a deep subaqueous fan depositional model for the palaeoarchaean 3 46 ga marble bar cherts warrawoona group western australia the 3 46 ga marble bar chert member of the east pilbara craton western australia is one of the earliest and best preserved sedimentary successions on earth here we interpret the finely laminated thin bedded cherts mixed conglomeratic beds chert breccia beds and chert folded beds of the marble bar chert member as the product of low density turbidity currents high density turbidity currents mass transport complexes and slumps respectively integrated into a channel levee depositional model the marble bar chert member constitutes the oldest documented deep sea fan on earth with thin bedded cherts breccia beds and slumps composing the outer levee facies tracts and scours and conglomeratic beds representing the channel systems

mechanisms of iron oxide transformations in hydrothermal systems abstract coexistence of magnetite and hematite in hydrothermal systems has often been used to constrain the redox potential of fluids assuming that the redox equilibrium is attained among all minerals and aqueous species however as temperature decreases disequilibrium mineral assemblages may occur due to the slow kinetics of reaction involving the minerals and fluids in this study we conducted a series of experiments in which hematite or magnetite was reacted with an acidic solution under h 2 rich hydrothermal conditions t 100 250 c p h 2 0 05 5 mpa to investigate the kinetics of redox and non redox transformations between hematite and magnetite and the mechanisms of iron oxide transformation under hydrothermal conditions the formation of euhedral crystals of hematite in 150 and 200 c experiments in which magnetite was used as the starting material indicates that non redox transformation of magnetite to hematite occurred within 24 h the chemical composition of the experimental solutions was controlled by the non redox transformation between magnetite and hematite throughout the experiments while solution compositions were controlled by the non redox transformation in the first 3 days in a 250 c experiment reductive dissolution of magnetite became important after 5 days and affected the solution chemistry at 100 c the presence of maghemite was indicated in the first 7 days based on these results equilibrium constants of non redox transformation between magnetite and hematite and those of non redox transformation between magnetite and maghemite were calculated our results suggest that the redox transformation of hematite to magnetite occurs in the following steps 1 reductive dissolution of hematite to fe aq 2 and 2 non redox transformation of hematite and fe aq 2 to magnetite

model test of failure modes of high embankment and aseismic measures for buried strike slip fault movement in this article a series of model tests for a scaled high embankment which is located at the yun gui railway have been carried out the purpose of the model tests was to ascertain failure modes of high embankments and the efficiency of the aseismic measures for buried strike slip fault movement the results show 1 failure mode of the high embankment for buried strike slip fault movement is the tensile failure 2 the model with cfg pile foundation sand blanket and geogrid has the best aseismic effect followed by the model with sand blanket and geogrid when dislocation displacement is small the sand blanket under the embankment can achieve better aseismic efficiency but when the dislocation displacement is large the sand blanket under the embankment may lose its aseismic efficiency and may cause an adverse effect on the embankment

evidence for free oxygen in the neoarchean ocean based on coupled iron molybdenum isotope fractionation abstract most geochemical proxies and models of atmospheric evolution suggest that the amount of free o2 in earth s atmosphere stayed below 10 5 present atmospheric level pal until the great oxidation event goe that occurred between 2 2 and 2 4 ga at which time free o2 in the atmosphere increased to approximately 10 1 to 10 2 pal although photosynthetically produced o2 oases have been proposed for the photic zone of the oceans prior to the goe it has been difficult to constrain absolute o2 concentrations and fluxes in such paleoenvironments here we constrain free o2 levels in the photic zone of a late archean marine basin by the combined use of fe and mo isotope systematics of ca mg carbonates and shales from the 2 68 to 2 50 ga campbellrand malmani carbonate platform of the kaapvaal craton in south africa correlated fe and mo isotope compositions require a key role for fe oxide precipitation via oxidation of aqueous fe ii by photosynthetically derived o2 followed by sorption of aqueous mo to the newly formed fe oxides a dispersion reaction model illustrates the effects of fe oxide production and mo sorption to fe oxides and suggests that a few to a few tens of m free o2 was available in the photic zone of the late archean marine basin consistent with some previous estimates the coupling of fe and mo isotope systematics provides a unique view into the processes that occurred in the ancient shallow ocean after production of free o2 began but prior to oxygenation of the deep ocean or significant accumulation of free o2 in the atmosphere these results require oxygenic photosynthesis to have evolved by at least 2 7 ga and suggest that the neoarchean ocean may have had a different oxygenation history than that of the atmosphere the data also suggest that the extensive iron formation deposition that occurred during this time was unlikely to have been produced by anoxygenic photosynthetic fe ii oxidation finally these data indicate that the ocean had significant amounts of o2 at least 150 myr prior to previously proposed whiffs of o2 at the archean to proterozoic transition

hematite formation by oxygenated groundwater more than 2 76 billion years ago geoscientific drilling in the marble bar area of the pilbara craton western australia resulted in the discovery of locally abundant hematite in archean basalts 200 m below the present land surface the hematized basalts occurring along a bedding parallel shear zone are cross cut by pyrite veinlets 3 mm in width and contain euhedral pyrite grains 10 500 m in diameter with sharp crystal edges indicating that the hematite formed before the pyrite we have dated the pyrite in the veinlets at 2 763 0 016 ga using the re os method therefore the hematite formed prior to 2 763 ga the basalts containing the hematite belong to the apex basalt of the warrawoona group and were erupted onto the archean seafloor at 3 46 ga due to 2 9 ga orogenic deformation and subsequent deep erosion the apex basalt was exposed at the surface of a continental landmass prior to 2 77 ga sometime in the period between 2 9 ga and 2 77 ga the basalt section we describe was less than 200 m below the late archean land surface and within range of groundwater percolation through the shear zone in the basalts geological mineralogical and geochemical lines of evidence strongly suggest that the infiltration of o2 rich groundwater through the bedding parallel shear in the basalts formed hematite prior to 2 76 ga and hence oxygenated surface environments at least localized and or short lived emerged more than 300 million years before the widely accepted great oxidation event during 2 45 and 2 32 ga

