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

[ D e r w a r t h e z e i t l i c h e Z e d l i t z e r S a n d e r s ü d l i c h d e s T r e b n i t z e r K a t z e n g e b i r g e s , S c h l e s i s c h e s T i e f l a n d , s ü d w e s t l i c h e s P o l e n : e i n e N e u ü b e r p r ü f u n g n a c h fünfz ig J a h r e n ] K u r z f a s s u n g : Der Zedli tzer Sander (S ied lec Sandur) in Schles ien , im südwest l ichen Polen ge l egen , wurde zuerst von M. SCHWARZBACH im J a h r 1942 beschr ieben . Er wurde als e in warthezei t l icher Sander gedeutet , der am Südrand der S tauchmoräne (Trzebn ica Hügel , T rzebn ica Katzen­ geb i rge ) ents tanden war. Einige n e u e r e Untersuchungen widersprechen dieser Interpretat ion und negieren das Auf­ treten warthezei t l ichen Eises in Südwest -Polen . Der vor­ l i egende Beitrag präsentiert neue sed imento log i sche Un­ te rsuchungen aus den Ab lagen ingen des Siedlec Sanders . Das wicht igste Ergebnis d ieser Studien ist e ine detaillierte B e s c h r e i b u n g einiger klassischer , s c h o n von SCHWARZ­ BACH b e s c h r i e b e n e r und e in iger neue r Aufschlüsse. Aus d iesen Aufschlüssen wurde gesch lossen , daß der S ied lec Sander e inen eiszei t l ichen S c h w e m m f ä c h e r mit S e dimentstrukturen repräsent iere , wie sie auch in S c h w e m m *) Address o f the outhor: Dr. D. KRZYSZKOWSKI, Geographical Institute, University o f W r o c l a w pi. Uniwersytecki 1, 5 0 1 3 7 Wroc l aw , Poland fächern semiarider Kl imate vorkommen. D a s glaziofluviatile Material des S c h w e m m f ä c h e r s legt nahe , d a ß seine Sedi­ men ta t ion in einer kal ten Polarwüste erfolgte. Dieser S c h l u ß spricht für SCHWARZBACHS Deutung und nicht für die se ine r Opponen ten , und er belegt indirekt das Auftreten warthezei t l ichen Eises in Schlesien. Im vor l iegenden Be i ­ trag ward außerdem die mögl iche Ausdehnung des Eises in das Trebni tzer Ka tzengeb i rge diskutiert. 1 I n t r o d u c t i o n MARTIN SCHWARZBACH in his work "Das Diluvium Schlesiens" (1942 ) discussed broadly the problem o f extent and sediment stratigraphy o f the Wartanian (War the) stage in Middle Silesia. His major data c a m e from the Trzebnica Hills (Trebnitzer Katzenge­ bi rge) and from its southern foreland. SCHWARZBACH ( 1 9 4 2 ) definitevely established that the maximum extent o f the Wartanian stage in Middle Silesia is on the top o f the Trzebnica Rampart. T h e main argu­ ments were the till o f this age which was found in several sections near Trzebnica and because the Wartanian outwash plain was found (Zedlitzer San­ der, Siedlec Sandur) in the southern foreland o f the rampart. Now, after fifty years, the discussion on sta­ tus o f the Wartanian stage in Silesia is coming back. A series o f papers has presented data which suggest that there ist no Wartanian deposits in Middle Silesia (WINNICKI 1990, 1991 , WINNICKI & SKOMPSKI 1991) . Fortunately, some o f the "classical" sections, which w e r e examinated by SCHWARZBACH ( 1 9 4 2 ) , have been lately again exposed . This make possible to re­ examine SCHWARZBACH'S interpretation and discuss m o r e critically the "Wartanian problem" in south­ western Poland. T h e paper presents detailed data from Pierwoszow (Pürbischau) outcrop (SCHWARZ­ BACH 1942, page 212-218 , figures 6 -10) and from two n e w outcrops which are located southwards the Trzebnica Hills, on the plain which has been sup­ p o s e d to represent the Wartanian proglacial sandur (Fig. 1) . 