grain size characteristics of red clay deposits on the eastern edge of chinese loess plateau and its implications for neogene evolution of east asian winter monsoon loess and red clay on the chinese loess plateau provides a detailed history of the east asian monsoon in the neogene based on grain size analysis of a shilou red clay section in shanxi china the eolian origin of shilou red clay was demonstrated then the evolution of the east asian winter monsoon was explored the results showed that most of the particles were fine grained with a median size of 5 9 m the sand fraction 63 m in most samples was less than 5 the particle size distribution shows a unimodal pattern with a modal size of 2 30 m the grain size content agreed with the decreasing north southward trend of eolian deposits on the chinese loess plateau implying that the red clay particles were carried mainly by northerly low level winds all the evidences point to an eolian origin for the shilou red clay sediments according to the variation of 10 70 m coarse content 43 m and the u ratio of the shilou grain size record the neogene evolution of the east asian winter monsoon was divided into five stages 11 0 7 5 7 5 5 6 5 6 4 8 4 8 3 1 and 3 1 2 6 ma during the period of 11 0 7 5 ma the grain size varied more frequently and with larger amplitude implying large fluctuations in the winter monsoon after 7 5 ma the grain sizes decreased slightly indicating that the winter monsoon gradually weakened between 5 6 and 4 8 ma the grain sizes showed extreme variation with the highest and lowest values across the whole section indicating large changes in the winter monsoon from 4 8 ma the grain sizes increased slightly then changed dramatically after 3 1 ma which is evidence that the winter monsoon strengthened gradually and intensified later this new finding indicates that the evolution of winter monsoon is closely related to tibetan plateau uplift and global paleoclimate change

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

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

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

equatorial undercurrents associated with indian ocean dipole events during contrasting summer monsoons 1 positive indian ocean dipole iod events generally tend to be accompanied by intensified summer monsoon flows and above normal precipitation over the sub continent although strong monsoons have not always coincided with positive iod events numerical simulation experiments and supplementary data diagnostics are performed to understand the iod sub surface dynamics in relation to the monsoon strength the model experiments when forced by iod winds during strong monsoon periods generated a strong subsurface zonal pressure gradient along the equator and an eastward equatorial undercurrent euc leading to supply of cold subsurface waters to the upwelling regions in the eastern equatorial indian ocean however the simulations when forced with iod winds during weak monsoon periods were unable to set up the subsurface pressure gradients and the euc thus resulting in weak sst cooling in the east these results raise the possibility that iod monsoon interactions during strong monsoon years might favor intensification of the iod

the record of changing hematite and goethite accumulation over the past 22 myr on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy 1 high field isothermal remanence hirm and diffuse reflectance spectroscopy drs wereusedto characterize hematite and goethite in a suite of bulkand particle sized fractioned samples from the chinese loess plateau representing the main changes in magnetic mineralogy over the past 22 myr the record of drs defined hematite largely reflects variations in the pedogenic fraction 8 mm makes the main contribution to goethite concentrations in the bulk samples pedogenic goethite concentrations generally vary inversely with those of hematite the lack of consistent correlations between hirm inferred mineral content and drs measurements casts doubt on the validity of using hirm to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution the progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction reflecting changes in the source region possibly involving increased aluminum substitution the good correlation between drs defined hematite and frequency dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite the results shed new light on using hirm to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 myr in the dust source regions and on the loess plateau

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

identifying eolian dust in the geological record abstract recognition of terrestrial dust in geological records is essential for reconstructing paleoenvironments and quantifying dust fluxes in the past however in contrast to eolian sands silt sized dust is difficult to recognize in pre quaternary records due to a lack of macroscopic features indicating eolian transport and mixing with alluvial sediments windblown dust deposits are commonly identified by comparing their sedimentological and petrological features with quaternary examples of dust known as loess here we review the characteristics of terrestrial dust deposits and conclude that most of these features are not exclusively windblown and may be formed by alluvial deposits as well we therefore synthesize a set of criteria which enable a reliable identification and quantification of dust while acknowledging potential contributions of alluvial components these methods include quartz grain surface morphology analysis to distinguish eolian and alluvial transport modes provenance studies to identify local and extrabasinal sources grain size shape end member modelling to quantify the various sedimentary contributions to the record and a basin scale stratigraphic approach to derive regional patterns and avoid interpretation of local phenomena we reassess the eocene to pliocene records of the chinese loess plateau and conclude that these strata represent both alluvial and eolian sediments deposited in extensive mudflat systems quaternary loess by contrast is almost exclusively composed of windblown dust the early pleistocene shift from mudflat to loess deposits is associated with a significant increase in accumulation rates likely due to increased dust production upwind overwhelming and blanketing the local mudflat systems in central china

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

dating vertebrate microfaunas in the late neogene record of northern china abstract chinese paleontologists have ordered neogene strata in time on the basis of their contained fossils small mammals in particular but biochronology alone attains limited accuracy in a biogeographically restricted system the chronology of terrestrial sediments can be refined when sound systematics of the contained fossils is combined with paleomagnetic data the geomagnetic polarity time scale has proven to be a useful independent reference system for dating the biochronology of continental deposits in north china long composites of successive microfaunas with faunal correlation at times of low endemism and age estimation through paleomagnetic correlation yield robust biochronologies that are well constrained in time the yushe basin shanxi province sequence which has magnetostratigraphic control provides a key reference for the late neogene of north china data from yushe basin identify the microfauna characteristic at the time of the miocene pliocene boundary in northern china the assemblage from near the village of jiayucun strongly resembles the rich microfauna of ertemte inner mongolia and occurs at the base of a reversed magnetozone correlated with chron c3r early gilbert chron latest miocene successive pliocene age assemblages from yushe basin resemble the jingle and youhe local faunas which were formerly used as reference faunas for north china nihewan like assemblages are correlated with the matuyama chron some being pre olduvai subchron and therefore pliocene in age by current definition later pleistocene time is represented in yushe basin by fossil sites in loam deposits the well known loess sequence of central china and other plio pleistocene reference faunas yield a date of ca 1 ma for a reddish loam microfauna from yushe basin

