crustal migration of co2 rich magmatic fluids recorded by tree ring radiocarbon and seismicity at mammoth mountain ca usa unrest at mammoth mountain over the past several decades manifest by seismicity ground deformation diffuse co2 emissions and elevated he3 he4 ratios in fumarolic gases has been driven by the release of co2 rich fluids from basaltic intrusions in the middle to lower crust recent unrest included the occurrence of three lower crustal 32 19 km depth seismic swarms beneath mammoth mountain in 2006 2008 and 2009 that were consistently followed by peaks in the occurrence rate of shallow 10 km 10 km depth earthquakes we measured c14 in the growth rings 1998 2012 of a tree growing in the largest 0 3 km2 0 3 km2 area of diffuse co2 emissions on mammoth mountain the horseshoe lake tree kill hltk and applied atmospheric co2 concentration source area modeling to confirm that the tree was a reliable integrator of magmatic co2 emissions over most of this area the tree ring c14 record implied that magmatic co2 emissions from the hltk were relatively stable from 1998 to 2009 nearly doubled from 2009 to 2011 and then declined by the 2012 growing season the initial increase in co2 emissions was detected during the growing season that immediately followed the largest february 2010 peak in the occurrence rate of shallow earthquakes migration of co2 rich magmatic fluids may have driven observed patterns of elevated deep then shallow seismicity while the relationship between pore fluid pressures within a shallow upper 3 km of crust fluid reservoir and permeability structure of the reservoir cap rock may have controlled the temporal pattern of surface co2 emissions

early cretaceous sediment failure in the southwestern sable subbasin offshore nova scotia conventional cores from lower cretaceous outer shelf and upper slope prodelta facies in the alma and glenelg fields of the scotian basin show a wide range of synsedimentary deformation storm dominated prodelta sandstone and mudstone beds have common load casts and structureless sandstone beds overlain by deformed sediment and sandstone dykes that are caused by storm or earthquake induced local liquefaction blocks of sediment 5 15 m 15 50 ft thick principally on the outer shelf have foliated mudstone at their base common internal shear zones in mudstone shear deformation of sandstone and are capped by intraclast conglomerates that are interpreted as debris flow deposits these are all features observed in shallow slides on the modern mississippi prodelta at the paleoshelf edge and upper slope larger slide blocks are recognized with zones of intense internal deformation and high angle thrusts near their base the lack of a basal foliated mudstone may be the result of more rapid slide motion than on the shelf resulting in hydroplaning in addition there is early postdepositional interstratal deformation as a result of loading by sandy delta distributaries and by slide blocks on the upper slope the scale of many deformation structures is below the limits of three dimensional seismic vertical resolution yet they are likely to substantially influence reservoir properties

source characterization for an explosion during the 2009 eruption of redoubt volcano from very long period seismic waves abstract the 2009 eruption of redoubt produced several very long period vlp signals associated with explosions we invert for the source location and mechanism of an explosion at redoubt volcano using waveform methods applied to broadband recordings such characterization of the source carries information on the geometry of the conduit and the physics of the explosion process inversions are carried out assuming the volcanic source can be modeled as a point source with mechanisms described by a a set of 3 orthogonal forces b a moment tensor consisting of force couples and c both forces and moment tensor components we find that the source of the vlp seismic waves during the explosion is well described by either a combined moment force source located northeast of the crater and at an elevation of 1 6 km asl or a moment source at an elevation of 800 m to the southwest of the crater the moment tensors for the solutions with moment and force and moment only share similar characteristics the source time functions for both moment tensors begin with inflation pressurization and execute two cycles of deflation reinflation depressurization repressurization although the moment force source provides a better fit to the data we find that owing to the limited coverage of the broadband stations at redoubt the moment only source is the more robust and reliable solution based on the moment only solution we estimate a volume change of 19 000 m3 and a pressure change of 7 mpa in a dominant sill and an out of phase volume change of 5000 m3 and pressure change of 1 8 mpa in a subdominant dike at the source location these results shed new light on the magmatic plumbing system beneath redoubt and complement previous studies on vulcanian explosions at other volcanoes

the detection of low magnitude seismic events using array based waveform correlation summary it has long been accepted that occurrences of a known signal are most effectively detected by cross correlating the incoming data stream with a waveform template such matched signal detectors have received very little attention in the field of detection seismology because there are relatively few instances in which the form of an anticipated seismic signal is known a priori repeating events in highly confined geographical regions have been observed to produce very similar waveforms and good signals from events at a given site can be exploited to detect subsequent co located events at lower magnitudes than would be possible using traditional power detectors even greater improvement in signal detectability can be achieved using seismic arrays running correlation coefficients from single sensors can be stacked over an array or network to result in a network correlation coefficient displaying a significant array gain if two events are co located the time separating the corresponding patterns in the wave train as indicated by the cross correlation function is identical for all seismic stations and this property means that the correlation coefficient traces are coherent even when the waveforms are not we illustrate the power of array based waveform correlation using the 1997 august 16 kara sea event the weak event that occurred 4 hr after the main event was barely detected using an sta lta detector on the spits array but is readily detected by signal matching on a single channel the main event was also recorded by the far more distant norsar array but no conventional detection can be made for the second event a clear detection is however made when the correlation coefficient traces are beamformed over all sensors of the array we estimate the reduction in detection threshold of a test signal on a regional seismic array using waveform correlation by scaling down a master signal and immersing it into seismic noise we show that for this case waveform correlation using a single channel detects signals of approximately 0 7 orders of magnitude lower than is possible using an sta lta detector on the array beam waveform matching on the full array provides an additional improvement of approximately 0 4 magnitude units we describe a case study in which small seismic events at the barentsburg coal mine on spitsbergen were detected using the signals from a major rockburst as master waveforms many spurious triggers occurred in this study whereby short sections of signal exhibited coincidental similarity with unrelated incoming wave fronts we demonstrate how such false alarms can almost always be identified and screened out automatically by performing frequency wavenumber analysis upon the set of individual correlation coefficient traces

cementation and porosity evolution of tight sandstone reservoirs in the permian sulige gas field ordos basin central china abstract tight sandstone gas reservoirs constitute an important type of unconventional gas resources and may be of crucial significance as environment friendly source of energy in the world however the dynamics of densification and evolution of the low porosity and low permeability sandstone reservoirs are intensively debated in literature recently the question of sequence of reservoir densification and hydrocarbon accumulation has arisen a typical tight sandstone reservoir the first member of the shanxi formation and the eighth member of shihezi formation in the permian sulige gas field in central china provides an excellent case study to probe these questions by using a variety of different methodologies such as scanning electron microscopy sem x ray diffraction xrd cathodoluminescence fluid inclusion analysis and confocal raman spectrometer analysis we identified different authigenic minerals such as illite kaolinite dickite chlorite and smectite illitization coexisting with siliceous and calcitic cements these authigenic minerals precipitated at different diagenetic stages related to the changing conditions during compaction and lithification and therefore changed the porosities of the host rocks during each of these stages the types of pores in the sulige gas field are dominated by illite and kaolinite intercrystalline pores matrix solution pores and primary intergranular pores the results of this study suggest that compaction and cementation are the reasons for the most distinct loss in porosity on the other hand kaolinite and illite preserve their intercrystalline pores which could be identified as the main reserve space of the tight gas reservoirs therefore the secondary porosity of the sandstone reservoirs forms the most important contributor to the gas reservoir potential in the sulige gas field in addition it could be inferred that the tight gas accumulation took place during the densification of the reservoirs the implications of the presented results may also help to understand the formation of other tight reservoirs world wide

facies provenance and paleoclimate interpretation using spectral gamma logs application to the lower cretaceous of the scotian basin abstract spectral gamma logging has been useful in some settings for correlation of wells for identification of sediment facies and for interpretation of hinterland paleoclimate we have taken advantage of the hundreds of geochemical analyses of sandstones and shales from conventional core that are available from the scotian basin to test the relationship of the elements k u and th measured by spectral gamma to sedimentary facies these elements are also known to be useful in characterising provenance of sediment to different parts of the basin the geochemical and spectral gamma data both show that there are subtle differences in k u and th in different lithofacies such as higher th u in low sedimentation rate facies but they are not sufficiently distinctive to identify the lithofacies of any unknown interval the main control on abundance of these elements is the effect of grain size that is the proportion of sand to mud in sediment volcanic sources have a high k th ratio and early albian sediments with relatively high volcanic component have unusually high k th in distal shale prone successions the grain size effect is sufficiently small that climate controlled variations in th k ratio are recognised in the early cretaceous with the ratio being higher at times of humid weathering on land the variations in th k ratio through time are broadly similar to those known from western european sections notably with topmost hauterivian and topmost aptian humid events overall this study provides an assessment of the use and pitfalls of spectral gamma logs in a deltaic succession

diagenetic alterations and reservoir heterogeneity within the depositional facies a case study from distributary channel belt sandstone of upper triassic yanchang formation reservoirs ordos basin china abstract diagenesis is of decisive significance for the reservoir heterogeneity of most clastic reservoirs linking the distribution of diagenetic processes to the depositional facies and sequence stratigraphy has in recent years been discipline for predicting the distribution of diagenetic alterations and reservoir heterogeneity of clastic reservoirs this study constructs a model of distribution of diagenetic alterations and reservoir heterogeneity within the depositional facies by linking diagenesis to lithofacies sandstone architecture and porewater chemistry during burial this would help to promote better understanding of the distribution of reservoir quality evolution and the intense heterogeneity of reservoirs based on an analogue of deltaic distributary channel belt sandstone in upper triassic yanchang formation 83 sandstone plug samples were taken from 13 wells located along this channel belt an integration of scanning electron microscopy thin sections electron microprobe analyses rate controlled porosimetry rcp gas flow measurements of porosity and permeability and nuclear magnetic resonance nmr experiments together with published data were analysed for the distribution mineralogical and geochemical characteristics of detrital and diagenetic components and the distribution of reservoir quality within the distributary channel belt distribution of diagenetic alterations and reservoir heterogeneity within the distributary channel belt sandstones include i formation of high quality chlorite rims in the middle part of thick sandstones with coarser grain sizes and a lower content of ductile components resulted from the greater compaction resistance of these sandstones providing larger pore spaces for chlorite growth leading to formation of the intergranular pore wide sheet like throat and intergranular pore intragranular pore wide sheet like throat 15 k 1md in the middle part of thick sandstones ii formation of thinner chlorite rims in the middle part of thinner sandstones is associated with the intergranular pore intragranular pore narrow sheet like throat 9 18 o vpdb 23 4 to 16 6 13 c vpdb 4 0 to 2 3 favoured in the top and bottom of the channel sandstone which near the sandstone mudstone bouding surface destroying pore space

