Issuu on Google+

Eiszeitalter

u.

Gegenwart

29

189—200 7 fig.

Hannover

1979

Remarks on the Genesis of Subglacial Channels in Northern Poland Upper Pleistocene, channel, fluviatile erosion, glacial erosion, glacier, glacial lake NW-Polish Lowlands MlCHAL PASIERBSKI *)

A b s t r a c t : The origin of the majority of subglacial channels and similar valleys in Nothern Poland, taking in account their character and differenciated shape (narrow, deep, long and curved) is connected w i t h erosional a c t i v i t y of subglacial waters. But the author based on several examples shows, that some of these channels have a more combined genesis, when the main factor has been the inland ice (narrow, small ice tongues). [Zur G e n e s e subglaziärer R i n n e n t ä l e r im nördlichen Polen] Kurzfassung: Die Entstehung der meisten subglaziären Rinnentäler sowie ähnlicher Talformen in Nordpolen w i r d ihrer Eigenschaften wegen (eng, tief, lang und gewunden) allge­ mein mit der Erosionstätigkeit der subglazialen Wässer in Verbindung gebracht. Der Verfasser zeigt an ausgewählten Beispielen, daß ein Teil dieser Rinnentäler eine mehrfach kombinierte Entstehung aufweist, wobei als Hauptagens schmale und kleine erodierende Eisloben infrage kommen. S t r e s z c z e n i e : Geneza wiekszosc.i rynien subglacjalnych oraz dolin o podobnym charakterze w Polsce Polnocnej, biorac pod uwage^ ich zroznicowany ksztalt (wqskie, glebokie, dlugie i kr^te) u w a z a n a jest powszechnie jako w y n i k erozyjnej dzialalnosci wod subglacjalnych. Autor w oparciu o w y b r a n e przyklady wykazuje, ze niektöre z tych rynien majq bardzicj zlozona, genez^, gdzie g l o w n y m czynnikiem w ich formowaniu ostatecznego ksztaltu byl l^dolod (w^skie, male loby lodowcowe). Preface S u b g l a c i a l channels a r e l a n d f o r m s c h a r a c t e r i s t i c of a g l a c i a l e n v i r o n m e n t , t h e y occur in a r e a s of ground m o r a i n e s a n d o u t w a s h e s as w e l l a s of e n d m o r a i n e s , a n d t h e y cut across p r a d o l i n a s a n d f l u v i a l v a l l e y s . A l s o c h a r a c t e r i s t i c is t h a t as r u l e t h e y r u n p a r a l l e l to each o t h e r . W h e r e t h e y meet an o b s t r u c t i o n t h e y e i t h e r e n d t h e i r run, or t h e y k e e p going m e r e l y c h a n g i n g t h e i r direction. S o m e t i m e s t h e y a p p e a r in a f a n - l i k e p a t t e r n , s h o w i n g differences i n w i d t h s a n d c h a n g e s in d e p t h s , it a l s o h a p p e n s t h a t such channels cross each other a t v a r i o u s angles. T h e floor r e l i e f of the s u b g l a c i a l channels is r a g g e d a n d u n e v e n , their l o n g p r o f i l e s show n u m e r o u s steps a n d o v e r d e e p e n i n g s , these l a t t e r fil­ led w i t h l a k e w a t e r . N e a r the i n l a n d ice m a r g i n t h e s u b g l a c i a l channels b r e a k off, e n d i n g t h e i r run, this f e a t u r e GALON ( 1 9 6 5 ) considers e v i d e n c e of the f a r t h e s t e x t e n t of the L a s t G l a c i a t i o n . After M A J D A N O W S K I

( 1 9 5 0 ) the s u b g l a c i a l c h a n n e l s o c c u r in highest

concentration

in the e n d m o r a i n e z o n e , n e x t come m o r a i n e p l a t e a u s w h i l e o u t w a s h sheets r e v e a l differ­ ences in channel d e n s i t y . W h e r e a s a l l c h a r a c t e r i s t i c f e a t u r e s of s u b g l a c i a l c h a n n e l s a r e Address of the author: Dr. M. P a s i e r b s k i , Dep. of Geogr. Nicholas Copernicus Univer­ sity, ul. Fredry 8. 87-100 Torun, Poland.


1.90

Michal Pasierbski

k n o w n for a l o n g t i m e , t h e p r o b l e m of t h e i r o r i g i n c o n t i n u e s to be one of t h e m o o t p o i n t s l a c k i n g a s a t i s f a c t o r y e x p l a n a t i o n i n g l a c i a l e n v i r o n m e n t , a n d therefore is often t h e o b 足 ject of c o n t r o v e r s i e s .

