recovery of small strain stiffness following blast induced liquefaction based on shear wave velocity measurements changes in soil fabric following liquefaction have been studied using various in situ methods and often return inconclusive or conflicting observations the time rate variation of stiffness when

results of rock magnetic investigations and relative paleointensity determinations on lacustrine sediments from birkat ram golan heights israel i detailed rock magnetic investigations including the analysis of the laboratory installed magnetizations the measurement of hysteresis parameters and the high temperature dependency of the saturation magnetization were carried out on sediments from birkat ram golan heights israel the 550 cm long composite profile composed of three single cores is supposed to span the late holocene i e the last 4400 years at least titanomagnetites in the pseudo single domain range were identified as the main magnetic carrier minerals in the homogenous sediments the variations in concentration and grain size of the magnetic fraction are only partly reflected in the sediment lithology the relative paleointensity was estimated by normalizing the intensity of the natural remanent magnetization nrm after demagnetization at 20 mt j nrm 20 mt by different concentration parameters the median destructive field of the nrm mdf nrm is coherent with the relative paleointensity estimates indicating that a sedimentary effect has not sufficiently been removed by the normalization process the morphologies of these estimates however correspond to the archeomagnetic records from bulgaria and greece therefore a second normalization based on the linear relationship between the paleointensity estimates and the mdf nrm was applied resulting in an improvement of the records

high resolution palaeosecular variation in northern europe during the last 3200 years variations in the declination inclination and relative palaeointensity of earth s magnetic field during the last 3200 yr have been recorded from a sequence of annually laminated sediments in lake pohjajarvi lat 62 n central finland the magnetic mineralogy is uniform with only small variations in concentration of magnetite of pseudo single domain psd grain size the variations in direction were found to be very similar to records reconstructed from other lakes in finland and northwest russia while the relative palaeointensity curve can be correlated accurately with archaeomagnetic data from central europe

reconstructing holocene geomagnetic field variation new methods models and implications reconstructions of the holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long term solar terrestrial relationships and as relative dating tools for geological and archaeological archives here we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts igneous rocks and sediment records a new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data to reduce the influence of a few individual records all sedimentary data are resampled in 50 yr bins which also means that more weight is given to archaeomagnetic data during the inversion the sedimentary declination data are treated as relative values and adjusted iteratively based on prior information finally an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model as a result of the data adjustments power has been shifted from quadrupole and octupole to higher degrees compared with previous holocene geomagnetic field models we find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr the new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder possibly originating from the equator less

holocene palaeoecology of the golan heights near east investigation of lacustrine sediments from birkat ram crater lake abstract lacustrine deposits of the crater lake birkat ram located in the northern golan heights have been used as a paleoecological archive preliminary sedimentological and palynological investigations based on a composite profile allow the reconstruction of the environmental history of the last 6500 years fluctuations of the pollen composition trees and shrubs versus herbs values of oak and olive tree correspond to changes in different sediment parameters total organic carbon magnetic susceptibility which can be interpreted as the effects of human impact on the geo biosphere four phases with strong settlement activities can be identified for the northern golan heights 1 during the chalcolithic period early bronze age 2 during the hellenistic roman byzantine periods 3 during the crusader period and finally during modern time these periods were interrupted by wooded regeneration phases with low anthropogenic activities

rare earth element geochemistry of ferromanganese crusts from the hawaiian archipelago central pacific abstract the rare earth element ree composition of ferromanganese deposits from the hawaiian archipelago was determined as part of a geochemical investigation into the origin and environment of deposition of crusts most samples exhibit shale normalized ree patterns which are typical of hydrogenous ferromanganese deposits patterns of two todorokite and manjiroite rich crusts are significantly different from those of the other samples the range of concentrations in typical hawaiian crusts sum of ree 0 15 0 25 wt is in the uppermost portion of that reported for deep sea fe mn nodules shallow water 2000 m as well as slightly greater ree fractionation large positive ce anomalies attributed to the oxidative scavenging at the mno 2 surface are observed on all samples except one the slight light ree lree depletion in shallow water crusts relative to deeper samples is discussed in terms of variations in the ree concentrations in the water column and the relative complexing behavior of the ree no significant trend in ce concentration with depth is observed partition coefficient calculations suggest that concentrations of trivalent ree in crusts are affected by their availability in seawater to a greater extent than by the composition of the scavenging ferromanganese oxide flocs

paleosecular variations since 9000 yr bp as recorded by sediments from maar lake shuangchiling hainan south china abstract high resolution paleosecular variation psv can play an important role in sediment dating and for understanding the temporal characteristics of the geodynamo of the earth s magnetic field in this article based on magnetic susceptibility correlation a composite sediment profile has been compiled from a 16 m long core hn 2 and a 8 m deep well hn 3 in shuangchiling maar lake a crater basin located on hainan island southern china fine and homogeneous silty clay corroborates with a stable continuous and undisturbed deposition a u channel based paleomagnetic study constrained by ams14c chronology derived from leaves plant debris and woods and supported by rock magnetic data indicates that the lake sediments document a reliable paleosecular variation psv record since 9000 cal year bp comparison of our psv features with other records from lakes biwa japan erhai china baikal russia as well as archaeomagnetic records demonstrate that the inclination pattern is generally synchronous within chronological uncertainties suggesting further psv dating may be valuable for stratigraphic correlation on a regional scale

environmental magnetism of antarctic late pleistocene sediments and interhemispheric correlation of climatic events abstract recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences studies of these changes contribute to the reconstruction of climate history for the glacial interglacial cycles of the late pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years here we show that sharp coercivity minima observed in fine grained sediments from the continental rise of the western antarctic peninsula correlate to the major rapid cooling events of the northern atlantic heinrich layers we interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation which reflect changes in the input of detrital organic matter controlled by sea ice extent with the inherent uncertainties in age controls the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous but interhemispheric time lags or leads of the order of 1 2 kyr such as those recently reported from the greenland and antarctic ice cores are also compatible with the data

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

high resolution paleomagnetic records from holocene sediments from the palmer deep western antartic peninsula thick holocene sedimentary sections 45 m cored in the palmer deep by the united states antarctic program usap and during ocean drilling program odp leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes after removal of a low coercivity drilling overprint the sediments display a stable single component remanent magnetization two short cores that recovered the uppermost 2 6 m of sediment have inclinations that fluctuate about the present day inclination 57 measured at faraday station and several features with wavelengths of 10 to 20 cm appear to be correlative however shipboard measurements of inclination fluctuations on split core samples from three holes drilled at odp site 1098 do not correlate well with each other even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole gad inclination the correlation is improved dramatically by using inclinations measured on u channels taken from the pristine center of a split core consequently the anomalous directions and the resulting poor between hole correlation of inclinations obtained from shipboard data can be attributed to coring induced deformation which is common on the outer edge of odp piston cores and or measurement artifacts in the split core data our preferred inclination record is thus derived from u channel results the upper 25 m represents continuous sedimentation over the past 9000 yr with an average sedimentation rate exceeding 250 cm kyr 0 25 cm yr given that remanence measurements on u channels average over an interval 7 cm long we obtained independent measurements of the paleo geomagnetic field that average over only 30 yr this high resolution record is characterized by an inclination that fluctuates within 15 of the current gad inclination

