Palaeodrainage on Marajó Island, northern Brazil, in ... · Dilce F. Rossetti, 1* Márcio M. Valeriano,Ana M. Góes2 and Marcelo Thales3 (1Instituto Nacional de Pesquisas Espaciais-INPE,

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from continental areas was interrupted, leading to abandonment ofnumerous channels.

A model has been proposed that considers a large channelizedfunnel-shaped morphology related to an Upper Pleistocene toHolocene estuarine system in Lake Arari area, eastern MarajóIsland, a product of decreasing continental inflows (Rossetti et al.,2007b). Without significant flow discharge, the estuary was nolonger fed by riverine-derived sediments. A complex interplay oftectonics and sea-level changes would have promoted the replace-ment of this system by a north–south oriented lake, ie, Lake Arari,which is a major feature in eastern Marajó Island that parallels themargins of the funnel-shaped feature related to the palaeoestuary.

Both sides of Lake Arari display a network of palaeochannelswith an overall northeast/southwest orientation, which are notice-ably wider than modern channels in that area, suggesting signifi-cant environmental change(s). The goal of this paper is to providea detailed characterization of this palaeodrainage network (Figure2A and B) in order to understand both their mode of formation and

Introduction

Marajó Island (Figure 1A and B) encompasses a low-lying area upto 400 000 km2 at the mouth of the Amazon River, where a com-plex network of palaeochannels is exceptionally well preserved(Bemerguy, 1981; Porsani, 1981; Vital, 1988). Previous studieshave shown that these palaeochannels are related to a large, northto northward[AQ] oriented palaeovalley resulting from tectonicreactivations in late Pleistocene to Holocene time (Rossetti andValeriano, 2006; Rossetti et al., 2007a). According to theseauthors, this palaeovalley originated when a palaeo TocantinsRiver was flowing north/northwestward, a direction that is oppo-site to its modern northeast direction in the lower Amazon mouth.This process gave rise to the opening of Marajó Bay, with a con-sequent separation of Marajó Island from the mainland. As theisland became established, the delivery of sediments supplied

Palaeodrainage on Marajó Island,northern Brazil, in relation to Holocenerelative sea-level dynamicsDilce F. Rossetti,1* Márcio M. Valeriano,1 Ana M. Góes2 and Marcelo Thales3

(1Instituto Nacional de Pesquisas Espaciais-INPE, OBT/DSR Rua dos Astronautas 1758-CP 515, 12245-

970 São José dos Campos-SP, Brazil; 2Universidade de São Paulo-USP, Instituto de Geociências –

Programa de geologia Sedimentar e Ambiental Rua do Lago, 562 Butantã 05508-080 São Paulo, SP,

Brazil; 3Museu Paraense Emílio Goeldi Av. Magalhães Barata 376-CP 399, 66040-170 Belém-PA, Brazil)

Received 12 September 2007; revised manuscript accepted 8 January 2008

Abstract: A large area in northeastern Marajó Island, northern Brazil, has been characterized geomorphologi-cally, applying information acquired from Landsat imagery. This study was combined with detailed sedimen-tologic analysis of continuous cores, which provided a record of depositional settings developed in this areathrough the Holocene. The results revealed well-preserved, meandering to anastomosed drainage networks ofwide palaeochannels that were superimposed by a narrower palaeochannel system. In both cases, the sedimen-tary record consists of sands, heterolithic deposits and muds, locally rich in plant debris. The strata are organ-ized into fining upward successions that reach approximately 18 m thick in the wide channels and 4 m thick inthe narrow channels. Sedimentary features suggestive of a coastal location for the wider palaeochannels andreworking of sediments by tidal currents include the prevalence of well to moderately sorted, rounded to sub-rounded, fine- to medium-grained sands displaying foreset packages separated by mud couplets, suggestive oftidal cycles. The data presented herein point to a rise in relative sea level reaching the Lake Arari area duringthe early to late/mid Holocene. This event was followed by a relative sea level drop. Tectonics seem to havecontributed to an overall lowering in relative sea level in the study area since the mid-Holocene, which does notfollow the same pattern recorded in other areas along the northern Brazilian coast.

Key words: Remote sensing, geomorphology, sedimentology, palaeochannel, Holocene, Marajó Island, rela-tive sea level, tectonics, Brazil.

The Holocene 18,5 (2008) pp. 01–12

© 2008 SAGE Publications 10.1177/0959683608091798

*Author for correspondence (e-mail: [email protected])

11-091798-Rossetti.qxd 4/30/2008 6:25 PM Page 1

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LYthe their controlling mechanism(s). This research was motivatedby the advances in remote sensing data collection. Unlike most ofAmazonia, the study area is dominated by grassland vegetation,being suitable for accurate geomorphological analysis using opti-cal (Landsat) imagery. This approach was complemented by inte-grating remote sensing with sedimentologic data in order tounequivocally document the palaeochannels. This type of investi-gation has not been done before in the study area, and might pro-vide significant data to discuss the causes that led to changes inchannel dynamics through time, as well as the possible influenceof relative sea-level fluctuation in this low-lying area of northernBrazil.

Physiography and geology

Northeastern Marajó Island is a flat-lying area with altitudes averaging 4–6 m above modern sea level. Climate is tropical, withmean annual temperature of 28°C and precipitation of 2500 to3000 mm/yr. Vegetation is mostly primary, with dense forests andopen vegetation prevailing in the west and east sides of the island,respectively, the latter displaying additionally elongated andhighly sinuous belts of forest vegetation selectively developedupon slightly raised areas of palaeochannels.

Geologically, northeastern Marajó Island has been consideredas part of the Pará Platform (Figure 1A), which corresponds to alarge area of the crystalline Precambrian and sedimentaryPalaeozoic substrates that remained tectonically stable relative toadjacent sedimentary basins. However, as highlighted in a previ-ous study (Azevedo, 1991), this platform might display narrow,

but deep, troughs that are up to 3500 m deep. Lake Arari is locatedin a north–south elongated depression connected northward to theMexiana Sub-basin. This sub-basin is part of Marajó GrabenSystem (Figure 1A), a structure defined by NW–SE and NE–SW normal faults reactivated from basement (Azevedo, 1991;Villegas, 1994; Costa and Hasui, 1997). The rift experienced twoextensional phases. The first one is related to the opening of theEquatorial South Atlantic Ocean in the late Jurassic and earlyCretaceous (Szatmari et al., 1987[AQ]; Azevedo, 1991), with asecond, and more important, extensional episode taking place inthe Aptian–Albian transition.

