seismic potential of the dead sea fault in the northern gulf of aqaba elat new evidence from liquefaction seismic reflection and paleoseismic data abstract the cities of elat israel and neighboring aqaba jordan are major economic cultural and seaport centers they are located on the northern shore of the gulf of aqaba elat gae directly on the dead sea transform yet the precise location of the fault trace and its tectonic activity are lacking the interpretation of seismic reflection profiles across the gae beach and paleoseismic trench data located 2 2 km north of the shoreline provide evidence that the active offshore mapped avrona fault extends onland along the eastern side of the elat sabkha mudflat where three prominent fault strands crosscut the sedimentary fill mismatch of reflector geometry across the faults and flower structures indicate strike slip faulting with a normal slip component subsurface data from two trenching sites provide evidence for a minimum of two surface ruptures and two paleoliquefaction events faulting is constrained by radiocarbon dating for an event 1 between 897 and 992 ce and event 2 after 1294 ce we suggest that the historically documented 1068 ce and at least one later earthquake in 1458 or 1588 ce ruptured the elat sabkha site based on fault mapping we suggest a minimum value of m 6 6 for the 1068 ce earthquake whereas no surface rupture was observed for the 1212 ce historical earthquake fluidized strata radiocarbon dated to before 1269 1389 ce identified as paleoliquefaction may be attributed to it two liquefaction sand blows mapped in the trench likely formed after 1337 ce and before 1550 ce which possibly occurred at the same time as in the second faulting event our data suggest that no large event occurred along the avrona segment in the past 430 550 years given a 5 mm yr slip rate we conclude that a significant period of time passed since the last surface rupturing on the avrona fault increasing its seismic potential

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

gaw khuni basin an active stepover structure in the sanandaj sirjan zone iran the gaw khuni basin is located in the central part of the sanandaj sirjan zone on the northeastern margin of the zagros orogen this basin is one of the continuous zones of sanandaj sirjan zone basins that is filled by pliocene holocene sediments the gaw khuni basin is surrounded by an en echelon to parallel arrangement of active faults in dextral strike slip fault zones that indicate a right step dilational stepover structure the boundary faults of this basin are the eastern and western gaw khuni ramsheh and nain dehshir faults earthquake distribution determined along the faults dissection and displacement of holocene sediments and also the development of pull apart basins filled with holocene deposits along the faults confirm that these faults are active the gaw khuni stepover was formed during transtensional movements produced between two dextral strike slip faults nain dehshir and ramsheh also the gaw khuni pull apart basin and the eastern and western gaw khuni faults developed in a releasing step between the faults and grew in two directions during the time of their formation

phosphogenesis and weathering of shelf sediments from the southeastern united states implications for miocene δ13c excursions and global cooling the enormous phosphorite deposits of the southeastern united states indicate intense upwelling but contain small amounts of organic carbon the authors propose that deposition of organic rich sediment on continental shelves in the southeastern united states and elsewhere during marine transgressions in the late oligocene and early to middle miocene resulted in global positive delta sup 13 c shifts and the formation of early diagenetic phosphorite multiple reworking and supergene weathering from subaerial exposure during miocene marine regressions oxidized most of the organic carbon and resulted in the return of delta sup 13 c to its preexcursion value the estimated phosphorite content of the southeastern united states requires sufficient organic carbon burial 10 sup 15 kg carbon to support a 1 per thousand delta sup 13 c excursions sea level fluctuations organic carbon burial phosphogenic episodes and possibly global cooling during the cenozoic

seismic imaging of the three dimensional architecture of the cinarcik basin along the north anatolian fault the cinarcik basin is a transtensional basin located along the northern branch of the northern north anatolian fault naf in the sea of marmara the eastern half of which has been identified as a seismic gap during the seismarmara 2001 experiment a dense grid of multichannel seismic reflection profiles was shot covering the whole cinarcik basin and its margins the new seismic images provide a nearly three dimensional view of the architecture of the basin fault system at depth and sedimentary infill and provide insight into its tectonic evolution along both northern and southern margins of the basin seismic reflection data show deep penetrating faults hence long lived features which have accommodated a large amount of extension there is no indication in the data for a single throughgoing strike slip fault neither a cross basin fault nor a pure strike slip fault running along the northern margin faster opening is presently observed in the eastern part of the basin the cinarcik basin seems to have developed as a transtensional basin across strike slip segments of the northern naf for the last few million years

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

strain partitioning and stress perturbation around stepovers and bends of strike slip faults numerical results abstract stepovers and bends along strike slip faults are where push up ranges and pull apart basins are formed they are also commonly where fault ruptures terminate field study and analogue models suggest that the configuration of faults plays a key role in crustal deformation around bends and stepovers but the related mechanics of stress perturbation strain partitioning and fault evolution remains poorly understood here we present results of systematical mechanical models of stress changes and strain partitioning around simple stepovers and bends using three dimensional viscoelasto plastic finite element code our model predicts elevated deviatoric stress around all stepovers and bends with higher stresses around the restraining ones narrow stepovers localize strain between the fault gaps to form connecting faults whereas wide stepovers localize strain on the tips of fault segments so the stepovers may evolve into subparallel faults we explored how various configurations of stepovers and bends change the stress field and strain distribution and show that these results can help explain some key differences between the pull apart basins in the dead sea trough and death valley and the push up ranges along the san andreas fault

high spatial resolution in vertical slice ocean acoustic tomography most studies of ocean acoustic tomography have assumed that little horizontal information is available from the many acoustic multipath travel times observed in a single vertical plane slice between source and receiver moorings there is in fact significant small scale information present in such data sets we examine single vertical slice tomography in spectral terms and show that the acoustic measurements resemble a high pass filter which is more sensitive to small scales shorter than 100 km than to longer scales with the exception of the mean which is well measured the sensitivity extends to scales smaller than 10 km in theory although the level of the ocean energy spectrum is so low at these scales that even small data errors limit the measurement we use analytical calculations supplemented by numerical simulations with realistic data sets to show that accurate reconstructions of the high wave number features are possible out to the limits of the parameterization 9 2 km wavelength when the power spectrum of the ocean features is white or red the total measurement error is 1 ms and multiple receivers are used the ultimate limit of spatial resolution may be smaller still depending on array configuration measurement errors and the shape of the power spectrum

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

relationship between tectonism and volcanism along the great sumatran fault zone deduced by spot image analyses abstract satellite images provide evidence for numerous stepovers pull apart grabens and volcanic structures along the nw trending right lateral great sumatran fault zone high resolution spot images permit us to analyze the relationship between volcanic and tectonic structures this analysis reveals that releasing stepovers and pull aparts are ephemeral structures along the great sumatran fault zone and that the geometry of the strike slip fault evolves permanently through time the interpretative structural maps obtained from spot image analysis reveal that the formation of huge peculiarly shaped volcanic calderas has occurred in large releasing stepover fault zones and that the bounding faults of rectangular pull apart basins are analogous to the circular ring faults of calderas in particular detailed study of the segments at the southernmost 150 km long termination of the great sumatran fault zone from northwest of ranau lake to semangka bay allows us to describe the development of the ranau collapse caldera this caldera is located within a pull apart basin bounded by a stepover its peculiar rectangular shape and its relatively large size about 200 km 2 are controlled by the evolution of the extinct ranau releasing stepover similarly the toba elliptical caldera one of the largest volcanic caldera in the world is elongated parallel to the present trace of the great sumatran fault and appears to be related to a releasing stepover associated with a wide pull apart basin that is not active at present

organic matter apatite pyrite relationships in the botneheia formation middle triassic of eastern svalbard relevance to the formation of petroleum source rocks in the nw barents sea shelf abstract the middle triassic botneheia formation of eastern svalbard edgeoya and barentsoya comprises an organic carbon rich fine grained clastic succession 100 m thick that makes the best petroleum source rock horizon in the nw barents sea shelf the succession records a transgressive regressive interplay between the prodelta depositional system sourced in the southern barents sea shelf black shale facies of the lower and middle parts of the muen member and the open shelf phosphogenic system related to upwelling and nutrient supply from the panthalassic ocean phosphogenic black shale facies of the upper part of the muen member and the blanknuten member the relationships between organic matter authigenic apatite and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation the accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing upward productivity related to early transgressive phase and retrogradation of the prodelta system the phosphogenic black shale facies deposited in an oxygen minimum zone omz of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity suppressed sedimentation rates and changing bottom redox the phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of omz including high input of autochthonous organic matter into sediment oxic to dysoxic episodically suboxic and or anoxic conditions intense phosphogenesis and recurrent reworking of the seabed the massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of omz during high stand of the sea high input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis in mature sections in eastern svalbard the petroleum potential of the botneheia formation rises from moderate to good in the black shale facies and from good to very good in the phosphogenic black shale facies attaining maximum in the massive phosphatic mudstone

