chemical remagnetizations in the illizi basin saharan craton algeria and their acquisition process summary during remagnetization chemical changes limited to moderate grain growth from pre existing single domain sd grains do not modify the palaeomagnetic direction carried by these grains palaeomagnetic direction from new sd grains on the contrary is that of the magnetic field during remagnetization the resulting direction becomes intermediate between the directions carried by previous and new sd grains as it appears often in case of a partial magnetic overprint if the growth of pre existing grains is more important these grains become large multidomain md and loose the primary magnetization stable magnetization is then only related to the new sd grains which carry the total remagnetization in the illizi basin saharan platform these different cases of partial or total magnetic overprint have been observed resulting from palaeomagnetic studies of different palaeozoic and mesozoic formations

a facies model for a quaternary andesitic composite volcano ruapehu new zealand ruapehu composite volcano is a dynamic volcanic sedimentary system characterised by high accumulation rates and by rapid lateral and vertical change in facies four major cone building episodes have occurred over 250 ka from a variety of summit flank and satellite vents eruptive styles include subplinian strombolian phreatomagmatic vulcanian and dome related explosive eruptions and extrusion of lava flows and domes the volcano can be divided into two parts a composite cone of volume 110 km3 surrounded by an equally voluminous ring plain complementary portions of ruapehu s history are preserved in cone forming and ring plain environments cone forming sequences are dominated by sheet and autobrecciated lava flows which seldom reach the ring plain the ring plain is built predominantly from the products of explosive volcanism both the distal primary pyroclastic deposits and the reworked material eroded from the cone much of the material entering the ring plain is transported by lahars either generated directly by eruptions or triggered by the high intensity rain storms which characterise the region ring plain detritus is reworked rapidly by concentrated and hyperconcentrated streams in pulses of rapid aggradation immediately following eruptions and more gradually in the longer intervals between eruptions

discriminant function analysis of late quaternary tephras from five volcanoes in new zealand using glass shard major element chemistry abstract the microprobe determined glass shard major element chemistry of tephras derived from five north island new zealand volcanoes mayor island okataina taupo tongariro and mount egmont and younger than ca 20 000 yr b p was subjected to discriminant function analysis four separate approaches were adopted to test the match of the tephras with their known sources 1 an analysis of raw microprobe data 2 an analysis of normalized data 3 an analysis of the data transformed by calculating the log 10 of oxide scores divided arbitrarily by the chlorine content and 4 a repeat of 3 with multivariate outlier scores as determined by principal components analysis deleted all yielded excellent classification functions efficiencies of 91 100 with the eruptives associated with each of the five volcanoes being chemically distinct from one another in each approach the first two canonical discriminant functions accounted for 90 of the variation between groups the removal of multivariate outliers from the data set had only minor effects on the performance of the discriminant function procedures separate discriminant function analysis of the relatively alike taupo and okataina eruptives gave a greater degree of multivariate separation the numerical classifications generated should enable unidentified tephras erupted since ca 20 000 yr b p from the five volcanoes to be provisionally matched with their sources

pollen and radiolarian records from deep sea core rc14 103 climatic reconstructions of northeast japan and northwest pacific for the last 90 000 years using modern pollen and radiolarian distributions in sediments from the northwest pacific and seas adjacent to japan to interpret floral and faunal changes in core rc14 103 44 02 n 152 56 e we recognize two major responses of the biota of eastern hokkaido and the northwest pacific to climatic changes since the last interglaciation relatively stable glacial environments 80 000 20 000 yr b p were basically cold and wet 8 c and 1200 mm mean annual temperature and precipitation respectively supporting climax broadleaf deciduous forest with quercus and ulmus zelkova with surface waters in the northwest pacific characterized by warm 1 5 c winter and cold 10 4 14 3 c summer temperatures climatic evidence from rc14 103 shows a high degree of local and regional variation within the context of global climatic change correlative ocean and land records provide the detailed input necessary to assess local regional responses to variations in other key elements i e solar radiation monsoonal variations of the northeast asian climate system

geological history of the north eastern ring plain of ruapehu volcano new zealand abstract continuous exposures along the upper waikato stream provide new insights into the north eastern ring plain of ruapehu volcano extending the known stratigraphy beyond 22 6 ka time control in the sequence is provided by five rhyolitic tephra units erupted from central north island volcanoes comprising kawakawa okaia omataroa hauparu and rotoehu tephras the sequence is dominated volumetrically by diamictons and fluvial deposits resulting both from volcanic events and periods of instability on the flanks of ruapehu within the sequence are 60 individual andesitic lapilli units derived primarily from ruapehu volcano via mostly sub plinian eruption mechanisms an average eruption rate of more than one lapilli eruption per 1000 years is estimated for the ca 60 ka record the style of deposition on the ring plain changes over time and appears to reflect climate change over the last glacial period in periods of severe climatic conditions during marine 18 o stage 4 porewan stadial and the last glacial maximum of marine 18 o stage 2 ohakean the north eastern ring plain aggraded rapidly with deposition of thick continuous diamicton sequences the other recognized cool period in the southern north island the stadial of late 18 o stage 3 ratan did not appear to induce major aggradation on the north eastern ring plain during periods of mild climate within the last glacial deposition on the north eastern ring plain was dominated by fall accession of either tephra or material reworked from other parts of the ring plain by aeolian processes

climatic and environmental changes at southeastern coast of lake biwa over past 3000 years inferred from borehole temperature data abstract in order to infer past climatic change in central japan we measured temperatures in a borehole at the karasuma site on the southeastern coast of lake biwa and reconstructed sediment surface temperature history during the last 3000 years the reconstructed temperature history shows apparent medieval warm period little ice age and contemporary temperature warming however the large amplitude of the temperature changes up to 4 5 k cannot be explained by past climatic change only suggesting that there was some other cause of the larger amplitude temperature changes the onsets of temperature decrease in the late 12th century a d and temperature increase in the mid 17th century a d appear to coincide with occurrences of two destructive earthquakes 1185 and 1662 a d that caused water level changes of lake biwa it suggests that the reconstructed sediment surface temperature history reflects the environmental change due to tectonically induced water level changes of the lake if the annual mean of the ground surface temperature was higher than that of the bottom water temperature in a shallow part of the lake which is consistent with the present day data the large amplitude of the sediment surface temperature change may be attributed to a combined effect of past climatic and environmental changes thus we suggest that the borehole temperature at the karasuma site preserves information not only on past climate changes but also on environmental changes due to tectonically induced water level changes

lago grande di monticchio southern italy a long record of environmental change illustrated by sediment geochemistry abstract bulk geochemical analysis has been carried out on a 51 m sediment core from lago grande di monticchio in southern italy the record which may extend from the present back through more than one glacial cycle displays major variations in indicators of palaeoproductivity such as organic carbon and biogenic silica the most prominent change occurs at the holocene boundary lower in the sequence zones of moderately enhanced productivity highlight either interstadial or interglacial periods c n ratios and hydrogen indices provide possible indications of the sources and diagenetic state of the bulk organic matter but must be interpreted carefully as it is difficult to isolate the effects of these two factors changes in the clastic fraction e g na al ratio suggest that tephra deposition in the lake and its catchment has significantly altered the sedimentation this may also have influenced the biological productivity of the system

palaeomagnetic results from the early permian copacabana group southern peru implication for pangaea palaeogeography abstract samples collected from folded carbonate rocks of the early permian copacabana group exposed in the peruvian subandean zone have been subjected to detailed palaeomagnetic analysis thermal demagnetisation of most samples yield stable high unblocking temperature directions dominantly carried by titanomagnetite minerals this remanence identified in 32 samples 43 specimens is exclusively of reverse polarity consistent with the permian carboniferous reversal superchron pcrs the overall directions pass the fold test at the 99 confidence level and are considered as being a pre folding remanence acquired in early permian times the copacabana group yields an overall mean direction of d 166 i 49 95 4 5 k 131 5 n 9 sites in stratigraphic coordinates and a corresponding palaeosouth pole position situated at 68 s 321 e a95 5 2 k 100 combining this pole with the coeval high quality data from south america africa and australia results in a mean pole for gondwana situated at 34 4 s 065 6 e a95 4 9 k 73 6 n 13 studies in african coordinates this pole position supports a pangaea b palaeogeography in early permian times in contrast the combined pole for gondwana diverges from the coeval laurasian mean pole when assuming the pangaea a type configuration poor quality of the gondwana dataset and inclination shallowing in sediments seem to play no role in the misfit between the permian triassic poles from gondwana and laurasia in pangaea a reconstruction

organization of tropical convection in a gcm with varying vertical resolution implications for the simulation of the madden julian oscillation experiments using a gcm with two different vertical resolutions show differences in the amount of variability in the tropical upper tropospheric zonal wind component associated with the madden julian oscillation mjo the gcm with lower vertical resolution shows very little variability in this quantity whereas when the vertical resolution is doubled in the free troposphere the gcm produces variability which is of the same strength as observations however the eastward propagation of an enhanced convective region from the indian ocean into the west pacific is not well represented in either simulation of this atmospheric gcm a water covered or aqua planet version of the same gcm is used to investigate the behaviour of tropical convection when the vertical resolution is doubled when the vertical resolution is increased the spectrum of tropical cloud types changes from a bimodal distribution with peaks representing shallow cumulus and deep cumulonimbus clouds to a trimodal distribution with a third peak in mid troposphere near the melting level associated with periods when these mid level congestus clouds are dominant the detrainment from these clouds significantly moistens the mid troposphere the appearance of these congestus clouds is shown to be partly due to improved resolution of the freezing level and the convective processes occurring at this level however due to the way in which convective detrainment is parametrized in this model the vertical profile becomes rather noisy and this too contributes to the change in the nature of the convective clouds the resulting cloud distribution more closely resembles observations particularly during the suppressed phase of the mjo when cumulus congestus is the dominant cloud type

