berriasian aptian black shales of the maiolica formation lombardian basin southern alps northern italy local to global events the lower cretaceous maiolica formation represents the classic pelagic succession of the apulian margin of the tethys ocean in the southern alps it consists of white calcilutites with minor marly layers and black shales a multidisciplinary study including lithostratigraphy nannofossil assemblage composition and organic geochemistry was performed on two composite sections in order to characterise the marl shale layers that record production and storage of organic matter om and terrigenous input in the berriasian aptian interval such layers are associated with turbidite deposition and bottom current activity in the late berriasian earliest valanginian late valanginian and early aptian the uppermost hauterivian barremian black shales alternate with pelagic calcilutites forming an interval barren of redeposited layers the quantity of organic carbon increases from the berriasian to the barremian the background composition of the kerogen is continental dominated with varying proportions of marine derived om preservation of om did not necessarily occur under anoxic conditions on the contrary storage of om probably resulted from enhanced terrestrial input of nutrients siliciclastics woody and herbaceous fragments inducing mesotrophic conditions and increased primary productivity higher fertility of surface waters during the late valanginian and early aptian is reflected by distinctive decreases in abundance of oligotrophic nannoconids and increase in abundance of mesotrophic diazomatholithus in the valanginian during the barremian the rhythmic establishment of eutrophic conditions documented by the highest amounts of marine om determined high frequency fluctuations in nannoconid abundance the early aptian nannoconid crisis is interpreted as the result of a major climate change and enhanced primary productivity variations of calcareous nannofloras as well as changes of lithology and om which we describe in the lower cretaceous maiolica formation of the lombardian basin can also be recognised in coeval units from other sites of the apulian side of the tethys similar episodes of siliciclastic and terrestrial om accumulation and major changes in calcareous nannofossils are also recorded in the upper valanginian and lower aptian pelagic sediments of the tethys atlantic and partly pacific oceans such nannofossil variations are coeval with positive excursions of the 13c curve and suggest perturbations of the bio geochemical cycles at a global scale additional minor changes in siliciclastic and terrestrial om accumulation as well as in nannofloras are probably the result of local events strictly related to the physiography and evolution of the tethyan margin

borehole response studies at the garner valley downhole array southern california the garner valley downhole array gvda consists of a set of seven downhole strong motion instruments ranging from 0 to 500 m depth one of the objectives of this experiment is to estimate site response and study wave propagation as the energy travels from the bedrock underneath the site up through the soil column the gvda velocity structure is studied by computing synthetic accelerograms for a small event located at an epicentral distance of 10 km these synthetics simulate well the data recorded at the borehole stations in addition theoretical transfer functions are calculated using the obtained velocity model and compare well with the empirical transfer functions from 54 recorded events it is also observed that the downgoing wave effect is predominant in the first 87 m and is strongly reduced at depth using the velocity structure at gvda and the transfer function results it has also been possible to develop a simple method to compute the incident wave field which is needed in nonlinear site response for instance recently there have been many comparative studies between horizontal to vertical h v spectral ratios and traditional spectral ratios although many of these studies show that h v spectral ratios can reproduce the shape of the site response curve most show differences in the amplitude level in the case of garner valley where we have both surface and multiple borehole instruments we find that this discrepancy in amplitude of the site response estimates is because the vertical component has significant site response associated with it due to s to p conversions that begin in the weathered granite boundary at 87 m depth manuscript received 27 august 2001

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

tethyan carbonate carbon isotope stratigraphy across the jurassic cretaceous boundary an indicator of decelerated global carbon cycling the carbon isotope record in four pelagic carbonate sections from the southern alps northern italy across the jurassic cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy the carbon isotope curve from bulk carbonates shows a decrease from kimmeridgian to early tithonian cm24 cm22 values of 13c 2 07 0 14 to late tithonian and berriasian cm18 cm14 values of 13c 1 26 0 16 the change in the carbon isotope record coincides with changes in tethyan calcite and silica accumulation rates with a drop in the calcite compensation depth in the atlantic and tethys oceans and with changes in organic carbon burial along the eurasian margin of the tethys reduced surface water productivity due to diminished transfer rates of biolimiting elements into the atlantic and tethys oceans can explain these observations the decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the tethys and atlantic oceans the proposed changes in tithonian berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles

crustal structure across the pacific margin of nicaragua evidence for ophiolitic basement and a shallow mantle sliver seismic wide angle measurements across the pacific margin of nicaragua were carried out using ocean bottom hydrophones and land stations recording marine airgun shots the structure and the p wave velocity of the subducting cocos and overriding caribbean plates were determined by modelling wide angle data and further constrained by coincident seismic reflection borehole and gravity data the oceanic crust of the cocos plate is 5 5 km thick with a thin pelagic sediment cover the plate boundary can be traced to 40 km depth and is generally similar to configurations derived earlier from the local seismic network a major feature of the upper plate is an 80 km wide high velocity high density rock unit reaching from the front of the margin to about the middle of the shelf this wedge shaped unit is 15 km thick beneath the shelf edge and is composed of a 5 km thick upper part with velocities increasing from 3 5 km s 1 near the trench to 5 2 km s 1 at the shelf break overlying a 10 km thick lower part with velocities of 6 0 km s 1 analysis of the gravity field requires densities of 2 6 2 7 g cm 3 for the upper part and 2 9 g cm 3 for the lower part of this unit these velocities and densities suggest that the margin wedge is composed of ophiolitic rock similar to those sampled offshore guatemala and exposed on the nicoya peninsula costa rica the velocity structure of this ophiolitic unit ends about 50 km offshore landward the basement underneath the sandino basin is formed by older igneous rock drilled beneath upper cretaceous sedimentary rock onshore nicaragua beneath the ophiolitic basement we find a sliver with velocities typical of mantle material that begins at depths of 12 18 km and coincides with the down dip limit of the seismogenic zone mantle densities are required for the sliver to match the gravity data in a tectonic reconstruction the suture of an oceanic plateau on the farallon plate against the chortis block in upper cretaceous time is suggested suturing left the former trench and margin in deep water consistent with the late cretaceous to palaeocene deep water sediment of the rivas formation at the base of the sandino basin suture of the farallon plate and chortis block might have initiated the strike slip movement along the motagua polochic fault system the development of a new subduction zone in eocene oligocene times left the ophiolitic basement and a sliver of oceanic mantle attached to the chortis block and shifted the volcanic arc about 70 km southwestwards close to its present position

a revised correlation of mesozoic polarity chrons and calpionellid zones investigation of four sections of tithonian to valanginian pelagic limestone have led to refinement of the correlation of calpionellid zones to the magnetic polarity time scale the correlations are self consistent but differ slightly from those previously published the discrepancy with the published correlation from the bosso section 1 has been resolved by re evaluation of the biostratigraphy of this sequence the revised correlation places the base of thechitinoidella zone in the lower part of polarity chron cm21n the base of zone a near the top of cm20n the a b boundary at the base of cm18 theb c boundary in the upper part of cm17 thec d boundary at the top of cm16 and thed e boundary at the top of cm14

geochemical prospecting for rare earth elements using termite mound materials the blockspruit fluorite prospect located in north west state of the republic of south africa occurs within an actinolite rock zone that was emplaced into the kenkelbos type granite of proterozoic age there are a large number of termite mounds in the prospect for geochemical prospecting for rare earth elements rees in total 200 samples of termite mound material were collected from actinolite rock and granite zones in the prospect geochemical analyses of these termite mound materials were conducted by two methods portable x ray fluorescence xrf spectrometry and inductively coupled plasma mass spectrometry icp ms comparison of the two methods broadly indicates positive correlations of rees la ce pr nd and y in particular y and la having a strong correlation as the result of modal abundance analyses the actinolite rock at surface mainly consists of ferro actinolite 89 89 wt and includes xenotime 0 26 wt and monazite 0 21 wt grains as ree minerals termite mound materials from actinolite rock also contain xenotime 0 27 wt and monazite 0 41 wt grains in addition termite mound materials from the actinolite rock zone have high hematite and fe silicate contents compared to those from granite zone these relationships suggest that ree minerals in termite mound materials originate form actinolite rock geochemical anomaly maps of y la and fe concentrations drawn based on the result of the portable xrf analyses show that high concentrations of these elements trend from sw to ne which broadly correspond to occurrences of actinolite body these results indicate that termite mounds are an effective tool for ree geochemical prospection in the study area for both light rees and y but a more detailed survey is required to establish the distribution of the actinolite rock body

