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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.
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114
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Buenos Aires. Jeunel oI South AnwIcan Earth Sciencea, 2(4):385-389.
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paleocIimate and sea levei changes. New approaches and resuIts from the AntarctIca PenlnsuJa and
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115