the emplacement of ophiolites by collision ophiolites recognized in most of the world s orogenic belts are generally interpreted to be oceanic crust and upper mantle lithosphere fragments that have been incorporated into continental margins at consuming plate boundaries we suggest that the mechanism for ophiolite emplacement is the same in both the alpine and andean type orogenes in both geological settings obduction of oceanic lithosphere onto the continental lithosphere is caused by the convergence of light buoyant bodies such as oceanic plateaus continental slivers island arcs or old hot spot traces for example the troodos ophiolite complex previously interpreted by some workers as resulting from continental collision may have been emplaced by the collision of cyprus with the eratosthenes plateau embedded in the oceanic eastern mediterranean crust on the other hand the upper jurassic coast range ophiolites of california previously interpreted as resulting from typical oceanic subduction may be the result of a continuous injection of thick nonsubductable packages of light continentally derived sedimentary rocks seamounts and plateaus into the subduction zones many other ophiolite complexes may be similarly related to accreted terranes

effect of burial and compaction on soil magnetic properties results from soil paleosol sequences in the himalayan foreland india abstract the study based on 395 stratigraphically ordered pedogenic and associated non pedogenic horizons in the himalayan foreland basin indicated a significant depth control for the routine rock magnetic parameters lf fd arm sirm b cr and s ratio the study representing eight fluvial sections with overburdens varying from 0 to 5 km for holocene to 11 ma interval spread over an area of 9000 km 2 infer at least three major phases of mineral magnetic response to soil physico chemical changes these are phase i early burial compaction dissolution and diagenetic changes up to an overburden of 1 5 km leading to substantial loss in ultra fine pedogenic ferrimagnetic oxides phase ii late burial diagenetic transformations up to 2 5 km of overburden leading to formation of antiferromagnetic oxides probably accelerated by the high crustal heat flows of the region and phase iii development of stable antiferromagnetic phase after 2 5 km of burial consequent to phase ii these results indicate a greater control of burial related changes over the routine mineral magnetic parameters than that due to paleoclimatic variations for paleosols of 1 5 km overburden or 2 ma of age in the himalayan foreland basin

comment on mudflat distal fan and shallow lake sedimentation upper vallesian turolian in the tianshui basin central china evidence against the late miocene eolian loess by a m alonso zarza z zhao c h song j j li j zhang a martin perez r martin garcia x x wang y zhang and m h zhang sedimentary geology 222 2009 42 51 abstract alonso zarza et al 2009 argued that the miocene sedimentary sequence near qinan qa i guo et al 2002 north to tianshui in central china represents mudflat distal fan and shallow lake sediments here we show that they 1 did not take into account extensive observational evidence supporting an eolian origin 2 erroneously correlated deposits of different origins and small lateral extent occurring in different geomorphic units 3 inferred a common origin for distal fans in the tianshui and qinan regions despite contrasting tectonic and geomorphic conditions and 4 in some cases misinterpreted features typical of eolian deposits accordingly their study is not a sufficient basis for challenging earlier interpretations of asian paleoclimates

late neogene evolution of the east asian monsoon revealed by terrestrial mollusk record in western chinese loess plateau from winter to summer dominated sub regime article i nfo more and more evidence indicates that the onset of the east asian ea monsoon can be traced back to the oligocene miocene boundary at about 23 ma however the process of its evolution is still less well known until now here we investigate its late neogene evolution by analyzing a terrestrial mollusk sequence from the chinese loess plateau clp covering the period between 7 1 and 3 5 ma considering the modern ecological requirements of these organisms we were able to define two groups of cold aridiphilous ca and thermo humidiphilous th species representing the ea winter and summer monsoon variations respectively as previously defined in the quaternary glacial interglacial cycles variations in these two groups indicate two different monsoon dominated periods during 7 1 3 5 ma first between 7 1 and 5 5 ma the ea winter monsoon with a 100 kyr periodicity was dominant second between 5 1 and 4 ma the ea summer monsoon dominated with a 41 kyr periodicity furthermore our mollusk record yields valuable evidence for a late miocene pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated associated with a periodicity transition from weak 100 kyr to 41 kyr the strengthened winter monsoon interval with a 100 kyr periodicity is coeval with orbital scale global ice volume changes in conjunction with the uplift of the tibetan plateau which probably reinforced the winter monsoon sub regime conversely closures of the panama and indonesian seaways associated with changes in obliquity between 5 1 and 4 ma are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency favoring heat and moisture transports between low and high latitudes to allow th mollusks to grow and develop in the clp

recognition of cryptochron in the polarity subchron c3ar palaeomagnetic results of the late miocene lava sequence from noma peninsula kyushu island japan

neogene and quaternary coexisting in the geological time scale the inclusive compromise removing the tertiary and quaternary periods whilst conserving the paleogene and neogene periods in the geological timescale 2004 caused a storm of protest one response was to advocate restoring an enlarged quaternary and consigning the neogene to a minor role within the tertiary amongst an array of practical traditional sentimental and anthropocentric reasons for this response the one hard core justification was that the rigidly nested hierarchy of the geological timescale must be preserved the central objective of this paper is conserving the historically legitimate miocene present neogene period and system there are two options for conserving the quaternary concurrently with the neogene i an inclusive compromise in a flexible hierarchy and ii an upgrading of pliocene and pleistocene divisions to the level of epoch in the inclusive compromise there coexist alternative pathways through the hierarchical ranks thus geohistorians and biohistorians have two options for traversing the hierarchy from era to age as in this example using the hierarchical positioning of the calabrian age and stage either cenozoic era neogene period pleistocene epoch calabrian age or cenozoic era quaternary subera pleistocene epoch calabrian age we reaffirm that the inclusive compromise is entirely viable in so doing we i challenge the necessity of the rigidly nested hierarchy which should be capable of a little flexibility ii reject all analogies of the arbitrary and conventional chronostratigraphic hierarchy with three natural biological hierarchies iii reaffirm the integrity of the neogene extending to the present and iv see no reason to doubt the harmonious coexistence of the two options preserving the quaternary and neogene traditions in an orderly working and stable time scale in the alternative schema conserving the neogene divisions of the pliocene and pleistocene are upgraded so that the late pleistocene early pleistocene and late pliocene epochs comprise the quaternary subperiod itself equivalent to late neogene the inflexibly nested hierarchy is preserved but the tertiary is lost

