chronological sequence of the early pleistocene gigantopithecus faunas from cave sites in the chongzuo zuojiang river area south china abstract since 2004 five new early pleistocene cave sites with gigantopithecus blacki and other fossil mammals have been discovered in the chongzuo zuojiang river area guangxi zhuang autonomous region guangxi zar south china these sites include baikong cave of liyu mountain juyuan cave of boyue mountain sanhe and queque caves of wuming mountain and wuming cave of mulan mountain the present study provides a preliminary account of these newly discovered gigantopithecus faunas and discusses their taxonomic composition evolutionary trends and chronology based on recent biostratigraphic and geochronological studies combining faunal and paleomagnetic data the gigantopithecus faunas from the zuojiang river area can be divided into three temporal stages during the early pleistocene the early stage 2 6 1 8 ma is represented by the baikong and boyue faunas which include some neogene relics e g sinomastodon hesperotherium dicoryphochoerus dorcabune and cervavitus and several species that make their first appearance during the pleistocene e g sinicuon dubius pachycrocuta licenti ailuropoda microta sinomastodon jiangnanensis stegodon huananensis and tapirus sanyuanensis the middle stage 1 8 1 2 ma is represented by the sanhe fauna which is characterized by the appearance of ailuropoda wulingshanensis cuon antiquus and tapirus sinensis the late stage 1 2 0 8 ma is represented by the queque fauna which is characterized by a marked decrease in neogene relics and the appearance of a few species that are more typical of the middle pleistocene e g ailuropoda baconi and stegodon orientalis evolutionary trends in the early pleistocene gigantopithecus faunas include a gradual increase in dental size in some of the typical taxa such as g blacki ailuropoda and tapirus and the successive turnover of representative species such as a microta a wulingshanensis a baconi thus far eleven g blacki sites of early pleistocene age have been recorded in southern china and these are primarily concentrated in guangxi zar where more than 70 of early pleistocene g blacki cave sites are known given this temporal and geographic distribution it is possible to infer that guangxi zar represents an important early evolutionary and zoogeographic center for g blacki

origin of the late early cretaceous granodiorite and associated dioritic dikes in the hongqilafu pluton northwestern tibetan plateau a case for crust mantle interaction we present a detailed study of geochronology mineral chemistries bulk rock major and trace element abundances and sr nd hf isotope compositions of the granodiorite and associated dioritic dikes in the hongqilafu pluton at the northwestern margin of the tibetan plateau the granodiorite and dioritic dikes yielded zircon u pb ages of similar to 104 ma and similar to 100 ma respectively the dioritic dikes comprise varying lithologies of gabbroic diorite diorite porphyry and granodiorite porphyry exhibiting a compositional spectrum from intermediate to felsic rocks their mineral compositions display disequilibrium features such as large major element compositional variations of plagioclase clinopyroxene and amphibole crystals these dioritic dikes are enriched in incompatible elements ba rb th u k and sr nd hf isotopes sr 87 86 sri 0 7066 to 0 7071 epsilon nd t 5 3 to 7 4 epsilon hf t 3 6 to 6 2 we suggest that the dioritic dikes were most likely derived from partial melting of mantle wedge metasomatized by the subducted subducting seafloor with a sediment component followed by afc processes with fractional crystallization of clinopyroxene amphibole and plagioclase and assimilation of lower continental crust the mantle wedge derived magma parental to the dioritic dikes underplated and induced the lower continental crust to melt forming the felsic crustal magma parental to the granodiorite with mantle melt signatures and having more enriched isotope compositions sr 87 86 sri 0 7087 to 0 7125 epsilon nd t 9 5 to 11 6 epsilon hf t 10 3 to 14 1 than those of the dioritic dikes the hongqilafu pluton is thus the product of mantle crust interaction at an active continental margin subduction setting over the period of several million years this understanding further indicates that the closure timing of the shyok back arc basin and the collision between the kohistan ladakh arc and the karakoram terrane may have taken place later than similar to 100 ma c 2016 elsevier b v all rights reserved

the effect of floodplain grass on the flow characteristics of meandering compound channels abstract laboratory experiments were conducted in a large scale meandering compound channel to investigate the effect of floodplain grass on the main flow field in the channel three dimensional velocity fields turbulences and reynolds shear stresses were measured along half a meander the experiments revealed that flexible artificial grass planted on a floodplain can significantly reduce the conveyance capability of the entire channel two parallel stage discharge curves increased with increasing flow depth the additional resistance of the floodplain grass increased the streamwise velocity and conveyance in the main channel along a meander an analysis of the generation mechanism of secondary flows in the main channel indicated that the secondary current consisted of an enhanced original secondary cell that was strengthened by the centrifugal force and a component of the upstream floodplain flow the relative dominance of these two components in the secondary flows was primarily determined by the angle between the floodplain flow and the main channel ridge and also the floodplain roughness at the same flow depth the secondary flow in cases with grass on the floodplain was generally stronger than that in the case of a smooth meander bend although it was weaker near the middle cross over section floodplain grass enhanced the intensity of the lateral turbulence above the bankfull level and significantly modified the turbulence structure although it had a negligible effect on the vertical turbulence except at the bend entrance floodplain grass also affected the reynolds shear stresses in the main channel generating stronger lateral shear stresses at a low flow depth in contrast at a high flow depth the distribution of the interface shear stresses changed entirely while its magnitude remained the same when the floodplains were grassed the vertical shear stress that was induced by secondary flows was greater at the apexes but reduced at the cross over sections these observations highlight the important effects of floodplain grass on the main channel flow

a multivariate mixing model for identifying sediment source from magnetic measurements a sequential method for quantitative identification of sediment source components based on magnetic measurements has been developed and tested for sediments from the rhode river maryland simulated mixing tests and multiple regression were employed to establish numerical relationships between source component proportions and the magnetic measurements of mixtures on the basis of these multivariate mixing models source components of three estuarine sediment cores were estimated by linear programming the results strongly support the previous studies on this catchment which indicated a dramatic change in sediment source some 150 to 200 yr ago quantitative calculations are more useful and informative than purely qualitative descriptions