gradual carbonate to clastic transition and provenance of quartz along the nw trento plateau southern alps italy abstract over the drowned site of the nw trento carbonate platform a gradual transition from early cretaceous pelagic carbonate to more siliciclastic sedimentation during the early tertiary is denoted by mineralogical and geochemical trends decreasing oxygen isotope ratios of quartz in the matrix from 34 33 to 18 47 smow suggest a mainly biogenic origin for the silica with insignificant terrigenous quartz input during the early cretaceous and only minor introduction of terrestrial quartz during the late cretaceous and early tertiary the insignificance of terrigenous input during the late cretaceous and early tertiary is consistent with existing depositional models that involve bypassing of the nw trento plateau margin the bulk of the terrigenous deposition being funnelled into the adjacent lombardian flysch basin bernoulli and winkler 1990 during the eoalpine tectonic phase doglioni and bosellini 1987

isotopic evidence for late jurassic early cretaceous climate change abstract strontium oxygen and carbon isotope ratios have been determined from late jurassic early cretaceous belemnites from the volga basin russia and kawhia harbour new zealand 87sr 86sr ratios derived from well preserved belemnites from the volga basin support a middle tithonian age derived from the analysis of the endemic ammonite fauna the kawhia harbour section records a gradual rise in 87sr 86sr values and in comparison with the published 87sr 86sr curve suggests that the lower part of the section is latest oxfordian in age whilst the upper part of the section correlates well with the biostratigraphic correlation suggestion of an early middle tithonian age although the published strontium calibration curve shows a degree of scatter our new data confirm the uniform rise in 87sr 86sr values from the late jurassic into the early cretaceous such an increase may result from either a decrease in mid oceanic ridge spreading and or an increase in weathering rates and flux of radiogenic strontium although a eustatic drop in sea level and concurrent western cordillera uplift suggests that weathering may have been the controlling factor of late jurassic seawater strontium isotope composition palaeotemperatures derived from the well preserved belemnite 18ocarb values from the volga basin indicate that the middle volgian late kimmeridgian was warm 14 20 c followed by a slight cooling and a subsequent gradual increase to the jurassic cretaceous boundary the 18ocarb values from new zealand located at a palaeolatitude of 80 s if interpreted in terms of palaeotemperature indicate a high degree of variability such variability may not be related to palaeotemperature but to changes in oceanic chemistry resulting from the formation and dissolution of an ice sheet and or snow during the oxfordian kimmeridgian carbon isotope trends for the late jurassic show a fall in values from the oxfordian with lowest values occurring in the early middle tithonian before rising but without reaching values obtained in the oxfordian the overall low 13ccarb may be related to a global increase in continental weathering and or upwelling of cooler oceanic water enriched in oxidised organic carbon 12c enriched

site amplification and attenuation via downhole array seismogram inversion a comparative study of the 2003 miyagi oki aftershock sequence weak motion geotechnical array recordings at 38 stations of the japanese strong motion network kik net from the 2003 m w 7 0 miyagi oki aftershock sequence are used here to quantify the amplification and attenuation effects of near surface formations to incident seismic motion initially a seismic waveform optimization algorithm is implemented for the evaluation of high resolution low strain velocity v s attenuation q s and density profiles at the sites of interest based on the inversion results v s versus q s correlations are developed and scattering versus intrinsic attenuation effects are accounted for in their physical interpretation surface to downhole traditional spectral ratios ssr cross spectral ratios c ssr and horizontal to vertical h v site response estimates are next evaluated and compared while their effectiveness is assessed as a function of the site conditions classified on the basis of the weighted average vs of the upper 30 m v s30 of the formations single and reference station site response estimates are successively compared to surface to rock outcrop amplification spectra and are evaluated by deconvolution of the downhole records based on the inversion results comparison of the observed ssr and estimated surface to rock outcrop amplification spectra illustrates the effects of destructive interference of downgoing waves at the downhole instrument level as a function of the site class site amplification factors are successively computed in reference to the national earthquake hazards reduction program nehrp b c boundary site conditions v s30 760 m sec and results are compared to published values developed on the basis of strong motion data and site response analyses finally weak motion ssr estimates are compared to the mainshock spectra and conclusions are drawn for the implications of soil nonlinearity in the near surface results presented in this article suggest that currently employed site classification criteria need to be reevaluated to ensure intraclass consistency in the assessment of amplification potentials and nonlinearity susceptibility of near surficial soil formations

