Annotation of the results obtained in 2021
Completed works During the reporting period, fieldwork was carried out to study the structure of the Upper Pleistocene and Holocene loess-paleosoil series of Ciscaucasia. The work included core drilling, description of sections, and sampling in the following areas: Stepnoe (Stavropol Territory), Ust-Labinsk (Krasnodar Territory), Mikhailovskoye (Rostov Region), Temizhbekskaya (Krasnodar Territory). Reference samples of alluvial and eolian sands were taken for lithological and geochemical studies to search for potential mineral dust sources. The joint laboratory of OSL dating of Moscow State University and the Institute of Geography RAS performed luminescence dating of 10 samples from the Temizhbekskaya section. Together with the earlier datings, this made it possible to build a reliable age model for the Temizhbekskaya section. Sixteen samples from the OT-20 well (Otkaznoye) and ten samples from the U-Lab well (Ust-Labinsk) underwent preliminary preparation. A series of lithological and geochemical studies was performed for Otkaznoye-2020, Stepnoe, Temizhbekskaya, Pyatiletka, Ust-Labinsk, Mikhailovskoye cores: granulometric analysis, determination of the content of organic matter and carbonates, magnetic susceptibility, the frequency dependence of magnetic susceptibility, color measurement, bulk chemical analysis. The results of climate modelling of the PMIP4 project were used to analyze the influence of climatic conditions on dust emission for the following periods: the last glacial maximum (LGM, 21 ka), the Holocene optimum (midHolocene, 6 ka), the Mikulin interglacial (lig127k, 127 ka). The results of paleoexperiments were compared with a control experiment on the reproduction of the preindustrial climate (piControl). The results of two models INMCM and MIROC were analyzed. Model changes in the intensity of dust sources were considered. These data reflect the climatic conditions of dust formation - predominantly humid conditions. Meteorological data were analyzed, including wind direction and speed and their relationship to dust storms. Data were received from the All-Russian Research Institute of Hydrometeorological Information - World Data Center (VNIIGMI-MCD) website. Data have been received from 7 weather stations in Ciscaucasia since 1966. Wind roses have been constructed that takes into account wind directions at any speed, with a speed of more than 10 m/s (wind speed capable of carrying the sand fraction) and during dust storms. During the reporting period, project members took part in three Russian conferences, where they made oral presentations on the project results. Three articles were submitted and accepted for publication. All articles will be published in journals indexed in WoS and/or Scopus. Main scientific results It has been established that three phases of soil formation are distinguished in the structure of the Mezin pedocomplex in all upland areas. The Bryansk interval is much less expressed; it is often enormously extended and has 2-3 independent subphases of embryonic soil formation. In almost all studied LPSs, two noticeable peaks of sand are distinguished, which correspond to the beginning of MIS 2 and MIS 5b. The Kuban LPS are distinguished by a characteristic pattern of changes in particle size distribution with depth; the main feature is a sharp increase of the sand content in MIS 2 - MIS 1. There is a strongly marked relationship between the content of the sand fraction in the loess and the distance to the massifs of alluvial sands and sandy loams, the main of which are located in the east Caspian lowland and on the terraces of the Don and Kuban rivers. An anomalously high thickness of Upper Pleistocene and Holocene LPS is observed in the Stepnoe area. Thus, according to preliminary estimates, more than 23 m of loess-like sandy loam has accumulated in Stepnoe over the past 60 thousand years. Holocene loess thickness can exceed 3 m in this area. The results of luminescent dating of the Temizhbekskaya section made it possible to estimate the age of the LPS above volcanic ash layer (Upper Pleistocene), volcanic ash layer (~220 ka), and loess-like loam strata under volcanic ash layer (230–260 ka). Based on our own and published materials (data on the structure of the LPS in 25 controversial sections and boreholes of Ciscaucasia), the average sedimentation rates for stratigraphic units of the Upper Pleistocene were calculated. The collected data conclude that the loess accumulation rates are related to the distance to the sandy massifs undergoing deflation. Moreover, the area of these deflation areas (sources of mineral dust) correlates with the average loess accumulation rates in the adjacent loess-paleosol series. In terms of time, there is a clear division according to the average sedimentation rate. In cryochrones MIS 4 and MIS 2, the average rates of loess accumulation throughout Ciscaucasia were 1.5 and 2.5 times higher, respectively, than the average rates established for thermochrones (MIS 5, MIS 3, and MIS 1). A spatial analysis of the structure and composition of the loess cover showed that the Caspian lowland has been and remains the dominant source of mineral dust for the territory of Ciscaucasia over the past 130 thousand years. Massifs of sandy and sandy loam deposits formed by the alluvium of the Terek, Kuma and Volga rivers are deflated by strong easterly winds in the arid climate, and masses of mineral dust are transported far to the west up to the Sea of Azov. The content of the sandy fraction in loess and the average rate of loess accumulation naturally decreases from east to west, from the Terek-Kuma lowland to the Sea of Azov. Terraces and alluvial estuarine plains of the Don and Kuban rivers are secondary sources of mineral dust, increasing the content of the sand fraction in loess and the rate of loess accumulation in the areas adjacent to the valleys. Based on the results of model experiments, it is shown that the general localization of the main sources of mineral dust has not changed dramatically in the studied region over the past 130 thousand years. The intensity of dust formation in warmer epochs was generally lower than in cold ones. At the same time, when comparing experiments on the INMCM and MIROC models, significant differences in dust emission volumes are revealed, which are probably associated with differences in the boundary conditions of model experiments and with a low spatial resolution of the models. Archival meteorological data show that the western and eastern wind directions are predominant for all the considered meteorological stations of Ciscaucasia. The northern and southern winds share does not exceed 10-20%. During dust storms, the east wind direction sharply prevails, more than 80%. Based on the data obtained, it can be concluded that the transport of mineral dust from east to west dominates in dust storms.

