reservoir assessment using non invasive geophysical techniques this paper describes the use of three geophysical techniques to detect potential seepage that could jeopardise the integrity of reservoir embankments could induce partial or total collapse and pose a risk to the population nearby a fast scanning geophysical technique using two dipole electromagnetic em profile apparatus gem2 provided the first step to detect the weakest points on the selected dams in order to proceed to a more detailed analysis and visualisation of the soil erosion fissuring or piping using electrical resistivity tomography ert finally self potential surveys were carried out to relate to the em and ert anomalies that could be pathways for seepage and changes of the water displacement inside the embankment the three geophysical techniques used were evaluated in one case study of reservoir in a location relevant to flooding issues in czech republic a risk approach based on the geophysical results was undertaken for the reservoir embankment the three techniques together were compared for the same problematic section and confirmed seepage by showing similar results conclusions were also drawn on the efficiency of using these three techniques as a package to give a comprehensive non invasive assessment to be used as common practice by local authorities and environment agencies whereby remedial action could be recommended to protect assets and civilians

shallow seismic refraction used to map the hydrostratigraphy of nukuoro atoll micronesia abstract results from a shallow seismic refraction survey on nukuoro indicate that the distribution of fresh and brackish groundwater on that atoll island is controlled by a three dimensional mosaic of carbonate facies each facies is characterized by a distinct seismic velocity which is dependent on the grain size composition and abundance of carbonate cement the refraction survey further indicates that the upper saturated zone is composed of mostly unconsolidated sediments underlain by highly permeable well indurated limestone the fresh water lens and associated transition zone of fresh to saline groundwater occur within the upper unconsolidated sediments measurements of chloride ion concentrations in water samples collected from sites across the island indicate an asymmetric fresh water lens with the thickest part of the lens located near the lagoon shoreline during the 1983 drought saline water intruded into the island s central topographical depression where taro is cultivated the intrusion was caused by tidal pumping upward movement of brackish water underlying a reef flat plate which forms a confining layer over a significant part of the island

the resolving power of cross borehole tomography the data collected in a cross borehole tomography problem is inherently incomplete since the boreholes do not completely surround the media under study the ability of the experiment to resolve structure is therefore limited by poor experimental geometry we use the method of backus and gilbert to investigate the ability of this technique to resolve variations in acoustic velocity and attenuation between the two boreholes both integrals that appear in the backus gilbert formulation can be performed analytically thus expediting the calculations the resolving kernels have significant horizontal width demonstrating that the horizontal position of structures can be only poorly resolved

palaeoenvironmental significance of rounded pyrite in siliciclastic sequences of the late archaean witwatersrand basin oxygen deficient atmosphere or hydrothermal alteration petrographic and sulphur isotope studies support the long held contention that rounded grains of pyrite in siliciclastic sequences of the late archaean witwatersrand supergroup originated as placer grains the grains areconcentrated at sites where detrital heavy minerals are abundant within quartz pebble conglomerates and quartzose sandstones depositional sites with abundant pyrite are 1 within the matrix of bar type clast supported conglomerates 2 on scoured or winnowed surfaces and 3 on stratification planes the grains are internally compact or porous with truncation of internal structure at outer margins indicating fragmentation and rounding of pyritic source rocks during erosion and sediment transport a large range in textures reflects source rock lithologies with known varieties linked to sedimentary hosted diagenetic pyrite volcanic hosted massive sulphide deposits and hydrothermal pyrite laser ablation sulphur isotope analysis of pyrite reveals a broader range in 3 4 s values 5 3 to 6 7 than that of previously reported conventional bulk grain analyses 1 to 4 rounded pyrite from the steyn reef has significant variation in 3 4 s values 4 7 to 6 7 that establishes heterogeneous sulphur compositions with even adjacent grains having diverse isotopic signatures the heterogeneity supports a placer origin for rounded pyrite euhedral pyrite and pyrite overgrowths which are undoubtedly authigenic have restricted 3 4 s values 0 5 to 2 5 are chemically distinct from rounded pyrite and are probably the products of metamorphism or hydrothermal alteration the placer origin of rounded pyrite indicates that pyrite was a stable heavy mineral during erosion and transport in the early atmosphere its distribution in three sequences witwatersrand supergroup ventersdorp contact reef and black reef and in other sequences not linked to witwatersrand type au u ore deposits implies deposition of redox sensitive detrital heavy minerals during the late archaean consequently rounded grains of detrital pyrite are strong indicators of an oxygen poor atmosphere while not confirming a placer origin for gold in witwatersrand au u ore deposits the palaeoenvironmental significance of rounded pyrite negates its link to hydrothermal mineralization

tunnel signature prediction for a cross borehole seismic survey seismic location of tunnels or voids with a cross borehole survey is examined with field data and theory the field data were taken at a site with a 2 2 m high by 2 7 m wide roughly rectangular cross section tunnel using a newly developed 1 to 5 khz system employing a p wave sparker source the synthetic records were obtained using a 2 5 d boundary valued solution for an explosive point source near a cylindrical void and the solution was evaluated with the method of steepest descent the synthetic waveforms compared well to the field data both showed a maximum reduction of amplitude in the tunnel shadow of 8 db and a maximum first arrival delay of 0 1 ms additional theoretical modeling was used to examine the variations of the received signals with tunnel size and frequency and showed amplitude reduction increased with frequency and tunnel size calculations showed that s waves scattered from the tunnel are more than 20 db smaller than the primary p wave on hydrophones and more than 12 db smaller on