hierarchical tropical cloud systems in an analog shallow water model abstract recent observations have revealed an hierarchy of cloud clusters and superclusters within the madden julian oscillation of the equatorial troposphere the authors here report on the results of simulations with a model based on a simple nonlinear analog of the shallow water equations the model consists of a troposphere represented by single values of vertical velocity and temperature and in which the horizontal motions are assumed always to represent the first baroclinic mode the troposphere overlies a subcloud layer of fixed depth in which the evolution of moist entropy is predicted the model is driven by specified values of radiative cooling and sea surface temperature and a newtonian relaxation of the surface wind toward a specified value the system is horizontally homogeneous except for an anisotropy owing to the equatorial effect an eastward propagating low wavenumber disturbance containing an hierarchy of superclusters and cloud clusters is spontaneously generated from a random initi

slab melting as an explanation of quaternary volcanism and aseismicity in southwest japan two volcanoes on the quaternary volcanic front in southwest japan have erupted medium k andesite and dacite which are chemically similar to adakites i e high al 2 o 3 sr y low y and steep rare earth element ree patterns with no negative eu anomalies unlike other subduction related volcanoes in japan earthquake data and the extrapolated position of the philippine sea plate from its near trench position indicate that the leading edge of the plate is 75 100 km deep beneath these volcanoes melting of the plate at this depth would leave a garnet eclogite residual accounting for the y and heavy ree depletion the lack of seismic data and active volcanism in southwest japan can be attributed to the attenuated seismic response of the plate due to melting and to the atypical nature of magma generation

correlation of fluvial terraces within the hikurangi margin new zealand implications for climate and baselevel controls abstract a correlation of fluvial terraces is presented for eight non glacial catchments of the eastern north island new zealand within the actively uplifting hikurangi margin using a combination of loess and tephra coverbed stratigraphy and radiocarbon and osl dating of fluvial deposits and loess coverbeds we demonstrate correlation of four fill terraces t1 t4 the available age constraints suggest t1 15 30 ka t2 31 50 ka t3 50 70 ka and t4 115 ka but the association and temporal link with loess deposits suggest correlation with cold periods and thus the refinement of t2 late mis 3 31 40 ka t3 mis 4 55 70 ka t4 mi substage 5b 90 ka 5d 110 ka or mis 6 140 160 ka the ability to correlate terraces between catchments plus the lack of independent evidence for tectonic triggering events indicates terraces have probably formed in response to either climate terrestrial or baselevel sea level control climate control is indicated by the temporal link of post glacial incision with re establishment of forest cover and of lgm aggradation with limited grass and shrub cover and periglacial processes aggradation due to increased sediment supply under reduced vegetation is dramatically demonstrated by formation of the taupo pumice alluvium terrace in response to inundation by volcanic deposits unwelded ignimbrite following the 1 8 ka taupo eruption and the response to post settlement

stratigraphy chronology styles and dynamics of late quaternary eruptions from taupo volcano new zealand taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite dominated central portion of the taupo volcanic zone in the north island of new zealand taupo has an average magma output rate of 0 2 m 3 s 1 over the past 65 000 years and is one of the most frequently active and productive rhyolite volcanoes known the structure of the modern inverse volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 c years bp oruanui eruption and has been little modified since except for collapse following the 1850 14 c years bp eruption the products of 28 eruptions labelled psi omega a ldots z all of which post date the oruanui eruption are defined and described here twenty seven of these eruptions are represented by pyroclastic deposits of which three were accompanied by a mappable lava extrusion and one eruption z solely by evidence for a lava extrusion the deposits of seven eruptions b c e s v x and y largely correspond to previously defined tephra formations karapiti poronui opepe waimihia whakaipo mapara and taupo respectively the previously defined motutere and hinemaiaia tephras are reinterpreted to represent the products of 12 eruptions g to r while the remaining eight deposits and one eruption are newly recognized eruption psi occurred at ca 17 200 14 c or 20 500 calibrated years bp and eruption z about 1740 calibrated years bp eruption volumes vary by more than three orders of magnitude between 0 01 and more than 44 km 3 and repose periods by more than two orders of magnitude from ca 20 to 6000 years the eruption deposits reflect great variations in parameters such as volume the dispersal characteristics of the fall deposits the presence or absence of intraeruptive time breaks the formation of pyroclastic flows the degree of magma water interaction the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions all but seven fall deposits are plinian in dispersal two y1 and probably w are sub plinian one y5 has been termed ultraplinian while psi and a are too poorly preserved for their dispersal to be assessed the lengths of repose periods in the post oruanui sequence range are not randomly distributed but show self similar properties fractal dimensionality repose intervals r in years of not more than 350 years follow n 53 5r 0 21 and those of not less than 350 years follow n 2096r 0 83 where n is the number of eruptions the shorter repose periods may reflect triggering processes such as regional extension affecting magma bodies during their viable lifetimes while longer repose intervals i e not less than 350 years may reflect an episodicity of major rifting events or the production of magma bodies below the volcano bulk volumes v in km 3 of the eruption products also show self similar properties fractal dimensionality with n 6 17v 0 46 however there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible the post oruanui activity at taupo represents noise superimposed on the more uniform longer term activity in the central taupo volcanic zone where large greater than 100 km 3 eruptions such as the oruanui occur at more evenly spaced intervals of one per 40 60 000 years

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

unravelling a complex volcanic history from fine grained intricate holocene ash sequences at the tongariro volcanic centre new zealand abstract holocene volcanism at the tongariro volcanic centre tgvc at the south western end of the taupo volcanic zone tvz new zealand involved eruptions from at least three centres and was dominated by numerous small eruptions of vei 1 4 these produced very thin grey to black fine to coarse ash deposits of basaltic andesite to andesitic composition being unable to uniquely recognise and correlate these deposits presented a challenge in documenting the complete eruption record from the tgvc and to distinguish the periods of activity associated with each centre previous studies combined fine and poorly distinguishable tephras into mappable formations comprising many tens of units bracketed by rhyolitic marker tephras derived from the tvz caldera centres to the north very fine scaled mapping and analysis of glass of holocene tephras in the tgvc were used to document the comprehensive explosive eruption record over the last 12 000 cal years glass compositional analyses distinguished the tephras from the three main centres of the tgvc mt ruapehu mt ngauruhoe and red crater the latter two being part of the mt tongariro complex the three vents are sufficiently distinctive to be defined by ratios of major element oxides in the glasses with the oxide pair k 2 o feo being the most diagnostic ruapehu sourced tephras are generally higher in k 2 o 1 4 4 wt and lower in feo 3 7 8 3 wt than tongariro derived units red crater and ngauruhoe the diagnostic analyses provided the basis for correlating multiple tephra packages on the ring plains surrounding the tgvc and for establishing a revised eruption frequency for each of the volcanoes the new data show that ngauruhoe began erupting about 7000 cal years ago up to 4500 cal years earlier than previously thought

late quaternary uplift rate inferred from marine terraces muroto peninsula southwest japan forearc deformation in an oblique subduction zone abstract tectonic uplift rates across the muroto peninsula in the southwest japan forearc the overriding plate in the southwest japan oblique subduction zone were estimated by mapping the elevations of the inner edges of marine terrace surfaces the uplift rates inferred from marine terraces m1 and m2 which were correlated by tephrochronology with marine isotope stages mis 5e and 5c respectively include some vertical offset by local faults but generally decrease northwestward from 1 2 1 6 m ky 1 on cape muroto to 0 3 0 7 m ky 1 in the kochi plain the vertical deformation of the muroto peninsula since mis 5e and 5c was interpreted as a combination of regional uplift and folding related to the arc normal offshore muroto misaki fault a regional uplift rate of 0 46 m ky 1 was estimated from terraces on the muroto peninsula and the residual deformation of these terraces was attributed to fault related folding a mass balance calculation yielded a shortening rate of 0 71 0 77 m ky 1 for the muroto peninsula with the muroto misaki fault accounting for 0 60 0 71 m ky 1 but these rates may be overestimated by as much as 10 given variations of several meters in the elevation difference between the buried shoreline angles and terrace inner edges in the study area a thrust fault model with flat 5 10 dip and ramp 60 dip components is proposed to explain the shortening rate and uplift rate of the muroto misaki fault since mis 5e bedrock deformation also indicates that the northern extension of this fault corresponds to the older muroto flexure

new moscovian palaeomagnetic pole from the edjeleh fold saharan craton algeria summary a palaeomagnetic study was carried out in the moscovian y305 ma formation in the edjeleh anticline the only area where important dips can be observed in the upper palaeozoic series of the illizi basin algeria this study shows the existence of three magnetization components two of them are interpreted as cenozoic and permian remagnetizations their poles are 88 8un 164 0ue k 262 a95 3 3u and 43 4us 61 7ue k 93 a95 5 9u respectively the third component is determined by both welldefined chrms and remagnetization circles analysis its associated fold test is positive and significant because the folding started before or during the autunian this third component was acquired very early and is very probably the primary magnetization its corresponding palaeomagnetic pole 28 3us 58 9ue k 157 a95 4 2u is close to the poles from the saharan platform obtained from neighbouring periods the positive fold test of this study thus validates these previous upper palaeozoic poles this new result is in agreement with the geodynamical model matte 1986 henry et al 1992 which proposed the occurrence of a large clockwise rotation of africa during the carboniferous such a motion agrees with the permian pangaea a2 reconstruction

dynamical aspects of twin tropical cyclones associated with the madden julian oscillation abstract a nonlinear shallow water model on the sphere is used to study barotropic aspects of the formation of twin tropical disturbances by madden julian oscillation mjo convection in the model the effect of mjo convection upon the lower tropospheric tropical circulation was simulated by an eastward moving meridionally elongated mass sink straddling the equator the intensity and propagation speed of the mass sink were chosen to simulate observations that mjo convection intensifies while nearly stationary in the eastern equatorial indian ocean weakens while moving eastward over the maritime continent again intensifies once it reaches the west pacific ocean and finally becomes stationary and dies off near the date line this mass sink produced twin cyclones in the two regions where it was stationary namely where it was initially turned on and where it was turned off in addition the mass sink produced two zonally elongated cyclonic potential vorticity anomalies straddling the equator in the reg

