recognizing and dating prehistoric liquefaction features lessons learned in the new madrid seismic zone central united states the new madrid seismic zone nmsz which experienced severe liquefaction during the great new madrid missouri earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes is a superb laboratory for the study of world class earthquake induced liquefaction features and their use in paleoseismology in seismically active regions like the nmsz frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret lessons learned studying liquefaction features in the nmsz may help to unravel the paleoseismic record in other seismically active regions soil characteristics of liquefaction features as well as their structural and stratigraphic relations to native american occupation horizons and other cultural features can help to distinguish prehistoric liquefaction features from historic features in addition analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features also new methods for dating liquefaction features are needed

reactive transport modelling of reflux dolomitization in the arab d reservoir ghawar field saudi arabia it has long been recognized that the arab d reservoir in ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir previous studies indicated that dolomite occurs with either a stratigraphic or non stratigraphic distribution when mapped dolomite tends to form several parallel linear trends across the field although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits non stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below this study focuses primarily on these non stratigraphic dolomites and proposes that i these dolomites initially formed via seepage reflux but were reinforced by late stage hydrothermal dolomitization and ii reflux is also responsible for the formation of parallel linear trends of dolomite the reflux model hypothesizes that an evaporative lagoon which is the source of dolomitizing fluids formed during the falling stage systems tract of a depositional sequence and that with continuing sea level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the ghawar field leaving behind lines of dolomite bodies along a series of temporary coastlines two dimensional reactive transport models have been built to test this hypothesis and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non stratigraphic dolomite as well as the mapped lateral distribution of the dolomite trends in addition the major ion compositions of late jurassic seawater are calculated based on fluid inclusion data in the literature using jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over dolomitization than using modern seawater

diagenetic stabilization of the upper permian dalan formation persian gulf basin abstract the upper permian dalan formation is a supergiant gas reservoir in the persian gulf basin reservoir quality is controlled by the original facies type dolomitization and anhydrite cementation this study focuses on the texture petrographic analysis bulk stable isotope values and trace element composition in order to identify the original mineralogy of carbonate grains and cements and to assess the synsedimentary and diagenetic processes including the timing and setting of dolomitization the limestone data suggest that the initial precipitation of isopachous acicular to fibrous aragonite cements in the marine phreatic environment was followed by dissolution of aragonite grains and cements in the meteoric phreatic zone and neomorphism and low mg calcite cementation blocky and drusy crystals syntaxial overgrowths in the active freshwater phreatic zone the relatively pristine 18o and 13c values low mn and relatively high sr and na contents indicate that this meteoric diagenesis was relatively limited the remaining porous space was cemented by blocky calcite later during burial four types of dolomites are identified within a complex mixture of texturally and isotopically different dolomites dolomicrite dolomicrosparite dolosparite and saddle dolomite dolomicrite formed syndepositionally from the evaporated permian seawater or by reflux of dense evaporated brines during shallow burial the second major episode of dolomitization dolomicrosparite and dolosparite was driven by reflux of warmer and more saline fluids at greater depth which affected both previously non dolomitized and dolomitized sediments the final diagenetic stabilization during deep burial is associated with extensive pressure solution fracturing vein filling of calcite and dolomite cements and crystallization of saddle dolomite

paleoaquifer and deep burial related cements defined by regional cathodoluminescent patterns middle ordovician carbonates virginia middle ordovician ramp carbonates virginia were deposited in a subsiding foreland basin bordered on the southeast by tectonic highlands ramp carbonates were lithified in part by turbid marine cements but major cementation was by nonferroan clear rim and equant cements zoned defined by cathodoluminescence clear cements consist of nonluminescent oldest bright and dull youngest cements the zonation relates to increasingly reducing conditions of pore waters zoned cements in peritidal beds best developed in southeastern belts have complex zonations pendant to pore rimming fabrics and are associated with crystal silt which abuts all cement zones solutional cavities and erosional surfaces which locally truncate dull cement these cements are meteori vadose to shallow phreatic cements in northwestern exposures of peritidal beds are dominated by non zoned dull cement which lacks abundant evidence of early near surface precipitation major cementation of subtidal facies occurred under burial conditions burial cements best developed in southeastern belts have a simple zonation reflecting progressive burial up to 7 5 km 4 5 mi of the carbonate ramp shallow burial nonluminescent cement formed from oxidizing meteoric waters which expelled anoxic connate marine waters these meteoric waters were carried by aquifers from tectonic upland recharge areas on the southeastern basin margin bright cement formed under more reducing conditions following stagnation of the paleoaquifer with burial and possibly was precipitated at depths of 2 to 3 km 1 to 2 mi burial cements in northwestern exposures of subtidal beds are dominated by dull cement initial generations of which precipitated from downdip portions of aquif rs deeper burial dull calcite and ferroan dolomite cements largely formed at burial depths of 2 to 3 km 1 to 2 mi and temperatures of 75 to 135 c 165 to 275 f or more associated with hydrocarbon formation emplacement during the late devonian to mississippian latest clear dull cement fills tectonic fractures and was emplaced during late paleozoic alleghenian deformation probably at temperatures of 200 to 300 c 390 to 575 f and depths of 5 to 7 km 3 to 4 5 mi deeper burial diagenesis appears to be genetically linked to late paleozoic mississippi valley type mineralization in the southern appalachians zoned peritidal and burial cements are confined mainly to southeastern portions of the ramp where cementation was influenced by meteoric waters shed from tectonic uplands on the southeast and carried northwest by paleoaquifers northwestern portions of the ramp were influenced very little by upland sourced meteoric waters and nonzoned dull cements precipitated from relatively reducing waters the distribution of nonluminescent cement in middle ordovician subtidal facies defines the regional distribution of oxidizing portions of the paleoaquifer system such incursion of upland sourced oxidizing meteoric waters into ramp carbonates should be a common feature of foreland basin carbonates deposited adjacent to tectonic uplands furthermore foreland basin carbonates that undergo progressive burial should show a simple nonluminescent to bright to dull sequence of cement zones the close association of zoned cements and regional uplands in the middle ordovician sequence indicates the importance of assessing regional geologic relationships environmental parameters geologic history and tectonics in understanding regional cementation patterns and cementation processes of anci nt carbonate platforms

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

deposition and textural evolution of cool water limestones outcrop analog for reservoir potential in cross bedded calcitic reservoirs the eocene miocene te kuiti group is a succession of cool water carbonate and siliciclastic rocks on the north island of new zealand the limestones are subtidal bioclastic and largely composed of bryozoans echinoderms and benthic foraminifers these rocks can be divided into a horizontally bedded facies assemblage and a cross bedded facies assemblage the horizontally bedded facies assemblage represents deposition on a wave storm dominated shelf and is composed of grainstones and packstones containing textures resulting from biologic processes the cross bedded facies assemblage represents deposition on a current dominated shelf and consists of grainstones with textures formed chiefly by physical processes the te kuiti group can be used as an outcrop analog for cross bedded calcite dominated hydrocarbon reservoirs porosity permeability and reservoir potential of the horizontally bedded facies assemblage decreased rapidly during late shallow burial owing to mechanical compaction and to the fine grain size close packing and ineffective early cementation of the rock coarser grain size open framework and earlier cementation within the cross bedded facies assemblage resulted in significant heterogeneity and good reservoir potential before moderate burial tabular lens shaped and sigmoidal reservoir units are proposed primary porosity and early developed traps are essential to reservoirs formed of cool water limestones and those carbonates from calcite seas the influence of depositional setting extends into the eventual bedding style texture physical properties and reservoir potential of the rock

impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir the case of the oolithe blanche formation bathonian paris basin france the oolithe blanche formation was studied in three quarries located at the south eastern edge of the paris basin france heterogeneities in reservoir properties were assessed through a sedimentological diagenetic and petrophysical study the relationships between depositional settings diagenesis and petrophysical properties were analysed using detailed petrographic studies image analysis nano ctscans and petrophysical measurements the carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso and macroporosity early cementation vs early compaction processes mainly grain interpenetration may have considerable influence on fluid flow properties and parameters such as permeability acoustic velocities and tortuosity better reservoir properties are found when compaction processes begin before cementation from statistical analyses e g principal component analysis and linear discriminant analysis a sedimentological diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work

lower silurian reefs and post reef beds of the attawapiskat formation hudson bay platform northern ontario outcrop exposures along the attawapiskat river in the hudson bay lowlands of northern ontario clearly reveal the morphology of silurian upper llandoverian reefs of the attawapiskat formation and the relationships between reef cores flanking beds and post reef beds these relationships indicate that the reefs had a syndepositional relief of at least 8 10 m the relief of the reefs is indicated by debris flow lenses encased within flanking beds a debris flow fan at the base of a reef thin reef flanking beds truncated against a vertical reef face penecontemporaneous brachiopod beds on the flanks of reefs and three large slide blocks that apparently slid over the side of a reef reefs of the attawapiskat formation are largely limestones with a wide range of lithologies from stromatoporoid coral and cement rich boundstones to alga cement rich boundstones thick laterally extensive nuia grainstone beds a product of widespread nuia monocultures in supratidal to intertidal ponds are present above t

dolomite formation and biogeochemical cycles in the phanerozoic summary based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation the abundance and distribution of dolomite throughout the phanerozoic remains an enigma sometimes referred to as the dolomite problem comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it the recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective a biogeochemical approach to the dolomite problem reveals a plausible connection between phanerozoic geochemical cycles and dolomite formation in particular periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans lowered oxygen levels would have fostered a more active community of anaerobic microbes including sulphate reducing bacteria which in turn could have led to more extensive dolomitization of marine carbonates