Evolution

of o p i n i o n s

about

the origin

of s u b g l a c i a l

channels

T h e oldest c o n c e p t of h o w such c h a n n e l s m a y h a v e d e v e l o p e d w a s w h a t w a s c a l l e d t h e " t e c t o n i c c o n c e p t " a t t h a t t i m e p u t f o r w a r d b y BERENDT ( 1 8 6 3 ) . S e v e r a l y e a r s l a t e r BERENDT ( 1 8 7 9 ) t o o k it for g r a n t e d t h a t these c h a n n e l s h a d o r i g i n a t e d i n i c e c r e v a s s e s as t h e effect of m e l t w a t e r a c t i o n . N e x t i t w a s JENTZSCH ( 1 8 8 4 ) in w h o s e belief these channels w e r e of s u b g l a c i a l o r i g i n , a n d i n h i s o p i n i o n t h e d i r e c t i o n of s u b g l a c i a l s t r e a m s m i g h t often h a v e been i n d e p e n d e n t of t h e d i r e c t i o n in w h i c h t h e ice w a s m o v i n g . In KOZARSKI'S ( 1 9 6 6 / 7 ) o p i n i o n JENTZSCH c a m e v e r y n e a r to i n t r o d u c i n g h y d r o s t a t i c p r e s s u r e i n t o t h e process of channel f o r m a t i o n , b u t finally i t w a s USSING ( 1 9 0 3 ) , a n d after h i m W E R T H ( 1 9 0 7 ) , w h o took this s t a n d . I n this m a t t e r u n c o m m o n l y i m p o r t a n t w e r e t h e o b s e r v a t i o n s m a d e b y USSING. O n J u t l a n d this scientist observed a close i n t e r r e l a t i o n b e t w e e n s u b g l a c i a l c h a n n e l s a n d t h e s t a r t i n g p o i n t s of o u t w a s h sheets i s s u i n g from chan足 nel o u t l e t s in t h e s h a p e of w i d e s p r e a d c o n e s . USSING'S d i s c o v e r y of this r e c u r r e n c e b e c a m e a n i m p o r t a n t e l e m e n t in c o n t r o v e r s i e s a b o u t t h e e r o s i v e character of s u b g l a c i a l channels. T h e problematics introducted b y USSING w e r e later considerably e x p a n d e d a n d documen足 ted by WERTH ( 1 9 0 8 / 9 ) .

A s e p a r a t e p a g e in i n v e s t i g a t i o n s of s u b g l a c i a l channels refers to research w o r k b y W O L D S T E D T ( 1 9 2 3 , 1 9 2 6 , 1 9 5 2 , 1 9 5 4 ) . I n i t i a l l y he w a s i n full a c c o r d w i t h U S S I N G ' S ( 1 9 0 3 )

a n d WERTH'S ( 1 9 0 8 / 9 ) opinions, t r y i n g t o s u p l e m e n t t h e m b y his o w n field w o r k in t h e n o r t h e r n p a r t s of G e r m a n y a n d P o l a n d . H o w e v e r , g r a d u a l l y WOLDSTEDT c o m e to p r e f e r a different c o n c e p t : h e assumed t h a t p a r t of t h e s u b g l a c i a l channels those of c o n s i d e r a b l e w i d t h , m a y h a v e o r i g i n a t e d from t h e e r o s i v e a c t i o n of g l a c i e r lobes. T h i s e x p l a i n s w h y in 1 9 2 9 h e m a i n t a i n e d t h a t a n y sort of channels f o r m a t i o n is c o n n e c t e d w i t h g l a c i a l erosion, this belief h e k e p t u p u n t i l 1 9 5 2 , w i t h t h e definite assertion t h a t i n t h e a r e a of t h e L a s t G l a c i a t i o n t h e s u b g l a c i a l c h a n n e l s h a v e r e s u l t e d from a n e r o s i v e a c t i o n of t h e i n l a n d i c e , w h i l e n o t d i s p u t i n g s o m e c o - a c t i o n of m e l t w a t e r s t r e a m s i n t h i s process, he e m p h a s i z e d t h a t t h e i r p a r t used to be l i m i t e d to t h e i n i t i a l stage of dissection of t h e s u b 足 s t r a t u m w h i c h , s u b s e q u e n t l y , w a s s c u l p t u r e d b y t h e i n l a n d ice. In h i s field e x a m i n a t i o n s WOLDSTEDT u s e d t o scrutinize t h e w i d e l y r a d i a t i n g e n d depressions k n o w n f r o m t h e A l p i n e f o r e l a n d . I n h i s a t t e m p t of d i s c e r n i n g r e s e m b l i n g e x a m p l e s i n l o w l a n d a r e a s h e d i s c o v e r e d s i m i l a r i t i e s i n t h e O d r a l o b e w h e r e he b e l i e v e d t h e channels of t h e P r e n z l a u a n d t h e R a n d o w r i v e r s a s w e l l a s t h e v a l l e y s of t h e l o w e r O d r a a n d of L a k e M i e d w i e to h a v e been s c u l p t u r e d b y t h e a c t i o n of n a r r o w g l a c i a l lobes. In a d d i t i o n WOLDSTEDT i n d i c a t e d e x a m p l e s f r o m N o r t h A m e r i c a ( L a k e M i c h i g a n ) , from t h e B a l t i c b a s i n a n d from F e n n o s c a n d i a w h e r e h e a l s o b e l i e v e d t h e c h a n n e l s to h a v e d e v e l o p e d d u e to g l a c i a l erosion. H o w e v e r , some v a c i l l a t i o n in w h a t h e u s e d to b e l i e v e c a n l a t e r be o b s e r v e d i n W O L D STEDT'S book " D a s E i s z e i t a l t e r " p u b l i s h e d i n 1 9 5 4 , w h e r e h e s p e a k s less d e c i s i v e l y a b o u t t h e g l a c i a l o r i g i n of s u b g l a c i a l c h a n n e l s . WOLDSTEDT'S c o n c e p t s g a i n e d b o t h s u p p o r t e r s a n d opponents. O n e of t h e f o r m e r w h o t o o k u p a n d p u r s u e d this concept w a s JASPERSEN ( 1 9 5 3 ) w h o d u r i n g h i s field studies on the C y m b r i a n p e n i n s u l a a t t e m p t e d t o a p p l y to f u r t h e r a r e a s t h e results he o b s e r v e d here. A l s o a f o l l o w e r of a g l a c i a l o r i g i n of t h e c h a n n e l s seems to h a v e been LIEDTKE ( 1 9 7 5 ) . T h i s scientist, c o m m e n t i n g upon USSING'S ( 1 9 0 3 ) s u g g e s t i o n s about t h e close r e l a t i o n s of o u t w a s h sheets t o g l a c i a l channels, a r r i v e d a t t h e c o n c l u s i o n t h a t o u t w a s h sheets d o not


