Varve chronology of the glacial sediments in Blekinge and northeastern Skåne, southeastern Sweden

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velocity of the ice recession, c. 90 m/year in northeastern Skåne, shows good agreement with the work of Antevs, whose unpublished diagrams have been re-worked and used in this investigation.     

A local clay-varve chronology and proglacial sedimentary environment in glacial Lake Peipsi, eastern Estonia

Ten cores consisting of varved clay from the northern part of Lake Peipsi in eastern Estonia have been correlated using varve thickness variations and specific marker varves into a 375-year floating varve chronology. Continuous sedimentation during gradual ice recession is concluded from a clear transition from proximal to distal varves. Cyclic variations in varve thickness are caused mainly by thickness changes of clayey winter layers. This is interpreted to indicate increased influx of finer material due to faster melting of the glacier. The cyclic pattern of thickness change is explained by alternating periods of increased and decreased melting of the ice. Simultaneous accumulation of varved clay in glacial Lake Peipsi and in the Luga and Neva basins of Russia is concluded from the good visual correlation between the mean varve thickness diagrams for the three chronologies. Because the varve chronologies from northwestern Russia have been tentatively correlated to the Swedish varve chronology, the timing of the clay accumulation in glacial Lake Peipsi is placed between c . 13 500 and 13 100 varve years BP.     

Revision of the lateglacial Swedish varve chronology

A survey of the revised lateglacial varve chronology is given. Almost all revisions are based on new, independent measurements not yet finished. Compared with the old time scale, the preliminary datings (calendar years ± a margin of error) of the ice margin retreat are 'older', mainly due to the fact that the postglacial varve chronology has been extended by 365 years. This implies that the so-called zero year ( sensu De Geer 1940: limit of late glacial and beginning of postglacial varve sedimentation). earlier estimated at 6,923 B.C. (Nilsson 1964), is now dated 7,288 B.C. According to the new time scale, deglaciation from Stockholm to the area of zero-year formation in Indalsälven's valley lasted about 1,190 ± 40 years, compared with 1,073 years in De Geer's (1940) time scale or 1,092 in Jarnefors' (1963). Preliminary varve graph correlations, which are still very weak concerning the Fennoscandian moraine zone, indicate that the ice receded from Högsby, northwest of Kalmar at approximately 10,700⁺²⁰⁰₋₃₀₀ B.C. At localities just to the north of the Fennoscandian moraines, deglaciation started about 8,750⁺⁵⁰₋₁₅₀ years B.C. according to the new varve measurements, and the ice front receded in southern Stockholm 8,470⁺⁴⁰₋₁₄₀ B.C. Varve dating now gives older ages (calendar years) than ¹⁴C-dating; about 200–400 years older regarding some ice margin positions in south Sweden.     

Late Pleistocene and early Holocene drainage events in the eastern Fehmarn Belt and Mecklenburg Bight,SW Baltic Sea

The Fehmarn Belt is a key area for the Late Pleistocene and Holocene development of the Baltic Sea as it was a passage for marine and fresh water during its different stages. The pre‐Holocene geological development of this area is presented based on the analysis of seismic profiles and sedimentary gravity cores. Late Pleistocene varve sediments of the initial Baltic Ice Lake were identified. An exceptionally thick varve layer, overlain by a section of thinner varves with convolute bedding in turn covered by undisturbed varves with decreasing thicknesses is found in the Fehmarn Belt. This succession, along with a change in varve geochemistry, represents a rapid ice‐sheet withdrawal and increasingly distal sedimentation in front of the ice margin. Two erosional unconformities are observed in the eastern Mecklenburg Bight, one marking the top of the initial Baltic Ice Lake deposits and the second one indicating the end of the final Baltic Ice Lake. These unconformities join in Fehmarn Belt, where deposits of the final Baltic Ice Lake are missing due to an erosional hiatus related to a lake‐level drop during its final drainage. After this lake‐level drop, a lowstand environment represented by river deposits developed. These deposits are covered by lake marls of Yoldia age. Tilting of the early glacial lake sediments indicates a period of vertical movements prior to the onset of the Holocene. Deposits of the earliest stages of the Baltic Sea have been exposed by ongoing erosion in the Fehmarn Belt at the transition to the Mecklenburg Bight.     

