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The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied.
INTRODUCTION
The specific features of modern geodynamic movements in Northwest Russia, including shelf seas surrounding the Baltic Shield, are currently being discussed and represent a relatively new problem.
Some researchers insist that these processes manifested themselves both in the entire Quaternary stage of regional development and in the Late Neopleistocene and Holocene [2, 5‒7, 10, 11, 21‒24, 29, 34, 37, 45, 47, 49, 55, 56, 64].
Other researchers deny the significant influence of block neotectonic movements on the formation of the modern relief, giving preference to gouging and isostatic processes during the development of ice sheets [1, 13, 48–50, 63].
Particularly clear views on isostasy as a leading factor in modern vertical movements are being developed in Norway [53]. However, for the Baltic (Fennoscandian) Shield, numerous manifestations have been revealed of both neotectonic processes (rectilinear areas of the relief, vast areas of development of the structurally predetermined relief), and direct evidence of tectonic events in the Holocene—primarily, numerous seismic dislocations established both in the north and other regions of Karelia [11, 20, 45].
The implementation of new methods of geophysical research, including high-resolution multichannel seismoacoustic profiling and multibeam echo sounding, have shown that many features of the relief and Quaternary cover of glacial shelf seas, which include the Barents Sea, White Sea, and part of the Kara Sea, are associated not only with neotectonic movements; they also manifest themselves precisely in the Holocene, including the second half of this period.
As well, seismotectonic processes are triggers for underwater gravitational processes, which significantly affect the distribution of bottom sediments.
The aim of this article is to study the influence of modern geodynamic processes on the geomorphology of the seabed and lithology of bottom sediments of the White Sea, where we have conducted research for many years, participating in marine geological surveys and thematic research.
GEOLOGICAL SETTING
Western Arctic Shelf
The marginal seas (Barents and Kara), as well as intrashelf seas (White and Baltic) in Northwest Russia are glacial shelf seas, i.e., a shelf that was covered by continental and shelf glaciers in the Quaternary [31].
The White Sea Basin is part of the structure of the eponymous sea basin; it is the northern part of the sea and has the shape of a funnel. The structure of the White Sea Basin includes (Fig. 1):
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Fig. 1.
Sketch map of study region (after [66], modified).
— The Central Basin, along with Kandalaksha, Onega, and Dvina bays;
— the White Sea Gorlo Strait;
— the Voronka Inlet (a structure that is the funnel-shaped, northern part of the White Sea, with the cone facing the Barents Sea, with the outer zone of the cone being called the White Sea Voronka Inlet).
It is assumed that the contour of the modern White Sea depression is predetermined by a system of Riphean grabens that formed on the passive margin of the Baltica Paleocraton in 1263–1080 Ma ago [5].
This depression predetermined the position and morphology of Kandalaksha Bay, the most northwestern and deep-water, which today is a deep-sea trench with steep walls. Its formation is associated with activation of faults along the Riphean grabens in the Quaternary.
The final formation of this morphostructure was determined by two factors: endogenic tectonic stresses directly in the considered part of the Baltic Shield, as well as dynamic loads associated with the development and degradation of the Scandinavian glacier [5]. This activation is also observed in present day. A significant, the deepest, part of this trench is filled with a thick layer of Riphean sandstones [4].
The Barents Sea is also characterized by large structural faults.
M.L. Verba [5, 8] indicated the rift-related nature of deep faults of the Barents–Kara shelf. The formation of both the largest sedimentary basins in the northern and southern parts was associated with deep faults of the Barents Sea and the distribution of the main morphological forms of the Barents Sea inherited from a system of ancient rifts—trenches and uplifts separating them [8].
Research conducted on the Western Arctic shelf by GIN RAS (Moscow, Russia) together with JSC MAGE (Murmansk, Russia) clearly linked modern neotectonic activity to the position of moving blocks in the upper mantle and the deep fault network, which reach the seabed surface [39].