Remarks on trie Genesis of Subglacial Channels in Northern Poland

191

a l w a y s h a v e t o be c o n n e c t e d w i t h g l a c i a l c h a n n e l s . A s an e x a m p l e h e i n d i c a t e s t h e 7 0 0 k m p a r t of a P o m e r a n i a n e n d m o r a i n e w h e r e o u t w a s h p l a i n s c o v e r a s much as 6 5 0 k m w h i l e the a r e a of a g r o u n d m o r a i n e is l i m i t e d t o 5 0 k m . This e v i d e n c e m a d e h i m a s s u m e t h a t g l a c i a l c h a n n e l s w e r e b y n o m e a n s the o n l y s o u r c e t h a t used to s u p p l y the s a n d y deposits forming o u t w a s h p l a i n s . A n a d d i t i o n a l a r g u m e n t p u t f o r w a r d b y LIEDTKE ( 1 9 7 5 ) , i n ­ c i d e n t a l l y e n d o r s i n g WOLDSTEDT'S concept, is t h e presence of s t e p s in t h e s u b g l a c i a l chan­ nels, he c o m p a r e s them w i t h s i m i l a r steps o b s e r v e d in fiords a n d A l p i n e v a l l e y s . F u r t h e r ­ more LIEDTKE c a l l s a t t e n t i o n t o a n o t h e r of h i s o b s e r v a t i o n s : h o w t h e s u b g l a c i a l channels g r o w m o r e n a r r o w a n d less d e e p w h e r e t h e y a p p r o a c h the l i n e of t h e i n l a n d i c e m a r g i n . In his o p i n i o n , t h e g e o m o r p h o l o g i c a l a c t i o n of w a t e r should b e most effective a t p l a c e s w h e r e s u b g l a c i a l w a t e r s issue, therefore h e r e t h e channels s h o u l d be deepest. N o t w i t h ­ s t a n d i n g a l l t h e a b o v e a r g u m e n t s , LIEDTKE a l s o p e r c e i v e d o t h e r e v i d e n c e t h a t c o n t r a d i c t s a g l a c i a l o r i g i n of the c h a n n e l s , such a s : t h e i r w i n d i n g r u n , t h e i r f a n - l i k e p a t t e r n , a n d other d e t a i l s . U l t i m a t e l y h e a d m i t s this p r o b l e m t o be a difficult one, a n d t h a t i n d e l i ­ b e r a t i n g a b o u t t h e o r i g i n of t h e channels m a i n l y i n t o a c c o u n t s h o u l d be t a k e n : g l a c i a l erosion, e r o s i o n b y s u b g l a c i a l w a t e r s , p a r t l y a l s o specific t e c t o n i c s even processes of salt leaching c a u s i n g t h e f o r m a t i o n of i n i t i a l d e p r e s s i o n s . H e a d v i s e s t h a t , u p to t h e t i m e a definite e x p l a n a t i o n of t h e o r i g i n of these c h a n n e l s is s e c u r e d , t h e y should be c a l l e d glacial channels. In P o l i s h l i t e r a t u r e WOLDSTEDT'S o p i n i o n s w e r e t a k e n u p b y KONDRACKI ( 1 9 6 5 ) in whose belief t h e channel d i m e n s i o n s ( t h e i r c o n s i d e r a b l e w i d t h s ) p r e c l u d e a s s u m i n g t h e m to h a v e o r i g i n a t e d from a n e r o s i v e a c t i o n of f l o w i n g w a t e r . O n t h e o t h e r h a n d K O Z A R S K I ( 1 9 6 6 / 7 ) i n s i s t s , t h a t o n l y a m i n o r p a r t of t h e channels o b s e r v e d i n P o l a n d a n d i n the G e r m a n P l a i n m a y h a v e been formed b y g l a c i a l erosion. H e feels u n a b l e to a g r e e w i t h WOLDSTEDT'S concepts in t h e i r full scope, b e c a u s e in his o w n o p i n i o n most of t h e chan­ nels a r e s m a l l a n d r u n in a w i n d i n g course, a n d n e a r g l a c i t e c t o n i c d i s t u r b a n c e s t h e y a r e altogether lacking.

