The study examined the geochemical characteristics of the bottom sediments of lakes Pyasino and Melkoye located in the paleo-glacial zone of the Russian Arctic. This contributes to a better understanding of geochemical processes in these specific Arctic limnic systems and their ecological significance. The data obtained showed a significant enrichment of the sediments with elements typical of the Norilsk ore province, primarily Ni and Cu. Increased concentrations of Ni, Cu, Zn, Co, Cr, and Mo in the upper 10 cm sediment layer in Lake Pyasino are the result of anthropogenic influence on the lake ecosystem. Pore water of the sediment, which was first studied in the region, was enriched with NO3- and PO4 3- biogenic compounds and dissolved organic carbon as a consequence of microbial decomposition of organic matter (OM). This resulted in the migration of labile OM components into pore water and the appearance of the reduction conditions. Increased concentrations of Fe, Mn, Al, As, B, Ba, Co, Mo, Ni, Si, Sr, V, and Y in the pore water compared to lake water are due to diagenetic processes in the bottom sediments. Our data demonstrate the role of organic matter in changes in the mineral composition of the sediments and in the formation of authigenic minerals (pyrite and calcite). In addition, low levels of reduced forms of sulfur indicate low intensity of bacterial sulfate-reduction processes in the sediments.

A complex of mineralogical and geochemical data from the south of Western Siberia indicates that the middle Holocene warm and dry epoch ended 5.5–4 cal ka BP with the further onset of more humid and cold conditions in the region. Significant changes in the regional climate probably occurred about 3.6–3.1 cal ka BP that is marked by an increase in the content of carbonates in the sediments, and by changes in vegetation. A general trend in the content of Mg in the carbonate fraction of lake sediments clearly shows a variation in water salinity as a response to climate change. There was a cyclical change of periods of drying/humidification of the Holocene climate of southern Western Siberia.

A 6-meter core of Holocene sediments from Lake Dukhovoe was studied. As shown by the radiocarbon dating of lacustrine sediments, Lake Dukhovoe was formed in the Early Holocene (10 cal ka BP). The upper 180 cm of sediment is represented by sapropel, and the boundary of lake sediments is at 293 cm. This is an early stage of lake evolution, devoid of biogenic sedimentation. The microbiological studies of the sediment were carried out, which showed a high total number of heterotrophic bacteria in the upper (0–15 cm) and deeper (110–180 cm) sapropel intervals. Mineral bottom sediments (180–293 cm) are characterized by the presence of groups of phosphorus-reducing and ferromanganese bacteria. The contents of Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr and Cr in sapropel are within the average concentrations for the earth’s crust, and U and Mo exceed them.

Elongated biconvex Carex fossil fruits are relatively common in fossil assemblages, but they are of much uncertain taxonomic affinity. Three fossil-species have been erected to accommodate the materials from the respective type localities (C. klarae, C. paucifloriformis and C. paucifloroides) and a number of superficially similar-looking fossils were reported from other sites. The formerly proposed affinities mostly pointed to the extant C. pauciflora (subgen. Euthyceras) or Carex sect. Cyperoideae (subgen. Vignea), depending on the authors. But despite the similar superficial resemblance of the fossil remains to these not very closely related sedge taxa, other groups are also possible matches. We used a comparative approach employing stereomicroscope and SEM to analyze the affinities of several Old World “mummified” fossils (ca. 23 to 0.1 Ma) of elongated biconvex fruits. Several samples showed a fair preservation of previously unattested microscopic characters. In particular, one of them allowed us to detect an indirect record of fine silica body morphologies (impressions) on the periclinal walls, which permitted the sound taxonomic placement of the remains from the Miocene of Siberia as a Carex sect. Cyperoideae. In all the other fossils analyzed, the epidermal cell outline and the central position of the main silica body were sufficient to discard assignment to subgen. Euthyceras, despite a purported affinity to C. pauciflora reported in previous literature. In the absence of detailed information on silica bodies, epidermal cell (exocarp) details in fossil specimens do not seem to be determinant for the systematic placement. However, the addition of diagnostic style characters pointed to sect. Cyperoideae as the best match with the available information. Our data support a continued presence of Carex sect. Cyperoideae in the Old World since the Miocene, which candidates Eurasia as a possible place of origin for it, despite DNA-based reconstructions alone proposed North America. This study underlines the importance of detailed taxonomic studies to properly address the identity of fossils and unravel the biogeographic history of plants.

