spatial and temporal patterns of aeolian activities in the desert belt of northern china revealed by dune chronologies abstract as a part of the inqua project a global digital database and atlas of quaternary dune field and sand seas 337 age records from the desert dunes of china and 20 from mongolian dune fields have been compiled in the database this has opened the possibility of exploring and synthesizing the quaternary environmental changes in the asian mid latitudes dune fields directly from the on site aeolian sand archives this paper assessed the sand dune chronologies in terms of geographical distribution data quality and their implications for late quaternary palaeoenvironmental reconstructions the available ages are concentrated mainly in the last 20 ka and many are from the fields of stabilized dunes in the eastern portion of the desert belt in northern china the number of records and the ratio between the records of stable state and the total records could act as a proxy for the palaeoenvironmental interpretation the aeolian sand activities deciphered from the chronological data in the eastern portion of the desert belt in northern china show a reasonable correlation with the general global climatic curves at the glacial interglacial timescales the limited aeolian sand records from the glacial period however hamper the understanding of the detailed features e g forms and processes of the dune fields during glacial times in the last two millennia however there has not been any meaningful correlation between aeolian dune activity and climatic variation at the centennial time scales probably due to the complexity of the aeolian sand systems and human interventions extending the coverage of dune chronology both temporally and spatially is urgently needed for a full understanding of the environmental changes in the dune fields

paleoenvironment of the central himalaya during late mis 3 using stable isotopic compositions of lacustrine organic matter occluded in diatoms and sediments abstract marine isotope stage mis 3 was an interstadial stage in the climate history of the earth where the last phase 40 30 ka showed relatively warmer climate over the northwest china tibetan plateau and northwestern india compared to other regions of the world however not many studies are reported for climate variability during this period from the himalayan region here an attempt has been made to understand the paleoenvironment of the central himalaya during 45 29 ka using stable isotopic compositions of carbon 13ctoc and nitrogen 15ntn along with their elemental ratios toc tn in bulk organic matter and occluded organic matter within diatom frustules 13cdiatom of a paleolake sequence the variabilities in 13cdiatom 13ctoc and toc tn ratios indicated intermittent changes in the lake carbon dynamics from bicarbonate dominated system to carbon dioxide dominated regime these changes in lacustrine carbon cycling provided evidence for existence of sporadic dry events in the central himalaya during 45 29 ka in agreement with the records from the northwest china tibetan plateau and northwestern india our results also confirm the existence of a relatively wet and humid period during 40 32 ka in the central himalaya therefore it appeared that compared to other parts of the world relatively wet and humid climate existed throughout this region however the mechanism behind this wet and humid phase remains to be explored and warrants a high resolution paleoclimate study in the himalaya

boron occurrence in halite and boron isotope geochemistry of halite in the qarhan salt lake western china abstract previous studies have investigated boron b isotope composition of salt lake brines in the qaidam basin western china however the research on b isotope geochemistry of halite from a sediment core in a typical sedimentary basin has been very limited in this study a 102 m long drill core isl1a was recovered from qarhan salt lake in eastern qaidam basin forty three halite samples from upper 44 0 m in isl1a were collected and analyzed for chemical compositions k na ca 2 mg 2 cl so 4 2 sr 2 and b 3 and b isotopes in order to investigate their relationships and b isotope fractionation between halite and brines in the qarhan salt lake the results show that 1 more b 3 and mg 2 values in halite are low concentrations and more concentrated and low b 3 concentrations have a strong correlation with low mg 2 in halite which imply that they might be the same source 2 low mg 2 values in halite from isl1a have a similar trend with m mg 2 molarity of fluid inclusion brines from two sediment cores east to isl1a about 50 km in the study area suggesting that low b 3 and mg 2 concentrations should derive from fluid inclusions in halite based on x ray diffraction results in isl1a that no borate and small amount of magnesium salts were deposited 3 11 b values of halite in isl1a range from 0 35 to 5 84 which are in the range of those of river water and brines 1 0 to 9 6 and almost overlapped with those of brines 2 9 to 7 5 in the qarhan salt lake these results suggest that no or minor b isotope fractionation between halite and brine occurred

late pliocene quaternary evolution of redox conditions in the western qaidam paleolake ne tibetan plateau deduced from mn geochemistry in the drilling core sg 1 abstract manganese mn in lake sediments reacts strongly to changes of redox conditions this study analyzed mn concentrations in oxides carbonates and bulk phases of the calcareous lacustrine sediments of a 938 5 m long core sg 1 taken from the western qaidam basin well dated from 2 77 ma to 0 1 ma comparisons of extractions from diluted hydrochloric acid acetic acid and citrate bicarbonate dithionite demonstrate that variations of mn concentrations from acetic acid leaching mnhoac are mostly responsible for mn ii fluctuations in the carbonate phase taking into account the relevant processes during weathering transportation deposition and post deposition of mn bearing rocks we conclude that mn input from catchment weathering and paleolake redox condition provide the primary controls on variations in the mn records of carbonate and oxide phases we propose mnhoac as a new sensitive indicator of paleolake redox evolution and catchment scale climate change the mnhoac variations show a long term upward decreasing trend indicating a long term decrease of mn input from catchment weathering associated with increasing oxygen content in the paleolake bottom water the great similarities of the mnhoac record with other regional and global records suggest that paleolake redox changes and climatic drying in the qaidam basin may be largely related to global cooling

