cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

analysis of a guided wave along a conducting structure in a borehole a guided wave along a borehole is often observed in borehole radar measurements these guided waves deform the antenna pattern and can cause artefacts in radar measurements a water filled borehole or a conducting logging cable can function as a waveguide for electromagnetic waves under some conditions we describe the theoretical characteristics of such a guided wave in a borehole and compare them with our experiments the measured signal discussed was obtained with a directional borehole radar this radar uses a cylindrical conformal array antenna as receiver and is a model of a conducting structure in a borehole the induced field around the borehole was compared with the theory the most fundamental symmetrical and asymmetrical modes were tm 01 and he 11 and they were identified in the measured signals using time frequency distribution analysis and by observation of the azimuthal field distribution of the magnetic field

evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years although old diagrams have been extensively used the recent ones based on discriminant functions of ratio variables with or without log transformation proposed during 2004 2010 for the discrimination of four tectonic settings of island arc continental rift ocean island and mid ocean ridge were newly evaluated to show their high success rates of 57 3 100 and 58 5 100 for major element and immobile element based diagrams respectively for the continental arc of the andes evaluated for its similarity to island arc these four sets of diagrams showed success rates of 62 1 83 8 these four sets of five diagrams per set were therefore used to infer tectonic setting of the mexican volcanic belt mvb los tuxtlas volcanic field ltvf and central american volcanic arc cava using this approach the mvb especially its western central and eastern parts and the ltvf of southern mexico show a dominantly continental rift setting and the cava shows an arc setting the west central part of the mvb is consistent with dual tectonics of arc and rift these results confirm the application of an unusual mantle upwelling rift model for the mexican on land volcanism whereas the conventional plate tectonic subduction model seems to be applicable for the cava from guatemala to north western costa rica

mom analysis of dipole antennas in crosshole borehole radar and field experiments in this paper we propose a method of moments mom analysis that includes the borehole effects on crosshole borehole radar and we verify that the mom represents the crosshole borehole radar data correctly we derive the far field approximation of an electric field radiated by an electric point source in this derivation we assume that the point source is in a cylindrically layered medium while the observed electric field is in another cylindrically layered medium the equations that are derived are used as a transfer function to connect the two impedance matrices one for the transmitting antenna and the other one for the receiving one in these matrices the influence of the scattered field by the borehole is included completely we conducted field experiments in granite with a controlled borehole medium in order to investigate the influence of the borehole in this paper we estimated the relative amplitude and the group delay of the received signals between the water filled borehole case and the air filled borehole case this paper showed that the estimated amplitude and delay depend on the frequency and that the proposed mom could predict these frequency dependencies

forcing mechanisms for mid cretaceous black shale formation evidence from the upper aptian and lower albian of the vocontian basin se france calcareous nannoplankton palynomorph benthic foraminifera and oxygen isotope records from the supraregionally distributed niveau paquier early albian age oceanic anoxic event 1b and regionally distributed niveau kilian late aptian age black shales in the vocontian basin se france exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid cretaceous low latitudes to quantify surface water productivity and temperature changes nutrient and temperature indices based on calcareous nannofossils were developed the nutrient index strongly varies in the precessional band whereas variations of the temperature index reflect eccentricity since polar ice caps were not present during the mid cretaceous these variations probably result from feedback mechanisms within a monsoonal climate system of the mid cretaceous low latitudes involving warm humid and cool dry cycles a model is proposed that explains the formation of mid cretaceous black shales through monsoonally driven changes in temperature and evaporation precipitation patterns the lower albian niveau paquier which has a supraregional distribution formed under extremely warm and humid conditions when monsoonal intensity was strongest bottom water ventilation in the vocontian basin was diminished probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes surface water productivity in the vocontian basin was controlled by the strength of monsoonal winds the upper aptian niveau kilian which has a regional distribution only formed under a less warm and humid climate than the niveau paquier low latitude deep water formation was reduced to a lesser extent and or on regional scale only the threshold for the formation of a supraregional black shale was not reached the intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale at least in the vocontian basin the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity

high resolution carbon isotope records of the aptian to lower albian from se france and the mazagan plateau dsdp site 545 a stratigraphic tool for paleoceanographic and paleobiologic reconstruction high resolution carbon isotope stratigraphy is established for the aptian to lower albian of the vocontian basin se france and correlated to the carbon isotope record of the mazagan plateau dsdp site 545 the carbon isotope stratigraphy of the vocontian basin is proposed as a standard reference curve for the aptian to lower albian due to the completeness and high temporal resolution of the stratigraphic succession the good biostratigraphical time control and the frequent occurrence of regional to global black shale horizons including oceanic anoxic events 1a oae 1a of the lower aptian and oae 1b of the lower albian the carbon isotope record appears better suited for long distance short term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types however the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography and to correlate regional to global black shale horizons in different marine environments this combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species based on the demonstrated diachroneity of important biostratigraphic markers of the aptian albian boundary the globally observed break point between the end of the uppermost aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13c values is an alternative criterion the distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the aptian to lower albian

borehole effects on downhole seismic measurements there are increasing interests in acquiring crosshole and vsp surveys at frequency up to 1 khz or more with the intention to resolve the fine details of structures and lithology between wells bregman et al 1989 harris 1988 tura 1991 however at frequencies on the order 1 khz the existence of the fluid filled borehole has a strong influence on the downhole measurements depending on the frequency and angle of incidence as well as the formation properties the measured displacements on the borehole wall or pressure at the center of borehole may be significantly different from those of the incident wave without taking proper care of this effect any imaging or inversion algorithm which utilizes both the amplitude and phase information of recorded energy will produce erroneous results

