morphological change and sediment dynamics of the beach step on a macrotidal gravel beach abstract the morpho sedimentary evolution of a pure gravel beach step over a tidal cycle is examined during fairweather conditions using detailed measurements of nearshore hydrodynamics morphological and sedimentary change and nearshore sediment transport the characteristics of the beach step are analysed with specific reference to the concurrent dynamics of the beachface a departure from previous studies which have treated the step as a feature isolated from the nearshore region as a whole the step and berm are both accretionary features strongly linked to tidal stage yet their temporal evolution is independent the relaxation time of the berm being linked to the spring neap tidal cycle and that of the more transient step linked to the semi diurnal tide over this time scale the beachface is a closed sedimentary unit although the beach step may be differentiated from the beachface using sedimentary moments indeed despite the location of the step in the region of wave breaking it has relatively stable sedimentology remaining characteristically coarser and more leptokurtic than the swash zone co spectral analysis between nearshore bed motion and cross shore current velocity reveals that significant nearshore sediment transport occurs at sub incident frequencies in response to wave groups motion of the nearshore bed is not a linear function of velocity magnitude or direction so it is likely that there is a role for the various mechanical properties of the bed therefore a better description of nearshore sediment transport in the region of the beach step would require instantaneous sediment size information allowing the use of a time variant friction factor

petrography and genesis of spicular and columnar geyserite from the whakarewarewa and orakeikorako geothermal areas north island new zealand domal masses of geyserite which surround many geyser vents in the whakarewarewa geothermal area are formed largely of spicules spicule columns and shrub columns the non branching spicules and the branches of branching spicules individually up to 3 cm high and 1 mm diameter have a laminated core encased by siliceous cortex silicified microbes are rare in the core but common in the cortex silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules shrub columns up to 5 cm high and 1 5 cm in diameter are formed of opal a that was precipitated around a three dimensional branching shrub like microbial structure the shrub branches which are hollow with scalloped walls do not contain any evidence of the original microbes or minerals that formed them silicified microbial mats are present between the columns microbial boring and etching by acidic steam led to local diagenetic degradation of these columns in the geyserite mounds at whakarewarewa spicules and spicule columns are common whereas shrub columns are rare interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate however that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents petrographic evidence shows that the spicules spicule columns and shrub columns grew through a combination of biotic and abiotic processes

a markov model for beach changes on the holderness coast of england markov models offer an objective and quantitative method of assessing beach changes for a stretch of the holderness coast a beach classification scheme was devised and a probabilistic first order matrix model based on surveyed profile data was produced this could describe and predict transitions between beach types and between different time periods different profile types dominated different coastal locations and seasonal variations were seen in order to improve the accuracy of prediction throughout the year a second winter model was added to the original summer one although the models had been prepared independently of wave conditions a comparison of the wave record and beach transitions revealed that waves under 0 3 0 5 m high produced fairly static beaches when waves were between 0 5 and 1 0 m the beach was more dynamic and variable while waves over 1 0 m led to the depletion of the upper beach this was broadly in accordance with published theory markov models have the advantage that they can be adjusted periodically if conditions change and are thus useful for prediction on coasts for which no wave records exist

chronology and dynamics of a large silicic magmatic system central taupo volcanic zone new zealand the central taupo volcanic zone in new zealand is a region of intense quaternary silicic volcanism accompanying rapid extension of continental crust at least 34 caldera forming ignimbrite eruptions have produced a complex sequence of relatively short lived nested and or overlapping volcanic centers over 1 6 m y silicic volcanism at taupo is similar to the yellowstone system in size longevity thermal flux and magma output rate however taupo contrasts with yellowstone in the exceptionally high frequency but small size of caldera forming eruptions this contrast reflects the thin rifted nature of the crust which precludes the development of long term magmatic cycles at taupo 11 refs 4 figs 1 tab

evaluation of possible gas microseepage mechanisms petroleum microseepage anomalies over petroleum accumulations are commonly explained by rapid vertical migration of colloidal gas bubbles through fracture networks this article is a theoretical anal ysis of this mechanism and of continuous gas phase flow in frac tures the gas bubble ascent mechanism is much slower than re ported microseepage velocities so it cannot account for observed microseepage in contrast continuous gas phase flow through frac tures can equal or exceed reported microseepage velocity while maintaining total flux low enough so that petroleum accumulations can exist for geological lengths of time fracture entry pressure for bubbles is more than twice that of a continuous gas phase so con tinuous gas phase migration also requires a lower pressure threshold before initiating seepage vertical microseepage is therefore best explained by the same mechanism interpreted for macroseepage although this article provides a theoretically justified mecha nism for microseepage it also shows why interpretation of surface microseepage signals is problematic fracture geometry controls seepage velocity and flux so geochemical anomalies may indicate an increase in fracture aperture as well as possible subsurface ac cumulations larger fractures require very low gas capillary entry pressures so in some settings surface seepage could result from fractures over stratal migration pathways as well as over petroleum accumulations

australian offshore natural hydrocarbon seepage studies a review and re evaluation abstract surprisingly few natural hydrocarbon seeps have been identified in australia s offshore basins despite studies spanning thirty years early studies of natural hydrocarbon seepage around the australian margin were generally based on the geochemical analysis of stranded bitumens water column geochemical sniffer sampling synthetic aperture radar or airborne laser fluorosensor later studies involved the integration of these remote sensing and geochemical techniques with multi channel and shallow seismic a review of these earlier studies indicates that many seepage interpretations need to be re evaluated and that previous data sets when placed in a global context often represent normal background hydrocarbon levels low recent burial and subsidence rates are not favourable for high rates of seepage there are also difficulties in proving seepage on high energy shallow carbonate shelves where seabed features may be rapidly re worked and modern marine signatures are overprinted on authigenic seep carbonates thus the relatively few sites of proven natural hydrocarbon seepage in australia s offshore sedimentary basins can be reconciled relative to their geological occurrences and the dominantly passive margin setting active thermogenic methane seepage on the yampi shelf the only proven documented occurrence in australia is driven by deposition of a thick late tertiary carbonate succession and late miocene tectonic reactivation therefore to increase the success of detecting and correctly interpreting natural hydrocarbon seepage data need to be analysed and integrated within the context of the local geological setting and with an understanding of what is observed globally

geophysical and geochemical evidence for subsurface hydrocarbon leakage in the bering sea alaska abstract geophysical and geochemical surveys were conducted on the bering sea shelf to investigate whether hydrocarbons found in the surficial sediment particularly in association with certain geophysical events indicate the presence and nature of more deeply reservoired oil and gas deposits surface sediment samples were obtained at 1000 sites where high resolution seismic data indicated the presence of gas seepage and or surface faulting in addition sites for background measurements were occupied away from areas of gas seepage results of the geophysical survey show seismic wipeout zones to be present throughout the bering sea shelf sediment samples obtained within the shallow wipeout zones confirm that these features are caused by gas in addition compositional and isotopic analyses indicate that the gas is of biogenic and thermogenic origins the thermogenic leakage appears to be related to localized faulting and shallow structuring the high resolution seismic data therefore provide an excellent tool for locating leakage points thereby enhancing the opportunity of finding migrated thermogenic hydrocarbons in surficial sediments an examination of vertical variability shows the hydrocarbon concentrations to be strongly related to various processes occurring in the surficial sediments core samples must be taken from below the zone of maximum disturbance to obtain unaltered hydrocarbon samples

