Climatic Events During the Late Pleistocene and Holocene in the Upper Parana River: Correlation with NE Argentina and South-Central Brazil Joseh C

Quaternary International 72 (2000) 73}85

Climatic events during the Late Pleistocene and Holocene in the Upper Parana River: Correlation with NE Argentina and South-Central Brazil JoseH C. Stevaux* Universidade Federal do Rio Grande do Sul - Instituto de GeocieL ncias - CECO, Universidade Estadual de Maringa& - Geography Department, 87020-900 Maringa& ,PR} Brazil

Abstract

Most Quaternary studies in Brazil are restricted to the Atlantic Coast and are mainly based on coastal morphology and sea level changes, whereas research on inland areas is largely unexplored. The study area lies along the ParanaH River, state of ParanaH , Brazil, at 223 43S latitude and 533 10W longitude, where the river is as yet undammed. Paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes. Sedimentological and pollen analyses plus TL and C dating were used to establish the following evolutionary history of Late Pleistocene and Holocene climates:

First drier episode ?40,000}8000 BP First wetter episode 8000}3500 BP Second drier episode 3500}1500 BP Second (present) wet episode 1500 BP}Present

1. Introduction the excavation of Sete Quedas Falls on the ParanaH River (today the site of the Itaipu dam). Barthelness (1960, Geomorphological and paleoclimatological studies of 1961) de"ned a regional surface in the Guaira area de- the Upper ParanaH River Basin are scarce and regional in veloped at the end of the Pleistocene (Guaira Surface) nature. King (1956, pp. 157}159) de"ned "ve geomor- and correlated it with the Velhas Cycle. In an overview of phological cycles in the Brazilian landscape (Gondwana, Central Brazil geomorphology and paleoclimatology, Post-Gondwana, Sul-Americano, Velhas and Paraguac7 u Bigarella and Ab'Saber (1964) de"ned some important cycles) and correlated them within southern Africa. pediments, pediplanes and terraces. These were linked to Later, Braun (1971), using aerial photography and radar the Velhas and Paraguac7 u cycles. images, updated King's work and provided more details Pioneer work in the Quaternary paleoclimatology in (Table 1). Central Brazil was undertaken by Cailleux and Tricart King's (1956) last two cycles have been correlated with (1957). Bigarella and Ab'Saber (1964) proposed the "rst some morphological features recognized in the Upper tentative correlation of glacial events and semi-arid con- ParanaH River area by other authors. Maack (1968, p. 254) ditions in Brazil. Basing their studies on arkosic sands in compared the beginning of the Velhas Cycle (end of the Brazilian Continental Shelf, Damuth and Fairbridge Pliocene) with the di!erentiation of the ParanaH and (1970) outlined the climatic mechanisms and climatic Uruguay River basins (Stevaux, 1994b, for a resume) and conditions in South America during the last glacial event. However, Milliman et al. (1975) and Irion (1984) are of the opinion that the feldspar of this sand comes from * Corresponding author. Tel.: #55-44-263-2285; fax: #55-44-263- the Andes or has originated from deep erosion of the 5116. Amazon River during periods of lower sea level. Colin- E-mail address: [email protected] (J.C. Stevaux). vaux (1996) pointed out that in this case, the deposits of

Table 1 Brazilian geomorphological cycles (after King, 1956; Braun, 1971)

Epoch Geomorphological cycle Main events

Holocene Paraguac7 u Terrace processes, mainly #uvial systems Pleistocene Plio-Pleistocene Velhas Coastal and #uvial plains construction, shelf sedimentation Pliocene to Eocene Sul-Americano Pediplanization phase (aggradation), laterization, karstic drainage Paleocene to Cenomanian Denudation phase, tectonic activity (graben and horst) Turonian to Aptian Post-Gondwana Pediplanization phase (aggradation), end of basaltic volcanism Barremian to Berriasian Denudation phase Upper Jurassic to Paleozoic Gondwana Basaltic volcanism, desert formation Great sedimentary basins

