187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

late pliocene caribbean surface water dynamics and climatic changes based on calcareous nannofossil records abstract quantitative analyses of nannofossil assemblages from two odp sites were performed to determine changes in the surface water structure in the caribbean sea and implications for climatic changes during the late pliocene analysis was made by calculation of accumulation rates and division of nannofossils into ecological groups based on their depth distributions and trophic regime oligotrophic vs eutrophic between 3 5 and 2 7 ma separate surface water masses existed in the northern and southern caribbean the northern surface water was strongly oligotrophic with a deep thermocline nutricline prior to 3 1 ma the southern caribbean was characterized by a shallower thermocline nutricline with minor upwelling induced by the presence of the past itcz intertropical convergence zone after 3 1 ma the thermocline nutricline deepened in the southern caribbean and the upper water became oligotrophic as a result of the completion of the closure of the isthmus after an episodic invasion of cooler surface waters associated with high latitude cooling at approximately 2 7 ma coccolith productivity in the caribbean was at its lowest a deep thermocline existed between 2 7 and 2 4 ma and nutrient depleted waters spread on the suw subtropical under water in the caribbean after 2 4 ma the increase of terrigenous materials from the south american continent caused an abundance of eutrophic taxa this suggests that recent climate systems were established due to the intensification of the northern hemisphere glaciation

temporal correlation between seismic moment and injection volume for an induced earthquake sequence in central oklahoma the rapidly increased earthquake rate in the central united states has been linked with wastewater injection while the overall understanding appears clear at large scales the interaction between injection and faulting at smaller scales within individual sequences is still not clear for an earthquake sequence in central oklahoma we conduct finer scale analysis of the spatiotemporal evolution of seismicity and pore pressure modeling the pore pressure modeling suggests that nearby wells show much stronger correlation with earthquake sequence evolution detailed temporal analysis found correlation between earthquake rate seismic moment and injection rates from wells in close proximity however the observed maximum magnitude mmax is about one order of magnitude smaller than expected based on a theoretical relationship between mmax and cumulative volume this discrepancy may point toward additional parameters such as fault size and stress which influence mmax the lower mmax is consistent with the truncated gutenberg richter distribution observed from matched filter detected catalog overall the detailed observations suggest that it is possible to resolve relationships between individual disposal wells and induced earthquake sequences

effect of early pliocene uplift on late pliocene cooling in the arctic atlantic gateway despite the undisputed role of the arctic ocean in the modern and pliocene climate system the arctic has only recently attracted public awareness that ongoing fundamental change in the arctic cryosphere could be a response to global warming clarification of the arctic s role in global climate during the pliocene is however largely hampered by equivocal stratigraphic constraints from a well dated pliocene sequence from the yermak plateau off nw spitsbergen we present sedimentological and geochemical data indicating that 4 million years ago terrigenous sediment supply and sources changed abruptly in response to a regional tectonic uplift event we argue that this event together with contemporary uplift and tilting along the northwestern european continental margin preconditioned the landmasses for glacial ice build up during intensification of the northern hemisphere glaciation inhg our data further suggest that the final deepening widening of the arctic atlantic gateway the fram strait between 6 5 and 5 ma gradually caused increased deep water mass exchange which in turn likely contributed to the intensification of the north atlantic thermohaline circulation coupled to the north atlantic warm pool as a regional moisture source declining atmospheric co2 levels and other feedback mechanisms during the pliocene the regional tectonic activities in the high northern latitudes caused decreased summer ablation and thus allowed the initial build up of glacial ice both in scandinavia and the sub aerially exposed svalbard barents sea culminating in the first large scale coastline shelf edge glaciations at 2 75 ma

spatiotemporal pore pressure evolution due to fluid mass point sources in dynamic poroelasticity summary the spatiotemporal behaviours of pore pressure induced by a fluid mass point source in quasi static and dynamic poroelasticity are compared and contrasted explicit results for the pore pressure in time domain are derived using the known fundamental solution of dynamic poroelasticity in frequency domain depending on the frequency content of the source function different regimes can be identified first the diffusive regime where only the diffusive slow wave exists the latter is equivalent to the process of pore pressure diffusion second there is the propagation diffusion regime where slow and fast wave modes coexist it is shown that the amount of induced pore pressure due to the diffusive slow wave is different for quasi static loadings e g fluid injection experiments and transient loads e g propagating low frequency seismic waves the results are discussed in the context of fluid injection experiments where short term fluctuations of the injection rate can create both the fast compressional wave and the slow diffusive wave the results can be used in order to generate synthetic seismograms and validate numerical schemes for pressure disturbances in dynamic poroelasticity

bayesian inversion of pressure diffusivity from microseismicity we have considered the problem of using microseismic data to characterize the flow of injected fluid during hydraulic fracturing we have developed a simple probabilistic physical model that directly ties the fluid pressure in the subsurface during the injection to observations of induced microseismicity this tractable model includes key physical parameters that affect fluid pressure rock failure and seismic wave propagation it is also amenable to a rigorous uncertainty quantification analysis of the forward model and the inversion we have used this probabilistic rock failure model to invert for fluid pressure during injection from synthetically generated microseismicity and to quantify the uncertainty of this inversion the results of our analysis can be used to assess the effectiveness of microseismic monitoring in a given experiment and even to suggest ways to improve the quality and value of monitoring

tracing sources of pollution in soils from the jinding pb zn mining district in china using cadmium and lead isotopes abstract systematic variations in the cd and pb isotope ratios in polluted topsoils surrounding the jinding pb zn mine in china were measured so that the sources of the metals could be traced the average 114 110cd value and 206pb 207pb isotope ratio in background soils from the region were 0 41 and 1 1902 respectively whereas the contaminated soil samples had different values with the 114 110cd values varying between 0 59 and 0 33 and the 206pb 207pb isotope ratios varying between 1 1764 and 1 1896 we also measured the cd and pb isotopic compositions in oxide ores sulfide ores and slags and found that binary mixing between ores and background soils could explain almost all of the variations in the cd and pb isotope ratios in the contaminated soils this suggests that cd and pb pollution in the soils was mainly caused by the deposition of dust emitted during anthropogenic activities mining and refining the pb and cd isotope ratios clearly showed that contamination in soils in the northeastern part of the area was caused by surface mines and zinc smelters and their slagheaps while contamination in soils in the southwestern part of the area also came from tailing ponds and underground mines the main area of soil polluted by dust from pb zn mining processes roughly extended for up to 5 km from the mine itself