54 DARII 'SZ KRZYSZKOWSKI i o o coutour lines m a s I distinct scarps I sites with the Wirtanian till WartQnion sandurs lolluvial fans) forested areas on the sandur m sires investigated in detail geological cross-sections see Fq 3 Fig. 1: Locat ion o f the S ied lec Sandur southwards the Trzebnica 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 ts s o u t h e r n f o r e l a n d 2 . 1 H i s t o r i c a l b a c k g r o u n d The Trzebnica Hills we re for many years the strato­ type region for the Silesian Pleistocene stratigraphy. FRECH ( 1 9 0 1 , 1904) descr ibed two tills in superpositi­ on in Trzebnica outcrops: the Elsterian and the Saalian one ; both were deformed together with Neogene clay in substratum. Later, TIETZE (1910, 1 9 1 5 ) and FRECH ( 1 9 1 3 ) found that two Pleistocene tills occur also southwards the Trzebnica Hills, near Wroclaw. DNTRICIT ( 1914 ) and then MEISTER ( 1 9 3 5 ) and SCHWARZBACH (1942) descr ibed the next till near Trzebnica , which overlay discordantly deformed, older tills and Neogene clay. This till, which was supposed to represent the Wartanian (SCHWARZBACH 1942) , w a s found only in few sections: G luchow Corny, T a c z o w Wielki, Radlow, Raszyn, Trzebnicki Las B u k o w y and Droszow (DITTRICH 1914, MEISTER 1935, SCHWARZBACH 1942) . In all cases, it was only 2-4 m thick, usually covered by loess and its lateral extent w a s unknown, presumably small. At the same time, there was discussion on genesis o f the Neogene/Qtia ternary sediment deformation found in Trzebnica Hills. Older authors prefered tectonic (endogenic) genesis (FRECH 1 9 0 1 , 1913, OLBRICHT 1924, CZAJKA 1931 , MEISTER 1 9 3 5 ) . How­ ever, s ince the work of BERGER (1937) , the glaciotectonic genesis (push mora ine) have been usually pre­ fered and the age o f deformation was related to the Wartanian stage (SCHWARZBACH 1942, W O L D S T E D T 1954, 1955, KRYGOWSKI 1950, WALCZAK 1951 , PACIIUCKI 1952, ROZYCKI 1957, 1968, ROTNICKI I 9 6 0 , 1967) , although G O L A B ( 1 9 5 1 ) and LYCZEWSKI ( 1 9 6 4 ) still advocated arguements on their tectonic genesis . 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 Recent geological investigations indicate that the Silesian Lowland (Wroc law region) can b e subdivid­ ed into two regions: the Wroclaw Basin with 4 0 8 0 m thick Pleistocene s equence , which is surrounded by areas with thin ( b e l o w 20 m) or no Pleis tocene deposits and with N e o g e n e clays at the ground sur­ face (CZERWONKA & KRZYSZKOWSKI 1992) . Th ree PleisThe Wartanian Siedlec Sandur (Zedlitzer Sander ) 5 5 t ocene glacial units, including three tills have been found in