a computer assisted thin section study of lake baikal sediments a tool for understanding sedimentary processes and deciphering their climatic signal a freeze drying technique for cutting thin sections of soft sediments without disturbance is used to study several lake baikal sedimentary microstructures image analysis methodology is applied to selected thin sections this new technique provides quantification of the size shape orientation and packing of the objects forming the sedimentary structures sedimentary processes which were previously poorly documented have been identified and others are better understood spheroidal lens like pure aggregates of the diatom genus synedra are found in hemipelagic sediments providing a new insight into their traditional paleoecological interpretation they are possibly related to a transportation mechanism from the littoral zone or to lacustrine snow laminae of aulacoseira have also been recorded evidence of rapid sedimentation suggests they are due to massive algal blooms the depositional mechanism that was suggested by other studies for explaining the laminations at the buguldeika uplift is confirmed the hemipelagic sedimentation is interrupted by terrigenous pulses due to discharge events the sedimentation rate appears to be increasing during these pulses preliminary results from the academician ridge show stronger microbioturbation during cold periods this observation strengthens the hypothesis of intense water circulation during colder times thin section image analysis provides crucial information for deciphering lacustrine records and their regional and palaeoclimatic significance

biological forcing of hemipelagic sedimentary laminae evidence from odp site 893 santa barbara basin california core observation x radiography and scanning electron microanalysis of distinctly laminated indistinctly laminated and nonlaminated sediments from odp site 893 show that laminated as well as nonlaminated i e massive hemipelagic sediments can form in the absence of bioturbation this view contrasts with conventional sedimentological interpretations equating laminated hemipelagic sediments with anoxic water masses i e absence of bioturbation and nonlaminated sedimentary intervals exclusively with oxygenation episodes that permitted infaunal colonization we conclude that heterogeneities in the texture and or composition of sediment supply are necessary for the production of laminated sediments the absence of hydraulic and biological reworking permits their preservation laminae at site 893 have two prominent components biosilica and terrigenous detritus compositional contrasts between adjacent laminae in x radiographs reflect short term seasonal and subseasonal heterogeneities in sediment flux core intervals with large contrasts in density and or composition between adjacent laminae are termed as having high bimodality hb hb couplets produce distinctly laminated sediments that intergrade vertically with indistinctly laminated and nonlaminated sediments adjacent laminae in indistinctly laminated sediments possess minimal contrasts in bulk density and composition nonlaminated sediments are compositionally and texturally homogeneous many biosiliceous laminae responsible for distinctly laminated hb couplets record mass flocculation and sedimentation of ungrazed diatom frustules formed during discrete bloom events ecological interpretation of diatomite laminae suggests that many were effectively self sedimenting i e the production of gelatinous exudates by phytoplankton facilitated their aggregation and rapid sedimentation the results indicate that lamination style preserves meaningful ocean climate data concerning episodicity heterogeneity and export efficiency of biologically mediated sedimentary flux in upwelling dominated coastal ecosystems

clay fabric of selected submarine sediments fundamental properties and models abstract clay fabric of selected mississippi delta sediment and a red clay from the eastern equatorial pacific is related to void ratio and depth of burial relatively high void ratio naturally consolidated delta sediment is characterized by a fabric of randomly oriented domains and short linking chains with particles in edge to face and face to face contacts lower intermediate void ratio sediment showed greater particle to particle packing but a consistent predominance of randomly oriented domains with a few chains and a slight development of larger domains than observed in the high void ratio sediment the deeply buried very low void ratio sediment has highly oriented domains and thin long voids the red clay sample is characterized by flocs connected by long linking chains and a very hi h void ratio domains and turbostratic type clay fabric are characteristic of high porosity high void ratio mississippi delta sediments highly oriented domains and long chains are diagnostic of the deeply buried very low porosity delta muds the clay fabric of natural undisturbed samples was compared with laboratory remolded samples for comparison with models suggested by earlier researchers observations using the transmission electron microscope tem support the proposed fabric models for remolded sediment selected samples were studied using the scanning electron microscope sem tentative clay fabric models for undisturbed submarine sediment are proposed and related to void ratios

