Pewjunon

1040--6182(93)E0012--F

Quaternary International, Vol. 21, pp. 143-161, 1994. Copyright © 1994 INQUA/Elsevier Science Ltd.

Printed in Great Britain. All rights reserved. 1040-6182/94 $26,00

THE UPPER PARAN/~, RIVER (BRAZIL): GEOMORPHOLOGY, SEDIMENTOLOGY AND PALEOCLIMATOLOGY

Jos6 C. S tevaux Universidade Estadual de Maringd, Department of Geography, N~cleo de Pesquisa era Limnoiogia lctiologia e

Aqiiicultura (NUPELIA ), Grupo de Estudos Multidisciplinares do Ambiente ( GEMA ), 87020-900 Maringd, PR, Brazil

This study involves the geomorphological, sedimentological and paleoclimatologicai aspects of the Upper Paran~ River at Porto Rico (State of Paran(t, Brazil). The alluvial plain is composed of a braided system (main channel) with island and sandy bars, and an anastomosing system (involving secondary channels, tributaries and a complex of swamps, pools and natural levees). River discharge in its upper course varies from 8400 to 13,000 m3/s (minimum of 2550 m3/s and maximum of 33,740 m3/s). Solid discharge reaches 27 x 106 tons/year for suspended sediments and 3 x 106 tons/year for load sediments. Through eehobathymetric survey, bed forms were grouped in ripples, megaripples, dunes and sand waves.

A detailed study of the sedimentology, heavy minerals and facies architecture was applied to the two major geomorphic provinces and their subenvironments: channel province (with sand bar and bed form deposits) and overbank province (with natural levee, flood basin, crevasse and island deposits).

Palynological preliminary studies show that during the Late Pleistocene the area was dominated by grassland and savannas under drier climatic conditions. Since the beginning of the Holocene there has been a generalized transition to a humid phase and the present Broadleaf Forest occupies the area.

Some hypotheses can be formulated for the evolution of the area. (1) The first order architectural element channel (CH) was generated during the Pleistocene associated with climatic changes and tectonism. The alluvial valley was filled up by alluvial colluvial deposits at the end of the Pleistocene (channel deposits present > 40 ka BP). (2) Tectonism and climatic changes (Atlantic Climatic Optimum) generated a new valley bottom (5-8 m below the former level) and a wide meandering plain was built up (4000-4500 BP). (3) A recent fluvial system created a new terrace 3 m above the normal water level.

I N T R O D U C T I O N

The ParaWi River is the tenth largest river in the world as measured by discharge; the second largest catchment in South America and the principal river of the Rio de La Plata Basin. From its source, at the confluence of the Paranalba and Grande Rivers, Brazil (lat. 20°S), to its mouth in the Plata Estuary near Buenos Aires, Argentina Oat. 34°S), the Paran~i River is about 3780 km long. The Paran~i River Basin has an area of 2,800,000 krn 2 and drains all south-central South America, from the borders of the Andes to the Serra do Mar just along the Atlantic Coast (Fig. 1).

The Paran~ River 's hydrological basin consists chiefly of sedimentary and volcanic rocks of the Paran~i and Chaco Sedimentary Basins, whose borders are constituted by highlands of the eastern flank of the Andes and Precambrian rocks of the Brazilian Shield on the north and east (Petri and Fulfaro, 1983).

The Paran~i River alluvial trench is divided into three major parts: an upper course, from its source to the Itaipu Dam near Foz do Iguaqu; a middle course along the Paraguay-Argentina Border; and a lower course from the Paraguay River confluence near Corrientes (Argentina) to the Rio de La Plata Estuary.

The Upper Parantt River, with an extension of 809 km and a basin of 820,000 km 2, has only 500 km not impounded, and half of that will be modif ied by the Porto Primavera Reservoir, to be finished in 1995 (Agostinho et al., 1991). The Ilha Grande Hydroelectric Project, whose construction was suspended, would eliminate the last lotic reach of the

upper course of the river. From 1972 to 1978, the Upper Paran~i River presented, just upstream of Sete Quedas Falls, a total solid discharge between 9.89 x 106 and 30 x 106 tons/year, 9.59 x 106-27 × 106 tons/year for suspended sediments and 0.3 x 10-6-3 x 10 -6 tons/year for bed load sediments (Itaipu Binacional, 1990).

The Brazilian part of the Paran~i River Basin has had its hydrological and limnological regime considerably altered in the last decades. At the beginning of the sixties the total dammed area was approximately 1000 km 2, whereas at present this area is close to 20,000 km 2 (Fig. 2).

Porto Rico Area The studied area is situated near the town of Porto Rico

(lat. 22°43'S, long. 53°10 'W) between the mouths of the Paranapanema River and Ivai River (Figs 1 and 3). At this point the hydrological basin area is about 670,000 km 2. Here, the Paran~i River has a large, braided channel, 3.4 ~.0 km in width, with an extensive alluvial plain in its right margin. This plain is drained by a complex involving the Paran~i secondary channels, Ivinheima and Baia Rivers.

There are many lakes, back swamps and secondary streams, forming a typical meander ing-anas tomosing alluvial plain. The wide area may present fairly recent subsidence m possibly some type of small neocratonic basin

where the Ivinheima River, which comes from the State of Mato Grosso do Sul, is situated.