improved characterization of fine texture soils using on ground gpr full waveform inversion ground penetrating radar gpr uses the recording of electromagnetic waves and is increasingly applied for a wide range of applications traditionally the main focus was on the analysis of the medium permittivity since estimates of the conductivity using the far field approximation contain relatively large errors and cannot be interpreted quantitatively recently a full waveform inversion fwi scheme has been developed that is able to reliably estimate permittivity and conductivity values by analyzing reflected waves present in on ground gpr data it is based on a frequency domain solution of maxwell s equations including far intermediate and near fields assuming a 3 d subsurface here we adapt the fwi scheme for on ground gpr to invert the direct ground wave traveling through the shallow subsurface due to possible interference with the airwaves and other reflections an automated time domain filter needed to be included in the inversion in addition to the obtained permittivity and conductivity values also the wavelet center frequency and amplitude return valuable information that can be used for soil characterization combined geophysical measurements were carried out over a silty loam with significant variability in the soil texture the obtained medium properties are consistent with theta probe electromagnetic resistivity tomography and electromagnetic induction results and enable the formulation of an empirical relationship between soil texture and soil properties the permittivities and conductivities increase with increasing clay and silt and decreasing skeleton content moreover with increasing permittivities and conductivities the wavelet center frequency decreases whereas the wavelet amplitude increases which is consistent with the radiation pattern and the antenna coupling characteristics

light elements and li isotopes across the northern portion of the central american subduction zone 1 quaternary mafic rocks have been erupted from volcanoes both on and behind the volcanic front in southeastern guatemala and western el salvador behind the front volcanism extends almost continuously some 110 km from the front b and li contents as well as b nb and li yb ratios are generally higher in the mafic volcanic rocks of the volcanic front and lower in those behind the front beryllium concentrations show the opposite relationships with generally higher values behind the front in addition many behind the front samples have lower 7li 2 3 versus 4 6 for the volcanic front guatemalan volcanic rocks in general have lower 7li than those found along the remainder of the central american margin the light element variations across northern central america clearly indicate that the volcanic front receives a much more pronounced fluid contribution from dehydrating subducting cocos lithosphere than the behind the front region this dehydration pulse occurs at slab depths between 85 and 105 km and selective enrichments of b cs and cl in volcanic rocks of the volcanic front suggest that the source of this pulse is dehydrating serpentinite in addition the dehydration pulse from subducted serpentinite is likely superimposed on a continuous dehydration signal provided by subducting oceanic crust which continues behind the volcanic front to slab depths 200 km the enhanced fluid contributions at the front produce higher degrees of wedge melting thus explaining the lower be contents of front samples there are two possible explanations of the lower 7li of many behind the front volcanic rocks from southeastern guatemala western el salvador selective loss of 7li during progressive dehydration of subducting cocos lithosphere or diffusive fractionation accompanying late stage selective crustal contamination since the slightly lower 7li of guatemalan volcanic rocks in general is consistent with a minor crustal overprint the second explanation is favored and could be relevant to the few subduction zones where lower li isotopic values characterize back arc regions light element variation across southeastern guatemala and western el salvador is consistent with the operation of decompression melting behind the volcanic front be zr ratios across the northern portion of the central american subduction zone may indicate some mobility of be

statistical evaluation of elemental concentrations in shallow marine deposits cretaceous lusitanian basin abstract the elemental geochemistry of ancient shallow marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways complex multi parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the lusitanian basin ericeira portugal are presented and interpreted the section comprises marly carbonate and sandstone rich coastal marine deposits of early albian to early cenomanian age principal component analysis of bulk elemental abundance ca mg sr fe and mn lead to define four geochemical clusters based on common elemental attributes siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration but still preserve information on paleoshoreline position mixed carbonate siliciclastics and limestone facies bear evidence for relative sea level position and relevant paleoclimatic information in their elemental record accordingly mid albian mixed carbonate siliciclastic deposits present variable degrees of continental influx specifically a sharp increase of fe and mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands the progressive transition towards more marine conditions is accompanied by higher ca and sr content and represented by limestone facies corresponding to a higher sea level position during late albian to early cenomanian times moreover this facies records a trend towards warmer and more arid conditions early diagenetic stabilization and or dissolution of aragonite into low mg calcite can account for major elemental variations including higher sr content strongly coupled with ca content along with lower mg fe and mn concentrations data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits when combined with conventional sedimentology and thin section petrography allow for elaborate conclusions on their depositional environment and diagenetic pathways cored wells and facies specific reservoir properties can be addressed by these methodologies able to detect and quantify changes in patterns both industry and academy can therefore benefit from approaching such a complex interplay

the source of central american lavas inferences from geochemical inverse modeling the rate earth element chemistry of a large suite of samples from the central american volcanic front has been determined to understand their petrogenesis different segments of the volcanic front are compared on the basis of their calculated source rare earth patterns as deduced from inverse modeling the results yield a range in the extent of light rare earth enrichment of the source as well as in source mineralogy moderateto strong lree enrichment and high modal garnet contents are observed for the sources of both guatemala and central costa rica whereas slight lree depletion and little or no garnet occurs in the nicaraguan source region although distinct source regions beneath each central american segment are permitted by the modeling it is more likely that the mantle wedge is broadly homogeneous but locally heterogeneous small volume relatively enriched garnet bearing veins surrounded by a matrix of isotopically depleted mantle periodotite could exist throughout the mantle wedge apparently distinct sources occur due to the variation in partial melting beneath the different segments controlled by the amount of subduction generated flux per unit wedge volume which in turn is a function of the dip of the subducted lithosphere

paleoceanography of the northwestern pacific during the albian abstract the deep ocean conditions and circulation during the cretaceous have been characterized mainly by the sediments from the tethys sea and the proto atlantic ocean because sedimentological data from the pacific basin from that period have been quite limited here we present new geochemical measurements from sediments that we collected from two sites in hokkaido japan that were presumably deposited in the northwest pacific during the albian 112 ma the low organic carbon and carbonate contents combined with other measurements from our study suggest that the mid depth northwest pacific during the time of deposition was corrosive to sedimentary carbonate but oxic we also use a simple box model of the ocean biogeochemistry to investigate the conditions of carbonate preservation and suggest that the northwest pacific hydrography was quite distinct from the tethys sea and the proto atlantic ocean

