petrological significance of manganese carbonate inclusions in spessartine garnet and relation to the stability of spessartine in metamorphosed manganese rich rocks idioblastic spessartine garnet pervasively developed in mn rich rocks and impure manganese carbonate ore at the lower proterozoic nsuta manganese deposit western ghana contains abundant inclusions of micritic and microconcretionary carbonates and to a lesser extent quartz detailed mineralogical and microprobe studies indicate all the carbonate phases i e carbonate inclusions in garnet carbonates coexisting with garnet and carbonates not directly in contact with garnet the latter hereafter referred to as matrix carbonates lie within the rhodochrosite kutnahorite solid solution series i e mn55 80 ca mg 20 45co3 to ca42 mn mg 58 co3 2 minor compositional differences occur in the various carbonate phases but partition of major elements among coexisting phases indicate most carbonate minerals strongly fractionate ca and mg over coexisting spessartine the nature composition and textural relationship of coexisting minerals and inclusions in porphyroblastic spessartine indicate that the latter formed from metamorphic reactions in which rhodochrosite and or kutnahorite and quartz were consumed in part corroborating earlier observations on a rhodochrosite precursor for spessartine spessartine formation is thus envisaged to have taken place when the predominantly mn carbonate quartz assemblage became unstable in the presence of minor amounts of an unknown aluminous phase because all the carbonates appear to be low temperature phases with no indications of significant recrystallisation or homogenisation it could be argued that the spessartine rhodochrosite kutnahorite quartz pyrite assemblage stabilised during very low grade greenschist facies metamorphism under relatively low but uniform fo2 conditions these observations also suggest the stability field of spessartine could extend to relatively lower temperatures than currently envisaged

geomorphologic indicators of sea level and lowstand paleo shelf exposure on early middle miocene sequence boundaries abstract relationships between clinoformal sequence boundaries and relative sea level change in particular locations of lowstand shorelines and amounts of paleo shelf exposure represent a key topic in sequence stratigraphy this paper uses 3d seismic data to analyze morphologies of two sequence boundaries in the early middle miocene section of the northern carnarvon basin of the australian northwest shelf a step like discontinuity is recognized on the outer paleo shelf of sequence boundary dls4 based on reflection truncation and seismic facies change vertical offset at this step varies from 7 to 65 m increasing along strike from sw to ne the trace of this discontinuity comprises both linear and arcuate segments in coherence time slices isolated mounds and small platforms also occur on this sequence boundary basinward of the discontinuity underlying sub sequence boundary dls3 1 displays a smaller step like discontinuity together with u and v shaped incisions as well as numerous isolated depressions the latter occurring within two large arcuate concave basinward features on coherence slices we discuss several possible origins for these discontinuities we conclude that step like discontinuities on dls4 and dls3 1 represent buried wave cut terraces or sea cliffs erosion is presumed to have occurred at or near ambient sea level the incisions of dls3 1 are karst together these interpretations imply significant lowstand paleo shelf exposure of early middle miocene sequence boundaries

identification of fractured carbonate vuggy reservoirs in the s48 well area using 3d 3c seismic technique a case history from the tarim basin

an improved cylindrical surface fitting related method for fault characterization abstracton the basis of the similarity of seismic waveforms and shapes of the reflectors the coherence and curvature attributes can be derived respectively to characterize faults coherence is effective for characterizing relatively large faults when the distortion of seismic waveforms at a fault is not obvious the curvature attribute may play a complementary role in detecting the fault according to geometric features of the faulted strata the rate of change of curvature has recently been developed to improve fault characterization through an application to the real seismic data from the western tazhong area of the tarim basin china it was demonstrated that curvature change rate has advantages in detecting subtle faults having quite small throws and heaves however when the dip angle of a faulted stratum is smaller than 45 the curvature change rate derived from its fitted surface has multiple extreme values associated with one fault plane which cause a low signal to noise ratio s n of a co

