influence of th rich mineral phases on u th radioactive disequilibrium ages of sulfide deposits from the okinawa trough abstract many samples of hydrothermal sulfide minerals from the okinawa trough yield 234u 230th radioactive disequilibrium ages that are inconsistent with the ages of coexistent barite obtained using electron spin resonance esr method these results contrast strongly against results obtained for the southern mariana trough for which the u th radioactive disequilibrium ages are roughly consistent with the esr ages sulfide minerals from the okinawa trough show large variation in u and th abundances suggesting open system behavior we infer that the interaction of hydrothermal fluids with thick terrigenous sediment caused large scale migration of u and th in the okinawa trough the 234u 230th 232th 230th plots for the sulfide samples from the hatoma knoll and the izena hole show two mixing trends for each site the presence of th rich phase with high 230th 234u ratio seems to cause incorrect age estimates of the sulfide deposits

climatic and tectonic controls on sedimentation and erosion during the pliocene quaternary in the qaidam basin china the qaidam basin is an internally drained basin located in the northeastern tibetan plateau presently over 50 of the basin floor exposes thick 1 km sections of pliocene quaternary strata that are deformed by folding and faulting we investigated this nearly continuous pliocene quaternary sedimentary record for the effects of global climate change and deformation on basin sedimentation new detailed stratigraphic magnetostratigraphic and stable isotope 18 o 13 c data from the pliocene shizigou and pleistocene qigequan formations along the southwestern flank of an intrabasin fold within the north central qaidam basin are presented here strata reveal climatically controlled meter scale parasequences within shallow lacustrine marginal lacustrine and deltaic lithofacies paleocurrents shift from eastward at the base to southwestward for the majority of the section but they abruptly shift toward the south southeast in the upper 400 m twenty two magnetozones constrain deposition between 5 2 ma and ca 0 8 ma and reveal that sedimentation rates were fairly constant 474 34 m m y from 5 2 to 3 0 ma after which time rates abruptly decreased to 154 40 mm yr before increasing again to 750 m m y since 1 2 ma the 18 o values shift from relatively constant values avg 6 8 range 9 6 to 4 5 relative to vienna peedee belemnite vpdb to less negative values avg 1 2 range 1 2 to 2 7 vpdb between 3 1 and 2 6 ma and to extremely variable values avg 2 9 range 8 3 to 4 0 after ca 2 6 ma the post 2 6 ma extreme variability in stable isotopes reflects the same timeframe of enhanced climatic cyclicity associated with northern hemisphere glaciation the 13 c values remain relatively constant average 4 0 range 5 7 to 1 0 until ca 0 9 ma when the values increase to 0 3 range 1 0 to 1 5 vpdb the appearance of growth strata at 3 0 ma shallow water evaporite deposition after 2 6 ma and the observation of paleoyardangs buried wind sculpted landforms within lake marginal strata at 2 4 ma imply that emergence of the adjacent anticline was followed by the shallowing and partitioning of the lake basin and subaerial exposure and erosion of marginal lake sediments these data reflect a significant change to a more arid climate in the qaidam basin between ca 3 1 ma and 2 6 ma overlapping with the onset of significant northern hemisphere glaciations and basin floor deformation lake level cycles were on 230 000 yr frequency from 2 6 ma to 1 2 ma before increasing to 12 000 yr frequency suggesting increased aridity and broad subaerial exposure of lake sediments after the pliocene quaternary transition deformation of intrabasin sediments by at least 3 0 ma caused uplift of the basin floor which provided an environment rich in friable material for wind deflation of the qaidam basin a likely source for sediments on the chinese loess plateau and nutrients for the pacific ocean carried by westerly winds by 2 6 ma deformation of the qaidam basin created closed depressions that facilitated evaporite sedimentation that continues today coeval intrabasin deformation combined with increasing aridity after 3 1 ma thus controlled both deposition and erosion within the region

rapid exhumation at 8 ma on the liupan shan thrust fault from apatite fission track thermochronology implications for growth of the northeastern tibetan plateau margin abstract the liupan shan mountain is one of the outermost ranges in northeastern tibetan plateau the onset of its uplift provides insight on whether the plateau grew sequentially outward or broad areas of the plateau deformed simultaneously the apatite fission track method can be used to date rapid cooling as the result of unroofing of rocks in response to tectonically induced vertical motion fission track data from apatite in early cretaceous sedimentary strata exposed on the hanging wall of liupan shan thrust fault in northeastern tibet suggest that a late cenozoic rapid cooling events occurred at 7 3 8 2 ma or 8 ma this age apparently dates fault activity of the liupan shan thrust in response to northeastward growth of the tibetan plateau uplift and lateral growth which continues today numerous studies of the tibetan plateau suggest that the onset of deformation in eastern and northern margin of tibetan plateau occurred in the latest miocene