the Wroclaw Basin (CZKRWONKA & KRZYSZ­ KOWSKI 1 9 9 2 ) . The lowermost till, the Pietrzykowice Till, is characterized by large predominance o f Scan­ dinavian, crystalline rocks; the middle till, the Wierzbno Till, is characterized by a predominance o f Baltic limestones; and the uppermost, the Smolna Till, is again characterized by predominance o f Scan­ dinavian crystalline rocks. On the other hand, the locally-derived rocks s h o w palaeotransport from NW to SE for both Pietrzykowice and Wierzbno Tills and from NE to SW for the Smolna Till. These tills were interpreted to represent two stadials o f the Elsterian (Pietrzykowice and Wierzbno Til ls) and the older Saalian (Drenthe, Odranian) stage (Smolna Till) (CZERWONKA & KRZYSZKOWSKI 1 9 9 2 ) . In the northern part of the Wroclaw Basin, at the southern margin o f the Trzebnica Hills, this s equence is covered additionally by 1 0 3 0 m thick series o f sands and gravels the Siedlec Formation, and by 0 , 5 1 ,5 m thick loess (Figs 2 and 3 ) . T h e Pleistocene geology o f ..the Trzebnica Hills is more complex. Most o f outcrops have only one till, which most problably represent an equivalent of the Smolna Till (the Odranian-Drenthe s tage) (WINNICKI & SKOMESKI 1 9 9 1 ) . This till is usually deformed together with glaciofluvial and glaciolacustrine de­ posits and/or with Neogene clay forming fold or thrust zones. KRZYSZKOWSKI ( 1 9 9 2 ) descr ibed in the northern part o f Trzebnica Hills, from both outcrops and borings, a set o f synclines and anticlines which comprise at least two tills. The lower till may corre­ spond with the Wierzbno Till and the upper one with the Smolna till o f the Wroclaw Basin. Other parts o f Trzebnica Hills has even less valuable data. Most o f borings have only s imple lithological description o f deposits with no petrological data. Hence , lithostratigraphic correlation o f deposits is very difficult, although it seems that at least two tills occur here, similarly to the northern part o f Trzebnica Hills (Fig. 2 ) . Some o f bor ings comprise several alternating sequences o f tills, sands, glaciolacustrine silts and Neogene clays. O the r borings, in turn, comprise only Neogene deposi ts with 5 1 0 m thick till or loess at the top. Such s e q u e n c e s can be easily interpreted as representing thrust structures (Fig. 3 a ) . T h e age o f sediment deformation in Trzebnica Hills, as in whole Silesian Rampart, is recently related rather to the Odranian (Dren the) stage than to the Wartanian (Warthe) (SZCZEEANKIEWICZ 1 9 6 9 , BRODZIKOWSKI 1 9 8 2 , 1 9 8 7 ) . The rampart is interpreted as push moraine overrided by an ice-sheet during a continuous ad­ vance . The margin o f the Odranian ice-sheet is lo­ cated about 7 0 8 0 km sosuthwards from the Trzeb­ nica Hills. T h e occurrence o f the Wartanian till in Trzebnica Hills cannot be confirmed or rejected by recent in­ vestigation. The conclus ion by WINNICKI (WINNICKI northern port of the Trzebnica Hills Trzebnica southern part of the Trzebnica Hills GTUCHDW northernmost part of the Wroclaw Basin