The annual range of temperature varies from 10.3 (winter) to 33.6°C (summer), with an average of 22°C, and an annual rainfall of 1200 mm (University of Maringa Meteorological

143

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~ - IttZILIAN SlilS*LD

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ITAIPU RESERVOIR

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FIG. 1. Studied area in the geological and hydrological

Station), so that the region has a tropical-subtropical climate. In the Fluvial Station of Port S. Jose (Fig. 4), in the Paranapanema River mouth, the Paranfi River has a discharge that varies from 8400 m3/s in the dry season of June, July and August to 13,000 m3/s in the wet season from November to March, with the highest discharge registered as 33,740 m3/s (in 1983, with a recurrence of 27 years) and the lowest 2550 m~/s (in 1969). In the study area the gradient of the Paran~ River is about 0.096 m/kin.

The area belongs to the Highland of Alto Paranfi Geomorphological Region (Justus, 1985), which is dominated by very smooth hills gently tilting to the Paran~i River. Four major geomorphological units can be found along the alluvial trench (Fig. 5).

Unit Porto Rico This unit consists of the Mesozoic eolic sandstone of the

Caiua Formation covered by a 1-8 m autochthonous sandy soil layer associated with colluvial deposits named the Paranavai Formation (Popp and Bigarella, 1975), and forms almost all the high and steep eastern bank of the river. The landscape is constituted of low hills ranging between 250 and 320 m in altitude, with a hydrographical net of rivers not longer than 20 km (except the Paranapanema River), and

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STATE OF

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STATE OF s~o ~ o (IRAZIL)

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J contexts (after Iriondo, 1988 and Agostinho et al., 1991 ).

high gradient (4.2 m/km). They develop rapids in relatively deep and narrow canyons eroded on the Caiua Formation.

Unit Taquarugu This occurs in the NW and Western portions of the area

~ o !

1910-19 i 1~0-25 1930-39

1950-59

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amularJ.m arm (h tx 100o)

4 8 12 16 20

I = - - - L 18.

20 /~ 60 18 108 118 of m

FIG. 2. Upper Paran~ River hydrological basin. Impounded area evolution (after Agostinho etal., 1991, Fig 2).

The Upper Paran~ River (Brazil) 145

FIG. 3. The Porto Rico area. MS, State of Mato Grosso do Sul; PR, State of Paran~i; SP, State of SAo Paulo, Brazil. Landsat image (black bar on the top is 10 km).

and 15--45 m above the Paran~i normal water level. It consists of a high colluvium terrace where hundreds of small lakes can be found. These lakes probably originated by pseudo- karstic processes during ancient dry periods very similar to the forms described by Popolizio (1975, 1992) in the Paran~--Corrientes River area in Argentina.

Unit Fazenda Boa Vista This unit is a typical alluvial-colluvial terrace rising 8-10

m above the Parami River water level. It is formed exclusively by sand and irregular lenses of gravel with many levels bearing limonite cement. A great number of paleo channels and levees suggests that this unit was strongly reworked by the ancient Ivinheima River meandering system.

Unit Rio Parand This unit is the proper Paranh River alluvial plain and

consists of high and low flood plains, island, bars and a secondary anastomosing system. Almost all lakes and back swamps in this unit are flooded every year during the wet season.

Two levels of limonite-cement gravel, identified by Fulfaro (1974) and Boggiani et al. (1985) as 'Quartzite and Agate Generations', are possibly the oldest deposits in area related with the geomorphological and sedimentologieal history of the Upper Paranfi River. They occur in the highest altitude of the northwestern portion of the study area (Fig. 5) and paleocurrent analysis show that these deposits have come from the north and northwest. Fulfaro and Suguio (1974) attributed a Neogenic age to these deposits.

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FIG. 4. BoUom: discharge of the Paran~ River at Port $6o Josu Fluvial Station from 1960 to 1990. The catastrophic flood of 1983 reached 33,740 mVs. Top: Variation in areal extent of a group of islands from 1953 to 1990.

146 J.C. Stevaux

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FIG. 5. Geomorphological units of the Porto Rico area.

+

The Upper Parar~ River (Brazil) 147

POIl'fO Ille~

.a,

FIG. 6. Block diagram showing the Parar~ River channel asymmetry (after Femadez, 1990, Fig. 22).

Fluvial Geomorphology The channel pattern in the Parana River from the

Paranapanema mouth to the Sere Quedas Falls canyon (covered by the Itaipu Hydroelectric Dam) is typically braided, with a large number of islands and sandy bars (Fig. 3). However, an accurate analysis shows that this segment has a mixed pattern. The main channel is braided but the secondary channels, in the flood plain on the fight margin, are anastomosed according to the concept of Smith (1976).

The strong asymmetry of the alluvial trench geometry (See Fig. 19B, C) shows a possible tectonic control on the

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3O

IC 5

FIG. 7. Upper Para~ at Port Sic) Jo~. Relationship between concentration of suspended material (mg/l) and liquid discharge (QI). Note the anti-

clockwise cycle for the 1988-1989 flood.

fluvial dynamic. There is almost no flood plain along the left margin, so that the fiver continuously erodes the Mesozoic sandstone of the Caiua Formation. However, in its right margin the Paran~ River built up a large flood plain. The multichannel morphology occurring in the main channel can be divided according to its fluvial characteristics (Fig. 6). Along its south side, erosional-depositional dynamics have been intense such that the talweg has totally shifted to the left

t . ~ r t ~ . k ~ ( m h po~t)

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• s A I

1 ~ 0 1970 1 ~ 0 . 1990

FIG. 8. Talweg migration in three cross-sections in a braiding oftbe Upper Q1 (m s . 8 - ] - ) Parm~ S~-tion port Sgo Jos~ is a node point where the talweg presents high

stability (migration velocity 2.7 m/year); section University of Maringa Lab. is in the upslremn part of a braid (migration velocity 13.4 m/year) and section Porto Rico is in the middle of a braid (migration velocity 56.6

m/year). Localization on Fig. 9.

