The Physical Basis of Ice Sheet Modelling (Proceedings of the Vancouver Symposium, August
1987). IAHS Publ. no. 170.
Zonal arrangement of thermal regimes of Pleistocene
ice sheets as indicated by field data from Poland
Jerzy Liszkowski
Dept. of Earth Sciences
Silesian University
ul. Mielczarskiego 60
41-200 Sosnowiec, POLAND
ABSTRACT Field observations from Poland indicate a radially distributed pattern of thermal regimes of Pleistocene ice sheets centered on the Scandinavian
center of glaciation. Nearest the center of glaciation is a belt 500-750 km wide
where the thermal regime of the ice sheet was cold. Hundreds of massive glacial rafts up to 10 m3 in volume were eroded from the pre-Quaternary
bedrock. This belt comprises Pomerania and Masuria in north and north-east
Poland. The ice flow regime was compressional here. Next is a 250 km wide
zone where the thermal regime was temperate, ice movement was due to basal
sliding, and the flow regime was extensional. This is reflected in the relatively
faint bedrock erosion and low total thickness of Quaternary deposits, suggesting ineffective debris entrainment and glacial deposition. This zone comprises
the central parts of the North German-Polish Plain. Within the marginal zones
of individual ice sheets, the thermal regime was temperate, with large quantities
of subglacial, englacial and supraglacial water. The ice flow regime was
compressive. Rapid glaciofluvial deposition occurred in locally strongly
differentiated environments. Push moraines and intensive glacio-tectonic deformations related to bedrock failure are common here. These observed patterns
are related to bedrock geology and geohydrology and particularly to the
different geothermal heat flow within different geotectonic units crossed by the
ice sheets.
Arrangement zonal des regimes thermiques de calottes glaciaires du
Pleistocene, comme indiqué par des données de terrain en Pologne
RESUME Des enquêtes sur le terrain en Pologne indiquent une distribution
radiale des régimes thermiques de calottes glaciaires du Pleistocene partant du
centre Scandinave de glaciation. Tout d'abord, une zone de 500 à 700 km où
le régime thermique de la calotte était froid se trouve près du centre de glaciation. Des centaines de blocs de roches du pré-quaternaire atteignant 107 m3,
ont été érodées du lit rocheux. Cette zone comprend la Poméranie et la
Masurie au nord, nord-est de la Pologne. Le régime d'écoulement de la glace
y était compressionel. Ensuite se trouve une zone de 250 km où le régime
thermique était tempéré, le mouvement de la glace était dû au glissement sur le
fond, et le régime d'écoulement était extensionel. Ceci se reflète dans l'érosion
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Jerzy Liszkowski
relativement minime du lit rocheux et la faible épaisseur totale des dépôts du
quaternaire qui suggèrent un entrainment de fragments de roche et un dépôt
glaciaire négligeables. Cette zone comprend les parties centrales de la plaine
Nord-Germano-Polonaise. Dans les zones marginales de calottes individuelles,
le régime thermique était tempéré avec d'importantes quantités d'eau sousglaciaire, intraglaciaire et supra-glaciaire. Le régime d'écoulement de la glace
était compressif. Des dépôts fluvio-glaciaires sont survenus dans des
environnements qui sont localement fortement différenciés. Des moraines'
compressionelles et des déformations glaciotectoniques intenses reliées aux ruptures du lit rocheux sont courantes à cet endroit. Les distributions étudiées
sont reliées à la géologie et la géohydrologie des lits rocheux, et plus
particulièrement au différent flux de chaleur géothermique dans différentes
unités géotectoniques traversées par les calottes glaciaires.
INTRODUCTION
One of the main purposes of reconstructing Pleistocene ice sheets is to enable reasonable estimates of ice thickness to be made. These can in turn be used as input data for ice sheet
models or as output data of Quaternary ice sheets when inverse problems are considered. The
first step in the reconstruction of Pleistocene ice sheets is to recognize the extent of glaciations
by using moraines and other ice contact features and geological evidence. Moreover, realistic
reconstruction of Pleistocene ice sheets requires knowledge of the chronology of glacial events.
If these data are known with some accuracy, it is possible to calculate ice sheet thicknesses
using gradients of outlet glaciers of recent Greenland or Antarctic ice caps as general checks.