palaeovegetation and palaeoclimate changes around lake biwa japan during the last ca 3 million years abstract the palaeovegetation and palaeoclimate history in and around the lake during the last 3 ma based on pollen analyses of the upper 900 m of a 1400 m core is presented and a provisional global correlation is made the upper 900 m of the core is subdivided into 37 pollen zones during glacial stages or stadials vegetation typical of the subpolar zone occurred in the mountainous area around lake biwa while in the lowland area around the lake plants characteristic of the cool temperate zone occurred during interglacial stages or interstadials the vegetation of the mountainous area was generally characterized by plants of the temperate zone and or cool temperate zone while in the lowland area the vegetation was composed mainly of broadleaved deciduous and evergreen trees of the temperate and warm temperate zones the climatic history of the last 500 ka shows remarkable parallels with the palaeotemperature record of the caribbean and pacific oceans sedimentary cycles of the mediterranean sea environmental change in central europe and the record of sea level change in japan and new guinea

the apparent polar wander path for south america during the permian triassic abstract many of the controversies that arise in global reconstructions for permian triassic time could be resolved by taking into account the large latitudinal and counter clockwise movement of gondwana during that interval of time the proper trace of the apparent polar wander curve should differentiate one position for the early permian another position for the late permian and yet another for the triassic by doing so and comparing the apparent polar wander paths apwp of south america and africa it is easy to see that both curves have the same shape therefore it is possible to arrive at a good fit between them which previous analyses were unable to achieve this new proposed permian triassic track of the apwp reveals a hook not hitherto recognized that should be accounted for in global reconstructions

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

tectonic and climatic record of the lake biwa japan region provided by the sediments deposited since pliocene times abstract the sediments of lake biwa japan contain a potential record of eastern asian paleoclimates that date from the early pliocene a continuous drilled core of lake sediments with a recovery of 70 was obtained in 1982 1983 to allow study of this record dating of core samples by a combination of tephrochronology magnetostratigraphy and fission track methods has revealed that parts of the sedimentary record apparently are missing even though obvious discontinuities cannot readily be detected from lithostratigraphic and seismic data tectonically induced migration of the basin center from its former more southerly location may be responsible for several hiatuses in the sedimentary record which are more common in its earlier part the record during the brunhes epoch appears to be relatively complete sediments indicate warm cold changes in land vegetation which may record glacial cycles deeper sediments contain evidence of warmer climate late neogene flora tectonic events can be inferred from changes in sediment type and in sedimentation rates

a marker tephra bed close to the lower middle pleistocene boundary distribution of the ontake byakubi tephra bed in central japan abstract tephrochronology is an exceptionally important tool in the precise regional correlation of early and middle pleistocene sedimentary strata in japan the present study reveals that the yukawa tephra 5 yut5 derived from the older ontake volcano the nezumigawa nzg and mitamitajima mtj tephras of the ina bazin and the byakubi e tephra byk e of the boso peninsula are the same tephra on the basis of their lithofacies bulk grain composition mafic mineral composition major element composition of hornblende and stratigraphic relationships with the dated tephras we propose to call the series of tephras correlated with byk e the ontake byakubi tephra bed on byk tephra following the naming convention in which the tephra name consists of the names of the source volcano and the type location the matuyama brunhes chronozone boundary occurs just above byk e in the type section of the kokumoto formation in the kazusa group which is a candidate global boundary stratotype section and point gssp for the lower boundary of the middle pleistocene subseries therefore on byk tephra becomes a critically important marker tephra bed for the early middle pleistocene boundary in central japan the present study indicates that the major element composition of hornblende can be a useful tool for identification and correlation of strongly weathered tephra layers such as nzg and mtj in which all the volcanic glass shards have been altered

late quaternary volcanism in new zealand towards an integrated record using distal airfall tephras in lakes and bogs studies on distal airfall tephra layers preserved in lake sediments and peats in northern new zealand have documented the stratigraphic chronologic and compositional relationships of 46 eruptives aged c 17000 700yr bp which originated from six north island volcanic centres taupo 9 tephras okataina 8 maroa 1 rhyolitic mayor island 2 peralkaline tongariro 11 egmont 15 andesitic sources were distinguished by mineralogy and composition field relations and 14c chronology all known rhyolitic tephra producing eruptions from taupo okataina and maroa volcanoes since c 17000yr bp are represented but only a small proportion of the known tephras erupted from tongariro egmont or mayor island volcanoes is recorded the distal tephras from these latter volcanic centres may thus reflect atypically powerful or oblique eruptions or dispersal by strong winds an improved record of volcanism for the tongariro egmont and mayor island centres might be obtainable from suitable lakes or bogs more proximal to them

analysis of titanomagnetite within weathered middle pleistocene kmt tephra and its application for fluvial terrace chronology kanto plain central japan abstract the widespread kaisho kamitakara tephra kmt derived from the source vent located in the hida mountains is a favorable marker tephra for the chronological study of the middle pleistocene in the kanto plain central japan as the kmt in aeolian sediments is strongly weathered the chemical composition of titanomagnetite resistant to weathering was determined for its identification the age of the kmt was estimated at 0 62 ma mis 16 0 by nakazato 2006 horizon and age of kaisho kamitakara tephra from the inubo group in the northeastern part of chiba prefecture central japan programme and abstracts japan association for quaternary research 36 106 107 in japanese revising a previous estimate of 0 58 0 69 ma by suzuki 2000 kaisho kamitakara tephra erupted from the hida mountains in early half of middle pleistocene and its significance for geomorphic chronology of central japan geographical review of japan 73 1 25 in japanese the stratigraphic position of the kmt in the azuyama and sayama terrace surfaces in southwest kanto and the kitsuregawa upper terrace surface in north kanto indicates that these terraces are correlative it is assumed that the dissected fluvial terrace surfaces were formed a few tens of thousands of years prior to the deposition of the kmt alluvial fan deposits constituting these terrace surfaces were formed during the period from mis 17 3 to 16 2 during a transition from interglacial to glacial geomorphic conditions during this period of the middle pleistocene were stable allowing the formation of broad fans

an air sea coupled skeleton model for the madden julian oscillation this work is an extension and improvement of the minimal madden julian oscillation mjo skeleton model developed by majda and stechmann which can capture some important features of the mjo slow eastward propagation quadrupole vortex structure and independence of frequency on wavelength but is unable to produce unstable growth and selection of eastward propagating planetary waves with the addition of planetary boundary layer frictional moisture convergence these deficiencies can be remedied the frictional boundary layer selects the planetary scale eastward propagation as the most unstable mode but the dynamics remains confined to atmospheric processes only here the authors study the role of air sea interaction by implementing an oceanic mixed layer ml model of wang and xie into the mjo skeleton model in this new air sea coupled skeleton model the features of the original skeleton model remain additionally the air sea interaction under mean westerly winds is shown to produce a strong instability that selectively destabilizes the eastward propagating planetary scale waves although the cloud shortwave radiation seasurfacetemperature crs feedbackdestabilizesbotheastwardand westward modes theair sea feedback associated with the evaporation and oceanic entrainment favors planetary scale eastward modes over the western hemisphere where easterly background winds prevail the evaporation and entrainment feedbacks yield damped modes indicating that longitudinal variation of the mean surface winds plays an important role in regulation of the mjo intensity in addition to the longitudinal variation of the mean sea surface temperature or mean moist static stability this theoretical analysis suggests that accurate simulation of the climatological mean state is critical for capturing the realistic air sea interaction and thus the mjo

towards characterising rhyolitic tephra layers from new zealand with rapid non destructive μ xrf core scanning abstract tephra layers are of importance for the construction of reliable age control in late quaternary paleoenvironmental and volcanic hazard studies especially in volcanically active settings such as the north island of new zealand however their identification involves time consuming and destructive processing steps making the application of non destructive xrf core scanners potentially advantageous for tephra identification here we investigate the potential of the itrax xrf core scanner to differentiate between rhyolitic tephra layers sourced from various northern new zealand rhyolitic volcanic centres deposited in maar lakes of the auckland volcanic field in their macroscopic form these tephra layers are usually visibly distinct when surrounded by a dark organic rich sediment matrix although their attribution to source volcanic centre and eruption typically requires examination of their mineral assemblages combined with chemical fingerprinting of the rhyolite glass shards we demonstrate that xrf core scanning of rhyolitic tephra layers from the taupo volcanic zone and tuhua volcanic centre can also allow identification and sometimes differentiation of the tephra using xrf derived elemental counts especially high si k ca and very low br and ti different rhyolite tephra layers vary in their relative abundances of major minor and trace elements as is evident from electron microprobe and la icp ms analyses of their glass shards mo tube based xrf cannot detect na nor mg and is of lower reliability for the lighter elements ca al which play an important role in traditional tephra fingerprinting nevertheless we are able to demonstrate that xrf core scanning data can distinguish between previously identified tephra layers using multivariate statistics furthermore the study emphasises the need for a standard protocol for xrf core scanning of tephra layers for this approach to be more widely applicable especially to aid or be a substitute for conventional geochemical approaches used for tephra fingerprinting

climatic change at the end of the last glaciation in japan inferred from pollen in three cores from the northwest pacific ocean abstract late glacial pollen time series from high sedimentation rate marine cores kh79 3 c6 ch84 04 and ch84 14 show the rise of successional vegetation typified by betula during the replacement of boreal forest types picea and pinus by thermophilous quercus forests variations in these three marine pollen records replicate the trends and timing of pollen records from japan and the structure and timing of vegetation and climatic changes on the pacific coast of japan since the last glacial maximum in marine cores kh79 3 c6 ch84 04 and ch84 14 oxygen isotope and or marine faunal data have been interpreted as evidence of a cooling event in the northwest pacific ocean which is coeval with the younger dryas chronozone pollen records from these northwest pacific cores like those from japan do not exhibit a regionally replicated statistically robust pollen assemblage which can be unambiguously interpreted as evidence of a late glacial climatic reversal between ca 11 000 and 10 000 yr b p the apparent disparity between the terrestrial pollen and marine evidence for a climatic oscillation during the younger dryas chron in northeast asia further complicates the variable record of this brief late glacial event

