aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

evolution of mesozoic sandstone compositions southern junggar northern tarim and western turpan basins northwest china a detrital record of the ancestral tian shan abstract sandstone compositional data can be a powerful tool in the interpretation of tectonic and climatologic influences on sedimentary basin fill in addition to yielding important information about porosity in sandstone petroleum reservoirs in order to explore these relationships a modified gazzi dickinson point counting technique was used to analyze the composition of 143 mesozoic sandstone samples from the southern junggar northern tarim and western turpan basins of northwestern china results indicate that a mesozoic ancestral version of the tian shan physiographically separated the junggar and tarim basins and provided sand of very different composition to each basin mesozoic sandstone from the northern tarim basin is diverse in composition and lithic rich qm41f14l45 qp42lvm26lsm32 is locally micaceous and contains common radiolarian chert grains and few dense accessory minerals inferred source rocks include upper paleozoic alkali granite and metamorphic complexes thick silurian bedded chert sequences and lower paleozoic strata of a passive continental margin in contrast sandstone from the southern junggar and western turpan basins is uniformly volcanic rich qm21f21lt58 qp13lvm68lsm19 and contains abundant dense accessory minerals and only local radiolarian chert and mica inferred principal source rocks are devonian carboniferous andesitic arc volcanics the effect of sampling scale on sandstone composition outweighs that of plate tectonic setting samples were derived mostly from medium and coarse grained fluvial systems that likely drained only portions of the ancestral tian shan and hence preserve local source rock signatures rather than an integrated compositional signal that can be directly compared to plate tectonic petrofacies models in addition though mesozoic basins of western china were most akin to broken foreland basins mesozoic sandstone is considerably more compositionally diverse and lithic rich than that of modern or ancient broken foreland basins because of the variety of accreted terranes constituting the ancestral tian shan temporal changes in sandstone composition are consistent with episodes of mesozoic deformation in the tian shan each deformational episode increased physiographic relief of the ancestral range produced renewed downcutting and erosion of source rocks and resulted in the deposition of compositionally very immature sandstone in adjacent basins although a regional early mesozoic megamonsoon and an early cretaceous rain shadow cast across the northern tarim basin are interpreted from regional facies and paleontologic data neither paleoclimatic phenomenon appears to have significantly modified sandstone composition in the study area calculations of intergranular volume porosity cement indicate that porosity in sandstone from the tarim and junggar basin depocenters was reduced principally by burial compaction and that the rate of porosity reduction was highest for lithic rich samples

review of fossil chemosynthetic assemblages in japan abstract seventy five fossil chemosynthetic assemblages of cretaceous to holocene age have been discovered in japan many are interpreted to have been cold seep dependent and one is associated with a whale fall fossil hydrothermal vent assemblages have not been found in japan non seep assemblages of solemyids lucinids and or thyasirids are not included in this study various combinations of five diagnostic features characterize cold seep assemblages 1 the abundant and often exclusive occurrence of large invertebrate taxa suspected of harboring chemosynthetic bacteria 2 associated authigenic carbonates greatly depleted in 13c 3 a three dimensional distribution of the assemblage that is laterally restricted 4 associated pockmark or diapir related sedimentary structures and 5 the presence of conduit related tectonic or sedimentological structures such as faults slumps or debris flows excluding the whale fall assemblage we can divide cenozoic fossil chemosynthetic assemblages in japan into three types regardless of geochronologic age type i is dominated by vesicomyid bivalves and or tube worms characterized by its allochthonous or parautochthonous mode of occurrence in deep water greater than 1000 m settings along with tectonically or sedimentologically induced structures such as faults slumps diapirs or debris flows likely dependent on seepage controlled by subduction related tectonism and or on methane coming from the drastic decomposition of gas hydrate type ii is dominated by vesicomyid bivalves in most cases the species differ from those in type i and is characterized by autochthonous occurrences in muddy sediments from less than 1000 m water depth type iii is dominated by lucinoma and or conchocele and characterised by autochthonous occurrences in muddy sediments from depths of less than 300 m a living community similar to the type ii and iii assemblages has not yet been observed in the seas around japan it is noteworthy that no tectonically or sedimentologically induced structures have been observed in and around the type ii and iii fossil localities although the muddy sediments sometimes show brecciated facies that suggest an explosive effusion of methane

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

relationships between meso cenozoic denudation in the eastern tian shan and uranium mineralization in the turpan hami basin nw china constraints from apatite fission track study abstract the eastern tian shan tectonic belt located in the southern domain of the central asian orogenic belt consists of the bogda mountain range turpan hami tuha basin and choltagh mountain range from north to south understanding the meso cenozoic denudation history of the eastern tian shan is critical to unravel the genesis of sandstone type uranium u mineralization in the tuha basin in this paper thirteen granite and sandstone samples were collected along two north south transects in the west of the eastern tian shan for apatite fission track thermochronological study the apatite fission track ages obtained in this study in combination with the thermal history modeling results and previous thermochronological data indicate three main episodes of denudation in the eastern tian shan since the mesozoic i e late jurassic to early cretaceous 160 135 ma late cretaceous to early eocene 100 50 ma and late eocene to early miocene 35 20 ma the late cretaceous denudation events are related to the kohistan dras arc accretion collision that affects the tian shan mountain range extensively whereas the cenozoic ones are related to the india asia collision regional distribution of apatite fission track ages in the eastern tian shan and comparison with u mineralization ages in the tuha basin suggest that the choltagh mountain range began to denudate in the late jurassic exposing high u bearing volcanic rocks on the surface and resulting in significant u mineralization in the southern part of the tuha basin in the cretaceous whereas the bogda mountain range in the north did not experience significant denudation until the late eocene due to the relatively low exhumation of the bogda mountain range and limited exposure of u bearing rocks u mineralization in the tuha basin is minor during the cenozoic but the newly deposited sediments helped the preservation of the u deposits that were formed in the cretaceous

