structural evolution of the latakia ridge and cyprus basin at the front of the cyprus arc eastern mediterranean sea abstract the active deformation front between the african and anatolian plates in the eastern mediterranean is delineated by the cyprus arc present plate kinematic vectors and earthquake data suggest that the movement along the eastern extent of the cyprus arc is largely sinistral strike slip it is however widely accepted that subduction took place beneath cyprus until the early miocene subduction has since thought to have become impeded by the collision of the eratosthenes seamount with the island of cyprus the deformation front of the cyprus arc is dominated by the latakia ridge a steep narrow high which merges gradually with the lower slope of the broad hecataeus rise in the west and extends to the northern levantine coast in the east where the expression of the ridge changes to a number of narrow northeast trending ridges and basins the latakia ridge has previously been interpreted as either a thrust culmination or a positive flower structure this study uses high resolution marine seismic reflection profiles to delineate the stratigraphic and structural architecture of the deformation front from seismic profiles four stratigraphic units bounded by major basin wide unconformities can be identified these units are eocene lower miocene miocene uppermost miocene messinian and pliocene quaternary the timing of deformation determined from growth stratal architectures on the flanks of the major structures show that two main phases of deformation characterize the structural history of the deformation front each of these phases represents a different kinematic regime a compressional regime dominated during the miocene whereas a strike slip regime dominated in the pliocene quaternary

a study on the regulation of the concentrations of some trace metals rb sr zn pb cu v cr ni mn and mo in saanich inlet sediments british columbia canada abstract bulk metal concentrations were measured in the sediments of saanich inlet in an attempt to establish the occurrence of trace metal enrichment in the anoxic central basin ba ni v cr zn pb cu and mo were found to be enriched in the anoxic ooze over the possible contributions from lithogenic sources spatial and seasonal variations in the chemical composition of the settling particulates collected with interceptor traps gave further indications of the mode of incorporation of these metals biogenic ba and cr appeared to be associated with opaline silica although alternative explanations are also possible particularly for ba zinc seemed to be added to the sediment essentially in association with planktonic materials while cu required an additional source directly linked to the anoxic environment similarly ni v and mo were added to the anoxic sediments by reactions occurring at the sediment water interface in the nearshore environment studied here these metals particularly ni and mo were not associated to any significant extent with planktonic materials of all the elements analyzed mo showed the largest enrichment in the anoxic sediments of saanich inlet

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

rare earth element geochemistry of the metamorphosed volcanogenic massive sulfide deposits of the manitouwadge mining camp superior province canada a potential exploration tool trace and rare earth element bee geochemistry indicates that rocks in the manitouwadge mining camp were derived from three major lithological units mafic volcanic rocks acid volcanic tuffs and dacites the geco willroy willecho and big nama creek cu zn ag deposits are contained within the 2720 ma acid volcanic tuffs our study suggests that the thickness of the felsic volcanic unit acid tuffs and volcaniclastics may be significantly underestimated in the area medium to high grade metamorphism upper amphibolite lower granulite gave rise to specific alteration assemblages which crystallized during several episodes of deformation and plutonism because major element geochemistry of the rocks was modified during ore forming processes and later by several episodes of metamorphism and tectonism the present alteration minerals merely reflect the cumulative effect s of these episodes and are often misleading in the identification of the protoliths thus due to extensive alteration the protoliths of various lithological units can be positively identified only from trace and rare earth element geochemistry extensive up to 97 light ree depletion was observed in the felsic volcanic rocks around the geco willroy and willecho deposits the positive correlation between bee mobility and mineralization suggests that ree geochemistry can be successfully used in the exploration for volcanogenic massive sulfide deposits around the manitouwadge mining camp the absence of a well defined discordant alteration pipe at geco and localized enrichment in fe al or k at the willroy willecho big nama creek and geco deposits implies that they may be highly metamorphosed equivalents of mattabi type deposits where the original iron rich carbonates have recrystallized to calc silicate or amphibole rich assemblages during regional metamorphism localized enrichment in fe al and k in the felsic tuffs could be used to identify possible alteration pipes or semicomformable alteration zones associated with mineralization

influence of sedimentation on enrichment of manganese and growth of ferromanganese micronodules bengal fan india abstract based upon down core variations in o mn ratio in sediment and in micronodules mn content organic carbon and abundance of micronodules in two box cores from high and low sedimentation regions of the bay of bengal 0 20 and 0 40 cm levels were identified as mn oxidation zone in the western and the eastern regions of the bay despite similarity in bottom water o 2 and organic carbon contents of the region a higher abundance of micronodules down to the deeper levels was observed in the area of low sedimentation but in the upper surfaces increased enrichment of mn was observed in core 1 located in the area of higher sediment accumulation rapid recycling of mn faster burial transfer to mn reduction zone mn dissolution and its upward diffusion re precipitation increasing upward flux of mn ii and associated higher consumption of o 2 limits the width of mn oxidation zone and appears to be responsible for enhanced enrichment of mn in the area of high sedimentation the results of the present study also suggest that though the availability of mn controls the formation of micronodules their resident time in mn oxic zone regulates their growth and influences their morphology

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

the oxidation state of manganese in marine sediments and ferromanganese nodules marine sediments and ferromanganese nodules from the pacific ocean have been analyzed for the omn ratio of solid manganese we tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples we choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences the ferromanganese nodules that we analyzed were all from manop site h and had mnfe ratios that ranged from 5 6 to 70 these nodules were invariably highly oxidized with omn values ranging from 1 90 to 2 00 our most precise analyses suggest that less than 1 of the total manganese is present as mn ii we also analyzed red clay and hemipelagic sediments from the eastern tropical pacific baja borderland and manop site h and carbonate ooze samples from the equatorial pacific these sediments are also highly oxidized omn 1 90 to 2 00 except when mn ii appears in the interstitial water as dissolved mn ii increases the value of the omn ratio in the solid phase decreases the omn ratio decreases to values as low as 1 40 this decrease appears to be due to a decrease in oxidized manganese by reduction however an increase in reduced manganese in the solid sediments by adsorption or mnco3 formation can not be ruled out in all cases

geochemical and oxygen isotope signature of sea floor alteration associated with a polydeformed and highly metamorphosed massive sulfide deposit ruostesuo central finland massive sulfide deposits in the vihanti pyhasalmi district central finland are hosted by a highly deformed and metamorphosed bimodal volcanic sequence alteration zones that envelop these deposits are composed of cordierite orthoamphibole garnet bearing rocks referred to as cor rocks belonging to upper amphibolite to granulite facies outcrops of mafic and felsic cor rocks mcor and fcor in the vicinity of the ruostesuo zn cu deposit define mappable layers with distinctive metamorphic mineral assemblages orthoamphibole cordierite plagioclase quartz m1cor garnet orthoamphibole cordierite plagioclase quartz m2cor quartz cordierite biotite orthoamphibole cummingtonite garnet plagioclase f1cor and quartz cordierite garnet sillimanite f2cor these rocks are interlayered with or grade into typical amphibolites i e hornblende plagioclase and quartz plagioclase bearing rocks that are interpreted as least altered mafic and felsic metavolcanic rocks respectively whole rock geochemical data for least altered metavolcanic rocks and cor rocks at ruostesuo define three mafic suites primitive basalts basaltic andesites and ferrobasalts and two felsic suites r1 and r2 rhyolites using a combination of high field strength element ratios and rare earth element profiles cor rocks can be assigned to all five volcanic suites calculated mass changes for the majority of exposed cor rocks at ruostesuo are similar to those reported for chlorite quartz assemblages found within the inner core of alteration pipes located below some sea floor massive sulfide deposits relative to least altered precursors mafic cor rocks have gained fe mg s and lost variable amounts of si ca na k rb ba sr and eu which resulted in an average net mass loss of about 10 percent the bulk composition of most altered mafic cor rocks near total loss of ca na k reflects the proportion of chlorite to quartz within the premetamorphic alteration assemblages and the composition of the chlorite mass change results for altered mafic rocks indicate that basalts at ruostesuo were altered by an evolved fe rich hydrothermal fluid at high water rock ratios mass changes for cor rocks of the r2 felsic volcanic suite are similar to those of the mafic rocks enriched in fe mg and depleted in ca na k rb ba sr and eu except for significant additions of si that resulted in net mass gains of 20 to 30 percent felsic cor rocks of the r1 volcanic suite show gains in k rb and ba that are attributed to the formation of premetamorphic sericite during an alteration stage dominated by hydrothermal seawater in comparison to least altered metavolcanic rocks mafic and felsic cor rocks are depleted in 18o with delta 18o values 2 to 5 per mil lower than precursor rocks estimated temperatures of alteration were 270 to 350 c these data indicate that the signature of a high temperature 300 c sea floor hydrothermal upflow zone is preserved within upper amphibolite to granulite facies rocks at ruostesuo the stratigraphic boundary between strongly chloritized mafic volcanic rocks and silicified felsic volcanic rocks marks a transition from net mass losses associated with hydrothermal fluid dominated alteration to net mass gains associated with seawater dominated alteration silicification at or near the boundary between mafic and felsic volcanic rocks may have been the result of conductive cooling or mixing with seawater from above in the absence of textural or crosscutting relationships indicative of a younging direction a stratigraphic model is proposed on the basis of the above geochemical constraints altered basalts at ruostesuo represent the exposed base of a chloritic stockwork zone that passes upsection into altered felsic volcanic rocks that host massive zn cu sulfides this stratigraphic model has significance for the interpretation of other massive sulfide deposits in the vihanti pyhasalmi district and exploration strategies that couple chemostratigraphy with mass change results more significantly the preservation of premetamorphic oxygen isotope values for strongly metamorphosed and locally migmatitic cor rocks indicate that oxygen isotope mapping is a viable exploration tool in the district and in other mineralized upper amphibolite to granulite facies terranes worldwide

