run out of cut slope landslides mesh free simulations this study uses an incompressible smoothed particle hydrodynamics isph model to investigate the run out and deposit morphology of granular materials flowing down cut slopes the primary aim is to study the influence of various factors on the run out and to summarise a quantitative relationship for direct use in landslide hazard management in the model the granular materials are modelled as a rigid perfectly plastic material with a coulomb yield surface the coupled continuity equation and momentum equation are solved by a semi implicit algorithm the model is first validated and its results are carefully compared with various controlled experiments regarding granular flows the model reproduces the flows and correctly predicts the deposition profiles under various conditions then the computational results are used to study the run out and mobility of landslides for granular columns collapsing onto a flat surface a normalised run out and a new scaling relationship are proposed which are supported

fluid inclusion and stable isotope c o and s constraints on the genesis of the high grade langdu cu skarn deposit in yunnan sw china abstract the langdu cu skarn deposit is the highest grade cu deposit average 6 49 cu in the zhongdian polymetallic district in sw china skarns and ore bodies occur primarily in the contact zone of upper triassic qugasi formation fm and late triassic ca 217 ma intrusions disseminated massive stockwork and vein like sulfide ores occur in the skarn quartz calcite veins porphyry and marble skarn minerals include pyroxene garnet actinolite and epidote four types six subtypes of fluid inclusions fis are identified in the sulfide bearing quartz veins type i liquid rich two phase fis have varying vapor liquid ratios and yielded homogenization temperatures of 110 338 c and salinities of 1 7 29 5 wt nacl eqv type ii vapor rich fis contain ch4 n2 bubbles and homogenized to vapor at 262 425 c type iii fis are single phase at room temperature 20 c a vapor phase is present at below 120 c and the fis homogenized at 117 to 114 c type iv daughter mineral bearing fis homogenized by halite disappearance at 295 392 c and have salinities of 37 8 46 6 wt nacl eqv such characteristics suggest that fis were trapped by fluid immiscibility and phase separation the 34scdt values of chalcopyrite and pyrrhotite are of 5 3 to 0 7 on the 34s histogram all langdu data show a cluster of 32s rich 34scdt 5 3 to 4 6 and a cluster of 34s rich 34scdt 1 1 to 0 7 type i calcite in skarn and type ii calcite in quartz sulfide vein have 13cpdb and 18osmow values of 8 4 to 7 8 6 3 to 6 1 and 10 1 to 12 3 and 12 0 to 13 0 respectively type iii calcite from calcite sulfide veins has 13cpdb 5 6 to 0 2 and 18osmow 12 5 to 16 3 biotite garnet and pyroxene syn ore quartz and chlorite yielded 18osmow values of 6 9 4 1 5 13 2 15 3 and 6 8 respectively sulfur carbon and oxygen isotopic features of these hydrothermal minerals and the fis microthermometric data suggest that the ore forming fluids were magmatic sourced and contaminated by meteoric formation water during ascent and or fluid wallrock interactions low 34s 5 3 to 4 6 in sulfides and the ch4 in the fis are interpreted to reflect the reaction between the magmatic fluids and the carbonaceous slate in qugasi fm the methane likely expanded the vapor liquid immiscibility field and reduced the sulfates so42 to sulfides s2 and extensive water rock reaction and fluid mixing may have occurred leading to the high grade cu mineralization at langdu

jurassic and cretaceous paleomagnetic data from the southern alps italy jurassic and cretaceous paleomagnetic data from 46 sites in the venetian alps trento plateau and se lombardian basin have been compiled nine of these site mean directions have been previously published the sites can be divided into four age groups senonian hauterivian barremian kimmeridgian tithonian and callovian oxfordian for three of the age groups positive regional fold tests indicate at the 99 confidence level that the characteristic magnetization components predate the deformation structural mapping in the venetian alps allowed us to assign sites to individual thrust sheets and we observe no significant relative rotation of thrust sheets in the nappe pile indeed we observe remarkable consistency in mean direction throughout the entire sampling area for each of the four age groups the senonian and hauterivian barremian pole positions lie close to coeval poles on african apparent polar wander paths apwps this result is consistent with previous analyses of middle and late cretaceous data from the venetian alps the new jurassic poles deviate significantly from recently published african apwps reflecting either the poor definition of the african apwp in the late jurassic or about 20 anticlockwise rotation of the southern alps relative to africa during early cretaceous time the former of the two possibilities is favored by a new late jurassic early cretaceous pole from north america and by early permian paleomagnetic data from the southern alps which are consistent with coeval african data implying that the movement of the southern alps was similar to that of africa since early permian

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

the savage hutter avalanche model how far can it be pushed the savage hutter sh avalanche model is a depth averaged dynamical model of a fluid like continuum implementing the following simplifying assumptions i density preserving ii shallowness of the avalanche piles and small topographic curvatures iii coulomb type sliding with bed friction angle delta and iv mohr coulomb behaviour in the interior with internal angle of friction phi or delta and an ad hoc assumption reducing the number of mohr s circles in three dimensional stress states to one we scrutinize the available literature on information regarding these assumptions and thus delineate the ranges of validity of the proposed model equations the discussion is limited to relatively large snow avalanches with negligible powder snow component and laboratory sand avalanches starting on steep slopes the conclusion of the analysis is that the sh model is a valid model for sand avalanches but its mohr coulomb sliding law may have to be complemented for snow avalanches by a second velocity dependent contribution for very small snow avalanches and for laboratory avalanches starting on moderately steep and bumpy slopes it may not be adequate

analysis of run up of granular avalanches against steep adverse slopes and protective barriers the purpose of this study was to determine whether run up of rapid landslides or avalanches against protective dykes or walls placed perpendicular to the path can be predicted using a dynamic model based on shallow flow assumptions a series of laboratory experiments were carried out involving rapid flow of dry sand in a flume arrested by a steep adverse slope the barrier slope was varied and included a perpendicular wall a curved transition of varying radius separated the path from the barrier the dynamic internal and basal friction angles of the sand were determined by independent testing the results were analysed using a savage hutter type model a shock wave was observed as the flow approached the barrier toe and the model had to be improved by an original velocity smoothing algorithm to prevent numerical instability the new model is capable of simulating the entire process of run up of the leading edge against the barrier face deposition of the sand behind the barrier and backward migration o

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

paleomagnetism and paleogeography of jurassic radiolarian cherts from the northern apennines of italy oriented samples of jurassic radiolarian chert were collected from the tuscan domain continental margin and the ligurid domain oceanic of the northern apennines for paleomagnetic study to determine the paleogeographic origins of these rocks the oceanic rocks are all thermochemically overprinted by a mostly reversed polarity component of magnetization b that was likely acquired during late miocene regional uplift of the northern apennines this component also dominates the lower brittle chert of the tuscan cherts but disappears upsection in the more clay rich and ductile siliceous marlstones in addition the tuscan cherts retain an inferred primary magnetization c isolated at temperatures between 560 and 660 c which passes a fold test and shows a polarity stratigraphy this component indicates a paleolatitude of 11 4 n and a counterclockwise vertical axis rotation of 29 9 with respect to the southern alps of italy of 49 8 with respect to africa and of 91 8 with respect to eurasia our results suggest that the tuscan domain was farther south than other deep water continental margin sections of adria and that transcurrent faulting might have played a significant role in the orogenic evolution of the northern apennines

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

meteoric versus burial control on porosity evolution of the smackover formation whole rock 13c 18o and sr compositions of the uppermost ooid grainstones of the smackover formation at black creek field in mississippi reveal characteristics of a meteoric system in this area the trend in 13c signatures indicates that meteoric water acquired its low carbon values at a soil zone and was buffered completely with the host rock before entering the meteoric lens identical 18o data suggest that allochems stabilized at the same temperatures in waters of similar 18o compositions during early meteoric diagenesis that is calcitization continued to completion before the onset of burial sr concentrations reveal differential transformation mechanisms low sr values in the phreatic zones are attributed to slow stabilization by exchange with the bulk solution high sr compositions in the vadose zone resulted from rapid incremental transformation meteoric cementation was sparse therefore grainstones entered the burial realm with all of their porosity intact modification of porosity was a burial process and was directly related to the intensity of chemical compaction which itself was controlled by three factors 1 the degree of early cementation 2 grain type and 3 grain size early cemented intervals experienced low to moderate compaction regardless of grain size or grain type in the absence of early cementation grain type and grain size were the dominant factors of porosity control coarse grained intervals that were composed of micritic grains experienced less compaction than fine grained oolitic intervals average volumetric percentages of cements as determined by point counting of 63 samples are as follows 1 marine and meteoric cements 1 5 2 prebitumen calcite 6 5 3 saddle dolomite 1 4 postbitumen calcite 4 3 5 pyrobitumen 1 total cement sum of 1 5 total burial cement sum of 2 5 and total burial carbonate cement volumes sum of 2 4 average 14 13 and 12 respectively out of an original porosity of 40 13 porosity units were lost by cementation and 27 porosity units were reduced by compaction mechanical and chemical present day intergranular porosity of these grainstones is zero whether they belonged to the vadose zone or the phreatic interval burial cementation and compaction destroyed all intergranular porosity regardless of early diagenetic overprint or textural variables the reservoir became compartmentalized during burial some intervals were active producers of calcium carbonate others were passive recipients

primary and diagenetic isotopic signals in fossils and hemipelagic carbonates the lower jurassic of northern spain stable isotope and trace element analyses of 230 jurassic pliensbachian toarcian samples from northern spain have been performed to test the use of geochemical variations in fossils belemnites and brachiopods and whole rock hemipelagic carbonates as palaeoceanographic indicators although the succession analysed reinosa area westernmost basque cantabrian basin has been subject to severe thermal alteration during burial diagenesis the samples appear to be well preserved the degree of diagenetic alteration of the samples has been assessed through the application of integrated petrographic chemical and cathodoluminescence analyses it is demonstrated that brachiopods and whole rock carbonates although widely used for palaeoceanic studies do not retain their primary marine geochemical composition after burial diagenesis in contrast there is strong evidence that belemnite rostra preserve original isotopic values despite pervasive diagenesis of the host rock well preserved belemnite shells non luminescent to slightly luminescent typically show stable isotope values of 4ae3 to 0ae7 d 13 c 0ae7 to 3ae2 d 18 o and trace element contents of 950 l gg 1 sr and sr mn ratios 80 this study suggests that the degree to which diagenesis has affected the preservation of an original isotopic composition may differ for different low mg calcite fossil shells and hemipelagic bulk carbonates behaviour that should be considered when marine isotopic signatures from other ancient carbonate rocks are investigated multiple non luminescent contemporaneous belemnite samples passed the petrographic and geochemical tests to be considered as palaeoceanic recorders yet their d 13 c and d 18 o values exhibited moderate scatter such variability is likely to be related to the palaeoecological behaviour of belemnites and or highfrequency secular variations in sea water chemistry superimposed on the longterm isotopic trend a pronounced positive carbon isotope excursion up to 4ae3 is documented in the early toarcian serpentinus biozone which correlates with the toarcian d 13 c maximum reported in other european and tethyan regions

