Loess Layers Research Articles

New dates of a Northern Italian loess deposit (Monte Orfano, Southern pre-Alps, Brescia)

Loess in Northern Italy has been usually considered deposited during the MIS 4-2 period, which corresponds to the last Pleistocene glacial cycle. In particular, no absolute dating evidenced loess depositions older than ca. 89 ka. We investigated two strongly rubified soil profiles in the southern margin of the Alpine range in Lombardy to prove their aeolian origin and age of formation. We analysed the granulometry of all genetic horizons of these strongly rubified soils, and a total of 8 samples were collected for luminescence dating purpose. Most of the analysed soil horizons were dominated by silt and were characterized by the s-shaped granulometric curve, typical of loess materials. A particularly high clay content evidenced a strong weathering degree. A deep horizon was particularly clay rich, and it was interpreted as a typical Terra-Rossa horizon. Luminescence dates increased with depth, reaching 122 ka for the deepest loess layer and 453 ka (minimum age) for the Terra-Rossa horizon. The deepest observed loess layer represents the oldest quantitatively dated aeolian deposition in Northern Italy up to now.

Weathering and paleoprecipitation indices in a Late Pleistocene–Holocene loess–paleosol sequence in central Argentina

A Late Pleistocene–Holocene loess–paleosol sequence in central Argentina was studied to obtain a weathering insight and to probe geochemical tools as paleoclimatic proxies. Three paleosols and a buried soil interlayered with loess mantles compose Corralito I sequence (32°00′7″ S, 64°11′08″ W, 469 m a.s.l). Several weathering indices (CIA, CIA-K, and LWI) and elemental ratios (∑Bases/Al2O3, Rb/Sr, CaO/TiO2, Na2O/TiO2) were calculated. An incipient weathering degree throughout the sequence was detected, denoting that the parent material (i.e., loess mantles) has not been substantially modified by pedogenesis. Although a statistically significant correlation between magnetic susceptibility and several weathering indices was identified, the weathering intensity was not strong enough to produce a decrease in the magnetic signal of the paleosols, which is, in part, inherited from the detrital fraction. Paleoprecipitation indices, calculated using geochemical data, suggest slightly wetter conditions during paleosol formation when compared to loess. Paleosols were formed during humid conditions (paleosols II and II during MIS 5e, and paleosol I during MIS 3) with sedimentation pause and soil development, whereas loess layers were deposited during more arid conditions.

Permeability and paleoenvironmental implications of loess–paleosol sequence from Jingyang Loess Plateau

Eolian loess in China contains abundant information about paleoclimate evolution, but there have been few studies of the relationship between the changing permeability of loess and the paleoenvironment. To investigate how loess–paleosol permeability responds to climate change, 342 undisturbed soil samples were collected from the Jingyang Loess Plateau in the Guanzhong Basin. Permeability was measured by a TST-55 permeameter and soil microstructures were observed with a scanning electron microscope (SEM). The results showed that: (1) the permeability of the loess layers was higher than that of the paleosol layers; (2) loess–paleosol sequence permeability had a four-stage accumulation history; (3) the degree of permeability anisotropy (DPA) of most of the loess was greater than 1, whereas that of the paleosol layers were less than 1; (4) loess and paleosol microstructures were consistent with the results obtained by permeability, whose changes had been mainly caused by the pedogenesis controlled by the Quaternary climate. The higher permeability of the loess layers was largely the result of lower pedogenesis intensity due to the cold/dry climatic conditions at the time when the sediments were deposited. Conversely, the lower permeability of the paleosol layers was the result of higher pedogenesis intensity under warm/wet climatic conditions. Based on the permeability, DPA, and soil microstructures, we concluded that the gradual uplift of the Qinling Mountains and the changes in the intensity of the East Asian monsoon had played important roles in controlling the evolution of the climate in the Guanzhong Basin. Therefore, loess permeability can reflect Quaternary climate change and provide a new research method for interpreting the characteristics of the Jingyang Loess Plateau.

Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and −10° joints and weathered mudstone with 0°, 10°, and −10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

Shaking table test on the characteristics of seismic acceleration responses at the portal section of the loess tunnel

A large-scale shaking table test was conducted to study the dynamic response at the portal section of a tunnel based on the loess tunnel of the Baoji–Lanzhou high-speed railway as an engineering background. A wavelet packet transform method was applied to analyze seismic acceleration responses. The pattern of changes in energy in the loess tunnel under the seismic load was obtained. Results reveal that (1) the acceleration amplification factor of the slope surface increases with elevation, but a turn exists at the inverted arch of the tunnel because the stiffness of the tunnel is greater than that of the slope soil. As such, the tunnel elicits a certain protective effect on the slope soil below it. (2) The amplification effect of the internal slope soil decreases gradually outward, and the tunnel portal is affected by the amplification effect of the slope surface. The peak ground acceleration (PGA) of the tunnel vault is greater than that of the inverted arch of the tunnel. Thus, the vicinity of the tunnel vault should be the key seismic fortification area. (3) The loess layer causes an amplification effect on low-frequency-band seismic waves (0–12.51 Hz) and a filtering effect on the high-frequency-band seismic waves. The changes in the energy of the slope surface and the inside tunnel gradually stabilize as the seismic load increases. This study can provide a reference for the seismic fortification of the tunnel portal section of the loess slope–tunnel system under a seismic action.

Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India

Kashmir valley receives the rainfall owing to the dominant westerly winds and experiences less impact of the southwest monsoonal rains (SWM). In this valley, loess and loess paleosols occur as a thin veneer covering the landscape. The loess paleosols form an important proxy for paleoclimate reconstruction and understanding the late Quaternary paleoenvironmental shifts. For this purpose, the loess, paleosols within the loess lithosections were lithologged and the sediment samples were subjected to various grain-size textural and geochemical analysis. The U-ratio of the sediments supported by parameters such as TOC, CaCO3 content, ratios of Zr/Rb, Rb/Sr, Ba/Sr, K/Ba, K/Rb, chemical index of alteration (CIA) and clay mineralogy indicate that the loess paleosols have undergone weak to moderate degree of pedogenesis. The U-ratio and Zr/Sr ratio also reflect variations in the wind velocity ranging from weak to moderate conditions for the loess deposition. The Ba/Sr and Rb/Sr ratios signify varied precipitation conditions, particularly with higher precipitation during the paleosol formation. The A–CN–K plot exhibits weaker to intermediate type of weathering of the loess horizons. TiO2% vs. Al2O3% binary plot illustarates mostly basaltic to rhyolite/granite type of rock source and the Panjal Traps is one of the major sources of the loess deposition. The lower end of the exposed Choori and Burzahama lithosections were dated by OSL method to 54 ± 2 ka at 9.5 m depth and 52 ± 2 ka at 8 m of depth, respectively. Geochemical analysis and OSL dating of the Choori and Burzahama lithosections reveal that climate during the marine isotope stage 3 (MIS 3) was dominantly warm and dry (stadial conditions) in Kashmir valley when the loess layers covered the valley and since then the loess horizons have undergone weak to intermediate, moderate type of weathering in cool and dry conditions.

Microstructure and soil-water retention behavior of compacted and intact silt loess

There are an increasing number of mega engineering projects of removing the top of hills to fill in the valley for new land creation in the Loess Plateau of China, which significantly changes the hydrological and geological equilibrium state of the site. The formation of a new hydrological equilibrium state is associated with the water movement in the compacted and intact loess layers. Most disasters occurring in the loess area are related to water. The soil-water retention curve (SWRC) is the key to the implementation of unsaturated soil mechanics in engineering practice and is required to numerically model the movement of water in the soil. In this study, the SWRCs and microstructure of intact and compacted specimens from Lanzhou and Yan'an, two typical cities that have new land creation projects, are investigated. The SWRC is obtained using the filter paper method. The mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) techniques are used to explore the microstructure. The results highlight that the intact loess has a higher air occlusion value (AOV) and a similar slope of SWRC in the transition zone compared with the remolded specimens that compacted at the natural water content. The normalized SWRC (i.e., degree of saturation versus suction/AVO) of the intact specimen is approximately the same as the remolded specimens compacted at the natural water content. The difference in the microstructure between intact and compacted specimens originates from different existing states of the clay particles and further contributes to the variation of the SWRC.

