geochemical evolution of the precambrian old rag granite virginia u s a testing a uth exploration model abstract the old rag granite is one of several recognized units within the virginia blue ridge complex generally composed of grenville age gneisses and granitoid intrusive rocks chemical variation in the old rag granite indicates simple orthomagmatic crystallization from the borders to the core of the pluton fractional crystallization of plagioclase oxides apatite and zircon accounts for much of the variation some trace elements however show anomalous behavior in the central part of the pluton y and sr and possibly ba and nb are enriched whereas rb and total ree are depleted in the central part of the pluton late crystallization of monazite could contribute to the observed ree patterns it could not however account for rb depletion and sr enrichment and no clear relationship between ree data and th u ratios are observed the geochemical patterns indicate overall orthomagmatic crystallization overlain by a late stage hydrothermal event an exploration model for uraniferous granites based upon the uranium deposits at rossing and bokan mountain included the precambrian basement of central and northern virginia in a list of proposed target areas geological mineralogical and whole rock chemical characteristics show a close association between the old rag granite and the rossing type deposits the uranium mean 6 9 ppm range 0 1 19 8 ppm and thorium mean 43 ppm range 3 5 114 ppm values are anomalous th u ratios average 7 5 and are widely variable indicating a decoupling of uranium from thorium neither u nor th are lognormally distributed within the old rag granite requiring an explanation beyond simple removal of u by weathering rayleigh fractionation modeling shows that both u and th although probably distributed originally by closed system fractionation have been subsequently mobilized uranium can be lost in an oxidized form by secondary processes such as weathering or hydrothermal alteration thorium however will be affected only by hydrothermal processes it is concluded that although primary fractionation was orthomagmatic the old rag granite was affected by late hydrothermal alteration whereby u was lost from the body and th was redistributed three primary avenues for u migration are possible 1 the rocks of the saddleback mountain intrusive suite which may have been contemporaneous with the old rag granite 2 paleozoic fault zones that cut the old rag pluton and 3 quartz veins pegmatites cupolas and roof pendants of the country rock nellysford gneiss that have been lost to erosion the last option is preferred on geological and geochemical grounds it is possible that the sedimentary uranium deposits of the adjacent triassic culpepper basin were derived from eroded upper levels of the old rag granite and like intrusives of the virginia blue ridge complex

identification of karst features using seismic p wave tomography and resistivity anisotropy measurements a football stadium with a capacity of a hundred thousand spectators is under construction over a karst terrain 10 km west of the old town of istanbul turkey a large cavity of approximately 30 m3 was detected beneath the sports field through a number of boreholes so that a geophysical survey was required to further investigate a portion of the sports field we utilized seismic refraction tomography and dc electrical method with rotated wenner array to delineate zones with solution voids and cavities total core recovery tcr was 5 15 from boreholes where zones with low velocities were identified through tomographic inversion whereas tcr values were above 60 in zones with higher velocities both low velocity zones in the tomographic images and increasing resistivity anisotropy with depth appear to indicate that the cavity extends toward the west and south at a depth of approximately 8 m although the southward and westward extension changes in character

hydrological response of loess slopes with reference to widespread landslide events in the heifangtai terrace nw china abstract in the heifangtai terrace nw china flooding irrigation is common for the cropland production and has increased the groundwater table by 20 30 m over the past five decades it is believed that excessive irrigation has induced a large number of loess landslides in this area however these loess landslides responses to hydrological changes have still not been well understood therefore 43 boreholes and 51 2d electrical resistivity tomography ert profiles with a total length of 40 km have been investigated to analyze the hydrological characteristics for the whole terrace and characterize the effects of hydrological changes on the occurrence of different types of loess landslides our main findings are as follows 1 three groundwater domes are found in the center and eastern part of the heitai terrace and the groundwater table is gradually rising in the whole terrace based on the ert results 2 the rising rate of groundwater table at the center of the terrace is twice greater than that at the margin of the terrace and it takes approximately 4 months for irrigation water to penetrate from the top surface to the saturated layer 3 landslide deposits could block drainage channels of groundwater increase the localized hydraulic gradient and result in rising of local groundwater table at the edge of the terrace 4 the resultant hydraulic gradient impels the groundwater from the center to seep out on the eastern and southern margins and new landslides are prone to occur in the main scarp of landslides with rising groundwater table the type and magnitude of landslides are affected by groundwater seepage and movement in order to fundamentally control the occurrence of landslides effective drainage system and the restrained amount of irrigation water are needed