A series of papers has presented data which suggest that there ist no Wartanian deposits in Middle Silesia (WINNICKI 1990, 1991, WINNICKI & SKOMPSKI 1991).
Fortunately, some of the "classical" sections, which were examinated by SCHWARZBACH (1942) 2 Geology of the Trzebnica Hills and its southern foreland

Historical background
The Trzebnica Hills were for many years the strato type region for the Silesian Pleistocene stratigraphy.FRECH (1901FRECH ( , 1904) ) described two tills in superpositi on in Trzebnica outcrops: the Elsterian and the Saalian one; both were deformed together with Neogene clay in substratum.Later, TIETZE (1910, 1915) and FRECH (1913) found that two Pleistocene tills occur also southwards the Trzebnica Hills, near Wroclaw.DNTRICIT (1914) and then MEISTER (1935) and SCHWARZBACH (1942) described the next till near Trzebnica, which overlay discordantly deformed, older tills and Neogene clay.This till, which was supposed to represent the Wartanian (SCHWARZBACH 1942), was found only in few sections: Gluchow Corny, Taczow Wielki, Radlow, Raszyn, Trzebnicki Las Bukowy and Droszow (DITTRICH 1914, MEISTER 1935, SCHWARZBACH 1942).In all cases, it was only 2-4 m thick, usually covered by loess and its lateral extent was unknown, presumably small.
At the same time, there was discussion on genesis of the Neogene/Qtiaternary sediment deformation found in Trzebnica Hills.Older authors prefered tectonic (endogenic) genesis (FRECH 1901, 1913, OLBRICHT 1924, CZAJKA 1931, MEISTER 1935).How ever, since the work of BERGER (1937), the glaciotectonic genesis (push moraine) have been usually pre fered and the age of deformation was related to the Wartanian stage (SCHWARZBACH 1942, WOLDSTEDT 1954, 1955, KRYGOWSKI 1950, WALCZAK 1951, PACIIUCKI 1952, ROZYCKI 1957, 1968, ROTNICKI I960, 1967), although GOLAB (1951) and LYCZEWSKI (1964) still advocated arguements on their tectonic genesis.1990, 1991, WINNICKI & SKOMPSKI 1991), that he did not find the Wartanian tili in Trzebnica Hills during his geological mapping is rather wrong.None of the outcrop described by MEISTER (1935) and SCHWARZ BACH (1942) have been re-examined, simply because these outcrops are completely destroyed and vege tated.Hence, it seems that the older descriptions are still correct and can be adopted to recent strati graphy.If so, the possible Wartanian till is a till lying discordantly on older glacial and Neogene deposits.3 The Siedlec Sandur

General morphology and geology
The Siedlec Sandur (Siedlec Formation) is a sandygravelly, cone-shaped deposit lying on the Smolna till in the southern foreland of the Trzebnica Hills (Fig. 3 a & b).The plan view of these deposits is fanshaped and the contours bow downlope from two apexes, one near Pierwoszöw and other near Skarszyn, which lie at the border of ice-pushed ridge (Fig. 1).The cross fan profile is convex and radial profiles are usually flat or concave in the uppermost part but they are convex in the lowermost part of the fan.The slope inclination varies from 0,50 % to 1,67 %.Gen erally, three segments of the fan can be recognized from its morphology: the upper part of the fan with slope inclination ranging from 1,0 % to 1,33 %, the middle part of the fan with slope inclination be tween 0,5 % to 0,67 % and the lower part of the fan, near its southernmost margin, with slope inclination up to 1,67 %.The thickness of deposits decreases systematically from apex zones (ca.30 m) to its south ern margin, where is only thin (below 10 m) sandy cover on the hill.The southern margin of the Siedlec Sandur is marked by scarp, which represent also a sharp lithological boundary, between a sand and a till (Fig. 1).The last one forms a widespread till plain around the Siedlec Sandur.The boundary between the sandur and till plain sometimes visible as boundary between a forest and fields (Fig. 1).There are no good traces of outflow from the sandur to the Odra river valley, being south, from the time of its formation.The Siedlec Sandur is probably dissected only by younger valleys, infilled with Weichselian and Holocene fluvial deposits (Fig. 1).In the north ern part of the sandur, sandy-gravelly deposits are covered by 0,5 -1,5 m thick loess cover, which con tinues northwards, into a thick loess cover in Trzeb nica Hills (6 -20 m) (Fig. 2).

