Ejina Basin Research Articles

Tectonic–thermal evolution since the Mesozoic in the Suhongtu Depression, Yingen–Ejina Basin: Constraints from Apatite fission track and vitrinite reflectance

The Yingen–Ejina Basin (YEB) located in the western part of the North China Plate is a significant area for petroleum exploration. During the Early Cretaceous, the YEB witnessed the extensive development of source rocks. However, the subsequent tectonic evolution and multi‐stage thermal history of these source rocks have posed challenges to oil and gas exploration in the basin. This study focuses on the Mesozoic and Cenozoic tectonic evolution of the YEB, utilizing Apatite fission track (AFT) and vitrinite reflectance (Ro) data of samples from Well BC‐1 in the Suhongtu Depression, northern YEB. The central ages of six AFT samples ranged from 28 ± 2 to 49 ± 3 Ma with corresponding track lengths between 10.8 ± 1.9 and 12.3 ± 1.5 μm. Combining with the study of Ro and thermal history simulation, the thermal history of the YEB is summarized as follows: In the late Early Cretaceous, the study area experienced tectonic elevation, as evidenced by the discontinuous change in Ro values along the vertical column. Towards the end of the Late Cretaceous, there was a subsidence in the study area. The Ro data indicate that the Early Cretaceous source rocks, although experiencing several tectonic uplifts, had remained within the hydrocarbon generation temperature range, and reached the maximum thermal uplifts before the end of the Late Cretaceous. Therefore, hydrocarbon generation from early Cretaceous source rocks is an important exploration target in the study area and will be the focus of oil and gas exploration in the future.

Simulating River/Lake–Groundwater Exchanges in Arid River Basins: An Improvement Constrained by Lake Surface Area Dynamics and Evapotranspiration

Surface water–groundwater interactions in arid zones are characterized by water exchange processes in a complex system comprising intermittent streams/terminal lakes, shallow aquifers, riparian zone evapotranspiration, and groundwater withdrawal. Notable challenges arise when simulating such hydrological systems; for example, field observations are scarce, and hydrogeological parameters exhibit considerable spatial heterogeneity. To reduce the simulation uncertainties, in addition to groundwater head and river discharge measurements, we adopted remote sensing-based evapotranspiration data and lake area dynamics as known conditions to calibrate the model. We chose the Ejina Basin, located in the lower reaches of the Heihe River Basin in arid northwest China, as the study area to validate our modelling approach. The hydrological system of this basin is characterized by intensive, spatiotemporally variable surface water–groundwater interactions. The areas of the terminal lakes into which all river runoff flows vary significantly depending on the ratio between river runoff and lake evaporation. Simulation results with a monthly time step from 2000 to 2017 indicate that river leakage accounted for approximately 61% of the total river runoff. Our study shows that for areas where surface water and groundwater observations are sparse, combining remote sensing product data of surface water areas and evapotranspiration can effectively reduce the uncertainty in coupled surface water and groundwater simulations.

Assessing shallow groundwater level using RTI model and long-term MODIS data in Ejina Basin, Northwest China

The present study aims to exploit the thermal inertia model to assess the shallow groundwater level distribution, as an attempt to address agricultural water shortage and ecological degradation in arid and semi-arid regions. Apparent thermal inertia (ATI) model is one of the most commonly used and successfully implemented models, whereas in some cases, the scales of the results achieved on different dates are inconsistent, which poses a serious difficulty when monitoring soil moisture over time. To address this restriction, we introduce a soil moisture indicator, called RTI, which derives an approximation of soil thermal inertia, from flexible multi-temporal MODIS observations covering a 2-year period. Taking the Ejina Basin in arid area as an example, to more accurately assess the shallow groundwater level distribution, ATI and RTI models were adopted based on the long time series MODIS data to assess the multi-temporal soil moisture content in the study area. The data of groundwater level measured by observation well and thermal inertia were employed to generate scatter diagrams. Subsequently, a nonlinear equation was developed. Based on the thermal inertia, the temporal and spatial distribution map of the shallow groundwater level in the whole study area was generated with the inverse calculation of the nonlinear equation. It was found that the shallow groundwater level distribution in Ejina Basin tended to be shallower from south to north, as well as from summer to winter. As revealed from the results, both ATI and RTI models can effectively assess the shallow groundwater level in arid areas. The RTI model could better reflect the seasonal changes of soil moisture content and groundwater level.