kimmeridge clay sedimentation a new cyclic model abstract the kimmeridgian upper jurassic fine clastic sequences of the boulonnais northern france and dorset southern england represent oxygen controlled environments five facies types with increasingly deteriorating living conditions ranging from normal shelf environments to submarine lifeless desert have been distinguished the widespread occurrence of this facies in the late jurassic north atlantic shelf sea and the palaeogeographic situation require a large scale model to explain the kimmeridge clay sedimentation anoxic conditions are generally explained by one of three models none of which applies directly to the kimmeridge clay a new model derived from the overall palaeogeographic and palaeoclimatic situation is therefore proposed in this model water mass stratification and anoxic bottom conditions refer to a high latitude monsoonal type wind circulation causing a water current and counter current system in the north atlantic shelf sea and the arctic ocean variations in the amount of oxygen in the bottom waters allow recognition of four different cycles with periods ranging from seasonal to 3 107 years they influenced the counter current system and the resulting anoxic conditions

a jurassic tongue of the ocean infilled with oolitic sands the belluno trough venetian alps italy abstract the belluno trough is a narrow and elongate basin on the northwestern corner of the apulian plate continental margin it acquired topographic identity in early liassic time during the breakup of a widespread upper triassic carbonate shelf at the beginning liassic the belluno trough was a starved depression accumulating euxinic mudstone and bounded by two shallow water carbonate banks trento and friuli platforms this typical bahamian physiography lasted until late liassic time when the shallow water trento platform collapsed tectonically and suddenly drowned tilting northward and breaking along an old tectonic line it became therefore a submerged pelagic plateau in the meantime the western edge of the friuli platform now the windward margin of an oceanic platform turned into a prolific super producing oolite factory quite soon the oolite sands of the friuli margin started to flow down the slope reaching the basin through numerous entry points and gradually building a complex of coalescent deep sea fans which prograding westward infilled the belluno trough the fans terminated westward against the faulted edge of the trento plateau on which above a karst like surface locally encrusted with manganese red nodular ammonitic limestone was slowly accumulating northward where the topographic relief decreased the oolite fans could spill over the escarpment onto the edge of the plateau by the end of middle jurassic time the belluno trough was no longer a submarine depression but a gentle slope connecting the friuli platform to the deep pelagic trento plateau in callovian time probably because of a short drop in sea level large parts of the friuli platform were exposed to subaerial diagenesis during the subsequent oxfordian transgression the resulting rocky bottom became the substratum for an extensive growth of reefal organisms hydrozoans corals rudists which fringed the friuli platform for the whole malm and cretaceous times

biostratigraphic correlation of mesozoic polarity chrons cm1 to cm23 at capriolo and xausa southern alps italy abstract two pelagic limestone sections in the southern alps spanning the kimmeridgian late jurassic to barremian early cretaceous interval yield magnetostratigraphies which can be correlated to oceanic magnetic anomalies m1 m3 and m8 m23 this includes the interval m11 m13 which has not previously been correlated to a sedimentary section detailed investigations of nanofossils and calpionellids in these sequences allow precise correlation of polarity chrons to biostratigraphic events and these results compare favorably to those of previous studies the close correspondence in polarity pattern between that interpreted from the m8 to m15 interval in the hawaiian lineations and that recorded at the capriolo section suggests that sedimentation rates in this sequence and spreading rates in the hawaiian lineations were rather constant during this interval in contrast the sedimentation rate at the xausa section appears to increase up section with the facies transition from the rosso ammonitico to the maiolica formation