The sedimentary fill of the Mexiana Sub-basin (Figure 1C) ismostly based on sub-surface data (Galvão, 1991; Villegas, 1994).It encompasses sandy deposits of the Breves/JacarezinhoFormations (Aptian–Cenomanian), and silty mudstones of theAnajás Formation (early Cretaceous). These units, attributed todepositional environments ranging from fluvial to shallow marine,are overlain by sandstones, mudstones and conglomerates of theLimoeiro Formation (late Cretaceous), also related to fluvial-shallow marine settings (Villegas, 1994). Tertiary deposits overlying the Cretaceous succession consist of mixed siliciclastic-carbonates of the Marajó Formation (Palaeocene–Eocene), as wellas of the Pará Group (Miocene to Holocene), altogether includedin transitional to shallow marine depositional settings. The latterencompasses sandstones of the Tucunaré Formation and mud-stones of the Pirarucu Formation, which are age equivalent to theBarreiras Formation and the post-Barreiras sediments recorded inthe surface (Rossetti et al., 1989, 1990; Rossetti, 2000, 2001).

The Barreiras Formation and post-Barreiras sediments areexposed along coastal cliffs in eastern Marajó Island. In this area,

2 The Holocene 18,5 (2008)

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Figure 1 (A) and (B) Location map of the study area in northeastern Marajó Island, northern Brazil. The inside box in (A) locates (B). Note in(B) the location of Lake Arari upon a main palimpsest morphology related to a palaeoestuary setting. (C) Summary of the stratigraphic frameworkof the study area


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Dilce F. Rossetti et al.: Palaeodrainage and relative sea-level dynamics, Brazil 3

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Figure 2 (A) 4(Red), 5(Green), 7(Blue) Landsat composition (A) and corresponding map (B) of the palaeodrainage networks preserved on bothsides of Lake Arari, northeastern Marajó Island. Note the dominance of a drainage system consisting of wide and continuous palaeochannels tothe east of the lake, which contrasts with more segmented palaeochannels to the west. Observe also, in the eastern sector, a drainage network con-sisting of relatively narrower channels locally superimposed upon wider palaeochannels. These two figures also show that Lake Arari parallels amuch larger palimpsest funnel-shaped geomorphologic feature that is typical of an estuary, with its mouth to the north. A set of parallel struc-tures is seen in the inner margin of this feature, which resembles lateral accretion bars. (I–II locates the profile presented in (C) and the numberslocate the studied drills, except for number 4 that locates a trench). (C) A topographic profile obtained from SRTM digital elevation data illus-trating a large area to the north in the western sector that is slightly more depressed than the terrains located to the south (see (A) for profile loca-tion). The three highest topographic peaks are caused by the selective development of forest vegetation over palaeochannels


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the post-Barreiras deposits are only a few metres thick, but thisunit becomes rapidly thicker westwards in the sub-surface, reach-ing up to 120 m in the Arari Lake area, where it unconformablyoverlies sandstones and mudstones of the Barreiras Formation.

Methods

The geomorphological characterization presented in this paper wasbased on analysis of Landsat 5-TM (Ref. 224-060 and 225-061,INPE) and Landsat 7-ETM+ (Ref. 223-060 and 223-061, GLCF)images, acquired in August 2001. These scenes were free of cloudsin most of the eastern side of Marajó Island, favouring their use forthe detailed geomorphological mapping proposed here. A R(Red),G(Green), B(Blue) band composition scheme was applied usingthe SPRING software. The composition 4(R), 5(G), 7(B) revealedthe palaeochannels with a higher degree of precision when com-pared with other Landsat optical compositions because of its spec-tral contrast relative to surroundings areas. The processed Landsatimages obtained provided a better visualization of the features ofinterest than any other radar products, such as L-band syntheticaperture radar images of the Japanese Earth Resources Satellites(JERS-1) and interferometric synthetic aperture radar (InSAR)from the Shuttle Radar Topographic Mission (SRTM). Despitelimitations, the latter data were additionally used in this work forproviding digital elevation models in places with good resolution.

The sedimentological data consisted of detailed descriptions ofcores collected with shallow drills using a RKS percussion drillingsystem, model COBRA mk1. This system allowed sampling ofcores with 5 cm diameter up to a depth of 24 m. Descriptionsincluded definition of sedimentary features based on lithology,structure (physical and biogenic) and the vertical facies distribu-tion. The sedimentary facies were properly photographed andrecorded in lithostratigraphic profiles.

The chronology was based on radiocarbon analysis undertaken atthe Beta Analytic Radiocarbon Dating Laboratory. Samples of peat,wood and organic sediments were dated by scintillation spectrome-try or, for small samples, accelerator mass spectrometry (AMS).The samples were pre-treated with acid to remove carbonates andweaken organic bonds, washed with alkali to remove secondaryorganic acids, and then combined with acid again to provide more

accurate dating. Conventional 14C ages were calibrated to calendaryears using the Pretoria Calibration Procedure program, based ontree-ring data as calibration curves (Talma and Vogel, 1993).

Geomorphology

The area surrounding Lake Arari displays a set of geomorphologi-cal features that include palaeochannels and sandy bars, the lattermostly developed in its eastern margin (Figures 3 to 5). Thepalaeochannels vary in size when both sides of the lake are com-pared. Hence, the area located to the east contains a series of well-defined and highly continuous channels displaying widths up to 1.2km, with an average between 0.6 and 0.9 km (Figures 2A, B, 3A,B). These are interconnected, configuring an anastomosing tomeandering pattern, with channels showing a main northeast/south-east orientation. Floodplain areas between channels might presentlakes >4 km in length. An interesting feature on this side of the lakeare sets of sandy bars elongated in a main north–south direction,which parallels the lake margin but continues southward beyond thelake boundaries, delineating the margin of the palimpsest estuarinechannel morphology upon which Lake Arari became established(Rossetti et al., 2007b). Two main palaeochannels in the centre ofthis sector are sharply truncated by these bars. A few narrowerpalaeochannels averaging 0.2 km wide are observed in the northeastpart of this sector, where they cross over the wider palaeochannels,and also over each other (see Figures 2A, B and 4A).

