tectonic implications of 40ar 39ar muscovite dates from the mt haley stock and lussier river stock near fort steele british columbia the mt haley and lussier river stocks are located northeast of cranbrook b c near the south end of the western main ranges of the southern canadian rocky mountains both are multiphase potassium feldspar porphyritic monzonite plutons that intrude lower paleozoic miogeoclinal strata they crosscut and thermally overprint the lussier river fault and the thrust and fold structures in the east flank of the purcell anticlinorium and the west limb of the porcupine creek anticlinorial fan structure muscovite from the mt haley stock yielded a 40ar 39ar plateau age of 108 2 0 7 ma 2 and a single crystal step heating analysis of muscovite from a skarn in the metamorphic aureole adjacent to the lussier river stock gave a plateau date of 108 7 0 6 ma 2 these dates constrain the timing of thrusting and folding in this portion of the western rocky mountains and of the displacement along the lussier river st mary fault to pre middle albian

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

may 18 1980 mount st helens deposits in south coldwater creek washington beginning at 0832 pacific daylight time pdt mount st helens washington produced a rockslide debris avalanche and a lateral explosion blast that generated a laterally directed pyroclastic surge called here a blast surge the resulting deposits are thickest in the east west trending valley of north fork toutle river immediately north of the volcano but are almost as thick in south coldwater creek a small tributary of the toutle river in the lee of an east west trending ridge johnston ridge just north of the north fork toutle river the avalanche surmounted johnston ridge 300 m relief and flowed down the valley of south coldwater creek closely following the avalanche and in part contemporaneously with it the blast surge left thin up to 0 5 m deposits on johnston ridge and thick up to 15 m deposits in south coldwater creek these deposits have a lower layer layer a1 which is friable massive poorer in fines particles 1 16 mm and more poorly sorted than the upper layer layer a2 layer a2 is less friable because it contains more silt and clay sized material beneath layer a1 is a zone containing a small percentage of debris from the blast surge mixed with products eroded from the underlying surface this zone designated as layer a0 is a poorly mixed layer containing schlieren of soil shattered volcanic fragments and considerable quantities of organic material layer a1 is strongly sorted and fines depleted and is interpreted to have been deposited from just behind the turbulent head of the blast surge layer a2 is interpreted to have been deposited from the body of the blast surge which is believed to have been less turbulent than the head layer a0 is interpreted to have formed by shearing at the base of the head of the blast surge in the region between the front and the back of the head of the blast surge it is concluded that a strongly fines depleted basal layer of a pyroclastic flow or surge deposit underlain by a thin sheared zone is the signature of an extremely high velocity particulate density current

lithic breccia and ignimbrite erupted during the collapse of crater lake caldera oregon abstract the climactic eruption of mount mazama 6845 y b p vented a total of 50 km3 of compositionally zoned rhyodacitic to basaltic magma from a a single vent as a plinian pumice fall deposit and the overlying wineglass welded tuff and b ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of crater lake caldera new field and grain size data for the ring vent products are presented in this report the coarse grained poorly bedded clast supported lithic breccia extends as far as 18 km from the caldera center like the associated ignimbrite the breccia is compositionally zoned both radially and vertically and silicic mixed and mafic types can be recognized based on the proportion of rhyodacitic pumice matrix fractions in silicic breccias are depleted of fines and are lithic and crystal enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement ignimbrite occurs as a proximal veneer deposit overlying the breccia a medial 8 to 25 km from the caldera center compositionally zoned valley fill as much as 110 m thick and an unzoned distal 20 km facies which extends as far as 55 km from the caldera breccia within 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring vent eruption columns expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks as recently postulated for some turbidity currents an inflection in the rate of falloff of lithic clast size within the lithic breccia at 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure the onset of ring vent activity at mt mazama was accompanied by a marked increase in eruptive discharge pyroclastic flows were emplaced as a semicontinuous stream as few ignimbrite flow unit boundaries are evident as eruption from the ring vents progressed flow runout distance and the extent of breccia deposition decreased due to a greater internal flow friction and b decreasing eruption column heights effect b probably resulted from a progressive decrease in magmatic gas content and discharge rate waning discharge may have been promoted by the tapping of more viscous crystal rich magma collapse of conduit walls and declining caldera collapse rate