a tephrochronologic method based on apatite trace element chemistry geochemical correlation of ash fall beds with conventional tephrochronologic methods is not feasible when original glass composition is altered thus alternative correlation methods may be required initial studies of heavily altered paleozoic tephra k bentonites have suggested the potential for employing trace element concentrations in apatite as ash fall bed discriminators to further test the utility of apatite trace element tephrochronology we analyzed apatite phenocrysts from unaltered volcanic rocks with an electron microprobe nine samples from rocks erupted during the quaternary and one sample from a rock erupted during the paleogene the resulting apatite trace element data provide unique bed discriminators despite within crystal variability each of the volcanic rocks studied possesses unique trends in mg cl mn fe ce and y concentrations in apatite the results from this study establish an important tephrochronologic method that can be applied to nearly all portions of the phanerozoic stratigraphic record and greatly assist development of an advanced timescale in addition to establishing a fingerprint for a particular eruption apatite chemistry provides useful information about the source magma

palaeomagnetism of the early permian mount leyshon intrusive complex and tuckers igneous complex north queensland australia summary this study provides reliable precisely defined and well dated early permian 286 6 ma palaeomagnetic poles for australia from the mount leyshon intrusive complex mlic and the tuckers igneous complex tic both complexes are associated with prominent negative magnetic anomalies indicating the presence of rocks carrying stable remanence of reverse polarity with a koenigsberger ratio greater than unity the characteristic remanence carried by the intrusive phases and by locally remagnetized contact metamorphosed host rocks is always of reverse polarity consistent with acquisition during the permo carboniferous kiaman reverse superchron the corresponding palaeopoles confirm that australia occupied high latitudes in the early permian the pole positions are mlic lat 43 2 s long 137 3 e dp 6 0 dm 6 4 q 6 tic lat 47 5 s long 143 0 e dp 6 0 dm 6 6 q 6 permian palaeomagnetic overprinting is detectable at considerable distances from the mlic 2 3 km well beyond the zone of visible alteration the primary nature of the early permian palaeomagnetic signature is established by full baked contact aureole tests at both localities other new data from australia are consistent with the poles reported here comparison of the australian african and south american apparent polar wander paths apwp suggests that mean permian and triassic poles from west gondwana particularly from south america are biased by remagnetization in the jurassic cretaceous and that the late palaeozoic mesozoic apwp for gondwana is best defined by australian data the australian apwp exhibits substantial movement through the mesozoic provided only that the time averaged palaeofield was zonal the early triassic palaeomagnetic data from australia provide an important palaeogeographic constraint that the south geographic pole was within or very close to se australia around 240 ma the new early permian poles are apparently more consistent with pangaea b type reconstructions of gondwana and laurussia than with the pangaea a2 configuration this may be partly an artefact of reconstruction problems within gondwana as systematic differences between approximately coeval apparently reliable permo carboniferous poles from africa south america and australia are evident in standard gondwana reconstructions these discordances require a tighter fit of the southern continents suggesting that some attenuation of continental margins not accounted for in the reconstructions has occurred during breakup of gondwana or that the fit between east and west gondwana needs to be substantially modified if stretching of continental margins during breakup of supercontinents is a general phenomenon it may help to ameliorate but not solve the long standing controversy regarding pangaea reconstructions although alternative pangaea reconstructions such as pangaea b may reconcile poles from laurussia with australian poles in the late carboniferous early permian no plausible reconstruction can bring the early triassic poles into agreement this suggests that persistent departures from a pure dipole field may have been present in the early triassic lesser but still significant non dipole effects may also have been present during the late carboniferous and permian and may help resolve the pangaea a versus b controversy without requiring substantial attenuation of continental margins or intracontinental deformation we suggest that the most parsimonious interpretation of the palaeomagnetic and geological information is that laurussia and gondwana remained in a pangaea a2 type configuration through the permian and triassic discordance between the apwps for these two supercontinents is attributable mainly to persistent non dipole components of the geomagnetic field which were most important in the early triassic

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

paleomagnetic results from permian rocks of the northern saharan craton and motions of the moroccan meseta and pangea abstract the characteristic magnetization of redbed samples from the upper part of the serie d abadla probably early permian 31 n 2 7 w has a mean direction derived from 13 sites of d 129 i 11 k 59 95 6 and a corresponding south paleopole at 29 s 60 e a 95 5 all directions have reversed polarity the paleolatitude of the northern fringe of the saharan craton was 6 3 s which is in excellent agreement with that for the moroccan meseta therefore in all probability there has been no paleolatitudinal displacement greater than about 500 km of the moroccan meseta relative to africa since permian time comparison of results from sedimentary rocks shows no evidence for relative rotation of the moroccan meseta since permian time small apparent rotations are indicated by evidence from massive trachyandesite lavas from morocco but we argue that these could have arisen from the incomplete averaging of secular variation and uncertainties in estimates of paleohorizontal rather than from true tectonic rotations the combined latest carboniferous early permian paleopole for the saharan craton and the meseta differs form the path of apparent polar wandering for north america when the continents are assembled in wegener s pangea pangea a in which northwest africa is opposite north america it is in reasonable agreement when the continents are assembled in the pangea b configuration northwest africa opposite europe

vegetation and climate history since the last interglacial in kurota lowland western japan abstract the pollen record of a long core from the kurota lowland of central honshu in western japan provides a continuous vegetation and climate history from beyond 120 000 to 25 000 yr bp the chronology is based on widely dispersed tephra and six conventional 14c dates prior to 120 000 yr bp forests were composed predominantly of abies tsuga picea and pinus haploxylon which indicate a cold climate probably corresponding to oxygen isotope stage 6 during the last interglacial around 120 000 yr bp cryptomeria japonica was dominant in forests with a small amount of evergreen oaks the early stage of the last glacial period is characterised by dominance of c japonica with two increases at 105 000 and 90 000 80 000 yr bp of pinaceous conifers and cool temperate deciduous broad leaved trees between 70 000 and 60 000 yr bp pinaceous conifer vegetation developed indicating a dry and cold climate and this was succeeded by a cool temperate deciduous broad leaved forest composed mainly of fagus crenata and deciduous oaks indicating a wet and cool cold climate from 55 000 to 40 000 yr bp temperate coniferous forests composed of c japonica and cupressaceae associated mainly with tsuga and deciduous oaks occurred after 40 000 yr bp mixed forests of c japonica tsuga and cool temperate deciduous broad leaved trees such as fagus crenata and deciduous oaks prevailed in a wet and cool climate at 28 000 yr bp an abrupt decrease of c japonica and development of forests composed of tsuga pinus haploxylon and betula with some deciduous broad leaved trees imply climatic deterioration to the lgm the vegetation history since the lgm has been revealed previously at iwaya site in kurota lowland time series of these pollen records can be correlated with the marine oxygen isotope stages 1 through 6

correlation of middle pleistocene crystal rich tephra layers from daisen volcano southwest japan based on the chemical composition and refractive index of mafic minerals abstract analyses of chemical compositions and refractive indices of mafic minerals have been effective correlation tools especially for crystal rich tephra layers containing isolated volcanic glass shards the analyses are applied to the correlation of the middle pleistocene tephra layers in the kinki and chubu districts central japan with those erupted from daisen volcano in the chugoku mountains west of the districts on the basis of chemical compositions of hornblende phenocrysts and refractive indices of hornblende orthopyroxene and cummingtonite phenocrysts four groups of tephra layers in the kinki and chubu districts are successfully correlated to bvs2 cpm gpm and hpm1 or dop tephra layers of the lowermost member of the daisen tephra formation the correlation reveals that two tephra layers bvs2 and cpm with estimated eruption ages of 410 ka and 370 400 ka respectively are present in the kinki district the hpm1 tephra about 210 ka is also widespread and recognized at the eastern foot of yatsugatake volcanoes about 400 km east of the source these tephra layers can contribute to establishing the regional correlation and chronology of the middle pleistocene sequences in central japan especially for the time from mis 7 to mis 11

construction of volcanic records from marine sediment cores a review and case study montserrat west indies detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing frequency and style of future eruptions and for the identification of potentially at risk areas subaerial volcanic stratigraphies are often incomplete due to a lack of exposure or burial and erosion from subsequent eruptions however many volcanic eruptions produce widely dispersed explosive products that are frequently deposited as tephra layers in the sea cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies at least for explosive eruptions nevertheless problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits consequently cryptotephras in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye may be the only record of many explosive eruptions additionally thin reworked deposits of volcanic clasts transported by floods and landslides or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers leading to the construction of inaccurate records of volcanism this work uses samples from the volcanic island of montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores with a particular relevance to cores sampled in relatively proximal settings i e tens of kilometres from the volcanic source where volcaniclastic material may form a pervasive component of the sedimentary sequence visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic deposit detection techniques including point counting of grain types component analysis glass or mineral chemistry colour spectrophotometry grain size measurements xrf core scanning magnetic susceptibility and x radiography this study demonstrates that a set of time efficient non destructive and high spatial resolution analyses e g xrf core scanning and magnetic susceptibility can be used effectively to detect potential cryptotephra horizons in marine sediment cores once these horizons have been sampled microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits by using specific criteria related to clast morphology and sorting standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits and to distinguish fallout deposits from other volcaniclastic deposits

paleomagnetisme dans les hellenides internes analyse des aimantations superposees par la methode des cercles de reaimantation there are very few reliable and well dated paleomagnetic data on the internal hellenides which were strongly affected by successive tectonic events we have analysed 268 samples from two separate sedimentary formations of this domain these correspond to two important moments in the geotectonic evolution of the hellenides the toarcian and the jurassic cretaceous boundary we show that all the analysed samples probably contain both detrital magnetite and secondary haematite and generally carry at least two components of superimposed magnetization the diversity and convergence of the remagnetization circles allow us to show that these two components are antiparallel and to determine their directions because of tectonic disruption the calculated declinations are only of local interest on the other hand inclinations remain significant for calculating paleolatitudes these constitute important constraints on reconstructions of the jurassic paleogeography of the hellenic domain in light of our results