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

model for a passive to active continental margin transition implications for hydrocarbon exploration this paper proposes a model for the transition of a passive atlantic type continental margin to an active one with reverse polarity prior to its ultimate collision with an island arc or continent significant morphological and stratigraphic patterns which are believed to characterize this transition include 1 reactivation as reverse faults of preexisting listric normal faults not gulf coast type growth faults but those affecting basement as well that were established during the margin s most recent period of extension 2 landward migration with time of this fault rejuvenation 3 development of deeper water shallower water deeper water or deeper water unconformity deeper water stratal assemblages on the margin 4 regional flexure of the continental margin a in to that known for the outer rise area of oceanic plates landward of the subduction zone and 5 landward migration of major unconformities coeval with continental margin flexure this model creates implications for hydrocarbon exploration because 1 it predicts the presence or absence of unconformities and thus potential stratigraphic traps among units of a particular basin 2 provides spatial and temporal constraints for secondary porosity development in potential reservoirs 3 allows more accurate interpretations to be made of thermal or burial history diagrams constructed for the purpose of determining relative thermal maturities of potential source units and 4 helps distinguish between basement reactivation and decollement or gulf coast type growth faulting the orogenic phase of the margin s development however may later overprint or conceal these morphological and stratigraphic patterns to the extent that they might be unrecognizable because they have implications from both academic and economic perspectives the role of these patterns in the margin s evolution should not be overlooked

magnetostratigraphy of the xihe loess soil sequence and implication for late neogene deformation of the west qinling mountains summary theqinlingmountainrangeformsanimportantclimatebarrierbetweensouthernandnorthern china its western part referred to as the west qinling constitutes a unit of northeastern tibetan plateau the uplift history of qinling during the neogene is still a contentious issue magnetostratigraphic results from the 150 m thick xihe loess soil sequence nl vi located on the alluvial highlands surrounding an intermontane basin from the west qinling indicate 17 reverse and 17 normal magnetozones they are correlative with the interval from chron c5n to chron c2ar in the geomagnetic polarity timescale the age of the nl vi section can thus be palaeomagnetically constrained to a period from 10 5 to 4 2 ma the middle portion of the section has been affected intermittently by surface erosion processes as loess is sensitive to any erosion that may have been induced by substratum deformation and tectonic uplift this sequence indicates that the intermontane basin ridge pattern of the west qinling had already been formed by 10 5 ma thus providing suitable topographic conditions for aeolian deposition this timing is consistent with a significant deformation phase between 14 and 10 ma reported for the tibetan plateau meanwhile the complete preservation of the nl vi loess soil sequence precludes both intense deformation of the substrate and rapid uplift of the west qinling between 10 5 and 4 2 ma although the erosion affected portion of the nl vi section reflects some degree of tectonic instability from 8 3 to 6 9 ma the intensity must have been sufficiently weak to prevent the erosion of the aeolian deposits these further suggest that the late miocene growth of the tibetan plateau has not significantly affected the west qinling thus the studied nl vi aeolian sequence provides not only independent evidence for the uplift history of the west qinling within an accurate chronological framework but also provides new insights into the tectonic changes on the northeastern tibetan plateau

magnetostratigraphy and palaeoclimatic significance of late tertiary aeolian sequences in the chinese loess plateau summary the aeolian red clay sequence in the central part of the chinese loess plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records from the results we deduce that aeolian dust accumulation and the related east asia palaeomonsoon system began at least 7 6 myr ago and that the tibetan plateau had reached a significant elevation by that time the late tertiary palaeoclimatic history of the red clay as reflected by magnetic susceptibility is reconstructed for the time period 7 6 2 5 ma increases in aeolian dust accumulation for the last 7 6 myr appear to have a close relation with the uplift processes of the tibetan plateau the remarkable increase of aeolian dust accumulation beginning at 3 2 ma appears to reflect the influence of an increasing global ice volume on the east asian monsoon and aeolian dust accumulation

the magnetic properties of loess and paleosol samples from the chinese loess plateau spanning the last 22 million years abstract magnetic measurements susceptibility isothermal and anhysteretic remanence and quotients derived from these are presented for a suite of loess and paleosol samples from sites on the chinese loess plateau the three sites xifeng dongwan and qinan qa i together span most of the last 22 million years the results provide the first multi parameter magnetic measurements from pre pleistocene loess paleosol sequences that began accumulation in the early miocene mass specific measurements have been corrected for carbonate concentrations which peak in the loess layers and range up to 57 all the magnetic properties recorded indicate variability on both orbital and supra orbital timescales the changing magnetic properties allow the record to be divided into a sequence of eight sample groups that broadly parallel the main supra orbital changes in magnetic susceptibility the pre pleistocene parts of the record include intervals mainly late miocene and pliocene during which loess as well as paleosol layers are characterized by high values for properties such as frequency dependent susceptibility fd usually associated with strong weathering most of the miocene record prior to 8 5 ma with the exception of a brief interval from ca 14 4 to 15 9 ma shows reduced values for indicators of pedogenic ferrimagnetic concentrations in both the loess and paleosol layers as well as a low amplitude of variability between loess and paleosol values the palaeoenvironmental implications of this part of the sequence are unclear since they hinge on the type of model of pedogenic magnetic mineral formation adopted high field remanence measurements indicate that the coercivity of the antiferromagnetic minerals represented declined progressively throughout the whole period in both the loess and the paleosol samples though there is no unambiguous evidence for long term diagenetic alteration of the magnetic properties on timescales beyond the orbital ones that drive the loess paleosol alternations the present results suggest caution in applying existing climofunctions based on magnetic susceptibility to deposits spanning the whole of the last 22 ma

aeolian silt transport processes as fingerprinted by dynamic image analysis of the grain size and shape characteristics of chinese loess and red clay deposits abstract this study applied dynamic image analysis dia sympatec qicpic to characterize the grain size and shape of chinese aeolian sediments in order to fingerprint their transportation processes this is the first time this technique has been applied to late neogene and quaternary silt particles 2 63 m from the chinese loess plateau clp we selected four well studied quaternary loess palaeosol sequences along a north south transect across the clp and compared their grain size distribution obtained by dia with that yielded by laser diffraction particle size analysis ld fritsch analysette 22 and sympatec helos kr this comparison demonstrated that dia is successfully able to differentiate loess units from palaeosols and to characterize clearly spatiotemporal variations in the grain size records of loess palaeosol sequences formed during the last two glacial and interglacial periods this is consistent with grain size results obtained using ld dia is also able to characterize spatial variations in the more fine grained aeolian red clay deposits underlying the quaternary loess and allows the quantification of the fluvial contribution to red clay sequences dia of the characteristics of grain shapes in loess palaeosol sequences and red clay deposits revealed a systematic pattern whereby the aspect ratio decreased with increasing grain size indicating that systematic shape sorting occurred during the aeolian transportation of these dust particles it could be inferred from our study that particles in a certain grain size range correspond to a specific aspect ratio range and may in turn be aerodynamically distinguishable from each other and further correlated with the wind velocity strength also evident from analysis of our dia data was a subtle but systematic downwind decrease in the aspect ratio of the particles in the loess units this observation suggests that elongated and or flat particles with a low aspect ratio were transported further downwind than more symmetrically shaped particles with a high aspect ratio this study indicates that dia of grain size and shape characteristics can be an additional powerful tool for identifying grain size and shape sorting trends determining the dominant mode of transport and reconstructing transport pathways of silt sized aeolian sediments