enigmatic chambered structures in cryogenian reefs the oldest sponge grade organisms abstract previously undescribed chambered structures are common and widespread in the cryogenian post sturtian glacial carbonates of the oodnaminta reef complex adelaide geosyncline south australia the rasthof berg aukas formation namibia and the gauss formation namibia these carbonate structures have millimetre to centimetre scale chambers separated by well defined and generally thin micritic walls chamber walls now consist of dolomite but were probably originally aragonitic the chambers may have a lobate polygonal or dendritic morphology and are often further divided into smaller chambers chambered structures occur as reefal growth frameworks as cavity fillings in neptunean dykes and growth cavities and as intercolumnar material within stromatolite frameworks in the oodnaminta reef complex these structures are only present in the sub photic deep water framework these structures probably represent the calcified remains of an organism or community of organisms that was globally distributed and widespread for a significant time period following the sturtian glaciation no precisely analogous structures have been previously described from modern or ancient settings but the complexity and degree of organization suggests a significant evolutionary advance over older proterozoic fossils the closest morphological analogues for the structures are a some types of reef dwelling sponges and b some complex microbialites from archaean and paleoproterozoic carbonates the structures lack spicules and ostia found in sponges ruling out a true poriferan origin however it is plausible that they are proto sponges sponge grade organisms or complex microbial precursors to sponge grade organisms whatever their affinity we suggest these structures record a significant evolutionary event on the path towards organic complexity

near shore hypoxia in the chesapeake bay patterns and relationships among physical factors near shore shallow waters in the chesapeake bay periodically experience episodes of anoxia or severe hypoxia during summer in order to examine the severity and temporal pattern of hypoxia and environmental factors that may lead to such episodes dissolved oxygen salinity and temperature were measured at 15 min intervals during the summers of 1987 and 1988 in a western shore oyster bed bottom dissolved oxygen concentrations averaged lower at a 4 m site than at a 2 m site at the 4 m site dissolved oxygen concentrations dropped below 2 mg l 1 during approximately 40 of days and below 1 mg l 1 during approximately 10 of days each summer however diel fluctuations in oxygen concentrations were sufficiently large that even on days of the most severe oxygen minima dissolved oxygen concentrations always reached or exceeded a level tolerable by most estuarine organisms during some part of the day during episodes of severe hypoxia on the western shore of the chesapeake bay oxygen minima 1 coincided with increased salinities and ebb tides 2 were preceded by winds from the s sse minima of 0 5 1 mg l 1 or sw minima of 0 6 1 1 mg l 1 and 3 were reached during 22 00 06 00 hours severe hypoxia at the study site therefore appeared to result from intrusions of bottom water which were most effectively driven by southerly winds tidal currents were required to provide the final force that brought deep water close to shore the diel pattern of intrusions is most likely caused by winds which were often either too strong or had too weak a southerly component to permit intrusions without near shore mixing and reaeration to occur during afternoon early evening hours and the diel periodicity of tides short term fluctuations in temperature and salinity were not as great as fluctuations in dissolved oxygen when compared to seasonal fluctuations of each parameter for many organisms short term fluctuations in temperature and salinity may therefore be less likely to influence the habitability of areas such as the near shore chesapeake bay than are similar duration fluctuations in dissolved oxygen concentrations

diagenetic alteration of chamositic clay minerals to ferric oxide in oolitic ironstone abstract in the clinton oolitic ironstone silurian of pennsylvania ooids that were initially composed of chamositic clay minerals were diagenetically altered to ferric oxide evidence for this alteration includes the preservation of intermediate stages in a variety of partly altered ooids finely laminated chamositic ooids in marginal zones of ferric oxide storm beds bed parallel transitions of ooid compositions in bioturbated oolite and spastolithic shapes of ferric oxide ooids electron microprobe analysis demonstrates that this oxic alteration did not leave significant abundances of residual silicon and aluminum based on textural characteristics and on a permian age of remagnetization the most likely time for the alteration was during early phases of the alleghany orogeny recognitio that the ooids were initially chamositic clay minerals resolves at least part of the oxidation reduction paradox maynard 1986 for ferrous phyllosilicate could presumably accumulate in the low oxygen conditions associated with the medial silurian oceanic anoxic event

a lacustrine record of paleomagnetic secular variations from birkat ram golan heights israel for the last 4400 years abstract detailed paleo and rock magnetism investigations were carried out on three sediment cores from birkat ram golan heights israel based on high resolution logs of magnetic susceptibility a 5 4 m long composite profile was created that spans the last 4400 years the time interval covered by a single sample is about 26 years characteristic remanent magnetisation chrm of all 288 samples was determined by analysis of the results of progressive alternating field af demagnetisation the brown to olive coloured homogenous sediments show a fairly stable magnetisation and the obtained inclination and declination records agree with the archaeomagnetic records from iraq egypt and israel comparison of the psv records from birkat ram with those from bulgaria and hungary yielded a different behaviour of the earth s magnetic field vector over the near east and southeast europe during the last 1000 years

holocene geocentric dipole tilt model constrained by sedimentary paleomagnetic data paleomagnetic data although undeniably limited have been used to constrain complex time varying geomagnetic field models here we present four different versions of a time varying geocentric dipole model for the past approximately 9000 years based on a limited selection of sedimentary paleomagnetic data with good spatial coverage the robustness of the modeling approach is evaluated using modern magnetic observation station data provided by the world data centre for geomagnetism in edinburgh and we discuss the magnitude of the error introduced by insufficient data coverage the prediction in terms of directional variations is tested against paleomagnetic data from 63 different sedimentary sites and compared to results from recently published spherical harmonic geomagnetic field models we find that the dipole estimate can explain the paleomagnetic data almost as well as the more complicated spherical harmonic models specific areas and records are identified where there are significant differences between the performance of the dipole estimate and the spherical harmonic models our results suggest that many of the differences between the dipole model predictions and the paleomagnetic data can be related to poor paleomagnetic quality and or the lack of accurate and precise time control inherent to some of the records these results agree with valet et al 2008 who suggested that the cals7k 2 model probably underestimates the dipole contribution in order to reduce the misfit between the inversion and the data we conclude that better paleomagnetic data and associated time control are needed to improve global geomagnetic field models less

origin and palaeogeographical distribution of the viruan iron and phosphate ooids in estonia evidence from mineralogical and chemical compositions abstract the occurrence of iron ooid beds in the ordovician sequence of baltoscandia has been known for a long time in estonia the best developed ooid beds are known to occur at two levels in the lower oelandian to middle ordovician viruan boundary interval being restricted to the kunda and aseri lasnamagi stages respectively according to outcrop and subsurface data these ooid beds can be traced from hiiumaa island estonia to the st petersburg area russia in the east the geographic and stratigraphic distribution of the viruan oolite body indicates that the source material was derived from a land area located northwest to north northwest of tallinn the presence of well developed hardgrounds at the base of viruan oolite suggests that ooid formation took place during a deepening event two mineralogically different ooid groups have been identified in this study brown ooids composed of iron oxy hydroxides and apatite and light grey ooids composed primarily of carbonate fluorapatite the latter probably formed through early diagenetic alteration of the brown ooids brown ooids contain over 60 of iron oxy hydroxide and remnants of an unidentified silicate mineral the concentric lamination is composed of alternating laminae of phosphate francolite and iron oxy hydroxide the trace element abundances in the ooids are strongly influenced by the phosphate content as is the observed ree distribution pattern the chondrite normalized ree patterns are characterized by enrichment of the lighter ree and have a typical negative eu anomaly of about 0 7 shale normalized ree patterns have a hat shape similar to ree patterns found in conodonts and other biogenic apatite thin volcanic ash beds have been recorded at this level in sweden in estonia however there are no visible indications of volcanic material