boron geochemistry of the central american volcanic arc constraints on the genesis of subduction related magmas boron contents were measured in representative quaternary lavas from the central american volcanic arc to evaluate along strike variations in subduction processes despite the significant range in b concentrations 2 37 ppm in the mafic lavas b la ratios vary in a systematic fashion along the arc higher values 1 are typical between guatemala and northern costa rica whereas low values most 0 5 typify central costa rica and western panama b la is highly correlated with 10be 9be r2 0 94 excluding one sample and appears to be a useful indicator of subduction contributions to the magma sources if enrichments of both b and 10be are proportional to the flux of subducted sediment along strike variations in b la suggest at least a twofold variation in this flux with maximum values below western nicaragua and minimum values below costa rica and western panama where the cocos ridge is being subducted these data may also reflect significant differences in thermal state of the descending slab which in turn differentially affects release patterns of fluids and fluid mobile trace elements and possibly melting processes beneath different parts of the arc the following scenario is suggested to explain the geochemical results beneath the northwestern part of the arc steep subduction of older relatively cold slab favors more efficient subduction of fluid components to depths beneath the volcanic front the released fluids carry fluid mobile elements to the overlying mantle which upon melting produces calcalkalic magmas shallow subduction of warmer slab beneath the southeastern part of the arc favors shallow release of fluids and limits fluid related metasomatism of sub arc mantle beneath the volcanic front under such conditions b la and ba la ratios in the sub arc mantle vary little from values seen in oceanic island basalts magmas in this part of the arc nevertheless display the highest la yb and lowest ba la and b la ratios which are consistent with prior light rare earth element enrichment in the source significantly lower degrees of melting or a combination thereof because some of the largest volcanoes occur in costa rica and magma flux there is nearly an order of magnitude higher than elsewhere in the arc source enrichment is considered to be the more plausible explanation it is proposed that quaternary magma production below costa rica involved lithospheric sources containing trapped or stored melt components but this enrichment process is unlikely to have involved typical arc magmas or subduction fluids because we see no b enrichment

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

mid cretaceous radiolarian zonation for the north atlantic an example of oceanographically controlled evolutionary processes in the marine biosphere this paper is included in the special publication entitled geological evolution of ocean basins results from the ocean drilling program edited by a cramp c j macleod s v lee and e j w jones mid cretaceous aptian turonian sediments from seven deep sea drilling project and ocean drilling program sites in the north atlantic have been investigated in order to establish a mid cretaceous radiolarian biostratigraphy for the north atlantic one of the results a new zonation for mid cretaceous north atlantic radiolaria is presented here from parallel investigations of calcareous sections in central italy an accurate calibration to standard planktonic foraminiferal zonations is possible the evolution of mid cretaceous radiolaria appears to be strongly related to sea level changes nutrient supply and the extension of the oxygen minimum zone a model was proposed that explains extinction radiation events of mid cretaceous radiolaria as being controlled by sea level fluctuations and resulting changes of productivity these are the parameters that control the dimensions of the oxygen minimum zone the fluctuation of which destroys and creates habitats

nejapa tephra the youngest c 1 ka bp highly explosive hydroclastic eruption in western managua nicaragua nejapa maar 2 5 1 4 km c 120 m deep the largest maar along the 15 km long holocene nejapa miraflores lineament nml is the source vent of the youngest relatively widespread basaltic tholeiitic tephra blanket nejapa tephra nt in western central nicaragua as shown by isopachs and isopleths rausch and schmincke 2008 the nt covers an area of 10 km2 in w nw managua the minimum total magma volume erupted is estimated as 0 09 km3 juvenile dominantly slightly vesicular 20 40 vol basically tachylitic cauliflower shaped lapilli with an average density of 2 1 g cm3 make up 90 vol of the deposit while lithoclasts comprise 10 vol except proximally this the paucity of fine grained tuffs and the dominant plane parallel bedding all suggest fragmentation by shallow interaction of a rising magma starting to vesiculate and fragment pyroclastically with external water the complex particles so generated erupted in moderately high eruption columns at least 7 10 km and were dominantly deposited as dry to damp warm to cool fallout minor surge transport is inferred from fine grained locally cross bedded tephra beds chiefly north of nejapa and just west of asososca maars synvolcanic faulting along the nml is inferred faults in the study area indicate that activation of the n s trending nejapa miraflores fault nmf representing the western flank of managua graben preceded deposition of nt and underlying masaya tuff c 1 8 ka bp chiltepe pumice c 1 9 ka bp and masaya triple layer 2 1 ka bp the nt deposit is underlain regionally by a paleosol and topped by a soil the basal paleosol contains pottery sherds made by the usulutan negative technique during the late formative period 700 bce 300 ce 2 7 1 7 ka bp the soil overlying nt contains pottery related to the ometepe technique dated as between 1350 and 1550 ce 650 450 a bp these and the radiocarbon dates of the pottery bearing paleosols 1245 125 and 535 110 a bp obtained by pardo et al 2008 indicate that nejapa maar erupted between c 1 2 and 0 6 ka bp future eruptions in this area of similar magnitude eruptive and transport mechanisms would represent a major hazard and risk to the densely populated western suburbs of managua a city expanding rapidly westward assuming a similar eruption scenario poor quality roofs common in nicaragua would be prone to collapse up to 12 km peripheral to nejapa maar or another close by eruptive site and buildings at a distance of up to 500 m are likely to be severely affected in view of the past frequency of eruptions along the nml further eruptions are likely to occur in the near future

