the late maastrichtian nannofossil record of climate change in the south atlantic dsdp hole 525a abstract the phytoplankton response calcareous nannofossils to the late maastrichtian climate evolution is investigated in the south atlantic dsdp hole 525a and compared to published geochemical and micropaleontological data the results point to a succession of dramatic climatic fluctuations cool water indicators ahmuellerella octoradiata kamptnerius magnificus and nephrolithus frequens suggest cool surface water conditions prevailed during chron c30n at the top of c30n their sudden drop in abundance the last occurrence of b constans and the concomitant increase in the tropical species micula murus suggest warming and lower surface water productivity an m murus acme within chron c29r reflects maximum warming during the last 100 kyr of the maastrichtian the decrease in m murus and increase in cool water indicators reflect rapid cooling with the cool climate persisting over the calcareous nannoplankton response to climate change correlate with similar findings in the equatorial atlantic hole 1258a and parallels the stable isotope record of planktic and benthic foraminifera of dsdp hole 525a as well as the decline in 187os 188os comparison of this marine record and the continental climate record in north america suggests a link between deccan volcanism and the late maastrichtian warm event

the barremian aptian arid phase in western europe abstract evidence is presented from nine areas in western europe speeton yorkshire southern north sea channel and weald basins southern england jeanne d arc lusitanian and aquitanian basins of the north atlantic continental margins lower saxony basin north germany the paris basin and southern france for a phase of aridity which began during the hauterivian middle barremian and continued to dominate the climate of the region until the mid aptian although conditions during this period were not uniformly dry throughout criteria for recognising arid environments include the occurrence of evaporites abundances of carbonate rich sediments red beds firmgrounds carbonate nodules and pyrite concretions depletion of kaolinite spore assemblages of limited morphological diversity and the presence of numerous coniferalean and cheirolepidiacean pollen grains the change from generally humid to dry climates during the barremian is thought to have been linked to a lowering of sea level the arid phase clearly falls within the time span of the first cretaceous oceanic anoxic event

late mesozoic north atlantic land bridges abstract current palaeogeographical reconstructions suggest that since the onset of the late jurassic and during the whole cretaceous period the landmasses of north america and west eurasia have been separated by seaway s exposed on the north atlantic rift system such a palaeogeographical setting should have limited the possibility of direct overland dispersals between the biotas of the two continents strong faunal affinities between the two sides of the north proto atlantic ocean presuppose faunal exchanges between the landmasses however suggesting the existence of ephemeral land bridges around the jurassic cretaceous boundary and the mid early cretaceous this study reviews the current faunal evidence and discusses palaeogeographical evidence that might better elucidate the existence of the postulated land bridges evaluation of the evidence leads to the conclusion that two land bridges were exposed 1 between east north america and iberia during the late kimmeridgian 154 ma and 2 between north america and fennoscandia via the barents shelf around the hauterivian barremian boundary 131 ma the former land bridge was terminated in the earliest tithonian 151 ma and the latter was terminated in the late early barremian 129 ma furthermore the latter land bridge was contemporaneous with regressive stages in both the mid polish trough and the sea strait crossing the russian platform allowing broad direct terrestrial communication among north america europe and asia in the earliest barremian

latest jurassic early cretaceous events and the late cimmerian unconformity in north sea area each of several regional or local unconformities may have been identified locally as the late cimmerian unconformity a supposed major break at the base of the valhall formation or roedby formation over most of the north sea the base of the valhall formation is isochronous and conformable with underlying sediments it is detected on seismic reflection profiles because it represents a widespread facies change marking the late ryazanian transgression most of the unconformities are of eustatic origin and the effects of eustatic sea level changes were never completely masked by local tectonics thus in the modeling of individual oil fields the possibility of sedimentary breaks occurring can be predicted in part by reference to regional or eustatic events modified journal abstract

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

sensitivity analysis of drilling parameters in rock rotary drilling process based on orthogonal test method abstract drilling exploration is the main method for geological studies of rocks and soil selecting reasonable drilling parameters is important for ensuring the safety and economic benefits of a project according to the force limit equilibrium of rock during rotary drilling and using the energy equilibrium method the relationship between the vertical drilling efficiency and drilling parameters such as the speed of rotation thrust force and rotation torque were deduced in this study through improvements in the drilling process monitoring dpm system it was possible to quickly efficiently and quantitatively obtain the drilling parameters during rock drilling an in situ drilling test of granite using the improved dpm system showed the sensitivity of the drilling efficiency to each drilling parameter via an orthogonal test the results indicated that the optimal drilling efficiency 13 2 was achieved under the following test conditions a rotation speed of 128 r min thrust force of 788 kpa and a rotation torque of 64 n m the influence of the thrust force on the drilling efficiency was extremely significant the sensitivity of this parameter was high and the weight value of the thrust force had a 57 87 influence among the others furthermore the influence of the rotation torque on the drilling efficiency index was significant the sensitivity to this parameter was neither high nor low and its weight value was 36 82 in contrast the influence of the rotation speed on the index was insignificant sensitivity to this parameter was low and its weight value was 5 31 the research methods and results presented herein can serve as references for the optimum design of drilling construction and the reasonable selection of drilling parameters

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

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

ammonoid and nannoplankton abundance in valanginian early cretaceous limestone marl successions from the southeast france basin carbonate dilution or productivity a quantification of calcareous nannofossil and ammonoid absolute abundance was carried out in the valanginian limestone marl alternations of the vergol section drome located in the epicontinental vocontian basin southeast france this section is characterised by four centimetric organic carbon rich layers barrande layers b1 b4 the aim of this work is to reconstruct changes in the distribution of nutrients in the water column on the base of the analysis of fossil organisms at different levels of the food chain calcareous nannofossil abundance correlates negatively with carbonate content thus calcareous nannoplankton probably did not produce the bulk of carbonates in the valanginian of the studied section nannofossil abundance was more likely controlled by carbonate mud produced and exported from shallow platform environments to the basin variations of carbonate export controlled by climate and hydrodynamics are responsible for the limestone marl alternations the levels of highest abundance of nannoplankton are interpreted as mainly linked to a reduced accumulation rate and to a minor extent to variations in primary production a dilution by allochthonous carbonate mud is further evidenced by the relationship between total organic carbon toc and calcium carbonate caco3 toc content decreases with increasing caco3 content except for one of the organic carbon rich layers b4 both taphonomy and dilution factors may have partly controlled the variations in macrofauna abundance these can be more likely interpreted as a response to palaeoenvironmental changes of the various taxa with different palaeoecological affinities the high abundance and dominance of bochianitids orthocone ammonoids in the layer b4 can be explained by their opportunistic behaviour and their deep nektonic possibly nektobenthic mode of life their great capacity for vertical mobility may have permitted brief feeding incursions to the bottom waters when the trophic resources were higher in depth than in the surface waters high trophic levels at the sea bottom may have also benefited the bivalves and gastropods which are very abundant in layer b4 the mode of life of different ammonoid families is also discussed