compositional variations in manganese carbonate micronodules from the lower proterozoic nsuta deposit ghana product of authigenic precipitation or post formational diagenesis abstract detailed petrographic and microprobe studies of micronodules identified in the manganese carbonate orebody and adjacent mn rich rocks at the 2 2 ga nsuta deposit ghana indicate distinct lithologic control on nodule structure and chemical composition nodules in the mn rich rocks adjacent to the manganese carbonate orebody conform with the well banded nature of the rock and are distinctly zoned into alternating bands compositionally dominated by mg kutnahorite and mg ca rhodochrosite individual nodules are partially or completely cemented by thin dark silica and carbonates of ca mg mn solid solution nodules in the orebody on the contrary are generally massive homogeneous consist predominantly of rhodochrosite and are only partially cemented by dark silica based on the stratigraphic relationship of the nodule bearing rocks to the manganese carbonate orebody and the variations in texture and composition observed in the nodules it would appear that the mn carbonate nodules precipitated diagenetically in response to changing pore water chemistry and or metal mn and ca supply the overall mineralogical and geochemical features indicate in addition that the nodules may have preserved original carbonate compositions both metastable and stable during burial diagenesis and low grade regional metamorphism

mud volcanism by repeated roof collapse 3d architecture and evolution of a mud volcano cluster offshore nigeria abstract using 3d seismic data we document the subsurface architecture of a cluster of 3 mud volcanoes located on the upper continental slope offshore nigeria in a background of gently dipping stratified sediments the subsurface of the cluster contains 8 seismic sequences made of one subcircular syncline 1 3 km in diameter and adjoining unstratified units synclines flatten out upward through intercalation of unstratified concave up lenses between stratified units and are eventually filled by a convex up unstratified lens onlapped by background sediments the lower boundary of each sequence is a 0 5 1 5 km deep bowl shaped unconformity across which high dip strata rest above truncated low dip series we interpret each seismic sequence as a mud volcano system mvs sourced from a connected region and evolving through episodes of roof collapse three are associated with the surface mud volcanoes and another 4 to fossil ones mud volcano systems are dynamic features that record the evolution of 1 the material extruded from one single connected source region depletion zone as it grows downwards and stepwise becomes depleted 2 the basal unconformity which joins strata originally separated by material evacuated in the remobilization process by analogy with salt tectonics we propose to call it a mud weld 3 the conduits and 4 the successive collapsed roofs of the depletion zone the evolution of each mud volcano system in this interpretation records progressive growth of the depletion zone by downbuilding punctuated by episodes of roof collapse and extrusion the geometry and evolution of this type of mvs can be interpreted in the light of analogue models of magmatic caldera development in early stages the thin roof experiences downsagging while remobilized material is extruded through an axial pipe like conduit in later stages the thickened roof undergoes piston like subsidence and mud extrusion occurs along the peripheral fault

modern 3 d seismic interpretation three dimensional seismic surveys are applied to the whole range of problems from exploration to development and exploitation they provide constraints for detailed reservoir characterization for planning and executing enhanced oil recovery strategies and for monitoring the changes in reservoirs as they are developed and produced modern 3 d seismic interpretation involves the use of interactive workstations and the application of both the hardware and software technologies to accurately and efficiently interpret large volumes of data the 3 d interpreter must not only understand the concepts of geology and seismology but must also develop an understanding of the various algorithms implemented in computer aided interpretation tools to effectively use these systems

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

graphitization of organic matter and fluid deposited graphite in palaeoproterozoic birimian black shales of the kaya goren greenstone belt burkina faso west africa palaeoproterozoic black shales form an essential part of the birimian volcanosedimentary belt in burkina faso west africa the mean rmax values and the atomic h c values of the bulk carbonaceous matter bcm together with rock structures and mineral assemblages indicate that these carbon rich rocks were metamorphosed to sub greenschist and low grade greenschist facies x ray diffraction reveals that the 002 graphite peak width in half maximum fwhm ranges from 0 43 to 0 71 2 in sub greenschist facies and from 0 27 to 0 41 2 in greenschist facies rocks but the d 002 values in both groups of rocks are approximately the same 3 35 a the bcm of individual samples is composed of particles with very variable shape reflectance and raman spectra type i particles that predominate in sub greenschist facies are fine grained irregular or elongate bodies 1 to 3 m in size their maximum reflectance rmax ranges between 2 5 and 8 2 and raman parameters r1 and r2 range from 0 5 to 1 4 and 0 5 to 0 8 respectively type ii particles are lath shaped up to 40 m large bodies commonly arranged parallel to white mica flakes the number of these particles increases from sub greenschist to greenschist facies maximum reflectance varies between 6 and 11 2 and r1 and r2 raman parameters range from 0 05 to 0 7 and from 0 1 to 0 5 respectively type iii particles occur in hydrothermally altered and sheared rocks these are nodular aggregates composed of grains up to 10 m in size this type of particles has very high reflectance rmax 11 15 and its raman spectra indicate a very high degree of structural ordering corresponding to well ordered graphite type i particles represent original organic matter in the metasediments type ii particles are believed to have been formed either in situ by solid state transformation of type i particles or by crystallization from metamorphic fluids gradual graphitization of the type i organic particles and the growth of lath shaped type ii particles from a fluid phase is assumed to have taken place under the peak metamorphic conditions associated with the burial of birimian sediments during thrust tectonism progressive tectonic accretion and crustal thickening during the d1 event of the eburnean orogeny the growth of equant high reflectance postkinematic nodular aggregates of type iii particles is ascribed to the reduction of co2 rich fluids during a hydrothermal event associated with late eburnean d2 exhumation and strike slip movements type i carbonaceous particles were only slightly affected by high temperature low pressure contact metamorphism during intrusion of late eburnean magmatic bodies whereas formation of type ii or iii particles was not recorded in contact metamorphosed rocks at all