missing molluscs as evidence of large scale early skeletal aragonite dissolution in a silurian sea in the silurian carbonate platform succession of gotland sweden interreef limestone and marl sequences have shallow marine shelly assemblages dominated by brachiopods typical of many paleozoic benthic faunas locally from similar facies where early skeletal silicification occurred associated with bentonites there are rich and diverse assemblages of originally aragonitic molluscs quantitative faunal analysis suggests that massive depletion of skeletal aragonite chiefly molluscs took place and the entire molluscan fauna may generally be underrepresented by at least 100 fold previous workers on the gotland succession have already shown that abundant diagenetic limestones were sourced by early aragonitic remobilization our findings indicate molluscs as the probable source of this diagenetic calcite not aragonite mud as was previously thought the taphonomic window represented by the silicified faunas illustrates the importance of aragonitic shells among the original silurian shelf benthos and raises the possibility that the paucity of such shells among many fossil faunas may be largely an early taphonomic effect

selective and reversible carbonate silica replacements in lower cretaceous carbonate bearing turbidites of the eastern alps in the diagenetic history of calcareous sandstones silicacementation and silicification may be followed by carbonatecementation and replacement and vice versa and the change over from one to the other may occur more than once this is well illustrated by calcareous and siliciclastic turbidites of the gault formation aptian to albian of the eastern alps which have been interpreted as deep sea trench plain and deep sea fan deposits in these turbidites silicification selectively affects ooids and a few other biogenic carbonate fragments rich in organic matter algae and bryozoans which form a small fraction of the bulk sediment the type and sequence of diagenetic changes are largely controlled by host rock composition and may vary vertically within individual beds as a result of compositional grading in the carbonate turbidites silicification follows widespread calcite cementation the process is slow resulting in relatively coarsely crystalline replacement quartz in ooids with quartz nuclei rim quartz forms mostly monocrystalline overgrowths by outward replacement of the concentrically laminated carbonate cortex this type of silicification is often incomplete leaving parts of the ooid cortices unaffected in quartz arenites and sublitharenites silicification precedes calcite cementation there the process is rapid forming microcrystalline quartz even if the ooid nucleus consists of quartz a syntaxial overgrowth does not normally form the replacement quartz is almost always polycrystalline late stage diagenetic calcite and dolomite which develop euhedral crystal shapes and cut across grain boundaries may replace the earlier secondary rim quartz of the ooids as well as other minerals possible sources of the silica are pressure solution of quartz dissolution of opaline silica of radiolarian tests and of sponge spicules and feldspar in the host bed in a number of examples an increase in the degree of silicification can be observed towards the lower bedding planes of individual turbidites requiring an additional external source of silica which seems to necessitate cross formational flow of pore solutions silicification in both the carbonate and the siliciclastic turbidites probably took place at about the same time in the carbonate turbidites it was preceded however by calcite cementation which significantly reduced porosity and permeability before silicification took place the greater degree of alteration experienced by the gault turbidites of the falknis and tasna nappes which are more internal structural units of the alps compared to the flysch zone of the eastern alps is reflected by the growth of quartz beards and spikes from the ooids in the direction perpendicular to maximum stress this is the only case observed where the rim quartz of the ooids grows beyond the original grain boundaries

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

a mesozoic carbonate hot spring deposit in the hartford basin of connecticut abstract limestone at coe s quarry in north branford connecticut is characterized by a variety of cross cutting discontinuous textural facies the environmental significance of most textural features is ambiguous but cellular tufa and abundant spherulite strongly suggest a boiling hot spring setting the cellular tufa consists of a thin polygonal framework of micritic calcite which surrounds and interconnects irregular elongate voids the void space is filled with spherulites and locally derived carbonate detritus cemented by sparry calcite and dolomite spherulites nucleated and grew in suspension to diameters of 0 1 mm or more before settling in the cellular tufa and other nearby depositional settings spherulites may form distinct geopetal fabrics in the pores of the cellular tufa dem nstrating that some indistinct layering in tufa had high primary dips other important depositional facies are algal bacterial tufa micritic and banded travertine and siliciclastic limy sandstone all units are abruptly discontinuous laterally and are also found as intraclasts mixed in with other facies the spherulites indicate rapid precipitation of carbonate from highly supersaturated bicarbonate waters formed by flash boiling of co2 rich water the cellular textures are similar to microterrace deposits and encrusted organic grains and mats in modern hot springs saddle dolomite which is an important early cement suggests temperatures of at least 60 c we infer that the limestone was deposited from a hot spring which periodically flash boiled in violent geyserlike eruptions the talcott basalt which immediately underlies the limestone is in places totally replaced by ferroan carbonates we infer that the same circulating groundwater heated by deeper intrusive equivalents of the talcott basalt locally altered the basalt and reached the surface at hot springs like the one from which the limestone at coe s quarry precipitated

in situ raman spectroscopic quantification of aqueous sulfate experimental calibration and application to natural fluid inclusions abstract sulfate is an important component of geological fluids which is often encapsulated in fluid inclusions fis analyses of the composition of such fis can provide important information on the origin and properties of the fluids inside however conventional microthermometric analyses are often hampered due to the complex composition of such fluids alternatively in situ raman spectroscopy is a powerful method to determine the aqueous sulfate concentration of fis unfortunately the effect of a common component chloride on the analytical results has not been well addressed yet in addition disagreements also exist in the current spectrum processing method which also prevents the application of this method in various geological cases in this study a series of fused silica capillary capsules fsccs containing aqueous na2so4 0 01 1 5 mol kg and na2so4 nacl mna2so4 0 05 and 0 5 mol kg mnacl 0 1 4 0 mol kg solutions were prepared as standards in situ raman spectra for the stretching vibration of so42 v1 so42 the bending vibration v2 h2o and the stretching vibration vs h2o of water were collected at room temperature results show that for sulfate solutions both v2 h2o and vs h2o bands can be used as internal standards for the determination of aqueous sulfate concentration mso42 the peak area a ratios between v1 so42 and v2 h2o or vs h2o bands increased nearly linearly with mso42 in na2so4 solutions consequently the relationships between mso42 and the spectral parameters i e a v1 so42 a v2 h2o and a v1 so42 a vs h2o were established however the calculated mso42 will be underestimated when applying the above calibration curve to nacl na2so4 solutions using a v2 h2o as an internal reference in this case the influence of chloride on the calculated mso42 will be largely eliminated when using a vs h2o as an internal reference or fitting the vs h2o band with two gaussian components at 3230 cm 1 and 3450 cm 1 and then using the total peak area as internal reference it should be noted that our calibration results allow comparisons across different laboratories because the spectral intensity was corrected to reduce the response function of the spectrometer and the temperature and wavenumber dependence then the a v1 so42 a vs h2o mso42 relationship was applied to natural fis in fluorite from the dalucao hydrothermal ree deposit southwestern china and in halite from the paleogene evaporite in the jianghan basin south china the mso42 in pre ree stage fluorite hosted fis can reach 0 37 mol kg indicating that sulfate are responsible for the hydrothermal transport of ree the mso42 in the halite hosted fis were found to be in close association with the mineral assemblage serving as an indicator for the degree of evaporation or sedimentary facies

cathodoluminescence and composition of calcite cement in the taum sauk limestone upper cambrian southeast missouri abstract study of calcite cements in the taum sauk limestone upper cambrian southeast missouri using cathodoluminescence petrography and microprobe analysis has shown that 1 distinct luminescent zones correspond to distinct compositional zones 2 the degree of luminescent intensity of a particular calcite zone appears to be controlled by the fe mn ratio of the zone not by the absolute concentrations of either cation 3 manganese may induce luminescence in calcite at concentrations as low as 300 ppm and 4 there may be no critical concentration of ferrous iron in calcite above which there can be no luminescene

depositional environment sequence stratigraphy and geochemistry of lower cretaceous carbonates fahliyan formation south west iran abstract the fahliyan formation is a carbonate sequence of lower cretaceous berriasian hauterivian age and was deposited in the zagros sedimentary basin iran in this investigation the fahliyan formation at the type section and in the subsurface has been studied facies analysis and petrographic studies led to the recognition of 10 microfacies that were deposited in three facies belts lagoon shoal and open marine the observed facies patterns indicate a carbonate rimmed shelf depositional environment based on field observations microfacies analysis and sequence stratigraphic concepts two third order sequences in the type section and three third order sequences in the subsurface section were identified the transgressive deposits display a predominance of deep subtidal facies while highstand deposits show shallow subtidal facies some petrographic evidence such as an abundance of aragonite skeletal and non skeletal components shows that this formation was deposited in a sub tropical environment with original aragonite mineralogy geochemical evidence such as high sr na ratios also support original aragonite mineralogy 18o and 13c values suggests that alteration occurred during burial diagenesis in a closed system with low water rock interaction palaeotemperature calculation based on the heaviest oxygen isotope value in micritic samples of the fahliyan limestone shows that ambient water temperature was around 24 c during the deposition of this formation

