Regressive Stage Research Articles

Geology aspects and formation of the erosional structure of Upper Miocene deposits of the Western Cicaucasus

The results of regional studies of the Early Miocene deposits of the Western Ciscaucasia, carried out on the basis of seismic stratigraphic analysis, are presented. The spatial pattern of sediment accumulation is analyzed and the paleogeographic conditions during the regressive stages of the Late Miocene in the Western Ciscaucasia are clarified. Erosion incisions of several levels were identified, which developed during the fall of the erosion base level during major regressions in the studied time interval. By spatial correlation of paleochannels based on a selected series of intersecting seismic profiles, the buried river valleys of the Paleo-Don and Paleo-Donts were reconstructed and constructed at the Sarmatian‒Meotis boundaries and within the Late Meotis‒Late Pontian interval.

Characteristics of the hydrological regime of the periglacial moraine lakes in the Altai

In the last decade glaciers of Inner Asia have been shrinking with acceleration, and the number of glacial lakes has been growing significantly, including those with a high probability of outburst and high-water discharge. The hydrological regime of lakes in the Altai is understudied in comparison with lakes in other high mountain countries. The article is based on our extensive field material on hydrological and morphometric characteristics of moraine lakes collected in the Russian and Mongolian parts of the Altai Mountains and combined with the Earth remote sensing data. We have proposed detailed indicators (criteria) of transgressive, regressive and post-regressive stages of lake development. It allows allow to determine at a qualitative level at what stage a lake is at and to assess its further development. The characteristics of hydrological regime of Altai lakes at different stages of development are described for the first time. Based on the criteria proposed, the classification of glacial and moraine lakes in the Altai high mountains was carried out. It shows that at present most of the lakes are in the transgressive stage. Over the last 22 years, the number of lakes has increased significantly: on the territory of the North Chuya Ridge – from 28 to 60, on the South Chuya Ridge – from 39 to 73, on the Katun Ridge – from 57 to 89, on the territory of the Tavan-Bogdo-Ola massif – from 11 to 19, and on the territory of the Mongun-Taiga massif – from 8 to 11 lakes.

U–Pb Age and Mineral Inclusions in Zircon from Diamondiferous Garnet–Pyroxene Rocks of the Kumdy-Kol Microdiamond Deposit in Northern Kazakhstan

Abstract ––This paper describes the results of studying inclusions and determining the U–Pb age in zircon from the diamondiferous garnet–pyroxene rock of the Kumdy-Kol metamorphogenic diamond deposit, located in the Kokchetav subduction-collision zone. The distribution of rare earth elements in garnet and clinopyroxene is used as a basis for estimating the equilibrium pressure (5.5 ± 0.3 GPa) and temperature (993 ± 24 °C), which correspond to the diamond stability field. The composition of mineral inclusions in zircon indicates its formation at both the progressive and the regressive stage of metamorphism. The concordia diagram shows that the figurative points of zircon lie on a discordia with an upper intersection at 1953 ± 139 Ma and a lower intersection at 512 ± 4 Ma. The main peak on the graph of the probability density distribution of zircon ages corresponds to an age of 519 Ma. The presence of grossular–almandine garnet inclusions in zircon confirms the previous assumption that the basement rocks of the Kokchetav massif act as protoliths of garnet–pyroxene rocks.

Fluid inclusions in quartz of the gold-ore occurrences and gold-quartz intergrowths from placers in the Sololi uplift of the Olenyok arch (Yakutia)