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

the stable isotope record in cervid tooth enamel from tantang cave guangxi implications for the quaternary east asian monsoon abstract studies have shown that stable isotope oxygen o and carbon c composition of mammal tooth enamel can provide information on a region s paleoclimate and paleoecology stable isotope analysis has been used to investigate the impact of the qinghai tibetan plateau uplift on the development and strength of the asian monsoon however due to sparse data from southern china a region dominated by the east asian monsoon o and c isotope analysis of mammal tooth enamel has been unable to fully inform on the impact of the monsoon environment in the region here we present the results of the analysis of stable isotopes on a set of cervid tooth enamel from late middle pleistocene tantang cave in bubing basin guangxi southern china and compare them with comparable isotope data from nearby early early pleistocene mohui and middle early pleistocene sanhe caves the results of the oxygen isotope analysis indicates that tantang cave 8 70 to 6 39 is similar to mohui cave 8 71 to 6 34 with both sites being more negative than sanhe cave 4 77 to 1 20 we suggest the east asian summer monsoon was stronger during the tantang and mohui mammal occupations and weaker during the lifetime of the sanhe mammals this result is indirectly corroborated by vertebrate paleontological evidence murid rodents implying an open grassland and somewhat drier climate are found in great numbers in sanhe the carbon isotope results from tantang 17 70 to 10 26 mohui 15 27 to 12 51 and sanhe 16 63 to 14 71 overlap extensively suggesting these various faunas primarily lived in a closed forest environment the implications of these findings from stable isotope studies from tantang are discussed in their broader context

the new hominid skeleton from sterkfontein south africa age and preliminary assessment a new hominid skeleton from sterkfontein member 2 attaches to foot bones recovered from loose blocks during the 1980s and first described in 1995 several flowstone horizons are present above and below the skeleton and have given clear palaeomagnetic signatures five changes in magnetic polarity have been identified when constrained by the available biostratigraphy this sequence can be placed confidently between 3 22 and 3 58 ma interpolation of sedimentation rates over the small intervals between reversals allows this range to be reduced to 3 30 3 33 ma the skeleton is thus the oldest yet discovered and is considered to belong to a species of australopithecus other than africanus copyright 1999 john wiley sons ltd

stratigraphy and remanence acquisition of a palaeomagnetic reversal in alluvial siwalik rocks of pakistan a high resolution record of a palaeomagnetic reversal is documented in miocene alluvial rocks of pakistan we examined lateral variability of lithostratigraphy and palaeomagnetic stratigraphy through the same palaeomagnetic reversal in six correlated sections each section contains one or more palaeomagnetic sites with directions between fully reversed and fully normal the position of the reversal illustrates local relief in the study area and the time transgressive nature of certain stratigraphic units variability in the thickness of the transitional interval indicates contemporaneous variability in sediment accumulation rates different characteristics of palaeomagnetic remanence are associated with the depositional and postdepositional history of these sediments variability in patterns of remanence behaviour is the basis for inferences about post depositional processes we discuss two magnetic parameters that express coherency of palaeomagnetic samples the maximum angle of deviation and the circular standard deviation of particular interest are samples with incoherent palaeomagnetic signals the incoherency of samples is inversely correlated with the thickness of the transitional interval a low rate of sediment accumulation suggested by a thin transitional interval may facilitate a prolonged period of remagnetization through pedogenic or hydrological processes alternatively transition intervals defined by coherent magnetization may be thin as a result of pedogenically induced incoherency

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

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

timing of the nihewan formation and faunas abstract magnetostratigraphic dating of the fluvio lacustrine sequence in the nihewan basin north china has permitted the precise timing of the basin infilling and associated nihewan mammalian faunas the combined evidence of new paleomagnetic findings from the hongya and huabaogou sections of the eastern nihewan basin and previously published magnetochronological data suggests that the nihewan formation records the tectono sedimentary processes of the plio pleistocene nihewan basin and that the nihewan faunas can be placed between the matuyama brunhes geomagnetic reversal and the onset of the olduvai subchron 0 78 1 95 ma the onset and termination of the basin deposition occurred just prior to the gauss matuyama geomagnetic reversal and during the period from the last interglaciation to the late last glaciation respectively suggesting that the nihewan formation is of late pliocene to late pleistocene age the nihewan faunas comprising a series of mammalian faunas such as maliang donggutuo xiaochangliang banshan majuangou huabaogou xiashagou danangou and dongyaozitou are suggested to span a time range of about 0 8 2 0 ma the combination of our new and previously published magnetostratigraphy has significantly refined the chronology of the terrestrial nihewan formation and faunas

mid pleistocene acheulean like stone technology of the bose basin south china stone artifacts from the bose basin south china are associated with tektites dated to 803 000 3000 years ago and represent the oldest known large cutting tools lcts in east asia bose toolmaking is compatible with mode 2 acheulean technologies in africa in its targeted manufacture and biased spatial distribution of lcts large scale flaking and high flake scar counts acheulean like tools in the mid pleistocene of south china imply that mode 2 technical advances were manifested in east asia contemporaneously with handaxe technology in africa and western eurasia bose lithic technology is associated with a tektite airfall and forest burning

determination of stream incision rate in the appalachian plateaus by using cave sediment magnetostratigraphy paleomagnetic dating of clastic fluvial sediments contained in caves within the walls of a steeply incised gorge allowed calculation of a maximum incision rate for the east fork obey river the maximum incision rate for this major stream on the western margin of the cumberland plateau north central tennessee was found to be 0 06 m ka this rate was determined on the basis of the paleohydraulic relation between the caves and the surface stream the presence of a normal to reverse polarity transition in clastic fluvial sediments deposited within the caves and the vertical distribution of polarity found in sediments throughout the gorge the dating results indicate that this highly developed fluviokarst containing several of the longest known caves in the united states developed wholly within the pleistocene and holocene

magnetostratigraphic and uranium series dating of fossiliferous cave sediments in jinyuan cave liaoning province northeast china abstract chronological sequences of quaternary terrestrial mammalian faunas can provide important information about the evolutionary history of mammals regional biostratigraphy and paleoenvironmental changes here we report the results of studies of a thick nearly continuous sedimentary sequence from jinyuan cave in liaoning province northeast china the sequences contains four mammalian faunas ranging in age from the late pliocene to the late middle pleistocene detailed paleomagnetic and u series age determinations date the upper unit of the sedimentary sequence to 2 2 0 3 ma the results suggest that cave development and infilling were closely associated with the tectonic evolution of the bohai basin including the subsidence of the basin and the uplift of the surrounding mountains such as luotuo hill together with the large mammalian faunas from both south and north china we suggest that these mammalian faunas were smaller in size and lower in species diversity during the middle pleistocene transition mpt 1 2 0 7 ma than in the earlier and later pleistocene this indicates that major climatic variations during the mpt in north china may have reduced their taxonomic abundance and diversity the extremely warm and wet interglacial climates that followed the mpt in monsoonal east asia provided an ecological niche for the evolution and migration of these mammalian faunas resulting in an increase in the numbers and diversity of mammals in east asia

estimation of flow direction in meandering compound channels abstract the flow in the main channel of a meandering compound channel does not occur in the ridge direction because of the effect of the upstream floodplain flows this study proposes a model for estimating the flow direction in the depth averaged two dimensional domain depth averaged flow angles between the entrance and the apex sections detailed velocity measurements were performed in the region between the meander entrance section and apex section in a large scale meandering compound channel the vertical size of the secondary current cell is highly related to the depth averaged flow angle thus the means of the local flow angles above the secondary current cell and within the cell are separately discussed the experimental measurements indicate that the mean local flow angle above the cell is equal to the section angle whereas the mean local flow angle within the cell is equal to zero the proposed model is validated using published data from five sources good agreement is obtained between the predictions and measurements indicating that the proposed model can accurately estimate the depth averaged flow direction in the meandering compound channels finally the limitations and application ranges of the model are discussed

