The Baltic Ice Lake in the southwestern Baltic: Sequence-, chrono- and biostratigraphy

ArticleinBoreas 26(3):217-236 · September 2008with 62 Reads
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Abstract
Jensen, J. B., Bennike, O., Witkowski, A., Lemke, W. & Kuijpers, A. 1997 (September): The Baltic Ice Lake in the southwestern Baltic: sequence-, chrono- and biostratigraphy. Boreas, Vol. 26, pp. 217–236. Oslo. ISSN 0300–9483. This multidisciplinary study focuses on late-glacial deposits in the Mecklenburg Bay -Arkona Basin area. The sequence stratigraphical method has been used on shallow seismic and lithological data, in combination with biostratigraphical work and radiocarbon dating. Glacial-till deposits underlie sediments from two Baltic Ice Lake phases. Varved clay deposits from the initial phase cover the deepest parts of the basins. A prograding delta is observed at the western margin of the Arkona Basin, prograding from the Darss Sill area. The delta system is possibly related to a highstand dated at 12.8 ka. A maximum transgression level around 20 m below present sea level (b.s.l.) is inferred, followed by a drop in water level and formation of lowstand features. The final ice lake phase is characterized by a new transgression. The transgression maximum as observed in the Mecklenburg Bay is represented by transgressive and highstand deltaic deposits. These also indicate a maximum shore level of 20 m b.s.l. The deltaic sediments that contain macroscopic plant remains and diatoms have yielded Younger Dryas ages. Mapping of the late-glacial morphology of the Darss Sill area reveals a threshold at 23 to 24 m b.s.l. This means that the Baltic Ice Lake highstand phases inundated the Darss Sill, which implies that the westernmost extension of the Baltic Ice Lake reached as far as Kiel Bay. Forced regressive coastal deposits at the western margin of the Arkona Basin mark a lowstand level of around 40 m b.s.l. caused by the final drainage of the Baltic Ice Lake. The lowstand deposits predate lacustrine deposits from the Ancylus Lake, which date to approximately 9.6 ka BP.

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    Recent reconstructions suggest that the British-Irish and Fennoscandian ice sheets coalesced and covered the central and northern North Sea from ca. 26cal. ka BP and until ca. 19cal. ka BP. At ca. 19cal. ka BP the Norwegian Channel Ice Stream started to retreat and the ice sheets broke apart at ca. 18.7cal. ka BP. This led to a drainage of an ice-dammed lake in the southern North Sea northwards via the Norwegian Channel into the SE Nordic Seas. In this paper we combine information from high resolution TOPAS profiles, bathymetric records and shallow borings to study the ice-dammed lake outburst, a common deglaciation process but which rarely has been evidenced in such a detail from the marine realm. A 12m deep and 3km wide incision at the northeastern part of the Dogger Bank is suggested to represent the point where the ice-dammed lake breached. The glacial lake outburst flood, which had an estimated peak discharge of 9.8×10⁴-2.9×10⁵ m³/s and lasted for about 5-15months, flowed between the withdrawing British-Irish and Fennoscandian ice sheets following the crest of the Ling Bank northwards. Along this path, about 300km downstream of the break-through point, an up to 10m thick sediment package with a prograding-aggrading sedimentation pattern, typical for ice-dammed lake outburst deposits, has been deposited. This sediment package was deposited in a high-energy environment, immediately following extensive erosion of the underlying till unit of Last Glacial Maximum age. An oxygen isotope anomaly and an associated ultra-rapidly deposited meltwater plume on the Norwegian continental margin, dated to ca. 18.7cal. ka BP, also witness this lake outburst. The ice-dammed lake outburst flood occurred when evidence suggest a sea level at least 110m lower than at present in the region. As the sea level rose, following the melting of the Last Glacial Maximum ice sheet, the Ling Bank Delta developed on top the outburst deposits. The delta, indicating a sea level close to 80m below present, has an extent of 80km and up to 12m deep fluvial channels are associated with the topset beds. This fluvial environment may have lasted until the end of the Younger Dryas time period when the Ling Bank was submerged and attained its present water depth.
  • Article
    The Bornholm Basin has experienced a complex history linked closely to the structural development of the Tornquist Zone strike-slip fault system. The latest major tectonic development was late Cretaceous and early Tertiary Rønne Graben inversion caused by dextral transpressional strike-slip movements focused around rigid blocks such as Bornholm. By applying the strike-slip concept, it is possible to show that the Rønne Graben inversion push-up structure was created by restraining left step-over. The fault system continues northwest and north of Bornholm where the strike-slip movement resulted in right step-over and the formation of a pull-apart basin: the northern part of the Bornholm Basin. Detailed seismo-acoustic and sediment core studies show that, despite a rather uniform present bathymetry in the central part of the Bornholm Basin, the Quaternary deposits mirror the pull-apart basin synsedimentary depositional pattern with depocentres close to the major normal faults, bounding the Christiansø Ridge. IODP Site M0065 penetrated a secondary fault zone and provided detailed information on neotectonic events and on environmental changes during the Holocene. The generally rather homogeneous sediments in the cores indicate a dominance of oxic conditions in the Bornholm Basin during the Holocene. However, strong internal seismic reflectors, indirectly reflecting variations in the sediment density and the reflection coefficient, were caused by a shift to stronger laminated, organic-rich sediments that were deposited during the Medieval Warm Period (MwP). The variable depth positions of the MwP-related strong reflectors indicate large differences in the spatial and temporal sedimentation pattern in the Bornholm Basin. These differences in the depositional environment may have been caused by local neotectonic events in the basin.
  • Article
    Full-text available
    Acoustic profiling methods are commonly used in the geosciences to obtain knowledge about the sedimentary structures of marine deposits. However, their interpretation and the correlation of acoustic reflectors with sedimentological boundaries remain difficult. The gradient in acoustic impedance determines the intensity of acoustic reflectors, which are not necessarily sedimentary boundaries. Suitable geo-acoustic models that cover a wide range of sediment types have not yet been developed for the Baltic Sea. Based on comprehensive investigations of sediment cores from Mecklenburg Bay and the Arkona Basin, we developed geo-acoustic models that enable the transfer of laboratory p-wave velocity measurements to in situ conditions while considering changes in pressure, salinity, temperature and the frequency dependence of the p-wave velocity (i.e. acoustic dispersion). This modelling allows the calculation of the wet bulk density and in situ p-wave velocity (from which the acoustic impedance is calculated) from core logging and selected sedimentological data, such as the water content, loss on ignition, and grain size. Precise plotting of core data into the acoustic profiles is now possible and represents a crucial step towards the interpretation of these profiles. Modelled p-wave velocities are used to convert two-way-travel-time to depth. The average sedimentological parameters for the different development phases of the Baltic Sea are calculated using geo-statistical methods and may allow for rough p-wave estimations if core logging data are not available.