high altitude aeolian research on the tibetan plateau aeolian processes and their role in desertification have been studied extensively at low elevations but have been rarely studied at high elevations in areas such as the tibetan plateau where aeolian processes were active in the geologic past and remain active today in this review we summarize research that improves our understanding of aeolian processes on the tibetan plateau including the distribution characteristics and provenance of aeolian sediments the history of aeolian activity aeolian geomorphology and wind driven land degradation contemporary aeolian processes primarily occur in dry basins in wide river valleys on lakeshores on mountain slopes and on gravel pavements sediment characteristics suggest a local origin and provide interesting contrasts with those of china s loess plateau the history of aeolian activity and its paleoclimatic implications reconstructed based on aeolian archives is short mostly since the late glacial and shows wide regional differences aeolian geomorphology is simple and suggests short formation time wind driven land degradation is less severe than previously thought driven by different factors in different areas and exhibited complex interactions with freeze thaw processes aeolian research has been conducted within the general framework of aeolian science but addresses issues specific to the tibetan plateau that arise due to the low air temperature low air density and the presence of a cryosphere we propose six priorities for future research aeolian physics the effect of freeze thaw cycles comparisons with other areas regional differences effects of wind driven land degradation and integrated observation and monitoring

environmental implications of the magnetic record in pleistocene lacustrine sediments of the qaidam basin ne tibetan plateau abstract the application of magnetic proxies in paleoclimate studies has the advantage of fast and non destructive measurement procedures which is an important precondition for obtaining high resolution datasets within a manageable time frame here we demonstrate the advantage of using magnetic proxies for a 940 m long drill core comprising lacustrine sediments from the qaidam basin ne tibetan plateau which was previously dated by magnetostratigraphy and optical stimulated luminescence osl dating comparison of three independent mass specific magnetic susceptibility datasets confirms the horizontal homogeneity of the drill core at scales of several cm 3 the potential linkage of to astronomical forcing is suggested by spectral analysis magnetic grain size and mineralogy dependent parameters were used to evaluate possible scenarios explaining the variation moreover using additional palynological results we demonstrate the correlation of with climatic constraints thereby showing the climate sensitivity of higher and lower values are related to dry and more humid conditions respectively our results lead us to conclude that variations are caused by the interference of two driving mechanisms low temperature oxidation in the catchment area and a changing catchment area in summary this study confirms the informative value of magnetic proxies for detecting paleoenvironmental change in high resolution

how to find high quality petroleum source rocks in saline lacustrine basins a case study from the cenozoic qaidam basin nw china abstract despite having made significant contributions to global hydrocarbon occurrences source rocks in saline lacustrine basins show great mineralogical and organic geochemical heterogeneity and the controlling mechanism is weakly studied here we use the cenozoic qaidam basin as an example to compare the organic and inorganic parameters of fine grained sediments in different lacustrine facies and to figure out the characterization and distribution of effective petroleum source rocks in saline lacustrine systems organic inorganic database of six selected boreholes show that in the bench margin high gradient lacustrine system fine grained sediments in sublittoral brackish mesosaline zones containing low chlorides

climate changes in the qaidam basin in nw china over the past 40 kyr abstract little is known about the climate and environmental changes that have occurred in the extremely arid regions of china since mis marine isotope stage 3 59 29 cal kyr bp when most regions in northwestern china and the tibetan plateau featured warm and humid conditions in this paper we present a record of the climate changes in the qaidam basin in arid northwestern china over the past 40 kyr based on the mineralogy of a 35 m long sediment core recovered from qarhan salt lake our results show that the lake was a saline or hyper saline lake saturated with respect to gypsum between 40 and 33 cal kyr bp beginning at 33 cal kyr bp evaporite formation was dominated by halite precipitation indicating that the lake salinity had increased extensively and that the climate became drier during 33 24 5 cal kyr bp the lake salinity then increased continuously resulting in the appearance of bischofite between 24 5 and 14 6 cal kyr bp the disappearance of bischofite and the increase in gypsum indicate that the salinity of the water decreased slightly between 14 6 and 8 3cal kyr bp however during the last 8300 years the lake has dried up and is now a playa generally the climate was wet in late mis 3 arid in mis 2 29 11 7 cal kyr bp and hyperarid in the holocene the relatively humid conditions may have resulted from weak evaporation caused by the relatively low insolation and intense ice albedo feedback in late mis 3 the decreased insolation and dramatically increased eurasian ice volume in mis 2 may have led to limited precipitation which resulted in persistent dry climate conditions in the qaidam basin in the holocene the reduction in ice volume reduced the albedo and this change in conjunction with increased insolation may have led to evaporation exceeding local precipitation resulting in hyperarid climate conditions in the qaidam basin