paleoceanographic changes across the jurassic cretaceous boundary the calcareous phytoplankton response abstract calcareous nannoplankton experienced rapid diversification at the jurassic cretaceous boundary including the appearance of several highly successful and long ranging cretaceous genera this study examines at high resolution calcareous nannofossil assemblages and bulk rock oxygen and carbon isotopes of lower tithonian to lower berriasian 151 to 142 ma sediments recovered in deep sea drilling project hole 534a central atlantic ocean the results show major changes in assemblage composition and abundance of three genera conusphaera nannoconus and polycostella conusphaera dominates the nannolith assemblage in the late middle tithonian conusphaera world while the nannoconid dominance nannoconus world began in the berriasian the acme peak of the genus polycostella in the late tithonian partially superimposes that of conusphaera although these genera are indicators of warm oligotrophic surface waters stable isotope data suggest that the individual taxa may flourish in slightly different ecological regimes nannoconus flourished under warmer and possibly more nutrient depleted surface waters than polycostella a genus that thrived in relatively cooler waters these findings imply paleoceanographic changes across the j k boundary interval with a cooling in the late tithonian followed by a temperature increase in the berriasian because the transfer of these heavily calcified nannolith taxa to the seafloor is more efficient than that of average coccolithophorids the j k evolutionary event changed carbonate cycling and burial in the oceans

correlation of terrigenous and biogenic sediment fluxes in the north atlantic ocean during the past 150 my the depositional history of the north atlantic ocean is described on the basis of about 120 deep sea drill sites sediment fluxes were quantified by calculating accumulation rates g cm 2 my 1 of terrigenous and calcareous biogenic sediment components they were plotted versus an absolute time scale into palinspastic maps and into age versus paleodepth diagrams

are early cretaceous environmental changes recorded in deposits of the western part of the silesian nappe a geochemical approach abstract the organic matter om rich relatively monotonous sequence of upper barremian albian deposits in the western part of the silesian nappe in the polish outer carpathians was investigated using geochemical proxies to show environmental changes the amounts of organic carbon 0 4 4 32 wt of toc co vary with the concentration of s and or redox sensitive trace elements rste mo u co v as kerogen is present as type iii and mixed type ii iii maceral assemblages consist of vitrinite inertinite and liptinite the carbon isotopic composition of the organic matter 13 c org varies between 25 38 and 21 31 with an outlier at 15 14 during the early cretaceous the proto silesian basin was the site of om accumulation in a detrital oceanic anoxic event as a result of increased sedimentation rates of terrestrial organic matter runoff of terrestrial organic matter was accompanied by the production of plankton on an occasional basis the marine matter contribution is inferred from occurrence of siliceous microfauna the domination of short chain n alkanes the distribution of sterane and prevalence of cholestane and enrichment in nutrient elements p 2 o 5 ba ag cd the bottom waters could have been dysoxic to anoxic with a mid water oxygen minimum zone omz developed owing to the oxidation of organic matter anoxia is inferred from the lamination pyritization patterns rste concentration and low pr ph and c 23 t c 30 h ratios intervals enriched in toc and rste in the ve ovice formation record pulses of marine productivity preceded by volcanic teshenite and hydrothermal activity they are referable to the following episodes the taxy barremian aptian early aptian selli fallot and paquier during the late aptian and at the aptian albian boundary the initiation of turbidite deposition during the albian led to bottom ventilation the lhoty formation records the late albian toolebuc episode marked by a toc peak which resulted from the detrital flux acidic solution was responsible for reducing conditions in the sediment

nehrp soil classification and estimation of 1 d site effect of dehradun fan deposits using shear wave velocity abstract shear wave velocity of the near surface soil at nearly 50 sites in the sub himalayan mountain exit covering doon fan deposits was determined using multi channel analysis of surface waves masw a seismic reflection technique based on the average shear wave velocity of the upper 30 m soil column sites in the dehradun fan are predominantly classified as class d 180 360 m s similarly sites located on the northwestern eastern and southeastern sides of the fan deposit have shear wave velocities in the upper 30 m soil greater than 360 m s thereby classifying them as class c 360 760 m s in accordance with nehrp provisions some of the sites towards the southwestern side of the fan deposits had average shear wave velocities less than 180 m s and could be classified as soil class e one dimensional site effects including amplification and dynamic period were calculated for the majority of the sites however some of the representative suite of sites across the north south profile of dehradun fan has been discussed here although the attenuation is greater on the southwestern side of the dehradun fan deposits i e thicker low velocity sediments and the sites had been classified as class d and e but the site amplification tends to be greater in the northern and northwestern part of the city due to large impedance contrast with in the near surface soils