  • Article
    Studies of plant and animal macrofossils have been carried out on early-Holocene lake marls from the southwestern Baltic. The records have been dated to the interval from c. 8500 to 7800 14C years BP by correlating pollen assemblages to an onshore radiocarbon dated pollen diagram. The sediments contain from 5 to 81% carbonate, and only few macroscopic remains of wetland and terrestrial taxa. The plant and animal (mainly mollusc) macrofossils reflect deposition at the outer edge of the belt with submerged macro-limnophytes, in the lower littoral, perhaps at water depths at 4–7 m. The ratio between the shells and opercula of the snail Bithynia tentaculata points to some post-mortem disturbance, but it can be concluded that the water was highly alkaline and mesotrophic.
  • Article
    Full-text available
    We give an extensive list of Recent, Holocene and Pleistocene ostracods from Mecklenburg-Vorpommern based on a review of publications, unpublished reports and diploma theses as well as some new studies. The list contains additional data on the stratigraphic distribution and occurrence of the reported taxa within different types of waters from the study area. A total of 138 Quaternary ostra-cod species are known so far from Mecklenburg-Vorpommern, of which 115 live today in the study area. Twenty three of the 67 documented fossil and subfossil species are extinct here today. The Recent fauna contains 28 marine, 13 brackish and 74 freshwater species. A bibliography on Quaternary ostra-cods from Mecklenburg-Vorpommern is given as a reference for work on biogeography, ecology, stra-tigraphy and taxonomy of ostracodes from the Baltic Sea region. Resumen Se proporciona en este trabajo una lista extensiva de los ostrácodos del Reciente, Holoceno y Pleistoceno de Mecklenburg-Vorpommern (Alemania), basada en la revisión de las publicaciones, informes no publicados y tesis de diplomatura, así como algunos estudios nuevos. La lista contiene datos adicionales de la distribución estratigráfica y presencia de los taxones referidos en diferentes tipos de aguas del área de estudio. Un total de 138 especies de ostrácodos del Cuaternario son cono-cidos hasta ahora en Mecklenburg-Vorpommern, de las cuales 115 viven todavía en el área de estu-dio. Veintitrés de las 67 especies fósiles y subfósiles documentadas no aparecen actualmente en este área. La fauna del Reciente contiene 28 especies marinas, 13 de aguas salobres y 74 de aguas dulces. Se proporciona una bibliografía de los ostrácodos del Cuaternario de Mecklenburg-Vorpommern, como referencia para futuros trabajos acerca de la biogeografía, ecología, estratigrafía y taxonomía de los ostrácodos en la región del Mar Báltico.
  • Article
    Full-text available
    This thesis is based on the work carried out while I was a Ph. D. student at the Department of Geology, GeoBiosphere Science Centre, Lund University, between September 1999 and November 2003. The results of this work have been presented in six separate papers listed below as appendices (I-VI) and are hereafter referred to by their Roman numerals. The papers have been submitted to peer-reviewed international journals. Three of them will appear soon and the other three are still under consideration.
  • Article
    A study of changes in siliceous microfossil assemblages and chemical analyses in a well-dated offshore sediment core from the Bornholm Basin, southwestern Baltic Sea, is carried out with the objective of increasing knowledge of the Holocene history of the area. The core covers about 11300 calendar years from the brackish phase of the Yoldia Sea stage to the present. The first weak marine influence in the Ancylus Lake stage is recorded about 10100 cal. yr BP (c. 8900 14C BP), indicating a complex transition to the Litorina Sea with different phases of brackish-water inflow. The lithology, organic carbon content and C/N and C/S ratios indicate no major changes in the sedimentary environment during the Litorina-Post-Litorina Sea stages. A high productivity event recorded in the Post-Litorina Sea stage around 950 cal. yr BP correlates with the Medieval warm event. A biostratigraphical change indicating a colder climate is recorded in the sediment at about 800 cal. yr BP, which might mark the beginning of the Little Ice Age.
  • Article
    Rößler, D., Moros, M. & Lemke, W. 2010: The Littorina transgression in the southwestern Baltic Sea: new insights based on proxy methods and radiocarbon dating of sediment cores. Boreas, 10.1111/j.1502-3885.2010.00180.x. ISSN 0300-9483. The Littorina transgression is one of the most pronounced environmental events in the Holocene history of the Baltic Sea. It changed the hydrographic system from the freshwater Ancylus Lake into the brackish-marine Littorina Sea. Here, 18 cores from two western Baltic basins, Mecklenburg Bay and the Arkona Basin, were analysed. We show that, besides biological indicators, sedimentary organic carbon, C/N ratio, bulk δ13C isotope values and carbonate content display clearly the transition from Ancylus Lake to the Littorina Sea. The first appearances of benthic foraminifers, marine molluscs and ostracods represent the onset of brackish-marine conditions in the bottom waters. Central Arkona Basin sediments display more abrupt shifts in geochemical parameters and microfossil records at the transition from Ancylus Lake to the Littorina Sea than those from Mecklenburg Bay. Mixing of reworked Ancylus material with Littorina Sea stage material was stronger in Mecklenburg Bay, resulting in less pronounced proxy parameter changes and older bulk material dates. Radiocarbon dating of both calcareous material (benthic foraminifers, mollusc shells) and bulk fractions at the transgression horizon shows large age discrepancies. Based on calcareous fossil dates it appears that marine waters began to enter Mecklenburg Bay c. 8000 cal. a BP. In the Arkona Basin the first marine signals are recorded approximately 800 years later, c. 7200 cal. a BP. This indicates a transgression pathway via the Great Belt into Mecklenburg Bay and then into the Arkona Basin.
  • Article
    Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region.
  • Article
    In the narrow offshore border zone between Germany and Denmark, 550 km of high-density 3·5-kHz subbottom seismic reflection profiles were recorded within a 70-km2 area in order to reconstruct the seismic stratigraphy of late Pleistocene to early Holocene lacustrine and fluvial environments. Using detailed line drawings, seismic facies analyses and a hierarchy of bounding surfaces, a depositional unit was recognized and subdivided into subunits 4a (oblique-parallel), 4b (mound, oblique-tangential), 4c (sigmoid, oblique), 4d and 4e (shingled and parallel). The base of this seismic facies association defines a wide U-shaped valley with well-defined scours and, in the valley sides, ‘steps’ are located above deep steep-dipping reflections. Stratigraphic control was available from 32 coring sites (5- to 12-m-deep vibrocores). Subunit 4b represents coarsening-up silt and sand, and samples from subunit 4d show fining-up fine sand, silt and clay. The seismic facies association is proposed to have formed by a fluvial event of short duration some time in the period between 10·3 14C ka BP and 9·0 14C ka BP. Subunits 4a to 4e represent gradually decreasing flow power. A peak flow initiated the fluvial event, after which water discharge and level fell rapidly. Subsequently, the normal background discharge from the Baltic Sea area dominated the flow style. Reflections beneath the ‘step’-like valley side with high dip angles are interpreted as faults. This tectonic activity resulted in subsidence in the analysed area and could possibly have influenced the fluvio-dynamic development. The seismic stratigraphic succession reveals a high-resolution record of sediments in this area. In particular, the stepwise uncovering of the morphology of the subunits, preserved in high-resolution seismic facies associations, is proposed as a useful tool in modelling the dynamic development of the near sea-floor environment.