processes of deep water renewal in lake baikal deep water renewal in lake baikal siberia the world s deepest lake and largest lake by volume is relatively fast water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr relative saturation of dissolved oxygen typically exceeds 80 the equation of state of baikal water was determined including the effect of dissolved ions and silicic acid based on nearly 600 ctd profiles taken between 1993 and 1995 two mechanisms of deep water mixing were identified 1 in spring cold and relatively saline water from the selenga the major inflow to the lake forms a density plume that reaches the bottom of the central basin during april and early may due to entrainment of lake water the plume transports about 125 km of water per year to the deepest part of the basin later in spring the river water forms the thermal bar observed along the eastern shore there are indications that parts of the selenga are also plunging to the deep part of the southern basin 2 at academician ridge separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin horizontal mixing results in a water mass that can sink on either side of the sill whereas in the central basin the water mass stays at intcrmediatc depth in the northern basin it sinks to the decpcst part more detailed data are needed to quantify this density flux no indication of a wind induced thermobaric instability was found

disequilibrium partitioning of oxygen isotopes associated with sector zoning in quartz fractionation of oxygen isotopes during crystal growth is commonly assumed to be an equilibrium process we present evidence here that large variations in delta 18 o values in a zoned vein quartz crystal are the result of disequilibrium partitioning between fluid and crystal within a single crystal vith well developed concentric and sector zoning delta 18 o values determined with laser extraction techniques on milligram to submilligram sized samples range from 4 7 parts per thousand to 7 3 parts per thousand core to rim variations within single growth sectors fluctuate by 2 6 parts per thousand whereas differences between adjacent sectors along the same growth zone can exceed 2 0 parts per thousand in contrast fluid inclusion homogenization temperatures and salinities are relatively constant and show no effect of grow th or sector zoning differences in delta 18 o values between sectors along the same growth zone cannot result from variations in the oxygen isotope composition of the fluid and strongly suggest disequilibrium partitioning of oxygen isotopes between fluid and the growing crystal the cause of this disequilibrium is believed to be due to differences in surface structure and or growth mechanisms between nonequivalent faces

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

revealing hidden structures the application of cathodoluminescence and back scattered electron imaging to dating zircons from lower crustal xenoliths abstract the use of cathodoluminescence cl and or back scattered electron bse imaging techniques with in situ ion probe analyses of zircons can help unravel complex crustal histories of metamorphic rocks that otherwise might remain elusive using these techniques we have imaged zircons from three lower crustal xenolith suites that have previously been dated by shrimp sensitive high resolution ion microprobe in all three cases the zircons are featureless in transmitted light but cl and bse reveal internal structures that correlate with distinct growth events generally cl and bse images reveal similar structures with cl showing finer detail neither imaging technique is capable of delineating all growth features in every sample and the best results are obtained using a combination of the two techniques igneous cores in zircons commonly emit a different color cl emission in many cases zoning in the cores is truncated indicating that the zircons either spent time in the supracrustal environment after their initial crystallization and prior to the granulite facies event s or that part of the core zircon was resorbed during the subsequent metamorphic event metamorphic rims when present are commonly 10 to 30 m thick and are nearly always unzoned and featureless igneous cores and metamorphic overgrowths commonly have distinctive cl emission spectra and trace element concentrations however the cl spectra can only be used to qualify chemical differences as a linear relationship has not been shown to exist between cl intensity and trace element concentration in natural zircons in many cases the hf y p u and the heavy rare earth elements hrees concentrations can be correlated to igneous and metamorphic growth using a combination of cl and bse imaging techniques and in situ trace element analyses with either the electron microprobe or pixe particle induced x ray emission