calcite and aragonite precipitation from seawater solutions of various salinities precipitation rates and overgrowth compositions abstract the reaction rate and composition of calcite and aragonite overgrowths precipitated from seawater solutions of various salinities i e s 5 15 25 35 44 were determined at 25 c and 10 2 5 atm co2 partial pressure using a constant disequilibrium seeded technique the rate data were fitted to an empirical rate law of the form log r n c or a 1 log k where n is the empirical reaction order and k is the rate constant calcite precipitation rates in seawater solutions do not vary appreciably as a result of salinity variations over the range investigated while those for aragonite show an increase in going from the higher i e s 35 44 to the lower i e s 5 15 25 salinity range this study also confirms previously published findings that above a given saturation state i e c 2 6 aragonite precipitates more rapidly than calcite at 25 c the incorporation of sr2 in aragonite and mg2 in calcite overgrowths are independent of the precipitation rate the partition coefficient of sr2 in aragonite is approximately equal to unity and is unaffected by salinity variations between 5 and 44 however the mg2 partition coefficient in calcite increases with decreasing salinity of the parent seawater solutions possibly as a result of variations in the sulfate content of the solutions and solids the experimental results were discussed in the context of a number of geological environments

grounded source tem modelling of some deep seated 3d resistivity structures long offset transient electromagnetics lotem is now regarded as a suitable electrical method for deep exploration along with magnetotellurics mt in this method the vertical magnetic field impulse response and occasionally the horizontal electric field step response of a grounded wire source on the surface of the earth are measured here these two responses are computed for 3d models of three deep resistivity structures of interest in hydrocarbon exploration i a faulted graben in a resistive basement rock at a depth of 4 km beneath a conductive overburden ii a facies change in a resistive layer buried at a depth of 2 km in the conductive overburden above a resistive basement and iii an anticlinal uplift of a resistive layer at a depth of 1 km in the conductive overburden above a resistive basement the results show that the sensitivity of the electric field response to model perturbation is generally greater than that of the magnetic voltage response further the electric field sensitivity is confined to early and intermediate times while that of the magnetic voltage response is confined to intermediate and late times hence it is recommended that both electric and magnetic recordings are made in a lotem survey so that the final results can be presented as apparent resistivity curves derived from the two responses jointly as well as separately

instantaneous shaking liquefaction induced by the m7 2 1995 southern hyogo prefecture earthquake japan the sand boils induced by the 1995 southern hyogo prefecture earthquake m7 2 occurred in many locations along the nojima earthquake surface rupture zone some concentric circles of sand boils that occurred along the surface rupture zone were displaced by surface rupturing at the ogura location in the central part of the rupture zone this indicates that liquefaction was caused by instantaneous strong ground shaking before surface rupturing the grain size distribution patterns of sand boils show that the sand boils are in the range of grain size to generate liquefaction liquefaction induced by earthquakes is generated by the horizontal vibration of s waves in noncohesive soil under increased pore pressure and induced effective stress in the ogura location however field evidence and seismic data indicate that the liquefaction induced by the 1995 southern hyogo prefecture earthquake formed during 3 s to 4 s after the main shock mainly by the vertical vibration of p waves rather than the horizontal vibration of s waves we define this as instantaneous shaking liquefaction

permian oolitic carbonates from the baoshan block in western yunnan china and their paleoclimatic and paleogeographic significance marine carbonate ooids are environment sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions this paper describes permian ooids from the baoshan block in western yunnan china in order to offer a new means to refine the uncertain paleogeographic details of this gondwana derived block four major types of ooids micritic ooids compound ooids leached ooids and half moon ooids are documented from the hewanjie formation in the northern and the shazipo formation in the southern baoshan block these ooids are dated via biostratigraphic analysis to be wordian early wuchiapingian and signify an ameliorated shallow marine temperature for the guadalupian strata of the baoshan block results of this study coupled with literature data reveal diachronous debut of permian ooids among the gondwana derived blocks mostly sakmarian in central taurides of turkey central iran central pamir and karakorum block versus wordian capitanian in baoshan block peninsular thailand and south qiangtang in contrast asselian sakmarian strata of baoshan block as well as peninsular thailand and south qiangtang are characterized by glaciomarine diamictites these observations suggest that the baoshan block was probably situated at a considerably higher paleolatitude under distinct influence of gondwana glaciation during the asselian sakmarian than those blocks yielding sakmarian ooids moreover marine ooids are virtually absent nearby the equator within the permian tethys similar to the modern situation the baoshan block is accordingly interpreted to drift to warm water southern mid latitudes during the wordian capitanian and remain to the south of central iran karakorum block and south china which were equatorially located in the capitanian

geochemical indicators of depositional and early diagenetic facies in holocene carbonate muds and their preservation potential during stabilisation holocene carbonate muds 63 m fraction and macro organic matter were collected from marine subtidal mudbanks and supralittoral mud islands of florida bay and freshwater marshes of the florida everglades u s a geochemistry sedimentology and mineralogy were used to determine whether carbonate mud formation in specific marine and freshwater environments was geochemically distinct and to assess the importance of early diagenetic reactions on mud chemistry and mineralogy significant variations were found in the relative amounts of carbonate minerals not just between the marine and freshwater environments but also within florida bay in particular mg calcite is enriched in crane key muds by 10 relative to nearby cross bank the mg calcite appears to precipitate in the surface living cyanobacterial mats of the key and seems to be linked to mg chelation by the cyanobacterial organic matter this mg calcite has a distinct 13c around 4 6 lighter than mg calcite derived from thalassia epibionts in the cross bank muds dolomite was found just below the cyanobacterial mats forming in the only part of the core where reactive organic carbon has been completely removed by sulphate reducing bacteria the 13c values of this dolomite at least 4 are consistent with previously published 13c values of dissolved inorganic carbon in pore waters at this horizon which support dolomite formation in situ mg supply for dolomite formation may be from dissolution of the overlying cyanobacterial mat mg calcite the various types of organic matter have distinctive 13c values ranging from 25 mangrove and sawgrass to 10 cyanobacterial mats and 8 thalassia seagrass values intermediate between these end members record mixing of the organic matter types which shows particularly the time when the bank muds became dominated by thalassia organic matter i e were relatively removed from mangrove vegetation five holocene mud suites bank key cyanobacterial mats mangrove swamp and freshwater everglades swamp show distinct chemical signatures in their mean 13c 18o mgco3 and sr values na distinguishes between seawater and non seawater influenced environments but fe mn and p are mainly controlled by non carbonate materials comparison with published stable isotope and elemental data for pleistocene limestones in the south florida area suggests that only the facies diagnostic signatures of 13c and mg will be resolvable once the muds have been stabilised to micrite alteration of the 18o and sr values during stabilisation will probably be more severe to the extent that original facies variations are destroyed

time specific aspects of facies state of the art examples and possible causes abstract the term time specific facies tsf was introduced to the scientific community by the late otto h walliser to refer to unique facies typical of particular narrow intervals some of which were related to bioevents in some senses however the concept was recognized much earlier and is even engrained in the very names of some geologic periods the concept of time specific facies is expanded slightly herein to include distinctive or unique regional to global characteristics of the sedimentary record that characterize particular intervals of geologic time the recognition of time specific and widespread processes in the sedimentary record is a critical step in unraveling the interplay between processes of differing scale these range from very short term but widespread facies that overlap with event deposits to general facies types that may persist for intervals up to 10s of millions of years in duration this paper briefly summarizes the history of development of the tsf concept provides examples to illustrate a few of the key aspects of time specific facies and offers a few tentative explanations for this phenomenon among the factors that control tsfs abrupt changes in redox conditions and early diagenetic mineralization sedimentary condensation often associated with abrupt sea level change altered climate and paleoceanography and biotic evolution and extinction seem to be most critical and permit a preliminary genetic classification of tsfs inevitably however many tsfs reflect multiple effects and some remain largely unexplained

enhanced carbonate petrography using fluorescence microscopy abstract fluorescence microscopy can recognize depositional facies and delineate diagenetic fabrics and porosity relationships in certain highly dolomitized or recrystallized limestones previously uninterpretable using standard petrographic techniques this tool has other valuable applications in the study of carbonate rocks these other applications include differentiating carbonate cements from neomorphic spar enhancing depositional and diagenetic fabrics rapidly evaluating mineralogical stabilization and recrystallization in holocene and pleistocene deposits and improving delineation of porosity and pore geometries in sedimentary rocks fluorescence microscopy is a rapid easily used and nondestructive technique that can be applied to unpolished thin sections or rock slabs by itself or in conjunction with other petrographic and geochemical tools it has the potential to expand our understanding of carbonate diagenetic processes and products in particular dolomitization and neomorphism and carbonate porosity evolution we strongly encourage routine usage of fluorescence microscopy in future carbonate petrographic studies

