laboratory gouge friction seismic like slip weakening and secondary rate and state effects 1 we investigate experimentally the frictional response of a thick sample of simulated fault gouge submitted to very high shear displacements up to 40 m in an annular simple shear apparatus acsa the frictional strength of our granular material exhibits velocity weakening consistent with classical rate and state dependent friction laws the length scale involved in the latter phenomenon is dc 100 m however the evolution of friction is largely dominated by a significant slip weakening active over decimetric distances l 0 5 m interestingly these decimetric frictional length scales are quantitatively compatible with those estimated for natural faults during shearing a thin and highly sheared layer emerges from the thick and slowly deforming bulk of the sample because of the intermittent and non local coupling observed between these two zones we relate the large frictional length scales in our data to the slow structuring of the thick interface

a new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge i present results of a series of slide hold slide tests on granite surfaces separated by a layer of simulated granite gouge the shear stress during the hold period hold was controlled and used as a major control parameter of the experiments in addition to the time of hold time dependent fault healing which has been observed in many previous similar experiments was observed only at very high hold above 90 of the sliding friction a time independent strengthening termed consolidation strengthening occurred at all hold with a magnitude proportional to the reduction of hold the magnitude of this strengthening was as large as 25 of the residual friction the consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time dependent healing the friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening on the basis of these results together with earlier authors results of the measurements of porosity change under similar conditions i conclude that the time independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress under a constant normal stress and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement dilatancy during shearing the rate and state dependent friction rsf law was extended to incorporate the present findings

geochemistry of daihai lake sediments inner mongolia north china implications for provenance sedimentary sorting and catchment weathering abstract to advance the understanding of sediment distribution catchment weathering hydraulic sorting and sediment provenance in a tectonically stable basin the geochemistry of surface sediment samples from daihai lake in north china is presented mud bulk sediments were analyzed for 10 major and 30 trace elements organic carbon and nitrogen and for 87sr 86sr ratios in silicate fraction acid insoluble ai and carbonates acid soluble as enrichment in fe2o3 cao mno mgo k2o and p2o5 and their positive correlation with al2o3 rb sr ratios and bivariate discrimination diagrams of k vs rb and th u vs th suggest low chemical weathering intensity under semiarid conditions in the daihai catchment accumulation of clays in deeper water sites by sedimentary sorting results in an evident distribution of sediment composition with the lake water depth although similar chondrite normalized ree rare earth element patterns of lake sediment samples with lree light rare earth element enrichment negative eu anomalies and an almost flat hree heavy rare earth element pattern may suggest similar sedimentary source rocks original sediment provenance can be recognized on the basis of their distinctive 87sr 86sr ai ratios and immobile th zr ti and nb trace element signature separating from weathering and sedimentary processes as well as from grain size effect

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

reconstruction of woodland vegetation and firewood exploitation in nine mile canyon utah based on charcoal and pollen analysis abstract anthracological charcoal and pollen analysis conducted on samples from multiple sites in nine mile canyon utah western united states of america were used to reconstruct the woodlands of this region and interpret firewood exploitation during the formative period ad 200 1300 the pollen record identifies constituents of the paleoenvironment of this region reflecting species that grew in the vicinity of the site and in the broader area wood charcoal reflects various trees and shrubs that were used as fuel or for construction by the prehistoric occupants settled in nine mile canyon pollen results elucidate a portion of the spectrum of wood taxa which varies in different parts of the canyon depending on elevation and the canyon s topography while micro charcoal analysis has a long and rich tradition in association with pollen analysis anthracological analysis is different in that it focuses on macroscopic pieces of archaeological charcoal here anthracology using sem imagery helps define local woody taxa by identifying macroscopic pieces of archaeological charcoal these two analytical tools build a complementary record of local woodland vegetation through aerial pollen transport and fuel wood selection while the pollen record is affected by aerial transport the anthracological assemblages in most cases reflect species growing in the vicinity of the prehistoric settlements but can be affected by natural transport within the drainage recovery of douglas fir pseudotsuga menziesii charcoal from the lower portions of the canyon containing steep walls and natural conditions not favorable for douglas fir growth indicates presence of drift wood or debris flow deposits

determining the spatial and temporal patterns of climate changes in china s western interior during the last 15 ka from lacustrine oxygen isotope records china s western interior is a climatologically complex region where climatic conditions are primarily controlled by the westerly jet stream and the asian monsoon system observations reveal that the 18o signatures of these atmospheric elements as expressed in their meteoric waters are different and these differences are reflected in the lacustrine systems that are ultimately fed by the meteoric waters empirical orthogonal function eof decomposition of 17 lacustrine 18o records from this area clearly reveals the spatial and temporal structures of climate changes during the last 15 ka the first eof mode dominated by sites in the nw sector captures the temperature effect on the variability of the 18o dataset we interpret the variations through time in the amplitude of this mode to be indicative of changes in summer air temperature the second eof mode heavily weighted by sites in the se sector reveals the amount effect on 18o and thus its amplitude time series indicates changes in the intensity of the asian summer monsoon our eof based reconstructions of regional climate are generally consistent with the 18o records of ice cores cave speleothems and marine carbonates copyright 2008 john wiley sons ltd

cosmogenic 10be inferred lake level changes in sumxi co basin western tibet abstract most tibetan lakes are surrounded by conspicuous regressive shorelines attesting to high water levels in the past concentrations of the in situ produced cosmogenic radionuclide 10 be in bedrock from the three highest terraces surrounding sumxi co situated in western kunlun indicate that the highest lake level appeared before 10 000 11 500 yr and most likely between 11 000 and 12 800 yr younger ages for the two lower terraces imply regression of sumxi co during the early mid holocene the concurrency of the highest lake level with orbitally induced maximum northern hemisphere summer insolation suggests that the increase in water supply to sumxi co was most likely associated with increased recharge from melting glaciers we conclude that the enhanced indian monsoon during the early holocene did not penetrate the tibetan plateau and affect the northwestern part of tibet significantly

geomorphic response to climatic and environmental changes along a central asian transect during the holocene abstract this paper discusses the geomorphic response to late quaternary climatic changes and to some extent human impact along an asian transect running from eastern siberia via mongolia and tibet to india the prevailing aridity of the asian interior is controlled by distance from oceans and the existence of high mountain ranges modifying the circulation of air masses another factor is the existence of permafrost expanding to the temperate zone the contrasting characteristic of continentality are expressed in the asymmetry of present day slope processes caused by differences in temperature and humidity differences in altitude generate altitudinal and horizontal zones late quaternary climatic changes are reflected in latitudinal and altitudinal shifts in upper and lower tree lines the snow line and the permafrost limit the warming trend in the early holocene gave way to cooling in the last 3 5 ka bp this was accompanied by a rise in humidity which started ca 10 ka bp in the southern part under monsoonal influences and later 8 7 ka bp in the northern part under the influence of westerlies increased aridity was more or less coincident with the later cooling trend across asia in recent millennia this has been accompanied by deforestation cultivation and overgrazing which have in turn caused accelerated runoff and soil erosion

the tempo of holocene climatic change in the eastern mediterranean region new high resolution crater lake sediment data from central turkey this study presents results from a multi proxy analysis of cores taken in a crater lake sequence from eski acigol in central turkey which cover the period from pre c 16000 cal yr bp to the present the sediments comprise an upper unit of generally non laminated banded to massive silts and peats of mid to late holocene age overlying a laminated unit of late pleistocene to early mid holocene age the laminae comprising mainly aragonite amorphous silica diatom frustules and organic matter were formed in a relatively deep dilute meromictic lake pollen data indicate an abrupt replacement of artemisia chenopod steppe by grass oak terebinth parkland during the period of laminae deposition marking the start of the holocene a gradual increase in tree pollen during the early holocene came to an end c 6500 cal yr bp u series and adjusted c 14 timescale when mesic deciduous taxa declined at the same time as lake levels fell human impact on regional vegetation is inferred from a sharp decline in oak around 4500 4000 cal yr bp diatom isotopic and mineralogical data indicate that during the second half of the holocene the lake became relatively shallow and oscillated between fresh and brackish evaporated water conditions the contrast between wetter early and drier late holocene climatic conditions is matched by other eastern and central mediterranean proxy climate data while the eski acigol sequence resembles holocene hydroclimatic changes in the saharo arabian zone and was also apparently linked to orbital forcing it is unlikely to have had the same direct cause i e an expansion and subsequent retreat of monsoon rainfall