To the west of Lake Arari, there are two well-defined palaeo-drainage networks. One consists of palaeochannels as wide asthe ones of the eastern sector, but with channels that are less con-tinuous, resulting in several isolated segments with straightedges that are particularly abundant in the middle and northernpart of the sector (Figure 2A and B). These areas have slightlylower topography than nearby terrain, as indicated by the digitalelevation model (DEM) obtained from SRTM data (Figure 2C).The depressed areas coincide with features known in MarajóIsland as mondongos, referring to lands that remain flooded allyear round. Modern channels wider than average, and whichgrade into irregular ponds, are present in this area (Figure 4B).More continuous, also larger (up to 1.6 km wide), palaeochan-nels occur to the west in this sector. Although less defined than


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Figure 3 (A) A 4(R), 5(G), 7(B) Landsat composition and corresponding drawing highlighting details of the palaeodrainage consisting of widechannels that is typical in the eastern sector of Lake Arari. The two arrows indicate locations where main palaeochannels in the centre of this sec-tor are sharply truncated by the set of migrating bars from the inner lake margin


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in the eastern sector, this drainage network displays many chan-nels that are also northeast/southwest oriented, with some chan-nel confluences indicating northeastward palaeoflows.

The other palaeodrainage network from the western margin ofLake Arari is formed by a myriad of narrow channels (Figure 4C)that are locally superimposed upon wider palaeochannels, par-tially obliterating their presence on the landscape.

In the western sector, there are both wide and narrowpalaeochannels that are either laterally displaced or suddenly

interrupted by modern rivers that follow an overall straight pattern(Figure 4C to F). Where lateral channel displacements areobserved, strike-slip faults with dextral motion are suggested(Figure 4C, D and E).

In addition to the palaeodrainage networks that occur on both mar-gins of Lake Arari, there are a few palaeochannels within the shal-lower part of the lake that correspond to the seaward-most portion ofthe Arari palaeoestuary (Figure 5). These palaeochannels show goodcontinuity with those from the western margin of the lake.


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Figure 4 (A) Narrow channels superimposed on large channels to the northeast of Lake Arari. (B) to (F) Details of the western side of the studyarea, illustrating: (B) the depressed area characterized in the SRTM digital topographic data shown in Figure 2C (single head arrows = channelswider than average; double head arrows = average channels). Note that channels flow into irregular ponds (northeast side of the image, where wateris indicated by blue colors. (C) Palaeodrainage (shown in bright orange) consisting of a myriad of narrow palaeochannels superimposed upon widerpalaeochannels, eastern sector of the study area. The inset box indicates a palaeochannel disrupted by a fault with lateral offset, whose plane canbe traced northward into a straight modern channel (double head arrow). (D) and (E) Landsat image (D) and corresponding drawing with the inter-pretation (E) of a wide palaeochannel disrupted by a fault with lateral offset. (F) A wide palaeochannel complex (dotted lines) sharply truncated bya straight modern river (arrows). The palaeochannel disappears northward for a distance of more than 2 km. All figures were obtained from a 4(R),5(G), 7(B) Landsat composition, except for (B), which is a 5(R), 4(G), 3(B) composition


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Sedimentology

Seven drills with continuous cores were available for this study(Figure 6). Four of them are from the western side of Arari Lake,with one recording a wide (drill #1) and a narrow (drill #5) channelmorphology, and the other two (drills #2 and #3) derived from inter-channel areas. The fifth drill (drill #6) was collected within thenorthern part of Lake Arari. Another two drills were obtained in theeastern side of the lake, one (drill #7) recording a wide channel mor-phology right at the margin of the lake, and the other (drill #8)recording an area southeastward of Lake Arari. Additionally, atrench (#4 in Figure 2) was made around 1.7 km south of drill #3.

Analyses of cores obtained on the narrow and widepalaeochannel morphologies revealed sedimentary successionsencompassing sandy, streaky to wavy heterolithic, and muddy

facies (Figure 7A–C), typically configuring fining upward trends.Cores on wide palaeochannels did not reach the base of the suc-cessions. However, the recorded deposits are up to 18 m thick,and mostly include sandy portions formed by several, 2–4 mthick, sharp-based cycles with normal grading of coarse tomedium and fine to very fine grain sizes (Figure 6, profiles 1 and7). Upward, the sandy deposits grade into heterolithic and muddydeposits, characterizing overall fining upward cycles. The sedi-mentary record of the narrow palaeochannel indicates a main,sharp-based (Figure 7D), fining upward succession only 4 mthick (Figure 6, profile 5), which is internally composed of sev-eral smaller-scale (0.2–0.3 m thick) cycles. The sandy depositscut into a muddier package consisting of laminated and massivemuds that might contain several thin, sharp-based sandy layersthat fine upward. A trench in a narrow channel to the north of the


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Figure 5 (A) A 4(R), 5(G), 7(B) Landsat composition and the corresponding drawing with the interpretation of large palaeochannels crossingover the shallower, northernmost part of Lake Arari


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study area (Figure 6, profile 4) also revealed a sharp-based sandysuccession up to 0.5 m, with abundant, though mostly undeter-mined, invertebrate trace fossils, with thick traces resemblingOphiomorpha (Figure 7E).

