self weight consolidation of soft soils an experimental and theoretical study soil is laid down by sedimentation through water passing through the phases of a fluid supported suspension through a loose structure to a soft soil the stiffness of which then gradually increases under additional load consolidation is caused by the self weight of the soil and while the sediment is soft is accompanied by large strains to predict magnitudes and rates of movement the physical processes must be understood and used as the basis of a theoretical model this paper describes laboratory experiments on the development and consolidation of a soft soil in settling columns with measurement of density using an accurate non destructive x ray technique total stress pore pressure and settlement the results are compared with an earlier theoretical model modifications made to the model in the light of observed experimental features allow it to be used to predict the laboratory consolidation le sol est depose par sedimentation a travers l eau il a d abord la forme d une suspension soutenue

importance of clay in iron transport and sediment reddening evidence from reduction features of the abo formation new mexico u s a abstract petrographic and geochemical data from reduction features in the abo formation permian of central new mexico provide insight into the source of iron for hematite precipitation in red beds reduction features in the abo formation include isolated reduction spots as well as zones of reduction associated with fractures and coarser grained beds the reduction features contain less iron and more copper than the host rock mean values in ppm host rock fe 6456 cu 9 reduced fe 3730 cu 113 hematite relics are present in reduced areas associated with fractures and reduced bedding but are absent in reduction spots hematite apparently never formed in the reduction spots because of localized reducing conditions present at the time of pervasive reddening reduced fractures and bedding most likely result from migration of reducing pore fluids flowing through more permeable areas and postdate hematite precipitation iron bearing sand and silt grains which are typically regarded to be the principal source of iron for hematite precipitation in red beds are uncommon average 1 in the abo formation where present these grains are not significantly altered in either red host rock or in the white reduction features therefore detrital iron bearing clay size material is the primary source of iron in the abo formation although compositionally variable the clay rich areas contain a mean of 8 4 feo total in the host rock and a mean of 4 6 feo total in reduction spots chemical and mineralogical data from clay rich areas suggest that ferric oxyhydroxides associated with the clays are a more important iron source than iron from the clay crystal structure low whole rock iron content of the abo formation relative to other red bed units is consistent with clay and associated ferric oxyhydroxides being the principal iron source the abo formation may represent a clay dominated end member in a continuum of red beds in which the iron needed for reddening is derived from clays and coarser iron bearing framework grains

identification and characterization of the encrusting materials in a coastal liquefied petroleum gas storage cavern an examination was carried out of the encrusting materials on the seepage removal pumps in a bottom sump of an undersea liquefied petroleum gas lpg cavern the studied cavern constructed at 8 km off the western coast of korea facing the yellow sea is at 130 150 m below the seabed since the first filling of the lpg into the cavern it has suffered from the unexpected problem of a thick encrustation of unknown materials on the seepage removal pumps of the cavern the xrd and xrf analyses revealed that the encrustation materials were mainly iron hydro oxides and carbonate mineral aragonite based on the geological setting below the cavern site it was inferred that iron oxides found in the pleistocene sandy sediment and the precambrian gneiss might be supplying ferrous iron to the cavern waters under an anaerobic condition evidenced by low dissolved oxygen and negative redox potential in the cavern water a significant change in the hydraulic condition near the pump intake and mixing the cavern water with oxic waters supplied through re circulated seawater and terrestrial groundwater discharge would precipitate the dissolved iron precipitation of the carbonate mineral is thought to have occurred due to over saturation of calcium and bicarbonate which may have resulted from the dissolution of cement grouting materials used during the undersea cavern construction and submarine groundwater discharge sgd this study reports the iron and carbonate precipitation in the man made undersea cavern which is affected by the surrounding hydrogeological condition and the sgd

factors governing abundance of hydrolyzable amino acids in the sediments from the n w european continental margin 47 50 n fifty six samples representing 6 sediment cores taken along the n w european continental margin from the shelf slope and abyssal plain of the goban spur and meriadzek terrace were quantitatively analysed for total hydrolyzable amino acids thaa and clay minerals in descending order the five most abundant amino acids making up more than 70 of the total were aspartic acid glycine serine alanine and glutamic acid clay mineral proportions were typical for the n e atlantic in order of descending abundance illite kaolinite chlorite smectite and mixed layers the meriadzek terrace area is characterised by fine grain suspension sedimentation with a low pelagic carbonate input and the lowest content of thaa in contrast the goban spur transect is characterised by much higher carbonate inputs and more vigorous hydrodynamics as judged from granulometry and the high abundance of minerals of shelf and continental origin and a generally higher thaa content the pelagic portion of thaa deposited at the sea floor is more readily mineralised during early diagenesis than the more refractory clay mineral associated continental portion along this margin the average mineralization of thaa down to 25 cm in the sediment is about 54 there is a significant affinity between chlorites and amino acids which we suggest may involve the formation of ionic bonds between the octahedral layers of the clay and the amino acids