a seismic refraction study of the oregon cascades a 275 km long reversed refraction profile in the oregon cascades two shallow earthquakes of magnitude 5 in southern washington a shallow earthquake of magnitude 4 6 in northern california and a previously published analysis of the bouguer gravity field are used to develop a crustal p wave velocity model for the oregon cascades travel time analysis of the refraction profile indicates a crustal structure characterized by surface layers with p wave velocities that vary from 2 9 to 5 2 km s and thicknesses that vary from 2 5 to 5 0 km upper crustal velocities of 6 1 to 6 5 km s between the depths of 3 and 29 km lower crustal velocities near 7 0 km s between the depths of 29 and 44 km and a mantle reflector at a depth of 44 km comparison with synthetic seismograms supports this structure and shows that the lower crustal and mono transitions can be better modeled by continuous velocity gradients than by first order discontinuities arrival times from two shallow earthquakes in southern washington in 1981 across 14 telemetry stations in the oregon cascades show an apparent velocity of 7 62 km s on the basis of a previously published gravity analysis the mean north south component of the dip to the crust mantle boundary is estimated at 1 down dip to the south the apparent velocity from the earthquakes and the dip estimate from gravity indicate that the true pn velocity is 7 70 km s arrival times from a shallow earthquake in northern california in 1978 across telemetry stations in the washington cascades are consistent with this model and indicate that the upper mantle velocity reaches 8 20 km s at a depth of approximately 100 km

jemez mountains volcanic field new mexico time term interpretation of the cardex seismic experiment and comparison with bouguer gravity the jemez mountains volcanic field jvf is centered astride the western flank of the rio grande rift in north central new mexico near the center of the volcanic field are the valles and toledo calderas the sites of two cataclysmic eruptions of silicic tephra and subsequent caldera collapses these calderas are among the largest and most recent 1 1 and 1 4 ma of the world s giant volcanic calderas the valles caldera especially has associated highly developed hydrothermal systems and may still contain residual magma within a cooling compositionally zoned pluton at shallow crustal depths the main goal of our study was to estimate the complex shallow crustal structure beneath the jemez volcanic field using data from a seismic refraction experiment that encompassed the central part of the field a time term technique was used to process first arrival time data from the network of temporary seismic stations of the caldera and rift deep seismic experiment cardex refraction experiment the data set consisting of 290 time distance pairs was processed to yield time terms at 84 locations 78 recording stations and 6 explosion sites the p wave velocity of the precambrian basement refractor was estimated to be 5 86 0 01 km s station time terms are highly correlated to bouguer gravity anomalies and thus tend to corroborate models for which the crystalline basement outcrops along the western margins of the rift and western flank of the jvf and dips generally eastward to depths of at least 600 m below sea level beneath sediment filled axial basins of the rift

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

carbon isotope excursions in boreal jurassic cretaceous boundary sections and their correlation potential abstract the jurassic cretaceous j k boundary is one of the most problematic points on the geological timescale the boundary is not defined by a global stratotype section and point gssp because of the absence of well defined by significant faunal turnover widely correlatable biostratigraphic levels to fix the base of the berriasian a distinct earliest berriasian positive carbon isotope excursion is identified in the boreal marine carbonate belemnites carbon records from the maurynya river northern urals and the nordvik peninsula northern east siberia the excursion is found within the top part of the upper volgian craspedites taimyrensis ammonite zone slightly above the j k boundary which was established by palaeomagnetic data because a significant positive 13 c shift was also observed immediately above the j k boundary in the tethyan guppen heuberge pelagic carbonate section switzerland this positive carbon isotope event can be regarded as a useful marker for a panboreal and boreal tethyan correlation of j k boundary beds this 13 c excursion is interpreted as a record of increased rates of organic carbon burial the 13 c data obtained previously for the upper volgian and ryazanian in different boreal regions are also analysed in this paper other well documented carbon isotope excursions with less global significance allow the creation of a composite carbon isotope curve for boreal regions that characterises the upper volgian and ryazanian in detail

the mt hood region volcanic history structure and geothermal energy potential the volcanic history of the mt hood region in the last 15 m y shows a slow migration of six to eight volcanic centers from a position about 20 km west of mt hood to the most recent volcanic center in the series this migration was accompanied by the development of the structural setting visible in the mt hood region today mt hood stands on a swell which runs north and south along the cascade range within this swell is a graben the high cascades graben which is parallel to the axis of the swell and has the hood river fault as its eastern boundary fault superimposed on this graben is the mt hood subsidence block subsidence of this block and graben is presumably related to withdrawal of magma from beneath the block and eruption of this material on top of the block to form mt hood the overall structure is one of broad uplift and narrow subsidence that is at least 5 m y old and presumably still active cutting across the entire mt hood region and most of the pacific northwest is a set of northwest southeast right lateral strike slip faults these are numerous around mt hood but the offset on any single fault is small a few meters and in some cases vertical these faults are also young and indicate east west extension and north south compression an older and probably inactive set of northeast southwest folds and thrust faults is evident in the region particularly in the miocene columbia river basalt group these may be related to a long history of north south compression the volcanic history and structure are presumably a result of subduction of the juan de fuca plate beneath the north american plate this subduction is oblique leading to a substantial component of right lateral motion which in turn leads to north south compression in the pacific northwest crustal thinning associated with volcanism has resulted in an elevated geothermal gradient around mt hood this high gradient makes it possible to tap water in excess of 80 c within 1500 m of the surface if these thermal waters can be produced in large volumes they might provide a substantial amount of economically competitive energy for space heating and industrial processes in the region adjacent to the cascades a simple geothermal resource calculation shows that a 1000 km2 area around mt hood could produce beneficial heat which if supplied by electricity would require over 1000 mw for 30 years