rapid creation and destruction of sedimentary basins on mature strike slip faults an example from the offshore alpine fault new zealand abstract seismic reflection profiles and multibeam bathymetric data are integrated to analyse the structure of the 25 km long strike slip dagg basin associated with the marine section of the alpine fault fiordland new zealand the basin is developing in almost 3000 m water depth at a releasing bend whilst contemporaneous transpression results in inversion of its southern end fiord derived glacio marine sediments flooded the basin during the last glaciation and provide a stratigraphic framework for structural analysis geometrical analysis enables an estimation of 450 1650 m of dextral displacement on the alpine fault at the releasing bend since the development of an unconformity estimated to have formed at between 30 and 110 ka this implies a dextral slip rate ranging from a possible minimum of 4 mm yr to the maximum of 35 mm yr constrained by the pacific australian plate motion rate despite total dextral displacement of 480 km on the alpine fault zone and a growth history spanning 15 20 myr this geomorphically well expressed and structurally complex strike slip basin developed and evolved rapidly during the late pleistocene and thus represents only the latest phase in the evolution of the alpine fault upward splaying structures within the fault zone exhibit a rapid spatial evolution in pleistocene strata which may reflect the interactions between high fault slip rate voluminous sedimentation supply inherited structural complexities in the basement rocks and deeper cover sequence and interactions between adjacent faults the present through going releasing bend at the northern end of the basin may have evolved from a more complex pull apart basin that developed between separate segments of the alpine fault the results from dagg basin illustrate the rates at which structural complexities and sedimentary basins can develop within highly active very mature through going continental wrench faults strike slip basins on the scale of 40 80 km 2 on such faults may be ephemeral features that can be developed and destroyed on a time scale of 10 5 10 6 years

miocene to recent cariaco basin offshore venezuela structure tectonosequences and basin forming mechanisms abstract the cariaco basin located 40 km off the central part of the coast of venezuela is the largest 4000 km 2 and bathymetrically deepest 1400 m bsl neogene fault bounded basin within the right lateral strike slip plate boundary zone that separates the caribbean and south american plates using subsurface geophysical data we test two previously proposed tectonic models for the age distribution and nature of east west striking strike slip faults and basin forming mechanism for the two main depocenters of the cariaco basin the earliest interpretation for the opening of the twin cariaco depocenters by schubert 1982 proposes that both depocenters formed synchronously by extension along transverse north south normal faults at a 30 km wide rhomboidally shaped pull apart basin between the right lateral east west striking and parallel san sebastian and el pilar fault zones a later model by ben avraham and zoback 1992 proposes that both depocenters formed synchronously by a process of transform normal parallel extension or rifting in a north south direction orthogonal to the east west striking and parallel strike slip faults we use more than 4000 km of 2d single and multi channel seismic data tied to 11 wells to map 5 tectono stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both cariaco depocenters evolved from paleogene to the present comparison of fault and isopach maps for dated horizons from paleogene to late neogene in age show three main phases in basin development 1 from middle miocene to pliocene the west cariaco basin formed as a rhomboidally shaped pull apart at a 30 km wide stepover between the northern branch of the san sebastian fault and the el pilar fault zone 2 during the early pliocene a new strike slip fault transected the west cariaco basin southern branch of the san sebastian fault and caused extension to cease and 3 during the early pliocene to recent a lazy z shaped pull apart formed along the curving connection between the southern branch of the san sebastian and el pilar fault zones

anthropogenic versus natural control on trace element and sr nd pb isotope stratigraphy in peat sediments of southeast florida usa 1500 ad to present abstract analysis of a well dated peat core from blue cypress marsh bcm provides a detailed record of natural and anthropogenic factors that controlled the geochemical cycles of a number of trace elements in florida over the last five centuries the trace elements were divided into natural and anthropogenic groups using concentration trends from the bottom to the top of the core the natural group includes li sc cr co ga ge zr nb cs ba hf y ta th and ree rare earth elements these elements show similar concentrations throughout the core indicating that changes in human activities after european arrival in the new world did not affect their geochemical cycles the anthropogenic group includes pb cu zn v sb sn bi and cd upcore enrichment of these elements indicates enhancement by anthropogenic activities from the early 1500s to present fluxes of the anthropogenic metals to the marsh increased significantly with modern accumulation rates several fold e g v to hundreds of times e g zn greater than pre colonial rates the dominant input mechanism for trace elements from both groups to the marsh has been atmospheric deposition atmospheric input of a number of the elements including the anthropogenic metals was dominated by local sources during the last century for several elements long distant transport may be important for instance ree and nd isotopes provide evidence for long range atmospheric transport dominated by saharan dust the greatest increase in flux of the anthropogenic metals occurred during the 20th century and was caused by changes in the chemical composition of atmospheric deposition entering the marsh increased atmospheric inputs were a consequence of several anthropogenic activities including fossil fuel combustion coal and oil agricultural activities and quarrying and mining operations pb and v exhibit similar trends with peak accumulation rates in 1970 the principal anthropogenic source of v is oil combustion the decline in v accumulation after 1970 in the bcm peat corresponds to the introduction of low sulfur fuels and the change from heavy to distilled oils since the 1970s after the 1920s pb distribution in the peat follows closely the history of alkyl lead consumption in the us which peaked in the 1970s pb isotopes support this inference and furthermore record changes in the ore sources used to produce leaded gasoline idaho ores dominated the peat pb isotope record until the 1960s followed by pb from mississippi valley type deposits from the 1960s to the 1980s enhanced fluxes of cu zn cd sn sb bi and to some extent ni during the last century are likely also related to fossil fuel combustion local agricultural activities may also have influenced the geochemical cycles of cu and zn the peat record shows enhanced u accumulation during the last century possibly related to phosphate mining in western florida sr isotopes in the peat core also reflect anthropogenic influence the 87sr 86sr ratio decreases from natural background values in the basal part of the core to lower values in the upper part of the core the sr isotope shift is probably related to quarrying operations in florida and marks the first time an anthropogenic signal has been detected using the sr isotope record in a peat core

growing folds and sedimentation of the gosau group muttekopf northern calcareous alps austria analysis of the three dimensional geometry of upper cretaceous clastics in the muttekopf area northern calcareous alps austria indicate fold and fault structures active during deposition coniacian continental to neritic sedimentation lower gosau subgroup was contemporaneous with displacements on nw trending faults and minor folding along ne trending axes from the santonian onwards sedimentation of the deep marine upper gosau subgroup the nw trending faults were sealed and large folds with wsw trending axes developed the direction of contraction changed to n s after the end of gosau deposition in the danian paleocene synorogenic sedimentation patterns indicate continuous contraction from the coniacian to the late maastrichtian danian therefore large scale extension as observed in the central part of the eastern alps cannot be documented in the western parts of the northern calcareous alps a combination of subduction tectonic erosion for the frontal parts and gravitational adjustment of an unstable orogen after nappe stacking for the internal parts possibly accounts for the different development of gosau basins in the frontal and trailing regions of the austroalpine wedge

long range inversions for ocean acoustic tomography ocean acoustic tomography was proposed by munk and wunsch 1979 as a method for making measurements of ocean variability over large areas after the successful demonstration of the feasibility of the idea in the 1981 three dimensional mesoscale experiment ocean tomography group 1982 the tomography group has proposed a new experiment to be carried out in 1986 in the eastern pacific ocean on ranges as long as the subtropical gyre scale in this paper the gyre scale experiment is simulated in the model ocean using holland s eddy resolving general circulation quasi geostrophic model the paper addresses the following issues 1 measurement of the heat content vertical profile horizontally averaged along the tomographic section 2 adequacy of the linearized inverse over very long ranges and the need for its improvement 3 possible improvements in the specification of the field statistics to obtain more accurate estimates and to measure properties like average pycnocline trends 4 relationship of possible range dependent information from the inversion to the assigned noise level the results of the modeling simulation can be summarized as follows 1 the linearized stochastic inversion needs to be improved for gyre scale ranges providing estimates of the average heat content that have warm or cold biases iteration is used and shown to provide good estimates of the average heat content 2 a smaller number of iterations is necessary if the initial estimate is improved this can be done by including a spatial mean in the horizontal covariance function for regions of the ocean where the energy level in the mean and in the long length scales may be even more important than the mesoscale energy peak 3 general trends like average pycnocline slopes can be estimated very well by including an inhomogeneous covariance in the inversion 4 the estimates of the mean heat content values and of the average slopes are rather insensitive to the specified noise level 5 the type and number of eigenrays used is not a critical factor in the inversion estimates as long as the eigenrays provide a good sampling of the interior water mass increasing the number of eigenrays does not significantly improve the estimate of the average values 6 range dependent information is primarily a function of the assigned noise for too high a noise the basic quantities that can be measured are the mean value and the average trend

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

long range propagation of sound through oceanic mesoscale structures assumptions related to the feasibility of ocean acoustic tomography are investigated utilizing range dependent sound speed profiles the models include a warm midocean eddy and a cold core gulf stream ring superposed on a latitudinal geographic variation covering 1000 km the results show that changes in the acoustic travel times produced by mesoscale features can be nonlinear that the ray paths are substantially displaced by a mesoscale eddy and that information from a single source and receiver can be used to infer the distance to a mesoscale disturbance