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

fault reactivation in the junggar region northwest china the role of basement structures during mesozoic cenozoic compression basement structures exposed at the margins of the junggar basin were created during the altaid orogeny in the late palaeozoic the most prominent structures are backstops to subduction accretion complexes north tien shan fault or major thrusts within these complexes dalabute and kelameili faults both types of basement structure are far more common in accretionary turkic type orogens such as the altaids than true sutures probably the only suture sensu stricto in the junggar area is cryptic and lies under the junggar basin s thick mesozoic cenozoic cover the exposed palaeozoic fault zones have been reactivated by mesozoic cenozoic compressional events which are the long distance expression of orogenies at the southern margin of asia latest palaeozoic and mesozoic events reactivated a larger number of fault zones than have been affected by the cenozoic india asia collision possibly because of an increase in the strength of the junggar basement over time following late permian rifting cenozoic strain is partitioned between strike slip motion on basement structures within the palaeozoic orogenic belts around the junggar basin and numerous thrusts and transpressive faults in regions marginal to and within the basin itself most major strike slip faults are reactivated structures and occupy narrower zones than their palaeozoic precursors thrust zones follow the palaeozoic basement grain but active faults have propagated into the mesozoic cenozoic cover

migration velocity analysis in factorized vti media one of the main challenges in anisotropic velocity analysis and imaging is simultaneous estimation of velocity gradients and anisotropic parameters from reflection data approximating the subsurface by a factorized vti transversely isotropic with a vertical symmetry axis medium provides a convenient way of building vertically and laterally heterogeneous anisotropic models for prestack depthmigration the algorithm for p wave migration velocity analysis mva introduced here is designed for models composed of factorized vti layers or blocks with constant vertical and lateral gradients in the vertical velocity vp0 the anisotropic mva method is implemented as an iterative two step procedure that includes prestack depth migration imaging step followed by an update of the medium parameters velocity analysis step the residual moveout of the migrated events which is minimized during the parameter updates is described by a nonhyperbolic equation whose coefficients are determined by 2d semblance scanning

hydrothermalism in the mediterranean sea abstract hydrothermalism in the mediterranean sea results from the collision of the african and european plates with the subduction of the oceanic part of the african plate below europe high heat flows in the resulting volcanic arcs and back arc extensional areas have set up hydrothermal convection systems most of the known hydrothermal sites are in shallow coastal waters

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

feasibility of nonhyperbolic moveout inversion in transversely isotropic media inversion of reflection traveltimes in anisotropic media can provide estimates of anisotropic coefficients required for seismic processing and lithology discrimination nonhyperbolic p wave moveout for transverse isotropy with a vertical symmetry axis vti media is controlled by the parameter or alternatively by the horizontal velocity vhor which is also responsible for the influence of anisotropy on all time processing steps including dip moveout dmo correction and time migration here we recast the nonhyperbolic moveout equation originally developed by tsvankin and thomsen as a function of vhor and normal moveout nmo velocity vnmo and introduce a correction factor in the denominator that increases the accuracy at intermediate offsets then we apply this equation to obtain vhor and from nonhyperbolic semblance analysis on long common midpoint cmp spreads and study the accuracy and stability of the inversion procedure our error analysis shows that the horizontal velocity becomes relat

depth domain velocity analysis in vti media using surface p wave data is it feasible the main difficulties in anisotropic velocity analysis and inversion using surface seismic data are associated with the multiparameter nature of the problem and inherent trade offs between the model parameters for the most common anisotropic model transverse isotropy with a vertical symmetry axis vti media p wave kinematic signatures are controlled by the vertical velocity v0 and the anisotropic parameters e and however only two combinations of these parameters nmo velocity from a horizontal reflector vnmo 0 and the anellipticity coefficient can be determined from p wave reflection traveltimes if the medium above the reflector is laterally homogeneous while vnmo 0 and are sufficient for time domain imaging in vti media they cannot be used to resolve the vertical velocity and build velocity models needed for depth migration here we demonstrate that p wave reflection data can be inverted for all three relevant vti parameters v0 e and if the model contains nonhorizontal intermediate i

cenozoic tectonic and geodynamic evolution of the kyrgyz tien shan mountains a review of geological thermochronological and geophysical data abstract the complex crustal structure of the tien shan has a strong impact on the distribution of strain induced by the india eurasia collision with intracontinental deformation in eurasia s interior as a distant effect the northward propagation of the india eurasia deformation front is suggested by the rejuvenation of mountain ranges and intermittent intramontane basins the tien shan basement is formed by the rigid heterogeneous precambrian blocks microcontinents of tarim issyk kul or central tien shan and aktyuz boordin surrounded by a soft matrix of paleozoic accretion collision belts the kyrgyz tien shan mountains are situated between the active structures of the tarim plate and the pamir indenter south and the stable kazakhstan shield north underplating by the tarim plate and thrusting by the pamirs are responsible for the building of the cenozoic tien shan the reactivation of its inherited structural fabric and the tectonic layering of the upper lithosphere underlying the area large earthquakes m 6 delineate the northern and southern margins of the issyk kul microcontinent indicating that crustal heterogeneity influenced the location of active structures in the northern kyrgyz tien shan

3 d moveout inversion in azimuthally anisotropic media with lateral velocity variation theory and a case study reflection moveout recorded over an azimuthally anisotropic medium e g caused by vertical or dipping fractures varies with the azimuth of the source receiver line normal moveout nmo velocity responsible for the reflection traveltimes on conventional length spreads forms an elliptical curve in the horizontal plane while this result remains valid in the presence of arbitrary anisotropy and heterogeneity the inversion of the nmo ellipse for the medium parameters has been discussed so far only for horizontally homogeneous models above a horizontal or dipping reflector here we develop an analytic moveout correction for weak lateral velocity variation in horizontally layered azimuthally anisotropic media the correction term is proportional to the curvature of the zero offset traveltime surface at the common midpoint and therefore can be estimated from surface seismic data after the influence of lateral velocity variation on the effective nmo ellipses has been stripped the generalized dix equat

anisotropic migration velocity analysis application to a data set from west africa although it is widely recognized that anisotropy can have a significant influence on the focusing and positioning of migrated reflection events conventional depth imaging methods still operate with isotropic velocity fields here we present an application of a 2d migration velocity analysis mva algorithm designed for factorized v x z vti transversely isotropic with a vertical symmetry axis media to an offshore data set from west africa by approximating the subsurface with factorized vti blocks it is possible to decouple the spatial variations in the vertical velocity from the anisotropic parameters with minimal a priori information since our method accounts for lateral velocity variation it produces more accurate estimates of the anisotropic parameters than those previously obtained with time domain techniques the values of the anellipticity parameter found for the massive shales exceed 0 2 which confirms that ignoring anisotropy in the study area can lead to substantial imaging distortions such as mis stacking and mispositioning of dipping events while some of these distortions can be removed by using anisotropic time processing further marked improvement in image quality is achieved by prestack depth migration with the estimated factorized vti model in particular many fault planes including antithetic faults in the shallow part of the section are better focused by the anisotropic depth migration algorithm and appear more continuous anisotropic depth migration facilitates structural interpretation by eliminating false dips at the bottom of the section and improving the images of a number of gently dipping features one of the main difficulties in anisotropic mva is the need to use a priori information for constraining the vertical velocity in this case study we successfully reconstructed the time depth curve from reflection data by assuming that the vertical velocity is a continuous function of depth and estimating the vertical and lateral velocity gradients in each factorized block if the subsurface contains strong boundaries with jumps in velocity knowledge of the vertical velocity at a single point in a layer is sufficient for our algorithm to determine all relevant layer parameters