characterisation and correlation of active hydrocarbon seepage using geophysical data sets an example from the tropical carbonate yampi shelf northwest australia abstract for the first time in australia active present day hydrocarbon seepage has been imaged on the tropical carbonate yampi shelf in 50 and 90 m water depth seepage is evidenced by gas plumes in the water column that are associated with seabed features such as clusters of reflective blocks hard grounds pockmark fields and mounds seepage activity and intensity seems to vary with changes in pressure related to macro tidal cycles the seabed features coincide with sub surface features such as areas of seismic signal attenuation under high amplitude reflectors seismic discontinuities and bright spots hydrocarbon migration seepage pathways appear to be controlled by the reactivation of pre existing fractures and dykes within the basement the types of seabed features and their preservation on a tropical carbonate shelf are strongly influenced by the coarse bioclastic nature of sediments and the high energy of macro tidal currents and storm reworking

shoreline recovery on wave dominated sandy coastlines the role of sandbar morphodynamics and nearshore wave parameters abstract this study quantifies and characterises the temporal variability of shoreline recovery on a high energy sandy coastline using a 10 year dataset of daily shoreline and sandbar positions from a coastal imaging station at narrabeen collaroy beach australia following a total of 82 individual storm events rates of the cross shore return of the shoreline to its pre storm position were analysed observed rates during shoreline recovery were characterised by an overall mean of 0 2 m day temporal variability in rates was most evident at shorter timescales of 1 2 weeks and included rates most frequently between 0 and 0 3 m day less frequent more rapid rates of up to 2 m day and also minor landward movements this temporal variability was significantly correlated with nearshore forcing parameters describing the ratio of wave height to wave period the cross shore proximity and attachment of the sandbar to the shoreline and the rate of cross shore sandbar migration these findings are summarised in a new conceptual model that characterises temporal phases and rates of shoreline recovery corresponding to stages of onshore sandbar migration following a storm from fully detached storm deposited sandbar morphology through to complete sandbar welding with the shoreline more gradual shoreline recovery rates are observed with fully detached and semi attached sandbar conditions in contrast more rapid rates of shoreline recovery occur when sandbars are closer and attached to the shoreline observed to be on average 3 4 times greater than for detached sandbars in conditions with attached and semi attached sandbars shoreline recovery rates are negatively correlated to the forcing of nearshore wave steepness and dimensionless fall velocity and coupled with concurrent rates of onshore sandbar migration the findings provide insight into key parameters influencing shoreline recovery following storms

acceleration of sinter diagenesis in an active fumarole taupo volcanic zone new zealand siliceous sinters form where nearly neutral ph alkali chloride waters discharge at the surface 100 c they may preserve biogenic and abiogenic material and therefore archive paleoenvironmental settings freshly precipitated sinters undergo diagenesis through a five step series of silica mineral phase changes from opal a to opal a ct to opal ct to opal c to quartz transformation rates vary among sinters because postde positional conditions can accelerate or retard diagenesis meanwhile preserving or destroy ing biosignals we monitored alteration and diagenesis of newly precipitated filamentous microbe rich sinter during a two year field experiment where sinter was suspended inside a fumarole at orakei korako taupo volcanic zone new zealand patchy and complex diagenesis resulted from changes in environmental conditions including variations in tem perature ph and the intermittent deposition of sulfur throughout the experiment opal a was dissolved by acidic steam condensate and reprecipitated locally quartz crystals grew on the sinter surface within 21 weeks previous reports of transformation rates from opal to quartz are on the order of thousands of years in duration thus our results show that fumarolic overprinting accelerates diagenesis microbial preservation was not favor able because primary filamentous fabrics were obscured by deposition of opal a micro spheres smooth silica infill and sulfur if ancient hydrothermal systems were among the likely places where early life flourished it is necessary to distinguish between depositional features and those inherited during diagenesis this near real time experiment enabled observations on environmental controls of diagenetic change in silica minerals and illus trated the variability of conditions that can occur in nature during this complex process

recognizing and compensating for interference from the sediment s background organic matter and biodegradation during interpretation of biomarker data from seafloor hydrocarbon seeps an example from the marco polo area seeps gulf of mexico usa abstract a suite of seep samples from the vicinity of the marco polo field in the green canyon area of the gulf of mexico provides an exceptional opportunity to study the impact of interference from sediment background organic matter and alteration by biodegradation on thermogenic hydrocarbons from seafloor seeps these seep samples contain a range in both the concentration of seeped hydrocarbons present and level of biodegradation experienced in addition the subsurface oil that sources the seepage was available for comparison the results of the study show that it is essential to have the biomarker data from the sediment s background organic matter when dealing with low concentration seepage these data provide a means to characterize the contribution of background organic matter to the biomarker distributions this in turn allows the identification of thermogenic hydrocarbons when the concentration of seeped oil in seafloor sediments is low in high concentration seepage the hopanes and regular steranes were found to be more susceptible to near surface microbial alteration while tricylic tetracyclic terpanes diasteranes monoaromatic steroids and triaromatic steroids were more resistant if biodegradation is severe enough all biomarker compounds are vulnerable to alteration and very little information is preserved in an effort to reconstruct the altered distributions low temperature pyrolysis of the seeped oils asphaltenes was done to liberate occluded biomarkers compounds although biomarkers were recovered they did not resemble the parent oil characteristics of some of the recovered biomarker distributions suggest alteration by biodegradation this implies the three dimensional structure of the asphaltenes may not offer complete protection from microbial attack these results demonstrate why interpretation of biomarker data from seafloor seeps can be a difficult task care must be taken to recognize contributions from the sediment s background organic matter as well as identify alteration by biodegradation failure to understand these processes can lead to erroneous interpretations being made about the seep s parent oil and source rock

hydrocarbon seeps in petroliferous basins in china a first inventory abstract natural hydrocarbon seepage is a widespread phenomenon in sedimentary basins with important implications in petroleum exploration and emission of greenhouse gases to the atmosphere china has vast petroleum oil and gas bearing sedimentary basins but hydrocarbon seepage has rarely been the object of systematic studies and measurements based on the available chinese literature we report a first inventory of 932 hydrocarbon seeps or seepage zones 710 onshore seeps and 222 offshore seeps including 81 mud volcanoes 449 oil seeps 215 gas seeps and 187 solid seeps bitumen outcrops the seeps are located within the main 20 mesozoic cenozoic petroliferous sedimentary basins especially along the marginal regional and local faults the type of manifestations oil gas or mud volcano reflects the type and maturity of the subsurface petroleum system and the sedimentary conditions of the basin oil seeps are particularly abundant in the junggar basin gas seeps mostly developed in the lunpola basin in smaller basins of the eastern guizhou and yunnan provinces onshore taiwan and in the offshore yinggehai basin mud volcanoes developed in basins junggar qaidam qiangtang onshore and offshore taiwan that experienced rapid sedimentation which induced gravitative instability of shales and diapirism in comparison to available global onshore seep data bases china results to be the country with the highest number of seeps in the world the massive gas seepage in china could represent a considerable natural source of methane to the atmosphere and a key process that may drive future hydrocarbon exploration

