iriondo, 1989. quaternary lakes of argentina

7/22/2019 Iriondo, 1989. Quaternary Lakes of Argentina.

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Palaeogeography, Palaeoclimatology, Palaeoecology, 70 (1989): 81-88 81Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

Q U T E R N R Y L K E S O F R G E N T IN

M I R I O N D OCONICET, Casilla de Correo 487, 3100 Parand Argentina)(Received September 14, 1987; accepted J anu ary 20, 1988)

A b s t r a c tIriondo, M., 1989. Quaternary lakes of Argent ina. Pa laeogeogr., Palaeoc limato l., Palaeoecol., 70:81 88.

The Quaternary lakes of Argentina are grouped into eight main environments: swamps and playas of theHernandaries Formation (Middle Quaternary of northe astern Argentina) Pampean swamps; Chaco swamps; swampsand shallow lakes of the Paran h system; salt lakes of the Puna; northwestern salt lakes and playas; glacial lakes of thesouthern Cordillera; and Patagonian closed depressions.

I n t r o d u c t i o nQuaternary lacustrine sediments are exten-

sive in Argentina, and show considerablediversity. This paper synthesizes the presentknowledge about the main environments fromthe continental regions of the country. TheQuat ernar y lakes of Tierra del Fuego, theMalvinas and other islands are not analyzed.

The continental surface of Argentina is2,759,000 km 2. Its extr eme la ti tu di na l poin tsare locat ed at 21 47'S a nd 52 23'S. The nor th-south length is 3300 km and the maximal widthis 1500 kin. The distr ibut ion of altit udes r angesfrom the 7000 m of the Acon cagua m ount ain inthe Cordillera, to the few meters above the sealevel of the Buen os Aires coastal plain, andeven below sea level in some Patagoniandepressions. The large ext ent and geographicaldiversity of the co untry results in a wide rangeof climates, from humid tropical in the north-east to periglacial in the far south, with largeareas of high mountain climate in the west.Such climatic and geographical diversity isresponsible for a great variety of lacustrineenvironments. The morphology and sediments

of the Quaternary lakes remain basicallyunaltered, and most of them are still notcovered by younger deposits.

The main data source for the present study isthe geomorphological map of the SouthAmeri can plains (still unfinished), a subprojectof IGCP-201. According to the available re-sults, lacust rine envir onments similar to thoseof Argent ina also occur in Chile, Parag uay anda large sector of Bolivia as far north as latitude18S.T h e Q u a t e r n a r y o f A r g e n t i n a

The dominant geomorphological and sedi-mentary processes during Quaternary times inArgentina are strongly correlated with thegeography of the country. In a simplifiedscheme, three first-order geomorphological re-gions can be defined: the Andes Cordill era andassociated mountains, the Great Plains, andPatagonia.

In the Cordillera the principal processes ofsignificance to lacustrine development weretectonics, mass movements and glacial events(see Clapperton, 1983; Mercer, 1984; Lauer and

0031-0182/89/$03.50 1989 Elsevier Science Publishers B.V.


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82F r a n k e n b e r g , 1 9 8 4 ; R a b a s s a e t a l . , 1 9 8 4 ) . V o l -c a n i c a c t i v i t y w a s a l s o s i g n i f i c a n t a t t i m e sd u r i n g t h e P l e i s t o c e n e a n d H o l o c e n e . D e v e l o p -m e n t o f l a c u s t r i n e e n v i r o n m e n t s w a s p o ss i b l ei n t e c t o n i c d e p r e s s i o n s a n d i n g l a c i a l l y e x c a -v a t e d v a l l ey s .

T h e G r e a t P l a i n s , w h i c h c o v e r t h e c e n t r a la n d n o r t h w e s t e r n p r o v i n c e s , a r e t h e s i t e o fe x t e n s i v e c o n t i n e n t a l s e d i m e n t a t i o n o f m a i n l ys a n d a n d p e l it e s. T h e r e g i o n i s c h a r a c t e r i z e db y v e r y l o w s lo p e s a n d s i g n i f i c an t n e o t e c t o n i ca c t i v i t y . A s u c c e s s i o n o f h u m i d a n d d r y c li -m a t e s o c c u r r e d d u r i n g t h e Q u a t e r n a r y ( Ir -i o n d o , 1 9 8 4 ) . T h e g e o m o r p h o l o g i c a l c h a r a c t e r -i s t ic s o f t h e p l a i n s r e s u l t e d i n a n i m p o r t a n td e v e l o p m e n t o f l a c u s t r i n e e n v i r o n m e n t s , e s pe -c i a l l y s w a m p s .

