Greater Caucasus Mountains Research Articles

წყალტუბოს (დასავლეთი საქართველო) „თეთრა მღვიმის“ პრაქტიკული სარგებლიანობის პოტენციალი

Tskaltubo is one of the oldest balneological resorts in Georgia. The city is located in the gorge of the river Tskaltubostskali at an altitude of 95-150 meters above sea level. To the north-east, the city is bordered by the southern slope of the Samgurali Range (Greater Caucasus Mountains), and to the south by the Colchis Plain, which opens to the Black Sea. The hills around the resort are covered with rich subtropical vegetation, evergreen shrubs and deciduous forests (oak, beech, elm). The surroundings of Tskaltubo are also known for karst caves, among which "White Cave", "Sataplia" and in 1984 Vakhushti Bagrationi are distinguished by their significant popularity and attractiveness. Cave of Tskaltubo ("Prometheus") discovered by the expedition squad of the Institute of Geography. Tskaltubo municipality is rich in many historical-cultural and natural monuments. Therefore, in addition to the resort-medical functions, the city is attractive for both foreign and local tourists and vacationers. In the early seventies of the last century, the "Tetra" cave was used to treat patients with diseases of the cardiovascular and respiratory systems. This practice has been stopped in Georgia since the 90s of the previous century. Recent investigations have revealed that its characteristic radioactive and ionizing state has been restored in the cave. The stated circumstance is also confirmed by the present paper. This is a prerequisite that the "white" cave can still be used for medical, tourist or other useful purposes, which will not harm the cave, cave formations and the environment.

Slope deformation, reservoir variation and meteorological data at the Khoko landslide, Enguri hydroelectric basin (Georgia), during 2016–2019

Abstract. The Greater Caucasus mountain belt is characterized by deep valleys, steep slopes and frequent seismic activity, the combination of which results in major landslide hazard. Along the eastern side of the Enguri water reservoir lies the active Khoko landslide, whose head scarp zone affects the important Jvari–Khaishi–Mestia road, one of the few connections with the interior of the Greater Caucasus. Here, we present a database of measurement time series taken over a period of 4 years (2016–2019) that enables us to compare slope deformation with meteorological factors and human-induced perturbations owing to variations in the water level of the reservoir. The monitoring system we used is composed of two digital extensometers, placed within two artificial trenches excavated across the landslide head scarp. The stations are also equipped with internal and near-ground surface thermometers. The dataset is integrated by daily measurements of rainfall and lake level. The monitoring system – the first installed in Georgia – was set up in the framework of a NATO-funded project, aimed at assessing different types of geohazards affecting the Enguri artificial reservoir and the related hydroelectrical plant. Our results indicate that the Khoko landslide displacements appear to be mainly controlled by variations in hydraulic load, in turn induced by lake level oscillations. Rainfall variations might also have contributed, though this is not always evident for all the studied period. The full databases are freely available online at the following DOI: https://doi.org/10.20366/unimib/unidata/SI384-2.0 (Tibaldi et al., 2020).

Potential practical potential of Tskaltubo (Western Georgia) "White Cave"

Tskaltubo is one of the oldest balneological resorts in Georgia. The city is located in the gorge of the river Tskaltubostskali at an altitude of 95-150 meters above sea level. To the north-east, the city is bordered by the southern slope of the Samgurali Range (Greater Caucasus Mountains), and to the south by the Colchis Plain, which opens to the Black Sea. The hills around the resort are covered with rich subtropical vegetation, evergreen shrubs and deciduous forests (oak, beech, elm). The surroundings of Tskaltubo are also known for karst caves, among which "White Cave", "Sataplia" and in 1984 Vakhushti Bagrationi are distinguished by their significant popularity and attractiveness. Cave of Tskaltubo ("Prometheus") discovered by the expedition squad of the Institute of Geography. Tskaltubo municipality is rich in many historical-cultural and natural monuments. Therefore, in addition to the resort-medical functions, the city is attractive for both foreign and local tourists and vacationers. In the early seventies of the last century, the "Tetra" cave was used to treat patients with diseases of the cardiovascular and respiratory systems. This practice has been stopped in Georgia since the 90s of the previous century. Recent investigations have revealed that its characteristic radioactive and ionizing state has been restored in the cave. The stated circumstance is also confirmed by the present paper. This is a prerequisite that the "white" cave can still be used for medical, tourist or other useful purposes, which will not harm the cave, cave formations and the environment.