attenuation and velocity structure for site response analyses via downhole seismogram inversion a seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude downhole array recordings based on a global optimization scheme in the wavelet domain complemented by a local least square s fit operator in the frequency domain the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space whereas the best fit model detection is substantially accelerated through the local deterministic inversion results presented for selected aftershocks of the mw 7 0 sanriku minami earthquake in japan recorded by the kik net strong motion network illustrate robustness of the impedance structure estimation by contrast the attenuation structure is shown to be sensitive to the frequency content of seismic input data attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple scattered energy sensitivity analyses illustrate that for the same forward model results can be substantially different based on the definition of the objective function it is concluded that even for engineering purposes inversion should aim to decouple intrinsic and scattering attenuation mechanisms

changes in shear moduli of liquefied and nonliquefied soils during the 1995 kobe earthquake and its aftershocks at three vertical array sites acceleration records of the 1995 kobe earthquake and its first after shocks provided by vertical arrays at port island pi sgk and tks sites were used to estimate changes in the shear moduli of subsurface soils caused by strong ground motion shear moduli estimates are based on stress strain relations deter mined for consecutive time intervals during the mainshock and aftershocks we found that in the upper 0 13 m at pi reclaimed fill above the groundwater level the shear modulus decreased by 80 90 of its initial value owing to liquefaction signs of its recovery appeared 3 5 min after the decrease in the intensity of strong motion at depths of 13 18 m reclaimed fill below the water level and 27 32 5 m water saturated sand at pi 0 11 m at sgk and 0 14 m at tks water saturated alluvium the shear modulus decrease was estimated at about 80 50 60 60 70 and 50 respectively recovery began immediately after the decrease in the intensity of strong motion and was completed within a few minutes the results show that the behavior of the upper layers at sites pi and sgk where the highest accelerations were recorded was dynamically unstable so far as the method can be applied to any site where vertical array records and profiling data are available ac cumulation of representative data on nonlinear soil behavior during strong motion for various soil conditions is desirable summarizing and generalizing these data we may be able to predict soil behavior in future earthquakes

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

what is a reference site many methods for estimating site response compare ground motions at sites of interest to a nearby rock site that is considered a reference motion the critical assumption in these methods is that the surface rock site record reference is equivalent to the input motion at the base of the soil layers data collected in this study show that surface rock sites can have a site response of their own which could lead to an underestimation of the seismic hazard when these sites are used as reference sites data were collected from local and regional earthquakes on digital recorders both at the surface and in boreholes at two rock sites and one basin site in the san jacinto mountains southern california the two rock sites keenwild and pinon flat are located on granitic bedrock of the southern california peninsular ranges batholith the basin site garner valley is an ancestral lake bed with watersaturated sediments on top of a section of decomposed granite which overlies the competent bedrock ground motion is recorded simultaneously at the surface and in the bedrock at all three sites when the surface rock sites are used as the reference site i e the surface rock motion is used as the input to the basin the computed amplification underestimates the actual amplification at the basin site for frequencies above 2 to 5 hz this underestimation by a factor of 2 to 4 depending on frequency and site results from the rock sites having a site response of their own above the 2 to 5 hz frequencies the near surface weathering and cracking of the bedrock affects the recorded ground motions at frequencies of engineering interest even at sites that appear to be located on competent crystalline rock the bedrock borehole ground motion can be used as the reference motion but the effect of the downgoing wave field and the resulting destructive interference must be considered this destructive interference may produce pseudo resonances in the spectral amplification estimates if one is careful the bedrock borehole ground motion can be considered a good reference site for seismic hazard analysis even at distances as large as 20 km from the soil site

a mobile multi depth borehole sensor set up to study the surface to base seismic transfer functions abstract the best method to evaluate the seismic site response is by means of borehole vertical arrays that use earthquake records from different depths in this paper we introduce the implementation of a single borehole sensor system synchronized to a sensor on the surface that is fixed at variable depths within a single well this system is used for recording small amplitude earthquake signals at variable stiffness conditions in depth to compute empirical borehole transfer functions the computed average empirical borehole transfer functions allow the estimation of an s wave velocity model that is constrained using the frequency peak observed in the h v ratio curve pairs of surface and borehole earthquake records were obtained with the borehole sensor placed at 10 20 50 and 100 m depth in a test site in managua nicaragua the average velocity of the final model down to 100 m appeared to be in good agreement with the average velocity computed via cross correlation using the surface and borehole signals likewise an inverted masw profile and h v ratio at the same site agree with the s wave velocity model obtained

