stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

inverse square root dependence of mid ocean ridge flank roughness on spreading rate the topographic roughness of mid ocean ridge flanks is known to increase with decreasing spreading rate1 4 but the exact form of this relationship has not been established as the topographic features that make up ridge flank roughness abyssal hills are created near the axes of mid ocean ridges by faulting and volcan ism5 7 the relationship between roughness and spreading rate may shed light on the process of crustal accretion at spreading centres here i present measurements of ridge flank roughness on profiles crossing the world mid ocean ridge system which show that roughness is proportional to the inverse square root of the spreading rate this result is consistent with some very simple inferences of how the topographic roughness of mid ocean ridge flanks scales with the lithospheric thickness near ridge axes as determined by thermal models

constructional features of the troodos ophiolite and implications for the distribution of orebodies and the generation of oceanic crust the map pattern of the troodos ophiolite in cyprus is an expression of a simple elongate anticlinal structure the cross sectional form of the anticline can be described by a sinusoidal dip model on the northern flank of the anticline the thickness of various units number of gossans etc were measured along profiles at 2 5 km intervals normal to strike using existing maps supplemented by new observations profiles are approximately perpendicular to the spreading direction during crustal construction and uncertainties in unit thickness are smaller than the range of unit thicknesses data on the profiles were analyzed quantitatively by harmonic analysis using the fourier transform method the harmonic analysis discloses cyclic variation in the thickness of major units number of gossans etc that provides a link with the regular spacing of five groups of cu fe zn orebodies groups of orebodies occur preferentially where sheeted dikes are at a shallow crustal depth sheet and massive flows and dike

regression analysis of vs30 using topographic attributes from a 50 m dem abstract the average shear wave velocity for the top 30 m v s30 is one of the simple predictors of earthquake ground motion amplification we performed a multiple linear regression analysis of the logarithm of observed v s30 at 1646 locations in japan with three topographic attributes slope gradient surface texture and the logarithm of elevation calculated from a 50 m dem a v s30 map was created using the partial regression coefficients the determination coefficient was 0 318 the development of the estimation method of v s30 from a dem will be useful for earthquake vulnerability assessment

the relation between site amplification factor and surficial geology in central california abstract site amplification factors at frequencies of 1 5 3 6 and 12 hz were determined for 132 stations of the usgs seismic network in central california from coda waves of 185 local earthquakes in this area using a recursive stochastic inversion method we found that the site amplification at a station is systematically related to the geology underlying that station the site amplification is high for young quaternary sediments and decreases with increasing geologic age at all frequencies between 1 5 and 12 hz the rate of decrease varies with frequency where site amplification at low frequencies shows a faster rate of decrease with age than at higher frequencies to quantify the relation between site amplification factor and site geology the surface geology of station sites was classified into five groups namely 1 quaternary sediments 2 pliocene sediments 3 miocene through cretaceous sediments 4 franciscan formation and mesozoic granitic rocks and 5 pre cretaceous metamorphic rocks the station site amplification factors for each group were logarithmically averaged and the mean value was assigned to the median geologic age of that group a smooth power law relation was found between the mean site amplification and the median geologic age this relation provides a simple way of estimating site effect at a specific site with known surficial geology our site amplification factors were compared with magnitude station residuals determined by eaton 1990 for the same network a remarkable linear correlation was found between the logarithmic coda amplification factor and the magnitude station residual value confirming that the coda method provides an effective means of estimating site amplification factor comparison of our site amplification factor with strong motion results obtained from the loma prieta earthquake boore et al 1989 maley et al 1989 shakal et al 1989 chin and aki 1991 suggests that weak and strong motion site amplification factors correlate well in the region outside the epicentral source region beyond epicentral distances of about 50 km within the epicentral source region however the weak motion amplification factors estimated from coda waves do not agree with the observed for strong ground motion suggesting a nonlinear behavior at sediment sites these results together with studies on the correlation between weak motion site amplification and earthquake intensity borcherdt 1970 borcherdt and gibbs 1976 chavez garcia et al 1990 king et al 1990 demonstrate the importance of in situ determination of weak motion site amplification for seismic zonation

depth to bedrock using gravimetry in the reno and carson city nevada area basins sedimentary basins can trap earthquake surface waves and amplify the magnitude and lengthen the duration of seismic shaking at the surface poor existing gravity and well data coverage of the basins below the rapidly growing reno and carson city urban areas of western nevada prompted us to collect 200 new gravity measurements by classifying all new and existing gravity locations as on seismic bedrock or in a basin we separate the basins gravity signature from variable background bedrock gravity fields we find an unexpected 1 2 km maximum depth trough below the western side of reno basin enhancement of the seismic shaking hazard would be greatest in this area depths throughout most of the rest of the truckee meadows basin below reno are less than 0 5 km the eagle valley basin below carson city has a 0 53 km maximum depth basin depth estimates in reno are consistent with depths to bedrock in the few available records of geothermal wells and in one wildcat oil well depths in carson city are consiste

nd isotopic excursion across cretaceous ocean anoxic event 2 cenomanian turonian in the tropical north atlantic late cretaceous fish debris from demerara rise exhibits a dramatic positive excursion of 8 nd units during ocean anoxic event 2 oae2 that is superimposed on extremely low nd t values 14 to 16 5 observed throughout the rest of the studied interval the oae2 nd excursion is the largest yet documented in marine sediments and the majority of the shift is estimated to have occurred over nd values on demerara rise are explained as the nd isotopic signature of the south american craton whereas eruptions of the caribbean large igneous province or enhanced mixing of intermediate waters in the north atlantic could have caused the excursion

interaction of submarine volcanic and high temperature hydrothermal activity proposed for the formation of the agrokipia volcanic massive sulfide deposits of cyprus the results of drilling near the spreading ridge type volcanic hosted massive sulfide deposits of agrokipia cyprus are described mineralization and associated argillic hydrothermal alteration occur over intervals of 5 130 m and at depths of 80 230 m beneath the original surface of the oceanic crust mineralization occurs in massive flows that probably represent a locally ponded sequence up to 300 m thick abundant glass aphanitic basalt transitions are present from about 100 m below the surface of the ponded sequence with glass abundances locally reaching 60 of the section a novel hypothesis involving the presence of active high temperature hydrothermal vents beneath the cooling ponded sequence with the passage of hydrothermal fluids through the still molten lava is proposed to account for the observations while this hypothesis is reasonable the inferred processes have not as yet been demonstrated under either laboratory or field conditions the seafloor expression of this system was proba

cretaceous deep water formation in the indian sector of the southern ocean 1 the role that meridional overturning circulation moc patterns played in poleward heat transport during the extreme warmth of the early to late cretaceous is a fundamental and unresolved question in climate dynamics in order to address this question we must determine where deep waters formed and how they may have circulated during periods of extreme warmth here we present late albian through maastrichtian 105 to 65 ma nd isotope records from deep sea drilling project dsdp and ocean drilling program odp sites in the proto indian ocean and the tropical pacific comparison of these data with previously published records indicates deep water formation in the indian sector of the southern ocean began at least 105 ma extending the record of high latitude convection back into the early cretaceous prior to the peak warmth of the mid cretaceous the growing body of data supports a mode of moc in part characterized by high latitude downwelling during the peak of greenhouse warmth of the mesozoic and cenozoic however this mode of moc likely was characterized by numerous locations of deep convection that were regionally important but not significant in terms of a globally overturning circulation due to paleogeographic and bathymetric barriers