first evidence of widespread active methane seepage in the southern ocean off the sub antarctic island of south georgia an extensive submarine cold seep area was discovered on the northern shelf of south georgia during r v polarstern cruise ant xxix 4 in spring 2013 hydroacoustic surveys documented the presence of 133 gas bubble emissions which were restricted to glacially formed fjords and troughs video based sea floor observations confirmed the sea floor origin of the gas emissions and spatially related microbial mats effective methane transport from these emissions into the hydrosphere was proven by relative enrichments of dissolved methane in near bottom waters stable carbon isotopic signatures pointed to a predominant microbial methane formation presumably based on high organic matter sedimentation in this region although known from many continental margins in the world s oceans this is the first report of an active area of methane seepage in the southern ocean our finding of substantial methane emission related to a trough and fjord system a topographical setting that exists commonly in glacially affected areas opens up the possibility that methane seepage is a more widespread phenomenon in polar and sub polar regions than previously thought

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

neotethyan late cretaceous volcanic arc hydrothermal vent fauna the barite polymetallic ore zone of the late cretaceous madneuli volcanogenic massive sulfide vms deposit in the republic of georgia contains large tube worm fossils that represent the first ancient hydrothermal vent fauna to be identified from a volcanic arc setting and very likely the shallowest ancient example yet found the fossil tube walls are formed of an unusual quartz barite pyrite and galena mineral assemblage rather than only pyrite as in other vent fossils this probably reflects the low temperature high salinity vent chemistry at the time of preservation as deduced from fluid inclusion analyses the madneuli vent fauna is one of three examples that occurred over a time span of 6 m y in an area of the neotethyan ocean that was as tectonically complex as the present day west pacific the ancient and modern vent faunas appear to occur in a similar range of tectonic settings and bathymetry

vti anisotropic corrections and effective parameter estimation after isotropic prestack depth migration in the method for applying anisotropic corrections after isotropic prestack depth migration psdm the correction which is calculated and implemented in the depth domain is defined as a time difference between isotropic and anisotropic traveltimes under the assumption that the vertical velocity is known the definition of this correction uses a special postmigration common image gather cig ordering which collects the migrated data according to the input trace s source and receiver distance from the surface cig location in this postmigration domain the dip of the events can be directly related to their horizontal position in the cig called the imaging offset and the separation of flat and dipping reflectors becomes easy to perform the dependency of the seismic anisotropic effect on the subsurface dip angle is well pronounced in these cigs after application of an isotropic psdm effective anisotropic parameter estimation is performed at selected cig locations by using a simple two parameter scan procedure the optimal anisotropic parameters can be used to perform a final anisotropic psdm or to apply a residual correction to the isotropically migrated data we demonstrate the method for p wave data in 2d media with vertical transverse isotropy vti symmetry by using both synthetic and real data we also present a strategy for handling the ambiguity between the vertical velocity and the anisotropic parameters

multi stage exhumation of the ne tarim precambrian bedrock nw china constraints from apatite fission track thermochronology in the kuluketage area terra nova 23 324 332 2011 abstract fourteen samples of precambrian bedrocks from the kuluketage area located in the north eastern tarim craton yield apatite fission track ages ranging from 166 to 82 ma these ages are far younger than their precambrian age of stratigraphy or metamorphism indicating that the samples experienced total annealing before mesozoic exhumation the samples were subdivided into three groups based on locations and ages multi stage mesozoic exhumation is linked to collisions of the qiangtang lhasa and kohistan terranes with the south eurasian continental margin the three cooling phases are also shown by stratigraphy and seismology considering modelling results with different constraint boxes seismic profiles and the stratigraphic sequences of surrounding sedimentary basins faint cenozoic reheating and recooling were likely to take place in the kuluketage area by northwards propagating deformation from india eurasia collision and continued convergence

vent fluid chemistry in bahia concepcion coastal submarine hydrothermal system baja california sur mexico abstract shallow submarine hydrothermal activity has been observed in the bahia concepcion bay located at the gulf coast of the baja california peninsula along faults probably related to the extensional tectonics of the gulf of california region diffuse and focused venting of hydrothermal water and gas occurs in the intertidal and shallow subtidal areas down to 15 m along a nw se trending onshore offshore fault temperatures in the fluid discharge area vary from 50 c at the sea bottom up to 87 c at a depth of 10 cm in the sediments chemical analyses revealed that thermal water is enriched in ca as hg mn ba hco3 li sr b i cs fe and si and it has lower concentrations of cl na so4 and br than seawater the chemical characteristics of the water samples indicate the occurrence of mixing between seawater and a thermal end member stable isotopic oxygen and hydrogen composition of thermal samples plot close to the local meteoric water line on a mixing trend between a thermal end member and seawater the composition of the thermal end member was calculated from the chemistry of the submarine samples data by assuming a negligible amount of mg for the thermal end member the results of the mixing model based on the chemical and isotopic composition indicate a maximum of 40 of the thermal end member in the submarine vent fluid chemical geothermometers na li na k ca and si were applied to the thermal end member concentration and indicate a reservoir temperature of approximately 200 c the application of k mg and na li geothermometers for vent fluids points to a shallow equilibrium temperature of about 120 c results were integrated in a hydrogeological conceptual model that describes formation of thermal fluids by infiltration and subsequent heating of meteoric water vent fluid is generated by further mixing with seawater

velocity independent layer stripping of pp and ps reflection traveltimes buildingaccurateintervalvelocitymodelsiscriticallyimportant for seismic imaging and avo amplitude variation withoffsetanalysis here weadaptthepp ps ssmethodtodevelopanexacttechniqueforconstructingtheinterval traveltime offset function in a target zone beneath a horizontally layered overburden all layers in the model can be anisotropic with an essential assumption that the overburden hasahorizontalsymmetryplanei e up downsymmetry our layer stripping algorithm is entirely data driven and in contrast to the generalized dix equations does not require knowledgeofthevelocityfieldanywhereinthemedium important advantages of our approach compared to the dixstyle formalism also include the ability to handle mode converted waves long offset data and laterally heterogeneous targetlayerswithmultiple curvedreflectors numericaltests confirm the high accuracy of the algorithm in computing the interval traveltimes of both pp and ps waves in a dipping transversely isotropic layer with a tilted symmetry axis tti mediumbeneathananisotropicoverburden in combination with the inversion techniques developed forhomogeneousttimodels theproposedlayerstrippingof pp and ps data can be used to estimate the interval parameters oftti formations in such important exploration areas as thecanadianfoothills potentialapplicationsofthismethodology also include the dip moveout inversion for the p wave time processing parameter and stable computation of the interval long spread nonhyperbolic moveout for purposes ofanisotropicvelocityanalysis