beyond black shales the sedimentary and stable isotope records of oceanic anoxic events in a dominantly oxic basin silurian appalachian basin usa abstract episodes of instability in the global climato oceanic system have become the hallmark of the silurian period these events are marked by six large positive carbon isotope excursions associated with major extinctions the widespread environmental consequences of these perturbations of the global carbon cycle remain poorly documented a high resolution chronostratigraphic reconstruction of the appalachian foreland basin afb provides a framework to evaluate environmental signatures of two of these carbon isotope excursions valgu and ireviken events telychian sheinwoodian at a regional scale integration of published biostratigraphic range data mapping of sequence stratigraphic surfaces and facies and generation of high resolution carbon isotope profiles for several transects provides precise correlation of the basin stratigraphy yielding a high resolution temporal framework this chronostratigraphic reconstruction of the afb highlights the importance of time specific facies tsf during these intervals for instance packages of red green and gray marine rocks separately occupied discrete time intervals cutting across local facies belts indicative of shallow to deep marine environments similarly widespread iron mineralization occurred during discreet time slices as bathtub rings rimming the margins of the basin changes from one time specific facies to the next are coincident with changes in carbon isotope values indicating a genetic link between fractionation of the global carbon reservoir and redox changes from generally oxic to anoxic oceanic conditions in parts of the afb the basal part of the study interval was deposited during the valgu event this first event begins with an unconformity marking global lowstand this fall in sea level was coincident with rising carbon isotope values as recorded in adjacent basins a slight sea level rise and flooding of the subaerial unconformity occurred near the peak in carbon isotope values oxidized iron minerals were deposited in a zone that extended from the lower shoreface into the basin center pinching out into shallower parts of the basin thin pyrite phosphorite glauconite layers associated with black shales in the basin center were deposited over these ferruginous strata as the event ended and carbon isotope values shifted negatively to a more stable baseline temperatures warmed sea level reached a silurian high and oxic conditions associated with very low rates of organic carbon oc burial were established these conditions were relatively stable for nearly four million years this long period of stasis was punctuated by the ireviken event which displays a strikingly similar progression of tsf patterns yet more intense and longer lived than the preceding valgu event with the first positive shift in carbon isotopes at the onset of the ireviken event the basin redox system changed from largely oxidizing to reducing coincident with a rapid drop in sea level and an abrupt reappearance of iron mineralization on the basin margins the sea level fall associated with the shift to peak values of the carbon isotope excursion is marked by the progradation of a significant body of sand well out into the basin during this sea level drop conditions in the basin center became highly reducing and periodically sulfidic widespread ironstones and ankeritic carbonates were deposited isochronously rimming the shallow basin margins where they alternated with light gray pyritic shales indicating fluctuating redox conditions a large negative carbon isotope excursion of 3 is coincident with a shift from regression to transgression suggesting glacial melting via methane release continued deposition of ironstones through this time interval suggests a primary link to shallow marine redox processes rather than large scale transgression or regression of the shoreline the ironstones are overlain by gray to black pyritic shales deposited across all environments revealing a final stage of redox progression into sustained sulfidic conditions as peak values of the carbon isotope excursion returned to a high stable baseline near 4 the similar expression of tsfs within the afb of these two global events demonstrates that fractionation of the global atmospheric and oceanic carbon reservoirs had a predictable cascading impact on shallow sea floor environments the associated redox processes reveal the dynamic regional interactions of a shallow oxic epicontinental water mass with a broader anoxic oceanic water mass providing valuable insight into the origin of some of the largest extinctions in the silurian period

geomagnetic secular variations over the last 6500 years as recorded by sediments from the lakes of south argentina summary regional type curves depicting secular variations in declination and inclination through the last 6700 calendar years constructed for southwestern argentina about 41 s 71 30 w by stacking palaeomagnetic data derived from lake sediment cores are described and analysed the data consist of records from four lakes which have been previously studied el trebol brazo campanario moreno and escondido and are here integrated within lake correlation was based on magnetic susceptibility and intensity of the natural remanent magnetization nrm interlake correlation was derived from declination and inclination patterns and a set of radiocarbon age determinations the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the spectrum obtained from spectral analysis of declination d and inclination i at the same time shows major peaks at periodicities of about 3400 1600 and 1200 yr for both parameters in order to test the stability of the periodicities obtained spectral analysis has been applied to every 3500 yr time span at intervals of 500 yr for both records patterns of circularity during the last 6700 yr appear to recur with a near constant interval of about 2000 yr both open and closed loops are associated with clockwise and counter clockwise circularity

compaction of alluvial sands by deep blasting the jebba hydroelectric development nigeria presently under construction features a 42 m high zoned rockfill embankment founded on river alluvium up to 70 m in depth the riverbed alluvium comprises fine to medium to coarse grained quartzitic sands with traces of gravel the relative densities of the sands vary appreciably in both the vertical and horizontal directions during the dam design it was found that it would be necessary to densify the loose to medium dense portion of the river sands to maintain settlements within acceptable limits and to withstand design earthquake forces the top 25 m of the river alluvium is densified by the vibrocompaction method and below this level down to depths of 40 m the alluvium is densified by blasting there is no precedent found in the literature for densification by blasting at such depth this paper presents details of a test program and the production work test results conclusively show increases in static cone penetration resistance in loose sand layers

effects of clay mineralogy and the electrical conductivity of water on the acquisition of depositional remanent magnetization in sediments new experiments on the interrelationship of clay minerals solution properties and postdepositional remanent magnetization pdrm provide interesting insights into pdrm acquisition we have found that clay mineral content composition and solution conductivity affect pdrm strongly with increasing clay concentration or electrolyte concentration pdrm intensity decreases clay minerals may also be responsible for the inclination shallowing of pdrm different clay minerals behave differently for example montmorillonite diminishes pdrm intensity more rapidly than kaolin anson and kodama 1987 have suggested an electrostatic model to explain their results of a similar study however we cannot explain all of our results by using their electrostatic model to us it seems that colloid coagulation is the key to explaining the results two kinds of forces exist in a colloidal solution electric repulsion and van der waals attraction in low electrolyte concentration solutions repulsion is larger than attraction strong brownian motion is therefore required to enable the particles to cross over the repulsive energy barrier in order to stick to each other but in high electrolyte concentration solutions repulsion becomes relatively small and particles stick together much more easily thus the effective mass of the grain becomes larger clay magnetite but the magnetic moment remains the same and hence the magnetic torque is relatively less effective as a result the magnetic carriers do not align effectively in the direction of the ambient field making the pdrm intensity weaker

high resolution record of geomagnetic secular variation from late pleistocene lake lisan sediments paleo dead sea we measured geomagnetic secular variation in lake lisan sediments paleo dead sea more than 1500 oriented samples were collected from a 27 3 m section of alternating aragonite and detritus laminae in the dead sea basin ranging in age from 67 to 32 ka the natural remanent magnetization nrm is carried by titanomagnetite in the detrital laminae whereas the aragonite is diamagnetic the nrm is very stable and was acquired several hundred years after deposition the mean direction of 878 horizons is dd 005o id 45o 95d 1o d 22 we observed three modes of directional geomagnetic variation as a function of and by inference time very rapid inter sample changes slow variation in mean direction and inclination shallowing of about 1o m the overall rate of change in direction is 0 57 0 57o year not significantly different from zero for about 83 of the record the rate of change is less than 1o year and comparable to historical values high rates of change are observed more frequently in the lisan than in historical records and peak rates are up to ten times faster a smoothed curve resulting in a maximum rate of change of 0 66o year and a mean 0 10 0 10o year may be a more realistic representation of the field behavior no reverse nrms were observed but geomagnetic field excursions may be present where the vgps deviate by more than 40o from the geographic north at about 52 and 41 ka the latter may represent the laschamp event 1998 elsevier science b v all rights reserved