petrology and oxygen isotope geochemistry of a fossil seawater hydrothermal system within the solea graben northern troodos ophiolite cyprus hydrothermal mineral zonations and o isotope patterns of the northern troodos complex do not parallel the ophiolite pseudostratigraphy but reflect the convective geometry of an upper cretaceous seawater hydrothermal system large areas of the sheeted intrusive complex sic including the subaxial region of the solea graben are composed of 18o rich subgreenschist mineral assemblages and may represent regions of diffuse seawater recharge other areas of the sic are recrystallized to distinctive epidosite rocks granular high variance assemblages of epidote quartz chlorite that are depleted in 18o al2o3 na2o k2o zr cu and zn and are enriched in cao and sr compared with other mafic volcanic and dike rocks of the solea graben epidosite alteration occurred at temperatures of 310 370 c and involved fluids with 18o values and salinities similar to those of upper cretaceous seawater the epidosite zones are discordant with earlier mineral o isotope zonations and with the axis of spreading in the solea graben suggesting a postspreading off axis origin the seawater hydrothermal system responsible for solea graben massive sulfide deposits was probably driven by hypabyssal intrusions not exposed emplaced in a terminal failed spreading episode the geometries of o isotope surfaces within the solea graben imply that the epidosites formed in fossil upflow and deep recharge conduits depletions in base metals show that epidosite alteration liberated cu and zn to mineralizing fluids within the fossil upflow zone

biostratigraphy and paleoceanography of the cretaceous seaway between norway and greenland abstract the narrow seaway between greenland and norway in cretaceous time was over 1500 km long and 300 km wide and partly of bathyal water depth during aptian through campanian it received a large volume of fine grained siliciclastic sediments with intercalated gravity flow sandstone wedges as a conduit for heat transport between the low latitudes and polar region atlantic watermasses particularly affected the eastern norwegian margin of this seaway despite its high latitude setting calcareous and few siliceous planktonic microfossils thus play an important role in regional stratigraphy and facies analysis and a majority of fossil events correlate to nw european basins the eastern margin sedimentary succession may be subdivided in several broad lithologic units 1 thin multicolored marly sediments of hauterivian barremian age with a shallow marine falsogaudryina nodosariid ostracod assemblage 2 dark mudstones and minor sands aptian early cenomanian in age with an upper bathyal agglutinated assemblage and monotypic hedbergella floods 3 thick mudstone facies with thin slope apron turbidite sands and an impoverished benthic planktonic assemblage of late cenomanian coniacian age deposited in an upper bathyal oxic dysaerobic environment where turonian sedimentation rates are low a planktonic foraminiferal assemblage with whiteinella hedbergella dicarinella and marginotruncana occurs 4 grayish laminated mudstones santonian campanian in age with local sands in the north a low diversity middle to upper bathyal benthic planktonic foraminiferal assemblage and an inoceramus prisms and radiolarian diatom flood a campanian agglutinated foraminiferal bloom also is known from the atlantic oceanic realm 5 more marly sediments of maastrichtian age with a low diversity planktonic benthic foraminiferal assemblage using the distribution of 1755 foraminiferal and dinoflagellate microfossil events in over 30 exploration wells a rasc ranking and scaling probabilistic zonation served as a template to build a cretaceous zonal model with 19 assemblage and interval zones including over 100 events variance analysis ranks 72 events according to reliability in correlation three new index taxa include uvigerinammina una and ammoanita globorotaliaeformis albian and fenestrella bellii campanian widespread planktonic flood events occur in late albian through early cenomanian early mid turonian late santonian earliest campanian and mid maastrichtian the result of northwards shifts of warmer water masses and disruptions in water stratification in the dysaerobic basins an earliest cretaceous hiatus separates jurassic from cretaceous strata ongoing block faulting coupled to thermal subsidence and global sealevel rise increased water depth in aptian albian time from neritic to bathyal and created sand accommodation space in dysaerobic restricted settings in cenomanian coniacian time sedimentation rates in the central basin increased 10 fold whereas paleo waterdepth did not deepen this relatively brief less than 10 m y tectonic episode resulting in deposition of deep water sands is tentatively linked to stress re orientation in the rockall area a widespread upper maastrichtian danian hiatus the result of shoulder uplift reflects break up prior to the onset of paleogene seafloor spreading in the norwegian sea

hydrothermal sulfide and oxide deposits on seamounts near 21 n east pacific rise hydrothermal deposits were sampled by submersible from the calderas and summit benches of two seamounts 20 and 30 km west of the east pacific rise at 21 n the deposits document a wide variety of off axis hydrothermal activity including samples from the interiors of seafloor sulfide deposits in contrast to most mid ocean ridge deposits sulfide deposits on green seamount are rich in si fe and cu are poor in zn and contain abundant quartz sulfide chimneys grew by quenching of hydrothermal fluids and deposition of walls of colloform pyrite marcasite zn sulfide and minor galena whereas coarse grained pyrite and chalcopyrite were deposited at higher temperatures 250 c in chimney interiors as chimney walls grew outward into sea water increased temperatures in the inner walls resulted in recrystallization to pyrite and deposition of pyrite and chalcopyrite in pore space cooling in the outer portions of chimneys caused deposition of opal at temperatures of about 80 170 c as chimneys coalesced and opal rich material was heated in the interiors of sulfide edifices opal was recrystallized to chalcedony and quartz faulting has exposed the interiors of sulfide deposits where further recrystallization and deposition of chalcopyrite and quartz occurred at temperatures of 230 320 c clogging of chimneys changes in flow paths and cooling of the deposits led to the deposition of late mixed layer illite smectite iron sulfides fe poor sphalerite opal and barite the sulfide deposits formed over a time span of at least 140 000 to 70 000 yr ago probably coincident with caldera and pit crater formation the ages of the sulfide deposits provide constraints on the last volcanic and tectonic activity and they also suggest that it took a maximum of 260 000 yr for the seamount to reach its present height red seamount is presently hydrothermally active and deposits consisting predominantly of amorphous fe oxyhydroxide are forming on small pillow cones in the caldera at temperatures of 10 15 c hydrothermal nontronite deposits capped by mn oxide crusts cover much of the southern summit bench of red seamount and formed at temperatures of around 30 c iron rich talc and sulfide grains in nontronite provide evidence of former high temperature activity and suggest that a sulfide deposit is present nearby

