Ordos Plateau Research Articles

Restriction of groundwater recharge and evapotranspiration due to a fluctuating water table: a study in the Ordos Plateau, China

Improved understanding of interactions among the atmosphere, soil water and groundwater can be achieved by observing time-series of soil-water content and water-table fluctuations in a soil profile. Field observations at a site in China show that from mid-June to mid-September, when evapotranspiration is strong, direct groundwater recharge does not occur, and variations in soil-water content in the shallow part of the unsaturated zone are mainly controlled by atmospheric conditions; however, in the deeper part they are controlled by the fluctuating water table. Therefore, a one-dimensional (1D) model with a variable-head lower boundary condition (BC) is built to interpret the responses of soil-water flow to changes in atmospheric and groundwater conditions, and a 1D model with a fixed-head lower BC corresponding to the mean water-table depth is built for comparison. The model with a variable-head lower BC reproduces the observed variations in soil-water content, and results in much smaller groundwater evapotranspiration than the compared model. Moreover, the model with a variable-head lower BC shows a two-sided damping of variations in the soil-water flux from the surface and from the bottom, thus producing a stable middle layer with limited variation in soil-water flux. The limited but stable upward flux in the middle layer indicates restriction of both the direct recharge and evapotranspiration of groundwater. Therefore, this study enhances understanding of interactions between the atmosphere and groundwater in arid regions, and also on the appropriate selection of the lower BC of 1D variably saturated flow models.

Physical and Mechanical Properties of Pisha Sandstone with Different Corlors in Ordos Plateau

Pisha sandstone with different colors is widely distributed in Ordos Plateau, showing different engineering properties. Therefore, basic physical and mechanical properties of two kinds of common Pisha sandstones with different colors (purplish red and yellow) are studied through laboratory tests. Because of the capillary pressure in the soil, the Shear resistance of Pisha sandstone will increase first and then decrease with the increase of water content; when the water content is nearly saturated, the shear strength indexes of two Pisha sandstones are significantly reduced.

The process of moisture and temperature change of soil profile in Pisha sandstone area

The Pisha sandstone area in Ordos Plateau is a cross zone of water, wind and freeze-thaw erosion. Freeze-thaw erosion is one of the important erosion modes in this area, and soil moisture and temperature are the two key factors affecting it. In order to reveal the change process of soil moisture and temperature with time in the Pisha sandstone area, we took the small watershed of Erlaohugou in Huangfuchuan as the study area. Two sets of EM50 full-automatic collection systems were set up on a typical slope in the area, and the change process of moisture and temperature of the slope from March to September was continuously observed. The results showed that the changes of soil moisture and temperature in this area were greatly affected by seasons and climate. Soil moisture exhibited significant temporal and spatial differentiation, while soil temperature had significant temporal differentiation but not obvious spatial differentiation.

Comparative analyses of leaf cuticular lipids of two succulent xerophytes of the Ordos Plateau (Gobi Desert), Tetraena mongolica maxim and Zygophyllum xanthoxylum (Bunge) Engl

Tetraena mongolica Maxim, a relic shrub of the paleo-Mediterranean flora, is normally accompanied in the Western Ordos desert by another plant species in the same taxonomic family, Zygophyllum xanthoxylum (Bunge) Maxim, and together they play a vital role in the ecology of the local environment. Z. xanthoxylum has been identified as having stronger drought tolerance than T. mongolica. As an important water barrier, cuticles were compared between these two relatives to better reveal the mechanism of their different drought tolerance. Z. xanthoxylum possesses more flattened wax crystals, lower epidermal permeability and higher water use efficiency (WUE) than T. mongolica. The composition of cuticular lipids were analyzed, and the results showed that Z. xanthoxylum had significantly higher total amounts of both cuticular wax and cutin monomers than T. mongolica, with all wax class (especially alkanes) and cutin monomer amounts being much higher in Z. xanthoxylum. Cuticle-associated genes were analyzed by transcriptome sequencing, and the results showed that more alkane synthesis genes were up-regulated in Z. xanthoxylum. These findings provide different cuticles on these two succulent xerophytes and reveal the relationships with their different drought tolerance. This study is helpful to reveal the function of plant cuticle in adaptability to extreme environments.

