shrimp zircon u pb dating of quartz porphyry from zhongjia tin polymetallic deposit in longyan area fujian province and its geological significance mineralizations of the zhongjia tin polymetallic deposit in longyan area of fujian province are composed of vein type ore bodies in the external contact zone and veinlet disseminated sn wo mineralization in the inner contact zone belonging to post magmatic hydrothermal type related to quartz porphyry of the area shrimp u pb dating of twenty zircon grains from the quartz porphyry gived the weighted mean age of 98 5 1 7 ma n 29 mswd 1 8 suggesting that the quartz porphyry in the deposit was produced by regional tectono magmatic activities during the late stage of early cretaceous tin polymetallic mineralization of the zhongjia deposit occurred in late cretaceous instead of in early jurassic and constituted a part of late yanshanian metallogenic activity on the margin of the south china tungsten tin and polymetallic province as evidenced by regional metallogenic correlation the authors hold that the prospecting targets of tin polymetallic deposits in southwestern fujian province should be late yanshanian granitic bodies and their external contact zones

was the 16 august 1997 seismic disturbance near novaya zemlya an earthquake the reviewed event bulletin for 16 august 1997 produced by the prototype international data center pidc reported a small seismic disturbance in the vicinity of the northern russian test site at novaya zemlya at about 02 11 utc initial reports suggested that this disturbance was caused by a small nuclear explosion whereas others identify the source as an earthquake using vertical component s p ratios however other authors show evidence that questions the validity of the s p method for this region and conclude that the disturbance cannot be positively identified as an earthquake using seismological evidence the apparent attenuation from the 16 august 1997 disturbance to spits spitsbergen distance 1280 km azimuth 317 is reported to be weak similar low attenuation is suggested from high frequency observations at kev kevo finland 1130 km azimuth 268 thus high frequency p and s waves propagate efficiently across the barents sea leading to the possibility that the radiation pattern of the source may be inferred we show using a grid search method that the high frequency sv sh amplitude ratios observed at spits and kev measured from the complex envelopes of the free surface corrected three component seismograms combined with simple p n signals with positive first motion at hfs hagfors sweden and nores norway are consistent with a double couple source with a range of orientations we compute synthetic seismograms for one such double couple source oriented at 255 115 120 similar to that reported for the 1 august 1986 kara sea earthquake the synthetic p n seismograms at hfs and nores and the relative sv sh amplitudes of the synthetic s n seismograms at kev and spits match those observed reasonably well our model also predicts 1 weak p n at nri norilsk russia suggesting that the emergent p n onset and low signal to noise ratio observed is related to the focal mechanism and 2 the negative p first motion and large sh sv ratio observed at amd amderma 360 km azimuth 152 thus we conclude that the 16 august 1997 seismic disturbance was an earthquake beneath the kara sea and that identification is possible using only data that would normally be available to the pidc assuming kev can be used as an alternative for the nearby station arces which was not working at the time of the disturbance

associations between burial diagenesis of smectite chemical remagnetization and magnetite authigenesis in the vocontian trough se france results of a paleomagnetic rock magnetic geochemical and petrographic study on jurassic and cretaceous carbonates in the vocontian trough support a hypothesized connection between burial diagenetic alteration of smectite and the widespread occurrence of a chemical remanent magnetization crm carried by magnetite where smectite has altered to other clay minerals limestones are characterized by a prefolding secondary normal polarity magnetization throughout the basin the magnetization is interpreted to be a crm based on low burial depths which cannot cause thermoviscous resetting where significant smectite is still present the crm is absent weakly developed and where the clays show no evidence for burial alteration the units are characterized by a primary magnetization crm intensity also varies with the amount of smectite and burial isothermal anhysteretic and natural remanent magnetization intensities increase where smectite has altered both stratigraphically and geographically this is interpreted to indicate magnetite authigenesis associated with clay diagenesis superparamagnetic magnetite is more dominant in highly altered units based on the results of low temperature experiments all sections away from the alps have 87sr 86sr values that are similar to coeval seawater and stable isotopes of carbon and oxygen show no sign of alteration orogenic type fluids therefore are not a likely agent of remagnetization near the alps the rocks are characterized by an additional reversed polarity component which is interpreted to reflect acquisition of the crm through a reversal a postfolding magnetization is also present there and strontium isotopic ratios are higher than elsewhere in the basin and might indicate some alteration by orogenic type fluids we conclude that burial diagenesis of smectite is the likely cause for the development of the widespread crm in the vocontian trough and that this mechanism might explain widespread chemical remagnetization elsewhere

regional metallogeny of tungsten tin polymetallic deposits in nanling region south china abstract the nanling region gains its reputation for abundant mineral resources especially w sn sb bi pb zn li be ta nb and ion adsorption ree within weathering crust as well as uranium these dominant mineral resources are mainly formed in the yanshanian period with intimate genetic relationship to yanshanian granitoids spatially tungsten and tin deposits separately occurred in the eastern and western parts of nanling region respectively the complicated genetic relationships between tungsten tin polymetallic deposits and nanling granitoids demonstrate a regularity for mineralization we named this metallogenic specialization reflected in the aspects of specialized metallogenic compositions age spatiality alteration and its geological background the metallogenic specialization regional metallogeny is important to discover mineralization lay the foundation a new exploration model named five levels basement was proposed in this paper now it became a prospecting guidance in nanling region recently the ongoing prospecting of large tungsten deposits in nanling and its adjacent region using this model indicates a northward expanding for tungsten deposits in the south part of study area and westward expanding for that in the eastern part in practice the model also can be used in deep prospecting e g deep seated bedded or bed like orebodies as well as not limited to tungsten deposits other mineral deposits

seismic models of a prograding carbonate platform vercors south east france abstract the southern vercors area south east france displays superb exposures of a lower cretaceous prograding carbonate platform these exposures allow a geometrical sequence analysis to be combined with detailed outcrop observations two dimensional seismic modelling techniques were used to determine the seismic response of three of these exposures the montagnette the archiane valley and the rocher de combau the outcrops display prograding and retreating series of clinoforms interfingering with fine grained basinal sediments photographs from different angles of view combined with detailed field observations were used to construct lithological profiles with a resolution of f few metres p wave velocities and bulk densities were measured from cored hand specimens and selected values were assigned to lithostratigraphic units in each profile the vertical incidence modelling technique was then used to compute migrated time sections of reflectivity these were convolved with source wavelets of different frequencies to produce the final synthetic seismic profiles none of the modelled outcrop geometries is correctly portrayed seismically at 25 50 hz frequencies not only do the synthetic seismic profiles show less detail they also show misleading geometries in most seismic models for instance pseudo unconformities are present that correspond to rapid changes in dip and in facies in outcrop furthermore the seismic tool is not able to resolve between stratal patterns punctuated by unconformities and those with gradual shifts in facies belts accompanied by complex interfingering relationships this implies that an unconformity recognized on a real seismic line should not automatically be assumed to represent a true stratal unconformity large outcrops are often used to show the validity of sequence stratigraphy a concept mainly based on the analysis of seismic lines this study however shows that there is no one to one relationship between geometries observed in outcrop and in seismic lines seismic modelling of outcrops therefore provides a means for evaluating outcrop geometries in terms of seismic stratigraphy

barremian platform carbonates from the eastern vercors massif france organization of depositional geometries the vercors massif of southern france constitutes a world class and unique opportunity to visualize depositional geometries and diagenetic transformations of a barremian early aptian early cretaceous carbonate system the urgonian platform at a seismic scale and thus to constrain the three dimensional continuity and connectivity of reservoir prone facies deposited during periods of high and low sea level the integration of detailed outcrop analysis including diagenetic transformations with the sequence stratigraphic interpretation of cliff provides opportunities to study the precise relationship between sea level changes and facies distribution including reservoir prone examples such as slope and fan deposits to understand how local tectonics affect accommodation space and effects on sedimentation rates this integrated stratigraphic framework developed at surface conditions provides an analog for major petroleum systems of the middle east where platform carbonates are involved such as the aptian shu aiba or the cenomanian turonian mishrif formation

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

the detection of low magnitude seismic events using array based waveform correlation summary it has long been accepted that occurrences of a known signal are most effectively detected by cross correlating the incoming data stream with a waveform template such matched signal detectors have received very little attention in the field of detection seismology because there are relatively few instances in which the form of an anticipated seismic signal is known a priori repeating events in highly confined geographical regions have been observed to produce very similar waveforms and good signals from events at a given site can be exploited to detect subsequent co located events at lower magnitudes than would be possible using traditional power detectors even greater improvement in signal detectability can be achieved using seismic arrays running correlation coefficients from single sensors can be stacked over an array or network to result in a network correlation coefficient displaying a significant array gain if two events are co located the time separating the corresponding patterns in the wave train as indicated by the cross correlation function is identical for all seismic stations and this property means that the correlation coefficient traces are coherent even when the waveforms are not we illustrate the power of array based waveform correlation using the 1997 august 16 kara sea event the weak event that occurred 4 hr after the main event was barely detected using an sta lta detector on the spits array but is readily detected by signal matching on a single channel the main event was also recorded by the far more distant norsar array but no conventional detection can be made for the second event a clear detection is however made when the correlation coefficient traces are beamformed over all sensors of the array we estimate the reduction in detection threshold of a test signal on a regional seismic array using waveform correlation by scaling down a master signal and immersing it into seismic noise we show that for this case waveform correlation using a single channel detects signals of approximately 0 7 orders of magnitude lower than is possible using an sta lta detector on the array beam waveform matching on the full array provides an additional improvement of approximately 0 4 magnitude units we describe a case study in which small seismic events at the barentsburg coal mine on spitsbergen were detected using the signals from a major rockburst as master waveforms many spurious triggers occurred in this study whereby short sections of signal exhibited coincidental similarity with unrelated incoming wave fronts we demonstrate how such false alarms can almost always be identified and screened out automatically by performing frequency wavenumber analysis upon the set of individual correlation coefficient traces