numerical climate modeling a frontier in petroleum source rock prediction results based on cretaceous simulations organic productivity and preservation are primary controls of the distribution of petroleum source beds both organic productivity and preservation are in part a function of geographic setting and climate therefore the prediction of paleoclimates is a major frontier in petroleum source rock prediction a climate model based on the fundamental laws thought to govern atmospheric circulation is applied here to the prediction of upwelling regions associated with very high productivity and bottom conditions that may become anoxic despite a high oxygen supply the potential and limitations of climate modeling in the prediction of upwelling regions are examined by 1 demonstrating the ability of the model to predict present day winds and upwelling regions 2 demonstrating t at the model and the location of upwelling regions is sensitive to geography continental positions sea level and topography and 3 investigating whether the model sensitivity to past geographies is realistic i e if predicted upwelling regions for the cretaceous period correspond to source rock localities the model predictions of ocean and coastal upwelling compare very favorably with present day observations and with estimates of primary productivity the location of middle latitude and high latitude upwelling locations are sensitive to model specified geography the location of low latitude upwelling is less sensitive to changes in global geography if coastlines are oriented appropriately despite some limitations a comparison of source rock localities with model predictions is promising the results of these studies suggest that numerical climate modeling is a potential tool in petroleum source rock prediction

planktonic foraminiferal zonation in the cretaceous yezo group central hokkaido japan abstract the mudstone of the yezo group exposed in central hokkaido yields abundant microfossils of calcareous nannofossils foraminifers radiolarians and dinoflagellates benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence while specimens of planktonic foraminifers are generally fewer than benthics in all samples we recognized the following 13 planktonic foraminiferal zones assigned to the late aptian to early campanian in the oyubari and haboro kotanbetsu areas 1 globigerinelloides spp 2 ticinella primula 3 biticinella breggiensis 4 rotalipora subicinensis rotalipora ticinensis 5 rotalipora appenninica 6 rotalipora globotruncanoides 7 rotalipora cushmani 8 whiteinella archaeocretacea 9 helvetoglobotruncana helvetica 10 marginotruncana pseudolinneiana 11 marginotruncana sinuosa 12 contusotruncana fornicata 13 globotruncana arca the globigerinelloides spp to h helvetica zones late aptian to early turonian can be correlated with standard zones in the tethyan regions whereas the assemblages from the m pseudolinneiana to g arca zones lack tropical zonal markers of dicarinella concavata d asymetrica and globotruncanita elevata in many studied sections the scarcity or lack of tropical zonal species during the late turonian to early campanian suggests that the oyubari and haboro kotanbetsu regions in hokkaido were located in the transitional to boreal biogeographical provinces

introduction seismic wave scattering in three dimensionally heterogeneous earth the classical earth model of spherical symmetry or layered structure is undergoing a revolution the earth has been revealed to be laterally heterogeneous everywhere from the crust mantle to the core with scale from the grain size of rocks to the lowest orders of global spherical harmonics figure 1 shows the strength and scale length of heterogeneities in the crust and mantle of the earth in terms of v the perturbation index of seismic p or s wave speed defined as the r m s fractional variations of wave speed over the measured region the scale length of heterogeneities revealed by seismic waves not including the laboratory measurements of rock samples spans 8 orders of magnitude these heterogeneities with different scales have different effects to seismic waves the velocity and density heterogeneities can cause the change in waveform phase or travel time and amplitude fluctuation as well as apparent attenuation of the direct arrivals they can also generate coda waves such as the p coda s coda and lg coda caused by the lithospheric heterogeneities and precursory waves such as the scattered pkp waves as the precursors to pkikp caused by the heterogeneities near the core mantle boundary the near source or near receiver structures can modify the seismic waveforms by resonance and other effect rough topography or rough interface can cause the coupling between body wave and surface wave aligned cracks in the crust can produce the effective anisotrophy a great complexity arises when heterogeneities have interaction with anisotrophy and nonlinearity

volcanogenic upwelling of anoxic nutrient rich water a possible factor in carbonate bank reef demise and benthic faunal extinctions the middle cretaceous oceans were characterized by widespread anoxia high sea levels reef carbonate bank extinctions and at least in the pacific by intense widespread mid plate volcanism the demise of reefs on numerous pacific atolls has left a large number of guyots this synthesis explores the possibility that the middle cretaceous demise of mid pacific and other carbonate bank communities and related extinctions elsewhere reflects sporadic possibly volcanogenic upwelling of anoxic water the upwelling would have had to be rapid enough to overwhelm surface reoxygenation and frequent widespread enough to suppress recolonization according to the hallock schlager hypothesis upwelling of nutrient rich waters destroyed the carbonate bank communities nutrient excess and anoxia may well have worked together the globally widespread presence of at least mid depth anoxia h 2 s is reasonably well established the cenomanian turonian oceanic anoxic event perhaps was an extreme example as is the mortality of modern benthic invertebrates at o 2 levels below about 0 15 ml l recolonization times for modern reef corals imply that upwelling catastrophes if localized need have recurred on approximately decade time scales previously postulated cretaceous sea level fluctuations raising sea level at rates on the order of 5 10 m in 10 4 10 5 yr would then have sufficed to carry the intermittently stressed reef surfaces below the 5 to 10 m deep high carbonate production zone below which reef recovery chances diminish thus the episode of frequent localized but widespread upwelling events need have lasted only about 10 4 10 5 yr although intermittent deep water ventilation is known to have occurred on milankovitch time scales during the cretaceous thereby bringing anoxic and or nutrient rich waters to the surface geologic and ocean modeling evidence is necessary to establish whether a significant amount of rapid upwelling did or could occur because mid plate submarine volcanism was widespread and intense in the middle cretaceous pacific volcanogenic hydrothermal heating and entrainment of nutrient rich anoxic waters is one possible mechanism for catastrophic buoyant upwelling rudistid bank extinction and guyot formation the efficacy of this process depends principally on the buoyancy that is heat energy flux and the buoyancy brunt vaisala frequency typical hydrothermal plumes along the mid oceanic ridge axis rise only to 150 to 400 m heights above the sea floor but megaplumes rising 1 000 m are known simple plume models imply that only basalt eruptions comparable to the largest historically known would be sufficiently energetic 10 12 10 14 j s to bring bottom water to the ocean surface from normal mid oceanic ridge axial depths 3 km over much of the present ocean however these models are conservative through neglect of momentum overshoot and gas exsolution to the extent that higher eruption rates and lower brunt vaisala frequencies due to lower vertical temperature gradients prevailed in the middle cretaceous pacific anoxic deep waters would more readily have reached the ocean surface most cretaceous guyots are now in the north pacific but were carried across the equator by pacific plate motion normal tendencies to upwelling and oxygen deficiency along the equator would have made the carbonate banks most vulnerable during their equatorial transit