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

seismicity of the forearc marginal wedge accretionary prism three different types of seismic data have been examined for seismic events occurring within the zone called the accreted wedge or forearc marginal wedge that underlies the inner trench wall of some arcs these types of data are 1 teleseismically recorded earthquakes that have been reported in the literature as occurring in major arc trench regions these events fail to demonstrate that earthquakes occur within the accreted wedge because the uncertainty of focal depth usually exceeds the depth dimension of the accreted wedge these data include many tsunamigenic earthquakes 2 local earthquakes located by combined ocean bottom seismograph and land networks in the arc trench region in the new hebrides and the central and eastern aleutian trench none of the more reliable of these hypocenters lies within the accreted wedge 3 s p intervals measured at stations on islands located on the outer ridge or at ocean bottom seismograph stations on the forearc marginal wedge these data do not show the existence of events occurring within the accreted wedge e g from 18 ocean bottom seismograph stations with a cumulative operation time of about 1 year the smallest s p time is about 2 5 s for events in the new hebrides and about 4 s for events in the adak and kodiak regions we found no s p time smaller than 2 s from 6 years of seismograms recorded at middleton island alaska and no s p time smaller than 4 s from 25 years of seismograms recorded on barbados all of the events could have occurred outside the forearc marginal wedge although we have located no events with hypocenters which are situated unambiguously within the accreted wedge we have located many events which occurred in the vicinity of the accreted wedge some occur in the upper portion of the benioff zone shallower than about 40 km and others occur in the leading edge of the overriding plate these locations reported in this paper which are within or close to the seismic networks comprise some of the most reliably located shallow events ever reported in convergent margins of island arcs the absence of seismic activity within the accreted wedge in any island arc that we studied suggests that the deformation evident in this region occurs aseismically

record of emergent continental crust 3 5 billion years ago in the pilbara craton of australia isotopic data for the earth s oldest rocks1 7 imply that a considerable volume of continental crust existed during the early archaean aeon 3 0 gyr ago but it is not known when this crust first began to form emergent landmasses sedimentary geochemistry suggests8 9that the area of exposed continent was negligible until late in the archaean10 a contention supported by the fact that until now all greenstone supracrustal volcanic and sedimentary successions shown to have been deposited on eroded continental basement have yielded ages of 3 0 gyr here we report the discovery of an angular unconformity an ancient erosion surface beneath rocks of the 3 46 gyr warrawoona group in the pilbara craton of australia currently the oldest known well preserved greenstone succession below the unconformity low grade greenstones older than 3 5 gyr were intruded by voluminous granitoids before erosion as the overlying warrawoona rocks are only mildly metamorphosed slightly deformed and were deposited near sea level we infer that they accumulated on crust that was already rigid cool and buoyant thus by 3 46 gyr ago the sub warrawoona rocks formed an emergent block of continental crust the most ancient known

the depths of the deepest deep earthquakes the maximum depth of seismic activity is a fundamental observation providing a constraint on models of mantle dynamics although most recent investigations of mantle seismicity and dynamics state that seismicity extends to about 700 km focal depths of 720 km have been reported for large earthquakes as well as depths greater than 800 km for small events we have examined focal depths of events in several catalogs and conclude that 1 the deepest reliable focal depths are at about 670 680 km and events with focal depths beneath 600 km occur in several widely separated geographic regions 2 observations supporting focal depths exceeding 680 km are usually few poor or inconsistent 3 the reduction of seismic activity beneath about 650 km is quite abrupt however we cannot determine whether activity stops completely at 670 680 km or the maximum size of events decreases gradually beneath 650 km with magnitudes of 6 5 7 0 occasionally occurring at 650 km magnitudes of 5 5 6 0 at 680 km 4 0 4 5 at 695 km etc several models can explain the absence of seismic activity in the lower mantle two models are consistent with the abrupt termination of activity at about 650 680 km in widely separated areas a barrier which resists penetration by the subducting lithosphere or a phase transition which modifies the properties of the subducted material as it goes into the lower mantle

application of time lapse ert imaging to watershed characterization time lapse electrical resistivity tomography ert has many practical applications to the study of subsurface properties and processes when inverting time lapse ert data it is useful to proceed beyond straightforward inversion of data differences andtakeadvantageofthetime lapsenatureofthedata weassess various approaches for inverting and interpreting time lapse ertdataanddeterminethattwoapproachesworkwell thefirst approachismodelsubtractionafterseparateinversionofthedata from two time periods and the second approach is to use the inverted model from a base data set as the reference model or prior information for subsequent time periods we prefer this second approach data inversion methodology should be considered when designing data acquisition i e to utilize the second approach it is important to collect one or more data sets for which the bulk of the subsurface is in a background or relatively unperturbed state athird and commonly used approach to time lapse inversion invertingthedifferencebetweentwodatasets localizes the regions of the model in which change has occurred however varying noise levels between the two data sets can be problematic to further assess the various time lapse inversion approaches weacquiredfielddatafromacatchmentwithinthedry creek experimental watershed near boise idaho u s a we combined the complimentary information from individual static ertinversions time lapseertimages andavailablehydrologicdatainarobustinterpretationschemetoaidinquantifyingseasonalvariationsinsubsurfacemoisturecontent