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

carbon isotope stratigraphy of the upper kharaib and shuaiba formations implications for the early cretaceous evolution of the arabian gulf region the carbon isotope profiles of shallow marine carbonates from the barremian aptian kharaib and shuaiba formations of the arabian gulf region range between 0 5 and 7 pmil dgr13c pdb peedee belemnite systematic variations can be correlated with isotope profiles reported from tethyan pelagic limestone sequences the detailed correspondence between the isotopic signature of the relatively well dated pelagic limestones and the poorly dated shallow water limestones from the arabian gulf region suggests that global marine carbon isotope changes apparently affected deep sea and shallow water carbonate sediments similarly and at a similar time resolution although oxygen isotopes have been reset during diagenesis carbon isotopes appear to have maintained their primary marine signature through time no evidence has been found to connect carbon isotope trends to subaerial exposure or later meteoric diagenesis in combination with other data the investigated carbon isotope profiles can be used for basin to platform and regional correlations beyond the current resolution of biostratigraphy in shallow water limestones carbon isotope stratigraphy confirms significant hiatuses in the investigated shallow water carbonate sequences using carbon isotope trends as a proxy for sea level fluctuations the carbon isotope cycles of the late early cretaceous of the arabian gulf region may represent four cycles of rising and falling sea level with a duration corresponding to that of third order sea level fluctuations regional correlations derived from isotope trends provide a scenario for the larger scale stratigraphic evolution of the arabian peninsula during the end of the early cretaceous differential rates of aggradation between realms influenced by siliciclastics and those characterized by siliciclastic poor clean carbonate deposition apparently caused the development of a pronounced basin platform topography during the early aptian shuaiba intrashelf basin and platform

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

evaluation of δ13c chemostratigraphy for intrabasinal correlation vendian strata of northeast siberia integrated sedimentologic stratigraphic and geochemical 13 c 18 o fe mn and sr data from vendian cambrian carbonate ramp deposits of the northeast siberian platform olenek uplift and kharaulakh mountains region are used to constrain primary time dependent oscillations in the carbon isotope record and to evaluate 13 c chemostratigraphy for high resolution intrabasinal correlation the vendian 13 c record of northeast siberia reflects global variations seen elsewhere by displaying in ascending order a strong positive isotopic shift to values near 6 herein named the p interval an intermediate interval of relatively little isotopic change i interval which shows in some sections a monotonic decrease in 13c from 2 at the base to near 0 at the top and a negative excursion to 4 n interval just beneath the vendian cambrian boundary in addition to secular isotopic shifts these strata exhibit local small scale signals related to intrabasinal variations in subsidence erosion and diagenetic alteration e g degradation of organic matter dolomitization and hydrothermal and burial effects these local intrabasinal processes in some cases have modified both the magnitude and form of the primary isotopic excursions which are used as the basis for correlation in all studies carbon isotope profiles provide an important method to evaluate intrabasinal variations in subsidence erosion and stratigraphic completeness these profiles reflect increasing subsidence along the platform to basin transition whereas progressive truncation of isotopic profiles along this trend illustrate pronounced uplift and erosion of ramp strata along unconformity surfaces

pinning points a method providing quantitative constraints on relative sea level history abstract quantitative constraints on the history of relative sea level allow for a better understanding of the controls on depositional sequence development the constraints are provided by pinning point curves plots of ancient relative sea level elevations pinning points versus time constructing a pinning point curve requires identification of ancient stratigraphic positions of sea level through interpretation of facies and surfaces formed at sea level then their ancient relative elevations are determined through reconstructing aspects of ancient paleotopography upper miocene strata from las negras southeastern spain preserve paleotopography contain ancient surfaces of subaerial exposure and contain facies deposited near sea level the pinning point curve illustrates a complex relative sea level history with large and small scale relative sea level fluctuations defined by 31 pinning points

effects of misclassification costs on mapping mineral prospectivity abstract mineral prospectivity mapping is a classification process because in a given study area a specific region is classified as either a prospective or non prospective area the cost of false negative errors differs from the cost of false positive errors because false positive errors lead to wasting much more financial and material resources whereas false negative errors result in the loss of mineral deposits traditional machine learning algorithms using for mapping mineral prospectivity are aimed to minimize classification errors and ignore the cost sensitive effects in this study the effects of misclassification costs on mapping mineral prospectivity are explored the cost sensitive neural network csnn for minimizing misclassification costs is applied to map fe polymetallic prospectivity in china s southwestern fujian metalorganic belt sfmb a csnn with a different cost ratio ranging from 1 10 to 10 1 was used to represent various misclassification costs the cross validation results indicated a lower misclassification cost compared to traditional neural networks through a threshold moving based csnn the csnn s predictive results were compared to those of a traditional neural network and the results demonstrate that the csnn method is useful for mapping mineral prospectivity the targets can be used to further explore undiscovered deposits in the study area

chemostratigraphic correlation of barremian and lower aptian ammonite zones and magnetic reversals based on carbon isotope stratigraphy we correlate the ammonite dated barremian reference section near angles se france with the magneto and biostratigraphically dated succession at cismon northern italy the results confirm the previous correlation of the lower barremian ammonite and magnetostratigraphy by channell et al 1995 and show that the base of cm0 selected as the stage boundary between the aptian and the barremian coincides with the stage boundary defined by ammonite stratigraphy the upper barremian carbon isotope record of the cismon section displays two positive 13c excursions whereas the data from angles show only one shift towards more enriched values the absence of the second upper barremian 13c excursion at angles indicates that up to 50 of the barremian stage is missing in the selected reference section the gap occurs most probably within the giraudi ammonite zone and is related to the 12d maximum flooding surface of jacquin et al 1998

recognition of geochemical anomalies using a deep variational autoencoder network abstract deep learning dl algorithms have received increased attention in various fields in the field of geoscience dl has been shown to be a powerful tool for mining complex high level and non linear geospatial data and for extracting previously unknown patterns related to geological processes in this study a deep variational autoencoder vae network was used to extract features related to mineralization and these features were then integrated as a anomaly map in support of mineral exploration based on geochemical exploration data which consist of cu pb mn zn and fe2o3 various experiments were conducted to determine the optimal parameters of the vae the structure of the vae in which the network depth and number of hidden units were 24 12 3 12 24 was built to recognize geochemical anomalies related to fe polymetallic mineralization in the southwest fujian province china the geochemical anomalies recognized by the vae show a close spatial correlation with known fe polymetallic deposits meanwhile the areas with high probability are located in or around the yanshanian intrusions and the contact zones of the carboniferous permian formation and yanshanian intrusions these results suggest that the anomalous areas identified by the vae are meaningful for mineral exploration

data driven predictive mapping of gold prospectivity baguio district philippines application of random forests algorithm the random forests rf algorithm has recently become a fledgling method for data driven predictive mapping of mineral prospectivity and so it is instructive to further study its efficacy in this particular field this study carried out using baguio gold district philippines examines a the sensitivity of the rf algorithm to different sets of deposit and non deposit locations as training data and b the performance of rf modeling compared to established methods for data driven predictive mapping of mineral prospectivity we found that rf modeling with different training sets of deposit non deposit locations is stable and reproducible and it accurately captures the spatial relationships between the predictor variables and the training deposit non deposit locations for data driven predictive mapping of epithermal au prospectivity in the baguio district we found that a the success rates of rf modeling are superior to those of weights of evidence evidential belief and logistic regression modeling and b the prediction rate of rf modeling is superior to that of weights of evidence modeling but approximately equal to those of evidential belief and logistic regression modeling therefore the rf algorithm is potentially much more useful than existing methods that are currently used for data driven predictive mapping of mineral prospectivity however further testing of the method in other areas is needed to fully explore its usefulness in data driven predictive mapping of mineral prospectivity

spatial analysis and visualization of exploration geochemical data abstract this paper briefly reviews the application of geoinformatics in exploration geochemistry from the perspective of spatial analysis and visualization and demonstrates the advantages of geoinformatics in exploring geochemical patterns and identifying geochemical anomalies in particular the application of geoinformatics to geochemical mapping recognition of geochemical anomalies and simulation of geochemical patterns are discussed the benefits of geoinformatics include 1 overlay of geochemical data on a geological map which helps geochemists to understand spatial geochemical patterns and visualize geochemical anomalies 2 local neighbourhood spatial analysis which considers the local spatial structure of geochemical patterns as a powerful tool to identify weak geochemical anomalies and 3 geochemical patterns simulation based on geological constrains which helps to understand geological processes future researches should focus on development and application of various functions for processing geochemical data in a gis to promote the progress of geoinformatics in both geochemical exploration and environmental studies

the mineralization age of the makeng fe deposit south china implications from u pb and sm nd geochronology the makeng fe deposit is located in the southwestern fujian district south china the sm nd isochron ages of seven samples of pure garnet and five of pure magnetite separates from the makeng ores yielded an isochron age of 157 15 ma laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of the nearby exposed the dayang juzhou dj porphyritic biotite granite and fine grained syenogranite yielded 206pb 238u ages of 140 2 1 1 and 140 1 1 0 ma respectively these results suggest that the intrusion of the dj granite and the makeng skarn alterations and fe mineralization are contemporaneous the dj granite exhibits geochemical characteristics of a type granites including high values of na2o k2o 8 13 8 92 wt feot mgo 3 4 21 5 and ga al 2 64 3 45 10 4 and low al2o3 10 71 13 29 wt value chondrite normalized rare earth element patterns are characterized by obviously negative eu anomalies eu 0 02 0 28 and primitive mantle normalized spidergrams show the enrichment in high field strength element and depleting in sr ti ba and eu the geochemical characteristics of dj granite suggest that the granite was derived from partial melting of the paleoproterozoic metasedimentary rocks of the cathaysia basement and some underplating of mafic magma in the lower tholeiitic crust and or depleted mantle might be involved and provide the heat source for the partial melting the dj granite also fits the spatiotemporal distribution of the jurassic cretaceous coastward migration of both extensional and arc related magmatism and fills the a type granites gap in the early stage of the early cretaceous 145 125 ma therefore it is suggested that the late jurassic and early cretaceous magmatism in southwestern fujian district were generated in an extensional environment responding to the slab rollback and concomitant retreating arc system of the paleo pacific plate within the south china block and the fe metallogeny in southwestern fujian district is genetically linked with the magmatism during this period

