antarctic link to deep flow speed variation during marine isotope stage 3 in the western north atlantic the western boundary undercurrent wbuc off eastern america is an important component of the atlantic meridional overturning circulation and is the principal route for southward transport of north atlantic waters and southward return of southern source water ssw here a direct flow speed proxy mean grain size of the sortable silt is used to infer the vigour of flow of the palaeo wbuc at blake outer ridge odp site 1060 depth 3481 m during marine isotope stage mis 3 the overall shape of the flow speed proxy record shows a complex pattern of variability with generally more vigorous flow and larger scale flow variations between 35 and 60 ka than in the younger part of mis 3 and mis 2 b35 ka six events of reduced bottom flow vigour slow events ses occur these appear uncorrelated with heinrich events but are instead synchronous with the warming phases of antarctic warm events a 1 to a 4 with one new one a 1a and one poorly defined a 0 this indicates that antarctic climate exerts a stronger control on deep flow vigour in the north atlantic during mis 3 than northern hemisphere climate the correspondence of ses with antarctic warming suggests a weaker wbuc flow due to reduced volume flux at ssw source or reduced ssw density because the variability of the lower limb of the wbuc was not connected to sharp north atlantic changes in temperature it is unlikely that the dansgaard oeschger cycles were associated with a mode of moc variation involving wholeocean overturn but more likely with perturbations of only the shallow glacial gulf stream glacial northern source intermediate water cell nutrient proxies benthic carbon isotopes and cd ca of uvigerina peregrina at this site show similar trends to the grip 18 o record this correlation has previously been attributed mainly to hydrographic and flow changes but is here shown to be better explained by variations in surface ocean productivity and subsequent decomposition of 12 c rich organic material on the

abrupt changes in deep atlantic circulation during the transition to full glacial conditions 1 six ocean drilling program odp sites in the northwest atlantic have been used to investigate kinematic and chemical changes in the western boundary undercurrent wbuc during the development of full glacial conditions across the marine isotope stage 5a 4 boundary 70 000 years ago sortable silt mean grain size ss measurements are employed to examine changes in near bottom flow speeds together with carbon isotopes measured in benthic foraminifera and planktic foraminiferal fragmentation as proxies for changes in water mass chemistry a depth transect of cores spanning 1 8 4 6 km depth allows changes in both the strength and depth of the wbuc to be constrained across millennial scale events ss measurements reveal that the flow speed structure of the wbuc during warm intervals interstadials was comparable to modern holocene conditions however significant differences are observed during cold intervals with higher relative flow speeds inferred for the shallow component of the wbuc 2 km depth during all cold stadial intervals including heinrich stadial 6 and a substantial weakening of the deep component 3 4 km during full glacial conditions our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation involving glacial north atlantic intermediate water that was quantitatively distinct from preceding cold stadial events furthermore our chemical proxy data show that the physical response of the wbuc during the last glacial inception was probably coupled to basin wide changes in the water mass composition of the deep northwest atlantic

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

method of estimating the amount of in situ gas hydrates in deep marine sediments abstract the bulk volume of gas hydrates in marine sediments can be estimated by measuring interval velocities and amplitude blanking of hydrated zones from true amplitude processed multichannel seismic reflection data in general neither velocity nor amplitude information is adequate to independently estimate hydrate concentration a method is proposed that uses amplitude blanking calibrated by interval velocity information to quantify hydrate concentrations in the blake ridge area of the us atlantic continental margin on the blake ridge blanking occurs in conjunction with relatively low interval velocities the model that best explains this relation linearly mixes two end member sediments hydrated and unhydrated sediment hydrate concentration in the hydrate end member can be calculated from a weighted equation that uses velocity estimated from the seismic data known properties of the pure hydrate and porosity inferred from a velocity porosity relationship amplitude blanking can be predicted as the proportions of hydrated and unhydrated sediment change across a reflection boundary our analysis of a small area near dsdp 533 indicates that the amount of gas hydrates is about 6 in total volume when the interval velocity is used as a criterion and about 9 5 when amplitude information is used this compares with a calculated value of about 8 derived from the only available measurement in dsdp 533

geophysical and geochemical logs from a copper oxide deposit santa cruz project casa grande arizona in support of an in situ leaching experiment five holes drilled into a copper oxide deposit have been logged with geophysical and geochemical tools developed for use in the petroleum industry when combined with geological description chemical analyses and mineralogical data from core and cuttings the logs provide information regarding the alteration fracturing copper distribution porosity and permeable zones correlations among sonic velocity rock strength from mechanical tests on core and alteration indicators from neutron and potassium logs demonstrate a close link between the state of alteration and the mechanical state of the rock neutron activation natural gamma ray and density logs in combination correlate so well with copper assays that log based prediction of copper content is possible in addition an estimate of whole rock mineralogy is presented in log format based on comparisons of flow logs and acoustic logs obtained in the same holes reductions in acoustic velocity appear t

surface sediment response to deepwater circulation on the blake outer ridge western north atlantic paleoceanographic implications abstract two transects of box core hydrographic and photographic stations were made along the blake outer ridge on the southeastern u s continental rise to study how circulation patterns affect surface sediment properties circulation is strongest at 4200 m on the flanks of the ridge and is reflected in the suspended particulate distribution a second turbidity maximum at 3600 m suggests that there may be a second axis of circulation at this depth the intense circulation on the flanks of the ridge has resulted in winnowing of the sediment revealed by coarsening and flattening of the grain size distribution in the detrital silt fraction and concentration of carbonate by the formation of a foraminiferal lag deposit the mean grain size of the detrital silt fraction on the crest of the ridge decreases southeastwards with increasing distance from upstream sediment sources shifts in the position and strength of the western boundary undercurrent affect the distance that relatively coarse silt is transported downcore changes in grain size can therefore be used as paleoceanographic proxy for changes in deepwater circulation

geological interpretation of a low backscatter anomaly found on the new jersey continental margin abstract an enigmatic low backscatter acoustic anomaly occurs on the new jersey continental margin between hudson and wilmington canyon channels the presence of the low backscatter anomaly as seen with 6 5 and 12 khz data indicates a change in the physical properties of the seafloor or near sub surface analyses of seafloor and sub surface acoustic data with previously collected sediment cores suggest the low backscatter feature corresponds to an outcrop of older strata uncovered by erosion and non deposition by the western boundary undercurrent wbuc the decrease in backscatter strength is enhanced by the presence of gas in the sub surface sediments found in the buried chesapeake drift

