paleoclimatic significance of magnetic properties on the red clay underlying the loess and paleosols in china abstract the red clay unit of northern china is a widespread miocene pliocene 7 2 2 5 ma aeolian deposit that underlies much of the quaternary loess paleosol sequence in the central loess plateau it comprises a sequence of highly developed soils and interbedded layers of less weathered loess like material here referred to as reddish loess in common with the loess paleosol alternations of the overlying quaternary deposits the soil reddish loess alternations are interpreted to represent climatic fluctuations in this case between warm humid and relatively dry cool conditions however while magnetic susceptibility variations in the quaternary deposits provide a good proxy for pedogenic intensity in the red clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis in an attempt to resolve this issue we have investigated a red clay section and overlying loess paleosol sequence at xifeng and have supplemented these data with samples from the red clay at lingtai our study indicates that the red clay and loess paleosol sequence have a common magnetic mineralogy comprising magnetite maghemite and hematite and possibly goethite and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic sp component this implies that susceptibility enhancement in the red clay is strongly related to the magnitude of the sp content a component that is widely recognised as having a pedogenic origin in quaternary deposits further support for a correlation between pedogenesis and magnetic susceptibility in the red clay is provided by a good correlation between magnetic susceptibility and the rb sr ratio an independent weathering index however differences in the magnetic mineralogy of the two units are also evident the minimum magnetic susceptibility of the red clay is less than half the value of the overlying quaternary deposits at locations such as xifeng and lingtai while the maximum sp content is relatively larger than for the quaternary deposits while we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units climate may also be a contributory factor in explaining these differences precipitation is a major control on magnetic enhancement in paleosols maher and thompson 1995 quat res 44 383 391 liu et al 1995 palaeogeogr palaeoclimatol palaeoecol 113 243 248 but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive central loess plateau china magnetic enhancement negative alaska siberia magnetic destruction or uncertain pakistan argentina new zealand cycles of enhancement and destruction while our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the red clay they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary but independent techniques more work is required to deconvolve the climatic record of the red clay but the reward may be the extension of the record of paleomonsoon evolution back into the pliocene and late miocene

nd and sr isotopic variations in chinese eolian deposits during the past 8 ma implications for provenance change a record of changes in nd and sr isotopic composition of the eolian deposits from the central loess plateau has been determined for the past 8 ma the isotopic records of the silicate fraction of the quaternary and tertiary eolian deposits allow interpreting the interplay between the sr isotopic variations in the eolian deposits and the late cenozoic tectonic and climatic changes the results indicate that the temporal variations of nd and sr isotopes show remarkable changes around the beginning of the quaternary the lower values of the 143 nd 144 nd and the decreasing trend of the 87 sr 86 sr ratios after 2 58 ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late cenozoic uplift induced glacial grinding in the high orogenic belts in central asia in this context the substantial changes in climate and tectonics have modified dust sources significantly and the quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the tertiary red clay d 2005 elsevier b v all rights reserved

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

what controlled mid late miocene long term aridification in central asia global cooling or tibetan plateau uplift a review abstract debate continues over whether global cooling or uplift of the tibetan plateau provided the first order driver for the aridification moisture levels of central asia throughout the mid late miocene between about 17 and 5 ma this review attempts to throw new light on the relations between the aridification and these two key factors this paper examines the evolution of miocene climate both moisture and temperature within five separate regions of eurasia to help understand the large scale controls of long term moisture in central asia the five regions include 1 europe 2 high latitude asia 3 the east asian monsoon region 4 the south asian monsoon region and 5 central asia itself because moisture reaching central asia has to firstly cross at least one of the other four regions temperature proxy data compiled from these five regions correlate with ocean temperatures from the global deep sea oxygen isotope records furthermore compiled moisture proxy data from the four regions surrounding central asia co vary and correlate with each other this can be explained by positive feedbacks between drying and cooling and supports the assumption that global cooling provides a dominant driving factor for the drying of eurasia global cooling reduces the amount of water vapor held in the atmosphere and thereby can cause terrestrial drying however in central asia the moisture evolution shows less similarity with its surroundings the uplift of the tibetan plateau including the tianshan mountains could provide a possible explanation for this difference the changing topography resulting from uplift events over time and space strongly influenced the moisture patterns in central asia during miocene times future research on the spatial timing and amplitude of tibetan plateau uplift should be useful to understand the moisture processes in central asia during the miocene