The impact of groundwater depth on the spatial variance of vegetation index in the Ordos Plateau, China: A semivariogram analysis

As important sensitive feedback of ecosystems, spatial distribution and patterns of vegetation can remarkably reflect eco-environmental conditions in arid and semiarid areas, where groundwater plays a significant role. The impact of groundwater depth (GD) on the spatial variance in remote-sensing vegetation index is highlighted in this study over the Ordos Plateau, China. The 250 m resolution mean annual Enhanced Vegetation Index (EVI) data are analyzed and compared to the same resolution data of altitude, air temperature, aridity index and GD. A linear regression analysis indicates a significant weak correlation between the EVI and the climatic and topographic controls at the regional scale. A semivariogram analysis is introduced to quantify the GD-dependent variance in the residual EVI (WEVI) filtered from this linear regression. The pixel-to-pixel dependency of WEVI on GD is nonlinear and significant only when GD is smaller than 10 m. The semivariance of WEVI increases with the lag distance and slightly fluctuates around the sill when the distance is sufficiently larger than 5 km. The sill of WEVI variance in the situation of GD ≤ 5 m is significantly higher than that in deeper groundwater situations. The semivariogram range of WEVI in the middle zone of the study area is lowest due to the lowest semivariogram range of GD. The nugget effect in the WEVI variance is weak but positively related to the nugget of GD variance when groundwater is shallow. High sensitivity of the vegetation cover to the shallow groundwater should be considered in the regulation of groundwater resources for ecological benefits.

Using Isotopes (H, O, and Sr) and Major Ions to Identify Hydrogeochemical Characteristics of Groundwater in the Hongjiannao Lake Basin, Northwest China

Hongjiannao Lake is the largest desert freshwater lake in the Ordos Plateau, China, and the relict gull is an endangered species that uses the lake for its habitat, with the largest colonies being located there. Using hydrochemical parameters, stable hydrogen and oxygen isotopes, and strontium isotopes, we investigated the hydrogeochemical characteristics of groundwater. As a result, the major cations of the groundwater were found to be Ca2+ and Na+, the major anion was found to be HCO3−, and the hydrochemical facies were mainly found to be HCO3–Ca, HCO3–Na. and HCO3–Ca–Na. The hydrochemical formation of groundwater was controlled by both evaporation and water–rock interactions, and carbonate and sulfate minerals dissolved or precipitated in the groundwater. On the basis of isotope analysis, groundwater was affected by evaporation and δ18O enrichment, and the higher salinity of Hongjiannao Lake suffered from intensive evaporation. The higher 87Sr/86Sr ratio and lower concentrations of Sr2+ in the groundwater were derived from the dissolution of silicate minerals, whereas the opposite concentrations were due to the dissolution of carbonate and sulfate minerals. Based on this work, such results can be used to research groundwater recharge into the lake and to protect water quality.

Isostatic state and crustal structure of North China Craton derived from GOCE gravity data