Kinematic variability of late Cenozoic fault systems and contrasting mountain building processes in the Alxa block, western China

Abstract In this study, new structural field data and geological observations are coupled with remote sensing analysis and compilation of previous published work to establish a new kinematic framework for the neotectonic reactivation of the Alxa block, China. The Alxa block occupies a key position in Central Asia north and east of the contractional and sinistrally transpressive deforming zones of the Qilianshan-Hexi Corridor-easternmost Altyn Tagh Fault and Beishan deforming belts, south of the sinistrally transpressive southernmost Gobi Altai, and west of – or overlapping with - Ordos block extensional and transtensional graben systems. In addition, the Alxa block is internally transected by important fault systems (Bayan Nuru, Bayanwula, Chahanbulage) that record previously unrecognized Late Cenozoic activity. Active mountain building processes in the Alxa block show remarkable variation from large extensional horst blocks (Helanshan, SW Langshan, SW Yabrai) to localized uplifts along sinistral wrench-belts (Bigesitai) to dominantly contractional (Longshoushan) and sinistral transpressional ranges (Helishan). The triangular wedge-shape of the Alxa block likely pre-disposed it to eastward extrusion in response to NE-directed India-Eurasia collision-derived compressional stresses from the south, and E-W tensional forces driven by Pacific margin rollback to the east. A combination of inherited regional lithospheric structure and the modern east-directed geodetically derived crustal velocity field led to: 1) crustal thinning and subsidence of the Ejina basin to the west in the wake of the eastward extruding Alxa block, and 2) distributed sinistral transtension and crustal extension within the Alxa block interior, and in the Hetao and Yinchuan grabens to the east.

Sediment history mirrors Pleistocene aridification in the Gobi Desert (Ejina Basin, NW China)

Abstract. Central Asia is a large-scale source of dust transport, but it also held a prominent changing hydrological system during the Quaternary. A 223 m long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstruct the main modes of water availability in the area during the Quaternary. The core was drilled from the Heihe alluvial fan, one of the world's largest alluvial fans, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical–mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, pollen and non-pollen palynomorphs, and n-alkanes with leaf-wax δD) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grain-size endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the pre-Quaternary quartz- and plagioclase-rich “Red Clay” formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110 m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0 m is composed of mainly silty to sandy sediments derived from the Heihe that have accumulated in a giant sediment fan until modern time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative of different environments. Mixed-layer clay minerals (chlorite/smectite) are increased in the basal Red Clay and reworked sediments, smectite is indicative of lacustrine-playa deposits, and increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma. At this time Heihe broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the northern Tibetan foreland (i.e. the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese Loess Plateau, suggesting that the Heihe alluvial fan may have served as a prominent upwind sediment source for it.

Geomorphological Evolution and Palaeoenvironmental Change in the Western Alashan Plateau, China