distinguishing climatic and current effects in mid pleistocene sediments of hatton and gardar drifts ne atlantic samples taken from dsdp sites 552 and 553 on hatton drift and site 611 on gardar drift in the northeast atlantic ocean were examined by analyses of carbonate content coarse fraction amount and composition fine fraction size and composition and oxygen isotope ratios the age of both sections is the mid pleistocene ranging from the end of the jaramillo normal event to the boundary between the matuyama and brunhes epochs about 0 77 0 96 ma records of this time show a change from a dominance of 23 ka to longer periodicity at about 0 818 ma this is marked at site 552 but less so at site 611 the grain size is mainly controlled by coccoliths foraminifera and ice rafted material all of which are related to glacial interglacial changes zones barren of and abundant in coccoliths are sensitive indicators of climatic effect carbonate increase lags behind foraminiferal oxygen isotope records of surface warming in several glacial to interglacial transitions at both drifts different types of carbonates oozes occur on hatton and gardar drifts of several possible factors influencing these bottom current effects seem more significant than others deduced from size analysis of the fine fraction sedimentological results in this study further confirm that sediment drifts in the ne atlantic have maintainted their basic characteristics at least since the mid pleistocene

provenance stratigraphic architecture and hydrogeologic influence of turbidites on the mid ocean ridge flank of northwestern cascadia basin pacific ocean abstract the northwestern edge of cascadia basin north pacific ocean is unusual because late pliocene to holocene turbidites lap onto juvenile oceanic crust of the juan de fuca ridge subsidence of the ridge flank combines with irregular westward progradation of the turbidite facies to create a stratigraphic section that coarsens and thickens upward the sand provenance is mixed individual turbidity currents have funneled into the area through several shelf slope and abyssal floor conduits including vancouver valley juan de fuca channel barkley canyon and nitinat canyon local bathymetric blockage deflection and reflection of flow paths by basement relief remobilization by intrabasinal submarine slides and debris flows episodic channel switching and sporadic overbank flooding have combined to produce erratic recurrence intervals for the turbidity currents only the tallest basement highs have remained isolated from turbidite deposition during the last 500 000 years spatial and temporal differences in sediment accumulation are important because they modulate the three dimensional responses of compaction and consolidation those changes in physical properties govern where and when hydraulic communication with the underlying basement shuts down the basal hemipelagic layer of cascadia basin transforms to an effective hydrologic seal seepage rates 1 mm yr once the sediment basalt interface is buried by 100 150 m of strata rapid accumulation of turbidites therefore accelerates the hydrogeologic conversion of igneous basement from open to sealed

chronology for climate change developing age models for the biogeochemical ocean flux study cores we construct age models for a suite of cores from the northeast atlantic ocean by means of accelerator mass spectrometer dating of a key core bofs 5k and correlation with the rest of the suite the effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation the degree of bioturbation is estimated by comparing modeled profiles with dispersal of the vedde ash layer in core 5k and we find a mixing depth of roughly 8 cm for sand sized material using this value we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years with lesser effect on fine carbonate 10 mu m ages the bioturbation model illustrates problems associated with the dating of instantaneous events such as ash layers and the heinrich peaks of ice rafted detritus correlations between core 5k and the other cores from the bofs suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes magnetic susceptibility water and carbonate content and via marker horizons in x radiographs and ash beds

the ediacaran to cambrian rift system of southeastern south america tectonic implications abstract the tectonic evolution of southeastern south america from the middle ediacaran to the early cambrian is marked by a series of small fault bounded siliciclastic and volcaniclastic basins and voluminous coeval granites traditionally associated with the compressional or transpressional tectonics of the late stages of the pan african brasiliano orogeny most existing models consider these basins separately with distinct tectonic evolutionary histories according to local geological settings however new and recently published age constraints lithological similarities and structural aspects point to the correlation of all ediacaran to cambrian basins in southeastern south america within a common basin system more than 1500 km long the interpretation of a common origin for all ediacaran to cambrian basins of southeastern south america implies that all the different terranes of the brasiliano orogenic collage in the region were already united in a single plate at approximately 600 ma an extensional

late glacial and holocene palaeocurrents around rockall bank ne atlantic ocean core samples and hydrographic data from 50 to 60 n and 15 to 25 w in the northeast atlantic ocean are used to study changes in current activity from the last glacial to present we establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis changes in current speed are recorded by the mean size of the sortable coarse noncarbonate silt component which increases with current vigor by winnowing away of fines our method involves the definition of an ideal sortable silt input function recorded at a site accumulating unmodified pelagic flux only the ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths the upper surface of southern source water ssw probably shoaled during the glacial as indicated by the covariation of sortable silt records from sites presently covered by ssw and lower north atlantic deep water lnadw the data suggest that production of lnadw was suppressed during the glacial increased following the last glacial maximum and declined at the start of termination 1a a second pulse of production occurred immediately before the younger dryas event intermediate waters were generally faster flowing during the glacial and may have expanded their depth domain such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m