The crustal structure between different subregions of the North China craton (NCC) plays an important role in improving our understanding on the craton evolution. Here we present a flexural Moho map and isostatic residual gravity field of the NCC derived from the GO_CONS_GCF_2_TIM_R3 model.We first investigate the influence of additional sources on the forward flexure calculation, especially the distinct thinning of the lithospheric thickness from west to east. After removing the gravity effects of the LAB undulations, the flexural Moho and isostatic residual gravity field of the NCC are calculated using the Vening-Meinesz regional isostasy models. There are high to medium positive residual anomalies beneath the Eastern block and Trans-North China Orogen, while negative residual anomalies delineate the Yinshan block, Ordos plateau and Khondalite belt. This obvious disparity is consistent well with the decreasing depth of the flexural Moho from west to the east. A profile across the Eastern block, Trans-North China orogen and the Western block was employed to construct a density structure of the crust and uppermost mantle. By comparing the surface topography, Bouguer gravity, isostatic Moho and seismological Moho undulations, we find that the flexural Moho is much shallower than the seismic Moho beneath the northern margin of the Ordos block, possibly indicating the over-compensated isostatic state caused by the dominant NW–SE oriented compressional deformation in the lithospheric processes. Density modeling results further predicted that a high density body may exist in the lower crust beneath the northern margin of the Ordos block, which could be a westward-dipping upper-middle crust remnant stagnating in the lower crust beneath the Western block. Medium to high pressure metamorphism of granulite facies or eclogite facies, resulting from subsequent continental thickening during the continental collision may be responsible for modifying the remaining subduction remnant.

Long‐Term Elimination of Grazing Reverses the Effects of Shrub Encroachment on Soil and Vegetation on the Ordos Plateau

AbstractConversion from grasslands to shrublands resulting from overgrazing occurs worldwide and is reinforced by the global climatic change. The functioning, biogeochemical cycles (e.g., carbon and water), and the stability of grassland ecosystems are significantly affected by the conversion. To best manage and use those grassland ecosystems, it is imperative to examine how the shrub‐encroached grasslands can be restored to native grassland ecosystems. In this study, aboveground biomass of all species, root biomass, soil water content, and soil texture in a set of fenced and unfenced plots were observed every three years from 1992 to 2011 in a semishrub encroached grassland on the Ordos Plateau of China. In the fenced plots, aboveground biomass increased for grass species and decreased for semishrub species. Root biomass and soil water content in the 0–10‐cm soil layer increased, but decreased in the 10–30‐cm soil layers. The fraction of soil particle sizes less than 0.01 mm increased in the 0–10‐cm soil layer. In contrast, these variables remained constant in the unfenced plots over the experimental period. The semishrub encroached grassland dominated by Artemisia ordosica was replaced with a native perennial grass, Stipa bungeana, when grazing was eliminated in the fenced plots. Changes in soil texture and moisture after fencing were correlated with the native grassland restoration from semishrub encroached grasslands. This study suggests that, to restore the native grassland, grazing should be eliminated in the study region.

Experimental study of sediment transport processes and size selectivity of eroded sediment on steep Pisha sandstone slopes

The Pisha sandstone area on the Ordos Plateau of China is the primary source of coarse sediment (with a particle size d > 0.05 mm) of the Yellow River. Sediment size distribution and selectivity greatly affect sediment transport and deposition. Hence, sediment transport processes and size selectivity by overland flow on Pisha sandstone slopes were investigated in this study. Experiments were run with Pisha sandstone soil (bulk density of 1.35 g cm−3) under rainfall intensities of 87 and 133 mm h−1 with a 25° slope gradient, and the duration of simulated rainfall was 1 h. Sediment and runoff were sampled at 2-min intervals to examine the size distribution change of the eroded sediment. The particle composition, enrichment rate, fractal dimension, and time distribution characteristics of median grain size (d50) of eroded sediment were comprehensively analyzed. Statistical analyses showed that Pisha sandstone slope generated a large amount of coarse sediment during the erosion. >40% of eroded sediment particles were coarse sediment, which will become the main sediment in the lower reaches of the Yellow River bed. The particle size of eroded sediment tended to gradually decrease with the continuous rainfall but remained larger than the initial value of Pisha sandstone soil after refinement. The fractal dimension was positively correlated with the slope flow velocity, while the d50 was negatively correlated with the slope flow velocity. Overall, these findings indicates that the selectivity and transportation of sediment particles on the Pisha sandstone slopes is mainly influenced by the hydrodynamic parameters of overland flow. The reason for the large amount of coarse sediment generated during the erosion in Pisha sandstone area is not only related to the large porosity and a small cohesive force of sand, but also related to the hydraulic conditions of the Pisha sandstone slopes. In the Pisha sandstone area, we should control soil erosion mainly by reducing the initial erosion dynamics, such as reducing splash erosion, increasing soil infiltration and surface resistance. This study provides a methodology and data references for studying the particle selectivity characteristics of eroded sediment and provides a scientific basis for revealing the mechanism of erosion and sediment yield in the Pisha sandstone area of China.