The sandy facies ranges in colour from medium grey to brownin the sub-surface and, more rarely, white to pale yellow and yel-

low to dark brown near the surface due to iron staining. Sandsare, in general, well to moderately sorted, rounded to subrounded,micaceous, and fine- to medium- or medium- to coarse-grained.When present, the dominant sedimentary structure consists ofparallel and cross-lamination or cross-stratification (Figure 7A);otherwise sands are massive. Mud drapes and/or highly frag-


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Figure 6 Lithostratigraphic core profiles obtained from seven drills (1 to 3 and 5 to 8) and one trench (4), representing wide palaeochannels (1 and 7), narrow palaeochannels (5), and interchannel areas (1–3, 6 and 8)


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8 The Holocene 18,5 (2008)1cm

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Figure 7 Details of the sedimentary facies recorded in the studiedcores. (A) Laminated sand facies from a large palaeochannel succession,with lamination marked by dark layers (white arrows) composed of plantdebris. The dark layer between the two black arrows contains plantdebris. (B) Heterolithic bedded facies formed by mud with isolated fineto very fine sand lenses (white arrows). (C) Laminated mud facies. (D)A detail from the base of the narrow channel deposit in profile 5, illustrating massive sand facies (Sm) sharply truncating (dotted line)underlying laminated mud facies (Ml). (E) A detail from asharp-based narrow

Figure 7 (Continued)

channel deposit exposed in a trench (profile 4), where highly bioturbatedsands (Sm; arrow = burrows) sharply overlies underlying massive mud(Mm). (F) A sandy channel deposit displaying thin mud laminae(arrows) between alternating thicker and thinner sand layers formingcouplets attributed to flood/ebb tidal fluctuations. (G) A detail of a mud facies with a fragment of wood (arrow). (H) Peat from mud facieslaterally correlatable to channel deposits in the study area

mented plant remains (Figure 7A) are often observed mantlinglaminations, foreset packages and set boundaries. Double muddrapes configuring alternating thicker and thinner sand bundlesare also present (Figure 7F).

The muddy deposits at the top of the sandy fining upwardcycles consist dominantly of thin streaks or lenses of well-sorted, brownish massive muddy silt to fine grained sands,greenish grey and grey massive mud, and heterolithic facies.Sandier heterolithic deposits locally form flaser bedding. Theheterolithic deposits may grade into either massive or laminatedmud facies (Figure 7C) that may contain dispersed plant debris(Figure 7G).

The cores obtained on interchannel areas are dominantlymuddy, comprising greenish grey and grey laminated and massivemud, endured green/yellow to brownish massive mud, brownishmassive muddy silt, and heterolithic facies. These lithologies aresimilar to the ones recorded at the top of the fining upward cyclesdescribed above. Plant debris and fragments of coal are present inseveral places throughout the profiles, and peat deposits (Figure7H) were recorded between 2–4 m and 11.3–13.2 m in drill #3,and between 3 and 3.7 m in drill #8.

The muddy deposits in drills #2, 6 and 8 are overlain by muddyhorizons that are frequently interbedded with layers and lenses ofwell-sorted, fine- to very fine-grained sands and are locally pres-ent within the muddy deposits, forming either fining or coarseningupward cycles up to 5 m thick.

Radiocarbon age and stratigraphy

Twenty samples were dated using radiometric or AMS dating.Together with mapping of discontinuity surfaces (Figure 6), theresults (Table 1) establish the following stratigraphy for the stud-ied deposits, represented by three units.

The lower unit comprises mudstones with plant debris that areinterbedded with fining upward sand layers recording radiocarbonages between 55 082 (±12 354) and 41 582 (±1432) 14C yr BP.The top of this unit is marked by a palaeosol characterized byendured, oxidized, greenish to brownish and yellowish massivedeposits having fragments of pyritized biogenic tubes and pebblesof sandstones. An irregular discontinuity surface with a relief ofseveral metres (at least 14 m, considering the recorded profiles)separates this unit from overlying deposits.

The intermediate unit consists of muddy deposits that areinterbedded, at the base, with either heterolithic or sandy deposits,forming coarsening upward cycles. In drills #1 and 7, these strataare coeval with cross-stratified and flaser laminated sands that fineupward. Radiocarbon ages recorded in this unit range from 10 577(±43 14C yr BP and 6300 (±80) 14C yr BP.

The upper unit follows the same overall lithological patternas observed in the intermediate unit. Even where lithology doesnot change, a sharp surface with up to 2 m of relief (consideringonly the recorded profiles) is recognized, separating depositsthat are slightly oxidized below from deposits with no evidenceof oxidation above. Recorded radiocarbon ages range from 6190(±60) 14C yr BP and 3500 (±40) 14C yr BP.


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LYInterpretation of the depositionalsettingThe mapping of palaeochannels in the Lake Arari area based onLandsat imagery allowed us to distinguish, for the first time, twopalaeodrainage systems consisting of channels that were consider-ably wider and sandier than the average channels present today inthat area. These characteristics are consistent with comparativelyhigher-energy palaeoflows during the latest Quaternary. The factthat the palaeodrainage system composed of narrower channels issuperimposed upon the palaeodrainage system with wider chan-nels, locally cutting through them, is good evidence that the latterhad an earlier stage of development with respect to the narrowpalaeochannels. Analsysis of sedimentary facies and the strati-graphic architecture helped to further demonstrate the nature ofthese depositional environments.

Despite the presence of a discontinuity surface between theintermediate and upper units, the radiocarbon ages indicate thatthese units are genetically related, as no significant time gap existsbetween them. Therefore, the discontinuity surface at the base ofthe upper unit is related to a short break in sedimentation due to anauthochtonous process related to environmental dynamics. Forthis reason, they will be analysed together here as part of a con-temporaneous depositional system.

Intermediate and upper unitsThe sedimentological analysis of the upper unit reveals typical finingupward successions, indicative of decreasing flow energy, in placeswhere channel morphologies were mapped in surface. Although suchlithological organization is present in a variety of depositional set-tings, the channel morphology assures that these deposits recordupward decreasing energy associated with confined, channelizedflows, as typical of many channel deposits (Miall, 1985). Drills #1and #7 illustrate two wide channel morphologies in the uppermostunit, with thicker (at least 18 m thick) sedimentary successions rela-tive to the uppermost fining upward sandy succession recorded in drill#5 (where a narrow channel morphology is observed). The widerchannels, however, display sedimentary successions that result, infact, from amalgamation of fining upward sandy cycles, with a breakin sedimentation being suggested between 9 and 10 m depth. Thissuggests that the channels were not continuously filled. After filling,the channels became progressively abandoned and filled with mud-

dier deposits, forming the uppermost portions of the fining upwardsuccessions. Hence, the lower sandy portion of the channel succes-sion is attributed to higher energy sediment bedload deposition dur-ing active channel development, while the upper muddy deposits arerelated to sediment deposition from suspensions during channel aban-donment, when flow energy was dominantly low.

