genesis of marginal moraines in the caucasus

Genesis of marginal moraines in the Caucasus LEONID R. SEREBRYANNY AND ANDRE1 V. ORLOV

Serebryanny, Leonid R. & Orlov, Andrei V. 1982 1201: Genesis of marginal moraines in the Caucasus. Borear, Vol. 11, pp. 27%289. Oslo ISSN 0300-9483.

Composition and fabric of different moraines in the glaciated areas of Central Caucasus were studied to elucidate sedimentary environments and geomorphological processes. Methods used included particle- size distribution, pebble and mineral counts, shape analysis of pebbles, and till fabric analysis. Samples were taken from superglacial and basal debris, marginal moraine ridges and till horizons, and quantitative parameters were established for different glacial environments and till accumulation processes. Consider- able differences in composition and fabric of superglacial and basal debris were caused by their specific transport conditions. Most marginal moraines consist of material similar to basal debris and only the topmost parts of some ridges have a noticeable incorporation of superglacial debris. These results point to considerable erosion of mountain valleys by temperate glaciers. Previous geomorphological investigations have emphasized the importance of superglacial debris in the formation of marginal moraines by alpine glaciers, but this viewpoint is not supported by the studies performed.

Leonid R. Serebryanny and Andrei V . Orlov, Institute of Geography, USSR Academy of Sciences, Staromonemyi 29, 109017 Moscow, USSR; 6th December, 1980 (revised 22nd June, 1981).

B o w

In mountain areas, marginal moraines have been studied mainly as morphological features taken to represent former stationary positions of ice margins. The genesis of these landforms has been investigated less thoroughly due to the ap- parent simplicity of the problem. The application of analytical methods began only relatively re- cently, providing quantitative information about the composition and fabric of marginal moraines and making it possible to determine the diagnostic peculiarities of these landforms in mountains.

Direct observations of ice margins began in alpine regions at the end of the 18th and the beginning of the 19th centuries and contributed to the understanding of marginal moraines as a result of debris accumulation near the glacier front. The dominating assumption was that the debris falling down from the glacier front is the most important factor in this process. The par- ticipation of basal debris in the formation of marginal moraines was investigated very little and therefore the erosion of temperate glaciers in mountain areas was underestimated (Boulton 1970). Nevertheless, an unbiased estimation of superglacial and subglacial processes is necessary to clarify the distinctive features of glacial mor- pholithogenesis.

In this paper we have aimed at elucidating the genesis of marginal moraines in the Caucasus with the aid of particle-size analysis (with such statistical parameters as mean diameter d and sorting coefficient So), shape analysis of pebbles,

lithological analyses (pebble counts, mineral counts), and till fabric analysis. The following formulas were used: d =Zd;Pi/lOO, where d; is the mean particle size in each fraction and P; is the percentage of the given fraction; and $0 = m, where P3 is the third quartile, and P I is the first quartile or particle sizes corre- sponding to the contents of 75 and 25 % in cumulative curves. All the methods mentioned were used for the study of the composition of marginal moraines in high mountains of Central Cauca- sus, where temperate glaciers are widely distrib- uted (Fig. 1). These glaciers occupied larger areas in the past and left numerous morphological landmarks (Kovalev 1967).

Marginal moraines of Central Caucasus In Central Caucasus marginal moraines do not only appear as classic horseshoe-formed ridges with convex slopes downvalley, but very often as isolated hills near valley slopes (Figs. 2 and 3). These moraines are 5-6 m, seldom 8-10 m high and from 2-3 to 4-5 m and more wide. The distal slopes are higher and steeper than the proximal ones.

The sizes of marginal moraines may be strongly depending on the lithological composition of rocks outcropping in the upglacial parts of Val- leys. Even small glaciers may create thick mar-

19 - Boreas 4/82

280 Leonid R . Serebryanny and Andrei V . Orlov BOREAS 11 (1982)

1:8000 000

1:2500000

Fig. 1 . Localization map. Investigated glacier regions are marked by cir- cles: 1 - Sakeni, 2 - Ushba, 3 - Adishi, 4 - Shaurtu, Bashil, 5 - Be- zenghi, 6 - Dykhsu, 7 - Khalde, 8 - Shtula, 9 - Tanatsete, 10- Zey, 11 - Karaugom, 12 - Roshka.

