Quaternary Science Journal - The Wartanian Siedlec Sandur (Zedlitzer Sandur) southwards the Trz... by Geozon Science Media

Eiszeitalter

Gegenwart

53 — 66

Hannover

9 fig., 1 tab., 1 pi.

1993

The Wartanian Siedlec Sandur (Zedlitzer Sander) southwards the Trzebnica Hills, Silesian Lowland, Southwestern Poland: re-examination after fifty years DARIUSZ KRZYSZKOWSKI*)

P u s h m o r a i n e , stratigraphic c o r r e l a t i o n , s a n d u r deposit, s e d i m e n t o l o g i c a l i n v e s t i g a t i o n s , classical s e c t i o n s , W a r t a n i a n i c e - s h e e t , S i e d l e c Sandur, S o u t h w e s t e r n P o l a n d

A b s t r a c t : T h e S i e d l e c S a n d u r ( Z e d l i t z e r S a n d e r ) in Silesia,

f ä c h e r n s e m i a r i d e r K l i m a t e v o r k o m m e n . D a s glaziofluviati-

S o u t h w e s t Poland, w a s at first d e s c r i b e d b y M. SCHWARZ

le Material d e s S c h w e m m f ä c h e r s legt n a h e , d a ß seine Sedi

BACH in 1 9 4 2 . It w a s i n t e r p r e t e d a s t h e W a r t a n i a n proglacial

mentation

outwash,

S c h l u ß spricht für SCHWARZBACHS D e u t u n g u n d nicht für d i e

formed

at t h e s o u t h e r n

margin o f ice-pushed

in e i n e r

kalten

Polarwüste

erfolgte.

Dieser

ridge ( T r z e b n i c a Hills, T r e b n i t z e r K a t z e n g e b i r g e ) . S o m e

seiner Opponenten,

r e c e n t investigations r e j e c t this interpretation

w a r t h e z e i t l i c h e n E i s e s in S c h l e s i e n . Im v o r l i e g e n d e n

and denay

u n d e r b e l e g t indirekt d a s Auftreten Bei

t h e o c c u r r e n c e o f t h e W a r t a n i a n i c e - s h e e t in S o u t h w e s t e r n

trag ward a u ß e r d e m d i e m ö g l i c h e A u s d e h n u n g d e s Eises in

P o l a n d . T h e p a p e r p r e s e n t s n e w s e d i m e n t o l o g i c a l investi

d a s T r e b n i t z e r K a t z e n g e b i r g e diskutiert.

g a t i o n s from d e p o s i t s o f t h e S i e d l e c Sandur. T h e m a i n result o f this study is d e t a i l e d d e s c r i p t i o n o f s o m e classical, d e s c r i b e d b y SCHWARZBACH, a n d s o m e n e w s e c t i o n s . F r o m t h e m , it w a s c o n c l u d e d that t h e S i e d l e c S a n d u r r e p r e s e n t s

1 Introduction

t h e p r o g l a c i a l alluvial fan with s e d i m e n t a r y structures typi cal for fans d e p o s i t e d in semi-arid c l i m a t e s . In turn, t h e g l a ciofluvial material o f t h e fan s u g g e s t s that

sedimentation

MARTIN

SCHWARZBACH

his w o r k

"Das

Diluvium

t o o k p l a c e in p o l a r d e s e r t c o n d i t i o n s . T h i s c o n c l u s i o n c o n

S c h l e s i e n s " ( 1 9 4 2 ) d i s c u s s e d broadly t h e p r o b l e m o f

firms rather SCHWARZBACH'S v i e w , t h a n v i e w s o f his o p p o

e x t e n t and s e d i m e n t stratigraphy o f t h e Wartanian

n e n t s , a n d confirms indirectly a n o c c u r r e n c e o f t h e W a r t a

(Warthe)

n i a n i c e - s h e e t in Silesia. T h e p a p e r d i s c u s s also a p o s s i b l e

c a m e from the T r z e b n i c a Hills ( T r e b n i t z e r K a t z e n g e

e x t e n t o f this i c e - s h e e t in T r z e b n i c a Hills.

b i r g e ) a n d from its s o u t h e r n foreland. SCHWARZBACH (1942)

stage

Middle

Silesia.

definitevely e s t a b l i s h e d that

His

major

the

data

maximum

e x t e n t o f the W a r t a n i a n stage in Middle Silesia is o n [Der warthezeitliche Zedlitzer S a n d e r südlich d e s

t h e t o p o f the T r z e b n i c a Rampart. T h e main

T r e b n i t z e r K a t z e n g e b i r g e s , Schlesisches Tiefland,

m e n t s w e r e the till o f this age w h i c h w a s found in

südwestliches Polen: eine Neuüberprüfung n a c h fünfzig J a h r e n ]

several

sections n e a r

Trzebnica and

argu

because

the

W a r t a n i a n o u t w a s h plain w a s found (Zedlitzer San

K u r z f a s s u n g : D e r Z e d l i t z e r S a n d e r ( S i e d l e c S a n d u r ) in S c h l e s i e n , im s ü d w e s t l i c h e n P o l e n g e l e g e n , w u r d e zuerst

d e r , S i e d l e c S a n d u r ) in t h e southern foreland o f the r a m p a r t . Now, after fifty years, the d i s c u s s i o n o n sta

v o n M. SCHWARZBACH i m J a h r 1 9 4 2 b e s c h r i e b e n . Er w u r d e

tus o f t h e Wartanian s t a g e in Silesia is c o m i n g b a c k .

als e i n w a r t h e z e i t l i c h e r S a n d e r g e d e u t e t , d e r a m S ü d r a n d

A s e r i e s o f p a p e r s h a s p r e s e n t e d data w h i c h suggest

der Stauchmoräne (Trzebnica Hügel, Trzebnica Katzen

that t h e r e ist n o W a r t a n i a n deposits in Middle Silesia

gebirge) entstanden war. Einige n e u e r e

(WINNICKI

Untersuchungen

1 9 9 0 , 1 9 9 1 , WINNICKI & SKOMPSKI

1991).