Diversification and historical demography of the rapid racerunner (Eremias velox) in relation to geological history and Pleistocene climatic oscillations in arid Central Asia

Late Cenozoic stepwise aridification has transformed Central Asia into an arid environment, and the Pleistocene climatic oscillations exerted further ecological impact. Therefore, both aridification and glaciation would have considerably influenced the evolution of many midlatitude species in arid Central Asia (ACA). However, strong biotic evidence supporting this role is still lacking. Here, we test this perspective using a phylogeographic study of Eremias velox, which is an arid-adapted lizard, across ACA using sequences from mitochondrial cytochrome b and 12S rRNA genes. Phylogenetic analyses of the concatenated data, including 595 specimens from 107 localities, revealed ten geographically correlated lineages that diverged by 1.1–15.4% for the cytochrome b gene and 1.0–10.3% for the 12S rRNA gene, which were estimated to have coalesced ∼6.23 million years ago. Ancestral area estimations suggested that E. velox originated from the Iranian Plateau and then dispersed into Central Asia. The intensification of aridification across Central Asia during the Late Pliocene may have facilitated the rapid radiation of this arid-adapted lizard throughout this vast territory. Subsequently, the geological events (e.g., uplift of the Kopet-Dagh, Tianshan and Greater Caucasus Mountains) and glacial oscillations during the Pleistocene triggered the progressive diversification of E. velox. The most recent common ancestor of the Caucasus-Central Asia clade was dated to approximately 2.05 Ma. Specifically, the diversification between the Caucasus clade (VI, VII) and the Central Asia clade (VIII, IX, X), and within the Central Asia clade may have been established and partially maintained by repeated transgressions of the Caspian Sea during the Pleistocene and Holocene. In contrast to demographic and/or range contractions in response to climatic changes during the Last Glacial Maximum (LGM) of the populations (Clades VI and X) from the Caucasus-Central Asia clade, mitochondrial evidence and ecological niche modeling support the signature of demographic and range expansions during the LGM for the Clade V populations (E. v. roborowskii, being endemic to the Turpan Depression). The effect of Pleistocene climatic changes on the historical demography of this arid-adapted species may be lineage-specific, depending predominantly on animal physiology and geography. Finally, we discuss the taxonomic implications, such as the appearance of the Turkmenistan populations as a distinct species, and E. v. roborowskii deserving a full species status.

Spatial and temporal variability of Paleocene–Miocene organofacies of the Kura Basin, eastern Azerbaijan, and implications for basin evolution and petroleum generation

Fine-grained Paleocene–Miocene strata of eastern Azerbaijan record the evolution of the Kura Basin from an open marine system connecting the South Caspian Basin to the Paratethys of eastern Europe to an isolated epicontinental sea. Tectonic uplift associated with the Greater Caucasus mountains in Azerbaijan resulted in exposure of these strata over much of the northeastern part of the basin, allowing detailed observation and sampling over a broad area. Four hundred Paleocene–Miocene samples collected in eastern Azerbaijan demonstrate spatial and temporal geochemical heterogeneity within the predominately mudstone succession, indicating a complex evolution of this elongate basin. Through detailed organic geochemical analysis of samples, trends can be seen in the distribution of total organic carbon (TOC), pyrolysis characteristics, and biomarker results from a subset of twenty-four samples. In addition to confirming the well-documented regional basin restriction during the Oligocene to early Miocene deposition of the Maikop Series, heterogeneity of these geochemical indicators across the study area shows spatial variability in oxicity and terrestrial organic input within the basin on a sub-regional scale.Observed geochemical variability suggests a complex evolutionary history of the Kura Basin during the Paleocene–Miocene, and this has important implications for hydrocarbon prospectivity in the region. Within the 400 collected samples, total organic carbon (TOC) values range from 0.3 to 6.3%, with Oligocene–Miocene samples showing average values of 1.4%, compared to lower TOC values found in Paleocene–Eocene strata (average=0.3%). Rock-Eval pyrolysis shows that the majority of strata are organic lean, immature, and mixed oil/gas to gas prone (Type II/III to Type III), with a smaller group of latest Eocene–Early Miocene samples having better oil prone source potential. Gas chromatography and biomarker analysis of 24 samples reinforces the immaturity of most samples, shows varying levels of terrestrial input in all samples, suggests well-oxygenated waters prevailed with periodic suboxic to dysoxic/anoxic events, highlights gross differences between the Paleocene–Eocene and Oligocene–Miocene stratigraphic intervals, and shows generally good lateral correlation between samples. These interpretations reinforce what is seen through inorganic geochemical evaluation of trace metals, bulk composition, and stable isotopic ratios, and offer more detail as to the evolution of this basin and the implications for oil and gas prospectivity of the region.