temporal variations of mineral dust biogenic tracers and anthropogenic species during the past two centuries from belukha ice core siberian altai 1 in july 2001 a 140 m long ice core was recovered from the belukha glacier 49 48 26 n 86 34 43 e 4062 m a s l in the siberian altai the ion chemistry of the upper 86 m covering the last two centuries is characterized by biogenic emissions ammonium and formate aeolian dust calcium magnesium chloride and sodium and anthropogenic species sulfate nitrate and ammonium particularly high ammonium and formate concentrations indicate pronounced emissions from siberian forests the inferred fire frequency does not show a long term trend but distinct periods of enhanced activity sulfate has the highest industrial to preindustrial ratio and an anthropogenic contribution of more than 80 variations in this record reflect sulfur dioxide emissions in siberia and kazakhstan sulfate concentrations remained low until 1950 then sharply increased and peaked in the 1970s the decrease in the 1980s is attributed to the economic political and social crises and to the replacement of coal with gas rising nitrate concentrations since 1960 reflect traffic growth and enhanced fertilizer application increasing ammonium concentrations since the 1950s are attributable to population inflow in southern siberia with the associated enhancement of agricultural activity a nitrate peak of short duration in 1908 is thought to be the atmospheric signature from the tunguska event on 30 june 1908

assessing tectonic and climatic controls for late quaternary fluvial terraces in guide jianzha and xunhua basins along the yellow river on the northeastern tibetan plateau abstract this study focused on well preserved fluvial terrace sequences that span the past 100 ka in the guide jianzha and xunhua basins along the yellow river that drained the northeastern tibetan plateau new geomorphic stratigraphic sedimentologic and chronologic data from twelve depositional sequences within terraces yielded better constraints on rates of incision degradational and aggradational phases for the yellow river age control was established by sixteen osl ages on quartz grains from fluvial sediments three fluvial aggradational phases were identified between 100 and 80 ka 53 and 40 ka and 21 and 12 ka associated with terrace levels respectively at 120 to 95 61 to 45 and 25 to 15 m above river level these aggradational phases reflect multiple processes including enhanced fluvial discharge sediment availability with glaciation deglaciation and increased monsoonal precipitation the initiation of fluvial degradation was linked to mega floods released from landslide dammed lakes at ca 76 38 and 16 ka though these changes may also reflect variations in sediment load discharge relations with climate change the apparent net incision rate is 1 13 0 11 mm yr for the past 100 ka and is consistent with late cenozoic tectonic uplift rates 0 5 2 mm yr and recent gps based rates the fluvial dynamics of the upper reach of the yellow river was variably controlled by climate induced changes in discharge sediment load relations on stadial to interstadial timescales episodic mega floods from the breach of landslide dams and with net incision in the past 100 ka in response to tectonic uplift of the tibetan plateau

chemical and boron isotope compositions of non marine brines from the qaidam basin qinghai china the general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the qaidam basin northern qinghai xizang tibet plateau china this basin is a large tectonically active system isolated from the ocean and composed of thick clastic and evaporite sediments the modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites the chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources 1 inflow of hot springs enriched in sodium sulphate and boron evaporation of these waters leads to a high na cl ratio 1 a na cl so4 brine and an evaporite mineral assemblage of halite mirabilite borate lakes daqaidam and xiaoqaidam 2 inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a na mg cl solute type with low na cl 1 brcl licl and bcl ratios and 3 ca chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes evaporation and salt crystallization of mixtures of the latter two types leads to a marine like brine e g na mg cl type nacl ratio 1 and mineral assemblages similar to that predicted for progressive evaporation of seawater e g qarhan playa halite sylvite carnallite bischofite the 11 b values of the input waters to the qaidam basin range of 0 7 to 10 9 vs nbs 951 and brines from salt lakes 0 5 to 15 0 are similar to those of associated granitic rocks 11b 2 3 to 3 7 n 3 and hence indicate the non marine origin of these fluids the highest 11b values are associated with fluids with low bli ratios indicating selective removal of elemental boron and 10b by adsorption onto clay minerals the magnitude of 11b enrichment due to adsorption is 15 20 and thus non marine brines are well distinguished from marine derived brines 11b of 39 to 59 preserving the large isotopic difference 40 of their source waters it is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace

ground penetrating radar measurements of subsurface structures of lacustrine sediments in the qaidam basin nw china possible implications for future in situ radar experiments on mars abstract the stratigraphic profile of paleolakes on mars preserves a record of past climatic hydrological and sedimentary environment radar could be used to detect the structure and distribution of buried lacustrine sediments but orbiter radar sounders rarely detect the internal structure or the bottom of the ancient martian lake deposits future martian missions will employ ground penetrating radar gpr onboard rovers to investigate the shallow subsurface structure of paleolake basins in this case ground experiments are necessary to test the potential of gpr detection this study reports on gpr experiments operating at 100 mhz and 200 mhz carried out in the qaidam basin one of the analogue sites for martian paleolake environments to detect the subsurface structure of lacustrine sediments and measure the relative permittivity of sediments with both laboratory instrument and gpr data two gpr measurements were performed on top of yardangs representing layered lacustrine sedimentary outcrops another survey site is a polygonal patterned ground which is a common landform in the qaidam basin and on mars the observations revealed by gpr experiments show that 1 sediments of three sites have varied compositions density and porosity and have a wide range of relative permittivity values from 1 56 to 4 56 2 the detection depth of our measurements could reach 20 m 3 the interfaces between sedimentary layers can be seen in radargrams but reflectors in radargrams may not always match with exposed layers of the yardang outcrops due to the undetected change of permittivity values or thin thickness of layers 4 a distinct and continuous reflector is observed beneath the polygonal terrain which we interpret as a subsurface layer with low water brine content our ground experiments suggest that a similar gpr on martian rover could detect the near surface structure of lacustrine sediments e g deposition anomaly interfaces of drastic permittivity change such as buried ice brine considering that the design frequency is close to our equipment

pliocene pleistocene climate change at the ne tibetan plateau deduced from lithofacies variation in the drill core sg 1 western qaidam basin china abstract the pliocene pleistocene sedimentologic evolution of the western qaidam basin at the ne tibetan plateau was studied on the nearly thousand meter deep drill core sg 1 spanning ca 2 8 0 1 ma recovered from the chahansilatu sub depression with an average recovery rate of 95 lithofacies variation records the regional climatic change in relation to asian drying and tibetan plateau uplift sedimentary textures and structures demonstrate a continuous slight coarsening and an increase of evaporites upward we recognized five lithofacies 1 gray black laminated mudstone 2 gray massive mudstone and siltstone 3 bedded halite 4 loose muddy halite and 5 brownish yellowish saliferous siltstone and mudstone representing 1 semi deep fresh to semi brackish lake 2 shallow brackish lake 3 perennial saline lake 4 playa saline lake and 5 saline mudflat conditions respectively variation of the lithofacies through the core demonstrates a clear trend of lake shrinkage since the late pliocene and the final termination of the chahansilatu paleolake accelerations of lake shrinkages are observed at ca 2 5 ma 2 2 ma 1 6 ma 1 2 ma 0 9 ma 0 6 ma and 0 1 ma our results suggest that the long term stepwise drying of the asian inland may have been forced by the change of the global ice volume

pleistocene paleoenvironmental changes in the high mountain ranges of central china and adjacent regions abstract during several joint chinese german expeditions the quaternary landscape and paleoclimatic evolution of the mountain ranges and grabens surrounding the loess plateau of central china was studied the results are compared with proxy data from the interior loess plateau to help reconstruct atmospheric circulation during late pleistocene times middle to late pleistocene alluvial terraces and fans capped with loess units and paleosols show that aggradational episodes correlate with periods of glaciation and increased loess accumulation in turn degradation correlates with interglacials or interstadials and increased soil formation this implies that climate is the primary control on quaternary paleohydrology and alluvial sedimentation and erosion the high mountains which barely reached the last glacial ela were only glaciated during the most favourable climatic period of glaciation the glaciation the glacial and alluvial forms point to a cool early to maximum glacial period with increased precipitation and to a maximum to final period with cold dry conditions during the last glaciation the maximum advance of the small glaciers took place towards the end of a relatively humid and cold period between ca 32 and 23 ka the following dry cold stage between ca 23 and 13 ka was rather unfavourable for glacial advance proxy data from the loess plateau supports the view that glaciations were more or less dominated by cold dry winter monsoon climate whereas during the interglacial interstadials a warmer and more humid climate prevailed implying a strengthening of the summer monsoon influence the results prove variations of the monsoon that in turn modulates paleohydrology periglacial dynamics glacier advances dust flux and soil formation

