REGIONAL GLACIATION OF
SOUTHERN & EASTERN BALTIC
James S. Aber
|Clay mine at Jaroszów, southwestern Poland. Tertiary clay (gray) is overlain by glacial sediments (brown). Such geology is typical throughout much of central Europe between the Baltic Sea and alpine mountains. Photo date 8/93; ©; by J.S. Aber.|
|Tatra Mountains, near Zakopane, southern Poland. The Tatra Mts. are part of the Carpathian Mountain system of central Europe. The Tatras supported many small alpine glaciers during the Pleistocene, but were not reached by any advances of the Scandinavian ice sheets. Photo date 8/93; © by J.S. Aber.|
Poland was glaciated repeatedly by continental ice sheets during the Pleistocene, and small alpine glaciers existed in the Carpathian Mountains. North-flowing river systems were blocked during glaciations. Rivers and melt-water runoff were diverted to the west--North Sea, south--Black Sea and east--Caspian Sea--see Fig. 14-2. During interglacial and interstadial intervals, environmental conditions ranged from periglacial, to temperate, to subtropical.
These hills rise >100 m above lowlands to the north and south. They are
composed of deformed Tertiary strata and older glacial sediments. Trzebnica Hills, for example, are a well-known
ice-pushed ridge--see Fig. 14-4. The hills rise about 100 m above
the lowland to the south and around 150 m above the lowland to the north.
They consist of deformed Pleistocene sediment, Pliocene gravel, and clayey strata of the Miocene Poznan Formation. These strata are thrust into a composite structure above a horst in underlying
hard Triassic bedrock. Deformation of Trzebnica Hills and other ice-shoved
hills of the Silesian Rampart is traditionally ascribed to the Wartanian
phase of Saalian Glaciation (Aber et al. 1995). However, some
geologists attribute primary deformation of the hills to older
Southwestern Poland was glaciated by at least four major ice advances, two
Esterian and two Saalian--see Fig. 14-3. The older glaciations
crossed the Odra valley and terminated on the northern flank of the Sudeten
Mountains. These ice advances were regionally derived from the northwest,
with the exception of the Odranian which apparently came from the
northeast. Local ice movement directions were much more variable. Large
ice-shoved hills of the Silesian Rampart are among the most conspicuous
glacial features of the region.
These hills rise >100 m above lowlands to the north and south. They are composed of deformed Tertiary strata and older glacial sediments. Trzebnica Hills, for example, are a well-known ice-pushed ridge--see Fig. 14-4. The hills rise about 100 m above the lowland to the south and around 150 m above the lowland to the north. They consist of deformed Pleistocene sediment, Pliocene gravel, and clayey strata of the Miocene Poznan Formation. These strata are thrust into a composite structure above a horst in underlying hard Triassic bedrock. Deformation of Trzebnica Hills and other ice-shoved hills of the Silesian Rampart is traditionally ascribed to the Wartanian phase of Saalian Glaciation (Aber et al. 1995). However, some geologists attribute primary deformation of the hills to older glaciations.
|View over glacial foreland south of Trzebnica Hills, which are visible as the higher ridge on horizon. The hills rise about 100 m above the foreground terrain. These and similar ice-shoved hills mark the Silesian rampart in southwestern Poland. Photo date 8/93; ©; by J.S. Aber.|
|Deformed glacial sediment within Trzebnica Hills. Laminated clay is disrupted into a breccia of broken fragments. Thrust blocks of deformed Miocene clay (Poznan Fm.) are also found within Trzebnica Hills at other sites. Photo date 8/93; © by J.S. Aber.|
The Silesian Rampart is associated with the Odra fault zone, which continues into eastern Germany as the Fläming Rampart. The Odra faults form a complex of horsts and grabens in hard Paleozoic and Triassic bedrock below softer Tertiary strata. Ice-pushing of soft sediments took place above these buried bedrock obstacles. The Silesian and Fläming Ramparts are parts of a glaciotectonic belt that extends westward across Germany and the Netherlands, and reaches onto the North Sea floor. Ice-shoved hills of this belt vary greatly in age and genesis, but most are associated with buried hard-rock structures (Aber et al. 1995). This situation demonstrates an important principle--buried bedrock features may strongly influence Quaternary geology and geomorphology.
Uplands adjacent to the delta/bay display various evidences for
glaciotectonism--see Fig. 14-6. The eastern flank of the Pomeranian
upland has numerous bedrock rafts, small ice-shoved hills, and dislocations
of Quaternary strata. Much of the ice-shoved material was presumably
derived from Gdansk Bay. The great depth of Gdansk Bay is a result of
combined strong glacial erosion and glaciotectonism by major ice streams or
lobes during repeated glaciations.