case history using time lapse vertical seismic profiling data to constrain velocity saturation relations the frio brine pilot co2 injection author s al hosni m caspari e pevzner r daley tm gurevich b abstract 2016 european association of geoscientists a engineers co2 sequestration projects benefit from quantitative assessment of saturation distribution and plume extent for field development and leakage prevention in this work we carry out quantitative analysis of time lapse seismic by using rock physics and seismic modelling tools we investigate the suitability of gassmann s equation for a co2 sequestration project with 1600 tons of co2 injected into high porosity brine saturated sandstone we analyze the observed time delays and amplitude changes in a time lapse vertical seismic profile dataset both reflected and transmitted waves are analyzed qualitatively and quantitatively to interpret the changes obtained from the vertical seismic profile we perform a 2 5d elastic finite difference modelling study the results show a p wave velocity reduction of 750 m s in the proximity of the injection well evident by the first arrivals travel time delays and amplitude change and reflected wave amplitude changes these results do not match with our rock physics model using gassmann s equation predictions even when taking uncertainty in co2 saturation and grain properties into account we find that time lapse vertical seismic profile data integrated with other information e g core and well log can be used to constrain the velocity saturation relation and verify the applicability of theoretical models such as gassmann s equation with considerable certainty the study shows that possible nonelastic factors are in play after co2 injection e g co2 brine rock interaction and pressure effect as gassmann s equation underestimated the velocity reduction in comparison with field data for all three sets of time lapse vertical seismic profile attributes our work shows the importance of data integration to validate the applicability of theoretical models such as gassmann s equation for quantitative analysis of time lapse seismic data

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

pore pressure distribution of a mega splay fault system in the nankai trough subduction zone insight into up dip extent of the seismogenic zone we use the pore pressure distribution predicted from a waveform tomography wt velocity model to interpret the evolution of the mega splay fault system in the nankai trough off kumano japan to map pore pressure around the mega splay fault and plate boundary decollement we integrate the high resolution wt velocities with laboratory data and borehole well log data using rock physics theory the predicted pore pressure distribution shows that high pore pressures close to lithostatic pressure along the footwall of the mega splay fault extend seaward to the trough region and the normalized pore pressure ratio is nearly constant over that extent this continuity of the overpressured zone indicates that a coseismic rupture can potentially propagate nearly to the trough axis we interpret a high pressure belt within an accretionary wedge on the landward side of the present mega splay fault as evidence of the ancient mega splay fault because the ancient mega splay fault soles into the active mega splay fault the active mega splay fault may function as a basal detachment fault and is directly connected to the seaward plate boundary decollement

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

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

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

deepwater circulation on blake outer ridge western north atlantic during the holocene younger dryas and last glacial maximum three depth transects containing a total of 33 sediment cores were investigated along the blake outer ridge in the western subtropical north atlantic sortable silt mean grain size and stable isotope records were used to assess the position and relative intensity of the western boundary undercurrent wbuc during the holocene the last glacial maximum lgm and the younger dryas yd intervals the holocene reconstruction is consistent with modern physical and chemical hydrographic measurements in the area suggesting a deep position for the fast flowing core of the wbuc 3000 4000 m deepening to 4500 m water depth on the ridge flanks and a water column dominated by north atlantic deep water nadw the lgm and yd reconstructions show that a comparable hydrographic regime was present during both these intervals suggesting a similar mode of circulation that was appreciably different from the holocene reconstruction the wbuc s zone of maximum flow speed during these intervals is suggested to have shifted above 2500 m water depth consistent with nutrient depleted glacial north atlantic intermediate water formation with an increasing influence of southern source water ssw beneath below 4000 m water depth results hint at increased ssw flow vigor during both the lgm and yd with higher flow speeds than during the holocene this study provides a framework for aiding the interpretation of time series records of paleocurrent flow speed changes in the region of the wbuc

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

fluctuations in deep western north atlantic circulation on the blake outer ridge during the last deglaciation variations in the mean grain size of the detrital silt fraction from four piston cores along a depth transect on the blake outer ridge were used to examine paleocirculation patterns and intensity between 2650 and 3818 m for the late pleistocene and holocene prior to 12 kyr circulation was focused on the upper part of the ridge above 2700 m and may have corresponded to enhanced levels of intermediate water production in the north atlantic deepwater circulation during deglaciation underwent a two step decrease to minimum speeds from 15 5 to 13 5 kyr followed by a three step increase to maximum speeds at 10 kyr minima in circulation at 13 5 and 12 kyr can be directly associated with oxygen isotopic evidence for advection of reduced salinity surface water to the north atlantic additional circulation minima at 15 and 10 5 kyr may also be the result of reduced salinity from high latitude meltwater discharge evidence for a drop to moderate circulation intensity during the holocene is supported by isolated geochemical records but could also be explained by decoupling of ocean ventilation rates from bottom circulation or a change in sediment provenance at the end of deglaciation

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

glacial interglacial instabilities of the western boundary under current during the last 365 kyr from sm nd ratios of the sedimentary clay size fractions at odp site 646 labrador sea we present 40 sm nd isotope measurements of the clay size 2 m fractions of sediments from the sout hern greenland rise odp 646 that span the last 365 kyr these data track changes in the relative supply o f fine particles carried into the deep labrador sea by the western boundary under current wbuc back to the fourth glacial interglacial cycles earlier studies reveal ed three general sources of particles to the core s ite i precambrian crustal material from canada greenland and or scandinavia north american shield nas ii palaeozoic or younger crustal material from east gr eenland nw europe and or western scandinavia young crust yc and iii volcanic material from iceland and the mid atlantic ridge mar clay size fractions from glacial sediments have the lowest nd isotopic ratios supplies of young crustal particles were si milar during glacial oxygen isotope stages ois 2 6 and 10 i n contrast the mean volcanic contributions decrease d relative to old craton material from ois 10 to ois 6 and the n from ois 6 to ois 2 the glacial ois 8 interval d isplays a mean sm nd ratio similar to those of interglacials ois 1 5 and 9 compared with other interglacials ois 7 was marked by a higher yc contribution but a similar 3 0 mar supply the overall nas contribution dropped by a factor of 2 during each glacial interglacial tran sition with the mar contribution broadly replacing it during interglacials to decipher between higher supplies and or dilution particle fluxes from each end memb er were estimated glacial nas fluxes were systematically h igher than interglacial fluxes during the time int erval examined fine particle supplies to the labrador se a were strongly controlled by proximal ice margin e rosion and thus echoed the glacial stage intensity in con trast the wbuc carried mar supplies from the eastern basins did not change significantly throughout the last 36 5 kyr except for a marked increase in surface sedi ments that suggests unique modern conditions distal wbuc controlled inputs from the northern and ne north atlant ic seem to have been less variable than proximal suppl ies linked with glacial erosion rate

