carbonate diagenesis in ice the fine particles created by glacial comminution of carbonate minerals are susceptible to interaction with meltwater and the isotopic composition of fine carbonate in glacial deposits has the potential of recording this interaction here we focus on the carbonate fraction of glacial sediment and debris within basal ice at the tsanfleuron glacier switzerland size separates of basal ice debris and melt out tills show a collinear isotopic trend interpreted as a mixing line between detritus 18 o pdb 5 and 13 o pdb 0 6 and authigenic calcite which in one case had 18 o values as light as 18 7 and 13 c values as light as 5 7 in most cases the finer fractions with calcite crystals as small as 0 1 m are enriched in the isotopically light component which is interpreted to form largely by freezing in basal ice the isotopic compositions of ice and included gases could be influenced by this process melt out tills inherit the authigenic calcite thus carbonate bearing till should no longer be regarded simply as clastic sediment

cryogenic cave calcite from several central european caves age carbon and oxygen isotopes and a genetic model abstract cryogenic cave calcite ccc formed by segregation of solutes during water freezing was found in three central european caves this calcite type forms accumulations of loose calcite grains on cave floor the calcite grains are of highly variable crystal morphology and of sizes ranging from less than 1 mm to over 1 cm the most typical feature is their accumulation as loose uncemented crystals u series dating indicates the formation of ccc in the studied caves during several climatic oscillations of the weichselian between 61 and 36 ka bp in the chelsiowa jama jaskinia jaworznicka cave system in poland between 34 and 26 ka bp in the buml cave in the czech republic and between 26 and 21 ka bp in the stratenska jasky a cave system slovakia at the time of ccc formation the studied caves were lying in a periglacial zone detailed c and o stable isotope study of ccc samples revealed that slow water freezing under isotope equilibrium was the dominant formational process in the studied polish and czech caves significantly higher 13 c values of ccc in the stratenska jasky a cave indicate either water freezing in a more opened system with continuous co 2 escape rayleigh fractional separation or participation of another co 2 source the model of slow water freezing under isotope equilibrium is supported by isolated character of the caves having limited ventilation in contrast modern cryogenic cave calcite powders sampled directly on the ice surface of two recently iced caves in slovakia with high ventilation showed much higher 18 o and 13 c data similar to cryogenic calcites obtained in experimental rapid water freezing

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

detection and extraction of fault surfaces in 3d seismic data we propose an efficient method for detecting and extracting fault surfaces in 3d seismic volumes the seismic data are transformed into a volume of local fault extraction lfe estimates that represents the likelihood that a given point lies on a fault surface we partition the fault surfaces into relatively small linear portions which are identified by analyzing tilted and rotated subvolumes throughout the region of interest directional filtering and thresholding further enhance the seismic discontinuities that are attributable to fault surfaces subsequently the volume of lfe estimates is skeletonized and individual fault surfaces are extracted and labeled in the order of decreasing size the ultimate result obtained by the proposed procedure provides a visual and semantic representation of a set of well defined cleanly separated one pixel thick labeled fault surfaces that is readily usable for seismic interpretation

structural evolution of the pematang reservoirs kelabu dingga gas fields sumatra the kelabu jingga area located in the kiri trough of the central sumatra basin produces gas from the paleogene pematang group the pematang group consists of sandstones claystones organic rich shales and conglomerates deposited in fluvial and fresh water deltaic and lacustrine environments deposition occurred during regional tectonism associated with a major plate reorganization in the pacific and indian oceans during the paleogene subsequent rifting and basin development occurred in the kiri trough area in central sumatra syngenetic listric faults and associated rollover folds formed during rifting the pematang group was deposited in deep transtensional pull apart grabens and shallow extensional rifts tectonics strongly influenced the geometry and lateral continuity of the fluvial deltaic sands during the neogene oblique convergence of the indian ocean plate with the asian plate resulted in a regional dextral wrenching event in the central sumatra basin that overprinted the earlier extensional style of faulting in the kiri trough both extensional and compressional features are evident interpretation of a 3d seismic survey wireline logs including dipmeter and fms data and core data has delineated fault styles and depositional trends within the pematang group in the kelabu jingga fields the resultant maps and cross sections reveal hydrocarbon reserves and new drilling opportunities