paleomagnetism and paleogeography of the northern calcareous alps austria prefolding magnetization components have been resolved at 38 sites of liassic adnet limestones in the central northern calcareous alps nca and at one site in the drauzug the site mean directions are northeasterly and down and are closer to coeval european directions than to southern alpine african directions the western end of both the nca and of the drauzug yield different site mean directions and negative fold tests indicating remagnetization the sampling localities have been rotated relative to one another during thrusting however comparison of paleomagnetic poles with the european apparent polar wander path implies an average clockwise rotation of about 30 for the nca relative to europe larger scale clockwise rotations in excess of 80 relative to the southern alps are implied by comparison with the southern alpine african polar wander path facies analysis of jurassic and lower cretaceous basinal sediments in the central part of the nca suggests that liassic subsidence was related to presently e w sinistral strike slip faults whereas malm berriasian subsidence was controlled by presently e w south dipping normal faults both paleomagnetic and facies data tend to indicate that the nca did not undergo the african rotation seen in southern alpine paleomagnetic data this implies the existence of a short lived tract of triassic jurassic ocean floor between the nca and the southern alps which linked the pindos ocean to the ligurian trough and allowed adria to rotate independently from the nca during the late jurassic eo alpine deformation and metamorphism are associated with the early cretaceous closure of this hallstatt trough

the influence of rock fabric and mineralogy on thermochemical sulfate reduction khuff formation abu dhabi abstract thermochemical sulfate reduction tsr is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce h2s and calcite in this study of the dolomite hosted hydrocarbon gas reservoirs in the permo triassic khuff formation abu dhabi a geochemically well constrained rock gas system we demonstrate for the first time a clear influence of rock texture and mineralogy on the rate and extent of tsr reactions and thus on h2s concentration in the gas phase the controls on the rate on h2s accumulation were tsr reaction kinetics tsr became significant as temperature exceeded 140 c a critical threshold temperature for chemical reaction between aqueous sulfate and aqueous methane anhydrite dissolution rate once initiated the subsequent reaction rate was controlled by the rate of supply of aqueous sulfate to the reaction site sulfate limitation is indicated by the lack of fractionation of sulfur isotopes between sulfate and sulfide i e suggesting total reaction for each unit of sulfate that dissolves also finely crystalline anhydrite began reacting at a lower temperature than coarse crystalline anhydrite likely a result of relative surface area suggesting that anhydrite dissolution was the rate limiting step transport rates are unlikely to have been rate limiting at the earliest stage of reaction because anhydrite was replaced in situ by calcite on the very edges of anhydrite nodules and crystals transport rate later as tsr proceeded it became transport controlled as calcite growing on the surface of anhydrite crystals began to isolate them from dissolved methane tsr ceased once calcite had effectively armor plated totally isolated the remaining anhydrite finely crystalline anhydrite underwent more extensive and more rapid tsr than coarser anhydrite crystals because these had a greater ratio of surface area to volume allowing more and faster dissolution and requiring more calcite to isolate them from methane localized loss of h2s occurred in the reservoir by reaction with indigenous fe bearing clays consequently reservoirs with a relatively high siliciclastic content have less h2s than would be expected from the advanced state of anhydrite replacement by calcite in order to predict tsr related h2s concentration in hydrocarbon gases it is thus important to understand the diagenetic and textural characteristics of the reservoir as well as the thermal and petroleum emplacement history

an improved landslide mobility model a relatively simple and versatile numerical model known as dan developed by oldrich hungr for the assessment of landslide mobility has been enhanced to incorporate the consideration of a trapezoidal shaped flow channel for more realistic modelling purposes this enhanced debris mobility model dmm has been programmed to run on a spreadsheet and has been calibrated against detailed landslide data in hong kong in contrast to previous work the enhanced dmm eliminates the limitations inherited from the assumption of a rectangular flow channel with frictionless side boundaries when using dmm no predefined width of landslide is needed the dmm simulates landslide mobility with the flow resistance on the whole wetted perimeter of the channel calculates the surface width of the landslide based on the cross sectional geometry of the channel and is capable of predicting a lobe shaped debris deposition area this technical note presents details of the enhancement to the dan formulation key words landslides

stratigraphy and sedimentology of jurassic bedded chert overlying ophiolites in the north apennines italy in the north apennines of italy upper jurassic bedded chert stratigraphically overlies ophiolitic rocks and is overlain by lower to middle cretaceous pelagic limestone and shale and upper cretaceous flysch the bedded chert best exposed in east liguria and on elba is typically 30 80 m thick but occasionally reaches 150 200 m thickness it consists of two main alternating lithologies siliceous mudstone sm and radiolarite r chert sections commonly show characteristic stratigraphic changes lower cherts display a striking rhythmic alternation of r and ferruginous sm beds in middle cherts sm beds are much less ferruginous and shalier intercalations are locally present in upper cherts r beds are less frequent and sm beds are essentially non ferruginous r beds are generally 1 4 cm thick and consist of 80 90 quartz 5 15 clays and usually 1 hematite they are commonly parallel laminated and rarely size graded in size graded beds large radiolaria are more abundant near the bed base commonly together with ophiolitic or sm clasts and small radiolaria more abundant near the bed top sorting is poor throughout most r beds r beds are interpreted as turbidites cf nisbet price 1974 model calculations suggest that typical settling velocities of radiolaria during redeposition are 1 cm sec 1 which is low and of restricted range relative to the 1 10 cm sec 1 settling velocities of clastic grains of comparable size range radiolaria therefore should have only a limited tendency to grade and sort during deposition from a turbulent current sm beds are commonly 1 7 cm thick although much thicker ones occur near the base of sections and consist mainly of 50 70 quartz 15 35 clays and 0 15 hematite microscopic clay silica aggregates and highly corroded remnants of radiolaria are common sm beds are interpreted as mainly ambient pelagic sediment which accumulated slowly in topographic lows and which was modified by near surface dissolution of biogenic silica in sm beds which contain two texturally different layers the lower one is interpreted as the top of the underlying radiolarian turbidite north apennine cherts represent the first sediment deposited on oceanic crust formed during the opening of the north apennine part of the tethys the ophiolitic basement had a rugged topography which favoured the redeposition of siliceous sediment hematite and local mn enrichments in sm beds in the lower chert sections represent hydrothermal precipitates inferred to have originated at a spreading axis during seafloor spreading accumulation of siliceous sediments progressively reduced the topography deposition of ophiolitic detritus within the sediments phased out during early chert sedimentation and the hydrothermal contribution during early middle chert sedimentation as local basins filled during late chert sedimentation radiolarian turbidites became less frequent the first limestones at the top of chert sections are calcareous ooze turbidites derived from above the ccd and deposited slightly below it gradual descent of the ccd to ocean floor depths at the end of the jurassic bosellini winterer 1975 led to the replacement of siliceous by carbonate sedimentation

simulation of interactions between debris flow and check dams on three dimensional terrain abstract debris flows are rapid gravity driven flows of sediment water mixture which can be greatly destructive due to its huge volume high velocity and large impact force check dam is essential protective structure for controlling debris flow however it is a challenging work to assess the interactions between debris flow and check dam especially when involving complex topography and dam destruction a numerical method was developed in this study to investigate the interactions between debris flow and check dam on three dimensional terrain the debris flow and check dam were simulated by smoothed particle hydrodynamics sph method and finite element method fem respectively the method was validated by a dam break problem and a granular flow flume test an actual debris flow event originated from failure of tailings dams on 19 july 1985 in stava italy was simulated as an example the results indicate that the proposed method is a practical tool to simulate the runout characteristics of debris flow e g flow velocity flow depth impact area and interactions between debris flow and check dam e g impact force destruction of check dam interception by check dam given similar total dam volume increasing the number of dams will improve the hazard mitigation effect moreover it is recommended to construct dams in downstream area with straight channel this study will contribute to a better understanding of the flow structure interaction and is helpful for rational design of check dams

thermochemical sulfate reduction and fluid evolution of the lower triassic feixianguan formation sour gas reservoirs northeast sichuan basin china the dolomite hosted lower triassic feixianguan formation from the northeast sichuan basin china is an economically important reservoir that contains sour natural gas these reservoirs were initially filled with oil later replaced by gas during burial to 7000 m 22 965 ft followed by uplift to about 4000 m 13 123 ft we have studied the souring process thermochemical sulfate reduction tsr and diagenetic evolution of the feixianguan formation using detailed petrology fluid inclusion studies and stable isotope data from carbonate minerals pre tsr diagenesis included in time order the eodiagenetic main stage of dolomitization by a reflux mechanism fracture related calcite cementation barite quartz celestite and fluorite mineralization and a dolomite recrystallization stage thermochemical sulfate reduction resulted in anhydrite replacement by calcite petroleum destruction formation of sulfur rich pyrobitumen and elemental sulfur and generation of large volumes of and diagenesis during tsr can be subdivided into oil stage tsr and gas stage tsr with oil stage tsr defined by the presence of primary oil and bitumen inclusions in the tsr calcite based on aqueous inclusion homogenization temperatures oil stage tsr commenced at a temperature of 116 c with a mode between 130 c and 140 c gas stage tsr started at a temperature of 135 c and continued to maximum burial temperatures of about 220 c trace amounts of pyrite barite quartz and celestite grew during tsr post tsr diagenesis was dominated by fracture related calcite precipitation as well as celestite and anhydrite crystallization formation water salinity increased from depositional values 3 5 wt up to 24 wt during pre tsr dolomite recrystallization probably because of an influx of evaporite associated water from the overlying jialingjiang formation although pre tsr barite quartz celestite and fluorite mineralization was associated with a transient decrease in water salinity during tsr formation water salinity decreased from 26 wt to as low as 4 wt as a result of water being produced during tsr reactions

alteration of solid bitumen by hydrothermal heating and thermochemical sulfate reduction in the ediacaran and cambrian dolomite reservoirs in the central sichuan basin sw china abstract solid bitumen in reservoir rocks is an allochthonous organic matter formed from bitumen or liquid hydrocarbons by various alteration processes in this study two types of altered solid bitumen have been identified in both the ediacaran dengying and cambrian longwangmiao formations in the central sichuan basin using petrographic microthermometric chemical and isotopic data the hydrothermally altered bitumen type 1 is associated with the pore filling saddle dolomite and quartz in which homogenization temperatures of some fluid inclusions are more than 10 c higher than the maximum burial temperature of the dengying formation it has various anisotropic textures with significantly high bireflectance values rbmax rbmin between 3 89 and 9 21 moreover the hydrothermal alteration led to 13c enrichment in the type 1 bitumen compared to the normally matured bitumen derived from the same source on the other hand the thermochemical sulfate reduction tsr altered bitumen type 2 has s c atomic ratios of up to approximately 0 06 the 34s values of type 2 bitumen are close to those of the carbonate associated sulfate and similar to the tsr derived h2s in the same reservoirs a strong negative correlation exists between s c atomic ratios and 13c values in the type 2 bitumen in the dengying formation which is interpreted as a result of an increasing incorporation of the 13c depleted ethanethiol into the bitumen during tsr this interpretation is consistent with the fact that the remaining ethane became isotopically heavier as tsr proceeded in addition the reactive sulfate for tsr was primarily derived from the hydrothermal sulfate such as barite this is evidenced by the replacement of hydrothermal barite by the 34s enriched pyrite and the small differences in 34s value between the barite and the type 2 bitumen or the tsr derived h2s in the same strata we suggest that tsr in the ediacaran and cambrian hydrocarbon reservoirs was probably initiated by hydrothermal activity

