Quaternary Science Journal - Examples of Weichselian environments: local versus regional develo...

Eiszeitalter

u.

16-19 4 Fig.

44

Gegenwart

Hannover

1994

Examples of Weichselian environments: local versus regional developments ELSE

KOLSTRUP*)

W e i c h s e l i a n . climate, p a l a e o e n v i r o n m e n t ,

A b s t r a c t : In this p a p e r s o m e factors o f u n c e r t a i n t y to the reconstruction of ice age palaeoenvironments

a r c discus­

sed. T h e discussion u s e s t w o e x a m p l e s o f d e v e l o p m e n t o n land, n a m e l y the e x a m p l e s o f frost m o u n d s a n d fires, and e m p h a s i s e s t h e d e v e l o p m e n t s with relation t o l o c a l versus regional e n v i r o n m e n t a l c h a n g e s . It is d e m o n s t r a t e d

that a

c h a n g e in local, n o n - c l i m a t i c factors c a n result in deposits w h i c h c a n b e mistaken as Ixjing the result o f climatic change.

It

is

proposed

that

future

investigations

can

provide

m u c h additional i n f o r m a t i o n o n past e n v i r o n m e n t a l

deve­

l o p m e n t s a n d their c o m p l e x cause-effect r e l a t i o n s h i p s o n land, b u t in order to m a k e holistic r e c o n s t a i c t i o n s it is ne­ c e s s a r y to l o o k out for t h e p o s s i b l e effects o f b o t h climatic and

non-climatic

developments

when

environmental

c h a n g e s are r e c o n s t r u c t e d .

[Beispiele weichselzeitlicher Umweltbedingungen: lokale Entwicklungen i m Gegensatz zu regionalen] K u r z f a s s u n g : In der v o r l i e g e n d e n Arbeit w e r d e n einige Unsicherheitsfaktoren Umweltbedingungen

bei der Rekonstruktion

v o n Paläo-

diskutiert. In d e r D i s k u s s i o n w e r d e n

z w e i B e i s p i e l e aus d e m terrestrischen B e r e i c h n ä m l i c h Frosthügel und B r ä n d e : w o b e i d e r

angeführt,

Schwerpunkt

der U n t e r s u c h u n g e n auf d e m G e g e n s a t z v o n l o k a l e n zu re­ gionalen

Umweltveränderungen

striert, d a ß l o k a l e V e r ä n d e r u n g e n ,

liegt.

E s wird

die k e i n e

demon­

klimatischen

Ursachen haben, Ablagerungen entstehen lassen

können,

die d e n Eindruck e r w e c k e n , als seien sie d a s E r g e b n i s kli­ matischer Veränderungen. ge Untersuchungen über

Es wird festgestellt, d a ß

e i n e F ü l l e zusätzlicher

Paläo-Umweltentwicklungen

Beziehungen

hinsichtlich

und

ihre

Lirsache und

künfti­

Informationen komplexen

Wirkung

liefern

k ö n n e n . Um aller s c h l ü s s i g e R e k o n s t r u k t i o n e n m a c h e n zu k ö n n e n , ist e s n o t w e n d i g , m ö g l i c h e Effekte s o w o h l klima­ tisch als a u c h nicht k l i m a t i s c h induzierter zu

Entwicklungen

untersuchen.

1 Introduction F r o m various sources, s u c h as for e x a m p l e d e e p sea c o r e s a n d ice cores, it is k n o w n that temperature c h a n g e s took place during the ice age, a n d b y n o w a g o o d temperature framework has b e e n established (e. g. J O H N S E N et al., 1 9 9 2 ) . However, the temper­ ature is only o n e environmental parameter, and it is b e c o m i n g increasingly understood that if g o o d palae*) A d r e s s o f t h e author: Frau Dr. E. KOLSTRUP, M o s e v e j 12 Blans, DK - 6400 Sonderborg,

Denmark

frost m o u n d s , fires, l o c a l c o n d i t i o n s

o e n v i r o n m e n t a l reconstructions are to b e made, o t h e r environmental parameters will a l s o have to b e included with the reconstructions. In particular the d e v e l o p m e n t s that t o o k place on land can give information on c o m p l e x cause-effect interrelation­ ships. In present landscapes there is a great diversity o f e n v i r o n m e n t s and subenvironments, s o m e t i m e s within short distance, and there is n o reason lo p r e s u m e that there w a s less complexity in the past.

