Marginal Moraines Research Articles

Time regularities of strontium concentration in drinking groundwater distant from the sea coast.

This paper confirms the regularities of the formation of increased concentrations of strontium (Sr) in fresh groundwater used for drinking water supply, depending on the time they are residen in the carbonate deposits of the aquifer. On average, every thousand years, the Sr concentration increases by 2.1-3.5mgL-1. In addition, high strontium content is positively correlated with altitude and well depth and negatively correlated with redox conditions in the aquifer. Large relief elevations are associated with the development of marginal moraine deposits from the Last Glacial Period composed predominantly of clay, which contributes to a decrease in water exchange. The high Sr content is associated with the dissolution of significant formations of celestite and strontianite, up to their ore occurrences. For this reason, the saturation indices (SIs) for celestite and strontianite correlate with TDS and rise to - 1.42 and 2.05, respectively. Low Sr values do not correlate with the residence time of groundwater in the aquifer or the depth of wells and tend to depressions in the relief, with a virtual absence of overlying sediments and positive Eh values, which indicates an active water exchange. The low level of Sr is associated with the dissolution of gypsum, calcite, and dolomite containing strontium as an impurity. This causes the SIs for gypsum, calcite, and dolomite to correlate with TDS, while for celestite and strontianite, the SI drops to - 5.02 and - 0.92, respectively. The established patterns make it possible to more reasonably choose places for the construction of water wells to obtain drinking water of standard quality.

Glacial geomorphology of the northwest Laurentide Ice Sheet on the northern Interior Plains and western Canadian Shield, Canada

ABSTRACT The majority of the Northwest Territories of mainland Canada was covered by the Laurentide Ice Sheet during the Last Glacial Maximum. The increasing coverage of high resolution remotely sensed data provides new opportunities to map the glacial geomorphology and study the glacial history of this remote location. Here we present a comprehensive map of glacial landforms within the northern Interior Plains and adjacent areas of the Canadian Shield, comprising around 6% of the Laurentide Ice Sheet bed. Twelve landform types were mapped from the high resolution ArcticDEM: ice flow parallel lineations, subglacial ribs, crevasse-squeeze ridges, major and minor moraine crests, hummocky terrain complexes and ridges, shear margin moraines, major, minor and lateral and submarginal meltwater channels, esker ridges and complexes, glaciofluvial complexes, perched deltas, raised shorelines and aeolian dunes. Together, these landforms provide a record of the highly dynamic behaviour of the northwest sector of the Laurentide Ice Sheet.

Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits

AbstractLandforms and sediments on the palaeo–ice stream beds of central Alberta record glacitectonic raft production and subsequent progressive disaggregation and moulding, associated substrate ploughing, and grooving. We identify a subglacial temporal or developmental hierarchy that begins with incipient rafts, including en échelon hill-hole complexes, hill-hole pairs, and strike-slip raft complexes, all of which display patterns typical of transcurrent fault activation and pull apart. Many display jigsaw puzzle–style fragmentation, indicative of substrate displacement along shallow décollement zones and potentially related to patchy ice stream freeze-on. Their gradual fragmentation and smoothing produces ice flow-transverse ridges (ribbed moraine), hill-groove pairs, and paraxial ridge and groove associations. Initiator scarp and megafluting associations are indicative of raft dislodgement and groove ploughing, leading to the formation of murdlins, crag-and-tails, stoss-and-lee type flutings and drumlins, and Type 1 hogsback flutings. Downflow modification of rafts creates linear block trains (rubble stripes), stoss-and-lee type megaflutings, horned crag-and-tails, rubble drumlinoids, and murdlins, diagnostic of an immature palaeo–ice stream footprint. Lateral ice stream margin migration ingests disaggregated thrust masses to form ridged spindles, ladder-type morphologies, and narrow zones of ribbed terrain and Type 2 hogsback flutings, an assemblage diagnostic of ice stream shear margin moraine formation.