Mud drapes mantling foresets and cross-set boundaries insandy channel deposits can be produced in a variety of settingswhenever mud is available and the flow fluctuates, allowingalternation between sand deposition and mud settling from sus-pension. Frequent mud drapes, however, indicate constant varia-tions in flow velocity, which is naturally found in tidal settings.The frequent mud drapes in deposits representative of wide chan-nels and, in particular, the double mud drapes configuring alter-nating thicker and thinner sand bundles, resemble many featuresattributed to the action of tidal current fluctuations (Boersma and Terwindt, 1981; Mowbray and Visser, 1984; Yang and Nio,1985; Leckie and Singh, 1991; Shanley et al., 1992; Hori et al.,2001; Plink-Bjorklund, 2005). The good to moderate sorting,good roundness and dominantly fine grain sizes are sedimentaryfeatures that conform to a coastal location for these drainage sys-tems. Additionally, the high degree of bioturbation, with proba-ble Ophiomorpha traces, as observed in a trench representative ofnarrow channel deposits, is also consistent with a coastal influ-ence. Thus, although core data provide only limited informationconcerning the sedimentary features, the available informationsupports the theory that the studied palaeochannels were formed,at least in part, in a coastal setting, and most likely under theinfluence of tidal currents.

Below channel successions, or where channel morphology isabsent in the surface, low energy muddy deposits prevail.Considering the proposed interpretation of tidal influence in thechannel deposits, the muddy counterparts might include depositsrelated to adjacent muddy tidal flats and mangroves. Our ongoing palinologic studies reveal the frequency of Rhyzophorapollens throughout the intermediate and upper units, which con-firms this interpretation. However, the coarsening upward sandycycles at the base of the intermediate unit, and their upward gra-dation into muddy deposits that may reach up to almost 12 mthick, lead to propose a standing body of water of low energy,with episodic sand inflows. Despite the limited core informationrelative to the size of the study area, the tidal influence, the


Table 1 Radiocarbon ages obtained for the studied deposits in Marajó Island (see text for explanations)

Profile sample # Depth (m) Type of material 14C yr BP Cal. yr B.P. 2-sigma calibration (type of analysis)

1/MR-228 12.0 peat 8850 (±110) 10 220–9550 (radiometric)2/MR-166 4.7 wood 4770 (±40) 5600–5460; 5380–5340 (AMS)2/MR-179 13 organic sediment 10 276 (±34) (AMS)2/187 16.3 organic sediment 10 577 (±43) (AMS)3/268 2.1 organic sediment 5279 (±38) 6031–5909 (AMS)3/277 9.5 organic sediment 5561 (±37) 6402–6270 (AMS)3/MR-282 12.5 peat 6300 (±80) 7410–7000 (radiometric)4/MR-153 0.7 organic sediment 3500 (±40) 3870–3670 (AMS)4/MR-233 3.2 organic sediment 4930 (±40) 5740–5600 (AMS)5/205b 5.6 organic sediment 5863 (±36) 6680–6496 (AMS)5/MR-212 8.8 peat 6630 (±70) 7610–7420 (radiometric)5/MR-216 9.8 peat 6690 (±60) 7940–7680 (AMS)5/MR-218 10.6 organic sediment 9770 (±70) 11 250–11 100 (AMS)6/MR-241 7.7 organic sediment 7450 (±40) 8360–8180 (AMS)6/248 11.8 organic sediment 41 582 (±1,432) (AMS)6/MR-249 12.5 organic sediment 42 580 (±1,430) (AMS)7/MR-265 10.3 plant remains 7320 (±40) 8190–8020 (AMS)8/MR-291 1.3 peat 6190 (±60) 7250–6900 (radiometric)8/MR-311 17.8 organic sediment 41 080 (±810) (AMS)8/304 12.8 organic sediment 55 082 (±12 354) (AMS)


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occurrence of Rhyzophora pollens, and the palimpsest estuarinemorphology recognized in Lake Arari area (Rossetti et al.,2007b), together defend the hypothesis that these muddydeposits might have been formed also in central estuarine basins.Either riverine or tidal inflows could have produced suspendedlobes as bayhead deltas or tidal deltas and washovers, recordedby coarsening upward cycles. Additionally, lacustrine paludalsedimentation is expected to occur in the uppermost portions ofcores, for instance the one located within Lake Arari.

Lower unitBased only on facies interpretation, the lower unit does not seemto record any abrupt change in depositional conditions. Like theuppermost two units, this unit records settings displaying lowenergy flows that alternated with higher energy flows, responsi-ble for deposition of muds and sand layers, respectively. The lat-ter could be related to shallow channels, given the sharp base andthe fining upward nature. These deposits, however, show no evi-dence of tidal reworking, which could be taken as an indicationof an increasing influence of continental conditions, probablywith a higher proximity to fluvial inflows. Thus, the interbeddedmud deposits would be more properly attributed to flooplain settings, though eventually it could include also lacustrine andpaludal deposits.

The presence of and, particularly, the significant relief of thestratigraphic surface at the top of the lower unit, its associationwith ferruginization and palaeosol formation, and the relativelyolder (late Pleistocene) radiocarbon ages, all indicate that thesedeposits record a separate depositional episode in Lake Arariarea.

Depositional history and linkage torelative sea level

This work leads to the conclusion that the study area had a verydynamic depositional evolution during late Pleistocene toHolocene time. The physical environment changed from onewith increased continental influence to a tidally influenced set-ting, which evolved, in turn, to the lacustrine and associatedpaludal system represented by Lake Arari and nearby areas. Thisstratigraphic framework points to a transgressive phase takingplace in the early Holocene to late mid-Holocene. Subsequently,there was a return to the more continental conditions that prevailtoday in this study area. The implications of this architecturalreconstruction for approaching the causes of relative sea-levelchanges are discussed below.

