biogenicity of silica precipitation around geysers and hot spring vents north island new zealand abstract before anthropogenic modifications ohaaki pool broadlands ohaaki and dragon s mouth geyser wairakei emitted waters at temperatures of 93 98 c the siliceous sinter that precipitated around their vents has the characteristics of geyserite a dense laminated deposit of presumed abiogenic origin that was precipitated from waters too hot 73 c to support microbes other than thermophilic bacteria petrographic and sem examinations of the sinters that surround the vent of dragon s mouth geyser and form the pool rim dam of ohaaki pool show that they incorporate columnar stromatolites and silicified laminated stromatolitic mats that contain well preserved filamentous microbes at both localities the microbes lack evidence of desiccation or shrinkage which implies that they were silicified rapidly at or shortly after their death microbe preservation is commonly spectacular even the trichome is recognizable in many specimens although replacement by silica preserved the cells of the trichome cell walls and septae were not preserved possibly because they were destroyed by autolysis before silicification the sheath that surrounded the trichome is normally well preserved however late silica precipitation produced thick external encrustations of amorphous silica around many sheaths although boiling and very hot 90 c waters were discharged temperatures at many sites surrounding the vents remained sufficiently low and moist to support a microbial community that included thermophilic bacteria and cyanobacteria in these cooler niches the microbes and their biofilms served as highly favorable templates for the nucleation and growth of amorphous silica and collectively provided a microbial framework for the laminated accretionary sinter silica was supplied from supersaturated spring and geyser fluids that were delivered to sites of sinter precipitation as air cooled spray as proximal runoff or as the result of oscillations in the surface level of the spring or geyser pool waters in the field and in hand specimen the resulting columnar sinter appear to be identical in morphology to that inferred to originate from abiotic silica precipitation in a sterile environment consequently some columnar spicular and stratiform geyserites are probably not abiotic precipitates but are true silica stromatolites

microstructure of high temperature 73 c siliceous sinter deposited around hot springs and geysers yellowstone national park the role of biological and abiological processes in sedimentation slightly alkaline hot springs and geysers in yellowstone national park exhibit distinctive assemblages of high temperature 73 c siliceous sinter reflecting local hydrodynamic conditions the main depositional zones include subaqueous pool and channel bottoms and intermittently wetted subaerial splash surge and overflow areas subaqueous deposits include particulate siliceous sediment and dendritic and microbial silica framework silica framework forms thin porous microbe rich films coating subaqueous surces spicules with intervening narrow crevices dominate in splash zones surge and overflow deposits include pool and channel rims columns and knobs in thin section subaerial sinter is composed of i dark brown nearly opaque laminated sinter deposited on surfaces that evaporate to dryness ii clear translucent silica deposited subaqueously through precipitation driven by supersaturation iii heterogeneous silica representing silica encrusted microbial filaments and detritus and iv sinter debris brownish laminations form the framework of most sinter deposited in surge and overflow zones pits and cavities are common architectural features of subaerial sinter and show concave upward pseudo cross laminations and micro unconformities developed through migration marked birefringence of silica deposited on surfaces that evaporate to dryness is probably a strain effect repeated wetting and evaporation often to dryness and capillary effects control the deposition morphology and microstructure of most high temperature sinter outside of the fully subaqueous zone microbial filaments are abundant on and within high temperature sinter but do not provide the main controls on morphology or structuring except in biofilms developed on subaqueous surfaces millimetre scale lamination cyclicity in much high temperature sinter represents annual layering and regular seasonal fluctuations in silica sedimentation

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

seamount topography by least squares inversion of altimetric geoid heights and shipborne profiles of bathymetry and or gravity anomalies summary altimetric measurements of sea surface heights have long been used to locate uncharted marine features newly available data sets geosat gm ers 1 and topex poseidon now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper this method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and or gravity anomalies when available furthermore uncertainties can be computed together with the topography which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases tests are performed using simulated data in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling these errors can be maintained under the 100 m level rms for altimetric data with a measurement noise of 5 cm rms or less which is achieved for geosat ers 1 and topex poseidon altimeters an example of inversion of seasat data is presented in the case of a seamount in french polynesia

siliceous shrubs in hot springs from yellowstone national park wyoming u s a many of the siliceous hot springs in yellowstone national park contain subaqueous spinose siliceous precipitates up to 5 cm high that occupy shallow terracettes in siliceous terraced mound accumulations discharge channels etc these siliceous shrubs are composed of opal a with an arborescent or branching pattern and have strong morphological similarities to bacterial shrubs from carbonate precipitating hot springs siliceous shrubs constitute a major precipitate style associated with discharge channel flow path facies throughout most of the 20 m of flow path at cistern spring norris geyser basin they are found in siliceous spring waters ranging in temperature from 76 4 to 16 2 c and ph from 6 0 to 7 4 at every scale siliceous shrubs contain abundant evidence of microbial life in the form of bacterial body fossils and extracellular polymeric substances the presence of relict organic constituents and bacterial morphological fossils indicates that the shrub fabric and architecture are dominated by bacteria i e there is potentially a strong biotic effect on the precipitation process precipitation of opal in siliceous shrubs is very likely the result of either active bacterially induced precipitation or passive mediation through organic templates on a larger scale siliceous shrubs contain abundant evidence of former microbial activity in hot springs thus they are good microbial biomarkers resume plusieurs sources thermales siliceuses de yellowstone contiennent des precipites siliceux subaquatiques et en forme d aiguilles jusqu a 5 cm de haut qui occupent de petites terrasses peu profondes dans des accumulations en forme de monticules en terrasses dans les chenaux d ecoulement etc ces arbrisseaux siliceux sont composes d opale a avec un patron arborescent ou a branches et ont de fortes similitudes morphologiques aux arbrisseaux de bacteries de sources thermales precipitant du carbonate les arbrisseaux siliceux constituent un style commun de precipitation associe au facies de chenal de decharge chemin d ecoulement a travers la plus grande partie des 20 m du chemin d ecoulement a la source cistern du bassin du geyser norris ils se retrouvent dans les eaux de sources siliceuses dont la temperature varie de 76 4 a 16 2 oc avec un ph variant de 6 0 a 7 4 a toutes les echelles les arbrisseaux siliceux contiennent de nombreuses evidences de vie microbienne sous la forme de fossiles de corps bacteriens et de substances extracellulaires polymeriques la presence de constituants organiques reliques et de fossiles morphologiques bacteriens indique que la texture et l architecture des arbrisseaux sont dominees par les bacteries c a d qu i lyau n fortpotentiel d un effet biotique sur le processus de precipitation la precipitation de l opale dans les arbrisseaux siliceux est tres probablement le resultat d une precipitation active induite par les bacteries ou d une aide passive a travers des gabarits organiques a une plus grande echelle les arbrisseaux siliceux contiennent de nombreuses evidences d activite microbienne anterieure dans les sources thermales ils forment donc de bons marqueurs biologiques traduit par la redaction guidry and chafetz 1583

eocene to present subduction of southern adria mantle lithosphere beneath the dinarides we modeled global positioning system measurements of crustal velocity along a n13 e profile across the southern adria microplate and south central dinarides mountain belt using a one dimensional elastic dislocation model we assumed a n77 w fault strike orthogonal to the average azimuth of the measured velocities but we used a constrained random search algorithm minimizing misfit to the velocities to determine all other parameters of the model the model fault plane reaches the surface seaward of mapped sw verging thrusts of eocene and perhaps neogene age along the coastal areas of southern dalmatia consistent with sw migrating deformation in an active fold and thrust belt p wave tomography shows a ne dipping high velocity slab to 160 km depth which reaches the surface as adria dips gently beneath the foreland and becomes steep beneath the dinarides topographic high the thrust plane is located directly above the shallowly dipping part of the slab the pattern of precisely located seismicity is broadly consistent with both the tomography and geodesy deeper earthquakes down to 70 km correlate spatially with the slab and shallower earthquakes are broadly clustered around the geodetically inferred thrust plane the model fault geometry and loading rate ages of subaerially exposed thrusts in the fold and thrust belt and the length of subducted slab are all consistent with adria eurasia collision involving uninterrupted subduction of southern adria mantle lithosphere beneath eurasia since eocene time