w i d e r s p r e c h e n d i e s e r I n t e r p r e t a t i o n u n d n e g i e r e n das Auf

Fortunately, s o m e o f t h e "classical" s e c t i o n s , w h i c h

treten w a r t h e z e i t l i c h e n E i s e s in S ü d w e s t - P o l e n . D e r v o r

w e r e e x a m i n a t e d b y SCHWARZBACH ( 1 9 4 2 ) , h a v e b e e n

l i e g e n d e Beitrag präsentiert n e u e s e d i m e n t o l o g i s c h e U n tersuchungen aus d e n Ablageningen d e s Siedlec Sanders. D a s w i c h t i g s t e E r g e b n i s d i e s e r Studien ist e i n e detaillierte Beschreibung

einiger

klassischer,

schon

v o n SCHWARZ

BACH b e s c h r i e b e n e r u n d e i n i g e r n e u e r Aufschlüsse. Aus

diesen

Aufschlüssen

wurde

geschlossen,

daß der

S i e d l e c S a n d e r e i n e n e i s z e i t l i c h e n S c h w e m m f ä c h e r mit S e d i m e n t s t r u k t u r e n r e p r ä s e n t i e r e , w i e s i e a u c h in S c h w e m m -

lately

again

exposed.

This make

p o s s i b l e to

e x a m i n e SCHWARZBACH'S interpretation m o r e critically t h e

and

"Wartanian p r o b l e m "

south

w e s t e r n Poland. T h e p a p e r p r e s e n t s d e t a i l e d from

Pierwoszow (Pürbischau) outcrop

discuss

data

(SCHWARZ

BACH 1 9 4 2 , p a g e 2 1 2 - 2 1 8 , figures 6 - 1 0 ) a n d from t w o new

outcrops

which

are

located southwards

the

T r z e b n i c a Hills, o n t h e plain w h i c h h a s b e e n sup *) Address o f the outhor: D r . D . KRZYSZKOWSKI, G e o g r a p h i c a l Institute, University o f W r o c l a w pi. U n i w e r s y t e c k i 1, 5 0 - 1 3 7 Wroclaw, Poland

p o s e d to r e p r e s e n t t h e Wartanian p r o g l a c i a l sandur (Fig. 1 ) .

D A R I I ' S Z KRZYSZKOWSKI

ioo-

coutour lines m a s I

distinct scarps

I sites with the Wirtanian till

Fig. 1: L o c a t i o n o f t h e S i e d l e c S a n d u r

forested areas on the sandur

WartQnion sandurs lolluvial fans)

s o u t h w a r d s t h e T r z e b n i c a Hills.

2 G e o l o g y o f t h e T r z e b n i c a Hills a n d i t s southern foreland 2.1 H i s t o r i c a l b a c k g r o u n d

At t h e s a m e time, there w a s discussion o n g e n e s i s o f the N e o g e n e / Q t i a t e r n a r y sediment deformation found in Trzebnica Hills. Older authors prefered t e c t o n i c ( e n d o g e n i c ) g e n e s i s (FRECH 1 9 0 1 , 1 9 1 3 , OLBRICHT

The T r z e b n i c a Hills w e r e for many years t h e strato type r e g i o n for the Silesian Pleistocene stratigraphy. FRECH ( 1 9 0 1 , 1904) d e s c r i b e d two tills in superpositi o n in T r z e b n i c a outcrops: t h e Elsterian a n d t h e Saalian o n e ; b o t h were d e f o r m e d together with Neog e n e clay in substratum. Later, TIETZE ( 1 9 1 0 , 1 9 1 5 ) and FRECH ( 1 9 1 3 ) found that t w o Pleistocene tills o c c u r also s o u t h w a r d s the T r z e b n i c a Hills, n e a r W r o c l a w . DNTRICIT ( 1 9 1 4 ) a n d t h e n MEISTER ( 1 9 3 5 ) a n d SCHWARZBACH ( 1 9 4 2 ) d e s c r i b e d t h e next till near T r z e b n i c a , which overlay discordantly d e f o r m e d , older tills a n d N e o g e n e clay. This till, w h i c h w a s s u p p o s e d t o represent t h e Wartanian (SCHWARZBACH 1 9 4 2 ) , w a s found only in few sections: G l u c h o w C o r n y , T a c z o w Wielki, Radlow, Raszyn, T r z e b n i c k i Las

geological cross-sections see Fq 3

m sires investigated in detail

B u k o w y a n d D r o s z o w (DITTRICH 1 9 1 4 , M E I S T E R

1935, SCHWARZBACH 1 9 4 2 ) . In all cases, it w a s only 2-4 m thick, usually c o v e r e d b y loess a n d its lateral extent w a s unknown, p r e s u m a b l y small.

1 9 2 4 , CZAJKA 1 9 3 1 , MEISTER

1935).

How

ever, s i n c e the work o f B E R G E R ( 1 9 3 7 ) , t h e g l a c i o t e c tonic g e n e s i s (push m o r a i n e ) have b e e n usually pre fered a n d the age o f deformation was related t o t h e Wartanian 1954,

stage

1955,

(SCHWARZBACH

KRYGOWSKI

PACIIUCKI 1 9 5 2 , ROZYCKI

1950,

1942,

WOLDSTEDT

WALCZAK

1951,

1 9 5 7 , 1 9 6 8 , ROTNICKI I 9 6 0 ,

1 9 6 7 ) , although G O L A B ( 1 9 5 1 ) and LYCZEWSKI ( 1 9 6 4 ) still a d v o c a t e d a r g u e m e n t s o n their t e c t o n i c g e n e s i s .