 

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Annotation of the results obtained in 2022
During the second year of the project implementation, field work was carried out in eight key areas of Ciscaucasia in order to obtain materials on the structure and composition of the Upper Quaternary loess-soil series (LPS). During the work, drilling with core sampling, clearing of outcrops and pitting, description and documentation of cores and section walls, sampling for luminescence dating, lithological and geochemical studies, petro- and paleomagnetic studies, paleosol studies were carried out. Preliminary results of luminescence dating of a new series of 16 samples for core OT-20 (Otkaznoe plot) were obtained. The dates confirm the Upper Pleistocene age of the exposed LPS and detail the earlier stratigraphic subdivision scheme. At the Otkaznoye site, in three mine workings at the level of the Krutitskaya paleosol (MIS 5c), previously unexposed volcanic ash was found, dispersed in the loess. In terms of its stratigraphic position, the ash presumably corresponds to the Elbrus tephra described in the core from the Sarmatskaya well (SARM) in the bottom sediments of the Caspian Sea, the age of which is estimated at 84.6±7.4. For the first time, the structure of the Mezin pedocomplex (MIS 5), which was previously available only in well cores, was uncovered for the Otkaznoye site in clearing. On the basis of morphological and micromorphological features, the Krutitsa (MIS 5c) and Salyn paleosols (MIS 5e) were diagnosed. The Krutitskaya paleosol belongs to Calcic Gypsic Kastanozem Cambic Siltic Tephric according to the international classification WRB (2015). The Salyn soil was defined as Calcic Gypsic Kastanozem Siltic Cambic and is similar to the modern Holocene soil. The Salyn soil was formed under alternating wet and arid conditions, as evidenced by the abundance of carbonate nodules and large ferruginous-manganese nodules and spots. As a result of the petro- and paleomagnetic study of the loess-soil series in two sections (OT-22R and OT-22Sh2) at the Otkaznoye site, it was found that the prevailing direction of paleowinds in the study area at the beginning of the Late Pleistocene was ESE–WNW. During the first paleomagnetic studies in the sections, it was not possible to reveal the excursion of the Blake geomagnetic field expected for this time interval (~120 ka), which may be due to the peculiarities of the paleomagnetic record in the loess-soil deposits of the region or partial erosion of the sedimentary sequence and requires more detailed research. An analysis of the array of geochemical data showed that the loesses of Ciscaucasia have a very similar, predominantly granodiaritic composition, enriched in carbonates and clay. They were significantly altered by weathering processes prior to eolian sedimentation. Reliable geochemical trends indicating the sources of aeolian material have not yet been identified. Age models of sedimentation and maps visualizing the change in sedimentation rates and sand content in LSL were constructed for the main thermo- and cryochrons of the late Pleistocene and Holocene. From these results, it can be seen that the content of the sand fraction in loess and the average rate of loess accumulation naturally decrease from east to west, from the Tersko-Kuma lowland to the Sea of Azov. In loess formed during cryochrons (MIS 4 and MIS 2), the sand content is on average 1.3 times higher than in loess of thermochrons (MIS 5, MIS 3 and MIS 1). It is confirmed that the Caspian lowland has been and remains the dominant source of mineral dust for the territory of Ciscaucasia over the past 130 thousand years. In the Caspian Sea, massifs of sandy and sandy loam deposits in an arid climate are blown away by strong easterly winds. The wind carries masses of mineral dust far to the west up to the Sea of Azov. The terraces and alluvial estuarine plains of the Don and Kuban are secondary sources of mineral dust, increasing the content of the sand fraction in the LPS in the territories adjacent to the valleys. The results of comparison of reference sections of the Late Quaternary LPS of the Ciscaucasia with global and regional indicators of paleoclimate allow us to draw the following preliminary conclusions: 1) changes in sedimentation rates and average sizes of loess particles are generally consistent with changes in climate humidity in Europe and the extratropical space of the Northern Hemisphere; 2) the likely leading factor influencing the change in the rate of accumulation of mineral dust is the degree of aridity in the areas of deflation - the Caspian region; 3) the second most important factor influencing the intensity of loess accumulation is the degree of development of the vegetation cover in the areas of accumulation of mineral dust; 4) Fluctuations in the level of the Caspian Basin are a secondary factor in the accumulation of loess even in the eastern regions of the distribution of the LPS of Ciscaucasia.

 

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