marine geologic evidence for a levantine sinai plate a new piece of the mediterranean puzzle marine geophysical data recorded offshore egypt illustrate the presence of an active fault belt trending n145 e that obliquely transects the eastern nile deep sea fan this belt more than 150 km long consists of a series of linear transtensive faults with an apparent right lateral horizontal component these fault zones bound thick sediment filled grabens where linear salt ridges and diapirs represent likely messinian salt reactive response to regional transcurrent geodynamics we infer that this tectonic belt might correspond to an offshore extension of the gulf of suez rift system if our hypothesis is correct this fault belt might represent the western boundary of a levantine sinai microplate locked between the major arabia and africa plates and the anatolian aegean microplate

a model for the deposition of hydrothermal manganese near ridge crests a two stage scavenging model is used to describe the transport of hydrothermal mn to the sediments adjacent to ridge crests dissolved mn is hypothesized to be scavenged by slowly settling metal depositing capsuled bacteria which in turn are incorporated into rapidly settling macroaggregates upon reaching the seafloor the mn is subject to resuspension in particulate form and to remobilization within the sediment column and release back into the water column as dissolved mn measured mn distributions in the vicinity of the southern juan de fuca ridge and estimated values of process rate constants are used to limit the range of possible model outcomes the results present a picture of water column distributions and fluxes of dissolved fine particulate and large particle associated mn in a plume advecting off axis the model and best available parameter values suggest that more than 80 of the hydrothermal mn is deposited within several hundred kilometers of the ridge crest though dissolved mn concentrations beyond that distance exceed background levels by many times the residence time of hydrothermal mn in the water column is of the order of several years an off axis component of advection of the order of 0 1 0 3 cm s is needed to make similar the model and measured distributions of mn depositing in the sediments

multiple opening and closing of the eastern mediterranean and south china basins the eastern mediterranean east of crete and the south china basin are small ocean basins surrounded by continental masses and are currently undergoing closure they were both formed by the rifting of continental fragments away from large continents a comparison of the geological evolution of the two basins indicates a remarkable similarity in the sequence of evolutionary stages that took place in both basins although the age of these stages is probably different for each of the two the formation of the two basins is a consequence of a much larger process in which large lithospheric plates south and north of the basins move toward each other africa including sinai and arabia toward eurasia and india australia toward eurasia and the pacific each basin went through several stages of evolution during which oceanic crust was created and destroyed during each stage the area of the newly formed oceanic crust was smaller than the area formed in the previous stage it appears as if similar evolutionary patterns also occurred in other marginal and small ocean basins formed by continental rifting

alexandria nile delta coast egypt update and future projection of relative sea level rise previous studies have indicated that the nile river deltaic plain is vulnerable to a number of aspects including beach erosion inundation and relatively high rates of land subsidence this issue motivates an update and analysis of new tide gauge records from which relative sea level changes can be obtained estimated rates from five tide gauges are variable in terms of magnitude and temporal trend of rising sea level analysis of historical records obtained from tide gauges at alexandria rosetta burullus damietta and port said show a continuous rise in mean sea level fluctuating between 1 8 and 4 9 mm year the smaller rate occurs at the alexandria harbor while the higher one at the rosetta promontory these uneven spatial and temporal trends of the estimated relative sea level rise rslr are interpreted with reference to local geological factors in particular holocene sediment thickness subsidence rate and tectonism are correlated with the estimated rates of relative sea level change from the relatively weak correlation between them we presume that tectonic setting and earthquakes both recent and historical ones contribute more to accelerated rslr than that of dewatering and compression dewatering of holocene mud underlying the nile delta plain as a result large areas of the coastal plain have been subsided but some sectors have been uplifted in response to tectonic activities of thick underlying older strata projection of averaged sea level rise trend reveals that not all the coastal plain of the nile delta and alexandria is vulnerable to accelerated sea level rise at the same level due to wide variability of the land topography that includes low lying areas high elevated coastal ridges and sand dunes accretionary beaches and artificially protective structures interaction of all aspects tectonic regime topography geomorphology erosion rate and rslr rate permitted to define risk areas much vulnerable to impacts of sea incursion due to accelerated sea level rise

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

manganese authigenesis in the landsort deep baltic sea abstract manganese mineralogy because of its redox sensitivity is a valuable parameter for interpreting water column anoxia and sediment diagenesis in the baltic and especially the landsort deep the relatively widespread occurrence of mn carbonates and the unique observations of authigenic mn sulphides in sedimentary environments need to be accounted for within the models proposed for mn authigenesis in diverse settings in this study stratigraphic changes in the geochemistry and mineralogy are documented in two gravity cores using petrographic microscopy xrd sem eds analyses of c and s content 13 c isotopes icp ms cation determinations and electron microprobe element profiling the lamination in the bottom sediments of the landsort deep suggests essentially continuous anoxic conditions at the sediment surface during the last ca 4500 14 c years the most striking variations in the sediments are related to the occurrence of two mn ii precipitate rich sapropel intervals recent and 1390 1990 14 c years bp sapropel deposition is associated with relatively slow detrital sedimentation allowing the concentration of organic matter the sediment c org content is influenced by the variations in the primary production as well as the supply of terrestrial c org but a major control appears to be detrital dilution the precipitation of mn carbonate as individual aggregates of spherical particles dispersed within clayey sediment matrix and as laminae with semi seasonal cyclicity is believed to be largely induced by the high alkalinity in connection with organic matter deposition and degradation where h 2 s has exceeded fe availability mns has also precipitated most commonly as well developed hexagonal crystals but also as the cubic variety alabandite which has not previously been reported from a sedimentary environment an expansion of the anoxic bottom water conditions during sapropel deposition is interpreted by correlation with laminated intervals on the slope of the deep basin budget calculations for the supply of mn to the basin during mn rich sapropel formation can be better balanced by the addition of mn from dissolution of oxides formed prior to the anoxic expansion the importance of alkalinity for the precipitation of mn carbonates and sulphides does not exclude the need for considerable mn concentrations but the model argued in several recently published studies stressing mn availability as the major control does not seem appropriate for the landsort deep and may be too restrictive in many other settings as well

the composition and diagenesis of interstitial solutions ii fluxes and diagenesis at the water sediment interface in the high latitude north and south atlantic studies of the major element composition of in situ sampled pore waters are reported for the north atlantic and southern ocean between africa and antarctica the pattern of diagenetic modification of pore water composition is similar throughout the entire atlantic enrichment of na ca2 and alkalinity and depletion of mg2 and k are nearly universal only siliceous oozes consistently provide very limited evidence of cation diagenesis the changes observed and the calculated fluxes across the seawater sediment interface are much the same as those reported previously for other areas of the atlantic and caribbean fluxes of the major cations across the interface continue to be indicated as a major factor in the geochemical cycling of these elements particularly na mg2 and k diagenetic modelling indicates that aerobic oxidation of organic matter and consequent dissolution of caco3 is a dominant reaction throughout the north atlantic the data indicate that o2 oxidation to at least 30 cm is prevalent at nearly all stations dissolution of caco3 in response to the introduction of metabolic co2 can lead to significant post depositional modification of the sediments the modelling also indicates a 1 1 stoichiometric relationship between na release and mg2 uptake by sedimentary components although dissolved silica concentrations in biogenic siliceous sediments are among the highest yet reported 700 m calculations demonstrate that solubility control cannot be through equilibria with the mineral sepiolite further the influence of cation silicate surface phases generally upon solubility is contraindicated by si oh 4 mg2 h relationships evaluation of the influence of fluid advection on pore water profiles indicates that at the stations studied in the north atlantic it is small a more general consideration of the potential contribution of fluid advection to shaping interstitial water profiles demonstrates that advection can be a dominant factor in such circumstances serious misinterpretation of the nature of diagenetic reactions may result from a lack of knowledge and consideration of fluid advection

change detection of the coastal zone east of the nile delta using remote sensing the coastal zone of the nile delta is a promising area for energy resources and industrial activities it also contains important wetland ecosystems this coastal area witnessed several changes during the last century a set of four satellite images from the multi spectral scanner mss thematic mapper tm and systeme pour l observation de la terre spot sensors were utilized in order to estimate the spatio temporal changes that occurred in the coastal zone between damietta nile branch and port said between 1973 and 2007 image processing applied in this study included geometric rectification atmospheric correction on screen shoreline digitizing of the 1973 mss and 2007 spot images for tracking the shoreline position between damietta promontory and port said and water index approach for quantifying manzala lagoon surface area change using 1973 mss 1984 tm and 2003 tm images results showed that coastal erosion was severe near damietta promontory and decreased eastward however accretion was observed near port said about 50 of the coastal strip was under erosion and 13 was under accretion in addition a remarkable decline 34 5 of the manzala lagoon surface area was estimated these changes were attributed mainly to the control of the river nile flooding and the land use change by anthropogenic activities