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

seismotectonic model of the kangra chamba sector of northwest himalaya constraints from joint hypocenter determination and focal mechanism the existing seismological network in the kangra chamba sector has been upgraded with 12 three component digital seismometers to obtain new insight on the nature and sources of continued clustered seismicity in this part of northwest himalaya a combination of travel time distance plots and travel time inversion of p and s phases have been used to derive a 1d velocity model for the region the mini mum 1d velocity model divides the average 44 km thick crust into four layers the top 10 km thick layer represents the metamorphosed sediments of the chamba nappe that dominates the surface geology of the study area suggestion of a thin low velocity layer at 15 km depth possibly marks the detachment zone separating the downgoing indian plate from the overriding wedge the improved locations of epicenters show close clustering of seismic events immediately northeast of the epicenter of the 1905 kangra earthquake while away from this zone the seismicity in the chamba sector has more even distribution in the later sector space depth distribution of hypocenters suggests that strain resulting from the ongoing collision of the indian plate with asia is being consumed by reverse fault movement on the chamba thrust the clustered seismicity in the kangra sector has three distinct source regions and mechanisms 1 southward displacement of the thick chamba nappe sheet over the panjal imbricate zone along the panjal thrust accounts for the seismicity at shallow depths of less than 7 km 2 the nucleation of strains where the northeast dipping main boundary thrust mbt merges with the detachment plane produces focused seismicity near this junc tion and 3 the seismicity in a small pocket below the plane of detachment appears to be a consequence of stresses generated at the base of the northeast dipping detachment plane by the transverse structure

an 11 ma old red clay sequence on the eastern chinese loess plateau abstract older red clay deposits on the chinese loess plateau contain information of early paleomonsoon evolution and tectonic history of the ordos platform and the tibetan plateau a well conserved eolian red clay sequence was recently discovered at shilou on the eastern chinese loess plateau paleomagnetic measurements demonstrate that polarity zones recorded in the shilou red clay profile correspond well with polarity zones between c2an 1n and c5n 2n of the gpts and the basal age of the study profile is approximately 11 0 ma field observation grain size frequency distribution and quartz grain morphology suggest a wind blown origin for this sequence this indicates that the eastern loess plateau began to accumulate dust deposits at 11 ma ago implying earlier establishment of the east asian paleomonsoon probably owing to uplifting of the tibetan plateau and ongoing global cooling it also demonstrates that the eastern loess plateau belonging to the ordos platform was slowly uplifted and suffered from erosion in the early neogene and has no conserved eolian deposits older than 11 ma as in the western chinese loess plateau

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

preliminary magnetostratigraphy of a thick eolian red clay loess sequence at lingtai the chinese loess plateau magnetic remanence and bulk susceptibility measurements are reported for a 305 m eolian loess red clay sequence at lingtai the chinese loess plateau polarity zonation defined by about 680 remanence data yields a basal age of about 7 05 ma for the section which represents the oldest wind blown dust deposited continuously in north central china during the late cenozoic the resultant magnetostratigraphic scheme implies a nearly linear accumulation rate about 2 98 cm ka of atmospheric dust on the loess plateau during the period of 7 05 to 2 58 ma comparison of the bulk susceptibility record with the pedogenic characteristics of the red clay observed in the field suggests that magnetic susceptibility in the red clay is not as useful as in the loess soil sequence to indicate summer monsoon variations

astronomical forcing of the east asian monsoon mirrored by the composition of pliocene south china sea sediments abstract high precision major and minor element records of pliocene core intervals from ocean drilling program odp site 1145 located in the northern part of the south china sea were generated at a 5 cm approximately 2 kyr resolution from the geochemical data distinct proxies those indicating changes in detrital matter provenance as well as those indicating productivity variations could be derived both the terrigenous input to the northern south china sea k si and variations in productivity ba al show a response to insolation forced monsoon variability while the fluvial input k si responds to changes in the summer monsoon productivity increases as documented by ba enrichments seem to reflect variations in winter monsoon intensity a stronger winter monsoon may have increased nutrient availability via dust input and or upwelling phenomena according to our geochemical proxy records summer and winter monsoons are approximately 180 out of phase this may imply forcing of the winter monsoon through southern hemisphere summer insolation maxima the k si ratio shows a linear correlation with the la90 1 0 5 northern hemisphere summer insolation record and has therefore been used to create an astronomical timescale for the investigated sediments of odp site 1145 carbonate contents and corresponding color reflectances display 41 and 100 kyr cycles we propose that these do not reflect glacial cycles but are rather the result of an interference signal of dilution by fluvial and eolian terrigenous material and carbonate production burial flux a sudden onset of gradual changes in sediment composition occurs after 3 0 ma this is also documented by an increase in sedimentation rates and may be caused by enhanced fluvial input from the pearl river due to intensified weathering rates on the asian continent this may be linked to tectonic processes around the himalayan tibetan complex and its consequences regarding land sea heating and atmospheric circulation

the chinese loess in xifeng ii a study of anisotropy of magnetic susceptibility of loess from xifeng summary measurements of specimens from the loess profile of xifeng gansu province china all show original magnetic fabric for sediments i e nearly horizontal foliation and the commonly oblate magnitude ellipsoid the degree of anisotropy always shows a strong correlation with the foliation f rather than with the lineation l specimens from wind blown loess redeposited water lain loess and red clay show their own distribution areas respectively in a diagram of l versus f magnetic fabric provides evidence for the suggestion that the red clay like the overlying wind blown loess is aeolian in origin the data points from the red clay all falling within the distribution area of the wind blown loess data points the magnetic fabric measured from present day palaeosols may still represent the features of the parent loess although the orientation of fabric has been slightly weakened through pedogenesis as shown in the present study