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

arctic vs north atlantic water mass exchanges in fram strait from pb isotopes in sediments surface sediment samples n 10 collected between spitzbergen and greenland and two cores raised east c04 and west c16 from fram strait were analyzed for their chemical and isotopic pb compositions to trace the source of sediments and water masses exchanging between the arctic and the north atlantic oceans in surface sediments variable major and trace element concentrations suggest variations in both the mineralogy carbonate and quartz dilution of other silicate minerals and source regions of detrital supplies based on th zr and to a lesser extent on th u ratios each core site shows specific but nearly constant th zr ratios indicating homogeneous source supplies at both core sites pb concentrations and isotopic compositions display similar patterns homogeneous low pb and radiogenic crustal signals below 5 10 cm contrasting with high pb and less radiogenic anthropogenic inputs at core tops however the differing pre anthropogenic pb isotopic ratios in c04 and c16 confirm the involve

ocean ventilation during the last 12 000 years hypothesis of counterpoint deep water production abstract available radiocarbon data on selected planktonic foraminifera species suggest that differential dissolution reduces the 14 c c ratio in planktonic tests removing 14c rich specimens from assemblages of surface dwelling species the effect is analogous to that observed for stable isotope composition in planktonic foraminifera other disturbing factors apparently affect benthic radiocarbon data as well thus radiocarbon stratigraphies are difficult to interpret in terms of history of deep water ages that is deep ocean mixing the best data at hand south china sea after corrections for differential dissolution and benthic vital deviations suggest a high variability of deep water mass ages in the late glacial period which is explained in terms of vertical motion of deep water mass boundaries across the recording sites the fluctuations are ascribed to sporadic increases in deep water production in the north pacific during cold periods and to the presence of a glacial bottom water mass which resisted mixing during deglaciation

crustal heterogeneity and subduction processes 3 d vp vp vs and q in the southern north island new zealand summary along the southern hikurangi subduction zone in the southern north island new zealand the subduction zone changes from volcanic with moderately weak interseismic coupling to non volcanic with strong coupling in wellington to investigate how material heterogeneity relates to subduction processes we compute 3 d seismic properties using 342 earthquakes and 2 shots recorded by a 165 station seismic array the time base for some telemetered temporary stations was not stable which required revising the inversion code to allow an additional origin time related to the telemetered stations progressive inversions from 2 d to fine 3 d were carried out for vp vp vs and qp combined interpretation of these three seismic properties highlights features of the subduction zone the subducted slab is imaged as a high velocity high q feature in the overlying crust from southeast to northwest there is low velocity in the accretionary wedge high velocity in the axial ranges and low velocity in the wanganui basin high vp vs and low qp characterize the crust east of the north island dextral fault belt high vp vs is imaged above the subducted slab to 40 km depth in the northern half of the study area low qp is also prominent above the slab particularly trenchwards of the volcanic region in marked contrast to the high vp vs the low qp above the slab extends as a continuous feature up to the low qp in the shallow crust underlying the volcanic region the low qp and high vp vs are correlated with the region of weaker coupling and are consistent with significant subducted sediments with associated fluid release vp vs is particularly sensitive to overpressured fluid in the compressional forearc whereas qp also images the hydrostatically pressured fluid transport in the more permeable extensional volcanic region the rheology of the lower crust of the overlying plate is a factor in large scale subduction coupling as evidenced by the terrane boundaries and haast schist in the section near wellington the changing rheology of the lower crust of the overlying plate in the southern north island also provides a possible explanation for the southward cessation of volcanism

composition microstructures and petrophysics of the mozumi fault japan in situ analyses of fault zone properties and structure in sedimentary rocks from shallow crustal levels 1 we characterize the chemical microstructural and geophysical properties of fault related rock samples from the 80 100 m wide mozumi fault zone north central honshu japan the fault is exposed in a research tunnel 300 400 m below the ground and we combine geological data with borehole geophysical logs to determine the elastic and seismic properties of the fault zone detailed mapping within the tunnel reveals that the fault zone consists of two zones of breccia to foliated cataclasites 20 and 50 m thick two narrow tens of centimeters wide principal slip zones on which most of the slip occurred bound the central fault zone the dominant deformation mechanisms within the fault zone were brittle fracture brecciation slip localization plastic deformation and vein formation in a sericite calcite rich matrix clay alteration patterns are complex within the fault zone with clay rich fault breccia enriched in smectite illite and kaolinite relative to the kaolinite and illite dominant in the host rock whole rock geochemical analyses show that the fault related rocks are depleted in fe na k al mg and si relative to the host rock the fault zone exhibits depressed electrical resistivity values by 10 100 ohm m relative to the wall rock values of vp and vs values that are 0 30 and 0 40 km s 10 20 less than protolith values the spontaneous potential logs indicate that the fault zone has increased freshwater content relative to formation waters wellbore based measurements of vp and vs in fault related rocks to enable us to calculate values of young s modulus from 16 2 to 44 9 gpa and poisson s ratio for the fault zone of 0 263 to 0 393 the protolith has young s modulus of 55 4 gpa and a poisson s ratio of 0 242 lowest calculated values of young s modulus and highest calculated values of poisson s ratio correspond to fault breccia with increased porosity high fluid content and low resistivity values taken together these data show that the shallow portion of the mozumi fault consists of a complex zone of anastomosing narrow slip zones that bound broad zones of damage fluid rock alteration and deformation created altered fault related rocks which have resulted in overall reduced interval velocities of the fault zone these data indicate that seismic waves traveling along the interface or internally reflected in the fault zone would encounter rocks of differing and reduced elastic properties relative to the host rocks but that in detail material properties within the fault may vary

estimation of rock frame weakening using time lapse crosswell the frio brine pilot project abstractco2 injection into subsurface reservoirs leads to pressure and saturation changes furthermore co2 brine minerals interaction could result in dissolution or reprecipitation of rock frame forming minerals observed time lapse seismic associated with co2 injection into poorly consolidated sandstone at the frio co2 injection site texas usa could not be predicted using classical rock physics models i e models involving elastic changes in the rock frame due to saturations and or pressures changes only and assuming no changes in the rock microstructure that and the changes in the fluid chemistry after co2 injection suggests that the assumption of a constant rock microstructure might be violated using high resolution time lapse crosswell data we have developed a methodology for estimating changes in the rock frame by quantifying the rock frame drained moduli before and after co2 injection based on rock microstructure diagnostics we found that the changes in the drained frame elastic prope