quantification of bioturbation in hemipelagic sediments via thin section image analysis traditional ichnofabric descriptive semiquantitative l schemes rely upon subjective estimates of the degree to which original sedimentary fabrics have been disrupted this paper presents an objective method of quantifying bioturbation in hemipelagic sediments based on a thin section image analysis technique in order to perform these analyses optical or backscattered electron micrographs are processed in order to obtain black and white images in these images black pixels are silt size larger grains and the clay size sedimentary matrix are white pixels once the initial processing has been accomplished an index h is defined to quantify the horizontal orientation of the larger grain size fraction of the sediment h is low for bioturbated fabric and high for laminated sediments in hemipelagic suspension deposits h can he used to quantify bioturbation assuming that no other sedimentary processes have disrupted the original depositional fabric the quantitive bioturbation scheme described here is consistent with existing semiquantitative bioturbation schemes in addition it is objective and provides higher resolution descriptions of biological processes that disrupted the sediment after deposition applying this quantitative scheme should refine future paleoecological reconstruction derived from lacustrine and marine successions

synsedimentary fracturing fluid migration and subaqueous mass wasting intrastratal microfractured zones in laminated diatomaceous sediments miocene monterey formation california u s a abstract thinly laminated diatomaceous sediments from the miocene monterey formation contain intrastratal microfractured zones imzs with a layer specific stratigraphic distribution imzs are a hybrid fault vein structure that are stratally bounded by undeformed sediments imzs record synsedimentary extension brittle fracture and en echelon normal faulting and are intimately associated with a well ordered record of sediment and fluid redistribution in sigmoidal mud filled vein arrays outcrop microscope and sem observations suggest that imzs are attributable to intrastratal faulting and vein propagation within shallowly buried diatomaceous sediments we interpret that imzs formed in a setting of bedding parallel shear on a submarine slope proximal to a region of active tectonism measuring the spatial orientation of imzs and correctly interpreting their vergence direction permits accurate estimation of paleoslope direction the unique physical properties of organic rich diatomaceous sediments contributed substantially to the formation of imzs associated sediments record contemporaneous fluidization slumping disharmonic folding complex fracturing and brecciation suggesting that imzs are part of a rheological continuum of synsedimentary slope failure the presence of cobbles and boulders bearing imzs and related structures within and directly subjacent to soft sediment conglomerates and breccias further substantiates the synsedimentary origin of imzs and suggests that stratigraphic horizons bearing imzs may have acted as detachment surfaces for some slope failure and subsequent mass movement events although the trigger for initiation of failure remains uncertain our kinematic model and the apparent restriction of imzs and comparable structures to transpressive and convergent tectonic margins suggests that imzs and some associated rudite deposits may record the signature of seismic events upon shallowly buried hemipelagic sediments

large thin slicing a new method for the study of fabrics in lithified sediments this paper outlines a new method for the study of sedimentary fabrics in well lithified facies the technique involves the cutting of large thin slices of rock that can then be viewed in transmitted light the utility of this methodology is demonstrated in sandstone soft siltstone and even schist the technique is particularly pertinent to sedimentary geologists studying lithologically homogeneous sediments in which physical and biogenic sedimentary fabrics are difficult to discern due to a lack of contrast

variation in biogenic and detrital fluxes and formation of laminae in late quaternary sediments from the peruvian coastal upwelling zone abstract studies of laminated sediments from the peru margin using back scattered electron imagery bsei provide a high resolution record of variation in detrital and biogenic fluxes and highlight the uncertainty involved in preserving a record of surface processes in bottom sediments intermittently laminated sediments which predominate in the peru forearc basins record episodic major diatom bloom events from which there was adequate flux to counteract water column processes of dissolution and comminution a distinctive sub millimetre lamination with a limited occurrence during isotope stage 5 comprises a regular alternation between silt rich and clay rich couplets which may represent annual deposition with irregularly interlaminated diatom ooze containing near monospecific bloom assemblages the absence of diatom ooze layers between silt clay couplets may be controlled by variation of either the intensity of upwelling and or the nutrient content of upwelled waters macroscopically obvious 0 5 3 cm thick pelleted or homogeneous zones which occur throughout the sub millimetre laminated sequence represent periods of increased oxygenation with a probable 8 16 year duration occurring at irregular intervals of a few years to a few hundred years a slight but pervasive microscopic bioturbation is common within laminated intervals which would macroscopically be described as anaerobic sediments