New evidence for the rank of the Wartanian cold period (Pleistocene, MIS 6): a case study from E Poland

In the stratigraphic division of the Saalian (Middle Pleistocene) in Europe, the Wartanian cold period has the rank of a stadial of the Odranian Glaciation, correlated with MIS 6. The authors demonstrate the higher rank of this cold period, on the basis of an analysis of the sedimentary succession in eastern Poland, at an exposure of the terminal moraine of the Wartanian ice sheet. At the Wólka Zagórna site, three stratigraphic units were distinguished: A (lower glacigenic deposits – glaciofluvial deposits and subglacial till), A/B (fossil soil of lessivé type), B and C (a periglacial horizon with deflation pavement, involutions, frost-wedge structures and upper glaciofluvial deposits and flow till, with ice-wedge casts). Two distinct periods of climatic cooling, associated with the youngest Saalian ice sheets, were recorded in this succession in E Poland: Odranian (unit A, an ice-sheet transgression marked by the deposition of glaciofluvial deposits dated as 365–226 ka, ending with the deposition of subglacial till), and Wartanian (units B and C, an ice sheet transgression marked by development of a periglacial zone, dated as 180–126 ka, and then deposition of glacigenic sediments at the front of the ice sheet and formation of a marginal moraine). Each of these periods of ice-sheet transgression occurred at a different time (in the MIS 8 and MIS 6 positions) and were separated by a warm period. It is documented by unit A/B – a fossil soil with a very well developed Bt horizon – which attests to its formation in an illuviation process beneath a complex of mixed forests during an interstadial warming that occurred in MIS 7. From this palaeoclimatic reconstruction, it is inferred that the Wartanian cold period should be viewed as a separate glaciation in MIS 6 and the Odranian period should be assigned to MIS 8 in the stratigraphic schema of the Quaternary.

Application of geomorphons for analysing changes in the morphology of a proglacial valley (case study: The Scott River, SW Svalbard)

The progressive degradation of the cryosphere of High-Arctic areas causes an increase in the dynamics of geomorphic processes that shape the valleys of rapidly retreating glaciers. Those especially sensitive to global environmental changes are the small, land-ending valley glaciers that are in the phase of strong retreat. Under these conditions, the river valley's floors that are drained by proglacial waters are constantly undergoing intensive changes. For the analysis of these changes, two methods were used simultaneously (as a synthesis) to allow for quantitative and qualitative evaluation. The first one is the increasingly more common DoD method (DEM of difference), which allows quantifying volumetric changes as a result of topographic differentiation. The second one, which was applied for the first time on a small-valley spatial scale, is the geomorphons method that makes it possible to assess the stability of landforms and to determine the directions of their new development. To judge the applicability (advantages and disadvantages) of both methods for analysis of geomorphic changes in rapidly changing proglacial environments, the study was carried out over a 3.3 km distance of the non-glaciated section of the Scott River valley course (NW Wedel-Jarlsberg Land, SW Svalbard). This area (1.3 km2) is currently shaped by a braided gravel-bed river. More accurately, the study focused on the section spanning from the glacier terminus, which is the source of the Scott River, to its outlet at the Rechersche Fjord (Bellsundfiorden). The foundation for the development of comparative elevation models was a collection of terrestrial laser scanning (TLS) surveys that were taken with a Leica ScanStation C10 scanner during the 2010 and 2013 snowmelt seasons. On the basis of these surveys and with the use of TIN interpolation, high-resolution (0.2 m) digital terrain models (DTMs) were generated. The DTM models that had been prepared in this manner were used for the analysis of surface changes by employing Geomorphic Change Detection (GCD) software, and by simultaneously generating geomorphons maps for four selected test areas that covered characteristic fragments of the valley bottom (1- on the close forefield of the Scott Glacier terminus; 2- in the immediate vicinity of the narrow valley outlet at the foot of the marginal moraine ridge; 3- in the enlargement of the central section of the non-glaciated valley floor; 4- within the alluvial fan (outlet to the fjord)). A comparison of the obtained results (DoD and geomorphons maps; zonal statistics) as well as a compilation of both the quantitative assessment of the scale of changes and the qualitative assessment of the transformation's direction allowed for reconstructing the range and rate of three-year-long changes in morphology at the analysed sections of the valley floor. It was found that the pattern and rate of changes were closely related to the location of the test areas in the Scott River's catchment system. Significant differences in the dynamics of processes shaping the valley landforms along the longitudinal valley course were found.