In the last two decades, developments in glaciology have led to new interpretations of the
origin of many Pleistocene glacigenic features, sequences and landforms. In particular, glaciological studies on recent ice sheets provides a new explanation of the close relation of glacial
erosion and deposition to thermal regimes of the ice. In the Polish Quaternary literature, however, there are very few attempts to relate glacigenic deposition models to flow conditions and
thermal regimes of ice sheets. Thus the aim of the paper is threefold: (a) to outline the
Quaternary stratigraphy and glacial extent in Poland, (b) to reconstruct ice sheet thickness for
the last distinct North Polish (Weichselian) glacial stade, and (c) to present a general picture of
thermal regimes of the Late North Polish Glaciation.
OUTLINE OF QUATERNARY STRATIGRAPHY AND GLACIAL EXTENT IN
POLAND
The dominant morphogenetic and sedimentary events of the last 1.8 Ma (i.e., the Quaternary)
in Poland have been repeated glaciations depositing offlapping, progressively younger séries of
glacigenic sediments. The area of Poland, like other terrains in north, north-central and
northeast Europe, was affected by several distinct Pleistocene glaciations. Although different
stratigraphie schemes were and are currently applied, most Quaternary geologists and geomorphologists agree that Poland was glaciated at least three times. In order of age, these were the
South Polish (Elster), the Middle Polish (Saale), and the North Polish (Weichselian) Glaciations, interrupted by two interglacial cycles. Geological mapping of glacial deposits and landforms has produced convincing evidence of major stillstands and/or readvances during general
Middle Polish and North Polish déglaciations. However, only a few of these have yet been
shown to represent widespread ice sheet readvances. Thus, each of the distinct glaciations is
subdivided into a few glacial stades (for details see Mojski, 1985).
The southward extension of the South Polish Glaciation was the greatest, that of the
North Polish Glaciation the least. The limit of the South Polish Glaciation is poorly defined
Zonal arrangement of thermal regimes
123
and is marked by the forerunners of the Carpathian and Sudetes Mountains (Fig. 1). As a
result of long term erosion, the glacial landforms and glacigenic series of this glaciation have
been strongly denuded. Thus, bedrock structure, lithology, fluvial processes and periglacial
weathering all play a fundamental role in landscape formation. Ground conditions are for the
most part of the periglacial terrain type described by Eyles & Dearman (1981).
Within the limit of the Middle Polish Glaciation, outward of the North Polish Glaciation,
both glacial landforms and glacigenic deposits are better preserved. Ground conditions of all
three glacial terrain models distinguished by Eyles & Dearman (1981), i.e., subglacial, supraglacial and glaciated valley terrains, can be recognized and mapped. In southeast Poland, the
extent of the Middle Polish Glaciation is marked by numerous ice-pushed pressure ridges with
heights up to 50-100 m above their surroundings and linear extent up to 200 km.
FIG. 1 Extent of main Pleistocene ice sheets in Poland. 1 (hachured): extent
of individual ice sheets. S: South Polish Glaciation; MidPo: Maximal (Odra)
stade of the Middle Polish Glaciation; MidPw: Warta stade of the Middle Polish Glaciation; NI: Leszno (Brandenburg) glacial phase of the late North Polish Glacial stade; Npm: Pomeranian glacial phase of the late North Polish
glacial stade. 2 (dash-dot): Southern boundary of widespread occurrence of
glacial rafts.
124
Jerzy Liszkowski
Within the limit of the North Polish Glaciation, youthful glacial landforms and thick glacigenic sequences of the late (main) glacial stade occur. Glacigenic series of two older glacial
stades (Kaszuby glacial stade, 11.5-9.5 ka BP, and Pre-Grudziadz glacial stade, 7.5-5.35 ka
BP; see Mojski, 1985) are known from borings and outcrops along lower Vistula river banks
only. Glacigenic sequences typical of supraglacial terrains (Eyles & Dearman, 1981) with a
high glaciofluvial component are most common.
The margins of former ice sheets of each distinct glaciation and glacial stade are marked
by more or less continuous moraine belts and other ice contact deposits. Thus, the extent of
individual Pleistocene ice sheets in Poland is known with reasonable accuracy. Figure 1 can
therefore be interpreted to represent the first step in reconstruction of Pleistocene ice sheets and
as hard facts for input data in ice sheet modelling. These data are also included in the work of
Aseyev et al. (1973) and CLIMAP (1976).
RECONSTRUCTION OF LATE NORTH POLISH GLACIAL STADE ICE SHEET
As mentioned above, the configuration and extent of Pleistocene ice sheets in Poland is known
with reasonable accuracy. However, the chronology of glacial events is known in some detail
for the late North Polish glacial stade only. A tentative reconstruction of the ice sheet of this
glacial stade will be presented below. Older glaciations are harder to reconstruct because associated 14C data are nonexistent.