from seismic data to core data an integrated approach to enhance reservoir characterization abstract integrated structural analyses of seismic and various well data are necessary to optimize hydrocarbon reservoir characterization however there are many published examples from the oil and gas industry where single data types are analysed but not integrated this may lead to erroneous interpretations and drainage strategies as illustrated by an example from the area around well 34 10 b 12 in the north sea gullfaks field integrated structural interpretation should typically utilize all available seismic surveys well log correlation data dipmeter data and core data interpretation of seismic data helps in the understanding of large scale structural and stratigraphic geometries time lapse 4d seismic helps to identify changes in reservoir properties caused by injection and production well log correlation data are used to document variations in zonation thickness caused by sedimentological or structural changes dipmeter data tie observations of bedding orientation from seismic data to subseismic scale core data represent the most detailed millimetre to metre scale data available and can yield information on rock properties as well as sedimentological and micro structural features small scale deformation structures such as deformation bands and fractures can typically be identified and characterized in addition it is possible from unorientated cores to find the orientation of bedding and deformation structures this information is compared to observations from dipmeter data well log correlation data and seismic data to improve the interpretation well 34 10 b 12 is a hanging wall injector near one of the large scale faults in the gullfaks field several 3d seismic surveys are available from the area as are standard well log data dipmeter information and cores together the data range from millimetre to kilometre with some overlap between the data types through integrated analysis pitfalls such as interpreting any linear feature on timedip attribute maps as faults has been avoided also a geometric relation between core scale and seismic scale faults has been established and it has been possible to relate small scale and large scale structures in a model which is consistent with all the available data

control of internal structure and fluid migration pathways within the barbados ridge decollement zone by strike slip faulting evidence from coherence and three dimensional seismic amplitude imaging the application of three dimensional seismic reflection and coherence imaging to the study of the decollement zone of the barbados ridge accretionary complex has provided new insights into the relationships among internal structure fluid flow and previously unrecognized strike slip faulting combined coherence and seismic amplitude imaging of the decollement zone reveal anomalous northeast trending lineaments parallel to and abutting zones of high amplitude negative polarity reflections analysis of these lineaments shows them to be penetrative structures dipping southeast with apparent reverse dip slip offset isopach mapping of the accretionary wedge indicates significant right lateral displacement across these structures these faults apparently channel fluid flow within the decollement zone and the prominent northeast trending conduits so formed are readily visible as high amplitude negative polarity reflections additionally north northeast trending zones of variable coherence and high positive amplitude are inferred barriers to up structure fluid migration pathways movement along strike slip structures probably alternates with displacement along the decollement zone northeast trending strike slip faults extend for 13 km crossing the length of the survey area and into the incoming oceanic plate active arc oblique strike slip faulting of the decollement zone beneath the barbados ridge accretionary wedge implies a stress regime in that 1 is fixed and 2 and 3 either transpose with time or are nearly equal this state of stress may be a common occurrence in forearc tectonism and may have led to the formation of many as yet unrecognized arc oblique strike slip faults at convergent margins

