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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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... After the last deglaciation, the Baltic Sea underwent a complex salinity history and dynamic shore-level development with several lacustrine and marine stages: the Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the Littorina Sea (Björck 1995). In connection with shallow seismic profiling in the south-western Baltic Sea, two marked and widespread erosional unconformities have been identified (Jensen et al. 1997(Jensen et al. , 1999Lemke et al. 1998;Larsen 2004). The older unconformity occurs within sediments deposited in the Baltic Ice Lake, whereas the younger one separates Baltic Ice Lake sediments from Holocene lake and mire deposits. ...
... Cladium mariscus was recorded from late-glacial deposits in south-eastern Denmark by Bennike & Jensen (1995), but its presence was probably due to down-core contamination, and there are no secure records of it from late-glacial deposits in Denmark (Iversen 1954;Jensen et al. 1997;Bennike et al. 2004). Its northern geographical limit during the Allerød may thus have been located near the coring site. ...
... The sediment is fine-grained and was probably deposited at a water depth of several metres, and we suggest that the shore level during deposition was around 40 m lower than at present. Both before and after this lowstand episode, the relative shore level was around 20 m below the present sea level according to Jensen et al. (1997). This implies that the shore-level fall towards the end of the Allerød chronozone was of the same magnitude as the fall at the Younger Dryas -Holocene transition, i.e. considerably more than 5-10 m as suggested by Björck (1995). ...
Article
Full-text available
After the last deglaciation, the Baltic Sea underwent a complex salinity history and dynamic shore-level development with several lacustrine and marine stages: the Baltic Ice Lake, the Yoldia Sea, the Ancylus Lake and the Littorina Sea (Björck 1995). In connection with shallow seismic profiling in the south-western Baltic Sea, two marked and widespread erosional unconformities have been identified (Jensen et al. 1997, 1999; Lemke et al. 1998; Larsen 2004). The older unconformity occurs within sediments deposited in the Baltic Ice Lake, whereas the younger one separates Baltic Ice Lake sediments from Holocene lake and mire deposits. The latter unconformity is dated to the transition between the Younger Dryas and the Holocene, corresponding to c. 11.7 cal. ka BP and formed due to a sudden drop in the level of the icedammed Baltic Ice Lake of around 25 m, caused by ice recession from Mt. Billingen in south central Sweden.
... Subsequently, between ~14 and 13 ka the Baltic Ice Lake shoreline was raised due to shoaling of the meltwater spillway to the Kattegat as erosion reached more resistant bedrock under ongoing isostatic rebound (Sandgren and Snowball, 2001;Andrén et al., 2011). The maximum Baltic Ice Lake shoreline level prior to ~13 ka ranged from ~20 m below the present sea level near the German and Danish straits (Jensen et al., 1997;Feldens & Schwarzer, 2012) to > 200 m above present sealevel in east central Sweden (Påsse and Daniels, 2015;Muschitiello et al., 2016). Surface exposure ages suggest that ice retreat from the southern Baltic Sea and, consequently, deposition on top of the diamicton at Site M0064, a subglacial deposit, commenced after ~14.4 ka (Figure 1, Cuzzone et al., 2016). ...
... Deposition in a smaller Baltic Ice Lake resumed, but a second and final lake drainage event occurred near the end of the Younger Dryas cold period at ~11.7 ka (Jacobsson et al., 2007). After the second drainage, deposition in the shallower, rebounded, southern Baltic Sea basin ceased due to a 25-m drop in water level, which is marked by an unconformity in the seismic stratigraphy of both the Hanö Bay and the Bornholm Basin (Jensen et al., 1997;. In the Landsort Deep (Site M0063), however, deposition continued (Obrochta et al., 2017). ...
... Ice retreat outpaced glacio-isostatic adjustment leading to the development of a Baltic Ice Lake that was significantly deepening upstream. The retreat of the grounding line increased the volume of the freshwater storage as long as the ice blocked drainage of meltwater prior to ~ 12.9 ka BP (Jensen et al, 1997;Muschitiello et al., 2016). ...
Article
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The rapid retreat of the Baltic Ice Stream and the development of the Baltic Ice Lake is assessed using data from sediment cores retrieved from three sub-basins in the southern Baltic Sea. Hydraulic piston coring by the International Ocean Discovery Program (IODP) recovered for the first time intact glacial lake sequences overlying diamictons and other ice-contact deposits at Sites M0063, M0064 and M0065. Based on the particle size and bulk sediment chemical composition the glacial lake sediments were subdivided into a proximal and a distal varve sequence. The origin of a dark, lithologically distinct horizon between the proximal and distal varves is attributed to a lake drainage event following the opening of a spillway in central Sweden. Available age constraints suggest that the Baltic Ice Lake developed during the Bølling-Allerød interstadial and reached its maximum size at ∼13 ka. Ice retreat was forced by surface melt, and amplified by calving in the upstream deepening lake environment. Furthermore, rapid ice retreat and glacio-isostatic processes allowed for the storage of substantial amounts of meltwater in the Baltic Ice Lake during the Allerød warm period. Subsequent lake drainage into the North Atlantic took place through a conduit at higher latitude than previous drainage pathways. The pronounced changes in meltwater storage and routing caused by the rapid retreat of the Baltic Ice Stream may have contributed to abrupt climate change through the effects of changing freshwater supply on Atlantic overturning circulation.
... At 12 800 cal. a BP, the re-advancing Scandinavian Ice Sheet blocked that outlet and the subsequent water-level rise initiated the final Baltic Ice Lake (BILf) stage (Andr en et al. 2011), which inundated the Darss Sill threshold. A lake level of À20 m in the FB area was reached (Jensen et al. 1997(Jensen et al. , 1999. The Arkona Basin, MB, Great Belt (Bennike et al. 2004) and even Kiel Bight (Jensen et al. 1997 were connected during the BILf highstand via the FB (Novak & Bj€ orck 2004). ...
... A lake level of À20 m in the FB area was reached (Jensen et al. 1997(Jensen et al. , 1999. The Arkona Basin, MB, Great Belt (Bennike et al. 2004) and even Kiel Bight (Jensen et al. 1997 were connected during the BILf highstand via the FB (Novak & Bj€ orck 2004). Fine laminated layers of clay and silt, lacking organic material, are found in the FB and adjacent basins. ...
... Kostecki et al. 2015;Endler et al. 2016). During the lake highstand, sandy clinoforms developed along the eastern MB margin, generated by sediment discharge from the ancient Warnow River (Jensen et al. 1997). ...
Article
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TheFehmarn 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, onemarking the top of the initial Baltic IceLake depositsandthe secondone 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 environmentrepresentedbyriver deposits developed. These deposits arecoveredbylake marls ofYoldia 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.
... The Baltic Ice Lake lasted from approximately 16,000 to 11,600 cal yr BP (BjörckBj¨Björck, 2008) and is separated into an initial (BILi) and a final (BILf) phase. The maximum water level of the BIL in Mecklenburg Bay and the Arkona Basin is given with 20 m below sea level (b.s.l.) (Jensen et al., 1997), while 18 m b.s.l. is reported in the Darss Sill area (Lemke et al., 1994). Local lakes in Mecklenburg Bay area were possibly connected to the Baltic proper, flooding the Darss Sill (Jensen et al., 1997) during the period of the BILf highstand (Lemke, 1998), when the BIL may have extended into the Great Belt (Bennike et al., 2004). ...