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

eocene early miocene foreland basin development and the history of himalayan thrusting western and central nepal sedimentologic petrographic and u pb detrital zircon ages from middle eocene through early miocene sedimentary rocks in the lesser himalayan zone of western and central nepal indicate that a peripheral foreland basin system had developed in the eastern himalayan collision zone by middle eocene time the shallow marine eocene bhainskati formation accumulated in a back bulge depozone between a southward migrating forebulge and the indian craton migration of the forebulge through this region during eocene oligocene time produced a regional unconformity that spans 15 20 myr by early miocene time the forebulge unconformity was onlapped by the distal fringes of the southward migrating foredeep depozone represented by fluvial deposits of the dumri formation continued southward migration of the foredeep during the neogene accommodated the fluvial siwalik group light mineral provenance data and u pb detrital zircon ages suggest that the bhainskati was derived partly from tethyan sedimentary rocks of the tibetan himalayan zone during initial growth of the himalayan fold thrust belt the dumri was derived from metasedimentary and crystalline rocks of the greater himalayan zone during emplacement of the main central thrust and contemporaneous tectonic unroofing by normal faulting along the south tibetan detachment system the lesser himalayan crystalline thrust sheets were emplaced soon after deposition of the dumri formation 15 10 ma paleocurrent and lithofacies data from the dumri formation indicate deposition by west southwestward flowing rivers that drained into the indus portion of the himalayan foreland basin system during the early miocene thick channel sandstones in the lower dumri may represent the early miocene counterpart of the modern ganges river eastward diversion of the ganges drainage system to near its present location had occurred by 15 ma as the high standing aravalli range on the northern indian shield approached the front of the fold thrust belt assuming reasonable values for the flexural rigidity of indian lithosphere the time span of the forebulge unconformity yields a velocity of 14 33 mm yr for the southward migration of the fold thrust belt relative to india this range of values is consistent with neogene and present day estimates and suggests that only one third to one half of india eurasia convergence has been accommodated by shortening in the himalayan fold thrust belt since the onset of collision

condensation and phosphatization of the middle and upper ordovician limestones on the malopolska block poland response to paleoceanographic conditions abstract the growth fault activity in the late middle ordovician resulted in the establishment of a horst like submarine paleohigh in the northern malopolska block this topographic submarine swell was the site of carbonate deposition characterized by a low overall net sediment accumulation rate the sedimentary and ecological conditions on this paleohigh were controlled by a paleocurrent that flowed along the northern margin of the malopolska block however seasonal intense storms associated with the mid latitude location of this terrane cannot be excluded the paleocurrent induced seasonal upwelling of nutrient rich waters from deeper parts of the current system that shifted onto the paleohigh and caused phosphatization of the sediment the winnowing and reworking of sediment together with slow carbonate production by a temperate water biota and relatively long periods of omission resulted in low accumulation rates and sediment condensation the cessation of the paleocurrent and associated phosphatization coincides with changes in the oceanic circulation system due to the late ordovician collision of avalonia with baltica and gradual closure of the tornquist sea

canlex full scale experiment and modelling a major aim of the canadian liquefaction experiment canlex was to verify analysis procedures for pre dicting liquefaction phenomena towards this purpose two loading events were carried out a field event comprising a clay embankment built over a loose sand foundation layer and a centrifuge test performed on a model of a sand em bankment structure both the field event and the centrifuge model were planned so as to induce a static liquefaction failure and were instrumented to observe their response in terms of displacement and pore pressure the fundamental mechanical characteristics of the foundation layer were determined from laboratory element tests triaxial and simple shear these tests formed the basis for the stress strain modelling used in the numerical analyses two fundamentally different modelling techniques were used one involved a fully coupled plasticity model and the other involved a model based on a collapse surface approach the model and prototype structures were then analyzed and the predicted results in terms of displacements and pore pressures were compared with the measured values the results from both approaches were found to be in reasonable agreement with the measurements provided allowance was made for direc tion of loading and drainage effects were accounted for resume un but principal du canadian liquefaction experiment canlex etait de verifier les procedures d analyse pour predire les phenomenes de liquefaction a cette fin deux cas de chargement ont ete realises un chargement sur le terrain comprenant la construction d un remblai d argile sur une couche de fondation de sable meuble et un essai au centrifuge realise sur un modele d une structure de remblai de sable tant le remblai sur le terrain que le modele dans le centrifuge ont ete planifies de facon a induire une rupture par liquefaction statique et ont ete instrumentes pour ob server leurs reponses en termes de deplacement et de pression interstitielle les caracteristiques mecaniques

iron rich carbonate tidal deposits angepena formation south australia a redox stratified cryogenian basin abstract the cryogenian angepena formation ca 650 ma of south australia records deposition in a peritidal environment equivalent to and landward of the balcanoona reef complex and offers valuable insights into shallow marine chemistry during the nonglacial interlude between two global ice ages the sedimentary facies comprise an iron rich marine red bed succession and include red mudcracked dolomitic shales tepee dolostone crossbedded intraclastic ooid grainstone and tepee related sheet cavities with marine cements these facies are interpreted to have been deposited in a cryogenian tidal flat to subtidal setting that is laterally equivalent to the reefal and back reef environments of the balcanoona formation marine cements from this environment are characterized by well preserved non and bright cathodoluminescent zoning and strong negative to slightly positive cerium ce anomalies ce ce we suggest that the angepena formation is indicative of intermittent synsedimentary iron oxide precipitation in an oxidized peritidal environment in an otherwise strongly ferruginous and anoxic oceanic setting large negative ce anomalies develop over a narrower depth range when compared to modern oxic marine settings highlighting the importance of dissolved mn and fe concentrations in controlling the magnitude of the negative ce anomalies overall coupled sedimentological and geochemical evidence suggest a neoproterozoic shallow marine system at the interface of an oxidizing atmosphere and an anoxic ferruginous marine system

a comparative study of the arm and isr of some natural magnetites of md and psd grain size summary arm and isr stability with respect to alternating field and low temperature treatment were measured for a set of artificial rock specimens each of the specimens contained a known amount of a natural magnetic mineral of a known grain size the following minerals were used a homogeneous natural magnetite a natural titanomagnetite with submicroscopic fe rich inclusions and a natural titanomagnetite and a natural titano maghemite that both show exsolution phenomena the grain size of the fractions varied from 5 to 250 m it is found that the stability of arm and irs of multi domain grains with respect to alternating fields and low temperature treatment is similar whereas for the smallest grains studied 5 m arm is more stable than isr multi domain arm data from this study are in agreement with current multi domain arm theory low temperature behaviour of arm and isr can be explained either in terms of a model in which stable moments in the bulk of the grains are screened by the surrounding matrix or in terms of a model in which regeneration of the bulk remanence plays a role and in which stable moments are situated on the surfaces of the grains

spline analysis of holocene sediment magnetic records uncertainty estimates for field modeling 1 sediment and archeomagnetic data spanning the holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia in global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates uncertainties in sediment magnetic records arise from 1 imperfections in the paleomagnetic recording processes 2 coring and sub sampling methods 3 adopted averaging procedures and 4 uncertainties in the age depth models we take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of holocene magnetic records smoothing spline models that capture the robust aspects of individual records are derived this involves a cross validation approach based on an absolute deviation measure of misfit to determine the smoothing parameter for each spline model together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock in depth departures from the spline models provide information concerning the random variability in each record temporal resolution analysis reveals that 50 of the records have smoothing times between 80 and 250 years we also perform comparisons among the sediment magnetic records and archeomagnetic data as well as with predictions from the global historical and archeomagnetic field models combining these approaches we arrive at individual uncertainty estimates for each sediment record these range from 2 5 to 11 2 median 5 9 interquartile range 5 4 to 7 2 for inclination 4 1 to 46 9 median 13 4 interquartile range 11 4 to 18 9 for relative declination and 0 59 to 1 32 median 0 93 interquartile range 0 86 to 1 01 for standardized relative paleointensity these values suggest that uncertainties may have been underestimated in previous studies no compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of holocene sediment magnetic records the analysis highlights the importance of collecting oriented cores publishing and archiving unprocessed raw paleosecular variation determinations and presenting a detailed chronology so that changes in the sedimentation rate can be assessed with regard to future field models workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high latitude declination records

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

dissolved rare earth elements in the southern ocean cerium oxidation and the influence of hydrography abstract analysis of dissolved ree distributions in the southeastern atlantic ocean has revealed that progressive oxidative removal of dissolved ce from deepwater 1 km occurs over the mixing time of the oceans ce anomaly ce ce values measured in deep waters from the southeastern atlantic are similar to but slightly higher than those from deep ocean stations throughout the indian and pacific oceans typically falling in the range 0 08ce ce 0 12 only deepwater samples from the north atlantic exhibit values greater than ce ce 0 12 with the exception of southeastern atlantic bottomwaters which are influenced by antarctic bottomwater covariation of dissolved ree concentrations with salinity and or dissolved si concentrations at this site has allowed dissolved ree compositions for various southern ocean water masses to be predicted end member concentrations for antarctic bottom water aabw derived in this way indicate high dissolved ree concentrations similar to average pacific deep water but with significantly enhanced dissolved ce concentrations and less pronounced hree enrichment this result is consistent with the proximity of our study site to active aabw deepwater formation and evolution of that water mass during transport to the pacific ocean

the stratigraphic expression of a large negative carbon isotope excursion from the ediacaran johnnie formation death valley the rainstorm member of the ediacaran johnnie formation of the southern basin and range us records a large negative excursion in carbon isotope ratios of carbonate strata 13 c vpdb 6 the character of the excursion raises fundamental questions about whether this isotopic pattern is accurately capturing the time series behavior of marine dissolved inorganic carbon dic or is a product of diagenesis to explore this issue we examined the expression of this isotopic excursion within the johnnie oolite a 2 m thick marker bed which records the highest rate of change in 13 c sedimentologically the oolite unit is thought to be time transgressive if the isotopic excursion reflects time series behavior of the carbon cycle its expression in the oolite across the basin should systematically align the sections according to their slight diachroneity detailed carbon and oxygen isotopic stratigraphy of the oolite at seven different locations indicates the magnitude of the excursion at the base of the oolite is spatially variable such that after a palinspastic reconstruction the sections align along a systematic north to south gradient in the isotopic data the oolite preserved in the old dad mountains the most southerly section measured is an outlier to this trend and the most difficult to ordinate accurately in the reconstruction showing the largest isotopic range between the onset of carbonate deposition and top of the oolite several hypotheses are congruent with these data but the sum of observations is best explained by a scenario wherein the oolite is time transgressive and deposited in a north to south manner throughout the onset of the isotopic excursion if correct this implies that the stratigraphic 13 c pattern reflects time series behavior of marine dic

synsedimentary diagenesis in a cryogenian reef complex ubiquitous marine dolomite precipitation abstract analysis of the synsedimentary diagenetic phases from a pervasively dolomitised cryogenian 650 ma reef complex south australia reveals a fundamentally different style of marine diagenesis to that of phanerozoic carbonates textural evidence from dolomitised and undolomitised lithologies of the oodnaminta reef complex indicates that depositional components were precipitated initially as calcium carbonate aragonite and calcite dissolution textures and preserved fabrics in ooids indicate an originally aragonitic mineralogy early fibrous marine cements that have well preserved fibrous crystallographic fabrics with a length fast optical character are likely to have precipitated as high magnesium calcite however following this very early phase of diagenesis the dominant marine process occurring in these reefs was dolomite precipitation this involved the dolomitisation of earlier depositional and diagenetic phases as well as the precipitation of fibrous dolomite cements these fibrous marine cements include the newly described radial slow fascicular slow radiaxial slow and rhombic dolomite cements the cements have optical properties chemical zonation and cathodoluminescent characteristics indicating that they were direct marine precipitates dolomite precipitation during marine diagenesis in this reef complex suggests that the oceans of the cryogenian were chemically different to those of the phanerozoic abundant dolomite formation appears to be linked to anoxic magnesium rich seawater during this time marine dolomite precipitation under these conditions may explain the abundance of dolomite in the precambrian sedimentary record

cretaceous oceanic red beds corbs different time scales and models of origin abstract the cretaceous oceanic red bed corb is a newly opened window on global oceanic and climate changes during the cretaceous greenhouse world as a result of the international geoscience programmes 463 494 and 555 2002 2010 corbs have been documented in many places by numerous publications the principle goal of this paper is to summarize scientific advances on corbs including chronostratigraphy sedimentology mineralogy elemental and isotopic geochemistry and their relationship to oceanic anoxic events oaes palaeoclimate and palaeoceanography we propose a new geochemical classification of the corbs using cao al 2 o 3 and sio 2 values which lithologically refer to marly clayey and cherty corbs respectively detailed mineralogical studies indicate that hematite goethite and mn 2 bearing calcite are the minerals imparting the red color of corbs hematite clusters of several to tens of nanometers in the calcite structure are the main cause of the red coloring of limestones and the mn 2 bearing calcite gives additional red color goethite was thought to form originally with hematite and was subsequently transformed to hematite during late diagenesis chronostratigraphic data allow the distinction of two groups of corbs by their durations short term corbs are generally less than 1 myr in duration and seem to be on the scale of milankovitch cycles during the deposition of cretaceous reddish intervals from odp cores 1049 and 1050 low primary productivity and relatively high surface temperature resulted in low organic carbon flux into the sediments which reduced oxygen demand and produced oxidizing early diagenetic conditions in such an oxic environment iron oxides formed imparting the reddish color the long term corbs depositional events lasted longer than 4 myr and may be a possible consequence of the oaes enhanced amounts of organic carbon and pyrite burial during and after the oaes would have resulted in a large and abrupt fall in atmospheric co 2 concentration which probably induced significant global climatic cooling during and after the oaes global cooling would have enhanced formation of cold deep water increasing its oxidizing capacity due to the greater content of dissolved oxygen and would promote formation of oceanic red beds sedimentological mineralogical and geochemical data indicate that corbs were deposited under highly oxic oligotrophic conditions probably at a low sedimentation rate the cretaceous red and white limestones from italy have similar compositions of terrestrial input sensitive elements al ti k mg rb zr higher contents of fe 2 o 3 and depleted redox sensitive elements v cr ni and u and micronutrient elements cu zn indicating similar provenance sources but red limestones were deposited under more oxic conditions at the sediment water interface than white limestones the cretaceous red shales such as those from the north atlantic and tibet have similar mineralogy and geochemistry as the late cenozoic red clays in the pacific ocean and the environment where both are formed was well oxidizing at a very low sedimentation rate we compiled seventeen published stratigraphic examples of phanerozoic oceanic red beds including the late cenozoic red clays in the pacific different hypotheses explain the origin of red pigmentation of limestones and shales including 1 detrital origin of iron derived from continental weathering 2 iron bacterial mediation at the time of sedimentation and 3 iron oxidation in oligotrophic highly oxic environment additional research on phanerozoic oceanic red beds is needed in order to better document their origin and palaeoceanographic and palaeoclimatic significance