glacial induced closure of the panamanian gateway during marine isotope stages mis 95 100 2 5 ma the final phase of the closure of the panamanian gateway and the intensification of northern hemisphere glaciation nhg both occurred during the late pliocene glacial interglacial g ig variations in sea level might therefore have had a significant impact on the remaining connections between the east pacific and the caribbean here we present combined foraminiferal mg ca and 18o measurements from ocean drilling program odp site 1241 from the east pacific and odp site 999 from the caribbean the studied time interval covers the first three major g ig marine isotope stages mis 95 100 2 5 ma 2 5 ma after the intensification of nhg analyses were performed on the planktonic foraminifera neogloboquadrina dutertrei and globigerinoides sacculifer representing water mass properties in the thermocline and the mixed layer respectively changes in sea water temperature relative salinity and water column stratification strongly suggest that the panamanian gateway temporarily closed during glacial mis 98 and 100 as a result of changes in ice volume equivalent to a drop in sea level of 60 90 m reconstructed sea surface temperatures sst from g sacculifer show a glacial decrease of 2 5 c at site 1241 but increases of up to 3 c at site 999 during glacial mis 98 and 100 suggesting that the panamanian gateway closed during these glacial periods the mg ca temperatures of n dutertrei remain relatively stable in the east pacific but do show a 3 c warming in the caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification we infer that the glacial closure of the gateway allowed the western atlantic warm pool to extend into the southern caribbean increasing sst g sacculifer and deepening the thermocline n dutertrei additionally ice volume appears to have become large enough during mis 100 to survive the relatively short lasting interglacial mis 99 so that the gateway remained closed towards the end of mis 98 during mis 97 and into mis 96 temperatures on both sides are mostly similar suggesting water masses exchanged again additionally caribbean variations in sst and 18owater follow a precession like cyclicity rather than the obliquity controlled variations characteristic of the east pacific and many other tropical areas suggesting that regional atmospheric processes related to the trade winds and the intertropical convergence zone itcz had a dominant impact in the caribbean

biogeography of neogene calcareous nannofossils in the caribbean and the eastern equatorial pacific floral response to the emergence of the isthmus of panama abstract principal components analysis of nannofossil assemblages in five odp sites in the caribbean and the eastern equatorial pacific was used to monitor neogene surface water circulation changes in 15 83 10 71 ma floral distributions clearly show the existence of the circum tropical current between the caribbean and the eastern equatorial pacific and no surface water communication between the northern and southern caribbean in 10 71 9 36 ma the circum tropical current weakened and the northward intra caribbean current had been initiated northern and southern caribbean surface waters again became separated in 8 35 3 65 ma and the circum tropical current was regenerated after 2 76 ma the northward intra caribbean current has completely been established and the circum tropical current disappeared this suggests that a barrier to the circum tropical current had formed indicating the final closure of the isthmus of panama

a preliminary study of cadmium mass fractionation in lunar soils abstract this preliminary investigation reports evidence of linear mass fractionation in cd in lunar soil samples the isotopic and elemental abundance of cadmium in five lunar samples has been measured with high precision using thermal ionization mass spectrometry and the stable isotope dilution technique respectively although both positive and negative mass fractionation for cd have been identified in meteorites this is the first time that cd isotope fractionation has been observed in lunar materials three of the four lunar soil samples analyzed gave positive in the sense that the heavy isotopes of cd are enriched with respect to a laboratory standard mass fractionation ranging in magnitude from 0 34 to 0 63 per mass unit cadmium is a volatile element and its elemental abundance in these fractionated lunar soil samples ranges from 57 to 112 ng g as compared to the solar system abundance of 686 ng g there is a possible inverse correlation between the magnitude of the mass fractionation and the concentrations for the same samples the fourth lunar soil sample which has a cd concentration approximately 11 times greater than the mean of the other soil samples gave zero mass fractionation the fifth sample is an orange colored glass spherule which gave a small negative mass fractionation volatilization by micrometeorite impact and ion sputtering are both likely to have contributed to the mass fractionation observed in these lunar soils it is also possible that redeposition of isotopically fractionated cd may have been a factor in the magnitude of the observed effect

characterization of hydraulic properties of rocks using probability of fluid induced microearthquakes the use of borehole fluid injections is typical for exploration and development of hydrocarbon or geothermal reservoirs such injections often induce small magnitude earthquakes the nature of processes leading to triggering of such microseismicity is still not completely understood here we consider induced microseismicity using as examples two case studies of geothermal reservoirs in crystalline rocks and one case study of a tight gas sandstone reservoir in all three cases we found that the probability of induced earthquakes occurring is very well described by the relaxation law of pressure perturbation in fluids filling the pore space in rocks this strongly supports the hypothesis of seismicity triggered by pore pressure moreover this opens additional possibilities of using passive seismic monitoring to characterize hydraulic properties of rocks on the reservoir scale with high precision

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

fields of multi kilometer scale sub circular depressions in the carnegie ridge sedimentary blanket effect of underwater carbonate dissolution offshore ecuador the carnegie ridge is a volcanic ridge with a carbonate sediment drape during the salieri cruise multibeam bathymetry was collected across carnegie ridge with the simrad em120 of the r v sonne the most conspicuous features discovered on the carnegie ridge are fields of circular closed depressions widely distributed along the mid slope of the northern and southern flanks of the ridge between 1500 and 2600 m water depth these circular depressions are 1 4 km wide and typically 100 400 m deep most are flat floored and some are so densely packed that they form a honeycomb pattern the depressions were carved into the ridge sedimentary blanket which consists of carbonate sediment and has been dated from upper miocene to upper pleistocene several hypotheses including pockmark origin sediment creeping paleo topography of the volcanic basement effects of subbottom currents and both marine and subaerial karstic origins are discussed we believe that underwater dissolution process merits the most serious consideration regarding the origin of the closed depression

circulation through the central american seaway during the miocene carbonate crash changes in circulation associated with the shoaling of the isthmus of panama and the caribbean carbonate crash in the miocene were investigated using nd isotopes from fossil fish teeth and debris from two sites in the caribbean basin ocean drilling program sites 998 and 999 and two sites in the eastern equatorial pacific sites 846 and 1241 the total range for nd values measured from 18 to 4 5 ma in the caribbean is 7 3 to 0 these values are higher than atlantic water masses 11 and range up to values equivalent to contemporaneous pacific water masses confirming that flow into the caribbean basin was composed of a mixture of pacific and atlantic waters with an upper limit of almost pure pacific sourced waters throughout the caribbean record particularly during the carbonate crash 10 12 ma low carbonate mass accumulation rates mars correlate with more radiogenic nd values indicating increased flow of corrosive pacific intermediate water into the caribbean basin during intervals of dissolution this flow pattern agrees with results from general ocean circulation models designed to study the effect of the shoaling of the central american seaway low carbonate mars and high nd values also correlate with intervals of increased northern component water production and therefore enhanced conveyor circulation suggesting that the conveyor may respond to changes in circulation associated with shoaling of the central american seaway reduced pacific throughflow related to shoaling of the seaway led to a gradual increase in carbonate preservation and more atlantic like nd values following the carbonate crash

evidence for middle eocene and younger land emergence in central panama implications for isthmus closure the rise of the isthmus of panama linked to a number of climatic paleoceanographic and biological events has been studied mostly from indirect often distal geochemical and biotic evidence we have upgraded existing geologic mapping in central panama with more than 2000 field stations over 40 petrographic analyses and more than 30 new geochronological and thermochronological analyses this data set suggests that the isthmus was an uninterrupted chain above sea level from late eocene until at least late miocene times the basement complex of central panama is a folded faulted 3 km thick arc sequence intruded by granitoid bodies and onlapped by mildly deformed upper eocene and oligocene strata six u pb zircon ages in the granitoids along with published geochronological data reveal intense late paleocene to middle eocene magmatism 58 39 ma a temporary cessation of magmatic activity between 38 and 27 ma and renewed magmatism between 25 and 15 ma in a position 75 km south of the former magmatic axis thermochronological analyses in zircon eight u th he ages and in apatite crystals four u th he ages and nine fission track ages obtained from a subset of 58 54 ma granitoid bodies record a concordant lutetian age 47 42 ma cooling from 200 c to 70 c in 5 m y and cooling below 40 c between 12 and 9 ma cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed upper eocene to oligocene terrestrial to shallow marine strata above exhumation and erosion of the basement complex are independently confirmed by lower miocene strata that have a detrital zircon signature that closely follows the central panama basement complex age distribution these results greatly restrict the width and depth of the strait separating southern central america from south america and challenge the widely accepted notion that the central american seaway closed in late pliocene time when the ice age began

