Quaternary Science Journal - Quaternary climatic changes in the Caribbean and N. South-America

Eiszeitalter

und

Gegenwart

Band 19

Seite

203-208

Öbringen/Württ.,

31. Oktober

1968

Quaternary climatic changes in t h e Caribbean and N. South-America B y J . I. S. Z O N N E V E L D , U t r e c h t

S u m m a r y . This paper gives an inventarization o f the available data concerning quater­ nary climatic changes in the Caribbean and the northern parts o f South America.

It appears that in Colombia, N . W. Venezuela, the Leeward Islands o f the Netherlands Antilles and Barbados the pluvial periods coincided with the glacial periods in higher latitudes.

The evidence for G u y a n a and Surinam is still insufficient to establish definitely the climatic evolution, altough the available data seem to indicate that during the glacial periods the climate was less humid than at present: this would correspond with a shifting o f the "arid" belt over some 10 degrees.

Z u s a m m e n f a s s u n g . Es wurden in dieser kurzen Arbeit Literaturangaben über die quartären Klimaänderungen gesammelt, die aus dem karibischen Gebiet und den benachbarten Teilen Südamerikas bekannt sind. Man kann feststellen, daß in Kolumbien, Nordwest-Venezuela, Aruba, Curacao, Bonaire und Barbados pluviale Perioden etwa synchron waren mit den Glazialen in Gebieten höherer Breite.

Die Daten aus Guyana und Suriname lassen zwar noch keine endgültigen Schlüsse zu, doch deutet vieles darauf hin, d a ß dort während der Glazialzeiten trockenere klimatische Bedingungen herrschten als heute. D a s würde einer Verschiebung der „ariden" Zone um etwa 1 0 ° entsprechen.

R e c e n t p a l a e o c l i m a t i c research in A f r i c a h a s i n d i c a t e d t h a t o n l y p a r t o f t h e pluvials t h a t w e r e r e c o g n i z e d in different r e g i o n s o f t h e c o n t i n e n t , were s y n c h r o n o u s w i t h the g l a c i a l periods o f m o r e p o l e w a r d r e g i o n s ( c f . T R I C A R T , M I C H E L a n d V O G T , 1 9 5 7 ; BERNARD,

1 9 6 2 ; B Ü D E L , 1 9 6 3 ; F A I R B R I D G E , 1 9 6 4 ; see a l s o P E N C K , 1 9 1 3 ) .

A s a general rule i t a p p e a r s t h a t d u r i n g t h e g l a c i a l periods, the b o u n d a r i e s o f the different c l i m a t i c belts shifted towards t h e e q u a t o r . I n these periods t h e m e s o t h e r m a l zones as w e l l as t h e a r i d z o n e s o f the n o r t h e r n h e m i s p h e r e w i l l h a v e m o v e d s o u t h w a r d a n d t h e b e l t o f the e q u a t o r i a l r a i n f o r e s t n a r r o w e d . E v e n in e q u a t o r i a l r e g i o n s eolian sands w e r e deposited ( D E H E I N Z E L I N , 1 9 5 2 ) . O n l y in t h e z o n e o f the c l i m a t o l o g i c a l ( o r t h e r m a l ) e q u a t o r , some degrees s o u t h w a r d o f the a s t r o n o m i c a l one , t h e t r o p i c a l rain­ forest c o u l d survive. D u r i n g t h e i n t e r g l a c i a l s t h e c l i m a t i c belts shifted a g a i n t o w a r d s the poles ( c f . t h e diagram p u b l i s h e d b y F A I R B R I D G E in 1 9 6 1 a n d 1 9 6 4 ) .

A l t h o u g h the shifting o f the c l i m a t i c b e l t s w a s n o t a s simple as i n d i c a t e d a b o v e , w e m a y a c c e p t t h a t in t h e N . S a h a r a the p l u v i a l periods c o i n c i d e d with t h e g l a c i a l s b u t t h a t in t h e m o r e southern r e g i o n s , pluvial p e r i o d s h a v e t o b e c o r r e l a t e d with i n t e r g l a c i a l times.

