Explore the vast range of titles available.

Analysis of data published on basement faulting in the Baltic region makes it possible to distinguish the >700 km long East European Craton (EEC) interior fault zone extending from the Leba Ridge in the southern Baltic Sea across the Latvian cities of Liepaja and Riga to Pskov in Russia (LeRPFZ). The complex geometry and pattern of its faults, with different styles and flower structures, suggests that the LeRPFZ includes a significant horizontal component. Exceptionally high fault amplitudes with signs of pulsative activities reveal that the LeRPFZ has been acting as an early Palaeozoic tectonic hinge-line, accommodating bulk of the far-field stresses and dividing thus the NW EEC interior into NW and SW halves. The LeRPFZ has been playing a vital role in the evolution of the Baltic Ordovician–Silurian Basin, as a deep-facies protrusion of this basin (Livonian Tongue) extending into the remote NW EEC interior adheres to this fault zone. The Avalonia–Baltica collision record suggests that transpression with high shear stress, forcing the SE blocks in the LeRPFZ to move obliquely to the NE, reigned in the Ordovician. In the Silurian, the LeRPFZ with surrounding areas became increasingly affected by Laurentia–Baltica interaction and compression from the NW, while the orogenic load by Avalonia–Baltica collision flexed the foreland basin along the NW margin of the EEC. As a highly mobile basement flaw liable to differentiated tectonic movements, the LeRPFZ has experienced tectonic inversion in accordance with the stress-field changes induced by Avalonia–Baltica–Laurentia interaction. Being an axial area of the Livonian Tongue in Ordovician–early Silurian time, by the Devonian, due to the progressing Caledonian Orogeny and growing compression from the NW, the LeRPFZ became the most uplifted and intensively eroded zone in the NW EEC interior.

Located in the interior of the East European Craton (EEC), the Baltic Ordovician–Silurian Basin hosts an elongated tongue-like deep-marine depression, the Livonian Tongue (LT), which extends from Sweden across Latvia and separates the Estonian and Lithuanian shallow-marine shelves. The tectonic origin of the LT has been suggested already since its discovery in the early 1960s. However, the nature of tectonic forces and mechanisms behind the evolution of this narrow intracratonic subsidence zone in the Ordovician–Silurian of the Baltic Basin has remained poorly understood. The origin of the LT can be related to an extensive intracratonic dislocation zone known as the Leba Ridge–Riga–Pskov Fault Zone (LeRPFZ) that coincides largely with the axis of the LT. The LeRPFZ reveals some heavily uplifted basement blocks and has, therefore, been considered as an up-warped anticline-type structure. Recent studies show that the LT has developed in highly complex and changing stress field conditions during the Caledonian orogeny. The subsidence and widening phase of the LT in the Ordovician and early Silurian coincides with, and was possibly governed by, the Avalonia collision with Baltica from the SW when high shear stress forced LeRPFZ blocks to move obliquely towards the NE. As Laurentia was approaching Baltica and finally collided with it in the mid-Silurian, the shear stress became progressively mingled with compression from the NW and the subsidence of the LeRPFZ became reversed, triggering LT withdrawal to the SW. Thus, being once the deep-water centre of the Baltic Ordovician–Silurian Basin, the LT became the most uplifted and intensely eroded EEC interior zone by the Devonian.

Bedrock relief with the basics (subdivision and thickness) of the overlying Quaternary sequence was studied by means of seismo-acoustic profiling beneath the Suur Strait in the West Estonian Archipelago. Reaching ca 15–20 m below sea level (b.s.l.) in the watershed area in the NE corner of the Gulf of Riga, the bedrock surface beneath the strait drops along two channels, divided by the islet of Kesselaid rising ca 15 m above sea level (a.s.l.), into a large depression more than 60 m b.s.l. in the interior of the Väinameri. A similar setting indicates that the low-lying bedrock surface between the Estonian mainland and the islands of Muhu and Saaremaa was formed by combining erosions of preglacial river(s) and Pleistocene glaciers. The large depression NW of the islet of Kesselaid possibly represents a section of an east-west running preglacial river, heavily reworked by Pleistocene glaciers. Although supported by preliminary data from the Soela Strait, the latter opinion still needs additional profiling between the islands of Hiiumaa and Saaremaa. The thickness of the Quaternary sequence around the strait follows the general height and ruggedness of the bedrock surface; it is occasionally missing in the nearshore bedrock plateaus (submarine alvars) and reaches ca 50 m in the depression NW of Kesselaid.

This paper represents one output of the extensive seismo-acoustic profiling performed by the Estonian Geological Survey in the Väinameri, the shallow sea in the West Estonian Archipelago, during the geological mapping conducted in 2019–2022. Based on recordings from boomer-type sound transmitters, this study describes and analyses the bedrock relief to assess a prior suggestion that there exists a NE–SW trending pre-Quaternary river valley traversing the Väinameri, extending across the central Baltic Sea. The bedrock relief map and 3D model reveal a valley-like structure with distinctive cuesta elements crossing the central Väinameri. The cuesta plateau, along with the cuesta escarpment (Silurian Klint) that emerges faintly in the Bay of Matsalu, has been substantially reshaped by Pleistocene glaciers around the Muhu depression in the very centre of the Väinameri and is best preserved between Saaremaa and Hiiumaa islands. The general drainage pattern also points towards a fluvial erosion component in shaping the bedrock depression below the Väinameri. Despite that, the age and genesis of this valley-like feature with the Silurian Klint below the Väinameri remain open. The hypothesis that a pre-Quaternary Eridanos River System might have eroded these bedrock structures contradicts the altitude of the klint base below the Baltic Sea, which remains far below the presently estimated reach of the Eridanos fluvial erosion. Further studies are needed to specify the possible genesis and age of the klints and buried bedrock valleys in Estonia, which, in many aspects, reveal the characteristics of pre-Quaternary fluvial denudation rather than Pleistocene glacial erosion.