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

biogeochemistry and paleoclimate variability during the holocene a record from mansar lake lesser himalaya investigation of biogeochemistry and amino acids on a 30 m long core from mansar lake has thrown light on palaeoclimate variability during the holocene period the c n ratio between 6 and 10 with some deviations and 13c mostly between 20 and 22 in the shallow core as well as a c n ratio greater than 13 reaching from 19 to 20 and correspondingly lower 13c of 28 in the deeper core suggest an aquatic source of carbon in the former and a cellulose rich land plant source in the latter this is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core which indicates a hot and wet climatic regime during the early holocene and dry and cold during the late holocene period the amino acid data aa c c and aa n n are higher in shallow sediments compared to deeper sediments indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core the lower percentage of the non protein amino acids alanine ala and amino butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin the higher amino acid ratio asp ala 16 99 av and glu aba 18 18 av in the shallow core and lower ratios 10 32 and 12 41 av in the deeper core and asp glu 1 52 av and ala aba 1 61 av ratios in the former which are potential indicators of the nature of the organic matter are higher in the shallow core relative to the deeper core 1 33 and 1 23 av indicating relative biodegradation of organic matter in deeper sediments it has been observed that the organic matter associated with the dry season is relatively less biodegraded as evidenced from their higher ratios and is more biodegraded in the wet season as their ratios are lower in the river sediments in the absence of a bacterial contribution of organic matter from the soil source in this lake since mansar lake is a non drainage type it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments therefore the c n ratio and 13c values supported by amino acid data the latter being significant in revealing primary productivity and a terrestrial source of organic matter suggest a hot and wet climatic regime during the early holocene ca 7580 bp and a dry and cold in the late holocene period ca 4050 bp

from the allerod to the mid holocene palynological evidence from the south basin of the caspian sea pollen and dinoflagellate cysts have been analysed in a core from the south basin of the caspian sea providing a picture of respectively past vegetation and water salinity for the late pleistocene to middle holocene a relatively sharp lithological change at 0 86 m depth reflects a shift from detrital silts to carbonates rich fine silts from this depth upwards a holocene chronology is built based on ten radiocarbon dates on ostracod shells and bulk carbonates from the vegetation point of view the late pleistocene deserts and steppes were partially replaced in the most sheltered areas by an open woodland with pinus juniperus hippophae elaeagnus and even alnus quercus pterocarya and fraxinus related to the allerod palynozone this was interrupted by the younger dryas palynozone when artemisia reaches a maximum in a first instance followed by a very dry phase with only a slight return of pinus and quercus and the rare presence of ulmus zelkova from 11 5 to 8 4 cal ka bp an open landscape dominated by shrubs such as ephedra and progressively increasing quercus appeared the final spread of diverse evergreen and deciduous trees is delayed and occurs after 8 4 cal ka bp it is suggested that this delay is caused by an arid climate in the early holocene linked to high insolation and perhaps to a lake effect the dinocyst assemblages fluctuate between slightly brackish pyxidinopsis psilata and spiniferites cruciformis 7 psu and lower and more brackish impagidinium caspienense w13 psu in the lateglacial khvalynian highstand the assemblages remained dominated by relative low salinity taxa a late and brief increase of salinity occurred prior to 11 2 cal ka bp associated with the mangyshlak lowstand it is suggested that it was caused by a brief drop in meltwater flow from both the north and the southeast uzboy and a likely evaporation increase this lowstand occurs quasi at the same time as the end of a longer lowstand in the black sea the freshest waters are then inferred as having occurred between 8 4 and 4 4 cal ka bp linked to a connection with the amu darya and the melting glaciers on the pamir mountains

quaternary glaciations of the rongbuk valley tibet randomisation tests on boulder weathering data distinguish moraines of four different ages in the rongbuk valley all deposited by valley glaciers flowing northward into tibet from the himalaya lichenometry utilising subgenus rhizocarpon distinguishes two groups of moraines those 100 yr old and those older than several thousand years the degree of soil development has a similar limited utility in relative age dating these moraines the radiocarbon ages of calcium carbonate coatings in the lower horizons of moraine soils provide minimum limiting ages of 1900 yr bp for the penultimate advance of the rongbuk glacier samdopo moraine and 9500 yr bp for the rongbuk moraine the moraine suggested by previous workers to represent the last glacial maximum equilibrium line depression associated with the rongbuk moraine probably was slight 200 m the small magnitude of this depression relative to glaciers in other mountain ranges could relate to a weakening of the monsoon in full glacial times recent tectonic uplift and or to the insensitivity of these high altitude glaciers to lowering temperatures in the rain shadow of mount everest

late quaternary climatic changes in the eastern kumaun himalaya india as deduced from multi proxy studies abstract an event of neotectonic activity on an ne sw trending subsidiary fault in the zone of e w running intracrustal boundary thrust south almora thrust in the champawat district of eastern kumaun himalaya resulted in creation of a lake at ca 21 5 bp the lake drained in the late holocene leaving behind a 5 0 m thick sedimentary sequence of mostly black and carbonaceous mud with a minor magnetic reversal between 20 5 and 19 7 ka bp at the base the profile studied by using multi proxies e g carbon isotopes pollen analysis palaeo and mineral magnetism and clay minerals has recorded globally well established abrupt climatic events in the last 20 000 years such as the lgm older dryas od younger dryas yd holocene warming 8 2 ka and 4 2 ka events most events estimated assuming a constant rate of sediment accumulation for similar lithologies may be related to the rapid changes in the local climate and albedo structure the itcz may have played a key role in controlling the behavior of the southwest monsoon from the lgm

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

first tectonic geomorphology study along the longmu gozha co fault system western tibet abstract the longmu gozha co left lateral strike slip fault system lgcf is located in remote western tibet forming a triple junction with both the altyn tagh fault atf and the karakorum fault kf the two major strike slip faults in the region the ashikule gozha co and longmu co faults are clear and distinct left stepping en echelon faults together forming the lgcf system although poorly documented quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost tibetan plateau indeed the karakax fault nw segment of the atf lgcf and kf together control the tectonics of western tibet which itself controls the extrusion of tibet towards the east with the lgcf acting as a natural boundary for eastward motion of the tibetan plateau due to india s northward impingement the lgcf system shows clear and impressive morphological indications of left lateral active shear that we quantify using field measurements terrestrial lidar along with 10 be surface exposure dating our data suggest a slip rate 9 and 8 mm yr respectively yielding a few mm yr of extension accommodated most likely in the ashikule graben and surroundings located between the atf and karakax faults numerous evidences of recent tectonic related events are present in the vicinity such as the 1951 volcanic eruption as well as the 2008 and 2014 ms 7 3 yutian earthquakes attesting of its high activity in addition the lgcf s en echelon geometry and identical direction with the atf as well as smaller geological offsets and lower slip rate compared to those on the surrounding faults suggest that this segment of the atf may be the most recent

paleoclimatic changes on the southern tibetan plateau over the past 19 000 years recorded in lake pumoyum co and their implications for the southwest monsoon evolution abstract the paleoclimatic changes in the southern region on the tibetan plateau tp after the lgm were studied by multi proxy analysis including pollen ca carbonates toc 13 c toc plant macrofossils and sands with sediment cores from lake pumoyum co close to the east end of the himalayas the following paleoclimatic changes characteristic of the southern tp were suggested by comparing with the paleoclimatic records from various regions within the southwest sw monsoon domain on the tp soon after the lgm deglaciation in the southern tp had already started at 18 5 ka bp and more actively increased after ca 16 5 ka bp with the hydrological circulation oscillating in ca 1200 2000 and 4000 year periods an abrupt increase in humidity under the reduced sw monsoon intensity occurred at 15 0 ka bp as part of further deglaciation processes subsequently the climate amelioration in the southern region started from 15 0 ka bp a few centuries earlier than other regions of the tp and then was further intensified by synchronizing with the bolling allored b a event over the b a period the sw monsoon intensity in the southern region almost continuously and sharply increased unlike many regions on the tp the southern region experienced almost no or substantially small impact of the younger dryas yd event and also other major dry cold reversals such as heinrich 1 event the 8 2 kyr event and an abrupt spell occurring between 5 and 4 ka bp the monsoon intensity in the southern region after the yd event started to rapidly increase from 11 4 ka bp and reached a maximum between 10 8 and 10 0 ka bp after the lgm which lagged about 1200 years behind the maximum insolation in the northern hemisphere from ca 9 6 ka bp the gradual decrease in humidity in the southern tp started and continued until 4 2 ka bp it s aridification trend was characterized by three stepwise transition observed at 9 6 7 7 and 5 5 ka bp however the aridification in the southern tp was rather weak and the climatic conditions were sustained fairly humid and comparably stable the humidity between 4 2 and 2 5 ka bp essentially increased despite the weakened sw monsoon intensity at that time whereas from 2 5 ka bp to the present the climatic conditions became most arid and instable during the holocene as a consequence the holocene climate optimum in the southern region lasted from 11 4 ka bp until 2 5 ka bp and was marked by the earliest start and the latest end timings within the sw monsoon domain on the tp the comparison of the start timings from various paleoclimatic records indicated that the first sw monsoon on the tp after the yd event generated at 11 4 ka bp in the southern region subsequently according to the degree of the recovery of positive vegetation albedo feedback system in each region the monsoon probably extended from the southern tp over the entire tp taking 3000 4000 years based on these results the possible key factors and mechanisms responsible for the paleoclimatic changes in the southern region and also the possible processes as to the evolution of the sw monsoon over the tp are discussed

