a 160 k y old record of el nino southern oscillation in marine production and coastal runoff from santa barbara basin california usa a 160 k y old laminated sediment record from the santa barbara basin california analyzed using scanning electron microscope techniques provides a history of interannual variability of marine production and coastal runoff we used backscatter electron imagery to measure the components of the varve these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3 1 and 8 4 yr in the terrigenous series these are indistinguishable within the frequency resolution of the spectra from significant periodicities of 3 5 and 7 6 yr in the diatomaceous series the 3 1 and 3 5 yr periodicities record el nino modulation of coastal runoff and marine production the 8 4 and 7 6 yr periodicities are consistent with modulation by strong to very strong el nino events this is supported by the results of cross spectral analysis of the terrigenous and diatomaceous records which reveal inverse or antiphase relationships at 3 5 and 7 6 yr our work adds to a body of evidence that suggests that el nino has been a persistent feature of late quaternary climate variability

amethyst bearing lava flows in the parana basin rio grande do sul brazil cooling vesiculation and formation of the geodic cavities size distribution data obtained from detailed field study of bubbles and amethyst geodes in the basaltic lava flows of the serra geral formation ametista do sul rio grande do sul brazil are used in cooling and vesiculation models to infer the origin and the formation processes of the geodic cavities coupled field observations and modelling results emphasize that 1 the formation of geodes in the studied lava flow can be explained qualitatively and quantitatively by the exsolution of magmatic gas from the supersaturated melt with no need for external surface water supply 2 the vertically elongated habits of the geodes result from higher cooling rate of the magma in contact with the accumulating bubbles and 3 the abnormal metre sized geodes with their branching habits result not only from the diffusive decompressive bubble growth but also from the coalescence of inwards progressing tubular cavities

factors affecting the durability of selected weak and clay bearing rocks from turkey with particular emphasis on the influence of the number of drying and wetting cycles weathering can induce a rapid change of rock material from initial rock like properties to soil like properties the resistance of a rock to short term weathering is described through a durability parameter called the slake durability index as durability is an important engineering parameter particularly for weak and clay bearing rocks it was assessed by a number of tests the main purpose of this study is to assess the influence of the number of drying and wetting cycles and controls of mineralogical composition and strength on durability for this purpose 141 samples of different types of weak and clay bearing rocks were selected from different parts of turkey and relationships between the above mentioned rock characteristics were statistically investigated the samples were subjected to multiple cycle slake durability testing x ray diffraction xrd analysis and uniaxial compression testing in addition to assess the influence of mineralogical composition on durability the mineral contents of the original material and the material passing from the drum of the slake durability apparatus after each cycle were also determined by xrd the results indicate that the type and amount of clay minerals are the main factors influencing the variations of the slake durability index in all samples the durability of the clay bearing rocks studied correlates best with the amount of expandable clay minerals a strong relationship between the uniaxial compressive strength and the fourth cycle slake durability index is found only for the marls among the rock types studied assessment of gradation results of the spoil pile materials consisting of clay bearing rocks also reveals that the increase in percentage of fines in old piles is indicative of material degradation as is evident by multiple cycle slaking it is emphasized that two cycle conventional slake durability testing did not appear to offer an acceptable indication of the durability of weak and clay bearing rocks when compared with multiple cyclic wetting and drying comments on the performance of the test are made that aim to make the testing process and interpretation of the results more reliable

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

effects of magmatic processes serpentinization and talc carbonate alteration on sulfide mineralogy and ore textures in the black swan disseminated nickel sulfide deposit yilgarn craton the black swan disseminated orebody occurs predominantly within the partially carbonated serpentinite core of a zoned serpentinite talc carbonate ultramafic cumulate body of komatiitic parentage the black swan disseminated sulfides depart significantly from the characteristic pattern observed in otherwise similar deposits in western australia and canada which display magnetite bearing pentlandite rich sulfide aggregates blebs in serpentinites and s rich millerite bearing assemblages in talc carbonates the black swan disseminated ores in contrast are dominated by millerite pyrite polydymite assemblages in both serpentinites and talc carbonates with no evident relationship to the progression of carbonation sulfides show three types of intergrowth with gangue minerals which can occur separately or all together intergrowth with magnetite at least some of which appear to be primary magmatic in origin fine intergrowth with interlocking lath textured antigorite and intergrowth with carbonate minerals carbonate commonly replaces the core of sulfide blebs while retaining the primary magmatic outline carbonate replacement of sulfide roughly parallels the overall progression of carbonation of the whole rock but no systematic relationship of the other intergrowth types to carbonate content is observed in the serpentinites serpentine mineralogy determined by microbeam raman spectroscopy comprises lizardite which occurs in pseudomorphic mesh textures after olivine and antigorite formed by variable degrees of overprinting of original lizardite mesh textures ranging to a completely overprinting interlocking texture with no relic igneous texture this progression is interpreted as the result of mild thermal metamorphism of original lizardite serpentinite this progression is completely independent of carbonate content and is also apparently independent of extent of sulfide antigorite intergrowth which is interpreted as being early and related to volume expansion during initial sea floor serpentinization talc is almost completely absent from serpentinites while carbonate content varies widely whole rock ni and s data are very strongly correlated in millerite poor pentlandite rich samples and poorly correlated in samples where millerite is the dominant ni bearing sulfide on this basis we conclude that the pentlandite assemblages are slightly modified survivors of the original magmatic event while the millerite pyrite assemblages formed during the earliest stages of serpentinization overprinting of the early serpentinization event by talc carbonate had essentially no effect on sulfide mineralogy other than inducing intergrowth with carbonate a number of distinctive features such as magnetite rich bleb cores the association of sulfides with segregation vesicles and chromite shells the subspherical morphology of the blebs and preferential replacement of bleb cores are considered to be inherited from the magmatic phase and are attributed to an original high but variable oxygen and halogen content of the sulfide melt component exsolution of this component during solidification of the blebs in some cases produced sulfide centered bubbles now preserved as segregation vesicles while in other cases oxygen was retained within the bleb forming magnetite sulfide intergrowths chromite shells formed as a result of exsolved oxygen interacting with komatiite magma volatile rich blebs solidified in some cases with hollow or porous cores which were subsequently exploited by carbonate replacement

new ams dates stratigraphic correlations and decadal climatic cycles for the past 4 ka at lake turkana kenya abstract new ams radiocarbon dates and stratigraphic correlations of 7 piston cores recovered from lake turkana east africa show that the frequency of cyclic variability is greater than previously reported for a single piston core almost 60 new ams dates of various carbonate fractions indicate that large 150 m ostracode carapaces yield the most accurate chronology for the sediment record due to the input of old fine grained carbonate stratigraphic correlations among the cores by carbonate abundance and magnetic susceptibility profiles provide supporting evidence for the ostracode based chronology this chronology refines earlier estimates of sediment accumulation that impacts the recurrence interval of lamination deposition from one lamination every two years to one lamination per year in two north basin cores the record of carbonate content within the north basin of the lake reflect its dilution with terrigenous sediments input from the omo river but direct paleoclimatic interpretations are complicated by lateral migrations of the delta channels with changing lake levels time series analysis of both individual cores and a combined carbonate profile show significant spectral peaks at 1000 76 32 22 18 6 and 11 yr the latter three suggest an important link between the sediments accumulating in lake turkana and global cycles of climatic variability

persistent late pleistocene holocene seasonal upwelling and varves off the coast of california abstract seasonal production of siliceous phytoplankton and a seasonal flux of terrigenous clastic material produced varved sediments along the continental slope off california during the late pleistocene to mid holocene light colored sediment within laminations and in sediment trap samples was deposited during summer upwelling and contains an abundance of the diatoms skeletonema costatum and chaetoceros spp resting spores dark colored sediment deposited in the fall and winter contains abundant thalassiosira pacifica and has more terrigenous material distribution of diatoms in varves shows that seasonal upwelling has persisted along the california coast and has remained strongly seasonal since the late pleistocene

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

the varve microcosm propagator of cyclic bedding changes in the proportion of seasonal components within varves accumulate over time to produce cyclic bedding a varve couplet is therefore a microcosm of bedding at a larger scale within the same stratigraphic unit cyclic bedding arises from a differing physical response or a phase shifted temporal response to climatic forcing an example from the permian castile formation suggests that the skipping of climatic cycles by the bedding response may be a common occurrence leading to erroneous estimates of the frequency of cyclic bedding seasonal changes that generate cyclic bedding occur in two domains of episodic sedimentation separated by a megathreshold between pelagic and advective environments cumulative changes responsive to seasonality within either domain can produce several types of cyclic bedding over a broad range of frequencies extending into the milankovitch band

geotechnical study on kordofan tropical black soils sudan republic abstract a study was made of the applicability of south kordofan tropical black clays sudan as a construction material for small earth dams in rural areas the broad task is to determine the design parameters and develop simplified design criteria for low cost small earth dams in semi arid regions the present work concentrates on the geological and basic geotechnical characteristics of kordofan tropical black clays soil samples were collected from ten locations in south kordofan province classification grain size distribution compaction tests and shear strength swelling chemical and mineralogical tests indicate that south kordofan black clays are very plastic expansive generally of low permeability and of moderate to low density most of the samples show an irregular compaction curve with peaks at very low water content 6 12 and at higher water content 19 26 probably attributable to the interaction between the physical e g fabric and chemical properties and the mineralogical composition some samples are moderately dispersive as a general conclusion these clays could be used for small earth dams successfully if attention is paid to compaction placement water content shrinkage fissures and filter design

