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  • 1. Gerok, Dmitrij
    et al.
    Gelumbauskaite, Leonora Zivile
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Grigelis, Algimantas
    Bitinas, Albertas
    New data on the palaeo-incisions network of the south-eastern Baltic Sea2014In: Baltica: an International Yearbook for Quaternary Geology and Palaeogeography, Coastal Morphology and Shore Processes, Marine Geology and Recent Tectonics of the Baltic Sea Area, ISSN 0067-3064, E-ISSN 1648-858X, Vol. 27, no 1, p. 1-14Article in journal (Refereed)
    Abstract [en]

    The present study area is located within the south-eastern segment of the Baltic Sea framed by 55 degrees 30'-56 degrees 30' N and 19 degrees 00'-21 degrees 15'E. The area is re-visited with the aim to describe in more detail the geologic prerequisite for development of the palaeo-incisions as well as the timing of their subsequent infillings. The channels form distinctive features in the sedimentary bedrock along the outer limits of pre-Weichselian ice sheets, on average reaching depths into the bedrock of 50 m in the nearshore zone of Lithuania to 100 m along the slope to the Gotland depression in the west. The development of palaeo-incisions system is governed by the easily eroded late Palaeozoic to Mesozoic bedrock of the present area. Only rare occurrences of channels have been reported from the middle and lower parts of the Palaeozoic further west in the Baltic. The present investigation supports a mechanism that the channels formed below the ice near the ice sheet margin by melt water erosion under high pressure. The channels start at random where a fracture in the ice develops forming outlet of water contained below the central part of the ice sheet. The channels often merge together in the direction of the ice margin, possibly gradually adapting to previous fracture systems in the bedrock. The investigated incisions were infilled prior to the advance of the Weichselian ice sheet and some have been reopened and repeatedly infilled.

  • 2.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Multiple re-advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat, south-central Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 4, p. 619-637Article in journal (Refereed)
    Abstract [en]

    Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice-sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high-resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74-m sediment record recently acquired by drill coring, and with onshore LiDAR-based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying > 120-m deglacial sequence. Three distinct retreat-re-advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re-advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag-and-tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north-central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a(-1). The pronounced topography of the Vättern basin and its deep proglacial-dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier.

  • 3.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björck, Svante
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lif, Arne
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koyi, Hemin
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Major earthquake at the Pleistocene-Holocene transition in Lake Vattern, southern Sweden2014In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, no 5, p. 379-382Article in journal (Refereed)
    Abstract [en]

    Lake Vattern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vattern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake floor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vattern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infillings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vattern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the significance of glacio-isostatic unloading.

  • 4.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Anderson, Leif
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björk, Göran
    Cronin, Thomas M.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    Mayer, Larry
    Noormets, Riko
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Ananiev, Roman
    Barrientos Macho, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cherniykh, Denis
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gemery, Laura
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Jerram, Kevin
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Khortov, Alexey
    Mohammad, Rezwan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Semiletov, Igor
    Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10365Article in journal (Refereed)
    Abstract [en]

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions41-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (similar to 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  • 5. Suuroja, Sten
    et al.
    Suuroja, Kalle
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A comparative analysis of two Early Palaeozoic marine impact structures in Estonia, Baltic Sea: Neugrund and Kardla2013In: Bulletin of the Geological Society of Finland, ISSN 0367-5211, Vol. 85, p. 83-101Article in journal (Refereed)
    Abstract [en]

    Kardla and Neugrund are two Early Palaeozoic offshore impact structures located some 50 km apart along the Estonian coast of the Baltic Sea. They share many similarities but differing features are also found. The Kardla impact structure is located at the NE coast of Hiiumaa Island (58 degrees 58'N, 22 degrees 46'E). The inner crater has a 4 km rim-to-rim diameter and a c. 130 m high central uplift, surrounded by a ring fault, c. 12 km in diameter. The well-preserved buried inner crater is outlined in the landscape by a circular ridge of uplifted bedrock. The perimeter of the outer crater is outlined on the seafloor by a semicircular ridge of narrow shoals. The variable height of the rim wall (50-240 m above the crystalline basement level) and the asymmetric location of the inner crater is obviously a result of an oblique impact in a layered target and partial collapse of the rim wall. Shortly after the impact in a shallow epicontinental sea during Late Ordovician time (c. 455 My), calcareous biodetritic muds were deposited and the crater was buried. The Neugrund impact structure is located in the seabed at the entrance of the Gulf of Finland (59 degrees 20'N, 23 degrees 31'E). The inner crater has a 7 km rim-to-rim diameter and the outer limit of the structure passes through the Osmussaar Island to the southwest of the impact centre. The crater was buried in a shallow epicontinental sea with siliciclastic deposition shortly after the impact at Early Cambrian time, c. 535 My. It was partially re-exposed by erosion during Pliocene. The target had a three-layered composition: Precambrian metamorphic rocks covered by Ediacaran and Early Cambrian siliciclastic rocks (c. 150 m) and water (c. 100 m). The structure has been studied with seismoacoustic and sidescan sonar profiling, and by diving and sampling of submarine outcrops. Several hundred samples of impact breccias have been collected and investigated from erratic boulders distributed by glacial action in the west Estonian mainland, islands and sea floor.