Reconstructing the late Quaternary relative sea-level behaviouralong northern Brazilian coastal areas and particularly decipheringthe main controlling mechanism (eustasy, tectonics or sedimentsupply), are issues that need further information. Pollen data haveindicated an early- to mid-Holocene relative sea-level rise similarto the modern one in the states of Maranhão (Behling and Costa,1997) and Pará (Behling and Costa, 2000, [AQ]2001; Behling,2001; Behling et al., 2001a,b; Vedel et al., 2006). In addition,many of these studies have suggested a mid-Holocene relative sea-level low, followed by a transgression, from the mid to lateHolocene on the northern Brazilian coast. An increased relativesea-level has been also reported for the past decades in theBragança Peninsula, northeastern Pará (Souza Filho andParadella, 2003; Cohen et al., 2004, 2005a,b).

Based on these studies, it can be concluded that, except for ashort mid-Holocene regression, the northern Brazilian coastalareas have remained under an overall transgression since, at least,the early Holocene. The data presented here lead us to state that,whatever happened along the coastline, the effect of this main

transgression is not reproducible inland in northeastern MarajóIsland. In fact, there was a time for relative sea-level rise beforethe late to mid Holocene, as recorded by the deposits of the inter-mediate unit. Deciphering when this transgression started is prob-lematic with the available data. A previous publication hadestablished that the palimpsest estuarine morphology preserved inthe Lake Arari area results from a transgressive event initiatedduring the late Pleistocene. However, during the late Holocene,the study area started to prograde, a process that would have cul-minated with estuary abandonment and the modern establishmentof lacustrine to paludal conditions. The change to more stagnantlacustrine conditions may have favoured local formation of peatdeposits on the lake bottom.

The change in drainage network from wider to progressivelynarrower channels through Holocene, as recorded in the studyarea, supports the above interpretation. The wider palaeochan-nel deposits indicate a minimum age of 8770 (±110) 14C yr BP,though they might have started to be filled with sediment ear-lier, as the base of these deposits was not reached. The sharptruncation of these palaeochannels at the Lake Arari edge sug-gests that the beginning of channel sedimentation pre-dated themain phase of lake sedimentation. In particular, the fact thatthe wide palaeochannels are truncated by the bars in the innerside of Lake Arari is an indication that they were active beforelateral bar migration took place, which mostly likely occurredwhen the palaeoestuarine system was converted into a lakedepositional setting. Thus, the wide palaeochannels were, atleast in part, contemporaneous to the palaeoestuary and earlystages of the lake establishment. As the lake evolved, the widepalaeochannels also started to be abandoned in the landscape.As this process took place, these channels no longer developedinland in northeastern Marajó Island because they werereplaced by a much narrower drainage system that eroded, inpart, the pre-existing one.

The narrow channels were formed in the late Holocene, as indi-cated by the fact that they cut into deposits with recorded ages of3500 (±40) 14C yr BP and 5863 (±36) 14C yr BP. Such a changecould reflect a climatic gradation towards progressively more aridconditions, with decreasing humidity promoting reduction inchannel size. The history of climate fluctuations in the Holocenein this area has not been reconstructed yet, but data availablefrom other areas of the Brazilian Amazonia have indicated anopposite pattern of increased humidity since the beginning of theHolocene (Baker et al., 2001; Sifeddine et al., 2001; Rossetti et al., 2004, 2005), which would have ultimately led to expansionof the rainforest as we see today. Under such climatic conditions,and disregarding all other factors, variation from narrow intowide rivers would be expected, contrary to what has beenrecorded for the study area.

Linking the low relative sea level to a low eustatic episode inthis instance would be inconsistent with the overall trend for a risein sea level during the Holocene worldwide (Mörner, 1996). Thishypothesis is also inconsistent with the above-cited reconstruc-tions of an overall Holocene transgression for northern Brazilianareas, again all other factors remaining constant.

Considering the improbability of all the above-mentionedfactors to explain the evolution of the drainage system recon-structed in northeastern Marajó Island, a tectonic influenceremains as the most likely. Numerous publications have high-lighted the importance of neotectonics related to fault reactiva-tions in the Quaternary evolution of the north equatorialBrazilian margin and related areas of Amazonia (Costa et al.,1993, 1996, 1997, 2001; Souza Filho, 2000; Souza Filho et al.,2000[AQ]; Bemerguy et al., 2002; Souza Filho and Paradella,2003; Rossetti and Valeriano, 2006; Rossetti et al., 2007a, b).Even a small offset along fault planes has the potential to



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imprint a significant rearrangement of drainage patterns in thislowland area. Palaeochannels that are either laterally displacedor sharply interrupted by modern straight rivers constitute solidevidence for the influence of recent fault displacements in thewestern sector of the study area. Additionally, the numeroussegments of palaeochannels with sharp edges in this sector andtheir association with naturally depressed areas are highly con-sistent with this interpretation, pointing to locally subsidingareas. The presence of modern channels, anomalously widerthan average, coinciding with these depressions conforms tothis proposition.

Although a detailed tectonic study is beyond the scope of thiswork, a preliminary model can be hypothesized as the most likelyto explain the recorded changes in drainage patterns throughHolocene in Marajó Island. As highlighted in a separate publica-tion (Rossetti et al., 2007b), and mentioned above, the establish-ment of a palaeoestuary in the Lake Arari area and itsabandonment is related to the late-Quaternary tectonic history ofthe island, which became detached from continental areas asMarajó Bay, formed in the lowest Tocantins River, opened alonga NE–SW oriented strike-slip fault zone (see also Costa andHasui, 1997). After a relative sea-level rise that resulted in theestuary infill, the network of mostly southeastward-flowing widechannels was developed over the study area. However, as thecontinental inflow was cut off and the estuary became aban-doned, wide channels could no longer persist, becoming also pro-gressively abandoned in the landscape. This process of channelabandonment might have coexisted with establishment of LakeArari. In the late Holocene, relatively higher lands adjacent tosubsiding areas of the eastern sector were prone to develop a net-work of narrower channels. The continuity of some of thesepalaeochannels over areas located to the north of Lake Ararishows that this area was probably already emerged since thisdrainage system developed.