  • Chapter
    Palaeoenvironmental reconstructions can provide important information into the processes influencing the long-term development of the Baltic Sea since the Last Glacial Maximum. This paper uses lithological and diatomological evidence from two sediment cores to reconstruct the palaeoenvironments of the mouth of the Rega Valley, Poland. We use the ecological preferences of diatoms to qualitatively reconstruct changes in salinity over the same period. Results between the two cores correspond, and demonstrate that both basins have experienced a series of marine transgressions, coastal aggradation, and lagoon development over the Late Glacial and Holocene. Surprisingly, our high-resolution core profiles demonstrate that conditions varied between fresh brackish and brackish fresh for most of the Holocene (Boreal through Subatlantic Chronozones), whilst the well-documented mid-Holocene peak in salinities between 6.000 and 5.000 cal. BP was not observed in our records. It is likely that this indicates the buffering of the Baltic waters from freshwaters from the south, and demonstrates the importance of terrestrial-hydrological processes for determining the long-term stability of the salinities in the southern Baltic coastal zone.
  • Article
    Full-text available
    The small limpet Ancylus fluviatilis is reported from two sediment cores from the south-western Baltic Sea. One of the occurrences, from Mecklenburg Bay, is dated to the late-glacial, corresponding to the Baltic Ice Lake stage of the Baltic Sea. The other occurrence, from the south-western part of the Bornholm Basin, is dated to the earliest Holocene, corresponding to the Yoldia Sea stage. These appear to be the first reports of Ancylus fluviatilis shells from submarine deposits from the Baltic Sea.
  • Article
    Shallow seismic profiling indicated the presence of a drowned lagoon–barrier system formed during the transgression of the southern Kattegat, and investigations of core material have confirmed this. Studies of plant and animal macrofossils show that the lagoonal sediments contain a mixture of marine, brackish, lacustrine, telmatic and terrestrial taxa, and analyses of foraminifers indicate brackish-water conditions. Low oxygen isotope values obtained on shells of marine molluscs also point to lowered salinity. The lagoonal sediments are situated at depths between 24 and 35 m below present sea level. They are dated to between c. 10.5 cal. ka BP and c. 9.5 cal. ka BP, and reflect a period characterized by a moderate relative sea level rise. The lagoonal sediments are underlain by lateglacial glaciomarine clay and silt, which are separated from the Holocene deposits by an unconformity. The earliest Holocene sediments consist of littoral sand with gravel, stones and shells; these sediments were formed during the transgression of the area before the barrier island–lagoon system was developed. The lagoonal sediments are overlain by mud, which contains animal remains that indicate increasing water depths.
  • Article
    Full-text available
    Four sediment cores from the southern part of the Arkona Basin were analyzed in terms of their geochemical composition, age and stratigraphy. The main stages of the Baltic Sea: the Baltic Ice Lake, the Ancylus Lake and the Littorina Sea were identified in all the analyzed cores. The data confirmed the high water fluctuation and significant environmental changes during the Baltic Sea evolution in the Late-Glacial and the Holocene. The signs of the second regression of the Baltic Ice Lake, dated at around 11 000 cal BP, were identified at a depth of 24 m b.s.l. Regression of the Ancylus Lake, dated at 9300 cal BP, was identified at a depth of 23 m b.s.l. The most pronounced period was the transition stage between the Ancylus Lake and the Littorina Sea. The record of the Littorina Sea onset in the sediments of the Arkona Basin is marked as a sudden increase in loss on ignition, biogenic silica, magnesium, calcium, iron and strontium. The age of the Littorina Sea in the Arkona Basin was estimated as younger than 8200 cal BP.
  • Article
    Late Glacial and Holocene subfossil molluscs along the Lithuanian Baltic Sea coast are found in the outcrops of Ventes Ragas Cape and squeezed lagoon gyttja at Nida and in offshore boreholes at Butinge, north of Klaipeda, Smiltyne, Nida on the Curonian Spit. They are also found in boreholes drilled in the Curonian Lagoon and River Nemunas delta water areas. During the Late Glacial and the first Litorin 3, Sea transgression, a small shallow freshwater basin or a semi-enclosed lagoon of the larger basin covered an area of the recent Curonian Spit and Lagoon. Subfossil molluscs of the Litorina Sea discovered near Butinge, Melnrage and Smiltyne are typical of shallow littoral zones with sandy and somewhat muddy bottoms. As concerns the Yoldia Sea and Ancylus Lake periods, the water level was considerably lower than present sea level, thus sediments and subfossil molluscs of these basins are absent along the Lithuanian coast.
  • Article
    Full-text available
    Arkona Basin (southwestern Baltic Sea) is a seasonally-hypoxic basin characterized by the presence of free methane gas in its youngest organic-rich muddy stratum. Through the use of reactive transport models, this study tracks the development of the methane geochemistry in Arkona Basin as this muddy sediment became deposited during the last 8 kyr. Four cores are modeled each pertaining to a unique geochemical scenario according to their respective contemporary geochemical profiles. Ultimately the thickness of the muddy sediment and the flux of particulate organic carbon are crucial in determining the advent of both methanogenesis and free methane gas, the timescales over which methanogenesis takes over as a dominant reaction pathway for organic matter degradation, and the timescales required for free methane gas to form.
  • Article
    Full-text available
    Subglacial lakes are common features of contemporary ice masses. However, they are rarely identified in the geological record. This is due to the difficulty in discriminating between subglacial and proglacial lake sediments; a proglacial origin is typically preferred as the ‘simplest’ explanation. We hypothesise that numerous deposits currently interpreted to record proglacial lake sedimentation may actually have a subglacial origin. Here we try and find ways of distinguishing proglacial from subglacial lake sediments by investigating three sites along the Dänischer Wohld Peninsula, northern Germany, which have been interpreted to record both proglacial and subglacial sedimentation. We identify two major phases of ice activity and associated lake formation during the Late Weichselian glaciation. (1) Proglacial lake formation at ∼23 ka in front of the advancing Baltic Ice Stream. This lake was subsequently overridden and the sediments glaciotectonised as ice continued to advance to its maximum extent. (2) Retreat of ice back into the Baltic Basin at ∼19 ka and formation of a proglacial lake that persisted for ∼4 ka. We suggest that subglacial lake activity may have occurred at two of the sites between 23 and 19 ka. This is based on the presence of aggrading sediment deposits characterised by stratified/laminated diamictons and interbedded tabular to channelized sorted sediments, the juxtaposition of relatively undeformed waterlain sediment and subglacial till, absence of glaciotectonic thrusting and folding or of fining/coarsening successions and the geomorphic association with tunnel valleys to the south of the study area. The style of sedimentation and deformation provided the greatest insight into the discrimination of proglacially vs subglacially deposited glaciolacustrine sediments. The luminescence signal palaeodose distributions also offers a potentially powerful means of fingerprinting sediment transport pathways of young glacial systems.