148 J.C. Stevaux

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HG. 9. Eehosnun of longitudinal sections (localization at the top). A-A' : main channel (in a braid); the first order bed forms are dunes, the second order are r ~ g m i l ~ s and the third order are ripples. B-B ' : secondary channel (in a braid); the first order bed forms are mes,luipplcs and the second

order are ripples. C--C': unichm~nel (in a node point), the first order bed form is large and flat with isol~ed megmpples and tipples.

margin. Here the channel is about 13 m deep with a flow velocity of 1.4 m/s. On the opposite side, the fluvial dynamics are reduced, the depth does not exceed 5 m and the flow velocity is less than 0.9 m/s. Thus, the asymetry of the alluvial deposits suggests tilting of the right block towazds the high left margin. Here the channel depth is about 13 rn with a flow velocity of 1.4 m/s. On the opposite side the fluvial dynamic is reduced, the depth does not exceed 5 m

and the flow velocity is less than 0.9 m/s. Thus, the channel and alluvial deposits' asymmetry suggests fairly tilted subsidence of the right block against the high one of the left margin.

The anastomosed channels of the external border of the flood plain comprise a complex with the Baia, Curu;aba and Ivineima Rivers and secondary channels of the Paran~i River. These channels present low to high simuosity (1.2 to 2.1).

The Upper Parar~ River (Brazil) 149

LEFT I N ISLAND

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-4 PEMLE

-2 COARSE SAND

O IIEDiUM SAND

+2 FINE SAND

+4 V. FINE SANO

3 - 4 POOIqL¥

FIG. 10. Comparation of grain size and sorting distribution in a main channel of the Upper Paran~ River. Grain size average (-) varies from +1.0 to +1.5 phy; standard deviation (+) varies from 0 to 1.

Actually, since 1953, studies from aerial photographs confirm the low activity of these channels, restricted to which is lateral accretion, natural levee build up and mainly avulsion processes that may separate channels many kilometers long. As this complex is controlled by the Parana and Ivinheima regimes, the water in the secondary channels may flow downstream or 'upstream' according to the relative discharge of each.

There are many lakes and swamps associated to the anastomosed branch of the Parana River, and they are very important environment for local ecosystems (Agostinho et al., 1991).

Water Regime and Suspended Sediments In spite of two great dams just upstream of the area

(Rosana in the Paranapanema and Porto Primavera in the Paran,t), the Paran~i River section at Port S. Jos6 is very important to the local hydrology, because it constitutes a node point controlling the braided reach downstream. The main influence of the dam on the river system dynamic is probably the great decrease of load sediment, especially of coarse material. Suspended solid concentration in the Paran~ River at this section varies from 30 to 6 mg/l. Suspended sediment concentration and water discharges during 1988--1989 (Fig. 7). From April to November (dry season) there was an increase in solid concentration, and a decrease from December to January, during the flood period.

During the normal floods the channel water invades the plain by overflowing the natural levee and abandoned channels. The flood is gradual and calm, with no effective unidirectional flow, except locally where levee crevasses may occur. At these points the flow is more intensive, and

ephemerous channels with associated splay may occur, or abandoned channels may even become reactivated.

The anastomosed secondary channels are influenced not only by the water of the Paran,~i River but by the Ivinbeima- Baia floods as well. The interrelation between the floods of the Paran~f and Ivinheima-Baia systems controls the magnitude of 'catastrophic floods'. In this case, the water totally invades the alluvial plain, forming a large channel 8 km wide.

Bed Form Bed forms and bars morphology change drastically and

talweg tends to drift continuously in the Paran~i braided channel. Drago (1990) characterized these movements in two distinctive types: (1) gradual and continuous transverse movements and (2) sudden shifts from one position to another. The magnitude of the movement of the talweg from a stable marker is studied in three different cross-sections (Fig. 8). Cross-section Port S. Jos~ shows a talweg shifting about 2.7 m/year. This section is a node point that operates as a zone of bypass of energy in the system. On the other hand, section Porto Rico shows a significant displacement of the talweg, reaching 56.6 m/year. The intermediate section University of Maringa Lab. shows an average shift of 13.4 m/year.

Using the same terminology proposed by Drago (1990), four bed forms can be found in this reach of the Paran6 River:

(1) Ripples: are forms with wave height from few to 30 cm. Generally, the ripples are superimposed on the upstream face of large bed forms.

(2) Megaripples: range from 30 cm to 1.5 m and are

150 J.C. Stevaux

(A)

I I )

TYP( - A -) BANK BANK

TYIq[ - II TYPE - C

[ I I

BANK NENINT

FLOW VILOCITY

TRANIVIHIIIAL PROIrlLE

l i t O M ~ OF MATEIIIAL

e lU~Ut .MIETRY

A T V ~ • TW'G c

H i l l LOW LOW

NIGH NIOtl LOW

STEEP STEEP IIfJITLE

RAPtO RAPIO SlOW

gOdtRIll F I M

I I

FIG. 11. A, B and C mar~n types of the Upper Paran~ River and their fi~olo~c, topograp~c and erosional characteristics (after Fernandez, 1990).

linguoid and lunete in shape. Megaripples are forms with high mobility, like ripples.

(3) Dunes: have wave heights ranging from 1.5 to 7.5 m and lengths from 50 to 500 m. They are perhaps the most common forms in the upper course of the Paranfi River.

(4) Sand waves: are the largest forms with heights reaching 13 m and lengths of 1000 m. Sand waves are

probably related to the catastrophic floods and responsible for the bar construction.