spatial and temporal analysis of water chemistry records 1958 2000 in the huanghe yellow river basin 1 the chemistry of major dissolved ions ca2 mg2 na k hco3 so42 cl and dissolved silica sio2 in the river water of the huanghe yellow river china was studied from historical records at 100 stations in the drainage basin for the period 1958 2000 not all the parameters were continuously monitored during the entire period this river system 750 000 km2 presents an exceptional temporal and spatial water chemistry variability compared to other major rivers the total dissolved solid tds concentration of the huanghe varied over 2 to 3 orders of magnitude throughout the basin with a median tds concentration of 452 mg l which is about 4 times the world spatial median value wsm in particular the concentrations of na k so42 and cl were 10 20 times higher than in other major world rivers similar to the changjiang yangtze river and many other himalayan rivers the tds at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2 0 despite a water dilution of fourfold to fivefold in the summer flood season in addition to chemical weathering of sedimentary rocks evaporation and fractional crystallization were found to be the major natural process controlling the major element chemistry of the huanghe owing to the abundance of loess and clastic rocks under arid and semiarid climates a persistent increasing trend from year to year has been observed in the concentrations of tds and all the salts except for hco3 at all main channel stations except for the uppermost lanzhou the rate of increase in the tds concentration was the highest in the middle reaches 10 52 mg l yr 1 at toudaoguai and remained to be unusually high in the lower reaches 5 5 mg l yr 1 at stations luokou and lijin the increasing trend coincided with a significant decrease in water discharge at most of the main channel stations in the past 40 years and is attributed to increasing regulations of reservoirs and intensive water withdrawal for irrigation and diversions as well as many other anthropogenic processes despite the increasing trend in tds concentrations the seaward tds flux to the sea by the huanghe has decreased dramatically from more than 20 109 kg yr in the 1960s to less than 10 109 kg yr at present due to the sharp decrease in water discharge sometimes completely dried up in the lower reaches of the river the significant decreases in sea ward fluxes of water and dissolved salts are expected to have profound physical ecological and socio economic impacts on the lower reaches of the river the coastal areas and the bohai sea

spatial pattern of grain size in the late pliocene red clay deposits north china indicates transport by low level northerly winds abstract the confirmation of an eolian origin of the tertiary red clay from north china would make it a valuable terrestrial paleoclimatic record however it is still controversial as to which wind primarily transported the dust forming the red clay onto the loess plateau careful consideration of this question is a prerequisite for better understanding the history of atmospheric circulation in central and east asia during the miocene and pliocene epochs in this paper the grain size distributions of bulk samples and chemically isolated quartz grains of the late tertiary red clay were investigated to explore the potential transportation mechanisms of the dust as well as the atmospheric circulation at the time of deposition the samples were taken from six localities spanning across 550 km on the loess plateau the results show that the mean grain size of both bulk and quartz samples decreases southward as does the coarse fraction content 42 m these data not only give new evidence for the eolian origin of the red clay but also indicate that the red clay was probably transported mainly by northerly low level winds or the winds at least had a strong northerly component therefore the spatial distribution of grain size of the red clay is comparable to that of the overlying quaternary eolian loess which demonstrates a remarkable northwest southeast decrease in grain size sedimentation rate and thickness during the last glacial coinciding with the dominant wind direction of the northwesterly east asian winter monsoon however the grain size of the red clay is generally finer than the corresponding loess this indicates that the red clay may have been transported by a weaker winter monsoon associated with stronger pedogenic modification and or the dust source area was not extensive compared to that during the quaternary moreover the high content of grains coarser than 19 m transported mainly by energetic low level winds over short distances suggests that the dusts were not transported by upper level westerly

relevance of seismicity in kumaun garhwal himalaya in context of recent 25th april 2015 m w 7 8 nepal earthquake abstract due to the continuous movement of underthrusting indian plate beneath the eurasian plate the strain energy accumulates which is released substantially in the form of great earthquakes it is yet to be released in the unruptured zone which lies between the two great earthquakes viz 1934 bihar nepal earthquake and 1905 kangra earthquake this zone has been termed as the central seismic gap csg the occurrence of previous great earthquakes and recent nepal earthquakes gives a clue to the probable location of future great earthquake on the basis of analysis of seismicity in the locked portion and the stress drop analysis the csg has been redefined and location of probable zone of future great earthquake has been demarcated