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

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

magnetostratigraphy of a late miocene pliocene loess soil sequence in the western loess plateau in china 1 eolian deposits of pliocene age have never been reported from the western loess plateau in china here a 73 7 m eolian sequence is dated using magnetostratigraphic method and micromammalian fossils the polarity zonation correlates with the geomagnetic polarity timescale gpts from chron 3br 1r to chron 2an 3n indicating an age from 7 10 to 3 52 ma bp the sequence is characterized by clear expression of eighty four pairs of loess and soil layers while individual soils are basically indefinable for the eolian deposits of the same age in the eastern loess plateau suggesting that the later has experienced other geological processes this sequence extends the upper limit of the previously reported miocene loess soil sequences at qinan into the pliocene about 3 52 ma bp

a model for the crustal evolution of southern scotland in the late silurian southern scotland was a mature accretionary active margin of sumatra type on the southeastern edge of north america while england was on a passive margin on the opposite side of the iapetus ocean southward subduction below england during the middle ordovician produced a magmatic arc which now lies close to the iapetus suture and thus argues for a missing forearc terrane tectonic erosion or strike slip removal may be responsible for some of this missing terrane to the north of the lake district but we now suggest that underthrusting below southern scotland may also be an important cause if the ordovician forearc terrane of northern england is now below the southern uplands we would have an explanation for the evidence for similar lower crustal foundations on either side of the surface trace of the iapetus suture velocity structure from the lispb study sr u pb isotopic signatures and geophysical attributes of the c 400 ma granites the under thrusting model still leaves room for considerable modification of both margins by large strike slip faults seismic refraction profiles of modern accretionary active margins sumatra sw japan allow us to propose a likely velocity profile for late silurian southern scotland we choose a mesozoic forearc truncated by strike slip faulting the queen charlotte islands margin of the ne pacific as an analogue for the late silurian southern iapetus margin following previous suggestions of highly oblique and slow convergence during the final stages of closure of iapetus we combine the two profiles by under thrusting the southern margin to produce a model which involves minimal shortening in the collision zone the crustal profile resulting from such a collision would be very similar to the modern southern scotland profile both in terms of the scale of the tectono stratigraphic terranes involved and of the resulting crustal velocity structure the cessation of accretion after the mid wenlock may be related to impingement of the english continental crust against the scottish trench subsequent uplift of the southern uplands may be connected with the appearance of coarse detritus in the lake district during the silurian

the depositional environment of the late pliocene red clay jing le basin shanxi province china abstract red silty clays of late pliocene age are widely distributed in northern china at the type section in the jing le basin in shanxi province they overlie alluvial and lacustrine sands and gravels and underlie loess new data on grain size grain shape fabric chemistry floral pollen content and previously catalogued faunal evidence suggest sedimentation of the silty clays in a warm temperate and sub humid environment as a weathered mantle transported down gentle slopes by creep and rainwash the jing le formation represents a transition from dominantly alluvial deposition in the upper pliocene to dominantly aeolian deposition in the lower pleistocene

wind blown origin of dongwan late miocene pliocene dust sequence documented by land snail record in western chinese loess plateau recently the first late miocene pliocene eolian deposits from the western chinese loess plateau have been reported these deposits would complement the eolian record between quaternary loess paleosol sequences and miocene loess sequences if their wind blown origin could be documented however although several lines of evidence indicate the eolian origin of this sequence it is still necessary to address this issue through further efforts among these biological approaches are of particular value here we analyze the composition and preservation conditions of mollusk assemblages in the dongwan section our results show that all mollusk fossil individuals are preserved in perfect condition without indicating any reworking all identifiable mollusk species are terrestrial and are mostly identical to those identified in the quaternary loess paleosol sequences of the chi nese loess plateau generally the cold aridiphilous species are dominant in the loess layers while thermo humidiphilous species are mostly encountered in the paleosols the close similarity of the mollusk record in both the dongwan late miocene pliocene deposits and the quaternary loess sequence in the chinese loess plateau supports the supposition that the dongwan section is a typical loess paleosol sequence and is without any doubt of wind blown origin

magnetostratigraphy of an early middle miocene loess soil sequence in the western loess plateau of china 1 stratigraphy and magnetic susceptibility of the quaternary eolian deposits at different sites in china can be closely correlated confirming their spatial coherence and temporal continuity the extent to which these conclusions are true for the miocene loess soil sequences remains to be addressed here a 231 9 m eolian section qa iii is geomagnetically dated yielding an age span of 21 4 11 4 ma with the portion older than 19 6 ma being partially water reworked the magnetozones litholigic structure and magnetic susceptibility of the sequence are highly correlative with the qa i and qa ii sections 30 km west of qa iii these sequences demonstrate that the miocene loess deposits are also spatially correlative in stratigraphy present a near continuous sequence of paleoenvironment changes and that magnetic susceptibility is a useful tool for stratigraphic correlation the basal age of qa iii confirms again the onset of asian inland deserts and monsoon dominate climates by the early miocene

middle miocene eolian sediments on the southern chinese loess plateau dated by magnetostratigraphy abstract we present the results of a magnetostratigraphic grain size and geochemical investigation of a well preserved sequence of eolian sediments of miocene age at duanjiapo on the southern chinese loess plateau the paleomagnetic results demonstrate that the basal age of the studied interval is about 11 ma the results of the grain size and geochemical analyses show strong similarities between the eolian miocene silts and the overlying red clay and loess units this leads us to conclude that all formations have a similar eolian origin although the miocene silts include evidence of fluvial sediments derived from river originating in the qinling mountains to the south of the study site our results indicate that the accumulation of eolian dust in the southern chinese loess plateau area began at least 11 ma ago