geochemistry of the pliocene red clay formation in the chinese loess plateau and implications for its origin source provenance and paleoclimate change abstract recent field observations and sedimentological studies suggest the eolian origin of the late tertiary red clay formation underlying the pleistocene loess soil sequence in the loess plateau thereby extending the wind blown record from 2 6 ma down to 7 0 ma in north central china to address the source provenance of the red clay major and trace element concentrations were analyzed on the samples from a north south loess transect of the loess plateau and a red clay section at jiaxian results show that there is a good agreement of both major and trace element compositions between the last glacial interglacial loess soil units and the jiaxian red clay record the ree distribution patterns of the loess soil and red clay samples are remarkably similar in shape with enriched lree and fairly flat hree profiles and clear negative eu anomaly the geochemical features of the red clay are also identical to those of upper continental crust these chemical characteristics provide further evidence for eolian sedimentation of the red clay from the relations both between na2o al2o3 and k2o al2o3 ratios and between u pb and th pb ratios the eolian loess and red clay materials must have been subject to thorough sedimentary differentiation and moderate chemical weathering in the source area the chemical similarity between soil unit s1 and the red clay implies that such an environment as occurred in the last interglacial period may have already formed in northwestern china during the late tertiary comparison of down section variations in elemental ratios with field observations of pedogenic development of the red clay suggests that cao al2o3 sr rb and sr ba are more sensitive to climate changes than magnetic susceptibility and can be used to reconstruct the climate history of the late cenozoic

holocene climate changes over the desert loess transition of north central china a 2 m trench section at the desert loess transition of north central china was analyzed at 2 cm intervals for grain size distribution md m and total organic carbon toc ams 14c time series of the md and toc records provides direct information on variations of the east asian monsoon climate during the last 10 000 yr md is considered to represent the wind strength and high md reflects strong winter monsoon winds toc denotes the degree of vegetation cover a function of the intensity of summer monsoon circulations from ca 10 000 to 7000 cal yr bp the climate was dominated by a strong winter monsoon and a very weak summer monsoon as indicated by high md and low toc values subsequently climatic conditions became warmer gradually from ca 7000 to 5500 cal yr bp the period between ca 5500 and 2700 cal yr bp displayed the highest toc and lowest md values over the last 10 000 yr marking a stable state of a warm humid climate i e the holocene climatic optimum of china during the interval of ca 2700 1500 cal yr bp the expansion and intensification of agrarian activities could have led to desertification and acceleration of deposition of coarse grained particles resulting in a decreased organic carbon accumulation rate however the toc during this interval still has values as high as during the episode of ca 7000 5500 cal yr bp reflecting a relatively stronger summer monsoon circulation since ca 1500 cal yr ago high amplitude fluctuations of toc that fluctuate in phase with the clay size fraction imply that the climate experienced three major oscillations with a prominent peak of enhanced summer monsoon circulation at ca 1300 cal yr ago and with two intervals of increased winter monsoon strength occurring around ca 1000 and 300 cal yr ago the md and toc records over the past 5000 yr demonstrate a good correlation with the archaeological phenological and historical records of china climate changes in the east asian monsoon region were not only related to the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but were also controlled by the pattern and intensity of the atmospheric circulation

spatial self organization in geomorphology from periodic bedforms and patterned ground to scale invariant topography a rich diversity of spatial order can be discerned in landforms and small scale features of landscapes with spatial order ranging in scale from 107 m to 10 2 m and in geometry from pronounced two dimensional periodicity to three dimensional scale invariance ripples of wind blown sand with their strikingly uniform spacing and mountainous topography with its fractal characteristics illustrate the range of geomorphic self organization patterns on the land surface are often very distinct easily observed and readily studied because of their accessibility and yet the systematic quantitative study of geomorphic self organization is only in its infancy it offers difficult challenges but also exceptional opportunities particularly for those versed in modern techniques used in studies of self organization in this overview diverse examples of spontaneous organization in geomorphic systems and recent pertinent studies are described starting with spatial structures that are generally most distinct and best understood they include 1 periodic structures that form on various substrates as water or air transports erodes and deposits sediments ripples and dunes meanders and bar pool topography of rivers and rhythmic shoreline features 2 polygonal patterns that result either from the growth cracks in such contrasting media as freezing lava and frozen ground or from freeze thaw alternations in soils 3 large scale periodic structures dictated by the deformation of magma or of the earth s crust linear arrays of evenly spaced volcanoes and sequences of alternating valleys and mountain ranges and 4 scale invariant structures revealed in drainage networks and topography