periodicities of palaeoclimatic variations recorded by loess paleosol sequences in china abstract palaeoclimatic periodicity recorded by chinese loess paleosol sequence has been investigated for a number of years however conclusions from previous investigations are still controversial and interpretation of cycle evolution is quite equivocal in this study two typical loess paleosol sequences 148 and 191 m in thickness respectively in the central chinese loess plateau are sampled 3872 samples total and measured for grain size distribution and magnetic susceptibility in order to reconstruct the palaeoclimatic changes over the past three million years on the basis of a new sensitive proxy indicator of palaeoclimate and a newly developed independent time scale not orbitally tuned two time series of asian dust storm variations which are highly related to the palaeoclimate system changes are obtained wavelet and spectrum analyses indicate that there are approximately 400 200 100 66 57 41 31 27 and 22 kyr cycles in these typical loess paleosol records some orbital driven cycles are weak and are not well presented in the new time series while some non orbital cycles are found since the eccentricity frequencies of the solar irradiance of approximately 400 and 100 kyr are preserved in these palaeoclimatic sequences the lack of relatively short time orbital cycles of 41 kyr obliquity and 22 kyr precession cycles in part of the two time series may be explained by the relatively low time resolution of the loess paleosol deposits through an astronomical estimate the obliquity and precession cycles should leave stronger footprints on records of palaeoclimatic variations at the middle latitudes of the northern hemisphere the presence of non orbital cycles may be explained by unstable dust deposition processes and pedogenic processes in the paleosol units which could misrepresent or obliterate the imprint of the solar irradiance frequency this conclusion may indicate that one should be cautious when investigating specific palaeoclimatic changes e g at sub orbital time scales recorded in loess deposits especially in the paleosol units

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

gps measurements from the ladakh himalaya india preliminary tests of plate like or continuous deformation in tibet observations of relative motion in a geodetic network in ladakh india and across southern tibet indicate slow shear on the karakorum fault rapid east west extension across the whole of southern tibet and constant arc normal convergence between india and southern tibet along the himalayan arc measurements of ten campaign style and six permanent sites with global positioning system gps precise geodesy provide these bounds on the style and rates of the large scale deformation in the tibet himalaya region divergence between sites at leh ladakh india and shiquanhe western tibet as well as slow relative motion among sites within the ladakh network limit right lateral slip parallel to the karakorum fault to only 3 4 5 mm yr this low rate concurs with a recent estimate of 3 4 mm yr for late holocene time but disagrees with the much higher rate of 30 35 mm yr that has been used to argue for plate like behavior of the tibetan plateau convergence between ladakh and the indian subcontinent at 18 8 3 mm yr at 224 17 1 differs little from estimates of convergence across the central segment of the himalaya finally lengthening of the baseline between leh ladakh and lhasa in southeastern tibet at 17 8 1 mm yr or between leh and bayi farther to the southeast at 18 3 mm yr is consistent with an extrapolation of rates of east west extension of the tibetan plateau based both on shorter gps baselines e g lhasa simikot and on diverging slip vectors of earthquakes in the himalaya we interpret these results to indicate that tibet behaves more like a fl uid than like a plate

one dimensional reference velocity model and precise locations of earthquake hypocenters in the kumaon garhwal himalaya we report an optimum 1d velocity model of the kumaon garhwal himalaya based on analysis of 5000 seismograms generated at 50 digital broadband seismic stations in the region during april 2005 and june 2008 these include data from 385 local earthquakes with azimuth gaps of 180 each of which had a minimum of seven p and five s phase readings this velocity model was then used to map the locations of 1150 earthquakes 1 m 5 that occurred in the region a majority 75 of these earthquakes occurred in the upper 20 km of the crust largely above the main himalayan thrust and forms an 10 km wide band along the surface trace of the munsiari thrust however we also find another parallel band of earthquakes about 70 km to its southwest through the tehri dam in the lesser himalaya and a significant number 15 both in the tethys himalaya and within the flexed crust of the underthrusting indian plate beneath the ganga basin furthermore unlike the reported absence of seismicity in the lower crust of the nepal himalaya and its reappearance in the shallow mantle the kumaon garhwal himalayan crust is found to be seismically active throughout with no event reliably recorded in the shallow mantle of this region during the epoch of our seismic recording online material figures show constrains and distribution of data used in joint inversion and table shows p and s wave corrections obtained from travel time inversion

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

wind blown origin of the pliocene red clay formation in the central loess plateau china abstract in order to determine the depositional processes of the pliocene red clay formation deposited directly beneath the plio pleistocene loess in the chinese loess plateau four red clay sections spanning over 400 km are studied grain size analysis of closely spaced samples in the sections shows that the particles of the red clay are very fine with the sand fraction 63 m being negligible and that all the curves indicating changes in different grain size parameters have a similar pattern the grain size records in the upper part of the four sections are almost identical with the median grain size centered at 4 8 m the ree patterns of 28 samples from the jiaxian red clay section are all characterized by lree enrichments relatively flat hree and slight negative eu anomaly being similar to those of eolian loess and the average upper continental crust these lines of evidence point to a wind blown origin of the red clay deposits accumulation of the loess soil sequences in the chinese loess plateau during the past 2 6 ma can be therefore regarded as the continuation of the pliocene atmospheric dust deposition observations of spatial grain size changes in the loess plateau suggest that the eolian red clay might be transported mainly by the westerlies differing significantly from the overlying loess that was transported essentially by the east asia winter monsoonal winds