glaciomarine sedimentation and palaeo glacial setting of maxwell bay and its tributary embayment marian cove south shetland islands west antarctica abstract high resolution 3 5 khz and multi channel seismic profiles and piston cores were collected from maxwell bay and its tributary embayment marian cove in the south shetland islands antarctica during the korea antarctic research program 1992 93 and 1995 96 to elucidate the glaciomarine sedimentation processes and recent glacial history of the area seismic data from maxwell bay reveal a rugged bay margin and flattened basin floor covered with well stratified hemipelagic muds on the base of slope acoustically transparent debris flows occur indicating downslope resedimentation of glaciomarine sediments despite the subpolar and ice proximal settings of marian cove the seafloor is highly rugged with a thin sediment drape suggesting that much of the area has been recently eroded by glaciers sediment cores from the cove penetrated three distinct fining upward lithofacies 1 basal till in the lower part of the core accumulated just seaward of the grounding line of the tidewater glacier 2 interlaminated sand and mud in the middle part deposited in ice proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping and 3 pebbly mud in the upper part deposited in ice distal zone by both surface meltwater plume and ice rafting from the glacier front a reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling maxwell bay in late wisconsin time and grounding of the tidewater glacier in marian cove until about 1300 yr bp

composition and provenance of turbidite sands late quaternary madeira abyssal plain abstract late quaternary sediments from the madeira abyssal plain map consist of metre thick fine grained distal turbidites separated by centimetre thick layers of pelagic clay marl and or ooze three major compositional groups of turbidites have been defined by previous work volcanic organic rich and calcareous the coarse to medium grained sand fraction from the basal parts of the volcanic turbidites is predominantly composed of volcanic glass pumice and foraminifera whereas heavy mineral and plagioclase feldspar grains plus basalt and trachyte clasts become more abundant in the overlying fine grained sands and silts the bases of organic rich turbidites consist of fine grained sands and silts which are rich in foraminifera quartz and alkali feldspar grains and altered lithic clasts calcareous turbidites have bases composed of medium to fine grained foraminiferal sand devoid of terrigenous coarse grained material new mineralogical data are used to define grain assemblages in the sand silt fraction from these turbidite groups these assemblages are comparable to mineral assemblages from alkali olivine basalts trachybasalts to trachyandesites and trachytes phonolites on the azores canary islands and madeira and with sediments from the continental margin of northwestern africa volcanic glass chemistry however distinguishes the canary islands as the principal island provenance of the volcaniclastic sands volcaniclastic material probably originated either from reactivation of basic volcanism on tenerife and gran canaria in the quaternary or during the development of the western islands of la palma and hierro 5 ma recent trachytic and phonolitic material was derived from the more fractionated volcanic complexes on the central and eastern islands of the canary islands tenerife gran canaria fuerteventura and lanzarote organic rich turbidites consist of two mineralogical subgroups which originated from two distinct source areas along the continental margin of northwestern africa 1 north of the canaries off morocco 2 south of the canaries off senegal differences in the mineralogy between source areas reflect geographical variations in the weathering of continental granitic rocks which were subsequently transported off shore mainly by aeolian processes calcareous turbidites were derived from the great meteor cruiser seamount chain west of the map

abrupt wind regime changes in the north atlantic ocean during the past 30 000 60 000 years 1 the inputs of higher plants in blake outer ridge subtropical western north atlantic during marine isotope stage 3 mis3 have been recorded at high resolution by quantification of c23 c33 odd carbon numbered n alkanes and c20 c30 even carbon numbered n alkan 1 ols in sediment sections of ocean drilling program site 1060 the changes of these proxies at this open marine site are mainly related to eolian inputs their concentrations and fluxes exhibit major abrupt variations that are correlated with dansgaard oeschger d o patterns in greenland ice cores the ratios between interstadials and stadials range between 2 and 9 times the intense flux increases in the d o stadials are linked to strong enhancements of the westerly wind regime at these subtropical latitudes during stadials the observed variation was paralleled by changes in wind blown dust and the polar circulation index in greenland ice which is in agreement with previously hypothesized atmospheric teleconnections between northern and middle low latitudes of the northern hemisphere the close correspondence between sedimentary and ice core proxies is evidence that crossings of the glacial climate thresholds involved major reorganizations of the troposphere the observed large rise in higher plant biomarkers indicates that climate stabilization in the d o stadial conditions led to main increases in wind intensity

