trace metal signatures of eastern mediterranean sapropels abstract sapropel samples of pliocene to pleistocene age recovered during odp leg 160 from sites 964 ionian basin 969 mediterranean ridge 966 967 top and northern slope of the eratosthenes seamount south of cyprus and 968 cyprus margin were analysed for major and trace elements eastern mediterranean sapropels are characterized by high organic carbon and sulphur contents and by significant enrichments in several redox sensitive and or sulphide forming trace metals bi cd co cr cu mo ni re sb tl u v enrichment factors relative to average shale are comparable to those found in ctbe black shales the re content is extremely high in the sapropels studied with maximum values up to 1000 ng g re mo ratios averaging 2 7 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to an anoxic water column during sapropel formation additionally enhanced ba concentrations in the sapropels support the assumption that bioproductivity was also high during these episodes trace metal signatures of sapropels originating from different drill sites on a transect across the eastern mediterranean are not only influenced by water depth but also by their location in the eastern mediterranean metal enrichments seem to be higher at the western sites compared with the eastern sites this probably reflects a change in the circulation pattern during periods of sapropel formation pliocene sapropels exhibit elevated trace metal contents in comparison with pleistocene examples therefore different palaeoceanographic conditions may have developed during the pleistocene compared with the pliocene altering palaeoceanography was probably controlled by climatic change which may be related to the onset of glaciation of the northern hemisphere decreasing summer precipitation throughout the late pliocene and the pleistocene may also have influenced sapropel deposition

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

magnetofossil spike during the paleocene eocene thermal maximum ferromagnetic resonance rock magnetic and electron microscopy evidence from ancora new jersey united states previous workers identified a magnetically anomalous clay layer deposited on the northern united states atlantic coastal plain during the paleocene eocene thermal maximum petm the finding inspired the highly controversial hypothesis that a cometary impact triggered the petm here we present ferromagnetic resonance fmr isothermal and anhysteretic remanent magnetization first order reversal curve and transmission electron microscopy analyses of late paleocene and early eocene sediments in drillcore from ancora new jersey a novel paleogeographic analysis applying a recent paleomagnetic pole from the faeroe islands indicates that new jersey during the initial eocene had a 6 9 degrees lower paleolatitude 27 3 degrees for ancora and a more zonal shoreline trace than in conventional reconstructions our investigations of the petm clay from ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria this result the first identification of ancient biogenic magnetite using fmr argues that the anomalous magnetic properties of the petm sediments are not produced by an impact they instead reflect environmental changes along the eastern margin of north america during the petm that led to enhanced production and or preservation of magnetofossils

an appalachian amazon magnetofossil evidence for the development of a tropical river like system in the mid atlantic united states during the paleocene eocene thermal maximum on the mid atlantic coastal plain of the united states paleocene sands and silts are replaced during the paleocene eocene thermal maximum petm by the kaolinite rich marlboro clay the clay preserves abundant magnetite produced by magnetotactic bacteria and novel presumptively eukaryotic iron biomineralizing microorganisms using ferromagnetic resonance spectroscopy and electron microscopy we map the magnetofossil distribution in the context of stratigraphy and carbon isotope data and identify three magnetic facies in the clay one characterized by a mix of detrital particles and magnetofossils a second with a higher magnetofossil to detrital ratio and a third with only transient magnetofossils the distribution of these facies suggests that suboxic conditions promoting magnetofossil production and preservation occurred throughout inner middle neritic sediments of the salisbury embayment but extended only transiently to outer neritic sediments and the flanks of the embayment such a distribution is consistent with the development of a system resembling a modern tropical river dominated shelf

magnetic anisotropy magnetostatic interactions and identification of magnetofossils 1 single domain magnetite particles produced by magnetotactic bacteria mtb and aligned in chains called magnetosomes are potentially important recorders of paleomagnetic paleoenvironmental and paleolife signals rock magnetic properties related to the anisotropy of magnetosome chains have been widely used to identify fossilized magnetosomes magnetofossils preserved in geological materials however ambiguities exist when linking magnetic properties to the chain structure because of the complexity of chain integrity and magnetostatic interactions among magnetofossils that results from chain collapse during post depositional diagenesis in this paper magnetic properties of three sets of samples containing extracted magnetosomes of the culturedmagnetospirillum magneticumstrain amb 1 were analyzed to determine how chain integrity and particle concentration influence magnetic properties intact mtb and well dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions but progressive chain breakup and particle clumping significantly increase the degree of magnetostatic interaction this results in a change of the magnetic signature toward properties typical of interacting single domain particles i e a decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization decreasing in the crossing point of the wohlfarth cisowski test and in the delta ratio between losses of field and zero field cooled remanent magnetization across the verwey transition as well as vertical broadening of the first order reversal curve distribution we propose a new diagram that summarizes the verwey transition properties with diagnostic limits for intact and collapsed chains of magnetosomes this diagram can be used in conjunction with other parameters to identify unoxidized magnetofossils in sediments and rocks