  • Article
    It is well known that the former view of three or four Quaternary glacial periods in northern or south-central Europe, respectively, cannot be kept any longer, because much more qualitatively different interglacial vegetation-sequences have since been discovered. Yet the question is how many of these different interglacial periods had existed in reality? The comparison with deep-sea isotope-curves, which is practised repeatedly now, cannot be accepted as a reliable way of argumentation, because firm stratigraphical connections between terrestrial and oceanic sediment sequences are generally lacking. Thus, one has to construct, on the continents, palaeoclimatological, geological and palaeoecological sequences independently from changes in the deep-sea curves of stable isotopes. Another problem is the timing and ways of immigration of the exacting taxa from their glacial refuge areas when at the beginning of interstadial or interglacial periods the climate began to improve. Here, too, the comparison with stable isotope curves of deep-sea foraminifera is of no help, because the dating quality of older deep-sea sediments is restricted. Finally, exact quantification of the palaeoecological consequences of early human activities has rarely been attempted in various regions of Europe. Thus, very often one cannot reliably differentiate between climate and man, both being factors which strongly influenced the palaeoecological situation in various regions of Europe at a very early period.
  • Article
    The stratigraphy of a core taken from the bottom sediments of Mecklenburg Bay in the southern Baltic is studied. Radiocarbon dates of a peat layer about 26 m below sea level show that the peat was formed approx. 9,500 BP. Pollen and diatom analyses were made from the profile. Some features in the biostratigraphy are difficult to explain, but a consistent picture can be drawn of the outline of the postglacial development in this region. The Ancylus transgression did not extend to Mecklenburg Bay, which was inundated by saline water during the Litorina Sea stage of the Baltic.
  • Clirnatic Changes on a Yearly to Millenniul Basis, 37 56 Allererd-Younger Dryas sea-level changes in southwestern Sweden and their relation to the Baltic Ice Lake dcvelopment
    • Karlen
    • W Reidel
    • Dordrecht
    • S Bjorck
    • G Digerfeldt
    & Karlen, W. (eds.): Clirnatic Changes on a Yearly to Millenniul Basis, 37 56. Reidel, Dordrecht. Bjorck, S. & Digerfeldt, G. 1991: Allererd-Younger Dryas sea-level changes in southwestern Sweden and their relation to the Baltic Ice Lake dcvelopment. Boreas 20, 115-133.
  • Geologische Untersuchungen an spitglazialen und holoziinen Sedimenten dcr Liibecker und Mecklenburger Bucht
    • D Lange
    Lange. D. 1984: Geologische Untersuchungen an spitglazialen und holoziinen Sedimenten dcr Liibecker und Mecklenburger Bucht. Unpublished PhD thesis, Institute of Marine Research in Warnemunde, 166 pp.
  • Siliciclastic sequence stratigraphy in well logs, cores and outcrops. Americun A.ysociution of' Petroleutlz Geologists, Mrlltoils E.~ploratiori, Ser. 7. 45 pp. von Post, L. 1929: Svea, Gota och Dan 6lvar
    • J C Van Wagoner
    • R M Mitchum
    • K M Champion
    • V D Rahmanian
    Van Wagoner, J. C., Mitchum, R. M., Champion, K. M. & Rahmanian, V. D. 1990: Siliciclastic sequence stratigraphy in well logs, cores and outcrops. Americun A.ysociution of' Petroleutlz Geologists, Mrlltoils E.~ploratiori, Ser. 7. 45 pp. von Post, L. 1929: Svea, Gota och Dan 6lvar. Ywer 49, 1-33. van Proschwitz, T. & Bennike, 0. in press: Late Quaternary land snails from the southwestern Baltic Sea. Juirrnul of C'oncologj~.
  • Article
    Studies of ancient Baltic sediments obtained from isostatically uplifted lake basins near Helsinki, on the south coast of Finland, have yielded diatom sequences across the transition from Ancylus Lake to Litorina Sea strata. The apparent discrepancy between the littoral and off-shore records may be due to differential response to the change by the littoral and off-shore diatom assemblages.- from Author
  • Article
    Marine geological investigations including shallow seismic surveys and corings have been carried out in the shallow waters of Fakse Bugt (Bay) and Hjelm Bugt near to the island of Møn, Denmark. A combined sequence- and lithostratigraphy has been established and supplemented with biostratigraphic data and 14C datings. The data show that a sequence of varved glaciolacustrine sediments mapped east of Møn and in Hjelm Bugt, can be followed into the Arkona Basin. Correlation of these glaciolacustrine deposits with Baltic Ice Lake deposits in Blekinge, southern Sweden indicates the existence of a major lake basin: the initial Baltic Ice Lake. In Sweden the initial phase of the Baltic Ice Lake is dated to about 12,500 14C years BP.In the Møn area transgression of the Baltic Ice Lake is indicated in the central part of Fakse Bugt by the development of a transgressive freshwater barrier beach ridge-lagoon system following the initial onlapping sedimentation of varved deposits.The freshwater coastal system was initiated during the Allerød stage and the final maximum transgression level (13 m below present sea level) was reached in the upper part of Younger Dryas just prior to the final drainage of the Baltic Ice Lake.
  • Article
    Today, about 73% of the water exchange between the Baltic and the North Sea takes place through the Darss Sill area. In hydrographic terms the Darss Sill is a major morphological unit separating the deeper areas of the Mecklenburg Bay and the Arkona Basin from each other. It is characterized by an average water depth of 16 m. The main bathymetric features are the Gedser Reef with a water depth of less than 10 m and the Kadet Channel which has a maximum water depth of 32 m.According to previous authors there are two different ice marginal lines between Falster (Denmark) and the Darss peninsula (Germany). The recent Kadet Channel is regarded as a large glacial valley cutting the ice marginal lines.Joint Danish and German investigations in the Darss Sill area (1989–1991) indicate the existence of only one marginal line in this region, which is represented by a till cropping out in the area between Falster and the German coast.The formation of the marginal line ca. 13,500 BP caused a damming of a pre-existing subglacial drainage system in the Gedser Reef area.Southeast of the recent Kadet Channel glaciofluvial drainage occurred towards the NE through a deep channel into the Baltic Ice Lake immediately after the retreat of the ice.During the Baltic Ice Lake transgression the channel was filled by sandy sediments from sources east of the investigated area. This accumulation process resulted in the blocking of the channel at the time of the Baltic Ice Lake highstand maximum. At this time occasional overflow in the Kadet Channel area must have started. The main erosion and deepening of the Kadet Channel must, however, be ascribed to the Ancylus Lake overflow.
