spatial pattern of late glacial and holocene climatic and environmental development in western mongolia a critical review and synthesis abstract the effective humidity resulting from the balance between evapotranspiration and precipitation largely controls the environmental conditions under the highly continental semi humid to arid climate of mongolia minor variations of temperature and precipitation have resulted in considerable environmental changes over the holocene affecting vegetation composition and density soil formation geomorphological activity desertification processes lake level and glacier distribution thus various paleoclimatic archives have been investigated in several studies over the last decades here we present an overview of the existing reconstructions of climatic changes over the late glacial and holocene the aim of this work is to obtain a spatially differentiated synthesis of the currently available paleoenvironmental information and to point to existing contradictions and knowledge gaps our results suggest that during the late glacial dry and cold conditions dominated whereas the early holocene was warm and characterized by increasing humidity 6000 years ago the temperature began to decrease enhanced aridity occurred in the rain shadow east of the altai and khangai mountains pointing to increasing influence of the westerlies in the valley of great lakes east of the altai mountains the late glacial was characterized by high lake levels that steadily decreased over the holocene in the valley of gobi lakes south of the khangai mountains high lake levels persisted from the early holocene until the beginning of the mid holocene in contrast the lake level of telmen nuur north of the khangai mountains remained low until the end of the mid holocene periods of enhanced eolian transport and deposition occurred from the late glacial until the early holocene and again during the late holocene in between during the mid holocene no soil erosion by eolian and fluvial processes took place over large areas the present state of research shows that the limited number of investigated archives and the unbalanced spatial distribution of the studied sites hamper an integrative reconstruction with appropriate spatial and temporal resolution paleoclimate interpretations by different authors which were derived from the same archives or from neighboring archives in the same region diverge in paleotemperature and humidity thus paleoclimate at a regional scale of up to 100 km as well as the timing of climate changes at a temporal scale of several centuries is still ambiguous in mongolia further challenges include the multiple possible causes of lake level changes and the difficulty to distinguish i between climatic and anthropogenic impacts on vegetation and landscape and ii between local regional and global signals in the proxy data in addition there are ambiguities with respect to the ages of various materials that are obtained by radiocarbon and luminescence dating

avo and devonian reef exploration difficulties and possibilities although avo has proven useful in hydrocarbon exploration in shallow gas sands there are few examples of its application to carbonate exploration this paper presents a conjecture that avo can help differentiate between shale and porous dolomite in devonian reefs a critical problem in canada where oil production from nisku reefs in the devonian formation accounts for a large part of industry activity devonian formations have generated 60 of canadian oil production and 25 of gas production

quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

history of late pleistocene glaciations in the central sayan tuva upland southern siberia abstract this work describes the history of late pleistocene glaciations in the central sayan tuva upland southern siberia geological and geomorphological analysis as well as 10 be surface exposure dating revealed the glacier fluctuations in this continental area the available published data show that the glaciers were formed in the mis 6 and probably survived in the mis 5 data are also available concerning glacial advances in different periods of mis 4 mis 3 and mis 2 elas were 2030 2230 m two distinct 10 be exposure ages groups are highlighted reflecting the time of formation of glacial deposits in the mis 2 associated to the big sayan ridge outlet glaciers the sentsa sailag group terminal moraine has a mean exposure age of 16 44 0 38 ka the jombolok terminal moraine jombolok outwash plain group has a mean exposure age of 22 80 0 56 ka the last glaciation that occurred at mis 2 is characterized by the absence of ice cap on the azas volcanic plateau and of ice field in the todza basin the thickness of the valley glacier was 300 400 m at mis 2 the terminal moraines were 1300 1400 m a s l in the tissa sentsa jombolok and sailag river valleys

influence of secular variation of the geomagnetic field on production rates of in situ produced cosmogenic nuclides abstract scaling factors are presented that allow a full description of the cosmic ray flux modulation during secular variation of the geomagnetic field these scaling factors are analogous to those determined in a similar work dunai t j earth planet sci lett 2000 176 157 169 that were accurate for field strengths equivalent to present day field strength but cannot accommodate field strength variations strategies to derive the relevant geomagnetic field parameters are discussed and are tested with existing production rate calibrations for 3 he a production rate of 103 4 2 atoms g olivine yr sea level and for zero cutoff rigidity was derived from calibration sites from hawaii western usa and canary islands covering the time range of 2 281 kyr

characteristics of late quaternary monsoonal glaciation on the tibetan plateau and in east asia abstract glaciers fed by monsoonal precipitation are mainly located on the tibetan plateau and easternmost asia these are characterized by simultaneous accumulation and ablation in summer season the southeast part of the tibetan plateau experiences monsoonal precipitation in excess of 1000 mm yr resulting in maritime temperate glaciers in contrast precipitation in the middle and northwest part of the tibet plateau decreases from 1000 to 200 mm yr resulting in the formation of continental cold glaciers during the last glacial the regions of heavy monsoonal precipitation were restricted to the southeast corner of the plateau the westerly weak precipitation zone shifted southward and occupied the major northwest part of the plateau where the extreme continental type glaciers greatly expanded in the eastern margin of asia including taiwan central japan hokkaido and probably mount changbai maritime type glaciers were more extensive because of higher monsoonal precipitation especially heavy snowfall in northwest japan owing to the rich moisture content of the winter monsoon over the japan sea the millennial scale monsoon intensity and glacial cycle in the tibetan plateau are strongly affected by the precession cycle and the orbit inclination cycle which dominate the solar irradiance variation in low latitudes as the high radiation and strong monsoon caused the warmer and wetter climate during 40 30 ka the low radiation produced a weak monsoon and large depression of temperature and precipitation around 21 ka this climatic pattern differs from that in the high latitudes where the eccentricity cycle is prominent the temperature during the last glacial maximum lgm was 6 9 c lower than today on the tibetan plateau and the equilibrium line altitude was depressed by about 1000 m in the southeast part and in the east south and west margins of the plateau where precipitation was high the equilibrium line depression was 500 300 m in the inner and especially the west part of the plateau this variation in equilibrium lines might be caused by the combined effect of the decrease in precipitation the expansion of extreme continental glaciers and the active uplift of glaciated mountains the estimation of a glaciated area of about 350 000 km2 in the tibetan plateau and roughly 500 000 km2 in high asia based on observations of prominent features of lgm glacier extension may be the direct evidence that shows there was no quaternary unified ice sheet developed in the tibetan plateau

inversion and interpretation of a 3d seismic data set from the ouachita mountains oklahoma acoustic impedance inversion ai and simultaneous angle dependent inversion sadi of a 3d seismic data set characterize reservoirs of mississippian morrowan age in the triangle zone of the frontal ouachita mountains oklahoma acoustic impedance of the near angle seismic data images the 3d spatial distributions of wapanucka limestone and cromwell sandstone lame parameters density and and sections are derived from the p wave and s wave impedance ip and is sections produced by the sadi lithology is identified from the gamma logs and the vp vs and are interpreted in terms of a hydrocarbon distribution pattern the ip is used to identify high ip regions that are consistent with high sand shale ratio the estimated impedances and derived lame parameter sections are consistent with the interpretation that parts of the wapanucka limestone and cromwell sandstone contain potential gas reservoirs in fault bounded compartments the cromwell sandstone contains the main inferred

quaternary glacial history of the kanas valley chinese altai nw china constrained by electron spin resonance and optically stimulated luminescence datings abstract the chinese altai is located on the northern edge of central asia rich geological records of quaternary glaciations are preserved in this area however the glacial history in the chinese altai has hardly been investigated this study aims to rebuild the regional glacial history in the kanas valley of the chinese altai we present 14 electron spin resonance esr ages and 3 optically stimulated luminescence osl ages from glacial landforms by integrating with ages from previous studies five major glacial advances are identified during marine oxygen isotope stages mis 6 5 4 3 and 2 with ages of 167 0 16 0 123 0 18 0 ka 97 0 19 0 78 0 7 0 ka 76 0 16 0 73 1 6 6 ka 52 1 7 8 34 4 4 2 ka and 28 0 3 3 16 1 1 5 ka respectively the glacial advance during mis 5 is the local last glacial maximum and glaciers became successively more restricted from mis 5 to mis 2 in addition the extensive mis 3 glacial advance in the chinese altai contrasts with the absence of mis 3 glacial advance in the mongolia altai these glacial patterns reflect that precipitation brought by the westerlies might play a primary role on driving glacial advances during the last glacial in the chinese altai this glacial chronology is in reasonable agreement with existing glacial chronologies from other parts of the altai tian shan and pamir indicating similar climate controls on the patterns of quaternary glaciation across central asia highlands