The Idre marginal moraine – An anchorpoint for Middle and Late Weichselian ice sheet chronology

We here report the results of luminescence and cosmogenic exposure dating of the Idre marginal moraine, located in the southern Scandinavian Mountains. This particular moraine is targeted because it is morphologically distinct and marks the margin of a former ice sheet. The till in the moraine contains erratics that provide strong evidence of flow from an ice sheet centred over Norway. The area immediately outside the moraine margin is an older residual soil. Luminescence ages of three samples taken from a sand lense within the moraine indicate that it formed at around 55 ka, during the early warm part of Marine Isotope Stage (MIS) 3. Median exposure ages (10Be) of ten samples from boulders embedded in the surface till indicate that about 30 ka of ice-free time have elapsed since formation of the moraine. The difference between the age of the ridge and the duration of exposure provides a measure of the time of ice-cover in the ice sheet core area. Previous research indicates that final deglaciation of the site occurred at approximately 10 ka ago, which in combination with our results implies that the area around the Idre marginal moraine was ice free for ca. 20 ka, i.e. from around 55 ka to around 35 ka. Thereafter, the area was glaciated and the marginal moraine was covered by the Late Weichselian ice sheet for around 25 ka without experiencing any significant erosion or morphological destruction. While earlier studies have already pointed towards MIS 3 ice free conditions in northern and central Sweden, this study contributes a measurement-based duration estimate for the MIS 3 interstadial.

Wet subglacial bedforms of the NE Greenland Ice Stream shear margins

AbstractWe describe elongate, wet, subglacial bedforms in the shear margins of the NE Greenland Ice Stream and place some constraints on their formation. Lateral shear margin moraines have been observed across the previously glaciated landscape, but little is known about the ice-flow conditions necessary to form these bedforms. Here we describe in situ sediment bedforms under the NE Greenland Ice Stream shear margins that are observed in active-source seismic and ground-penetrating radar surveys. We find bedforms in the shear margins that are ~500 m wide, ~50 m tall, and elongated nearly parallel to ice-flow, including what we believe to be the first subglacial observation of a shear margin moraine. Acoustic impedance analysis of the bedforms shows that they are composed of unconsolidated, deformable, water-saturated till. We use these geophysical observations to place constraints on the possible formation mechanism of these subglacial features.

High-resolution landform assemblage along a buried glacio-erosive surface in the SW Barents Sea revealed by P-Cable 3D seismic data

The Quaternary sedimentary record in the Arctic captures a diverse and evolving range of landscapes reflecting climate changes. Here we study the geological landform assemblage of the Upper Regional Unconformity (URU) in the SW Barents Sea. The aims are (i) to characterize buried geological landforms on a meter-scale resolution, (ii) to understand their link with underlying structures, and (iii) to reconstruct paleo-ice-sheet dynamics and configurations. The data consist of a high-resolution three-dimensional (3D) P-Cable seismic cube with an extent of c. 200 km2 and an inline separation of 6 m. Dominant frequencies of c. 150 Hz allow to image landforms at URU with a vertical resolution of 1–5 m and a horizontal resolution of 3–6 m. We conduct detailed horizon-picking and seismic attribute analysis of the buried URU horizon. We identified four sets of mega-scale glacial lineations, and shear band ridges located to the west of a shear margin moraine. Other characteristic features include hill-hole pairs, transverse ridges, rhombohedral ridges and depressions, iceberg ploughmarks and pockmarks. Polygonal faults below URU and deeper faults have a strong effect on the location of structures observed on URU. Bedrock packages deformed down to 30 m below URU and up to 5 m-high transverse ridges at URU are imprints of glacio-tectonic activity. Deformed strata below URU indicate normal faulting superimposed by glaciotectonic deformation. The four sets of mega-scale glacial lineations indicate four streaming events with thawed glacial beds, with shear band ridges forming in the shearing zone during one of these streaming events. Hill-hole pairs and rhombohedral ridges are frozen-bed features which indicate a polythermal regime at the base of the Barents Sea Ice Sheet during multiple streaming phases. This study therefore shows that paleo-ice streams have been temporarily frozen to the ground in the SW Barents Sea, and that landforms evidencing this freezing are associated with underlying faults.