... The maximum water level of the BIL in Mecklenburg Bay and the Arkona Basin is given with 20 m below sea level (b.s.l.) (Jensen et al., 1997), while 18 m b.s.l. is reported in the Darss Sill area (Lemke et al., 1994). Local lakes in Mecklenburg Bay area were possibly connected to the Baltic proper, flooding the Darss Sill (Jensen et al., 1997) during the period of the BILf highstand (Lemke, 1998), when the BIL may have extended into the Great Belt (Bennike et al., 2004). The regression of the initial and final phases of the BIL took place through outlets at O ¨ rsesund and Mt. ...
... The regression of the initial and final phases of the BIL took place through outlets at O ¨ rsesund and Mt. Billingen (SW Sweden) at 13,000 and 11,600 cal yr BP (BjörckBj¨Björck, 1995; Jensen et al., 1997; BjörckBj¨Björck, 2008). Following the regressions of the BIL, the water level in the southern Baltic east of the Darss Sill was situated at approx. ...
Article
The Baltic Ice Lake, Yoldia Sea, Ancylus Lake and Littorina Sea stages of regression and transgression controlled the history of the Baltic Sea since the last glacial period. Many details regarding their development remain unknown, including the question whether the regression of the Ancylus Lake (between 10,700 and 10,200 cal yr BP) took place west of the Darss Sill, or elsewhere. This study addresses whether a drowned river system in Fehmarn Belt (SW Baltic Sea) can be related to the drainage of the Ancylus Lake. The river channel is cut into glacial till in the western part of Fehmarn Belt. Here, the channel reaches an incision depth of up to 12 m at a base level of 40 m b.s.l. (below sea level). Near Mecklenburg Bay, the buried channel is incised down to 60 m b.s.l. and widens rapidly from several hundred meters to more than 1 km, fading towards east. It was mainly shaped as part of a glacial meltwater system at a maximum water level of 30 m b.s.l., and is therefore not related to the Ancylus Lake drainage. During the lowstand of the Baltic Ice Lake, local shallow water bodies covered the study area. A previously reported westward directed drainage of a lake in the eastern Fehmarn Belt could be restricted to a time interval between the highstand of the Ancylus Lake and prior to the Littorina Transgression. Timing, water level and potential water discharge of this event suggest a connection to a partial drainage of the Ancylus Lake. It is concluded that the threshold separating the Ancylus Lake from the North Sea needs to be located west of Fehmarn Belt.
... The Bj?rck, 2005) available at the website http://www.geol.lu.se/personal/seb/Maps%20of%20the%20Baltic.htm [27 Jan 2005], except for the paleo-shoreline of Norway, which was modified after Figure 12of Jensen et al. (1997). The paleo-shoreline west of 9?E is modified from map 6 of Stabell and Thiede (1986), except for the paleo-shoreline of Norway, which was erroneous due to a misprint (pers. ...
... The opening of the Danish Straits and ?resund was complex, and several periods of transient flow through these straits occurred over an extended time period (starting at 10.1 kyr, Andr?n et al., 2000), before full marine conditions in these straits were established between 9 and 8 kyr (Bj?rck, 1995; Lambeck, 1999; Andr?n et al., 2000; Bennike et al., 2004; Berglund et al., 2005). Jensen et al. (1997) conclude that the marine ingression through the Great Belt occurred at about 9.0-8.7 kyr (recalibrated, Table 2event 8c), and through the ?resund slightly later. The oldest reported marine shells from the Great Belt were dated to 8.1 kyr, but brackish water conditions prevailed for some centuries before that (Bennike et al., 2004). ...
... The record from ca 0.9 kyr until the present is characterized by a strongly " Danish " mineral magnetic signal (Figure 9), indicating sediment transport dominated by Atlantic water and the Jutland Current (currents 1, 4, and 5, Figure 8) (Paper III). (1999), except for the ?resund and the Great Belt, which were probably open at 8.1 kyr (Bj?rck, 1995; Conradsen, 1995; Jensen et al., 1997; Lambeck, 1999; Andr?n et al., 2000; Bennike et al., 2004; Berglund et al., 2005). The paleo-shoreline west of 9?E is modified from Figure 3hof Lambeck (1995). ...
... It can therefore be expected that dramatic water-level drops, which occurred during the Baltic Sea's Late Pleistocene and Holocene history (Björck 1995), are recorded in the sediments of the Arkona Basin. Previous studies have focused on deposits from the shallower south-western (Kolp 1976;Lange & Wulff 1980;Jensen et al. 1997), south-eastern (Kolp 1983(Kolp , 1986) and north-eastern margins (Abelmann 1985;Schubert 1991) of the Arkona Basin. Only six publications address sediment cores from the deeper basinal part (Neumann 1981;Rother 1989a, b;Gingele & Leipe 1997Sohlenius et al. 2001). ...
... In places where it is located shallower than 49 m b.s.l. it is the only re ector. Compared to the seismostratigraphy proposed by Jensen et al. (1997), the subdivision presented here is of higher resolution. This might be due to the fact that our study was performed in the deeper central part of the Arkona Basin, while the data of Jensen et al. (1997) were gathered mainly in its marginal parts. ...
... Compared to the seismostratigraphy proposed by Jensen et al. (1997), the subdivision presented here is of higher resolution. This might be due to the fact that our study was performed in the deeper central part of the Arkona Basin, while the data of Jensen et al. (1997) were gathered mainly in its marginal parts. Moreover, the difference in resolution potential of the different equipment used in these studies has to be taken into account. ...
Article
Full-text available
Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS 14C data and biostratigraphic information were gathered. Based on this multi-proxy approach, seven lithostratigraphic units (AI, AII, B to F) were distinguished. These consist of fine-grained clay, silt and mud, and are separated from each other by thin basin-wide traceable sandy layers (Sab-Sef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain-size fraction >63μm. In addition, some of the quartz-grain-dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin-wide water-level low-stand conditions. These low stands resulted from water-level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine-grained units AI, AII to F, in which coarser material is absent, represent water-level high-stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen-1 regression, respectively. We assign the most prominent sandy layer Sab to the final drainage of the Baltic Ice Lake (Billingen-2), whereas the sandy layers between units B, C., D and E are related to the Yoldia Sea and Ancylus Lake regressions of the Baltic Sea's history. The uppermost fine-grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well-visible sediment colour change from reddish/brown-to-grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised.
... For more detailed information on the seismic interpretations, macrofossil and diatom analysis and radiocarbon dating we refer to earlier publications (Jensen & Stecher 1992;Lemke & Kuijpers 1995;Jensen et al. 1997;Lemke et al. 1997). (Svensson 1991), whereas much fewer studies have been carried out in the southwestern area (Lemke et al. 1994;Eronen et al. 1990). ...