Fluid inclusions have been studied in vein quartz with gold sulfide mineralization from metamorphosed sandstones of the Eekite series and metarhyolites of the Early Proterozoic, in quartz breccia from the zone of overlapping gold mineralization on the Early and Middle Permian sandstones, as well as in the gold quartz intergrowths from the Sololi River placer. It has been revealed that formation of quartz breccias occurred within a wide temperature interval from 230 to 425 ºC, with predominance of carbon dioxide and nitrogen in the vapor phase. It is suggested that the increased nitrogen content may be associated with a chemical reaction between the fluid and ammonium-containing silicates of host rocks, in which nitrogen in the form of NH4+ isomorphically replaces potassium at the regressive stage of metamorphism. At the same time, it is possible that mantle nitrogen, which was transported along the Anabar-Eekite deep fault, participated in formation of the studied breccias. The close homogenization temperatures and similar nature of the water-salt composition for the fluid inclusions of quartz veins that inject the Eekite series meta-rocks and meta-rhyolites indicate the synchronism of their formation and attribute them to the common stage of ore formation. Quartz veins with gold sulfide mineralization were the primary sources of pebbles with gold-quartz intergrowths from the Sololi River, this is evidenced by similarity of principal characteristics of fluid inclusions. Oxidizing conditions of the mineralization serve as favorable factor for the Au deposition, it is indicated by the predominant CO2 content in fluid inclusions, keeping role of a geochemical barrier and leading to an elevated gold content in quartz veins.

Evolution of Coniacian facies and environments in the Iberian basin: a longshore current controlling siliciclastic sand distribution on a carbonate platform

The Coniacian carbonate sediments of the Iberian basin were deposited on a homoclinal ramp that grades upwards into a distally steepened ramp, with a major shoreline siliciclastic fringe. Twenty-three facies have been identified and grouped into three main depositional environments: outer, mid, and inner ramp. The last include barrier (shoal), lagoon, carbonate tidal-flat and shoreface sub-environments. The more prominent biogenic components show a mixture of sunlight-dependent phototrophic organisms (mainly large benthic foraminifera) and nutrient-dependent heterotrophic organisms (mainly rudists), with a remarkable rare occurrence of corals. Nutrients supplied from the emergent mainland probably promoted the development of heterozoan organisms. The vertical evolution of the ramp shows: a basal transgressive stage with facies retrogradation; a maximum flooding stage, and a regressive stage with aggradation and progradation of a distally steepened ramp. The presence and distribution of siliciclastics are problematic, since sands coming into the basin are likely to be rapidly and widely redistributed along the basin, taking into account the common storm, wave, and tidal processes preserved by the sedimentary facies. The presence of a clockwise NW-flowing longshore current is postulated to account for this distribution, which was likely induced by both dominant external currents around Iberia and wind-driven currents. These clockwise gyres facilitated the invertebrate dispersion into this enclosed basin and the local presence of upwelling. This could have been another source of episodic nutrient-rich waters from the deep ramp, which may have favored heterozoan development even in the more proximal and relatively shallower-water facies.

Long-term surveillance of the feline leukemia virus in the endangered Iberian lynx (Lynx pardinus) in Andalusia, Spain (2008–2021)

Feline leukemia virus (FeLV) infection is considered one of the most serious disease threats for the endangered Iberian lynx (Lynx pardinus) Over 14 years (2008–2021), we investigated FeLV infection using point-of-care antigen test and quantitative real-time TaqMan qPCR for provirus detection in blood and tissues in lynxes from Andalusia (Southern Spain). A total of 776 samples from 586 individuals were included in this study. The overall prevalence for FeLV antigen in blood/serum samples was 1.4% (5/360) (95% CI: 0.2–2.6), FeLV proviral DNA prevalence in blood samples was 6.2% (31/503) (95% CI: 4.1–8.6), and FeLV proviral DNA in tissues samples was 10.2% (34/333) (95% CI: 7–13.5). From a subset of 129 longitudinally sampled individuals, 9.3% (12/129) PCR-converted during the study period. Our results suggest that FeLV infection in the Andalusian population is enzootic, with circulation of the virus at low levels in almost all the sampling years. Moreover, since only one viremic individual succumbed to the infection, this study suggests that lynxes may therefore control the infection decreasing the possibility of developing a more aggressive outcome. Although our results indicate that the FeLV infection in the Iberian lynx from Andalusia tends to stay within the regressive stage, continuous FeLV surveillance is paramount to predict potential outbreaks and ensure the survival of this population.