structure of the southernmost okinawa trough from reflection and wide angle seismic data abstract during a passive seismic experiment in the okinawa trough the shots of two reflection profiles were recorded by ocean bottom seismometers obs both profiles include 3 ocean bottom instruments are about 65 km in length and located in the axial portion of the southwestern okinawa trough processing of the reflection seismic data images recent deformation of the sedimentary units forward modelling of the wide angle data on both profiles reveals a 1 2 km thick sedimentary infill overlying an acoustic basement characterised by seismic velocities between 3 2 and 3 5 km s crustal thickness could only be modelled on one profile and was determined to be around 10 km thickening towards the ryukyu arc in the south gravity modelling was used to additionally constrain both profiles especially the deep structure of profile 1

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

dating iron skarn mineralization using hydrothermal allanite la u th pb isotopes by laser ablation icp ms abstract trace elements and u th pb isotopes of hydrothermal allanite from the beiminghe iron skarn deposit eastern north china craton were simultaneously analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms to demonstrate the suitability and robustness of the u th pb system in this phase as a geochronometer of ore forming processes allanite grains from the beiminghe deposit typically exhibit optical and chemical zoning and are intergrown or texturally equilibrated with prograde and or retrograde skarn assemblages mainly consisting of tremolite diopside magnetite and garnet in addition they contain abundant aqueous two phase or daughter mineral bearing three phase aqueous fluid inclusions confirming their hydrothermal origin most grains have high la ce ratios 1 19 1 74 and thus are classified as allanite la a notable feature of the hydrothermal allanite la is the lack of common pb with values comparable with those of the zircon standards 91500 and gj 1 used in this study la icpms spot analyses reveal remarkable variation in ca rees rare earth elements fe al and mg within a single grain consistent with the substitution of ree3 mg fe2 for ca al fe3 in the mineral structure traverses of zoned grains show that the rims have th u ratios ranging from 0 73 to 11 55 significantly higher than the core areas 0 07 1 81 fifty nine spot analyses beam size of 32 m or 60 m on 5 allanite la grains yield reproducible 206pb 238u ages of 134 7 to 139 6 ma with a weighted mean 206pb 238u age 206pbexcess corrected 206pb 238u age of 136 1 ma 2 of these 34 analyses on allanite rims have a weighted mean 208pb 232th age of 139 2 ma 2 that is within error of the 206pb 238u age the dating results showed that an increase of beam size from 32 to 60 m significantly reduces the analytical uncertainties 2 petrographic and textural data have demonstrated that the allanite la grains formed during skarn alteration and notably have close paragenetic relationships with retrograde skarn assemblages and iron oxide minerals their u th pb ages therefore are interpreted as the timing of iron skarn mineralization at beiminghe thirteen zircon grains from the ore related diorite intrusion have a weighted mean 206pb 238u age of 136 2 ma 2 consistent with and thus confirming the reliability of the allanite la u th pb ages when interpreted as the formation age of the beiminghe iron deposit our results suggest that hydrothermal allanite with low th and u is a promising u th pb geochronometer and can provide reliable constraints on the timing of hydrothermal mineralization without requiring a matrix matched external standard the present dating results also indicate that the u pb rather than th pb isotope system is preferable for u th pb dating of low th u allanite

tracing the provenance of fine grained dust deposited on the central chinese loess plateau eolian dust deposits in north china provide an excellent means of determining past variations in continental paleoclimate and atmospheric circulation however debate still exists on which deserts in east asia are the dominant sources of chinese loess and whether the dust provenance has shifted significantly at different time scales here we present new constraints on the provenance of fine grained dust deposited on the central chinese loess plateau clp by combining electron spin resonance signal intensity and crystallinity index of fine grained quartz contained in samples from two loess paleosol sequences our results show that the fine grained dust deposits on the clp originate mainly from the gobi desert in southern mongolia and the sandy deserts in northern china primarily the badain juran and tengger deserts rather than from the taklimakan desert in western china at least during the last climatic cycle the dominant source of fine grained dust varied significantly from southern mongolia during cold periods to northern china during warm periods the glacial interglacial provenance fluctuations are strongly coupled with changes in the intensity of the near surface northwesterly winter monsoon

binary sources of loess on the chinese loess plateau revealed by u pb ages of zircon the age distribution of detrital zircon has been used to trace sediment sources existing datasets show great similarity of zircon ages between the loess on the chinese loess plateau clp and the sediments from the north tibetan plateau ntp implying that eolian dust is delivered from the ntp to the clp by westerly winds or via the yellow river however ntp dust can also be transported by northwesterly winds from the alxa arid lands aals where materials are received from both the ntp and the gobi altay mountains gams here we report u pb zircon ages for aals sands and ntp and clp loess the results show that the zircons in the aals are mixed from ntp and gams zircons ntp loess is mainly derived from local sources mixing of materials from the ntp and gams defines the zircon ages of the loess on the clp better than the pure ntp source no temporal and spatial heterogeneities of zircon ages have been observed for the loess on the clp which suggests that the well mixed materials in the aals likely have an eolian source