arkosic sand does not require an arid climate in the di!erent from that proposed by Bonetto et al. (1986, Amazon Basin. Bigarella and Backer (1975) made a syn- 1990) which excludes the Brazilian reach of the river. Out thesis of paleoclimatical changes in Southern Brazil dur- of the 909 km constituing the Upper ParanaH River (fed by ing the Quaternary. Ab'Saber (1977, 1982) published an a basin area of 820,000 km), only a stretch of 250 km is integration of the knowledge on Central Brazilian undammed. paleoclimatology available at the end of the 1970s. The object of this study lies near the village of Porto Paleoclimatological studies in the last two decades con- Rico (Fig. 2), state of ParanaH (223 43S and 533 10W), cerning the Brazilian continental Quaternary involved Brazil. The annual range of temperature of the area is mainly local approaches (Ledru, 1993; van der Hammer, 10.3 to 33.63C, with a mean of 22.43C, and an annual 1991; Servant et al., 1989; Sifeddine et al., 1994). rainfall of 1200 mm. Thus, the region has a tropi- Markgraf (1989) made an extensive climatic review of cal}subtropical climate (Cwa in KoK ppen's classi"cation). Central and South America since 18,000 BP, based on The ParanaH River, a wide (3.4}4.0 km in width) anas- pollen data. Clapperton (1993, pp. 202}205) gave a tomosing-braided system (Stevaux and Santos, 1998), has general review of the environmental changes in South an extensive alluvial plain developed only along its right America during the Last Glacial Maximum based on (northwestern) margin. geomorphological evidence. Thomas and Thorp (1995, The area comprises the geomorphological region 1996) compared the humid and sub-humid tropics in termed the Alto ParanaH highland by Justus (1985), char- South America and Africa during the Late Pleistocene acterized by smooth hills with altitudes ranging from 250 and Early Holocene. to 320 m. Stevaux (1994a) outlined four main geomor- An important contribution for the understanding of phological subdivisions that can be recognized along the the ParanaH River Valley evolution has been made by alluvial valley: Porto Rico, Taquaruc7 u, Fazenda Boa Ruiz (1963) and Fulfaro and Suguio (1974), who studied Vista, and Rio Parana Geomorphological Subdivisions the occurrence of gravel deposits within the eastern part (Fig. 2 and Table 2). of the basin. Basically, they found two generations of Structurally, the study area is situated between the Sa o gravels with di!erent compositions at di!erent altitudes, Jeronimo-Curiuva and Rio Alonso lineaments (Ferreira, and related them to the uplift of the Serra de Maracaju, 1982; Fulfaro et al., 1982). These features correspond to the headwaters of the ParanaH and Paraguay rivers. diabase dikes, fractures and faults oriented in NW}SE direction and delimit a series of tectonic blocks in the northeastern portion of the ParanaH Sedimentary Basin. 2. Study area of the upper ParanaH River Basin Jabur (1992) identi"ed an alternation of high and low blocks along the longitudinal pro"le of the ParanaH River The ParanaH River Basin is divided into four major that are correlated with the former lineaments. Using the parts (Fig. 1): upper course: from its source at the con#u- longitudinal pro"le of Jabur (1992) plus geotechnical well ence of the ParanamH ba and Grande rivers (lat. 203S, long. data from the Primavera Dam and Doutor Camargo 513W) to the Itaipu Dam (site of the Sete Quedas Falls); bridge over the ParanaH , Stevaux (1994a) concluded that middle course: along the Argentine and Paraguayan bor- the tectonic lineaments and blocks control the river pat- ders to the con#uence of the Paraguay River near Cor- tern, particularly the occurrence of node points and rientes (Argentina); lower course: corresponding to a vast braided reaches. alluvial plain as far south as Rosario; and delta course: Maack (1968, p. 252.) thought that the ParanaH River from the con#uence of Carcarana River to the La Plata channel followed a vertical fault (probably Late Me- Estuary (lat. 343S, long. 583W). This division is slightly sozoic) in the area of `ParanaH Canyona. Iriondo and J.C. Stevaux / Quaternary International 72 (2000) 73}85 75

Fig. 1. ParanaH River Hydrographic Basin.