衡阳盆地始新世含鱼地层的成因分析

衡阳市郊五马归槽始新世鱼化石保存在黑色湖相纹层中。根据纹层序列的对比,发现该地的鱼化石均为同一层位;根据鱼化石在纹层序列中的具体位置及鱼化石的保存状况,笔者推测鱼群的死亡并非由于季节更替,而是由气候干旱引起的湖水盐度升高所控制;黑白纹层的变化是由大气降雨所致。     

Late Weichselian pollen stratigraphy, clay varve chronology and palaeomagnetic secular variations in Lake Bolmen, Småland, south Sweden

Pollen analysis, glacial varve chronology and palaeomagnetic measurements were carried out on Late Weichselian lake sediments from southwestern Smaland, south Sweden. The sequence is correlated to the GRIP event stratigraphy, expressed in calendar years BP, and covers the period from the deglaciation at c. 14 400 to 11 300 calendar years BP. The series encompasses c. 930 varves and has been connected to the local varve chronology. Varve thickness increases markedly after the Older Dryas stadial, which indicates an accelerated deglaciation and melting of dead ice. The pollen diagram displays the vegetation development from the deglaciation at c. 14 400 calendar years BP to the transition to the Holocene. The vegetation succession starts with an arctic pioneer vegetation at the deglaciation, changes to a more stable tundra environment and displays a development which concurs with the traditional lateglacial pollen stratigraphy for southern Sweden. A palaeo-magnetic secular variation curve is presented displaying two westerly declination swings at 14200-13800 and 12 800-11 600 calendar years BP, respectively. The upper one can be recognized from other palaeomagnetic stratigraphies from southern Sweden and Estonia.     

Younger Dryas deglaciation at Mt. Billingen, and clay varve dating of the Younger Dryas/Preboreal transition

A clay varve chronology has been established for the Late Weichselian ice recession east of Mt. Billingen in Västergötland, Sweden. In this area the Middle-Swedish end moraine zone was built up as a consequence of cold climate during the Younger Dryas stadial. A change-over from rapid to slow retreat as a result of climatic deterioration at the Alleröd/Younger Dryas transition cannot be traced with certainty in the varve sequences, but it seems to have taken place just before 11,600 varve years BP. The following deglaciation was very slow for about 700 years — within the Middle-Swedish end moraine zone the annual ice-front retreat was only c . 10 m on average. A considerable time-lag is to be expected between the Younger Dryas climatic event and this period of slow retreat. The 700 years of slow retreat were succeeded by 200 years of more rapid recession, about 50–75 m annually, and then by a mainly rapid and uncomplicated retreat of the ice-front by 100–200 m/year or more, characterizing the next 1500 years of deglaciation in south and central Sweden. The change from about 50–75 m to 100–200 m of annual ice-front retreat may reflect the Younger Dryas/Preboreal transition. Clay-stratigraph-ically defined, the transition is dated at c . 10,740 varve years BP, with an error of +100 to -250 years. In the countings of ice layers in Greenland ice cores (GRIP and GISP-2) the end of the Younger Dryas climatic event is 800–900 years older. However, a climatic amelioration after the cold part of the Younger Dryas and in early Preboreal should rapidly be reflected by for example chemical components and dust in Greenland ice cores, and by increasing δ¹³C content in tree rings. On the other hand, the start of a rapid retreat of the inland ice margin can be delayed by several centuries. This can explain at least a part of the discrepancy between the time-scales.     

Glaciomarine varves and the character of deglaciation, Säveån valley, southwestern Sweden

Glaciomarine varves, in contrast to glaciolacustrine varves, are primarily dependent upon sedimentation from meltwater overflow. They are usually developed in proximal positions and are a more reliable reflection of deglaciation character within a specific area than 'classical' glaciolacustrine varves, which are generally more distal and greater influenced by bottom topography. The close relationship with ice-front processes in the glaciomarine environment is discussed and utilized to suggest correlations between the varve stratigraphy, ice-front positions and climate shifts during the deglaciation of the Savean valley, where two varve localities have been documented. A varve sequence outside this valley shows similar general trends in varve-thickness variation, and comparison between localities may help in extending the lines connecting positions of concurrent ice-marginal deposition. The study of glaciomarine varves provides a more continuous record of changes in the ice-front character than can be obtained from intermittent moraine positions.     