  • Article
    Full-text available
    Four taxa of rodents have been recovered from submarine deposits from the southwestern Baltic Sea. A find of Arvicola terrestris represents the first record of Younger Dryas age from this region. A Late Boreal record indicates that this species was formerly a member of the Bornholm fauna. Finds of Apodemus flavicollis and Microtus sp. probably date from the Middle Holocene. the Late- and Postglacial history of these rodents in northwestern Europe is reviewed.
  • Article
    The Billingen area in the Middle Swedish endmoraine zone has been studied with respect to climatic changes and their effects between c.11 300 and 9500 yr BP. In the later part of the rather warm Allerod Chronozone the Baltic Ice Lake was drained and the glacier retreated north of Mt Billingen. A significant glacier readvance occurred in the early, cool part of the Younger Dryas Chronozone once again damming the huge glacial lake in the east. Around 10 500 yr BP a significant climatic amelioration created prerequisites for a normal vegetational succession and the final retreat of the glacier from the area. The last drainage of the Baltic Ice Lake occurred and after another c.600 years the area for a short time was influenced by marine water some hundred years before the whole area was lifted above sea level. Since the climatic amelioration in the middle of the Younger Dryas Chronozone no significant climatic change seems to have occurred during the time-period studied. - from Authors
  • Article
    Full-text available
    The Pleistocene deposits of Denmark are largely composed of: 1) tills, and 2) waterlaid outwash material. Using a combined set of glacial-stratigraphic methods, about 200 selected localities in the central part of Denmark have been investigated over the past ten years. Studies at eight principal localities and two key localities, some of which are classical exposures, provide the foundation for a litho-stratigraphic model for the till units. The results are used to establish a detailed chronology from the Elsterian to the late Weichselian. -from Author
  • Article
    The fundamental concept on which sequence stratigraphy is based is that stratal architectures develop in response to the interaction between base-level change and sediment flux. A small lucustrine fan-delta at East Coulee, Alberta, illustrates these principles and demonstrates that sequence stratigraphic concepts are scale- and time-independent. This fan-delta formed in a matter of days in a roadside drainage ditch as water level rose and then fell. Changes in the subaqueous space available for sediment to fill (ie accommodation) resulted in the development of a succession of systems tracts analogous to those formed within sedimentary basins over much longer time frames. -from Authors
  • Article
    Full-text available
    Shallow seismic investigations and sediment sampling were carried out in the Hjelm and Fakse Bugt (Bay) off the island of Mon, Denmark. Ribbed moraine morphology is observed in the Hjelm Bugt area while results from seismic studies in Fakse Bugt reveal two different late-glacial sequences: 1; glacial diamict and 2; proglacial, delta - ice take and fluvial deposits. These deposits originate from the final Late Weichselian deglaciation. Within sequence 1 two units can be distinquished. Unit La consists of glacial deposits dislocated by thrusting that form asymmetrical ridges on the sea floor, unit 1.b is not pre-consolidated, (soft) diamict interpreted as supraglacial flow diamict. Sequence 2 can likewise be subdivided in two units a and b. These can be characterized as delta deposits formed in a glacial lake in which a sudden lowering of the water-level caused a break of the sedimentation. Earlier studies from the Skane area (southern Sweden) report a similar depositional pattern during deglaciation. The deposits consist here of asymmetrical ridges, interpreted as Rogen moraines. They were resting on and covered with flow diamict deposits and water layered deposits, thought to have been formed by an arctic glacier with a cold-based compressive marginal zone. From the comparison of onshore glaciotectonic and morphological data with the offshore data presented, it is concluded that the Mons Klint cliff section was formed under glaciotectonic compression between two ice lobes, one from a north-eastern and another from a south-eastern direction. The formation of Mons Klint was thus associated with a final Weichselian readvance.
  • Bacillariophyceae 1, Navicullaceae
    • K Krammer
    • H Lange-Bertalot
    Krammer, K. & Lange-Bertalot, H. 1986: Bacillariophyceae 1, Navicullaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (eds.): Siissivasserfloru uon Mitteleuropa 211. Fischer, Stuttgart.
  • Article
    BOREAS Foged, N. 1978 03 01: Diatoms from the Middle and Late Weichselian and the Early Flandrian period on Andøya, north Norway. Boreas, Vol. 7, pp. 41–47. Oslo. ISSN 0300–9483. From cores from a depth of 9.9 m up to 5.1 m below the present surface of a mire situated approx. 36 m above sea level on Andøya, north Norway, 47 samples were analysed for diatoms. Some 240 taxa were recorded, chiefly in Late Weichselian and Early Flandrian material. They were subdivided according to their halobion and pH relation. On the whole, the pH reaction of the environment was neutral, but it changed from faintly acid to faintly alkaline during the sedimentation of the Late Weichselian material.
  • Article
    To a varying degree the Middle and Late Pleistocene ice sheets in northern Eurasia redirected the drainage of major catchments in Europe and western Siberia from the North Sea and Arctic Ocean south to the Caspian, Black Sea, and ultimately the Mediterranean. During the Late Weichselian, glacial meltwater reached the Mediterranean through the Dniepr and Don catchments and to a minor extent through the Danube. During the Warthe Substage of the Saalian, meltwater from the Volga was most likely added. During the Drenthe Substagc of the Saalian the watershed shifted Par to the east, and meltwater reached the Mediterranean also from the Oh. Irtysh, Yenisei, and Tunguska catchments in Siberia. Depending on the extent of the ice sheets, the increase in freshwater supply during deglaciations resulted in reductions of Mediterranean overflow into the North Atlantic. Such overflow reductions may have reduced vapour transport to the ice sheets and thus accelerated wastage.