fluctuations in biosiliceous production and the generation of early cretaceous oceanic anoxic events in the pacific ocean shatsky rise ocean drilling program leg 198 integration of geophysical logs with sedimentological biostratigraphic and physical properties data from poorly recovered chert rich sequences at ocean drilling program leg 198 sites 1207 and 1213 allows us to propose an aptian albian early cretaceous depositional history for shatsky rise north pacific ocean the logs indicate that the lower aptian and lower albian deposits are relatively lithified and unporous compared to contiguous sediments these characteristics are best explained by increased siliceous cementation that resulted from an elevated flux of radiolarians to the seafloor the intervals of increased biosiliceous production may record a biotic response to enhanced nutrient delivery coeval with but longer in duration than oceanic anoxic events oaes 1a early aptian and 1b early albian on shatsky rise oae 1a is represented by organic carbon rich sediments but oae 1b is not thus black shale deposition in the pacific ocean was only possible when a carbon burial threshold was crossed we speculate that this threshold was related to the balance between productivity and carbon oxidation and that ultimately the supply of biolimiting nutrients through hydrothermal alteration of basalt may have been the key to the development of black shale in the pacific basin

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

a simultaneous inversion of seismic traveltimes and amplitudes for velocity and attenuation it is possible to efficiently use traveltime and amplitude information to infer variations in velocity and q with little additional computation terms accounting for source radiation pattern and receiver coupling may be included in the inversion the methodology is based upon a perturbation approach to paraxial ray theory the perturbation approach linearizes the relationship between velocity deviations and traveltime and amplitude anomalies using the technique we infer the velocity and attenuation structure at a fractured granitic site near raymond california a set of four well pairs are examined and each is found to contain two zones of strong attenuation the velocity variations contain an upper low velocity region corresponding to the uppermost attenuating zone the location of these zones agrees with independent well log and geophysical data the velocity and attenuation anomalies appear to coincide with extensively fractured sections of the borehole and may indicate fracture zones rather than individual fractures

borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1 this paper discusses the borehole radar system ramac developed within the framework of the international stripa project which can be used in three different measuring modes single hole reflection cross hole reflection and cross hole tomography the reflection modes basically provide geometrical data on features located at some distance from the borehole in addition the strength of the reflections indicate the contrast in electrical properties single hole reflection data are cylindrically symmetrical with respect to the borehole which means that a unique fracture orientation cannot be obtained a method has been devised where absolute orientation of fracture zones is obtained by combining single hole reflection data from adjacent holes similar methods for the analysis of cross hole reflection data have also been developed and found to be efficient the radar operates in the frequency range 20 60 mhz which gives a resolution of 1 3 m in crystalline rock the investigation range obtained in the stripa granite is approximately 100 m in the single hole mode and 200 300 m in the cross hole model variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross hole tomographic imaging to yield maps of radar velocity and attenuation the cross hole measurement configuration coupled withmore tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties the analysis of the radar data has provided a consistent description of the fracture zones at the stripa cross hole site in agreement with both geological and geophysical observations less

a new estimate of the caco3 to organic carbon export ratio 1 we use an ocean biogeochemical transport box model of the top 100 m of the water column to estimate the caco3 to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate we find a global average molar export ratio of 0 06 0 03 this is substantially smaller than earlier estimates of 0 25 on which a majority of ocean biogeochemical models had based their parameterization of caco3 production contrary to the pattern of coccolithophore blooms determined from satellite observations which show high latitude predominance we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres our results suggest a dominant contribution to global calcification by low latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods

influence of oceanic anoxic events on the evolution of mid cretaceous radiolaria in the north atlantic and western tethys abstract mid cretaceous aptian turonian extinction radiation events of radiolaria from the north atlantic and western tethys are summarized in relation to oceanic anoxic events oae from investigations of radiolarian faunas black shales and stable carbon isotopes extinction and radiation events of radiolaria can be observed from the late early aptian the earliest albian the latest albian and the cenomanian turonian boundary these events correlate well with organic carbon rich sediments that contain type ii kerogen and show positive 13c excursions they correspond to the oceanic anoxic events oae in the early aptian oae 1a selli level early albian oae 1b late albian oae 1d and latest cenomanian oae 2 bonarelli level detailed investigations of the two most significant events the selli and the bonarelli level in the umbria marche basin of central italy show that extinctions coincide with the first occurrence of marine black shales type ii kerogen and the most prominent rise of 13corg values stepwise extinctions and continuous radiations precede and follow the events similar patterns are evident for the oae 1b and 1d black shales dominated by terrestrial organic matter type iii kerogen e g oae 1c are not characterized by isotopic excursions or by radiolarian extinction radiation events contemporaneous drowning events documented from carbonate platforms around the investigated basins provide a link to a model where flooding of lowlands and leaching of nutrients during a relative rise of sea level lead to an increased productivity and an expansion of the oxygen minimum zone omz because of the loss of deep habitats deeper dwelling forms become extinct shallower dwelling radiolarians survive a narrowing of the omz during highstands and relative sea level falls together with a coupled decrease of the nutrient supply leads to the development of new niches and therefore to radiation