variations in the provenance of the late neogene red clay deposits in northern china abstract the voluminous loess red clay deposits in northern china forming part of the chinese loess plateau clp are valuable terrestrial archives of climatic evolution for the late cenozoic era fundamental in reconstructing the late miocene and pliocene wind patterns and aridification history is a detailed knowledge of the provenance of these deposits this paper provides end member modelling of bulk grain size distributions and u pb dating of detrital zircons for three distant red clay sequences in the northeastern baode southern lantian and western dongwan clp data show that these different sections each display a distinctive compositional structure indicating variable depositional processes but they also share two significant zircon age populations of 200 300 ma and 400 500 ma while the permian triassic 200 300 ma group accounts for a larger proportion of zircons ages in the northeastern ne clp the ordovician silurian 400 500 ma component is dominant in the southern and western clp it is suggested that the red clay in the southern and western clp was mainly derived from the northern tibetan plateau ntp and the taklimakan desert by low level westerly winds samples of the ne clp show an increased signature of sediments transported by near surface northwesterly winds from the broad area of the central asian orogen belt caob this spatial transport and deposition pattern is supported by the results from the backtrace trajectory modelling of the dominant dust transport pathways in the clp it is noted that the red clay sample of around 3 6 ma obtained from the ne clp shows increased detrital contributions from its west possibly indicating an intensified westerly wind strength and or aridity of the ntp and taklimakan desert due to the uplift of the tibetan plateau and tianshan mountains in the pliocene the onset of enhanced drainage of the yellow river caused by the increased denudation of the netp since 3 6 ma could also have contributed to this

rock magnetic properties confirm the eolian origin of miocene sequences from the west of the chinese loess plateau abstract diagnostic rock magnetic characteristics of miocene sequences from the western part of the chinese loess plateau are used to confirm the eolian nature of sections the origin of which has been a matter of recent dispute alonso zarza et al 2009 2010 guo et al 2010 the key magnetic properties include i detailed correlation of both the orbitally timed and supra orbital variations in magnetic properties between widely separated sections ii the bi modal distribution of magnetic properties with respect to particle size reflecting in situ neoformation alongside the deposition of detrital minerals derived from the source areas iii the consistent presence in the clay fractions of fine ferrimagnetic grains close to the superparamagnetic stable single domain transition all within the size range characteristic of those formed by weathering and pedogenesis under at least partially aerobic conditions and iv absence of evidence for lacustrine indicators such as bacterial magnetosome assemblages sub oxic diagenesis or greigite formation

hysteresis and thermomagnetic properties of particle sized fractions from loess and palaeosol samples spanning 22 myr of accumulation on the chinese loess plateau summary hysteresis loop measurements and thermomagnetic experiments were carried out to characterize magnetic mineralogy and magnetic grain size in a suite of particle size fractioned samples from the chinese loess plateau representing the main changes in magnetic properties over the last 22 myr we find that 1 the ferrimagnets in the detrital fractions 8 m younger than 14 ma show a magnetite type curie temperature whereas those older than 15 ma have a curie temperature slightly over 600 c owing to low temperature oxidation 2 the dominant ferrimagnets in the clay fractions 2 m are most likely to be maghemite 3 both the hysteresis plots and thermomagnetic experiments reinforce previous indications from low temperature experiments that paramagnetic minerals make a major contribution to the clay fractions in all the samples considered 4 the degree of oxidation indicated by the thermomagnetic curves is highest in the clays and next highest in the oldest coarse fractions 5 day plots provide limited and potentially misleading information on the differences between fine grained pedogenic and coarse grained detrital ferrimagnetic assemblages even when allowance is made for the effects of hematite on the quotients used this study reinforces the view that measurements on bulk samples alone obscure critical distinctions between pedogenic and detrital components

accretionary processes at subduction zones in the eastern mediterranean abstract the tectonic history of the eastern mediterranean as well as the present tectonic style are affected by the collision and accretion of oceanic plateaus at subduction zones small but distinct oceanic plateaus exist today in the eastern mediterranean away from the plate boundary many other oceanic plateaus crowd the plate boundary particularly in the hellenic arc area their presence results in the unusual complexity of this subduction zone as is evidenced by the seismicity and bathymetry patterns the present two arcs system in this region the hellenic and cyprean arcs is probably the consequence of the collision of a large continental plateau with an older arc this plateau has been thrusted over the continental mass of anatolia and pieces of it are to be found in the region between the two arcs active subduction in the hellenic arc takes place in the outer trenches particularly in the ionian and strabo trenches subduction of mediterranean lithosphere in the pliny and ptolemy trenches is limited to their western parts inner segments of these trenches served as the main subduction trenches before the subduction zones migrated outward following the collision of oceanic plateaus

multichannel seismic evidence bearing on the origin of bowers ridge bering sea bowers ridge is a large arcuate sub marine ridge that extends north and west from the aleutian ridge and separates the abyssal aleutian and bowers basins in the bering sea two multichannel seismic reflection lines recorded in 1976 over bowers ridge and the adjacent basins confirm the existence of 8 to 10 km thick sediment wedges on the north side of bowers ridge and at the base of the bering continental margin deformed sediment within the bowers wedge indicates that subduction of the adjacent ocean crust beneath the ridge probably occurred prior to middle cenozoic time flat lying reflectors near the bottom of the trench suggest that a bathymetric trough and large ridge existed in mesozoic time the major period of underthrusting subsidence and in filling of the trench probably occurred from mesozoic to early tertiary time small amounts of underthrusting may have continued after the early tertiary development of the aleutian ridge however by middle miocene time the formerly subaerial bowers ridge had subsided below sea level the multichannel seismic data do not show evidence for a buried spreading center within the eastern aleutian basin consequently the sediment wedges trenches at both bowers ridge and the bering continental margin are believed to be the consequence of subduction that occurred during the convergence of the ridge and the margin the large size of bowers ridge suggests that a large amount of convergence has occurred since mesozoic time if bowers ridge was a large feature in mesozoic time as suggested by the apparent bathymetric trough then the ridge may be as old or older than the aleutian ridge to which it connects

magnetostratigraphy and sedimentology of the jingchuan red clay section and correlation of the tertiary eolian red clay sediments of the chinese loess plateau a 325 m thick loess and red clay sequence was recently discovered at jingchuan which is situated about 45 km north of the previously studied lingtai section in the middle part of the chinese loess plateau the jingchuan section is composed of 199 m of pleistocene loess and 126 m of tertiary red clay deposits paleomagnetic studies show that the jingchuan red clay has a basal age of at least 7 7 ma which represents the oldest red clay deposits presently known in the loess plateau field observations and grain size analyses both suggest an eolian origin of the red clay thus extending available records of the eolian deposits in the loess plateau from about 7 0 ma to 7 7 ma correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late cenozoic red clay records in the loess plateau have a general continuous nature thereby providing potential for deriving long term climatic evolution signals from this eolian loess and red clay sequence