Drainage network reveals patterns and history of active deformation in the eastern Greater Caucasus

The Greater Caucasus Mountains are a young (∼5 m.y. old) orogen within the Arabia-Eurasia collision zone that contains the highest peaks in Europe and has an unusual topographic form for a doubly vergent orogen. In the east-central part (45°E–49°E), the range is nearly symmetric in terms of prowedge and retrowedge widths and the drainage divide is much closer to the southern margin of the range (prowedge side) than it is to the northern margin (retrowedge side). Moreover, the divide does not coincide with the topographic crest, but rather the crest is both shifted northward by as much as 40 km and traversed by several large north-flowing rivers. Both the topographic crest and drainage divide appear to coincide with zones of active rock uplift, because they are characterized by bands of high local relief and normalized channel steepness values (>300). This uplift pattern could result from a synchronous initiation of the two uplift zones or propagation of deformation either northward or southward. The two propagating scenarios differ fundamentally in their predictions for the relative ages of topographic features; northward propagation predicts that the topographic crest is younger than the drainage divide, and the southward scenario predicts the converse. Because available geologic and topographic data are consistent with both propagation directions, we use a landscape evolution model to test all three scenarios. Model results indicate that the current topography and drainage network is best explained by a northward propagation of deformation from the south flank into the interior of the east-central Greater Caucasus. Such propagation implies recent out-of-sequence deformation within the Greater Caucasus due to reactivation or development of new structures within the core of the orogen. It remains unclear if such deformation is a transient response to an accretion cycle or stems from a fundamental change in the structural architecture of the orogen.

Glacier reaction to temperature and precipitation change in Central Caucasus, 2001–2010

This paper examines changes in surface area and terminus retreat of glaciers in the Greater Caucasus Mountains between 2001 and 2010 using ASTER imagery. The use of consistent high-resolution imagery such as ASTER significantly reduces uncertainties in measurements of glacier shrinkage and retreat and enables assessments at decadal intervals which are important for both scientists and regional decision-makers. Two ASTER images acquired on 15 September 2001 and 29 September 2010 covering central sector of the Greater Caucasus Ridge and the Elbrus glaciated massif were used for glacier mapping. Outlines of 179 glaciers were mapped of which 108 glaciers are located on the northern macroslope of the Greater Caucasus and on Mt Elbrus in the Baksan River catchment (Russia) and 71 are located on the southern macroslope in the Inguri River catchment (Georgia). In total, glaciers lost 5% of their area. Glacier wastage was higher in the Inguri catchment at 5.6%; in the Baksan catchment, glaciers lost 4.3% of their area. Termini positions of 28 valley glaciers were measured on ASTER and aerial photographs to compare rates of glacier retreat in 2001–2010 and 1987–2001.The rate of this recession increased, this fact confirmed by field studies in Baksan basin. Glacier mass balance observations at Garabashi glacier indicate strong reduction in cumulative mass balance since 1998 providing further evidence on glacier wastage. The observed shrinkage of Caucasus glaciers is mainly connected with increasing in summer temperatures.Increase in precipitation has not compensated for an increase in temperature between 1987–2001 and 2001–2010 periods.

Deglaciation of the Caucasus Mountains, Russia/Georgia, in the 21st century observed with ASTER satellite imagery and aerial photography