relative dating of quaternary moraines rongbuk valley mount everest tibet implications for an ice sheet on the tibetan plateau abstract relative dating studies applied to high altitude moraines 5000 5500 m in the rongbuk valley on the northern flank of mt everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests these differences serve to define three intervals of major pleistocene glaciation that on the basis of the degree of weathering are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation either interpretation indicates that some of these moraines are considerably older than their previously assigned ages the magnitude of equilibrium line lowering during neoglacial and late pleistocene times is calculated to be ca 50 100 and 350 450 m respectively the data described here are incompatible with the recently proposed model kuhle 1987 for large scale ice sheet development on the tibetan plateau the reconstructed equilibrium line lowering in the everest region is only 30 of that cited in the ice sheet model moreover the flow patterns and geometry of the former rongbuk glaciers are in opposition to those proposed by the model based on the data from the everest region it appears that valley glaciation rather than ice sheet growth characterized the southern margin of the tibetan plateau during the middle and late pleistocene glaciations

the influence of climate hydrology and permafrost on holocene peat accumulation at 3500 m on the eastern qinghai tibetan plateau peatland of the eastern qinghai tibetan plateau lies at the convergence of the east asian and indian monsoon systems in eastern asia to understand the evolution of this peatland and its potential to provide new insights into the holocene evolution of the east asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near hongyuan the age depth profile was determined using 16 14c ams age dates the peat analysed for a range of environmental variables including carbon nitrogen and hydrogen concentration bulk density 13c and the associated spring water analysed for hydrogen and oxygen isotopes the age depth profile of the recovered peat sequence covers the period from 9 6 to 0 3 kyr bp and is linear indicating that the conditions governing productivity and decay varied little over the holocene using changes in carbon density organic carbon content and its 13c cold dry periods of permafrost characterised by low density and impeded surface drainage were identified the low 18o and d values of the spring water emanating around the peat deposit down to 13 8 and 102 vsmow respectively with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day in view of the current annual mean air temperature of 1 c this suggests conditions in the past have been conducive to permafrost inferred periods of permafrost correspond to independently recognised cold periods in other holocene records from across china at 8 6 8 2 7 8 5 6 4 2 3 1 and 1 8 1 5 kyr bp the transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at hongyuan are of longer duration than equivalent cold dry periods over central and eastern china light dark banding peat on a scale of 15 30 years from 9 6 to 5 5 kyr bp may indicate a strong influence of decadal oscillations possibly the pacific decadal oscillation and a potential link between near simultaneous climatic changes in the northwest pacific enso movement of the intertropical convergence zone and the east asian monsoon

effects of the extrusion of fault gouge on frictional sliding thick gouge is extruded from between sample contacts of simulated fault zones thin gouge is locally extruded by irregularities of the fault surfaces extrusion causes the simple shear strain rate e to vary as a function of position within the gouge and with time the local shear traction thus varies from its macroscopic value the case of thick gouge is quantitatively modeled extrusion does not significantly affect experiments measuring a and b in the traditional formula for the instantaneous coefficient of friction 0 aln e e 0 bln where 0 is the steady state coefficient of friction at the reference strain rate e 0 and the state variable depends on the previous history of the sample other effects are modest and most likely to be observable when a b implying that the strain rate does not spontaneously localize the macroscopic coefficient of friction for a b is decreased by an amount which is less than the short long aspect ratio of the gouge zone measurments of frictional dilatancy in velocity stepping experiments and of the effects of sudden changes of normal traction on shear traction are not compromised if the plates bounding the fault gouge behave as rigid parallel planes the changes in shear traction after a sudden change in normal traction are strongly affected if the walls confining the gouge are compliant and do not remain parallel then the local ratio of the new normal traction to the old normal traction varies with position on the fault surface

strain rate effect on frictional strength and the slip nucleation process abstract kato n yamamoto k yamamoto h and hirasawa t 1992 strain rate effect on frictional strength and the slip nucleation process in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 269 282 the strain rate dependence of frictional strength is investigated in relation to sliding behaviour by biaxial compression tests of large scale granite samples frictional sliding is generated by increasing shear strain at a constant rate under a constant normal stress on the fault the ram displacement is held constant for a prescribed time interval between two successive sliding events so as to have the same time effect of stationary contact between sliding surfaces we obtained the following results as the strain rate increases 1 sliding becomes more unstable 2 the nucleation zone size of stick slip decreases and 3 frictional strength logarithmically increases result 3 is consistent with the previous study by dieterich 1979a and 1 and 3 are similar to the strain rate effects on failure characteristics of intact rocks reported in the literature result 3 can be explained by a rate and state dependent friction law our results suggest that the strain rate dependence of the fault strength plays an important role in controlling the nucleation process of faulting

climatic variations and geomorphology of the indus river valley between nimo and batalik ladakh nw trans himalayas during late quaternary abstract the indus river valley is tectonically unstable exhibiting complex topography landscape relief and varied sedimentation the major geomorphic landforms are alluvial fans debris cones fluvio lacustrine deposits scree and talus cones in the present work a transect between nimo and batalik along the river was studied to consider the geomorphological landform evolution during the quaternary based on the distribution of the sediments along the valley mass movements catastrophic land sliding and tectonic activity transported material from steep slopes to valley bottoms which were responsible for forming lakes preserved as thick piles of fine sediment while the outburst floods redistributed sediment down valley three phases of lake formation are recorded in the 136 km stretch 35 000 26 000 bp lamayuru palaeolake 17 000 13 000 bp rizong palaeolake occupying 35 km of the valley length and 14 000 5000 bp khalsi saspol palaeolake 55 km in length and having the highest lake levels the lake formation is attributed to deglaciation after the last glacial maximum lgm and holocene warming tectonic activity seismites are concentrated only at 10 and 6 ka

holocene environmental variations recorded by organic related and carbonate related proxies of the lacustrine sediments from bosten lake northwestern china we reconstructed a multiproxy record of the holocene climate changes from a 9 53 m core from bosten lake in the southern xinjiang of northwestern china based on a chronology supported by nine ams 1

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

9th millennium plant subsistence in the central anatolian highlands new evidence from pinarbasi karaman province central anatolia plant macrofossil analysis phytolith analysis and ams radiocarbon dating at pinarbasi in central anatolia confirm the presence and continuity of plant gathering practice as a key subsistence strategy from c 9000 7700 cal bc results demonstrate the use of almond terebinth and hackberry as food plants similar to palaeolithic epipalaeolithic subsistence strategies in the antalya region crop and or crop progenitor use is unsupported with sporadic cereal macrofossils rare and shown by direct radiocarbon dating to be intrusive a conclusion supported by the phytolith analysis seed exploitation is also rejected results confirm the presence of sedentary foragers from 9000 cal bc in central anatolia contemporary with the levantine ppna early ppnb suggest a different plant subsistence focus to contemporary forager societies in the fertile crescent and indicate economic differences with contemporary sites in central anatolia which were already cultivating crops

isotopic hydrology and paleohydrology of the madagi kenya natron tanzania basin during the late quaternary abstract three generations of stromatolites mark the recent extension of paleolakes in the magadi natron basin on the border between tanzania and kenya the last two generations are observed some 50 m above the modern lakes level they are respectively attributed to the beginning of the last interglacial and to the pleistocene holocene transition analysis of the morphology and texture of the stromatolites reveals an ecological zonation between 0 and 10 14 m below the shoreline their relatively high 18o and 13c values reflect a long residence time for the paleolake water which would have been favorable to the establishment of an isotopic equilibrium between atmospheric co2 and the dissolved inorganic carbon despite deep carbon inputs in relation to carbonititic volcanism a study of the 18o 2h and 13c contents in the hydrothermal springs perennial rivers and lacustrine brines indicates that during the last period of significant renewal of the deep saline groundwater precipitation was depleted in heavy isotopes when compared to modern precipitation this difference corresponds to a drop of about 600 1000 m in altitudinal hydroclimatic zones finally a comparison between the modern and paleohydrological data leads us to believe that the stabilization of the paleolake shorelines at the same altitude can be attributed to control by the water table level in the aquifer of the basaltic plateaus east of the basin

distribution of bacterial and archaeal ether lipids in soils and surface sediments of tibetan lakes implications for gdgt based proxies in saline high mountain lakes bacterial and archaeal lipids such as glycerol dialkyl glycerol tetraethers gdgts and dialkyl glycerol diethers are increasingly used as proxies for specific environmental parameters such as air temperature and soil ph in lacustrine environments little is known however about the distribution and applicability of bacterial and archaeal lipids on the tibetan plateau we investigated nine different watersheds across the plateau by way of sediments from lakes and rivers as well as the surrounding soils our transect study included a salinity gradient and focused on saline lakes which are rarely examined we analyzed archaeal isoprenoid i and bacterial branched b gdgts as well as archaeol to trace their sources and environmental factors influencing their distributions we could show that igdgts were produced in situ and bgdgts were primarily soil derived although we could not exclude in situ production of bgdgts in the lakes the most important environmental variables correlating with gdgt distributions were temperature and salinity bacterial gdgt distributions correlated mainly with salinity while archaeal lipid distributions correlated with temperature based on the correlation of methylation mbt and cyclisation cbt indices of bgdgts with ph and mean annual air temperature maat we established local calibrations for the tibetan lakes tex86 could also be applied to reconstruct temperature which was strongly biased towards measured summer lake water temperature indicating enhanced production of igdgts in the summer months existing proxies show therefore potential for palaeoclimate reconstruction on the tibetan plateau if local calibrations are applied