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

a plate kinematic framework for models of caribbean evolution abstract we define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the caribbean region newly determined poles of rotation defining the approximate spreading histories of the central north and the south atlantic oceans are given for the late jurassic early cretaceous anomaly sequence of the central north atlantic we have used previously published definitions of fracture zone traces and magnetic anomaly picks redetermining the pole positions and angular rotations for various isochrons on an evans and sutherland interactive graphics system for magnetic anomalies younger than the cretaceous quiet period in both oceans we 1 used seasat altimeter data to help define fracture zone traces and 2 identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones by the finite difference method the relative paleopositions and the relative motion history between north and south america were computed this analysis defines the size and shape and the rate at which the size and shape changed of the interplate region between north and south america since the middle jurassic thus a plate kinematic framework is provided for the larger plates pertaining to the caribbean region in which can be derived more detailed scenarios for gulf of mexico and caribbean evolution north and south america diverged to approximately their present relative positions from late triassic to early campanian about 84 m y ago time this is the period during which the gulf of mexico and a proto caribbean seaway were formed since the campanian only minor relative motion has occurred from early campanian through to middle eocene times south america diverged only another 200 km and since the middle eocene minor n s convergence has occurred these very minor post early campanian motions have probably been accommodated by imperfect shear and compression along the atlantic fracture zones to the east of the lesser antilles and along the northern and southern borders of the caribbean plate accordingly it is suggested that from campanian time to the present the relative motions between the north and south american plates have had only minor effects on the structural development of the caribbean region primarily using the data of engebretson et al the convergence history of pacific plates with north america was calculated for two points near the western caribbean by completing finite difference solutions the convergence history of the pacific plates with the caribbean and south american plates can be approximated the direction and rate of convergence of the pacific plates with the americas may have controlled the style of subduction and possible microplate migration along the north american south american and western caribbean boundaries that define the eastern pacific plate margin

closing of the central american seaway and the ice age a critical review 1 what role did the closing of the central american seaway play in enabling continental ice sheets to wax and wane over north america and fennoscandia a summary of relevant evidence presented here permits a causal relationship between them but can be interpreted to show none the common denominator of such evidence is the approximate simultaneity of that closing with global cooling and the first major ice advance at the resolution of paleoclimate however geologic evidence from central america places only weak constraints on when interchange between pacific and caribbean water ceased the strongest evidence for when north and south america became connected by a continuous land bridge the great american exchange of vertebrates assigns climate change the causal role for an arid central american climate typical of glacial times seems necessary for animals that inhabited savannas to pass through panama paleoceanographic and geochemical studies of environments and water masses in the eastern pacific western caribbean and atlantic in general call for continual change since 6 ma or earlier if evidence concurrent with global change near 3 5 3 ma seems more widespread than for other times hypothesized connections between a closed seaway and glaciation commonly call for profoundly different north atlantic ocean circulation but simulations using general circulation models provide a spectrum of differences in circulation for open and closed seaways might much not all of the evidence implicating the closing of the seaway in global climate change in fact be a consequence of that change and blind to central america s tectonic development

the solar nebula redox state as recorded by the most reduced chondrules of five primitive chondrites abstract mafic minerals in the most reduced chondrules of five primitive meteorites were analyzed with an electron microprobe to determine the lower limit on their feo contents the accuracy obtained was 0 01 weight percent feo the thermodynamic relationship between mole fraction fesio 3 and po 2 of the ambient nebular gas at the time of mineral equilibration was established and was used to infer the local o h ratio of the nebular gas during chondrule formation the lowest ferrosilite compositions reflected equilibration at 1500k with a gas 2 18 times more oxidizing than a gas of solar composition olivines in low feo uoc chondrules are uniformly more feo rich than coexisting pyroxenes this discrepancy suggests that a significant change in the o h ratio of the nebular gas occurred between the time of olivine and pyroxene crystallization in the region of the nebula where uocs formed mineral compositions in the chondrules of two c2 chondrites studied suggest they formed in a more homogeneous region of the nebula than the uocs

seismic hydraulic fracture migration originated by successive deep magma pulses the 2011 2013 seismic series associated to the volcanic activity of el hierro island in this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of el hierro canary islands during 2011 2013 we estimated temporal variations of the gutenberg richter b value throughout the period of analysis and performed high precision relocations of the preeruptive and syneruptive seismicity using a realistic 3 d velocity model our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust these magma pulses occurred within a small and well defined volume resulting in the emplacement of fresh magma along the crust mantle boundary underneath el hierro we analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust our results suggest that very high earthquake rates underneath el hierro represent the response of a stable lower crust to stress perturbations with pulsatory character linked to the injection of magma from the mantle magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms the absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity had diffusive character we conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the moho we suggest within this framework that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

development of a pliocene mixed carbonate siliciclastic reef limon costa rica the miocene to pleistocene limon group of costa rica is a mixed carbonate siliciclastic succession that formed in association with the emergence of the central american isthmus our study focuses on a lower late pliocene reef unit the newly excavated contact cut which is located at the contact between the siliciclastic sediments of the rio banano formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the quebrada chocolate formation the siliciclastic sediments were deposited in a thick deltaic setting sourced by erosion of the cordillera de talamanca deposits of the limon group preserve a sequence of progressively shallowing near shore sediments that were exposed by uplift during the early to middle pleistocene the contact cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of caribbean coral reef predominance in the neogene it shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea level highstand three stages of reef evolution are recognized based on faunal diversity the contact cut reef complex is comparable to the time equivalent reef of the las islas roadcut situated west of limon which shows a rapid burial of the corals by siliciclastics both reefs document a distinct facies diversification during the final stages of the closing of the central american seaway the reefs developed in an environment stressed by siliciclastic input which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs the biotic composition of the patch reefs that occurred during the sea level rise las islas and contact cut did not differ from the reefs that developed during the final highstand in sea level the reefs of the overlying moin formation limon group differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs with a very fast give up scenario for las islas reef and a catch up followed by a give up phase for contact cut reef