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

ray based gridded tomography for tilted transversely isotropic media reflection tomography in the migrated domain can help reconstruct heterogeneous anisotropic velocity fields needed for accurate depth imaging of complex geologic structures the presence of anisotropy however increases the uncertainty in velocity analysis and typically requires a priori constraints on the model parameters here we develop a 2d p wave tomographic algorithm for heterogeneous transversely isotropic media with a tilted symmetry axis tti and investigate the conditions necessary for stable estimation of the symmetry direction velocity vp0 and the anisotropy parameters e and the model is divided into rectangular cells and the parameters vp0 e and the tilt of the symmetry axis are defined at the grid points to increase the stability of the inversion the symmetry axis is set orthogonal to the imaged reflectors with the tilt interpolated inside each layer the iterative migration velocity analysis involves efficient linearized parameter updating designed to minimize the residual moveout in image gathers for all available reflection events the moveout equation in the depth migrated domain includes a nonhyperbolic term that describes long offset data which are particularly sensitive to e synthetic tests for models with a quasi factorized tti syncline i e e and are constant inside the anisotropic layer and a tti thrust sheet demonstrate that stable parameter estimation requires either strong smoothness constraints or additional information from walkaway vsp vertical seismic profiling traveltimes if the model is quasifactorized with a linear spatial variation of vp0 it may be possible to obtain the interval tti parameters just from long spread reflection data

deep sea and shallow water hydrothermal vent communities two different phenomena hydrothermal vent communities from 76 areas lying at depths from 0 to 4100 m were split into two groups bdeepq and bshallow waterq based on the occurrence of vent obligate restricted to hydrothermal vents taxa of a high rank genus and family the two groups were then compared based on a large set of environmental faunistic and community parameters the degree of obligacy of fauna sharply changes at the depth of approximately 200 m in 21 shallow water areas located at depths b200 m vent obligate taxa are absent or their taxonomic rank does not exceed a species the total number of vent obligate species in shallow water is 8 and their obligacy is uncertain data from 55 areas lying at depths from 200 to 4100 m indicate there are ca 400 obligate species in 47 of these areas obligate vent taxa of the genus or the family rank are present obligate taxa of the genus rank appear at 200 m depth and of the family rank at 386 m the depth ca 200 m corresponds well with differences in community structure and composition and environmental parameters deep sea n200 m hydrothermal communities differ from shallow water ones b200 m in a much higher ratio of vent obligate taxa deep sea vent communities are also distinguished by the lack of diatom and algae bacterial mats phytoplankton lower species richness the development of large sulphide structures higher role of active vents in structuring communities in space replication of a set of dominant taxa in communities within large regions reproduced through the succession at newly formed vent fields more pronounced concentric and vertical zonality higher biomass of macrofauna the important role of symbiotrophic forms dominating the biomass the ratio of species with a bpointq species range endemic to small areas is higher in the deep sea there are no significant differences between the vent and non vent biogeography both in shallow waters and the deep ocean modern deep sea hydrothermal vent communities have a longer evolutionary history than their shallow water counterparts to explain major differences between deep and shallow water hot vent communities evolutionary processes need to be analysed over long geological periods and within global vertical zones it is suggested that the proportion of organic matter derived from chemosynthesis and photosynthesis plays a crucial role in evolution when calculated for global zones this proportion increases with depth to a certain critical level that separates deep and shallow water hot vent communities and fauna vertical zonation in the distribution of obligate taxa in hydrothermal vent communities indicates that this level is reached at approximately 200 m depth

primary uranium sources for sedimentary hosted uranium deposits in ne china insight from basement igneous rocks of the erlian basin carboniferous permian triassic and jurassic igneous basement rocks around the erlian basin in northeast china have been investigated through detailed mineralogical whole rock geochemistry geochronological data and sm nd isotope studies carboniferous permian biotite granites and volcanic rocks belong to a calc alkaline association and were emplaced during the late carboniferous early permian 313 1 286 2 ma these rocks are characterised by positive end t 3 3 5 3 and fairly young t dm model ages 485 726 ma suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks triassic biotite granites belong to a high k calc alkaline association and were emplaced during the middle triassic 243 3 233 2 ma their negative end t 2 to 0 1 and higher t dm model ages 703 893 ma suggest a contribution from precambrian crust during the magma generation processes leading to a strong enrichment in k and incompatible elements such as th and u highly fractionated magmas crystallised in u rich biotite up to 21 ppm u and two mica granites in biotite granite the major u bearing minerals are uranothorite and allanite they are strongly metamict and the major part of their uranium 90 has been released from the mineral structure and was available for leaching mass balance calculations show that the triassic biotite granites may have at least liberated 14 000 t u km3 and thus correspond to a major primary uranium source for the u deposits hosted in the erlian basin

analysis of image gathers in factorized vti media because events in image gathers generated after prestack depth migration are sensitive to the velocity field they are often used in migration velocity analysis for isotropic media here we present an analytic and numerical study of p wave image gathers in transversely isotropic media with a vertical symmetry axis vti and establish the conditions for flattening such events and positioning them at the true reflector depth application of the weak anisotropy approximation leads to concise expressions for reflections in image gathers from homogeneous and factorized v z media in terms of the vti parameters and the vertical velocity gradient kz flattening events in image gathers for any reflector dip requires accurate values of the zero dip nmo velocity at the surface vnmo z 0 the gradient kz and the anellipticity coefficient for a fixed error in vnmo and kz the magnitude of residual moveout of events in image gathers decreases with dip while the moveout caused by an error in initially incr

provenance constraints on the xishanyao formation southern yili basin northwest china evidence from petrology geochemistry and detrital zircon u pb geochronology we conducted petrographic geochemical and new u pb laser ablation inductively coupled mass spectrometry analyses of detrital zircons in the sandstone samples from the important mengqiguer sandsto

deep sea hydrothermal communities in southwestern pacific back arc basins the north fiji and lau basins composition microdistribution and food web abstract during the year 1989 two diving cruises of the french deep sea submersible nautile were devoted to the study of hydrothermal vent biology in spreading centers of two southwestern pacific back arc basins lau basin and north fiji basin in both cases two major active sites were visited white lady and mussel valley in the north fiji basin and hine hina and vai lili in lau basin the faunal associations clustered around active vents are dominated by two species of snails ifremeria nautilei and alviniconcha hessleri and one or two species of mytilids belonging to bathymodiolus these species are associated with chemoautolithotrophic bacteria in intracellular symbiosis as detected by the activity of the calvin benson cycle diagnostic enzyme rubpcase pedunculate and sessile barnacles dominated the outer rim of the site and are analogs of the fiter feeding serpulids living in the epr sites the hot extremes of the sites are poorly or not colonized by alvinellids or other taxa in the lau basin cold seep sites are found at the periphery of active hot or warm ventsand are dominated by vestimentiferans and pogonophorans no major differences were seen between associations of the two back arc basins at the generic level with the exeption of the abundance of synaptid holothurians associated with bathymodiolus in side the mussel valley site