T h e r e f o r e , by increasing the efforts o n p a l a e o e n v i r o n m e n t a l reconstmction from land d e p o s i t s it may, apart from temperattires, also b e c o m e p o s s i b l e to in­ c l u d e and understand hydrology- and w i n d conditi­ o n s , as well as various geological p r o c e s s e s from dif­ ferent types o f areas. In turn such factors c a n b e seen in relation to soil, vegetation and fauna.

O n e of the problems in the reconstructions is that g e o l o g i c a l localities c a n b e regarded as points in the l a n d s c a p e and that deposits from different localities c a n b e difficult to correlate in time and with relation to their p a l a e o g e o g r a p h i c development. Y e t , it is crucial that deposits a n d p h e n o m e n a that are used for reconstruction o f a certain time span elate from the s a m e period, so that similar e n v i r o n m e n t s from different periods are not correlated in time.

In o t d e r to m a k e realistic palaeoenvironmental re­ constructions it is n e c e s s a r y to k n o w h o w various p h e n o m e n a d e v e l o p u n d e r relatively s t a b l e climat­ ic c o n d i t i o n s today, a n d further to m a k e qualified e s t i m a t e s o f the g e o l o g i c a l effects o f m a j o r climatic c h a n g e s . In other worcis, if regularities o f single en­ vironmental factors through time, as d e d u c e d from c o m p l e x palaeosituations, are to be outlined, it is nec­ essary to find out what could have t a k e n p l a c e as a result o f regional climatic changes on t h e o n e hand, a n d w h a t could have h a p p e n e d owing t o local de­ v e l o p m e n t s that o c c u r e d without climatic c h a n g e on the other.

In t h e following, two e x a m p l e s are given o f devel­ o p m e n t s which might at first sight b e t a k e n as indi­ cations o f climatic, i. c \ , regional c h a n g e ; but o n c e additional information o n underlying factors are in­ c l u d e d with the interpretation, it appears that their d e v e l o p m e n t might equally well b e interpreted as the result o f local, site specific conditions.

E x a m p l e s o f W e i c h s e l i a n e n v i r o n m e n t s : local v e r s u s regional d e v e l o p m e n t s

2 T h e e x a m p l e o f frost m o u n d s

17

A pollen diagram from S t o k e r s d o b b e in the Nether­ lands (Fig. 2 ) represents a vegetation radiocarbon

The first e x a m p l e relates t o t h e d e v e l o p m e n t a n d d e ­ dated to around 18.000 ± 2 0 0 B P with dwarf birch, cay o f frost mounds. From palaeogeographic investi­ gations it is k n o w n that frost m o u n d s existed during the last i c e a g e in N W - E u r o p e ( D E G A N S , 1 9 8 1 , PisS A R T , 1 9 8 3 , W A T S O N , 1 9 7 7 ) . Frost mounds o f various kinds, such as pingos a n d palsas, develop a n d d e ­ cay naturally within permafrost e n v i r o n m e n s t o d a y without c h a n g e s o f climatic conditions ( M A C K A Y ,

Figure 2: L o c a t i o n o f S t o k e r s d o b b e ( S ) , F r o s l e v ( F ) a n d Vittarp ( V ) .

grasses, s e d g e s and herbs ( P A R I S et al., 1 9 7 9 ) . A sim­ plified version o f this diagram is s h o w n in Fig. 3 . If n o further information h a d b e e n available from this locality it might have b e e n suggested that this v e g e -

ETJ ic.

ORGANIC D I R E C T I O N OF F L O W

Figure 1: S c e m a t i c outline o f g r o w t h a n d d e c a y o f a frost m o u n d . T h e y o u n g e s t part is at t h e t o p . and the a g e o f t h e form i n c r e a s e s d o w n w a r d o f t h e figure.

1 9 7 9 ) . Figure f shows t h e s c e m a t i c d e v e l o p m e n t o f a frost m o u n d under present periglacial c o n d i t i o n s .

Frost m o u n d s have a c o r e o f ice, and with time this core g r o w s in hight rather than in diameter ( M A C K A Y , 1 9 7 9 ) . With time the sides b e c o m e steeper, s o that o p e n c r a c k s d e v e l o p at t h e summit, and the sedi­ ment a n d vegetation o n t h e sides b e c o m e unstable and c r e e p s / s l u m p s d o w n w a r d w h e r e it a c c u m u l a t e s along the perimeter o f t h e form. O n c e the i c e c o r e has b e c o m e e x p o s e d to t h e air a n d sun, melting o c curs ( M A C K A Y , 1 9 7 9 ) . W h e n t h e i c e core has m e l t e d ,

a lake remains surrounded b y a ring wall, a rampart, o f sediments a n d plant r e m a i n s that originate from the sides o f the p i n g o ( M A C K A Y ,

1986).