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

garner valley downhole array of accelerometers instrumentation and preliminary data analysis the garner valley downhole array gvda in southern california 33 41 60 n 116 40 20 w is a five element array of three component dual gain force balance accelerometers that are capable of measuring accelerations from 3 10 6 to 2 0 g over a frequency range from 0 0 to 100 hz the accelerometers are placed at depths of 0 6 15 22 and 220 m the lithostratigraphy is 19 m of soil overlying a 24 m layer of weathered granite below which is granite tonalite the array only 7 km from the san jacinto fault is located at the northern end of the anza seismic gap on the san jacinto fault where an m 6 5 or greater earthquake can be expected it is only 35 km from the indio segment of the san andreas fault which last ruptured with an m 8 earthquake around 1700 a d from its installation in july 1989 through july 1991 gvda has recorded 280 earthquakes with magnitudes ranging from 1 2 to 4 7 and epicentral distances ranging from from 0 to 110 km the maximum acceleration recorded was 89 cm sec 2 from an m l 4 2 earthquake 15 8 km hypocentral distance from gvda the average amplification of the apparent seismic moment between 220 m depth and the surface is about 13 for over five orders of magnitude in the size of the recorded earthquakes the spectral ratio 0 220 of horizontal acceleration amplitude spectrum shows a mean amplification of about 10 for the frequency range of 2 0 to 30 hz for 17 events resonance peaks exist at about 1 7 3 0 and 12 0 hz where the spectral ratio 0 220 is nearly 40 analysis of the acceleration spectra of two specific earthquakes that have nearly the same hypocenter but with different magnitudes m 4 2 and 2 5 shows that the weathered granite zone beneath the soil strongly attenuates the spectral amplitudes for frequencies greater than 40 hz the impedance of the soil relative to the weathered granite amplifies all frequencies by about a factor of 3 leading to spectral levels that are greater at the surface than at 22 m depth near the top of the weathered granite the acceleration spectra at each depth show resonant peaks at the same frequencies the spectra at each depth are well correlated for both earthquakes the acceleration spectrum at 220 m is nearly constant for frequencies less than 60 hz which implies that there is little or no attenuation

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

determination of shallow s wave attenuation by down hole waveform deconvolution a case study in istanbul turkey summary the estimation of shear wave velocity and attenuation in near surface geology is of primary importance in engineering seismology in fact their knowledge is essential for site response studies when preparing improved seismic hazard scenarios in this study we propose two approaches for estimating the average shear wave quality factor qs by using recordings of a vertical array of accelerometers the methods are mainly based on the deconvolution of the wavefield recorded in a borehole with that recorded at the surface the first method requires the fourier transform of the deconvolved wavefield to be fitted with a theoretical transfer function valid for the vertical or nearly vertical in the case at hand up to 30 incidence angle propagation of s waves the second method is based on the spectral fitting of the fourier transform of only the acausal part of the deconvolved wavefield with a theoretical transfer function both methods can be applied without any prior knowledge of the subsoil structure since they are based on empirical data analysis and do not require a precise knowledge of the azimuthal orientation of the sensors in the boreholes which is seldom available first we describe the theoretical framework of the proposed methodologies for qs estimation which are based on the assumption that the structure in the borehole is weakly heterogeneous in the vertical direction i e no large impedance contrast exists between the borehole sensor and the surface second by using synthetic accelerograms we verify that in a realistic subsoil structure the assumption of vertical homogeneity can hold and we investigate the robustness and the suitability of the proposed methods finally only the method that was shown to provide the more stable results based on fitting the borehole to surface spectral ratio with a theoretical function is applied to earthquakes signals recorded by a vertical array of accelerometers installed in atak oy western istanbul results show that using borehole data provides a fair and robust estimate of an average qs of about 30 46 and 99 for the 0 50 0 70 0 140 m depth ranges respectively that can be used for numerical simulations of ground motion