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

dynamics of the 2015 m7 8 nepal earthquake the 2015 m7 8 nepal earthquake ruptured part of the main himalayan thrust beneath kathmandu to study the dynamics of this event we compute p wave spectra of the main shock and of two large aftershocks to estimate stress drop and radiated energy we find that surface reflections depth phases of these shallow earthquakes produce interference that severely biases spectral measurements unless corrections are applied measures of earthquake dynamics for the main shock are within the range of estimates from global and regional earthquakes we explore the azimuthal and temporal variations of radiated energy and highlight unique aspects of the m7 8 rupture the beginning of the earthquake likely experienced a dynamic weakening mechanism immediately followed by an abrupt change in fault geometry correlation of backprojection results with frequency dependent variations in the radiated energy rate and with the suggested geometry of the main himalayan thrust yields new constraints on dynamic ruptures through geometrical barriers

tectonic and climatic controls on provenance changes of fine grained dust on the chinese loess plateau since the late oligocene abstract provenance variations of late cenozoic aeolian deposits on the chinese loess plateau clp were closely associated with regional tectonic activity and climatic change previous studies however have not reached a consensus regarding the nature and origin of past variations in source this study presents the results of oxygen isotope 18 o analyses of fine grained quartz 18 o variations exhibit distinct trends and patterns of variation over six time intervals i e 25 20 20 12 12 7 7 2 6 2 6 1 2 and 1 2 0 ma in comparison with quartz 18 o results from east asian dust sources and previous provenance studies of the same aeolian sequences we identify three significant composition changes of the dust source system at around 20 12 and 2 6 ma the dust source system was also rather unstable at 25 20 12 7 and 1 2 0 ma while three stable stages occurred at 20 12 7 2 6 and 2 6 1 2 ma the correlation between the provenance changes and paleoclimatic and tectonic evidence suggests that both tectonic and climatic factors were important in driving the observed stepwise provenance changes however the changes were mainly constrained by tibetan plateau uplift prior to the quaternary and by global climate change thereafter

surface deformation in the region of the 1905 kangra mw 7 8 earthquake in the period 1846 2001 1 one century after the mw 7 8 kangra earthquake of 4 april 1905 we report weak constraints on its rupture parameters based on the remeasurement of historic triangulation points in the epicentral region the western corner of the 1905 rupture is constrained to within 20 km and its sw edge strikes n135 15w the down dip width of the rupture is inferred from the location of the interseismic locking line to have been less than 55 km scaling laws and revised msk intensities suggest an along arc rupture length of 100 km with uniform slip of 4 m because the earthquake ruptured 60 of the width of the plate boundary and released a fraction of the inferred slip deficit complacency about its re rupture in the distant future is unwarranted the kangra rupture could fail again today in a mw 7 5 earthquake 1 4 m of slip or as part of a much larger earthquake mw 8 6

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

the status of central seismic gap a perspective based on the spatial and temporal aspects of the large himalayan earthquakes abstract the central himalaya considered as a prominent seismic gap is generally believed to be the most vulnerable segment due for a great plate boundary earthquake m 8 two significant historical earthquakes are known to have occurred in this region in ad 1505 and 1803 interpreted by some workers as great earthquakes occurrences of these events question the validity of central himalaya being a seismic gap here we analyze the macroseismal data from the central himalaya and the gangetic plains and suggest that neither of these earthquakes can be qualified as a plate boundary type event and the size of at least the 1803 does not exceed mw 7 7 our studies further indicate that the central himalayan frontal thrusts may be undergoing a quiescence of 1000 years in terms of generation of great earthquakes assuming a steady elastic strain accumulation due to plate convergence and its simple translation as periodic great earthquakes such long quiescence may appear intriguing we suggest that the long term quiescence and the spatial and temporal clustering that characterize the distribution of large earthquakes in the himalaya is a manifestation of the tectonic deformation associated with a highly evolved fold and thrust belt our analyses also indicate that the large moderate earthquakes are mostly concentrated on higher level thrusts these structures probably accommodate most of the seismogenic slip in the himalaya and the rest of the strain could possibly be expended on passive folding consequently great earthquakes m 8 are relatively infrequent as in the case of central himalaya apparently leading to long periods of quiescence