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

nonlinear 3d tomographic least squares inversion of residual moveout in kirchhoff prestack depth migration common image gathers velocity model estimation with seismic reflection tomographyisanonlinearinverseproblem wepresentanewmethodforsolvingthenonlineartomographicinverseproblemusing 3d prestack depth migrated reflections as the input data i e our method requires that prestack depth migration psdmbeperformedbeforetomography themethodisapplicable to any type of seismic data acquisition that permits seismic imaging with kirchhoff psdm afundamental conceptofthemethodisthatwedissociatethepossiblyincorrect initialmigrationvelocitymodelfromthetomographicvelocity model we take the initial migration velocity model and the residual moveout in the associated psdm common image gathers as the reference data this allows us to consider themigrateddepthoftheinitialpsdmastheinvariantobservation for the tomographic inverse problem we can therefore formulate the inverse problem within the general framework of inverse theory as a nonlinear least squares data fitting between observed and modeled migrated depth the modeledmigrateddepthiscalculatedbyraytracinginthetomographic model followed by a finite offset map migration in the initial migration model the inverse problem is solved iteratively with a gauss newton algorithm we applied the method to a north sea data set to build an anisotropic layer velocitymodel

apatite fission track thermochronology of the precambrian aksu blueschist nw china implications for thermo tectonic evolution of the north tarim basement the precambrian aksu blueschist is located in the northwestern margin of the tarim block nw china in recent decades many studies were carried out with focus on the metamorphic age however a complete understanding of the evolution of the tarim block requires the cooling history of the precambrian metamorphic rocks and the time temperature paths as determined by low temperature thermochronometry therefore apatite fission track aft technique was applied on the precambrian aksu blueschist to reveal the thermo tectonic evolution of the north tarim basement all of the six blueschist samples analysed in this study yielded aft ages spanning 107 5 62 5 ma much younger than the blueschist facies metamorphic age of neoproterozoic and confined track lengths are between 10 46 and 12 12 m based on regional stratigraphic sequences the aft thermal history modeling as well as previous chronological results the thermo tectonic evolution of the aksu blueschist can be roughly reconstructed with four stages 1 the precambrain aksu blueschist exhumed to the surface soon after its formation erosion during the early sinian is indicated by the lack of sedimentation until the late sinian 2 the late sinian strata are continuous while the middle upper silurian and the lower middle carboniferous strata are absent the total thickness of the late sinian and paleozoic strata probably reached 10 000 m and resulted in the total annealing and thermal resetting of aft ages 3 the aft ages in the cretaceous are related with the widespread uplift in tian shan and its adjacent regions that restarted the aft clock during the late mesozoic these reflect a distant effect of the collision of the lhasa terrane with eurasia in the late jurassic early cretaceous and 4 sediments of cenozoic are documented in the aksu area the aksu blueschist was heated to partial annealing zone with the overlying cenozoic sediments during miocene time the aksu blueschist was re exhumed which was probably a distant response to the ongoing india eurasia convergence

late oligocene early miocene initiation of shortening in the southwestern chinese tian shan implications for neogene shortening rate variations abstract the cenozoic tian shan is one of the preeminent examples of an intracontinental orogen however there remains a significant controversy over when deformation related to the india asia collision commenced and therefore how shortening within the mountains has been partitioned over time one approach has been to look at the modern shortening rate as measured by geodetic studies combined with estimates of the total shortening across the range and extrapolate backwards this approach suggests that the onset of range construction was ca 10 ma k y abdrakhmatov s a aldazhanov b h hager m w hamburger t a herring k b kalabaev k b kalabayev v i makarov p molnar s v panasyuk m t prilepin r e reilinger i s sadybakasov b j souter y a trapeznikov v y tsurkov a v zubovich relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates nature 384 6608 1996 450 453 an alternate method is to determine the age of the onset of exhumation using thermochronology we present 19 new apatite fission track aft results from the southwestern chinese portion of the belt this region represents the first area exhumed during the late tertiary along a transect at ca 76 e exhumation commenced at the oligocene miocene boundary 24 ma along the maidan and muziduke thrusts which bound the southern side of the kokshaal range subsequently deformation propagated ca 20 km south to the kashi basin bounding thrust kbt which was exhumed by no earlier than 18 9 3 3 ma three detrital aft samples from plio pleistocene strata deposited ca 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20 9 7 0 5 3 ma to 15 9 5 4 4 0 ma with a fairly constant lag time of 16 to 18 ma these ages combined with structural data suggest that both the hanging wall and the footwall of the kbt experienced a renewed episode of exhumation during the latest cenozoic the discrepancy between the late oligocene miocene initiation of significant exhumation shown herein and the 10 ma initiation estimate from geodesy suggests that the tian shan has undergone a complex late cenozoic shortening history assuming that the present shortening rate could account for the total amount of cenozoic shortening in 10 ma and realizing that shortening initiated at least 15 myr earlier we conclude that the shortening rate must have varied over time possibly in pulsed southward migrating events and that the present rate may not reflect the average rate since initiation of range uplift

tracking the multi stage exhumation history of the western chinese tianshan by apatite fission track aft dating implication for the preservation of epithermal deposits in the ancient orogenic belt abstract the western chinese tianshan located in the southern domain of the central asian orogenic belt caob was originally established by multiple accretion collision processes in the paleozoic and was modified by complicated intracontinental tectonic evolution in the mesozoic to cenozoic understanding the timing and mechanism of the latter geological processes is critical to unravel the preservation conditions of the epithermal deposits in the western chinese tianshan this work presents new apatite fission track aft data for three mountain ranges keguqinshan wusunshan and nalatishan of the western chinese tianshan to track their exhumation history our aft data gave a wide range of ages from 76 8 5 5 ma to 182 3 9 9 ma and the mean confined fission track lengths are between 9 8 0 5 m and 12 3 0 2 m the new data in combination with the thermal history modeling results allow us to summary three main episodes of exhumation in the western chinese tianshan including the early permian 300 280 ma late triassic late jurassic 230 140 ma and late oligocene early miocene 30 20 ma the first episode may have been caused by terrane accretion collision in the late paleozoic leading to uplift of the keguqinshan that supplied abundant sediments to form a critical cover of ca 4 km thick on these epithermal deposits the second episode was likely related to closure of the mongol okhotsk ocean in the mesozoic and an extremely slow exhumation rate ca 0 0083 mm y as well as a moderate erosion of ca 0 8 km thick are estimated the last episode is regarded to be the result of collision between the indian plate and the eurasia plate in the cenozoic and this significant tectonic event triggered rapid exhumation up to ca 0 1 mm y of the whole region in the western chinese tianshan which removed more than ca 3 2 km pre cenozoic sedimentary cover and sent the epithermal deposits to the subsurface level

