The Lesser Caucasus region is located in the northern part of the Armenian Highland, within the active Arabia-Eurasian collision zone. Numerous and various geological hazards, such as large earthquakes can be observed in this region. They can reach M7 +/- magnitude inducing surface ruptures and strong ground shaking that in turn can trigger landslides and liquefaction phenomena. One of the most important sources of earthquakes is the PambakSevan-Syunik fault (PSSF), which crosses the entire Armenian territory including Lake Sevan with population estimated at 280,000 around it. In this work, we conducted a paleoseismological study along the VanadzorArtanish segment of the PSSF, on the northern shore of the Lake Sevan. Our findings indicate that this fault produced a Mw 7.2 earthquake between 901 and 2333 cal. BC resulting in a surface rupture of at least 22 km and a vertical displacement component of approximately 2 m. Based on our observations, this large earthquake most likely triggered associated phenomena such as landslides and a lake tsunami. These new results demonstrate that characterizing the paleoseismology of active faults in mountainous regions, especially in densely populated areas like Armenia, must be combined with the analysis of potential associated phenomena to provide a complete geohazards assessment.

The history of studying glacial complexes in North-Eastern Siberia goes back more than 150 years. During this period, extensive geological and geomorphological features were obtained, which made it possible to determine the stages, nature and extent of glaciations. At the same time, the lack of direct dating of the glacial relief obtained by geochronological methods does not allow for full-fledged paleogeographic reconstructions. This leads to discussions in both Russian and English literature about the possibility of the existence of glaciation in the mountains of North-Eastern Siberia. In this regard, to determine the size and time of glaciation in the southern part of the Chersky Range, we carried out a complex of geomorphological and geochronological studies, which are part of the international project “Searching for the missing ice sheet in Eastern Siberia”. Because of fieldwork in the Ohandya Ridge, in the Malyk-Sien River valley, three terminal moraine ridges have been identified, reflecting different stages of glaciation. Based on the dating of exposed boulders within three terminal moraine complexes, 22 10Be cosmogenic dates were obtained. The average exposed age for the outer moraine is 120.8±13.7 ka, for the middle one North-Eastern 37.7±4.9 ka and for the internal moraine North-Eastern 13.8±2.2 ka. The age of the terminal moraine complexes testifies to the mountain-valley character of the glaciation of the Chersky Range in the Middle and Late Pleistocene, and emphasizes the trend towards a gradual decrease in the maximum length of glaciers in Northeast Asia. The successive reduction of glaciers from MIS 6 to MIS 2 indicates an increase in the deficit of atmospheric precipitation and a significant cryoaridization of the region. The decreasing trend may be related to the sharply continental conditions observed in the interior of Eurasia and western North America. This trend contrasts with much of the glaciated areas in the Northern Hemisphere, where the maximum area of Late Pleistocene glaciers is reconstructed for LGM time (MIS 2). The obtained datings of the glacial complexes of the Chersky Ridge confirm that at the end of the Middle and Late Pleistocene glaciations here were of a limited nature and there was no single ice cover in the mountains.

The North Darhad Fault, a major N-S fault at the SW Baikal Rift, demonstrates weak present-day activity, but several morphotectonic features indicate the occurrence of strong surface-rupturing earthquakes in the past. The seismic potential of the North Darhad Fault has not been accurately assessed, leaving a gap in the assessment of the seismic hazard. In this paper we present remote and field morphotectonic and paleoseismological studies carried out along this fault system. A detailed topographic mapping of the fault scarp in alluvial surface and trenching across the fault revealed two paleoseismic events responsible for the scarp formation. Dating of organic remnants found in the cross-section allow estimating a Holocene age for the paleoearthquakes and bracket the vertical slip rates along the North Darhad Fault between 0.3 +/- 0.06 mm/yr (min) and 0.6 +/- 0.12 mm/yr (max) over the last - 8.4 ka. The obtained morphotectonic and paleoseismological data suggest that the North Darhad Fault has produced two magnitude Mw7 earthquakes separated by mean recurrence period of - 3.5 ka. We have demonstrated that within the SW Baikal Rift the - M7-7.5 earthquakes likely occur during temporal clusters along the faults separated in space by up to 250 km. The slip rates along the North Darhad Fault allowed us to compute the age of the Darhad Basin at 6.5-3.3 Ma, suggesting a synchronous formation of fault-controlled horstgraben systems throughout the SW Baikal Rift. The opening of the Darhad Basin fits well into the pull-apart model of deformation between the two largest strike-slip fault systems - Bulnay in the south and MondyTunka-Sayan in the north.