The Holocene temperature conundrum, the discrepancy between proxy-based Holocene global cooling and simulated global annual warming trends, remains controversial. Meanwhile, reconstructions and simulations show inconsistent spatial patterns of terrestrial temperature changes. Here we report Holocene alkenone records to address spatial patterns over mid-latitude Eurasia. In contrast with long-term cooling trends in warm season temperatures in northeastern China, records from southwestern Siberia are characterized by colder conditions before ~6,000 years ago, thus long-term warming trends. Together with existing records from surrounding regions, we infer that colder airmass might have prevailed in the interior of mid-latitude Eurasian continent during the early to mid-Holocene, perhaps associated with atmospheric response to remnant ice sheets. Our results challenge the proposed seasonality bias in proxies and modeled spatial patterns in study region, highlighting that spatial patterns of Holocene temperature changes should be re-considered in record integrations and model simulations, with important implications for terrestrial hydroclimate changes.

The Itmurundy Zone of Central Kazakhstan is a key structure in the core of the Kazakh Orocline representing a typical Pacific-type orogenic belt hosting accretionary complex, ophiolite massifs and serpentinite mélange. The main controversies in the existing tectonic models of the Itmurundy Zone are about the timing of subduction and accretion, the direction and kinematics of subduction and the number of oceanic plates. A new model for the early Paleozoic tectonic story of the Itmurundy Zone is postulated in this paper, based on new detailed geological and U–Pb detrital zircon age data, combined with previously documented geological, U–Pb age, microfossil, geochemical and isotope data from igneous rocks, deep-sea sediments and greywacke sandstones. The present study employs the Ocean Plate Stratigraphy (OPS) model to explain the tectonic processes involved in the evolution of the Itmurundy Zone and to present a holistic story of Ordovician oceanic plate(s), which accretion formed an accretionary complex. The detailed mapping allows distinguishing three types of OPS assemblages: (1) Chert-dominated, (2) OIB-hosting, and (3) MORB-hosting. The U–Pb ages of detrital zircons from sandstones of OIB and Chert types show unimodal distributions with similar main peaks of magmatism at 460–455 Ma in the provenance, and their maximum depositional ages (MDA) span 455–433 Ma. Two samples from OPS Type 3 show the peaks of magmatism both at ca. 460 Ma and the MDA of 452 Ma and 459 Ma, respectively. The MDA of sandstones and microfossils data from chert show the younging of strata to the south and SE in Types 1 and 2 and to NEE for Type 3 (in present coordinates) suggesting double-sided subduction to the NNW and SEE and, accordingly, the co-existence of pieces of two oceanic plates in Ordovician time. The U–Pb zircon data from both igneous and clastic rocks indicate a period of subduction erosion in early Ordovician time. As a whole, the accreted OPS units of the Itmurundy Zone record the timing of subduction and accretion from the early Ordovician to the early Silurian, i.e., 60 Ma at shortest.

Chemical composition of bottom sediments and pore waters of organic-mineral sediments (sapropel) of Lake Kotokel (Eastern Baikal region) has been studied, based on long drilling cores, 14.5 and 16.5 m. A reduction type of diagenesis has been established, during which destruction of organic matter, transformation of the chemical composition of pore waters and the formation of authigenic minerals occur. Even in the uppermost intervals of sapropel, organic matter is being profoundly transformed and differs significantly in composition from that of bioproducers (plankton). The major role in diagenetic transformations of organic matter belongs to different physiological groups of microorganisms, primarily heterotrophic, amonifying and sulfate-reducing bacteria. During diagenesis, the basic chemical composition of pore waters (HCO3-, SO42-, Cl-, Ca2+, Mg2+, K+, Na+) changes, trace elements (Fe, Mn, Sr, Ba, Pb, As, Co, Ni) redistribute, concentrations of HCO3-, NH4+, PO43- and Si increase; this is caused by destruction of organic matter. In the process of bacterial sulfate reduction in pore waters, the concentration of SO42- decreases along the depth of the section, and in the sediment the proportion of reduced forms of sulfur increases and the isotopic composition of sulphur delta 34S changes. Transformation of chemical composition of pore waters and the activity of microorganisms leads to the formation of authigenic pyrite, rhodochrosite, and barite.