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

geology and diagenetic history of overpressured sandstone reservoirs venture gas field offshore nova scotia canada deep exploratory wells in the scotian basin offshore nova scotia canada have encountered overpressured formations with pressures 1 9 x the normal hydrostatic gradient the overpressures occur over an area of approximately 10 000 sq km in the venture field the abnormal pressures are confined below a depth of 4500 m and are associated with upper jurassic lower cretaceous gas and condensate bearing sandstone reservoirs the overpressures occur within normally compacted shales containing numerous overpressured sandstone reservoir beds the development of overpressures seals and secondary reservoirs are all diagenetically driven the volumetric increase achieved by kerogen to petroleum gas conversion and hydrocarbon expulsion are believed to be the main driving forces or venture overpressures three secondary porosity depth levels which top at 2500 m 65 degrees c 3700 m 95 degrees c and 4600 m 130 degrees c correlate with major steps in the organic matter maturation in the basin secondary porosity is initially achieved by alumosilicate dissolution with ferroan sparry calcite cement dissolution dominating below 4000 m porosity enhancement and preservation is not the result of a single diagenetic event but instead the result of a series of diagenetic events that overlapped in time formation of dynamic diagenetic barriers within the zone of peak gas generation helps retard the diffusive migration of hydrocarbons and other fluids expelled during shale diagenesis resulting in pressure build up the preservation of up to 32 percent porosity under 500 1000 atm of pressure could not be achieved without simultaneous pressuring of developing voids thus the expansion of secondary reservoirs in the overpressured zone also had to be late 50 ma or younger and about synchronous with pressurizing of the reservoirs significant for hydrocarbon exploration is that venture type diagenetic overpressures are not associated with undercompacted sediments and hence they cannot be predicted from compaction trends during drilling petrographic diagenetic and lithofacies studies can be instrumental in predicting potential areas of deep subsurface secondary reservoirs development

facies related diagenesis and multiphase siderite cementation and dissolution in the reservoir sandstones of the khatatba formation egypt s western desert in the fluvio deltaic quartz arenitic sandstones of the jurassic khatatba formation in the salam field egypt9s western desert diagenesis and sedimentary facies control reservoir quality fluvial channel sandstones have the highest porosities 10 15 and permeabilities 100 600 md in part because of siderite cementation which 1 inhibited compaction and quartz cement and 2 was later dissolved creating intergranular secondary porosity 1 4 of total porosity fluvial crevasse splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolin matrix and pervasive shallow burial fe dolomite cement respectively siderite precipitation was multiphase and separated by distinct dissolution events the earliest siderite precipitated near surface within suboxic tropical coastal swamps containing predominantly meteoric waters some influence of marine waters is indicated by local enrichments in mg and ca the next major siderite generation shows a trend to decreasing mn and ca contents and is of shallow burial origin the last major siderite phase is mg rich and interpreted as deeper burial in origin some dissolution occurred during shallow burial related to climatically controlled meteoric water fluxing under unconformities the most important dissolution however occurred during deep burial resulting in 1 a major corrosion surface predating the last mg rich zone 2 selective dissolution of some earlier zones and 3 secondary porosity this burial dissolution is interpreted to have been caused by cooling of compactional waters expelled from the basin along major faults other diagenetic phases observed include early diagenetic pyrite kaolin quartz bitumen and late diagenetic barite and illite kaolinite precipitated at shallow depths 130 c during and or after rapid late cretaceous burial quartz developed in two phases separated by oil migration this paper illustrates that in fluvio deltaic quartz arenites deposited under the influence of humid tropical climate reservoir quality can be largely controlled by the contrasting pathways of carbonate diagenesis followed by the different sedimentary facies this paper also documents a case in which siderite dissolution generated significant secondary porosity in reservoir sandstones and where both siderite cementation and dissolution took place in multiple phases during different diagenetic stages including early shallow burial and deep burial diagenesis the present study also shows that in multiphase siderite cements the earlier growth zones can be selectively dissolved and replaced by later siderite zones i e recrystallized during burial diagenesis these findings contrast with the general thought that siderite cements are not susceptible to generation of significant secondary porosity by dissolution and that earlier formed siderites are essentially stable during diagenesis

impact of sequence stratigraphy depositional facies diagenesis and co2 charge on reservoir quality of the lower cretaceous quantou formation southern songliao basin china abstract the fourth member of the lower cretaceous quantou formation in southern fuxin uplift zone of the southern songliao basin is typical tight oil reservoir which has recently been explored and produced for effective exploration and development the evaluation and control factors of the reservoir quality of the k1q4 sandstones should be thoroughly studied the study focused on the control of the combination of sequence stratigraphy depositional facies and diagenesis on the reservoir quality and identified the impact of co2 charging based on the core and thin section observation xrd sem fluid inclusion and isotope testing and analysis the fourth member of the lower cretaceous quantou formation consists of lowstand system tracts lst transgressive system tracts tst and highstand system tracts hst the k1q4 sandstones were mostly deposited in distributary channels and crevasse splays of a delta plain within the lst and tst and underwater distributary channels and sheet sands of a delta front within the hst the k1q4 sandstones mostly silt to medium grained medium to well sorted and are mostly lithic arkoses and feldspathic litharenites have undergone significantly diagenetic alterations such as compaction quartz cementation unstable grains feldspar and volcanic fragments dissolution carbonate cementation and clay minerals cementation the reservoir quality of the k1q4 sandstones are poor with low porosity and permeability showing variations among the different system tracts and depositional facies and are influenced by the charging of co2 and controlled by the combination of sequence stratigraphy depositional facies and diagenesis the sandstones with high reservoir quality are mostly deposited in high energy environments including the underwater distributary channel sandstones especially the lst distributary channel sandstones with the best reservoir quality among the lst tst and hst sandstones which can be ascribed to larger grain size and better sorting resulting in larger intergranular pore space after compaction and less content of carbonate cements illite and mixed layer i s and more pore lining chlorite and more effectively dissolution the poor reservoir quality of sandstones from crevasse splay and sheet sand is due to the small grain size and bad sorting which resulted in extensive compaction and the resulting weak dissolution the charging of co2 has dual impact on the reservoir quality of the k1q4 sandstones the co2 charging can induce the dissolution of unstable detrital grains and the precipitation of dawsonite the former create new secondary pore space while the latter occupy the intergranular pore space the co2 charging is harmful to the reservoir quality when the dawsonite content exceeds a threshold of 5

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

early diagenesis of inner shelf phosphorite and iron silicate minerals lower cretaceous of the orpheus graben southeastern canada implications for the origin of chlorite rims wells in the orpheus graben encountered the most proximal part of the deltaic lower cretaceous rocks of the scotian basin more distal sandstones are important gas reservoir rocks with good reservoir quality where fe rich chlorite chamosite rims on framework grains have inhibited quartz cementation cutting samples from the orpheus graben show the presence of fe rich sheet silicates berthierine or chamosite and early diagenetic phosphorite these minerals were analyzed by electron microprobe and their textures were mapped with backscattered electron images studies in the north sea have shown a relationship between high phosphorus and the presence of good chlorite rims in reservoir rocks the mineralization of pore water phosphorus instead of its return to seawater is favored by fe rich sediments and sorption on iron oxides during shallow sea floor diagenesis the fe ti and p contents are uncommonly high in scotian basin shales compared with global average shale compositions the uncommon occurrence of inner shelf phosphorite in this study is interpreted to be a consequence of the same high fe content of the sediment that also favors the formation of fe rich sheet silicates in rapidly deposited deltaic sandstones of the offshore reservoirs the dominance of type 3 kerogen led to sulfate depletion occurring at depths of tens of meters and a corresponding great thickness for overlying eh oxidation potential controlled diagenetic zones the thick fe reduction zone allowed the formation of early diagenetic berthierine which on burial formed the chamosite rims that resulted in the improved reservoir quality in sandstones the distribution of phosphorus minerals may be an indicator of conditions suitable for berthierine formation

coated phosphate grains proxy for physical chemical and ecological changes in seawater irrespective of geologic age phanerozoic coated phosphate grains deposited beneath productive surface waters in organic rich paleoenvironments are of only two types unconformity bounded grains contain internal discordances and erosional surfaces attributable to multiple episodes of phosphogenesis and sedimentary reworking during periods of stratigraphic condensation redox aggraded grains consist of concordant concentric phosphate laminae that are intimately interlayered with circumgranular layers containing pyrite chamosite or barite recording in situ diagenetic mineralization driven by changes in pore water redox potential such changes can be attributed to variations in biological oxygen demand within suboxic pore water environments resulting from fluctuations in sedimentation rate of organic carbon redox aggraded grains are thus sensitive indicators of variations in organic carbon export and record changes in primary productivity and or ecological dynamics of the surface ocean this concept of coated grain formation necessitates a long residence time just below the sediment water interface if sedimentation rate is too high grains are rapidly buried and so removed from the zone of active phosphate precipitation coated phosphate grains can therefore be considered the granular equivalents of condensed beds these concepts are equally applicable to the interpretation of other types of coated grains and concretions that contain eh sensitive minerals such as iron bearing ooids and polymineralic concretions

the 1998 1999 seismic series at deception island volcano antarctica abstract during the 1998 1999 antarctic summer the pattern of seismic activity at deception island volcano changed significantly the change was characterized by the occurrence of an intense swarm of volcano tectonic vt earthquakes more than 2000 vt earthquakes with s p times smaller than 4 s were recorded in the period january february 1999 pure volcanic events were also detected especially long period lp events volcanic tremor and some hybrid events seismic monitoring was performed using two short period small aperture arrays among other instruments based on their signal to noise ratios we selected 863 vt earthquakes 350 lp events and tremor episodes and 9 hybrid events for analysis we estimated apparent slowness and back azimuth for all events using the zero lag cross correlation array technique combining this information with s p times and other indirect evidence we identified two different source regions lp seismicity is located less than 1 1 5 km southwest of the fumarole array site these events are likely to have a hydrothermal origin vt earthquakes and hybrid events are located at depths of 0 3 10 km in an area under the bay of deception island the area extends from the fumarole array to the northeast with epicentral distances that range from 0 5 to 12 km most hypocenters are clustered in a small volume of around 8 km3 the sources of the lp seismicity and the vt earthquakes are spatially distinct which indicates that they are not produced by the same mechanisms moment magnitude analyses of the vt earthquakes provide an average magnitude of 0 5 and very low average stress drop around 1 bar a study of first motion of the p waves suggests that the events in this small source region should have a variety of source mechanisms this is supported by the existence of families of events with the same waveforms the occurrence of repeating fracture processes with low stress drop and small fault dimensions can be explained by the lubrication of pre existing zones of weakness by pressurized fluids the most probable hypothesis that explains the generation of this seismic series at deception island is a seismic series caused by the stress generated by the uplift of the source area due to a magmatic injection in depth we favor this hypothesis since it is compatible with the majority of the characteristics of the seismicity and explains the spatial and temporal behavior of the series

seismic source mechanism of degassing bursts at kilauea volcano hawaii results from waveform inversion in the 10 50 s band the current march 2008 to february 2009 summit eruptive activity at kilauea volcano is characterized by explosive degassing bursts accompanied by very long period vlp seismic signals we model the source mechanisms of vlp signals in the 10 50 s band using data recorded for 15 bursts with a 10 station broadband network deployed in the summit caldera to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account the vlp signals associated with the bursts originate in a source region 1 km below the eastern perimeter of halemaumau pit crater the observed waveforms are well explained by the combination of a volumetric component and a vertical single force component for the volumetric component several source geometries are obtained which equally explain the observed waveforms these geometries include 1 a pipe dipping 64 to the northeast 2 two intersecting cracks including an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east 3 a pipe dipping 58 to the northeast intersecting a crack dipping 48 to the west southwest and 4 a pipe dipping 57 to the northeast intersecting a pipe dipping 58 to the west southwest using the dual crack model as reference the largest volume change obtained among the 15 bursts is 24 400 m3 and the maximum amplitude peak to peak of the force is 20 gn each burst is marked by a similar sequence of deflation and inflation trailed by decaying oscillations of the volumetric source the vertical force is initially upward synchronous with source deflation then downward synchronous with source reinflation followed by oscillations with polarity opposite to the volumetric oscillations this combination of force and volume change is attributed to pressure and momentum changes induced during a fluid dynamic source mechanism involving the ascent expansion and burst of a large slug of gas within the upper 150 m of the magma conduit as the slug expands upon approach to the surface and more liquid becomes wall supported by viscous shear forces the pressure below the slug decreases inducing conduit deflation and an upward force on the earth the final rapid slug expansion and burst stimulate vlp and lp oscillations of the conduit system which slowly decay due to viscous dissipation and elastic radiation consideration of the fluid dynamic arguments leads us to prefer the dual crack vlp source model as it is the only candidate model capable of producing plausible values of length scales and pressure changes the magnitudes of the vertical forces observed in the 15 bursts appear consistent with slug masses of 104 to 106 kg