sedimentology and stratigraphy of box cores from the hebble site on the nova scotian continental rise abstract fifty box cores were obtained from the 2 4 km site of the high energy benthic boundary layer experiment hebble on the lower nova scotian continental rise at 4820 m the oldest unit occurring in two gravity cores is a pre holocene dark grey gravelly mud probably of debris flow origin above this is a soft grey mud overlain by brown sandy mud whose sand is largely foraminiferal with some terrigenous material from interbedded turbidites in some places this unit has a stiff brown gravelly mud at its base which is always overlain by sandy mud containing dispersed gravel it is suggested that the dispersed gravel originated from the underlying gravelly mud and has been dispersed upwards by the action of burrowing organisms foraminifera indicate a holocene age down to about 65 cm and thus a net accumulation rate of about 6 cm ka 1 the surface unit of brown mud named the hebble mud is spatially variable in both thickness and sand content which average about 4 cm and 6 respectively sand percentage is not related to silt size or percentage but varies inversely with deposition rate and thickness suggesting a relation to local winnowing the size and peak height of the main silt mode 10 17 m are closely correlated and the peak height is inversely related to the percentage of clay this is attributed to fractionation during deposition of the mud wherein fine silt and clay deposition is suppressed at flow speeds from 10 to 18 cm s 1 leaving coarser silt there is more clay on the upstream and downstream sides of a low spur suggesting spatial variation of shear stress that may be due to a standing internal wave added to the mean flow silt mode size is variable downcore although clay percentages are similar to those at the surface the overall silt size is probably controlled by turbidite input thus silt size is likely to be an unreliable indicator of current speeds down core though peak height of the silt mode may be satisfactory

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

mesozoic felsic arc magmatism and continental olivine tholeiites in zhejiang province and their relationship with the tectonic activity in southeastern china abstract the mesozoic geology of zhejiang province in southeastern china is characterized by two distinct geodynamic settings separated by a major tectonic event during the late jurassic early cretaceous a continental magmatic arc developed with a westward subduction of the kula or izanagi plate under the south china block during the development of this magmatic arc microsyenite porphyries and quartz bearing porphyries were emplaced in western zhejiang about 124 ma ago these porphyritic rocks intruded felsic tuffs that rest unconformably on carboniferous and permian folded strata geochemically they are enriched in lil and light rare earth elements lree which are features of acid shoshonitic suites isotopically they are characterized by negative nd t 124 5 3 to 4 7 values and high initial 87 sr 86 sr ratios 0 7079 0 7084 later in eastern zhejiang quartz phyric ignimbrites and subordinate acid andesites were emplaced and intruded by nearly contemporaneous microsyenitic and rhyolitic domes during the cretaceous about 97 ma ago all these rocks belong to the high k calc alkaline suites they show geochemical features of volcanic arc granites emplaced in an active continental margin and are characterized by negative nd t 97 8 8 to 7 1 and high initial sr isotopic ratios 0 7081 0 7089 the negative nd t 97 values of all the cretaceous calc alkaline and shoshonitic rocks of intermediate to acid composition suggest that these rocks were probably derived from a mantle wedge source contaminated by variable amounts of old crustal components likely represented by the proterozoic basement rocks of the south china block the contemporaneous igneous rocks in vietnam as well as in the fujian and guangdong provinces china represent the lateral counterparts of the zhejiang calc alkaline plutonic and volcanic rocks in the late early cretaceous an important tectonic event occurred which provoked the ending of the inagazi or kula plate subduction and affected the continental magmatic arc this tectonic event is likely related to the collision of the china indochina margin with the west philippine block after this tectonic event in the beginning of the late cretaceous continental stretching and crustal attenuation affected the south china block leading to the development of ne sw faulted basins in which continental olivine tholeiites and minor alkaline rhyolites were erupted both characterized by low nd t 97 ratios ca 4 meanwhile continental conglomerates and sandstones were also deposited this rifting process began likely before the india asia indentation and lasted at least until the late tertiary

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

turbidites and megaturbidites from the herodotus abyssal plain eastern mediterranean unrelated to seismic events abstract a transect of 9 piston and gravity cores was taken across the southeast flank of the mediterranean ridge the transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge each core contains two or more turbiditic layers which belong to two discrete types here called a and b type a essentially consists of black plastic clays rich in smectite with silt fraction of terrigenous nature source area is the nile cone and age is middle or late pleistocene type b turbidites are pale brown to whitish in color coarse grained carbonate rich and bioclastic in composition with shallow water fossils dominant they are poor in smectite and the silt fraction is very rich in carbonates calcite and aragonite the source area is the north african shelf south of the abyssal plain a megabed belonging to type b turbidites is correlatable from core to core with a thickness in excess of 10 m in the abyssal plain and an estimated volume of 10 km 3 its stratigraphic position in the latest pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head during a low sea level stand the source areas of the two discrete turbidite types belong to the essentially aseismic north african continental margin although they are presently recorded on the tectonically active mediterranean ridge no seismic events are required to account for the presence of either type of turbidite

time and method dependent size distributions of fine grained sediments with increased interest in fine grained sediments it is imperative that a firm basis exist for comparative studies of these cohesive sediments in this study the size distributions of continental slope and rise muds are shown to be dependent on both method and duration of sample pretreatment statistical analysis of 171 size distributions indicates that of the four most frequently used sample preparation methods soak stir shake and ultrasonify the time required to reach a terminal distribution beyond which no fine shift was detected varied from 15 minutes to 90 hours for a given sample solely as a function of preparation method data from this study also indicate that sample preparation by simple soaking alone will probably yield fine grained sediments which when analysed by pipette or microsedimentation accumulation balance undergo a continuous change in size distribution during analysis and may never reach a terminal distribution during the analysis time on the other hand stirring and ultrasonification were shown to be the most rapid and consistent methods for obtaining a sample s terminal distribution