the impact of cover rock rheology on the style of folding in the zagros fold thrust belt abstract the present day morphology of the zagros fold thrust belt is dominated by magnificent exposures of nw se trending folds these folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock the cover rock succession of the zagros consists of a sequence of competent and incompetent units which vary both along and across the belt field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation during the shortening linked to the current convergence of the arabian and iranian plates the incompetent units act as detachment horizons which localise thrusting and which act as decollement above which detachment folds form in addition where these incompetent units are thick e g 1 km they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur as a result the folds above and below the incompetent units in the central part of the zagros folded belt have significantly different geometries and wavelengths as the zagros folds host the majority of the hydrocarbon reserves in iran and iraq an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region

factors governing subaqueous siliceous sinter precipitation in hot springs examples from yellowstone national park usa siliceous sinter precipitation within hot spring systems has been attributed to a variety of mechanisms evaporative concentration cooling changes in ph and cation effects repetitive in situ t ph alkalinity etc and laboratory major minor and trace elemental stable isotopic analyses of the waters plus observations of silica precipitation on natural e g twigs pine cones as well as artificial substrates glass slides and copper plates in the waters substantiate that subaqueous precipitation is occurring throughout the vent to distal end of flow in both cistern spring norris geyser basin and deerbone spring lower geyser basin yellowstone national park wyoming usa quartz and sodium potassium geothermometers indicate that cistern spring is fed by a subsurface reservoir that is between 232 and 272 c calculated reservoir temperatures are significantly lower at deerbone spring 182 197 c based on a suite of measured and theoretical saturation indices downflow changes in the system resulting from evaporative concentration e g cl increases 10 changes in ph e g 5 6 7 1 and cation effects al and fe are of negligible importance in the subaqueous precipitation of hot spring opal a similarly at the macroenvironmental scale potential biotic effects on opal a precipitation appear to be minimal modelling of the two active siliceous sinter precipitating systems indicates that cooling e g 80 17 c is the predominant process governing subaqueous mineral precipitation

geological setting of the early devonian rhynie cherts aberdeenshire scotland an early terrestrial hot spring system abstract the drilling of nine cored boreholes including a deep hole 233 m to a gabbroic basement in the vicinity of the rhynie chert locality has resulted in a major revision of the structure and stratigraphy of the area the main new structural element recognized is a low angle extensional fault system which defines the western edge of a half graben containing the early devonian succession the fault system was the main conduit for the fluids that fed the hot springs and a heat source to the southeast of rhynie is indicated rapid and unexpected lateral and vertical variations in lithology together with new lithological units have been identified the latter include a thick unit of intensely altered lapilli tuffs which are unique to the rhynie basin and to other devonian basins in ne scotland analysis of these lithologies in conjunction with the new structural model allows the succession at rhynie to be correlated with the succession in the rest of the basin and a model of basin evolution and hot spring development to be constructed siliceous sinters were deposited by multiple episodes of hot spring activity and are variably interbedded with shales sandstones and minor tuffs in a unit about 35 m thick sinter deposition was ultimately controlled by repeated subsidence along the basin margin geothermal activity was probably widespread in northern britain in the early devonian but the surface deposits are unlikely to be preserved the rhynie deposit has survived due to a fortuitous combination of circumstances

combined control of decollement layer thickness and cover rock cohesion on structural styles and evolution of fold belts a discrete element modelling study abstract a series of numerical experiments based on the discrete element method were performed to simulate the formation of fold belts with varied decollement layer thickness and cover rock cohesion to investigate their controls on structural styles of fold belts each model consists of a weak unbonded basal decollement layer with a relatively low to high thickness and a bonded cover with a relatively low to high cohesive strength horizontal shortening of the particle assemblage was achieved by horizontal motion of a vertical boundary wall resulting in deformations in the system the results show that shortening was mainly accommodated by detachment folds sinusoidal and box folds fault related folds and opening mode fractures in the models the combination of a lower cohesion and a thinner decollement resulted in more distributed strain and a larger number of folds whilst the combination of a higher cohesion and a thicker decollement led to more pronounced strain localisations in fewer folds surface uplift and fold amplitude diapir height are mainly positively affected by the decollement thickness i e the thicker the decollement is the greater the surface uplift and fold amplitude are the propagation rate of deformation is predominately controlled by the cover rock cohesion a lower cohesion led to a higher propagation rate of deformation the model with a relatively low cohesion and decollement thickness produced regularly spaced box folds which are comparable to those in the southern zagros fold and thrust belt the models presented demonstrate that the combined effect of decollement layer thickness and cover rock cohesion can play a critical role in the structural styles and kinematic evolution of fold belts

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

effects of initial rift inversion over fold and thrust development in a cratonic far foreland setting abstract the effects of initial rift inversion over the geometry of a far foreland intracratonic fold and thrust belt are investigated a total of 25 seismic reflection lines and stratigraphic data from 9 wells are used in association to digital elevation and field geological data to investigate the geometric relationship between shallow thrust development and initial positive inversion of buried rift faults in a cratonic environment where inversion tectonics is not common the study case is conducted in the meeting region of the opposed verging brasilia and aracuai foreland fold and thrust neoproterozoic belts located in central brazil formed in the first stages of west gondwana amalgamation seismic reflection sections are used to map buried paleorift faults and trust ramps the best 5 sections are also interpreted in detail in terms of fold and thrust geometry and their relationship to the inverted rifts is analyzed they show high correlation between shallow fold and thrust geometry and the shortening of synrift strata caused by rift inversion results indicate that initial positive rift fault reactivation exerts a determinant control over the locus of thrust ramp nucleation by causing syn rift strata to overfold and drape fold the passive folding propagates upwards forming gentle folds in the decollement plane where thrust ramps tend to nucleate back thrust forethrust pairs tend to form over elevated horsts where higher topographic plateaus are preserved multiple thrusting and lower relief occur over buried rifts with multiple inverted faults strata over non rifted basement remain practically unaffected by thrusting and folding moreover the development of thrust salients and recesses are demonstrated to be conditioned by the morphology of buried rifts the study also contributes with a more precise mapping of the buried rift system and thrust system in the area and brings new insights about the structural evolution of the brasiliano pan africano orogeny affecting the sao francisco craton basement and covers

experiments on simultaneous faulting and folding above a basement wrench fault abstract wrench zones commonly show en echelon patterns of folds in the stratified cover above a basement fault examples are the darien basin in panama and the inglewood fault trend in california folds are often associated with synthetic and antithetic wrench faults but the time relationships between folds and faults may not be obvious we have done experiments where simultaneous faulting and folding occur above a basement fault four experiments were performed using a simple apparatus capable of imposing localised strike slip motions this apparatus consists of two plastic plates one can be moved laterally past the other by a piston thus modelling lateral motion on a single basement fault models were properly scaled to account for gravitational forces brittle behaviour of sandstone and ductile behaviour of clay or shales in the upper crust each model is a vertical succession of silicone layers and sand layers each layer is 2 mm thick except for the basal silicone layer which is 2 4 6 or 8 mm thick in experiments 1 2 3 or 4 respectively all models were deformed at the same slip rate on the basal fault 1 cm h 1 experiments 1 2 and 3 with 8 cm total horizontal sinistral offset were designed to investigate the influence of basal silicone layer thickness on the deformation of a multilayered model experiment 4 with 20 cm of total offset was designed to investigate the influence of an increasing left lateral offset on folding and faulting with a 2 mm thick basal silicone layer experiment 1 synthetic strike slip faults appeared en echelon above the basement fault no folds were visible at the surface of the experiment but the interfaces between sand and silicone layers showed millimetric folds en echelon above the basement fault with a 4 mm thick basal silicone layer experiment 2 en echelon synthetic strike slip faults and folds appeared above the basement fault faults and folds rotated progressively anticlockwise and synclines were activated as dextral antithetic shear zones with a 6 mm thick basal silicone layer experiment 3 synthetic faults and en echelon folds appeared as before but the fold amplitude was larger than in experiment 2 an increasing left lateral offset produced anticlockwise rotation of faults and folds as before and synclines were activated as dextral antithetic shear zones in experiment 4 after 16 cm of left lateral offset the anticlockwise rotation of the folds was such that antithetic dextral shear zones became almost parallel to the basement fault and were then reactivated as synthetic sinistral shear zones