Early-Holocene glacier fluctuations of northern Grovabreen, western Norway

Marginal moraines on the northern side of Grovabreen, a plateau glacier in inner Sunnfjord, Western Norway, have been mapped and morphostratigraphically correlated with the Erdalen Event and possibly the Finse Event and the ‘Little Ice Age’. Schmidt-hammer exposure-age dating was used to evaluate the age of the most distinct marginal moraines by measuring the degree of surface weathering on boulders. The lithostratigraphy of lake sediments was analysed in a core from Dalevatnet in order to correlate this stratigraphy with the marginal moraines in the catchment area of the lake and reconstruct the early-Holocene history of Grovabreen. The lake catchment was deglaciated at 10,750 cal. yr BP. Two readvances of an outlet glacier in Fagredalen were dated to between 10,340 and 9960 cal. yr BP, correlated with the two-peaked Erdalen Event. A readvance shortly after 8450 cal. yr BP can most probably be correlated with the 8200 cal. yr BP Finse Event.

Shear margin moraine, mass transport deposits and soft beds revealed by high-resolution P-Cable three-dimensional seismic data in the Hoop area, Barents Sea

Abstract High-resolution seismic data are powerful tools that can help the offshore industries to better understand the nature of the shallow subsurface and plan the development of vulnerable infrastructure. Submarine mass movements and shallow gas are among the most significant geohazards in petroleum prospecting areas. A variety of high-resolution geophysical datasets collected in the Barents Sea have significantly improved our knowledge of the shallow subsurface in recent decades. Here we use a c. 200 km 2 high-resolution P-Cable 3D seismic cube from the Hoop area, SW Barents Sea, to study a 20–65 m thick glacial package between the seabed and the Upper Regional Unconformity (URU) horizons. Intra-glacial reflections, not visible in conventional seismic reflection data, are well imaged. These reflections have been mapped in detail to better understand the glacial deposits and to assess their impact on seabed installations. A shear margin moraine, mass transport deposits and thin soft beds are examples of distinct units only resolvable in the P-Cable 3D seismic data. The top of the shear margin moraine is characterized by a positive amplitude reflection incised by glacial ploughmarks. Sedimentary slide wedges and shear bands are characteristic sedimentary features of the moraine. A soft reflection locally draping the URU is interpreted as a coarser grained turbidite bed related to slope failure along the moraine. The bed is possibly filled with gas. Alternatively, this negative amplitude reflection represents a thin, soft bed above the URU. This study shows that P-Cable 3D data can be used successfully to identify and map the external and internal structures of ice stream shear margin moraines and that this knowledge is useful for site-survey investigations.

Ice-stream dynamics of the SW Barents Sea revealed by high-resolution 3D seismic imaging of glacial deposits in the Hoop area

Recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics. This study focuses on a new high-resolution P-Cable 3D seismic cube located in the Hoop area in the SW Barents Sea. The scientific motivations of the study are (1) to document glacial landforms on a meter-scale, (2) to study the link of these landforms with the subsurface, and (3) to understand ice-stream dynamics by detailed interpretation of main horizons, including the seabed, intra-glacial horizons, and Upper Regional Unconformity (URU). The horizons are assessed using the concept of seismic geomorphology, and compared with interpretations derived from conventional 3D seismic and state-of-the-art multibeam echosounder technologies to discuss the benefits and limitations of the different geophysical technologies. A well-defined intra-glacial seismic reflection is imaged in the eastern part of the P-Cable cube. This reflection has an overall NE-trending ridge-shaped morphology, which is up to 50 m high and 5–10 km wide, and interpreted as a shear margin moraine. The top of the moraine displays well-defined iceberg ploughmarks and clear slope failure events along its eastern flank. The seabed geomorphology, which has been directly shaped by glacial processes related to multiple phases of ice streaming, appears to be influenced by the buried shear margin moraine. Mega-scale glacial lineations (MSGLs) indicative of fast-flowing ice streams characterize the seabed west of the moraine. Infilled MSGLs and different sets of iceberg ploughmarks with large berms dominate the seabed geomorphology above the moraine. The seabed east of the moraine, characterized by a smooth morphology and few pockmarks, is inferred to reflect more slowly-moving ice. Not resolved by other geophysical techniques, seismic attribute maps of P-Cable 3D allowed the identification of smaller ploughmarks and corrugated ridges related to paleo tides. Eroded by the larger iceberg ploughmarks, these small ploughmarks are suggested to be linked to an earlier rapid disintegration of the Barents Sea Ice Stream. The new high-resolution 3D seismic data have led to the development of a revised ice-stream model of the Barents Sea, linking the glacial deposits to different ice stream events.