I

ginal moraine ridges in the areas of soft rocks such as shales and such easy weathering rocks as diabases. A series of such moraine ridges up to 25-30 m high was observed near the margin of a receding glacier in the upper part of the valley of Roshka River (the basin of Khevsurskaya Aragvi), where intrusive diabases form the mas- sives of Chaukhi and Roshka-khorkhi (Maruash- vili 1971). Moraine ridges up to 12-15 m high are found near the margin of Bulre Glacier in the upper part of Karasu Valley composed of cristal- line schists.

No distinct relationships can be found between the number of marginal moraines and the shape of glacial valleys. The most representative series of 6-8 marginal moraines occur in flat, broad parts of such valleys, but in the narrow and steep parts these landforms are usually not well expressed. Avalanches, mudflows, rockfalls, land- slips and river erosion tend to destroy marginal moraines, making their distribution fragmentary. Our observations near the margin of Bezenghi Glacier point to a rapid erosion of marginal moraines. For example, during the glacier advance in 1977-79 a morainic ridge 5 m high was totally

destroyed due to changes in the run-off systems of glacier meltwaters.

Origin of glacial debris Superglacial and basal debris as sources of material of marginal moraines differ strongly by their composition and texture. Such differences have also been reported from other regions (Slatt 1971; Drake 1974; Mills 1977a, b, c; Boulton 1978; Eyles & Rogerson 1978). We tried to esti- mate relationships of these sources of accumulation in the study area.

The superglacial debris is composed mainly of rough fragments provided from the slopes around fim areas. The cover of superglacial debris has an uneven spatial distribution; the mean values of its thickness seldom reach 0.3-0.4 m. The thickest accumulations of debris are along the medial and lateral moraines stretching along the sides and axes of glacial tongues.

An almost continuous cover of superglacial debris is formed due to uneven ablation on ice margins where ice flow is retarded, and englacial

BOREAS 11 (1982) Marginal moraines in the Caucasus 281

Fig. 2. Marginal moraine ridges near the snout of the Adishi Glacier, Caucasus.

Fig. 3. Isolated moraine hills of the Early Subatlantic (2,800 years B.P.). 6 km below the Snout of the Bezenghi Glacier, Caucasus.

282 Leonid R. Serebryanny and Andrei V. Orlov BOREAS 11 (1982)

Fig. 4. Five-class roundness scale of A. V. Khabakov (1946).

debris is melted out and redistributed. This cover is very noticeable on the surface of glaciers.

The visible effect of superglacial debris sliding off the ice front does not exclude another source of marginal moraine formation. We have seen thick (up to 5 m) layers of debris-laden ice with considerable concentration of debris in their basal strata in crevasses and cavities at the margins of Bezenghi, Dykhsu, Shaurtu, Bashil, Khalde, Ushba and other glaciers. During the melting-out from ice this debris is being accumulated and forms marginal moraines.

We observed such processes at the margin of the Adishi Glacier, where there was no supergla- cia1 debris at all due to the form of the firn basin. Another example was observed in the middle part of the Khalde Glacier, where a large outcropping rock riegel is exposed in the zone of coalescence of three confluent glaciers. The riegel is being eroded by one of these glaciers, and thick horizons of debris-laden ice or basal debris are exposed in the marginal fissures of the glacier. They are thrusted upon the glacier surface and accumulated in a series of marginal moraines.

These examples of marginal moraine formation totally of basal debris may be considered as exceptions from the general rule. Usually at least some superglacial debris is included in marginal moraines together with the basal debris.

Particle-size distribution In the superglacial debris (fractions less than 20 mm) studied in the frontal parts of ice margins, the small amount of clay-silt particles is typical:

the total contents of particles less than 0.01 mm does not exceed 1 %. The amount of fine debris is increased slightly only in transported glacial drift composed of shales.

As all the samples of the superglacial debris studied are composed of no more than 50 % of gravel (3-5 mm) and pebbles (10-20 mm), the mean diameter d has values from 4.0 to 7.6 mm. This distribution has more than one maximum, a sign of poor sorting; the sorting coefficients vary from 1.5 to 4.1 with the mean value 2.4.

Basal debris is essentially different from superglacial debris by grain-size distributions mainly because of larger amounts of fine particles. It is a result of debris inclusion in basal ice layers and subsequent attrition and grinding during glacial transport. There are clear maxima in the fractions of fine sand (0.14.25 mm), and coarse sand (0.5-2.0 mm). Sometimes maxima are present also in gravel and pebble fractions. The proportion of clay and silt particles (less than 0.01 mm) may amount up to 9%, and the total amount of the sand fraction may reach 70 %. The value of the mean diameter d varies from 1.8 to 5.0 mm and so from 2.9 to 5.2, with the mean value 4.2.