The chronology and extent of the late North Polish glacial stade in Poland is summarized
in the form of a time-distance diagram in Fig. 2. Several of the main time-controlling 14C
dates are also presented. The reconstruction of the ice sheet was based on the procedure used
by Andrews (1975, 1980), using gradients of the Antarctica ice cap as a general check (see
also Buckley, 1969, and Paterson, 1981). The reconstructed profiles are presented on Fig. 3.
The center of glaciation was located in Angermanland, central Sweden. Thicknesses of the ice
sheets of individual glacial phases were estimated to be 3.4-3.7 km, which are larger figures
than those given by Aseyev et al. (1973) and CLIMAP (1976) and accepted by Mbrner (1980),
but which agree well with estimates made by Balling (1980) on the basis of gravity data
analysis.
It is worth noting that there are some indications that the ice sheet thickness near the
margins of the Leszno (Brandenburg) and Poznan (Frankfurt) glacial phases in west-central
Poland was significantly less than that predicted using a conventional parabolic ice sheet
profile. This hypothesis is schematically shown on Fig. 3 by the dashed line labelled la. A
similar picture was obtained by Andrews (1980) for the Baffinland and Clyde stades of the
Foxe glaciation. This phenomenon was likely related to some form of instability (or nonstationarity), but the causes are as yet not well understood. It seems, however, that this
phenomenon was more the rule than the exception.
THERMAL REGIMES OF PLEISTOCENE ICE SHEETS WITHIN POLAND
Within the Quaternary of Poland there are some phenomena that suggest spatial differentiation
of thermal regimes and modes of flow of Pleistocene ice sheets. These include (a) the
widespread occurrence of massive glacial rafts within distinct zones in northwest and northeast
Poland; (b) the marked reduction of the total thickness of Quaternary deposits within a part of
the Polish Lowland; and (c) the strong glaciotectonic deformation of Pliocene and Miocene
deposits below the base of the Quaternary.
Zonal arrangement of thermal regimes
125
FIG. 2 Time-distance diagram for the late North Polish QNeichselian) glacial
stade of the last distinct Pleistocene glaciation. Npz: Poznan (Frankfurt) glacial phase; Ngo: Gothian (Low Baltic) glacial phase; Nsa: Central Swedish
and Salpausselkas glacial phases. Other symbols as on Fig. 1.
4000
1
^3000
co
LU
| 2000
o
E 1000
0
250
500
DISTANCE
750
(km)
1000
1250
FIG. 3 Reconstructed cross-sections through the late North Polish ice sheet.
Curve 1: Poznan glacial phase (theoretical); curve la: same but based on field
evidence; curve 2: Pomeranian glacial phase (theoretical).
126
Jerzy Liszkowski
The occurrence of huge agglomerations of massive glacial rafts (called Schollen in the
German Quaternary literature) is a specific feature of the Quaternary of northwest and northeast
Poland. They occur within glacigenic sequences of each distinct glaciation, although it seems
that they are most common within glacial series of the Middle Polish Glaciation. More than
1000 glacial rafts have been recognized. Some of the glacial rafts are up to 6 km long and
130 m thick. They consist of either unconsolidated Tertiary sediments or lithified rocks of
Cretaceous to Jurassic age. Most common are rafts of Miocene to Pliocene sandy-silty deposits, as well as Cretaceous chalks and chalky or cherty marls. They occur at different levels
within the glacigenic series of a given glaciation, i.e., in the bottom, median or top position.
The rafts vary in shape from regular, flat sheets over folded and thrasted subvertical masses to
irregular, strongly jointed and slickensided blocks. The contact surfaces between them and the
surrounding glacigenic deposits, mainly tills, are very sharp. The travel distance of individual
rafts vary between tens of meters (parautochthonous rafts, upthrusts) to hundreds of kilometers.
The southern limit of mass occurrence of glacial rafts is given on Fig. 1.
A part of these rafts is undoubtedly related to local or subregional heights of bedrock
topography, escarpments or slopes of buried river valleys incised in bedrock. However, the
greatest part of the rafts was eroded from a distinct zone now lying offshore of the Polish
southern Baltic coast and along the southern slope of the Peribaltic (Lithuanian) syneclise. The
huge agglomeration of these rafts indicates that in the area situated somewhat north of the
northern limit of the deposition, the Pleistocene ice sheets were cold; the bedrock below the
base of the ice sheets was frozen to the depth of several to tens of meters. The thickness of
this frozen zone increased with increasing permeability of the rocks or sediments. The rafts of
sediments frozen to the ice sheet sole were sheared away from the parent bedrock either along
surfaces of weakness or just below the base of the frozen ground.