Final remarks

Detailed mapping and sedimentary characterization ofpalimpsest drainage systems based on integration of remotesensing and core data information indicate a dynamic evolu-tion of physical environments in northeastern Marajó Islandduring the Holocene. As opposed to an overall rise in relativesea level, as recorded in several localities along the northernBrazilian coast during this period, the study area seems tohave been under the effect of an overall lowering in relativesea level since the late Holocene. This is suggested by the pro-gressive abandonment of an estuarine system that gave rise toa lake surrounded by a drainage network of wide channels,which became progressively narrower through time. Consi-dering the very low-lying nature of the study area, where themean relief is around 4 to 6 m above modern sea level, itwould be expected that even a slight rise in sea level of a fewmetres would result in significant shoreline retreat and flood-ing of land areas. As this seems not to have happened in thestudy area, it can be concluded that either the relative rise insea level recorded along the northern Brazilian coast was notsignificant enough to leave imprints in inland areas of north-eastern Marajó Island, or the rise was locally compensated byanother influencing factor.

The data presented here is in agreement with previous studiesthat propose tectonics as an important mechanism to have deter-mined the distribution of Holocene deposits along the northernBrazilian coast. Despite the overall rise in sea level since the earlyHolocene, the relative sea level varied from place to place, beingcontrolled mostly by local fault reactivations.

Acknowledgements

This work was funded by FAPESP (Project#004/15518-6). Thethree first authors are scholarship holders of CNPq. The GoeldiMuseum and the City Hall of Santa Cruz do Arari are acknowl-edged for helping with logistic support during fieldwork.

References

Azevedo, A.T. 1991: Tectonic evolution of Brazilian EquatorialContinental Margin Basins. Ph.D. Thesis, University of London.Baker, P.A., Seltzer, G.O., Fritz, S.C., Dunbar, R.B., Grove, M.J.,

Tapia, P.M., Cross, S.L., Rowe, H.D. and Broda, J.P. 2001: Thehistory of South American tropical precipitation for the past 25,000years. Science 291, 640–43.Behling, H. 2001: Late Quaternary environmental changes in theLagoa da Curuça region (eastern Amazonia, Brazil) and evidence ofPodocarpus in the Amazon lowland. Vegetation History andArchaeobotany 10, 175–83.Behling, H. and Costa, M.L. 1997: Studies on Holocene tropical veg-etation, mangrove and coast environments in the State of Maranhão,NE Brazil. Quaternary of South America and Antarctic Peninsula 10,93–118.


TBelém

Belém

TBelém

TBelém

Figure 8


PRO

OF

ON

LY

––— 2000: Holocene environmental changes from the Rio Curuárecord in the Caxiuanã region, eastern Amazon Basin. QuaternaryResearch 53, 369–77.Behling, H., Cohen, M.C.L. and Lara, R.J. 2001a: Studies onHolocne mangrove ecosystem dynamics of the Bragança pensinsula innortheastern Pará, Brazil. Palaeogeography, Palaeoclimatoogy,Palaeoecology 167, 87–101.Behling, H., Keim, G., Irion, G., Junk, W. and Nunes de Mello, J.

2001b: Holocene environmental changes in the Central Amazon Basininferred from Lago Calado (Brazil). Palaeogeography, Palaeoclimatoogy,Palaeoecology 173, 87–101.Bemerguy, R.L. 1981: Estudo sedimentológico dos paleocanais daregião do Rio Paracauari, Soure, Ilha do Marajó, Estado do Pará.M.Sc. Thesis, Universidade Federal do Pará.Bemerguy, R.L., Costa, J.B.S., Hasui, Y., Borges, M.S. and Soares,

J.R.A.V. 2002: Structural geomorphology of the Brazilian Amazonregion. In Klein, E.L., Vaseques, M.L. and Rosa Costa, L.T., editors,Contribuições à Geologia da Amazônia. Sociedade Brasileira deGeologia-Núcleo Norte, 245–58.Boersma, J.R. and Terwindt, J.H.J. 1981: Neap-spring tidesequences of internal shoal deposits in a mesotidal estuary.Sedimentology 28, 151–70.Cohen, M.C.L., Lara, R.J., Szlafsztein, C.F. and Dittmar, T. 2004:Mangrove inundation and nutrient dynamics under a GIS perspective.Wetlands Ecology And Management 12, 81–86.Cohen, M.C.L., Behling, H. and Lara, R.J. 2005a: Amazonian man-grove dynamics during the last millennium: the relative sea-level and theLittle Ice Age. Review of Palaeobotany and Palynology 136, 93–108.Cohen, M.C.L., Souza Filho, P.W.M., Lara, R.J., Behling, H. andAngulo, R.J. 2005b: A model of Holocene mangrove developmentand relative sea-level changes on the Bragança Peninsula (NorthernBrazil). Wetlands Ecology and Management 13, 433–43.Costa, J.B.S. and Hasui, Y. 1997: Evolução geológica da Amazônia.In Costa, M.L. and Angélica, R.S., editors, Contribuições à geologiada Amazônia. Sociedade Brasileira de Geologia-Núcleo Norte, 15–19.Costa, J.B.S., Borges. M.S., Bemerguy, R.L., Fernandes, J.M.G.,

Costa, J.R. and Costa, M.L. 1993: A evolução cenozóica da regiãode Salinópolis, nordeste do Estado do Pará. Geociências 12, 373–96.Costa, J.B.S., Bemerguy, R.L., Hasui, Y., Borges, M.S., Ferreira,

C.R.P., Jr, Bezerra, P.E.L., Costa, M.L. and Fernandes, J.M.G.