A u t h o r s l i k e NECHAY

(1932),

MAJDANOWSKI ( 1 9 5 0 ) ,

GALON

(1965)

a n d others a g r e e in t h e i r p u b l i c a t i o n s t h a t t h e p r i n c i p a l a g e n t f o r m i n g these channels must h a v e b e e n m e l t w a t e r s t r e a m s . Even so, t h i s in no w a y p r e c l u d e s the p o s s i b i l i t y t h a t the channels m i g h t h a v e been s e c o n d a r i l y t r a n s f o r m e d b y n a r r o w g l a c i e r lobes. E x a m p l e s of such processes, t h o u g h b u t f e w , a r e k n o w n f r o m l i t e r a t u r e ( G A L O N 1 9 5 2 ; ROSZKOWNA 1 9 6 4 ; K O Z A R S K I 1 9 6 5 ; PASIERBSKI 1 9 7 3 , 1 9 7 5 ) .

As c a n b e seen, this brief s u r v e y of r e l e v a n t l i t e r a t u r e discloses t h a t , o u t s t a n d i n g a n d c o n s t a n t l y r e c u r r i n g in c o n t r o v e r s i e s a b o u t t h e o r i g i n of t h e c h a n n e l s , a r e t w o c o n c e p t s in which t h e m a i n a g e n t is e i t h e r g l a c i a l e r o s i o n or erosion b y s u b g l a c i a l w a t e r s . H o w ­ ever, i t s h o u l d be k e p t i n m i n d t h a t often t h e s e t w o processes w e r e s u p e r i m p o s e d u p o n each other, t h a t one m a y h a v e c l e a r e d the w a y t o t h e other, a n d c o n v e r s e l y .

Area

of

research

In the p r e s e n t s t u d y t h e a u t h o r p u r p o s e l y s e l e c t e d such c h a n n e l s in N o r t h e r n P o l a n d w h o s e f e a t u r e s a d m i t t e d t h e a s s u m p t i o n t h a t t h e y h a v e r e s u l t e d from the c o - a c t i o n of g l a c i a l lobes a n d relief m a d e it possible t o c o r r e l a t e them w i t h l a n d f o r m s c l a s s i c a l in this respect, such a s t h e T o l l e n s e - S e e Becken ( J A N K E 1 9 6 1 ) a n d t h e M a l c h i n e r Becken (REIN­ HARD & RICHTER 1 9 5 8 ) , b u t w h e r e definite g e o l o g i c a l e v i d e n c e w a s l a c k i n g . W o r t h m e n ­ tioning a r e : 1 . t h e channel of Z a r n o w i e c k i e L a k e , 2 . the channel of C h a r z y k o w y L a k e , 3 . the channel of L a k e M i e d w i e (Fig. 1 ) .


Fig. 1: Subglacial channels of the last glaciation in Poland (after GALON 1 9 7 2 ) . 1. subglacial chan足 nels; 2 . subglacial channels transformed by rivers; 3 . areas discussed by the author.


Remarks on the Genesis of Subglacial Channels in Northern Poland

193

1. T h e channel of Z a r n o w i e c k i e L a k e S i t u a t e d f a i r l y close t o t h e B a l t i c shore this c h a n n e l passes t w o g e n e t i c a l l y d i v e r g e n t g e o m o r p h o l o g i c a l u n i t s : a m o r a i n e p l a t e a u a n d a n a c c u m u l a t i o n l o w l a n d . T h e l e n g t h of this channel i s s o m e 1 2 k m , 2 / 3 of which is o c c u p i e d b y Z a r n o w i e c k i e L a k e . I n i t s n o r ­ t h e r n p a r t w h e r e t h e t w o g e o m o r p h o l o g i c a l u n i t s a d j o i n each o t h e r , t h e channel is w i d e s t , u p t o a b o u t 3 k m , i n s o u t h w a r d d i r e c t i o n it g r o w s n a r r o w e r t o a b o u t 2 k m a n d a t t h e channel o u t l e t a r a d i a l s y s t e m of channels c a n b e o b s e r w e d t h a t b e a r s features different from those d e s c r i b e d a b o v e . A l o n g both slopes of t h e channel t h e m o r a i n e p l a t e a u rises to 1 1 0 m a.s.l., f u r t h e r on s u b s i d i n g g r a d u a l l y s o m e 4 0 m — s e e m i n g l y this is t h e p i c t u r e of a n a s y m e t r i c a l r i d g e s u r r o u n d i n g t h e c h a n n e l f r o m east a n d w e s t . T h e c o n s i d e r a b l e difference b e t w e e n t h e s u r f a c e of t h e m o r a i n e p l a t e a u a n d t h e w a t e r level in t h e l a k e a m o u n t i n g t o 8 0 — 1 0 0 m — l e d to h e a v y d i s s e c t i o n of t h e c h a n n e l scarps b y r a i n f a l l a n d g r o u n d w a t e r . Z a r n o w i e c k i e L a k e o c c u p i e s a l m o s t t h e w h o l e w i d t h of t h e c h a n n e l , its floor is l e v e l c o n s t i t u t i n g w h a t is c a l l e d a c r y p t o d e p r e s s i o n . I t w a s p r o b a b l y t h e s h a p e of t h e channel a n d of e l e v a t i o n s u r r o u n d i n g t h e channel t h a t m a d e SONNTAG ( 1 9 1 1 ) p u t f o r w a r d h i s thesis t h a t a n arch of e n d m o r a i n e s i s s u r r o u n d i n g t h e channel, a n d t h a t these e n d m o r a i n e s a r e t h e result of a d i l a t i o n of t h e c h a n n e l b y a n a r r o w g l a c i a l lobe. T o s o m e e x t e n t SONNTAG'S o p i n i o n w a s c r i t i c i z e d b y P A W L O W S K I ( 1 9 2 2 ) a n d , l a t e r on, b y Z A B O R S K I