... This assemblage is found in core 564016, 564024, 560007, MB01/94 and MBOU94, and it is dominated by the following taxa: Amphora pediculus, Cavinula scutelloides, Cocconeis pseudothumensis, Epithemia argus, E. frickei, Fragilaria brevistriata, F. martyi, Navicula submuralis. The dominating taxa are associated with a number of less frequent taxa, including Achnanthes clevei, A. joursa-cense, A. calcar, Amphora copulata, A. thumensis, Cavinula cocconeifomis, C. jaemefeltii, C. jentzschii, Cocconeis disculus, C. placentula, Fragilaria microstriata, F. lapponica, F. pseudoconstruens, F. robusta, Fragilaria sp. 1 and Fragilaria sp. 2 (sensu Jensen et al. 1997), Geisslena schoenfeldii, Navicula aboensis and N. submuralis. Although their percentage values vary between cores, the taxa mentioned are always present within samples referred to the littoral assemblage. ...
Article
One of the most discussed stages in the history of the Baltic Sea is the Ancylus Lake phase. This paper presents detailed information from the Darss Sill threshold area as well as the adjacent basins, i.e. the Mecklenburg Bay and Arkona Basin located in the southwesternmost Baltic. The threshold area was transgressed at the Baltic Ice Lake maximum phase and during the following regression about 10.3 ka BP a river valley was incised in the Darss Sill to a level of 23–24 m below present sea level (b.s.l.). Preboreal sediments in the study area show lowstand basin deposition in the Arkona Basin and the existence of a local lake in Mecklenburg Bay. The lowstand system is followed by the Ancylus Lake transgression that reached a maximum level of 19 m b.s.l. Thus, at the maximum level the water depth was about 5 m over the threshold, and the shore level fall during the Ancylus Lake regression must be in the same range. The Darss Sill area is the key area for drainage of the Ancylus Lake, and if the previously suggested regression of 8–10 m in southeastern Sweden is to be achieved, isostatic rebound must also play a role. The existence of the so-called Dana River in the Darss Sill area cannot be supported by our investigations. We observed no signs of progressive erosion of the Darss Sill area in the Early Holocene, and there are no prograding systems in Mecklenburg Bay that can be related to the Ancylus Lake regression. On the contrary, local lakes developed in Mecklenburg Bay and in the Darss Sill threshold area. In the Darss Sill area, marl was deposited in a lake in the valley that developed after the final drainage of the Baltic Ice Lake. Studies of diatoms and macrofossils, combined with seismic interpretation and radiocarbon dating, provide detailed information about the chronology and the relative shore level of these lake phases as well as about environmental conditions in the lakes.
... The limnic fauna includes Lepidurus sp., Cristatella mucedo and the snails Valvata cristata, V. piscinalis, Lymnaea peregra, L. truncatula, Gyraulus albus and Armiger crista. L. truncatula is characteristic of temporary ponds, often living at the transition between water and land, and it appears to be new to the Younger Dryas fauna of Denmark (Johansen 1904;Bennike & Jensen 1995;Jensen et al. 1997;Noe-Nygaard & Heiberg 2001). However, apart from this species, the flora and fauna are characteristic of Younger Dryas deposits in the region (Jensen et al. 1997). ...
... L. truncatula is characteristic of temporary ponds, often living at the transition between water and land, and it appears to be new to the Younger Dryas fauna of Denmark (Johansen 1904;Bennike & Jensen 1995;Jensen et al. 1997;Noe-Nygaard & Heiberg 2001). However, apart from this species, the flora and fauna are characteristic of Younger Dryas deposits in the region (Jensen et al. 1997). ...
Article
Full-text available
On the basis of shallow seismic records, vibrocoring, macrofossil analyses and AMS radiocarbon-dating, five stratigraphical units have been distinguished from the deepest parts of the central Great Belt (Storebælt) in southern Scandinavia. Widespread glacial deposits are followed by two lateglacial units confined to deeply incised channels and separated by an erosional boundary. Lateglacial Unit I dates from the time interval from the last deglaciation to the Allerød; lateglacial Unit II is of Younger Dryas age. Early Holocene deposits show a development from river deposits and lake-shore deposits to large lake deposits, corresponding to a rising shore level. Lake deposits are found up to 20 m below the sea floor, and the lake extended over some 200–300 km2. The early Holocene freshwater deposits are dated to the time interval c. 10900 to c. 8800 cal. yr BP and the oldest shells of marine molluscs from the Great Belt are dated to c. 8100 cal. yr BP.
... Sediment sections from the various regions (Kalm et al., 1996; Sohlenius et al., 1996; Heinsalu et al., 2000; Winterhalter, 2001; Емельянов и др., 1995, 2001 and others) show that in every sea basin sedimentation processes were proceeding differently because of morphological properties of the bottom relief, peculiarities of water dynamics, sources of sedimentary matter and other causes. In one of such regions – the Arkona Basin situated in the westernmost part of the Baltic Sea – significant traces of the reaction between the sea and the ocean had to be reflected best in the compositional changes of sediment (Jensen et al., 1997Jensen et al., , 1999 Lemke et al., 2001; Moros et al., 2002 and others). The level of the Baltic Sea changed many times after the recession of the glacier. ...
... The boundary between different clay layers is distinct and slanting, allowing to consider the interruption of sedimentation, which could result not only from non-deposition of sediments, but also from their washout. These events took place in the southwestern Baltic Sea region, which at the beginning of the Preboreal was the land (Блажчишин, 1984; Emelyanov, 1995) and the area of the section PSh-5441 was near the shoreline of the Baltic Ice Lake (Jensen et al., 1997; Moros et al., 2002). It should be pointed out that in the 285 cm horizon there is a thin (0.5 cm) dark grey silt (sand?) streak. ...
Article
Full-text available
The Arkona Basin, situated in the westernmost part of the Baltic Sea, underwent a specific Late Glacial and post-glacial evolution reflected in the layers of bottom sediments. The lithostratigraphy of the representative section PSh-5441 of this basin (at a depth of 46 m) was established based on the results of the sedimentological analysis and radiocarbon (14C) dating. Spores-pollen spectra were used for biostratigraphy, while diatom analysis was carried out to evaluate the sedimentary environment. The sediment section from the northern part of the Arkona Basin consists of the Late Glacial and post-glacial clays and silts which accumulated after territory deglaciation. Layers of brown and grey clays separated from each other by sedimentation hiatus had been developing under very changeable sedimentation conditions which could exist in the shallow basin at the end of the Baltic Ice Lake stage and in the later period. This time of development is marked by active processes of re-deposition. During the Litorina Sea stage two phases of sedimentation are distinguished. In the first phase, the water salinity was rather high and sedimentation took place under sub-littoral environmental conditions. In the second phase, it was possible to observe a slight raise of water level, and water salinity slightly increased as well. Sedimentation took place in the shallow sea.
... Significant Holocene post glacial sea-level variations have led to the flooding of Arkona Basin's western barrier (the Darss Sill), producing 4-5 distinct stratigraphical stages (Björck, 1995). (1) The Baltic Ice Lake stage beginning roughly 13.5 kyr before present (BP) as a result of deglaciation (Jensen, 1995;Jensen et al., 1997). During this stage, evidence points toward probable drainage of Arkona Basin waters through Øresund ( Fig. 1) (Jensen, 1995). ...