2.2 R e s u l t s o f r e c e n t g e o l o g i c a l i n v e s t i g a t i o n s R e c e n t geological investigations indicate that t h e Silesian Lowland ( W r o c l a w region) can b e subdivid ed into t w o regions: the Wroclaw Basin with 4 0 - 8 0 m thick P l e i s t o c e n e s e q u e n c e , which is s u r r o u n d e d by a r e a s with thin ( b e l o w 2 0 m ) or n o P l e i s t o c e n e deposits and with N e o g e n e clays at t h e g r o u n d sur face (CZERWONKA & KRZYSZKOWSKI 1 9 9 2 ) . T h r e e Pleis-

The Wartanian Siedlec S a n d u r (Zedlitzer S a n d e r ) t o c e n e glacial units, including three tills h a v e b e e n found in the Wroclaw B a s i n (CZKRWONKA & KRZYSZ KOWSKI 1 9 9 2 ) . T h e l o w e r m o s t till, the P i e t r z y k o w i c e

Till, is characterized b y large p r e d o m i n a n c e o f Scan dinavian, crystalline r o c k s ; the middle till, the W i e r z b n o Till, is characterized by a p r e d o m i n a n c e o f Baltic limestones; a n d the uppermost, t h e Smolna Till, is again characterized b y p r e d o m i n a n c e o f Scan dinavian crystalline r o c k s . O n the o t h e r hand, the locally-derived rocks s h o w palaeotransport from NW to SE for both Pietrzykowice and W i e r z b n o Tills and from NE to SW for t h e Smolna Till. T h e s e tills w e r e interpreted to represent t w o stadials o f the Elsterian (Pietrzykowice a n d W i e r z b n o Tills) and the o l d e r Saalian (Drenthe, Odranian) stage (Smolna Till)

(CZERWONKA &

KRZYSZKOWSKI

1992).

the

northern part o f the W r o c l a w Basin, at t h e southern margin o f the Trzebnica Hills, this s e q u e n c e is c o v e r e d additionally b y 1 0 - 3 0 m thick series o f sands a n d gravels - t h e Siedlec Formation, and by 0 , 5 - 1 , 5 m thick loess (Figs 2 and 3 ) .

northern part o f T r z e b n i c a Hills, from b o t h outcrops a n d borings, a s e t o f synclines and anticlines w h i c h c o m p r i s e at least t w o tills. T h e l o w e r till may corre s p o n d with the W i e r z b n o Till and the u p p e r o n e with the Smolna till o f t h e Wroclaw Basin. O t h e r parts o f T r z e b n i c a Hills h a s e v e n less valuable data. Most o f b o r i n g s have only s i m p l e lithological description o f deposits with n o petrological data. H e n c e , lithostratigraphic correlation o f deposits is very difficult, although it s e e m s that at least t w o tills o c c u r here, similarly to the n o r t h e r n part o f T r z e b n i c a Hills (Fig. 2 ) . S o m e o f b o r i n g s comprise several alternating s e q u e n c e s o f tills, sands, glaciolacustrine silts a n d N e o g e n e clays. O t h e r borings, in turn, comprise o n l y Neogene d e p o s i t s with 5 - 1 0 m thick till o r loess at t h e top. Such s e q u e n c e s can b e easily interpreted as representing thrust structures (Fig. 3 a ) . T h e age o f sediment deformation in Trzebnica Hills, a s in w h o l e Silesian Rampart, is recently related rather to t h e Odranian ( D r e n t h e ) stage than to t h e Wartanian ( W a r t h e ) (SZCZEEANKIEWICZ 1 9 6 9 , B R O D Z I K O W S K I 1 9 8 2 ,

1 9 8 7 ) . T h e rampart is interpreted a s p u s h moraine overrided by a n i c e - s h e e t during a continuous a d v a n c e . T h e margin o f the Odranian ice-sheet is l o c a t e d about 7 0 - 8 0 k m sosuthwards from the Trzeb n i c a Hills.

T h e Pleistocene g e o l o g y o f ..the T r z e b n i c a Hills is m o r e c o m p l e x . Most o f outcrops have o n l y o n e till, w h i c h most problably represent an equivalent of the S m o l n a Till (the Odranian-Drenthe s t a g e ) (WINNICKI & SKOMESKI 1 9 9 1 ) . T h i s till is usually deformed t o g e t h e r with glaciofluvial a n d glaciolacustrine de posits a n d / o r with N e o g e n e clay forming fold or

T h e occurrence o f t h e Wartanian till in Trzebnica Hills cannot b e c o n f i r m e d or rejected b y recent in

thrust z o n e s . KRZYSZKOWSKI ( 1 9 9 2 ) d e s c r i b e d in the

vestigation. T h e c o n c l u s i o n by W I N N I C K I (WINNICKI

northern

port of the

Trzebnica

Hills

Trzebnica

GENERAL CHRONOSTRATCRAPHY

southern part of the

northernmost p a r t of

Trzebnica

the Wroclaw

Hills

GTUCHDW

—

LIIHOSTRATGRAPHY

Basin

Siedlec Sandur

TaczOW

till

GENERAL LITHOSTRATKjRAPHY alluvium

CHRCN3STRATIGRAPHY

(informal)

Siedlec

Formation \

Smolna HU

general angular

PILICA INTERSTADIAL

\unconfornity

ODRANIAN (DRENTHEI ELSTERIAN Wierzbno

till

(YOUNGER STADIAL I

Pietrzykowice

ELSTERIAN

till

(OLDER STADIAL) r^—;—I fluvial deposits (mainly re - deposited loess]

I . »I

t r a v e l lag

1 1

IIIiII O

''"

loess

Poznan

EOS

glaciolacustrine deposits

glaciafluvia' deposits

r L

Formation

]" preglacia!" fluvial J deposits

clay

Fig. 2: Stratigraphy o f P l e i s t o c e n e d e p o s i t s o f t h e n o r t h e r n part o f Silesian L o w l a n d ( W r o c l a w B a s i n ) a n d T r z e b n i c a

Hills.