( 1 9 3 3 ) . B o t h d i s p u t e d t h e e x i s t e n c e of a n e n d m o r a i n e arch s u r r o u n d i n g t h e l a k e ; after ZABORSKI these e l e v a t i o n s w e r e f o r m e d b y some d i l a t i o n of t h e c h a n n e l b y a g l a c i e r lobe, b u t t o h i m t h e y d o n o t b e a r t h e features of e n d m o r a i n e s . L a t e r o n this opinion w a s a l s o u p h e l d b y ROSZKOWNA ( 1 9 6 4 ) w h o reports s u c c e s s i v e stages of f o r m a t i o n a n d d e c a y of the g l a c i e r lobe a n d i n d i c a t e s t h a t d r a i n a g e used t o p r o c e e d h e r e i n s o u t h w a r d d i r e c t i o n .

Fig. 2: Areal distribution of floes of Tertiary deposits around of Zarnowieckie Lake. 1. floes of Tertiary deposits; 2. altitudinal poinM. 13

Eiszeitalter u. Gegenwart


Michal Pasierbski

194

F i e l d i n v e s t i g a t i o n s c a r r i e d on b y the p r e s e n t a u t h o r in the s p r i n g of 1 9 7 7 r e v e a l e d on the f r i n g e of t h e coastal l o w l a n d a n d in t h e v i c i n i t y of the c h a n n e l the p r e s e n c e of M i o c e n e floes in t h e Q u a t e r n a r y d e p o s i t s ( F i g . 2 ) . F u r t h e r m o r e , a d e t a i l e d a n a l i s i s of t h e g e o l o g i c a l s t r u c t u r e , d o w n w a r d f r o m the surface of the m o r a i n e p l a t e a u to the c h a n n e l b o t t o m , d i s c l o s e d g l a c i t e c t o n i c d i s t u r b a n c e s of a n a s y m m e t r i c a l t y p e ; u p r i g h t folds, a n d h o r i z o n t a l shifting of s t r a t a ( F i g . 3 ) . M o s t d i s t i n c t l y v i s i b l e w e r e t h e s e p h e n o m e n a h a l f ­ w a y d o w n t h e channel s c a r p , f u r t h e r d o w n t h e y a r e concealed b y s a n d y deposits, w h i c h h e r e form n a r r o w level of k ä m e t e r r a c e .

TT!! Fig. 3: Simplified geological section across of the Zarnowiec channel. 1. boulder c l a y ; 2. sands and gravels with boulders; 3. sands; 4. peat.

T h e p r e s e n c e of floes as w e l l as t h e d i s c o v e r y of g l a c i t e c t o n i c s t r u c t u r e s in the c h a n n e l e n t o u r a g e c o n s t i t u t e the missing l i n k a m o n g testimonies for a g l a c i a l o r i g i n of the Z a r n o w i e c k i e L a k e channel. T h i s confirms h o w c o r r e c t w a s SONNTAG'S ( 1 9 1 1 ) c o n c e p t a n d the o p i n i o n s of ZABORSKI ( 1 9 3 3 ) a n d ROSZKOWNA ( 1 9 6 4 ) a s w e l l , a l l of w h o m c o n ­ t e m p l a t e d this p r o b l e m b y k e e p i n g g e o m o r p h o l o g i c a l elements in m i n d . The a n a l y s i s of t h e l o c a l g e o l o g i c a l s t r u c t u r e i n d i c a t e s in the s u b s t r a t u m of the c h a n n e l the e x i s t e n c e of a fossil v a l l e y of c o n s i d e r a b l e d e p t h , b e c a u s e in t h e a x i s of this v a l l e y a l l g l a c i a l d e p o s i t s h a v e been d e s t r o y e d . This o b s e r v a t i o n is in so f a r essential as it s h o w s the p a r t p l a y e d b y depressions a n d b y v a l l e y s r u n n i n g p a r a l l e l w i t h the d i r e c t i o n of a d v a n c i n g i n l a n d ice, t h e y f a c i l i t a t e d differences in t h e r a t e of t h e ice motion w i t h i n the zone of t h e ice m a r g i n , a n d in consequence l e d to t h e f o r m a t i o n of g l a c i e r lobes of different sizes.