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

new constraints on climate forcing and variability in the circum mediterranean region from magnetic and geochemical observations of sapropels s1 s5 and s6 eastern mediterranean sapropels are organic rich layers whose formation was triggered during boreal summer insolation maxima precession minima sapropel formation is associated with increased precipitation and runoff from europe and north africa although the relative influence of high and low latitude climate mechanisms is not fully resolved likewise it remains uncertain how centennial scale interruptions in conditions that give rise to sapropels may reflect atmospheric circulation changes in low latitudes we present magnetic geochemical and diffuse reflectance spectroscopy data from three sapropels that are representative of glacial s6 and interglacial s1 s5 conditions in the eastern mediterranean sea to assess environmental changes associated with sapropel formation the extent of diagenetic magnetite dissolution and authigenic formation of fine grained greigite in these sapropels and their underlying dissolution intervals are linked to enhanced sulphidic conditions during sapropel formation aeolian hematite and goethite are largely unaffected by this reductive dissolution except within the interglacial sapropel s5 and its underlying dissolution interval which formed under relatively stronger sulphidic conditions nevertheless low hematite contents indicate that the three studied sapropels accumulated under reduced aeolian dust inputs in response to an intensified african monsoon which resulted in expansion of savannah landscapes into ne saharan dust source areas small variations in goethite contents across sapropels indicate additional aeolian entrainment of goethite that formed under previous wet phases in the ne sahara or in subtropical savannahs located further south we link short lived dust abundance peaks within sapropels s1 and s6 to centennial scale periods of enhanced bottom water circulation reported previously for these sapropels although these sapropel interruptions are driven by high latitude cooling events our results indicate that such centennial scale episodes of atmospheric reorganization affected not only the eastern mediterranean northern borderlands but also subtropical north africa overall our results point to a dominant low latitude forcing on sapropel formation via boreal summer insolation maxima and intensification of the african monsoon

modes of sapropel formation in the eastern mediterranean some constraints based on pyrite properties abstract pyrite formation within and directly below sapropels in the eastern mediterranean was governed by the relative rates of sulphide production and fe liberation and supply to the organic rich layers at times of relatively high so2 4 reduction sulphide could diffuse downward from the sapropel and formed pyrite in underlying sediments the sources of fe for pyrite formation comprised detrital fe and diagenetically liberated fe ii from sapropel underlying sediments in organic rich sapropels input of fe from the water column via fe sulphide formation in the water may have been important as well rapid pyrite formation at high saturation levels resulted in the formation of framboidal pyrite within the sapropels whereas below the sapropels slow euhedral pyrite formation at low saturation levels occurred 34s values of pyrite are 33 to 50 below the sapropels 34s is lower than within the sapropels as a result of increased sulphide re oxidation at times of relatively high sulphide production and concentration when sulphide could escape from the sediment the percentage of initially formed sulphide that was re oxidized was estimated from organic carbon fluxes and burial efficiencies in the sediment it ranges from 34 to 80 varying significantly between sapropels increased palaeoproductivity as well as enhanced preservation contributed to magnified accumulation of organic matter in sapropels

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

fuzzy c means cluster analysis of early diagenetic effects on natural remanent magnetisation acquisition in a 1 1 myr piston core from the central mediterranean abstract the influence of early diagenesis on the natural remanent magnetisation nrm in sediments from the calabrian ridge central mediterranean is analysed with the help of fuzzy c means fcm cluster analysis and non linear mapping nlm the sediments are variably coloured white beige purplish greenish and grey layers occur with occasionally intercalated sapropels the nrm acquired depends on both depositional conditions and diagenetic processes to describe these fcm was performed with in arm caco3 ba mn and s as variables an eight cluster model was derived with the clusters belonging to two categories one expressing mainly diagenetic processes i e dissolution and precipitation and the other expressing mainly depositional conditions the impact of diagenesis on nrm acquisition is profound and not restricted to the close vicinity of the anoxic sapropelitic layers as a consequence the influence of diagenetic processes on the nrm should be thoroughly assessed when selecting samples e g for the determination of the relative palaeointensity of the geomagnetic field application of multivariate classification techniques appears to be useful because it links rock magnetic parameters to the geochemical environment in the present piston core three short reversed geomagnetic events in the brunhes chron are preserved and indeed occur in clusters expressing no or minor diagenesis the recording of the blake event however has been prevented by later precipitation of magnetite in the corresponding interval