Although neotectonic activity is considered to be the main factor of theterrain evolution of the Qinghai Tibet Plateau and its surrounding high-altitude areas, further geomorphological analysis and literature analysis areneeded for the understanding of the geomorphic evolution and the Quaternary environment change of the western area of the Alxa Plateau nearthe northern Tibet Plateau. The purpose of this study is to investigate thedistribution of site-specific geomorphic units of the landforms developedin the vast topography of Ejina Basin (Western Alxa), in order to identifythe geostructural and climatic causes of the geomorphic landscape and itsimpact on the change of paleoenvironment. At present, the climate andhydrological conditions in Ejina are relatively monotonous and stable. Inaddition to tectonic dynamic factors, the most widely distributed landform in the basin is climate landform. There are both geomorphologicaland sedimentological anomalies of Aeolian landforms occurred in thewhole basin, indicating that the underlying surface effect (retention effect) of river (Ejina River) and its related uneven ground and weak winderosion (deflation) process in the nearby area may be the important factors controlling the formation of Ejina dunes, rather than the arid climate.It is believed that the extensive interaction between the aeolian and fluvialprocesses is the main mechanism of the regional geomorphic difference inEjina Basin. According to the comparability of regional geomorphologyand sedimentology, the period of the formation of relic geomorphologyin the edge of Ejina Basin can be reasonably attributed to the local glacialmaximum of the last glacial. The geomorphic transformation from quasiplain and desert valley to desert plain, the appearance of widely movingsand dunes and the presence of large ancient lake geomorphology allindicate that the drought index of Ejina Basin is increasing on the scaleof geomorphic formation. Paleogeomorphological and chronological evidences show that the climatic and hydrological conditions of the basin inthe last glacial period and the early Holocene are much better than thoseat present. For example, the average annual precipitation in the area before 39-23ka BP is between 60-350 mm (about 36 mm today), but thereare large waves in the Holocene. The coexistence of various climates andlandforms in Ejina Basin and the resulting geomorphic diversity shouldbe the composite result of various geomorphic processes and surface processes besides glaciation. The low aridity (relative humidity) in the EjinaRegion in the late Pleistocene may be the result of the enhancement of thewesterly rain belt and the weakening of the Asian Winter Monsoon in thearid region of Central Asia.

A Study on the Groundwater Contamination by the Agriculture Fertilizer Inputs and its Spatial Distribution Pattern in the Zhangye Basin, Northwest China

The Heihe River is one of the largest rivers in Gansu province in China, which originates from Qilian Mountains and terminates at Ejina Basin in Gobi desert. The river is the only water source of the region, which is highly dependent on agriculture-based economy. The recent changes of economic and environmental sectors have been affected the sustainable agricultural practices of the region. Those changes may give adverse impacts on water quality. In this context, this study focuses on the water quality of both shallow-groundwater and deep-groundwater in the middle reaches of the Heihe River basin, the main agricultural region of the basin. Total of 35 water samples are used for measure water quality, i.e NO3− , NO2−, NH3 and pH. The water quality measurement results indicate two different spatial distribution patterns of chemical contamination respectively for shallow and deep ground water. This paper discusses the current spatial pattern of nitrogen contamination of the groundwater and its temporal change through the comparison with the past studies.

Orbital scale lake evolution in the Ejina Basin, central Gobi Desert, China revealed by K-feldspar luminescence dating of paleolake shoreline features

The Ejina Basin in the central Gobi Desert contains the terminal lakes of the Heihe River. Paleoenvironmental changes in the basin are important since its deposits are a significant source of Northern Hemisphere dust. In this study we employed a K-feldspar pIRIR dating technique to date shoreline features ≥940 m at multiple locations in the Ejina Basin ∼45–50 m above the modern basin floor. Internal checks of luminescence characteristics were employed to test the reliability of the pIRIR dating. In combination with our previously reported stratigraphy and chronology of shorelines at ≤927 m in the Ejina Basin, these results imply that a paleolake was present in the basin prior to ∼350 ka. Other high stands in the basin occurred at ∼320-310 ka, 240-180 ka, 120-80 ka, and ∼5 ka, corresponding to MIS 9, MIS 7, MIS 5 and the mid Holocene (MIS 1), respectively, indicating a strong link with glacial-interglacial cycles. Extensions of the East Asian Summer Monsoon (EASM) during interglacial periods, possibly interacting with the Westerlies, apparently caused higher precipitation and lake formation. The impact of orbital eccentricity on the EASM/Westerlies appears to be responsible for the formation of major lake/desert cycles on the northeastern margin of the Tibetan Plateau.