making the material the formation of silt sized primary mineral particles for loess deposits abstract in 1911 e e free wrote it may be well to point out that there are really two problems of the loess a problem of the origin of material and a problem of deposition the problem of the origin of material has been relatively neglected in comparison to problems of deposition of the formation of deposits and latterly in comparison to studies of loess stratigraphy if we are to understand the true nature of loess this fascinating material we need to be aware of all the significant events in the processing of the particles which form a deposit a large amount of silt sized primary mineral material has to be produced to make a loess deposit loess is a quaternary phenomenon and we see the entire process being completed in quaternary times some powerful quaternary forces are able to produce very large amounts of granular material glacial grinding vigorously supported by smalley 1966a provides an obvious source for some loess material but the vast deposits of north china and central asia have no obvious glacial connection however they are adjacent to high asia a region of vast tectonic activity and an enormous release of terrestrial energy in the last several million years high asia is a large producer of loess silt much of which finds its way south to make the ganges delta but large amounts are moved north and east to make huge loess deposits africa presents a problem recent work e g coude gaussen 1987 suggests that there is a region of peri saharan loess but earlier observations e g penck indicate quite clearly that the sahara region is free of loess rathjens 1928 in his study of tripolitania indicated the presence of loess like deposits and described their nature but he did point out that 90 of the granular material was greater than 100 pm in diameter which would remove it from a strict loess definition on the soil taxonomy map of africa there is a belt of soil d3 which could include considerable loess deposits it stretches from the matmata loess in tunisia across northern libya to the western part of the egyptian coastal region if d3 contains loess this points to a genuine desert loess particle producing mechanism operating in the sahara

submarine hydrothermal mineralization in the okinawa trough sw of japan an overview abstract the okinawa trough is a heavily sedimented rifted back arc basin formed in an intracontinental rift zone submarine hydrothermal activity is located within the six back arc rifts located in the middle and southern okinawa trough and its distribution is controlled principally by tectonic factors subduction of the daito and gagua ridges beneath the ryukyu arc has resulted in fracturing of the brittle lithosphere beneath the okinawa trough hydrothermal activity is strongest in the volcanic arc rift migration phenomenon vamp area plus the jade site and southernmost part of the okinawa trough spot area which form the prolongation of these two ridges these areas are characterized by extremely high heat flow locally submarine hydrothermal fluids from the okinawa trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and nh 4 concentrations of the fluids the fluids also contain high concentrations of co 2 of magmatic origin submarine hydrothermal mineralization in the trough is diverse the clam site consists principally of carbonate chimneys interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site this is most probably a sediment hosted deposit in which sulphide minerals have deposited within the sediment column leaving spent ore fluids to emerge at the seafloor the jade site consists of active and inactive sulphide sulphate chimneys and mounds the zn pb rich sulphides at this site contain the highest concentrations of pb ag and au so far recorded in submarine hydrothermal sulphide deposits at minami ensei knoll and hatoma knoll active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor an intense black smoker has recently been discovered at yonaguni knoll in the spot area if it is confirmed that sulphide mineralization is dominant at this site this could be a highly prospective area the most prospective areas for economic grade minerals in the okinawa trough appear to be the jade site and the spot area

the age of the taklimakan desert the taklimakan desert is located in the foreland basin of the tibetan plateau we report here the results of stratigraphic investigations of a 1626 meter thick sequence with interbedded wind blown silt from the southern marginal taklimakan desert because the studied section is located downwind of the desert the eolian silt accumulation is closely linked to desert formation our new evidence indicates that shifting sand dunes prevailed in the tarim basin by at least 5 3 million years ago as they do today we attribute this event to late cenozoic climatic deterioration as well as to changes in atmospheric circulation induced by tibetan plateau uplift

signatures of mountain building detrital zircon u pb ages from northeastern tibet although detrital zircon has proven to be a powerful tool for determining provenance past work has focused primarily on delimiting regional source terranes here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance and we demonstrate its ability to detect source changes for terranes separated by only a few tens of kilometers for such an analysis to succeed for a given mountain discrete intrarange source terranes must have unique u pb zircon age signatures and sediments eroded from the range must have well defi ned depositional ages here we use 1400 single grain u pb zircon ages from northeastern tibet to identify and analyze an area that satisfi es these conditions this analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete punctuated changes in local source terranes by tracking eroding rock units chronologically through the stratigraphic record this sensitivity permits the detection of the differential rock uplift and progressive erosion that began ca 8 ma in the laji shan a 10 25 km wide range in northeastern tibet with a unique u pb age signature