rapid in situ silicification of microbes at loburu hot springs lake bogoria kenya rift valley microbial mats located along the margins of hot spring pools and outflow channels at lake bogoria kenya are commonly silicified forming friable laminated crusts columnar microstromatolites composed of silica and calcite are also forming at several springs in sites of oscillating water level or spray silicification of the microbes involves impregnation of organic tissue by very fine amorphous silica particles and encrustation by small 2 m silica spheroids rapid silicification of the microbes which may begin while some are still alive can preserve sheaths and in some examples the filaments capsules and cells although this provides evidence of their general morphology the biological features that are required for taxonomic identifications are commonly poorly preserved the silica precipitation results mainly from evaporative concentration and rapid cooling of spring waters that have been drawn upward through the mats and microstromatolites by capillary processes almost all the silica at the loburu springs nucleates on microbial substrates this affinity of silica for functional groups on microbial surfaces contributes to the rapid silicification of the microbes and their preservation in modern and ancient cherts

diatomaceous origin of siliceous shale in eocene lake beds of central british columbia the abundance of diatoms in neogene lacustrine sediments and their apparent scarcity in paleogene deposits have long perplexed geoscientists but siliceous shales from eocene lake beds of central british columbia provide new insights major element geochemistry x ray diffraction patterns and relict diatom frustules suggest that eocene beds at horsefly mcabee and princeton originated as lacustrine diatomite that underwent diagenetic alteration to produce siliceous shale the combination of high sio2 and low al2o3 values and the presence of opal ct x ray diffraction peaks provide a distinctive geochemical fingerprint for biogenic silica deposits that have been remineralized the discovery of diatomaceous geochemical signatures in siliceous shales may prove to be a useful tool for extending the geologic record of diatoms perhaps helping to reduce the apparent discrepancy between fossil evidence and evolutionary interpretations based extant species

sedimentary and structural controls on seismogenic slumping within mass transport deposits from the dead sea basin abstract comparatively little work has been undertaken on how sedimentary environments and facies changes can influence detailed structural development in slump sheets associated with mass transport deposits mtds the nature of downslope deformation at the leading edge of mtds is currently debated in terms of frontally emergent frontally confined and open toed models an opportunity to study and address these issues occurs within the dead sea basin where six individual slump sheets s1 s6 form mtds in the late pleistocene lisan formation all six slumps which are separated from one another by undeformed beds are traced towards the ne for up to 1 km and each shows a change in sedimentary facies from detrital rich in the sw to more aragonite rich in the ne the detrital rich facies is sourced predominantly from the rift margin 1 5 km further sw while the aragonite rich facies represents evaporitic precipitation in the hyper saline lake lisan the stacked system of mtds translates downslope towards the ne and follows a pre determined sequence controlled by the sedimentary facies each individual slump roots downwards into underlying detrital rich layers and displays a greater detrital content towards the sw which is marked by increasing folding while increasing aragonite content towards the ne is associated with more discrete thrusts the mtds thin downslope towards the ne until they pass laterally into undeformed beds at the toe the amount of contraction also reduces downslope from a maximum of 50 to

depositional setting and paleobotany of permian and triassic permineralized peat from the central transantarctic mountains antarctica abstract silicified peat is known from two sites in the central transantarctic mountains both are within a 2 km thick permo triassic sandstone shale sequence that was deposited by braided streams in a rapidly subsiding foreland basin along the paleo pacific margin of antarctica upper permian permineralized peat occurs as scattered boulders just above a channel form sandstone in the upper part of the buckley formation on skaar ridge overlooking the beardmore glacier these boulders are erosional remnants of fine grained deposits that accumulated in shallow lakes or swamps on a flood plain at fremouw peak the peat occurs near the top of the fremouw formation in strata that are probably middle to late triassic in age the peat consists of large blocks that were rafted into a sandy braided stream channel during a flood and then stranded and buried as flood waters receded both sites are characterized by exceptionally well preserved plant material although the composition and diversity of the two floras are very different permineralization apparently took place rapidly and was enhanced by the dissolution of siliceous volcanic detritus that is abundant in both formations

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

sea surface topography retrieved from gnss reflectometry phase data of the geohalo flight mission sea surface topography observations are deduced from an airborne reflectometry experiment a gnss global navigation satellite system receiver dedicated for reflectometry was set up aboard the german halo high altitude long range research aircraft flights were conducted over the mediterranean sea about 3500 m above sea level a signal path model divided into large and small scale contributions is used for phase altimetry the results depict geoid undulations and resolve anomalies of the sea surface topography for the whole experiment 65 tracks over the mediterranean sea are retrieved and compared with a topography model tracks differ between right handed and left handed circular polarization the difference however is not significant for this study precision and spatial resolution decrease disproportionately at low elevations eight tracks with centimeter precision are obtained between 11 and 33 of elevation at higher elevation angles the number of tracks is significantly reduced due to surface roughness in future such retrievals could contribute to ocean eddy detection

fracture patterns and petrophysical properties of carbonates undergoing regional folding a case study from kurdistan n iraq abstract the zagros taurus fold and thrust belt hosts a prolific hydrocarbon system most hydrocarbon reserves are stored in naturally fractured reservoirs and such fracture systems can therefore have a significant impact on reservoir performance fractures are one of the most important paths for fluid flow in carbonate reservoirs and industrial geoscientists and engineers therefore need to understand and study fracture patterns in order to optimise hydrocarbon production the observed fracture patterns in outcrops may have implications on fluid flow and reservoir modelling in subsurface reservoirs and we have therefore undertaken a case study of fracturing associated with regional folding in iraqi kurdistan in this area some exploration wells currently target upper triassic dolostones kurra chine formation and or lower jurassic limestones and dolomitised limestones sehkaniyan formation in both units hydrocarbon production comes mainly from secondary porosity created by dolomitisation dissolution and fracturing both formations have undergone multiple phases of deformation associated with burial uplift folding and thrusting we investigate some fracture pattern characteristics and some petrophysical properties of these units using selected outcrops around the gara ora and ranya anticlines that form folds directly traceable for 25 70 km our outcrop data is compared with subsurface fracture and petrophysical datasets reported from wells in the nearby shaikhan and swara tika fields the 1 2 3d fracture attributes collected from outcrops are fracture orientation type spacing intensity length and cross cutting and abutting relationships fracture orientations show a clear relationship to the local fold axis in both the outcrop and subsurface although in some cases they appear to relate more to the present day in situ maximum horizontal stress direction or local strike slip faulting three stages of fracturing are proposed pre folding early folding and post folding fractures in addition we report petrophysical properties porosity permeability and acoustic velocity of both the kurra chine and sehkaniyan formations in relation to their structural position within folds and faults and stratigraphic level the highest porosities and permeabilities are recorded in the hinges and backlimbs of the gara anticline the best reservoir quality highest porosity and permeability is often found in areas associated with replacement dolomite i e solution vugs and intercrystalline porosity the kurra chine formation displays similar trends in velocity porosity data at both outcrop and the subsurface however the sehkaniyan formation displays lower acoustic velocity for a given porosity at outcrop compared to the subsurface