nonlinear ground response analysis of turkey flat shallow stiff soil site to strong ground motion blind predictions of ground response at the turkey flat vertical array site during the 2004 parkfield earthquake were performed using a series of nonlinear and equivalent linear ground response analysis codes in this article we report the out come of the blind predictions compare the predictions to measurements released after the predictions were made and provide discussion on residuals between the data and model predictions the prediction exercise considered various sources of material variability and model variability specifically these analyses utilized five dif ferent nonlinear analysis codes each exercised with a suite of small strain shear wave velocity profiles and modulus reduction damping curves that encompass the range of reported material properties below the site frequency of about 5 hz velocity profile variability dominates the computed response variability upon full release of strong motion data from the site the predictions were generally found to be biased towards underprediction at high frequencies sensitivity analyses and results of recent geophy sical testing at the site suggest this underprediction bias is most likely a result of in accuracies in prior estimates of near surface shear wave velocities analyses performed with the recent profile show no significant bias except at the site frequency where the response is overpredicted

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

downhole receiver function a case study receiver function is defined as the spectral ratio of the radial component and the vertical component of the ground motion it is used to characterize converted waves we extend the use of the receiver function to downhole data using waves recorded in a borehole excited by an earthquake of magnitude 4 0 near san fran cisco california on 26 june 1994 the focal depth of the event was 6 6 km and the epicenter was located at a distance of 12 6 km from the borehole array six three component sensors were located at different depths in a borehole to extract a co herent response of the near surface from the incoherent earthquake waves we de convolve the waves recorded by the sensors at different depths with the waves recorded by the sensor on the surface deconvolution applied to the waves in the s time window recorded by the radial component result in an upgoing and adowngoing wave propagating with s wave velocity for the waves in the p time window re corded by the radial component deconvolution also gives an upgoing and a down going wave propagating with s wave velocity this interesting result suggests a p to s conversion at a depth below the deepest sensor to diagnose this we compute the receiverfunction forthe borehole recording of the earthquakewaves thereceiver function shows an upgoing wave with an arrival close to time t 0 for the deepest sensor the agreement of the upgoing wave in the receiver function with the travel time curve for the p to s converted wave calculated using the p and the s wave velocity profile supports the hypothesis of a pronounced p to s conversion we present a synthetic example to illustrate that the first arrival of the receiver function applied to borehole data gives the upward propagating p to s converted wave to corroborate the observation of the mode conversion we apply receiver function to a different earthquake data recorded by the same borehole array in 1998 the focal depth of the event was 6 9 km and the epicenter was located at a distance of 13 km from the borehole array the receiver function for these data also show an upgoing wave with a pulse close to time t 0 at the deepest sensor the moveout of the upgoing wave agrees with the travel time curve for the p to s converted wave hence supporting our observation of the mode conversion

hualien seismic downhole data analysis abstract the hualien taiwan large scale seismic test lsst was initiated in 1993 by a consortium of industrial and research enterprises from five countries japan usa taiwan france and korea this in situ lsst includes two five accelerometer free field downhole arrays that recorded site response during seven earthquakes 1993 1995 in this paper the seismic site response during two of these events is analyzed correlation analyses of the recorded downhole accelerations are performed to calculate an average shear wave velocity profile in addition the actual seismic shear stress strain histories are directly calculated from the recorded downhole lateral accelerations these histories are then used to estimate soil stiffness and material damping in the linear small strain range the estimated soil stiffness is found to be significantly different in the longitudinal and transverse directions which suggests a marked azimuthal variation of soil properties anisotropy in a recent study of seismic site response ueshima and okano further investigation of seismic response of soil and embedded structure in hualien lsst program proceedings of eleventh world conference on earthquake engineering acapulco mexico 1996 also arrive at this interesting conclusion in addition this anisotropic soil response appears to have been manifested during earlier in situ experimental studies of foundation impedance functions barros and luco 1995 identification of foundation impedance functions and soil properties from vibration tests of the hualien containment model soil dynamics and earthquake engineering 14 229 248 finally the identified linear soil properties are shown to represent adequately the recorded seismic site response at small strains