temporal variations in pb isotopes and trace element concentrations within chinese eolian deposits during the past 8 ma implications for provenance change article i nfo the pb isotopes and trace element compositions of the silicate fraction of airborne dust from the chinese loess plateau were analyzed to infer provenance change during the past 8 ma the results indicate that the composition of eolian dust changed at 2 6 ma coincident with initiation of the northern hemisphere ice sheet the change in trace element composition at 2 6 ma indicates that a larger component of the eolian dust was derived from felsic rocks after this time pb isotopic evidence demonstrates that the source material of tertiary red clay differs to some extent from that of quaternary eolian deposits although chemical weathering may result in compositional changes in eolian deposits such a scenario is not supported by the present evidence given that glacial grinding and frost weathering processes have been active in the peaks of high mountains during the quaternary eolian dust of this age contains a large proportion of material derived from areas of high topographic relief and relatively little material from low lying cratonic regions such alpine processes played an important role in controlling the distinct changes in pb isotopes and trance element concentrations recorded at around 2 6 ma 2010 published by elsevier b v

high resolution magnetostratigraphy of the neogene huaitoutala section in the eastern qaidam basin on the ne tibetan plateau qinghai province china and its implication on tectonic uplift of the ne tibetan plateau abstract the closed inland qaidam basin in the ne tibetan plateau contains possibly the world s thickest 12 000 m continuous sequence of cenozoic fluviolacustrine sedimentary rocks this sequence contains considerable information on the history of tibetan uplift and associated climatic change however work within qaidam basin has been held back by a paucity of precise time constraints on this sequence here we report on a detailed paleomagnetic study of the well exposed 4570 m huaitoutala section along the keluke anticline in the northeastern qaidam basin where three distinct faunas were recovered and identified from the middle miocene through pliocene constrained by these faunal ages the observed thirty three pairs of normal and reversed polarity zones can be readily correlated with chrons 2n 5br of the gpts this study assigns the age of the section to the interval between ca 15 7 ma to 1 8 ma in addition the widely used stratigraphic units the xia youshashan shang youshashan the shizigou and qigequan formations were formed at 15 3 ma 15 3 8 1 ma 8 1 2 5 ma and

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

late cenozoic deformation and uplift of the ne tibetan plateau evidence from high resolution magnetostratigraphy of the guide basin qinghai province china the cenozoic intramontane gonghe guide basin in qinghai province china is tectonically controlled by the sinistral strike slip framework of the kunlun and altyn tagh south qilian faults in the northeastern tibetan plateau the basin is filled with thick cenozoic clastic sedimentary formations which provide important evidence of the deformation of this part of the plateau although they have long lacked good age constraints detailed magnetostratigraphic and paleontologic investigations of five sections in the guide basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit the guide group into six formations where ages are now magnetostratigraphically well established they are given in parentheses the amigang 1 8 2 6 ma ganjia 2 6 3 6 ma and herjia formations 3 6 to ca 7 0 7 8 ma and the older miocene ashigong garang and guidemen formations these rocks document a generally upward coarsening sequence characterized by increasing accumulation rates increasing gravel content and sizes of its components changes of bedding dips and source rock types and marginal growth faults collectively reflect accelerated deformation and uplift of the ne tibetan plateau after 8 ma punctuated by a sharp increase in sedimentation rate at ca 3 2 ma that reflects the boulder conglomerates of the ganjia formation interestingly much of the vergence of the compressional deformation in the basin is to the south accommodated by a sequence of six thrusts f1 f6 which become active one by one progressively later toward the south undoubtedly contributing to the uplift of this part of the plateau f1 likely initiated the guide basin due to crustal flexure in the oligocene f2 was active in the early miocene f4 and f5 at ca 3 6 ma and f6 was active in the early pleistocene the detailed late miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and hence uplift of northeastern tibet which when compared with ages for events on other parts of the plateau provides important boundary conditions for the geodynamical evolution of tibet

