late pleistocene and holocene loess sedimentation in central and western qilian shan china revealed by osl dating abstract the knowledge of loess accumulation in the central and western qilian shan was restricted to the time span since 13 11 ka until present loess deposits prior to this period have not yet been reported in this study 23 loess samples from the northern piedmont of central and western qilian shan area have been dated using fine grained quartz optically stimulated luminescence osl dating technique to set up a chronological framework for the loess sedimentation in this region our results demonstrate that the deposition of dust was widespread since the last deglaciation 13 ka until 3 6 ka in the northern piedmont of the central and western qilian shan area furthermore the chronology of the loess sedimentation has been extended back at least to 81 ka which is remarkably older than previously thought the existence of suitable environmental conditions e g vegetation cover for loess accumulation can be deduced in the central and western qilian shan for the holocene and late pleistocene however the loess sedimentation has been revealed to be discontinuous before 13 ka as indicated by its episodic occurrence

terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

gypsum dehydration agent of salt diapirism abstract one to ten percent anhydrite is present in gulf coast domal salt probably deposited as primary gypsum because the conversion to anhydrite occurs during burial and after the salt has recrystallized enough to become impermeable the water of dehydration does not escape this geopressured water will greatly increase the mobility of salt and aid diapirism the depths and temperatures that cause diapirism may be similar to those that cause gypsum dehydration but none of the four parameters is well understood gypsum dehydration may join differential load temperature depth and thickness as a factor strongly influencing diapirism

development of asymmetric shale pull aparts in evaporite shear zones abstract antithetically rotated lozenge shaped shale pull aparts are quite common in the shallow domains of the evaporite shear zones of the jura in northern switzerland the pull aparts are formed by synthetic shear fractures related to a transpressive strain field that also induces the antithetic rotation of the pull aparts immediately after their formation a simple analytical model shows that the acute angle of fracture and the antithetic rotation are determined by structural and rheological parameters and the direction of maximum compressive stress the pull aparts are commonly separated by sulphate veins as the elongation resulting from antithetic rotation does not compensate for the bulk elongation despite this some pull aparts are bordered by synthetic drag zones antithetically rotated pull aparts are indicative either of compression normal to shear zone boundaries in decollement type shear zones or in shear zones deformed by simple shear of an initial obliquity of the dismembered layers relative to the shear zone boundary resemblance of the shale pull aparts to type 1 asymmetric pull aparts and book shelf structures both of which rotate synthetically demonstrates that rotated and asymmetric pull aparts may be ambiguous kinematic indicators

chemical and physical responses to deformation in micaceous quartzites from the tauern window eastern alps micaceous quartzites from a subvertical shear zone in the tauern window contain abundant quartz clasts derived from dismembered quartz tourmaline veins bulk plane strain deformation affected these rocks at amphibolite facies conditions shape changes suggest net shortening of the clasts by 11 64 with a mean value of 35 quartz within the clasts accommodated this strain largely via dislocation creep processes on the high stress flanks of the clasts however quartz was removed via solution mass transfer pressure solution processes the resulting change in bulk composition allowed growth of porphyro blastic staurolite chlorite kyanite on the clast flanks matrix sio2 contents decrease from c 83 wt away from the clasts to 49 58 in the selvages on the clast flanks the chemical changes are consistent with c 70 volume loss in the high stress zones calculated shortening values within the clast flanks are similar to the volume loss estimates and are greatly in excess of the shortening values calculated from the clasts themselves flow laws for dislocation creep versus pressure solution imply large strain rate gradients and or differential stress gradients between the matrix and the clast selvages in a rock containing a large proportion of semirigid clasts weakening within the clast flanks could dominate rock rheology in our samples however weakening within the selvages was self limiting 1 growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution and 2 overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix which would have reduced the driving force for solution transfer creep extreme chemical changes nonetheless occurred over short distances the necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities and overall weakening of the rocks may result solution transfer creep may be a major process whereby weakening and strain localization occur during deep crustal metamorphism of polymineralic rocks

holocene climatic changes revealed by aeolian deposits from the qinghai lake area northeastern qinghai tibetan plateau and possible forcing mechanisms previous palaeoclimatic studies in the northeastern qinghai tibetan plateau netp during the holocene mainly using lake sediments have deepened our understanding of the climatic system in this remote region the timing and forcing mechanisms of climatic change in this region are still controversial however aeolian sand and silt deposits which are widely distributed in the netp can be readily dated by optically stimulated luminescence osl techniques and reveal the sensitive response of the landscape to climatic change in this study aeolian sand and loess at six sites around qinghai lake were studied to reconstruct millennial scale climatic changes during the holocene multiproxy data along with 24 osl age determinations show that low effective moisture and aeolian activity occurred at c 13 ka 10 9 1 ka and 8 9 7 8 ka periods of greater effective moisture may have occurred at 11 ka and 9 ka and there is evidence for a previously undocumented wet climate at 4 3 ka these results show that mi

creep of wet gypsum aggregates under hydrostatic loading conditions abstract gypsum dominated evaporite sequences are known to play an important role in controlling the mechanics of foreland thrust and nappe tectonics as well as occasionally forming large scale halokinetic structures associated with oil and gas accumulations however relatively little is known regarding the relevant deformation mechanisms and mechanical behaviour of gypsum in this study attention is focused on determining the compaction creep behaviour of wet granular gypsum aggregates with the aim of assessing the importance of pressure solution hydrostatic compaction experiments were performed at room temperature and applied effective pressures in the range 0 4 3 9 mpa using grain sizes ranging from 15 to 125 m the microstructure of the wet tested samples showed that compaction occurred by a process of dissolution within grain contacts and precipitation on pore walls in addition for most of the range of conditions investigated the mechanical data were found to be broadly consistent with models for interface reaction controlled grain boundary diffusional pressure solution combining the mechanical data with kinetic data taken from the crystal growth dissolution literature it is suggested that for the bulk of conditions studied creep of our wet granular gypsum aggregates was probably rate limited by precipitation on the pore walls this is in sharp contrast to the diffusion controlled pressure solution creep behaviour recently reported for highly soluble salts such as nacl and nano3 under similar conditions