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

palynological and stable isotopic study of palaeoenvironmental changes on the northeastern tibetan plateau in the last 30 000 years abstract the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere however only a few continuous palaeoclimate records are available here we present a 30 000 year pollen and carbon stable isotope record of two lacustrine sections from the zoige plateau on the northeastern tibetan plateau the pollen spectra show that the territorial palaeovegetational evolution experienced 7 stages in the following order 1 30 0 26 0 kyr b p alpine desert and desert grassland vegetation 2 26 0 18 0 kyr b p grassland and alpine meadow vegetation 3 18 0 14 2 kyr b p alpine desert 4 14 2 10 0 kyr b p grasslands and meadows with islet forests 5 10 0 9 4 kyr b p marsh and meadow vegetation 6 9 4 4 0 kyr b p dark conifer islet and marsh and finally 7 4 0 kyr b p present marsh and subalpine meadows with scattered islets of dark conifer the palaeoclimate was inferred from these variations in palaeovegetation and in particular the variation in the last 12 000 years was confirmed by the 13 c curve of the no 2 pit section major post glacial climatic events are clearly identified in the two study sequences including the late glacial series of bolling allerod old dryas and younger dryas and the holocene optimum the climate records in the two sequences also indicate a long term trend towards aridity in the study area

palaeoenvironments and palaeohydrology of a tropical closed lake lake asal djibouti since 10 000 yr b p in eastern africa republic of djibouti the hypersaline lake asal occupies an exceptional geological topographical and hydrological situation at 155 m below sea level and at 12 km from the sea it lies in the youngest and the deepest basin in a chain of closed depressions of central afar decreasing in elevation from west to east and represents the hydrogeological low of the whole system presently infiltration of marine water represents the major water input to the lake due to high evaporation conditions halite precipitates halocene water level fluctuations 315 m sedimentary conditions from fresh oligosaline waters to heavy brines and palaeohydrology are reconstructed field observations are supported by 85 14c dates on inorganic carbonates mollusc shells stromatolites and hydrothermal travertines stable isotope analyses on carbonates and sulphates mineralogy geochemistry and studies of biological remains discussion of the water balance for the major stages is based on reasonable assumptions about holocene conditions of precipitation and evaporation after an arid terminal pleistocene phase marked by coarse deposits due to exceptional floods the holocene cycle begins with complex strontium rich carbonate phases aragonite high and low mg calcites and dolomite these carbonates could reflect the first underground marine supply and waters concentrated through evaporation a high lake level ca 160 m a s l from ca 8600 to 6000 yr b p corresponds to the deposition of high mg calcite precipitated in a deep fresh water lake lake asal was draining the awash river system ethiopian plateau and escarpment through groundwater circulations the terminal basin of the system was probably the present day marine gulf of ghoubbat al kharab hydrologically separated from the open ocean by a sill at 4 m below sea level possibly due to fracture opening a dramatic regression in the lake level from 160 to 150 m occurred between ca 6000 and 5000 yr b p the inputs of continental water were consequently overwhelmed by marine infiltrations the carbonate phase exhibits clear resemblance with that of the transgressive episode from 5000 yr b p lake asal experienced minor water level fluctuations aragonite rich carbonates precipitated followed by calcium sulphates and halite stable isotopes of gypsum reflect its marine origin and various diagenetic processes the holocene evolution of asal which clearly differs from that of the neighbouring closed basins is due to both its specific geological and hydrological setting and to the regional climatic changes

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

microphysical model predictions of fault restrengthening under room humidity and hydrothermal conditions from logarithmic to power law healing the maximum fault strength and rate of interseismic fault strengthening healing are of great interest to earthquake hazard assessment studies as they directly relate to event magnitude and recurrence time previous laboratory studies have revealed two distinct frictional healing behaviors referred to as dieterich type and non dieterich type healing these are characterized by respectively log linear and power law increase in the strength change with time to date there is no physical explanation for the frictional behavior of fault gouges that unifies these seemingly inconsistent observations using a microphysical friction model previously developed for granular fault gouges we investigate fault strengthening analytically and numerically under boundary conditions corresponding to laboratory slide hold slide tests we find that both types of healing can be explained by considering the difference in grain contact creep rheology at short and long time scales under hydrothermal conditions favorable for pressure solution creep healing exhibits a power law evolution with hold time with an exponent of 1 3 and an apparent cutoff time of hundreds of seconds under room humidity conditions where grain contact deformation exhibits only a weak strain rate dependence the predicted healing also exhibits a power law dependence on hold time but it can be approximated by a log linear relation with of a few seconds we derive analytical expressions for frictional healing parameters i e healing rate cutoff time and maximum healing of which the predictions are consistent with numerical implementation of the model finally we apply the microphysical model to small fault patches on a natural carbonate fault and interpret the restrengthening during seismic cycles

holocene environmental changes in bangong co basin western tibet part 2 the pollen record abstract a better knowledge of environmental variations in key regions such as the tibetan plateau which plays a fundamental role in the indian monsoon dynamics and thus on the whole northern hemisphere atmospheric circulation is of great importance we present here a detailed paleoenvironmental study based on pollen analyses of a sediment core from lake bangong results on the modern pollen rain are also discussed as they give valuable information for the interpretation of the fossil pollen data the pollen results of the bangong sequence and their paleoclimatic interpretation are integrated into a chronological framework on the basis of palynostratigraphical methods because of dead carbon in the lake system it has been difficult to establish a reliable chronology of the bangong sequence using a geochemical model for correcting measured 14c ages the pollen record from lake bangong compares well with the record from lake sumxi in western tibet lake bangong core provides a continuous holocene pollen record before 9600 yr b p the dominance of desertic elements in the pollen record reflects an arid environment at about 9600 yr b p an abrupt shift to steppe vegetation suggests the onset of moister conditions and from 9500 to 6200 yr b p proxy data indicate conditions warmer and wetter than today proxy data also indicate short term changes during this interval climate instability is suggested by the development of a local palustral flora which peaks at 7700 yr b p and is interpreted as a lake regression in phase with increase in the percentage of littoral and saline water diatom species between 8600 and 7700 yr b p the first humid pulse culminating at 9000 8500 yr b p is thus followed by drier conditions around 8000 7700 yr b p the interval between 7200 and 6500 yr b p regarded as optimal for vegetation growth from the pollen record corresponds to a second humid pulse a trend towards aridity is observed during the following period with dry events centered around 5500 3900 3200 and 700 yr b p

application of rate and state friction laws to creep compaction of unconsolidated sand under hydrostatic loading conditions 1 rate and state variable friction laws describe the time dependent fault normal compaction that occurs during holds in slide hold slide friction tests on unconsolidated materials this time dependent deformation is qualitatively similar to that observed during volumetric creep strain tests on unconsolidated sands and shales under hydrostatic loading conditions to test whether rate and state friction laws can be used to model volumetric creep processes in unconsolidated sands the rate and state formulation is expanded to include deformation under hydrostatic stress boundary conditions results show that the hydrostatic stress form of the rate and state friction law successfully describes the creep strain of unconsolidated sand more importantly values obtained for rate and state friction parameters by fitting these data are in the same range as those obtained from more traditional tests by fitting the fault normal compaction of simulated gouge during a hold in a laboratory friction experiment