causation and mechanism of magnetic susceptibility trend in upper miocene pliocene red clay deposits of the eastern chinese loess plateau abstract the upper miocene pliocene red clay deposits of the chinese loess plateau clp like the overlying quaternary loess have recorded abundant paleoclimatic evolution information in this study we found that the variation in the magnetic susceptibility of seven sections across a north south climate gradient in the eastern clp exhibited an oscillatory upward trend prior to this research much less was known about the causation and mechanism of this trend among the seven sections the jiaxian and duanjiapo sections are located in the northernmost and southernmost of the climatic gradient respectively these representative sections were therefore selected to investigate the causation and mechanism of the aforementioned trend using magnetic measurements the results were as follows 1 the absolute and relative content of fine grained ferrimagnetic minerals displayed an oscillatory upward increasing trend in both of the red clay sequences which was the primary reason for the susceptibility increase in fluctuations 2 the absolute content of antiferrimagnetic minerals was nearly equivalent in each red clay sequence 3 based on the combination of the results of present study and previous study findings we found that the weathering and pedogenesis intensity of the red clay sequence showed an oscillatory upward trend during 7 2 6 ma which was closely linked with the strengthened east asian summer monsoon in oscillations these findings are probably the main cause for the oscillatory upward increasing fine grained ferrimagnetic minerals in upper miocene pliocene red clay sequence further this is likely the mechanism for the oscillatory upward increase of in the red clay sequence

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

major element rare earth element and sulfur isotopic composition of a high elevation firn core sources and transport of mineral dust in central asia 1 the arid region extending from the caspian sea into china contains some of the most extensive dust aerosol production areas in the world major element al fe ca and s rare earth element ree and isotopic 34s and 18o data from a 14 4 m long firn core recovered on the inilchek glacier tien shan mountains kyrgyzstan 5100 m elevation are presented and used to investigate the composition sources and transport of mineral dust to this central asian site the combination of geochemical compositions points to three distinct types of mineral deposits loess calcium carbonate and gypsum which do not covary in a linear fashion during the period recorded in the firn core 1992 1998 loess identified by its ree composition is characterized by distinct large scale deposition events and by ubiquitous background deposition at other times significant interannual scale variability is evident with the two largest loess events occurring within a single accumulation year 1997 and background conditions prevailing during 1994 1996 ree compositions specifically nd yb ratios point to multiple sources and transport directions of loess to inilchek glacier nonloess sources provide a significant fraction of the total ca and s deposited at the inilchek glacier hence the downcore profiles of ca and s reflect variability in the deposition of calcium carbonate and gypsum differences in the sulfur isotopic composition 34s of high dust period 15 0 and low background dust period 5 4 samples provide strong evidence for two sources of sulfate the former isotopic composition reflects a marine evaporite source of which there are many to the west of the tien shan mountains the latter composition indicates that a major portion of the atmospheric so42 was derived from anthropogenic emissions while the deposition of non loess ca calcite and non loess s gypsum is also high during the periods of high loess deposition there is pronounced ca and s variability during background loess periods 1994 1996 we suggest that the observed geochemical variability in the firn core can be explained by changes in local to regional scale atmospheric circulation and associated transport from multiple dust sources western kyrgyzstan kazakhstan versus the taklimakan desert china

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

magnetostratigraphy of the baoji loess paleosol section in the north central china loess plateau the baoji section is judged to be the most complete accessible quaternary loess paleosol section in the north central china loess plateau it is located 5 km north of the city of baoji it contains 37 paleosols and was recently named the type pedostratigraphic section the pedostratigraphic units geosols of the baoji section can be correlated throughout the loess plateau by a combination of magnetostratigraphy and character position and association of pedostratigraphic units magnetic properties were determined from 483 samples taken from 159 m of loess that overlies the red clay formation all major reversals that occurred in the last 2 5 ma were recorded the brunhes matuyama boundary occurs at a depth of 58 5 m within loess unit l8 the jaramillo subchron between 72 0 m in loess unit l10 and 76 4 m in paleosol s11 the olduvai subchron between 125 5 m in loess unit l25 and 131 5 m in loess unit l27 and the gauss matuyama boundary at 157 8 m within loess unit l33 just above the contact with the red clay formation this is the only known site where all major magnetic reversals are clearly defined in distinct field identifiable loess soil units in one section the magnetostratigraphy of the baoji section is thus recommended as the type section for the loess plateau

a preliminary reconstruction of the paleoecological and paleoclimatic history of the chinese loess plateau from the application of biomarkers abstract this study provides a preliminary reconstruction of paleoecological and paleoclimatic history over the central chinese loess plateau clp during the last 8 1 ma based on biomarker records from the earliest of the chaona stratigraphic section throughout the section we found variations in n alkane and n alkan 2 one distributions and dramatic changes in six other biomarker proxies 1 n alkanes c27 c29 c31 c33 ratios 2 n alkanes c27 c31 ratios 3 cpi carbon preference index values for cpi h alk 4 values for cpi h ket 5 n alkane mean chain lengths acl alk and 6 n alkan 2 ones c29 c31 ratios the c29 n alkanes dominate the red clay sediments with little variability indicating that trees dominated the clp and that the climate was relatively stable and less variable during the 8 1 2 6 ma period in contrast the c31 n alkanes dominate the loess paleosol sediments and biomarkers vary with relatively greater amplitude and higher frequency indicating that grasses dominated the clp and the climate was more arid and variable these biomarker records chronicle a drying and cooling trend on the clp since 4 ma these records can be further divided into four stages with boundaries around 5 6 3 8 and 2 6 ma indicating that the clp vegetation and climate experienced four evolutionary phases broadly consistent with those inferred from other available proxy data