quaternary glaciation of the tashkurgan valley southeast pamir the quaternary glacial history of tashkurgan valley in the transition between the pamir and karakoram in xinjiang province china was examined using remote sensing field mapping geomorphic analysis of landforms and sediments and 10be terrestrial cosmogenic nuclide dating moraines were assigned to four glacial stages 1 the dabudaer glacial stage that dates to the penultimate glacial cycle and or earlier and may represent one or more glaciations 2 the tashkurgan glacial stage that dates to early last glacial most likely marine oxygen isotope stage mis 4 3 the hangdi glacial stage that dates to mis 2 possibly early mis 2 and 4 the kuzigun glacial stage that dates to the mis 2 possibly the global last glacial maximum and is younger than the hangdi glacial stage younger moraines and rock glaciers are present at the heads of tributary valleys but these were inaccessible because they are located close to politically sensitive borders with pakistan afghanistan and tajikistan glaciers during the dabudaer glacial stage advanced into the central part of the tashkurgan valley during the tashkurgan glacial stages glaciers advanced several kilometers beyond the mouths of the tributary valleys into the tashkurgan valley glaciers during the hangdi and kuzigun glacial stages advanced just beyond the mouths of the tributary valleys glaciation in this part of the himalayan tibetan orogen is likely strongly controlled by northern hemisphere climate oscillations although a monsoonal influence on glaciation cannot be ruled out entirely

a late pleistocene glacial chronology from the kitschi kurumdu valley tien shan kyrgyzstan based on 10be surface exposure dating abstract surface exposure dating has become a helpful tool for establishing numeric glacial chronologies particularly in arid high mountain regions where radiocarbon dating is challenging due to limited availability of organic material this study presents 13 new 10be surface exposure ages from the kitschi kurumdu valley in the at bashi range tien shan three moraines were dated to 15 21 and 56 ka respectively and corroborate previous findings that glacial extents in the tien shan during marine oxygen isotope stage mis 2 were limited compared to mis 4 this likely documents increasingly arid conditions in central asia during the last glacial cycle morphological evidence in the kitschi kurumdu valley and a detailed review of existing numeric glacial chronologies from the tien shan indicate that remnants of the penultimate glaciation mis 6 are preserved whereas evidence for mis 5 glacier advances remains equivocal reviewed and recalculated exposure ages from the pamir mountains on the other hand reveal extensive mis 5 glacial extents that may indicate increased monsoonal precipitation the preservation of mis 3 moraines in the tien shan and the southern pamir does not require any monsoonal influence and can be explained alternatively with increased precipitation via the westerlies

pleistocene glaciations of central asia results from 10be surface exposure ages of erratic boulders from the pamir tajikistan and the alay turkestan range kyrgyzstan abstract we have determined the timing of glaciations in the pamir tajikistan and the alay turkestan range kyrgyzstan using 10be surface exposure dating glacial advances in the area have occurred 93 136 60 80 40 55 27 25 22 20 19 17 16 15 15 13 and 11 9 cal ka bp all late pleistocene glaciers in the pamir and the alay turkestan ranges have been valley glaciers except for the most extended glaciers on the pamir plateau which have formed local piedmont glaciations in the eastern pamir these are characterized by ela depressions of 370 380 m thar 0 5 in the turkestan range and alay range ela depressions at the same time were 750 and 600 m respectively late pleistocene glacier advances all over western high asia were contemporaneous with climatic cold phases rather than monsoonal maxima their maximum extent and that of the western hemisphere ice sheets were asynchronous due to increasing aridity in the region over the course of the last glacial late pleistocene climate in central asia seems to have been influenced by the interplay of the westerly circulation and the siberian anticyclone some indirect monsoonal influence in the eastern pamir may be responsible for the existence of some of the lateglacial moraine stages in this area high altitude glaciers seem to have reached their maximum extent earlier mis 5 4 than low altitude glaciers first half of mis 3 possibly due to prolonged glacial aridity imparting with moisture advection onto high altitude sites inducing glacial retreat but prolonged cold during the same time imparting with glacier ablation at lower altitude sites inducing glacial advance

timing and style of late quaternary glaciation in northeastern tibet glacial successions in the anyemaqen and nianbaoyeze mountains of northeastern tibet are reassessed and new glacial chronologies are presented for these regions cosmogenic radionuclide and optically stimulated luminescence dating indicates that two glacial advances occurred in marine isotope stage mis 3 and mis 2 in the anyemaqen mountains a third advance occurred in the early holocene we suggest that glaciation was synchronous in the anyemaqen and nianbaoyeze mountains as well as in other glaciated areas of tibet and the himalaya that are influenced by the asian monsoon the maximum extent of glaciation occurred early in the last glacial cycle mis 3 during a time of increased insolation when the monsoon intensified and supplied abundant precipitation as snow at high altitude to feed high altitude glaciers this suggests that precipitation as snow is fundamental in controlling glaciation in these regions however the occurrence of glacial advances during the insolation minimum of mis 2 suggests that despite reduced precipitation at this time the annual temperatures were cold enough to maintain positive glacier mass balances the numerically defined chronologies for the anyemaqen and nianbaoyeze mountains presented here provide a framework for comparing glacial advances in other parts of high asia

tectonic influences on carbonate deposition and diagenesis buckhorn asphalt deese group desmoinesian arbuckle mountains oklahoma abstract the dry branch section is a mixed siliciclastic carbonate sedimentary sequence containing carbonate rocks that experienced incomplete diagenesis due to early introduction of oil from the oil creek formation ordovician the section is part of the deese group desmoinesian exposed in the western portion of the mill creek graben arbuckle mountains oklahoma the sequence was deposited in shallow marine shelf setting within a tectonically active basin deposition was strongly influenced by adjacent terrigenous coastal depositional environments the section was synclinally deformed by wrench faults to the north which were active soon before and after deposition two of these faults cut both the dry branch section and the underlying oil creek formation a known petroleum reservoir and t e source of fault related oil seeps throughout the central arbuckle region these faults acted as avenues for reservoir fluids to enter section as a result of remigration driven by orogenic stress carbonate rocks which show evidence of diagenesis influenced by reservoir fluids are present in the upper part of the section limited cementation overcompaction and arrested carbonate diagenesis resulted from the effects of interstitial asphalt which formed as a result of intraformational biodegradation of oil creek oil stratigraphic variation in petrologic characteristics suggests that oil introduction into dry branch sediments occurred as a single event within 10 000 years of deposition of uppermost part of section coinciding regionally with the desmoinesian ouachita orogenic pulse dia enesis has resulted in moderate isotopic depletion of altered fossils 418o 3 5 13c relative to unaltered skeletal aragonite 18o 0 to 1 13c 3 7 to 5 0 petrographic and stable isotopic study shows that two phases of early carbonate cementation affected dry branch carbonates 1 early clear spar that is more depleted in 18o 5 than the altered fossils 2 later spar which contains asphalt inclusions microspar and poikilotopic sparry cement present in the upper dry branch are anomalously depleted in 13c 20 this is close to the isotopic compositional range of asphalt in the section indicating that organic carbon derived from oil biodegradation was present in the porewater during diagenesis carbonate geochemical and petrographic evidence and the early post depositional tectonic introduction of oil indicate that subsurface water was a principal diagenetic agent

east asian monsoon climates and gobi dynamics in marine isotope stages 4 and 3 abstract several thick last glacial loess sequences in the western part of the chinese loess plateau and an eolian colluvial sequence in the central mongolian plateau are used to understand how the summer and winter monsoons responded to global forcing factors during marine isotope stages mis 4 and 3 the magnetic susceptibility data are compared with other climatic proxy data to improve the well publicized reconstruction of the past monsoons this study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages which were characterised by cold and wet climates in the western part of chinese loess plateau after forest steppe in mis 5 coniferous forest emerged at the mis 5 mis 4 transition in cold and moist conditions these imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior and that the mongolian high became dominant when the northern insolation entered a stadial state mis 4 coniferous forest dominated mis 4 but thereafter deteriorated to a steppe towards the end of the mis 4 probably because the lower latitude oceans failed to supply water vapour to the interiors a coniferous forest emerged again at the mis 3 mis 2 transition after forest steppe in mis 3 consequently the southern boundary of the gobi desert retreated northwards during the coniferous tree dominated periods between 73 and 60 ka and between 27 and 19 ka and expanded to maxima between 60 and 50 ka and between 19 and 10 ka the extent of the gobi desert was considerably smaller for several times around 47 ka and 41 ka and 27 ka during mis 3 than during the holocene and the northern boundary retreated 5 times around 20 ka 24 ka 29 ka 31 ka and 34 ka in just the later part of mis 3