timing of deposition and deformation of the moodies group barberton greenstone belt south africa very high resolution of archaean surface processes abstract thin and largely discontinuous volcanic tuff beds in the alluvial fluvial and marginal marine siliciclastic strata of the middle archaean moodies group barberton greenstone belt bgb contain rare to abundant zircon dating of magmatic zircon grains from five tuff beds and one cross cutting dike yield ages which span the entire spectrum of bgb history from ca 3550 ma to 3215 ma and show variable degrees of post depositional alteration until ca 2500 ma the youngest pristine zircon grains in all tuff samples analyzed by ca id tims chemical abrasion ion dissolution thermal ion mass spectrometry yield upper intercept and concordia ages between 3227 6 0 3 and 3216 0 3 ma and those grains analyzed by la sf icp ms laser ablation sector field inductively coupled plasma mass spectrometry and shrimp sensitive high resolution ion microprobe yield ages between 3228 9 and 3214 9 ma most of these ages are either identical within error or significantly older than a ca id tims age of 3223 4 0 3 ma obtained from zircon grains of a tuff horizon of the schoongezicht formation at the top of the underlying fig tree group we interpret this age to mark the time of volcanic eruption whereas the significantly older and overlapping ages of the stratigraphically higher moodies tuff zircon grains point either to a high degree of magmatic inheritance and or a detrital contribution from surrounding sedimentary rocks during or after ash tuff deposition the minimum age for deposition of moodies group sediments and deformation is provided by a la icp ms zircon u pb age of 3219 9 ma obtained from an undeformed felsic dike which crosscuts folded moodies strata this age overlaps with a precise ca id tims u pb zircon age of 3216 0 0 3 ma obtained from a tuff horizon of the upper moodies group overall the new age data collectively imply that the up to 3 7 km thick sandstone dominated moodies group was deposited and deformed within

parsimonious surface wave interferometry we thank the sponsors for supporting the consortium of subsurface imaging and fluid modeling csim we also thank kaust for providing funding by the crg grant ocrf 2014 crg3 2300 for computer time this research used the resources of the it research computing group and the supercomputing laboratory at kaust

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

paleoarchean sulfur cycle and biogeochemical surface conditions on the early earth barberton south africa abstract this study presents the first multiple sulfur isotope dataset on sulfides from the ca 3 5 3 2 ga onverwacht group in the paleoarchean barberton greenstone belt bgb of south africa in situ 34 scdt and 33 s values of pyrite n 568 are reported from a wide range of hydrothermal volcanic and sedimentary environments and are used to explore mid archean biogeochemical sulfur cycling samples are from fresh drill core collected by the barberton scientific drilling project that intercepted cherts metabasalts and sheared ultramafics of the 3 3 3 35 ga kromberg formation the sedimentary units of the 3 432 ga noisy formation and the unconformably underlying metabasaltic pillow lavas of the 3 472 ga hooggenoeg formation pyrite in quartz carbonate veins in the lower diamictite of the noisy sequence records the largest range and most negative 34 scdt values so far reported from an archean terrain 34 s cdt 55 04 to 27 46 the noisy sediments also contain detrital and diagenetic pyrites with a significant variation in 33 s of between 0 62 to 1 4 and 34 scdt of between 7 00 and 12 6 interpreted to reflect tectonic exposure of these early sediments to atmospheric shallow marine conditions early marine pyrites from the kromberg cherts also display strong positive 33 s values up to 2 50 with narrow range in 34 scdt values 6 00 to 1 50 whereas hydrothermal veins in the basal ultramafic shear zones preserve magmatic values 0 this study reveals a potential proto tectonic control on atmospheric geodynamic and hydrothermal environments available for early sulfate reducing and or methanogenic microbes in the paleoarchean no evidence for microbial sulfate reduction or disproportionation was identified in the kromberg cherts despite previous morphological claims for microbial life highly variable and negative 34 scdt values were found in the noisy turbidites and hooggenoeg pillow lava breccia supporting the presence of microbial sulfate reduction in early tectono sedimentary basins and in the paleoarchean sub seafloor respectively in light of current controversies surrounding sulfur isotope studies in similar aged rocks of the pilbara craton west australia we argue that microbial elemental sulfur disproportionation was not a preferred metabolic pathway on the paleoarchean earth

faulting process of the august 8 1993 guam earthquake a thrust event in an otherwise weakly coupled subduction zone we study a large mw 7 7 earthquake that occurred on june 8 1993 slightly offshore and under the island of guam in the southern mariana island arc from a complete study of p and sh body waves a relocation of the aftershocks and the subevents of the main shock we propose a relatively simple model of the rupture process of this event we propose that this earthquake ruptured a shallow dipping thrust fault that corresponds to the subduction interface under guam like many other earthquakes this event started with a small foreshock and was followed by two large energy release events located to the northeast of the epicenter along the subduction zone the rupture process had a relatively short duration of about 32 s with a weak starting phase that lasted about 8 s seismic moments estimated from body waves surface waves and global positioning system gps are very similar of the order of 4 5 1020 n m the displacement field produced by our best model was compared to the gps measurements of coseismic slip obtained by beavan et al 1994 we find an excellent agreement both in displacement direction and magnitude between the predicted and observed gps displacements this appears to be then the largest earthquake to have occurred on a shallow dipping thrust fault in the mariana subduction zone during this century its occurrence requires a reassessment of the concept of seismic coupling in this subduction zone

weathering and sediment generation in the archean an integrated study of the evolution of siliciclastic sedimentary rocks of the 3 2ga moodies group barberton greenstone belt south africa abstract alluvial and braided fluvial deposits of the 3 2 ga moodies group in the barberton greenstone belt south africa are analyzed petrographically and geochemically to identify their source rocks provenance and assess the degree and type s of weathering required to produce the observed moodies sediment compositions conglomerate sandstone and shale data give somewhat differing pictures of provenance and weathering due to derivation from different components within the source terrane and size and compositional fractionation during transport the results suggest that shale geochemistry provides the most accurate estimate provenance although both rare earth element and trace element th sc zr cr and ti data must be used in combination to give the best results the source area for moodies group sediments was dominated by tonalite felsic volcanic rock komatiite basalt and granite based on mineralogical and major element divergence from estimated source area composition the moodies group sediments are remnants of an aggressive weathering environment labile materials such as komatiite basalt and coarse plagioclase grains decomposed almost entirely to clays and solutes and the chemical index of alteration for moodies shale is well above the global average an aggressive weathering environment in the archean may have been achieved by increased rainfall higher temperatures and or higher atmospheric p c o 2 more likely a combination of these conditions worked to offset the inhibitory weathering effects of a plant free environment