spatial characteristics of rock joint profile roughness and mechanical behavior of a randomly generated rock joint abstract barton s formula is one of the most widely used equations for estimating the shear strength of rock joints the joint roughness coefficient jrc in the equation is a crucial parameter of the shear strength because it controls the roughness of the profile to explore the spatial characteristics of the roughness of a rock joint profile a total of 86 actual rock joint profiles were collected from published researches and digitalized the profile height variation phv for each profile group was analyzed statistically the standard deviation of the phv was found to depend strongly on the jrc value this correlation of the standard deviation of the phv with the jrc can be used easily to estimate the jrc of a given joint profile owing to the above statistical features of the phv any random profile with a given jrc can be generated for further analysis therefore direct shear ds tests were simulated for two joint profiles a randomly generated profile with jrc 19 6 and barton s standard profile with jrc 18 20 using the discrete element method dem the simulation results revealed that both of the joint profiles have similar joint shear strengths indicating that the randomly generated jrc profile can function as a good artificial profile in an engineering simulation finally dem simulation also indicated that the shear strength of rock joints originates from the roughness of the joints and shearing off of the joints occurs at a normal stress larger than 4 mpa

mechanical behavior of structurally reconstructed irregular columnar jointed rock mass using 3d printing abstract baihetan hydropower station is one the most famous hydroelectric projects in china the columnar jointed rock mass cjrm is widely distributed in this area such as at the dam site and drainage tunnel the rocks surrounding cjrm are usually unstable due to its discontinuity therefore the investigation of mechanical properties of cjrm is essential to designing relevant structures in recent years several previous studies have been conducted to determine the mechanical properties of regular cjrm reconstructed using the mixture of water cement and sand however few studies have been conducted on the irregular cjrms formed in nature because of their structural uniqueness in this study the mechanical properties of irregular cjrms reconstructed using 3d printing technology was investigated and verified through laboratory test first the sampling window method was adopted to obtain the structural characteristics of columnar jointed basalts cjbs after this the mechanical properties i e uniaxial compressive strength ucs uniaxial tensile strength uts peak shear strength residual shear strength failure mode and acoustic emission ae characteristics of the reconstructed and natural cjbs in the laboratory tests were compared based on the similarity constant the results show that the mechanical properties of irregular cjrm reconstructed using 3d printing are consistent with the in situ specimens when considering the similarity constant finally based on a detailed discussion of the reconstructed and original irregular cjrm a new method to accurately reconstruct the structure of irregular cjrms using 3d printing is suggested and verified this method could be used to design irregular cjrms in rock engineering

shear behaviors of real natural un matching joints of granite with equivalent joint roughness coefficients abstract contact planes of a natural unfilled rock joint often portray dissimilar roughness characteristics particularly at shallow depth some researchers investigated shear strength behaviors of un matching joints i e joints with dissimilar surface morphologies through laboratory experiments using mimicked discontinuities this study aimed to explore shear behaviors of real natural un matching joints with similar averaged joint roughness coefficients jrcs in the singhbhum granite india based on laboratory investigations direct shear tests were performed on a total of 18 encapsulated jointed samples split into three groups under a three different low normal stresses 0 70 mpa with increasing values b three different high normal stresses within a range of 0 98 1 99 mpa with increasing values and c one particular intermediate normal stress 0 99 mpa for five times where direction of shearing was kept same as the dip direction of the joints in situ shear behaviors of the investigated joints portray diverse patterns moreover most of the obtained behavioral patterns look different from the typical shear stress shear displacement graph in the literature that are based on direct shear test results in case of matching rock discontinuities influence of surface morphology on shear behavior shear stress fluctuations with displacement variation of jrc values with the increase in normal stresses and observations on peak friction angle were critically analyzed effect of cycles of shearing on shear strength was also examined plausible reasons behind the uniqueness of the results were explained

