On the borders of the upper hydrogeodynamic zone in the Caspian artesian basin

This article provides the results from studying the upper part of the section of the entire Caspian artesian basin. The stratification map, the profile section and the isohyps map of the roof of the upper hydrogeodynamic zone were compiled on the basis of generalization of geological and general hydrogeological data. Systematized hydrogeological data on the depositional conditions, structural features and nature of the distribution within the upper hydrogeodynamic zone of the Caspian artesian basin, as well as the supply zones and the areas of transit and discharge of underground waters are provided. The borders of the upper hydrogeodynamic zone of the basin have been drawn as a result.     

布尔津盆地西部凹陷铀成矿水文地球化学条件初探

根据水成铀矿床理论，本在论述布尔津盆地水动力及水化学特征的基础上，通过资料综合整理，着重分析西部凹陷第三系层间水的铀水迁移分带规律，对层间氧化带砂岩型铀矿成矿水地球化学条件进行初步探讨。     

Model for Sr accumulation in the Carboniferous deposits of the Moscow artesian basin

Statistical and thermodynamic analysis of hydrogeochemical information on Sr accumulation in the waters of Carboniferous deposits in the Moscow artesian basin indicates that Sr concentration increases mostly with increasing salinity of the aqueous solution and its Mg and sulfate contents. The highest Sr concentrations are 8–10 mg/l, and Sr accumulation in groundwaters is constrained by the precipitation of strontiantie in the system aqueous solution + dolomite + calcite + strontianite. An increase in Sr concentrations in the Carboniferous waters is symbate with the accumulation of F, and the accumulation of Sr (as well as F) is largely controlled by two factors: a change in the hydrogeochemical type of the groundwaters toward its transition and an overprinted process of the slowing of water filtration from the recharge area of the aquifers (where the Carboniferous deposits are exposed at the surface) down the dips of the water-hosting strata.     

Model for the formation of fluorine-bearing rocks in the Carboniferous deposits of the Moscow artesian basin

The paper presents the results of the statistical and thermodynamic analysis of hydrogeochemical information on the genesis of F-bearing waters in the Carboniferous deposits of the Moscow artesian basin. The F concentration is demonstrated to increase with increasing salinity of the aqueous solution. As follows from the analysis of mineral equilibria, the saturation concentrations of the aqueous phase with respect to fluorite in association with calcite and gypsum is less than 2–3 mg of F/l. At the saturation of the aqueous phase with respect to fluorite in association with dolomite, the equilibrium concentration of F increases with increasing Mg concentration and decreasing equilibrium partial CO₂ pressure and can reach 8–10 mg of F/l. The main reason for this enrichment of the aqueous phase in F is certain features of mineral equilibria in the system of aqueous solution with Ca and Mg carbonates. An increase in the Mg²⁺ concentration in the aqueous phase decreases the Ca²⁺ concentration in the solubility equilibrium of dolomite, and this, in turn, decreases the F^? concentration in the solubility equilibrium of fluorite.     

The role of pressure in thermocatalytic processes in the sedimentary complex of the South Caspian basin

The role of overpressures in thermochemical processes in the South Caspian basin is considered. The studies, which take the world experience into account, suggest that the South Caspian basin (mainly its deep-water part), as well as other basins with abnormally high fluid pressures, is characterized by retarded kerogen and oil cracking and reaction of clay-mineral transformation. These processes can be periodically intensified by the development of diapirs and mud volcanoes, which are centers of pulsed hydrocarbon discharge from the system. The conclusion is made that deeply buried deposits in basins with fluid overpressure are promising in terms of hydrocarbon pools.     

盆地砂岩型铀矿区域评价中的水文地质分析

盆地砂岩型铀矿区域评价的主要目的是初步划分环境带和圈定成矿有利地段，为下步较详细工作提供依据。其中水地质工作着重从以下几个方面来进行：水地质单元划分；承压含水系统和目的层的确定；水动力条件分析；水地球化学环境分析；占水地质分析；氧化还原带和成矿有利地段的圈定。     

Structure of the crust and upper mantle of the Black and Caspian Seas

Many geophysical characteristics of the Caspian and Black Seas' deep basins are similar, having: suboceanic type of the crust, low average seismic velocity, absence of earthquakes and relatively small variation of magnetic anomalies. However, the sediments in the Caspian Sea deep basin are folded whereas in the Black Sea they are approximately horizontal. The Caspian Sea also has a far greater thickness of sediment accumulation.