Analytical Solutions for Steady-State Multiwell Aquifer Tests in Rectangular Aquifers by Using Double Fourier Transform: A Case Study in the Ordos Plateau, China

Straightforward solutions have long been expected for the analysis of multiwell aquifer tests. In this paper, we derive series analytical solutions of steady-state groundwater flow in a rectangular-shaped aquifer with pumping/injection wells for both confined and unconfined conditions. Double Fourier Transform (DFT) technique is applied to deal with different combinations of impermeable and specified head boundaries on sides. The obtained solutions are compact and concise in mathematics and flexible in terms of well number, well locations, and pumping/injection rates. Hatoucaidang, a groundwater resource field in the Ordos Plateau, Northwestern China, is introduced as a field case study, where a multiwell aquifer test was conducted. One of the analytical solutions derived herein is used to estimate hydraulic conductivities by applying a direct calculation method and a least square estimation method regarding observed versus calculated drawdowns. By comparing with nearby single-well pumping tests, the reliability of the derived analytical solutions is proven. This study facilitates utilizing the multiwell aquifer test to analyze the general behavior of groundwater movement in aquifer systems.

Determining the Age of Terrace Formation Using Luminescence Dating—A Case of the Yellow River Terraces in the Baode Area, China

Dating fluvial terraces has long been a challenge for geologists and geomorphologists, because terrace straths and treads are not usually directly dated. In this study, the formation ages of the Yellow River terraces in the Baode area in China were determined by dating fluvial deposits overlying bedrock straths using optically stimulated luminescence (OSL) dating techniques. Seven terraces (from the lowest terrace T1 to the highest terrace T7) in the study area were recognized, and they are characterized by thick fluvial terrace deposits overlaid by loess sediments. Twenty-five samples from nine terrace sections were dated to about 2–200 ka. The OSL ages (120–190 ka) of the fluvial samples from higher terraces (T3–T6) seem to be reliable based on their luminescence properties and stratigraphic consistency, but the geomorphologic and stratigraphic evidence show that these ages should be underestimated, because they are generally similar to those of the samples from the lower terrace (T2). The formation ages of the terrace straths and treads for the T1 terrace were deduced to be about 44 ka and 36 ka, respectively, based on the deposition rates of the fluvial terrace deposits, and the T2 terrace has the same strath and tread formation age of about 135 ka. The incision rate was calculated to be about 0.35 mm/ka for the past 135 ka, and the uplift rate pattern suggests that the Ordos Plateau behaves as a rigid block. Based on our previous investigations on the Yellow River terraces and the results in this study, we consider that the formation ages of terrace straths and treads calculated using deposition rates of terrace fluvial sediments can overcome problems associated with age underestimation or overestimation of strath or fill terraces based on the single age of one fluvial terrace sample. The implication is that, for accurate dating of terrace formation, terrace sections should be systematically sampled and dated.

Changes in levels of enzymes and osmotic adjustment compounds in key species and their relevance to vegetation succession in abandoned croplands of a semiarid sandy region.