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

chemical and physical studies of type 3 chondrites iii chondrules from the dhajala h3 8 chondrite abstract fifty eight chondrules were separated from the dhajala h3 8 chondrite and their thermoluminescence properties were measured chips from 30 of the chondrules were examined petrographically and with electron microprobe techniques the bulk compositions of 30 chondrules were determined by the fused bead technique porphyritic chondrules especially 5 which have particularly high contents of mesostasis tend to have higher tl mass normalized than non porphyritic chondrules significant correlations between log tl and the bulk cao al 2 o 3 and mno content of the chondrules and between log tl and the cao al 2 o 3 sio 2 and normative anorthite content of the chondrule glass indicate an association between tl and the abundance and composition of mesostasis unequilibrated chondrules i e those whose olivine is compositionally heterogeneous and high in ca have low tl whereas equilibrated chondrules have a wide range of tl depending on their chemical and petrographic properties we suggest that the tl level in a given chondrule is governed by its bulk composition which largely determined the abundance and composition of constituent glass and by metamorphism which devitrfied the glass in those chondrules with high ca glass to produce the tl phosphor we also suggest that one reason why certain chondrules in type 3 ordinary chondrites are unequilibrated while others are equilibrated is that the mesostasis of the unequilibrated chondrules resisted the devitrification this devitrification is necessary for the diffusive communication between chondrule grains and matrix that enables equilibration

isotope fractionation of cadmium in lunar material abstract the double spike technique has been used to measure the isotope fractionation and elemental abundance of cd in nine lunar samples the brownfield meteorite and the columbia river basalt bcr 1 by thermal ionisation mass spectrometry lunar soil samples give a tightly grouped set of positive isotope fractionation values of between 0 42 and 0 50 per mass unit positive isotope fractionation implies that the heavy isotopes are enhanced with respect to those of the laboratory standard a vesicular mare basalt gave zero isotope fractionation indicating that the cd isotopic composition of the moon is identical to that of the earth a sample of orange glass from the taurus littrow region gave a negative isotope fractionation of 0 23 0 06 per mass unit presumably as a result of redeposition of cd from the cd rich vapour cloud associated with volcanism cadmium is by far the heaviest element to show isotope fractionation effects in lunar samples the volatile nature of cd is of importance in explaining these isotope fractionation results although a number of mechanisms have been postulated to be the cause of isotope fractionation of certain elements in lunar soils we believe that the most likely mechanisms are ion and particle bombardment of the lunar surface

evolution of the northern nicaragua rise during the oligocene miocene drowning by environmental factors abstract possible causes to explain platform drowning have been hotly debated by carbonate sedimentologists for more than a decade now in this paper we present multiple evidence to explain the drowning of a carbonate megabank that covered most of the modern northern nicaragua rise nnr during an interval spanning from late oligocene to early miocene by the interaction of several environmental factors the recovery during odp leg 165 of late oligocene to middle miocene sedimentary sequences in the sub seafloor of the modern channels and basin pedro channel and walton basin respectively that dissect the nnr site 1000 and south of the rise in the colombian basin site 999 combined with information from dredged rock samples allows us to explore in more detail the timing and possible mechanisms responsible for the drowning of the megabank and its relationship to miocene climate change the modern system of isolated banks and shelves dissected by a series of intervening seaways and basins on the nnr has evolved from a continuous shallow water carbonate megabank that extended from the honduras nicaraguan mainland to the modern island of jamaica available information suggests that this megabank broke apart and partially drowned in the late part of the late oligocene at around 27 ma and finally foundered during the late early miocene around 20 ma resulting in limited neritic coral growth in the areas where the modern isolated carbonate banks and shelves are occurring today available information also suggests that the southern and central parts of pedro channel were already a deep water area before the major episode of platform drowning and its formation predates the initiation of the caribbean current however after the partial drowning of the megabank the channel has become a major pathway for the caribbean current stratigraphic units identified in deep water carbonates sampled at odp sites 999 and 1000 help to constrain the environmental setting leading to the drowning of the banks changes in lithology and mass accumulation rates of both the carbonate and non carbonate fraction parallel stable isotope shifts and likely indicate regional changes in climate and circulation during the late oligocene middle miocene interval carbonate mass accumulation rates mars at site 999 suggest increased regional productivity during the early miocene terrigenous mars at both sites 999 and 1000 show a general increase from the burdigalian through the serravallian the temporal association among episodes of neritic platform deposition followed by increased productivity as identified by higher carbonate mars and positive excursion in carbon isotopes suggests that oceanographic changes such as local upwelling and nutrification have led to the partial drowning of the nnr megabank

late neogene paleoceanography of the eastern caribbean the gulf of mexico and the eastern equatorial pacific abstract calcareous nannofossil census data from the late neogene of the caribbean the gulf of mexico and the eastern equatorial pacific were subjected to a multifold analysis in order to extract the paleoceanographic history of the region a detailed nannofossil biostratigraphy is the basic time framework the paleoenvironmental signals are deduced from fluctuations of diversity dominance and equitability through time by clustering of assemblages through time and examining the composition of cluster groups by comparison of fluctuations in carbonate content and coarse fraction with time and by factor analysis of the assemblage these measures variously reflect surface water characteristics such as productivity bottom water characteristics such as corrosiveness dissolution and conditions of sedimentation such as dilution of the pelagic biogenic carbonate diversity dominance and equitability which are determined by surface water characteristics show similar trends often in considerable detail in the caribbean and the gulf of mexico from the late miocene through pleistocene broad but definite similarities exist in these measures between the caribbean gulf of mexico and the eastern equatorial pacific in the late miocene to mid pliocene but not in the late pliocene clustering groups assemblages in a broad biostratigraphic pattern corresponding approximately to a major assemblage zone the structure and composition of cluster groups indicate strong similarity between the caribbean and the gulf of mexico during the late miocene through pleistocene but only weak similarity of the caribbean and gulf of mexico to the eastern equatorial pacific and only during the early pliocene surface water productivity is generally similar at the three locations into the late pliocene but seemingly diverges in the eastern equatorial pacific after about 2 4 m y variations in dissolution intensity have generally similar trends in the late miocene and early pliocene in the caribbean and the gulf of mexico but the trends diverge in the late pliocene and are dissimilar in the pleistocene in the eastern equatorial pacific dissolution intensity increases with the inferred thermal subsidence of the crust variations in the calcium carbonate content of the sediment essentially pelagic carbonate follow different trends at the three sites which is attributable to different sedimentary histories at the sites tectonic plus eustatic sea level changes for the caribbean eustatic sea level changes alone for the gulf of mexico and dilution by biogenic silica plus dissolution for the eastern equatorial pacific the various measured and derived parameters indicate that as late as the mid pliocene approximately 3 8 m y a deep water connection existed between the pacific and the caribbean gulf of mexico a shallower seaway permitting exchange of surface water between the pacific and gulf of mexico seems to have existed into the late pliocene to between 3 0 to 2 2 m y and final closure probably coincided with the sea level draw down associated with the initial buildup of a northern hemisphere ice sheet during the late pliocene and early pleistocene surface productivity oscillates markedly but seemingly with different intensities in the caribbean and the gulf of mexico the most important floral change occurs in both basins at about 0 9 m y when the smallgephyrocapsa dominated high productivity nannoflora of the preceeding 0 3 m y was replaced abruptly by a moderate productivity flora this turnover marks a major change in ocean circulation towards a relatively warm stably stratified tropical surface ocean which seems to have been affected remarkably little by some of the intense late pleistocene high latitude climatic changes