distribution and genetic types of loess landslides in china abstract in this study 14 544 loess landslides collected from the loess plateau of china are used to reveal their distribution and origins main factors considered include landslide density regional tectonics soil properties geomorphic structure rainfall distribution seismic activity and human activity based on these factors the loess plateau is divided into eight zones with high possibilities of landslides that are classified into six genetic types the first genetic type of clustering distribution of loess landslides is related to several main regional active faults the second type is related to broken pieces of loess geomorphic structures the third type is considered to be due to unloading of the geomorphic peripheral slope that can cause the internal structural plane to open and thus controls the prototype and scale of the loess landslide change of hydrogeological conditions in the slope softens the loess pedestal and the slippery layer forming a softening zone and thus controlling the shear crack and slip model of the fourth type of loess landslides the fifth type is due to seismic activities that can generate additional stress to the earth s surface and landform slopes causing the opening of joints and seismic liquefaction the last type of landslides is caused by human activities by changing the geological structure hydrogeological conditions and the inner stress balance of slopes

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

a unified landslide classification system for loess slopes a critical review abstract over the last few decades many landslide classification systems have been developed inconsistencies across these systems have inevitably led to ambiguity confusion and contradictions specifically there has been no consensus on what types of slope movements and failures constitute landslides as a result landslide classification systems based on the same criteria do not always include the same types of slope failures on the other hand general landslide classification systems do not take into account the unique characteristics of slope failures in loess which covers about 6 7 of the earth s land surface most literature on loess is in chinese and the nomenclature both within the chinese literature and between the chinese and english literature is often not readily comparable therefore there is a need for a consistent and comprehensive system for classification of loess slope failures to be developed to better manage these particular geohazards as the presence and interactions of humans with the environment in loess areas continue to increase in this paper a critical review of landslide classification systems was conducted to identify their limitations as well as their relevant criteria for classifying loess slope failures understanding the mechanisms underlying the failure of loess slopes is critical for creating a realistic and comprehensive classification system for slope failures the classification systems of loess slope failures unified in this paper are based on detailed analyses of the possible mechanisms underlying each class of failure the primary classification criteria are types of movement and materials with other descriptive criteria used to explain differences among different classes for each class one or two typical case histories are presented a comprehensive collection of the literature reviewed in this study will facilitate future research on loess geohazards

binary sources of chinese loess as revealed by trace and ree element ratios abstract chinese loess is generally accepted to be one of the most important archives for establishing the average geochemical compositions of the upper continental crust ucc assuming numerous upper crustal recycling processes however the effect of such recycling processes on elemental fractionation has still not been systemically and quantitatively assessed this study investigates the trace and rare earth elements ree of the

geometrical appearance and spatial arrangement of structural blocks of the malan loess in nw china implications for the formation of loess columns abstract loess as one of the main quaternary deposits covers approximately 6 of the land surface of the earth although loess is loose and fragile loess columns are popular and they can stand stably for hundreds of years thereby forming a spectacular landform the formation of such special column shaped soil structures is puzzling and the underlying fundamentals remain unclear the present study focuses on quantifying and examining the geometrical shape and spatial alignment of structural blocks of the malan loess at different locations in the loess plateau of china the structural blocks under investigation include clay and silt sized particles aggregates fragments lumps and columns which vary in size from microns to tens of meters regardless of their size the structural blocks of the malan loess are found to be similar in shape i e elongated with a length to width ratio of approximately 2 6 the aggregates fragments lumps columns and macropores between aggregates exhibit strong concentration in the vertical or subvertical alignment these phenomena imply that the malan loess is anisotropic and it is composed of a combination of vertically aligned strong units and vertically aligned weak segments based on this vertiloess structure is proposed to denote this combination the vertiloess structure prevents horizontal erosion but favors spalling peeling toppling falling and cracking sliding of vertical loess pieces thereby forming loess columns

evaluation of gully head retreat and fill rates based on high resolution satellite images in the loess region of china the acceleration of large gully erosion in the loess environments of china is a matter of concern because of the changing land use and urban expansion this paper evaluates the gully head retreat and landfill rates in the huoxianggou watershed in the loess region of china for the period between 1969 and 2017 high resolution satellite imageries and ground truths allowed us to estimate the linear and volumetric change rates of gully head the digital elevation model dem derived from unmanned aerial vehicle uav was used to calculate the geometric parameters of the gully bottom and the linear and volumetric gully parameters were obtained using the 1969 2004 and 2017 satellite images of the study area we estimated the average annual linear retreat rate rl for the study area between 1969 and 2003 rl was found to be 1 41 0 98 m y 1 the average annual volumetric retreat rate rv was 63 79 96 62 m3 y 1 the average annual linear fill rate fl was 3 87 4 09 m y 1 and the average annual volumetric fill rate fv was 1002 46 1633 87 m3 y 1 between 2004 and 2017 rl was 0 82 0 80 m y 1 rv was 1 80 1 37 m3 y 1 fl was 3 86 4 99 m y 1 and fv was 708 62 1787 21 m3 y 1 we also estimated the retreat and fill rate of gullies within various land use classes when the land use type near the gully head was road the volumetric retreat rate of the gully was threefold that of the farmland and the rate of the gully head landfill was fourfold that of the farmland moreover the volumetric change rate cv and linear change rate cl of all gully heads under the influence of a road including gully retreat and landfill had a power exponential relationship cv 13 29 c l 2 14 r2 0 71 the gullies near the roads in the thick loess area were cut at an abnormally rapid rate which has not received sufficient attention previously therefore the effect of road construction on gully erosion in the loess area of china should be reassessed