Testing on loess collapse of expressway subgrade reinforced by lime-soil compaction piles

The engineering constructed on loess ground have been threatened by loess collapse upon water. In Western China a new provincial expressway now has been built on loess ground. The depth of the loess layer is more than 20 meters. The loess ground was improved by five methods to reduce the collapsibility. The reinforcement was then verified by various in-situ tests and further tests were made on laboratory to explore the effect of ground reinforcement by lime-soil compaction piles. The laboratory tests show the dry density has increased by nearly 20% and the main reason for the increase of shear strength is the increase of cohesion index by 27% when the internal friction is basically the same. The collapsibility coefficients at different depths are examined and concluded that the collapsibility has been notably eliminated. Conclusion is drawn that the expressway subgrade shall not be influenced by reinforced loess ground.

New insights into Southern Caucasian glacial–interglacial climate conditions inferred from Quaternary gastropod fauna

ABSTRACTIn the present study, we performed gastropod analyses on loess–palaeosol sequences from northeast Armenia (Southern Caucasia) covering at least three glacial–interglacial cycles. The elaborated ecostratigraphy shows significant patterns of species composition related to the succession of pedocomplexes and loess, respectively. Pedocomplexes included species that can be associated with high‐grass to forest‐steppe biomes, indicating increased humidity for these sections compared to the loess layers. In contrast, loess layers that relate to glacial periods are associated with gastropod species of semidesert environments with shrub‐ and shortgrass‐steppes, indicating semiarid to arid conditions. Furthermore, the loess deposits do not show any evidence for cold‐adapted gastropod species. Therefore, we suggest that average July temperatures in the study area were above 10 °C, even during periods of loess deposition. Consequently, we propose that the limiting factor for tree growth during glacial periods was aridity, rather than temperature. In addition, we observe environmental differences between the various glacial times, with our results indicating a trend towards steadily increasing aridity in Southern Caucasia across the Middle to Late Pleistocene.

Law of Movement of Discontinuous Deformation of Strata and Ground with a Thick Loess Layer and Thin Bedrock in Long Wall Mining

The surface discontinuous deformation caused by coal mining has great damage to the ecological environment and threatens the safety of human lives. Focusing on the problem of discontinuous deformation (ground fissures and collapsed pits) in mining areas with a thick loess and thin bedrock, this paper uses a coal panel in southern Shanxi in China as research background, and uses field investigation, theoretical analysis and the particle flow code 2D (PFC2D) numerical simulation method to study the movement of overburden and discontinuous ground deformation of mining areas with a thick loess layer and a thin bedrock. The results show that with the continual advance of the working face, the failure of the overlying rock, the changing of force chain shape and the development of cracks under this geological and mining condition have their unique rules. This study analyzes the law of movement of overburden in coal seam mining, explains why discontinuous deformation of the surface occurs in case of a thick loess layer and thin bedrock, and provides reference for the prediction of fracture development under the same geological conditions and the application of the PFC2D in coal seam mining in different geological conditions.

Full-scale experimental study of methane emission in a loess-gravel capillary barrier cover under different seasons

The methane emission in a loess-gravel capillary barrier cover (CBC) in winter and summer was investigated by constructing a full-scale testing facility (20 m × 30 m) with a slope angle of 14.5° at a landfill in Xi’an, China. Weather conditions, methane emission, gas concentration, temperature, and volumetric water content (VWC) in the CBC were measured. The temperature and moisture in the CBC showed a typical seasonal pattern of warm and dry in summer and cold and wet in winter. Accordingly, the maximum methane oxidation rate and methane emission were higher in summer. The mean methane influx and methane emission decreased significantly as the VWC increased beyond 40% (i.e., a degree of saturation 0.85) at a depth of 0.85 m, which was near the loess/gravel interface. At this depth, more water was presented in the loess layer in the downslope direction due to capillary barrier effects, which increased the upslope methane emission. More dominant methane emission in the middle- and upper-section of the CBC occurred in summer than in winter as there was less soil moisture to facilitate methane transfer. The LFG balance showed that a significant fraction of the loaded LFG was not accounted in the flux chamber measurements due to the preferential flow along the edges of the CBC. The maximum methane oxidation rate was 93.3 g CH4 m−2 d−1, indicating the loess-gravel CBC could mitigate methane emissions after landfill closure.