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

what do we learn from peaks of uranium and of manganese in deep sea sediments abstract uranium and manganese are two redox sensitive trace elements with complementary behavior under anoxic conditions u is immobile while reduced mn is dissolved in pore water of sediments uranium diffuses from sea water into reducing sediments and is enriched there the depth of the reducing layers and the sediment accumulation rate determine the enrichment of authigenic uranium on the contrary mn is dissolved in the reducing sediment sections diffuses in pore water and forms peaks of mn oxide as soon as oxygen is available thus the profiles of both mn and authigenic u record the depth of the redoxcline during periods of oxygen limitation in the sediments estimates of the depth of incorporation of uranium during the last glacial were derived for several cores at localities in the atlantic numerical modeling of the redoxcline as a function of the oxygen content of the water column and of the flux of organic matter to the sediments constrains these values during periods of extreme shallow redoxcline depths burn down of organic matter and deepening of the redoxcline during the holocene may have significantly altered the organic matter and uranium signals of glacial sediments at present day conditions sediments accumulating at rates smaller than 2 cm ky 1 may have lost the u signals peaks of manganese are then the only reliable record for a less ventilated sediment column in the past

the behaviour of manganese in atlantic carbonate sediments abstract manganese porewater and solid phase data are considered from two different atlantic carbonate sediments both with good geochemical characterisation the first case is a continuously accumulated alternating pelagic marl carbonate ooze where there is a correlation in post oxic conditions between mn ii porewater levels and an acetate leachable mn fraction of the sediment this leachable mn appears to have an association with calcite and in this example the leached residue mn content approximates to that of shale in the second case a very recent compositionally homogeneous calcareous turbidite is underlain by mn oxyhydroxide at the former sediment surface which is now acting as a source of mn ii by reduction sorption of mn by the turbidite sediment and shale like leached residue mn levels in anoxic conditions are again observed as mn ii diffuses towards present oxic conditions although no unique equilibrium is achieved similar older buried turbidites have concentration decreases in solid phase mn content preserved from bottom to top as relict evidence that this process has occurred in these turbidites 54 64 of the total mn is leachable by the acetate method and therefore presumed to be sorbed by calcite the oldest example has persisted for 125 kyr it is suggested that the slow breakdown of metastable mn oxyhydroxide and sorption of mn ii to calcite surfaces are important controls on the behaviour of mn in pelagic carbonates in mildly reducing conditions where accumulation fluctuations occur these processes act together with accumulation to limit overall mn migration and to prevent the large mn enrichments seen near the sediment surface in more reducing environments

a model of suboxic sedimentary diagenesis suitable for automatic tuning and gridded global domains and solid phase mno2 the model misses some of the very high sediment surface mno2 concentrations observed in for example the california borderlands we believe that these sites must receive a higher input of reactive mn than the crustal abundance of the clay rain the model was deployed on every 2 2 grid point below 1000 m of the global seafloor using gridded maps of organic carbon rain to the seafloor and overlying water chemistry the deep sea carbon burial efficiency is 7 with 95 of respiration by oxic metabolism the model was also run against a new depth oxygen hypsometry of the global ocean with sediment area as a function of overlying oxygen concentration and average depth related to carbon fluxes to include the effects of shallow water sediments this analysispredictsthat shallow waters 1000 m account for 88 ofrespiration and oxygen accounts for 66 of respiration overall denitrification is closely coupled to organic nitrogen fluxes to the sediment and the global rate is estimated to be 1 4 10 14 mol yr 1 a factor of 6 8 higher than the corresponding estimate from middelburg et al 1996 throwing the nitrogen cycle in the ocean into imbalance index terms 4863 oceanography biological and chemical sedimentation 4851 oceanography biological and chemical oxidation reduction reactions 4804 oceanography biological and chemical benthic processes benthos 4805 oceanography biological and chemical biogeochemical cycles 1615 keywords diagenesis

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

tilt depth method a simple depth estimation method using first order magnetic derivatives aeromagnetic data are routinely presented as contour or color shaded maps of the total magnetic intensity tmi an interpreter s task is to identify features anomalies contained within the map and qualitatively and or quantitatively interpret them into geologic structures at depth if the map contains anomalies that have large magnetic intensities the bodies might be considered to have large magnetizations or to be at shallow depths small amplitude anomalies superimposed on these anomalies could be masked or even missed by an interpreter thus the task of the interpreter is to use the spectral content of the anomalies to try and resolve these ambiguities part of this process is also to obtain estimates of the depth and shape of the body causing the anomalies

oxidation state of marine manganese nodules analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98 of the mn in deep ocean nodules is present as mn iv the samples were collected from three quite different areas the hemipelagic environment of the guatemala basin the pelagic area of the north pacific and seamounts in the central pacific results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry k na ca ba 33 mg cu ni 76mn5o22 h2o 3 2

early diagenetic processes fluxes and reaction rates in sediments of the south atlantic abstract porewaters recovered from sediment cores gravity corers box corers and multicorers from various subrogions of the south atlantic amazon river mouth equatorial upwelling congo river mouth benguela coastal upwelling area and angola basin were investigated geochemically objectives included determination of eh ph oxygen nitrate sulfate alkalinity phosphate ammonium fluoride sulfide cal mg sr fe mn and si in order to quantify organic matter diagenesis and related mineral precipitation and dissolution processes porewater profiles from the eastern upwelling areas of the south atlantic suggest that sulfate reduction in the deeper parts of the sediment may be attributed mainly to methane oxidation whereas organic matter degradation by sulfate reduction is restricted to the near surface sediments further a prominent concentration gradient change of sulfate and related mineralization products occurred typically in the upwelling sediments at a depth of 4 to 8 m far below the zone of bioturbation or bioirrigation because other sedimentological reasons seem to fail as explanations an early diagenetic sulfide oxidation to sulfate within the anoxic environment is discussed porewater profiles from the sediments of the amazon fan area are mainly influenced by reactions with fe iii phases the remarkable linearity of the concentration gradients of sulfate supports the idea of distinct reaction layers in these sediments in contrast to the upwelling sediments the sulfate gradient develops from the sediment surface to a sulfate reduction zone at a depth of 5 3 m probably because a reoxidation of sulfide is prevented by the reaction with iron oxides and the formation of iron sulfide minerals a comparison of organic matter degradation rates from the different areas of the south atlantic show the expected relationship to primary productivity oxygen is the dominating oxidant whereas organic matter degradation by nitrate mn iv and probably also fe iii reduction is several orders of magnitude lower sulfate reduction is quantitatively of similar importance as oxygen respiration in the organic rich sediments but may also include methane oxidation reoxidation of ammonium and mn2 by oxygen or nitrate do not alter significantly the estimation of organic matter degradation in the oxic zone but may contribute to the nitrate reduction in suboxic layers

evidence of bioturbation in the cap ferret canyon in the deep northeastern atlantic in the sedimentary column a combined quantification of burrows and macrobenthic community provides evidence of bioturbation features in the submarine canyon of cap ferret between 2000 and 3000 m depth an image processing technique allows accurate quantification of burrow volumes with depth in the sedimentary column the major bioturbation mode seems to be different in the channel compared to the interfluve macrobenthic activity is more inclined to mix the sediment in the channel in response to increased organic matter supplies sediment mixing leads to burrow destruction in the upper mixed layer of sediment in the canyon burrows are better preserved on the interfluve where mixing is slower under the mixed zone the volume of recorded burrows is higher when sedimentation rate increases as in the upper canyon in this transition layer the burrow volume is estimated to be between 3 and 64 of the total sediment volume depending on the sediment depth the fill down of numerous burrows with surface sediment by bioregeneration suggests that anaerobic degradation of fresh organic matter is dominant in this canyon in the sedimentary column the negative relationship between carbonate content and macrobenthic abundance confirms that carbonate dissolution is largely influenced by bioturbation