distribution of diagenetic alterations in siliciclastic shoreface deposits within a sequence stratigraphic framework evidence from the upper jurassic boulonnais nw france the distribution of diagenetic alterations in upper jurassic siliciclastic shoreface sediments from nw france has been linked to the sequence stratigraphic framework calcite cement in mudrocks and sandstones of the transgressive tst and lower part of the highstand hst systems tracts is microcrystalline and occurs as continuously cemented layers and stratabound concretions the average delta 18 o v pdb 2 6 omicron and sr 87 sr 86 0 7078 compositions of microcrystalline calcite indicate precipitation from largely marine pore waters calcite cement in sandstones of the forced regressive wedge frwst and lowstand lst systems tracts is poikilotopic and occurs mainly as stratabound concretions complete dissolution of the carbonate grains and concomitant precipitation of poikilotopic calcite cement with low average delta 18 o 5 3 omicron and radiogenie sr isotope 0 70882 signatures suggest incursion of meteoric waters into sandstones during relative sea level lowstand the poorly lithified sandstones interbedded with sandstones cemented by poikilotopic calcite concretions display evidence of diagenesis under episodes of and to semiarid paleoclimate including i partial cementation by opal chalcedony gypsum and minor vadose calcite cement ii mechanically infiltrated clays and fe oxides and iii secondary porosity owing to partial dissolution of carbonate grains the integration of diagenesis into sequence stratigraphy allows better elucidation and prediction of the spatial and temporal distribution of diagenetic alterations and related reservoir quality modifications in shoreface sediments

source mechanism of vulcanian degassing at popocatepetl volcano mexico determined from waveform inversions of very long period signals 1 the source mechanism of very long period vlp signals accompanying volcanic degassing bursts at popocatepetl is analyzed in the 15 70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium the waveforms of two eruptions 23 april and 23 may 2000 representative of mild vulcanian activity are well reproduced by our inversion which takes into account volcano topography the source centroid is positioned 1500 m below the western perimeter of the summit crater and the modeled source is composed of a shallow dipping crack sill with easterly dip of 10 intersecting a steeply dipping crack northeast striking dike dipping 83 northwest whose surface extension bisects the vent both cracks undergo a similar sequence of inflation deflation and reinflation reflecting a cycle of pressurization depressurization and repressurization within a time interval of 3 5 min the largest moment release occurs in the sill showing a maximum volume change of 500 1000 m3 pressure drop of 3 5 mpa and amplitude of recovered pressure equal to 1 2 times the amplitude of the pressure drop in contrast the maximum volume change in the dike is less 200 300 m3 with a corresponding pressure drop of 1 2 mpa and pressure recovery equal to the pressure drop accompanying these volumetric sources are single force components with magnitudes of 108 n consistent with melt advection in response to pressure transients the source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds such source behavior is consistent with the opening of a pathway for escape of pent up gases from slow pressurization of the sill driven by magma crystallization the opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles assuming a penny shaped crack at ambient pressure of 40 mpa the observed pressure and volume variations can be modeled with the following attributes crack radius 100 m crack aperture 5 m bubble number density 1010 1012 m 3 initial bubble radius 10 6 m final bubble radius 10 5 m and net decrease of gas concentration in the melt 0 01 wt

a new conceptual model for the structural evolution of a regional salt detachment on the northeast scotian margin offshore eastern canada in this study we examine using seismic data in conjunction with numerical modeling a regional scale salt detachment and associated synkinematic sediments from the scotian margin offshore eastern canada this part of the scotian margin is characterized by an up to 4 5 km 2 8 mi thick and approximately 175 km 108 mi long synkinematic wedge of jurassic sediments with internal sigmoidal landward dipping reflectors the synkinematic wedge is laterally extensive encompassing an area of approximately 30 000 km2 11 600 mi2 and soles into an interpreted salt detachment the jurassic synkinematic wedge which is interpreted to have formed as an open ended allochthonous salt nappe was loaded by prograding sediments during the jurassic this loading squeezed the salt seaward and caused the overlying sediments to undergo extension and gravity spreading and gliding detaching on the salt sheet the open ended nappe model provides a mechanism for producing a large amount of extension with very little compensating contraction numerical model results indicate that high rates of extension detaching on even a thin salt layer can result in similar sigmoidal landward dipping strata based on the numerical modeling and seismic interpretation results we propose a new conceptual model for the jurassic paleogene structural evolution of the study area this model may also have implications for other passive margin salt basins with regional salt detachments

controls on diagenesis of lower cretaceous reservoir sandstones in the western sable subbasin offshore nova scotia abstract lower cretaceous deltaic sandstones of the scotian basin offshore eastern canada are important gas reservoirs the influence of several factors on diagenesis has been investigated depositional lithofacies sea level changes chemistry of basinal sediments and basinal fluid flux during burial the distribution and chemistry of diagenetic minerals was determined from nine wells located along a dip section of the sable subbasin mineral type and paragenesis were characterized using a combination of optical petrography back scattered electron images and electron microprobe analyses siderite is unusually abundant in marine sediments of the scotian basin and has thus been studied in detail siderite occurs in several generations early and late siderites are similar in chemical composition suggesting buffering by pre existing siderite but rare low mg siderite is related to a greater contribution of meteoric water siderite has locally dissolved to create microporosity and has suppressed quartz overgrowths siderite is most common in those muddy prodeltaic lithofacies where there is the highest availability of detrital ilmenite reactive fe released by breakdown of this ilmenite is responsible for the unusual presence of early siderite in marine sediments with the ca and mg content of the siderite indicating fully marine waters lithofacies have a strong influence on early diagenetic mineral assemblages lithofacies deposited in the transgressive system tract have abundant early fe calcite and siderite early kaolinite occurs principally in proximal fluvial and river mouth lithofacies where meteoric water was most likely available during the deposition contrary to other studies we find little impact of sequence stratigraphy on diagenetic minerals except in the transgressive system tract mesogenetic minerals are related to flux of formation water and maturing hydrocarbon products resulting first in pyrite and siderite and later in ankerite and ferroan calcite the principal controls are interpreted to be high fe 2 and low ca 2 of formation waters and vertical movement of the waters along faults overall the bulk chemical composition of terrigenous sediments and the depositional lithofacies are the most important factors controlling diagenetic minerals in the lower cretaceous of the scotian basin

glacier advances in northeastern turkey before and during the global last glacial maximum abstract our study in the basyayla valley in northeastern anatolia showed evidence of four glacier advances that built terminal and lateral moraines surface exposure dating of boulders on these moraines showed that the maximum ice extent mie was asynchronous with the global last glacial maximum lgm 22 1 4 3 thousand years ka the local mie took place at least 57 0 3 5 ka ago the extent of the basyayla glacier during this advance is not known exactly because the boulders are only preserved on a lateral moraine the next advance was prior to 41 5 2 5 ka and it descended down the valley to approximately 2320 m above sea level m a s l with a glacier length of 5 3 km during the early global lgm the basyayla glacier extended for a distance of 4 9 km down to approx 2430 m a s l the last recorded advance occurred during the global lgm this extension was 0 7 km smaller than the local mie and its terminus reached 2490 m a s l only the exposure ages of boulders in a retreat position at an altitude of approx 3045 m a s l indicate that the valley has remained ice free since the lateglacial period therefore the lateglacial extent was limited to the cirque system in the uppermost part of the catchment furthermore holocene glacier oscillations seem to be either absent or restricted to solifluction in the whole catchment and to rock glacier movements in the southern tributary of the basyayla valley system

diagenetic evolution and its impact on reservoir quality of tight sandstones a case study of the triassic chang 6 member ordos basin northwest china abstract the triassic chang 6 member sandstones are important oil reservoirs in the ordos basin of north western china and are actually considered to be typical tight sandstone reservoirs diagenetic alterations play a prominent role in considerably impacting the reservoir quality in this study an integrated approach of thin sections scanning electron microscopy sem x ray diffraction xrd cathodoluminescence cl fluid inclusions laser raman spectrographic analysis and stable isotope analysis was applied to examine the diagenetic history recorded in the chang 6 tight sandstones and investigate the influences of diagenesis on reservoir quality the sandstones consist of fine grained moderated to well sorted arkoses q48 5f40 9r10 6 and lithic arkoses q54 3f29 1r16 6 with an average porosity and permeability of 9 10 and 0 39 md respectively the sandstones have undergone complex diagenetic processes dominant eogenetic features include mechanical compaction leaching of feldspar in meteoric water chlorite coats originating from the transformation of precursor clays and precipitating directly from interstitial water calcites filling intergranular pores as poikilotopic cements and quartz and albite overgrowths on surfaces of grains subsequent mesogenetic events include ankerite cements filling porosity and replacing framework grains extensive dissolution of feldspars and precipitation of kaolinites due to emplacement of organic acids and secondary quartz overgrowths in the late period of mesogenesis early calcite is characterized by 13c 13cpdb ranging from 3 45 to 0 30 mean 2 00 and 18o 18opdb varying from 16 70 to 5 80 mean 10 50 while late ankerite is rich in 12c 13cpdb ranging from 10 71 to 0 80 mean 3 58 and 16o 18opdb varying from 24 30 to 15 80 mean 19 93 moreover calcite hosts single liquid fluid inclusions two phase fluid inclusions are contained in ankerite cements with mean homogenization temperature th of 96 0 c and salinity estimates from 11 47 to 18 96 eq wt nacl these data indicate that the calcite originated from meteoric water and the ankerite was associated with organic matter and recrystallization of the early calcite cements furthermore the metallic ions such as fe2 mg2 and ca2 required for ankerite precipitation were produced through alterations of volcanic fragments feldspars and biotites in comparison compaction has more important role than cementation in the loss of original porosity although cementation exerts enormous influence on reducing porosity quantitatively the compactional porosity loss reaches 54 9 while the cementation porosity loss accounts for up to 42 8 carbonate cements and the other authigenic products quartz and albite overgrowth and kaolinite mostly fill intergranular pores thus reduce porosity chlorite coats have effects in inhibiting compaction and restraining the development of quartz overgrowth thereby protect the intergranular porosity to some extent early secondary porosity was enhanced by leaching and dissolution of feldspar in the eogenetic period however these processes did not increase the net porosity in the mesogenetic stage

diagenetic controls on the quality of the middle permian lucaogou formation tight reservoir southeastern junggar basin northwestern china abstract the middle permian lucaogou formation in the southeastern part of the junggar basin in china is a typical tight oil reservoir with low to medium porosity average 11 2 and ultra low permeability average 0 01 md here we investigate lucaogu formation reservoir diagenesis and its impact on reservoir quality to effectively explore appraise and develop this complex tight oil reservoir core and thin section analyses scanning electron microscopy x ray diffraction xrd electron probe analyses fluid inclusions isotopic analysis pressure controlled mercury injection rate controlled mercury injection and micro nanometer x ray computer tomography ct imaging were performed on core samples from the lucaogou tight reservoir the sweet spots in the lucaogu formation are composed of siltstone tuffaceous siltstone and silty dolomite which underwent two stages of carbonate cementation primarily calcite dolomite and ankerite clay mineral alteration and dissolution and one stage of quartz cementation the major authigenic mineral cements derived from the original formation water clay mineral alteration dissolution of acid soluble components and the compaction and drainage of the interbedded mudstone are also a probable source of ions it is likely that oil emplacement occurred after quartz cementation and the first stage of carbonate cementation and feldspar dissolution but before the second stage of calcite cementation and feldspar dissolution organic acids produced during hydrocarbon generation contributed to the dissolution of the feldspar and tuffaceous components locally preventing a decrease in porosity by concurrent cementation and compaction carbonate cementation decreased the porosity and permeability of the silty dolomite substantially in the siltstone decreased permeability is largely attributed to cementation of clay minerals the pore structure of the sweet spot is controlled not only by the various cementation events but also by other geological factors such as heterogeneous dissolution of the tuffaceous component

origin and timing of siderite cementation in upper ordovician glaciogenic sandstones from the murzuq basin sw libya the origin and timing of siderite cementation have been constrained in relation to depositional facies and sequence stratigraphy of upper ordovician glaciogenic sandstones from the murzuq basin sw libya optical microscope backscattered electron imagery and carbon and oxygen stable isotope analysis have revealed that siderite is of eo and mesogenetic origin eogenetic siderite is mg poor with a mean composition of fe91 7mg1 5ca0 3mn6 5 co3 and occurs in paraglacial tide dominated deltaic highstand systems tract hst sandstones in paraglacial foreshore to shoreface hst sandstones and in postglacial gilbert type deltaic lowstand systems tract lst sandstones this siderite is typically of meteoric water origin that influxed into the lst and hst sandstones during relative sea level fall and basinward shift of the strandline mesogenetic siderite which engulfs and thus postdates quartz overgrowths and illite is mg rich with a mean composition of fe72 2mg21 7ca0 8mn5 3 co3 and occurs in the paraglacial tide dominated deltaic hst sandstones in paraglacial foreshore to shoreface hst sandstones in glacial tide dominated estuarine transgressive systems tract tst sandstones in postglacial gilbert type deltaic lst sandstones and in postglacial shoreface tst sandstones 18ov pdb values of this siderite which range between 22 6 and 13 8 suggest that precipitation has occurred from evolved formation waters with 18o values between 14 0 and 1 0 and was either meteoric mixed marine meteoric and or marine in origin by assuming postdating quartz overgrowths and illite temperature between 80 and 130 c

authigenesis of amphibole and its relationship to the diagenetic evolution of lower cretaceous sandstones of the potiguar rift basin northeastern brazil abstract authigenic amphibole occurs in the fan delta front arkoses and lithic sandstones of the neocomian pendencia formation in the potiguar rift basin northeastern brazil as overgrowths fracture healing and replacement of detrital amphibole the amphibole which is closely associated with diagenetic albite chlorite and sphene has precipitated from k na cl brines enriched in ti fe mg at temperatures 100 c these ions were derived from the diagenetic alteration of detrital amphibole and pyroxene chloritization of volcaniclastic sediments at the base of the formation and from brines that ascended along faults from the underlying basement

repeating coupled earthquakes at shishaldin volcano alaska since it last erupted in 1999 shishaldin volcano aleutian islands alaska has produced hundreds to thousands of longperiod 1 2 hz lp earthquakes every day with no other sign of volcanic unrest in 2002 the earthquakes also exhibited a short period 4 7 hz sp signal occurring between 3 and 15 s before the lp phase although the sp phase contains higher frequencies than the lp phase its spectral content is still well below that expected of brittle failure events the sp phase was never observed without the lp phase although lp events continued to occur in the absence of the precursory signal the twophased events are termed bcoupled eventsq reflecting a triggered relationship between two discrete event types both phases are highly repetitive in time series suggestive of stable non destructive sources waveform cross correlation and spectral coherence are used to extract waveforms from the continuous record and determine precise p wave arrivals for the sp phase although depths are poorly constrained the sp phase is believed to lie at shallow b4 km depths just west of shishaldin s summit the variable timing between the sp and lp arrivals indicates that the trigger mechanism between the phases itself moves at variable speeds a model is proposed in which the sp phase results from fluid moving within the conduit possibly around an obstruction and the lp phase results from the coalescence of a shallow gas bubble the variable timing is attributed to changes in gas content within the conduit the destruction of the conduit obstacle on november 21 2002 resulted in the abrupt disappearance of the sp phase published by elsevier b v

mass transfer between mudstone sandstone interbeds during diagenesis as revealed from the type and distribution of carbonate cements in the eocene beach bar sandstones bohai bay basin abstract the characteristics heterogeneous distribution and origins of carbonate cements within beach bar sandstones in the boxing sag and implications on the mass transfer from mudstone to sandstone during diagenetic process was investigated systematically by an integrated analysis invoking petrography carbon and oxygen stable isotopes and porosity permeability with specific references to the contrasts among the sharp s change lithology s mudstone s sandstone interbeds the gradual g change lithology g mudstone g sandstone interbeds and the center of sandstones there are distinct differences in the occurrence content distribution carbon and oxygen isotopic compositions and precipitation temperatures of the carbonate cements among the s sandstone g sandstone and center of sandstone material sources of carbonate cements in the s sandstones are mainly derived from the diagenetic alterations of the nearby s mudstones through mass transfer with the participation of organic co2 while in the g sandstones the material sources are mainly internal and originated from the calcareous matrix dissolution of feldspars and conversion of clay minerals provided the main materials for the precipitation of carbonate cements in the center of sandstones mass transfer of carbonate cements mainly occurred between the s mudstones and the s sandstones with limited transmission distance which controlled the distribution of carbonate cements in the s mudstones there was almost no mass transfer between the g mudstones and g sandstones because of the small concentration gradient instead the depositional components and recrystallization controlled the carbonate distribution of the g sandstones

diagenetic f rich ferroan calcite and zircon in the offshore scotian basin eastern canada significance for understanding thermal evolution of the basin in the scotian basin offshore eastern canada an unusual combination of high heat flow in the cretaceous and the abundance of halite has resulted in unusual diagenetic minerals such as sphalerite the newburn h 23 well is the most distal well in the basin with good core samples and has two previously unknown diagenetic mineral occurrences fluorine rich ferroan calcite and diagenetic zircon this study uses sem backscattered electron images and eds analyses emp wds mineral analyses and raman spectroscopy to determine mineral chemistry and textures to investigate the diagenetic and thermal significance of these minerals late diagenetic fe calcite contains 1 2 5 wt fluorine mostly from adsorption but rarely as small fluorite crystals fluoride is also adsorbed on the surfaces of some framework minerals and chlorite fluoride was transported in highly saline formation brines derived from the argo salt formation zircon grains 20 40 m in size have crystal outlines that are straight adjacent to pores partially lobate filling porosity and cross cutting other grains these may be diagenetic some zoned detrital zircon grains show 1 3 m wide diagenetic outgrowths neoformation of diagenetic zircon requires temperatures of 250 c transport of zirconium is favored by ligands in low ph solution principally fluoride and phosphate anions with zirconium mobilized during the alteration of metamict detrital zircon under low grade metamorphic conditions the presence of diagenetic sphalerite and the documented mid cretaceous thermal event in the scotian basin indicate conditions that could have been suitable for the formation of diagenetic zircon in this well suitable geological conditions for such diagenetic formation of zircon will be found in a subsiding rift basin with early evaporites that are affected by a subsequent phase of volcanism due to new rifting or subduction

burial dolomitization and dissolution of upper jurassic abenaki platform carbonates deep panuke reservoir nova scotia canada a large gas reservoir was discovered in the previously unproductive jurassic aged abenaki carbonate margin in 1998 most of the reservoir porosity is developed in dolostones these dolostones replaced preexisting wackestones packstones and grainstones associated with reefal and adjacent depositional environments many dolomites were subsequently recrystallized or dissolved accounting for much of the preserved secondary porosity subsequent fracturing helped enhance reservoir permeabilities enhanced petrographic techniques established that dissolution of previously dolomitized fabrics generated much of the secondary porosity in these dolostones diffused plane polarized light revealed relict grains and textures invisible with standard microscopic observations petrographic and geochemical observations also confirmed that dissolution occurred under deep burial conditions after incipient pressure solution dissolution was not confined to the centers of dolomitized grains as is commonly seen when remnant calcitic grains dissolve out during the advanced stages of replacement dolomitization instead dissolution was random within relict grains as isolated dolomite crystals were also variably dissolved the geochemistry of these dolomites and associated late stage calcites implied precipitation from basinal hot fluids as well as hydrothermal fluids later diagenetic fluids either acidic or calcium rich or perhaps both at different times based on associated mineralization seemingly promoted dolomite dissolution the presence of tectonic fractures and stylolites helium gas and faults observed in seismic data implied that dolomitization and subsequent dissolution along the abenaki platform margin were controlled by reactivated wrench faults tied to basement on a finer scale diagenetic fluids moved through fractures and pressure solution seams the data collected to date support our contention that the dolomitization and dissolution process which has created most of the porosity in the abenaki reservoir was poststylotization and deeper burial in origin given the timing of tectonic activity in the area and its inferred connection to diagenesis it is probable that at least a part of the diagenetic fluids were hydrothermal in nature

geochemical identification of clastic sediment provenance from known sources of similar geology the cretaceous scotian basin canada abstract this study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology petrological studies indicate that at least three distinct rivers draining reactivated horsts of the appalachian orogen supplied sediment to the lower cretaceous deltaic sandstones and mudrocks in the offshore scotian basin ninety five samples mostly from conventional core were analyzed for 44 major and trace elements the data were first screened for variability unrelated to provenance including changes in elemental abundance due to weathering and diagenesis and the effects of grain size and sorting on element variation the effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources multivariate statistical analysis by principal component analysis pca was used to test the hypothesis of three discrete sources suggested by the petrologic model major element pca on sandstones discriminated the sources but results from trace element pca required further investigation using element biplots to understand their significance only a few elements were found to be diagnostic of different sources namely k rb sr u th nb and ti with the latter two of value only for sandstones all of these are elements that are abundant in the granites of the appalachians most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources in other basins with quite different hinterland geology other elements are known to be of value in discriminating provenance thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources rather systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry informed by at least semiquantitative petrographic data

long period lp events on mt etna volcano italy the influence of velocity structures on moment tensor inversion since a few decades volcanic long period lp events have been recorded on many active volcanoes and their study has been recognized as an important tool to characterize volcanic activity lp event analyses through moment tensor mt inversions have led to kinematic descriptions of various source mechanisms the main challenge in these inversions is to strip out the propagation effect in order to isolate the source hence the velocity model used controls the accuracy of the retrieved source mechanism we first carry out several synthetic tests of inversions on mt etna volcano italy four geological models with topography are considered with increasing complexity the most complex model is used to generate synthetic data while the other three models are used to calculate the greens functions for inversions the retrieved solutions from the three velocity models are similar the mt solutions for a deeper source are well retrieved while a shallower source test suffers from high uncertainties and strong misinterpretation of the source orientation the homogeneous model gives the lowest misfit value but source location and mechanism decomposition are inaccurate when a complex model different from the true one is used a high misfit value and a wrong solution is obtained we then incorporate our findings into the mt inversion of an lp event recorded on mt etna in 2008 we obtain very different solutions among the three models in terms of source location and mechanism decomposition the overall shape of the retrieved source time functions are similar but some amplitude differences arise especially for the homogeneous model our work highlights the importance of including the unconsolidated surface materials in the computation of green s functions especially when dealing with shallow sources

determining the seismic source mechanism and location for an explosive eruption with limited observational data augustine volcano alaska 1 waveform inversions of the very long period components of the seismic wavefield produced by an explosive eruption that occurred on 11 january 2006 at augustine volcano alaska constrain the seismic source location to near sea level beneath the summit of the volcano the calculated moment tensors indicate the presence of a volumetric source mechanism systematic reconstruction of the source mechanism shows the source consists of a sill intersected by either a sub vertical east west trending dike or a sub vertical pipe and a weak single force the trend of the dike may be controlled by the east west trending augustine seldovia arch the data from the network of broadband sensors is limited to fourteen seismic traces and synthetic modeling confirms the ability of the network to recover the source mechanism the synthetic modeling also provides a guide to the expected capability of a broadband network to resolve very long period source mechanisms particularly when confronted with limited observational data

the geology of venture a geopressured gas field offshore nova scotia the venture gas field is a potential giant gas accumulation discovered in 1979 by the mobil et al venture d 23 well drilled by petro canada on a farm in from mobil this well was completed at a total depth of 4 945 m 16 224 ft the field is located on the scotian shelf 5 16 km 3 10 mi off the east end of sable island 300 km 186 mi east of halifax nova scotia water depths across the field range from 12 to 23 m 39 to 75 ft participants in the venture field include mobil texaco petro canada and nova scotia resources venture is the largest discovery on the scotian shelf offshore nova scotia with initial estimates of ultimate gas recovery exceeding 1 5 tcf the venture structure is an elongate east west anomaly on the downthrown side of a normal east west trending fault currently five wells define a gas bearing area of about 3 000 ha 7 400 ac within structural closure in the venture field gas occurs in multiple sandstone reservoirs from late jurassic to early cretaceous age over a stratigraphic interval of 1 600 m 5 250 ft the venture gas bearing productive section consists of one to four hydropressured sandstones and up to 17 geopressured sandstones with pressure depth ratiosmore of up to 0 8 psi ft venture sandstones exhibit abnormally high porosities for their depth possibly both preserved primary porosity and secondary solution porosity the reservoirs are often characterized by high water saturations and very high salinity formation water less

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

the roles of pedogenesis and diagenesis in clay mineral assemblages lower cretaceous fluvial mudrocks nova scotia canada abstract clay mineral assemblages in alluvial mudrocks are important for paleoclimatic interpretation and for understanding burial diagenetic cementation in sandstones but it is commonly difficult to unravel the relative importance of source weathering pedogenesis and diagenesis in their origin the clay mineral assemblages in fluvial overbank mudrocks from the lower cretaceous chaswood formation in central nova scotia investigated by x ray diffraction analysis of the

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

diagenesis of tight sandstone reservoirs in the upper triassic yanchang formation southwestern ordos basin china abstract in order to better predict the petrophysical properties of the tight sandstone reservoirs in the upper triassic yanchang formation ordos basin china the nature of the diagenetic system involved was investigated using a suite of petrographic and geochemical techniques including thin section and x ray diffraction analysis scanning electron microscopy maps mineralogy cathodeluminescence electron probe microanalysis and fluid inclusion analysis on a set of selected tight sandstone samples the sandstones investigated are texturally mature but compositionally immature with an average framework grain composition of q32f41l27 authigenic quartz calcite and chlorite coatings are the major cements while feldspars are partially dissolved two groups of quartz cement are present in the tight sandstone reservoirs smectite to illite conversion provided silica source for the first group of quartz overgrowth qo i while the silica source for the second quartz overgrowth qo ii was mainly originated from feldspar dissolution calcite cements consist of two types namely ca i and ca ii the ca i calcite cement contains no chlorite coatings and have higher concentrations of fe2 and mg2 whereas the ca ii calcite cement developed over the chlorite coatings plagioclase dissolution appears to be always accompanied by calcite cementation while k feldspar albitization forms euhedral albite locally the burial diagenesis processes were in most cases not episodic but occurred as slow adjustments in response to increased burial depths and temperatures in all the studied diagenetic minerals elemental distributions appear to be strictly constrained by the interaction of authigenic minerals involved indicating that the chemical reactions during the diagenesis comply well with the general principle of mass balance the diagenesis in the upper triassic yanchang formation tight sandstones was thus mainly developed in a closed geochemical system where mineral dissolution and precipitation are approximately balanced and diagenetic fluids were not affected by external sources significantly mechanical compaction has played a more important role in destroying the primary porosities of the upper triassic yanchang formation than the cementation

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

disseminated jigsaw piece dolomite in upper jurassic shelf sandstones central north sea an example of cement growth during bioturbation unusual textural and chemical characteristics of disseminated dolomite in upper jurassic shelf sediments of the north sea have provided the basis for a proposed new interpretation of early diagenetic dolomite authigenesis in highly bioturbated marine sandstones the dolomite is present throughout the franklin sandstone formation of the franklin and elgin fields as discrete non ferroan generally unzoned subhedral to highly anhedral jigsaw piece crystals these are of a similar size to the detrital silicate grains and typically account for 5 of the rock volume the dolomite crystals are never seen to form polycrystalline aggregates or concretions or ever to envelop the adjacent silicate grains they are uniformly dispersed throughout the sandstones irrespective of detrital grain size or clay content dolomite authigenesis predated all the other significant diagenetic events visible in thin section the dolomite is overgrown by late diagenetic ankerite and bulk samples display stable isotope compositions that lie on a mixing trend between these components extrapolation of this trend suggests that the dolomite has near marine delta18o values and low positive delta13c values the unusual textural and chemical characteristics of this dolomite can all be reconciled if it formed in the near surface zone of active bioturbation sea water provided a plentiful reservoir of mg and a pore fluid of regionally consistent delta18o labile bioclastic debris e g aragonite mg calcite supplied isotopically positive carbon to the pore fluids during shallow burial dissolution such dissolution took place in response to the ambient calcite sea conditions but may have been catalysed by organic matter oxidation reactions bioturbation not only ensured that the dissolving carbonate was dispersed throughout the sandstones but also prohibited coalescence of the dolomite crystals and consequent cementation of the grain framework continued exchange of mg2 and ca2 with the sea water reservoir maintained a sufficient mg ca ratio for dolomite rather than calcite to form irregular crystal shapes resulted from dissolution of both the dolomite and the enclosed fine calcitic shell debris before ankerite precipitation during deep burial diagenesis

diagenesis and reservoir quality of the lower cretaceous quantou formation tight sandstones in the southern songliao basin china abstract the lower cretaceous quantou formation in the southern songliao basin is the typical tight oil sandstone in china for effective exploration appraisal and production from such a tight oil sandstone the diagenesis and reservoir quality must be thoroughly studied first the tight oil sandstone has been examined by a variety of methods including core and thin section observation xrd sem cl fluorescence electron probing analysis fluid inclusion and isotope testing and quantitative determination of reservoir properties the sandstones are mostly lithic arkoses and feldspathic litharenites with fine to medium grain size and moderate to good sorting the sandstones are dominated by feldspar quartz and volcanic rock fragments showing various stages of disintegration the reservoir properties are quite poor with low porosity average 8 54 and permeability average 0 493 md small pore throat radius average 0 206 m and high displacement pressure mostly higher than 1 mpa the tight sandstone reservoirs have undergone significant diagenetic alterations such as compaction feldspar dissolution quartz cementation carbonate cementation mainly ferrocalcite and ankerite and clay mineral alteration as to the onset time the oil emplacement was prior to the carbonate cementation but posterior to the quartz cementation and feldspar dissolution the smectite to illite reaction and pressure solution at stylolites provide a most important silica sources for quartz cementation carbonate cements increase towards interbedded mudstones mechanical compaction has played a more important role than cementation in destroying the reservoir quality of the k 1 q 4 sandstone reservoirs mixed layer illite smectite and illite reduced the porosity and permeability significantly while chlorite preserved the porosity and permeability since it tends to be oil wet so that later carbonate cementation can be inhibited to some extent it is likely that the oil emplacement occurred later than the tight rock formation with the porosity close to 10 however thicker sandstone bodies more than 2 m constitute potential hydrocarbon reservoirs

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

diagenetic barite and sphalerite in middle mesozoic sandstones scotian basin as tracers for basin hydrology cementation of sandstone by minor late barite and sphalerite is widespread in the scotian basin at burial depths 2 km 1 mi providing information on fluid flow in the basin the texture and geochemistry of these minerals were analyzed by scanning electron microscopy and electron microprobe on samples from conventional core barite and sphalerite postdate silica and carbonate cementation occurring in veins or occupying secondary porosity they occur with diagenetic chlorite kaolinite pyrite titania minerals kutnohorite and mn siderite this study relates barite and sphalerite to the salt tectonic evolution of the basin based on seismic interpretation and the thermal history of the basin based on fluid inclusion studies barite is readily transported in basinal fluids 100 c 212 f yet is consistently a very late diagenetic mineral this implies that the source of ba is because of the late diagenetic breakdown of k feldspars at 2 3 km 1 2 mi depth which is confirmed by covariation of ba and rb in sandstones sulfur isotope data suggest that the was derived from argo formation evaporites that include 1 7 anhydrite sphalerite is mobile only in saline formation water 140 c 284 f and requires long distance transport through sandstones with zn rich fe ti oxides active detachment faults on salt welds provide potential pathways and a source of salt for migrating formation water the particularities of source and transport of both barite and sphalerite allow the pathways of basinal fluids and their relationship to active salt tectonics to be inferred providing indirect dating of the later stages of diagenetic paragenesis corresponding to times of hydrocarbon charge

radiocarbon studies of plant leaves and tree rings from mammoth mountain ca a long term record of magmatic co2 release evaluation of 14c in tree rings provides a measure of the flux of magmatic co2 from mammoth mountain both before and after 1994 when copious diffuse emissions were first discovered and linked to tree kill we analyzed the annual rings of trees with two main purposes 1 to track changes in the magnitude of magmatic co2 emission over time and 2 to determine the onset of magmatic co2 emission at numerous sites on mammoth mountain the onset of co2 emission at different areas of tree kill was determined to be in 1990 closely following the seismic events of 1989 at horseshoe lake hsl co2 emission was found to have peaked in 1991 and to have subsequently declined by a factor of two through 1998 the tree ring data also show that emissions of magmatic carbon from cold springs below the tree kill areas occurred well before 1989 trees located on the margins of the kill areas or otherwise away from zones of maximum gas discharge were found to be better integrators of magmatic co2 emission than those located in the center of tree kills although quantitative extrapolations from our data to a flux history will require that a relationship be established between 14c depletion in tree rings and average annual magmatic co2 flux the pattern of 14c depletion in tree rings is likely to be the most reliable indicator of the long term changes in the magnitude of co2 release from mammoth mountain

an investigation into pore structure and petrophysical property in tight sandstones a case of the yanchang formation in the southern ordos basin china abstract the complex and heterogeneous pore structures caused by complex diagenesis and sediment properties such as rock compositions and grain size play a critical role in macroscopic evaluating tight sandstone reservoir performance in order to gain insight into the genetic mechanism of the pore structure and evaluate reservoir quality in tight sandstone reservoirs this study investigated the impacts of diagenesis and sediment properties on pore structures and the relationship between microscopic pore structure parameters and macroscopic petrophysical performance based on the analysis of pore structure features including the morphology pore throat types sizes combinations distribution of combinations and pore connectivity sedimentary and diagenetic features and petrophysical properties samples from tight sandstones of the yanchang formation in southern ordos basin in china were evaluated by integrating scanning electron microscopy sem thin sections mercury injection porosimetry mip nuclear magnetic resonance nmr and gas n2 he porosity and permeability measurements three pore throat combinations were identified which represent the full range distribution of pores mp micropores dominanted pore throat combination iap intragranular pores dominanted pore throat combination and iep intergranular pores dominanted pore throat combinations the type and intensity of diagenesis and sediment properties grain size and ductile component content were found to result in differences in pore throat size and the distribution of pore throat combinations sandstones with coarser grain size and lower concentrations of ductile components have experienced weak compaction thick chlorite rim and minor kaolinite carbonate cementation were found to retain large iep pore space and wide strip shaped throat formed the intergranular pore throat inter t and intergranular pore intragranular pore throat inter intra t the intra intst t intragranular pore group of interstitial cement pores throat sandstones were characterized by intense dissolution and kaolinite cementation which resulted in small iep pore space and large mp iap pore space the intst t group of interstitial cement pores throat sandstones were characterized by intense compaction and kaolinite carbonate cementation compaction and cements destroyed iep pore space and formed mp pore space effectively connected pore space volume of iep and throat radius were positively correlated to porosity and permeability four pore structures are distinguished according to the proportion of effectively connected pore space and the radii of strip shaped throats the macroscopic behaviors and the geological genesis of the four pore structures are investigated

authigenesis of titania minerals and the mobility of ti new evidence from pro deltaic sandstones cretaceous scotian basin canada titania tio2 minerals are minor diagenetic phases in many sandstone shale successions but the conditions of ti mobility and titania authigenesis are poorly known here new modes of occurrence of authigenic titania minerals filling pores and replacing phytodetritus are documented from lower cretaceous prodeltaic sandstones in the offshore scotian basin of southeastern canada textural relationships suggest that titania minerals formed at the same time as kaolinite most commonly below lowstand sequence boundaries related to flux of meteoric water such authigenic titania is most abundant in thin bedded sandstones interbedded with thick prodeltaic mudstone in which fine grained detrital ti rich minerals are concentrated textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near surface eodiagenesis eogenetic titania is enriched in phosphorus 0 6 p2o5 and may co occur with authigenic fluorapatite and crandallite crystals such titania resulted from prolonged flow of meteoric water that dissolved p from apatite and feldspar thereby enhancing ti solubility in basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water the assumption that ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid probable mesodiagenetic titania has low p content suggesting that ti mobility under these conditions was facilitated by some other agent probably organic acids the results of this study illustrate that even in cases where titania minerals are volumetrically insignificant their microtextures and trace element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks

albitization of detrital plagioclase in triassic reservoir sandstones from the snorre field norwegian north sea abstract detrital plagioclase an12 an28 in triassic reservoir sandstones of the lunde formation in the snorre field offshore norway has been partially to completely albitized during burial diagenesis depths of about 2 500 3 000 m 75 100 c present temperature calcite caco3 99 mole and kaolinite were formed as by products of plagioclase albitization sodium rich detrital plagioclase an2 an11 are usually unalbitized detrital k feldspar is fresh or rarely partly albitized differences in albitization behavior of detrital plagioclase and k feldspar are shown to be related to the chemistry of formation waters reactivity of kaolinite and temperature the diagenetically formed albite pseudomorphs are very pure ab 9 well ordered low albite dark luminescent vacuolized mostly untwinned and comprised of numerous euhedral albite crystals some of the microporosity within the albite pseudomorphs is caused by volume reduction during albitization of the detrital plagioclase the amount of albite formed in the pseudomorphs is related to the molar proportion of albite component in the detrital unstable ca rich plagioclase the microporosity formed during albitization is proportional to the anorthite component which is believed to have dissolved and resulted primarily in the formation of calcite and kaolinite the albitization of detrital plagioclase in the studied sandstones can thus be explained without assuming the consumption of significant amounts of na from pore solutions

real time monitoring and massive inversion of source parameters of very long period seismic signals an application to stromboli volcano italy 1 we present a comprehensive processing tool for the real time analysis of the source mechanism of very long period vlp seismic data based on waveform inversions performed in the frequency domain for a point source a search for the source providing the best fitting solution is conducted over a three dimensional grid of assumed source locations in which the green s functions associated with each point source are calculated by finite differences using the reciprocal relation between source and receiver tests performed on 62 nodes of a linux cluster indicate that the waveform inversion and search for the best fitting signal over 100 000 point sources require roughly 30 s of processing time for a 2 min long record the procedure is applied to post processing of a data archive and to continuous automatic inversion of real time data at stromboli providing insights into different modes of degassing at this volcano

distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework evidence from the upper ordovician of the murzuq basin sw libya abstract the spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the upper ordovician glaciogenic quartzarenite sandstones in the murzuq basin sw libya which were deposited during the haritanian glaciation when the basin was laying along the continental margin of gondwana eogenetic alterations encountered include i replacement of detrital silicates mud matrix and pseudomatrix by kaolinite in paraglacial tide dominated deltaic in foreshore to shoreface highstand systems tract hst and in post glacial gilbert type deltaic lowstand systems tract lst sandstones particularly below the sequence boundaries sb kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline ii cementation by calcite 18 o vpdb 3 1 to 1 1 and 13 c vpdb 1 7 to 3 5 and mg rich siderite in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones in the glacial tide dominated estuarine transgressive systems tract tst sandstones and in the post glacial shoreface tst sandstones is interpreted to have occurred from marine pore waters iii cementation by mg poor siderite which occurs in the post glacial gilbert type deltaic lst sandstones and in the paraglacial tide dominated deltaic and foreshore to shoreface hst sandstones is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline iv pervasive cementation by iron oxides has occurred in the glacial shoreface offshore tst sandstones and post glacial shoreface tst sandstones immediately below the maximum flooding surfaces mfs which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor v formation of grain coating infiltrated clays mainly in the glacial fluvial incised valley lst sandstones and in the post glacial gilbert type deltaic lst sandstones as well as less commonly in the paraglacial foreshore to shoreface hst sandstones and in the tide dominated deltaic hst sandstones below the sbs mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial fluvial incised valley lst sandstones post glacial gilbert type deltaic lst sandstones and glacial shoreface tst sandstones in which early carbonate cements are lacking illite chlorite and albitized feldspars which occur in small amounts are most common in the glacial tide dominated estuarine tst sandstones and paraglacial shoreface hst sandstones this study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir quality evolution in glacial paraglacial and post glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework

origin of authigenic mn fe carbonates and pore water evolution in marine sediments evidence from cenozoic strata of the arctic ocean and norwegian greenland sea odp leg 151 early diagenetic mn fe carbonates occurring in thin layers nodules and burrows were recovered from cenozoic silts and clays from the arctic ocean and the norwegian greenland sea during ocean drilling program leg 151 at sites 909 fram strait miocene quaternary and 911 yermak plateau pliocene quaternary fine crystalline siderite enriched in ca and or mg is the predominant carbonate variable 13c values 21 8 to 7 9 pdb suggest that dissolved carbon was derived from the fe reduction suboxic zone the oxidation of marine organic matter in the bacterial sulfate reduction zone and the early stages of methanogenesis the range of 18o values for siderite 6 3 to 5 1 pdb indicates precipitation over a temperature range of 4 56 c during successive burial at site 913 east greenland margin eocene quaternary concentrically zoned microspherules and rhombohedra of ferroan rhodochrosite and manganoan siderite 20 600 m in diameter are the main authigenic carbonates although they have low 13c values 22 3 to 13 8 pdb elevated pore water sulfate concentrations indicate low sulfate reducing activity and suggest that dissolved carbon may have been partially derived from thermogenic methane the variable 18o values for rhodochrosite 11 9 to 1 5 pdb and siderite 11 4 to 10 3 pdb suggest precipitation at elevated temperatures 60 100 c during progressive burial the close association with barite cement suggests that carbonate precipitation at site 913 may have been influenced by hydrothermal fluids however active circulation of hydrothermal fluids is precluded by the occurrence of geochemical gradients in site 913 pore waters pore waters at the three sites reflect various evolutionary pathways that are partly due to variations in the extent of interaction with volcanic ash layers and the underlying basaltic crust which led to an overall decrease in mg2 k and 18o and an increase in ca2 with depth however pore waters at site 913 have evolved more extensively to na ca cl brines the sources of freshwater that cause the downhole decrease in cl and na concentrations at sites 909 and 913 are poorly constrained the possible influence of meteoric water incursion is suggested by the d 18o relationship of pore waters and the low 18o values of site 913 authigenic carbonates

authigenic minerals related to wettability and their impacts on oil accumulation in tight sandstone reservoirs an example from the lower cretaceous quantou formation in the southern songliao basin china abstract oil accumulation being difficult and complicated is an important issue in petroleum exploration researches authigenic minerals such as carbonate cements and chlorite can in certain reservoirs alter the wettability of some pore spaces from water wet to oil wet generally these oil wet pore spaces are favorable for oil accumulation the alteration of reservoir wettability induced by authigenic minerals and the impacts on oil accumulation in tight sandstone reservoirs were investigated using a suite of mineralogical and geochemical characterization techniques including thin section observation sem eds xrd qemsem cl quantitative grain fluorescence qgf fluorescence spectral analysis contact angle measurement and sealed coring oil saturation testing on the fourth member of the lower cretaceous quantou formation k1q4 in the southern songliao basin china the study shows that the tight sandstone reservoirs are compositionally immature with detrital grains distributed homogeneously quartz carbonates and clay minerals that show heterogeneous distribution characteristics are the major authigenic minerals in some parts of the intergranular pores the detrital mineral assemblage suggests that the reservoir rocks at deposition and before diagenesis had characterized by strong water wet properties with the development of authigenic minerals carbonate cements and authigenic chlorite tend to alter the wettability of some parts of the existing pore spaces from water wet to oil wet in the k1q4 sandstone reservoirs oil prefers to accumulate in the cemented residual pore spaces around carbonate cements and chlorite reservoirs containing about 4 5 carbonate cements are suggested to be more preferable to oil accumulation these reservoirs are mainly located between sandstone mudstone interfaces and central parts of the sand bodies chlorites have mainly two effects on one hand chlorite alters the wettability of existing pore spaces and provides preferential accumulation sites for oil in the tight sandstone reservoirs on the other hand it can reduce the adhesion of oil through forming clay oil flocs and promote further migration consequently the reservoirs with moderate amount of carbonate cements or chlorite always show relative high oil saturation in the k1q4 tight sandstones

phase weighted stacking applied to low frequency earthquakes abstract we apply phase weighted stacking pws to the analysis of low frequency earthquakes lfes in the parkfield california region and central cascadia the technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal to noise ratio snr of the stack we find that for picking lfe arrivals for the parkfield california region and for lfe template formation in central cascadia pws is extremely effective for lfes in the parkfield california region pws yields many more usable phases than standard linear stacking and for lfe detection in cascadia pws produces templates with much higher snr than linear stacking

thermal and hydrocarbon charge history and the relationship between diagenesis and reservoir connectivity venture field offshore nova scotia eastern canada11geological survey of canada contribution 20100418 fluid inclusions in diagenetic cements in upper jurassic lower cretaceous sandstones offshore nova scotia provide constraints on the fluid migration history in gas reservoirs of the scotian basin

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

review of diagenetic facies in tight sandstones diagenesis diagenetic minerals and prediction via well logs abstract the tight sandstones are characterized by low porosity low permeability complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones diagenetic facies which is the comprehensive description of the diagenesis and diagenetic minerals determines the formation and distribution of sweet spot by correlating the diagenetic facies to well log responses the subsurface distribution of porosity and permeability can be predicted however the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task this paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones and establishes a model for prediction of diagenetic facies via well logs as assessed from peer reviewed papers in the literature as well as from the authors personal experiences this review begins with reviewing the impacts of compaction cementation dissolution and various types of diagenetic minerals on reservoir quality evolution the definition and classification schemes of diagenetic facies are then discussed and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized the same diagenetic facies commonly display similar compositional and textural attributes matrix and cement as well as porosity systems the well log responses gr ac den cnl and rt of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections by translating the diagenetic facies to conventional well logs a predictable model which can be used for subsurface reservoir quality prediction is established then the theory of ecs logs is reviewed and the application of ecs logs in diagenetic facies evaluation is discussed at last the quantitative characterization for various type and degree of diagenesis is reviewed and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss cementational porosity loss and dissolution porosity content via well logs correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones this review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones

seismic activity at koryakski volcano in 1994 hybrid seismic events and their implications for forecasting volcanic activity abstract a small swarm of 80 earthquakes was observed beneath koryakski volcano between march 1 and may 31 1994 these earthquakes ranged from 0 to 8 km in depth and from 2 0 to 1 5 in magnitude ml the swarm under koryakski volcano was primarily of volcano tectonic character although a special type of event has been identified with a small amplitude signal preceding the p wave onset these precursory signals had varying durations ranging between a few seconds and a few tens of seconds the source of the signal invariably coincided with the hypocenter of the subsequent earthquake the origin of these signals may be conjectured to be magma emplacement into weakened zones which generated a rupture giving rise to a normal tectonic earthquake the existence of this kind of signals may indicate magmatic activity under the volcano and provide a method for estimating futher development of volcanic activity

provenance and burial history of cement in sandstones of the northbrook formation carboniferous western newfoundland canada a geochemical investigation abstract the carboniferous north brook formation western newfoundland canada consisting of fluvial lacustrine arkosic litharenites has undergone two cementation cycles the first cycle comprises chlorite followed by minor quartz and calcite mono phase aqueous fluid inclusions hosted in first cycle calcite reflect precipitation in a near surface meteoric diagenetic environment chlorite linings and cements generally inhibit precipitation of quartz overgrowths thus maintaining open pore space until a subsequent cycle when temperatures are within the oil window the second cycle comprises chlorite followed by calcite which hosts two phase fluid inclusions with homogenization temperatures ranging from 91 7 to 120 7 c and salinity from 6 3 to 8 4 eq wt nacl these results suggest conditions in line with a deep burial environment and calculated fluid inclusion isochors stipulate a trapping temperature of around 132 c and pressure of 500 bar 5 km hydrostatic pressure for these cements quantitative fluid inclusion gas analysis further confirms that fluids were sourced from evolved meteoric fluids with fluctuating co2 ch4 n2 ratios manganese analysis confirms an oxidizing environment for the first cycle calcite cement but a reducing one for the infilling second cycle cement both cements have similar ree signatures are slightly lree depleted and during migration the fluids were influenced by the sedimentary host rock although there is a prominent negative ce anomaly there is no eu anomaly in the cements the 13c and 18o values are mostly in the negative in the calcite cement hosted in the coarse grained clastics which were influenced by migrating brines and or hydrocarbons in the diagenetic history of this sedimentary basin the first cementation event is characterized by chlorite quartz and calcite emplaced under shallow oxidizing meteoric water conditions and appropriate temperatures a diagenetic hiatus ensued until the units were more deeply buried at this stage a second generation of cement characterized by minor chlorite and major calcite infilled vugs and voids under higher temperatures equivalent to the upper limit of the oil window and 5 km burial depth the lack of porosity precludes the north brook formation from being a petroleum reservoir although limited petroleum may have been sourced during the geologic history