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach argillaceous rocks cover about one thirds of the earth s surface the major engineering problems encountered with weak to medium strength argillaceous rocks could be slaking erosion slope stability settlement and reduction in strength one of the key properties for classifying and determining the behavior of such rocks is the slake durability the concept of slake durability index sdi has been the subject of numerous researches in which a number of factors affecting the numerical value of sdi were investigated in this regard this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices for the purpose different types of rocks marl clayey limestone tuff sandstone weathered granite were broken into chunks and were intentionally shaped as angular subangular and rounded and tested for slake durability before testing the aggregate pieces of each rock type their surface roughness was determined by using the fractal dimension despite the variation of final values of sdi test results values of id the rounded aggregate groups plot relatively in a narrow range but a greater scatter was obtained for the angular and subangular aggregate groups the best results can be obtained when using the well rounded samples having the lowest fractal values an attempt was made to analytically link the surface roughness with the id parameter and an empirical relationship was proposed a chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed the method proposed herein becomes efficient when well rounded aggregates are not available in such condition the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected id value the results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks

spoil pile instabilities with reference to a strip coal mine in turkey mechanisms and assessment of deformations with the increasing adoption of the surface mining of coal problems associated with spoil pile instability which affects resource recovery mining cost and safety and presents environmental hazards have become a matter of prime concern to mine planners and operators the study of geotechnical aspects is thus very important in the rational planning for the disposal reclamation treatment and utilization of spoil material a strip coal mine one of the largest open pit mines in turkey is located in central anatolia and provides coal to a thermal power station coal production is carried out in two adjacent open pits the central pit and south pit a large scale spoil pile instability over an area of 0 3 km2 occurred within the dumping area of the central pit in addition small scale movement occurred in the outside dumping area this paper outlines the results of field and laboratory investigations to describe the mechanisms of the spoil pile instabilities and to assess deformations monitored over a long period following the failure shear test results indicate that the interface between the floor and spoil material dumped by dragline has a negligible cohesion and is the most critical plane of weakness for spoil pile instability back analyses based on the method of limit equilibrium and the numerical modelling technique and observations in the pit revealed that failure occurred along a combined sliding surface consisting of a circular surface through the spoil material itself and a planar surface passing along the interface between the spoil piles and floor the analyses also indicated that pore water pressure ratios of about 0 25 satisfy limiting equilibrium condition and that rainfall about one month before the failure may be a contributing factor to the instability movement monitoring data obtained following the failure over a 1 5 year period suggested that the ongoing deformations were mainly due to compaction of the spoil material based on the monitoring data and the results of the analyses the failure mode of the local instability occurring at the outside dumping area was considerably similar to that of the large instability

district to camp controls on the genesis of komatiite hosted nickel sulfide deposits agnew wiluna greenstone belt western australia insights from the multiple sulfur isotopes the agnew wiluna greenstone belt of western australia is the largest komatiite hosted nickel sulfide belt in the world and contains two world class ni cu pge deposits and a host of smaller deposits this study focuses on the broader scale geology of this greenstone belt in order to understand the key controls on the genesis of the komatiite hosted ni cu pge deposits with specific focus on camp to district controls we apply multiple sulfur isotopes to this geologic framework and conclude not only that the addition of crustal sulfur is a prerequisite for ore genesis in komatiite systems but above all that the sulfur required to generate world class deposits is most likely derived from barren volcanic massive sulfide lenses which are spatially and genetically associated with felsic volcanic and volcaniclastic sequences that were emplaced coevally with large komatiitic sills and channelized lava flows multiple sulfur isotope data can be utilized in exploration at the deposit to district scales at the deposit scale the spatial pattern of mass independent s isotope values 33 s provides crucial insight into the identification of proximal high grade and high tenor ores in mineralized systems in fact sulfur data reflect the assimilation process that occurred upon komatiite emplacement whereby hot turbulent magma thermomechanically eroded and assimilated exhalative sulfides spatially located close to vent with negative to near zero 33 s values whereas less turbulent flows interacted with distal sulfidic shales having 33 s values above 0 per mil accordingly the spatial variation of multiple sulfur isotope values in magmatic sulfides and associated host rocks may be utilized as a vector towards high grade ores of poorly known systems at the district scale rather than ascertaining what controls the distribution of komatiite hosted ni cu pge deposits the appropriate question to ask is what controls the distribution of country rock sulfides considering that exhalative sulfides may be crucial to ore genesis in komatiite systems we propose that felsic lava domes unambiguously mark their vents and can be directly mapped or inferred from gravity data this work provides the first step in identifying district scale control on komatiite hosted ni cu pge deposits this is the scale that has high impact on exploration for new komatiite hosted nickel sulfide belts globally

bubble coalescence in basaltic lava its impact on the evolution of bubble populations morphological properties bubble number density porosity mean radius specific surface area of vesicular rocks provide quantitative information on the rates of bubble nucleation growth and coalescence in magmas when measured as a function of time such data are useful in constraining the timing and style of gas release during volcanic eruptions volcanic rocks commonly show strong zonation with respect to bubble size and porosity indicating a variation in the amount of bubble growth and coalescence preserved within a single sample morphological properties and bubble size distributions bsd s were measured in a suite of zoned alkali basalts using image analysis and the data were compared to theoretical predictions our data indicate that at porosities greater than 35 extensive coalescence occurred during the growth of bubbles with restricted nucleation at lower porosities vesiculation is dominated by nucleation and diffusion with no coalescence the interiors of many of our samples have undergone 4 7 binary coalescence events after eruption in a time of around 15 min the ostwald ripening effect has not significantly modified the bsd s

thermomechanical erosion of ore hosting embayments beneath komatiite lava channels textural evidence from kambalda western australia abstract archean komatiite hosted nickel deposits at kambalda western australia are located in embayments within channelized lava flows the origin of these embayments is controversial the currently favoured model invokes pre existing topographic features filled in by the komatiite and sulfide melt and subsequently modified by thermomechanical erosion new evidence from sulfide deposits on the eastern limb of the kambalda dome includes well preserved magmatic textural relationships of the sulfides with the surrounding rocks suggesting the entire embayment was formed by thermomechanical erosion these textures are particularly well preserved within the moran deposit of the long victor complex which lacks the younger intense structural deformation that other kambalda deposits have undergone the vestiges of an older broad concave embayment are represented by sediment sulfide textures present on the flanks up to 150 m away from the younger steep sided embayment sediment sulfide contacts are marked here by a globular silicate sulfide intergrowth interpreted as emulsion and cumulate like mono sulfide solid solution mss grains surrounded by interstitial silicate melt textures preserved from the formation of a steep sided embayment are frozen into the basalt sulfide contact and include an undulating contact with sulfide filled microfractures and a ferrichromite layer basalt sulfide breccia and interpreted crystallized silicate sulfide liquid emulsions and basalt plumes rising into the sulfides textures from the last step of embayment formation are found in the pinchouts i e where the massive sulfide ore is bounded top and bottom by basalt they include the same textures that were formed during the excavation of the steep sided embayment but they also feature interpreted basalt sulfide emulsions on the upper contact cm scale silicate sulfide ferrichromite layering on the upper contact and a vesicular basalt scum layer floating on the sulfides beneath the solid older basalt all these textures represent frozen examples of different stages during the excavation and formation of the embayment and reflect physical processes responsible for thermomechanical erosion the initial disposition and orientation of ore hosting channels was controlled by paleo topography probably defined by syn volcanic faults but the textures we describe show that within the channel the geometry of the entire embayment was the product of erosion the sulfide melt itself played a major role in the process owing to its high density high heat content and very low viscosity but the hydrated nature of the underlying altered basalt was also critical fluids were released from the basalt due to the high temperature in the 1 2 cm immediately beneath the sulfide melt with instant flash boiling creating a network of microfractures pre existing fracture networks and breccia in the basalt allowed the sulfide melt to locally infiltrate the substrate to a greater depth increasing the hydraulic head at the tip of the fracture thus accelerating the erosion process once a critical sulfide melt thickness is reached partly aided by a growing pile of matrix net textured sulfides the pressure difference on the embayment floor compared to the basalt at the bottom edges of the embayment becomes high enough to allow the liquid sulfides to melt sideways to form a pinchout