An echogram survey was made in three different longitudinal profiles in Paran~ River channels (Fig. 9). In the echogram from the mare channel, with d e ~ above the cfist ran~ng from 5.5 to 7.5 m and flow velocity near the water surface of about 1.3 ntis (Fig. 9A), the fLrst order forms are

A

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i " ] ,

. . d c

J ~ ~ ~ V O ~ I W E m ~ m ~ ~ m J i m

1 ~ 1 ~ 9

FIG. 12. Correlation of hydrological conditions, rainfall and erosion rates for three types of margin from July 1988 to August 1989 (after Fernandez, 1990).

The Upper Paranl River (Brazil) 151

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C

\ I"

i ~ 1 m t l s m ~ m a n t a M I B U

HG. 13. Types of bars in the Upper Paran& (A) central bar and (B) lateral bar (modified from Santos et al., 1989, Hg. 3).

dunes 2 to 3 m in height and 200-400 m long. They are not simple forms but incorporate secondary ones as megaripples and ripples. The second echogram (Fig. 9B) made in a secondary channel of braided system with depth less than 3 m (above the crests) and flow velocity 0.9 m/s. The bed forms are essentially megaripples 0.5-1.9 m in height and length ranging from 30 to 150 m. The third echogram (Fig. 9(=) was profiled in the unichannel reach of the river near Port S. Jos6 (node point). The most spectacular form in this

profile is a planar wave gently dipping upstream (1.3 m/1000 m), where only isolated ripples and megaripples appear.

Grain size of the bed load in a transversal section at Porto Rico ('Fig. 10) is very homogeneous and well sorted, with the mean between 1 and 2 phi (medium to fine sand) and standard deviation lower than 1.0.

Bank Line Alteration

Banks are continuously altered by shifting of erosion and deposition zones. Fernandez (1990) classified the Paranfi River margins in three types:

(1) Stable bank: occurs along almost all of the left margin of the river, constituted by the highly resistant sandstone of the Caiua Formation.

(2) Accretion bank: this margin is a type of 'lateral bar' that normally develops downstream of islands or pre-existant margin. It has high depositional rates and is generally covered by vegetation.

(3) Erosion bank: this is the margin that presents continuous recession. It forms steep faced banks with heights ranging from a few centimeters to 3 m above the water level.

Fernandez (1990) measured the rates and processes of eroding banks between 1988 and 1989 using a pins and pegs method. Thirty active eroding banks were monitored and grouped in three prominent types: A, B and C (Fig. 11). The morphological and sedimentological bank conditions and the flow characteristic were the basic parameters used in this classification. The mean annual erosion rates for A, B and C types were 4.08, 1.40 and 0.51 m/year, respectively. The correlation between data of hydrological conditions, rainfall amounts and erosion rates for three types of bank are shown in Fig. 12. There are two main erosion processes, corrosion and slumping, that increase activity during the flood period. Rotational sliding occurs secondarily in some high, very cohesive clay-rich banks.

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90

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70

6 0

50

40

30

~K: C N8 F vF

20

10

90.

'80,

70

60

50,

40

• C C N F vF

30

FIG. 14. Cumulative frequency curve for samples from lateral bars and central bar.

m k

~1s97

152 J C. Stevau×

TABLE 1. Lithofacies classification, from Miall (1978. rood.

Facies code Lithofacies Sedimentary. structures Interpretation

Gins massive matrix supported gravels grading debris flow deposits Gm massive or crudely bedded gravel horizontal bedding, imbrication longitudinal bars, lag and sieve

deposits Gt gravel trough crossbeds ~rtinor channel fills Br* resedimented blocks massive Sp sand medium to coarse and pebbly planar crossbeds dune and megaripples Sr sand, very fine to medium mud ripple drift and climbing, drape and lenses low velocity flow Sm sand fine to coarse massive fluidization So't sand fine to very fine, organic-rich mud lamination, bioturbation and mottled Sh sand fine to medium planar stratification main channel bed form S1 sand fine to mud planar lamination low velocity flow Fm silt and clay massive, rootlets overbank deposits FI mud and fine to very fine sand planar and rhythmic lamination levee deposit

*Stevaux (1993). tSantos (1991).

The fluvial channel dynamic is controlled by the river regime, so that intensity, duration and recurrence of flood are responsible for the modeling of the erosional or depositional forms. The area variation of a group of islands was monitored for 37 years (Fig. 4). In 1953 the area was about 2.7 km 2 and this value increased until 1966, reaching 3.6 km 2. At this period the increase in area coincided with the increase in the highest and medium annual discharges. Since then, the group of islands has been dominated by the erosional process and presented a reduction of 0.42 km 2 in area in 1970 (corresponding to 11% of the area in 1966). This reduction coincided with a strong decrease on the maximum and mean annual discharges. From 1970 a new cycle was initiated with an increase of 0.2 krn 2 in the area of the group of islnnds (about 15,000 m2tyear). For the same period the discharge also increased, reaching a peak of 34,000 m3/s in the historical flood of 1983.

SEDIMENTOLOGY, F A C I O L O G Y AND MO R P HOGENES IS

Fluvial sediments were described using the lithofacies classification of Miall (1977, 1985), with two additional specific facies observed in these deposits. Lithofacies, with their respective sedimentary structures and interpretation, are shown in Table 1. Six major deposits were identified for the alluvial and associated sediments, and could be grouped into three geomorphic provinces (Table 2).

Channel Province

middle of main channels with a length of 200-1000 m and length/width ratio of 3 : 1. The sand varies from very fine to very coarse (Fig. 14), with prominent granulometric alternation among the sets. Subordinately thin levels of mud may occur without expressive lateral continuity. The deposits are composed essentially of quartz (>95%) and mica (5%); the main heavy minerals are opaque (magnetite), amphibole, pyroxene, staurolite, kyanite and sillimanite (Table 3).