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

diagenetic evolution of a late silurian reef platform gaspe basin quebec based on cathodoluminescence petrography carbonate units of two facie of the platformal upper reef complex of the late silurian west point formation gaspe peninsula quebec were studied to decipher their diagenetic evolution the two facies were a reef margin facies and a back reef to lagoonal facies under the light microscope only three broad cement phases were recognized in contrast cathodoluminescence observation revealed seven distinct generations of cements and a plethora of additional diagenetic features such as fracturing internal brecciation sulfatization and stylolitization the first four generations of cement were early marine and confined to the reef margin facies the subsequent three cement generations evolved in shallow to deeper burial environments and affected the reef margin facies and the back reef to lagoonal facies c and o stable isotope data support these deductions fracturing internal brecciation stylolitization sulfatization and the generation of the latest cements occurred during compaction and postcompact

diagenetic alteration of early marine cements of upper silurian stromatactis stromatactis is a spar network whose elements in cross section have flat to undulose lower surfaces and digitate upper surfaces the network is composed principally of isopachous crusts of centripetal cement and commonly occurs embedded in finely crystalline limestone it is the cement filling of interconnected cavities stromatactis of upper silurian red stromatactis limestone from gaspe peninsula quebec appalachians exhibits two types of cements 1 an isopachous cement that lined the walls of the conduits and is interpreted as early marine and 2 a later blocky cement that occupies the centres of cavities the first cement is composed exclusively of non ferroan calcite whereas the second cement is mixed non ferroan and ferroan calcite the early isopachous cement is white on polished slabs and has a turbid aspect under transmitted light in a few samples the relative homogeneity of this early cement is broken by the presence of distinctive grey clear calcite under cathodoluminscence the grey clear calcite is non luminescent and exhibits well defined bladed crystal shapes whereas the white turbid cement has a dull orange luminescence and indistinct crystal shapes the relationships between the two cements indicate that the dull luminescent cement is a secondary form of the non luminescent cement and it is concluded that the dull cement is the product of alteration of the non luminescent cement by burial or meteoric fluids the later blocky cement has the same dull luminescence as the white turbid cement and is thought to have been precipitated from the same fluids as those responsible for the alteration of the early marine cements oxygen isotopic values of the dull cement of the early isopachous crusts mean 18o 6 8 o are intermediate between those of the non luminescent early marine cement mean 18o 5 3 o and the dull luminescent blocky cement mean 18o 11 8 o while carbon isotopic values do not differ significantly 13c 2 9 2 4 and 2 6 o respectively the alteration also has affected the distribution of some trace elements particularly mg both unaltered and altered cements contain less than 1 microdolomite inclusions but the mg content of the background calcite of unaltered cement is three times that of altered cement 14171 vs 5502 ppm precursor early marine cement is thought to have been low mg calcite the mean 18o value 5 3 o of unaltered early marine cement is higher than values for the oxygen isotopic signature of silurian oceans provided by brachiopod shells

electromagnetic sounding of the kapurdi lignite deposit in western rajasthan india in the kapurdi block of the barmer lignite field in western rajasthan india lignite occurs as a number of discontinuous seams of varying thickness up to a few m the country rock is a succession of clay sand and various members of the clay sand family the overburden comprising sand fuller s earth bentonitic clay clayey sand sandy clay and clay is thick and electrically highly conductive both its thickness 40 90 m and conductivity 0 5 1 0 s m are highly variable the lignite seams may occur anywhere in the clay sand sequence below this overburden a ten layered electrical model of the kapurdi area was parameterized on the basis of galvanic resistivity sounding and core drilling results this model was then validated by electromagnetic sounding measurements made with a 200 200 m square loop transmitter and energizing current of variable frequency 80 hz to 11 khz using central induction sounding techniques with a loop of this size only formations in the overburden could be mapped subsequent computer modeling has shown that a larger loop of size say 800 m and a frequency band of 30 500 hz are required to map formations below as well as those within the overburden even then only various clay sand interfaces can be mapped i e only over burden thickness and the likely depth range of lignite seams if they occur can be estimated direct mapping of lignite seams is not feasible in practice this is true of loop dipole as well as central induction sounding it is interesting that skin depth need not always be a factor limiting depth of exploration in electromagnetic prospecting

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

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

impact of basin burial and exhumation on jurassic carbonates diagenesis on both sides of a thick clay barrier paris basin ne france several diagenetic models have been proposed for middle and upper jurassic carbonates of the eastern paris basin the paragenetic sequences are compared in both aquifers to propose a diagenetic model for the middle and late jurassic deposits as a whole petrographic optical and cathodoluminescence microscopy structural fracture orientations and geochemical 18o 13c ree studies were conducted to characterize diagenetic cements with a focus on blocky calcite cements and their connection with fracturation events four generations of blocky calcite cal1 cal4 are identified cal1 and cal2 are widespread in the dominantly grain supported facies of the middle jurassic limestones about 90 of the cementation whereas they are limited in the oxfordian because grain supported facies are restricted to certain stratigraphic levels cal1 and cal2 blocky spars precipitated during burial in a reducing environment from mixed marine meteoric waters and or buffered meteoric waters the meteoric waters probably entered aquifers during the late cimmerian jurassic cretaceous boundary and late aptian early cretaceous unconformities the amount of cal2 cement is thought to be linked to the intensity of burial pressure dissolution which in turn was partly controlled by the clay content of the host rocks cal3 and cal4 are associated with telogenetic fracturing phases the succession of cal3 and cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water rock ratios these meteoric fluids circulated along pyrenean oligocene and alpine fractures and generated both dissolution and subsequent cementation in oxfordian vugs in mud supported facies and in poorly stylolitized grainstones however these cements filled only the residual porosity in middle jurassic limestones in addition to fluorine inputs fracturation also permitted inputs of sulphur possibly due to weathering of triassic or purbeckian evaporites or h2s input during paleogene times

facies architecture and high resolution sequence stratigraphy of an upper cretaceous platform margin succession southern central pyrenees spain abstract excellent exposures of upper cretaceous santonian carbonate platforms on the northern flank of sant corneli anticline southern central pyrenees provide detailed information of facies architecture in both depositional strike and dip directions basic accretional units are differentiated by facies contrast across mappable surfaces these surfaces do not show clear evidence of subaerial erosion and are correlated basinward with bedding planes across which there are subtle changes in skeletal composition two types of basic accretional units have been identified based on bedding patterns internal facies architecture and skeletal composition 1 rudist buildups consist of a rudist and coral belt at the platform margin passing landward into a slender hippuritid lithosome locally overlain by a bioclastic blanket that passes basinward into bioclastic apron like clinobeds and into fine grained packstone wackestone 2 calcarenite wedges consist of yellow brown benthic foraminifer rich grainstones to grain dominated packstones with scattered rudist shells and small coral colonies passing basinward into mud dominated packstones to wackestones with variable siliciclastic content quartz sand to silt and clay rudist buildups and calcarenite wedges alternate although not rhythmically these changes in platform skeletal composition reflect changes in the dominant type of carbonate producing biota independently of the changes in accommodation both types of basic accretional units rudist buildups and calcarenite wedges form simple sequences and parasequences according to internal lithofacies arrangement and inferred sea level cyclicity cycles or paracycles high frequency sea level cyclicity fits in the milankovitch frequency band long term changes in accommodation governing aggradation progradation and backstepping of basic sequences and parasequences reflect tectonic influence rather than long term changes in eustatic sea level

the response of two tethyan carbonate platforms to the early toarcian jurassic oceanic anoxic event environmental change and differential subsidence chemostratigraphic analyses 87 sr 86 sr d 13 ccarb of limestones from two jurassic platform carbonate sequences in italy trento and campania lucania platforms illustrate previously established trends found in pelagic sediments and skeletal carbonates from biostratigraphically well calibrated sections elsewhere in europe chemostratigraphic correlations between the platform carbonate successions and appropriate intervals from well dated reference sections allow the application of high resolution stratigraphy to these shallow water peritidal carbonates and furthermore elucidate the facies response to the early toarcian oceanic anoxic event oae lower jurassic toarcian levels of the western trento platform southern alps northern italy contain spiculitic cherts that appear where rising carbon isotope values characterize the onset of the oae a palaeoceanographic phenomenon interpreted as driven by increased nutrient levels in near surface waters there is a facies change to more clay rich facies at the level of the abrupt negative carbon isotope excursion also characteristic of the oae higher in the section the campania lucania platform southern apennines southern italy records a change to more clay rich facies where carbon isotope values begin to rise at the beginning of the oae but the negative excursion higher in the section occurs within oolitic facies although in both examples the early toarcian oae can be recognized by a change to more clay rich lithologies this facies development is diachronous and in neither case did the platform drown although the trento platform in the south west sector studied here was adversely affected by the oae it did not drown definitively until late aalenian time the campania lucania platform persisted throughout the jurassic and cretaceous differential subsidence rates which can be calculated using comparative chemostratigraphy are identified as a crucial factor in the divergent behaviour of these two carbonate platforms relatively fast in the case of the trento platform relatively slow in the case of the campania lucania platform it is proposed that where water depths remained as shallow as a few metres during the oae campania lucania platform dissolved oxygen levels remained high nutrient levels relatively low and conditions for carbonate secretion and precipitation remained relatively favourable whereas more poorly ventilated and or more nutrient rich waters trento platform adversely

climate change on tectonic time scales abstract observational and modeling studies relevant to climate change on tectonic time scales are reviewed probably the most significant climate result from this time scale involves inferences about nearly ice free conditions for some intervals of earth history some additional results suggest relatively rapid transitions between climate states modeling studies indicate that although tectonic changes significantly modify the atmosphere and ocean circulation in most cases such modifications do not appear to be sufficient to explain ice free climates increased atmospheric co2 levels 5 10 presentvalues may be needed to completely reconcile models and data although the co2 paradigm has received widespread attention in the last few years the results summarized herein indicate that co2 is only one of several important factors influencing climate i believe the time is appropriate for contemplating climate change on tectonic time scales in terms of a post co2 synthesis in which direct tectonic factors are approximately equal in importance to co2 fluctuations in the last few years modeling studies have progressed from a state of virtually no work on the topic to one where the models are in some respect ahead of the observations in the sense that data have not been compiled to test even some of the most basic model predictions in particular information is needed on past atmospheric co2 levels tropical sea surface temperatures seasonality of continental interiors and locations and production rates of deep waters initial steps are being taken to integrate observational and modeling activities on tectonic time scales and some of these shortcomings may be rectified over the next few years