––We present the results of comprehensive studies of Holocene bottom sediments from the shallow hypersaline (mineralization up to 282 g/L) Lake Bolshoi Bagan, located in the East Baraba lowland (south of Western Siberia). The research methods include X-ray diffractometry (XRD), IR spectroscopy, laser granulometry, scanning electron microscopy, elemental analysis of sediments and pore water, radiocarbon (14C AMS) dating. It has been found that during the Holocene an intensive authigenic mineral formation took place in the lake basin; gypsum, halite and carbonates of calcite-dolomite series dominate among the newly formed mineral phases. Mg-calcites with different Mg contents, excess-Ca dolomites, aragonite and occasionally Mg-siderite have been found in the assemblage of carbonate minerals by mathematical modeling of complex XRD patterns. Mineralogical and crystallochemical studies, supplemented by the results of geochemical analyses, allowed us to identify four stages of the evolution of Lake Bolshoi Bagan in the Holocene, due to regional climate variations. The boundaries of the stages in general correspond to the boundaries of the climatostratigraphic phases by the Blytt–Sernander system: Stage I (the end of the Boreal) – the lake formation, humid climate; Stage II (Atlantic) – climate aridization, shallowing of the lake; Stage III (Subboreal) – unstable climate, frequent change of conditions; Stage IV (Subatlantic) – moderately cool and dry climate.

Lake Chany is the largest endorheic lake in Siberia whose catchment is entirely on the territory of Russia. Its geographical location on the climate-sensitive boundary of wet and dry landscapes provides an opportunity to gain more knowledge about environmental changes in the West Siberian interior during the Holocene and about the evolution of the lake itself. Sediment cores obtained from the Yarkov sub-basin of the lake in 2008 have been comprehensively studied by a number of approaches including sedimentology and AMS dating, pollen, diatom and chironomid analyses (with statistical interpretation of the results), mineralogy of authigenic minerals and geochemistry of plant lipids (biomarker analysis.). Synthesis of new results presented here and published data provides a good justification for our hypothesis that Lake Chany is very young, no older than 3.6 ka BP. Before that, between 9 and 3.6 ka BP, the Chany basin was a swampy landscape with a very low sedimentation rate; it could not be identified as a water body. In the early lake phase, between 3.6 and 1.5 ka BP, the lake was shallow, 1.2–3.5 m in depth, and it rose to its modern size, up to 6.5 m in depth, during the last millennium. Our data reveal important changes in the understanding of the history of this large endorheic lake, as before it was envisioned as a large lake with significant changes in water level since ca. 14 ka BP. In addition to hydrology, our proxies provide updates and details of the regional vegetation and climate change since ca. 4 ka BP in the West-Siberian forest-steppe and steppe. As evolution of the Chany basin is dependent on hydroclimatic changes in a large region of southern West Siberia, we compare lake-level change and climate-change proxies from the other recently and most comprehensively studied lakes of the region.

—A 6-meter core of the Holocene sediments in Lake Dukhovoe is studied. The material composition of the core is heterogeneous and has clear bedding. Lacustrine sediments are represented by the upper 293 cm. Each bed of the sediments is subjected to microbiological analysis. A high total number of heterotrophic bacteria is revealed in the upper (0–15 cm) and deeper (110–150 cm) sapropel intervals. Sulfate-reducing bacteria are identified only in Chrysophyceae cysts. The CaO/Fe2O3 ratio shows the degree of “carbonate content” of bottom sediments. It is low in the lake sapropel (0.2), which indicates the geochemical specificity (carbonate-free sapropel). Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr, and Cr concentrations in sapropel are within the average concentrations for the Earth’s crust, shale, and oceanic pelagic clays, while U and Mo concentrations exceed them. Phytoplankton is enriched in phosphorus (biogenic element) and chalcophile elements (Zn, Cd, Sn, Sb, Hg, Pb, and Cu), which characterize the pollution of the modern atmosphere of the Baikal region. Diagenetic processes result in the transformation of the pore waters, namely an increase in mineralization as compared to lake water, an increase in the concentrations of biogenic components (HCO3-, NH4+, NO3-, and PO43-) and a decrease in SO42-. Pyrite framboid accumulations are revealed in organomineral sediments below the horizon of 200 cm, and iron phosphates represented by vivianite are identified in sapropel.