magnetochronological sequence of the early pleistocene gigantopithecus faunas in chongzuo guangxi southern china abstract the gigantopithecus fauna the most important mammalian fauna during the early pleistocene in southern china was usually excavated from cave or fissure deposits without precise age constraints here we present new magnetostratigraphy results for four cave sedimentary sequences in chongzuo guangxi zhuang autonomous region of southern china from the highest and oldest to the lowest and youngest including baikong cave juyuan cave sanhe cave and queque cave magnetite was identified as the major carrier of characteristic remnant magnetizations in the cave deposits correlation to the geomagnetic polarity time scale was achieved by combining magnetostratigraphic and biochronologic data our correlation suggests that the cave sedimentary sequences span from the pre olduvai matuyama chron to the jaramillo subchron the combined magneto biochronology leads to the establishment of a chronological framework for the early pleistocene gigantopithecus faunas in chongzuo area the gigantopithecus faunal succession of early pleistocene were assigned to estimated ages of 2 0 ma baikong cave 1 8 ma juyuan cave 1 2 ma sanhe cave and 1 0 ma queque cave respectively the river incision rate in chongzuo area during this time span was estimated to be 14 mm ky

the earliest evidence of hominid settlement in china combined electron spin resonance and uranium series esr u series dating of mammalian fossil teeth from longgupo cave abstract longgupo cave located in chongqing municipality china was discovered in 1984 sixteen gigantopithecus teeth and two hominid fossils accompanied with abundant mammalian fossils and stone artifacts were unearthed from the site previous dating result is questioned because of the complexity of deposition history in this study seventeen mammalian fossil teeth collected from different layers of unit c ii and c iii c iii during the 2003 2006 sino franco joint excavation were analyzed by combined esr and u series methods and calculated with a us esr model in situ dose rates were remeasured in detail in 2012 in order to refine the external dose rate determination uranium series analyses indicate that no obvious uranium leaching has occurred and all the teeth underwent a very recent uranium uptake history except one from layer c iii 3 of the south wall the us esr results show that the ages of ten teeth from unit c iii of the north wall are consistent in general about 2 35 ma the ages of seven samples from south wall are not in accordance with the stratigraphic order three teeth are much younger than the other four probably attributed to the relative higher uranium concentration and u th ratio in the dental tissues and significant higher in situ gamma dose rate nevertheless the three teeth from c iii of the south wall give an average age of 2 48 ma the fossil ages obtained in this work combined with paleontological evidence and new paleomagnetic results place longgupo at the very beginning of the early pleistocene compared with other early hominid settlements longgupo is one of the earliest evidences of hominid settlement in china and east asia to date

magnetostratigraphic dating of hominoid bearing sediments at zhupeng yuanmou basin southwestern china abstract the hominoid fossils found in the yuanmou basin southwestern china are among the key fossils for understanding the evolution of early hominoids in eastern asia and their relationship with coeval hominoids in europe and africa however their exact ages have not yet been well determined we provide a new high resolution magnetostratigraphy for the zhupeng profile which is one of the fossil bearing type sections in the region based on magnetostratigraphy of 227 remanent directions together with the age of micromammalian fauna indicate that the hominoid bearing layer is dated within polarity chron 3br 2r or 3br 1r i e within the interval 7 43 7 38 ma or 7 34 7 17 ma this unambiguously indicates that the yuanmou hominoid has a late miocene age which therefore makes it the youngest hominoid found in eurasia it is possible that the yuanmou basin provided a refuge for hominoids during a time of major environmental changes

flow patterns in compound channels with vegetated floodplains understanding the hydraulics of flow in a compound channel with vegetated floodplains is very important for determining the stage discharge curve and for supporting the management of fluvial processes in this paper the flow patterns over different types of vegetation such as tree shrub and grass are described based on an experimental study for vegetation on the floodplain the authors choose plastic grass duck feathers and plastic straws as model grass shrubs and trees respectively a 3d acoustic doppler velocimeter was used to measure the local flow velocities for different types of vegetation on the floodplain and the total discharge and flume slope were measured independently in the cases of nonvegetated floodplains all measured streamwise velocity distributions followed the logarithmic distribution but for vegetated floodplains they followed an s shaped profile exhibiting three zones for all cases the fluctuating velocity followed a normal distribution the influence of different types of vegetation on the distributions of the secondary currents turbulence intensities and reynolds shear stresses were also analyzed

sem and magnetic fabric study of a compacting sediment scanning electron microscopy sem anisotropy of magnetic susceptibility ams and anisotropy of anhysteretic remanence aar studies were conducted on kaolinite magnetite samples compacted to pressures between o and 0 2 mpa to determine if clay and magnetic fabric development mimic a change in compaction behavior marked by a break in slope in the compaction curve this break in slope indicates that the rate of void ratio decrease with increasing pressure abruptly slows down at pressures of about 0 04 mpa about one half of a compaction caused inclination decrease occurs at pressures less than 0 04 mpa sem photomicrographs show that horizontal clay fabric develops inhomogeneousiy within a sample at pressures below the break in slope since pore spaces are larger than magnetite grains at low pressures below the break in slope the observed pattern of inclination decrease during compaction may be due to magnetite grains being attached to clay particles and constrained to follow clay fabric development this interpretation is supported by the observation that aar minimum axes become vertical at pressures above the break in slope this may indicate that magnetic fabric is developing at low pressures and that most of the magnetite particles are constrained to lie subhorizontally the ams maximum axes tend to lie 90 from a strong remanence in these samples suggesting single domain magnetic behavior measurement of ams after alternating field demagnetization yields maximum axes which cluster near to the aar maximum axes suggesting multidomain behavior this apparent contradiction aay be due to magnetic conditions prior to ams aeasurement controlling domain wall nucleation

magnetostratigraphy late devonian iridium anomaly and impact hypotheses paleomagnetism sedimentology and fine scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the late devonian of western australia thermal demagnetization experiments were carried out on 93 specimens of marginal slope limestone form the northern canning basin samples are from a condensed sequence of deep water 100 m frutexites microstromatolites frutexites is a shrublike cyanobacterial organism that probably precipitated hematite or a metastable precursor from sea water when plotted within the microstratigraphic framework for the study area the observed characteristic directions from the sampled interval 14 5 cm thick are in five discrete layer parallel normal and reversed polarity zones the measured northeast southwest declinations and shallow inclinations probably record late devonian magnetostratigraphy on a centimetre scale the frutexites bed studied there occurs close to the frasnian famennian late devonian boundary a time of mass extinction of a wide variety of marine organisms throughout the world anomalously high iridium concentrations observed in the frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact this study concludes that iridium which is present over the span of five layer parallel magnetic reversals was concentrated over a long period of time by biologic processes thus the canning basin iridium anomalymore may be unrelated to meteorite impact less