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2. T h e channel of C h a r z y k o w y L a k e S i t u a t e d w h e r e t h e B r d a o u t w a s h p l a i n a n d t h e K r a y n a P l a t e a u a r e in c o n t a c t , t h i s channel r u n s in N — S d i r e c t i o n a n d in its l e n g t h of 17 k m s h o w s a c o n s i d e r a b l e w i d t h , from 2 to 2,5 k m . T h e southern b a n k of the c h a n n e l , incised in a m o r a i n e p l a t e a u , is e n ­ closed b y an a s y m m e t r i c a l arch of e n d m o r a i n e s , c r e a t i n g the i m p r e s s i o n of a w i d e s p r e a d a m p h i t h e a t r e . T h e e a s t e r n w i n g of this arch is r a t h e r i n d i s t i n c t d u e to t h e presence t h e r e of m a n y n a r r o w c h a n n e l s e x t e n d i n g a t different e l e v a t i o n s ; in t h e i r p a t t e r n t h e y r e s e m b l e a f a n issuing f r o m o u t l e t of the c h a r z y k o w y c h a n n e l . Both the s h a p e a n d the p a t t e r n of t h e s u b g l a c i a l c h a n n e l s which occur here in a f a i r l y dense n e t w o r k , w i t h N — S , N W — S E a n d N E — S W d i r e c t i o n s p r e v a i l i n g c l e a r l y i n d i c a t e t h e i r being of a n o l d e r a g e t h e n t h e w i d e c h a r z y k o w y c h a n n e l w h i c h — a l t h o u g h s e e m i n g l y it m a y h a v e d e v e l o p e d from o n e of t h e s u b g l a c i a l c h a n n e l s — its p r e s e n t - d a y a p p e a r e n c e is d e f i n i t e l y d u e to the e r o s i v e a c t i o n of a n a r r o w g l a c i e r lobe ( F i g . 4 ) . B y t h e w a y , this a u t h o r h a s been v o i c i n g t h i s s a m e o p i n i o n a t a n e a r l i e r d a t e w h i l e s t u d y i n g t h e g e o l o g i c a l s t r u c t u r e of this r e g i o n (PASIERBSKI 1 9 7 5 ) .

Fig. 4: Arrangement and width of subglacial channels in comparison with C h a r z y k o w y L a k e basin. 1. subglacial channels. In their m a j o r i t y t h e s u b g l a c i a l channels of t h e K r a y n a P l a t e a u a r e n a r r o w , w i n d i n g a n d v e r y deep. S o m e of t h a n dissect the Q u a t e r n a r y deposits to such e x t e n t t h a t t h e i r b o t t o m s l i e often i n M i o c e n e deposits. U n d e r t h e l a c u s t r i n e a n d o u t w a s h deposits a p p e a r s in t h e c h a r z y k o w y channel the b o u l d e r c l a y of t h e P o z n a n S t a g e ( F r a n k f u r t ) ( F i g . 5 ) . T h i s b o u l d e r c l a y a p p e a r s also in the southern b a n k of the channel w h e r e it is s p r e a d o v e r some glacitectonically upthrusted sands and g r a v e l s . 13

*


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Micha! Pasierbski

3. T h e channel of L a k e M i e d w i e S i t u a t e d in the c e n t r a l p a r t of the O d r a l o b e a n d e x t e n d i n g i n N — S d i r e c t i o n , t h i s channel is the l a r g e s t a m o n g those described so f a r . Its l e n g t h is a b o u t 2 0 k m . Its m e a n w i d t h 2 , 5 k m , t h o u g h in t h e southern p a r t t h e w i d t h exceeds 4 k m (Fig. 6 ) . T h e first to p o i n t out the g l a c i a l c h a r a c t e r of this channel w a s WOLDSTEDT ( 1 9 5 2 ) w h o a s c r i b e d a s i m i l a r o r i g i n to the v a l l e y s of the l o w e r O d r a , t h e P r e n z l a u a n d t h e R a n d o w a l s o . L a t e r on KARCZEWSKI ( 1 9 6 5 ) e s t a b l i s h e d , w h i l e s t u d y i n g the g e o m o r p h o l o g y of the P y r z y c e L o w l a n d t h a t t h e channel of t h e L a k e M i e d w i e h a s been f o r m e d b y a n a r r o w g l a c i e r lobe a n d in s u p p o r t i n g this a s s e r t i o n he i n d i c a t e s t h e r i d g e s of u p t h r u s t e d end m o r a i n e s f l a n ­ k i n g the southern a n d s o u t h e a s t e r n b a n k of t h e channel, he e v e n e n t e r s these r i d g e s i n his m a p . H o w e v e r , t h r e e y e a r s l a t e r KARCZEWSKI ( 1 9 6 8 ) changes his v i e w point r e g a r d i n g the o r i g i n of t h e channel of L a k e M i e d w i e , b y a s s u m i n g t h a t t h e b a s i n of L a k e M i e d w i e a n d the w h o l e channel h a d o n c e been filled b y d e a d ice. A s p r o o f of this a s s u m p t i o n h e m e n t i o n s t h e o c c u r r e n c e of s e t t l i n g structures i n the i c e - d a m m e d deposits. M o r e v e r he b e l i v e s , t h a t a l s o the steep d e e p of the s t r a t a o b s e r v e d in t h e u p t h r u s t e d end m o r a i n e s a n d the p r e s e n c e of h i g h l y fissil b o u l d e r c l a y m a y be e v i d e n c e of the settling w h i c h fol­ l o w e d the d e a d ice m e l t i n g . T h e i n t e r p r e t a t i o n s u g g e s t e d b y KARCZEWSKI ( 1 9 6 8 ) c o n t a i n s some i n a c c u r a c i e s . E a s t of L a k e M i e d w i e the P y r z y c e L o w l a n d w h e r e h e d i s t i n g u i s h e d a set of levels, s h o w s a diversified r e l i e f a n d often b o u l d e r c l a y can be seen on its s u r f a c e — a fact not m e n t i o n e d b y K A R C Z E W S K I . T h e r i m s of these l e v e l s a r e i n d i s t i n c t a n d often t h e y s i m p l y p a s s i n t o each o t h e r . T h e m o r a i n e p l a t e a u , s t u d d e d w i t h d r u m l i n s , p a r t of w h i c h KARCZEWSKI ( 1 9 6 5 ) a t least b e l i e v e s to be of e r o s i v e o r i g i n , differs i n n o w a y from t h e g r o u n d level a d j o i n i n g it. N e x t to the d r u m l i n s o c c u r e s k e r r i d g e s b o t h on the p l a t e a u a n d on the h i g h e s t l e v e l of the P y r z y c e L o w l a n d . T h e close v i c i n i t y of t h e s e t w o l a n d f o r m s r e v e a l s t h a t t h e y w e r e f o r m e d d u r i n g different p e r i o d s the d r u m l i n s w h i l e the a r e a suffered g l a c i a t i o n , t h e e s k e r d u r i n g d e g l a c i a t i o n . P u t t o g e t h e r , these few r e m a r k s c o m b i n e i n t o a l o g i c a l t o t a l i n d i c a ­ t i n g the e r o s i v e o r i g i n of t h i s p a r t of the O d r a l o b e . T h e p a t t e r n in which the d r u m l i n s a n d the n a r r o w s u b g l a c i a l channels r u n n i n g p a r a l l e l w i t h t h e d r u m l i n s seem t o p r o v e t h e i r being of i d e n t i c a l a g e . O n the o t h e r h a n d t h e w i d e channel o c c u p i e d b y L a k e M i e d ­ w i e is here of l a t e r a g e , a s e c o n d a r y f o r m a t i o n , t h e s o u t h w a r d e x t e n s i o n of this c h a n n e l c a n be t r a c e d b e y o n d the O d r a lobe, but h e r e it t u r n s i r r e g u l a r a n d w i n d i n g .