Experimental study on bearing characteristics of pile foundation in loess area of Longdong

In order to study the bearing characteristics of pile foundation in the deep loess layer of Longdong area, field tests were carried out on the basis of a project in Huachi County, Qingyang City. Three test cast-in-place piles of the basement were selected for static load tests. The Q-S curve of the three test piles was gentle, without obvious steep drop. The S-lgt curve was arranged in a gentle and regular way, with high bearing capacity, uniform and small settlement. So it can be used as the foundation of buildings bearing large loads. In the test, the load is mainly borne by the reaction force provided by the side friction of the pile; the axial force distribution of the pile body with depth is not only related to the load on the top of the pile, but also to the nature of the soil around the pile.

First results of multidisciplinary investigations for the hydrogeological conceptual modelling of loess deposits in eastern Croatia

Loess is a widespread continental aeolian sediment. Groundwater generally represents the most important source of potable water in loess areas, where loess is the aquitard overlying the aquifer system. This work investigates loess deposits of eastern Croatia that overlie a sandy aquifer exploited for potable and agricultural purposes. The genesis of the deposit and the depositional and post-depositional processes affecting its structure were reviewed in this work and integrated with the estimated hydrogeological properties of the material to propose a preliminary hydrogeological conceptual model of the loess-sand system. The results of published granulometric analyses were used to calculate the effective porosity and the hydraulic conductivity of the material employing an analytical approach. The eastern Croatian loess is a silty deposit originated during Middle-Upper Pleistocene glacial periods. The sediments produced by glacial grinding were transported and deposited by the Danube fluvial system and subsequently remobilised by wind forming the loess. During the interglacial periods, the pedogenesis of the deposit occurred, with bioturbations and discontinuities by living organisms at the micro- and macro-scale. The deposition of a new loess layer compacted and consolidated the previously deposited loess leading to the development of a sub-vertical pore structure and sub-vertical cracks at the micro- and macro-scale, respectively. The calculations from the grain size distributions point to the low effective porosity (5-12%) and hydraulic conductivity (~10-9 m/s) of both loess and pedocomplexes supporting their aquitard behaviour. The infiltration of surficial waters and their flow toward the underlying sandy aquifer is locally enhanced by the post-depositional discontinuities that constitute preferential flow paths within the loess aquitard. These results highlight the need of detailed hydrogeological investigations in loess deposits to address the impact of post-depositional processes on their hydrogeological behaviour and the upscaling of their hydrogeological properties for proposing specific groundwater protection strategies in loess areas.

Permeability and Groundwater Enrichment Characteristics of the Loess-Paleosol Sequence in the Southern Chinese Loess Plateau

To determine the permeability characteristics and the groundwater enrichment conditions of loess and paleosol layers, this article systematically investigated the permeability, magnetic susceptibility, porosity, and carbonate mass percentage of representative loess-paleosol layers (L1 to S5) on the Bailu tableland in the Chinese Loess Plateau south. The result of in situ permeability measurements showed that the average time to reach quasi-steady infiltration of loess layers is shorter than that of paleosol layers. In addition, loess layers have higher porosity and better water storage spaces than paleosol layers and were prone to form aquifers. Paleosol layers, on the contrary, are more likely to form aquitards. The difference between loess and paleosol in permeability, porosity and groundwater enrichment conditions is largely attributed to lower intensity pedogenesis of loess, which is in turn ascribed to the colder and drier palaeoclimatic conditions. It is worth mentioning that the CaCO3 concretion layer is a good aquifuge for its compact structure. Generally, the empirical formula of the Koctakob formula is applicable for describing the permeability rule of loess and paleosol layers, and the parameters of the empirical formulas can provide an important reference for hydrological and agricultural departments. In this regard, the Quaternary climatic change theory can contribute to the hydrogeology of the Chinese Loess Plateau, and the regional climatostratigraphy can be regarded as a baseline for local water resource positioning and revegetation in such a semi-arid area, which broadens the application field of Quaternary climatic change theory. Meanwhile, it also provides a reference path for solving water shortages of other loess distribution areas in China and other countries.