the barremian aptian turnover of biota in northwestern europe evidence from belemnites abstract neocomian valanginian barremian and gault aptian albian are lithostratigraphic terms used in the last century to divide the sub chalk cretaceous of northern europe the division is based on significant palaeoceanographic and palaeogeographic changes in the early aptian these changes are linked to a major turnover of marine floras and faunas which occurred simultaneously in the boreal realm the tethys and the indo pacific ocean various floral and faunal elements became extinct in the aptian both in the tethys and in the boreal realm while on the other hand new genera and species evolved marked changes in the diversification rate were observed for organisms with a different mode of life plankton nekton benthos apart from calcareous nannofossils foraminifera and ammonites this turnover also occurs in belemnites and the suborder belemnitina was completely replaced by the suborder belemnopseina the northwestern european barremian is characterised by the very successful belemnite family oxyteuthididae belemnitina which was completely replaced by the genus neohibolites belemnopseina in early aptian times this aptian turnover which is expressed by a homogenisation of marine floras and faunas is best explained by significant palaeoceanographic changes occurring in the early aptian the sea floor spreading rate which increased at the barremian aptian boundary significantly peaked in the late early aptian a mantle plume in the pacific possibly caused an additional production of oceanic crust both processes caused a major sea level rise this in turn resulted in a major change of the palaeoceanographic setting and restricted marginal seas like the northwestern european basins in barremian times became drowned the more open oceanic setting of the aptian enabled cosmopolitan floras and faunas to spread worldwide the aptian saw the radiation of planktonic foraminifera which played only a minor role in pre aptian times these palaeoceanographic changes from restricted marginal seas to a more homogeneous pelagic setting are considered to be the main cause for the significant changes in the composition of belemnite faunas

a magnetic investigation of mount hood oregon aeromagnetic data over the mount hood area of oregon are dominated by the topographic expression of highly magnetized cenozoic volcanics three dimensional magnetic modeling of the mount hood volcanic cone indicates that the bulk of the cone above approximately 1650 m elevation is composed of magnetically similar andesites the andesites are magnetized in a normally polarized direction i 80 0 d 28 3 and with a magnetization of 2 9 a m the chief exception to this is the possible remains of an old cone which underlies the northwest slope of the mount hood cone calculations show that this old cone is magnetized with a direction approximately opposite to the earth s present field and with a magnitude of magnetization of 3 9 a m

nannoplankton productivity fluctuations and rhythmically bedded pelagic carbonates of the greenhorn limestone upper cretaceous abstract comparison of calcareous nannofossil assemblages from rhythmically interbedded calcareous shales and adjacent bioturbated chalks of the greenhorn limestone cenomanian turonian of the western interior basin indicate significant changes in phytoplankton paleocommunity structure between lithotypes significantly higher shannon diversity and evenness values in the chalk assemblages indicate more stable surface water conditions with lower fertility three taxa indicative of high surface water fertility are significantly more abundant in marlstone assemblages which suggests that calcareous shale marlstone deposition corresponded with fluctuating surface water conditions with relatively high fertility the higher surface fertility and concomitant production of organic matter resulted in sediment anoxia during marlstone deposition leading to high rates of organic carbon storage reduced phytoplankton production during chalk deposition allowed oxygenation of the sea floor and establishment of diverse benthic invertebrate communities

evidence for a shallow pluton beneath the goat rocks wilderness washington from gravity and magnetic data a gravity and aeromagnetic study was conducted in and adjacent to the goat rocks wilderness area washington this work was done in conjunction with geologic and geochemical studies which were critically important to our interpretation the bouguer gravity anomaly map displays a large central positive gravity anomaly and three superimposed smaller positive anomalies the main anomaly about 26 by 11 km with an amplitude of about 16 mgal seems to delineate a dense large pluton or sheeted dike complex intruding less dense older volcanic and sedimentary rocks lying directly below the volcano the pluton or sheeted dike complex may have fed the goat rocks volcano throughout its 1 2 m y history three small feeders mapped on the surface as andesite intrusions may be the cause of three smaller gravity anomalies superimposed on the main anomaly the magnetic anomaly maps also exhibit a large central anomaly whose source is the goat rocks pluton the magnetic data suggest that the three shallow intrusive cupolas have undergone a significant amount of hydrothermal alteration in addition to some extent the magnetic data reflect the terrain of the area topographic highs produce magnetic highs and topographic lows produce magnetic lows the deviations from this pattern delineate subsurface geology magnetic lows may be of particular interest in locating zones of mineralization where magnetic minerals have been altered and have become significantly less magnetic

calcareous nannofossils and milankovitch cycles the example of the albian gault clay formation southern england a quantitative study of calcareous nannofossil assemblages was carried out on the albian gault clay formation england this unit consists of grey marly claystones and marlstones with phosphatic nodules and glauconitic layers as minor lithologies two cores were analyzed in detail to focus on changes in nannofloral assemblages and consider their significance preservation of calcareous nannofossils is excellent and therefore diagenesis cannot be invoked to explain not even partially the changes registered in assemblages fast fourier spectral analysis was performed on percentages of selected nannofossil species fluctuations in abundance of both biscutum constans and watznaueria barnesae regarded as fertility and non fertility indices respectively appear to be orbitally driven because spectral analysis showed periodicities of approximately 41 kyr obliquity cycle and 100 kyr short eccentricity cycle in all the spectra the axial obliquityc cycle is a strong signal as expected at these high latitude sites from the boreal realm the same pattern was observed in another fertility controlled taxon zygodiscus cf erectus but cross correlation shows that its abundance plot is displaced with respect to that of b constans orbital perturbations induce variations in climate and ocean circulation because they influence the earth s insolation and seasonality during times of high seasonality strong gradients cause vigorous oceanic circulation a better cycling of nutrients and higher fertility whereas during times of low seasonality low gradients induce more sluggish circulation and lower fertility the carbonate content of the gault clay cores is not correlatable to the higher fertility indices as the abundance curves of b constans w barnesae and z cf erectus are displaced with respect to caco3 content variations this also means that cyclicity in nannofossil assemblages is not a result of diagenesis but an original signal abundance fluctuations of repagulum parvidentatum and combined parhabdolithus asper p splendens colder and warmer water indicators respectively provide evidence for orbital periodicities suggesting that also cyclic variations of surface water temperature might have influenced the nannofossil assemblage patterns within the gault clay