Shape analysis The differentiation of particle-size spectra of superglacial and basal debris is combined with diagnostic differences shown by shape analysis. The roundness of particles expressed in the five- classes scale of Khabakov (1946) is used here (Fig. 4). The material of superglacial debris has no signs of glacial abrasion, because it is transported passively on the surface and in the upper ice layers influenced only by the breaking process of physical weathering. These debris have much common in appearance with avalanche and hillside waste materials. (Fig. 5).

The amount of angular clasts does not exceed 20 % in basal debris, but most basal debris pebbles show clear signs of glacial action and belong to the lowest roundness classes. Well rounded pebbles are present at some sites. These pebbles were probably incorporated in the glacier from underlying water-transported sediments. The surface of pebbles and boulders of less durable rocks have grooves, striae and other marks of glacier transport. The most representative are wedge-shaped shears and signs of cutting of fragments along one of their axes.

In the course of morphometrical investigations


three main axes (A, B, C) of each pebble were measured and indices of elongation (B/A) and flatness (C/B, CIA) were calculated. Pebbles from superglacial debris were distinguished by their higher flatness mean values: CIS = 0.6, C/ A=0.4. Most pebbles had the following axial ratios according to the classification proposed by Gaigalas (1965): B/A > 2 3 and 113 < CIB < 213, 113 < B/A < 213 and 113 < C/B < 13 . Pebbles with values B/A>2/3 and CIB< 1/3 were also present, but there were no isometric pebbles (Fig. 6a). According to Cailleux (Cailleux & Tri- cart 1963), the flat angular pebbles composed of different petrographical varieties are most probably a result of physical weathering of rocks. It is likely that the leading role in this process is exfoliation under the influence of sharp variations of diurnal temperatures typical of high mountain climate (Tricart & Cailleux 1965). Our conclusion is also supported by the absence of pebbles with clear signs of glacial treatment in superficial tills.

Contrary to superglacial debris the basal debris has a dominance of more isometric pebbles. The mean values of flatness indices C/B are equal to 0.7 and C/A to 0.5. One third of the pebbles were spheroidal with axial ratios BlA>2/3 and C/B > 2/3 (Fig. 6b).

Petrographic composition Petrographic pebble analyses showed that superglacial debris is dominated by rock fragments from firn areas, but basal debris contains many clasts transported from nearby rock outcrops under glacial tongues. For eframple, in superglacial debris from the tongue of Bezenghi Glager there are no quartz diorites and granodiorites outcropping for 5 km above the glacier margin upvalley. But the amount of such pebbles is over 18 % in debris-laden ice (basal debris) and young frontal moraines, and in some moraine ridges reaches 40 %. A similar situation is observed in the valley of the Khalde Glacier, where shales crop out on slopes in the lower part of glacier tongue, but superglacial debris does not contain such pebbles. Nevertheless, the amount of fragments reaches 32 % in some frontal marginal moraines. Mills (1977b) has reported similar data from the Athabaska Glacier.

The considerable differences in mineral counts of superglacial and basal debris due to different sources of material are also revealed by X-ray diffractometer analysis. For example, supergla-

Fig. 5. Typical appearance of superglacial debris.

cia1 debris of the Bashil Glacier contained a high share of chlorite: 78% in the fraction less than 0.001 mm, as compard to 45% in debris-laden ice, and approximately the same value (40 %) in frontal moraine. In superglacial debris we found lower contents of hydromica (25%) in silt-clay fractions (less than 0.01 mm) as compared to 40 % in debris-laden ice and 30 % in frontal moraine.

The shares of basal and superglacial debris The above-mentioned analytical data permit to distinguish clearly between the two possible sources of the formation of marginal moraines. The frontal ridges contain material lithologically similar with basal debris. This material is consoli- dated and coherent to a great extent due to higher contents of clay-silt particles. The maxima are in the same sand fractions as in basal debris. Superglacial debris material is usually present only in the topmost parts of ridges, but separate ridges may be composed entirely of this material. Additional diagnostic criteria of such marginal moraines are the presence of great amounts of interstices between large boulders and the absence of fine particles, which is also peculiar to scree and avalanche deposits.