on the characteristics of local geology and their influence on ground motions generated by the loma prieta earthquake in the san francisco bay region california strong ground motions recorded at 34 sites in the san francisco bay region from the loma prieta earthquake show marked variations in characteristics dependent on crustal structure and local geological conditions peak horizontal acceleration and velocity inferred for sites underlain by rock generally occur on the transverse component of motion they are consistently greater with lower attenuation rates than the corresponding mean value predicted by empirical curves based on previous strong motion data theoretical amplitude distributions and synthetic seismograms calculated for 10 layer models suggest that bedrock motions were elevated due in part to the wide angle reflection of s energy from the base of a relatively thin 25 km continental crust in the region characteristics of geologic and geotechnical units as currently mapped for the san francisco bay region show that average ratios of peak horizontal acceleration velocity and displacement increase with decreasing mean shear wave velocity ratios of peak acceleration for sites on soil alluvium fill bay mud are statistically larger than those for sites on hard rock sandstone shale franciscan complex spectral ratios establish the existence of predominant site periods with peak amplifications near 15 for potentially damaging levels of ground motion at some sites underlain by alluvium and fill bay mud average spectral amplifications inferred for vertical and the mean horizontal motion are respectively 1 1 for sites on the franciscan complex kjf 1 4 1 5 for sites on mesozoic and tertiary rocks tmzs 2 1 2 0 for sites on the santa clara formation qts 2 3 2 9 for sites on alluvium qal and 2 1 4 0 for sites on fill bay mud qaf qhbm these mean values are not statistically different at the 5 significance level from those inferred from previous low strain data analyses suggest that soil amplification and reflected crustal shear energy were major contributors to levels of ground motion sufficient to cause damage to vulnerable structures at distances near 100 km in the cities of san francisco and oakland

a shallow shear wave velocity transect across the reno nevada area basin in october and november 2001 we performed an urban shear wave velocity transect across 16 km of the reno nevada area basin using the refraction microtremor method of louie 2001 we determined shear wave velocity versus depth profiles at 55 locations shear wave velocity averaged to 30 m depth vs30 is one predictor of earthquake ground motion amplification in similar alluvium filled basins and it is the basis of site hazard classification under national earthquake hazards reduction program uniform building code nehrp ubc provisions a geologic map based nehrp classification along nearly all of our transect line would be nehrp d but our measurements of vs30 revealed that 82 of the transect is classified nehrp c relatively stiff tertiary sediments underlie the surface of the reno basin and weaker soils occur east of downtown reno in the floodplain of the truckee river although 53 of our locations were on the geologically youngest and most active fluvial units these sites showed vs30 values ranging from 286 m sec nehrp d to 849 m sec nehrp b mapped geologic and soil units are not accurate predictors of vs30 measurements in this urban area a test model based on gravity results showed quaternary alluvium depth can be combined with transect vs30 mea surements to predict vs30 across the reno basin

interpretation of aeromagnetic anomalies in terms of hydrothermal alteration in cretaceous normal polarity superchron extrusives of the troodos cyprus ophiolite one hundred and twenty two meters altitude aeromagnetics and ground data over the cretaceous normal polarity extrusives of the troodos ophiolite have allowed source modeling these data have been digitized and recontoured in gridded and reduced to the pole rtp formats the principal result is confirmation of large anomalies with amplitudes of several thousand nanoteslas and dimensions of 1 6 km since the extrusives are everywhere normally magnetized anomalies must have an explanation other than polarity reversals strong magnetization of overlying little altered extrusives and dikes and weak magnetization of underlying hydrothermalty altered material allows forward modeling in terms of source layer thickness detailed modeling was carried out for 50 km2 subarea containing two highs separated with 3000 nt contrast by a low for which ground information had been specifically acquired the low coincides with a thick series of sheet flows containing former hydrothermal flow ways gossans modeling of a former reservoir of hydrothermal fluid beneath the low with reduction of the magnetic source layer from 1000 to 250 m is consistent with observations for the extrusives as a whole gossans are weakly associated with relatively low rtp field although individual gossans are too small to perturb the kilometer scale anomalies they do show several relationships with anomalies gossans are absent from areas of very high 6500 nt and very low 1500 nt rtp field and within the intervening range they are bimodally distributed reconsideration of the nature of gossans accounts for some of these features

evaluation of methods for estimating linear site response amplifications in the los angeles region we have evaluated two methods of estimating linear site response amplifications and the standard index for classifying sites by comparing the results of each technique to observed ground motions at 33 sites in the los angeles region using velocity and density profiles from 33 boreholes we evaluated the use of the average 30 m shear wave velocity and associated site classifications the quarter wavelength method and the haskell propagator matrix method we correlated the average 30 m shear wave velocity and nehrp site classification at the borehole sites colocated within 290 m of a site with observed ground motion the observed data follow the expected trend of higher ground motion amplifications for lower average shear wave velocities but there is a significant degree of variability also there is a great deal of scatter in the observed amplifications within each national earthquake hazards reduction program nehrp class we used the velocity and density information in the database to calculate the average frequency dependent site response in the frequency ranges 1 3 hz 3 5 hz and 5 7 hz for a one dimensional flat layered structure using the haskell propagator matrix method and the quarter wavelength method there is a general correlation with the ground motion data however once again there is a great degree of scatter although slightly less for the quarter wavelength method we note that both the observed and predicted amplifications can change dramatically over a distance as small as 1 km or less even though all techniques considered give results that follow the expected trend of higher amplifications for softer sediments the predicted site response at any particular site with the current level of information may not be representative of the shaking that will actually occur during an earthquake the disparity between observed and predicted amplifications appears to be a result of oversimplification inherent in the amplificationestimation methods such as the use of average or assumed values for the site conditions in the absence of measured values the smoothing effect of using an average velocity limiting the properties considered to the uppermost 30 m of material and complexities in the wave propagation that are not addressed by these methods

strontium isotope stratigraphy in the upper cenomanian shallow water carbonates of the southern apennines short term perturbations of marine 87sr 86sr during the oceanic anoxic event 2 abstract strontium isotope stratigraphy of shallow water carbonates from the southern apennines italy indicates that the late cenomanian early turonian evolution of marine 87sr 86sr is not accurately depicted by the marine reference curve using the low mg biotic calcite of well preserved rudist shells as a study material and carbon isotope stratigraphy for correlation to the standard ammonite biozonal scheme of northern europe new 87sr 86sr values are proposed for four different stratigraphic levels the middle and uppermost part of the guerangeri zone the lower and upper part of the geslinianum zone the southern apennines data suggest that a sharp positive shift at the onset of oceanic anoxic event 2 precedes the well known sr isotope negative shift the positive shift is interpreted in terms of enhanced rates of chemical weathering driven by global warming forced by volcanogenic co2 outgassing a stratified ocean is invoked to reconcile the high gradient and the short lag time of the perturbation with estimates of present day total mass and residence time of strontium in the ocean the sharp switch to the negative shift is related to the collapse of water column density gradient driven by thermal instability during a late cenomanian cool event more active ocean circulation suddenly delivered to surface waters the signal of increased submarine volcanism that had accumulated in deep waters

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

formation of southern component water in the late cretaceous evidence from nd isotopes constraining deep ocean circulation during past greenhouse climatic periods such as the cretaceous is important for understanding meridional heat transfer processes controls on ocean anoxia and the relative roles of climate and tectonics in determining paleocirculation patterns ocean circulation models for the late cretaceous and early paleogene suggest that significant deep water production occurred in the southern ocean but cannot constrain when this process commenced or what the temporal relationship was between opening tectonic gateways and late cretaceous climatic cooling nd isotope data obtained from biogenic apatite fish teeth and bones are presented from lower bathyal and abyssal sites in the south atlantic and indian oceans during the mid cretaceous relatively radiogenic nd isotope values suggest that deep water circulation in these basins was sluggish with inputs likely dominated by seawater particle exchange processes and possibly easily weathered volcanic terranes in the campanian maastrichtian the nd isotopic composition of proto indian and south atlantic deep waters became less radiogenic suggesting the onset of deep water formation in the southern ocean southern component water scw consistent with paleogene reconstructions and ocean circulation models a combination of southern hemisphere cooling and the opening of tectonic gateways during the campanian likely drove the onset of scw