earthquake induced ground failures in italy abstract the national catalog of ground failures induced by strong earthquakes in italy cedit is described the catalog holds data on ground failures triggered by the earthquakes that occurred in italy in the last millennium and which had a nominal epicentral intensity equal to or greater than viii in the mercalli cancani sieberg mcs intensity scale the ground effects reported in the catalog are the following landslides fractures liquefaction surface faulting and topographic changes of the ground level subsidence settlements tilting and so on each effect is described in terms of seismological parameters of the triggering earthquake site coordinates and administrative code lithology and kinematic type of the ground failure the catalog represents a tool to assess the susceptibility of geologic materials to ground shaking and to validate predictive models of seismically induced ground displacements scenarios of earthquake induced geologic risks in the context of this study a simple statistical analysis of the database yielded useful relations between the parameters of the triggering earthquakes and the related effects

cellularly preserved microbial fossils from 3 4 ga deposits of south africa a testimony of early appearance of oxygenic life abstract fossil record of earliest earth s life is scant and restricted to simple kerogenous filaments spheres and lenticular microfossils which origin and taxonomic affiliation are still ambiguous here we report clusters of cell like bodies found in massive and weakly laminated black cherts of the 3 4 ga kromberg formation onverwacht group barberton greenstone belt south africa known earlier for benthic microbial mats and microfossils morphological traits and mineralization of the kromberg microfossils match those known from modern and fossil cyanobacteria micro raman and sem eds analyses showed that the cell like bodies fossilized mostly due to early mineralization with al silicates enclosing dispersed carbonaceous kerogenous matter derived from their thermally altered cell remains although in widespread opinion the early archean life is predominantly represented by benthic microbial mats the random non laminated distribution of the studied cyanobacteria like microfossils in the kromberg cherts is suggestive for probably benthic planktonic life cycle of these microbiota the paper also discusses how the morphological similarity of the kromberg fm cell like microfossils to geologically much younger and extant coccoidal cyanobacteria may influence the debate concerning the time of origin of earth s oxic atmosphere

reconciling seismic and geodetic models of the 1989 kilauea south flank earthquake 1 the inconsistency in depth between geodetic and seismic models of the 1989 kilauea earthquake has long been puzzling previous attempts to incorporate elastic heterogeneity have deepened geodetic models substantially bringing them closer to the seismic depth however recent studies that have included heterogeneity for other faults indicate that the effect is not so great we show here that elastic heterogeneity has a relatively minor effect on the geodetic model depth for this earthquake also however by combining three different sets of geodetic data we are able to get a more accurate estimate of the depth which does in fact coincide with the hypocentral depth at the 95 confidence level when we consider that static elastic parameter values are commonly less than dynamic values the agreement is even better furthermore the depth is consistent with the earthquake having occurred at the interface between the volcanic pile and the pre volcanic seafloor

u rich archaean sea floor sediments from greenland indications of 3700 ma oxygenic photosynthesis abstract 3700 ma metamorphosed pelagic shale from west greenland contains up to 0 4 wt reduced carbon with 13c values down to 25 6 pdb peedee belemnite the isotopic signature and mode of occurrence suggest that the carbon derived from planktonic organisms the pb isotopic composition shows that the shale had high primary u th this indicates that organic debris produced a local reducing environment which precipitated u transported to the site of sedimentation by oxidized ocean water the existence of highly productive plankton that fractionated c isotopes strongly and set up oxidation contrast in the environment suggests that oxygenic photosynthesis evolved before 3700 ma

stromatolite reef from the early archaean era of australia the 3 430 million year old strelley pool chert spc pilbara craton australia is a sedimentary rock formation containing laminated structures of probable biological origin stromatolites determining the biogenicity of such ancient fossils is the subject of ongoing debate however many obstacles to interpretation of the fossils are overcome in the spc because of the broad extent excellent preservation and morphological variety of its stromatolitic outcrops which provide comprehensive palaeontological information on a scale exceeding other rocks of such age here we present a multi kilometre scale palaeontological and palaeoenvironmental study of the spc in which we identify seven stromatolite morphotypes many previously undiscovered in different parts of a peritidal carbonate platform we undertake the first morphotype specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation finally we argue that the diversity complexity and environmental associations of the stromatolites describe patterns that in similar settings throughout earth s history reflect the presence of organisms

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

primary haematite formation in an oxygenated sea 3 46 billion years ago the timing of the origin of photosynthesis remains controversial the discovery of ancient haematite crystals that formed in a jasper formation in australia which was created in a marine setting suggests that oxygen was being produced at least locally by photosynthesis as early as 3 46 billion years ago

origin and global tectonic significance of early archean cherts from the marble bar greenstone belt pilbara craton western australia abstract five sections of bedded chert in mafic ultramafic rocks of the archean warrawoona group in the marble bar greenstone belt pilbara craton were analyzed in order to understand their depositional environment and to provide some constraints on early archean tectonics the sections are divisible into two types based on their field occurrence mineralogy and geochemistry thicker ones a and b that overlie fe rich low k tholeiites and thinner ones c1 c2 and c3 overlying komatiitic basalts the thickest ferruginous section a 45 m thick is the marble bar chert of the towers formation and is interpreted to have been an in situ precipitate derived from a high t hydrothermal solution emanating from a mid oceanic ridge mor the following geochemical features are similar to those of modern hydrothermal iron rich sediments at a mor i p v zn and y are positively correlated with fe ii a positive eu anomaly normalized to chondrite decreases from 6 6 to 1 3 and the magnitude of a negative ce anomaly decreases from 0 6 to 1 0 as ree and lree hree increase the 13 m thick b section in the apex basalt dominated by sio2 and containing significant amounts of ba up to 4330 ppm originated from a low t mor hydrothermal solution this section is characterized by an association with massive black gray silica veins that were hydrothermal feeders in normal fault zones in the spreading center geochemical evidence from the greenstones underlying the b section indicates that they are of morb origin in contrast to a and b c1 c2 and c3 sections are intercalated conformably with komatiitic basalts of the apex basalt and are 3 6 m thick the geochemical signatures of these three sections suggest that they were most likely formed by low t weak hydrothermal activity that may have been associated with hot spot volcanism they show strong enrichment of cr and ni reflecting a significant contribution of komatiitic basaltic detritus during sedimentation the presence of volcaniclastic chert in their uppermost beds indicates a decrease of hydrothermal silica precipitation due to waning hydrothermal activity among the three sections the uppermost c3 exhibits greater enrichment in zr nb hf and th and higher th sc and la yb n relative to the lower c1 and c2 sections this could mean that the depositional environment of c3 was relatively closer to a continent or to island arcs composed of granitoids and or their volcanic equivalents siliceous mudstones and sandstones of the uppermost clastic rocks t section panorama formation have geochemical signatures analogous to those of felsic plutonic volcanic rocks high th sc negative eu anomalies and high ree in some siliceous mudstones from this unit imply that differentiated granitoids or volcanic equivalents were already exposed erupted at least locally in the pilbara at this time this study shows these warrawoona group cherts were deposited in a variety of environments ranging from a mid oceanic spreading center to a convergent plate boundary via a hot spot this variation was most likely due to horizontal plate motions which accordingly support the operation of plate tectonics in the early archean