an experimental study on the effects of phenocrysts on convection in magmas abstract the effect of phenocrysts on convection in magma chambers is investigated experimentally using small heavy particles in convecting fluids the particles are initially uniformly distributed in a fluid which is either heated from below or cooled from above the system is allowed to evolve and temperature and particle concentration profiles are measured as functions of time when the concentration of particles is sufficiently small convection is basically unaffected by their presence when the concentration is above a critical value however the convective motion is considerably altered the effect of particles on the subsequent fluid behaviour is different in the cases of heating from below and cooling from above in the former case there are strong convective motions confined to a sedimentary layer of decreasing thickness beneath a clear layer which displays rather weak convective motions with time the destabilizing increase of temperature in the lower layer overcomes the stabilizing contribution to the bulk density due to the particles and the layer overturns quite suddenly in the situation of cooling from above a critical condition separates a case of continual overturn from a case of no overturn at all with the sedimentary layer falling unimpeded to the bottom theoretical analysis suggests that the critical value is determined primarily by the ratio of the contribution to the bulk density of the suspension due to particles to the change in fluid density due to the thermal effect the size distribution of the particles can also modify the fluid behaviour applying our general results to geological situations we suggest that the presence of relatively small concentrations of phenocrysts can critically influence the mode of convection in magmas

orbital forcing of bottom current enhanced sedimentation on feni drift ne atlantic during the mid pleistocene feni ridge is a plastered sediment drift deposited along the northwestern flank of rockall trough ne atlantic under the influence of deep geostrophic currents formed by intermittent overflows of arctic intermediate water from the norwegian sea across the iceland scotland ridge nsow lower deep water ldw a derivative of antarctic bottom water from the south atlantic mixed with old north atlantic deep water nadw also bathes the lower flanks of the drift below 2500 m deep sea drilling project site 610 was drilled in a sediment wave field on the surface of feni drift 2417 m though the sediments recovered proved to be typically pelagic preserving a high resolution 5 cm kyr 1 quaternary record of orbitally modulated ice rafting and biogenic productivity cycles but showing little evidence of current affected deposition from particle size and compositional analyses of the biogenic and lithogenic 10 m silt which we then compared with records of the percentage and flux of ice rafted detrital ird sand foraminifera and coccoliths for the same interval cross spectral comparisons were then made between these records and variations in a model of northern hemisphere ice volume ice sheet growth and decay in response to orbitally forced insolation changes at 65 n variations in the relative proportions and fluxes of ird sand foraminifera and coccoliths all covary closely with orbitally forced ice volume fluctuations but with differing amplitude coherency and phase relationships at each milankovitch frequency however there is a significant component of variance in pelagic and ice rafted sedimentation which is controlled by bottom currents and this shows excellent phase and coherency agreement with the ice volume model at all orbital frequencies the relative enrichment coarseness and flux of the contourite silt fraction of feni drift sediments all increase during glacial or cold stages of the mid pleistocene relative to warm stages suggesting that currents were stronger during these periods possible explanations for such changes in current activity include 1 an increased flux of nsow via the wyville thompson ridge into the rockall trough during glacials but not due to increased production of nsow 2 ldw presently lying below 2500 m rises during glacials by at least 50 60 m thereby flooding over the surface of feni ridge at site 610 3 the path of a major recirculation gyre in the lower nadw ldw system presently situated marginally south of site 610 encroaches upon the southern tip of feni ridge during glacials and 4 the rockall trough itself is a site of deep water formation during glacials analogous to labrador sea deep water formation today

deposition of ungraded muds from high density non turbulent turbidity currents turbidity current deposits of mud have recently been found up to 10m in thickness resulting from single depositional events1 2 turbidites 1 5 m thick from the madeira abyssal plain3 4 display long segments with little vertical change of grain size5 6 this suggests that the currents froze in some way making them unable to sort sediment here we suggest that a decline in flow speed of these currents led to a concentration gradient in silt close to the bed that was sufficiently steep to stratify the flow a concentration gradient of 18 kg m 3 over 1 5 m height gives a layer richardson number above the critical value of 0 25 for damping of turbulence we propose that with turbulence severely damped a dense suspension of fine material consolidates like a static suspension while continuing to flow downslope the current changes from a fully turbulent flow to a decelerating flow with suppressed turbulence and increasing density in the latter state interparticle forces prevent differential settling of the coarser grains

a computer interfaced sedigraph for modal size analysis of fine grained sediment a system has been developed allowing the direct storage on disc of size data from the x ray scanning settling tube sedigraph 5000et processing of the cumulative percentage data output to produce smooth frequency curves is described this allows rapid 15 min and precise m 0 1o discrimination of size modes peak heights median and silt and clay percentages of fine grained sediments an example of a mud turbidite is given showing systematic changes in bulk and modal properties not visible by eye lack of size segregation in the 1 m thickness of this turbidite shows that it may have been deposited from a highly concentrated flow rather than from a dilute waning turbidity current such flows may explain ungraded poorly graded muddy sediments also known as homogenites unifites or megaturbidites by other authors