Vertical distribution characteristics of soil moisture with different strata in deep profile in Guanzhong Basin, China

The distribution of soil moisture in loess-paleosol sequences is a critical factor that impacts the regional environment in the Chinese Loess Plateau (CLP). In this study, samples were collected from the Xiushidu (XSD) profile at the southern edge of the Jinghe River in Guanzhong Basin; specifically, the Holocene-Middle Pleistocene Lishi strata loess. They were then dry weighed, and moisture content and grain size distribution were determined using the grain size testing method. The impacts of different soil textures, sedimentary environments and other factors on the XSD profile moisture distribution in the study area were examined. The results showed that: (1) During the sequence change process from top to bottom, the soil moisture content of the loess-paleosol sequence increased and the overall average moisture content of the XSD profile was ranked in a descending order as: the middle layer of Middle Pleistocene Lishi loess > the upper layer of Middle Pleistocene Lishi loess > the Holocene > the Late Pleistocene; (2) When film water was predominant, the correlation coefficients for soil moisture content and clay, fine-silty sand, coarse silt sand and microsand content were 0.389, 0.394, − 0.419 and − 0.451, respectively; (3) In adjacent loess and paleosol layers, the soil moisture content of the overlying loess layer was always greater than the underlying paleosol layer. (4) In the same loess layer, minimum moisture content values were subject to the East Asia winter monsoon; as such, they often appeared in the middle layer of this glacial period. In the same paleosol layer, the opposite trend was observed.

Climate Change and Vegetation Evolution during the Transition from Marine Isotope Stage 5 to 4 Based on Two Typical Profiles at the Southern Chinese Loess Plateau

The geological transitional period from the Marine Isotope Stage (MIS) 5 to 4 during the Quaternary period is a multidimensional change involving monsoon and precipitation variation, vegetation dynamics, and environmental evolution. The first loess layer (L1) and the first paleosol layer (S1) in the Chines Loess Plateau provide excellent high-resolution terrestrial sediment record for this transition. In this work, grain size (GS), CaCO3 content, magnetic susceptibility (MS), and pollen composition were measured at intervals of 2-cm in two representative L1/S1 profiles in the southern Chinese Loess Plateau to reconstruct records of climatic and vegetative changes during this transition. Our results showed that, in general, the paleo-vegetation type was forest-steppe, with Pinus being the commonest tree, and Chenopodiaceae and Artemisia being common herbs in the study area. The topography had a significant impact on the distribution of paleo-vegetation. The increase of coarse particles, the decrease of magnetic susceptibility, and the rising percentage of Gramineae, Artemisia and Chenopodiaceae pollen, all indicated that the paleoclimate became cooler and drier over the transitional period. Besides, we identified a cool event at about 76.8 ka B.P. as revealed by grain-size curves, and in response to this event, the vegetation changed significantly but lagged several hundred years behind the grain size record. This study confirmed the cooling and drying tendency during the MIS 5 to 4 transition phase in the southern margin of the Chinese Loess Plateau. These findings shed light on the climatic change on vegetation evolution during the MIS 5 to 4 transition period.

Influence of Quaternary paleoclimate change on the permeability of the loess–paleosol sequence in the Loess Plateau, northern China