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

the tectonic regime of the southeastern mediterranean continental margin abstract the continental margin of the southeastern mediterranean off israel and sinai is transected by a series of nw se trending faults evidence of lateral displacements along these faults is presented the faults off israel were found to terminate at the eastern edge of the levant basin whereas the faults of the same series which transect the sinai continental margin were found to extend hundreds of kilometers further northwestwards the levant basin and the adjacent continental margin are both covered by a thick sedimentary sequence but whereas the basin is underlain by an oceanic crust the margin is underlain by a continental crust the effects of these two types of crust on the structure of the continental margin are discussed it is suggested that at least since the late neogene the marine province was under a tectonic regime of regional subsidence the continental province was affected by rifting and faulting and the tectonics of the continental margin reflect the superposition of these two regimes

generation of the benthic foraminiferal assemblage theory and preliminary data abstract the production of benthic foraminiferal communities is filtered through taphonomic mainly destructive processes within the sediments to generate the fossil assemblage both the production and the taphonomy depend on bottom water oxygen content and flux of organic carbon to the seabed an examination of the relationships of processes generating the fossil assemblage to oxygen and organic carbon supply is made using pore water geochemical measurements to estimate carbon flux for locations in the gulf of mexico and the central california margin the locations are plotted in a three dimensional field with bottom water oxygen content organic carbon flux and sediment depth as the axes then the response of foraminiferal standing stock taphonomic processes and the developing fossil assemblage to the field is investigated variation in the vertical stratification of foraminiferal standing stock and test production species stratification taphonomic process intensity and stratification and sediment bioturbation lead to marked differences in the way the fossil assemblage is generated across the oxygen content organic carbon flux field the result is that the oxygen carbon flux field has a significant impact on the fossil assemblage through the interaction of biological and biogeochemical processes in the sediments a model of this interaction is investigated to show how its elements change across the oxygen carbon flux field and how these affect the generation of the fossil assemblage

nd and sr isotope study of hydrothermal scheelite and host rocks at omai guiana shield implications for ore fluid source and flow path during the formation of orogenic gold deposits omai is a high tonnage low grade world class gold deposit located in the paleoproterozoic guiana shield it is the second most important gold deposit in the guiana shield after las cristinas venezuela and one of the largest in south america 4 0 million oz sm nd and sr isotope data are presented for host rocks and for scheelite from auriferous quartz carbonate scheelite sulfide telluride veins from the omai deposit gold bearing veins are hosted by the paleoproterozoic barama mazaruni supergroup a greenstone belt sequence consisting of mafic volcanic rocks interbedded with sedimentary rocks that are intruded by quartz feldspar porphyry and rhyolite dikes this lithologic sequence was folded and metamorphosed to lower greenschist facies during the paleoproterozoic trans amazonian orogeny the volcano sedimentary unit was intruded by a post tectonic quartz monzodiorite diorite hornblendite stock initial nd isotope ratios for the omai volcanic rocks range from nd 2 1 to 4 2 these values suggest that this part of the guiana shield was a site of new crust formation during the paleoproterozoic and was not contaminated by older archean reworked continental crust initial nd isotope ratios for the omai stock range between 0 5 and 2 3 which suggest limited contamination with previously formed continental crust although the nd isotopic ratios of gold related scheelites overlap with those of the host rocks particularly the tholeiitic basalts at the interpreted time of vein emplacement the lack of both isotopic mixing and significant nd movement during the hydrothermal process suggest that the nd isotope composition can be used to determine the isotopic characteristics of the ore fluid source area at omai the ore fluid is largely derived from a radiogenic nd source represented by mantle or lower crustal reservoirs strontium isotope ratios for the scheelites cluster tightly between 0 7019 and 0 7021 the sr isotope data suggest that unlike nd sr was significantly mobile during the hydrothermal process the fluids responsible for the omai deposit may have picked up sr along the flow path the constant low sr isotope values of scheelites probably reflect the key role that the local tholeiitic basalts played as the main source of sr in the fluids whereas nd isotopes identify the fluid source area the sr isotopes map the fluid flow paths

non steady state diagenetic record in eastern equatorial atlantic sediments abstract the radiocarbon age profile of a sediment core from the eastern equatorial atlantic shows a marked decrease in both clay and carbonate accumulation rates at the end of the last glacial period with overall rates of 3 2 and 8 1 cm kyr for the holocene and late glacial respectively the transition from glacial to postglacial conditions recorded in the sediments at 39 cm is above the visual fe ii fe iii redox boundary at 48 cm which has been used in the past to identify the glacial section and even further above the increase in preserved organic carbon content at 55 cm it is concluded from the present organic carbon profile and recent observations in this area and elsewhere that organic diagenesis in these sediments is not steady state instead it is suggested that the uppermost glacial sediments lost carbon through oxic remineralisation at the change to postglacial conditions and that this process is now continued with nitrate as the electron acceptor these observations suggest that the double mno x solid phase peak which occurs in these and similar sediments is a direct consequence of an adjustment of the oxic layer depth following the decrease in carbon flux at the onset of the holocene

continental slope processes off northern israel and southernmost lebanon and their relation to onshore tectonics abstract the continental terrace of israel and lebanon consists of a 1 2 km thick pliocene quaternary sediment wedge that narrows steepens and deepens from south to north the continental terrace is the product of 1 nile derived sediment accumulation whose bulk and rate of deposition decrease along the active levant continental margin with increasing distance from the nile mouths and 2 of the vertical tectonic uplift of israel and lebanon versus the subsidence of the adjacent submarine levantine basin which increases to the north collapse of the entire seaward facing part of the continental terrace off northern israel caused by large scale halokinetic rotational slumping has further accentuated its steep and narrow wedge form in the study area intensive mass wasting and canyon cutting over the steep continental slope have shaped its present furrowed morphology canyon incision is fault controlled the faults being submarine extensions of the continental fault system effected by drag of the sinai sub plate along the dead sea jordan beqa a transform that has controlled the tectonics and the structure of israel and lebanon since the late miocene the canyon heads at the continental shelf lie opposite the mouths of the continental rivers canyon cutting processes are not however connected to fluvial erosion of the emergent continental shelf during the last glacial lowered sea level stand canyon incision started on the continental slope and advanced downslope and upslope toward the shelf embryonic slope valleys canyons confined to the continental slope a canyon in the process of breaching the shelf break and mature canyons that indent the continental shelf to nearshore distances were mapped and are described

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

tectonic significance of the eratosthenes seamount a continental fragment in the process of collision with a subduction zone in the eastern mediterranean ocean drilling program leg 160 abstract one of the objectives of odp leg 160 in the eastern mediterranean sea april may 1995 was concerned with the study of processes of genesis and incipient collision of an inferred crustal fragment the eratosthenes seamount with the active margin of the eurasian plate to the north represented by southern cyprus the upper part of the eratosthenes seamount i e upper several hundred metres was found to include both shallow and deep water carbonates dating back to early cretaceous time shallow water platform carbonate deposition similar to that of the onshore levant continental margin to the east i e part of the north african plate was followed by submergence to bathyal depths 1000 m in the late cretaceous to middle eocene punctuated by depositional and tectonic hiatuses tectonic uplift approximately 1 km was followed by shallow water carbonate deposition in the early miocene the platform was exposed during the messinian desiccation crisis during the early pliocene the platform subsided to bathyal depths associated with localised accumulation of limestone debris flows subsidence accelerated in the late pliocene early pleistocene reaching a present day maximum depth of ca 2500 m deformation of the eratosthenes seamount i e subsidence and high angle faulting resulted from crustal flexure induced by southward overthrusting of the cyprus active margin tectonic subsidence of the eratosthenes seamount was approximately synchronous with rapid surface uplift of the over riding plate the troodos ophiolite of southern cyprus this uplift is explained in terms of incipient collision of an eratosthenes continental fragment with a subduction trench coupled with the effects of diapiric protrusion of serpentinite located within the core of the troodos ophiolite the eratosthenes drilling thus documented a modern analogue of subduction collisional processes leading to accretion of continental fragments and carbonate platforms in orogenic belts

on the occurrence of ferromanganese micronodules from the sediments of the bengal fan a high terrigenous sediment input region studies of 13 samples 10 surface sediments and 3 cores from across the middle fan region of the bay of bengal reveal the presence of micronodules area 0 22 million km2 over the entire bay these micronodules have two dominant morphological forms botryoidal in the eastern bay and spheroidal in the central and the western regions of the bay the abundance of the micronodules was found to be higher in the eastern region of the bay in the cores the micronodules were generally found to decrease in abundance down core the core from the eastern region had micronodules down to deeper levels than the western side todorokite is the manganese mineral present in the micronodules associated mineral phases are quartz feldspar and phillipsite these micronodules have high mn 19 20 32 13 rather low fe 1 20 1 83 ni 0 10 1 14 zn 0 10 0 30 and co 0 01 0 04 and their mnfe ratio ranges from 10 55 to 25 42 the contents of mn ni cu and zn and the mnfe ratio decrease down core based upon the variations in the abundance morphology mnfe ratio of the micronodules and the elemental distributions and the omn ratio in the sediments remobilization of mn from deeper levels and its precipitation at the upper surfaces of the sediment column in an oxic environment is suggested the results of the present study also suggest that a high rate of sedimentation is not a limiting factor for the formation of micronodules although it might affect their growth

manganese deposition through geological time dominance of the post eocene deep sea environment abstract the total terrestrial manganese ore deposits amount to about 6 4 10 9 tonnes of which 5 3 10 9 tonnes 82 are precambrian and 1 1 10 9 tonnes 18 mesozoic and cenozoic deep sea manganese nodules formed since the lower miocene unconformity 12 ma b p hold about 10 11 tonnes mn about 16 times the manganese in terrestrial deposits the development of deep sea manganese nodules is a reflection of global cooling and resulted from the transition of the sluggish cretaceous ocean with warm saline bottom water to the post eocene ocean with cold well oxygenated bottom curents important climatic and oceanographic events occurred at the eocene oligocene boundary and more particularly at the lower miocene unconformity which marks the period of increased antarctic bottom water circulation by contrast the giant shallow water manganese deposits of the lower jurassic to oligocene are associated with anoxia and high sea level stands the two types of deposit reflect different oceanographic conditions and tend not to be contemporaneous mass balance considerations suggest that the present day input of manganese into the oceans is in balance with its deposition in manganese nodules and sediments with perhaps 90 of the input being from hydrothermal sources although this is speculative the scale of present day deep sea manganese nodule formation suggests that we live in the manganese era