geochemistry of cambro ordovician arbuckle limestone oklahoma implications for diagenetic δ18o alteration and secular δ13c and variation abstract isotopic analyses of 227 limestone samples from the cambro ordovician arbuckle group oklahoma document slow secular changes in the chemistry of the limestones from late cambrian to early ordovician the 18o values of the limestones increase from 10 to 7 pdb 13c values decrease from 0 to 2 pdb and 87 sr 86 sr ratios decrease from 0 7091 to 0 7088 the light 18o values suggest that all arbuckle limestones underwent diagenetic alteration probably caused by meteoric water recharged during the development of the overlying pre middle ordovician unconformity the gradual 18o increase from late cambrian to early ordovician reflects reduced 18o depletion with decreasing burial temperature during alteration although the presence of additional primary secular 18o variation cannot be ruled out the 13c and 87 sr 86 sr variations in accord with 13c and 87 sr 86 sr variations in the literature represent primary secular variations the variations indicate that the 13c value and 87 sr 86 sr ratio of early paleozoic surface seawater decreased from late cambrian to early ordovician the 13c variation during this time period seems to correlate with sea level variation specifically during sea level fall an increase in the rate of oxidation of organic matter caused 13c depletion of inorganic bicarbonate in seawater as a result early ordovician carbonates probably deposited during the regression stage of the latest precambrian to latest early ordovician cycle became 13c depleted relative to late cambrian carbonates the decrease of seawater 87 sr 86 sr ratio from late cambrian to early ordovician may have resulted from decreased riverine sr input caused by decreased rate of continental weathering

geologic evidence for recurrent moderate to large earthquakes near charleston south carolina multiple generations of earthquake induced sand blows in quaternary sediments and soils near charleston south carolina are evidence of recurrent moderate to large earthquakes in that area the large 1886 earthquake the only historic earthquake known to have produced sand blows at charleston probably caused the youngest observed blows older late quaternary sand blows in the charleston area indicate at least two prehistoric earthquakes with shaking severities comparable to the 1886 event

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

bimodal magmatism and associated sedimentary facies with particular reference to the correlation between orogeny and regression it is stressed that a thorough investigation of the subtle and still poorly understood relationships between orogeny magmatism and associated sediments is warranted certain types of sediments appear to be commonly linked to specific magmatic contexts this is especially true for the oceanic crust but it may be equally valid for bimodal continental magmatism with the development of granite grand scale regression with the formation of continental detrital deposits could represent the response to mantle upwelling and or plume activity

burial diagenesis and porosity evolution upper jurassic smackover arkansas and louisiana the jurassic upper smackover ooid lime grainstone of the central gulf coast has been a major hydrocarbon exploration target for nearly half a century study of the geologic and sedimentologic framework petrography two phase fluid inclusions and trace element and stable isotope chemistry indicates the following diagenetic history the upper smackover is a blanket ooid grainstone ranging in thickness from 300 to 400 ft 91 to 122 m and covering at least 4 000 sq mi 10 400 sq km in the northern part of the arkansas shelf a regional meteoric water system was established in the grainstone shortly after deposition and prior to significant burial this meteoric water system gave way to conditions which were increasingly more marine toward the south near the louisiana arkansas state line the fresh to marine hydrologic gradient is responsible for the strong precompaction regional diagenetic overprint that eventually controlled available diagenetic pathways for the unit during burial three diagenetic zones are present 1 a northern zone dominated by oomoldic porosity and preburial spar cementation 2 a sou hern zone characterized by compaction effects late subsurface cement primary porosity preservation and late secondary subsurface porosity generation and 3 a transitional zone having characteristics common to both the northern and southern zones during the shallow burial phase compaction became increasingly more important to the south in zones dominated by marine connate fluid whereas rock integrity and a secondary oomoldic porosity system had already been established in the northern zone as burial increased brine originating in the underlying louann salt reached the shelf grainstone and began to displace the original connate fluid the brine triggered the inversion to calcite of remaining grains and cement composed of unstable mineralogy when the louann brine had displaced the original connate fluid caso4 replacement as gypsum and anhydrite was common across all three diagenetic zones also precompaction fine cement associated with oomoldic porosity was recrystallized and reequilibrated with the concentrate brine localized replacement dolomitization may well have developed throughout the burial history of the sequence but was most commonly postcompactional postcompaction poikilitic calcite cement and baroque dolomite were precipitated from the louann brine under conditions of elevated temperature and pressure as subsidence continued organic material from the basinward equivalents of the upper smackover lime grainstone arrived on the shelf and catalyzed so4 reduction resulting in pyrite and galena replacement in the southern and transitional zones as hydrocarbon maturation continued in the fine grained equivalents of the upper smackover h2s and co2 by products of these processes began to increase in the brine of the southern and transitional zones ultimately causing regional dissolution of existing carbonate and significantly enhancing preserved porosity porosity in the northern zone was established early and preserved through moderate burial although porosity is well developed permeability has been largely destroyed by recrystallization dolomitization is a prerequisite for economic reservoir development in the northern zone porosity in the southern zone is solution enhanced preserved primary intergranular porosity compaction is the most important porosity destruction process compaction in the absence of an early diagenetic overprint is affected primarily by grain type and secondarily by size and sorting pellets and oncolites compact easily yet destroy porosity during burial ooids and rhodolites resist compaction during burial therefore are related to porosity preservation grain type distribution as well as size and sorting are controlled by depositional environment processes with the most favorable areas for porosity development concentrations of ooids and rhodolites associated with early salt related structural movement porosity distribution in the southern zone therefore can be outli ed with the aid of geophysical end page 597 techniques porosity in the transitional zone is early secondary or preserved primary intergranular or a combination porosity in this zone therefore is highly unpredictable and a strong potential exists for diagenetic traps unrelated to structure or original depositional environment documentation of significant deep subsurface secondary porosity possibly associated with hydrocarbon maturation opens the potential for hydrocarbon exploration in deeply buried carbonate dominated basins this would include carbonate rocks heretofore thought to be well below the depth of carbonate porosity maintenance because of lithostatic load

contrasting diagenesis of two carboniferous oolites from south wales a tale of climatic influence two oolites in the dinantian mississippian lower carboniferous of glamorgan sw britain were deposited in similar depositional environments but have contrasting diagenetic histories the brofiscin and gully oolites occur in the upper parts of shallowing upward sequences formed through strandplain progradation and sand shoal and barrier growth upon a southward dipping carbonate ramp the brofiscin oolite is characterized by a first generation cement of equant calcite spar preferentially located at grain contacts and forming non isopachous fringes around grains interpreted as meteoric vadose and phreatic in origin isopachous fibrous calcite fringes of marine origin are rather rare and occur only at a few horizons burial compaction was not important and porosity was occluded by poikilotopic calcite spar fitted grain grain contacts locally occur and could be the result of near surface vadose dissolution compaction syntaxial overgrowths on echinoderm debris are common pre compaction overgrowths are cloudy inclusion rich and probably of meteoric origin and post compaction overgrowths are inclusion free by contrast the gully oolite has little first generation cement however marine fibrous calcite is common in oolitic intraclasts as isopachous fringes of acicular calcite crystals closely associated with peloidal internal sediment and early equant drusy calcite spar occurs in the uppermost part of the gully beneath a prominent palaeokarst where pedogenic cements also occur the major feature of gully diagenesis is burial compaction resulting in extensive grain grain dissolution and microstylolitic grain contacts and post compaction poikilotopic spar occluded remaining porosity the brofiscin oolite is pervasively dolomitized up dip but the gully oolite for the most part only contains scattered pre compaction dolomite rhombs and late veins of baroque dolomite with less pervasive dolomitization the difference in diagenetic style of the two dinantian oolites is attributed to prevailing climate the paucity of early meteoric cements in the gully is a result of an arid climate and this is supported by the nature of the capping palaeokarst the abundant meteoric cements in the brofiscin reflect a more humid climate and effective meteoric recharge also resulted in up dip pervasive mixing zone dolomitization the style of early diagenesis in these two oolites exerted a major control on the later burial diagenesis in the brofiscin the early cements inhibited grain grain dissolution and pressure solution while these processes operated extensively in the gully oolite thus prevailing climate can influence a limestone s diagenetic history from near surface through into deep burial

storm dominated mixed carbonate siliciclastic shelf sequence displaying cycles of hummocky cross stratification late proterozoic wonoka formation south australia abstract the regressive late proterozoic wonoka formation of the adelaide geosyncline in south australia contains a thick mixed carbonate siliciclastic interval of middle to inner shelf origin the shelf was storm dominated and displays abundant hummocky cross stratification hcs of varying scales and other wave formed sedimentary structures some parts of this sequence are notably cyclic two kinds of cycles are described here the first average cycle 8 m thick consists of the alternation of silty and argillaccous limestone with fine grained hummocky cross stratified calcareous sandstone climatic cyclicity e g milankovitch cycles involving alternate wet and dry periods or minor sealevel fluctuations along a low gradient shoreline are considered the most likely cause of the observed sediment cyclicity carbonate deposition predominated during dry periods or high sealevel followed by influxes of sand from deltaic sources during wet periods or times of low sealevel the prevalence of hcs in the sandstones is most likely due to much slower rates of lithification in comparison to the limestones which give evidence of rapid lithification on the seafloor the second type of cycle average cycle 5 10 m thick is characterised by the cyclic appearence of red hummocky cross stratified glauconitic and phosphatic limestones within a sequence dominated by grey green stylonodular limestone tempestites the most likely origin of the red limestone involves contributions of volcanic ash fall material the resulting sediment did not undergo the rapid seafloor lithification of the associated grey green limestones and thus was involved in considerable storm wave reworking before deposition the micritic shelf carbonates of the wonoka formation are considered to represent direct inorganic precipitation into the middle shelf environment rather than reworking of detrital material from shallow carbonate banks