The close relationship between ancient faults and those activated in the Quaternary led to dissection of the seabed surface relief characteristic of the Western Arctic shelf (and uncharacteristic of shelf seas). This relationship can be seen in digital models of the Barents and White seas recently compiled at the Shirshov Institute of Oceanology of the Russian Academy of Sciences (IO RAS, Moscow, Russia) (Fig. 2).
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Fig. 2.
Bottom relief of White Sea (after [19]).
The nature of the relief largely determines both the distribution of Quaternary and modern bottom sediments and the direction of sedimentation processes. The steep slopes of the modern deep-sea basin of Kandalaksha Bay determine the development gravitational processes on the slopes [31].
The presence of trenches on the Barents–Kara shelf is the reason for the appearance of glacioturbidites on their slopes, which arose during the deglaciation of shelf areas [15, 30].
The distribution of Quaternary sediments on the bottom of the Western Arctic seas is also influenced by the direction of neotectonic movements in the Late Quaternary. The ongoing isostatic uplift of the Barents Sea bed leads to a sharp reduction in the thickness of Quaternary sediments, primarily modern nepheloid marine sediments [37, 42].
In the White Sea, neotectonic uplift of the block of the Kola Peninsula and accompanying subsidence of the axial part of Kandalaksha Bay leads predominantly to the formation at depths of up to 50–60 m of a cover of thin perluvium, formed during the erosion of glacial–marine and glacial deposits [31].
Thus, we see a close relationship between the geological structure of the seas of the glacial zone and specific features in the formation of the Quaternary cover, as well as with bottom sediments directly overlying the seabed surface.
MATERIALS AND METHODS
Specific Features of Modern Geodynamic Processes in the Western Arctic Seas
The widespread concept of neotectonics, firmly established in the geology of Quaternary deposits, implies the study of tectonic movements in the crust and lithosphere that occurred in the Late Cenozoic (~35 Ma) and continue at the present stage of evolution of territories. These are vertical movements that are multidirectional in nature and lead to uplift or subsidence of the Earth’s surface.
In Northwest Europe, these are predominantly upward movements of the Baltic (Fennoscandian) Shield, compensated by subsidence of the crust in the countries of Central Europe, in particular, Holland.
These movements in northern regions that experienced Quaternary glaciation are overprinted by isostatic movements associated with subsidence of the Earth’s surface under the weight of a glacier and compensatory uplift after removal of the glacial load.
All these movements are very slow and have a long-term effect. In addition to direct instances of seismic phenomena, an example of which may be the Kaliningrad earthquake in 2004 [25] or the Teriber earthquake in 1917 [23], there is an ever-increasing body of data on earthquakes in platform areas, as evidenced by numerous seismic dislocations discovered in Karelia and on the Kola Peninsula [20, 44].
Therefore, it became necessary to introduce a definition for the neotectonic stage of development of the crust—modern geodynamic movements. This definition refers to movements of the Earth’s surface in real time, which usually correlates with the Holocene stage of evolution of territories, i.e. the last 10–12 ka [14]. Such a conceptual definition existed before, but it mainly covered high-precision measurements of displacement of the Earth’s surface using geodetic methods. However, recently, this concept has been increasingly augmented with data on geodynamic transformations of the crust (ruptures, seismic shocks, etc.).
These representations are significantly related to structures of the Baltic Shield, practically devoid of sedimentary cover, except for a thin Quaternary cover. At the same time, along with the important geodynamic factor of modern terrestrial morphogenesis of the Earth’s surface, glacial processes play a major role in the formation of the bottom relief against a decrease in the activity of the Late Valdai glacier.
Quaternary cover glaciers have actively altered the rocks of the Arctic Ocean floor, and during breakdown of the ice sheet, they left behind accumulative glacial and water–glacial landforms.
Seismoacoustic Profiling
Continuous seismoacoustic profiling (CSP) plays a vital role in geomorphological constructions, because this method has made it possible to obtain information about morphological forms, and from the geometric ratio of forms, to obtain indirect information om the age of structures.
An important characteristic of seabed landforms is the age of their formation, which can only be determined by geological sediment thickness studies, carried out by geological sampling with heavy soil corers, as well as drilling of unconsolidated sediments in their entire thickness.