Reclamation of cropland from grassland is regarded as a main reason for grassland degradation; understanding succession from abandoned cropland to grassland is thus crucial for vegetation restoration in arid and semiarid areas. Soil becomes dry when cropland is reverted to grassland, and enzyme and osmotic adjustment compounds may help plants to adapt to a drying environment. Croplands that were abandoned in various years on the Ordos Plateau in China, were selected for the analysis of the dynamics of enzymes and osmotic adjustment compounds in plant species during vegetation succession. With increasing number of years since abandonment, levels of superoxide dismutase increased in Stipa bungeana, first decreased and then increased in Lespedeza davurica and Artemisia frigida, and fluctuated in Heteropappus altaicus. Levels of peroxidase and catalase in the four species fluctuated; levels of proline, soluble sugar, and soluble protein either decreased or first increased and then generally decreased. According to a drought resistance index, the drought resistance of the four species was ranked in descending order as follows: S. bungeana > A. frigida > H. altaicus > L. davurica. The drought resistance ability of the different species was closely linked with vegetation succession from communities dominated by annual and biennial species (with main accompanying species of L. davurica and H. altaicus) to communities dominated by perennial species (S. bungeana and A. frigida) when soil became dry owing to increasing evapotranspiration after cropland abandonment. The restoration of S. bungeana steppe after cropland abandonment on the Ordos Plateau is recommended both as high‐quality forage and for environmental sustainability.

降水对鄂尔多斯高原克隆植物分布的影响

降水对鄂尔多斯高原克隆植物分布的影响

Vegetation response to climatic variation and human activities on the Ordos Plateau from 2000 to 2016

Determination and analysis of the effects of climatic variation and human activities on vegetation changes since the implementation of intensive ecological projects in 2000 are critically important for the restoration of vegetation on the Ordos Plateau, one of the areas that suffer from the worst vegetation degradation, the most concentrated coal and gas exploitation, and the highest ecological risks in China. This study was performed to establish and validate a nonlinear regression model to express the relationships between the normalized difference vegetation index (NDVI), precipitation, and air temperature in areas with scarce human activities, as identified from the Global Human Influence Index Datasets. This model was then applied to the whole plateau with data on cumulative precipitation and average air temperature with the consideration of the delayed effects to simulate temporal NDVI changes induced by climatic variation. The residual trend was then computed as the slope of the difference between the actual NDVI and the simulated value to analyze the human impact on vegetation. The results show that the plateau’s vegetation had experienced a significant greening trend from 2000 to 2016 under a warmer and wetter climate and with the impact of human activities; compared to air temperature, precipitation played a leading role in vegetation greening in most parts of the plateau, and human activities had a significant positive impact in 22.0% of the plateau and a significant negative impact in 0.66% of the plateau (p < 0.1). More effective programs of ecological protection and restoration must still be conducted by the government and other organizations.

Diversion of the paleo‐Yellow River channel in the Qingtongxia area of Ningxia, China: Evidence from terraces and fluvial landforms

The Qingtongxia Grand Canyon (QGC) of the Yellow River is a region of intense tectonic deformation that is located in the southern Yinchuan Basin, at the junction of the western margin of the Ordos Plateau and the northeast arcuate structural belt of the Qinghai–Tibetan Plateau. The Yellow River makes a 90° turn as it traverses the Qingtongxia area, incising the hard Ordovician sandstones of Niushou Mountain, while leaving the relatively soft Quaternary sediments on the northern side of the channel undisturbed. Despite this apparent inconsistency with the expected pattern of river erosion, there has been no significant research to date on the formation of the QGC. Here, we utilize remote sensing, surficial geomorphology, and shallow coring to confirm the evolution of the Yellow River channel and formation of the QGC. Using Landsat Thermic Mapper and ASTER imagery, we identified a N–S‐oriented zone of high water‐content in the northern part of the QGC that is characterized at the surface by marsh and wetlands. Shallow cores reveal the zone is underlain by Yellow River gravel, while seismic profiling confirms anomalous seismic structures relative to the surrounding strata. Together, these data document a paleo‐Yellow River channel in the northern Qingtongxia area. We selected four representative profiles of the Yellow River terraces in the Qingtongxia and adjacent areas to acquire measurements on above water level and age. The uppermost terraces preserved at the entrance, central section, and exit of the QGC are labelled T6, T9, and T3, respectively. Our data indicate that the flow direction during the construction of T9 was different to that of the modern Yellow River and that canyon incision occurred during the development of T3, which we constrain to 65–85 ka. Ultimately, we (a) document a paleo‐Yellow River channel north of the QGC, which may have been affected by tectonic activity since the late Pleistocene and (b) show that the Yellow River has since been diverted towards the Yinchuan Basin via the QGC.