a new proxy for bottom water ventilation in the eastern mediterranean based on diagenetically controlled magnetic properties of sapropel bearing sediments magnetic properties of eastern mediterranean sediments recovered during leg 160 of the ocean drilling program odp provide insight into non steady state diagenetic reactions associated with accumulation and degradation of organic matter in sapropels according to their magnetic properties sapropels can be classified as one of three types that correspond to increasingly anoxic conditions at the time of sapropel formation a combination of magnetic and geochemical data suggests a causal relationship that enables determination of the relative role of bottom water ventilation versus productivity in the resulting diagenetic stage reached for the three types of sapropels it appears that increased productivity is a prerequisite for sapropel formation but once organic matter is available in sufficient amounts variable efficiencies in bottom water ventilation are more important for modulating the diagenetic context in which different types of sapropels formed magnetic properties are more sensitive to variations in bottom water ventilation than to productivity and can be used to establish relative variations in bottom water ventilation both at and after periods of sapropel formation magnetic results and the distribution and type of sapropels at odp site 966 eratosthenes seamount between 2 3 and 4 0 ma suggest that bottom water ventilation was modulated by the orbital eccentricity component with ventilation being restricted during 400 kyr eccentricity maxima and enhanced during eccentricity minima enhanced ventilation during eccentricity minima as indicated by magnetic data is consistent with the occurrence of red intervals at site 966 and at other eastern mediterranean sites drilled during odp leg 160 and also with astronomically modulated variations in caco3 content found in mediterranean land sections this suggests that variations in bottom water ventilation modulated by 400 kyr eccentricity cycles operated at a basin wide scale

chemical cycles in pliocene sapropel bearing and sapropel barren eastern mediterranean sediments abstract high resolution 3 4 cm investigations of major and minor elements were carried out on sediment cores from odp leg 160 sites 964 ionian basin 969 mediterranean ridge 967 and 966 northern slope and top of eratosthenes seamount south of cyprus at site 967 element al ratios display pronounced cyclic records that are related to astronomically forced climatic variations sediments from the top of eratosthenes seamount site 966 show a similar pattern to those from site 967 but they are more disturbed by bioturbation and also strongly influenced by long term variations in sediment dispersal sediments from site 969 display similar trends to those from site 964 i e they are characterized by higher mg al slightly higher k al and lower ti al ratios during sapropel formation higher ti al ratios at site 969 compared with sediments from site 964 may be explained by a westward transport of material from a source in the east where ti al ratios are highest sites 966 and 967 elevated mg al ratios at site 969 during sapropel intervals are due to river derived material transported through the kithira strait between peloponnesus and crete from the northwestern aegean sea which originates from ultramafic rocks a change in intermediate water currents current reversal during sapropel formation may explain the enhanced supply of mg rich and the relatively diminished supply of ti rich material we propose that during deposition of the reddish intervals at site 969 a change in circulation did not occur because a drastic decrease in ti al ratios is not evident in these sediments ba peaks indicative of former sapropels are not present ba enrichments in the same sapropel barren intervals at site 967 northern slope of eratosthenes seamount suggest that during such intervals the burn down process was more effective than during the sapropel bearing intervals mn contents in all investigated pliocene sediments correlate with the carbonate contents higher mn contents of the sapropel barren sediments suggest that during time intervals of sapropel formation either mn accumulation at the margins of the permanently oxic upper water column or mn export into the western mediterranean might have occured the latter could only be explained by sub or anoxic conditions in large parts of the water column

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

using non negative matrix factorization in the unmixing of diffuse reflectance spectra abstract diffuse reflectance spectrophotometry drs often termed simply color scanning is a technique applied commonly to marine sediments to provide records of compositional variations measured drs spectra however represent the bulk response of a sediment s constituents and are therefore difficult to interpret in their raw form a quantification technique will be proposed and discussed which approaches the analysis of drs data sets as a linear mixing problem and applies a non negative matrix factorization nmf algorithm in their decomposition the presented methodology allows the spectra of the end member sediment constituents and their fractional abundances to be determined using only the measured data set unlike other drs data processing techniques nmf only allows additive combinations of end members to explain the data set and will therefore return only positive abundances analysis of sediments from the eastern mediterranean sea demonstrates the applicability of the nmf approach and the new method of orbital cycle stacking establishes that the unmixed data is consistent with expected environmental change