loessification and hydroconsolidation there is a connection abstract loessification can be defined as the acquisition of loessic characteristics by ground systems hydroconsolidation in this context is the collapse of the loess ground structure under the influence of loading and wetting loess on aeolian deposition is metastable a pre requisite for eventual collapse the actual collapse mechanism is dependent on the presence of a critical amount of clay mineral material at major particle contacts this clay accumulates via post depositional processes processes which can be described as part of loessification and as a contribution to collapsibility studies at ospringe in kent england support observations made in the bohemian massif in the czech republic about the nature of the loess ground system and the role of clay minerals and calcite crystals fragipan formation another important post deposition event could depend on hydroconsolidation in loess ground

detrital zircon evidence for the ternary sources of the chinese loess plateau abstract the provenance of chinese loess is fundamental for understanding its origin transportation and climatic significance in this paper eight samples were collected for detrital zircon age analysis five from different deserts and three from the jingbian section in the northern chinese loess plateau covering an age range of 2 6 0 03 ma the new results integrated with knowledge of relevant topography and wind patterns demonstrate that the age spectra of the detrital zircons in the loess are different from those of the sands from the tarim junggar and qaidam basins implying that these basins were not the sources of the silts of the loess plateau further analysis suggests that the three sources for the loess are 1 clastic materials eroded from the mountains of the central asian orogenic belt especially the gobi altai and hangay 2 clastic loess sized materials generated by erosion of the qilian mountains in the ne tibetan plateau and 3 minor clastic debris derived from the mountains of the north china craton thus silts of the loess plateau have a complex origin although inland basins long believed to be important sources have only a minor role at most

influence of structure on shear characteristics of the unsaturated loess in lanzhou china abstract loess is typically a kind of soil with metastable structure which makes loess sensitive to collapse and sliding upon wetting such structure has thus profound influence on loess s mechanical behavior however there have been arguments about how the metastable structure influences on loess s mechanical behavior and what the mechanism behind is in this study the influence of structure on shear characteristics of the unsaturated loess in lanzhou city of china was investigated with comparison of variation of shear strength and its parameters between six pairs of the undisturbed and remolded samples it is found that the peak shear strength and strength parameters of the loess significantly reduced once its structure was destroyed while shear behavior of the loess showed little change strength parameter c was much more sensitive to structure of the loess than shear strength reduction of the loess due to change of structure should be largely attributed to breaking up of cementation bonds between particles evidenced by the difference in pore size distribution and microstructure of soil fabrics between the undisturbed and remolded samples the bonds provided by clays and carbonates contributed the most to structure of the loess with minor by soluble salts while matric suction played little role in structure of the loess

petrology and petrogenesis of the bokan granite complex southeastern alaska the bokan granite complex is a peralka line ring dike complex emplaced into marine shales volcanic flows and tuffs and plutonic rocks mineralogically and chemically the complex is composed of i type granites aegirine and riebeckite bearing granite aplites porphyries and pegmatites comprise twelve distinct intrusive episodes the aegirine bearing rocks occur in an outer annular zone formed during early crystallization subsequent rocks are riebeckite bearing due to devolatilization of the magma chamber during a collapse ring dike emplacement event early crystallization of alkali feldspar occurred during magma ascension from a lower crustal upper mantle source at shallow depths subsolvus crystallization allowed microcline and albite to dominate local bodies of aegirine syenite were formed during the early collapse ring dike emplacement in response to the magma devolatilization the riebeckite granites reflect lower po2 and possibly declining peralkalinity the granitic rocks at bokan all exhibit na2o contents greater than k2o lithophile elements are concentrated in all the rocks especially in zones where hydrothermal albite and chlorite formed rb sr ratios increase in progressively younger rocks in the complex agpaitic ratios vary from 0 92 to 2 08 for the granitic rocks

loess genesis and worldwide distribution abstract loess formation generally involves the four main stages of production deflation transportation and deposition of loess particles traditionally loesses are classified as glacial desert or other types based only on source area characteristics without taking into account provenance and transportation research on loess genesis is often local with only a few attempts at systematically overviewing worldwide loess distribution both the local and few global studies lack information on the variability in loess thickness continuity and areal extent this review integrates a large body of information on loess source areas and transportation pathways and the existence of desert transition zones three modes of loess genesis 1 continental glacier provenance river transport 2 mountain provenance river transport and 3 mountain provenance river transport desert transition were identified global distribution maps of provenance and transport pathways of major loess areas and their different genesis modes were meticulously prepared maps showing the spatial distribution thickness and continuity of loess deposits were also composed and the sizes of loess covered areas of each continent were re estimated the main features related to the distribution of the loess deposits on each continent are summarized for different regions or as a whole depending on the coverage of the source maps and references

characterization of macropore structure of malan loess in nw china based on 3d pipe models constructed by using computed tomography technology abstract malan loess is a grayish yellow or brownish yellow clastic highly porous and brittle late quaternary sediment formed by the accumulation of windblown dust the present day pore structure of malan loess is crucial for understanding the loessification process in history loess strengths and mechanical behavior this study employed a modern computed tomography ct device to scan malan loess samples which were obtained from the east part of the loess plateau of china a sophisticated and efficient workflow for processing the ct images and constructing 3d pore models was established by selecting and programming relevant mathematical algorithms in matlab such as the maximum entropy method medial axis method and node recognition algorithm individual pipes within the malan loess were identified and constructed by partitioning and recombining links in the 3d pore model the macropore structure of malan loess was then depicted using quantitative parameters the parameters derived from 2d images of ct scanning included equivalent radius length and aspect ratio of pores porosity and pore distribution entropy whereas those derived from the constructed 3d structure models included porosity coordination number node density pipe radius length length density dip angle and dip direction the analysis of these parameters revealed that malan loess is a strongly anisotropic geomaterial with a dense and complex network of pores and pipes the pores discovered on horizontal images perpendicular to the vertical direction were round and relatively uniform in shape and size and evenly distributed whereas the pores discovered on vertical images varied in shape and size and were distributed in clusters the pores showed good connectivity in vertical direction and formed vertically aligned pipes but displayed weak connectivity in horizontal directions the pipes in vertical direction were thick long and straight compared with those in horizontal directions these results were in good agreement with both numerical simulation and laboratory permeability tests which indicate that malan loess is more permeable in the vertical direction than in the horizontal directions

changes in tensile strength and microstructure of loess due to vibration abstract loess soils typically have an open and metastable structure humidification and vibration can modify their microstructure and thus influence their mechanical behavior in the present study to investigate the influence of train vibration on the tensile strength behavior of loess the tensile tests were performed on loess specimens that had been vibrated at a low amplitude for a long period using a modified horizontal extensograph in addition the microstructures of vibrated and non vibrated loess specimens before and after the tensile tests were characterized changes in the loess microstructure due to vibration and that in the tensile test were analyzed the results show that the relationship between uniaxial tensile strength and water content in soil specimen could be represented using a power function the axial displacement at failure varies at the same manner as tensile strength with respect to water content in comparison to intact loess occurrence of less clay bridges and clay buttresses between aggregates or coarse particles is identified in the disturbed specimens while aggregates are seen to be a very little more loose in vibrated specimens after the tensile tests than that before the tensile tests this indicates that vibration reduces the tension resistance and ductility of loess soil structure which could be attributed to loss of bonding strength as a result of breakage of clay cementations and disintegration of aggregates in the tensile test the soil structure goes through two distinct phases of change i e stretching phase and cracking phase in the stretching phase the tensile deformations take place throughout the specimen without altering the contacts between soil particles significantly in the cracking phase weak cementations fail to resist tensile deformation and suffer from breakage once a through crack is developed the specimen breaks in two leading to a catastrophic drop of tensile stress

experimental case study of seismically induced loess liquefaction and landslide abstract the 1920 haiyuan ms 8 5 earthquake induced a large number of fluidized loess landslides in china characterized by low slope angles long run out distances and fluidized movement the mechanism of these landslides has aroused considerable interest although additional research is needed to understand more fully the behavior of the loess and the failure mechanism field investigation was conducted on the shibeiyuan landslide and loess samples collected for later laboratory analysis by conventional geotechnical tests triaxial compression tests and ring shear tests the field survey revealed that the shibeiyuan landslide occurred on a concave slope