deposition of the bear gulch limestone a carboniferous plattenkalk from central montana the carboniferous bear gulch limestone of the central montana big snowy trough is a lithographic limestone analogous to the plattenkalk carbonates of the mesozoic european middle eastern tethyan belt it contains an excellently preserved chitinous and phosphatic marine fauna petrographic and field studies synthesized with palaeontological data provide insights into depositional history tectonic activity initiated development of small en echelon basins rims of these basins were sites of high primary productivity photosynthesis by subtidal cyanobacterial mats and algae caused in situ precipitation of micrite cyanobacteria and algae also provided a food source for benthic and nektonic organisms which provided food for predators respiration in turn provided carbon dioxide for continued photosynthesis thus a balanced ecosystem evolved productivity in the water column used up available oxygen resulting in dysaerobic to anaerobic conditions in the bottom waters and sediments this plus high sedimentation rates of carbonate ooze transported downslope aided in preservation of whole body fossils there are no likely modern analogues known for the bear gulch limestone however comparisons with mesozoic plattenkalke demonstrate that it is most closely analogous to those deposited in shallow water back reef areas of the tethyan carbonate platform rather than to those deposited in the deeper water shelf edge environment this is in agreement with the water depth of roughly 40 m estimated for the bear gulch limestone

fault slip analysis along the northern margin of the eastern alps molasse helvetic nappes north and south penninic flysch and the northern calcareous alps fault slip data are analyzed and paleostress tensors computed from 84 stations along the northern margin of the eastern alps between liechtenstein and vienna most fault sets resulted from more than one deformation heterogenous sets are divided into homogenous subsets by cross cutting relationships observed in the field and stress tensors are calculated separately for each subset the deviatoric stress tensors fall into six distinct groups that are regionally consistent in orientation stress ratio and relative age throughout the northern margin of the eastern alps from oldest to youngest the tensor groups are as follows 1 1 subhorizontal e w 3 subvertical thrusting related e w compression this group is only encountered in the south penninic flysch and the northern calcareous alps 2 1 subhorizontal n s 3 subvertical thrusting related n s directed compression 3 1 subhorizontal n s 3 subhorizonal e w strike slip faulting conjugate to n s compression 4 1 subvertical 3 subhorizontal e w e w directed subhorizontal extension 5 1 subhorizontal e w 3 subhorizontal n s strike slip faulting during e w compression and 6 1 subvertical 3 subhorizontal about n s 3 trajectories are oriented perpendicular to the general strike of the eastern alps and parallel topographic gradients the six trensor groups correlate with distinct steps in the cretaceous and the post eocene tectonic evolution of the northern units of the eastern alps 1 1 thrusting related e w compressional structures in the south penninic flysch and the northern calcareous alps are correlated to cretaceous top to w directed thrusting in the south penninic and austroalpine domains 2 2 thrusting related n s compressional structures encompass large scale folds with e w trending axes rare e w oriented thrust branch lines and cut off lines and s dipping ramps in the rhenodanubian flysch tensors reflect the stresses during northward thrusting in the late eocene early miocene 3 3 4 strike slip faults and extensional structures depicting n s compression and e w extension formed during the eastward lateral extrusion of the eastern alps prominent reactivations of strike slip faults during subhorizontal extension in the east and permutation between 1 and 2 reflecting periodic superposition of strike slip and normal faulting in the western eastern alps during overall e w extension suggest a close relationship of both tensor groups deformation resulted in the eastward lateral motion of the northern units of the eastern alps that started during the miocene 4 5 the significance of late miocene e w directed compression reactivating pre existing fractures and faults is presently not well understood we tentatively relate this event to a major change of boundary conditions within the miocene 5 6 the youngest deformation recorded is caused by surface uplift and gravitational collapse of the eastern alps

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

evidence for a warm humid climate in arid northwestern china during 40 30 ka bp abstract former shorelines and sedimentary records from several lake basins in northwestern china xinjiang qinghai give evidence for warm and humid climatic conditions during 40 30 ka bp further indications of this favorable climate period are derived from palaeosols from the ili loess and from cemented calcareous layers on the terraces of the keriya river at the southern margin of the tarim basin and in the badain jaran desert in inner mongolia at that time annual mean temperature in the qaidam basin was 2 c higher and in the western part of inner mongolia even 2 3 c higher than today precipitation in most parts of northwestern china was between 60 300 mm greater than today these changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the earth s precessional cycle as a result of these orbital changes it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern china

a new terrestrial analogue site for mars research the qaidam basin tibetan plateau nw china abstract remote sensing observations and rover missions have documented the presence of playas salts and wind erosion landforms of lacustrine sediments on mars all of these observations suggest mars was aqueous in its early history however abundant questions remain how wet was the environment what were the properties of the liquids and the possibility of ancient habitability and what kinds of geological processes shaped the present landforms to explore these unknowns analogue studies can play a key role in this contribution we introduce the qaidam basin tibetan plateau northwestern china as a new and unique analogue site for studying the past aqueous and present arid environments of mars the qaidam basin the highest and one of the largest and driest deserts on earth is located in a dry cold and high uv environment similar to the surface of mars we demonstrate a variety of landforms and also their counterparts on mars which include aeolian dunes and yardangs polygons gullies valleys and fluvial fans in the qaidam basin various environmental regimes for the formation of linear and asymmetric barchans have been described saline lakes and playas representing different stages of lake evolution in arid environment are also present in the qaidam basin and provide promising cases for studying the habitability in mars like environments results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present martian habitability moreover the remote but ready accessibility of the qaidam basin make it a potential site for engineering testing in regards to future martin exploration missions we propose that the variety of exogenic and endogenic geomorphic types lacustrine sediments evaporite mineral assemblages and mars like extreme environments collectively point to the qaidam basin as an optimal