life cycle of a geyser discharge apron evidence from waikite geyser whakarewarewa geothermal area north island new zealand abstract waikite a geyser located in the whakarewarewa geothermal area on the north island new zealand has a history of eruptive dormancy cycles that have been attributed to natural and anthropogenic causes the last cycle involved an active period from 1932 to 1968 69 that was followed by a period of dormancy that continues today such cycles are important because they control the temporal development of the discharge apron when the geyser is active growth of the discharge apron is dictated by the precipitation of opal a which is controlled by factors such as discharge patterns water chemistry ph temperature rate of cooling and the resident microbiota with dormancy conditions change radically because water no longer flows down the discharge apron instead the discharge apron lapses into a phase of degradation that on waikite is evident from 1 deflation of the apron surface 2 blocks splaying off the apron margins along margin parallel fractures 3 tension fractures 4 saucer shaped collapse zones 5 increasingly unstable surfaces resulting from subsurface opal a dissolution 6 fractures from which steam and other gases emanate and 7 incursion of native vegetation around the edge of the apron and on the distal parts of the discharge apron when the geyser becomes active again silica precipitation will resume and the discharge apron will once again accrete vertically and expand laterally analysis of the waikite system shows that successions that develop on geyser discharge aprons are formed of unconformity bounded packages of sinter that reflect the eruptive dormancy history of the parent geyser

observed relation of soil magnetic susceptibility and soil gas hydrocarbon analyses to subsurface hydrocarbon accumulations magnetic susceptibility ms studies on soils over 19 oil and gas fields showed anomalously large amounts of diagenetic magnetic minerals in shallow depth samples in about 89 of the cases tested soil ms anomalies were compared with soil gas hydrocarbon ghc anomalies over 12 oil and gas fields including several stratigraphic traps and one gas storage reservoir samples were collected along the same profiles six examples are presented with detailed data listings our goal is to test the utility of soil magnetic susceptibility and soil gas hydrocarbons as petroleum prospecting methods we emphasize statistical evaluation of anomalies and their empirical correlation with producing areas and leads identified by other geochemical geological or geophysical data for direct comparison of anomaly strengths data are expressed statistically in terms of the appropriate background mean and standard deviation soil ms and soil ghc data complement each other providing better guidance to productive areas than either data set alone when used in an integrated exploration program their combined positive evidence of hydrocarbon presence under prospects could result in fewer dry holes than when drilling with structural information only

influence of thermophilic bacteria on calcite and silica precipitation in hot springs with water temperatures above 90 c evidence from kenya and new zealand hot and boiling springs in kenya and new zealand that are emitting water with temperatures more than 90 c are commonly characterized by a complex array of caco3 and sio2 precipitates that have been formed through abiogenic and biogenic processes thermophilic bacteria are the only microbes that can survive in the boiling water that is discharged into pools around the spring orifice analysis of modern substrates from various springs in the kenya rift valley and the taupo volcanic zone in new zealand shows that they are inhabited by a diverse array of coccoid and filamentous bacteria in some areas these bacteria produce copious amounts of mucus that coat the substrates although the coccoid and filamentous bacteria provide substrates for caco3 and sio2 precipitation the microbes do not seem to have any direct influence on the morphology of the precipitates that are produced conversely the mucus found in these hot spring pools selectively takes up elements such as si mg al and fe but is not calcifi

impact of seasonal changes on the formation and accumulation of soft siliceous sediments on the discharge apron of geysir iceland abstract unconsolidated highly porous permeable siliceous sediments found in shallow water pools on the middle and distal parts of geysir s discharge apron are formed of cryogenic opal a coa opal a spheres opal a cement silicified microbes and detrital lithic grains silicified leaves and silica coated grass stems and twigs are locally present with these pool sediments and microbial mats commonly cover the sediment surface partially consolidated layers 0 5 cm thick form when the constituent grains are bound together by filamentous microbes exopolysaccharides and or opal a cement most components of the sediment can be related to processes that are controlled largely by seasonal variations low temperatures in winter promote freezing of the medial to distal discharge waters and lead to formation of coa in ice when the ice melts the released coa grains become part of the pool sediments microbial mats trap and bind sediment and provide templates for silica precipitation during spring and summer but become semi dormant during the constant darkness that iceland experiences during winter when the waters are sufficiently supersaturated opal a precipitates as spheres in the water column and cement in pool deposits in some pools seasonal changes are evident from the alternation of soft and hard partly cemented laminae elsewhere however the distinction between the different time dependent components is lost because they become superimposed on each other or as aperiodic changes in flow patterns affect different pools

depositional evolution of an extinct sinter mound from source to outflow el tatio chile siliceous sinter deposits from el tatio chile preserve a wide variety of depositional environments and biosignatures from high temperature 85 c vent proximal facies to distal deposits dominated by silicified microbial mats four cores were drilled into an el tatio sinter mound and associated distal apron to investigate changes in hydrothermal environments over geologic timescales sedimentary and geochemical analysis of multiple sinter cores records the initiation and accretion of diverse depositional features still observed today in el tatio facies adjacent to hydrothermal vents are dominated by laminated sinter crusts on the steep margins of a high temperature pool with sparse microbial preservation outer margins of the same pool contain extensive sinter columns up to ten centimeters in length precipitated during repeated cycles of pool overflow and subsequent evaporation low relief hydrothermal pools also form minor deposits within distal debris aprons and analogous pools are still active close to sampling locations debris aprons are dominated by palisade tufted and arborescent microbial fabrics with distinct mat textures revealing well preserved microfossils surficial deposits in all cores feature detrital rich and microbially influenced sinters overlying higher temperature facies indicating a relative decrease in hydrothermal activity over time geochemical proxies for hydrothermal fluids and de trital input match depositional interpretations based on sedimentary structures 14 c ages from core deposits extend the mound s history by 11 000 years recording at least three thousand years of sinter deposition on top of glacial sandstones 13 337 10 232 y cal bp importantly this work provides a detailed depositional model unavailable through surficial sedimentology alone

the role of microorganisms in phytokarst development on dolostones and limestones grand cayman british west indies phytokarst is spectacularly developed on the hard finely crystalline dolostones of the oligocene miocene bluff formation and to a lesser extent on the soft limestones of the pleistocene ironshore formation on grand cayman the black weathered surfaces which are a reflection of an organic coating contrast sharply with the white colour of the unaltered host rocks which lack an organic coating on the dolostones this organic coating is formed principally of fungal sporangia and spores associated with mucilage along with lesser numbers of algae and bacteria endolithic and epilithic filamentous microorganisms are rare on the limestones the organic coating is formed principally of endolithic and epilithic filaments and mucilage fungal spores are rare and no sporangia were found the limestones of the ironshore formation are characterized by an intensely bored zone beneath the weathering surface in contrast the dolostones of the bluff formation have relatively few endoliths penetrating from the w