asynchronous glaciations in arid continental climate abstract mountain glaciers at 26 19 ka during the global last glacial maximum near the end of the last 10 5 yr glacial cycle are commonly considered on the basis of dating and field mapping in several well studied areas to have been the largest of the late quaternary and to have advanced synchronously from region to region however a numerical sensitivity model rupper and roe 2008 predicts that the fraction of ablation due to melting varies across central asia in proportion to the annual precipitation the equilibrium line altitude of glaciers across this region likely varies accordingly in high altitude cold and arid regions sublimation can ablate most of the ice whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone but extend downhill until higher temperatures there cause them to melt we have conducted field studies and 10 be dating at five glaciated sites along a precipitation gradient in mongolia to test the rupper roe model the sites are located in nearby 1 875 1 875 cells of the rupper roe model each with a different melt fraction in this little studied region the modern environment of the sites ranges from dry subhumid in the north 47 7 n to arid in the south 45 n our findings show that the maximum local advances in the dry subhumid conditions predated the global last glacial maximum and were likely from mis 3 however we also found that at 8 7 ka a cirque glacier in one mountain range of the arid gobi desert grew to a magnitude comparable to that of the local maximum extent this holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the pleistocene glaciers globally this asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature although precipitation also plays a role our findings are consistent with and support the rupper roe model which calls for glaciation in arid conditions only at high altitudes of sub freezing temperatures where the melt fraction in ablation is low we expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions an individual glacier advance should not be necessarily interpreted as evidence of cooling climate

paleoshoreline geomorphology of boon tsagaan nuur tsagaan nuur and orog nuur the valley of lakes mongolia abstract we conducted a preliminary study of paleoshoreline features associated with boon tsagaan nuur tsagaan nuur and orog nuur lakes located in the gobi altai transition zone of the valley of lakes dolina ozor which stretches from central to western mongolia the paleoshoreline features were first identified on radarsat satellite sar imagery we investigated the features during the 1998 field season of the joint mongolian russian american archaeological expedition to the gobi altai region we identified paleoshorelines of multiple elevations in the field which are considered to be relict beach ridges and wave cut terraces other paleolake landforms include spits and gilbert type deltas these landforms are complex large and well established implying that the paleolakes were stable for extended periods the reconstructed paleolakes cover extensive areas of the valley floor implying that hydrological and climatic conditions were very different in the past paleolake expansions may have occurred under a variety of circumstances one hypothesis is that the high lake stands occurred during the wetter period corresponding to the oxygen isotope stage 3 prior to the last glacial maximum lgm during the warmest early holocene and the late holocene or during all these periods if low evaporation rates due to lower temperatures glacier meltwater and possibly increased precipitation are important factors then the expansions may have occurred during the terminal late glacial period after the last glacial maximum the greatly expanded lakes in the gobi altai could have significantly affected the quaternary human demography and migration in the region

distribution and timing of holocene and late pleistocene glacier fluctuations in western mongolia despite being a key location for paleoglaciological research in north central asia with the largest number of modern and pleistocene glaciers and in the transition zone between the humid russian altai and dry gobi altai little is known about the precise extent and timing of holocene and late pleistocene glaciations in western mongolia here we present detailed information on the distribution of modern and late holocene glaciers and new results addressing the geomorphological differentiation and numerical dating by optically stimulated luminescence osl of pleistocene glacial sequences in these areas for the mongolian altai geochronological results suggest large ice advances correlative to marine isotope stages mis 4 and 2 this is in contrast to results from the khangai mountains central mongolia showing that significant ice advances additionally occurred during mis3 during the pleistocene glacial equilibrium line altitudes elas were 500 to 1000m lower in the more humid portion of the russian and western mongolian altai compared to 300 600 m in the drier ranges of the eastern mongolian altai pleistocene elas in the khangai mountains were depressed by 700 1000 m suggesting more humid conditions at times of major glaciation than in the eastern mongolian altai this paleo ela pattern reveals that the precipitation gradient from the drier to the more humid regions was more pronounced during glacial times than at present

seismic impedance inversion and interpretation of a gas carbonate reservoir in the alberta foothills western canada acoustic and simultaneous elastic impedance inversions of a 2d land seismic data set are performed to characterize a carbonate reservoir of mississippian age in the turner valley formation in the rocky mountain foothills of western canada the inversions produce p wave and s wave impedance sections ip and is respectively from which lame parameter density and sections are derived the ip data provide a separation between the clastics and carbonates the data provide an estimate of porosity distribution within the dolomitized limestone target deviations from baseline curves for water saturated carbonates of versus porosity versus porosity and is versus ip are interpreted as indicators of gas potential these indicators all provide similar spatial patterns of areas of high gas potential and are consistent with the gas occurence observed in a well

documenting the sand shale crossover all types of velocity data i e surface seismic and well log or sonic log data indicate that velocity in shallow unconsolidated sands is lower than in associated shales while velocity in older sands in more consolidated rock sequences is higher than in their associated shales as the low velocity sands compact to become the high velocity member in the sand shale sequence sand and shale velocities must become equal or crossover at some age and depth of burial if the same type of velocity data is used consistently this crossover occurs at the same depth and age of rocks in the geologic sequence as would be indicated by other types of velocity data even though the different kinds of velocities would not agree elsewhere if all rocks in the province are older and compacted this crossover of sand and shale velocities may not be observed or if observed may be very near the surface

asymmetric late pleistocene glaciations in the north basin of the baikal rift russia new morphological sedimentological and radiocarbon data of quaternary deposits from the northern baikal rift document at least three extensive late pleistocene glaciations at 50 ka 40 35 ka and 26 13 ka respectively during these periods valley glaciers advanced from the high rift shoulders 2500 m down to the present day coast of lake baikal 456 m in places the glaciers advanced beyond the present day shoreline into the lake basin as indicated by large moraines exposed in steep cliffs along the lakeshore furthermore stratigraphic relations between lacustrine sequences and glacial deposits as well as 14 c ages of two palaeo shorelines 10 and 4 m above the present lake level show that the last and the penultimate glaciations were followed by relative lake highstands these land based observations document a significant influence of late pleistocene glaciations on the sedimentary development of this lacustrine rift basin the northern baikal rift is characterized by an asymmetric half graben geometry that controls river drainage and sedimentation this asymmetry greatly influenced the development and spatial distribution of pleistocene glaciers on both rift margins on the western flank tilted fault blocks parallel to the rift served as topographic barriers for valley glaciers advancing toward the lake basin only in two locations glaciers could reach the present day coast on the eastern rift flank in contrast structure and drainage conditions allowed the development of numerous consequent streams providing thoroughfares and space for recurrent valley glaciations thus the glaciers on the eastern flank could advance beyond the present day lakeshore into the lake basin in numerous locations these observations indicate that asymmetric rift structure in combination with the effects of global cooling were the important controls on the pleistocene glacial development of the baikal rift

the relationship between acoustic properties and the petrographic character of carbonate rocks laboratory studies of the detailed relationships between acoustic properties and the petrographic character of brine and air saturated carbonate rocks with a wide range of facies porosities lithologies and rock fabrics indicate that porosity is the major factor influencing both p and s wave impedance and velocity primary lithology and secondary mineralogy have only a small influence on impedance and velocity combined use of p and s wave velocity data discriminates porosity changes from lithologic changes all other variables including pore fluid type and petrographic fabric have no significant influence on velocities laboratory measurements of p wave velocity under simulated in situ conditions reproduce well log velocity values reliably laboratory porosity velocity trends agree with the time average equation when the correct matrix velocities are used rock property results were used to interpret porosity lithology variations for an inverted seismic section from the williston basin where well