transition from the farallon plate subduction to the collision between south and central america geological evolution of the panama isthmus this paper presents new geological constraints on the collision of southern central america with south america and the resulting deformational episodes that have affected the panama isthmus since the late cretaceous the panama isthmus is located in southwestern central america and it represents the zone of contact between the two land masses central america and south america this collision event is still active today it has resulted in regional uplift since the late miocene pliocene and is responsible for the great american biotic interchange between south and north america depending on the methods of investigation used and due to the lack of data available the time when this collision began is still widely debated and poorly constrained to better constrain this age we have studied the rock formations and the tectonic deformations in central and eastern panama that have occurred since the late cretaceous this study presents new rock ages field work documentation and analyses and seismic line interpretations and it is complemented by spatial images for the eastern panama area during the middle eocene a number of changes suddenly appeared in the geological records that were synchronous with the break up of southern central america into two smaller blocks chorotega and choco our main results identify the prevalence of an extensional tectonic regime from the middle eocene to the middle miocene that caused the formation of horst and graben structures with thick sedimentary basin fills and a synchronous clockwise block rotation here we propose that these geologic events are associated with the initiation of the oblique collision of southern central america with south america the first contact of the southeastern extremity of central america occurred around 40 ma to 38 ma and then propagated northwestwards we describe here this long term collision episode in relation to the history of the panama isthmus

a method to allow temporal variation of velocity in travel time tomography using microearthquakes induced during hydraulic fracturing abstract hydraulic injections produce fluid filled fractures that reduce the seismic velocity of the rock compared to intact rock the travel times of microearthquakes induced by the injections may be used to discern changes in the rock velocities as well as locating the microearthquakes determining the volumes of rock where the velocities have changed provides indirect evidence for the location of the injected fluid and the character of the changes produced in the fractured rock available data are generally insufficient to resolve both the spatial and temporal changes within the rock to extract information about temporal changes and to obtain an improved image of the velocity structure we chose a parameterization scheme in which the velocities of each block are allowed to change from the background velocity only after a threshold number of microearthquakes have occurred in the block regularizing by constraining the velocity of all the altered blocks to be similar helps stabilize the inversion the regularization can be relaxed somewhat to allow the velocity of an altered block to be different from other altered blocks if the travel time data are compelling the parameterization scheme is justified since observations show that the volume of the seismically stimulated rock increases linearly with the volume of the injected fluid we applied the method to data collected in a region of precambrian crystalline rock that was injected with 21 600 m 3 of water we use travel times from a total of 3886 microearthquakes that were induced by the injection the mean rms travel time residual decreases about 7 the velocity structure contains a low velocity zone located near the injection region other distinct low velocity zones are identified the pattern of microearthquake locations found using our method appears to contain more structure than the pattern found in locations determined using a homogeneous velocity structure two clear low velocity regions found near the point where water was injected into the rock are separated by a region whose velocity did not change the region of unaltered velocity had a large number of microearthquakes

chemical and physical studies of type 3 chondrites 2 thermoluminescence of sixteen type 3 ordinary chondrites and relationships with oxygen isotopes thermoluminescence tl sensitivity values for sixteen type 3 ordinary chondrites fourteen of them from antarctica have been measured the values obtained normalized to the tl sensitivity of the dhajala meteorite range from 1 6 allan hills a77216 to 0 010 allan hills a77176 and include two reckling peak a80207 and allan hills a77176 that are particularly low they fill a hiatus in the tl distribution that previously existed between st mary s county and bishunpur the latter being a meteorite with one of the lowest tl sensitivities known the histogram of tl sensitivity values now shows a single distribution with higher values preferred it resembles the histogram for l chondrites occupying the petrologic types 3 4 5 and 6 there is a tendency for the tl sensitivity of meteorites to decrease as 18o increases equilibrated meteorites have tl sensitivities of 5 50 and 18o 4 5 to 5 0 while the most primitive meteorites with tl 0 01 have 18o 5 7 to 6 2 meteorites with intermediate tl have intermediate 18o theoretically it is possible that the range of 18o values observed may reflect progressive loss of o in the form of co at very low temperatures but very restrictive physical conditions and a complex history seem to be required

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

evolution of eastern pacific warm pool and upwelling processes since the middle miocene based on analysis of radiolarian assemblages response to indonesian and central american seaways a quantitative racholarian study at ocean drilling program site 1241 in the eastern tropical pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle miocene today this site is located just under the eastern pacific warm pool epwp based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes it is suggested that three notable changes occurred at 10 6 9 8 and 4 2 ma in the region four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following 1 stratified seawater 12 0 to 10 6 ma 2 a shallowing of the thermocline and an increasing of upwelling 10 6 to 9 8 ma 3 significant inflow of warm water to the eastern tropical pacific caused by an intensified northern equatorial countercurrent necc resulting in the formation of epwp 9 8 to 4 2 ma and 4 the reduction of the epwp and the necc and an increase in upwelling 4 2 to 0 ma the timing of these paleoceanographic events indicated the strong relations with the opening and closing of the indonesian and central american panama seaways the reduction of the epwp this study and the deepening of the thermocline in western pacific at about 4 2 ma cannariato and ravelo 1997 chaisson and ravelo 2000 indicated a change from a state resembling el nino in the late miocene and the early pliocene time to a state resembling la nina by the late pliocene c 2009 elsevier b v all rights reserved

benthic foraminiferal response to the emergence of the isthmus of panama and coincident paleoceanographic changes abstract late cenozoic benthic foraminiferal faunas from the caribbean deep sea drilling project dsdp site 502 3052 m and east pacific dsdp site 503 3572 m were analyzed to interpret bottom water masses and paleoceanographic changes occurring as the isthmus of panama emerged major changes during the past 7 myr occur at 6 7 6 2 3 4 2 0 and 1 1 ma in the caribbean and 6 7 6 4 4 0 3 2 2 1 1 4 and 0 7 ma in the pacific prior to 6 7 ma benthic foraminiferal faunas at both sites indicate the presence of antarctic bottom water aabw after 6 7 ma benthic foraminiferal faunas indicate a shift to warmer water masses north atlantic deep water nadw in the caribbean and pacific deep water pdw in the pacific flow of nadw may have continued across the rising sill between the caribbean and pacific until 5 6 ma when the pacific benthic foraminiferal faunas suggest a decrease in bottom water temperatures after 5 6 ma deep water to intermediate water flow across the sill appears to have stopped as the bottom water masses on either side of the sill diverge the second change recorded by benthic foraminiferal faunas occurs at 3 4 ma in the caribbean and 4 0 3 2 ma in the pacific at this time the caribbean is flooded with cold aabw which is either gradually warmed or is replaced by glacial bottom water gbw at 2 0 ma and by nadw at 1 1 ma these changes are related to global climatic events and to the depth of the sill between the caribbean and atlantic rather than the rising isthmus of panama benthic foraminiferal faunas at east pacific site 503 indicate a gradual change from cold pdw to warmer pdw between 4 0 and 3 2 ma the pdw is replaced by the warmer poorly oxygenated piw at 2 1 ma although the pdw affects the faunas during colder intervals between 1 4 and 0 7 ma the piw remains the principal bottom water mass in the guatemala basin of the east pacific