rare earth element association with foraminifera abstract neodymium isotopes are becoming widely used as a palaeoceanographic tool for reconstructing the source and flow direction of water masses a new method using planktonic foraminifera which have not been chemically cleaned has proven to be a promising means of avoiding contamination of the deep ocean palaeoceanographic signal by detrital material however the exact mechanism by which the nd isotope signal from bottom waters becomes associated with planktonic foraminifera the spatial distribution of rare earth element ree concentrations within the shell and the possible mobility of ree ions during changing redox conditions have not been fully investigated here we present ree concentration and nd isotope data from mixed species of planktonic foraminifera taken from plankton tows sediment traps and a sediment core from the nw atlantic we used multiple geochemical techniques to evaluate how where and when rees become associated with planktonic foraminifera as they settle through the water column reside at the surface and are buried in the sediment analyses of foraminifera shells from plankton tows and sediment traps between 200 and 2938 m water depth indicate that only 20 of their associated nd is biogenically incorporated into the calcite structure the remaining 80 is associated with authigenic metal oxides and organic matter which form in the water column and remain extraneous to the carbonate structure remineralisation of these organic and authigenic phases releases ions back into solution and creates new binding sites allowing the nd isotope ratio to undergo partial equilibration with the ambient seawater as the foraminifera fall through the water column analyses of fossil foraminifera shells from sediment cores show that their ree concentrations increase by up to 10 fold at the sediment water interface and acquire an isotopic signature of bottom water adsorption and complexation of ree3 ions between the inner layers of calcite contributes significantly to elevated ree concentrations in foraminifera the most likely source of ree ions at this stage of enrichment is from bottom waters and from the remineralisation of oxide phases which are in chemical equilibrium with the bottom waters as planktonic foraminifera are buried below the sediment water interface redox sensitive ion concentrations are adjusted within the shells depending on the pore water oxygen concentration the concentration of ions which are passively redox sensitive such as ree3 ions is also controlled to some extent by this process we infer that a the nd isotope signature of bottom water is preserved in planktonic foraminifera and b that it relies on the limited mobility of particle reactive ree3 ions aided in some environments by micron scale precipitation of mnco3 this study indicates that there may be sedimentary environments under which the bottom water nd isotope signature is not preserved by planktonic foraminifera tests to validate other core sites must be carried out before downcore records can be used to interpret palaeoceanographic changes

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

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

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin

application of high field strength elements to discriminate tectonic settings in vms environments high field strength element ratios in felsic volcanic rocks reflect the tectonomagmatic evolution of a region th ta th hf ta hf th yb and ta yb ratios collectively help to define the tectonic environment of volcanism separating oceanic arcs active continental margins and within plate volcanic zones on the basis of the above empirical observations the tectonic environments of selected archean and post archean volcanogenic massive sulfide deposits were reexamined published data sets plotted on discriminant diagrams represent twelve volcanogenic massive sulfide vms deposits from two distinct tectonic environments the volcanic rocks of the kuroko deposits japan san nicolas mexico and bathurst new brunswick canada plot within the active continental margin field on all diagrams whereas volcanic rocks from archean deposits of the superior province canada kidd creek kamiskotia geco winston lake mattabi lyon lake noranda selbaie and south bay plot in the within plate volcanic zone field the discriminant diagrams demonstrate that although the chemical character of rhyolites has not changed significantly since the archean the range of geotectonic setting of vms deposits probably has it is suggested that archean deposits most likely formed in an ensimatic rift environment whereas post archean deposits formed in subduction related rift zones of arc environments subduction related rhyolites of vms deposits are variably enriched in th and the light rare earth elements with respect to ta nb and the heavy rare earth elements

variations of element distribution in ferromanganese nodules and its bearing on growth rates mineralogical chemical and radiochemical analyses of nodules sampled at various distances from the east pacific rise indicate that the mineralogical composition is not clearly linked to distance but chemical composition seems to be the pelagic nodules accrete at a lower rate and are on the whole richer in manganese uranium and thorium and poorer in lead and silicon than nodules from the ridge the deep seated nodules display a marked decrease in thorium concentration toward their centers which can be explained in several ways one hypothesis involves a decrease in the growth rate as the plate moves away from the ridge and manganese flux diminishes as suggested in previous studies some dissolution of the bottom of the nodules may occur and contribute to abnormal element distributions

seismic images at the convergence zone from south of cyprus to the syrian coast eastern mediterranean abstract multichannel seismic profiles from cruise 5 of the r v akademik nikolaj strakhov provide the first deep seismic reflection images and extensive coverage south and east of cyprus five nw se trending seismic lines cross an area of active continental collision main tectonic structures are the eratosthenes seamount collision zone the hecateaus rise and the latakia larnaca ridge systems the levantine basin extends to the south all over the area the data required careful processing due to the low fold coverage the reverberatory character of the signal and the strong multiple energy the seismic results clearly image the thick sedimentary sequence of the levantine basin this basin is observed to terminate abruptly at the junction with the hecateaus rise south of cyprus to the east and north the deformation appears to be partitioned along two separated structures next to the latakia and larnaca ridges they correspond to major oblique fault systems

thermo tectonic evolution of an archean accretionary complex u pb geochronological constraints on granulites from the quetico subprovince ontario canada abstract u pb geochronological data have been obtained for a granulite zone in the quetico subprovince an archean accretionary complex of the superior province north of manitouwadge ontario canada this granulite zone represents the culmination of a low pressure high temperature regional metamorphism in the quetico subprovince and an apparent continuation of a northward increase in metamorphic grade in the wawa subprovince and across the quetico wawa boundary a u pb zircon age of 2666 1 ma from a concordant magnetite bearing granitic pegmatite in the quetico granulite zone is consistent with the inferred timing of regional metamorphism in amphibolite facies zones 2671 2665 ma and indicates that the low pressure high temperature metamorphism in the quetico subprovince commenced during the main compressional deformation titanite in a calc silicate rock from low leucosome fraction layered migmatites that might represent incipient melting gave a 207pb 206pb age of 2658 1 ma the timing of the granulite facies metamorphism is constrained by u pb zircon ages of 2650 2 and 2651 3 ma from mafic granulite and garnet bearing tonalitic leucosome respectively that are similar to reported u pb ages for mafic granulites in the upper levels of the kapuskasing structural zone the present u pb data suggest a diachronous development of peak metamorphic conditions of the regional metamorphism in the quetico and wawa subprovinces this diachronous development and the zonal distribution of the regional metamorphism are probably related to oblique collision at a convergent plate margin and differential rates of erosional uplift away from the quetico wawa boundary

active tectonic trends and crustal modeling of the eastern mediterranean sea deduced from geophysical data the eastern mediterranean sea is considered as a highly tectonic region evolving from the progressive african eurasian collision the current research is an attempt to resolve the problems related to the geodynamic evolution of this region to delineate the main tectonic trends the nature and thickness of the crust these tectonic trends have played a very significant role in the most recent discovery of large gas fields in the mapped region this has drawn the attention to the needs to investigate this region more thoroughly published gravity and magnetic data are utilized and analyzed using the most recent proposed techniques the integration of the implemented methods revealed more new tectonic trends the nw se trend is the major trend that is associated with temsah and misfaq bardwil trend while the ne sw trend that is associated with rosetta and eratosthenes seamount trends the n s trend that is associated with baltim fault trend and another e w trend is associated with the neogene hinge zone and the cyprian arc moreover a nne ssw related to the tartus thrust trend and the gulf of aqaba was observed in addition to an ene wsw trend relates to the kyrenia missi trend the observed wnw ese direction relates to the animaxander seamount trend and finally the nnw ssw trend based on the delineated tectonic trends the mapped region was classified into four main basins namely the shelf basins the margin dominated basins the deep basins and the levantine basin to the east the depth to the basement is an irregular surface and gradually changes from more than 13 km in the northern part and decreases to less than 6 km in the southeastern mediterranean sea

cordierite gedrite rocks from the central metasedimentary belt boundary thrust zone grenville province ontario mesoproterozoic metavolcanic rocks with affinities to the composite arc belt cordierite gedrite rocks in the southern grenville province occur near the base of the central metasedimentary belt boundary thrust zone interpreted by some as a crustal suture between the 1 29 1 24 ga composite arc belt and 1 4 ga rocks of laurentia major and trace element compositions of these rocks are consistent with volcanic protoliths that range in composition from basalt to dacite these cordierite gedrite rocks have low cao average 1 2 wt and major element and oxygen isotope ratios suggestive of hydrothermal alteration before metamorphism rare earth element ree compositions also indicate igneous protoliths although some ree patterns have been modified by local melt extraction the trace element compositions of cordierite gedrite rocks and neodymium isotope systematics are similar to those of metavolcanic rocks in the composite arc belt and are consistent with the extension of the composite arc belt to the base of the boundary thrust zone

manganese scavenging and oxidation at hydrothermal vents and in vent plumes abstract hydrothermal vents provide a major source of dissolved mn ii to the oceans where concentrations range from 5 mm within the 350 c hot smokers to just above ambient seawater concentration in far field vent plumes the mn ii rich environments within warm vents and vent plumes provide a suitable habitat for mn ii oxidizing bacteria in order to compare rates of scavenging and oxidation of mn ii proximally within vent fields