the cryogenian balcanoona reef complexes of the northern flinders ranges implications for neoproterozoic ocean chemistry abstract the cryogenian balcanoona reef complexes of south australia consist of several dolomite platforms with well defined backreef reef margin and slope basinal facies the mature platforms have prograded large distances into the basin 15 km and have high relief margins over 1 km of relief at the platform margin backreef facies are dominantly ooidal peloidal grainstones with abundant tepees and marine cemented sheet cavities the reef margin facies consists of upper stromatolitic boundstones and where present deeper water non stromatolitic chambered and clotted boundstones the deepwater chambered and clotted boundstones grew on near vertical escarpments below 150 m paleo water depths and consist of a complex array of marine cemented cavernous and calcimicrobial material the strongly prograding platforms range from accretionary low angle stromatolitic boundstone margins through to more mature escarpment margins the mature escarpment margins 200 m high escarpment are characterized by the development of both stromatolitic and non stromatolitic boundstones the slope basin facies of the mature escarpment margins consists of coarse debris deposits talus debrites and allochthonous blocks proximal to the platforms and calcareous dolomitic mudrocks distal to the platforms the development of an accretionary escarpment margin together with the large proportion of deepwater boundstone suggests that these cryogenian reefs were fundamentally different from phanerozoic reefal systems the enormous volume of deepwater boundstone in these reefs may be due to a severely anoxic water column that prevailed during this period of the cryogenian anoxia led to greater degrees of carbonate saturation at depth that enabled the development of deepwater boundstones with escarpment margins a community of anoxic adapted non photosynthetic organisms that were perhaps similar in their ecology to phanerozoic coelobiontic reefal communities may have constructed the enigmatic deepwater boundstone just prior to the final termination of the reef the system was subject to large scale erosion and margin collapse producing a major regional unconformity following this the reefs briefly re grew before final and complete cessation of the reef complexes the large scale margin collapse event may have been triggered by sea level fluctuation and or changes in ocean chemistry associated with late cryogenian oxygenation

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

geomagnetic secular variations in greece through the last 6000 years obtained from lake sediment studies summary geomagnetic declination and inclination secular variation curves have been constructed back to 6000 yr bp from palaeomagnetic measurements of sediments cored in lakes volvi trikhonis and begoritis greece they have been dated by palynological studies and by comparison with observatory and archaeomagnetic records radiocarbon ages are all affected by the old carbon factor cores from all three lakes contain a thin ash layer which we associate with the pompeii eruption of vesuvius in ad 79 averaged curves of secular variations of declination and inclination have been computed for the whole study the broader scale pattern of secular variations is basically similar to lake sediment records from the uk poland and switzerland though finer detail in the structure of some of the principal features is resolved

processes of holocene ferromanganese coated grains oncolites in the nearshore shelf of cameroon abstract brown fe and black fe mn coated grains are present at a water depth of 25 30 m in the subsurface reworked deposits of the sanaga pleistocene delta cameroon most are former fecal pellets with concentric layering composed of one to four layers brown grains are composed of a medium to well crystallized goethite black grains commonly have a metallic luster and show todorokite microcrusts on the surfaces of the goethite rims cyanobacterial microstructures that developed in the voids between the nuclei and the cortices of the grains as well as between successive layers within the cortices suggest a weakly microlaminated oncolite and biomediation of the oxidation these grains were generated between c 9600 and 8000 yr bp by successive centripetal coatings the most likely environment is thought to be oxygenated seawater over offshore bars near the mouth of the sanaga river successive steps are involved in the buildup of fe mn coatings 1 upward flux of mn2 and fe2 from the sediment column to the sediment water interface 2 fe3 precipitation as fe oxyhydroxide and catalyzed deposition of mn4 on the oxyhydroxide iron surface and 3 bacterial biomediation of the fe mn oxidation modern nearshore sediments on the cameroonian shelf and modern and quaternary sediments on other west african shelves contain only goethite coated grains the todorokite formation off the sanaga mouth appears to have no modern analog on the basis of the present day factors high sea water temperature 30 31 c low salinity 24 28o oo high bacterial activity and high concentration of mno 0 27 in the suspended matter of the upstream sanaga waters we consider the formation of the analyzed coated grains to have resulted from the same enhanced factors associated with the early holocene transgressive environment

uranium in iron formations and the rise of atmospheric oxygen abstract the concept of the great oxidation event goe during which atmospheric oxygen rose precipitously and perhaps to near modern levels around 2 4 2 1 billion years ago ga has become entrenched in our views on secular atmospheric evolution multiple proxies confirm a permanent shift towards more oxygenated conditions at some time near the archean proterozoic boundary however it remains unclear precisely when this transition occurred due in part to the likely temporal variability in those early levels and different sensitivities of the proxies utilized to track atmospheric oxygen partial pressures here we provide a new look at the timing and magnitude of early atmospheric oxygenation through the record of uranium u concentrations in iron formations if just as if are important archives of the redox state of seawater concentrations of redox sensitive u in if are faithful proxies for oxidative continental weathering and associated delivery of dissolved u to seawater our dataset suggests that there was an increase in u redox cycling and transport at ca 2 47 ga just before the permanent loss of mass independent sedimentary sulfur isotope anomalies traditionally used to define the onset of the goe further there is significant temporal variability in the if u record that we propose reflects dynamic precambrian redox conditions we provide additional support for earlier suggestions that the goe was a protracted event marked by vacillating oxygen levels

densification of pond ash by blasting fly ash from thermal power plants is disposed in huge quantities in ash ponds which occupy large land areas otherwise useful for agriculture housing or other development for effective rehabilitation of ash ponds densification of the slurry deposit is essential to increase the bearing capacity and to improve its resistance to liquefication extensive field trials were carried out to evaluate the effectiveness of deep blasting for densification of deposited fly ash ninety explosions comprising 15 single blasts with varying depths and quantities of charges and 3 group blasts each having 25 charges placed at various spacings were carried out the compaction achieved in terms of an increase in relative density was evaluated from surface settlement measurements extensive field monitoring was undertaken through pore water pressure measurements vibration measurements penetration tests and block vibration tests for the average charge of 2 4 g of explosive per cubic meter of untreated deposit the average relative density was found to improve from 50 to 56 58 analysis of the test results indicates that deep blasting may be an effective technique for modest compaction of loose fly ash deposits the field testing program presented in this paper provides valuable information that can be used for planning blast densification of fly ash deposits

effect of gas on the mechanical behavior of medium dense sands abstractthis paper presents the results of monotonic and cyclic triaxial tests performed on gassy medium dense sand specimens these sands are representative of conditions in a loose sand deposit that was densified using multiple blasting passes at a site in south carolina the equipment and laboratory testing procedures used to reproduce the postblast densification conditions observed at a field test are described in detail results of undrained and drained compression tests showed that the gassy specimen responses were bounded by the fully saturated drained and undrained responses the undrained test results showed that the presence of gas even in small amounts made the soil more compressible and restricted the buildup of excess pore water pressures as compared with those pressures observed in fully saturated specimens additionally the shear strengths of gassy medium dense sand specimens were similar to those observed in saturated loose sands sheared under drained conditions for a given cyclic s

regional modeling of the geomagnetic field in europe from 6000 to 1000 b c we have developed a first low degree regional geomagnetic model for the european continent valid for the period 6000 1000 b c from a selected compilation of sedimentary and archeomagnetic data the scha dif 8k model this model provides information about both direction declination and inclination and intensity of the earth s magnetic field by connecting it with our previous model scha dif 3k valid from 1000 b c to 1900 a d and the igrf we furnish continuous geomagnetic field information for the last 8000 years in europe it has been developed using the revised spherical cap harmonic analysis in 2 dimensions technique r scha2d and using the norm of the earth s magnetic field to constrain the inversion problem the size of the cap is 22 and the maximum degree of the expansion is 2 the linearization problem was solved by using the truncated taylor s series applied to the expressions representing the relationship between the declination inclination and intensity data and the cartesian components of the geomagnetic field we used the geocentric axial dipole gad field as our initial or reference field for time we used the classical sliding overlapping window method the size of the window was set to 100 years shifted by 50 years we compared the model s prediction with the input data with the global cals7k 2 model and with new independent data the regional model shows a better fit to the input and to the independent data than the global model especially in terms of intensity and agrees with the virtual axial dipole moment given by other studies for the last 8000 years the european geomagnetic field has recorded rapid changes or archeomagnetic jerks the average field for the last 8000 years in europe is indistinguishable from the gad field