a 40 000 year record of aridity and dust activity at lop nur tarim basin northwestern china abstract the taklamakan desert is a major dust source area for northwestern china the history of aridification and sandstorm activity of the desert is recorded in the lacustrine sediments of the lop nur paleolake on the eastern margin of the desert in this study we used accelerator mass spectrometry 14c dating the ln al ca ratio and the grain size of the non biogenic fraction of sediment core ky01 taken from the center of lop nur to produce a 40 kyr record of local climate change during mid late marine isotope stage mis 3 increases in the ln al ca ratio alluvial mud content and atmospheric dust content and a decrease in the dust storm content indicate an overall wet climate during mis 2 marked decreases in the ln al ca ratio and alluvial mud content especially during the last glacial maximum and heinrich event 1 cold interval indicate lowered atmospheric temperatures as also recorded in greenland ice cores during mis 2 fluvial input to the site was reduced and almost ceased suggesting extreme aridity at lop nur very strong low altitude winds and frequent dust storms during early mis 1 the contribution of dust storms to the lake sediments fell gradually and was then relatively constant even during the younger dryas cold interval this result might be ascribed to the increased supply of meltwater from snow and ice to lop nur representing a response to the rise in atmospheric temperatures during the deglacial accompanied by strong high level winds during 9 7 kyr bp there was an increase in the input of sediment from sandstorms and hence an increase in low level wind strength possibly relating to the 8 2 kyr bp cold event from 7 0 to 1 5 kyr bp there was a decrease in sandstorm input and thus a gradual weakening of the strength of low level winds however after 1 5 kyr bp the sandstorm input increased overall we conclude that dust storm activity in the region of lop nur since 40 kyr bp has been controlled mainly by northern hemisphere cold events with atmospheric dust providing a background sedimentary component that was dominant during warm intervals our findings contribute to an improved understanding of the dynamics of dust transport and to the history of dust activity and the lacustrine sedimentary record in northwestern china

radiocarbon dating of playa lake hydrologic changes examples from northwestern china and central australia accurate radiocarbon dating of arid zone playas is restricted by shortage of suitable organic matter analyses from two large systems in australia lake frome and china qarhan playa in the qaidam basin demonstrate the problems associated with the use of carbonates for dating organic carbon although requiring treatment of large samples 1 2 kg provides the most accurate basis for establishing chronologic control in qarhan a deposit of halite averaging about 30 m thick extends over an area of 5800 km2 carbonate in the system is dominantly derived as clastics from loess transported by northwesterly winds the large component of dead carbon thus involved explains anomalous patterns of dates derived from these materials such results are consistently much older than those based on organic carbon in lake frome subject to a more maritime climate in central australia the carbonate component is dominantly authigenic lacustrine in origin contaminated by a small detrital component it provides ages about one half life older than those from organic carbon the sequence from qarhan supplemented by evidence of lacustral pluvial episodes in two other sub basins in qaidam kunteyi and xiao qaidam illustrates the presence there of expanded waterbodies persisting from at least 40 000 to about 15 000 yr b p in areas where little surface water persists today the large evaporite deposits formed between about 25 000 to sometime after 15 000 yr b p holocene climate appears to have remained hyperarid like that of today at lake frome an early lacustral phase gave way before 18 000 yr b p to drying and aeolian activity water had returned to the system by 16 000 yr b p signalling a decline if not the end of aridity lacustrine conditions persisted through early holocene with drying and development of playa facies about 7000 yr b p after a brief return to lacustrine conditions between about 6000 4000 yr b p a dry playa environment has continued to the present day the frome and qarhan playas although in comparable latitudes lie in very different climatic and tectonic settings their palaeohydrologic records are neither in phase nor in distinct anti phase emphasizing the complexity of comparing palaeoclimatic records from different circulation systems