magnetostratigraphic dating of the xiashagou fauna and implication for sequencing the mammalian faunas in the nihewan basin north china the nihewan basin sedimentary sequences in northern china are rich in mammalian fossil and paleolithic sites thus providing insights into our understanding of quaternary land mammal biochronology and early human settlements in east asia here we present high resolution magnetostratigraphic results that place stringent age controls on the xiashagou xsg fauna that is the well known nihewan fauna sensu stricto in the nihewan basin northern china results show that the xsg sequence recorded the brunhes normal chron the matuyama reverse chron and the late gauss normal chron the xsg fauna resides in the matuyama reverse chron between the pre reunion matuyama chron and the post olduvai matuyama chron yielding an estimated age of ca 2 2 1 7 ma the pliocene pleistocene boundary gauss matuyama boundary is located in the lower part of the xsg section the combination of our study and previously published magnetostratigraphic data suggest that the mammalian fossil sites in the eastern nihewan basin can be placed between the gauss matuyama geomagnetic reversal and the matuyama brunhes geomagnetic reversal 2 58 0 78 ma leading to a time range of ca 2 6 0 8 ma for the nihewan mammalian faunas

subduction versus accretion of intra oceanic volcanic arcs insight from thermo mechanical analogue experiments we perform thermo mechanical laboratory experiments designed to explore the behaviour of the volcanic arc during intra oceanic arc continent collision following oceanic subduction and subsequent back arc opening the overriding oceanic lithosphere is made of two layers representing the oceanic crust and the lithospheric mantle this lithosphere carries a volcanic arc and is thinned and weakened beneath both the arc and the back arc basin the subducting plate contains three parts one layer oceanic and two layer crust and mantle continental lithosphere with a continental margin between them when the continental margin reaches the trench and starts subducting the overriding plate undergoes growing horizontal compression and finally fails in the vicinity of the back arc spreading centre which is the weakest part of this plate the failure can result in subduction of the whole arc plate comprised between the trench and the back arc spreading centre during subduction of the arc plate the mantle part of this plate subducts completely while the behaviour of the arc crust depends on its thickness and strength which is a function of composition and temperature we tested four cases with different arc crust thicknesses and composition rheology with total lithosphere thickness in the arc being constant three types of tectonic evolution have been obtained complete arc subduction complete arc accretion and partial arc subduction accretion the result is largely controlled by the crustal thickness of the arc a thin arc thickness equivalent to v16 km in nature made of the same strong material as the oceanic crust subducts completely without leaving any trace at the surface on the contrary a thick arc equivalent to v26 km in nature made of the same material is scraped off and accreted to the overriding plate the lower crust of such an arc is hotter therefore its strength at moho depth and coupling between crust and mantle are small in addition the thick arc has a high isostatic relief and hence a greater mechanical resistance to subduction therefore the arc is scraped off if the arc is made of a weaker continental like material or contains a weak layer low friction interface it is completely or partially scraped off even if it is small when there is no back arc opening before collision no thin and weak lithosphere in the rear of the arc the overriding plate fails in the arc area which may result in a complete fore arc block subduction with the volcanic arc remaining at the surface the obtained models are compared with mountain belts with nearly no trace of arc activity oman with accreted arc kohistan and with small remnants of subducted arc southern tibet 2003 elsevier science b v all rights reserved

late cenozoic paleomagnetism and chronology of andean basins of bolivia evidence for possible oroclinal bending new paleomagnetic and radioisotopic data are reported from two late tertiary high elevation non marine basins in the eastern cordillera of bolivia 1 quebrada honda located at 22 s lat consists of a 300 m thick section containing abundant santacrucian or friasian middle miocene fossil mammals this locality is constrained by mean 40 k 40 ar ages of 12 83 0 11 ma and 11 96 0 11 ma and the local magnetostratigraphy is correlated to chrons c5aa through c5a on the magnetic polarity time scale mpts the fossil mammals from quebrada honda have an extrapolated age of about 13 0 to 12 7 ma 2 micana located at 17 s lat consists of a 205 m thick section containing late miocene fossil mammals including a megatheriid sloth and the tiny mesothere microtypotherium cf m choquecotense this locality is constrained by a fission track age determination of 6 9 1 1 ma and the local magnetostratigraphy is correlated to chron 7 on the mpts the fossil mammals from this section have an extrapo

palynological analysis of the late early pleistocene sediments from queque cave in guangxi south china abstract palynomorphs extracted from the sediments in queque cave of the late early pleistocene in chongzuo guangxi zhuang autonomous region were investigated to reconstruct the paleoenvironment in the study area while the sediments are pollen poor they are sufficiently productive to carry out a paleoenvironmental analysis the source vegetation reflected by the palynomorphs from the unfossiliferous layer was temperate to warm temperate deciduous and evergreen broadleaved forest while it was warm temperate to subtropical deciduous and evergreen broadleaved forest from the mammalian horizons climatic parameters obtained using the coexistence approach indicate that the unfossiliferous layer mat 11 3 15 4 c map 601 1 1076 1 mm was cooler and drier than that from the mammal bearing layers mat 12 6 18 6 c map 784 7 1523 1 mm

vortex structure and sediment deposition in the wake behind a finite patch of model submerged vegetation abstracta submerged patch of finite width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes this experimental study used velocity and deposition measu

prediction of the depth averaged two dimensional flow direction along a meander in compound channels abstract for overbank flows in meandering channels the flow direction along a meander varies and is affected by floodplain vegetation this study proposes a model for predicting the depth averaged two dimensional flow direction depth averaged flow angle along a meander in smooth and vegetated meandering compound channels laboratory experiments were performed in smooth and vegetated channels measurements show that the height of the secondary current cell in the main channel is increased by dense floodplain vegetation comparing with that in a non vegetated channel a method of determining the height of the cell is proposed at the middle section between the apex and exit sections where the secondary current cell is absent the depth averaged flow angle is independent of the height of the cell beyond the middle section a new secondary current cell is formed and the flow angle is highly dependent on the height of the cell the proposed model is thoroughly verified using the flume experimental and field observed data good agreement is obtained between predictions and measurements indicating that the proposed model is capable of accurately predicting the depth averaged flow angle along a meander in smooth and vegetated meandering compound channels

tectonic evolution of the hengshan wutai fuping complexes and its implication for the trans north china orogen abstract the hengshan wutai fuping complexes comprise the central segment of the trans north china orogen tnco in the north china craton ncc the tectonic evolution of these complexes is regarded as representative for the entire tnco although the timing of the events has been controvesial on the basis of new nd isotope and structural data and a re appraisal of published geochemical and geochronological data a refined model for the tectonic evolution in the neoarchean to paleoproterozoic has been proposed a major ocean named the proto north china ocean developed between the western and eastern blocks prior to 2565 ma northwest ward intra oceanic subduction resulted in the formation of a proto arc as represented by the 2565 2540 ma wutai granitoids the proto arc was rifted and a back arc basin propagated and extended to form an intra oceanic arc basin system at about 2540 2525 ma the main products during the development of this system were a morb arc back arc basalt adakite association in the wutai greenstone belt and synchronous granitoids in the wutai complex the main subduction accretion process involving multiple subduction zones occurred at 2525 2475 ma resulting in closure of the wutai back arc basin and the formation of diverse arc magmas although the tectonic history between 2 5 and 1 8 ga remains uncertain final collision between the eastern and western blocks and the buildup of the tnco most likely took place at 1 9 1 8 ga the tectonic evolution of the tnco is characterized by subduction accretion processes and the development of arc basin systems thus it is more likely a cordilleran type orogen than a simple continent continent collisional orogen