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

modification and complete removal of eastern mediterranean sapropels by postdepositional oxidation sapropels unusually dark organic rich sediment layers whose origin is controversial are widespread in the eastern mediterranean the upper surfaces of these layers appear sharp and show little evidence of bioturbation it has been suggested that postdepositional oxidation may have removed the dark coloration from the upper part of the original layer so that the top of the visible layer now lies somewhat below the original position of the sapropel top such a diagenetic alteration has considerable implications for the interpretation of the sedimentary record where the tops of dark layers are usually correlated with the cessation of sapropel formation geochemical data demonstrate that all visual evidence of a thin example of the most recent eastern mediterranean sapropel has been removed from the sedimentary record by oxidation processes such a process may have thinned all sapropel units by several centimetres the most recent period of sapropel formation probably ended as recently as 5 ka cf cited values between 6 0 and 7 6 ka

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

quantitative three dimensional description of a rough surface and parameter evolution with shearing note roches reference lmr article 2002 005view record in web of science record created on 2006 11 09 modified on 2016 08 08

review of recent advances in the interpretation of eastern mediterranean sapropel s1 from geochemical evidence abstract the sediments of the eastern mediterranean basin contain c org enriched layers sapropels interbedded with the c org poor sediments which form by far the greater part of the record while it is generally appreciated that different surface ocean productivity and bottom water conditions are necessary for the formation and preservation of these two sediment types less attention has been paid to diagenetic effects which are an expected consequence of transitions between dramatically different bottom water oxygenation levels a geochemical interpretation has emerged of post depositional oxidation of the most recent sapropel s1 initially based on the relationship of the mn fe c org and s concentration depth profiles observed around s1 and the characteristic shapes of these elemental profiles known from other situations this indicates that post depositional oxidation has removed approximately half of the visual evidence of the sapropel 6 cm from a total of 12 cm in the deep basin the oxidation interpretation from redox sensitive element redistribution profiles has subsequently been consolidated with evidence from pore water o 2 no 3 mn 2 and fe 2 studies from characteristic solid phase ba profiles which yield palaeoproductivity records and from oxidation sensitive indicator trace elements i and se so far these geochemical observations have been concentrated in the deeper central parts of the basin where sediment accumulation rates are lower than on the basin margins and radiocarbon dating indicates that s1 formation occurred between 5 3 and 9 0 ky uncorrected conventional radiocarbon time it remains to be demonstrated whether or not these times are applicable to the entire e mediterranean basin the implications of these findings to guide sampling in future work on the s1 productivity episode and on older sapropels for palaeoenvironmental investigations are discussed

shear strength of discontinuities in sedimentary rock masses based on direct shear tests abstract accurate estimation of the shear strength of rock discontinuities is of great importance in many rock engineering practices especially for the stability assessment of dam foundations and rock slopes this study was conducted through both in situ and laboratory direct shear tests on rock discontinuities under the constant normal load cnl boundary condition focusing on the influence of the length of discontinuities on the shear strength the results of more than 109 direct shear tests carried out on rock discontinuities at the bakhtiary dam site were analyzed to consider the size effect on rock discontinuities strength the surface roughness of discontinuities was described by fractal dimension using a modified divider method moreover numerical simulations of direct shear tests were carried out on discontinuities with different lengths in order to establish an empirical relationship that can link the shear strength of discontinuities of laboratory scale to in situ scale from the experimental and numerical results it was confirmed that the peak shear strength of the discontinuity decreases as a function of the discontinuity length

observations of highly regular oscillations in the overflow plume downstream of the faroe bank channel 1 the faroe bank channel fbc is the deepest connection between the atlantic ocean and the nordic seas this work describes the dynamic properties of the plume of dense overflow water descending from the faroe bank channel using time series data for velocity and temperature from a network of 25 moorings deployed west of the faroe bank channel between july 1999 and february 2001 the cold water plume was identified using mean velocity and temperature data a regular pattern of strong velocity and temperature oscillations with 88 4 hours period was the most striking feature observed in the fbc overflow plume these oscillations are initiated in a region where observations indicate supercritical conditions and compare well to recent model results for the fbc overflow plume by ezer 2006