ductile creep compaction and rate and state dependent friction within major fault zones the shear traction on major strike slip faults during earthquakes is much lower than that expected on a frictionally sliding surface in equilibrium with hydrostatic pressure the low shear traction is explained if the fluid pressure at the time of the earthquake is much greater than hydrostatic pressure ductile creep within mostly sealed fault zones compacts the matrix and thus increases fluid pressure between earthquakes frictional dilatancy during earthquakes decreases fluid pressure below hydrostatic and over the earthquake cycle the fault zone is in long term equilibrium with the country rock this ductile mechanism is formally unified with rate and state theory for time dependent friction when the difference between a critical porosity where the rock loses all strength and the actual porosity of cracks is used as a state variable this choice is justified by percolation theory of mostly broken lattices time dependent behavior associated with changes in normal traction in the laboratory is explained by the formalism instability earthquakes sometimes occurs in the numerical experiments however fairly small amounts of frictional dilatancy during initial frictional creep decrease fluid pressure and preclude unstable sliding two coupled mechanisms for producing dilatancy on faults once an instability is well underway are evident 1 expansion of pore fluids associated with frictional heating increases fluid pressure offsetting the effects of increased pore volume during earthquakes there is some tendency for pore volume increase to balance fluid expansion so that fluid pressure stays relatively constant 2 production of isolated voids that do not immediately decrease fluid pressure throughout the fault zone during earthquakes can occur to the extent that the fault zone is not significantly strengthened although the extent of both processes is constrained by energy considerations the variation of fluid pressure during earthquakes is not yet well enough understood to predict stress drop from observable material properties

mineral magnetic study of late quaternary south caspian sea sediments palaeoenvironmental implications summary magnetic properties of sediments from a core 10 m long in the southern basin of the caspian sea have been investigated varying concentrations of greigite fe 3 s 4 dominate the magnetic fraction in late pleistocene sediments the synsedimentary formation of greigite indicates that the late pleistocene caspian sea was a brackish or fresh water poorly ventilated basin and suggests a water level higher than at the present the variation in magnetic parameters with the detrital magnetite bearing fraction remaining constant is interpreted in terms of greigite grain size variation and related to the slight variation in water salinity the holocene sediments are characterized by detrital magnetite this indicates better ventilation of the basin and suggests lower water levels than in the late pleistocene the gradual change in magnetic properties of the sediments between 90 and 60 cm depth with decreasing quantities of greigite indicates stepwise establishment of oxic conditions in the holocene

biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

characteristics of δ13cdic in lakes on the tibetan plateau and its implications for the carbon cycle dissolved inorganic carbon isotope 13cdic is an important tool to reveal the carbon cycle in lake systems however there are only few studies focusing on the spatial variation of 13cdic of closed lakes here we analyze the characteristics of 13cdic of 24 sampled lakes mainly closed lakes across the qiangtang plateau qtp and identify the driving factors for its spatial variation the 13cdic value of these observed lakes varies in the range of 15 0 to 3 2 with an average value of 1 2 the 13cdic value of closed lakes is close to the atmospheric isotopic equilibrium value much higher than that in rivers and freshwater lakes reported before the high 13cdic value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved co2 induced by the strong evaporation of lake water the 13cdic value of closed lakes has a logarithmic correlation with water chemistry tds dic and pco2 also suggesting that the evapo concentration of lake water can influence the 13cdic value the 13cdic value shows two opposite logarithmic correlations with lake size depending on the 13cdic range this study suggests that the 13c in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on qtp copyright 2011 john wiley sons ltd

late neogene environmental changes in the central himalaya related to tectonic uplift and orbital forcing the linkage between tectonic forces and climate evolution remains a matter of much debate and speculation here we present high resolution oxygen and carbon isotope data from an ancient lake basin in the central himalaya these data together with sedimentologic evidence reveal major changes in drainage systems and depositional settings at 7 2 5 5 and 3 2 ma these environmental changes appear to be driven by regional scale tectonics the oxygen isotope record also reveals alternating wet and dry climates with periodicities of 24 and 100 kyr that were likely controlled by orbital forcing paleo temperatures estimated using a fossil based oxygen isotope paleo thermometer are 21 6 ca t 7 ma which is 19 6 c higher than the present day mean annual temperature in the same area the much warmer environment inferred here is consistent with fossil mammalian and pollen assemblages and sediment clay mineralogy as well as carbon isotope data from fossil tooth enamels and paleosol carbonates the estimated temperature difference would require the study area to have been raised by 2 2 5 km since 7 ma to its current elevation of 4100 4500 m above sea level this result can be interpreted as either indicating the presence of a low altitude intermountain basin in the hanging wall of the already formed main central thrust or a protracted development of a north trending rift basin that has experienced changes in drainage system and depositional environment through time

river inflow and salinity changes in the caspian sea during the last 5500 years abstract pollen spores and dinoflagellate cysts have been analysed on three sediment cores 1 8 1 4 m long taken from the south and middle basins of the caspian sea a chronology available for one of the cores is based on calibrated radiocarbon dates ca 5 5 0 8 cal ka bp the pollen and spores assemblages indicate fluctuations between steppe and desert in addition there are some outstanding zones with a bias introduced by strong river inflow the dinocyst assemblages change between slightly brackish abundance of pyxidinopsis psilata and spiniferites cruciformis and more brackish dominance of impagidinium caspienense conditions during the second part of the holocene important flow modifications of the uzboy river and the volga river as well as salinity changes of the caspian sea causing sea level fluctuations have been reconstructed a major change is suggested at ca 4 cal ka bp with the end of a high level phase in the south basin amongst other hypotheses this could be caused by the end of a late and abundant flow of the uzboy river now defunct carrying to the caspian sea either meltwater from higher latitudes or water from the amu daria a similar later clear phase of water inflow has also been observed from 2 1 to 1 7 cal ka bp in the south basin and probably also in the north of the middle basin

late holocene climatic record from a glacial lake in ladakh range trans himalaya india a multi proxy study using mineral magnetism sediment texture total organic content palynofacies and diatoms was conducted in one of the highest proglacial lake situated at north pulu 5098 m a s

environmental change during the holocene in western china on a millennial timescale recent data on the evolution of the inland lakes loess palaeosol sequences and glacier variations in western china are briefly reviewed the lake history shows three distinct stages in the holocene i e low water levels before 7500 bp a stage of expansion during the climatic optimum between 7500 and 3500 bp and contraction after 3500 bp three stages wooded grassland mixed woodland wooded grassland becoming steppe also appear indicated by the holocene loess palaeosol sequence in the lanzhou region the optimal period for soil development being between 7500 and 3500 bp there were seven periods of glacier advance the continental glaciers advanced at about 8300 5700 4000 and 400 bp in northwestern china and the maritime glaciers advanced at about 3000 2000 1000 and 200 bp it is suggested that the climatic changes show two periodicities during the holocene namely at intervals of about 2500 and 1000 years

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

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

last glacial holocene geochronology of sediment cores from a high altitude tibetan lake based on ams 14c dating of plant fossils implications for paleoenvironmental reconstructions abstract we obtained three sediment cores from a high altitude lake lake pumoyum co altitude 5020 m asl on the southern tibetan plateau for reconstruction of environmental changes during the last glacial holocene transition in this study we established the first reliable chronology for sediment cores from lake pumoyum co ca 18 5 cal ka bp at the bottom by 14c analyses of terrestrial plant residue concentrates prc 125 m and aquatic plant residues the calibrated ages of the prc fraction in the surface sediment were nearly modern 0 1 0 1 cal ka bp and the 13c values 22 to 24 were agreed well with those of modern terrestrial c3 plants in addition we estimated 14c reservoir ages of macrophyte remains from changes in their 13c values the major climate boundary layers in the cores transitions to bolling allerod 14 5 0 5 cal ka bp younger dryas 12 8 0 1 cal ka bp and preboreal 11 6 cal ka bp were confirmed by our new 14c chronology the transition to the bolling allerod warm phase from the last glacial 14 5 0 5 cal ka bp coincided with an obvious lithologic boundary a rapid decrease in the abundance of the macrophyte remains in the lake pumoyum co sediment cores

potential forcing mechanisms of holocene lake level changes at nam co tibetan plateau inferred from the stable isotopic composition of shells of the gastropod radix the timing of lake level fluctuations on the tibetan plateau and their relationship with climatic changes is still under debate and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes here we present the results of analyses of the shell geochemistry of radix sp from an exposed terrace of nam co lake on the south central tibetan plateau optically stimulated luminescence osl dating reveals that deep water lacustrine sediments formed between ca 4 4 and 2 2 ka suggesting a high and stable lake level significantly above the present the results of sr ca 13c and 18o analyses of the fossil shells of radix sp indicate that during the mid to late holocene lake level variations in nam co were mainly controlled by variations in the indian summer monsoon a trend of decreasing evaporation also played an important role comparison with other results suggests a consistent pattern of mid to late holocene lake level changes acro