research on time frequency analysis method of active earth pressure of rigid retaining wall subjected to earthquake aiming at the drawback existing in the analysis methods of seismic active earth pressure of rigid retaining wall the time frequency computational method is proposed based on the elastic wave theory and hilbert huang transform which is full 3d nonlinear time history analysis method it not only can consider the effect of three factors peak ground acceleration frequency and duration of the bidirectional seismic wave on the seismic active earth pressure but also can provide some valuable references for the time frequency seismic design of other types of retaining structures the reasonability of this method is verified by the shaking table test results and it is more accurate than some representative methods such as limit equilibrium method and coordinated deformation method at last some rules and conclusions can be obtained by the parameters study as shown in the following with the increase in pga the critical rupture angle decreases the resultant force of seismic active earth pressure increases and its application point of resultant force gradually moves up with the increase in frequency the critical rupture angle and the resultant force of seismic active earth pressure are distributed in the shape of saddle and the handstand saddle respectively and they achieve the maximum value when the frequency is close to natural frequency of rigid retaining wall but the application point essentially is unchanged

decoupling photochemical fe ii oxidation from shallow water bif deposition abstract oxidized fe minerals in archean paleoproterozoic banded iron formations bifs are commonly taken to indicate the presence of biogenic o 2 or photosynthetic fe ii oxidizing bacteria in the oceans photic zone however at least one viable abiogenic oxidation mechanism has been proposed prior to the rise of atmospheric oxygen and the development of a protective ozone layer the earth s surface was subjected to high levels of ultraviolet radiation bulk ocean waters that were anoxic at this time could have supported high concentrations of dissolved fe ii under such conditions dissolved ferrous iron species such as fe 2 and fe oh would have absorbed radiation in the 200 400 nm range leading to the formation of dissolved ferric iron fe iii which in turn would have hydrolyzed to form ferric hydroxide fe oh 3 at circumneutral ph cairns smith a g 1978 precambrian solution photochemistry inverse segregation and banded iron formations nature 76 807 808 braterman p s cairns smith a g and sloper r w 1983 photo oxidation of hydrated fe 2 significance for banded iron formations nature 303 163 164 this process has been invoked to account for bif deposition without need for biology francois l m 1986 extensive deposition of banded iron formations was possible without photosynthesis nature 320 352 354 here we evaluate the potential importance of photochemical oxidation using a combination of experiments and thermodynamic models the experiments simulate the chemistry of ambient precambrian seawater mixing with fe ii rich hydrothermal fluids with and without uv irradiation we find that if fe ii was effused from relatively shallow seamount type vent systems directly into an anoxic photic zone the photochemical contribution to solid phase precipitation would have been negligible instead most of the fe ii would have precipitated rapidly as an amorphous precursor phase to the ferrous silicate mineral greenalite fe 3 si 2 o 5 oh 4 and or the ferrous carbonate siderite feco 3 depending on different simulated atmospheric pco 2 levels conversely in experiments where fe ii was exposed either to phototrophic fe ii oxidizing bacteria or to o 2 ferric hydroxide formed rapidly and the precipitation of ferrous iron phases was not observed if as suggested on mass balance grounds bif deposition requires that fe be sourced from shallow seamount type systems then we are driven to conclude that oxide facies bif are the product of a rapid non photochemical oxidative process the most likely candidates being direct or indirect biological oxidation and that a significant fraction of bif could have initially been deposited as ferrous minerals

u th pb isotope data indicate phanerozoic age for oxidation of the 3 4 ga apex basalt abstract the occurrence of ferric oxides in archean rocks has played an important role in discussions on the amount of free oxygen in the atmosphere of the ancient earth recognizing that post archean weathering may also produce oxide minerals drill cores have been used to obtain samples beneath the depth of phanerozoic weathering the first core of the archean biosphere drilling project abdp 1 documented hematite as alteration products in 3 4 ga basalts from the marble bar area of the pilbara craton nw australia and this has been used to infer the presence of an o2 bearing atmosphere in the archean it is possible however that despite recovery of samples from 100 m depth oxidation of the basalts occurred much younger than the depositional age in this study the age of oxidation of the apex basalt from the abdp 1 drill core at marble bar is constrained by u th pb geochronology lead and u concentrations of the basalts from the abdp 1 drill core vary greatly between

numerical simulation and shaking table test of geotextile bag retaining wall structure this study analyzed the dynamic behavior of flexible retaining walls constructed with geotextile bags the behavior of geotextile bag retaining wall system was simulated using a large scale shaking table in which 1 g n of one directional dynamic load was applied the dynamic behavior of the retaining wall was analyzed with simulated ground consisting of a geotextile bag in which 0 154 0 44 g n of ground acceleration was applied using historic and artificial seismic waves by el centro and hachinohe dynamic characteristics of the geotextile bag retaining wall structure in response to acceleration displacement and earth pressure were also analyzed based on results of large scale shaking table test and numerical analysis with the finite element method results showed that the dynamic active earth pressure increased with increasing ground acceleration at an action point of 0 6 h in addition the higher the point of passive positive earth pressure and the lower the increment of active positive earth pressure the more gradual the slope of the geotextile bag retaining wall