However, geological methods for studying the bottom relief in shelf seas are still used to a limited extent. Under these conditions, CSP remains the only source of information about the genesis and age of seabed landforms. Currently, the information content of seismoacoustic methods can be increased by using equipment with different emission frequencies, as well as multichannel profiling, which crosses over to precise metric methods of morphometric analysis.
According to CSP classification, high-resolution seismic survey (HRS) in the oscillation frequency range of 80–375 Hz yields the greatest sounding depth (up to 1 km) for seabed sediments with a relatively high vertical resolution (4–1 m).
Super-high-resolution seismic survey (SHRS) is used) in the frequency range of 375–1500 Hz with a resolution of ≤1 m. SHRS is the most popular research method.
Ultra-high-resolution seismic survey (UHRS) is carried out in the frequency range of 1.5–13 kHz with a resolution ≤25 cm and sounding depth ≤30 m for clay deposits [9, 44].
MODERN GEODYNAMICS OF THE WHITE SEA
Kandalaksha Bay
Previous studies have confirmed that the coasts and islands of the White and Barents seas are experiencing vertical movements [12, 18, 20, 40].
S.V. Pobedonostsev and L.L. Rozanov [23], based on studies of Holocene and modern tectonic movements of the coasts of the White and Barents seas, identified a vast zone next to Holocene uplifts on the Kandalaksha and Karelian coasts of the White Sea.
The coastal zones of the Onega Peninsula and Solovetsky Islands and Zhuzhmui and Zhizhgin islands in Onega Bay are also undergoing uplift.
In addition, Holocene subsidence of the following structures is significant in terms of extent [23]:
— southeastern part of the Kola Peninsula;
— southern part of the Kanin Peninsula;
— western coast of Chosha Bay;
— Kolguev Island;
— estuarine zones of the Northern Dvina and Onega rivers.
Coastal movements were associated with similar movements on the seabed.
B.I. Koshechkin [38] pointed out that the uplift and formation of the Kandalaksha tundra was accompanied by regression in the adjacent part of Kandalaksha Bay.
These data coincided with our observations of the bottom relief during marine geological surveys, during which the regressive level was identified at the –50 to –60 m marks and below; Holocene sediments were almost completely absent [30].
The White Sea is attributed to the intrashelf seas of the glacial zone and is characterized by a fairly dissected and, most importantly, diverse bottom relief. The maximum depths in it exceed 200 m, while the most striking feature of the relief of the White Sea Basin is the Kandalaksha Bay deep-sea depression, which largely determines the contour of the modern sea basin.
The genesis of this relief is polygenetic, but the main factors are tectonic and glacial. The relationship between these factors in the morphogenesis of the seabed surface is due to the fact that until now, the main direction in marine geomorphological research is zoning of the seabed morphology [16].
Seismotectonic Activation and Morphostructures
The White Sea is an intraplate morphostructure located at the boundary of the Baltic (Fennoscandian) Shield. The contour of the modern White Sea depression has inherited the structural plan of the Riphean system of grabens that arose on the passive margin of the Baltica Paleocraton 1263–1080 Ma ago [4, 62].
The system of faults that bound these Late Proterozoic structures was repeatedly activated; dikes were often emplaced along them, which are visible on Kasyan Island in the Velikaya Salma Strait.
One of the last stages of seismotectonic activation occurred in the Quaternary. The final formation of the White Sea morphostructure was governed by the interaction of two factors [5]:
— endogenic tectonic stresses in the basement;
— exogenic static and dynamic loads generated by the Scandinavian ice sheet.
The glacial load generated by this glacier led to subsidence of the underlying surface. After this load was removed, the Earth’s surface rebounded, which predetermined the complex combined influence of tectonic and isostatic factors on the late glacial relief. However, the reality of the uplift in the Kola region proved more complex.
Discussing the history of evolving views on development of the morphostructure of the Kola Peninsula, S.A. Strelkov et al. [38] showed that the initial scheme of glacial isostasy was developed by V. Ramsay [60].
At the end of the 1990s, when systematic study of sediments of lake basins isolated from the sea due to isostatic uplift commenced, it was established that the key position of isostasy, in which accumulation of glacier thickness leads to uplift of the territory after it melts, was significantly violated on the Kola Peninsula.