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

a simulation of mid cretaceous climate a series of general circulation model experiments utilizing genesis have been completed for the mid cretaceous based on geography variable atmospheric carbon dioxide concentrations 2 to 6 times present day concentrations and variable poleward oceanic heat flux 6 to 1 2 1015 w increased from present day by combining all three major variables co2 geography and oceanic heat flux the distribution of mid cretaceous temperatures can be achieved in the simulations increased co2 is required to promote global warmth and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of co2 four times present day co2 with 1 2 1015 w provided the best match to the distribution of mid cretaceous data the best match to the cretaceous observations was achieved with a globally averaged surface temperature increase of 6 2 c at the lower end of past estimates of mid cretaceous warmth this value may be a better estimate of mid cretaceous global warming finally the model experiments can be used to provide a paleocalibration of the global warming expected for a doubling of atmospheric carbon dioxide the best estimates for the mid cretaceous appear to be a 2 5 to 4 0 c sensitivity in the mid to upper range of the sensitivity of current climate models used to assess future global change

numerical modeling of borehole georadar data high frequency electromagnetic em wave propagation phenomena associated with borehole georadar experiments are complex to improve our understanding of the governing physical processes we present a finite difference solution of maxwell s equations in cylindrical coordinates this approach allows us to model the full em wavefield associated with borehole georadar experiments and to assess the adequacy of ray based methods currently used to interpret the observed amplitudes our results indicate that because shallow boreholes are often water filled the finite length of the boreholes as well as changes in material properties along a borehole wall can have major effects on the amplitude behavior of borehole georadar data as a result of waveguide phenomena the radiation pattern of a vertical electric dipole source located in a water filled borehole may be distorted significantly with respect to the corresponding reference radiation pattern in a homogeneous medium even greater distortions of the radiation pattern result when the electric dipole source is located near material boundaries or near the upper or lower end of a borehole this study indicates that some of the basic assumptions of conventional ray based amplitude tomography often are not fulfilled for borehole georadar data and that the derived constraints on the attenuation and conductivity structure should be regarded as qualitative in nature the algorithm and the results presented in this study do however offer the perspective to alleviate some of these inherent problems and thus help to make ray based georadar attenuation tomography a more reliable and effective tool for probing the shallow subsurface

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

geochemical characterization of surface waters and groundwater resources in the managua area nicaragua central america abstract this paper reports new geochemical data on dissolved major and minor constituents in surface waters and ground waters collected in the managua region nicaragua and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area the peculiar geological features of the study site an active tectonic region nicaragua depression characterized by active volcanism and thermalism combined with significant anthropogenic pressure contribute to a complex evolution of water chemistry which results from the simultaneous action of several geochemical processes such as evaporation rock leaching mixing with saline brines of natural or anthropogenic origin the effect of active thermalism on both surface waters e g saline volcanic lakes and groundwaters as a result of mixing with variable proportions of hyper saline geothermal na cl brines e g momotombo geothermal plant accounts for the high salinities and high concentrations of many environmentally relevant trace elements as b fe and mn in the waters at the same time the active extensional tectonics of the managua area favour the interaction with acidic reduced thermal fluids followed by extensive leaching of the host rock and the groundwater release of toxic metals e g ni cu the significant pollution in the area deriving principally from urban and industrial waste water probably also contributes to the aquatic cycling of many trace elements which attain concentrations above the who recommended limits for the elements ni 40 g l and cu 10 g l limiting the potential utilisation of lake xolotlan for nearby managua

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

distribution of biogenic silica and quartz in recent deep sea sediments all available quartz and biogenic silica concentrations from deep sea surface sediments were intercalibrated plotted and contoured on a calcium carbonate free basis the maps show highest concentrations of biogenic silica opal along the west african coast along equatorial divergences in all oceans and at the polar front in the southern indian ocean these are all areas where upwelling is strong and there is high biological productivity quartz in pelagic sediments deposited far from land is generally eolian in origin its distribution reflects dominant wind systems in the pacific but in much of the atlantic and indian oceans the distribution pattern is strongly modified by turbidite deposition and bottom current processes

multivariate analysis of cross hole georadar velocity and attenuation tomograms for aquifer zonation 1 we have investigated the potential of combining cross hole georadar velocity and attenuation tomography as a method for characterizing heterogeneous alluvial aquifers a multivariate statistical technique known as k means cluster analysis is used to correlate and integrate information contained in velocity and attenuation tomograms cluster analysis allows us to identify objectively the major common trends in the tomographic data and thus to reduce the information to a limited number of characteristic parameter combinations the application of this procedure to two synthetic data sets indicates that it is a powerful tool for converting the complex relationships between the tomographically derived velocity and attenuation structures into a lithologically and hydrologically meaningful zonation of the probed region in addition these synthetic examples allow us to evaluate the reliability of further petrophysical parameter estimates we find that although absolute values of the tomographically inferred petrophysical parameters often differ significantly from the actual parameters the clustering approach enables us to reliably identify the major trends in the petrophysical properties finally we have applied the approach to a cross hole georadar data set collected in a well studied alluvial aquifer a comparison of the clustered tomographic section with well log data demonstrates that our approach delineates the hydrostratigraphic zonation

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

analysis of eccentered dipole antenna for borehole radar a dipole antenna in a borehole may be placed away from the center of the borehole and this eccentricity produces additional complicated electromagnetic fields which may influence borehole radar signals in this paper we analyze an eccentric dipole antenna in a borehole for borehole radars our approach is an extended version of the pseudoanalytical formulation that was previously applied for analyzing an induction logging tool and a dielectric logging tool the proposed equations are suitable for modeling the finite dipole antenna utilizing a method of moments the eccentricity of the radar sonde has two consequences first it modifies the antenna characteristics such as its impedance and second it changes the electromagnetic field inside the borehole owing to the change of the structure of the cylindrical layers these two changes are evaluated by the proposed algorithm and two types of experiments the first one is a measurement of the input impedance of a monopole antenna which is in cylindrical layers on a ground plane in air the second one is about the transmission between two antennas one of which is eccentered in cylindrical layers this experiment was done in granite at a field test site and on a ground plane in air in the field experiments we controlled the position of the radar sonde in a borehole and made the antenna eccentered artificially we found that a 4 cm displacement resulted in changes of 4 db in amplitude and 4 ns in time delay comparing the experimental and calculated data obtained by the present method shows the validity of the proposed analytical formulation