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

empirical site response and comparison with measured site conditions at anss sites in the vicinity of reno nevada we empirically evaluate spectral amplification relative to a nearby rock site at 18 advanced national seismic system strong motion stations within the basin containing the urban areas of reno and sparks nevada the near surface site conditions have a strong effect on ground motion which is clearly demonstrated through analysis of weak motion the study uses multiple regional earthquake events of varying azimuth averages of these empirical amplifications grouped by generalized geological formations volcanic rock pliocene and early to mid quaternary sediments and younger quaternary sedimentary sites show dependence on the geology however when the stations are grouped according to v s 30 values the mean amplifications are more distinct indicating that v s 30 is a more useful predictor of amplification for the reno sparks nevada urban area spectral amplifications computed from ground motions of the local mogul nevada 2008 earthquake swarm m l 0 6 4 7 anderson et al 2009 have similar spectral shapes for 8 of the 12 stations where comparisons could be made but the absolute amplitudes are slightly inconsistent four stations show unexplained peaks in the amplitude spectral ratios from the mainshock ground motions the comparisons verify that multiple regional ground motions can be used to obtain relative site response amplification functions for seismic hazard applications but the discrepancies are a reminder that directional effects contribute uncertainty to the amplification functions online material tables describing earthquakes recorded in the vicinity of reno nevada and figures of the fourier spectral ratios fsrs and of the amplitude and basin depth relationships

deep sea magnetic vector anomalies over the hakurei hydrothermal field and the bayonnaise knoll caldera izu ogasawara arc japan 1 we conducted deep sea magnetic measurements using autonomous underwater vehicles in the bayonnaise knoll caldera the izu ogasawara island arc which hosts the large hakurei hydrothermal field we improved the conventional correction method applied for removing the effect of vehicle magnetization thus greatly enhancing the precision of the resulting vector anomalies the magnetization distribution obtained from the vector anomaly data shows a 2 km wide belt of high magnetization trending nnw sse going through the caldera and a low magnetization zone 300 m by 500 m in area extending over the hakurei site comparison between the results obtained using the vector anomaly and the total intensity anomaly shows that the magnetic field is determined more accurately especially in areas of sparse data distribution when the vector anomaly rather than the total intensity anomaly is used we suggest a geologically motivated model that basaltic volcanism associated with the back arc rifting occurred after the formation of the caldera resulting in the formation of the high magnetization belt underneath the silicic caldera the hakurei hydrothermal field lies in the intersection of the basaltic volcanism belt and the caldera wall fault suggesting a mechanism that hot water generated by the heat of the volcanic activity has been spouting out through the caldera wall fault the deposit apparently extends beyond the low magnetization zone climbing up the caldera wall this may indicate that hot water rising from the deep through the alteration zone is transported laterally when it comes near the seafloor along fissures and fractures in the caldera wall

volcanic glass compositions of the troodos ophiolite cyprus fresh volcanic glass is preserved throughout the extrusive section of the troodos ophiolite which indicates that the lavas have not been pervasively metamorphosed glass compositions reveal the existence of two major magma suites apparently corresponding to distinct stratigraphic intervals the basal 400 500 m of the sequence consists of an andesite dacite rhyolite assemblage containing abundant hyaloclastites the remainder of the section comprises a basalt basaltic andesite assemblage with high mgo and low tio 2 and total iron the lower sequence is interpreted as an evolved arc tholeiite suite the upper has some similarities to boninitic lavas the close association in time and space of these two suites is similar to that observed in the mariana and bonin arcs and suggests that all of the troodos lavas were erupted in a subduction zone environment most probably in an incipient arc or fore arc

geological setting and mineralogical and geochemical investigations on sulfide deposits near 13 n on the east pacific rise geological mineralogical and geochemical investigations of hydrothermal deposits on one of the most studied segments of the east pacific rise near 13 n show that sulfides occur in four main tectonic settings these are 1 in the middle part of the central graben where active zones are located 2 at the top of the central graben where a second line of deposits is observed 3 on the marginal high which has sulfides both on its western tectonic side and at its top where a large deposit is located and 4 on the flank of the southeastern seamount which is the site of the most important deposit of the area the nature of the distribution of the samples through the area studied shows that hydrothermal activity has existed for more than 20 000 years mineral assemblages are dependent on the sample location the sulfide samples exhibit a wide range of mineralogical assemblages varying from high temperature hydrothermal cu fe rich chimneys black smokers which are characteristic structures of young edifices to mature cu fe rich massive sulfides similar to those found in the core of massive sulfide lenses mined on shore with respect to these observations a classification into nine types of sulfide assemblages is proposed hydrothermal activity at the axis is now increasing in intensity increase in temperature decrease in f s2 and f o2 the relative paucity of zn rich massive sulfides on the off axis structures is likely to be a consequence of the depletion of zn in the hydrothermal fluids r mode factor analysis applied to a population of nineteen representative bulk chemical analyses shows fractionation of the reduced sulfur fluid during the discharge into three main groups cu fe co se ca sr zn cd ag as pb and si ba displaying the principal types of sulfide samples collected in the 13 n area microprobe investigations conducted on sulfide minerals define the distribution of trace metal elements such as ag co se cd and as during the process of hydrothermal maturation of the deposits

high resolution magnetic signature of active hydrothermal systems in the back arc spreading region of the southern mariana trough high resolution vector magnetic measurements were performed on five hydrothermal vent fields of the back arc spreading region of the southern mariana trough using shinkai 6500 a deep sea manned submersible a new 3 d forward scheme was applied that exploits the surrounding bathymetry and varying altitudes of the submersible to estimate absolute crustal magnetization the results revealed that magnetic anomaly derived absolute magnetizations show a reasonable correlation with natural remanent magnetizations of rock samples collected from the seafloor of the same region the distribution of magnetic anomaly derived absolute magnetization suggests that all five andesite hosted hydrothermal fields are associated with a lack of magnetization as is generally observed at basalt hosted hydrothermal sites furthermore both the pika and urashima sites were found to have their own distinct low magnetization zones which could not be distinguished in magnetic anomaly data collected at higher altitudes by autonomous underwater vehicle due to their limited extension the spatial extent of the resulting low magnetization is approximately 10 times wider at off axis sites than at on axis sites possibly reflecting larger accumulations of nonmagnetic sulfides stockwork zones and or alteration zones at the off axis sites