intra seasonal hydrological processes on the western tibetan plateau monsoonal and convective rainfall events at 7 5 ka abstract the tibetan plateau and the himalayas influence monsoonal circulation patterns and represent the water towers of humanity modern coupling of atmospheric circulation and the hydrological cycle over and on the plateau can be observed and delineated and the factors that control lake levels can be identified recent monitoring of lakes has shown that many have grown for decades due to higher meltwater inflow or stronger rainfall from different sources depending on the location the long term dynamics of lakes however can be best described by using high resolution climate archives we focus here on the often controversial discussion of holocene lake development and use the bangong co drainage basin on the western tibetan plateau as a case study we aim to identify the factors that influence lake level such as monsoonal or convective precipitation and meltwater to accomplish this shells of the aquatic gastropod genus radix were collected from an early middle holocene sediment sequence in the nama chu subcatchment of the eastern bangong co and sclerochronlogical isotope patterns for five shells were obtained at a weekly to submonthly resolution our data suggest that at ca 7 5 ka monsoonal rainfall was higher than it is today however summer precipitation was not continuous but occurred as extended moisture pulses this result implies that the northern boundary of the sw asian monsoon was similar to that today we identify convective rainfall events significantly stronger than today and relate these events to higher soil moisture and larger lake surface areas under higher insolation conditions the regional amount of meltwater corresponds with the westerly derived winter snowfall exceptionally heavy 13c values archived in the shells were likely at least partly triggered by biogenic methane production we suggest that our approach is suitable for studying other lake systems on the tibetan plateau from which fossil radix shells can be obtained

global nature of the younger dryas cooling event inferred from oxygen isotope data from sulu sea cores the younger dryas an approximately 1 000 year long return to near glacial conditions interrupted the glacial holocene climate transition during which most of the northern hemisphere ice sheets melted evidence for the younger dryas event has been found mainly in sediments from the north atlantic ocean and northwest europe and this has led to the idea that the event was caused by an injection of meltwater into the north atlantic ocean1 3 this model however has been recently questioned in the light of coral reef data on the rate of sea level changes during this transition4 here we present high resolution oxygen isotope records from benthic and planktonic foraminifera from two radiocarbon dated cores in the sulu sea showing that the younger dry as occurred synchronously in the surface and deep waters of the sulu sea and the northern atlantic ocean by combining our results with other palaeoclimate data we suggest that the younger dry as event was a global phenomenon and we believe it to have been caused by low atmospheric co2concentrations

primary and diagenetic carbonates in the anoxic sediments of lake bosumtwi ghana cores of organic rich muds from the tropical meteorite crater lake bosumtwi ghana contain laminae of authigenic calcite polyhedra and aragonite needles as well as scattered diagenetic calcite mg calcite spherulites and aggregates of dolomite crystals their respective origins are traced by analyses of oxygen and carbon stable isotopes anoxic dolomite and mg calcite formed in pore waters reflecting highest degrees of evaporative concentration and high rates of methanogenesis carbon dioxide reduction must have been the dominant methanogenic pathway producing diagenetic carbonates with delta sup 13 c values up to 27 pdb this example shows the inherent problems of interpreting bulk samples with progressive mineralogical sequences of calcite to mg calcite to aragonite to dolomite merely in terms of mg sup 2 ca sup 2 in lake waters it provides a model for the interpretation of ancient lacustrine carbonates from organic rich environments

amorphous material in high strain experimental fault gouges the microstructures of gouges produced in room temperature rotary shear sliding experiments were examined by transmission electron microscopy gouges were produced by sliding on ground surfaces of granite quartzite or marble except for one experiment in which a 1 mm thick simulated gouge layer was used water was added to the sliding surfaces of all but one sample crystal plastic processes play no role in the granite and quartzite gouges and a minor role in the marbles all of the gouges consist of mostly submicron crystalline fragments in addition the granite gouges contain 5 60 amorphous material and the quartzite gouge contains 50 amorphous material in the granite samples the composition of the amorphous material commonly lies between k rich and na ca rich feldspars although portions may be silica rich the microstructural relations suggest that the amorphous material forms by comminution of fragments rather than by melting the amount of amorphous material increases and the size of the largest crystalline fragments decreases with an increase in average shear strain although the microstructure is nearly uniform throughout each granite gouge layer these observations suggest that after slip becomes localized on y shear surfaces and or r1 riedel shears the entire gouge layer must continue to undergo deformation it is suggested that cyclic deformation in the gouge must occur to accommodate the passage of geometric irregularities on the active slip surfaces

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

the roles of time and displacement in velocity dependent volumetric strain of fault zones the relationship between measured friction a and volumetric strain during frictional sliding was determined using a rate and state variable dependent friction constitutive equation a common work balance relating friction and volume change and two types of experimental faults initially bare surfaces of westerly granite and rock surfaces separated by a 1 mm layer of 90 m westerly granite gouge the constitutive equation is the sum of a constant term representing the nominal resistance to sliding and two smaller terms a rate dependent term representing the shear viscosity of the fault surface direct effect and a term which represents variations in the area of contact evolution effect the work balance relationship requires that a differs from the frictional resistance that leads to shear heating by the derivative of fault normal displacement with respect shear displacement d n d s an implication of this relationship is that the rate dependence of d n d s contributes to the rate dependence of a experiments show changes in sliding velocity lead to changes in both fault strength and volume analysis of data with the rate and state equations combined with the work balance relationship preclude the conventional interpretation of the direct effect in the rate and state variable constitutive equations consideration of a model bare surface fault consisting of an undeformable indentor sliding on a deformable surface reveals a serious flaw in the work balance relationship if volume change is time dependent for the model at zero slip rate indentation creep under the normal load leads to time dependent strengthening of the fault surface but according to the work balance relationship no work is done because compaction or dilatancy can only be induced by shearing additional tests on initially bare surfaces and gouges show that fault normal strain in experiments is time dependent consistent with the model this time dependent fault normal strain which is not accounted for in the work balance relationship explains the inconsistency between the constitutive equations and the work balance for initially bare surface faults all rate dependence of volume change is due to time dependence similar results are found for gouge we conclude that a reflects the frictional resistance that results in shear heating and no correction needs to be made for the volume changes the result that time dependent volume changes do not contribute to a is a general result and extends beyond these experiments the simple indentor model and particular constitutive equations used to illustrate the principle

holocene lake level variations of longmu co western qinghai tibetan plateau longmu co is surrounded by conspicuous regressive shorelines attesting to high water levels in the past in this study we dated paleoshoreline sediments around the lake using optically stimulated luminescence osl infrared stimulated luminescence irsl and radiocarbon dating then explored the forces that drove holocene lake level variations we found that 1 osl irsl ages are consistent with geomorphic sequences and some extant cosmogenic and u th shoreline ages however inorganic evaporite crust 14c ages are much older than corresponding osl irsl ages due to varying lake reservoir effects and should be used with caution 2 the highest lake levels of longmu co 160 145 m above present lasted from 12 8 to 11 3 ka two periods of abrupt lake level declines occurred at 11 3 and 7 4 ka lake level dropped 44 and 45 m respectively with a gradual regression of 18 m between these two intervals the lake expanded moderately from 7 to 5 5 ka then declined once more after 5 5 ka with this regression accelerating during the last 1 5 ka 3 the deglacial lake level transgression was likely due to glacier melt waters the indian summer monsoon reached the longmu co watershed and brought precipitation during the early holocene middle to late holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration

comparison of smectite and illite rich gouge frictional properties application to the updip limit of the seismogenic zone along subduction megathrusts along plate boundary subduction thrusts the transformation of smectite to illite within fault gouge at temperatures of 150 c is one of the key mineralogical changes thought to control the updip limit of seismicity if correct this hypothesis requires illite rich gouges to exhibit frictionally unstable velocity weakening behavior here we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay rich gouges we sheared 5 mm thick layers of commercially obtained pure ca smectite a suite of smectite quartz mixtures and natural illite shale grain size ranging from 2 to 500 m in the double direct shear geometry to shear strains of 7 30 at room humidity and temperature xrd analyses show that the illite shale contains dominantly clay minerals and quartz within the clay sized fraction 40 mpa our data specifically the velocity strengthening behavior of illite shale under a wide range of conditions do not support the hypothesis that the smectite illite transition is responsible for the seismic aseismic transition in subduction zones we suggest that other depth and temperature dependent processes such as cementation consolidation and slip localization with increased shearing may play an important role in changing the frictional properties of subduction zone faults and that these processes in addition to clay mineralogy should be the focus of future investigation

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

carbonate isotopes from high altitude tso moriri lake nw himalayas provide clues to late glacial and holocene moisture source and atmospheric circulation changes abstract high resolution isotopic 18 o and 13 c investigations on endogenic carbonates calcite aragonite from tso moriri lake nw himalaya show dramatic fluctuations during the late glacial and the early holocene and a persistent enrichment trend during the late holocene changes in this lake are largely governed by the input meltwater monsoon precipitation evaporation i e ratio also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest i e using new isotopic data on endogenic carbonates in combination with the available data on geochemistry mineralogy and reconstructed mean annual precipitation we demonstrate that the late glacial and early holocene carbonate 18 o variability resulted from fluctuating indian summer monsoon ism precipitation in nw himalaya this region experienced increasing ism precipitation between ca 13 1 and 11 7 cal ka and highest ism precipitation during the early holocene 11 2 8 5 cal ka however during the late holocene evaporation was the dominant control on the carbonate 18 o regional comparison of reconstructed hydrological changes from tso moriri lake with other archives from the asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels after 8 cal ka in central asia was not strongly felt in nw himalaya

