The section at Lundarvatn

(1)

F O S S I L I C E W E D G E S A N D G R O U N D W E D G E S I N S E D I M E N T S B E L O W T I L L A T V O S S ,

W E S T E R N N O R W A Y

JAN MANGERUD & SVEIN ARNE SKREDEN

M a n g e r u d , J . & S k r e < l e n , S . A . : F o s s i l i c e w e d g e s a n d g r o u n d w e d g e s i n s e d i m e n t s b e l o w t i l l a t V o s s , w e s t e r n N o r w a y ' N o r s k G e o l o g i s k T i d s s k r i f t ' V o l . 5 2 , p p . 7 3 - 9 6 . O s l o 1 9 7 2 .

I n a 3 t o 4 m h i g h s e c t i o n , t h e f o l l o w i n g f o u r d i s t i n c t s e d i m e n t u n i t s e x i s t : A t t h e b a s e a w e l l - s o r t e d s a n d o f u n c e r t a i n o r i g i n ; a b o v e t h i s a b e d o f t i l l ( b e l i e v e d t o b e l o < l g e m e n t ti l l ) ; a b o v e t h i s b e d d e d s a n d , s i l t a n d c l a y , p r e s u m - a b l y d e p o s i t e d i n a n i c e - d a m m e d l a k e ; a n d o n t o p , a y o u n g e r l o d g e m e n t t i l l ' A l l t h e i e d i m e n t s b e l o w t h e u p p e r t i l l a r e c u t t h r o u g h b y t w o d i f f e r e n t t y p e s of we<lge-like structures. The wedges of the first type are filled with unsorted s e < l i m e n t s a n d a r e i n t e r p r e t e d a s f o s s i l i c e w e d g e s . T h e s e c o n d t y p e c o n s i s t s o f v e r t i c a l l y l a m i n a t e d c l a y a n d s i l t , p r e s u m a b l y a k i n d o f g r o u n d w e d g e ' T h e s e d i m e n t s a n < J t h e w e d g e s t r u c t u r e s a r e b e l i e v e d t o b e o f e i t h e r A l l e r d d / Younger Dryas age, or from older Weichselian interstadials'

J . M a n g e r u d , G e o l o g i s k i n s t i t u t t , a v d . B , ( J n i v e r s i t e t e t i Bergen,5014 Bergert- U n i v e r s i t e t e t , N o r w a Y .

s . A . S k r e t l e n , G e o l o g i s k i n s t i t u t t , a v d . B , ( J n i v e r s i t c t e t i Bergen, 5014 Bergen- U niv ersitetet, N o rwaY.

Introduction

Voss is situated in a broad and deep west Norwegian valley. The valley floor is45_15 m a.s.l., while the surrounding mountains rise to between 1300 and 1400 m a.s.l. (Figs. 1 and 2). Bedrock is exposed in most of the mountain area, while considerable deposits of till and glacio-fluvial sediments occur in the valleys.

Examination of the glacial striae (Skreden 1967) shows that the oldest ice movement was approximately towards the west (Figs. 1 and 2). Roughly speaking, this movement was independent of the topography, and is interpreted as representing a period of complete glaciation of the area. During this period the ice spread radially from an ice shed over the mountains further east.

Later the ice movement changed direction towards SW and s (Fig. 2).

During this later period the ice spread radially from an ice shed in the mountain areas between voss and Sognefjorden, northwest of voss. As the ice melted it became increasingly influenced by the topography, and finally became valley glaciers (Fig. 2, youngest) with outlets through the valleys of Voss-Granvin and Voss-Evanger. The final deglaciation of the Voss area seems to have taken place in Pre-Boreal time (Mreland 1963, Skreden 1967).

(2)

74 J . M A N G E R U D & S . A . S K R E D E N

t

/-- )

- - \

' ) \

F i g . 1 . M a p o f t h e V o s s a r e a . Glacial striae according to Skreden (1967). Numbr a l t i t u d e i n r n a . s . l . T h e d e s c r i b e d section at Lundarvatn is situated where the till fabric i s p l o t t e d . I n s e t i s a k e y m a p of southern Norway.

The section at Lundarvatn

During field work in 1965, an interesting section was discovered in a building excavation near Lundarvatn (Fig. 1). The field work was carried out by Svein Arne Skreden under Jan Mangcrud's guidance, and although this article has been written by Mangerud most of the field descriptions used are from Skreden's thesis (Skreden 1967).

Thick deposits forming an inclined ledge of 5-600 m in length along the western side of the valley are found here (Fig. 4). The building site is situated

130 m a.s.l. on a projecting ridge (remnant ridge) between two ravines cutting through thc ledge. The ravines fall from between 150 to 80 m a.s.l.

Profiles along the ridge and ravines (Fig. 3) show that the sediments are at least 20 m thick, probably considerably more.

(3)

FOSSIL ICE WEDGES AND GROUND WEDGES AT VOSS 75

Fig. 2. Schematic map showing the different ice based on an interpretation of the glacial striae.

@

0 5 1 0 k m

C o n t o u r ; n t e r v a l 5 0 0 m

€ l , u . t a b o v c 1 0 0 0 m

movements in the Voss area mainly

l Y o u n g c .

+Lpro""t

. , 1 , , - , , , i \ ,

< . - - . - \ ( Y o u n g c s t

- P r o f i l e I - - - - P r o f i t e I I

B u i t d i n g s i t e

275 250 2 2 5 200 175 1 5 0 125 100

? - - -

L u n d a r v a t n ,

Fig. 3. Profiles along the valley side at Voss. Profile I along the remnant ridge where the building site was located. Profile II in the ravine just north of the building site.

9 0 0 500

m . a . s . t .

(4)

76 J. MANGERUD & S. A. SKREDEN

Fig. 4. on the valley floor Lundarvatn can be seen to the right in the foreground. The building site is indicated by an arrow. (photo towards SW.)

Fig. 5. Profile along the excavated walls. A sketch map of the building site is inset in the upper right corner. The corners in the building site are denoted by letters also shown in the profile. The excavated wall BC thus lies at right angles to walls AB and CD.

V o s s C l a y a n d 5 i l t [_Fis 6______-_-]

c l a y m a r k e r b e d

l o w e r t i l l L u n d a r v a l n S a n d

f o s s i l e i c e - w e d g e

t a m i n a t e d w e d g e s a n d v e l n s c r e e p ( s o l i f l u c t i o n ) d e p o s i t s

- . - - - - e r a " u " , " a

a \ J o

V L q '

D

N o t e x c a v a t e d

(5)

FOSSIL ICE WF,DGES AND GROUND WEDGES AT VOSS

The main characteristics of the section are shown in Fis. 5 with four well defined units:

On the top a bed of till; upper till.