triassic evaporites and plio quaternary diapirism in western greece wide triassic evaporite outcrops run parallel to the strike of hellenide thrust faults in western greece they crop out along the leading edges of thrust sheets emplaced as part of the foreland migrating fold and thrust belt the evaporites acted as the plane of decollement for thrust sheet emplacement over much of the external hellenides plio quaternary diapirs occur locally within the broad outcrops of triassic evaporite they are the result of local mobilization of evaporite after its emplacement their rise may have been initially triggered by hellenide thrust sheet loading and subsequently accentuated by plio quaternary subsidence geophysical records and onland exposures show that diapiric rise controlled local sedimentation patterns above the sites of earlier hellenide thrusts the subsequent intrusion of diapirs into these cover sediments caused localized extensional structures to develop this is best seen in se zakinthos where strain hardened conjugate faults developed in friable pliocene sandstones early in the intrusion history principal strains calculated from these sets demonstrate patterns of extension sub orthogonal to intrusion margins they are comparable with patterns known from other field and experimental examples but contrast with some recent studies on diapir related strains

influence of pore fluid salinity on pressure solution creep in gypsum abstract the uniaxial compaction creep behaviour of wet granular gypsum is investigated under chemically closed drained conditions known to favour pressure solution the experiments were performed using applied stresses of 1 to 4 mpa and grain sizes in the range 50 to 280 m at room temperature the tests were carried out using saline pore fluids with a nacl concentration of 0 01 to 6 m saturated with respect to the unstressed gypsum starting material since gypsum is almost always associated with other evaporite minerals such as halite pore fluid compositions in gypsum will generally be highly saline data on the effect of pore fluid salinity on pressure solution in gypsum are thus directly relevant to the behaviour of gypsum in geological situations the results obtained in terms of mechanical behaviour and microstructures developed are in good agreement with the results obtained in previous experiments performed using nacl free pore fluids however the absolute creep rates obtained here are up to 50 times faster than in the nacl free tests comparison with theoretical models for pressure solution creep and crystal growth data reveals that diffusion is unlikely to be the rate controlling mechanism of pressure solution in the present experiments since the growth rate of gypsum increases with nutrient salinity the observed effect of nacl on pressure solution is consistent with the possibility of rate control by the precipitation reaction however the absolute creep rates observed are one to two orders of magnitude slower than creep rates predicted by a precipitation rate limited model so that the detailed mechanism remains unclear

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

clay mineral composition of pampean loess argentina abstract this paper summarizes current knowledge on clay minerals on the pleistocene and holocene pampean loess detrital illite is the predominant clay mineral of the vitroclastic loess with minor amounts of montmorillonite and kaolinite minerals the illite with a small k content corresponds to a highly illitic illite smectite component in paleosols its crystallinity index decreases and there are more expandable interlayers as in the chinese loess

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

new perspectives on the li isotopic composition of the upper continental crust and its weathering signature abstract lithium isotopes are increasingly used to trace both present day and past weathering processes at the surface of the earth and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust ucc yet the previous estimate of average 7li of the ucc has a rather large uncertainty hindering the use of li isotopes for this purpose new 7li for desert and periglacial loess deposits windblown dust from several parts of the world europe argentina china and tajikistan demonstrate that the former are more homogeneous than the latter and may therefore serve as excellent proxies of the average composition of large tracts of the ucc the li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered fine grained end member dominated by phyllosilicates and having low 7li and an unweathered coarse grained end member that is a mixture of quartz and plagioclase having higher 7li we use correlations between insoluble elements ree nd hf and fe2o3 sio2 li concentrations henceforth referred as li and 7li to estimate a new more precise average li isotopic composition and concentration for the ucc li 30 5 3 6 2 ppm and li 7 0 6 0 6 2 the 7li for desert loess deposits is anti correlated with the chemical index of alteration cia using this relationship along with our average 7li we infer that 1 the present day cia of the average ucc is 61 2 4 2 higher than the common reference value of 53 and 2 the average proportion of chemically weathered components is as high as 37 10 17 2 at the surface of the earth

holocene climatic change revealed by aeolian deposits from the gonghe basin northeastern qinghai tibetan plateau a climate record for the gonghe basin in the northeastern qinghai tibetan plateau during the holocene period was determined from a 3 90 m aeolian deposit as revealed by the variation of proxies including sedimentary facies magnetic susceptibility the total organic carbon toc content grain size and geochemical parameters the regional climatic evolution during this period can be divided into the following stages there was a cold and dry phase in 11 8 10 1 ka probably related to the younger dryas yd event prior to the holocene an optimum stage with relatively warmer and wetter climate dominated the region between 10 1 ka and 8 7 ka the climate tended to relatively dry condition from 8 7 ka to 4 7 ka although weak paleosol weakly developed paleosol developed during this period this is inconsistent with the megathermal maximum in the holocene or holocene optimum a relatively warm and wet climate emerged in 4 7 0 7 ka and an obviously cold and dry stage emerged since 0 7 ka thereafter the regional climate became warmer in addition eight cold events were recorded including the yd event around 11 8 ka 9 8 9 5 ka 9 2 8 7 ka 8 1 7 6 ka 7 0 6 1 ka 5 3 4 7 ka 3 1 1 5 ka and since 0 7 ka these events are coincident with cold phases revealed by aeolian depositions and lake records in the northeastern qinghai tibetan plateau and also with the evidence of deteriorated climate phases in the high and low latitudes of the northern hemisphere on a millennial scale such as in hongyuan peat and drift ice tracers in the north atlantic ocean in the holocene

aeolian process and climatic changes in loess records from the northeastern tibetan plateau response to global temperature forcing since 30 ka the response of surface processes to global climatic changes since the last glacial is critical to understanding the mechanism of climatic changes on the tibetan plateau in this study loess from the northeastern tibetan plateau netp was closely spaced dated to provide an independent high resolution record of dust accumulation processes and millennial scale climatic changes optically stimulated luminescence ages reveal episodes of rapid dust deposition at approximately 12 3 ka 16 ka 21 23 ka 25 28 ka and possibly also at 30 33 ka these episodes are broadly correlated with high latitude and marine records cold climatic events such as the younger dryas heinrich event 1 and the last glacial maximum this correlation implies that dust storms in the netp represent episodic aridification and wind strengthening which is ascribed to the southward shift of the polar front and the intensification of the siberian high pressure cell that was forced by millennial scale cooling in high northern latitudes