biogenic magnetite as a primary remanence carrier in limestone deposits abstract studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at sugarloaf key fl u s a and calcareous laminated sediments from laguna figueroa baja california mexico have revealed the existence of magnetotactic bacteria and ultrafine grained single domain magnetite in both environments magnetotactic bacteria were identified by light and electron microscopy the single domain magnetite was detected by coercivity spectra analysis with a squid magnetometer and examined under the transmission electron microscope the similarity in terms of size and shape between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine grained magnetite in these two marine environments was biologically formed these results combined with the common occurrences of ultrafine grained magnetite in limestone deposits detected rock magnetically suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks several cambrian limestone samples separately collected from siberia china and kazakhstan were examined for the presence of bacterial magnetite samples from the lower cambrian sinskian formation at siberia platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component post cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them assessing the potential role of biogenic magnetite as a primary remanence carrier in other phanerozoic limestone deposits ought to be further pursued

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

the early pleistocene gigantopithecus sinomastodon fauna from juyuan karst cave in boyue mountain guangxi south china abstract as one of the most important quaternary mammalian faunas in southern china the gigantopithecus sinomastodon fauna has received much attention the large primate fossil teeth newly collected from juyuan karst cave in boyue mountain guangxi zhuang autonomous region of southern china can be identified as gigantopithecus blacki the morphology and size of these g blacki teeth differ from those of the middle pleistocene gigantopithecus teeth which hold evidently larger dental dimensions and more complex crenulations from hejiang cave also in guangxi and tham khuyen cave in vietnam however the g blacki teeth from juyuan cave are relatively similar to those from early pleistocene mohui cave and liucheng gigantopithecus cave both in guangxi which suggests that the three cave sites have similar age the juyuan fauna associated with gigantopithecus blacki consisting of 45 mammalian species such as sinomastodon yangziensis ailuropoda wulingshanensis stegodon huananensis and rhinoceros fusuiensis is a typical early pleistocene gigantopithecus sinomastodon fauna of southern china the juyuan fauna is mostly similar to mohui fauna also implying their contemporaneity paleomagnetic analyses demonstrate that the fossil bearing sediments in juyuan cave are dominated by normal polarity combining the faunal analysis and magnetostratigraphic evidence the juyuan sediments can be best correlated with the olduvai normal subchron giving an estimated age of 1 8 ma

inclination shallowing in deep sea sediments from the north atlantic paleomagnetic data from miocene to recent deep sea sediments recovered during leg 94 of the deep sea drilling project dsdp in the north atlantic exhibit a systematic shallowing of inclinations with depth at some sites this shallowing is coincident with a downhole decrease in water content and is observed only in sediments with a carbonate content consistently greater than 80 compaction due to overburden pressure is believed to be responsible for the shallow inclinations observed in these unconsolidated sediments at sites where the carbonate content of the sediments is consistently below about 80 no significant downcore decreasing trends in the water content or inclination record are observed

geochronology of ailuropoda stegodon fauna and gigantopithecus in guangxi province southern china abstract pleistocene faunas from south china are difficult to subdivide based on the long temporal ranges of many taxa and a reduced number of genera in comparison to faunas from temperate north china in south china the ailuropoda stegodon fauna is a very general one and includes a relatively stable suite of genera that apparently persisted for long periods of time these attributes have made constraining its time range difficult application of electron spin resonance esr dating of tooth enamel constrains the ages well where uranium uptake was minor where uranium uptake into teeth was significant an approach combining esr and 230th 234u isotopic analysis also yields excellent ages previous estimates of early middle and late pleistocene time ranges previously determined by biostratigraphic seriation for the ailuropoda stegodon fauna are confirmed in all cases but are made more precise with our approach including specific time ranges for certain archaic taxa absolute dating also yields an extended time range for gigantopithecus blacki of 1200 to 310 ka

evidence for a relationship between hydrocarbons and authigenic magnetite establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to 1 elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite 2 developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods and 3 evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool the direct association of hydrocarbon migration and the precipitation of authigenic magnetite has however not been established in this paper we report palaeomagnetic rock magnetic petrographic and geochemical results of a study of samples from permian spelebthems and gilsonite found in the ordovician arbuckle group in southern oklahoma the results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic magnetite

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

speleology and magnetobiostratigraphic chronology of the buffalo cave fossil site makapansgat south africa speleological stratigraphic paleomagnetic and faunal data is presented for the buffalo cave fossil site in the limpopo province of south africa speleothems and clastic deposits were sampled for paleomagnetic and mineral magnetic analysis from the northern part of the site where stratigraphic relationships could be more easily defined and a magnetostratigraphy could therefore be developed for the site this is also where excavations recovered the fossil material described a comparison of the east and south african first and last appearance data with the buffalo cave fauna was then used to constrain the magnetostratigraphy to produce a more secure age for the site the magnetostratigraphy showed a change from normal to reversed polarity in the basal speleothems followed by a short normal polarity period in the base of the clastic deposits and a slow change to reversed directions for the remainder of the sequence the biochronology suggested an optimal age range of between 1 0 ma and 600 000 yr based on faunal correlation with eastern and southern africa a comparison of the magnetobiostratigraphy with the gpts suggests that the sequence covers the time period from the olduvai event between 1 95 and 1 78 ma through the jaramillo event at 1 07 ma to 990 000 yr until the bruhnes matuyama boundary at 780 000 yr the faunal bearing clastic deposits are thus dated between 1 07 ma and 780 000 yr with the main faunal remains occurring in sediments dated to just after the end of the jaramillo event at 990 000 yr

esr u series and paleomagnetic dating of gigantopithecus fauna from chuifeng cave guangxi southern china several gigantopithecus faunas associated with taxonomically undetermined hominoid fossils and or stone artifacts are known from southern china these faunas are particularly important for the study of the evolution of humans and other mammals in asia however the geochronology of the gigantopithecus faunas remains uncertain in order to solve this problem a program of geochronological studies of gigantopithecus faunas in guangxi province was recently initiated chuifeng cave is the first studied site which yielded 92 gigantopithecus blacki teeth associated with numerous other mammalian fossils we carried out combined esr u series dating of fossil teeth and sediment paleomagnetic studies our esr results suggest that the lower layers at this cave can be dated to 1 92 0 14 ma and the upper layers can be dated to older than 1 38 0 17 ma correlation of the recognized magnetozones to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic biostratigraphic and esr data the combined chronologies establish an olduvai subchron 1 945 1 778 ma for the lowermost chuifeng cave sediments we also analyzed the enamel 13c values of the gigantopithecus faunas our results show that southern china was dominated by c3 plants during the early pleistocene and that the gigantopithecus faunas lived in a woodland forest ecosystem