The Vistula delta and Gdansk Bay region is a classic area for research on
Eemian deposits and environments in northern Poland. Much of the modern
Vistula delta and Zalew Wislany were submerged in a shallow sea or lakes
during the Eemian--see Fig. 14-5. Thick marine, lacustrine, and
fluvial deposits accumulated, and fossils suggest that climatic conditions
were subtropical during the Eemian. During glacial advances, Gdansk Bay
and the Vistula delta were often submerged by proglacial lakes.
Uplands adjacent to the delta/bay display various evidences for glaciotectonism--see Fig. 14-6. The eastern flank of the Pomeranian upland has numerous bedrock rafts, small ice-shoved hills, and dislocations of Quaternary strata. Much of the ice-shoved material was presumably derived from Gdansk Bay. The great depth of Gdansk Bay is a result of combined strong glacial erosion and glaciotectonism by major ice streams or lobes during repeated glaciations.
|High bluffs along the Baltic coast northwest of Gdansk Bay. These hills are underlain by thick glaciolacustrine strata, which indicate that proglacial lakes once existed within the Gdansk Bay lowland and adjacent Baltic basin. Unconsolidated Miocene sand and silt are also present at the base of the cliffs. Photo date 9/93; © by J.S. Aber.|
|Orlowo cliff, on the western side of Gdansk Bay, near Sopot, Poland. This cliff reveals strongly deformed Quaternary and Tertiary strata shoved out of the Gdansk depression. Photo date 9/93; © by J.S. Aber.|
|Closeup view at Orlowo cliff showing massive till (upper right) thrust over sand and gravel that stand in vertical position (left center) beneath the thrust. Photo date 9/93; © by J.S. Aber.|
Elblag Upland is a complex glaciotectonic feature that consists almost entirely of deformed Pleistocene sediments. The upland stands nearly 200 m above surrounding lowlands--see Fig. 14-7. The upland covers approximately 390 km², which makes it the largest single ice-shoved landform in Poland or anywhere else in the southern Baltic region. Within the upland, many deformed strata are anomalously thick and situated high above their normal levels. For example, Eemian marine and lacustrine strata are locally >100 m thick within the hill and occur at elevations up to 80 m above present sea level. Equivalent strata are only 10-20 m thick with their tops located 10-30 m below sea level, where undisturbed beneath the adjacent delta plain and estuary.
|View westward from Frombork, the home of Copernicus. Elblag Upland is the large hill visible through low clouds on the horizon. The water body is Zalew Wislany, the coastal lagoon. The upland rises to nearly 200 m above sea level. Photo date 9/93; © by J.S. Aber.|
|Large block of Elblag Clay (dark gray) shoved into vertical position along with glacial sand/gravel (tan). This exposure reaches about 75 m elevation; the Elblag Clay was presumably thrust up from near or below sea level by ice pushing. The clay mine is located at Kadyny on the northern margin of Elblag Upland. Photo date 7/93; © by J.S. Aber.|
|Closeup view of Elblag Clay in the mine at Kadyny. The clay is strongly fractured and brecciated. Photo date 7/93; © by J.S. Aber.|
|Landscape in the central portion of Elblag Upland, near Majewo. Elongated hill on the horizon is an ice-shoved ridge that was later overridden and slightly smoothed. This ridge is part of the eastern arcuate morphologic belt of Elblag Upland. Photo date 9/93; © by J.S. Aber.|
Two morphologic patterns are well defined in the upland: (1) eastern arcuate belt, concave toward the northeast, and (2) western arcuate belt, concave to the west. These two sets converge near the center of the upland, in the vicinity of several small lakes, including Lake Stare. The greatest amount of deformation is documented in the zone of convergence, where strata stand in vertical position, and in which reworked Tertiary strata are found at elevations up to 130 m. The morphologic trends of Elblag Upland suggest two directions of local ice movement: (1) eastern section deformed by ice advance from the northeast, and (2) western portion pushed from the west. Structural evidence confirms dominant ice pushing from the northeast, and drumlins indicate final ice overriding from the NNW.
Elblag Upland represents a very large cupola hill that was formed by local ice movements from the northeast, west, and NNW (Aber and Ruszczynska-Szenajch 1997). All these ice advances took place during the late Vistulian glaciation. It is possible that Elblag Upland was created in an interlobate position, as local ice-lobes surged into a proglacial lake dammed in the Gdansk Bay basin--one ice lobe was situated to the east in the till-plain lowland, and another to the west in Vistula delta/lagoon depression.
|Kite aerial photographs|
of Polish lowlands.