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

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

enhancement and sharpening the migration images of the gravity field and its gradients potential field migration represents a rapid technique for imaging the subsurface based on gravity data however migration transformation usually produces a smooth and unfocused image of the targets due to the diffusive nature of the potential fields in this paper we introduce a method of the migration image enhancement and sharpening based on the application of the hybrid focusing stabilizer which combines the edge preserving smoothing filter with the minimum support functional the method is based on the model resolution matrix of the migration operator we also improve the migration image with a novel target oriented migration method the developed method of migration image enhancement and sharpening is illustrated by synthetic model studies and case studies the case study involves imaging the full tensor gravity gradient data collected in the nordkapp basin of the barents sea

grain fabric in hummocky cross stratified storm beds genetic implications abstract a detailed analysis of grain fabric in samples from hummocky cross stratified hcs storm beds suggests that these shallow marine sandstones were deposited from waning combined oscillatory unidirectional flows particle a axis orientations in the deposits in plan view parallel to visible lamination vary widely but have a mean orientation approximately normal to unidirectional paleoflow indicators sole marks and subparallel to regional shoreline this alignment of a axes is attributed to deposition under combined flows with a multidirectional oscillatory component produced by wind induced surface gravity waves with a modal crest orientation approximately parallel to the shoreline imbrication of particles varies in both the horizontally laminated and hcs intervals of the hcs stor beds due to waxing and waning of boundary shear stress caused by the oscillatory component of the flow in the basal horizontally laminated interval of an hcs storm bed grain imbrication angles vary about a mean of approximately 13 from the horizontal dipping into the paleoflow inferred from sole marks this preferred imbrication direction is attributed to boundary shear stress influenced by the unidirectional component of the combined flow however quasi cyclic variation in imbrication angle over a broad range and periodic reversal of imbrication direction suggest that the oscillatory component was also significant during deposition of the horizontally laminated interval in hcs intervals imbrication angles vary about a mean that is parallel to visible laminae suggesting th t oscillatory flow had become predominant the sequence of structures and changing patterns of fabric through these hcs storm beds is consistent with deposition under waning combined flows erosional scour forming the sharp base and unidirectional sole marks occurred in response to combined flows with an effective unidirectional component the unidirectional component continued to influence the direction of boundary shear stress during deposition of the horizontally laminated sands but waned and became negligible relative to a strong oscillatory component during formation of hcs

quantitative estimation of bioturbation based on digital image analysis quantitative determination of modification of primary sediment features by the activity of organisms i e bioturbation is essential in geosciences some methods proposed since the 1960s are mainly based on visual or subjective determinations the first semiquantitative evaluations of the bioturbation index ichnofabric index or the amount of bioturbation were attempted in the best cases using a series of flashcards designed in different situations recently more effective methods involve the use of analytical and computational methods such as x rays magnetic resonance imaging or computed tomography these methods are complex and often expensive this paper presents a compilation of different methods using adobe photoshop software cs6 for digital estimation that are a part of the idiap ichnological digital analysis images package which is an inexpensive alternative to recently proposed methods easy to use and especially recommended for core samples the different methods similar pixel selection method spsm magic wand method mwm and the color range selection method crsm entail advantages and disadvantages depending on the sediment e g composition color texture porosity etc and ichnological features size of traces infilling material burrow wall etc the idiap provides an estimation of the amount of trace fossils produced by a particular ichnotaxon by a whole ichnocoenosis or even for a complete ichnofabric we recommend the application of the complete idiap to a given case study followed by selection of the most appropriate method the idiap was applied to core material recovered from the iodp expedition 339 enabling us for the first time to arrive at a quantitative estimation of the discrete trace fossil assemblage in core samples