the processes and mechanisms of severe sandstorm development in the eastern hexi corridor china during the last glacial period abstract dust transported by sandstorms has been an important feedback in climate change in the past and its environmental effects are predicted to have a great impact on future global climatic change investigating the grain size classes and the standard deviations of the modern sandstorm samples and the samples in the shagou section situated in the eastern hexi corridor lead us to suggest that the sand fraction within the range of 275 4 550 m in this section can be used as a sensitive indicator of severe sandstorms we selected the size range in the l1 stratum of the shagou loess section as indicative of temporal changes in sandstorm intensity in the eastern hexi corridor and found that during the last glacial period severe sandstorms in the eastern hexi corridor occurred with high frequency during these periods i 70 54 ka b p ii 51 48 ka b p iii 45 42 ka b p iv 38 33 ka b p v 31 28 ka b p and vi 26 12 ka b p in general the frequency and intensity of dust storms in the early mis 4 and late mis 2 periods were both high but they were reduced in the middle period mis 3 the primary factors controlling severe sandstorms are hydrology and wind power followed by the expansion of the source extent reduced precipitation caused the source region of sandstorms to expand in addition wind speeds also increased at this time these factors may have directly contributed to the abundance of severe sandstorms based on the grain size from a loess section the shagou section in the eastern hexi corridor we propose an evolutionary sequence of the severe sandstorms during the last glacial period this sequence is consistent with the dust records in the arctic the antarctic and low latitude the central equatorial pacific areas thus globally synchronous periods of high dust activity occurred in the last glacial period the strong winds proposed here provide a potential explanation for the global consistency of dust flux changes during the last glacial period

lake evolution during the past 30 000 years in china and its implications for environmental change abstract taking china as a whole lake expansion occurred 500 b c 0 a d 650 950 a d and 1250 1650 a d over the past 3000 yr the expansions were mainly due to climatic fluctuations and correspond to frequent flood reports three regional characteristics of lake development have been recognized 1 fluctuations of near coastal lakes and those in other regions as well were out of phase during 500 b c 500 a d which possibly resulted from out of phase fluctuations of climate and sea level on 10 to 100 yr time scale 2 as the lower yellow river channel migrated southward the lakes in the south of the north china plain formed and reached their largest sizes much later than those in the north 3 for the lakes in the middle and lower yangtze river valley the higher a lake basin lies above a neighboring river and the further the lake is from the river s mouth in general the younger the lake is through land reclamation the ancient chinese have changed most of the lakes greatly however human activities were also constrained in certain ways by the natural changes of the lakes reclamation usually was banned and farmland was abandoned to repair reservoirs while lakes were expanding

evaporite minerals of the lower 538 5 m sediments in a long core from the western qaidam basin tibet abstract qaidam basin is a tectonically controlled mesozoic cenozoic depression on the northern margin of the tibetan plateau a 938 5 m long core was drilled in the qahansilatu sub basin in the western qaidam basin with an average core recovery of 95 it revealed alternating salt layers and carbonate clay layers samples were collected at 10 40 cm intervals for mineralogical analysis by xrd and chemical analysis by icp oes the lower 538 5 m sediments are composed of halite gypsum anhydrite gaylussite calcite aragonite ankerite dolomite and an unnamed mineral mg0 92ca0 08co3 3h2o with trace eugsterite the mother brines could be na type na ca type na ca mg type ca na type ca mg na type and trace ca mg na reflux and bacterial activity could be suitable for the formation of dolomite deep burial diagenesis could have played an active role in the formation of ankerite and anhydrate the continuous presence of halite suggested the paleo lake water was highly brackish or saline with high evaporation since 2 77 ma salt layers in the lower 538 5 m long sediments were present from 2221 ka to 2052 ka corresponding to pleistocene salt formation in the qaidam basin as hydrated carbonate minerals both gaylussite and the unnamed mineral are deposited under high precipitation rates with microbial activity gaylussite was deposited from na ca enriched solutions with molar ratios of na ca more than 2 from 691 m 2226 ka to 413 6 m 1222 ka the un named mineral mg0 92ca0 08co3 3h2o was found from 523 4 m 1728 ka to 724 2 m 2308 ka anhydrite could be transformed from gypsum under deep burial from 657 42 m 2052 ka to 867 m 2556 ka alternating salt and clay layers in the lower part of the core recorded arid and relatively wet climatic oscillations and the evolution of brine as a tectonic sub basin tectonic activities could change the local climate during episodes of uplift and subsidence the dominant minerals in the chahansilatu sub basin are similar to those of the other sub basins in the western qaidam basin but have asynchronous evolutionary stages of brine

late eocene clay boron derived paleosalinity in the qaidam basin and its implications for regional tectonics and climate abstract the qaidam basin located on the northeastern tibetan plateau and containing cenozoic sediments with a maximum thickness of 12 000 m is an ideal place to study the phased uplift of the ne tibetan plateau and regional climate change the estimation of the paleosalinity of sedimentary environments not only helps to evaluate the evolution of lakes in this region but offers insights into contemporaneous climate change we present detailed geochemical and mineralogical investigations from the lacustrine interval of the hongliugou section in the northern qaidam basin to reconstruct salinity fluctuations in the paleolake during the late eocene era 42 0 35 5 ma the clay mineral assemblages mainly contain smectite illite chlorite kaolinite and irregular illite smectite mixed layers clay boron derived paleosalinity estimates equivalent boron content couch s paleosalimeter and b ga ratios along with other proxies sensitive to salinity changes e g rb k ratios and ostracod assemblages collectively indicate an overall brackish sedimentary environment with a higher salinity period at approximately 40 0 39 2 ma this higher salinity period indicates a more arid environment and is probably related to global cooling however the global cooling in late eocene cannot explain the overall stable long term salinity pattern implying that other factors exist we propose that the migration of the yiliping depression depocenter in the northern qaidam and increased orographic rainfall induced by late eocene tectonic activity at the northern margin of the basin might have partly offset the increase in salinity driven by global cooling