empirical methods to estimate the strength of jointed rock masses abstract the ultimate strength and deformation of jointed rock mass are important parameters that designers look for in selecting sites for foundations of civil and mining engineering structures in rocks in the field it is extremely difficult to stress a rock mass to its ultimate failure stress consequently the field tests are performed up to a certain predefined stress level it is shown in this study that the results of these tests can be used to arrive at the ultimate strength of the rock mass a large number of uniaxial compressive strength ucs tests were conducted on the specimens of jointed block mass having various combinations of orientations and different levels of interlocking of joints four dominating modes of failure were observed the strength and the tangent elastic modulus values of the mass for a specific failure mode when plotted on the deere miller classification chart are found to follow an empirical straight line indicating strong correlation between them using the gradient of this empirical line correlations have thus been suggested to assess the ultimate strength of the jointed rock mass the findings of the study have been verified by applying it to estimate the ultimate rock mass strength of nine rock types from few dam sites in the lower himalayas the ultimate strength obtained by the present methodology is compared with that obtained through the q classification system it is concluded that reasonably good estimates on field strength of jointed rocks are possible by using the correlations suggested in this study

evaluation of existing criteria in estimating shear strength of natural rock discontinuities abstract as evident from the literature there are a number of shear strength criteria proposed by different researchers in spite of that barton s jrc jcs model is probably the most widely used criterion in routine engineering environments ease of determining the input parameters and efficiency in estimating the shear strength are the two key aspects which make this criterion widespread in rock engineering activities when the shear strength criteria existing in the literature had been analyzed by the authors it became apparent that the difficulty levels or eases involved in determining the input parameters of eleven criteria including barton s criterion are broadly comparable however the existing criteria do not seem to have been compared in terms of their practicality applicability while estimating shear strength of real natural rock discontinuities in the present investigation a total of 196 direct shear tests were performed on natural discontinuities of three distinct rock types i e granite quartzite and sandstone from india at normal stresses within a range of 0 22 2 01 mpa the estimated shear strengths were compared to the determined shear strengths the efficacies of the eleven shortlisted criteria in estimating shear strength of real natural rock discontinuities were critically evaluated the criteria emerged to be the most efficient in this regard were highlighted and plausible reasons behind all the findings of this study were also explained

asperity degradation characteristics of soft rock like fractures under shearing based on acoustic emission monitoring abstract shear failure of rock masses along pre existing discontinuities is one of the predominant failure modes of rock slopes and underground tunnels the monitoring and prediction of the impending shear failure is of great significance to ensure the stability of the rock structures and the safety of the workers in this study direct shear tests under normal stress ranging from 0 5 to 10 mpa are conducted on rock fractures analogous to soft rock discontinuities which are obtained by artificial splitting during which the ae parameters are monitored test results show that the ae parameters hit energy and events increase with the shear stress and peak at or near the peak shear strength after which the aes gradually decay with the decrease of shear stress the number of ae events first increases and then decreases with increasing normal stress which may be associated with the ductile deformation of the porous structure of cement mortar under higher normal stress the degradation of asperities on the fracture surface can be inferred from the accumulative ae hits and events which are characterized by s shapes and can be divided into slow growth fast growth and slow growth stages conceptual and mathematical asperity damage models are proposed respectively based on the temporal characteristics of ae events and the curve fitting which can be used to predict the asperity damage for a given shear stress curve the ae b value fluctuates and remains high in the shear process there is no strong correlation between the shear stress and the b value which indicates that the b value may not be an effective index to predict the quasi static shear failure of jointed rock masses possessing similar properties like cement mortar results of this study will not only contribute to a better understanding of the asperity degradation characteristics but also provide valuable knowledge for ae monitoring applications in jointed rock masses

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

three million years of monsoon variability over the northern sahara we present a 3 million year record of aeolian dust supply into the eastern mediterranean sea based on hematite contents derived from magnetic properties of sediments from ocean drilling program site 967 our record has an average temporal resolution of 400 years geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the sahara we deduce that the aeolian hematite in eastern mediterranean sediments derives from the eastern algerian libyan and western egyptian lowlands located north of the central saharan watershed 21 n in corroboration of earlier work we relate dust flux minima to penetration of the african summer monsoon front to the north of the central saharan watershed this would have enhanced soil humidity and vegetation cover in the source regions in agreement with results from green sahara climate models our results indicate that this northward monsoon penetration recurred during insolation maxima throughout the last 3 million years as would be expected this orbital precession scale mechanism is modulated on both short 100 kyr and long 400 kyr eccentricity time scales we also observe a strong expression of the 41 kyr obliquity cycle which we discuss in terms of high and low latitude mechanisms that involve southern hemisphere meridional temperature contrasts and shifts in the latitudes of the tropics respectively we also observe a marked increase in sub milankovitch variability around the mid pleistocene transition 0 95 ma which suggests a link between millennial scale climate variability including monsoon dynamics and the size of northern hemisphere ice sheets

experimental and numerical study of asperity degradation in the direct shear test abstract in this paper the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches pfc2d was used for numerical simulations in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes the damage process is simulated the joint interfaces were simulated by a newly developed modified smooth joint model in which micro scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box in order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests a comparative study was carried out against the physical experiments experimental and numerical direct shear tests were carried out on saw tooth triangular joints with the base angles of 20 and 30 under different normal stresses three shearing mechanisms of sliding surface wear and asperity shearing off were observed in these experiments the comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

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

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

estimating the relation between surface roughness and mechanical properties of rock joints discontinuities in rock masses have an important influence on deformational behaviour of blocky rock systems for a single rock joint the roughness of its surface is of paramount importance to its mechanical and hydraulic properties such as friction angle shear strength and dilatancy aperture many methods have been used to characterize the surface roughness of rock joints such as joint roughness coefficients jrc root mean square rms value structure function sf etc however most of these methods can only be used in the 2 d models in this study we carried out direct shear experiments on rock joints under both constant normal load cnl and constant normal stiffness cns conditions and measured the surfaces of rock joints before and after shearing using a 3 d laser scanning profilometer system by using a 3 d fractal evaluation method of roughness characterization the projective covering method pcm and a direct shear apparatus of high accuracy the relation between mechanical properties of rock joints under different boundary conditions and the change of their fractal dimensions in both 2 d and 3 d models have been examined which gives a new approach to accurately evaluate the evolution of roughness of rock joint surfaces and its influence on the hydro mechanical behaviours of rock joints

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

geological constraints on tidal dissipation and dynamical ellipticity of the earth over the past three million years the evolution of the solar system has been shown to be chaotic which limits our ability to retrace the orbital and precessional motion of the earth over more than 35 50 myr ref 2 moreover the precession obliquity and insolation parameters can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the earth induced by glacial cyclicity and mantle convection here we determine the average values of these dissipative effects over the past three million years we have computed the optimal fit between an exceptional palaeoclimate record from the eastern mediterranean sea and a model of the astronomical and insolation history by testing a number of values for the tidal dissipation and dynamical ellipticity parameters we find that the combined effects of dynamical ellipticity and tidal dissipation were on average significantly lower over the past three million years compared to their present day values determined from artificial satellite data and lunar ranging this secular variation associated with the plio pleistocene ice load history has caused an average acceleration in the earth s rotation over the past 3 myr which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean climate system through time

evidence for bacterial palaeoecological origin of mineral magnetic cycles in oxic and sub oxic tasman sea sediments abstract sediments from the tasman basin in the southwest pacific ocean show a cyclic pattern of variation in mineral magnetic properties including susceptibility and remanence over the brunhes chron the magnetic pattern is dominated by fluctuations in the concentration of a single domain ferrimagnetic component identified as bacterial magnetofossils by tem investigation of the magnetic fraction the intervals of low bacterial magnetite concentration occurring in glacial periods are accompanied by a change of the bacterial magnetosome morphology assemblage interpreted as recording a change in bacterial species assemblage there is no evidence of iron or sulphate reducing conditions during low bacterial magnetite intervals concentrations of bacterial magnetite are low when oxygen concentrations in surface sediment pore waters dropped either as the result of variation in bottom water oxygen concentration or sedimentation rate the variations in the magnetic signal are therefore interpreted as resulting primarily from bacterial palaeoecological control rather than dissolution or alteration the bacteria in this deep sea environment are apparently aerophilic and grow near the sediment surface within the oxic zone implying that magnetic remanence is also acquired near the surface but up to tens of centimetres below where the oxic zone is very thick