Then follows stratified sand, silt and clay, which we call Voss Clay and Silr.

A b e d o f t i l l ; l o w e r t i l l .

In the bottom there is sand which we call Lundarvatn Sand.

The three lower units are cut through by younger wedge structures which rve will discuss in detail.

LUNDARVATN SAND

The Lundarvatn Sand is exposed in excavation rvalls AB and CD, as well as in a ditch from corner D (Fig. 5). Except for some clay which was found under the sand in this ditch, the material below the sand is unknown. The Lundarvatn Sand is mainly fine and is well sorted. Fig. 12 shows the grain size distribution of three samples from different levels in wall cD. The sand is very homogeneous with few visible structures. weak stratification was seen in only a few places.

In wall CD (Fig. 5) the sand was more consolidated in the upper part.

Analysis of the porosity, both in a natural, undisturbed condition as well as in the laboratory, by artificially decreasing the porosity by stamping, shows that the higher consolidation is partly due to tight packing.

The origin of the sand is uncertain. but is most probably glacio-fluvial.

- F i n l O - _

' - - r - : - I

T - " o A " ' : 3 S

t;5:o??b':::

:#i*,fl

F F i s l 3 a - - - 1

.--:._]- ! s f

,-, o E_;-- .Y <) o"^ol

J V A' JV

a V Y 6 v O

(6)

Fig. 6. Photo of wa1l cD (Fig. 5). The length of the spade is 70 cm. The natural surface is indicated by the unbroken line. The upper and lower boundaries of voss clay and Silt are indicated by stippled lines.

LOWER TILL

The lower till is exposed in all the excavated walls (Fig. 5). The thickness varies from 0.5 m to at least 1.5 m. The boundary between the till and the sand below is very well defined, and only small amounts of sand seem to be incorporated in the lower till. The upper boundary of the till is very uneven (Fig. 6); this is partly because of later deformation. The till is nonsorted (see sample l taken in corner A, Fig. 11). In wail cD the boulder content is normal for lodgement tills, while it is poor in wall AB. we do not attach any importanca to this difference which is believed to be accidental.

rn wall cD a fabric analysis of the longest axes for 100 pebbles was carried out (Fig. 7). This revealed a maximum in the sector w-NW or E-sE.

we have interpreted this till as a lodgement till; the fabric indicates the direction of the ice movement. The till contains approximately 5% anorthositic rocks in the pebble fraction. Anorthosite occurs only E of voss, therefore the most probable ice movement seems to have been towards N-NW. This movement was diagonally across the valley, and parallel with the oldest glacial striae in the area (Figs. 1 and2). Accordingly we assume that the till was deposited simultaneously with the ice movement indicated by these striae.

VOSS CLAY AND SILT

The thickness of voss clay and Silt varies from 0.5 to 2 m. In places some beds are eroded and many deformations of the primary beds can be seen.

(7)

! p p e r r r L l

l l

l - l

5 5 p e b b l e s S

Orientation of longest axes of 100 stones in each of the two beds of till

About the middle of the sequence, however, there is a bed of dark clay, 5-6 cm thick, which differs much from the rest of the sequence. We call this the 'clay

marker bed' (Fig. -5), and the continuity of the bed shows an ab- sence of faulting or displacement to any measurable degree.

The sequence is complete in wall AB (to the right in Fig. 10) and will be described below. The base q)nsists of about 20 lamina of well-sorted clay and silt, 20 cm thick. Isolated pebbles in the lamina must have been dropped from drifting ice simultaneously with the deposition of clay and silt. This is particularly evident at the top, where a clay lamina with many pebbles occurs. Above the latter lamina follow sand and silt (Fig. 12, sample 8) decreasing in grain size upwards to the mentioned 'clay

marker bed'. This consists of fine-grained bluish, black clay, with c. 45/c clay (12 y) (Fig. 12, sample 7). The part of the sequence below the 'clay marker bed' with sand, silt and clay, can be regarded as an irregular type of graded bedding. There is, however, no real continuous decrease in grain size upwards. Sand and silt beds alternate several times, the thickness varying considerably. Above the 'clay marker bed' there is a new irregular graded bedding with sand and gravel near the base, above this sand (Fig. 12, sample 6) and silt, and at the top there are seven well-defined, thin lamina with clay. This part of the sequence is repeated once with sand grading into silt and a bed of clay 7 cm thick. At the top of the Voss Clay and Silt, sand is found with a thin lamina of clay.

It is obvious that all the fine-grained beds of clay must have been deposited in quiescent water, and the Voss Clay and Silt must accordingly be lacustrine or marine sediments. As will be described below, the sediments are practically void of fossils. The Late Weichselian marine limits is 97 m a.s.l.

(Skreden 1967) while the described section is situated 130 m a.s.l. This does not exclude the possibility that the sea may previously have reached this level. The many changes between in the lamina, however, indicate that these

(8)

8 0

5 0

I. MANGERUD & S. A. SKREDEN

u p p e r ti l t l o w e r t i l l

Fig. 8. Roundness analyses of pebbles in the tills according to Pettijohn's (1957) clas- sification. 100 pebbles in each sample.

sediments have been deposited in an ice-dammed lake. In any case one must assume that the pebbles found here and there in the sediments have been dropped from drifting ice.

U P P E R T I L L

The upper till can be found in large parts of the section, but is disturbed by creep (solifluction) on the slopes. The lower boundary is indistinct in most places, with a gradual transition from the underlying sediments. About 0.5 m has been removed from the top, but this seems to have been weathered soils and creep sediments derived from the till. The till can be characterized as having a normal content of boulders, and is completely unsorted (Fig. 11, sample 2).

An important question is whether the till is lying in situ, or if it has been redeposited by creep or slide. We concluded that it is a lodgement till in situ on the basis of the following observations. The upper till is tightly packed and the fissility structures are typical of lodgement tills. A fabric analysis of

100 pebbles (Fig.7) shows a well-defined maximum of the longest axes in the direction NE-SW. This direction cuts obliquely across the slope of the valley side, and it is therefore unlikely that it is due to creep or other mass movements (Johansson 1965).

If one accepts that this is a lodgement till, the fabric shows that it has been deposited by an ice movement towards SW, cutting diagonally across the valley. The upper till contains many rounded pebbles (Fig. 8) indicating that older fluvial or glacio-fluvial sediments have been eroded by the ice and incoroorated in the till.