F o r t h e c o r r e s p o n d i n g regions in t h e N e w W o r l d , v i z . t h e C a r i b b e a n a n d t h e a d j a c e n t p a r t o f S o u t h - A m e r i c a i t seems w o r t h w h i l e t o g a t h e r t h e e q u i v a l e n t p a l a e o c l i m a t i c i n ­ f o r m a t i o n in order t o l o o k f o r similar c o n c l u s i o n s , a l t h o u g h a d m i t t e d l y o u r k n o w l e d g e o f t h e Q u a t e r n a r y c l i m a t i c changes in t h i s p a r t o f t h e w o r l d is rather i n c o m p l e t e . I n this p a p e r d e d i c a t e d t o t h e m a s t e r o f q u a t e r n a r y research, P r o f . D r . P . W O L D S T E D T , w e will a t t e m p t t o p r o v i d e a b r i e f i n v e n t a r i s a t i o n o n this s u b j e c t ) .

1

P a l a e o c l i m a t i c changes manifest t h e m s e l v e s b y t h e f o l l o w i n g p h e n o m e n a : A. B. C. D. E. F.

m o v e m e n t s o f the levels o f seas a n d l a k e s changes in t e m p e r a t u r e o f t h e s e a w a t e r p e d o l o g i c a l changes, i n c r u s t r a t i o n s changes i n t h e v e g e t a t i o n changes in g r o u n d w a t e r c o n d i t i o n s changes in the g e o m o r p h o l o g i c a l processes.

i) The author is much indebted to Prof. J . B . B I R D , Montreal and Dr. K. DUPHORN, Hannover, who kindly gave him some valuable references and to Mrs. M . VAN DER M A E S E N and D r . H. BOISSEVAIN, who corrected the manuscript linguistically.

204

J . I. S. Zonneveld

a d A . Q u a t e r n a r y m o v e m e n t s o f s e a l e v e l , m o s t l y r e c o r d e d b y fossil — e i t h e r e l e v a t e d or s u b m e r g e d — coastlines a n d t e r r a c e s , are c a u s e d b y the a c c r e t i o n o r m e l t i n g o f g r e a t masses o f i n l a n d ice. T h e y h a v e n o d i r e c t r e l a t i o n w i t h local c l i m a t i c changes in r e g i o n s l i k e the C a r i b b e a n . Y e t t h e s t u d y o f f o r m e r l e a l e v e l s in this a r e a is v e r y i m p o r ­ t a n t as it offers t h e p o s s i b i l i t y to c o m p a r e t h e t i m i n g o f t h e l o c a l c l i m a t i c sequences w i t h t h o s e o f t h e e x t e n s i o n a n d s h r i n k i n g o f t h e g r e a t ice masses.

I n the C a r i b b e a n a n d a l o n g the n o r t h c o a s t o f S o u t h A m e r i c a m a n y d a t a a r e a v a i l ­ a b l e c o n c e r n i n g m a r i n e t e r r a c e s a n d s u b m a r i n e benches. I t is true t h a t t e c t o n i c m o v e m e n t s w i l l h a v e changed t h e o r i g i n a l height o f s o m e o f these " w a t e r m a r k s " , e s p e c i a l l y the o l d e r o n e s . Y e t the influence o f the c h a n g e d sealevels, b o t h a b o v e a n d b e l o w t h e r e c e n t one is e v i d e n t . H i g h sealevels i n d i c a t e d b y m a r i n e t e r r a c e s ( a b r a s i o n terraces as w e l l as a c c u ­ m u l a t i v e benches) h a v e been m e n t i o n e d b y J U K E S - B R O W N E a n d H A R R I S O N ( 1 8 9 1 ) , M O L E N GRAAFF ( 1 9 2 9 ) , R U T T E N ( 1 9 3 2 ) , WESTERMANN ( 1 9 3 2 ) , PIJPERS ( 1 9 3 3 ) , ZONNEVELD

(1960),

D E B U I S O N J E ( 1 9 6 4 ) a n d m a n y o t h e r s . L o w sealevels, e v i d e n c e d b y d r o w n e d v a l l e y s y s t e m s a n d s u b m a r i n e benches are d e s c r i b e d e. g. b y M O L E N G R A A F F ( 1 9 2 9 ) a n d N O T A ( 1 9 5 8 ) . T h e s e w a t e r m a r k s are the m o r e v a l u a b l e i f — as is t h e case in s o m e instances — a b s o l u t e datings are a v a i l a b l e .