1996: Neotectônica da região amazônica-aspectos tectônicos, geo-morfológicos e deposicionais. Geonomos 4, 23–44.Costa, J.B.S.C., Bemerguy, R.L., Hasui, Y. and Borges, M.S. 2001:Tectonics and paleogeography along the Amazon River. Journal ofSouth American Earth Sciences 14, 335–47.Costa, M.L., Moraes, E.L., Behling, H., Melo, J.C.V., Siqueira,

N.V.M. and Kern, D.C. 1997: Os sedimentos de fundo da Baía deCaxiuanã. In Lisboa, P.L.B., editor, Caxiuanã. Museu Paraense EmílioGoeldi, 121–37.Galvão, M.V.G. 1991: Evolução Termodinâmica da Bacia do Marajó,Estado do Pará, Brasil. M.Sc. Thesis, University Ouro Preto.Hori, K., Saito, Y., Zhao, Q., Cheng, X., Wang, P., Sato, Y. and Li,

C. 2001: Sedimentary facies of the tide-dominated paleo-Changjiang(Yangtze) estuary during the last transgression. Marine Geology 177,331–51.Leckie, D.A. and Singh, C. 1991: Estuarine deposits of the Albian PaddyMember (Peace River Formation), and lowermost Shaftesbury Formation,Alberta, Canada. Journal of Sedimentary Petrology 61, 825–49.Miall, A.D. 1985: Architectural-element analysis: a new method offacies analysis applied to fluvial deposits. Earth Science Review 22,261–308.Mörner, N.A. 1996: Sea level variability. Zeitschrift fuerGeomorphologie Neue Folge 102, 223–32.Mowbray, T. and Visser, M.J. 1984: Reactivation surfaces in subti-dal channel deposits, Oosterschelde, southeast Netherlands. Journal ofSedimentary Petrology 54, 811–24.Plink-Bjorklund, P. 2005: Stacked fluvial and tide-dominated estu-arine deposits in high-frequency (fourth-order) sequences of theEocene central Basin, Spitsbergen. Sedimentology 52, 391–428.

Porsani, M.J. 1981: Paleocanais, uma opção para prospecção de águasubterrânea na Ilha de Marajó. M.Sc. Thesis, Universidade Federal doPará.Rossetti, D.F. 2000: Influence of low amplitude/high frequency rela-tive sea-level changes in a wave-dominated estuary (Miocene), SãoLuís Basin, northern Brazil. Sedimentary Geology 133, 295–324.––— 2001: Late Cenozoic sedimentary evolution in northeastern Pará,Brazil, within the context of sea level changes. Journal of SouthAmerican Earth Sciences 14, 77–89.Rossetti, D.F. and Valeriano, M.M. 2006: Evolution of the lowestAmazon basin modeled from the integration of geological and SRTMtopographic data. Catena 70, 253–65.Rossetti, D.F., Truckenbrodt, W. and Góes, A.M. 1989: Estudopaleoambiental e estratigráfico dos Sedimentos Barreiras e Pós-Barreiras na região Bragantina, nordeste do Pará. Boletim do MuseuParaense Emílio Goeldi Série Ciências da Terra 1, 25–74.Rossetti, D.F., Góes, A.M. and Truckenbrodt, W. 1990: A influên-cia marinha nos Sedimentos Barreiras. Boletim do Museu ParaenseEmílio Goeldi Série Ciências da Terra 2, 17–29.Rossetti, D.F., Toledo, P.M., Moraes-Santos, H.M. and Santos,

A.E.A., Jr 2004: Reconstructing habitats in Central Amazonia usingmegafauna, sedimentology, radiocarbon and isotope analysis.Quaternary Research 61, 289–300.Rossetti, D.F., Toledo, P.M. and Góes, A.M. 2005: New geologicalframework for Western Amazonia (Brazil) and implications for bio-geography and evolution. Quaternary Research 63, 78–89.Rossetti, D.F., Góes, A.M., Valeriano, M.M. and Miranda,

A.C.C. 2007a: Quaternary tectonics in a passive margin: MarajóIsland, northern Brazil. Journal of Quaternary Science 22 inpress.[AQ]Rossetti, D.F., Valeriano, M.M., Góes, A.M. and Thales, M. 2007b:An Abandoned estuary within Marajó Island: implications for LateQuaternary paleogeography of northern Brazil. Estuaries and Coasts30 in press.[AQ]Shanley, K.W., McCabe, P.J. and Hettinger, R.D. 1992: Tidal influ-ence in Cretaceous fluvial strata from Utah: a key to sequence strati-graphic interpretation. Sedimentology 39, 905–30.Sifeddine, A., Marint, L., Turcq, B., Volkmer-Ribeiro, C., Soubiès,

F., Cordeiro, R.C. and Suguio, K. 2001: Variations of the Amazonianrainforest environment: a sedimentological record covering 30,000years. Palaeogeography, Palaeoclimatology, Palaeoecology 168,221–35.Souza Filho, P.W.M. 2000: Tectonic control on the coastal zone geo-morphology of the northeastern Pará State. Revista Brasileira deGeociências 30, 523–26.Souza Filho, P.W.M. and El Robrini, M. 2000: Coastal zone geo-morphology of the Bragança Area, Northeast of Amazon Region,Brazil. Revista Brasileira de Geociências 30, 518–22.Souza-Filho, P.W.M. and Paradella, W.R. 2003: Use of syntheticaperture radar for recognition of coastal geomorphological features,land-use assessment and shoreline changes in Bragança coast, Pará,northern Brazil. Anais da Academia Brasileira de Ciências 75,341–56.Talma, A.S. and Vogel, J.C. 1993. A simplified approach to calibrat-ing C14 dates. Radiocarbon 35, 317–22.Szatmari, P., Françolin, J.B.L., Zanotto, O. and Wolff, S. 1987:Evolução tectônica da margem equatorial brasileira. Revista Brasileirade Geociências 17, 180–88.Vedel, V., Behling, H., Cohen, M.C.L. and Lara, R.J. 2006:Holocene mangrove dynsamics and sea-level changes in northernBrazil, inferences from the Taperebal core in northeastern Pará State.Vegetation History And Archaeobotany 15, 115–23.Villegas, J.M.C. 1994: Geologia Estrutural da Bacia do Marajó.M.Sc. Thesis, Univ. Fed. Pará, Belém.Vital, H. 1988: Estudo do geossistema do Lago Arari, Ilha do Marajó,Pará. M.Sc. Thesis, Universidade Federal do Pará.Yang, C.S. and Nio, S.D. 1985: The estimation of paleohydrody-namic processes from subtidal deposits using time series analysismethods. Sedimentology 32, 41–57.



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Palaeodrainage on Marajó Island, northern Brazil, in ... · Dilce F. Rossetti, 1* Márcio M. Valeriano,Ana M. Góes2 and Marcelo Thales3 (1Instituto Nacional de Pesquisas Espaciais-INPE,