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

evidence for volcanic eruption on the southern juan de fuca ridge between 1981 and 1987 the formation of new ocean crust at mid ocean ridges is known to be a discontinuous process in both space and time but little is known about the frequency and duration of eruptions along an active ridge segment here we present evidence from sea beam surveys and underwater photography for the eruption of lavas along a segment of the juan de fuca ridge between 1981 and 1987 although previous studies have inferred volcanic activity on ridges in areas where recent seismicity or young lava flows have been observed1 4 none has yet had direct evidence to date such a recent submarine eruption the temporal coincidence between this eruptive episode and the megaplumes huge sudden emissions of hot mineral laden water observed over this part of the ridge5 6 in 1986 and 1987 supports previous suggestions5 10 that megaplumes are caused by sea floor spreading events

shallow shear velocity and seismic microzonation of the urban las vegas nevada basin las vegas valley has a rapidly growing population exceeding 1 5 million subject to significant seismic risk surveys of shallow shear velocity performed in the las vegas urban area included a 13 km long transect parallel to las vegas blvd the strip and borehole and surface wave measurements of 30 additional sites the transect was completed quickly and economically using the refraction microtremor method providing shear velocity versus depth profiles at 49 locations the lowest velocities in the transect nehrp d class are near intrabasin faults found near interstate 15 and lake mead blvd calcite cementation of alluvium a k a caliche along the las vegas strip elevates vs30 values to 500 600 m sec nehrp c class our transect measurements correlate poorly against geologic map units which do not predict the conditions of any individual site with accuracy sufficient for engineering application some usda soil map units do correlate and vs30 predictions based on measurements of soil units match transect measurements in the transect area extending soil map predictions away from the area of dense measurement coverage generally failed to predict new measurements further for several test sites the predictions were not conservative in that the soil model predicted higher vs30 than was later measured predicting lesser potential ground motion subsurface information is needed to build a vs30 model extending predictions throughout las vegas valley a detailed stratigraphic model built by correlating 1100 deep well logs in las vegas predicts vs30 better than surface maps but again only in parts of the valley well measured for velocity the stratigraphic model yields good predictions of our transect vs30 measurements it is less accurate although at least conservative when extended to sites away from the transect

refraction microtremors data analysis and diagnostics of key hypotheses surface wave methods are quite popular for site characterization in geotechnical earthquake engineering among these techniques a particular role is taken by passive methods for their ability to yield information on the low frequency range and consequently on large depths one such passive method the refraction microtremors remi technique has been proposed as a simple alternative to 2d array techniques to estimate surface wave dispersion by using linear arrays of geophones the technique owes its name to the use of widely available instruments also adopted for seismic refraction the basic hypotheses underlying remi are that noise is distributed isotropically in azimuth or is aligned exactly with the array these conditions often are not met and in most cases they are not verified because such analysis requires an accurate approach to data processing that is rarely applied we have developed an algorithm that verifies remi s basic hypotheses by analyzing experimental data in addition we have propo

developing a map of geologically defined site condition categories for california consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion the importance of amplification by soil conditions has long been recognized but though many seismic instrument sites have been characterized by their geologic conditions there has been no consistent simple classification applied to all sites as classification of sites by shear wave velocity has become more common the need to go back and provide a simple uniform classification for all stations has become apparent within the pacific earthquake engineering research center s next generation attenuation equation project developers of attenuation equations recognized the need to consider site conditions and asked that the california geological survey provide site conditions information for all stations that have recorded earthquake ground motion in california to provide these estimates we sorted the available shear wave velocity data by geologic unit generalized the geologic units and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials this new map is different from the california geological survey preliminary site conditions map of california in that 19 geologically defined categories are used rather than national earthquake hazards reduction program categories although this map does not yet cover all of california when completed it may provide a basis for more precise consideration of site conditions in ground motion calculations

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

geometry conditions and timing of off axis hydrothermal metamorphism and ore deposition in the solea graben the recent discovery of fossil spreading axes along the northern margin of the troodos ophiolite1 provides a unique opportunity to compare a fossil seawater hydrothermal system with systems of modern oceanic spreading centres2 6 whereas previous accounts of ophiolite hydrothermal systems7 13 including troodos14 16have elucidated many aspects of sea floor hydrothermal metamorphism earlier workers have not placed ophiolite hydrothermal features within any specific spreading centre structural framework most ophiolites exhibit complex histories of post accretion deformation that mask or obliterate early structures related to seafloor spreading the troodos ophiolite is apparently still in the process of being emplaced 17 and most structural elements at troodos appear to have originated beneath a cretaceous sea floor1 we have discovered an extensive area of intense seawater hydrothermal alteration within the sheeted dyke complex of the solea graben fig 1 the metamorphic petrology and oxygen isotope geochemistry of 100 dyke samples from this graben reveal the size and three dimensional geometry of the hydrothermal system and yield estimates of temperature salinity oxygen isotope composition and recharge discharge geometry for fluids that transported the constituents of massive sulfide orebodies geometric discordance between the trends of the hydrothermally altered area and of earlier seafloor spreading structures compels us to consider a post spreading off axis origin for the orebodies of the solea graben

high resolution near bottom vector magnetic anomalies over raven hydrothermal field endeavour segment juan de fuca ridge high resolution near bottom vector magnetic data were collected by remotely operated vehicle jason over the raven hydrothermal vent field 47 57 3 n 129 5 75 w located north of main endeavour vent field on the endeavour segment of the juan de fuca ridge the survey was part of a comprehensive heat flow study of the raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field raven hydrothermal activity is presently located along the western axial valley wall while additional inactive hydrothermal deposits are found to the nw on the upper rift valley wall magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow while crustal magnetization is representative of the static time averaged effect of hydrothermal alteration a general nw to se trend in reduced magnetization across the raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the raven site is approximately 15 106 m3 in volume

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

a transect of 200 shallow shear velocity profiles across the los angeles basin this study assesses a 60 km north northeast south southwest transect along the san gabriel river for shallow shear velocities in san gabriel valley and the los angeles basin of southern california we assessed a total of 214 sites 199 along the transect at 300 m spacing during a one week field campaign with the refraction microtremor remi technique the transect9s maximum 30 m shear velocity vs30 occurs in coarse alluvium of san gabriel valley where the san gabriel river exits the san gabriel mountains at 730 m sec upper national earthquake hazards reduction program nehrp site class c much of the northeast section of the transect in san gabriel valley is also nehrp class c or near the cd class boundary the section of the transect south from whittier narrows to seal beach shows nehrp d velocities in active alluvium the transect9s lowest vs30 230 m sec at the alamitos bay estuary is also classed as nehrp d an increase toward the nehrp cd class boundary occurs at the shoreline beach outside alamitos bay confirmed by additional measurements on seal beach our measured vs30 values generally show good correlation with published site classification maps and existing borehole data sets there is no evidence in our data for an increase in velocity predicted by wills et al 2000 at their cd to bc site classification boundary at the san gabriel mountains front nor for any decrease at their d to de class boundary at alamitos bay very large vs30 variations exist in soil and geologic units sampled by our survey the vs30 variations we measured are smaller than vs30 variations of 30 or more we found between closely spaced

depth trends in magnetic properties in an area of prolonged cold seawater drawdown in uppermost troodos type oceanic crust study of the oxide minerals and measurements of the magnetic properties of about 100 samples distributed over a 475 m continuous drill core section from the uppermost part of an extrusive sequence of the troodos cyprus ophiolite close to 35 02 n 33 11 e in the vicinity of malounda yields the following principal results 1 low temperature alteration is intense to a depth of 260 m below which it is relatively much subdued 2 saturation magnetization natural remanence intensity and initial susceptibility all increase continuously with depth throughout the section 3 curie temperature decreases with depth to 260 m below which a change in the style of the thermal decay of magnetization behaviour takes place 4 pillowed and massive flows differ in their magnetic properties the results are consistent with the downwards decrease in low temperature alteration also noted by k gillis from the distribution of secondary minerals the downwards variations in magnetic properties closely follow in both