N O T A , for i n s t a n c e , f o u n d t h a t his 4 0 a n d 1 2 f a t h o m levels off the A t l a n t i c c o a s t o f G u y a n a c o u l d be d a t e d as resp. 1 1 . 0 0 0 a n d 8 . 0 0 0 y e a r s a g o , i . e . d u r i n g t h e l a t e - a n d p o s t g l a c i a l rise o f t h e s e a l e v e l .

B R O E C K E R et a l . ( 1 9 6 7 ) show t h a t in B a r b a d o s the l o w e r three e l e v a t e d t e r r a c e s o r i g i ­ n a t e d b e t w e e n 8 2 . 0 0 0 a n d 1 2 2 . 0 0 0 y e a r s B . P . after e v a l u a t i o n o f the t e c t o n i c influence a n d c o m p a r i s o n w i t h t h e a v a i l a b l e d a t a c o n c e r n i n g s e a w a t e r t e m p e r a t u r e s in the a d j a c e n t seas ( E M I L I A N I , 1 9 6 5 , 1 9 6 6 ) . T h e a u t h o r s indeed e v i d e n c e t h a t the high sealevels c o r r e ­ s p o n d e d w i t h high t e m p e r a t u r e s o f t h e s e a w a t e r a n d o c c u r r e d in a p e r i o d k n o w n as an i n t e r g l a c i a l ( t h e last i n t e r g l a c i a l ) .

I n A f r i c a t h e a n c i e n t c o a s t l i n e a l o n g the great l a k e s p l a y e d an i m p o r t a n t role in the h i s t o r y o f p a l a e o c l i m a t i c research ( c . f. N I L S S O N , 1 9 3 1 ; K E N D A L L , 1 9 6 5 ) . I n n o r t h e r n S o u t h A m e r i c a o n l y t h e vicissitudes o f t h e ( f o r m e r ) L a k e o f B o g o t a , C o l o m b i a , c o u l d be t a k e n in c o n s i d e r a t i o n (see ad D ) . a d B . E s p e c i a l l y t h e p u b l i c a t i o n s o f E M I L I A N I ( 1 9 6 5 , 1 9 6 6 ) a n d E R I C S O N C . S . , 1 9 6 4 ) give interesting d a t a c o n c e r n i n g t h e changes in t e m p e r a t u r e o f the C a r i b b e a n s e a w a t e r .

As has been said b e f o r e , these d a t a c a n b e c o r r e l a t e d w i t h those c o n c e r n i n g h i g h e r a n d l o w e r s e a l e v e l s : h i g h sealevels p r o v e t o b e synchronous w i t h high w a t e r - t e m p e r a t u r e s a n d v i c e versa. a d C . U n d e r c e r t a i n c l i m a t i c c o n d i t i o n s deposition o f c a r b o n a t e s ( a n d o t h e r m a t e r i a l s ) can result in t h e f o r m a t i o n o f t r a v e r t i n e masses o r caliches. W I L H E L M Y ( 1 9 5 4 ) m e n t i o n s suchlike fossil i n c r u s t a t i o n s in n o r t h e r n V e n e z u e l a , e s p a c i a l l y on t h e peninsula o f G u a j i r a f o r which he postulates c l i m a t i c c o n d i t i o n s t h a t were m o r e h u m i d t h a n t h e present (very dry) ones.