geotechnical characteristics of post glacial organic sediments in lake bergsee southern black forest germany in lake bergsee southern germany the upper 13 m of gyttja and detritus mud were deposited during the latest pleistocene and holocene these have been investigated for physical properties using mainly geotechnical methods and x ray computed tomography these deposits are extremely weak even compared with similar deposits in scandinavia and elsewhere it has been possible to recognise a significant change in the density and in the undisturbed undrained shear strength at a depth of 6 5 m which can be related to a change in the sediment type other variations in properties can be related to organic fibre length and mineral growth although compressibility has not been measured directly the deposits have the properties of a highly compressible sediment and estimates of effective stress and compression have been made the sediment column seems to have experienced very little shortening apparently because the microstructure of the organic sediments would hinder the movement of water under the expected sediment loads

patterns and causes of millennial scale climate change in the pacific northwest during marine isotope stages 2 and 3 abstract a high resolution pollen record from fargher lake washington shows a series of millennial scale changes in vegetation and climate during marine isotope stages mis 3 and 2 a comparison of fargher lake with pollen records from little lake oregon and carp lake washington reveals regional patterns of change during the early part of mis 3 ca 60 000 45 000 cal yr bp fargher and carp lakes indicate transitions between open and closed vegetation and cold dry and warm wet conditions between 45 000 and 27 500 cal yr bp all three records show shifts between low and high elevation taxa that indicate a series of temperature changes these temperature changes are similar to those in the santa barbara basin and may be explained by changes in the strength of the aleutian low during mis 2 27 500 14 000 cal yr bp shifts between wet and dry adapted taxa were most prominent at little lake there is also evidence for two minor warmings mis 2 climate variations do not correlate well with those in the santa barbara basin however precipitation changes in the pacific northwest during mis 2 correlate with evidence of ice sheet surges into the north atlantic and were probably related to variations in the strength and position of the glacial anticyclone and the jet stream

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

facies architecture of an archean komatiite hosted ni sulphide ore deposit victor kambalda western australia implications for komatiite lava emplacement nickel sulphide mineralisation is located in structural embayments or troughs at the base of thick basal komatiite lava flows at the victor ore body kambalda western australia primary contact relations and textural and vesicle distribution of the host komatiite lavas particularly the development of coherent or quench fragmented margins is consistent with emplacement of komatiites under laminar flow conditions however the absence of sedimentary units beneath komatiites with coherent flow tops in the ore environment seems contradictory and suggests both turbulent and passive laminar emplacement respectively the presence of erosive basal contacts in the ore environment suggests the komatiite lava was initially turbulent and probably open channel fed it is during this initial stage that both erosion and deposition of the nis deposits occurred as the flow evolved widened and thickened laminar flow conditions prevailed the komatiites are inferred to have flowed in a laminar state through the development of interior magma tubes beneath surface crusts and to have grown endogenously

stability of waste spoils in an area strip mine geological and geotechnical considerations results of investigations into the stability of coal mine spoil consisting of thick clay saturated sand and shale overburden in an areal strip mine are presented atterberg limits particle size distributions and compaction tests were performed to provide index characteristics of the materials unconsolidated undrained and consolidated undrained triaxial compression test results on 10 2 cm diameter samples of compacted shale and shale soil mixtures were used to investigate the short term and the long term conditions respectively of the spoil slope there is evidence that the failure envelope of mine spoil made up of shale or shale soil mixture is curved however stability analyses reveal that the use of strength parameters defined by a linear mohr coulomb envelope yields results that are comparable with those obtained when the non linear failure envelope is used provided that such strength parameters are defined at the operating normal stress level on the failure surface the study illustrates a very good case of spoil instability resulting from very thick overburden soils of low strength and high water content results show that the key to achieving stability in such areas lies in an almost total segregation of the soils from the rocks

geotechnical and geoenvironmental characteristics of man made underground structures in cappadocia turkey underground cities and semi underground settlements most of which are 1500 years at least exist in the cappadocia region of turkey these man made rock structures are carved in soft tuffs and the best examples of long term performance of man made structures in the field of rock engineering the tuffs also have good thermal isolation properties to be used as housing and storage of foods in this article the authors are only concerned with physical and short term mechanical characteristics due to the wide spectrum of the theme and the in situ characterization of the cappadocia tuffs and the results of investigations are presented in addition a critical overview on possible engineering geological problems at cappadocia with mechanical aspects of historical and modern rock structures and their implications in rock engineering is made from the experimental results in the field it is evident that the engineering characteristics of these rocks do not show significant changes in vertical and horizontal directions however they are prone to atmospheric conditions in addition temperature and humidity measurements at different floors of the underground cities and various parts of semi underground settlements indicated that variations in climatic conditions of the openings are very small when compared to those outside the ground surface

zoophycos cyclicity during the last 425 ka in the northeastern south china sea evidence for monsoon fluctuation at the milankovitch scale in a deep sea piston core covering the last 425 ka from the northeastern south china sea power spectrum analysis of several core data from sediment parameters has been conducted and compared with

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

engineering geological characterization of coal mine waste material and an evaluation in the context of back analysis of spoil pile instabilities in a strip mine sw turkey abstract coal mine waste material which usually consists of a mixture of coarse grained particles to rock fragments grading to fine grained particles causes geotechnical and environmental problems on disposal a study of the geotechnical aspects of the problem is therefore important in rational planning for the disposal reclamation treatment and use of such material spoil pile instability has been a continuing problem in the eskihisar strip coal mine of southwestern turkey particularly shallow seated circular failures appearing along the haul road and instabilities covering large agricultural areas outside the dumping yard increase the importance of spoil pile stability the fact that the height of spoil piles dumped by trucks on both sides of the haul road will increase much more in the future has focused the attention of the miners to this problem this study outlines the geotechnical characteristics of waste material from the tertiary coal bearing rocks derived from field and laboratory investigations and describes the causes and mechanism of spoil instabilities which threaten the safety of the haul road and the agricultural areas in the vicinity of the pit gradation results suggest that fines and coarser material were approximately equally represented in the spoil the percentage of fines is indicative of material degradation as evidenced by slaking tests site observations and numerous back analysis of investigated failures reveal that the failures do not penetrate the foundation material and only occur along circular surfaces through the spoil material it is also noted that surface water infiltration reducing the effective shear strength of the spoil material contributes to failures shear test results indicate that the spoil is a nearly cohesionless material with a residual internal friction angle of about 33 which confirms the values derived from standard penetration tests it is also noted from back analyses that the spoil material exhibits a shear strength at or approaching the residual value at the time of failure the use of shear strength parameters defined by the linear mohr coulomb envelope yields results that are comparable with those obtained when the non linear failure envelope is used provided that such strength parameters were defined at the operating normal stress levels on the failure surfaces

reply to comments by s yagiz on determination of strength parameters and quality assessment of denizli travertines sw turkey by ibrahim cobanoglu and sefer beran celik engineering geology 129 130 2012 38 47

ichnofabrics of a pleistocene slope succession new jersey margin relations to climate and sea level dynamics abstract trace fossil and sedimentologic data were collected at 10 cm intervals throughout a virtually continuous 520 m thick upper pleistocene siliciclastic succession recovered at odp site 1073 new jersey margin these data were examined in the context of isotopic seismic and palynologic proxies to document depositional and ichnologic responses to quaternary climate and sea level dynamics in an upper slope setting two broad texturally defined sedimentary facies assemblages are recognized the clay rich assemblage reflects relatively rapid deposition in part from turbidity currents and suspended plumes and appears to be linked to cooler sea level fall and lowstand phases the sand rich assemblage reflects overall slower sedimentation by offshelf spillover and periodic winnowing and erosion under the influence of contour and other bottom currents during warmer transgressive highstand phases facies of the sand rich assemblage muds sandy muds muddy sands and sands are completely bioturbated and are characterized by high densities of biogenic structures including distinct burrow forms in contrast the clay rich assemblage includes facies that exhibit limited biogenic disruption laminated clay silty clay and graded silt or fine sand to clay couplets and on the whole is characterized by lower densities of biogenic structures most of which are diffuse burrow mottles these ichnofabric trends reflect changes in ecological and taphonomic parameters e g substrate stability and consistency residence time of sediments in the benthic boundary layer and degree of inter and intrabed textural variability many of which were governed by variations in sedimentation rate as mediated by glacio eustacy recurring identifiable ichnofossils are most common in facies of the sand rich assemblage in the upper half of the pleistocene succession finer grained components of this assemblage e g muds and sandy muds representing quieter phases of highstand deposition are characterized by a low diversity distal cruziana ichnofacies assemblage dominated by schaubcylindrichnus and phycosiphon anconichnus both of which represent the work of deposit feeding worms narrow facies transitions that correspond to phases of rapid transgression are marked by occurrences of thalassinoides these crustacean burrow systems were excavated in coarser grained higher energy facies sands and muddy sands and in closely associated firmground substrates produced by exhumation of consolidated muds by bottom currents and or mass wasting processes the association of firmground ichnofabrics with marine flooding events in an upper slope setting demonstrates that the sequence stratigraphic utility of the glossifungites ichnofacies extends beyond shelf depositional sequences to deeper water deposits the distribution of texturally defined facies and general ichnofabric parameters e g degree of bioturbation appears to respond to glacio eustatic cycles through the entire pleistocene record however the schaubcylindrichnus phycosiphon assemblage and thalassinoides are rare or absent altogether in the lower half of the succession indicating that biological responses to and the ichnologic record of climate and sea level dynamics may be strongly dependent on margin physiographic and bathymetric evolution