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

early diagenetic dolomitization and dedolomitization of late jurassic and earliest cretaceous platform carbonates a case study from the jura mountains nw switzerland e france early diagenetic dolomitization is a common feature in cyclic shallow water carbonates throughout the geologic record after their generation dolomites may be subject to dedolomitization re calcification of dolomites e g by contact with meteoric water during emersion these patterns of dolomitization and subsequent dedolomitization frequently play a key role in unravelling the development and history of a carbonate platform on the basis of excellent outcrops detailed logging and sampling and integrating sedimentological work high resolution sequence stratigraphic interpretations and isotope analyses o c conceptual models on early diagenetic dolomitization and dedolomitization and their underlying mechanisms were developed for the upper jurassic lower cretaceous jura platform in north western switzerland and eastern france three different types of early diagenetic dolomites and two types of dedolomites were observed each is defined by a distinct petrographic isotopic signature and a distinct spatial distribution pattern different types of dolomites are interpreted to have been formed by different mechanisms such as shallow seepage reflux evaporation on tidal flats and microbially mediated selective dolomitization of burrows depending on the type of dolomite sea water with normal marine to slightly enhanced salinities is proposed as dolomitizing fluid based on the data obtained the main volume of dolomite was precipitated by a reflux mechanism that was switched on and off by high frequency sea level changes it appears however that more than one dolomitization mechanism was active pene contemporaneously or several processes alternated in time during early diagenesis percolating meteoric waters obviously played an important role in the dedolomitization of carbonate rocks that underlie exposure surfaces cyclostratigraphic interpretation of the sedimentary succession allows for estimates on the timing of early diagenetic de dolomitization these results are an important step towards a better understanding of the link between high frequency probably orbitally forced sea level oscillations and early dolomitization under mesozoic greenhouse conditions

modeling of cu au prospectivity in the carajas mineral province brazil through machine learning dealing with imbalanced training data abstract machine learning ml is becoming an appealing tool in various fields of earth sciences especially in mineral prospectivity mapping mpm to support mineral exploration ml algorithms are designed to assume a relatively balanced amount of training data for the estimation of the decision boundaries between the classes of interest i e in mpm mineralized and non mineralized locations however in mpm the numbers of mineralized and non mineralized locations are naturally imbalanced as the number of known mineral deposit occurrences as a proxy of mineralized or positive class are naturally much smaller than the number of non mineralized locations the negative class the use of imbalanced data leads to difficulties in the training of ml models for mpm due to the learning bias towards the features of the predominant i e negative class in the present study using support vector machine for cu au prospectivity modeling in the carajas mineral province brazil we evaluated the effects of synthetic minority over sampling technique smote which addresses the issue of imbalanced training data on the performance of mpm the original training data for the positive i e minority class was modified by over sampling the mineralized locations using smote and by randomly under sampling the non mineralized locations at different proportions producing 400 training datasets with proportions of mineralized to non mineralized samples ranging from 600 30 to 30 600 each of these individual training datasets was used to evaluate the performance of mpm under different proportions of mineralized to non mineralized samples the performance of each prospectivity model was objectively evaluated using the f1 score and the success rate curve the results show that smote can significantly increase the performance and the spatial efficiency of mpm the main differences between the performances of the derived prospectivity models illustrate the sensitivity of mpm to the number of samples and distribution of classes in the training data according to the results better performance is achieved using smote when the prospectivity models are trained with an equal number of mineralized and non mineralized samples the best prospectivity model trained with a modified dataset with 600 600 proportion of mineralized to non mineralized samples resulted in 100 classification of the training mineralized locations and almost 80 of the testing mineralized locations and outlined only 7 of the study area as prospective

temporal consistency between granite evolution and tungsten mineralization in huamei ao southern jiangxi province china evidence from precise zircon u pb molybdenite re os and muscovite 40ar 39ar isotope geochronology abstract the large huamei ao tungsten deposit with total wo 3 reserves of 67 400 tons at an average grade of 1 334 wo 3 is located in the convergent zone of the eastern nanling e w trending tectono magmatic belt and the western wuyishan nne ssw trending tectono magmatic belt in southern jiangxi province china the tungsten mineralization in this deposit is mainly found in quartz wolframite veins with most orebodies distributed at the outer contact zone between concealed late jurassic granitic stocks and sinian weakly metamorphosed sandstones and phyllites zircons collected from medium to fine grained biotite granite in a diamond drill hole at a sea level of ca 10 m yield a crystallization age of 159 9 1 2 ma through laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms u pb dating molybdenite and muscovite that were both separated from quartz wolframite veins yield a re os isochron age of 158 5 3 3 ma and an 40 ar 39 ar weighted plateau age of 157 9 1 1 ma respectively these dates obtained via three independent geochronological techniques constrain the ore forming age of the huamei ao deposit and link the genesis of the ore and the underlying granite analyses of available high precision zircon u pb molybdenite re os and muscovite 40 ar 39 ar radiometric ages of major w sn deposits in southern jiangxi province indicate that there is no significant time interval between w sn mineralization and its intimately associated parent granite emplacement interval of 0 6 ma these deposits formed over three intervals during the mesozoic 240 210 170 150 and 130 90 ma with large scale w sn mineralization occurring mainly between 160 and 150 ma the majority of w sn deposits in this region are located in southern jiangxi and southern hunan provinces

improvements to seismic monitoring of the european arctic using three component array processing at spits abstract the detectability of low magnitude seismic events in the european arctic is determined primarily by the small aperture international monitoring system arrays arces and spits in august 2004 the spits array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 hz most important however for the detection and location of small magnitude seismic events was the deployment of three component instruments at six of the nine sites detection and correct classification of secondary phases are of paramount importance for events observed by only a small number of stations at regional distances and in the absence of the strong lg phases typically observed for continental propagation paths multiple three component stations were deemed necessary to exploit the higher s phase amplitudes anticipated on the horizontal sensors we demonstrate improved signal to noise ratios snrs for s phases on horizontal beams for several events close to novaya zemlya horizontal component f k analysis improves direction estimates and phase classification for low snr signals we demonstrate secondary phases that are misidentified by vertical only f k analysis but which are correctly classified by three component array processing a significant problem with array processing at spits is the overlap in slowness space of regional p and s phases phase identification is improved greatly by comparing the coherence between vertical traces with the coherence between horizontal traces considerations in the routine array processing of spits data are reviewed including the need for elevation corrections in slowness estimation and the need to take into account azimuth dependent variation of apparent velocity estimates for regional phases

geochemistry of pelagic and hemipelagic carbonates criteria for identifying systems tracts and sea level change the elemental si ti al mn ca zr and carbon stable isotope 13 c geochemistry of a biostratigraphically well constrained cenomanian turonian upper cretaceous chalk succession on the isle of wight southern england shows systematic variation that corresponds closely to a published sequence stratigraphic model for the cenomanian six sequences and their constituent systems tracts defined elsewhere using sedimentological criteria are clearly distinguishable from bulk sediment elemental profiles and an additional upper cenomanian sequence previously identified in spain is recognized in england from these geochemical data the manganese curve is particularly instructive exhibiting minima around sequence boundaries and through lowstands rising values from the transgressive surfaces through transgressive systems tracts maxima around maximum flooding surfaces and declining values through highstands silica and trace element ti zr aluminium ratios peak around transgressive surfaces and maximum flooding surfaces indicating pulses of increased siliciclastic input positive 13 c excursions are confirmed at the base of the middle cenomanian and spanning the cenomanian turonian boundary but are not evident in other sequences variation in mn is related to bulk sedimentation rate and detrital versus biogenic supply which control the mn flux and the efficiency of the diagenetic mn pump that leads to elevated mn contents in sediments manganese peaks do not generally correlate with positive 13 c excursions and although near coincident mn and 13 c peaks occur around the cenomanian turonian boundary the former is not necessarily linked to the oceanic anoxic event occurring at that time the global oceanic mn flux may have been enhanced during the cenomanian as a result of hydrothermal activity during rapid sea floor spreading and oceanic plateau formation elemental chemostratigraphy provides a new tool for developing sequence stratigraphic models in pelagic and hemipelagic carbonate successions