B A R K E R ( 1 9 6 0 ) f o u n d t h a t u n d e r t r o p i c a l r a i n f o r e s t , g r a n i t e s are a t t a c k e d b y c h e m i c a l w e a t h e r i n g in such a w a y t h a t m i n e r a l s l i k e e p i d o t e a n d h o r n b l e n d e p r a c t i c a l l y dis­ a p p e a r . I f , h o w e v e r , t h e forest is a b s e n t , these m i n e r a l s a r e resistant a g a i n s t w e a t h e r i n g .

T h e s a m e a u t h o r m e n t i o n s the o c c u r r e n c e o f e p i d o t e a n d h o r n b l e n d e in a s a m p l e f r o m a l a t e r i t i c l a y e r in t h e h u m i d forest o f S u r i n a m a n d c o n c l u d e s that this must p o i n t t o p a l a e o c l i m a t i c c o n d i t i o n s u n f a v o r a b l e f o r h u m i d t r o p i c a l forests. a d D . A v e r y i m p o r t a n t i n d i c a t o r f o r p a l a e o c l i m a t e s is t h e v e g e t a t i o n ( a l t h o u g h it is k n o w n t h a t t h e v e g e t a t i o n n o t a l w a y s is a p t to k e e p p a c e with the c l i m a t i c changes a n d that sometimes other factors than climate m a y cause vegetational changes). U p till n o w quaternary palaeobotanical data are known from Costa R i c a , C o l o m b i a and

Quaternary climatic changes in the Caribbean and N . South-America

205

Guyana. I n Costa Rica ( M A R T I N , 1 9 6 4 ) a n d C o l o m b i a (VAN D E R H A M M E N and G O N Z A L E Z , 1 9 6 0 ) p o l l e n a n a l y s i s r e v e a l e d that d u r i n g t h e g l a c i a l p e r i o d s the t i m b e r - l i n e in t h e m o u n t a i n s w a s some 1 0 0 0 m l o w e r than a t p r e s e n t t i m e s . T h e last m e n t i o n e d a u t h o r s also s h o w e d t h a t during the p e r i o d s with a h i g h t i m b e r - l i n e ( t h e i n t e r g l a c i a l s ) , t h e l e v e l o f t h e L a k e o f B o g o t a was l o w e r e d , a p p a r e n t l y d u e t o a decrease o f t h e p r e c i p i t a t i o n . I n o t h e r w o r d s : i n t e r p l u v i a l s c o u l d be c o r r e l a t e d w i t h i n t e r g l a c i a l s .

F r o m t h e l o w l a n d s o f t h e L l a n o s o f C o l o m b i a a n d V e n e z u e l a no p a l a e o c l i m a t i c d a t a are k n o w n f r o m p l e i s t o c e n e t i m e s . W I J M S T R A a n d V A N D E R H A M M E N ( 1 9 6 6 ) a n a l y s e d some p o l l e n o u t o f the L l a n o s O r i e n t a l e s o f C o l o m b i a , but the oldest samples o n l y d a t e f r o m a p p r o x i m a t e l y 6 . 0 0 0 y e a r s B . P . I n G u y a n a t h e same a u t h o r s i n v e s t i g a t e d a profile t h a t yielded s t r a t a as o l d as 9 . 0 0 0 — 1 0 . 0 0 0 B . P . T h e p o l l e n e v i d e n c e a p p e a r s t o p o i n t t o closed d r y forest o r c l o s e d s a v a n n a w o o d l a n d c o n d i t i o n s d u r i n g late g l a c i a l times in a region t h a t n o w has a s a v a n n a character ( R u p u n u n i ) . P r o f . H I L L S o f M c G i l l U n i v e r s i t y , M o n t r e a l ( o r a l c o m m u n i c a t i o n ) , h o w e v e r , e x p l a i n e d t h a t t h e l a k e w h e r e t h e samples were t a k e n , is in fact a k i n d o f an o x b o w l a k e ; so it is n o t e x c l u d e d t h a t in f o r m e r times this l a k e h a d an open c o n n e c t i o n w i t h t h e I r e n g R i v e r . T h i s r i v e r d r a i n s a l a r g e a r e a c o v e r e d w i t h different t y p e s o f forests a n d s a v a n n a s . I n o t h e r w o r d s : there is a p o s s i b i l i t y t h a t p a r t o f t h e pollen c o n t e n t o f the s a i d profile e s p e c i a l l y o f the o l d e r p a r t , does n o t p r o v i d e i n f o r m a t i o n a b o u t the ( f o r m e r ) v e g e t a t i o n o f t h e p r o p e r surroundings b u t o f t h e (forest) v e g e t a t i o n o f h i g h e r parts o f the d r a i n a g e basis o f t h e I r e n g R i v e r .