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

a possible mechanism for growth of calcite speleothems without participation of biogenic carbon dioxide abstract using plummer et al s 11 rate equations on the dissolution and deposition of caco3 in h2o co2 systems we have calculated deposition rates of caco3 to stalagmites in caves which are covered by glaciers or bare karst in this case no biogenic co2 from vegetated soil is available and the deposition of caco3 involves only atmospheric co2 the mechanism of deposition proceeds by a temperature effect cold melting waters of about 0 c dissolve caco3 under open system conditions at the surface of the rock when this solution saturated with respect to caco3 flows through the limestone rock its temperature increases by several degrees therefore it becomes supersaturated and caco3 is deposited under open system conditions in the warmer cave maximal growth rates of about 10 3 cm year are possible from the kinetics of the deposition of caco3 from the thin water films present at the surface of stalagmites we are able to estimate the isotopic composition of carbon in the caco3 deposited on the stalagmites to be approximately 13c 8 which is close to some observed values from our data we conclude that substantial growth of stalagmites is possible during glacial periods as well as in areas of bare karst a question which was not resolved up to now

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

oblique extensional tectonics in the malawi rift africa the malawi rift is the southern segment of the western branch of the east african rift system there has been little agreement as to whether this rift is opening perpendicularly or obliquely to its north south axis and little agreement on a mechanism for the formation of the asymmetric basins that make up the rift our analysis combines landsat image interpretation and field measurement of the latest slip direction on faults to produce a kinematic model of rift evolution the fault slip data are consistently compatible with a late cenozoic northwest southeast directed divergence between the nubian and somalian blocks plates across the rift the northwest striking livingstone fault at the northern limit of the malawi rift and the northwest striking zambezi fault zone to the south serve as dextral intracontinental transform zones between left stepping segments of the western branch of the east african rift system within the rift second order northwest striking transfer faults separate adjacent asymmetric basins the transform and transfer faults form a pattern that is similar to overlapping right stepping strike slip faults with a releasing geometry fault surfaces with two sets of striations indicate a progression from predominantly strike slip toward oblique normal faulting we hypothesize that during initial rift formation most northwest striking faults were dextral and that fault interaction between these structures resulted in curved stress trajectories and a pull apart component arcuate north to northeast striking border faults and subsiding basins then formed between these northwest striking faults in response to the right stepping dextral shear the maximum distance over which fault interaction is significant may control basin dimensions as opening of the rift proceeds slip partitioning and gravity failure result in increasing normal slip perpendicular to major escarpments and decreasing strike slip parallel to them

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

enhanced structural interpretation from 3d seismic data using hybrid attributes new insights into fault visualization and displacement in cretaceous formations of the scotian basin offshore nova scotia abstract meta or hybrid attributes extracted from seismic data through artificial neural networks enhance structural details in subsurface strata cretaceous units within the penobscot prospect are devoid of such interpretations although these units are plausible zones for hydrocarbon generation and accumulation the role of geologic structures responsible for such entrapment is poorly understood the present study enlightens these latter geological structures through a case study that uses 3d time migrated seismic data from the penobscot prospect in the scotian basin a modern data conditioning approach used together with multi attribute analyses and a supervised neural network have brought out the minute details of subsurface geologic structures through a hybrid attribute called the fault probability cube fpc the present fault displacement analysis reveals that the major fault of the prospect has evolved by the coalescence of different fault segments grown over space and time and has demonstrated a predominant nnw sse structural trend such a geometry has structurally modulated the cretaceous units the logan canyon the dawson canyon and the wyandot formations giving rise to different horst graben structures and fracture networks as shown by the fpc attribute this generates complicated structural deformation and accommodation space thereby enabling different trapping zones for hydrocarbon accumulation within these units such a detailed structural understanding will provide significant input to the future exploration and development programme in the penobscot prospect

generating a relative geologic time volume by 3d graph cut phase unwrapping method with horizon and unconformity constraints abstractconstruction of a relative geologic time rgt volume is vital to seismic geomorphological and sedimentological interpretation seismic instantaneous phase unwrapping provides an excellent approach for generating an rgt volume although several 2d or 3d seismic phase unwrapping results have been published there is a clear need for discussions on concrete methods for seismic phase unwrapping we have developed the graph cut phase unwrapping method which performs well in the interferometric synthetic aperture radar image processing it has advantages of strong discontinuity preserving ability and high computing efficiency to make it suitable for 3d seismic phase unwrapping the method is improved by extending it from 2d to 3d and by introducing the seismic horizon and unconformity constraints the strong and continuous conformable seismic events which can be easily tracked by certain autopicking methods are introduced as horizon constraints for guiding the phase unwrapping to ensure a constant

a texture based region growing algorithm for volume extraction in seismic data we present a novel approach to automated volume extraction in seismic data and apply it to the detection of allochthonous salt bodies using a genetic algorithm we determine the optimal size of volume elements that statistically according to the u test best characterize the contrast between the textures inside and outside of the salt bodies through a principal component analysis approach this information was used to implement a seeded region growing algorithm to directly extract the bodies from the cube of seismic amplitudes we present the resulting three dimensional bodies and compare our final results to those of an interpreter showing encouraging results