volcanic degassing hydrothermal circulation and the flourishing of early life on earth a review of the evidence from c 3490 3240 ma rocks of the pilbara supergroup pilbara craton western australia abstract new data gathered during mapping of c 3490 3240 ma rocks of the pilbara supergroup in the pilbara craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism for most cherts fossil hydrothermal fluid pathways are preserved as silica barite fe bearing veins that cut through the footwall and up to the level of individual bedded chert units but not above indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events silica barite fe bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units and occurred under alternating high sulphidation and low sulphidation conditions these veins provided pathways to the surface for elements leached from the footwall e g si ba fe and volcanogenic emissions from underlying felsic magma chambers e g co 2 h 2 s hs so 2 stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of warrawoona group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and or degassing of these magmas heat from these intrusions drove episodes of hydrothermal circulation listric normal faulting during caldera collapse produced basins with restricted circulation of seawater eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components thereby providing habitats suitable for early life forms fossil stromatolites from two distinct stratigraphic units in the north pole dome grew in shallow water conditions but in two very different geological settings with different morphologies stratiform and domical stromatolites in the stratigraphically lower c 3490 ma dresser formation of the warrawoona group are intimately associated with barite and chert precipitates from hydrothermal vents suggesting that component microbes may have been chemoautotrophic hyperthermophiles evidence of shallow water to periodically exposed conditions active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water tectonically active caldera and concentrated therein to produce an extreme habitat for early life widespread conical and pseudocolumnar stromatolites in the c 3400 ma strelley pool chert at the base of the unconformably overlying kelly group occur in shallow marine platform carbonates silicification was the result of later hydrothermal circulation driven by heat from the overlying newly erupted euro basalt the markedly different morphology and geological setting of these only slightly younger stromatolites compared with the dresser formation suggests a diversity of microbial life on early earth the biogenicity of putative microfossils from this and younger hydrothermal silica veins in the warrawoona group remains controversial and requires further detailed study

landslides on ancient embankments in the kinki district japan strong motion seismoscope of the 1596 keichou fushimi earthquake landslides on ancient embankments burial mounds of imashiro zuka and nishimotome zuka induced by historical earthquakes related to the tectonic movement of active fault systems located between northern osaka and kobe are discussed the geological conditions of the foundation of the mounds the lithology stiffness and the position of the mound relative to the fault systems contributed to the collapse of the mounds obvious interior structures of landslides revealed the inherent deformation process and provided significant insight into landslide mechanisms rapid increasing pore water pressure was necessary to facilitate sliding along the almost horizontal slip surfaces developed in the main part of the landslide bodies on the imashiro zuka mound liquefaction analysis using both the results of dynamic triaxial compression tests and earthquake response analysis showed liquefaction in the foundation of the mound was a possible landslide mechanism on the nishimotome zuka mound landslides of embankments are unavoidable over long periods of time if any weaknesses are present at the foundation of the construction the total quality of an artificial soil structure very much depends on the conditions of its foundation bed today these ancient burial mounds in the kinki district are located in both rural and urban regions and landslides on these mounds provide unique information about issues related to the long term stability of modern large scale construction activities