. : ] "

,rl

,tl

t :

> o 6 u t

6 q q c o

oC

0 9 )o

o o

> o o !

l c c 9 6 - t

@ G g L

1 l

o , : c o o

^ o o

l o o

o

(9)

FOSSII- ICE WEDGES AND GROUND WEDGES AT VOSS 81

Wedge-like structures

In the section two different types of wedge structures were found (Figs. 10 and 13). we describe them as unsorted. n-edges and. laminated wedges. wedge structures can be formed in several ways (Johnsson 1959, Dylik & Maarleveld 7967, Paepe & Pissart 1969). However, it seems obvious that the described wedges were formed by thermal (frost) contraction in frozen ground (a short literature survey on such wedges is given below). It should be mentioned here that many other deformations of the primary beds in voss clay and Silt exist. They will not be discussed in this article, but we would like to draw attention to the fact that they resemble involutions which are usually interpreted as fossil periglacial structures (West I96g).

REMARKS ON LITERATURE

wedges formed by thermal (frost) concentraction can be genetically divided into four groups (Dylik 1966, Dylik & Maarlevetd 1961, p6w6 et al. 1969):

Ice wedges, fossil ice wedges, ground weclges, seasonal irost crack.s. Lce wedges and ground wedges can only be formed in permafrost.

Ice wedges (ice f issures)

There seems to be general agreement on Leffingwells 'contraction theory' on the formation of ice wedges (Lachenbruch 1962, Dylik 1966, p6w6 et al.',969).

According to this there are three important processes: During cold periods in winter, the frozen ground contracts and cracks into polygons. In spring, melt-water flows into the fissures and freezes because the ground temperature is below 0 "c. During summer, only the surface (the active layer) melts, but in the perennially frozen ground below, the temperature also rises causing an increase in volume. As the fissure formed during the winter is now filled with ice, expansion takes place, usually as an upturning near the fissures, through deformations in the frozen sediments. The ice-filled fissures are now supposed to be zones of weakness, and therefore the processes described are repeated in the same zones in succeeding years. The ice-filled fissures grow in thickness (Fig. 9) and become wedge-like in cross section; this is the origin of the term 'ice wedge'.

Fossil ice wedges (ice-wedge casts)

From a geological point of view, it is very important that ice wedges consist of foliated, but nearly pure ice. This is probably due to the fact that the ice wedge is filled with ice early in spring while the ground is still covered by snow. At any rate the formation of fossil ice wedges requires a replace- ment of the ice by sediments. This occurs during climatic changes which cause the permafrost to melt. The ice wedges also eventually melt, and in the open spaces formed, sediments fill from above and from the sides. These processes are discussed among others by Dylik (1966) an<l p6w6 er al. (1969). Depend- ing on topography, climate, types of sediments and other factors. the oro-

(10)

I C E W E D G E F O R M A T I O N F O S S I L I C E

C o l l o p s e o b o v e r c e w e d g e ,

P c r m o f r o s l

J

r / r e 9 u l r . s l u m 0 r n g o n d

l s t F o l l

, - O p e n c r o c k

W E D G E F O R M A T I O N

I w o r m i n g

W r n t e r

N r h f o r f

Fig. 9. Schematic illustrations showing the formation of ice wedges and fossil ice wedges (from P6w6 et al. (1969)).

cesses, and accordingly also the fossil ice wedges, vary from place to place.

F i g . 9 s h o w s h o w P 6 w 6 e t a l . ( 1 9 6 9 ) t h o u g h t t h e w e d g e s in t h e D o n e l l y Dome Area in Alaska had been formed. We draw attention to the fact that the walls here consist of sand and gravel, and therefore collapse easily.

O p e n c r o c k S i l l o n d s o n d

u o s h e d l n b y s u r f o c e w o l e r , /4----_-:::-===

_lJ--:_-- -:-

a / ' - -

/zZi:.- -.-r-'-=.->

- - \ \ - \ \ \

r-i oilo Z o) e .

- - : < l _ - - \

^ . r r v e . l = 0 Y e ,

- : - - - - :

(11)

FOSSII- ]C]E WEDGES AND GROUND WEDGES AT VOSS

walls of silt and clay are more stable and the form of the ice wedge will accordingly be better preserved. It is typical of fossil ice wedges that they consist of unstratified sediments.

(]round wedges (ground fissures)

Permafrost cracks where the fissures have filled primarily with sediments, and not with ice, have recently been described, and Dylik (1966) suggests that they should be named ground wedges. They were probably formed in the same way as ice wedges, but as the wedge is filled primarily with sediments, small changes (if any) take place during the transition into a fossil stage. As a good example of ground wcdges, the sand wedges described by Pew6 (1959) from the Antarctic can be mentior.red. These are filled with unstratified sand, and are dependent on an extremely arid climate so that the cracks fill with dry sand during spring and summer.

wedges consisting of ice and sand in vertical lamination from an extremely arid permafrost area in canada are described by pissart (1968). This type must be classified as an intermediate type between ice wedges an<1 ground wedges. Pissart (1968) maintains, however, that the structures will be so well preserved when the ice melts that they will be recognized in fossil wedges.

Seasona! lrost cracks

As the term indicates, these cracks are formed during seasonal frozen ground, and in fossil form it is very important to distinguish them from fossil ice wedges and fossil ground wedges, which indicate permafrost at the time of formation. However, the mode of formation almost corresponds to that of ice wedges and ground wedges (Dylik 1966, P6w6 et al. 1969) with cracking due to rapid and great falls in temperature in the winter and filring in of sediments in the cracks during spring. The formation of frost cracks during severe frost in frozen ground outside the permafrost areas has been observecl by a number of workers (Washburn et al. 1963, Thorarinsson 1964, Seppiilei 1 9 6 6 , D y l i k 1 9 6 6 , S v e n s s o n 1 9 6 7 , P 6 w 6 e t a l . 1 9 6 9 ) . In s o m e o f these cases the frost cracks are isolated occurrences not resulting in any further crack development. Seppiilri (1966) describes wedges filled with sediments without internal structures. According to Dylik (1966) seasonal frost cracks with vertical lamination have been described in Soviet literature.

UNSORTED WEDGES

ln the section, five wedges filled with unsorted sediments were found. The most regular is shown in Fig. 10. This wedge is approximately 2 m high and 0.5 m wide at the top. It cuts mainly well-sorted, stratified sediments (voss CIay and Silt) and is very distinct. Along the sides of the wedge, the clay beds are downturned and broken, frequently in such a way that parts of the clay bed are incorporated in the wedge. The top of the wedge reaches slightly above the base of the upper till. The boundaries here are also well-defined.