P a t a g o n i a i s a c o m p l e x l a n d s c a p e d o m i n a t e db y m e s e t a s ( G o n z ~ le s D i a z a n d M a l a g n i n o ,1 98 4). T h e m e s e t a s c o n s i s t o f b a s a l t i c p l a t e a u xa n d t e c t o n i c a l l y u p l i f te d , c o a r s e g r a i n e d f a n so r i g i n a t i n g i n t h e C o r d i l l e r a . I n t h e P a t a g o -n i a n l a n d s c a p e n u m e r o u s c l o s e d d e p r e s s i o n sw e r e f o r m e d b y a e o l i a n e r o s i o n i n p e l i te s o fT e r t i a r y a g e ( F e r u g l i o , 1 9 5 0 ; F i d a l g o , 1 9 7 2 ) .T h e i r p a s t a n d p r e s e n t e v o l u t i o n i s d o m i n a t e db y t h e w i n d; p l a y a a n d s a l in e s e d i m e n t s a r e o fs e c o n d - o r d e r i m p o r t a n c e .

h e l a c u s t r i n e e n v i r o n m e n t s

T h e Q u a t e r n a r y l a k e s o f A r g e n t i n a c a n b eg r o u p e d i n t o e i g h t m a j o r g e o g r a p h i c a l e n -v i r o n m e n t s ( F i g. l) : t h e H e r n a n d a r i a s F o r m a -t i o n a n d a s s o c i a t e d d e p o s i t s , P a m p e a ns w a m p s , C h a c o s w a m p s , s w a m p s a n d s h a l l o wl a k e s o f t h e P a r a n ~ s y s te m , s a l t l a k e s o f t h eP u n a , n o r t h w e s t e r n s a l t l a k e s a n d p l a y a s ,g l a c i a l l a k e s o f t h e s o u t h e r n C o r d i ll e r a, a n dP a t a g o n i a n c l o s e d d e p r e s s io n s .Hernandarias Formation and associateddeposits

L a r g e s w a m p s a n d p l a y a s d e v e l o p e d du r i n gt h e M i d d le Q u a t e r n a r y i n n o r t h e a s t e r n A r g e mt i na . T h e s e c o v e r T e r t i a r y a n d l o w e r Q u a t e r -n a r y c o n t i n e n t a l f o r m a t i o n s , a n d a r e c o m p o s e d

Fig.1. Quaternary lacustrine regions of Argentina. a = Her-nandarias Fm. and associated dep osits, b=Pam peanswamps, c=C haco swamps, d=Pa ranfi system, e=S altlakes of the Puna. f Northwestern salt lakes and p layas.g Glacial lakes of the southern Cordillera. h = Patago-nian closed depressions.

o f s i l ty c l a y a n d c l a y e y s i l t 1 0 - 2 0 m t h i c k ,c o v e r i n g a t o t a l a r e a o f 6 1 , 0 0 0 k m 2. T h em o n t m o r i l l o n i t e g r o u p d o m i n a t e s t h e c l a yf r a c t i o n . T h e s c a r c e s a n d i s c o m p o s e d o f f i n ea n d v e r y f i n e g r a i n s o f q u a r t z ; z i r c o n , s i l l i m a n -i t e a n d s t a u r o l i t e a r e t h e m o s t i m p o r t a n t h e a v ym i n e r a l s .

T h e m o s t s i g n i f i c a n t g e o l o g i c a l u n i t i n t h i se n v i r o n m e n t i s t h e H e r n a n d a r i a s F o r m a t i o n ,w h i c h c o v e r s a s u r f a c e a r e a o f 2 5, 00 0 k m 2 i nE n t r e R i o s ( I r io n d o , 1 98 0). T h e l o w e r b e d s a r ec o m p o s e d o f 2 - 4 m o f g r a y i sh g r e e n s i l ty c l a y ,


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83massive and highly plastic, with numerousirregular desiccation cracks and slickensides.Concret ions of CaCO 3 and black patches ofmanganese minerals are common. Irregulargypsum ellipsoids composed of large crystals,with a max imum diam eter of 25 cm can befound in the vicinity of Hernandarias andsurrou nding areas. More th an 90% of the clayminerals are montmorillonite, beidellite andnon tro nit e (Romero, 1985). Paleochan nels , up to100m wide and 3m deep within the clays,contain medium to t hin beds of very fine quartzsand. The source of the sediments were thebasalts and sandstones of the CretaceousParangL basin.

The upper section is formed of a 6-8 m thickplastic clayey silt, reddish brown with greenand grey zones. Abundant patches of Mnminerals, CaCO 3 concre tion s and gypsum crys-tals less than 5mm long are typical. Theessential component of the sediment is anaeolian silt derived from the southwesternPampas and mixed with the clay and sand ofthe Paranfi basin (Rubinstein, 1983). A layer ofloess up to 1 m thick can be fou nd in severallocalities.

The environment of sedimentation of theHernandarias Formation was predominantlypaludal. The colours of the lower sectionindicate anoxic conditions in permanent ornearly permanent water bodies. In the uppersection oxidation predominated, with intervalsof complete dryness. Gypsum ellipsoids andisolated crystals are widespread throughoutthe formation, with larger concentrations atthe bottom. Their origin has been related toplaya processes (Bowler and Teller, in Torger-sen et al., 1986). Hence, periods of dryness canbe postulated for the Hernandarias swampsthroug hout the time of sedimentation.