seismic monitoring of diffraction images for detection of local heterogeneities diffracted waves contain valuable information regarding both the structure and composition of the media they are in in seismic data processing however these waves are usually regarded as noise in this paper we present an attempt to use scattered diffracted waves for the detection of local heterogeneities the method is based on the detection of diffracted waves by concentrating the signal amplitudes from diffracting points on the seismic section this is done using a correlation procedure that enhances the amplitude of the seismic signal at the location of the diffractors on the common diffraction point section d section the new local time correction for diffraction traveltime curve parameterization is based on the radius of curvature of the diffracted wavefront and near surface velocity we use the idea of seismic monitoring for detection and delineating local objects which may occur within the subsurface resulting from human activity or fast geological processes the method consists of continuou

imaging discontinuities on seismic sections in routine seismic processing normal moveout nmo corrections are performed to enhance the reflected signals on common depth point or common midpoint stacked sections however when faults are present reflection interference from the two blocks and the diffractions from their edges hinder fault location determination destruction of diffraction patterns by poststack migration further inhibits proper imaging of diffracting centers this paper presents a new technique which helps in the interpretation of diffracting edges by concentrating the signal amplitudes from discontinuous diffracting points on seismic sections it involves application to the data of moveout and amplitude corrections appropriate to an assumed diffractor location the maximum diffraction amplitude occurs at the location of the receiver for which the diffracting discontinuity is beneath the source receiver midpoint since the amplitudes of these diffracted signals drop very rapidly on either side of the midpoint an appropriate amplitude correction must be applied also because the diffracted signals are present on all traces one can use all of them to obtain a stacked trace for one possible diffractor location repetition of this procedure for diffractors assumed to be located beneath each surface point results in the common fault point cfp stacked section which shows diffractor locations by high amplitudes the method was tested for synthetic data with and without noise it proves to be quite effective but is sensitive to the velocity model used for moveout corrections therefore the velocity model obtained from nmo stacking is generally used for enhancing diffractor locations by stacking finally the technique was applied to a field reflection data set from an area south of princess well in alberta

time lapse monitoring of fluid induced geophysical property variations within an unstable earthwork using p wave refraction abstracta significant portion of the uk s transportation system relies on a network of geotechnical earthworks cuttings and embankments that were constructed more than 100 years ago whose stability is affected by the change in precipitation patterns experienced over the past few decades the vulnerability of these structures requires a reliable cost and time effective monitoring of their geomechanical condition we have assessed the potential application of p wave refraction for tracking the seasonal variations of seismic properties within an aged clay filled railway embankment located in southwest england seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals for a total period of 16 months p wave first break times were picked from all available recorded traces to obtain a set of hodocrones referenced to the same spatial locations for various dates along the surveyed period of time traveltimes extracted from each acquisition were then compared to trac

pyrite in a sulfate poor paleoarchean basin was derived predominantly from elemental sulfur evidence from 3 2 ga sediments in the barberton greenstone belt kaapvaal craton abstract multiple sulfur isotope variability in archean sedimentary rocks provides constraints on the composition of the earth s earliest atmosphere the magnitude and sign of mass independent anomalies reflect not only atmospheric processes but also transformations due to the archean marine sulfur cycle prior to preservation into sedimentary pyrite the processes affecting the archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear here we combine iron fe and multiple sulfur s isotope data in individual pyrite grains with petrographic information and a one dimensional reactive transport model to investigate the sources of fe and s in pyrite formed in a paleoarchean sedimentary basin pyrites were selected from mudstones sandstones and chert obtained from a drill core in the ca 3 2 ga mapepe and mendon formations of the fig tree and onverwacht groups respectively in the barberton greenstone belt kaapvaal craton south africa pyrite textures and 56 fe distinguish early diagenetic pyrite formed with pore water ferrous iron disseminated grains with average 56 fe pyrite 0 from late diagenetic pyrite formed through sulfidation of iron oxide minerals layered and aggregate forms with average 56 fe pyrite 1 mass dependent s isotope variability in pyrite was small 34 s pyrite ranged from 1 1 to 3 3 with a correspondingly minor spread in 33 s pyrite ranging from 0 3 to 2 1 and 36 s pyrite ranging from 3 08 to 0 27 that indicates a lack of post depositional re working with other distinct sulfur sources our combined fe and s isotope data are most readily explained with pyrite sulfide derived from microbial reworking of solid elemental s iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed the lack of a negative 33 s signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis consistent with low sulfate concentrations in the paleoarchean ocean

iron oxyhydroxide and sulphide mineralization in hydrocarbon seep related carbonate submarine chimneys gulf of cadiz sw iberian peninsula this paper aims to investigate the iron mineralization hosted in the submarine hydrocarbon seep related carbonate chimneys from the gulf of cadiz continental slope sw iberia chimneys are made of a general fine groundmass of major fe rich dolomite ankerite and calcite small grains of quartz and phyllosilicates and some foraminifer tests and ostracod shells primary porosity is frequently generated inside foraminifer chambers and ostracod shells and is filled with closely packed microcrystals of iron oxyhydroxide and sulphide minerals forming framboids some extremely peculiar multiframboidal textures are also detected corresponding to microcrystal groups spherical framboids and euhedral crystals without framboidal texture the mineralogy observed is mainly goethite pyrite pseudomorphs traces of tiny grains of pyrite were also observed cubic octahedral and pyritohedral are the habits observed in both minerals chemical analyses of framboids and euhedral crystals display high often erratic amounts of as co ni and mo in oxyhydroxides and mo pb v and co in sulphides versus almost always negligible concentrations of cu and zn a textural geochemical and mineralogical evolution is proposed to explain the coexistence of different morphologies in the multiframboidal texture a growth and aggregation of microcrystals as typical framboidal type mineralogical associations b development of euhedral habits c coalescence and homogenization of the microcrystal into large size euhedral to anhedral crystals and d formation of euhedral crystals or polycrystalline masses with complete loss of framboidal texture along this process an increase of the concentration of fe s mn and ti linked to a decrease in mg si al as p ca and v was observed the study of the iron mineralization in the gulf of cadiz is a first and can give clues to understand the complex geobiological interactions in this and other similar extreme hydrocarbon bearing submarine ecosystems