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

effects of shear stress applied to surfaces in stationary contact on rock friction in this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact we develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test a series of experiments conducted at a single normal stress of 5 mpa show the following effects first unloading the shear stress during the hold period increases frictional resistance by up to 10 20 a decrease in shear stress linearly increases the frictional resistance of the interface secondly the static friction coefficient increases with the logarithm of contact time the friction coefficient increases by 0 01 per decade of contact time at near zero shear stress levels and by more than 0 02 at shear stress levels that are greater than half the sliding friction

woodland vegetation and fuel exploitation at the prehistoric campsite of pinarbasi south central anatolia turkey the evidence from the wood charcoal macro remains this paper presents the results of the analysis of wood charcoal macro remains from the multi period prehistoric rock shelters of pinarbasi in the konya plain south central anatolia retrieval and analytical methods are also reported in detail together with some methodologies previously untested in the field of charcoal analysis aiming at the quantitative description of context related variation in the preservation status of archaeological wood charcoal assemblages the patterns observed in the charcoal record are interpreted as a reflection of the prehistoric strategies for firewood exploitation in their local and regional palaeoenvironmental context

towards a general state variable constitutive relation to describe granular deformation triaxial compression experiments were performed on cylindrical quartz sand packs to explore the universality of statevariable constitutive relations used to describe granular deformation samples were subjected to relaxation creep experiments similar to slide hold slide tests from friction studies for relaxation creep tests a constant rate of axial shortening was interrupted by time intervals for which the applied shortening rate was set to zero during holds loadforce decayed exponentially with time and the total stress relaxation scales with the logarithm of hold time consistent with friction tests on reloading after holds stress monotonically increases to the pre hold steady state levels without displaying the restrengthening of static friction often observed from shear tests on granular layers we find that the existing rate and state variable friction laws can model the transient strength behavior during relaxation creep and subsequent reloading by using simple assumptions about the deformation of cylindrical sand packs in triaxial compression by analogy with the rate and state friction constitutive relations we propose a generalized state variable expression for granular deformation in simple and pure shear although additional experiments under a variety of load boundary geometries and load paths will be needed such a general constitutive relation may ultimately describe granular deformation under a broad range of conditions e g for large variations in loading rate shear stress normal stress mean stress and may be applicable to a variety of research problems that involve deformation within granular media d 2005 elsevier b v all rights reserved

ams 14c chronology of 40 0 cal ka bp continuous deposits from a crater lake lake massoko tanzania abstract lake massoko tanzania 8 20 s 33 45 e 870 m a s l is a freshwater maar lake belonging to the rungwe volcanic area 15 km northwest of the livingstone mountains and lake malawi the rainfall regime is driven by the yearly oscillation of the intertropical convergence zone which determines a wet summer and a dry and windy winter the presence of lake malawi to the south and high ranges to the north result in a higher annual precipitation than that observed at a regional scale air masses overloaded with humidity bypassing lake malawi are submitted to ascending currents producing rainfall up to 2400 mm yr 1 in the lake massoko area important exchanges between the lake and groundwater reservoirs have been demonstrated from hydrological and isotopic balances of lake massoko on a regional scale these exchanges are superimposed on groundwater circulation the hydrological setting of lake massoko is also influenced by the tectonics of the region dominated by the northwest southeast tilt of tectonic blocks the sedimentary sequences of lake massoko cored in 1995 and 1996 under the eec project rukwa rukwa project final report 1997 likely register the palaeoenvironmental changes on the catchment the sediment record is nearly continuous due to the near constant high water level of the lake in contrast with many other lacustrine sequences in which reduced deposition rates discrepancies and or gaps characterise arid periods such as the last glacial maximum and the younger dryas event all the ams 14c dates on authigenic organic samples fit with the stratigraphy and the palaoenvironmental record of lake massoko exhibits a constant mean sedimentation rate of 0 628 mm yr 1 for the last ca 40 cal ka bp

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

time dependent friction of granite implications for precursory slip on faults frictional forces were measured during sliding between saw cut cylinders of barre granite deformed in a servo controlled triaxial loading machine two different effects occur depending on the type of loading when steady shortening of a stably sliding sample is halted suddenly slip continues at a diminishing rate which depends on the logarithm of the initial sliding velocity thus the frictional strength of the surface is decreasing with time when shortening at a constant rate resumes after the holding period however the frictional resistance temporarily rises to a peak proportional to the logarithm of time of no driving showing a well known increase in friction with time the subsequent decrease in resistance from this peak is continuous the observed frictional resistance of a surface thus results from the interaction of several processes and is not a constant in general but depends on the immediate and preceding deformation when shortening is resumed after a period of holding slip rate across the friction surface temporarily accelerates above the driving rate the slip rate can then either decrease to the driving rate and remain stable or accelerate further and lead to stick slip motion at stress levels below the peak value there is no apparent difference in the frictional resistance until the unloading rate of the loading machine is exceeded between slip episodes which settle stably to the constant driving rate and those which become unstable and result in stick slip the stick slip failure criterion is not a peak stress but rather loss of strength more rapidly that the unloading rate of the loading machine the evidence that accelerating motion before stick slip is due to the time variable strength of rock suggests that accelerating slip will occur before earthquakes unfortunately for easy observation experiments indicate that slip need not be uniform over a fault surface also to be established is whether slip will be sufficiently large in the earth to be detectable nevertheless a plausible mechanism for generating observable phenomena prior to earthquakes is suggested by the laboratory observations

palaeoclimatic interpretation of a topographic profile across middle holocene regressive shorelines of longmu co western tibet most lakes and closed basins in tibet are surrounded by abandoned shorelines attesting for high water levels in the past two such lakes longmu co and sumxi co western tibet were the focus of detailed palaeoclimatic work during the 1989 sino french expedition based on the study of lake sediments and analysis of a piston core here it is shown that additional information may be deduced from the abandoned shorelines around longmu co a 1800 m long topographic profile was levelled from 75 m up to 230 m above the present lake elevation 5008 m on which the shorelines form a flight of horizontal terraces separated by more or less degraded scarps the elevations of the terraces were spaced regularly about 1 35 m except for 3 5 m high lacunae reccurring every 15 16 m the potential annual evapo transpiration was computed based on meteorological data collected at tien shui hai from 13 08 89 to 11 09 90 using a modified penman formula a value of 1 60 0 3 m yr was obtained under close system conditions no outlet and a synthetic curve of lake regression was derived which appears to be consistent with the measured shoreline heights it is concluded that the 1 35 m terraces represent annual regression of the lake level by contrast the 3 5 m high lacunae might reflect the periodic return about every 9 12 yr of particular climatic conditions responsible for a perturbation of the annual process of shoreline formation all the shorelines of this profile have formed probably within one century during a continuous and abrupt regression of the lake such evolution has also been identified in the sediments of a piston core collected at sumxi co and dated at about 6 5 5 kyr b p the lake level must have been at its highest stand shortly before that major regression the mechanism responsible for this middle holocene high stand and for the major sudden drop of the lake level remains uncertain

evolution of wear and friction along experimental faults we investigate the evolution of wear and friction along experimental faults composed of solid rock blocks this evolution is analyzed through shear experiments along five rock types and the experiments were conducted in a rotary apparatus at slip velocities of 0 002 0 97 m s slip distances from a few millimeters to tens of meters and normal stress of 0 25 6 9 mpa the wear and friction measurements and fault surface observations revealed three evolution phases a an initial stage slip distances 50 mm of wear by failure of isolated asperities associated with roughening of the fault surface b a running in stage of slip distances of 1 3 m with intense wear rate failure of many asperities and simultaneous reduction of the friction coefficient and wear rate and c a steady state stage that initiates when the fault surface is covered by a gouge layer and during which both wear rate and friction coefficient maintain quasi constant low levels while these evolution stages are clearly recognizable for experimental faults made from bare rock blocks our analysis suggests that natural faults bypass the first two stages and slip at gouge controlled steady state conditions

modern hydrology and late holocene history of lake karakul eastern pamirs tajikistan a reconnaissance study abstract lake karakul in the pamirs tajikistan is a deep brackish water lake in a closed basin at almost 4000 m above sea level water samples from the catchment area and lake karakul and a 104 cm sediment core from its shallow eastern sub basin were investigated and provide a first lake record from the region spanning the last 4200 cal yr bp multi proxy analyses revealed the following a relatively high meltwater inflow from glaciers snow fields and frozen ground in the catchment as a result of relatively warm conditions was reconstructed for the period between 4200 and 3500 cal yr bp the shift to colder climatic conditions around 3500 cal yr bp was probably abrupt total organic carbon values displayed the most dramatic drop for the entire core within less than 40 years in contrast the subsequent re establishment of warmer conditions occurred gradually over several centuries a higher meltwater supply to the lake and warmer conditions were recorded since ca 1900 cal yr bp with two slightly colder intervals between 1200 and 800 cal yr bp and between 400 and 100 cal yr bp the abrupt shift to significantly colder and drier conditions around 3500 cal yr bp in the eastern pamirs is seen also in records from the aral sea and the guliya ice core from the western tibetan plateau however more palaeoclimate studies in this highly continental part of central asia are needed to assess the spatial and temporal patterns of the holocene climate in the region