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

influence of weathering and hydrothermal alteration on the ree and δ56fe composition of iron formation caue formation iron quadrangle brazil abstract continental margin superior type iron formation of the caue formation iron quadrangle brazil is composed of a laminated magnetite rich chemical meta mudstone that was altered during hydrothermal circulation of basinal fluids greenschist to amphibolite facies metamorphism and subsequent supergene enrichment of fe the absence of traction current deposits and storm generated structures suggests that deposition occurred on the distal shelf possibly as deep as the continental slope paragenesis based lithogeochemical analyses of two drill cores with contrasting alteration styles highlight the importance of hydrothermal metamorphic and supergene processes on the rare earth element plus yttrium ree y and 56fe compositions of iron formation the first drill core penetrates to a depth of 540 m in the ouro fino syncline ofs where lithofacies have experienced intense hydrothermal and supergene alteration the second core is from the gandarela syncline gs and contains 450 m of metamorphosed iron formation that has undergone later supergene enrichment of fe petrographically euhedral to subhedral magnetite in the ofs and gs is fabric destructive and depending on the style and degree of alteration can co occur with dolomite siderite goethite and or martite synsedimentary magnetite and other primary fe oxide phases are absent the effect of supergene enrichment and weathering is best captured along the depth profile of each core by the inverse relationship between sio2 and fe2o3 sio2 values are lowest and fe2o3 values highest near the surface the presence of goethite to 500 m records the maximum depth of these processes in the subsurface the ree y and y anomalies from the deepest and least altered lithofacies in both cores are typical of deposition in a redox stratified water column the weathered lithofacies show several changes in the ree y patterns ce anomalies and absence of y anomalies caused mainly by fluid percolation the change in fe isotopic composition with depth is more complex in drill core from the ofs negative 56fe values shift from 0 91 at depth to less negative values of 0 6 near the surface the most altered samples do not lie on this trend because they are characterized by positive values of 0 30 and 1 33 the 56fe values from the gs increase linearly from 0 11 to 1 23 towards the surface with the most negative values 0 7 and 1 16 near the top the most negative values from the ofs could reflect synsedimentary microbial dissimilatory fe reduction and the positive values from the gs may be related to partial fe2 oxidation between the hydrothermal fe source and fe oxyhydr oxides however when interpreted together with mineralogical and ree data these data likely record the various alteration processes that affected the caue iron formation such findings highlight the importance of coupling sedimentologic analysis with elemental and isotopic chemistry to understand iron formation deposition and fe ore forming processes

outcrop versus core and geophysical log interpretation of mid cretaceous paleosols from the dakota formation of kansas abstract paleosols of the mid cretaceous late albian to early cenomanian dakota formation in kansas and nebraska are well exposed in road river and clay pit exposures but show systematic overprinting by modern weathering examination of deep drill cores reveals that modern weathering effects include 1 oxidation of pyrite to jarosite 2 reaction of jarosite and calcite to clear selenite and 3 oxidation of sphaerosiderite and siderite nodules to hematite surface oxidation in this region extends no deeper than 2 m from the surface hematite nodules and coatings of leaves are found in core only at one stratigraphic horizon which was not as appears in outcrop a laterite transformed matrix density and photoelectric absorption logs of cores reveal that kaolinite clays are most abundant within deeply weathered paleosols sayela pedotype at this stratigraphic level near the albian cenomanian boundary when angiosperm forests were especially diverse and lived in a subtropical humid climate other paleosols of the early cenomanian were less deeply weathered and fossil plants of this age included temperate humid angiosperm mangal and swamp woodland but conifer dominated floodplain forests this short lived mid cretaceous warm wet spike has also been recognized in other paleosols of minnesota utah nevada and new mexico and coincides with marine black shale of the breitstroffer event midcontinental marine transgression a sequence stratigraphic boundary and a marked increase in early angiosperm diversity

research on time frequency analysis method of seismic stability of covering layer type slope subjected to complex wave aiming at the covering layer type slope a new analysis method of seismic slope stability is put forward and its rationality is verified by using results of shaking table tests and numerical simulations this method can consider the effect of shaking duration and frequency and amplitude of the seismic waves on the stability of the slope at the same time the results of shaking table tests and the numerical simulations show that the sliding process of the two side slope is a balanced and progressive process and the landslide mechanism analysis results show that non consistent movement and reduction of strength of the structural plane are two of the major influence factors which induce the landslide

continuous uplift near the seaward edge of the prince william sound megathrust middleton island alaska middleton island located at the seaward edge of the continental shelf 50 km from the base of the inner wall of the aleutian trench affords an opportunity to make land based measurements of uplift near the toe of the prince william sound megathrust site of the 1964 m 9 2 alaska earthquake leveling surveys 1973 1993 on middleton island indicate roughly uniform tilting 1 rad a down to the northwest of the island and gps surveys 1993 2012 show an uplift rate of 14 mm a of the island relative to fixed north america the data are consistent with a combined coseismic and postseismic uplift in meters due to the 1964 earthquake as a function of time years after the earthquake u 3 5 1 21 log10 1 1 67 h where 3 5 is the coseismic uplift and h is 0 for 0 and 1 otherwise the current uplift on middleton island is attributed to continuous slip on a fault splaying off from the megathrust and the long term uplift is the superposition of the effects of past earthquakes each earthquake being similar to the 1964 event then the predicted uplift at time t due to a sequence of earthquakes at times ti would be iut ti from studies of strandlines associated with the uplifted terraces on middleton island plafker et al 1992 estimated the occurrence times of the last six earthquakes and measured the present day elevations of those strandlines the predicted uplift is in rough agreement with those measurements about half of the predicted uplift is due to postseismic relaxation from previous earthquakes

biogeochemistry deepening the early oxygen debate the timing of the earliest production of oxygen by photosynthesis is hotly debated haematite crystals from pilbara australia may provide evidence for a deep ocean that was at least occasionally oxygenated by photosynthetic microbes 3 46 billion years ago

seismic passive earth pressure coefficients for sands by taking the failure surface as a combination of the arc of a logarithmic spiral and a straight line passive earth pressure coefficients in the presence of horizontal pseudostatic earthquake body forces have been computed for an inclined wall placed against cohesionless backfill material the presence of seismic forces induces a considerable reduction in the passive earth resistance the reduction increases with an increase in the magnitude of the earthquake acceleration the effect becomes more predominant for loose sands the obtained results compared well with those reported in the literature using curved failure surfaces however the results available in the literature on the basis of a planar failure surface are found to predict comparatively higher passive resistance