surface temperatures of the mid pliocene north atlantic ocean implications for future climate the mid pliocene is the most recent interval in the earth s history to have experienced warming of the magnitude predicted for the second half of the twenty first century and is therefore a possible analogue for future climate conditions with continents basically in their current positions and atmospheric co2 similar to early twenty first century values the cause of mid pliocene warmth remains elusive understanding the behaviour of the north atlantic ocean during the mid pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change under the framework of the pliocene research interpretation and synoptic mapping prism sea surface reconstruction we synthesize mid pliocene north atlantic studies by prism members and others describing each region of the north atlantic in terms of palaeoceanography we then relate mid pliocene sea surface conditions to expectations of future warming the results of the data and climate model comparisons suggest that the north atlantic is more sensitive to climate change than is suggested by climate model simulations raising the concern that estimates of future climate change are conservative

hydraulic fracturing controlled dynamics of microseismic clouds 1 several dynamic processes related to propagation of hydraulic fracture modify the stress state in rocks and therefore they are relevant for triggering of microseismicity for instance these are the creation of a new fracture volume fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the pore space of surrounding rocks and inside the fracture using real data we show that some of these processes can be seen from features of spatio temporal distributions of the induced microseismicity especially the initial stage of fracture volume opening as well as the back front of the induced seismicity starting to propagate after termination of the fluid injection can be well identified and used for reservoir engineering

mass dependent cadmium isotopic variations in nature with emphasis on the marine environment abstract we report a survey of natural mass dependent cadmium isotope fractionation measured by thermal ionization mass spectrometry using a double spike technique ds tims over sixty samples of natural terrestrial cd from diverse environments including morb oib continental loess hydrogenic and hydrothermal ferromanganese deposits and sphalerites both oceanic and from major continental ore deposits were analysed our results are expressed in terms of e 112 110 cd which are deviations in 112 cd 110 cd from our in house jmc cd standard in parts per 10 4 the total e 112 110 cd variation is relatively small with a range of only 5 e units and is one to two orders of magnitude smaller than that previously found in meteorites the morb oib and loess e 112 110 cd values are similar and provide a good estimate for the bulk silicate earth bse value which is 0 95 0 12 relative to our cd standard e 112 110 cd 0 16 relative to munster jmc cd taken together these data suggest little cd isotope fractionation takes place during crust mantle segregation cd isotopic compositions of continental sphalerite zns deposits worldwide and high temperature oceanic hydrothermal sulphides show remarkably similar e 112 110 cd values consistent with our estimate for the bse in contrast mid temperature oceanic sulphides from a single extinct hydrothermal chimney display over 4 e units variation along with the most negative values these variations are most probably caused by precipitation redissolution of sulphide phases en route within the hydrothermal system the e 112 110 cd variability found in worldwide marine fe mn deposits reflects the seawater cd isotope signal upon precipitation from ambient seawater a decrease in e 112 110 cd is observed in passing from shallow water fe mn deposits to those from deeper waters 2000 m depth this shift is explained by biological fractionation related to the uptake of dissolved seawater cd by phytoplankton in the upper water column the relatively uniform e 112 110 cd values close to zero at great depths are consistent with regeneration and remineralization of cd at depth our data suggest that cd isotopes much like the cd ca ratio in foraminifera could potentially serve as a proxy for past changes in biological productivity the temporal cd isotope record in a fe mn crust archive at 2000 m depth from the ne atlantic suggests no gross long term changes in cd cycling took place over the past 8 ma

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2

cadmium mass fractionation in unequilibrated ordinary chondrites abstract measurements of the isotopic composition of cadmium in whole rock samples of a number of unequilibrated ordinary chondrites have shown the presence of significant fractionation in the abundances of the isotopes some meteorites are enhanced in the light isotopes with respect to a laboratory standard whilst the reverse effect is exhibited in other meteorites the mass fractionation is linear over the range 106 116 within the limits set by experimental error the extent of the mass dependent fractionation varies from 2 1 per mass unit for light isotope enrichment for the ll3 chondrite semarkona to 2 7 per mass unit for thell3 chondrite bishunpur this is the first time that negative mass fractionation has been reported for cadmium in meteoritical material the cause of the fractionation is not known if rayleigh distillation were responsible then some correlation with cd concentration would be expected but this is not observed there does not appear to be a correlation between the magnitude of cadmium fractionation and abundance in whole rock samples of unequilibrated ordinary chondrites

late middle miocene segmentation of an eocene early miocene carbonate megabank on the northern nicaragua rise tied to the tectonic activity at the north america caribbean plate boundary zone the northern nicaragua rise nnr is comprised today of the eastern honduras nicaragua and southern jamaica carbonate shelves and a series of relatively small detached carbonate banks i e pedro rosalind serranilla diriangen and bawika banks separated from each other by intervening basins and seaways the nnr basins and seaways because of their common north trending orientation have been previously interpreted as paleocene eocene and possibly oligocene rifts becoming progressively younger from the eastern to the western part of nnr results from three recent 1988 and 1992 high resolution seismic surveys within these major seaways and basins 1 walton basin 2 pedro channel and 3 seaways and serranilla basin on the western side of the nnr show that the present bank and basin configuration evolved from a once continuous megabank that covered the entire length of the nnr including the island of jamaica from eocene through early miocene times in the late middle miocene this megabank progressively broke up into a series of smaller banks basins and seaways mainly as the result of tectonic movements related to the overall strike slip displacement within the north american and caribbean plate boundary zone of the cayman trough at the same time late middlemore miocene the most eastern portion of the megabank was uplifted and today forms most of central and south jamaica the timing of the megabank segmentation has tentatively been constrained by dating several blocks of shallow water limestone dredged from parts of the megabank outcropping on the sea floor of different seaways less

late neogene benthic stable isotope record of ocean drilling program site 999 implications for caribbean paleoceanography organic carbon burial and the messinian salinity crisis we report on epibenthic foraminiferal 18o and 13c and percentage coarse fraction records from caribbean ocean drilling program odp site 999 12 44 n 78 44 w water depth 2828 m spanning the interval from 8 5 to 5 3 ma low epibenthic 13c values and low amounts of sand sized particles mostly foraminifer shells indicate a poorly ventilated deep caribbean throughout the late miocene at this time the deep caribbean was dominated by a nutrient rich and corrosive water mass a generally constant 13c gradient between the caribbean and deep atlantic records during the late miocene suggests that the fluctuations in 13c reflect global changes in 13c of the dissolved inorganic carbon due to varying erosion of organic carbon from terrigenous soils and shelf sediments the observed 100 kyr cyclicity of epibenthic 13c is in good accordance with the variability of terrigenous input to the equatorial atlantic as recorded by magnetic susceptibility records of the ceara rise however some short term gradient changes between 7 0 and 4 5 ma indicate a poorer ventilation of the deep atlantic related to a reduced production of deep water in the atlantic the messinian salinity crisis between 6 0 and 5 3 ma did not affect the intermediate to deep water gradient between the caribbean and the atlantic comparison to the bahama platform record of odp site 1006 however indicates a poorer ventilation of the shallower northern caribbean basins coincident with the isolation of the mediterranean sea