Comparative Study of Hybrid-Wavelet Artificial Intelligence Models for Monthly Groundwater Depth Forecasting in Extreme Arid Regions, Northwest China

Prediction of groundwater depth (GWD) is a critical task in water resources management. In this study, the practicability of predicting GWD for lead times of 1, 2 and 3 months for 3 observation wells in the Ejina Basin using the wavelet-artificial neural network (WA-ANN) and wavelet-support vector regression (WA-SVR) is demonstrated. Discrete wavelet transform was applied to decompose groundwater depth and meteorological inputs into approximations and detail with predictive features embedded in high frequency and low frequency. WA-ANN and WA-SVR relative of ANN and SVR were evaluated with coefficient of correlation (R), Nash-Sutcliffe efficiency (NS), mean absolute error (MAE), and root mean squared error (RMSE). Results showed that WA-ANN and WA-SVR have better performance than ANN and SVR models. WA-SVR yielded better results than WA-ANN model for 1, 2 and 3-month lead times. The study indicates that WA-SVR could be applied for groundwater forecasting under ecological water conveyance conditions.

Evaluating the best evaporation estimate model for free water surface evaporation in hyper-arid regions: a case study in the Ejina basin, northwest China

Free water surface evaporation is an important process in the hydrologic and energy cycle. Accurate calculation of free water evaporation helps in evaluating the reliability of data on the distribution and quantity of water resources. However, the applicability of evaporation models to the calculation of free water surface evaporation in hyper-arid regions is still uncertain. Moreover, the accuracy of previously used evaporation models should be evaluated for hyper-arid regions. In this study, the Ejina basin in the hyper-arid region of northwest China was selected to address this issue. Measured meteorological data (1993–2008) were used to calculate free water surface evaporation using the Dalton model, Penman formula, and energy balance equations. Results from two different Dalton models were higher and lower than the results from E601 pan evaporation, respectively. Results from the Penman formula were lower than results from E601 pan, whereas results from the energy balance equations are higher than the results from E601 pan. The results indicate that previous evaporation models are not suited for calculating free water surface evaporation in hyper-arid regions if not modified. Using meteorological data and radiation data (1993–2000), the Dalton model, energy balance equations, and Penman formula were modified to calculate free water surface evaporation for 2001–2008. The average annual evaporation from the three modified models was slightly lower than the evaporation from E601 pan during 2001–2008. However, the errors in the values were only 11–14 mm, which were much lower than in previous models. The modified Dalton model and Penman formula yielded a higher accuracy of the calculation, whereas the modified energy balance equations had the lowest accuracy.

Discriminating sediment archives and sedimentary processes in the arid endorheic Ejina Basin, NW China using a robust geochemical approach

Geochemical characteristics have been intensively used to assign sediment properties to paleoclimate and provenance. Nonetheless, in particular concerning the arid context, bulk geochemistry of different sediment archives and corresponding process interpretations are hitherto elusive. The Ejina Basin, with its suite of different sediment archives, is known as one of the main sources for the loess accumulation on the Chinese Loess Plateau. In order to understand mechanisms along this supra-regional sediment cascade, it is crucial to decipher the archive characteristics and formation processes. To address these issues, five profiles in different geomorphological contexts were selected. Analyses of X-ray fluorescence and diffraction, grain size, optically stimulated luminescence and radiocarbon dating were performed. Robust factor analysis was applied to reduce the attribute space to the process space of sedimentation history. Five sediment archives from three lithologic units exhibit geochemical characteristics as follows: (i) aeolian sands have high contents of Zr and Hf, whereas only Hf can be regarded as a valuable indicator to discriminate the coarse sand proportion; (ii) sandy loess has high Ca and Sr contents which both exhibit broad correlations with the medium to coarse silt proportions; (iii) lacustrine clays have high contents of felsic, ferromagnesian and mica source elements e.g., K, Fe, Ti, V, and Ni; (iv) fluvial sands have high contents of Mg, Cl and Na which may be enriched in evaporite minerals; (v) alluvial gravels have high contents of Cr which may originate from nearby Cr-rich bedrock. Temporal variations can be illustrated by four robust factors: weathering intensity, silicate-bearing mineral abundance, saline/alkaline magnitude and quasi-constant aeolian input. In summary, the bulk-composition of the late Quaternary sediments in this arid context is governed by the nature of the source terrain, weak chemical weathering, authigenic minerals, aeolian sand input, whereas pedogenesis and diagenesis exert only limited influences. Hence, this study demonstrates a practical geochemical strategy supplemented by grain size and mineralogical data, to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central Asia.

