The aim of this study was to review old and new evidence for the readvance and retreat of the Low Baltic ice stream. The review is based partly on new field observations from southernmost Sweden and new dates relating to the marginals of the ice stream. The diamicton deposited by the Low Baltic ice stream is mainly a subglacial till (Malmo till) rich in clay and chalk. In addition, there are clasts and microfossils in the till derived from the bedrock in the Baltic area. This suggests that they were transported up to 700 km. The likelihood is that the ice moved upon a subglacial bed of mainly fine-grained, deformable sediments. It is also possible to think that the ice shut-down of the deforming bed-driven ice stream, was the result of sediment exhaustion. The sharp limits and low level of the Malmo till, and the sharp limit between an area of low relief hummocky moraine and an area of high relief hummocky landscape, are indicative of deposition from a lowland ice stream. The dating of the deglaciation of the Low Baltic ice stream shows that the ice stream existed approximately 18 000 to 14 600 calendar years BP. At the end of this period the first stage of the Baltic Ice Lake opened.

A number of correlated varve sequences from the local varve chronology in southeastern Sweden have been selected to make a 1040 varve years long mean varve thickness curve. Pollen analyses were carried out over an interval of 373 varve years in the northern part of the study area. The pollen stratigraphical data have been divided into local pollen assemblage zones which have been correlated with the radiocarbon‐dated regional pollen assemblage zones. Based on variations in herb and tree pollen content of the analysed varve sequences, it has been possible to identify well‐documented lateglacial pollen zones for southern Sweden, i.e. the Bölling interstadial (GI‐1e), the Older Dryas cold event (GI‐1d) and the early part of the Alleröd interstadial (GI‐1c). The event stratigraphy in this study, based on varying varve thicknesses and the composition of the pollen flora in the varves, has been correlated with the oxygen isotope stratigraphy of the GRIP ice‐core on Greenland between 13600 and 14400 GRIP ice‐core years BP. It is concluded that five decadal warm events and one centennial warm event (15–60 and 100 varve years long, respectively) occur in the clay varve record along with one centennial cold event (150 varve years long), the Older Dryas (GI‐1d).

A local varve chronology from southeast Sweden between the town of Karlskrona in the province of Blekinge and Hultsfred in the province of Smaland is presented. The chronology covers approximately 800 varve-years. The glaciolacustrine varves were deposited in the Baltic Ice Lake during the Late Weichselian deglaciation. The study includes 60 connected and 56 unconnected varve series and shows that the ice recession rates vary between 75-125 m/year and 250-340 m/year in the southern and northern parts of the area, respectively. An abrupt change from thin to thick clay varves was found in the northern part of the area. The change has been correlated with a similar change of silty varves in the bottom bed of one of the delta plains close to the highest shoreline. This change in the meltwater deposition has been hypothetically correlated with the transition between the Older Dryas (GI-1d) and Allerod (GI-1c) chronozones, or around 13,750 GRIP years.

The lateral displacement of a subglacial conduit, consisting of an area of subglacial conduit-mouth deposits covered by various subglacial and flow tills, is recognized in an abandoned gravel pit at Horn (near Nyköping). The displacement took place during a cold period (Younger Dryas) when the subglacial discharge of meltwater towards a proglacial basin was low. The sedimentary succession contains glaciofluvial deposits overlain by lodgement and flow tills. The superposition of tills may reflect oscillations of the ice in the frontal zone of the Scandinavian ice sheet during the Younger Dryas stadial. The tills are suggested to have been deposited in the conduit-mouth environment. The larger extent of the glaciofluvial unit, as compared to the limited range of the outcropping flow tills, is interpreted as evidence of lateral movement of the subglacial conduit in the frontal zone of the ice sheet. The study confirms a limited subglacial meltwater drainage in the study area during the Younger Dryas.

Image analysis is evaluated as a method to study the nature of the rhythmites in thick proximal varves in the bottom bed of the Bredakra glaciolacustrine delta, southeastern Sweden. The method used was greyscale and colour profiling on digital images. The greyscale curve reflects the relative grain size of the sediment and the results show that it is possible to graphically reproduce both the thickness variations of the rhythmites and the gradation between the different sublayers. Data confirm earlier field observations from the area that the rhyhmites in the proximal varves reflect the diurnal transportation in the meltwater streams. The mean value of six measured varves shows that the summer layers consist of c. 50 diurnal couplets. If the analysed laminae are formed of unmistakable diurnal couplers the duration of the intense melting period was c. 50 days during the Late Weichselian deglaciation of the Bolling Chronozone (G1-1e) in southeastern Sweden. Future work will show if the image analysis can be used to determine the duration of the intense melting periods regionally and in that connection also as a tool to determine the abrupt climate changes between the different chronozones during the Late Weichselian deglaciation.