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

significance of hydrocarbon seepage relative to petroleum generation and entrapment near surface indications of migrating hydrocarbons provide the petroleum systems analyst critical information about source organic matter type maturation organic maturity migration migration pathway delineation and in selected geologic settings specific prospect hydrocarbon charge all petroliferous basins exhibit some type of near surface signal but the hydrocarbon leakage to surface is not always detectable with conventional seep detection methods understanding the petroleum seepage system hence petroleum dynamics of a basin is key to understanding and using near surface geochemical methods for basin assessment and prospect evaluation the relationships between near surface hydrocarbon seepage and subsurface petroleum generation and entrapment are often complex the petroleum seepage system contain four key elements seepage activity qualitative expressions of relative leakage rates active vs passive and episodic vs continuous seepage type concentration of migrated thermogenic hydrocarbon relative to in situ material macro vs micro migration focus major direction of bulk flow leakage relative to the subsurface hydrocarbon generation and or entrapment and near surface seep disturbances near surface processes which can greatly alter or block seepage signals the rate and volume of hydrocarbon seepage to the surface greatly control near surface geological and biological responses and thus are the best method of sampling and analysis to detect hydrocarbon leakage effectively to properly predict subsurface petroleum properties interpretation of near surface geochemical data must recognize many potential problems including recent organic matter input transported hydrocarbons bacterial alteration mixing contamination and fractionation effects surface geochemical data should always be integrated with other geological data calibration datasets to determine the utility of near surface geochemical techniques within particular basinal settings are essential when evaluating prospects for hydrocarbon charge

temporal and spatial scales of beach profile change duck north carolina abstract an 11 year time series of high resolution beach profile surveys made on an atlantic ocean beach was analyzed for spatial and temporal characteristics of beach profile change approximately 300 profile surveys most extending from the dune to 8 m depth were available for the analysis on each of four cross shore lines together with electronically recorded and statistically processed wave time series from a nearshore gage located seaward of the survey site the profile survey data set was analyzed for such quantities as depth change frequency of depth change general seasonal shape of the profile seasonal depth change and change in the profile produced by extreme storms the morphodynamics of an inner and outer longshore bar were also examined including depth to bar crest bar height and length and speed of bar movement onshore and offshore several properties of depth change were related to wave characteristics representative results were average profile elevation change from 4 m to 4 m was symmetric about the mean sea level shoreline the average spring and autumn profile shapes were almost identical and occurred as transitional states between the summer and winter profile shapes the depth of active profile movement within survey accuracy of about 0 025 m was 4 m for the summer and 6 m for the winter and the 10 year frequencies of maximum absolute depth change in depths of 2 4 6 and 8 m were 1 64 1 38 0 22 and 0 12 m respectively a surprising result was that typical large storms transported sand into the nearshore from the seaward end of the profile from a depth of about 6 8 m

surface and subsurface signatures of gas seepage in the st lawrence estuary canada significance to hydrocarbon exploration abstract the seabed of the st lawrence estuary is characterized by many fluid releasing features on multibeam bathymetric images these features correspond to crater like depression pockmarks predominantly found on the northwestern shoulder of the 300 m deep laurentian channel as well as on the channel floor aligned pockmarks which define segments up to 12 km long are frequent in the laurentian channel whereas they are preferentially associated with submarine landslides on the northwestern shoulder of the channel on high resolution seismic profiles pockmarks found in the laurentian channel are characterized by seismic chimneys that may be traced down to the autochthonous paleozoic rocks st lawrence platform suggesting a thermogenic origin for the gas on the northwest shoulder of the laurentian channel the seismic signature of pockmarks does not extend downward to the reflector that corresponds to bedrock st lawrence platform and or grenvillian province suggesting together with high sedimentation rate a biogenic origin for the gas these results are discussed in the light of the data collected in the onshore parts of the st lawrence platform and suggest the presence of a mature hydrocarbon source the conclusions are supportive arguments for the hydrocarbon prospectivity of both the onshore and offshore segments of the paleozoic autochthonous domain st lawrence platform

upper jurassic travertine at el macanudo argentine patagonia a fossil geothermal field modified by hydrothermal silicification and acid overprinting the deseado massif hosts numerous late jurassic 150 ma fossil geothermal systems related to an extensive volcanic event developed in a diffuse extensional back arc setting detailed mapping petrography and mineralogical observations of el macanudo outcrops verify that it represents a hot spring related travertine partially replaced by silica and delineated by six sedimentary facies these are large concentric cones f1 laminated vertical columnar structures f2 porous layers f3 shrubby and irregular lamination f4 low amplitude wavy bedding f5 and mounds and breccias f6 the macanudo norte outcrop rocks constitute a silica replaced travertine sequence with development of large conical stromatolites in a deep pool or geothermally influenced shallow lacustrine environment surrounded by a subaerial travertine apron terrace whereas the macanudo sur outcrop is a subaerial travertine mound sequence structurally controlled vent areas occur in both northern f1 and southern f6 outcrops mainly located along regional nne and ene trending faults the other sedimentary units display a concentric distribution of travertine facies with respect to the interpreted vent areas the el macanudo palaeo hot spring deposit is situated in an eroded jurassic volcanic centre and records a complex evolutionary fluid history the sediments archived three different jurassic events when large and long lasting hydrothermal systems were active across the region this relative temporal sequence was formed by 1 travertine precipitation 2 development of a silica cap where early silicification was responsible for exceptional preservation of some stromatolitic fabrics and 3 acid alteration recorded by dissolution textures and clay formation and caused by a palaeo phreatic water level drop

seasonal changes in beach topography and beach volume in delaware abstract a beach study was conducted along a shore segment of the delaware coast from march 1982 through to april 1983 results indicate that beach topography and beach volume varied with changes in wave climatic regimes the regimes in turn were generally in phase with the winter and summer seasons because both the magnitude and frequency of storm waves were higher during winter than in summer the winter beach shape was concave upward following the winter storms of 1981 1982 swells rebuilt the beach in two stages from march through to august 1982 in the first stage the beach vertically accreted aggraded and in the second it laterally accreted prograded the aggrading stage involved the welding of a swash bar to the foreshore thereafter swash overtopping caused deposition on and landward of the bar in time the swash bar attained a berm and swale topography the prograding stage started when the swash could no longer overtop the berm crest which confined deposition to the foreshore this stage occurred following a minor or moderate storm event that shifted the berm crest upward and landward or during a neap tidal stage that occurred after the construction of a spring tide berm between march and the end of august 1982 60 m 3 of sediments per 1 m of beach were deposited on the shore of this value 67 was attributed to aggradational processes while the remaining 33 was attributed to progradational processes swells as well as storm waves caused vertical accretion storm waves contributed 20 of the total sediment volume deposited on the beach when the shore was at its maximum sediment volume for 1982 the beach topography was convex upward an inverse relationship existed between the mean monthly sediment volume and the mean monthly surge variability the surge level was used as an index of wave conditions high surge levels were associated with large waves while low surge levels were associated with small waves when surge variability was high during the winter sediment volume on the beach was low and conversely when surge variability was low in summer sediment volume was high correlation analysis showed that 80 of the variance of the mean monthly sediment volume was explained by the mean monthly surge variability