pedogenic and diagenetic influences on void coating formation in lower cretaceous paleosols of the mill creek formation southwestern alberta canada abstract pedogenic and diagenetic influences on void coating formation were studied in two paleosols from the lower cretaceous albian mill creek formation in southwestern alberta canada using detailed micromorphological mineralogical and geochemical methods the paleosols consist of alternating decimetre scale beds of red grey green and variegated mudstone intermediate horizons red and grey green variegated mudstones contain associations of pale yellow clay coatings dark red clay coatings fe depletion hypo coatings and fe oxide quasi coatings sem edx ray analyses indicate that the dark reddish coatings are dominated by si al and fe with subordinate amounts of k na ca mg and ti pale yellow clay coatings have a higher si content and lower al k na ca and fe contents relative to reddish coatings within the paleosol profiles the distribution of clay minerals indicates 1 an increase in discrete clay minerals downward 2 a decrease in mixed layer illite smectite downward and 3 an increase in chlorite upward x ray diffraction indicates that the pale yellow and dark red clay void coatings are polymineralic pale yellow clay coatings have a higher proportion of mixed layer illite smectite and kaolinite less chlorite and are less crystalline than dark reddish coatings despite a diagenetic overprint including development of diffusion gleyans degradation of organic matter burial reddening and probably some smectite illitization both compositional and morphological gradients exist in the paleosol profiles and void coatings these gradients are most likely related to depositional variations and to pedogenic development in the original soils under variable eh ph conditions in the presence of organic matter therefore although the void coatings are altered diagenetic features their morphology mineralogy and perhaps even some of their microchemistry is attributable to the presence of pedogenic precursors initially formed in soils similar to modern temperate alfisols and glossic soils

comparison of the rainy ridge analcime phonolite sill and the crowsnest volcanics alberta canada a 5 7 m thick analcime phonolite sill occurs in the middle of the proterozoic gateway formation in southwest alberta the sill consists of sanidine aegirine augite magnesian hastingsite melanite with hydrogrossular rims titanite and minor biotite apatite and opaque minerals mineralogical and chemical similarities to the analcime rich phases of the cretaceous crowsnest formation found some 20 km to the north suggest a genetic relationship major differences are the presence of amphibole and hydrogrossular minerals not reported in the crowsnest formation the presence of amphibole as a primary hydrous phase in the rainy ridge sill indicates crystallization from a hydrous magma microprobe studies indicate a progressive enrichment of sodium in amphiboles and pyroxenes an apparent difference in chemical composition and alteration behavior of primary analcime phenocrysts and groundmass analcime is interpreted to reflect crystallization of analcime from a hydrous melt at depth followed by rapid trans

evidence for pyroclastic emplacement of the crowsnest formation alberta the middle cretaceous crowsnest formation west of coleman alberta is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows surges fallout of material from vertical eruption columns and minor mud flows emplaced the deposits textural evidence in the form of plastically deformed volcanic fragments chilled deposit margins baked rock fragment margins recrystallization and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature massive deposits containing a fine grained basal zone are interpreted as the product of pyroclastic flows whereas deposits characterized by a block rich base overlain by a thin layer of block depleted stratified material are interpreted as the product of density stratified surges deposits exhibiting pronounced stratification were emplaced by ash cloud surges thickly bedded breccias

stratified flow in pyroclastic surges stratified flow theory is applied to pyroclatic surges in an effort to gain insight into transport dynamics during explosive eruptions particle transport is assumed to be by turbulent suspension and calculations contained herein show that this is likely for many cases including the 18 may 1980 blast at mount st helens the discussion centers on the rouse number pn which represents a ratio of particle settling velocity to scale of turbulence the brunt vaisala frequency n which is the maximum possible frequency of internal waves the froude number fr representing the ratio of inertial forces to gravitational forces and the richardson number ri a ratio of buoyant restoring forces to turbulent mixing forces the velocity or flow power dependence of bed form wavelength in surge deposits is related to a velocity dependence of wavelength of internal waves in the turbulent surge this produces a decrease in dune wavelength with increasing distance from vent migration direction of bed forms is related tofr as it is defined for a continuously stratified flow proximal to distal facies variations in surge deposits reflect increasingpn andri as the flows move away from their sources this produces the progression from sandwave to massive to planar facies with increasing distance from vent where the long axis of topography is at low angles to the flow direction massive facies in topographic lows may from concurrently with sandwave facies on highs due to the higher particle concentration in the lows where long axis of topography is at high angles to flow direction denser lower parts of the surge may be dammed or blocked blocked material tends to form massive flows that may move down slope independent of the overriding surge a model incorporating turbulent transport stratified flow and time evolution of pyroclastic surges is proposed for deposits which have been attributed to both pyroclastic flow and pyroclastic surge transport by various workers during the initial high energy waxing phase of the eruptive event pn is sufficiently low that only coarse but poorly sorted material is deposited to form relatively coarse bottom layers as the event wanes remaining finer material is deposited through a thin bed load to produce overlying bedded and cross bedded veneer deposits throughout most of the event blocking occurs to produce relatively thick and massive deposits in valley bottoms