arctic reappraisal of global carbon cycle dynamics across the jurassic cretaceous boundary and valanginian weissert event abstract late jurassic early cretaceous global carbon cycle dynamics have mainly been inferred from tethyan atlantic and pacific carbon isotope 13c records these records indicate a steady deceleration of the carbon cycle in late jurassic and jurassic cretaceous j k boundary times followed by a major mid valanginian carbon cycle perturbation demarcated by the well documented positive excursion named the weissert event however this model remains to be confirmed in boreal records which are rare and typically difficult to correlate with the global 13c signal in this study the first continuous and biostratigraphically calibrated organic carbon isotope 13corg stratigraphy is established for the bathonian lower barremian representing 30 myr of the boreal realm based on high resolution sampling of bulk rock marine shale from four time equivalent sections in arctic svalbard supplemented by existing 13corg data the 13corg stratigraphy displays several distinctive trends notably i a kimmeridgian positive excursion followed by a large negative excursion 6 4 in the upper kimmeridgian middle volgian consistent with existing boreal 13c records ii an upper volgian ryazanian overall positive recovery across the j k boundary and iii a prominent positive excursion 5 5 in the valanginian interpreted to represent the weissert event followed by steady high values into the lower barremian with no apparent excursion decay time calibrated correlation of the observed trends with existing 13c records representative of the entire exchangeable carbon reservoir reflects major global carbon cycle adjustments including i boreal decoupling from the global carbon reservoir during late jurassic and j k boundary times due to basinal isolation and ii global carbon cycle recoupling at the onset of the weissert event coinciding with incipient oceanographic connectivity boreal carbon cycling was inherently controlled by the basin configuration the new 13corg stratigraphy provides a well calibrated tool for boreal and boreal tethyan correlations and confirms that the weissert event represents an important perturbation of the global carbon cycle

seismicity of mount hood and structure as determined from teleseismic p wave delay studies a 16 station seismic network was established in the mount hood area of oregon in 1977 as part of a multidisciplinary study to evaluate the geothermal potential of a typical cascade volcano the immediate objective was to monitor local seismicity and to study the p wave velocity structure of the crust and upper mantle during the 13 months the network was in operation 10 local earthquakes were recorded all these events are spatially associated with the volcano and occurred at shallow depths roughly defining a zone striking north northwest the largest earthquake a magnitude 3 4 event was preceded by a single foreshock and followed by three locatable aftershocks these and the five other located earthquakes were of magnitude less than 2 0 fifty five teleseisms were recorded by the network and used in a teleseismic p wave delay study the residuals from the p delay study indicate that there is no significant velocity anomaly associated with the mount hood volcano and only small velocity variations in the mount hood region

upper crustal structure of the mount hood oregon region as revealed by time term analysis seismic refraction data with a dense areal distribution were collected to study the seismic structure of mount hood and the surrounding region this area is typical of cascade volcanoes and is geologically quite complex the prime goals of this project were to search for velocity variations in the upper crustal rocks and to determine if the velocity of these rocks is anisotropic a new system including 100 remote recording units was developed to facilitate the collection of data in this type of survey the data collected in this study reveal a large variation in velocity and thickness of the uppermost crustal rocks that is probably typical of the high cascade province a regional structural pattern surrounding mount hood where there is a marked thinning of low velocity near surface rocks suggests that the present edifice of mount hood lies on top of a much larger structure possibly the roof of a large batholith that was emplaced prior to the eruption of the volcanic rocks that form the modern mountain a straightforward time term analysis of the data reveals this structure when the time terms are used to correct the travel time observations for the variation in structure under each station the remaining set of residuals indicates a variation of travel time with azimuth while a systematic error in the time term reduction cannot be ruled out this variation is probably the result of anisotropic velocity structure in the underlying refractor the alignment of the direction of maximum velocity with the direction of maximum principal stress and the decrease in anisotropy with depth suggest that the anisotropic velocity structure is related to the opening and closing of fractures in the present stress field the direction of maximum velocity is about n25 w and the degree of anisotropy appears to vary with depth from about 3 near the surface to zero at depths below 8 km

the azimuthal variation of teleseismic p wave travel times summary results of earlier studies of p wave travel time anisotropy are compared with the p wave velocity anisotropy obtained by other authors for different regions of the earth the azimuthal relationship of p wave travel times from surface sources on the siberian platform is investigated it is found that the direction of the minimal travel time of p waves for the siberian platform as well as that for european regions is close to north south

locations and spectral properties of earthquakes accompanying an eruption of mount st helens a joint hypocenter determination routine has been developed to accurately determine the locations of earthquakes occurring under mount st helens the method has a special application to mount st helens where most of the earthquakes are suspected to occur at shallow depth in a rather limited volume under the volcano differences in elevation among stations are allowed for in this routine the location procedure determines a best half space velocity and one station correction for each station simultaneously with earthquake hypocenters arrival time data from an array of portable digital seismic event recorders are supplemented with data from stations of the permanent university of washington seismic network operating at the volcano earthquakes are found to occur along a line trending south east of the dome inside the crater the shallowest events occur near the dome with hypocentral depth increasing with increasing distance from the dome station corrections can be interpreted to imply the existence of a high velocity body beneath the crater which extends at least between depths of 5 and 2 1 km beneath the crater floor spectra are calculated from earthquake waveforms recorded at three stations the spectra show very little evidence for local site or path effects on frequency content of waveforms stress drops of earthquakes are calculated from measurements of corner frequency and low frequency spectral amplitude stress drops of earthquakes vary between 5 and 5 bars there is no evidence for a limiting corner frequency for small earthquakes as has been found for earthquakes occurring in mammoth lakes california data fit well a linear trend between log seismic moment and log source radius fit to data for earthquakes ranging in size from 1014 to 1027 dyn cm suggesting that there is no limiting source radius observed for earthquakes in this range of size