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

major changes in east asian climate in the mid pliocene triggered by the uplift of the tibetan plateau or global cooling since the mid pliocene east asian climates have experienced significant changes one view suggests that significant uplift of the tibetan plateau during this period could have been responsible for these dramatic changes in the strength of the east asian monsoon and for asian interior acidification while some other authors attribute these changes to the ongoing global cooling and rapid growth of the arctic ice sheet up to the present which factor dominates the major changes of east asian climate in the mid pliocene is still a contentious issue this study presents an analysis of several climate proxies including grain size cao na2o mgo tio2 ratio na ka ratio and dust accumulation rates of the xifeng red clay sequence in the eastern chinese loess plateau and the xihe pliocene loess soil sequence in west qinling they reveal that aridity in the continental interior and winter monsoon circulation both intensified whereas the east asian summer monsoon showed a weakening rather than intensifying trend since the mid pliocene these changes are also supported by the other multi proxy records from various regions in east asia previous numerical modeling studies have demonstrated that uplift of the tibetan plateau would have simultaneously enhanced continental scale summer and winter monsoon strength as well as central asian aridity the mid pliocene climate changes in east asia are therefore unlikely to be a response to plateau uplift on the contrary our recent modeling results give support to the view that ongoing cooling could have intensified both the aridity of the interior and the strength of the winter monsoon but weakened the summer monsoon in east asia c 2012 elsevier ltd all rights reserved

chronological sequence and subdivision of chinese neogene mammalian faunas six land mammal ages are recognized for the neogene of east asia the ages are based upon updated large and small mammal faunas and replace or redefine the land mammal stages erected by li et al 1984 comparisons and correlations are made to faunas in europe northern and southern asia and north america in addition methods of utilizing mammalian faunal data to define and recognize geochronologic ages are discussed

an active east asian monsoon at the oligocene miocene boundary evidence from the sikouzi section northern china abstractthe east asian monsoon forms a significant element of the global climatic system we here present detailed sedimentologic investigations of the oligocene to early miocene succession in the sikouzi section northern china to determine monsoon evolution during this time the particle size characteristics and grain surface structures in combination with the large scale cross bedding arrangements graded bedding laminations and small scale deformation structures type the oligocene red beds in association i as eolian attributable to large dune forms rare earth element results imply that the oligocene sediments are possibly sourced from a local provenance in the west qinling mountains excluding a more regional wind system during this time packages of thick bedded dark red mudstone silty mudstone as well as subordinate medium bedded pale gray fine to medium grained sandstone and thin bedded gypsum with the massive mudstone silty mudstone taking dominance point to a lacustrine deposition with d

a new record of late pliocene early pleistocene aeolian loess red clay deposits from the western chinese loess plateau and its palaeoenvironmental implications abstract the loess red clay sequences in northern china provide high resolution terrestrial records of asian monsoon evolution and aridification of the asian interior to date however aeolian deposits of late pliocene early pleistocene age 3 5 2 4 ma have only rarely been reported from the western chinese loess plateau clp which significantly hinders our understanding of the distribution of aeolian deposits and the palaeoenvironmental evolution of the region here we present magnetostratigraphic lithologic and magnetic susceptibility results for two recently drilled boreholes from the north bank of baxie river central linxia basin which are highly correlative with those of the loess red clay deposits spanning the interval from 3 6 to 2 4 ma in the eastern clp our results provide the first direct evidence for the occurrence of late pliocene early pleistocene aeolian deposits in the western clp and provide new insights into the distribution of aeolian deposits in northern china the spatial coherence of the magnetic susceptibility fluctuations further indicates that magnetic susceptibility is a powerful tool for stratigraphic correlation of late pliocene aeolian deposits in the western clp in addition our results demonstrate that erosional events may have occurred in the early or middle pleistocene and they may provide new insights into the reasons for the absence of loess red clay deposits from 3 5 to 2 4 ma in most parts of the western clp

oceanic plateaus the fragmentation of continents and mountain building many anomalous rises in today s oceans may be submerged continental fragments detached from previous continents ancient island arcs or basaltic piles formed by hot spots and spreading centers these rises are embedded in their respective moving oceanic plates and are fated to be consumed at active margins where such rises are being consumed at present e g the nazca ridge they cause cessation of volcanism disruption of the downgoing slab and possible shifts in plate boundary configuration many past rises including numerous continental fragments have been recognized within mountain belts as allochthonous terranes they constitute a large portion of the orogenic belts in the north pacific from mexico through western north america alaska east siberia japan and in new zealand the orogenic deformation in these belts is possibly the result of the accretion of the allochthonous terranes many terranes have been accreted with substantial deformation also in the alpine chain well before major continent continent collisions it is suggested therefore that the accretion of fragments may be the common process of the deformation phase of mountain building subduction of normal oceanic crust may be insufficient for deformation whereas full continent continent collision may not be necessary the general validity of this conclusion depends critically on whether allochthonous terranes caused orogenic deformation in the andes or not most of the accreted fragments with continental affinities in the mesozoic cenozoic orogenic belts of the world can be traced back to the breakup of gondwana beginning with a pacifica domain in the permian through a larger india domain in the early mesozoic and continuing through the separation of the somalia plate in the near future the reasons for this 250 million year breakup process are not known but some kind of thermal process possible of mantle wide scale is implied