Two bodies of the till are found in the upper part of the wedge, and in the

(12)

84 J. MANGERUD & S. A, SKREDEN

2

7 l a m i n a c l a Y

c l a y m a r k e r b e d

t . f , c l a y w r t h

b b l e s a . 2 0 l a m i n a c l a y a n d s i l t

L u n d a r - v a t n

N o t e x c a v a t e d

Fig. 10. Sketch showing the most regular of the unsorted wedges (fossil ice wedge), (see Fig. 5). The sketch also gives the lithostratigraphy in more detail.

base some large cobbles (minimum diameter about 10 cm) and lumps of clay are found. Apart from these lumps, the material in the wedges is totally unsorted (Fig. 11, sample 3). The wedge reaches the lower till, but here the boundaries are poorly-defined.

The other wedges are much ,the same, apart from two features' Firstly, they are more irregular in sbape, especially in the basal parts where they can be cornpared with some of the wedges P6w6 et al. (1969) describe. Secondly, some of the wedges have less well-defined boundaries against the overlying till. The horizontal extent of all unsorted wedges are unknoryvn.

The wedges are all too large to be seasonal frost cracks; the large cobbles in the wedges also contradict such a theory. Annual expansion of thermal

:ii:.:ri.,"ii.!i"

l.:,-tl:.+' r ' . . . ' ' , ' : : :

ii

.^s.o

0

(13)

1 1 2 5 6

Fig. 1.1. Grain size distributions, cumulative upper till; Sample 3: unsorted wedge (fossil wedge (ground wedge).

: 5 0 : c !

c u r v e s . S a m p l e 1 : l o w e r t i l l ; i c e w e d g e ) ; S a m p l e s 4 a n d 5

Sample 2:

laminated

Fig. I2.Crain size distributions, cumulative.rruo. rurnpre 6: sand just abov] clay marker bed; Sample 7: clay marker bed; Sample 8: silt immediately below clay marker bed; Samples 9, 10 and 11: Lundarvatn Sand.

contraction cracks is no more than a few mm (P6w6 1966, Dylik & Maarle- veld 1967), neither in seasonal frozen ground nor in permafrost. The latter condition and the structures in the walls clearly indicate that they are not ground wedges. The unsorted wedges have, however, almost all the characteristics described for fossil ice wedges (Dylik & Maarleveld 1961), and in accordance with this theory, all the observations given above can be ex- plained. For this reason we draw the conclusion that the unsorted wedges are lossil ice wedges.

(14)

The next problem was the stratigraphical situation of the wedges, which are clearly younger than voss clay and Silt. since bodies of upper till occur in the wedges, fossilization is undoubtedly younger than this till. Accordingly, a possible interpretation is that both the formation of the ice wedse and

(15)

subsequent fossilization are younger than the upper till, and that the part of the till overlying the wedges shows the active layer (Fig. 9). However, several observations of the wedge in Fig. 10 contradict this theory. It has a well- defined boundary against the till, and at the top (higher than the Voss Clay and Silt, Fig. 10) a mixture o,f sand, clay and till is found. The till above is densely packed, and has the same fissility structures as the adjoining till.

Fig. 13b. Close up photo of the laminated wedge (Fig. 13a) in Lundarvatn Sand.

(16)

There are no signs of collapse either in the till or on the surface as a result of ice melting in the ice wedges.

We therefore suggest the following interpretation. The formation of the ice wedges took place after the deposition of Voss Clay and Silt. Then followed an ice advance over the area while there was still permafrost. At the base of a temperate glacier the ice is at pressure melting-point, and the permafrost condition ceases to exist. Thus the fossilization of the wedges took place below the ice, and the wedges were partly filled from the top with already deposited lodgement till. The sharply defined upper boundary might be a somewhat younger erosional surface formed by the same glacier, and as the tops of the wedges reach above Voss Clay and Silt, they must have been more resistant to glacial erosion.

A possible fossil ice wedge from south Norway has earlier been described by Rye (1966). From north Norway a series of fossil ice wedges and fossil ice-wedge polygons (named 'tundra polygons' by Svensson) have been described by Svensson (1962,1963) and Svensson et al. (1967). Recently fossil ice wedges have been found at Jreren, southwest Norway (Bergersen & Fol- l e s t a d 1 9 7 1 ) .

LAMINATED WEDGES

The most striking structures in the described section were some vertical or inclined wedges and veins with well-sorted clay, silt and some sand. As it seems quite evident that the vertical internal structures are primary bedding formed by sedimentation, we have described the wedges as laminated wedges.

The largest laminated wedge is found in wall AB about 5 m from A (Figs.

5 and 13a). We will mainly describe and discuss the formation of this. The visible part of the wedge is approximately 2 m high, but where it disappears into the unexcavated ground it is still 18 cm wide. On the floor of the excavation, 1.5 m of the wedge is exposed. In the wall the wedge occurs mainly in Lundarvatn Sand, and here it is vertical. In the upper parts the wedge is tilted and the conditions are less clear because of later disturbances. There can be no doubt, however, that the wedge penetrates the lower parts of Voss Clay and Silt (Figs. 5 and 13a). The upper part of Voss Clay and Silt and upper till is redeposited here by later creep, and it also seems as if a greater part of the tilting of the wedge is due to these processes. The maximum width of the wedge is 25-30 cm, and in the sand it divides into branches which gradually become more and more narrow downwards. There are well-defined boundaries between the wedge and the sand, but the sand is partly impreg- nated by fine-grained material from the wedge. The material of the wedge is mainly sitt (Fig. 11. sample 4). but it contains thin dark lamina of clay, and also lamina of sand. The individual lamina and lenses are approximately vertical and fairly parallel but extremely irregular (Figs. 13b and |4), inter- section also sometimes taking place (Fig. 14, upper part). ln addition to what has already been stated about the boundaries of the wedge, it should be mentioned that Lundarvatn Sand is slightly folded upwards along it. Between

(17)

FOSSIL ICE WEDGES AND GROUND WEDGES AT VOSS

Fig. 14. The same laminated wedge as shown in Fig. 13a. Close up of a cast made according to the lacquer film method as described by Voigt (1949).

the wedge and corner A, faults occur in Lundarvatn Sand but they do not continue into the wedge.

The stratigraphical situation of this wedge is uncertain. It is younger than the lower part of Voss Clay and Silt, while its relation to the upper part of Voss Clay and Silt and upper till cannot be established.

The lamination, the fine-grained clay lamina and the continuity and plastic shape of the lamina show that the sediments must have been deposited in water. The fissure cannot initially have been opened to its full width, as this would have resulted in a horizontally laminated deposition from the base of the fissure and upwards. On the contrary we presume that during the deposition each individual lamina had well-defined boundaries to both sides.