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

jurassic radiolarites in a tethyan continental margin subbetic southern spain palaeobathymetric and biostratigraphic considerations abstract a region of the pelagic subbetic basin within the southern iberian continental margin is studied in lithostratigraphical and biostratigraphical detail jurassic radiolarites jarropa radiolarite formation bathonian oxfordian interbedded with shallow water marine limestones have been recognized underlying the radiolarites camarena formation bajocian are oolitic limestones showing shallowing upward cycles with karstic surfaces on the top corresponding to deposition on an isolated carbonate platform on volcanic edifices the milanos formation upper kimmeridgian tithonian overlying the radiolarites contains calciclastic strata with hummocky cross stratification which indicate outer carbonate ramp deposition in the jarropa radiolarite formation some calcisiltite strata with hummocky cross stratification have been found the bathymetry of the subbetic jurassic pelagic sediments including the radiolarites is considered as moderate or shallow in depth we suggest that the pelagic character of the jurassic sediments in this margin and their equivalents in other alpine domains is a consequence of distance from the continent beyond the pericontinental platform but not necessarily of depositional depth

two dimensional water flood and mudflow simulation flo 2d is a two dimensional finite difference model that simulates clear water flood hazards mudflows and debris flows on alluvial fans and urban floodplains interactive flood or mudflow routing between channel street and floodplain flow is performed using a uniform grid system to describe complex floodplain topography a quadratic rheological model developed from field and laboratory mudflow data enables appropriate simulations of flooding conditions ranging from clear water to hyperconcentrated sediment flows computer aided design cad graphics of predicted time sequenced flood depths automates the delineation of flood hazards replication of the 1983 rudd creek mudflow in utah demonstrates the capability of the model

mesozoic alpine facies deposition as a result of past latitudinal plate motion the fragmentation of pangaea as a consequence of the opening of the atlantic ocean is documented in the alpine mediterranean region by the onset of widespread pelagic sedimentation1 shallow water sediments were replaced by mainly pelagic limestones in the early jurassic period radiolarian cherts in the middle late jurassic period and again pelagic limestones in the late jurassic cretaceous period1 during initial extension basin subsidence below the carbonate compensation depth ccd is thought to have triggered the transition from early jurassic limestones to middle late jurassic radiolarites1 it has been proposed that the transition from radiolarites to limestones in the late jurassic period was due to an increase in calcareous nannoplankton abundance when the ccd was depressed below the ocean floor1 but in modern oceans sediments below the ccd are not necessarily radiolaritic here we present palaeomagnetic samples from the jurassic cretaceous pelagic succession exposed in the lombardian basin italy on the basis of an analysis of our palaeolatitudinal data in a broader palaeogeographic context we propose an alternative explanation for the above facies tripartition we suggest that the lombardian basin drifted initially towards and subsequently away from a near equatorial upwelling zone of high biosiliceous productivity our tectonic model for the genesis of radiolarites adds an essential horizontal plate motion component to explanations involving only vertical variations of ccd relative to the ocean floor it may explain the deposition of radiolarites throughout the mediterranean and middle eastern region during the jurassic period

geochemical characteristics of natural gases related to late paleozoic coal measures in china abstract by 2013 more than 20 gas fields related to late paleozoic coal measures have been discovered in china primarily distributed in the bohai bay ordos sichuan and junggar basins the total proven reserve in these gas fields is more than 3200 109 m3 accounting for 30 1 of the proven gas reserves in china after analyzing the molecular compositions stable carbon isotopes and helium isotopes of 375 gas samples genetic types and origins of the natural gas as well as the secondary alterations it experienced are discussed in this study most of the natural gas related to the late paleozoic coal measures are coal type gas with some of the gases from the sichuan basin and the jingbian gas field in the ordos basin being oil type gases generated from marine mudstones in the permian longtan formation and marine carbonates in the ordovician majiagou formation respectively the equivalent vitrinite reflectance values based on stable carbon isotopes of natural gases vary from 0 8 to 2 5 indicating the mature to over mature stage positive carbon isotope series 13c ch4 13c c2h6 and 13c ch4 13c c3h8 the form of 13c ch4 13c c2h6 is primarily resulted from the mixing of oil type gases of different maturities while the form of 13c ch4 13c c3h8 is primarily resulted from the mixing of coal type gases of different maturities high concentrations of hydrogen sulfide in natural gas from the sichuan basin and the chenghai gas field in the bohai bay basin are resulted from thermochemical sulfate reduction tsr which causes to some extent the fractionation of carbon isotopes by contrast the fractionation of methane carbon isotopes resulting from the tsr effect is not clear carbon dioxide from the bohai bay and junggar basins is primarily biogenic generated via the thermal decomposition of organic matter while that from the ordos basin sichuan basin and chenghai gas field is generated via the thermal decomposition of carbonates carbon dioxide related to the tsr effect has also contributed to the sichuan basin and chenghai gas field

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

controls on reservoir development in a shelf carbonate upper jurassic smackover formation of alabama hydrocarbon reservoirs of the upper jurassic smackover formation in alabama are predominately oolitic and pelletal dolostone pore systems are dominated by moldic and secondary intraparticle pores intercrystalline pores or mixtures of these pore types all smackover reservoirs in alabama have been strongly affected by early cementation dissolution of calcium carbonate allochems and dolomitization marine phreatic cement occluded primary interparticle porosity in much of the smackover reservoirs in alabama dolomitization of the smackover in alabama included penecontemporaneous early burial and late deep burial episodes early burial dolomite predominates fabric selective dolomitization yielded reservoirs strongly influenced by both depositional fabric and diagene is nonselective dolomitization yielded reservoirs with intercrystalline pore systems shaped primarily by diagenesis porosity evolution was controlled regionally by level of thermal exposure mode of dolomitization and proximity to the wiggins arch thermal exposure is inversely related to porosity but the relationship is weak r2 0 5 fabric selective dolostone is slightly more porous than nonselective dolostone when averaged over the entire study area averages of 18 1 and 15 1 respectively p 0 0001 but nonselective dolostone is more porous at a given level of equivalent vitrinite reflectance smackover fields on the north flank of the wiggins arch are unusually porous given their level of thermal maturity and are unusual in other ways as well local porosity variation was controlled by depositional fabric early cementation dissolution and burial compaction and cemen ation regional permeability variation cannot be explained using existing data permeability is locally controlled by pore throat size the effects of dolomite crystal size distribution early cementation fracturing and burial compaction and cementation pore throat size exhibits the strongest overall correlation with permeability r2 0 54 permeability and porosity are strongly correlated locally but the regional correlation is weak

remagnetization and northward coastwise transport of franciscan complex rocks northern california a reinterpretation of the paleomagnetic data previous paleomagnetic studies of accreted oceanic rocks within the franciscan complex of northern california have concluded that these rocks originated far to the south of their present positions with respect to the north american continent based on positive fold tests the characteristic remanent magnetizations were inferred to predate accretion related deformation and metamorphism and to have been acquired during or soon after deposition of these rocks thus the paleomagnetic data were thought to provide direct information on ancient oceanic plate motions however the plate motions implied by some of these paleomagnetic data are problematic e g exceptional plate velocities and uniform polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization recent work on oceanic rocks in similar subduction complexes of japan and mexico have shown that they were most likely chemically remagnetized during accretion prior to disruption of the original stratigraphic sequences modern analogs indicate that the oceanic rocks in mexico were probably remagnetized while still part of a shallow dipping subducting slab 10 at the base of an accretionary prism assuming these rocks were near horizontal at the time of remagnetization paleolatitudes at which these rocks were subducted and subsequent arc parallel displacements along the western margin of north america can be inferred in this paper franciscan rocks in northern california are reinterpreted as also having been remagnetized prior to accretion related deformation this scenario satisfies both geologic and paleomagnetic constraints for these rocks and resolves conflicts between data indicating both remagnetization and tectonic displacement transport of the laytonville limestone from the southern hemisphere is not required paleolatitudes of subduction and remagnetization in the northern hemisphere 12 to 33 appear to be inversely proportional to age of accretion middle cretaceous to oligocene for the franciscan rocks subsequent northward diplacements 800 to 3700 km and clockwise rotations 56 and 154 of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of north america during late mesozoic and cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models

finite element analysis for rockfall and debris flow mitigation works1 landslide risks arising from boulder falls and debris flows are commonly mitigated using rigid and flexible barriers debris barrier interaction is a complicated process so current design methods

estimating total resisting force in flexible barrier impacted by a granular avalanche using physical and numerical modeling flexible barriers are a promising tool for protection against extremely rapid landslides such as debris flow and debris avalanches with landslide impacts of any size the total force induced withi

evidence for multiple stages of oil cracking and thermochemical sulfate reduction in the puguang gas field sichuan basin china the puguang gas field is the largest gas field found in marine carbonates in china marine carbonate reservoirs in this field were buried to a depth of about 7000 m 22 966 ft and experienced maximum temperature up to 220c before uplift to the present day depth of 5000 5500 m 16 404 18 045 ft with present day thermal maturity between 2 0 and 3 0 equivalent vitrinite reflectance ro sulfur rich pyrobitumens with reflectance up to 3 5 are widespread in the reservoirs and resulted from thermal cracking of crude oils most likely generated from upper permian source rocks and thermochemical sulfate reduction tsr natural gases in the puguang gas field have wide variations in nonhydrocarbon gas contents with h2s contents between 5 1 and 58 3 and co2 contents between 7 9 and 18 0 the hydrocarbon gases originated mainly from thermal cracking of accumulated oil but were altered by tsr thermochemical sulfate reduction in the study area exerted different effects on the isotope compositions of different hydrocarbon gas components at different tsr stages the differential increase of 13c values for different gas components reflects transformation from a heavy hydrocarbon gas dominated tsr stage to a methane dominated tsr stage this caused a decrease of 13cmethane13cethane values and a corresponding conversion from reversed to normal isotope distributions thermochemical sulfate reduction in the study area appears to have been limited by sulfate concentrations in the reservoirs a successive three stage tsr series namely liquid hydrocarbon involved tsr heavy hydrocarbon gas dominated tsr and methane dominated tsr occurred in reservoirs with sufficient sulfate concentration methane can be the dominant organic reactant for tsr but only at elevated temperature and after most c2 hydrocarbons are exhausted