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

late quaternary atmospheric and oceanographic variations in the western pacific inferred from pollen and radiolarian analyses abstract pollen and radiolarian analyses of sediment from four piston cores located along a south north transect 28 44 n off the east coast of japan yield detailed records of variations in terrestrial and marine climate of this region for the last 140 ka the last interglacial climate of the southern half of japan was characterized by increased temperature and precipitation at least across central japan compared with today off southern japan surface were cooler during summer than at present off central japan both summer and winter sea surface temperatures were cooler than today early glacial 115 71 ka bp climate across central and southern japan alternated between wet and dry warm temperate with surface waters offshore warmer in summer and winter than during the penultimate interglacial temperatures and precipitation in japan reached low levels early during the full glacial phase and remained relatively low throughout much of the full glacial 71 14 ka bp cold sea surface temperatures at all our sites coincided with these cold conditions on land temperatures across much of japan began to increase steadily during the deglacial with surface waters offshore remaining at or near their glacial lows holocene vegetation patterns which continued to reflect an increase in temperature reached a maximum during early to mid holocene surface waters offshore however remained relatively cool during the early holocene with temperature maxima at most western pacific sites occurring in mid to late holocene we propose specific changes in the seasonal positions of atmospheric pressure cells to explain these climate variations that have occurred across the northeast asian northwest pacific region through the most recent interglacial glacial cycle results of this exercise show that there are no major discrepancies between climate reconstructions for mainland japan inferred from pollen and those for the western pacific derived from radiolarians

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal bearing sediments offshore shimokita peninsula japan iodp site c0020 sediments recovered at integrated ocean drilling program iodp site c0020 in a forearc basin offshore shimokita peninsula japan include numerous coal beds 0 3 7 m thick that are associated with a transition from a terrestrial to marine depositional environment within the primary coal bearing unit 2 km depth below seafloor there are sharp increases in magnetic susceptibility in close proximity to the coal beds superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence we investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record using isothermal remanent magnetization irm thermal demagnetization anhysteretic remanent magnetization arm iron speciation and iron isotopes magnetic mineral assemblages in all samples are dominated by very low coercivity minerals with unblocking temperatures between 350 580 c that are interpreted to be magnetite samples with lower unblocking temperatures 300 400 c higher arm higher frequency dependence and isotopically heavy 56fe across a range of lithologies in the coal bearing unit between 1925 1995 mbsf indicate the presence of fine grained authigenic magnetite we suggest that iron reducing bacteria facilitated the production of fine grained magnetite within the coal bearing unit during burial and interaction with pore waters the coal peat acted as a source of electron donors during burial mediated by humic acids to supply iron reducing bacteria in the surrounding siliciclastic sediments these results indicate that coal bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time within the subsequent deep biosphere

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects

reinterpretation of late quaternary sediment chronology of lake biwa japan from correlation with marine glacial interglacial cycles a review of published stratigraphic records of pollen sediment grain size diatoms and organic matter composition from lake biwa japan identifies four pre holocene episodes of milder climate increased surface runoff and enhanced aquatic productivity indicating intervals of warmer and wetter conditions which are interpreted as being interglacial correlation of these episodes to times of marine interglacial periods revises the age scale of the lake biwa sediment sequence which has been based on fission track dating the revised chronostratigraphic scale proposes an age of ca 430 000 yr b p for the base of the 250 m thick t bed instead of the former age of ca 700 000 yr b p

a new multiscale model for the madden julian oscillation abstract a multiscale model of the mjo is developed here that accounts in a simplified fashion for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic scale circulations in a moving convective envelope as well as direct mean heating on planetary scales this model involves idealized thermally driven congestus synoptic scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope the model self consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the mjo including the vertical structure in both the westerly onset region and the strong westerly wind burst region as well as the horizontal quadrupole planetary vortex structure the westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transpor

fatty acid geochemistry of a 200 m sediment core from lake biwa japan early diagenesis and paleoenvironmental information abstract fatty acids fas and hydroxy acids dicarboxylic acids and n alkanes were studied in a 200 m sediment core taken from lake biwa japan fas showed bimodal distribution with peaks at c 16 and c 22 c 28 their distribution patterns clearly changed with depth from lower molecular weight c 12 c 19 predominance to higher molecular weight c 20 c 32 predominance in the upper 20 m interval analyses of related compounds and hydroxy acids and dicarboxylic acids suggest that and oxidative degradation of c 12 c 19 fas has occurred in the sediments the ratio of bound c 12 c 19 to unbound fas increases with depth in the upper 0 1 m sediments suggesting that unbound fas are more labile however the ratio varies significantly in deeper sections and may be associated with water temperature in the sediments deeper than 20 m in depth c 12 c 19 fas gradually decrease on the other hand higher molecular weight fas hfas c 20 c 32 which were probably derived from terrestrial plants increase in concentration from 20 m to 100 m suddenly decrease at 100 m and show progressively lower concentration in deeper sediments these fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin hydroxy c 20 c 30 acids and c 20 c 30 dicarboxylic acids show a distribution pattern similar to hfas branched chain fas hydroxy acids and c 9 c 19 dicarboxylic acids show a major peak around 3 15 m in depth this peak is probably caused by increased bacterial activity in the water column and surface sediments in the past which may be associated with an increase in primary production of the lake

postglacial environmental change of the pacific ocean off the coasts of central japan abstract downcore changes in microfossil assemblages and oxygen isotope ratios in three piston cores recovered from the northwestern pacific off central japan show that the subtropical kuroshio front was located to the south of c 4 core site lat 33 n during the last glacial the front then advanced northward passing over the c 4 site and the c 6 site 34 6 n at about 13 ka and 10 ka respectively and reached the c 1 core site 36 n at about 7 ka after 5 5 ka it retreated to the area between the c 1 and c 6 sites a brief but significant cold event the readvance of the cold oyashio current is recognized between 11 and 10 ka in the two northern cores but the current did not reach the southern c 4 site a contemporaneous cold event is known in the north atlantic and the cooling was probably a global phenomenon likely to be associated with lowering of sea level contamination of isotopically light water is apparent between 14 and 11 ka in the marked change in isotopic composition of benthic foraminifers oxygen isotope ratios of planktonic foraminifers show that prior to the advance of the kuroshio front the surface water at these core sites was isotopically lighter than the kuroshio water at that time

a new late triassic liasic palaeomagnetic pole from superimposed and juxtaposed magnetizations in the saharan craton summary palaeomagnetic measurements in the late triassic liasic zarzaytine formations of the la recul6e area showed the existence of superimposed and juxtaposed magnetizations the separation of the juxtaposed magnetizations yielded late triassic liasic magnetization directions of normal and reversed polarities the new corresponding palaeomagnetic pole agrees well with a pangea a configuration it confirms from autunian to lias a latitudinal displacement of stable africa towards the north with important anti clockwise rotation contrary to laurussia which did not undergo significant rotation this transition of pangea from a2 to a ended before the late triassic it corresponds to dextral movements in the hercynoappalachian collision area and perhaps to part of the northwards drift of microcontinents of gondwanian origin located north of the arabian promontory

paleomagnetism of the newcastle range northern queensland eastern gondwana in the late paleozoic 1 the newcastle range is an extensive 2500 km2 and well exposed caldera system erupted on the trailing edge of eastern gondwana between 325 and 295 ma paleomagnetic samples were collected from ignimbrites and associated microgranitoid intrusions from the central northern and southern calderas from which three components of magnetization are recognized component 1 is considered to be a viscous magnetization acquired during the brunhes chron a presumed permian component c2 is found in seven paleomagnetic sites with a mean pole at 30 9 s 139 7 e k 13 9 a95 16 8 asd 21 7 agreeing with previously reported permian data from australia carboniferous units have a well defined characteristic component c3 distinguished by dual polarity predominantly reversed and moderate to steep inclination directions paleomagnetic polarities in the newcastle range volcanics are formation dependent and new constraints on the timing of carboniferous volcanism 325 317 ma are consistent with recent reanalysis of the base of the permo carboniferous reversed superchron pcrs a mean paleomagnetic pole calculated from 15 vgps lies at 63 4 s 125 e k 26 22 a95 7 6 asd 15 8 suggesting that australia remained at midlatitudes into the middle carboniferous this paleomagnetic pole is consistent with similarly aged poles from western gondwana the conformity of which indicates contributions from nondipole components of the earth s paleofield were probably not significant in the time immediately preceding the pcrs

thermal demagnetization of some carboniferous lavas for palaeomagnetic purposes summary thermal demagnetization of the natural magnetization of carboniferous basalts from scotland has successfully revealed the original direction of magnetization although the specimens had badly scattered directions at room temperature

andesitic plinian eruptions at mt ruapehu quantifying the uppermost limits of eruptive parameters new tephro stratigraphic studies of the tongariro volcanic centre tgvc on the north island new zealand allowed reconstruction of some of the largest andesitic explosive eruptions of mt ruapehu large eruptions were common in the late pleistocene before a transition to strombolian vulcanian and phreatomagmatic eruptive styles that have predominated over the past 10 000 years considering this is the most active volcano in north island of new zealand and the uppermost hazard limits are unknown we identified and mapped the pyroclastic deposits corresponding to the five largest eruptions since 27 ka the selected eruptive units are also characterised by distinctive lithofacies associations correlated to different behaviours of the eruptive column in addition we clarify the source of the 10 9 7 ka pahoka tephra identified by previous authors as the product of one of the largest eruptions of the tgvc the most common explosive eruptions taking place between 13 6 and 10 ka cal years bp involved strongly oscillating partially collapsing eruptive columns up to 37 km high at mass discharge rates up to 6 108 kg s and magnitudes of 4 9 ejecting minimum estimated volumes of 0 6 km3 our results indicate that this volcano as well as the neighbouring andesitic mt tongariro can generate plinian eruptions similar in magnitude to the chaiten 2008 and askja 1875 events such eruptions would mainly produce pyroclastic fallout covering a minimum area of 1 700 km2 ese of the volcano where important touristic agricultural and military activities are based as for the 1995 1996 eruption our field data indicate that complex wind patterns were critical in controlling the dispersion of the eruptive clouds developing sheared commonly bilobate plumes