The Sayan-Tuva Upland is the northernmost positive relief of Central Asia, associated with the India-Asia collision. It formed on the boundary of the Siberian Craton in late Miocene-early Pliocene time and is characterized by uplift and shear displacement of lithospheric blocks. In this study, we answer the question of how deformation is distributed within the Sayan-Tuva Upland and what are the rates and age of horizontal displacements. Using morphotectonic and palaeoseismological analyses, we have calculated the displacement rates and onset of activation of three faults: Erzin-Agardag, Sayan-Tuva and Kaakhem, which are fragments of large strike-slip fault systems that cut across the entire Sayan-Tuva Upland. For the Erzin-Agardag Fault, the rate of left-lateral displacement is 0.7-1.4 mm/yr and the age of strike-slip reactivation is estimated to be 2.1-1.1 Ma. For the Sayan-Tuva and Kaakhem faults, the minimum horizontal displacement rates are 0.9 +/- 0.1 and 0.6 +/- 0.1 mm/yr, and the maximum ages of the onset of strike-slip displacements are 2.4 Ma and 5 Ma, respectively. We propose that 1.1-2.1 Ma ago there was a kinematic change that activated left-lateral strike-slip faults, leading to the formation of the modern kinematic model, characterized by eastward movement of lithospheric blocks along inherited fault systems between the Hangay Dome and the Siberian Craton. Analysis of slip distribution and trenching across the Erzin-Agardag Fault allowed estimating the mean recurrence interval of the similar to M7.8 earthquakes between 9.4 and 4.7 ka. The Erzin-Agardag Fault has produced multiple displacements with an amplitude of similar to 6.6 m and follows a characteristic slip model.

A combined geomorphological and geochronological investigation was carried out aiming at determining the cause of the Darhad paleolake formation and dating the Darhad megaflood. Based on the analysis of satellite image mapping, new data were obtained revealing conditions of glacial dams along the Shishkhid Gol valley. We hypothesize that large glaciers in Khara-Baryangiin Gol and Ikh-James Gol downstream of the Tengis Gol mouth were the main causes of the highest Shishkhid Gol backwater. The estimated height of this glacial dam there was about 300 m. The presence of paleolake shorelines at an altitude of 1713 m in the immediate vicinity of this glacial dam confirms its dominant role for the formation of the Darhad paleolake. Based on cosmogenic 10Be exposure ages obtained on boulders from four fields of gravel dunes and of an erratic boulder exposed within a bar along the Yenisei River valley in the Tuva Basin, we infer that two among the three age peaks observed may correspond to megafloods at 36-38 ka and 18-23 ka.

The Early Cretaceous topographic evolution of Transbaikalia was largely governed by the tectonic evolution of the Mongol-Okhotsk orogen. The collapse of the Mongol-Okhotsk orogen triggered the formation of metamorphic core complexes and associated extensional basins, widespread throughout Transbaikalia, North Mongolia, and North China. Numerous lithofacies and biostratigraphic studies have been carried out from the sedimentary deposits of the Transbaikalia basins. However, the absence of absolute ages for the sedimentary series, as well as sediment source-to-sink analysis do not allow to accurately characterize the regional topographic evolution. We focused our study on the Gusinoozersk Basin of Western Transbaikalia, where extensive sedimentary sections of Lower Cretaceous deposits have been preserved. We provide new U/Pb (LA-ICP-MS) data on detrital zircons from sedimentary series and 40Ar/39Ar data on intruding rocks. We review the paleontological data to clarify the age of the paleogeographic events associated with the collapse of the Mongol-Okhotsk orogen, as well as to correct the age of faunal complexes in Western Transbaikalia. Our geochronological results show that the formation of the Cretaceous basins of Transbaikalia began around 136–130 Ma, accompanying the main episode of extension associated with the exhumation of the metamorphic core complexes. The lowest coarse-clastic formation characterizes the rapid subsidence and the predominance of proximal sediment sources. Distal provinces also made a contribution to sedimentation indicating the rise of a positive topography characterizing the exhumation of the metamorphic core complexes. Overlying fine-grained formations indicate a significant smoothing of the topography, suggesting that from middle Aptian, Western Transbaikalia developed in a relatively calm tectonic regime. We also show that the basins of Transbaikalia were formed both in conjunction with the exhumation of metamorphic cores complexes and reactivated structural sutures. Revised data on dinosaur fauna and palynology, together with the dating of host deposits, provide insights on the Early Cretaceous paleoenvironmental evolution.