influence of precipitation seasonality on glacier mass balance and its sensitivity to climate change numerical calculations are described aimed at evaluating the influence of precipitation seasonality summer and winter on glacier mass balance first equilibrium line altitudes elas are modeled using idealized meteorological variables modeled climatic conditions summer mean temperature and annual precipitation at the ela of glaciers located within a winter accumulation pattern confirm the observational results of earlier studies however the ela of glaciers located within a summer accumulation climate pattern locates in a colder environment than that of glaciers located within a winter accumulation climate pattern this difference is mainly due to the annual snow accumulation and the surface albedo a warming test 1k reveals higher sensitivities for the glaciers located within a summer accumulation pattern than for the glaciers located within a winter accumulation pattern in a humid environment a significant decrease in snow accumulation on the glaciers located within a summer accumulation pattern directly causes higher sensitivities in an arid environment on the other hand the decreased summer snow induces accelerated melting by lowering the surface albedo and thus increasing absorption of solar radiation on the glaciers located within a summer accumulation pattern both influences are due to significant differences in summer precipitation this study shows the importance of precipitation seasonality on the climatic sensitivity of glacier mass balance which in previous studies has been linked only with annual precipitation

lp norm deconvolution1 the purpose of deconvolution is to retrieve the reflectivity from seismic data to do this requires an estimate of the seismic wavelet which in some techniques is estimated simultaneously with the reflectivity and in others is assumed known the most popular deconvolution technique is inverse filtering it has the property that the deconvolved reflectivity is band limited band limitation implies that reflectors are not sharply resolved which can lead to serious interpretation problems in detailed delineation to overcome the adverse effects of band limitation various alternatives for inverse filtering have been proposed one class of alternatives is l p norm deconvolution l 1 norm deconvolution being the best known of this class we show that for an exact convolutional forward model and statistically independent reflectivity and additive noise the maximum likelihood estimate of the reflectivity can be obtained by l p norm deconvolution for a range of multivariate probability density functions of the reflectivity and the noise the l norm corresponds to a uniform distribution the l 2 norm to a gaussian distribution the l 1 norm to an exponential distribution and the l 0 norm to a variable that is sparsely distributed for instance if we assume sparse and spiky reflectivity and gaussian noise with zero mean the l p norm deconvolution problem is solved best by minimizing the l 0 norm of the reflectivity and the l 2 norm of the noise however the l 0 norm is difficult to implement in an algorithm from a practical point of view the frequency domain mixed norm method that minimizes the l 1 norm of the reflectivity and the l 2 norm of the noise is the best alternative l p norm deconvolution can be stated in both time and frequency domain we show that both approaches are only equivalent for the case when the noise is minimized with the l 2 norm finally some l p norm deconvolution methods are compared on synthetic and field data for the practical examples the wide range of possible l p norm deconvolution methods is narrowed down to three methods with p 1 and or 2 given the assumptions of sparsely distributed reflectivity and gaussian noise we conclude that the mixed l 1 norm reflectivity l 2 norm noise performs best however the problems inherent to single trace deconvolution techniques for example the problem of generating spurious events remain for practical application a greater problem is that only the main well separated events are properly resolved

relic permafrost structures in the gobi of mongolia age and significance relict permafrost structures ice wedge casts and cryoturbation structures are present in the gobi of southern mongolia luminescence dates of sediments are presented to constrain the age of formation of permafrost structures these data show that there was a phase of permafrost development during the latter part of the last glacial after about 22 to 15 ka that resulted in cryoturbated sediments and ice wedge casts furthermore permafrost degradation occurred during late pleistocene times 13 10 ka and was absent during the early holocene these permafrost structures mark the southernmost evidence of permafrost in northern asia during late quaternary times and indicate that the mean annual air temperature was below approximately 6 c during their formation 1998 john wiley sons ltd

trace based and geostatistical inversion of 3 d seismic data for thin sand delineation an application in san jorge basin argentina argentina s san jorge basin which straddles the southern provinces of chubut and santa cruz in the heart of patagonia has been producing hydrocarbons since 1907 the region currently accounts for 32 of the country s production the existence and early geologic evolution of the basin is due to the same rift process responsible for the opening of the atlantic ocean in early jurassic times extensive direct faulting and local erosion accompanied the rift evolution thereby facilitating the accumulation of chiefly nonmarine terrigenous sediments well into the early cretaceous at this point andean tectonism became a major source of pyroclastic concentration in the sedimentary column it was also responsible for pervasive batholitic intrusions clastic deposition in the hydrocarbon producing zone is characterized by thick shale laminations of lacustrine and floodplain origin interspersed with much thinner and laterally sparse sand bodies the hydrocarbon reservoirs

lake surface fluctuations since the late glaciation at lake daihai north central china a direct indicator of hydrological process response to east asian monsoon climate abstract sediment retrieved by coring from the center of enclosed lake daihai in north central china and lacustrine sediments obtained from lake terrace outcrops were employed to reconstruct the lake surface fluctuations and the relationships with monsoon climate since the late glaciation based on accelerator mass spectrometry ams radiocarbon chronology before ca 13 ka bp the surface of the lake was lower indicating a deficiency of effective precipitation and dry climate the result of relatively decreased monsoon precipitation during ca 13 11 ka bp the lake surface ascended to a relatively higher level marking a significant increase of effective precipitation the climate became humid indicating strengthened monsoon rainfall then the lake surface experienced a sharp decline ca 11 10 ka bp this could suggest a severe reduction of effective monsoon precipitation and drier climate ca 10 9 0 ka bp the lake surface area expanded temporarily as the level rose denoting the amelioration of monsoon related effective precipitation and a relatively humid climate subsequently the lake surface declined at ca 9 0 7 3 ka bp reflecting the prevalence of dry climate and relatively decreased monsoon precipitation higher lake level and larger lake depth indicated large scale expansion of the lake surface at ca 7 3 3 2 ka bp despite some secondary fluctuations this implied plentiful monsoon related effective precipitation and more humid climate in the lake basin since ca 3 2 ka bp the lake surface has experienced a severe fall except for a minor rise around 2 0 ka bp indicating dry climate as a whole from waning monsoon precipitation and relatively increased evaporation the effective precipitation variations revealed by lake surface fluctuations in lake daihai since the late glaciation are not only related to forcing factors such as insolation and temperature driven air masses from the continent and the ocean but are also influenced by regional feedback from topography vegetation coverage and hydrological status

too young or too old evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages cosmogenic exposure dating has greatly enhanced our ability to define glacial chronologies spanning several global cold periods and glacial boulder exposure ages are now routinely used to constrai

paleoclimatic evolution of the uvs nuur basin and adjacent areas western mongolia abstract the investigations presented in this paper focus on the shifts in pleistocene glaciations and the geomorphic changes in landforms as well as lake level changes and aeolian deposits of the last glacial interglacial cycle including the holocene geomorphic evidence and high lake levels show that the climate was more humid before the last glacial maximum lgm however at least one arid phase also occurred during the second half of the lgm the climate was dry and cold turning to wet and cold during the late glacial of the last ice age fluctuations in humidity and temperature occurred during the holocene since about 2000 yr bp the impact of human activity has increased

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

paleotopography and erosion rates in the central hangay dome mongolia landscape evolution since the mid miocene abstract standing over 2 km above the surrounding topography and flanked by orogen scale strike slip faults the hangay dome in central mongolia is characterized by long wavelength high topography basaltic eruptions spanning 30 million years and an abundance of flat topped summit plateaus however despite decades of research the origin and timing of the intraplate hangay dome uplift continues to be debated using landsat imagery gis and cosmogenic beryllium 10 we employ geomorphic investigations of 1 paleotopography preserved beneath basalt flows of known age 2 erosion rates at various temporal scales and 3 the relative contribution of glacial activity to total erosion to provide insight into the nature of landscape evolution in the egiin davaa region of the central hangay dome since the middle miocene reconstruction of paleo valleys cut into paleozoic basement rock that exhibit a degree of local relief 600 m similar to the modern landscape sluggish mean erosion rates