fluvial archives a valuable record of vertical crustal deformation abstract the study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms but also for identifying the nature of crustal deformation and its history in recent decades geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens here we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions the effects of horizontal deformation are not addressed channel long profiles have received considerable attention in the literature and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady state characteristics then we review the literature dealing with the transient response of rivers to tectonic perturbation through the production of knickpoints propagating through the drainage network inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories finally we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes as well as the erosional imprint of tectonic forcing sedimentary deposits such as fluvial terrace staircases are also considered as a classical component of tectonic geomorphology we show that these studies have recently benefited from rapid advances in dating techniques allowing more reliable reconstruction of incision histories and estimation of incision rates the combination of progress in the understanding of transient river profiles and larger more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation i e extrapolation of local data to entire profiles finally planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the dis equilibrium state of drainage systems across regional drainage divides

new african lower carboniferous paleomagnetic pole from intrusive rocks of the tin serririne basin southern border of the hoggar algeria a paleomagnetic study has been conducted on intrusive doleritic rocks cropping out within devonian horizontal tabular formations of the saharan craton tin serririne basin south of hoggar shield the 40k 40ar dating of the dolerites gave an age of 347 6 8 1 ma i e tournaisian the paleomagnetic data present three different directions the first has a paleomagnetic pole close to the previous african poles of permian age this direction is therefore interpreted as a permian remagnetization the second direction which is defined by both linear regression and remagnetization circles analysis is considered as the primary magnetization it yields a new african tournaisian paleomagnetic pole 18 8 s phi 31 2 e k 29 a95 7 5 very close to the ben zireg tounaisian pole aifa t feinberg h pozzi j p 1990 devonian carboniferous paleopoles for africa consequences for hercynian geodynamics tectonophysics 179 288 304 the third direction has intermediate orientation between those of the first or second directions and that of the upper cenozoic field it is interpreted as related to a composite magnetization this new tin serririne pole improves the apwp of gondwana for this key period of the evolution of the pangea this apwp confirms the previous paleogeographic reconstruction which shows that the pre hercynian ocean between gondwana and laurussia is still not close during the beginning of the carboniferous

characterization and correlation of cryptotephras using major element analyses of melt inclusions preserved in quartz in last interglacial marine sediments southeastern shikoku japan although sediments underlying marine terraces in se shikoku southwest japan contain no visible tephra layers late pleistocene cryptotephras were detected in a paleosol within the sediments the cryptotephras contained little or no glass but they were characterized through major element analyses of glass preserved as melt inclusions in quartz grains extracted from the paleosol the analyses enabled correlation of the cryptotephras with known eruptives from volcanoes on kyushu namely the kikai tozurahara tephra mis 5 2 5 3 the aira tn tephra 28 6 cal ka and the kikai akahoya tephra 7 5 cal ka these correlations enabled dating of the marine terrace surface known as the murotomisaki 1 surface in se shikoku as being older than mis 5 2 5 3 probably mis 5 5 in age in the absence of glass or mafic minerals because of weathering the analysis of melt inclusions in resistant quartz grains demonstrably provides a powerful method for characterizing cryptotephras to facilitate their correlation and thus their application as a linking and dating tool

detection and correlation of widespread cryptotephras in middle pleistocene loess in ne japan using cummingtonite geochemistry we used cummingtonite chemistry to detect strongly weathered widespread cryptotephras within middle pleistocene loess and fluvial terrace deposits and to correlate them with previously reported tephras in central and ne japan we correlated a cummingtonite bearing cryptotephra widely distributed in ne japan below the ichihasama pumice 108 146 ka and above the iwadeyama pumice iwp 160 240 ka with the iizuna kamitaru c tephra iz ktc which erupted from iizuna volcano central japan iz ktc is thus a widespread middle pleistocene tephra covering both central and ne japan moreover we detected the adachi medeshima tephra ac md which had been previously inferred to be a late pleistocene tephra 80 100 ka below the iz ktc and iwp tephras 125 150 ka and above the hagimori white ash tephra 210 250 ka therefore ac md must be a middle pleistocene tephra with an eruptive age older than 125 150 ka and younger than 210 250 ka we also detected a cummingtonite bearing tephra older than 210 250 ka and younger than 250 300 ka in the isawa area of ne japan and correlated it with a previously reported tephra in central japan thus like iz ktc this tephra is a widespread middle pleistocene tephra

stratigraphic and chemical correlation of volcanic ash beds in the terminal proterozoic nama group namibia at least twenty silicified volcanic ash beds have been identified in the kuibis and schwarzrand subgroups of the terminal proterozoic nama group of namibia nineteen of the nama ash beds are in the schwarzrand subgroup in the witputs subbasin two of these are in the siliciclastic dominated lower part of the subgroup which consists of the nudaus formation and nasep member of the urusis formation and comprises two depositional sequences identification and correlation of these ash beds are very well known based on stratigraphic position sixteen ash beds are contained within the carbonate dominated strata of the huns feldschuhhorn and spitskop members of the urusis formation these strata comprise four large scale sequences and eighteen medium scale sequences ash beds have been found in three of the large scale sequences and seven of the medium scale sequences correlations are proposed for these ash beds that extend over large changes in facies and stratal thickness and across transitions between the seaward margin depocentre and landward margin of the huns spitskop carbonate shelf a study of whole rock and in situ phenocryst compositions was conducted to evaluate the feasibility of independently testing sequence stratigraphic correlations by geochemically identifying individual ash beds whole rock abundances of al fe mg k and ti vary inversely with si reflecting variations in phenocryst concentration due to air fall and hydrodynamic sorting these sorting processes did not substantially fractionate whole rock rare earth element abundances ree which vary more widely with si ree abundances are higher in samples of the nudaus ash bed than in samples of the nasep ash bed independent of position in bed phenocryst abundance or grainsize providing a geochemical means for discriminating between the two beds variations in the position of chondrite normalized whole rock ree plots similarly support suspected correlations of ash beds between widely separated sections of the spitskop member abundances of fe mg and mn in apatite plot in distinct clusters for spitskop ash beds that are known to be different and in clusters that overlap for ash beds suspected of correlating between sections abundances of ree in monazites differ for the nudaus nasep and spitskop ash beds in which these phenocrysts were identified multivariate statistical analysis provided a quantitative analysis of the discriminating power of different elements and found that whole rock abundances of ge nb cs ba and la discriminate among the whole rock compositions of the nudaus and nasep ash beds and the spitskop ash beds that are thought to correlate between sections each of the above geochemical signatures by itself is not definitive because the differences between beds are comparable to the variability within beds and because some signatures are shared by beds known to be different taken together however weight of evidence arguments based on multiple components and phases can successfully discriminate among nama ash beds results from this study support sequence stratigraphic correlations of spitskop ash beds that document stratal truncations and gaps in the record related to onlap and erosion

北関東 東北地方南部のテフロクロノロジー 現状と展望

diagenetic changes of lignin compounds in a more than 0 6 million year old lacustrine sediment lake biwa japan a vertical profile of lignin in the upper 700 m layer of a 1400 m sediment core of lake biwa an oligotrophic freshwater lake in japan was determined using a cuo oxidative degradation method the results indicated that lignin is found throughout the core demonstrating lignin to be very stable for over 0 6 million years moreover the upper 250 m approximately 0 6 million years old segment of the sediment core was investigated to determine the apparent long term degradation rate of lignin a downward lignin concentration decrease is observed over the upper 250 m of the core which corresponds to a calculated half life of at least approximately 40 104 years assuming that lignin decrease is due to its in situ degradation diagenesis

devonian carboniferous paleopoles for africa consequences for hercynian geodynamics abstract paleomagnetic analysis of marine formations in the northwestern sahara algeria yields the following results three sites in the lower devonian orthoceras bearing limestones of beni abbes 29 67 n 2 15 w indicate a mean direction of remanence dm 149 6 im 1 6 95 6 8 this typical permian direction implies a complete remagnetization of the sites the famennian griotte limestones of the ben zireg anticline 31 92 n 1 82 w show high remanent magnetization intensities in this structure which has undergone polyphase tectonism multicomponent analysis evidences a high unblocking temperature htb component carried by haematite leading to a positive fold test after partial unfolding at the 95 confidence level with a mean direction d 156 4 i 47 6 95 0 9 and attributed to the early carboniferous 355 ma with a paleopole at 25 3 s 21 1 e dp 0 8 dm 1 2 an intermediate unblocking temperature itb component of magnetization carried probably by magnetite also present satisfies a positive fold test after tilt correction with a mean direction d 154 9 i 54 3 95 3 7 this pre folding direction of magnetization is attributed to the famennian it gives a paleopole at 19 2 s 19 8 e dp 3 7 dm 5 3 comparison with previous results shows a significant s n crustal shortening of about 2500 km during carboniferous times accompanied by a clockwise rotation of the saharan region of about 25 these new results give information about the tectonic phenomena involved in the collision between gondwanaland and laurasia they argue for a pangea a2 dominating model and define mean values for shortening rate and plate velocity comparable to the present ones 3 cm yr

discriminant function analysis of glass chemistry of new zealand and north american tephra deposits major trace and rare earth element analyses of volcanic glass are used separately or in combination for correlating quaternary tephras often by graphical or simple comparative methods we have taken a statistical approach using discriminant function analysis dfa to assess the relative discriminating power of the different elements in volcanic glasses from several tectonovolcanic provinces we found that major oxides are powerful discriminating variables for widespread tephras from the taupo volcanic zone in new zealand and here they can be more discriminating than trace elements a wide selection of tephras from the western united states can also be distinguished on major oxides alone particularly those from cascade range volcanoes for tephras from large intracontinental calderas such as long valley or yellowstone ree and trace elements are more effective at discriminating than major oxides however tephras erupted from the long valley area can be distinguished on major oxide composition by dfa despite their similar chemistry the selection and relative significance of different elements for discriminating tephras depends on the total data set being compared as well as the source volcano and the individual eruptive events caution must be exercised in the nonstatistical selection of compositional data for characterizing tephras dfa is a more powerful and objective tool for the comparison of tephra chemistry