aeolian origin and palaeoclimatic implications of the red clay north china as evidenced by grain size distribution the red clay is an important deposit underlying the quaternary loess palaeosol sequence in the chinese loess plateau being regarded as an excellent record of palaeoclimate changes in the late tertiary several properties of the red clay have been measured previously in order to derive climatic information however the sedimentary processes involved and the origin of the materials remain controversial here we present results of grain size analyses of the red clay from four representative sites in the chinese loess plateau in particular their grain size distribution is compared with that of typical quaternary aeolian loess palaeosol as well as lacustrine and fluvial sediments it appears from the sedimentological evidence that the major part of the red clay is of aeolian origin it is rather similar in some of its properties to the quaternary loessic palaeosols the dust forming the red clay was transported by a wind system that was weaker than that involved in the accretion of the quaternary loess furthermore the red clay sediment has been modified by post depositional weathering copyright 2001 john wiley sons ltd

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

possible influence of subducting ridges on the himalayan arc and on the ruptures of great and major himalayan earthquakes abstract subduction of bathymetric features such as ridges seamounts fractures etc on the subducting plate influences the arc morphology and earthquake ruptures we analyse their effect on the development of the arcuate shape of the himalayan arc and on the ruptures of great and major himalayan earthquakes besides the two most prominent ridges in the indian ocean namely the chagos laccadive deccan ridge and the 90 e ridge which are assumed to extend up to the himalayan arc at least three major subsurface ridges have been mapped on the underthrusting indian plate under the indo gangetic plains it appears that the subduction of the two most prominent ridges contributed to the development of the arcuate shape of the himalayan arc the interaction and subduction of the other subsurface ridges probably influenced the himalayan arc morphology by causing a localised cusp in the frontal topography also these ridges probably acted as barriers to the ruptures of the major and great himalayan earthquakes

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

a study of source parameters site amplification functions and average effective shear wave quality factor qseff from analysis of accelerograms of the 1999 chamoli earthquake himalaya the accelerograms of the 1999 chamoli earthquake and nine of its aftershocks which occurred in uttaranchal himalaya have been analyzed to investigate their source parameters the site amplification functions and the average effective shear wave quality factor qseff in the region the fault plane solution of the main shock is obtained using the spectral amplitudes of sh waves approximated by transverse components of accelerograms of the high energy packets observed in the accelerograms of the main shock it is found to be comparable with the reported solutions in other studies similarly the other source parameters viz seismic moment 5 03 1 7 1025 dyne cm stress drop 65 bars source duration 5 2 s and moment magnitude 6 4 estimated for the main shock are consistent with the values obtained in other studies the stress drops estimated for the aftershocks vary from 23 bars to 153 bars and the seismic moment from 1 4 1023 dyne cm to 2 9 1023 dyne cm the average estimated values of the effective shear wave quality factor qseff vary from 655 359 in the uttaranchal sector of himalaya and 1475 130 in the delhi region in general the qseff value increases with an increase in the epicentral distance reflecting the penetration of the waves into deeper layers of the crust as the epicentral distance of the observation point increases these values of qseff indicate that in general the curst is at low temperatures that will promote brittle behavior and conditions for episodic failure as compared to creep under the accumulated strains from plate collision at the himalaya plate boundary the site amplification characteristics at sites have been identified from the frequency bands of significant amplification observed in the spectral ratios of the horizontal to the vertical component records the decay of peak ground acceleration pga values with distance has been investigated using the empirical regression curves vis a vis the site amplification factors

soil properties and charcoal dynamics of burnt soils in the tyrolean limestone alps abstract we investigated soil samples of four burnt slopes in the tyrolean limestone alps of varying age after fire wildfires occurred in 2003 1962 1946 and in 1250 ad as well as of the surrounding soils that were not affected by combustion charcoal content of the o and a horizons was determined as well as ph soil organic matter content and c n ratio the results showed a background value of charcoal in all soils with a dominance of charcoal in the o horizon of the youngest burnt slope 2003 with vegetation and soil recovery charcoal concentrations decreased and zones of maximum charcoal accumulation shifted further down in the soil profile soil organic matter contents significantly decreased on burnt slopes which is due to vegetation combustion long term vegetation changes and intensified erosion however in the long term re accumulation occurs due to the recovery of vegetation soil ph increased by combustion and was further modified by an altered vegetation composition c n ratios remained largely stable with the soil n content reacting more sensitive to combustion the results demonstrate that alpine regions react sensitively to wildfires due to the steep slope angle which causes not only short term but also long term modification in vegetation composition and erosion