Massifs such as the Khibiny or Kandalaksha tundras did not fit this concept. In addition, the dominance of strike-slips among neotectonic faults was established [10]. B.I. Koshechkin considered that tectonic movements prevailed over isostatic [38].
Kandalaksha Bay
Kandalaksha Bay is located within two grabens [5, 43]:
— the Kandalaksha graben (in the southeast of the bay), which inherited the ancient Riphean trough of the Late Proterozoic paleorift and was activated (recreated) in the Neopleistocene before the onset of the Valdai glacier;
— Kolvitsa graben (in the northwest of the bay—this part of the bay is called Kandalukha).
The grabens are separated by an interdepression bridge between Velikiy Island and Porya Bay. Here, tensile stresses are transferred from the southwestern (southern part of the rift zone) to the northeastern side (northern part of the rift zone) [5, 47].
Our seismoacoustic studies here showed that this bridge is a structural uplift, dissected by small faults, while in the upper part of this uplift, a block of Riphean rocks has been preserved (Fig. 3).
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Fig. 3.
Seismoacoustic profile I‒I′ of eastern slope of uplift of Srednie Ludy Islands in Kandalashska Bay. During visualization, trace normalization of amplitudes with gain of 0.3 was used. Purple lines, block of layered rocks—relict of Riphean sandstone cover.
The studies revealed numerous seabed landforms associated with modern geodynamic movements expressed in the distribution of both Quaternary and seabed surface sediments. It was found that many mesoforms of the relief, frequently expressed on the surface of Kandalaksha Bay as rocky shoals and banks, as well as islands, reflect the small-block structure of the bedrock basement, represented by Archean and Lower Proterozoic crystalline rocks.
These block differentiated movements occur against the background of the inherited general uplift of the western part of the White Sea Basin with a relative subsidence of the eastern part, currently at a rate of +4 mm/year and –1 to –2 mm/year, respectively [46]. On seismograms, stepped slopes with significant gradients between the edge and the foot are distinctly seen (Fig. 4).
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Fig. 4.
Seismoacoustic profile II‒II′ of southwestern slope of Kandalaksha Bay depression intersecting Velikaya Salma Strait. Inset: Profile II‒II′. Seismogram identifies from displacement of seismic horizons multiple activated faults and associated landslides.
The largest gradients are associated with a scarp (edge of the Sambalud shelf), which stretches from the southern frame of the bay southeast to the Onega Peninsula [31, 63].
A. A. Nikonov et al. [24] identified the structure of the scarp as a regional seismic lineament, along which strong earthquakes that occurred in Neopleistocene and Holocene were noted.
In the area of greatest depths of Kandalaksha Bay, which is located between Cape Turiy Nos and the Karelian coast, narrow troughs were identified (using White Sea relief models [18]), the tectonic origin of which is emphasized by their geometric shape and association with sharp bends in the relief. As well, these troughs formed as a result of not only vertical, but also shear displacements in transverse and diagonal directions to the strike of the Kandalaksha graben [24].
Deep-Water Depression Fault System
The walls of the largest deep-water depression, located opposite Cape Turiy Nos, are 30–80 m in height; they are associated with the diagonal and transverse directions of displacements that formed the fault systems.
A diagonal fault system can be traced to the west in the area of the Velikaya Salma Strait and to the east, determining the position of the axis of the Kandalaksha graben closer to its northern (Kola) side.
The transverse fault system is associated with longitudinal grabenlike depressions with shear of the axial part, which is most clearly traced from Chupa Bay to the Turii Peninsula. The tectonic nature of these faults, clearly visible along the scarps in the bottom relief, is confirmed by our seismic profiling materials (see Fig. 4).
The seismograms clearly show displacements of a few to tens of meters of postglacial sediments along tectonic faults located in the rear suture of these scarps [35].
This led to the formation on the floor of Kandalaksha Bay of a dense system of numerous grabenlike forms (Fig. 5).
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Fig. 5.