geochemical constraints on the genesis of the ekou banded iron formation shanxi province north china the ekou banded iron formation bif in the wutai area is hosted within the late archean baizhiyan formation the mineral assemblage is used to identify oxide and silicate facies the oxide facies is composed of magnetite and quartz and the silicate facies is characterized by the presence of silicate minerals a geochemical analysis shows that the major elemental compositions are dominantly sio2 and fe2o3t with very little al2o3 and tio2 and minor abundances of incompatible elements and transition elements these results indicate that negligible terrigenous materials were involved in the bif deposition the rare earth elements rees normalized by post archean australian shale exhibit the characteristics of light ree lree depletion heavy ree hree enrichment and positive la y and eu anomalies the y ho ratios are superchondritic these results indicate that the material that formed the ekou bif originated from the mixing of seawater and submarine hydrothermal fluids a ce anomaly deficiency and heavy fe isotope enrichment indicate that the ekou bif formed in an anoxic marine environment the 30sinbs 28 values for quartz in the ekou bif are similar to those of other bifs with distribution ranges of modern sinters and black smokers the 18ov smow distribution is similar to that of hydrothermal sedimentary siliceous rocks these results suggest that the formation of the ekou bif was closely connected to submarine volcanic exhalation activity

nonredox transformations of magnetite hematite in hydrothermal systems the transformation of magnetite to hematite or hematite to magnetite in nature has generally been considered a redox reaction and linked to a specific redox state of fluid however a nonredox reaction fe2o3 hm fe2 h2o fe3o4 mt 2h may have been the principal mechanism for the transformations of iron oxides in nature especially in hydrothermal environments for example the transformation of goethite and or hematite primary precipitates to magnetite in banded iron formations bifs probably occurred through nonredox reactions with fe2 bearing hydrothermal fluids during the accumulation of a bif sequence rather than through redox reactions involving organic matter during and or after the bif deposition the proposed mechanisms for the transformation of magnetite to hematite provides new exploration strategies for hematite rich secondary ores extending the target for orebodies to much deeper zones below the paleosurface another important implication of the proposed mechanism is that the presence or absence of magnetite and or hematite in geologic formations may or may not provide meaningful information on the redox state of fluid

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

hematite replacement of iron bearing precursor sediments in the 3 46 b y old marble bar chert pilbara craton australia the history of atmospheric oxygen prior to the great oxidation event 2 45 2 2 ga is not well understood hematite in the marble bar chert from a nasa funded drill hole abdp1 in the pilbara craton australia has been cited as evidence for an oxygenated ocean 3 46 b y ago however isotopic data from the same drill hole have been used to argue for an anoxic ocean it is generally agreed that the hematite is primary representing either a direct hydrothermal precipitate or a dehydration product of iron oxyhydroxides that formed during anoxygenic photosynthesis here we present new petrographic evidence from the marble bar chert in drill hole abdp1 that shows that hematite in jasper bands formed via mineral replacement reactions the hematite mostly occurs as sub micron sized inclusions within chert so called dusty hematite that are typically arranged into polygonal clusters surrounded by a rim of clear quartz resembling shrinkage structures the lateral transition from laminated chert enclosing minute inclusions of greenalite siderite and magnetite to chert dominated by dusty hematite provides evidence for in situ replacement of iron bearing minerals the presence of hematite rich bands containing octahedral crystals with residual cores of magnetite indicates that some of the hematite was derived from the replacement of magnetite this interpretation is supported by the widespread occurrence of magnetite in jasper displaying progressive stages of replacement from unaltered octahedral inclusions in quartz to hematite pseudomorphs along quartz grain boundaries the occurrence of dusty hematite in fractures sedimentary laminae and the outer margins of polygonal clusters containing greenalite is consistent with fluid mediated oxidation of iron rich precursor minerals the presence of syn sedimentary chert breccias comprising rotated fragments of laminated chert indicates that the precursor sediment was silicified shortly after deposition the abundance of dusty greenalite inclusions which are texturally the earliest components of the laminated chert suggests that the precursor sediment contained an iron rich clay mineral our results show that hematite has replaced ferrous rich minerals after deposition and provide a mechanism to explain the origin of hematite in the marble bar chert which is consistent with the origin of hematite in adjacent basalts a secondary origin for hematite invalidates arguments for an oxygen bearing ocean 3 46 b y ago and provides a viable explanation for the formation of archean jasper bands our findings show that misinterpretations about the origin of hematite in early precambrian cherts could lead to false conclusions about the chemistry of the ancient ocean and atmosphere

oxygenation of the earth s atmosphere ocean system a review of physical and chemical sedimentologic responses abstract the great oxidation event goe is one of the most significant changes in seawater and atmospheric chemistry in earth history this rise in oxygen occurred between ca 2 4 and 2 3 ga and set the stage for oxidative chemical weathering wholesale changes in ocean chemistry and the evolution of multicelluar life most of what is known about this important event and the subsequent oxygenation history of the precambrian earth is based on either geochemistry or data mining published literature to understand the temporal abundance of bioelemental sediments bioelemental sediments include iron formation chert and phosphorite which are precipitates of the nutrient elements fe si and p respectively because biological processes leading to their accumulation often produce organic rich sediment black shale can also be included in the bioelemental spectrum thus chemistry of bioelemental sediments potentially holds clues to the oxygenation of the earth because they are not simply recorders of geologic processes but intimately involved in earth system evolution chemical proxies such as redox sensitive trace elements cu cr v cd mo u y zn and ree s and the ratio of stable isotopes 56fe 53cr 97 95mo 98 95mo 34s 33s in bioelemental sediments are now routinely used to infer the oxygenation history of paleo seawater the most robust of these is the mass independent fractionation of sulfur isotopes mif which is thought to have persisted under essentially anoxic conditions until the onset of the goe at ca 2 4 ga since most of these proxies are derived from authigenic minerals reflecting pore water composition extrapolating the chemistry of seawater from synsedimentary precipitates must be done cautiously paleoenvironmental context is critical to understanding whether geochemical trends during earth s oxygenation represent truly global or merely local environmental conditions to make this determination it is important to appreciate chemical data are primarily from authigenic minerals that are diagenetically altered and often metamorphosed because relatively few studies consider alteration in detail our ability to measure geochemical anomalies through the goe now surpasses our capacity to adequately understand them in this review we highlight the need for careful consideration of the role sedimentology stratigraphy alteration and basin geology play in controlling the geochemistry of bioelemental sediments such an approach will fine tune what is known about the goe because it permits the systematic evaluation of basin type and oceanography on geochemistry this technique also provides information on how basin hydrology and post depositional fluid movement alters bioelemental sediments thus a primary aim of any investigation focused on prominent intervals of earth history should be the integration of geochemistry with sedimentology and basin evolution to provide a more robust explanation of geochemical proxies and ocean atmosphere evolution