Geomorphology under ice streams: Moving from form to process

AbstractIce streams are integral components of an ice sheet's mass balance and directly impact on sea level. Their flow is governed by processes at the ice‐bed interface which create landforms that, in turn, modulate ice stream dynamics through their influence on bed topography and basal shear stresses. Thus, ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics. This paper reviews developments in our understanding of ice stream geomorphology from a historical perspective, with a focus on the extent to which studies of modern and palaeo‐ice streams have converged to take us from a position of near‐complete ignorance to a detailed understanding of their bed morphology. During the 1970s and 1980s, our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in Antarctica. Very few palaeo‐ice streams had been identified with any confidence. During the 1990s, however, glacial geomorphologists began to recognise their distinctive geomorphology, which included distinct patterns of highly elongated mega‐scale glacial lineations, ice stream shear margin moraines, and major sedimentary depocentres. However, studying relict features could say little about the time‐scales over which this geomorphology evolved and under what glaciological conditions. This began to be addressed in the early 2000s, through continued efforts to scrutinise modern ice stream beds at higher resolution, but our current understanding of how landforms relate to processes remains subject to large uncertainties, particularly in relation to the mechanisms and time‐scales of sediment erosion, transport and deposition, and how these lead to the growth and decay of subglacial bedforms. This represents the next key challenge and will require even closer cooperation between glaciology, glacial geomorphology, sedimentology, and numerical modelling, together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Ice stream reorganization and glacial retreat on the northwest Greenland shelf

AbstractUnderstanding conditions at the grounding‐line of marine‐based ice sheets is essential for understanding ice sheet evolution. Offshore northwest Greenland, knowledge of the Last Glacial Maximum (LGM) ice sheet extent in Melville Bugt was previously based on sparse geological evidence. This study uses multibeam bathymetry, combined with 2‐D and 3‐D seismic reflection data, to present a detailed landform record from Melville Bugt. Seabed landforms include mega‐scale glacial lineations, grounding‐zone wedges, iceberg scours, and a lateral shear margin moraine, formed during the last glacial cycle. The geomorphology indicates that the LGM ice sheet reached the shelf edge before undergoing flow reorganization. After retreat of ~80 km across the outer shelf, the margin stabilized in a mid‐shelf position, possibly during the Younger Dryas (12.9–11.7 ka). The ice sheet then decoupled from the seafloor and retreated to a coast‐proximal position. This landform record provides an important constraint on deglaciation history offshore northwest Greenland.

Glacial Geomorphology of Mt. Munkh Saridag in the Khuvsgul Mountain Range, Northern Mongolia

This study reconstructs palaeoglacial extent in the Khuvsgul Mountain Range in northern Mongolia based on the mapping of glacial landforms of Mt. Munkh Saridag. For the accurate reconstruction of palaeoglaciations in the Khuvsgul Mountain Range, glacial landforms including glacial valleys, glacial cirques, end moraines, medial moraines, marginal moraines and glacial lineations were mapped at a scale of 1:100.000 for Mt. Munkh Saridag. Mapping was conducted using Google Earth, 30 m resolution ASTER DEM data and 30 m resolution Landsat 5TM satellite imagery. This mapping revealed abundant glacial erosional and depositional landforms in the Khuvsgul Mountain Range, in particular, large end moraine complexes mark palaeoglacial advances in the mountain valleys of Mt. Munkh Saridag. Results indicate that Mt. Munkh Saridag, the center of Khuvsgul Mountain Range, had lost 42.6% of its total glacier area between 1970 (900 m²) and 2007 (384 m²) when the equilibrium-line altitudes (ELAs) of the glaciers were retreated by 47 m and 80 m on north and south aspects, respectively. The outer limits of these glacial landforms show development of small ice caps on peaks and ice fields in valleys of Mt. Munkh Saridag where their maximum glaciation was reconstructed to have covered 186 km². The spatial analyses show the dynamic change of the modern glaciers in Mt. Munkh Saridag, and how this depends on topographical elements of elevation and aspects, durations of solar radiation and vulnerability to the solar insolation. This study demonstrates that spatial analysis of the glacial landforms is crucial for reviewing the extent of palaeoglaciers that could be detailed with dates in further work.