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

paleomagnetism of red cherts a case study in the inuyama area central japan this study is an attempt to isolate and identify the primary magnetization in red cherts red chert samples from a middle triassic sequence in the inuyama area 35 4 n 137 0 e central japan have a multicomponent magnetization which is delineated by thermal demagnetization two of the components have high coercivity and high blocking temperatures one is carried by hematite and the other by magnetite the former was concluded to be the primary magnetization for two reasons 1 it predates intraformational folding and 2 it records geomagnetic reversals the other component which accounts for the dominant part of natural remanent magnetization was probably acquired at a time long after the deposition two paleomagnetic results were drawn from the middle triassic red chert sequence 1 the mean inclination of the samples in the sequence was 1 4 6 8 therefore the paleolatitude amounts to 0 7 3 4 in contrast to the paleolatitude expected from the paleopole of eurasian continent which is about 70 and 2 the magnetostratigraphy of this sequence indicates that two geomagnetic epochs in the middle triassic are considerably longer more than several million years than the average of those in the cenozoic

diagenetic trends in the siliceous facies of the monterey shale in the santa maria region california x ray diffraction and oxygen isotopic analyses of outcrop and subsurface samples of siliceous rocks were used to reconstruct thermal and diagenetic histories of the miocene monterey shale near santa maria california within many stratigraphic sections soft porous diatomaceous rocks change gradationally to underlying hard and brittle chert porcellanite and siliceous shale the accompanying silica mineral zones are in descending stratigraphic order 1 biogenic silica opal a 2 cristobalitic silica opal ct and 3 microcrystalline quartz boundaries between silica mineral zones and stratigraphic horizons are often discordant within the opal ct zone the d 101 spacing of opal ct decreases in a smooth non linear fashion from about 4 10 a to 4 04 a in the santa maria valley and bradley oil field areas the thicknesses of the opal ct zones are greater and the present thermal gradients less than in the adjacent orcutt oil field thin opal ct zones at shallow maximum burial depths apparently correlate with higher thermal gradients using present thermal gradients and reconstructed maximum burial depths from well data in the santa maria region the ranges in temperatures for the top and base of the opal ct zone are 38 54 c and 55 110 c respectively the temperature difference between these two boundaries ranges from 17 to 60 c in comparison temperature ranges for these two boundaries computed from oxygen isotopic compositions of opal ct and quartz extrapolated experimental quartz water fractionations and assuming o18 0 o for the isotopic composition of the equilibrating fluid are 18 56 c and 31 80 c for the top and base of the opal ct zone respectively the temperature difference between these boundaries is 11 36 c using this method thermal gradients and sedimentation rates strongly influence rates of silica transformations reconstructed thermal and diagenetic histories of siliceous rocks of the monterey shale at four well sites in the santa maria region demonstrate that most silica conversions probably occurred during the last 3 4 myr in response to accelerated rates of sedimentation and therefore burial heating during the pliocene

generation of isotopically and compositionally distinct water during thermochemical sulfate reduction tsr in carbonate reservoirs triassic feixianguan formation sichuan basin china abstract thermochemical sulfate reduction tsr the reaction of petroleum with anhydrite in reservoirs resulting in the growth of calcite and the accumulation of h2s has been documented in the feixianguan formation dolomite reservoir in the sichuan basin china fluid inclusion salinity and homogenization temperature data have shown that tsr results in a decrease in salinity from a pre tsr value of 25 wt down to 5 wt as a result of water created as a byproduct of progressive tsr we have studied the isotopic character of the water that resulted from tsr in the feixianguan formation by analyzing the oxygen isotopes of tsr calcite and determining the oxygen isotopes of the water in equilibrium with the tsr calcite at the temperatures determined by aqueous fluid inclusion analysis we have compared these tsr waters to water that would have been in equilibrium with the bulk rock also at the temperatures determined by aqueous fluid inclusion analysis we have found that the tsr waters are relatively depleted in oxygen isotopes by up to 8 compared to what would be expected at equilibrium between the bulk rock and water since this type of water was specifically derived from anhydrite the generation of relatively large volumes of low salinity low 18o water associated with advanced tsr in the feixianguan formation has also been reported in the permian khuff formation in abu dhabi and from sour devonian fields in the western canada basin this suggests that tsr derived water may be a common phenomenon the effects of which on mesogenetic secondary porosity and reservoir quality have previously been underappreciated

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

wiggins arch southern mississippi new exploratory data from 3 d seismic newly released data from a 65 mi2 168 km2 3 d three dimensional seismic survey on the south flank of the wiggins arch reopens the question of exploratory opportunity in this sparsely drilled region although surrounded by significant production from deep jurassic and more shallow cretaceous reservoirs the wiggins has not yet been the site of successful exploration only nine deep tests however exist within an area over 2000 mi2 5180 km2 in size thus previous interpretations of low potential on the wiggins suffer from limited data the recently completed 3 d survey in conjunction with systematic evaluations of existing sample well log and 2 d two dimensional seismic information shifts the focus of attention from the smackover formation to overlying haynesville and cotton valley intervals data suggest that large scale oolite shoals exist in the upper haynesville immediately below the bossier shale potential shoals coincide in occurrence with a major northeast southwest trending anticlinal structure changes in the character of the haynesville reflector imply significant porosity development while time structure mapping and isochron thinning in the haynesville cotton valley interval indicate an important degree of potential entrapment in cotton valley sandstones a well planned for an updip portion of the anticline should yield extremely valuable information for future analyses of wiggins arch geology

paleomagnetic evidence for a post eocene 90 ccw rotation of internal apennine units a linkage with corsica sardinia rotation we report on an extensive paleomagnetic study 36 sites of the tuscan nappe succession from the northern apennines arc aimed to reconstruct the tectonic evolution of the internal sector of this chain we analyzed eocene pelagic foreland ramp deposits scaglia toscana formation and oligocene lower miocene siliciclastic turbidites macigno and falterona formations paleomagnetic results show that the internal sector of the northern apennines underwent large counterclockwise ccw rotations with respect to the adria africa foreland a decrease in the rotation magnitude was observed from the southern to the northern sector of the arc from 91 to 36 this trend is opposite to that observed in the more external units of northern apennines and demonstrates that the oroclinal bending model which has been proposed for the external units of the chain is not appropriate to explain the evolution of the internal sector of the arc on the basis of the observed paleomagnetic pattern we propose a new tectonic model in which the tuscan and falterona cervarola units in the southern area were first rotated ccw along with the corsica sardinia block during its lower miocene rotational drifting and were later involved in the main phases of rotational emplacement and translation toward the outermost sector umbria domain thus yielding the final curved shape of the northern apennines chain data from this study represent the first paleomagnetic evidence of the influence of the corsica sardinia ccw rotation in the apennines orogenic wedge deformation in the general framework of the geodynamic evolution of the central mediterranean subduction system

origin of deep sour natural gas in the ordovician carbonate reservoir of the tazhong uplift tarim basin northwest china insights from gas geochemistry and formation water abstract deep sour gases are found in the ordovician carbonate reservoir of the tazhong uplift in the tarim basin northwest china all sour gases in this field are dominated by gas hydrocarbons c1 c4 with varying amounts of h2s most of the gases in the eastern tazhong are characterized by high gas dryness coefficients 0 95 13c enriched methane 13c1 ranging from 44 6 to 35 8 and small difference between values of the 13c2 and 13c1 13c2 1 in contrast the gases in the western tazhong are characterized by relatively low gas dryness coefficients mostly

peri equatorial paleolatitudes for jurassic radiolarian cherts of greece abstract radiolarian rich sediments dominated pelagic deposition over large portions of the tethys ocean during middle to late jurassic time as shown by extensive bedded chert sequences found in both continental margin and ophiolite units of the mediterranean region which paleoceanographic mechanisms and paleotectonic setting favored radiolarian deposition during the jurassic and the nature of a tethys wide change from biosiliceous to biocalcareous mainly nannofossil deposition at the beginning of cretaceous time have remained open questions previous paleomagnetic analyses of jurassic red radiolarian cherts in the italian apennines indicate that radiolarian deposition occurred at low peri equatorial latitudes similar to modern day deposition of radiolarian rich sediments within equatorial zones of high biologic productivity to test this result for other sectors of the mediterranean region we undertook paleomagnetic study of mesozoic mostly middle to upper jurassic red radiolarian cherts within the aegean region on the peloponnesus and in continental greece sampled units are from the sub pelagonian zone on the argolis peninsula the pindos olonos zone on the koroni peninsula near karpenissi in central greece and the ionian zone in the varathi area of northwestern greece thermal demagnetization of samples from all sections removed low temperature viscous and moderate temperature overprint magnetizations that fail the available fold tests at argolis and koroni however the cherts carry a third high temperature magnetization that generally exhibits a polarity stratigraphy and passes the available fold tests we interpret the high temperature component to be the primary magnetization acquired during chert deposition and early diagenesis at kandhia and koliaky argolis the primary declinations and previous results indicate clockwise vertical axis rotations of 40 relative to stable europe due to ambiguities in hemispheric origin n or s and thus paleomagnetic polarity the observed declinations could indicate either clockwise cw or counterclockwise ccw vertical axis rotations thus at adriani koroni the primary declinations indicate either cw or ccw rotations of 95 or 84 depending on paleomagnetic polarity and age the primary inclinations for all peloponnesus sites indicate peri equatorial paleolatitudes similar to those found for coeval radiolarian cherts exposed in other mediterranean orogenic belts our new paleomagnetic data support the interpretation that mesozoic radiolarites within the tethys ocean were originally deposited along peri equatorial belts of divergence and high biologic productivity

the effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate gas reservoirs abstract thermochemical sulfate reduction tsr is a well known process that can lead to sour h2s rich petroleum accumulations most studies of tsr have concentrated upon gas chemistry in this study we have investigated palaeoformation water characteristics in a deep anhydrite bearing dolomite sour gas reservoir of permian age in abu dhabi using fluid inclusion stable isotope petrographic and gas chemical data the data show that low salinity isotopically distinct water was generated within the reservoir by reaction between anhydrite and methane the amount of water added to the reservoir from tsr indicated by reduced fluid inclusion salinity and water 18o values varied systematically with the extent of anhydrite reaction with methane water salinity and isotope data show that the original formation water was diluted by between four and five times by water from tsr thus we have shown that large volumes of very low salinity water were generated within the gas reservoirs during diagenesis following gas emplacement the salinity of formation water in evaporite lithologies is therefore not necessarily high modelling based upon a typical khuff gas reservoir rock volume suggests that initial formation water volumes can only be increased by about three times as a result of tsr the extreme local dilution shown by the water salinity and 18o data must therefore reflect transiently imperfect mixing between tsr water and original formation water the creation of large volumes of water has important implications for the mechanism and rate of thermochemical sulphate reduction and the interpretation of gas volumes using petrophysical logging tools

microbial sulfate reduction in deep sea sediments at the guaymas basin hydrothermal vent area influence of temperature and substrates abstract microbial sulfate reduction was studied by a 35 s tracer technique in sediments from the hydrothermal vent site in guaymas basin gulf of california mexico in situ temperatures ranged from 2 7 c in the overlying seawater to 120 c at 30 cm depth in the hydrothermal sediment sulfate reduction was measured in intact cores of hydrothermal sediment at 3 20 35 50 70 and 90 c the maximum rates of sulfate reduction were found in the upper 0 2 cm of the sediment and ranged from 32 nmol cm 3 d 1 at 90 c to 1563 nmol cm 3 d 1 at 70 c the rates of sulfate reduction rapidly decreased with depth in the upper 0 10 cm of the sediment and the maximal depth integrated rate 0 10 cm was 70 3 mmol so 4 2 m 2 d 1 at 70 c in comparison the sulfate reduction rate in nonhydrothermal sediment from the vent area was 0 85 mmol m 2 d 1 at the in situ temperature of about 3 c the high subsurface rates of sulfate reduction in the hydrothermal vent area was attributed to an enhanced local substrate availability in slurries of hydrothermal sediment incubated at 10 120 c microbial sulfate reduction extended to 102 c and different temperature groups of microbial sulfate reducers had optimum temperatures at around 34 70 and 80 88 c the overall temperature response of thermophilic sulfate reduction was similar in hydrothermal sediment sampled at different sites addition of short chain fatty acids and yeast extract to the sediment slurries stimulated sulfate reduction rates at all incubation temperatures no sulfate reduction was detected in the temperature range from 102 120 c microbial rather than thermochemical sulfate reduction could be a possible source of h 2 s in sulfide deposits with formation temperatures at about 100 c

reaction path modelling illustrating the fluid history of a natural co2 h2s reservoir despite the increasing interest in geologic co sequestration of co2 and h2s the long term consequences of the chemical interactions involved in this process remain largely unknown on a reservoir s

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

paleomagnetism of jurassic radiolarian chert above the coast range ophiolite at stanley mountain california and implications for its paleogeographic origins upper jurassic red tuffaceous chert above the coast range ophiolite at stanley mountain california lat 35 n long 240 e contains three components of remanent magnetization the first component a removed by 100 200 c has a direction near the present day field for southern california and is probably a recently acquired thermoviscous magnetization a second component b removed between 100 and 600 c is identical to that observed by previous workers in samples of underlying pillow basalt and overlying terrigenous sedimentary rocks this component has constant normal polarity and direction throughout the entire section although these rocks were deposited during a mixed polarity interval of the geomagnetic field the b magnetization therefore is inferred to be a secondary magnetization acquired during accretion uplift or miocene volcanism prior to regional clockwise rotation the highest temperature component c removed between 480 and 680 c is of dual polarity and is tentatively interpreted as a primary magnetization although it fails a reversal test possibly due to contamination by b separation of the b and c components is best shown by samples with negative inclination c directions and a corrected mean direction using only these samples indicates an initial paleolatitude of 32 n 8 paleobiogeographic models relating radiolarian faunal distribution patterns to paleolatitude have apparently been incorrectly calibrated using the overprint b component few other paleomagnetic data have been incorporated in these models and faunal distribution patterns are poorly known and mostly unquantified the available data therefore do not support formation of the coast range ophiolite at stanley mountain near the paleoequator or accretion at 10 n paleolatitude as has been previously suggested based on paleomagnetic data but indicate deposition near expected paleolatitudes for north america 35 n 4 during late jurassic time

back analysis of geophysical flows using three dimensional runout model predicting the mobility and delineating the extent of geophysical flows remains a challenge for engineers the accuracy of predictions hinges on the reliability of input parameters of runout models

origin and distribution of hydrogen sulfide in the yuanba gas field sichuan basin southwest china abstract the yuanba gas field in the permian changxing formation p2c which exhibits wide variations in its hydrogen sulfide h2s concentration 1 20 12 16 is a typical sour gas field in the northern sichuan basin the sulfur rich reservoir s solid bitumen atomic s c ratios are 0 032 0 142 and late calcite cement 13c values which are smaller than the 13c values of the host dolostone indicate that the h2s originated from thermal sulfate reduction tsr and oil was involved in tsr the gas souring index gsi of p2c s gases is generally lower than 0 1 the ethane 13c values increase as the gsi increases although no obvious increase was observed in the methane 13c values the calcite cements 13c values 15 36 to 4 56 in dolostone are heavier than the typical reported values which implies that only limited heavy hydrocarbon gases were involved in tsr no anhydrites developed in p2c s reservoirs and dissolved sulfate anions so42 were mainly enriched during dolomitization insufficient dissolved so42 most likely caused the lower h2s concentrations in the permian to triassic reservoirs in the northeastern sichuan basin compared to the permian khuff formation in saudi arabia and the jurassic smackover formation in mississippi except for the so42 in residual water in paleo oil zones so42 from bottom water may also be involved in tsr therefore oil reservoirs with bottom water have more so42 and can produce more h2s than pure oil reservoirs this phenomenon may be the main cause of the great difference in the h2s concentrations between reservoirs while gravitational differentiation during late uplift most likely creates differences in h2s concentrations in a single reservoir carbon dioxide co2 which has a relatively heavy 13c value 3 9 to 0 3 may be the combined result of tsr the balance between co2 and inorganic fluid systems and carbonate decomposition

pure siliceous ooze a diagenetic environment for early chert formation the formation of marine opal ct nodules or layers as early diagenetic deposits has been documented only in antarctic deep sea sediments in contrast porcellanites and cherts in land sections and deep sea drilling project and ocean drilling program drill sites are usually found in sediment sections of miocene age and older during r v polarstem cruises ant ix 3 and 4 young porcellanites were recovered for the first time in contact with their host sediment in two cores from the atlantic sector of the southern ocean chemical and mineralogical studies of these deposits and their surrounding sediments have increased knowledge about very early chert formation in both cores the porcellanites are embedded in sediments rich in opal a with extremely low levels of detrital minerals an environment that seems conducive to a rapid transformation of biogenic silica into porcellanites

origin of vein hydrothermal carbonates in triassic limestones of the espadan ranges iberian chain e spain dolomitization and hg bearing veins in the lower triassic limestones of the espadan ranges iberian chain e of spain

tsr altered oil with high abundance thiaadamantanes of a deep buried cambrian gas condensate reservoir in tarim basin abstract the first exploratory well the zs1c well with 158 545 m 3 daily gas production was discovered in 6861 6944 m deep strata of the cambrian gypsolyte layer of the tarim basin china in 2014 the discovery opens a new target for the cambrian reservoired oil and gas exploration and directly leads to large scale oil and gas exploration of the deep reservoired cambrian oil and gas fields in the basin comprehensive two dimensional gas chromatography time of flight mass spectrometry and a comprehensive two dimensional gas chromatography flame ionization detector revealed the presence of abundant adamantane compounds 2 thiaadamantanes and 2 thiadiamantanes and a large amount of sulfur containing compounds in the condensate oil the formation of organic sulfur containing compounds such as 2 thiaadamantanes is an indication of sulfur incorporation from the gypsum in the stratum into oil and gas in the course of tsr this reservoir has apparently suffered severe tsr alteration because 1 high content of h 2 s 2 h 2 s sulfur isotopes 3 co 2 carbon isotopes and others abundant data to support this findings similar sulfur isotopic composition of h 2 s oil condensate and the gypsum in the cambrian strata indicate that the produced condensate is experienced tsr alteration therefore the deep accumulated cambrian oil reservoir has experienced severe tsr alteration and accumulated natural gas and condensate contains high sulfur content

a hydroclimatic threshold for landslide initiation on the north shore mountains of vancouver british columbia landslides triggered by rainfall are the cause of thousands of deaths worldwide every year one possible approach to limit the socioeconomic consequences of such events is the development of climatic thresholds for landslide initiation in this paper we propose a method that incorporates antecedent rainfall and streamflow data to develop a landslide initiation threshold for the north shore mountains of vancouver british columbia hydroclimatic data were gathered for 18 storms that triggered landslides and 18 storms that did not discriminant function analysis separated the landslide triggering storms from those storms that did not trigger landslides and selected the most meaningful variables that allow this separation discriminant functions were also developed for the landslide triggering and nonlandslide triggering storms the difference of the discriminant scores cs for both groups is a measure of landslide susceptibility during a storm the variables identified that optimize the separation of the two storm groups are 4 week rainfall prior to a significant storm 6 h rainfall during a storm and the number of hours 1 m3 s discharge was exceeded at mackay creek during a storm three thresholds were identified the landslide warning threshold lwt is reached when cs is 1 the conditional landslide initiation threshold ctli is reached when cs is zero and it implies that landslides are likely if 4 mm h rainfall intensity is exceeded at which point the imminent landslide initiation threshold itli is reached the lwt allows time for the issuance of a landslide advisory and to move personnel out of hazardous areas the methodology proposed in this paper can be transferred to other regions worldwide where type and quality of data are appropriate for this type of analysis

jurassic magnetic stratigraphy from umbrian italian land sections the umbrian apennines were the site of pelagic sedimentation throughout most of the jurassic magnetic stratigraphy from four sections spanning many of the jurassic stages indicates that the geomagnetic field at this time was characterized by two intervals of mixed polarity separated by an interval of predominantly normal polarity corresponding to the jurassic quiet zone in the oceanic magnetic anomaly record unfortunately ammonites are poorly preserved or absent throughout most of these sections the duration of this quiet interval cannot be well defined although it is probably restricted to the callovian and oxfordian stages