blast densification multi instrumented case history a comprehensive blast densification field study was conducted at a test site in south carolina to densify a loose soil layer at a depth between z 8 13 m the study included extensive laboratory and field characterizations and four carefully monitored blast events results revealed that densification is not an instantaneous phenomenon underlying time dependent processes involve resedimentation drainage of excess pore pressure as the granular skeleton deforms and the effective stress recovers and secondary settlement effects which do not involve excess pore pressure dissipation the degree of densification decreased in successive blasting events and the soil gradually evolved toward an asymptotical terminal density associated with blast densification the blasting sequence and detonation delays appeared to have a minor effect on shear induced movements the increase in penetration resistance manifested 2 years after four blasting drainage events instead surface settlement using standard surveying te

extreme ocean anoxia during the late cryogenian recorded in reefal carbonates of southern australia abstract the neoproterozoic was a time of great change in the earth s surface and marine environments including extensive climate variability the widespread oxygenation of the oceans and the accompanying rise of animal life however the timing of ocean oxygenation remains uncertain particularly in regard to cryogenian seas which were disrupted by large periods of global glaciation interglacial cryogenian reef complexes in the northern adelaide fold belt of australia contain abundant primary marine dolomite cements these cements have well preserved textural and growth zonation indicating they preserve their original marine chemistry and can be used as geochemical proxies for late cryogenian paleooceanography analysis of marine cements from peritidal nearshore facies shallow platformal facies and deep framework facies of the reef complexes reveals significant geochemical gradients with paleo depth while nearshore cements have low fe contents and commonly contain iron oxide inclusions the shallow and deep cements have very high fe concentrations chalcophile elements cu cd pb zn etc are most abundant in the nearshore cements whereas rare earth elements are found in highest concentrations in the deeper facies cements rare earth element profiles are unusual with shallow and deep facies having convex profiles with negligible ce ce anomalies and positive eu eu anomalies being constrained by sedimentology this carbonate geochemistry provides a window into interglacial cryogenian ocean chemistry and structure the marine cements reveal pronounced chemical stratification in this late cryogenian ocean a thin veneer of oxic surface waters existed at the ocean surface in peritidal facies with increasingly anoxic and fe rich seawater at depth the distribution of strongly chalcophile elements like cd and cu across the chemocline suggests that although ferruginous deeper anoxic waters probably contained some dissolved sulphide these conditions describe a ferro sulfidic ocean and encompass some of the most extreme anoxia yet documented during the late precambrian a return to archean like ocean conditions at this time suggests large scale disruption of the ocean system during the neoproterozoic

near east paleomagnetic secular variation recorded in sediments from the sea of galilee lake kinneret abstract paleomagnetic records of declination and inclination from sediments recovered from the bed of lake kinneret 32 4 n 35 7 e have been dated by radiocarbon techniques the sediments span the last 5000 yr the changes in inclination down the sediment cores are more pronounced than the declination fluctuations and are repeatable between the three coring sites which are several kilometers apart magnetic susceptibility logs display 13 maxima in the 5 m long sequences with a pronounced susceptibility minimum about 1000 yr b p many of the susceptibility maxima and minima can be easily correlated between coring sites and are shown to be dominantly related to changes in sediment carbonate content the natural remanent magnetization intensity follows a similar pattern to that of susceptibility and the natural remanence of the kinneret sediments is presumed to reside in detrital magnetite grains carried into the lake by the river jordan from the basalt rich bedrock of the rift floor and the golan heights the 14c chronology is strongly supported by a pollen study in which pronounced changes in the proportion of olive pollen were interpreted as being due to extensive cultivation of olives around galilee in the hellenistic and byzantine periods the kinneret paleosecular variation records if accurately dated point to a complex spatial pattern of holocene secular variation with significant variations over distances as small as 1000 2000 km

neoproterozoic aragonite dolomite seas widespread marine dolomite precipitation in cryogenian reef complexes the extraordinary abundance of dolomite in the proterozoic challenges our understanding of precambrian marine environments here we show that synsedimentary marine dolomite precipitation was pervasive within cryogenian reef complexes from the adelaide fold belt south australia although these reefs are composed of dolomite textural evidence indicates an originally aragonitic mineralogy for depositional components in common with many other neoproterozoic carbonates allochthonous slope debris from the reefs invariably contains both limestone and dolomite clasts indicating synsedimentary dolomitization in the reefs we describe several new forms of fibrous marine dolomite cement from the reefs that have a length slow optical character these fascicular slow radial slow and rhombic dolomite cements have finely preserved cathodoluminescent growth zones and optical characteristics that indicate they originally precipitated as dolomite rather than replacing calcite or aragonite cements abundant early marine dolomite precipitation implies a radically different seawater chemistry for the cryogenian perhaps these aragonite dolomite seas are associated with extreme neoproterozoic glacial events and or ocean anoxia

eolian action and the distribution of cambrian shales in north america prolonged eolian action on the barren prevegetation craton provides a better explanation for the absence of shale in the cambrian and lower ordovician orthoquartzite carbonate suite of east central and arctic north america than does marine bypassing it is hypothesized that paleo trade winds transported much of the missing silt and clay to the southern and western united states and southwestern canada while the remainder diffused radially off the craton under the influence of variably directed storm winds the distribution of shale in the sauk sequence supports this and indicates that the orthoquartzite carbonate suite of upwind regions is replaced by a shale carbonate suite in downwind areas

origin of negative ce anomalies in mixed hydrothermal hydrogenetic fe mn crusts from the central indian ridge abstract layered fe mn crusts from the off axis region of the first segment of the central indian ridge north of the rodrigues triple junction were studied geochemically and mineralogically vernadite mno2 is the main mineral oxide phase 230thxs and co concentrations suggest high growth rates of up to 29 mm myr and a maximum age of the basal crust layer of 1 ma whereas most of the major and minor elements show concentrations which are typical of hydrogenetic formation co pb ni and ti concentrations are strikingly lower concentrations and distribution of the strictly trivalent rare earths and yttrium rey are typical of hydrogenetic ferromanganese oxide precipitates but in marked contrast the crusts are characterized by negative cesn shale normalized anomalies and ce pr sn ratios less than unity profiles through the crusts reveal only minor variations of the rey distribution and ce pr sn ratios range from 0 45 to 0 68 compared to ratios of up to 2 for typical hydrogenetic crusts from the central indian basin the apparent bulk partition coefficients between the crusts and seawater suggest that for the strictly trivalent rey the adsorption desorption equilibrium has been reached positive ce anomalies in the partition coefficient patterns reveal preferential uptake of ce but to a lesser extent than in normal hydrogenetic crusts a new parameter excess ce cexs to quantify the degree of decoupling of ce from rey iii is established on the basis of partition coefficients cexs cebulk ratios suggest that the cir crusts formed by precipitation of fe mn oxides from a hydrothermal plume and that in hydrothermal plumes and normal seawater the enrichment of ce results from the same oxidative sorption process the growth rates calculated with 230thxs data as well as with the co formula are inversely related to cexs

llanvirnian ord iron ooids in baltoscandia element mobility ree distribution patterns and origin of the ree abstract the chemical and mineralogical compositions of llanvimian ordovician iron and associated phosphate ooids from sweden estonia and russia have been examined the oolites are generally thin and lean mud supported and dominated by fe oxyhydroxide goethite limonite ooids one swedish oolite contains a mixture of chamosite goethite and hematite ooids and it is suggested that the two latter types were derived from chamosite ooids by early diagenetic alteration the ree distribution patterns were unaffected by these reactions all ooids in the area show a typical negative eu anomaly inherited from the source material major and minor element contents in limonite and chamosite ooids are similar whereas their ree patterns are different limonite ooids have a lree hree ratio from 1 to 2 4 and chamosite ooids from 3 to 5 the amounts of ree in the ooids are strongly dependent on the amount of phosphate

the secular variation of the geomagnetic field in egypt in the last 5000 years the palaeo intensities fa of the geomagnetic field in egypt at some ages are determined by archaeomagnetic measurements and found to be fa 36 2 t at 3100 b c fa 46 8 t at 3000 b c fa 36 5 t at 2780 b c 49 0 t at 2500 b c 36 4 t at 2200 b c 57 5 t at 1990 b c 62 1 t atca 1400 b c 61 5 t at 1400 b c 69 9 t at 600 b c 59 3 t at 550 b c 79 9 t at 460 b c 73 7 t at 450 b c 69 7 t at 320 b c 56 2 t at a d 50 64 9 t at a d 400 54 4 t at a d 300 57 5 t at a d 700 and 43 0 t at a d 1975