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

early evolution of the bering sea by collision of oceanic rises and north pacific subduction zones three major bathymetric features exist in the bering sea shirshov ridge bowers ridge and umnak plateau new refraction data over umnak plateau and previous geophysical data across bowers ridge indicate that a thickened welt of crustal material is present beneath both features the crustal structure is transitional between oceanic and continental types various models for the origin of these features have been investigated one that has not been proposed previously assumes that the protostructures of bowers ridge and umnak plateau could have formed outside of the present bering sea according to this model before formation of the aleutian ridge in late mesozoic or earliest tertiary time these protostructures moved into their present bering sea positions prior to the arrival of these two structures in the bering sea oceanic crust was subducted along the bering continental margin connecting alaska and siberia the collision of the umnak plateau protostructure with the southeastern edge of the margin may have caused subduction to terminate here and move southward the new southerly position of subduction beneath the aleutian ridge was therefore controlled by late mesozoic or early tertiary locations of umnak plateau bowers ridge and possibly the north trending shirshov ridge farther to the west

orbital forcing of plio pleistocene climate variation in a qaidam basin lake based on paleomagnetic and evaporite mineralogic analysis abstract inland asian aridification is threatening the global ecological system under continued global warming requiring a full understanding of its forcing mechanisms past geological studies in this region focus mainly on initiation timing and million year timescale variations in aridification few studies address the relationship between aridification and insolation forcing here we present a paleomagnetic and evaporite mineralogic study of the 476 m long huatugou htg section ca 3 9 to 2 1 ma from the western qaidam basin the results show that the drying of this part of the basin began by at least 3 9 ma furthermore we show that the relative content variation of evaporite minerals was dominated by 100 kyr cyclicity during the pliocene this is consistent with the result from the xining area during the late eocene these results suggest that mid latitude lacustrine evaporite minerals in semi arid to arid regions are particularly sensitive to eccentricity forcing improving understanding of aridification forcing at orbital timescales

magnetostratigraphic constraints on the age of the hipparion fauna in the linxia basin of china and its implications for stepwise aridification abstract late cenozoic sediments in the linxia basin of china on the northeastern tibetan plateau bear abundant fossils of the hipparion fauna from late miocene times these sections record a history of aridification in the asian interior the evolution of the east asian monsoon and multiple uplifts of the tibetan plateau in this paper a new detailed magnetostratigraphic study of a sedimentary sequence from the duikang dk section containing the hipparion fauna is presented to better understand interconnected ecologic and environmental changes the 90 m thick section reveals nine normal and nine reversed zones that span from chron c5n 2n to chron c3ar or from chron c4n 2n to chron c2ar yielding magnetostratigraphic ages of 8 1 ma 3 7 ma for the studied section and 5 3 ma for the hipparion fauna bearing bed combined with all the previous magnetostratigraphic ages of the fauna bearing sediments in the linxia basin hipparion can be distinguished as mainly having lived during five periods phase i 11 5 ma phase ii 8 2 ma phase iii 6 3 ma phase iv 5 3 ma and phase v 2 5 ma based on comparison of climate records in the linxia basin with aridification records from surrounding regions and global cooling during the late cenozoic we suggest that the evolution of hipparion from the linxia basin was mainly driven by continuous global cooling and tectonic uplift of the northeastern tibetan plateau since the late miocene

geochemical evidence for provenance diversity of loess in southern china and its implications for glacial aridification of the northern subtropical region abstract the thick xiashu loess in southern china is distributed not only in the yangtze river valley but also and most extensively in the region between the qinling mountains and the lower reaches of the yangtze river however there are few studies of the provenance and climatic implications of the xiashu loess in this latter region here we present the results of a provenance study of last glacial loess samples from twenty two typical xiashu loess sections using the major and trace element composition as a provenance indicator seventeen of the sites are located to the north of the yangtze river and our primary aim was to determine the provenance of the xiashu loess within this region our results indicate that the alluvial plain located mainly in the present drainage area of the huai river was the primary dust source for the xiashu loess in this region the occurrence of multiple local dust sources within this alluvial plain suggested by their geochemical heterogeneity indicates that the alluvial plain experienced intensified aridity which caused it to become a dust source for local loess deposits in northern subtropical china during the last glacial our study provides strong evidence to challenge the long held view that the occurrence of xiashu loess resulted from the southward incursion of the clp loess deposits sourced from deserts of the asian interior and it confirms the substantial role of aridification of the present humid northern subtropical region for dust emission to the climate system during the last glacial

characterising chinese loess stratigraphy and past monsoon variation using field spectroscopy abstract the loess record in china constitutes one of the most important archives of past environmental change and specifically the east asian monsoon system changes in summer monsoon driven pedogenesis are commonly inferred from magnetic susceptibility of loess however there is still controversy as to the signal s origin and the uncertain effects of sediment accumulation rates this is linked to a wider problem that is emerging from recent work that of the relative importance on proxy records such as magnetic susceptibility of both regional climate patterns i e the monsoon and local site specific influences particularly modulated through site specific sedimentation rate at present this is poorly constrained and significantly increases the degree of uncertainty over the wider scale applicability of climate reconstructions from individual sites to resolve this issue for sub orbital timescales a rapidly deployable technique is needed that can be used to test multiple sites and differentiate between local and regional signals this research develops the first use of full spectrum reflectance spectroscopy in studying loess in the field at one site on the south of the loess plateau and utilises statistical analyses to compare such data with magnetic susceptibility records establishment of loess reflectance as a proxy for climate variability will potentially allow extension of the technique from point measurements to an imaging system and so enable the compilation of large data sets in order to investigate lateral facies variations in loess profiles this may allow the extraction of a broad scale climate record field spectra were obtained from 350 to 1100 nm with red edge reflectance spectra indicating the presence of iron oxides previously demonstrated to be indicators of pedogenesis through laboratory measurements an off the shelf camera was also tested with visible wavelength spectra being useful for rapid but general profile characterisation in order to mitigate the effects of bidirectional reflectance distribution function a potential problem in field measurements further laboratory measurement was made of powdered samples 400 2400 nm absorption features indicative of montmorillonite and illite muscovite were noted and stepwise regression modelling utilising absolute reflectance first derivative spectra and continuum removed spectra indicated strong predictive relationships with magnetic susceptibility particularly against the presence of montmorillonite the abundance of such clay minerals could be used to infer weathering rates and hence be used as a proxy for pedogensis reconstructions for the studied site are presented and demonstrate the potential power of loess reflectance environmental reconstruction