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

paleomagnetism of mesozoic red chert from cedros island and the san benito islands baja california mexico revisited previous paleomagnetic study of mesozoic subduction complex rocks on cedros island and the san benito islands mexico shows that these rocks have been remagnetized a single polarity magnetization was found in chert sections and underlying pillow basalt deposited during a mixed polarity interval of the geomagnetic field reanalysis of the cedros and san benito chert samples 101 total shows that 13 samples also retain a high blocking temperature component of magnetization 600 to 680 c indicating a polarity stratigraphy and deposition of the bedded chert near 2 3 paleolatitude these data are similar to those for red chert in california and japan implying that many of the mesozoic ophiolitic chert sequences now exposed around the pacific rim were initially deposited within the equatorial zone of high biologic productivity these new data also support accretion of the cedros and san benito chert to the american margin at tropical paleolatitudes requiring significant northward translation and clockwise rotation to bring them to their present position with respect to the continental interior

chemical and carbon isotopic fractionations of gaseous hydrocarbons during abiogenic oxidation abstract the variations of chemical and carbon isotopic compositions in gaseous hydrocarbons upon abiogenic oxidation by sulfates hematite and both in laboratory studies were clearly demonstrated through a unique two step experimental approach in the first step a large number of small gold capsules containing gaseous hydrocarbons were prepared by kerogen pyrolysis experiments which were conducted under the same condition 450 c and 50 mpa for 72 h using the same kerogen the analytical results demonstrated that the chemical and carbon isotopic compositions of gases were almost identical among the capsules in the second step each of these gaseous hydrocarbon bearing capsules along with mineral oxidant hematite or magnesium sulfate heptahydrate or both and deionized water 15 of the amount of the oxidant was placed into a large gold capsule after welding sealing the small gaseous hydrocarbon bearing capsule was forced to leak while the large capsule remained undamaged by compressing the large capsule from the outside at the position where this small capsule was located then these large capsules containing gas and mineral reactants were heated isothermally at 350 c and 50 mpa for 72 144 216 and 288 h respectively the results of the oxidation experiments with increasing heating time can be outlined as follows 1 the amount of methane remained almost unchanged in the experiments using hematite and the mixed oxidants hematite mgso4 while it increased substantially in the experiment using mgso4 after 72 h indicating methane was one of the final products of c2 oxidation 2 the amounts of c2 c5 hydrocarbons decreased consistently and more rapidly in the experiment using mgso4 than that using hematite and the mixed oxidants 3 the oxidation rates of gas hydrocarbons increased with increasing carbon number of hydrocarbons 4 the oxidation rates of i butane and i pentane were substantially higher than those of the corresponding n butane and n pentane 5 the amount of h2s increased substantially in the experiment using mgso4 whereas it was below the detection level in the experiments using hematite and the mixed oxidants 6 the 13c values of c1 c5 hydrocarbons became less negative and the isotopic fractionation extent increased with increasing carbon number of hydrocarbons and oxidation extent 7 carbon isotopic fractionation factor k12 k13 decreased with increasing oxidation rate of gas hydrocarbons and 8 the rate of thermochemical sulfate reduction tsr was strongly dependent upon the presence and concentrations of h2s

dynamic analysis of an extraordinarily mobile rock avalanche in the northwest territories canada the pre historic rock avalanche at avalanche lake was a spectacularly mobile rock avalanche that resulted in the largest documented runup of any landslide on earth the runout of the 200 mm3 event was a complex and three dimensional process that created three distinct depositional lobes there is some controversy as to whether the presence of glacial ice played an important role in the dynamics of this event to investigate this hypothesis an advanced three dimensional numerical landslide runout model was used to reconstruct the dynamics of this event it was found that a conventional runout model is able to reproduce the bulk characteristics of this event including its spectacular runup without accounting for glacial ice a sensitivity analysis was performed to determine the factors that control the mobility of this event it was found that low strength in the source zone as well as the presence of significant internal strength is required to reproduce the 600 m runup this has important implication

diagenetic alteration of permian strata at oil fields of south central oklahoma usa abstract many oil fields in south central oklahoma including cement velma carter knox and eola have a chimney of altered rock within slightly deformed permian red beds the chimneys occur above and within the oil reservoirs where the chimneys crop out the altered rock is commonly well exposed the alteration consists chiefly of removal of haematite from sand grains cementation of sandstone by pyrite marcasite calcite and dolomite and at the cement field replacement of a bed of gypsum by calcite the total volume of these late diagenetic minerals is vast many hundreds of millions of tons the diagenetic alteration of red beds occurred when crude oil and abundant natural gas migrated vertically from major anticlines in pennsylvanian and older strata into the gently folded gypsum bearing permian red beds during cementation the rush springs sandstone in the cement field had a high porosity 40 50 which suggests that here alteration occurred before substantial burial in the red beds anaerobic bacteria mediated the oxidation of ch 4 and possibly alkanes within crude oil to co 2 and simultaneously reduction of so 4 4 anions to h 2 s the cementation resulted when carbonate species reacted with ca 2 and mg 2 and the bleaching resulted when sulphide species reacted with fe 3 and fe 2 the evidence for the bacterially mediated alteration is the anomalously low isotopic values for carbon and sulphur carbonate minerals have 13 c values as low as 39 2 0 and most values are less than 15 0 o sulphide minerals have 32 s values as low as 37 9 and most values are less than 8 5 0

constraining the fluid history of a co2 h2s reservoir insights from stable isotopes ree and fluid inclusion microthermometry reservoirs that host co2 h2s bearing gases provide a key insight into crustal redox reactions such as thermochemical sulphate reduction tsr despite this there remains a poor understanding of the extent duration and the factors limiting this process on a reservoir scale here we show how a combination of petrography fluid inclusion rare earth element ree and carbon 13c oxygen 18o and sulphur 34s stable isotope data can disentangle the fluid history of the world s largest co2 accumulation the labarge field in wyoming usa the carbonate hosted labarge field was charged with oil around 80 ma ago which together with nodular anhydrite represent the reactants for tsr the nodules exhibit two distinct trends of evolution in 13c with both 34s and 18o that may be coupled to two different processes the first trend was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulphur and the oxidation of organic compounds and associated precipitation of calcite during tsr in contrast the second trend was interpreted to be the result of the hydrothermal co2 influx after the cessation of tsr in addition mass balance calculations were performed to estimate an approximate tsr reaction duration of 80 ka and to identify the availability of organic compounds as the limiting factor of the tsr process such an approach provides a tool for the prediction of tsr occurrence elsewhere and advancing our understanding of crustal fluid interactions

equatorial origin for lower jurassic radiolarian chert in the franciscan complex san rafael mountains southern california lower jurassic radiolarian chert sampled at two localities in the san rafael mountains of southern california 20 km north of santa barbara contains four components of remanent magnetization components a b and b are inferred to represent uplift miocene volcanism and subduction accretion overprint magnetizations respectively the fourth component c isolated between 580 and 680 c shows a magnetic polarity stratigraphy and is interpreted as a primary magnetization acquired by the chert during or soon after deposition both sequences are late pliensbachian to middle toarcian in age and an average paleolatitude calculated from all tilt corrected c components is 1 3 north or south this result is consistent with deposition of the cherts beneath the equatorial zone of high biologic productivity and is similar to initial paleolatitudes determined for chert blocks in northern california and mexico this result supports our model in which deep water franciscan type cherts were deposited on the farallon plate as it moved eastward beneath the equatorial productivity high were accreted to the continental margin at low paleolatitudes and were subsequently distributed northward by strike slip faulting associated with movements of the kula farallon and pacific plates upper cretaceous turbidites of the cachuma formation were sampled at agua caliente canyon to determine a constraining paleolatitude for accretion of the jurassic chert sequences these apparently unaltered rocks however were found to be completely overprinted by the a component of magnetization similar in situ directions and demagnetization behaviors observed in samples of other upper cretaceous turbidite sequences in southern and baja california imply that these rocks might also give unreliable results

study of thermochemical sulfate reduction of different organic matter insight from systematic tsr simulation experiments abstract a series of thermochemical sulfate reduction tsr simulation experiments were carried out involving different organic matter crude oil solid bitumen type ii kerogen type iii kerogen and different sulfate species anhydrite and mgso4 to address the chemical and carbon isotopic variations of the hydrocarbon h2s and co2 the increase of main peak carbons of residual saturated hydrocarbon and the decrease of gaseous hydrocarbons from control treatment to corresponding sulfate treatments suggest that tsr promote the consumption of both liquid and gaseous hydrocarbons the 13c1 3 values generally shift positively from control treatment to sulfate treatments and the 13cethane 13cmethane values in sulfate treatments are higher than that in control treatments the variation of 13c1 3 in tsr is controlled by the isotope fractionation during the generation and consumption of c1 3 in tsr mgso4 is more reactive than anhydrite in tsr a certain amount of h2s is incorporated into solid bitumen as the result of secondary alteration we believe that the reactivity order of different organic matter in tsr is crude oil solid bitumen type ii kerogen type iii kerogen the reactivity of organic matter in tsr depends on the hydrocarbon generation kinetics of each organic matter the dissolution decomposition and precipitation of carbonate control the yield of co2 in sour reservoirs the negative shift of 13co2 with increasing tsr extent is mainly due to the inheritance effect of carbon isotope from hydrocarbons inorganic co2 sourced from the thermal decomposition or acid dissolution of carbonate mineral impose significant influence on 13co2 the h2s yields decrease with ch4 yields and increase with 13ch4 value the 13ch4 values increase with residual amount of gaseous alkane 1 h2s residual alkane h2s suggesting that methane acted as reactant in tsr the 13co2 13ch4 values decrease significantly with increasing temperature and the 13co2 is even more negative than 13ch4 in 450 c mgso4 treatments involving type ii and type kerogen accordingly methane acted as a predominant reactant in 450 c sulfate treatments in our experiment it is possible for natural gas with high gas dryness to experience methane dominated tsr in geological reservoirs