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

fluctuations in surface height of active lava lakes during 1972 1974 mauna ulu eruption kilauea volcano hawaii an active lava lake is one that forms directly on top of a magma column as opposed to an inactive one formed by passive ponding of lava within a preexisting crater two active lava lakes operating within summit craters of newly constructed volcanic shields at mauna ulu and alae were the longest lived of any observed in a hawaiian rift zone to date small scale fluctuations a few to 20 m in the height of lake surfaces are typically associated with degassing gas piston activity larger fluctuations as great as 200 m reflect major changes in eruptive activity measurements of surface height fluctuations of mauna ulu lake show gross positive correlation with variation in summit tilt which in turn reflects the inflation deflation state of kilauea s summit magma reservoir a more tenuous conclusion is that a sympathetic variation possibly exists between surface heights of the mauna ulu and alae lakes collectively these observations 1 require the existence of a fully engorged connected open and hydraulically efficient magma conduit system linking the summit reservoir with the lava lakes 2 provide additional evidence for the postulated regime of quasi steady state magma transfer that characterized much of the eruption 3 imply that fluctuations in lake surface reflect variation in magma supply rate to the reservoir and or outflow rate from the mauna ulu alae vents and 4 suggest undetected episodes of magma intrusion or storage in kilauea s east rift zone during 1973

the magnetization of oceanic crust contribution to knowledge from the troodos cyprus ophiolite an extensive study of a segment of the troodos cyprus ophiolite using both outcrop and drill core samples and extending from the sediment extrusive interface through sheeted dikes to cumulate ultramafics has allowed a number of key questions regarding the magnetization of oceanic crust to be addressed these include the number of strongly magnetized intervals with depth their lateral variability and controls on their occurrence comparison has also been made with the section in ocean drilling program odp hole 504b and a reinterpretation of its constructional setting is offered two strongly magnetized intervals occur in the area studied the upper is in the extrusive sequence extends on average from 0 2 to 0 6 km depth and has a thickness of 0 4 km here magnetization is dominated by remanence the lower interval extends from the lowest level at which flows occur with dikes average depth 0 9 km into the sheeted complex average depth 1 2 km and has a thickness of 0 3 km here magnetization is dominantly induced no other strongly magnetized intervals occur in the section the extent of dike intrusion is closely related to the position of the lower limit of the highremanence layer and to the occurrence of the high induced magnetization layer in both cases the replacement of primary magnetite which can carry a strong remanence by magnetically soft secondary magnetite appears to be the controlling process comparison of the troodos and hole 504b magnetization profiles shows close similarity in the upper remanence dominated magnetic interval the absence of the deeper interval of high induced magnetization in the hole 504b profile is interpreted as meaning that sheeted dikes have not been penetrated by the drill hole

last glacial maximum paleochemistry and deepwater circulation in the southern ocean evidence from foraminiferal cadmium south atlantic benthic foraminiferal cd ca shows no glacial interglacial variation suggesting that the glacial contribution of north atlantic deep water to the southern ocean was not much different than at present in contrast cd ca in southeast indian ridge cores show lower glacial bottom water cd comparable to levels in intermediate depths of the north atlantic and significantly lower than in the deep south atlantic low glacial cd ca was also recorded in planktonic foraminifera suggesting a substantial decrease in the nutrient concentration of subantarctic surface water during the glacial maximum which most likely was caused by increased biological productivity the cd data are inconsistent with low glacial benthic foraminiferal 13c which suggest higher nutrient concentration we propose that the low cd ca in the southeast indian ridge records reflects a local source of nutrient depleted deepwater formed during the last glacial maximum by open ocean convection near the antarctic polar front downstream of the kerguelene plateau if this source was limited to the southeast indian basin then its impact on the overall chemistry of glacial circumpolar deepwater was rather small however if during glaciations open ocean convection became the dominant mode of bottom water formation it might have had a greater impact on cpdw chemistry

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

northridge earthquake damage caused by geologic focusing of seismic waves despite being located 21 kilometers from the epicenter of the 1994 northridge earthquake magnitude 6 7 the city of santa monica experienced anomalously concentrated damage with mercalli intensity ix an intensity as large as that experienced in the vicinity of the epicenter seismic records from aftershocks suggest that the damage resulted from the focusing of seismic waves by several underground acoustic lenses at depths of about 3 kilometers formed by the faults that bound the northwestern edge of the los angeles basin the amplification was greatest for high frequency waves and was less powerful at lower frequencies which is consistent with focusing theory and finite difference simulations

new discoveries of massive sulfides on the east pacific rise abstract newly discovered massive sulfide occurrences were mapped on the east pacific rise between 18 and 24 s large occurrences of sulfides are restricted to zones in which there is more tectonic strain than usual for sea floor spreading centers these sites are also characterized by a relatively shallow bathymetric position and greater coverage with sheet lava than with pillow lava several hydrothermal sources with no sulfide precipitate on the sea floor suggest precipitation of sulfide below the sea floor stockwork mineralization animal communities that depend on sulfide oxidation are scarce and small at least that is the fauna that is large enough to be recognized in underwater photographs the animal communities around hydrothermal sources which profit from the larger food supply provided by the primary fauna are present in dense populations over relatively large areas the enrichment of the hydrothermal component in the sediments adjacent to a spreading center is not typical of hydrothermal fields along the east pacific rise it can be concluded from the evaluation of the sediment that the hydrothermal activity increases northwards

variability of site response in the los angeles urban area this article addresses the variability of site response in the los angeles area and possible structural causes for the observations aftershock records from 231 sites in the san fernando and los angeles basins and the surrounding mountains are used in this study spectral ratios taken with respect to a low amplitude reference site are used to document the variation in site amplification in the frequency range 2 to 6 hz both spatially and with backazimuth to the source at higher frequencies 6 to 10 hz spectral ratios are shown to have greater spatial variability interstation spectral ratios are used to measure the standard deviation among source as a function of station separation an increase in the variation in ground motion is shown to take place at a station separation of 1 km relative site response estimates between nearby stations are used to demonstrate that preferred directions of motion can exist even in areas with no surface topographic effects significant variations in site response exist over short baselines up to a factor of 2 over 200 m that are not explained by differences in surficial geology or shallow shear wave velocity a variety of investigative approaches is used including spectral ratios arrival time variations 1d and 2d waveform modeling and comparison with seismic reflection lines to determine the most likely causes of these observations a correlation is demonstrated between late arrival times of p and s waves and larger site amplification in sherman oaks and northridge this observation in conjunction with waveform modeling and seismic reflection profiles is used to infer that sedimentary structures in the upper 1 to 2 km and topography on the sediment basement interface play an important role in determining site amplification these structures in the form of folds and buried basins focus energy in spatially restricted areas at the surface comparison of displacement waveforms at nearby stations having disparate site amplifications complemented by known shallow shear wave velocities at selected sites is used to support the argument that these structures in some cases can be the dominant factor in the modification of local ground motions

constructional features of troodos type oceanic crust relationships between dike density alteration magnetization and ore body distribution and their implications for in situ oceanic crust quantitative relationships are demonstrated between dike density and hydrothermal alteration magnetization location of volcanic massive sulfide vms ore bodies and a number of other properties in a 40 by 15 km segment of the extrusive series of the troodos ophiolite low temperature alteration extends from the sediment extrusive interface to close to the 25 dike density surface while the onset of greenstone type alteration is closely associated with the 50 dike density surface these associations are explained in terms of the regional scale variations in the dike density contour surfaces following the form of the top of the gabbroic layer of the ophiolite an upper magnetic zone characterized by stable high remanence terminates just below the 25 dike density surface a deeper magnetic zone characterized by high induced magnetization straddles the top of the sheeted complex volcanic massive sulfide bodies are concentrated in a narrow depth range centered about 0 1 km above the 25 dike density surface a model for the postridge crest evolution of ore bodies accounts for this optimum depth range for preservation physical property changes with dike density and the depth distribution of vms ore bodies and prospects for the ophiolite as a whole support this model similar relationships appear to be present in the samail macquarie island newfoundland and chilean ophiolites and icelandic crust as a result of relationships found in the troodos ophiolite an alternative is proposed to the current lithologic profile for ocean drilling program hole 504b