The sandur deposits
The principal deposit of the Siedlec Sandur is a coarse sand with a varying amount of gravel, low-Fig.4: General stratigraphy and sediment characteristic in Pierwoszöw outcrop.
1 2 Pig. 5: Detailed section of the Pierwoszöw outcrop (location is in Fig. 5) with levels of shallow troughs and gravels and clay balls, separated by horizontally bedded sands and pebble sands.angle or horizontally bedded.The latter sediment (Sh fades) dominate in the general picture of sandur se quence (Tabula 1, A). Gravels and/or clay balls may be concentrated in levels or be present in an isolated position.The lateral extension of horizontal strata is general in the order of some tens of metres.The thickness of these strata varies from several decime tres to several metres.The low-angle units have average lenght from some decimetres to some me tres and smaller thickness, reaching up to 0,5 m.These sediments are thought to represent sheetflood deposit (BULL 1972), deposited over large area by a shallow, supercritical flow during short periods with considerable discharge (MCKEE, CROSBY & BERRYHILL 1967, WILLIAMS 1971, MIALL 1977, FROSTICK & REID 1977, TUNBRIDGE 1981).The erosional surfa ces between deposits from different sheet-floods are often marked by small scour-and-fill structures (Sc fades) (Tabula 1 D).They are usually 2-6 centime tres deep and 10 -20 centimetres long, infilled by co arser material than in horizontal laminae.Small scours were formed locally during the sheet-floods.
In the sandur deposits described, the channel depo sits are less frequent and represent two types of channel-fills: shallow, single depressions (troughs) and trough cross-bedded sets with thickness up to 2 m (st fades).The shallow troughs are up to 0,5 m deep and about 1 -2 m wide and they usually have "festoon" lamination, parallel to the lower profile of trough (Tabula 1 B, C).The shallow troughs are of ten concentrated in levels, occurring in horizontally bedded deposits (Fig. 4,5 & 6).The shallow troLighs formed most probably during the vanning stages of floods, when low discharge occurred.Channel-fills formed during the next sheet-flood.The levels of shallow channels are believed to represent a former fan surface.In turn, the thick trough cross-bedded sets, which are usually interbedded with thin beds with horizontal bedding and some planar cross bed ding (Sp fades) Fig. 7), represent most probably large channel fills (BULL 1972, CHURCH & GILBERT 1975, BOOTHROYD & ASHLEY 1975, MIALL 1977, 1978, 1985, ALLEN 1983).
Very rare deposit, found in two sections, is a mas sive, fine sand to sandy silt.It is usually poorly sort ed deposit (diamicton, Dm fades).This fades forms 10 -15 cm thick, laterally extensive layers.Most prob ably, this fades represent an overbank deposit, form ed after main floods.
Additional feattire of the sandur deposits are normal faults (Tabula 1 E and Fig. 6).They were found in one outcrop (Biedrzyce), which is located on the valley bank.The faults cross all deposits, from the top to the bottom of outcrop.It seems, that they re present completely post-depositional feature, for med during the sediment gravity relacation on the slope.
tig. 7: The stratigraphy and sedimentary stmcaires of deposits in Wisznia Mala outcrop.

3-3 The Pierwoszöw outcrop
This outcrop is located in the main apex zone of the Siedlec Sandur, near village Pierwoszöw (Fig. 1).It was described at first by SCHWARZBACH (1942).Recent outcrop is 7 -8 m deeper than the SCHWARZBACH'S outcrop, with a section up to 17 m high (Tabula 1).
The section comprises almost only horizontally bed ded pebble sand and shallow channels, and a thin loess cover at the top (Fig. 4).The shallow channels are concentrated in two levels, one near bottom of the outcrop and other one about 5 -6 m from its bot tom.The uppermost part of the section (the old outcrop) has no shallow channels, containing only 8 -10 m thick, horizontally bedded strata (Fig. 4).Moreover, there are observed several, up to 0,5 m thick, horizontally bedded levels with gravels and clay balls (Fig. 4).In place, large clay balls are very concentrated, forming the "clay ball lags" (Fig. 5).
The clay balls are formed of Tertiary green clay and they have varying size, from a few millimetres up to 0,3 m, occasionally single clay balls may reach up to 0,5 m.The size of gravels is less changeable, from 1 to 10 centimetres.
The lower level of shallow channels have, in fact, at least three sub-levels of channels, which are sepa rated by horizontally bedded sands (Fig. 5).Neverthe less, all these channels occur within the bed with thickness of 1 m.The channels are formed practical ly of coarse sand, except two small troughs with gra vels.In turn, the upper level of shallow channels is more concentrated, contains larger troughs and it is formed in majority of gravels, although no clay balls have been observed (Fig. 5).Palaeocurrent measu rements from troughs show that there is no diffe rence between two levels mentioned, and that the transport of material was from north (Fig. 4).