data processing and recognition of seepage and microseepage anomalies of acid extractable hydrocarbons in the south slope of the dongying depression eastern china abstract the successful use of near surface anomalous signals exhibited in all petroliferous basins must lead to great development in petroleum exploration the elementary equations and methods for objective and accurate separation of anomalous signals from background signals are the most critical requirements in these surface geochemical surveys therefore we have worked up a series of fundamental equations and methods for eliminating surface interference and influences of geological conditions on anomaly intensities and recognizing multi type anomalies of uni and multi variates by using statistics fractal geometry wavelet analysis and artificial neural networks these equations illustrate that the threshold i e the boundary between background and micro seepage anomalies is determined by means standard deviations and prior probabilities of background and micro seepage anomalies when multi normality is met and that the traditional equation for the threshold background mean plus one or two standard deviations is not correct in the face of many new equations and methods it is important how to comprehensively use them to resolve the problems in geochemical surveys a geochemical survey in the south slope of the dongying depression eastern china provides a good opportunity to address this issue the anomalies obtained with the traditional equation do not reflect oil gas fields this study reveals three problems in the previous data processing and anomaly recognition 1 the surface interference caused by the variation of soil composition was not identified and removed 2 the influence of caprock thickness on anomaly intensities was not revealed and eliminated and 3 the micro seepage related to oil gas pools and seepage related to faults anomalies were not separated and correctly recognized furthermore the interaction of these problems makes the data processing and anomaly recognition more difficult to ensure effective elimination of the surface interference and caprock thickness influence and correct recognition of uni variate anomalies we iteratively applied the wavelet analysis based methods to eliminate the surface interference and caprock thickness influence and statistical methods with new fundamental equations to recognize uni variate anomalies of seepage and microseepage and then multi variate anomalies of seepage and microseepage were recognized with our fundamental equations and the corresponding methods in the results the seepage anomalies display a string bead shaped pattern and are distributed along faults and the micro seepage anomalies are ring shaped and coincide with oil gas pools sandbodies or traps therefore reprocessing of geochemical data with our fundamental equations and methods combined in an iterative manner can resolve the complicated problems in data processing and anomaly recognition and thus greatly improve the predictive capability of surface geochemical survey

surface sediment gases as indicators of subsurface hydrocarbons examining the record in laboratory and field studies abstract near surface sediment gases are commonly examined in surface geochemistry surveys to evaluate subsurface hydrocarbon generation and entrapment sediment gases reside in interstitial spaces bound to mineral or organic surfaces and or entrapped in carbonate inclusions characterizing migrated sediment gases with minimal compositional and isotopic fractionation is challenging and different methods are currently in use to extract and analyze surface sediment gases these methods have not been compared in controlled laboratory experiments the key to calibration experiments is to know the charge gas composition and thus have a basis to evaluate the sediment gas extraction procedure for this laboratory study marine sediments were homogenized and cleansed of in situ light hydrocarbons and bacteria replicate sediment samples were prepared and charged with two different hydrocarbon gas compositions and two concentration levels along with the requisite blank control samples the sediment gases were characterized by four laboratories using a variety of gas extraction procedures three headspace interstitial two adsorbed acid extraction and one ball mill occluded the results have been compared to the charge gases and each method evaluated the laboratory calibration experiments demonstrated that selected interstitial gas extraction methods examined do provide sediment gas compositions and compound specific isotopes similar to the charge gases however some of the results indicate that systematic sampling and or laboratory procedures associated with the adsorbed and ball mill gas extraction methods have altered the original charge gas compositions thus it is our recommendation to use a headspace interstitial gas extraction method in conjunction with a tight sealing storage container and water preparation procedure to best extract and analyze migrated sediment gases

the geological history of geysir iceland a tephrochronological approach to the dating of sinter the vertical succession through the discharge apron of geysir up to 3 5 m thick is formed of five lithological units a e units a b c and e are formed of siliceous sinters whereas unit d is a brown ash bed tephra grains in units c d and e came from katla hekla and vei ivotn katla tephra in unit d has been largely altered to palagonite integration of tephrochronological ages historical records and geological and geomorphological relationships shows that the geysir succession developed in four main phases during phase i c 10 000 4000 years ago laminated sinters formed from hot spring waters phase ii initiated c 3300 years ago saw the termination of sinter formation and blanketing of the area with tephra from katla and hekla phase iii c 3000 900 years ago represented by the boundary between units d and e was characterized by weathering and little sinter deposition phase iv was initiated with the re birth of geysir 800 900 years ago sinter deposited from the discharged waters has however been largely confined to the southern part of the discharge apron only limited opal a precipitation has occurred since 1916 because of a decline in geysir9s eruptions

beachrock occurrence characteristics formation mechanisms and impacts beachrocks are hard coastal sedimentary formations consisting of various beach sediments lithified through the precipitation of carbonate cements the objectives of this contribution are to a collate and review information on the reported occurrences characteristics and formation mechanisms of beachrocks and b consider their impacts on the coastal zone the analysis of the available information has shown that a beachrock formation is a global and diachronic phenomenon and b the great majority of beachrocks are found in tropical subtropical and low temperate latitude microtidal coasts the cementing agents of beachrocks are composed predominantly of the metastable carbonate phases high magnesian calcite hmc and aragonite ar appearing in a diverse crystalline morphology it has been suggested that cement precipitation in the coastal environment is controlled by i the physicochemical conditions ii the presence of organic compounds and microbes iii the magnitude and distribution of the wave energy along the coast and iv the textural characteristics of the constituent sediments various theories have been proposed to explain beachrock formation itself linking the phenomenon to either physicochemical or biological processes these theories however do not seem to be of universal validity and acceptance as each is able to explain only some of the reported occurrences the presence of beachrocks appears to affect beach morphodynamics by i locking the beach profile ii modifying the nearshore hydrodynamics iii changing the porous character of the beach and thus its response to wave forcing and iv differential bed erosion at the margins of the beachrock outcrops that can alter significantly the long and particularly the cross shore sediment transport therefore although relict submerged beachrock outcrops may provide some coastal protection by reducing the wave energy impinging onto the coastline modern beachrocks may promote offshore loss of unconsolidated beach sediments and buried beachrock outcropping finally the presence of beachrocks may have also significant ecological impacts as the indigenous mobile substrate fauna and flora of the beach is replaced by hard substrate benthic assemblages which are commonly arranged in hydrodynamically controlled zones

oil source correlation in the slope of the qikou depression in the bohai bay basin with discriminant analysis abstract the commonly used tools for oil source correlation such as mass chromatograms of biomarkers and bivariate cross plots of geochemical parameters cannot deal with multiple geochemical parameters and plenty of samples simultaneously leading to uncertainties in the results and even failures sometimes in this paper the discriminant analysis da is selected from supervised machine learning algorithms as it is superior to the commonly used tools as well as other multivariate statistical methods with the accumulation of geochemical data of source rocks and oils in the slope of the qikou depression the main source rocks in the third es3 and first members es1 of the paleogene shahejie formation were deposited in similar depositional environments the source rocks cannot be distinguished with the commonly used tools we firstly extended geochemical parameters and then used stepwise da to select informative parameters and to develop a discriminant model for oil source correlation the 22 selected parameters are supported by geochemical characteristics of the source rocks in the study area the da of these parameters for oil source correlation achieved a high correct rate of original validation 96 8 and leave one out cross validation 89 4 indicating a sufficient discriminatory power the oil source correlation results with high posterior probabilities showing strong similarity between the sources and oils coincide with geological conditions and illustrate that there is still much exploration potential in the study area especially for the es3 petroleum system all these illustrate that da is one of the most useful tools for oil source correlation with the accumulation of geochemical data of source rocks and oils