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

deep submarine pyroclastic eruptions theory and predicted landforms and deposits submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows however that significant pyroclastic activity can occur even at depths in excess of 3000 m in order to document and illustrate the full range of submarine eruption styles we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions 1 no gas exsolution 2 gas exsolution but no magma disruption 3 gas exsolution magma disruption and hawaiian style fountaining 4 volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse 5 magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity and 6 volatile content builds up in the top of a dike leading to vulcanian eruptions we also examine the role of bulk interaction steam explosivity and contact surface steam explosivity as processes contributing to volcaniclastic formation in these environments we concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities the most likely circumstance is the quiet effusion of magma with minor gas exsolution and the production of somewhat vesicular pillow lavas or sheet flows depending on effusion rate the amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption the most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity due to the localized concentration of volatiles in magma that has a low rise rate magmatic gas collects by bubble coalescence and ascends in large isolated bubbles which disrupt the magma surface in the vent producing localized blocks bombs and pyroclastic deposits another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions these deposits being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater should be easily distinguishable from strombolian and hawaiian eruptions however we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles in this case a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian style activity the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile induced hawaiian eruption specifically typical pyroclast sizes might be smaller fountain heights may exceed those expected for the purely magmatic hawaiian case cooling of descending pyroclasts would be more efficient leading to different types of proximal deposits and runout distances for density flows would be greater potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer in addition flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles and thus extremely poor in vesicles relative to typical flows associated with hawaiian style eruptions in the primary magmatic gas case we examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid ocean ridges furthermore the latter stages of development of volcanic edifices seamounts formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth but also to 1 the presence of a summit magma reservoir which favors the buildup of magmatic foams enhancing hawaiian style activity and episodic dike emplacement which favors strombolian style eruptions and 2 the common occurrence of alkalic basalts the co2 contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts these models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles

episodic negative anomalies of cerium at the depositional onset of the 2 65 ga itabira iron formation quadrilatero ferrifero of minas gerais brazil abstract magnetite bands in sericitic phyllite of the batatal formation mark the transition to the overlying 2 65 ga itabira iron formation or caue itabirite in the quadrilatero ferrifero of minas gerais brazil the magnetite bands have low non crustal th u ratios suprachondritic y ho ratios and sporadic anomalies of ce that are characterised as truly negative the data point to mild oxygenation of sea water at the depositional onset of the itabira iron formation some 200 ma before the great oxidation event

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

landslides induced by the 2008 wenchuan earthquake sichuan china the 2008 wenchuan earthquake with a magnitude of mw 7 9 induced numerous slope movements on the hanging walls of fault surface ruptures and on steep inner valleys along the minjiang river landslide moving directions showed preferred orientations normal to the fault ruptures indicating the effect of the directivity of the seismic wave the most common landslides were of carbonate rocks which are easily dissolved and decrease the contact surfaces the largest non volcanic landslide in history was induced in bedded dolomite by the earthquake and was preceded by gravitational deformation with ridge top depressions valley fill materials were mobilized at 36 locations probably by pore water pressure build up

the use of chromium reduction in the analysis of organic carbon and inorganic sulfur isotope compositions in archean rocks one of the most serious issues with deciphering the evolution of organisms and their biogeochemical environments from the ancient rock record is the difficulty in obtaining well preserved samples although not much can be done to avoid diagenetic and metamorphic alteration when they have occurred alteration due to weathering can be avoided by working on drill core samples this implies however that the amount of sample is limited which may in turn restrain the number of possible chemical and isotopic analyses that can be performed in order to save sample we show here that the chemical protocol used for the sulfur sulfide extraction for later sulfur isotope analyses is also suitable to decarbonate samples for later organic carbon isotope analyses in the case of carbonated rocks both sulfur sulfide extraction and decarbonation require high amounts of sample so that coupling them may save a significant amount of sample and time in addition it allows both organic carbon toc and 13c and sulfur isotope composition measurements to be performed on the exact same powder which is essential when trying to understand couplings between s and c cycles in heterogeneous samples we thus tested the efficiency of the acidic chromium solution commonly used to extract sulfur from sulfide for sample decarbonation on various archean rocks our results show that no significant carbon isotope fractionation is caused by this new decarbonation protocol even for the samples with low organic carbon content the chromium solution seems to be perfectly adapted for the analysis of organic matter in the ancient rock record at least when the rock samples have experienced low greenschist facies metamorphism further tests will be needed to verify if this protocol can also be used for less mature organic matter

microtremor measurements for the microzonation of dinar the geotechnical site conditions in dinar town located in western turkey were investigated after the 1995 dinar earthquake based on borings in situ penetration tests seismic wave velocity measurements and microtremor records the variation of damage distribution within the town was evaluated with respect to 23 district damage ratios calculated based on the detailed damage survey conducted by the general directorate of disaster affairs site amplifications were estimated from microtremor spectral ratios and microzonation was performed using a gis methodology the results of in situ penetration tests and seismic wave velocity measurements as well as the damage distribution were compared with the amplification zonation obtained from microtremor records the results indicate the applicability of microtremor spectral ratios for assessing the local site conditions and site amplifications