The stratotype and facies of the glacial Lower Vendian Nichatka Formation, Chara River basin, Central Siberia

Sediments of the Nichatka Formation are facially studied and thoroughly described, the sections are correlated, and the subformations are recognized. The formation represents a key stratigraphic unit to reveal the origin of the Central Siberian glacial horizon and to correlate it with glacial horizons in other regions of the world, namely, with the Laplandian Horizon of the Lower Vendian, Nantou and Marino tillites, etc. The Nichatka Formation is correlated with the glacial Bolshoi Patom (Dzhemkukan) Formation of the Vendian reference section at the Ura Uplift. Unlike the latter, it is mainly composed of continental glacial deposits and is marked by a complex facies composition. The glacial origin of the Nichatka Formation is reliably determined on the basis of a set of diagnostic characters. This permits a more complete reconstruction of the Early Vendian depositional environments. In addition to typical basal tillites and marginal moraine deposits, the formation includes glaciolacustrine and fluvioglacial sediments along with aquatillites, allotillites, and the glacial fan, including subaqueous, deposits.

Glacial geomorphology of the Maidika region, Tibetan Plateau

ABSTRACTWe present a glacial geomorphological map at a scale of 1:200,000 of the Maidika region in the southeastern part of the central Tibetan Plateau covering 13,600 km2. Based on the 90 m resolution SRTM elevation model, the 30 m resolution ASTER GDEM elevation model, and the Landsat ETM+ satellite imagery of 30/15 m resolution, we have mapped glacial valleys, marginal moraines, glacial lineations, and hummocky terrain. Glacial landforms occur frequently and indicate extensive past glaciation with alpine style valley glaciers as well as more extensive ice fields. Of particular interest is the presence of glacial lineation swarms, which is unusual for the Tibetan Plateau glacial landform record. Based on the distribution of glacial landforms, we present a generalized maximum glacial extent reconstruction covering 6045 km2 or 44% of the map.

Glacial geomorphology of the Parlung Zangbo Valley, southeastern Tibetan Plateau

ABSTRACTWe present a glacial geomorphological map (1:825,000) of the Parlung Zangbo Valley in the southeastern Tibetan Plateau based on Google Earth imagery and the 30 m ASTER Global Digital Elevation Model (ASTER GDEM). The mapped region covers 2.9 × 104 km2, including abundant glacial landforms such as glacial valleys, marginal moraines (including terminal moraines and lateral moraines), and hummocky moraines. Glacial valleys are distributed mainly above 2100 m a.s.l. with lengths from 1 to 130 km. Multiple marginal moraines occur along the glacial valleys, indicating the presence of multiple glacial events. The lowest moraines are distributed mainly at the mouth of each valley between 2400 and 4000 m a.s.l. Hummocky moraines are mainly distributed in the two main tributary valleys: the Bodui Zangbo Valley and the Yigong Zangbo Valley. One ice-dammed paleolake was mapped with a surface area of 12.5 km2. The mapped glacial features (including contemporary glaciers) cover 1.2 × 104 km2, about 40% of the mapped area, representing the minimum extent of maximum glaciation. This map provides a useful data set for reconstructing the timing and extent of paleoglaciations in this area.

Directions of ice flow during the last glaciation in counties Meath, Westmeath and Cavan

Ice flow direction indicators in north-west County Meath and adjacent parts of Westmeath and Cavan are described. Drumlins. striae, roche moulonnees. and oilier streamlined features, as well as till fabrics, suggest a general How during glacial maximum of north-west to south-east when combined with erratic carriage data. Analysis of the configuration of ice marginal moraines and subglacially deposited esker ridges deposited during glacial retreat, as well as till fabric analysis of deglacial sediments, suggest a more complicated retreat of ice, with margins oriented south-wesI to north-east prevailing in the south and cast of the study area. Further to the west and south-west there seems to be an element of retreat towards the west, with a north-south trending ice margin. This is suggested as providing evidence for a decoupling of the ice into separate lobes in that area.