glaciomarine sedimentation and its paleoceanographic implications along the fjord margins in the south shetland islands antarctica during the last 6000 years abstract two 3 m long cores were collected from maxwell and admiralty bays on king george island one of the south shetland islands west antarctica these cores were examined for their benthic foraminifer globocassidulina biora 18o and 13c records diatom abundance counts and biogenic constituents carbon and silica these high resolution data were used to reconstruct the paleoceanography of the bays and to link the marine record with deglaciation of the south shetland islands ice cap in maxwell bay extremely low diatom abundance the depletion of total organic carbon toc and biogenic silica biosi and enriched 18o between 6200 and 4000 bp indicate that this period was characterized by cold conditions with deposition of waterlain till unit 1 just seaward of the grounding line low sedimentation limitation of primary production on surface water and lack of meltwater supply deglaciation along the maxwell bay margin was dated from about 4000 bp until at least 2700 bp with increasing toc biosi and diatom abundance and decreasing the c n ratio up core at this time subglacial meltwater streams began to emanate from the glacier front sediment laden meltwater plumes from these streams deposited interlaminated sand and mud unit 2 in the ice proximal zone deglaciation was followed by marked climatic warming at around 2700 bp with evidence of toc and biosi maxima depleted 18o and markedly increased diatom valves with further glacier recession diatomaceous pebbly mud unit 3 was deposited in open marine conditions a large influx of organic materials by enhanced production during this period caused both rapid depletion of caco3 in sediment and resulted in marked increase in sedimentation since 2700 bp at 200 m water depth along the maxwell bay margin core s 19 in contrast the shallower platform along the admiralty bay margin core s 2 was deglaciated later about 1900 bp that is 2000 years after the maxwell bay margin this is possible as core s 19 is situated 200 m water depth more distal to the fjord head glacier while core s 2 in admiralty bay lies on a shallower platform

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

late glacial to holocene climatic and oceanographic record of sediment facies from the south scotia sea off the northern antarctic peninsula two gravity cores were collected from the south scotia sea located off the northern antarctic peninsula during the 2002 2003 korea antarctic research program karp expedition to determine the late quaternary climatic and oceanographic history reassessment of previous sedimentological geochemical and micropaleontological analyses combined with established age model of ams 14c dates represent the reliable record of late pleistocene climatic oceanographic change for the scotia sea region of antarctica during the last glacial maximum lgm the south scotia sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated weddell sea continental margin drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area the bottom current deposits during the glacial phase comprise two lithologic units 1 bioturbated gravelly sandy mud facies 1 formed by sluggish bottom current caused by reduced dense water production originated from the ice sheet on the weddell shelf 2 indistinctly layered diatomaceous mud as shown by total organic carbon toc highs in the facies 1 deposited by sporadic bottom currents caused by intensified sea ice formation in polynya during the glacial stage the lgm is characterized by greater and longer sea ice coverage and a restricted weddell scotia summer communication as evidenced by a relative decrease in percentage thalssiosira antarctica and chaetoceros resting spores which are more abundant close to the weddell ice shelf deglaciation about 13 000 9000 14c yr bp in the south scotia sea was characterized by increasing toc diatom abundance and decreasing magnetic susceptibility and sand contents up core at this time subglacial meltwater streams began to emanate from the weddell ice sheet with peak of ice rafting sediment laden turbid plumes from melting glacier and deglaciated weddell shelf have probably been joined into the realm of contour currents weddell gyre circulation ultimately forming indistinctly laminated gravelly mud facies 2 in the south scotia sea these currents probably resulted from water exchange between the weddell ice shelf and circumpolar warm deep water during the retreating phase of the last glaciation the deglaciation was probably followed by a period of open marine conditions with variable extent of sea ice variable toc content between about 9000 and 3000 14c yr bp bottom water production occasionally appears to have diminished or ceased due to the disintegration of some of the weddell ice shelf and biogenic input became increased forming bioturbated diatomaceous mud and ooze facies 3 the climatic amelioration could have restored the weddell scotia communication during the summer as evidenced by a relative increase of t antarctica and c resting spore in facies 3 at the onset of neoglacial about 3000 14c yr bp a decrease in toc and diatom abundance and an increase of sand content reflect the formation of more extensive and seasonally persistent multiyear sea ice the weddell ice shelf advanced with increased sea ice coverage at this time and as a result bottom water might play a role in transporting terrigenous sediments and reworked fossil diatoms into the south scotia sea forming diatomaceous sandy mud facies 4 during this time it is possible that the weddell scotia communication would have been partly restricted as evidenced by a reduction of the numbers of t antarctica and c resting spores our results indicate environmental variability throughout the late quaternary that was consistent across most portions of the maritime antarctic peninsula in addition the timing of climatic transitions correlates with the northern hemisphere indicating the possibility of coherent climatic variability during the late quaternary at least for the higher latitudes