late cretaceous to early tertiary structural elements of west kalimantan abstract recent geological and geophysical mapping in west kalimantan has allowed the definition of three domains with distinct geological and geophysical characteristics which were imprinted on the region by early cretaceous to eocene convergent tectonic events subduction related granitoids intruded low grade regional metamorphic rocks during the early cretaceous forming the schwaner mountains domain extending east west across the southern and central part of west kalimantan this is flanked in the northwest by a complex sequence of sedimentary and volcanic rocks ranging in age from late carboniferous to cretaceous which comprise the northwest kalimantan domain deformed cretaceous flysch deposits east of the northwest kalimantan domain form an accretionary complex representing the southern continuation of the extensive dominantly tertiary accretionary wedge in sarawak the boundary between the cretaceous accretionary domain and rocks of the northwest kalimantan domain is a fault which we interpret as a transform that marked the western limit of late cretaceous southward subduction beneath west kalimantan growth of the accretionary complex resulted in uplift of a ridge of melange and flysch deposits on which a half graben extensional basin formed and accumulated thick lacustrine deposits a sedimentary basin developed between continental rocks to the south and the emergent ridge comprising accretionary complex rocks and outer shelf deposits to the north in the position of a forearc basin as accretion proceeded the locus of underthrusting migrated northward and a second melange ridge and sedimentary basin developed farther to the north the evidence for accretionary processes and the association of these with sedimentary basin formation supports the hypothesis that an ancient south dipping subduction zone existed in the eastern part of west kalimantan during late cretaceous to early tertiary times

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

a workflow to skeletonize faults and stratigraphic features abstractimproving the accuracy and completeness of subtle discontinuities in noisy seismic data is useful for mapping faults fractures unconformities and stratigraphic edges we have developed a workflow to improve the quality of coherence attributes first we apply principal component structure oriented filtering to reject random noise and sharpen the lateral edges of seismic amplitude data next we compute eigenstructure coherence which highlights the stratigraphic and structural discontinuities we apply a laplacian of a gaussian filter to the coherence attribute that sharpens the steeply dipping faults attenuates the stratigraphic features parallel to the seismic reflectors and skeletonizes the unconformity features subparallel to the reflectors finally we skeletonize the filtered coherence attribute along with the fault plane the filtered and skeletonized seismic coherence attribute highlights the geologic discontinuities more clearly and precisely these discontinuous features can be colo

environmental setting micro morphologies and stable c o isotope composition of cold climate carbonate precipitates a review and evaluation of their potential as paleoclimatic proxies abstract given the growing interest in carbonate deposits from polar regions as paleoclimatic proxies this review paper first provides a classification of the various types of cold climate carbonate precipitates followed by a summary of the 13 c and 18 o composition of the carbonate deposits and parent water from which the carbonates precipitated the cold climate carbonate precipitates were classified into three broad categories powders crusts and speleothem the carbonate powders include those that precipitated in relation to aufeis aggradation cryogenic aufeis calcite and in relation to the growth of various annual perennial ice formations in freezing caves cryptocrystalline calcite and calcite pearls the carbonate crusts can be further subdivided based on their lithic environment those that precipitated on the upper surface of bedrock clasts i e subglacially precipitated calcite and evaporative calcite crusts those that are located on the underside of clasts i e pedogenic carbonates and those that precipitated in rock outcrop fissures i e endostromatolites the cold climate carbonate precipitates have a highly variable isotopic composition with 18 o values ranging between 6 5 and 28 vsmow and 13 c values in the 10 20 vpdb range however each type of carbonate precipitates has a specific 13 c and 18 o range suggesting that their environmental setting and the mechanism by which they formed controls their 13 c and 18 o signature it was found that carbonate deposits that precipitated under equilibrium physico chemical conditions had a 13 c value that is in equilibrium with that of the parent water while its 18 o composition was more variable as it is in part controlled by the temperature of reaction and by the 18 o and calcite saturation state of the parent water by contrast the 18 o composition of biologically precipitated carbonate deposits endostromatolites reflect that of the parent water while its 13 c composition was enriched over that of the parent water due to bacterial methanogenesis in the case of kinetically precipitated carbonate deposits the 18 o and 13 c values are out of equilibrium relative to that of the parent water due to the faster rate of reaction

delineation of tectonic features offshore trinidad using 3 d seismic coherence seismic coherence allows interpreters to quickly visualize and map complex fault systems calibration to well control adds the ability to recognize important stratigraphic features and potential gas water contacts applying coherence technology to an offshore trinidad 3 d survey reduced exploration cycle time and improved understanding of tectonic elements in the area the following shows some ways in which coherence may be used to identify complex fault systems and speed up interpretation