CaCO3 concretions. The mineralogy of theclastic fraction is a mixture of plagioclase andlithic fragments (approximately 30% each)with lower percentages of quartz and potassicfeldspar (INTA, 1984). Volc anic glass is pres entin variable quantities, shifting randomly inSante Fe from 4 to 30%. The clay fraction ispredominant ly illite.Althou gh tradit ionall y considered as lo-ess , recent studies show that a significantproportion of the pampean sediments accumu-lated in swamps (Iriondo, 1980; Manev ella andIriondo, unpublished). The main paludal areas,cove ring a t ota l surf ace o f almost 39,000 km z inthe provinces of Buenos Aires, Sante Fe andC6rdoba, occur in the Late Pleistocene Pam-pean Formation. The granulometry and struc-tures of the sediment are similar to those in thepresent swamps of the Pampa, showing abreccia-like structure produced by the growthof the abundant roots of ortaderia and otherswamp grasses.

Two paludal facies can be identified, differ-ing principally in colour: one is brown, theothe r green. Both are composed of silt andclayey silt, forming lenses and tabular bodies.The facies are characterized by a structureformed of two components, one pale and soft,the other darker and compact. Both arecomposed of irre gula r f ragmen ts 5-30 mm indiameter which interpenetrate in a chaoticmanner. Compact mangan ese nodules to 2 cmin diameter, and irregular concretions ofCaCO 3 are very frequent. Int ern al stratifica-tion is absent or weak; the contact withadjacent facies is in most cases sharp andirregular. The brown facies represent deposi-tion in seasonally desiccated swamps; thegreen facies were formed in permanentswamps.

Pampean swamps haco swampsIn Argent ina the word pamp ean defines asystem of Quaternary geological units, which

occur in the plains lying between latitudes30S and 38S. They are composed basically ofbrown silt with variable concentrations of

The Chaco is a tropical plain occupying840,000 km 2 in Arg ent ina , Bolivia and Para-guay. It has been formed from the largealluv ial fans of four rivers whi ch flow east fromthe western mountains. The uppermost sedi-


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84ments of the fans are of Late Quaternary age.Swamps are extensively developed in the distalareas of the fans.

The Argentinian sector of the Chaco com-prises the alluvial fans of the Bermejo andSalado rivers and a sector of the Pil comayofan. The swamps fill old fluvial belts, developedby the rivers during humid periods of theUpper Pleistocene and Holocene. Importantfactors for the development of swamps aretectonic sinking and a humid local climate;both are typical of the E astern Chaco. Themajor swamps, 100-200 km long and 3-10 kmwide, are typi call y less t ha n 1 m deep. Thewater s urface is covered by paludal vege tationGramineae and Cyperaceae) and floatingplants Eichornia and Pistia). The central areaof the swamp is often free of vegetati on in anirregula r belt of slowly flowing water. Bottomconditions are anoxic, with accumulation ofdead vegetation.

In the Bermejo and Salado fans the swampsare the headwat ers of local hydrograph ic nets,discharging dissolved organic matter and col-loids to the lower channels (Iriondo, 1986).Local rains provide most of the wa ter to th eswamps. Minor contributions produced by theoverflow of the large rivers can be impressive:in 1980 a spill out of the Pilc omayo river formeda swamp 250km long and 7 to 12 km wide,which has been supplied with large volumes ofwater by every flood since th at time.

At present, the Chaco rivers transport anddeposit silt, very fine sand and illitic clay.Pleistocene sediments pertaining to the sameriver fans, on the other hand, are composed ofsilt with montmorillonite (Morris et al., 1980).The Quaternary paludal deposits and presentswamps cover an are a of 65,000 km 2 in theArgentinian Chaco.Swamps and shallow lakes of the Parandsystem

The Paran~ h ydrogra phic basin is the secondlargest fluvial system in South America, withan area of 2,310,000 km z and a m ean an nu alprecipitation of 1300 mm. The lower section of

the river crosses the Argentinian plains. Pre-sent and past fluvial processes have producedseveral types of swamps and shallow lakeswhich cover more th an 32,000 km 2 in Argen-tina. Three genetically different areas can berecognized: the Iber~ swamps, the pres ent floodplain, and the Paranfi delta.

The Iberfi swamps, in the province of Corri-entes, parti ally cover an old alluvial fan of theParanfi. The swamps occupy an area 450 kmlong and u p to 75 km wide, but th e free watersurface comprises less tha n 10% of the t otalarea. The most significant product of thisenvironment is tropical peat, whose evolutionbegins with the growing of a carpet of floatingvegetation. The dead plants do not sink, butremain afloat, partially decomposed, and act assupport for the living vegetation. A slowgrowth in thickness results, forming embalsa-dos (rafts) 1-2 m thick, composed of a satu-rated sponge-like mass of part iall y decomposedvegetal tissues. During exceptionally dry yearsthe water level sinks and the rafts can reachthe bottom. Their own weight then causescompaction and adhesion to the bottom. In thefollowing humid season the water regains itsnormal level, leaving the rafts at the bottom.The process of raft grow th th en begins anew.Several geomorphological units character-ized by swamps, ponds and sh allow lakes, hav edeveloped in the 600 km long Para n~ floodplain (Iriondo, 1987). The forma tion of an a readominated by standing water begins when themain channel is diverted. The subsequentstages of the evolution are determined by theneotectoni c setting of the areas. On upliftedblocks the channels gradually disappear,changes occurring in the following sequence:first the channels become widened, then theygradually evolve into ponds and lakes, andfinally become raised areas with scatteredlakes.On gradually subsiding blocks, the areacovered by ponds and swamps increases. Themorphological sequence here is as follows:areas with widened channels, areas wit h lakesand associated channels, permanently sub-merged areas.