east asian monsoon variation and climate changes in jeju island korea during the latest pleistocene to early holocene a 4 96 m long sediment core from the hanon paleo maar in jeju island korea was studied to investigate the paleoclimatic change and east asian monsoon variations during the latest pleistocene to early holocene 23 000 9000 cal yr bp high resolution toc content magnetic susceptibility and major element composition data indicate that jeju island experienced the coldest climate around 18 000 cal yr bp which corresponds to the last glacial maximum lgm further these multi proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14 000 cal yr bp which represents the commencement of the last major deglaciation after the last major deglaciation the toc content decreased from 13 300 to 12 000 cal yr bp and from 11 500 to 9800 cal yr bp thereby reflecting the weakening of the summer monsoon the lgm in jeju island occurred later in comparison with the chinese loess plateau such a disparity in climatic change events between central china and jeju island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central china and by the buffering effect of the pacific ocean

depositional fluxes palaeoproductivity and ice rafting in the ne atlantic over the past 30 ka over the last 30 ka sediment flux to the northeast atlantic ocean has been strongly influenced by the growth and decay of northern hemisphere ice sheets input of ice rafted detritus the migration of the polar front and associated changes in patterns of biological productivity we examined cores from 47 n to 60 n along 20 w to determine the flux of components including carbonate organic carbon and terrigenous material and divided into size fractions during the glacial period fine carbonate flux was low and ice rafted input high burial flux during the holocene became dominated by coccolith and foraminiferal carbonate with minor organic matter and biogenic silica estimates of palaeoproductivity are ambiguous a method which corrects for water depth and sedimentation rate suggests no clear glacial to holocene change whereas a method based on percentage of organic carbon suggests increased productivity from glacial to holocene of around 60 sites of sediment focusing saw a change from enhanced fine terrrigenous flux in the glacial to enhanced fine carbonate in the holocene after compensating for sediment focusing glacial ice rafted flux distribution shows a decrease from south to north across the area reflecting cyclonic surface water circulation deposition of ice rafted detritus during heinrich events h1 and h2 led to enhanced preservation of organic matter immediately beneath the layers indicating a rapid accumulation rate

sedimentation on the feni drift and late glacial bottom water production in the northern rockall trough abstract between the last glacial maximum 18 ka and the present day a variety of contrasting oceanographic conditions including changes in surface and bottom water circulation patterns have existed in the north atlantic evidence for the presence of bottom currents in winnowed silt horizons in the feni drift suggests that deep water may have been produced in this region during glacial deglacial intervals current activity and thus perhaps deep water production was apparently intermittent and may have been controlled by a process analogous to the formation of labrador sea water this involves cooling and deep ocean convection during winter months physical factors controlling this production would be temperature and salinity of upper waters which would govern the density and wind stress necessary for vertical overturn coupled with absence of ice cover evidence of bottom current activity suggests that deep water production occurred in the rockall trough throughout termination 1a which closely corresponds to fairbanks 1989 meltwater pulse 1a mwp 1a production of deep water in this region apparently ceased shortly after the decline in influence of the meltwater influx

late holocene glacier reconstruction reveals retreat behind present limits and two stage little ice age on subantarctic south georgia observational data show that climate in the southern ocean region is rapidly changing however past the instrumental period our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records alpine glaciers present on many southern ocean islands may provide such data because changes in their mass balance extent and erosion rates often mark a response to climate shifts rock flour the fine grained fraction of the glacial erosion process is suspended in meltwater streams and transferred into the sediments of downstream lakes continuously recording glacier variations here we utilize this relationship to present a reconstruction of the late holocene glacier history of subantarctic south georgia using sediments from the glacier fed middle hamberg lake to fingerprint a glacial erosion size signal we used titanium counts validated against changes in sediment density and grain size allowing a continuous reconstruction of glacier variations over the past similar to 1250 years together with local moraine evidence and supporting evidence from other southern hemisphere glaciers on new zealand and in patagonia our findings reveal a series of consecutively diminishing late holocene advances in addition to a glacier maximum before 1250 cal a bp these include a twostage litle ice age with advances around 300 and 120 cal a bp in line with evidence from southern patagonia in addition we present evidence for an unreported retreat behind present limits around 500 cal bp

textural and dispersal patterns of thick mud turbidites from the madeira abyssal plain abstract the madeira abyssal plain is the site of a thick sequence of thick pleistocene turbidites that are almost entirely of material less than 63 m in grain size the major turbidites are 1 to 5 m in maximum thickness concentrating on three turbidites cored at 24 locations detailed patterns of thickness and vertical and lateral grain size changes reveal flow paths on the plain in general the bases of the units are of graded silt showing thick and thin planar lamination and occasionally ripple cross lamination a new idealised sequence of changes in size and structures with distance along the flow path is developed closer to source the beds comprise a graded structured silty base overlain by structureless mud which may also be graded down current the silty base becomes thinner with less apparent structure and the upper homogeneous part becomes thicker and more uniform in an overall thickening trend at the distal end uniform beds up to 5 m in thickness are found in one turbidite the modal size structure shows some silt modes which are hydrodynamically sorted and change size vertically and spatially while one particular mode is constant in size due to a particular species of coccolith the turbidites originated from slumps on the northwest african continental margin and from the vicinity of madeira and the canaries some of which exceeded 100 km3 in volume