impacts of post depositional processes on rapid monsoon signals recorded by the last glacial loess deposits of northern china abstract rapid east asian monsoon oscillations recorded by chinese loess are thought to be dynamically linked to north atlantic climate however few efforts have been made to assess the effects of post depositional processes e g surface mixing and pedogenesis on loess paleoclimatic records here a detailed optically stimulated luminescence dating of a thick loess sequence from the western loess plateau is presented offering a reliable chronology for last glacial deposits magnetic susceptibility and mean grain size records from three loess paleosol sequences along a northwest southeast transect are investigated to evaluate impacts of post depositional processes on these loess based proxy records our results indicate that 1 loess sequences developed within the flat tableland of the central and western loess plateau are nearly continuous during the last glaciation and 2 post depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions in the central loess plateau rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity in the northwestern loess plateau however due to high sedimentation rate and relatively weak pedogenesis high resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the greenland ice core and hulu cave stalagmite

sedimentation and diagenesis of chinese loess implications for the preservation of continuous high resolution climate records chinese loess has been extensively utilized to produce continuous and high resolution climate records of the late cenozoic such work assumes uninterrupted loess deposition and limited diagenesis here closely spaced optically stimulated luminescence osl dates are used to characterize the holocene and late pleistocene sedimentation histories of three sites across a nw se transect of the chinese loess plateau the results suggest that sedimentation is episodic at subglacial interglacial time scales with rates rapidly varying within units and between sites unconformities noneolian deposition and mixing of sediments also appear to be common existing understanding of loess deposition therefore requires reexamination while previous reconstructions of rapid climate change not dated using absolute methods should be regarded with caution loess deposits may still yield detailed climate records from specific high sedimentation rate strata and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating the rapid changes in sedimentation presented here indicate the east asian monsoon has the capacity to vary on millennial scales

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

last deglacial and holocene lake level variations of qinghai lake north eastern qinghai tibetan plateau qinghai lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid latitude westerlies and the low latitude asian summer monsoon asm most published lake level histories of qinghai lake are interpreted from drill core proxies here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial the results indicate that two periods of highstands occurred during the last deglacial approximate to 16 14 9 and approximate to 12 6 12 2 ka and that lake levels were 6 7 4m higher than at present lake levels dropped abruptly during the younger dryas and were generally low with frequent fluctuations during the early holocene qinghai lake reached its highest holocene level 9 1m higher than modern at approximate to 5 ka and has regressed during the past 2 ka we propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters supplemented by enhanced westerlies precipitation and decreased evaporation during heinrich event 1 approximate to 16 14 9 ka and increased asm rainfall during the bolling allerod warm period approximate to 14 12 ka lake level fluctuations during the holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland china

the shear strength of gypsum single crystals on three cleavage planes abstract single crystals of gypsum were strained to failure in simple shear at low confining pressures 1 10 bar the crystals were sheared on the 010 principal cleavage plane in seven directions and they showed both elastic and ductile behavior prior to failure mean critical resolved shear stresses c range from 0 20 to 0 52 mpa for shear on the 010 plane on the two secondary cleavages 100 and 011 the mean values for c are 14 0 mpa and 10 5 mpa respectively the ultimate shear strengths u in each of the seven directions on the 010 plane range from 0 58 to 1 36 mpa the minimum ultimate shear strength is in the 103 direction which has been previously identified by other workers as the preferred translation glide direction gypsum crystals strained to failure on two secondary cleavages 100 and 001 have much higher ultimate shear strength than any of the seven shear directions measured on 010 strengths range from 18 5 mpa on 100 to 14 3 mpa on 011 the static modulus of rigidity on 010 ranges from 0 07 gpa to 0 16 gpa and the values of dynamic rigidity obtained from ultrasonic pulse measurements range from 2 85 to 2 02 gpa the range of values of static rigidity on the two secondary cleavages is 0 90 to 3 0 gpa approximately one order of magnitude higher than the values on the 010 plane the work of fairbairn 1935 can be cited to demonstrate how the results can be applied to field studies of gypsum deformation

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

the utility of desert sand dunes as quaternary chronostratigraphic archives evidence from the northeast rub al khali abstract the distributions of optically stimulated luminescence osl ages from dunes are affected by palaeoenvironmental changes complex dune dynamics and sampling strategy extracting the relative importance of these factors when interpreting discontinuous osl chronologies from sand dunes has proven difficult and is particularly hindered in contexts where the internal sedimentary structures of dunes are not visible in this study samples for osl dating were taken from three major dune exposures in the rub al khali united arab emirates each showing clear internal structure with the aim of addressing these problems specific objectives were to assess how ages of individual sedimentary units represent dune accumulation as a whole and how the dune record in turn reflects known past environmental changes final ages were calculated using the oxcal software package by incorporating the known relative stratigraphy through the application of bayesian methods the results show that stratigraphy alone is not sufficient at these sites to guide osl sampling that is chrono and lithostratigraphic boundaries do not necessarily coincide where chronological hiatuses are present internal sediment stratigraphy can be a useful tool in identifying potential problems of under sampling the full dune record the implications of these findings for reconstructing quaternary climates from dune chronologies are considered

holocene climate change inferred from stratigraphy and osl chronology of aeolian sediments in the qaidam basin northeastern qinghai tibetan plateau abstract paleoclimatic reconstruction based on aeolian sediments in the eastern qaidam basin qb has been hindered by the limited chronological data here we present 61 optically stimulated luminescence osl ages on the basis of these osl ages and the lithologic stratigraphy we propose the effective moisture index emi for aeolian sediments to reconstruct the effective moisture change based on the emi from twelve sections the effective moisture change moisture sources and relevant mechanisms for paleoclimatic change in the eastern qb are discussed the results indicate that 1 aeolian deposition started at least before 12 4 0 7 ka during the deglaciation the paleosols developed at the early and mid holocene and aeolian sand and loess accumulated at mid and late holocene 2 effective moisture history was hyper arid at 12 8 11 6 ka humid and variable at 11 6 8 3 ka moderately humid and stable at 8 3 3 5 ka and increasingly arid at 3 5 0 ka 3 the effective moisture change was mainly controlled by the asian summer monsoon asm which mainly followed the change of northern hemispheric summer insolation and the westerlies strengthened and increased the aridity in the qb when the asm shrank