Two faciological associations related to the genetical phase of the central bars are found in a typical vertical profile (Fig. 15A). The initial phase, denominated protobar (Santos, 1991), is constituted essentially of Sp facies at the bottom and St facies at the top. These facies were deposited as dunes and megaripples during the sub-aquatic phase of bar construction. In the second phase, the bar was reworked by shallow water processes relating to flood reflux and by wind action. The faciological association of this phase is composed by facies Sr and So originated by ripple bed forms, facies S1 (eolic) and facies Fm (suspension).

During the floods, small 'natural levees' are deposited at the bar's upstream face (Fig. 13), forming protected shallow pools in the inner part of the bar. In these places, primary herbaceous vegetation may develop, contributing to bar stabilization. These deposits can migrate hundreds of meters or even totally disappear in the intensive floods (Santos, 1991).

Lateral bars develop beside the margins and island due to shadow zones originated by topographical particularities (Fig. 16). In these zones the flow velocity falls below 0.9

Sand bar deposits Paramt River sand bars were characterized by Santos et al.

(1989) and Santos (1991) as central and lateral bars according to faciology and channel position (Fig. 13).

Central bars are elongated sandy bodies deposited in the

TABLE 2. Geomorphic province and major deposits

G-eomorphological provinces Deposits

Channel sand bar, bed form Overharak natural levee, flood basin (swamps and

ox-bow lakes), crevasse and island

TABLE 3. Heavy mineral composition (%)

Lateral bar Central bar

Opaque 60.1 65.1 Kyanite 7.7 6.5 Staurolite 5.4 4.3 Tourmaline 5.2 3.1 Garnet 4.1 3.8 Epidote 3.7 4.6 Amphibole 7.1 7.5 Sillimanite 3.0 2.3 Zircon 0.7 0.7 Andalusite 0,7 0.2 Pyroxene 0.8 O. 2 Ruffle 0.3 ~).5

The Upper Paran6 River (Brazil) 153

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FIG. 15. Faciological vertical profiles in channel bars: (A) central bar and (B) lateral bar in the Porto Rico area, Uper Parana River (after Santos, 1991, Fig. 14).

m/s, creating a location with high depositional rate. These bars are formed by quartzose fine sand with high sorting (Fig. 14), with important layers of mud intercalated. Heavy minerals arc less than 2%, prevalently opaques, amphibole and kyanite (Table 3). The occurrence of unstable minerals (amphibole and pyroxene) associated with metastablc material (kyanitc, sillimanite, staurolite) suggests a source area composed of metamorphic aluminum-rich rocks, probably originated from the Brazilian Shield, with recent deposition in the fluvial system (Santos and Fernandez, 1992).

These deposits present an alternation of muddy facies Fm and F1 with sandy facies Sp, Sr and So (Fig. 15B). Occurrence of drape and flaser structures indicates fall-out and a tractive process. Frequent leaf banks are associated with the shallow pools in the inner portion of the bar.

The evolution of a lateral bar in the Porto Rico area was observed over the last 36 years (Fig. 17). In 1953, the process began with a shadow zone formation created in the right margin of the main channel. By 1970, with the intensive sedimentation, the protobar attached to the margin and the bar surface was covered by herbaceous vegetation. In 1980,

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FIG. 16. Topographic control in the lateral bar formation in the Upper Parana River.

154 J.C. Stevaux

l m j

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FIG. 17. Lateral bar evolution from 1953 to 1989 in the Upper Paran~i River, Porto Rico are,~ 1953, a sandy lateral bar is deposited; 1970, this lateral bar is covered by herbaceous vegetation; 1980, the first lateral bar is covered by arboreal vegetation and a new sandy lateral bar is deposited; 1989, the

second lateral bar is covered by herbaceous vegetation.

as the hydrological and morphological characteristics remained the same, a new protobar began to be deposited and the latter herbaceous vegetation was replaced by arboreous. By 1989, the last protobar became a lateral bar covered by herbaceous vegetation and a new bar began to be deposited ( t989)

When a new lateral bar is formed, a narrow channel ('ressaco') develops between the bar and the a0cient margin. With the continuity of the process, each new channel being formed beside the last one generates a very typical pattern in aerial photography (Fig. 18).

Bed form deposits This reach of the river presents a sandy mobile bottom,

except in some places with limonite cemented gravel, sandstone or basalt. Ripples, megaxipples and dunes are very common in this area; on the other hand, sand waves are restricted to catastrophic floods.

A very significant outcrop could be studied in Porto Primavera Dam, just upstream of Port S. Jos6 where, in a continuous trench of 13 kin, all alluvial deposits are totally exposed. Thus, it is possible to apply the Architectural Elements concepts of Miall (1985). Figure 19 reunites the Architectural Elements identified in that exposition. Figure 19B presents the CH element (channel) in regional scale, where it is about 11 km wide--this is one of the largest expositions of this element in the world. In Fig. 19C it is possible to distinguish the spatial distribution of the present Paran~i River, where the element SG and, secondarily, GB (respectively 'sediment gravity flow' and 'gravelly bars and bedforms') occur in the basal portion of the sequence. Architectural elements FM, LS ('forset macro form' and 'laminated sand') and GB are present in the middle of the sequence and LA ('lateral accretion') in a thin layer on the top.

The three vertical profiles in Fig. 19A present different characteristics of this sedimentary environment. In profile 1,

FIG. 18. Typical active-inactive channel pattern made by lateral bar processes in the Porto Rico area, Upper Paranfi River. Aerial photograph taken in July, 1970 (black bar on the left is 1000 m).