basin to platform chemostratigraphy and diagenesis of the early cretaceous vercors carbonate platform se france abstract cathodoluminescence petrography has been combined with bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses to reconstruct the diagenetic history of lower cretaceous barremian limestones exposed at the southern margin of the vercors carbonate platform in southeastern france stratigraphic and geographic trends in these analyses coupled with mass balance water rock interaction modeling have been used to constrain the chemical composition source and relative timing of the groundwaters responsible for diagenetic alteration this study was completed on the montagnette outcrop which is composed of two stacked 70 m thick units of prograding platform margin limestones that interfinger with marly basinal sediments the montagnette exposure is exceptional in that it is a single complete outcrop of basin to platform limestones that are preserved in their original lateral depositional continuity cathodoluminescence petrography indicates that the limestones have experienced a complex sequence of carbonate dissolution precipitation and fracturing events over one hundred bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses were completed to characterize each major event of deposition and diagenesis bulk rock analyses from the montagnette basin to platform transect exhibited no significant variations in 87 sr 86 sr 0 707523 to 0 707555 these values are consistent with estimated barremian seawater 87 sr 86 sr ratios in contrast micro sampled shell material in the platform margin and platform top deposits exhibit large variations in 87 sr 86 sr 0 706910 to 0 707450 the least radiogenic sr lowest 87 sr 86 sr occurs in shell material located toward the platform while the more seawater like ratios occur in sections without shells that are located toward the basin this pattern implies that selective diagenetic alteration of the shell material took place after basinal brines flowed up into the platform and spread out laterally the sr in the diagenetic waters was probably derived from water rock interaction with jurassic basinal sediments in the vocontian trough this conclusion is based on 1 the extremely low 87 sr 86 sr composition of shell material in the platform limestone 2 modeled co variation trends in 87 sr 86 sr 13 c and 18 o and 3 the absence of another nearby source of less radiogenic sr in the vercors region

stratal patterns sediment composition and sequence stratigraphy at the margin of the vercors carbonate platform lower cretaceous se france abstract conventional sequence stratigraphic concepts relate the large scale stratal architecture of sediment bodies to changes in relative sea level this paper evaluates the relationship between stratal geometry and sea level stand based on a study of large semicontinuous outcrops of cretaceous carbonate platform strata in the vercors southeastern france multiple lines of evidence for sea level change are combined including stratal geometry detailed quantitative microfacies analyses and diagenetic patterns at platform top hardground surfaces the studied outcrops of the cirque d archiane show two main prograding platform tongues both over 100 m thick the stratal geometries at the boundary between these platform tongues including an apparent pinchout of a wedge of slope sediments suggest the presence of a major lowstand unconformity however this stratal boundary does not coincide with the horizon containing the most extensive meteoric alteration furthermore detailed platform to basin correlation shows that the wedge of slope sediments is not basin restricted but makes a thin drape over the platform top the sedimentologic and diagenetic evidence suggest incipient drowning of the platform at the boundary between the two main platform tongues preceded by a minor exposure event only internally the main platform tongues consist of smaller 10 30 m thick units that prograde towards the basin and aggrade on the platform top and which are interpreted as stacked highstand wedges these wedges are usually topped by hardground surfaces with minor evidence for subaerial exposure the platform top horizon with the most extensive subaerial diagenesis and erosion correlates with a distinct but relatively thin unit of lithoclastic debris on the slope a pronounced scour in the clinoforms of the vercors does not correlate with a major exposure surface on the platform top this study shows that stratal geometries alone are a rather ambiguous guide to sea level history without the accompanying sedimentologic and diagenetic evidence for sea level change most of the stratal architecture of the vercors platform can be explained by either changes in accommodation or changes in carbonate production

the seismic disturbance on 1986 august 1 near novaya zemlya a source of concern summary on 1986 august 1 a small seismic disturbance occurred to the east of a soviet nuclear test site at novaya zemlya reported attempts to identify the nature of the source using only short period seismological data recorded at regional distances were unsuccessful however by using teleseismic p wave data it is possible to identify the source as an earthquake which occurred within the crust at a depth of 24 km the source is shown to have a double couple mechanism with a well constrained fault plane solution the identification as an earthquake is supported by the mb ms evidence

clinoform composition and margin geometries of a lower cretaceous carbonate platform vercors se france the concept of sequence stratigraphy uses the stratal geometries at the margins of carbonate platforms to define depositional sequences and systems tracts the aim of this study was to research if prograding purely aggrading and retrograding phases of a cretaceous carbonate platform showed differences in the composition and facies type of the slope sediments the vercors plateau in se france provides excellent outcrops to study this relationship continuous exposure of the platform to basin transition allowed direct examination of the margin geometries five successions were measured and sampled in great detail samples were thin sectioned and point counted using point count groups characterizing palaeoenvironments along the platform to basin transect the composition logs as well as the numerical analysis of the point count data both show a clear relationship between grain composition and stratal geometry the prograding and purely aggrading intervals are similar in composition as they are both relatively coarse grained and enriched in platform biota and limeclasts retreating units are relatively fine grained and rich in basinal grains small benthic foraminifers sponge spicules non carbonate grains and embedding material these observations suggest that the retreating intervals represent incipient drownings of the platform however rather than distinctly separated groups the different phases of platform development form a continuous range of variation between high platform input and high basinal input compared to the prograding units the purely aggrading intervals are relatively rich in peloids which may be suggestive of relatively low energy conditions on the platform during aggradation the compositional analysis also revealed significant variation in the frequency of ooids but these variations showed no relationship with the progradation aggradation or retreat of the platform

identification of presumed shallow underwater chemical explosions using land based regional arrays abstract seismic events located in the gulf of bothnia the baltic sea and the north sea recorded at the regional seismic arrays noress and finesa have characteristics of underwater blasts observed hydroacoustically spectral analysis of regional phases associated with the events reveals strong time independent spectral scalloping indicating that the waveforms are made up of correlated pulse echo type signals cepstral analysis gives consistent delay times between the pulse echo pairs with the most common delays between 400 and 600 msec some cepstra also have negative peaks at quefrencies between 150 and 350 msec the cepstral peaks are observed in all phases associated with the event and events recorded at both arrays have the same delay times the higher time delays are consistent with bubble pulse delays commonly observed in underwater blasts recorded hydroacoustically the lower quefrency negative peaks are caused by echoes with reversed polarities relative to the primary pulse and are consistent with reflections from the top of the water column generally these events have large pn lg amplitude ratios similar to those observed from quarry blasts somewhat smaller high frequency pn lg ratios are observed for baltic sea events compared with the north sea events which may be due to differences in the water bottom geologies of the two regions simple source models of underwater blasts explain many of the features of the observed cepstra and indicate that the shot depths had to be shallow around 40 to 80 m for shot sizes between 75 and 150 kg this study shows that the seismic sensor network called for by the comprehensive test ban treaty ctbt can augment the smaller network of hydroacoustic stations for the detection and identification of clandestine under water nuclear explosion tests in the near offshore environment

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

pn attenuation for a spherically symmetric earth model this paper presents the results of a theoretical study of the sensitivity of pn attenuation to the elastic and anelastic structure of the uppermost mantle for frequencies between 1 and 15 hz and distances between 200 and 1000 km synthetic seismograms are computed using wavenumber integration for an elastic model consisting of a crastal layer over an upper mantle with a slight linear velocity gradient approximately equal to the earth flattening transformation of a spherically symmetric homogeneous upper mantle these are compared to synthetic seismograms for a crustal layer over a mantle halfspace pure elastic head wave we find that earth sphericity alone causes a significant departure in pn attenuation from that of a canonical head wave almost two orders of magnitude at 1000 km and 15 hz and that high frequencies attenuate less rapidly than low frequencies if the spherical earth velocity gradient is greater than or equal to zero this implies that methods that assume frequency independent pn geometric spreading will produce biased estimates of the anelasticity of the upper mantle this is demonstrated using synthetic seismograms computed for an anelastic spherical earth model these results show that the velocity structure must be carefully considered when relating observed pn spectral amplitudes to the anelastic structure of the upper mantle

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

crustal structures from the wuyi yunkai orogen to the taiwan orogen the onshore offshore wide angle seismic experiments of the taiger and atsee projects abstract knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern china and adjacent areas in this study we integrated the datasets from the taiger taiwan integrated geodynamic research and atsee across taiwan strait explosion experiment projects to resolve onshore offshore deep crustal seismic profiles from the wuyi yunkai orogen to the taiwan orogen in southeastern china three seismic profiles were resolved and the longest profile was 850 km unlike 2d and 3d first arrival travel time tomography from previous studies we used both refracted and reflected phases pg pn pcp and pmp to model the crustal structures and the crustal reflectors in total data from 40 shots 2 earthquakes and approximately 1 950 stations were used 15 612 arrivals were selected among three transects using these data we determined the complex crustal evolution since the paleozoic era involving the closed paleozoic rift basin in central fujian the cenozoic extension due to the south china sea opening beneath the coastline of southern fujian and the on going collision of the taiwan orogen the shape of the moho which also reflects the crustal evolution can be summarized as follows 30 km deep to the west of fujian deepening toward central fujian 35 km becoming shallower toward the taiwan strait 28 km deepening again toward the mountain belt of taiwan 42 km and becoming shallower toward the pacific ocean 10 km

machine learning predictive models for mineral prospectivity an evaluation of neural networks random forest regression trees and support vector machines abstract machine learning algorithms mlas such us artificial neural networks anns regression trees rts random forest rf and support vector machines svms are powerful data driven methods that are relatively less widely used in the mapping of mineral prospectivity and thus have not been comparatively evaluated together thoroughly in this field the performances of a series of mlas namely artificial neural networks anns regression trees rts random forest rf and support vector machines svms in mineral prospectivity modelling are compared based on the following criteria i the accuracy in the delineation of prospective areas ii the sensitivity to the estimation of hyper parameters iii the sensitivity to the size of training data and iv the interpretability of model parameters the results of applying the above algorithms to epithermal au prospectivity mapping of the rodalquilar district spain indicate that the rf outperformed the other mla algorithms anns rts and svms the rf algorithm showed higher stability and robustness with varying training parameters and better success rates and roc analysis results on the other hand all mla algorithms can be used when ore deposit evidences are scarce moreover the model parameters of rf and rt can be interpreted to gain insights into the geological controls of mineralization