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

valanginian to aptian calcareous nannofossil stratigraphy and correlation with the upper m sequence magnetic anomalies abstract calcareous nannofossil stratigraphy has been investigated in lower cretaceous italian sections at gorgo a cerbara presale and frontale all in the umbrian apennines and at cismon southern alps a modified sample preparation technique has allowed a thorough stratigraphic study of the well lithified maiolica limestone and although nannofossil preservation is generally quite poor the major valanginian to aptian marker species can be detected nine nannofossil events can be determined and correlated to magnetic stratigraphies previously established in these sections nannofossil stratigraphy confirms most magnetostratigraphic correlations made between sections and allows a more precise correlation of magnetic chrons m 0 to m 11 with the valanginian hauterivian barremian and aptian stages the results obtained differ considerably from previous timescales nannofossil events recorded in the various sections may be time transgressive by as much as one magnetic chron probably due to differential preservation

instrumented borehole drilling for subsurface investigation the successful application of instrumented borehole drilling techniques in offshore exploration has encouraged its further use on shore as a ground investigation tool the drilling of holes for grouting tubes creates the potential for obtaining supplementary ground information which may be valuable to the succeeding tunnel construction the instrumented drilling system was therefore investigated to determine its power to discriminate between ground strata the configuration of the drilling system in terms of plant equipment and testing procedures was standardized and applied at a site in kennington park in london the general characteristics of the measured drilling parameters are given and qualitative and quantitative methods of interpreting the drilling parameters are demonstrated the possible soil machine interactions that are responsible for the measured drilling characteristics are examined a new method of data interpretation is proposed for identifying soil formation changes previously published correlations and analyses of drilling were examined and tested by comparing the trend lines of drilling data in london clay against known undrained strength data the degree of correlation was found to be limited doi 10 1061 asce 1090 0241 2002 128 4 283 ce database keywords boreholes drilling subsurface investigation gravel clay field tests

the tethyan pacific during late jurassic and cretaceous times abstract during mesozoic times the pacific ocean occupied almost an entire hemisphere plus a great wedge of ocean that lay between eastern gondwana and laurasia and extended westward from the pacific into the gradually widening tethys sea in the mediterranea atlantic and gulf of mexico as the atlantic widened the pacific narrowed apace and the pacific plate expanded at the expense of bordering plates during the late jurassic and cretaceous connections between the atlantic and pacific via passageways between small continental plates in central america gradually widened permitting a globe circling mainly west flowing current system in low latitudes except for tectonic slices preserved along the adjacent american and asian continents all pre jurassic pacific oceanic sediments have been subducted middle and late jurassic oceanic crust is inferred from magnetic data and one drill hole reached middle jurassic crust pacific cretaceous pelagic sedimentary rocks are typically nannofossil limestone above the calcite compensation depth and brown zeolitic clay and radiolarian mudstone below chert is common as nodules in both limey and clayey sediments and siliceous sediments appear to have been deposited over a wide band of latitudes in the cretaceous lower cretaceous black shale is present on several plateaus at paleodepths of 500 1500 m but contemporaneous sediments in adjacent basins are oxidized cretaceous vulcanism was on a stupendous scale in the western equatorial pacific a region of about 4x106 km2 centered on the ontong java plateau is covered almost entirely by mid plate tholeiitic flood basaltic flows and sills probably emplaced mainly during the earliest aptian emplacement of these huge masses in a relatively short time may have had important consequences not only for global sea level but also for the chemistry of the oceans and atmosphere a striking link to tethyan facies in the other hemisphere is the presence of shallow water platform and reefal sediments on the summits of many pacific cretaceous seamounts several dozen early cretaceous seamounts built to heights above sea level and doubtless many more existed on crust now subducted along the margins of the pacific as the seamounts subsided shallow water rudist coral platforms gradually covered them eventually forming atolls the platforms are the pacific expression of the urgonian platforms of the tethys many perhaps most of the pacific early cretaceous platforms drowned in the latest albian and are guyots today new volcanic chains rose later in the cretaceous but there is a gap in rudist reef development from the cenomanian through the santonian campanian and maestrichtian rudist reefs flourished in equatorial latitudes but hermatypic reefs appear to have been absent during the paleocene

weathered rock characterization using drilling parameters the characterization of weathered rocks by the use of drilling parameters is presented drilling parameters obtained from the drilling process monitoring system during the installation of soil nails into weathered rocks are used in this investigation a new drilling index pi simplified from the concept of the specific energy is used in an attempt to differentiate weathered rocks with pi or the penetration rate boundaries of weathered rocks between 1 soil and rock ranges and 2 grade ii and grade iii rocks in accordance with the six fold rock material decomposition grade are identified for weathered rocks in the soil range quantitative characterization has been established in this study by using the drilling parameters an empirical equation has been established for estimating the standard penetration resistance n value from the drilling parameter pi which is used in turn to determine the mohr coulomb friction angle based on the work of schmertmann although this approach tends to yield a slight

high northern palaeolatitude jurassic cretaceous palaeotemperature variation new data from kong karls land svalbard abstract the traditional view of warm equable global climates in the mesozoic with weakly developed latitudinal temperature gradients has been challenged by several recent studies however reliable high palaeolatitude palaeotemperature data is still rare in this study palaeotemperature data based on oxygen stable isotope palaeothermometry of well preserved mid jurassic to lower cretaceous belemnites from kong karls land svalbard are presented these data show cool high latitude marine isotopic palaeotemperatures for endemic species during the lower to mid valanginian 7 7 c which may be compatible with the formation of high latitude ice middle bathonian to kimmeridgian samples give warmer isotopic palaeotemperatures 9 4 c whilst samples from the aalenian to bajocian give isotopic palaeotemperatures which are warmer still 12 7 c comparison of the callovian temperatures with those from a mid latitude location shows them to be warmer than would be expected if previous latitudinal temperature gradients are correct this may be due to the ameliorating effect of oceanic heat transport pole wards from the panthalassa ocean via the south anyui ocean

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

seismic studies of crustal structure during the past four years seismology has continued its role as the key technique for determination of the structure of the continental and oceanic crust by and large however the field and analysis methods used bear little resemblance to those of ten years ago a continued push to increase the number of recording channels has led to the routine use of ocean bottom seismometers sonobuoys and multichannel streamers in oceanic studies and to the use of large sets of portable instruments and multichannel seismic reflection strings on land in studies using earthquakes as sources local and regional arrays provide a capability for obtaining geologically useful two and three dimensional information about the crust