... In this study, we assume that the initial HORM deposition in the southwestern Baltic Sea began 8.0 kyr BP (Jensen, 1995;Jensen et al., 1997Jensen et al., , 1999Witkowski et al., 2005). This date is consistent with the averaged date for the Littorina Sea Stage in the Baltic Sea given by Gustafsson and Westman (2002) if one considers this event in Arkona Basin preceded the averaged date for the Baltic Sea by 500 yr. Figure 2 shows a general overview of the two most recent stages of the Baltic Sea and the chronostratigraphy employed in the model. ...
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.
... All taxa can be classified as pioneer species. Most of them have been reported from both early lateglacial and interstadial deposits from the region (Bennike and Jensen, 1995;Jensen et al., 1997). C. lacustris is found on muddy substrates of large cold-water lakes. ...
... C. lacustris is found on muddy substrates of large cold-water lakes. It is quite common in deposits from the southwestern part of the Baltic Ice Lake (Jensen et al., 1997) and in lateglacial deposits from the region. It is typical of oligotrophic or mesotrophic conditions. ...
... All taxa can be classified as pioneer species. Most of them have been reported from both early lateglacial and interstadial deposits from the region (Bennike and Jensen, 1995;Jensen et al., 1997). C. lacustris is found on muddy substrates of large cold-water lakes. ...
... C. lacustris is found on muddy substrates of large cold-water lakes. It is quite common in deposits from the southwestern part of the Baltic Ice Lake (Jensen et al., 1997) and in lateglacial deposits from the region. It is typical of oligotrophic or mesotrophic conditions. ...
... Jakobsson et al. (2007) showed that at ca. 11,700, the BIL level had dropped 25 m during 1-2 years, and approximately 7800 km 3 of water drained with average water discharges in the range 120,000-250,000 m 3 s -1 . The studies done in south-western areas of the Baltic Sea drainage area have shown that before the final drainage of the BIL, there had been a transgression when the lake had extended as far as into the Kiel Bay (Jensen et al., 1997). According to Jensen et al. (1997), after the Billingen drainage, the relative lake level dropped up to 25 m at the Baltic Proper, but only to 4-5 in the Mecklenburg Bay area. ...
... The studies done in south-western areas of the Baltic Sea drainage area have shown that before the final drainage of the BIL, there had been a transgression when the lake had extended as far as into the Kiel Bay (Jensen et al., 1997). According to Jensen et al. (1997), after the Billingen drainage, the relative lake level dropped up to 25 m at the Baltic Proper, but only to 4-5 in the Mecklenburg Bay area. ...
Article
The Middle and Late Pleistocene glaciations of northern Eurasia had a great impact on the evolution of the modern drainage system. This paper presents a review and synthesis on the palaeogeography of glacial lakes, their drainage and impact on the re-organization of the drainage systems during the last two glacial-interglacial cycles. We will focus on four regions: (1) northern Central Europe and Fennoscandia, (2) the central part of the East European Plain, (3) the west Siberian Plain and (4) the Aral – Caspian – Black Sea area. The main findings of the last decade(s) include the improved chronology of some major river system formation and of meltwater overflows across the continental drainage divides. Major drainage systems of the north-central and west-central part of the East European Plain (upper Volga, upper Dnieper) formed due to overspill of glacial lakes in late MIS 6 with a partial re-organization (upper Dnieper) in MIS 2. The Aral – Caspian – Black Sea cascade acted as a sink for glacial meltwater from the north. The major meltwater yield to the Aral and Caspian seas occurred in MIS 6 and late MIS 5. In MIS 2, the meltwater delivery via the Volga valley into the Caspian Sea was low and therefore had only a minor influence on the sea level. Considerable meltwater discharge to the Black Sea through the Dnieper River system occurred around the maximal stage of the MIS 2 glaciation and ceased very quickly after the onset of deglaciation.
... Its shallow-water character with a depth of 28 m in its deepest part was also the cause of many environmental and water level changes during the initial stages of the Baltic Sea. Firstly, after deglaciation took place in Mecklenburg Bay at around at 16,000 cal BP (Houmark-Nielsen and Kjaer, 2003), the Baltic Ice Lake appeared and reached a water level of À20 m during highstand (Jensen et al., 1997). After the final drainage of the Baltic Ice Lake at 11,600 cal BP (Kortekaas, 2007) to a depth of around À40 m (Jensen et al., 1997;Bennike and Jensen, 2013), this area developed into a lacustrine environment. ...
... Firstly, after deglaciation took place in Mecklenburg Bay at around at 16,000 cal BP (Houmark-Nielsen and Kjaer, 2003), the Baltic Ice Lake appeared and reached a water level of À20 m during highstand (Jensen et al., 1997). After the final drainage of the Baltic Ice Lake at 11,600 cal BP (Kortekaas, 2007) to a depth of around À40 m (Jensen et al., 1997;Bennike and Jensen, 2013), this area developed into a lacustrine environment. During the next transgression of Ancylus Lake at around 10,300 cal BP the water level reached À19 m (Lemke, 1998;Jensen et al., 1999) and a local lake was established in Mecklenburg Bay, presumably connected with Ancylus Lake (Lemke and Kuijpers, 1995;Jensen et al., 1999;Lemke et al., 2001). ...
Article
Multi-proxy studies of the sediment cores and acoustic profiles from Mecklenburg Bay display a more detailed picture of the evolution of the environment in the Holocene. Studies of diatoms, geochemistry, grain size and radiocarbon dating clearly reveal the age and character of freshwater and marine transgressions and regressions. After the final regression of the Baltic Ice Lake, a local lake and swamp environment was recorded by peat gyttja sediments. This environment existed until the Ancylus Lake transgression dated ca 10,500 cal BP. During the Ancylus Lake period, the area remained a shallow-water lake, transitional isolated from the main Baltic Basin. The first slightly brackish marine inflows confirmed by the appearance of planktonic, mesohalobous and halophilous diatoms were identified at the beginning of the Initial Littorina Sea stage and dated ca 8800 cal BP. The boundary between the Ancylus Lake and the Initial Littorina Sea is marked by increasing contents of biogenic silica and iron. The Initial Lit-torina Sea stage was characterized by increasing mesohalobous and polyhalobous diatom forms and decreasing oligohalobous species. The Initial Littorina Sea environment was recorded as a slightly brackish reservoir sporadically affected by weak marine inflows. The Littorina transgression appeared in the Mecklenburg Bay at ca 7500e7700 cal BP and is reflected by the domination of polyhalobous di-atoms, increasing mean grain size, biogenic silica, and calcium and magnesium contents. The Initial Littorina Sea was a 1500-year-long period in Mecklenburg Bay, existing until the Littorina transgression. The main Littorina transgression first appeared in Mecklenburg Bay around 7700 cal BP and after a few hundred years at around 7200 cal BP in the Arkona Basin.
... All taxa can be classified as pioneer species. Most of them have been reported from both early lateglacial and interstadial deposits from the region (Bennike and Jensen, 1995;Jensen et al., 1997). C. lacustris is found on muddy substrates of large cold-water lakes. ...
... C. lacustris is found on muddy substrates of large cold-water lakes. It is quite common in deposits from the southwestern part of the Baltic Ice Lake (Jensen et al., 1997) and in lateglacial deposits from the region. It is typical of oligotrophic or mesotrophic conditions. ...