The deep basins of the Caspian, Black and Mediterranean seas represent a sequence having similar crustal structures but with a decreasing thickness of sediments and consolidated layer, in that order. It is possible that the intensive sinking and accumulation of sediments began earliest in the Caspian Sea and spreaded continuously to the Black Sea and then the Mediterranean Sea. The Caspian and Black Sea deep basins have existed for long time (perhaps from Paleozoic time or even earlier) as areas with a specific and related type of evolution.     

新疆三塘湖盆地水文地质条件及铀成矿前景分析

新疆三塘湖盆地是具有正向水文地质和水文地球化学分带的渗入型坳陷盆地,区内含水层发育良好,具有较好的泥-砂-泥结构模式,盆地铀源丰富,地下水中铀元素的分布规律有利于其在氧化还原过渡带中沉积富集,具有较好的铀成矿前景。     

Changes in the water regime of the caspian sea

The article deals with issues of structure and dynamics of the Caspian Sea water balance. On the base of historical, paleogeomorphological and other data the evolution history of the Caspian Sea and its basin has been observed for different time intervals down to 400 thous. years ago. Presented are computerized data on water balance components in the current centenary obtained from instrumental observations, revealed are causes of the sea-level fluctuations within that time interval and anthropogenic factor contribution to this process. Based on the analysis of this material, an attempt has been undertaken to present a scenarion of a possible sea-level position of the Caspian Sea with the expected versions of climatic changes at the end of the XX and beginning of the XXI centuries.     

Identification of hydrochemical facies in the Roswell Artesian Basin,New Mexico (USA), using graphical and statistical methods

Analysis of groundwater chemistry can yield important insights about subsurface conditions, and provide an alternative and complementary method for characterizing basin hydrogeology, especially in areas where hydraulic data are limited. More specifically, hydrochemical facies have been used for decades to help understand basin flow and transport, and a set of facies were developed for the Roswell Artesian Basin (RAB) in a semi-arid part of New Mexico, USA. The RAB is an important agricultural water source, and is an excellent example of a rechargeable artesian system. However, substantial uncertainties about the RAB hydrogeology and groundwater chemistry exist. The RAB was a great opportunity to explore hydrochemcial facies definition. A set of facies, derived from fingerprint diagrams (graphical approach), existed as a basis for testing and for comparison to principal components, factor analysis, and cluster analyses (statistical approaches). Geochemical data from over 300 RAB wells in the central basin were examined. The statistical testing of fingerprint-diagram-based facies was useful in terms of quantitatively evaluating differences between facies, and for understanding potential controls on basin groundwater chemistry. This study suggests the presence of three hydrochemical facies in the shallower part of the RAB (mostly unconfined conditions) and three in the deeper artesian system of the RAB. These facies reflect significant spatial differences in chemistry in the basin that are associated with specific stratigraphic intervals as well as structural features. Substantial chemical variability across faults and within fault blocks was also observed.     

Density inhomogeneities, isostasy and flexural rigidity of the lithosphere in the Transcaspian region

The 3-D lithospheric-density model for the southeastern part of the Caspian Sea and the Transcaspian area, practically coinciding with the territory of the Turkmen Republic, has been constructed based on geophysical data and in accordance with the principle of isostasy. From the model selected the anomalous density of the subcrustal layer between the Moho discontinuity and the 100-km depth level is found to be — 100 kg/m³ under the Tien-Shan, − 50 kg/m³ under the Kopet-Dag mountain area, + 80 kg/m³ under the central region of the South Caspian basin, −50 kg/m³ under the eastern part of the basin, known as the West Turkmenian depression, and + 45 kg/m³ under the Murgab depression.

