- worldwide influence and the coastal dynamics sequence of the tectonic phenomenon still active and tectonic activities had only local influence. during the course of the Quaternary. The eustatic changes have the same direction Some coastal plains, predominantly formed throughout the Earth’s surface during a certain by Quaternary sediments, such as that of the period. However, the tectonic changes and coas-
An. Acad bras. Ci&nc., (19763, 48, (Suplemento) . QRSTOM Fonds Wumentaire 326 KENITIRO SEGUI0 arid LOUIS MARTINS
tal dynamics may increase or diminish the effects other phenomena become relatively more im- of the glaciation events. portant. As a consequence, it will be during these It is on the last transgressive-regressive periods of eustatic quiet that we can try to cycle that we have the most data. A certain estimate the tectonic influence. For example, number of sea level changing curves was outli- we can try to verify if there are differences of ned in several parts of the world. It may be levels of the ancient strandline during the last concluded that those curves vary in details 6,000 years.
because the local phenomena are not the same. Two zones, in particular, of the brazilian t Let us consider an example of a curve coastline, where the geologic evolution during established at the Ivory Coast, Africa (Fig. 2), the Quaternary seems to have been affected by according to Martin (1973,. It is verified that the tectonic movements, are here considered. the sea level changed from - 60 to little more These are the coastal regions of the States of than - 110 m in relation to the present sea Bahia and São Paulo. level, between 23,000 to 18,000 years B. P. As n consequence, a change of about 50 m in 5,000 THE EVOLUTION OF THE STATE years was verified. Similarly, between 17,000 OF BAHIA COASTLINE and 7,000 years B. P. the sea level changed from - 110 to about - 10 m. The sea level changed, This: part of the brazilian coastline is geolo- in this case, 100 m in 10,000 years. Nevertheless, gically characterized by the presence of the during the last 6,000 gears the sea level did not Recôncavo Sedimentary Basin, which is a change more than some meters, and in some .. BRAZILIAN COASTLINE QUATERNARY FORDTATIONS - THE STATES OF SAO PAULO 327 m m .Io 10 + Some meters in 6,000years~ + - O. - 0 - 10 10 20. 20 30 i 30’ A O 40 O 40 3 50 -. 3 50 --L 60 -0 60 O O 70 Y 70 (D n 7 80 cn 80 .. “00 90 -90 Y (D 100 n 100 110 .11 o 12c -120 26 24 22 20 18 16 54 12 IO 8 6 4 .Z O Years B.P x 1.000 FIGURE 2 - EXAMPLE OF SEA LEVEL CHANGING CURVE VARIATIONS AT IVORY COAST(AFRICA). AFTER MARTlN(1973) An. Acad. bras. Ci6nc., (1976), 48, (Suplemento) 328 RENITICO SEGUI(J and LOUIS XAETINS N T -50 Km ++{ ILHÉUS + GEOLOGIC SCHEME OF THE SALVADOR REGION ITAPARICA IS. MADRE DE DEUS IS. J Holocene sytrandline 1 I I I i Present &andline I II I 'I l !I W E =I+ + Lei te GEOLOGIC SECTION OF THE REC~NCAVO BASIN FIGURE 3 - NFLUENCE OF THE REC~NCAVOGRABEN ON THE HOLOCENE STRANDLINES. AIG. Arad. bras. C"iE?zc., (19T61, 48, (Suplemento) BRAZILIAN COASTLINE QUATERNARY FORMATIONS - THE STATES OF SAO PAULO 329 cavo Basin was still a subsident zone during the lated with the Pariquera-Acu Formation of Bi- Recent Quaternary, with the exception of the garella and Mousinho (19651, probably Pliocene zone materialized by the Itaparica and Madre in age (Fig. 5). de Deus Islands. Above, we find a formation that is argilla- It is interesting to verify that the transition ceous in its basal part and sandy on the top, between the different zones is very rapid. There called Cananéia Formation (Suguio and Petri, is no gradual transition from an emergence 1973). Its altitudes range from 5 to 6m seaward morphological zone to a submergence morpholo- and 9 to 10 in near the crystalline basement gical zone. rocks. Studying the nlicroorganisms, Petri and Suguio (1973) showed that the basal argillaceous THE EVOLUTION OF THE STATE OF unit was deposited in a transitional, brackish SÃ0 PAULO COASTLINE water environment, changing from a continental to a salt water environment. At the bottom of The State of São Paulo coastline, with an the sandy unit it is possible to see indications average NE-SW trend, is limited by 23 and of a transgressive phase, followed by emersion 250 southern latitude and 43 and 459 western in a regressive phase toward the top (Martin longitude (Fig. p). and Suguio, 1975). Many fossil Callianassid It shows mixed morphological configurations burrows that are situated in increasing levels with emergence characteristics in the southern toward the continent indicated that the sea level part and submergence features in the northern was rising at that time. The first radiocarbon part. The São Sebastião region forms approxi- dating taken from a fossil wood fragment con- mately the limit between two zones of different tained in the argillaceous formation gave behaviour. 