evidence for a stronger oxygen minimum zone off central california during late pleistocene to early holocene of 31 deep sea cores collected along the central california continental slope 18 have distinctly laminated sediment at depth but none have laminations in the top few centimetres the cores with laminated facies are restricted to water depths between 508 and 1508 m but not all cores taken from this depth interval have laminated facies 14 c dates yield an extrapolated age of 4700 b p for the top of the uppermost laminated unit comparisons of the diatom flora in the laminated couplets with diatom floras in a 13 month sediment trap record suggest that the laminations are varvelike couplets of seasonal sedimentation the laminated facies represent a period from the last global deglaciation to early holocene when the oxygen minimum zone along the northeastern pacific ocean was stronger than at present a stronger oxygen minimum zone during this time is inferred to be the result of intensified upwelling

vesicular komatiites 3 5 ga komati formation barberton greenstone belt south africa inflation of submarine lavas and origin of spinifex zones komatiites of the 3 5 ga komati formation are ultramafic lavas 23 mgo erupted in a submarine lava plain environment newly discovered vesicular komatiites have vesicular upper crusts disrupted by synvolcanic structures that are similar to inflation related structures of modern lava flows detailed outcrop maps reveal flows with upper vesicular zones 2 15 m thick which were 1 rotated by differential inflation 2 intruded by dikes from the interior of the flow 3 extended forming a flooded graben and or 4 entirely engulfed the largest inflated structure is a tumulus with 20 m of surface relief which was covered by a compound flow unit of spinifex flow lobes the lava that inflated and rotated the upper vesicular crust did not vesiculate but crystallized as a thick spinifex zone with fist size skeletal olivine instead of representing rapidly cooled lava the spinifex zone cooled slowly beneath an insulating upper crust during inflation overpressure of the inflating lava may have inhibited vesiculation this work describes the oldest vesicular komatiites known illustrates the first field evidence for inflated structures in komatiite flows proposes a new factor in the development of spinifex zones and concludes that the inflation model is useful for understanding the evolution of komatiite submarine flow fields

holocene glacier and deep water dynamics adelie land region east antarctica abstract this study presents a high resolution multi proxy investigation of sediment core md03 2601 and documents major glacier oscillations and deep water activity during the holocene in the adelie land region east antarctica a comparison with surface ocean conditions reveals synchronous changes of glaciers sea ice and deep water formation at milankovitch and sub milankovitch time scales we report 1 a deglaciation of the adelie land continental shelf from 11 to 8 5 cal ka bp which occurred in two phases of effective glacier grounding line retreat at 10 6 and 9 cal ka bp associated with active deep water formation 2 a rapid glacier and sea ice readvance centred around 7 7 cal ka bp and 3 five rapid expansions of the glacier sea ice systems during the mid to late holocene associated to a long term increase of deep water formation at milankovich time scales we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier sea ice ocean system throughout the holocene in the adelie land region in addition the orbitally forced seasonality seems to control the coastal deep water formation via the sea ice ocean coupling which could lead to opposite patterns between north and south high latitudes during the mid to late holocene at sub milankovitch time scales there are eight events of glacier sea ice retreat and expansion that occurred during atmospheric cooling events over east antarctica comparisons of our results with other peri antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier sea ice ocean interactions and their holocene evolutions reflect a more global antarctic holocene pattern

warm water mollusc assemblages from northern chile mejillones peninsula new evidence for permanent el nino like conditions during pliocene warmth although results have been controversial understanding the tropical pacific climatic state during the pliocene warm interval c 4 5 3 0 ma is crucial if insight is to be gained into the dynamic processes of present and future global warming in the multi proxy effort to reconstruct ancient climates a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature sensitive marine molluscs shallow water strata of the mejillones peninsula northern chile 23 s contain dense faunal assemblages in which molluscs exclusive to or characteristic of pliocene deposits chlamys simpsoni chlamys vidali chorus blainvillei concholepas nodosa fusinus remondi herminespina mirabilis coexist with surprisingly abundant and varied populations of extant warm water species bulla punctulata cerithium stercusmuscarum olivella sp turbo cf fluctuosus anomia peruviana argopecten ventricosus donax peruvianus dosinia ponderosa mexicardia procera undulostrea megodon most of which have their current southern zoogeographical limit at 6 s these tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures sst along the northern chile coast were at least 2 c warmer in the mid pliocene than at present and that these very different conditions lasted long enough to allow stable colonization of the area such a significantly warmer sst pattern strongly resembles general climatic conditions accompanying modern el nino events when warm tropical waters propagate southward along the western margin of south america this supports the existence in this area of persistently el nino like conditions during the mid pliocene

vesicles in thick komatiite lava flows kambalda western australia traditionally vesicles have been considered to be rare in komatiites however field studies at kambalda western australia and critical literature examination suggest that vesicle presence and content in komatiites are grossly underestimated at kambalda vesicles are observed in significant amounts up to 30 in internal horizons within komatiite lavas the vesicular horizons are inferred to represent bubbles frozen in place below the upper crust during multiple episodes of flow through of bubble rich lava we conclude that vesicle and crystal distribution are compatible with many komatiites being emplaced under laminar flow conditions analogous to models for basalt lava emplacement

komatiites and nickel sulfide ores of the black swan area yilgarn craton western australia 2 geology and genesis of the orebodies the black swan ultramafic succession hosts a number of magmatic fe ni cu pge sulfide ore shoots ranging from high grade massive ore to low grade disseminated sulfides of these the most economically significant is the silver swan massive sulfide orebody associated with the basal contact of the succession the deposit varies in thickness between 5 and 20 m reaches a n s strike length of 75 m extends for at least 1 2 km of vertical plunge and is open at depth overlying matrix net textured ore is rare inclusions of dacite are abundant within the lower 5 m of the massive sulfide they range from angular fragments through smooth sinuous and plumose morphologies to fine lace like intergrowths with the sulfide matrix and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures some well above their liquidus temperature the composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30 komatiite the consistent thickness of the inclusion bearing basal layer within the massive sulphide is interpreted as the extent of 3 d physical connectivity between the inclusions and a partially molten underlying hybrid layer primary contacts between the silver swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse grained chevron textured chromites with skeletal textures compositions of these chromites match those from kambalda perseverance and other localities and are inconsistent with a metamorphic origin they are interpreted as markers of primary magmatic contacts the combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates taken together with observations on the internal fractionation of platinum group elements within the massive ores these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube the floor of the tube had been previously heated by passage of large volumes of lava such that it had reached its melting range the felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma this constitutes strong evidence for the operation of thermo mechanical erosion during ore emplacement the disseminated cygnet and black swan orebodies show a number of distinctive features cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip up transport and redeposition of sulfides from a pre existing massive sulfide orebody of which black duck may be a remnant the black swan orebody by contrast does not show xenolithic features but is characterised by an association of sulfide blebs with segregation vesicles and by unusually coarse grained olivine the black swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals

pelletal structures in peruvian upwelling sediments late quaternary sediments from the peru upwelling zone have been investigated using backscattered electron imagery the dysaerobic to anaerobic conditions which persist within the strong oxygen minimum zone intersecting the shelf and upper slope sediments have resulted in the preservation of a wide range of microscopic fine structure relating to biological activity two forms of pelletal structures are present pellets and aggregate structures 1 pellets are oval in cross section with a mean diameter of 610 m and sharp boundaries three common pellet types have been identified a crushed diatom and clay pellets b intact diatom pellets and c silt pellets 2 aggregate structures are smaller than pellets with a mean diameter of 360 m they have indistinct boundaries and may be composed either of pure diatom ooze or a mix of clay silt and diatoms the size shape and mode of occurrence of aggregate structures suggest that they are the product of a meiofauna redistributing the topmost sediment during periods of very slight increases in oxygen most of the crushed diatom clay pellets and intact diatom pellets are probably also the product of a surficial deposit feeding fauna tolerant of low dissolved oxygen levels such as polychaete worms silt pellets may record the chamber building activities of agglutinating foraminifera