present day stress field in egypt based on a comprehensive and updated earthquake focal mechanisms catalog the present day stress field in egypt has been investigated on the basis of updated earthquake focal mechanism catalog covering the period from 1951 to 2017 our catalog contains 234 focal mechanisms compiled from previous studies in addition to 22 new source mechanism solutions achieved in this study according to the distribution of the recent earthquake epicentres egypt is divided into nine seismotectonic regions the available fault plane solutions in egypt demonstrate a spatial variability of source mechanisms which categorize the study area into three groups the first group includes dahshour beni suef cairo suez district northern central gulf of suez and southern gulf of suez which characterized by pure normal faulting mechanism to normal faulting with strike slip component pure strike slip faulting has clearly characterised aswan and gulf of aqaba regions in the second group however the third group which contains abu dabbab and the northern egyptian continental margin is characterized by thrust and strike slip faulting to calculate the orientation of the principle stress axes and the shape ratio we have applied the stress inversion technique the present day stress regime shows a variability of the tectonic stresses including extensional tectonic transtensional and strike slip the transtensional stress regime with a maximum horizontal extensional nne stress axis represents the dominant stress field pattern in egypt the results exhibit a good agreement with the tectonic settings and recent deformations in egypt

a textural and geochemical guide to the identification of hydrothermal monazite criteria for selection of samples for dating epigenetic hydrothermal ore deposits hydrothermal monazite is one of the most reliable geochronometers for u pb dating of epigenetic or hydrothermal ore deposits because its blocking temperature at ca 700 c is higher than that of most metamorphic conditions although igneous monazite is routinely used for age dating igneous rocks only a few ore deposits have been dated by hydrothermal monazite this is due to the similar morphology of hydrothermal and igneous monazite which prevents the reliable distinction of hydrothermal monazite in particular we demonstrate that hydrothermal monazite can be distinguished from igneous monazite by its unique geochemical signature its local abundance and to common association with hydrothermal mineral assemblages our data and the data of others reported in the literature suggest that the low tho 2 content of hydrothermal monazite 0 1 wt is distinct from that of igneous monazite 3 to 5 wt and may be used to determine their genesis

tectonic framework and late cenozoic tectonic history of the northern part of cyprus implications for earthquake hazards and regional tectonics abstract located near the triple junction of the african arabia and eurasian plate cyprus has had an active and complex neotectonic history which includes devastating historical earthquakes investigations into the tectonic framework of the northern part of cyprus provide important insights into regional tectonism of the eastern mediterranean and middle east the northern part of cyprus is divided into two tectono stratigraphic terranes the boundary of which is the ovgos fault zone in the middle miocene the ovgos fault zone was a marine platform margin which separated open marine platform carbonates from deep marine turbidites transpressive movement along easterly and northeasterly trending structures dominated the late miocene deposition and preservation of messinian evaporites occurred in grabens at intersections of these trends n s compression began in the early pliocene and produced contractional tectonism along east west trends including major thrusting of allochthonous rocks in the kyrenia range quaternary deformation has been dominated by strike slip faults along northeast and northwest trends movement during the pleistocene occurred on several of these faults holocene movement is documented on one of these faults a seismic hazard is implied for the nicosia area because its proximity to the quaternary faults since the miocene cyprus has been continuously uplifted but the tectonic setting is controversial as some researchers invoke a subduction zone setting and others ascribe to a regime of strike slip tectonics our neotectonic framework is consistent with a restraining bend model for cyprus in a regional strike slip regime

diagenetic separation of cadmium and manganese in suboxic continental margin sediments abstract the vertical distribution of cd differs from that of mn in sediment cores taken from the continental margins of the arctic and atlantic oceans the oxic surface sediment is depleted in cd and enriched in mn whereas the subsurface sediment is enriched in cd and depleted in mn in some cores the distributions of solid phase and dissolved mn are offset the porewater profiles indicate that mn is being precipitated relatively deep in the sediment whereas the solid phase distributions indicate that mn has been precipitated very close to the sediment surface in the recent past at one deep site located near the base of the continental slope 3000 m the offset may be caused by a relatively recent decrease in ocean productivity a corresponding decrease in the organic carbon flux to the sediment and a subsequent migration of the redox boundary deeper into the sediment however at a site where the upper sediment layers have accumulated during the last few decades this explanation cannot account for the offset distributions we propose that a fluctuating input of organic matter to the sediment on seasonal or decadal timescales causes the position of the redox boundary to fluctuate the fluctuating redox boundary pumps dissolved mn upward and concentrates it as mn oxide in a distinct layer at the upper limit of the redox excursion at the same time it pumps cd downward and concentrates it in a distinct layer at the lower limit of the redox excursion the net result of a fluctuating redox boundary is to increase the spatial separation of cd and mn during the early diagenesis of suboxic sediments

geochemistry of ferromanganese micronodules and associated mn and trace metals diagenesis at high terrigenous depositional site of middle fan region bay of bengal abstract the influence of sedimentation on the morphology growth and geochemistry of the micronodules and on mn enrichment in the sediments of the bay of bengal has been evaluated mn accumulation is 307 219 mg cm2 kyr 1 in cores having 20 17 cm kyr 1 sedimentation rate but drops to 34 17 7 mg cm2 kyr 1 in cores with 3 4 cm kyr 1 sedimentation rates however mn enrichment zone becomes thinner with increased sedimentation the abundance of the micronodules increases and they have been observed down to the deeper levels with higher contents of mn ni cu and zn from the areas of the lower sedimentation the results of the present study reveal that though the higher sedimentation may be conducive for higher mn accumulation in the upper surfaces of the sediments the growth abundance and enrichment of mn ni cu and zn in the micronodules are mostly regulated by their residence time within mn oxidation zone the influence of residence time on the morphology and the internal structures of the micronodules are also evaluated

new insights into magnetic derivatives for structural mapping magnetic and gravity derivatives can be likened to seismic attributes in that they can help define estimate the physical properties of the source structure causing the anomaly this contribution looks at the tilt derivative first reported in 1994 and more recently used to derive the local wavenumber 1997 we will show that the combination of the tilt derivative and its total horizontal derivative are highly suitable for mapping shallow basement structure and mineral exploration targets and that they have distinct advantages over many conventional derivatives we provide the simple theory behind the derivatives use a range of simple 2d models to illustrate their response and apply them to mapping a mineral target in namibia

kinetic and thermodynamic factors controlling manganese concentrations in oceanic waters abstract data are presented describing the changes in the distribution of dissolved and particulate mn observed over a 16 month period in the periodically anoxic waters of saanich inlet a fjord located on the coast of vancouver island british columbia during the spring and summer when the bottom waters were anoxic a dense cloud of particulate mn was found at mid depths where mn 2 enriched anoxic bottom waters were mixing with oxygenated waters then during the autumn aand winter following an intrusion which reoxygenated the bottom water an intense precipitation of mn was observed throughout the entire water column during this latter period dissolved mn concentrations in the bottom water which exceeded 1000 nmol l under anoxic conditions decreased towards a lower limit of 1 6 nmole l a value comparable to that observed in pacific ocean waters of similar ph and dissolved oxygen content mn in the particulate matter collected just above the oxic anoxic interface was found to have an average oxidation number of 3 05 and on this basis it is proposed that dissolved mn concentrations in oceanic waters are controlled by the precipitation of the metastable oxide mineral manganite mnooh a hypothesis consistent with the fact that dissolved mn values in subsurface pacific ocean waters closely approach the equilibrium solubility of this phase temporal and spatial gradients in the particulate mn distribution were used to calculate the in situ rate of mn precipitation and the results of these calculations then were fitted to theoretical rate equations which suggest that the precipitation of mn is controlled by 2 parallel processes bacterial oxidation and an inorganic autocatalytic oxidation reaction

seismic refraction profiles between cyprus and israel and their interpretation summary a long seismic refraction profile was carried out between southern israel and cyprus the seismic energy was generated by 33 sea shots each of 0 8 t explosives and was recorded by land stations in israel and cyprus and by ocean bottom seismographs deployed along the profile the results showed that the continental crust of southern israel thins towards the mediterranean underneath a northward thickening sedimentary cover cyprus is underlain by a 35 km thick continental crust thinning south wards and extending to mt eratosthenes between mt eratosthenes and the israel continental shelf the crystalline crust is composed of high velocity 6 5 km s 1 material and is about 8 km thick it is covered by 12 14 km of sediments and may represent a fossil oceanic crust

subsurface structural trends of the offshore nile delta area egypt evidences from gravity and magnetic data subsurface structural trends and tectonics affecting the offshore nile delta area egypt have been studied through the interpretations of gravity and magnetic data reduced to the pole regional residual separation tilt derivative and euler deconvolution techniques are applied for the processing and interpretations of the magnetic and gravity data the average depth of the sedimentary cover estimated from the two dimensional power spectrum technique ranges between 8 km and 13 km the interpretation of the gravity and magnetic data indicates that the study area is affected by many subsurface structural trends the nw se is the major trend related to el temsah and misfaq bardwil trend the ne sw direction is the second dominant trend related to the rosetta trend other trends defined through the interpretation of gravity and magnetic data include the n s direction related to the baltim fault trend the e w direction related to the neogene hinge line and the nne ssw related to the gulf of aqaba accessory trends include the ene wsw wnw ese and finally the nnw ssw