Suguio (1981) and Iriondo (1988) suggested that the 3. Materials and methods Amazonas and ParanaH rivers are in#uenced by neotectonic movements. Iriondo (1988) proposed that the The sediments were studied by using outcrops along ParanaH River in its middle reach (Corrientes-Santa Fe, the ParanaH River. These were supplemented by pits and Argentina) runs for 600 km along a tectonic lineation of trenches, 10 vibro cores (2}4 m deep with 7.5 cm diameter Pleistocene age. This lineation created a complex of tec- aluminium tubes), and 15 motor-auger holes (2}5 m deep tonic blocks di!ering in vertical displacement. On the and 7.5 cm diameter). Vibro core drilling in pans and wet other hand, geotechnical reports prepared for hydroelec- areas was performed from a light barrel raft. The cores tric dam construction excluded any neotectonic activity were split up, described, photographed and sampled for in the area (Washburn, 1930; Ruiz, 1963). textural, composition, palynological and dating analyses. Stevaux (1994a) identi"ed some neotectonic evidence After splitting, the cores were opened in a light-protected in the area, such as small faults in alluvial deposits and room and the halves were immediately covered with an lineaments observed on satellite images (Taquaruc7 u- opaque plastic "lm for later thermoluminescence samp- Anaurila( ndia and Porto Rico-Rosana lineaments). He ling. Textural analysis was undertaken by using conven- thought that the principal evidence of neotectonics is the tional laboratory procedures. Pollen analysis was strong asymmetry of the channel and small faults identi- performed by Jabur (1992) and Stevaux et al. (1997). "ed in geological cross sections in the river channel. Nine C samples were processed at Centro de Energia This study provides insights into climatic evolution Nuclear na Agricultura * CENA, University of Sa o during the Late Pleistocene and Holocene in the Upper Paulo, Brazil; and at laboratories of Beta Analytic INC., ParanaH River basin and its correlation with the north- Florida, USA. Four samples for thermoluminescence eastern plains of Argentina and the Brazilian Highlands. dating were processed at the Department of Geology, 76 J.C. Stevaux / Quaternary International 72 (2000) 73}85

Brazil, and X-ray di!ractometry of clay was made by PETROBRAS, Rio de Janeiro, Brazil (Table 3).

4. Pans of the Taquaruc7 u Geomorphological Subdivision

The unit has hundreds of small pans with diameters varying from 300 to 6000 m (Fig. 3) very similar to those described by Goudie (1991) in South Africa and Austra- lia, and by Klammer (1982) in South America. The origin of these pans is controversial. Popolizio (1975, 1992) suggested that similar water bodies in the Middle ParanaH River plain, near Corrientes, Argentina, were formed by pseudokarst processes during dry periods. Justus (1985) and Pires Neto et al. (1994) thought that the small pans (`lagoasa) were formed by colluviation in"lling of an ancient drainage pattern. Iriondo (1997) suggested that wind de#ation processes formed the pans. Based on core descriptions, four facies associations were recognized in the pan deposits: massive sandy mud, pollen-rich mud, massive sand and organic deposits Fig. 2. Hydrology and geomorphology of the studied area (after (Table 4 and Fig. 4). Stevaux, 1994a). Massive sandy mud: The deepest sediments cored (1.5}2.0 m depth) consist mostly of light grey (5Y5/2) to olive grey (5Y6/2) patchy mud, with 20% consisting University of Peking, China, and at the Institute of of matrix-supported grains of "ne to very "ne, Physics, University of Sa o Paulo, Brazil. SEM photo- well-sorted sand. The largely massive nature of the mud graphs were made in IBLC * UNESP, Ribeira o Preto, isthe result of burrowing organisms, as indicated by

Table 2 Geomorphological subdivisions in the Porto Rico area (modi"ed from Stevaux, 1994a, b)

Geomorphological Subdivision Sedimentary composition Description

Porto Rico Sandstone, sandy soil and colluvium Smooth hills Taquaruc7 u Sandy colluvium Hundreds of pans Fazenda Boa Vista Sand and gravelly sand Alluvial terrace and fan ParanaH River Sand, mud Present alluvial plain

Table 3 Carbon and thermoluminescence data

Lab. code! Material Localization and depth Method Age

Nogueira Jr. (1988) Woods Channel, ca. 10 m Standard-C '40,000 CENAC110 Woods Channel, 11.0 m Standard-C '40,000 CENAC112 Organic clay Flood plain, 4.5 m Standard-C 4870$100 BETAC92912 Leaves Terrace, 11.0 m Standard-C 31,140$1760 BETAC92911 Woods Terrace, 10.0 m AMS-C 42,520$1700 BETAC92010 Woods Flood plain, 1.6 m Standard-C 3160$80 BETAC92909 Leaves Flood plain, 1.5 m Standard-C 3150$90 BETAC92908 Leaves Island, 2.0 m Standard-C 270$60 BETAC92907 Woods Flood plain, 3.5 m AMS-C 1990$80 UPC0107 Fine sand Pan, 0.7 m Additive dose-TL 1540$730 UPC0104 Fine sand Pan, 1.8 m Additive dose-TL 23,540$2240 UPC0105 Fine sand Pan, 0.6 m Additive dose-TL 3230$750 UPC0108 Fine sand Pan, 1.7 m Additive dose-TL 5290$450

!CENA: Centro de Energia Nuclear na Agricultura, Brazil; BETA: BETA Analytic, USA; UP: University of Peking, People's Republic of China. J.C. Stevaux / Quaternary International 72 (2000) 73}85 77