The Badar Sand Field is a geomorphological phenomenon representing a dome structure that dominates the topography of the subsiding Tunka Depression in the SW Baikal Rift. Many interpretations of its origin, including tectonic uplift, have been proposed, but the question remains open. We propose a new model to explain its genesis, based on a thorough analysis of both new and previously published geomorphological and sedimentological data. We suggest that the accumulation of the Badar Sand Field occurred in two stages: aquatic and aeolian. The lower part of the sandy deposits accumulated during the long-term existence of a landslide-dammed paleolake within the Tunka Depression. The upper part was formed after the drainage of the paleolake due to aeolian redeposition of sands. New results of OSL-dating from the vertical 40-m geological cross-section "Badar" showed that the accumulation of lake sediments occurred in the period 24-15 thousand years ago (MIS2). Based on the analysis of satellite images, we modeled the paleolake and determined that it arose as a result of landslides that dammed the antecedent section of the Irkut river valley in the Elovsky Spur. The analysis of the Irkut river terraces showed the absence of tectonic uplift within the Tunka Depression in the Holocene. The incision of the Irkut River at 40-90 m into the Badar dome occurred as a result of the restoration of equilibrium in the longitudinal profile of the river due to changes in sedimentation conditions in the post-glacial period.

The Mondy Fault is a 90 km long E-W trending active structure belonging to the southwestern part of the Baikal rift system, connecting the Tunka depression to the East to the Hovsgol rift to the West. The fault is well expressed in the morphology and formed during the Neogene within a transtensional strain regime (left-lateral + normal) contemporaneously with the opening of the Baikal Rift. On April 4th, 1950, the fault produced a large earthquake with a moment magnitude of Mw 6.9, and a left-lateral focal mechanism. Along with other structures of the Tunka depression such as the Tunka and Sayan faults, it represents a seismic hazard for the cities in the region as the Irkutsk agglomeration (1 million people). To characterize its potential activity, we combined morphotectonic and paleoseismological investigations at two sites along the eastern and western parts of the fault, respectively. Our study shows that cumulative left-lateral displacements are associated with a strong reverse component. This indicating that the previous Neogene normal vertical component has been reversed, consistently with the inversion of the tectonic regime observed within the SW Baikal Rift region in the Late Pleistocene-Holocene. We estimated the slip rate along the fault to be 0.9-1.5 mm/yr over the last similar to 13 ka, and identified four large surface-rupturing events with minimum magnitude of 7.4 separated by an average recurrence interval of 3.9-4.6 ka.

Late Quaternary slip rates characterize the seismic potential of an active fault in terms of estimating the average expected recurrence period for rupturing episodes. Along the Baikal Rift faults the slip rate distributions are poorly understood. This study provides morphotectonic and paleoseismological analyses of the Kichera Fault that stretches within the North Baikal Rift over a length of 100 km. Exposure ages of key displaced terraces of the Neruchanda River from in-situ produced cosmogenic 10Be depth profiles show that the highest terrace T5 is older than 315 ka, intermediate terrace T3 was abandoned 100.0 ± 30 ka ago and the lowest terrace T1 is as old as 48.3 ± 19.9 ka. These exposure ages, coupled with terrace elevation from the actual Neruchanda River bed, allow us to estimate the incision rates for the corresponding time periods which are 0.1 (maximum), 0.16 ± 0.05 and 0.19 ± 0.08 mm yr−1, respectively. Using the cumulated amplitudes of the terrace displacement, we estimate the vertical slip rates along the Kichera Fault are 0.42 ± 0.13 and 0.19 ± 0.08 mm yr−1 over the last ~100 ka and ~48.3 ka, respectively. Paleoseismological studies including morphomertic analyses of the tectonic scarp and trenching across the fault allowed estimating the age (5.4 ka) and minimum magnitude (6.8) of the last Kichera Fault rupture. Using the estimates of short- and long-term slip rates, we propose mean recurrence intervals of 5.3 and 2.4 ka, respectively. The last interval is shorter than the time since the last earthquake, indicating that the future event could be of greater magnitude to maintain the long-term average slip rate.