paleomagnetism of the lower permian redbeds of the abadla basin algeria abstract one of the reference permian paleomagnetic poles for the african apparent polar wander path apwp was determined by morel et al 1981 earth planet sci lett 55 65 74 in the upper unit of the 2000 m thick abadla redbeds formation 31 2 n 2 7 w unfortunately this upper unit remains undated although its age was presumed to be autunian whereas microflora fossils characteristic of the autunian were discovered in the lower unit of the same formation the paleomagnetic data n 11 d 130 1 i 13 0 k 138 95 3 6 and pole 29 1 s 57 8 e a95 2 0 obtained from the better dated autunian levels must take the place of the previous abadla pole for the autunian part of the african apwp this new pole is very close to the morel et al s pole determined from the unfossiliferous upper unit of the abadla formation giving an autunian age for this upper unit consequently the subsidence of the abadla basin and the deposition of the whole succession occurred during a period not longer than 20 25 myr

sea level variations during marine isotope stage 7 and coastal tectonics in the eastern seto inland sea area western japan relative sea level rsl observations for marine isotope stage mis 7 were obtained from three sites higashinada kakogawa and mitsu of the eastern seto inland sea area western japan we evaluated the magnitude of sea level highstands during mis 7 and the local tectonics based on rsl records of this coastal area for this purpose we analyzed diatom assemblages and sedimentary sulfur and carried out tephra analysis we also constructed a linear age model to determine the depositional ages of the sediments using altitudes of astronomical age control points obtained mainly from the present diatom data at the mitsu site rsls were estimated to be 22 87 0 50 m at the mis 7 5 highstand peak 234 6 ka below 20 17 m at 211 2 ka and below 20 00 m at 209 9 ka with a tectonic subsidence rate of 0 11 0 02 m ka since the last interglacial maximum at the mitsu site the elevation of the tectonically corrected mis 7 5 highstand peak may have been 2 94 5 19 m the tectonically corrected sea level elevations during mis 7 3 are inferred to have been below 3 06 4 72 m at 211 2 ka and below 3 09 4 70 m at 209 9 ka comparisons between the diatom inferred rsls and the isotopically derived sea level curve indicate that the mis 7 3 highstand peak was above 18 m and may have been lower than the mis 7 5 and 7 1 highstands based on the isotopically derived sea level curve and the rsl data from higashinada and kakogawa a tectonic subsidence rate of 0 26 0 32 m ka was derived for higashinada and a tectonic uplift rate of 0 17 m ka and 0 43 m ka and 0 26 m ka and 0 42 m ka these values indicate the intensity of crustal movements associated with active faulting of the rokko awaji fault system along this tectonically active coast

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

palaeomagnetism of the stephano autunian lower tiguentourine formations from stable saharan craton algeria summary palaeomagnetic studies have been carried out in a stephano autunian formation of the saharan craton despite the presence of a strong recent magnetic overprint some samples give a well defined characteristic remanent magnetization direction moreover a new approach using the remagnetization circles has been used to confirm the significance of this direction the obtained stephano autunian pole 35 3 s 60 3 e allows a substantial improvement of the apparent polar wander path apwp for stable africa this apwp clearly shows that the clockwise rotation of africa which occured during the hercynian orogeny was stopped during the stephano autunian period

identification and correlation of visible tephras in the lake suigetsu sg06 sedimentary archive japan chronostratigraphic markers for synchronising of east asian west pacific palaeoclimatic records across the last 150 ka abstract the lake suigetsu sg06 sedimentary archive from honshu island central japan provides a high resolution palaeoenvironmental record including a detailed record of explosive volcanism from japan and south korea thirty visible tephra are recorded within the 73 m long sg06 core which spans the last 150 ka here we describe and characterise these tephras based on major element glass composition which is useful for the identification and correlation of these tephras and the age models of the records in which they are found utilising the large number of radiocarbon measurements n 600 from terrestrial plant macrofossils in the lake suigetsu sg06 record we are able to provide precise and accurate ages for the tephras from eruptions within the last 50 ka glass compositional data of some of the largest eruptions from japan k ah at aso 4 aso a aso d and ata sampled at proximal outcrops are also presented these data show that the major element glass chemistry is distinctive for many of the visible sg06 tephra units and allows some of the layers to be correlated to known eruptions from volcanoes in japan and south korea namely k ah sg06 0967 u oki sg06 1288 at sg06 2650 aso 4 sg06 4963 sg06 4979 k tz sg06 5181 aso abcd sg06 5287 and ata sg06 5181 the following ages were obtained for the sg06 tephra units 3 966 4 064 cal ka bp 95 4 probability range for the sg06 0588 tephra 10 242 10 329 cal ka bp 95 4 probability range for sg06 1293 19 487 112 sg06 2012 ka bp 2 for sg06 1965 28 425 194 sg06 2012 ka bp 2 for sg06 2504 28 848 196 sg06 2012 ka bp 2 for sg06 2534 29 765 190 sg06 2012 ka bp 2 for sg06 2601 29 775 191 sg06 2012 ka bp 2 for sg06 2602 43 713 156 sg06 2012 ka bp 2 for sg06 3485 46 364 202 sg06 2012 ka bp 2 for sg06 3668 49 974 337 sg06 2012 ka bp 2 for sg06 3912 50 929 378 sg06 2012 ka bp 2 for sg06 3974 and improved ages for two of the most important tephra markers across japan the k ah 7 165 7 303 cal ka bp at 95 4 probability range sg06 0967 and at tephra 30 009 189 sg06 2012 ka bp at 2 sg06 2650

toward a comprehensive upper quaternary tephra and ignimbrite stratigraphy in new zealand using electron microprobe analysis of glass shards abstract new zealand quaternary marine and terrestrial sequences contain numerous tephras or volcanic ash horizons that are the distal correlatives of voluminous welded ignimbrite sheets erupted from central north island electron microprobe analyses of glass shards from the distal tephras demonstrate their homogeneity and are shown to identify each tephra examined by matching tephras from stratigraphically controlled sequences the first comprehensive tephra stratigraphy spanning from 50 000 to 700 000 yr ago and covering the new zealand region is advanced analyses on glass shards from the unwelded base of ignimbrite sheets are comparable to the distal tephra analyses and allow correlation between ignimbrites and to the distal tephras the better exposed tephra record constrains the number of separate eruptive events and the stratigraphy of the ignimbrites both of which were previously confused by lack of outcrop samples from pumiceous marine sediments were found to contain two or more chemically distinct populations of glass the pumice is in cross bedded sands or sand lenses within conglomerate attesting to a shallow high energy environment where reworking could occur however each glass population could be matched to older known tephras

multiscale atmosphere ocean interactions and the low frequency variability in the equatorial region abstractin the present study a simplified multiscale atmosphere ocean coupled model for the tropical interactions among synoptic intraseasonal and interannual scales is developed two nonlinear equatorial plane shallow water equations are considered one for the ocean and the other for the atmosphere the nonlinear terms are the intrinsic advective nonlinearity and the air sea coupling fluxes to mimic the main differences between the fast atmosphere and the slow ocean suitable anisotropic multispace multitime scalings are applied yielding a balanced synoptic intraseasonal interannual el nino sinen regime in this distinguished balanced regime the synoptic scale is the fastest atmospheric time scale the intraseasonal scale is the intermediate air sea coupling time scale common to both fluid flows and el nino refers to the slowest interannual ocean time scale the asymptotic sinen equations reveal that the slow wave amplitude evolution depends on both types of nonlinearities analytic solution

late quaternary cryptotephra detection and correlation in loess in northeastern japan using cummingtonite geochemistry abstract we detected late pleistocene cummingtonite bearing cryptotephras in loess deposits in ne japan and correlated them with known tephras elsewhere by using major element compositions of the cummingtonite this is the first time cryptotephras have been identified by analysis of a crystal phase rather than glass shards in central ne japan four cummingtonite bearing tephras the ichihasama pumice the dokusawa tephra the naruko nisaka tephra and the adachi medeshima tephra are present in late pleistocene loess deposits because the cummingtonite chemistry of each tephra is different and characteristic it is potentially a powerful tool for detecting and identifying cryptotephras an unidentified cummingtonite bearing cryptotephra previously reported to be present in the late pleistocene loess deposits at kesennuma pacific coast did not correlate with any of the known cummingtonite bearing tephras in central ne japan but instead with the numazawa kanayama tephra erupted from the numazawa caldera southern ne japan although kesennuma is well beyond the previously reported area of the distribution of the numazawa kanayama tephra three new cummingtonite bearing cryptotephras in the mid and late pleistocene loess deposits estimated to be less than 82 ka 100 200 ka and ca 250 ka on the isawa upland were also detected

planktonic foraminifera in the western north pacific during the past 150 000 years comparison of modern and fossil assemblages abstract planktonic foraminiferal abundance variations in 186 deep sea piston core tops from the western north pacific were used to create a calibration set to characterize the present day kuroshio gyre system q mode factor analysis helped identify six faunal assemblages 93 variance related to modern water masses two tropical assemblages differing in relative dissolution three assemblages representing subtropical subpolar and transitional conditions and a gyre margin assemblage lying between the kuroshio current and the mainland of asia multivariate regression produced transfer functions relating observed summer august and winter february sea surface temperatures sst to the assemblages with standard errors of estimate of 1 5 c and 2 5 c respectively data from 24 piston cores was used to interpret variations of the kuroshio gyre system during the past 150 000 yr stratigraphic control is based on oxygen isotopic measurements the extinction of pink pigmented globigerinoides ruber at 120 000 b p coiling direction changes in neogloboquadrina pachyderma north of 30 n and dissolution variations between resistant and fragile taxa major dynamic changes in the circulation of the kuroshio gyre occurred during the last two glacial maxima at 15 20 000 b p isotopic stage 2 and at 140 150 000 b p isotopic stage 6 these intervals are characterized by 1 lowered sea levels which reduced flow into the sea of japan and sea of okh okhotsk 2 advance of the polar front from its modern position at about 42 n to 35 38 n 3 southward penetration of the oyashio current along the pacific coast of japan to tokyo 4 2 3 c lowered sst in tropical areas little or no change in subtropical areas and a 4 6 c decrease in transitional areas and 5 an overall decrease in carbonate dissolution relative to interglacial stages the maximum interglacial at 120 000 b p isotopic substage 5e shows a retreat of the polar front north of its modern position and an overall relative increase in interglacial carbonate dissolution that does not become severe until substage 5d