the relationship between microseismicity and high pore pressures during hydraulic stimulation experiments in low permeability granitic rocks several hundred microearthquakes with local magnitudes ranging between 4 and 2 were recorded during hydraulic stimulation experiments at the hot dry rock demonstration site fenton hill new mexico these events are probably caused by shear failure induced by high pore fluid pressures since the event locations seem to cluster in a narrow band near the hydraulic fracture we were able to use micro seismic techniques to locate the hydraulic fracture and monitor its growth we calculate the minimum pore pressure increase necessary to induce rock failure using a simple model of slippage on preexisting fractures by comparing a pore pressure distribution calculated using a one dimensional diffusion model with the distribution of event foci we demonstrate that high pore pressures are a probable cause for these microearthquakes stress drops for these microearthquakes calculated from spectral parameters increased by a factor of 3 during the course of the experiment the stress drop increase correlates with a migration of seismic activity away from the injection well bore which suggests relatively low in situ shear stresses near the well bore caused by strain release in this region during previous pressurizations

late miocene washhouse climate in europe abstract we present two eight million year long proxy records of precipitation for southwest and central europe covering the middle to late miocene 5 3 13 ma at a temporal resolution of about 60 kyr and 150 kyr respectively the estimates of precipitation are based on the ecophysiological structure of herpetological assemblages amphibians and reptiles from 13 0 ma until about 9 ma both records show a similar trend evolving from a long dry period 13 11 ma into a washhouse climate 10 2 9 8 ma characterized by global warm conditions and several times more precipitation than present the transition from washhouse to a dryer climate between 9 7 and 9 5 ma and the concomitant cooling episode appear to have triggered a severe biotic event known as the vallesian crisis which included the extinction of hominoids in western europe a second washhouse period 9 0 8 5 ma coeval with a global warm episode was unprecedentedly intense in southwest europe but less pronounced in central europe from 8 ma onward a divergence in the two precipitation records is observed with southwest europe staying wetter and central europe becoming dryer than present both precipitation records are combined into a common run off curve as a measure of the relative intensity of the hydrological cycle for moderate latitudes of continental europe the run off curve shows a remarkable positive correlation with atlantic deep water temperatures from ceara rise by lear et al 2003 which are significantly higher up to 3 c during the two washhouse periods and show no other positive excursion of comparable magnitude we discuss potential links and the role of the coeval temporary restriction of the central american seaway on ocean and atmosphere circulation

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

drastic change in the geographical distribution of the cold water nannofossil coccolithus pelagicus wallich schiller at 2 74 ma in the late pliocene with special reference to glaciation in the arctic ocean abstract we reconstruct the late pliocene to quaternary paleoceanography of the pacific and atlantic oceans based on the geographical distribution of coccolithus pelagicus wallich schiller which has been regarded as a typical cold water species at 2 74 ma the distribution of c pelagicus defines a biogeographical boundary in the marginal seas of mid to high latitude regions of the pacific such as near the japanese islands kuril islands kamchatca peninsula aleutian islands alaska and the northeastern pacific off canada the relative abundance of c pelagicus is greater than 80 in these marginal sea areas in the north pacific and japan sea on the basis of characteristics of the nannofossil assemblages and recent nannoplankton biogeography in the norwegian greenland sea the change in the relative abundance of c pelagicus at 2 74 ma is thought to be the result of the southward migration of most species except c pelagicus with the onset of heavy glaciation the results also indicate that the geographical distribution of c pelagicus changed in three steps at 2 75 1 65 and 1 2 ma and it became rare to barren in low latitude regions

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

abrupt intensification of north atlantic deep water formation at the nordic seas during the late pliocene climate transition knowledge of the evolution of north atlantic deep water nadw is key to understanding the past evolution of the climatic system here we developed a new rock magnetic method to determine the constituent magnetic minerals of sediments and report on the evolution of nadw during 2 2 2 9 ma we measured isothermal remanence acquisition curves of north atlantic deep sea sediments drilled at the gardar drift and decomposed the first derivatives of these curves into high coercivity and low coercivity components residuals of the decomposition were sufficiently small throughout the study interval confirming that the gardar drift sediments represent a mixing of the two end members fractional changes of the high coercivity component represent variation of the iceland scotland overflow water a branch of nadw formed at the nordic seas the high coercivity component increased significantly during an interglacial period just after 2 68 ma which suggests that nadw formation in the nordic seas abruptly intensified at this time

pushing the limit of earthquake detection with distributed acoustic sensing and template matching a case study at the brady geothermal field template matching has been widely applied in the detection of earthquakes and other seismic events due to its power in detecting weak signals recent studies using synthetics have shown that application of template matching to large n arrays can potentially detect earthquakes substantially below the noise level here we apply template matching to the distributed acoustic sensing das data recorded in the brady hot springs geothermal field nevada using 5 catalogued events we detect 116 events and find 68 of them well below the noise level we confirm 112 events are true earthquakes by examining the patterns of their sensor to sensor cross correlation sections this demonstrates that the combination of das and template matching has capability to detect microseismicity below the noise level which is unusual for conventional seismic arrays and methods with the updated catalogue we observe a surge of earthquakes during the shutdown of a geothermal power plant nearby in addition the rapid increases in the downhole pressure record coincide with intense swarms of earthquakes these observations show a strong correlation between the seismicity frequencies and the downhole pressure changes finally we investigate several factors that may affect the detection performance and compare different strategies for spatial down sampling in order to provide helpful insights for future large n design and data processing

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

unequilibrated ordinary chondrites a tentative subclassification based on volatile element content for unequilibrated ordinary chondrites uoc two measures of primitiveness are available volatile content in principle reflecting accretion conditions from the solar nebula and metamorphism reflecting reheating in the parent bodies these two measures do not always correlate and we have therefore developed a tentative classification scheme based on volatile content that complements the searset al 1980 scheme based on metamorphism like the latter it subdivides type 3 chondrites on a scale of 3 0 to 3 9 the notation 3 4 0 indicates a meteorite that is subtype 3 4 according to metamorphism and 3 0 according to volatile content the classification is based mainly on c and xe two elements that are little affected by shock induced reheating and to a lesser extent on ar36 bi in and tl of 22 meteorites considered the majority have concordant classifications 0 2 on the two scales however 5 meteorites are richer in volatiles than their metamorphic grade indicates sharps 3 4 0 alha 77011 3 5 0 ngawi 3 6 3 alha 77299 3 7 4 and mezo madaras 3 7 3 it remains to be seen whether these differences indeed denote a more primitive nature some new clues to the formation of chondrites may eventually come from xe and c their concentrations in uoc s vary by more than 5 but the xec ratio remains nearly constant at 3 4 10 3 of the solar system ratio even the ratios for other chondrite classes differ only slightly from that for uoc s e g c3o 1 5 and e3 4 0 4 either the 4 factors determining this ratio t t p and internal surface area of the carbon varied in complementary fashion or more probably they varied only slightly in the entire source region of chondrites