formation of calcareous nodules in loess paleosol sequences reviews of existing models with a proposed new per evapotranspiration model abstract loess is a product of aeolian deposition during quaternary glaciation cycles loess paleosol sequences are rich in calcareous nodules cns in the literature two models are widely cited for the formation of cns namely per descendum and per ascendum however there has been no direct testing or monitoring to support either of these contradictory models this paper reviews a large number of multidisciplinary literature to evaluate the consistency reliability and rationality of these two models three main conclusions are drawn 1 the causative factors variation of ph value along loess paleosol sequence decrease of co2 partial pressure and reduction of solvent water that are used to support the per descendum model do not completely explain the supersaturation of infiltration solution with caco3 thereby making this model questionable 2 the per ascendum model explains the formation of cns along narrow horizons through upward evaporation however it fails to produce sporadic distributions and irregular shapes of nodules on loess slope faces and the frequent appearance of nodules around plant roots in order to reconcile these deficiencies we conducted an extensive field survey in various parts of shanxi province based on this new set of observations it was concluded that the per ascendum model can be extended to explain all occurrences of cns this extended model is called per evapotranspiration

geology and uranium thorium mineral deposits of the bokan mountain granite complex southeastern alaska abstract the bokan mountain kendrick bay uranium thorium deposits are associated with a late jurassic peralkaline granite ring dike complex the uranium thorium deposits form pipe like bodies along contacts or occur as pods in en echelon northwest striking shear zones the host intrusive is a multiphased body consisting mainly of riebeckite granite porphyry and subordinately of pegmatite aplite aegirine granite porphyry and eight other lesser rock types the ore is closely associated with an albitized aegirine syenite the ore consists of thorium and rare earth rich rock containing uranothorite uraninite and generally less than 2 of sulfide species about 100 000 tons 89 000 t of ore have been mined at an average grade of about 1 u3o8 and nearly 3 tho2 mainly from the ross adams pipe the pipe itself lies along the contact of aegirine syenite and aegirine granite porphyry it is as much as 24 m across and was mined along strike for over 300 m the ore in shear zones occurs in lenses as much as 3 m thick and 30 m in strike length wallrock alteration within and adjacent to orebodies consists of pervasive hydrothermal albite and lesser amounts of chlorite fluorite calcite quartz sericite and tourmaline hematite is present in the outer distal parts of the ore zones the minerals produced to date occur within the outer annular zone of the bokan granite complex in which aegirine is present as the major alkali ferro magnesian mineral ore emplacement occurred during the first subsidence event in association with devolatilization of the magma chamber the pod like ore zones appear to have formed during regional faulting synchronous with magma crystallization and subsequent hydrothermal events subsequent magma crystallization yielded riebeckite granites that were depleted in u and th filling temperatures in ore stage fluid inclusions within quartz range from 320 to 331 c with pressure corrections increasing the temperature of formation to 420 c or higher depending on dissolved gas content sulfur isotopic analyses on pyrite galena sphalerite and pyrrhotite indicate disequilibrium but 34sh2s is estimated at 7 6 carbon and oxygen isotopic analyses on ore stage calcite yield 18oh2o of 6 8 to 8 1 and 13c c of 4 3 to 7 0 the oxygen and carbon isotopic data support a magmatic origin for the calcite and associated thorium uranium deposits

partial melting fractional crystallisation liquid immiscibility and hydrothermal mobilisation a recipe for the formation of economic a type granite hosted hfse deposits abstract a number of a type granites host resources of the high field strength elements hfse including the rare earth elements ree that have been considered for economic exploitation the best known of them is the strange lake pluton canada with a resource of 20 mt grading 1 44 wt ree2o3 of which 50 are heavy rare earth oxides in this paper we examine the various processes that are likely to be responsible for the hyper enrichment of the hfse starting with the generation of a parental magma through a very low degree of partial melting of a mantle plume or a metasomatically enriched mantle in both cases below a continental crust continental rift we trace the evolution of this magma olivine nephelinite through fractional crystallisation of olivine and clinopyroxene followed by plagioclase k rich alkali feldspar and arfvedsonite to the final residues of hyper enriched hfse granitic pegmatites in so doing we show that at least two additional steps are essential to the process of hfse enrichment the first of these is the abrupt termination of plagioclase crystallisation prior to the final consumption of ca or assimilation of a ca source and the resulting exsolution of an immiscible ca fluoride melt that sequesters the lree and y the second of these steps is prolonged crystallisation of arfvedsonite which delays saturation of the magma with an aqueous phase and ensures the development of an agpaitic assemblage of na bearing hfse minerals e g na zirconosilicates and na titanosilicates finally we show that saturation of the magma with an aqueous carbonic fluid which evolves to a very acidic composition is an essential ingredient in the recipe for the formation of an economic a type granite hosted hfse deposit