variations chimiques et isotopiques de l eau du sol lors de la reprise en gel d une couche active sur pergelisol continu presqu ile de brogger svalbard the isotopic and chemical composition of soil waters in a periglacial environment was studied during a 2 month period 89 10 07 to 89 11 09 the experimental site chosen is located near ny alesund

use of a computational fault extraction process with calibrations to characterize a fractured basement reservoir yufutsu japan the yufutsu oil and gas field located in hokkaido northern japan produces hydrocarbon from a typical fracture type reservoir composed of very tight cretaceous granitic basement and overlying conglomerate of the eocene here delineations of faults accompanying large open fractures are essential for optimal developments to capture fault distribution objectively various seismic attribute estimates ascribed to fault distributions are derived from three dimensional seismic data by computational procedures however to use the estimates properly calibrating them with independent observations other than seismic data is important we present a calibration scheme by coupling seismic data with microseismic data and in situ stress data to delineate active faults under a strike slip faulting stress regime in the yufutsu field active faults are interpreted to be fluid pathways formed by shear dilation in the calibration two kinds of parameter sets are tuned one controls linkages of fault responses fragmented by artificial noises caused by seismic acquisition and processing to adjust spatial continuities of fault surfaces properly another limits extracted fault strikes with respect to mohr coulomb failure criterion to highlight active faults the calibrated seismic attribute estimates show a qualitative consistency with the microseismic hypocenter distribution observed during a massive hydraulic stimulation in addition a large difference in gas productivity observed at four wells from very high productivity to no gas flowing is clearly related to an existence of distinct lineation with strong magnitudes of the calibrated seismic attributes it suggests that the calibrated estimate becomes a criterion to judge an economic viability of a well

fissure calcretes in the arctic a paleohydrologic indicator abstract the effects of modern climate warming are expected to be amplified in northern periglacial regions paleohydrological reconstructions in the arctic provide important insights into natural climatic variations during the pleistocene and holocene with which to compare predictions of modern impacts here the authors describe a new material calcrete found in fissures in arctic carbonate terrains which record hydrogeological and climatic conditions during climatic optimums in the north 234 u and 230 th activity ratios suggest growth during northern insolation maxima these fissure calcretes strongly resemble biogenic calcite precipitates endostromatolites and grow on the external face within fissures in carbonate bedrock in periglacial environments in thin section samples are finely laminated and are composed of diverse fabrics including a uniformly present basal layer with regularly spaced columns from several microns to 3 cm in length their surface morphology is often preserved in the relief of the adjacent fissure face in a micro lapies texture strongly suggestive of a dissolution reprecipitation mechanism whereby the fissure widens in lock step with column growth their highly enriched 13 c 0 to 8 4 composition suggests that methanogenenic bacteria supported by a substrate of soil derived organic matter control growth in a network of groundwater saturated near surface fissures extending to a depth of 3 to 5 m accordingly 18 o holds valuable paleotemperature information

the properties genesis and environmental significance of calcitic pendents from the high arctic spitsbergen abstract calcitic pendents occurring beneath coarse clasts were investigated from a well drained profile near ny alesund spitsbergen developed on fluvio glacial deposits with a few carbonate rock fragments micromorphological study was combined with mineralogical geochemical and isotopic investigations to determine the relationships of calcitic pendent characteristics to soil conditions calcitic pendents are observed at all depths beneath clasts and display a succession of five types of laminae with strongly differentiated overall characteristics the number of laminae and their specific attributes are nearly unchanged with depth and with the petrographic nature of the host clast each lamina consists of weakly differentiated micro laminae that are grouped into six morphological facies precipitation of pedogenic carbonates is shown to be currently active throughout the profile induced by supersaturation of solutes with respect to calcite during the initial stage of freezing this process would form beneath clasts the calcitic pendents that are suggested to successively grow at all depths following the gradual progression of the frost front carbonate dissolution appears to mainly affect the fine soil mass from the surface down to the permafrost level controlled by summer biological activity differences of isotopic values of the whole calcitic pendents from those that would precipitate in equilibrium with present day soil conditions are explained by changes in soil conditions during the accretionary process 14 c values suggest that accretion of the pendents integrates phases which occurred during earlier episodes than the holocene the complex layering of calcitic pendents provides a sequential record of evolving soil forming conditions during a time period possibly longer than the last glacial cycle previous conditions are interpreted in relation to present conditions of precipitation the succession of micro laminae is thought to reflect minor climatic fluctuations and marked changes between adjacent laminae are thought to indicate significant climatic changes