the active temperate glacial landsystem a model based on breiðamerkurjokull and fjallsjokull iceland accurate interpretations of ancient glaciated terrains rely heavily on our knowledge of process form relationships in contemporary glacierized basins a landsystems model for temperate actively receding glaciers is presented based upon brei amerkurjokull and fjallsjokull iceland historical documentation maps and or aerial photography documenting recession since 1903 provide a unique series of snapshots of the evolving glacial geomorphology at these snouts this documentation is employed in association with sedimentological investigations to assess the evolution of sediment landform assemblages at active temperate glacier margins using the wealth of geomorphological and sedimentological information produced during the recent recession of brei amerkurjokull and fjallsjokull three depositional domains are recognized 1 areas of extensive low amplitude marginal dump push and squeeze moraines derived largely from material on the glacier foreland and often recording annual recession of active ice 2 incised and terraced glacifluvial forms such as recessional ice contact fans and hochsandur fans and simple and complex anabranched eskers and small areas of pitted outwash 3 subglacial landform assemblages of flutes drumlins and overridden push moraines located between ice marginal glacifluvial depo centres the lack of supraglacial sediment in active temperate glaciers like brei amerkurjokull and fjallsjokull generally precludes the widespread development of chaotic hummocky moraine the hummocky terrain previously termed kame and kettle topography has mostly evolved by melt out into a complex network of anabranched eskers over the period 1945 1998 or actually comprises pitted or kettled outwash sandar the tills across the foreland were emplaced by subglacial deformation and lodgement and comprise materials derived from pre existing stratified sediments in addition to localized abrasion of rock surfaces and patches of lake sediments till sequences thicker than 2 m have been constructed by the sequential plastering of till layers onto stratified sediments and bedrock because this stacking is a sub marginal process it is suggested that complex till sequences similar to those observed at brei amerkurjokull fjallsjokull may be employed in the reconstruction of ancient glacier margins additionally the geomorphology of the active temperate landsystem at east brei amerkurjokull may contain subtle surge signatures verifying the historical record of small surges by this part of the glacier this illustrates the danger of employing landform sediment associations from restricted study areas e g parts of landsystems as representative process form models for glaciated terrains

late holocene vegetation history suggests natural origin of steppes in the northern mongolian mountain taiga abstract insular occurrences of steppe vegetation are a common feature of the northern mongolian mountain taiga steppe vegetation is limited here to southern slopes whereas northern slopes and valley bottoms are principally wooded with light and dark taiga forests in a case study in the valley of the river eroo at khonin nuga research station in the western khentey mountains we searched for evidence of an anthropogenic versus natural origin of steppe vegetation on the southern slopes pollen data of three profiles covering the last 2500 years showed continuous presence of steppe throughout the late holocene with human influence restricted to the recent past virtual absence of charcoal in the soil on and beneath three steppe slopes suggested that the present steppe grasslands are not replacing former forests burnt by humans or lightning the floodplains in the center of the eroo valley were recently deforested this is suggested by the pollen analysis and by interviews with local people on landuse history steppe grasslands of the study area have probably never been used as pastures pastoral nomads traditionally avoided the eroo valley near khonin nuga because of difficult access and high densities of wolves and bears all our data suggest that the present vegetation pattern of the western khentey with steppes and single small ulmus pumila trees on south facing slopes occurring as islands in the mountain taiga is driven by climate and relief and is not the result of human activities as suggested for other regions of asia

surface exposure dating reveals mis 3 glacial maximum in the khangai mountains of mongolia abstract this study presents results from geomorphological mapping and cosmogenic radionuclide dating 10be of moraine sequences at otgon tenger 3905 m the highest peak in the khangai mountains central mongolia our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during marine oxygen isotope stage mis 3 large ice advances also occurred during mis 2 at 23 and 17 16 ka but these advances did not exceed the limits reached during mis 3 the results indicate that climatic conditions during mis 3 characterized by a cool wet climate with a greater than today input from winter precipitation generated the most favorable setting for glaciation in the study region yet glacial accumulation also responded positively to the far colder and drier conditions of mis 2 and again during the last glacial interglacial transition when precipitation levels increased viewed in context of other pleistocene glacial records from high asia the pattern of glaciation in central mongolia shares some features with records from southern central asia and ne tibet i e ice maxima during interstadial wet phases while other features of the mongolian record i e major ice expansion during the mis 2 insolation minimum are more in tune with glacier responses known from siberia and western central asia

constraining the timing of the most recent cataclysmic flood event from ice dammed lakes in the russian altai mountains siberia using cosmogenic in situ 10be ice dammed lakes were repeatedly formed in intermontane basins in the russian altai mountains throughout the pleistocene these cataclysmic outburst floods caused by ice dam failures were documented as earth9s largest flood waves by other geoscientists using in situ 10 be we successfully dated surfaces of flood associated boulders located in a former lake basin and downvalley from a former ice dam our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15 8 1 8 ka the field location of the boulders implies that they were deposited by the largest late pleistocene flood that drained the chuya katun lake completely following initial dam failure a published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers the failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern russia this flooding event in the headwaters of the ob river coincides with a freshwater peak as recorded in isotopic records of the kara sea and the arctic ocean

the late pleistocene glaciation in the bogchigir valleys pamir tajikistan based on 10be surface exposure dating abstract glacial chronologies from the pamir may not only provide insights into past changes in temperature but also into past changes in precipitation related to the northern hemispheric westerlies and the monsoonal circulation we present 18 new exposure ages from the bogchigir valleys that complement and refine our previous studies in these valleys the most extensive dated glaciation in the area occurred 100 ka during marine oxygen isotope stage mis 5 and indicates increased precipitation likely from both the westerlies and the monsoonal circulation a subsequent glacier advance which deposited characteristic chukur moraine lobes occurred at 80 75 ka circumstantial evidence points to glacial advances at 65 and 40 ka the latter likely also documenting increased monsoonal moisture supply during mis 3 less extensive glacial advances occurred during mis 2 at 28 and 24 ka and reflect the aridization trend during the course of the last glacial cycle deglaciation started 21 ka interrupted by minor stillstands or readvances at 16 and 12 ka local calibration sites and glacier climate modeling would be very helpful to reduce the systematic methodological uncertainties still at least 10 and to draw more detailed paleoclimatic conclusions

high time resolution ams 14c data sets for lake baikal and lake hovsgol sediment cores changes in radiocarbon age and sedimentation rates during the transition from the last glacial to the holocene abstract high time resolution 14 c dating of lake baikal sediment cores indicates negative and positive anomalies of calculated linear sedimentation rate lsr 1 1 and 35 6 cm ka respectively during the period of climate transition from the last glacial to holocene the timing of the lake baikal apparent lsr anomalies is consistent with that of the changes in the atmospheric radiocarbon concentration 14 c during younger dryas rapid cooling event 14 c dating of lipids in the lake baikal surface sediments revealed that the sources of sedimentary lipids were different in each basin in the northern basin of lake baikal the 14 c age of total lipids from the surface sediment 4 0 14 c ka was found to be older than that of toc 1 6 14 c ka by contrast the 14 c age of total lipids in the southern basin was younger than that of the toc by ca 0 7 3 0 ka in the lake hovsgol sediment cores ages of the main lithologic boundaries during the last glacial interglacial transition were estimated based on new 14 c data sets toc concentration in the cores started to rapidly increase at 13 8 0 3 14 c ka at the base of the basinwide finely laminated layer deposited during bolling allerod the base of the layer diatomaceous mud corresponds to the end of younger dryas event 10 6 0 1 14 c ka

late pleistocene glaciers in darhad basin northern mongolia abstract late pleistocene glaciers around darhad basin advanced to near their maximum positions at least three times twice during the zyrianka glaciation at 17 19 ka and 35 53 ka and at least once earlier the zyrianka glaciers were smaller than their predecessors but the equilibrium line altitude ela difference was 14 c and luminescence dating of lake sediments confirm the existence of paleolake highstands in darhad basin before 35 ka geologic evidence and 10 be cosmic ray exposure dating of drift suggests that at 17 19 ka the basin was filled at least briefly by a glacier dammed lake 140 m deep however lake sediments from that time have not yet been recognized in the region a shallower paleolake briefly occupied the basin at 11 ka but between 11 and 17 ka and after 10 ka the basin was probably largely dry the timing of maximum glacier advances in darhad appears to be approximately synchronous across northern mongolia but different from siberia and western central asia supporting the inference that paleoclimate in central asia differed among regions

avo analysis in high impedance sandstone reservoirs avo analysis is now established as an effective hydrocarbon detection tool in many exploration provinces in most areas in which it is widely used the impedance of the reservoir rocks is less than or equal to the impedance of the surrounding rocks the avo response of low impedance reservoirs is an increase in amplitude with offset methodologies for detecting and analyzing these types of avo anomalies have been developed and have resulted in greatly increased drilling success ratios for some formations such as the yegua formation of onshore texas