  • Article
    The dynamic history of the Baltic Sea during the millennia following the last deglaciation has been one of the main topics for many generations of Quaternary geologists around the Baltic Sea. Based on the present-state-of-knowledge and certain hypotheses, a model for the development during the Baltic Ice Lake, Yoldia Sea, and Ancylus Lake stages are presented. The Öresund Strait was the threshold of the initial stage of the Baltic Ice Lake and was eroded down to bedrock as a result of the isostatic uplift. The emerging threshold forced the Baltic Ice Lake to rise above sea level at ca. 12.0 ka BP. This gradual up-damming ended at ca. 11.2 ka BP when the large glacial lake was lowered 5–10m by possible subglacial drainage at Mt. Billingen. A glacial readvance during the Younger Dryas ended a ca. 400 year long land-bridge between Sweden and the continent, by blocking the former drainage route. Once again the Baltic Ice Lake had to rise above sea level to be drained over the öresund Strait. At ca. 10.5 ka BP a gradual ice recession began, and 200 years later, when the receding ice sheet could not withhold the up-dammed water masses, the final drainage of the Baltic Ice Lake occurred, which rapidly lowered the water level within the Baltic basin with ca. 25 m and ended the Baltic Ice Lake stage. The next stage, the Yoldia sea, was characterized by a complex pattern of relative sea level changes with large differences within the Baltic basin, a very restricted Baltic Sea in the south, and thus an extensive landbridge. At ca. 9.9 ka BP a short (100–200 years) saline ingression is seen in the Baltic sediment records from Stockholm in the north to the southernmost parts of the Yoldia sea. The gradually shallower strait in south central Sweden (The Närke Strait) ended the saline influence. 300–400 years later the two remaining outlets west of Lake Vänern, Göta Älv and Otteid-Steinselva, had become too shallow to ‘swallow’ the outflowing Yoldia Sea waters. At this stage the Baltic/Lake Vänern level could thus not fall in pace with the relative sea level fall outside the outlet areas. This was the isolation of Lake Vänern and the Baltic from the sea and the beginning of the Ancylus Lake. Since the water depth of the (larger) Göta Älv outlet had to be more or less maintained, the Ancylus Lake level had to rise in pace with the uplift of the outlet region. This caused a significant and rapid transgression (10–30 m in ca. 300 years) in the southern Baltic, which flooded large areas with recently immigrated (pine) forests. Since the Öresund Strait, during the Yoldia Sea stage, had been uplifted more than southerly areas, the Ancylus transgression ended with a new drainage pathway at ca. 9.2 ka BP: through the Darss Sill area in the southern Baltic and northwards through the Store Belt Strait. This so-called Dana River had cut off the former large land-bridge. The Quaternary deposits of this new threshold were eroded and a fairly rapid regression set in. At ca. 9.0 ka BP the Dana River had eroded down to the sea level, which isolated Lake Vänern from the Ancylus Lake and created a land-bridge between southern Sweden and northwards. Ca. 800 years later, when the sea level rose above the Öresund threshold, marine water could enter the Baltic, and at ca. 8.0 ka BP brackish water characterized the southern Baltic. This marks the end of the Ancylus Lake.
  • Article
    Two profiles of the diatom assemblages in lake sediments of Late Devensian age have been analysed in detail to substantiate a zonation based upon the diatom assemblages from the nearby Loch Sionascaig site, in northern Scotland. The profiles bear out the original divisions into three diatom assemblage zones and indicate some subdivisions; there is close correlation with stratigraphic, pollen and chemical changes. The Cam Loch assemblages did not include the planktonic phase found in the Sionascaig Diatom Zone 2 sediments of Allerød age, despite the proximity of the two sites and a geological location that would suggest a possibly richer environment.It is concluded that the best pioneer forms are those of cosmopolitan distribution and that in the benthos at least there was an alkaline environment with sufficient nutrient status for diatoms typical of present day eutrophic lakes to occur during the period of greatest diatom diversity. The open water planktonic environment probably remained nutrient-poor with little diatomaceous plankton, a condition resembling some present-day alpine lakes.The final cold phase of the late-glacial is characterized by the temporary disappearance of many taxa and the presence of several indicator taxa. Solifluction of the surrounding land surface is indicated by the presence of some subaerial forms. This is also a feature of an earlier slight climatic recession indicated by correlation of pollen and diatom analyses and now correlated with the Bølling/Allerød stade.
  • Book
    This book is designed specifically to promote the utilisation of sequence stratigraphic analysis as a powerful technique in the exploration for and production of oil and gas. It emphasises also the importance of coupling borehole logs/cores with high resolution seismics for more accurate subsurface correlation of time and facies. Following an introduction and definition of the main terms, the bulk of the book examines parasequences, parasequence sets and sequences in both theoretical and practical terms. There are examples from both the subsurface and outcrop. The book is illustrated with coloured figures including fold-outs. -from Authors
  • Book
    The glacial unloading and resulting isostatic land uplift have together with hydro-isostasy, eustatic rise of sea-level and geoidal changes, ruled the shore displacement of Fennoscandia. Within the Baltic basin, periods of damming and shifts of outlet further complicated the shore displacement during the period studied, c. 12,200-8400 BP. Information on the Baltic history was derived from shoreline observations and studies on sediment cores from lakes formerly directly affected by the Baltic. These cores were analysed with respect to pollen, diatoms, and lithology to determine sequences of Baltic sediments, and dated by a combination of radiocarbon dates and biostratigraphy. The studied areas of southeastern Sweden, mainly central Gotland and the Oskarshamn area, eastern Småland, display a similar course of shore displacement. The Late Weichselian period shows a regression of a slightly decreasing rate between c. 12,200 and 10,300 BP. Then followed a fast drop (25 m) of the Baltic's water level; the final drainage of the Baltic Ice Lake. During the next c. 700 yr, the Yoldia stage, a regression of c. 17 m occurred. This period is mainly characterized by fresh-water diatoms in the Baltic, but at c. 10,000 BP there is evidence of a shortlasting (100-150 yr) period with brackish water. The Ancylus transgression, of c. 11 m, began c. 9600 BP and culminated c. 9300 BP. It was followed by a fast regression of 5-10 m, thereafter the rate of regression decreased. Shoreline gradients shows that the fastest shoreline tilting occurred around 10,000 BP, thus c. 2000 years after deglaciation.
  • Article
    On the basis of synchronization of three carbon-14 (14C)-dated lacustrine sequences from Sweden with tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 ± 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Δ14C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.
  • Article
    Full-text available
    A summary account is given of the development of a small Late-Glacial lake at Snellegem-St. Andries, Belgium. Sedimentation, hydrology, water quality and biotic succession clearly depended on climatic conditions and catchment processes (soil stability and leaching, vegetation). Special attention is drawn to a period of low water level near the end of the Allerød and the abundance of Fragilaria in certain periods.