pangea b and the late paleozoic ice age abstract the late paleozoic ice age lpia was the penultimate major glaciation of the phanerozoic published compilations indicate it occurred in two main phases one centered in the late carboniferous 315 ma and the other in the early permian 295 ma before waning over the rest of the early permian and into the middle permian 290 ma to 275 ma and culminating with the final demise of alpine style ice sheets in eastern australia in the late permian 260 to 255 ma recent global climate modeling has drawn attention to silicate weathering co2 consumption of an initially high greater variscan edifice residing within a static pangea a configuration as the leading cause of reduction of atmospheric co2 concentrations below glaciation thresholds here we show that the best available and least biased paleomagnetic reference poles place the collision between laurasia and gondwana that produced the greater variscan orogen in a more dynamic position within a pangea b configuration that had about 30 more continental area in the prime equatorial humid belt for weathering and which drifted northward into the tropical arid belt as it transformed to pangea a by the late permian the presence of widespread equatorial coal basins with euramerica flora in the footprint of the greater variscan orogen during the late carboniferous is more compatible with a heterogeneous horst and graben morphology characterized by uplifted crystalline massifs acting as loci of intense silicate weathering co2 consumption and supplying sediment for proximal basins as venues of organic carbon burial than a contiguous high mountain plateau as assumed in recent climate modeling of the lpia and its demise the culminating phase of the lpia occurred at about 275 ma with the transformation from pangea b to pangea a and the attendant reduction of continental area in the equatorial humid belt as well as with continued northward drift that placed what remained of the greater variscan orogen into the zechstein arid belt in the late permian by which time the geologic landscape was largely blanketed with siliciclastics the resulting warming from reduced silicate weathering and thus increasing pco2 was interrupted at 260 ma with a cooling trend that coincided with emplacement of the emeishan large igneous province on the equatorial south china craton as well as the drift of the cimmerian continental blocks through the equatorial humid belt due to opening of the neo tethys a return to ice age conditions from the increase in silicate weathering uptake of co2 was avoided by drift of the emeishan large igneous province out of the equatorial belt that in conjunction with massive outgassing from emplacement of the siberian traps in high latitudes at the end of the permian 252 ma helped steer the climate system to sustained non glacial conditions

関東平野西縁 上鹿山面 狭山面の古地磁気による編年 58 69 kmt kmt brunhes chron

a multiple parameter approach to andesitic tephra correlation ruapehu volcano new zealand abstract a multi parameter approach was used to correlate andesitic tephras in a complex tephra sequence ranging in age from ca 23 to ca 75 ka on the eastern ring plain of ruapehu volcano north island field properties combined with ferromagnesian mineral assemblages and mineral compositions were required to map and correlate this sequence three tephra units could be identified based on their unique physical appearance but other tephras could not be correlated on this basis alone hornblende and olivine proved to be valuable marker minerals enabling further distinction of two of the marker units recognised by field properties as well as defining two further marker tephras unweathered titanomagnetite crystals present in all of the tephras were subjected to major element analysis by electron microprobe canonical discriminant function analysis dfa of these analyses enabled the grouping and discrimination of tephra units further aiding the identification of defined marker units as well as defining new marker units the titanomagnetite chemistry showed a strong relationship to the ferromagnesian mineralogy showing that the ferromagnesian phenocrysts formed from the same melt or under the same melt conditions prior to eruption of each tephra canonical dfa was also applied to hornblende and olivine mineral analyses to identify further marker beds and to confirm identifications of previously defined units this statistical analysis was found to be invaluable in reducing the large amount of compositional data from this study into a useable form for andesitic tephra correlation and mapping

use of amphibole chemistry for detecting tephras in deep sea sequences chikyu c9001c cores and developing a middle pleistocene tephrochronology for ne japan abstract using amphibole crystals we detected tephras in deep sea sequences chikyu c9001c cores and correlated marine and terrestrial tephras in ne japan then we reconsidered some previously reported tephra ages by using the age model of the cores we identified 50 spikes in amphibole grains numbered a1 a50 from top to bottom among these 12 spikes a38 49 corresponded to a thick non tephric sand layer we selected 20 spikes containing amphibole grains with glass coatings as likely primary tephras and analyzed their chemistry for tephra characterization on the basis of its amphibole chemistry we correlated spike a34 with the tn cii ciii layers of the tanabu c tephra tn c which erupted from osore volcano on shimokita peninsula we then showed that spike a34 represents primary tephra deposition not secondary deposition through bioturbation or bottom current reworking because amphibole grains with homogeneous chemistry were accumulated only in sediment near the spike within 10 cm we also showed that the chemical variation within each amphibole grain was not as great as the variation between grains which further supports the correlation between spike a34 and tn cii ciii these findings show that amphibole grains which are resistant to weathering can be used for characterization and correlation of weathered tephras from which glass shards have been removed by dissolution the glass shard chemistry of the 16h6a 60 80 tephra at 4 58 m below spike a34 which does not correspond to an amphibole spike suggests that this tephra likely correlates with the amphibole free tn ci layer in the terrestrial sequences non tephric sediments marine sand and lahar deposits occur between tn ci and tn cii ciii suggesting that some time elapsed after the deposition of tn ci before tn cii ciii were deposited by using the stratigraphic information of the 16h6a 60 80 tephra and spike a34 together with the 18o stratigraphy of the deep sea sequence we re assigned the eruptive age of tn c from the previously reported zircon fission track age of 180 40 ka to mis 8 257 263 ka

using discriminant function analysis to identify holocene tephras based on magnetite composition a case study from the sunwapta pass area jasper national park the magnetite composition from three sets of samples of mazama st helens set y and bridge river tephras from jasper and banff national parks are used to test whether discriminant function analysis can unambiguously distinguish these tephras the multivariate method is found to be very sensitive to the change in reference samples st helens set y tephra is clearly distinguished however discrimination between mazama and bridge river tephras is less distinct a set of unknown tephras from the sunwapta pass area was used to test the classification schemes unknown tephras are assigned to different tephra types depending on which reference tephra set is used in the discriminant function analysis

reconstructing the largest explosive eruptions of mt ruapehu new zealand lithostratigraphic tools to understand subplinian plinian eruptions at andesitic volcanoes we analysed the tephra record of mt ruapehu for the period 27 097 957 to 10 000 cal years bp to determine the largest scale explosive eruptions expected from the most active new zealand andesitic volcano from the lithostratigraphic analysis a systematic change in the explosive behaviour is identified from older deposits suggesting dry magmatic eruptions and steady eruptive columns characterised by frothy to expanded pumice fabrics to younger deposits that are products of unsteady conditions and collapsing columns characterised by microvesicular fibrous and colour banded pumice fabrics the end members were separated by eruptions with steady columns linked to water magma interaction and highly unstable conduit walls dry magmatic eruptions producing steady plinian columns were most common between 27 097 957 and shortly after 13 635 165 cal years bp following this time activity continued with eruptions that produced dominantly oscillating unsteady columns which engendered pyroclastic density currents until 10 ka when there was an abrupt transition at mt ruapehu since which eruptions have been an order of magnitude lower in intensity and volume these data demonstrate long period transitions in eruption behaviour at an andesitic stratovolcano which is critical to understand if realistic time variable hazard forecasts are to be developed

time variations of erosional force and grain size in pleistocene lake sediments abstract theoretical investigations on models of the developmental processes of erosional features show that the time variations in erosional force have more sensitive influence on the time fluctuation of eroded material such as sediments in lakes than that of the quantity representing erosional features such as volume of mountains time sequences of grain size distributions from the pleistocene sediments in lake biwa central japan indicate dominant periodicities of about 40 000 and 20 000 yr very close to those predicted from the milankovitch theory the time variations of the grain size parameters which may be indicators of erosional forces are very similar to that of the caloric summer insolation in the northern hemisphere

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

a numerical approach toward the classification of magnetites from tephra in southern alberta high titanium glass encased magnetites associated with intermixed tephras in upper subalpine soils in banff national park are shown to be characteristic of mazama tephra and of regional significance similar magnetites occur in a mazama layer above a paleosol at fish creek alberta and within a sample of mazama ash ua 396 from windy point alberta detailed sampling and analysis of the fish creek tephra indicate that the magnetites do not represent a separate eruptive event or an older ashfall cluster analysis of glass encased magnetites from reference samples of mazama st helens y and bridge river ashes revealed composite grouping of mazama and bridge river magnetites and separate and strong groupings of high tio2 magnetites discriminant analysis identifies mgo tio2 and al2o3 as the most significant chemical discriminants between the various ashes discriminant function analysis identifies the high titanium magnetites as mazama in type and successfully classifies 96 of the tephra derived magnet

geodynamical implications of a moscovian palaeomagnetic pole from the stable saharan craton illizi basin algeria abstract four different characteristic remanent magnetization chrm orientations have been isolated in the el adeb larache formation of the algerian sahara 27 45 n 8 9 e two of them are interpreted as overprints developed respectively during recent and permian times the two others give new moscovian 28 7 s 55 8 e and probably stephano autunian 38 5 s 57 5 e palaeopoles in good agreement with those previously obtained from the sahara but significantly different from the dwyka varves pole mcelhinny and opdyke 1968 comparison with lower carboniferous results shows that the latitudinal displacement of africa during the carboniferous is mainly related to a clockwise rotation about 25 around an axis close to the northeastern border of africa such a motion of africa agrees well with geological observations and with the pangea a2 hypothesis

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general