pathways of organic carbon oxidation in three continental margin sediments we have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of denmark and norway rates of nh4 and sigma co2 liberation sediment incubations were used with o2 penetration depths to conclude that o2 respiration accounted for only between 3 6 17 4 of the total organic carbon oxidation dentrification was limited to a narrow zone just below the depth of o2 penetration and was not a major carbon oxidation pathway the processes of fe reduction mn reduction and sulfate reduction dominated organic carbon mineralization but their relative significance varied depending on the sediment where high concentrations of mn oxide were found 3 4 wt mn only mn reduction occurred with lower mn oxide concentrations more typical of coastal sediments fe reduction and sulfate reduction were most important and of a similar magnitude overall most of the measured o2 flux into the sediment was used to oxidized reduced inorganic species and not organic carbon we suspect that the importance of o2 respiration in many coastal sediments has been overestimated whereas metal oxide reduction both fe and mn reduction has probably been well underestimated

seismic triggering of catastrophic failures on shear surfaces in saturated cohesionless soils this paper is concerned with an analysis of the seismic performance of infinite slopes in undrained conditions the material assumed on the sliding surface is a loose saturated sand susceptible to a gradual loss in undrained shear strength after failure with the progress of unidirectional shear displacement the undrained monotonic and cyclic shear behavior of this sand was investigated through an experimental study based on ring shear tests with initial stresses corresponding to the static conditions on the sliding surface of the analyzed slopes these tests provide the experimental framework for a modified sliding block method to estimate the earthquake induced undrained shear displacements for conditions of no shear stress reversals on the sliding surface the proposed estimation procedure incorporates the shearing resistance obtained from undrained monotonic ring shear tests to approximate the undrained yield resistance at a certain displacement during an earthquake the term catastrophic failure is

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

mineral chemistry of igneous melanite garnets from analcite bearing volcanic rocks alberta canada the mineral chemistry of melanite garnets from the crowsnest volcanic rocks of sw alberta canada has been investigated by using electron microprobe scans quantitative analyses and multivariate statistical analysis the garnets occur with aegirine augite sanidine analcite and rare plagioclase as phenocrysts in trachyte and phonolite flows agglomerates and tuffs wavelength dispersive microprobe scans reveal complex zonation patterns both normal and oscillatory the results of fifty quantitative analyses were subjected to r mode factor analysis to delineate the chemical exchanges producing the zonation the chemical zonation of the garnets may be attributed to four independent binary exchanges al fe3 si ti ca mn and mg fe2 the stoichiometry of these garnets based on microprobe and wet chemical fe analyses combined with the strongly antithetic behavior of si and ti lead us to infer that the ti in these garnets is dominantly tetravalent it is clear from this study that quantitative modelling of the processes of crystal growth and zonation of melanite garnets in alkaline undersaturated igneous rocks should be aimed at simulating the four chemical exchanges listed above