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

semi automatic fault fracture interpretation based on seismic geometry analysis abstract fault and fracture interpretation is a fundamental but essential tool for subsurface structure mapping and modelling from 3d seismic data the existing methods for semi automatic automatic fault picking are primarily based on seismic discontinuity analysis that evaluates the lateral changes in seismic waveform and or amplitude which is limited by its low resolution on subtle faults and fractures without apparent vertical displacements in seismic images this study presents an innovative workflow for computer aided fault fracture interpretation based on seismic geometry analysis first the seismic curvature and flexure attributes are estimated for highlighting both the major faults and the subtle fractures in a seismic volume then fault probability is estimated from the curvature and flexure volumes for differentiation between the potential faults and non faulting features in the geometric attributes finally the seeded fault picking is implemented for interpreting the target faults and fractures guided by the knowledge of interpreters to avoid misinterpretation and artefacts in the presence of faulting complexities as well as coherent seismic noises applications to two 3d seismic volumes from the netherlands north sea and the offshore new zealand demonstrate the added values of the proposed method in imaging and picking the subtle faults and fractures that are often overlooked in the conventional seismic discontinuity analysis and the following fault interpretation procedures

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

the paradox of tropical karst morphology in the coral reefs of the arid middle east despite differences in reef growth between the arabian gulf and the red sea a common distinctive pattern of polygonal sills surrounding ponded depressions consistently occurs in shallow water viewed from a satellite these seafloors are reticulated and maze like despite little current rainfall this patterning is best explained by karst dissolution of limestone during periods of lower sea level this is a paradox since such fine scale karstification is confined to areas with considerably more precipitation than currently observed in arabia we resolve this apparent contradiction by developing a pleistocene holocene chronology of sea level and climate for the red sea and arabian gulf and through the use of pattern analysis and computer simulation reveal the mechanism of formation for these structures we demonstrate that this patterning can be taken as a quaternary signature of paleohumidity in the now hyperarid red sea and arabian gulf

quaternary activity of the range front thrust system in the longmen shan piedmont china revealed by seismic imaging and growth strata reliable estimates of quaternary or cenozoic upper crustal shortening in the longmen shan fold and thrust belt are rare in this paper we report on our use of high resolution 2 d and 3 d seismic reflection profiles at various scales together with borehole data to investigate the structural geometry of the longmen shan piedmont the results reveal a thrust system beneath the longmen shan termed the range front thrust system which consists of the range front blind thrust and its upward splay faults moreover on these faults we identified growth strata that provide an excellent opportunity for assessing the activity of this thrust system analyses of the growth strata reveal early to late pleistocene activity on the range front blind thrust with minimum dip slip and horizontal shortening rates of 1 1 0 2 mm yr and 1 mm yr accordingly the maximum accumulated slip on the range front blind thrust is calculated to be 7 5 0 3 km in the longmen shan using the new horizontal shortening rate and other published data we also estimated that the long term shortening rate across the longmen shan fold and thrust belt is 1 3 mm yr which is comparable to the short term gps rate the similarity of these rates suggests that the longmen shan attained a steady state condition over the past 2 myr an additional highlight of our results is that we show quaternary activity around the tibetan plateau to have been nearly synchronous in different regions including in the longmen shan the himalayas the western kunlun shan and the northern qilian shan

autotracking of faults on 3d seismic data manual fault mapping in 3d seismic interpretation is labor intensive and time consuming complex fault geometries and the distortion of the seismic signal close to faults complicate full automation of the fault mapping process we present a semiautomatic fault tracking method for 3d seismic data that consists of fault highlighting followed by model based fault tracking fault highlighting uses log gabor filters for emphasizing oriented amplitude discontinuities at faults in the presence of noise subsequent fault tracking fits an active contour to the highlighted fault voxels the active contour searches for a connected smooth curve which fits the data and disambiguates misleading or missing information the fault tracker requires the interpreter to place the active contour close to a fault on one initial seismic inline 2d pick the active contour deforms to the closest amplitude dis continuity highlighted this tracking result is then projected forward to the next inline providing an initial fault pick on this section that is again optimized by the active contour tracking results on a series of successive seismic sections finally constitute a 3d fault surface user interaction is solely required for an approximate fault pick on the first inline and in cases where the fault line is lost due to insufficient signal use of the autotracker prototype provides a fast solution for the mapping of complete 3d fault surfaces of constant dip and for the automated tracking of fault portions within distinct dip domains if fault surfaces are curved i e listric the method was applied to a series of high quality reflectivity sections extracted from a 3d seismic volume from shallow offshore nigeria with the tracking results generated within seconds comparing well with manually interpreted fault surfaces