Fig. 3: G e o l o g i c a l cross sections t h r o u g h o u t the S i e d l e c Sandur a n d s o u t h e r n m o s t part o f T r z e b n i c a Hills. Location ol s e c t i o n s is in Fig. 1.

Fig. 3 : G e o l o g i c a l c r o s s s e c t i o n s t h r o u g h o u t t h e S i e d l e c S a n d u r a n d s o u t h e r n m o s t part o f T r z e b n i c a Hills. Location o f s e c t i o n s is in Fig. 1.

DARIUSZ KRZYSZKOWSKI

1990,

1 9 9 1 , WINNICKI & SKOMPSKI 1 9 9 1 ) , that h e did

not find t h e Wartanian tili in T r z e b n i c a Hills during his g e o l o g i c a l mapping is rather wrong. N o n e o f the o u t c r o p d e s c r i b e d b y MEISTER ( 1 9 3 5 ) a n d SCHWARZ

BACH ( 1 9 4 2 ) have b e e n r e - e x a m i n e d , simply b e c a u s e these o u t c r o p s are c o m p l e t e l y destroyed a n d v e g e tated. H e n c e , it s e e m s that t h e older descriptions a r e still c o r r e c t a n d c a n b e a d o p t e d to recent strati graphy. I f so, the possible Wartanian till is a till lying discordantly o n older glacial a n d N e o g e n e deposits. I p r o p o s e a lithostratigraphic n a m e for this till - the T a c z ö w Till, from T a c z o w outcrop, d e s c r i b e d in detail b y MEISTER ( 1 9 3 5 , p. 8 ) ( F i g 2 ) . T h e similar s e q u e n c e w a s then d e s c r i b e d in t h e next village B r o c h o c i n ( B r o c k o t s c h i n e = Moltketal) b y SCHWARZ BACH ( 1 9 4 2 ) . All sites with the T a c z o w Till m e n t i o n e d by

MEISTER

(1935)

and

SCHWARZBACH

(1942)

are

s h o w n approximately in Fig. 1 a n d they mark possible southernmost extent o f t h e Wartanian i c e sheet in T r z e b n i c a Hills.

3 The Siedlec Sandur 3.1 G e n e r a l m o r p h o l o g y a n d g e o l o g y The S i e d l e c Sandur ( S i e d l e c F o r m a t i o n ) is a sandygravelly, c o n e - s h a p e d deposit lying o n the S m o l n a till in t h e southern foreland o f t h e T r z e b n i c a Hills (Fig. 3 a & b ) . T h e plan v i e w o f these deposits is fans h a p e d a n d the contours b o w d o w n l o p e from t w o a p e x e s , o n e near P i e r w o s z ö w a n d other near Skarszyn, w h i c h lie at the b o r d e r o f i c e - p u s h e d ridge (Fig. 1). T h e c r o s s fan profile is c o n v e x a n d radial profiles

are usually flat o r c o n c a v e in t h e uppermost part b u t they are c o n v e x in the lowermost part o f the fan. T h e s l o p e inclination varies from 0 , 5 0 % t o 1,67 %. G e n erally, three s e g m e n t s o f the fan c a n b e r e c o g n i z e d from its morphology: the upper part o f the fan w i t h s l o p e inclination ranging from 1,0 % t o 1,33 %, t h e middle part o f t h e fan with s l o p e inclination b e t w e e n 0,5 % t o 0 , 6 7 % and the l o w e r part o f the fan, n e a r its s o u t h e r n m o s t margin, with s l o p e inclination up t o 1,67 % . T h e thickness o f deposits d e c r e a s e s systematically from a p e x zones ( c a . 3 0 m ) to its south ern margin, w h e r e is only thin ( b e l o w 10 m ) s a n d y c o v e r o n the hill. T h e southern margin o f the S i e d l e c Sandur is marked b y scarp, w h i c h represent also a sharp lithological boundary, b e t w e e n a sand a n d a till (Fig. 1). T h e last o n e forms a w i d e s p r e a d till plain around the Siedlec Sandur. T h e b o u n d a r y b e t w e e n the sandur a n d till plain s o m e t i m e s visible a s b o u n d a r y b e t w e e n a forest and fields (Fig. 1). T h e r e are n o g o o d traces o f outflow from t h e sandur t o t h e Odra river valley, b e i n g south, from t h e time o f its formation. T h e Siedlec Sandur is p r o b a b l y d i s s e c t e d only b y y o u n g e r valleys, infilled with W e i c h s e l i a n and H o l o c e n e fluvial deposits (Fig. 1 ) . In the north ern part o f the sandur, sandy-gravelly deposits a r e c o v e r e d by 0,5 - 1,5 m thick loess cover, which c o n tinues northwards, into a thick l o e s s c o v e r in T r z e b nica Hills ( 6 - 2 0 m ) (Fig. 2 ) .

3.2 T h e s a n d u r d e p o s i t s T h e principal deposit o f the S i e d l e c Sandur is a c o a r s e sand with a varying a m o u n t o f gravel, l o w -

Fig. 4: G e n e r a l stratigraphy a n d s e d i m e n t c h a r a c t e r i s t i c in P i e r w o s z ö w o u t c r o p .

T h e Wartanian S i e d l e c Sandur (Zedlitzer S a n d e r )

1 i

Pig. 5: D e t a i l e d section o f the P i e r w o s z รถ w o u t c r o p ( l o c a t i o n is in Fig. 5 ) with levels o f s h a l l o w troughs a n d g r a v e l s a n d clay balls, s e p a r a t e d by horizontally b e d d e d s a n d s a n d p e b b l e sands. 1

12 m

Fig. 6: T h e stratigraphy and s e d i m e n t a r y structures o f d e p o s i t s in B i e d r z y c e o u t c r o p . T w o l e v e l s o f s h a l l o w t r o u g h s a n d o n e level o f c l a y balls are visible in l o w e r part o f t h e s e c t i o n .