Determining the fault displacement rates and the sequence of formation of intra-rift structures are essential aspects in the study of the evolution of intracontinental rifts. To better understand the development of the Tunka system of basins (Baikal Rift) and the influence of tectonics on landscape evolution, we conducted a morphometric analysis of the Tunka Fault and its transverse drainage network. We studied geomorphic parameters of 64 facets and 74 drainage basins within the Tunka mountain-front in the footwall of the Tunka Fault; these parameters include mountain front sinuosity, the ratio of facet height and width to base length, basin shape, hypsometric integral, asymmetry factor, and the valley width to height ratio. Our main objectives were to determine long-term throw rates for specific mountain front segments and estimate the timing of corresponding geomorphic structures, to characterize the geomorphological response of the transverse drainage systems to fault movements, and to understand the relationship between the morphometry and kinematics of different segments along the Tunka Fault. The analysis of the Tunka mountain front reveals evidence for strong tectonic control on its morphology. We found that the morphological features are strongly influenced by the Late Pleistocene - Holocene kinematic inversion along the eastern part of the Tunka Fault. The Late Pliocene-Quaternary throw rates estimated for specific geomorphic structures vary in the range of 0.8-1.0 mm year(-1), which is compatible overall with the long-term throw rates of other basins of the Baikal Rift. Based on these rates, we estimate the age of fault-controlled subsidence of the Tunka and Khoytogol basins and Nilovsky Spur to be between 3.5 and 1.5 Ma. We also show that geomorphological response of the transverse drainage varies along the Tunka Fault, indicating a close relationship between fault kinematics and landscape response.

The debate regarding the history of water‐level fluctuations in Lake Baikal extends back to the late 19th century and is rooted in the interpretation of the sequence of palaeo‐shoreline terraces observed around the Baikal trough. Modern studies identify terraces up to 200 m above and down to 40 m below the present‐day Lake Baikal water level, and opinions are split between (i) those who regard the lake‐level fluctuations as a function of shifts in water balance associated with glacial and interglacial periods, and (ii) those who attribute the changes to predominantly tectonic factors, permitting water‐balance fluctuations of not more than a few tens of metres. In either case, a definitive lake‐level scheme must also constrain the relative elevation of the Baikal's outlet, which has not been fixed over time. Here, we focus upon the lake‐level changes over the past 50 000 years with a new set of observations from an outstanding sequence of palaeo‐shoreline terraces on Bolshoi Ushkanii Island located in central Lake Baikal. By determining the 14C age of soils rapidly buried by beach deposits on two terraces, we provide direct evidence of lake‐level highstands at ~120–122 and ~72–83 m during Marine Isotope Stage (MIS) 3 (Karginsk interstadial). By integrating these results with the repeated subsidence of Baikal's outlet threshold since MIS 5e, we show that lake‐level fluctuations closely align with swings in glacial and interglacial climate.

The Late Paleozoic–Early Mesozoic Mongol-Okhotsk Ocean extended between the Siberian and Amur–North China continents. The timing and modalities of the oceanic closure are widely discussed. It is largely accepted that the ocean closed in a scissor-like manner from southwest to northeast (in modern coordinates), though the timing of this process remains uncertain. Recent studies have shown that both western (West Transbaikalia) and eastern (Dzhagda) parts of the ocean closed almost simultaneously at the Early–Middle Jurassic boundary. However, little information on the key central part of the oceanic suture zone is available. We performed U-Pb (LA-ICP-MS) dating of detrital zircon from well-characterized stratigraphic sections of the central part of the Mongol-Okhotsk suture zone. These include the initial marine and final continental sequences of the East Transbaikalia Basin, deposited on the northern Argun-Idemeg terrane basement. We provide new stratigraphic ages for the marine and continental deposits. This revised chronostratigraphy allows assigning an age of ~165–155 Ma, to the collision-related flexure of the northern Argun-Idemeg terrane and the development of a peripheral foreland basin. This collisional process took place 5 to10 million years later than in the western and eastern parts of the ocean. We demonstrate that the northern Argun-Idemeg terrane was the last block to collide with the Siberian continent, challenging the widely supported scissor-like model of closure of the Mongol-Okhotsk Ocean. Different segments of the ocean closed independently, depending on the initial shape of the paleo continental margins.