laminae development in opal a precipitates associated with seasonal growth of the form genus calothrix cyanobacteria rehai geothermal area tengchong yunnan province china abstract the western discharge apron at meinuquan rehai geothermal area yunnan province china which incorporates the upper terrace terrace front and lower terrace is covered with laminated opal a precipitates that have formed from the spring waters that flow across its surface laminae are formed of silicified calothrix mats or featureless opal a that contains no microbes scattered spherical and rod shaped microbes and or rare calothrix rapid silicification of the calothrix led to preservation of their basal heterocysts vegetative cells trichomes tapering filaments and laminated and splayed sheaths the calothrix mats grew during the dry season when there was maximum sunlight because of low cloud cover during this time the mats grew under stable conditions because the water that flowed across the discharge apron was sourced from the springs and temperature and water geochemistry was more or less constant growth of the calothrix mats decreased during the wet season april to late september when sunlight is reduced due to the extensive cloud cover associated with the monsoonal rains during the wet season water flowing over the discharge apron is a mixture of rainwater runoff from the surrounding hillsides and spring water such variable flow conditions water temperatures and water geochemistry curtailed microbe growth and impacted silica precipitation the precipitates at meinuquan are like those associated with some icelandic hot springs although growth of calothrix is controlled by sunlight in both settings the periods of maximum sunlight in china october march and iceland june august are at different times of the year because of their geographic locations

the hot spring and geyser sinters of el tatio northern chile abstract the siliceous sinter deposits of el tatio geothermal field in northern chile have been examined petrographically and mineralogically these sinters consist of amorphous silica opal a deposited around hot springs and geysers from nearly neutral silica saturated sodium chloride waters water cooling and evaporation to dryness are the main processes that control the opal a deposition in both subaqueous and subaerial settings in close spatial relation to microbial communities all fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse cyanobacteria green bacteria and diatoms the most important ecological parameter is the temperature gradient which is closely related to the observed depositional settings 1 geyser setting water temperature 70 86 c boiling point at el tatio 4200 m a s l coarse laminated sinter macrostructure with rapid local variations biota comprises non photosynthetic hyperthermophilic bacteria 2 splash areas around geysers water temperature 60 75 c laminated spicule and column macrostructure locally forming cupolas

source transport inversion an application of geophysical inverse theory to sediment transport in monterey bay california application of forward coastal sediment transport models in situations involving large temporal and spatial scales or topographically complex environments can be highly problematic since the distribution of hydrodynamic parameters is rarely adequately known where rocky topography is present flow patterns may be altered and sediments trapped by topographic barriers a frequently employed approach to these problems is the application of the statistical technique known as empirical orthogonal function eof analysis one limitation of eof analysis of grain size and mineralogical data is that eof is a purely geometric technique which does not allow incorporation of a priori knowledge we may have regarding the physical environment in fact there is no guarantee that a meaningful physical interpretation of the results of an eof analysis actually exists this is not true of geophysical inverse theory which is capable of incorporating diverse forms of information and is not limited to purely geometric manipulations of data we have formulated an inverse theoretical approach to study sediment transport which we call sti short for source transport inversion sti relaxes the nonphysical assumption of orthogonal endmembers and can handle many forms of a priori information sti has been developed initially in the context of modeling the sediment supply and dispersal system of monterey bay california using the geographical distribution of heavy mineralogy data significant sources are identified and sediments traced from those sources along transport pathways model results are encouraging both in terms of goodness of fit between model and data and in terms of the agreement of model results with the sediment sourcing and dispersal patterns inferred in previous studies model results indicate that beach sediments are primarily derived from the open coast north of the bay that a littoral cell boundary exists in the center of the bay at moss landing and that beach deposits produced by paleolittoral drift during a sea level low stand lie along the 100 m isobath

restudy of acid extractable hydrocarbon data from surface geochemical survey in the yimeng uplift of the ordos basin china improvement of geochemical prospecting for hydrocarbons abstract two geochemical surveys were conducted in 1992 and 2000 respectively in the yimeng uplift of the ordos basin china the earlier survey grid had 1 5 km spacing and the later survey grid had 0 5 0 5 km spacing the acid extractable hydrocarbons of both surveys show similar geochemical trends however the anomalies obtained with traditional statistical methods do not correlate with existing oil gas fields this study reveals two problems in the data and their processing the first one is interference caused by the variation of soil composition we applied a wavelet analysis based method to eliminate this interference in the data of the later survey the second is that micro seepage anomalies did not identify existing oil gas fields and seepage anomalies related with faults had not been previously recognized we modified the logic multiplication cluster analysis and applied a multi fractal model and a back propagation artificial neural network to recognize these two types of anomalies that cannot be recognized with typical statistics in the study area the recognized seepage anomalies display a string bead shaped pattern and some are distributed along a large fault in this area the fault is the main pathway for hydrocarbon migration the micro seepage anomalies are ring shaped and are mostly distributed close to the fault they coincide with oil gas field and structure traps therefore reprocessing of existing geochemical data using these new methods can greatly improve their usefulness in hydrocarbon exploration

the spatial and temporal variability of sand bar morphology the spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years the data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology lippmann and holman 1989 the morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria the most frequently observed morphologies are the longshore periodic rhythmic bars observed in 68 of the data linear bars occur under highest wave conditions h s 1 78 m and are unstable mean residence time 2 days shore attached rhythmic bars are the most stable mean residence time 11 days and generally form 5 16 days following peak wave events non rhythmic three dimensional bars are very transient mean residence time 3 days eighty seven percent of transitions to lower bar types defined in text occurred one state at a time supporting our selection of the ordering of states and suggesting the suitability of a sequential morphology model transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states with more substantial changes in morphology resulting from larger wave increases this suggests that up state erosional transitions based on offshore bar migration are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance principal component analysis was used to decompose bar position into two dimensional linear and three dimensional longshore variable components cross shore linear bar position ranges 50 m about the 2 year mean 27 m standard deviation and dominates bar variability 74 6 three dimensional bar structure accounts for 14 of the variance 12 m standard deviation changes in incident wave height precede cross shore bar migration by less than 1 day changes in longshore variability are inversely correlated to changing wave conditions with bar morphology becoming linear rapidly during storms on time scales of less than 1 day evolution to significantly three dimensional structure typically occurs over 5 7 days following peak wave events

control of hydrocarbon seepage intensity on level of biodegradation in sea bottom sediments offshore surface geochemical surveys which target the surface expression of potential migration pathways for sampling such as fault scarps or diapiric features have become a commonly applied approach in the petroleum industry results of such surveys help to reduce risk on key exploration play elements and are used to evaluate prospects and to predict hydrocarbon phase and expected properties based on geochemical surveys conducted by exxonmobil in many basins worldwide there is an interrelation of the seep intensity concentration and level of biodegradation results from offshore west africa where many active macroseeps show moderate to severe biodegradation and a frontier basin offshore united kingdom rockall trough where active microseeps show no evidence of biodegradation are compared the specific biochemical controls on the difference in biodegradation proneness are not known although it appears that a certain threshold of oil concentration is needed to sustain an active bacterial community or to exceed clay adsorption capacities that may protect microseeps from biodegradation it is notable that the 25 norhopane series often considered an indication of severe biodegradation in reservoir oils has not been recognized in even ultra severely biodegraded seeps this suggests that different biodegradation pathways may be followed in marine surface seeps versus those in subsurface hydrocarbon accumulations a likely scenario in light of the fact that physiologically diverse bacterial communities are prevalent under different physiochemical conditions