Analysis of data published on basement faulting in the Baltic region makes it possible to distinguish the >700 km long East European Craton (EEC) interior fault zone extending from the Leba Ridge in the southern Baltic Sea across the Latvian cities of Liepaja and Riga to Pskov in Russia (LeRPFZ). The complex geometry and pattern of its faults, with different styles and flower structures, suggests that the LeRPFZ includes a significant horizontal component. Exceptionally high fault amplitudes with signs of pulsative activities reveal that the LeRPFZ has been acting as an early Palaeozoic tectonic hinge-line, accommodating bulk of the far-field stresses and dividing thus the NW EEC interior into NW and SW halves. The LeRPFZ has been playing a vital role in the evolution of the Baltic Ordovician–Silurian Basin, as a deep-facies protrusion of this basin (Livonian Tongue) extending into the remote NW EEC interior adheres to this fault zone. The Avalonia–Baltica collision record suggests that transpression with high shear stress, forcing the SE blocks in the LeRPFZ to move obliquely to the NE, reigned in the Ordovician. In the Silurian, the LeRPFZ with surrounding areas became increasingly affected by Laurentia–Baltica interaction and compression from the NW, while the orogenic load by Avalonia–Baltica collision flexed the foreland basin along the NW margin of the EEC. As a highly mobile basement flaw liable to differentiated tectonic movements, the LeRPFZ has experienced tectonic inversion in accordance with the stress-field changes induced by Avalonia–Baltica–Laurentia interaction. Being an axial area of the Livonian Tongue in Ordovician–early Silurian time, by the Devonian, due to the progressing Caledonian Orogeny and growing compression from the NW, the LeRPFZ became the most uplifted and intensively eroded zone in the NW EEC interior.

Located in the interior of the East European Craton (EEC), the Baltic Ordovician-Silurian Basin hosts an elongated tongue-like deep-marine depression, the Livonian Tongue (LT), which extends from Sweden across Latvia and separates the Estonian and Lithuanian shallow-marine shelves. The tectonic origin of the LT has been suggested already since its discovery in the early 1960s. However, the nature of tectonic forces and mechanisms behind the evolution of this narrow intracratonic subsidence zone in the Ordovician-Silurian of the Baltic Basin has remained poorly understood. The origin of the LT can be related to an extensive intracratonic dislocation zone known as the Leba Ridge-Riga-Pskov Fault Zone (LeRPFZ) that coincides largely with the axis of the LT. The LeRPFZ reveals some heavily uplifted basement blocks and has, therefore, been considered as an up-warped anticlinetype structure. Recent studies show that the LT has developed in highly complex and changing stress field conditions during the Caledonian orogeny. The subsidence and widening phase of the LT in the Ordovician and early Silurian coincides with, and was possibly governed by, the Avalonia collision with Baltica from the SW when high shear stress forced LeRPFZ blocks to move obliquely towards the NE. As Laurentia was approaching Baltica and finally collided with it in the mid-Silurian, the shear stress became progressively mingled with compression from the NW and the subsidence of the LeRPFZ became reversed, triggering LT withdrawal to the SW. Thus, being once the deep-water centre of the Baltic Ordovician-Silurian Basin, the LT became the most uplifted and intensely eroded EEC interior zone by the Devonian.

This paper represents one output of the extensive seismo-acoustic profiling performed by the Estonian Geological Survey in the Vainameri, the shallow sea in the West Estonian Archipelago, during the geological mapping conducted in 2019-2022. Based on recordings from boomer-type sound transmitters, this study describes and analyses the bedrock relief to assess a prior suggestion that there exists a NE-SW trending pre-Quaternary river valley traversing the Vainameri, extending across the central Baltic Sea. The bedrock relief map and 3D model reveal a valley-like structure with distinctive cuesta elements crossing the central Vainameri. The cuesta plateau, along with the cuesta escarpment (Silurian Klint) that emerges faintly in the Bay of Matsalu, has been substantially reshaped by Pleistocene glaciers around the Muhu depression in the very centre of the Vainameri and is best preserved between Saaremaa and Hiiumaa islands. The general drainage pattern also points towards a fluvial erosion component in shaping the bedrock depression below the Vainameri. Despite that, the age and genesis of this valley-like feature with the Silurian Klint below the Vainameri remain open. The hypothesis that a pre-Quaternary Eridanos River System might have eroded these bedrock structures contradicts the altitude of the klint base below the Baltic Sea, which remains far below the presently estimated reach of the Eridanos fluvial erosion. Further studies are needed to specify the possible genesis and age of the klints and buried bedrock valleys in Estonia, which, in many aspects, reveal the characteristics of pre-Quaternary fluvial denudation rather than Pleistocene glacial erosion.

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.