sedimentary structures on the bengal shelf a multi scale approach to sedimentary fabric interpretation abstract sedimentary structures on the bengal shelf are examined using x radiographic thin section and scanning electron microscopic sem techniques which reveal contrasting depositional processes for the inner and middle shelf as well as for either side of a major submarine canyon indenting the western shelf margin the inner shelf is characterized by tidally produced interlaminated silts and muds that reveal a neap spring cyclicity the cyclicity is more pronounced for the winter season when high discharge monsoon conditions do not obscure the tidal signature on the middle shelf alternating beds of silts and muds probably represent high discharge and low discharge conditions respectively silty beds on the western margin of the submarine canyon are thinner than those found on the eastern margin the western margin receives predominantly fine grained ganges sediments in contrast to the eastern area which receives both ganges and coarser brahmaputra sediments these observations indicate that the submarine canyon presently intercepts westward along shelf sediment transport muddy beds and laminae that appear internally homogeneous in the x radiographs and exhibit faint bedding in thin sections often are composed of resistant protruding and less resistant recessed microlaminae as observed with the sem on the inner shelf resistant microlaminae are composed of fine grained polymineralic equant particles the less resistant microlaminae are composed of large platy illite grains rimmed by smaller platy or lath like illite particles resistant and less resistant microlaminae within middle shelf muddy sediments have the same textural characteristics observed on the inner shelf however both types essentially are monomineralic on the middle shelf the smallest particles within the less resistant microlaminae exhibit an open flocculated structure that may result from higher salinity and or decreased bottom shear stress associated with tidal currents biological structures predominantly occur on the western inner and middle shelf particularly in intervals of high smectite concentrations this relationship may exist because of a preferential organic affinity for expandable minerals providing a favorable substrate for benthic organisms

an image analysis technique to measure grain size variation in thin sections of soft clastic sediments this paper presents a simple and fast image analysis technique to measure grain size variation in thin sections of soft elastic sediments optical and backscattered electron microscope photographs are digitised from thin sections cut by freeze drying to avoid disturbing the sediments processing of the 256 grey scale images produces binary black and white images where white pixels represent the clay rich sedimentary matrix and black pixels represent elastic grains data measured include grain surface grain perimeter and centre of gravity two indices are defined to quantify grain size d 0 equivalent disk diameter and p phase percentages the technique is applied to silt and clay laminations attributed to the d division of a distal turbidite from lake baikal the data obtained using image analysis are similar to the conventional descriptions of such deposits indices calculated on very small samples e g on a single lamina allow for greater precision in interpretation of sedimentary processes compared to photomicrographs backscattered electron microscope images have better qualities and allow to quantify variations in the grain size along a sediment core the technique produces objective and quantified grain size observations in less time than conventional petrographic methods c 1998 elsevier science b v all rights reserved

the hydraulic equivalence of mica abstract settling experiments performed on silt to fine sand sized mica flakes with a holographic micro velocimeter revealed that mica is the hydraulic equivalent of quartz spheres having diameters a factor of 4 to 12 times smaller mica in the very fine to fine sand sizes has been traditionally used by sedimentologists to delineate areas of deposition or nondeposition and potential winnowing of fines and is here found to be the hydraulic equivalent of silt sized particles but not of clay experiments also showed that mica flakes tend to settle at orientations which are neither perpendicular nor parallel to the gravitational vector and tend to generally maintain their orientation throughout equations for the settling of a disc in lerman and others 1974 and that developed by komar and reimers 1978 are shown to be mathematically similar for the coarse silt to fine sand ranges of discs and are adequate predictors of settling rates of mica flakes a comparison of the hydraulic equivalency of quartz spheres to coarse silt through fine sand sized mica flakes is presented