This takes a cyclic process for granted, with formatio,n of a fissure which was later filled with sediments, renewed opening of fissure, sedimentation and so on. This cycle has to be repeated 30-50 times. As the lamina intersect in places, no regular deposition from one side to the other could have taken place. Another important point is the improbability that a water-bearing fis-

(18)

J. MANGERUD & S. A. SKREDEN

Table 1. Number of pollen and spores in 10 g samples of sediments.

Voss C l a y

. a n d

L o w e r s i r r T i i l ( c l a y. - ; "

m a r k e t b e d )

L a m i -

l - o s s r l L a m i -

. n a l e u

U n o c r i c e , n a t e d

: . . . . w e o g e

T i l l w e d e e . - . - - : : .

w e d s e .

r r i c . l o t r r r g ' rr ' ' s i l i

. - c t a y

P i r t u " ' Pi<:ea B e t u l a Cory lus G r a m i n e a e C y p e r a c e a e E r i c a l e s Artenri.sia C o m p o s i t a e l i g . R u n t e x Dryopteris lype S p h o g n u n t N o t i d e n t i f i e d

l l 1 1

T o t a l 1 l

sure could exist at a depth of 2 m without the sand (Lundarvatn Sand) having had a greater shear strength than at present.

The formation of this wedge is difficult to interpret. Some few similar structures have been described earlier; a ground wedge (sand wedge) which Black (1969) mentioned from Poland, the ice- and sand-filled wedges described by Pissart (1968) from Canada rvhich are discussed above, and above a l l t h e ' p e c u l i a r ty p e o f f o s s i l ic e f i s s u r e ' w h i c h M a c a r ( 1 9 6 9 ) d e s c r i b e s f r o m Belgium. We have every reason to believe that the laminated wedges we describe, and the ones that Macar (1969) described, are of the same genesis.

M a c a r ( 1 9 6 9 ) in t e r p r e t s t h e w e d g e s a s a ' p e c u l i a r t y p e o f i c e w e d g e ' , b u t i s unable to give a detailed explanation of the formation. Neither are we able to suggest other possible modes of formation other than a type of thermal contraction crack, either a ground wedge or a seasonal frost crack with preserved primary bedding. Both the extensive depth and width necessitate a rejection of the theory of seasonal frost cracks. We can therefore conclude that the laminated wedge is a type ol lossil ground h'edge. The weakness of this theory is in the assumption that the fissures fill with sediments when little or no water is present (p. 83), because the water would freeze and ob- struct further supply of sediments. However, we have interpreted the structures as aqueous. Accordingly, we must presume a heat regime in the fissure during spring, which makes a filling of sediment-loaded water possible. We must also assume that this water does not freeze until so much sediment has been deposited that a complete particle lattice is established.

I 1 2 1

1 1 8

t 7 I

I

I 2 1 2

21 33

(19)

F O S S I L IC E W E D G E S A N D G R O U N D W E D G E S A T V O S S 9 1

Fossils

No macro-fossils were found in the sediments. In samples from the 'clay marker bed' we looked for diatoms and foraminifers. but none were found.

Several samples were investigated for pollen, and a few grains were found.

Samples of 10 g were taken as it was evident that the sediment had a low content of organic matter. The samples were treated according to the HF method (Frgri & Iversen 1964). A repeated treatment \,vas necessary to re- move all mineral matter. In spite of repeated heating with HCl, not all the fluorides formed by HF treatment disappeared. A great part could however be removed by dispersion with NHr and decantation (Nilsson 1961). Never- theless, all the preparations were of poor cluality. The result of the pollen analysis is shown in Table 1. It appears that the sediments are poor in pollen and spores. We assume that pollen could be preserved in the impermeable 'clay

marker bed', and that the low pollen content in this bed is due to an original dearth of pollen. Apart from this, it is difficult to decide if the low pollen content is caused by modest primary sedimentation of pollen, or by p o s t - d e p o s i t i o n a l c o r r o s i o n .

The only sample that gives any clue about the vegetation is from the laminated wedge, and it suggests a vegetation of birch and herbs. On the whole, the little pollen that was found indicates an Arctic type vegetation, but there was not enough to emphasize this result.

Genesis and age of the sediments and wedge structures

The oldest sediment we have described is Lundarvatn Sand. which has obviously been deposited by running water, but otherwise has an uncertain genesis. Underneath the Lundarvatn Sand there are another 15-20 m of unconsolidated sediments (Fig. 3) which are unfortunately unknown.

An ice advance tor,vards W has then deposited the lower till on top of the Lundarvatn Sand. This is possibly the same ice niovement as the oldest found in the study of glacial striae (Fig. 2). The ice has then retreated from the area, and Voss Clay and Silt has been deposited, probably in an ice-dammed lake. After the deposition of Voss Clay and Silt, the climate must have been severe with permafrost and the formation of ice-wedge polygons and possibly also ground-wedge polygons. The permafrost period was succeeded by a new advance of ice which deposited the upper till. At one particular period this ice movement had a southwesterly direction. This parallels younger, but not the youngest striae in the area.

If our correlations between the two beds of till and striae are correct, the transition of direction of ice movement from W to S (as shown in Fig. 2) cannot have been continuous, because Voss Clay and Silt must have been deposited in the period between the formation of the westerly and the southwesterly striae. Another possible interpretation is that all the ice movement

(20)

J. MANGERUD & S. A. SKREDEN

shown in Fig. 3 is younger than Voss clay and Silt and that the lower till consequently originates from still older stages.

It has not been possible to date the sediments by the aid of fossils or by the crr-method. For voss clay and Silt, some alternatives can be considered by interpretation of lithostratigraphy and fossil ice wedges.

Several factors are decisive for the formation of ice wedges. The mean air temperature is not an obvious criterion, but it gives an approximate measure. lt has frequently been assumed that ice wedges can develop when the mean annual air temperature is - 3-4oc or lower (Dylik & Maarleveld 1967) while P6w6 (1966a, b) discloses rhat ice wedges in Alaska can only be formed when the mean annual temperature is -6-g oc or lower. Today the mean annual temperature for voss is *5.2 oc (Bruun 1967). The winter is cold with a mean temperature for the coldest month (January) of - 5.0 oc, and the lowest recorded air temperature is -36.1 oc (Bruun 1967). The formation of ice wedges at voss would seem to require a mean annual tem- p e r a t u r e a t l e a s t 8 o c l o w e r than today (maybe l1-13.c). with the same precipitation as today this would rapidly result in a complete glaciation of the area. If we compare with the conditions at the end of the last glaciation (Anur-rdsen & Simonsen 1967), a lowering of somewhat more than 3 oc would seem to be sufficient for a complete glaciation of the voss area.

This leads us to the following conclusion: The formation of ice wedges at voss can only have taken place if one or both of the followine conditions have prevailed:

Immediately after a rapid deterioration of climate and during the span of time which was necessary for the glaciers to advance to Voss.

Under a sufficiently cold but dry climate, so that no formation of glaciers could take place.

These conditions may }rave existed during Early, Middle or Late weichselian. we know little about Early weichselian in Norway, but recently fossil ice wedges of this age were described from Jreren, south-west Norway (Ber- gersen & Follestad r911). From Middle weichselian a number of c1a-datings (Mangerud 7970a) indicate that at times parts of Norway must have been free of ice. More recently B. G. Andersen (pers. comm.) has had a number of c1r-datings carried out from Jreren giving cla-ages between 2g 000 and 42 000 years B.P., which may be correlated with the Upton warren Inter- stadial complex in England (west 1968). we cannot discuss the possible Early or Middle weichselian age any further, due to the lack of information from western Norway. we will, however, conclude that it is possible that the described sediments and fossil ice wedges at voss formed duringthese periods.

Another possibility is that the formation took place during the Late weichselian; to be more precise during Allerrid/Younger Dryas. This alternative comprises two problems which will be discussed in more detail.

voss must have been free of ice during the (Late) Allerrid Interstadial and Voss Clay and Silt must have been deposited during this period.

(21)

FOSSII- ICE WEDGES AND GROUND WEDGES AT VOSS 93

C L ] M A T O I G R

L D E R D R Y A S B O L t N G O i D E S I O R Y A S

B L O M O I 0 k m

B h R G E N 3 0

r ' C 5 S 8 ! k m

c e l v e d g e I o r n r a l o n v o 5 s C l a ! a n d S L l l

F i g . 1 5 . c r o s s s e c t i o n b e t w e e n the west coast of Norway near llergen and voss, ap- p r o x i m a t e l y p a r a l l e l to direction of the ice movement. The straight lines indicate the s i t u a t i o n o f t h e i c e f r o n t a t v a r i o u s stages. The sections of the curve exten<iing west o f B e r g e n a r e d r a w n a c c o r d i n g to Mangerud (1970b) and are based on several cl.l d a t i n g s . T h e s t i p p l e d p a r t b e t w e e n Bergen and voss and the location of the becls an<I s t r u c t u r e s a t V o s s o u t l i n e a p o s s i b l e interpretation of the sediments and the age ol the wedses.

The climate early in the Younger Dryas Stadial must have made the formation of the ice wedges possible.

In the Early Allercid the ice front retreated rapidly from the area west of Bergen (Fig. 15) (Mangerud 1970b). Even if rhe retreat had continued at a much reduced speed, there would have been sufficient time for the ice front to retreat east of voss if the climate had been warm enough. Based on paleo- botanical considerations, Mangerud (1970b) found that the mean summer temperatures in that area during Late Allercid were 2-2.5 "c lower than present. Anundsen & Simonsen (1961) assume that the ice front almost reached voss during the deposition of the Eidefjord-osa moraines (Early Holocene), as they calculate the summer temperature to have been not more than 2.5 oc below the present. There are necessarily many uncertain factors attached to such calculations, but one might nevertheless draw the conclusion that, on the basis of paleoclimatological estimates, it is not improb- able that Voss became free from ice during the Late Allercjd.

As for the possibility of the formation of ice wedges in youngcr Dryas Stadial, fossil ice wedges, presumably formed during younger Dryas, have been described from northern Norway (Svensson et al. 1967), Finland (Don- ner et al. 1968), south Sweden (Johnsson 1962, 1963, Svensson 1962, 1964, Tak-Schneider |968a) and also from areas outside Scandinavia, e.g. Holland/

Belgium (Maarleveld 7964, van der Hammen et al. 1967, Zagwijn & paepe 1968, Tak-Schneider 1968b) and Scotland (Galloway 1961). A few of these wedge structures might be fossil seasonal frost cracks, but this does not change the general picture. From this geographical distribution it seems quite certain that ice wedges could have been formed at Voss during younger Dryas if the area was free from ice.

(22)

J . M A N G E R U D & S . A . S K R E D E N

we will not discuss the climatic aspects any further, but would rike to draw attention to one fact. Accorcling to Andersen (196g), during the younger Dryas the snow-line was 525 + 50 m lower than today alonglhe south-west coast of Norway. Reite (1969) found a difference of 600 m at More. If the precipitation was the same as it is today. this wourd impry that the summer temperature was only 3-4 oc lower than today (Andersen 196g, Reite l96g).

If the summer temperature was even lower, the winter precipitation must have been correspondingly Iess (Andersen 196g). The fossil ice wedges from the Younger Dryas Stadial mentioned above, strongly indicate that ihe lowering of temperature wasl in fact, considerably greater. F'or instance, arong the coast of Skine the annual mean temperature today is more than 7 oc (Atlas civer Sverige, maps 31-32), and the formation of ice wedges during the Younger Dryas consequently suggests that the annual mean temperature was as least 10-13o lower than today. This low annual mean temperature can partly depend on low winter temperatures, but all things considered, the fossil ice wedges from Younger Dryas Stadial indicate that the climate was very c o l d a n d d r v .

Ackrttsw'ledg.ratrts. - Dr. Bjdrn Andersen, cand. real. Tore Vorren and cand. mag.

lng.e Aarseth kindly read the manuscript. cand. mag. Kjell Htiyvik provi<ied exceilent assistance during field work. The figures were drawn by Miss EIen rrgens. cand. mag.

Berit Maisey translatecl the manuscript. Mr. Knut Nedkvitne (ownei of the building :l:tl c"l: us,permission ro carry our rhe field work. To ail these persons we proffer our srncere tnanks-

March 1971

REFERENCES

Andersen, B. G. 1968: Gracial georogy of western Troms, North Norway. Norges geor.

understikelse 256, L60 pp.

Anundsen, K. & Simonsen, A. 1967: Et preborealt breframstpt pi Hardangervidda og i omradet mellom Bergensbanen og Jotirnheimen. Ltttiv. Bergert. Arbok, {4ut.-N(ttrrrvit.

S e r . 1 9 6 7 , N o . 7 , 4 2 p p .

Atlus tiver svcrige 195-J. Generalstab. I-it. Anst. Fcirrag. stockhorm.