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T h r e e g e o m o r p h o l o g i c a l u n i t s o f t h e P a r a n ~d e l t a c o v e r i n g a p p r o x . 5 0 00 k m 2 h a v e s ig n if i-c a n t l a c u s t r i n e d e v e l o p m e n t s ( I r i o n d o a n dS c o t t a , 1 9 7 9 ) : ( a ) T h e p o o r l y - d r a i n e d d e l t ap l a in , c h a r a c t e r i z e d b y n u m e r o u s s h a l l o wl a k e s , p o n d s a n d s w a m p s , c r o s s e d b y s m a l la d v e n t i t i o u s c h a n n e ls . ( b ) T h e l a g o o n fo r m e db y t h e H o l o c e n e t r a n s g r e s s i o n , w h i c h i s i n u n-d a t e d f o r s e v e r a l m o n t h s o f t h e y e a r b y f l oo d sf r o m a m a j o r t r i b u t a r y , t h e G u a l e g u a y R i v e r .( c ) T h e l o w e r d e l ta , s u b j e c t t o t id a l a c t i o nw h i c h i s c h a r a c t e r i z e d b y s o u p p l a te - l ik ei s la n d s , f o r m e d b y a p e r i p h e r a l l e v e e a n d w i t ha c e n t r a l p o n d c o v e r i n g m o s t o f t h e t o t a ls u r f a c e .

T h e s e d i m e n t s c a r r i e d b y t h e P a r a n ~ a r e a tp r e s e n t p r e d o m i n a n t l y f in e q u a r t z s a n d a n di l l i t i c c l a y s .Salt lakes of the Puna

T h e P u n a d e A t a c a m a i s l o c a t e d a t h ig ha l t i t u d e ( 3 0 0 0 - 4 0 0 0 m a .s .1 .) i n t h e N W c o r n e ro f A r g e n t i n a . I t c o n s t i t u t e s t h e s o u t h e r n p a r to f t h e A l t ip l a n o , b u t i n s t e a d o f a m e s e t am o r p h o l o g y a s i n P e r u a n d B o l i v i a , i t i s h e r ec h a r a c t e r i z e d b y a s e r ie s o f f a u l t e d b l o c k s w i t hN - S s t r i k e . T h i s s t r u c t u r a l p a t t e r n c r e a t e s ab a s i n a n d r a n g e l a n d s c a p e w i t h l o c a l r e li e f o f8 0 0 - 1 0 00 m . T h e c l i m a t e i s a r i d , w i t h a n a n n u a lp r e c i p i t a t i o n o f t h e o r d e r o f 2 0 0 m m . T h eh y d r o g r a p h y i s c o m p o s e d o f s e v e r a l e n d o r h e i ca r r o y o n e t s f l o w i n g i n t o l a r g e d r y s a l t l a k e s ;s e v e n s u c h l a k e s e x c e e d 1 00 0 k m 2 i n a r e a .

T h e s a l t l a k e s , w h i c h c o n s t i t u t e t h e p r e s e n tl a c u s t r i n e b o d i e s, a r e H o l o c e n e i n a g e. T h e yd e v e l o p e d u p o n P l e i s t o c e n e l a c u s t r i n e s ed i-m e n t s , w h i c h n o w a p p e a r a s t e rr a c e s , w i t h am a x i m a l h e i g h t o f 2 0 m o v e r th e s a l t l a k el e ve l. M o s t o f th e s a l t c o m e s f r o m T e r t i a r ye v a p o r i t e s . H y d r o t h e r m a l p r o c e s s e s a r e i m -p o r t a n t i n s e v e r a l a r e a s ( A l o n s o a n d G u t i ~ r re z ,1984).Northwestern salt lakes and playas

I n t h e s e m i a r i d v a l l e y s o f t h e n o r t h w e s t e r np r o v i n c e s p l a y a s a n d s a l t l a k e s a r e w i d e s p r e a d .

85T h e l a r g e s t s a l t l a k e i s t h e S a l i n a s G r a n d e s ,w i t h a n a r e a o f 5 00 0 k m 2.Glacial lakes of the southern ordillera

A l a r g e r s e r i e s o f d e e p l a k e s o f g l a c i a l o r i g i ni s l o c a t e d b e t w e e n 4 0 S a n d 5 4 S i n t h e v a l l e y so f t h e P a t a g o n i a n C o r d i ll e r a. T h e m e a n a r e a o ft h e l a k e s i s 77 k m 2 ; t h e d e p t h i s f r e q u e n t l yg r e a t e r t h a n 1 0 0 m , w i t h t h e th e r m o c l i n e a t3 0 - 4 0 m i n s u m m e r ( Q u i r b s a n d D r a g o , 1 98 5).T h e m i n e r a l o g y o f t h e s e d i m e n t s i s d o m i n a t e db y v o l c a n i c m a t e r i a l s ( M a z z o n i , 1 9 83 ).