Figure 3: Simplified pollen d i a g r a m f o n n S t o k e r s d o b b e . T h e d e p t h s are in c m a b o v e s e a level. After PARIS et al. ( 1 9 7 9 ) .

IS

ELSE KOLSTRUP

tation c o u l d represent a relatively warm phase b e ­ tween t w o colder periods. H o w e v e r , the geological information provided b y P A R I S et al. ( 1 9 7 9 ) indi­ cates that the organic material w a s found in a pingo rampart. Therefore it is p r o b a b l e that the vegetation represented by the pollen diagram should b e s e e n as a slope product, w h i c h represents the time o f pingo growth. T h e o n s e t a n d termination o f accumulation o f organic material might c o n s e q u e n t l y b e interpret­ ed as t h e result o f a local p h e n o m e n o n without c h a n g e o f climatic conditions.

This c o n c l u s i o n d o e s not e x c l u d e the possibility o f climatic c h a n g e as an underlying factor for the devel­ opment, but o n c e there are natural, non-climatic al­ ternative explanations to the reconstruction o f a s u c ­ cession o f events, a proposal o f climatic change from such data n e e d s additional e v i d e n c e from c o n t e m ­ poraneous comparable developments.

3 T h e e x a m p l e o f fires In the Taiga o f NW-Canada a n d Alaska natural fires ignited b y lightning o c c u r regularly ( V I E R E C K ,

1983).

This m e a n s that in areas with thLtnderstorms and p r e s e n c e o f w o o d y material, there is a possibility o f fires a n d s u b s e q u e n t deposition o f btirnt organic material.

It is s o m e w h a t umisual t o find traces of fires in ice age sediment, but during the last years, 3 Weichseli­ an localities with burnt w o o d o r charcoal particles have b e e n found in D e n m a r k .

O n e locality is located near Froslev in southern Den­ mark (Fig. 2 ) . In that area large p i e c e s o f btirnt w o o d of juniper (Juniperus) w a s found with regular intervals over s o m e kilometers ( K O L S T R U E & H A V E M A N N , 1 9 8 4 ) .

In most localities the w o o d w a s found within fluvial sediments and therefore redeposited, but in two lo­ calities it w a s found in situ overlain by aeolian sedi­ ment. Radiocarbon dates o f c. 5 0 . 0 0 0 BP places the burning o f a vegetation with juniper growth within the Weichselian.

In t w o localities near Varde in western Jutland microscopic charcoal particles w e r e found during pollen countings o f a deposit which may b e o f O d derade

or

post-Odderade

age ( K O L S T R U P

1992).

A

simplified pollen diagram from the locality, Vittarp 1, is shown in Fig. 4 . T h e diagram has s o m e Pinus a n d Betula as well as C y p e r a c e a e a n d P o a c e a e . Further there is p r e s e n c e o f Calluna w h i c h has a m a x i m u m in sample 4 coinciding with a m a x i m u m o f charcoal particles longer than 1 0 pm. A b o v e that level the per­ centage o f Pinus decreases a n d that o f Betula in­ creases. It is thought that a fire d a m a g e d the vegeta­ tion in the surroundings. Calluna w h i c h can reestab­ lish itself relatively well after fires benefited from the fire in the competition with other taxa. It is possible that Pinus b e c a m e d a m a g e d b y the fire, and that the

,

50'/^

L . ' . ' l SILT.SMC

W vi Figure

a::::

4 : Simplified

pollen

diagram

from

Vittarp.

After

KOLSTRUP ( 1 9 9 2 ) .

c h a n g e in the p o l l e n diagram represents a c h a n g e in the local vegetation after the fire. I f that was the c a ­ se, it m e a n s that c h a n g e s in local vegetation a n d e n ­ vironment, c o u l d h a v e taken p l a c e without c h a n g e o f climatic conditions. It is also p o s s i b l e that the ter­ mination o f deposition o f organic material might merely represent a supply of m i n e r o g e n i c sediment owing to e x p o s e d soil surfaces.

Also this kind o f situation has c o n s e q u e n c e s for the palaeoclimatic reconstruction; b e c a u s e , if a c c u m u l a ­ tion o f organic material was intermpted due t o soil surface instability (in this case restilting from fire), it m e a n s that t h e reconstruction o f past vegetational developments m a y turn out to b e very c o m p l e x , a n d that great care h a s to b e taken w h e n using, for e x ­ ample, the mutual AP and NAP p o l l e n p e r c e n t a g e relationship for climatic reconstruction ( s e e also KOLSTRUP,

1990).