Sedimentation in a deep glacier-fed lake—Lake Tekapo, New Zealand

ABSTRACT Surface sediments, cores and seismic reflection profiling delineate sedimentary environments and processes of sedimentation in Lake Tekapo. Sedimentation is dominated by the Godley River which forms an extensive delta in the northern third of the lake. Delta growth accounts for 55% of annual sediment deposition. In winter sandy muds are deposited at the top of the delta slope, where they may move under gravity as a surficial slide. Oversteepening of the upper slope also generates deep seated failures. The entire 20 km² of delta slope is subjected to rotational slumping which episodically reworks large volumes of sediment. Down the delta slope sedimentation rates decrease, surface sediments get finer and varves become better developed.
In the lake basin sediments are parallel bedded varves, which contain typical winter-summer annual cycles as well as minor, non-annual flood varves. Annual varve thickness and semi-annual varve frequency are determined by variations in the discharge of the Godley River. Sedimentation in the basin accounts for 40% of the budget and sedimentation rates decrease with distance from the delta, except at the distal end of the basin, where turbid underflows are stopped by the rising lake floor. Beyond the basin, sedimentation rates decrease abruptly. Coriolis deflection of inflowing river water increases sedimentation rates down the eastern shore. The remaining 5% of the sediment is deposited on the lateral slopes and shoulders where sediments form a thin muddy veneer over basement, which occasionally slumps to the basin floor.     

Centennial-scale oscillations in oxygen and carbon isotopes of endogenic calcite from a 15,500 varve year record of the Piànico interglacial

The palaeolake record from Piànico (Southern Alps) comprises a sequence of 15,500 continuous calcite varves formed during peak interglacial conditions around 400 ka ago. The varved nature of these deposits allows precise sub-sampling of five varve year intervals for stable isotope analyses. All samples consist of calcite precipitated in the epilimnion of the lake, with contents of detrital carbonate below 4%. Four significant negative δ¹⁸O oscillations occurred during the upper half of the interglacial. The most prominent of these oscillations has an amplitude of −1.1‰ and lasted 780 varve years. The three other oscillations are shorter (125–195 varve years) and of lower amplitude (0.4–0.9‰). An additional major drop in δ¹⁸O occurs 315 varve years before the end of continuous calcite precipitation in the lake. This shift marks the end of long interglacial conditions and the beginning of harsher climate conditions and glacier advances in the Southern Alps. In contrast, the four δ¹⁸O oscillations within the period of continuous formation of calcite varves reflect natural intra–interglacial climate dynamics.     

The Pleistocene/Holocene boundary: a proposed boundary-stratotype in Gothenburg, Sweden

The boundary between the last two geological epochs, the Pleistocene and the Holocene, is placed at 'the date 10,000 B.P., measured in radiocarbon years'. In the European chronostratigraphy, this corresponds to the Younger Dryas/Preboreal boundary, the pollen zone III/IV boundary and the Late Glacial/Postglacial boundary. The stratal sequence in the Botanical Garden of Gothenburg is proposed as a suitable boundary-stratotype of the Pleistocene/Holocene that fulfils the stratigraphical rules of marine environment and accessibility. A core, labelled B 873, has been analyzed for multiple parameters by various authors. The suggested Pleistocene/Holocene boundary in Core B 873 is indicated by a lithologic boundary, a palynological change tentatively correlated with the pollen zone III/IV boundary, and a distinct palaeomagnetic intensity maximum, the 'Gålön Magnetic Intensity Maximum', identified in numerous other cores at the Younger Dryas/Preboreal boundary and at the drainage of the Baltic Ice Lake in varved clay sequences (with the peak dated at the drainage ±4 varves). This boundary is closely radiocarbon dated at 10,000 B.P. (10,000–9950 B.P.) in terrestrial-lacustrine sequences within the proposed type area in Gothenburg and in Southern Sweden, the established type region for the Pleistocene/Holocene boundary. The corresponding varve date is 9965 varves B.P. (De Geer's varve –1073). The various parameters directly and indirectly connected with the study of Core B 873 make global correlations possible. Because every region has its own local characteristics, however, it will be necessary to establish regional type sections, hypostratotypes.     

Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 1

Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257‐year‐long varve chronology from southeastern Sweden spanning the regional late Allerød–late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice‐Core Chronology 2005 using the time‐synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice‐rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS‐1; 12 846 years before AD 1950). With the support of a simple ice‐flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice‐sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central‐western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS‐1 in Greenland ice‐cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere–ocean circulation changes in the North Atlantic.     