hemipelagic and turbiditic mudstone facies associations in the upper cretaceous gosau group of the northern calcareous alps austria abstract turbiditic and hemipelagic mudstones from the upper cretaceous to lower paleocene nierental formation of the northern calcareous alps austria can be differentiated by employing relatively simole laboratory and higher hemipelagic mudstones turn out to be characterized by finer grain sizes of the non carbonate fraction and higher carbonate contents sediment colour bioturbation distribution of microfossils weathering characteristics and bed sequence analysis were used as additional criteria to recognize the genetically different mudstone types for acquiring the non carbonate grain size data the samples were leached in hydrochloric acid and the remaining siliciclastic material was used for analysis with a sedigraph the median values of the grain size distributions of the turbidite mudstones reach up to 9 7 whereas the hemipelagic median values lie between 9 5 and 10 8 carbonate contents of the turbidite mudstones range between 22 and 68 those of the hemipelagic mudstones between 58 and 82 single bed profiles show distinct vertical trends of both grain size and carbonate content values for the turbidite mudstone division no such trends exist in the hemipelagic mudstone beds five basic types of turbiditic and or hemipelagic mudstones can be recognized 1 turbidite hemipelagite couplets 2 pure hemipelagic mudstone sequences 3 hemipelagic mudstone sequences with very thin turbiditic interacalations 4 a thorouthly mixed turbiditic hemipelagic mudstone type which is characterized by intense bioturbations and 5 mud turbidites without any hemipelagic intervals most of these types occur simultaneously at different localities of the nierental formation

terrigenous sediment supply along the chilean continental margin modern regional patterns of texture and composition the regional patterns of texture and composition of modern continental slope and pelagic sediments off chile between 25 s and 43 s reflect the latitudinal segmentation of geological morphological and climatic features of the continental hinterland grain size characteristics are controlled by the grain size of source rocks the weathering regime and mode of sediment input eolian off northern chile vs fluvial further south bulk mineral assemblages reveal a low grade of maturity regional variations are governed by the source rock composition of the different geological terranes and the relative source rock contribution of the coastal range and andes as controlled by the continental hydrology the relative abundance of clay minerals is also predominantly influenced by the source rock composition and partly by continental smectite neoformation latitudinal variations of illite crystallinities along the chilean continental slope and west of the peru chile trench clearly reflect modifications of the weathering regime which correspond to the strong climatic zonation of chile

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

tectonics of se china new insights from the lushan massif jiangxi province in south china the lushan massif forms a topographic high of the south china block south of the qinling dabie belt the lushan massif consists of two main lithotectonic units separated by a major tectonic contact a neoproterozoic upper sinian paleozoic unit comprising primarily unmetamorphosed sandstones overlies a paleoproterozoic unit mainly composed of low pressure high temperature gneisses and micaschists both units are cut by cretaceous granitic intrusions three primary tectono metamorphic and magmatic events are recognized the eastern part of the lushan massif is cut by a nne ssw trending ductile normal fault d3 deformation coeval to the emplacement of a 100 110 ma leucogranite dated by 40ar 39ar laserprobe on biotite and muscovite d2 deformation is responsible for the formation of a decakilometer scale ne sw trending upright anticline characterized by ne sw stretching and nw se shortening the age of this folding event is defined by a 127 1 2 ma u pb titanite date obtained for a syntectonic granodiorite and 40ar 39ar ages of 133 ma for amphibole this cretaceous age also corresponds to the 40ar 39ar ages of 126 ma found on syntectonic muscovites at the base of the sinian unit an older deformation event d1 characterized by a top to the nw extensional decollement of the sinian paleozoic series above proterozoic metamorphic rocks is related to the triassic tectonics of the dabieshan lastly in the lower part of sinian rocks the occurrence of kyanite cataclased during d1 documents an older poorly preserved late paleozoic early mesozoic tectonometamorphic event dx related to a blind thrust in the continental crust of the south china block in the southern foreland of the dabieshan

meso cenozoic taphrogeny and dispersion in the continental margin of southeast china and adjacent seas abstract the area from the continental margin of south china to the central basin of the south china sea can be divided into several meso cenozoic fault sag zones i e continental upwarp continental slope and oceanic central fault sag zones the fault sags are of five types continental upwarp fault sags embryonic continental rifts intracontinental rifts continental slope transitional rifts and oceanic rifts these extensional structures are the products of different stages of taphrogeny from the continental margin to the ocean there are several fault sags and rifts formed in various stages the study area lies within the interaction zone of the eurasia pacific and indo australia plates where the extensional structures are related to this interaction but not directly to the subduction mechanism the distribution of the fault sags is controlled by the previous tectonic framework shallow tectonic movements induced the motion of deep seated materials mantle diapirism in turn promoted crustal thinning as well as rifting and influenced the development of shallow tectonics