It follows that a l s o the example with carcoal points to the necessity t o include and integrate a n u m b e r o f c o n t e m p o r a n e o u s developments in order t o d e c i d e if a recorded c h a n g e was the result o f climatic o r local c h a n g e .

4 T h e importance o f dating T h e possibilities o f alternative interpretations as t o local versus regional palaeoenvironmental c h a n g e s put a hard pressure o n the available dating m e t h o d s , but s o m e results with relation t o the present discus­ sion have already b e e n obtained. F r o m radiocarbon datings it s e e m s as if there is, for e x a m p l e , n o l o n g e r a clustering o f clatings within what w a s previously thought to b e Middle Pleniglacial interstadials.

Instead the datings are more e v e n l y distributed ( R A N , 1 9 9 0 ) an argument in favour o f t h e idea o f vegetations having b e e n dependant o n local condi­ tions in addition t o climatic c h a n g e ( s e e also KOLSTRUP,

1990).

Future investigations might, apart from the 1 4 C m e ­ thod, also m a k e u s e o f the t h e r m o l u m i n e s c e n c e a n d the optically stimulated light m e t h o d s o n W e i c h s e l i ­ an aeolian s e d i m e n t s collected at geologically thorougly investigated localities.

E x a m p l e s o f W e i c h s e l i a n e n v i r o n m e n t s : local v e r s u s regional d e v e l o p m e n t s

J.,

5 Conclusions T h e a b o v e e x a m p l e s are o n l y s i n g l e o n e s , and m a n y m o r e form o t h e r g e o l o g i c a l situations, such as for e x a m p l e d u n e slacks and a b a n d o n e d stream c h a n ­ nels, c o u l d h a v e b e e n m e n t i o n e d . B e s i d e s , b o t h t h e e x a m p l e o f frost m o u n d a n d fire are r e p r e s e n t e d b y single localities, a n d t h e r e f o r e t h e y provide insuffi­ cient data t o m a k e general c o n c l u s i o n s from. It fol­ lows that t h e present p a p e r c a n only b e regarded as a basis for d i s c u s s i o n with relation to future s y s t e m ­ atic investigations. If s u c h investigations c a n

take

into a c c o u n t t h e discussion o n local versus r e g i o n a l conditions from land data for a n u m b e r o f localities, it may b e c o m e possible to establish holistic p i c t u r e s o f past e n v i r o n m e n t s at a g i v e n time, and

subse­

quently to a r r a n g e these p i c t u r e s c h r o n o l o g i c a l l y s o that m a n y - s i d e d , detailed d e v e l o p m e n t s c a n b e re­ c o n s t r u c t e d . I f such an a p p r o a c h o f effect-cause r e ­ lationship c a n b e successfully m a d e , it will lead to an i m p r o v e d understanding of t h e c o m p l e x i t y that w a s also p r e s e n t in the nature o f the past, and t h e r e b y it can serve as a strong tool in t h e prediction o f future climatic a n d e n v i r o n m e n t a l c h a n g e s .

Acknowledgements I am very grateful to Dr. J . Klostermann w h o stimu­ lated m e t o write this p a p e r b a s e d o n a lecture g i v e n at the D E U Q I I A meeting in Kiel and for his translati­ on o f t h e Kurzfassung. T h e field investigations that provided t h e D a n i s h data w e r e financially s u p p o r t e d by the C a r l s b e r g Foundation a n d the Danish Natural S c i e n c e R e s e a r c h Council.

6 References (1981): T h e D r e n t s c h e Aa valley system. A stu­ dy in q u a t e r n a r y g e o l o g y . T h e s i s Vrije Universiteit te A m s t e r d a m . - R o d o p i A m s t e r d a m . 132 pp.

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STAUFFER,

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W A T S O N , E . ( 1 9 7 7 ) : T h e Periglacial E n v i r o n m e n t . T h e p e ­ riglacial e n v i r o n m e n t o f G r e a t Britain d u r i n g t h e D e v e n s i a n . - Phil. Trans. R. S o c . Lend. B . 2 8 0 : 1 8 3 - 1 9 8 ; G r e a t Britain.

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K . , G U N D E S T R U P , N . , H A M M E R , C . U . . EVERSEN, P . J O U Z E L ,

19

Manuscript a c c e p t e d 19. 1 1 . 1 9 9 2