fluorine mobility during early diagenesis of carbonate sediment an indicator of mineral transformations abstract the abundant occurrence of calcium carbonate minerals in marine sediment their well documented dissolution or precipitation during diagenesis and their high f content suggest that carbonate mineral diagenesis may be an important influence on f behavior in marine sediment to test this hypothesis we have examined the geochemistry of f in shallow carbonate mud bank sediment of florida bay usa the f content of biogenic calcium carbonate in florida bay varies with mineralogy positively correlates with the mg content of calcite and occurs in similar abundance to sr high mg calcite f sr 2 4 mol mol aragonite 0 53 0 79 mol mol low mg calcite 0 22 mol mol models of porewater distributions direct solute flux measurements and reaction rate estimates over the upper 0 16 cm of sediment from bob allen key bank predict net fluxes out of the sediment of 170 mol f m2 d 230 mol sr m2 d and 5 6 mmol ca m2 d the net solute flux ratio of f sr 0 71 mol mol is consistent with dissolution of aragonite or high mg calcite but f ca and sr ca ratios 28 mmol mol and 40 mmol mol respectively are 3 10 that of biogenic carbonate sources selective dissolution of a high f and sr content phase or more likely based on dissolution experiments concurrent dissolution and reprecipitation of phases with different f and sr contents account for this discrepancy the loss of f sr and ca to fluorapatite precipitation as predicted from a stoichiometric model of phosphate release can be added to the transport reaction model predicted net fluxes a resulting more complete mass balance model incorporating both carbonate mineral reactions and fluorapatite formation yields total release estimates of f sr and ca of 770 mol 332 mol and 53 mmol m2 d respectively calcium carbonate minerals apparently undergo transformation whereby 34 mmol high mg calcite m2 d and 19 mmol aragonite m2 d dissolve and 46 mmol low mg calcite m2 d precipitates ignoring other cations besides ca if no fluorapatite formation occurs the required fluxes are that 23 mmol aragonite m2 d dissolves and 3 4 mmol high mg calcite m2 d and 14 mmol low mg calcite m2 d precipitate net loss of caco3 from the deposit by dissolution is 6 7 mmol m2 d 3 of the accumulation flux the magnitude of these fluxes could cause significant mineralogical and chemical changes on rapid time scales in nearshore carbonate sediment fluorine is probably mobile in other carbonate deposits undergoing diagenetic alteration on short and longer time scales and is a powerful additional constraint on the rates and nature of carbonate mineral diagenesis

carbon isotopic composition and lattice bound carbonate of peru chile margin phosphorites new light stable carbonate carbon isotope and lattice bound co2 data from quaternary peru chile margin phosphatic nodules crusts and pelletal grains and from associated dolomicritic concretions are presented which provide constraints on the timing and mechanisms of growth of these phases in organic carbon rich sediments comparison of 13c values from carbonate fluorapatite cfa nodules and pelletal grains 4 8 to 0 0 and 2 9 to 1 0 pdb respectively with pore water total dissolved 13c values from these sediments suggests early authigenic cfa precipitation from pore waters within a few centimeters of the sediment water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter in contrast the dolomicritic cores of nodules recovered from about 12 s display both strongly negative to positive 13c values 10 8 to 6 1 characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes the amount of structural carbonate in cfa suggests that carbonate substitution generally increases as 13c in cfa decreases a probable consequence of increasing carbonate and accompanying charge balancing substitutions in the cfa lattice in response to increasing pore water carbonate ion concentrations with depth below the sediment water interface in one buried upward growing nodule decreasing cfa 13c and increasing structural co2 also correspond to decreasing cfa growth rates these data suggest that in addition to other constraints such as pore water phosphorus and fluoride availability the lower limit of cfa precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations in organic rich peru chile margin sediments this depth threshold appears to be at approximately 5 10 cm below the sediment water interface where maximum cfa co2 contents of about 6 wt occur in less organic rich settings greater depths of precipitation of cfa may be anticipated below this relatively shallow depth of cfa precipitation on the peru shelf high pore water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates

a comparison of measured and predicted broadband acoustic arrival patterns in travel time depth coordinates at 1000 km range broadband acoustic signals were transmitted from a moored 250 hz source to a 3 km long vertical line array of hydrophones 1000 km distant in the eastern north pacific ocean during july 1989 the sound speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph xbt conductivity temperature depth ctd and air launched expendable bathythermograph axbt casts while the transmissions were in progress this experiment is unique in combining a vertical receiving array that extends over much of the water column extensive concurrent environmental measurements and broadband signals designed to measure acoustic travel times with 1 ms precision the time mean travel times of the early raylike arrivals which are evident as wave fronts sweeping across the receiving array and the time mean of the times at which the acoustic reception ends the final cutoffs for hydrophones near the sound channel axis are consistent with ray predictions based on the direct measurements of temperature and salinity within measurement uncertainty the comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km which is not resolved by the direct measurements significantly 25 ms peak to peak affects the time mean ray travel times the final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100 200 m off the sound channel axis nongeometric effects such as diffraction at caustics partially account for this observation

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

recurrent patterns in surface thermal fronts associated with cold filaments along the west coast of north america abstract previous studies indicate that cold filaments off northern california have sharp southern s type and diffuse northern d type thermal boundaries in this study 44 avhrr satellite images taken from three coastal regions in the california current system northern central and baja california over a period of 10 years were used to examine the regional variation in surface frontal structure associated with cold filaments the images were specifically chose from months where past mean wind conditions indicated upwelling occurred because cold filaments appear to be more abundant during the upwelling season the images also were chosen to provide independent realizations of filament structure distributions of average gradient magnitude as a function of gradient angle were used to provide a more compact representation of the frontal information contained in each image an analysis of these distributions shows that the sharp diffuse boundary structure associated with cold filaments observed in shipboard data dominates the total surface frontal structure found in satellite data for two of the three regions studied the recurrent ubiquitous patterns found in the satellite determined frontal structure are discussed in terms of their potential effects on acoustic propagation and regional implications on ecological community structure in the california current system

extinction of pull apart basins numerous pull apart basins are present along the haiyuan fault zone in northwestern china detailed geological mapping of these basins reveals an evolution of faulting and subsidence that leads toward extinction of some pull apart basins the most common cause of pull apart basin extinction appears to be the development of new strike slip faults along one of the basin margin normal faults or diagonally across the basin the strike slip faults may develop together with normal faults to form a complex zone within the basin the migration of boundary strike slip faults toward the basin center can also cause the extinction of pull apart basins the extinction of these pull apart basins suggests that there is probably a tendency for a strike slip fault zone to straighten itself and the examples show how this takes place

4d analogue modelling of transtensional pull apart basins abstract scaled sandbox models were used to investigate the 4d evolution of pull apart basins formed above underlapping releasing stepovers in both pure strike slip and transtensional basement fault systems serial sectioning and 3d volume reconstruction permitted analysis of the full 3d fault geometries results show that very different pull apart basins are developed in transtension compared to pure strike slip both types of models produced elongate sigmoidal to rhomboidal pull apart systems but the transtensional pull apart basins were significantly wider and uniquely developed a basin margin of en echelon oblique extensional faults dual opposing depocentres formed in the transtensional model whereas a single central depocentre formed in pure strike slip in transtension a distinct narrow graben system formed above the principal displacement zones pdzs cross basin fault systems that linked the offset pdzs formed earlier in the transtensional models sequential model runs to higher pdz displacements allowed the progressive evolution of the fault systems to be evaluated in cross section transtensional pull aparts initiated as asymmetric grabens bounded by planar oblique extensional faults with increasing displacement on the pdzs basin subsidence caused these faults to become concave upwards and lower in dip angle due to fault block collapse towards the interior of the basin in addition strain partitioning caused fault slip to become either predominantly extensional or strike slip the models compare closely with the geometries of natural pull apart basins including the southern dead sea fault system and the vienna basin austria

role of a ductile decollement in the development of pull apart basins experimental results and natural examples abstract traditional models describe pull apart basins as graben or half graben basins with normal or normal oblique slip master faults analogous to death valley california yet many pull aparts are characterized by asymmetric basins with strike slip master faults indicating that not all pull apart basins conform to the simple death valley models we present analogue modelling results that show developmental sequences and structural styles of pull aparts are dramatically different when overburden rides over a ductile horizon and that thickness of the ductile horizon exerts control on basin development in our models synthetic and antithetic strike slip faults control basin geometries while localized normal faulting and local oblique slip on strike slip faults accommodate basin subsidence faults evolve from initial strike slip to normal oblique and normal dip slip to form a system of either isolated sub basins in the case of thick ductile layers or coalescing sub basins in the case of thin ductile layers these results demonstrate distinct differences between non ductile and ductile decollement pull apart structures basin boundaries dominated by normal faults suggest a decollement within or at the base of a non ductile layer similar to death valley california basin bounding faults dominated by strike slip and oblique slip faults indicate basin formation over a ductile layer similar to the gulf of elat aqaba or gulf of paria venezuela and trinidad

northward migration of the southern diagonal fault of the hula pull apart basin dead sea transform northern israel abstract the hula valley located in northeastern israel is a 4 million year old pull apart basin bounded by two left stepped segments of the dead sea transform basic models of pull apart basins suggest four faults at all sides of the basin a situation which is not always the case in the hula pull apart basin the longitudinal n s faults are clearly evident while the transversal e w faults are less explicit an nw oriented lineament expressed as a north facing continuous scarp 1 3 m high was recognized in the southern part of the valley morphological seismic and sedimentary considerations suggest that this scarp is the surface expression of a deep seated fault this fault termed the yesod hama ala fault forms the present southern boundary of the hula pull apart basin and appears to be the southern diagonal fault which links the jordan fault in the east with the yammunneh fault in the west it is suggested that this fault scarp formed a shallow morphological barrier that partly blocked the southern outlet of the valley enabling a permanent lake in the southern part of the hula valley thus the uplifted southern block determined the sw shoreline of the lake it is proposed that the hula basin is a version of the classic pull apart model it is also suggested that in the absence of upwelling mantle material and extension along the length of the basin a crustal thinning and subsidence might have occurred through normal faulting of the upper brittle crust the thick depositional sequence within the southern part of the basin shows that the present margins have been a major depositional site for a long time and that the hula valley has thus developed as an asymmetric pull apart rhomb shaped basin bounded by steep north striking boundary normal as well as strike slip faults w nw striking and northward dipping normal faults and a south facing bending flexure as activity within the basin continued and northward migration of the faulting occurred a new fault developed according to this perception the present active fault is the yesod hama ala fault while the future fault will be located northward as can be presumed from the present micro seismic activity in the valley

strike slip faulting in the central part of the sanandaj sirjan zone zagros orogen iran abstract the sanandaj sirjan zone ssz is one of the main basement tectonic blocks located close to the northeastern margin of the zagros orogenic belt new observations in the central part of the zone indicate that the fault pattern is dominated by nw trending longitudinal faults the components of movement on the fault planes are interpreted as dextral oblique thrusting and dextral strike slip the identified structures along the faults were associated with the strike slip faults e g hasan robat and najafabad dextral restraining stepovers and rotated tectonic blocks arranged in a domino configuration near to the foladshahr and kolah ghazi mountains along the longitudinal faults the dextral offsets of the rock units streams alluvial deposits and rivers were measured the dextral offset values range from 2 4 to 2 7 km while the estimated offsets based on the geomorphological features are between 50 and 61 m for streams up to approximately 50 m for alluvial deposits and up to 2 2 km for rivers the dextral strike slip component on the fault planes occurs along the northern and southern margins of the ssz as well as directly within the zone west and east of the study area the evidence for strike slip faulting in the internal part of the zone suggests that the central part of the ssz probably was horizontally sheared in a manner consistent with a simple shear card deck model