reappraisal of purported ca 3 7 ga stromatolites from the isua supracrustal belt west greenland from detailed chemical and structural analysis abstract the biogenicity of proposed stromatolite structures from eoarchean ca 3 71 ga rocks of the isua supracrustal belt isb in west greenland is under debate the structures in question are found within a suite of multiply deformed greenschist to amphibolite facies metamorphic rocks to assess their premise as primary sedimentary features as opposed to products of strain localization in layered variably ductile rocks we report new field mapping at the appropriate scale and resolution from the original discovery sites reported by nutman et al 2016 our new map was used to guide micro and macro structural investigations and comprehensive geochemical sampling here we report detailed field characterization and structural analysis to show that the structures are linear inverted ridges aligned with azimuths of local and regional fold axes and parallel to linear structures they are not deformed conical stromatolites combined major element e g ca mg si scanning xrf maps and electron backscatter diffraction ebsd patterns collected on fresh surfaces cut perpendicular and parallel to the ridges attest to the lack of any residual sedimentary laminae e g compositional layering within these structures cores internal layering previously inferred for these features instead arises from variable weathering of outcrop surfaces that otherwise conceals granoblastic quartz dolomite cored boudins that sit between semi continuous competent layers of enveloping quartzite in a calc silicate schist the morphology of boudins reflects viscosity contrasts of the different ductile layers during deformation therefore these features are not of sedimentary origin furthermore discontinuous field relationships and absence of primary sedimentary structures that could serve as way up indicators preclude confident assignment of these outcrops as being structurally overturned as originally argued collectively our results show that the isua structures are the expected result of a tectonic fabric that preserves no fine scale primary sedimentary structures and were probably never stromatolites

the organic geochemistry of coal from plant materials to coal coalification is a process that transforms plant remains under the influence of time temperature and possibly pressure to a black generally lustrous solid organic fossil fuel having a very complex chemistry although much has been learned in the past two centuries on coal chemistry we still have little knowledge of the way plant materials undergo these transformations the problem has been the existence of adequate characterization tools the advent of some new tools for structural elucidation of macromolecules has led to some revised thinking on coalification originally thought to be a process involving the full degradation of plant remains and subsequent reconstitution of these remains the general consensus today is that the process involves a selective preservation of certain resistant plant components followed by some minor reorganization of the biopolymers that survive the major components of plants do degrade and the resistant ones often constitute only a small fraction of the original mass of the plant materials this paper examines the most recent literature concerning coalification and focuses on the chemistry associated with coalification of certain recognizable plant remains that have been at the center of research activity for the past two decades thus we examine the recent knowledge of the chemistry of resistant biopolymers in extant and fossil wood cuticles resins spores and algae knowledge that has been assembled to establish the reaction pathways towards coal macromolecules

the owens river as a tiltmeter for long valley caldera california in the lower 11 km of its course around the resurgent dome of long valley caldera the owens river displays two parallel meander belts comparable in meander wavelength and amplitude but unequal in age elevation and discharge it appears the two belts take turns carrying the river s flow depending on whether the dome is inflating or subsiding the inboard belt some 200 300 m closer to the dome and now 30 60 cm higher in elevation contains an underfit stream and is now being abandoned the outboard channel formed in a series of avulsions apparently induced by recent uplift of the dome in the upper 4 km of the two channel reach avulsion occurred between 1856 and 1878 as inferred from the original u s coast and geodetic survey mapping in the caldera avulsion had already occurred by 1856 in the lower 4 km of the river suggesting a possible migration of the center of uplift through time muted remains of older oxbows in the outboard meander belt indicate an earlier occupancy by the river and thus an

the origin and tectonic significance of asymmetrical meander belts in the hebgen lake area of sw montana the madison and south fork rivers occupy the northeast sides of their respective meander belts the form of the abandoned meander loops within these asymmetric meander belts indicates that they were produced by gradual northeast migration of the active channels this progressive migration can be related to tectonic tilting produced by regional extensional faulting at a high angle to the original channel belt axis which ran down a gently sloping outwash cone asymmetric channel sandstone bodies in the rock record can be recognized by the preferred dip of successive lateral accretion units in meander loops together with soft sediment deformation facies and thickness variations they may indicate tectonic deformation of the sedimentary surface

airborne gravimetry of geohalo mission data processing and gravity field modeling airborne gravimetry is a crucial method to improve our knowledge about the earth gravity field especially in hard to access regions generally the accuracy of airborne gravimetry is several milligals which is suitable for filling the so called polar gaps in satellite derived global gravity field models here some investigations based on airborne gravity measurements from the geohalo mission over italy are presented to subtract the vertical accelerations from the values measured by the gravimeter four different versions of kinematic accelerations were derived from global navigation satellite systems gnss recordings to remove the high frequency noise a low pass filter with a cutoff wavelength of 200 s was applied to both chekan am measurements and kinematic accelerations from gnss to investigate how future airborne gravity campaigns could be designed a dedicated flight track was repeated two times showing that the equipment worked well also at higher altitude and speed from the final best results follows an rms of gravity differences at crossover points of 1 4 mgal which according to the law of error propagation implies the accuracy of a single measurement to be 1 4 2 1 mgal to demonstrate how a satellite only gravity field model can be improved by airborne measurements a gravity field model for the geohalo region has been computed to compute also an improved regional geoid model the point mass modeling pmm and the remove compute restore rcr technique using a recent satellite only model and residual terrain modeling rtm were applied finally gnss leveling points have been used to check the quality of the regional point mass model

new antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in antarctica gravity surveying is challenging in antarctica because of its hostile environment and inaccessibility nevertheless many ground based airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s we present the first modern antarctic wide gravity data compilation derived from 13 million data points covering an area of 10 million km2 which corresponds to 73 coverage of the continent the remove compute restore technique was applied for gridding which facilitated levelling of the different gravity datasets with respect to an earth gravity model derived from satellite data alone the resulting free air and bouguer gravity anomaly grids of 10 km resolution are publicly available these grids will enable new high resolution combined earth gravity models to be derived and represent a major step forward towards solving the geodetic polar data gap problem they provide a new tool to investigate continental scale lithospheric structure and geological evolution of antarctica

quantifying deformation processes in the se pyrenees using u pb dating of fracture filling calcites it is difficult to quantify the timing of the deformation processes in brittle fold thrust belts because minerals suitable for dating and well preserved growth strata sediments are scarce or absent here we quantify the duration of thrust sheet emplacement and shortening rates in the se pyrenean thrust sequence using u pb dating of fracture filling calcites the obtained u pb dates reveal a minimum duration for the emplacement of each thrust unit 18 7 ma for the boixols upper pedraforca 11 6 ma for the lower pedraforca and 14 3 ma for the cadi thrust sheets and show that piggy back thrusting was accompanied by post emplacement deformation of the upper thrust sheets above the lower sheets during their south directed tectonic transport we calculated shortening rates of 0 6 3 1 and 1 1 mm a 1 from the older to younger emplaced thrust sheets our results also reveal the formation of local normal faults during the late oligocene as a result of the late stages of compression and exhumation in the se pyrenees we observed that temperatures 110 c could be a limiting factor when applying the u pb dating method supplementary material u pb analytical results concordia plots and fracture data are available at https doi org 10 6084 m9 figshare c 5078862

an unusual modern silica carbonate sinter from pavlova spring ngatamariki new zealand a silica carbonate deposit is forming from the dilute alkali chloride waters of pavlova spring a small thermal pool and outflow channel 85 to 10 times lower accumulation rates than typical siliceous sinters in the tvz and deposition of both silica and calcite is controlled by microchemical conditions and local temperature gradients rather than by bulk spring water chemistry

experiments on faulting in a two layer cover sequence overlying a reactivated basement fault with oblique slip abstract two series of experiments were undertaken to investigate the development of faults in a cover sequence overlying a reactivated basement fault with oblique slip the experiments represent physical models properly scaled to account for gravitational forces brittle behaviour of the upper cover and ductile behaviour of evaporites in the lower cover models were made with a coulomb layer sand overlying a newtonian ductile layer silicone putty in each series the thickness of the silicone layer was varied from each experiment to the next in all normal wrench experiments a domain of faults appeared in the brittle layer vertical offsets were mostly of normal sense but some reverse faults occurred in experiments with thick silicone layers the thicker the silicone the wider the fault domain the deformation zone was in all cases limited to the faulted domain in the reverse wrench experiments discrete reverse riedel faults appeared without a silicone layer as the silicone layer became thicker the importance of the reverse faults diminished with the thickest layer of silicone 3 cm no faults appeared in the overburden but a monoclinal flexure accommodated the dip slip component in the presence of silicone the deformation zone was not limited to a faulted domain and the strike slip component was accommodated by a bulk shearing of the overburden in the uplifted compartment these experiments demonstrate that in basins deformed in oblique slip mode any deformation that is localized along discrete faults at the basement level becomes distributed over a much wider zone of overburden when this overlies an interval of evaporites

inversion of geohalo aerogravimetry to infer ocean bottom topography application to the tyrrhenian ionian and adriatic seas