Jabur (1992) and Stevaux et al. (1997) presented a pollen diagram from the cores of Taquaruc7 u Geomor- phological Unit with four pollen zones. Zone I: The TL date at the base of this interval is 23,540$2240 BP (Stevaux, 1994a). The low concentration of pollen with the predominance of Gramineae, Umbelliferae and Palmae suggests savanna vegetation. The presence of mud-supported grains of sand associated with a low content of organic carbon also supports the assumption of semi-arid climate with high wind activity in the area. Zone II:TwoTLagesof5290$450 and 3230$250 BP were obtained at the base and top of this zone. Pollen diagrams show forest elements including Myrtaceae, Moraceae, Araceae and Rapanea with a low concentration of savanna elements such as Gramineae, Compositae, Umbeliferae, Polygonaceae, Acanthaceae and Mal- Fig. 3. Aerial photograph of pans of the Taquaruc7 u Geomorphological Subdivision (Black bar is 1.0 km). vaceae. The increase in pollen abundance associated with low percentage of sand grains is best interpreted as a humid climate with more vegetation and less eolian activity. tubes of 0.5}2.0 mm diameter with olive grey clay coat- Zone III: In spite of the absence of dating within this ings. Smectite and detrital kaolinite form the predomi- interval, the time range of the zone can be estimated nant clay minerals. Sand percentages decrease upward, using the age of underlying and overlying units as about whereas organic, pollen and sponge content, increase ca. 3000 to 1540 yr BP. Sandy facies, decreasing in pollen toward the top. The upper part of this unit consists of abundance, and the predominance of savanna elements medium to dark grey (5Y5/1}4/1) massive sandy mud, associated with low percentage of organic content sug- with high contents of vegetal remains and abundant root gest a short period of semi-aridity. bioturbation. This unit is interpreted as lacustrine sus- Zone IV: This zone corresponds to the present depo- pension deposits with wind-blown sand forming a mud- sitional pan processes. The pollen diagram contains supported sand grain fabric. forest elements (Myrtaceae, Rubiaceae, Moraceae, Pollen-rich mud: This unit is mostly composed of black Bignoniaceae, Leguminosae) and less-abundant savanna to very dark grey (5Y2.5/1}5Y6/1) organic mud, massive, elements. Pollen and facies suggest a climatic change mottled by bioturbation, with a high percentage of towards a more humid condition (present-day climate) vegetal remains and high pollen and sponge content. since 1540$100 BP, as dated at the base of the zone. Sand grains are mostly absent in the pollen-rich mud. Massive sand: This unit consists of white to light grey (5Y7/1}7/2) "ne to very "ne quartzose, well-sorted sand. 5. Terraces of the Fazenda Boa Vista Geomorphological It consists of a single bed 0.3 m thick with an abrupt and Subdivision irregular basal contact. Organic deposit: This unit is mainly composed of The unit was "rst described by Suguio et al. (1984) and vegetal remains (leaves and logs) and peat, with few black Nogueira Jr. (1988). It is about 10 m thick and consists of organic mud layers rich in pollen and sponges. Thin gravelly sand and gravel (Gm, Gt, Sm and Sp facies) with layers of spongolith (5 cm) can also be found. a predominance of muddy sand and sandy mud (Sr and

Table 4 Facies associations and sedimentary processes of pan deposits of Taquaruc7 u Geomorphological Subdivision

Facies association Facies description Processes TL age Pollen zone!

Organic deposit Black organic mud Suspention Present IV Massive sand Light grey "ne to very "ne sand Wind-blown ca. 3000 to 1540$100 BP III Pollen-rich mud Black to very dark grey Suspension 5290$450 to 3230$250 BP II organic mud Massive sandy mud Burrowed, light grey to olive mud, Suspension and 23,540$2240 BP I "ne to very "ne sand wind-blown

!Stevaux et al. (1997). 78 J.C. Stevaux / Quaternary International 72 (2000) 73}85

Fig. 4. Pan deposits of the Taquaruc7 u Geomorphological Subdivision.

Table 5 Facies description and sedimentary processes/environment of Fazenda Boa Vista Geomorphological Unit

Facies unit Age Thickness Description Facies code! Environment

Massive "ne sand 3500 to 1500# '1 m Very "ne to "ne Sm Alluvial fan massive sand Fine sandy to sandy mud ? 1 m Very "ne sand to mud Sr, Fm Flood palin (mixed-braided/ anastomosed Gravelly sand 42,520$1700; 7}8 m Gravel, "ne-medium Sm, Sp (Gms, Gt) Psamitic anastomosed channel 31,140$1760" gravelly sand Polymictic gravel ? 1 m Agates, chalcedony, Gm, Gt Gravel bar in braided channel quartz, quartzite

!Facies code from Miall (1985). "From C dating. #From stratigraphic correlation (Stevaux and Santos, 1998).