the influence of 14c reservoir age on interpretation of paleolimnological records from the tibetan plateau there is a great deal of controversy regarding the fate of glaciers and ice fields on the tibetan plateau in the face of continued anthropogenic global warming paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the tibetan plateau to changing conditions specifically the numerous lakes distributed across the tibetan plateau can provide high resolution spatial and temporal climate reconstructions to investigate past changes in the climate system in this paper we review the primary limitation to exploiting these valuable paleoclimate archives errors in radiocarbon based age models we review the techniques that have been used to estimate 14 c reservoir ages on the tibetan plateau and compile the published 14 c reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties using site specific evaluations of bangong co and lake qinghai we demonstrate that 14 c age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records we also examine 14 c induced uncertainties in the spatial climatic response on the tibetan plateau to 1 the termination of the last glacial maximum and 2 the holocene thermal maximum we conclude with recommendations for reducing uncertainties in future lake based paleoclimate studies on the tibetan plateau

diapiric deformations in the quaternary deposits of the central ebro basin spain from a study of 24 outcrops in neogene and quaternary deposits of the central ebro basin a number of diapiric deformations have been recognized two principal types being differentiated domal or pillow structures and piercement or intrusive structures the former are incipient diapirs of gypsum piercing structures have reverse faulted contacts not caused by halokinesis here neogene marls are the active plastic material contrasting with the competent behaviour of gypsum these intrusive structures are viscous diapirs which easily pierce the non consolidated low strength quaternary gravel overburden and submit it to a horizontal compressive stress as a consequence reverse faults and flexures develop in it generally normal faults and tension cracks do not appear underlying gypsum beds are frequently pulled up into diapirs and they constitute the structural core density contrast and conditions for plastic flow exist at the marl gravel boundary it seems to have been specially common at the time of quaternary fluvial sedimentation so that much deformation is synsedimentary diapiric phenomena have been very active during early to middle pleistocene time becoming weaker afterwards

holocene aeolian activity and climatic change in qinghai lake basin northeastern qinghai tibetan plateau abstract aeolian deposits in the qinghai lake basin on the northeastern qinghai tibetan plateau netp were studied in order to reconstruct changes in aeolian activity related to climatic changes over the last 12 5 ka we used 20 optically stimulated luminescence and conventional radiocarbon dates to construct chronological frameworks for four aeolian sections the results indicate that aeolian activity occurred episodically at 12 5 ka 11 2 ka 9 0 ka 8 5 ka 5 5 ka 2 6 2 4 ka and 1 0 9 ka paleosols developed mainly during 9 5 4 ka the field stratigraphy of the sections together with measurements of grain size magnetic susceptibility ms and total organic carbon toc indicate that aeolian activity was strong during the last glacial period following the younger dryas yd holocene interglacial conditions began to develop in the qinghai lake basin at 12 ka with the strengthened asian summer monsoon asm and the decrease in insolation the climate became warm and humid according to the record of aeolian activity the early holocene can be divided into two intervals before and after 9 5 ka aeolian activity remained strong from 12 ka 9 5 ka although the climate was more humid than that of the last glacial period between 9 5 ka and 8 5 ka the aeolian activity weakened and the climate became warm and wet but variable following the mid holocene climatic optimum the climate became significantly drier at 4 ka and aeolian activity strengthened again overall the asm dominated aeolian activity in the qinghai lake basin during the holocene with enhanced aeolian activity corresponding to a weakened asm paleosol development exhibited a lagged response to the strengthened asm and therefore aeolian sand layers in the section do not always indicate a cold and dry climate

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

late pleistocene and holocene aeolian sedimentation in gonghe basin northeastern qinghai tibetan plateau variability processes and climatic implications abstract although stratigraphic sequences of aeolian deposits in dryland areas have long been recognized as providing information about past environments the exact nature of the environmental processes they reflect remains unclear here we report the results of a detailed investigation of eight outcrop sections in the gonghe basin northeastern qinghai tibetan plateau measurements of sediment grain size and chemical composition indicate that the deposits are primarily of aeolian origin consisting of interbedded well sorted sand silty sand loess and or palaeosol however their occurrence varies from site to site fossil dune sands mainly occur in or close to the currently stabilized or semi stabilized dune fields whereas loess is distributed along the downwind marginal areas this pattern of basin scale differentiation was controlled mainly by spatial variability of sediment supply due to the antecedent sedimentary patterns within the basin together with previously published optically stimulated luminescence osl ages 24 new osl dates are used to elucidate the history of aeolian activity and its relationship to climatic changes there is no apparent relationship between past dune activity and downwind loess deposits deposition of silty sand probably occurred during past phases of windy dry and cold climate in the late pleistocene however climatic factors alone cannot explain the occurrence of silty sand deposition this is because the deposition of silty sand was always preceded by episodes of fluvial deposition prior to river incision thereby indicating the importance of an activated sediment supply associated with fluvial processes deposition of well sorted sand occurred episodically not only during the late pleistocene but also during the early to mid holocene vegetation conditions controlled either by the occurrence of intervals of moisture deficit during the late pleistocene or by changes in the balance between precipitation and evapotranspiration at a local scale played an important role in sand mobility and deposition the effect of vegetation on sand mobility is also suggested by independent evidence of aeolian activity from genggahai lake in the gonghe basin here the deposition of aeolian sand in the basin during the early to mid holocene indicates a low level of effective moisture caused by high evaporation induced by higher summer insolation despite the coeval increased regional precipitation recorded by lacustrine sediments in contrast late holocene palaeosols represent a high level of effective moisture and their formation did not necessarily require increased regional precipitation overall our results suggest that the relationship between aeolian activity and regional climate change is complex and that sand accumulations do not represent the consistent action of surface processes that are related to climatic changes