depositional environments organic carbon accumulation and solar forcing cyclicity in smackover formation lime mudstones northern gulf coast upper jurassic smackover lime mudstones a major hydrocarbon source rock in the u s gulf coast show three distinct lithofacies the basal laminated lithofacies consists of organic and siliciclastic rich lamina sets that alternate with organic poor clean carbonate lamina sets both lamina sets are composed of lamina couplets interpreted to be varves this lithofacies lacks current induced structures allochems and rip up clasts benthic and planktonic fossils are absent one organic rich lamina set and one organic poor lamina set comprise one cycle 0 5 3 cm thick the middle thin bedded lithofacies is composed of organic and siliciclastic rich carbonate beds that alternate with organic poor clean carbonate beds both bed types are internally laminated one organic rich bed and one organic poor bed comprise one cycle 2 60 cm thick the upper burrowed lithofacies is extensively bioturbated massive shows no evidence of cyclicity and contains little organic carbon sedimentologic characteristics suggest that the basal laminated lithofacies was deposited under anoxic conditions below storm wave base in a basinal environment the middle thin bedded lithofacies is copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received march 5 1996 revised manuscript received august 2 1996 final acceptance december 10 1996 2basin research institute louisiana state university baton rouge louisiana 70803 3lss international 1440 lake front circle suite 180 the woodlands texas 77380 formerly with department of geology and geophysics louisiana state university baton rouge louisiana 70803 4department of geology and geophysics louisiana state university baton rouge louisiana 70803 the study was supported by grants from the center for energy studies and the basin research institute of louisiana state university we thank h d klemme and g t moore for providing unpublished data p meyers and l m pratt reviewed an earlier version of the manuscript and offered valuable comments j wrenn kindly provided characteristics of organic matter we thank j kropog w s leblanc k lyle p o neill and b simpson for technical assistance we appreciate the helpful comments of r l folk b kirkland and c h moore critical comments by k t biddle n b harris b a prather and p d wagner significantly improved the quality of concepts presented

plate tectonics and pelagic facies late jurassic to early cretaceous deep sea sediments of the ybbsitz ophiolite unit eastern alps austria abstract pelagic sediments of the ybbsitz unit are part of an ophiolite sequence within the penninic unit in the eastern alps cherts and calpionellid limestones of late jurassic to early cretaceous age were deposited on oceanic basement sedimentation near an oceanic spreading center below the calcium compensation depth ccd is represented by chert clay rhythmites cherts display hydrothermal fe and mn mineralizations that are characterized by low contents of co ni and cu as well as by high fe2o3 tio2 and mno tio2 ratios as the site of deposition migrated away from the spreading center hydrothermal influence ceased due to the late jurassic drop of the ccd calcareous radiolarian ooze was deposited on intrabasinal topographic heighs downslope transport of this ooze to sites below the ccd by turbidity currents resulted in intercalations of calcareous and carbonate free sediments apparently the drop of the ccd was greater than the rate of cooling induced basement subsidence as calcareous radiolarites overly this sequence carbonate contents gradually increase upsection and micritic limestones terminate purely pelagic sedimentation at the jurassic cretaceous boundary plate drift moved the site of deposition towards an active continental margin producing a coarsening upward clastic sequence this sequence starts with turbidite and breccia intercalations in pelagic limestones followed by the deposition of early cretaceous flysch it marks the onset of subduction of the ybbsitz unit under the austroalpine continental margin

enigmatic origin of the largest known carbon isotope excursion in earth s history carbonate rocks from the middle ediacaran period in locations all over the globe record the largest excursion in carbon isotopic compositions in earth history this finding suggests a dramatic reorganization of earth s carbon cycle named the shuram excursion for its original discovery in the shuram formation oman the anomaly closely precedes impressive events in evolution including the rise of large metazoans and the origin of biomineralization in animals instead of a true record of the carbon cycle at the time of sedimentation the carbon isotope signature recorded in the shuram excursion could be caused by alteration following deposition of the carbonate sediments a scenario supported by several geochemical indicators however such secondary processes are intrinsically local which makes it difficult to explain the coincident occurrence of carbon isotope anomalies in numerous records around the globe both possibilities are intriguing if the shuram excursion preserves a genuine record of ancient seawater chemistry it reflects a perturbation to the carbon cycle that is stronger than any known perturbations of the modern earth if however it represents secondary alteration during burial of sediments then marine sediments must have been globally preconditioned in a unique way to allow ordinary and local processes to produce an extraordinary and widespread response

origin of high h2s concentrations in the upper permian changxing reservoirs of the northeast sichuan basin china abstract intense thermochemical sulfate reduction tsr and up to 18 h 2 s are found in the upper permian changxing formation p 3 ch in the northeast ne sichuan basin china despite that rare gypsum or anhydrite was found in this formation here we present new concentration data of carbonate associated sulfate cas from carbonate host rocks c o and sr isotope data for tsr related calcites and s isotope data for sulfur compounds obtained during this study these data along with spatial temporal changes in palaeogeopressure conditions hydraulic conductivity and the physical capacity indicate that the h 2 s was generated locally from tsr within the p 3 ch reservoirs we propose that the reactive sulfates were derived from cas released during dolomitization and recrystallization of earlier dolomite within the p 3 ch fm and from the cross formational migration of evaporative brines from the lower triassic feixianguan formation t 1 f to p 3 ch fm our calculation shows that the two sources could provide enough so 4 2 for the generation of h 2 s within the p 3 ch reservoirs early downward migration of sulfate rich evaporative brines from the t 1 f formation occurred in near surface and shallow burial diagenetic settings mainly 3 ch fm subsequently tsr calcites precipitated from the pore water have high sr concentrations up to 7767 ppm close to the t 1 f tsr calcites and 87 sr 86 sr ratios mainly from 0 7074 to 0 7078 which are significantly higher than those of late permian seawater but within the range of early triassic seawater

paleomagnetic data from umbria italy implications for the rotation of adria and mesozoic apparent polar wander paths abstract sixteen new jurassic and cretaceous paleomagnetic sampling sites are located in northern umbria along three river valleys bosso burano sentino the late jurassic and early cretaceous data are consistent in declination but not inclination with previously published data from these valleys early jurassic data from eight sites give site mean declinations which are significantly different from the two site mean declinations of this age which were previously available comparison of the data with cretaceous and jurassic mean directions from the southern alps indicate 20 anticlockwise rotation relative to the southern alps of this part of northern umbria during neogene deformation of the umbrian fold and thrust belt if the umbrian mean directions are rotated to compensate for the tectonic rotation the early jurassic and cretaceous umbrian and southern alpine pole positions coincide closely with a recently derived african apparent polar path apwp implying that adria moved with africa since at least early jurassic times the late jurassic umbrian and southern alpine poles however are not consistent with current apwps and imply rapid apparent polar wander in both african and north american coordinates from high latitude to lower latitude between bathonian and oxfordian times

the complexity secondary geochemical process genetic mechanism and distribution prediction of deep marine oil and gas in the tarim basin china abstract most paleozoic marine craton basins in china are rich in natural gas except the tarim basin where both oil and gas are prolific various hydrocarbon types have been found in this basin including deep ultra heavy oil heavy oil normal oil volatile oil condensate and natural gas petroleums with diverse types even coexist within a single reservoir generally the ordovician and cambrian reservoirs are deeply buried 5500 8000 m and intensively altered after initial oil and gas accumulations bringing challenges to physical property prediction before drilling and evaluation of exploration targets based on recent exploration discoveries and experimental data we systematically analyzed the origin of oil and gas demonstrated the mechanisms and processes of secondary geochemical alteration e g biodegradation gas washing fractionation tsr and high temperature cracking moreover the preservation mechanism of ultra deep normal oil was also clarified and the distribution patterns of oil and gas were predicted tarim basin has been uplifted and shallowly buried in the early accumulation stage then rapidly and deeply buried in the late stage resulting in various geochemical alteration processes at different burial stages through the reconstruction of complex deep strata oil and gas accumulation histories the spatial distribution of deep petroleum types were predicted this review has provided detailed assessment with case studies in the tarim basin and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums in addition to massive gas accumulations liquid oils still have great exploration potential in strata deeper than 8000 m in the tarim basin

field observations rheological testing and numerical modelling of a debris flow event debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy we investigate the dynamics and the rheological properties of a 90 000 m3 debris flow event triggered by a rapid regressive landslide with high water content field evidence revealed a maximum flow depth of 7 8 m with an estimated peak discharge of 350 400 m3 s 1 depositional evidence and grain size distribution of the debris pose the debris flow in an intermediate condition between the fluid mud and grain flow behaviour the debris flow material has silt clay content up to 15 per cent the rheological behaviour of the finer matrix was directly assessed with the ball measuring system the measurements performed on two samples at 45 63 per cent in sediment concentration by volume gave values of 3 5 577 pa for the yield strength and 0 6 27 9 pa s for the viscosity based on field evidence we have empirically estimated the yield strength and viscosity ranging between 4000 200 pa and 108 134 pa s respectively we used the flo 2d code to replicate the debris flow event we applied the model with rheological properties estimated by means of direct measurements and back analyses the results of these models show that the rheological behaviour of a debris flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts for debris flows composed by a significant number of coarse clasts a back analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows in these cases the back estimated coefficients do not adequately describe the rheological properties of the debris flow copyright 2006 john wiley sons ltd

limited thermochemical sulfate reduction in hot anhydritic sour gas carbonate reservoirs the upper jurassic arab formation united arab emirates abstract limited thermochemical sulfate reduction tsr in hot 130 160 c and anhydrite rich sour gas reservoir carbonates of the arab formation upper jurassic is manifested by rare calcitization of anhydrite with slightly lower 13cvpdb values 3 2 to 0 1 than calcite precipitated in equilibrium with late jurassic seawater fluid inclusion microthermometry of calcite that has replaced anhydrite indicates that tsr occurred between 130 c and 160 c the lack of evidence for extensive tsr despite the suitable current temperatures and abundant sulfates in the gas reservoir coupled with the relatively more common tsr related calcite in the flanks water zone than crest gas zone indicate that 1 gas emplacement while the reservoir was buried at shallower depth slowed down or inhibited tsr in the crest even when it subsequently reached depths where extensive tsr would occur and 2 h2s up to 38 vol has migrated from the underlying permo triassic and or jurassic sulfate carbonate deposits this study demonstrates that constraining the timing of hydrocarbon emplacement within the context of burial thermal history is crucial for a better understanding of the origin and distribution of h2s in hot anhydrite rich sour gas reservoirs

hidden terranes in the northern apennines italy a record of late cretaceous oligocene transpressional tectonics we propose that a very oblique or transpressional tectonic regime was dominant during the early pre collisional orogenic evolution of the northern apennines late cretaceous to early oligocene this hypothesis resolves many inconsistencies in the previous reconstructions of this orogenic belt which were based on a classic model of orthogonal convergence between the european and adriatic plates the crucial lines of evidence that point to a major role of oblique tectonics in the structuring of the northern apennines are 1 the plate tectonics framework that indicates left lateral oblique convergence along the europe adria plate margin 2 the lack of a magmatic arc during the entire pre collisional convergent history of the chain a time span 45 m y from late cretaceous to early oligocene 3 the long 20 m y residence time of turbidite sequences in the trench the dormant trench 4 the multiple source areas of turbidites from both sides of the basin and the associated coarse gravity d

permian wolfcamp limestone reservoirs powell ranch field eastern midland basin discussion the open quotes ep however its economic importance and geological complexity and the question of whether his model can be extended to other areas in the permian basin warrant this discussion