velocities and quality factors of sedimentary rocks at low and high effective pressures summary techniques for measuring acoustic velocities and quality factors q of sedimentary rocks in the laboratory are sufficiently accurate to establish closely fitting regression curves which represent the variation of these acoustic properties with pressure ultrasonic p and s wave measurements of velocity v v and q q q were made on 16 different water saturated sandstone samples at various effective pressures using an ultrasonic reflection technique and the data were fitted using a simple regression equation containing a constant plus linear and exponential pressure dependent terms the redundancy of the linear term in the regression of q data suggests that microcracks alone govern the pressure variation of q whereas velocities are additionally dependent on another mechanism consistent with the changes in elastic moduli caused by intergranular compression causing small reductions in porosity the implied rates of microcrack closure with increasing effective pressure in all samples were found to be comparable the regression equations describe the data closely enough to enable the extrapolation of acoustic properties to both low and high effective pressures this is of practical use since laboratory techniques can produce uncertain results at low pressures due to coupling problems and low signal strengths whilst high pressures require large confining vessels low pressure and high pressure data are applicable to shallow seismic surveys and hydrocarbon exploration respectively

deep circulation changes in the labrador sea since the last glacial maximum new constraints from sm nd data on sediments sm nd concentrations and nd isotopes were investigated in the fine fraction of two labrador sea cores to reconstruct the deep circulation patterns through changes in sedimentary supply since the last glacial stage three sources are involved the north american shield palaeozoic rocks from northeastern greenland and mid atlantic volcanism the variable input of these sources provides constraints on the relative sedimentary supply in conjunction with inception of deep currents during the last glacial stage a persistent but sluggish current occurred inside the labrador basin an increasing discharge of volcanic material driven by the north east atlantic deep water is documented since 14 3 kyr signaling the setup of a modern like deep circulation pattern throughout the labrador irminger and iceland basins during the last deglacial stage the isotopic record was punctually influenced by erosion processes related mainly to ice sheet instabilities especially 11 4 10 2 and 9 2 kyr ago

sources of labrador sea sediments since the last glacial maximum inferred from nd pb isotopes pb isotopes have been measured in the clay size fraction of late glacial and holocene deep sea sediments recovered from two labrador sea piston cores that have been previously analyzed for nd isotopes the newly acquired pb isotopic data allow us to better constrain the different source areas that supplied clay size material during the last deglaciation until 8 6 kyr calendar ages nd pb data can be modeled mainly as a mixture between a precambrian crust and lower paleozoic material originating from the denudation of the pan african orogen the old material originates mainly from the archean lower proterozoic or both terranes of greenland and also probably corresponding terranes of labrador although minor input of other precambrian material is recorded in some detrital carbonate rich deglacial samples from orphan knoll the phanerozoic crustal end member consists of sediment material mainly originating from northwestern europe this source area is found to be the only significant source of young crustal material in early holocene sediments from the greenland rise no significant input from the mid atlantic volcanism is apparent this study puts further constraints on the deep circulation pattern during the last deglaciation it is concluded that at that time european phanerozoic material was carried from the norwegian sea through the wyville thompson ridge into the iceland basin by the north east atlantic deep water no evidence for an overflow is found either south of the iceland iceland scotland ridge or through the denmark strait

the contour current flow along the southern iceland faeroe ridge as documented by its bedforms and asymmetrical channel fillings abstract the iceland faeroe ridge is a natural barrier to the exchange of water masses between the norwegian greenland sea and the north atlantic basin the main overflow of cold and dense water from the norwegian greenland sea through the faeroe channels results in the generation of an intense contour current flow below 600 m water depth along its southern flank side scan sonar surveys revealed an extensive pattern of various bedforms with current indicators matching well with contour flow directions previously inferred from oceanographic measurements in the shallow ridge crest area only minor current induced bedforms were observed reflecting the relatively weaker intensities of overflow across the ridge in addition to the observed bedforms surveys of a nearby ridge parallel channel system also located on the southern flank of the iceland faeroe ridge document an asymmetrical sedimentation pattern with northern channel flanks displaying condensed sedimentation this asymmetrical sedimentation pattern is attributed to the influence of the coriolis force which is the ultimate driving mechanism for the generation of contour current systems

prediction of elastic wave velocities in sandstones using structural models elastic wave propagation in fluid saturated sandstones depends upon two sets of rock features 1 the volume fractions and elastic constants of the rock constituents quartz clay water etc and 2 microstructural geometry grain contacts pore aspect ratios while the former data are usually obtainable the latter are relatively inaccessible we present a new method for determining microstructural data using idealized but physically representative models of sandstone the key to the method is the simulation of certain depositional and diagenetic processes in a manner that completely specifies the geometry of the resulting models hence the geometric features of the grain space and void space required for various theories of elastic propagation can be calculated directly from the models we find good agreement between predictions and measurements of compressional and shear wave velocities in both clean and clay bearing saturated sandstones in contrast with previous efforts at predicting velocitie

modelling of pliocene pleistocene abyssal mudwaves using synthetic seismograms abstract the geological significance of seismic reflectors within pliocene pleistocene mudwaves at dsdp site 603 has been examined using synthetic seismograms the seismograms generated from physical properties in hole 603c show good agreement with field seismic profiles the travel time to depth conversion permits accurate location of the reflectors in the borehole impedance contrasts in the late pliocene to early pleistocene part of the section are controlled predominantly by density which are related to mean grain size variations grain size is inferred to have been controlled by fluctuations in the velocity of the deep western boundary undercurrent