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

rayleigh scattering by aqueous colloidal silica as a cause for the blue color of hydrothermal water abstract thermal waters in hydrothermal ponds bathing pools and the brines of geothermal electric power plants commonly have a characteristic blue color although many researchers have assumed that the blue color is due to a colloidal suspension and or absorption by dissolved ferrous iron or by water itself there has been no specific effort to identify the physical nature of this phenomenon we have tested in synthetic and natural solutions whether aqueous colloidal silica is responsible for the blue color aqueous colloidal silica is formed by silica polymerization in thermal waters of the neutral chloride type which contain initially monomeric silica in concentrations up to three times above the solubilities of amorphous silica the hue of the blue thermal waters in the pools tested agrees with that of a synthesized colloidal silica solution grain size analyses of aqueous colloidal silica in the blue colored thermal waters demonstrate that the color is caused by rayleigh scattering from aqueous colloidal silica particles with diameters 0 1 0 45 m smaller than the wavelengths of visible radiation

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

experiments on fault reactivation in strike slip mode abstract experiments were undertaken to investigate how faults reverse or normal in a cover sequence become reactivated when an underlying basement fault is itself reactivated in strike slip mode physical models properly scaled for gravity were deformed in a large 2 1 5 m apparatus divided into two halves one half can be moved laterally or vertically past the other models were constructed with a coulomb layer sand overlying a newtonian ductile layer silicone three different configurations of the basement fault reverse normal or vertical defined three series of experiments each consisted of 1 brittle model 6 cm of sand and 2 brittle ductile models 5 cm of sand overlying 1 cm of silicone or 4 cm of sand overlying 2 cm of silicone each model was deformed in two steps 1 a pure dip slip stage and 2 a reactivation in pure strike slip mode in surface views little reactivation was observed but in all cases the deformation imposed during the strike slip episode was localized by pre existing dip slip structures in cross sections however faults were seen reactivated at depth on the basis of these experiments we suggest that 1 a previously faulted zone can control the deformation of a strike slip zone and 2 reactivation of faults in strike slip mode can occur at depth without being visible at the surface we attribute the higher probability of reactivation at depth to the mechanical properties of the sand especially cohesion

global gravity bathymetry and the distribution of submarine volcanism through space and time 1 the seafloor is characterized by numerous seamounts and oceanic islands which are mainly volcanic in origin relatively few of these features 0 1 however have been dated and so little is known about their tectonic setting one parameter that is sensitive to whether a seamount formed on near or far from a mid ocean ridge is the elastic thickness te which is a proxy for the long term strength of the lithosphere most previous studies are based on using the bathymetry to calculate the gravity anomaly for different values of te and then comparing the calculated and observed gravity anomaly the problem with such an approach is that bathymetry data are usually limited to single beam echo sounder data acquired along a ship track and these data are too sparse to define seamount shape we therefore use the satellite derived gravity anomaly to predict the bathymetry for different values of te by comparing the predicted bathymetry to actual shipboard soundings in the vicinity of each locality in the wessel global seamount database we have obtained 9758 te estimates from a wide range of submarine volcanic features in the pacific indian and atlantic oceans comparisons where there are previous estimates show that bathymetric prediction is a robust way to estimate te and its upper and lower bounds te at sites where there is both a sample and crustal age show considerable scatter however and there is no simple relationship between te and age nevertheless we are able to tentatively assign a tectonic setting to each te estimate the most striking results are in the pacific ocean where a broad swath of on ridge volcanism extends from the foundation seamounts and ducie island easter island ridge in the southeast across the equator to the shatsky and hess rises in the northwest interspersed among the on ridge volcanism are flank ridge and off ridge features the indian and atlantic oceans also show a mix of tectonic settings off ridge volcanism dominates in the eastern north atlantic and northeast indian oceans while flank ridge volcanism dominates the northeastern indian and western south atlantic oceans we have been unable to assign the flank ridge and off ridge estimates an age but the on ridge estimates generally reflect we believe the age of the underlying oceanic crust we estimate the volume of on ridge volcanism to be 1 1 106 km3 which implies a mean seamount addition rate of 0 007 km3 yr 1 rates appear to have varied through geological time reaching their peak during the late early cretaceous and then declining to the present day

reprint of comparison of modern fluid distribution pressure and flow in sediments associated with anticlines growing in deepwater brunei and continental environments iran abstract differences in fluids origin creation of overpressure and migration are compared for end member neogene fold and thrust environments the deepwater region offshore brunei shale detachment and the onshore arid central basin of iran salt detachment variations in overpressure mechanism arise from a the availability of water trapped in pore space during early burial deepwater marine environment vs arid continental environment and b the depth temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development chemical reactions associated with smectite rich mud rocks in iran occur shallow 1900 m smectite to illite transformation causing load transfer related moderate overpressures whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore brunei the basal detachment in deepwater brunei generally lies below temperatures of about 150 c where chemical processes and metagenesis are inferred to drive overpressure development overall the deepwater brunei system is very water rich and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines the result is a wide variety of fluid migration pathways and structures from deep to shallow levels particularly mud dykes sills laccoliths volcanoes and pipes fluid escape pipes crestal normal faults thrust faults and widespread inflationary type overpressure in the central basin the near surface environment is water limited mechanical and chemical compaction led to moderate overpressure development above the upper red formation evaporites only below thick early miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms fluid leakage episodes across the evaporites have either been very few or absent in most areas locations where leakage can episodically occur e g detaching thrusts deep normal faults salt welds are sparse however in both iran and brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds

cyclic sedimentation in the eocene allenby formation of south central british columbia and the origin of the princeton chert fossil beds extensive deposits of eocene conglomerate sandstone shale and sub bituminous coal occur within a half graben at princeton british columbia these strata comprise 2000 m of fluvial sediment interbedded with tephra and volcanic flows near the southeast margin of the basin 200 m of rhythmically bedded strata are exposed along the similkameen river cyclic deposition resulted from repeated episodes of hydrologic and topographic change related to seismic activity along the boundary fault on the east flank of the princeton basin where allenby formation sediments are juxtaposed against metamorphic and metavolcanic rocks of the upper triassic nicola group interbedded carbonaceous shale and tuffaceous sandstone record influxes of distal lahar deposits into a lowland swamp coal breccia transitions originated when debris flows along the scarp carried volcanic debris into adjacent wetlands coal chert rhythmites are inferred to be evidence of hydrologic changes associated with floodplain tilt events that c