Research on Ordos Model Based on Sustainable Development Perspective

In order to achieve the sustainable development of the region, aiming at the ecological degradation characteristics of the soil matrix and climate control in the Ordos Plateau and the ecological environment caused by the single model. This paper analyzes the ecological degradation characteristics of the regional ecosystem, the restoration of different degraded vegetation, the soil complex Erosion management technology, regional ecological security technology,regional eco-industrial development and reconstruction of human settlements in five areas to carry out sustainable development model for the implementation of the model to provide theoretical and technical research ideas, and strive to weaken the local ecological degradation rate, Promote the adjustment of local industrial structure, enhance the local green economy development rate, accelerate social development and ecological civilization construction.

Sources and origins of eolian dust to the Philippine Sea determined by major minerals and elemental geochemistry

AbstractWe investigated the microscopic mineral characteristics of modern eolian dust particulates and the trace-element compositions of the siliciclastic fractions of these samples, collected from the Philippine Sea in 2014 and 2015, and conducted an air mass backwards trajectory analysis of dust particulates in the spring and winter of 2015, to better constrain the provenances and transport dynamics of dust delivered to this region. The microscopic minerals show obvious signatures of dust deposition and physical abrasion, indicating long-distance wind transport from the Asian deserts. The trace-element compositions (Zr–Th–Sc) display a binary mixture of eolian materials derived from the eastern Asian deserts and the central Asian deserts, which is similar to the result of the Sr–Nd isotopic compositions of modern sediment trap sediments collected on the Benham Rise in 2015. We demonstrate that modern dust sediments in the Philippine Sea primarily originate from the Ordos Desert (generally &gt; 80%), while the contributions of the Taklimakan Desert and the Badain Jaran Desert are small. Eolian dust particulates raised from source regions are predominantly transported to the Philippine Sea by the East Asian winter monsoon, but not by the westerlies. In addition, our results indicate that increased precipitation in the source regions can result in relatively low dust fluxes in the Philippine Sea, and there is a period of 6–7 days for eolian dust originating from source areas to be delivered to the Philippine Sea.

Spatio-Temporal Variations in Precipitation Extremes in the Endorheic Hongjian Lake Basin in the Ordos Plateau, China

Precipitation extremes have important implications for regional water resources and ecological environment in endorheic (landlocked) basins. The Hongjian Lake Basin (HJLB), as the representative inflow area in the Ordos Plateau in China, is suffering from water scarcity and an ecosystem crisis; however, previous studies have paid little attention to changes in precipitation extremes in the HJLB. In this study, we investigated the spatio-temporal variations of the core extreme precipitation indices (i.e., PRCTOT, R99p, Rx1day, Rx5day, SDII, R1, R10, CWD, and CDD) recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI), and analyzed the climatic dry–wet regime indicated by these extreme indices during 1960–2014 in the HJLB. The results show that the nine extreme indices had large differences in temporal and spatial variation characteristics. All the nine extreme precipitation indices showed a large fluctuation, both in the whole period and in the three detected different sub-periods, with variation magnitudes of 13%–52%. Most extreme indices had non-significant downward trends, while only the consecutive wet days (CWD) had a significant upward trend. The eight extreme wet indices increased from northwest to southeast, while the consecutive dry days (CDD) had the opposite change direction. Each index had a different trend with different spatial distribution locations and areas. The nine extreme indices revealed that the climate in the HJLB has become a drought since the early 1980s. This was specifically indicated by all four extreme precipitation quantity indices (PRCTOT, R99p, Rx1day, Rx5day) and the extreme intensity index (SDII) declining, as well as the number of heavy precipitation days (R10) decreasing. When the dry–wet variations was divided into the different sub-periods, the climatic dry–wet changes of each index demonstrated more inconsistency and complexity, but most indices in the first sub-period from 1960 to the late 1970s could be regarded as a wet high-oscillation phase, the second sub-period after the early 1980s was a relatively dry low-oscillation phase, and the third sub-period after the late 1990s or early 21st century was a dry medium-oscillation phase. It is worth noting that most extreme indices had an obvious positive linear trend in the third sub-period, which means that in the last 20 years, the precipitation extremes showed an increasing trend. This study could provide a certain scientific reference for regional climate change detection, water resources management, and disaster prevention in the HJLB and similar endorheic basins or inland arid regions.