is the middle cretaceous pulse of rapid sea floor spreading real or necessary it is commonly accepted that the major control on long term eustasy is variation in sea floor spreading rate the middle cretaceous sea level highstand in particular has been correlated with a postulated pulse of rapid spreading in the pacific basin this inferred event took place during the cretaceous normal superchron cns and has also been used as evidence for the existence of superplumes from the deep mantle giving a causative link between core mantle interactions and the record of sea level change there are reasons however to question the foundation upon which this linkage is based recent studies of marine geochemistry show no evidence for large hydrothermal fluxes during middle cretaceous time that require major increases in oceanic spreading rates plate reorganizations in the pacific during the cns show evidence of ridge jumps indicating that more of the sea floor of this age may be preserved than has been presumed improvements in the mesozoic time scale indicate that the cns was longer than previously assumed reducing the need for rapid spreading rates in the pacific basin middle cretaceous rapid plate generation rates are not needed to explain the history of sea level change long term eustasy can easily be accounted for by supercontinent breakup variations in the distribution of crust consumed at subduction zones and other effects because the inferred pulse of spreading was in part used to argue for the existence of a superplume the basis for this hypothesis is diminished the phenomena attributed to deep mantle plumes can be accounted for by plate tectonic forces and plate reorganization hence we question the basis and need for the cretaceous pulse of rapid sea floor spreading

nannofossil assemblages fine fraction stable isotopes and the paleoceanography of the valanginian barremian early cretaceous north sea basin calcareous nannofossil assemblages have been investigated in three sections from around the margins of the early cretaceous north sea basin both absolute number of nannofossils per gram and relative percent of the assemblage of different taxa abundance data have been collected absolute abundances up to 10 billion nannofossils per gram are somewhat higher than those reported previously from other stratigraphic intervals stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large uniform water masses stable over long 0 5 to 1 m y time periods these water masses contained a characteristic nannoplankton which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters which in turn may have been controlled by relative sea level fine fraction isotopic data show fluctuations on shorter time periods 0 1 to 0 5 m y we postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the boreal sea these oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals data are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 001 2 50 payment must accompany order

isotopic evidence for temperature variation during the early cretaceous late ryazanian mid hauterivian oxygen and carbon isotopic compositions have been determined from the belemnite genera acroteuthis and hibolites sampled from the early cretaceous ryazanian hauterivian interval of the speeton clay formation filey bay england the speeton clay formation consists of a series of claystones and calcareous mudrocks deposited in an epicontinental sea 18 o values from belemnites which met petrographic and chemical criteria for well preserved skeletal carbonate indicate warm marine palaeotemperatures c 12 15 c for much of the early valanginian whilst cool temperatures

investigations of water inrushes from aquifers under coal seams in many coal mines limestone confined aquifers underlie coal seams during coal extraction from these mines water inrushes occur frequently with disastrous consequences this paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams it then presents the water inrush mechanism the main factors which control water inrushes include strata pressure mining size geologic structures and the water pressure in the underlying aquifer analysis shows that reduction of confinement due to mining is the major cause of the water conducting failure in the floor strata the depth of the failure zone is strongly dependent on the mining width this paper also presents field observation results of the water conducting failure in the floor strata and applies the finite element method coupled with stress dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction finally theoretical and empirical methods to predict water inrushes are given and technical measures for improving mine design and safety for coal extraction over aquifers are presented these measures include fault and fracture grouting and mining method modification such as changing long wall to short wall mining

preservation of delta 18 o and delta 13 c in belemnite rostra from the jurassic early cretaceous successions stratigraphic collection of 263 belemnite rostra guards from jurassic to lower cretaceous sediments in the moscow area of russia northern germany england new zealand and morocco were analyzed to determine temporal variations in their delta 18 o and delta 13 c as a proxy for isotopic composition of surface seawater internal structures of the rostra were studied using cathodoluminescence and sem techniques their trace element fe mn mg and sr and the stable carbon and oxygen isotope compositions the average stratigraphic resolution is about 1 ma these samples represent a broad range of paleolatitudes and paleoceanographic settings ranging from 42 degrees n to 82 degrees s covering boreal to subtropical brackish to open marine shelf paleoenvironments the rostra originally contained domains enriched in organic matter that were later replaced by luminescent diagenetic calcite thereby generating an impression of seasonal growth rings diagenetic calcite accounts for up to 6 8 percent of the rostrum the trace element content of the rostra range from 227 to 3935 ppm for mg 379 to 1514 ppm for sr and up to 305 and 3662 ppm for mn and fe respectively however selective drilling of only primary calcitic domains resulted in 90 percent of all analyzed samples to fall within the range of trace element values typical for modern low mg calcite shells the chemical and textural data suggest that the primary calcite of the rostra is well preserved as is its isotopic signature the delta 13 c and delta 18 o measurements define oscillating temporal bands of about 3 to 4 per mil width around more or less modern marine values of 2 and 1 per mil respectively oxygen isotopes in the well preserved rostra most likely reflect temperature variations within a approximately 14 or 8 degrees c range the observed 3 to 4 per mil spread of values between contemporaneous specimens which is comparable to the scatter of data reported for modern low mg calcitic brachiopod shells probably reflects the diversity of local ecosystems although some of the spread may be due to real short term temporal variations within single biozones the delta 13 c values of the rostra define a band similar to that of the oxygen isotopes and the temporal oscillations of both isotope curves are commonly in phase the above dataset complemented by the results of jones jenkyns and hesselbo 1994 and jones and others 1994 yields a composite delta 18 o and delta 13 c variations in belemnite guards for the entire jurassic early cretaceous interval for delta 18 o the oscillating band indicates that the most negative values occur at times of independently postulated global and or regional anoxic events such as those in the toarcian and kimmeridgian as well as the aptian these oaes appear to be characterized by up to 10 degrees c higher seawater temperatures than the intervening background times the delta 13 c record shows 13 c depletion for the kimmeridgian event but enrichment for the other two suggesting that the delta 13 c temporal oscillations and oaes are not simply a reflection of surficial productivity due to operation of the biological pump but rather of changing oceanic circulation patterns due to variations in latitudinal surface temperature gradients

mesozoic palaeoceanography of the north atlantic and tethys oceans summary the biogeography and preservation of calcareous nannofossil assemblages allow mapping of surface water fertility patterns and put constraints on carbonate dissolution in the global oceans of the middle cretaceous cyclic changes in carbonate dissolution and surface water biologic productivity in the cretaceous oceans were linked to oceanographic and climatic changes that had frequencies close to the milankovitch cycles tens of thousands to hundreds of thousand years evolution of calcareous nannoplankton during the jurassic and cretaceous periods occurred in two primary cycles of about 75 ma duration that were punctuated by major diversification events occurring every 15 30 ma that marked the beginning of periods of increased marine organic matter production and preservation stagnation events calcareous nannoplankton evolved largely in shallow seas during the rhaetian to kimmeridgian in the latest jurassic calcareous nannoplankton conquered the oceanic realm became major producers of pelagic carbonates and are thus responsible for the shift of carbonate deposition from shallow seas to the deep ocean in the late cretaceous chalk seas nannofossils replaced shallow water benthos as major carbonate producers warm climates due to high atmospheric co 2 concentrations and increased albedo during high sea level stands caused by global tectonic processes made these tiny creatures flourish during the late mesozoic