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

the nickeliferous late archean reliance komatiitic event in the zimbabwe craton magmatic architecture physical volcanology and ore genesis the widespread komatiitic reliance lithostratigraphic unit of the late archean bulawayan supergroup consists of many submarine flow fields directly or indirectly overlying the sedimentary manjeri unit which varies from a generally carbonaceous sulfide rich deep water basinal facies in the north and west parts of the zimbabwe craton to a generally sulfide poor shallow water platformal facies in the south and east the flow fields are associated with high level subvolcanic feeder sills intruded into pre manjeri basement made up of the conformable sulfide bearing felsic koodoovale unit and older barren granitoid greenstone crust in the north and west and south and east respectively the sills and flow fields together constitute largely discrete sill flow complexes very approximately 100 km in diameter of which five are well preserved in the north and west and three in the south and east parts of the craton the reliance sills up to 40 km in diameter and 2 000 m thick some composite and locally overlapping to slightly discordant mostly comprise a thick lower dunite peridotite and a relatively thin to intermittent upper pyroxenite gabbro other larger probably related sills intruded at greater structural depths link adjacent complexes and form midcrustal magma chambers the reliance sills are interpreted as an interconnected system of flow through feeders at different crustal levels the reliance flow fields are 33 to 85 km in diameter and up to 2 500 m thick dominantly of komatiitic basalt composition of very low height breadth aspect ratio locally linked to the sills via structures interpreted as fissure vents and partly extrusive cryptodomes and thin out toward their lateral margins most display a simple coherent volcanological growth sequence from sheet and or channelized sheet flows and lava channel complexes in lower and proximal positions to marginal lava lobes in upper and distal positions comparable in general organization and probable emplacement processes to those of hawaiian and flood basalt flow fields flow field development was influenced by episodic eruption preexisting topographies and penecontemporaneous sedimentation and felsic and mafic volcanism and some flow fields in the south and east were partly emergent sills in the north and west are weakly mineralized but those in the south and east are barren the principal reliance nickel sulfide deposits are confined to flow fields in the north and west occur within lava channel complexes trojan and shangani mines damba silwane and hunters road prospects and a fissure vent epoch mine and include type 1 basal sequences of massive to matrix to disseminated sulfides lowermost flows trojan shangani and type 2 central accumulations of weakly disseminated sulfides hunters road upper flows trojan shangani epoch and shangani occupy central flow field positions whereas hunters road and damba silwane are proximal trojan may be either distal or proximal field evidence does not directly support the origin of the reliance deposits solely by magmatic erosion of sulfidic substrate during flow emplacement as proposed for komatiite hosted nickel deposits elsewhere instead the deposits origin and asymmetric distribution across the craton may be mainly due to assimilation of sulfidic felsic wall rocks during magma passage through the subvolcanic sills in the north and west possibly combined with sulfur degassing due to very shallow water lava emplacement in the south and east

expression of seasonal and enso forcing in climatic variability at lower than enso frequencies evidence from pleistocene marine varves off california abstract upper pleistocene marine sediments along the upper continental slope off northern and central california contain alternations of varved and bioturbated sediments and associated changes in biota and sediment composition these alternations can be related to conditions that accompany el nino and anti el nino enso circulation anti el nino conditions are characterized by increased upwelling and productivity and by low concentrations of dissolved oxygen in the oxygen minimum zone that resulted in varve preservation el nino conditions are characterized by little or no upwelling low productivity and higher concentrations of dissolved oxygen that resulted in zones of bioturbation alternations of varves and zones of bioturbation that range from decades to millennia occur through the upper pleistocene section the inferred long term alternations in el nino and anti el nino conditions appear to be a re expression of enso s primary 3 7 year cycle decadal to millennial cycles of productivity associated with el nino and anti el nino conditions may have served as a carbon pump and transferred atmospheric co 2 to the marine reservoir changes in sediment composition and organisms associated with el nino or anti el nino conditions can be related to both seasonal and enso phenomena expression of these changes at lower than enso frequencies may be partly explained by adding the effects of seasonal variability to effects produced by a self oscillating enso system however deterministic mechanisms including solar modulation of enso may also contribute to long term alternations of el nino and anti el nino conditions

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

peru coastal currents during el nino 1976 and 1982 year long measurements of subsurface current and temperature on peru9s continental shelf included the onset of el nino in 1976 and 1982 the peru coastal undercurrent more than doubled in speed and advected anomalously warm water poleward el nino began in different seasons in 1976 and 1982 but the current and temperature responses were very similar acceleration of poleward flow at 10 s occurred several days after sea level rose at the galapagos islands in october 1982 suggesting the onset of el nino propagated as a kelvin wave

facies analysis and correlation of high order sequences in middle outer ramp successions variations in exported carbonate on basin wide δ13ccarb kimmeridgian ne spain carbonate mud that accumulated in the deep parts of a late kimmeridgian carbonate ramp iberian basin ne spain was partly derived by resedimentation from shallow water production areas high frequency sea level changes probably driven by climatic changes in tune with precession and short eccentricity cycles affected carbonate production and the amount of exported sediment facies analysis and correlation of three outcrops located in middle and outer ramp settings allows a comparison of high order sequences bundles of beds and sets of bundles across a ramp transect and an assessment of the carbonate factory analysis of the storm deposits found in middle ramp settings identifies deepening to shallowing high frequency cycles based on the level of exported carbonate in outer ramp areas many of the bundles exhibit a thinning trend indicating a progressive decrease of carbonate production and hence carbonate export during periods of high frequency sea level rise 13ccarb values show a gradual increase through the studied long term transgressive interval ranging from 1 5 to 2 8 within this long term evolutionary trend short term 13ccarb fluctuations occur that correspond with some of the high order cycles defined from sedimentary facies analysis these short term 13ccarb shifts are interpreted as shifts in carbonate export from shallow reef regions to the outer ramp a consequence of this study is that variation in 13ccarb can be used for correlation in outer ramp successions at least on a basin wide scale

komatiites and nickel sulphide orebodies of the black swan area yilgarn craton western australia 1 petrology and volcanology of host rocks the black swan succession is a bimodal association of dacitic and komatiitic volcanic rocks located about 50 km nne of kalgoorlie within the 2 7 ga eastern goldfields greenstone province of the yilgarn craton the komatiite stratigraphy comprises a steep dipping east facing package about 700 m in maximum thickness and about 2 5 km in strike length fig 1 which hosts a number of economically exploitable ni sulphide orebodies including the silver swan massive ore shoot approximately half a million tonnes at about 10 5 ni the sequence can be subdivided into a lower felsic unit comprising coherent and autobrecciated facies of multiple dacite lava flows an upper eastern and lower western ultramafic unit each showing marked lateral facies variation and an upper felsic unit coeval with the eastern ultramafic unit the komatiite sequence has been metamorphosed at sub greenschist facies in the presence of high proportions of co2 rich fluid giving rise to pervasive talc carbonate and talc carbonate quartz assemblages with extensive preservation of pseudomorphed igneous textures cores of lizardite serpentinite are present in the thickest parts of the ultramafic succession the degree of penetrative deformation is generally very low and original stratigraphic relationships are largely intact in much of the sequence the eastern ultramafic unit and western ultramafic unit are interpreted as components of a single large komatiite flow field representing overlapping stages in the emplacement of a series of distributory lava pathways and flanking sheet flows the western ultramafic unit which hosts the bulk of the high grade massive and disseminated ores is a sequence dominated by coarse grained olivine cumulates 2 km wide and up to 500 m thick with major magma pathways represented by thick homogenous olivine mesocumulate piles at its northern and southern ends respectively 400 and 200 m thick the sequence between the two major pathways consists of olivine orthocumulates ooc with minor spinifex textured intervals the unit is capped by a persistent spinifex textured crust less than 1 m thick and is locally vesicular the eastern ultramafic unit contains the black swan cumulate zone a 500 m thick sequence of very coarse grained hopper textured locally vesicular ooc containing disseminated sulphides in its lower 200 m the zone is flanked to the north and south by complexly interdigitated sequence of highly irregular spinifex capped olivine cumulate rich flow lobes between 1 and 100 m thick and dacitic lavas and tuffs the complexity of the 3 d spatial relationship of these units suggests a combination of simultaneous eruption of dacite and komatiite combined with thermal or thermomechanical erosion the eastern and western units are interpreted as the result of more or less continuous prolonged eruption of olivine charged komatiite lava which developed localised thermo mechanical erosion channels in the dacitic substrate komatiite and dacite eruption was synchronous giving rise to complex interdigitation and extensive contamination and hybridisation

a komatiite analog to potential ultramafic materials on io ultramafic volcanism is one model which fits currently available data for some eruptions on jupiter s moon io assuming that such activity does occur it is possible to apply komatiitic analogs and terrestrial ultramafic flow models to io we have used such analogs and models along with galileo data to investigate the nature of ultramafic materials that are assumed to occur at high temperature hotspots on io the unusual komatiites of the commondale greenstone belt south africa are consistent with available galileo data on the temperatures and composition of potential ionian ultramafic materials these komatiites had high sio2 50 wt and mgo 31 wt contents which are inferred to result in high liquidus temperatures 1610 c low dynamic viscosities 0 2 pa s and low densities 2680 kg m and in the crystallization of orthopyroxene phenocrysts not found in other komatiites we used the commondale composition and the model of williams et al 1998 to investigate potential ultramafic flow behavior on io compared to their terrestrial counterparts ionian ultramafic lava flows would have less potential for turbulent flow lower maximum emplacement distances and lower thermal erosion rates because of the lower ionian gravity and their more silicic composition shallow 10 m thermal erosion channels seem less likely on io unless 1 lavas are superheated 2 lavas are more ultramafic 31 mgo 3 eruption rates eruption durations or flow volumes are high or 4 substrates are unconsolidated partly consolidated or volatile rich and thus more erodable if volatiles are present in the lava as vesicles then increasing lava vesicularity results in decreasing maximum emplacement distances decreasing thermal erosion rates and decreasing erosion channel depths for given eruption durations