fe isotopes of a 2 4 ga hematite rich if constrain marine redox conditions around the goe abstract the hematite and manganese rich hotazel iron formation griqualand west basin south africa was deposited at a key moment in time close to the goe between 2 4 and 2 3 ga it stratigraphically overlies the ongeluk formation comprising thick flood basalts which in turn interfinger with and cover the makganyene formation diamictites the inferred remnants of the first paleoproterozoic snowball earth interval no extensive research has been conducted to date on the basal part of the hotazel formation due to poor exposure though it constitutes an important link between a period of large scale ice cover extensive volcanism and the onset of atmospheric oxygenation here we present a detailed petrographic geochemical and fe isotope study of a roughly 3 metre long drill core exposing the ongeluk to hotazel contact our results show that after the cessation of ongeluk volcanism primary precipitation of fe iii oxyhydroxides from the photic surface zone of the original basin became the dominant sedimentation mechanism negative 56fe values between 0 26 and 0 50 in micro drilled hematite rich chert indicate that surface water 56fe compositions at the time of deposition were depleted yet 56fe and bulk rock fe mn values are still substantially higher 1 2 than those reported higher up in the mn rich layers of the hotazel sequence suggesting that redox potentials were still comparatively limited during the earliest stages of the hotazel depositional environment the base of the hotazel formation thus forms a transitional interval between precipitation from essentially ferruginous seawater as recorded in the ghaap group bifs and from isotopically and chemically highly evolved surface waters as demonstrated by the hotazel mn rich layers in the absence of fe ii as a strong reducing agent large volumes of photosynthetic oxygen may have eventually escaped into the atmosphere leading to the onset of atmospheric oxygenation our results thus contradict previous models that place the onset of the goe before the hotazel formation concurrent with and mechanistically linked to the makganyene and ongeluk events instead we show that the hotazel basal sediments are still pre goe consistent with their circa 2 4 ga age and the continuation of mif s higher in the stratigraphic record

strain accumulation across the prince william sound asperity southcentral alaska the surface velocities predicted by the conventional subduction model are compared to velocities measured in a gps array surveyed in 1993 1995 1997 2000 and 2004 spanning the prince william sound asperity the observed velocities in the comparison have been corrected to remove the contributions from postseismic 1964 alaska earthquake mantle relaxation except at the most seaward monument located on middleton island at the seaward edge of the continental shelf just 50 km landward of the deformation front in the aleutian trench the corrected velocities qualitatively agree with those predicted by an improved two dimensional back slip subduction model in which the locked megathrust coincides with the plate interface identified by seismic refraction surveys and the back slip rate is equal to the plate convergence rate a better fit to the corrected velocities is furnished by either a back slip rate 20 greater than the plate convergence rate or a 30 shallower megathrust the shallow megathrust in the latter fit may be an artifact of the uniform half space earth model used in the inversion backslip at the plate convergence rate on the megathrust mapped by refraction surveys would fit the data as well if the rigidity of the underthrust plate was twice that of the overlying plate a rigidity contrast higher than expected the anomalous motion at middleton island is attributed to continuous slip at near the plate convergence rate on a postulated listric fault that splays off the megathrust at depth of about 12 km and outcrops on the continental slope south southeast of middleton island

early earth microbes and the rise of oxygen reconstructions of atmospheric chemistry and microbial life early in the earth s history have been contentious observations increasingly point to the evolution of complex and variable environments earlier in time

coseismic slip distribution of the 2002 mw7 9 denali fault earthquake alaska determined from gps measurements 1 on 3 november 2002 an mw7 9 earthquake occurred in central alaska the earthquake ruptured portions of the susitna glacier denali and totschunda faults inversion of the gps measured displacement field indicates that the event was dominated by a complex right lateral strike slip rupture along the denali fault gps sites closest to the epicenter show the effect of thrust motion on the susitna glacier fault the preferred coseismic slip model with m w 7 8 indicates relatively low slip on the western part of the rupture and high slip from about 60 km east of the hypocenter extending to the junction of the denali and totschunda faults we find mostly shallow slip from the surface to 15 km depth but the inversion suggests one large deep slip patch about 110 km east of the hypocenter our model predicts surface slip in good agreement with surface geological observations where model resolution is good

experimental evidence for non redox transformations between magnetite and hematite under h2 rich hydrothermal conditions abstract transformations of magnetite fe ii fe 2 iii o 4 to hematite fe 2 iii o 3 and vice versa have been thought by many scientists and engineers to require molecular o 2 and or h 2 thus the presence of magnetite and or hematite in rocks has been linked to a specific oxidation environment however the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions here we report the results of hydrothermal experiments in mildly acidic and h 2 rich aqueous solutions at 150 c which demonstrate that transformations of magnetite to hematite and hematite to magnetite occur rapidly without involving molecular o 2 or h 2 fe 3 o 4 mt 2h aq fe 2 o 3 hm fe aq 2 h 2 o the transformation products are chemically and structurally homogeneous and typically occur as euhedral single crystals much larger than the precursor minerals this suggests that in addition to the expected release of aqueous ferrous species to solution the transformations involve release of aqueous ferric species from the precursor oxides to the solution which reprecipitate without being reduced by h 2 these redox independent transformations may have been responsible for the formation of some iron oxides in natural systems such as high grade hematite ores that developed from banded iron formations bifs hematite rich deposits formed on mars corrosion products in power plants and other industrial systems

modern weathering in outcrop samples versus ancient paleoredox information in drill core samples from a mesoarchaean marine oxygen oasis in pongola supergroup south africa there is growing evidence from mo and fe stable isotope tracers that shallow water sediments of the 2 95 ga mozaan group pongola supergroup in south africa were deposited under oxidizing conditions while mineralogical elemental and s isotopic evidence favors the contemporaneous atmosphere to have remained reducing in contrast the first reported cr stable isotope data for white mfolozi riverbed outcrop samples of the ijzermijn iron formation if mozaan group and drill core samples of the underlying paleosol of the nsuze group were interpreted to require oxidative weathering conditions during the time of deposition more recent cr isotope data of at least the ijzermijn if samples of the same white mfolozi riverbed outcrop however suggested that modern weathering effects can superimpose oxidative signatures on paleo redox proxies this study compares 234u 238u activity ratios along with stable mo and fe isotope data of corresponding drill core and white mfolozi riverbed outcrop samples in order i to test 234u 238u disequilibria as a potential tool to identify samples affected by modern weathering and ii to further investigate weathering effects on outcrop samples particularly with regard to the stable mo and fe isotope systematics all drill core samples from the ijzermijn if have 234u 238u activity ratios that are within uncertainties of secular equilibrium i e a value of 1 and thus were not significantly affected by modern weathering related u gain or loss or other sub recent rock water interaction by contrast the outcrop if and shale samples from the white mfolozi riverbed show very strong deviations from the secular equilibrium 234u 238u activity ratio furthermore these deviations are accompanied by the observations that i outcrop samples have on average heavier 56 54fe values 0 96 than drill cores 1 59 and ii positive correlations in drill core samples between log fe mn and 98 95mo or 56 54fe are disrupted by inclusion of the outcrop samples as are negative correlations between log mno and 98 95mo however 56 54fe and 98 95mo of our outcrop samples do not correlate with the extent of 234u 238u disequilibria as such 234u 238u activity ratios fail to act as a direct identification tool for modern weathering effects on stable fe and mo isotopes in outcrop samples overall this study confirms the adsorption of isotopically light mo onto mno2 particles in oxic surface water conditions in the epicontinental pongola sea reduction of the mn oxides together with microbial fe reduction in the reduced sediment pile of the pongola basin led to the formation of mn and fe carbonates during early diagenesis storing the observed stable fe and mo isotopic signatures we thus extend the so called mno2 shuttle first proposed for the neoarchean 2 46 ga old koegas if to late mesoarchean shallow marine depositional settings