A l s o in t h e coastal a r e a s o f G u y a n a V A N D E R H A M M E N ( 1 9 6 1 ) m a d e s o m e v e r y i n t e r ­ esting i n v e s t i g a t i o n s . H e s h o w e d t h a t in t h e subsoil o f G e o r g e t o w n a s a v a n n a - l i k e v e g e ­ t a t i o n c o u l d be c o r r e l a t e d w i t h a ( g l a c i a l ) l o w s e a l e v e l . After a rise o f t h e sealevel a ( m a n g r o v e ) v e g e t a t i o n c a m e into the p i c t u r e . A c t u a l l y this m a n g r o v e v e g e t a t i o n itself does n o t p o i n t to c l i m a t i c changes; it is a n e v i d e n c e for t h e ingression o f t h e sea u n d e r influence o f the rising s e a l e v e l . T h e s a v a n n a v e g e t a t i o n , h o w e v e r , c o u l d i n d i c a t e a c l i m a t e w i t h a treeless v e g e t a t i o n in an a r e a w h e r e in present times the n a t u r a l c o n d i t i o n s tend to a h u m i d rain f o r e s t . a d E . T A M E R S ( 1 9 6 6 , 1 9 6 7 ) recently p u b l i s h e d some i n t e r e s t i n g d a t a c o n c e r n i n g the age o f g r o u n d w a t e r masses in the n e i g h b o u r h o o d o f M a r a c a i b o a n d on t h e p e n i n s u l a of G u a j i r a in N . W . V e n e z u e l a .

I n t h e s e areas, at p r e s e n t , the p o t e n t i a l e v a p o r a t i o n is a p p r o x i m a t e l y f o u r t o five times h i g h e r t h a n the p r e c i p i t a t i o n . T h e r e f o r e r e c e n t r a i n w a t e r is n o t in a s i t u a t i o n t o reach t h e g r o u n d w a t e r r e s e r v o i r . R e c h a r g e o f the g r o u n d w a t e r basins c o u l d o n l y h a v e o c c u r r e d d u r i n g periods w i t h more p r e c i p i t a t i o n ( a n d p e r h a p s less e v a p o r a t i o n ) , i. e. during p l u v i a l periods. A c c o r d i n g to r a d i o c a r b o n d a t i n g s published b y T A M E R S ( 1 9 6 7 ) most o f t h e g r o u n d w a t e r samples in the n e i g h b o u r h o o d o f M a r a c a i b o are a p p r o x i m a t e l y 1 0 . 0 0 0 — 3 5 . 0 0 0 years o l d . T h e pluvial p e r i o d d u r i n g which t h e recharge o f t h e a q u i f e r has t a k e n p l a c e e v i d e n t l y c o i n c i d e d w i t h t h e last ( W ü r m , Weichsel, W i s c o n s i n ) g l a c i a l p e r i o d . I n G u a j i r a T A M E R S ( 1 9 6 6 ) f o u n d ages in the r a n g e o f 5 . 0 0 0 — 8 . 0 0 0 y e a r s , t h e time o f t h e H o l o c e n e c l i m a t i c o p t i m u m . H e c o n c l u d e s t h a t here the g r o u n d w a t e r reser­ v o i r c o u l d h a v e been c h a r g e d during a p l u v i a l t h a t c o u l d c o r r e s p o n d w i t h t h e p e r i o d o f higher p r e c i p i t a t i o n r e c o g n i z e d b y B U T Z E R ( 1 9 6 1 ) in t h e M e d i t e r r a n e a n r e g i o n s . ad F . F i n a l l y some g e o m o r p h o l o g i c a l p h e n o m e n a m a y p o i n t t o a l t e r n a t i o n s o f p l u v i a l a n d i n t e r p l u v i a l p e r i o d s in the C a r i b b e a n a n d t h e n o r t h e r n p a r t o f S o u t h A m e r i c a .