a new 14 c age for the oruanui wairakei eruption new zealand the oruanui eruption was the largest known outburst of taupo volcano new zealand and is among the larger quaternary eruptions documented the eruption deposits are variously known as the oruanui wairakei kawakawa tephra or aokautere ash formations and represent a bulk volume probably exceeding 500 km 3 four new 14 c age determinations on carbonized vegetation in the non welded oruanui ignimbrite are combined to give a conventional age of 22590 230 yr b p compared with the previously accepted figure of 20000 yr b p this new age resolves the anomaly of apparently older 14 c ages being obtained from a demonstrably younger new zealand deposit and strengthens correlation of this eruption with an antarctic ice core acid anomaly the trace of this eruption has great potential as a time plane marker in the antarctic just prior to the last glacial maximum the close similarity in ages between the oruanui and a comparable sized eruption ito aira tn in japan suggests that this period of activity may represent the best chance of resolving any linkages between large scale explosive silicic volcanism and climate changes

anatomy of siliceous hot springs examples from yellowstone national park wyoming usa abstract numerous siliceous hot spring systems in the norris and lower geyser basins of yellowstone national park wyoming provide insights into spring geometries depositional facies and lithofacies associated with modern hot springs analyses of active cistern spring octopus spring deerbone spring and spindle geyser and inactive pork chop geyser siliceous hot springs have facilitated the construction of a facies model for siliceous hot spring deposits at yellowstone yellowstone s siliceous springs tend to group into four broad morphological categories siliceous spires and cones domal mounds terraced mounds and ponds siliceous spires cones are subconical accumulations up to 5 7 m high and about 2 m in diameter and are common deposits in yellowstone lake domal mounds are characterized by siliceous precipitates with a broad lens or shield geometry 2 3 m in vertical relief discharge channels and an areal accumulation of approximately 150 m2 in contrast terraced mounds have a stair step morphology a substantial pool 8 10 m in diameter shrubby precipitates and occupy areas of 2000 m2 siliceous ponds are variable in size have little outflow and exhibit low amounts of silica precipitation of these morphological varieties domal mounds and terraced mounds are thought to have the best long term preservation potential the four spring morphotypes are composed of up to eight cumulative hot spring depositional facies 1 vent 95 c 2 proximal vent precipitation of siliceous sinter is the result of abiotic and biotic processes abiotic precipitational processes are dominant in the vent area whereas biotic influences on the precipitate fabric become progressively more important downflow

sedimentology and allostratigraphy of post 240 ka to pre 26 5 ka lacustrine terraces at intracaldera lake rotorua taupo volcanic zone new zealand abstract lake rotorua partially occupies a nearly circular 20 km diameter volcano tectonic depression formed at c 240 ka by eruption of the voluminous mamaku ignimbrite three distinct lacustrine littoral terraces defined on the basis of contrasting geomorphology and field relations and separated by tephrostratigraphically dateable unconformities and basin floor disconformities fringe much of the lake basin they are here correlated with former high stands of the lake which resulted from the blockage and re establishment of a number of alternative outlets due to tectonic activity and volcanism at both the host and adjacent volcanic centres the unconformities allow division of the deposits into three allostratigraphic units each of which is then characterised by elevation and sediment provenance the

geothermal mineralization i the mechanism of formation of the beowawe nevada siliceous sinter deposit the siliceous sinter deposit at beowawe nev has a volume of 7 71 x 10 sup 7 m sup 3 and contains 1 28 x 10 sup 11 kg silica this silica precipitated from geothermal solutions that welled up along the malpais fault a graben bounding fault sinter formation involved three steps 1 geothermal solutions saturated with quartz in the reservoir moved to the surface where they cooled and became supersaturated with amorphous silica 2 amorphous silica particles nucleated heterogeneously to produce a colloidal suspension 3 the amorphous silica particles agglomerated and were cemented together by amorphous silica precipitating in the embayments between the particles at least 5 58 x 10 sup 14 kg of geothermal solution must have been produced over time to account for the mass of silica in the beowawe deposit this fluid would have carried at least 4 95 x 10 sup 17 kj of heat to the surface 21 references 6 figures 1 table

shoreline variability via empirical orthogonal function analysis part i temporal and spatial characteristics empirical orthogonal functions eofs or principal components were used to extract the significant modes of shoreline variability from several data sets collected at three very different locations although eofs have proven to be a valuable tool in the analysis of nearshore data most applications have focused on the ability of the technique to describe cross shore or profile variability here however eofs were used to help identify the dominant modes of longshore shoreline variability at duck north carolina the gold coast australia and at several locations within the columbia river littoral cell in the u s pacific northwest in part one of this analysis characteristic patterns of shoreline variability identified by the eof analysis are described in detail at each site the dominant modes consisting of the first four eigenfunctions were found to describe nearly 95 of the total shoreline variability at both duck and the gold coast several interesting longshore periodic features suggestive of sand waves were identified while boundary effects related to natural headlands and navigational structures entrances dominated the pacific northwest data sets

geyser eggs from te whakarewarewatangaoteopetauaawahiao north island new zealand waikorohihi and mahanga two geysers located on geyser flat at te whakarewarewatangaoteopetauaawahiao new zealand discharge chloride waters with a ph of 8 5 9 25 at 100 c many large up to 10 8 5 cm coated grains composed of amorphous silica opal a that are informally termed geyser eggs surround the vent of waikorohihi whereas smaller 3 cm geyser eggs are present in the proximal outflow channel of mahanga the geyser eggs have nuclei of detrital sinter or rhyolitic tuff their cortices are formed of thin concentric laminae and or spicular geyserite most cortical laminae contain a low diversity biota that includes filamentous microbes three types and scattered spherical microbes silicified grains of pinus radiata pollen are common in some laminae multiple phases of silica encrustation around the filamentous microbes disguised most features that are needed to confidently identify them most filaments are probably cyanobacteria variations in the microporosity and or microbe concentrations define individual cortical laminae growth of the geyser eggs in the pool around waikorohihi vent was controlled by the eruptive behavior of the geyser the eggs are submerged by boiling water during eruptions during dormant phases the geyser eggs are subaerially exposed while exposed their surfaces may remain moist from steam or rainwater or they may desiccate the low microbial diversity in the geyser eggs is probably related to their periodic inundation by boiling water and the highly variable conditions the abundant microbial laminae in the geyser eggs confirm that microbial templates are found in siliceous coated grains from almost all environmental settings in siliceous thermal spring systems

hot spring and geyser sinters the integrated product of precipitation replacement and deposition complex ornate sinter deposits are found in many hot spring and geysers systems throughout the world including those located in the taupo volcanic zone on the north island of new zealand those sinters are formed of opal a that replaced microbes opal a precipitated as cement accessory minerals e g kaolinite jarosite calcite biological detritus e g leaves wood pollen grains and lithic detritus the opal a is compositionally variable because of the amount of water oh and h2o and in some cases accessory elements e g au ag bound into its structure the composition and fabric of the siliceous sinter found at any locality reflect the relative balance among the processes of replacement precipitation and deposition the microbes that inhabit these systems are of critical importance because they are commonly replaced by and or encrusted with opal a in many settings copious amounts of opal a are precipitated as cement around the frameworks of silicified filaments the cementation pro