mediterranean fossil whale falls and the adaptation of mollusks to extreme habitats the hypothesis that sunken carcasses of mesozoic marine reptiles and cenozoic whales acted as evolutionary stepping stones to deep sea reducing habitats is underlain by the question of whether vent like chemosymbiotic specialization fi rst evolved at shelf depths fossil skeletons of large whales have long been known from ancient shallow water strata but they have never been considered as a source of information on ecosystem development we present a study on a 3 ma old fossil whale fall and a survey of other pliocene fossil skeletons to show that the associated biota is dominated by heterotrophs with subsidiary chemoautotrophs the taphonomy of the mediterranean shelf whale falls shows some differences with respect to deep water studies quantitative analyses of abundance data within a large data set on fossil and modern mollusk families confi rm that deep and shallow water communities at reducing habitats are composed of a different set of taxa i e specialists occurring only below the shelf break mediterranean carcasses sunken in coastal settings do not seem to be favorable for the evolution of whale fall specialists among the mollusks the situation reverses as the shelf break is approached

hydrothermal venting within a coral reef ecosystem ambitle island papua new guinea shallow water 5 10 m hydrothermal venting in a nearshore coral reef environment at ambitle island in the tabar feni island arc east of papua new guinea occurs as focused discharge of boiling fluid from discrete ports 10 15 cm in diameter and as dispersed discharge of diffuse bubble streams that issue through the sandy mixed carbonate volcaniclastic sea floor abiotic aragonite and microcrystalline ferroan low mg calcite interlaminated with fe oxyhydroxides are the prominent hydrothermal precipitates geochemical attributes of aragonite 18o 13c and fluid inclusions suggest that cements formed from a solution with salinities 5 at temperatures of 100 c with probable contribution of hydrothermal co2 sr isotope ratios in abiotic hydrothermal aragonite 0 704 15 are similar to those in island arc basalt and denote considerable subsurface water rock interaction of meteoric water derived from the adjacent volcanic island the sr isotope ratio of a coral sample 0 707 46 collected adjacent to a vent portal suggests coral growth within a mixed seawater hydrothermal environment

migration velocity analysis for ti media in the presence of quadratic lateral velocity variation abstractone of the most serious problems in anisotropic velocity analysis is the trade off between anisotropy and lateral heterogeneity especially if velocity varies on a scale smaller than the maximum offset we have developed a p wave mva migration velocity analysis algorithm for transversely isotropic ti models that include layers with small scale lateral heterogeneity each layer is described by constant thomsen parameters e and and the symmetry direction velocity v0 that varies as a quadratic function of the distance along the layer boundaries for tilted ti media tti the symmetry axis is taken orthogonal to the reflectors we analyzed the influence of lateral heterogeneity on image gathers obtained after prestack depth migration and found that quadratic lateral velocity variation in the overburden can significantly distort the moveout of the target reflection consequently medium parameters beneath the heterogeneous layer s are estimated with substantial error even when borehole informa

image gathers of sv waves in homogeneous and factorized vti media reflection moveout of sv waves in transversely isotropic media with a vertical symmetry axis vti media can provide valuable information about the model parameters and help to overcome the ambiguities in the inversion of p wave data here to develop a foundation for shear wave migration velocity analysis we study sv wave image gathers obtained after prestack depth migration the key issue addressed using both approximate analytic results and kirchhoff migration of synthetic data is whether long spread sv data can constrain the shear wave vertical velocity vs0 and the depth scale of vti models for homogeneous media the residual moveout of horizontal sv events on image gathers is close to hyperbolic and depends just on the nmo velocity vnmo out to offset to depth ratios of about 1 7 because vnmo differs from vs0 flattening moderate spread gathers of sv waves does not ensure the correct depth of the migrated events the residual moveout rapidly becomes nonhyperbolic as the offset to depth ratio approaches two with the migrated depths at long offsets strongly influenced by the sv wave anisotropy parameter although the combination of vnmo and is sufficient to constrain the vertical velocity vs0 and reflector depth the tradeoff between and the thomsen

reconstructing early himalayan tectonic evolution and paleogeography from tertiary foreland basin sedimentary rocks northern india the latest paleocene middle eocene subathu formation and the oligocene miocene dagshai and kasauli formations of the indian foreland basin record the early evolution of the himalayan fold thrust belt sandstone petrography of the subathu formation shows a predominantly recycled sedimentary source with a distinct ophiolitic and volcanic influence that was drastically reduced by the time of deposition of the dagshai formation sandstones in the dagshai and kasauli formations consist predominantly of metapelitic detritus the metamorphic grade of metapelitic lithic grains increases with time from dominantly very low grade at the base of the dagshai formation to dominantly low grade in the kasauli sandstones mudstone geochemistry documents the presence of a mafic ultramafic source during the time of deposition of the subathu formation that becomes significantly less important by the time of deposition of the dagshai formation compositions of subathu formation detrital spinels show they were either derived from both mid ocean ridge basalt type and arc type ophiolites or from an ophiolite of composite origin and that southerly derivation from the deccan trap continental flood basalts is unlikely kasauli formation garnet compositions suggest derivation from medium grade metamorphic rocks to amphibolite facies subathu formation composition reflects provenance influence from the indus suture zone during latest paleocene middle eocene time indicating initiation of continent continent collision and development of the foreland basin by this time suture zone influence was drastically reduced by the time of deposition of the dagshai formation when the embryonic thrust belt provided a barrier sufficient to partially separate the suture zone from the himalayan foreland basin the first appearance of himalayan metamorphic detritus occurs in the dagshai formation at the close of oligocene time whereas the kasauli formation records erosion to deeper metamorphic levels during earliest miocene time the occurrence of garnet and higher grade metamorphic lithic grains during early neogene time is coincident with the timing of displacement along the main central thrust and south tibetan detachment zone composition of early foreland basin sediments from pakistan balakot murree and kamlial formations to nepal bhainskati and dumri formations and bangladesh kopili barail formations surma group indicates diachronous arrival of ophiolitic to low grade metamorphic detritus derived respectively from the indus suture and early himalayan thrust sheets in the north this is consistent with progressively later closure of neotethys along the suture from latest paleocene time in the west to eocene time or even later in the east