high resolution osl dating of aeolian activity at qinghai lake northeast tibetan plateau abstract qinghai lake is the largest lake on the tibetan plateau tp located between the extremely arid qaidam basin to the west and the severely desertified gonghe basin to the south extensive aeolian sediment at qinghai lake is ideal material to reconstruct regional aeolian activity and to better understand the relationship between desertification and climatic change in the lake basin aeolian sand accumulation is usually accompanied by erosion hence depositional hiatuses and disconformities must be identified for reliable reconstruction of regional aeolian activity to date the low density of age sampling around qinghai lake has hindered identification of hiatuses in this study we report the first high density osl dating 41 osl ages were obtained from two aeolian sand sections dongwei dw and niaodao nd sand accumulation trends recorded in the high density osl sampling sections were consistent with previously published probability density function pdf ages for the northeast tp the middle holocene 7 to 4 ka was characterized by very low accumulation rates with rapid sedimentation in the late glacial to early holocene 14 to 7 ka and the late holocene after 4 ka a 3 ka hiatus in accumulation between 7 to 4 ka was identified in the dw section but the nd section showed successive accumulation since the late glacial 14 ka on sub orbital and millennial scales our environmental reconstructions are consistent with previously published aeolian data and paleoshorelines records the combined evidence shows strong aeolian activity since 14 ka to 9 ka initiation of pedogenesis at 9 to 7 ka intensified soil development between 7 ka and 4 ka with the most intense pedogenesis and least aeolian activity between 6 to 4 ka relatively weak paleosol formation from 4 to 2 ka and renewed aeolian activity after 2 ka

cation exchange capacity and mineralogy of loess soils with different amounts of volcanic ashes the cation exchange capacity of soils cec is largely affected by the mineralogy of their parent material soils of the argentinean pampas develop on illitic loess mixed in variable proportions with volcanic ashes it is whether a question of how pedogenesis can modify this mineralogy affecting cec differentially in order to answer this question we analyzed four soils two of them placed in semiarid conditions and developing on parent materials with high volcanic ash contents and two placed in the humid pampas developing on ash free parent materials results indicated that pedogenesis transformed coarse lithogenic illites into smaller illites in ash free soils accumulating them not only in clays but also in silts in ash enriched soils illites were not altered by pedogenesis but they were the volcanic glasses which were transformed into less crystallized smectites these smectites accumulated mainly not only in clays but also in fine silts the mineral fraction of ash free soils had higher cec 15 07 cmolc kg 1 than ash enriched soils 9 50 cmolc kg 1 being the contribution of the 50 m sized fractions to the total cec similar in all the studied soils on average 54 as a consequence of this clays and silts of ash free soils made a relatively low contribution to the total cec while poorly crystallized smectites of ash enriched soils made a relatively high contribution this was explained on the basis of the kind of minerals present smectitic minerals with high cec rather than on the proportion of the mineral fraction itself in ash enriched soils and on the relatively high content of the mineral fractions rather than on their mineralogy illites with low cec in ash free soils the contribution of silts to cec was similar and relatively high in all the studied soils 17 5 of the total cec and 32 of the mineral fraction cec these results confirm that the electrochemical properties of the studied soils are defined not only by clays but also by silts mainly those with sizes between 2 and 20 m

kinetics of precipitation of gypsum and implications for pressure solution creep in order to model the role of gypsum in crustal deformation and in trapping hydrocarbons a quantitative mechanism based understanding of the deformation and compaction behaviour of gypsum is needed previous laboratory experiments indicate that intergranular pressure solution is an important deformation mechanism in gypsum and may be controlled by the kinetics of gypsum precipitation to examine this further the growth kinetics of gypsum were investigated using seed crystals and super saturated aqueous solutions prepared from natural gypsum powders the results showed both nucleation and growth dominated behaviour results relating purely to seed over growth showed that at low driving forces

gypsum nucleation and crystal morphology in analog saline terrestrial environments abstract gypsum crystals were grown in experimental conditions analogous to saline terrestrial environments within bentonite clay gels by diffusion control at three different temperatures four brine salinities and four tannic acid a model terrestrial humic substance concentrations the resulting crystals correspond to natural gypsum formed in terrestrial environments prismatic gypsum typically grew at both high and low temperatures in the absence of the organic additive with increasing organic acid concentrations the prismatic crystals progressively became flattened perpendicular to 001 and two temperature dependent trends developed at low temperatures a hemi bipyramidal habit dominated by 1111 faces developed whereas the lenticular e103 dominated habit forme at higher temperatures with progressively greater concentrations of organic material a 100 penetration twinning developed secondary complex nucleation occurred near the twin interfaces and finally rosette and rosette like aggregates formed higher temperatures generally favored better formed and larger rosettes the presence of 5 and 15 nacl greatly decreased nucleation density and resulted in larger single crystals and crystal aggregates the a 100 penetation twins appear to be diagnostic of gypsum growth in natural terrestrial sediments at a ph greater than 7 5

genesis of subtropical soils with stony horizons in ne argentina autochthony and polygenesis abstract deep red soils combining characteristics of highly weathered materials together with a significant degree of clay illuviation and with stony horizons close to the saprolite are found in the province of misiones northeastern argentina two basic types of stony horizons have been found which with the fine grained material above are together considered autochthonous the first one is a ferruginous nodular horizon composed mainly of in situ goethitic nodules of gravel size resulting from weathering and glaebulization processes of basalt the second are siliceous horizons which are also in situ derived from pre existing quartz veins within the basalt in contrast different analytical evidences particularly the vertical and geographical variations in the som stable carbon isotope ratios and the mineralogical composition of fine and coarse fractions suggest that these red subtropical soils are polygenetic being the result of a two fold process linked to paleoecological fluctuations in the framework of these results different interpretations about the origin of these soils and their parent materials and particularly the tropical loess theory are discussed