integrated geological and geophysical interpretation case study and lame rock parameter extractions using avo analysis on the blackfoot 3c 3d seismic data southern alberta canada blackfoot field southeast of calgary alberta canada has produced oil and gas from a glauconitic compound incised valley system the glauconitic compound incised valley has three cycles of incision and valley fill lower lithic and upper incised valleys the upper and lower incised valleys are the main reservoirs the geophysical interpretation of compressional pp seismic data resulted in the definition of the compound valley extent and in the mapping of the upper and lower incised valleys a stratigraphic well log template was built using the most significant lithological information and well logs to integrate both geological and geophysical interpretations the well log cross sections and corresponding depth converted seismic were superimposed furthermore a detailed geological facies interpretation of the upper and lower incised valleys was undertaken and incorporated a good correlation was found between the interpreted geological facies and the seismic data response information about the natu

last glacial maximum climate of the former soviet union and mongolia reconstructed from pollen and plant macrofossil data an improved concept of the best analogues method was used to reconstruct the last glacial maximum lgm climate from a set of botanical records from the former soviet union and mongolia terrestrial pollen and macrofossil taxa were grouped into broad classes plant functional types pfts defined by the ecological and climatic parameters used in the biome1 model pft scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from eurasia and north america in contrast to individual taxa which exhibit great variability and may not be present in the palaeoassemblages even in suitable climates pfts are more characteristic of the vegetation types the modified method thus allows climate reconstruction at time intervals with partial direct analogues of modern vegetation e g the lgm at 18 kbp mean temperatures were 20 29 degrees c colder than today in winter and 5 11 degrees c colder in summer in european russia and ukraine sites from western georgia show negative but moderate temperature anomalies compared to today 8 11 degrees c in january and 5 7 degrees c in july lgm winters were 7 15 degrees c colder and summers were 1 7 degrees c colder in siberia and mongolia annual precipitation sums were 50 750 mm lower than today across northern eurasia suggesting a weakening of the atlantic and pacific influences reconstructed drought index shows much drier lgm conditions in northern and mid latitude russia but similar to or slightly wetter than today around the black sea and in mongolia suggesting compensation of precipitation losses by lower than present evaporation

altai megafloods the temporal context abstract pleistocene floods from ice dammed lakes in the russian altai mountains are among the largest freshwater megafloods in earth history improved dating techniques have led to new dates constraining the timing of flood erosional and depositional events in addition to a variety of interpretations and explanations of event histories a proliferation of dates may increase confusion with respect to the characteristics and chronology of the flood events in a succinct review the main ice dammed lakes features the outburst floods and their repeated formation are presented among other indicators interbedded units of lacustrine deposits and outburst flood sediments in inya river valley demonstrate conclusively that there was a series of outburst floods with significant evidence for at least three high magnitude flood events prior study focussed on the interpretation of lake sediments shorelines giant bars gravel dunes dated by radiocarbon luminescence and cosmogenic nuclide assay the literature presents sometimes contradictory findings with respect to flood chronology these different interpretations evidence and arguments are reviewed for plausibility and consistency this consideration includes methodical and technical dating problems limited bleaching for luminescence techniques low purity for cosmogenic nuclide dating contamination of samples dated by radiocarbon assay at the current stage of knowledge the main period of repeated high magnitude outburst floods occurred between 28 ka and 15 ka bp indicators of earlier events are less distinct possible younger smaller floods can be identified after 15 ka bp but it is difficult to relate these to catastrophic lake draining rather they may relate to non catastrophic draining of residual small lakes within the larger basins the termination of the lake period took place before 9 9 0 3 ka cal bp in the kuray basin and in the chuya basin before 8 2 0 2 ka cal bp indicators are lacking for any drainage events after 7 7 0 6 ka as indicated by osl ages of aeolian deposits at low elevations in the katun valley relating the outburst floods to the temporal and spatial dynamics of the impounding glacier is challenging as with regard to pleistocene glaciation several conceptual models have been established supported by field evidence that in part can be contradictory during the period of the high magnitude outburst floods the extension thickness of the impounding valley glaciers were sufficient to form deep glacial lakes around the time of the last glacial maximum lgm yet the timing of the lgm remains controversial transferring glacial chronologies from mountain areas adjacent to the russian altai mountains to the environment of the megafloods does not provide a clearer picture as there is evidence for maximum stages at mis 4 and mis 3 in addition to recent postulations of a lgm in mis 2 for the russian altai mountains the russian altai mountains are located in a climatic transitional zone across which different lgm stages could be developed due to different moisture availability and temperature chronologies the effects of spatially variable rain shadows influencing the supply of moisture from the regional prevailing winds and local moisture sources from expanded ice dammed lakes complicates the picture and require further investigations

geomorphological investigations and luminescence dating in the southern part of the khangay and the valley of the gobi lakes central mongolia geomorphological investigations in the catchment area of the baydragiyn river along the southern slope of the khangay and in the valley of the gobi lakes in western mongolia provide evidence for late quaternary glaciations and lake level changes thermoluminescence tl and infrared optically stimulated luminescence irsl dating of aeolian and colluvial sediments from the central khangay place the sediments that overlie fluvial and glaciofluvial terraces in the holocene an age of 21 ka is determined for a sand deposit overlying the terrace that is related to the last glacial ice margin lacustrine sediments from higher beach lines in the valley of the gobi lakes provide evidence for a slightly more humid period around 1 5 ka and a larger extent of the lakes in the early holocene at about 8 5 ka as also reported from other parts of central asia remnants of lacustrine sediments buried by alluvial gravel and indicating a huge palaeolake in the basin of the orog nuur however date to the early stage of the last glaciation around 70 ka copyright 2001 john wiley sons ltd

toward a late holocene glacial chronology for the eastern nyainqentanglha range southeastern tibet abstract monsoonal affected temperate glaciers in the eastern nyainqentanglha range southeastern tibet are highly sensitive to climate change knowledge about their late holocene dynamics is still however widely lacking the few studies on glacial chronology which are available for this region tend to mainly focus on dating results without sufficiently considering the geomorphological setting often leading to misinterpretations in this complex high mountain environment in this study two selected glacier forelands are investigated using a multi proxy approach encompassing detailed geomorphological mapping dendrochronology sedimentology and optically stimulated luminescence as well as radiocarbon dating the starting point was the creation of a consistent morphosequence which was validated by remote sensing of further glacier forelands from the wider region similarities and differences between the investigated settings were analyzed in detail to identify the relevant morphological and topoclimatic forcing mechanisms we found evidence of climatic events affecting the whole region during the little ice age resulting in similar configurations and numbers of moraines the geomorphological settings of the glacier forelands are however remarkably different making investigations of the landform and sediment configuration an indispensable condition for their interpretation subsequently constraints from different methods of relative and numerical dating were evaluated critically and included into a conceptual chronosequence if applicable our results suggest that the late holocene maximum glacier advance comprised several successive advances from mid 17th to mid 18th century none of our observations supports an earlier neoglacial advance reaching further than the lia maximum after the lia maximum continued retreat that was only interrupted by short phases of stability followed as evidenced by 2 3 recessional moraines in the investigated settings

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

late quaternary lake level record from northern eurasia lake records from northern eurasia show regionally coherent patterns of changes during the late quaternary lakes peripheral to the scandinavian ice sheet were lower than those today but lakes in the mediterranean zone were high at the glacial maximum reflecting the dominance of glacial anticyclonic conditions in northern europe and a southward shift of the westerlies the influence of the glacial anticyclonic circulation attenuated through the late glacial period and the westerlies gradually shifted northward such that drier conditions south of the ice sheet were confined to a progressively narrower zone and the mediterranean became drier the early holocene shows a gradual shift to conditions wetter than present in central asia associated with the expanded asian monsoon and in the mediterranean in response to local monsoon type circulation there is no evidence of mid continental aridity in northern eurasia during the mid holocene in contrast the circum baltic region was drier reflecting the increased incidence of blocking anticyclones centered on scandinavia in summer there is a gradual transition to modern conditions after ca 5000 yr b p although these broad scale patterns are interrupted by shorter term fluctuations the long term trends in lake behavior show a clear response to changes in insolation and glaciation