Climate-Driven Landformof the Ejina Basin (NW China) in Central Asia and Its Paleoenvironmental Implications

<p>Though neotectonic activity is believed to be the major factor in the evolution of the topography of the Ejina Basin in Central Asia, detailed documentation and analysis of climatic landscape features and their environmental implications are lacking. The present study is a site-specific documentation of landforms developed in the wide part of the Ejina Basin, with the aim to identify the climatic landforms based on the method of climatic geomorphology and to evaluate its landscape evolution and response to palaeoclimate changes. The morphodynamics of older landscapes are recognized by making comparison with the present climate and its corresponding landscapes. Clear evidences testifying the basin-scale shifting and transformation of different morphoclimatic zones in the basin are observed, which prove that the main geomorphic unit is changed from an alluvial-lacustrine plain to a desert plain. The coexistence of diverse landscapes and the consequent geomorphodiversity in the basin should be a compound result of surficial processes other than glaciations. The climate and hydrological conditions of the basin during the last glaciation and during the Early Holocene were much better than at present, possibly having an average annual precipitation ranged between 60~350 mm on <del cite="mailto:unknown" datetime="2015-11-27T09:00"> </del>the basin during ca. 39-23 ka BP but great fluctuations during Holocene. The periods of lower aridity during the late Pleistocene in the bain could be induced by an increase of the westerlies and a weakening of the Asian winter monsoon on the arid areas of the central Asia.</p>

Seismites as indicators for Holocene seismicity in the northeastern Ejina Basin, Inner Mongolia

Abstract This paper contributes to the understanding of palaeoseismology in slowly deforming regions by demonstrating the interpretation of soft-sediment deformation to be a valuable tool in identifying palaeoseismicity where the present-day seismicity is low and the geomorphology initially does not indicate active tectonics by the presence of fault scarps, surface ruptures or diverted rivers. The Ejina Basin (also known as the Gaxun Nur Basin or Juyan Lake Basin) in Inner Mongolia exhibits highly variable endorheic lakes, such as the Late Quaternary Juyanze Palaeolake. We assessed the Holocene tectonic activity of the Western Juyanze Palaeolake Basin, situated within the Ejina Basin, by identifying seismites and a previously unknown normal fault. Deformation mechanisms other than earthquakes, such as landslides or cryoturbation in permafrost, can be excluded. Far-field and near-field seismic sources are considered to have generated the soft-sediment deformation structures. As the occurrence of seismites is restricted to the Western Juyanze Palaeolake Basin and there is Pleistocene–Holocene activity on the Tienehu Fault, a near-field source is most likely.

Quartz and K-feldspar luminescence dating of a Marine Isotope Stage 5 megalake in the Juyanze Basin, central Gobi Desert, China