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

a review of ocean acoustic tomography 1987 1990 the techniques and instruments used in acoustic tomography of the oceans are surveyed and results are summarized sections are devoted to theoretical studies and numerical simulations mesoscale mapping vertical slice tomography flow imaging and nonlinear bias series of tomographic experiments analyses to identify global changes and outstanding problems the forward and inverse problems and ocean physics typical data are presented in tables and graphs and a comprehensive bibliography is provided 72 refs

quaternary tectonic evolution of the northern gulf of elat aqaba along the dead sea transform the northern gulf of elat aqaba is located in the transition between the deep marine basins of the gulf and the shallow onland basins of the arava valley interpretation of 500 km of high resolution seismic reflection data collected across the northern shelf reveals the tectonic structure and evolution of this transition six nne trending faults and one e w trending transverse fault are mapped slip rates are calculated based on measured offsets and age determination based on a radiocarbon calibrated sedimentation rate and a quaternary age model the most active fault is the evrona fault that absorbs most of the left lateral slip within the basin with an average sinistral slip rate of 0 7 0 3 mm yr through the late pleistocene and 2 3 3 4 mm yr during the holocene two intrabasin faults east of the evrona fault that have been inactive for the last several tens of thousands of years were mapped and motion from these faults has likely transferred to the evrona fault the basin is flanked on the west by the elat fault and on the east by the aqaba fault both faults are marked by large bathymetric escarpments based on displaced seismic reflectors we calculate a holocene vertical slip rate of 1 0 0 2 and 0 4 0 1 mm yr for the elat and aqaba faults respectively the geometry slip rates and slip history of the northern gulf of elat aqaba faults show that during the late pleistocene several intrabasin faults became dominant across the basin but that during the holocene the evrona fault accommodates most of the strike slip

sr and nd isotopic analysis of phosphorite sedimentation through one miocene high frequency depositional cycle on the north carolina continental shelf abstract a well developed seismic litho and biostratigraphic data base with good models for the formation and deposition of phosphate rich sediments exist for the upper cenozoic sediments on the north carolina continental margin this provides a unique opportunity to evaluate the potential of utilizing strontium and neodymium isotopic analyses to help unravel a complex genetic history of phosphate formation and deposition thirty one samples from three vibracores in onslow bay supplied hand picked concentrate subsamples of five phosphate grain types and thirty one concentrate subsamples of phosphate peloids for stratigraphic analysis all subsamples were analyzed for their sr isotope composition while only thirteen were analyzed for nd isotopes the 31 peloid samples represent three different stratigraphic units and include 1 holocene surficial sands with highly variable concentrations and types of reworked phosphate 2 pleistocene moldic carbonates with minor concentrations of black peloidal phosphate and 3 miocene mid burdigalian frying pan sequence unit 1 fps 1 of the pungo river formation with very high concentrations of multiple types of phosphate grains that decrease upsection and change grain types with changing lithofacies the latter unit represents deposition during one high frequency sea level cycle stratigraphic analysis utilized one grain type phosphate peloids for comparative purposes with the depositional model of riggs and mallette 1990 the sr and nd data cluster into significant categories that are coincident with these three major stratigraphic units sr and nd isotope compositions of selected phosphate grains from three phosphate rich depositional sequences are utilized to 1 date the initial miocene transgression of unit fps 1 of the pungo river formation 2 decipher processes of formation and deposition of major phosphate grain types through one miocene sea level cycle including the processes of in situ formation versus reworking 3 develop a sr and nd chronostratigraphy for evaluating changing patterns of continental margin sedimentation through high frequency depositional cycles 4 determine effects of reworking and weathering on the isotope signals between miocene pleistocene and holocene sediments 5 evaluate the suitability of utilizing sr and nd isotopes for detailed chronostratigraphic analysis of phosphorite sedimentation and 6 refine our understanding of the upper cenozoic evolutionary history of north carolina s continental margin

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

cenozoic history of phosphogenesis recorded in the ferromanganese crusts of central and western pacific seamounts implications for deepwater circulation and phosphorus budgets abstract ages of seamount phosphatization episodes have been revised for 14 mid plate seamounts in the western and central pacific using the most up to date marine sr isotope curve and 87 sr 86 sr data from the literature the new ages provide a composite geologic history of phosphatization consistent with cenozoic climate history phosphatization on mid pacific seamounts took place only between 36 and 12 ma and it peaked at the eocene oligocene e o transition 34 ma the unprecedented appearance of prominent amounts of phosphorites at the e o transition and frequent recurrences of it afterwards suggests that a new mechanism came into play at that time namely the intensification of the advective flow of bottom water which accelerated the phosphorus cycle in contrast the absence of phosphorites younger than 12 ma suggests another fundamental change in process associated with the shift to a dry and cold climate that probably resulted in a decrease in the riverine input of labile phosphorus the drastic decrease in the frequency of hiatuses in ocean floor depositional records also indicates weakened bottom currents as a possible explanation for the absence of seamount phosphorite since 12 ma a phosphorus flux is a critical variable in modeling the response of the earth system to climate forcing in the geologic past thus the changes in phosphorus flux across the e o boundary and around 12 ma justify further study

closing up structures alternatives to pull apart basins the effect of bends in the north anatolian fault turkey fault blocks passing bends or stepovers in a fault zone must adapt their margins to the uneven fault trace two cases of adaption are distinguished for extensional bends or stepovers transtension 1 the fault margins close up behind a single bend knickpoint of a strike slip fault and a closing up structure new term arises or 2 fault block margins are extended behind a releasing bend double bend or stepover parallel to the displacement and a pull apart basin originates the dosing up described here is accomplished by acute angled synthetic strike slip faults that dissect the straight fault in front of a knickpoint to form a zig zag block boundary behind it crustal extension is also involved in the closing up structure but in a different way from typical pull apart basins the closing up structure illustrated was developed behind an extensional knickpoint in the north anatolian fault west of lake abant nw turkey where the process of closing up continues to this day the kinematic model of this closing up structure is supported by displacements and ruptures observed during the 1967 mudurnu valley earthquake and the 1957 abant earthquake

physical analog modeling of pull apart basin evolution abstract pull apart basins are structural depressions formed by localized extension along strike slip fault systems typically at releasing bends or steps in the fundamental strike slip system analog modeling is used to evaluate the sequence of structural evolution of pull apart basins and factors that control their degree of structural asymmetry and geometry basin evolution internal structure and overall symmetry are investigated for oblique releasing step angles and with varying rates of displacement between brittle and ductile crust on opposing sides of the strike slip system while maintaining relative rates between brittle crust on opposing sides of the basin pull apart basin evolution is separated into three stages incipient early and mature incipient pull apart basins are characterized by formation of a normal fault bounded graben or half graben parallel to the oblique step between main strike slip zones in the early stage of formation additional normal faults form toward the basin interior from the original bounding faults and cross basin strike slip faults cut diagonally across the basin interior basin bounding normal fault systems are characterized by lateral variations of fault throw and localized relay ramps in the mature stage of evolution strike slip and normal faults join to completely bound the pull apart basin analog model results indicate that displacement associated with cross basin faults causes development of a through going strike slip fault that links the two main strike slip displacement zones ultimately resulting in a decline in normal fault activity asymmetric symmetric and hybrid pull apart basins all follow the same overall deformation sequence just described the asymmetry of a pull apart basin is controlled by the degree of decoupling between brittle and ductile crust beneath the two crustal blocks in relative motion this is modeled by maintaining a constant relative rate of motion between opposing fault blocks in all models but varying the rate between the blocks and the fixed model basement absolute rate models in which one side of the detachment is fixed with respect to the basement form asymmetric pull apart basins defined by a half graben with the master fault on the mobile side in models where opposing sides of the fault system are equally decoupled from the basement symmetrical pull apart basins form defined by horst and graben structures and master fault dominance switching sides along the length of the basin fault segmentation associated with relatively immature pull apart basins may be capable of arresting earthquake rupture late linkage of main strike slip zones by a cross basin fault could extend potential rupture area dramatically increasing the possibility for large magnitude earthquakes