SEAFLOOR MORPHOLOGY OF THE OB RIVER GULF, KARA SEA

The article presents the results of an extensive study of the bottom topography of the Ob River Gulf in the Kara Sea, which is a follow-up to the long-term studies of the authors. It refines the existing ideas and aims at solving a fundamental problem of reconstructing the conditions for the formation of bottom topography in the shallow bays of the Kara Sea in the Late Pleistocene and Holocene. The work aims to create a regional characteristic of the geomorphologic structure of the Ob River Gulf bottom. The initial data on the bottom topography were taken from marine navigational maps and sounding boards at a scale of 1:50 000 - 1:100 000. We processed and interpreted the collected cartographic material to create a detailed DEM of the bottom and a bathymetric map at a scale of 1:200 000 with an isobaths interval of 1 m. In addition to bathymetric data, the compilation of a geomorphologic map engaged a large amount of literature and stock materials on geomorphology, geology, and geocryology of the region. The original morphogenetic legend was elaborated with due account of current ideas regarding the conditions for the formation of periglacial plains relief at the regressive stage of the Kara Sea shelf evolution. It was found that the relict fluvial relief prevails within the gulf and was partly modified by subaqueous processes during post-LGM transgression and the current epoch. We have indicated the most critical features of the structure and pattern of the flooded pravalley of the Ob River, as well as the total ancient erosion network. The selected individual forms and relief elements take into account the scale of objects and the degree of their generalization on the map and give an idea of the development of relief-forming processes both at the subaerial stage and under subaqueous conditions, including specific features of modern dynamics of the coastal and bottom relief.

The Pleistocene ice-sheet dynamics in north-central Poland based on magnetic fabrics of tills and landform analysis

Abstract This research was carried out in north-central Poland, which was occupied by the ice sheet of the Saalian (Marine Isotope Stage [MIS] 6) and Upper Stadial of the Weichselian (MIS 2) glaciation. The application of the anisotropy of magnetic susceptibility (AMS) method supported by a digital elevation model (DEM) analysis of the orientation of glacial landforms allowed for the reconstruction of ice-sheet extent and ice movement directions of these two Pleistocene glaciations. The research used an innovative method of collecting AMS till samples from the glacial plateau areas. Based on the research, it was found that during the general recession of the ice sheet of the Saalian glaciation, a previously undescribed glacial transgression occurred, characterized by a different direction of ice-sheet movement. On the basis of detailed geomorphological studies of the area of terminal moraines, previously described in fragments, the maximum extent of the ice sheet during the Weichselian glaciation was clarified. The recession of the ice sheet of the Weichselian glaciation from the area of north-central Poland took place in four regressive or transgressive–regressive stages with variable directions of ice-sheet movement. The results obtained indicate the great potential of the AMS method in paleoenvironmental studies of glaciated areas.

Failure Prediction of Open-Pit Mine Landslides Containing Complex Geological Structures Using the Inverse Velocity Method

In the field of open-pit geological risk management, landslide failure time prediction is one of the important topics. Based on the analysis of displacement monitoring data, the inverse velocity method (INV) has become an effective method to solve this issue. To improve the reliability of landslide prediction, four filters were used to test the velocity time series, and the effect of landslide failure time prediction was compared and analyzed. The results show that the sliding process of landslide can be divided into three stages based on the INV: the initial attenuation stage (regressive stage), the second attenuation stage (progressive stage), and the linear reduction stage (autoregressive stage). The accuracy of the INV is closely related to the measured noise of the monitoring equipment and the natural noise of the environment, which will affect the identification of different deformation stages. Compared with the raw data and the exponential smoothing filter (ESF) models, the fitting effect of the short-term smoothing filter (SSF) and long-term smoothing filter (LSF) in the linear autoregressive stage is better. A stratified prediction method combining SSF and LSF is proposed. The prediction method is divided into two levels, and the application of this method is given.

ОСОБЕННОСТИ ВЕЩЕСТВЕННОГО СОСТАВА, ПАРАМЕТРЫ МЕТАМОРФИЗМА И ПРОТОЛИТЫ ГРАНУЛИТОВ ЛАРБИНСКОГО БЛОКА ДЖУГДЖУРО-СТАНОВОЙ СКЛАДЧАТОЙ ОБЛАСТИ

The article focuses on the issues related to the primary nature and metamorphism of gneisses from the Larba block of the Dzhugdzhur-Stanovoy fold area, which are based on the study of the mineralogical composition of supracrustal rocks. PT-parameters for the highest temperature and pressure metamorphic transformations of rocks of the Larba block are estimated as P = 6.5–8.5 kbar and T > 800°C. Relatively low-temperature garnet-biotite, garnet-biotite-chlorite mineral parageneses were formed at the regressive stage of metamorphism at ~4–6 kbar and temperatures up to 500–600°C. Wide variations in paragneiss compositions indicate that protoliths of the studied gneisses differed in composition. Overall, Larba metasedimentary rocks had weakly and moderately weathered source areas. Most of the compositions of paragneisses are localized in the field of chlorite-montmorillonite, montmorillonite-kaolinite-hydromica and chlorite clays formed from the mafic substrate. Low alkalinity in combination with a high MgO content indicates the presence of rock erosion products with a significant admixture of basic volcanic material in the detrital material. Migmatization of rocks is the most significant factor distorting the reconstruction of the original rock composition.

Holocene stable oxygen isotope record from the North Caspian Rybachya core

The first results of 22 δ18Oost measurements on ostracod shells from the Rybachya core in the North Caspian Sea are presented. The stable oxygen isotope record here confirms previous studies of Upper Quaternary and Holocene sediments of the Rybachya core area, where it was suggested that a paleovalley was formed during the Mangyshlak regressive stage and then gradually filled during the Holocene transgressive stage. We recorded three local isotopic stages, each characterized by δ18Oost values. The hydrological variability and sea level changes associated with the transgressive-regressive rhythm of the Caspian Basin and the climatic changes in the Northern Hemisphere led to the δ18Oost changes obtained in this work. Relatively depleted δ18Oost values from sediments filling the paleovalley allowed to interpret the isotope record in terms of freshwater influx. The average δ18O enrichment of ostracod shells is taken as evidence for the isolation of the paleovalley during the Caspian Sea level retreat. However, the higher δ18Oost values obtained for the last (modern) stage of Caspian history are under the strong control of host water salinity, which is higher than during the paleovalley filling episode.

Continental depositional record of climate and tectonic evolution around the Eocene-Oligocene transition in southeast France: perpectives from the Vistrenque Basin (Camargue)

Based on detailed sedimentological analyses of cores, interpretation of well logs and a set of geochemical measurements performed on lacustrine sedimentary rocks, the palaeoenvironmental evolution and the sedimentary architecture of the Paleogene continental Vistrenque Basin (SE France) have been reconstructed. The analysis of sedimentary archives revealed three main stages of basin infill evolution: (1) a deep-lake basin (Priabonian-earliest Rupelian) whose sedimentation was dominated by terrigenous gravity-driven deposits during a period of high subsidence rate and strike-slip fault activity and under a prevailing humid climate; (2) an evaporative deep lake (early Rupelian) characterized by a drastic reduction in lake volume (forced-regression), terrigenous supplies and deposition of evaporites in disconnected sub-basins; (3) an overall long-term normal regressive stage (middle Rupelian to earliest Chattian) of lake infill characterized by an increase in terrigenous supplies and a vertical upward transition from deep-lake gravity-driven deposits to marginal lake and floodplain sedimentation. The onset of lake volume reduction and forced regression during the early Rupelian is associated with (1) the reworking of marginal lake carbonates into the deep lake areas, (2) the deposition of organic-rich sediments (TOC > 10%) coupled with sulphate-reduction processes in the deepest areas of the lake, (3) an important decrease in terrigenous supplies and (4) a long-term increase in δ18O of matrix-supported carbonates. This early Rupelian forced regression of the Vistrenque lacustrine system is interpreted to result from a regional decrease in precipitation in response to global cooling during the Eocene-Oligocene Transition (EOT). The final infill of the Vistrenque lake system (late Rupelian-early Chattian) and the onset of a floodplain occurred in more humid conditions during a stage of decreased activity of the Nîmes Fault, prior to or during an early stage of the Liguro-Provençal rifting.

Different graphitization degrees of carbon matter in rocks of a same metamorphic evolution

Two X-ray diffraction methods were chosen to determine the degree of structural order (degree of graphitization) of natural carbonaceous matter. Factors influencing the graphitization processes during the progressive and regressive stages of metamorphism are examined. The correlation of the degrees of structural order of the carbonaceous material with the sequence of mineral growth allows the metamorphic history of the graphite-bearing rocks to be traced. The obtained data can be used for the evaluation of graphite as a raw material.

Shallow‐marine calciclastic mass‐transport deposits in an evolving thrust‐top basin: A case study from the North Dalmatian foreland basin, Croatia

AbstractMass‐transport deposits are products of resedimentation phenomena involving a broad spectrum of gravity‐driven processes, and commonly have a high preservation potential in deep‐marine environments. This study documents various types of mass‐transport deposits that are interbedded with intensely bioturbated shallow‐marine calciclastic sediments deposited along a reflective coast during the middle and late Eocene. The sedimentary succession, located in the vicinity of Novigrad in northern Dalmatia, Croatia, comprises sediments deposited in a range of nearshore and carbonate ramp environments, and represents the infill of a thrust‐top (piggyback) basin of the North Dalmatian foreland basin. Five types of mass‐transport deposits, ranging in thickness from 13 cm to 6 m, have been identified: (i) calcilutite and calcarenite slumps; (ii) conglomeratic slump‐debrites with a ‘dough‐like’ appearance; (iii) blocky‐flow deposits bearing large blocks of beachface and/or shoreface deposits; (iv) rockfall deposits comprising scattered blocks of beachface conglomerates and shoreface calcarenites; and (v) ‘classical’ matrix‐supported debrites. Calciturbidites are rare and mainly comprise Ta and Tb divisions. Conglomeratic slump‐debrites are mostly found in association with offshore‐transition deposits, suggesting that mass flows were triggered above the storm‐wave base likely due to a combined effect of: (i) strong earthquakes related to the tectonic development of the basin; (ii) sediment destabilization due to pore‐water overpressure during forced regressions; and (iii) storm‐wave loading affecting the shallow seabed. Progressive deepening likely favoured mass‐flow transformations, although the overall paucity of turbidites suggests relatively short mass‐flow transport distance and turbidity current bypass to deeper realms. Multiple erosion phases and resedimentation processes from the Cretaceous to the late Eocene contributed to the diverse suite of extraformational clasts in the mass‐transport deposits studied. The mass‐transport deposits may be triggered and emplaced in shallow‐marine settings mainly during regressive stages of basin development, as the diverse gravel clast composition suggests significant tectonic influence. Although the mass‐transport deposits reported herein are relatively small, some of their peculiar sedimentary features and occurrence within shallow‐marine calciclastic deposits render them rather unique and suitable for a re‐assessment of the nature and evolutionary continuum of processes involved in subaqueous sediment mass transport, as well as the preservation potential of sedimentary features in high‐energy wave‐reworked environments.

Self-Stigma's Effect on Psychosocial Functioning Among People With Mental Illness.

Consequences of self-stigma exhibit a four-step regressive model from being aware of public stigma, to agreeing with it, to applying it to oneself, to resulting harm on the self. We hypothesize the relationship between self-stigma and psychosocial functioning is mediated by three constructs: the why try effect, stigma stress coping resources, and personal recovery. Two hundred eight people with depressive and bipolar disorders participated the study. Data partially supported the regressive model of self-stigma. Awareness was not found to be associated with other regressive stages. The model representing the path between self-stigma-harm and psychosocial functioning was significant and robust. The path was mediated by the why try effect and personal recovery. Findings echo the growing body of research attempting to describe outcomes of self-stigma, in this case, psychosocial functioning. Programs meant to erase self-stigma, and its effect on functioning should incorporate the why try effect and personal recovery as strategic ingredients.

Inlet migration during the turning point between transgressive and regressive stages at the Guaratuba Holocene barrier, Paraná - Southern Brazil

This paper analyzes the sedimentary record of a paleo-inlet that evolved in association with a coastal barrier, using data that provides a high-resolution stratigraphy. During the evolution of the Guaratuba Holocene barrier, autogenic factors associated with the paleo-estuary dynamics compete with allogenic factors of RSL (Relative Sea Level) variation and the influence of climate on sediment input. The integration of geological mapping, vibrocore, GPR (Ground Penetrating Radar), and radiocarbon dating techniques allowed for recognizing of a paleo-inlet migrating east-southeast during the turning point between the transgressive and regressive stages, cyclically affected by episodes of aggradation and reversal in the direction of lateral migration. This dynamic, conditioned by shadow zones of bedrock elevations and the littoral drift of sediments, modifies the stratigraphy and the barrier's depositional architecture, defining diachronous surfaces and lateral variations in the stratigraphic stacking. These features exemplify how barrier-inlet systems are affected by the combination of high frequency, climate-defined events and local coastal processes during their evolution.

P-T parameters of metamorphism of the rocks of the differentiated body of the Misaelga complex (western slope of the Southern Urals)

The article presents materials on the P-T parameters of metamorphism of the rocks of the differentiated body of the Misaelga complex. Based on the study of metamorphogenic minerals and mineral associations: amphibole, amphibole-plagioclase, amphibole-garnet, epidote-garnet, muscovite, chlorite, ilmenite-titanomagnetite, a gradual decrease in temperature and pressure was established from the final stages of the magmatic stage of formation of rocks of the Misaelga complex to the beginning of the metamorphogenic stage.
 It is shown that the process of amphibolization begins immediately when the temperature of the residual melt drops by ~100°С (from 800°С to 700°С), which indicates the autometamorphic character of rock alteration. At the same time, the decomposition of the solid solution in titanomagnetite and ilmenite begins (766–588°С). Further changes include alteration (albitization) of plagioclase (550–>400°С), sericitization (~ 300°С) and chloritization (333–157°С).
 The association of minerals with garnet, distributed in a narrow interval of the section at a depth of 341.5 m with a horizon thickness of no more than 2–2.5 m, is a zone in which dynamothermal metamorphism manifested itself, due to fluid working out of the substrate of the Taratash complex in shear deformation zones, identified in the interval 1400–1200 Ma. The P-T parameters of dynamothermal metamorphism, determined by the garnet-epidote association, correspond to 550–580°С at a pressure of 2 kbar, and according to the garnet-amphibole geobarometer – 300–400°С. At the same time, it should be emphasized that these associations characterize the regressive stage of metamorphism.

On the Allocation of Regional Geological Monuments of the Main Devonian Field

Abstract—Using the example of two particularly valuable geological objects of the Main Devonian Field (Ilmen glint and the valley of the Velikaya River in the area of the Vybuty rapids), the features of the allocation and protection of geological monuments of regional significance are considered. Ilmen glint is a complex (stratigraphic, paleontological, ore-litho-petrological, hydrogeological) geological monument of regional significance. The authors substantiate the paleogeographic value of the object, which consists in the possibility of studying various ecological complexes of the macrofauna of the Middle Frasnian Sea, reflecting both regressive and transgressive stages of its development. Also, for the Ilmen glint are recommended two new criteria: a historical criterion (reflection of information about a geological object in the classical geological literature) and (for the first time) the introduction of a new historical and geographical criterion (the relationship of geological and geographical features with the history of settlement and development of the region). As a unique geological object, Ilmen glint has been studied by outstanding Russian and foreign researchers. The sections of the glint and the near-glint region are stratotypic for a number of sub-regional and local subdivisions of the Middle Frasnian of the Main Devonian Field. The features of the geological structure (close occurrence to the surface of carbonate rocks of the Upper Devonian), proximity to Novgorod and convenient communication with it by water influenced the fact that this area became one of the areas of ancient mining back in the days of Veliky Novgorod. Due to the location at the crossroads of important roads, the surroundings of glint often turned out to be the scene of important historical events, so in the village of Korostyn, located at the western tip of glint, the famous Korostyn Peace was concluded. The Vybuty Rapids tract is not a protected area, although it also has a clear scientific value from the paleogeographic (interesting complexes of ichnofossils are observed in the outcrop and extremely valuable in the reconstruction of paleogeographic conditions of the hardground facies) and historical and geographical points of view (a large ford was the strategic place in the Middle Ages for Pskov). The article considers the influence of natural and anthropogenic hazards on the condition of the described geological objects. In the described unique outcrops, there is an active manifestation of landslide processes and weathering processes. At the same time, the terrain features (the presence of local plicative and disjunctive structures that contribute to the formation of zones of increased fracturing) are aggravated by the active traffic load in the areas adjacent to the coastal cliffs.

Morphology and genesis of the Yaselda glacial valleys in Belarus

Geological mapping revealed the oldest Yaselda (Don (on the territory of Russia), Sanian 1 (on the territory of Poland)) generation of valleys in the Quaternary strata. Valleys are widespread in marginal and inner zones of the Yaselda glaciation area. They are located in the pre-Yaselda lowlands, in the areas of deformable deposits that lie above the more hard rocks protrusion and in fault systems. The distribution of glacial valleys is depends on the radial-sectoral structure and dynamics of the Yaselda glacier, which predetermined both the common and regional features of the valley regularity and morphology. The common features are the location in lobed sectors, occurrence in heterochronous ice marginal complexes, the predominance of polygenetic valleys. The regional features include isolated position, submeridional and meridional orientation, smaller size and weak expression of valleys in the maximum phase relief, the predominance ofvalleys of glacial exaration and extrusion and tunnel valleys. Valleys of the younger (Novogrudok) phase are located in the marginal complexes of the Middle Neman, Naliboky and Middle Berezina ice lobes and tongues. Valleys are characterised by connection with the belt of marginal highlands, sublatitudinal large-festoon ordering on the area of the lobes and a fan structure in the tongues, large size and maximum depths, clear expression in relief. Here, mainly polygenetic basins and trough valleys, extrusion valleys and subglacial tunnel valleys have been established. Basins arose simultaneously with the advance of outlet glaciers and are the result of exaration and glaciotectonic overthrusts of substrate rocks in the territory of the Belarusian anteclise and lowlands enveloping from the north. Their formation became possible at the regressive stage, when the readvances of the ice lobes led to the extrusion of a large amount of bed material and its accumulation in the basin borders. Trough valleys arose due to the wedging of outlet glaciers into paleovalleys or selective linear erosion along zones of structural weakening. In areas of rock bed, they were formed by plucking and abrasion, and in areas of soft substrate – by plucking, removal of thrust blocks. Numerous extrusion valleys appeared due to the extrusion in the Meso-Cenozoic deposits from under the glacial tongues into the marginal zones during the glacial retreat phase. Tunnel valleys originated as a result of canal erosion of sediments during rapid outbursts of water from subglacial lakes established for the glacier reduction phase. Most of the large valleys are of polygenetic origin.

Tectono-sedimentary evolution of the Paleogene Qikou Sag, Bohai Bay Basin, NE China

The Qikou Sag is a petroliferous tectonic unit within the Bohai Bay Basin, northeast China. The depositional system evolved temporally, spatially, and episodically in five rifting stages (stages 1–5) during the Paleogene and Neogene, with sedimentation responding to regional subsidence. This study focuses on the tectono-sedimentary evolution through stages 2–4, while the main oil-bearing sedimentary rocks were deposited in the Bohai Bay Basin. The depositional system exhibited retrogradation and then progradation during the rifting stage 2 (43–36.7 Ma), retrogradation in stage 3 (36.7–32.8 Ma), and upward coarsening and progradation in stage 4 (32.8–24.6 Ma). This vertical superposition corresponded to three episodic stages of rising and falling lake levels during the Paleogene, which were equivalent to a transgressive with regressive (stage 2), transgressive (stage 3), and then regressive (stage 4) cycle. The sediment fills coincided with the tectonism and the regional subsidence history of the Qikou Sag, which is composed of uplift areas and sub-sags. In this respect, the boundary fault activity around the sub-sags decreased from stages 2–4, leading to the migration of sub-sag depocenters from near faults to the center of sub-sags, which suggests that faults released control over the sedimentation. Secondly, tectonism and the total subsidence rate decreased from SQ1 to SQ7 (stages 2–3) and then accelerated at the end of stage 4 (SQ10 to SQ11). The tectonic subsidence rates decreased quicker than the total subsidence rate; this demonstrates that major rift faulting was the dominant geological process in the early Paleogene, whereas overall subsidence was dominant in the late Paleogene.