... Bryozoans live on firm objects, often on macrolimnophytes. All the taxa have been reported from Lateglacial deposits from the region (Bennike & Jensen 1995;Jensen et al. 1997;Bennike et al. 2004a). Cytherissa lacustris is found on muddy substrates of large cold-water lakes. ...
... Cytherissa lacustris is found on muddy substrates of large cold-water lakes. It is quite common in deposits from the southwestern part of the Baltic Ice Lake (Jensen et al. 1997) and in Lateglacial deposits from the region. It is typical of oligotrophic or mesotrophic conditions. ...
Article
Coring through glaciotectonically stacked Quaternary sediments situated below sea level on the island of Møn, Denmark, recovered a succession of interstadial sediments of Middle Weichselian age. Plant and animal remains including insects found in laminated sand and mud indicate deposition in a lake surrounded by dwarf shrubs, herbs, mosses and rare trees. The insect fauna indicates a mean July temperature of 8–12 °C, suggesting an arctic to sub-arctic environment, while winter temperatures around −8 to −22 °C suggest periglacial conditions with permafrost. Luminescence dating of sediment samples gave ages from 48–29 ka, and radiocarbon dating indicates deposition of plant fragments between 45 and 36 ka BP. The fossil assemblage from Møn shows close resemblance to those from other sites with similar ages found in the vicinity of the western Baltic Basin.
... We assume that theriver either drained large parts of Germany, or the Fennoscandian Ice Sheet. In the latter scenario the river might have followed the southem margin of the ice sheet and the so-called urstrom valleys in northem Germany, before the outlet in the southwestem part of the Baltic Sea (Jensen et al. 1997). The delta deposits are found above til1 (Sequence 1) from the last glaciation of the region, and they are divided into two parts (sequence 2 and 3) that are separated by an unconformity. ...
... Apparently, these shells were washed out from the land areas to the south. The silty sediments were deposited at a shore level of 22-23 m b.s.l., corresponding to the threshold between the Arkona Basin (Jensen et al. 1997). According to the sequence stratigraphical terrninology, these coastal deposits belong to sequence 3, B: profile 564016 from Mecklenburg Bay. ...
... Significant Holocene post glacial sea-level variations have led to the flooding of Arkona Basin's western barrier (the Darss Sill), producing 4-5 distinct stratigraphical stages (Björck, 1995). (1) The Baltic Ice Lake stage beginning roughly 13.5 kyr before present (BP) as a result of deglaciation (Jensen, 1995;Jensen et al., 1997). During this stage, evidence points toward probable drainage of Arkona Basin waters through Øresund ( Fig. 1) (Jensen, 1995). ...
... In this study, we assume that the initial HORM deposition in the southwestern Baltic Sea began 8.0 kyr BP (Jensen, 1995;Jensen et al., 1997Jensen et al., , 1999Witkowski et al., 2005). This date is consistent with the averaged date for the Littorina Sea Stage in the Baltic Sea given by Gustafsson and Westman (2002) if one considers this event in Arkona Basin preceded the averaged date for the Baltic Sea by 500 yr. Figure 2 shows a general overview of the two most recent stages of the Baltic Sea and the chronostratigraphy employed in the model. ...
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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.
... The proglacial lakes and the subsequent Baltic Ice Lake (c. 12–10 14 C kyr BP) that formed in the Baltic Sea basin, filled by melt water from the retreating ice sheet, are considered the beginning of the modern Baltic Sea (Jensen et al. 1997; Kabailienė 1999). They were cold freshwater lakes inhabited by sub–arctic flora and fauna. ...
Article
Late Glacial and Holocene subfossil molluscs along the Lithuanian Baltic Sea coast are found in the outcrops of Ventės Ragas Cape and squeezed lagoon gyttja at Nida and in offshore boreholes at Būtingė, north of Klaipėda, Smiltynė, 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 Litorina 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 Būtingė, Melnragė and Smiltynė 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.
... In many palaeogeographical reconstructions, the shallow southern and western parts of the Kattegat are shown as land during the Lateglacial (Jensen et al., 1997(Jensen et al., , 2002bLambeck, 1999). However, until now no Lateglacial non-marine deposits with plant or animal remains have been reported from the Kattegat (M€ orner, 1969;Bennike et al., 2000;Jensen et al., 2002a;Bendixen et al., 2017). ...
Article
Lateglacial submarine lake sediments are reported for the first time from the Kattegat Sea in southern Scandinavia. The Lateglacial sediments were collected from a vibrocore that contained, from top to bottom, Holocene marine muddy sand, Holocene brackish‐water mud, Early Holocene peat with remains of Betula pubescens and telmatic plants, Lateglacial lake deposits that are the focus of this paper, and homogenous sand. Radiocarbon dating of terrestrial plant remains from the Lateglacial sediments gave ages between 12 400 and 12 800 cal a bp, corresponding to the Younger Dryas. The Lateglacial sediments contain remains of Betula nana and other plants indicating a tundra‐like open landscape with dwarf shrub heaths, which is typical for the region. Remains of macrolimnophytes indicate shallow carbonate‐rich, cool lake waters. Remains of larvae of Trichoptera and Chironomidae dominate the invertebrate fauna and indicate a fairly species‐rich fauna. Half of the trichopteran taxa today have their distribution north of Denmark or show a generally northern distribution in Europe. The lake sediments are found at ∼ 24 m below sea level, and the presence of lake sediments shows that this part of Kattegat had not been transgressed by the sea during the Younger Dryas.
... Macrofossils and pollen of Salix are present, probably from the dwarf species Salix polaris or S. herbacea. These species were among the first vascular plants to colonize former glaciated areas in Denmark (Bennike and Jensen, 1995;Jensen et al. 1997;Bennike et al. 2004b) and southern Sweden (Jönsson, 1988). With its capability to grow on unstable raw soil and to withstand low summer temperatures S. polaris was an important pioneer plant (Rønning, 1979;Korsager et al. 2003). ...
... High stands of the water level, interrupted by dramatic drops, were recorded in the Arkona Basin sediments. After the last deglaciation, the first high stand of the water level of −20 m (Jensen et al., 1997) appeared as the Baltic Ice Lake and was interrupted by regressions to a depth of around −40 m: the first at around 12,800 cal BP (Bennike and Jensen, 2013) and the second as final drainage at 11,600 cal BP . The period of the Baltic Ice Lake (BIL) recorded in the Arkona Basin as grey and reddish-brown clay sediments with sandy layers corresponded to the abovementioned drainage events (Moros et al., 2002). ...