DARIUSZ KRZYSZKOWSKI

angle o r horizontally bedded. T h e latter s e d i m e n t (Sh f a d e s ) d o m i n a t e in t h e general picture o f sandur s e q u e n c e ( T a b u l a 1, A). Gravels a n d / o r clay balls m a y be c o n c e n t r a t e d in levels o r b e present in a n isolated position. T h e lateral e x t e n s i o n o f horizontal strata is general in the order o f s o m e tens o f metres. T h e t h i c k n e s s o f these strata varies from several d e c i m e tres t o several metres. T h e low-angle units h a v e average lenght from s o m e decimetres t o s o m e m e tres a n d smaller thickness, reaching u p to 0 , 5 m. T h e s e sediments are thought to represent sheetflood d e p o s i t (BULL 1 9 7 2 ) , deposited o v e r large area by a shallow, supercritical flow during short periods with c o n s i d e r a b l e discharge ( M C K E E , C R O S B Y &

trough (Tabula 1 B , C ) . T h e s h a l l o w troughs are of ten concentrated in levels, occurring in horizontally b e d d e d deposits (Fig. 4 , 5 & 6 ) . T h e shallow t r o L i g h s formed most p r o b a b l y during t h e vanning stages o f floods, w h e n l o w discharge o c c u r r e d . Channel-fills formed during t h e n e x t sheet-flood. T h e levels o f shallow channels a r e believed to represent a former fan surface. In turn, t h e thick trough cross-bedded sets, which are usually interbedded with thin b e d s with horizontal b e d d i n g a n d s o m e planar cross b e d ding ( S p f a d e s ) Fig. 7 ) , represent most probably large c h a n n e l

fills

( B U L L 1 9 7 2 , CHURCH & G I L B E R T

1975,

B O O T H R O Y D & ASHLEY 1 9 7 5 , MIALL 1 9 7 7 , 1 9 7 8 ,

1985,

ALLEN 1 9 8 3 ) .

BERRYHILL 1 9 6 7 , WILLIAMS 1 9 7 1 , MIALL 1 9 7 7 , FROSTICK & R E I D 1 9 7 7 , TUNBRIDGE 1 9 8 1 ) . T h e e r o s i o n a l surfa

ces b e t w e e n deposits from different sheet-floods are often m a r k e d b y small scour-and-fill structures ( S c f a d e s ) ( T a b u l a 1 D ) . T h e y are usually 2 - 6 c e n t i m e tres d e e p a n d 1 0 - 2 0 centimetres long, infilled b y c o arser material than in horizontal laminae. Small scours w e r e formed locally during t h e sheet-floods. In t h e s a n d u r deposits described, the c h a n n e l d e p o sits a r e less frequent a n d represent t w o types o f channel-fills: shallow, single d e p r e s s i o n s ( t r o u g h s ) and t r o u g h cross-bedded sets with thickness up to 2 m (st f a d e s ) . T h e shallow troughs are u p to 0 , 5 m d e e p a n d about 1 - 2 m wide and they usually have "festoon" lamination, parallel to the l o w e r profile o f

Very rare deposit, found in t w o sections, is a m a s sive, fine sand t o sandy silt. It is usually poorly sort e d deposit (diamicton, D m f a d e s ) . This fades forms 1 0 - 1 5 c m thick, laterally extensive layers. Most prob ably, this f a d e s represent an o v e r b a n k deposit, form e d after main floods. Additional feattire o f the sandur deposits are normal faults (Tabula 1 E a n d Fig. 6 ) . T h e y were found in o n e outcrop ( B i e d r z y c e ) , w h i c h is located o n t h e valley bank. T h e faults cross all deposits, from t h e t o p to the bottom o f outcrop. It s e e m s , that they re present c o m p l e t e l y post-depositional feature, for m e d during the s e d i m e n t gravity relacation on t h e slope.

tig. 7: T h e stratigraphy a n d s e d i m e n t a r y s t m c a i r e s o f d e p o s i t s in Wisznia Mala o u t c r o p .

The

Wartanian Siedlec Sandur (Zedlitzer S a n d e r )

3-3 T h e P i e r w o s z ö w o u t c r o p T h i s outcrop is l o c a t e d in the main a p e x zone o f t h e Siedlec Sandur, n e a r village P i e r w o s z ö w (Fig. 1). It w a s described at first by SCHWARZBACH ( 1 9 4 2 ) . R e c e n t o u t c r o p is 7 - 8 m deeper than t h e SCHWARZBACH'S outcrop, with a section up to 17 m high (Tabula 1 ) . T h e section c o m p r i s e s almost o n l y horizontally b e d d e d p e b b l e sand a n d shallow c h a n n e l s , and a thin l o e s s c o v e r at t h e t o p (Fig. 4 ) . T h e shallow c h a n n e l s are concentrated in two levels, o n e n e a r bottom o f t h e outcrop and o t h e r o n e about 5 - 6 m from its b o t tom. T h e u p p e r m o s t part o f t h e section (the o l d o u t c r o p ) has n o shallow c h a n n e l s , containing o n l y 8 - 10 m thick, horizontally b e d d e d strata (Fig. 4 ) . Moreover, there are observed s e v e r a l , up to 0,5 m thick, horizontally b e d d e d levels w i t h gravels a n d clay balls (Fig. 4 ) . In place, large c l a y balls are v e r y concentrated, forming the "clay ball lags" (Fig. 5 ) . T h e clay balls are formed o f Tertiary green clay a n d they have varying size, from a f e w millimetres up t o 0,3 m, occasionally single clay balls m a y reach up t o 0,5 m. T h e size o f gravels is less c h a n g e a b l e , from 1 to 10 centimetres. T h e lower level o f shallow c h a n n e l s have, in fact, at least three sub-levels o f channels, w h i c h are s e p a rated by horizontally bedded sands (Fig. 5). Neverthe less, all these c h a n n e l s occur within the b e d with thickness o f 1 m. T h e channels are formed practical ly o f coarse sand, e x c e p t two small troughs with gra vels. In turn, the u p p e r level o f shallow channels is m o r e concentrated, contains larger troughs and it is formed in majority o f gravels, a l t h o u g h no clay b a l l s h a v e b e e n o b s e r v e d (Fig. 5). P a l a e o c u r r e n t m e a s u rements from troughs s h o w that t h e r e is no diffe r e n c e b e t w e e n t w o levels m e n t i o n e d , and that t h e transport o f material was from n o r t h (Fig. 4 ) .