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

structural model of the san bernardino basin california from analysis of gravity aeromagnetic and seismicity data 1 the san bernardino basin is an area of quaternary extension between the san jacinto and san andreas fault zones in southern california new gravity data are combined with aeromagnetic data to produce two and three dimensional models of the basin floor these models are used to identify specific faults that have normal displacements in addition aeromagnetic maps of the basin constrain strike slip offset on many faults relocated seismicity focal mechanisms and a seismic reflection profile for the basin area support interpretations of the gravity and magnetic anomalies the shape of the basin revealed by our interpretations is different from past interpretations broadening its areal extent while confining the deepest parts to an area along the modern san jacinto fault west of the city of san bernardino through these geophysical observations and related geologic information we propose a model for the development of the basin the san jacinto fault related strike slip displacements started on fault strands in the basin having a stepping geometry thus forming a pull apart graben and finally cut through the graben in a simpler bending geometry in this model the san bernardino strand of the san andreas fault has little influence on the formation of the basin the deep central part of the basin resembles classic pull apart structures and our model describes a high level of detail for this structure that can be compared to other pull apart structures as well as analog and numerical models in order to better understand timing and kinematics of pull apart basin formation

evidence from coseismic slip gradients for dynamic control on rupture propagation and arrest through stepovers received 30 july 2008 revised 14 november 2008 accepted 18 december 2008 published 27 february 2009 1 analysis of historic slip distributions from large magnitude continental strike slip earthquake ruptures reveals a pronounced correlation between the distance over which slip decreases as a rupture approaches a structural step in the fault and the ability of the rupture to propagate through the step our analysis of coseismic slip gradients near these stepovers indicates that in earthquakes in which slip decreases gradually toward a step rupture will not continue on the next segment conversely in earthquakes in which slip decreases abruptly rupture commonly renucleates on the next segment the fact that ruptures that stopped had low slip gradients near stepovers relative to those that continued indicates that rupture dynamics control the propagation of rupture through stepovers these results corroborate dynamic rupture models that show that ruptures in which slip decreases abruptly at a step generate strong seismic waves that serve to renucleate rupture on the opposite side of the structural step there are several potential causes for gradual decrease of displacement as rupture approaches a stepover including transference of deformation onto subsidiary structures rheological contrasts that could dictate favored rupture propagation directions the existence of stress shadows from previous earthquakes within the system or other material or frictional heterogeneities all of these are potentially observable and if mapped systematically could provide the basis for a strong constraint on the likely end points of future earthquakes inasmuch as earthquake magnitude is strongly dependent on the size of the rupture such predictions would be of great utility as a basic component of scenario based earthquake rupture forecasts

analog modeling of pull apart basins scaled sandbox models have successfully simulated the geometries and progressive evolution of pull apart basins developed in a weak sedimentary cover above right stepping releasing dextral strike slip fault systems in rigid basement synkinematic basin infill was added progressively as the models were deformed vertical and horizontal sectioning of the completed models has allowed the full three dimensional architecture of the pull apart system to be analyzed we present three representative end member experiments 30 underlapping releasing sidestep 90 sharp nonoverlapping releasing sidestep and 150 overlapping releasing sidestep the pull apart basin geometries are typically sigmoidal to rhombic grabens the geometries of which are dependent upon the architecture of the underlying basement fault systems underlapping releasing sidestepping faults offset angles of 30 75 typically form elongate rhomboidal grabens 90 releasing offset sidesteps produce shorter squat rhomboid pull apart basins and overlapping releasing sidesteps 115 150 produce box like grabens with highly kinked basin sidewalls the pull apart basins are bounded by terraced oblique slip extensional sidewall fault systems that link the laterally offset principal displacement zones pdz of the main dextral strike slip faults the sidewall faults show changes in kinematics from dominantly dip slip extension in copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received june 24 1996 revised manuscript received november 20 1996 final acceptance june 10 1997 2fault dynamics project geology department royal holloway university of london egham surrey tw20 oex united kingdom supported by the fault dynamics project sponsored by arco british limited petrobras u k ltd bp exploration conoco u k limited mobil north sea limited and sun oil britain we also acknowledge additional funding from sun oil britain landsat thematic mapper data courtesy of rtz mining and exploration limited south american division jurrian reijs is thanked for field data relating to the salina del fraile pull apart basin chris elders is thanked for reviewing earlier versions of this manuscript and j crowell c morley and k biddle are thanked for constructive reviews of the manuscript the contents of this paper have been

tomographic resolution of mesoscale eddies in the marginal ice zone a preliminary study the adequacy of ocean acoustic tomography to resolve mesoscale eddies in the marginal ice zones miz in the vertical plane containing the acoustic multipaths connecting a pair of transceivers is studied using simulation inversions based on realistic eddy profiles obtained from conductivity temperature depth data resolution in this plane is seen to be strongly dependent upon the characteristics of the sound channel for optimal minimum mean square error estimators resolution is directly related to accuracy with better resolution implying higher accuracy for unaided acoustic tomography i e no supplementary measurements using only non bottom interacting paths horizontal and vertical resolution lengths of the order of 40 km and 200 m respectively are found in the upper water column for a transmission range of 150 km the implication is that the horizontal resolution is marginally adequate to resolve miz eddies but the vertical resolution is not since the horizontal scale of the eddies is of the same order whereas the vertical scale is much shorter the incorporation of bottom reflected arrivals is found to improve resolution significantly however the improvement only occurs in the horizontal direction and saturates when more than 14 of these arrivals are included beyond this point additional travel time observations give mostly redundant information on the other hand the disappearance of less stable non bottom interacting ray paths can result in a significant loss of resolution but only vertically the deficiency in vertical resolution is a result of the upward refracting nature of the miz sound channel it is also demonstrated that the inclusion of point temperature measurements on the acoustic transceiver moorings can dramatically increase the vertical resolution of the overall system particularly within a horizontal correlation length of the mooring with the inclusion of satellite radiometry surface temperature measurements adequate vertical resolution is achieved over the entire range considered

the tectonic framework of a complex pull apart basin seismic reflection observations in the sea of galilee dead sea transform abstract a multi channel seismic reflection survey consisting of 20 lines with a total length of 180 km was conducted in the sea of galilee the data provide new insights into the pliocene quaternary evolution of the kinarot beit shean pull apart basin kbsb along the dead sea transform two distinct zones are defined beneath the lake 1 a graben that underlies most of the lake bounded by steep north south longitudinal strike slip faults and 2 shallow pre rift units underlying the northwestern wider part of the lake we suggest that before approximately 4 ma the kbsb grew due to northward movement of the korazim plateau and by crustal stretching along the rift axis since the pliocene 4 ma lateral slip has been transferred from the southern segment of the basin s western marginal fault to normal faults in the galilee and to the eastern margin of the korazim plateau by the newly formed almagor fault which makes a restraining bend along the transform n s lithospheric stretching below the kbsb has diminished and the korazim plateau has changed from being a detached block to a compressional saddle a phase of rapid subsidence and formation of a half graben structure in the northern part of the basin approximately 1 ma ago was coeval with major deformation in areas adjacent to the kbsb indicating major reorganization of the plate boundary in the region currently most transform motions are probably taken up along a single fault on the eastern side of the kbsb implying that the main trough under the sea of galilee is in a late stage of growth as a pull apart

degree of supersaturation and precipitation of organogenic dolomite this paper integrates the degree of carbonate saturation into a general model for the origin of dolomite in organic rich marine sediments degradation of organic matter by sulfate reducing bacteria promotes early dolomite precipitation by simultaneously increasing the carbonate alkalinity and lowering the sulfate ion concentration to near zero the interstitial water in organic rich sediments of several deep sea drilling project sites where dolomite is believed to be precipitating is up to 10 sup 3 times supersaturated with respect to near ideal dolomite and up to 10 times supersaturated with respect to calcite the highly supersaturated interstitial waters appear to overcome low temperature kinetic barriers to precipitate a nonideal fine grained calcian dolomite the degree of supersaturation with respect to dolomite decreases and the interstitial water approaches carbonate equilibrium with increasing burial depth at several of these sites removal of sulfate ion is important because sulfate ion may inhibit dolomite precipitation a calcareous sediment is not required but the presence of calcite or aragonite appears to greatly enhance dolomitization by providing an additional source of ca and carbonate ions

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

geophysical analysis of fault geometry and volcanic activity in the erzincan basin central turkey complex evolution of a mature pull apart basin abstract the erzincan basin is one of several neogene sedimentary basins developed by prolonged right lateral strike slip along the north anatolian fault zone nafz the intracontinental transform defining the present boundary between the eurasian plate to the north and accreted anatolian terranes to the south the basin has a strong asymmetry and young

how well do surface slip measurements track slip at depth in large strike slip earthquakes the importance of fault structural maturity in controlling on fault slip versus off fault surface deformation abstract comparisons of observed surface displacements with geodetically inferred slip at depth in six large m w 7 1 strike slip earthquakes reveal a correlation between the structural maturity of the fault and the ratio of deep slip to surface slip that occurs on localized zones of surface rupture specifically structurally immature faults 25 km of total displacement manifest only 50 60 of total slip on narrow fault surface traces versus 85 95 for structurally mature faults 85 km total slip the same pattern holds when structurally simple parts of a surface rupture are analyzed separately from parts that exhibit obvious structural complexity e g discontinuous or multiple traces or significant dip slip these results imply that geologic measurements of surface slip along structurally immature faults are likely to significantly underestimate the true slip at depth in large earthquakes this observation has implications for a number of important problems including determination of fault slip rates which are based on surface offsets earthquake probability assessments which are based on geologic fault slip rates comparisons of geologic and geodetic rate data in the search for strain transients the structural evolution of fault zones estimation of paleo earthquake magnitudes based on geomorphic offsets analyses of the relative importance of faulting vs distributed deformation in accommodating relative plate motions in continental crust the design and construction of infrastructure built near active faults and possibly for the prediction of strong ground motions which may at least partially depend on the degree of slip localization to the surface

origin and age of phosphorite from the last glacial maximum to holocene transgressive succession off the orange river south africa a major erosional unconformity between upper cretaceous sediments and the last glacial maximum lgm transgressive succession occurs on the inner continental shelf off the orange river vibracores from 122 m water depth consist of upper pleistocene shelly phosphatic sands deposited in a high energy shoreface environment during the lgm lowstand between 22 and 19 ka the gravel rich shoreface sand grades into condensed shell rich delta front sands as sea level rose between 19 and 14 3 ka an abrupt facies transition to prodelta muddy sands corresponds to the rapid rise in sea level associated with melt water pulse mwp 1a at 14 3 ka and the facies transition to clayey silt corresponds to mwp 1b at around 11 ka a large decrease in macro and microfossil diversity indicates low oxygen conditions as the sea level rose phosphorite recovered from throughout the succession includes large interior mollusc moulds sand size peloids and friable nodules sr derived ages of the phosphorite range from early miocene to quaternary x ray amorphous friable ca phosphate nodules occur in organic rich holocene mud deposits quaternary sediment on the shelf represents a complex condensed section in which reworked phosphorite pebbles show multiple episodes of phosphogenesis often separated by millions of years within individual pebbles the phosphorite indicates that organic rich mud deposition on the shelf was prevalent during the early to middle miocene marine transgressions and sea level highstands that were associated with increased upwelling as indicated by the extensive early to middle miocene eolianites of the tsondab sandstone formation most friable phosphorite that formed during quaternary marine transgressions and highstands was probably fragmented and transported off shelf during succeeding marine regressions