A n e s t i m a t i o n o f t h e p r e s e n t e v o l u t i o n o fL a k e M a s c a r d i w a s m a d e b y t h e a u t h o r o f t h i sp a p e r ( I r i o n d o , 1 9 7 4 ) . L a k e M a s c a r d i i s at y p i c a l C o r d i l l e r a n l a k e , 3 8 k m 2 i n e x t e n t a n dw i t h a m a x i m u m d e p t h o f 21 8 m . T h e e v o l u t i o nw a s m o d e l e d b y c a l c u l a t i o n o f s u s p e n d e d a n db e d l o a d d i s c h a r g e , d i s t r i b u t i o n o f s e d i m e n t s i nt h e l a k e a n d c o m p a c t i o n o f p e l i t e s. T h e f o l lo w -i n g v a l u e s r e s u l t e d : T h e l a k e r e c e i v e s 2 5 , 3 0 0t o n / y r o f s u s p e n d e d l o a d a n d 2 50 0 t o n / y r o f b e dl o a d (1 7, 00 0 t o n / y r o f d i s s o l v e d s o l i d s c r o s s t h el a k e t o t h e o c e a n ) . T h e b a s i n i s b e i n g e r o d e d a ta m e a n r a t e o f 22 m m / 1 0 0 0 y r ; 8 m m o f w h i c hi s d u e t o c h e m i c a l e r o s i o n . B y i n t e g r a t i n g t h es e d i m e n t i n p u t a n d t h e c o m p a c t i o n e x p e c t e do v e r l o n g p e r i od s , t h e a r e a a n d v o l u m e o f t h el a k e 3 0 ,0 0 0 y e a r s a f t e r t h e p r e s e n t w a sp r e d i c t e d . A c c o r d i n g t o t h e m o d e l , a n d p r o v i d -i n g t h a t n e i t h e r c l i m a t i c c h a n g e s n o r c a t a -s t r o p h i c e v e n t s w i l l o c c u r , t h e l a k e w i l l b ec o m p l e t e l y f i l l e d u p i n 2 2 8 , 0 0 0 y e a r s .Patagonian closed depressions

P a t a g o n i a i s a c o m p l e x l a n d s c a p e , m a i n l yc h a r a c t e r i z e d b y b a s a l t i c p l a t e a u x a n d t e c to n i -c a l l y u p l i f t e d p e b b l e f a n s o r i g i n a t i n g i n th eC o r d i l l e r a . F i n e - g r a in e d , u n c o n s o l i d a t e d s e d i-m e n t s o f T e r t i a r y a g e u n d e r l i e t h e Q u a t e r n a r yf o r m a t i o n s . T h e c l i m a t e , w h i c h i s d r y a n d c o l d ,i s d o m i n a t e d b y s t r o n g w e s t e r l y w i n d s , re s u l t -i n g i n s e v e r e a e o l i a n e r o s i o n . T h e t o t a l s u r f a c ei s a b o u t 5 2 0 , 0 0 0 k m 2. C l o s e d d e p r e s s i o n s o fd i f f e re n t t y p e s a r e c h a r a c t e r i s t i c o f t h e P a t a g o -n i a n l a n d s c a p e . K e i d e l ( 1 9 7 1 ) a n d F r e n g u e l l i


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86(1 95 7) d e f i n e t w o m a i n t y p e s : l a r g e a n d

s m a l l d e p r e s s i o n s .I n m o s t o f P a t a g o n i a , t h e s m a l l d e p r e s s i o n s

a r e s h a l l o w d e f l a t i o n h o l l o w s , e x c a v a t e d i no u t c r o p s o f s o f t T e r t i a r y s e d i m e n t s. L u n e t t e sa r e o f t e n d e v e l o p e d a l o n g t h e e a s t e r n( l e a w a r d ) s i d e o f t h e s e d e p r e s s i o n s . F i d a l g o(1 97 2), s t u d y i n g a l a r g e a r e a o f c e n t r a l P a t a g o -n i a , o b t a i n e d t h e f o l l o w i n g s i g n i f i c a n t f i g u r e sf o r 1 00 h o l l o w s : e l l i p t i c - t o - c i r c l e f o r m s 5 0 -5 0 00 m i n d i a m e t e r ; 1 - 3 m d e e p ; f r e q u e n c y o fs l o p e g r e a t e r t h a n 2 : 1 h o l l o w i n 1 40 k m 2. T h eh o l l o w s a r e f l o o d e d a f e w d a y s i n t h e y e a r ,w h e n t h i n d e p o s i t s o f c l a y a n d s i l t a c c u m u l a t e .