28,000 +. 2,000 years B. P. (Sample Ba-227). The Precambrian basement rocks touch the Since the dating was made under adverse con- sea almost everywhere, with the exception of ditions, this sample should be older than the indi- narrow plains mostly constituted by Quaternary cated age. Although this dating had not been marine deposits, such as Ubatuba and Caraguata- perfect, it showed that the Cananéia Formation tuba coastal plains in the north. In the southern was deposited during the penultimate great part of the São Sebastião Island there are a transgression. series of plains essentially formed by Quaternary Situated stratigraphically above the Cana- marine sediments separated by advanced points néia Formation but topographically below, the of crystalline basement that reach the sea. At following formations are found: the present, only the greatest of these plains was studied in detail. That is the Cananéia- a) A coastal marine formation essentially Iguape plain situated in the southern State of constituted by fine to very fine sands, never higher than 3 m -: It is formed by the same São Paulo. It is more than 100 lun long with a sand as the Cananéia Formation, as a result of maximum width of 40 km. A detailed mapping and radiocarbon dating permitted to identify a the reworking of that formation. Radiocarbon certain number of formations (Martin and dating showed that it was deposited during the last transgressive episode. Suguio, 1975). In contact with the Precambrian crystalline b) Mangrove formation that fills up the rocks, there occur rudaceous sediments of a ancient bays carved in the Cananéia For- continental formation that can be roughly corre- mation -: Raised mangrove sediments fornied 330 KENITIRO SEGUIU and LOUIS BIARTINS during a period when the sea level was higher during 3,900 to 3,400 years E. P. Afterwards, than nt present, also occur. the sea level was again about 3 m higher, relative to the present, near 3,000 and 2,500 years B. P. e) Fluviatile-lagoonal formations that are sandy and argillaceous sediments deposited by Consequently, it was verified that in the the Ribeira de Iguape River and its tributa- southern coastal plain of the State of São Pauh ries -: They are found in the eroded zones of (area with emersion morphology) there were th6 Cananéia Formation that were occupied by >ea levels higher than the present during the a lagoonal system during the periods when the Holocene. One of the purposes of this work sea levels were higher than at present. is to verify that the same levels occur in the It is interesting to verify the presence of northern littoral (area with submergence mor- phology), especially see if they have the same some evidence of a formation more elevated than to the Cananéia Forniation 115 to 18 m above the altitude, and to check the possible influence of average sea level) on the Iguape island, near the tectonics in the Holocene coastal evolution. Icapara Village. This would be evidence of a Unfortunately till now we don't have suf- transgressive period older than that of the Ca- ficient calculated data to elucidate the question. nanéiin Formation. However, from now on, we can reach some interesting conclusions. From the north to south Some sambaquis (Kjökkenmoddings) and the areas and the widths of the marine sedi- fossil plant debris, associated to these morpho- mentation Quaternary plains grow regularly logical periods, permitted the establishment of (Fig. 4). In the Ilha Grande Bay (State of a sea level changing curve for the Cananéia- Rio de Janeiro) the marine Quaternary fornia- Iguape region (F'ig. 6). tions show little development and some genuine From these data it was possible to deduce &as> are found in the Parati region. However, that the sea level was approximately 3 m above it was seen that the marine Quaternary plain the present sea level 5,000 years E. P. This higher of the CananBia-Iguape region has a considerable sea level was followed by a period when the sea surface area (maximum dimensions: 100 X 40 level probably was lower than the present one kml. The importance of the Pleistocene form- FIGURE 5 - INTERPRETATIVE PROFILE ACROSS SEVERAL FORMATIONS OF THE CANANÉIA-IGUAPE REGION (S.PI. CANANÉIA ISLAND I r Fine sand = Holocene "Call~ono;sid"burrows horizon ._ Cananeio Formation = Pleistocene 2' 0 Fine sand Penultimate transgression m 10 L EEI Silty cloy 5 Potiquera-A$u Formation (Pliocene?) Scale O (rccI Crystalline rocks = Precambriun Kmnmi An. dcad. bras. CiLizc., (19761, 48, ISuplemento) BRAZILIAN COASTLINE QUATERNARY FORMATIONS - THE STATES OF SÄO PAULO 331 