Taken from Estonia in the Baltics.
|Crystalline erratic boulders on the beach on the island of Vormsi, northwestern Estonia. Such boulders are useful to establish sources and directions of ice movement. Photo date 8/00, © J.S. Aber.|
|Digital elevation model for Estonia and surrounding areas. The islands and western mainland of the country are generally less than 30 m above sea level. Uplands (>100 m high) are found in the north-central and southern portions of Estonia, and Lake Peipsi occupies a large depression along the eastern edge of the country. Elevation data obtained from GLOBE. Raw DEM data resampled into UTM grid. Click on the small image to see a larger (55 kb) version. Image processing by J.S. Aber ©.|
Most of Estonia is less than 100 m above sea level. Higher uplands are found in the north-central (Pandivere), south (Sakala), and southeast (Otepää and Haanja) portions of the country--see Figure 14-8. The Pandivere and Sakala uplands are composed primarily of bedrock. Pandivere was an area dominated by glacial erosion, and its sediment cover is often less than 5 m. Sakala has an average 20 m cover of glacial sediment. In contrast, the Otepää and Haanja uplands are composed of thick (>100 m) Quaternary sediments representing several episodes of glaciation. These sediments were strongly deformed by ice pushing in interlobate positions and may be considered as large glaciotectonic massifs (Rattas and Kalm 1999).
|View over Haanja Upland terrain taken from an observation tower at Suur Munamägi, the highest point in Estonia (318 m). Photo date 8/00, © J.S. Aber.|
|View from the top of the ski jump at the Olympic training center in the Otepää Upland. Photo date 8/00, © J.S. Aber.|
Major ice lobes flowed through lowlands across western and easternmost Estonia, and ice flow diverted around the uplands to form local ice lobes. This led to complicated patterns of ice flow directions--see Figure 14-9. The northern coastal cliff, formed in Ordovician limestone underlain by soft Cambrian clay, was subjected to widespread glaciotectonic deformation--see Figure 14-10. Conspicuous drumlin fields are found in lowlands of central Estonia. These drumlin fields record both southeasterly and southwesterly directions of ice movement. Most of the drumlins consist of older Quaternary sediments that were deformed and molded into streamlined hills during the last glaciation (Rattas and Kalm 1999).
|Saadjärv drumlin field, east-central Estonia--see Figure 14-11. Lake Saadjärv (left) occupies an elongated trough, and a long, smooth drumlin extends into the distance on right. Another lake, Soitsjärv, can be seen at extreme upper right. Kite aerial photograph, 9/00, © J.S. Aber.|
At least five distinct till beds have been identified along with associated stratified drift, although intervening nonglacial strata are scarce--see Table 14-1. Considerable information is available for the last glaciation--Võrtsjärve, as its deposits are widely preserved in the modern landscape of Estonia--see Table 14-2. Five phases during the general retreat of the last ice sheet have been identified along with lesser glacial limits. These phases represent either stillstands or readvances of the ice margin.
|Formation||Genesis||Russian||W. European||Järve: Võrtsjärve|
|Valdaian ||Weichselian ||Prangli ||Forest vegetation|
|Mikulinan ||Eemian ||Ugandi: upper|
|Middle Russian ||Saalian ||Karuküla ||Forest vegetation ||Likhvinan ||Holsteinian ||Sangaste ||Glacial till ||Oka ||Elsterian|
|Phase||Extent||Direction||Age*||Palivere ||Northwestern Estonia ||SE ||11,200 ||Pandivere ||Northern Estonia ||S-SW ||12,000 ||Sakala ||Central Estonia ||SE ||12,250 ||Otepää ||Southern Estonia ||SE ||12,600 ||Haanja ||Nearly whole Estonia ||SE ||13,000 |
|View southeast along esker peninsula at Rumpo, southern Vormsi. The road follows the crest of the esker, which bends to the east in the distance. This esker extends several km across the seafloor to the southeast. Kite aerial photograph, 8/00, © J.S. Aber.|
|View toward the northwest at Rumpo, southern Vormsi. The road follows the crest of the esker across the island interior. Villages and agricultural fields are located on the higher, better drained esker ridge. Kite aerial photograph, 8/00, © J.S. Aber.|
The eskers of Vormsi and surroundings demonstrate a regular pattern in their distribution, which represents the preserved portions of a subglacial drainage network that was essentially braided in character. The esker network is located along the central pathway of the Väinameri ice lobe, and the overall direction of drainage was toward the Palivere glacial limit. Similar esker systems have been identified on the Baltic Sea floor between Estonia and Sweden--see Fig. 14-13.
|Landsat image of Vormsi and the Väinameri region, northwestern Estonia. Compare with Figure 14-12 for positions of eskers and the Palivere glacial limit. Blue colors of the Väinameri reflect variations in water depth (1 to 10 m). Image acquisition date 7/86; image processing by J.S. Aber ©.|
Along and south of the Palivere ice limit, an extensive proglacial lake was developed, which represents an early phase of the Baltic Ice Lake (Raukas 1993). The existence of a proglacial water body is documented further by the water-laid nature of the upper portion of the Palivere diamicton on the western Estonian islands (Kadastik and Kalm 1998). The Palivere phase has been interpreted as a significant readvance of the ice sheet following complete deglaciation of Estonia after the Pandivere stade (Karukäpp and Raukas 1997). The Palivere readvance may have taken place as a local ice-lobe surge into a proglacial lake and during which a substantial volume of subglacial meltwater was released.