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

lake evolution in the tengger desert northwestern china during the last 40 000 years climatic changes inferred from lacustrine deposits and lake level fluctuations in northwestern and central china are mainly based on paleoclimatic records from the tibetan plateau while there is still a lack of data relating to the semiarid arid desert regions of inner mongolia in the tengger desert different paleolake levels at baijian hu are documented by six paleoshorelines and stratified lake carbonates the highest lake level occurred ca 39 000 14c yr b p and prevailed over about 16 000 km2 from sediment structure geochemical composition and ostracods we infer humid cool conditions until 23 000 14c yr b p in the northern badanjilin desert at gaxan nur sogu nur high lake levels can be deduced from mollusc bearing paleobeaches and lake carbonates which have been dated to 34 000 14c yr b p and indicate a lake that covered some 32 000 km2 after ca 20 000 yr b p the climate became dry with increased eolian activity and decreasing lake levels reestablishment of wet conditions occurred ca 13 000 yr b p the holocene is represented by stratified lake deposits that alternate with fluvial and eolian deposits indicating a longterm oscillating trend toward arid conditions the existence of widespread freshwater lakes during the late pleistocene indicates a semihumid climate without an accompanying fall in temperature to arctic conditions

complex patterns of glacier advances during the late glacial in the chagan uzun valley russian altai abstract the southern part of the russian altai mountains is recognized for its evidence of catastrophic glacial lake outbursts however little is known about the late pleistocene paleoglacial history despite the interest in such reconstructions for constraining paleoclimate in this study we present a detailed paleoglaciological reconstruction of the chagan uzun valley in the russian altai mountains combining for the first time detailed geomorphological mapping sedimentological logging and in situ cosmogenic 10be and 26al surface exposure dating of glacially transported boulders the chagan uzun valley exhibits the most impressive glacial landforms of this sector of the altai with extensive lobate moraine belts deposited in the intramontane chuja basin reflecting a series of pronounced former glacial advances observations of hillside scale folding and extensive faulting of pre existing soft sediments within the outer moraine belts together with the geomorphology strongly indicate that these moraine belts were formed during surge like events identification of surge related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate but instead largely influenced by various internal and external factors therefore no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the chagan uzun valley chuja basin in contrast the inner up valley glacial landforms of the chagan uzun valley were likely deposited during retreat of temperate valley glaciers close to equilibrium with climate and so most probably triggered by a general warming cosmogenic ages associated with the outermost innermost and intermediate moraines all indicate deposition times clustered around 19 ka however the actual deposition time of the outermost moraine may slightly predate the 10be ages due to shielding caused by subsequent lake water coverage this chronology indicates a marine isotope stage mis 2 last maximum extent of the chagan uzun glacier and an onset of the deglaciation around 19 ka this is consistent with other regional paleoclimate proxy records and with the northern hemisphere glaciation chronology finally this study also highlights the highly dynamic environment in this area with complex interactions between glacial events and the formation and drainage of lakes

changes in the volume and salinity of lake khubsugul mongolia in response to global climate changes in the upper pleistocene and the holocene two gravity cores 1 1 and 2 2 m long of deep water bottom sediments from lake khubsugul mongolia were studied the holocene biogenic silica and organic matter rich part of the first core was subjected to ams radiocarbon dating which placed the date of dramatic increase of pelagic diatoms 40 cm below sediment surface at a calendar age of 11 5 cal ky bp icp ms analysis of weak nitric acid extracts revealed that the upper pleistocene compared to the holocene samples were enriched in ca cinorg sr mg and depleted of u w sb v and some other elements transition to the holocene resulted in an increase of total diatoms from 0 to 108 g 1 of bisi from 1 to 20 of organic matter from 6 the bolling allerod younger dryas holocene abrupt climate oscillations manifested themselves in oscillations of geochemical proxies a remarkable oscillation also occurred at 22 cm ca 5 5 ky bp the pleistocene section of the second longer core was enriched in carbonate co2 up to 10 and water extractable so42 up to 300 times greater than that in holocene pore waters all this evidence is in an accord with the earlier finding of drowned paleo deltas at ca 170 m below the modern lake surface of the lake dokl akad nauk 382 2002 261 and suggests that due to low ca 110 mm regional precipitation at the end of the pleistocene lake khubsugul was only 100 m deep and that its volume was ca 10 times less than today

aspects of late quaternary geomorphological development in the khangai mountains and the gobi altai mountains mongolia abstract the reconstruction of geomorphological processes as a result of environmental change is approached by investigating and dating some fluvial aeolian and lacustrine archives at specific locations that form a n s basin and range transect across the khangai mountains south to the eastern gobi altai mountains in mongolia geomorphological processes varied a spatially with different climatic conditions and vegetation cover in relation to different elevation and latitude and b temporally due to climatic shifts during the late quaternary in total 15 sections from three distinct sub regions along that transect were dated by 22 osl ages the khangai mountain sub region exhibits mainly late glacial to holocene aeolian silty to sandy cover sediments mainly in the upper catchment reaches 1800 m a s l sections in the northern and central gobi represent river terraces and alluvial fans in basin areas as well as aeolian sediments in the mountains above 2200 m a s l the oldest terrace surface found in this study t2 nga1 dates to the penultimate glacial cycle the t1 terrace surfaces on the northern khangai mountain front and in the central gobi sub region yield a maximum accumulation during the global last glacial maximum glgm and late glacial time during the glgm phase represents rather sheetflow dominated transport built the alluvial fans and in late glacial times the sediments exhibit more debrisflow controlled accumulation incision forming the t1 terrace edges is therefore supposed for the pleistocene holocene transition and subsequent early holocene the geomorphic evidence is interpreted as stronger fluvial morphodynamics induced by enhanced humidity under beginning interglacial conditions these processes coincided with the development of aeolian mantles at higher altitudes in the khangai and gobi altai mountains where higher temperatures and humidities supported the formation of a vegetation cover that served as a dust trap at least since late glacial times and reduced the sediment supply on the alluvial fans

palaeoglaciology of bayan har shan ne tibetan plateau exposure ages reveal a missing lgm expansion the bayan har shan a prominent upland area in the northeastern sector of the tibetan plateau hosts an extensive glacial geological record to reconstruct its palaeoglaciology we have determined

reservoir characterization of the flag sandstone barrow sub basin using an integrated multiparameter seismic avo inversion technique editor s note this material was presented at the 17th aseg geophysical conference and exhibition a series of oil and gas fields have been discovered since 1979 in the early cretaceous flag sandstone in the barrow sub basin of western australia s carnarvon basin the flag sandstone is a lowstand complex of gravity flow sandstones deposited beyond the shelf edge of the barrow delta figure 1 shows a stratigraphic chart the permeable flag sandstone forms a consistent high quality reservoir that is capped by the impermeable muderong shale in the area immediately adjacent to and south of varanus island the main trapping mechanism is four way dip closed anticlines formed by drape compaction structural closure alone does not appear sufficient for oil emplacement as a limited number of prominent closed structures have been drilled and found water wet the known oil fields are nearing depletion and the goal is to properly locate additional wells to ensure complete development of the area figure 1 stratigraphic chart for carnarvon basin showing the early cretaceous flag sandstone and overlying muderong shale barrow sub basin the identification of the closed anticlinal structures on seismic data is complicated due to a poor p impedance contrast between the flag sandstone and the overlying muderong shale however a strong v p v s contrast exists between the sandstone and shale resulting in reasonably consistent avo class ii effects a far angle stack with an angle range of 30 45 has been used successfully to map the structure on the top of the flag sandstone the difficulty with this mapping technique is that it is subject to tuning effects and assumes a consistent avo response however some wells in the area demonstrate an avo response that does not match a simple model thus a more robust technique was required that could model the true avo response provide an accurate pick