stable carbon isotope geochemistry of adsorbed alkane gases in near surface soils of the saurashtra basin india abstract the stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near surface soil and sediments from the saurashtra basin were characterized for their origin and maturity saurashtra is considered geologically prospective for oil and gas reserves however a major part of the basin is covered by the deccan traps hindering the exploration of mesozoic hydrocarbon targets surface geochemical prospecting based on micro seepage of hydrocarbons from subsurface accumulations could be advantageous in such areas in light of this 150 soil samples were collected from the northwestern part of saurashtra around the jamnagar area where a thick sedimentary sequence of about 2 3 km exists under 1 1 5 km of deccan basalt the concentration of acid desorbed alkane gases from soil samples was found to vary in ppb as methane c 1 3 518 ethane c 2 0 430 propane c 3 0 331 i butane ic 4 0 297 n butane nc 4 2 116 i pentane ic 5 0 31 and n pentane nc 5 0 23 respectively fifteen samples with high concentrations of alkane gases were measured for their 13 c 1 13 c 2 and 13 c 3 compositions using gas chromatography combustion isotope ratio mass spectrometry gc c irms the values for methane varied from 27 to 45 4 ethane from 20 9 to 27 6 and propane from 20 4 to 29 1 versus the vienna peedee belemnite vpdb the carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter likely to be mainly a terrestrial source rock with a partial contribution from a marine source these gases may have migrated to the near surface environment where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity the maturity scale 13 c versus log ro applied to the surface sediment samples of the jamnagar area indicated the source material to be capable of generating oil and gas the detection of thermogenic alkane gases in near surface sediments offers the possibility of hydrocarbons at depth in saurashtra

model for hydrocarbon microseepage and related near surface alterations despite recent advances in surface and near surface geochemical methods there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits we have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man years of our experience to contribute to that end evidence indicates that hydrocarbon micro seepage from reservoirs most probably involves buoyant colloidal size microbubbles of light hydrocarbons principally methane through the butanes ascending relatively rapidly through a water filled network of fractures joints and bedding planes bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide which may alter sediments producing detectable modifications in geomorphic seismic magnetic and radiometric properties we have used combinations of 1 airborne microwave sensing and laboratory analyses of soil gas hydrocarbons 2 shallow source aeromagnetic and soil magnetic susceptibility measurements 3 aerial and surface gamma ray measurements and 4 geomorphology to find productive oil and gas deposits results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings however these surface methods cannot reveal depth size or quality of reservoirs or even if producible hydrocarbons will be found

the quantitative description of beach cycles abstract a quantitative method is developed to describe sequential changes in beach profile morphology dominant cycles in temporal eigenfunctions computed by empirical eigenfunction analysis and rotary component analysis are defined and used to construct a sequence of profiles representing the energetic portions of beach cycles five sets of beach profile data from torrey pines beach in southern california were analyzed with these techniques because the first and second eigenfunctions account for between 65 and 90 of the variability of the data the beach profiles are accurately described with only these two variables and the mean profile using rotary component analysis beach changes represented by the two dominant eigenfunctions can be separated into many elliptical components each representing a particular frequency associated with cycles in beach state profiles are reconstructed using points from the perimeter latera recta of these beach state ellipses a frequency of 1 cpy is the most energetic frequency in the first and second eigenfunctions corresponding to the cyclic onshore offshore sediment movement associated with bar and berm profiles profiles constructed from points on the elliptical path associated with annual cycles graphically depict the sequential development of bar and berm during the beach cycle beach cycles corresponding to a frequency of 2 cpy are also significant primarily due to the energy of the second eigenfunction no other frequencies are consistently found to be as significant as the annual and semi annual cycles at this beach in particular monthly beach cycles have little energy associated with them the method described provides a uniform way to objectively discriminate energetic beach cycles and yields a concise representation for beach modeling and prediction it should be a valuable tool for uniform quantitative intercomparison of beaches and beach cycles

field observations of waves generated by passing ships a note this short contribution reports the results of a field study on the nearshore characteristics of waves generated by both conventional and high speed passenger ferries the field observations took place in the late summer of 2005 at a beach close to the port of mytilene island of lesbos greece and involved the visual observation of ship waves using digital video recordings and image processing techniques the results showed that passage of the fast ferry was associated with a longer more complex and energetic nearshore event this event not only did include higher nearshore waves up to 0 74 m and was organised in different wave packets but it was also an order of magnitude longer 680 s than the conventional ferry event regarding the effects on beach sediment dynamics the fast ferry waves were estimated to be very efficient in mobilising the nearshore sediments in contrast to those of the conventional ferry the fast ferry service appears to generate daily prolonged nearshore events which contain waves with higher energy than those expected from the normal summer wind wave regime of the area these events also include some high and very steep waves which can be particularly erosive therefore fast ferry wakes may have considerable impacts on the seasonal beach sediment dynamics morphodynamics and the nearshore benthic ecology as well as they may pose significant risks to bathers affecting the recreational use of the beaches exposed to fast ferry traffic finally the study has shown that satisfactory field observations of the nearshore characteristics of ship generated and wind waves can be obtained using inshore deployments of calibrated poles digital video cameras and appropriate image processing algorithms

facies architecture in depositional systems resulting from the interaction of acidic springs alkaline springs and acidic lakes case study of lake roto a tamaheke rotorua new zealand the facies architecture in hot spring systems tends to become more varied and complicated as the degrees of freedom in the system increase discharge aprons fed by waters from a single vent will for example be characterized by predictable downslope facies changes that reflect downslope changes in water chemistry and temperature the facies architecture however becomes exponentially more intricate when more factors start to impact the system this phenomenon is readily apparent in the geothermal area around lake roto a tamaheke located in the whakarewarewa thermal village rotorua new zealand where the facies architecture developed in response to the interactions between acid lake acid hot spring and alkaline hot spring depositional regimes with additional extraneous sediment being brought into the area by volcanic ash clouds wind blown pollen and surface run off from the surrounding drainage basin much of the complexity in the facies architecture of this system stems from the temporal varianc

yampi shelf browse basin north west shelf australia a test bed for constraining hydrocarbon migration and seepage rates using combinations of 2d and 3d seismic data and multiple independent remote sensing technologies abstract the yampi shelf on australia s north west shelf is highly prospective with two discrete hydrocarbon sources producing dry gas and oil to reduce exploration uncertainty relating to gas flushing and poor top seal capacity a study was undertaken to characterise hydrocarbon migration in the area it used a combination of seismic amplitude and structural data integrated with shipboard water column geochemical sniffer wasi data satellite synthetic aperture radar or sar data and aircraft acquired airborne laser fluorosensor alf data data were acquired synchronously and in staged programs to allow both direct comparison and time series analysis of results massive natural dry gas and oil seepage was detected though the relative abilities of wasi sar and alf to detect and characterise this seepage were markedly different the spatial distribution concentration and relative composition of the detected seepage were controlled principally by the regional seal s thickness and capacity rather than by the inherent composition and flux of the migrating hydrocarbons wasi preferentially identified gas seepage often in basin ward locations because the high relative permeability of gas favoured its early leakage even through thick seals sar preferentially identified oil seepage which was episodic and largely restricted to the basin margin at the regional zero edge of seal reflecting the low relative permeability of oil even through thin seals it leaked late alf principally detected low level oil seepage from charged traps and was hence most useful for trap ranking the ability of these remote sensing tools as well as that of seismic data itself to detect hydrocarbons appears critically dependant upon interplays between the relative sensitivity of the assorted tools to detect various hydrocarbon phases and the capacity of the top seal itself the study has demonstrated that the interactions between geology and hydrocarbon charge are predictable and that understanding these interactions is crucial for the reliable interpretation of remote sensing data