diapiric features in the southeastern mediterranean sea possible indication of extension in a zone of incipient continental collision abstract several types of diapiric structures were studied in the zone between the nile deep sea fan and the eratosthenes seamount in the se mediterranean sea the study discovered four stages in the structural evolution of the diapiric features starting as a domal piercement structure and developing into initial basin as seawater dissolution starts to effect the diapiric salt subsequently v shaped and then mature u shaped basins formed as products of dissolution sedimentary collapse and sediment deposition the structures both protrusions and depressions are aligned along discrete lineaments most of them trending ne sw and a few nw se the ne sw lineaments are probably a series of normal faults and the nw se ones seem to be strike slip faults the development of extensional structures on the underthrust edge of the african plate as it approaches the subduction zone are commonplace in the mediterranean and elsewhere and the occurrence of normal faults in this area is compatible with the intensive subsidence of the eratosthenes seamount in the plio pleistocene the lithostatic load of the nile deep sea fan could have contributed to the subsidence and thus enhanced the diapirism in the se mediterranean

the distribution and behaviour of 230th and 231pa at an ocean margin baja california mexico uranium th and pa isotopes were measured in sediments collected by box core along a transect normal to the baja california continental margin six cores were analyzed ranging in depositional environment from manganese nodule bearing pelagic red clay to hemipelagic sediments displaying mn reduction in the upper 5 cm in the hemipelagic cores solid phase mn peaks due to diagenetic remobilization occur within the upper layers which are well mixed with respect to unsupported sup 230 th and sup 231 pa the fact that sup 230 th and sup 231 pa are not concentrated at the mn peaks suggests that little mobility of these nuclides occurs within the sediment column unsupported sup 230 th sup 231 pa activity ratios in the biomixed layer of the sediments range from 10 9 to 6 6 generally decreasing towards the inshore stations the flux of sup 230 th and sup 231 pa across the sediment water interface is almost in balance with the theoretical water column supply in the most distal core but rapidly increases inshore this evidence from the sediment column confirms that enhanced sup 230 th and sup 231 pa removal occurs at ocean margins and that sup 231 pa is removed from the water column to the sediments in preference to sup 230 th

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

the oxidation state of manganese in surface sediments of the deep sea iodometric titration of deep sea sediment from cores at manop sites m and h indicate a particulate mn oxidation state between 3 3 and 3 9 in the top 5 cm results from site h show a minimum in the mn oxidation state at 1 5 cm depth indicating mn reduction is occurring above the zone of pore water mn oxidation using a simple box model the rate of reduction is calculated to be 19 mg cm2 kyr 77 mg cm2 kyr at least 5 times the flux of mn to nodules in this region although no mn oxidation state minimum is observed in site m sediments oxic reduction is inferred from a particulate mass balance indicating that a large fraction of the mn rain to this site is not preserved in the sediments and must be remobilized we suggest that the process of reduction in oxic or suboxic environments near the sediment water interface may be an important mechanism controlling the concentration of mn in sediments and provides a mechanism for supplying diagenetic mn to the nodules at site h

climate change and its impacts on the coastal zone of the nile delta egypt the main objectives of the current work are 1 to determine historic pattern of shoreline changes erosion and accretion along the north coast of the nile delta 2 to present a future view on what to be expected regarding climate change impacts sea level rise slr scenarios expected land losses and alteration of some soil characteristics 3 to recognize negative impacts of slr on the nile delta coast and 4 to assess and suggest protection measures the current investigation was conducted using the advanced techniques of remote sensing and geographic information system the investigated area with 394 measured locations is located along the northern coast of the nile delta between alexandria and eltina plain in sinai peninsula exactly between 29 20 and 32 40 e and 29 54 and 31 35 n with the minimum erosion values of 1 11 m2 maximum of 6 044 951 64 m2 and total of 16 02 km2 on the other hand 177 sites showed minimum accretion values of 0 05 m2 maximum of 2 876 855 86 m2 and total of 13 19 km2 slr was determined by applying the quadrant equation for 10 year intervals using 1990 as the base year mediterranean slr along the nile delta coast could be estimated considering three different scenarios low 0 20 m medium 0 50 m and high 0 90 m impacts of slr are divided into 1 primary and 2 secondary impacts over the coming decades the nile delta will face greater threat due to slr and land subsidence as well regarding climate change and its impacts on soil characteristics rapid increase in salinity values during the former three decades were found this increase may be due to the intrusion of salty water of the mediterranean on the other hand organic matter content decreased due to higher temperature especially during the summer season some protection measures were assessed and suggested to combat or tackle slr

lithospheric boundaries and plate motions in the cyprus area abstract accurate location of earthquakes recorded by seismographs and reliable fault plane solutions of strong recent earthquakes are used to define the plate boundaries and the pattern of plate motion in cyprus and surrounding area spatial distribution of shallow h

late tertiary structure and stratigraphy of north sinai continental margin new seismic data provide information on the structural development and late tertiary stratigraphy of the continental slope and rise off northern sinai the upper continental slope is characterized by a marginal plateau composed of a series of platforms or steps the lower continental slope is smooth except for a low ridge paralleling the western part numerous diapiric structures along the continental margin north of the sinai peninsula emerge from an evaporitic layer of late tertiary age the diapirs usually are aligned along west northwest trending faults a salt ridge 90 km long produces a submarine ridge in the lower continental rise two main fault trends have been mapped in the western part of the continental margin they trend west northwest and in the eastern part northeast these trends parallel the continental slopes of northern sinai and southern israel respectively the structural grain of the sinai margin appears to be controlled by two main tectonic elements 1 rejuvenated basement faults of the continent ocean transition zone and 2 salt diapirism due to loading of messinian evaporites with nile derived upper tertiary clastics

delineation the active subsurface structures at fayoum cairo district egypt using magnetic and magnetotelluric tools in this work we present a reconnaissance study to elucidate and delineate subsurface fault structures for an active tectonics area that lies between cairo and el fayoum provinces and consider major sources of seismicity in egypt well logging aeromagnetic land magnetic and magnetotelluric data have been used the well logging data were used for several drilled wells along w e direction the magnetic data were analyzed using trend analysis 3d magnetic modeling and werner deconvolution techniques the magnetotelluric data were interpreted using 2d tm te modeling techniques the results show that there are eight major fault structures having e w n s and nw se directions these faults extend downward for about 20 km at the dahshour and qatrani areas the epicenter sources of the earthquakes are clustering around the intersections of these structures the kattaniya horst structure has been interpreted as a regional structure that exceeds the limits previously determined by geologists the depth to this horst reaches about 1 8 km at the nw and more than 4 3 km at the southern parts the interpreted values of magnetic susceptibility at the horst zone indicate that they are ultrabasic basic intrusion bodies

particulate manganese dynamics in gulf stream warm core rings and surrounding waters of the n w atlantic manganese has been measured in size fractionated paniculate matter profiles obtained by large volume in situ filtration of the upper 1000 m of the n w atlantic as part of the warm core rings experiment wcre in 1982 environments sampled included warm core rings wcr 82b and 82h the entrainment zone at the edge of these rings the slope water surrounding rings and the gulf stream gs and sargasso sea ss from which the rings formed manganese concentrations ranged from 10 pmol kg 1 to 10 000 pmol kg 1 with the extreme values observed in the quasi isolated core waters of wcr 82b and in a tongue of shelf water at the periphery of wcr 82b respectively the majority of the mn was in the 1 53 m particle size fraction and most mn was probably close to 1 m in size mn showed no correlation with major biogenic phases indicating that formation by local biological processes was not an important source instead most paniculate mn present in the waters sampled originated in reducing sediments at the continental margin a manganese budget for the quasi isolated core waters of wcr 82b between february and june 1982 showed that most mn removal was by the aggregation of the small mn oxyhydroxide particles into fecal material followed by sedimentation calculations show that wcrs cause offshore particulate mn transports from the continental margin between 66 w and cape hatteras of 8 5 104 to 14 104 mol d 1 with most derived from the continental shelf only 4 of the shelf derived mn becomes entrained into wcrs and the rest is left to disperse in the slope water or enter the circulation of the gulf stream the wcr induced offshore mn transports may account for a large fraction of the mn flux to sediments on the continental slope and upper continental rise

