BoI.IG-USP, Publ.Esp., 8:109-115, 1991.

THE PATAGONIAN GLACIATIONS AND THE ONSET OF GENERAL QUATERNARV­

TYPE GLACIATIONS ON THE GLOBE

NAMómer'

CALDENIU5 (1932) mapped four extensive and impressive glaciatlons trom the

Argentlne-ChOian mountaln chaln (Flg.1). By analogy anel supposed correlatlon with the Scandlnavian

chronology, he - untortunately - named these stagas the Inltioglacial, the Danlglacial, the Gothiglacial and

the Flnlglacial. This Implles that the last three stagas would date at 20 Ka, 13 Ka and 10 Ka, raspectJvely.

ADALGO & RUGGI (1965) accepted this and proposed that the Initloglacial represented the earty phase of

the last glaciatlon In the northem hemisphere some 60 Ka ago.

The mapping of CALDENIU5 (1932) was masterty done and seems to be generally

correct. The chronology, on the other hand, was completely hypothetical. 5tOl (and In absence of

anythlng e1se), the chronology of Caldenius has been widely usad. Both MERCER (e.g., 1976) and

CLAPPERTON (1983) have notlced this weakness.

We have taken up this problem and applied paleomagnetism on a number of locaIities

and In a number of dlfferent projects. Thls Includas both stratlgraphias associated to the glacial moraines

a10ng the Andas and stratigraphies in the coastal region with loess depositlon as possIble signs of

glaclatlons (FIg. 1).

First, we have identlfied at least 5 (not 4) main moralne zonas, which we interprete as

slgns of gtaclation or "Ice ages". In the Lago Buenos Aires area (MORNER & 5YLWAN, 1987, 1989 and

MORNER, 1989a), these tive moraine zonas include as many as 15 separate terminal moralne ridges,

representlng phases of the maln glaciatlons. The oIdest (outermost) moralne zone (a part of Caldenius

Initloglacial complex) has a quite dlfferent geomorphological appearance and must be conslderably oIder

than the others.

The two 11)0raine zones, our I and 11, belonging to Caldenius Initioglacial, were both

1 PaJeogeophysica & Geodynamica, Geologicallnstitute, 8-10691 Stockholm, Sweden.

Figure 1 - Extension of the 5 glaciation maxima (I-V) in Patagonia (primarilyas mapped by CALDENIUS, 1932). Black tringles mark locaJities investigated by us as to paleomagnetism and glacial chronology. The record from Lago Buenos Aires (Lago B.A.) serves as a type area. The first glaciation maximum (I) at about 2.3 Ma had the widest extension and was the only one fully to cross the Tierra dei Fuego area.

110

formed durlng a perlod ot reversed geomagnetlc poIarity. We bellave that our zone I Is ot early Matuyama

age or about 2.3 Ma oid. and·that our zona 11 is ot late Matuyama age or 1.2 Ma oId. Thls fits well wIth the

occurrence ot 108ss-Uke deposJts In a magnetostratlgraphically very well dated strataJ sequence at Mar dei

PIsta (RUOCCO. 1989 and RUOCCO & MORNER. 1987). Our zona 11 g1aclatlon (the flrst wIth a -rre&h"

appearance) would. In thls case. correlate wIth MERCER's (1976) K/ Ar dated maxlmum glaciatlon.

BIDEGAlN (1989) has shown wIth magnetostratlgraphy that an "oId lcess" In Entre Rios Is ot upper

Matuyama age (fIttIng well with a 1.2 Ma age ot the zona 11 gIacIatIon).

The zona 111 or ·DanlglaclaJ· glaciatlon Is well fIxecI at the Brunhes/Matuyama transIdon;

the InItiaI phase balng ot raversed poIarIty and the maln phase ot normal poIarIty. Thls Implles a

fundamental and drastlc revlsion ot the oid chronology. It has been recorded In severa! places and Is

consIdered a major and clear flndlngs.

The zona IV or GothlglaclaJ gIaciatIon remalns undated. It occurred somewhere wlthln

the Brunhes NonnaI Epoch.

The zona V or "AnJglaclaJ· glaclatlon Includes severa! phases (as do the oider zonas). the

Iast one ot whlch must have ended shortIy batere about 14.000 BP accordlng to radlocarbon dates and

secular paleomagnetlc changes In a varved clay sequence cf 887 Individuai varves (SYLWAN. 1987).

Our record trom the Lago Buenos Aires ares Is shown In Figure 2 and the general

chronology estabIlshed for the Patagonian glaciations Is shown In Agure 3.

From the paleomagnetlc record at Mar dei PIata (RUOCCO. 1989). we learn that cycllc

alternatlons between wetter and dryer and between cooIer and warmer perlods began In the upper Gauss

shortIy after 2.9 Ma. Thls seems to represent a general climatlc-environmental change (FIg. 2) and to be

related to paleo-oceanographlc changes. judglng trom the Isotopic signals descrlbed by SHACKLETON &

OPDYKE (19n).

A short marlne episode is deterrnlned at around 2.9-2.7 Ma both in the Paraná basln

(BIDEGAlN. 1989) and In Patagonia (MORNER et ai .• In prep.).

The system and chronology ot g1aclatlons establlshed In Figure 3 does not Indlcate any

clear correlatlon with northem hemisphere records nor with the oceanlc hlgh-frequency glaclaJ/lnterglaciaJ

changes. ThIs abeence ot correlation may ba signiflcant and real.

The late glacial and postglaclal short-term glacial cllmatlc changes saem rather to be out

ot phasethan In phase wlth the northem European changes (MORNER. 1984. 1988) and to represent the

redlstrlbutlon ot energy CNer the g10be via ocean circulatlon changes (rather than g1oba1ly synchronous rlses

and faIIs In temperature). This seerns also to be the case wIth so-caIled Younger Dryas effects and

correlatlons. It is true that the oceanic and atmospheric clrculatlon was severely upset, but thls lead to the

redlstrlbutlon cf energy (heat) CNer the globe. not to a general fali CNer the globa. Thls concurs wIth the

Interpretatlon by MARKGRAF (1987) ot the cllmatlc changes In southem South Arnerlca. but dlfter to the

111

I I I I -10 km O 10 20

~ N N N N O o.... BRUNHES

r-: ::: 60

<t = 30 ..J I ::: O o....

= -30 ~ > = -60

I 30

R RR

?

I 40

1

D 7 8

I 50

RR

O? '~r--, ,

I +60 km

MATUYAMA ?

N 60 -

30 -

0--30 -

-60 -5

Rgure 2 - Terminal moraines and morainas zonas along three profllas (A-C) east to northeast of Lago Buenos Airas showing the

change trom 4 main zonas Q.e., F=Rniglacial, G= Gothiglacial, 0= Daniglacial, 1= Initioglacial accordlng to Caldenius

nomelJclature), to our tive maio zonas (I-V) and 15 individual moraines (1-15). Horizontally bedded subtill proglacial sedimenta have

been sampled for paJeomagnetism in 8 locaJitias (1-8). The distancea are given with respect to the innermost moraine poeitIon. The

paleornagnetic resulta (after complete demagnetization) are given at the base; the polarity reoords (N, R) trom the eight locaIitias,

the Brunhes-Matuyama zonation, and the VGP latitudinal reoord indicating a c1ear zonation between reversed and normal polarity

(encircled star reter to our varved c1ay reoord). The Matuyama/Brunhas boundary occurred somewhere within the Daniglacial

moraine zone (111) .

interpretatlon by HEUSSER (1987).

In 1989, we extended our studies to the Antarctic Peninsula (MORNER et ai., 1989a,

1989b) in connectlon wIth the Swedish Expeclltion (SWEDARP -88/89) to Antarctica. In the James Ross

area, there was a rnaximum glacial expansion after the deposltion of the "Pecten Conglomerate" on

Cockbum Island. We believe that the rnarine episode that deposited the "Pecten Conglomerate" is identical

to the events established ali along the Argentine and BrazUian coasts (MORNER. 1989b) and dated at about

2.9-2.7 Ma (BIDEGAlN. 1989 and MORNER. 1989a). This is consistent with paleornagnetlc data obtained

from the "Pecten Conglomerate" and trom possible corretative beds on Livingstone Island (MORNER. in

prep.). The "Pecten Conglomerate" is covered byerratic material of a glacial phase of considerable size.

This phase represents the rnaximum glaciation within this area. As it post-dates the Pecten Conglomerate.

its age should be younger than 2.7 Ma (provided the Pecten Conglomerate is properly dated). This is close

112

o tJ) Va 11.-15 >11. KA W

FINIGLACIAL Vb 12-13 <120 KA

I Z GOTHIGLACIAL rl 9-11 MID-B ::> a:: CO DANIGLACIAL m 5-8 "'0.7 MA

1 J

« INITIOGLACIAL fi 2-1. . ",1.2 MA ~ « >-::> ~

2 ~

INITIOGLACIAL I ",2.3 MA

tJ) tJ)

3 ::> GENERAL « "'3.0 MA

(!) CHANGE

Agure 3 - SyntheaIa 01 the magneto8b atigraphic poaItion 01 the 5 main glaciatlon8 (ar "Ice ages") In Patagonla (oroaa-hatched

zones), correspondlng map-unita accordlng 10 CALDENIUS (1932), our numbering 01 the fIve moraIne zonea (I-V) and Individuai

terminal moralnes (1-15) In the Lago Buenos Aires area and ages 01 the 5 moraIne zones (Ice ages). lhe general change at around

3.0 Ma representa th. beglnning 01 an alternating cllmatic regimen. N. about 2.9-2.8 Ma, there waa a ahort but draatlc marln •

• piaod •.

to the establlshed age of the maximum glaciation In Patagonla of about 2.3 Ma (MORNER, 19898). lhe Ice

caps on the Antarctlc Peninsula anel in southern South America seen, therefore, to have reached their

maximum at the same time. This seerns quite reasonable, reallzing that the first glaciation maximum In

Patagonla was the onIy glaclatlon that crossed the entire TIerra dei Fuego ·and exhlbited a major dome In the

south (FIg. 1).

Furthennore, the European and North American continental Ice caps expertenced a first

maximum in the lowermost part of the Matuyama Reversed Chron at about 2.4-2.3 Ma. SimBarty, the first

loess beds in China began at about 2.4 Ma.

It seems, therefore, clear that the entire globe experienced a first glacial episode at about

2.4-2.3 Ma. This would, of course, be the logicallower boundary of the Quatemary.

113

The paJeomagnetic dating 01 the onset ofQglaciations in Patagonia, forms the base for

presently avalJable possibUlties of establishing correlations both with Antarctica anel with the northem

hemisphere.

REFERENCES

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SYMPOSIUM ON GLOBAL CHANGES IN SOUTH AMERICA DURING THE QUATERNARY. São Paulo

1989. Speclal Publlcation, 1: Program, Abstracts 8nd General Informatlona. São Paulo,

ABEQUAjlNQUA 1989. p.46-48.

CALDENIUS, C. (1932) Las glaciaciones cuaternarias en la Patagonia y Tierra dei Fuego. Geografiska Ann,

14:1-164.

CLAPPERTON, C.M. (1983) The glaciation ot the Andes. Quaternary Science Reviews, (2):83-155.

FIDALGO, F. & RIGGI, J.C. (1965) Los Rodados Patag6nlcos en la Meseta dei Guenguel y A1rOOedores

(Santa Cruz). Revista de la Asoclación Geológica Argentina, 20:273-325.

HEUSSER, C.J. (1987) Oimate 01 southem South America during the last glacial maximum inferrOO from

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MARKGRAF, V. (1987) PaleocIimate data model comparison trom the Southem Hemisphere. In: 12th

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MERCER, J.H. (1976) Glacial history 01 southemmost South America. Quaternary Research, 6:125-166.

MõRNER, NA (1984) Oimatic changes on a yearty to mUlennial basis. Concluding remarks. In: MôRNER,

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MôRNER, NA (1988) Terrestrial variations within given energy, mass anel momentum budgets;

paJeocIimate, sea levei, paJeomagnetism, differentiaJ rotation anel geodynamics. In: STEPHENSON,

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114

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MORNER, NA (19898) The Patagonian glaciations. In: INTERNATIONAL SYMPOSIUM ON GLOBAL

CHANGES IN SOUTH AMERlCA DURING THE QUATERNARY. São Paulo, 1989. SpecI8l Publlcation,

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MORNER, NA (1989b) Changes in the coastaI sedimentary envlronments. The South Amerlcan case and

Impllcations on Global Changes. In: INTERNATIONAL SYMPOSIUM ON GLOBAL CHANGES IN SOUTH

AMERICA DURING THE QUATERNARY, São Paulo. 1989. SpecI8l PUbIlcaUon, 1: Program,

Ab8Iracta and Gen .. llnformatioM. São Paulo, ABEQUA/INQUA. p.216-220.

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MORNER, N.A. & SYLWAN, C. (1989) Magnetostratigraphy of the Patagonian moraine sequence at Lago

Buenos Aires. Jeunel oI South AnwIcan Earth Sciencea, 2(4):385-389.

MORNER, NA; MUJICA, A.; DA ROCHA, P. ~n press) Cenozolc rnagnetostratlgraphy, sedlrnentary

dynamlcs, paleocIil'l'l8taogy, sea levei changes and related problema. SCAR reporl

MORNER, NA; MUJICA, A.; DA ROCHA, P. (In press) Paleomagnetlsm, sedlmentary dynamics,

paleocIimate and sea levei changes. New approaches and resuIts from the AntarctIca PenlnsuJa and

South Shetland Islands. SCAR report.

RUOCCO, M. (1989) A 3 Ma paleomagnetic record of coastaI continental deposJts In Argentina.

Palaeogeography, Palaeoclimatology, Palaeoecology, 72(1/2): 1 05-113.

RUOCCO, M. & MORNER, NA (1987) Late Cenozoic IItho-and rnagnetostratlgraphy of continental deposits

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SHACKLETON, N.J. & OPDYKE, N.D. (1977) Oxygen isotope and paleomagnetic evidence for earty

Northern hemisphere g1aciation. Natura, 270:216-219.

SYLWAN, C. (1987) Annua! paleomagnetic record from late glacial varves in Lago Buenos Aires, Patagonia.

Argentina. Quatemary oI South America and Antarctic Peninsula, 5:181-196.

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