quantitative controls on location and architecture of carbonate depositional sequences upper miocene cabo de gata region se spain abstract sequence stratigraphy pinning point relative sea level curves and magnetostratigraphy provide the quantitative data necessary to understand how rates of sea level change and different substrate paleoslopes are dominant controls on accumulation rate carbonate depositional sequence location and internal architecture five third order 1 10 my and fourth order 0 1 1 0 my upper miocene carbonate depositional sequences ds1a ds1b ds2 ds3 tcc formed with superimposed higher frequency sea level cycles in an archipelago setting in se spain overall our study indicates when areas of high substrate slope 15 are in shallow water independent of climate the location and internal architecture of carbonate deposits are not directly linked to sea level position but instead are controlled by location of gently sloping substrates and processes of bypass in contrast if carbonate sediments are generated where substrates of low slope 15 6 cm ky to 2 cm ky and overall relative sea level rose at rates of 17 21 4 cm ky higher frequency sea level rates were about 111 to more than 260 cm ky producing onlapping fining deepening upward cycles decreasing accumulation rates resulted from decreasing surface area for shallow water sediment production drowning of shallow water substrates and complex sediment dispersal related to the archipelago setting typical systems tract and parasequence development should not be expected in bypass ramp settings facies of onlapping strata do not track base level and are likely to be significantly different compared to onlapping strata associated with coastal onlap basal and upper ds2 reef megabreccias indicating the transition from cool to warmer climatic conditions were eroded from steep upslope positions and redeposited downslope onto areas of gentle substrate during rapid sea level falls 22 7 cm ky of short duration such rapid sea level falls and presence of steep slopes are not conducive to formation of forced regressive systems tracts composed of downstepping reef clinoforms the ds3 reefal platform formed where shallow water coincided with gently sloping substrates created by earlier deposition slow progradation 0 39 1 45 km my is best explained by the lack of an extensive bank top progressively falling sea level and low productivity resulting from siliciclastic debris and excess nutrients shed from nearby volcanic islands although ds3 strata were deposited during a third order relative sea level cycle a typical transgressive systems tract is not recognizable indicating that the initial relative rise in sea level was too rapid 19 cm ky downstepping reefs forming a forced regressive systems tract were deposited during the relative sea level fall at the end of ds3 indicating that relatively slow rates of fall 10 cm ky or less over favorable paleoslope conditions are conducive to generation of forced regressive systems tracts consisting of downstepping reef clinoforms the tcc sequence consists of four shallow water sedimentary cycles that were deposited during a 400 ky to 100 ky time span such shallow water cycles typical of many platforms form only where shallow water intersects gently sloping substrates the relative thicknesses of cycles 2 m to 15 m thick magnitudes of relative sea level fluctuations associated with each cycle 25 30 m high rates of relative sea level fluctuations minimum of 25 120 cm ky and the widespread distribution of similar tcc cycles in the mediterranean and elsewhere are supportive of a glacio eustatic influence with rates of sea level change so high typical systems tracts do not form

mapping mineral prospectivity through big data analytics and a deep learning algorithm abstract identification of anomalies related to mineralization and integration of multi source geoscience data are essential for mapping mineral prospectivity in this study we applied big data analytics and a deep learning algorithm to process geoscience data to identify and integrate anomalies related to skarn type iron mineralization in the southwestern fujian metallogenic zone of china based on the geological setting and environment for the formation of skarn type iron mineralization 42 relevant variables including two geological one geophysical and 39 geochemical variables were analyzed and integrated for detecting anomalies related to mineralization using a deep autoencoder network the results indicate that the mapped prospectivity areas have a strong spatial relationship with the locations of known mineralization and demonstrate that big data analytics supported by deep learning methods is a potential technique to be considered for use in mineral prospectivity mapping

mapping mineral prospectivity for cu polymetallic mineralization in southwest fujian province china abstract in this study both the fuzzy weights of evidence fwofe and random forest rf methods were applied to map the mineral prospectivity for cu polymetallic mineralization in southwestern fujian province which is an important cu polymetallic belt in china recent studies have revealed that the zijinshan porphyry epithermal cu deposit is associated with jurassic to cretaceous yanshanian intermediate to felsic intrusions and faulting tectonics evidence layers which are key indicators of the formation of zijinshan porphyry epithermal cu mineralization include 1 jurassic to cretaceous intermediate felsic intrusions 2 mineralization related geochemical anomalies 3 faults and 4 jurassic to cretaceous volcanic rocks these layers were determined using spatial analyses in support by geodas and arcgis based on geological geochemical and geophysical data the results demonstrated that most of the known cu occurrences are in areas linked to high probability values the target areas delineated by the fwofe occupy 10 of the study region and contain 60 of the total number of known cu occurrences in comparison with fwofe the resulting rf areas occupy 15 of the study area but contain 90 of the total number of known cu occurrences the normalized density value of 1 66 for rf is higher than the 1 15 value for fwofe indicating that rf performs better than fwofe receiver operating characteristics roc were used to validate the prospectivity model and check the effects of overfitting the area under the roc curve auc was greater than 0 5 indicating that both prospectivity maps are useful in cu polymetallic prospectivity mapping in southwestern fujian province

improving shallow water carbonate chemostratigraphy by means of rudist bivalve sclerochemistry deep time shallow marine carbonate platforms record distinct biotic responses to climatic and environmental stressors unfortunately precise temporal assignment of these biotic responses is often problematical due to poor biostratigraphic control and or a significant diagenetic overprint of the neritic bulk carbonate chemostratigraphic inventory an accurate stratigraphic framework is essential to better understand the causal relation between biotic events recorded by carbonate platforms and environmental changes that for instance culminated in mass extinction events or prolonged episodes of oceanic anoxia here we provide an integrated carbon and strontium isotope stratigraphy of the early cretaceous subtropical provence carbonate platform in se france that is based solely on pristine low mg calcite from rudist bivalves carbon isotope data of geochemically screened rudist fragments enabled reconstruction of a characteristic barremian pattern including the mid barremian event mbe that allowed for a precise correlation with stratigraphically well constrained tethyan shallow water and hemipelagic reference sections in order to evaluate ontogenetic carbon isotope changes and the overall variability of the shell derived carbon isotope data numerous sclerochronological carbon isotope profiles of individual large rudist shells are presented strontium isotope stratigraphy supports the carbon isotope based age of the studied sections but also provides unequivocal evidence for a major hiatus in the depositional record covering large parts of the late barremian in contrast to biostratigraphic and bulk carbonate chemostratigraphic archives the here established chronostratigraphy of carbonate platform evolution in the southern provence region demonstrates a twofold resurgence of rudist rich carbonate platform production during the early aptian and arguably the latest early aptian

the level of deterrence provided by data from the spits seismometer array to possible violations of the comprehensive test ban in the novaya zemlya region summary the yield threshold at which a fully decoupled explosion can be identified has been a recurring issue in the debate on whether the comprehensive nuclear test ban ctb can be adequately verified here we assess this yield threshold for the novaya zemlya nz and kola peninsula regions by analysing seismograms from six small body wave magnitude mb 3 5 seismic disturbances recorded at regional distances 1050 1300 km by the seismometer array at spitsbergen spits multiple filter analysis of the seismograms shows clear high frequency pn f 14 hz except from a calibration explosion on the kola peninsula from four of the disturbances studied we observe clear high frequency sn the explosion showed no clear high frequency sn and the data from the remaining disturbance was potentially contaminated by a data glitch frequency domain analysis indicates that the pn and sn attenuation across the barents sea is similar to that observed across stable tectonic regions shields we define a spectral magnitude for the 2 5 3 5 hz passband that is tied to teleseismic mb from nz explosions the six disturbances considered have 2 3 mb 3 5 three component data are available from spits for four of the disturbances considered including the explosion from the explosion the s p ratios on the vertical z radial r and tangential t components in the 3 0 6 0 hz passband are all less than unity the s p ratios for the same passband on the z component from the remaining three disturbances are less than unity but the ratios on the r and t components are significantly greater than unity we argue that s p ratios 3 0 6 0 hz passband of less than unity on all of the z r and t components at spits may indicate a potential treaty violation in the kola peninsula and nz regions the temporal variation of seismic noise in the 3 0 6 0 hz passband at spits suggests that our three component s p criterion will be effective 95 per cent of the time for disturbances with mb 2 8 we suggest that mb 4 25 b log10w where w is the explosive yield in kilotons kt with b 0 75 for w 1 and b 1 0 for w 1 is suitable for conservatively estimating the yield threshold of a potential violation of the ctb in the nz region from this we infer that a 35 ton fully coupled explosion in the nz region is likely to be identified as suspicious under the ctb using the three component s p criterion simulations show that the low frequency decoupling factor df for a fully decoupled nuclear explosion in hard rock is about 40 suggesting that such an explosion with a yield of 1 6 kt in the nz region is likely to be identified using data from spits the conservatism likely to be employed by a potential violator and uncertainties in the dfs for nuclear explosions in hard rock cavities together with data from stations other than spits within 2000 km of the nz region suggest that the yield at which a potential violator of the ctb could confidently escape detection using decoupling in the nz region is in reality probably less than 0 5 kt