structures and kinematics in the northeastern mediterranean a study of an irregular plate boundary abstract extensional structures are prominent in the northeastern mediterranean a unique sector of the africa eurasia plate convergence zone to explain this paradoxical situation we analyse here the young tectonics of this region by examining its structural elements and plate kinematics offshore multichannel seismic reflection profiles and onland geology show that the stuctural settings are different on the two sides of the northeastern mediterranean triple junction afr arb ana on the east stuctures controlled by strike slip and by compression coexist whereas on the west compression is not very conspicuous here deep basins separated by a partly submerged ridge are prominent we interpret the ridge which comprises the kyrenia misis andirin unit at its core as a large flower structure which extends from southeastern turkey to cyprus the adana cilicia and the iskenderun latakia mesaoria basins on its flanks are interpreted as due to extension this interpretation agrees with the relative motions between the africa arabia eurasia and anatolia plates in this region analysis of the local plate kinematics reveals that strike slip predominates along the southern boundary of the anatolia plate in this region as a result of anatolia s westward escape east of the triple junction this motion is associated with comparable shortening transverse to the plate boundary whereas west of the triple junction the motion transverse to the plate boundary varies between slight compression to extension depending mainly on the local strike of the plate boundaries these variations calculated from regional data correlate well with the observed structural changes along the northeastern mediterranean sector of the plate convergence zone the structural kinematic analysis explains both the lateral changes in the deformation style and the existence of local extension in the northeastern mediterranean

gravity anomalies of the cyprus arc and their tectonic implications abstract continental crust forms from structurally thickened remnants of oceanic crust and overlying sediments which are then invaded by arc magmatism understanding this process is a first order problem of lithospheric dynamics the transition in young mountain belts from ocean crust through the agglomeration of arc systems with long histories of oceanic closures to a continental hinterland is well exemplified by the plate margin in the eastern mediterranean the boundary between the african plate and the aegean anatolian microplate is in the process of transition from subduction to collision along the cyprus arc in the west north of the oceanic herodotus basin subduction may be continuing in the east microcontinental blocks such as the eratosthenes seamount are already colliding with cyprus to the north of the suture the changes in crustal structure along and across this convergent zone are not known except by inference from bathymetry and from a couple of deep penetrating wide angle seismic transects on the african plate margin in this contribution we model four bouguer gravity profiles across the cyprus arc the profiles are similar in showing a gravity low over the plate boundary suture attributed to thick sediments with bouguer highs over oceanic or transitional crust to the south and over ophiolites and thinner sediments on thin continental crust to the north bouguer lows at the northern ends of the profiles are characteristic of elevated continental crust well sedimented oceanic or transitional crust on the african plate margin is replaced north of the suture by variably sedimented basement in which continental crustal thickness increases from 10 km to 30 km over the forearc region the models involve assumptions about characteristic densities and trade offs between sediment and crustal thicknesses but they do provide well defined targets for future wide angle seismic tests

combining sedimentological trace metal mn mo and molecular evidence for reconstructing past water column redox conditions the example of meromictic lake cadagno swiss alps here we present sedimentological trace metal and molecular evidence for tracking bottom water redox state conditions during the past 12 500 years in nowadays sulfidic and meromictic lake cadagno switzerland a 10 5 m long sediment core from the lake covering the holocene period was investigated for concentration variations of the trace metals mn and mo xrf core scanning and icp ms measurements and for the presence of anoxygenic phototrophic sulfur bacteria carotenoid pigment analysis and 16s rdna real time pcr our trace metal analysis documents an oxic intermediate sulfidic redox transition period beginning shortly after the lake formation similar to 12 5 kyr ago the oxic period is characterized by low sedimentary mn and mo concentrations as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria enhanced accumulation preservation of mn up to 5 6 wt in the sediments indicates an intermediate mn enriched oxygenation state with fluctuating redox conditions during a similar to 2300 year long transition interval between similar to 12 1 and 9 8 kyr bp we propose that the high mn concentrations are the result of enhanced mn2 leaching from the sediments during reducing conditions and subsequent rapid precipitation of mn oxyhydr oxide minerals during episodic and short term water column mixing events mainly due to flood induced underflows at 9800 130 cal yr bp a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of mo in the sediments up to 490 ppm accompanied by an abrupt drop in mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column persistently high mo concentrations 80 ppm provide evidence that sulfidic conditions prevailed thereafter until modern times without any lasting hypolimnetic ventilation and reoxygenation hence lake cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over similar to 12 kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment possibly depicting analogous conditions in an ancient ocean our study underscores the value of combining sedimentological geochemical and microbiological approaches to characterize paleo environmental and redox conditions in lacustrine and marine settings

mapping the fluid flow of the mariana mounds ridge flank hydrothermal system pore water chemical tracers we present a conceptual model of fluid circulation in a ridge flank hydrothermal system the mariana mounds the model is based on chemical data from pore waters extracted from piston cores and from push cores collected by deep sea research vessel alvin in small meter sized mounds situated on a local topographic high these mounds are located within a region of heat flow exceeding that calculated from a conductive model and are zones of strong pore water upflow we have interpreted the chemical data with time dependent transport reaction models to estimate pore water velocities in the mounds themselves pore water velocities reach several meters per year to kilometers per year within about 100 m from these zones of focused upflow velocities decrease to several centimeters per year up to tens of centimeters per year a larger area of low heat flow surrounds these heat flow and topographic highs with upwelling pore water velocities less than 2 cm yr in some nearby cores downwelling of bottom seawater is evident but at speeds less than 2 cm yr downwelling through the sediments appears to be a minor source of seawater recharge to the basaltic basement we conclude that the principal source of seawater recharge to basement is where basement outcrops exist most likely a scarp about 2 4 km to the east and southeast of the study area

natural and anthropogenic influences in the northeastern coast of the nile delta egypt landsat enhanced thematic mapper imagery etm of 2002 and aerial photography of 1955 combined with published charts and field observations were used to interpret coastal changes in the zone between kitchener drain and damietta spit in the northeastern nile delta previously recognized as a vulnerable zone to the effects of any sea level rise resulting from global warming the interpretation resulted in recognition of several changes in nine identified geomorphological land types beach and coastal flat coastal dunes agricultural deltaic land sabkhas fish farms manzala lagoon saltpans marshes and urban centers reclamation of vast areas of the coastal dunes and of manzala lagoon added about 420 km to the agricultural deltaic land about 48 km of backshore flats marshes salt pans and manzala lagoon have been converted to productive fish farms the main urban centers have expanded nearly 12 1 km2 have been added to their areas and new urban centers damietta harbor and the new damietta city with total area reach of 35 3 km2 have been constructed at the expense of vast areas of manzala lagoon coastal dunes and backshore flats as a consequence of human activities the size of manzala lagoon has been reduced to more than 65 shoreline changes have been determined from beach profile survey 1990 2000 and comparison of 1955 aerial photographs and etm satellite image of 2002 reveal alongshore patterns of erosion versus accretion the short term rate of shoreline retreat 1990 2000 has increased in the downdrift side of damietta harbor 14 m year whereas areas of accretion exist within the embayment of gamasa and in the shadow of ras el bar detached breakwaters system with a maximum shoreline advance of 15 m year a sandy spit 12 km long has developed southeast of damietta promontory these erosion accretion patterns denote the natural processes of wave induced longshore currents and sediment transport in addition the impact of man made coastal protection structures

the oxidation state of manganese in ferromanganese nodules and deep sea sediments from the central indian ocean abstract ferromanganese nodules from different sediment facies including siliceous ooze pelagic clay sediments from transition zone of siliceous and pelagic clay and seamount crusts from the central indian ocean were analysed for chemical composition mineralogy and bulk oxidation state of mn by the iodometric method despite considerable variation in chemical composition mn fe ratio times from 1 35 to 7 42 and mineralogy the o mn ratio or mno x solid hydrous manganese oxide does not vary much from 1 73 to 1 81 suggesting most of the mn in the manganese nodules in mn iv the oxidised upper zone in the sediment cores decreases in thickness from 15 cm in the north 5 s to 11 cm in the southern part 14 s of the central indian ocean iodometric titration of deep sea sediments yields o mn ratios of 1 29 1 95 sediments from the manganese nodule field have maximum solid mn concentrations and lower o mn ratios in the core top 0 3 cm with minimum mn and o mn ratios at 11 cm depth and thus may reflect the mechanism controlling the supply of diagenetic mn to the nodules in contrast sediments from the non manganese nodule field have comparatively low solid phase mn concentrations in the core top 0 3 cm and almost uniform o mn ratios with depth indicating that mn is not preserved in the sediments but may be remobilised and deposited somewhere else

chemical evidence for advection of hydrothermal solutions in the sediments of the galapagos mounds hydrothermal field pore water profiles of ca mg f po4 3 and mn in the galapagos mounds hydrothermal field are believed to reflect in part upwelling of hydrothermal solutions through the sediments concentration depth profiles in a low heat flow area just north of the mounds field display diagenetic changes typical of those found in pore waters underlying highly productive surface waters consistent with the inference of no water flow or very slow downwelling w 5 cm yr of bottom water through these sediments rates of upward advection calculated from mounds field pore water profiles of ca mg and f profiles agree well with each other averaging about 1 cm yr in the pelagic sediments near the mounds and 15 30 cm yr within the hydrothermal mounds themselves the upward advection also modifies the shape of po4 3 and mn profiles advection rates inferred from the pore water data are generally in reasonable agreement with those made from heat flow data the higher ca and lower mg f po4 3 and mn concentrations in mounds field pore waters compared with those of the low heat flow area suggest chemical exchange between the solution and basalt prior to upwelling li k rb sr and so4 concentrations are indistinguishable from bottom water this suggests very high effective water rock ratios during the reactions which produced the upwelling solutions perhaps due to extensive prior alteration of basalt adjacent to the flow path of water through the crust inferred reaction temperatures are between 70 150 c