  • Article
    A new numerical method for determination of pH variation through time in Holocene lake sediment has been developed. Normal probability curves and a parabolic curve were adjusted to the plotted values of percentages for the five pH preference groups of diatoms (alkalibiontic, alkaliphilous, indifferent, acidophilous and acidobiontic) in surface sediment samples from 24 lakes with known mean pH. Based on these curves a transfer function for pH inference was derived. A multiple regression formula based on the same data base was also developed. An attempt to create a single Index formula for the whole pH interval, based on the same idea as the known Index B, failed, and three different indices had to be derived. The results of regression line statistics on the calculated pH values for the 24 lakes, compared to the observed pH values, are presented in diagram form together with values for the standard error of estimate (Sy), the squared coefficient of correlation (r2), and regression line equations. In order to show the applicability of the different methods, they have been used on a sediment core from Lake Trummen, southern Sweden.
  • Article
    The Tornquist zone is a fundamental structural lineation representing the SW margin of the East European/Fennoscandian Precambrian basement platform. It is characterized by complex, often rejuvenated, dip-slip and strike-slip faulting and frequently by tectonic inversion. The zone extends across Poland, beneath the S Baltic into Skane and N Denmark. Evidence obtained from offshore oil and gas exploration suggests that the zone extends beneath the S Norwegian North Sea at least as far as the line of the Viking graben, some 500 km beyond its commonly assumed termination at the line of the Oslo graben.-G.R.
  • Article
    Full-text available
    Mt. Kroppefjall is situated just south of the Middle Swedish (Younger Dryas) ice-marginal zone. Its abundance of lake basins makes it very suitable for detailed shore displacement studies close to the Younger Dryas ice margin. Altogether 12 lakes at altitudes between 157 and 78 m were studied and all but one situated above the marine limit contained marine sediments. The dating of their isolation from the sea resulted in a shore displacement curve from c. 11,200 to c. 98M)BP. The relative uplift almost ceased between 10,900 and 10,300 BP, which is mainly related to an ice readvance in the Lake Vanern basin. This period of balance between uplift and sea level rise was preceded by a relative uplift rate of 5 m/lW yr and followed by as high rates as 7–8 m/100 yr, possibly caused by a delayed uplift effect and perhaps also a local fall in sea level caused by the rapidly receding ice margin. The time difference between the formation of two delta surfaces at Odskolts Moar is estimated at 60&800 years. Shoreline diagrams along the Swedish west and east coasts, mainly based on a number of shore displacement curves, reveal large anomalies that are believed to have been caused by dammings and drainages of the Baltic basin. The southwards extrapolated shorelines indicate that the bedrock threshold in the Oresund Strait, between Denmark and Sweden, functioned as the outlet threshold for the Baltic Ice Lake during its dammed stages, while the erosion of the Store Balt and Darss Sill straits began at the culmination of the Ancylus transgression and continued during the rapid IS20 m Ancylus regression.
  • Article
    From stratigraphic investigations of 38 piston and vibro cores, four fine-grained Late Weichselian sediment units can be defined in the southern Kattegat. A continuous stratigraphic record of the Late Weichselian sediments cannot be established from single cores due to the uneven distribution of the units, but by compilation of relative stratigraphies a composite record can be determined for sediments deposited between approximately 13,500 and 10,000 BP. The sediments contain both lithological and biostratigraphical evidence that the Baltic Ice Lake was suddenly drained through the Öresund Strait at about 12,700 BP. This drainage route appears to have been unchanged until about 10,300 BP when a passage opened in south central Sweden through which the final drainage of the Baltic Ice Lake took place. The Younger Dryas cold event appears to have had only marginal effects on the marine benthic life in the region. The data also indicate that drainage of fresh Baltic water through the Öresund Strait was the driving force for an inflow of marine water from the Skagerrak North Atlantic Ocean into the southern Kattegat, as occurring at the present. This paper is a contribution to IGCP 253, Termination of the Pleistocene.
  • Article
    Thirteen Norwegian lake basins isolated during the Late Weichselian and Holocene are studied. Fragilaria shows a predominance in sediments deposited around the isolation independent of when the basins were isolated. Predominance of Fragilaria spp. seems to develop in accordance with the local environment and more or less independently of the regional differences. The large Fragilaria abundances might be caused by the same effect as in recently deglaciated basins situated above marine limit in Late Weichselian, mainly dependent on the nutrient supply. -from Author
  • Article
    Shallow seismic, sedimentological and macrofossil data and AMS radiocarbon dates on terrestrial plant remains from submarine deposits in Fakse Bugt in the southwestern part of the Baltic Sea are presented. The sediments were deposited near the shore of the Baltic Ice Lake, mostly in barrier-lagoon environments, during two highstand episodes dated to around 12.5–12.2 14C ka BP and 10.6–10.3 ka BP. Coastal sediments from the highstands indicate maximum water levels of 13–15 m and 13 m below present sea level, respectively. During the first episode Salix polaris was widespread in the land area, and during the second episode Dryas octopetala and Betula nana were the most common woody plants. During the lowstand episode Betula pubescens woods dominated. The flora and fauna of the Baltic Ice Lake were rather diverse, reflecting the long and increasing distance to the margin of the Fennoscandian Ice Sheet. Calcium-carbonate-rich, mesotrophic water characterized the Baltic Ice Lake in Fakse Bugt.
  • Article
    This paper presents evidence on the timing and pattern of the Late Weichselian deglaciation in SW Scandinavia, particularly in the Öresund–Kattegat region before the Allerød interstadial. New radiocarbon ages and evaluated older dates demonstrate that active glacier ice had left eastern Denmark, southern Halland and western Skåne before 14,000 BP. The deglaciation in the Öresund region took place mainly under glacioestuarine conditions in a narrow fjord or inlet with some marine influence, as indicated by radiocarbon-dated finds of Polar Cod (Boreogadus saida) and the vertebra of a Ringed Seal (Phoca hispida). The Swedish west coast experienced glaciomarine and deltaic ice proximal conditions, where Vendsyssel was at the same time under full marine conditions with little evidence of ice rafting. A paleogeographic interpretation illustrates land, sea and ice configurations around 14,000 BP. We suggest that a subsequent lateglacial transgression reached the entire region almost simultaneously and peaked around 13,300 BP. This led to deposition of an ice-rafted diamicton (the Öresund diamicton) in Skåne and Sjælland, and of glaciolacustrine mud in Halland. We propose that the complex transgression and regression events recorded in the region were governed by interaction of the eustatic sea level rise, isostatic reponse to glacier unloading and possibly also by damming by an ice stream in the Skagerrak and northern Kattegat.
  • Chapter
    There has been a proliferation in recent years of applications of sequence-stratigraphic concepts since the publications by Vail et al. (1977a,b), Posamentier et al. (1988), Posamentier and Vail (1988a,b) and Van Wagoner et al. (1990). The use of this approach to enhance understanding of geological relationships within a time-stratigraphic framework clearly has achieved widespread acceptance. Along with the rapid acceptance of these concepts, however, has come a number of problems that are addressed in this paper.The inevitable introduction of a morass of terminology as well as occasional misunderstanding and misapplication of the stratigraphic model has led to considerable confusion. Moreover, certain key contentious issues within sequence stratigraphy remain that need to be resolved. Most importantly, however, sequence stratigraphy must be viewed as a tool or approach rather than a rigid template. The conceptual stratigraphic models are based on first principles and it is the understanding of these first principles rather than memorization of the model that is the key to successful application of sequence stratigraphy.