The Biedrzyce outcrop
This outcrop is located in the apex zone of the small fan, tributary to the main alluvial fan, which is lo cated between villages Skarszyn and Biedrzyce (Figs. 1 and 6).Recent outcrop is 11 -12 metres high.
The Biedrzyce section, like in Pierwoszöw, com prises almost only horizontally bedded pebble sands and shallow channels and additionally a 10 -15 cm thick layer of massive, sandy diamicton.The shallow channels form two levels.The lower one is about 1 m thick and contains three sub-levels of troughs, se parated by horizontally bedded sands.The channels are formed both of coarse sands and pebble sands, although the latter are less common (Fig. 6).The lower level of shallow channels is followed by thin layer of massive, fine sand to sandy silt (sandy dia micton) (Fig. 6).This bed is laterally continuous, at least 4-5 metres.The upper level of shallow chan nels lies about 1,5 m above the lower one and it is formed of only one, 0,2-0,5 m thick bed with troughs.Some troughs of this level are, however, much larger than troughs of the lower level (Fig. 6).Moreover, these troughs contains usually pebble sands and gravels (with diameter up to 20 cm).
Within the horizontally bedded sand, only one level with clay balls and several levels of gravels can be observed (Fig. 6).Single clay balls are also observed in other horizontal beds and troughs.Palaeocurrent measurements from troughs indicate transport directly from north (Fig. 6).

The wisznia Mala outcrop
This outcrop is located near the western margin of the Siedlec Sandur, near village Wisznia Mala (Figs. 1 and 7).The section investigated is only 4 m high.
The Wisznia Mala section is threefold.The lower part of the section comprises an alternating cross bedded and horizontally beddes sands or pebble sands.The cross bedded sets are represented by large troughs, small troughs and planar sets.These de posits are followed by thin, but laterally continuous, massive, sandy silt with single, floating gravels (san dy diamicton).The middle part of the section, about 1 m thick, is represented by horizontally bedded sand with one shallow channel (Fig. 7).This sedi ment, although thin, is veiy similar to sediments from Pierwoszöw and Biedrzyce outcrops.The up per part of the section is occupied by planar cross bedded sand, representing, most probably, a part of similar sequence as in its lower part.The important fact is that no clay balls have been found in Wisznia Mala outcrop.The palaeocurrent measurements from trough and planar corss-bedding indicate trans port from north-east (Fig. 7).
Very interesting is the vertical succession of sedi ments (Fig. 8).In Pierwoszöw outcrop, there are three distinct layers which differ in grain size.The lower and upper one are represented mostly by me dium to coarse sands with only rare gravel beds, whereas the middle one is represented by pebble sands with common gravel beds.The coarser layer PIERWOSZÖW 180,0 m Q.s.1.comprises deposits from a bottom of upper level of shallow channels up to the uppermost gravel level, 3 -4 m below the loess (Figs. 4 & 8).The Biedrzyce section have almost the same stratigraphy: the lower layer with medium to coarse sands and coarser layer lying above.The latter starts from the bottom of up per level of shallow channels and continues up to the top of the section (Figs. 6 & 8).The thickness of sediments in the Wisznia Mala outcrop is small, prob ably not enough for inter pretation of vertical succes sion of grain size.Neverth eless, coarser deposits are more common in lower part of the outcrop, and probably they represent an equivalent of coarse, mid dle layer in Pierwoszöw.

Gravel petrography
The gravel petrography have been examined in two outcrops: Pierwoszöw and Biedrzyce.In the first one, samples have been ta ken from lower and upper part of the sequence.The size of examined gravels was 1-10 cm; the number of gravels in single sample varied from 128 (Pierwos zöw) to 192 (Biedrzyce).The results are presented in Table 1.Generally, gravel petrography shows for gla cial origin of deposits, most probably derived from a till.The time of deposition is rather young, because of large content of Baltic lime stones, comparable with the limestone content in tills.Lacking of large num ber of flint suggests, in turn, that the source material (till) was also not rich in flint.
The Smolna Till (Odranian, Drenthe), lying on the top of Trzebnica Hills is a flint-poor till (KRZYSZKOWSKI 1992), and it is one possible source of gravels.On the other hand, it seems that the source gla cial deposits may be also the Taczow Till (Wartani an, Warthe) or directly glacial material (moraine) de rived from the Wartanian ice sheet and transported by subglacial and proglacial streams.
The occurrence of non-resistant Mesozoic lime stones and Tertiary mudstones as well as large number of clay balls in deposits of uppermost part of the san- dur suggest that transport of material was not long.The distance from outcrops investigated to the first outcrops of the Taczow or Smolna Tills and Tertiary clays beeing northwards is about 2 km (MEISTER 1932, WINNICKI 1988).

Palaeoenvironmental interpretation
The Siedlec Sandur is a typical alluvial fan.This is considered from its fan-shaped geometry, texture of deposits and sedimentary structures (BULL 1972, HEWARD 1978).The specific feature is that the sandur plan is formed of two fans with apexes about 6 km each from the other.The apexes occur at the mouths of deep valleys cutting the margin of the ice-pushed ridge (Fig. 9).The sandur was formed by proglacial meltwater flowing from north, from the stagnating ice-sheet.The proglacial streams eroded both older glacial deposits and Tertiary clays at the basement, forming 2 km long, narrow and deep valleys before they have reached the margin of the ridge.The pre domination of horizontal or low angle bedding in the sandur deposits with only minor channel sedi mentation suggest sedimentary conditions typical for alluvial fans in arid climates (BULL 1972).Glacial origin of the fan material suggest, in turn, the cold (periglacial) conditions, most probably a polar desert.Generally, the sandur has two sedimentary zones: the fanheads with practically only sheet flood depo sition intermpted locally by minor scouring and fur ther towards the bordering ice pushed ridge a lower fan with braided channels and limited number of sheet floods (Fig. 9).Both fans, forming the sandur plain, have similar stratigraphic and sedimentary se quences suggesting that they were formed simulta neously and due to the same processes, in spite of different source area.This well correspond with pro glacial origin of the fan.The episodic floods occur red only during the melting of an ice-sheet, which is controlled regionally by changing year seasons.At first, the fanheads were characterized by frequent sheet floods intermpted by dry fan conditions with formation of only small channels.In turn, the next phase of fan development was characterized by ra pid but more episodic floods.The accumulated ma terial was usually coarser and no minor channels were formed, suggesting larger water discharge at this time.Probably, this change of sedimentary envi ronment is a result of increasing aridity.The flood water was channelized into braided channels at the lower fan during both phases described.These channels were, most probably, also ephemeral.Lacking of outflow from the fan suggests that water might have evaporated or infiltrated almost at the fan.This probably agrees with the fan morphology.The middle segment of the fan is very flat, sug gesting high aggradadion rates.The same processes might also have created the steep slope of the lowermost segment of the fan.