new type of compositional zoning in calcite insights into crystal growth mechanisms compositional zoning of trace elements is observed in time equivalent regions within 10 overline 1 4 growth sectors of natural and synthetic calcite single crystals and has been called intrasectoral zoning to distinguish it from conventional sectoral zoning differential interference contrast microscopy shows that 101 overline 1 4 faces grow by the spiral mechanism cathodoluminescence microscopy and electron probe microanalyses reveal that trace element partitioning differences on 101 overline 1 4 faces correspond exactly to crystallographically controlled orientations of growth steps effective partitioning of mg and mn varies up to a factor of four between time correlative growth steps spreading in different directions effective sr partitioning varies by approximately 20 and is inversely correlated with enrichment trends of mg and mn preferential incorporation of different aqueous species at different growth steps may provide an explanation for morphological and chemical variation in natural calcites

quantification of depositional changes and paleo seismic activities from laminated sediments using outcrop data abstract measurements of laminations from marine and limnic sediments are commonly a time consuming procedure however the resulting quantitative proxies are of importance for the interpretation of both climate changes and paleo seismic activities digital image analysis accelerates the generation and interpretation of large data sets from laminated sediments based on contrasting grey values of dark and light laminae statistical transformation and correlation of the grey value signals reflect high frequency cycles due to changing mean laminae thicknesses and thus provide data monitoring climate change perturbations e g slumping structures seismites and tsunamites of the commonly continuous laminae record seismic activities and obtain proxies for paleo earthquake frequency using outcrop data from i the pleistocene lisan formation of jordan dead sea basin and ii the carboniferous permian copacabana formation of bolivia lake titicaca we present a two step approach to gain high resolution time series based on field data for both purposes from unconsolidated and lithified outcrops step 1 concerns the construction of a continuous digital phototransect and step 2 covers the creation of a grey density curve based on digital photos along a line transect using image analysis the applied automated image analysis technique provides a continuous digital record of the studied sections and therefore serves as useful tool for the evaluation of further proxy data analysing the obtained grey signal of the light and dark laminae of varves using phototransects we discuss the potential and limitations of the proposed technique

the high sensitivity of the palynological record in the vico maar lacustrine sequence latium italy highlights the climatic gradient through europe for the last 90 ka the palynological study of the vice maar lacustrine sequence italy is realized from the correlation of three drillholes the time span covers a period from the end of oxygen isotope substage 5b till the beginning of stage 1 from ca 90 to ca 10 ka bp at the base of the pollen diagram pollen zone 0 a younger dryas like fluctuation is observed after pollen zone 1 which is a well developed forest period substage 5a the forests of pollen zones 3 and 5 correspond to extensive climate improvements these last two zones are correlated to the ognon complex of the grande pile france and to interstadial periods 20 and 19 defined in the grip ice core greenland 72 6 66 2 ka before the stage 5 4 transition these two interstadial periods are global events found in the greenland and antarctica ice sheets as well as in north atlantic marine cores in other pollen records from north of the alps changes have been recorded but they are less pronounced than in vico pollen zone 7 stage 3 shows ca 7 warm humid fluctuations that might have a link to the dansgaard oeschger events greenland during zone 9 the lateglacial interstadial is recorded as well as the younger dryas event the localization of vice near plant refugia and far from the ice cap enables its pollen diagram to record abrupt and intense response to climate changes possibly through a link to the atlantic ocean via westerly winds c 1996 elsevier science ltd