structural analysis of a previously unknown active fault that triggered the 2013 mw 5 8 awajishima earthquake southwest japan the m w 5 8 awajishima earthquake occurred on 13 april 2013 in southwest awaji island 25 km southwest of the epicenter of the 1996 m w 6 8 kobe earthquake southwest japan analyses of aerial photographs and 3d perspective images field investigations and structural analysis of fault rocks reveal that 1 a previously undocumented fault here called the yamada fault strikes northwest southeast and dips southwest at 86 along a topographic lineament at the geological boundary between mesozoic granitic rocks and the late pliocene quaternary osaka group composed of interbedded sandstone and mudstone 2 the main shear zone of the yamada fault consists of a fault core with a 10 cm wide zone of fault gouge generally 1 5 cm a fault breccia zone of 100 cm wide and a damage zone of 10 50 m wide composed of cataclastic rocks and fractures 3 foliations characterized by s c fabrics that have developed in the shear zone indicate a dominantly thrust fault sense consistent with that revealed by the focal mechanism and 4 coseismic surface ruptures occurred locally along the main trace of the yamada fault consisting of numerous short fissures ranging in length from centimeters to several meters and concentrated in a zone 5 m wide our findings show that the newly identified yamada fault is an active fault and that it is probably the fault on which the 2013 m w 5 8 awajishima earthquake occurred therefore it is necessary to construct a fault model to better understand the deformation characteristics of the seismogenic source fault and for reassessing the seismic hazards on the densely populated awaji island of southwest japan

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

history of carbonate ion concentration over the last 100 million years abstract instead of having been more or less constant as once assumed it is now apparent that the major ion chemistry of the oceans has varied substantially over time for instance independent lines of evidence suggest that calcium concentration ca2 has approximately halved and magnesium concentration mg2 approximately doubled over the last 100 million years on the other hand the calcite compensation depth and hence the caco3 saturation has varied little over the last 100 my as documented in deep sea sediments we combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration co32 over this period of time from the calcite saturation state which is proportional to the product of ca2 times co32 but also affected by mg2 we can calculate seawater co32 our results show that co32 has nearly quadrupled since the cretaceous furthermore by combining our co32 proxy with other carbonate system proxies we provide calculations of the entire seawater carbonate system and atmospheric co2 based on this reconstructed atmospheric co2 is relatively low in the miocene but high in the eocene finally we make a strong case that seawater ph has increased over the last 100 my

evolution of the mg ca ratio of cretaceous seawater implications from the composition of biological low mg calcite abstract for the evaluation of variations in the cretaceous seawater mg ca ratio 12 shells of rudist bivalves ranging in age from the late barremian 112 2 ma to the early campanian 81 4 ma have been analysed for intra shell variations in chemical mg sr fe mn and isotopic 18 o 13 c compositions of low mg calcite preservation of fibrous prismatic ultrastructure low fe and mn concentrations as well as sr concentrations within the range of marine biological calcite indicate only very minor diagenetic alteration in all studied shells mg concentrations and 18 o values show a more or less well defined inverse covariance this pattern is similar to the conditions observed in modern skeletal calcite and interpreted to result from a combination of a temperature effect and an unidentified metabolic control on the incorporation of mg into calcite average mg concentrations in rudist calcite are significantly lower than those of modern bivalves and increase from the barremian albian to the campanian while slopes of 18 o mg regressions are similar to those of modern bivalves assuming that the mg incorporation is linearly dependent on the mg ca ratio of seawater and that mg incorporation into calcite of modern bivalve mollusks follows the same metabolic pathway than in their extinct cretaceous relatives the mg ca molar ratio of cretaceous seawater increased from 1 in the late barremian to 3 in the early campanian this trend matches previous model predictions of seawater composition and experimental results from fluid inclusions in halite a very low mg ca ratio of seawater is confirmed here to have occurred before the onset of the significant mid cretaceous increase of seafloor production rates in the late barremian uncertainties in the secular variations of seafloor spreading are discussed as hydrothermal alteration of young oceanic crust is an important driver of changes in the seawater mg ca ratio

origin of shallow burial cements in the late visean of the campine basin belgium abstract the diagenesis of late visean buildup and shelf carbonates from three boreholes in the campine basin northern belgium has been studied to determine the early diagenetic pore fluid evolution in the basin the earliest cementation occurred by isopachous fibrous and radiaxial fibrous calcites which precipitated in a marine environment under oxidizing conditions neomorphism during subsequent diagenesis altered these cements extensively precipitation of these first stage cements was followed by an episode of dissolution of carbonate components gastropods pelecypods and echinoderms after this episode non bright and dull luminescent stages successively developed in the shelf carbonates in response to the pore waters becoming progressively more anaerobic fluid inclusions and oxygen stable isotopes in the dull luminescent stage indicate that this cement formed in a meteoric fluid at relatively low temperatures 30 c and thus under burial conditions of a few hundred metres buildup carbonates from the shelf margin show a similar diagenetic evolution but dull luminescent cements appear to have precipitated at higher temperatures 45 c than in the shelf carbonates the meteoric waters responsible for the cementation are interpreted to have been sourced from near the brabant massif where dissolution of visean limestones could have taken place when the limestones to the north were already buried underneath namurian strata lateral gravity driven groundwater flow may be a very important type of fluid flow causing the cementation of shelf carbonates fracturing of the late visean strata started before the precipitation of the meteoric cements but was most intense just before and during the precipitation of the dull luminescent calcites this fracturing probably took place during the sudetic phase at the end of the visean and early namurian times

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

repeated large subduction zone earthquakes in the nankai suruga trough evidence from submarine liquefactions 1 subduction zones are generally characterized by large earthquakes that contribute about 90 of the total seismic moment worldwide and can cause great damage from tsunamis such as the 2004 sumatra mw 9 0 earthquake here we report recurrent large subduction zone earthquakes revealed by extensive submarine liquefactions formed in the nankai suruga trough where the philippine sea plate is subducting beneath the eurasian plate field evidence and grain size analysis of liquefied deposits show that the multiple liquefactions were repeatedly induced by strong earthquake shaking during the pleistocene in the eastern nankai suruga subduction zone the recognition and analysis of submarine liquefactions provide reliable paleoseismic evidence in the nankai suruga subduction zone

palaeoatmospheres in the phanerozoic except in the recent geological past palaeoatmospheric composition cannot be measured but only inferred from palaeontological or geochemical observations the likely controls on atmospheric composition are reviewed and the role of organisms stressed as monitors recorders motors and moderators of palaeoatmospheric changes whereas there is a good general case for changes in po 2 and pco 2 during phanerozoic time proposals for timing and mechanism in the earlier phanerozoic are speculative at present it seems probable that the late palaeozoic spread of land plants raised o 2 and reduced co 2 levels in the atmosphere the end cretaceous crisis had a transient impact on the atmosphere whose general constancy through geological time is one of the most remarkable features of earth history

long term earthquake clustering a 50 000 year paleoseismic record in the dead sea graben the temporal distribution of earthquakes in the dead sea graben is studied through a 50 000 year paleoseismic record recovered in laminated sediments of the late pleistocene lake lisan paleo dead sea the lisan represents more than 10 times the 4000 years of historical earthquake records it is the longest and most complete paleoseismic record along the dead sea transform and possibly the longest continuous record on earth it includes unique exposures of seismite beds earthquake induced structures associated with slip events on syndepositional faults the seismites are layers consisting of mixtures of fragmented and pulverized laminae the places where the seismites abut syndepositional faults are interpreted as evidence for their formation at the sediment water interface during slip events on these faults thicker sediment accumulation above the seismites in the downthrown blocks indicates that a seismite formed at the water sediment interface on both sides of the fault scarps modern analogs and the association with surface ruptures suggest that each seismite formed during a m l 5 5 earthquake the 230 th 234 u ages of a columnar section obtained by thermal ionization mass spectrometry give a mean recurrence time of 1600 years of m l 5 5 earthquakes in the dead sea graben the earthquakes cluster in 10 000 year periods separated by quiet periods of similar length this distribution implies that a long term behavior of the dead sea transform should be represented by a mean recurrence of at least 20 000 year record this observation has ramifications for seismic hazard assessment based on shorter records

grounded source transient e field modeling of a shallow resistive layer with 3 d inhomogeneity there is growing interest in the use of transient electromagnetic tem sounding for shallow geotechnical environmental and groundwater investigations two commonly used transmitterreceiver configurations for tem sounding are 1 loop loop or its variation in loop configuration and 2 wire loop configuration the less common configuration of a horizontal electric dipole hed transmitter and receiver is treated in this study and called wire wire configuration