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

seismicity and source parameters for small scale earthquakes along the splays of the north anatolian fault naf in the marmara sea summary major discrepancy between present day fault models in the marmara sea is closely related to structural development of depression areas beneath the sea therefore in this study the marmara sea and especially its major basins are investigated by means of recent seismological observations consisting of microseismicity 1 2 md 3 6 2002 may 2006 may focal mechanisms 2 4 md 5 0 1999 2006 and stress analysis based on the focal mechanisms in the cinarcik basin where either pull apart model or negative flower structure is proposed northeastern margin is represented by strike slip sources having a nw alignment probably corresponding to a cross basin strike slip fault developing in a matured pull apart basin this suggestion is directly relevant to experiments of sand box analogue models these experiments indicate that such a cross basin strike slip fault is produced after the pull apart basins attain their mature stage eventually resulting in less vertical displacements attributed to normal faults bounding the basin this experimental decline may be corroborated by the paucity of normal mechanisms in the basin extensional motion in this region is more influential outside of the basin especially to the area where an onshore seismic activity is monitored on the land on the other hand another strike slip activity in the cinarcik basin is distributed on a possible strand parallel to the northern coastline of the marmara sea in the armutlu peninsula this may indicate that one or more short strands of the northern splay extend to the west by bounding the basin from the south in the central basin the existence of a right lateral strike slip faulting on an east west trending fault is supported by similar strike slip focal mechanisms located at both extremities of the basin to the west dominant style of deformation gradually shifts from strike slip faulting to transpression along the western coastline of the marmara sea where the northern splay joins with the offshore continuation of the ganos fault finally focal mechanisms in the marmara sea are inverted for the best fitting stress tensor characterized by a subvertical 2 axis and two subhorizontal stress axes of 1 and 3 oriented nw se and ne sw respectively conclusively this study infers that the current tectonics of the marmara sea is mainly governed by a strike slip regime ascribed to both submarine splays of the naf and partly dominated by extensional and compressional features indicating shallow processes at local scales

neotectonics of the owen fracture zone nw indian ocean structural evolution of an oceanic strike slip plate boundary the owen fracture zone is a 800 km long fault system that accommodates the dextral strike slip motion between india and arabia plates because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the early pliocene the fault is clearly observed on bathymetric data it is made up of a series of fault segments separated by releasing and restraining bends including a major pull apart basin at latitude 20 n some distal turbiditic channels from the indus deep sea fan overlap the fault system and are disturbed by its activity thus providing landmarks to date successive stages of fault activity and structural evolution of the owen fracture zone from pliocene to present we determine the durability of relay structures and the timing of their evolution along the principal displacement zone from their inception to their extinction we observe subsidence migration in the 20 n basin and alternate activation of fault splays in the vicinity of the qalhat seamount the present day owen fracture zone is the latest stage of structural evolution of the 20 myr old strike slip fault system buried under indus turbiditic deposits whose activity started at the eastern foot of the owen ridge when the gulf of aden opened the evolution of the owen fracture zone since 3 6 myr reflects a steady state plate motion between arabia and india such as inferred by kinematics for the last 20 myr period the structural evolution of the owen fracture zone since 20 myr including fault segments propagation and migration pull apart basin opening and extinction seems to be characterized by a progressive reorganisation of the fault system and does not require any major kinematics change

a first deep seismic survey in the sea of marmara deep basins and whole crust architecture and evolution abstract increased source strength streamer length and dense spatial coverage of seismic reflection profiles of the seismarmara leg 1 allow to image the deep structure of the marine north marmara trough nmt on the strike slip north anatolian fault naf west of the destructive izmit 1999 earthquake a reflective lower crust and the moho boundary are detected they appear upwarped on an e w profile from the southern central basin eastwards towards more internal parts of the deformed region thinning of the upper crust could use a detachment suggested from an imaged dipping intracrustal reflector that would allow upper crustal material to be dragged from beneath it and above the lower crust accounting for the extensional component but also southwest motion of the southern margin of the nmt sections across the eastern half of the nmt crossing the cinarcik and imrali basins reveal several faults that are active reaching into the basement and have varying strike and proportions of normal and strike slip displacement they might be viewed as petals of a large scale negative flower structure that spreads over a width of 30 km at surface and is rooted deeper in the lithosphere under the central basin a very thick sediment infill is revealed and its extensional bounding faults are active and imaged as much as 8 km apart down to 6 km depth we interpret them as two deep rooted faults encompassing a foundering basement block rather than being merely pulled apart from a jog in a strike slip above a decollement the deep basin lengthening would account for only a modest part of the proposed 60 km finite motion since 4 myr along the same direction oblique to the nmt that sidesteps the shear motion from its two ends thus differential motion occurred much beyond the deep basins like subsidence involving the nmt bounding faults and the intracrustal detachments the complex partitioned motion localized on active faults with diverse natures and orientations is suggested to represent the overburden deformation induced from horizontal plane simple shear occurring in depth at lithospheric scale and in front of the north anatolian fault when it propagated through the region

transtensional faulting patterns ranging from pull apart basins to transform continental margins an experimental investigation abstract seventeen small scale experiments were performed to study the deformation induced in brittle ductile models by a releasing stepover between two transform faults and by intersection between transform and divergent plate boundaries in both cases faulting depends on the rheological layering presence and strength of a ductile layer at depth and the width of the basal stepover successive types of pull apart basins are observed in the first set of experiments which are compared with natural examples firstly a lazy z shaped basin appears which is bounded by y faults above transform boundaries and r faults propagating from each corner of the stepover then r faults replace r faults leading to a rhomb shaped graben at every stage the basin length to width ratio remains between 2 2 and 3 8 suggesting that scale independence of pull apart basins is related to the geometrical shape of bounding faults in a second set of experiments deformation at the end of a transform boundary is characterized by a horsetail splay bounding a divergent basin within the horsetail splay block tilting and block rotation about vertical axes lead to a surface slope perpendicular to the slope of the divergent basin a feature that can be compared with marginal ridges at transform margins

on the time mean state of ocean models and the properties of long range acoustic propagation 1 receptions on three vertical hydrophone arrays from basin scale acoustic transmissions in the north pacific during 1996 and 1998 are used to test the time mean sound speed properties of the world ocean atlas 2005 woa05 of an eddying unconstrained simulation of the parallel ocean program pop and of three data constrained solutions provided by the estimating the circulation and climate of the ocean ecco project a solution based on an approximate kalman filter from the jet propulsion laboratory ecco jpl a solution based on the adjoint method from the massachusetts institute of technology ecco mit and an eddying solution based on a green s function approach from ecco phase ii ecco2 predictions for arrival patterns using annual average woa05 fields match observations to within small travel time offsets 0 3 1 0 s predictions for arrival patterns from the models differ substantially from the measured arrival patterns from the woa05 climatology and from each other both in terms of travel time and in the structure of the arrival patterns the acoustic arrival patterns are sensitive to the vertical gradients of sound speed that govern acoustic propagation basin scale acoustic transmissions therefore provide stringent tests of the vertical temperature structure of ocean state estimates this structure ultimately influences the mixing between the surface waters and the ocean interior the relatively good agreement of the acoustic data with the more recent ecco solutions indicates that numerical ocean models have reached a level of accuracy where the acoustic data can provide useful additional constraints for ocean state estimation

variability in magnitude of paleoearthquakes revealed by trenching and historical records along the haiyuan fault china paleoseismology provides fundamental data for generalizing earthquake recurrence behavior by revealing past surface rupturing events determining the size of paleoseismic events is notoriously more challenging than their timing paleoearthquakes exposed in trenches are vaguely defined as large enough to break to the surface and often assumed to be similar in size here we show an example where the paleoseismic record includes events of both moderate and large magnitudes at the salt lake site on the active left lateral haiyuan fault northern tibetan plateau a high resolution stratigraphic sequence recorded three and possibly four events since a d 1500 constrained by accelerator mass spectrometry 14 c dating historical accounts of earthquake damage in the study region suggest that several earthquakes exposed in the trenches markedly differ in magnitude with the exception of the most recent m 8 earthquake that occurred in a d 1920 two earlier events which occurred in a d 1760 or 1709 and 1638 respectively are considerably smaller with magnitude m 7 and more likely m 6 or less thus this section of the haiyuan fault that broke during moderate magnitude events failed again after a short interval during a large m w 7 8 8 3 earthquake as part of a larger multisegment rupture our study shows that moderate magnitude events can be preserved in the stratigraphy and exposed by paleoseismic trenching under ideal conditions for instance if sedimentation is fast enough and there is no hiatus in deposition eventually the data presented add to the growing body of paleoseismic records containing events of different magnitudes with a large variability in rupture length and coseismic slip