3.4 T h e B i e d r z y c e o u t c r o p This outcrop is l o c a t e d in the a p e x z o n e o f the small fan, tributary to t h e main alluvial fan, which is l o c a t e d b e t w e e n villages Skarszyn a n d B i e d r z y c e (Figs. 1 and 6 ) . R e c e n t outcrop is 1 1 - 12 metres high. T h e Biedrzyce section, like in Pierwoszöw, c o m prises almost o n l y horizontally b e d d e d pebble s a n d s and shallow c h a n n e l s and additionally a 10 - 15 c m thick layer o f massive, sandy d i a m i c t o n . T h e shallow c h a n n e l s form t w o levels. T h e l o w e r o n e is a b o u t 1 m thick and contains three sub-levels o f troughs, s e parated by horizontally bedded s a n d s . T h e c h a n n e l s are formed b o t h o f coarse sands a n d pebble s a n d s , although the latter are less c o m m o n (Fig. 6 ) . T h e l o w e r level o f s h a l l o w channels is followed by thin layer o f massive, fine sand to s a n d y silt (sandy dia

m i c t o n ) (Fig. 6 ) . This b e d is laterally continuous, at least 4-5 metres. T h e upper level o f shallow c h a n nels lies about 1,5 m a b o v e the l o w e r o n e and it is formed o f o n l y o n e , 0,2-0,5 m thick b e d with troughs. S o m e troughs o f this level are, however, m u c h larger t h a n troughs o f the l o w e r level (Fig. 6 ) . Moreover, t h e s e troughs c o n t a i n s usually p e b b l e sands and gravels (with diameter u p to 2 0 c m ) . Within the horizontally b e d d e d sand, o n l y o n e level with clay balls a n d several levels o f gravels can b e observed (Fig. 6 ) . Single clay balls are also observed in other horizontal b e d s and troughs. Palaeocurrent measurements from troughs indicate transport directly from north (Fig. 6 ) .

3.5 T h e w i s z n i a M a l a o u t c r o p This outcrop is located near the w e s t e r n margin o f the Siedlec Sandur, near village Wisznia Mala (Figs. 1 and 7 ) . T h e s e c t i o n investigated is o n l y 4 m high. The Wisznia Mala section is threefold. T h e l o w e r part o f the s e c t i o n comprises a n alternating cross b e d d e d and horizontally b e d d e s sands or p e b b l e sands. The cross b e d d e d sets are represented by large troughs, small troughs and planar sets. T h e s e d e posits are f o l l o w e d by thin, but laterally continuous, massive, sandy silt with single, floating gravels (san dy diamicton). T h e middle part o f t h e section, about 1 m thick, is represented by horizontally b e d d e d sand with o n e shallow channel (Fig. 7 ) . This sedi ment, although thin, is veiy similar to sediments from P i e r w o s z ö w and Biedrzyce outcrops. T h e up per part o f the section is o c c u p i e d b y planar cross b e d d e d sand, representing, most p r o b a b l y , a part o f similar s e q u e n c e as in its lower part. T h e important fact is that n o clay balls have b e e n found in Wisznia Mala outcrop. T h e palaeocurrent measurements from trough a n d planar corss-bedding indicate trans port from north-east (Fig. 7 ) .

3-6 G r a i n s i z e d i s t r i b u t i o n Most o f sandur deposits are m e d i u m sands to p e b b l e sands. Mean size varies from 1.84 0 to -1.22 0 sort ing varies from 0 , 5 7 0 to 2 . 2 5 0. Sporadically o c c u r fine sands ( M 2.91 0, o 0 . 6 8 0) o r sandsy diamiclons ( M 1.87-2.17 0, o 0.90-1.73 0) (Fig. 8 ) . z

Very interesting is the vertical s u c c e s s i o n o f sedi ments (Fig. 8 ) . In P i e r w o s z ö w o u t c r o p , there are three distinct layers which differ in grain size. T h e lower and u p p e r o n e are represented mostly by m e dium to c o a r s e sands with o n l y rare gravel b e d s , whereas the m i d d l e o n e is r e p r e s e n t e d by p e b b l e sands with c o m m o n gravel b e d s . T h e coarser layer

D A R U J S Z KRZYSZKOWSKI

PIERWOSZÖW 180,0 m Q.s.1. STRATIGRAPHY 4,69

2,50

1,29

-,.

WISZNIA 158,5

-1,13

1,97

-0.11

1,64

0,85

1,45

-122 1.04 1.47 0,88 2,91

203 1,17 1,01 0.77 0,68

1,76

1,62

1.87

1,73

Formation

1,8 t -1,15

0.57 2,19

(Sandur)

Siedlec

frequent

(Sandur)

3.7 Gravel p e t r o g r a p h y

fret^ent clay balls

i „;

MALA

m Q.S.1. rn

Siedlec

BIEDRZYCE 165,0

m Q.S.1. gravity fajlts throughout the section

Siedlec

g | | S g

126

Formation 2.25

2,62 1,56 0,90 0,57 1,26

Sh Dm Sh/St Sh

•

• . sandy silt I " I (diamicton) |y v :| sand 0

(Sandur)

rrrrn loess 1°

s e d i m e n t s in the W i s z n i a Mala outcrop is small, p r o b a b l y not e n o u g h for inter pretation o f vertical s u c c e s sion o f grain size. Neverth e l e s s , coarser d e p o s i t s are m o r e c o m m o n in l o w e r part o f the o u t c r o p , and p r o b a b l y they r e p r e s e n t an equivalent o f c o a r s e , mid dle layer in P i e r w o s z ö w .