The Tunka Basin is a broad, emerging basin situated between the Baikal Lake to the east and the the Hodvsgodl Lake to the west. The basin is bounded to the north and to the south by the Tunka and the Khamar-Daban mountain ranges, respectively. The Tunka normal fault, located at the southern foothills of the Tunka moun-tain range, is the main structure that controlled the development of the Tunka Basin during the Neogene. Paleoearthquake-surface ruptures attest of its present activity; and show that its western and eastern terminations are undergoing a tectonic inversion characterized by left-lateral-reverse deformations. The southern edge of the Tunka Basin is classically interpreted as being tectonically controlled. In this paper, we present the results of a geomorphological and stratigraphic analysis within its southwestern and southeastern parts suggesting that there is no active fault affecting the foothills of the Khamar-Daban mountain range. The different features observed in the Quaternary deposits are interpreted to be the result of periglacial processes induced by alternating episodes of permafrost aggradation and degradation during the Holocene. Our study concludes that the Khamar-Daban Range and the Tunka Basin are uplifting together, and that the Tunka and Mondy faults are the two main triggers of regional earthquakes.

The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the Mongol-Okhotsk Ocean that separated Siberia from Mongolia-North China continents. Following the oceanic closure, the tectonic evolution of that region was characterized by collisional uplift and subsequent extension that gave rise to the formation of metamorphic core complexes. This complex tectonic setting prevailed simultaneously between 150 Ma and 110 Ma both in Transbaikalia, North Mongolia, and within the North China Craton. Published paleobotanical and paleontological data show that the oldest Mesozoic basins had formed in western Transbaikalia before the estimated age of extension onset. However no precise geochronological age is available for the onset of extension in Transbaikalia. The Tugnuy Basin, as probably the oldest Mesozoic basin in western Transbaikalia, is a key object to date the onset of extension and following changes in tectonic setting. In this study, U-Pb (LA-ICP-MS) dating of detrital zircons from three key Jurassic sediment formations of the Tugnuy Basin are used to identify the potential source areas of the sediments, understand the changes in sediment routing and provide insights on the topographic evolution of western Transbaikalia. Our results show several significant changes in tectonic regime after the closure of the Mongol-Okhotsk Ocean. A wide uplifted plateau formed during the closure of the Mongol-Okhotsk Ocean, determining the Early Jurassic drainage system reaching the Angara-Vitim batholith to the north and shedding sediments to the continental margin to the South. The following collisional event at the end of the Early Jurassic led to the uplift of the collision zone, which partially inverted the drainage system toward the North. A strike-slip displacement induced by the oblique collision initiated some of the early Transbaikalian depressions, such as the Tugnuy Basin at about 168 Ma. A phase of basin inversion, marked by folding and erosion of the Upper Jurassic sediments, could correspond to the short-term collision event that took place during the latest Jurassic-earliest Cretaceous in the eastern Central Asian Orogenic Belt. The following inversion in tectonic regime from compression to extension is consistent with the mid-lower-crustal extension that led to the formation of the numerous metamorphic core complexes throughout northeastern continental Asia during the Early Cretaceous.

The first Sm–Nd isotopic data and U–Pb (LA–ICP–MS) detrital zircon ages from sandstones of the Prisayan and Kuda Formations (the Irkutsk Basin, southern part of the Siberian Platform) have been obtained. They demonstrate that during accumulation of the sediments in the Irkutsk Basin, the contribution of local erosion sources decreased over time, while input from the Paleo–Transbaikalia sources increased. The change in provenance areas was triggered by tectonic rebuilding in Paleo–Transbaikalia caused by the closure of the Mongol–Okhotsk Ocean.