Asian Summer Monsoon‐Related Relative Humidity Recorded by Tree Ring δ18O During Last 205 Years

AbstractTo deeply understand the Asian summer monsoon (ASM) strength variation in its fringe region, we established a 205‐year stable oxygen isotope (δ18O) chronology based on four individual Pinus tabulaeformis Carr. from Ordos Plateau, China. First, we found that δ18O in tree rings inherits the signals of summer (June to August) monsoonal precipitation δ18O (δ18OP). Second, relative humidity (RH) was observed to have a large effect on the δ18O of pine trees. The tree ring δ18O series significantly correlates with the observed local RH from June to August (RHJJA) with r = −0.65 (N = 56, p &lt; 0.001). The RH over Ordos Plateau is greatly influenced by ASM‐related precipitation. As such, it could well reflect the variations of ASM intensity. Thus, we reconstructed the RHJJA over Ordos, the center of the ASM fringe region (ASMFR), for the last two centuries. Our reconstructed RHJJA series has a large geographical and spatial representativeness, which is well compared with other precipitation reconstructions in ASMFR and jointly reflects ASM variations in the past. The RHJJA reconstruction showed that the 1870s–1890s were the wettest years in the entire reconstruction, while the middle‐late 1920s were the driest. From 1930 to 2012, the RH of the study area continuously decreased. We found significantly negative correlations between RHJJA and the Central Pacific sea surface temperature. This finding means that if the El Niño–Southern Oscillation of the Central Pacific continues to increase in the future, the aridification in the ASMFR will be intensified.

The implication of the geophysical data and drilling records for the formation and paleoenvironment of the Hobq Desert, China

The Hobq Desert (HD) locates at the northern margin of the Ordos Plateau, China and the transition zone to the Hetao Basin. It is one of the main proximal deserts of the Loess Plateau, and its formation was controlled by the evolution of the Yellow River and the Ordos Plateau. It is still worthy of discussing the regional structure to enhance the understanding of the desert formation and paleoenvironment, especially with the additional works in the eastern part. Geophysical methods including gravity, magnetic, EM (electromagnetic) are often used to analyse the regional and near-surface structure. As for drilling records, they could show the lithology sequence directly and be applied for the environmental study (e.g., OSL dating). Therefore, in this paper, we used the satellite gravity data, GPR (Ground Penetrating Radar), TEM (Transient electromagnetic method) and drilling records with borehole resistivity data to analyse the desert structure from different scales and the paleoenvironment. Trough the upward continuation and Park-Oldenburg calculation for the gravity data, the thickness of Quaternary deposits is 0.85–1.55 km. The inferred faults indicated the performance of the Hetao Basin and the Ordos Plateau's uplift in Pleistocene, which also contributed to HD's formation and existing topography. A three-part structure within 350 m was revealed in the profile at eastern HD by EM data. The upper layer within 80–90 m was the aeolian dry sand, the middle one was mainly fluviolacustrine saturated sand with the occurrence of clay and grey calcareous root tubes, and the lower one might be the aeolian sand. This near-surface structure was consistent to the western part, and the forming period for the sand in the upper zone was thereby estimated no earlier than 80 Ka. Moreover, during this period, millennial-scale changes in paleo-effective moisture occurred although it was dominated by the arid climate.