Fm at the top). The terraces of the Fazenda Boa Vista a braided sandy river and "nally to an anastomosed Subdivision have four facies associations: polymictic system (gravelly sand, "ne sand to sandy mud, respective- gravel; gravelly sand; "ne sand to sandy mud and massive ly). Dating of the bottom of the gravelly sand unit yielded "ne sand (Table 5 and Fig. 5). ages of 42,580$1700 and 31,140$1760 BP. The facies associations of the Fazenda Boa Vista A thin 0.5}1.0 m layer of "ne massive sand (Sm facies) Geomorphological Subdivision suggest that the basal rests over the alluvial sediments described above. This deposits were generated by a gravel-carrying, high-en- sandy deposit belongs to an inactive alluvial fan system ergy braided river (basal association) that evolved into constructed by Baile and other brooks (Fig. 2). J.C. Stevaux / Quaternary International 72 (2000) 73}85 79

Fig. 5. Pro"le of deposits in the Fazenda Boa Vista Geomorphological Subdivision.

6. Alluvial plain of the ParanaH River Geomorphological The upper interval consists of a strati"ed sand and Unit gravelly sand unit (channel facies Sp, St and Sr facies) overlying a sandy mud unit (#ood plain facies Fm). In general, the alluvial deposits of the ParanaH River This facies association is believed to have been depos- form a wedge whose thickness varies from 6 to 10 m in ited in an anastomosing river environment. Three the #ood plain, and up to 10}15 m in the channel (Fig. 6). C and two thermoluminescence determinations Three main sedimentary units are identi"ed within the gave the following ages: 4870$100, 3150$90 and alluvial deposits of the ParanaH River: sandy gravel; strat- 2050$80 BP for the basal portion of the #ood plain i"ed and gravelly sand; and sandy mud. The "rst and deposits. second units are found in the channel and in the #ood In spite of the islands' occcurrence in the channel, plain; the third one occurs only on the #ood plain the sedimentary processes are closely related to the over- (Table 6). bank environment. These forms originated from channel The transverse section of alluvial deposits of the bars followed by aggradation produced by #ood pro- ParanaH River (Fig. 6) has two intervals with di!erent cesses (Stevaux, 1994a). There are two main groups facies corresponding to changes in hydrologic regime of islands: depositional and erosional islands. The during the Late Quaternary. The lower interval formed latter form the main group and are probably related by the sandy gravel facies association (Gm, Gt and Sp to a vertical channel incision at the beginning of the facies) suggests deposition in a braided river environ- Second (Present) Wet Episode (see below). Island de- ment. Two C dates in the sandy facies (Sp) of this posits are of di!erent ages according to their position deposit indicate ages higher than the method's resolu- related to the water level of the river: 2450$350 tion. No organic material was found in sediments of the and 870$30 BP, respectively, at 4.50 and 1.25 m upper limit of this interval. However, through strati- depth (below the river medium water level), and 270$60 graphic correlation it is possible to assume an age of ca. and 60 BP for minor abandoned channels on the #ood 8000 BP (Stevaux, 1994a; Stevaux and Santos, 1998). plain. 80 J.C. Stevaux / Quaternary International 72 (2000) 73}85

Fig. 6. Alluvial plain deposits (channel and #ood plain) of the Upper ParanaH River at the section of Porto Sa o JoseH . Note the strong channel asymmetry.

Table 6 Facies description, sedimentary processes and environment of the Rio ParanaH Geomorphological Subdivision sediments

Facies association Years BP Thickness Structure Facies! Environment

Sandy mud 4780$100";1}4 m Massive and laminated Fm, Sr Flood plain, crevasse, 3160$80"; natural levee (islands) 3150$90"; 2450$350$ 2050$80" 870$30$ 270$602" Present Strati"ed sand and 8000}present# 10}12 m Lenses and blankets of sand Sp, St, Ss (Sr) Mega ripple and dune in gravelly sand anastomosed sandy channel Sandy gravel '40,000" 0.5}1 m Crudely strati"ed imbricated to Gm, Gms, Gt Flash #ood, grain #ow in massive gravel braided river

!Facies code from Miall (1985). "From C dating. #From stratigraphic correlation (Stevaux and Santos, 1998). $From TL dating.