lake level variations of qinghai lake in northeastern qinghai tibetan plateau since 3 7 ka based on osl dating abstract qinghai lake is the largest internally drained lake in china and its unique location makes it sensitive to climate changes late glacial climate changes associated with variation in qinghai lake levels have been intensively investigated for the past 40 years with particular attention paid to lake level fluctuation histories between the last interglacial and the holocene however the details of lake level fluctuations during the holocene are still unclear using both optically stimulated luminescence osl dating of quartz for 22 samples and infra red stimulated luminescence irsl of feldspars only for sample hyw1 whose irsl age is 37 15 years a total of 23 samples are dated from paleoshoreline deposits fluvial sediments and aeolian sands a total of 13 sections near the modern lake shore with ages from 37 15 to 3710 350 years these ages are used to reconstruct the lake level fluctuation history spanning the last 3700 years the results indicate that 1 the youngest irsl age of 37 15 years is in agreement with the independent age of 39 29 years suggesting that luminescence dating is able to date decadal samples for sediments from the study area 2 the lake experienced several oscillations imposed on an overall regressive trend during the past 3700 years 3 the dated paleoshoreline deposits are generally related to warm and wet periods suggesting that those shoreline deposits formed during cold and dry periods if any may have been modified by later transgressions 4 lake level fluctuations during the period of 3700 240 years ago are generally consistent with the climate conditions identified in other proxies with the highest lake level occurring about 1770 years ago and 5 after 240 years ago the lake level dropped more rapidly which is inconsistent with the proxy records showing a warmer and wetter phase

paleoenvironmental changes recorded in a luminescence dated loess paleosol sequence from the tianshan mountains arid central asia since the penultimate glaciation abstract mid latitude arid central asia aca is one of the driest regions in the world and is a key source area of global atmospheric dust loess records of paleoclimatic changes in aca are complex and interpretations are problematic due primarily to the lack of robust chronologies quartz osl and k feldspar pirir dating methods were employed to date 8 quartz and 30 k feldspar samples from a 30 m loess sequence byh10 section on the northern slope of the tianshan mountains central aca northwest china the reliability of quartz and k feldspar ages was monitored by internal checks of luminescence characteristics and by comparison of the quartz and k feldspar ages the section lithology proxy indexes of grain size and magnetic susceptibility and the high resolution osl chronology together indicate 1 quartz osl dating can be used to date aca loess samples less than 40 ka while k feldspar pirir dating is reliable for loess samples at least as old as 150 ka from aca 2 aeolian loess began to be deposited on the northern slope of tianshan mountains beginning at least 145 ka ago and was deposited primarily during the penultimate and last glaciation periods 3 rapid loess deposition occurred during mis 6 mis 4 to early mid mis 3 and mis 2 but little or no loess deposition occurred during mis 5 mis 3a and mis 1 4 this loess depositional sequence is comparable to previously published stalagmite growth records in the region on glacial interglacial cycles rapid dust deposition and lack of stalagmite growth during glacials and lack of loess deposition and stalagmite growth during interglacials indicate a climatic pattern of wet warm interglacial and dry cold glacial climatic regimes on orbital cycles in aca 5 variation in the loess deposition rates in aca was much larger than in the central loess plateau during the last glaciation 6 depositional hiatuses of 50 kyr occur in aca loess sequences and high resolution chronologies are needed when reconstructing past climatic changes

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

rates of dust deposition between 50 ka and 20 ka revealed by osl dating at yuanbao on the chinese loess plateau abstract a new chronology has been constructed for an 18 m section of malan loess at yuanbao near linxia on the western edge of the chinese loess plateau the chronology has been obtained using the optically stimulated luminescence signal from coarse silt sized grains of quartz extracted from eighteen samples collected at approximately 1 m intervals down the section in the upper 9 m the dust deposition rate was 1 11 m ka covering the time period from 26 1 1 9 ka to 17 5 1 2 ka and there is no evidence of hiatus at this scale of analysis at greater depths the average rate of dust deposition is lower although there was a short period of higher deposition between 37 ka and 34 ka no large breaks 5 ka in deposition were deduced from the osl ages for the lower part of the loess section dating from 51 2 4 6 ka to 30 0 2 5 ka the age of the boundary at 9 1 m between the more uniformly deposited upper loess and the lower loess is compared to the age of the transition in the marine record between marine isotope stages 3 and 2 the chronological information at yuanbao is also used to challenge the previous use at this section of an age model based on changes in grain size

holocene moisture and east asian summer monsoon evolution in the northeastern tibetan plateau recorded by lake qinghai and its environs a review of conflicting proxies abstract climatic and environmental changes in the northeastern tibetan plateau are controlled by the asian summer monsoon asm and the westerlies two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern asia during the past few decades a series of holocene palaeoclimatic records have been obtained from sediment cores from lake qinghai and from various other geological archives in the surrounding area of the northeastern tibetan plateau however because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used the nature of holocene climatic changes in the region remains unclear and even controversial here we review all major classes of the published data from drilled cores from lake qinghai as well as other evidence from lakes and aeolian deposits from surrounding areas in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the holocene combining the results of moisture and precipitation proxies such as vegetation history pollen based precipitation reconstruction aeolian activity lake water depth lake level changes salinity and sediment redness we conclude that moisture and precipitation began to increase in the early holocene reached their maximum during the middle holocene and decreased during the late holocene similar to the pattern of the east asian summer monsoon easm in northern china it is clear that the region experienced a relatively dry climate and weak easm during the early holocene as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations generally low lake levels of lake qinghai and the adjacent lake hurleg and lake toson in the qaidam basin and widely distributed aeolian sand deposition in the lake qinghai basin and the nearby gonghe basin to the south and in the eastern qaidam basin to the west we argue that the ostracod 18o record which is widely used as a proxy of effective moisture and summer monsoon intensity in lake sediments at least in lake qinghai and which exhibits light values in the early holocene and heavier values thereafter cannot be used to reflect the strength of the easm or the intensity of monsoon precipitation as is also the case for leaf wax 2h records rather we argue that as is the case of the chinese speleothem 18o record which also is often interpreted as an easm proxy it reflects variation in the 18o of precipitation overall we suggest that the easm significantly affected precipitation in the northeastern tibetan plateau during the holocene and that it increased in strength during the early holocene reached a maximum during the middle holocene and decreased during the late holocene

late pleistocene holocene clay mineral record from the great rann of kachchh basin western india implications for palaeoenvironments and sediment sources abstract the present study uses clay mineralogy to delineate a 17 ka record of palaeoenvironmental palaeoclimatic changes in the recently uplifted palaeogulf of arabian sea i e great rann of kachchh grk situated on continental margin of indian subcontinent and flanked by indus delta the grk basin has preserved continuous record of post glacial sedimentation clay mineral studies on two long cores 60 m and 50 m long show more abundance of physical weathering products illite and chlorite over the chemical weathering products smectite and kaolinite we show that the grk sediments depict multiple sources of sediment input dominance of illite chlorite suggests grk received sediments dominantly from the himalayan terrain with minor contribution from adjacent regions we present the oldest clay mineralogical signature of an interval of intensified monsoon conditions during the late pleistocene 17 7 16 3 cal ka b p monsoon became stronger before 8 4 cal ka b p and whereas the mid holocene weakening of monsoon occurred after 7 cal ka b p despite the differences in source region and composition of clay mineral records from the grk with northeastern and southeastern arabian sea the sedimentation responded to major climatic shifts that have occurred since the lgm