The cumulative curves of size distribution of heterogeneous glacial drift of the Khalde Glacier and its forefield (Fig. 7) show that typical curves of superglacial and basal debris are situated in the concentration field of curves derived from marginal moraines.

The established regularities are also clearly expressed in the graph of relationship between the mean diameter d and the sorting coefficient so of all the heterogeneous glacial drift studied in the Central Caucasus (Fig. 8).

284 Leonid R. Serebryanny and Andrei V. Orlov BOREAS 11 (1982)

30

20

10

0

b

20

f0 1 0

$>$

Axial ratio Axial ratio Fig. 6. Histograms of shape ratios of clasts in superglacial debris (a), basal debris (b) and marginal moraines (c) in glaciated areas of the Central Caucasus.


a -/ -4- 2 _-.-. Fig. 7. The concentration field of cumulative curves of grain-size distributions in marginal moraines and the cumulative curves of grain-size distributions in superglacial and basal debris. The samples were collected on the Khalde Glacier and its forefield. (1) limits of the concentration field of cumulative curves of grain-size distribution in marginal moraines; (2) typical cumulative curves of grain-size distributions of superglacial debris; (3) typical cumulative curves of grain-size distributions in basal debris.

The results of shape analysis support our conclusion that material from the glacier bed is dominant in marginal moraine ridges. This material is ice-reworked, the mean values of the roundness coefficient exceeding 20 %. This coefficient was calculated as K O = (On, + Inl + 2nz + 3n3 + 4n4) 25 %:loo, where no. . .n4 are numbers of particles in each roundness class (Khabakov 1946). It is worth noting that the basal tills from some Alaskan glaciers include rounded pebbles probably incorporated from fluvioglacial deposits (Slatt 1971). Mills (1977b), who made shape analysis of tills from the Athabaska Glacier in Cordilleras, found that pebbles in basal till had indications of glacier abrasion. Our results show that since some Cau- casian marginal moraines include well-rounded pebbles with preserved crust of mountain var- nish, they probably derive from reworked old fluvial gravels. Usually there are many pebbles with axial ratios (like in Fig. 6c) in marginal moraine ridges as well as in basal debris.

As shown above, some marginal moraine

I

k 8 '1 I 4 I" ' A

A

A A

I f 0 2 A 3 Fig. 8. The distribution field of mean diameter ( d ) and sorting coefficient (so) of grain-size distributions in different glacial drifts: (1) superglacial debris, (2) basal debris, (3) marginal moraine.

286 Leonid R. Serebryanny and Andrei V . Orlov BOREAS 11 (1982)

ridges are formed from the material falling from the glacier front. This accumulation mode pro- vides the supply of flat angular pebbles.

Certainly, during the formation of marginal moraines one may also observe changes of different sedimentary environments reflected in the material composition and structure of these landforms. For example, in the valley of the Khalde Glacier we have seen a ridge composed of basal till in the axial part of valley and of superglacial till close to valley slopes.

Ell fabric analysis The study of material composition permits distin- guishing material of different genesis in marginal moraines, but does not give exact information about their accumulation process. Such information may be obtained from orientation analysis of elongated pebbles. The theory of the dominant orientation of pebbles along the ice movement was formulated by Richter (1931) on the basis of studies from Central Europe and from regions of present glaciation. Later this idea was confirmed by other scientists (e.g. Hoppe 1952; Okko 1955; Galloway 1956; Slatt 1971, 1972; Olszewski & Szuprynynski 1975; Mills 1977a). It is possible to use fabric analysis to clarify the conditions of till accumulation in mountains with ice movement direction depending upon the valley course.

We measured pebble orientation of marginal moraines on horizontal surfaces in excavated pits at a depth of not less than 1.5 m, in order to avoid the influence of cryogenetic and slope processes (upwarping of pebbles to the surface, solifluction ground flow) acting in seasonally-frozen sediments (Lundqvist 1949; Rose 1974). Each pebble was measured in seven parameters: sizes along the A, B and C axes, and azimuths and dips of the A and B axes. We used only pebbles with index BIA not more than 0.5. At each site we usually measured 100 pebbles and sometimes only 50.