  • 6.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Regional deglaciation and postglacial lake development as reflected in a 74m sedimentary record from Lake Vättern, southern Sweden2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, p. 336-354Article in journal (Refereed)
    Abstract [en]

    The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vattern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vattern have been available. Here, we present the results from a unique, 74m borehole in southern Lake Vattern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (approximate to 13.8-13.4cal.kaBP). After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vattern basin (approximate to 13.0cal.kaBP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Allerod.

  • 7. Tsyrulnikov, Arkady
    et al.
    Tuuling, Igor
    Kalm, Volli
    Hang, Tiit
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Late Weichselian and Holocene seismostratigraphy and depositional history of the Gulf of Riga, NE Baltic Sea2012In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 41, no 4, p. 673-689Article in journal (Refereed)
    Abstract [en]

    The Lateglacial and postglacial sequence in the northern Gulf of Riga is sedimentologically subdivided into nine distinctive layers. In the seismo-acoustic sequence these layers are correlated with seven seismic/acoustic units, which largely reflect different stages in the development of the Baltic Sea. A uniform layer of the Late Weichselian till, a layer of waterlain glacial diamicton (WGD), a varved succession of the Baltic Ice Lake, a brackish-water/freshwater sandy/silty clay of Yoldia Sea, a FeS-rich layer of Ancylus Lake and discordantly bedded sand of the Litorina Sea and present-day gyttja are revealed both in sediment cores and in acoustic recordings. In general, the lateral extent of the distinguished sediment layers is gradually shrinking upwards in the Quaternary sequence towards the deepest, central depression of the gulf. Two distinguished regional discontinuities divide the Lateglacial and postglacial sediment sequence into three allounits: glacial diamicton deposits in the lower part; ice-proximal WGD, glaciolacustrine and postglacial lake/marine deposits in the middle; and brackish-water marine deposits in the uppermost part of the sequence. The presented detailed seismostratigraphic subdivision of the Quaternary sediment sequence of the Gulf of Riga permits a correlation/comparison with similar sequences across the Baltic Sea and in other former glaciated basins.

  • 8. Tuuling, Igor
    et al.
    Floden, Tom
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland: subdivision, thicknesses and correlation, based on marine seismic studies2009In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 267, no 02-jan, p. 55-70Article in journal (Refereed)
    Abstract [en]

    The Llandovery-lowermost Wenlock sequence in the Baltic Sea between Saaremaa and Gotland has been studied by means of high resolution seismic reflection profiling. The number and the positions of the seismic reflectors within this sequence change considerably even within short distances, thus showing a high lateral inconsistency both in lithology and thickness. Stratigraphically two unambiguous (S-1 and S-2) and two roughly fixed trans-Baltic seismic reflectors (S-5 and S-7) enabled us to distinguish the pre-Adavere, the Adavere (S-1-S-2 and S-2-S-5) and the Mustjala seismic units (S-5-S-7) and to follow their east-westerly changes across the Baltic. The seismic signatures and thicknesses of these units undergo a sharp transformation midway Baltic, dividing between the Saaremaa type and the Gotland type of Llandovery-lowermost Wenlock sections. This is due to a short and steep northeast-southwest facies transect that was induced by a well differentiated bathymetry in the intracratonic Palaeobaltic basin, thus clearly distinguishing the shallow-shelf (basinal), the slope (transitional) and the deep-shelf (basinal) areas. The slope is furthermore accentuated by the intensive submarine erosion and channelling during the Late Ordovician and Early Silurian times. Thus, the Saaremaa type of section includes the inner to outer shallow-shelf transect, where the pre-Adavere and Adavere units are decreasing in thickness, and the Mustjala unit is increasing in thickness towards Gotland. In the slope area offshore Gotland, all the Llandovery-lowermost Wenlock units thin out rapidly towards the deep-shelf area in south to southeast and the thickness of the pre-Adavere and Adavere units approach zero. Similar features of submarine erosion on Gotland and around the Estonian Latvian border reveal that an unstable basinal slope, from the point of sediment accumulation, extended over large areas along the shallow-shelf edge of the Palaeobaltic basin during the latest Ordovician and earliest Silurian times. Seismic data suggest that the uppermost unidentified subsurface of the Silurian succession in northern Gotland includes a considerable amount of marlstone layers that are coeval with the Mustjala Member in Estonia. 