magnetostratigraphy and biostratigraphy of callovian oxfordian limestones from the trento plateau monti lessini northern italy abstract callovian oxfordian ammonitico rosso limestones from the trento plateau carry a characteristic remanent magnetization indicating frequent geomagnetic polarity reversals which can be correlated to callovian oxfordian ammonite zones the characteristic magnetization component has low coercivity and blocking temperatures below 600 c suggesting that magnetite is the carrier the age of the magnetization is not constrained by field tests although sedimentological evidence for early lithification and the close stratigraphic juxtaposition of normal and reversed component directions tend to indicate that acquisition of the magnetization occurred close to the sediment water interface stratigraphic gaps and the condensed nature of the sections inhibit the correlation of polarity reversals between sections the data suggest a reversed polarity bias for the oxfordian and a normal polarity bias for the callovian

paleomagnetic stratigraphy and time in sediments studies in alluvial siwalik rocks of pakistan sediments may acquire magnetic remanence upon deposition and shortly after deposition hence the paleomagnetic record of sedimentary rocks may provide a chronostratigraphic framework for rates and patterns of depositional and post depositional processes over time scales intermediate between those of modern observation and those of the dated geologic record two applications of high resolution magneto stratigraphy in miocene alluvial rocks of pakistan illustrate this point 1 transition stratigraphy the dense sampling of a magnetic reversal of correlated sections in the dhok pathan formation revealed high variability in sediment accumulation rates over several thousand to 10 000 yr time transgressive strata representing a paleosol and a floodplain marsh and a pervasive post depositional record mainly from pedogenesis 2 lateral tracing of paleomagnetic reversal boundaries in the chinji formation revealed a secular change in sediment accumulation rate and evidence for increased accumulation rate a

early late pliocene biochronology and surface water temperature variations in the mediterranean a high resolution magnetobiostratigraphy is presented for the early late pliocene in sicily paleomagnetic measurements on samples from 100 stratigraphic levels provide an unprecedented high quality polarity sequence which extends from the upper reversed gilbert to the upper normal gauss subchron the resultant chronology for the early late pliocene provides ages for the following principal mediterranean bioevents 1 fodgloborotalia crassaformis at 3 40 ma 2 prolonged absence ofgloborotalia puncticulata between 3 38 and 3 16 ma 3 loduvigerina rutila at 3 16 ma 4 lodsphaeroidinellopsis seminulina at 3 07 ma 5 lodgloboquadrina altispira at 3 04 ma 6 lodcibicides italicus at 2 96 ma summer and winter surface water temperature estimates for the period 3 50 to 2 92 ma are based on the abundances ofglobigerinoides sacculifer andgloborotalia puncticulata in 111 samples with an average resolution of some 5000 years short term variations in temperature of the surface water and in colour and carbonate content of the sediment are primarily controlled by the equinoxal precession a higher seasonality during deposition of the grey coloured carbonate poor facies suggests that at that time the summer solstice occurred near perihelion whereas an inverse alignment occurred at the time of deposition of white coloured carbonate rich layers this phase relationship between the precession cycle and grey coloured layers is also valid for the sapropels which began to intercalate in the grey coloured layers at 2 94 ma long term changes in surface water temperatures include a warming between 3 38 and 3 18 ma followed by a cooling from 3 18 to 3 03 ma the warming of mediterranean surface waters at 3 38 ma is believed to be associated with the final closure of the isthmus of panama consequent strengthening of the gulf stream injected larger volumes of warm surface water into the north atlantic drift and eastern boundary current and this caused surface water temperatures in the mid to high latitude northeast atlantic and mediterranean to rise the subsequent climatic cooling at 3 18 ma is linked to a first stage of northern hemisphere continental ice growth

geomorphic inheritance and the development of tower karst four genetic types of tower karst are identified the most typical consisting of residual hills protruding from a planed carbonate surface veneered by alluvium two extreme possibilities for tower karst evolution are recognized a direct development that is independent of any previous morphology and a sequential development that depends explicitly on the morphological characteristics of a previous cockpit karst phase examples of both are described although the latter appears the more common south china tower karst is examined in this light palaeomagnetic analysis of cave deposits in a tower near guilin indicate the feature to be a time transgressive landform four principal controls of tower development are discussed and a model of tower evolution is presented

heishan mafic ultramafic rocks in the qimantag area of eastern kunlun nw china remnants of an early paleozoic incipient island arc abstract the heishan mafic ultramafic complex in the qimantag mountains of the eastern kunlun orogen consists of olivine pyroxenites pyroxenites gabbros and massive basalts zircons from the gabbros have magmatic sector zoning with th u ratios of 0 5 2 3 and yield a shrimp age of 486 6 ma mswd 0 31 which is taken as the time of magma crystallization spinel pyroxene and plagioclase mineral compositions indicate that the rocks formed in an island arc environment the cumulates have low la yb n ratios 0 6 0 8 and depleted lree patterns high abundances of cr 3031 1185 ppm co 119 50 ppm and ni 953 291 ppm and end t values of about 8 0 the massive basalts have somewhat higher contents of tio2 1 0 1 3 na2o 2 6 2 8 total ree and mg s 55 63 than those of the cumulates the la yb n ratios of the basalts range from 0 8 to 1 2 and the chondrite normalized ree patterns are flat end t values of the basalts range from 7 7 to 9 4 the compositions of the cumulates and volcanic rocks especially their similar nd isotopes suggest that the rocks were derived from similar depleted mantle sources the primary magmas were probably generated in an initial arc environment we conclude that the heishan mafic ultramafic complex in the qimantag area preserves a record of proto tethyan oceanic lithosphere formed in the early paleozoic it possibly marks a suture between the qaidam and north kunlun terranes in the western segment of the eastern kunlun orogen

magnetostratigraphy of cave sediments wyandotte ridge crawford county indiana towards a regional correlation abstract the polarity of 42 sediment samples obtained from 21 sites in wyandotte cave and five smaller satellite caves in wyandotte ridge southern indiana is used as a basis for a magnetostratigraphic correlation with sediments in mammoth cave kentucky sediments in caves at elevations between 137 and 162 m have a normal polarity but the fill between 168 and 171 m exhibits a polarity reversal the reversal is interpreted to represent the most recent polarity change suggesting that the upper level of wyandotte cave was last active at about the same time not less than 0 78 ma as the c level in mammoth cave which lies at approximately the same elevation the local base level control in both cave systems is provided by tributaries of the ohio river thus the correlation is most likely a consequence of the contemporaneous abandonment of upper level passages in wyandotte and mammoth caves during the early pleistocene reconstruction of the ohio river drainage sediments in caves between 236 and 241 m have a normal polarity the fill in these little wildcat and galley door caves is probably at least 2 6 ma old it appears to correlate with the residuum that delimits the upper mitchell plain surface the pennyroyal plateau in kentucky and on the basis of our interpretation of the magnetostratigraphy is older than the fill in the highest a and b levels in mammoth cave