Abstract. Changes in the map area of 498 glaciers located on the Main Caucasus ridge (MCR) and on Mt. Elbrus in the Greater Caucasus Mountains (Russia and Georgia) were assessed using multispectral ASTER and panchromatic Landsat imagery with 15 m spatial resolution in 1999/2001 and 2010/2012. Changes in recession rates of glacier snouts between 1987–2001 and 2001–2010 were investigated using aerial photography and ASTER imagery for a sub-sample of 44 glaciers. In total, glacier area decreased by 4.7 ± 2.1% or 19.2 ± 8.7 km2 from 407.3 ± 5.4 km2 to 388.1 ± 5.2 km2. Glaciers located in the central and western MCR lost 13.4 ± 7.3 km2 (4.7 ± 2.5%) in total or 8.5 km2 (5.0 ± 2.4%) and 4.9 km2 (4.1 ± 2.7%) respectively. Glaciers on Mt. Elbrus, although located at higher elevations, lost 5.8 ± 1.4 km2 (4.9 ± 1.2%) of their total area. The recession rates of valley glacier termini increased between 1987–2000/01 and 2000/01–2010 (2000 for the western MCR and 2001 for the central MCR and Mt.~Elbrus) from 3.8 ± 0.8, 3.2 ± 0.9 and 8.3 ± 0.8 m yr−1 to 11.9 ± 1.1, 8.7 ± 1.1 and 14.1 ± 1.1 m yr−1 in the central and western MCR and on Mt. Elbrus respectively. The highest rate of increase in glacier termini retreat was registered on the southern slope of the central MCR where it has tripled. A positive trend in summer temperatures forced glacier recession, and strong positive temperature anomalies in 1998, 2006, and 2010 contributed to the enhanced loss of ice. An increase in accumulation season precipitation observed in the northern MCR since the mid-1980s has not compensated for the effects of summer warming while the negative precipitation anomalies, observed on the southern slope of the central MCR in the 1990s, resulted in stronger glacier wastage.

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

The Greater Caucasus Mountains, due to their youth (~5 Ma), provide an opportunity for insight into the early stages of orogen development during continent-continent collision. However, their recent tectonic evolution and first-order architecture remain unclear. Here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity, geodetic strain, bedrock geology, and foreland basin structure. We find that the range contains four zones along strike that differ in structural architecture, topography, and first-order tectonic history. In particular, two south directed, singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates. We hypothesize that the along-strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen, with the tips of the range preserving an early, singly vergent form and the center recording a more advanced orogen. The differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the Greater and Lesser Caucasus orogens, which initiated at ~5 Ma.

Rapid Pliocene exhumation of the central Greater Caucasus constrained by low‐temperature thermochronometry

Constraining the timing of onset and rates of deformation within the Greater Caucasus mountains is key to understanding their role in accommodating deformation across the Arabia‐Eurasia orogen. We present new low‐temperature thermochronometric constraints on the Cenozoic thermal evolution of the central Greater Caucasus that elucidate a three‐phase cooling history. Between 50 and 30 Ma, cooling within the range was negligible. In Oligocene time, cooling rates throughout the range increased to ∼4°C/Myr. These rates remained constant until the early Pliocene time, when they increased again, reaching ∼25°C/Myr along the axial part of the range. Rates and timing of Oligocene exhumation are consistent with previous results from the western Greater Caucasus and are proposed to result from onset of subduction of the Greater Caucasus back‐arc basin. Rapid exhumation of the Greater Caucasus, beginning in Pliocene time, contrasts with previously reported thermal histories for other portions of the range. Pliocene exhumation of the central Greater Caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the Arabia‐Eurasia plate boundary. We hypothesize that this exhumation, and regionally observed plate reorganization, results from the collision of the Lesser Caucasus with Eurasia, completing the subduction of oceanic lithosphere across this segment of the Arabia‐Eurasia plate boundary.

Forest snail faunas from Georgian Transcaucasia: patterns of diversity in a Pleistocene refugium

Thirty forest sites in Georgia were sampled to obtain inventories of their land snail faunas. The sites, in nine sampling areas, ranged from Batumi near the Turkish border to Lagodekhi near the Azerbaijan border, and included parts of both the Lesser and Greater Caucasus mountains and the Colchic lowlands. Abundance was generally low, and most sites held less than 20 species. Ninety species were found overall. Although sites within some sampling areas had very similar faunas, the overall levels of similarity among sites and sampling areas was low, especially when compared with similar forests from northern central Europe. Both climate and geographical position affected similarity: although these were correlated, independent effects of each were detected, and the effect of position alone was strongest. Despite this effect, most species have ranges extending into Turkey or Ciscaucasia, a few have very limited ranges, and there is no evidence of patterns of allopatric replacement among congeners. These patterns resemble those seen in faunas from forests in lower latitudes, and suggest a slow build-up of regional diversity by differentiation in situ, without the repeated restrictions to a multiplicity of small refugia that are characteristic of areas where fluctuations in aridity are important. The refugium has remained isolated, and has contributed little to the Holocene recolonization of areas further north. 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, , 239-250. ABSTRACT FROM AUTHOR Copyright of Biological Journal of the Linnean Society is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Relationship between Local Species Richness and Species Pool: A Case Study from the High Mountains of the Greater Caucasus