L e s s f re q u e n t s u b t y p e s o f h o l l o w s c a n b ef o u n d o n b a s a l t ic p l a t e a u x a n d g r a n i t i c t e r -r a i n s . M e t h o l ( 1 96 7) s t u d i e d t h e i r o r i g i n i nn o r t h e r n P a t a g o n i a , c o n c l u d i n g t h a t t h e f i rs to n e i s p r o d u c e d b y t h e s i n k i n g o f t h e m a n t l eo f b a s a l t a s a r e s u l t o f a s u f f u s i o n p r o c e s s i nt h e u n d e r l y i n g s e d i m e n t s , i n so m e p l a c e s o ft h e p r e b a s a l t i c d r a i n a g e n e t . O n g r a n it e s ,t h e d e v e l o p m e n t o f h o l l o w s r e s u l t s f r o m t h ew e a t h e r i n g o f f r a c t u r e s , p l u s s t r o n g a e o l i a ne r o s io n . A s s u m i n g f o r e n t i r e P a t a g o n i a t h ed a t a f r o m F i d a lg o , a n d e s t i m a t i n g a m e a n a r e ao f 1 k m 2 fo r e a c h h o l l o w , t h e t o t a l a r e a i sa p p r o x i m a t e l y 3 7 00 k m 2.

T h e l a r g e d e p r e s s i o n s a r e l o c a t e d i n t e c to n i -c a l l y s u n k e n b l o c k s. T h e i r a r e a s a r e i n t h eo r d e r o f a h u n d r e d t o a f e w t h o u s a n d s q u a r ek i l o m e t e r s . T h e m a i n m o r p h o g e n i c a g e n t s i nt h e d e v e l o p m e n t o f l a r g e c l o s e d d e p r e s s io n sa r e t e c t o n i c s u b s i d e n c e a n d d e f l a t i o n , w h i c he r o d e s e d i m e n t s a n d s o f t r o c k s t o t h e l e v e l o ft h e w a t e r t a b l e , o r t o h a r d r o c k . A l l u v ia l ,c o l l u v i a l a n d o t h e r p r o c e s s e s a r e o f se c o n d -o r d e r i m p o r t a n c e . T h e s e d e p r e s s i o n s b e g a n t of o r m p r o b a b l y d u r i n g t h e M i d d l e P l e i s t o c e n e ;t h e y a r e f l o o d e d s e v e r a l w e e k s i n t h e y e a r .

T h e G r a n B a j o d e l G u a l i c h o ( 65 - 40 0 1 5 S ) i so n e o f t h e l a r g e s t d e p r e s s io n s , w i t h a n a r e a o f3 0 00 k m 2 a n d a d e p t h o f 25 0 m . I t s l o w e s t p o i n ti s 6 0 m b e l o w s e a l e v e l ( L i z u a i n a n d S e p f d v e d a ,1 97 8). C o a l e s c e n t a r r o y o s e d i m e n t s c o v e r m o s to f t h e s u r f a c e , a n d s u r r o u n d a 2 00 k m 2 s a l tb o d y . T h e B a j o d e l a T i e r r a C o l o r a d a( 6 7 W - 4 3 S ) i s a n o t h e r i m p o r t a n t d e p r e s s i o n .

W i t h a n a r e a o f 8 5 0 k m 2, i t i s c o v e r e d b ys i l t a n d f i n e s a n d p i n k t o g r e y i n c o l o u r ,w i t h t h i n e v a p o r i t e d e p o s i t s i n t h e c e n t r a la r e a ( L a p i d o a n d P a g e , 1 9 7 8 ; L a p i d o , 1 9 8 1 ) .A r r o y o s e d i m e n t s i n t h e N W s e c t o r a n d as e q u e n c e o f b e a c h e s i n t h e N E f r in g e c a n b en o t e d .

A f ew l a r g e d e p r e s s i o n s a t p r e s e n t c o n t a i np e r m a n e n t , b u t p o o r l y k n o w n l a k e s . T h e m o s ti m p o r t a n t a m o n g t h e m a r e C o l h u 6 H u a p i( 6 0 0 k m 2 ) , M u s t e r s ( 4 0 0 k m 2) a n d C a r d i e l( 30 0 k in 2 ). A l l o f t h e m a r e f e d b y C o r d i l l e r a nw a t e r s .

A c a r t o g r a p h i c s u r v e y m a d e o n m a p s o f t h eA t l a s F i s i c o d e l a R e p ~ b l i c a A r g e n t i n a( C h i o z z a a n d F i g u e i r a , 1 9 8 1 ) i n d i c a t e s a t o t a la r e a o f 1 0, 70 0 k m 2 f o r t h e l a r g e c l o s e d d e p r e s -s i o n s o f P a t a g o n i a .C o n c l u s i o n s

T h e e x t e n t o f d i f fe r e n t Q u a t e r n a r y l a k e s i nt h e v a r i o u s r e g i o n s o f A r g e n t i n a i s s h o w n i nT a b l e I. S e v e r a l c o n c l u s i o n s e m e r g e f ro m t h i st a b l e :

- - T h e Q u a t e r n a r y l a k e s f o rm 9 .5 % o f t h et o t a l c o n t i n e n t a l s u r f a c e o f A r g e n t i n a .

- - S w a m p e n v i r o n m e n t s c o n s t i tu t e 75 .7 % o ft h e l a c u s t r i n e s u r f a c e s ; s a l t l a k e s a n d p l a y a s2 0 .9 % . D e e p l a k e s m a k e u p o n l y 3 . 4 % o f t h et o t a l .