As mentioned above, the rafts were sometimes transported distances of up to 450 km and
occur at any level within the glacial series of any glaciation. This suggests that the rafts were
transported from subglacial to englacial and supraglacial positions. Thrusting along curved,
concave upwards slip lines can contribute to rafts being brought up from the base to the ice
sheet surface. This implies, however, that a strong positive topographic gradient existed here
(related to the formation of the peripheral bulge connected with the glacioisostatic adjustment
to the surface load redistribution), causing longitudinal compression within the ice masses and
the formation of thrust planes within them.
The glacial rafts are accompanied by enormous masses of debris, ranging from erratic
boulders to sand-sized material. Thus, the ice sheets were overloaded with debris. As solid
ice is capable of limited erosion only, it is supposed that north of the cold-ice zone, where
entrainment of massive glacial rafts occurred, there was a zone of temperate ice. Debris-loaded
basal meltwater moving from the temperate ice zone into a cold one can refreeze in great quantities and enrich the basal ice sheet layers with debris. Overthrusting, as discussed above, carried these debris-rich basal layers into englacial and supraglacial positions in the terminal parts
of the ice sheet (see, e.g., Boulton, 1972a, 1972b, 1974). The southern limit of this temperate
ice zone runs nearly along the axis fo the southern Baltic Sea and along the axis of the Peribaltic Syneclise and coincides approximately with the northern boundary of Late Cretaceous rocks
at the bottom of the Recent South Baltic Sea (Rûhle, 1982). It is also worthy of note that the
southern limit of the supposed temperate ice zone coincides approximately with the zero isobase of Holocene glacioisostatic uplift of Fennoscandia (see M&rner, 1980, Fig. 4). The northern limit of this temperate ice zone is not known, but it is assumed that it extended to the
center of glaciation.
The reduction of the total thickness of Quaternary deposits in the northern and
northeastern parts of the Middle Polish Lowland and the southern part of the South Baltic Lake
Region is strong enough to warrant a search for an explanation. The area was at least twice,
Zonal arrangement of thermal regimes
127
and in the southern part of the South Baltic Lake Region thrice, covered by ice sheets. The
Quaternary deposits consist on the whole of one to three sheet-like, overconsolidated lodgment
and melt-out till layers and accompanying glaciofluvial deposits. The Quaternary deposits vary
in thickness from 10-35 m.
The reduction of the thickness of Quaternary deposits suggests at first postdepositional
erosion. This is true, however, only for the glacigenic series of the oldest South Polish Glaciation, since glacial series of the Middle Polish Glaciation and in the South Baltic Lake Region
of the late North Polish Glacial phases as well are rather complete and also well expressed in
glacial landforms. Thus it is assumed that the reduction of thickness of Quaternary deposits is
of primary nature and that this area was covered by either thinned ice sheets, debris-poor ice,
or both. Also within the area occupied by ice sheets of the earlier glacial phases (Leszno, or
Brandenburg, and Poznan, or Frankfurt) of the late North Polish glacial stade, there is strong
evidence of ice sheet thinning and rapid, surge-like advance of the ice. Both the thinning of
the ice sheets and their rapid advances may be the effect of a strong, positive velocity gradient
as the result of changed ice flow regime from compressional (see above) to tensional. Thus it
is suggested that ice thicknesses near the margins of the ice sheets were significantly less than
would be predicted using a conventional parabolic ice-sheet profile (curve la on Fig. 3).
The bedrock within the previously discussed area, in which there has been a marked
reduction of the total thickness of Quaternary deposits, is composed of clayey-silty deposits of
Pliocene age, underlain mostly by groundwater-bearing, sandy-silty sediments with brown coal
intercalations of Miocene age and partly by Mesozoic carbonate and siliceous carbonate rocks.
The bedrock deposits were strongly glaciotectonically disturbed and deformed. These disturbances include folding and thrusting (with amplitudes up to 250 m), fracturing, brecciation and
slickensiding of clayey deposits, differential compaction and overconsolidation, and mud and
clay diapirism (Liszkowski, 1975 and unpublished data). They were the result of rapid ice
loading and the formation of abnormal pore water pressures within the permeable Miocene
deposits. This indicates that the bedrock was unfrozen and therefore that the thermal regime of
the ice sheet was temperate in this zone. It is likely that the previously described thinning of
the ice sheet within the Middle Polish Lowland Region was partly controlled by the high
deformability of the bedrock deposits (Boulton & Jones, 1979).