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

stable isotopic characterisation of francolite formation stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits values of 13c and 34s in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions the exceptions are concretionary francolite from namibia which has an isotopic composition in keeping with its formation within organic rich sediments and that from offshore morocco which has an isotopic signature of the anoxic suboxic interface onshore deposits from jordan mexico south africa and possibly the permian phosphoria formation in the western u s a are substantially depleted in18o they appear to be too altered for deductions to be made about their environments of formation in other onshore deposits which are unaltered or minimally altered the isotopic composition suggests that some formed within sulphate reducing sediments sedhura morocco whilst francolite from the georgina basin of australia formed at the oxic anoxic boundary where oxidation of biogenic h2s decreases the 34s of pore water in general pelletal samples show non oxic isotopic signatures whilst non pelletal samples show oxic isotopic signatures but samples from namibia peru ica plateau and the californian and moroccan margins are exceptions to this rule morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature

evidence of quaternary and recent activity along the kyaukkyan fault myanmar abstract cenozoic right lateral shear between the eastern indian margin and eurasia is expressed by numerous n s trending fault systems inboard of the sunda trench including the sagaing fault the most easterly of these fault systems is the prominent 500 km long kyaukkyan fault on the shan plateau myanmar s largest recorded earthquake mw 7 7 on 23rd may 1912 focused near maymyo has been attributed to the kyaukkyan fault but the area has experienced little significant seismicity since then despite its demonstrated seismic potential and remarkable topographic expression questions remain about the kyaukkyan fault s neotectonic history in this study we document robust geologic evidence of fault activity along the kyaukkyan fault field investigation and interpretation of satellite imagery reveal deformation features developed along a fault system mostly indicative of quaternary dextral strike slip faulting clearly defined tectonic geomorphology including fault scarps and linear valleys are used to trace the northernmost and southernmost part of the fault the fault s central section is characterised by a complex pull apart system whose normal border faults show signals of relatively slow recent activity dextral transtensional activity along the kyaukkyan fault is recorded by geomorphic features such as sag ponds shutter ridges offset and beheaded streams triangular facets and low sinuosity mountain fronts the quaternary age of activity is demonstrated by short lived geomorphic features such as wind gaps offset and deformed alluvial fans and even offset of man made structures in the inle basin alluvial fan successions along the easternmost mountain front reveal a vertical transition from faulted and folded alluvial fan sequences adjacent to pre cenozoic flanking ranges to overlying gravels that appear less deformed conversely a locally buried cross basin fault system has fresh geomorphic expression even within the uppermost parts of the lacustrine fluvial basin fill this may indicate quaternary migration of dominant fault deformation from sidewall faults to a cross basin fault system which is indicative of a mature strike slip fault system and has been observed in other active strike slip faults around the world and in analogue models

middle pleistocene extinction process of pull apart basins along the north anatolian fault zone abstract numerous basins that present in northern turkey formed in plio quaternary period by the strike slip tectonics of the north anatolian fault zone these pull apart basins isolated from their surrounding topographies by major scarps of faults along their margins that mapped as active faults but the mapped recent traces in the pull apart basins are in disagreement about these marginal faults and commonly characterized by the faults that pass through basin floors in the cases of surface rupturings in great earthquakes during the last century these faults have migrated from the basin rims to the center of the basins in agreement with the extinction model of pull apart basins here we review observations about numerous basins along the north anatolian fault zone to show that the migration of these faults in middle pleistocene related with the maturity of basins through their evolution

sedimentation cycles and their diagenesis on the slope of a miocene carbonate ramp bahamas odp leg 166 numerous small scale depositional cycles are present in the miocene sediments of seismic sequence m along the margin of great bahama bank odp leg 166 these cycles consist of decimetre to metre scale alternations between light grey and dark grey black wackestones packstones the light grey layers are well cemented and nearly uncompacted they contain planktonic and benthic foraminifera and bioclasts bioturbation in these layers is moderate the dark grey wackestones packstones are uncemented strongly compacted and normally strongly bioturbated the main components are planktonic foraminifera and fine grained bioclasts the dark layers are rich in aragonite and organic carbon and contain around 80 carbonate the light layers show low aragonite and organic carbon contents combined with carbonate values of up to 97 5 light 13c and slightly negative 18o values were observed in the dark uncemented layers while the cemented intervals show heavy 13c values and slightly more positive 18o values the carbon isotope signal between the dark and the light layers shows variations of up to 1 45 both 13c and 18o co vary with carbonate content the formation microscanner images reflect the changes in carbonate mineralogy the natural gamma ray tool shows that variations in siliciclastic content of the examined succession displays a different frequency than the cyclic alternations in carbonate mineralogy the internal stacking pattern of the cycles is closely tied to sea level the dark layers are deposited during rising sea level while the light layers reflect sediment production and export during highstand and falling sea level these cycles thus represent a rather continuous sediment shedding pattern that is clearly related to the ramp morphology and differs from the highstand shedding pattern typical for rimmed flat topped platforms most measured parameters suggest that primary sediment composition played an important role in the cementation process the primary differences in composition were enhanced during shallow burial diagenesis the initially high content of metastable carbonate phases in the periplatform sediments triggered rapid cementation of the primary aragonite rich layers leading to the formation of the light beds dissolution of metastable high mg calcite and aragonite was followed by in situ precipitation of more stable dolomite and calcite diagenesis was enhanced by the coarse grain size of the primary aragonite rich layers in contrast the more pelagic dark calcite rich layers were only slightly affected by diagenesis and could preserve their aragonite content the uncemented layers subsequently were subject to strong mechanical compaction whereas the cemented beds stayed nearly uncompacted

origin and age of phosphorite from the south central florida platform relation of phosphogenesis to sea level fluctuations and δ13c excursions abstract francolite carbonate fluorapatite from predominantly peloidal phosphorite grains in the miocene hawthorn group from the babcock deep core southwestern florida is highly substituted with an average composition of ca4 61na0 22mg0 14k0 05sr0 02 po4 2 23 co3 0 62 so4 0 12 f 1 04 13c values of 1 0 7 8 pdb of the francolite co3 indicate a substantial contribution of c from an organic source the sulfur isotopic composition of francolite so4 is depleted to slightly enriched relative to miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction the uniformly high sr na mg so4 and co3 contents of the francolite the 18o values of the francolite co3 0 2 4 2 pdb and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation phosphorite from the babcock deep core has sr 87 86 ratios that range from 0 708148 0 708880 and sr derived ages that range from late oligocene 25 6 0 7 ma to early late miocene 9 2 1 4 ma the sr derived ages of relatively fragile calcareous benthic foraminifers are consistently younger than associated hard tightly cemented phosphorite and support textural evidence of extensive reworking the age of the host sediment ranges from early miocene to pliocene and its depositional history is related to sea level fluctuations approximately three quarters of the total phosphorite in the babcock deep core formed during or within 2 my before the major early to mid miocene positive 13cshift as recorded at dsdp site 588 southwest pacific one third of the total phosphorite formed just prior to the carbon shift in the short interval between 21 9 and 20 4 ma these results indicate that reworked phosphorite deposits may provide a proxy of organic carbon cycling on continental shelves that correspond to sealevel fluctuations and to variations in the 13crecord

late cenozoic phosphogenesis on the western shelf of south africa in the vicinity of the cape canyon abstract the strontium isotope 87 sr 86 sr composition of phosphorite carbonate fluorapatite cemented grains pcg phosphate cemented limestone pcl skeletal phosphorite grains spg and biogenic calcite mollusc shell benthic foraminifera and echinoid spines from sediment on the outer continental shelf in the vicinity of the cape canyon ranges from 0 707981 to 0 709167 and corresponds to an age range of late early oligocene to late pleistocene most biogenic carbonate sr ages agree with biostratigraphic ages but some samples contain significantly older and reworked robust 250 m benthic foraminifera although the sr ages of biogenic and phosphorite grains indicate that sedimentation was fairly continuous most sediment is reworked with only lower miocene upper pliocene and upper pleistocene successions generally preserved in the study area the initial phosphogenic episode from the latest oligocene to early early miocene 21 26 ma was the largest with additional phosphogenic episodes in the late early miocene 16 19 ma and middle miocene 10 15 ma most phosphorite occurs as pcg that formed during marine transgressions and highstands from the late oligocene warming event until the mid miocene climatic optimum a period of episodic antarctic glaciation and several positive marine 13 c excursions upper oligocene to lower miocene pcg have been extensively reworked and are associated with major erosional unconformities pcg vary from peloidal sands to gravel mollusc moulds and contain variable amounts of quartz glauconite and pyrite inclusions pcl formed from 9 to 17 ma by cementation and replacement of older calcareous sediment during the middle to late miocene marine regression phosphorite as well as associated glauconite and pyrite indicate that periods of rapid accumulation of organic rich terrigenous muds derived from the focusing of the suspended load of rivers and organic matter produced in areas of coastal upwelling have occurred episodically on the margin since the late oligocene the relative paucity of phosphorite younger than the middle miocene may result from frequent erosional events as documented by pronounced unconformities on the shelf that reflect lowered eustatic sea level tectonic uplift and high frequency high amplitude quaternary sea level fluctuations