Article
A multidisciplinary investigation performed on gravity cores, supplemented by a new radiocarbon dating of macrofossils, outlined the environmental evolution of Arkona Basin in the Holocene. Studies comprising the analysis of diatoms, geochemistry, grain size, and radiocarbon dating clarified the knowledge about the age and environmental changes during freshwater and marine transgressions and regressions. The acoustic profiling method allowed proper interpretation of the analysis results from sediment cores and created a proper lithostratigraphic model of the investigated basin. Baltic Ice Lake and Yoldia Sea sediment layers were identified acoustically and cores penetrated the final regression surface of the Baltic Ice Lake. The analyses of cores concentrated on Ancylus Lake and Littorina Sea sediments. Two phases of the Ancylus Lake stage were identified. The peaks of loss on ignition in the cores, observed as a strong acoustic reflector, were identified as a marker of Ancylus Lake regression between the first, high-water level phase and the second, shallow-water phase. The age of onset of Littorina transgression was estimated at around 7000–7200 cal BP and was younger than some previous estimations. The retrieved age confirmed the suggestion that the marine environment appeared first in Mecklenburg Bay and then after a few hundred years in Arkona Basin as an intensive transgression. The appearance of Littorina Sea revealed a fast shift of the environment from lacustrine to marine. The first phase of the Littorina stage was recognised as a rapidly increasing water level and high-energy environment; the second showed rapidly increasing salinity in the calmer conditions of sedimentation.
... Ice-dammed lakes develop supraglacially, subglacially or ice-marginally and their 43 formation and length of existence are strongly dependent on the dynamics of the ice sheet and 44 the character of the neighboring environment (Carriwick and Tweed, 2013). Well-studied 45 examples of paleo ice-dammed lakes are Lake Agassiz (Laurentide Ice Sheet) which existed 46 for a time period of 4000 years during the last deglaciation, the late Wisconsin Glacier Lake 47 Missoula (Coredellian Ice Sheet), and the Younger Dryas Baltic Ice Lake (Scandinavian Ice 48 Sheet) (e.g., Jensen et al., 1997;Teller et al., 2004;Alho et al., 2010). Such ice-dammed lakes 49 can cover considerable areas and contain huge volumes of water. ...
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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.
... Jensen (1992); Jensen et al. (1997); lemke et al. (1998); lemke, sCHWarzer, and Diesing (2002) have identified five seismostratigraphic units (E1 to E5) in the western Baltic Sea and the area around Rügen. An uppermost till (E1) was incised by late glacial channels, probably filled with glacio-lacustrine sediments (E2) of the early Baltic Ice Lake stage. ...
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The Late Quaternary history of the Baltic Sea is marked by a complex sequence of glacial, lacustrine and marine phases (late Pleistocene, Baltic Ice Lake, Yoldia Lake, Ancylus Lake, Littorina Sea). Boomer data, acquired in October 2004, permitted to improve the knowledge of the late Quaternary geological evolution of Tromper Wiek, a semienclosed bay, located in the north-eastern part of Rügen Island. The sedimentary deposits can be subdivided in 6 seismic units (U1 to U6). The upper part of the lowest unit (U1) corresponds to Pleistocene till. Channels incise the top of this till (surface S2), probably created during the first drainage of the Baltic Sea during the Late Glacial. Subsequent channel filling (U2) occurred in two phases beginning with chaotic deposits, probably fluviatile of origin, followed by graded deposits. This filling was stopped by an erosive period with the formation of surface S3, showing channels at the same location as S2. The facies of the channel filling (U3 and U4), during a second phase, is similar to the first one, but resembles a prograding sediment body, intercalated between the two units in the shallower part. U3 shows a bar-shaped deposit at its top. The facies of U4 is very similar to a barrier/back-barrier facies similar to the facies of unit U5, partly composed of gravel. The deposits of U6 correspond to the post-Littorina Sea deposits. The presence of gravel is linked to coastal cliffs, in which chalk layers, pushed up by glaciers, alternate with sections of till and meltwater deposits and with submarine outcrops of till. Gravel deposits are present in unit U5. They are strongly linked to the presence of a barrier. Four of the six units show a barrier facies (U2, U3, U4 and U5); gravel deposits could be present inside all of these units and would represent a larger deposit than estimated previously.
... 24,25). Die Entwässerung erfolgte über den Öresund in das Kattegat (BJÖRCK 1995, JENSEN et al. 1997. Vor etwa 13 000 Jahren wurden im Arkonabecken bereits -20 m HN erreicht. ...
... The Baltic Sea is one of the largest brackish water bodies on Earth and has several main basins of which the Arkona Basin with a mean water depth of 40-50 m is located in the southwestern part (Fig. 1). Stratigraphic analyses of the late glacial to Holocene sediments show alternating lacustrine and brackish/marine deposits (e.g., Bjö rck, 1995;Sohlenius et al., 1996;Jensen et al., 1997;Moros et al., 2002;Andrén et al., 2011). The changes in salinity are caused by the retreat of the Fennoscandian ice sheet and by opening or closing of gateways to the ocean following the termination of the last glaciation 14,000-13,000 yr BP (years before present). ...
Article
Towards the end of the last deglaciation more than 13,500 years ago the southern Baltic Sea was a freshwater lake, the Baltic Ice Lake, for several thousand years during which iron-rich, organic-poor clay was deposited. The modern brackish-marine stage started about 8600 years ago with the deposition of organic-rich mud, which is today characterized by high rates of sulfate reduction and high concentrations of free sulfide. We studied the iron–sulfur diagenesis in gravity cores from the Arkona Basin, SW Baltic Sea, to track the progressing sulfidization front in the buried Ice Lake sediment. The geochemical zonation was unusual as the sulfate concentration dropped steeply by two thirds below which it increased again due to a deep sulfate reservoir. The reservoir had been established during the early Holocene marine period as sulfate and other seawater ions diffused down into the lake sediment for several thousand years. Sulfur isotope analyses confirmed its origin as seawater sulfate, while its oxygen isotope composition indicated a microbially catalyzed equilibration with ambient interstitial water, decoupled from net sulfate reduction. Today, hydrogen sulfide diffuses from the marine mud down into the lake sediment where a black band with high magnetic susceptibility and high iron monosulfide, greigite and elemental sulfur content shows progressing sulfidization of the large pool of solid-phase reactive iron. Dissolved iron from the deep Ice Lake sediment diffuses up to the sulfide front and provides a small supplement to the solid Fe(III) pool as a sulfide sink. Pyrite formation at the sulfidization front may involve surface-bound zero-valent sulfur while, above the front, polysulfides are in equilibrium with the system hydrogen sulfide – polysulfide – rhombic sulfur and may not be important for further pyrite formation. The Holocene iron–sulfur diagenesis observed in the Arkona Basin represents an important transitional state for post-glacial transgressions with organic-rich marine sediment overlying lacustrine clay, such as in other areas of the Baltic Sea or in the Black Sea.
... Formation IVb is a basin-wide intermediate zone consisting of homogeneous clay that can be related to the first Baltic Ice Lake drainage that occurred during the late Allerød (Fig. 6). This drainage led to a 10-m drop in water level and to the formation of unconformities in the shallow parts of the southwestern Baltic Sea (Jensen et al. 1997;Bennike & Jensen 1998U scinowicz 2006). The relatively deep Bornholm Basin was covered by water even after this drainage event and the unconformity seen in shallow areas is replaced by a basinal correlative conformity. ...
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.
... Initial studies focused on the Fakse Bugt and Gedser Rev region and the history of the Baltic Ice Lake (Jensen & Stecker 1992; Lemke & Kuijpers 1995; Jensen et al. 1997) and were followed by detailed studies of the Ancylus Lake stage (Jensen et al. 1999). Further studies of relative shorelevel changes in the region (Bennike & Jensen 1998) and the Femer Baelt threshold (Lemke et al. 2001) showed that local ice lakes developed in front of the retreating Fennoscandian ice sheet. ...