river incision or diversion in response to bedrock uplift introductionmany researchers have examined the long term behavior of alluvialrivers i e schumm et al 1987 snow and slingerland 1990 paola et al 1992 on long time scales alluvial rivers act as sediment transport systemsthat broadly deposit sediment over low areas in their basins i e tucker andslingerland 1996 the behavior of bedrock rivers is less well understood although most workers agree that bedrock erosion is some function of streampower howard and kerby 1983 seidl and dietrich 1992 howard et al 1994 accordingly researchers addressing a river s response to bedrock up lift equate incision with relatively high stream power and diversion with rela tively low stream power e g burbank et al 1996 however these studiesassume that the erosion rate of the bedrock channel across the mountainrange controls the eventual outcome they have not examined the behavior ofthe alluvial river upstream and downstream of the uplift we propose to lookat the entire erosional and depositional river system and examine the long term response of a coupled alluvial bedrock river system to tectonic uplift our motivation is general and aims at a greater understanding offluvial and tectonic interactions but our model is necessarily both specificand simplified the tectonic uplift of a bedrock massif into the path of a later ally unconstrained alluvial river such a scenario has two possible out comes either the river maintains its original course and incises through theuplift or the river diverts and forms a new course around the uplift a sig nificant complication in the analysis of this scenario is that the evolvingriver system is partial alluvial and partial bedrock channeled because thebehaviors of these two river types are different modeling requires couplingdiverse systems we construct an analytical model to perform a first orderanalysis of this coupled system our objective is to identify the specific fac tors that determine the final outcome of river diversion or incision our model focuses on long time scales 10

subaqueous silicification of the contents of small ponds in an early devonian hot spring complex rhynie scotland the early devonian rhynie and windyfield cherts of northeast scotland originated as siliceous sinters deposited by hot springs silicification affected both subaerial and subaqueous environments preserving a diverse terrestrial and freshwater biota cherts originally deposited in small shallow pools can be recognised on the basis of both texture and fossil content textures comprise clotted and microcoprolitic textures bacterial coatings on plant axes that can be stromatolitic and a variety of bacterial and fungal meshworks the crustacean lepidocaris the euthycarcinoid heterocrania the charophyte alga palaeonitella and chytrid fungi are typical elements of the aquatic biota observations of modern hot springs in yellowstone national park wyoming u s a demonstrate that shallow ponds and streams on low angle outwash areas and dormant vent orifices provide suitable environmental analogues textures comparable to those described from rhynie are recorded from yellowstone sinters but examples of the

relationship between spring and geyser activity and the deposition and morphology of high temperature 73 c siliceous sinter yellowstone national park wyoming u s a abstract six classes of alkaline hot springs and geysers are here distinguished in yellowstone national park based on activity and eruptive style 1 non surging non boiling springs 2 gently surging non boiling springs 3 non surging to gently surging boiling springs 4 strongly surging springs 5 fountain geysers and 6 cone geysers each displays morphologically distinctive siliceous sinter deposits in the high temperature 73 c parts of the vent and outflow systems non surging and gently surging non boiling springs that do not overflow their rims develop thin digitate to lilypad like sinter rims that grow horizontally over the pool surfaces similar springs with rim overflow have rims that accrete vertically boiling springs often have nearly circular steep sided pools and rims dominated by splash and rim overflow and composed mainly of spicular and columnar sinter fountain geysers characterized by broad fountain like eruption bursts have a central vent surrounded by a zone of spicular sinter beyond which is a broad flat bottomed moat but lack steep sinter cones cone geysers have narrow vents jet like discharges that cool rapidly and fall close to the vent and steep sided spicule dominated sinter cones sinter deposition takes place within three main zones 1 fully subaqueous sides and bottoms of vent pools outflow basins and outflow channels 2 periodically wetted splash zones surrounding hot springs and geysers and 3 largely subaerial parts of the rim and outflow areas wetted mainly by overflow and surging and that dry quickly fully subaqueous surfaces are covered by fine earthy particulate siliceous sediment pss composed largely of amorphous silica spherules and spherule aggregates that appear to have precipitated around heterogeneous nuclei including microbes splash zones of hot springs and geysers are characterized by spicular sinter largely subaerial zones wetted mainly by rim overflow and surging with little or no splash show complex varieties of terraced columnar and knobby sinter the highest silica deposition rates occur where surfaces are wetted frequently and evaporate to dryness such as the tops of spicules columns and knobs associated lower areas and crevices that remain wet or moist show slow accumulation of pss most continuously wet surfaces in high temperature 73 c hot spring and geyser vent and outflow systems are probably covered by microbial biofilms although microbes may locally influence rates of silica deposition and sinter microstructure the results of this study suggest that the depositional sites morphology and macrostructuring of high temperature sinter are controlled largely by the processes of surface wetting evaporation and drying

a devonian auriferous hot spring system rhynie scotland the early devonian rhynie hot spring system is the oldest known and is of the low sulphidation type it extends for at least 1 5 km along a major fault zone defining the western margin of an outlier of fluvial and lacustrine sediments plant bearing sinters and andesitic lavas the age of sedimentation and hydrothermal activity has been determined by palynological pragian and radio metric 396 12 ma techniques the outlier is a half graben with a complex stepped western margin the devonian rocks show intense hydrothermal alteration along the fault zone the main alteration minerals are quartz k feldspar calcite hematite and illitic and chloritic clays multiple chert veining and brecciation are widely developed and geyserite and vent material are also present pyrite occurs in veins and all alteration facies sinters and altered rocks contain high concentrations of au as sb hg w and mo gold occurs in arsenian pyrite and as sub micron particles in oxidized rocks the fluid s responsible for most hydrothermal alteration were near neutral with low sulphur and oxygen activities and dominated by meteoric water however incursions of high temperature 300 440 c magmatic fluids occurred with d 65 and 18 o around 8 5 34 s pyrite and initial 87 sr 86 sr ratios vein calcite lie mainly within the ranges 3 4 to 8 5 and 0 71138 to 0 71402 respectively these data indicate that late proterozoic dalradian metasediments are a likely source for s and sr but other sources are possible 13 c values for caliche and vein calcite imply derivation of carbon from non organic sources the rhynie cherts were deposited from a low salinity fluid of probable meteoric origin 18 o chert 13 1 to 16 5 which had interacted with the basement rocks and sediments high xe ar br cl and i cl ratios plant bearing chert yielded an 40 ar 39 ar ratio 292 1 0 6 significantly less than that of modem air and may be the first valid determination of a sample of ancient atmosphere

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

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

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

karst dissolution along fracture corridors in an anticline hinge jandaira formation brazil implications for reservoir quality abstract folded fractured and karstified structures have been recognized in several carbonate reservoirs however they are rarely fully identified from seismic or well data and have been poorly described the present study investigates the geological and structural controls that regional anticlines may exert on solution enlarged fracture corridors and epigenic karst concentrations in folded fractured carbonate units we performed regional mapping based on 106 2d seismic lines 51 well logs unmanned aerial vehicle uav imagery of four major outcrop sites i ii iii and iv and field investigations to parameterize fracture and karstic features density spacing length and aperture the study area is potiguar basin brazil where we identified the gentle ne trending apodi fold 10 km wide and 20 km long the fold formed along an inverted extensional fault during the latest miocene quaternary stress field and the envelope of the meandering trend of the apodi river coincides with the ne trending fold axis the fracture pattern in the fold hinge zone consists of two orthogonal syn folding fracture sets a ne sw striking hinge parallel set and an orthogonal nw se striking set these fractures and superposed karstification are mostly concentrated in the hinge zone along fracture corridors in an area 1 5 km wide and 20 km long we conclude that fracture corridors in anticline hinges are likely sites to have high fracture densities and wide apertures these corridors provide reservoir spaces that are favorable for the formation of karst cavities with significant increases in permeability and porosity along the fracture sets these features act as important fluid pathways and storage areas where matrix porosity is low the findings can be used for first order prediction in karstified carbonate reservoirs

distribution of joints in the hinge line culmination of foreland verging overturned anticlines an example from the montagna dei fiori structure in the central apennines of italym francioni et al distribution of joints in overturned anticlines the distribution of joints veins and shear fractures in the montagna dei fiori overturned anticline is here reported two joint sets longitudinal and transverse to the nnw sse anticline axial trend and a conjugate system of shear fractures are recognized the transverse and longitudinal joint sets have a pre folding development likely related to the foreland foredeep flexure the transverse joints were reopened during layer parallel shortening along with the development of the shear fractures then during syn folding outer arc extension and hinge line culmination fold axial parallel extension both the longitudinal and transverse joints were enhanced and reactivated respectively