As a consequence of glaciation, the crust of the eastern Baltic region was depressed substantially. During late glacial and early Holocene times, large areas were submerged beneath the Baltic Ice Lake and early phases of the Baltic Sea--see Table 14-3. Marine and coastal deposits of the Litorina Sea and Limnea Sea are widespread on the western Estonian mainland and islands. Since deglaciation, western and northern Estonia has experience significant uplift, whereas southeastern Estonia has subsided. At present, western and northern Estonia is rising at rates that exceed 2 mm per year in places, while southeastern Estonia is sinking at < 1 mm per year. A hingeline of no change crosses through Võrtsjärv and Lake Peipsi. Recent crustal movement has markedly affected river drainage and lakes. For example, the southern end of Lake Peipsi is sinking at rates up to 0.8 mm per year (Hang and Miidel 1999). Medieval churches and villages on lake islands are now submerged.
|Beach gravel of the Limnea Sea, about 4000 years old. This old beach ridge is now several meters above sea level on the Rumpo Peninsula, island of Vormsi, northwestern Estonia. Photo date 8/00, © J.S. Aber.|
|Lake/Sea||Phase||Age *||Baltic Ice Lake ||Alleröd, early Younger Dryas ||10,500 ||Yoldia Sea ||late Younger Dryas, early Pre-Boreal ||10,000 ||Ancylus Lake ||late Pre-Boreal, Boreal ||9000 ||Litorina Sea ||Atlantic, early Sub-Boreal ||7000 ||Limnea Sea ||Sub-Boreal, Sub-Atlantic ||4000 |
Kite aerial photographs of Estonia--Estonian KAP.
During the last glaciation, the Scandinavian Ice Sheet contained several major and many minor, fast-moving ice streams, which extended as fan-shaped lobes at the ice margin--see Fig. 14-15. These ice streams/lobes were separated by interlobate zones in which ice movement was relatively slow. The locations of these dynamic features were controlled primarily by bedrock topography and secondarily by positions of ice domes and ice-marginal calving bays within lakes or seas. Ice-stream zones are marked by streamlined landforms that consist mainly of till or eroded bedrock. Interlobate zones are marked by accumulations of stratified melt-water deposits.
The dynamics of individual ice streams/lobes varied as the ice sheet waxed and waned, so that some streams were more active and expanded at times, and at other times different ones became dominant. In this way, time-transgressive and overlapping patterns of ice flow took place in many areas. Two patterns of ice flow record the last major glaciation.
Large ice-shoved hills are a characteristic part of the southern Baltic coastal landscape in northern Poland, northern Germany and southern Denmark. These hills are mainly products of Vistulian glaciation; in many cases deformation resulted from relatively late readvances. The ice-shoved hills of the southern Baltic are mostly associated with embayments or estuaries, in which ice lobes were active during deglaciation. Certain hills suffered multiple or changing directions of ice movement: Høje Møn
|Scale model of Møns Klint and the eastern part of the island of Møn, southeastern Denmark. View is toward west; maximum elevation is about 140 m. Notice the arcuate, ridged landscape formed by inland continuation of chalk masses that are exposed in the cliff. The northern (right) portion was deformed by ice advance from the northeast; southern (left) part was created by ice pushing from the south. These ice advances may have been separate events (Pedersen 2000), or glaciotectonic deformation may have occurred in an interlobate setting (Jensen 1993). Model displayed at the Geological Museum, Copenhagen, Denmark.|
|Space-shuttle photograph of northeastern Germany. Near-vertical view of the German island, Rügen (right-center) and mainland (lower portion); part of the Danish island of Møn is visible in upper left corner. Rügen and Møn were subjected to strong glaciotectonic deformation by ice advances from multiple directions. NASA Johnson Space Center, Imagery Services, STS045-152-156, 3/92.|
During late Vistulian deglaciation, major readvances took place within the western Baltic region--the Young Baltic advances. The advances are traditionally ascribed to ice streams that originated in the central Baltic region to the east and terminated in the Kattegat Sea to the northwest--see Fig. 14-16. These advances may have been major surges that effected the entire southern Baltic ice stream, which in turn triggered surges by local ice lobes and tongues in the embayments of the southern, western, and eastern Baltic region. Many of the large glaciotectonic hills may have formed during surges by Young Baltic ice lobes (Aber and Ruszczynska-Szenajch 1997).
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ES 331/767 © J.S. Aber (2008).