calcareous nannofossil paleoceanography of the cretaceous greenhorn sea two distinctive laterally traceable bentonite beds were used to construct three isochronous time slices through the marine sediments of the upper cretaceous greenhorn cyclothem of the western interior basin calcareous nannofossil assemblages from these time slices were analyzed from 40 localities to examine the paleoceanographic conditions in the basin deposition of the lower time slice x bentonite approximately corresponded to the time at which free communication between the basin and open oceanic systems first occurred the most striking trend is the presence of common to abundant nannofossils in the center of the basin and their absence from the eastern and western margins this indicates that open oceanic conditions conducive to large standing crops of calcareous nannoplankton existed only in a narrow centrally located channel conditions at the basin margins were probably unsuitable for large populations due to salinity constraints multivariate analyses indicate two distinct biofacies northern and southern which are interpreted to represent distinct surface water masses the geometry of the water mass boundary suggests that the northern surface water mass actively flowed southward into or over the relatively passive southern water mass the upper time slice hl 3 bentonite samples the nannofossil distributions at or near the maximum transgression of the greenhorn sea in this time slice nannofossils occur beyond the limits of the study area except in proximity to the frontier delta system diversities are significantly higher indicating water mass conditions more similar to those in open oceanic settings multivariate analyses indicate three distinct surface water masses northern southern and western the northern and southern water masses exhibit relationships similar to those during the x bentonite time slices the interaction between the northern and southern water masses promoted vertical stratification of the water column and resultant sediment anoxia the western biofacies may be indicative of a surface water mass with significant contributions from nearby fresh water influx

planktic foraminifera from the mid cretaceous barremian early albian of the north sea basin palaeoecological and palaeoceanographic implications abstract a marine cretaceous succession barremian albian of a cored borehole bgs 81 40 located in the central north sea basin has been examined with respect to its planktic and benthic foraminiferal content as well as for calcareous nannofossils the distribution patterns of foraminifera and calcareous nannofossils allow for a two fold division of the investigated interval 1 the barremian earliest aptian interval which reflects a marine temporary restricted setting this is indicated by sporadic occurrences of planktic foraminifera with very rare planispiral forms suggesting short term connections of the boreal and tethyan realms the benthic foraminiferal assemblages indicate aerobic sometimes dysaerobic bottom water conditions high abundances of nannoconids in the barremian suggest enhanced stratification and or warm oligotrophic surface water 2 the late aptian early albian interval which was characterised by an open oceanic environment with cool and aerobic surface water conditions planktic foraminifera are more abundant and diverse than in the lower interval trochospiral hedbergellids dominate the foraminiferal assemblages the episodic occurrences of planispiral clavate and trochospiral flattened planktic morphotypes indicate the existence of a seaway between the boreal and the tethyan realms aerobic to dysaerobic bottom water conditions are suggested by the composition of the benthic foraminiferal assemblages high abundances of cool water taxa within the calcareous nannofossil assemblages indicate a cooling trend across the latest aptian and earliest albian

deep earthquakes beneath mount st helens evidence for magmatic gas transport small magnitude earthquakes began beneath mount st helens 40 days before the eruption of 20 march 1982 unlike earlier preeruption seismicity for this volcano which had been limited to shallow events less than 3 kilometers many of these earthquakes were deep between 5 and 11 kilometers the location of these preeruptive events at such depth indicates that a larger volume of the volcanic system was affected prior to the 20 march eruption than prior to any of the earlier dome building eruptions the depth time relation between the deep earthquakes and the explosive onset of the eruption is compatible with the upward migration of magmatic gas released from a separate deep reservoir

evidence for glacial control of rapid sea level changes in the early cretaceous lower cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves strontium data from an interval spanning 7 million years in the berriasian valanginian imply that global sea level fluctuated about 50 meters over time scales of 200 000 to 500 000 years which is in agreement with the exxon sea level curve oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes if glaciation caused all the rapid sea level changes in the cretaceous that are indicated by the exxon curve then an antarctic ice sheet may have existed despite overall climatic warmth

a valanginian early cretaceous boreal nannoplankton excursion in sections from romania abstract in order to resolve both sea level and palaeoclimatic signals for the earliest cretaceous 161 calcareous nannofossil samples of berriasian to valanginian age have been studied from romania these samples are derived from three biostratigraphically well dated sections of tethyan litho and biofacies the nannofossil assemblages recorded are of high diversity reflecting stable warm water conditions typical for the earliest cretaceous of the tethys the floras are characterised by abundant watznaueria spp and nannoconus spp whereas other taxa are less common long term trends on the scale of 1 4 my are reflected by shifts from watznaueria spp dominated assemblages in the lower berriasian to nannoconus spp assemblages in the middle upper berriasian back to watznaueria spp in the upper berriasian lower valanginian and again to nannoconus spp in the upper valanginian these changes are thought to be caused by palaeoclimatic shifts periods with a dominance of cosmopolitan eurytopic watznaueria are thought to reflect cooler humid conditions and well mixed surface waters those with a dominance of nannoconus warmer conditions and a rather stabile surface water stratification crucibiscutum salebrosum very common at high latitudes is extremely rare in the romanian samples it occurs only at one specific interval of early late valanginian age saynoceras verrucosum ammonite zone associated with other rare boreal taxa also restricted to this particular level this boreal nannoplankton excursion is believed to be controlled by sea level rather than by climate since simultaneously tethyan ammonites found their way into the boreal realm

an empirical method for determining the mechanical properties of jointed rock mass using drilling energy abstract characterization of jointed rock masses and evaluation of their mechanical properties are challenging tasks in rock engineering this paper presents an experimental investigation of the response characteristics of drilling energy to the discontinuity of rock mass using a drilling method the linear relationship between the drilling energy and discontinuity frequency is revealed which only depends on the rock type and is independent of calculation units a new empirical method for determining the rock quality designation rqd versus the variation of drilling energy is proposed based on the discontinuity frequency comparison between the prediction and in situ investigation results demonstrates that the rqd can be estimated from this empirical method the em er modulus ratio and cm c strength ratio versus rqd relations are modified for the determination of rock mass strength and deformation modulus in order to consider the continuous variation of em er and cm c with the model parameter which is related to the drilling energy and modulus of elasticity of intact rock and the variation of drilling energy for rock mass the results show that the modified em er cm c versus rqd relations can give proper values compared with the field test results as well as compared with the various proposed relations from rmr q and gsi the modified relations can provide a practical fast and easy to use method for the estimated rock mass strength and deformation modulus but they are only a first approximation