The Upper Par~ River (Brazil) 155

A

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FIG. 19. Architectural elements and faciology of Para~ River channel &-posits at Porto Primavera dam. (A) Faciolosical profiles in the channel deposits; 03) CH element (present and ancient); and (C) spatial distribution of the architectural elements of the channel deposits

(after StevatLx, 1993).

the prevailing Gms facies indicates debris flow as the main sedimentary process. However, the relative sorting and roundness of the clasts suggest that these deposits had various cycles of transport and sedimentation.

Profile 2 presents facies Sp and St with few Gt interbedded. This profile is very similar to the Plate and Donjek Rivers described by Smith (1971, 1972), Williams and Rust (1969) and Rust (1972). The faciology is typical of the FM architectural element, whose generator bed forms are sandwaves, dunes and megaripples (Allen, 1983; Kirk, 1983; Cant and Walker, 1978; Haszeldine, 1983a, b). This profile

is the more representative on Paran~i River deposits, suggesting that the element FM is in adjustment to the present river pattern (Stevaux, 1993).

Gravel facies (Gm, Gms, Gt and Br) interbedded with sandy facies (Sp, St and Sh) are found in profile 3. Br facies shows reactivating phases and instability, with erosion and remobilization of pre-deposited sediments. Blocks of pebbly sand and sandy gravel suggest that sediments suffered some extensive diagenesis. In outcrops it is possible to identify gravity flow; slump and fluidization. However, the intensive actuation of traction flow reorganized the blocks and

156 J.C. Stevaux

GMd FMF corresponds to overbank environments involving a large number of sub-environments that may or may not be m connection with the Paranfi main channel, depending upon flood magnitude. It is interesting to emphasize the importance of overbank deposits, traditionally neglected by fluvial sedimentologists in favor of channel belt studies (Farrel, 1987). The overbank deposits give a more complete sedimentary history than the fragmentary channel records. Information about paleoclimate, paleocology, palinology, macro fossil, paleopedology and absolute dating are preferentially found in these deposits rather than in channel sequences.

FIG. 20. Faciological vertical profile and outcrop of levee deposits in the Upper Paran~i River, Porto Rico area. (G) coarse, (Md) medium, (F) fine and

(MF) very fine sand. Black bar on the left is 1 m.

pebbles, building up gravelly sand facies (Gp and Sp), common in the GB architectural element.

On the top of profile 3 (Fig. 19A) there is a sandy faciological association belonging to the LA element. This element is often referred to point bar deposits (Miall, 1985), where the sigmoidal foresets transversely shift the channel, generating a sequence of 'off lap'. However, this reach of the Paran~i River is straight, suggesting that lateral accretion was induced by talweg migration.

Overbank Province About 70% of the Porto Rico alluvial plain area

Natural levee deposits Natural levees in the Porto Rico area do not exceed 3 m

in height and occur in the main channel as well as in secondary ones. The natural levee faciology can be divided into three major faciological units (Fig. 20): (1) a basal unit, constituted by sandy facies Sp and St from the bar phase; (2) a middle unit, muddy borrowed facies deposited in the flood plain phase and (3) an upper unit, a thickening and coarsening upward sequence corresponding to the levee deposits, ubiquitous in almost all right margins of the Paran~ River. Figure 21 shows the evolution and idealized profile of a typical 'erosive margin levee'. Each growth phase (T~, T2, etc.) advances toward the flood plain, resulting in the characteristic coarsening-thickening upward sequence (Stevaux, 1993).

Flood basin deposits Six major units were identified in these deposits (Fig. 22).

Sandy mud with iron nodules unit. Light olive-gray sandy mud with nodular and root traces with iron oxide coating; SEM and X-ray diffraction analyses show kaolinite and smectite as clay minerals. Fe-oxide precipitant suggests that the environment was well drained, allowing for Fe 2÷ mobilization and subsequent precipitation as Fe 3.. Centimetrical to decimetrical layers of rooted sand can be

4 ' "

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FIG. 21. Diagram showing hypothetical evolution of natural levee along an erosional margin (after Stevaux, 19931

The Upper Paran~ River (Brazil) 157

STRATI¢i l tAPHIC SEQUENCE , FLOOD BASIN

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The environment of this unit is the same as the previous one, but in a more proximal splay position.

Sand grading to clay unit. This is one of the most common facies on the flood basin deposits in the area. Its granulometry varies from medium/fine cross-bedded sand with clay clasts in the base to medium gray borrowed organic-rich mud. This faciology is interpreted as small abandoned channels from Paran~i secondary anastomosing channels or local tributaries.

Clay clasts unit. This unit is constituted of thin levels of clay clasts in a sandy matrix and is interpreted as the product of sub-aerial exposure of the swamp bottom (mud cracks formation) and re-sedimentation in the next flood. This unit is very important in paleoregime studies, because it may identify periods of complete dessication of the flood basin.

Peat and clay unit. A 0.5-2.0 m layer of peat inter- fingered with organic-rich clay, with leaves and logs fragments; lamination is partially obliterated by bioturbation. This unit was deposited in back swamp or shallow pool environments.

Massive sand unit. This facies is derived from colluvial-alluvial processes on the sandy geomorphological units (Porto Rico and Fazenda Boa Vista) and it can be randomly associated with other units. When sand is deposited in thick layers inter-fingered with peat or organic- rich clay in a well drained part of the alluvial plain, the high pH of subsurface water can mobilize the Fe-oxide coatings of the grains, and the sand becomes very clean.