Oksyvos kultūra dešiniajame žemutinės Vyslos krante

Oksyvos kultūra, kaip nauja vėlyvojo ikiromėniškojo gele­žies amžiaus archeologinė kultūra, susidarė dėl keltų pasau­lio įtakos bei Pševorsko ir Jastorfo kultūrų impulsų III a. prieš Kr. (A1 periode). Kultūros vardas kilo nuo vietovės Oksywie (Oxhцft), šiandieninio Gdynės miesto dalies, apie 10 km į šiaurę nuo Gdansko, kur buvo atidengtas šios kul­tūros kapinynas. Pradžioje ši kultūra užėmė visą dešiniąją žemutinės Vyslos pusę ir sritį prie Chełmno (Kulmo). Kla­sikiniame periode A2 kultūra užėmė ir sritį Pomeranijoje. Archeologinių šaltinių duomenimis, čia buvo įsikūrusios vietinių gyventojų grupės – Pomeranijos kultūros tęsėjos. Dėl materialinės kultūros pokyčių ir galbūt gotų diktuoja­mų laidojimo papročių iš Oksyvos kultūros ikiromėniškojo laikotarpio A3 periodo pabaigoje ir romėniškojo laikotarpio B1 periodo pradžioje išsivystė Wielbarko kultūra. Archeologinę medžiagą, reprezentuojančią Oksyvos kul­tūrą šioje Vyslos srities dalyje, sudaro archyvinė medžiaga (apie radinius, aptiktus iki Antrojo pasaulinio karo) ir archeo­logijos paminklai. Svarbiausią grupę tarp prieškario kolekcijų sudaro archyvinė medžiaga, kurią surinko Waldemaras Hey­mas (Heym). Šis žmogus į archeologijos istoriją pirmiausia pateko kaip Heimatmuseum Marienwerder vadovas. Dėl Antrojo pasaulinio karo maišaties didžioji W. Hey­mo rinkinio dalis yra negrįžtamai dingusi arba išbarstyta. Likusi tik informacija apie pavienius artefaktus. Naujausi archeologiniai rinkiniai yra tik prieškario medžiagos papil­dymas. Jie nėra svarbiausia šio Vyslos srities regiono Oksy­vos kultūros kolekcijos dalis. Turimas medžiagos rinkinys reprezentuoja Oksyvos kul­tūrą visu ikiromėniškuoju laikotarpiu, t. y. nuo periodo A1 iki periodo A3. Dalis rinkinio yra iš to laikotarpio kapinynų, kaip antai Bystrzec (buv. Weisshof, Kreis Marienwerder) arba Stary Targ (buv. Altmark, Kreis Stuhm). Kapai, ku­riuose rasta ginklų (ietigalių, kalavijų, antskydžių), yra ypač svarbūs, tačiau jie žinomi tik iš A2 periodo ir A3 periodo baigiamosios stadijos. Iš minėto laikotarpio ankstyviausio horizonto galima kalbėti apie Pomeranijos varpinius kapus ir Jastorfo kultūros įtaką. Geriau pažįstama Pševorsko kul­tūros įtaka, ypač Oksyvos kultūros puodininkystei. Suma­nymas nustatyti Oksyvos kultūros gyvenviečių chronologiją pagal išlikusią medžiagą ir kaupiamą informaciją, kuri dau­giausia fragmentiška, yra sunkiai įvykdomas. Kitu atveju tai klausimas, į kurį turėtume atsakyti. Oksyvos kultūros arheologinė medžiaga iš šitos Vakarų Prūsijos srities yra svarbi bendram Oksyvos kultūros pa­veikslui identifikuoti, ji reikšminga ne tik šiam Vyslos re­gionui.Iš vokiečių kalbos vertė Mykolas Michelbertas

Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia

In this article, we present a map of the glacial geomorphology of the Altai and Western Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 m resolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.