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

stratigraphic carbon isotope fluctuations of detrital woody materials during the aptian stage in hokkaido japan comprehensive δ13c data from four sections of the ashibetsu area abstract geological and organic geochemical studies were performed on an aptian mid cretaceous sedimentary succession of the sorachi and yezo groups in the ashibetsu area central hokkaido northern japan microscopic observations of kerogen samples indicate that the constituents of sedimentary organic matter som are predominantly detrital woody materials opaque and translucent phytoclasts hydrogen carbon atomic ratios of the kerogen samples indicate that the som have not been affected by thermal alteration significantly and thus preserved the original 13c compositions it is found that 13cwood profiles of four sections from the ashibetsu area fluctuate systematically with stratigraphy the 13cwood profiles show a remarkable negative shift followed by a positive excursion of 3 6 from 25 4 to 21 8 exhibiting a bifurcate shape in the early aptian 13cwood values become nearly constant between 23 0 and 23 5 and then approximate to 24 0 in the late aptian a relatively small positive anomaly is also identified in the latest aptian the similarity in 13cwood profiles among different sections suggests that som with homogenized 13c values of c3 plants were deposited in sediments transportation for a long distance from the sufficiently large provenance is postulated to mix c3 plant materials resulting in the homogenization of 13cwood values the 13cwood profile is essentially conformable with that of pacific marine carbonates with their isotopic difference almost constant at all times such conformable marine and terrestrial 13c variations support the previous hypothesis that the temporal 13c change of the aptian ocean atmosphere biosphere system is precisely traced by bulk isotopic analyses of detrital woody materials and the supplemental paleoenvironmental effects onto 13cwood composition such as pco2 changes are probably negligible

shallow open system evolution of basaltic magma beneath a subduction zone volcano the masaya caldera complex nicaragua abstract lavas and pyroclastic material from the masaya caldera complex have a number of distinctive geochemical features relative compositional homogeneity low al2o3 and high feo contents a tholeitic differentiation trend and elevated large ion lithophile lil element concentrations e g ba 800 ppm on cmas projections their compositions always fall on or near low pressure cotectics in addition the basalts of masaya have unusually high 87sr 86sr and 10be masaya has exhibited medium term compositional cycles best exhibited by the sawtoothed changes in tio2 and feo mgo there are also a number of longer term compositional changes which are abrupt and generally coincide with caldera formation many of the geochemical characteristics of masaya coupled with a number of volcanological observations indicate masaya is underlain by a large shallow open system magma chamber perhaps on the order of 10 km3 in size although fractional crystallization is a significant magmatic process in masaya s open system chamber magma mixing contamination is equally important magma mixing is necessary to explain the discontinuous stratigraphic changes in magma composition observed at masaya and crustal contamination is necessary to explain their generally elevated 87sr 86sr and lil element concentrations two components therefore have been admixed into the magma chamber of masaya a lil poor basaltic component such has been erupted from the nearby nejapa and granada cinder cones and a lil rich acidic component such has been erupted from the nearby calderas of apoyo and apoyeque admixtures of the former have dominated admixtures of the latter ended with caldera formation ironically open system behavior has exerted fundamental control on the maintenance of relative compositional homogeneity

compositional and isotopic characteristics of organic matter for the early aptian oceanic anoxic event at shatsky rise odp leg 198 the occurrence of intervals of enhanced sequestration of organic matter om during the mid cretaceous collectively termed oceanic anoxic events oae reflect abrupt changes in global carbon cycling these episodes raise questions about the causes for such perturbations and their linkages to fluctuations in climate marine biota and ocean geochemistry preserved in the sedimentary record detailed assessment of the early aptian event oae1a in the pacific has been precluded by the limited recovery of this stratigraphic interval in contrast to the many records from the tethyan realm the recovery of pelagic sequences of om rich sediments at site 1207 on shatsky rise odp leg 198 corresponding to oae1a has enabled recognition of high resolution temporal variations in the elemental and isotopic compositions of this event in the pacific however the continuous 45 cm om rich interval recovered is likely only the initiation of oae1a rather than a complete section based on natural gamma and uranium logs which suggest that the full thickness of this interval is 1 2 m exceedingly high organic carbon corg 20 and total sulfur ts 5 contents among the highest ever recorded for pelagic cretaceous sequences attest to the enhanced sequestration of om during oae1a 13corg values are lowest 27 7 at the base of the recovered om rich interval followed by a 2 4 positive shift this isotopic profile resembles part of the 13ccarb record at resolution guyot and is comparable with segments c3 and c4 of the cismon 13corg record low 15n values 2 provide evidence for nitrogen fixation perhaps coupled with elevated cyanobacterial populations that suggest that the marine nitrogen cycle in the cretaceous was different from the modern overall the temporal fluctuations in elemental and isotopic data through oae1a at shatsky rise describe differences in production and preservation of om that likely reflect variations in ocean conditions associated with both local and global environmental changes