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Fig. 6: Geomorphologie outline of M i e d w i e Lake surroundings (partly after KARCZEWSKI 1965). 1. moraine plateau; 2. end moraines; 3. drumlins; 4. eskers; 5. levels of P y r z y c e ice-dammed basin.

T h e e x a m i n a t i o n of the g e o l o g i c a l s t r u c t u r e of v i c i n i t y of L a k e M i e d w i e discoloses m a r k e d d i v e r g e n c e s i n t h e a l t i t u d e of t h e T e r t i a r y w h i c h rises to p a r t i c u l a r heights some 7 m b e l o w g r o u n d s u r f a c e as much a s a l o n g t h e w e s t e r n b a n k of t h e channel. T h i s h i g h p o s i t i o n of the t o p of t h e T e r t i a r y a n d the differences in the Q u a t e r n a r y deposits a l o n g t h e eastern a n d w e s t e r n side of the channel ( F i g . 7) i m p l y the p a s t occurrence of g l a c i 足 tectonic disturbances. Considering in addition the upthrusted end moraines observed b y KARCZEWSKI w h i c h b y n o m e a n s f o r t u i t o u s l y s u r r o u n d a r c h l i k e t h e southern r i m of t h e channel, it c l e a r l y a p p e a r s t h a t this v a l l e y is f o l l o w i n g the l i n e of a s u b g l a c i a l c h a n n e l d e v e l o p e d , in c o n s e q u e n c e of the e r o s i v e a c t i o n of a n a r r o w g l a c i e r lobe. A p a r t from t h e a b o v e described c h a n n e l s w h o s e g l a c i a l o r i g i n is u n q u e s t i o n a b l e , t h e r e c a n be observed q u i t e a n u m b e r of o t h e r s in N o t h e r n P o l a n d w h i c h not o n l y on a c c o u n t


198

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amrj/ r~;>

&

Fig, 7 : Simplified geological section across of the Miedwie Lake. 3. Miocene deposits.

1. boulder clay; 2. sands;

of t h e i r s h a p e a n d t h e i r size c a n be l o o k e d u p o n as s u b g l a c i a l in o r i g i n . W o r t h m e n t i o n i n g a m o n g t h e m is t h e k i k o l s k a c h a n n e l s i t u a t e d on t h e Dobrzyfi P l a t e a u , some t i m e a g e d e s c r i b e d b y N E C H A Y ( 1 9 2 7 ) , the channel of K r e p s k i e L a k e on t h e K r a y n a P l a t e a u , as w e l l the channel issuing from the d r u m l i n field n e a r Zböjno i n v e s t i g a t e d b y NIEWIAROWSKI ( 1 9 5 7 ) . M o s t of these channels a r e m a r k e d b y d r u m l i n s s h o w i n g a u p t h r u s t e d i n t e r i o r s t r u c t u r e . N o t w i t h s t a n d i n g t h e f a c t these c h a n n e l s a r e b y m e a n s w i d e , the v e r y p r e s e n c e of d r u m l i n s is a p t to i n d i c a t e t h e i r o r i g i n .