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

geochronology of tag and snakepit hydrothermal fields mid atlantic ridge witness to a long and complex hydrothermal history geochronological studies of a large number of precipitates from the tag hydrothermal field and of few samples from snakepit hydrothermal field of the mid atlantic ridge show intermittent repeated hydrothermal events at both sites 210pb pb and 230th 234u measurements of sulfides iron and manganese oxides and 14c measurements of carbonates combined with observations of hydrothermal events recorded as discrete layers in sediment cores provide the basis for unravelling the temporal history of the fields the tag field shows intermittent activity over the past 120 000 years as evidenced by ages of low temperature mn oxides the presently active black smoker mound first formed about 40 000 50 000 years ago with precipitation of massive sulfides it has had intermittent pulsed high temperature activity every 5000 6000 years over the past 20 000 years which may reflect renewed magmatic activity at the ridge axis fluid flow is focussed at the mound site by structural and tectonic control suggested by the intersection of n s ridge parallel lystric normal faults and an e w transform fault periods of inactivity are marked by covering of the mound with pelagic carbonate ooze which is probably partially dissolved and reprecipitated as aragonite at the end of each high temperature event the snakepit field had an initial event about 4000 years ago probably shortly after the eruption of the volcanic ridge on which it sits a recent renewal still presently active was probably initiated by recent fissuring of the volcanic pile

comparison of sulphide deposits from the east pacific rise and cyprus submarine sulphide deposits of the east pacific rise discovered in 1978 at the mouth of the gulf of california are compared here with fossil massive sulphide ore bodies two main types of massive sulphide ore bodies are defined in relation to the associated volcanism the cyprus ore shows striking analogies with east pacific rise deposits the comparison is based on mineralogical observations and textural facies evidence these similarities suggest that the genetic processes were identical

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

elemental abundance anomalies in the late cenomanian extinction interval a search for the source s elemental abundances have been measured by neutron activation methods across the cenomanian turonian late cretaceous extinction interval in samples collected from sixteen sites in the western interior basin of north america and from twelve widely separated locations around the globe including six odp dsdp sites in most western interior basin sites in colombia and in western europe weaker two closely spaced elemental abundance peaks occur in the upper cenomanian 92 m y spanning the ammonite zones ofsciponoceras gracile throughneocardioceras juddii elements with anomalously high concentrations include sc ti v cr mn co ni ir pt and au the lower peak coincides with the disappearance extinction of the foraminiferrotalipora cushmani in north american sectionsr greenhornensis also disappears at or just below this horizon but in europe it disappears considerably earlier thanr cushmani a series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak the well documented positive 13c excursion begins just before the extinctions and the elemental anomalies and continues into the lower turonian well above the upper anomaly this carbon isotope excursion has been observed in east european sections where we find little or no evidence of the elemental anomalies suggesting that the two phenomena may not be tightly coupled elemental abundance ratios in the anomalies closely resemble those of mid atlantic ridge basalt or hawaiian lava tholeiitic but not those of c1 chondrite black shale average crustal rocks or lamproite and kimberlite of roughly similar age in southeastern kansas the excess ir and other siderophiles hint at possible large body impact s for the source however we have not located microspherules other than biogenic calcispheres or shocked mineral grains in any of our samples furthermore sc ti v and mn are not enriched in differentiated solar system bodies although the weak geochemical signal from comet impact s could be masked by the strong terrestrial like overprint these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep metal rich water associated with the large late cenomanian through early turonian eustatic rise and deep water opening of the south atlantic the flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component

exceptional ground motions recorded during the 26 april 2008 mw 5 0 earthquake in mogul nevada abstract an unusually shallow swarm of earthquakes in mogul a suburb in west reno nevada started 28 february 2008 and continued for several months temporary instruments in the epicentral region constrained event depths and locations and provided onscale recordings of the strong ground motions and supplemented a network of over 21 permanent advanced national seismic system anss strong motion stations deployed throughout the metropolitan reno area by the end of august the swarm had produced over 200 earthquakes with magnitude m l greater than 2 0 the largest earthquake in the sequence occurred at 06 40 utc on 26 april 2008 11 40 p m on 25 april local time with magnitude m l 4 7 m w 5 0 and a hypocentral depth of about 3 1 km in the m w 5 0 mainshock mean horizontal peak ground acceleration exceeded 0 6 g at three stations the strongest peak vector acceleration was 1164 cm sec 2 or about 1 19 g at the station mogl 0 4 km from the epicenter at a frequency of about 3 hz the mean horizontal peak velocity exceeded 12 cm sec at the four nearest stations and the peak vector velocity at the strongest was 54 cm sec the duration of the strongest shaking was about 2 sec at these stations the observed peak accelerations and peak velocities decreased more rapidly with distance than predicted to values below the median predictions at most stations in the reno metropolitan area the shallow source depth is to some degree a likely contributing factor to these unusual observations the motions in the residential neighborhood near the epicenter are significantly greater than the seismic forces required by the 1985 uniform building code zone 3 that was in effect when the mogul neighborhood was developed but damage to the wood frame structures in the neighborhood was minimal

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

blind shear wave velocity comparison of remi and masw results with boreholes to 200 m in santa clara valley implications for earthquake ground motion assessment multichannel analysis of surface waves masw and refraction micro tremor remi are two of the most recently developed surface acquisition techniques for determining shallow shear wave velocity we conducted a blind comparison of masw and remi results with four boreholes logged to at least 260 m for shear vel ocity in santa clara valley california to determine how closely these surface meth ods match the downhole measurements average shear wave velocity estimates to depths of 30 50 and 100 m demonstrate that the surface methods as implemented in this study can generally match borehole results to within 15 to these depths at two of the boreholes the average to 100 m depth was within 3 spectral amplifi cations predicted from the respective borehole velocity profiles similarly compare to within 15 or better from 1 to 10 hz with both the masw and remi surface method velocity profiles overall neither surface method was consistently better at matching the borehole velocity profiles or amplifications our results suggest masw and remi surface acquisition methods can both be appropriate choices for estimating shear wave velocity and can be complementary to each other in urban settings for hazards assessment