droplets and bubbles solidification of sulphide rich vapour saturated orthocumulates in the norilsk talnakh ni cu pge ore bearing intrusions

new approaches to the characterization of clay bearing densely jointed and weak rock masses various classification systems for rock masses have been used in engineering applications however these systems are not sufficient to classify clay bearing densely jointed and weak rock masses among the factors that cause this deficiency are the damaging effect of water on rocks which has not sufficiently been described in the existing classification systems this factor was allowed for by the inclusion of new parameters in the modified rock mass classification m rmr system developed in recent years the aim of this study is to make contributions to the m rmr classification system and to overcome the difficulties encountered in the classification procedure for this purpose data were collected for rock mass classification from 13 clay bearing densely jointed and weak rock masses in four regions yatagan soma baskoyak and guvenc located in the western and middle parts of turkey the discontinuity data were collected by the line survey technique and evaluated by statistical methods in addition to the uniaxial compressive strength test for the determination of the rating for intact rock strength the block punch index test was also considered as an alternative parameter and the slake durability index test and x ray diffraction analyses were performed on 104 samples collected from the studied rock masses further the weathering coefficient wc determined by schmidt hammer was considered as an alternative parameter for the determination of the rating for joint weathering as a result of statistical evaluation of data obtained from the field and laboratory studies it has been concluded that the block punch index bpi could be used as an alternative parameter for the determination of the rating for intact rock strength in the m rmr classification system it was also found that the slake durability index id determined at the fourth cycle would be a more effective approach than the second cycle index that has previously been used to express the unfavourable effect of water on the rock mass the propositions made in the present work to contribute to the m rmr system were tested in back analyses of three previously failed slopes and the performance of the system with the newly introduced improvements appeared to be satisfactory

geotechnical characterization of lignite bearing horizons in the afsin elbistan lignite basin se turkey abstract the afsin elbistan lignite deposit with its 3 4 billion metric tons of reserves is the biggest lignite basin and one of the most important resources for electrical energy production in turkey kislakoy mining field was selected as the first opencast mine to feed four power station blocks of 300 mw each slope instability has been a continuing problem in the kislakoy opencast mine particularly complex failures along a noncircular failure surface appearing at the final slope stage and covering large areas in the mine increase the importance of slope stability this study outlines the geotechnical characteristics of the lignite bearing horizons and describes the causes and mechanisms of slope instabilities which threaten the safety of the mine quantitative x ray diffraction xrd analyses were carried out using an interactive data processing system siroquant based on rietveld interpretation methods parametric slope stability analysis and backanalysis were carried out for the failure that occurred at the northwestern final slope stage of the mine the spencer wright limiting state equilibrium method was used in order to determine with confidence the most representative values of regional shear strength parameters to explain the failure mechanism and to assess the conditions at the time of failure in the analysis phreatic and piezometric surfaces were considered site observations and numerous backanalyses of the slope failure reveal that a compound slide occurred where gyttja contact zone layers rest directly on the lignite gyttja contact zone contains the weakest material within the system the analysis showed that the main cause of the northwestern slope instability was the presence of the groundwater flow within a quaternary aquifer through buried valleys reducing the effective shear strength of the slope materials it is also noted from backanalysis that the gyttja contact zone layer presents a shear strength at or approaching the residual value at the time of failure

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

climatically induced lake level changes at lake van turkey during the pleistocene holocene transition sediment core k10 from lake van eastern turkey provides a continuous varve record back to 14 570 calendar years b p before present 1950 the longest unbroken and non floating lake varve sequence yet described the underlying sediment is unvarved and hard changes in the aragonite calcite ratio the presence of protodolomite and magnesite in certain profile sections the annual record of the sedimentation rate the water content of the sediment the concentrations of organic carbon and opal and the texture of the sediments from this core provide a record of the lake level history the new chronology enabled us to redate the old pollen profile van zeist and woldring 1978a b and to establish an accurate timescale for the reconstructed lake level change carbon 14 dates show that the highest lake terrace corresponds to high lake level at around 19 000 years b p during the last glacial 70 m above its present level before 15 000 years b p the lake must have been completely dry marking a reduction of lake level by 500 m in maximum 4000 years beginning at 14 600 years b p and ending at 12 040 years b p the lake level recovered by 250 m to fall again during the next 1400 years by 10 600 years b p the lake began to rise and reached following another regression between 9000 and 8100 years b p the holocene highstand by about 7500 years b p dropping to today s level at about 3000 years b p

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

the volcanology of komatiites as deduced from field relationships in the norseman wiluna greenstone belt western australia abstract komatiites in the western part of the norseman wiluna greenstone belt in the yilgarn block of western australia display a wide variety of volcanic facies ranging from very thin differentiated munro township type flow units through to very thick olivine rich cumulate flow units containing high proportions of adcumulate dunite cumulate flow units have been mapped in detail in the agnew wiluna segment of the norseman wiluna greenstone belt in the yakabindie and mt keith areas thick lenticular bodies of olivine adcumulate are flanked and overlain by thinner sheet like sequences of finer grained olivine orthocumulates they show fine scale internal layering broad scale cryptic layering and upper fractionated sequences containing harrisites pyroxene bearing cumulates and in some cases gabbroic derivatives low grade disseminated sulphide mineralisation occurs within the dunite lenses in the stratigraphically equivalent kathleen east area adcumulate dunite grades laterally into olivine orthocumulates and spinifex textured flows a similar relationship is also seen further south where the perseverance ultramafic complex consists of a thick central dunite lens flanked on one side by thin fine grained orthocumulate sequences and on the other by intercalated orthocumulates and spinifex textured flows these field relationships indicate an extrusive origin for the adcumulate dunite bodies the walter williams formation in the west central part of the norseman wiluna belt is a very large cumulate flow unit 150 km long and 30 km wide in presently exposed extent it consists of a central sheet like body of adcumulate dunite underlain and overlain by olivine orthocumulates the adcumulate sheet is everywhere capped by a distinctive thin layer of olivine harrisite at its northernmost extent the flow unit consists of cyclically layered olivine and pyroxene bearing cumulates capped by gabbros dolerites and pyroxene spinifex textured material interpreted as a periodically replenished lava lake sequence both the lenticular dunite bodies of the agnew wiluna belt and the sheet like dunite body of the walter williams formation are interpreted as crystallisation products of very large submarine komatiite lava flows which erupted and flowed at very high rates the adcumulate dunites are interpreted as the products of in situ crystallisation at low degrees of supercooling at the top of upward and inward accreting crystal piles at the bases of the flows flanking and overlying olivine orthocumulates reflect higher rates of heat loss at the site of crystallisation due to lower lava flow rates field evidence from perseverance and the general geometry of the dunite lenses suggest that the lenses formed within large thermal erosion channels developed by turbulent lava rivers flowing over low melting felsic volcanic substrates the textural range exhibited by komatiites can be integrated into a comprehensive model for the geometry of large komatiite flow fields formed by rapid extrusion dunite sheets form close to the eruption sites and dunite lenses as a result of channellisation further away from the vent or close to the vent in the situation where the substrate is non refractory and thermal erosion can take place readily kambalda type volcanic facies develop in more distal environments where lava emplacement is channellised and episodic and munro type flow units represent small scale lava tubes formed at low flow rates on the distal flanks of major eruptions or close to the vent of very small ones waning eruption rates leads to proximal facies being overridden by distal ones a common observation in komatiite sequences the size of thermal erosion channels requires very rapid eruption rates comparable to those in phanerozoic flood basalt terrains

modern and palaeo oceanographic environments under benguela upwelling cells off southern namibia averaged benthic physical and chemical and key microfaunal ostracoda parameters of the bottom waters and substrate allow a ranking of the intensity of upwelling in the modern cells off southwestern africa b1 b6 b1 namib cell temperature salinity dissolved oxygen total organic matter 10 3 c 34 94 1 2 ml l 6 2 palmoconcha walvisbaiensis cytherella namibensis garciaella knysnaensis robusta and neocaudites lordi b2 walvis cell 11 0 c 35 00 1 0 ml l 9 2 palmoconcha walvisbaiensis cytherella namibensis garciaella knysnaensis robusta buntonia rogersi neocaudites lordi and ruggieria cytheropteroides leeward side only b3 luderitz cell 9 1 c 34 77 1 8 ml l 6 3 palmoconcha walvisbaiensis cytherella namibensis incongruellina venusta kuiperiana angulata and ruggieria cytheropteroides leeward side only b4 namaqua cell 10 0 c 34 82 2 4 ml l 3 1 pseudokeijella lepralioides and ruggieria cytheropteroides b5 columbine cell 8 3 c 34 70 3 1 ml l 3 9 ruggieria cytheropteroides pseudokeijella lepralioides poseidonamicus panopsus and ambostracon a flabellicostata b6 peninsula cell 8 9 c 34 63 3 6 ml l 1 9 pseudokeijella lepralioides ambostracon a keeleri cytherella dromedaria neocytherideis boomeri xestoleberis africana neocaudites osseus coquimba birchi and urocythereis arcana pleistocene palaeo upwelling characteristics of the shelf north west of luderitz are investigated by analysing the ostracod faunas sediment textures and mineralogy of three large volume gravity cores q mode factor analyses using previously published transfer functions allow predictions for benthic environmental parameters during the late pleistocene the area experienced less intense upwelling and lower primary productivity than at present in an environment equated with a modified peninsula cell b6 b7 cell 9 6 c 34 73 3 2 ml l 3 9 neocaudites lordi ambostracon a keeleri bairdoppilata simplex paracypris lacrimata parakrithella simpsoni xestoleberis hartmanni ruggieria cytheropteroides and pseudokeijella lepralioides in middle and early pleistocene late pliocene times the core sites lay closer inshore adjacent to evaporite halite and authigenic phosphorite rich lagoons with a high intensity upwelling walvis like cell b1 to the north west and a low intensity upwelling cell b7 to the south