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

origin of the fabric of laminated fine grained glaciolacustrine deposits abstract scanning electron microscope fabric analysis of laminated pleistocene glacial silty clay and clay from new york state provides evidence of two sedimentary processes suspension settling of flocculated aggregates followed by bioturbation of the upper parts of silty clay and clay laminae the glacial rhythmites in two pleistocene glacial lakes in new york state formed dominantly from episodic sedimentation of flocculated sediment graded bedding and random particle orientation indicate continuous deposition of flocculated sediment during the deposition of a typical glaciolacustrine couplet however during the interlude between rhythmite deposition of the flocculated silty clay and clay a second but more subordinate sedimentary process of bioturbation dominated nematode burrows found in the upper part of the clay portion of couplets are associated with preferred orientation of clay flakes this fabric found around the burrows was produced as the soft plastic moist flocculated clay sediment was sheared and reoriented by nematode movement between sedimentation events the preferred orientation between burrows in the upper part of the clay laminae resulted from postdepositional compaction due to the weight of overburden reorientation was limited however to only the upper part of the clay laminae random orientation present in the original flocculated sediment was preserved in the lower part of the couplet the study presents a model of how clay fabric can be used in determining sedimentary processes of glaciolacustrine deposits

introducing fiji and icy image processing techniques in ichnological research as a tool for sedimentary basin analysis abstract in recent years image treatment has been appraised as a very powerful tool to facilitate ichnological analysis especially in marine cores of modern sediments supporting the determination of certain ichnological features however it is still a new approach and detailed research is necessary to encounter a faster and more efficient method the present study focuses on two image processing techniques fiji and icy and their comparison with a refined version of the well established high resolution image treatment strengths and weaknesses of the methodologies for the determination of three main features were explored i visibility of trace fossils ii quantification of the percentage of bioturbated surface and iii penetration depth estimation refined high resolution image treatment gives the best results for enhanced visibility of trace fossils whereas fiji is found to be a sound and rapid option one disadvantage shared by fiji and icy is the binary character of the produced images which may impede later ichnotaxonomical differentiation both fiji and icy fiji are rapid alternatives for quantifying the bulk amount of bioturbated surface the magic wand method refineedge based on high resolution image treatment provides good results regardless of the contrast of the images and it additionally allows for a more detailed quantification the semi automatic character of icy favors quick estimation of penetration depth and facilitates differentiation between distinct tracemaker communities based on a rapid quantification of pixel values thus fiji and icy methods offer good results and are much less time consuming than high resolution image treatment they are proposed as faster alternatives for the estimation of ichnological features especially useful at the beginning stages of research when a large number of samples must be analyzed

speckled beds distinctive gravity flow deposits in finely laminated diatomaceous sediments miocene monterey formation california distinctive nonlaminated intervals we term speckled beds sbs are common in finely laminated diatomites of the monterey formation at celite quarry lompoc california sbs have sharp and bedding parallel upper and lower contacts tabular geometry and are less than or equal to 10 cm thick sbs are characterized by a bedding parallel arrangement of sand to granule size diatomaceous and detrital aggregates that are uniformly distributed in a fine grained matrix of macerated biosilica and detrital mud the unique physical properties of diatomaceous sediments provided cohesive substrates and high fluid content that were prerequisite for the formation of sbs abundant hybrid fault vein structures slump folds and complexly deformed laminae in the quarry attest to syndepositional deformation of laminated diatomaceous sediments on a subaqueous slope within the oxygen minimum zone the unique features of sbs permit an interpretation of stepwise rheological transformation during mass movement via passage through critical point transformations from bingham plastic slump and or slide block to turbulent fluid turbidity current to viscous fluid exhibiting laminar flow debris flow the recognition of sbs clarifies the origin of these distinctive yet problematic deposits and clearly differentiates them from other nonlaminated intervals sb composition indicates provenance from an oxygen minimum zone and further illustrates that a hiatus is not required to form cohesive firmgrounds in diatomaceous sediments the recognition of sbs as recorders of slope failure events complements paleoseismic studies of holocene diatomaceous laminites from saanich inlet british columbia ocean drilling program sites 1033 and 1034