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

organic matter and trace element rich sapropels and black shales a geochemical comparison a distinct pliocene eastern mediterranean sapropel i 282 recovered from three ocean drilling program odp leg 160 sites has been investigated for its organic and inorganic composition this sapropel is characterized by high organic carbon corg and trace element contents and the presence of isorenieratene derivatives the latter suggests that the base of the photic zone was sulphidic during formation of the sapropel combined with evidence of bottom water anoxia preservation of laminae high redox sensitive trace element contents and the abundance and isotopic composition of pyrite this leads to the tentative conclusion that almost the entire water column may have been anoxic this anoxia resulted from high productivity and not from stagnation because an approximation of the trace element budget during sapropel formation shows that water exchange with the western mediterranean is needed entire water column anoxia has been suggested earlier for several black shales with regard to the depositional environment and the corg content however only the cenomanian turonian boundary event ctbe black shales appear to be comparable to this sapropel the proposed trace element removal mechanism of scavenging and co precipitation in an anoxic water column is thought to be similar for both types of deposits the ultimate trace element source for the sapropel however is seawater whereas it is hydrothermal and fluvial input for ctbe black shales because they have a larger temporal and spatial distribution nonetheless the corg rich eastern mediterranean pliocene sapropel discussed here may be considered to be a younger analogue of ctbe black shales

comparative study on dynamic shear behavior and failure mechanism of two types of granite joint abstract frictional instability such as fault slip rockburst injection induced earthquake and landslide is frequently associated with the unstable sliding of pre existing discontinuities this study aims to investigate the influence factors and mechanism of the unstable sliding of granite joints two types of granite granite a and granite b which are mainly composed of microcline albite quartz and biotite are used to prepare a number of splitting joints with the average jrc values of 12 7 and 15 7 respectively direct shear tests are then conducted under various normal stresses during which acoustic emissions are monitored and recorded test results reveal that the peak shear strength is generally greater for joint b than joint a while the post peak failure intensity with respect to post peak stress drop amplitude of stick slip peak energy rate the sound emitted during stress drops for joint b are smaller than that of joint a especially under the high normal stress condition the underlying contributing factors are studied according to the petrographic observation and the two dimensional joint surface roughness analysis the higher peak shear strength for joint b is related to the rougher joint surface which is associated with a larger mineral grain size the more violent post peak failure intensity in joint a is related to its smaller mineral grain size compact structure and fewer inherent cracks which favor a greater energy build up in the asperities the present study suggests that not only the roughness of discontinuity plane but also the micro texture of the host rock should be considered in the assessment of the fault slip rockburst hazards caused by the unstable sliding results of this research contribute to the better understanding of mechanism and influencing factors of fault slip rockburst as well as the mitigation of geohazards induced by the dynamic shear failure of rock discontinuities

magnetic unmixing of first order reversal curve diagrams using principal component analysis we describe a quantitative magnetic unmixing method based on principal component analysis pca of first order reversal curve forc diagrams for pca we resample forc distributions on grids that capture diagnostic signatures of single domain sd pseudo single domain psd and multi domain md magnetite as well as of minerals such as hematite individual forc diagrams are recast as linear combinations of end member em forc diagrams located at user defined positions in pca space the em selection is guided by constraints derived from physical modeling and imposed by data scatter we investigate temporal variations of two ems in bulk north atlantic sediment cores collected from the rockall trough and the iberian continental margin sediments from each site contain a mixture of magnetosomes and granulometrically distinct detrital magnetite we also quantify the spatial variation of three em components a coarse silt sized md component a fine silt sized psd component and a mixed clay sized component containing both sd magnetite and hematite in surficial sediments along the flow path of the north atlantic deep water nadw these samples were separated into granulometric fractions which helped constrain em definition pca based unmixing reveals systematic variations in em relative abundance as a function of distance along nadw flow finally we apply pca to the combined dataset of rockall trough and nadw sediments which can be recast as a four em mixture providing enhanced discrimination between components our method forms the foundation of a general solution to the problem of unmixing multi component magnetic mixtures a fundamental task of rock magnetic studies this article is protected by copyright all rights reserved

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

progressive dissolution of titanomagnetites at odp site 653 tyrrhenian sea abstract magnetic properties microscopy and ferrous ferric iron ratio document increasing down core alteration of titanomagnetite to iron sulfide at odp site 653 leg 107 tyrrhenian sea changes in magnetic properties are interpreted to indicate a grain size increase in titanomagnetite to 40 m below seafloor bsf and a grain size decrease from this level to about 150 m bsf as dissolution affects first the fine grained and then the coarser grained magnetite the availability of dissolved sulfate from underlying messinian evaporites may account for the sulfide supply at depth and hence for the prolonged dissolution process dissolution at leg 107 sites adjacent to site 653 is less pronounced possibly by the availability of organic matter that can be metabolised by sulfate reducing bacteria