Bergersen, o. F. & Follestad, ts. A. i971: Evidence of fossir ice-wedges in Earry weichselian deposits at Foss-Eikjelan<J, Jeren, South west Norway. Nr,lsk ge.g. titt.sskr.25, 3945.

BIack, R' F. 1969: Climatically significant fossile periglacial phenomena in Northcentral United Srates. Biul. perl,glac. 20, 225_239. Lodz. poland.

Bruun, I. 1967: Standartl rtoilrtals 1931-60 ol tltt' uir tetnperature in Norwuy. Norske Met. Inst., 269 pp.

Donner, J. J., Lappalainen, v. & west, R. G. l96g: Ice weclges in south-eastern Finland.

Geol. f6ren. Stockltolnt F-6rh.90, 112-116.

Dylik' J' 1966: Problems of ice-wedge structures ancl frost-fissures polygons. Ilit.rl. pery- gluc. 15,241-291.

Dylik, J. & Maarleveld, G. c. 1967: Frost cracks, frost fissures and related polygons.

Med. Geol. Sticht., Nierye Ser. ig,7 21.

Fegri, K. & lversen, L 1964: Textbook ol poilen Anaryses.237 pp. Munksgaarcr, copen- hacen.

(23)

F O S S I L I C E W E D G E S A N D G R O U N D W E D G E S A T V O S S 9 5

G a l l o w a y , R . W . 1 9 6 1 : I c e w e d g e s a n d i n v o l u t i o n s i n S c o t l a n d . B i u l . P e r y g l a c . 1 0 , 1 6 9 - 1,93.

H a m m e n , T . v a n d e r , M a a r l e v e l d , G . C . , V o g e l , J . C . & Z a g w i j n ' W ' H . l 9 6 7 : S t r a t i - g r a p h y , c l i m a t i c s u c c e s s i o n a n d r a d i o c a r b o n d a t i n g o f l a s t g l a c i a l i n t h e N e t h e r l a n d s . G e o l . e r t M i i t $ o u t p 4 6 , 1 9 - 9 5 .

H i l l e f o r s , A . 1 9 6 6 : I s k i l a r i N o r r a H a l l a n d . S v e r r s f t G e o g . A r s b . 4 2 , 1 3 4 - 1 4 1 '

J o h a n s s o n , C . E . . 1 9 6 5 : S t r u c t u r a l s t u d i e s o f s e d i m e n t a r y d e p o s i t s . G e o I . f 6 r e n . S t c t c k - h o l n t F 6 r l t . 8 7 , 3 - 6 I .

J o h n s s o n , G . 1 9 5 9 : T r u e a n d f a l s e i c e - w e d g e s i n s o u t h e r n S w e d e n . G e o g . A r t r n l e r 4 1 ,

15-33.

J o h n s s o n , G . 1 9 6 2 : P e r i g l a c i a l p h e n o m e n a i n S o u t h e r n S w e d e n ' G e o g . A r t n a l e r 4 1 ' 3 7 8 - 404.

J o h n s s o n , G . 1 9 6 3 : P e r i g l a c i a l i c e - w e d g e p o l y g o n s a t H d s s l c h o l m , s o u t h e r n m o s t S w e - d e n S y e r r s k G e o g . A r s b . 3 9 , 1 7 3 - I 7 6 .

L a c h e n b r u c h , A . H . 1 9 6 0 : T h e r m a l c o n t r a c t i o n c r a c k s a n d i c e - w e d g e s i n p e r n l a f r o s t . U.S. Geol. Surv. Prof . Pap. 400-8, 8404-8406.

L a c h e n b r u c h , A . H . 1 9 6 2 : M e c h a n i c s o f t h e r m a l c o n t r a c t i o n c r a c k s a n d i c e - w e d g e p o l y g o n s i n p e r m a f r o s t . G e o l . S t t t ' . A t t t e r i c u S p e r ' . P u p . 7 0 , 6 9 p p .

L u n d q v i s t , I . L 9 6 2 : P a t t e r n e d g r o u n d a n d r e l a l e d f r o s t p h e n o m e n a i n S w e d e n . S v e r i g e s g a o l . u n t l e r s d k n i n g S e r . C 5 8 3 , 1 0 1 p p .

M a a r l e v e l d , G . C . 1 9 6 4 : P e r i g l a c i a l p h e n o m e n : r i n t h e N e t h e r l a n d s d u r i n g d i f f e r e n t p a r t s o f t h e W t i r m t i m e . B i u l . P e r y g l u c . i 1 , 2 5 I - 2 5 6 .

l V l a c a r , P . 1 9 6 9 : A p e c u l i a r t y p e o f f o s s i l i c e f i s s u r e s : I n P 6 w 6 , ' I . L . ( e d . ) T h e p e r i g l u - c i a l e n v i r o n n t e n l . M c G i l l - Q u e e n ' s U n i v c r s i t y P r e s s , M o n t r e a l , p p . 3 3 7 - 3 4 6 .

M a n g e r u d , I . 1 9 7 0 a : l n t e r g l a c i a l s e d i m e n t s a t F j d s a n g e r , n e a r B e r g e n , w i t h t h e f i r s t E e m i a n p o l l e n s p e c t r a f r o m N o r w a y . N o r s k 7 4 c t t l . t i d s s k r . 5 0 , 1 6 7 - 1 8 1 .

M a n g e r u d , J . 1 9 7 0 b : L a t e W e i c h s e l i a n v e g e t a t i o n a n d i c e - f r o n t o s c i l l a t i o n s i n t h e B e r g e n d i s t r i c t , W e s t e r n N o r w a y . N o r s k g a o g . t i d s s k r . 2 1 , 1 2 1 - 1 4 8 .

M r e l a n d , P . J . 1 9 6 3 : K v a r t i e r g e o l o g i s k e s t u d i e r i o m r i d e t m e l l o m G r a n v i n o g V o s s . U n - p u b l i s h e d t h e s i s , U n i v e r s i t e t e t i B e r g e n , B e r g e n .

N i l s s o n , T . 1 9 6 1 : K o n t p e n d i u n t i l < r ' n r t i i r p o l e o n t o l o g i o t ' l t k v u r t i i r p a l e o n t o l o g i s k a u r t d c r - s d k n i t t g s r n e t o d e r . L u n d s U n i v e r s i t e t , 2 3 8 p p .

P a e p e , R . & P i s s a r t , A . 1 9 6 9 : P e r i g l a c i a l s t r u c t u r e s i n t h e L a t e - P l e i s t o c e n e s t r a t i g r a p h y o f B e l g i u m . B i u l . P e r y g l u c . 2 0 , 3 2 1 - 3 3 6 .

P e t t i j o h n , F . J . 1 9 5 7 : S e t l i n t e n t u r y R o c k s . 2 n d e d . , 7 1 8 p p . H a r p e r & B r o t h e r s , N e w Y o r k .

P 6 w 6 , T . L . 7 9 5 9 : S a n d - w e d g e p o l y g o n s ( t e s s e l a t i o n s ) in t h e M c M u r d o S o u n d r e g i o n , A n t a r c t i c a . A n t . J o u r . S c i . 2 5 7 , 5 4 5 - 5 5 2 .

P 6 w 6 , T . L . 1 9 6 6 a : l c e - w e d g e s i n A l a s k a - c l a s s i f i c a t i o n , d i s t r i b u t i o n a n d c l i m a t i c s i g n i f i c a n c e . P r o c . I n t e r r t . P e r n u t f r o s t C o n f . , N u t l . A t ' u d . S c i . , N c t / . R e s . C o u r t t ' i l P u h . 1 2 8 7 , 7 6 - 8 1 , .

P 6 w 6 , T . L . 1 9 6 6 b : P a l e o c l i m a t i c s i g n i f i c a n c e o f f o s s i l e i c e w e d g e s . I l i t L l . P c r y g l u c . 1 5 , 6 5 1 3 .

P 6 w 6 , T . L . , C h u r c h , R . E . & A n d r e s e n , M . J . 1 9 6 9 : O r i g i n a n d p a l e o c l i m a t i c s i g n i f i - c a n c e o f l a r g e - s c a l e p a t t e r n e d g r o u n d i n t h e D o n n e l l y D o m e A r e a , A l a s k a . G e o l . S o t : A t n e r i c a S p e c . P a p e r 1 0 3 , 8 7 PP.

P i s s a r t , A . 1 9 6 8 : L e s p o l y g o n e s d e f e n t e d e g e l d c l ' l l e P r i n c e P a t r i c k . ( A r c t i q u e C a - n a d i e n - 7 6 " l a t . N . ) . I l i u l . P e r y g l a c . 1 7 , 1 7 1 - 1 8 0 .

R a p p , A . & R u d b e r g , S . 1 9 6 4 : S t u d i e s o n p e r i g l a c i a l p h e n o m e n a i n S c a n d i n a v i a 1 9 6 0 - 1 9 6 3 . B i t t l . P e r y g l a c . 1 4 , 7 5 8 9 .

R e i t e , A . 1 9 6 8 : L o k a l g l a c i a s j o n p i S u n n m i i r e . N o r g e s g e o l . u n t l e r s d k e l s e 2 4 7 , 2 6 2 - 2 8 7 . R y e , N . 1 9 6 6 : P e r m a f r o s t s t r u k t u r e r i F j o r d a n e , V e s t - N o r g e . N o r s k g e o l . t i d s s k r . 4 6 ,

203-213.

Seppiilii, M. 1966: Recent ice-wedge polygons in eastern Enontekiii, northmost Finland.

Publ. Inst. Geog. Univ. Turku, 42,211-287.

Skreden, S. A. 1967: Kvartrergeologiske underspkelser i omridet Voss - Bolstad@yri samt Bordalen. Unpublished thesis, Universitetet i Bergen, Bergen.

Svensson, H. 1962: Ett mpnster i marken. Svertsk Geog. Arsb. 38,95-104' Svensson, H. 1963: Tundra polygons. Norges geol. undarsikelse 223, 298-327.

(24)

9 6 J . M A N G E R U D & S . A . S K R E D E N

Svensson, H. 1964: Fossil tundramark pir Laholmssldtten. Sveriges geol. undersdkning, S e r . C 5 9 8 , 7 - 2 9 .

S v e n s s o n , H . 1 9 6 7 : J o r d s k a l v e n v i d H a l l a n d s f l s e n i f e b r u a r i 1 9 6 6 . G e o l . fbren. Stock- h o l n t F d r l t . 8 9 , 1 5 1 - 1 8 0 .

S v e n s s o n , H . , K : i l l a n d e r , H . , M a a c k , A . & O h r n g r e n , S . 1 9 6 7 : P o l y g o n a l g r o u n d a n d s c r l i f l u c t i o n f e a t u r e s . L t u r c l S t u d . G e o g . , S e r . A 4 0 , 6 7 p p .

T a k - S c h n e i d e r , U . v a n d e r 1 9 6 8 a : F o s s i l f r o s t f i s s u r e s i n t h e p r o v i n c e o f J 6 n k 6 p i n g , S w e d e n . G a o g . A r t t t . , S e r . A 5 0 , 1 0 9 1 1 0 .

T a k - S c h n e i d e r , U . v a n d e r 1 9 6 8 b : C r a c k s a n d f i s s u r e s o f P o s t - A l l e r p d a g e i n t h e N e t h e r l a n d s . B i u l . P e r y g l u c . 1 7 , 2 2 L - 2 2 5 .

T h o r a r i n s s o n , S . 1 9 6 4 : A d d i t i o n a l n o t c s o n p a t t e r n e d g r o u n d i n I c e l a n d w i t h a p a r t i c u l a r r e f e t e n c e t o i c e - w e d g e p o l y g o n s . B i u l . P e r y g l u c . 1 4 , 3 2 7 - 3 3 6 .

V o i g t , E . 1 9 4 9 : D i e A n w e n d u n g d e r l - a c k f i l n r - n r e t h o d e b e i d e r B e r g u n g g e o l o g i s c h e r r r n d b o d e n k u n d l i c h e r P r o f i l e . M i t t . G e o l . S t n a t s i n s t . H a n t b u r g 1 9 , 1 , 1 1 - 1 2 9 .

W a s h b u r n , A . L . , S m i t h , D . D . & G o d d a r d , R . H . 1 9 6 3 : F r o s t c r a c k i n g i n a m i d d l e - l a t i t u d e c l i m a t e . B i u l . P e r y g l u < ' . 1 2 , 1 1 5 - 1 8 9 .

W e s t , R . G . 1 9 6 8 : P l c i s t o c e r t e G e o l o g y a n d I l i o l o g l , . 3 7 7 p p . L o n g m a n s , G r e e n a n d C o . L t d . . L o n d o n .

Z a g w i j n , W . & P a e p e , R . 1 9 6 8 : l ) i e S t r a t i g r a p h i e d e r w e i c h s e l z e i t l i g e n A b l a g e r u n g e n d e r N i e d e r l a n d e u n d B e l g i e n s . E i s : . e i t a l t e r u n d G e g c n w u r t 1 9 , 1 2 9 - 1 4 6 .