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

seismic anisotropy and its impact on imaging the shallow alpine fault an experimental and modeling perspective the transpressional alpine fault in new zealand has created a thick shear zone with associated highly anisotropic rocks low seismic velocity zones lvz and high seismic reflectivity are recorded in the alpine fault zone but no study has explored the underlying physical rock parameters of the shallow crust that control these observations protomylonites are the volumetrically dominant lithology of the fault zone here we combine experimental measurements of p wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged numerical models that account for the porosity free real samples fabric elastic tensors from ebsd are calculated by mtex and a finite element model fem while microfractures are modeled with differential effective media dem theory at effective pressures representative of the alpine fault brittle zone experimental wave speeds are lower than those predicted by mtex fem a possible dem model suggests that a combination of random and aligned microfractures with aspect ratios increasing with pressure can explain the experimental wave speeds for pressures 70 mpa such micro porosity in the form of foliation and mica basal plane parallel microfractures and grain boundaries is validated with synchrotron x ray microtomography and tem images finally by modeling anisotropy of seismic reflection coefficients with angle of incidence we demonstrate that the high reflectivity and lvz observed at the alpine fault can only be explained if this microporosity is accounted for throughout the brittle fault zone even at depths of 7 10 km

paleoceanography of the deep western boundary undercurrent on the north american continental margin for the past 25 000 yr temporal fluctuations of silt mean particle size and foraminiferal indices were used to examine fluctuations in velocity and position of the axis of the deep western boundary undercurrent dwbuc on the north american continental margin from 25 to 17 ka the dwbuc axis was 500 m shallower and farther inshore than its present position on the lower rise current speed was high from 25 to 20 ka and then waned until 17 ka between 17 and 7 ka the major axis of the dwbuc shallowed to 4000 m current speed increased from 17 to 11 ka but slowed from h to 7 ka since 7 ka the dwbuc axis has deepened to its modern position at 4900 m the zone of maximum carbonate dissolution remained below the dwbuc the most intense dissolution was from 22 to 9 ka and 5 to 2 ka highest abundance of uvigerina and highest percent benthic foraminifera were immediately above the dwbuc from 22 to 7 ka after which values of both parameters fell to near zero

transport of carbonate sediment in the western north atlantic evidence from oxygen and carbon isotopes abstract in most deep ocean environments the carbonate component is usually considered to be of pelagic origin deposited on the sea bed without extensive transport even when evidence exists that carbonate fractions have been transported the transport is usually viewed as being intrabasinal stable isotope analyses 18 o and 13 c of the carbonate contained in the fine fraction m of eight cores from the north american continental margin and the west flank of the mid atlantic ridge mar suggest that carbonate sedimentation patterns may be influenced by transport to a greater extent than previously recognized in holocene sections of all the cores the fine fraction and foraminiferal isotopic signals are comparable in cores from the flanks of the mar the fine fraction and foraminiferal isotopic signals remain comparable during the entire glacial interglacial cycle on the north american margin however the pattern is strikingly different starting about 10 ka and extending back into glacial times the fine fraction isotopic signal in margin cores becomes increasingly depleted reaching a value of 8 pdb the foraminiferal signal from these same cores follows the typical glacial interglacial pattern and gets heavier during glacial time the holocene correspondence of foraminiferal and fine fraction isotope curves throughout the north american basin suggests that both have the same intrabasinal pelagic source however in late glacial age sediments from the north american margin the divergence of foraminiferal and fine fraction isotope signals indicates different sources for each component based on the isotopic signals and the timing of changes in the signal a substantial proportion of the fine fraction carbonate on the north american margin appears to be derived from diagenetically altered carbonate rock this fine carbonate sediment probably resulted from physical erosion of carbonate rock by glacial processes and deposition in the north american basin by the retreating wisconsin glacier

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

persistence of gulf stream separation during the last glacial period implications for current separation theories 1 we present stable oxygen isotope ratio 18o measurements on deep dwelling planktonic foraminifera from the western margin of the north atlantic in order to reconstruct the latitude at which the gulf stream separated from the western boundary of the atlantic ocean in the past the modern separation latitude can be reconstructed within one degree from 18o measured on the fossil shells of deep dwelling planktonic foraminifera globorotalia truncatulinoides from the holocene sediments representing the past 10 000 years of mild climate conditions similar to today the separation latitude is captured in a sharp 18o gradient which reflects the prominent hydrographic change across the boundary between the warm waters south and east of the gulf stream and the cold slope water to the north the latitudinal 18o profile from approximately the last glacial maximum shows that the gulf stream separated from the coast near cape hatteras at almost the same latitude as it does today we assess our finding in light of existing gulf stream separation theories and conclude that one of the theories the wind induced separation mechanism is not consistent with our paleoceanographic reconstruction

atlantic sediments glacial interglacial comparisons to assess the regional effects of glaciation on sedimentation in the atlantic ocean we compare sediment types distributions and rates between recent core top and last glacial maximum lgm 18 000 years b p stratigraphic levels based upon smear slides and carbonate analyses in 178 cores we find that glacial age carbonate content is generally lower than recent during both the recent and lgm carbonate content shows an east west asymmetry with western basins exhibiting lower carbonate values input of ice rafted detritus into the north atlantic during lgm time interrupts this topographic control on carbonate distribution considerably farther south than at present in the south atlantic this effect is minor comparison of lgm and recent sediment distributions indicates that the lgm seafloor was dominated by biogenic oozes calcareous clays and clays while the recent is dominated by biogenic oozes and marls coarse grained detritus is much more prevalent in lgm sediments derived not only from glacial input but also from fluvial and aeolian sources sedimentation rates calculated from lgm to recent sediment thickness in cores are 4 cm 1000 yr for most of the ocean higher rates are typical of the continental margin off the amazon river the north american basin and a small region off west equatorial africa

stress induced elastic anisotropy of the etnean basalt theoretical and laboratory examination 1 a theory the stress sensitivity approach has been developed which relates the elastic moduli of anisotropic rocks to the stress tensor and pore pressure for an arbitrary symmetry of the applied load the theory explains the stress induced changes of seismic velocities in terms of stress induced changes of the pore space geometry the stress dependent anisotropy is described in terms of thomsen s anisotropy parameters e and to test the theory we analyze the laboratory high frequency results of deformation of an isotropically crack damaged dry lava flow basalt from mt etna volcano the theory states that under an anisotropic i e axisymmetric triaxial load and in the case of an initially isotropic rock 1 the anisotropy parameters are linear functions of the stress exponentials i e exponential functions of principal stress components and 2 the ratio of these anisotropy parameters as a function of the stress is constant in order to verify these relationships the stress exponentials and the anisotropy parameters based on the measured velocities are computed as well as the expected ratio of the thomsen s parameters our experimental results are in very good agreement with the theoretically predicted relations