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

understanding linear dune chronologies insights from a simple accumulation model abstract dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition and are thus seen as potential archives of palaeoenvironmental information some dune types are more suitable for this purpose than others and linear dunes used here synonymously with longitudinal dunes have been most frequently employed they are commonly found in dryland and dryland marginal regions and they are apparently less migratory than some other dune forms thereby offering the potential for longer environmental histories most recent studies have employed optical osl dating surveys which directly date the emplacement of dune sands to attempt to produce a representative history of aeolian accumulation at a dunefield scale yet such studies have not always given due consideration to the geomorphology of linear dune accumulation although linear dunes do not rework their sand as readily as say barchans dunes it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield s surface for this reason all dune archives must be assumed to be discontinuous over long timescales the effect of sediment redistribution on dune preservation and thus palaeoenvironmental interpretation is difficult to observe and poorly understood we present a simplified probabilistic model to replicate deposition erosion of sand at a linear dune crest thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history the modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi millennial timescales of the model s duration periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history particularly when the events involve the system as a whole briefly functioning out of an equilibrium state i e the probabilities of deposition and reworking are not equal however under forcing conditions where the probabilities are unchanged throughout the duration of the model run the results can show apparent structure within the data when sample sizes are low although at large sample sizes the preservation potential decays with burial age according to a power law the model confirms the importance of rigorous sampling strategies for such studies but also suggests that if such precautions are taken the reworking inherent to linear dune aeolian systems does not preclude their use as a quaternary palaeoenvironmental archive of environmental change

deformed anhydrite nodules a new type of finite strain gauge in sedimentary rocks abstract the nodular anhydrite of many sedimentary basins has been deformed by halokinesis ductile faulting and regional folding deformed nodular anhydrite is common and particularly well exposed in the east central sverdrup basin axel heiberg island canadian arctic large oriented specimens containing closely packed nodules were collected on this island and used for a pilot study of the state of paleostrain owing to the asymmetry of many anhydrite nodules robin s method of strain analysis is better suited than most other techniques diameter ratios in about 50 nodule sections must be determined per deformation plane to achieve a reasonable analytical precision given the attitude of bedding and its stratigraphie facing one can split the total strain into two finite increments 1 1 an apparent or real compaction 2 2 the tectonic strain in view of the ubiquity of nodular anhydrite rocks in typical sedimentary piles the procedures described in this paper should be applicable in many regions

late quaternary aeolian activity in gonghe basin northeastern qinghai tibetan plateau china abstract aeolian deposits at four sites in the gonghe basin were used to reconstruct the history of aeolian activity over the late quaternary these deposits include well sorted aeolian sand paleosols and or loess aeolian sand represents dune field expansion and or dune buildup whereas paleosols indicate stabilization of dunes accompanying ameliorated vegetation cover on the basis of 25 dates by optically stimulated luminescence osl it appears that aeolian activities occurred episodically at 33 5 20 3 13 9 11 8 11 0 9 4 7 8 and 5 7 5 5 ka which is largely consistent with the recent findings from the adjacent semi arid areas aeolian sand mobility occurring during the early to mid holocene conflicts with a climatic optimum inferred from lacustrine records in the northeastern qinghai tibetan plateau this inconsistency may be resolved by interpreting aeolian activity as a response to decreased effective moisture due to enhanced evaporation induced by higher summer insolation at that time together with local terrain and its effects on moisture our results suggest that aeolian sand and paleosol cannot be simply ascribed to regional dry and wet climates respectively and they most likely reflect changes in effective moisture

environmental changes during the late pleistocene and the holocene in the gonghe basin north eastern tibetan plateau abstract different types of aeolian sediments are widespread in gonghe basin on the north eastern tibetan plateau despite that individual sections are often discontinuous the analysis of a large number of individual sections distributed in the entire basin provides a valuable archive for the reconstruction of environmental changes since the late pleistocene this study presents 43 new osl optical stimulated luminescence ages and combines them with 39 previously published ages from the gonghe basin for the last 16 ka from around 15 to 14 ka onwards an increase in moisture facilitated the formation of a vegetation cover and the fixation of loess sediments on the northern and southern side of the basin after enhanced mobility of aeolian sediments during the dry younger dryas greater than before precipitation fixated also the sands in the lower parts of the basin the increase in moisture can be attributed to the strengthening of the asian summer monsoon a comparison with the timing of aeolian sediment accumulation in the neighbouring basins probably indicates a time transgressive strengthening of the monsoon on the north eastern tibetan plateau aeolian sands were first permanently stored from around 17 ka at the qinghai lake in the north east of the area and at 10 5 ka at the donggi cona in the south west the gonghe basin is located in an intermediate position highest moisture values occurred during the mid holocene from around 7 5 until probably 2 5 ka in the gonghe basin in most parts of the basin aeolian activity was low during this time in the central part of the basin aeolian sand movement occurred sporadically since 2 5 ka aeolian activity in most parts of the basin resumed due to the late holocene weakening of the asian summer monsoon however the parallel accumulation of aeolian sands and silts indicates an increased human influence

mylonitic deformation of evaporites in decollements examples from the southern alps france abstract the ductile deformation of triassic evaporites is described in two decollements from the southern alps of france the arc de nice and arc de digne nappes we show that deformation is not chaotic as is commonly considered on the contrary it is commonly well organized and is consistent with progressive shearing typical shear structures include mylonitic foliation stretching lineations folds of various shapes and orientations a type folds and sheath folds asymmetrical pressure shadows composed of gypsum fibres shear bands and boudinage at two sites lineation directions and analysis of shear criteria allow the kinematics of nappe emplacement to be determined computer modelling of pressure shadows allows deformation mechanisms and strain measurements to be determined the results of the analysis can be placed in the context of the regional framework of the two decollements 1 deformation at the nice site corresponds to dextral wrenching on a lateral ramp of the decollement along the western limit of the arc de nice nappe deformation in the ductile fault zone is close to simple shear 2 deformation in the second site is associated with a ramp which affects the decollement in front of the arc de digne nappe the deformation corresponds to shearing towards the southwest including a pure shear component this result can be explained by taking into account the effects of the ramp geometry upon the deformation in the decollement this shows that deformation analysis of evaporites in decollements can be used to understand the mechanisms and kinematics of nappe emplacement