  • 9. Tuuling, Igor
    et al.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seismic correlation of Palaeozoic rocks across the northern Baltic Proper - Swedish-Estonian project since 1990, a review2009In: EST J EARTH SCI, ISSN 1736-4728, Vol. 58, no 4, p. 273-285Article in journal (Refereed)
    Abstract [en]

    After a short historical review of the correlation of Palaeozoic rocks between Estonia and Sweden, this paper focuses on the results of marine seismic studies, achieved during the cooperative Swedish-Estonian project since 1990. The most recent seismic correlation scheme of the Cambrian, Ordovician, and Silurian strata and their distribution at the seafloor across the northern Baltic Proper are presented. Thickness changes and trends, as well as the sedimentary structures, reef bodies, and erosional features of different seismic units, are treated in connection with structural and facies changes in the Palaeobaltic Basin. The immediate background of this project is outlined and the locations of the seismic lines shot during the joint expeditions to the Baltic Sea are shown.

  • 10. Tuuling, Igor
    et al.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Seismic stratigraphy, architecture and outcrop pattern of the Wenlock-Pridoli sequence offshore Saaremaa, Baltic Sea2011In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 281, no 1-4, p. 14-26Article in journal (Refereed)
    Abstract [en]

    The Wenlock-Pridoli sequence has been subdivided and mapped offshore Saaremaa in the Baltic Sea by means of high resolution seismic reflection profiling. The most striking and consistent seismic reflectors correlate with contrasting lithological boundaries of the Silurian regional stages, the Jaani/Jaagarahu (S(8)), the Jaagarahu/Rootsikula (S(10)), the Rootsikula/Paadla (S(11)). the Paadla/Kuressaare (S(12)), the Kuressaare/Kaugatuma (S(13)) and the Kaugatuma/Ohesaare (S(14)) stages, which often coincide with erosional disconformities on Saaremaa. The shallow-shelf Silurian sequence that crops out on Saaremaa is also exposed in the closest offshore area of the island. Due to the westerly to south-westerly increasing erosional cut below the Baltic, the deeper facies varieties that are concealed in southern Saaremaa, are revealed and exposed at the seafloor towards Gotland. This is particularly well expressed in the Jaagarahu Stage, which undergoes a fades change with significant increase in thickness on the basinal slope of the Baltic Silurian Basin, both onshore and offshore Saaremaa. The Silurian sequence overlying the Jaagarahu Stage does not show any considerable thickness or fades changes neither below nor offshore Saaremaa. Offshore Saaremaa, seismic reflectors limiting new deeper facies subunits in the Jaagarahu Stage become either successively or simultaneously exposed inside the Vilsandi (S(8)-S(9)) respectively the Maasi-Tagavere (S(9)-S(10)) seismic units towards Gotland. These outcrop patterns were largely formed by two different erosional agents that during different time periods have played a considerable role in the formation of the present day Baltic Sea depression. Hence, the gradually south-westerly deepening cuesta landscape formed by the Cenozoic erosion, namely the Silurian Klint and the plateaus north and south of it, discloses progressively deeper part of the Baltic Silurian Basin. The deeper facies subunits are exposed rapidly by the submeridional erosional incisions of the Pleistocene glaciers. Except for the erosional component, there appears also a distinct tectonic factor in the genesis of the present Baltic Sea depression. Today, the coeval Silurian rocks that once were formed in separate facies belts, i.e. in different depth intervals of the same sedimentary basin on Saaremaa and on Gotland, are presently located at about equal altitude.