Crevasse deposits The Paran~i River's natural levees are not continuous, so

that water floods often enter the plain before the levee overflows. This diminishes the channel water stress on levee walls, avoiding crevassing. The complex of channels originated by the lateral bar accretion process (Fig. 18) distributes the flood water, diminishing the stress. Thus, when the bankful level is reached, all of the plain is already inundated, and in strong floods, the plain, as a whole, operates as a great channel. In this case the bed load passes over the plain, generating bed forms like those found in the main channel. The predominance of Sp facies indicates that the 'crevasse' deposits in the Paran,'i River display the same faciology as the channel.

FIG. 22. Idealized faeiological profile for flood basin deposits in the Upper Paran~t River.

interpreted as splay lobes (Farrel, 1987). Sand grains dispersed in the mud suggest colic origin, probably under semi-arid conditions with limited plant cover in the area. The environment for this unit is interpreted as shallow back swamps subjected to crevasse activity (small channels and splay).

Silty sand unit. Silty and muddy dark gray fine sand, bioturbed by roots, with incipient planar lamination. Worm and root tubes may be infilled by peUetal clay iUuviation.

Island deposits In spite of the islands' occurrence in the channel, their

sedimentary processes are closely related to overbank environments. These forms are originated from channel bars followed by aggra~tion produced by flood process. Island morphology develops from depositional and erosional processes whose equilibrium defines its permanence or disappearance from the system.

A representative profile obtained from vibro corer and elucidates the island formation (Fig. 23). The fn'st phase bar deposition, and the second involves vertical accretion originated by the flood process. The island sequence is

158

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J.C. Stevaux

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FIG. 23. F a e ~ l vmic~ profile, del~tio~l e n v L , ~ t and ~ ~ ~ ('13' curve) in a c i ~ l i ~ of the U l ~ t ~ River, near PoFto Rico. 'G' curve is the distance between the margin and the profile. ( I ) ~ c l q ~ d t s - 'G' tempe in O;, (2)stable bar ~ - 'G' curve goes far from O; O) aggradation processes - - 'G' curve comimm far from O; (4) ~ i n e m l m l margin condilion-- "G' curve tends to O:. ( 5 ) ~

condition - - 'G' curve stable far from O; and (6) c=osional margin levee (pmaU s#mlion) ~ 'G' cm~e back to O (after Stevaux, 1993).

composed of bar deposits followed by natural levee deposits (depth 2.1-4,0 m.). About 2.5 m of muddy seAimcnts were dvposited in the flood plain environment. F/trolly, a natural levee sequence ends the island depositional history (depth 0.0-2.1 m.).

PAI ,EOCLIMATOLOGY

Pa_lynological studies in the area are very scarce and remitted to only a few samples collected in the main Upper Paramt River hydrographic sub-basins in the State of Parami

The Upper Paran~ River (Brazil) 159

TABLE 4. Correlation among palynological samples from Paran~ River sub-basins and the Porto Rico area (after Jabur, 1993 and Klein, 1975)

Epoch I H HI IV

Holocene Araucaria forest, Araucaria forest, Paran~Umguay Basin Pmmut Uruguay Basin broadleaf and savannah broadleaf and savannah Broad leaf forest Broad leaf forest

Pleistocene Gramineae Gramineae Gramineae Gramineae (Late) Compositae Compositae Compositae Compositae

Umbelliferae Umbelliferae Myrtacea Myrtacea Podocarpus Podocarpus Amaranthacea Mau.ritia sp.

Palmae Typha Palmae Typha Typha

Pleistocene Oenotheraceae Oenotheraeeae - - - - (Early) Urticaceae Urticaceae

Araceae Araceae

I, Tibagi River (S 25°10'50"/W 50°38'00"); If, Piquirivai River (S 24"07'50"/W 52°14'00"); HI, Umuarama (S 23030'00"/W 53°30'00"); IV, Porto Rico (S 22*00' 10"/W 53°06'00").

(Jabur, 1993). Table 4 presents an expeditious correlation between the palinology of these sub-basins and samples from the Parami River alluvial plain in the Porto Rico area. During the late Pleistocene (between 25 and 10 ka BP), the area was dominated by grassland and savannas under drier climatic conditions, as suggested by the low frequency of pollen (Fig. 24). Since the beginning of the Holocene there was a generalized transition to a humid phase, reaching a climatic 'optimum' at about 5 ka BP identified by Jabur (1993) as the 'Optimum Atlantica'. It is very suggestive that this event corresponds to the highest sea level in the SE Coast of Brazil according to the relative sea level variation curve presented by Suguio et al. (1985).

In this last humid phase, the Paran~ Basin was occupied by the present Broadleaf Forest (Klein, 1975). Nevertheless, a significant fall in the relative sea level curve between 3500 and 2000 BP seems to be correlated" with an interval of low frequency of pollen (drier climatic conditions?) in the profile of Fig. 24.

QUATERNARY EVOLUTION

Unfortunately, the greater part of the Upper Parami River and associated deposits are flooded by hydroelectric dams, hence the importance of the Porto Rico area as the last resort for the study of its Quaternary history. Based on analysis of

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FIG. 24. Pollen frequency, climate and vegetation during the Quaternary in the Upper Paran~ River hydrological basin (Source: Klein, 1975 and Jabur, 1993).

160 J.C. Stevaux

geomorphology, sedimentology and lithofacies associations, together with palynology, t4C and TL dating (Stevaux. 1993), several hypothesis can be put forward as to the Quaternary evolution of the Upper Paranfi River: - - Two different levels of conglomerate identified as the

'Quartzite and Agate Generations' (Fulfaro, 1974: Boggiani et al., t985) can be correlated with tectonics events that raised the western watershade between Paranfi and Paraguay hydrologic basins during the Neogene.