I sand & gravel

Dm Fm Sh Sp St Sc

— — — —

massive, sandy diamicton massive silt (loess) horizontally bedded sand gravel planar cross-badded sand/gravel trough cross-bedded sand/gravel scour & fill structures

The gravel petrography h a v e b e e n e x a m i n e d in t w o outcrops: P i e r w o s z ö w a n d Biedrzyce. In t h e first o n e , samples have b e e n ta k e n from lower and u p p e r part o f the s e q u e n c e . T h e size o f e x a m i n e d g r a v e l s w a s 1 - 1 0 cm; the n u m b e r o f gravels in single s a m p l e varied from 128 ( P i e r w o s z ö w ) to 192 ( B i e d r z y c e ) . T h e results are p r e s e n t e d in T a b l e 1. Generally, g r a v e l petrography s h o w s for gla cial origin o f deposits, m o s t p r o b a b l y derived f r o m a till. T h e time o f d e p o s i t i o n is rather young, b e c a u s e o f large content o f Baltic l i m e stones, comparable with the limestone c o n t e n t in tills. Lacking o f large n u m b e r o f flint suggests, in turn, that the source material (till) was also not r i c h in flint. The Smolna Till ( O d r a n i a n , D r e n t h e ) , lying o n the top o f T r z e b n i c a Hills is a flint-poor till (KRZYSZKOWSKI 1 9 9 2 ) , a n d

Fig. 8: T h e grain size distribution a n d vertical s u c c e s s i o n o f features o f d e p o s i t s o f the S i e d l e c Sandur.

c o m p r i s e s deposits from a b o t t o m o f upper level o f s h a l l o w c h a n n e l s up to t h e uppermost gravel level, 3 - 4 m b e l o w the loess (Figs. 4 & 8 ) . T h e B i e d r z y c e section h a v e almost the s a m e stratigraphy: the l o w e r layer with medium to c o a r s e sands and c o a r s e r layer lying a b o v e . T h e latter starts from the b o t t o m o f up per level o f shallow c h a n n e l s and continues u p to the t o p o f the section (Figs. 6 & 8 ) . T h e t h i c k n e s s o f

is o n e possible s o u r c e o f gravels. O n the o t h e r h a n d , it s e e m s that the s o u r c e gla cial d e p o s i t s m a y b e also t h e T a c z o w Till ( W a r t a n i an, W a r t h e ) o r directly glacial material ( m o r a i n e ) d e rived from t h e Wartanian i c e sheet and transported by subglacial and proglacial streams.

T h e o c c u r r e n c e o f non-resistant M e s o z o i c l i m e stones a n d Tertiary mudstones as well as large n u m b e r of clay balls in deposits o f u p p e r m o s t part o f t h e san-

T h e Wartanian S i e d l e c Sandur (Zedlitzer S a n d e r )

Tab. 1: Gravel petrography of deposits of the Siedlec Sandur near Trzebnica (%) Scandinavian crystalline rocks

Baltic limestones

Scandinavian quartzites & sandstones

flint

Pierwoszöw sample no 108

—

Pierwoszöw s a m p l e n o 105

Biedrzyce sample n o 119

dur suggest that transport o f material w a s not long. T h e distance from outcrops investigated to the first o u t c r o p s o f the T a c z o w or S m o l n a Tills and Tertiary clays b e e i n g northwards is a b o u t 2 km (MEISTER 1932, WINNICKI 1 9 8 8 ) .

3.8 Palaeoenvironmental interpretation T h e Siedlec Sandur is a typical alluvial fan. This is c o n s i d e r e d from its fan-shaped g e o m e t r y , texture o f deposits a n d sedimentary structures (BULL 1 9 7 2 , HEWARD 1 9 7 8 ) . T h e specific feature is that the s a n d u r plan is formed o f t w o fans with a p e x e s about 6 k m

quartz

Mesozoic limestones

Tertiary mudstones

syderite concretions

other rocks

e a c h from the other. T h e a p e x e s o c c u r at the mouths o f d e e p valleys cutting the margin o f the ice-pushed ridge (Fig. 9 ) . T h e sandur w a s formed b y proglacial meltwater flowing from north, from the stagnating ice-sheet. T h e proglacial streams e r o d e d both older glacial deposits a n d Tertiary clays at the b a s e m e n t , forming 2 k m long, narrow a n d d e e p valleys before they have r e a c h e d the margin o f the ridge. T h e pre domination o f horizontal or l o w angle bedding in the sandur deposits with only m i n o r channel sedi mentation s u g g e s t sedimentary conditions typical for alluvial fans in arid climates (BULL 1 9 7 2 ) . Glacial origin o f the fan material suggest, in turn, the c o l d (periglacial) conditions, most p r o b a b l y a polar desert.

Fig. 9: G e n e r a l p a l a e o g e o g r a p h i c interpretation o f the S i e d l e c Sandur in relation to position o f t h e Wartanian ice-sheet at t h e T r z e b n i c a Hills.