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The present-day Storebælt (Great Belt), the waterway between the islands of Fyn and Sjælland (Fig. 1), contains deeply incised valleys, locally more than 50 m deep, and is of crucial importance to the water exchange between the fully marine Kattegat and the brackish Baltic Sea. The role of this important gateway changed significantly during the late and post-glacial period (since 15000 B.P.), when the Baltic Basin experienced alternating freshwater, brackish and marine conditions as a result of changes in relative sea level (Figs 2, 3). The importance of the Storebælt in understanding the dynamics of the Baltic Basin is reflected in the large number of studies carried out (see Bennike et al. 2004). The first detailed sedimentological and stratigraphic studies in the Storebælt area that demonstrated the presence of early Holocene freshwater deposits below the seabed were those of Krog (1960, 1965, 1971), who also presented the first shore-displacement curve for the area (Krog 1979).
... Thus the high con- Fig. 3. Geochemical composition of the core EMB1218-3-3 from the Mecklenburg Bay tents of calcium, magnesium, and strontium were related to the clay minerals fluxes (Higgins and Schrag 2010). The unit MB-3-2 of peat gyttja with a high content of organic matter reflected the local lacustrine environment that developed after the final regression of the Baltic Ice Lake (Jensen et al. 1997). A similar peat gyttja layer was not found in the core taken from the deeper part of the Arkona Basin. ...
... The Arkona Basin has a relatively smooth morphology as a result of late and postglacial basin filling with muddy and sandy sediments (Lemke 1998). Detailed information about western Baltic Sea development can be found in Eronen et al. (1990), Jensen (1995, Jensen et al. (1997), Lemke (1998) and Andrén et al. (2000). The central sector is filled with greenish soft organic-rich mud, the organic material originating both from in situ primary production and terrestrial input (e.g. via the Oder River; Miltner and Emeis 2000). ...
Article
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Acoustic profiling methods are widely used to provide a rapid view into geological structures. For the interpretation of acoustic profiling results (single- and multi-beam), reliable geo-acoustic models are needed. Suitable geo-acoustic models covering a wide range of sediment types do not exist to date for the Baltic Sea. Based on surface sediment datasets, geo-acoustic models have been set up for the prediction of acoustical parameters derived from sedimentological data for south-western Baltic Sea surface sediments. Empirical relationships were created to predict key in situ parameters (p-wave velocity, wet bulk density) from sedimentological core data, notably grain density and water content. The Gassmann-Hamilton equations were used to set up a more generic physically based model. For the first time semi-empirical equations for the calculation of the elastic frame modulus and the solid sediment particle modulus were established by an iterative Gassmann-Hamilton fitting procedure. The resulting models have a remarkably good performance with, for example, a calculated sound velocity accuracy of about 17-32 m s-1 depending on model input data. The acoustic impedance of seafloor sediments can be estimated from single-beam echosounding if the contribution of seafloor reflectivity is extracted from the total acoustic signal. The data reveal a strong linkage between acoustic impedance and selected sediment properties (e.g. grain size, water content). This underlines the potential for effective mapping of seafloor sediment properties (e.g. habitat mapping). Furthermore, these geo-acoustic models can be used by marine geologists for a precise linkage between sediment facies identified in longer cores and corresponding acoustic facies recorded by high-resolution seismic profiling in future work.
... These fluctuations completely changed the existing ecosystems, which had to adapt to new environmental conditions. Since the 1990s, complex interdisciplinary studies concerning the reconstruction of the sea level and salinity of the Baltic Sea in the Holocene have been carried out in the Arkona Basin area (Jensen et al. 1997, Lemke et al. 2001, Witkowski et al. 2005. These studies determined the maximal extent of the Baltic Ice Lake, which flooded the Arkona Basin during its high level at 10 300 cal BP. ...
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This article presents the results of diatom studies from three cores taken from the Arkona Basin. The main stages of the Baltic Sea evolution in the Holocene – Ancylus Lake, Mastogloia Sea, Littorina Sea, and Post-Littorina Sea – were identified in diatom assemblages. The transition stage between Ancylus Lake and Littorina Sea, called Mastogloia Sea, was not such a long period as in the Mecklenburg Bay but was essential in the evolution of the Baltic Sea. The most pronounced feature of this period was an increase in the number of halophilous species, which reflected the existence of the littoral environment at the onset of this stage. The appearance and development of halophilous species was stimulated by stepwise inflows of saline waters. The composition of diatom assemblages reflected natural eutrophication of the Baltic Sea during the Littorina Sea stage.
... Glacial till sheets of Weichselian age were formed during several phases of ice decay and re-advances and were subsequently covered by glacial (occasionally varved) clays during the Baltic Ice Lake (BIL) phase in Mecklenburg Bay, the Arkona Basin, and the Bornholm Basin (e.g. Eronen et al., 1990;Hübscher et al., 2010;Jensen et al., 2008;Kögler and Larsen, 1979;Moros et al., 2002;Trimonis et al., 2008), where local lakes were dammed by stagnant ice and merged to the Baltic Ice Lake proper. Because isostatic uplift in the study area took place during that time, the BIL deposits can only be found at considerable water depths (Björck, 1995). ...
Article
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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.
... Bryozoans are an important component of ancient and recent fauna of the Baltic Sea area. Marine bryozoans dominate today whereas freshwater bryozoans are better presented in the past, because of statoblasts of Phylactolaemata are the only known fossils of Bryozoa from the Holocene of the Baltic Sea (JENSEN et al. 1997; BENNIKE et al. 2004). Ecologic preferences of the two bryozoan groups with respect to water salinity determine the main features of the Baltic Sea fauna, such as ecology, distribution, diversity and history of occurrence. ...
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The present study is a short overview of published data concerning the marine and freshwater bryofauna from the Baltic Sea area with focus on their history, ecology, distribution, species list and taxonomy. More than 140 years history of the Baltic Sea studies recorded in the literature were reviewed, and compared with results of our actual research conducted during 2001-2004 in Kiel Bay. One species of marine bryozoans – Electra arctica – was first documented in the Baltic Sea. Some main features of the Baltic bryozoan fauna such as fluctuating occurrences of species in response to oscillations in the hydrographic regime of the Baltic Sea and its open character in respect to Kattegat populations are discussed.
... Units have been identified, which are separated by a sharp uneven erosional unconformity (Bennike et al., 2004a). The older unit is related to melt water drainage of the retreating glacier whereas the younger unit reflects the drainage of the Baltic Ice Lake (Jensen et al. 1997). The Late-glacial Unit in Å rhus Bay is believed to correlate to the younger Great Belt Late-glacial Unit (LG II). ...