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

fault geometry at the rupture termination of the 1995 hyogo ken nanbu earthquake the source geometry and slip distribution at rupture termination of the 1995 hyogo ken nanbu earthquake were investigated using waveform inversion on the assumption of fault branching in the northeastern part of the rupture model possible branching of the okamoto fault is suggested both by the static displacement distribution and damage extension east of kobe nishinomiya area to exclude data contaminated by the basin edge diffracted wave in the waveform inversion process we examined the spatio temporal variation of its influence and from a comparison with a flat model we determined windows appropriate for the data three subevents were identified as was reported in previous works the largest was in the shallow part on the awaji side whereas the smaller two occurred at great depths 7km on the kobe side we found a smaller subevent in the deep part of the branch total variance reduction was larger and the abic value was smaller when we assumed the branch than when we did not which shows the superiority of the branching fault model resolution checks showed that the slips on proposed branched portions are physical and not caused by random data noise or systematic errors in green s func tions that arise from misestimation of velocity structures calculation of the relative static displacement between two leveling observation stations near the branching fault also showed the greater utility of the branching fault model the effect of slip on the branched fault has been shown in near source ground motion simulation using the 3d finite difference method iwata et al 1999 the characteristic distribution of ground motion in the near source region indicated by the damage distribution is well reproduced by the modeling of both the source process and wave propagation in the realistic 3d velocity structure slip on the branched fault affected the ground motion in eastern kobe nada and higashi nada wards ashiya and nishinomiya cities but its contribution is not dominant even in those regions about 30 to 50 maximum velocity in the frequency range of 0 1 to 1 0 hz we conclude that branching rupture of the okamoto fault during the hyogo ken nanbu earthquake is the preferable interpretation on the source process of this earth quake this supports the idea of a geometrical barrier suggested by geological ob servations

methanotrophs regulated atmospheric sulfur isotope anomalies during the mesoarchean tumbiana formation western australia abstract the 2 73 billion year old tumbiana formation of the fortescue group in the pilbara craton western australia preserves one of the best records of the fortescue negative carbon isotope excursion with organic 13 c values as low as 60 the prevailing environmental conditions at this biological excursion are not well understood here we present an integrated carbon 12 c 13 c and multiple sulfur 32 s 33 s 34 s 36 s isotopes study of a pristine diamond drill core through the tumbiana formation collected at meentheena by the pilbara drilling project our results show centimeter to meter scale heterogeneities in sulfur and carbon contents and isotope compositions organic 13 c values vary at the meter scale and display a bimodal distribution with peaks at about 44 and 34 this bimodal distribution is interpreted to reflect variations in the contribution of methanotrophic metabolism to the biomass the 34 s v cdt values of sedimentary pyrite vary from 5 73 to 2 75 sulfur isotopes sulfur contents and s c ratios are variable suggesting a complex local biotic sulfur cycling sedimentary pyrite preserves mass independent fractionation of sulfur mif s with 33 s v cdt ranging between 0 25 and 1 64 average 0 47 corresponding to the characteristic dampened mesoarchean anomalies positive correlation between sulfide mif s and a 13 c depletion of organic matter argues for a causal link between methanotrophs activity and the preservation of mif s anomalies in the rock record

spatial variability in oceanic redox structure 1 8 billion years ago the deposition of iron formations ceased about 1 84 billion years ago reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite inhibiting widespread iron oxide mineral deposition

source model of the 1995 hyogo ken nanbu earthquake and simulation of near source ground motion the 1995 hyogo ken nanbu earthquake struck the heavily populated kobe and adjacent cities in western japan more than 6400 people were killed and more than 150 000 buildings were destroyed the characteristics of mainshock ground motions in the heavily damaged area are needed to understand how buildings and bridges performed and why they reached failure unfortunately very few strong ground motions were recorded in the heavily damaged area during the mainshock in this study we attempt to estimate mainshock ground motions by using the em pirical green s function method egf method first we assume an initial source model with the asperities based on the rupture process obtained by inversion of strong ground motion records for simplicity we consider each asperity as a sub event with uniform stress drop in a finite extent then the initial model was improved by matching the synthetic and observed ground motions using a trial and error pro cedure the final model consists of three subevents subevent 1 with stress drop of 163 bars under the akashi strait around the rupture starting point subevent 2 with stress drop of 86 bars under the nojima fault in awaji island and subevent 3 with stress drop of 86 bars under kobe finally we estimate strong ground motions using aftershock records at sites where the mainshock was not recorded the near source motions in kobe synthesized with the best fit model are characterized by two large pulses with a duration of 1 to 3 sec the pulses are caused by forward rupture directivity effects from subevents 1 and 3 peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1000 cm sec 2 and 130 crrdsec respectively while those at a rock site in the near source region are about 300 crrdsec 2 and 60 cm sec