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

the evolution of dry lands in northern china and in the republic of mongolia since the last glacial maximum abstract the dry lands in china and mongolia include sand seas gravel deserts stable sand dunes desert steppe steppe and scrub woodlands environments distributed in a wide range of geomorphological and tectonic settings from 155 m below sea level to more than 5000 m asl in china the sandy deserts and gravel deserts are located in the arid regions mainly west of the helan mountains 106 e whereas the stable dune regions are distributed in the semi arid areas east of the helan mountains in mongolia deserts cover more than 40 of the country they are mainly distributed in the southern and southwestern part of the country in inter mountain valleys and basins of the altai mountains and in the uvs nuur basin in northwestern mongolia the desert regions enclose mainly gravel desert gobi and comprise some areas with sand fields and dune fields especially in western mongolia relict frost wedges and moraines in the chaidamu and tarim basins of china indicate that the coldest time of the last glaciation occurred at 30 25 ka in these two areas the stratigraphy of the dunes in the badain jaran desert high lake levels in the areas near and within the large deserts in china and in mongolia suggest a much more humid climate in western china and in mongolia during marine isotope stage three however the period after 24 ka to the end of the pleistocene was mostly characterised by increased temperature and reduced precipitation in the chaidamu and tarim basins paleoenvironmental conditions in the eastern part of the chinese desert belt were marked by an extensive widening of dune formation at 21 13 ka reflecting a weaker intensity of east asian summer monsoon during the holocene higher lake levels stratigraphy of dunes and results of palynological isotopical and sedimentological analyses of lacustrine sediments in the western china and mongolia suggest a few wetter periods especially in the earlier part of the holocene the holocene climatic conditions in the eastern part of the chinese deserts have enabled stabilisation of dunes and formation of soils the presently active dunes in this region are a result of desertification due to human influences recent investigations in the dry lands of china and mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates

late pleistocene evolution of salt lakes in the qaidam basin qinghai province china abstract the qaidam basin is a tectonically controlled depression at 2700 m altitude on the northern margin of the qinghai xizang tibet plateau rimmed by the high aljun qilian ranges to the north and kunlun peaks to the south rising above 5000 m the basin floor experiences hyper arid conditions with evaporation precipitation ratios exceeding 100 1 periglacial and glacial conditions prevail on montane peaks with permafrost above 3800 m on the basin floor small waterbodies lie on extensive halite salt flats on the largest the qarhan salt flat 5800 km2 in extent the small lakes dabuxun and taijinier represent contracted remnants of a once expansive water body throughout neogene time a succession of clastic sediments indicates lake depo centre migration from nw to se towards late pliocene evaporitic conditions developed with formation of gypsum halite celestite mirabilite and bloedite continued deformation through pleistocene time has developed a series of nw se trending domes and troughs this setting has continued to exert a controlling influence on basin and brine evolution with progressive development through sulfate to chloride brines as dry conditions intensified in late pleistocene expanded lake conditions qarhan mega lake corresponding to near the 2800 m contour indicate the existence of past climates much more humid than those of today a drilling program has defined the lateral and vertical extent of evaporitic halite deposits freshwater clastics and shell deposits which predate the halite phase indicate humid lacustral conditions until after 40 000 30 000 yr b p desiccation from about 25 000 yr until about 9000 yr b p resulted in deposition of halite to 60 m thick with thin parting muds representing brief returns to more humid environments high lake shorelines with aragonitic ooids surrounding the dry playa kunteyi and high level ostracod rich beach and near shore deposits on xiao qaidam attest to the presence of expanded late pleistocene lacustral conditions on lakes other than qarhan preceding the final evaporite stage clastic sediments associated with the halite are dominated by loessial silts equivalent to the late pleistocene malan deposits of central china simultaneous halite and loess deposition reflect the dry conditions that developed in the qaidam basin during the latter part of the last glaciation and which have persisted ever since the final evolution of brines has resulted in development of extensive potassium rich brines and salts with the mineral carnallite providing the basis for a large potash extraction industry near golmud the hydrologic history documented by the analyses of lake sediments reflects the interaction of tectonic deformation and climatic change in the development of brines to the potash stage

the polygonal surface structures in the dalangtan playa qaidam basin nw china controlling factors for their formation and implications for analogous martian landforms