provenance of aeolian sediment in the taklamakan desert of western china inferred from ree and major elemental data abstract to identify the provenance of aeolian deposits in the extensive dune field in the taklamakan desert is of great importance for understanding the formation of this the largest sand sea in china the opinions from earlier studies are quite dipolar and are as follows a local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages and b strong homogenization of the sands in the entire taklamakan on the basis of geochemical data from whole rock samples by separately examining the ree characteristics and major elemental composition in coarse and fine fractions of the samples from aeolian deposits this paper provides new data for interpreting sources of aeolian deposits in the taklamakan the sampling sites are distributed in four different fluvial systems i e the areas of the keriya river niya river and cele river in the southern part and the northern margin near the tarim river fig 1 our results show that there are some significant differences in concentrations of trace elements and in ree features between the coarse and the fine fractions of the aeolian sediment the major elemental and ree data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin the fine fractions mainly silts are more homogenized the regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin this confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east west direction it should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea in addition little variation is found between old and young sands in two sediment sequences in the central part of the desert indicating consistency of sand sources in a given site during the last 40 ka

geomorphic application of the hausdorff besicovich dimension an algorithm was developed and tested to produce a useful description of natural terrain texture first orthogonal calculation of the variance spectrum of an elevation matrix of a square terrain sample was made using a variation of standard methods to eliminate directional effects second the slope of the log log spectrum wavelength diagram was used to calculate the hausdorff besicovitch h b dimension of the terrain sample according to voss formula the algorithm was tested on samples from a 60 km 60 km digital terrain model from death valley california and las vegas nevada u s a three 12 km 12 km samples showed systematic variations in both the spectral signature and h b dimension one of the terrain samples was manipulated by smoothing and simulated erosion to test the sensitivity of the dimension a sloping artificial surface was subjected to several cycles of synthetic fluvial erosion with dimension increasing with erosion duration age a smoothed 60 km 60 km terrain model was subjected to extended cycles of synthetic erosion which produced a pali type landscape typical of the island of kauai

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

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

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

new evidence for the catastrophic demise of a prehistoric settlement the lajia ruins in the guanting basin upper yellow river nw china abstract the lajia ruins in the guanting basin nw china are a product of the prehistoric qijia culture like pompeii they are a rare example of an archaeological site preserved by a natural disaster and are therefore important in archaeology anthropology and geology however the nature of the disaster s responsible for the destruction of the site remains controversial most studies have focused on an earthquake and a red clay layer directly overlying the site and a detailed stratigraphic study of the mid holocene sedimentary strata combined with other intervals of red clay deposition hence possible disasters is lacking we identified a mid holocene paleosol sequence the shanglajia section at the site which contains two layers of red clay dated to 3950 a bp and 3500 a bp intercalated within the mid holocene paleosol s0 subsequent multi proxy analysis indicated that the characteristics of the two red clay layers resemble those of typical tertiary red clay deposits and the modern gully deposit at the foot of the great red hills but are distinctly different from those of the slackwater deposits of the yellow river and the mid holocene paleosol our results suggest that at 3950 a bp and 3500 a bp two large scale rainstorm induced mudflow events originating from the gullies to the north flooded the lajia area on the second terrace of the yellow river devastating and burying the human settlements we infer that the intensified erosion and mass wasting were caused by human activity in addition natural factors such as rainstorms and earthquakes may also have played an important role in triggering catastrophic mudflow events in the tertiary red clay deposits overall our results provide further insights into prehistoric man land relationships in this environmentally sensitive region which may have implications for modern land use in this region of china and elsewhere

sulfide geochronology along the endeavour segment of the juan de fuca ridge 1 forty nine hydrothermal sulfide sulfate rock samples from the endeavour segment of the juan de fuca ridge northeastern pacific ocean were dated by measuring the decay of 226ra half life of 1600 years in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years this dating method is effective for samples ranging in age from 200 to 20 000 years old and effectively bridges an age gap between shorter and longer lived u series dating techniques for hydrothermal deposits results show that hydrothermal venting at the active high rise sasquatch and main endeavour fields began at least 850 1450 and 2300 years ago respectively barite ages of other inactive deposits on the axial valley floor are between 1200 and 2200 years old indicating past widespread hydrothermal venting outside of the currently active vent fields samples from the half graben on the eastern slope of the axial valley range in age from 1700 to 2925 years and a single sample from outside the axial valley near the westernmost valley fault scarp is 5850 205 years old the spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift these relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