The paper presents new data and reviews previously obtained results on the late glacial to Holocene history of peatlands in the southern part of the Baikal region under conditions of regional climate changes. To better understand climate signals, we have combined vegetation and geochemical variation data in 4.6 m thick peat deposits in the Vydrino bog located on the Tankhoi piedmont plain south of Lake Baikal. The territory has been swamped since 13.1 cal ka BP when the peatland started developing as a fen upon a sedimentary substrate. The 13.1-9.5 cal kyr climate record included two events of warming separated by an excursion of dry cold climate. Warming continued till 9.0 cal ka BP and eutrophic peat formation occurred in favorable temperature and moisture conditions. Another warming episode between 9.0 and 8.4 cal ka BP ended up with the Holocene climate optimum while the bog became mesotrophic. About 7.3-6.5 cal ka BP, the temperature and moisture inputs were no longer optimal for fir and spruce forests in the Vydrino area, which led to dramatic changes in landscape and vegetation. The wet and warm climate gradually became drier and colder from 6.5 to 2.3 cal ka BP, with a brief warm excursion about 5.5-5.3 cal ka BP. The peat deposition was interrupted in a cold climate from similar to 2.3 cal ka BP to similar to 0.7 cal ka BP, and the bog became oligotrophic afterwards. The newly obtained data allowed us to compare the paleoclimatic indicators available for the south Baikal region to determine their compatibility and inconsistency. In addition, we provide a general view to the quality of the climate and environmental reconstructions in the Baikal region by comparison of the data on its peatland study.

This paper presents results of biogeochemical investigation of the Holocene organic-rich sapropelic sediments of Lake Dukhovoe situated not far from the Baikal. The main source of organic matter in Lake Dukhovoe is phytoplankton, which serves as a biogeochemical barrier where elements are accumulated from water and then buried in the bottom sediments. Microorganisms (e.g., bacteria, micromycete and actinomycetes) play significant role in decomposition of organic matter and formation of organic-mineral complexes in four distinguished types of sapropels: organic, organic-mineral, mineral-organic and mineral. Diagenetic transformations of the Lake Dukhovoe sapropels under influence of mechanical, biochemical, microbiological and physicochemical processes lead to transformation of element speciation. A boundary between oxidizing and reducing diagenesis conditions is at the depth of 167 cm in the sapropel core. Change of the conditions forms geochemical barrier in bottom sediments and control the formation of secondary phases (organic-mineral complexes, diatomite, framboidal pyrite, vivianite, carbonates, etc.) as well as processes of accumulation and leaching of chemical elements. Additionally, high contents of Fe, Mn, Cu, Zn, Pb, Cd, and Mo in the upper 10 cm of the sapropel might have been caused by forest fires and anthropogenic factors. The fact of marcasite formation in the stomatocysts of Chrysophyte algae (golden algae) is new and was established for the first time. Based on the results and geochemical equilibrium modelling, the stomatocysts of Chrysophyte algae can be considered as a microreactor for iron sulfide formation.

The results of lithological and mineralogical studies of the Holocene bottom sediments from the shallow hypersaline (mineralization up to 282 g/L) Bolshoi Bagan Lake, located in the East Baraba Lowland (southwestern Siberia), are presented. The research methods included X-ray diffractometry (XRD), infrared spectroscopy, laser grain size analysis, scanning electron microscopy, elemental composition study, and radiocarbon ( 14 C AMS) dating. It was found that intensive authigenic minerogenesis occurred in the lake basin during the Holocene. Halite, gypsum, and carbonates dominate among the newly formed mineral phases. Mg-calcites with different Mg contents, excess-Ca dolomites, aragonite, and occasionally Mg-siderite have been established in the assemblage of carbonate minerals by the mathematical modeling of complex XRD patterns. The mineralogical and crystallochemical studies, supplemented by the results of other analyses, allowed us to identify four stages of the evolution of Bolshoi Bagan Lake in the Holocene, due to variations in the regional climate. The boundaries of the stages generally correspond to the boundaries of the climatic stratigraphical phases by the Blytt–Sernander classification: stage I (the end of the Boreal), lake formation, humid climate; stage II (Atlantic), climate drying, shallowing of the lake; stage III (Subboreal), unstable climate, frequent change of conditions; stage IV (Sub-Atlantic), moderately cool and dry climate. The mineralogical signals of the global climatic Bond events in southwestern Siberia have been identified.