a margin wide bsr gas hydrate assessment canada s atlantic margin abstract it is the intent of this paper to explore a significant extent of an entire passive continental margin for hydrate occurrence to understand hydrate modes of occurrence preferred geologic settings and estimate potential volumes of methane the presence of gas hydrates offshore of eastern canada has long been inferred from estimated stability zone calculations but little physical evidence has been offered an extensive set of 2 d and 3 d single and multi channel seismic reflection data comprising in excess of 140 000 line km was analyzed bottom simulating reflections bsr were unequivocally identified at seven sites ranging between 250 and 445 m below the seafloor and in water depths of 620 2850 m the combined area of the bsrs is 9311 km 2 which comprises a small proportion of the entire theoretical stability zone along the canadian atlantic margin 715 165 km 2 the bsr within at least six of these sites lies in a sedimentary drift deposit or sediment wave field indicating the likelihood of grain sorting and potential porosity and permeability reservoir development although there are a variety of conditions required to generate and recognize a bsr one might assume that these sites offer the most potential for highest hydrate concentration and exploitation total hydrate in formation at the sites of recognized bsr s is estimated at 17 to 190 10 9 m 3 or 0 28 to 3 12 10 13 m 3 of methane gas at stp although it has been shown that hydrate can exist without a bsr the results from this regional study argue that conservative estimates of the global reserve of hydrate along continental margins are necessary

intermediate water links to deep western boundary current variability in the subtropical nw atlantic during marine isotope stages 5 and 4 records from ocean drilling program sites 1057 and 1059 2584 m and 2985 m water depth respectively have been used to reconstruct the behavior of the deep western boundary current dwbc on the blake outer ridge bor from 130 to 60 kyr b p marine isotope stage mis 5 and the 5 4 transition site 1057 lies within labrador sea water lsw but close to the present day boundary with lower north atlantic deep water lnadw while site 1059 lies within lnadw high resolution sortable silt mean inline equation grain size and benthic 13c records were obtained and changes in the dwbc intensity and spatial variability were inferred comparisons are made with similar proxy records generated for the holocene from equivalent depth cores on the bor during mis 5e inline equation evidence at site 1057 suggests slower relative flow speeds consistent with a weakening and a possible shoaling of the lsw sourced shallower limb of the dwbc that occupies these depths today in contrast the paleocurrent record from the deeper site suggests that the fast flowing deep core of the dwbc was located close to its modern depth below 3500 m during this interval the benthic 13c suggests little chemical stratification of the water column and the presence of a near uniform lnadw dominated water mass after 111 kyr b p the inline equation record at site 1057 increases to reach values similar to site 1059 for the rest of mis 5 the strengthening of flow speeds at the shallow site may correspond to the initiation of glacial north atlantic intermediate water formation also suggested by a divergence in the benthic 13c records with site 1057 values increasing to 1 2 coupled suborbital oscillations in dwbc flow variability and paleohydrography persisted throughout mis 5 comparison of these data with planktonic 18o records from the sites and alkenone derived sea surface temperature sst estimates from the nearby bermuda rise suggest a hitherto unrecognized degree of linkage between oscillations in subtropical north atlantic sst and dwbc flow

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

abyssal bedforms as indicators of changing bottom current flow examples from the u s east coast continental rise direct indications of circulation patterns in the deep sea especially along continental rises and sediment drifts can be obtained through the analysis of abyssal bedforms such as furrows and mud waves such direct evidence of current flow will supplement indirect indicators of circulation provide by paleochemical indicators preserved in ocean sediments water that sinks in the northern north atlantic forms part of the western boundary undercurrent along the continental rise of eastern north america and the understanding of temporal changes in the speed and depth of flow along this continental rise can provide important information on how the speed at which the global conveyor system is operating changes with time studies of furrows and mud waves along the blake bahama outer ridges show that they are active sedimentary features today and that bottom flow speeds near the time of the younger dryas were increased over later intervals a more detailed analysis of bedform structure and sediments is needed to more clearly show the timing and reason for this change in sedimentation pattern

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

changes in grain size and magnetic fabric at blake bahama outer ridge during the late pleistocene marine isotope stages 8 10 abstract odp sites 1055 1062 on the blake bahama outer ridge bbor are characterized by high sedimentation rates which allow high resolution analyses to reconstruct the behavior of the deep western boundary current dwbc as a function of depth along the bbor the odp sites provide an intermediate and deep water transect from 1800 to 4760 m water depths we focused on the time interval from 350 to 250 ka marine isotope stages mis 10 2 8 3 grain size and magnetic properties were analyzed with centennial to millennial scale time resolution integrating the results of grain size analyses lightness and magnetic properties the changes in the vertical position and the intensity of the dwbc core were inferred during glacial periods mis 10 2 and 8 4 8 3 the dwbc core was located at around 2200 m water depth whereas it deepened to 3000 m or more during warm periods interglacial stage 9 3 and interstadial 8 5 between these periods the dwbc core moved to shallower depth 2500 3000 m and its intensity increased which generally provided coarser sediments to a broad depth range from 2100 to 4800 m furthermore the magnetic properties imply that the dwbc supplied carbonate material other than terrigenous sediments to the deeper sites during mis 9 the depositional processes at site 1062 are characterized by sudden influxes of fine carbonate rich sediments which gradually decreased with time paleocurrent directions inferred from the direction of the great axis of the magnetic fabric are consistent with the modern topography at sites 1055 1056 1058 and 1060 during the relatively warm period from stages 9 3 to 8 5 at site 1062 the deepest site which exhibits a mud wave field the inferred flow direction is parallel to the bathymetric contours during warm periods while the nearly cross wave direction seemingly dominated during the other periods it appears that topographic position may have affected the scattering of azimuth plots moreover there is a possibility that the changes in flow direction correlate with climate changes

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

overburden 4d time shifts indicating undrained areas and fault transmissibility in the reservoir abstract production induced geomechanical stress changes cause velocity changes in the overburden that might be detected as 4d seismic time shifts the strength of the velocity changes depends on the degree of pressure changes and the elastic properties of the reservoir and overburden layers even small velocity changes less than 1 might accumulate into detectable seismic time shifts at the top reservoir since the overburden thickness typically ranges from one to several kilometers reservoir pressure changes inducing seismic time shifts are observed in the overburden of the snorre heidrun and statfjord fields all located on the norwegian continental shelf the strong correlation between overburden time shifts geomechanics and reservoir pressure changes is used to indicate undrained areas and transmissibility across faults which is useful information for increased oil recovery well planning and reservoir model updating 4d geomechanical models are built with input from simulated reservoir pres