Elements of Kandalaksha Bay morphostructure (after [46], modified). 1, linear elements of relief of coastal zone; 2, main tectonic scarps (graben boundaries); 3, paleoseismic dislocations (after [46]).
Confinement of paleoseismic dislocations to the transverse and diagonal directions of deformations confirms the seismic activity in the Neopleistocene, possibly the Holocene [47, 48].
Also in more shallow-water depressions, the relief is sharply differentiated, which is due to the fact that the basement blocks experiencing multidirectional and multitemporal movement have rectilinear boundaries that predetermine the appearance of linear landforms, and this rectilinearity often moves from one side of the depression to the other, encompassing the coastline (Fig. 6).
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Fig. 6.
Sketch map of distribution of modern disjunctives in head of Kandalaksha Bay according to analysis of satellite photos and obtained geophysical data (after [64, 65]).1, faults.
Longitudinal Asymmetry of Structures in Kandalaksha Bay
Kandalaksha Bay is characterized by longitudinal asymmetry associated with different bathymetric levels of the scarps framing the modern graben. The scarps extending along the Karelian coast have a height of up to 160 m, whereas the height of the scarps off the southern coast of the Kola Peninsula reaches only 100 m.
A similar asymmetry is observed in the eastern closure, where along the Onega Peninsula the height of the scarps is ~30 m; along the Zimny Coast, <2 m; sometimes these scarps are absent [48].
Similar scarps are shown in the seismograms, and their direct relationship with geodynamic zones makes it possible to identify similar landforms as structural-denudation (see Fig. 4).
An example of a structurally predetermined ridge relief is the head of Kandalaksha Bay (Kandalukha), where the typical skerry shape of the water area has features of distinct linear ordering Moreover, ridges of structural origin alternate with ridges covered with moraine deposits and characterized by developed vegetation.
The structural origin of this relief is emphasized by degassing along fissures, as well as hydrological measurements, which indicate the presence of relatively desalinated waters in the lower part of the water column [35].
This can be interpreted as a result of water exchange along tectonic fissures that we observed in coastal sections. At the same time, the thickness of the bottom water horizon and its mineralization changed at different times, which we believe is associated with periods of geodynamic activation and expansion of fissures or an increase in water exchange.
As a result, our opinion was confirmed when, after an oil spill on shore in the port of Vitinsky and proper containment of the spill, petroleum products penetrated through fissures into Kandalaksha Bay [32].
On a large number of islands, as well as on coastal land, in the zone where gabbroid rocks of the Kandalaksha tundra outcrop on shore, we identified a large number of seismic dislocations. It is characteristic that at one of the seismic dislocations, a displacement along the fault of the tidal line is visible at a distance of up to 1 m, which indicates its young origin (Fig. 7).
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Fig. 7.
Seismic dislocation on northern shore of Kandalaksha Bay. Displacement along tectonic fault line is 1.5 m. Displacement along tectonic fracture (dashed red line) of upper line of ferruginous zone associated with maximum tidal level (black line) is shown.
Another evidence of young postglacial geodynamic movements are the sharp and fresh edges of the microrelief of coastal scarps against a coast glacially smoothed, which clearly indicates their formation following the retreat of a glacier.
Velikaya Salma Strait
The Velikaya Salma Strait is located in the structure of Kandalaksha Bay.
The trough of the strait is an extensional zone that developed simultaneously with the Kandalaksha Bay depression [7].
The main features of the relief of the trench floor and surface of the basement within its boundaries are as follows [46]:
— increase in bottom depths from northwest to southeast from 40 to 140 m and subsidence of the surface of the basement to 300 m;
— increase in the thickness of the sedimentary sequence from 10 to 100–150 m;
— the presence of isolated basins with depths of up to 120 m, separated by sills with a relative height of several tens of meters;
— displacement of the trench axis to the southern wall, which forms a sharp transverse asymmetry with the steep, sharply dissected southwestern and gentle northeastern (Veliky Island) slopes.
The slopes of the depression of the strait according to seismometry data are steep and stepped (Fig. 8).
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Fig. 8.