Significant disturbances of the local isostasy are determined both in the northern and central areas of the South Caspian basin and also in the area of the Kara-Bogaz swell of the Turan platform and for the Kopet-Dag foredeep. indicating a high level of stresses in the lithosphere. The shape of the Turan plate determined by the seismic profiling is accounted for by elastic deformation resulting from the forces acting on the southern edge of the plate in the area of the Turan plate-Kopet-Dag collision. The elastic thickness of the Turan plate is estimated as 25 ± 5 km. The results obtained seem to confirm the idea that the decomposition of the Turan plate has taken place in the zone of the plates interaction and the decomposed material is situated under the Kopet-Dag ridge.

We propose that the Kara-Bogaz swell is supported by the mantle material upwelling whereas the subsidence of the adjacent part of the South Caspian basin may be due to the downgoing mantle flow i.e., a small convection cell is suggested in that area.     

Hydrogeology of the Ordos Basin,China

The Ordos Basin is located in the east of NW China that is composed of different aquifer systems. Karst groundwater is stored in the Carmbrian-Ordovician carbonates along the margins of the basin. Fissured-pore water is present in the Cretaceous strata in the central-western basin and pore water is stored in the overlying Quaternary deposits discontinuously. The main origin of groundwater in the basin is direct or indirect infiltration of precipitation. Groundwater flows from recharge areas to adjacent local discharge areas. Besides evaporation and abstraction, groundwater feeds springs and rivers, such as the Yellow River and its tributaries. According to the karst aquifer lithologic structure, the features of karst development and circulation, the karst aquifer is divided into three structural and circulation patterns. Based on the control of Cretaceous sedimentary environment, lithologic structure, lithofacies, and palaeogeographic characteristics, the Cretaceous system is divided into the northern desert simple plateau aquifer system and the southern loess plateau aquifer system. PACKER was used to obtain temperature, hydrogeochemical and isotope data at specific depths. Groundwater circulation is studied using hydrodynamic fields, temperature fields, isotopes, hydrogeochemical data and numerical simulations. According to the result, it is divided into local, intermediate and regional systems.     

Role of Subsurface Brines in Salt Balance: The Case Study of the Caspian Sea and Kara Bogaz Bay

The water level of the Caspian Sea fluctuated significantly during recent history, without consensus for the cause. The varied chemistry of the Caspian, Kara Bogaz and sediment a interstitial waters provides a further insight. Element concentrations and ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters were compared to those of Caspian and Kara Bogaz open waters, and of acid-leached extractable components. The ⁸⁷Sr/⁸⁶Sr ratios of the interstitial waters are explained by addition of subterranean waters similar to nearby spring waters. These subterranean waters yield chemical characteristics such as a Cl/SO₄, ⁸⁷Sr/⁸⁶Sr, Ca/Sr and K/Rb ratios of respectively 80, 0.7086, 250 and 1,800. However, their addition does not explain the large difference in the K/Rb ratio of the Caspian and Kara Bogaz waters, respectively at 7,630 and 17,550, which implies also a leaching of salt deposits by the upward migrating subterranean waters. The sediments of the southern Caspian basin, with low Na, Cl and SO₄ in their interstitial waters, deposited apparently in an anoxic environment. The related chemical changes in the waters are also indicative of a recent change in the hydrologic regime, possibly induced by a changing morphology of the drainage basin.     

Petroleum systems and the history of their formation in the northern Caspian Sea basin

This study presents the consideration of the geological history and petroleum systems in the northern Caspian Sea basin (on the basis of basin modeling using the TemisSuite2008 software package). The key patterns of the distribution of oil and gas fields and their phase composition are described. Kulaginskii Ridge and the adjacent areas are considered. The preceding data are generalized and new data are used.     

Application of the 3D geotemperature modeling for the calculation of conditions of organic matter catagenesis

Three dimensional modeling of the geothermal field was performed along geotraverses in the Barents Sea and Caspian Basin using data obtained by the method of reflected waves based on common depth point (MRW CDP) and deep drilling. Depths of the interval of catagenetic transformation of organic matter were calculated for different regions of the sedimentary basin. The smallest depth of this interval is confined to the South Barents Depression, where the highest hydrocarbon potential was found on the basis of geological prospecting. A thermal dome distinguished for the first time is confined to this region in 3D models. The same effect was also found in the Caspian Basin: thermal domes are located in the southern Emba, Mangyshlak, and Astrakhan arch regions, where hydrocarbon materials are mined extensively.     