biological fe oxidation controlled deposition of banded iron formation in the ca 3770 ma isua supracrustal belt west greenland the redox balance of the archean atmosphere ocean system is among the most significant uncertainties in our understanding of the earliest history of earth s surface zone most workers agree that oxygen did not constitute a significant proportion of the atmosphere until after ca 2 45 ga after the great oxidation event but there is less agreement on when o2 production began and how this may have been consumed by reduced species such as fe ii in the oceans the fe redox cycle through time has been traced using banded iron formations bifs and fe isotopes are increasingly used to constrain the conditions of earth s paleoenvironments including the pathways of formation of bifs iron isotope analyses of bifs from the 3 7 to 3 8 ga isua supracrustal belt isb obtained by micro sampling of magnetite rich layers and conventional analysis as well as by in situ femtosecond laser ablation fs la icp ms indicate a consistently narrow range of non zero 56fe values analysis of magnetite by fs la icp ms allows for precise and accurate micron scale analyses without the problems of orientation effects that are associated with secondary ion mass spectrometry sims analyses magnetite 56fe values range from 0 4 to 1 1 among different bands but within individual layers magnetite grains are mostly homogeneous although these bifs have been metamorphosed to amphibolite facies the metamorphism can neither explain the range in fe isotope compositions across bands nor that between hand samples the isotopic compositions therefore reflect primary low temperature sedimentary values the positive 56fe values measured from the isb magnetites are best explained by deposition of fe iii oxides produced by partial oxidation of fe ii rich ocean water a dispersion reaction model which accounts for rates of hydrothermal fe ii aq input rates of oxidation and rates of fe oh 3 settling suggests exceptionally low o2 contents 0 001 of modern o2 contents in the photic zone such low levels suggest an anoxygenic pathway is more likely and the data can be well modeled by anoxygenic photosynthetic fe ii oxidation comparison of the fe isotope data from the isua bifs with those from the 2 5 ga bifs from the hamersley and transvaal basins australia and south africa respectively suggests a striking difference in fe sources and pathways the 2 5 ga magnetite facies bifs of australia and south africa have 56fe values that range from 1 2 to 1 2 over small scales and are on average close to 0 which is significantly lower than those reported here from the isua bifs the wide range in fe isotope compositions for the hamersley and transvaal bifs in concert with c and o isotope data have been interpreted to reflect bacterial dissimilatory fe iii reduction dir the absence of low 56fe values in the isua bifs as well as the lack of fine scale isotopic heterogeneity may indicate formation prior to widespread dir

post depositional ree mobility in a paleoarchean banded iron formation revealed by la ce geochronology a cautionary tale for signals of ancient oxygenation abstract precambrian banded iron formations bif are chemical sedimentary deposits whose trace element signatures have been widely used to interrogate the chemical composition and redox state of ancient seawater here we investigated trace element signatures in bif of the 3 22 ga moodies group barberton greenstone belt south africa which are interbedded with near shore siliciclastic sedimentary rocks and represent one of the oldest known shallow water occurrences of bif unusual rare earth element ree signatures notably with pronounced negative ce anomalies in shale normalized spectra have been previously reported for chemical sediments of the moodies group which we confirm here through an expanded dataset for moodies bif spanning three different localities we find negative ce anomalies as low as 0 2 ce ce that are associated with unusual enrichment of lree relative to hree in the sample set while total ree abundances and certain ree features appear strongly related to the concentration of detrital indicators e g zr and are likely primary other features notably lree enrichment cannot be explained as a primary feature of the sediment this is better explained by later addition of ree from a lree enriched but ce depleted fluid that generated the significant negative ce anomalies observed in surface samples of moodies group bif this ree addition event influenced both sm nd and la ce isotope systematics the latter yielding an isochron of 60 32 ma thus constraining the timing of emplacement of the negative ce anomalies to the past 100 ma possibly upon surface exposure of the barberton greenstone belt to wetter conditions during the cenozoic our findings constitute a cautionary tale in that even the most immobile elemental redox proxies may be more sensitive to post depositional modification than previously thought and demonstrate the clear advantage offered by paleoredox proxies coupled to radiometric geochronometers to enable the direct dating of ancient signals of earth surface oxygenation

time frequency analysis method of acceleration amplification along hillslope based on elastic wave theory the time frequency analysis method of acceleration amplification along the hillslope is derived by using hilbert huang transform combined with modal analysis method and orthogonal theory its reasonability is verified by the results of shaking table test and numerical simulation this method can not only analyse the effect of peak ground acceleration frequency and duration of seismic waves on acceleration amplification along hillslope but also illustrate whiplash effect of hill theoretically

displacements and tilts from dip slip faults and magma chambers beneath irregular surface topography surface displacements and tilts due to buried deformation sources are influenced by topography the leading order corrections due to topography of arbitrary profile but small slope are determined for dip slip faults edge dislocations and magma bodies lines of inflation in a two dimensional elastic medium the vertical displacement correction is simply the product of the topography and the horizontal normal strain due to the source in a flat half space the correction for a normal fault beneath an idealized basin and range topography is a slight increase in the uplift on the range side the effect of topography for a line of inflation beneath a symmetric volcano is to reduce the central uplift failure to account for topographic influences can bias estimates of source depth and geometry