The causes of linear relationships between local species richness and the size of the actual species pool in closed subalpine meadow communities and open plant communities of the alpine stony substrate (the Greater Caucasus Mountains) were analyzed using a computer simulation model. The results demonstrated that this relationship is insufficient evidence for the variation of local species richness among communities is wholly or partly determined by regional processes (the species-pool hypothesis). A relatively proportional ratio between these variables can also arise where local species richness and the size of the species pool both depend on local processes, or where local species richness is determined by local factors alone while the size of the species pool is determined by both local and regional factors.

40Ar/ 39Ar and 18O/ 16O studies of the Chegem ash-flow caldera and the Eldjurta Granite: Cooling of two late Pliocene igneous bodies in the Greater Caucasus Mountains, Russia

Volcanic and intrusive rocks of the Chegem caldera and the nearby Eldjurta (Eldzhurtinskiy) Granite record a late Pliocene episode of silicic magmatism in the north-central Caucasus Mountains. Surface exposures, created by the recent rapid uplift and erosion of the Caucasus Mountains, span a 2 km vertical section of Chegem caldera fill and 1150 m of the Eldjurta Granite; cored mineral-exploration drillholes in the Eldjurta Granite extend the sampling to a depth of 4 km. The unique sampling range available in these two young igneous bodies affords an excellent opportunity to study their denudation and cooling histories, which we examine by means of 40Ar/ 39Ar and 18O/ 16O measurements on an extensive sample suite. Total-fusion biotite and sanidine ages from eight Chegem Tuff samples, both intracaldera and outflow, are analytically indistinguishable with a weighted mean of 2.82 ± 0.02 Ma. A cross-cutting granodiorite porphyry intrusion has a sanidine total fusion age of 2.84 ± 0.03 Ma, and whole-rock incremental heating of a post-caldera andesite flow, which caps the caldera fill, yields an age of 2.82 ± 0.02 Ma. Thus, caldera formation and post-caldera resurgence and volcanism all occurred within a very short time (< 50,000 yr). Biotite total-fusion ages of ten Eldjurta Granite samples, including seven from ∼ 500 m intervals in the 4 km deep drillhole, show a systematic linear decrease in age with depth from 1.90 Ma near the roof contact of the granite to 1.56 Ma at a depth of 3700 m. Assuming these ages were set at the same temperature, this age/depth gradient implies an isotherm migration rate of 13 mm/yr between 1.90 and 1.56 Ma. This migration rate is due to a combination of rapid denudation and downward relaxation of isotherms, with cooling rates between 200 and 500°C/Ma during this period. Oxygen isotopic compositions of quartz, K-feldspar, plagioclase and biotite from the drillhole samples below the 800 m depth are fairly uniform and record primary igneous δ 18O values with little evidence for subsolidus hydrothermal activity. However, in surface outcrop samples and in the shallowest drillhole sample, mineral δ 18O values have been lowered by up to 3‰ by interaction with an external (meteoric-hydrothermal?) fluid. The primary mineral δ 18O values of the Eldjurta Granite are distinctly higher than the corresponding phenocryst δ 18O values in the Chegem volcanic rocks, indicating that the two bodies evolved as separxate magma batches.

GLACIER TRENDS IN THE CAUCASUS, 1960s TO 1980s

Records of terminus positions for the 1960s to 1980s have been obtained for 51 glaciers in the Greater Caucasus Mountains between the Black Sea and Caspian Sea, between latitude 40° and 44° N and longitude 40° and 49° E. These records have been analyzed as percentage of glaciers observed retreating, advancing, and stationary, displayed as a five-year moving average. The main result is the absence of the clear trend towards glacier advance found in the Alps between the 1960s and 1980s by both Patzelt (1985) and Wood (1988), suggesting a phase difference in the climates of the Alps and the Caucasus. [Key words: glaciers, glaciology, Greater Caucasus Mountains, Alps.]