  • Article
    Full-text available
    The history of the recording and interpretation of the Fennoscandian uplift illustrates the main history of Earth sciences because the results obtained had (and still have) immediate impact of the interpretation of a large number of fundamental problems in Earth sciences. Thanks to a paper of De Geer in 1888, the glacial isostatic origin was established. Fennoscandia became the classic area of glacial isostasy, and its sea level records were used for geophysical calculations of the properties and dynamics of the mantle and crust. The varve dated sea level curve of Lidén (1938) from the center of uplift provided an exceptionally well dated record. With the radiocarbon method, the records of shorelines and shorelevel displacement curves were drastically improved providing a totally new basis for the understanding of the geodynamics of the Fennoscandian uplift and for the geophysical interpretation of the data obtained. This is especially true in combination with the repeated levelling data obtained during the last decades for Finland and Sweden. The Late Cenozoic long term movements of the Fennoscandian Shield are characterized by a considerable subsidence. The postglacial uplift of Fennoscandia is complex (an exponential and a linear factor) and caused by two different mechanisms. The total absolute movement in relation to the last glaciation is an elliptic uplift cone of 830 m height surrounded by a subsidence through of 170 m height. The mass in the uplift cone and in the subsidence through is as 1:1 with a volume 0.7 × 106km3. The disappearence/appearance of mass give evidence of a mass transfer in a low viscosity asthenosphere. The properties and conditions of the asthenosphere are found to be: 1–10 × 1020 Poises in viscosity, 3 × 10−14 − 3 × 10−16 sec−1 in strain rates, 0.7% of the melting temperature, 3 mm in grain size, and 5–0.4 bar in stress. The main isostatic uplift (the exponential factor) originates from an asthenospheric dislocation glide process which in early-mid Holocene time changed over into a diffusion creep process. The present linear uplift factor (identified through the last 8000 yrs) seems to originate from mesospheric motions under the following approximate conditions: 0.6% of the melting temperature, 2 × 1022 Poises in viscosity, 3 × 10−16 sec−1 in strain rates and 8 bars in stress. Uplift irregularities and neotectonism are frequently established and often reveal an old geodynamic inheritance (e.g. the Pre-Baikalian/Gothian bedrock seam of high geodynamic activity). The peak rates of glacial isostasy are associated with intensive fracturing, faulting and seismic activity.
  • Article
    Marine geological investigations including shallow seismic, sedimentological and stratigraphical studies were carried out in Fakse Bay, southwestern Baltic. Seismic sequence analytical methods were used, supplemented by detailed lithological descriptions, pollen analysis and 14C dating of core material. Detailed correlations between sediment facies units and seismic sequences resulted in the establishment of four depositional sequences: I. Glacial related deposits, II. lagoon/pond and freshwater coastal deposits, III. Lake-bog-lake deposits, and IV. Marine, (sub)littoral deposits. Most attention has been paid to Sequences II and III, showing the development of a transgressive freshwater barrier beach ridge and a following regression.Pollen spectra indicate Allerød and Younger Dryas Chronozone ages (11,500-10,000 14C yrs B.P.) for the development of a sheltered lagoon/pond basin behind the transgressive freshwater barrier beach ridge. The freshwater coastal deposits are interpreted as the southwesternmost marginal deposits of the Baltic Ice Lake and represent the transgression maximum. This transgression maximum reached a level of about 13 m below the present sea level. The final drainage of the Baltic Ice Lake resulted in the development of a sheltered basin behind the former beach ridge. A fluctuating groundwater level here favoured the deposition of alternating lake gyttja and bog peat deposits in the central part of the basin. Pollen analysis and 14C dating reveal that the lake deposits correspond to high groundwater levels associated with the Ancylus Lake (9000 yrs B.P.) and the Littorina Sea (7000 yrs B.P.) transgressions, while the bog sediments represent the low water stands in the early Holocene.
  • Article
    Full-text available
    To overcome inconsistencies in the Exxon sequence stratigraphic model as applied to silicielastic and carbonate shelf margins, it is proposed that an ideal sequence should consist of four systems tracts. In addition to the transgressive and highstand systems tracts, developed during rising base-level, it is suggested that there should be two systems tracts associated with falling and lowstands of relative sea-level. These are: the forced regressive wedge systems tract formed during falling base-level, bounded below by the ‘basal surface of forced regression’ and above by the sequence boundary, representing the lowest point of sea-level fall, and the lowstand prograding wedge systems tract, developed as relative sea-level begins to rise after sequence boundary formation. This systems tract downlaps the basin-floor forced regression deposits in a basinwards direction and onlaps forced regressive wedge sediments on the slope. The forced regressive wedge systems tract consists of shallow-water stranded parasequences deposited on the upper slope to the shelf, and basin-floor fan or apron sediments, deposited at the toe-of-slope and derived from erosion of the stranded parasequences and/or erosion of the previous highstand shelf and shelf-margin sediments.
  • Article
    New stratigraphy data especially diatom analyses are presented from the area north of Lake Onega relevant to the discussion on possible Lateglacial connection between the Baltic Sea and White Sea. Following the deglaciation 12,000–11,000 years ago Lake Onega basin was occupied by a system of ice dammed lakes which drained to the Lake Ladoga basin. When the ice retreated from the threshold leading to the White Sea 11,000 years ago the water level dropped and since that the lake was controlled by its thresholds to the White Sea and the Baltic basin. Lake Onega has remained distinctly above the sea level and no Late Weichselian sea connection existed between the White Sea and Baltic basins. The marine diatoms frequently found in sediments are reworked older fossils as also suggested by some earlier workers. Lake Onega drained to the White Sea basin over the Maselga threshold and also to Lake Ladoga between 11,000 and 10,000 radiocarbon years ago, and to the White Sea alone between 10,000 and 9500 years ago, and the present outlet of Lake Onega, River Svir, originated 9500 years ago.
  • Article
    Full-text available
    Sea level related radiocarbon, palynological and stratigraphical data from sediment cores in the Western Baltic have been tested against the existing sea level curves for the region. The relative sea level rise curves for the beginning of the Holocene show no significant deviations between the Kiel, Mecklenburg and Lubeck Bays and hence do not support the previously reported differences in the averaged regional subsidence rates for this time interval. The submarine terraces at -30 m and perhaps also at - 27 m were formed during the lacustrine phase of the Western Baltic when the water levels were controlled by the main thresholds in the Great Belt. -from Authors