p wave velocity measurements for preliminary assessments of the mineralization in seafloor massive sulfide mini cores during drilling operations highlight it is important to develop systems able to detect and classify mineralized zones from waste materials while drilling deep water seismic p wave velocities vp were measured on 40 sms and unmineralized mini cores the porosity was back calculated from vp the results were compared with electrical resistivity measurements using archie s law it is possible to observe that metallic conduction exists abstract deep sea mining exploration for seafloor massive sulfide sms deposits is currently increasing at present most exploration activities are surficial and use indirect methods to identify potential sites and perform first assessments for a proper resource estimate however drilling is inevitable by using seabed drill rigs exploration costs can be reduced considerably sms deposits are normally found at depths between 1000 and 4000 m and in order for deep sea mining to be implemented reliable technologies are needed additionally the development of geophysical systems that can detect and classify mineralized zones from waste materials while drilling could decrease costs and speed up offshore operations by limiting the amount of drilling of unmineralized materials this paper shows how the physical properties of sms can be used to discriminate between host rocks and mineralization seismic p wave velocities vp were measured on 40 sms and unmineralized mini cores by back calculating the porosity from vp comparing the results with electrical resistivity measurements and using archie s law it is possible to observe that metallic conduction exists for deep sea mineral exploration the combination of seismic tests electrical resistivity and magnetic susceptibility could support the preliminary discrimination of mineralized samples in the cores while drilling at the seafloor

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

extensive dilatancy anisotropy beneath mount hood oregon and the effect of aspect ratio on seismic velocities through aligned cracks the azimuthal variations of p wave velocity measured in u s geological survey usgs seismic refraction experiments around mount hood oregon are modeled by propagation through the effective anisotropy of parallel vertical cracks the three refractors at 1 3 7 and 8 5 km depth show different behavior the shallow refractor at 1 km displays p wave velocity variations typical of the parallel water filled vertical microcracks found throughout much of the upper continental crust the arrivals from the refractor at 3 7 km display velocity variations consistent with either dry cracks or more probably with cracks filled with supercritical water as one interpretation of the heat flow around mount hood suggests that temperatures at 3 7 km would be above the critical temperature for water at in situ pressures the velocity variations at the deepest refractor at 8 5 km depth are poorly constrained but again suggest liquid filled cracks the possibility of high temperatures suggests that at this depth the cracks could be thin skins of melt along grain boundaries the vertical cracks in all three refractors strike in the northwest to southeast quadrants which is consistent with the compressional quadrants in the mechanisms of local earthquakes shear wave splitting reported elsewhere indicates that there are stress aligned water filled microcracks extensive dilatancy anisotropy or eda throughout at least the brittle upper 10 or 20 km of the continental crust the high heat flow in the high cascades may confine the range of crack behavior usually spread over the whole thickness of the crust to the top 10 km beneath mount hood thus the p wave velocity variations beneath mount hood may indicate that eda cracks occur throughout the whole of the continental crust the large number of shot to recorder travel times measured by the usgs allows extensive dilatancy anisotropy to be recognized from the analysis of p wave velocity variations for the first time

numerical simulation of progressive rock failure and associated seismicity in this paper a numerical approach to modeling progressive failure leading to collapse in rock and associated seismicity is reported in the first part a newly developed numerical code rfpaz rock failure process analysis is introduced the program allows modeling of the observed evolution of damage and associated seismic events due to progressive failure leading to collapse in brittle rock there are three features distinguishing the approach from conventional numerical methods such as fem 1 by introducing heterogeneity of rock parameters into the model rfpaz can simulate non linear behavior in rock using a linear method 2 by introducing elastic modulus reduction for failed elements rfpa2d can process discontinuum mechanics problems by a continuum mechanics method and 3 by recording the event rate of failed elements the seismicities associated with the progressive failure in rock can be simulated in the second part of the paper the applications of rfpa2d in simulating geological process and in solving mining design problems are illustrated numerical simulation of a fault initiation process indicates that some of the important phenomena such as coalescence of microfracture the nucleation and growth of crack clusters fault initiation and development elastic rebound dilatation uplift and seismic behavior etc can be simulated with this numerical code the simulation of progressive failure leading to collapse in underground openings demonstrates the capacity of this code in solving mining design problems

early cretaceous calcareous nannofossils from high latitudes implications for palaeobiogeography and palaeoclimate abstract in order to better understand the palaeoceanography and palaeoclimate of the early cretaceous nannofossil data have been obtained from high latitudinal sites from offshore mid norway and from the barents sea no consistent nannofossil data are yet available for early cretaceous high latitudes which should more clearly reflect possible palaeoclimatic changes as recorded in fluctuations of diversity and abundance existing data from france italy romania poland and nw europe germany north sea england have been complemented by material from higher latitudes in order to record the arctic boreal nannofossil assemblages 400 samples from the norwegian shelf and the barents sea have been analysed sixty samples covering the berriasian barremian interval yielded calcareous nannofossils these are derived from cores between 63 and 73 n of present day latitudes the nannofossil assemblages recorded are generally of a low diversity and characterized by abundant watznaueria barnesae and crucibiscutum salebrosum whereas biscutum constans is less common c salebrosum rare or absent at low latitudes is extremely common in the norwegian samples it shows a bipolar distribution especially during valanginian hauterivian times in the early valanginian a distinctive latitudinal gradient in the abundance of c salebrosum impoverished in low latitudes and abundant in high latitudes possibly reflects latitudinal differences in temperature restricted palaeoceanographic settings caused by a sea level lowstand may have amplified these thermal gradients palaeoclimatically this implies the existence of climatic belts throughout parts of the early cretaceous early valanginian hauterivian resulting from considerable temperature gradients from north to south the palaeobiogeographic patterns discussed resulted in the formation of distinctive latitudinally bound nannofossil zones which to a certain extent are similar to those of modern oceans the palaeobiogeographic patterns described support the idea of an ice house phase for the early valanginian and disagree with the suggestion of a globally warm equable climate during that time