global cooling in marine climates and local tectonic events in southwest japan at the plio pleistocene boundary abstract this study reconstructs the temporal changes in water temperature and depth on the pacific coast of southwest japan from the latest pliocene to the earliest pleistocene ca 2 6 ma on the basis of the modern analog technique mat of fossil ostracodes and factor analysis of fossil planktonic foraminifera from the takanabe formation around the plio pleistocene boundary the mat results reveal that the mean annual warmest month and coldest month temperatures of bottom water were estimated at ca 6 17 6 17 and 6 16 c respectively the bottom water temperature before 2 6 ma was similar to modern temperatures of the study site since then the temperature dropped several degrees moreover the result of the analysis of fossil planktonic foraminifera suggests that the study site clearly changed from a marine climate under the influence of the axial part of the kuroshio current to that of transitional water at around 2 6 ma thus the results of the microfossil analysis reveal for the first time that a global cooling event at the plio pleistocene boundary influenced the pacific coast of sw japan the change in water depth at ca 2 6 ma in the study site was estimated to have been extremely large in comparison with the global sea level fluctuations during the late pliocene suggesting that the tectonic movement related to the rotation of the southern kyushu island southwest japan started at ca 2 6 ma and that subsidence occurred in the study area

middle to late miocene caribbean dinoflagellate assemblages and palynofacies dsdp leg 15 site 153 abstract changes in oceanic circulation and productivity patterns near central america have been explained using numerous different tools such as tectonics geochemistry and micropaleontology this paper aims to contribute to this discussion through the study of dinoflagellates and palynofacies in the drill core from dsdp site 153 based on foraminiferal data the studied section is divided into the middle and upper miocene and our dinoflagellate events also support an age model of 15 to 8 ma indval ecological indexes and the p g dinoflagellate ratios were used to develop paleoenvironmental inferences the indicator species are operculodinium centrocarpum and tectatodinium pellitum for the mm1 interval spiniferites spp and impagidinium strialatum for mm2 and selenopemphix armageddonensis lejeunecysta spp and l tenella for um3 intervals mm1 and mm2 are characterized by a dominance of gonyaulacoids and inner to outer neritic environments the um3 interval is interpreted as an outer neritic environment in the base middle portion and inner neritic in the uppermost part with a shift from gonyaulacoid to peridinioid dominance suggesting an increase in productivity during the middle miocene productivity is low due to intermittent marine circulation restrictions in the caribbean sea and there is a slight increase during the upper miocene following reestablishment of the global oceanic circulation this is directly connected to the occurrence of geotectonic and paleoceanographic events in the region during the miocene mainly by mass movements such as the panama gateway and the opening of the pedro channel to the north changing the surface conditions in the caribbean sea

pliocene pleistocene planktonic foraminifera from the east pacific ocean off costa rica and their paleoceanographic implications abstract planktonic foraminifera from the ocean drilling program holes 1039b 1040c and 1043a off costa rica in the east pacific ocean indicate that the surface seawater temperature abruptly declined four times during the late pliocene early pleistocene these events occurred in the lower part of zone n19 5 4 2 ma the basal part of zone n22 ca 2 ma the middle part of zone n22 ca 1 5 ma and the basal part of zone n23 ca 0 65 ma the maximum divergence of surface and intermediate water dwellers begins at the basal part of zone n22 ca 2 ma which signals cooling episodes and faunal changes suggesting responses to the closing of the central american seaway

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

paleoceanography and the diachrony of radiolarian events in the eastern equatorial pacific the development of an orbitally tuned time scale for the odp leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework with this framework we are better able to define which of the first and last appearances of species appear to be synchronous in addition the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped these maps not only provide information on the process of evolution migration and extinction they can also be related to water mass distributions and near surface circulation of the ocean of 39 radiolarian events studied at 11 sites in the eastern equatorial pacific 28 were found to have a minimum range in their estimated age that exceeded 0 15 m y the temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 ma these changes in the locations of high gradient regions suggest that the south equatorial current sec was north of its present position prior to approximately 7 ma there was a southward shift in the northern boundary of this current between approximately 6 and 7 ma and the development of a relatively strong gradient between the northeastern and northwestern sites between approximately 3 7 and 3 4 ma there was a very slight northward shift in the northern boundary of the sec and the steep gradients between the northeastern and northwestern sites may have disappeared this change is thought to be associated with the closing of the isthmus of panama the temporal spatial patterns of diachronous events younger than 3 4 ma are consistent with patterns of circulation in the modern ocean

influence of the amazon river development and constriction of the central american seaway on middle late miocene oceanic conditions at the ceara rise abstract sediment samples from odp 154 site 926a ceara rise western equatorial atlantic ocean spanning the neogene from 12 8 to 9 2 ma were investigated on their calcareous dinoflagellate contents to better understand the oceanographic changes in relation to the closure of the central american seaway and the development of the amazon river intervals with increased cyst accumulation rates and dissolution sensitive species occur from 12 4 ma onward they correspond to periods of enhanced north atlantic deep water production indicating the presence of this water mass at the research site during these intervals this suggests that pulses of north atlantic deep waters sporadically flew into the south atlantic related to uplift phases of the panama sill at about 11 2 ma the first appearance of leonella granifera indicates river influence at the sample site this first indication of river influence in the western equatorial atlantic can be linked to the developing amazon river the cyst association changes at about 11 2 ma from almost monospecific to highly diverse and the permanent presence and increased abundance of l granifera suggest that river waters were able to reach the study site by now probably as a result of the southward flowing north brazil current after 10 5 ma the cyst association indicates a decrease in amazon influence at site 926a this change can be correlated to a reducing inflow of pacific waters through the central american seaway leading to a reverse of the north brazil current to its modern northwards flow pattern

locating microearthquakes induced by hydraulic fracturing in crystalline rock microearthquakes induced by hydraulic fracturing in crystalline rock at a depth of 3 5 km were located with a precision of better than 30 m to obtain information about the geometry and dimensions of the fracture system produced the induced microseismicity was monitored by a network of five vorehole seismic stations a total of about 800 induced events were reliably located from arrival times event locations show a tabular distribution that strikes 350 sup 0 and dips 65 sup 0 east subparallel to the injection well the injection was intended to produce a fracture system that would hydraulically connect two subparallel wells a lack of fluid communication between them is consistent with a lack of induced microearthquakes near the target wellbore the 150 m thickness of the zone of seismicity far exceeds the relative locational uncertainties the injected fluid appears to have stimulated a zone of rock rather than simply a single fracture the distribution of microseismic events presumably envelopes the zone of fluid paths created by the fracture experiment

filtration fronts in pressure compliant reservoirs hydrofracturing is believed to be the major mechanism responsible for the migration of crust fluids and for the transport of hydrocarbons from overpressured fluid compartments in their analysis of the process of porosity reduction in the earth s crust and crustal pore pressure generation walder and nur 1984 point out that elevated pore pressure generated as a result of local porosity reduction may lead to brittle failure with partial relief of high pore pressure such episodic fracturing accompanied by crack healing may be a common process throughout most of the crust hunt 1990 also speculates that the generation of oil and gas within the compartments plus the thermal expansion of pore fluids eventually causes fracturing of the top compartment seal during periods of basin sinking seal fracturing causes a pressure drop with compartment fluids rushing to the breakout point episodic cycles of resealing and breakout may occur in intervals of thousands of years in rapidly sinking basins such as the u