pyrite framboids and their development a new conceptual mechanism it has been suggested that the two morphologies of sedimentary pyrite framboids and euhedra may reflect two distinct pathways of pyrite formation framboids form indirectly via iron monosulphides whereas euhedra form from direct precipitation from solution a third pathway which is bridging these two forms is proposed here namely the continuous growth from a monosulphide globule through framboids to a euhedral single crystal it is also suggested that framboids probably occur over a range of three orders of magnitude from the least complex microframboids through framboids to polyframboids

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

diffraction imaging by multifocusing correct identification of geologic discontinuities such as faults pinch outs and small size scattering objects is a primary challenge of the seismic method seismic response from these objects is encoded in diffractions our method images local heterogeneities of the subsurface using diffracted seismic events the method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities this is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local time correction formula to parameterize diffraction traveltime curves this time correction which is based on the multifocusing method depends on two parameters the emergent angle and the radius of curvature of the diffracted wavefront these parameters are estimated directly from prestack seismic traces the diffraction multifocusing stack dmfs can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area

double seismic zone beneath the mariana island arc a double zone of seismicity has been found beneath the northern marianas in the depth range 80 120 km the benioff zone undergoes a pronounced bend with radius of curvature about 200 km before straightening and descending nearly vertically to a depth of more than 600 km thus this is an ideal area in which to search for evidence of stresses associated with unbending of the subducted oceanic plate we relocated all teleseismic events from 1963 through 1975 by using a regional composite master event technique which significantly decreased the scatter of the hypocenters the three events of the lower seismic zone are separated from the upper zone by about 30 35 km the true thickness of the upper seismic zone is probably 20 km or less the limited focal mechanism data indicate that there is downdip tension in the lower zone and downdip compression in the upper zone the seismicity patterns could be generated either by thermal stresses or by unbending a plate which was originally deformed anelastically we show that an elastic perfectly plastic model of the rheology of the plate can account for the separation of the two seismic zones the focal mechanisms and the greater activity of the upper seismic zone

chemistry and mineralogy of precambrian paleosols at the base of the dominion and pongola groups transvaal south africa abstract we have studied alteration zones found between sedimentary rocks of the lowest proterozoic dominion and archean pongola groups and underlying granitic rocks transvaal south africa the alteration zones have a transitional lower boundary primary igneous minerals are gradually destroyed upward toward the contact with overlying sedimentary rocks ca mg na p and mn are progressively lost upwards in the zone the chemical and mineralogical variations and available stratigraphic evidence are all consistent with the interpretation that these zones are paleosols formed by precambrian weathering 2 8 3 0 ga ago after formation the paleosols underwent metasomatism and metamorphism sericite now present in the paleosols was probably formed by low temperature potassium metasomatism of original clays andalusite in the pre pongola paleosol was probably formed by metamorphism of original clays in impermeable zones which prevented groundwater flow and potassium metasomatism the dominion paleosol was investigated at three localities the effects of weathering were similar at the three sites except for the behavior of iron one site lost about 20 of iron whereas the other sites lost 75 and 80 of initial iron content the differences in iron loss may be due to variation in soil ventilation and diffusion of atmospheric gases as a function of grain size and topography variations in iron loss may be used to place some constraints on the composition of the precambrian atmosphere given constraints imposed by dominion paleosols overlying uraniferous conglomerates requirements for chemical weathering and the greenhouse effect and possible presence of non diffusing photochemical oxidants the partial pressures of oxygen and carbon dioxide gases probably are in the ranges po1 0 02 to 0 5 pal present atmospheric level and pco2 5 to 30 pal

practical techniques for 3d resistivity surveys and data inversion1 techniques to reduce the time needed to carry out 3d resistivity surveys with a moderate number 25 to 100 of electrodes and the computing time required to interpret the data have been developed the electrodes in a 3d survey are normally arranged in a square grid and the pole pole array is used to make the potential measurements the number of measurements required can be reduced to about one third of the maximum possible number without seriously degrading the resolution of the resulting inversion model by making measurements along the horizontal vertical and 45 diagonal rows of electrodes passing through the current electrode the smoothness constrained least squares inversion method is used for the data interpretation the computing time required by this technique can be greatly reduced by using a homogeneous half space as the starting model so that the jacobian matrix of partial derivatives can be calculated analytically a quasi newton updating method is then used to estimate the partial derivatives for subsequent iterations this inversion technique has been tested on synthetic and field data where a satisfactory model is obtained using a modest amount of computer time on an 80486dx2 66 microcomputer it takes about 20 minutes to invert the data from a 7 by 7 electrode survey grid using the techniques described below 3d resistivity surveys and data inversion can be carried out using commercially available field equipment and an inexpensive microcomputer