Holocene shore displacement and chronology in Ångermanland, eastern Sweden, the Scandinavian glacio-isostatic uplift centre

The shore displacement during the Holocene in southeastern Ångermanland, Sweden, has been investigated by means of radiocarbon-dating of isolation intervals in sediment cores from a total of nine new basins. Results from earlier investigations have been used in complement. There is a forced regression in the area from c. 9300 BP ( c . 10500 cal. yr BP) until c . 8000 BP ( c . 9000 cal. yr BP), on average c . 8 m/100 years, after which there is a gradually slowing regression of c . 2.5–1.0 m/100 years up to the present time. The most rapid regression occurs during the later phase of the Ancylus Lake stage, 9500–9000 cal. yr BP. There is no evidence of halts in the regression. Crustal uplift in the area since deglaciation is c . 310 m. The deglaciation of southeastern Ångermanland took place c . 9300 BP ( c . 10500 cal. yr BP); this is c . 900 years earlier than the age given by clay varve dating. The shore displacement curve provides a means of estimating the difference between the clay varve time scale and calibrated radiocarbon dates, by comparison with varve-dated altitudes of alluvial deltas of the River Ångermanalven. From c. 2500 to c. 8000 cal. BP there is a deficit in clay varves of some 300 years; further back in time this discrepancy increases significantly. The main explanation for the discrepancy is most likely lacking varves in the time-span 8500–10200 cal. yr BP, located along the upper reaches of River Ångermanalven below the highest shore level.     

The varve-related ice-dammed lake events in Glen Roy and vicinity: a new interpretation

This paper presents a new interpretation of the sequence of events in Glen Roy and vicinity during the Loch Lomond Stadial that can be inferred from a detailed varve record constructed by Palmer et al. (2010). 300 years of Younger Dryas glacier advance in the Scottish Highlands are recorded by very thin varves formed in an ice-dammed lake up to 35 km long. At a varve site now occupied by Loch Laggan the lake stood permanently at 260 m, but in Glen Roy varves were also laid down in a lake at 325 m and, later, 350 m caused by glacier advance. Initial ice retreat recorded by a gradual increase in varve thickness was soon followed by much thicker varves. The varve sequences are interrupted by a sand bed caused by sudden drainage of the 350 m lake. The major varves of the Glen Roy sequence show that storminess was still increasing in intensity at least 160 years after glacier retreat had begun. At the Loch Laggan site 15 cm of deformed sediments register an earthquake that produced 3 m faulted uplift of all three Glen Roy shorelines, a response to the abrupt removal of 5 km³ of water when the 260 m lake was catastrophically drained by jökulhlaup. The deformed sediments are immediately followed by varves deposited in a local lake, ice-dammed lake sedimentation now having ceased, having lasted more than 460 years.     

Correlation of stadial and interstadial events in the south Swedish glacial varves with the GRIP oxygen isotope record

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).     

Lake Mullsjön - a key site for understanding the final stage of the Baltic Ice Lake east of Mt. Billingen

The deglaciation pattern at Mt. Billingen, within the Middle Swedish end moraine zone, and its relationship with dramatic water level changes in the Baltic Ice Lake is a classic topic of Swedish Quaternary Geology. Based on data west of Mt. Billingen, the authors (in two earlier papers) presented a stratigraphic model associated with this subject. This study is an attempt to test the model east of Mt. Billingen, i.e. inside the Baltic Ice Lake itself. Lake Mullsjon is situated 30 km southeast of the drainage area of the Baltic Ice Lake and within the final drainage zone. About 8 m of Late Weichselian sediments (mostly varved clay) were recovered from the lake and analysed from different stratigraphic viewpoints, including lithology, grainsize, varve chronology, and pollen. These analyses show that the site was deglaciated in the later part of the Allerød Chronozone. Shortly thereafter the first drainage of the Baltice Ice Lake took place but without isolating Lake Mullsjon. After a short period of disturbed sedimentation varved clay continued to form as the glacier receded for another 120 varve years until the onset of the Younger Dryas cooling, as registered both in the pollen and in the varve stratigraphies. After c. another 120 varve years our analyses suggest that the Baltic Ice Lake was dammed once again. About 230 varve years of further ice readvance followed west of Mt. Billingen, while the ice margin in the east was more or less stationary. Rapid melting set in, at first producing coarse varves, but soon the clay was thin-varved and fine. This continued for 140 varve years until suddenly the lake became isolated. At this isolation thick beds of silty-sandy deposits were deposited on the lake floor. The isolation is dated to 10,400–10,500 ¹⁴C years B.P., which corresponds to the assumed age of the final drainage of the Baltic Ice Lake. It was also isolated at the same time as lakes (on the same isobase) situated 20 m lower, but west of Mt. Billingen, were raised above sea level. This strongly suggests that Lake Mullsjön was isolated as an effect of the drainage of the Baltic Ice Lake. Significant differences between the clay-varve and the ¹⁴C chronologies are also presented.     