Formation of the superdeep South Caspian basin: subsidence driven by phase change in continental crust

The large hydrocarbon basin of South Caspian is filled with sediments reaching a thickness of 20–25 km. The sediments overlie a 10–18 km thick high-velocity basement which is often interpreted as oceanic crust. This interpretation is, however, inconsistent with rapid major subsidence in Pliocene-Pleistocene time and deposition of 10 km of sediments because the subsidence of crust produced in spreading ridges normally occurs at decreasing rates. Furthermore, filling a basin upon a 10–18 km thick oceanic crust would require twice less sediments. Subsidence as in the South Caspian, of ≥20 km, can be provided by phase change of gabbro to dense eclogite in a 25–30 km thick lower crust. Eclogites which are denser than the mantle and have nearly mantle P velocities but a chemistry of continental crust may occur beneath the Moho in the South Caspian where consolidated crust totals a thickness of 40–50 km. The high subsidence rates in the Pliocene-Pleistocene may be attributed to the effect of active fluids infiltrated from the asthenosphere to catalyze the gabbro-eclogite transition. Subsidence of this kind is typical of large petroleum provinces. According to some interpretations, historic seismicity with 30–70 km focal depths in a 100 km wide zone (beneath the Apsheron-Balkhan sill and north of it) has been associated with the initiation of subduction under the Middle Caspian. The consolidated lithosphere of deep continental sedimentary basins being denser than the asthenosphere, can, in principle, subduct into the latter, while the overlying sediments can be delaminated and folded. Yet, subduction in the South Caspian basin is incompatible with the only 5–10 km shortening of sediments in the Apsheron-Balkhan sill and south of it and with the patterns of earthquake foci that show no alignment like in a Benioff zone and have mostly extension mechanisms.     

Isotopic composition (H,O, Cl,Sr) of ground brines of the Siberian Platform

New data on the geochemistry and isotopic composition of chloride brines of the Siberian Platform are presented. The distribution of stable isotopes (²H, ¹⁸O, and ³⁷Cl) in brines of the Tunguska, Angara-Lena, western part of the Yakutian and Olenek artesian basins and ⁸⁷Sr/⁸⁶Sr in brines of the western part of the Olenek artesian basin was studied in the context of the problem of genesis of highly mineralized groundwaters. Results of the study and comparative analysis of the geochemical and isotopic peculiarities of the Siberian Platform brines conform to the theory of brine formation through the interaction of connate waters with enclosing rocks.     

Correlation of upper quaternary deposits and paleogeography of the Black and Caspian seas

The evolution of the Black and Caspian seas is considered based on the analysis of new stratigraphic and paleogeographic data. Three transgression stages (Karangatian, Surozh, Black-Sea) and two regression stages (Post-Karangatian and New-Euxinian) were characterized for the Black Sea, as well as four transgression stages (late Khazarian, early Khvalynian, late Khvalynian, and New-Caspian) and three regression stages (Atelian, Enotaevkan, Mangyshlakian), for the Caspian Sea. The analysis of data on the absolute age of deposits allowed correlation of paleogeographic events for the basins, between them and with the stages of the Last (Valdai) Glaciation: the Karangatian and late Khazarian transgressions were correlated with the Mikulinian Interglacial; the post-Karangatian and Atelian regressions, with the Kalininan glaciation; the early Khvalynian and Surozh transgressions, with the middle Valdai Interstadial; the New-Euxinian and Enotaevkan regressions, with the Ostashkovian glaciation; the Black Sea, late Khvalynian, and New-Caspian transgression, with the late glaciation — post-glaciation periods; the Mangyshlakian regression, with the Older Dryas (?). The last connections between the Caspian and Black seas are dated to the middle Valdai time when waters of the early Khvalynian basin drained down to the Surozh basin.     

Groundwater recharge formation in the Heihe intermountain artesian basin

The Heihe intermountain artesian basin is situated in northwestern China. The basic types of formation of groundwater recharge have been identified, viz., the percolation of river waters in the mountain regions and infiltration from irrigation canals and fields in the plain areas with a well-developed irrigation system. Such sources account for about 90% of the overall groundwater recharge.