spatial sampling considerations and their applications to characterizing fractured rock and karst systems assessing the existence location and mapping of geologic anomalies such as fractures and cavities within soil and rock are common to both engineering and hydrologic project needs there are numerous measurement techniques available to detect map and characterize fractures and cavities a summary of the common methods available for fracture and cavity detection and mapping are presented along with their spatial sampling capabilities the remote sensing and geophysical methods are but a small part of this list but provide a wide range of tools to attack the problem they include some of the most effective methods for locating and mapping fractures and cavities and cover the complete range of spatial sampling from regional to no more than the surface of a borehole wall an understanding of all of the tools available and their spatial sampling limitations is a necessary part of planning and carrying out an effective fracture cavity investigation

origin and evolution of modern loess science 1824 to 1964 abstract loess is the most important aeolian deposit of the quaternary and plays an important role in explorations of the evolution of paleoclimate and paleoenvironment in recent years historians of science have been working on how loess research originated developed and was promoted in europe in the early 19th century the chinese community has a clear history of the loess research from the late 20th century however it remains unclear when and how modern loess studies were communicated between western and eastern academic societies and who contributed to the development and dissemination of modern loess knowledge especially from the western to the eastern societies based on books essays memoirs travel notes published letters and other types of records from geologists such as k leonhard 1779 1862 c lyell 1797 1875 and r pumpelly 1837 1923 the present study clarifies the way and process by which loess research originated from the rhine valley and spread to britain onto the united states and in particular china it was discovered that loess was formally defined in 1824 in the rhine valley in the 1830s l horner 1785 1864 and lyell introduced loess research from the rhine valley to britain at the same time lyell put forward the theory of the fluvial origin of loess and verified his theory by expanding study areas to the united states in 1866 pumpelly the first foreign geologist investigating chinese loess put forward lacustrine formation of loess pumpelly s hypothesis was soon argued against in 1870 by f von richthofen 1833 1905 who thought loess was formed via an aeolian mode based on a wide investigation in the loess plateau of china although the above main hypotheses originated based on investigations of chinese loess they were not disseminated to china and received by chinese scholars in a timely manner and the local loess research in china launched almost 130 years later by the stimulation from work by scholars of the soviet union

loess geology and surface processes an introductory note abstract loess is a type of quaternary sediments of the wind origin in arid and semi arid regions this type of sediment is widely and thickly distributed in china forming the loess plateau which is the largest bulk accumulation of loess on the earth the loess plateau of china has received great attention from scientific communities including geologists geophysicists and engineers worldwide accordingly a wealth of investigations has been undertaken on various problems arising in this area however some scientific questions remain relevant and unresolved these questions mainly present in the areas of evolution and surface processes of loess landform depositional environments of loess sediments impacts due to neotectonics and fault activities in loess areas and natural and man made geohazards in recent years extensive innovative studies have been carried out to further understand the above mentioned topics substantial new data theories and insights have become available this special issue provides a timely overview on the recent case histories theoretical advances laboratory and field testing and state of art methods in the theme of loess geology and surface processes the papers gathered in this special issue are introduced in this article

pleistocene climate change inferred from multi proxy analyses of a loess paleosol sequence in china abstract the aeolian loess blanketing the chinese loess plateau clp is sensitive to climate change in monsoonal east asia here we present a multi proxy climatic record from a pleistocene loess paleosol sequence from the lantian basin on the southern margin of the clp the measurements include magnetic susceptibility and related magnetic properties bulk median grain size color reflectance and the color inferred hematite versus goethite ratio hm gt a long term aridification and cooling trend during the interval from ca 2 22 0 43 ma is indicated by two magnetic grain size proxies corresponding to the global climatic cooling of the late cenozoic in addition at least four intervals of climatic extremes are evident in the record of hm gt ratio at 1 71 1 65 ma 1 26 1 24 ma 0 94 0 86 ma and 0 62 0 48 ma these intervals are characterized by distinct regional climates which contrast with the global climatic conditions represented in marine sediments for example a relatively arid climate is documented from 1 71 to 1 65 ma which was rapidly succeeded by a relatively humid climate which is associated with the earliest hominin with an age of ca 1 63 ma in the lantian basin