ocean acoustic tomography at 1000 km range using wavefronts measured with a large aperture vertical array broadband acoustic signals transmitted from a moored 250 hz source to a 3 km long vertical line array of hydrophones 1000 km distant in the north central pacific ocean were used to determine the amount of information available from tomographic techniques used in the vertical plane connecting a source receiver pair a range independent pure acoustic inverse to obtain the sound speed field using travel time data from the array is shown to be possible by iterating from climatological data without using any information from concurrent environmental measurements range dependent inversions indicate resolution of components of oceanic variability with horizontal wavelengths shorter than 50 km although the limited spatial resolution of concurrent direct measurements does not provide a strong cross validation since the typical cast spacing of 20 25 km gives a nyquist wavelength of 40 50 km the small travel time signals associated with high wavenumber ocean variability place stringent but achievable requirements on travel time measurement precision the forward problem for the high wavenumber components of the model is found to be subject to relatively large linearization errors however unless the sound speed field at wavelengths greater than about 50 km is known from other measurements or from a two dimensional tomographic array the high ocean wavenumber resolution that is in principle available from tomographic measurements is therefore achievable only under restricted conditions

organic matter in anoxic sediments off central peru relations of porosity microbial decomposition and deformation properties abstract microstructure of central peru continental margin sediments suggests that in environments of rapid hemipelagic sedimentation organic matter decomposition has a significant effect on geotechnical properties in highly porous surface sediments particles resembling the remains of fecal pellets appear to be coated by bacterial sheaths but after burial sheaths disappear as an increasingly uniform and closed structure of organo mineral aggregates develops interstitial water nutrient and solid phase c n and p profiles support the interpretation that this progression corresponds to decomposition and metabolite regeneration from labile organic matter by microbial sulfate reduction it is proposed that early aggregation has a strengthening effect and that this combined with the low density of near surface sediments results in an effective overburden pressure lower than experimentally determined preconsolidation pressures more basic knowledge of the lifetime of organo mineral aggregates and the influence of gross and local microstructure on the rates and products of diagenetic reactions is needed in order to verify the relationship between organic matter accumulation and sediment stability in continental margin environments

a mid pleistocene deformation transition in the hula basin northern israel implications for the tectonic evolution of the dead sea fault the dead sea fault dsf plate boundary has accommodated relative sinistral motion between the sinai and arabian plates since the neogene geologically based models point to a long term 5 0 ma n trending relative motion roughly parallel to the central sector of the dsf gps based calculations of present day relative motion between the sinai and arabian plates indicate a northward increasing convergent component across the dsf suggesting a kinematic change over the plio pleistocene period we study the evolving deformation of the hula rhomb shaped graben situated along the central sector of the dsf in order to examine the possible kinematic change the hula graben is widely accepted as a pull apart basin part of a series of basins extending southward we use a 3 d approach combining mapped surface structures with subsurface seismic reflection profiles 173 km and borehole data 38 boreholes gathered here into a single geographic information systems database results indicate that during the mid pleistocene a major tectonic transition modified the structure of the basin fill a subvertical nnw trending left lateral throughgoing strike slip fault developed diagonally across the basin consequently the basin entered a new geodynamic phase where subsidence was controlled by both the basin bordering faults and the diagonal fault while the vertical displacement across the transverse faults is minor synchronous structural changes recorded in additional localities along the dsf attests to a mid pleistocene 1 ma regional tectonic transition that was associated with a northward increasing convergent component across the central and northern sectors of the dsf

die muttekopfgosau lechtaler alpen tirol osterreich sedimentologie und beckenentwicklung in the eastern alps compression during orogeny in the upper cretaceous caused crustal thickening isostatic uplift and gravitational adjustment of the unstable orogenic wedge this process triggered extensional basin formation on the back of the orogen gosau basins the basin fill of the muttekopf gosau basin is arranged in megacycles the first one comprising alluvial fan sediments and inoceramus marls of the lower gosau complex faupl et al 1987 of santonian age three other cycles follow upper gosau complex campanian to maastrichtian consisting of turbiditic fining upward sequences that are indicative for extensional tectonics during basin formation as subsidence events prevent formation of autocyclic coarsening upward sequences and therefore prograding of the turbidite system deposition of the 1st and 2nd megacycle occured below the ccd carbonate compensation depth the carbonate rich 3rd megacycle was deposited probably below the ccd after a period of palaeogeographic reorganisation uplift in the source area

mineralogy of sedimentary apatites abstract members of the apatite family are the most common phosphate minerals apatites in igneous and metamorphic rocks generally approach fluorapatite in composition in sedimentary rocks the apatite is usually the carbonate fluorapatite variety francolite which produces x ray diffraction patterns similar to but distinctive from those of fluorapatite variations in francolite compositions and physical properties have also been identified the substitution of co 3 2 for po 4 3 from zero to about 25 of phosphate sites on a 1 1 basis influences all other changes in composition and crystallography of francolites statistical models have reduced the francolite composition to a single parameter problem the dominant factor being the variation in unit cell a value with increasing co 3 2 substitution within a deposit variations in francolite composition with stratigraphical position and particle size may indicate the extent and type of post depositional alteration replacements of so 4 2 for po 4 3 and ca 2 by na 2 and mg 2 are also discussed but these are of more limited significance

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

pacific miocene carbon isotope stratigraphy using benthic foraminifera abstract seven miocene pacific ocean deep sea drilling project sites from four different water masses planktonic foraminiferal biogeographic regions have been correlated using 18 prominent carbon isotopic events defined in the benthic foraminiferal 13c records in dsdp site 289 the correlations are based on the assumption that there are global or at least pacific wide controls on the 13c of deep water hco3 each of the individual 13c records is correlated to site 289 based on the shape of the curves in a manner analogous to that used to correlate sea floor magnetic anomaly patterns the results of this correlation experiment confirm that planktonic foraminiferal biostratigraphy and carbon isotopic stratigraphy are consistent within the tropical surface water mass and precise to 100 000 years correlations between surface water masses suggest that the precision of foraminiferal biostratigraphy is on the average less than 200 000 years due to the lack of cosmopolitan marker species and diachronism of species occurrences carbon isotope stratigraphy used in conjunction with biostratigraphy has the potential to provide an easily utilized globally applicable correlation tool with an interregional precision of 100 000 years or better as more continuous and undisturbed deep sea sections become available as a result of the hydraulic piston coring program

dating phosphogenesis with strontium isotopes authigenic and replacement francolites in modern phosphorite have values of sup 87 sr sup 86 sr within error of that of modern marine sr 0 70916 plus minus 2 during the phosphatisation of carbonate sr is not inherited from the carbonate but is totally exchanged with sr in ambient water the sup 87 sr sup 86 sr in shallow marine pore waters is indistinguishable from the value for modern marine sr so authigenic francolite which precipitates from pore water accurately records the isotopic ratio of contemporary marine sr by comparing the sup 87 sr sup 86 sr in francolite with published curves for the isotopic evolution of tertiary marine sr we have dated phosphogenetic events affecting the chatham rise 4 90 plus minus 0 35 ma the nambian margin 1 15 plus minus 0 25 ma and 4 70 plus minus 0 35 ma and the sechura desert peru 11 8 plus minus 0 5 ma

initiation evolution and extinction of pull apart basins implications for opening of the gulf of california abstract we present a model for the origin crustal architecture and evolution of pull apart basins the model is based on results of three dimensional upper crustal elastic models of deformation field observations and fault theory and is generally applicable to basin scale features but predicts some intra basin structural features geometric differences between pull apart basins are inherited from the initial geometry of the strike slip fault step over which results from the forming phase of the strike slip fault system as strike slip motion accumulates pull apart basins are stationary with respect to underlying basement and the fault tips propagate beyond the rift basin increasing the distance between the fault tips and pull apart basin center because uplift is concentrated near the fault tips the sediment source areas may rejuvenate and migrate over time rift flank uplift results from compression along the flank of the basin with increasing strike slip movement the basins deepen and lengthen field studies predict that pull apart basins become extinct when an active basin crossing fault forms this is the most likely fate of pull apart basins because basin bounding strike slip systems tend to straighten and connect as they evolve the models show that larger length to width ratios with overlapping faults are least likely to form basin crossing faults and pull apart basins with this geometry are thus most likely to progress to continental rupture in the gulf of california larger length to width ratios are found in the southern gulf which is the region where continental breakup occurred rapidly the initial geometry in the northern gulf of california and salton trough at 6 ma may have been one of widely spaced master strike slip faults lower length to width ratios which our models suggest inhibits continental breakup and favors straightening of the strike slip system by formation of basin crossing faults within the step over as began 1 2 ma when the san jacinto and elsinore cerro prieto fault systems formed

insights into active deformation in the gulf of cadiz from new 3 d seismic and high resolution bathymetry data the nature of active deformation in the gulf of cadiz is important for developing a better understanding of the interplate tectonics and for revealing the source of the 1755 great lisbon earthquake new high resolution 3 d seismic data reveal a classic pull apart basin that has formed on an east striking fault in the southern lobe of the gulf of cadiz accretionary wedge geometrical relationships between an array of faults and associated basins show evidence for both dextral and sinistral shear sense in the southern lobe strike slip faulting within the lobe may provide a link between frontal accretion at the deformation front and extension and gravitational sliding processes occurring further upslope inception of the strike slip faults appears to accommodate deformation driven by spatially variant accretion or gravitational spreading rates or both this implies that active deformation on strike slip faults in the southern lobe is unrelated to the proposed modern inception of a transform plate boundary through the gulf of cadiz and underscores the importance of detailed bathymetric analysis in understanding tectonic processes