7. Paleoclimatological interpretation the Upper Parana River Basin. Using the present climate as a reference base, the following four paleoclimate peri- The following paleoclimatological interpretations are ods are inferred: in accordance with the climatic episodes described by First drier episode: End of Pleistocene to Early Holo- Stevaux (1994a) for the Late Pleistocene and Holocene of cene ('40,000-ca. 8000 BP). The lack of absolute dates J.C. Stevaux / Quaternary International 72 (2000) 73}85 81 and the fragmentary sedimentary record do not allow Second drier episode: 3500}1500 BP: This short period a more detailed chronology for this episode. Dating of of more arid climatic conditions (not as severe as in the two logs at the base of the ParanaH River channel deposits "rst dry period) has been deduced from a decrease in produced ages older than the limits of the dating method. organic content and pollen association (pollen zone III) A dry climate may be inferred from these deposits. The in pan cores (Table 4). The alluvial fan, whose deposits sandy gravel facies unit is interpreted as having orig- rest over the Fazenda Boa Vista Geomorphological Unit, inated by #ash #ood and grain #ow processes in a typical was probably active at this period (Stevaux et al., 1995). dry climate braided channel river (Table 6). Drier condi- However, no date for this deposit is available. tions can also be deduced from the low percentage of Second (present) wet episode: 1500 BP to the present. organic and savanna pollen content (pollen zone I) asso- Present-day wet climate. ciated with grains of sand #oating in a muddy matrix in pan deposits. Intensive eolian activity in a forest-free area is thus inferred. Thermoluminescence dating yielded an 8. Regional correlation age determination of 23,540$2240 BP (Table 4). The same climate condition may be also interpreted from the The four climatic episodes presented in this paper are braided system identi"ed in the basal portion of alluvial in reasonable agreement with other areas of southern plain deposits (sandy gravel unit) and for the polymictic Brazil (Fig. 5). A close correlation is also obtained with gravel and gravelly sand from the Terraces of the the Argentine plains for the last 18,000 years in climatic Fazenda Boa Vista Geomorphological Unit. Two events (Table 7) described by Iriondo and Garcia (1993). C determinations at the base of these deposits yielded The First Drier Episode is correlated with the Last dates of 41,580$1700 and 31,140$760 BP (Table 5). Glacial Maximum and can be recognized in the study First wetter episode: ca. 8000}3500 yr BP. The cores of area as occurring in south-central Brazil and north- the lakes displayed an increase in organic material with eastern Argentina. Iriondo and Garcia (1993) de"ned an abundance in forest elements (pollen zone II), and a de- arid and cool period, with aeolian sand and loess depo- crease in #oating sand. These facts have been interpreted sition between 18,000 and 8500 BP in the Chaco-Pam- to indicate lesser eolian activity (more vegetation cover). pean plain, a result of extensive glaciation in the Andes Two thermoluminescence ages in this interval ranged (Clapperton, 1983). In the study area aeolian activity is from 5290$450 BP at the base to 3230$250 BP at the also identi"ed in the massive sandy mud facies unit in the top (Table 4). Alluvial deposits of the ParanaH River also pan deposits of the Taquaruc7 u Geomorphological Unit displayed a change in their sedimentary facies that could (Table 4). Further, the origin of these pans has been be interpreted as paleohydrological and climatic. Sandy interpreted to result from an ancient dune "eld formed gravel facies from the former braided system change to during this episode (Stevaux and Krammer, 1998). strati"ed sand and sandy mud facies, interpreted as being The First Wetter Episode is well characterized all over deposited in an anastomosed river system. A Carbon south-central Brazil and NE Argentina. The upper age date in these deposits yielded 4870$100 BP (Table 6). limit of this period varies from 10,000 to 7300 BP As organic material used in this dating was collected (Iriondo and Garcia, 1993; Iriondo, 1991, 1997; Stevaux, about 1.0 m from the base of deposits, it is possible to 1994a). Thomas and Thorp (1995) identi"ed a short suppose an age older than 4870 BP for the hydrological period of wet climate between 10,200 and 8200 BP, not change. Correlation with other areas in southeastern recognized in other areas. Brazil and northeastern Argentina suggests an age of ca. The beginning of the "rst wet episode varies from 8000 BP for these paleohydrological and climatical chan- 10,200 to 7300 BP, with the episode ending between 2500 ges (Thomas and Thorp, 1995; Barbosa et al., 1990; and 3500 BP. Ledru (1993) and Ledru et al. (1996) identi- Servant et al., 1989; Iriondo and Garcia, 1993; Jabur, "ed a short period of semi-arid conditions from 5200 to 1992; Stevaux et al., 1997). 4300 BP in Central Brazil. There is no general agreement

Table 7 Comparison of climatic events in the upper ParanaH River area and Argentine plains

Upper ParanaH River Argentine plains (Iriondo and Garcia, 1993)

Second (present) wet episode (1.5}Present) (a) Present climate: subtropical, humid (b) Little ice age: arid climate (c) 1.0-Little ice age: similar to the present climate Second drier episode (3.5}1.5 ka) Cordobense stage, dry subtropical climate (3.5}1.0 ka) First wetter episode (8.0}3.5 ka) Platense stage, humid subtropical climate, with Brazilian fauna First drier episode ('40.0}8.0 ka) Arid and cool, with eolian deposits (18}8.5 ka), with Patagonian fauna 82 J.C. Stevaux / Quaternary International 72 (2000) 73}85 about the termination of this period. On the basis of period of aridi"cation during the 18th Century and the pollen analysis in the Mendoza region of Argentina, beginning of the 19th Century in Buenos Aires Province. Markgraf (1989) estimated the end of this humid period Iriondo and KroK hling (1995) ascribed the sand of the SereH at about 3000 BP. D'Antoni (1983) suggested a date of Member of Las Islas Formation (Hurtado et al., 1985) to 3800 and 2300 BP. In this paper an age of 8000}3500 BP aeolian depositional processes related to the aridity of is assigned for the First Wetter Episode. the Little Ice Age. In several places this sand includes The second drier episode varies from 3500 to 1500 BP human (European) and faunal remains (Iriondo and in the Upper ParanaH Basin, and is identi"ed in Central Garcia, 1993). Brazil and NE Argentina. Within Argentina, Iriondo Although located in SE Brazil, the areas of Morro (1997) described a short period during the Late Holo- Itapeva (22347S, 45332W; 2030 m above sea level), Santa cene, from 3500 to 1200 BP, with warm and semiarid Catarina (26}283S, 49}483W; 1160 m asl), Serra Negra climate where dry winds produced wind-blown silt. He (19300S, 46345}46W; 1170 m asl) and Salitre (19300S, ascribed this event to a stationary cyclonic centre in 46346W; 1000 m asl), studied by Behling (1995, 1997), De Argentina and neighbouring regions in Paraguay and Oliveira (1992) and Ledru (1993) do not have a paleocli- Uruguay. Iriondo (1991) also identi"ed this dry period as matic evolution similar to that proposed in this paper. extending from 3500 to 1000 BP in the Argentine Litoral. Probably, the climatic history of these areas is locally In an overview paper discussing the e!ects of global in#uencend by their high altitude. change in South America, Coltrinari (1993) recognized a generalized dry event with concentration of man-in- duced "res and recession of humid Amazonia forest 9. Fluvial responses to climatic changes or neotectonism: ca. 5000 to 4000 BP. an open question The Little Ice Age, identi"ed in NE Argentina (Iriondo and Garcia, 1993), is not recognized in the studied area. The causes of changes in the hydraulic regime and Based on historical data, Politis (1984) recognized a short terrace formation in the Upper ParanaH River during the

Fig. 7. Correlation among climatic events in Southern Brazil, Argentine plains and the Upper ParanaH River area. (1) Thomas and Thorp (1995, 1996); (2) Ledru (1993); (3) Barbosa et al. (1990); (4) Laming-Emperaire (1968); (5) van der Hammer (1991); (6) Bombim and Klat (1974), Bombim (1976); (7) Bigarella and Andrade-Lima (1982); (8) Servant et al. (1989); (9) Iriondo and Garcia (1993) and (10) Jabur (1992), Stevaux (1994a). J.C. Stevaux / Quaternary International 72 (2000) 73}85 83

Holocene are not well understood. Were they caused by Barbosa, A.S., Ribeiro, Schimitz, P.I., 1990. Cultura e ambiente em climatic or tectonic in#uences? In spite of the lack of aH reas de cerrado do Sudoeste de GoiaH s. In: Pinto, M.N. (Ed.), 7 7 structural studies in the area, Iriondo (1988), Souza-Filho Cerrado * Caracterizacao, ocupacao e perspectivas. Universidade de BrasmH lia, pp. 67}100. (1993), and Stevaux (1994a) discussed some evidence of Barthelness, H., 1960. ComentaH rio geomorfoloH gico sobre o vale tectonic activity occurring during the climatic changes in do rio IvamH . Boletim Paranaense de Geogra"a, Curitiba, PR 1 (1), the Late Quaternary. Small faults in ancient alluvial 8}17. gravel deposits, the vertical incision of Fazenda Boa Barthelness, H., 1961. Infere( ncias de comportamento de uma Vista Geomorphological Subdivision, and the strong drenagem. Boletim Paranaense de Geogra"a, Curitiba, PR 1 (2}3), asymmetry of the alluvial sediment wedge (Fig. 7) are the 6}13. Behling, H., 1995. Investigation into the Late Pleistocene and Holocene main evidence for Quaternary tectonism. On the other history of vegetation and climate in Santa Catarina (S. Brazil). hand, the climatic episodes described above were strong Veget. Hist. Archaeobot. 4 (3), 127}152. enough to have caused di!erent paleohydrological re- Behling, H., 1997. Late Quaternary, climate and history from the gimes (braided to anastomosed pattern, Stevaux et al., tropical mountain region of Morro de Itapeva, SE Brazil. 1995, 1997) and to have generated terraces identi"ed in Paleogeography, Paleoclimatology, Paleoecology 129, 407}422. the Upper ParanaH River. Bigarella, J.J., Ab'Saber, A.N., 1964. PaleK ogeographische und paleK o- klimatische Aspekte der KaK enoziokums in SuK dbrasilien. Zeitschrift The paleoclimate studied in this work presented fuK r Geomorphologie 8 (3), 286}312. only qualitative aspects of the paleoenvironmental Bigarella, J.J., Backer, R.D., 1975. International Symposium on the variables. However, the elaboration of deterministic Quaternary. Curitiba, PR. Boletim Paranaense de Geocie( ncias, pp. models for paleoclimatic changes needs a quantitative 33}77. approach for these variables. Analysis of water and air Bigarella, J.J., Andrade-Lima, D., 1982. Paleoenvironmental changes in Brazil. In: Prance, G.T. (Ed.), Biological Diversi"cation in the temperature, rainfall, pH, salinity, sediment load and Tropics. Columbia, New York, pp. 27}39. #ow velocity are indispensable for this purpose. Quanti- Bombim, M., 1976. Modelo paleopedoloH gico evolutivo para tative analyses of variables will be possible according o NeoqaternaH rio da regia o da Campanha Oeste do Rio Grande do to the progress of studies on sponge, algae, benthic or- Sul. A Formac7 a o Touro Passo, seu conteuH do fossilmH fero e ped- 7 ganisms, and phytoliths, together with more accurate oge( nese poH s-deposicional. Vol. 15, Comunicacao do Museu de Cie( ncias da PontifmHcia Universidade CatoH lica do Rio Grande do Sul, surveys on sedimentology and stratigraphy. Moreover, Porto Alegre, pp. 1}90. the research area requires a progressive extension not Bombim, M., Kant, E., 1974. Evide( ncia paleoclimaH tica em solos do Rio only to the tributary valleys, but over the entire drainage Grande do Sul. Anais XXVIII Congresso Brasileiro de Geologia. basin. Porto Alegres 3, 183}194. Bonetto, A.A., Castello, H.P., Wais, I.R., 1986. Comparison between the di!erential impacts of dams on two large river basins in Argentina. Proceedings, International Symposium on the Impact of Large Acknowledgements Water Projects on the Environment, Paris, France, October 27}31, UNESCO Headquarters, 14 pp. ` Bonetto, A.A., Wais, I.R., Castello, H.P., 1990. The increasing damming This research is part of the project titled Upper of the ParanaH Basin and its e!ects on the lower reaches. Regulated Tertiary and Quaternary Paleoclimates in the Upper Rivers: Research and Management 4, 333}346. ParanaH River Basina supported by the Conselho Braun, O.P.G., 1971. Contribuic7 a oa` geomorfologia do Brasil central. Nacionalde Desenvolvimento CientmH"co e TecnoloH gico, Revista de Geocie( ncias XXXIII (32), 1}16. Brazil (CNPq 522456/94 and 520099/96-6). The NuH cleo Cailleux, A., Tricart, J., 1957. Zones phytogeographiques et morpho- cliamtiques du Quaternaire du BreH sil. Vol. 293, Comptes Rendues. de Pesquisas em Limnologia, Ictiologia e Aquicultura de la Societe de Biogeographie, Paris, pp. 7}13. * NUPELIA, University of MaringaH provided accom- Clapperton, C.M., 1983. The glaciation of the Andes. Quaternary modations and equipment for "eld work. The author Science Reviews 2, 83}155. would like to thank Vera Markgraf, MartmH n Iriondo and Clapperton, C.M., 1993. 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