Our results show that there are three orientation types (Fig. 9b, c, d) in marginal moraines, with maxima coinciding with ice movement direction (b-type), across this direction (c-type), and a combination of these (d-type). Comparison of orientation measurements with the material composition shows that the first type (Fig. 9b) is common in ridges of basal till; the second one (Fig. 9c) often occurs in ridges of superglacial till. Measurements of pebbles in the basal debris of Bezenghi and Khalde glaciers were made to

explain the obtained results. These measurements show that most pebbles are orientated along the ice movement direction and inclined across this direction (Fig. 9a). This is caused by ice movement in glacier margins influenced by structural characteristics of debris-laden ice. The results conform with measurements from other regions (Harris 1972; Drake 1974; Mills 1977a). The dips of the A axis vary from 0" to 30", with mean values from 5" to 10". The inclinations of the B axis have mean values of 0-5".

In ridges of basal till material pebbles dip along ice movement direction as well as across this movement. The dips of the A axis may be up to 80". The maxima have values of 0-5" and 10- 15".The B axis of most pebbles dips 5-20'. Such ridges probably formed as a result of the melting out of basal debris composing their core. We suggest that variations in dip values and lesser maxima in rose diagrams are influenced by ice- melting processes.

It is very difficult to explain the transverse orientation of pebbles in marginal moraines composed by superglacial till material. Investigations at the front of Khalde and Tanatsete glaciers show that pebbles falling from the glacier front have a dominant orientation parallel to the glacier margin. The formation of the transverse orientation (c) may be presented in the following way. Elongated pebbles falling from glacier front and then rolling on the slopes of the ridge are directed with their long axis across slope direction; a similar case may be illustrated by a pencil rolling down the inclined plane. The final posi- tion of pebbles is much influenced by microland- forms (Ehlers 1979), and therefore rose diagrams very often show only a general trend to the transverse orientation. This supposition is supported by the dips of the A axis not exceeding 0-5" in most pebbles and the dips of the B axis having values of 10-15". Our observations showed that the transverse orientation of stones is also clearly expressed in screes.

In some studies the transverse orientation of stones has been interpreted as caused by ice-push action (Hames 1972) or by compressive stress in moving ice (Boulton 1970). But in the Caucasus the transverse orientation of pebbles was mainly found in marginal moraine ridges formed of superglacial debris.

In some moraine ridges we observed a complex orientation with two maxima, one along and one transverse to the ice movement direction (Fig. 9d). To explain the formation of such orien-

BOREAS 11 (1982)

a 0

Marginal moraines in the Caucasw 287

b 0

0 C

480'

0 d

Fig. 9. The main types of orientation of elongated pebbles in basal debris (a) and marginal moraines (b, c, d). The ice movement direction is shown by an arrow. The roses represent the most typical individual cases.

288 Leonid R . Serebryanny and Andrei V . Orlov BOREAS 11 (1982)

Fig. 10. The formation of a marginal moraine ridge by the Shaurtu Glacier.

tation we made fabric analyses and roundness estimations of elongated pebbles. We found, for example, that in a moraine ridge on the left bank of the Tanadon River (the basin of the Urukh River) rounded pebbles are mostly directed along ice movement; angular ones are directed across it and almost parallel to the course of the ridge. To clarify the mechanism of such orientation we made special observations at the margin

Fig. 11. Accumulation of superglacial debris falling down the snout of the Khalde Glacier.

of Shaurtu Glacier in the Chegem Valley. The right part of this glacier showed signs of advance: it had formed a young moraine ridge. This ridge was separated from the glacier by an open cavity 0.4-0.5 m high (Fig. 10). Debris-laden ice layers were exposed in the basal part of the glacier, and stone fragments melted out gradually and re- built the ridge. Large rock fragments were observed preserving the orientation acquired during ice transport. Simultaneously the cavity was being filled up by material falling from the glacier front, leading to a complex orientation (cf. Fig. 11).

But the complex orientation with two maxima is also typical of marginal moraines composed totally of basal till. It is possible that such orientation is due to ice-push action (Hams 1972) or solifluction re-deposition of moraine material (Lundqvist 1949).

The term 'marginal moraine' is understod in geomorphological investigations not only as a specific group of glacial landforms, but also as a specific type of glacial deposits. We suggest that these accumulative formations do not represent a specific facies of glacial deposits, but may include different till facies. Marginal moraines are typi- cally formed only under exceptionally favourable conditions of accumulation of superglacial or basal debris or both of them, which leads to the creation of positive landforms against the general background of till accumulation.

The results of this investigation were established only for a definite glacio-geomorphological region and their application for other regions may be done only after similar analytical research. Our results are considered as an example of possibilities for genetic interpretation of glacial (or other) landforms by the analysis of their material composition and fabric.