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

magnetostratigraphic dating of early humans in china abstract china is a key area for research into human occupation in the old world after the initial expansion of early humans out of africa reliable age determinations are pivotal for assessing the patterns of human evolution and dispersal in this region this paper reviews magnetostratigraphic studies of some early pleistocene strata bearing hominin remains and or artifact stone tools from northern to southern china the quality and reliability of the paleomagnetic dates are also evaluated new magnetostratigraphic results for the xihoudu paleolithic site in north central china are also presented among the few hominin or paleolithic sites in china from the early pleistocene five have been well investigated three of these are in northern china at xiaochangliang donggutuo and gongwangling the remaining two in southern china at longgupo and yuanmou considerable progress has been made during the past three decades towards paleomagnetically dating these sites indeed the age estimates at xiaochangliang and gongwangling have been widely accepted magnetostratigraphic consensus about the age of the donggutuo site has also been reached however the age determination for the two sites in southern china is still contested the integration of rock magnetic stratigraphy with magnetic polarity stratigraphy has resulted in a determined age of 1 36 ma for a stone tool containing layer of lacustrine sediments at the xiaochangliang site in the nihewan basin lithostratigraphic constraints have significantly contributed to determining the age of lantian homo erectus at gongwangling which occurred in a loess paleosol sequence of the southern loess plateau its age paleomagnetically derived is about 1 15 ma these two paleomagnetic ages suggest an expansion and flourishing of human groups from northern to north central china during the early pleistocene this suggestion has been reinforced by our new magnetostratigraphic age estimate of about 1 27 ma for the xihoudu site as will be presented in this paper however more work is needed for the age determinations of the hominin bearing strata at the longgupo and yuanmou sites in southern china finally we stress that it is necessary to combine biostratigraphy lithostratigraphy and rock magnetic stratigraphy with the traditional magnetic polarity stratigraphy in order to obtain reliable age determinations for strata bearing hominin remains or stone artifacts

petrogenesis of tholeiite associations in kudi ophiolite western kunlun mountains northwestern china implications for the evolution of back arc basins the kudi ophiolite in the western kunlun mountains comprises harzburgites dunites cumulate dunites cumulate pyroxenites and gabbros diabase dikes and pillow and massive lavas and are fragments of a supra subduction zone ssz ophiolite from the early paleozoic the extrusive rocks can be classified into three groups of tholeiites back arc basin bab tholeiites low ti island arc tholeiites iat and lree enriched iat as shown by their distinctive geochemical characteristics the ssz type mantle peridotites the cumulate complex with arc tholeiite affinity and babb type diabase dikes and basalts constitute an upper mantle and crustal section of a back arc basin formed by coupling of morb type mantle upwelling with fluid efflux from slab devolatilization the low ti iat are characterized by low ti and hfse and slightly u shaped or lree depleted chondrite normalized ree patterns and represent melts derived from a depleted mantle source region extraction of babb magma modified compositionally by fluids and or melts from the subducting lithospheric slab during propagation and extension of the back arc basin we interpret the lree enriched iat as products of closure of the back arc basin because an interaction between the parental magma of this iat and the mantle peridotites formerly the upper mantle of the basin in a newly formed mantle wedge had occurred

magnetostratigraphy of sediments in mammoth cave kentucky clastic sediment deposits found within the caves of mammoth cave national park have yielded a magnetostratigraphic pattern of magnetic polarity reversals which indicates that they were deposited over a range of at least 1 million and most likely 2 million years

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

paleoenvironmental background of the early pleistocene gigantopithecus fauna in bubing basin south china thanks to the presence of the enigmatic gigantopithecus fossils vertebrate paleontologists have spent much time analyzing the pleistocene faunas of southern china although research has been conducted in the region for more than one half century the vast majority of this research has focused on the direct analysis of the associated vertebrate fossils particularly for taxonomic identification purposes in order to develop a firmer understanding of the paleoenvironment in which these various taxa lived there is still a relative paucity of data derived from other lines of evidence besides taxonomic identifications here we contribute to these paleoenvironmental reconstructions of southern china by presenting the results of clay mineral composition and geochemical analyses of the deposits from the early pleistocene mohui cave bubing basin guangxi in general the mohui cave clay mineral samples are dominated by kaolinite which indicates a warm and humid climate the relatively high content of smectite in unit ii implies a relatively long dry season within the overall context of the warm and humid environment based on the chemical index of alteration cia the estimated land surface temperature during the early pleistocene 27 c was much higher than today 21 9 c our results are consistent with previous environmental reconstructions based on vertebrate paleontological and isotopic studies of the gigantopithecus fauna in southern china that the environment during the early pleistocene was warmer and more humid than today

characteristics of pleistocene megafauna extinctions in southeast asia the extinction of large bodied taxa from the pleistocene in southeast asia is examined although the chronological resolution of these extinctions is poor and number of excavations in the region relatively few broad characteristics of these extinctions can be described many taxa which became extinct appear to have been endemic to regions within southeast asia while some taxa which experienced extinction or severe range reduction occurred in several regions members of the latter group include proboscideans stegodon and palaeloxodon the pygmy hippopotamus hexaprotodon the orangutan pongo hyenas crocuta and hyaena the giant panda ailuropoda tapirs tapirus and megatapirus rhinoceroses rhinoceros and the giant asian ape gigantopithecus the loss of these species cannot be assigned to a single cause rather their disappearance is likely tied to both climatic and human agents unlike other regions which experienced megafauna extinctions eustatic changes in sea level in southeast asia seems to have been an important factor

preservation assessments and carbon and oxygen isotopes analysis of tooth enamel of gigantopithecus blacki and contemporary animals from sanhe cave chongzuo south china during the early pleistocene abstract as one of the largest primates that ever lived the finding of gigantopithecus blacki mainly occurs in southern china during the early and middle pleistocene previous stable carbon isotope analysis of g blacki teeth showed that it relied on c3 based foods in the early pleistocene however the deficiency of preservation assessment other ape samples and oxygen isotope data may hinder the dietary interpretation and understanding the dietary preference of g blacki compared to human relative apes in this study xrd and ftir were used to assess the crystallinity variation of apatite in fossil enamel of g blacki and animals during the early pleistocene from sanhe cave chongzuo guangxi south china the results indicated that the carbonate group in enamel apatite still retained its biogenic signature although the crystallinity was enhanced during fossilization the carbon isotope values of all fossil animals suggest that they consumed c3 based foods most importantly the oxygen isotope values of all animal fossils show that g blacki as well as pongo was engaged in mixed feeding strategy perhaps relying on grasses plant leaves stems or possible roots that are depleted in 18o moreover lower oxygen isotope values of g blacki than those from pongo are observed suggesting that g blacki preferred plant roots or stems with lower 18o values