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

detecting clandestine tunnels using near surface seismic techniques abstractgeophysical detection of clandestine tunnels is a complex problem that has met with limited success multiple methods have been applied spanning several decades but a reliable solution has yet to be found we evaluated shallow seismic data collected at a tunnel test site representative of geologic settings found along the southwestern u s border our results demonstrated the capability of using p wave diffraction and surface wave backscatter techniques to detect a purpose built subterranean tunnel near surface seismic data were also collected at multiple sites in afghanistan to detect and locate subsurface anomalies including data collected over the escape tunnel discovered in 2011 at the sarposa prison in kandahar afghanistan which allowed more than 480 prisoners to escape and data from another shallow tunnel recently discovered at an undisclosed location the final example from afghanistan was the first time surface based geophysical methods have detected a tunnel whose presence and loca

mass independent isotope effects in archean 2 5 to 3 8 ga sedimentary sulfides determined by ion microprobe analysis we report sulfur isotope anomalies with 33 s the deviation from a mass dependent fractionation line for the three isotope system 34 s 32 s vs 33 s 32 s ranging up to 2 within individual archean sedimentary sulfides from a variety of localities our measurements which are made in situ by multicollector secondary ion mass spectrometry unequivocally corroborate prior bulk measurements of mass independent fractionations mif in sulfur and provide additional evidence for an anoxic atmosphere on the earth before 2 ga this technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record the presence of mif sulfur in sulfides from a 3 8 ga fe rich quartzite from akilia island west greenland is consistent with a marine sedimentary origin for this rock copyright 2003 elsevier science ltd

a land ocean bottom seismograph experiment in the mariana forearc abstract a network of land and ocean bottom seismographs in the north central mariana islands located 20 earthquakes during a 22 day recording period the locations of 14 subcrustal events define an inclined seismic zone extending to approximately 280 km depth with one isolated event at 580 km depth the geometry of this zone coincides with that defined by teleseismic earthquake locations no reliably located earthquakes occurred within the accretionary prism consistent with the hypothesis that deformation within the accretionary prism takes place aseismically

seismic modeling to monitor co2 geological storage the atzbach schwanenstadt gas field 1 we develop a petro elastical numerical methodology to compute realistic synthetic seismograms and analyze the sensitivity of the seismic response when injecting carbon dioxide co2 in a depleted gas reservoir the petro elastical model describes the seismic properties of the reservoir rock saturated with co2 methane and brine and allows us to estimate the distribution and saturation of co2 during the injection process the gas properties as a function of the in situ pressure and temperature conditions are computed with the peng robinson equation of state taking into account the absorption of gas by brine wave attenuation and velocity dispersion are based on the mesoscopic loss mechanism which is simulated by an upscaling procedure to obtain an equivalent viscoelastic medium corresponding to partial saturation at the mesoscopic scale having the equivalent complex and frequency dependent bulk dilatational modulus we include shear attenuation and perform numerical simulations of wave propagation at the macroscale by solving the viscoelastic differential equations using the memory variable approach the pseudo spectral modeling method allows general material variability and provides a complete and accurate characterization of the reservoir the methodology is used to assess the sensitivity of the seismic method for monitoring the co2 geological storage at the atzbach schwanestadt depleted gas field in austria the objective of monitoring is the detection of the co2 plume in the reservoir and possible leakages of co2 the leakages are located at different depths where the co2 is present as gaseous liquid and supercritical phases even though the differences can be very subtle this work shows that seismic monitoring of co2 from the surface is possible while the identification of shallow leakages is feasible the detection of the plume and deep leakages located in the caprock just above the injection formation is more difficult but possible by using repeatability metrics such as the normalized rms nrms images considering real data conditions affected by random noise a reference detection threshold for deep leakages and the co2 plume in the reservoir corresponds to a signal to noise ratio of about 10 db

imaging and monitoring of the shallow subsurface using spatially windowed surface wave analysis with a single permanent seismic source abstractdevelopment of shallow subsurface monitoring systems is important for monitoring the ground stability of shallow formation and also for conventional deep seismic monitoring because with cu

a numerical study of surface wave based tunnel detection at the black diamond mines regional preserve california author s sherman cs rector j dreger d glaser s abstract 2018 society of exploration geophysicists detecting underground voids such as old mine workings solution cavities in karst terrain or unknown tunnels such as illicit cross border tunnels is a challenging problem for geophysics and an important concern for geotechnical design public safety and domestic security seismic surface wave based detection methods have become increasingly popular for detecting relatively shallow and small targets however the theoretical limitations of these methods have thus far remained unclear we use a suite of 3d numerical simulations inspired by a tunnel detection experiment carried out at the black diamond mines regional preserve bdm in northern california the geophysical anomalies predicted by our numerical simulations at bdm agree with field observations and our estimates for the location of the primary tunnel target agree with historical records in the area using our calibrated numerical model we perform a parametric study to determine the effect of tunnel size depth of burial filling material and source characteristics to determine the range over which surface wave backscattering and attenuation based methods are effective in addition we perform a regression analysis to determine a relationship for the maximum depth at which a tunnel may be detected via these approaches given the target diameter wavelength of interest and the signal to noise ratio

microbial life and biogeochemical cycling on land 3 220 million years ago the colonization of emergent continental landmass by microbial life was an evolutionary step of paramount importance in earth history here we report direct fossil evidence for life on land 3 220 million years ago ma in the form of terrestrial microbial mats draping fluvial conglomerates and gravelly sandstones of the moodies group south africa combined field petrographic carbon isotope and raman spectroscopic analyses confirm the synsedimentary origin and biogenicity of these unique fossil mats as well as their fluvial habitat the carbon isotope compositions of organic matter 13corg from these mats define a narrow range centred on 21 in contrast to fossil mats of marine origin from nearby tidal deposits that show 13corg values as low as 34 bulk nitrogen isotope compositions 2 15n 5 are also significantly different from their marine counterparts 0 15n 3 which we interpret as reflecting denitrification in the terrestrial habitat possibly of an atmospheric source of nitrate our results support the antiquity of a thriving terrestrial biosphere during the palaeoarchaean and suggest that a complex and microbially driven redox landscape existed during the deposition of the moodies group with distinct biogeochemical cycling occurring on land by 3 220 ma microbial life colonized the land surface by 3 2 billion years ago forming complex communities distinct from those in nearby marine environments according to analyses of fossilized microbial mats in the moodies group south africa