strontium lead and zinc isotopes in marine cores as tracers of sedimentary provenance a case study around taiwan orogen abstract the active collision zone around taiwan orogen receives a variety of sedimentary inputs including terrigenous flux from taiwan and chinese rivers oceanic currents and atmospheric dust in order to determine the present day respective contributions of these different sources we analysed the pb and sr isotopic compositions of late quaternary sediments accumulated offshore east taiwan samples from the taiwan coastal range andesites sandstones conglomerate and peinan river terraces and suspended loads have also been analysed to constrain the mean taiwan isotopic signature mixing lines between the different sources of material indicate that the core located in the okinawa trough represents a mixture of about 60 of taiwan 30 of chinese loess and 10 of yangtze river contributions the southernmost core located close to luzon arc is influenced by taiwan 60 and volcanic material 40 the sr and pb isotopic compositions of samples cored in the manila trench and in the huatung basin are strongly influenced by the taiwan signature while the ryukyu trench core samples point to significant but variable contributions of chinese loess and yangtze river this work also reports zn isotopic variations in the silicate fraction of these marine core samples the overall variation in zn isotopic compositions expressed as 66zn is greater than 0 3 per mil for an analytical precision of 0 05 the zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material except for the manila trench core samples and the older sample from the huatung basin they present values heavier by 0 2 0 3 close to those obtained on all taiwan rocks and peinan river particulates these results show 1 the particular characteristics of taiwan zn isotopic compositions on a large scale and 2 the possible use of zn isotopes as a tracer of material sources

grain size information from the statistical properties of digital images of sediment abstract the autocorrelation technique for estimating grain size from digital images ofsand beds has been extended and validated for use on coarse sand 0ae7 mm and gravel up to 20 mm a number of aspects of the technique have beenexplored and some potential improvements suggested autocorrelation is justone suitable statistical method sensitive to the grain size of sediment in digitalimages four additional techniques are presented and their relative meritsdiscussed a collective suite of techniques applicable to the general problem ofgrain size estimation from digital images of sediment might broaden theapplicability to more sedimentary environments as well as improve itsaccuracy these techniques are compared using a large data set from a gravelbarrier beach in southern england based on over 180 samples mean grain sizeof sieved and imaged sediments correspond to within between 8 and 16 some theoretical aspects of the spatial arrangement of image intensity indigital images of natural sediments are addressed including the fractal natureof sediments in images which has potential implications for derivation ofgrain size distributions from images of sand sized material throughsegmentation and thresholding the methods outlined in this contributionmay also nd application in further uncovering the geometric structure ofsediment beds as well as in the simulation of sedimentation processes keywordsgrain size analysis digital images statistical models gravel beach introductiongrain size information from natural environ ments traditionally is obtained using methodssuch as sieving laser diffraction and settling which do not help measure equivalent propertiesof the sample in addition the slow and labour intensive nature of these methodologies has lim ited the spatial and temporal resolution at whichgrain size data are obtained where grain size isan important parameter such as in determiningsediment transport studies can be limited funda mentally by the dif culty in sampling for sedi ment at the required frequency a furtherdisadvantage is that sediment must be removedfrom the natural environment potentially alteringsubsequent system development in contrast photographic methods can be used to measuresediment size at a resolution comparable withmeasurements of hydraulic hydrodynamic andmorphological topographical conditions withoutdisrupting the sediment body by direct sampling the problem of deriving sediment size infor mation from digital images of sediment has beenapproached using two different families of tech niques the rst is based on edge detection andimage segmentation principles e g butler et al 2001 sime ferguson 2003 graham et al 2005 such techniques rely on marked image intensity contrasts between grains and gapsbetween grains interstices such that thresholdscan be speci ed to discriminate individual grainsfrom the background intensity levels e g sime ferguson 2003 thus far these methods aresedimentology 2009 56 421 438

an abrupt shift in dust source on the chinese loess plateau revealed through high sampling resolution osl dating abstract the source of dust that forms the extensive deposits of loess exposed on the chinese loess plateau is highly debated in particular it is not clear whether sources can change abruptly within individual loess units or whether local influences on source can override the influence of far travelled components high vertical sampling resolution 10 40 cm optically stimulated luminescence osl dating of sediments on the loess plateau in china has been successful in providing detailed independent age models for loess accumulation here osl behaviour is used to infer a shift in loess sediment source during the last glacial period osl dating procedures have often utilised the widely applied single aliquot regeneration sar protocol on quartz grains detailed sar osl dating of the last 45 ka of sedimentation at beiguoyuan section on the north of the loess plateau demonstrates anomalous and statistically significant age increases and scatter in age estimates in samples from a c 2 5 m unit at about 20 ka compared to samples above and below many of these samples also fail internal dose recovery tests and show anomalous luminescence signal properties deconvolution of osl decay curves into first order components reveals that many of the age overestimating samples have a significant ultrafast component this behaviour is restricted to the 2 5 m segment and is only likely to be uncovered using high sampling resolution luminescence analysis combined with heavy mineral grain size and geochemical evidence this suggests that the source of material in this unit abruptly shifted at the last glacial maximum potentially to a local source rather than well mixed and recycled multiple distant sources as appears to be the case at other times at the site and other studied sections on the loess plateau the environmental causes of this source shift may be tied to abrupt climate change during the last glacial maximum and demonstrate the highly dynamic nature of the locations of dust generation during the last glacial period the change in source also adds complexity to standard climate proxy analyses of loess using sediment properties