early pleistocene large mammal fauna associated with gigantopithecus at mohui cave bubing basin south china the mohui fauna associated with gigantopithecus blacki has been recovered from the pleistocene karst cave deposit in bubing basin guangxi south china the large mammalian assemblage derives from 28 species 15 of which have no historic descendants occurrence of some ancient species implies that this fauna is early early pleistocene such as hystrix magna sinomastodon yangziensis stegodon huananensis ailuropoda microta pachycrocuta licenti tapirus sanyuanensis hespertherium sp and dorcabune liuchengense comparisons to already dated early pleistocene faunas in south china combined with preliminary paleomagnetic electron spin resonance esr and u series analysis of this cave indicate mammalian fauna age around 1 7 ma comparisons to five faunal assemblages in the same basin show species level differences in ailuropoda stegodon hystrix tapirus and sus implying the large mammal fauna has passed through a slow process of evolution during the quaternary in east asia

biogenic magnetite in stromatolites ii occurrence in ancient sedimentary environments abstract in this paper we report the discovery of fossil bacterial single domain magnetite particles in ancient stromatolites the biogenicity of the crystals was determined by the following criteria 1 distinctive morphology and habit 2 composition and 3 environment of deposition stromatolites ranging in age from the middle archean to pleistocene composed of both carbonate and chert were analyzed for the presence of single domain magnetite using rock magnetic methods the granulometry and composition of the ultra fine grained magnetite crystals extracted were determined by transmission electron microscopy and electron diffraction the oldest magnetofossils were extracted from stromatolitic chert of the gunflint iron formation which is approximately 2000 ma old the implications of these findings and the potential uses of fossil bacterial magnetite in studies of the evolution of biomineralization and prokaryotic metabolic processes paleomagnetism and as an indicator of ancient oxygen levels are discussed bacterial magnetite represents the oldest evidence of biomineralization yet discovered in the fossil record

sediment deposition within and around a finite patch of model vegetation over a range of channel velocity the interaction between flow and vegetation creates feedbacks to deposition that vary with channel velocity this experimental study describes how channel velocity and stem generated turbulence influence the deposition within and around an emergent patch of model vegetation with a particular focus on deposition within the patch the reynolds number threshold for stem scale turbulence generation was determined using velocity spectra and flow visualization at high channel velocity resuspension occurred in the bare regions of the channel and a nonuniform spatial distribution of net deposition was observed around and within the patch in contrast at low channel velocity there was no or limited resuspension and a uniform distribution of net deposition was observed around and within the patch the deposition inside the patch was enhanced relative to a bare channel control only when the following two criteria were met 1 the absence of stem turbulence and 2 the presence of sediment resuspension in the bare channel comparison to previous lab and field studies further support these criteria

an island arc origin of plagiogranites at oytag western kunlun orogen northwest china shrimp zircon u pb chronology elemental and sr nd hf isotopic geochemistry and paleozoic tectonic implications abstract this paper presents detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope geochemistry of three intrusive plagiogranite bodies formed in an island arc setting within the oytag ophiolite suite of the oytag kuda suture zone shrimp zircon u pb dating of two of these intrusions shows that they were emplaced into the oytag volcanic rocks at 337 5 4 1 ma and 327 7 4 9 ma and that the younger intrusion contains inherited zircons ranging from 435 3 to 480 8 ma both intrusions are composed of low al trondhjemite and tonalite the rocks have low k 2 o and sr and high y contents with low sr y ratios they have relatively low rare earth element ree concentrations and are depleted in light ree lree and relatively enriched in heavy ree hree with marked negative eu anomalies in the chondrite normalized ree patterns they have initial 87 sr 86 sr ratios of 0 7048 to 0 7068 and e nd t values of 6 2 to 7 6 which are lower than those of typical morb in situ hf isotopic compositions of zircons with early carboniferous age from both intrusions are characterized by positive initial e hf values ranging from 12 5 to 19 5 similar to typical morb the inherited ordovician zircons in the younger intrusion have initial e hf values of 1 9 to 3 1 similar to zircons from ordovician granitoids in the region detailed elemental and isotopic data suggest that the oytag plagiogranites were formed in an oceanic island arc setting by differentiation of arc tholeiitic magmas that formed in response to the intra oceanic subduction the inherited zircons are interpreted as the xenocrysts captured from the incipient oceanic crust that contains relicts of discrete fragments of continental crust with ordovician zircons through which the plagiogranite was emplaced the oytag ophiolite suite might be the remnants of an ancient island arc the basement of which was the incipient oceanic crust the oytag kuda suture zone is suggested to be a multiple suture zone that represents the remnants of both the proto tethyan and paleo tethyan oceans the western kunlun orogen was therefore not a long lived active continental margin during the early and late paleozoic times it most likely underwent at least two orogenic cycles and thus might represent a multiple orogenic belt

magnetic stratigraphy of cenozoic terrestrial sediments and mammalian dispersal the existing literature on the correlation of the magnetic polarity timescale to vertebrate mammalian chronology for the cenozoic is reviewed for all continents except the soviet union the magnetostratigraphic data from north america is the most complete followed by the indian sub continent ten criteria for rating magnetostratigraphic studies are established and the papers reviewed are rated from 1 10 with 10 being the maximum score the timing of mammalian dispersal is examined against the background of information from magnetostratigraphic studies allied with radiometric dating north american land mammal ages are partly defined on immigrant taxa and the boundaries of the nalma are based on dispersal events it has been suggested that dispersal and evolutionary episodes observed in siwalik sediments were correlative to sea level change deduced from delta 18 o data from benthic foraminifera to test this possibility in the general case dispersal events into north america were determined by us

comparison of u th paleomagnetism and cosmogenic burial methods for dating caves implications for landscape evolution studies caves are useful in landscape evolution studies because they often mark the level of previous water tables and when dated yield incision rates dating caves is problematic however because their ages are only constrained by the oldest deposits contained within which may be far younger than the cave itself we dated cave deposits in the sierra nevada using u th dating of speleothems paleomagnetic dating of fine sediment and cosmogenic 26 al 10 be burial dating of coarse sediment the sampled caves formed sequentially as the water table lowered providing an important stratigraphic test for the dating methods large discrepancies between deposit ages from similar cave levels demonstrate that even when accurately determined deposit ages can seriously underestimate the timing of cave development drip type speleothems are most prone to this minimum age bias because they can accumulate long after caves form and because the u th method is limited to 400 ka paleomagnetic dating requires correlation with the global reversal chronology and is hindered by a lack of continuous stratigraphy the fine sediment analyzed for paleomagnetism is also highly susceptible to remobilization and deposition in cave passages well above base level cosmogenic 26 al 10 be dates bedload material deposited when caves were at or very near river level and can date material as old as 5 ma in the sierra nevada speleothem u th ages and sediment burial ages from the same cave levels differ by as much as an order of magnitude these results suggest speleothem ages alone may significantly underestimate cave ages