Ackmwledgementr. -We express our sincere gratitude to Prof. Aleksis Dreimanis for his kind attention and valuable help during the preparation of this paper.

References Boulton, G. S. 1970 On the origin and transport of englacial

debris in Svalbard glaciers. .I. Glaciol. 9, 213-229. Boulton, G. S. 1978 Boulder shapes and grain-size distribu-

tions of debris as indicator of transport paths through a glacier and till genesis. Sedimentology 25, 773-799.

Cailleux, A. & Tricart, J. 1963: Initiation ci I'Ctude des sables et des galen 1-3. 376 pp., 194 pp., 203 pp. CDU, Paris.

Drake, L. D. 1974: all fabric control by clast shape. Bull. Geol. SOC. Am. 85, 247-250.


Ehlers, J. 1979: Forms at the base of till strata as indicators of ice movement. J. Glaciol. 22, 345-355.

Eyles, N. & Rogerson, R. J. 1978: Sedimentology of medial moraines on Berendon Glacier, British Columbia, Canada: implications for debris transport in a glacierized basin. Bull. Geol. SOC. Am. 89, 16861693.

Gaigalas, A. 1965: Osobennosti krupnooblomochnogo materi- ala raznovozrastnykh moren yugo-vostochnoy Litvy i voz- mozhnosti ispolzovaniya dlya stratigrafii [The peculiarities of clastic material from the Pleistocene tills of different age in south-eastern Lithuania and possibilities to use them on stratigraphy]. Trudy Instintta geologii 2, 104-156. Vilnius.

Galloway, R. W. 1956: The structure of moraines, Lyngdalen, North Norway. J. Glaciol. 2, 730-733.

Harris, S. A. 1972: The nature and use of till fabrics. In Research Methods in Pleistocene Geomorphology, 4545. Guelph-Norwich.

Hoppe, G. 1952: Hummocky moraine regions with special reference to the interior of Norrhotten. Geogr. Ann. 34, 1- 72.

Khabakov, A. W. 1946: Ob indeksakh okatannosti galek [On the roundness indices of gravels]. Sov. geologiya 10, 9699.

Kovalev, P. V. 1967: Sovremennoye i drevneye oledeneniye Bolshogo Kavkaza [The present and ancient glaciation of Great Caucasus]. Mabrialy Kuvkazskoy ekspeditsii 8, 3-101. Kharkov.

Lundqvist, G. 1949: The orientation of the block material in certain species of flow earth. Geogr. Ann. 31, 335-347.

Maruashvili, L. I. 1971: Vostochnyi Kavkaz [Eastern Cauca-

sus]. In Geomo$ologiya Gruzii, 236-239. Mezniereba, Tbilisi.

Mills, H. H. 1977a: Basal till fabrics of modern alpine glaciers. Bull. Geol. SOC. Am. 88, 824-828.

Mills, H. H. 1977b: Differentiation of glacier environments by sediment characteristics: Athabaska Glacier, Alberta, Ca- nada. J. Sediment. Petrol. 47, 726737.

Mills, H. H. 1977c: Textural characteristica of drift from representative Cordilleran glaciers. Bull. Geol. SOC. Am. 88, 1135-1143.

Okko, V. 1956: Glacial drift in Iceland, its origin and morpho- logy. Acta Geogr. 15, 1-133. Helsinki.

Olszewski, A. & Szupryczynski, J. 1975: Texture of rock particles of the basal transport, Werenskiold Glacier. Butt. Acad. pol. sci. Ser. sci. terre 23, 5947.

Richter, K. 1932: Bewegungsrichtung des Inlandeises, rekon- struiert aus den Kritzen und Langsachsen der Geschiebe. Z. Geschiebeforsch. 8, 62-66.

Rose, J. 1974: Small-scale spatial variability of some sedimen- tatry properties of lodgement till and slumped till. Proc. Geol. Assoc. 85, 239-258.

Slatt, R. M. 1971: Texture of ice-cored deposits from ten Alaskan valley glaciers. 1. Sediment. Petrol. 41. 828-834.

Slatt, R. M. 1972: Texture and composition of till derived from parent rocks of contrasting textures: south-eastern New- foundland. Sediment. Geol. 7, 283-290.

Tricart, J. & Cailleux, A. 1965: Introduction ci la gdomorpholo- gie climatique. 306 pp. Sedes, Pans.

genesis of marginal moraines in the caucasus

Documents