spatial distribution and mechanisms of earthquakes in the southern new hebrides arc from a temporary land and ocean bottom seismic network and from worldwide observations in 1977 a wide aperture seismic network of land and ocean bottom stations obs was operated for 6 weeks in the southern new hebrides island arc data on the spatial distribution and mechanisms of small events recorded by this local network were integrated with worldwide observations of moderate to large size new hebrides earthquakes of the past 17 years to study the structure and deformational processes in the new hebrides subduction zone surprisingly small differences less than about 10 km were found between the locations of shallow and intermediate depth earthquakes as located by the temporary local network and by the international seismological centre using worldwide stations analysis of the p wave travel time data from the obs station closest to the trench shows limited evidence for a high velocity zone about 5 higher than the surrounding mantle associated with the descending plate the thrust zone between the descending and upper plates is defined mainly by the spatial distribution and focal mechanisms of moderate to large size events and their aftershocks but it is not very well defined by the spatial distribution of small size events located in this study shallow seismic activity located beneath the trench and beneath the interplate thrust zone indicates a lower limit of about 40 km for the thickness of the seismically active part of the descending plate beneath the thrust zone focal mechanisms of moderate to large size earthquakes located within the upper plate and geological observations on the islands suggest that the upper plate in the region of erromango and tanna is divided into a series of blocks that are differentially uplifted along mainly nw se striking faults during the obs experiment several shallow events were well located beneath the coriolis trough a riftlike feature located to the east of the volcanic arc well determined depths of these events are between 11 and 22 km the well located intermediate depth events define a 20 km thick benioff zone that has a dip of about 70 the spatial distribution of events within the descending slab is very strongly clustered in a persistent pattern that is seen in both the short term sample of small events determined by the local network and the long term sample of locations based on worldwide data several focal mechanisms of moderate to large size intermediate depth events show components of lateral extension along the strike of the arc and some show components of lateral compression both of which could be interpreted as the result of a lateral bending of the descending plate in the part of the southern new hebrides arc where the trench begins to curve around to the east

biogenic overgrowth on detrital pyrite in ca 3 2 ga archean paleosols regionally traceable paleosols in the lower moodies group of the barberton greenstone belt ca 3 22 ga northeastern south africa and swaziland contain locally abundant silicified nodules originally composed of pedogenic carbonates and sulfates interbedded with heavy mineral laminae dominated by pyrite pyrite grains show rounded detrital cores and secondary idiomorphic rims with trace element concentrations and 34 s ratios clearly different from those of the cores while cores have low co and ni concentrations and high co ni ratios rims show as much as 5 5 wt of these elements and low co ni ratios reflecting the weathering of nearby ultramafic rocks in situ sulfur isotope analyses of pyrite cores show 34 s vcdt vienna canyon diablo troilite values between 5 and 5 while the rims show 34 s vcdt values between 20 and 24 5 suggesting biogenic fractionation of sulfur the close spatial association and microtextural evidence for nearly contemporaneous formation of the pedogenic sulfate nodules and the secondary pyrite rims suggests microbial processing of sulfur in the paleosols which provided reduced and 34 s depleted sulfur for the growth of authigenic pyrite this indicates that vadose zone soil forming processes in the archean involved not only physical and chemical modification of moist unconsolidated sediment in a terrestrial environment but also already included its microbiological modification

earliest life on earth evidence from the barberton greenstone belt south africa abstract studies investigating the structure and diversity of earth s record of life older than 3 2 ga are restricted to two locations worldwide in which sedimentary rocks have escaped regional high grade metamorphism and penetrative deformation the pilbara craton of western australia and the barberton greenstone belt in the kaapvaal craton of south africa this paper provides a south african perspective on the evidence of paleoarchean life a record that is often overlooked in the literature it aims to summarize and critically review previously reported claims of early life in the bgb gives an overview of the latest findings and provides an outlook on potential future discoveries the 15 km thick volcanic sedimentary succession making up the barberton supergroup was deposited between 3 55 to ca 3 20 ga and can be subdivided in three stratigraphic units that provide a unique window into a diverse and widespread paleoarchean microbial ecosystem landscape putative biosignatures occur almost throughout the entire bgb stratigraphy and range from carbonaceous cherts containing filamentous spheroidal and lenticular microstructures traces of hydrothermal biofilms photosynthetic microbial mats remnants of pseudocolumnar stromatolites and large organic walled spheroidal microfossils of currently unknown affinity the bgb also contains one of the world s oldest known record of tufted microbial mats which extensively colonized tidally influenced siliciclastic shorelines and were most likely formed by filamentous photosynthesizers other mat associated biosignatures include silicified gas bubbles domes and lenses that likely formed due to metabolic activity or the decay of buried organic matter some of these subsurface voids beneath the cohesive mats were inhabited by the earliest known forms of cavity dwelling microbial communities that were probably dominated by chemotrophic or photosynthetic microbes recently discovered terrestrial microbial mats once thriving in a fluvial dominated setting represent the oldest macroscopically visible fossil traces of life on land which is also supported by the occurrence of nearby paleosols that carry signals of biogenic sulfur fractionation the wealth of preserved microbial biosignatures from marine fluvial hydrothermal and possibly planktonic settings combined with the high spatial and temporal resolution of the barberton greenstone belt deposits is truly exceptional consequently the bgb deserves an equal level of attention and protection for future generations like its australian counterpart