testing the tectonic significance of some parameters of longitudinal river profiles the case of the ardenne belgium nw europe the longitudinal profiles of 24 rivers of 3rd to 5th order have been analyzed in order to recognize the regional tectonic differentiation pattern of the ardenne a paleozoic massif of nw europe data collected exclusively from 1 25 000 topographic maps were used to define a set of parameters related to the geometry of the profile and proxies for river bedload and drainage area validation of the proxy defined for the bedload discharge ratio demonstrates its potential use for inter river comparison based on its value at the river mouth it is however inadequate to estimate the ratio changes along a given stream course this proxy has been computed to estimate the portion accounted for by hydrodynamic factors in the river bed profiling thus outliers to the correlation function linking it to the river bed gradient have been considered as undergoing other influences principally of lithologic or tectonic origin most indicative of the computed profile parameters are those related to the concavity of the profile four more or less regional longitudinal profile types are recognized which are partly determined by differential tectonic movement the combined analysis of all the parameters confirms the current uplift of the ne ardenne and points to a subsidence of the namur area with respect to its sw and se surroundings whether periglacial or tectonic in origin the upper pleistocene lowering of a local base level has also been identified in the famenne another conclusion of this study is that in order to evidence tectonic influences and to avoid any misinterpretation in a region of complex geologic and geomorphic history and moderate tectonic activity it is essential to consider a number of parameters and to consider their significance within the framework of detailed geologic setting and morphogenetic history

in situ silicification of an icelandic hot spring microbial mat implications for microfossil formation transmission electron microscopy and energy dispersive x ray analysis revealed that filamentous phototrophic bacteria resembling chlorojlexus aurantiacus underwent rapid silicification in an icelandic hot spring microbial mat the mineralization associated with the cells occurred both extracellularly within and on the external sheaths of the bacteria and intracellularly within the cytoplasm the exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites this results in the production of silica casts of the bacteria which bear a striking resemblance to microbial remains in ancient microfossil assemblages rcsumc les analyses par microscopie clectronique i transmission et par 1 6nergie dispersive des rayons x ont rcvcl6 que les bactkries filamenteuses phototrophes ressemblant b chlorojlexus aurantiacus ont subi une silicification rapide au sein d un tapis microbien de source therrnale en islande la mineralisation associee aux cellules se presente sous forme extracellulaire b l interieur de et sur la membrane externe des bacteries et sous forrne intracellulaire i l interieur du cytoplasme la preservation exceptionnelle de la membrane des bacteries est due b la presence de sites de nucleation minerale disperses le resultat est la production des moulages siliceux des bactkries affichant une resemblance remarquable avec les vestiges microbiens d anciens assemblages microfossiles traduit par la raaction fossil evidence of the earth s earliest biosphere shows that complex communities of microorganisms were abundant and well distributed throughout the precambrian era among the richest beds of microbial fossils are those found in the gunflint iron formation north of lake superior in canada barghoorn and tyler 1965 the early archaean apex chert of australia schopf and packer 1987 schopf 1993 and the riphean section of the anabar uplift in russia sergeev 1993 all ranging in age from 0 8 to 3 5 ga the distribution and types of microorganisms preserved as cellularly intact microfossils are remarkably similar to those in modern microbial mats in which organic rich layers formed by cyanobacteria and or other types of filamentous bacteria alternate with layers that are comprised of detrital inorganic sediment and authigenic mineral precipitates morse and mackenzie 1990 these benthic microbial communities are considered to be analogous and possibly homologous with those that were preserved billions of years ago as stromato

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

structural and fluid evolution of saraburi group sedimentary carbonates central thailand a tectonically driven fluid system abstract a stable isotopic study focused on calcite cements vein fill calcite and various bioclasts was conducted on variably deformed and thrusted lower and middle permian carbonates of the saraburi group samples were collected in quarry faces across 3 areas in the saraburi lopburi region of central thailand stable isotope crossplots carbon and oxygen using texture aware isotope samples defined variable but related fluid cement histories which are tied to regional burial and then orogenic overprints driven by the indosinian triassic orogeny this was followed by telogenetic overprints driven by late cenozoic uplift the studied carbonates were deposited along the western margin of the indochina block where they were deposited as isolated calcareous algal sponge and fusilinid rimmed platforms on highs bound by extensional faults the platform areas passed laterally and vertically into more siliciclastic dominated sequences deposited in somewhat deeper waters within probable fault bound lows regional post depositional mesogenetic fluid rock re equilibration of the isotope values in ongoing calcite precipitates occurred until the matrix permeability was occluded via compaction and pressure solution this regional burial regime was followed by collision of the indochina and sibumasu blocks during the indosinian triassic blocks which drove a set of structurally focused thrust plane related increasingly warmer set of fluids through the studied sequences the final diagenetic overprint seen in the isotopic values of the latest calcite cements occurs in a telogenetic uplift setting driven by cenozoic tectonics and isostatic uplift integration of isotope data with its structural setting establishes a clear separation in fluid events related to two time separate tectonic episodes its fluid chemistry defines the permo triassic closure of the paleotethys and its subsequent reactivation during the tertiary collision of india and asia the c o covariant plot fields in the permian carbonates of central thailand are so distinct that it is possible to use their signatures to separate burial from meteoric cements in drill cuttings and hence recognise equivalent subsurface unconformities and likely zone of porosity development in possible buried hill plays in thailand

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

industrial structural geology principles techniques and integration an introduction the authors wish to acknowledge the generous financial support provided in association with this volume to the geological society and the petroleum group by badley geoscience ltd bp cgg robertson dana petroleum ltd getech group plc maersk oil north sea uk ltd midland valley exploration ltd rock deformation research schlumberger and borehole image core specialists wildcat geoscience walker geoscience and prolog geoscience we would like to thank the fine team at the geological society s publishing house for the excellent support and encouragement that they have provided to the editors and authors of this special publication

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

seismic potential of southern italy abstract to improve estimates of the long term average seismic potential of the slowly straining south central mediterranean plate boundary zone we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs we express seismic potential long term average earthquake recurrence rates as a function of magnitude in the form of truncated gutenberg richter distributions for seven seismotectonic source zones seismic coupling seems to be large or even complete in most zones an exception is the southern tyrrhenian thrust zone where most of the african european convergence is accommodated here aseismic deformation is estimated to range from at least 25 along the western part to almost 100 aseismic slip around the aeolian islands even so seismic potential of this zone has previously been significantly underestimated due to the low levels of recorded past seismicity by contrast the series of 19 m6 7 earthquakes that hit calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration and seismic potential is revised downward the southern tyrrhenian thrust zone and the extensional calabrian faults as well as the northeastern sicilian transtensional zone between them which includes the messina straits where a destructive m7 event occurred in 1908 all have a similar seismic potential with minimum recurrence times of m 6 5 of 150 220 years this potential is lower than that of the southern apennines m 6 5 recurring every 60 to 140 years but higher than that of southeastern sicily minimum m 6 5 recurrence times of 400 years the high seismicity levels recorded in southeastern sicily indicate some clustering and are most compatible with a tectonic scenario where the ionian deforms internally and motions at the calabrian trench are small the estimated seismic potential for the calabrian trench and central and western sicily are the lowest minimum m 6 5 recurrence times of 550 800 years most zones are probably capable of generating earthquakes up to magnitudes 7 7 5 with the exception of central and western sicily where maximum events sizes most likely do not exceed 7