The Jurassic growth of mountain ranges along the southern edge of the Siberian platform occurred in an active tectonic setting related to the closure of the Mongol-Okhotsk Ocean. The oceanic subduction and subsequent continent collision events induced compressive deformations at the platform boundary. Understanding the paleogeography related to the Mesozoic closure of the Mongol-Okhotsk Ocean requires dating and correlation of the Jurassic Prisayan Formation in the Irkut basin and Tugnuyskaya Formation in southwestern Transbaikalia. This work presents structural and paleobotanic results within both formations. 40Ar/39Ar dating of underlying volcanics from the upper member of the Ichetuyskaya Formation is used to refine the age of the sediment series and provide probable correlation. The results show that the Tugnuyskaya Formation initiated at the end of the Middle Jurassic-beginning of the Late Jurassic and was not coeval with the Prisayan Formation, whose upper fine-grained members were deposited in the early Middle Jurassic. 40Ar/39Ar dating of volcanics from the upper member of the Ichetuyskaya Formation yielded a Middle Jurassic age of 167.7 +/- 1.2 Ma (Bajocian to Bathonian). The paleogeographic data analysis based on facies and mineralogical composition of sediments and on a study of source areas from Sm-Nd data and the U-Pb ages of detrital zircons from the deposits in the southern Irkut basin indicates that the deposition of the Prisayan Formation was followed by the intensification of relief building along the southern edge of the Siberian Platform. Our geochronological data show that active tectonic deformations in southwestern Transbaikalia evidenced in the volcanoclastic Ichetuyskaya Formation in the Tugnuy basin also occurred during the Middle Jurassic. The uppermost sediments of the Tugnuy basin were deposited at the end of the Middle Jurassic-Late Jurassic in a quiet tectonic setting with low relief and lacustrine-boggy depositional environments. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Lake Baikal is Earth's deepest lake and an iconic site of scientific study. This vast basin holds sedimentary archives of environmental change dating back to the Miocene and its array of palaeoshorelines and surrounding relief record the past ~1–3Ma of lake-levels and outflows. Here we present an extensive review of previous work alongside a new set of observations concerning the Quaternary development of Lake Baikal, with special focus on lake-level fluctuations and the formation and evolution of the lake's three known outlets. The sequence of shoreline terraces indicates that lake-levels were both higher and lower in the past. Lake Baikal stood ~200m higher during the Last Interglacial, i.e. Marine Isotope Stage (MIS) 5e and dropped to 40m below (present-day) during the Last Glacial Maximum (MIS 2). The relative lake-level variations reflect climate factors and gradual or sudden (coseismic) tectonic impacts on the elevation of the lake's outlet thresholds. Three successive outlets are known: i) the palaeo-Goloustnaya-Manzurka, associated with the Manzurka Alluvium; ii) the palaeo-Irkut, and iii) the currently-active Angara River outlet. We propose that the Manzurka Alluvium is the product of catastrophic events in Lake Baikal. The sudden (possibly coseismic) collapse of the ~15×3km Goloustnaya fault-block into Lake Baikal triggered a mega-tsunami that thrust overwash deposits across neighbouring drainage divides above Lake Baikal and the valleys of the Goloustnaya-Manzurka River system. The age of the Manzurka Alluvium remains poorly constrained, but the mega-tsunami is potentially traceable to an unconformity in drill-core sediments at ~0.8–1.0Ma, although older (late Pliocene) and younger (~125ka) ages have also been proposed. The Irkut outlet existed between MIS 6 and MIS 5 when lake-level was ~200m higher than present (~640–650masl) and a large bay extended into the Tunka rift at Baikal's south-west tip. Lake Baikal retreated from the Tunka rift when lake-level fell by up to 100m in early MIS 5e. We propose that the lake-level fall is connected to a partial collapse of Primorsky Ridge at Listvenichny Bay, which caused Baikal to overspill into the Angara River thereby forming a new outlet. The release of a >4000km3 megaflood down the Angara River valley caused large-scale modification and reworking of valley-fills (MIS 5e). At the end of MIS 2, further collapse of Primorsky Ridge lowered the outlet threshold an additional 50–60m and prompted a second megaflood down the Angara River valley, which left a widespread unconformity where horizontal-bedded sands (dated at ~11.8–13.4ka) overlie cryoturbated deposits of the earlier megaflood. The central role of catastrophic processes at Lake Baikal suggests that, rather than being rare events, coseismic landsliding and mega-tsunami may be more frequent than hitherto recognised.