refraction tomography over a buried waste disposal site determining the depth and geometry of a landfill s lower boundary is a difficult task potential field methods generally lack the necessary depth resolution and seismic reflection data are usually contaminated by source generated noise in the time range of interest 50 ms to address this problem we have developed a surface 2 d tomographic refraction scheme that is based on a fast finite difference eikonal solver and an inversion method that incorporates appropriate damping and smoothing constraints this new scheme has been applied to a first arrival traveltime data set collected across adjacent landfills in northern switzerland high quality seismic data were collected along five profiles that crossed the landfills and two that sampled undisturbed natural sediments seismic waves generated from multiple shots were recorded on large numbers of closely spaced receivers during quiet evening periods reliability of the resultant velocity tomograms was estimated on the basis of 1 ray diagrams 2 plot

climatic and geochemical implications of archean pedogenic gypsum in the moodies group 3 2 ga barberton greenstone belt south africa abstract lithic sandstones of braided fluvial to supratidal facies in the paleoarchean moodies group 3 22 ga barberton greenstone belt south africa include several regionally traceable units with common to abundant in places rock forming nodular concretions of megaquartz pseudomorphs after gypsum barite and calcite concretionary accumulations are stratiform and commonly associated with aqueously reworked fine grained tuffaceous sediment of originally rhyodacitic composition and can grow to fist sized agglomerates in crusts tens of m in lateral extent weathering of tuffaceous material and feldspar delivered alkali cations such as ca ba and k while carbonates were likely supplied by silicate weathering of mafic to ultramafic volcanic rocks during exposure to a co2 rich atmosphere sulfate ions were partly delivered by oxidative pyrite dissolution which may have included microbial and abiotic disproportionation of volcanic s or so2 concretionary growth apparently took place under pedogenic to early diagenetic conditions within unconsolidated granular sediment in the vadose zone dominated by seasonal fluctuations of the groundwater level under evaporitic conditions the concretions likely represent the oldest terrestrial evaporites known to date and form part of the oldest known compound paleosols their formation and composition constrain the local occurrence of sulfate in the archean atmo and hydrosphere their interaction with the emerging biosphere archean weathering regime local climate and vadose zone hydrodynamics

trace element zoning of sulfides and quartz at sheba and fairview gold mines clues to mesoarchean mineralisation in the barberton greenstone belt south africa abstract the fairview and sheba mines are two of the major gold mines in the paleoarchean barberton greenstone belt of southern africa at these mines gold is associated with quartz carbonate rutile veins and occurs both as invisible gold finely dispersed in sulfides primarily pyrite and arsenopyrite and as visible electrum grains hosted in pyrite up to approximately 1000 ppm au are contained in pyrite and up to approximately 1700 ppm in arsenopyrite mapping of trace element distribution in sulfide minerals using electron microprobe and proton probe techniques revealed multiple events of ore formation and au mineralisation at fairview mine three stages of pyrite formation were identified the last of which is associated with arsenopyrite electrum and other sulfide minerals sphalerite chalcopyrite galena gersdorffite and sb sulfides at sheba mine pyrite was deposited in two stages and electrum is associated with the second stage at both mines the last stage of sulfide formation is the main stage of au deposition and is associated with mobilisation of au as sb cu zn and ni the host rock composition seems to have affected the composition of pyrite since higher ni and co concentrations up to 1 4 and 1 6 wt respectively have been measured in meta ultra mafic host rocks in comparison with chert and metagreywacke arsenopyrite is chemically zoned and has sb and s rich cores and as and ni rich rims this zoning indicates variations in fluid compositions decreasing sb and increasing ni and crystallisation conditions increasing as content for increasing temperature geothermometric estimates based on the as content of arsenopyrite as 32 at indicate temperatures up to 420 c for the crystal rims petrographic and cathodoluminescence observations of quartz associated with gold mineralisation show only local brittle deformation and no plastic deformation this supports the notion that the ore transporting veins were emplaced late in the deformation history variations of cathodoluminescence of quartz are correlated with changing al contents al 0 16 wt and can be related to fluctuations in the ph of the mineralising fluids

a revised classification scheme of pyrite in the witwatersrand basin and application to placer gold deposits abstract pyrite is the most abundant ore mineral in gold bearing quartz pebble conglomerates qpcs of the witwatersrand basin and similar archaean sedimentary units much of the pyrite in archaean conglomerates is detrital in origin implying that it survived weathering transport and reworking under anoxic conditions detrital pyrite is generally found together with authigenic pyrite formed in situ as a result of syn to post depositional processes as pyrite is frequently associated with gold mineralization many authors have developed different pyrite classification schemes in order to better understand the nature and origin of the mineralization although the different classifications cannot always be easily compared as they are largely based on inferred pyrite genesis we propose a revised entirely descriptive classification scheme for detrital and authigenic pyrite in archaean qpcs the scheme was created in order to provide a consistent framework for the petrographic description of pyrite in clastic sedimentary rocks detrital pyrite is subdivided into massive inclusion bearing and coarsely crystalline types authigenic pyrite includes euhedral overgrowth infill aggregate and pseudomorphic types we evaluate the methods used in pyrite classification propose formation pathways for detrital and authigenic pyrites and apply the classification scheme to some well known occurrences of detrital pyrite bearing conglomerates

surface wave methods for anomaly detection abstractperimeter defense operations geohazard assessment and engineering characterization require the detection and localization of subsurface anomalies seismic waves incident upon these discontinuities generate a scattered wavefield we have developed various surface wave techniques currently being fielded that have consistently delivered accurate and precise results across a wide range of survey parameters and geographical locations we use the multichannel analysis of surface waves approach to study the multimode rayleigh wave the backscatter analysis of surface waves basw method to detect anomalies 3d visualization for efficient seismic interpretation basw correlation for attribute analysis and instantaneous amplitude integration in the complex basw method discrete linear moveout functions and f k filter designs are optimized for basw considering the fundamental and higher mode dispersion trends of the rayleigh wave synthetic and field data were used to demonstrate multimode basw and mod