the tianger bingdaban shear zone hosted gold deposit west tianshan nw china petrographic and geochemical characteristics abstract the wangfeng tianger saridala ore district consists of over 20 orebodies with total proven gold reserves exceeding 15 tonnes the district is located on the ew striking tianger bingdaban shear zone in west tianshan mountains northwest china the lensoid orebodies are distributed along the shear zone in a region about 25 km in length and 1 km in width enhanced fluid flow and fracturing controlled location and orientation of mineralized zones during deformation along narrow shear bands oriented oblique to the overall shear zone margins fabrics in fractures and strain shadow overgrowths generally plunge steeply parallel to the lineation in the surrounding cataclasite matrix consisting of new grains of quartz and minor amounts of micas native gold occurs in mylonitized granites or mylonitized sulfide mica quartz veins gold grade is closely related with the occurrence of sulfide quartz veins pyrite and pyrrhotite in gold bearing sulfide quartz veins contain inclusions of native gold chondrite normalized rare earth element ree distribution patterns for pyrite from the orebodies show light ree enrichments and negative eu anomalies relationships between gold contents and th u zr hf and la yb n values for pyrites imply that gold rich pyrites are different from gold poor pyrites thus indicate that the pyrites in the orebodies have a different origin compared with those in wall rocks a rb sr isochron for the mylonitized au bearing quartz veins indicates an age of 224 14 ma with an initial 87 sr 86 sr ratio of 0 7294 0 0089 mswd 1 1 this age is conformed by 40 ar 39 ar dating on muscovites 220 9 to 222 5 ma which is interpreted as the age of ore formation in the tianger deposit high initial 87 sr 86 sr ratios 0 7294 high 34 s values 11 2 to 16 5 low 18 o h2o values 1 67 to 3 07 and low d values 84 to 104 indicate that the ore forming fluid was unrelated to any magmatic process

dynamic character of the hydrothermal vent habitat and the nature of sulphide chimney fauna abstract a major substratum for vent organisms on juan de fuca and explorer ridges of the northeast pacific is the polymetallic sulphide chimney the deposition processes and subsequent growth of such chimneys provide a dynamic and extreme habitat that changes rapidly during initial venting stages colonization must await stabilization of the chimney structure as the porous anhydrite shell accumulates sulphide minerals protection from direct hot water contact increases for organisms colonizing the outer walls while sufficient vent water still diffuses for the support of chemosynthesis vestimentiferan worms are found on small sulphide mounds but the active growth and collapse of anhydrite spires is a major source of disruption and mortality high temperature venting and spire growth appear to attract alvinellid polychaetes which may be implicated in the process of strengthening and sealing the anhydrite spires fauna on the growing chimney is subject to changes in fluid flow patterns that can make the structure uninhabitable large chimneys are inhabited by more species indicating that a diversification of habitat results from variations in mineralization and fluid availability chimney fauna has become specialized in exploiting an unpredictable and unstable habitat in an extreme example of the control of biotic development by the physical environment

evidence of uranium biomineralization in sandstone hosted roll front uranium deposits northwestern china we show evidence that the primary uranium minerals uraninite and coffinite from high grade ore samples u3o8 0 3 in the wuyiyi wuyier and wuyisan sandstone hosted roll front uranium deposits xinjiang northwestern china were biogenically precipitated and psuedomorphically replace fungi and bacteria uranium vi which was the sole electron acceptor was likely to have been enzymically reduced post mortem accumulation of uranium may have also occurred through physio chemical interaction between uranium and negatively charged cellular sites and inorganic adsorption or precipitation reactions these results suggest that microorganisms may have played a key role in formation of the sandstone or roll type uranium deposits which are among the most economically significant uranium deposits in the world

seismic data processing in vertically inhomogeneous ti media the first and most important step in processing data in transversely isotropic ti media for which velocities vary with depth is parameter estimation the multilayer normal moveout nmo equation for a dipping reflector provides the basis for extending the ti velocity analysis of alkhalifah and tsvankin to vertically inhomogeneous media this nmo equation is based on a root mean square rms average of interval nmo velocities that correspond to a single ray parameter that of the dipping event therefore interval nmo velocities including the normal moveout velocity for horizontal events vnmo 0 can be extracted from the stacking velocities using a dix type differentiation procedure on the other hand which is a key combination of thomsen s parameters that time related processing relies on is extracted from the interval nmo velocities using a homogeneous inversion within each layer time migration like dip moveout depends on the same two parameters in vertically inhomogeneous media namely vnmo

the association of mafic ultramafic intrusions and a type magmatism in the tian shan and altay orogens nw china implications for geodynamic evolution and potential for the discovery of new ore deposits abstract the nw china region is characterised by tectonic and lithostratigraphic domains such as the tian shan and altay orogens the tarim junggar and turpan basins the tian shan and altay orogens are part of the central asian orogenic belt the nw china region was affected by a series of thermal events that occurred between the silurian and the triassic which resulted in the emplacement of numerous granitic plutons and mafic ultramafic intrusions a number of these granitic plutons are of a type affiliation which on the basis of the positive end values are likely to have been derived from mantle sources in addition at least two large igneous provinces lips can be recognised in nw china namely the 345 325 ma tian shan lip and the ca 270 280 ma tarim lip age and field data suggest a spatial and temporal relationship between the mafic ultramafic intrusions and a type granites within the lips in this paper we discuss mafic ultramafic intrusions that host magmatic ni cu sulphide deposits kalatongke in the altay huangshan and poyi poshi in the eastern tian shan these intrusions are typically zoned characterised by an envelope of early gabbroic rocks that enclose later ultramafic units these zoned mafic ultramafic intrusions have some features that are comparable with alaskan type complexes taking into consideration the spatial temporal relationship of the mafic mafic ultramafic rocks and a type granites we suggest that these magmatic events occurred during an extensional regime possibly related to a mantle superplume event that affected much of central asia during the permian of which the siberian traps and the emeishan continental flood basalts of sw china are part if the a type felsic magmatism took place during a superplume event we also suggest that these rocks may be conducive to host iron oxide copper gold iocg style mineralisation we conclude with a model that attempts to explain the relationship between the zoned mafic ultramafic intrusions and mantle plume activity in nw china during the permian

residual moveout in anisotropic angle domain common image gathers i develop the fundamental concepts for quantitatively relating perturbations in anisotropic parameters to the corresponding reflector movements in angle domain common image gathers adcigs after anisotropic wavefield continuation migration the proposed theory potentially enables the application of residual moveout rmo analysis of adcigs to velocity estimation in realistic anisotropic conditions i demonstrate that linearization of the relationship between anisotropic velocity parameters and reflector movements can be derived by assuming stationary raypaths this assumption leads to a fairly simple analytical derivation i then apply the general method to the particular case of rmo analysis of reflections from flat reflectors in a vertical transverse isotropic vti medium this analysis yields expressions to predict rmo curves in migrated adcigs these rmo expressions are functions of both the phase aperture angle and the group aperture angle several numerical examples demonstrate the accuracy of the rmo curves predicted by my kinematic analysis the synthetic examples also show that approximating the group angles with the phase angles in the application of the rmo expressions may lead to substantial errors for events reflected at wide aperture angles the results obtained by migrating a 2d line extracted from a gulf of mexico 3d data set confirm the accuracy of the proposed method the rmo curves predicted by the theory match the rmo function observed in the adcigs computed from the real data