The purpose of this investigation is to describe and interpret the sedimentology and petrography of Late Weichselian varves in southeastern Sweden in order to determine their nature and origin. It is focused on the microscopic evidence for glaciolacustrine varve sedimentation in the Baltic Ice Lake and the possibilities of making a detailed facies classification of the sediments in an area with an established varve chronology. The material examined was cores taken from five representative localities in an area below the highest shoreline of the Baltic Ice Lake in the provinces of Skåne and Blekinge, i.e., below an altitude of 55–65 m. The investigations included chemical analyses, XRD, microscopy (polarized) and SEM-EDX investigations of the summer and winter layers of the varves. The results of the chemical, clay mineralogy (XRD) and microscopic examinations of the bedrock and mineral fragments indicate that the material in the different facies of the varved clay is mainly produced by moderate alteration and erosion from the local bedrock of predominantly granitoid rocks and of residual kaoline deposits. It is possible to distinguish microscopic evidence of four varve types differing in texture depending on the water depth and how close to the ice the different facies were deposited, i.e., if they were deposited proximally, distally or extramarginally in relation to the ice margin. It is also possible to relate these differences to changes in the palaeoclimate during the deglaciation of the area in the Bölling and Older Dryas chronozones.

The Ekeby site, south of Stockholm, has been chosen to elucidate glaciofluvial sedimentation processes soon after the end of the Younger Dryas. Detailed lithofacies and grain-size analyses of gravel, sand and fine sediment sequences in a gravel pit reflect changes in the depositional environment. Four main facies assemblages have been distinguished. The lowermost part of the sequence was probably deposited in a subglacial conduit environment. The middle part of the sequence reflects a transition to a proglacial subaqueous environment. The upper part of the latter sequence probably occurred during increased melting of the ice. The sequence was then covered by beach gravel formed during the regression after the drainage of the Baltic Ice Lake.

Ever since the first clay-varve correlation was carried out by Gerard De Geer in 1884, a large quantity of clay-varve data has been collected in Sweden. Some of this material is stored at the Geochronological Institute of the Department of Quaternary Research, Stockholm University, while some is stored in individual research records. A large proportion of this clay-varve material forms the basis of the Swedish Time Scale which is more than 13,000 years long and covers both the deglaciation of Sweden and the postglacial time. In order to make this unique material available to the scientific community the data are now being compiled and transformed into digital form in a database. Clay-varve material can be stored in, at least, three different ways. The older, historical, material is, in many cases, available only as varve graphs, some of it is kept in numerical form and a limited part has been transformed into digital form. Material which is stored only as varve diagrams must, in one way or another, be transferred to the digital format. The database is a GIS related base using the GIS-program QUIKMap. By creating a database of this type it is possible to make a search for sites with clay-varves covering a specific time span but it is just as easy to search for all clay-varve sites within a restricted geographical area.

BoreasVolume 22, Issue 4 p. 347-347 A clay varve chronology workshop Bertil Ringberg, Bertil Ringberg Department of Quaternary Research, Stockholm University, Odengatan 63, S-113 22 Stockholm, Sweden.Search for more papers by this author Bertil Ringberg, Bertil Ringberg Department of Quaternary Research, Stockholm University, Odengatan 63, S-113 22 Stockholm, Sweden.Search for more papers by this author First published: December 1993 https://doi.org/10.1111/j.1502-3885.1993.tb00196.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume22, Issue4December 1993Pages 347-347 RelatedInformation

Landforms in Skåne have been analysed on the basis of two computer-made relief maps in 1:250 000. The relief is represented by hill shading. These maps give both an overview and a detailed view of the landforms. Information about the geology and bedrock topography under the Quaternary cover have also been taken into consideration in the interpretation. This analysis has resulted in three maps, one of the forms in the bedrock, another of the depositional forms in the Quaternary cover, and a third one of glacial spillways and other erosional valleys. Although Skåne is one of the most widely investigated parts of Sweden, several new discoveries were made. These include observations on the existence and extension of minor horsts, the pattern of Late Glacial spillways, the unexpectedly large number of drumlins, the pattern of small moraine ridges, and the distinct delimitation and areal extent of the hummocky moraine in the south (Backlandet).The information gained has been used for an analysis of the processes that led to the present landforms and of the timing of landforming events. Skåne has a varied bedrock due to its position within the Tornquist Tectonic Zone. Late Cretaceous inversion tectonics was succeeded by erosion on obliquely elevated bedrock blocks. There are two erosional levels in the raised areas at about 150 and 100 m a.s.l. The relief is interpreted to have been produced by erosion to successively lower base levels, including exhumation of sub-Mesozoic relief. The bedrock knolls of this relief, produced by Mesozoic etching and subsequent stripping, are now often cores in the drumlins, as also are the Jurassic volcanic necks. The present valley systems are almost all found to be influenced by the Late Glacial drainage and several water gaps occur. This focuses the attention to the relative importance of preglacial and glaciofluvial processes in the formation of the valleys.The deglaciation of the area was reconstructed with the aid of the Late Glacial erosional and depositional forms and the Quaternary lithostratigraphy. Two phases of the Late Weichselian deglaciation have been reconstructed: 1) The main recession during which a large body of ice stagnated in the south and was surrounded by diverging ice streams, and large glacial lakes were formed in the Vomb Basin; 2) The Low Baltic readvance with a renewed damming of a glacial lake in the Vomb Basin. During the recession of the ice several systems of glacial spillways formed or reshaped the valleys of Skåne.