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Detailed acoustic mapping have been carried out in the Århus Bay in order to establish the general Late Weichselian and Holocene stratigraphy, and to map the gas related acoustic blanking.The mapping results show that the oldest seismic unit is glacial till, probably related to the latest glacial advance in the region. The glacial till is covered by late-glacial ice-lake clay and silt reaching a thickness of up to 10m. In the deeper part of the bay, early Holocene organic material and peat has been recorded in a few cores. A thin seismic unit is observed, which probably represents an early Holocene lowstand period, when most of the Århus Bay was dry land. The three upper seismic units are related to the Holocene transgression of the region representing different hydrographical conditions. The lowermost unit (Marine unit 1) partly drapes the basin area with clay sediments and partly shows prograding sandy coastal deposits around glacial ridges. Marine shells from this unit date back to 8700cal.yearsBP which are the oldest marine shells found south of the threshold in the northern Great Belt. The next unit (Marine unit 2) consists in general of mud to sandy mud, which cover most of the western central part of the Århus Bay and in some places reach the present seabed in areas of erosion or non-deposition. The distribution of the youngest seismic unit (mud, Marine unit 3) is confined to the sub-recent to recent sedimentation basins in the eastern central part of the area. Acoustical blanking shows that the methane production takes place in the Holocene marine sediments. A map of the distribution and depth to free methane in the muddy sediments has been produced. Combined information from the different seismic equipment used allowed a mapping of the distribution and depth to free gas in the intervals 0.5–2, 2–4 and >4m. The map shows that acoustic blanking is found in the central part of Århus Bay about 4m below the seabed. In areas with high sedimentation rate, the acoustic blanking is found closer to the sediment surface and in selected key stations, pore-water chemistry have documented that depth to acoustical blanking is comparable to the methane saturation depth.Barotropic induced inflow dominates the present current system in the semi-enclosed Århus Bay. The inflow events create turbulence in the outer eastern parts of the bay, followed by high sedimentation rates. The recent situation is reflected in the seabed sediments in the eastern part of the bay, which are characterised as soft sandy mud deposits, with gas bubbles close to the seabed.Seismic investigations have not previously been used to identify recent sedimentation areas and the most vulnerable areas in respect to possible escape of methane and toxic hydrogen-sulphide. The results of the present survey show that future monitoring must be focused in shallow gas areas in the eastern-most part of Århus Bay.
... Jensen (1992); Jensen et al. (1997); lemke et al. (1998); lemke, sCHWarzer, and Diesing (2002) have identified five seismostratigraphic units (E1 to E5) in the western Baltic Sea and the area around Rügen. An uppermost till (E1) was incised by late glacial channels, probably filled with glacio-lacustrine sediments (E2) of the early Baltic Ice Lake stage. ...
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The Late Quaternary history of the Baltic Sea is marked by a complex sequence of glacial lacustine and marine phases (late Pleistocene Baltic Ice Lake Yoldia Like Ancylus Lake Littorina Sea) Boomer data acquired in October 2004 permitted to improve the knowledge of the late Quaternary geological evolution of Tiomper Wick a semi enclosed bay located in the north-eastern part of Rugen Island The sedimentary deposits can be subdivided in 6 seismic units (U1 to U6) The upper part of the lowest unit (U1) corresponds to Pleistocene till Channels incise the top of this till (surface S2) probably created during the fist drainage of the Baltic Sea during the 1 ate Glacial Subsequent channel filling (U2) occurred in two phases beginning with chaotic deposits probably fluviatile of origin followed by graded deposits This filling was stopped by an erosive period with the formation of surface SI showing channels at the same location as S2 The facies of the channel filling (U3 and U4) during a second phase is similar to the first one but resembles a prograding sediment body intercalated between the two units in the shallower part U3 shows a bar shaped deposit at its top The facies of U4 is very similar to a barrier/back barrier facies similar to the facies of unit U5 partly composed of gravel The deposits of U6 correspond to the post Littorina Sea deposits The presence of gravel is linked to coastal cliffs in which chalk layers pushed up by glaciers alternate with sections of till and meltwater deposits and with submarine outcrops of till Gravel deposits are present in unit U5 They tie strongly linked to the presence of a barrier Four of the six units show a barrier facies (U2 U3 U4 and U5) gravel deposits could be present inside all of these units and would represent a larger deposit than estimated previously
... The identification of the seismostratigraphic units extends the scheme of Jensen et al. (1997) and the seismic units are separated as follows: ...
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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
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.
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Denmark has the richest concentration of underwater Stone Age finds in the world, thanks to a combination of factors that include favourable conditions of preservation and a long tradition of professional and amateur interest in underwater prehistory. The majority of finds are from the central areas of the Danish Straits and date back to about 8500 years ago, when rising sea level finally created a marine connection between the North Sea and the Baltic Sea. Most are in shallow water, c. 2–5 m in depth, but sites at greater depth have also been identified. Most fall within the Ertebølle period, between 7400 and 5900 years ago, and include excavations at shoreline settlements such as Tybrind Vig, Ronæs Skov and Møllegabet II. These sites have yielded large assemblages of material including wooden artefacts such as remains of fish weirs, dugout canoes, bows, spear shafts and leister prongs, as well as remains of fibres and woven fabric. These materials owe their excellent state of preservation to the deposition in fine-grained marine sediments alongside settlement areas located on the shoreline, and to subsequent sea-level rise because of marine inundation, which has maintained the material in permanently waterlogged and anaerobic conditions. This chapter examines the conditions that have given rise to this unusual concentration of underwater sites, provides an overview and illustration of some of the most distinctive finds, discusses their wider significance and addresses future challenges.
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
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.
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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.
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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.
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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
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.
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
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.
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.
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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. Different facies within the general near-shore environment, from shallow littoral to moderately deep (10‒20 m) open bay, are represented. All the sediments deposited before 8000 B.P. contain oligohalobous diatom floras normally associated with the Ancylus Lake stage. Between 8000 and 7500 B.P., an interval often singled out as the Mastogloia stage, weakly brackish taxa are regularly introduced into the strictly littoral floras, whereas the floras deposited at the same time in deeper water remain unchanged and consist of ordinary Ancylus taxa. After 7500 B.P. rich brackish floras characteristic of the Litorina stage proper appear at all sites that retained their contact with the Baltic. These results confirm the earlier conclusions based on off-shore data that the Mastogloia stage can only be demonstrated in the littoral facies. Nevertheless, in view of its consistent and non-local occurrence after but not before a certain time point, this stage is considered to reflect a general change in conditions in the Baltic Sea history; 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.
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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.
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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
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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.
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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.
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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.
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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.
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A conceptual framework for understanding the effects of eustatic control on depositional stratal patterns is presented. Eustatic changes result in a succession of systems tracts that combine to form sequences deposited between eustatic-fall inflection points. Two types of sequences have been recognized: 1) a type 1 sequence, which is bounded at the base by a type 1 unconformity and at the top by either a type 1 or type 2 unconformity and has lowstand deposits at its base, and 2) a type 2 sequence, which is bounded at the base by a type 2 unconformity and at the top by either a type 1 or type 2 unconformity and has no lowstand deposits. Each sequence is composed of three systems tracts; the type 1 sequence is composed of lowstand, transgressive-, and highstand systems tracts, and the type 2 sequence is composed of shelf-margin, transgressive-, and highstand systems tracts. The type 1 sequence is associated with stream rejuvenation and incision at its base, whereas the type 2 sequence is not. Eustacy and subsidence combine to make the space available for sediment to fill. The results of this changing accommodation are the onlapping and offlapping depositional stratal patterns observed on basin margins -from Authors
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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.
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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
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
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
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
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.
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
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
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
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
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
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.