Seismogram of profile I‒I′ of zone of active development of landslide processes in Velikaya Salma Strait (Kandalaksha Bay). Notation (Arabic numerals): 1, landslide bodies; 2, slip plane of landslide; 3, zone of sediment accumulation with abnormally large thickness as result of gravity processes; 4, accumulation of modern nepheloid sediments formed due to SPM generated during landslides.
The studied features indicate the primary tectonic origin of the trench, the active subsidence of its floor trench in recent times, and sharp differentiation of tectonic movements [17].
Faults of the Roof of the Basement
According to CSP data obtained, in the basement and overlying Quaternary sediments, faults were revealed that determine the size of individual blocks at the level of the first few hundred meters, with vertical displacements manifested in the bottom relief, which indicates modern activity.
The displacement amplitude of the roof of the basement along faults is on average 10–12 m, reaching 35–40 m, and decreasing towards the roof of the sedimentary cover to first meters [36]. In the axial part, the strait is a contact of multiphase gravitational blocks sliding along both sides. There are practically no bottom sediments between them. A large number of landslide bodies are identified here and according to multibeam echo sounding data [28].
Due to the fact that the thickness of Quaternary sediments began to accumulate during the second stage of the Valdai glaciation 20–18 thousand years ago, the rate of vertical displacements can be estimated at 0.5–2 m/thousand years.
On the southwestern side of the graben, block landslides with a volume of up to 800 000 m3, which include both moraine deposits and blocks of crystalline grounds, which may be a confirmation of strong seismic events that occurred when the main base was destroyed. As a result, the slope has a stepped character, forming an almost vertical structure with scarps 100–200 m wide and steep slopes up to 20–30 m high (Fig. 6).
Rate of Uplift
Measurements of coastal uplifts in the area of the Kindo Peninsula in the northwestern part of the Kandalaksha Strait have shown very high rates of uplift of the strait over the last 9.5 ka cal BP—during this time, the coast of the peninsula rose by ~90 m [29].
At the beginning of the Holocene, 9.5–5 ka ago, the rate is estimated at 9–13 mm/year. The rate slowed in the Atlantic time (Tapes transgression), then intensified in the subboreal time and slowed again in the Sub-Atlantic time. Modern uplift rates are approximately 4 mm/year. In the bedding part bedding part of Kandalaksha Bay on the White Sea coast, the amplitudes of postglacial uplift were maximum up to 150 m or more [28].
High uplift rates in the Holocene caused significant tectonic stresses in the crust, which were relieved as a result of earthquakes, faults with different orientations, and activation of gravity processes.
This is confirmed by numerous rock scarps 15–40 m high on the shores of the strait, terracelike steps (subsidence blocks) on the slopes, deep (up to 2–3 m) fissures and ditches, as well as stone seismic dislocations on islands and the adjacent part of the Karelian coast [29]. The size of stone blocks in these seismic dislocations may be evidence of earthquakes with a magnitude M ≤ 9 points [48].
Seismic Structures of the White Sea Basin
Potential seismic structures were identified from seismoacoustic data in other parts of the White Sea Basin. The second largest, after Kandalaksha, is the Onega Bay graben, with narrowing troughs in the western part. Along the entire length, right up to the mouth of the Onega River in the east, both sides with scarp heights of 15–30 m can be traced near Onega Bay. At the junction of the Kandalaksha and Onega grabens transverse scarps up to 60 m high with a northeastern strike, as in the White Sea Gorlo Strait [48].
The morphostructure of the Gorlo Strait, which connects the White Sea Basin with the Barents Sea, has significant geological features. With the predominant northwestern strike in the White Sea, in the Gorlo Strait, the main tectonic elements, including those activated in the Quaternary, are directed to the northeast, parallel to the coast of the Kola Peninsula and eastern tip of the Zimny Coast.
We presumably attribute the multidirectional strike to fault tectonics, namely, a system of Late Cenozoic normal faults that delineated the boundaries of the modern graben to which the strait is confined. This is confirmed by our seismoacoustic profiling data.