the early jurassic bokan mountain peralkaline granitic complex southeastern alaska geochemistry petrogenesis and rare metal mineralization abstract the early jurassic ca 177 ma bokan mountain granitic complex located on southern prince of wales island southernmost alaska cross cuts paleozoic igneous and metasedimentary rocks of the alexander terrane of the north american cordillera and was emplaced during a rifting event the complex is a circular body 3 km in diameter of peralkaline granitic composition that has a core of arfvedsonite granite surrounded by aegirine granite all the rock forming minerals typically record a two stage growth history and aegirine and arfvedsonite were the last major phases to crystallize from the magma the bokan granites and related dikes have sio2 from 72 to 78 wt high iron feo tot 3 4 5 wt and alkali 8 10 wt concentrations with high feo tot feo tot mgo ratios typically 0 95 and the molar al2o3 na2o k2o ratio

evolving sources of eolian detritus on the chinese loess plateau since early miocene tectonic and climatic controls abstract the thick deposits of eolian dust on the chinese loess plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations here we report a 22 ma long nd and sr isotopic records of the eolian sources decreasing e nd values and increasing 86 sr 87 sr ratios of the eolian deposits has been observed from early miocene to about 7 ma which indicates growing material contribution from qilian mountains relative to the gobi altay mountains the source shift during 22 7 ma is interpreted to reflect the erosional response of the qilian mountains to its surface uplift between 7 ma and 1 2 ma the results show relative constant nd and sr isotopic compositions of the eolian deposits and thus suggest a constant source contribution between qilian mountains and gobi altay mountains synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution since 1 2 ma nd and sr isotopic records indicate that the relative debris input from qilian mountains drops rapidly as large scale topographic changes would not be expected in such a short time period the source shift since 1 2 ma might be by the differing erosional responses in qilian mountains and gobi altay mountains to the development of full glacial climate after the middle pleistocene transition this work shows that combined nd and sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale

prediction of the wetting induced collapse behaviour using the soil water characteristic curve abstract collapsible soils go through three distinct phases in response to matric suction decrease during wetting pre collapse phase collapse phase and post collapse phase it is reasonable and conservative to consider a strain path that includes a pre collapse phase in which constant volume is maintained and a collapse phase that extends to the final matric suction to be experienced by collapsible soils during wetting upon this assumption a method is proposed for predicting the collapse behaviour due to wetting to use the proposed method two parameters critical suction and collapse rate are required the former is the suction value below which significant collapse deformations take place in response to matric suction decease and the later is the rate at which void ratio reduces with matric suction in the collapse phase the value of critical suction can be estimated from the water entry value taking account of both the microstructure characteristics and collapse mechanism of fine grained collapsible soils the wetting soil water characteristic curve thus can be used as a tool five sets of data of wetting tests on both compacted and natural collapsible soils reported in the literature were used to validate the proposed method the critical suction values were estimated from the water entry value with parameter a that is suggested to vary between 0 10 and 0 25 for compacted soils and to be lower for natural collapsible soils the results of a field permeation test in collapsible loess soils were also used to validate the proposed method the relatively good agreement between the measured and estimated collapse deformations suggests that the proposed method can provide reasonable prediction of the collapse behaviour due to wetting

shallow karst exploration using mt vlf and dc resistivity methods1 a geophysical test was carried out over a well located and fairly embedded karstic conduit the mt vlf method was selected because of its high resolution and its ability to provide a resistivity parameter sensitive to water and clay this method was used together with dc resistivity methods which allow vertical adjustment of the vlf data and show consistency between the investigation and target depths after correcting the deformations due to the polarization of the primary field the mt vlf data show clearly in the central part of the site that the conduit does not coincide with an anomaly axis but coincides with the boundary between a conductive area and a resistive area 2d modelling confirms that direct detection of the conduit is not feasible and that the conduit is located close to a conductive zone corresponding to a completely clay filled fractured zone this situation was observed on the whole site and the conduit seemed systematically to thread its way between the conductive zones to join the outlet the distribution of the conductive fractured zones and the direction of the hydraulic gradient were two important elements in predicting the location of the conduits a 3d approach would increase the probability of finding the conduits in such a case

formation and development of the structure of collapsing loess in china abstract gao g 1988 formation and development of the structure of collapsing loess in china eng geol 25 235 245 it is well known that in china the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility gradually decreasing from the northwest to the southeast these differences are consistent with variations in climatic conditions this indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment based on the microstructure analyses it can be assumed that the formation and development of the structure of collapsing loess in china has undergone five stages the loessization stage the formation stage the development stage the degeneration stage and the clayization stage the five stages of loess regularly exist in different regions of the loess plateau this also shows that under the modern climatic condition the collapsing loess in the northwest of the loess plateau in china is still developing however the feature of collapsing loess is gradually disappearing in the southeast of the loess plateau