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

origin of vesicle layering and double imbrication by endogenous growth in the birkett basalt flow columbia river plateau abstract the 40 m thick birkett basalt pahoehoe flow at sentinel gap in the columbia river plateau has an unusually thick 15 m upper vesicular zone this zone includes a striking layering in which the layers have contrasted vesicle abundances and sizes most layers show a reverse grading of vesicle size and abundance the layering is interpreted to have grown endogenously by the cyclic injection of vesicular lava layers under the growing top crust accommodated by uplift of that crust grading of the layers resulted from vesicle growth and ascent each injection occurred at or near the boundary between vesicular and non vesicular lava of the preceding layer and split that layer into an upper vesicular part and a lower non vesicular part critical to this interpretation are 1 a pervasive foliation and lineation defined by the parallelism of strongly flattened and elongate vesicles transects the vesicle layers obliquely and 2 the magnetic fabric the anisotropy of magnetic susceptibility is oriented similarly to the vesicle foliation and also defines a cryptic foliation in the non vesicular zone having a dip opposed to that in the layered zone these foliations are interpreted to be opposed imbrications and indicate the flow azimuth of the lava they strongly support the concept of lava growth by successive thin sill like insertions of fresh vesicular lava between hot but static and effectively solid floor and roof

endogenous growth in channelized komatiite lava flows evidence from spinifex textured sills at pyke hill and serpentine mountain western abitibi greenstone belt northeastern ontario canada spinifex textured sills i e veins characterized by komatiitic magmas that have intruded their own volcanic piles have long been recognized for instance in the early 1970s pyke and coworkers in their classic work at pyke hill in munro township noted that not all spinifex bearing ultramafic rocks formed as lava flows rather some were clearly emplaced as small dikes and sills several hypotheses have been proposed to explain spinifex textured sills intrusion into a cold host filter pressing or drainage of residual liquid however these do not satisfactorily explain the phenomenon field and petrographic observations at pyke hill and serpentine mountain demonstrate that spinifex bearing komatiite sills and dikes were emplaced during channel inflation processes when new magma was intruded into a cooler semi consolidated but permeable cumulate material komatiitic liquids were intruded into the olivine cumulate rocks near the boundary between the spinifex and the cumulate zones of well organized to organized komatiite flows spinifex textured sills are generally tabular in morphology stacked one above another with curviplanar contacts sub parallel to stratigraphy some sills exhibit complex digitated apophyses thinner sills typically have a random olivine spinifex texture similar though generally composed of coarser crystals to that of komatiite lava flows thicker sills exhibit more complex organization of their constituent crystals characterized by zones of random olivine spinifex overlying zones of organized coarse spinifex crystals similar to those found in lava flows they have striking coarse dendritic spinifex zones composed of very large olivine crystals up to several centimetres long and up to 1 cm wide that are not observed in lava flows typically at the sill margins the cumulate material of the host flow is composed of euhedral to subhedral olivine crystals that are larger than those distal to the contact many of these margin crystals have either concentric overgrowth shells or dendritic olivine overgrowths that grew from the cumulate sill contact toward the sill interior the dendrites grew on pre existing olivine cumulate at the contact in response to a sharp temperature gradient imposed by the intrusion of hot material whereas the concentric overgrowths formed as new melt percolated into the unconsolidated groundmass of the host flow cumulate material spinifex textured sills and dikes occur in well organized to organized flows that are interpreted to have formed by breakouts above and peripheral to lava pathways channels conduits as a result of inflation that accompanied voluminous komatiitic eruptions responsible for the construction and channelization of komatiitic flow fields the spinifex textured dikes and sills represent komatiitic lava that was originally emplaced into the channel roof during periods of episodic inflation that resulted in lava breakouts and was subsequently trapped in the roof rocks during periods of channel deflation accordingly the occurrence of spinifex textured sills and dikes may indicate proximity to and aid in the identification and delineation of lava channel ways that could potentially host ni cu pge mineralization within komatiitic lava flow fields

bioturbated oxygenation event beds in siliceous facies monterey formation miocene california abstract predominatly laminated marine diatomaceous sequences deposited in oxygen deficient neogene basins typically contain bioturbated intervals that reflect episodes of improved benthic oxygenation excellent exposures of the siliceous facies of the miocene monterey formation near lompoc central california provided an opportunity to assess the ichnology and sedimentology of 200 such event beds in their general paleogeographic paleoclimatic and sea level context and hence to evaluate the character and causes of associated oxygenation episodes four recurring event bed types type i iv are distinguished on the basis of ichnologic characteristics these types fall into two general groups delineated on the basis of sedimentologic attributes primarily texture group 1 beds type i only have 1 homogeneous bioturbate primary strata that are more clastic rich and much coarser than surrounding laminated diatomites and 2 vertically extensive piped zones characterized by firmground thalassinoides paradoxicus glossifungites ichnofacies these characteristics indicate that group 1 events involve coincident increases in bottom current intensity clastic input and benthic oxygenation some group 1 beds may be the product of turbidity current transport of sediments trauma resistant crustaceans and allochtonous waters however most group 1 beds more likely record climate and sea level mediated migratio of incipient bank top conditions down the flank of a submergent topographic high group 2 beds types ii iii and iv are characterized by primary strata that are only slightly coarser and more clastic rich than surrounding laminites ichnofabrics and trace fossil assemblages which are dominated by burrows of deposit feeders thalassinoides suevicus meniscate backfilled structures and chondrites reflect normal softground substrates and quiet water pelagic deposition zoophycos ichnofacies differences in ichnologic parameters bed thickness adn presence diversity size and vertical extent of discrete burrows in primary strata and or piped zones among the bed types within this group reflect differences in magnitude duration and to a lesser extent frequency of oxygenationepisodes coincident increases in oxygenation and clastic content recorded by group 2 beds are attributed to e1 nino like climatic events gross temporal patterns in the intensity and frequency of these climatic events appear to be linked to the phases of a third order sea level cycle whereas shorter term variations 100 120 ka may have been mediated by milankovitch cyclicity relationships established between bioturbation events and relative water depth are of potential use in reconstructing basin paleogeography and or recognizing the signal of sea level change in the monterey formation and other neogene siliceous sequences

an investigation of landslide problems in spoil piles in a strip coal mining area west virginia u s a abstract spoil piles in coal mine areas in north central west virginia suffer from numerous landslide problems an investigation to determine the causes of these slides showed that the stratigraphic composition the nature of the foundation soils the seasonal high water table and the mining technique contributed to the instability the presence of red shales is identified as a key problem several models of failure were investigated based on inclinometer data these data suggest that multiple failure surfaces may develop in spoil piles in such cases the initial failure surface is better defined than other movement surfaces which either represent subsequent failures that occur in response to placement of additional spoil materials or are shear zones of readjustment following initial failure results show that failures are most likely initiated along the spoil natural ground interface and propagate slowly into the spoil mass

can the greenland climatic jumps be identified in records from ocean and land sharp jumps in climate punctuate the records from borings in the greenland ice cap during the time interval 60 000 to about 20 000 yr ago rapid fluctuations are also seen in foraminifera records for cores from the northern atlantic and in a pollen record from a core from a bog in the vosges mountains in france in this paper we present a new radiocarbon chronology for northern atlantic deep sea core v23 81 which permits comparison with the radiocarbon dated vosges mountains pollen record because of the lack of a 14c chronology for the greenland ice record and of distortions peculiar to each of the three records it is not yet possible to say whether or not the events are genetically related