- - O f t h e f i r s t - o r d e r g e o m o r p h o l o g i c a l r e -g i on s , th e p l a i n s w i t h 4 m a j o r e n v i r o n m e n t sa n d 7 5 . 7% o f t h e t o t a l s u r f a c e a r e c l e a r l y t h em o s t f a v o u r a b l e f o r t h e d e v e l o p m e n t o f l a c u -s t r i n e e n v i r o n m e n t s .

- - I n t h e C o r d il l er a a n d o t h e r m o u n t a i n s ,t h r e e l a k e e n v i r o n m e n t s o c c u r , w i t h 1 8 . 8 % o ft h e t o t a l a r e a l e x t e n s i o n .T h e P a t a g o n i a m e s e t a r e g io n i s g e n e r a l l yu n f a v o u r a b l e f o r l a k e d e v e l o p m e n t . T h e c l o s e dd e p r e s s i o n s a r e c o m p a r a t i v e l y m o d e s t i n a r e a le x t e n t ( 5. 5% o f th e t o t a l ) a n d c o n s t i t u t el a c u s t r i n e e n v i r o n m e n t s o n l y a f e w w e e k s int h e y e ar . T h e s e d i m e n t a t i o n b a l a n c e a p p e a r s t ob e n e g a t i v e i n m o s t o f t he m .- - T h e l a c u s t r i n e e n v i r o n m e n t s o f t h e p l a in sa r e c o m p o s e d o f d if f e r e n t t y p e s o f s w a m p s .


7/8

T A B L E IA r e a s o f l a k e s a n d s w a m p s i n m a j o r e n v i r o n m e n t s o f A r g e n t i n aM ~ o r e n v i r o n m e n t L o c a l i t y / g e o l o g i c a l A r e af o r m a t i o n

(km 2 )H e r n a n d a r i a s F m a n d A ss o c H e r n a n d a r i a s F m . 2 5, 00 0Othe r 36 ,000

( )

P a m p e a n s w a m p so t a l 61,000 23.5

B u e n o s A i r e s 2 5, 00 0S a n t a F e 1 1, 00 0C 6 r d o b a 2 5 5 0

C h a c o s w a m p sP a r a n d s y s t e m

o t a l 38,550 14.8o t a l 65,000 25.0

Iber~ 20,000F l o o d p l a i n 5 35 0De l t a 6 8 0 0

32,15014,40027,000

7420

o t a l

S a l t l a k es o f th e P u n a o t a lo t a lo r t h w e s t e r n s a l t l a k e s / p l a y a so t a ll a c i a l la k e s o f s o u t h C o r d i l l e r a

S m a l l h o l l o w sL a r g e d e p r e s s i o n s 370010,700o t a l 14,400

259,920

P a t a g o n i a n c l o s e d d e p r e s s i o n s

S w a m p sS a l t l a k e s / p l a y a sD e e p l a k e s

T o t a l Q u a t e r n a r y l a k e s a n d s w a m p s

12.45.5

10.42.9

5.5100.0

75.720.9

3.4

87

Such swamps developed under a diversity ofclimates, from humid tropical to arid.

The lakes formed in the mountains , on thecontrary, are related to extreme climaticconditions: aridity (salt lakes and playas) orglaciat ion (deep lakes).A c k n o w l e d g e m e n t s

The author thanks M. R. Talbot for helpfulcomments in an earlie r version of this paper.

R e f e r e n c e s

A l o n s o , R . a n d G u t i ~ r r e z , R . , 19 84 . Z o n a c i 6 n d e u l e x i t a e nl o s s a l a r e s d e l a P u n a a r g e n t i n a . R e v . A s o c . G e o l .Ar g e n t . , 3 9 : 5 2 5 7 .

C l a p p e r t o n , C ., 1 98 3. T h e g l a c i a t i o n o f t h e A n d e s . Q u a t y .Sc i . Rev . , 2 :83 155.

C h i o z z a , E . a n d F i g u e i r a , R . , 1 9 8 1 . A t l a s F i s i c o d e l aR e p f i bl i ca A r g e n t i n a . C e n t r o E d i t o r d e A m e r i c a L a t i n a ,B u e n o s A i r e s , 2 v o l s . , 41 7 p p .

F e r u g l i o , E . , 19 50 . D e s c r i p c i 6 n G e o l 6 g i c a d e l a P a t a g o n i a .Y a c i m i e n t o s P e t r o l l f e r o s F i s c a l e s , B u e n o s A i r e s , 3 v o l s. ,670 pp .