  • 11. Tuuling, Igor
    et al.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Silurian reefs off Saaremaa and their extension towards Gotland, central Baltic Sea2013In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 150, no 5, p. 923-936Article in journal (Refereed)
    Abstract [en]

    The Silurian reefs off Saaremaa in the Baltic Sea were studied by means of high-resolution seismic reflection profiling. The abundance and diversity of the reefs increases off Saaremaa concomitantly with the deepening of the Baltic Silurian Basin towards Gotland. The peak of the reefs around Saaremaa occurred during the Middle Wenlock. The reef facies retreated further off Saaremaa during the Late Wenlock, became episodically restored around the island during the early Ludlow and finally ceased during the late Ludlow. A similar SW-NE-SW migration of reefs reflects an alternating transgressive-regressive pattern in the nearshore shallow shelf environment, where already minor sea-level fluctuations strongly influenced the conditions for reef growth. During the early Wenlock, a bathymetric break with a large barrier-reef-like structure divided the shallow shelf offshore Saaremaa facially into back-reef and southerly sloping fore-reef areas. The width of this SW-migrating barrier (c. 8 km) and the extent of reef bodies within it (c. 4 km) are the largest known in the Baltic region. During the Silurian, the reefs between Saaremaa and Gotland were flourishing to a much larger extent than is visible today. The primary Silurian reef pattern was increasingly destroyed towards Gotland by later erosion. This has resulted in a large area void of Wenlock reefs off northern Gotland. Off southern Gotland, the narrow conical low-energy deeper-water reefs prevail, as the wave-agitated shallow-water facies with larger and lenticular Wenlock and Ludlow reefs are largely eroded around the Gotland Deep.

  • 12. Tuuling, Igor
    et al.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The Baltic Klint beneath the central Baltic Sea and its comparison with the North Estonian Klint2016In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 263, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Along its contact with the Baltic Shield, the margin of the East European Platform reveals a well-developed, flooded terraced relief. The most striking and consistent set of escarpments at the contact of the Lower Palaeozoic calcareous and terrigenous rocks, known as the Baltic Klint (BK), extends from northwest of Russia to the Swedish island of Oland. Marine seismic reflection profiling in 1990-2004 revealed the central Baltic Sea Klint (BSK) section in detail and enabled comparison of its geology/geomorphology with a classical klint-section onshore, namely the North Estonian Klint (NEK). The conception of the BK onshore, which is based on the land sea separating terraced relief in northern Estonia, is not fully applicable beneath the sea. Therefore, we consider that the BSK includes the entire terraced Cambrian outcrop. We suggest the term Baltic Klint Complex to include the well-terraced margin of the Ordovician limestone outcrop, which is weakly developed in Estonia. Because of a steady lithological framework of the bedrock layers across the southern slope of the Fennoscandian Shield, the central BSK in the western and the NEK in the eastern part of the Baltic Homocline have largely identical morphologies. The North Estonian Ordovician limestone plateau with the calcareous crest of the BK extends across the central Baltic Sea, whereas morphological changes/variations along the Klint base occur due to the east-westerly lithostratigraphic/thickness changes in the siliciclastic Cambrian sequence. The verge of the NEK, located some 30-50 m above sea level, starts to drop in altitude as its east-westerly course turns to northeast southwest in western Estonia. Further westwards, the BK shifts gradually into southerly deepening (0.1-0.2 degrees) layers as its crest drops to c. 150 m below sea level (b.s.l.) near Gotska Sandon. This course change is accompanied by a considerable decrease in thickness of the platform sedimentary cover, as below the central Baltic Sea the stratal sequence is 150-250 m thinner than in northern Estonia. This has facilitated a deviation of the terraced relief-forming Cenozoic rivers traversing east-westerly across the southern slope of the Fennoscandian Shield and forming different morphostructures in its eastern and western parts. Thus, a low-lying central Baltic Sea depression with well-developed asymmetrical cuesta valleys and terraces occur in the western half of the Baltic Homocline. In its eastern part, however, the only explicitly shaped cuesta valley along the shield-platform boundary forms a narrow east-westerly branch/gulf of the Baltic Sea (Gulf of Finland). The well-terraced southern margin of this gulf runs along the contact of the outcropping terrigenous and calcareous rocks, rises above the sea and forms a complex landform known as the NEK.

  • 13.
    Tuuling, Igor
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    The Ordovician-Silurian boundary beds between Saaremaa and Gotland, Baltic Sea, based on high resolution seismic data.2007In: Geological Quaternarly, Vol. 51, no 3, p. 217-229Article in journal (Refereed)
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