The Juyanze Basin, in the central Gobi Desert of China, contains one of three terminal lakes of the Heihe River, the second largest inland river in China. The paleoenvironmental record of the region is important since it is a significant global dust source region. In this study, a newly developed post-infrared(IR)-stimulated luminescence (IRSL) (pIRIR) dating technique, together with traditional quartz optically stimulated luminescence (OSL) dating, was applied to shoreline and deep water sediments obtained from a buried shoreline at ~927m in the Ejina Basin, ~33m above the basin floor. The reliability of K-feldspar pIRIR dating was confirmed by internal checks of a dose recovery test, an anomalous fading test, and a residual dose test. Internal checks of the quartz OSL dating, and comparison to K-feldspar pIRIR ages, indicate that the single-aliquot regenerative-dose protocol was reliable for samples from the shoreline, but that quartz ages older than 60ka may be underestimated. Our results indicate that three lacustrine sequences, separated by erosional unconformities and eolian deposition, span a period from ~122 to 73ka, covering most of Marine Isotope Stage (MIS) 5. At a depth of ~33m (~927m elevation), the paleolake covered more than 1800km2 in the Juyanze Basin during this period but fluctuated frequently. Whether or not this MIS 5 lake filled the entire Ejina Basin or merely overflowed the Juyanze Basin to partially fill the other Ejina sub-basins remains unknown. Regardless, the presence of such a large MIS 5 paleolake in the Ejina Basin suggests its lake history closely matches those from other closed-basin drainages originating in the Qilian Mountains. We suggest that the high stands appearing during MIS 5 in the Juyanze Basin likely were a response to moist climatic conditions during the last interglacial period.

Fault geometry and neotectonic fault activity of the Ejina Basin using integrated geological and geophysical data

Fault geometry and neotectonic fault activity of the Ejina Basin using integrated geological and geophysical data

Book review: Water Resources Research in Northwest China Helps to Deal with Water Issues in the Context of Climate Change and Human Activity

Water resource is one of the most important natural resources for sustaining the survivals ofanimals and plants, promoting the development of agriculture and industry, and maintainingecological diversity and environmental sustainability across the globe. In arid and semiaridareas, water resources are especially important. However, with global environmental change,especially climate change and ecological degradation, the global water cycle has beenchanged, and concerns on this change have been increased. The arid region of NorthwestChina covers over one fourth of the nation’s entire land area and forms one of the world’slargestaridregions.Waterresourceisakeyfactorrestrictingsocialandeconomicdevelopmentand influencing environmental change in Northwest China; issues regarding water resourcesare complex and serious in this area. Therefore, it is necessary and urgent to carry outinvestigations on water resources in Northwest China.Water Resources Research in Northwest China, edited by Yaning Chen, was recentlypublished by Springer in 2014 (Chen 2014, Springer, 444p, Hardcover ISBN 978-94-017-8016-2).Before the publication of this English book, several Chinese books on relevanttopicshave been published by some Chinese publishers, such as Groundwater Utilization and Eco-Environmental Protection in Ejina Basin, Heihe River, Northwestern China by Wu et al.(2004), Hydrologic Cycle and Water Resource Modeling for the Heihe River Basin inNorthwestern China by Wu et al. (2010), and Development, Utilization and Management ofWater Resources in Western China by Ren et al. (2012). This book, however, is the firstEnglish book, to the best of my knowledge, reporting water resources research results inNorthwest China and published by a world famous book publisher. The research reported inthisbookissupportedbytheNationalKeyBasicResearchProgramofChina(973Program)in

Support-Vector-Machine-Based Models for Modeling Daily Reference Evapotranspiration With Limited Climatic Data in Extreme Arid Regions

Evapotranspiration is a major factor that controls hydrological process and its accurate estimation provides valuable information for water resources planning and management, particularly in extremely arid regions. The objective of this research was to evaluate the use of a support vector machine (SVM) to model daily reference evapotranspiration (ET0) using limited climatic data. For the SVM, four combinations of maximum air temperature (T max ), minimum air temperature (T min ), wind speed (U 2 ) and daily solar radiation (R s ) in the extremely arid region of Ejina basin, China, were used as inputs with T max and T min as the base data set. The results of SVM models were evaluated by comparing the output with the ET0 calculated using Penman–Monteith FAO 56 equation (PMF-56). We found that the ET0 estimated using SVM with limited climatic data was in good agreement with those obtained using the conventional PMF-56 equation employing the full complement of meteorological data. In particular, three climatic parameters, T max , T min , and R s were enough to predict the daily ET0 satisfactorily. Moreover, the performance of SVM method was also compared with that of artificial neural network (ANN) and three empirical models including Priestley-Taylor, Hargreaves, and Ritchie. The results showed that the performance of SVM method was the best among these models. This offers significant potential for more accurate estimation of the ET0 with scarce data in extreme arid regions.