Conclusions
From description and interpretation above it is clear that the Siedlec Sandur may be considered as pro glacial alluvial fan deposited in periglacial, arid climate and formed at the margin of the ice-pushed ridge.The proglacial sandurs are rather common southwards the Trzebnica Hills (Fig. 9) and they prob ably have the same features as sandur described.The similar sand bodies, with the same sedimentary structures, fan morphology and similar geographic position at the margins of Saalian ice-pushed ridges have been also described as alluvial fans (sandurs) in the Netherlands (AUGUSTINUS & RIEZEBOS 1971, RUEGG 1977, 1981).
The age of Siedlec Formation (sandur) can be consi dered from its relation to Smolna Till -the till depo sited by the Odranian (Drenthe) ice-sheet, the san dur is undoubtedly younger, lying on the Smolna till (Fig. 2 & 3).Hence, it seems that it is a proglacial equivalent of the Taczow Till, deposited by the War tanian ice-sheet stagnating on the top of Trzebnica Hills.This interpretation agrees with the former view by SCHWARZBACH (1942) but contradicts the view of WINNICKI (1990WINNICKI ( , 1991)).The last author is interpreting the sand body of the Siedlec Formation as käme pla teau deposited during the decay of the Odranian (Drenthe) ice-sheet.
Although the alluvial fan genesis for the Siedlec For mation deposits seems to be unquestionable, there are some problems which are still unclear.First of all, there is small evidence for braided channel sedi mentation at the lower fan (one outcrop with section only 4 m high).Also, there is no outcrops at the steep slope of the lowermost segment of the sandurhence, the genesis of this slope is not solved satis factorily, yet.Periglacial conditions (polar desert) should be confirmed by an occurrence of frost fissu res or ice wedge casts or other permafrost indicators, but deposits investigated have no such periglacial stmctures.This is unexpected characteristic of the Siedlec Sandur, because for example the Weichse lian proglacial sandurs in Poland have large number of permafrost indicators (KOZARSKI 1974(KOZARSKI , 1992)).Fur ther sedimentological investigations of other Warta nian proglacial sandurs lying southwards the Trzeb nica Hills (Fig. 10) should examine whether the sheet flood deposition is only local feature of the Siedlec Sandur or is climatically controlled occurring in whole region.These investigations should solve definitevely the problem of outflow from sandurs to the river Odra valley and solve the stratigraphic rela tion between the sandurs and so known "upper" ter race of the river Odra valley, supposed to represent the Wartanian (SZCZEPANKIEWICZ 1959, ROZYCKI 1969).
Both problems have not been solved satisfactorily for the Siedlec Sandur.
his work "Das Diluvium Schlesiens" (1942) discussed broadly the problem of extent and sediment stratigraphy of the Wartanian (Warthe) stage in Middle Silesia.His major data came from the Trzebnica Hills (Trebnitzer Katzenge birge) and from its southern foreland.SCHWARZBACH (1942) definitevely established that the maximum extent of the Wartanian stage in Middle Silesia is on the top of the Trzebnica Rampart.The main argu ments were the till of this age which was found in several sections near Trzebnica and because the Wartanian outwash plain was found (Zedlitzer San der, Siedlec Sandur) in the southern foreland of the rampart.Now, after fifty years, the discussion on sta tus of the Wartanian stage in Silesia is coming back.

Fig. 2 :
Fig. 2: Stratigraphy of Pleistocene deposits of the northern part of Silesian Lowland (Wroclaw Basin) and Trzebnica Hills.

Fig. 3 :
Fig. 3: Geological cross sections throughout the Siedlec Sandur and southernmost part of Trzebnica Hills.Location ol sections is in Fig. 1.

Fig. 3 :
Fig. 3: Geological cross sections throughout the Siedlec Sandur and southernmost part of Trzebnica Hills.Location of sections is in Fig. 1.
I propose a lithostratigraphic name for this till -the Taczöw Till, from Taczow outcrop, described in detail by MEISTER (1935, p. 8) (Fig 2).The similar sequence was then described in the next village -Brochocin (Brockotschine = Moltketal) by SCHWARZ BACH (1942).All sites with the Taczow Till mentioned by MEISTER (1935) and SCHWARZBACH (1942) are shown approximately in Fig. 1 and they mark possible southernmost extent of the Wartanian icesheet in Trzebnica Hills.

Fig. 6 :
Fig. 6: The stratigraphy and sedimentary structures of deposits in Biedrzyce outcrop.Two levels of shallow troughs and one level of clay balls are visible in lower part of the section.
Fig. 8: The grain size distribution and vertical succession of features of deposits of the Siedlec Sandur.

Fig. 9 :
Fig. 9: General palaeogeographic interpretation of the Siedlec Sandur in relation to position of the Wartanian ice-sheet at the Trzebnica Hills.