Glaciomarine varves in late-Pleistocene clays near Göteborg, southwestern Sweden

Cyclic variations in the grain size, colour, carbonate content and organic content are interpreted as the result of proximal glaciomarine varve deposition along a fjord-like valley in southwestern Sweden. The sedimentological factors which allow varve development in this generally inhibiting environment arc considered by analogy with modern examples. Density stratification which is best developed during the spring and summer period of high discharge is suggested to have an essential influence on the cyclic character. Since sedimentation is interpreted to have occurred primarily from meltwater overflow the degree of mixing and salinity-induced coagulation largely governs fine-sediment sorting. Although these varves are not as well defined or as easily correlated as classical varves, they are considered useful in many comparable applications.     

Palaeomagnetic records from two varved clay sequences in the Middle Swedish ice marginal zone

Two varved clay sequences, at Rystad and Tottnäs, situated in the Middle Swedish ice marginal zone were analysed palaeomagnetically. Two parallel profiles were sampled and analysed at each site. The varved clay at Rystad was dated by floating varve chronology. The varves at Tottnäs can be linked to Swedish time scale, expressed in calendar years B.P. Due to the distance between the sites they cannot be correlated by means of varve diagrams. Palaemagnetic methods were used as an alternative. Based an AF demanetization of pilot samples, the palaeomanetic to be too low, in the order of15, compared to the site latitude. At Tottnäs the inclination records are very close to the expected inclination with respect to the site latitude. Because of a systematic inclination error in the Rystad profiles the correlation was based on the declination records. Statistical comparisons of these records between the two sites indicate that the sediment successions are partly synchronous. It is concluded that the deglaciation at Tottnäs started c. 130 years earlier than at Rystad. This mean that the Swedish ice marginal zone east of Rystad will have a more northeasterly extension than previously thought.     

A 750-yr record of autumn snowfall and temperature variability and winter storminess recorded in the varved sediments of Bear Lake, Devon Island, Arctic Canada

The varve record from High Arctic, proglacial Bear Lake reveals a regionally coherent hydroclimatic signal as well as complexities due to changing hydroclimatic and limnologic conditions. Varve formation is strongly dependent on underflows that exhibit variability in strength during the past 750 yr. Periods with reduced underflow sedimentation and accumulation rates fail to produce varves in the distal part of the lake. Isolated coarse silt and sand grains occur in 80% of the varves and are interpreted to be niveo-aeolian in origin. Coarse (>500 μm) sand grains deposited on the lake ice by strong winter winds are notably less common since A.D. 1850, likely due to reduced storminess. Regression of the varve thickness record with meteorological records indicates high correlations with autumn (September and October) temperatures and total monthly snowfall. These correlations are best at times when underflow activity is sufficiently strong to produce varves throughout the lake. The close association with warmer temperatures and snow-bearing synoptic systems moving north in Baffin Bay suggests that the primary climate signal in the varves is varying autumn snow pack that controls nival discharge in the following year. The similarity between the other records of melt season temperature and sea-ice cover and the Bear Lake record suggests that summer and autumn conditions were generally similar across the Baffin Bay region through much of the last millennium.     

Stratigraphy of a Lateglacial lake basin sediment sequence at Turret Bank,upper Glen Roy,Lochaber: implications for the age of the Turret Fan

New lithostratigraphical, pollen-stratigraphical and tephrostratigraphical data are presented for a sediment sequence at Turret Bank, a site that lies close to the confluence of the River Turret with the River Roy in Lochaber, the western Scottish Highlands. The site is also adjacent to the inner margin of a major gravel fan, the Glen Turret Fan, the age of which has been debated and has a crucial bearing on the overall sequence of events in Glen Roy, especially concerning the maximum limit of Loch Lomond Readvance (Younger Dryas) ice. Several lines of evidence point to the sediment sequence at Turret Bank having been wholly deposited during the Loch Lomond Stadial-early Holocene transition: (i) the pollen sequence is typical for this transitional period; (ii) varved deposits preserved in the sequence bear a strong resemblance to mid-Stadial varves in a regional master varve scheme for Glen Roy and vicinity (the Lochaber Master Varve Chronology); and (iii) an early Holocene tephra – the Askja-S Tephra – is preserved within the sequence. Some limitations with the new data are considered, but it is concluded that the coherent integration of lithostratigraphic, geomorphological, pollen-stratigraphical and tephrostratigraphical data point to the likelihood that Loch Lomond Readvance ice extended to the inner margin of the Glen Turret Fan, and that the fan was probably constructed by glacial meltwaters at this time.