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

the onset of radiolarian deposition in the ophiolite sequences of the northern apennines abstract the present paper concerns the radiolarian biostratigraphy of the lowest part of four sections of the monte alpe cherts a typical element of the steinmann trinity in the northern apennines the base of the volterraio section elba island yielded a radiolarian association most robably belonging to the middle oxfordian early kimmeridgian in the murlo section southern tuscany the basal samples richest in radiolaria show an association typical of the middle oxfordian lower kimmeridgian at rocchetta di vara eastern liguria the association found in our lowest yet not strictly basal fossiliferous samples indicates an upper oxfordian lower kimmeridgian age in the section of ii conventino monti rognosi eastern tuscany the radiolarian association permits only a reference to the upper callovian lower kimmeridgian interval in most of the examined sequences the time intervals in which the onset of radiolarian deposition is bounded include the uppermost oxfordian and lower kimmeridgian while this onset is distinctly older at rocchetta di vara the beginning of the deposition of the monte alpe cherts gives an upper age limit for basalt extrusion in each section

landslide mobility analysis for design of multiple debris resisting barriers multiple debris resisting barriers have been commonly used worldwide to mitigate debris flows in drainage lines however a well developed methodology to assess the mobility of debris flows with co

deposition of franciscan complex cherts along the paleoequator and accretion to the american margin at tropical paleolatitudes red radiolarian cherts from three localities within the franciscan subduction complex of northern california contain three components of remanent magnetization which are best isolated by progressive thermal demagnetization the first component usually removed by 300 c has an in situ direction similar to the present axial dipole field and is probably a recently acquired thermoviscous overprint a second component generally removed between 300 and 630 c has constant normal polarity and direction within each section and is interpreted to have been acquired by low temperature chemical alteration during subduction and accretion at the continental margin the third component isolated between 560 and 680 c has both normal and reversed polarities passes a fold test and is inferred to have been acquired during or soon after deposition the available paleomagnetic biostratigraphic and geochemical data indicate deposition of these cherts along the paleoequator 0 2 n or s paleolatitude between pliensbachian and oxfordian time as the oceanic plate moved eastward relative to north america beneath the equatorial zone of high biologic productivity between bathonian and cenomanian time the chert sequences apparently moved progressively away from the paleoequator 2 15 n or s and were soon after accreted to the american continental margin plate reconstruction models for the farallon plate corroborate low paleolatitude trajectories from ridge crest to subduction zone for example from 3 s to 11 n and they imply subsequent northward translation of the franciscan complex 4 000 km by strike slip faulting related to relative motions between the farallon kula pacific and north american plates

the role of s 3 ion in thermochemical sulphate reduction geological and geochemical implications thermochemical sulphate reduction tsr plays a crucial role in the global sulphur cycle in the earth s crust and may affect current and past sulphur isotopic records however the extrapolation of experimental reaction rates measured at high temperature above 200 degrees c towards lower temperatures as well as the interpretation of the sulphur isotopic fractionation recorded in natural samples require an accurate description of the elementary steps controlling these reactions we addressed this question through dedicated experiments based on in situ raman spectroscopy measurements we show that the trisulphur ion s 3 is the dominant intermediate sulphur valence species involved in abiogenic sulphate reduction processes initiated by h2s over a wide range of temperature 100 350 degrees c and solution compositions whatever the electron donor considered the in situ spectroscopic data reported here unambiguously demonstrate the presence of s 3 at temperatures as low as 100 degrees c the presence of s 3 is critical to achieve rapid sulphate reduction especially at low temperature we propose that any dissolved constituent which decreases the dielectric constant of water or which yields favourable s 3 coordination will stabilise the trisulphur ion thus promoting tsr at t and ph conditions that are less extreme than previously thought the importance of s in these processes should also be taken into account when discussing the mass independent sulphur isotopic compositions recorded in natural and or experimental tsr related samples

the fate of co2 derived from thermochemical sulfate reduction tsr and effect of tsr on carbonate porosity and permeability sichuan basin china abstract this article discusses the role of methane in thermochemical sulfate reduction tsr the fate of tsr derived co2 and the effect of tsr on reservoir porosity and permeability and the causes of the anomalously high porosity and permeability in the lower triassic soured carbonate gas reservoirs in the northeast sichuan basin southwest china the lower triassic carbonate reservoirs were buried to a depth of about 7000 m and experienced maximum temperatures up to 220 c before having been uplifted to the present day depths of 4800 to 5500 m but they still possess porosities up to 28 9 and permeabilities up to 3360 md the present day dry gas reservoirs evolved from a paleo oil accumulation and experienced varying degrees of tsr alteration as evidenced from the abundant sulfur rich solid bitumens and varying h2s and co2 concentrations tsr occurred mainly within the oil and condensate wet gas windows with liquid hydrocarbons and wet hydrocarbon gases acting as the dominant reducing agents responsible for sulfate reduction sulfur rich solid bitumen and h2s generation and calcite precipitation methane dominated tsr was a rather late event and had played a less significant role in altering the reservoirs intensive h2s and co2 generation during tsr resulted in calcite cementation rather than carbonate dissolution which implies that the amount of water generated during tsr was volumetrically insignificant 13c depleted co2 derived from hydrocarbon oxidation preferentially reacted with ca2 to form isotopically light calcite cements and the remaining co2 re equilibrated with the 13c enriched water rock systems with its 13c rapidly approaching the values for the host rocks which accounted for the observed heavy and relatively constant co2 13c values the carbonate reservoirs suffered from differential porosity loss by tsr involved solid bitumen generation and tsr induced calcite and pyrite precipitation intensive tsr significantly reduced the porosity and permeability of the intervals expected to have relatively high sulfate contents the evaporative platform dolostones and the platform margin shoal dolostones immediately underlying the evaporative facies early oil charge and limited intensity of tsr alteration together with very low phyllosilicate content and early dolomitization accounted for the preservation of anomalously high porosities in the reservoirs above the paleo oil water contact a closed system seems to have played a special role in preserving the high porosity in the gas zone reservoirs below the paleo oil water contact the closed system which is unfavorable for deep burial carbonate dissolution and secondary porosity generation was favorable for the preservation of early formed porosity in deeply buried carbonates especially sucrosic and vuggy dolostones have a high potential to preserve such porosity

mesogenetic dissolution its role in porosity development in carbonate reservoirs models of porosity formation in carbonate rocks have stressed subaerial exposure and attendant shallow meteoric diagenesis porosity formation also occurs in deep burial or mesogenetic settings as a result of dissolution enlargement of preexisting pores porosity enhancement and creation of new pore systems brines charged with organic acids carbon dioxide and or hydrogen sulfide derived from organic matter diagenesis and thermochemical sulfate reduction are the likely fluids causing significant mesogenetic dissolution enhanced and newly created mesogenetic pore types can mimic pore types formed in shallow meteoric environments and therefore the mesogenetic origin of some porosity may go unrecognized

burial diagenesis and thermochemical sulfate reduction smackover formation southeastern mississippi salt basin the smackover formation in the southeastern mississippi salt basin has been buried from 3 03 to 6 06 km and subjected to temperatures of 100 to 200c pre hydrocarbon migration burial diagenesis is characterized by precipitation of calcite cement followed by saddle dolomite and late anhydrite these phases formed at temperatures of less than 100c the oxygen isotopic composition of calcite ranges from minus 5 to minus 8 4 pdb and carbon isotopic composition ranges from 3 5 to 6 0 pdb the sulfur isotopic composition of late anhydrites ranges from 18 1 to 19 1 cdt post hydrocarbon migration burial diagenesis is dominated by replacement of previously formed late anhydrite by calcite or calcite plus elemental sulfur and precipitation of post bitumen calcite cement these diagenetic phases formed at temperatures above 150c and are present only in the deep part of the basin the oxygen isotopic compositions of calcites that replace anhydrite range from minus 3 0 to minus 4 0 pdb and carbon isotopic compositions range from minus 2 0 to 4 2 pdb the oxygen isotopic compositions of post bitumen calcites range from minus 3 4 to minus 5 6 pdb and carbon isotopic compositions range from minus 1 6 to minus 16 3 pdb two samples of elemental sulfur have sulfur isotopic compositions of 15 8 and 16 1 cdt the high temperature replacement of anhydrite by calcite more the presence of post bitumen calcite cement the sulfur isotopic composition of sulfates and elemental sulfur and high concentration of hydrogen sulfide indicate that rapid thermochemical reduction of solid sulfates is taking place in the deep part of the mississippi salt basin at temperatures as low as 150c less

biogenic carbonates are they a criterion for underlying hydrocarbon accumulations an example from the gulf of suez region egypt the gulf of suez petroliferous basin is characterized by the occurrence of a middle upper miocene evaporite cap field and subsurface investigations in the southwest gulf of suez region indicate that the evaporites usually contain two types of biogenic carbonates in addition to sulfur the first type of carbonate is biogenic syngenetic in origin and was formed in low temperature euxinic aquatic environments by the reduction of dissolved sulfates and the oxidation of organic matter by sulfate reducing bacteria the resulting carbonate and sulfur are stratigraphically restricted within the evaporite sequence and occur as interlaminated gypsum calcite sulfur or as sulfur ooids sulfur globules and stromatolitic sulfur that are enclosed in gypsum or calcite the biogenic syngenetic carbonate and sulfur did not originate from petroleum and have a significance of euxinic aquatic settings the second type of carbonate is a biogenic epigenetic carbonate that formed under low temperatures by biochemical reactions between seeping hydrocarbons and the overlying miocene evaporites the carbonate is vuggy is included within or caps the evaporites and usually shows hydrocarbon stains or emits a hydrocarbon smell the sulfur is usually yellow but may be brown to black due to bitumen staining carbonates replace gypsum or anhydrite and occur as aragonite calcite or dolomite the d13c mean values for carbonate minerals range from 7 8 to 27 2 pdb being relatively heavier than the d13c values of the nearby crude oil 28 1 to 29 3 pdb carbon isotope values indicate that these carbonates were formed from the heavier organic carbon dioxide under reducing conditions where the lighter methane is stable the occurrence of biogenic epigenetic carbonates and sulfur in the evaporite deposits of the gulf of suez petroliferous basin is similar to that recorded in other basins such as the gulf coast basins of texas louisiana and southern mexico the fergana and amudarya depression of central asia and the mesopotamian depression in iraq the biogenic epigenetic carbonates or sulfur in some regions is considered as a criterion for petroleum microseepage that may indicate a potential hydrocarbon bearing reservoir at depth