卷 56, 编号 3 (2025)

The article studies sediment accumulation processes in the upper reaches of a river with abundant sediment supply from slopes and subsequent river incision into the accumulative strata when the supply of slope sediments ceases. The object of study is the upper reaches of the Waipaoa River (New Zealand), where such processes are well studied and morphometric, hydrological and sedimentological information is available. The deformation equation using the Grishanin formula for calculating the transport rate of bedload was solved using numerical methods, regional morphometric relationships and an empirical formula for the rate of sediment supply from slopes to the head of the river. The result is a quantitative description of both sediment accumulation processes and the processes of river incision into them. Under conditions of sediment supply from slopes, a sediment accumulation area was formed, which expanded over time both upwards (regressively) and downwards (transgressively) along the river. The longitudinal profile of the channel straightened along the chord. Subsequent incision upon cessation of sediment supply occurred transgressively, starting from the upper section of the accumulation area. As a result, a cyclic chord terrace with time-transgressive downstream incision was formed. During the incision, sediments accumulated on the surface of the terrace in the middle and lower parts, which, despite subsequent erosion, could be preserved in the section of the alluvial layer. The use of numerical methods allows us to trace the details of the processes of formation of accumulative deposits of cyclic terraces and the incision of river flows into these deposits.

Based on the literature data and results of field research, the locations of karst remnants, the type and age of karsting rocks they formed in, as well as the morphology and morphometry of the remnants were determined. In the Southern Cis-Urals, the remnants were formed in gypsum of the Kungurian stage on the Pribelskaya plain and in the western foothills of the Southern Urals, as well as in limestones of the Sakmarian and Artinskian stages on the Ufa plateau. In the Southern Urals, they were formed in limestones and dolomites of the Upper Devonian and Early Riphean within the low-mountain ridges of the western slope. In the Southern Cis-Urals, karst remnants are represented by hills, ridges and outcrops of bedrock rising above the flattened surrounding terrain, and in the Southern Urals, they are isolated low mountains and pillars. The sizes of the remnants are small – a few tens of meters. In the Southern Urals, their sizes are larger than in the flat Cis-Urals, which is due to the higher hypsometric position of their locations and the formation of remnants in carbonate rocks that are more resistant to the effects of denudation agents than in sulfate rocks. Based on the analysis of the geological and geomorphological conditions of the locations of karst remnants and the leading exogenous geological process that determines their formation, all the characterized remnants are divided into three main types: erosion-karst, the formation of which is mainly due to the activity of river erosion, karst-denudation, associated with the phenomenon of unloading rock pressure in river valleys and kastogenic, formed in the bottoms of karst basins of collapse genesis. The most numerous remnants are erosion-karst, and the least common are kastogenic. The formation of karst remnants in the region presumably began in the Early Pleistocene, the formation of which continues at the present time.

The article is devoted to the study of the postglacial tectonic activity of the Imandra-Kolvitsky fault in the south-west of the Kola Peninsula based on the synthesis of signs of seismogenic deformations in the relief, bedrock of the crystalline basement and loose sediments. The studied area is located in a through-tectonic depression, in the low-mountain Kandalaksha Tundra massif, occupied by the basin of Lake Sredne Luvengskoye. Previously, a focus of paleoearthquakes was established here due to the presence of seismic deformations of various types and ages. The tasks of the work included the creation of a combined detailed digital relief model in the lake bed and on the coastal territory; analysis of the structure of the relief and the distribution of tectonic deformations on the surface; analysis of the structure and hierarchy of segments of the Imandra-Kolvitsky fault and minor ruptures; analysis of the deep structure of the quaternary cover and its relationship with the relief of the basement with the identification of zones of faults and deformation anomalies. The main methods used were geological and geomorphological (morphogenetic, morphotectonic, morphodynamic, paleoseismic) and geophysical (ground penetration radar (GPR) and electrotomography (ET)). The spatial and deep structure of the segments of the Imandra-Kolvitsky fault in relation to deformations of sediments and the surface of the basement and the probable period of maximum activity of 14.9–10.3 thousand years have been determined.

This study is devoted to the vegetation dynamics, hydroclimatic conditions and fires research in the northwestern macroslope foothills of the Eastern Sayan. The results of palaeoecological reconstruction obtained based on AMS dating, pollen, macrofossils, macrocharcoal and malacofaunal analyses of the Sosnovka mire deposits (right bank of the Yenisei River, southern part of the Rybinskaya Depression) covering the last ≈11,000 calendar years are presented. The grain size analysis of the mineral deposits underlying peat was performed and minerals of different size fractions were studied using scanning electron microscopy. The data show that about 10, 000 calendar years ago, a shallow water body experiencing periodic shallowing were formed in the floodplain of the Kan River. The process of mire formation began ≈9,700–8,500 cal. yr BP at the optimum of heat and moisture supply, when the dry valleys were covered with a mixed siberian pine-spruce-fir forest dominated by spruce and fir. During the Holocene Thermal Optimum (7,500–6,000 years ago) a reduction in spruce and fir in the composition of the forest stand, increased fire activity, clearing of forests, beginning of mire formation in the floodplains of rivers with catchments in the western part of the Eastern Sayan foothills occurred. The periods of decreased heat supply and increased humidity occurred at 5,500–5,200, 3,560–2,960, 2,300–2,000, 1,800–1,300 cal. yr BP. This, among other things, caused the expansion of the range of dark coniferous forests, with the most significant response in the range of 1,360–1,300 cal. yr BP. Changes in climatic conditions towards aridization and increased continentality 7,500–6,000 cal. yr BP, 3,800–3,600 and 2,000–1,800 cal. yr BP contributed to the rise of the lower boundary of dark coniferous forests and increased fire activity. The last 800 years have been characterized by strengthening of continentality, expansion of forests with Pinus sylvestris and the highest fire activity (in the last 100 years the rate of accumulation of macroscopic charcoal has been 80 particles/cm² per year).

Sedimentary paleoarchives of the Late- and Postglacial sediments accumulated in the Nizhnevarzugskaya tectonic depression and on its western flank were studied on the Tersky coast of the White Sea using lithostratigraphic analysis, radiocarbon dating, and GPR profiling. The consecutive succession of sedimentary setting from glacial through glaciolacustrine to marine has been established. For the first time on the White Sea coast the facial variability of basin sediments filling a large tectonic depression was revealed not only in the outcrops, but also laterally. The glaciolacustrine sediments represented by rhythmically bedded deposits were traced up to a height of 41 m a.s.l. Glaciolacustrine sediments documented at the bottom of the depression accumulated in a large proglacial lake, while on its side sediments accumulated in small depressions at the top of the till. At the bottom of the depression, glaciolacustrine rhythmites are overlaid above erosional surface by Holocene marine sediments consisting of two facies. The lower facie is represented by fine-grained cross-bedded sands with shells, which were deposited in the coastal shallow water at the beginning of the Holocene Tapes transgression (starting from ~9.4 cal. kyr BP). The relative sea level at that time was 9–10 m below the modern. The upper facie consists of mixed-grained layers of sand interlayered with gravel-pebble beds deposited later than 7.8 cal. kyr BP in the breakwater zone during the lowering of the relative sea level. According to existing geological and geomorphological data, the accumulation of marine sands at 43–22 m a.s.l. in the Nizhnevarzugskaya depression correlates with the Late Glacial-Early Holocene transgressive-regressive rhythm, and below 22 m a.s.l. with the Holocene transgression.

Late Pleistocene deposit including a bone-bearing horizon of mammoth fauna has been described in the series of sections along the lower reaches of the Semiyulyakh River (in the Tirekhtyakh River basin, the right tributary of the Indigirka River). The combination of the unit position between the lower and upper ice complex, radiocarbon date, and fossil complexes testify to the age corresponding to the beginning of MIS 3 (Late Neopleistocene). The lower and upper layers were formed in different environments. The lower layer was formed in the gradually degraded channels of a small river. The upper layer accumulated on a floodplain during meandering of a rather large river. Lenses with autochthonous detritus in the top of the lower layer contain the remains of mammoth fauna, including those with preserved soft tissues. The studied buried deposits are considered as natural resource for which paleoecological reconstructions are highly significant. The richness of the bone-bearing horizon could be explained by the spatial overlap of the in situ and the allochthonous deposits formed as a result of a number of crisis events and regular mortality under standard conditions. The necessary factors for the formation of both types of deposits were intensive meandering and, as a result, active thermal erosion of the sides and bottoms of the valley. The supposed source of the allochthonous deposit was the lower ice complex (MIS 4), mechanical barriers were formed under conditions of slowing down the flow velocity at the bends of overgrown secondary channels. At the same time, the in-situ deposit of mammoth fauna was formed as a result of the formation of marshy traps in under the permafrost melting conditions.

Archaeological sites of the Middle Sartan age are extremely rare within the Cis-Baikal region, and therefore are of a great interest to specialists. Our team discovered a new multi-layered geoarchaeological object of this age, called the Kitoi Most. The paper presents the results of comprehensive studies of the deposits hosting culture-bearing horizons at Kitoi Most. The section has a complete set of regional chronostratigraphic levels of the Upper Pleistocene. Sediments derived from the rocks of the Jurassic sedimentary basin. At the initial stage (MIS 5), the formation of the section occurred in alluvial environment, and subsequently (MIS 4–1) mainly in subaerial conditions with periodic manifestations of pedogenesis and an increased role of colluvial processes. The formation of the magnetic properties of deposits of the loess strata of the section corresponds to the "Siberian" mechanism, which is a superposition of two "Chinese" mechanisms, which explains the presence of superparamagnetic particles in soils as a result of pedogenesis, and the "Alaskan" (wind) mechanism, which causes differences in the magnetic susceptibility of loess and fossil soils by changes in the intensity of wind activity. In the subaerial deposits of the Sartan (MIS 2) age, the presence of nivean-eolian sands was established. These deposits overlap archaeological horizons and correspond to ~17–14.7 ka cal. BP period when sediment genesis was influenced by deep cryoaridization with the manifestation of extremely strong wind. Apparently, this climatic pressure influenced development of the system of human occupation in the region, which is currently expressed in the limited distribution of archaeological objects of this age in the territory of Cis-Baikal.