ations also increases regularly from the north The littoral of the State of São Paulo is to the south. It is necessary to note that the situated in the concave portion of the Ponta width of the continental shelf is more important Grossa tectonic arch that is located in an ancient in the southern part than in the northern part. positive zone. A certain number of evidences In the Parati Mountains region (north) the shows recent rising in the northern flank of isobath of 50 m is situated at 8 km from the the arch. It is a positive zone in the continent coastline, in the Santos region, it is located at followed by great faults more or less parallel 50 km, and in the Iguape region (south) it is at to the coastline. Some of these faults originated 60 km. the FIGURE 6-SCHEME OF SEA LEVEL CHANGES IN THE CANANÉIA-IGUAPE REGION (SPI BETWEEN 6,500 AND 2,500 YEARS B.P Martin 8 Suguio (1975). An. Acad. byas. C~&C., (1970, 48, (Suplemento) 332 KENITIRO SEGUIO and LOUIS MARTINS indicates the inflection point to the north on the If the block systems situated in the left continent. It then progresses towards the con- side of the inflection line uplift again, and if tinental shelf, continually swerving from the th? block systems at the right side submerge, coastline. This would explain the coastal plain's 8 iieit inflection period would begin and it regular growth in estent and width. \coxl;l fall into the general scheme. However, this inflection phenomenon is pro- Obviously this scheme is very simplified. Ne- bably not recognizable in the Holocene time vertheless, it is possible to reconstruct the State scale. Evidently the submerged and emerged of São Paulo coastal evolution after Tertiary. coasts differentiation did not occur only during Three main evolutive stages are distinguishable: the Holocene. The last transgression was perfor- the inflection period, the fracturation period and med on previously existing submersion niorpho- the renewed inflection period (Fig. 8) It seems logy. PTormsllj-, if the fnîlectioïi mechanism was that a continental zone uplift and an oceanic perceptible during the course of the Holocene, zone submergence occurred during the Tertiary, the same age levels slightly elevated in the thus generating an inflection line between these interior zones than in the exterior zones would two zones. When the tensional strength was be found. Unfortunately this difference of levels great enough, the fractures were produced, ori- together with the normal dipping seaward of ginating the ?Serra do Mar, on the continerit the sedimentary layers, would be very difficult and the Santos fault zone in the ocean. The to measure. erosion of the continent occurred in proportion to its uplifting. Simultaneously, the sedimn. CONCLUSIONS tation occurred in an incipient .;graben, in the area, occupied today by the Santos Basin. Pro- Numerous points of the Brazilian coastline bably thk fracturation period was not continuous show Holocene niarine levels indicating higher and c nme periods of interruption propitiated the sca levels than the present's. It would be inte- inflLctmn mechanism's renewal. resting to verify whether these ancient strand- linec were not submitted to deformations in order to estimate the role played by modern tectonism. In the Salvador region (State of Bahia), the Recòncavo Sedimentary Basin cutting the littoral, probably had a certain activity in the course of the Recent Quaternary. The transition between the areas with an uplifted Holocene coastline and the areas without an uplifted coastline occurs in a very abrupt way. The State of São Paulo littoral presents a submersion morphology in the north and an emersion morphology in the south. It is neces- I sary to observe that the transition between these zones is very gradual and not abrupt as in the case of the Salvador region. It seems that in this case the explanation of the changin coastline morphology must be looked for in the continental inflection phenomenon. ACKLOWJXERIIENTS This research has been financially supported by a grant from the FAPESP (Fundação de Am- paro S Pesquisa do Estado de SBo Paulo). The authors wish to express their thanks to Maria Morris for the revision of the English text. BRAZILIAN COASTLINE QUATERNARY FORMATIONS - THE STATES OF SÃ0 PAULO 333 Sea level INITIAL STAGE, zone f facture zone "Serra do Mar" Santos Basin + + ' +*u fault zone ++i ++++-!-++-I- l I +++++tt+t I +++ t t RENEWAL INFLECTION, I STA BI LIZ ED FRACTURE S. 'I 4 FIGURE 8- EVOLUTIVE SCHEME OF THE STATE OF SÃ0 PAULO CONTINENTAL MARGIN IN THE CENOZOIC. An. Acad.. bras. Ci&nc., (1976), 48, (Suplemento) 334 KENITIRO SEGUIO and LC)UIS MARTINS REFERENCES RARNES, E. and LEITE, D. 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