the viscosity of fine grained sediments a comparison of low to medium activity and high activity clays abstract viscosity is generally recognized as an indicator of landslide mobilization viscous behavior at relatively low high shear rates is an important predictor of the motion of slow fast moving landslides the viscosity in a modified bingham model at low and high shear rates was examined the viscous characteristics are primarily dependent on the physico chemical properties of the materials in question e g grain size mineralogy salinity in this context the viscous characteristics of low to medium activity and high activity clays bentonite with different salinities were compared empirical relationships exist between the liquidity index and the plastic viscosity regardless of the mineralogical composition this study also demonstrated a positive relationship between the liquidity index and the viscosity in a modified bingham model with n 1 the results showed that low to medium activity and high activity clays fall into a similar range for fine grained sediments mixed with salt water 30 g l however an effect of salinity was evident when using high activity clays mixed with fresh water modified bingham model is a useful and powerful tool for describing pre and post yield viscosity in engineering practice by correlating the geotechnical and rheological properties of fine grained sediments index properties can help to estimate the appropriate values for the rheological parameters of these soils

impact of early dolomitization on multi scale petrophysical heterogeneities and fracture intensity of low porosity platform carbonates albian cenomanian southern apennines italy abstract petrographic petrophysical and fracture analyses were carried out on middle cretaceous platform carbonates of the southern apennines italy that represent an outcrop analogue of the val d agri and tempa rossa reservoirs of the basilicata region the studied outcrops which are made of interlayered limestones and dolomites of inner platform environment were selected to study the impact of dolomitization on reservoir properties and the control of dolomite texture on fracture development two types of dolomites both formed during very early diagenesis were found interlayered at a metre scale with micrite rich limestones mainly mudstones and wackestones dolomite a is fine to medium crystalline and makes non planar mosaics dolomite b is coarse crystalline and makes planar s and planar e mosaics the intercrystalline space of the planar e subtype of dolomite b is either open or filled by un replaced micrite or by late calcite or saddle dolomite cement dolomite a and dolomite b have similar average porosities of 3 7 and 3 1 respectively which are significantly higher than the average porosity of limestones 1 4 their poro perm relationships are similar with the notable exception of planar e type b dolomites which generally display higher permeability values the intensity of top bounded fractures is distinctly lower in coarse crystalline dolomites than in fine crystalline dolomites and limestones both at the macro and the micro scale on the other hand neither lithology i e limestone vs dolomite nor dolomite crystal size control the intensity of perfect bed bounded fractures which is strictly controlled by the fracture layer thickness our results provide information that could be used as guidance for the characterization and modelling of fractured carbonate reservoirs made of interlayered limestones and dolomites

the timing and environment of tepee formation in a marinoan cap carbonate thin carbonate units capping marinoan age glacial diamictites contain atypical tepee like structures that have been interpreted as evidence of seafloor dolomite cementation at parachilna gorge in the adelaide fold thrust belt a marinoan age cap dolomite contains paired tepee and growth fault structures that demonstrate the tepees grew 3 5 7 1 m below the sediment water interface in the early diagenetic zone although generally much larger such tepees and their associated sheet veins have an external morphology and internal structure identical to that of inter tidal tepee structures formed through expansive crystallisation on the other hand cap carbonate hosted tepees lack the size chaotic internal bedding carbonate crust and concretionary morphologies and expected carbon isotope geochemistry to be cold seep structures expansive crystallisation during early diagenesis seems the most likely means of forming tepees in cap carbonates the only cement common to all cap carbonate tepees is microcrystalline dolomite the crystallisation of this mineral phase drove both tepee growth and the fluid overpressure fracturing that formed the sheet veins the same microcrystalline dolomite is the component of cap carbonates routinely selected for isotopic analysis with the resulting 13c values assumed to be representative of coeval marine bicarbonate however the parachilna gorge tepees suggest that the microcrystalline dolomite contains both primary and early diagenetic components their separation is not achieved by current analytical methods

tsunamigenic sources in an active european half graben gulf of corinth central greece abstract the gulf of corinth is an active half graben dissecting the mainland of greece along an east west axis the gulf is well known for its intense seismic activity and its rapid extension rates however published historical catalogues reveal that the gulf of corinth is also the site of frequent and relatively destructive tsunami occurrences this paper presents a comparative study of the potential of probable tsunami sources in the gulf of corinth by referring to published offshore geology data coseismic seafloor displacement along offshore faults and submarine mass failures are the active tsunamigenic sources the paper applies easy to use empirical and semi empirical equations that estimate the generated tsunami wave height just over the source area building upon the most probable worst case scenarios for both coseismic fault displacement and submarine mass failure generated tsunamis the tsunami potential of its case is explored a maximum probable 6 7 m w offshore earthquake would produce a rupture on the seafloor surface with a maximum displacement of 0 66 to 1 08 m in height in the gulf of corinth the tsunami which would be generated by the seafloor displacement would have a wave height of the same magnitude as the seafloor displacement furthermore existing evidence of submarine mass failures that took place over the last 3000 years in the eastern part of the corinth gulf had and would have the potential of generating tsunamis with a maximum wave height of 1 04 and 4 04 m and maximum wave length of 4 52 and 6 25 km

dolomites and dolomites in mesozoic platform carbonates of the southern apennines geometric distribution petrography and geochemistry abstract a multidisciplinary study of the dolomitized bodies present among the late triassic to late cretaceous carbonate deposits of the monti lattari belt southern apennines of italy compares the different dolomitization styles present within this succession of these mesozoic platform carbonates and furnishes an overview of their formative genetic models the revealing traces of the diverse modes of diagenesis in this region include both surface and subsurface mechanisms utilizing a geometric reconstruction of the dolomitized bodies an integrated facies and petrographic analysis of the components and a geochemical characterization of the sediments including detailed mineralogy and associated stable isotope values the data presented demonstrate that some intervals are characterized by surface related dolomitization processes middle late triassic and cretaceous while others latest triassic to lower middle jurassic and are mainly dominated by later large scale subsurface dolomitization processes all of the middle late triassic norian successions are pervasively dolomitized exhibit fabric preserving textures and have a distinctly heavy stable isotope signature their origin has been related to diagenesis due to particular climatic and palaeoceanographic conditions leading to the formation of extended blankets of shallow warm saline seawater this setting was terminated by climatic and palaeoceanographic changes during the latest triassic which dramatically reduced the significance of surface related dolomitization on a regional scale the overlying latest triassic rhaetian outcrops consist of a widespread coarse fabric destructive massive dolomite with a lighter isotopic signature these dolomites seem genetically related to the ones of the lower middle jurassic which share the same geometrical petrographic and geochemical characteristics caused by large scale fluid circulation this diagenetic pattern apparently started in the early jurassic during burial driven by thermal convection due to the different temperatures between the oceanic waters and the warmer carbonate platform the middle upper jurassic units feature local episodes of early dolomitization that partially replaced the muddy carbonate facies due to tidal pumping and reflux mechanisms dolomitization is not a pervasive feature during this phase of deposition in the cretaceous portion of the succession dolomites have a totally different and distinct character and are generally related to bedding and show variability in textures and mg ca ratios local association with evaporites geometry of dolomitized bodies and stable isotope geochemistry suggest processes comprising evaporative pumping and reflux all related to the surface environment this evidence points to a renewal of a climatic context more favorable for early dolomitization thus this study permits recognition of the presence of three quite different dolomitization styles within the carbonate platform succession of the southern apennines fold thrust belt one ascribed to the norian one to the rhaetian lower jurassic and one to the cretaceous

numerical analysis of the mobility of the palos verdes debris avalanche california and its implication for the generation of tsunamis abstract analysis of morphology failure and post failure stages of the palos verdes debris avalanche reveals that it may have triggered a significant tsunami wave our analysis of the failure itself indicates that the slope is stable under aseismic conditions but that a major earthquake with a magnitude around 7 could have triggered the slide a post failure analysis considering the debris avalanche as a bi linear flow shows that peak velocities of up to 45 m s could have been reached and that the initial movement involved a mass of rock less than 10 km wide 1 km long and about 50 80 m thick initial wave height estimates vary from 10 to 50 m tsunami waves propagating to the local shoreline would be significantly smaller such a range demonstrates our lack of proper knowledge of the transition from failure to post failure behavior related to mass movements further investigations and analyses of terrestrial and submarine evidence are required for a proper hazard assessment related to tsunami generation in the los angeles area

synsedimentary dolospar cementation a possible devonian example in the camsell formation northwest territories canada1 a unique association of beds containing fenestral pore filling medium crystalline dolomite with beds of dolospar and quartz sandstone occurs in the lower devonian camsell formation many of these sandstones consist almost entirely of dolospar sand sedimentological petrographic cathodoluminescent and chemical data indicate that the dolospar sands consist of grains that have been eroded and reworked during camsell deposition from fenestral dolostone beds that directly underlie these sandstones erosional truncation of individual dolomite crystals and of intracrystalline cathodoluminescent zonations along the edges of sand grains indicates that either dolomitization or dolomite cementation of the pore filling carbonate cements within fenestrae of the fenestral fabrics occurred before erosion and deposition of dolospar sand the fine details of the cathodoluminescent zonations suggest that the pore filling fenestral dolomite originated as primary cements that underwent some annealing recrystallization under the influence of high subsurface temperatures this unique occurrence may document synsedimentary devonian cementation by medium to coarsely crystalline dolomite

petrology petrochemistry and stromatolites of the middle to late proterozoic beck spring dolomite eastern mojave desert california the beck spring dolomite is the medial unit of the middle to late proterozoic pahrump group the oldest sequence of sedimentary rocks in eastern california stratigraphic sections of the beck sprin

retention of high permeability during shallow burial 300 to 500 m of carbonate grainstones abstract a progressive decrease in matrix permeability occurs with burial in the paleogene limestones of west central florida yet grainstones with permeabilities 400 md persist below burial depths of 300 m why some grainstones retain high permeability during passage through the shallow burial realm was investigated using 85 dominantly foraminifera and micritized grain grainstones from the eocene avon park formation twenty seven variables representing diagenesis stratigraphic packaging depositional energy grain types and pore network attributes were quantified permeabilities range from 23 to 7 160 md and thin section porosities range from 14 to 36 grain size lower coarse to upper fine sand covaries positively with sorting poor to very good the samples are from three different systems tracts within the avon park and sampled grainstone bodies ranged in thickness from 0 5 to 3 5 m evidence of diagenesis include mechanical and chemical burial compaction pre compaction cements and dissolution original interparticle porosity loss due to compaction copl and cementation cepl range from 0 to 35 3 and 1 6 to 26 2 respectively most original intraparticle porosity is occluded but most moldic porosity which ranges from 1 2 to 12 remains open multivariate regression reveals that 61 of the variance in permeability is attributed to grain size cepl copl and systems tract a proxy for relative abundance of compactable foraminifera versus robust micritized grains large grain size means a large initial permeability all other regression components reflect diagenetic reductions in permeability observed ranges in cepl and copl values mean they can reduce permeability by more than three orders of magnitude whereas the other regression parameters reduce it by only one order of magnitude retention of high 400 md permeability can occur by 1 cementation of 40 of the original interparticle pore space which inhibits subsequent compaction yet preserves high permeability or 2 a combination of cementation and compaction that destroys less than two thirds of the original interparticle pore space these relations derived from originally calcite rich sediments provide a quantitative reference by which to evaluate permeability preservation during shallow burial in numerical simulation of diagenesis and reservoir development capillary pressure data also support the hypothesis that pore geometries and hence permeability respond differently to compaction versus cementation cement dominated samples exhibit a dominance of porosity behind intermediate sized pores at higher permeabilities than compaction dominated samples compaction also does not yield a large change in the amount of porosity behind pore throats smaller than 1 at any permeability above 20 md whereas cementation dominated diagenesis generates significant amounts of pore space behind those small throats once permeability goes below 100 md these differences arise because cementation converts the original interparticle pores to a system of interparticle polyhedral and sheet like pores connected by progressively smaller pore throats between cement crystals whereas compaction merely constricts the original interparticle porosity behind smaller intergranular pore throats

flow behaviour and runout modelling of a complex debris flow in a clay shale basin identification of debris flow hazard areas necessitates the knowledge of the flow thickness and the runout distance both have been investigated using a numerical runout model on the faucon stream south french alps representative of clay shale basins results of various rheological tests and numerical experiments are presented and discussed the calibration of the model was undertaken using the results of both geomorphological surveys and sedimentological analyses rheological tests using either a parallel plate rheometer a coaxial rheometer slump tests and an inclined plane were carried out on several samples results have shown that the flow behaviour could be described by an herschel bulkley constitutive equation the rheological responses of several natural suspensions collected from surficial deposits sandstones moraines weathered black marls were also investigated in order to model the runout of the flow the model bing was used the model describes well the influence of each type of sediment on the behaviour runout distance deposit thickness of the flow although the velocities were significantly overestimated different risk scenarios are tested and discussed copyright 2005 john wiley sons ltd

comments and reply on precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites comment

mountain waves over mont blanc influence of a stagnant boundary layer abstract a stationary mountain wave embedded in southwesterly flow over mont blanc in the alps was observed simultaneously by three research aircraft and three types of remote sensing gps dropsondes airborne light detecting and ranging lidar and rapid scan satellite imagery these observations provide a basis for testing linear and nonlinear theories of how mountain waves over complex terrain are controlled by the ambient wind profile especially the effects of a low level stagnant layer and the jet stream aloft the layer of blocked flow near the ground reduced the amplitude of the wave generation the strong wind and weak stability in the upper troposphere forced the wave into a decaying evanescent state in spite of this evanescent condition no lee waves were observed the authors resolve this paradox by demonstrating that the stagnant layer below 3 km played an additional role it was able to absorb downward reflected waves preventing the formation of a resonant cavity linear theory inclu

the effects of dolomitization on petrophysical properties and fracture distribution within rift related carbonates hammam faraun fault block suez rift egypt abstract petrographic and petrophysical data from different limestone lithofacies skeletal packstones matrix supported conglomerates and foraminiferal grainstones and their dolomitized equivalents within a slope carbonate succession eocene thebes formation of hammam faraun fault block suez rift egypt have been analyzed in order to link fracture distribution with mechanical and textural properties of these rocks two phases of dolomitization resulted in facies selective stratabound dolostones extending up to two and a half kilometers from the hammam faraun fault and massive dolostones in the vicinity of the fault 100 metres stratabound dolostones are characterized by up to 8 times lower porosity and 6 times higher frequency of fractures compared to the host limestones precursor lithofacies type has no significant effect on fracture frequency in the stratabound dolostones at a distance of 100 metres from the fault massive dolostones are present which have 0 5 times porosity of precursor limestones and lithofacies type exerts a stronger control on fracture frequency than the presence of dolomitization undolomitized vs dolomitized massive dolomitization corresponds to increased fracture intensity in conglomerates and grainstones but decreased fracture intensity in packstones this corresponds to a decrease of grain crystal size in conglomerates and grainstones and its increase in packstones after massive dolomitization since fractures may contribute significantly to the flow properties of a carbonate rock the work presented herein has significant applicability to hydrocarbon exploration and production from limestone and dolostone reservoirs particularly where matrix porosities are low

perspectives on proterozoic surface ocean redox from iodine contents in ancient and recent carbonate abstract the proterozoic eon hosted the emergence and initial recorded diversification of eukaryotes oxygen levels in the shallow marine settings critical to these events were lower than today s although how much lower is debated here we use concentrations of iodate the oxidized iodine species in shallow marine limestones and dolostones to generate the first comprehensive record of proterozoic near surface marine redox conditions the iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters to assess the validity of our approach neogene quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate iodine contents despite the potential for diagenetic loss maximum proterozoic carbonate iodine levels are elevated relative to those of the archean particularly during the lomagundi and shuram carbon isotope excursions of the paleo and neoproterozoic respectively for the shuram anomaly comparisons to neogene quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends the baseline low iodine levels in proterozoic carbonates relative to the phanerozoic are linked to a shallow oxic anoxic interface oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes however the diagnostically low iodine data from mid proterozoic shallow water carbonates relative to those of the bracketing time intervals are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans this redox instability may have challenged early eukaryotic diversification and expansion creating an evolutionary landscape unfavorable for the emergence of animals

sea level sediments and the composition of seawater the composition of seawater changed significantly during the course of the phanerozoic in concert with long term changes in sea level which were largely the result of changes in the volume of mid ocean ridges these reflect changes in the rate of seafloor spreading and determine the rate of seawater cycling through mid ocean ridges spencer and hardie 1990 and hardie 1996 proposed that the changes in the cycling rate of seawater through mid ocean ridges have been responsible for the changes in the composition of seawater during the phanerozoic this explanation cannot account for the major changes in the composition of seawater during the cenozoic which was a time of nearly constant seafloor spreading rate however changes in the rate of deposition of shallow water carbonates and their penecontemporaneous dolomitization can explain the cenozoic changes in seawater composition this indicates that sedimentologic parameters have played a major role in the chemical evolution of seawater the more rapid cycling of seawater through mors during the mesozoic can explain semiquantitatively the fairly minor differences between the composition of seawater in the eocene and in the jurassic changes in the composition of seawater during the paleozoic were probably determined both by changes in the rate of dolomite and gypsum anhydrite deposition and by changes in the rate of seawater cycling through mid ocean ridges if the causes of these compositional changes are the same as those during the cenozoic and mesozoic then sedimentologic factors have been significantly more important than the rate of cycling of seawater through mors in shaping the chemical evolution of seawater during the phanerozoic

conceptual and numerical modeling of the big 95 debris flow western mediterranean sea abstract the big 95 debris flow affected 2 200 km2 of the ebro continental slope and rise in the western mediterranean sea the resulting deposit of sandy and silty mud has a volume of 26 km3 and is up to 150 m thick dating yields a minimum failure age of ca 11 500 cal yr bp swath bathymetry data very high resolution seismic reflection profiles side scan sonographs and sediment cores indicate that the debris flow consisted of two main components relatively coarse more mobile material which was mostly remolded during flow and finer more cohesive material which moved as independent blocks and partially kept its internal coherence these blocks were partially buoyant and were pushed and dragged up to 15 km by the mobile material during transport the blocks broke into smaller fragments the more mobile material kept on flowing reaching almost 2 000 m water depth in the valencia channel after traveling 110 km in this paper a conceptual and numerical model of the big 95 debris flow is investigated the more mobile component has been modeled as a bingham fluid with assigned rheological properties the more cohesive material has been idealized as consisting of rigid blocks using a simplified end member scenario the blocks are modeled as being at rest and then moved by interaction with the mobile material as the mobile material comes into contact with the blocks the latter are subjected to interaction forces the impact force static earth pressure force shear force and water drag in addition to gravity and the coulomb friction with the seafloor theoretical values for the internal friction angle of the blocks and the yield strength of the mobile material were adjusted to reproduce the observed run outs of 15 20 km for the blocks and 70 km for the mobile material the numerical results demonstrate that the proposed conceptual model is physically possible with input values of the order of 1 for the coulomb frictional angle and 800 pa for the yield strength such values even if certainly low are in line with recent estimates for other subaqueous debris flows and might be explained by processes aiding mobilization such as hydroplaning and entrapment of more mobile material underneath the blocks alternatively it might imply that the blocks were already in motion before the impact of the mobile material took place

1d numerical model of muddy subaqueous and subaerial debris flows a 1d numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented the model incorporates the herschel bulkley and bilinear rheologies of viscoplastic fluid the more familiar bingham model is integrated into the herschel bulkley rheological model the conservation equations of mass and momentum of single phase laminar debris flow are layer integrated using the slender flow approximation they are then expressed in a lagrangian framework and solved numerically using an explicit finite difference scheme starting from a given initial shape a debris flow is allowed to collapse and propagate over a specified topography comparison between the model predictions and laboratory experiments shows reasonable agreement the model is used to study the effect of the ambient fluid density initial shape of the failed mass and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows it is found that initial failure shape influences the front velocity but has little bearing on the final deposit shape in the bingham model the excess of shear stress above the yield strength is proportional to the strain rate to the first power this exponent is free to vary in the herschel bulkley model when it is set at a value lower than unity the resulting final deposits are thicker and shorter than in the case of the bingham rheology the final deposit resulting from the bilinear model is longer and thinner than that from the bingham model due to the fact that the debris flow is allowed to act as a newtonian fluid at low shear rate in the bilinear model

the landslide tsunami of november 3 1994 skagway harbor alaska we show that the tsunami of november 3 1994 in skagway alaska was generated by an underwater landslide formed during the collapse of a cruise ship wharf undergoing construction at the head of taiya inlet this event occurred at a time of extreme low tide and was not associated with a regional seismic event or incoming oceanic tsunami persistent wave motions with an amplitude of 1 m and a period of 3 min recorded by a tide gauge in skagway harbor following the landslide are linked to the formation of a cross inlet seiche and quarter wave resonance within the harbor the high q factor for the harbor q 20 indicates weak dissipation and strong resonance within the harbor

numerical modeling of an underwater bingham plastic mudslide and the waves which it generates underwater landslides are a common source of tsunamis in coastal areas theoretical and experimental studies on this problem however are scarce because of the difficulties in modeling and observing a submarine slide and the associated tsunami to study this problem we present a numerical model that simulates the coupling of a bingham plastic mudslide on a gentle uniform slope with the surface waves which it generates a formulation of the dynamics of the problem is presented where the landslide is treated as an incompressible bingham plastic flow and the water motion is assumed irrotational the long wave approximation is adopted for both water waves and the mudslide dispersion of waves and potential turbulent mixing are not considered the resulting differential equations are solved by a finite difference method we present the numerical results for successive profiles of the mud surface the horizontal velocity distributions of the slide the evolution of the surface elevations and the distributions of the particle velocity of the water motion three major parameters dominate the magnitude of the waves if the volume of the mud is fixed the density of mud the yield stress of the mud and the depth of water at the mudslide site because of the yield stress the slides stop on the slope when the shear stress exerted on the bottom become smaller than the yield stress the bingham plastic behavior of the mud significantly reduces the extent and the speed of the mudslide and also the magnitude of the surface waves generated comparison of the solution of the bingham plastic mudslide model with a snow flow test is presented the solution of a viscous fluid model has been derived as a special case of the present solution

a permeability model for naturally fractured carbonate reservoirs abstract based on a detailed structural study performed on a reservoir surface analogue a fracture permeability model for carbonate reservoirs is proposed this involves four hierarchical systems each one assumed to convey fluids exclusively to that of immediately higher order new basic equations are then provided simulating hydrodynamic reservoir response the large scale first order structures consist of faults to which high permeability structures damage zones are associated at the meter scale stratabound joint systems together with bedding joints bounding the mechanical layers form a connected network transporting fluids to the fault system at a lower scale down to crystal size non stratabound joints constitute a pervasive and capillary fracture network which conveys fluids within the rock mass the non fractured host rock constitutes the lower permeability system at the crystal scale as no published works include an effective integration of detailed structural and numerical models the present study aims at covering a significant gap in the literature also providing appropriate theoretical basis for subsequent studies on fracture network modeling and reservoir simulation besides its application in the field of reservoir development and management the illustrated model may also be useful in environmental studies involving ground fluids such as e g in the field of special toxic nuclear waste management

holocene to pliocene tectonic evolution of the region offshore of the los angeles urban corridor southern california 1 quaternary tectonism in the coastal belt of the los angeles urban corridor is diverse in this paper we report the results of studies of multibeam bathymetry and a network of seismic reflection profiles that have been aimed at deciphering the diverse tectonism and at evaluating the relevance of published explanations of the region s tectonic history rapid uplift subsidence in basins folds and thrusts extensional faulting and strike slip faulting have all been active at one place or another throughout the quaternary period the tectonic strain is reflected in the modern physiography at all scales los angeles la basin has filled from a deep submarine basin to its present condition with sediment impounded behind a large sill formed behind uplifts near the present shoreline newport trough to the south southeast of la basin also accumulated a large volume of sediment but remained at midbathyal depths throughout the period there is little or no evidence of quaternary extensional tectonism in either basin although as much as 6 km of subsidence which mainly occurred by sagging has been recorded in places since the middle miocene the uplifts include folded and thrust faulted terranes in the palos verdes hills and the shelves of santa monica and san pedro bays the uplifted areas have been shortened in a southwest northeast direction by 10 or slightly more and some folds are reflected in the bathymetry two large adjacent midbathyal basins santa monica and san pedro show strong evidence of subsidence and slight west northwest extension 10 during the same time folding was taking place in the uplifts the tectonic boundaries between uplifts and basins are folded normal faulted reverse faulted and strike slip faulted depending on location the rapid quaternary uplift and subsidence along with the filling of la basin have produced a reversal in the regional physiography in the early pliocene la basin was a submarine deep palos verdes and the shelves comprised a northeast basin slope and the present offshore basins and catalina island formed an emergent or shallowly submerged shelf since extensional compressional and lateral strains are all locally in evidence simple notions that this part of southern california underwent a change from miocene transtension to quaternary transpression fail to explain our observations

gravels in the daxing conglomerate and their effect on reservoirs in the oligocene langgu depression of the bohai bay basin north china abstract the daxing conglomerate reservoir has become an important exploration target in the langgu depression of the bohai bay basin in this paper gravel composition void space poroperm characteristics and hydrocarbon productivity of the daxing conglomerate in the third member of the oligocene shahejie formation es3 are studied in detail to understand the impact of gravel type on reservoir quality based on cores petrographic thin sections scanning electron microscope sem photos porosity permeability and well test data the daxing conglomerate is composed of limestone and dolomite gravels the void space of the daxing conglomerate includes intragravel and intergravel pores as well as fissures intragravel pores are dominated by gravel type they develop as intergranular pores intergranular dissolved pores intragranular dissolved pores and few intercrystalline pores in limestone gravels whereas in dolomite gravels they develop as intercrystalline pores intercrystalline dissolved pores dissolved pores and cavities few intergranular pores and intergranular dissolved pores the analysis shows that dolomite conglomerates provide better reservoir quality than limestone conglomerates microscopically areal porosity in dolomite gravels is higher than that in limestone gravels macroscopically porosity and permeability of conglomerates that are dominated by dolomite gravels dolomite conglomerates are better than those of conglomerates dominated by limestone gravels limestone conglomerates the dolomite conglomerates are superior to the limestone conglomerate with regard to hydrocarbon productivity at the level of parent rock and gravel properties poroperm characteristics and hydrocarbon productivity of dolomite reservoirs in the middle proterozoic changcheng and jixian systems parent rocks of dolomite gravels are better than those of the limestone reservoirs in the lower paleozoic cambrian and ordovician parent rocks of limestone gravels gravel properties including grain structure physical nature and dissolution velocity cause the dolomite conglomerates to have more intercrystalline pores fissures and secondary dissolved pores than limestone conglomerates

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

source and progression of a submarine landslide and tsunami the 1964 great alaska earthquake at valdez like many subduction zone earthquakes the deadliest aspects of the 1964 m 9 2 alaska earthquake were the tsunamis it caused the worst of these were generated by local submarine landslides induced by the earthquake these caused high runups engulfing several coastal towns in prince william sound in this paper we study one of these cases in detail the port valdez submarine landslide and tsunami we combine eyewitness reports preserved film and careful posttsunami surveys with new geophysical data to inform numerical models for landslide tsunami generation we review the series of events as recorded at valdez old town and then determine the corresponding subsurface events that led to the tsunami we build digital elevation models of part of the pretsunami and posttsunami fjord head delta comparing them reveals a 1500 m long region that receded 150 m to the east which we interpret as the primary delta landslide source multibeam imagery and high resolution seismic reflection data identify a 400 m wide chute with hummocky deposits at its terminus which may define the primary slide path using these elements we run hydrodynamic models of the landslide driven tsunamis that match observations of current direction maximum inundation and wave height at valdez old town we speculate that failure conditions at the delta front may have been influenced by manmade changes in drainage patterns as well as the fast retreat of valdez and other glaciers during the past century

the offshore morpho structure and tsunami sources of the viti levu seismic zone southeast viti levu fiji abstract new high resolution seabat 8160 multibeam bathymetry data reveal in detail the complex offshore morphology over part of the viti levu seismic zone vlsz in southeast viti levu the mapped seafloor is scarred by a complex network of linear submarine canyons and numerous submarine slides the submarine canyons are morphologic expressions of graben structures in the underlying basement rock submarine canyon faults are continuous with nearshore shelf faults and onshore fault controlled valleys and structural lineaments together these define continuous onshore offshore fault zones which combined form a structurally complex fault mesh of composite origin we attribute the development of the principal fault sets in the fault mesh to progressive distributed faulting in response to anticlockwise tectonic block rotations within the fiji platform during the neogene low occurrence of large earthquakes and a diffused pattern of seismicity currently observed in the vlsz may reflect complex coseismic faulting through the fault mesh the abundance of submarine slides over the vlsz which typically occur on the outer barrier reef edge as well as the submarine canyon heads and walls and mid slope imply that seismic shaking may be an important factor for triggering slope failure morphometric analysis and empirical modelling of the slides show that slides triggered in shallow water depths within 5 km of the coastline at the outer barrier reef edge and submarine canyon heads produce the largest near field tsunami amplitudes we interpret that such slides represent a significant local tsunami hazard

tsunami sources in the southern california bight 1 locally generated tsunamis due to faulting or slope failures offshore southern california threaten nearby coastal cities disruption of operations at port facilities due to tsunami attack could severely impact the regional and national economies this study examines three faults and two landslides scenarios as potential tsunami sources computed runup ranges from 0 5 to 6 m depending on the source and location bathymetric features such as the broad san pedro shelf are shown to contribute to tsunami wave focusing while retarding tsunami arrival times suggesting the usefulness of an early warning system

permeability loss with depth in the cenozoic carbonate platform of west central florida relationships between matrix permeability and depth in shallow buried 500 m cenozoic limestones of florida were investigated using more than 12 000 minipermeameter measurements on 1210 m of slim hole core these data are considered representative of the matrix permeability reduction that accompanies early burial of shallow water subtidal to peritidal nonreefal carbonates of sta ble cratonic margins platforms shelves and ramps measured matrix permeabilities range from less than 4 0 to 6450 md for both limestones and dolostones although the median permeability of limestones 88 md exceeds that for dolostones 15 md sucrosic dolostones which have high intercrystalline po rosities have median matrix permeabilities of 1000 md non sucrosic dolostones which are much less porous have median matrix permeabilities of only 13 md neither population of dolostones exhibits a permeability with depth trend low permeability limestones consist of mudstones wackestones tidal laminites pedogenetically altered limestone lime mud rich breccia and well cemented grain supported rocks these low permeability limestones all exhibit median matrix permeabilities less than 35 md and none exhibit permeability with depth trends in contrast high mud packstones low mud packstones very low mud packstones and grainstones exhibit larger median matrix permeabilities 69 129 181 and 418 md respectively and a systematic reduction with depth in their mean and maximum permeabilities least squares exponential regressions indicate that burial depth explains 22 31 of the permeability variance in these grain supported rocks the balance of the variability within each textural class is attributed to variation in facies grain types grain sizes sorting etc and the amount of early preburial cementation in the absence of permeability enhancement by deep subsurface diagenesis or fracturing extrapolation of the permeability with depth trends suggests that the limestones that have the best reservoir potential in the deeper subsurface are grain supported limestones that have higher than begin page 1254 average matrix permeabilities in the near surface realm petrographic analyses and consideration of diagenetic histories suggest that matrix permeability of the dolostones and low permeability limestones was determined by early near surface dolomitization and cementation respectively and has yet to be affected by burial processes petrographic observations also suggest that the depth signal in grain supported limestones results from mechanical compaction and the onset of grain to grain pressure solution extrapolation of the matrix permeability data indicates that permeability loss with burial occurs faster than the documented burial related porosity loss for the same group of rocks this indicates that limestone permeability is more sensitive to burial compaction than limestone porosity thus preservation of reservoir quality rock during burial is more dependent on permeability preservation than on porosity preservation

microbially catalyzed dolomite formation from near surface to burial abstract over the past century a number of models have been developed to explain the vast stratigraphic distribution of authigenic dolomite these models include hydrogeological geochemical and geomicrobiological interpretations that shed light on kinetic constraints on low temperature dolomite formation and in particular how certain microbes can overcome such limitations in this review we focus on the direct and indirect mechanisms by which microbes facilitate the nucleation and shallow burial diagenetic stabilization of dolomite in marine sediments we also consider the likely effects of local and global scale biogeochemical perturbations over the distribution and activities of subsurface microbes and thus potentially over the stratigraphic distribution of dolomite considering the many advances that have been made in the fields of geomicrobiology and biogeochemistry during the past 20 years investigating the important role microbes play in sedimentary systems will undoubtedly contribute to a more complete interpretation of dolomite formation in the rock record

carbonate rocks and petroleum reservoirs a geological perspective from the industry abstract carbonate oil reservoirs are sometimes regarded with apprehension in the petroleum industry since it can be difficult to predict the quality of and ensure high recovery factors from this rock family particular problems are the complex and heterogeneous nature of porosity in carbonate rocks often leading to large ranges in permeability for any given porosity and the organization of carbonate successions most commonly as vertically heterogeneous but laterally persistent layers important issues that arise time and again in carbonate reservoir description include a predicting reservoir quality at inter well scales and in uncored wells b recognizing problematic high permeability layers c determining the permeability component to allocate to fractures and connected vug systems and d populating reservoir models with representative physical parameters because porosity in carbonate rocks generally presents as diverse and heterogeneous conventional core plugs are seldom representative of large rock volumes and significant issues remain in terms of the scale compatibility of the various datasets for measured physical parameters that are used in carbonate reservoir description many of the world9s largest carbonate reservoirs were discovered and developed shortly after the second world war and are now showing signs of maturity expressed variously as poor pressure support water or gas breakthrough and stranded resources the proportion of the world9s conventional petroleum that is reservoired in carbonate rocks is commonly estimated at around 50 60 and many large carbonate reservoirs are likely to have a production lifetime beyond 50 years it is no coincidence then that the petroleum industry has been the primary source of funding of and promotion of research into carbonate rocks and depositional systems often with impacts extending well beyond oil and gas exploitation

late proterozoic aragonitic cement crusts bambui group minas gerais brazil the late proterozoic pedro leopoldo facies bambui group in the vicinity of belo horizonte brazil comprises alternating laminated microsparitic limestones 10 35 mm thick beds and fibrous limestones 10 55 mm thick the latter are composed of a mosaic of sparry calcite crystals these irregularly crosscut rays and fans are composed of feathery precursor crystal bundles with squared off growth zones ghosts of an original fibrous mineral hexagonal in cross section are visible the petrographic characteristics very high strontium content and low magnesium content of the fibrous beds as well as microspar beds strongly argue for an original aragonitic mineralogy the rays are interpreted as having formed by precipitation at the sediment water interface whereas the micrite was precipitated from the water column prior to deposition on the sea floor the lack of emergence features suggests widespread aragonite precipitation under persistently subtidal conditions

petrography and geochemistry of the magnesites and dolostones of the ediacaran ibor group 635 to 542 ma western spain evidences of their hydrothermal origin the ediacaran deposits between 635 and 542 ma of the central zone of the iberian massif consist of alternating siliciclastic and carbonate beds these carbonates are dolostones and magnesites which are interpreted to have been formed by the replacement of primary peritidal limestones through petrographic and geochemical analyses we recognize different types of dolomites d1 to d4 and magnesites m1 and m2 despite distinct petrographic features of the four types of dolomite their oxygen and carbon isotopes overlap with 18o values ranging from 15 45 to 17 51 smow and 13c from 0 13 to 3 21 pdb sr isotope values for d1 and d2 range from 0 7028 to 0 7091 magnesites m1 and m2 show oxygen values higher than 17 87 0 and 13c values show the same variability as for the dolomites d3 and d4 oxygen isotope values are between 18 91 and 19 61 and the carbon isotope values range are similar to the other diagenetic phases sr isotope values for the magnesites and late dolomites d3 and d4 are 0 7095 to 0 7104 being higher than those of the d1 and d2 dolomites d1 is a relatively early dolomite phase formed by the replacement of fine grained peritidal limestones the coarser crystal size of d2 which shows similar geochemical features as d1 suggests formation by dolomitization of coarser grained limestones the replacement of d1 and d2 by m1 and m2 advanced along stylolites fractures and bedding planes this replacement is interpreted to have occurred by hydrothermal fluids which is suggested by the presence of talc and forsterite d3 a coarse dolomite completely destroyed any previous texture and d4 dolomite cement post dates magnesite formation interactions of hydrothermal fluids with the prior carbonates reset the oxygen isotopes of the earlier dolomite the study of these magnesites and related dolostones may offer new insights into the model of formation of sparry magnesites hosted by mixed siliciclastic carbonate platform deposits the establishment of the factors and mechanism that control the diagenetic evolution of these carbonates has a great importance in order to understand and predicts porosity and permeability variations of rocks formed under similar geological conditions

diagenesis of carbonate cements in permo triassic sandstones from the iberian range spain evidence from chemical composition and stable isotopes petrographic chemical and stable isotope investigations have been made on calcite dolomite and fe dolomite ankerite from permian triassic clastic sequences from the iberian range spain calcite and dolomite cements have precipitated before the fe dolomite ankerite calcite however has also formed by calcitization of dolomite due to uplift the negative 13cpdb values 9 51 to 2 13 in these carbonates suggest derivation of carbon from oxidation of organic matter in the early carbonates and from decarboxylation of organic matter in the late fe dolomite ankerite early diagenetic dolomitic cements have heavier 13c 3 54 higher mn mn fe and mn mn mg and lower fe fe mg ratios than later diagenetic dolomitic cements the latters are also characterized by lighter 18opdb 10 64 than the early cements due to increase in temperature and to pore water mineral reactions

pacific basin tsunami hazards associated with mass flows in the aleutian arc of alaska abstract we analyze mass flow tsunami generation for selected areas within the aleutian arc of alaska using results from numerical simulation of hypothetical but plausible mass flow sources such as submarine landslides and volcanic debris avalanches the aleutian arc consists of a chain of volcanic mountains volcanic islands and submarine canyons surrounded by a low relief continental shelf above about 1000 2000 m water depth parts of the arc are fragmented into a series of fault bounded blocks tens to hundreds of kilometers in length and separated from one another by distinctive fault controlled canyons that are roughly normal to the arc axis the canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes the volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large scale sector collapse into the sea large scale mass flow deposits have not been mapped on the seafloor south of the aleutian islands in part because most of the area has never been examined at the resolution required to identify such features and in part because of the complex nature of erosional and depositional processes extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the aleutian islands because the aleutian arc is surrounded by deep open ocean mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources to test this hypothesis we present a series of numerical simulations of submarine mass flow initiated tsunamis from eight different source areas we consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope the flows have lengths that range from 40 to 80 km maximum thicknesses of 400 800 m and maximum widths of 10 40 km we also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse at four locations makushin cleveland seguam and yunaska sw volcanoes which represent large to moderate sized events in this region we calculate tsunami sources using the numerical model topics and simulate wave propagation across the pacific using a spherical boussinesq model which is a modified version of the public domain code funwave our numerical simulations indicate that geologically plausible mass flows originating in the north pacific near the aleutian islands can indeed generate large local tsunamis as well as large transoceanic tsunamis these waves may be several meters in elevation at distal locations such as japan hawaii and along the north and south american coastlines where they would constitute significant hazards

origins of microbial microstructures in the neoproterozoic beck spring dolomite variations in microbial community and timing of lithification abstract microbialite microstructures form at the scale of microbial processes and can preserve evidence of growth degradation and lithification in microbial communities understanding how these processes are preserved in microstructures will provide insights into microbial ecosystems and how microbial communities have evolved through time microbialites in the neoproterozoic beck spring dolomite southern california u s a contain microstructures that record variations in the morphology of microbial communities as well as the timing of degradation versus lithification in the communities these processes are represented by five end member microbial microstructures 1 distinct laminated microstructure 2 diffuse laminated microstructure 3 distinct clotted microstructure 4 diffuse and regular clotted microstructure and 5 diffuse and irregular clotted microstructure these microstructures are distinguished by fabrics defined by organic inclusions in distinct microstructures organic inclusions sharply define microbial features such as laminae that are laterally continuous for millimeters or 50 200 micron diameter microdots the contacts between distinct microstructures are always sharp in diffuse microstructures zones of organic inclusions lack distinct boundaries neighboring laminae and clots grade into each other within tens of microns and boundaries between microbial structures and encasing cements are indistinct diffuse microstructures grade into each other and into distinct microstructures in a systematic way that suggests that differences are due to variations in the timing of mineralization relative to growth and degradation of microbial communities sharply defined textures in distinct microstructures suggest that lithification started during growth of the microbial community and the close spatial association but lack of intergrading between distinct laminated and distinct clotted microstructures suggests that they formed from two distinct microbial communities that lived in the same environment by contrast diffuse microstructures formed where lithification occurred after the onset of decay and degradation of the primary growth structure the continuum from distinct microbial textures through more diffuse and irregular textures documents variations in the timing of lithification relative to growth and decay of the microbial community thus where petrographic preservation is extremely good such as in the beck spring dolomite sub millimeter scale microbial microstructures record a gradation between growth and degraded microbial structures depending on the relative timing of lithification and heterotrophic decay

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

tsunamigenic earthquakes past and present milestones we review a number of events which taken individually have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards notably through the development of warning algorithms starting with the 1700 cascadia earthquake we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics the diversity of earthquake cycles the development of warning algorithms the response of communities at risk to warnings and their education the latter being either formal or rooted in ancestral heritage we discuss in detail lessons from the 2004 sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004

sedimentology mineralogy and isotopic analysis of pellet lake coorong region south australia gravity cores of holocene sediments from a shallow ephemeral lake in the coorong region pellet lake southeastern coastal australia show a mineral assemblage and sequence particular to its hydrology the mineralogical sequence above an initial dolomitic siliciclastic sand reflects conditions of increasing salinity in the lower portions of the core i e organic rich aragonite to magnesite hydromagnesite aragonite followed by a relative decrease in salinity i e magnesite aragonite hydrornagnesite to aragonite hydromagnesite in the upper portions of the core this sequence is capped by 0 4 m of micritic dolomite and minor amounts of hydromagnesite with the relative abundance of dolomite increasing upwards three stratigraphically and spatially distinct dolomite units upper lower and margin are recognized using stable carbon and oxygen isotope data unit cell calculations and mgc03 mole per cent data of the dolomite detailed x ray diffraction xrd analyses of samples with more than 80 dolomite shows that the dolomite is ordered average unit cell parameters calculated from the xrd patterns indicate that the upper dolomite unit has crystal lattices expanded in the c direction c 16 09 a relative to ideal dolomite c 16 02 a and contracted in the a direction a 4 796 a relative to ideal dolomite a 4 812 a the mol fraction of mgc03 in the upper dolomite shows up to 4 0 f 2 0 mole per cent excess mg in the dolomite crystal lattice calculated from xrd this unusual dolomite crystal chemistry is probably generated by rapid precipitation from solutions which have greatly elevated mg ca ratios transmission electron microscopy reveals that the upper dolomite has a heterogeneous microstructure which also suggests rapid precipitation from solution the modulated microstructure found in calcium rich dolomite is completely lacking dolomite ordering reflections are present in electron diffraction patterns but are weak stable oxygen and carbon isotope values of the upper dolomite are tightly grouped ave 6l80 x 7 55 6i3c 4 10 yet show three upward lightening oxygen cycles the oxygen cycles correlate with three upward decreases in the calculated mg content of the dolomite zone these cycles may indicate the increased importance of rain water dilution of the brine at times when the water in the lake was at its shallowest levels analyses of the lower dolomite and the margin dolomite suggest that these units precipitated more slowly from less evaporitic brines than the upper dolomite unit the lower dolomite is close to stoichiometric has less evaporitic stable isotope values than the upper dolomite and has only a slightly expanded c axis the margin dolomite is ca rich has a more homogeneous microstructure and has expanded a and c axes the abundance of relatively soluble mg bearing phases such as hydromagnesite and magnesite may supply additional magnesium for the dolomitization of aragonite and calcite during subsequent diagenesis and burial of the sediment this process may leave a finely laminated dolomicrite deposit which retains little if any evidence of evaporite minerals

carbonate rocks and related facies with vestiges of biomarkers clues to redox conditions in the mesoproterozoic ocean abstract the raipur group of the chattisgarh basin preserves two major late mesoproterozoic carbonate platforms the lower platform is about 490 m thick separated from the upper platform 670 m thick by a 500 m thick calcareous shale carbonate strata cover almost 40 of the chattisgarh basin outcrop and represent two major platform types a a non stromatolitic ramp the charmuria sarangarh limestone and b a platform developed chiefly in the intertidal to shallow subtidal environment with prolific growth of stromatolites the chandi saradih limestone the first platform consists primarily of the black timarlaga limestone that is locally replaced by early diagenetic dolomite this carbonate platform experienced strong storm waves and was subsequently drowned by a major transgression during which extensive black limestone marl rhythmite was deposited followed by deposition of the gunderdehi shale the carbonate factory was later re established with development of an extensive stromatolite dominated charmuria sarangarh platform that ranged from restricted embayment to open marine conditions sea level change played a major role in controlling the broad facies pattern and platform evolution the 13 c signatures of the chattisgarh limestones falling within a relatively narrow range 0 to 4 are typical for upper mesoproterozoic carbonate rocks 18 o values however have a greater range 5 7 to 13 3 indicating significant diagenetic alteration of some samples likely dysoxic or anoxic conditions prevailed during deposition of the black timarlaga limestone and well oxygenated conditions during deposition of the gunderdehi shale and saradih chandi stromatolite the lack of 17 21 moretanes and high t max values suggest mature organic matter in the non stromatolitic ramp a paucity of diagnostic eukaryotic steroids indicates that algae were rare in the chattisgarh basin a high content of hopanes supports a generally bacterially dominated proterozoic ocean in which various stromatolites flourished

dolomite reservoirs porosity evolution and reservoir characteristics systematic analyses of the published record of dolomite reservoirs worldwide reveal that the majority of hydrocarbon producing dolomite reservoirs occurs in 1 peritidal dominated carbonate 2 subtidal carbonate associated with evaporitic tidal flat lagoon 3 subtidal carbonate associated with basinal evaporite and 4 nonevaporitic carbonate sequence associated with topographic high unconformity platform margin buildup or fault fracture reservoir characteristics vary greatly from one dolomite type to another depending upon the original sediment fabric the mechanism by which dolomite was formed and the extent to which early formed dolomite was modified by postdolomitization diagenetic processes e g karstification fracturing and burial corrosion this paper discusses the origin of dolomite porosity and demonstrates the porosity evolution and reservoir characteristics of different dolomite types

petroleum reservoir porosity versus depth influence of geological age average porosity values for the producing zones of oil and gas fields worldwide are examined as a function of the present depth for sandstone and carbonate lithologies divided into 10 groupings by reservoir depositional age precambrian silurian to pliocene pleistocene the wide variations in average reservoir porosity within each depth range reflect the extreme ranges in porosity controlling factors such as depositional facies early

assessment of source probabilities for potential tsunamis affecting the u s atlantic coast abstract estimating the likelihood of tsunamis occurring along the u s atlantic coast critically depends on knowledge of tsunami source probability we review available information on both earthquake and landslide probabilities from potential sources that could generate local and transoceanic tsunamis estimating source probability includes defining both size and recurrence distributions for earthquakes and landslides for the former distribution source sizes are often distributed according to a truncated or tapered power law relationship for the latter distribution sources are often assumed to occur in time according to a poisson process simplifying the way tsunami probabilities from individual sources can be aggregated for the u s atlantic coast earthquake tsunami sources primarily occur at transoceanic distances along plate boundary faults probabilities for these sources are constrained from previous statistical studies of global seismicity for similar plate boundary types in contrast there is presently little information constraining landslide probabilities that may generate local tsunamis though there is significant uncertainty in tsunami source probabilities for the atlantic results from this study yield a comparative analysis of tsunami source recurrence rates that can form the basis for future probabilistic analyses

regional porosity variation in thamama b reservoirs of abu dhabi abstract we present a large dataset of average porosity depth thickness and well locations for one of the earth s major oil bearing limestone reservoirs and discuss possible controlling factors petrologic data are not included in this study but regional petrology data from earlier studies and detailed results from one representative oilfield provide a useful basis for interpretation of the present compilation porosity decreases with depth similar to porosity depth trends from other limestone strata but the main data cluster representing the largest fields in the depth range 7000 9500 ft 2134 2896 m follows a much steeper trend approximately parallel with the crest flank trends of individual fields where crestal porosity has apparently been preserved by early arrival of oil maps of depth porosity thickness and departure of porosity from the overall trend illustrate the geographic variation of these parameters solidity thickness with porosity removed is constant from crest to flanks in the largest fields indicating that crest flank porosity differentiation took place by closed system compaction and cementation the principal value created by this work is the framework established for focusing continuing studies that can further constrain the controlling processes and thus develop predictive tools for this particular reservoir and similar micropore dominated limestones worldwide

fourier ray modeling of short wavelength trapped lee waves observed in infrared satellite imagery near jan mayen abstract a time dependent generalization of a fourier ray method is presented and tested for fast numerical computation of high resolution nonhydrostatic mountain wave fields the method is used to model mountain waves from jan mayen on 25 january 2000 a period when wavelike cloud banding was observed long distances downstream of the island by the advanced very high resolution radiometer version 3 avhrr 3 surface weather patterns show intensifying surface geostrophic winds over the island at 1200 utc caused by rapid eastward passage of a compact low pressure system the 1200 utc wind profiles over the island increase with height to a jet maximum of 60 70 m s 1 yielding scorer parameters that indicate vertical trapping of any short wavelength mountain waves separate fourier ray solutions were computed using high resolution jan mayen orography and 1200 utc vertical profiles of winds and temperatures over the island from a radiosonde sounding and an analysis system the radiosonde based simulations pr

model simulations of tsunamis generated by the storegga slides abstract a mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of water waves generated by the submarine storegga slides on the norwegian continental slope the equations are solved numerically by a finite difference technique computations of wave amplification effects reveal run up heights for the second storegga slide between 3 and 5 m in exposed areas along the eastern coast of greenland iceland and scotland and the western coast of norway the calculated run up heights agree remarkably well with possible tsunami wave heights deduced from geological evidences along the eastern coast of scotland the generated wave heights are strongly dependent on the acceleration of the slide the effects of shear stress at the interface between the water and the slide body has turned out to be important

momentum flux estimates for south georgia island mountain waves in the stratosphere observed via satellite abstract we show high resolution satellite observations of mountain wave events in the stratosphere above south georgia island in the remote southern atlantic ocean and compute the wave momentum fluxes for these events the fluxes are large and they imply important drag forces on the circulation small island orography is generally neglected in mountain wave parameterizations used in global climate models because limited model resolution treats the grid cell containing the island as ocean rather than land our results show that satellite observations can be used to quantitatively constrain mountain wave momentum fluxes and they suggest that mountain waves from island topography may be an important missing source of drag on the atmospheric circulation

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

origin of shallow submarine mass movements and their glide planes sedimentological and geotechnical analyses from the continental slope off northern norway submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy in which downslope movement is initiated however little is known about the sedimentology and physical properties of the sediments within these surfaces in this study we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit in combination with high resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated the initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments the 16 m long core comprising mostly undisturbed massive and laminated ice rafted debris rich clay penetrated this slab the base of the slab is characterized by a high amplitude semicontinuous reflection visible on the subbottom profiler data at about 12 5 m depth interpreted to originate from the glide plane on top of a plumite deposit this plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength movement probably started within contouritic sediments immediately above the glide plane characterized by higher sensitivities and higher water contents the occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope the slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass numerical models infinite slope bing and retrogressive slope models illustrate that the present day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger

large scale basement involved landslides california continental borderland large seafloor relief shallow metamorphic basement and seismic activity in the california continental borderland combine to produce major submarine slides capable of generating local tsunamis the catalina schist basement complex of the borderland contains melange units faults between metamorphic facies and foliation derived from a history of deep subduction underthrusting and subsequent tectonic exhumation along regional low angle fault systems neogene volcanic and sedimentary rocks covered the exhumed metamorphic basement forming an interface with a strong contrast in material properties neogene transtensional block faulting formed steep escarpments that cut through and elevated the low angle detachment surface providing slip surfaces with free faces susceptible to failure along the rheological boundary two basement involved slope failure examples west of san diego are described including large block glides and progressive rotational slumps along the steep northeast facing thirtymile bank escarpment and along the southwest flank of fortymile bank

origin and petrophysics of dolostone pore space abstract the common claim that dolomitization creates 12 porosity is based on the mole for mole replacement equation however in the past 50 years data have been collected demonstrating that dolomitization does not create porosity instead dolostones inherit the porosity and fabric of the precursor limestone and porosity is reduced by overdolomitization the porosity of the precursor limestone depends on the diagenetic history up to the time of dolomitization data show that 1 carbonates are born with high porosity and lose porosity gradually over a long period and 2 mud dominated fabrics compact more readily than grain dominated fabrics the problem of estimating the time of dolomitization is minimized by confining observations to young limestones and associated dolostones limited data from holocene dolomitic sediments suggest no change in porosity with dolomitization study of plio pleistocene carbonates in bonaire netherlands antilles demonstrates that precursor limestones are more porous than dolostones limestones average 25 porosity whereas dolostones average 11 porosity data from the neogene of the great bahama bank show that dolostones and adjacent limestones both have 40 porosity porosity studies of the jurassic arab d formation show that dolostones and associated grain dominated limestones have similar porosity ranges and that the decrease in porosity with increasing dolomitization results from compaction of the mud dominated fabrics these data suggest that porosity in dolostone is not created by a mole for mole replacement mechanism instead dolostone porosity is 1 inherited from the precursor limestone and 2 occluded by the process of overdolomitization palaeozoic dolostones however are commonly more porous than juxtaposed limestones the explanation for this observation is that limestones lose porosity through compaction and cementation whereas dolostones resist compaction and retain much of their porosity permeability studies have demonstrated that dolomitization of grain dominated limestones usually does not change porosity permeability relationships instead precursor limestone fabric controls pore size distribution the dolomite crystal size of a muddominated dolostone may however be larger than the carbonate mud size improving the porosity permeability relationship substantially hence there is a predictable relationship between interparticle grains or crystals porosity permeability precursor grain size and dolomite crystal size

rheological properties of loose sands subjected to upward flow the objective of this study was to investigate the rheological properties of loose sands subjected to upward flow by using a vane type rheometer that controlled upward flow in the loose sand specim

diagenetic effects on the well yield of dolomite aquifers in slovenia diagenetic effects upon the hydraulic parameters of dolomite aquifers were examined results indicate that dolomites affected only by late burial diagenesis are economically more interesting to exploit than those formed first by early and then also affected by late diagenesis as the values of most studied hydraulic parameters transmissivity specific capacity linearized specific capacity and maximum yields are higher in the former group data were collected from the hydrogeological reports of 298 wells in dolomites from permian to cretaceous age in slovenia classified in a relational hydrogeological database and analyzed by statistical methods the studied parameters are hydraulic conductivity k transmissivity t specific capacity q q s linearized specific capacity ql q d and maximum yields qmax values of the studied parameters are distributed log normally according to most normality tests and span several orders of magnitude statistical tests show significant differences between the late and early late groups for parameters q ql and t and non significant differences for k and qmax

the coupling of a submarine slide and the surface waves which it generates underwater landslides are a common source of small scale tsunamis in coastal areas they have been the object of only a few theoretical and experimental studies a numerical model is developed to study the coupling of a submarine landslide and the surface waves which it generates a formulation of the dynamics of the problem is presented where the landslide is treated as the laminar flow of an incompressible viscous fluid and the water motion is assumed irrotational long wave approximation is adopted for both water waves and the mudslide the resulting differential equations are solved by a finite difference method we present the numerical results which contrast the behavior of the mud flow under a fixed surface in the presence of one way coupling bottom deformations affect the free surface and with full coupling surface pressure gradients react on the mud flow it is found that three main waves are generated by a landslide starting from rest on a gentle uniform slope the first wave is a crest which propagates away from the mudslide site into deeper water this crest is followed by a trough in the form of a forced wave which propagates with the speed of the mudslide front the third wave is a relatively small trough which propagates shoreward two major parameters dominate the interaction between the slide and the waves it produces the density of sliding material and the depth of water at the mudslide site the two way interactions are significant for the cases of a smaller mud density and shallower waters for the cases of larger mud density and shallower waters the two way interactions are small but the waves generated are very large for larger initiation depth of the mudslide the interactions are weak and the waves generated are small we also examined the possibility of a resonance between the slide and the waves our numerical results indicate that a resonance is not expected in many practical cases

comments and reply on precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites comment

energy of water waves induced by submarine landslides water waves generated by submarine landslides may constitute a serious hazard for coastal population and environment these masses may be giant as documented by several examples in recent history and by numerous geological traces of paleo events a theoretical investigation on wave generation and wave energy is performed here by using a model that is based on some simplifying assumptions the landslide is treated as a rigid body moving underwater according to a prescribed velocity function water waves are governed by the shallow water wave equations where water velocity is constant through the water layer and vertical velocity is negligibly small geometrically simple basins are considered with either constant depth or constant slope since attention is focused on the fundamental characteristics of the generation process analytical 1 d solutions as well as 1 d and 2 d numerical results obtained by means of a finite element model are used to gain understanding of the energy transfer from a moving body to the water from the 1 d examples it is found that if slide duration is sufficiently long water usually gains energy in the form of waves until a saturation point is reached when body motion is no longer capable of producing a net transfer of energy from the rigid body to water finite duration motions of a body moving at constant speed along a flat ocean floor can be used as canonical examples since bottom slopes cannot significantly change the generated wave pattern typically two trough crest systems are developed that travel in opposite directions with the leading crest in the direction of the slide and the leading trough toward the other direction the amplitude of the former is generally higher with amplitude controlled by the froude number ratio of body velocity to long waves phase celerity and wavelength dictated by landslide length generation and propagation of 2 d cases show a more complicated pattern since lateral radiation plays an important role some of the features present in the 1 d models are observed in 2 d wavefields however substantial differences arise the most significant difference is that no energy saturation takes place in 2 d since the body transfers energy to the water as long as it moves

a probabilistic approach for determining submarine landslide tsunami hazard along the upper east coast of the united states abstract tsunami hazard assessment is critical for coastal communities emergency services and industry to develop regional risk and response management plans for catastrophic tsunami events such as the recent 1998 papua new guinea png and 2004 indian ocean tsunamis along the northeastern united states coastline tsunami hazard assessment is in its infancy mostly due to the lack of historical tsunami record and the uncertainty regarding the return periods of potential large scale events the latter includes large transoceanic tsunamis such as could be caused by a collapse of the cumbre vieja volcano in the canary islands or a large co seismic tsunami initiated in the puerto rican trench as well as large local tsunamis such as could be caused by a submarine mass failure smf occurring on the nearby continental slope in this region considerable geologic and some historical e g the 1929 grand bank landslide tsunami evidence suggests that the largest tsunami hazard may arise from tsunamigenic smfs triggered by moderate seismic activity the coastal impact of smf or landslide tsunamis indeed can potentially be narrowly focused and affect specific communities this research presents the development validation and results of a probabilistic geomechanical and coastal tsunami impact analysis of tsunami hazard on the upper northeast coast of the united states results are presented in terms of nearshore breaking wave height and runup caused by seismically induced tsunamigenic smf with a given return period a monte carlo approach is employed in which distributions of relevant parameters seismicity sediment properties type and location volume and dimensions of slide water depth etc are used to perform large numbers of stochastic stability analyses of submerged slopes along actual shelf transects based on standard pseudo static limit equilibrium methods the distribution of predicted slope failures along the upper u s east coast is found to match published data quite well for slopes that are deemed unstable for a specified ground acceleration with given return period the tsunami source characteristic height is found using empirical equations based on earlier numerical simulation work and corresponding breaking height and runup are estimated on the nearest coastline for a 0 2 annual probability ground acceleration for instance simulations yield a return period of tsunamigenic smfs of 3350 yr i e a 0 03 annual probability of occurrence the resulting estimate of the overall coastal hazard from 100 and 500 yr smf tsunami events is found to be quite low at most locations as compared to the typical 100 yr hurricane storm surge in the region 4 5 m specifically for the 100 yr event smf tsunami hazard is quite low with no coastal region exceeding a 1 m runup for the 500 yr event however two regions of relatively elevated hazard are found 1 near long island ny with a peak runup of 3 m and 2 near the new jersey coast with a peak runup of 4 m it should be stressed that these are only first order estimates and detailed tsunami inundation modeling is required to fully quantify tsunami runup and inundation at these sites this will be the object of more detailed studies in future work

selected characteristics of limestone and dolomite reservoirs in the united states data from the united states oil and gas file totl developed by the university of oklahoma norman oklahoma are used to characterize the lithology location state and basin geologic age year of discovery depth to top of pay porosity permeability water saturation volume of crude oil and nonassociated gas originally in place and net pay thickness of limestone and dolomite reservoirs in the united states distributions of these parameters representing thousands of reservoirs establish a framework to which individual carbonate reservoirs can be compared and provide insights into geologic processes affecting reservoir characteristics limestone reservoirs are more numerous in the united states than dolomite reservoirs by a ratio of about 3 to 1 because limestones are more abundant than dolomites however in the eight states that account for over 90 of united states carbonate reservoirs there is a statistical tendency for carbonate reservoirs to occur preferentially in dolomites dolomite reservoirs on the average are larger and deeper than those of limestone yet they often have lower matrix porosities and permeabilities this line of investigation offers supplemental evidence that dolomitization tends to improve the reservoir properties of a given formation and that effective fracture systems at reservoir depths are more likely to occur in dolomites than in limestones

geotechnical and rheological characteristics of waste rock deposits influencing potential debris flow occurrence at the abandoned imgi mine korea mass movements associated with abandoned mines are dangerous and destructive local communities near abandoned mine sites are often threatened by the effect of extreme precipitation events on these sites in this study the geotechnical and rheological characteristics of mine deposits were examined to delimit the hazardous areas near abandoned mines waste rock materials were collected from a pyrophyllite mine deposit in the mountainous region of korea and a sieve analysis was performed to determine the grain size distribution the yield stress in the debris flow modeling was determined using fall cone and rheometric tests rheological tests were performed on materials finer than 4 75 mm using a ball measuring system rheometer these samples were mainly composed of gravels and sands with small clay content the waste materials typically exhibited a shear thinning behavior within a given shear rate ranging between 10 5 and 102 s 1 the yield stresses obtained from the rheometric tests agreed well with those obtained from the fall cone tests for the input parameter we selected the yield stresses ranging from 100 to 500 pa as a case study the debris flow mobility associated with the abandoned mine was examined using a one dimensional flow dynamic model the runout distance and velocity of the waste materials are strongly dependent on the yield stress both factors significantly increase with decreasing yield stress however even under the highest yield stress i e 500 pa the failed mass can flow into the mountain stream thus the physico chemical contaminations of areas downslope of abandoned mines may be unavoidable with respect to extreme rainfall events

origin of dolostone reservoir rocks smackover formation oxfordian northeastern gulf coast u s a formation of regionally extensive dolostone reservoir rocks in the smackover can be understood despite the possible effects of recrystallization geochemical and petrographic data suggest that dolomitization took place in 1 seawater seepage 2 reflux 3 near surface mixed water 4 shallow burial mixed water and 5 deeper burial environments which overlapped in time and space to form a platform scale dolostone body composed of a complex mixture of dolomites seawater seepage and reflux dolomitization occurred in the near surface penecontemporaneously with deposition of the smackover and overlying haynesville formations dolomitization by seawater seepage occurred within an oolite grainstone sill which separated an intraplatform salt basin from the open sea seawater flowed landward through the sill in response to evaporitic drawdown of brines in the isolated intraplatform basin isolation of the salt basin occurred during the oxfordian when the shoreline retreated from the conecuh embayment dolomite located at the top of the smackover enriched in 18 o suggests additional dolomitization by reflux of hypersaline brines reflux occurred as buckner coastal sabkhas prograded over smackover oolite grainstone shoreface deposits vugs lined with shallow burial calcite and dolomite cements indicate flushing of the smackover grainstone aquifer with fresh water freshwater intrusion probably occurred following sea level lowstands during the late jurassic and early cretaceous leaching in the proximal portion of the freshwater aquifer produced excellent limestone reservoir rocks in the updip smackover dolomitization in the contemporaneous downdip mixed connate freshwater zone formed dolostone reservoir rocks with depleted isotopic compositions consistent with a shallow burial mixed water origin

potential tsunamigenic submarine landslides in active margins abstract a review of modern historical and submarine landslides from the geological record shows that landslides in active continental margins can generate tsunamis the tsunamis may damage coastal and seabed infrastructure and so represent an important element of marine geohazards research due to their potentially significant impacts on society the primary trigger mechanism of tsunamis in this type of setting was thought to be earthquake activity however there are also a number of alternative hypotheses regarding the likely initiation mechanism including the generation of submarine landslides in this paper we briefly review the geological features and trigger mechanisms of tsunamigenic submarine landslides on active margins large tsunamigenic submarine landslides appear to occur mostly on margins characterized by non accretion these observations have implications for tsunami warning systems as the japanese system does not consider the scenario of tsunami excitation by submarine landslides

analyse de la liquefaction et du comportement non draine des sables du delta de kenamu projet adfex jointly sponsored by france norway and canada the adfex project artic delta failure experiment aims at triggering a full scale submarine slide for that purpose a delta is destabilized by blasting to induce instantaneous liquefaction of the delta front the selected site is the delta of kenamu river at melville lake labrador located approximately 40 km northeast of goose bay the delta sediments are angular fine silty sands constituted mainly of quartz a series of consolidated isotropically and undrained triaxial tests was performed on specimens of reconstituted loose sands to establish the boundaries between the contracting and dilating behaviours steady state line or f line and the upper and lower limits of the boundaries within the bidimensional diagram void ratio mean effective stress a soil state above this boundary region constitutes a necessary condition to liquefaction the results of the triaxial tests are used to evaluate the liquefaction potential of kenamu delta key words liq

airflow over a two dimensional escarpment ii hydrostatic flow hydrostatically dominated forced flow over the asymmetric topography of the darling scarp western australia is modelled using a hydrostatic numerical mesoscale model and compared with observations simulations reproduce the essential features of wave overturning and the development of a shooting hydraulic flow this response is dependent on the wind profile but not on the existence of a critical level the high backsheared environment leads to a high ratio of the brunt vaisala frequency to wind speed throughout the profile resulting in short wavelengths high nonlinearity and overturning with the ratio of the halfwidth of the topography to the boundary layer depth being small the flow fields are shown to be sensitive to the boundary layer

model for how microbial methane generation can preserve early porosity in dolomite and limestone reservoirs in some dolomite and limestone hydrocarbon reservoirs protection from cementation is a primary factor in porosity preservation we present a model in which methanogens methane producing microorganisms produce methane gas ch4 g that outgasses from solution in pore space creating a two phase system that reduces effective hydraulic conductivity k protecting pore space from cementation methanogens have been implicated in dolomite formation and can generate methane to fill pore space of a model near surface carbonate sediment 37 5 primary porosity with ch4 g in 180 to 4650 yr depending on nutrient levels gas generation results in occlusion of the aqueous phase from pore spaces and throats creating a two phase flow regime reducing the effective hydraulic conductivity of model marine carbonate sand by about 50 from 2 8 to 1 2 cm day in as little as 55 yr therefore reducing aqueous fluid flow necessary for cementation despite rapid burial and complete cessation of methanogenesis effective hydraulic conductivity could take more than 100 000 yr to return to its original value if methanogenesis continues with burial the effective hydraulic conductivity is reduced to zero after 250 yr dolomites can preserve more primary porosity with depth than other carbonates we propose that in addition to increased structural resistance a biogenic model exists for porosity preservation in dolomites that is linked to the activity of methanogens this model represents specific end member cases and illustrates the effect of methane buildup in relationship to the extent of reservoir diagenesis

effects of glacial transport and neomorphism on precambrian dolomite crystal sizes late precambrian glacial rocks are notable for their association with dolostones1 and this has been regarded as a palaeoclimatological paradox2 5 however little detailed work has been carried out to determine the mode of origin of the dolomite in north east spitsbergen svalbard the vendian6 7 succession contains two glacial stratigraphical units8 9 which are dolomitic and are underlain and overlain by dolostones evidence from sedimentary structures and gross textures indicates that dolomite within the glacial units is detrital whereas at other levels it is a precipitate10 accordingly dolomite crystal sizes were analysed to determine whether evidence of glacial erosion and transport rock flour has been preserved allowing for the effects of later crystal enlargement aggrading neomorphism which vary within and between samples the results show a markedly higher proportion of very fine crystals in the inferred detrital dolostones compared with the precipitated dolostones the very fine crystals are interpreted as relics of rock flour the preservation of which demonstrates a novel means of testing the origin of dolostones associated with glacial sequences inorganic precipitation of dolomite during glaciation or secondary dolomitization of till are not required to explain the dolomite tillite association but pronounced climatic changes at the onset and close of glacial periods are indicated

evaluating the ca isotope proxy the use of ca isotopes as a proxy for mass flux imbalances in the ca cycle is evaluated critically a compiled ca isotope record for the last 45 ma derived from bulk nannofossil ooze and with a temporal resolution of 0 5 ma and an interpretation of the record are presented in the context of the global ca cycle this analysis which assumes that nannofossil ooze records isotopic variations in seawater indicates a dynamic ca cycle in the cenozoic such dynamic behavior has serious implications for the c cycle and suggests feedbacks between the ca and c cycles to stabilize or buffer the oceanic carbon reservoir alternative applications of the ca isotope proxy are investigated using numerical models to determine the extent to which ca isotopes are sensitive to other aspects of the ca cycle the results of the simulations are applied to specific cases in the cenozoic the simulations illustrate how variations in the global fractionation factor between calcium carbonate and seawater can produce trends similar to those observed when comparing previously published ca isotopic compositions of marine barite to the nannofossil ooze record the large drop in the 44 ca value of bulk nannofossil ooze near the eocene oligocene boundary can be reconciled in two ways either as a substantial increase in weathering relative to sedimentation or as an indicator of changing depositional mode within the ocean though the preferred interpretation is not clear at present it is evident that ca isotopes stand to be a unique proxy for ca cycling once the isotope systematics are elucidated

precambrian dolomites petrographic and isotopic evidence that they differ from phanerozoic dolomites dolomites are more common in precambrian than in phanerozoic rocks and from a petrographic isotopic study of the middle to upper proterozoic beck spring dolomite of eastern california it is suggested that precambrian dolomites are different from those of the phanerozoic petrographically all fabric details of precambrian dolomites studied are preserved just as if they were limestones and isotopically they show the same trend as limestones increasingly negative i8 o and to a lesser extent increasingly light i8 c from depositional components through early fibrous dolomite cements to later dolomite spar cements the data suggest that in precambrian time dolomite was the principal carbonate mineral precipitated from seawater and during diagenesis and this implies that precambrian seawater was different from that of the phanerozoic

porosity permeability relationships in interlayered limestone dolostone reservoirs porosity and permeability data from five carbonate platform successions of different settings ages and burial depths are examined to identify overall similarities and differences in the reservoir quality of interlayered limestones and dolostones each succession consists mainly of limestone and dolostone with subordinate proportions of intermediate partly dolomitized compositions in the three deeply buried platforms the key features are that limestones have much lower average porosity than associated dolostones and that limestones and dolostones show little difference in average permeability for given porosity in contrast the shallowly buried platforms show little difference in average porosity between limestones and dolostones and also display higher average permeability for given porosity in dolostones than limestones these data suggest the following general guidelines for depositional and diagenetic controls on reservoir architecture in carbonates consisting of interlayered limestone and dolostone 1 reservoir compartmentalization by the formation of tight limestone barriers is largely a burial diagenetic process involving calcite cementation locally produced by chemical compaction 2 both the pattern of early dolomitization and the distribution of clay minerals because they influence the localization of chemical compaction are key factors that determine the distribution of tight limestone barriers separating flow units thus the pattern of eventual burial compartmentalization follows a template that is hardwired into the stratigraphic architecture by depositional mineralogy and early diagenesis 3 after burial 2 3 km 1 2 1 8 mi dolostones should not be expected to have higher permeability for given porosity than associated limestones these rules assume dolomitization to occur early relative to chemical compaction which will commonly be the case because of combined hydrologic and mass balance constraints dolomitization and concentration of clay appear linked to cycle and sequence architecture in the present examples and thus may have a useful degree of predictability at least in terms of statistical parameters such as net gross and probability of flow unit thickness distribution

an organodiagenetic model for marinoan age cap carbonates abstract the nuccaleena formation cap carbonate is the global stratotype for the marinoan glaciation and ediacaran gssp a designation that emphasises the importance of cap carbonates to our current understanding of global neoproterozoic biogeochemistry sedimentology and stratigraphy however to date there is no agreed depositional model for cap carbonates and there remains minimal detailed paragenetic data for developing process based depositional models here an early diagenetic organodiagenetic dolomite cementation model for marinoan cap carbonate formation is hypothesised and explored it is demonstrated how this process based model can explain the three main atypical sedimentary structures that are the basis for correlation of marinoan age cap carbonates giant tepee like structures sheet veins and tubestones these features are interpreted to be products of fluid overpressure deformation induced by organodiagenetic expansive cementation giant tepee like structures the hallmark of marinoan cap carbonates conform to a simple structural analysis that is consistent with the predicted stress field induced by expansive cementation driven fluid overpressure the undeformed to highly deformed gradient of deformation features in cap carbonates is consistent with the range of rheologies in a shallowly buried cementing carbonate modification of matrix textures and bedding surfaces also conforms to the range of expected textures within this model overall it is hypothesised that the aggradational condensed section architecture of cap carbonates was the primary control over the generation of these atypical sedimentary features the available paragenetic analysis suggests that the geochemical data particularly the c isotopic data can be reinterpreted as supportive of the organodiagenetic model and that the neoproterozoic ocean was perhaps similar to that of today the proposed model indicates that the current criteria for the placement of the ediacaran gssp are non unique and potentially non isochronous perhaps the most important aspect of this model is that it is testable and is a call for focused research on the much overlooked paragenesis of cap carbonates

pliocene mass failure deposits mistaken as submarine tsunami backwash sediments an example from hornitos northern chile abstract in this study we question the former interpretation of a shallow marine backwash tsunami origin of a conspicuous pliocene coarse clastic unit at hornitos northern chile and instead argue for a debris flow origin for this unit we exclude a relation to a tsunami in general and to the eltanin impact in particular the observed deposit at hornitos was not generated either directly impact triggered tsunami or indirectly submarine mass flow caused by seismic shaking by an impact re calculation of the alleged impact tsunami including consideration of the van dorn effect shows that an impact in the southern ocean did not cause a significant tsunami at hornitos impact related seismic shaking was not able to trigger slides several thousands of kilometers away because the eltanin event was a deep sea impact that did not create a crater additionally the biostratigraphic age of 5 1 2 8 ma of the associated la portada formation is not concurrent with the newly established age of 2 511 0 07 ma for the eltanin impact instead we argue for an origin of the conspicuous unit at hornitos as a debris flow deposit caused by an earthquake in the andean subduction zone in northern chile our re interpretation considers the local synsedimentary tectonic background a comparison to recent submarine tsunami sediments and recent examples of mass wasting deposits along the chilean margin the increased uplift during the pliocene caused oversteepening of the coastal scarp and entailed a contemporaneous higher frequency of seismic events that triggered slope failures and cliff collapses the coarse clastic unit at hornitos represents an extraordinary potentially tsunami generating mass wasting event that is intercalated with mass wasting deposits on a smaller scale

massive formation of early diagenetic dolomite in the ediacaran ocean constraints on the dolomite problem paleozoic and precambrian sedimentary successions frequently contain massive dolomicrite camg co3 2 units despite kinetic inhibitions to nucleation and precipitation of dolomite at earth surface temperatures 100 c thus raising doubt about the validity of these deposits as archives of earth surface environments we present a high resolution 63 my long clumped isotope temperature t 47 record of shallow marine dolomicrites from two drillcores of the ediacaran 635 to 541 ma doushantuo formation in south china our t 47 record indicates that a majority 87 of these dolostones formed at temperatures of 100 c when considering the regional thermal history modeling of the influence of solid state reordering on our t 47 record further suggests that most of the studied dolostones formed at temperatures of 60 c providing direct evidence of a low temperature origin of these dolostones furthermore calculated 18o values of diagenetic fluids rare earth element plus yttrium compositions and petrographic observations of these dolostones are consistent with an early diagenetic origin in a rock buffered environment we thus propose that a precursor precipitate from seawater was subsequently dolomitized during early diagenesis in a near surface setting to produce the large volume of dolostones in the doushantuo formation our findings suggest that the preponderance of dolomite in paleozoic and precambrian deposits likely reflects oceanic conditions specific to those eras and that dolostones can be faithful recorders of environmental conditions in the early oceans

origin of dolomite and its spatial and chronological distribution a new insight abstract one of the oldest problems in sedimentology is the origin of dolomite dolomite camg co3 2 is one of the most common sedimentary carbonate minerals its density is 2 866 and calcite s density is 2 710 the absolute abundance of dolostones as well as the dolostone limestone ratio increase with geologic age changes in seawater magnesium concentration were invoked to explain these observations during the last 30 years for both scientific and economic reasons many attempts were made to explain the scarcity of recent dolomites carbonate rocks composed mainly of dolomite generally have high porosities and are important reservoir rocks for oil dolomite is the thermodynamically stable carbonate phase in seawater its relative scarcity in recent marine carbonate sediments therefore cannot be explained simply by the thermodynamic properties of dolomite dolomite formation appears to be inhibited by seawater most sedimentologists assumed that the formation of dolomite is mainly controlled by the dissolved magnesium calcium mg2 ca2 ratio in seawater the molar mg2 ca2 ratio in seawater is 5 3 it was therefore assumed that dolomite formation requires a still higher ratio this explanation however had to be abandoned when primarily during the last 2 to 3 years dolomite was observed as an important constituent of many modern marine organic rich sediments for example in th california borderlands gulf of california the japan trench cariaco basin off the coast of venezuela and the solar lake in israel in the guaymas basin for example dolomite actively forms from pore fluids with mg2 ca2 ratios of 1 to 2 similar dolomite formed in the miocene monterey formation either as penecontemporaneous or early diagenetic nodules or as laminated dolomite the dgr18o values of these dolomites range from 6 to 7 pmil pdb and their dgr13c values range from 30 to 20 pmil experiments conducted recently in our laboratory have shown that the important condition of dolomite formation is not high mg2 ca2 ratios but low dissolved sulfate so4 4 content which inhibits dolomite formation seawater contains 28 mmso42 dolomitization of calcite is already inhibited at sulfate concentrations of approximately 5 to 7 of seawater value aragonite dolomitization however though strongly retarded at these low dissolved so42 concentration values is inhibited at sulfate concentrations of approximately 50 of seawater s value we have also shown that dolomitization of caco3 proceeds through protodolomite a calcium rich disordered dolomite which would transform t dolomite if equilibrium were established dissolved so42 also retards the rates of protodolomite transformation to dolomite and dedolomitization sulfate ions adsorbed to the surfaces of calcite dolomite or aragonite may affect the kinetics of phase transformations in the carbonate system in a sulfate depleted environment sulfate is rapidly desorbed at 15 to 35 c 59 to 95 f the process is completed in 1 to 2 days thus favorable sites for dolomite formation in the marine environment are those where dissolved so42 concentrations are low the most effective processes of sulfate removal from or its dilution in marine pore fluids are microbial reduction in organic rich sediments and mixing of seawater with large amounts of fresh water this happens for example in continental margin sediments with high rates of deposition as in the gulf of california or in deeper water sediments associated with black shales the presence of much dissolved so42 in seawater also explains the almost absence of dolomite in apparently highly favorable environments for example in open marine carbonates the relative paucity of dolomite rich carbonate rocks dolostones formed during the last 100 to 120 million years as compared with their abundance in older sediments in particular in the precambrian and early paleozoic could be explained on the basis of changes in the depositional environments and in the carbonate mineralogy of the primary calcareous sediments these differences do not necessarily reflect changes in seawater magnesium concentrations end of article last page 2156

discrete element simulation of the jiufengershan rock and soil avalanche triggered by the 1999 chi chi earthquake taiwan we present contact dynamics discrete element simulations of the earthquake triggered jiufengershan avalanche which mobilized a 60 m thick 1 5 km long sedimentary layer dipping similar to 22 degrees se toward a valley the dynamic behavior of the avalanche is simulated under different assumptions about rock behavior water table height and boundary shear strength additionally seismic shaking is introduced using strong motion records from nearby stations we assume that seismic shaking generates shearing and frictional heating along the surface of rupture which in turn may induce dynamic weakening and avalanche triggering a simple slip weakening criterion was adopted to simulate shear strength drop along the rupture surface we investigate the mechanical processes occurring during triggering and propagation of an avalanche mobilizing shallowly dipping layers incipient deformation forms a pop up structure at the toe of the dip slope as the avalanche propagates the pop up deforms into an overturned fold which overrides the surface of separation along a decollement simultaneously uphill layers slide at high velocity 125 km h and are folded and disrupted as they reach the toe of the dip slope the avalanche foot forms a wedge that is pushed forward as deformed rocks accrete at its rear we simulated five cross sections across the jiufengershan avalanche which differ in the geometry of the surface of separation topographic and simulated surface profiles are similar the friction coefficient at the surface of separation determined from back analysis is abnormally low mu ss 0 2 possibly due to lubrication by liquefied soils the granular deposits of simulated earthquake and rain triggered avalanches are similar

ship waves in the lee of isolated topography abstract a three dimensional linear steady state model which has been designed for the purpose of simulating the internal wave field which is forced by stratified flow over topography is described in the present paper the model directly assimilates radiosonde data on wind and temperature and its primary purpose is to serve in the design of three dimensional nonlinear experiments as a test the model is used to predict a sequence of ship wave patterns which were observed in the lee of isolated islands in the norwegian and barents seas using radiosonde data from the islands themselves the model reproduces the observed wave patterns rather accurately