Conclusions T h e d e v e l o p m e n t of i n v e s t i g a t i o n s a n d p o l e m i c which since a l o n g t i m e d e a l w i t h the o r i g i n of the s u b g l a c i a l channels is c o n s t a n t l y y i e l d i n g a d d i t i o n a l f a c t s b r o a d e n i n g o u r k n o w l e d g e . H o w e v e r , there c o n t i n u e to be a n u m b e r of open q u e s t i o n s l a c k i n g e x p l a n a ­ t i o n w h i c h u l t i m a t e l y solved, m a y p r o v e c o r r e c t either one of t h e concepts u n d e r deliberation. T h e a n a l y t i c a l s t u d y of the p a t t e r n a n d t h e d i s t r i b u t i o n of channels in N o r t h e r n P o l a n d ( F i g . 1) i n d i c a t e t h a t in t h e i r v a s t m a j o r i t y these l a n d f o r m s a r e short. A p a r t f r o m f e w e x c e p t i o n s , t h e i r d i r e c t i o n is a l w a y s p e r p e n d i c u l a r to t h e l i n e in which t h e i n l a n d ice m a r g i n c a m e to rest. T h e r e s u l t of t h i s r u l e is a s p a t i a l difference in the r u n of the c h a n n e l s in the a r e a s of p a r t i c u l a r g l a c i a t i o n s t a g e s ( B r a n d e n b u r g , F r a n k f u r t , P o m e r a n i a n ) . E v e n so, t h e r e a r e c e r t a i n d i r e c t i o n s i n c o m m o n for a l l s t a d i a l s — s h o w i n g t h a t these c h a n n e l s d i d o u t l i v e the s t a d i a l s . W h a t t h e n a r e t h e y r e a l l y . R e p l i c a s of ice c r e v a s s e s , or of t h e results of g l a c i a l erosion? 1. If g l a c i a l erosion has t a k e n p l a c e , g l a c i t e c t o n i c structures s h o u l d be in e v i d e n c e a l o n g the c h a n n e l s . Y e t o b s e r v a t i o n s k n o w n so f a r i n d i c a t e t h a t in t h e end m o r a i n e s a d ­ j o i n i n g the channels g l a c i t e c t o n i c d i s t u r b a n c e s h a v e been o c c u r i n g a t l o w d e p t h s , f r o m 0 to 5 m o n l y b e l o w the g r o u n d s u r f a c e , w h i l e f a r t h e r d o w n the d e p o s i t s lie c o n f o r m a b l y (PASIERBSKI 1 9 7 3 ) . T h e channel b o t t o m s a r e i n c i s e d much deeper. 2. I n v e s t i g a t i o n s of channels p r o d u c t e d b y n a r r o w g l a c i e r lobes i n d i c a t e , t h a t t h e y a r e w i d e n e d sections of s u b g l a c i a l channels. T h e y occur a t c e r t a i n p l a c e s o n l y , i n spite of t h e r u n of t h e channel c o n t i n u i n g to be v i s i b l e .


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3.

199

T h e n u m e r o u s t r a n s v e r s e steps o b s e r v e d in t h e channels s h o w f e a t u r e s of a c c u m u ­

lation (GALON 1 9 6 5 ; KOZARSKI 1 9 6 6 / 7 ) .

4.

Difficult to a s c r i b e t o g l a c i a l e r o s i o n a r e the a r e a l l y v e r y s m a l l b u t e x c e p t i o n a l l y

d e e p k e t t l e s which o c c u r i n the channel.

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(1966/7): The origin of subglacial channels in the North Polish and North German Plain. — Bull, de la Soc. des Amis des Sei et des Lettres de Poznan, 20: 21—36; Poznan.

LIEDTKE, H. (1975): Die nordische Vereisung in Mitteleuropa. — 160 p., Bonn. MAJDANOWSKI, S. (1950): Zagadnienie r y n i e n jeziornych na Nizu europejskim. (Summary: The problem of lake-channels in the European Plain.) — Bad. Fizogr. nad Polska. Zach., 2: 3 5 — 116; Poznan. NECHAY, W. (1927): U t w o r y ladowcowe Ziemi Dobrzynskiej. — Spraw. Panstw. Inst. Geol., 4: 61—144; W a r s z a w a . —

(1932): Studia nad genezq jezior Dobrzynskich. (Resume: Etudes sur l a genese des lacs de Dobrzyn.) — Przegl. Geogr., 12: 1 2 4 — 1 7 7 ; W a r s z a w a .

NIEWIAROWSKI, W. ( 1 9 5 7 ) : Wybrane zagadnienia z bedan Mazowsze. — Dok. Geogr., 3: 24—37; W a r s z a w a .

geomorfologicznych

na

arkuszu

PASIERBSKI, M. (1973): Przebieg deglacjacji i formy terenu polnocnej cz^sci W y s o c z y z n y Krajenskiej. (Summary: The course of deglaciation and the landforms in the northern part of K r a y n a Plateau.) — Stud. Soc. Sei. Torunensis. Geogr. et Geol., 8: 99 p . ; W a r s z a w a . —

(1975): Uwagi o genezie niecki Jeziora C h a r z y k o w s k i e g o . (Summary: R e m a r k s on the genesis of the C h a r z y k o w y Lake basin.) — A c t a Univer. Nicolai Copernici Geogr., 1 1 : 101—113; Poznan.


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Quaternary Science Journal - Remarks on the Genesis of Subglacial Channels in Northern Poland