Geomorphoclimatic characteristics and landform information in the Ejina Basin, Northwest China

Natural environment of mid-latitude deserts of Central Asia is undergoing rapid changes. One of its elements is the relief. What needs to be particularly emphasized is its morphogenesis and landform evolution. In this study, a geomorphological research in the Ejina Basin (Inner Mongolia) is carried out with regard to identifying the main landforms and the contemporary geomorphic processes. We consider ancient and modern landforms as a unit and provide a general explanation for their evolution. Related environmental indications of existing landforms are discussed on the basis of climate geomorphology. Results show that the current basin is under the conditions favorable for the development and dominance of landforms originated from physical processes such as desiccation–deflation and aeolian. The landform system is characterized by its variable structure which is conditioned by specific hydrodynamics processes that existed during glaciations. It is suggested that landform patterns in Ejina are under the strong influence of rapid and/or intensive geomorphic processes. These signatures reflect the regional dynamics of landform evolution as characterized by a very effective integration of tectonic and climate-driven morphogenetic processes. Based on the present day climate data, we infer an obvious linkage of desert gorges and pediments in the basin to ancient humid phases, which provided high energy runoff for the formation of these landforms and were associated with erosional features under more humid and colder climate during the last glacial period. Desert plains and aeolian dunes in the central basin are the related products of contemporary climate. Clear evidences proving the landform inconsistency and landform instability in the Ejina are presented, indicating that the main geomorphic unit is experiencing transformation from alluvial plain to desert plain and then to aeolian dunes. However, the geomorphodiversity in the Ejina should be a compound result of complex surficial processes other than glaciation. Frost weathering, fluvial/alluvial action, desiccation–deflation and aeolian processes as well as climatic changes have played important roles.

Groundwater recharge and hydrogeochemical evolution in the Ejina Basin, northwest China

Groundwater plays a dominant role in the eco-environmental protection of arid/semi-arid areas. Understanding sources and mechanisms of groundwater recharge in the Ejina Basin, an arid inland river basin in northwest China, is important for water resource planning in this ecologically sensitive area. In this study, 90 water samples were collected from rainfall, rivers and lakes, and springs and pumping wells in 2009. Analysis of the aquifer system and hydrological conditions, together with hydrogeochemical and isotope techniques were used to investigate groundwater sources and their associated recharge processes. Our results show that shallow phreatic and deep confined groundwater differ greatly in their compositions, with a distinct spatial heterogeneity of phreatic groundwater TDS (from 365 mg/L to 5833 mg/L), which increase along the shallow groundwater flow paths. Groundwater chemical evolution is mainly controlled by rock dominance and the evaporation-crystallization process, and the dominant anion species change systematically from HCO3 to SO4 to Cl, and the dissolved ions within the groundwater system from Na- and K-rich minerals and sulfate phases also contribute significantly to the groundwater composition. The stable isotope levels (delta O-18 and delta H-2) of the surface water and the shallow phreatic groundwater confirm that the Heihe River and Badain Jaran Desert groundwater are the main sources recharging the phreatic aquifer in the Ejina Basin. Thus, river infiltration and desert front recharge should be considered as the two main recharge mechanisms of the Ejina aquifer. However, recharge from the Badain Jaran Desert aquifer to the Ejina Basin has occurred at a lower rate due to acidification since the middle Holocene. For this reason, the sustainable improvement of the ecological environment should be based on the shallow groundwater recharge of the phreatic aquifer in the Ejina Delta, which mainly takes place via seepage through the riverbed and direct infiltration during periods of environmental flow control. (C) 2012 Elsevier B.V. All rights reserved.

10Be in quartz gravel from the Gobi Desert and evolutionary history of alluvial sedimentation in the Ejina Basin, Inner Mongolia, China

10Be in quartz gravel from the Gobi Desert and evolutionary history of alluvial sedimentation in the Ejina Basin, Inner Mongolia, China