Contrasting moisture evolutions between westerlies‐dominated Central Asia and monsoonal Asia since the mid‐Holocene have been widely recognized. Yet, inconsistent hydrological records over the early Holocene from both regions hamper our understanding of hydroclimatic changes and associated mechanisms. Here we present isotopic and biomarker (alkenone) records from three Chinese lakes located at both regions to address a possible meltwater role in lake water budget. Our results show the occurrence of particularly depleted isotopic values of lake water associated with lake freshening within the deglaciation and early Holocene. Together with anomalously old 14 C dates, which were also documented in many other Asian lakes, our observations likely indicate substantial meltwater contribution to mid‐latitude Asian lake water budget, along with the climatic warming. Hence, the potential meltwater effect should be considered when inferring Asian summer monsoon and westerlies behavior over this critical period, with important implications to Holocene hydrological reconstructions and future hydroclimatic projections.

The Russian Arctic region is lacking in studies on geochemical changes reflecting early sediment diagenesis in lake environments. The paper presents new data on the compositions of bottom sediments and sediment pore water from two lakes of the Norilo–Pyasinskaya water system in Arctic Siberia. Lakes Pyasino and Melkoye occupy basins left by glaciers that originated from the Putorana Plateau during the Last Glacial Maximum (LGM). Clayey sediments were continuously deposited in the lakes, and the depositional environment has changed only slightly for the last ca. 20 ka. Two sediment cores with lengths of 4.0 and 3.2 m were collected in Lakes Pyasino and Melkoye, respectively, with a Livingstone-type piston corer providing undisturbed, stratigraphically consistent sedimentary sequences. Their analyses revealed a change from oxidized to reduced conditions at a depth of ~10 cm. The concentrations of Ca2+, Mg2+, Na+, and K+, as well as the HCO3−/Ca2+ ratio in pore water, showed a depthward increase indicating the progressive degradation of organic matter. Another trend was the gradual decrease in SO42− alongside increasing HCO3−/SO42− caused by bacterial sulfate reduction, although this was rather weak, judging by the low concentrations of S (II) bound to Fe-sulfides, H2S, etc. Additionally, the microbial digestion of organic matter caused a release of its mobile components, which led to the enrichment of the water in NO3−, PO43−, and DOC. Most of the analyzed elements (Al, B, Ba, Co, Cu, Mo, Ni, Si, Sr, V, and Zn) reach higher concentrations in the pore water than in the lake water above the water-sediment boundary, which is evidence of diagenetic processes. As a result of redox change, immobile Fe (III) and Mn (IV) natural oxides were reduced to mobile Fe (II) and Mn (II) species and migrated from the solid phase to the pore water, and eventually precipitated as authigenic Fe sulfides and Mn carbonates. The results are useful for better understanding the early diagenesis processes in different geographical settings over the huge Eurasian continent.

Abstract. The ostracod record from Lake Sargul infers details of two-stage development of the lake ecosystem during the Holocene.

Abstract. We present the results of study the Holocene sediments of Itkul Lake, a shal low brackish lake with carbonate sedimentation, located in the eastern part of Baraba lowland (Southwestern Siberia, Novosibirsk Region). A 1.8 m thick core of the Holocene (7.9 14C yr) sediments of Itkul Lake has been studied. Based on the geochemical and lithostratigraphic properties of the bottom sediments, we have established the following stages of the lake evolution: (I) the beginning of sedimentation, 7.8 7.0 14 ka; (II) extreme shallowing with a probable complete drying, ~7.0 5.5 14 ka; (III) rise in the water level, ~5.5 4.3 14 ka; (IV) repeated shallowing, 4.3 2.8 14 ka; and (V) subsequent watering, 2.8 0 14 ka. At present, the lake again tends to shallowing.