epithermal sinters of paleozoic age in north queensland australia silica sinters deposited from hot springs have been found associated with volcanic rocks of late devonian to late carboniferous age in north queensland australia these deposits have many features in common with modern hot spring sinters such as those of the taupo volcanic zone in new zealand they occur associated with subaerial volcanic rocks and are locally found with air fall tuffs and fluvial and lake deposits in which hydrothermal eruption breccias are common the associated rocks are extensively hydrothermally altered and are cut by silica veins showing characteristic epithermal vein textures the silica veins contain low salinity fluid inclusions trapped at epithermal temperatures and there is evidence of boiling textures preserved in the sinters are identical to those found in modern sinters they include columnar structures similar to bacterial stromatolites described from yellowstone national park as well as striated surfaces apparently resulting from silica deposition on filamentous algae plant fossils including oxroadia gracilis are abundant criteria applied to identify these ancient sinters may be applied to other possible sinter deposits and may provide evidence indicating the level of exposure of the former geothermal system which may be an important guide in exploration for epithermal precious metal deposits

neotectonic effects on sinuosity and channel migration belle fourche river western south dakota short term instability in the behaviour of a small meandering alluvial channel is identified from the relation between sinuosity and either floodplain slope or channel slope within 17 reaches along an 81 kilometre section of the belle fourche river in western south dakota in reaches 1 to 4 and 11 to 17 the channel is relatively stable and sinuosity varies inversely with channel slope in reaches 5 to 10 sinuosity is positively related to floodplain slope sinuosity increases markedly in reaches 5 6 and 7 which are immediately downstream from a discontinuity in the long profile of the floodplain in association with an increase in floodplain slope immediately upstream from the discontinuity bankfull channel depth and sinuosity decrease and the area of the floodplain reworked by meander migration between 1939 and 1981 increases in association with a decrease in floodplain slope channel behaviour in reaches 5 to 10 is best explained as a consequence of neotectonic activity as indicated by changes in elevation recorded along geodetic survey lines that cross lineaments that may delimit the eastern boundary of the black hills uplift sinuosity acts as a barometer of the effects of neotectonic activity on alluvial channels initial indications of channel and floodplain instability due to neotectonic activity may be derived from evidence of anomalously active channel migration as documented from photographic or topographic sources

the interplay between fluids folds and thrusts during the deformation of a sedimentary succession abstract in this paper field evidence is presented to support the idea that fluid pressures in excess of lithostatic pressure were operating during the initiation and reactivation of large thrusts and folds in the wenlock shales of llangollen north wales it is also argued that as major thrusts are reactivated and as major folds amplify into finite structures they in turn exert an influence on the subsequent migration and concentration of fluids within the deforming sedimentary succession

microbial silica interactions in icelandic hot spring sinter possible analogues for some precambrian siliceous stromatolites silicified deposits such as sinters occur in several modern geothermal environments but the mechanisms of silicification and crucially the role of microorganisms in their construction are still largely unresolved detailed examination of siliceous sinter in particular sections of microstromatolites growing at the krisuvik hot spring iceland reveals that biomineralization contributes a major component to the overall structure with approximately half the sinter thickness attributed to silicified microorganisms almost all microorganisms observed under the scanning electron microscope sem are mineralized with epicellular silica ranging in thickness from 5 lm coatings on individual cells to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick within the overall profile there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite microbial layers are predominantly consisting of filamentous intact vertically aligned biomineralized cyanobacteria identified as calothrix and fischerella sp and weakly laminated silica layers which appear to be devoid of any microbial component the microbial layers commonly have a sharply defined base overlying the weakly laminated silica and a gradational upper surface merging into the weakly laminated silica these cyclic laminations are probably explained by variations in microbial activity active growth during spring summer allows the microorganisms to keep pace with silicification with the cell surfaces facilitating silicification while during their natural slow growth phase in the dark autumn winter months silicification exceeds the bacteria s ability to compensate i e grow upwards at this stage the microbial colony is probably not essential to microstromatolite formation with silicification presumably occurring abiogenically when conditions once again become favourable for growth recolonization of the solid silica surface by free living bacteria occurs cell motility is not responsible for the laminations we have also observed that microbial populations within the microstromatolite some several mm in depth appear viable i e they still have their pigmentation the trichomes are not collapsed cell walls are unbroken cytoplasm is still present and they proved culturable this suggests that the bulk of silicification occurred rapidly probably while the cells were still alive surprisingly however measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light pal only transmitted through the uppermost 2 mm therefore the deeper microbial

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

depositional facies and diagenetic alteration in a relict siliceous hot spring accumulation examples from yellowstone national park u s a abstract siliceous precipitates from portions of an 11 m long core drilled through a relict yellowstone hot spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment most of the core consists of relatively low temperature siliceous sinter containing abundant plant diatom and microbial fossilized remains derived from the distal debris apron and discharge channel flowpath of the hot spring a few intervals contain stromatolitic horizons analogous to modern siliceous pool margin and discharge channel flowpath facies despite the abundance of silicified microbial remains e g silicified stromatolitic horizons as well as individual filamentous microbes diatoms distinctive organic biomarkers are not preserved in the core the apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high temperature chemically reactive fluids numerous diagenetic features have been superimposed on the siliceous sinter especially considering the relatively shallow depths of burial the uppermost interval 0 to 1 2 m consists of highly porous siliceous sinter opal a and interbedded travertine amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval below is a diagenetic facies 4 8 to 5 3 m that consists of opal ct and minor chalcedony the most pervasive diagenetic alteration in the core is the 6 8 to 11 2 m depth interval where abundant zeolites mordenite heulandite bladed cristobalite lepispheres chalcedony cements and calcite veins are present judging by the assemblage of plant and diatom remains most of this pervasive alteration is superimposed on relatively low temperature siliceous sinters and is likely the result of migration of hot waters through this interval the paragenesis of all these intervals is very complex involving numerous episodes of mineral precipitation and dissolution this diagenetic alteration is facilitated by the porous nature of the siliceous sinter thermal convection of superheated fluids or steam strongly oxidizing spring waters and fluctuating hydrochemical regimes rapid dissolution and or replacement of organic matter indicates that standard morphological means e g petrographic identification of body fossils may be the best method by which to identify that organisms were previously present in ancient hot spring accumulations

regional and local vegetation community dynamics of the eocene okanagan highlands british columbia washington state from palynology palynofloras from the middle early to early middle eocene okanagan highlands northern washington state and southern british columbia are used to reconstruct vegetation across a broad upland eocene landscape in this preliminary report forest floristic composition is reconstructed using palynological analysis of sediments from republic washington localities of the allenby formation in the princeton region hospital hill one mile creek and summers creek road hat creek mcabee falkland horsefly and driftwood canyon british columbia wind dispersed taxa were dominant in all samples consistent with floras preserved in lacustrine and paludal depositional environments pseudolarix was dominant in five of the floras but abies falkland or ulmus republic corner lot site were dominant in individual samples for some floras betulaceae were dominant for mcabee alnus and allenby formation betula matching megafloral data for these sites some taxa common to most sites suggest cool conditions e g

seasonal changes in silica deposition in hot spring systems abstract monthly monitoring of water chemistry at octopus spring yellowstone national park reveals no changes in the chemical composition over this eight month study differences in silica deposition are attributed to flow dynamics and seasonal air temperatures colder air temperatures in winter promote visible accumulation of siliceous sinter probably as a result of decreased solubility periodic drying promotes accumulation and subsequent dehydration of the silica this combination of intermittent supply and periodic dehydration may account for the laminated siliceous deposits observed in the geological record the processes described herein are important in the siliceous preservation of microbial fossils but the following observations underscore the difficulty in preserving microbial fabrics in the geological record pools populated by cyanobacteria are bounded by margins built of silicified microbial mats silicification of the pool margins occurs through an evaporative process called wicking silica rich water is transported upward through the microbial mats by capillary action depositing silica at the surface of the mat as water evaporates the upper surface of such wicking deposits is extremely resistant to brecciation but the underlying support is highly friable and would be difficult to preserve intact in winter months temporary isolation of some pools from active flow causes fragile silica deposition around biological and other debris film coated gas bubbles on the surfaces of microbial mats are observed during all seasons and probably are filled with oxygen released during photosynthesis although this has not been confirmed they become coated with silica during winter months presumably because of increased cooling possibly forming thin discontinuous silica sheets as observed in the geological record