W I L H E L M Y ( 1 9 5 4 ) c a l l e d a t t e n t i o n t o t h e " f o s s i l " c h a r a c t e r o f the v a l l e y s o f C u r a c a o which w o u l d reflect c o n d i t i o n s more h u m i d t h a n those o f r e c e n t times.

O n B o n a i r e and B a r b a d o s B L U M E ( 1 9 6 8 ) c o u l d establish t h a t along t h e f r o n t o f some c u e s t a - l i k e f o r m s s l u m p i n g a n d spring e r o s i o n must h a v e o c c u r r e d u n d e r c l i m a t i c c o n ­ ditions c o n s i d e r a b l y m o r e h u m i d than at p r e s e n t .

J . I . S. Zonneveld

206

T R I C A R T a n d C A I L L E U X ( 1 9 6 5 ) record an observation on Barbados where a large l i m e s t o n e block w h i c h during a h u m i d p e r i o d w a s m o v e d d o w n w a r d b y slumping, w a s r e c e n t l y a t t a c k e d b y sealevel s o l u t i o n . T h e l o c a l s i t u a t i o n leads them t o c o n c l u d e t h a t t h e s l u m p i n g t o o k p l a c e during t h e last g l a c i a l p e r i o d w h e n t h e sealevel w a s l o w e r t h a n at present.

A v e r y interesting study w a s c a r r i e d o u t b y D E B U I S O N J E ( 1 9 6 4 ) w h o p o s t u l a t e s t h a t s o m e m a r i n e t e r r a c e s ( r e p r e s e n t i n g f r i n g i n g a n d b a r r i e r reefs built up d u r i n g p e r i o d s w i t h h i g h sealevels) w e r e f o r m e d u n d e r r e l a t i v e l y a r i d c o n d i t i o n s . M o r e o v e r , he f o u n d e v i ­ d e n c e t h a t t h e l o w e r sealevels c o i n c i d e d w i t h m o r e h u m i d p e r i o d s .

R e c e n t l y G A R N E R ( 1 9 6 7 ) expressed t h e idea t h a t t h e i n t r i c a t e systems o f r a p i d s a n d w a t e r f a l l s t h a t a r e c h a r a c t e r i s t i c f o r m a n y r i v e r s in V e n e z u e l a ( a n d o t h e r t r o p i c a l regions) w o u l d be connected with a transition from dry to humid conditions: the rivers that h a d o r i g i n a t e d d u r i n g this t r a n s i t i o n w o u l d n o t y e t h a v e h a d t h e o p p o r t u n i t y t o d e g r a d e their b e d s a n d w o u l d o n l y find their w a y in u n c o n c e n t r a t e d a n d u n o r g a n i z e d c h a n n e l systems ( " r i v e r s in t h e m a k i n g " ) . I n m y o p i n i o n , h o w e v e r , this v i e w is based o n a m i s c o n c e p t i o n c o n c e r n i n g t h e e v o l u t i o n a n d c h a r a c t e r o f r i v e r s in h u m i d t r o p i c a l regions ( c f . Z O N N E ­ VELD, 1 9 5 2 , 1 9 6 8 ; TRICART, 1 9 5 9 ; BARKER,

1960).