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88Fidalgo, F., 1972. Consideraciones sobre los bajos situadosal norte de la provincia de Santa Cruz. In: Actas, VCongr. Geol. Argent., 5: 123-137.Frenguelli, J., 1957. Geografia de la Repfiblica Argentina-- Neozoico. Coni, Buenos Aires, 2, 113 pp.Gonzalez Diaz, E. and Malagnino, E., 1984. Geomorfologia

de la provincia de Rio Negro. Serv. Geol. Nac., BuenosAires, 159 pp.Igarzfibal, A., 1984. Origen y evolu ci6n geomorfol6gica delas cuencas avaporiticas cuartarias de la Puna argen-tina . In: Actas, IX Congr. Geol. Argent. , 3:595 607.INTA, 1984. Carta de suelos de la Repfiblica Argentina,Hoja 3363-30 Berabevfi. INTA, Buenos Aires, 141 pp.Iriondo, M., 1974. Modelo de sedimentaci6n en el lagoMascardi, provincia de Rio Negro. Rev. Asoc. Geol.Argent., 29: 349-358.Iriondo, M., 1980. Estudio geomorfol6gico de la cuenca delrio Salado en Santa Fe. In: Convenio UNL-INCYTH,Santa Fe, 48 pp.Iriondo, M., 1980. E1 Cuat ernario de Entre Rios. Rev. Asoc.Cienc. Nat. Litoral, 11: 125-141.Iriondo, M., 1984. The Quate rnary of northeaste rn Argen-tina. In: The Quaternary of South America and theAntarc tic Peninsula. Balkema, Rotterdam, 2, pp. 51 78.Iriondo, M., 1986. Dinhmica fluvial y transpo rte desedimentos en el arroyo Los Amores (Chaco-Santa Fe).In: Actas, Primera Reuni6n Argent. Sedimentol., LaPlata, pp. 19-21.Iriondo, M., 1988. A comparison between the Amazon andthe Paran~ river basins. Mitt. Geol. Pal~iontol. Inst.Univ. Hamburg, SCOPE-UNEP Sonderband, 66: 77-92.Iriondo, M. and Scotta, E., 1979. The ev olu tion of theParanh river delta. In: K. Sugulo, T. Fairchild, L. Martinand J. Flexor (Editors), Int. Symp. Coastal Ev olution inthe Quaternary, 1978, Inst. Geoci~nc., USP, Sao Paulo,pp. 405-418.Keidel, H., 1971. (~ber das patagonische Tafelland, daspatagonische GerSll und ihre Beziehungen zu denErscheinungen in argentinischen Andesgebiet und Lito-ral. Z. Dtsch. Wiss. Verein, 84: 219-245.Lapido, O., 1981. Descripc i6n geol6 gica de la Hoja44g-Cafiad6n inglesias. Bol. Serv. Geol. Nac., 185,46 pp.Lapido, O. and Page, R., 1978. Relaciones estratigrgtficasy estructura del Bajo de la Tierra Colorada (provincia

del Chubut). In: Actas, VII Congr. Geol. Argent. ,1: 299-314.Lauer, W. and Frankenberg , P., 1984. Late g lacia l glacia-tion and the development of climate in southern SouthAmerica. In: J. Vogel (Editor), Late Cainozoic Paleocli-mates of the Southern Hemisphere. Balkema, Rotter-dam, pp. 103-114.Lizuain, A. and Sepfilveda, E., 1978. Geologla del GranBajo del Gualicho (provincia de Rio Negro). In: Actas,VII Congr. Geol. Argent., 1: 407-422.Mazzoni, M., 1983. Dep6sitos volc anicl hsticos holocenos defondos lacustres. Rev. Asoc. Geol. Argent., 38: 84-100.Mercer, J., 1984. Late Cainozoic glacial variations inSouth America south of the Equator. In: J. Vogel(Editor), Late Cainozoic Paleoclimates of the SouthernHemisphere. Balkema, Rotterdam, pp. 45-58.Methol, E., 1967. Rasgos geomorfol6gicos de la meseta deSomuncur~ Rio Negro. Rev. Asoc. Geol. Argent., 22:295-311.Morrg~s, H., Postma, J ., Ferngmdez, M. and Scoppa, C.,1980. Mineralogla de arcilla de algunos suelos del nortede la provincia de Sante Fe. In: Actas, IX Reun. Argent.Cienc. Suelo, 3: 1185-1191.Quir6s, R. and Drago, E., 1985. Relaciones entre variablesfisicas, morfom~tricas y clim~ticas en lagos patag6nicos.Rev. Asoc. Cienc. Nat. Litoral, 16:181 199.Rabassa, J., Brandani, A., Boninsegna, J. and Cobos, D.,1984. Cronologla de la Pequefia Edad del Hielo en losglaciares Rio Manso y Castafio Overo, cerro Tronador,provincia de Rio Negro. In: Actas, IX Congr. Geol.Argent., 3: 624-639.Romero, S., 1985. Estudio geol6gico-econ6mi co del gtreayesifera de Piedras Blancas. Thesis. Fac. Cienc. Nat.Museo, Univ. Natl. Plata, 81 pp.Rubinstein, C., 1983. Estudio sedimentol6gico y ambientalde la Formaci6n Hernandarias. Thesis. Fac. Cienc.Exactas Nat., Univ. Nac. Buenos Aires, 45 pp.Spalletti, L., 1976. Sedimentologla de gravas glaciales,fluviales y lacustres de la regi6n del cerro San Lorenzo.Rev. Asoc. Geol. Argent., 31: 241-259.Torgersen, T., De Deckker, P., Chivas, A. and Bowler, J.,1986. Salt lakes: A discussion of processes influencingpalaeoenvironmental interpretation and recommenda-tions for future study. Palaeogeogr., Palaeoclimatol.,Palaeoecol., 54: 7-19.

iriondo, 1989. quaternary lakes of argentina

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