cover collapse sinkholes in the tournaisis area southern belgium abstract in the tournaisis area southern belgium cover collapse sinkholes have been reported since the beginning of this century in this area the relatively flat lying carboniferous limestone is overlain by an unconformable mesocenozoic cover recent research has shown that these sinkholes developed from reactivated paleokarsts the intensive pumping for domestic and industrial water supply combined with the dewatering due to deep limestone quarries operations resulted in the lowering of groundwater levels this triggered the reactivation of paleokarstic systems and thus the occurrence of cover collapse sinkholes these sudden and unexpected collapses have already had major impacts in the region in 1977 about thirty sinkholes opened up along the escaut river downstream from the city of tournai as a consequence the groundwater was polluted by an extensive loss of river water into the carboniferous aquifer more recently a house and industrial facilities were severely damaged by such cover collapse sinkholes in this context a geoharzard map would be a valuable tool as far as regional development is concerned this points at the importance to develop methods to locate and characterize hidden paleokarsts a study site has been chosen in an area where sinkholes have been opening up for about ten years a geophysical survey of the site which included electrical resistance mapping of the area has shown weakness lineaments these lineaments are parallel to a main fault affecting the region

landslides triggered by excavation in the loess plateau of china a case study of middle pleistocene loess slopes abstract the frequent occurrence of catastrophic landslides caused by excavation in a loess slope is one of the commonly encountered engineering problems in the loess plateau middle pleistocene loess slopes were selected as a case study for current research the distribution of excavation induced loess landslides was studied by field investigation on the basis of centrifuge model tests the deformation features and failure mechanism of a homogeneous loess slope and a double paleosol interlayer loess slope under different excavation slope angles were analyzed and compared it was shown that the response of horizontal earth pressures in the lateral region of the excavation zone has a close relationship with the failure of the slope displacement measurements showed that the deformation stages of loess slopes due to excavation are independent of the paleosol interlayer the excavation slope inclinations and soil properties significantly affected the failure process and division of the slope the characteristics that excavation induced loess landslides always occur in hysteresis and abruptness were interpreted by the analysis of the failure process the influence of blade penetration during the excavation performed was quantitatively estimated finally based on the result of stress path tests an improved unloading constitutive model was proposed to simulate the deformation of soils in the lateral and bottom of the excavation area

pedogenic components of xijin loess from the western chinese loess plateau with implications for the quaternary climate change abstract chinese loess deposits preserve abundant information on the aridification of the asian interior and asian monsoon evolution during the quaternary although substantial progress has been made in deciphering the paleoclimatic record of the thick loess deposits in the western chinese loess plateau clp the environmental significance of variations in the magnetic susceptibility and the ultrafine 40 m fractions of the 416 m long xijin loess core from the lanzhou basin northeastern tibetan plateau our results indicate that the 40 m fraction and marine oxygen isotope record consequently we conclude that the pedogenic component is a more accurate and sensitive indicator of weathering and soil formation than the record and it is well suited to reconstructing high resolution quaternary climatic change in the western clp furthermore the proportion of the pedogenic component increased systematically over the past 2 2 million years which may have been primarily caused by long term global cooling since the early pleistocene together with the episodic uplift of the tibetan plateau

the formation of loess deposits in the tashkent region and parts of central asia and problems with irrigation hydrocollapse and soil erosion abstract there are large problems of irrigation hydrocollapse and soil erosion associated with the loess deposits of central asia to get to grips with these we need a clear view of the nature and formation of the loess and in this region there are still disputes and disagreements and controversies important events in the loess deposit formation process can be identified and studied and relative significances assigned there are large loess deposits in the vicinity of tashkent in the north east of uzbekistan these were mapped and studied for many years by g a mavlyanov and associates they used a terminology which appears to be based on pavlov s nineteenth century usage and developed a polygenetic formation theory for loess deposits this was a formation theory very much associated with central asia and essentially favouring a proluvial mechanism a speculative look at the deposits near tashkent allows alternative terminologies and formation mechanisms to be considered in particular the widespread soviet antipathy to aeolian deposition can be examined the deposits associated with the chirchik river upstream of tashkent might be affected by the pavlov mechanisms but could be topped by aeolian deposits the collapse of loess when wetted is controlled by the nature of the ground and is a very significant interaction of soil and water in particular in central asia hydrocollapse and water erosion are closely related and are controlled by the complex nature of loess ground dust clouds in eastern uzbekistan are largely loess related but in the west dust material is raised from the drying aral sea bed this is often clay mineral agglomerate material and can carry dangerous pollutants