A

B

T h e o b s e r v a t i o n s , m a d e b y G A L O N ( 1 9 6 6 , 1 9 6 6 ) a r e m o r e i m p o r t a n t in t e r m s o f p a l a e o c l i m a t i c e v i d e n c e . G A L O N refers t o e r o s i o n a l f o r m s which a p p a r e n t l y w e r e m o u l ­ ded u n d e r s e m i a r i d c o n d i t i o n s (he f o u n d t h e same " b r a n c h e d slope i n c i s i o n s " in a c t i o n in a c t i o n in s e m i - a r i d regions) b u t w h i c h in p r e s e n t days a r e c o v e r e d w i t h t r o p i c a l r a i n ­ f o r e s t . A l s o Z O N N E V E L D ( 1 9 6 7 ) m e n t i o n s fossil l a n d f o r m s in southern S u r i n a m , r e s e m b l i n g fossil " l a v a k a s " , w h i c h must h a v e o r i g i n a t e d in p e r i o d s o f greater e x t e n s i o n o f t h e s a v a n n a s ( a c t u a l l y a l a r g e p a r t o f t h e r e c e n t s a v a n n a s in t h a t area h a s t o b e r e g a r d e d as a n t h r o p o g e n i c ) .

"When t h e d a t a r e v i e w e d a r e o v e r l o o k e d a n d c o n s i d e r e d , it becomes e v i d e n t t h a t t h e v a l u e o f the i n f o r m a t i o n is u n e q u a l . S o m e d a t a o n l y i n d i c a t e t h a t a t o n e t i m e o r t h e o t h e r c l i m a t i c changes d i d o c c u r , p a r t l y in regions t h a t a r e n o w r e l a t i v e l y d r y ( C u r a c a o , B o n a i r e , N . W . V e n e z u e l a a n d also B a r b a d o s ) , p a r t l y in t h e regions w i t h h u m i d t r o p i c a l c l i m a t e s (the n o r t h e r n p a r t o f S o u t h A m e r i c a ) . ) 2

O n the other hand other data provide more exact information a n d concern the r e l a t i o n b e t w e e n l o c a l c l i m a t i c changes a n d t h e sequence o f glacials a n d i n t e r g l a c i a l s .

The

evidence of C u r a c a o ( D E B U I S O N J E ,

ZALEZ,

1960),

Barbados ( T R I C A R T and

1964),

Colombia (VAN DER H A M M E N and

CAILLEUX,

1 9 6 5 ) and

GON­

Maracaibo (TAMERS 1 9 6 7 )

c l e a r l y p o i n t t o h u m i d c o n d i t i o n s d u r i n g t h e last g l a c i a l ( o r p a r t o f i t ) a n d t o ( r e l a t i v e ) a r i d i t y during interglacials.

T h e e v i d e n c e f r o m G u y a n a a n d S u r i n a m , h o w e v e r , is still insufficient t o establish t h e c l i m a t i c e v o l u t i o n in t h a t area, a l t o u g h t h e a v a i l a b l e d a t a seem t o i n d i c a t e t h a t i n t h e G u y a n a s t h e least h u m i d c o n d i t i o n s c o i n c i d e d w i t h g l a c i a l s . T h i s w o u l d m e a n t h a t d u r i n g t h e t r a n s i t i o n f r o m a n i n t e r g l a c i a l t o a g l a c i a l p e r i o d t h e ( s e m i - ) arid z o n e shifted south­ w a r d a n d t h a t it w e n t b a c k again w h e n t h e g l a c i a l w a s s u c c e e d e d b y t h e n e x t i n t e r g l a c i a l .

T h i s w o u l d c o r r e s p o n d w i t h a shifting o v e r some 1 0 degrees.

A t present it is p r e f e r a b l e t o a v o i d s p e c u l a t i o n a n d t o w a i t f o r t h e results o f n e w research t o be c a r r i e d o u t in eastern V e n e z u e l a , n o r t h e r n B r a z i l a n d t h e t h r e e G u y a n a s .

2

) One would expect that also in French Guyana such indications will be found, in spite o f the information already given by CAILLEUX ( 1 9 5 9 ) that in this country during the Pleistocene ap­ parently no important climatic changes had occurred.

Quaternary climatic changes in the Caribbean and N . South-America

207

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t h

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Anschrift des Verf.: Prof. Dr. J . I. S. Zonneveld, Utrecht, Drift 2 1 , Geografisch Instituut der Rijksuniversiteit, Utrecht, Nederland.