early aptian algal bloom in a neritic proto north atlantic setting harbinger of global change related to oae 1a pervasive growth of microencrusters lithocodium bacinella characterizes short lived stratigraphic intervals in lower aptian shallow water carbonate platform settings of the central and southern tethys although a causal relationship between this peculiar shallow water facies and the early aptian oceanic anoxic event oae 1a seems likely the temporal and spatial distributions of lithocodium and bacinella mass occurrences in the rock record point to a rather complex pattern possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event oae 1a slightly pre or postdating the deposition of dark organic rich black shales in pelagic basins this study presents evidence for a punctuated and well expressed early aptian bloom of the ulvophycean green algae lithocodium aggregatum observed at the proto north atlantic margin lusitanian basin portugal similar to southern and central tethyan sections a lithocodium dominated interval temporally replaces the rudist dominated platform ecosystem this lithocodium rich horizon is composed of oncoidal floatstones and boundstones including a well exposed biohermal level and reaches a thickness of up to 6 m high resolution carbon isotope stratigraphy shown here clearly argues for lithocodium to represent a biotic harbinger of environmental change in the run up of oae 1a chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto north atlantic was coeval with an early aptian carbonate platform drowning episode observed in the northern tethys prior to oae 1a a regionally enhanced nutrient level and a relative sea level rise are suggested to have triggered the transient mass occurrence of lithocodium microencrusters which also may have been influenced by elevated atmospheric co2 concentrations related to the emplacement of the ontong java large igneous province upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients which tentatively diminished and finally interrupted the metazoan carbonate platform factory

an integrated cathodoluminescence video capture microsampling system a new system is described that permits real time microdrilling of sedimentary grains and crystals within cathodoluminescence zonations low light cathodoluminescence photomicrograph images are captured with a thermoelectrically cooled color video camera and saved on a computer these cathodoluminescence images are then transparently superimposed on a standard color video image of the sample being microdrilled on a 20 m scale using a video mixer this integrated system can be applied to a wide variety of sedimentary rocks and minerals

an estimate of albian sea level amplitudes and its implication for the duration of stratigraphic hiatuses abstract carbonate platform tops are reliable but incomplete recorders of past sea level fluctuations as they are riddled with hiatuses of various durations basinal sections represent a more complete record but fail to register regressive transgressive events with small to moderate amplitudes we seek to avoid these problems by combining information on past sea level fluctuations from coeval platform top slope and basinal sections the outcome of this study is a semiquantitative albian sea level curve from the southern tethyan margin in oman in subaerial exposure surfaces the northern oman margin recorded 4 high amplitude 50 m 6 intermediate amplitude 30 m and 26 low amplitude 10 m regressive transgressive cycles hiatuses that cap the platform top depositional sequences might account for between 30 to 70 of the cycle duration the resulting platform top depositional sequences have frequencies in the order of 230 20 kyr i e they are in the time range of orbital eccentricity cycles it appears that at least some of these albian regressive transgressive cycles were rapid and punctuated as opposed to sinus shaped milankovitchian sea level oscillations

frequency dependent attenuation in the crust the shear wave attenuation q l in the crust beneath the northeastern us and scandinavia is determined as a function of depth and frequency using theoretical modeling of complete waveforms in comparison with observed data to determine attenuation in the upper crust of the northeastern us short period 0 25 t 2 sec rg waves recorded by linear arrays of seismometers are used for scandinavia rg and lg waves are combined to extend the investigation into the deeper crust the combination of rg waves and short period t 1 0 sec lg waves makes it possible to determine attenuation as a function of depth and frequency in the crust parameterized as q qo f to match the observations theoretical models for three mechanisms that contribute to attenuation in the crust frequency independent anelastic qa 1 and frequency dependent fluid flow qf 1 and scattering qs 1 are considered the best fitting models require low q q0 100 in the shallow crust that increases with increasing frequency as f0 5 above 1 hz in the middle crust between about 2 to 10 km depth q is moderate 100 q0 500 with a frequency dependence of f1 in the lower crust the attenuation is very low q 500 and its frequency dependence is difficult to establish the low intrinsic q and the frequency dependence in the uppermost crust can be explained by fluid flow in fractures in the middle crust the frequency dependence suggests scattering the increase of q in the lower crust is most likely due to annealing of microcracks under pressure and temperature as observed in the laboratory

the removal of free surface interactions from three component seismograms summary the effect of the free surface can be removed from three component seismic recordings to recover the incident upgoing wavefield if the slowness and azimuth of the current wavefront are known as a function of time for a single threecomponent station it is usually possible to estimate an azimuth for an event from the first arriving p waves but slowness estimates are less reliable when more than one wavetype is presented in the seismic wavetrain however the free surface correction operators are generally slowly varying functions of slowness and so some error in slowness can be tolerated effective approximations for the removal of the free surface effects can be made for hard rock sites to cover slowness bands for the main regional phases pn pg sn and lg by applying these operators in turn over group velocity windows appropriate to the particular phases the relative amplitude of the p sv and sh contributions to the wavefield can be estimated because the free surface amplification effects have been removed the amplitudes can be compared directly and provide useful constraints on the radiation characteristics of the source this procedure is therefore helpful for developing discrimination measures for different classes of sources

diagenesis of barremian aptian platform carbonates the urgonian limestone formation of se france near surface and shallow burial diagenesis the diagenesis of carbonate platform sediments is controlled by the original facies and mineralogy climate sea level changes and burial history these controls are clearly seen in the diagenesis of the urgonian platform carbonates of se france early diagenesis in the urgonian platform included the precipitation of marine cements dissolution of rudist shells and minor karstification diagenetic features produced during this phase were controlled by several falls in relative sea level during the barremian to mid aptian punctuating platform sedimentation the original mineralogy of the sediment and the prevailing semi arid arid climate in the region at this time following a relative sea level rise and further sedimentation progressive burial of the platform led to minor compaction followed by precipitation of coarse equant zoned to non luminescent calcite cement this cement was cut by later stylolites suggesting a relatively shallow burial origin stable isotope mean values 7 94 18o and 0 36 13c and trace element mean values of fe 334 ppm mn 92 ppm and sr 213 ppm data suggest that these cements precipitated from meteoric fluids at temperatures slightly elevated relative to depositional temperatures a variable thickness of replacive dolomite which occurs preferentially within the shelf margin facies of the lower part of the urgonian post dates mechanical fracturing and chemical compaction but pre dates the main phase of stylolitization it is probable that the dolomitizing fluid was sourced by the early compaction driven release of connate fluids held within the underlying muddy units the burial history of these rocks suggests that calcite cementation and dolomitization took place at relatively shallow burial depths 1 1 5 km the overall diagenetic history of the urgonian limestone formation is a reflection of the pre conditioning of the platform limestones by climate sea level tectonics and the shallow burial depths experienced by the platform during the later mesozoic

discrimination of earthquakes and explosions in southern russia using regional high frequency three component data from the iris jsp caucasus network high frequency regional records from small earthquakes magnitude 4 5 and comparable magnitude chemical explosions are analyzed to find a reliable seismic discriminant in southern russia near kislovodsk the digital three compo nent seismograms recorded during 1992 by the caucasus network operated by la mont doherty earth observatory since 1991 in the distance ranges 15 to 233 km are used mean vertical component pg lg spectral amplitude ratios in the band 8 to 18 hz are about 1 3 and 3 2 for earthquakes and explosions respectively in this region we find that the vertical component pg lg spectral ratio in the frequency band 8 to 18 hz serves quite well for classifying these events a linear discriminant function analysis indicates that the pg lg spectral ratio method provides discrimination power with a total misclassification probability of about 7 the pg lg spectral ratios of rotated three component regional records improve the discrimination power of the spectral ratio method over the vertical component pg lg ratios preliminary analysis indicates that distance corrected vertical component pg lg ratios improve the dis crimination power by about 4 over uncorrected ratios but we find that an even better discriminant is the pg lg spectral ratio of the three component regional records corrected for the free surface effect in the frequency band 8 to 18 hz the free surface corrected three component pg lg spectral ratio provides discrimination power with a total misclassification probability of only 2 6 free surface corrected and network averaged pg lg spectral ratios provide transportability of the spectral ratio method to various regions worldwide

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

mineral potential mapping with a restricted boltzmann machine abstract a restricted boltzmann machine can be trained to encode and reconstruct training samples from a training sample population with an unknown complex probability distribution small probability samples can be differentiated from the training sample population due to their comparatively larger encoded and reconstructed errors in mineral potential mapping mineral potential areas usually take up only a small proportion of the whole mineral exploration region and have specific evidence map patterns assume that the whole mineral exploration region is divided into uniform cells and a restricted boltzmann machine is then trained on all the cells as a small proportion of the total training cells mineral potential cells have much larger encoded and reconstructed errors compared to non mineral potential cells based on the encoded and reconstructed errors of the training cells asc and ase are thus defined as two mineral potential indicators for mineral potential mapping with the trained restricted boltzmann machine the altay district in northern xinjiang in china which is linked with a complex geological setting is chosen as a case study area restricted boltzmann machines with 12 visible units and differing hidden units are constructed and trained on 9582 training cells in the study area the asc ase posterior probability and deposit bearing probability are used to predict the mineral potential of each grid cell in the study area the auc area under the curve a measure of aggregated classification performance in machine learning is applied to measure the mineral potential mapping performance of these four mineral potential indicators the results show that the four mineral potential indicators perform similarly well therefore a restricted boltzmann machine can be trained to map mineral potentials and the asc and ase are two feasible indicators for the mineral potential mapping with the trained restricted boltzmann machine