DARIUSZ KRZYSZKOWSKI

G e n e r a l l y , the sandur h a s t w o sedimentary z o n e s : t h e fanheads with practically o n l y sheet flood d e p o sition intermpted locally b y m i n o r scouring a n d fur ther towards the bordering i c e p u s h e d ridge a l o w e r fan with braided c h a n n e l s a n d limited n u m b e r o f s h e e t floods (Fig. 9 ) . B o t h fans, forming t h e s a n d u r plain, h a v e similar stratigraphic a n d sedimentary s e q u e n c e s suggesting that they w e r e formed simulta n e o u s l y and d u e to the s a m e p r o c e s s e s , in spite o f different source area. This well c o r r e s p o n d with pro glacial origin o f the fan. T h e e p i s o d i c floods o c c u r red o n l y during the melting o f an ice-sheet, w h i c h is c o n t r o l l e d regionally b y c h a n g i n g year s e a s o n s . At first, t h e fanheads w e r e characterized b y frequent s h e e t floods intermpted b y dry fan conditions with formation o f only small c h a n n e l s . In turn, t h e n e x t p h a s e o f fan d e v e l o p m e n t w a s characterized b y ra pid b u t m o r e episodic floods. T h e a c c u m u l a t e d m a terial w a s usually coarser a n d n o m i n o r c h a n n e l s w e r e formed, suggesting larger water d i s c h a r g e at this time. Probably, this c h a n g e o f sedimentary envi r o n m e n t is a result o f increasing aridity. T h e flood w a t e r w a s channelized into braided c h a n n e l s at t h e l o w e r fan during both p h a s e s described. T h e s e c h a n n e l s were, most probably, also e p h e m e r a l . Lacking o f outflow from t h e fan suggests that w a t e r might have evaporated o r infiltrated almost at t h e fan. This probably agrees with t h e fan m o r p h o l o g y . T h e middle segment o f the fan is very flat, sug gesting high aggradadion rates. T h e s a m e p r o c e s s e s might also have created the s t e e p s l o p e o f t h e l o w e r m o s t segment o f the fan.

WINNICKI ( 1 9 9 0 , 1 9 9 1 ) . T h e last author is interpreting the sand b o d y o f the Siedlec Formation as k ä m e p l a teau d e p o s i t e d during the d e c a y o f the O d r a n i a n (Drenthe) ice-sheet. Although t h e alluvial fan g e n e s i s for the Siedlec F o r mation d e p o s i t s s e e m s to b e unquestionable, t h e r e are s o m e p r o b l e m s which a r e still unclear. First o f all, there is small e v i d e n c e for braided c h a n n e l s e d i mentation at t h e lower fan ( o n e outcrop with s e c t i o n only 4 m h i g h ) . Also, there is n o outcrops at the s t e e p slope o f t h e lowermost s e g m e n t o f the sandurhence, t h e g e n e s i s o f this s l o p e is not solved satis factorily, yet. Periglacial c o n d i t i o n s (polar d e s e r t ) should b e c o n f i r m e d b y a n o c c u r r e n c e o f frost fissu res o r ice w e d g e casts o r o t h e r permafrost indicators, but deposits investigated h a v e n o such periglacial stmctures. T h i s is u n e x p e c t e d characteristic o f t h e Siedlec Sandur, b e c a u s e for e x a m p l e the W e i c h s e lian proglacial sandurs in P o l a n d have large n u m b e r of permafrost indicators (KOZARSKI 1974, 1 9 9 2 ) . Fur ther s e d i m e n t o l o g i c a l investigations o f other W a r t a nian proglacial sandurs lying southwards the T r z e b nica Hills ( F i g . 1 0 ) should e x a m i n e w h e t h e r t h e sheet flood deposition is o n l y local feature o f t h e Siedlec Sandur o r is climatically controlled o c c u r r i n g in w h o l e region. T h e s e investigations should s o l v e definitevely t h e p r o b l e m o f outflow from sandurs t o the river O d r a valley a n d s o l v e the stratigraphic rela tion b e t w e e n t h e sandurs a n d s o k n o w n "upper" ter race o f t h e river Odra valley, s u p p o s e d to r e p r e s e n t the W a r t a n i a n (SZCZEPANKIEWICZ 1 9 5 9 , ROZYCKI 1 9 6 9 ) .

Both p r o b l e m s have not b e e n solved satisfactorily for the S i e d l e c Sandur.

4 Conclusions F r o m description and interpretation a b o v e it is c l e a r that t h e Siedlec Sandur m a y b e c o n s i d e r e d a s p r o glacial alluvial fan d e p o s i t e d in periglacial, arid climate a n d formed at the margin o f the i c e - p u s h e d ridge. T h e proglacial sandurs a r e rather c o m m o n southwards the Trzebnica Hills (Fig. 9 ) and they prob ably h a v e the s a m e features a s sandur d e s c r i b e d . T h e similar sand bodies, with t h e s a m e sedimentary structures, fan m o r p h o l o g y a n d similar g e o g r a p h i c position at the margins o f Saalian i c e - p u s h e d ridges h a v e b e e n also described a s alluvial fans ( s a n d u r s ) in

the

Netherlands

(AUGUSTINUS & RIEZEBOS 1 9 7 1 ,

RUEGG 1977, 1981).

T h e a g e o f Siedlec Formation (sandur) c a n b e c o n s i d e r e d from its relation to S m o l n a Till - t h e till d e p o sited b y the Odranian ( D r e n t h e ) ice-sheet, t h e san dur is undoubtedly younger, lying o n t h e S m o l n a till (Fig. 2 & 3 ) . Hence, it s e e m s that it is a proglacial equivalent o f the T a c z o w Till, d e p o s i t e d b y t h e W a r tanian ice-sheet stagnating o n t h e t o p o f T r z e b n i c a Hills. T h i s interpretation a g r e e s with the former v i e w by SCHWARZBACH ( 1 9 4 2 ) but contradicts t h e v i e w o f

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Manuscript accepted 3 0 . 1 1 . 1 9 9 2

Plate 1. T h e deposits o f S i e d l e c S a n d u r : A - t h e 7 - 8 m thick, m o n o t o n o u s s e q u e n c e o f h o r i z o n t a l l y b e d d e d s a n d s . B & C - e x a m p l e s o f s h a l l o w d e p r e s s i o n s (trougs m a r k e d b y a r r o w s ) lying w i t h i n t h e horizontally b e d d e d sands, D - s m a l l scour-and-fill structure, E - h o r i z o n t a l l y b e d d e d s a n d s with a level o f l a r g e c l a y balls ( a r r o w s ) , t h e n o r m a l fault is v i s b l e o n t h e left s i d e o f picture.