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

late quaternary environments in the gobi desert of mongolia vegetation hydrological and palaeoclimate evolution abstract considerable efforts have been devoted to decipher the late quaternary moisture and thermal evolution of arid central asia however disparate interpretations still exist concerning different proxies the spatial and temporal heterogeneities have inhibited a holistic understanding of general patterns and underlying mechanisms to address these issues two parallel cores onw i 6 00 m onw ii 13 35 m were retrieved in the gobi desert of mongolia from lake orog nuur multidisciplinary investigations including geomorphological mapping radiocarbon dating sedimentological palynological and ostracod analyses enabled us to gain a comprehensive dataset for vegetation development and hydrological variability over the last 45 kyr higher lake levels during the marine isotope stage mis 3 and early mis 2 35 24 kyr were probably caused by increased precipitation the sharp transition of termination i 11 kyr is indicated by sedimentological palynological and ostracod data during the late pleistocene the lower area of the orog nuur catchment was dominated by artemisia steppe and gradually altered to chenopodiaceae desert steppe in the holocene the early holocene is also characterized by a relatively humid environment the humid pulses during the mis 3 and the early holocene were also recorded in other archives and are possibly the trait of a larger scale phenomenon in arid central asia four major harsh climatic periods were documented in the core at 43 kyr 36 kyr during the global last glacial maximum and the younger dryas as playa phases reduced westerlies moisture transport and a retreated east asian summer monsoon influence probably caused those dry phases in the gobi desert of mongolia

timing of multiple late quaternary glaciations in the hunza valley karakoram mountains northern pakistan defined by cosmogenic radionuclide dating of moraines moraines and associated landforms in the upper hunza valley karakoram mountains northern pakistan provide an excellent record of multiple glaciations during the late quaternary glaciers advanced at least eight times by using 10 be and 26 al surface exposure dating on moraine boulders and scoured bedrock we determined the timing of glaciation for four of these glacial advances ca 54 7 43 2 ka borit jheel glacial stage ca 25 7 21 8 ka ghulkin i glacial stage ca 18 4 15 3 ka ghulkin ii glacial stage and ca 10 8 9 0 ka batura glacial stage for two of the older advances the yunz and shanoz glacial stages our data set a limit of 60 ka although at present the uncertainties in dating make it impossible to describe unequivocally the climate processes controlling glaciations in the hunza valley the results suggest that precipitation changes related to oscillations in the southwest asian monsoonal system combine with cooling that is broadly associated with heinrich events to cause glacial advances in this region

paleolakes in the gobi region of southern mongolia abstract numerous lakes and remnants of paleolakes exist in western and southern mongolia for six basins in the area detailed geomorphological maps were compiled based on extensive field studies and remote sensing datasets several phases of high and low lake levels were reconstructed and dated by radiocarbon and optically stimulated luminescence during the marine isotope stage mis 6 lakes in southern and western mongolia mostly disappeared in contrast large paleolakes existed during the last interglacial mis 5e and lasted probably until the beginning of the last glacial these huge lakes were caused by a strong east asian summer monsoon which reached southern and even western mongolia during the mis 3 the monsoon was considerably weaker and most of the lakes were relatively small or even disappeared higher lake levels of this period were only recorded at the orog nuur however at this time the lake was fed by glacial melt water from the khangai mountains the mis 2 was again a very dry period the previously supposed phase of synchronous high lake levels and glaciations in southern and western mongolia is not supported by the data presented here during the holocene lakes in the western and southern part of the study area evolved differently early holocene high lake levels were reconstructed for the western lakes while most of the southern lakes had highest lake levels in the mid holocene these differences can be attributed to different moisture bearing atmospheric systems in the late holocene lake levels were generally low and in the last 50 years most lakes completely disappeared due to a strong human usage of the water resources

palaeoclimate glacier and treeline reconstruction based on geomorphic evidences in the mongun taiga massif south eastern russian altai during the late pleistocene and holocene abstract little is known about the extent of glaciers and dynamics of the landscape in south eastern russian altai the effects of climate induced fluctuations of the glaciers and the upper treeline of the mongun taiga mountain massif were therefore reconstructed on the basis of in situ multiannual observations geomorphic mapping radiocarbon and surface exposure dating relative dating such as schmidt hammer and weathering rind techniques and palaeoclimate modelling during the maximal advance of the glaciers their area was 26 times larger than now and the equilibrium line of altitude ela was about 800 m lower assuming that the maximum glacier extent took place during mis 4 then the average summer temperatures were 2 7 c cooler than today and the amount of precipitation 2 1 times higher buried wood trunks by a glacier gave ages between 60 and 28 cal ka bp and were found 600 700 m higher than the present upper treeline this evidences a distinctly elevated treeline during mis 3a and c with a correction for tectonics we reconstructed the summer warming to have been between 2 1 and 3 0 c during mis 3c the glaciated area was reduced to less than 0 5 km2 with an increase of the ela of 310 470 m higher than today due to higher precipitation the glaciated area during mis 3a was close to the current ela exposure dating 10be would indicate that the maximum glacier extension was 24 ka bp but the results are questionable from a geomorphic point of view the maximum extent can more likely be ascribed to the mis4 stage we estimate a cooling of summer temperature of 3 8 to 4 2 c and a decrease in precipitation of 37 46 compared to the present day situation samples of wood having an age of 10 6 6 2 cal ka bp were found about 350 m higher than the present treeline it seems that the summer temperature was 2 0 2 5 c higher and annual precipitation was double that of the present day for that period the reconstructed glaciation area was 1 km2 less than today three neoglacial glacier advances were detected the glaciers covered about double the area during the little ice age lia summer cooling was 1 3 c with 70 of the present day precipitation the reconstructed amplitude of climatic changes and the shift of the altitudinal zones show that the landscape has reacted sensitively to environmental changes and that dramatic changes may occur in the near future

re evaluation of mis 3 glaciation using cosmogenic radionuclide and single grain luminescence ages kanas valley chinese altai previous investigations observed a period of major glacial advances in central asia during marine oxygen isotope stage mis 3 57 29 ka out of phase with global ice volume records we have re ex

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

climate variability in the salawusu river valley of the ordos plateau inner mongolia china during marine isotope stage 3 fluctuations in climatic proxies of the milanggouwan section in the salawusu river valley of the ordos plateau inner mongolia china during marine isotope stage 3 mis 3 coincide well with sedimentary cycles for palaeo mobile dune sands alternating with fluvial lacustrine facies and palaeosols we compared the palaeo mobile dune sands with modern mobile dune sands products of a cold and dry climate dominated by the east asian winter monsoon whereas the fluvial lacustrine facies and palaeosols were controlled by a wet warm climate similar to that of the east asian summer monsoon the mis 3 climate of the salawusu river valley appears to have experienced at least nine wet warm and ten cold dry fluctuations divided into five stages mis 3e 58 900 49500 yr bp mis 3d 49 500 40 700 yr bp mis 3c 40 700 36 900 yr bp mis 3b 36 900 27 000 yr bp and mis 3a 27 000 22 300 yr bp the 19 cold warm climatic fluctuations corresponded roughly to the grip and guliyan records and with fluctuations in the north atlantic climate notable peaks in the spectral analysis occurred at 19 500 yr 1020 yr 640 yr and 500 yr our results show that the millennial centennial climate was closely related to the relative strengths of east asian monsoons which are controlled by the north atlantic thermohaline circulation and which is also closely linked to the sun s precession period copyright 2008 john wiley sons ltd

extensive glaciation in transbaikalia siberia at the last glacial maximum abstract successively smaller glacial extents have been proposed for continental eurasia during the stadials of the last glacial period leading up to the last glacial maximum lgm at the same time the large mountainous region east of lake baikal transbaikalia has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations we have applied cosmogenic 10be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region based on eighteen exposure ages from five moraine complexes we propose that large mountain ice fields existed in the kodar and udokan mountains during oxygen isotope stage 2 commensurate with the global lgm these ice fields fed valley glaciers 100 km in length reaching down to the chara depression between the kodar and udokan mountains and to the valley of the vitim river northwest of the kodar mountains two of the investigated moraines date to the late glacial but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post lgm glacial history in addition to the lgm ice fields in the highest mountains of transbaikalia we report geomorphological evidence of a much more extensive ice cap type glaciation at a time that is yet to be firmly resolved

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s

late quaternary glaciation in the kyrgyz tien shan the tien shan of kyrgyzstan contains multiple moraines and drift from late quaternary glaciations the spatial temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture the dominant modern climatic signatures in northern central asia include orographic thunderstorms in summer cold and dry siberian high pressure cells in winter and westerly cyclonic storms from the north atlantic and eastern mediterranean in spring and fall changes in any of these systems during the late quaternary would have varied precipitation delivery to and glacier growth in the kyrgyz tien shan geomorphic mapping and reconnaissance level 10be cosmic ray exposure dating of moraine sequences in six drainages indicate that there were multiple maximum advances of similar extents and equilibrium line depressions across the range glaciers in the north and east of the kyrgyz tien shan last advanced to their maximum positions during marine oxygen isotope stage mis 5 and again during mis 4 while in the south and west of the range advance occurred during mis 3 in contrast to maritime europe and north america there is no evidence of a major glacial advance during mis 2 glacier advances during mis 2 and since were restricted to the vicinity of modern glaciers allowing the older glacial record to be preserved well