carbonate platform stratal geometries and the question of subaerial exposure abstract integrated petrographic geochemical and fluid inclusion analyses indicate that the most prominent exposure unconformity at the southern margin of the vercors carbonate platform in southeastern france does not coincide with the major break in depositional geometry therefore changes in sediment supply and dispersal strongly influenced the resulting stratal geometries and prevent direct reconstructions of sea level from the stratal patterns platform to basin transects exposed in the cirque d archiane contain two prograding grainstone tongues separated by a wedge of finer grained slope sediments that thin toward the platform diagenetic analyses have been done at several strategic platform top bedding planes to determine the extent to which these sedimentologic breaks represent subaerial exposure while many bedding planes contain some evidence of meteoric alteration one of these bedding surfaces is unique in that it exhibits several generations of overprinted meteoric calcite cements bladed to blocky morphology precipitation in biomolds extinct to zoned cathodoluminescence low mg and 18 o variable 13 c freshwater fluid inclusions that are cross cut by marine borings eroded dolomitized clasts derived from this exposure surface occur in the uppermost portion of the finer grained wedge this combined evidence indicates that a significant episode of subaerial exposure took place at this horizon prior to deposition of the overlying platform top sediments the most significant change in depositional style and therefore the most likely position for a sequence boundary defined by stratal geometry is the top of the lower grainstone tongue however the intensely altered exposure surface and its basinward equivalent in the wedge lie 50 m above the top of the lower grainstone tongue therefore the surface containing the most extensive record of meteoric diagenesis does not stratigraphically coincide with the surface representing the most significant lateral shift in depositional facies

comparison of location procedures the kara sea event of 16 august 1997 various location procedures and velocity models are compared for the ml 3 3 kara sea event of 16 august 1997 this event has been the subject of considerable discussion because of its geographical position and the difficulty in obtaining a reliable focal depth estimate a comprehensive data set was extracted by re reading the records from all available stations these readings have then been used in a sequence of location experiments to examine the effect of using different velocity models to describe the travel times of the phases and also to compare the use of a fully nonlinear scheme shakena sambridge and kennett 2001 and a linearized location algorithm hyposat schweitzer 2001 2002 a standard least squares misfit criterion has been used for direct comparisons between the two methods the results confirm both the importance of s wave information in assessing the depth of regional events and the need to apply a reliable velocity model to place the strongest constraints on the location of the event even with only a limited data set but an adequate velocity model it is possible to find the position of the kara sea event close to the most probable locations however there is then no depth resolution reported error ellipses from standard data centers tend to have relatively small error ellipses with the commonly made assumption that the reading errors and the a posteriori residuals have an unbiased normal distribution such inversion results may indicate an unreasonably high resolution and accuracy of the solution the epicenter estimates for the whole data set using the range of different tech niques agree quite well with some overlap of the estimated confidence regions the observed seismic source was most likely an earthquake in the middle or lower crust at about 10 30 km depth

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

evaluation of uncertainty in mineral prospectivity mapping due to missing evidence a case study with skarn type fe deposits in southwestern fujian province china in this paper the southwestern fujian metallogenic belt one of the important fe polymetallic belts in southern china was chosen as a case study area to evaluate the uncertainty due to missing evidence in mineral prospectivity mapping four geological features were considered important for mineral prospectivity mapping based on the geological model for skarn deposits in the belt 1 the yanshanian granitic intrusions because they provided energy fluids and part of the metal budget 2 faults because they served as pathways for hydrothermal fluids 3 the carboniferous permian carbonate sequences because they supplied part of the metal budget and served as host rocks for ore deposition and 4 geochemical anomalies because they indicate presence of skarn type alteration and mineralization four separate predictive evidence layers depicting each the above geological features were extracted from relevant geoscience data and were integrated using a modified fuzzy weights of evidence model which retains the advantages of both fuzzy weights of evidence and logistic regression modeling the results show that most of the known fe deposits occur in or near and thus have strong correlation with areas of high posterior probabilities as indicated by the delineated prospective areas that occupy only 4 6 of the studied region but contain 88 5 of the total number of known fe deposits different combinations of predictive evidence layers were used to examine prediction uncertainty related to missing evidence plots of accumulative number of fe deposits versus accumulative prospective areas show that the order of the most to the least important evidence of mineral prospectivity in the studied region is favorable rock types geochemical anomalies intrusive rocks faults results of blind testing the prospectivity models indicate that the geological model of fe mineralization in the belt is suitable for predicting exploration target areas for skarn type fe deposits and suggest that the highest risk in follow up exploration is related to sequences of carbonates in the carboniferous permian formations that were likely either not mapped or not represented at the present regional scale of mapping

a multilayered water column in the ediacaran yangtze platform insights from carbonate and organic matter paired δ13c abstract large carbon isotope fluctuations have been systematically reported for ediacaran carbonate rocks the meaning of which remains controversial in order to better understand the mechanisms behind such variations we present new paired 13c data on carbonates 13ccarb and their associated organic matter 13corg from a shelf margin section yangjiaping of the doushantuo formation in this section the doushantuo formation starts with cap dolostones presenting 13ccarb values around 5 and 13corg values between 30 3 and 27 6 up section phased variations in 13ccarb and 13corg describe positive and negative excursions while their difference 13cdol org 13ccarb 13corg remains around 29 2 these new data allow the first reconstruction of lateral variations of 13ccarb 13corg and 13ccarb org for a shelf to basin cross section of the yangtze platform south china after integration with results reported previously for two other sections across the yangtze platform the isotope signals reveal strong lateral heterogeneities with complex variations of 13ccarb and 13cdol org in the inner shelf section phased variations in the shelf margin section with positive 13ccarb and 13cdol org close to 29 and dominantly negative 13ccarb with 13corg as low as 35 in the basin these variations are incompatible with the idea that the 13ccarb can systematically be used as a proxy of ocean surface waters assuming that 13ccarb are acquired in bottom waters and or upper sediments we show that the heterogeneous 13ccarb and 13cdol org are compatible with a stratified water column composed of up to three layers i an oxic surface layer where dissolved inorganic carbon dic is probably in isotope equilibrium with the atmosphere ii an intermediate euxinic layer with a lower 13cdic due to organic matter oxidation by ongoing sulphate reduction iii a bottom euxinic layer that seems to be restricted to the inner shelf lagoonal facies lacking sulphate containing methane and with a higher 13cdic due to dic production by methanogenesis if our model holds true it suggests that not only negative but also positive ediacaran carbon isotope excursions may reflect ocean stratification the positive excursion possibly recording a sulphate free methanogenic layer at the bottom of restricted basins

carbon isotope stratigraphy of early cretaceous urgonian shoal water deposits diachronous changes in carbonate platform production in the north western tethys abstract carbonate platforms are highly sensitive ecological systems that typically show rapid and characteristic response modes to environmental and climatic changes acting both on a regional scale and global scale a widely accepted hypothesis proposes that the late barremian stepwise establishment of the urgonian carbonate platform on the northern tethyan shelf was related to a gradual change from predominantly humid towards more arid greenhouse conditions this climate change resulted in the reorganisation of the carbonate platform ecosystem from heterozoan towards photozoan dominated assemblages and a decrease of organic matter burial in tethyan and boreal basins in order to decipher the palaeoenvironmental and climatic boundary conditions of these major changes in neritic and pelagic settings a precise chronostratigraphy of urgonian carbonate platform evolution is needed here we provide an integrated stratigraphic framework of lower barremian to lower aptian urgonian carbonate platform sections cluses forclaz located at the northern rim of the tethys subalpine chains ese france with special focus on sedimentological analyses and high resolution carbon isotope stratigraphy a characteristic barremian aptian carbon isotope pattern permits precise platform to basin correlation with cyclostratigraphic and ammonite dated pelagic and hemipelagic tethyan sections in the vocontian trough angles combe lambert glaise and umbria marche basin gorgo a cerbara similar to helvetic shoal water settings the carbonate platform in the subalpine chains experienced a gradual transition from heterozoan to photozoan dominated ecosystems this biogenic pattern points to a gradual change of the carbonate platform after the so called early barremian crisis towards an oligotrophic rimmed platform system urgonian limestone formation according to the chronostratigraphy of urgonian carbonate platform evolution in the subalpine chains established here the installation of a photozoan dominated rudist rich platform ecosystem referred to as urgonian limestones sensu stricto occurred at the early late barremian transition the onset of changes in the carbonate production mode heterozoan versus mixed heterozoan photozoan versus photozoan clearly predates the onset of similar lithological changes in the helvetic realm by about 1 0 to 1 2 myr the established chronostratigraphic framework points to a link between the change towards photozoan dominated limestones and fading palaeoenvironmental perturbations related to the mid barremian event which is associated with major faunal turnovers and the onset of cyclic black shale deposition in the central tethyan realm judging from palaeoenvironmental proxies including kaolinite phosphorus and black marl limestone ratios oscillating predominantly humid and relatively arid greenhouse conditions modulated the observed pattern in urgonian carbonate platform production mode and the varying frequencies of black shale deposits in the tethyan and boreal realms transient blooms of the orbitolinid foraminifera palorbitolina lenticularis at the onset of a marked upper barremian positive carbon isotope shift are interpreted to reflect increasing nutrient influx most probably related to accelerated hydrological cycling and or sea level rise these strata do not represent an over regional correlatable lithostratigraphic unit but likely an expression of progressive northern tethyan environmental and oceanographic change possibly related to ontong java large igneous province volcanism in the prelude of oceanic anoxic event 1a oae