CONCLUSIONS AND CONSEQUENCES FOR ICE SHEET MODELLING
The most important conclusion resulting from the preceding analysis is that there was a zonal
arrangement of thermal regimes of Pleistocene ice sheets in Poland. The results of the preceding study are schematically shown on Fig. 4. Although this figure was drawn for the late
North Polish glacial stade only, it is stressed that a similar pattern of thermal regimes of ice
occurred during the Middle and South Polish Glaciations, too. The boundaries between the
individual thermal regime zones were probably somewhat dislocated and their width changed.
In general, however, the picture was similar.
It is important to emphasize that a similar zonal arrangement of thermal regimes of Pleistocene ice sheets probably existed in other Baltic countries, including the German Democratic
Republic and Denmark to the west and the Lithuanian and Belorussian republics of the USSR
to the east. In all these countries, a zone of huge agglomeration of massive glacial rafts can be
distinguished, and in all cases this zone is situated in the northernmost part of these countries.
This suggests that the thermal regime zonation obtained for Poland was probably a supraregional feature of the Scandinavian ice sheets.
The question now arises as to what controlling factors determined this zonal arrangement
of thermal regimes of Pleistocene ice sheets. Fundamentally, the thermal regime of ice sheets
depends on variables related to the climate (surface temperature and its long term fluctuations),
128
Jerzy Liszkowski
the thickness of the ice, the distribution of geothermal flux at the base of the ice sheet, the
bedrock topography, the lithology and physical properties of surface materials at the base of
the ice, and the hydrogeological conditions within the near-surface rocks and sediments at the
base of the ice cap. It is at this time impossible to quantify the contribution of each of the factors cited to the zonal pattern. Thus, only a qualitative discussion can be presented.
For the central (with respect to the center of glaciation) temperate ice zone of Fig. 4, the
most effective controlling factor was probably the great thickness (pressure) of the ice sheet. If
correct, this implies that the thermal regime of the ice within this zone changed with time from
cold to warm.
FIG. 4 Reconstructed zonation of thermal regimes of the late North Polish ice
sheet. T: temperate ice, C: cold ice, C/T: alternating cold and temperate ice.
The numbers 1-13 indicate distances in hundreds of km from the presumed
center of glaciation.
The formation of the cold ice zone of Fig. 4, which is critical for our considerations, was
probably mainly controlled by the lithology of the bedrock deposits at the base of the ice
sheets. As discussed above, these bedrock lithologies include Pliocene and Miocene sandysilty sediments and Late Cretaceous chalks and siliceous chalk and marls, which are all rocks
of high porosity, permeability and wetteability, and thus of high adfreezing susceptibility to ice.
Bedrock topography was a secondary controlling factor here, although only of minor, local
importance.
For the external temperate ice zone of the Central Polish Lowland Region, the most
important factor controlling ice temperature was the distribution of geothermal flux, i.e., the
geotectonic (age) province of the crystalline basement and the thickness of the sedimentary
Zonal arrangement of thermal regimes
129
layer of the Earth's crust. It is the only factor that explains the dislocation of the southern
boundary of the zone of widespread occurrence of glacial rafts in northeast Poland to the south
with respect to northwest Poland.
The southernmost narrow zone of differentiated (in space and time) thermal regimes of
ice sheets coincide with the terminal zone of the ice cap. Within this zone, the main controlling factors were short term climatic fluctuations and the thinning-out of the ice sheet.
The author considers the results presented as preliminary and needing more detailed
investigation. However, there is no doubt that the results obtained are of some importance for
ice sheet modelling. The extent of Pleistocene ice sheets (Fig. 1) and the reconstructed thickness of the ice sheets of the late North Polish (Weichselian) Glaciation could be used as hard
facts for input data. The thermal regime zonation of Pleistocene ice sheets, discussed and
examplified for the late North Polish Glaciation in Fig. 4, could be used as hard facts for output tests. The significance of the physical properties, especially the adfreezing susceptibility
and deformability of materials that directly underlie the base of the ice sheet, ought to be especially emphasized.
ACKNOWLEDGEMENTS I wish to thank J.S. Walder and Edwin D. Waddington for
thoughtful and constructive review of the manuscript. Financial support from the IAHS which
allows me to attend the Symposium on the Physical Basis of Ice Sheet Modelling and the XIX
General Assembly of the IUGG is gratefully acknowledged.
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