AbstractPermeability differences in multi‐cycle loess–paleosol aeolian sediments, which are still poorly understood, have the potential to significantly improve our understanding of climatic change during the glacial–interglacial periods of the Quaternary. In this study, the permeability of a well‐preserved and continuous loess–paleosol sequence in the South Jingyang Plateau was investigated. Weathering intensity was inferred using a series of climate proxies including grain‐size distribution, magnetic susceptibility and mineralogy. The results of laboratory tests showed that the average saturated hydraulic conductivity of loess layers is higher than that of paleosol layers. Also, clear differences between loess and paleosol were found in terms of depth variations of the vertical and horizontal saturated hydraulic conductivities. Differences in loess–paleosol were also found for other proxies for pedogenic weathering [i.e. clay content, sand content, Kd value (ratio of coarse silt to clay), magnetic susceptibility, dolomite content and the ratios of hornblende/illite and hornblende/chlorite]. Our results showed a high permeability of loess layers associated with weak pedogenic weathering during cold/dry paleoclimatic conditions in glacial stages. On the contrary, paleosol layers developed in a warm/humid climate during the interglacial stages experienced strong pedogenic weathering that resulted in lower permeability. Based on these results, we construct a connection between Quaternary climate change theory and the modern hydrological system. This provides a scientific basis for investigating the distribution and pollution of groundwater resources in the local region. © 2020 John Wiley & Sons, Ltd.

Numerical Simulation and Model of Deformation Features of Destabilized Mining Slope Under Fault-Controlled Conditions

This paper took the Fengmaoding slope, typically found in the mountainous areas of central Shanxi province, as its research area. The stratum structure of the Fengmaoding slope is a typical coal measures stratum covered by a layer of loess. There are communication towers on the slope mass and top of the slope; railways, roads, and rivers at the foot of the slope. There are many villages across from the slope, therefore, the buildings and structures nearby, even the lives of the villagers are threatened by the damages caused by the deformation of the slope. Tectonic development and mining activities have very profound effects on the stability of the slope. Considering the above, this paper analyzed the effects of the fault in controlling the deformation features of the destabilized slope during underground mining by adopting the method of numerical simulation from these perspectives including displacement, stress, strain, among others. under different circumstances (the faulted and unfaulted) so as to provide guidance for future studies about landslides of the same type and give preventive proposals for reference.

Active and passive source Rayleigh wave joint imaging of the shallow structure in the Caotan Camp area, southwestern Ordos Basin

The shallow surface of the southern Ordos Basin is a thick Quaternary loess layer with a loose and unstable structure, which threatens the stability of local infrastructure and has a great impact on oil and gas seismic exploration in this area. Therefore, identifying the internal velocity structure of the loess sediments is of critical importance. In this study, joint imaging of active and passive source Rayleigh waves was utilized to reveal the shallow shear-wave velocity (vs) structure in the Caotan Camp area, southwestern margin of the Ordos Basin. Active source Rayleigh waves were recorded by long-spread geophone array and processed by an improved F–K transform algorithm to extract multi-mode Rayleigh-wave dispersion curves. The passive source seismic signals were collected by broadband seismographs, and the phase velocities at discrete frequencies of the passive source Rayleigh wave were calculated by Aki's spectral formula. A nested genetic and damped least squares (DLS) algorithm was used for the joint inversion of the active and passive source Rayleigh wave dispersion curves. The two-dimensional vs section under the survey line reveals the thickness and stratification of loess sediments in the study area. The joint imaging of the active and passive source Rayleigh wave also effectively increases the investigation depth, allowing to obtain the bedrock interface below the loess sediments.

Terrace formation and river valley development along the lower Taohe River in central China

A flight of nine river terraces has been well developed and preserved along the course of the lower Taohe River. Based on optically stimulated luminescence (OSL), electron spin resonance (ESR), paleomagnetic and loess-paleosol stratigraphic analyses, we found that the accumulation ages of the gravel layers of terraces T9–T1 correspond to the loess layers L13, L9, L8, L6, L5, L4, L3-L2, L1-4 and L1-1, respectively. The chronologic results indicate that the formation and development of the modern river valley in this area occurred between 1.4 and 1.14 Ma. The topographic fluctuation caused by the Kunhuang Movement appears to have been the main reason for the reorganization of the river system and valley development in the area. In the context of this tectonic uplift, fluvial processes were coupled with the regional climate on a geomorphic equilibrium scale; i.e., over a glacial-interglacial cycle. That is, river aggradation appears principally to have occurred during glacial periods, while a graded state existed during interglacial periods. In addition, rapid river downcutting in response to climate change occurred during the transition periods from glacial to interglacial climates.