site response estimates in salt lake valley utah from borehole seismic velocities abstract the general correlation of salt lake valley sites located on soft saturated unconsolidated silty and clayey deposits that is deposits with low s wave velocity with high seismic amplification at the ground surface motivated our investigation of the relationship between the p and s wave seismic velocity v p and v s of these units and their corresponding observed site response we found that low near surface v s 1 5 is proportional to seismic amplification measured on the surface and suspected that we might be able to predict the site response if the near surface seismic velocity structure were known with this idea in mind we constructed plane layered seismic impedance models from borehole data in order to correlate impedance structure with variations in site response seismic travel times measured in a borehole at 2 m intervals were converted into compressional and shear wave seismic velocity profiles for 22 boreholes average depth 59 m in salt lake valley utah using this impedance model we estimated site response on the ground surface of the borehole site to within 12 of the measured value in the 0 7 to 1 0 hz frequency range for six of the twenty sites and within 20 for 55 of the sites all except two of our site response estimates are within a factor of two of the measured value thus high values of seismic amplification appear to be partially explained by a near surface high impedance contrast produced by the low s wave velocities comparing the downhole data with published salt lake valley ground motion data derived from nevada nuclear tests shows that increased site response sites of relative ground motion amplification is associated with 1 a lower value of v s 110 to 400 m sec and 2 high poisson ratios 0 45 to 0 49 derived from borehole v p and v s values the lowest s wave velocities found in the salt lake valley are comparable to other regions such as the muds around san francisco bay and the lake sediments of mexico city with low s wave velocities and a record of severe seismic wave amplification in previous earthquakes the very low velocity surface layer in salt lake valley is however about half as thick 10 to 14 m as the low velocity layers around san francisco bay and mexico city we also considered the influence of sedimentary basin fill on site response because coincidentally the sites of high seismic wave amplification correspond to the locations of thickest basin fill the valley fill impedance structure revealed in seismic reflection profiles we acquired indicate that a more dynamic impedance structure characterizes sites near the center of the valley where the basin fill is thickest the reflection data from mid valley sites typically have more high amplitude reflectors relative to basin edge sites the sites with a more dynamic impedance structure suggest that the site response would also be correspondingly different thus the broadband deep basin effect on site response might account for some of the discrepancy between observed and predicted site response in this study

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

characterization of near surface geology at strong motion stations in the vicinity of reno nevada abstract we evaluate site conditions at each of the 21 advanced national seismic system anss strong motion stations in the reno sparks nevada area shallow shear wave velocities are measured using the refraction microtremor remi technique louie 2001 average velocities to depths of 30 and 100 m are compared with local geological and soil classifications generalized 1 250 000 scale geological classifications show some variations in unit averages of the measured velocities but variations between units are much smaller than the standard deviations of velocities within units having multiple measurements site velocities are weakly correlated with the weight percent of gravel sand silt and clay in the soil unit at the surface predictions of site velocities based on these soil sediment percentages fall within 20 of measured values for all but two of the 21 sites

origin of magnetic highs at ultramafic hosted hydrothermal systems insights from the yokoniwa site of central indian ridge high resolution vector magnetic measurements were performed on an inactive ultramafic hosted hydrothermal vent field called yokoniwa hydrothermal field yhf using a deep sea manned submersible shinkai6500 and an autonomous underwater vehicle r2d4 the yhf has developed at a non transform offset massif of the central indian ridge dead chimneys were widely observed around the yhf along with a very weak venting of low temperature fluids so that hydrothermal activity of the yhf was almost finished the distribution of crustal magnetization from the magnetic anomaly revealed that the yhf is associated with enhanced magnetization as seen at the ultramafic hosted rainbow and ashadze 1 hydrothermal sites of the mid atlantic ridge the results of rock magnetic analysis on seafloor rock samples including basalt dolerite gabbro serpentinized peridotite and hydrothermal sulfide showed that only highly serpentinized peridotite carries high magnetic susceptibility and that the natural remanent magnetization intensity can explain the high magnetization of yokoniwa these observations reflect abundant and strongly magnetized magnetite grains within the highly serpentinized peridotite comparisons with the rainbow and ashadze 1 suggest that in ultramafic hosted hydrothermal systems strongly magnetized magnetite and pyrrhotite form during the progression of hydrothermal alteration of peridotite after the completion of serpentinization and production of hydrogen pyrrhotites convert into pyrite or nonmagnetic iron sulfides which considerably reduces their levels of magnetization our results revealed origins of the magnetic high and the development of subsurface chemical processes in ultramafic hosted hydrothermal systems furthermore the results highlight the use of near seafloor magnetic field measurements as a powerful tool for detecting and characterizing seafloor hydrothermal systems

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

trace element abundances in the rock canyon anticline pueblo colorado marine sedimentary section and their relationship to caribbean plateau construction and oxygen anoxic event 2 1 rapid eruption of submarine lava flows during formation of the caribbean plateau correlates closely with ocean anoxic event 2 oae2 which bracketed the cenomanian turonian boundary 93 5 ma these events also correspond with a positive excursion in carbon isotopic composition of seawater hydrothermal activity associated with large scale submarine volcanism may have been responsible for this abrupt change in ocean chemistry we determined the distribution of major minor and trace element abundances in the rock canyon marine sedimentary section pueblo colorado after normalizing element concentrations to zr to remove the variable contribution of terrigenous material to these sediments we detected an interval of concentrated metal abundance anomalies that coincides with the abrupt beginning of the positive 13c isotope excursion the metal abundance anomalies indicate that intermittent hydrothermal activity in the form of both water rock exchange and magmatic degassing introduced large concentrations of trace metals into the cretaceous ocean at the same time that extinctions of benthic species turnover in plankton communities and increases in isotopically light organic carbon burial occurred the stratigraphic position of this interval of trace metal anomalies matches events associated with oae2 and indicates that intermittent hydrothermal activity on a massive scale triggered abrupt changes in carbon burial and deep ocean oxygen contents

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

changing ocean circulation and hydrothermal inputs during ocean anoxic event 2 cenomanian turonian evidence from nd isotopes in the european shelf sea nd isotopes of fish debris collected from the english chalk at eastbourne sussex uk are used to reconstruct the history of ocean circulation in the nw european shelf sea during oceanic anoxic event 2 oae 2 cenomanian turonian the eastbourne end record exhibits a 1 unit negative excursion decreasing from 9 to 10 immediately followed by a 3 unit positive excursion reaching 7 the onset of the negative end excursion lags the global 13c rise characteristic of oae 2 suggesting stable patterns of ocean circulation in the nw european shelf sea at this time both negative and positive nd isotope excursions took place during a transient cooling episode within oae 2 the negative end excursion is interpreted as due to a change in ocean circulation with northerly sourced water masses becoming the dominant bottom waters at eastbourne the positive excursion is best explained by the transport of radiogenic nd derived from a volcanic source possibly the high arctic or caribbean large igneous province lip an input of volcanic nd may reconcile the eastbourne record with coeval end records on demerara rise in the western tropical atlantic the broad synchroneity of high end values 7 registered at both sites suggests a possible period with efficient oceanic mixing between the tropical atlantic and the nw european shelf sea during the cooling episode the eastbourne end record of oae 2 together with coeval temperature reconstructions provides evidence for the coincidence of changes in ocean circulation and transient climatic cooling implying a tight coupling between the two phenomena during this interval