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

geochemical differentiation of quaternary sediments from the pampean region based on soil phosphorus contents as detected in the early 20th century abstract data obtained in the early 20th century on the total phosphorus tp content in soil materials from the pampean region have been processed and plotted on maps of the region approximately 1200 subsoil data and 1400 surface horizon data obtained using the same analytical method have been processed according to differences in phosphorus content several areas have been demarcated limits and characteristics of these areas have been correlated with data from the more recent literature regarding the p distribution and with both mineralogical and sedimentological information on surface materials results suggest that a confluence of sediments from different provenances i e the andean range the pampean hills and the brazilian shield is found in the argentine pampean region

spatial variability of 14c reservoir effects in tibetan plateau lakes abstract radiocarbon dating of lake sediments is often hampered by the presence of a lake reservoir effect lre also dead carbon or old carbon effect especially in dry and cold regions with a sparse plant cover in the catchment the tibetan plateau became a hotspot of the palaeoenvironmental and climate research community in recent years and the assessment of present day lres is a crucial prerequisite for the establishment of reliable radiocarbon age depth relationships for lake sediment cores this paper examines the spatial variability of lres within individual lakes through a discussion of new data for lake donggi cona and a compilation of previously published data for five additional lakes where lre data are available for different sites lake reservoir effects for lake donggi cona on the northeastern tibetan plateau were determined for shells of aquatic snails collected alive close to the lake s shore the largest determined lre of 20 000 14 c years is significantly larger than previously reported lres from the central part of the lake and larger than any previously published lre for the tibetan plateau relatively low lres in the central regions of lakes higher lres towards the margins and high lres in tributaries and spring waters are apparently a common pattern of tibetan plateau lakes the differences in lres within individual lakes or catchment areas are attributed to the more prolonged exchange of the lake water s dissolved inorganic carbon with the atmospheric co 2 in central lake regions on the one hand and the increasing influence of 14 c free or poor stream and groundwater due to the dissolution of carbonaceous basement rocks towards its margins generally higher lres were recorded in the three tectonically active lake regions of the six examined catchments and it is speculated that rising crustal co 2 further contributes to the lres in these catchments in addition to these observations and inferences elevated 14 c levels of the atmosphere as a result of nuclear bomb testing are often ignored if lres for modern materials are reported by convention relative to the atmospheric 14 c activity of the year 1950 lre data reported in this way represent unrealistic minimum estimates

the argentine neotropical loess an overview abstract the neotropical loess primary and reworked covers a large part of argentina north of 30 s it is different in some ways from the loess of the pampa which is generally considered the typical argentine loess the mineralogical chemical and physical composition of the neotropical loess has been analyzed and is here compared with both pampean and northern hemisphere european and north american loess the distribution of neotropical loess is established following the former teruggi scheme and the bio stratigraphical data indicating a late pleistocene age is described the great climatic variability of this period is documented through description of a loess paleosol sequence that mantles the pre andean valleys the influence of loess influx upon the genesis of the paleosols and the stadial interstadial environmental changes are considered in relation to the generalized truncation of paleoedaphic sequences the migration of the polar front and the weakness of the pacific high pressure system are also analyzed in relation to south american environmental evolution during the upper quaternary in that sense the genesis of pre andean fluvial valleys and mega fans extending outward into the andean piedmont plains having sources on the eastern dry side of the andes would have been influenced by such a paleoclimatic situation

holocene climatic change and the nomadic anthropocene in eastern tibet palynological and geomorphological results from the nianbaoyeze mountains abstract our study provides detailed information on the lateglacial landscape and vegetation development of tibet based on a suite of geomorphological and palynological proxy data from the nianbaoyeze shan on the eastern margin of the tibetan plateau 33 n 101 e 3300 4500 m asl we reconstruct the current state as a function of climate history and the longevity of human influence study results constrain several major phases of aeolian sedimentation between 50 15 ka and various glacier advances during the late pleistocene the holocene and the little ice age increased aeolian deposition was primarily associated with periods of more extensive glacial ice extent fluvial and alluvial sediment pulses document an increase of erosion starting at 3926 79 cal yr b p coinciding with cooling neoglacial and a growing anthropo zoogenic influence evidence for periglacial mass movements indicate that the late holocene cooling started at around 2000 cal yr b p demonstrating increased surface activity under the combined effects of human influence and climate deterioration the onset of peat growth generally depended on local conditions that include relief meso climate and in more recent times also on soil compaction due to animal trampling we distinguish three initiation periods of peat growth 12 700 10 400 cal yr b p for flat basins inside last glacial terminal moraines 7000 5000 cal yr b p for the main valley floors and 3000 1000 cal yr b p for the higher terrace surfaces the holocene vegetation history started with an open landscape dominated by pioneer shrubs along braided rivers picea juniperus abies and betula trees accompanied by a successive closing of the vegetation cover by poaceae cyperaceae and herbs 9800 8300 cal yr b p first signs of nomadic presence appear as early as 7200 cal yr b p when temperatures were up to 2 c warmer than today forest remained very patchy with strong local contrasts during the following cooling phase 5900 2750 cal yr b p the natural vegetation was transformed by nomadic grazing to bistorta rich kobresia pygmaea pastures modern nomadic migration routes were established at least 2200 years ago overgrazing and trampling led to the shrinking of bistorta and the spreading of annual weeds short lived cold events 8000 6200 3500 cal yr b p impacted on the vegetation only temporarily as the transformation of the natural poaceae rich vegetation into kobresia pastures modified the influence of the tibetan plateau hot plate on the monsoon system our data even point to an early start of a nomadic anthropocene nearly 6000 years ago against the background of a very long grazing history modern tibet must be seen as a cultural landscape