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

manganese deposits of the oudalan province in the northeast of burkina faso and ansongo inlier in eastern mali abstract at least 15 manganese deposits crop out in the west african craton in mali burkina faso ghana and cote d ivoire there average grade estimates range from 17 to 52 total mn oxide and average volume of 5 19 mt of ore they consequently provide an attractive target for exploration and eventual exploitation the tambao and beliata mn oxide deposits in the oudalan province northeast of burkina faso and takavasita agualla and tondibi mn oxide deposits in the ansongo inlier eastern mali generally crop out as a saprolitic residuum that formed during the miocene to eocene and are enriched in manganese to 52 total mn oxide the saprolitic residuum is overlain by blocky to botryoidal manganese rich duricrusts that form part of the resource portfolio the residuum overlies deeply weathered manganese bearing carbonates shales and volcaniclastic siltstones of the birimian supergroup 2 3 2 1 ga that form a low grade resource and likely formed in a heat driven seawater convection system that provided hydrothermal solutions from submarine volcanic centers they are typically intercalated with mafic intermediate volcanic rocks

efficient volumetric extraction of most positive negative curvature and flexure for fracture characterization from 3d seismic data most positive negative curvature and flexure are among the most useful seismic attributes for detecting faults and fractures in the subsurface based on the geometry of seismic reflections when applied to fracture characterization and modelling of a fractured reservoir their magnitude and azimuth help quantify both the intensity and orientation of fracturing respectively however previous efforts focus on estimating only the magnitude of both attributes whereas their associated azimuth is ignored in three dimensional 3d seismic interpretation this study presents an efficient algorithm for simultaneously evaluating both the magnitude and azimuth of most positive negative curvature and flexure from 3d seismic data the approach implemented in this study is analytically more accurate and computationally more efficient compared with the existing approach the added value of extracting most positive negative curvature and flexure is demonstrated through the application to a fractured reservoir at teapot dome wyoming first the newly extracted attributes make computer aided fault fracture decomposition possible this allows interpreters to focus on one particular component for fracture characterization at a time so that a composite fractured reservoir could be partitioned into different components for detailed analysis second curvature flexure azimuth allows interpreters to plot fracture histogram and or rose diagram in an automatic and quantitative manner compared with the conventional plotting rose diagram based on manual measurements automatic plotting is more efficient and offers unbiased insights into fracture systems by illuminating the most likely orientations of natural fractures in fractured reservoirs

manganese occurrence in the mankwadzi area southern kibi winneba metavolcanic belt ghana typical or atypical palaeoproterozoic birimian mn mineralization

the paradox of tropical karst morphology in the coral reefs of the arid middle east comment using mainly satellite images of both the arabian gulf and portions of the red sea purkis et al 2010 1 applied sophisticated mathematical modeling to explain large polygonal seafloor features templates that are amplified in some areas by modern coral growth they conclude from their

characterization of the shallow structures of active fault zones using 3 d ground penetrating radar data 1 where they can be correlated with geological exposures and trenches 3 d ground penetrating radar gpr data can contribute critical subsurface information to paleoseismic investigations because active faults are typically characterized by complicated near surface structures that vary with the styles of faulting and the types of rock that are ruptured gpr data can be difficult to interpret we have acquired 3 d gpr data sets across three active fault zones within new zealand that have different deformation styles the strike slip wellington fault zone reverse faults of the ostler fault zone and normal faults of the maleme fault zone to improve our interpretation of the processed gpr volumes we employed two suites of geometric attributes the first suite was computed using a coherence based algorithm it provided estimates of the coherency azimuth and dip of reflections the second suite quantified the volumetric textures of reflections which allowed different reflection facies to be defined objectively we have demonstrated how some attributes were more successful at visualizing certain structural or depositional characteristics than others for example the coherency attribute was an excellent tool for highlighting normal faults within volcanic deposits of the maleme fault zone whereas the texture based attributes were most useful for discriminating between the gravel and metasediment units juxtaposed by the wellington fault zone our gpr data sets and associated attribute volumes showed details of near surface fault geometry that were not obvious from surface mapping and they revealed evidence of off fault deformation gravitational collapse and topple structures