millennial scale climate origins for stratification in cambrian and devonian deep water rhythmites western usa abstract basinal facies of the middle cambrian marjum formation western utah and middle devonian denay limestone central nevada are characterized by thin rhythmically interbedded limestone and marl layers deep water rhythmites limestone layers average thickness range of 4 3 5 5 cm are composed of laminated to massive pelleted lime mudstone marl layers average thickness range of 0 7 1 7 cm are characterized by laminated argillaceous dolomitic mudstone the absence of current or wave reworked features paucity of bioturbation and skeletal fossils stratigraphic relationships with adjacent facies and the dark color indicate that limestone and marl layers in both rhythmite successions were deposited in quiet dysaerobic waters below storm wave base both limestone and marl layers are composed of submillimeter thick graded laminae which represent discrete depositional events from dilute density currents generated by high frequency storms or distal turbidity currents fluctuations in primary pelagic productivity cannot account for variations in carbonate influx because calcareous microfossils did not evolve until the mesozoic instead the rhythmic interbedding is interpreted to reflect climatically controlled variations in fluvial and or eolian influx or changes in marine currents storm or distal turbidity currents which transported shallow platform derived carbonate material into the deep water region spectral analysis of carbonate time series were compared to lithologic rank series and particularly for the middle cambrian rhythmites were found to be statistically indistinguishable the durations of significant spectral peaks were estimated from calculating the average sedimentation rates from the two biostratigraphically controlled stratigraphic sections these rates range between 4 3 4 1 cm k y and 21 2 29 2 cm k y for the cambrian and 3 6 1 8 cm k y to 5 1 7 4 cm k y for the middle devonian application of these sedimentation rates to the marjum couplets suggests that individual couplets represent between 190 2100 years of time the denay couplets represent 800 1900 years the good agreement between empirical holocene hemipelagic sedimentation rates and the sedimentologic evidence of relatively high depositional rates for the paleozoic rhythmites supports this millennial scale interpretation these results combined with that from previous work in paleozoic evaporite and carbonate successions suggest that millennial scale paleoclimatic variations affected marine and marginal marine sedimentation as far back in time as the cambrian millennial scale climatic change appears to be a permanent feature affecting the oceans and atmosphere and is apparently largely unaffected by major changes in phanerozoic paleogeography tectonics and atmospheric composition

seismic hazard map of turkey using the deterministic approach abstract because the instrumental records of turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach an attempt was made in this study to accomplish it through the deterministic way in this regard all active faults of turkey small and large were evaluated together to obtain major fault systems then the procedure suggested by wells and coppersmith bull seismol soc am 4 1994 975 applied to those faults to obtain the maximum magnitude earthquake that they can generate to do this it was assumed that 1 3 of the total fault length would rupture to yield the maximum earthquake following that seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole turkey at 0 2 intervals using the computer model tumdes written in basic programming language the computed peak ground acceleration pga values were contoured and the iso acceleration map based on sadigh et al seismol res lett 1 1997 180 relationship was selected as the new seismic hazard map of turkey on which the seismic zonations were determined as following pga 0 3 g zone 1 0 3 g

komatiites of the wildara leonora belt yilgarn craton wa the missing link in the kalgoorlie terrane abstract the wildara leonora belt in the kalgoorlie terrane is located between the world class nickel provinces of the agnew wiluna belt to the north and the kambalda domain to the south it extends from the wildara station to the gold mining center of leonora and consists of a deformed package of mafic komatiitic and sedimentary rocks this package of rocks which hosts a number of small nickel sulfide occurrences has been explored extensively for komatiite hosted nickel deposits most recently within the sullivans unit in the south east of the wildara leonora belt lithostratigraphic similarities together with shared physical geochemical and textural properties support a common affiliation between the wildara leonora and the agnew wiluna belts on this evidence the wildara leonora belt represents the southern extension of the largest komatiite hosted nickel camp in the world the apparently lesser prospectivity for nickel sulfide deposits is interpreted as a consequence of contrasting volcanic facies assemblages komatiites in the wildara leonora belt present geochemical and volcanological characteristics consistent with turbulent lava flow emplacement however compared with the agnew wiluna belt the wildara leonora belt komatiites are not spatially associated with felsic volcanic units but rather overlie a thick sequence of pillowed basalts and sulfidic sediments the lower proportion of adcumulate greater degrees of fractionation and lower degrees of contamination are consistent with komatiites in the wildara leonora belt having been emplaced in a more distal position to the rift environment with lower magma flux and more tranquil emplacement than the agnew wiluna belt komatiites and consequently having lower potential for giant nickel sulfide deposits such as those at perseverance and mt keith

the petrogenesis of volcaniclastic komatiites in the barberton greenstone belt south africa a textural and geochemical study the onverwacht group of the 3 5 3 2 ga barberton greenstone belt south africa contains multiple stratigraphic units that include laterally extensive beds of komatiitic ash accretionary lapilli and lapilli these units have been affected by pervasive silicification serpentinization or less commonly carbonate metasomatism silicification resulted in sio2 k2o485 wt and depletion of most other major and trace elements most of these tuffs have prominent high hf hf and zr zr 0 5 12 which cannot result from normal magmatic processes but are due to the typically immobile rare earth elements migrating during post silicification fluid rock interaction similarly their low ce ce values do not reflect archean surface redox conditions but the circulation of later oxidizing fluids despite this intense alteration ratios of al2o3 and tio2 remain uniform and coherent within single volcanic units these ratios indicate that most silicified tuffs are not petrogenetically related to the underlying or overlying komatiitic flow rocks and that each originated from either separate mantle sources or different partial melting conditions serpentinized tuffs retain komatiitic element abundances but al2o3 fails to define a tight linear array with the demonstrably immobile elements ti and zr we speculate that this is due to post depositional mixing of al depleted and al undepleted tuff layers by aqueous currents excellent textural preservation of the silicified tuffs shows they are characterized by a dearth of phenocrysts low particle vesicularity and abundance of fine vitric ash suggesting the eruption and rapid quenching of superheated or near liquidus anhydrous magmas minor assimilation of hydrated basaltic or ultramafic crust within the dry magma may have enhanced the surface phreatomagmatic explosivity while still allowing the magma to rise close to an adiabatic ascent path however textural and geochemical evidence for such a process is scarce temporal and compositional constraints show that the diversity in the types of komatiites throughout the onverwacht group can be accounted for by variations in plume mantle dynamics and that komatiitic tuffs were deposited during intervals of volcanism characterized by low effusive eruptive volumes and or low emplacement rates

shear strength of rockfill a practical method for estimating the shear strength of rockfill is developed the peak drained friction angle prime is found to be closely related to that of rock joints in both cases the values of prime are dependent on sample size stress level surface roughness and on the uniaxial compression strength of the rock friction angles are therefore higher for smaller samples and very high where stresses are low as at the toe or near the face of a rockfill dam test data reviewed shows that the value of prime for rockfill can be quantified by a equivalent roughness r and an equivalent particle strength s the value of r depends on the porosity following compaction and on the degree of particle roundedness and surface smoothness a practical method is proposed for physically measuring the full scale shear strength of in place compacted rockfill

case study of slope failure during construction of an open pit mine in indonesia this paper presents back analyses of a failed slope at an open pit lignite mine in muara enim indonesia the slope which was being raised by the dumping of excavated material failed at a dump he

the summer 1997 eruption at pillan patera on io implications for ultrabasic lava flow emplacement galileo data and numerical modeling were used to investigate the summer 1997 eruption at pillan patera on io this event now defined as pillanian eruption style keszthelyi et al this issue included a high temperature 1600 c possibly ultrabasic 140 km high plume eruption that deposited dark orthopyroxene rich pyroclastic material over 125 000 km2 followed by emplacement of dark flow like material over 3100 km2 to the north of the caldera we estimate that the high temperature energetic episode of this eruption had a duration of 52 167 days between may and september 1997 with peak eruption temperatures around june 28 1997 galileo 20 m pixel 1 images of part of the pillan flow field show a widespread rough pitted surface that is unlike any flow surface we have seen before we suggest that this surface may have resulted from 1 a fractured lava crust formed during rapid low viscosity lava surging perhaps including turbulent flow emplacement 2 disruption of the lava flow by explosive interaction with a volatile rich substrate or 3 a combination of 1 and 2 with or without accumulation of pyroclastic materials on the surface well developed flow lobes are observed suggesting that this is a relatively distal part of the flow field shadow measurements at flow margins indicate a thickness of 8 10 m we have modeled the emplacement of putative ultrabasic flows from the summer 1997 pillan eruption using constraints from new galileo data results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50 150 km on a flat unobstructed surface which is consistent with the estimated length of the pillan flow field 60 km our modeling suggests low thermal erosion rates 20 m erosion channels was unlikely especially distal to the source we calculate a volumetric flow rate of 2 7 103 m3 s 1 which is greater than those for typical mauna loa kilauea flows but comparable to those for the 1783 laki eruption and the inferred flow rates of the roza flows in the columbia river flood basalts the differences in ultrabasic eruption styles on earth and io appear to be controlled by the different eruption environments plumes at sites of ultrabasic eruptions on io suggest strong magma volatile interactions on a low gravity body lacking an atmosphere whereas the geology at sites of komatiite eruptions on earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity