contact diagenesis the effect of an intrusion on reservoir quality in the triassic sherwood sandstone group northern ireland abstract intrusion of a dolerite sill into clay bearing arkosic triassic sherwood group sandstones with moderate porosity 22 and high but anisotropic permeability mode 500 md led to the progressive transformation of precursor diagenetic minerals in the host rock locally pore filling mg rich smectite saponite quartz and dolomite existing in the rock following earlier burial diagenesis reacted to produce grain coating flakes of talc at the lowest contact temperatures 130 180 c based on equilibrium reaction path and thermal history calculations at higher temperatures 200 230 c talc reacted with calcite to produce an actinolitic amphibole close to the intrusion at temperatures of 250 c bundles of acicular needles of actinolite protruding into open pores were produced by a second reaction involving saponite hematite and calcite framework feldspar minerals mainly k feldspars played little or no part in the reactions because there were no k al rich minerals produced by contact diagenesis and because the detrital feldspar grains are essentially unaltered thus while equilibrium may have been approached on the intrapore scale 10 m it was not achieved between grains e g detrital feldspars pore water and clays in the pores total porosity has been unaffected by the intrusion and consequent mineral reactions because reactions involved recrystallization of original pore filling minerals despite the contact diagenetic changes in the rock the permeability of the sandstone remained largely unaffected by intrusion

applications of geochemistry in tsunami research a review abstract much progress has been made since the first published studies of tsunami deposits nearly 30 years ago geochemistry is now a much more widely used proxy in tsunami research mainly due to its increasingly recognised value in the identification of historical and or prehistorical deposits at times even providing the conclusive proof when other proxies are missing or equivocal but also its significance in environmental impact assessments following recent tsunamis the rapid advance in analytical techniques has also made it a more approachable and popular method as it is now often faster and cheaper here we provide a review of the applications of geochemistry including the techniques used as well as a database of studies that used chemical proxies in their investigation of recent and old events including onshore and offshore tsunami deposits chemical signatures are often used as markers of marine inundation either as salinity indicators where they can also allow the identification of the limit of tsunami inundation or tracers of the incorporation of marine sourced carbonates their applications as indicators of source material are nevertheless expanding thereby potentially providing additional information on the hydrodynamic processes associated with tsunami inundation although they are largely site specific the effects of post depositional changes in different climatic regimes are examined with a particular emphasis on water leachable components and implications for post event recovery of coastal ecosystems we demonstrate the usefulness of chemical proxies in studies of the geological record of tsunamis extending back thousands of years suggest new approaches and discuss limitations and existing knowledge gaps

chemical multi isotopic li b sr u h o and thermal characterization of triassic formation waters from the paris basin this work reports chemical and isotope data and temperature estimates for seven water samples collected from triassic formations in the paris basin in france four samples were collected in the central part of the basin saline waters and three were collected at the edge of the basin near the recharge zone dilute waters the saline waters collected from the chaunoy and champotran boreholes have high salinities around 120 g l and very similar chemical and isotopic compositions the saline water sample from the la torche borehole has much higher salinity 168 g l and significantly different isotope characteristics the chemical geothermometers applied to these fluids from the centre of the basin give temperature values ranging between 80 and 100 c the fresh water samples collected at the edge of the basin have very different chemical and isotopic compositions these dilute water samples santenay and ch teauroux are shallow with colder temperatures of around 45 to 50 c the study of uranium activity ratios for these triassic formation waters allows us as a first approximation to estimate a mean apparent fluid circulation velocity of around 0 2 m yr which corresponds to a mean age slightly higher than 1 my for waters sampled in the chaunoy champotran and la torche fields in the centre of the basin the multi isotope characterization of triassic formation waters shows that our data are in agreement with literature values as concerns traditional isotope systematics delta18o deltad 87sr 86sr li and b isotope signatures in the centre of the paris basin are in a good agreement with a fluid signature derived mainly from water rock interactions involving clastic rocks with water essentially resulting from a seawater derived brine endmember diluted by meteoric waters the data reported in the present work for li and b isotopes could be used as a reference for future studies to characterize sandstone formation waters

deposits flow characteristics and landscape change resulting from the september 2009 south pacific tsunami in the samoan islands the september 29th 2009 tsunami caused widespread coastal modification within the islands of samoa and northern tonga in the south pacific preliminary measurements indicate maximum runup values of around 17 m okal et al 2010 and shore normal inundation distances of up to 620 m jaffe et al 2010 geological field reconnaissance studies were conducted as part of an unesco ioc international tsunami survey team survey within three weeks of the event in order to document the erosion transport and deposition of sediment by the tsunami data collected included a general morphology and geological characteristics of the coast b evidence of tsunami flow inundation flow depth and direction wave height and runup c surficial and subsurface sediment samples including deposit thickness and extent d topographic mapping and e boulder size and location measurements four main types of sedimentary deposits were identified a gravel fields consisting mostly of isolated cobbles and boulders b sand sheets from a few to 25 cm thick c piles of organic mostly vegetation and man made material forming debris ramparts and d surface mud deposits that settled from suspension from standing water in the tsunami aftermath tsunami deposits within the reef system were not widespread however surficial changes to the reefs were observed

multiple generations of high salinity formation water in the triassic sherwood sandstone wytch farm oilfield onshore uk abstract the origin and heterogeneity of oilfield formation water in the lower triassic sherwood sandstone at wytch farm in the wessex basin uk have been investigated using production data detailed water geochemistry and o s and h stable isotope data the formation waters are highly saline nacl type brines with tds values of up to 230 000 mg l there is a general decrease in salinity from the flanks of the field to the crest with cl decreasing from about 136 000 to 109 000 mg l the cl br ratio of the water shows that salinity was largely derived from the dissolution of upper triassic continental evaporites found off structure to the west and north of the field the water in the field had a meteoric source although variation in 2h values suggests that there may be meteoric waters of different ages in the oilfield reflecting recharge under different palaeoclimatic conditions at the crest of the field aqueous so 4 2 resulted from dissolution of anhydrite in the reservoir in contrast in other parts of the field there is an indication that some of the dissolved so 4 2 was derived from oxidation of pyrite at some point on the recharge path of meteoric water to the field there were two meteoric influx events bringing different cl concentrations and different 2h values the first was probably before the eocene oil influx and could have occurred in the lower cretaceous or early tertiary the second meteoric influx event probably occurred after or during oil migration into the wytch farm structure since the second meteoric water is found at the flanks of the field adjacent to the regions where salt is found in the stratigraphy the preservation of heterogeneities in oilfield formation water compositions suggests that there has been little aqueous fluid movement or diffusive flux for over 40 million years mass flux has been restricted by density stratification within the aquifer and the very low effective permeability for the aqueous phase in the oil filled reservoir

investigation of a high stress drop earthquake on august 30 1986 in the vrancea region abstract several source parameters of the intermediate depth vrancea earthquake from august 30 1986 were computed starting from strong motion data among them most striking for a mw 7 2 event is the high seismic energy 4 5 1023 erg corresponding to ms 7 9 and four independent estimates of effective stress about 1100 bar the high fracture energy per unit area of the fault 2 1010 erg cm2 and a somewhat low apparent stress about 400 bar are indicators of a low rupture velocity a single asperity with an area of about 160 km2 was identified on the 700 km2 fault area the rupture duration of about 4 s is in agreement with the inverse of corner frequency and with teleseismic determinations the depth of the main shock was checked against determinations from pp p intervals and so the initiation of rupture was fixed around 130 km depth

noble gases in crude oils from the paris basin france implications for the origin of fluids and constraints on oil water gas interactions in order to investigate the potential of noble gases to trace the dynamics of oil reservoirs we have analysed the abundance and isotopic composition of all noble gases he ne ar kr and xe in crude oils from the paris basin france using a new extraction and purification procedure the main oil reservoirs are presently located in the jurassic dogger limestone and in the triassic keuper sandstone but hydrocarbons originated from a common source rock formation located in the interbedded liassic sequence despite this common origin the abundance and isotopic ratios of the noble gases differ between the dogger and the keuper the isotopic compositions of kr and xe are indistinguishable from that of air 3he 4he ratios higher than those predicted from radiogenic production in the sediments or in the crust are attributed to the occurrence of mantle derived 3he in the basin each sedimentary sequence is characterised by well defined and homogeneous 21ne 22ne and 40ar 36ar ratios which average 0 0306 0 0008 and 312 10 for the dogger and 0 0367 0 0012 and 664 30 for the keuper respectively the main source of radiogenic noble gases appears to be the continental crust underlying the basin with possible regional contributions of noble gas isotopes produced in the sediments the helium and argon isotopic ratios of the dogger oils are very similar to those observed in geothermal waters flowing in the dogger aquifer throughout the basin demonstrating that noble gases in oils derive from associated groundwaters oil reservoirs in the paris basin therefore accumulate noble gases from wide regions of the continental crust through cross formational flow of groundwaters and subsequent partitioning into oil this observation implies that noble gases cannot be directly used to date oils but can provide time constraints if 1 water oil interactions are quantified and 2 the residence time as well as the noble gas characteristics of associated groundwaters are known oil water gas partitioning processes are well recorded in the fractionation of noble gas elemental abundance two distinct processes have been identified 1 accumulation of atmosphere derived ang and radiogenic noble gases both initially dissolved in groundwaters resulting in a positive correlation between absolute amount of ang and the extent of heavy noble gas fractionation and 2 subsequent fractional degassing resulting in a negative correlation between ang abundance and heavy noble gas fractionation degassing is particularly evident for the keuper oils and might have occurred in the reservoirs following hydrodynamic gas stripping the ang abundance in the dogger reservoirs requires that about one order of magnitude more water than presently observed has interacted with the oil given current estimates of the residence time for groundwaters in the dogger aquifer the duration of oil water interaction is in qualitative agreement with a palaeocene oligocene age for the major episode of secondary oil migration in the paris basin high xenon contents in keuper reservoirs suggest that they have experienced hydrodynamic interactions between flowing waters and oils for long time and that the trias might have reached hydrostatic condition only recently

evolution of porewater composition through time in limestone aquifers salinity and d h of fluid inclusion water in authigenic minerals jurassic of the eastern paris basin france past water circulations can significantly reduce the porosity and permeability of marine limestones this is particularly the case in the middle bathonian bajocian to upper oxfordian jurassic limestones from the eastern border of the paris basin the knowledge of the timing the temperature and composition of paleowaters is essential to model the hydrological evolution in this area where the callovian oxfordian claystones are studied for the storage of nuclear wastes in this way fluid inclusions hosted in low temperature 60 c authigenic calcite quartz and celestite crystals were analyzed by raman spectroscopy and mass spectrometry to determine the chlorinity and d h ratios chlorinity measurements mmol cl per liter of water in fluid inclusions trapped in authigenic crystals during the late jurassic early cretaceous period revealed unexpected high values up to 3800 mmol l 1 indicating that brines were involved in some of the diagenetic crystallization processes by contrast fluid inclusions in calcite cements of cenozoic age within the oxfordian limestones have low cl concentration less than 150 mmol l 1 thus showing that a dilution event caused by water infiltrations during the cretaceous uplift of this part of the basin has flushed out the original saline porewater by coupling d of fluid inclusion with 18o of calcite crystals we estimate that calcite precipitation occurred at temperatures between 25 and 53 c the hydrogen isotope composition of calcite forming water is different between the middle jurassic d ranging from 20 to 35 8 v smow and the overlying oxfordian limestone d from 59 5 to 44 8 v smow present day groundwaters are also of distinct composition on both sides of the oxfordian claystones indicating that limestone aquifers underwent independent hydrologic evolutions since the early diagenetic jurassic cementation

multi proxy evidence for trans pacific tsunamis in the hawai ian islands abstract the origin of two sand layers buried in polol wetland on the northeast coast of the island of hawai i was investigated using a multi proxy approach including radiometric dating sedimentology geochemistry micropalaeontology palynology and historical records based on 210 pb 137 cs and pollen data the lower sand unit extending 250 to 350 m inland is attributed to the 1946 aleutian tsunami while the upper sand unit was laid down by the 1957 aleutian tsunami chronological information does not appear to support any link between these deposits and historical storm events furthermore sedimentological geochemical diatom and pollen results suggest deposition of marine and near beach sediments under high energy conditions typically associated with tsunami inundation this work presents the first conclusive sedimentary evidence for distantly generated tsunamis on the hawai ian islands opening the way for more comprehensive historical and palaeotsunami studies indeed a brief review of archaeological data suggests that the hawai ian coast may have experienced similar large magnitude events in the past from both local and distant sources

the long term fate of co2 in the subsurface natural analogues for co2 storage abstract co 2 is a common gas in geological systems so that planned storage of co 2 in the subsurface may do no more than mimic nature natural co 2 has a wide number of sources that can be at least partly identified by carbon stable isotope geochemistry three pairs of case studies with different reservoir characteristics and co 2 contents have been examined to assess the natural impact of adding co 2 to geological systems carbonate minerals partially dissolve when co 2 is added simply because the co 2 dissolves in water and forms an acidic solution therefore carbonate minerals in the subsurface are not capable of sequestering secondary co 2 the addition of co 2 to a pure quartz sandstone or a sandstone in which the supply of reactive aluminosilicate minerals has been exhausted by excess natural co 2 addition will have no consequences the co 2 will simply saturate the water and then build up as a separate gas phase the addition of co 2 to carbonate cemented sandstone without reactive aluminosilicate minerals will induce a degree of carbonate mineral dissolution but no solid phase sequestration of the added co 2 when co 2 is naturally added to sandstones it will induce combined aluminosilicate dissolution and carbonate cementation if the aluminosilicate minerals contain calcium or magnesium or possibly iron examination of a co 2 filled porous sandstone with abundant reactive aluminosilicate minerals that received a huge co 2 charge about 8000 to 100 000 years ago reveals minimal evidence of solid phase sequestration of the added co 2 this indicates that either dissolution of reactive aluminosilicates or precipitation of carbonate minerals is relatively slow it is very likely that the slow dissolution of reactive aluminosilicates is the rate limiting step solid phase sequestration of co 2 occurs only when reactive aluminosilicates are present in a rock and when the system has had many tens to hundreds of thousands of years to equilibrate the two critical aspects of the behaviour of co 2 when injected into the subsurface are 1 that the rock must contain reactive ca and mg aluminosilicates and 2 that reaction to produce carbonate minerals is extremely slow on a human timescale the reactive minerals include anorthite zeolite smectite and other fe and mg clay minerals such minerals are absent from clean sandstones and limestones but are present in dirty standstones lithic arenites which are mineralogically immature and some mudstones the analysis of geological analogues shows that injection of co 2 into carbonate bearing rocks that do not contain reactive minerals will induce dissolution of the carbonate whether it is a matrix cement rock fragment fault seal or part of a top sealing mudstone

chemical signatures of palaeotsunamis a forgotten proxy article i nfo article history a range of diagnostic criteria are required to help identify palaeotsunami deposits although chemical signatures have long been used as indicators of palaeosalinity in sedimentary sequences their use in the studies of palaeotsunami deposits is rarely applied and is yet to be widely recognised the chemical composition of interstitial water in coastal ponds and sedimentary sequences in coastal marshes and lagoons has been used successfullyasanindicatoroftsunamiinundation chemicalsignaturescanalsoprovidecluesaboutthelandward limit of runup of a tsunami beyond the area of sediment deposition like most palaeotsunami proxies however the preservation of chemical signatures varies with environmental conditions

new insights into the origin of perylene in geological samples abstract the origin of the polycyclic aromatic hydrocarbon pah perylene in sediments and petroleum has been a matter of continued debate reported to occur in phanerozoic organic matter om fossil crinoids and tropical termite mounds its mechanism of formation remains unclear while a combustion source can be excluded structural similarities to perylene quinone like components present in e g fungi plants crinoids and insects potentially suggest a product precursor relationship here we report perylene concentrations 13c 12c and d h ratios from a holocene sediment profile from the qingpu trench yangtze delta region china perylene concentrations differ from those of pyrogenic pahs and rise to prominence in a stratigraphic interval that was dominated by woody vegetation as determined by palynology including fungal spores in this zone perylene concentrations exhibit an inverse relationship to the lignin marker guaiacol d h ratios between 284 and 317 similar to the methoxy groups in lignin as well as co variation with spores from wood degrading fungi 13c 12c of perylene differs from that of land plant wax alkanes and falls in the fractionation range expected for saprophytic fungi that utilise lignin which is isotopically lighter than cellulose and whole wood during progressive lignin degradation the relative carbon isotopic ratio of the perylene decreases we therefore hypothesise a relationship of perylene to the activity of wood degrading fungi to support our hypothesis we analysed a wide range of phanerozoic sediments and oils and found perylene to generally be present in subordinate amounts before the evolutionary rise of vascular plants and to be generally absent from marine sourced oils few exceptions being attributed perhaps to a contribution of marine and or terrestrial derived fungi anoxia especially under marine conditions and or contamination of core material by fungi a series of low molecular weight aromatic quinones bearing the perylene backbone were detected in devonian and cretaceous sediments potentially representing precursor components to perylene

scaling of source parameters for vrancea romania intermediate depth earthquakes the stress drop scaling of the vrancea romania intermediate depth earthquakes with seismic moments from 10 to 20 dyne cm is investigated the empirical green s function technique is used in order to retrieve the seismic source parameters for the smaller earthquakes 1021 1026 dyne cm available source parameters for the major vrancea earthquakes that occurred in 1940 1977 1986 and 1990 mw 6 9 as determined from teleseismic and local data were included a circular source model approximates well the deconvolved source time functions and source spectra for the analyzed earthquakes in case of the large earthquakes an equivalent circular area is considered corresponding to the zone of aftershocks the static stress drop is determined from seismic moment and source radius for brune s model a dependence of the stress drop on the seismic moment as m140 is outlined over the entire magnitude range

geothermometry and geobarometry of overpressured lower paleozoic gas shales in the jiaoshiba field central china insight from fluid inclusions in fracture cements the wufeng longmaxi organic rich shales host the largest shale gas fields of china this study examines sealed fractures within core samples of the wufeng longmaxi shales in the jiaoshiba shale gas field in order to understand the development of overpressures in terms of magnitude timing and burial in wufeng longmaxi shales and thus the causes of present day overpressure in these paleozoic shale formations as well as in all gas shales quartz and calcite fracture cements from the wufeng longmaxi shale intervals in four wells at depth intervals between 2253 89 m and 3046 60 m were investigated and the fluid composition temperature and pressure during natural fracture cementation determined using an integrated approach consisting of petrography raman spectroscopy and microthermometry many crystals in fracture cements were found to contain methane inclusions only and aqueous two phase inclusions were consistently observed alongside methane inclusions in all cement samples indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid homogenization temperatures of methane saturated aqueous inclusions provide trends in trapping temperatures that th values concentrate in the range of 198 5 c 229 9 c 196 2 c 221 7 c for quartz and calcite respectively pore fluid pressures of 91 8 139 4 mpa for methane inclusions calculated using the raman shift of c h symmetric stretching v1 band of methane and equations of state for supercritical methane indicate fluid inclusions trapped at near lithostatic pressures high trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of wufeng longmaxi shales at maximum burial and the early stage of the yanshanian uplift which can provide a key evidence for understanding the formation and evolution of overpressure our results demonstrate that the main cause of present day overpressure in shale gas deposits is actually the preservation of moderate high overpressure developed as a result of gas generation at maximum burial depths

chronology of fracture sealing under a meteoric fluid environment microtectonic and isotopic evidence of major cainozoic events in the eastern paris basin france abstract a detailed reappraisal of the sequence of tectonic stages that has affected the eastern part of the paris basin from the late jurassic to the end of cainozoic is presented in order to improve knowledge of the relationships between tectonics and fluid mass palaeo transfers in that basin this goal was performed in two steps i establishing a relative tectonic chronology on the basis of numerous observations and detailed analysis of geometrical relationships between striated planes vertical and bedding stylolites and tension gashes and ii discussing the geochemical signatures 18 o and 13 c of calcite from fracture infillings well positioned within the relative tectonic chronology the resulting tectonic sequence agrees with the main events described by previous papers but the present work details the pyrenean s l eocene oligocene and alpine miocene pliocene convergence stages and explains the mechanisms of the oligocene miocene transition between the two previous events the different tectonic stages are as follows i late jurassic to early cretaceous extension starting with a wnw ese direction but changing to e w ii the pyrenean convergence eocene changing from nne ssw to ne sw and finally ene wsw compression iii oligocene transition from pyrenean to alpine convergence marked by a drastic evolution of main stress which swaps from a horizontal position to a vertical one and radial extension marked by a strong reactivation of bedding stylolitisation iv the alpine convergence late miocene to present day changing from wnw ese to nnw sse direction of shortening 18 o and 13 c values of calcite from tension gashes associated to each tectonic stage spread from 18 to 27 smow and from 0 8 to 3 pdb respectively according to the maximum thermal history of this part of the basin t max 40 c or 60 c according to the available published estimates the calculated 18 o values of fluids 7 to 4 involved in mass transfer processes are interpreted as meteoric the lowest 18 o values 18 20 are located around the main regional faults and associated with 13 c values that are rather different from those of host rocks in contrast calcites from non faulted area present a higher 18 o 20 and 13 c values close to those of host rocks these data are explainable in terms of differences in the fluid rock ratios prevailing during carbonate redistribution the highest ratios being associated to discontinuities faults sometimes with hydraulic breccias that were active during the tertiary tectonic events outside the fault zones the isotopic compositions of calcite from tension gashes are similar at the regional scale to those of calcite from geodes or cements analysed in previous studies on localized areas as a result we emphasize the fact that a significant part of the carbonate redistribution in the middle to upper jurassic limestones from the eastern paris basin occurred during the tertiary s l enlightening the influence of distant orogenic systems extensive or compressive in the matter redistribution within sedimentary basins at variance of models inferring a porosity cementation predominantly during burial

predecessors to the 2009 south pacific tsunami in the wallis and futuna archipelago abstract multi proxy studies of trench sediments from futuna island in the wallis and futuna archipelago have produced a record of two palaeotsunamis dated to around 1860 2000 bp and c 470 bp one of the most useful proxies in this study has been the archaeological data associated with occupations that immediately underlie the deposits associated with both palaeotsunamis the reworking of the archaeological material into the palaeotsunami deposits and the additional chronological control provided by artefacts have added value to interpretations based upon more conventional earth science proxies the identification of tsunamigenic sources for these events is tentative and based upon known potential sources based upon a comparison between the effects of the 2009 south pacific tsunami and those recorded in the trenches event 1 1860 2000 bp appears most likely to be associated with a large tsunami sourced from the tonga kermadec trench region there are only rare contemporaneous events reported from around the region although this appears to be largely due to a lack of similar research as opposed to a lack of evidence event 2 c 470 bp is markedly larger than event 1 with sedimentary evidence indicating significant inland inundation and runup around the entire island there are several lines of evidence for a contemporaneous event in the south pacific around 470 bp although much of this needs further verification determining a source for this event is problematic because it must take in to account the regional signal and the significant impacts recorded on futuna we propose that the source for this younger event was either a larger tonga kermadec trench related earthquake or the kuwae caldera collapse in 1452 1453 ad we recognise that as further research is carried out in the pacific we will greatly improve our abilities to identify past sources and the magnitude and frequency of past events from these areas this can only serve to improve our understanding of the regional risk from tsunamis

secondary porosity formed by deep meteoric leaching botucatu eolianite southern south america the botucatu sandstone of the parana basin of brazil a jurassic eolianite exhibits unusually deep basinwide penetration of meteoric water this flow of dilute groundwater has removed calcite cement for an average distance of about 140 km from the outcrop and down to a burial depth of about 250 m feldspar has been leached from the framework for about 30 km downdip transforming what was deposited as a feldspathic sandstone into a diagenetic quartz arenite on outcrop these two dissolution processes have generated appreciable secondary porosity by weathering reactions at sites far removed from contact with the atmosphere between 100 and 500 pore volumes of water have passed through the aquifer system to produce this leaching making this an end member case of extensive meteoric diagenesis of sandstone consideration of other basins with meteoric incursion suggests that basin scale leaching is favored when uplift of one margin provides a steep gradient and there is a downdip escape route via faults or outcrop of the aquifer cratonic basins close to rifted continental margins seem to provide the best chance of meeting these conditions

source scaling of intermediate depth vrancea earthquakes summary source scaling properties are studied for the intermediate depth seismic nest in the vrancea region romania which has been the source of many destructive earthquakes we investigate spectral and time domain scaling properties using wide band digital records from 16 earthquakes 3 7 mw 7 4 all processing variants p or s waves spectral or time domain etc produce consistent results the observed corner frequency versus mw trend generally follows the constant stress drop model with typical stress drop values of 1 10 mpa this kind of scaling seen over the entire magnitude range analysed is similar to that observed for shallow events however this trend seems to be violated for the largest earthquakes mw 6 5 they show a clear tendency for higher static stress drops than shallow events and for magnitudes above 7 average stress drops exceeding 10 mpa may be expected these results are of particular significance for seismic hazard studies and specifically for the estimation of future strong motions

origin of salinity in produced waters from the palm valley gas field northern territory australia abstract the chemical composition and evolution of produced waters associated with gas production in the palm valley gas field northern territory has important implications for issues such as gas reserve calculations reservoir management and saline water disposal the occurrence of saline formation water in the palm valley field has been the subject of considerable debate there were no occurrences of mobile water early in the development of the field and only after gas production had reduced the reservoir pressure was saline formation water produced initially this was in small quantities but has increased dramatically with time particularly after the initiation of compression in november 1996 the produced waters range from highly saline up to 300 000 mg l tds with unusual enrichments in ca ba and sr to low salinity fluids that may represent condensate waters the sr isotopic compositions of the waters 87sr 86sr 0 7041 0 7172 are also variable but do not correlate closely with major and trace element abundances although the extreme salinity suggests possible involvement of evaporite deposits lower in the stratigraphic sequence the sr isotopic composition of the high salinity waters suggests a more complex evolutionary history the formation waters are chemically and isotopically heterogeneous and are not well mixed the high salinity brines have sr isotopic compositions and other geochemical characteristics more consistent with long term residence within the reservoir rocks than with present day derivation from a more distal pool of brines associated with evaporites if the high salinity brines entered the reservoir during the devonian uplift and were displaced by the reservoir gas into a stagnant pool which has remained near the reservoir for the last 300 400 ma then the size of the brine pool is limited at a minimum it might be equivalent to the volume displaced by the reservoired gas

unusually large tsunamis frequent a currently creeping part of the aleutian megathrust current models used to assess earthquake and tsunami hazards are inadequate where creep dominates a subduction megathrust here we report geological evidence for large tsunamis occurring on average every 300 340 years near the source areas of the 1946 and 1957 aleutian tsunamis these areas bookend a postulated seismic gap over 200 km long where modern geodetic measurements indicate that the megathrust is currently creeping at sedanka island evidence for large tsunamis includes six sand sheets that blanket a lowland facing the pacific ocean rise to 15 m above mean sea level contain marine diatoms cap terraces adjoin evidence for scour and date from the past 1700 years the youngest sheet and modern drift logs found as far as 800 m inland and 18 m elevation likely record the 1957 tsunami previously unrecognized tsunami sources coexist with a presently creeping megathrust along this part of the aleutian subduction zone

some source and medium properties of the vrancea seismic region romania abstract simple spectral theory of seismic sources was used to determine source parameters directly related to medium properties stress drop seismic efficiency and fracture energy and quality factors of the vrancea romania seismic region the results show an increase in maximum static stress drop maximum seismic efficiency and fracture energy with depth the seismic efficiency is magnitude independent but the stress drop is magnitude independent only for events with ml 3 8 below this value the logarithm of stress drop increases quasi linearly with magnitude in the depth interval 50 160 km the stress drop increases with a slope of about 2 3 bar km the fracture energy per unit area of the fault has values of the order of 105 108 erg cm2 the frequency independent quality factors indicate that the attenuation of p waves is generally higher than that of s waves and that qp values are in agreement with recent tectonic models for the vrancea region total decoupling of the slab now sinking gravitationally is present only in the southwestern part of the vrancea region as suggested by the spatial position of intermediate depth hypocenters

geochemistry of hco 3 na thermal water from the gudian slope insights into fluid origin formation mechanism and circulation in the yitong basin northeast china abstract the goal of this paper is to systematically analyze the geochemical and isotopic characteristics 18o d t 13chco3 and doc of a hco3 na thermal water to determine its origin formation mechanism and circulation pattern in the gudian slope yitong basin northeast china schoeller diagrams and isotope data indicate that this thermal water is not connected to groundwater or river water and that its recharge source is immature water with low 18o and d values that originates from the changbaishan area this result was also confirmed by its doc 13c value approximately 24 which indicates that the c originates from c3 plants the analysis of na k mg diagrams indicates that the thermal waters except for one sample sjxk are fully equilibrated this observation combined with the results of the analysis for 18o d t and cation geothermometry data for the thermal water indicates that no water underwent mixing with cold water before arriving at the surface instead high temperature immature water flowed up from a deep reservoir and mixed with old formation water approximately 35 4 in the eocene reservoir these data indicate the occurrence of an interesting phenomenon in which the thermal water samples of the gd area exhibit a regression line with a negative slope and similar 18o values potentially due to the fractionation of co2 gas and a buffer of high hco3 concentrations rather than their short circulation times the high so4 cl b cl f cl and hco3 cl ratios and 13chco3 values ranging from 0 84 to 1 24 of these samples imply that magmatic volatiles have been dissolved in the thermal water however we cannot ignore the contributions of 13c from the leaching of limestone with a13c value of approximately 3 4 which is further supported by the br cl and hco3 cl ratios thus we analyzed the geological background and data collected from well chang 27 and deduced that a limestone stratum exists below the study area magmatic volatiles flow up through the lithospheric faults along the northwestern and southeastern edges of the basin encounter changbaishan area recharge water in the limestone reservoir form hot water with high concentrations of hco3 and then recharged into the eocene sandstone reservoir long term mineral hydrolysis and transformation reactions in the reservoir cause the concentrations of na to increase and lead to the formation of hco3 na water

geochemistry and origin of formation brines from the paris basin france 2 saline solutions associated with oil fields abstract oil fields from the paris basin are located in three geological levels dogger middle jurassic rhaetian and keuper upper triassic the origin of water and dissolved salts in saline solutions associated with oil is investigated using the hypothesis that cl and br are conservative in solution in a diagram of cl br ratios vs cl the points of the dogger and the keuper aquifers lie in the zone of primary brines whereas those of the rhaetian are located in the zone of secondary brines the na cl ratio is very high in all of the saline solutions suggesting either a relatively poorly evolved brine at the beginning of halite deposition or some halite dissolution all of the saline solutions especially those from the dogger aquifer are clearly diluted dilution by meteoric waters would not alter the cl br ratio high concentrations of lithium rubidium and boron are attributed to the presence of an extremely evolved brine of marine origin in mixtures of secondary brines formed by dissolution of halite and small amounts of sylvite and ca sulphate mass balance calculations of the excess of cl with respect to na k allows the fraction x of water derived from the primary brine to be calculated assumptions are that all na and k is derived from the secondary brine and that the cl content of the primary brine is constrained by bischofite saturation at 11 000 mmol kg 1 the typical proportion of water from the primary brine waters is 0 7 in the dogger formation and 2 4 in the keuper values of the concentration factor cf expressed as the ratio of the molal concentration of a conservative ion in the evolved brine to its concentration in seawater have been calculated for lithium solutions from the dogger and keuper aquifers have cfli values of 1 8 103 and of 7 7 103 respectively in the rhaetian aquifer the linear relationship between heavy isotope contents of the brine 2h and 18o and the cl content indicates a mixture of two water sources the first one is meteoric water as defined by the intersection of the formation water line with the global meteoric water line 2 h 65 18 o 9 3 the other end member is enriched in heavy isotopes and in cl and is attributed to seawater that has dissolved evaporites mainly halite however the presence of small amounts of an extremely evolved brine is required to account for the bromide lithium rubidium and boron contents of the formation brine from the rhaetian aquifer as this contribution is very limited in amount it cannot affect the heavy isotope content of the formation water mass balance equations are solved for ternary mixtures of meteoric water seawater and brine the same constraints as above no na and k supplied by the primary brine and clbrine 11 000 mmol kg 1 are applied it is also assumed that the seawater component has the same ionic contents as modern seawater and that the salt content of the meteoric component is negligible the fraction of primary brines is x 1 4 according to the cl balance this estimate agrees with that obtained from the lithium balance assuming that the primary brine component was the same as that of the keuper formation water mass balance calculations also indicate that the so42 content of the rhaetian formation water is exclusively due to the secondary brine component in the three saline solutions the very high ca2 contents and high ca 2 mg 2 ratios may be attributed to reaction of the very evolved brine free of so2 4 with gypsum or anhydrite the result is an exchange of mg2 for ca2 which causes a release of ca2 to the solution and a precipitation of secondary mg sulphate this process can also account for the high strontium contents of the analysed samples values of the ratio 87 sr 86 sr are very high in the keuper formation water due to close contact of the solutions with the granitic basement or with granite derived detrital deposits values in the rhaetian and dogger aquifers equal those of upper triassic marine deposits the stable isotope 34s and 18o content of the dissolved aqueous so2 4 indicates a triassic origin for the bulk of sulphate involved in the evolution of formation waters from the rhaetian and from the dogger all geochemical indicators thus show a vertical migration of triassic brines however aqueous so2 4 from the keuper has a permian isotopic signature suggesting a reworking in solution of salts from this period

widespread cementation induced by inflow of continental water in the eastern part of the paris basin o and c isotopic study of carbonate cements abstract mesozoic limestones from the eastern part of the paris basin display mostly in strata rich in bioherms abundant macro cavities vugs and some connected micro fractures almost completely filled with euhedral calcite crystals late calcite spar the interparticle porosity of limestones is also filled with euhedral calcite spar cements similar to those observed in vugs and fractures and rarely displays the preservation of the structures typical of early marine cements these calcite spars both from vugs fractures infillings and from cemented porosity were studied in drilled cores cross cutting the kimmeridgian to bathonian series with the main objective of determining the nature and flow regime of the fluids responsible for the strong porosity reduction observed in that part of the paris basin mesozoic limestones the approach combined mineralogical and geochemical studies o and c stable isotopic compositions measured by conventional and sims methods with temperature estimates from fluid inclusion analyses the 13 c values of late calcite are close to those of the host limestones and correlate with the 13 c changes in host rocks indicating a local source of c by contrast late calcites from vugs fractures and also in the cemented interparticle porosity of limestones have 18 o values around 21 smow values which are distinct from those of bulk host limestones 25 to 27 the 18 o value of the fluid is estimated to be 6 8 to 2 5 for a crystallisation temperature between 32 and 42 c determined from fluid inclusion studies thus the parent fluid of cemented interparticle porosity and vug and fracture infillings likely contained a component of meteoric water in contrast to the previous belief that the reduction of porosity in those series was related to early marine diagenesis possible situations in which such meteoric fluid could have occurred are i a stage when the limestone aquifers were directly connected to surface water and or ii channelling of water from deeper zones in the basin through regional fault systems the o isotopic compositions of the calcite cements in the underlying 140 m thick callovo oxfordian argillites and those of the less recrystallised bathonian to kimmeridgian limestones are those expected for unmodified marine calcite 18 o ca 28 smow therefore from the isotopic point of view the callovo oxfordian argillites remained essentially unaffected by the paleo fluid circulation documented in the adjacent limestones series this indicates the argillites acted as an efficient permeability barrier in the past

u pb dating of geodic calcite new insights on western europe major tectonic events and associated diagenetic fluids this study presents the first application of the u pb dating method to highly pb depleted diagenetic geodic calcites of the jurassic formations of the paris basin that leads to a reappraisal of the palaeohydrological history of this region composite u pb ages from multiple geodes combined with 18 o analyses reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events dogger formations recorded a first diagenetic fluid episode at 147 8 3 8 ma i e at the very beginning of the emersion of the basin during the tithonian period and 30 ma earlier than previously assumed 18 o results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the cretaceous period oxfordian formations recorded another major meteoric fluid circulation at 33 5 2 8 ma related to the initial stage of the european cenozoic rift system ecris consequently the porosity of the mesozoic formations of the studied area may have been closed sooner than previously thought before the main ecris rifting phase of oligocene age this study shows that u pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins supplementary material pb pb diagrams 238 u and 235 u series isochron diagrams and effect of blank correction on u and pb isotopic compositions and on ages calculation are available at https doi org 10 6084 m9 figshare c 3886885

basin scale thermal and fluid flow histories revealed by carbonate clumped isotopes δ47 middle jurassic carbonates of the paris basin depocentre the reconstruction of past diagenetic conditions in sedimentary basins is often under constrained this results from both the analytical challenge of performing the required analyses on the minute sample amounts available from diagenetic mineral phases and the lack of tracers for some of the diagenetic parameters the carbonate clumped isotopes thermometry 47 opens new perspectives for unravelling the temperatures of diagenetic phases together with the source of their parent fluids two parameters that are otherwise impossible to constrain in the absence of exploitable fluid inclusions here is reported the study of a large number of sedimentary and diagenetic carbonate phases from middle jurassic reservoirs of the paris basin depocentre by combining detailed petrographic observations with a large number of 47 data n 45 on a well documented paragenetic sequence including calcite and dolomite burial cements the data reveal carbonate crystallization at temperatures between 29 c and 98 c from fluids with 18owater values between 7 and 2 in response to the progressive burial and uplift of the paris basin throughout 165 myr of basin evolution coupled to the time temperature evolution previously estimated from thermal maturity modelling these temperatures allow determining the timing of four successive cementation episodes the overall dataset indicates a history of complex water mixing with a significant contribution of hypersaline waters from the triassic aquifers migrated upward along faults during the cretaceous subsidence of the basin subsequent large scale infiltrations of meteoric waters induced a dilution of these pre existing brines in response to the paris basin uplift in the tertiary overall the data presented here allow proposing an integrated approach to characterize the cementation events affecting the studied carbonate reservoir units based on temperature oxygen isotope composition and salinity of the parent fluids as well as on petrographic grounds this article is protected by copyright all rights reserved

coastal plain stratigraphy records tectonic environmental and human habitability changes related to sea level drawdown upolu sāmoa coastal plain stratigraphy is often over looked in paleo sea level reconstructions because carbonate sediments do not precisely constrain former sea level pacific island sedimentology provides an invaluable record of geomorphic and environmental consequences of coastal evolution in response to changes in sea level and local tectonics a series of coastal auger cores obtained from eastern upolu reveal a subsurface carbonate sand envelope predominately composed of coral and coralline algae derived from the reef framework coupling the sedimentological record with geophysical models of holocene sea level we identify a critical value 0 3 1 0 m during the falling phase of the sea level high stand 1899 2103 cal yr bp that represents the transition from a transgressive to a regressive environment and initiates coastal progradation correlating the critical value with time we observe nearly a millennium of coastal plain development is required before a small human population is established our findings support previous studies arguing that s moa was colonized by small and isolated groups as post mid holocene drawdown in regional sea level produced coastal settings that were morphologically attractive for human settlement as future sea level approaches mid holocene high stand values lessons learned from pacific island sedimentological records may be useful in guiding future decisions related to coastal processes and habitat suitability

a renewed look at calcite cement in marine deltaic sandstones the brent reservoir heather field northern north sea uk wireline and seismic acoustic impedance imaging show that the marine part of the clastic brent group reservoir in the heather field northern north sea contains much calcite cement in the flank parts of the structure the non marine ness formation and crest parts of the structure contain negligible calcite cement this localised calcite cement has led to relatively poor reservoir performance since first oil in 1978 although a new suite of wells has boosted production with plans to keep the field active until 2030 understanding the origin and distribution of calcite cement would help the development of more realistic reservoir models and boost production rates through optimum well location we have thus used a suite of techniques including standard point counting sem eds mineralogy bse microscopy fluid inclusion thermometry and stable isotope analysis to develop new and improved models of calcite distribution calcite seems to have attributes of both early and late diagenetic cement 30 to 40 intergranular volume in calcite cemented beds seems to support pre compactional growth but high temperature fluid inclusions and the presence of primary oil inclusions suggests late growth much calcite may have developed early but it seems to have recrystallized and possibly undergone redistribution at close to maximum burial or had a late growth event calcite cement probably originated as marine derived micrite bioclasts or early marine cement but adopted the isotopic characteristics of high temperature growth as it recrystallized quartz grains have corroded outlines in calcite cemented areas with one sample with 79 calcite cement displaying signs of nearly total replacement of quartz grains by calcite the flank localisation of calcite remains to be explained although it could be due to primary depositional factors early diagenetic loss of calcite from crestal regions or late diagenetic loss of calcite from crestal regions controversially the growth of calcite seems to be associated with quartz dissolution although the geochemical and petrophysical cause of this remains obscure diagenetic loss of quartz from sandstones cannot easily be explained by conventional modelling approaches and yet seems to be an important phenomenon in heather sandstones

diagenesis and pore water evolution in the keuper reservoir paris basin france keuper upper triassic fluvial sandstones and nonmarine carbonate rocks form a major oil reservoir in the western paris basin at burial depths of nearly equal 2 km early diagenetic processes comprise red bed type diagenesis mechanical clay infiltration iron oxide precipitation and extensive dolocrete formation both in fluvial channels and in fine grained overbank sediments locally significant paleokarst created vuggy dissolution porosity in the carbonate units and probably also caused leaching of detrital alkali feldspar grains oxygen carbon and strontium isotope analyses of various eogenetic cements indicate a nonmarine pore water composition ferroan carbonates authigenic albite and potassium feldspar quartz sulfates sulfides and clay minerals formed subsequent to major mechanical compaction their isotopic compositions record significant changes in the chemistry of the parent pore water cl br relationships of the present day pore water reveal that fluids saturated with respect to halite flushed the reservoir during burial this is documented by the oxygen isotope composition of the burial cements based on radiogenic dating of illite cements influx of warm brines into the reservoir most likely occurred during the earliest cretaceous at this time the margins of the basin were uplifted by late cimmerian tectonism resulting in an unconformity at the jurassic cretaceous boundary we suggest that uplift of the vosges crustal block created a hydraulic head in the eastern part of the basin and established a gravity driven fluid flow system displacing interstitial brines from the keuper evaporites from the eastern part towards the western part of the basin fluid inclusion studies indicate that brine influenced cementation occurred at progressively higher temperatures reaching peak temperatures of 140 degrees c these high subsurface temperatures could not have been caused by advective heat transport but most likely resulted from a combination of maximum burial depth high surface temperatures and thermal blanketing during the late cretaceous a second gravity driven fluid flow system was established during the oligocene by major uplift and freshwater flushed the keuper reservoir mainly from the south causing brine dilution the present day pore water in the study area is still saline 50 100 g l tds and mass balance calculations indicate that the ratio of basinal brines to tertiary meteoric water is about 1 2

coupling δ47 and fluid inclusion thermometry on carbonate cements to precisely reconstruct the temperature salinity and δ18o of paleo groundwater in sedimentary basins abstract diagenetic minerals may provide information about the burial history of geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of sedimentary basins clumped isotope or 47 thermometry on carbonates opens a new avenue for interpreting carbonate formation temperature and thermal history of rocks yet most of current knowledge on 47 systematics has been acquired via theoretical or experimental studies with only limited validation by the rock record at geological conditions timescales here we investigate calcitic and dolomitic cements representative of three genetically different cementation phases from a well documented mineral paragenesis of a carbonate unit middle jurassic paris basin france we compare 47 with fluid inclusions microthermometry fim data that were independently obtained from the same calcite and dolomite crystal specimens the range of homogenization temperatures th found for cal1 cal2 and dol1 fluid inclusions fit remarkably well i e within 47 measurements t 47 for a temperature range between 60 and 100 c and salinities between 0 and 15 wt nacl eq this provides a consistent rock based validation of the experimentally determined 47 calibration with formation temperature for both calcite and dolomite mineralogy such findings also confirm the applicability of 47 thermometry in low temperature diagenetic environments i e below circa 100 c which provides higher precision than fim measurements i e typical uncertainties of 6 c with three 47 measurements though significantly less time consuming importantly this study underlines how the coupling of both techniques can help to evaluate the degree of preservation of the original temperature information captured by either fluid inclusions or 47 compositions and interpret each proxy as confidently accurately as possible moreover because both fim and 47 measurements can provide independent constraints on the geochemistry of diagenetic paleofluids via their salinity and 18 o composition this study also highlights the benefits of coupling both techniques to further unravel the nature of paleofuids finally we propose a practical guideline as a basis for future applications of combined fim and 47 thermometry

effects of fringing reefs on tsunami inundation american samoa abstract a numerical model of tsunami inundation delft3d which has been validated for the 29 september 2009 tsunami in tutuila american samoa is used to better understand the impact of fringing coral reefs and embayments on tsunami wave heights inundation distances and velocities the inundation model is used to explore the general conditions under which fringing reefs act as coastal buffers against incoming tsunamis of particular interest is the response of tsunamis to reefs of varying widths depths and roughness as well as the effects of channels incised in the reef and the focusing effect of embayments model simulations for conditions similar to tutuila yet simplified to be uniform in the alongshore suggest that for narrow reefs less than about 200 m wide the shoaling owing to shallow water depths over the fringing reef dominates inducing greater wave heights onshore under some conditions and farther inundation inland as the reef width increases wave dissipation through bottom friction begins to dominate and the reef causes the tsunami wave heights to decrease and the tsunami to inundate less far inland a sensitivity analysis suggests that coral reef roughness is important in determining the manner in which a fringing reef affects tsunami inundation smooth reefs are more likely to increase the onshore velocity within the tsunami compared to rough reefs a larger velocity will likely result in an increased impact of the tsunami on structures and buildings simulations developed to explore 2d coastal morphology show that incised channels similar to those found around tutuila as well as coastal embayments also affect tsunami inundation allowing larger waves to penetrate farther inland the largest effect is found for channels located within embayments and for embayments that narrow landward these simulations suggest that embayments that narrow landward such as fagafue bay on the north side of tutuila and that have an incised deep channel can cause a significant increase in tsunami wave heights inundation distances and velocities wide embayments similar in size to massacre bay induce some tsunami amplification but not as much as for the narrowing embayment

basin scale evolution of formation waters a diagenetic and formation water study of the triassic chaunoy formation paris basin abstract formation waters and their movements within basins are commonly attributed with responsibility for patterns of cementation and porosity loss within reservoirs and aquifers it is thus important to understand when and how waters move in the subsurface we have studied the evolution and movement of formation water in the triassic chaunoy formation of the paris basin nw europe to define the way in which the water has evolved and to interpret water movement patterns using mineral isotope and fluid inclusion data in conjunction with detailed formation water analyses the chaunoy formation is cemented with different types of dolomite calcite and quartz cement we have studied the evolution of waters in terms of oxygen carbon and strontium isotopes and salinity connate waters were meteoric in origin but strongly influenced by the proximity of a playa lake input of palaeo meteoric water which entered the chaunoy via eastern halite bodies resulted in highly saline formation water for the majority of the chaunoy formation from about 100 ma until and for some time after maximum burial saline waters spread into the aquifer initially taking a west north west trajectory and then switching to a west south west pattern in the eocene following the alpine orogeny and localised uplift of the basin margin the southern portion of chaunoy received fresh low salinity meteoric water it is likely that formation water was lost from the chaunoy in a more central part of the basin via sub vertical cross formational flow to the mid jurassic dogger formation to accommodate the influx of fresh water

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

dolomitization of gas reservoirs the upper permian changxing and lower triassic feixianguan formations northeast sichuan basin china abstract the lower triassic feixianguan formation and to a lesser extent the upper permian changxing formation contain more than ten giant recently discovered dolomite gas fields on either side of a paleo embayment kaijiang liangping bay sichuan basin china this study documents the origin of the dolomite using a combination of petrology fluid inclusion trace element geochemistry and stable isotope and radiogenic isotope analysis of samples from outcrop and core samples from producing gas fields three stages of dolomitization are revealed dolomicrite from the lagoon facies in the feixianguan formation and minor fabric retentive dolomite from reef facies in the changxing formation on the northeast side of kaijiang liangping bay represent the initial dolomite phase caused by reflux of feixianguan brine with salinity close to gypsum saturation 18 wt salinity during the first stage of diagenesis at 30 c the second and dominant dolomite phase fabric retentive dolomite in both the feixianguan and changxing formations on the both sides of kaijiang liangping bay is the result of reflux of diagenetic fluids with salinity ranging from normal feixianguan seawater 3 5 salinity up to mesohaline water 6 5 salinity during early burial diagenesis at about 35 40 c as shown by the dominance of single phase aqueous inclusions shallow formed stylolites that cut the second phase of dolomite and the early triassic marine carbon oxygen and strontium isotope and rare earth element and yttrium ree y signals the subordinate third dolomite phase fabric obliterative dolomite and dolomite cement was due to burial diagenetic recrystallization between 80 and 140 c in the feixianguan and changxing formations on both sides of kaijiang liangping bay the third phase of dolomitization involved water expelled from the slightly younger lower triassic jialingjiang formation marine evaporites and carbonates on the northeast side of kaijiang liangping bay revealed by the high salinity of the aqueous inclusions that homogenize at 80 to 140 c and elevated strontium isotope data the carbon isotope and ree y signals of the third phase of dolomite are similar to earlier dolomite cements confirming the lack of exotic input future exploration should be focused on dolomitized high energy sediments e g reef and oolitic shoal and bank in similar triassic tethyan paleogeographic settings that are associated with restricted facies but underlying dolomitized high energy permian strata may also be good exploration targets

recent storm and tsunami coarse clast deposit characteristics southeast hawaiʻi abstract deposits formed by extreme waves can be useful in elucidating the type and characteristics of the depositional event the study area on the southeast coast of the island of hawai i is characterized by the presence of geologically young basalts of known age that are mantled by recent wave derived sedimentary deposits the area has been impacted by large swells storms and tsunamis over the last century and in combination with known substrate ages makes this an ideal location to study recent deposits produced by such events three distinct coarse clast deposit assemblages can be recognized based on clast size composition angularity orientation packing elevation and inland distance of the deposit these deposits are characterized as one of three types 1 gravel fields of isolated clasts primarily boulder size material and scattered pockets of concentrated sand and gravel in topographic lows 2 shore parallel and cuspate ridges composed mostly of rounded basalt gravel and sand with small amounts of carbonate detritus the ridges range in height from about 1 to 3 m and are 10s of m wide 3 cliff top deposits of scattered angular and sub angular clasts along sea cliffs that are generally greater than 5 m elevation the gravel fields are primarily of tsunami origin from either the 1975 kalapana event or a combination of the 1975 tsunami and 1868 tsunami or earlier events the ridge deposits are presently active and sediment continues to be added during high wave events the cliff top deposits contain evidence of deposition by both tsunami and storm processes and require further investigation