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

geochemical evidence for the provenance of middle pleistocene loess deposits in southern china the provenance of middle pleistocene loess in the middle and lower reaches of the yangtze river the most intensively investigated loess deposits outside the loess plateau region in china remains controversial identification of the provenance will provide crucial insight into the environmental implications of this valuable sedimentary archive and into the potential role of the east asian winter monsoon in transporting the dust from deserts in the asian interior in this study geochemistry was used to compare the provenance of loess in the lower reaches of the yangtze river in southern china with that inferred for loess deposits on the loess plateau in northern china compared with samples from the loess plateau the 20 mm fraction in the loess deposits of southern china has higher tio2 al2o3 zr nb zr al zr ti zr hf y al and lan smn ratios and lower eu eu th nb y nb and al nb ratios the clear distinction in immobile element ratios between samples from the two regions indicates that the loess deposits in the two regions have different provenances the inferred difference in source area is also supported by variations in the major element composition of bulk samples obtained in this study and collected from published data these lines of evidence indicate that the deserts in the asian interior are not the primary provenance for the southern loess it is suggested that the adjacent floodplains to the north of yangtze river are the dominant dust sources and the occurrence of sustained loess deposits in the lower reaches of the yangtze river currently an area of northern subtropical climate is an indication of local aridification and strengthened winter monsoon activity during glacial periods as a regional response to the middle pleistocene climate transition around 0 8 ma the role of the east asian winter monsoon in transporting the dust from northern deserts to southern china has been overestimated in previous studies

terrestrial mollusk records from chinese loess sequences and changes in the east asian monsoonal environment abstract the terrestrial mollusk fossils found in chinese loess strata have been studied for over one hundred years however the greatest progress in these studies has been made only in the last two decades in this paper we review the advancements advantages and limitations of terrestrial mollusk studies in chinese loess deposits improvements in research methods and approaches have allowed the extraction of more detailed paleoenvironmental and paleoclimatic information from mollusk assemblages the broadened research scope and content have yielded many new findings and results the mollusk record has thus become one of the most important proxies in the paleoenvironmental and paleoclimatic reconstruction of loess paleosol sequences in china the greatest progress in the studies of terrestrial mollusks in chinese loess sequences can be summarized as follows 1 modern mollusk assemblages can be classified into four ecotypes based on their temperature and humidity requirements including eurytopic semi aridiphilous and sub humidiphilous cold aridiphilous and thermo humidiphilous types 2 quaternary mollusk assemblages can be modified into the following three ecological types glacial loess interglacial paleosol and interstadial weakly developed paleosol assemblages 3 mollusk records successfully reveal long term climatic and environmental changes reflective of the history of east asian monsoonal variations since the late cenozoic and the succession of mollusk species also indicate short term environmental changes such as millennial climate variability during last glacial maximum and unstable climatic fluctuations during glacial and interglacial periods and 4 more recently new analytical approaches have offered increased research potential in areas such as paleotemperature reconstruction using the isotopic compositions of modern and fossil mollusk shells combined with higher accuracy 14 c dating of quaternary loess deposits which will greatly improve future loess paleoenvironmental research

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

origin of the miocene pliocene red earth formation at xifeng in northern china and implications for paleoenvironments abstract in the eastern loess plateau region of northern china the quaternary loess soil sequences of the last 2 6 ma are underlain by the hipparion red earth formation magneto stratigraphic studies suggest that it is a near continuous terrestrial record for the period from 7 to 2 6 ma bp and therefore has great potential for the study of asian paleoclimates the origin of this formation is controversial and needs further study in this work the xifeng red earth section a type section for the eastern loess plateau region was studied using optical microscopic analysis grain size measurements and both major and trace element geochemical properties to address questions of its origin and environmental implications the results show that this formation consists of three parts the lower part 6 2 ma bp is a water reworked deposit related to alluvial and slope processes the middle part from 6 2 to 3 6 ma bp was derived from in situ eolian dust deposition but was significantly affected by groundwater oscillations and the upper part from 3 6 to 2 6 ma bp is an eolian formation similar to the quaternary loess soil sequence the grain size of the upper part is significantly coarser than for the middle part but finer than for the overlying loess because the eolian dust deposits in the middle reaches of the yellow river were mainly transported from the deserts in northern china by the northwesterly winter monsoon wind and the westerlies we interpret the eolian origin of the middle and upper red earth formation beginning approximately at 6 2 ma bp as an indication of the strengthening of the aridification of the asian continent desert lands in central asia must have been formed at or by that time to provide a significant source of dust however the generally finer grain size of the red earth suggests a weaker transporting wind and or a more remote source the latter implies a smaller extent of deserts than in the quaternary the high degree of similarity between the geochemical properties of the red earth and loess samples seems to suggest a rather similar source areas and comparable dust transporting trajectories the removal of the dust deposits from groundwater influence and the increase in grain size at 3 6 ma bp are attributable to both tectonic and climatic causes the initiation of these phenomena corresponds to an intensive uplift of the tibetan plateau and also to a simultaneous uplift of the sedimentary basins in the surrounding areas it is also approximately synchronous with an increase in eolian mass accumulation rate in the north pacific both suggesting an increased continental aridity in the asian dry lands and an increasing intensity of transporting winds

collisional processes in the eastern mediterranean in the eastern mediterranean the collision of the erastosthenes and the anaximander seamounts with the cyprus arc results in a unique tectonic setting due to the small size of the eastern mediterranean basin as a result of the collision some of the motion between the african plate and the eurasian plate is taking place by thrust faulting along the north african passive margin it seems that the stress at the plate boundary along the cyprus arc may be transmitted southward to cause the reactivation of a pre existing fault zone along the passive margin of eastern north africa

source to sink fluctuations of asian aeolian deposits since the late oligocene abstract the source to sink fluctuations of asian aeolian deposits have been investigated over the past two decades using multiple mineralogical and geochemical tracers these source tracers have substantially improved our understanding of the processes of production transport and deposition of asian dust cycling from the asian inland basins to the north pacific ocean however due to differences in the sensitivity and interpretation of these various tracers there is controversy about which regions were the dominant dust sources and whether the dust provenances were stable at tectonic and glacial interglacial timescales here we comprehensively review the source to sink system of asian aeolian deposits on the chinese loess plateau since the late oligocene by assessing the utility of recently employed provenance tracers we conclude that integrating different tracers can effectively distinguish major primary and secondary dust sources the combination of sr nd isotopes quartz esr ci 18o data and zircon age spectra can decipher the source to sink fluctuations of asian aeolian deposits at tectonic and glacial interglacial timescales comparison of these sensitive source tracers with tectonic and climatic evidence indicates that the phased growth of the northern tibetan plateau played a key role in asian dust production and transport during the late oligocene to miocene while the onset and expansion of the northern hemisphere ice sheets had a substantial impact on the source to sink fluctuations since the late pliocene