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

characteristics of dune bedded pyroclastic surge bedsets abstract the grainsize characteristics of dune bedded pyroclastic surge bedsets are surveyed the variance between coarsest and finest beds ranges from 1 to 6 phi in different surge bedsets and it increases as the grainsize of the coarsest bed increases reflecting an increasing velocity of emplacement deposits of wet surges identified as those which contain accretionary and ash coated lapilli tend to be finer and show less variance this partly because wet ash is cohesive but mainly because wet surges tend to be weaker dry surge bedsets are strongly fines depleted wet ones less so the lack of erosion of underlying ash layers shows that the environment is a strongly depositional one individual bedsets are demarcated by thin intervening fine ash fall layers which are the complementary ash cloud deposits settled or flushed out after the passage and decay of each turbulent surge surge deposits are generally less coarse than the coarsest associated airfall deposits which shows that they are formed by generally weaker events this study helps interpret the dune bedded parts of the landscape mantling may 18th 1980 blast deposit of mount st helens the blast was a very violent event but the variance and the grainsize of the coarsest bed are those of a relatively weak surge this suggests that the dune bedding was produced by a weak effect such as minor turbulence in a thin pyroclastic flow coming to rest in a mountainous terrain roughened by tree stumps and fallen logs

dynamic analysis of a slope failure from the 6 august 1979 coyote lake california earthquake abstract the coyote lake california earthquake of 6 august 1979 m l 5 7 provided a rare opportunity to perform a dynamic numerical analysis of a seismically induced slope failure using actual strong motion records the earthquake displaced a preexisting slump on the northeast shore of lake anderson and formed a fissure 20 m long offsets of 9 mm vertically and 18 mm horizontally were measured across the fissure the slump is 9 km northwest of the located epicenter but within 100 m of the mapped trace of the calaveras fault two strong motion records were written in the vicinity of the slump coyote creek 5 km to the southeast and gilroy 6 15 km to the southeast these records combined with field measurements of the slope estimates of the material properties and a dynamic numerical model based on the newmark analysis of seismic slope stability to calculate a predicted displacement for the landslide a displacement of 27 mm calculated using the n50 e component of the gilroy 6 record is in excellent agreement with the displacement measured in the field 21 mm however displacements of only 0 12 mm calculated using the 250 component of the coyote creek strong motion record reflect significant local variations in seismic shaking intensity because strong motion records and slope failures rarely coincide this landslide provides an important test case for our understanding of the dynamics of seismically induced landslides as well as a warning that local seismologic variations need to be considered in any design applications

mass dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles abstract sulfur isotope studies of post archean terrestrial materials have focused on the ratio 34s 32s because additional isotopes 33s and 36s were thought to carry little information beyond the well known mass dependent relationship among multiple isotope ratios we report high precision analyses of 33s and 36s values defined as deviations of 33s and 36s from ideal mass dependent relationships for international reference materials and sedimentary sulfides of phanerozoic age by using a fluorination technique with a dual inlet isotope ratio mass spectrometer measured variations in 33s and 36s are explained as resulting from processes involve branching reactions two or more reservoirs formed or mixing irreversible processes in closed systems rayleigh distillation amplify the isotope effect we outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation the isotope systematics discussed here cannot explain the much larger variation of 33s and 36s observed in archean rock records furthermore phanerozoic samples we have studied show a characteristic 33s and 36s relationship that differs from those measured in archean rocks and laboratory photolysis experiments thus high precision analysis of 33s and 36s can be used to distinguish small non zero 33s and 36s produced by mass dependent processes from those produced by mass independent processes in archean rocks and extraterrestrial materials

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved