remobilization events involving cd and zn from intertidal flat sediments in the elbe estuary during the tidal cycle in laboratory experiments the effect of periodic alternations between aerobic and anaerobic conditions on the mobilization of zn and cd from the surface layers of an intertidal sand and mud flat sediment was studied a percolation technique was used to simulate submersion and exposure to the air by controlling the concentrations of oxygen and nitrate within undisturbed 2 cm sediment layers zn and cd released from the sediment were removed from the pore water under anerobic conditions and maintained in the percolating water when aerobic conditions were established zn was mobilized immediately after re oxidation whereas cd mobilization was observed after a retention time of 53 to 180 min and 25 72 h in sand and mud flat sediments respectively from 0 3 to 1 8 of the total cd was then lost from these sediments the rates of particulate organic matter degradation calculated from the production of co 2 under aerobic and anaerobic conditions were similar the ph values in sand flat sediments used in the experiments were significantly higher than in mud flat sediments neither the rates of organic matter mineralization nor the variations in ph controlled the observed trace metal mobility the results strongly indicate that trace metals were precipitated as sulphides under anaerobic conditions the release of trace metals under aerobic conditions was attributed to the oxidation of sulphides and the mineralization of organic matter in the surface layer of the mud flat the rate of zn mobilization reached 8 79 10 7 mol g 1 s 1 in summer but was only 1 82 10 7 mol g 1 s 1 in winter cd was released from the same layer during the whole year at a constant rate of 5 89 10 9 mol g 1 s 1 calculations based on the percolation experiments indicate that in mud flat sediments from the elbe estuary a loss of up to 50 of the total cd occurs within one month

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

evidence for dynamic coupling of surface processes with isostatic compensation in the lower crust during active extension of western turkey western turkey in the eastern part of the aegean region is extending slowly with extension no faster than 0 5 mm yr 1 across any individual active normal fault up to 15 km of southward extension has occurred in the most active 100 km wide part of this region since 15 ma indicating a typical strain rate of 3 10 16 s 1 rivers carry a sediment flux of 4 106 m3 yr 1 westward to the aegean sea coast with offshore sedimentation at 1 mm yr 1 sediment loading causes coastal areas to subside much faster than would be expected from the extension alone most of this sediment is derived from regional erosion of inland areas to the east at a typical rate of 0 1 mm yr 1 this erosion being isostatically compensated by uplift it is suggested that the lower crustal material displaced by sediment loading near the coast flows east to isostatically compensate the erosion the average eastward velocity of this lower crustal channel flow beneath the aegean coast is estimated as 1 mm yr 1 the maximum velocity is 2 mm yr 1 this case study thus indicates the general point that isostatically compensated erosion and lower crustal channel flow can affect the evolution of sedimentary basins that are surrounded by eroding landmasses factors that are often neglected

control of manganese and iron in skagerrak sediments northeastern north sea three cores with variable physicochemical characteristics from different areas of the skagerrak northeastern north sea have been studied to understand the processes such as redox conditions caco3 bioturbation etc controlling the fe and mn abundance in sediments sequential extraction was performed to identify the partitioning patterns of these elements into sorbed and carbonate mn fe oxyhydroxide fe oxyhydroxide residual leachable and residual non leachable phases pore water fe and mn contents in the central skagerrak increase up to 100 mm depth while they reach maximum concentrations around 50 mm depth in the southern skagerrak sediments the fe redox boundary lies below the mn redox boundary whereas the latter coincides with the level of oxygen penetration extractable mn in the upper layers of the central basin sediments is 10 times higher than that present in sediments of the southern part 30 mmol kg 1 fe is present in all fractions extracted but mn occurs mainly in carbonate and fe mn oxyhydroxide phases total extractable fe is about three times less than that of total fe in all cores whereas total mn is nearly equivalent to the total extractable mn mn in sediments showed two peaks the surficial one due to precipitation of oxyhydroxides from the diagenetically upwelled and sedimented mn from overlying waters and the deeper one associated with diagenetically formed carbonate phase the substitution approach has been used to explain the presence of significant quantities of mn and fe in the carbonate phase the computed observed partition coefficients decrease with depth in general but increase with corresponding decrease in ca substantiating the ionic replacement reactions mn in the carbonate phase is negatively related to caco3 suggesting possible rhodochrosite formation evaluated observed and thermodynamic partition coefficients revealed the likelihood of siderite formation solutions to diagenetic equations showed contrasting behaviour of mn and fe in skagerrak sediments increased reduction of mn oxyhydroxides in the central parts compared to that in the southern skagerrak results in the significant enrichment rate of mn in pore water 1365 mol m 3 yr 1 in sediments of the former area large amounts of fe oxyhydroxides are reduced in southern parts compared to the skagerrak basin itself mn and fe fluxes from reducing to oxidizing zones are larger in the southern skagerrak 8 8 and 9 0 m mol m 2 yr 1 respectively than in central parts 5 3 and 4 6 m mol m 2 yr 1 respectively mn and fe also exhibit contradicting sedimentation patterns where the former has high deposition fluxes in the central skagerrak while the latter is deposited more in the southern skagerrak mn seems to be internally cycled within the skagerrak

faulting associated with historical and recent earthquakes in the eastern mediterranean region summary this paper summarizes evidence for surface faulting in historical and recent earthquakes in the eastern mediterranean region and in the middle east such information is particularly important for studies of active tectonics and for palaeoseismology we have found 78 cases of faulting pre 1900 and 72 post 1900 some of which show that faults that have apparently been inactive this century had already ruptured before 1900 for some cases faulting could not have been predicted from 20th century activity and in others it could have been expected but has not been observed during the instrumental period the data are suycient to allow the derivation of relationships between magnitude and rupture length

horizontal crustal motion in the central and eastern mediterranean inferred from satellite laser ranging measurements four campaigns to acquire satellite laser ranging slr measurements at sites in the mediterranean region have been completed these measurements to the lageos satellite made largely by mobile systems cover a time span beginning in november 1985 and ending in june 1993 the range data from 18 sites in the central and eastern mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network estimates of horizontal motion were placed into a regional northern europe fixed kinematic reference frame uncertainties are on the order of 5 mm yr for sites having at least four occupations by mobile systems and approach 1 mm yr for permanently located sites with long histories of tracking the resulting relative motion between sites in the aegean exhibit characteristics of broadly distributed pattern of radial extension but at rates that are about 50 larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater or across the region the motion estimated for sites in turkey exhibit velocity components associated with the westward motion of the anatolian block relative to eurasia these results provide a present day snapshot of ongoing deformational processes as experienced by the locations occupiedmore by slr systems less

geochemistry of surface sediments from the arabian sea we report new geochemical data si al na k rb sr mn cu ni fe zn co and pb for 126 surficial sediments and base metal partition data for limited samples from the deep arabian sea and discuss the controls affecting these elemental concentrations the geochemical nature of and differences between sediments from three physiographically tectonically distinct regions have been identified the spatial resolution allows us to discern the various processes operative in the deep arabian sea during the holocene epoch r mode factor analysis on the geochemical data suggests that four dominant factors are responsible for the observed geochemical variations in the samples namely carlsberg ridge hydrothermal activity terrigenous contribution hydrogenous authigenic precipitates and biological contribution

trace metals in metalliferous sediments manop site m interfacial pore water profiles we present data showing enrichments of metals mn cu v cr cd and ni and dissolved organic matter dom in surficial pore waters depths 1 cm at a metalliferous sediment site in the pacific we also present a model of metal release during particulate organic carbon poc oxidation and opal dissolution at the sediment seawater interface a comparison of measured interfacial metal concentrations with those predicted from the model suggest that cd ni and cr are released during oxidation of poc at the sediment seawater interface however for v cu and mn additional source s and or processes are required to account for the measured interfacial concentrations for cu recycling via interfacial remineralization and release to bottom waters with subsequent scavenging out of bottom waters by particulates probably provides the major additional source for v we suggest that in addition to some contribution from a benthic flux bottom water scavenging scenario complexation with dom at the interface serves as a trap to accumulate v released from particulates in the zone of oxygen reduction for manganese we suggest that most of the interfacial pore water content is produced from reduction of sedimentary mn iv by reactions with dom at the sediment seawater interface the calculated benthic flux of manganese as a result of this reaction may account for a large fraction of the particulate manganese rain that is apparently not preserved in the sediment at this site

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

the importance of the oxygen minimum zone and sediment geochemistry in the distribution of recent benthic foraminifera in the northwest indian ocean abstract the relationship between the distribution of benthic foraminifera and sediment type and depositional environment in the arabian sea is discussed the benthic foraminiferal fauna were sampled in nineteen recent surface sediment samples and geochemical variables of the sediment of the same samples were measured the water depths for the box core samples varies from 440 to 4040 m a total of 103 species and six species complexes were identified the geochemical properties were found to correspond well to the sediment type and depositional environment and six different sediment depositional environment types could be distinguished analysis of the benthic foraminiferal fauna reveals specific faunal assemblages that are closely related to these sediment depositional environment types

remobilization of transition metals in surficial pelagic sediments from the eastern pacific abstract the top thirty centimeters of sediment at two sites in the eastern equatorial pacific contain evidence of post depositional remobilization of mn fe co ni cu and zn remobilization takes place as mn and fe oxyhydroxides are released to the pore water during the microbially mediated decomposition of organic matter precipitation of the dissolved metals in near surface more oxic strata controls the solid phase distribution of mn fe and zn the solid phase redistribution of co and ni requires only suitable material for readsorption comparison of pore water fluxes with solid phase metal distributions in the solid sediment indicates no loss of dissolved metal to the overlying water column at the present time loss of mn during the quaternary is indicated by the composition of the sediments however leaching experiments suggest that portions of the mobile mn fe co ni and cu are fixed by incorporation in authigenic smectite in the surficial sediments

models of depth dependent bioturbation at manop site h in the eastern equatorial pacific the vertical distribution of excess 226ra sorbed to manganese rich sediments from a box core taken at manop site h 6 34 n 92 48 w in the eastern equatorial pacific can be modeled only if the rate of bioturbation decreases rapidly downward from the seafloor within the upper few centimeters of sediment independent bioturbation rates estimated by balancing dissolved and particulate diagenetic mn fluxes are compatible with the values obtained from the radium model such results are consistent with 210pb and 230th measurements reported here and with manop lander and porewater observations that rapid organic carbon degradation in these sediments consumes oxygen within a few centimeters of the sediment seawater interface the modeled decrease in bioturbation expressed as a biodiffusion coefficient is consistent with values of more than 25 cm2 kyr at the surface falling to less than 0 4 cm2 kyr at a depth of 14 cm

geochemical evaluation of diagenetic processes in a deep water carbonate abstract a 60 m section encompassing three separate lithofacies of the rancheria formation texas new mexico u s a a mississippian age deep water carbonate unit was collected for petrographic elemental and isotopic 87 sr 86 sr 18o and 13c analyses petrographic examination including cathode luminescence studies indicates that the samples have not been subjected to secondary diagenetic processes this is further supported by the results of the isotopic analyses insoluble residues were separated from the bulk carbonate through a 0 1 n hcl leach estimates of element mobility in the insoluble residue were determined through leaching studies performed on u s g s standards rgm 1 mag 1 and sco 1 elemental abundances were determined on bulk rock samples using x ray fluorescence and on bulk rock and insoluble residues using neutron activation analysis some oxides and elements e g mgo and co showed no variation throughout the section and may reflect diagenetic environment while others e g cao and sr appear to reflect lithofacies several elements e g sm eu lu and zn in both the carbonate and insoluble residue exhibit three episodes of increasing concentration upsection irrespective of lithofacies boundaries each of these gradients is terminated by a thin shale layer these gradients are viewed as developing through carbonate insoluble residue pore water interactions which lead to surface equilibrium and enrich the pore water in elements that are incompatible in the solid phases the pore water then migrates to overlying sediment layers repetition of these interactions further enriches the pore water in incompatible elements and establishes the chemical gradients in the solid phases d values were calculated from these gradients using the rayleigh equation and were used to model a second section of the rancheria the good agreement between the predicted and actual gradients seen in the second section of the rancheria is further support for the diagenetic model presented here

establishment of a continuous gps network across the kephalonia fault zone ionian islands greece abstract we report on the establishment of a continuous gps network across the kephalonia fault zone kfz central ionian islands greece the kfz is an important segment of the boundary zone between the rapidly moving aegean microplate and the apulian platform italy repeated gps measurements carried out between the northern ionian islands and the island of crete have shown rates of crustal motion of the aegean reaching 35 mm a oriented sw relative to southern italy the kfz coincides with a maximum shear strain rate 180 nano strain a and a very high level of seismicity in order to monitor the ongoing deformation across the kfz and correlate the strain accumulation with earthquakes a continuous gps network has been installed operating at a sampling rate of 5 s this paper describes the instrumental set up the data logging strategy and first preliminary results

tensile test of natural microbiotic crust abstract the mechanical properties of microbiotic crust are important to stabilize sandy surfaces in arid and semi arid regions we developed a new experimental approach to perform the tensile test of natural microbiotic crust the modulus of elasticity ultimate stress and one dimensional stress strain relation was obtained the microbiotic crust we measured exhibits linear elastic behavior firstly and then breaks this mechanical character was applied to the study of the rupture of microbiotic crust under the impact of one saltating grain a very simple dimensionless variable was suggested to quantitatively assess surface stability

transcurrent fault activity on the dead sea transform in lebanon and its implications for plate tectonics and seismic hazard fault activity within the lebanese transpression zone one of the classic examples of restraining bend development on a continental transform is here investigated using dated geomorphological features the northern part of the yammouneh fault commonly considered to be the principal active strand on this part of the dead sea transform has been inactive for the past 5 ma field observations show that basalts dated as late pliocene hi age apparently offset by the yammouneh fault unconformably overlie it the active transcurrent structure is principally perhaps exclusively the roum fault the lebanese transpressive zone has evolved through tune with migration of fault activity these results confirm the overlapping transform hypothesis for the dead sea system require the active triple junction between the transform and the tethyan collision belt to lie offshore se cyprus and have profound implications for assessing seismic hazard hi the levant

heavy metal distributions in peru basin surface sediments in relation to historic present and disturbed redox environments abstract heavy metal distributions in deep sea surface sediments and pore water profiles from five areas in the peru basin were investigated with respect to the redox environment and diagenetic processes in these areas the 10 20 cm thick mn oxide rich and minor metal rich top layer is underlain by an increase in dissolved mn and ni concentrations resulting from the reduction of the mno 2 phase below the oxic zone the mobilised associated metals like co zn and cu are partly immobilised by sorption on clay organic or fe compounds in the post oxic environment enrichment of dissolved cu zn ni co pb cd fe and v within the upper 1 5 cm of the oxic zone can be attributed to the degradation of organic matter in a core from one area at around 22 25 cm depth striking enrichments of these metals in dissolved and solid forms were observed offset distributions between oxygen penetration and mn reduction and the thickness of the mn oxide rich layer indicate fluctuations of the mn redox boundary on a short term time scale within the objectives of the german atesepp research programme the effect of an industrial impact such as manganese nodule mining on the heavy metal cycle in the surface sediment was considered if the oxic surface were to be removed or disturbed oxygen would penetrate deep into the formerly suboxic sediment and precipitate mn 2 and metals like ni and co which are preferably scavenged by mno 2 the solid enrichments of cd v and other metals formed in post oxic environments would move downward with the new redox boundary until a new equilibrium between oxygen diffusion and consumption is reached

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

episodic preservation of pteropod oozes in the deep northeast atlantic ocean climatic change and hydrothermal activity an up to 13 cm thick pteropod ooze covers the ocean floor of the northeast atlantic ocean at five stations between 44 n and 48 30 n at around 25 w at water depths of between 2800 and 3200 m subsurface pteropod horizons occur at least at two different stratigraphic levels pteropod shells both from the surface layers and from the subsurface horizons are fe mn stained with an intensity of staining that increases with age ams 14c ages of single pteropods are between 1700 yrs b p and the present for the surface layer and between 7600 and 3300 yrs b p for the upper horizon in the sediment the mn fe ratios of the pteropod coatings are between 0 24 and 0 40 indicating a hydrothermal source apparently episodic pteropod preservations record pulses of hydrothermally derived elevated mn and fe concentrations we conclude that pteropod preservation is the combined result of episodic climatically induced non dissolution and subsequent hydrothermally induced protective fe mn coating

87sr 86sr ratios in permo carboniferous sea water from the analyses of well preserved brachiopod shells abstract sr isotopic analyses of well preserved portions of permo carboniferous brachiopods distributed globally confirm the general shape of the sr isotope age curve established by previous workers for this time interval there is little variation between the sr isotopic composition of unaltered portions of brachiopods and that of portions of the same shell interpreted to be diagenetically altered based on cathodoluminescence elemental and stable isotopic data however the sr isotopic composition in diagenetically altered micritic matrix adjacent to the shell is more radiogenic the sr isotopic composition in the unaltered portions of calcitic megafossils has potential as a stratigraphie tool

active deformation and seismic potential in the serbomacedonian zone northern greece abstract the seismic potential in the central part of the serbomacedonian geological zone n greece is examined for 1 the lateral distribution of the rupture zones of the 1902 1932 and 1978 large shocks and 2 the potential stress drop stored in the area of these three shocks the distribution of rupture zones defines an area trending sse nnw and the whole length of the area examined has been ruptured since 1902 in the area of the 1902 and 1932 large earthquakes the slip accumulated is enough to generate more large shocks

the chemistry and mineralogy of haloed burrows in pelagic sediment at domes site a the equatorial north pacific the chemical and mineralogical composition of burrowed sediment recovered in 66 box cores at latitude 9 25 n and longitude 151 15 w in the equatorial pacific demonstrates the important role of infauna in determining the geochemistry of pelagic sediment haloed burrows approximately 3 cm across were present in many of the cores within early tertiary sediment that was covered by less than 5 cm of surface quaternary sediment in several cores the burrows in cross section consist of three units 1 a dark yellowish brown central zone of quaternary sediment surrounded by 2 a pale yellowish orange zone the halo of tertiary sediment which is surrounded by 3 a metal oxide precipitate the enclosing tertiary sediment is dusky brown several elements mn ni cu co zn sb and ce have been leached from the light colored halo whereas cr cs hf rb sc ta th u the rare earth elements exclusive of ce and the major oxides have not been leached the metal oxide zone 1 5 mm thick contains as much as 16 mno2 as the mineral todorokite the composition of the todorokite exclusive of the admixed tertiary sediment resembles the composition of the metal deficit of the halo and also the composition of surface ferromanganese nodules that have been interpreted as having a predominantly diagenetic origin thus bioturbation contributes not only to the redistribution of metals within pelagic sediment but also to the accretion of ferromanganese nodules on the sea floor

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

geochemical and mineralogical characteristics in two color core sediments from the korea deep ocean study kodos area northeast equatorial pacific abstract at sites 89 and 90 of the korea deep ocean study kodos located in the western part of the area between the clarion and clipperton fracture zones the topmost sediment column can be divided into two layers by a sharp color boundary an upper pale brown layer unit a and a lower dark brown layer unit b geochemical and mineralogical properties in units a and b are clearly different across the color boundary which can be interpreted to be a hiatus with an age gap of at least 3 ma the large gap in sediment ages results in an overall difference in sediment properties between units a and b that is older unit b sediment is higher in smectite contents more severe in fossil dissolution and lower in poc contents commonly due to prolonged diagenesis disappearance of the coarse mode 50 60 m of the size distribution in unit b is a result of prolonged dissolution of siliceous fossils however other phenomena occurring just below the color boundary the most severe dissolution of fossils the most frequent occurrence of coarse grained micronodules and smectite aggregates maximum value of metals mn cu ni and increased water contents can be explained by the active stirring of bottom sediments by intensified paleo bottom currents present during the hiatus that is turbulence as well as winnowing action caused by the paleo currents had respectively accelerated the dissolution of siliceous fossils and the concentration of coarse grains at the hiatus in addition micronodule formation was promoted by the efficient formation of oxygen depleted micro environments around in situ fauna remains which were buried efficiently by increased reworking and resedimentation of bottom sediments by the paleo current activity meanwhile increases in metal and water contents just below the color boundary are the results of the concentration of micronodules enriched in metals and probable formation of woodpile fabric by abundant spicules and spines respectively active stirring of bottom sediments by the intensified paleo bottom currents as well as the large gap in sediment age between units a and b are mostly responsible for the vertical variations of geochemical and mineralogical properties in two color core sediments

geochemical evolution of the central pacific ocean over the past 56 myr 1 we measured the elemental concentrations of 69 sediment samples collected at ocean drilling program site 1215 and employed a suite of statistical methods and elemental ratios to quantify the lithogenic biogenic and authigenic hydrogenous hydrothermal ahh components we show that the changes in their abundance record 1 northwestward migration of the pacific plate 2 changes in climatic and oceanographic processes associated with the transition from the eocene greenhouse into the oligocene icehouse and 3 changes in pacific spreading rates and plate reorganization the distributions of three separate lithogenic end members depend on the latitudinal positioning of the site underneath the different wind belts locations north of 22 n received material from asia which was transported to the central pacific via the westerlies locations between 20 and 22 n display a silicic volcanic composition and may reflect the boundary between westerlies and northeast trade winds locations south of 20 n are geochemically e g cr ta sc th etc distinct from locations north of 22 n and suggest a north american origin rb sc significantly increases from values of 2 8 g g 1 at 20 22 ma to 5 7 g g 1 in the modern recording the development of the east asian monsoon and formation of asian loess during the early to mid eocene 53 54 ma when site 1215 was located at 11 13 n and was above the carbonate compensation depth export production increased by 40 55 and was 25 greater than the modern value at 9 n the ahh component dominated from late eocene to the late miocene and during the late eocene may have been driven by elevated hydrothermal activity during increased seafloor spreading

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

genetic implications of trace element distributions in carbonate and non carbonate phases of limestones and dolostones from western cantabria spain abstract fe zn sr ba and pb contents are reported for carbonate and non carbonate clay fractions of lower cretaceous limestones and dolostones from western cantabria spain increases in the zn contents of both carbonate and non carbonate fractions are observed in association with the calcite dolomite transformation suggesting that the dolomitising fluids were probably enriched in this element relationships between regional geochemical trends for some elements zn in the carbonate fraction and zn ba and pb in non carbonate fraction the paleogeography of the area during the aptian and albian and the geographical positions of the localities studied lead to the conclusion that the dolomitising fluids originated from adjacent basinal mud rocks stable isotope and fluid inclusion data support this hypothesis

the effect of bioturbation and adsorption gradients on solid and dissolved radium profiles in sediments from the eastern equatorial pacific abstract remobilization of mn resulting from the diagenetic oxidation of organic carbon causes steep adsorption gradients within hemipelagic sediments of the eastern equatorial pacific transport of ra along these gradients is capable of maintaining marked 226ra 230th disequilibrium in the surface sediments pore water and solid phase 226ra profiles measured in cores from two sites in this area are modeled by adjusting the ra adsorption coefficient as a function of the depth varying mn content at manop site m the high organic carbon accumulation rate causes a sharp redox gradient within the upper 10 cm of sediment biological mixing is constant and rapid 500 cm2 kyr in this upper layer below which the mn content the ra adsorption coefficient and the 226 ra 230 th ratio are all sharply reduced at manop site h the organic carbon accumulation rate is less and therefore the redox gradient is expanded over a greater depth scale in the surface sediment biological mixing is slower decreases with depth and gradients in the adsorption coefficients and 226 ra 230 th ratio are less marked than at site m

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

the sinai triple junction revisited abstract this paper is a summary of a more detailed analysis of the kinematics of the sinai triple junction courtillot et al 1987 accurate kinematic data are lacking along the red sea and they can be supplemented by bathymetric topographic and geological data pertaining to the three arms of the entirely continental sinai triple junction motions across the northern red sea and along the gulf of elat are an order of magnitude larger than across the gulf of suez the direction of motion there remains a major uncertainty a possible kinematic model is highlighted in which right lateral strike slip motion and small pull apart basins occur along the gulf of suez in agreement with recent field observations in egypt early miocene is marked by major geodynamical changes all along the northern boundaries of the african and indian plates we suggest that rifting in the arabian sea gulf of aden red sea and gulf of suez was initiated at the end of the first phase of continental extrusion of indochina when the tibetan plateau began to rise and spreading in the south china sea came to a halt

atypical ferromanganese nodules from pelagic areas of the central indian basin equatorial indian ocean abstract two box core samples one each from red clay and siliceous ooze sediment provinces from the central indian basin indian ocean were studied both cores contained ferromanganese nodules at their tops the red clay sediment also hosts buried nodules at a depth of 82 cm chemical characterization of the sediments indicates that early diagenetic remobilization of transitional metals is pronounced in the siliceous ooze sediment while in the red clay no such effect is discernible this is further corroborated by the abundance and dissolution patterns of microorganisms and ferromanganese micronodules occurring in the two sediment columns bulk chemical analyses indicate that all the nodules are of the hydrogenetic b type vernadite and todorokite are the major minerals both of which constitute laminated nondirectional colloform and cuspate microstructures petrographic studies yield evidence of recrystallization of todorokite and partial transformation of vernadite to todorokite the former process being more advanced in buried nodules microprobe analyses revealed that primary todorokite has a lower mn fe ratio and higher ni content than recrystallized todorokite in the same sample the mineralogical reconstitution in the nodules is attributed to postdepositional intranodule diagenesis the present study does not reveal the correlation between mineralogy and microstructure in the nodules which has been suggested for the nodules from the pacific neither can any mineral or microstructure be considered specific for any particular genetic model the studied nodules are therefore atypical the mineralogical and chemical reordering in these ferromanganese nodules raises the question of the viability of radiometric methods in determining growth rates of such nodules

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

the itrf96 realization and its associated velocity field this text intends to present and to analyse the quality of the new 1996 edition of the international terrestrial reference system called the itrf96 the itrf96 represents a key step forward in the activity of the iers terrestrial system determinations a new physical combination model has been developed as well as a new stochastic model for the first time the level of accuracy has reached 1 cm or better in position for about 50 of itrf96 stations and 30 of the stations have their velocities determined free of any aditional tectonic plate model assumption with an uncertainty better than 3 mm yr the itrf96 also provides a more complete solution a new software has been developed which makes available the itrf96 full variance covariance matrix whereas this information was restricted to station positions in the previous itrf94 edition moreover the network coverage is clearly the largest set of globally distributed terrestrial space geodesy stations that have ever been computed 521 stations located among 290 sites in addition station velocities are also determined at a very accurate level allowing possible determination of kinematic plate motion models free of any geological assumption

fluxes of 226ra and barium in the pacific ocean the importance of boundary processes abstract the 226 ra ba ratio in particles collected in sediment traps decreases with depth fluxes of ba and al increase with depth these observations cannot be explained by simple vertical processes instead they require a component to the deep flux which originates at the ocean margins we suggest that the deep traps are enriched in ba through the advection of barite originally precipitated in biologically productive regions of the ocean margin this source is less important for 226 ra because some is lost by radioactive decay between the precipitation of barite on the margin and outward transport the boundary flux is an important source of material to the deep sea from 226 ra fluxes in the upper 1000 m of the water column we estimate that the residence time of 226 ra in the upper ocean is 400 years the removal of 226 ra in the particle flux is approximately balanced by the upwelling of waters enriched in 226 ra

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

authigenic magnetite formation in suboxic marine sediments the resolution and reliability of magnetostratigraphy and reconstructed time series of geomagnetic field behaviour depend critically on where remanence is acquired and fixed in the sediment column and whether the magnetization is altered chemically after deposition if authigenic magnetic minerals are formed at depth or if the magnetic carriers are changed after deposition then the nature and timing of magnetic events can be affected by depth offsets in remanence acquisition and mixing of detrital and authigenic signals using palaeo and rock magnetic and sediment geochemical analyses we have studied how early diagenesis affects the magnetic properties of suboxic hemipelagic sediments here we report evidence of the formation of fine grained authigenic magnetites near the commonly observed brown tan green colour boundary which marks the transition from fe oxidizing to fe reducing conditions we propose that biogenic magnetite produced by magnetotactic bacteria forms as part of the microbially mediated sequence of reactions involved in the oxidation of organic matter the magnetite is created as a metabolic by product of the microorganisms use of iron redox transitions as a source of energy active magnetite formation appears to be restricted to a zone between the levels of nitrate and iron reduction

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

the strontium isotopic composition of brigantian late dinantian seawater abstract strontium isotopic determinations of different fossiliferous biominerals from brigantian late dinantian carbonates in northern england reveal that many are affected by diagenetic overprinting of their original 87 sr 86 sr ratios only pristine non luminescent articulate brachiopod shell material can be used to gain reliable estimates of carboniferous and by deduction palaeozoic ocean chemistries conodonts are found to be the only type of phosphatic biomineral capable of preserving original palaeoseawater chemistries however this only applies to specimens subjected to minimal burial temperatures other phosphatic biominerals are conclusively shown to be readily susceptible to diagenetic overprinting of original sr isotopic ratios a brigantian strontium curve compiled from pristine brachiopod calcite shows a relatively complex evolution with time but it can be resolved into two separate components operating on different time scales a cyclic sinusoidally shaped component with a frequency of 1 ma appears to fluctuate about a longer term more gradual linear increase in the brigantian seawater isotopic composition

distribution of major trace and rare earth elements in surface sediments of the wharton basin indian ocean bulk chemical analyses of eighteen surface sediments taken on an east west transect lat 15 40 s in the wharton basin indian ocean were analysed for major trace and rare earth elements ree by inductively coupled plasma atomic emission spectrometry icp aes the relationship between al and k suggests in situ formation of authigenic phillipsite the relationship between p and ca suggests accumulation of biogenic apatite fish bone debris from high biological productivity waters which is confirmed by the linear relationship with p and cu a strong positive correlation among redox sensitive metals mn fe cu ni and zn suggests that they are incorporated into a ferromanganese oxide phase probably micronodules calcareous oozes from the transect have low ree abundance la 8 ppm with a very strong negative cece value 0 41 siliceous oozes have high ree abundance la 28 ppm with moderate positive cece 1 24 and red clays have highest ree abundance la 66 ppm with a weak positive 1 05 to moderate negative cece 0 73 shale normalized ree patterns and layb n ratios record similar enrichment of heavy ree hree relative to light ree lree in all sediment types this might be due to retention of the bottom water ree pattern and the presence of fish bone debris correlation coefficient and r mode factor analyses suggest a very strong positive association r2 0 9 of ree with p and thus most likely with biogenic apatite fish bone debris as p is directly associated with biological activity it is thus related to surface primary productivity ree in the wharton basin sediments appear to reflect a combination of surface water effects and diagenetic processes

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

growth of diagenetic ferromanganese nodules in an oxic deep sea sedimentary environment northeast equatorial pacific abstract to study the accretion mechanism of diagenetic ferromanganese nodules formed in an oxic deep sea sedimentary environment manganese nodules sediments and pore waters were sampled in the northeast equatorial pacific diagenetic ferromanganese nodules are ellipsoidal to discoidal in shape rough in surface texture enriched in cu ni and 10 a manganite and are ubiquitous on the abyssal plain hydrogenetic nodules are polynucleated irregular in shape smooth in surface texture enriched in co and mno 2 and occur dominantly on seamounts numerous microlayers with diagenetic or hydrogenetic characteristics occur successively in the nodules concentration of nitrate in sediment pore waters indicates that overall redox conditions are oxic however mn oxide grains on the walls of burrows and worm tubes are interpreted to be reprecipitated metal ions supplied from oxygen depleted microenvironments that formed in the oxic sediment column by decomposition of organic matter active mixing of bottom sediments by benthic fauna and bottom currents is indicated by ubiquitous burrows worm tubes and tracks and trails high values in sediment mixing coefficients 1 cm 2 yr and scattering of data points in depth profiles of pore water nitrate concentrations we suggest that diagenetic ferromanganese nodules in an oxic deep sea sedimentary environment grew from remobilized metal ions as well as reprecipitated mn oxide grains which were supplied to the nodules episodically during the stirring of bottom sediments by benthic fauna and intermittent strong bottom current flow

microplate versus continuum descriptions of active tectonic deformation whether deformation of continents is more accurately described by the motions of a few small rigid plates or by quasi continuous flow has important implications for lithospheric dynamics fault mechanics and earthquake hazard assessment actively deforming regions of the western united states central asia japan and new zealand show features that argue for both styles of movement but new observations are necessary to determine which is most appropriate and at what scale the description applies geologic geodetic seismic and paleomagnetic measurements tend to sample complementary aspects of the deformation field so an integrated observation program can utilize the strengths of each method and overcome their separate spatial or temporal biases provided the total relative motion across each region is known and the distribution of active faults is well mapped determination of fault slip rates can provide potentially decisive constraints reconnaissance geological studies supply useful slip rate estimates but precise values depend upon detailed intensive investigation of individual sites geodetic survey measurements can determine the spatial pattern of contemporary movements and extract slip rate information but the sometimes elusive effects of cyclic elastic strain buildup and relief must be accounted for in relating current movements to the long term deformation pattern earthquake catalogs can be applied to determine seismic strain rates and relative velocities but must be averaged over large regions and are usually limited by the inadequate duration of historical or instrumental seismicity catalogs paleomagnetic determinations of vertical axis rotations provide estimates of block rotation rates but are often locally variable and averaged over many millions of years which of the two descriptions of continental tectonics is more nearly correct depends on the local rheological stratification of the lithosphere especially the strength and thickness of the elastic crust relative to the ductile lithosphere and dynamical models can provide contrasting forecasts of observable features with testable consequences

origin of dolomites in the lower cambrian xiaoerbulak formation in the tarim basin nw china implications for porosity development abstract dolomites occur pervasively in the cambrian strata in the tarim basin nw china although the cambrian strata have been deeply buried and affected by multiple phases of dolomitization some intervals in the upper part of the lower cambrian xiaoerbulak formation developed high porosity the goal of this study is to understand the origin of different types of dolomites and the formation mechanism of the porosity in the xiaoerbulak formation the geochemistry of matrix dolomites suggests that they formed from middle rare earth element mree enriched anoxic pore fluids close to or within the zone of iron reduction the similar ree y patterns and overlapping 13 c values between pore filling and matrix dolomites indicate that the fluids that were responsible for the precipitation of pore filling dolomite apparently inherited the signatures of the formation waters that were stored in the host strata low 18 o values coupled with high ba zn and rare earth element ree content of pore filling dolomites indicate that pore filling dolomites were formed at elevated temperatures the precipitation of authigenic quartz and saddle dolomites and high mn content in pore filling dolomites indicate that hydrothermal fluids that mostly originated from cambrian basinal clastic units or basement rocks were involved the mixture of formation water and external hydrothermal fluids is the most likely explanation for the formation of significant porosity and precipitation of pore filling dolomites at depth breccia dolomite zebra dolomite and saddle dolomite occur mostly in areas that are close to faults which suggests that hydrothermal fluids passed through strike slip faults in this area when these faults were activated the development of permeable layers in the upper part of the xiaoerbulak formation overlain by impermeable layers of the wusongger formation suggests a possible potential diagenetic trap when the faults were activated high pressure and high temperature fluids flowed up through faults and hit low permeability beds at the base of the wusongger formation then the hydrothermal fluids flowed laterally into permeable dolomite strata at the top of the xiaoerbulak formation and encountered the formation brines large volumes of secondary porosity formed when host dolomite was leached by the mixing fluids and pore filling dolomites and other minerals formed soon afterward both the faults and original host facies exerted important influences on the lateral extent of the dissolution

why are there no clockwise rotations along the north anatolian fault zone mechanical analysis of lithospheric deformation associated with an intracontinental transform fault suggests that it should be associated with a pattern of vertical axis rotations governed by the length of the fault its displacement and the mechanical properties of the lithosphere paleomagnetic results from two transects across the north anatolian fault zone indicate that there have been no measurable clockwise rotations on a regional scale associated with neogene dextral strike slip motion along the fault the data come from two groups of volcanic rocks that have been dated by k ar whole rock geochronology and have yielded ages ranging from 45 3 3 1 m y to 41 8 1 3 m y eocene and 21 7 1 5 m y to 7 5 0 2 m y miocene the absence of clockwise rotations suggests one of the following explanations 1 in contrast to the assumptions underlying current mechanical analyses deformation in the upper crust may not directly reflect the flow in the lithosphere and is localized along a single fault trace 2 deformation is distributed but rotations have been prevented by the presence of elongate fault blocks subparallel to the trace of the main fault 3 displacement along the north anatolian fault may be too small or the rheologic properties of the lithosphere such that rotations about vertical axes cannot be resolved instead of the predicted clockwise rotations measured declinations show that there has been approximately 30 of anticlockwise rotation of both the eocene and miocene volcanic rocks this suggests that no significant rotation occurred between eocene and miocene times and that the anticlockwise rotation occurred either immediately before or concurrent with the plio pleistocene slip on the north anatolian fault

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

the strain rate field in the eastern mediterranean region estimated by repeated gps measurements we use the combined gps velocity field of the eastern mediterranean for the period 1988 to 1996 to determine crustal deformation strain rates in a region comprising the hellenic arc the aegean sea and western anatolia we interpret the velocity field and determine the strain rate tensor by the spatial derivatives of the collocated motion vectors the region following the line marmara sea north aegean trough northern central greece and the central ionian islands is associated with strong right lateral shear motion with maximum shear strain rates of 180 nano strain a 180 10 9 a in the central aegean sea n s oriented extensional processes prevail reaching 100 nano strain a the southern aegean is characterized by relatively small strain rates maximum extensional components of the strain rate tensor reaching 150 nano strain a in a n s direction are found in central greece the hellenic arc is associated with moderate arc parallel extension and strong compression perpendicular to it projections of the strain rates parallel to the major fault zones reveal that the northern aegean is governed by the westward continuation of the north anatolian fault zone which is associated with strong dextral shearing maximum 220 nano strain a accompanied by numerous large earthquakes in this century

geodetic strain of greece in the interval 1892 1992 a first order triangulation of greece was carried out in the 1890s reoccupation using global positioning system receivers of 46 of the 93 original markers yielded estimates of the deformation of the region over the intervening interval broad regions have similar geodetic strain over the 100 year time span strain north of the gulf of korinthos is predominantly north south extension though with a significant east west component the central peloponnisos is relatively stable whereas the gulfs of the southern peloponnisos are all characterized by uniaxial east west extension the seismic expression of strain for the entire region calculated from the seismic moment tensors of earthquakes of m s 5 8 during the past 100 years accounts for only 20 50 of the geodetically determined strain at a scale of 50 100 km the fraction of the strain that is expressed seismically varies much more than this range in particular whereas seismic strain in the eastern gulf of korinthos over the past 100 years is commensurate with the geodetic strain there is rapid extension across the western gulf of korinthos 0 3 strain yr 1 with negligible seismic strain for the 100 year period prior to 1992 the egion earthquake of june 1995 in the western gulf of korinthos released only a small proportion 20 of the elastic strain that had accumulated in that region the observed distribution of displacements can be explained by the relative rotation of two plates with a broad accommodation zone between them but it is equally consistent with the deformation that would be expected of a sheet of fluid moving toward a low pressure boundary at the hellenic trench a simple calculation implies that if the region does behave as a fluid then its effective viscosity is 10 22 10 23 pa s such viscosities are consistent with the deformation of a lithosphere obeying a rheological law similar to that obtained for olivine in the laboratory

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

ree fe variations in hydrothermal sediments implications for the ree content of seawater seafloor hydrothermal vent solutions exhibit rare earth element ree enrichments ranging between one to three orders of magnitude greater than average seawater to assess the impact of these hydrothermal inputs on ocean chemistry we have examined the behavior of rees for hydrothermal sediments collected adjacent to two pacific spreading ridge sites the east pacific rise at 19 s and the southern juan de fuca ridge at 4s n in general the ree fe ratios for both proximal and distal hydrothermal sediments are greater than vent solutions by a factor of 2 to 500 and these ratios increase with increasing distance away from the ridge axis an evaluation of these results in the context of previous models of ree behavior indicates that in fact seawater experiences a net depletion in rees as a result of hydrothermal activity this is due primarily to the large scavenging capacity of iron oxyhydroxides which precipitate from these solutions such an interpretation explains why the ree content of seawater collected in the vicinity of hydrothermal vents is anomalously lower than normal seawater sampled from a comparable depth

scientific objectives of current and future wegener activities abstract the wegener group has promoted the development of scientific space geodetic activities in the mediterranean and in the european area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research wegener currently has three scientific objectives which are related to plate boundary processes sea level and height changes and postglacial rebound in a full exploitation of the space geodetic techniques namely slr vlbi and gps the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories in the past particularly slr observations within wegener medlas have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the mediterranean with high precision with gps spatially denser site distributions are feasible and in several wegener projects detailed studies of tectonically active areas were possible on the basis of repeated episodic gps observations current projects associated with wegener are successful in separating crustal movements and absolute sea level variations as well as in monitoring postglacial rebound these tasks require high precision height determinations a problem central to all of the present wegener activities in these projects continuously occupied gps sites are of increasing importance time series of heights observed with continuous gps can be determined with a few centimeters rms error thus enabling the reliable estimates of vertical rates over relatively short time intervals regional networks of continuous gps sites are already providing results relevant for example for the study of postglacial rebound the mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes and the wealth of observations acquired in previous wegener projects together with new space geodetic observations will allow the test of geophysical hypotheses linking three dimensional deformations of the earth s surface to the dynamics of the earth s interior in particular it is anticipated that wegener projects will aim at a test of the slab detachment hypothesis the complex investigations on sea level fluctuations presently carried out at basin scale from the strait of gibraltar to the black sea make it possible to study the present and recent past interactions of ocean atmosphere and solid earth as well as to develop appropriate models to assess future aspects

the hydrothermal component in ferromanganese nodules from the southeast pacific ocean abstract statistical analyses of geochemical data from ferromanganese nodule samples representing a broad area of the southeast pacific ocean indicate nodule compositions are controlled by four factors 1 suboxic diagenesis 2 oxic diagenesis 3 hydrogenous precipitation and 4 hydrothermal precipitation the first three are identical to those identified in studies of nodules from the north pacific the fourth factor represents the first quantitative determination of a significant hydrothermal end member in ferromanganese nodules nodules apparently acquire a hydrothermal component through the accretion of colloidal sized hydrothermal precipitates which are widely dispersed from their origin at vents along the east pacific rise epr nodules recovered from beneath the shadow of the present day hydrothermal plumes emanating from the epr contain significantly higher amounts of hydrothermal material relative to nodules from other areas

source mechanism of the bartin earthquake of september 3 1968 in northwestern turkey evidence for active thrust faulting at the southern black sea margin abstract the bartin earthquake of september 3 1968 is the strongest instrumentally recorded earthquake to occur along the black sea margin in northwestern turkey the source mechanism of the bartin earthquake as determined in this study from long period p wave first motions and from the inversion of p and sh waves indicates thrust faulting with a strike of 28 dip of 38 and rake of 80 the average centroid depth is 4 km and the seismic moment is 3 9 10 25 dyn cm the bartin earthquake provides the first evidence for active thrust faulting at the southern margin of the black sea the black sea has probably evolved as a back arc basin resulting from the northward subduction of tethys seismicity fault plane solutions and other geophysical data suggest that at the present time the black sea is closing under north south compression

gps and geologic estimates of the tectonic activity in the marmara sea region nw anatolia a dense network of 52 global positioning system gps sites is used to determine the velocity field and strain rate pattern at the western end of the north anatolian fault zone nafz in the marmara sea region nw anatolia based on four gps campaigns carried out biannually between 1990 and 1996 the detailed kinematic field of crustal motion is calculated the southernmost station shows an average rate of 22 3 mm yr oriented westward relative to istanbul eurasia this value is indicative of the dextral strike slip motion of nw anatolia relative to the black sea the gps velocity field reveals that the sites located on the thrace black sea block show negligible motion relative to istanbul the gps based deformation pattern of three sections crossing the westward prolongation of the nafz is compared with neotectonic data both the gps and the neotectonic data give clear evidence that most of the deformation occurs along a relatively narrow e w oriented zone this belt extends from the single fault trace of the nafz through the gulf of izmit the marmara sea the arkoy region and the gulf of saros into the north aegean trough nat in addition the cross sections show the increasing influence of the n s oriented extension in the aegean sea region from the comparison of the directions and rates of shear and normal strain deduced from gps data with geologic and seismic observations we conclude that the most active zone of dextral shear follows a line along mudurnu valley the northern marmara sea and the saros trough where it joins the nat

global positioning system gps estimates of crustal deformation in the marmara sea region northwestern anatolia abstract in the marmara sea region the relative motion between the anatolian and eurasian lithosphere has been measured by means of the modern techniques of space geodesy using the global positioning system gps in order to resolve in detail the kinematic field within the active earthquake belts of northwestern anatolia two gps campaigns were carried out across a dense network consisting of 45 sites preliminary results reveal horizontal westward motion of anatolia relative to eurasia of 2 4 cm y on average that runs along the western end of the north anatolian fault zone e w oriented right lateral strike slip movement average 0 06 ppm y maximum 0 13 ppm y 1ppm y 1 strain y and ne sw extension average 0 06 ppm y maximum 0 21 ppm y can be obtained from the calculated strain field in the west strike slip motion trending wsw ene is observed these findings are compared to the stress pattern derived from seismology and neotectonics