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

botryoidal aragonite and its diagenesis botryoidal aragonite is a spectacular growth form occurring as mamelons up to 100 mm in diameter three examples of this particular carbonate cement have been discovered in two distinct areas in new caledonia small scale mamelons have been recognized within pleistocene reefal terraces at ouvea an island of the loyalty archipelago and in the red sea large scale mamelons of botryoidal aragonite exist within pleistocene reefal terraces along the um gheig region of the egyptian coast in addition a similar botryoidal cement partly dolomitized but exhibiting aragonite relics occurs within a miocene reef in the same region mamelons of botryoidal aragonite are isolated and or coalescent but grow only on fixed substrates they occur within cavities of varied origin their fabrics are characterized by fans of elongate euhedral crystals of aragonite fibres botryoidal aragonite can be preceded or followed by other types of cements or internal sediment despite similar mineralogy petrography and ultrastructure there are differences between the fabrics of the pleistocene botryoids from the red sea and ouvea and the miocene botryoids from the red sea the former are of submarine origin as confirmed by the strontium content 8500 10 500 ppm and isotopic composition 18o between 0 10 and 0 19 pdb the latter related to a miocene karst are rich in strontium average 13 600 ppm and have an isotopic composition average 18o 10 50 pdb indicative of non marine precipitation diagenesis of these botryoidal aragonites consists of slight dissolution for pleistocene botryoids and mineralogical transformation for the miocene botryoids the latter exhibit the diagenetic sequence aragonite calcite dolomite the aragonite to calcite transformation is a dissolution reprecipitation process the void distribution and size influencing the distribution and the size of the replacement calcite crystals

facies architecture and diagenesis of belgian late frasnian carbonate mounds abstract late frasnian petit mont member carbonate mounds occur in the southern part of the dinant synclinorium and in the philippeville anticline sw belgium these mounds are 30 to 80 m thick and 100 to 250 m in diameter they are embedded in shale nodular shale and argillaceous limestone based on facies mapping of 14 buildups and related off mound sediments these mounds typically started from below the photic and storm wave base zones and builtup into shallow water environments above an argillaceous limestone substrate the first carbonate mound facies consists of spiculitic wackestone with stromatactis pm1 which becomes progressively enriched in crinoids and corals pm2 then in peloids stromatoporoids and cyanobacteria pm3 pm4 consists of algal coral peloid wackestone and packstone with green algae and thick algal coatings a core of algal and microbial bindstone pm5 sporadically occurs within large mounds the uppermost part of these mounds may show a recurrence of facies pm2 and pm1 pm1 to pm3 are coloured red by hematite derived from microaerophilic iron bacteria pm4 and pm5 are grey the transition from the aphotic to the cyanobacterial photic zone is recorded in the succession pm2 pm3 the transition from the cyanobacterial to the green algal photic zone is recorded by pm3 pm5 storm wave base was reached within pm3 and fair weather wave base within pm5 this paleobathymetric interpretation suggests a depth of 100 150 m during initial establishment of pm1 three types of mounds can be distinguished on the basis of geometry and facies architecture 1 les bulants type mounds display a continuous vertical facies succession pm2 3 4 5 and low relief 2 although exhibiting the same facies succession as les bulants les wayons type mounds show a distinct relief with steep flanks and bioclastic talus 3 st remy mounds consist exclusively of pm1 and pm2 bioclastic flank deposits are not observed from 1 to 3 these mound types represent successive deepening down a ramp biostratigraphic correlation on a regional scale provides good evidence that relative sea level changes largely controlled lateral and vertical transitions of facies beyond that hypoxic conditions are indicated by the sponge and iron bacteria consortium in lower parts of the mounds this is in agreement with the general assumption of stratified water masses during late frasnian preceding the prominent lower kellwasser crisis cementation began with a radiaxial synsedimentary cement a fringe of meteoric phreatic cement initially nonluminescent then with a bright orange luminescence occurs in all mounds it is contemporaneous with a nonluminescent pervasive cement of grainstones deposited in littoral areas differentiation between the reducing mounds and the oxidizing littoral area resulted from better aquifer circulation in sedimentary bodies close to the recharge area late burial cements occlude all the remaining porosity and are contemporaneous with the opening of the variscan fracture system

diagenesis and compositional partitioning of quaternary cool water carbonate aeolianites southeastern australia abstract middle to late pleistocene stranded carbonate sea beaches adjacent aeolian dunes and pleistocene aeolianites together with holocene marginal marine calcareous sediments across southeastern australia contain the longest record of such deposition in the modern world stretching back to at least 900 ky mis 23 the grains are were derived from a suite of cool water heterozoan carbonate sediments produced on the adjacent offshore shelf most modern shelf carbonate sediments in the region today are aragonite rich but the aragonite is presently slowly being dissolved on or just below the seafloor before the deposits enter the rock record beach dune sediments are derived mainly from the shallow 30 meters deep adjacent seafloor they are mollusk rich but with most bryozoan particles having been destroyed in the surf zone the mollusks are dominantly aragonite these nearshore sediments are swept onshore before any significant seafloor diagenesis can take place and so are compositionally different from the eventual aragonite poor open shelf sediments aragonite skeletal fragments in the dunes progressively dissolve with time under a semi arid climate and produce diagenetic low magnesium calcite meteoric cements a well known process common in tropical aragonitic pleistocene aeolianites the loss of metastable minerals with time is matched by a progressive and well understood change in stable isotopes such alteration in this environment however seems to take longer than in tropical carbonates with lithification herein not beginning until 200 ka and complete cementation being achieved in 450 ky thus neither aeolianites nor offshore marine carbonates record the composition of the original sediment aeolianites lack the important bryozoan constituents whereas neritic deposits lack the prolific mollusks this partitioning revealed for the first time answers the conundrum as to why some cool water neritic shelf and coastal sediments in the rock record are compositionally different

tectonic controls of phanerozoic sedimentary rock cycling the cyclic nature of the phanerozoic sedimentary rock distribution carbon sulphur coupling and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors the distribution of preserved sedimentary mass in terms of rock mass remaining u geologic age shows a minimum c 300 350 ma ago which separates two subcycles of erosion and deposition of sedimentary rocks the older subcycle was interrupted because of the major continental collisions of the devonian and late carboniferous these collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses leading to a decline in the probability of destruction and an increase in half life of these older sediments a strong correlation exists between the long term cyclicity in the phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs this correlation is related to two principal tectonic modes of the phanerozoic oscillatory and submergent it is postulated that the submergent mode of active plate convergence obduction and subduction of sediments large ridge volume and high sea level gave rise to low erosion and sedimentation rates less restricted environments of carbonate deposition and relatively high atmospheric co 2 levels high temperatures resulting from an increased rate of production of co 2 from diagenetic and metamorphic reactions at subduction zones as sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir as sea level fell reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors these reservoir transfers are consistent with secular changes observed in the distribution of 13 c and 34 s in sedimentary materials during the phanerozoic petrographic examination of phanerozoic oolite formations shows that ooids with preserved calcitic relict textures are characteristic of pre carboniferous carbonate rocks whereas ooids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age these changes in ooid mineralogy may be interpreted as reflecting changes in co 2 levels of the ocean atmosphere system consistent with the above tectonic considerations atmospheric co 2 levels were higher prior to carboniferous time favouring formation of calcitic ooids and skeletal parts after the carboniferous co 2 levels fell and aragonite and mg calcites of greater than 8 mol mg increased in abundance as precipitates

co seismic displacements folding and shortening structures along the chelungpu surface rupture zone occurred during the 1999 chi chi taiwan earthquake abstract a nearly 100 km long surface rupture zone called chelungpu surface rupture zone occurred mostly along the pre existing chelungpu fault on the northwestern side of taiwan accompanying the 1999 chi chi ms 7 6 earthquake the chelungpu surface rupture zone can be divided into four segments based on the characteristics of co seismic displacements geometry of the surface ruptures and geological structures these segments generally show a right step en echelon form and strike ne sw to n s and dip to the east with angles ranging from 50 to 85 the co seismic flexural slip folding structures commonly occurred in or near the surface rupture zone from a few meters to a few hundreds of meters in width which have an orientation in fold axes parallel or oblique to the surface rupture zone the displacements measured in the southern three segments are approximately 1 0 3 0 m horizontally and 2 0 4 0 m vertically the largest displacements were measured in the northern segment 11 1 m horizontally and 7 5 m vertically respectively the amount of co seismic horizontal shortening caused by flexural slip folding and reverse faulting in the surface rupture zone is generally less than 3 m it is evident that the co seismic displacements of the surface rupture zone are a quantitative surface indicator of the faulting process in the earthquake source fault the relations between the geometry and geomorphology of the surface rupture zone dips of the co seismic faulting planes and the striations on the main fault planes generated during the co seismic displacement show that the chelungpu surface rupture zone is a reverse fault zone with a large left lateral component

aragonitic algae in calcite seas effect of seawater mg ca ratio on algal sediment production abstract secular variation in seawater mg ca would have subjected the aragonite producing codiacean algae to two intervals of low mg calcite seas mmg ca mmg ca 2 seas since their origin in the ordovician it is asserted that the aragonite high mg calcite affinity of modern and recent tropical seas mmg ca 2 has enabled the aragonitic codiaceae to act as major carbonate sediment producers in these seas to test this assertion specimens of the sediment producing codiacean alga udotea flabellum were grown in artificial seawaters formulated at mmg ca ratios 1 0 2 5 5 2 that have occurred in the oceans throughout the geologic history of the codiaceae while the u flabellum algae produced exclusively aragonite in both the artificial boundary seawater mmg ca 2 5 and the artificial aragonite high mg calcite seawater modern seawater mmg ca 5 2 the algae produced a portion 25 3 of their caco3 as low mg calcite 4 mol mgco3 in the artificial calcite seawater mmg ca 1 0 suggesting that their caco3 polymorph control can be partially overridden by ambient seawater chemistry primary productivity calcification and linear growth of the algae decreased with reductions in ambient mg ca despite increases in absolute ca concentration of the seawater reduced calcification in the lower mg ca seawaters is probably due to kinetic difficulties of producing aragonite from seawater that favors the nucleation of calcite the decreased linear growth and primary production are likely associated with reductions in the ambient co2 available for photosynthesis resulting from the reduced calcification these findings support the assertion that the dominant ecological and sedimentological roles of codiacean algae in recent tropical seas is facilitated by a seawater mg ca ratio that favors the nucleation of aragonite over calcite furthermore producing aragonite in seawater that favors the nucleation of low mg calcite mmg ca