paleohydrogeological and thermal events recorded by fluid inclusions and stable isotopes of diagenetic minerals in lower cretaceous sandstones offshore nova scotia canada upper jurassic lower cretaceous sandstones of the scotian basin offshore eastern canada are important gas reservoirs previous studies of fluid inclusions in jurassic limestones and apatite thermochronology of cretaceous sandstones have suggested a late mesozoic thermal event fluid inclusions in different authigenic cements were analyzed to determine the temperature and composition of basinal fluid at the time of precipitation and the timing of hydrocarbon migration and entrapment fifty one sandstone samples were analyzed for stable isotope composition 18o and 13c of carbonate cements trapping temperatures for primary aqueous inclusions hosted in quartz overgrowths 89 175c and in late carbonate cements 138 173c are higher than predicted by two dimensional modeling from burial alone based on postrift geothermal gradients these inclusions contain high salinity fluids mostly 19 22 wt nacl equivalent second predominantly aqueous inclusions have much lower salinities 5 2 6 7 wt nacl equivalent and some contain liquid hydrocarbons late fe calcite cement in hauterivian sandstone shows negative values of 13 17 to 9 2 whereas cements in deeper and shallower sandstones have higher 13c values these data indicate that high temperature high salinity fluids preceded hydrocarbon migration the oldest and youngest rocks studied show less effect of high temperatures than do rocks that were buried to depths of at least 2 km 1 2 mi after 135 ma and before 100 ma both fluid inclusions and 13c of carbonate cement suggest that highest temperatures were achieved during burial at 115 to 105 ma this early cretaceous thermal event had a geothermal gradient of at least 55c km it is earlier than the previously reported event based on apatite fission tracks but is consistent with the fission track data the event is synchronous with regional evidence of volcanism and its peak coincides with rapid salt tectonic deformation in the deep basin hydrocarbon charge to the outer shelf wells occurred after this thermal event and thus not before the late cretaceous

evidence for stratigraphically controlled paleogeotherms in the illinois basin based on vitrinite reflectance analysis implications for interpreting coal rank anomalies coal rank reflects the temperature of coalification with higher rank coal forming at higher temperatures if the temperature of coalification depended only on the earth s geothermal gradient then the maximum rank of coal in a sedimentary basin should be directly proportional to the thickness of strata above the coal this association does not occur in the illinois basin a continental interior basin in the midwestern united states where the overall coal rank observed is higher than can be explained by past burial depth alone recognition of this anomaly has led many authors to suggest that hot groundwater flowing from south to north during a paleozoic basin scale groundwater migration event increased coal rank we analyzed vitrinite reflectance formula 1 a measure of rank as a function of depth in wells across the basin to determine how paleogeotherms representing variation in temperature with depth change with location our results show that the basin can be divided into three zones 1 in the southern zone the paleogeotherm varies irregularly with depth in strata above the sub absaroka unconformity the contact separating pennsylvanian and mississippian strata 2 in the central zone the paleogeotherm displays a distinct inflection at the unconformity for the rate of increase in formula 2 with depth is greater above the unconformity than below the unconformity and 3 the observed inflection in the paleogeotherm dies out northward until in the northern zone the paleogeotherm has the same slope both above and below the unconformity we propose that the inflection in the paleogeotherm of the central zone indicates that the hot groundwater responsible for causing an increase in coal rank flowed through a high permeability zone just below the sub absaroka unconformity this flow which advected heat into pennsylvanian strata above cooled as it moved northward so it did not influence the paleogeotherm in the northern zone preliminary studies of vein paragenesis stable isotope composition and fluid inclusions as well as computer modeling of flow related heat advection support this proposal 1 embed mml math 1 gif 2 embed mml math 2 gif

study of magnitudes seismicity and earthquake detectability using a global network abstract based on 10 yr of observations reported in the international seismological centre bulletins 1971 1980 m b magnitudes for about 70 000 earthquakes have been recomputed using a maximum likelihood estimation technique reportings from a network of 115 globally distributed stations were used in these calculations comparison to conventional m b estimates show that the network magnitude bias problem is quite significant at low and intermediate magnitudes recurrence statistics based on the revised m b estimates give b values consistent with those obtained from lasa and norsar data and indicate that the number of earthquakes worldwide of m b 4 0 averages about 7 500 annually this number is much lower than previous estimates the teleseismic detection capability of the network requiring at least four detecting stations has been evaluated based on recurrence statistics the estimated 90 per cent incremental m b threshold ranges from 3 9 to 4 5 in the northern hemisphere and from 4 2 to 4 8 in the southern hemisphere this is consistent with results obtained by the networth approach

origin and significance of isotope shifts in pennsylvanian carbonates asturias nw spain abstract the primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water an inadequate understanding of this variability as well as different diagenetic environments severely limit the interpretation of the stable isotope record of shoalwater carbonates in order to investigate this primary and diagenetic variability along a bashkirian moscovian platform to basin transect 13c and 18o analyses have been performed on more than 1000 matrix micrite carbonate cement and brachiopod shell samples in isotope analysis these different carbonate materials tend to complement each other inasmuch as they have different advantages and shortcomings the resulting data reveal spatial trends in 13c and 18o signatures from platform top lower values to basin higher values in the case of 13c from pristine brachiopods this trend can be explained by the long residence time aging of platform top water masses in the case of brachiopod 18o this variance is interpreted to reflect temperature differences between warm surface and colder bottom water separated by a permanent thermocline at about 150 to 200 m beneath the shelf break micrite and marine cement isotopic values from the platform interior were reset lowered during pervasive early meteoric diagenesis in contrast micrite and marine cement isotopic values from the outer platform slope and basin show higher values close to the assumed pennsylvanian seawater isotopic composition this implies that isotopic data from shoalwater carbonates including pristine brachiopod shells might not necessarily reflect paleoceanographic trends of the open ocean water masses because of changes in coastal water mass isotope signature and interaction with early meteoric fluids

study of low magnitude seismic events near the novaya zemlya nuclear test site abstract a study of available seismic data shows that all but one of the 42 known underground nuclear explosions at novaya zemlya have been detected and located by stations in the global seismic network during the past 30 years only one seismic event in this area has been unambiguously classified as an earthquake 1 august 1986 m b 4 3 several other small events most of which are thought to be either chemical explosions or aftereffects of nuclear explosions have also been detected since 1990 a network of sensitive regional arrays has been installed in northern europe in preparation for the global seismic monitoring network under a comprehensive nuclear test ban treaty ctbt this regional network has provided a detection capability for novaya zemlya that is shown to be close to m b 2 5 three low magnitude events have been detected and located during this period as discussed in this article 31 december 1992 m b 2 7 13 june 1995 m b 3 5 and 13 january 1996 m b 2 4 to classify the source types of these events has proved very difficult thus even for the m b 3 5 event in 1995 we have been unable to provide a confident classification of the source as either an earthquake or explosion using the available discriminants a study of m b magnitude in different frequency bands shows as expected that the calculation of m b at regional distances needs to take into account source scaling effects at high frequencies thus when comparing a 4 to 8 or 8 to 16 hz filter band to a teleseismic 2 to 4 hz band the smaller events have relatively speaking significantly more high frequency energy up to 0 5 m b units than the larger events this suggests that a p wave spectral magnitude scale might be appropriate the problem of accurately locating small events using a sparse array network is addressed using the 13 january 1996 event which was detected by only two arrays as an illustrative example our analysis demonstrates the importance of using accurately calibrated regional travel time curves and at the same time illustrates how array processing can be used to identify an interfering phase from a local disturbance thereby avoiding location errors due to erroneous phase readings

source parameters of aftershocks of the 1991 costa rica and 1992 cape mendocino california earthquakes from inversion of local amplitude ratios and broadband waveforms abstract source parameters of aftershocks of the 22 april 1991 m w 7 7 costa rica and the 25 april 1992 m w 7 1 cape mendocino california earthquakes are determined using a grid search inversion of p sh and sv amplitude ratios recorded by sparse local networks of three component broadband and short period stations the inversion procedure consists of computing synthetic seismograms for three fundamental fault orientations for all source receiver pairs over a range of source depths calculating the complex envelopes of the observed and synthetic seismograms to determine peak amplitudes of p sh and sv waves combining the fundamental fault amplitudes for all possible values of strike dip and rake at 10 increments and determining the best fault orientation and depth as the one that yields the smallest misfit between observed and synthetic p sh p sv and sv sh amplitude ratios the ambiguity in the sense of motion on the nodal planes arising due to the use of amplitude ratios is resolved by examining p wave polarities the sensitivity of source parameters to uncertainties in earthquake location and crustal structure is explored for events with good station coverage focal mechanism determinations are stable for a wide range of assumed values of crustal structure earthquake location and depth source parameters for many of the largest events m 3 4 are also determined by inversion of broadband displacement waveforms using a similar grid search technique comparable results were obtained using both broadband waveforms and amplitude ratios focal mechanism solutions for 20 aftershocks of the costa rica earthquake reveal a complicated faulting geometry indicating active thrust normal and strike slip faults in the back arc of costa rica the 1992 cape mendocino earthquake occurred at the intersection of the north american gorda and pacific plates while the mainshock was associated with underthrusting of the gorda plate beneath the north american plate fault plane solutions for 70 of the 38 largest aftershocks indicate that these events result from either motion between the gorda and pacific plates or from internal deformation within the gorda plate

systems tracts and depositional sequences in a carbonate setting a study of continuous outcrops from platform to basin at the scale of seismic lines abstract the application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application the continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the southern vercors plateau western alps france confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems from the stratal patterns displayed in outcrop we determined that carbonate lowstand systems tracts are major components in the basin even in the deep pelagic realm transgressive and highstand systems tracts are very thin a response to starvation in contrast on the shelf transgressive and highstand systems tracts are the major components carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break it clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts especially of carbonate lowstand systems tracts are basically similar to those of siliciclastic systems tracts this study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand this is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments a second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts this paper demonstrates that the shoreline position for carbonates which indicates the facies transgression or regression is independent of prograding or retrograding shelf breaks the stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space i e on their position within the transgressive and regressive cycles