controls of diagenetic alteration on the reservoir quality of tight sandstone reservoirs in the triassic yanchang formation of the ordos basin china abstract the ordos basin is rich in tight oil resources and the upper triassic yanchang formation tight oil reservoir is one of the most important exploration targets in the study area the chang 63 tight sandstone reservoir exhibits lacustrine deep water lobe shaped delta deposits with low porosity low permeability and a complex diagenetic alteration history the reservoir quality is extremely heterogeneous because of the heterogeneity of the depositional lithofacies and diagenetic alterations this research integrates multiple techniques to investigate the depositional lithofacies the characteristics and distributions of various diagenetic alterations and their controls on reservoir quality four lithofacies are identified and the various lithofacies have different diagenetic characteristics and diverse reservoir qualities the chang 63 tight sandstone reservoir has experienced significant diagenetic alteration mechanical compaction and authigenic illite are the most important causes of the decrease in reservoir quality carbonate cementation preferentially occurs in sandstones of lithofacies i and ii near the mudstone sandstone contact surfaces sandstones within 1 m of adjacent mudstone sandstone contact surfaces are usually tightly cemented by carbonate cement illite can be divided into two types according to its morphology both types of illite lead to a decrease in reservoir quality ultimately by combining the relationship between depositional facies and lithofacies with the distribution of different diagenetic processes five evolutionary patterns are identified for reservoir quality in the lacustrine deep water lobe shaped delta deposits can be summarized by ratings of best moderate relatively poor poor and worst

temporal evolution of a hydrothermal system in kusatsu shirane volcano japan inferred from the complex frequencies of long period events 1 we present a detailed description of temporal variations in the complex frequencies of long period lp events observed at kusatsu shirane volcano using the sompi method we analyze 35 lp events that occurred during the period from august 1992 through january 1993 the observed temporal variations in the complex frequencies can be divided into three periods during the first period the dominant frequency rapidly decreases from 5 to 1 hz and q of the dominant spectral peak remains roughly constant with an average value near 100 during the second period the dominant frequency gradually increases up to 3 hz and q gradually decreases from 160 to 30 during the third period the dominant frequency increases more rapidly from 3 to 5 hz and q shows an abrupt increase at the beginning of this period and then remains roughly constant with an average value near 100 such temporal variations can be consistently explained by the dynamic response of a hydrothermal crack to a magmatic heat pulse during the first period crack growth occurs in response to the overall pressure increase in the hydrothermal system caused by the heat pulse once crack formation is complete heat gradually changes the fluid in the crack from a wet misty gas to a dry gas during the second period as heating of the hydrothermal system gradually subsides the overall pressure in this system starts to decrease causing the collapse of the crack during the third period

how sandstone porosity and permeability vary with diagenetic minerals in the scotian basin offshore eastern canada implications for reservoir quality abstract the scotian basin is an under explored offshore basin that has produced gas and minor oil from jurassic cretaceous deltaic sandstones reservoir quality is an important exploration risk in the basin this study evaluates whether there are systematic stratigraphic or geographic variations in diagenetic mineral assemblage control of reservoir porosity and permeability three data sets are used a compilation of all available core plug porosity and permeability measurements 3271 in total a subset of 577 corresponding to thin sections with lithofacies assignments and a subset of 35 thin sections principally from reservoir sandstones in which modal abundance of diagenetic minerals has been determined by image analysis of scanning electron microscope backscattered electron images abundances above a 4 threshold of diagenetic kaolinite calcite and ankerite correlate inversely with permeability but chlorite and possibly siderite correlate positively diagenetic assemblages show no systematic variation with stratigraphy or geography both of which may involve variable detrital supply permeability shows the well known variation with grain size and depth of burial but after correcting for these effects it is greatest in estuarine channel and river mouth turbidite sandstones this is because these facies preferentially develop chlorite rims on detrital quartz grains and are also the sites of enhanced flow of late basinal fluids resulting in secondary porosity local effects such as facies distribution architecture of channel sandstones fluid pathways related to complex salt tectonics and the effects of overpressure are more important than predictable basin wide effects in controlling sandstone reservoir quality

diagenetic sequences of continuously deposited tight sandstones in various environments a case study from upper paleozoic sandstones in the linxing area eastern ordos basin china an integrated analysis of the petrographic characteristics and types and distribution of diagenetic alteration in the upper paleozoic benxi taiyuan shanxi and xiashihezi formations provides insights into the controlling factors on variations in porosity and permeability in tight sandstones 85 of the sandstone samples display porosity values 10 and 90 of the samples exhibit permeability 1 md diagenetic alteration includes mesogenetic compaction cementation by dolomite ankerite and quartz dissolution of feldspar and illitization of smectite eodiagenesis includes compaction development of smectite cementation by pore filling quartz and disordered kaolinite and precipitation of calcite and fe calcite chlorite and quartz preserve primary pores against damage whereas kaolinite illite smectite i s mixed layer and illite significantly diminish reservoir quality via permeability reduction chlorite and i s content decrease abruptly as depth increases whereas the kaolinite content remains elevated at depth because of the complete destruction of k feldspar the transformation from smectite to illite provides silica ions for the widely distributed quartz overgrowths as the depositional environment transformed from fluvial xiashihezi to deltaic shanxi and to epicontinental taiyuan and benxi the dissolution effect increased monotonically feldspar dissolution is dominant in the shanxi formation whereas the benxi and taiyuan formations commonly contain quartz dissolution pores the taiyuan formation has markedly higher porosities than in the overlying and underlying formations caused by strong dissolution and high silica content the decrease in porosity in the benxi formation results from the extensive formation of clay minerals caused by high frequency transgressions in a transitional environment

long period seismic source characterization at popocatepetl volcano mexico 1 the seismicity of popocatepetl is dominated by long period and very long period signals associated with hydrothermal processes and magmatic degassing we model the source mechanism of repetitive long period signals in the 0 4 2 s band from a 15 station broadband network by stacking long period events with similar waveforms to improve the signal to noise ratio the data are well fitted by a point source located within the summit crater 250 m below the crater floor and 200 m from the inferred magma conduit the inferred source includes a volumetric component that can be modeled as resonance of a horizontal steam filled crack and a vertical single force component the long period events are thought to be related to the interaction between the magmatic system and a perched hydrothermal system repetitive injection of fluid into the horizontal fracture and subsequent sudden discharge when a critical pressure threshold is met provides a non destructive source process

influence of near surface volcanic structure on long period seismic signals and on moment tensor inversions simulated examples from mount etna 1 long period lp seismicity on volcanoes is thought to be associated with moving fluids or resonating fluid filled conduits hence lp moment tensor mt source inversions might have a direct bearing on our understanding of the plumbing system using 3 d full wavefield simulations and 2 d sensitivity kernels in a digital elevation model of mount etna we investigate the influence of near surface volcanic structure on lp signals and on moment tensor inversions contrary to common wisdom in crustal seismology we find that despite their relatively long wavelengths lps are severely distorted by near surface structures including layering and topographic features in particular near surface low velocity structures which are commonly observed on volcanoes play a critical role in controlling the nature of lp signals if not accounted for these path effects leak into the source solution leading to the emergence of erroneous source geometries spurious forces and incorrect source time functions this is particularly problematic if one adopts an unconstrained solution space for the source with many free parameters hence there is a fine balance in the trade off between the velocity model and the source in the absence of high resolution near surface velocity control we demonstrate the importance of employing a priori source information from other fields e g structural geology for shallow lps constraining the number of free parameters in the inversion a probabilistic approach should then be taken as the model with the best fit is not necessarily the true solution

relationship of diagenetic chlorite rims to depositional facies in lower cretaceous reservoir sandstones of the scotian basin the relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the lower cretaceous missisauga formation was investigated using a combination of electron microprobe bulk geochemistry and x ray diffraction data the succession studied comprises several stacked parasequences the delta progradational facies association includes i fluvial or distributary channel sandstones some with tidal influence ii thick bedded delta front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms and iii more distal muddier delta front and prodeltaic facies the transgressive facies association includes lag conglomerate siderite cemented muddy sandstone and mudstone and bioclastic sandy limestone chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles good quality chlorite rims are well correlated with ti in bulk geochemistry ti is a proxy for fe availability principally from the breakdown of abundant detrital ilmenite fetio3 under conditions of sea floor diagenesis the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate depletion level and of the overlying eh controlled diagenetic zones resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones this early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation this study thus shows that the preservation of porosity by chlorite rims is a two stage process rapidly deposited delta front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis

long period seismicity and very long period infrasound driven by shallow magmatic degassing at mount pagan mariana islands long period lp seismicity and very long period infrasound ivlp were recorded during continuous degassing from mount pagan mariana islands in july 2013 to january 2014 the frequency content of the lp and ivlp events and delay times between the two arrivals were remarkably stable and indicate nearly co located sources using phase weighted stacking over similar events to dampen noise we find that the lp source centroid is located 60 m below and 180 m west of the summit vent the moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike we model the seismoacoustic wavefields with a coupled earth air 3 d finite difference code the ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios so the ivlp is not the result of lp energy transmitting into the atmosphere at its epicenter based on crater shape and dimensions determined by structure from motion we model the ivlp as acoustic resonance of an exponential horn the source of the continuous plume from gas analysis is shallow magmatic degassing which repeatedly pressurized the dike sill portion of the conduit over the 7 months of observation periodic gas release caused the geologically controlled sill to partially collapse and resonate while venting of gas at the surface triggered resonance in the crater lp degassing only accounts for 12 of total degassing indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent

long period earthquakes in the long valley caldera region eastern california most earthquakes occurring near long valley caldera since the onset of recurring swarm activity in 1980 have the broad band signature typical of tectonic or volcano tectonic earthquakes with impulsive high frequency p and s waves with the mammoth mountain earthquake swarm in mid 1989 we began detecting occasional events with a marked deficiency in energy above 5 hz a feature typical of long period lp volcanic earthquakes these events occur beneath the southwest flank of mammoth mountain at focal depths ranging from 10 to 28 km distinctly deeper than the 2 to 10 km depth range for tectonic earthquakes in the area the lp events occur at intervals ranging from weeks to months individual occurrences typically consist of several events within 2 to 5 minutes where the largest event has never been first magnitudes range from 0 5 to 1 8 the mid crustal focal depths of the lp events are similar to occurrences at a number of areas with holocene volcanism in japan and the western united states they may indicate the movement of magmatic fluids but do not necessarily indicate an imminent volcanic eruption

varietal heavy mineral analysis of sediment provenance lower cretaceous scotian basin eastern canada abstract the origin of a major increase in sand supply in the early cretaceous of the scotian basin offshore eastern canada has been investigated by analysis of heavy mineral varieties the chemistry of detrital minerals from the scotian basin was compared with that of minerals from potential source rocks sampled from older sedimentary successions river sands and glacial tills on land heavy mineral varieties were established based on 1000 high quality electron microprobe emp analyses and used to classify heavy mineral types by mineral liberation analysis mla which uses a rapid scanning electron microscope particle analyser heavy mineral varieties were compared between the cretaceous quartz arenites and subarkoses and samples from potential source areas different chemical varieties of the same mineral group have different grain size distributions so that their relative modal abundances may be influenced by hydraulic sorting but modal abundance of different varieties of tourmaline garnet and spinel provides useful information widely used provenance sensitive mineral ratios are difficult to interpret because of the abundance of polycyclic sources comparisons of the shape parameters of the individual mineral types are also useful for provenance identification aspect ratio in elongate grains such as tourmaline and zircon is a measure of polycyclic reworking but is influenced by the initial shapes of minerals from different source rocks uniformity of varietal heavy minerals over a large area and stratigraphic range and the covariance of spinel and zircon with quite different crystalline sources indicate predominance of polycyclic sources to the central scotian basin probably principally from carboniferous and lower paleozoic sandstones in part sourced from western newfoundland ophiolites heavy mineral varieties in the west scotian basin can be closely matched to sources in the adjacent meguma terrane of the appalachians all the data show that the sands of the scotian basin were derived from reworking of crystalline basement of the appalachian orogen and its paleozoic sandstone cover uplifted during rifting of iberia from the grand banks there is no evidence of a significant supply of sand to the scotian basin from a proto st lawrence river