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

uplift of the luliang mountains at ca 5 7 ma insights from provenance of the neogene eolian red clay of the eastern chinese loess plateau abstract the luliang mountains located at the western margin of the trans north china orogen are thought to have undergone several uplift events during the late mesozoic and cenozoic due to far field effects of the india eurasia collision and or pacific plate subduction however the timing and mechanisms of late cenozoic uplift of the luliang mountains are not clear our investigation of the source characteristics of the shilou red clay sequence an eolian deposit on the eastern chinese loess plateau adjacent to the luliang mountains provides a new understanding of the relationship between the material composition of the eolian sediment and regional tectonic activity grain size data for the shilou red clay sequence reveal an abrupt increase at ca 5 7 ma and u pb detrital zircon geochronology indicates that the major source areas of shilou red clay shifted after ca 5 7 ma from the junggar basin western mu us desert and gobi alxa arid lands to the eastern mu us desert and the luliang mountains detrital zircons younger than 5 7 ma in the shilou red clay have similar u and th contents to zircons from the luliang mountains indicating that the mountains acted as a proto source for the red clay after ca 5 7 ma we suggest that the influx of coarser grained sediment is due to rapid uplift of the luliang mountains at ca 5 7 ma and that this timing is consistent with northeastward propagation of mountain uplift in response to the india eurasia collision

evolution of an active sea floor massive sulphide deposit hydrothermal circulation at oceanic spreading ridges causes sea water to penetrate to depths of 2 to 3 km in the oceanic crust where it is heated to 400 c before venting at spectacular black smokers these hydrothermal systems exert a strong influence on ocean chemistry1 yet their structure longevity and magnitude remain largely unresolved2 the active transatlantic geotraverse tag deposit at 26 n on the mid atlantic ridge is one of the largest oldest and most intensively studied of the massive sulphide mounds that accumulate beneath black smoker fields here we report ages of sulphides and anhydrites from the recently drilled3 tag substrate structures determined from 234u 230th systematics analysed by thermal ionization mass spectrometry the new precise ages combined with existing data4 5 show that the oldest material 11 000 to 37 000 years old forms a layer across the centre of the deposit with younger material 2 300 7 800 years old both above and below this stratigraphy confirms that much of the sulphide and anhydrite are precipitated within the mound by mixing of entrained sea water with hydrothermal fluid6 the age distribution is consistent with episodic activity of the hydrothermal system recurring at intervals of up to 2 000 years

u pb ages of detrital zircon and provenances of red clay in the chinese loess plateau abstract the chinese loess plateau clp which is located in the central part of china mainly contains two sequences the quaternary loess paleosol sequence and the late miocene pliocene red clay sequence u pb ages of detrital zircon from the quaternary loess paleosol sequences indicate that the current spatial pattern of central asian aridification was largely established during the early quaternary u pb ages of detrital zircon from the underlying red clay sequences demonstrate that the northern source regions were important contributors for the dust since the late miocene except for the periods of 8 ma and 5 5 to 4 ma these two periods correspond to increased and decreased dust deposition in the north pacific respectively ascribed to the late miocene aridification of the qaidam basin in the west of the clp and the early pliocene aridification of the tarim basin in the west of the clp we attribute the increase of the qaidam basin derived north pacific dust fluxes to the uplift of the ne tibetan plateau such uplift also controlled the climatic and environmental changes in central asian during the late miocene this study highlights the dynamical process of the central asian aridification during the late miocene pliocene

controls on uranium and thorium behaviour in ocean floor hydrothermal systems examples from the pindos ophiolite greece abstract a suite of hydrothermally altered basaltic rocks from the jurassic pindos ophiolite of greece was analysed for its u and th content samples taken from different levels within the ophiolite display variable degrees of hydrothermal alteration ranging from low water rock ratio recharge zone alteration to high water rock ratio discharge zone alteration most samples analysed exhibit constant u th ratios regardless of the degree of alteration however neither of these two elements correlate with any other immobile element zr y ti ree these results suggest that both u and th have been mobile during high temperature ocean floor hydrothermal alteration and indicate a common probably mineralogical control for both elements the chemical composition of hydrothermal fluids from modern tectonic settings equivalent to that of the pindos ophiolite east pacific rise guaymas basin was used to predict theoretical aqueous speciation and solubility of u and th during water rock interaction in these environments the results of this treatment agree with the above conclusions drawn from rock studies and indicate that oxide mineral phases uraninite thorianite control u and th solubility during hydrothermal alteration at oceanic spreading environments