The seismograms clearly show faults with a northeastern strike in the rocks underlying the Quaternary deposits in the central part of the graben. In the bottom relief, each of them corresponds to a negative shape in the form of a trough or ditch, which indicates the seismic activity of these faults in the Holocene [43].
Data on the modern geodynamic (seismotectonic) activity of this dislocation zone are confirmed by evidence of two earthquakes, one of which was recorded in 2006 in the Gorlo Strait at the intersection with the Chapom graben, and another earthquake that occurred in 1542 in the vicinity of the Solovetsky Islands [40].
DISCUSSION
The formation of the morphostructure of the White Sea Basin, which has an ancient origin in the Upper Proterozoic, continued in the Holocene under conditions of directed uplift in the western (significant) and central (moderate) parts and subsidence (significant) in the eastern. Sharp dissection of the seabed relief and the presence of fresh-looking rock ridges give grounds to consider that individual blocks of the relief are separated by currently active faults. Most are confined to the Kandalaksha graben but are also observed in other areas of the White Sea (Gorlo Strait, Solovetsky Islands) [49].
Modern geodynamic processes are not only an important relief-forming process; they also influence the distribution of the Quaternary sediment cover. Holocene nepheloid sediments have accumulated at the bottom of most depressions, but this is all but absent in the zones of modern uplifts.
In Kandalaksha Bay, at depths of <50–60 m, there is a sharp reduction in the thickness of Quaternary sediments, mainly due to the absence of marine Holocene clayey sediments. This is largely due to a sharp reduction in the input of detrital material to the White Sea Basin after glaciers retreated. In conditions of a small amount of detrital material, geodynamic processes became decisive in the distribution of sequences of noncoeval unconsolidated sediments.
Accordingly, vast areas of marine perluvium appeared on the seabed surface, with a thin layer overlying the sequence of glacial–marine and glacial formations. Moreover, alternating zones of modern uplifts or subsidences govern the distribution of the layer of surface (seabed) sediments, resulting in their mosaic distribution.
Modern geodynamic movements can lead to abnormally high accumulation of unconsolidated deposits. Gravity processes move significant amounts of detritus. These processes are largely due to modern geodynamic movements, because seismic shocks during earthquakes, in the conditions of water basins, trigger processes by which detrital material moves downslope.
The dissected seabed relief and the presence of slopes, including the steep walls of the modern Kandalaksha graben, create favorable conditions for the erosion of detrital material.
In the White Sea, especially in Kandalaksha Bay, all types of slope formations are present:
— block structural landslides (subsidence);
— gravitational landslides;
— water–gravity processes (slumps);
— grain flows (including turbidites).
The following factors contribute to the development and formation of slope landforms.
— Heavy saturation of sediments with water, especially if there is a near-surface clay horizon. In marine conditions, slopes of 1°‒2° are sufficient to detach a landslide body. Even smaller angles are sufficient for sediments to begin to slip.
— The presence of modern geodynamic movements, most often in the form of low-intensity seismic shocks—this is the main triggering factor in the development of slope processes. Even small shaking of the ground can cause its movement to lower bathymetric levels.
The Velikaya Salma Strait is an en echelon zone for the main tectonic fault running along the southwestern wall of the Kandalaksha depression. The shape of the strait is a deep, narrow, which promotes the sliding of sedimentary masses. The presence of a large number of seismic dislocations indicates that seismic activity in the region continues to this day [29, 47].
The activity of modern geodynamic movements is evidenced by the appearance of a relatively desalinated horizon of bottom water at the base of the water column at the head of Kandalaksha Bay [33]. Our data indicate not only the specific features of modern sedimentation processes in different areas of the White Sea, but also the presence of young tectonic processes. These are tectonic zones, in many of them, degassing has been recorded.
Geodynamic processes in the White Sea and, in particular, Kandalaksha Bay, lead to numerous changes in the morphological appearance of the basin, in particular, the appearance of distinct and extended linear landforms (shore–underwater scarp–island shore–bay shore). There are also the dissected relief of the seabed uncharacteristic of shelves outside the glacial zone, the widespread development of sandy-crushed sediments marking zones of neotectonic uplift, and the variable nature of hydrodynamic processes closely related to the features of the bottom relief.