tomographic image of a seismically active volcano mammoth mountain california high resolution tomographic p wave s wave and vp vs velocity structure models are derived for mammoth mountain california using phase data from the northern california seismic network and a temporary deployment of broadband seismometers an anomalous volume 5 1 109 to 5 9 1010m3 of low p and low s wave velocities is imaged beneath mammoth mountain extending from near the surface to a depth of 2 km below sea level we infer that the reduction in seismic wave velocities is due to the presence of co2 distributed in oblate spheroid pores with mean aspect ratio 1 6 10 3 to 7 9 10 3 crack like pores and mean gas volume fraction 8 1 10 4 to 3 4 10 3 the pore density parameter 3 4 na3 0 11 where n is the number of pores per cubic meter and a is the mean pore equatorial radius the total mass of co2 is estimated to be 4 6 109 to 1 9 1011 kg the local geological structure indicates that the co2 contained in the pores is delivered to the surface through fractures controlled by faults and remnant foliation of the bedrock beneath mammoth mountain the total volume of co2 contained in the reservoir suggests that given an emission rate of 500 tons day 1 the reservoir could supply the emission of co2 for 25 1040 years before depletion continued supply of co2 from an underlying magmatic system would significantly prolong the existence of the reservoir

paleohydrogeological and thermal events recorded by fluid inclusions and stable isotopes of diagenetic minerals in lower cretaceous sandstones offshore nova scotia canada upper jurassic lower cretaceous sandstones of the scotian basin offshore eastern canada are important gas reservoirs previous studies of fluid inclusions in jurassic limestones and apatite thermochronology of cretaceous sandstones have suggested a late mesozoic thermal event fluid inclusions in different authigenic cements were analyzed to determine the temperature and composition of basinal fluid at the time of precipitation and the timing of hydrocarbon migration and entrapment fifty one sandstone samples were analyzed for stable isotope composition 18o and 13c of carbonate cements trapping temperatures for primary aqueous inclusions hosted in quartz overgrowths 89 175c and in late carbonate cements 138 173c are higher than predicted by two dimensional modeling from burial alone based on postrift geothermal gradients these inclusions contain high salinity fluids mostly 19 22 wt nacl equivalent second predominantly aqueous inclusions have much lower salinities 5 2 6 7 wt nacl equivalent and some contain liquid hydrocarbons late fe calcite cement in hauterivian sandstone shows negative values of 13 17 to 9 2 whereas cements in deeper and shallower sandstones have higher 13c values these data indicate that high temperature high salinity fluids preceded hydrocarbon migration the oldest and youngest rocks studied show less effect of high temperatures than do rocks that were buried to depths of at least 2 km 1 2 mi after 135 ma and before 100 ma both fluid inclusions and 13c of carbonate cement suggest that highest temperatures were achieved during burial at 115 to 105 ma this early cretaceous thermal event had a geothermal gradient of at least 55c km it is earlier than the previously reported event based on apatite fission tracks but is consistent with the fission track data the event is synchronous with regional evidence of volcanism and its peak coincides with rapid salt tectonic deformation in the deep basin hydrocarbon charge to the outer shelf wells occurred after this thermal event and thus not before the late cretaceous

sand composition changes across key boundaries of siliciclastic and hybrid depositional sequences abstract sand composition of arenite successions is sensitive to a suite of factors operating between initial grain production and final diagenesis on a variety of spatial and temporal scales seven allogenic factors the relative importance of which relies upon the complex interaction between tectonics eustasy and climate play a decisive role in dictating petrofacies distribution within siliciclastic to hybrid depositional sequences these factors include i tectonic exhumation ii physical and chemical rock breakdown iii change in sediment flux iv change in source basin physiography v shelf colonization by organisms vi generation of chemical grains and vii volcanism autogenic processes may locally have a considerable influence on the type and amount of sediment supplied to the basin thus interfering with the external control based upon literature data a conceptual framework of expected compositional changes across the key surfaces for sequence stratigraphic interpretation is outlined two case histories from the miocene shelf to turbidite deposits of the northern apennines and the quaternary alluvial to nearshore succession of the adriatic coast respectively are used as references to illustrate how arenite petrofacies changes can be framed into a sequence stratigraphic scheme on multiple timescales

diagenetic controls on the reservoir quality of the tight gas collyhurst sandstone formation lower permian east irish sea basin united kingdom abstract the lower permian collyhurst sandstone formation is an important gas reservoir both offshore and onshore in the east irish sea basin of north western uk and is considered to be a tight gas reservoir diagenetic processes have significantly influenced the reservoir quality of the sandstone this study employs petrographic mineralogical and stable isotopic analyses on two different onshore core successions to investigate the composition and texture the diagenetic history and the impact of lithology and diagenesis on reservoir quality the collyhurst sandstone formation consists of fine to very coarse grained poorly to well sorted sub arkosic to lithic arenite sands the reservoir properties of the sandstone are relatively poor with average porosity and permeability of 6 6 and 0 387 md respectively on the basis of petrographic analyses five sandstone lithofacies were identified fine grained conglomeratic carbonate cemented quartz cemented and matrix free contrasting characteristics between the reservoir units suggest the development of divergent diagenetic pathways features observed during early diagenesis include compaction growth of pore filling early carbonate cements calcite i dolomite and siderite i and vermicular kaolinite late diagenetic features include further carbonate cementations ferroan dolomite ankerite calcite ii and siderite ii iii clay mineral cementation illite and chlorite with both grain coating and pore filling textures also common in late diagenesis are syntaxial quartz overgrowths albite barite and anhydrite are minor late diagenetic cement phases compaction processes rather than cementation accounts for the major destruction of the initial sandstone porosity but cementation still accounts for up to 32 of porosity loss carbonate cements mostly fill intergranular pores thus block pore throat and prevent migration of fluid clay minerals bridge and occlude pores resulting in further destruction of the reservoir quality the study provides insights into how lithofacies primary composition texture and sorting and diagenesis can influence reservoir qualities of tight gas sandstones

sequence stratigraphic distribution of diagenetic alterations in coal bearing paralic sandstones evidence from the rio bonito formation early permian southern brazil linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations and hence of reservoir quality a study of the coal bearing alluvial deltaic estuarine and shallow marine sandstones of the rio bonito formation early permian parana basin southern brazil reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework calcite dolomite siderite kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries transgressive and maximum flooding surfaces and is systematically distributed within lowstand transgressive and highstand systems tracts diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite detectable in resistivity wire line logs concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries particularly in the transgressive systems tract meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries transgressive and maximum flooding surfaces favoured the formation of grain rimming siderite the results of this study are relevant to the exploration of coal bed methane and other coal bearing reservoirs where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments

distribution of diagenetic alterations in fluvial and paralic deposits within sequence stratigraphic framework evidence from the petrohan terrigenous group and the svidol formation lower triassic nw bulgaria abstract elucidation of diagenetic alterations in the petrohan terrigenous group fluvial highstand systems tract hst sandstones and svidol formation tide dominated deltaic and tidal flat transgressive systems tract tst and highstand systems tract hst respectively sandstones and calcarenite lower triassic nw bulgaria was constrained within a sequence stratigraphic framework eogenetic alterations in the fluvial hst sandstones include i formation of grain coating infiltrated clays as a result of percolation of mud rich surface waters into underlying coarse grained and permeable channel fills and crevasse splay sandstones ii formation of pseudomatrix by mechanical compaction of mud intraclasts that were incorporated into the coarse grained channel sandstones during their lateral avulsion and iii cementation by calcite 18 o vpdb 6 5 to 3 13 c vpdb 5 1 to 0 6 and dolomite 18 o vpdb 6 1 to 0 3 13 c vpdb 7 2 to 5 8 in the crevasse splay and floodplain sediments mesogenetic alterations that are encountered in the fluvial hst sandstones include i illitization of grain coating clays mud intraclasts and mica possibly because of simultaneous albitization of feldspars ii cementation by calcite 18 o vpdb 14 5 to 8 4 13 c vpdb 7 7 to 0 6 and dolomite 18 o vpdb 15 8 to 5 13 c vpdb 7 9 to 1 5 and iii limited amounts of quartz overgrowths in the channel sandstones owing to occurrence of thick grain coating clays conversely the tide dominated deltaic tst sandstones and the tidal flat hst calcarenite were pervasively cemented by calcite 18 o vpdb 6 6 to 3 1 13 c vpdb 5 1 to 0 6 and siderite 18 o vpdb 7 2 to 5 7 13 c vpdb 0 3 to 0 9 particularly below marine and maximum flooding surfaces due to the presence of abundant bioclasts and prolonged residence time of the sediments under certain geochemical conditions along these surfaces the remaining open pores were cemented during mesodiagenesis by calcite 18 o vpdb 6 6 to 3 1 and 13 c vpdb 5 1 to 0 6 and dolomite 18 o vpdb 6 6 to 3 1 and 13 c vpdb 5 1 to 0 6 this study shows that constructing a conceptual model for the distribution of diagenetic alterations is possible by integration of diagenesis with sequence stratigraphy the model shows that tide dominated deltaic tst sandstones and tidal flat hst calcarenite were pervasively cemented by carbonates during near surface eodiagenesis owing to the presence of abundant bioclasts conversely fluvial lst sandstones remained poorly cemented during near surface eodiagenesis due to the lack of bioclasts but were cemented by mesogenetic calcite dolomite and quartz overgrowths instead

sediment geochemistry as a provenance indicator unravelling the cryptic signatures of polycyclic sources climate change tectonism and volcanism interpretation of bulk sediment geochemistry is one of several approaches for determining sediment provenance this study investigates the value added by bulk sediment geochemical analysis in interpreting provenance in a passive margin clastic basin the upper jurassic lower cretaceous deltaic sediments of the scotian basin provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant more than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km thus impacting principal component analysis and published weathering indices however multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the tithonian and barremian and changes in supply from major tectonic events such as the top aptian uplift in the labrador rift covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources geochemical analyses revealed a previously unsuspected tithonian alkali volcanic sediment source characterized by high niobium and tantalum the lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance published discrimination diagrams are of limited value statistical analysis of geochemical data is strongly influenced by diagenetic processes episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones single indicator elements for particular sources are generally lacking nevertheless careful consideration of geochemical variability on a case by case basis integrated with detrital mineral studies provides new insights into palaeoclimate sediment provenance and hence regional tectonics although there is no simple template for such analysis this study demonstrates an approach that can be used for other basins

microbial influence on the oxygen isotopic composition of diagenetic siderite abstract numerous early diagenetic siderite concretions previously described have been interpreted as the results of microbially mediated reactions interpretation of oxygen isotope data for such material requires an understanding of the effect of temperature on fractionation processes however whilst equilibrium fractionation of oxygen isotopes between siderite and water has been measured down to 33 c extrapolation to lower temperatures may be invalid furthermore inorganic measurements may not be applicable to microbial systems the specific iron reducing microorganism geobacter metallireducens has been cultured anaerobically in the laboratory using acetate as an organic substrate and amorphous feooh as an electron acceptor the acetate is oxidised to co2 with concurrent iron reduction and extracellular siderite precipitation rhombohedral siderite crystals up to 25 m in size have been precipitated over a range of temperatures 18 40 c stable isotopic analysis of these crystals and the solutions from which they precipitate shows that this microbial precipitation of siderite has an associated isotopic fractionation different from the published equilibrium and which is not simply a function of temperature in all cases 18o values of siderite are lower than predicted by inorganic equilibrium fractionation data this may explain the numerous anomalously low 18o values reported for early diagenetic marine siderites and previously attributed to mechanisms such as mixing with meteoric water sediment water interaction recrystallisation or variable isotopic fractionation despite a lack of supporting evidence