pleistocene fluctuations in the western boundary undercurrent on the blake outer ridge the mean grain size of the detrital silt fraction was analyzed in two piston cores from the crest of the blake outer ridge using electronic particle analysis the resultant profiles in the two cores are highly correlatable and are interpreted to reflect the paleospeed of the western boundary undercurrent wbuc for the past 90 kyr the record can be divided into three periods the first encompasses the past 12 000 years and begins with an abrupt acceleration marking the transition from slow glacial to more vigorous holocene conditions the later holocene is a period of strong but variable flow the second period extends from 30 to 12 10 years and is characterized by a steady reduction of wbuc strength through the last ice age the current continued to decelerate until 12 10 years when the polar front finally retreated northward past the passages connecting the norwegian sea to the north atlantic the third period from 30 to about 90 10 years was a time of strong and variable flow that was independent of the glacial interglacial signal that is seen in the oxygen isotope record during this time the core of maximum flow appears to have shifted up and down the flank of the blake outer ridge and may have been influenced as much by salinity as by temperature variations in the source areas of the wbuc

a 130 000 year record of levantine intermediate water flow variability in the corsica trough western mediterranean sea abstract sortable silt particle size data and stable isotope analyses from the corsica trough western mediterranean sea provide a continuous palaeoceanographic record of the inflow ventilation and vertical fluctuations of the levantine intermediate water liw in the northern tyrrhenian sea for the last 130 000 years the results presented herein reveal that climate changes drive the mediterranean intermediate circulation on milankovitch to millennial time scales intensified intermediate inflow and ventilation in the corsica trough occurred throughout the last glacial interval with a cold faster warm slower pattern existing between the dansgaard oeschger climatic oscillations including heinrich events and the liw variability by contrast a weak intermediate ventilation characterised the holocene and the last interglacial period especially during insolation maxima and the sapropel deposition in the eastern mediterranean this variability probably reflects the changes of the eastern mediterranean net evaporation as well as the propagation to the western mediterranean of the profound hydrographic adjustments of the levantine sea and adjacent areas to climate forcing the implications for the formation and ventilation of the western mediterranean deep water wmdw in the northwestern mediterranean basin as well as for mediterranean atlantic exchange through the strait of gibraltar are discussed

cloud aerosol and boundary layer structure across the northeast pacific stratocumulus cumulus transition as observed during cset abstractduring the cloud system evolution in the trades cset field study 14 research flights of the national science foundation g v sampled the stratocumulus cumulus transition between northern

sediment accumulation rates west of the mid atlantic ridge 35 n abstract although carbonate curves have a long history of use for temporal correlation only limited agreement concerning the reasons for down core carbonate variations has been reached in this study these variations are examined by analyzing absolute accumulation rates of both carbonate and terrigenous sediment components carbonate content was determined in nine cores from approximately 3000 5000 m water depth down core variation in carbonate was correlated to an oxygen isotope curve to establish a down core time stratigraphy weight percent carbonate carbonate accumulation rate and terrigenous sediment accumulation rate were plotted as a function of water depth and time 0 130 000 yrs b p the weight percent carbonate plot indicates that carbonate content decreases with increasing water depth however the carbonate accumulation rate data demonstrates that this decrease in weight percent carbonate does not result from a decrease in the carbonate accumulation rate in the deeper cores the accumulation rate of carbonate actually increases in these deep cores the increase in carbonate accumulation rate is offset by a larger increase in the accumulation rate of terrigenous sediment resulting in a decrease in weight percent carbonate high accumulation rates of both carbonate and terrigenous sediment in cores below 4250 m appears to result from transport and redeposition of sediment most of the carbonate sediment deposited in these deep cores appears to be derived from shallow areas of the mid atlantic ridge mar the terrigenous sediment probably results from deposition by deep currents

the inverse correlations between methane content and elastic parameters of coal bed methane reservoirs we investigated three coal bed methane cbm reservoirs in which there exist when we are careful about data quality and reduce environmental variations inverse correlations between methane content and the elastic properties of the coal beds such inverse correlations may exist in general in high and medium rank cbm reservoirs there is evidence that supports the generalization of such inverse correlations and factors that distort them these distorting factors may prevent identification of such inverse correlations in certain cbm prospects however they cannot negate the underlying inverse correlations such inverse correlations may play a role in cbm amplitude versus offset avo similar to the role played by gassmann biot theory gassmann 1951 biot 1956 1962 in avo technology for conventional gas reservoirs this may lay the first brick for a theoretical basis of cbm avo

practical seismic petrophysics the effective use of log data for seismic analysis a quick scan of the seg web site shows that the phrase seismic petrophysics has been used explicitly in the title of a paper or abstract six times the earliest of which was by williams et al in 1996 the hugoton cross well survey a direct look at stratigraphy seismic petrophysics and shale anisotropy however the first attempt at a definition and an expanded description of seismic petrophysics was published by wayne pennington in the leading edge in 1997 seismic petrophysics an applied science for reservoir geophysics he defines seismic petrophysics as follows the purposeful application of rock physics theory as calibrated by laboratory and well measurements to the interpretation of seismic data

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

porosity and elastic anisotropy of rocks under tectonic stress and pore pressure changes elastic properties of rocks depend on tectonic stress using the theory of poroelasticity as a constraint we analyze features of these dependencies related to changes in rock pore space geometry we develop a formalism describing elastic moduli and anisotropy of rocks as nonlinear functions of confining stress and pore pressure this formalism appears to agree with laboratory observations to a first approximation elastic moduli and seismic velocities as well as porosity depend only on the difference between the confining tectonic stress and pore pressure however in general both the confining stress tensor and the pore pressure must be taken into account as independent variables the stress dependent geometry of the pore space fully controls the stress induced changes in elastic moduli and seismic velocities specifically the compliant porosity plays the most important role despite the fact that in many rocks the compliant porosity is a very small part of total porosity changes in compliant porosi

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

the ability of rock physics models to infer marine in situ pore pressure pore fluid pressure is an important parameter defining the mechanical strength of marine sediments obtaining high spatial resolution in situ pore pressure measurements in marine sediments however is a challenge and as a result only a handful of in situ pore pressure measurements exist at scientific drill sites integrating rock physics models with standard iodp odp measurements provides a potentially widely applicable approach for calculating in situ pore pressure here we use a rock physics approach to estimate in situ pore pressure at two scientific ocean drill sites where in situ pressure is well constrained odp site 1173 used as reference for normal hydrostatic fluid pressures and odp site 948 where previous studies infer high fluid pressures 0 45 0 95 where the pore pressure ratio is defined as the pore pressure above hydrostatic divided by the difference between the largest principal stress and hydrostatic stress our analysis indicates that the rock physics method provides an accurate low precision method for estimating in situ pore pressure at these drill sites and sensitivity analysis indicates this method can detect modestly high 0 6 pore pressure at the 95 confidence level this approach has broad applicability because it provides an inexpensive high resolution meter scale method for retrospectively detecting and quantifying high pore pressure at any drill site where quality wireline logs and ocean drilling data exist