increased production of calcite and slower growth for the major sediment producing alga halimeda as the mg ca ratio of seawater is lowered to a calcite sea level abstract laboratory experiments were conducted to subject the calcareous alga halimeda a prolific producer of aragonite in the modern ocean to a variety of ambient mg ca ratios these experiments were based on three predictions 1 that halimeda would calcify at a lower rate when the ambient mg ca ratio was reduced from its high level in modern seawater 5 2 2 that this alga would grow more slowly under these conditions because its calcification yields as a byproduct co2 which is available for photosynthesis and 3 that the calcite content of halimeda s skeleton would increase as a percentage of total caco3 as predicted reduction of the mg ca ratio of ambient artificial seawater from its modern level to estimated early oligocene and early eocene levels 2 5 and 1 5 respectively resulted in progressively lower rates of calcification production of organic matter and linear growth for halimeda incrassata colonies the ambient mg ca ratio exerted a stronger influence over the rate of calcification than ca2 which in the geologic past has risen in seawater whenever the ambient mg ca ratio has declined thus although elevation of ca2 at such times would have promoted the calcification and growth of halimeda the concomitant decline of the mg ca ratio would have had a stronger negative effect in addition the percentage of skeletal material consisting of calcite rose from 8 in modern day seawater to 16 in artificial early oligocene seawater and 46 in artificial early eocene seawater magnesium was incorporated into this calcite as a function of the ambient mg ca ratio with a fractionation pattern differing only slightly from that of nonskeletal calcite halimeda exerts less biological control over its biomineralization than the related genera penicillus and udotea which in previous experiments produced only 22 25 of skeletal caco3 as calcite in seawater having a very low mg ca ratio 1 0 nonetheless it is likely that many taxa of green algae that produce little or no calcite today would have produced a substantial proportion of skeletal low mg caco3 as calcite in ancient seas such as those of the cretaceous whose mg ca ratios were close to unity

ooids in purbeck limestones lowermost cretaceous of the swiss and french jura ooids occurring in the shallow water purbeckian carbonate sediments of the jura mountains can be grouped into six types gradations from one type to another and coexistence of the various types are common type 1 ooids are small and well rounded they display fine concentric micritic laminae in many cases their cortices are dissolved and replaced by void filling spar microsparitic neomorphic replacement occurs locally type 2 ooids are large and have irregular shapes they show fine micritic laminae and occasional layers of fine radial crystals they commonly evolve into oncoids ooids of type 3 display many fine radial cortical laminae and are patchily micritized they are medium in size and mostly well rounded this type of ooid may pass into large irregularly shaped coated grains type 4 ooids have 1 to 4 cortical laminae with a fine radial structure and patchy micritization they are medium in size and well rounded type 5 ooids have only one lamina with a coarse radial structure they are small and well rounded associated are spherical grains containing bundles of elongate crystals ooids of type 6 show superpositions of two or more different radial and or fine micritic laminae the cortical structure may also change laterally in the same lamina the preferential dissolution of type 1 ooid cortices to form oomoulds indicates a primary composition of unstable carbonate sedimentological features and comparison with modern ooid occurrences point to formation on high energy sandbars in normal marine waters type 2 ooids grew in marine lagoonal environments with quiet water and abundant cyanobacteria the radially structured ooid cortices of types 3 4 and 5 show no dissolution features this implies that they were originally composed of stable carbonates or that an unstable carbonate phase was transformed into a stable one at an early stage of diagenesis type 3 ooids occur together with marine faunas and indicate high water energy ooids of type 4 and type 5 originated probably from relatively quiet water of variable salinity coexistence of different ooid types and mixed forms of type 6 implies gradual or rapid changes in hydrodynamic geochemical and microbiological conditions which were a feature of the purbeckian depositional environments

experimental calibration of mg isotope fractionation between dolomite and aqueous solution and its geological implications abstract hydrothermal experiments at 220 160 and 130 c were performed to calibrate the mg isotope fractionation factor between dolomite and aqueous mg hydrothermal experiments included synthesis of dolomite using different starting materials as well as exchange experiments that used poorly ordered proto dolomite the morphology of synthesized dolomite was dependent on starting mineralogy suggesting that dolomite was synthesized by different pathways hydrothermally synthesized dolomite was initially fine grained disordered or poorly ordered dolomite that with time recrystallized to coarser grained ordered dolomite isotopic exchange was monitored using 87 sr 86 sr ratios and 25 mg tracers and these indicated near complete isotope exchange between dolomite and aqueous solutions at the end of most hydrothermal experiments the mg isotope fractionation factor between dolomite and aqueous solution obtained from synthesis and exchange experiments converged with time and was independent of dolomite morphology suggesting attainment of isotopic equilibrium combining results from synthesis and exchange experiments the temperature dependent mg isotope fractionation factor for ordered dolomite is 26 mg dolo aq 0 1554 0 0096 10 6 t 2 where t is in kelvin in contrast poorly ordered dolomite has a 26 mg dolo aq fractionation factor that is up to 0 25 lower than that of ordered dolomite and this is attributed to longer mg o bonds in imperfectly ordered dolomite the experimentally calibrated 26 mg dolo aq fractionation factors lie between those calculated by schauble 2011 and rustad et al 2010 the 26 mg dolo aq fractionation factor extrapolated to lower temperatures using the 26 mg t function of this study matches the 26 mg dolo aq fractionation factor obtained by modeling of mg isotope compositions of odp drill core samples this study shows that significant mg isotope fractionation occurs during dolomite precipitation these results collectively demonstrate that mg isotopes in dolomite are a useful tool for studying mg global cycling and dolomitization

transient electromagnetic modeling of shallow a type sections with 3 d inhomogeneities a hard rock area underlain by granitic gneissic or basaltic rocks often has an a type three layer geoelectric section in which resistivity increases with depth the middle layer of moderate resistivity caused by fracturing fissuring that lies between the surface weathered layer and the substratum of unfractured rock is not a good target for a direct current dc resistivity sounding since it is generally suppressed in the observations moreover its definition requires expanding the electrode spacing to a length several times the depth of the target layer and this may be a drawback if the target layer is either laterally variable or limited in its horizontal extent we first studied the transient electric field of a horizontal electric dipole hed source excited by a step turn off current for a 1 d model of an a type geoelectric section the results of this theoretical study are presented as graphs of normalized apparent resistivity versus a time related dimensionless parameter irrespective of the sepa

calcitic aragonitic and mixed calcitic aragonitic ooids from the mid proterozoic belt supergroup montana a great variety of ooid types occurs within the siyeh and snowslip formations of the mid proterozoic belt supergroup montana cortical layers are inferred to have been composed either of calcite in a radial concentric or radial with dark rays fabric or aragonite in a radial or concentric fabric the calcitic cortical layers record their original fabrics but the originally aragonitic cortical layers have been replaced by calcite in a range of textures and by quartz and dolomite some formerly aragonitic cortical layers are replaced by calcite spar which contains relics of the original cortical structure others consist of calcite spar without inclusions or columnar calcite which grew radially from the nucleus commonly a calcitic ooid some ooids were wholly composed of calcite others were of aragonite but two phase ooids were common mostly consisting of an inner calcitic part and an outer aragonitic part probable microdolomite inclusions suggest a high mg content of the calcitic cortical layers the depositional environment of these oolites was probably analogous to baffin bay texas where a similar range of ooid types is forming today

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

active ooid growth driven by sediment transport in a high energy shoal little ambergris cay turks and caicos islands ooids are a common component of carbonate successions of all ages and present significant potential as paleoenvironmental proxies if the mechanisms that control their formation and growth can be understood quantitatively there are a number of hypotheses about the controls on ooid growth each offering different ideas on where and how ooids accrete and what role if any sediment transport and abrasion might play these hypotheses have not been well tested in the field largely due to the inherent challenges of tracking individual grains over long timescales this study presents a detailed field test of ooid growth hypotheses on little ambergris cay in the turks and caicos islands british overseas territories this field site is characterized by westward net sediment transport from waves driven by persistent easterly trade winds this configuration makes it possible to track changes in ooid properties along their transport path as a proxy for changes in time ooid size shape and radiocarbon age were compared along this path to determine in which environments ooids are growing or abrading ooid surface textures petrographic fabrics stable isotope compositions 13 c 18 o and 34 s lipid geochemistry and genetic data were compared to characterize mechanisms of precipitation and degradation and to determine the relative contributions of abiotic e g abiotic precipitation physical abrasion and biologically influenced processes e g biologically mediated precipitation fabric destruction through microbial microboring and micritization to grain size and character a convergence of evidence shows that active ooid growth occurs along the transport path in a high energy shoal environment characterized by frequent suspended load transport median ooid size increases by more than 100 m and bulk radiocarbon ages decrease by 360 yr westward along the 20 km length of the shoal crest lipid and 16s rrna data highlight a spatial disconnect between the environments with the most extensive biofilm colonization and environments with active ooid growth stable isotope compositions are indistinguishable among samples and are consistent with abiotic precipitation of aragonite from seawater westward increases in ooid sphericity and the abundance of well polished ooids illustrate that ooids experience subequal amounts of growth and abrasion in favor of net growth as they are transported along the shoal crest overall these results demonstrate that in the ambergris system the mechanism of ooid growth is dominantly abiotic and the loci of ooid growth is determined by both carbonate saturation and sediment transport mode microbes play a largely destructive rather than constructive role in ooid size and fabric