a coupled environmental system formed at about 2 5 ma in east asia abstract the somewhat abrupt commencement of loess deposition on a large scale in north central china is palaeomagnetically measured at about 2 5 ma the formation of the dynamical conditions responsible for windblown loess processes implies a reorganization of the atmospheric circulation over eastern asia it is speculated that at that time the accelerated uplift of the tibetan plateau had reached a threshold height giving rise to the intensification and northward shift of the siberian high and deepening of the cyclone in the lee of the tibetan plateau the uplift of tibet and the resulting reorganization of atmospheric circulation at about 2 5 ma would initiate a coupled environmental system tibetan plateau inland desert loess plateau in eastern asia that could be a key system in understanding the onset of glaciation in northern hemisphere and climatic change in the quaternary the climatic shift from near continuous warm condition before 2 5 ma to frequent and chaotic fluctuations after is speculated to be triggered to a significant extent by the uplift of the tibetan plateau an orography cold surge albedo temperature feedback mechanism is developed in explaining the harsher climate over east asia during glacial time and is thought to be one of the major contributors in promoting glacial development on the globe

paleomagnetic age of the tangxian planation surface northwestern zhongtiao shan of the shanxi graben system north china abstract a numerical formation age for the tangxian planation surface txps in north china is still controversial the txps beveled across paleoarchean basement rocks is overlain by late cenozoic conglomerate aeolian red clay and loess the magnetostratigraphy of two late cenozoic deposition sections is established and two other sections are recorded and measured in this work the magnetostratigraphy indicates six normal magnetozones n1 to n6 and six reverse magnetozones r1 to r6 these magnetozones are correlated to chron c1n through c2an 1r indicating that the txps was formed at 3 12 3 03 ma the characteristics of the zhongtiao shan tectonic uplift and its relationship with the tibetan plateau and ordos block are discussed in terms of tectonic uplift the txps formation and accumulation of the late cenozoic sediments are mainly controlled by tectonic activities the formation and uplift of the txps with a lag in the shanxi graben system is consistent with the activities of the tibetan plateau and ordos block implying that the ne extension of the tibetan plateau epeirogenic uplift advances successively

the onset of extensive loess deposition around the g m boundary in china and its palaeoclimatic implications abstract in northern china the red clay loess contact is palaeomagnetically defined at about the gauss matuyama boundary the red clay formation has recently been proposed as mostly of wind blown origin and can be interpreted as having been formed under climatic conditions of continuous warmth punctuated by small amplitude oscillations the shift from red clay development to extensive loess deposition exhibits a 3 fold abrupt increase in aeolian dust deposition rate and marks the beginning of frequent and chaotic climatic fluctuations this event implies a large scale reorganization of the atmospheric circulation over east asia in particular the northward shift and intensification of the siberian high which may have resulted from a dramatic uplift of the tibetan plateau compared to another climatic shift recorded by the chinese loess deposits which occurred at about the upper boundary of the olduvai subchron the red clay loess shift is much more pronounced and recognizable in the field it appears that in regional stratigraphic studies the g m magnetic reversal has a better correlation potential than the upper olduvai

preliminary magnetostratigraphy of the red clay underlying the loess sequence at baoji china magnetic remanence and bulk susceptibility measurements are reported from 93 samples spanning the uppermost 27m of the red clay underlying the loess sequence at baoji shaanxi province china if a new previously undetected short about 20ka excursion or reversed interval near 3 3ma be accepted then a reasonable fit to the standard time scale emerges a linear accumulation rate of 1 5cm ka is implied and the correlation coefficient is 0 992 no significant hiatus occurs between the red clay and the overlying loess so the 27m investigated reach back to about 4 3ma fourier analysis of the bulk susceptibility data yields a strong peak near 400ka in agreement with astronomical calculations of the orbital parameters responsible for climatic forcing

late cenozoic sporopollen records in the yangtze river delta east china and implications for east asian summer monsoon evolution abstract the late cenozoic east asian summer monsoon easm is generally linked with the tibetan plateau uplift and or global cooling in this study four cores zk004 zk005 sz03 and sz04 consisting of fluvial lacustrine deposits spanning the period of 8 0 0 ma were obtained from the yangtze river delta east china for sporopollen analysis to investigate trends in the easm evolution and its driving forces the results show that high percentages of arboreal taxa such as fagaceae ulmaceae juglandaceae taxaceae taxodiaceae liquidambar anacardiaceae rutaceae etc represent a relatively warm and humid climate between 8 0 and 2 6 ma the herb dominated vegetation poceae asteraceae cyperaceae etc is linked with a relatively cold and dry climate after 2 6 ma the compiled thermophilic percentages and ap arbors nap non arbors ratios of these four cores which show that the long term cooling and drying trends are similar to the global cooling since 8 0 ma imply that the easm experienced long term weakening coincident with the global cooling however over this super long time scale the thermophilic percentages and ap nap ratios have remained at roughly stable levels since 2 6 ma possibly due to the effects of the tibetan plateau uplifts