acoustic and petrophysical relationships in low shale sandstone reservoir rocks this paper describes the measurements of the acoustic and petrophysical properties of two suites of low shale sandstone samples from north sea hydrocarbon reservoirs under simulated reservoir conditions the acoustic velocities and quality factors of the samples saturated with different pore fluids brine dead oil and kerosene were measured at a frequency of about 0 8 mhz and over a range of pressures from 5 mpa to 40 mpa the compressional wave velocity is strongly correlated with the shear wave velocity in this suite of rocks the ratio v p v s varies significantly with change of both pore fluid type and differential pressure confirming the usefulness of this parameter for seismic monitoring of producing reservoirs the results of quality factor measurements were compared with predictions from biot flow and squirt flow loss mechanisms the results suggested that the dominating loss in these samples is due to squirt flow of fluid between the pores of various geometries the contribution of the biot flow loss mechanism to the total loss is negligible the compressional wave quality factor was shown to be inversely correlated with rock permeability suggesting the possibility of using attenuation as a permeability indicator tool in low shale high porosity sandstone reservoirs

three dimensional p velocity image of the oroville reservoir area california from local earthquake tomography this study images the p velocity structure of a region in the vicinity of the large artificial reservoir at oroville california the velocity structure of the upper crust to a depth of 12 km was obtained by simultaneous inversion of p arrivals of 168 aftershocks of the 1975 oroville earthquake a decrease in p wave velocity by 7 to 8 was observed across a known fault zone the hypocenters of the 1975 sequence are associated with a southwest dipping structure characterized by low velocity with most of the deeper activity occurring in adjacent regions of higher velocity resolution of the velocity structure was examined through inversions of synthetic travel times using different starting velocity models although the role of the reservoir in generating the low velocities remains speculative the structure is comparable to that of some active segments of the san andreas fault where fluid pressures are thought to be high

resolution limits of fluid overpressures from mineralogy porosity and sonic velocity variations in north sea mudrocks pore pressure identification in mudrocks largely relies on indirect methods including analyses of sonic velocity data the magnitude of pore pressure changes that can be resolved from such data depends on the impact of fluid pressures on well log responses and on the velocity responses to lithological variations that could be mistaken for indications of pore pressure changes analysis of relationships between sonic velocity mineralogy and porosity from 11 north sea wells demonstrated porosity variations of up to 5 from the mean value in mudrocks at any given depth between 1 and 3 5 km 3300 11 500 ft comparisons of these wells with seven wells from the norwegian sea demonstrated that the sonic velocity and density variations are influenced by the content of silica with a biogenic origin but that they can otherwise not in general be related to mineralogy and pore pressure variations the sonic velocity deviations from the mean value are of the same magnitude as those that would be caused by porosity changes of 8 in mudrocks of uniform lithology furthermore the deviations are not significantly reduced when the velocity data are compensated for changes in density porosity detection limits for mechanically compacting mudrocks that are at their maximum effective stress are equivalent to static mud density changes of 0 1 0 15 g cm3 these numbers apply to mudrocks with similar lithological variability to those analyzed in our data set but should be much higher when significant amounts of silica with a biogenic origin are present the impact of effective stress changes on the sonic velocities of chemically compacting as well as of mechanically unloading rocks is much less because small or no porosity changes follow from the effective stress changes in such cases the velocity responses for mechanically unloading and stress insensitive chemical compaction can only be identified from four dimensional time lapse seismic data unless the rocks are close to the fracturing limit these observations imply that reasonably accurate velocity based pore pressure identification in north sea mudrocks requires a knowledge of local mudrock heterogeneity and compaction that cannot easily be obtained as a result sonic velocity data should be treated with considerable caution in pore pressure evaluation

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

nd and pb isotope signatures of the clay size fraction of labrador sea sediments during the holocene implications for the inception of the modern deep circulation pattern holocene on the basis of sediment supply variations for the last 12 kyr three sources have contributed to the sediment mixture the north american shield the pan african and variscan crusts and the mid atlantic ridge clay isotope signatures indicate two mixtures of sediment sources the first mixture 12 2 6 5 ka is composed of material derived from the north american shield and from a young crustal source from 6 5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the midatlantic ridge since the significant decrease in proximal deglacial supplies the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the western boundary undercurrent over the past 8 4 kyr the progressive intensification of the western boundary undercurrent was initially associated mainly with the transport of the northeast atlantic deep water mass until 6 5 ka and with the denmark strait overflow water thereafter the establishment of the modern circulation at 3 ka suggests a reduced influence of the denmark strait overflow water synchronous with the full appearance of the labrador seawater mass our isotopic data set emphasizes several changes in the relative contribution of the two major components of north atlantic deep water throughout the holocene index terms 4267 oceanography general paleoceanography 4558 oceanography physical sediment transport 1040 geochemistry isotopic composition chemistry 9325 information related to geographic region atlantic ocean 9604 information related to geologic time cenozoic keywords clay size fraction sedimentary mixings deep circulation nd and pb isotopes north atlantic labrador sea

the role of deep water sedimentary processes in shaping a continental margin the northwest atlantic abstract the tectonic history of a margin dictates its general shape however its geomorphology is generally transformed by deep sea sedimentary processes the objective of this study is to show the influences of turbidity currents contour currents and sediment mass failures on the geomorphology of the deep water northwestern atlantic margin nwam between blake ridge and hudson trough spanning about 32 of latitude and the shelf edge to the abyssal plain this assessment is based on new multibeam echosounder data global bathymetric models and sub surface geophysical information the deep water nwam is divided into four broad geomorphologic classifications based on their bathymetric shape graded above grade stepped and out of grade these shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope accommodation this descriptive method of classifying continental margins while being non interpretative is more informative than the conventional continental shelf slope and rise classification and better facilitates interpretation concerning dominant sedimentary processes areas of the margin dominated by turbidity currents and slope by pass developed graded slopes if sediments did not by pass the slope due to accommodation then an above grade or stepped slope resulted geostrophic currents created sedimentary bodies of a variety of forms and positions along the nwam detached drifts form linear above grade slopes along their crests from the shelf edge to the deep basin plastered drifts formed stepped slope profiles sediment mass failure has had a variety of consequences on the margin morphology large mass failures created out of grade profiles whereas smaller mass failures tended to remain on the slope and formed above grade profiles at trough mouth fans or nearly graded profiles such as offshore cape fear