radio tomography and borehole radar delineation of the mcconnell nickel sulfide deposit sudbury ontario canada in an effort to reduce costs and increase revenues at mines there is a strong incentive to develop high resolution techniques both for near mine exploration and for delineation of known orebodies to investigate the potential of high frequency em techniques for exploration and delineation of massive sulfide orebodies radio frequency electromagnetic rfem and ground penetrating radar gpr surveys were conducted in boreholes through the mcconnell massive nickel copper sulfide body near sudbury ontario from 1993 1996 crosshole rfem data were acquired with a jw 4 electric dipole system between two boreholes on section 2720w ten frequencies between 0 5 and 5 0 mhz were recorded radio signals propagated through the sudbury breccia over ranges of at least 150 m at all frequencies the resulting radio absorption tomogram clearly imaged the mcconnell deposit over 110 m downdip signal was extinguished when either antenna entered the sulfide body however the expected radio shadow did not eventuate when transmitter and receiver were on opposite sides of the deposit two dimensional modeling suggested that diffraction around the edges of the sulfide body could not account for the observed held amplitudes it was concluded at the time that the sulfide body is discontinuous according to modeling a gap as small as 5 m could have explained the observations subsequent investigations by inco established that pick up in the metal cored downhole cables was actually responsible for the elevated signal levels both single hole reflection profiles and crosshole measurements were acquired using ramac borehole radar systems operating at 60 mhz detection of radar reflections from the sulfide contact was problematic one coherent reflection was observed from the hanging wall contact in single hole reflection mode this reflection could be traced about 25 m uphole from the contact in addition to unfavorable survey geometry factors which may have suppressed reflections included host rock heterogeneity disseminated sulfides and contact irregularity velocity and absorption tomograms were generated in the sudbury breccia host rock from the crosshole radar radar velocity was variable averaging 125 m mus while absorption was typically 0 8 db m at 60 mhz kirchhoff style 2 d migration of later arrivals in the crosshole radargrams defined reflective zones that roughly parallel the inferred edge of the sulfide body the mcconnell high frequency em surveys established that radio tomography and simple radio shadowing are potentially valuable for near and in mine exploration and orebody delineation in the sudbury breccia the effectiveness of borehole radar in this particular environment is less certain

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

low latitude sea surface temperatures for the mid cretaceous and the evolution of planktic foraminifera isotopic data from exceptionally well preserved foraminifera show that the subtropical north atlantic had sea surface temperatures ssts between 30 and 31 c during the late albian and early cenomanian these temperatures were warmer than average modern temperatures in the tropical western atlantic and support previous inferences based on diagenetically suspect material of albian tropical ssts of 30 c this finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle cretaceous greenhouse however our data do not support the concept of a super tethyan region of hypersaline waters in the western north atlantic during late albian and early cenomanian time because seawater salinities substantially higher than modern ones would require significantly higher ssts than those reported here isotopic analysis of mid cretaceous planktic foraminifera shows that planomalina ticinella and biticinella grew in surface waters and provide isotopic proxies for sst whereas deeper growing species include hedbergella rotalipora and praeglobotruncana none of these taxa display isotopic indications of photosymbiosis suggesting that this ecology did not evolve in planktic foraminifera before the late cretaceous contrary to previous hypotheses none of these species increased their depth habitat during their life cycles unlike many extant planktic foraminifera the rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

new perspective on aptian carbon isotope stratigraphy data from δ13c records of terrestrial organic matter carbon isotope analyses were performed on detrital woody materials in aptian mid cretaceous marine sediments of central hokkaido northern japan a positive 13cwood excursion from 25 4 to 21 8 following a remarkable negative isotope shift is recognized in the early aptian and a small positive anomaly is also found in the latest aptian this 13cwood profile is exactly in phase with the 13ccarbonate curve from a pacific guyot when the age of the guyot carbonates is revised using published sr isotope stratigraphies the highly conformable 13c profiles of pacific and hokkaido sections suggest that 13c compositions of aptian marine and terrestrial carbon reservoirs changed simultaneously by the same amplitude within the ocean atmosphere biosphere system fluctuation patterns of tethyan 13ccarbonate curves are slightly different from those of pacific and hokkaido sections such differences in 13c profiles may be attributed to the local paleoceanographic setting of the aptian mediterranean tethys

lead isotope composition of central american volcanoes influence of the galapagos plume 1 lead isotopic analyses of lavas from central america both along and behind the volcanic arc help to clarify source components in the mantle wedge analysis of previous pb isotopic data had implied that little or no marine sediment lead was added to the central american source region as all samples fell within the morb field in contrast to other information e g ba la 10be 87sr 86sr that indicated a high subduction component the data presented here include several analyses of local marine sediment showing it to be exceptionally unradiogenic in pb and thus permitting high sediment contributions to the mantle source region without significant changes in pb isotopes combined pb nd and pb sr isotopic diagrams clearly illustrate the influence of crustal contamination for samples from guatemala and honduras and of subducted sediment for all lavas of the volcanic front samples collected behind the volcanic front are derived from mixing between enriched and depleted mantle sources and in central costa rica extending to the back arc overlap pb sr and nd isotope values for both cocos island and some components of the galapagos hot spot the restricted geographical occurrence of the enriched mantle signature in central america coupled with the persistence of the signal well into the back arc region imply that these lavas are sampling galapagos plume influenced mantle the presence of this plume component beneath southern central america and extending to the northeast beneath the caribbean confirms a galapagos hot spot origin for this part of caribbean plate

effects of gas and water filled boreholes on the amplitudes of crosshole georadar data as inferred from experimental evidence a special packer system is developed that replaces the water in a borehole with a gas and thus allows us to isolate the effects of the borehole filling media on crosshole georadar measurements we demonstrate experimentally that the radiative characteristics of borehole georadar antennas differ substantially for gas and water filled boreholes the main differences are a spectral shift to lower frequencies and a less focused radiation pattern in the case of a water filled borehole these effects are correctly predicted by a basic finite difference time domain fdtd modeling approach which offers the prospect for improving the quality of amplitude inversions from crosshole georadar data

litho and biofacies of early cretaceous rudist bearing carbonate sediments in northeastern japan abstract carbonate blocks of late aptian lower cretaceous age occur in the lower yezo group of central hokkaido in northeast japan the shallow water carbonates were emplaced by gravity sliding and rock fall into a deep water flysch basin various lithofacies can be distinguished within the blocks including massive wackestone bedded packstone and micro oncoid grainstone containing corals rudists an oyster gastropods calcareous algae and an orbitolinid foraminifer facies and palaeoecological analyses suggest deposition of low energy biostromes and sand banks in open lagoonal and restricted environments with local higher energy shoals and beaches the presence of calcareous sandstones and abundant insoluble residues in limestones suggest deposition in an attached carbonate platform close to a supply of terrigenous material rather than deposition upon seamounts within an oceanic setting a narrow rimmed shelf in tropical subtropical conditions would have been the depositional environment for these carbonates which were subsequently deformed into blocks and transported into deep water as a result of the tectonic collapse of the platform