paleovalley related uranium deposits in australia and china a review of geological and exploration models and methods abstract the features and similarities in the geology of paleovalley related uranium mineralizing systems in australia and china can be used to refine strategies for exploration paleovalley related uranium resources include sandstone lignite and calcrete style deposits that are developed within the host sediments deposited in paleovalleys the paleovalleys incise either crystalline bedrock or older sedimentary rocks and uranium was deposited and concentrated by the influx of oxidized reduced groundwaters flowing in aquifers within the paleovalley fill the critical features of paleovalley related uranium deposits include sediment and uranium sources geological setting depositional environment age and relative timing of mineralization aquifer characteristics availability and distribution of reductants and preservation potential of the uranium mineral system this set of information provides a basis to establish the uranium mineralization model which can then be used to assist with generating targets for uranium exploration and prospectivity analysis of a region with respect to sino australian examples paleovalley related uranium deposits form mostly around the margins of sedimentary basins and the mineralization is commonly hosted within channel fills contained within paleovalleys developed upon or proximal to precambrian crystalline rocks that contain primary uranium sources the deposits that have been well studied show remarkably similar factors that controlled the formation of paleovalley related uranium deposits basement bedrocks with above background 2 8 ppm u levels of uranium 10 100 ppm that are linked to and or incised by paleovalleys are associated with these deposits and are the inferred source of the uranium in these regions extensive fluvial systems developed particularly during mesozoic and cenozoic times uranium from the bedrock was first dispersed into the sediments and then concentrated to form deposits through successive chemical remobilization precipitation and concentration the deposits formed in continental or marginal marine environments and commonly are associated with reduced lithologies containing pyrite and dispersed organic matter and or seams of lignite or show evidence of infiltrated hydrocarbons the mineralization is developed where oxidizing fluids carrying dissolved u reacted with reductants in the sediments geological geophysical and geochemical features of the paleovalleys and related uranium deposits are used to construct models to understand host sediment distribution fluid flow and ore genesis that can assist exploration for paleovalley hosted uranium deposits precise geometric definition of the basin margin and paleovalley architecture is important in identifying exploration targets and improving the effectiveness of drilling refinements in remote sensing geophysical and data processing techniques in combination with sedimentological and depositional interpretations provide an efficient approach for outlining the principal drainage patterns and channel dimensions to help reduce risk an exploration strategy should combine these technologies with a detailed understanding of the physicochemical parameters controlling uranium mobilization precipitation and preservation

seismic anisotropy in exploration and reservoir characterization an overview recent advances in parameter estimation and seismic processing have allowed incorporation of anisotropic models into a wide range of seismic methods in particular vertical and tilted transverse isotropy are currently treated as an integral part of velocity fields employed in prestack depth migration algorithms especially those based on the wave equation we briefly review the state of the art in modeling processing and inversion of seismic data for anisotropic media topics include optimal parameterization body wave modeling methods p wave velocity analysis and imaging processing in the p domain anisotropy estimation from vertical seismic profiling vsp surveys moveout inversion of wide azimuth data amplitude variation with offset avo analysis processing and applications of shear and mode converted waves and fracture characterization when outlining future trends in anisotropy studies we emphasize that continued progress in data acquisition technology is likely to spur transition from t

exceptional crinoid occurrences and associated carbonates of the keasey formation early oligocene at mist oregon usa abstract an unusual concentrated zone of well preserved fossil crinoids corals and other organisms exists with carbonates in an otherwise barren outcrop of fine grained sandstone and siltstone of the early oligocene keasey formation at mist oregon the origin of this lagerstatte has long puzzled paleontologists taxonomically similar modern isocrinids have a strong preference for indurated substrates the mist carbonates may have provided seafloor hardgrounds for the isocrinids a physical limiting factor on the formation and distribution of the crinoid lagerstatte other paleoenvironmental factors such as currents sedimentation rates and food flux also may have affected crinoid community development stable carbon and oxygen isotopic analyses of micritic slabs concretions and sparry veins in several lithologic units at mist indicate that most of the carbonates formed in the zone of archaeal methanogenesis enrichment in 13ccarbonate with values as high as 9 5 vpdb the carbonates may be a late diagenetic feature entombing the faunal material following burial depletion in 18ocarbonate to 7 8 vpdb and therefore have no temporal relation to the crinoids alternatively the carbonates could have formed in the methanogenic zone deep in the sediment pile later exhumed by erosion and colonized again with no temporal affiliation to the epifauna finally the carbonates at mist could have precipitated in an unusually shallow zone of archaeal methanogenesis induced by seepage from the subsurface resulting in availability of reduced organic compounds and bacterial consumption of sulfate near the sediment water interface in this case the sulfate reduction zone must have been thin and the upward advection of deep sourced isotopically evolved fluids sufficient to impart negative 18o and positive 13c signatures to the carbonates forming possibly at only a few centimeters depth further evidence that supports a shallow methanogenic origin for the mist carbonates includes 1 presence of an infaunal low oxygen and or chemosymbiotic fauna 2 pristine preservation of molluscan shell secreted in isotopic equilibrium with seawater bicarbonate 3 lack of major erosional surfaces associated with the carbonates and 4 the occurrence of reservoir rocks beneath mist that were charged with natural gas during the early oligocene locally mapped faults and or clastic dikes of this age may have conveyed methane to the near surface with crinoid growth occurring upon indurated calcareous sediments that were intermittently exposed by minor current winnowing of the draping bottom silts

wave equation migration velocity analysis for vti models abstractanisotropic models are needed for wave simulation and inversion where a complex geologic environment exists we extended the theory of wave equation migration velocity analysis to build vertical transverse isotropic models because of the ambiguity between depth and in the acoustic regime we assumed can be accurately obtained from other sources of information and inverted for the nmo slowness and the anellipticity parameter we combined the differential semblance optimization objective function with the stacking power maximization to evaluate the focusing of the prestack image in the subsurface offset domain to regularize the multiparameter inversion we built a framework to adapt the geologic and the rock physics information to guide the updates in nmo slowness and this regularization step was crucial to stabilize the inversion and to produce geologically meaningful results we tested the proposed approach on a synthetic data set and a 2d gulf of mexico data set starting with a fairly

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data