Different methods have been used to produce a new informal upper Late Weichselian lithostratigraphy for western Skäne. Special attention is payed to the genesis of the uppermost diamicton, the Malmö till, which was formed during the Low Baltic readvance. The different opinions about the latter unit and the existence of the Low Baltic ice stream are discussed. The lithostratigraphy related to the shoreline displacement during the Late Weichselian and to the outbursts of the Glacial Lake Vomb during the final deglaciation is shown. The 100 years old finds of the arctic codfish (Boreogadus saida) in the Lomma clay is 14C dated and the most reliable age is 13,700 B.P. The expected age was 12,800–13,000 B.P. The latter age is calculated from the shore displacement curve and corresponds to the final deglaciation at the beginning of the Bölling chronozone.

The area of study is strategically placed 250–500 km inside the border of the Weichselian glaciation. The low relief of the area, the surrounding of a shallow sea and the varying bedrock have all influenced the physical nature of the ice. Different methods, including analyses of reworked microfossils, have been used to produce a new informal lithostratigraphy for the area. The glacial striae have been studied and grouped according to orientation and relative age. Correlation is drawn between the ice‐flow pattern determined by the lithostratigraphy and the pattern determined by the glacial striae. The correlation shows the general ice flow during the different glacial events in he Late Weichselian. It is possible to broadly correlate these events with the events in Denmark. The record of glacial advances between 21,000 and 13,000 B.P. starts and ends with an ice stream following the topographyy of the Baltic. The ice streams show low profile and longitudinal axial, lobatic flow. The flow pattern during the Main Weichselian advance indicates a radially flowing dome over the mainland. There is no geologic evidence of separate ice domes in the southern Baltic during the Late Weichselian.

Varve series of fine‐grained glacial sediments have been studied in an area of the Baltic Ice Lake near the border between the provinces of Blckinge and Smalånd, southeastern Sweden. The main purpose of the investigation was to establish a more reliable connection than earlier between the varve chronologies of the Karlskrona area (Ringberg 1971 and 1979) and the Kalmar area (Rudmark 1975). The varve series have been linked to the local chronology of Antevs (1915) as the most recent revision of the Swedish time scale has not yet been completed. The investigation has led to two alternative connections. There are no differences between the alternatives in the southern part of the study area. In the middle of the area there is a difference of 17 years and in the northern part of the area there is a difference of 85 years between the two alternatives. Continued investigations will show which is the most reliable alternative. At present, the uncertainty of the ice recession chronology is at most 85 years in the investigation area.

In sections and cores from an area of the Baltic Ice Lake in Blekinge complete varve series of fine‐grained glacial sediments have been found. It is possible to divide the series, from bottom to top, into four varve types. A core from Karlshamn in Blekinge shows most varves of the investigated localities, in all 355 varves. Antevs' (1915) local chronology has been used, as the most recent revision of the Swedish time scale has not yet been completed. The chronology in this investigation ranges from ‐ 325 to + 315, or 640 years. The varve chronology and the velocity of the ice recession, c. 90 m/year in northeastern Skåne, shows good agreement with the work of Antevs, whose unpublished diagrams have been re‐worked and used in this investigation.

Mörner (1975a and b) has attempted to extend the Fjärås line (the Gothenburg end moraine) from the west coast of Sweden to the Bredåkra delta in Blekinge, south-eastern Sweden. He has revised the present author's account of the genesis of the Bredåkra delta (Ringberg 1971) and tried to establish a correlation on palaeomagnetic grounds between the Fjärås stadial (dated at 12,350–12.400 B.P., Mörner 19756) and the Bredåkra delta. In this note, the author shows that this revision is based on unreliable calculations and that Mörner's palaeomagnetic work is not dated in a reliable way. The conclusion is that Mörner has not succeeded in his efforts to extend the Fjärås line to the Bredåkra delta and that the relation between the genesis of the delta and the deglaciation of the west coast of Sweden is still unclear.