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

the holocene climatic optimum and pollen records of sapropel 1 in the eastern mediterranean 9000 6000 bp abstract the most recent sapropel in the deep eastern mediterranean sea has been deposited between 9 and 6 ka bp climate conditions as revealed by the pollen records of this sapropel in marine cores were most favorable for temperate deciduous trees which is in agreement with the inferences from records of peripheral land pollen sites the abundance of deciduous oak pollen is much higher than that of artemisia sage brush indicating that annual precipitation in the mid elevation borderlands was at least 550 mm without summer drought but more probably in the range 800 1300 mm the pollen of pistacia which formed a savanna at low elevations is also at its highest abundance and signals the absence of frost in winter while being capable of withstanding summer drought the early holocene therefore appears as the post glacial climatic optimum with the highest moisture and mildest winters in southwest asia this is also the time of the neolithic population explosion with incipient domestication of cereals possibly following natural selection of the tough rachis mutation in wheat and barley by the extreme aridity of the preceding younger dryas

chronology and stratigraphy of late quaternary sediments in the konya basin turkey results from the kopal project abstract the late quaternary environmental history of the konya plain in south central turkey is used to examine sediment facies changes in a shallow non outlet basin which has experienced major climatically driven changes in lake extent two principal types of sedimentary archive are used to reconstruct a palaeoenvironmental record namely alluvial sequences on the carsamba alluvial fan and sediments from residual lakes the latter have been used to investigate broader climatic and vegetational histories via palaeolimnological techniques including pollen diatom and stable isotope analysis these changes are dated here by radiometric techniques including radiocarbon ams and conventional osl and u th chronological agreement is generally good between the different dating techniques although typically there is greatly reduced precision beyond ca 25 ka lake sediment cores investigated have basal ages beyond the range of 14c dating but contain hiatuses as a result of subsequent alternation between phases of lacustrine sedimentation and aeolian deflation in contrast to most deepwater non outlet lake systems the konya basin may have been occupied by a single extensive lake for as little as 10 of late quaternary time mainly around the time of the lgm this lake highstand was followed by an important arid interval in the absence of unbroken chronostratigraphic sequences palaeohydrological investigation of shallow non outlet lakes may require analysis of basin wide changes in sedimentation rather than reliance on single core records stratigraphic continuity in such sedimentary environments cannot be assumed and requires independent chronological control through radiometric dating

weathering and anthropogenic influences on the water and sediment chemistry of wular lake kashmir himalaya this paper presents a study on the wular lake which is the largest fresh water tectonic lake of kashmir valley india one hundred and ninety six 196 water samples and hundred 100 sediment samples n 296 have been collected to assess the weathering and anthropogenic impact on water and sediment chemistry of the lake the results showed a significant seasonal variability in average concentration of major ions being highest in summer and spring and lower in winter and autumn seasons the study revealed that lake water is alkaline in nature characterised by medium total dissolved solids and electrical conductivity the concentration of the major ion towards the lake central showed a decreasing trend from the shore line the order of major cations and anions was ca2 mg2 na k and hco3 so4 2 cl respectively the geochemical processes suggested that the chemical composition lake water is mostly influenced by the lithology of the basin carbonates silicates and sulphates which had played a significant role in modifying the hydrogeochemical facies in the form of ca hco3 mg hco3 and hybrid type chemical index of alteration values of wular lake sediments reflect moderate weathering of the catchment area compared to upper continental crust and the post archean shale the sediments have higher si ti mg and ca contents and lower al fe na k p zn pb ni cu content geoaccumulation index igeo and us environmental protection agency sediment quality standards indicated that there is no pollution effect of heavy metals zn mn pb ni and co the study also suggested that wular lake is characterised by both natural and anthropogenic influences

a synthesis of hydrogen isotope variability and its hydrological significance at the qinghai tibetan plateau abstract hydrogen isotope ratios of sedimentary biomarkers are known to record the climatic variability in terrestrial and marine environments however there is still a lack of calibration studies that can quantitatively retrace the driving forces especially at the tibetan plateau here we elaborate the actual influence of environmental parameters such as temperature evapotranspiration salinity and biosynthetic fractionation on d values of n alkanes we measured hydrogen isotope values d of n alkanes in recent sediment and plant samples as well as d values of different water sources lake and inflow water precipitation as well as leaf root and soil water from six tibetan lakes along a 10 spanning longitudinal transect covering an aridity gradient as expected the deuterium record can be used to distinguish two water pools at the plateau i precipitation water which supplies water for the lake inflow and terrestrial plants and ii enriched lake water having a clear evaporative signal based on significant correlations of the source water and d values of n alkanes d of alkane n c 23 record the lake water isotope composition and track the evaporative enrichment of the lake system in contrast d of alkane n c 29 can be used to retrace the isotope composition of the inflow displaying the integrated rainfall signal in the vegetation period modified by soil and leaf water evaporation while temperature changes are less pronounced across the tibetan transect the isotopic difference between c 23 and c 29 could potentially be used as a proxy to reconstruct effective moisture precipitation minus evaporation areas with lower precipitation amounts and higher evaporation rates are characterized by higher d c 23 c 29 values this relationship is more pronounced in regions with mean annual precipitation below 350 mm even in contrasting environments the application of the d proxies is very promising combining other tibetan studies it is possible to present a comprehensive picture of the usage of compound specific hydrogen isotopes of n alkanes on the tibetan plateau

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

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

petrological record of co 2 influx in the dongying sag bohai bay basin ne china abstract dawsonite occurs in sandstones of the fourth member of the shahejie formation dongying sag bohai bay basin northeastern china the paragenesis sequence formation temperatures carbon dioxide co2 and aqueous medium origin of dawsonite from the binnan area were studied to understand the formation of dawsonite as a possible mechanism for mineral trapping of co2 in carbon capture and storage ccs programs the petrological and geochemical characteristics of the dawsonite bearing sandstones were identified using polarizing microscope examination scanning electron microscope x ray fluorescence x ray diffraction and stable isotopic analyses the paragenesis sequence of the authigenic minerals are mainly quartz overgrowth early stage calcite a ferrocalcite dawsonite late stage calcite b ankerite siderite the carbon and oxygen isotope compositions of dawsonite reveal that 13c values of dawsonite range from 2 27 to 3 50 indicating inorganic co2 the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite range from 7 2 to 1 6 suggesting that co2 originated mainly from degassing of mantle derived magmas and partly from thermal decomposition of carbonate rocks as supported by regional magmatic activities rifting and observation of carbonate during drilling in well bin76 the 18o values of dawsonite vary from 17 2 to 19 8 and the calculated 18o values of h2o in isotopic equilibrium with dawsonite range from 2 1 to 0 4 the mixed aqueous medium was mainly connate water influenced by magmatic activities and meteoric water influx during the formation of dawsonite according to oxygen isotope data the formation temperatures of dawsonite in the binnan area range from 77 c to 95 c which are consistent with the estimated paleo temperatures 79 c to 85 c indicating that the dawsonite formed at the late stage of the diagenetic phase

evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions an experimental study we performed flow through laboratory experiments on five cylindrically cored samples of ultramafic rocks in which we generated a well mated through going tensile fracture to investigate evolution of fracture permeability during serpentinization the samples were tested in a triaxial loading machine at a confining pressure of 50 mpa pore pressure of 20 mpa and temperature of 260 c simulating a depth of 2 km under hydrostatic conditions a pore pressure difference of up to 2 mpa was imposed across the ends of the sample fracture permeability decreased by 1 2 orders of magnitude during the 200 330 h experiments electron microprobe and sem data indicated the formation of needle shaped crystals of serpentine composition along the walls of the fracture and chemical analyses of sampled pore fluids were consistent with dissolution of ferro magnesian minerals by comparing the difference between fracture permeability and matrix permeability measured on intact samples of the same rock types we concluded that the contribution of the low matrix permeability to flow is negligible and essentially all of the flow is focused in the tensile fracture the experimental results suggest that the fracture network in long lived hydrothermal circulation systems can be sealed rapidly as a result of mineral precipitation and generation of new permeability resulting from a combination of tectonic and crystallization induced stresses is required to maintain fluid circulation