The block structure of the seabed at the head of Kandalaksha Bay leads to the appearance of a peculiar skerry relief, where small islands composed of crystalline rocks, sometimes covered by moraine deposits, alternate with deep, narrow straits, where depths can reach almost 100 m.
The uplift of land is the reason for the formation of meromictic lakes, i.e., bays that are gradually separated from sea basins as a result of the emergence of sills at their mouths that block penetration of salt water.
All these phenomena, described with the example of the northwestern White Sea, are found in the Baltic Sea and Lake Ladoga and Lake Onega, which are also inland waterbodies of the glacial zone [26, 32, 62].
Modern geodynamic processes are hazardous geological processes, the study of which is actively growing in together with the beginning of economic development of the seabed.
Marine research in recent years [46], carried out as part of scientific expeditions, indicates the great role of modern geodynamic processes in the formation of the bottom relief and Quaternary sediment cover for the Barents and Kara glacial-shelf seas.
CONCLUSIONS
Modern geodynamic movements, which we examined using the example of the White Sea, are a powerful factor of morphosedimentogenesis in the seas of the tectonically quiescent glacial zone in northwest European Russia.
The level of activity of these processes is not comparable with the Far Eastern seas and their coasts, especially Kamchatka, but individual seismic events can lead to significant destruction of engineering structures. An example is the Kaliningrad earthquake of 2004, when copious damage to infrastructure on the coast was recorded on land [3, 25, 54].
Modern geodynamic movements make a vast contribution to the formation of the Murmansk and Karelian coasts, and are also one of the main reasons for the peculiarity and dissected nature of the bottom relief of both inland seas and large lakes, as well as the marginal Barents and Kara seas. These are associated with anomalous hydrological processes at the bottom of Kandalaksha Bay, which are related to the influx of reservoir–pore water through activated tectonic fissures. This allowed proposals for the use (measurement) of the hydrochemistry of the bottom layer of the water column to forecast the modern tectonic activity of the region [35].
Modern geodynamics can be considered a trigger for the gravitational movement of sediments downslope in tectonically predetermined trenches, which leads to the formation of a peculiar stepped relief, as well as the appearance of layers of clayey deposits that are difficult to explain from the standpoint of normal sedimentation. This is largely a consequence of the deposition of SPM stirred up during displacement of underwater landslides. Cases have been recorded when modern seismotectonic events were briefly recorded even on the surface of nepheloid silty sediments [28].
The study showed that modern geodynamic processes are an important factor in the modern lithomorphogenesis of the shelf seas of Northwest Russia and they should be taken into account both in modern geological cartography and marine engineering-geological surveys.
The study of modern geodynamic processes acquires practical importance in assessing hazardous geological processes and phenomena in shelf economic development zones. All of the major deposits and gas fluid occurrences in the Barents and Kara seas are associated with zones of tectonic processes.
ACKNOWLEDGMENTS
The authors thank our colleagues S.V. Shvarev (Insitute of Geography RAS, Moscow, Russia), L.R. Semenov (Russian Geological Research Institute (VSEGEI), St. Petersburg, Russia), and Yu.A. Zhuravlev (MAGE LLC, Murmansk, Russia) for joint research, in which we were able to take a new approach to studying the structures discussed in the article.
Our colleague, the dearly departed geologist A.A. Nikonov (Schmidt Institute of Physics of the Earth RAS, Moscow, Russia), who devoted his entire life to studying neotectonic movements, will remain forever in our memory.
The authors thank the reviewers, Doctor of Geology and Mineralogy A.A. Peyve (Geological Institute RAS, Moscow, Russia) and Dr. Geology and Mineralogy N.P. Chamov (Geological Institute RAS, Moscow, Russia) for useful comments, and editor M.N. Shoupletsova (Geological Institute RAS, Moscow, Russia) for careful editing.
FUNDING
The study was carried supported by the Russian Science Foundation (grant no. 22-17-00081).
CONFLICT OF INTEREST
The authors of this work declare that they have no conflicts of interest.
Publisher’s Note.
Pleiades Publishing remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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