- - Many authors attribute to the excavation of the first order architectural element channel (CH) an age about at the limit of the Pliocene/Pleistocene (King, 1959; Bigarella and Ab'Saber, 1964; Braun, 1971; Bertheleness, 1961; Fulfaro and Suguio, 1974; Suguio et al., 1984; Stevaux, 1993). Several recent ~4C age determinations in samples from the channel deposits of the Paranfi River in Porto Rico and Porto Primavera dam and from geomorphologic unit Taquarupu show an age superior to 40 ka BP. This emphasizes the hypothesis that during the Pleistocene, under predominant dry climate, the valley was filled with typical braided system and colluvium.

- - Wet climatic conditions (Atlantic Climatic Optimum) probably associated with tectonic reactivation changed the river channel pattern and a new valley bottom was generated (corresponding to the surface of the high flood plain and major islands). A fluvial meandering system with large flood plain was formed at this time (6(D0--4000 BP). The sandy deposits of the ancient braided system were covered by the muddy meandering deposits.

--- The recent fluvial system was reactivated probably by tectonic movements, creating a new terrace 3 m above the present active flood plain. This terrace is flooded only during major floods that occur cyclically every 7 years. The present flood plain is 1 to 2 m above the normal water level and is flooded every year. This last rectivation exposed part of the ancient braided system and thus liberated a great amount of sand

A C K N O W L E D G E M E N T S

Special thanks are extended to my colleagues from GEMA (Grupo de Estudos do MOo Ambiente of the University of Maringfi, Department of Geography), Dr lssa C. Jabur, Mantel Luiz dos Santos, Oscar V.Q. Fernandez and Edvard E. Souza Filho who worked with me in all phases of this project. To CNPq, FlNEP and CONCITEC funding agencies for this research. I am also grateful to Dr Thomas R. Fairchild (University of S/to Panlo, Brazil) who reviewed the English text. To Professor Shigueo Watanabe (University of S~o Paulo, Brazil) and Professors Mu Zhiguo and Zheng Gonwang (Peking University, China) for the TL analysis.

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Allen, J.R.L. (1983). Studies in fluviatile sedimentation: Bars, bar- complexes and sandstone sheets (low-sinuosity braided streams) in the Brownstone (L. Devonian), Welsh Borders. Sedimentary Geology, 33, 237-293.

Berthelenness, H. (1961). Interfer~ncia de comportamento de uma drenagem, Boletim Paranaense de Geografia, 2-3, 6-13.

Boggiani, P.C., Coimbra, A.M. and Fairchild, T.R. (1985). Seixos silicosos

das cascalheiras dos nos Parami e Araguam: nomenctatura ¢ provenifmcia. In: Simpfsio Regional de Geologia 5. S~lo Paulo. Boletim de Resumos.

Braun, O.P.G. (1971). Contribuiq~lo ~ Geomorfologia do Brasil Central Revista Brasileira de Geografia, 32(32), 1-36.

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Fan-el, K M (1987). Sedimentology and facies architecture of overbanK deposits of Mississippi River, False River region, Louisiana. In: Ethridge, F.G., Flores, R.M. and Harvey, M.D. reds), Recent Developments in Fluvial Sedimentology. Society of Economic Paleontologists and Mineralogists, Special Publication no. 39, pp. 111-120.

Fernandez, O.V.Q. (1990). Mudanqas no canal fluvial do rio Parami e processos de erosio nas margens: regiio de Porto Rico. P.R. Master dissertation, Instituto de Geoci~ncias e Ci~ncias Exatas, Universidade Estadual Paulista (UNESP), Rio Claro, SP, 96 pp.

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Haszendine, R.S. (1983a). Fluvial bars reconstruction from a deep, straight channel, Upper Carboniferous coal field of Northeast England. Journal of Sedimentary Petrology, 53, 1233-1248.

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Justus, J.O. (1985). Subsfdios para interpretaq~to morfogen~tica atrav~s da utilizaqfio de imagens de radar. Masters dissertation, Bahia State University, Brazil, 204 pp.

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Klein, R.M. (1975). Southner Brazilian phytogeographic features and the probable influence of Upper Quaternary climatic changes in floristic distribution. In: Bigarella J.J. and Becker, R.D. (eds), Special Contribution, International Symposium on the Quaternary., pp. 67- 8s

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Miall, A.D. (1985). Architectural-element analysis applied to fluvial deposits. Earth Science Review, 22, 261-308.

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Petn. S. and Fulfaro, V.J. (1983). Geolog da Chapada dos Parecis, Matt Grossg, Brasil. Revista Brasileira de Geociencias, VII, 274-282.

Popolizio, E. (1975). El seudokart y su importancia en los estudios hidrologicos del Nordeste Argentino. Centro de Geoeiencias Aplieadas. Serie C. Investigacion n. 1, Universidad Nacional de Noroeste Argentino. Resistencia, Chaco, Argentina, 14 pp.

Popolizio, E. (1982). Geomorphology of the Argentina Northeast. Water International, 7, 162-177.

Popp, J.H. and Bigarella, J.J. (1975). Fornm~lo de solos cenozficos do Noroeste do Paran~i. Anais da Academia Brasileira de Ci~ncias, Rio de Janeiro, 47, 465--472 (suplerr~nto).

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I

The Upper Parar~ River (Brazil) 161

Geoci~ncias e Ci~ncias Exatas, Universidade Estadual Paulista (UNESP), Rio Clato (SP), Brazil, 100 pp.

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