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

rock magnetism of greigite bearing sediments from the dead sea israel summary detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the dead sea israel the sediments are heterogeneous composed of fine clastic layers alternating with authigenic aragonite the magnetic remanence is carried by ti magnetite and greigite reflecting a detrital as well as an authigenic phase directions of the characteristic remanent magnetization were obtained from stepwise af demagnetization of the natural remanent magnetization and subsequent principle component analysis the acquisition of a gyroremanent magnetization in a noticeable amount of the samples could be linked to core disturbances the depth age models based on ams 14c datings on plant remains yielded an age of 10 04 ka cal bp for the base of the longest profile from site ein gedi a continuous lacustrine sediment sequence the profiles from the two other sites representing near shore sedimentation are interrupted by a hiatus in sedimentation comparison of the inclination and declination records from all dead sea cores and nearby sited lakes suggest that low frequency variations documented in the dead sea sediments are likely of geomagnetic origin

greigite detected as dominating remanence carrier in late pleistocene sediments lisan formation from lake kinneret sea of galilee israel summary a rock magnetic investigation of three sedimentary cores of lisan formation of late pleistocene age from lake kinneret sea of galilee northern israel demonstrates that the magnetization of these sediments is controlled by various degrees of a secondary chemical remanent magnetization crm carried by greigite fe3s4 this crm is superimposed on a primary detrital remanent magnetization drm that resides in ti magnetite this finding is independently confirmed by x ray diffraction xrd measurements performed on magnetic extracts of the sediments the domain state of the greigite is largely single domain behaviour sd thus dominating the magnetization therefore the magnetic record retrieve from of these sediments is not reflecting geomagnetic variations but rather chemical rock magnetic properties resulting from diagenetic processes the results of our study suggest that paleomagnetic record of greigite bearing sediments should be interpreted with caution because of the following reasons 1 geomagnetic secular variations can be biased due to large coercivity overlap between magnetite and greigite 2 alternating field af demagnetization can produce erroneous directions due to vector distortion by acquisition of a gyro remnant magnetization grm 3 estimation of relative paleointensity can be hampered by large scale variations in natural remnant magnetization nrm intensity caused by the acquisition of a secondary crm of unknown age and unknown extent superimposed on the drm the precipitation of greigite requires reducing conditions at the sediment water interface and or interstitial water associated with the presence of sulphur and iron oxides reducing conditions are typical of stratified lakes and other stratified water bodies such as the dead sea paleo lake lisan temporarily the eastern mediterranean sea the caspian sea the black sea and many other marine basins according to our findings paleomagnetic records from such environments carried dominantly by greigite therefore should be treated with care

petrographic microchemical studies and origin of the agbaja phanerozoic ironstone formation nupe basin nigeria a product of a ferruginized ooidal kaolin precursor not identical to the minette type the campanian maastrichtian agbaja ironstone formation of the nupe basin nigeria forms a major part of the about 2 billion tons of iron ore reserves of the middle niger embayment the ironstone deposits were previously reported to be similar to the minette type ironstones because of their depositional patterns composition and inferred origin four rock types are recognized within the agbaja ironstone formation ooidal pack ironstone pisoidal pack ironstone mud ironstone and bog iron ore in the ironstones kaolinite of both the groundmass and the ooids pisoids is of lateritic origin whereas the associated quartz mica and heavy minerals are of detrital origin ooids and pisoids were formed by mechanical accretion of platy kaolinite crystals by rolling on the sea floor in a near shore environment and were subsequently transported and deposited together with a fine grained kaolinitic groundmass pyrite mainly framboidal and siderite both exclusively occurring as pseudomorphs of goethite and or hematite are diagenetic whereas goethite is post diagenetic in origin resulting from the ferruginization of the kaolinitic precursor crandallite gorxeicite goyazite bolivarite and boehmite are also post diagenetic in origin hematite was formed from the dehydration of goethite whereas gibbsite restricted to the upper part of the deposit is of recent and in situ lateritic origin the presence of newly formed authigenic pyrite and siderite now replaced by hematite and goethite are indicators of a reducing environment during diagenesis the absence of diagenetic chamositic clay minerals evidently caused by a low mg concentration suggests that fully marine conditions were not established during sedimentation this is supported by the lack of fossils brecciated shell materials and bioturbation features in the deposit reworking and redeposition of the primary constituents are inferred from broken pisoids nuclei of pisoidal ooidal fragments in pisoids and high iron concentrations present in the pisoids and ooids compared to that of the groundmass these observations indicate that the agbaja ironstone deposits of the lokoja study area exhibit some environmental and mineralogical characteristics that are markedly different from other known deposits of minette type where primary chamositic clay minerals generally form the protore for the ironstones the recognition of kaolinite as the precursor constituent and the occurrence of similar deposits of the same age late cretaceous in nigeria sudan and egypt have implications for the paleoenvironmental interpretations of phanerozoic ironstone deposits

origin of hematite carrying a late paleozoic remagnetization in a quartz sandstone bed from the silurian rose hill formation virginia usa abstract paleomagnetic and petrographic studies of a quartz sandstone bed from the silurian rose hill formation of the central appalachians show that hematite carrying a late paleozoic remagnetization is authigenic comparison of paleopole positions from the rose hill formation with late paleozoic poles for north america suggests a synfolding remagnetization the sandstone cement is characterized by pore lining hematite pore filling berthierine and intergrowths of hematite berthierine and quartz these cements postdate pressure solution of detrital quartz grains late paleozoic cementation is a consequence of diagenesis associated with alleghanian deformation detrital fe mg silicate grains are believed to have been a local source of fe for some authigenic hematite and berthierine although mass balance calculations suggest that an external source is also required some berthierine aggregates are pseudomorphic after detrital fe bearing silicate grains trace amounts of detrital tourmaline are the only remnants of the detrital fe mg silicates

modern iron ooids from a shallow marine volcanic setting mahengetang indonesia an unconsolidated submarine deposit of iron ooids and pisoids located offshore the volcanic island mahengetang indonesia is described herein the deposit occurs in a shallow marine setting in an area characterized by venting of hydrothermal fluids and expulsion of gas across the sediment water interface the ooid deposit is essentially pure to a minimum depth of 0 5 m and covers an area of at least 1000 m 2 ooids are composed of concentric accretionary layers of limonite admixed with amorphous silica precipitated around andesitic rock fragments the smallest layers forming the ooids are about 10 min thickness the iron rich precipitate is 50 iron by weight ooid formation is likely promoted by precipitation of iron and silica from exhalative fluids rising up through the substrate concentric layering is thought to result from constant agitation of ooids associated with currents and expulsion of gas from the sediment