carbon geochemistry of cold seeps methane fluxes and transformation in sediments from kazan mud volcano eastern mediterranean sea abstract despite growing concerns about potential enhancement of global warming and slope failure by methane produced by gas hydrate dissociation much uncertainty surrounds estimates of gas hydrate reservoir sizes as well as methane fluxes and oxidation rates at the sea floor for cold seep sediments of the eastern mediterranean sea depth dependent methane concentrations and rates of anaerobic oxidation of methane aom are constrained by modeling the measured pore water sulfate profile the calculated dissolved methane distribution and flux are sensitive to the advective flow velocity which is estimated from the depth distributions of conservative pore water constituents na b near complete anaerobic oxidation of the upward methane flux of 6 0 mol m 2 yr 1 is supported by the depth distributions of indicative biomarkers and the carbon isotopic compositions of organic matter and dissolved inorganic carbon pore water and solid phase data are consistent with a narrow depth interval of aom 14 18 cm below the sediment water interface based on an isotopic mass balance the biomass of the microbial population carrying out oxidation of methane coupled to sulfate reduction at the given methane flux represents 20 of the total organic carbon which is a significant pool of in situ formed organic matter model results indicate that the asymptotic methane concentration is reached a few meters below the sediment surface the predicted asymptotic concentration is close to the in situ saturation value with respect to gas hydrate suggesting that the rate of shallow gas hydrate formation is controlled by the ascending methane flux the proposed model approach can be used to predict the formation of gas hydrate and to quantify methane fluxes plus transformation rates in surface sediments where fluid advection is an important transport mechanism

the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

a quaternary solution model for white micas based on natural coexisting phengite paragonite pairs a thermodynamic model for the quaternary white mica solid solution with end members muscovite mg celadonite paragonite feceladonite ms mgcel pg fecel is presented the interaction energies for the mgcel pg join the fecel pg join and the ternary interactions were obtained from natural coexisting phengite paragonite pairs phengite paragonite pairs were selected based on the criteria that their chemical compositions may be represented as a linear combination of the model end member compositions and that the respective formation conditions 350 650 c 4 21kbar are accurately known previously published excess free energy expressions were used for the ms pg ms mgcel and ms fecel binaries the suggested mixing model was tested by calculating multicomponent equilibrium phase diagrams this proved to be particularly well suited to reproduce compositional variations of white micas from amphibolite facies metapelites

menes caldera a highly active site of brine seepage in the eastern mediterranean sea in situ observations from the nautinil expedition 2003 abstract this paper reports the first in situ seafloor observations of fluid escape structures in a fault controlled caldera type depression of about 8 km diameter named the menes caldera in the eastern mediterranean sea off egypt western province of the nile deep sea fan a detailed analysis of seven nautile dives performed during the nautinil cruise in 2003 focused on determining the nature origin importance mechanisms and environmental impacts of the fluid escape processes from the geological observations seafloor maps constructed from direct visual observations and video records made from the submersible and sampling results for three mud volcanoes of the caldera cheops chephren and mykerinos show differences in activity but many common characteristics the three volcanoes show a crater like depression the study reveals a strong contrast between mykerinos where no seepage activity was found and the craters of cheops and chephren where an intense activity of brine seepage was discovered on cheops a dome of dark grey mud raises slightly above the brine surface in the central part of the brine lake and shows numerous circular vents of 1 2 m diameter that become gradually colonized by microbial mats chephren hosts a deep 200 m and warm 45 c brine lake alternations of areas void of or covered with microbial mats at the surface of the chephren brine lake indicate large surface disturbances that may result from the occurrence of several active vents at the bottom of the lake a special feature at chephren is a brine overflow at the western edge of the crater also indicative of the very high activity of brine seepage the nautinil observations indicate that the menes caldera in the eastern mediterranean is a highly active site of brine seepage growth faults rooted in pre messinian sediment layers provide pathways for warm fluids to escape pressurized source levels below the messinian salt

reversals in fe mg partitioning between chloritoid and staurolite chloritoid and staurolite coexist with al silicate chlorite or garnet or biotite in precambrian quartzite and schist from northern new mexico the observed fe mg reversal is not related to variable p t or minor element content including fe super 3 however it could arise from any of three factors 1 fe and mg may occur on several crystallographic sites in one or both minerals 2 some mg may not be exchangeable with fe in staurolite or 3 fe and mg may mix non ideally in one or both phases modified journal abstract

ferrimuscovite and celadonite substitutions in muscovite from fe3 rich low grade psammitic rocks northern apennines italy abstract electron microprobe and wet chemical data of muscovites from pyrophyllite or k feldspar bearing fe 3 rich rocks of the verrucano metasediments are reported a close relationship has been found between muscovite composition and bulk rock chemistry the extent of celadonite and ferrimuscovite substitutions increases progressively from pyrophyllite to k feldspar bearing samples the mutual cation substitutions reveal 1 an almost ideal tschermak substitution 2 a close positive correlation between the mg fe 2 and fe 3 contents and 3 a negative correlation between the octahedral and interlayer occupancies the extent of celadonite and ferrimuscovite substitutions of muscovite from magnetite bearing rocks has been constrained at moderate pressure in low temperature metamorphism

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

stratigraphic and structural relationships of multiply deformed precambrian metamorphic rocks in the rio mora area new mexico the contact between a proterozoic greenstone belt and a proterozoic quartzite terrane is exposed in the rio mora area new mexico metavolcanic rocks of the vadito group forming the northern edge of the pecos greenstone belt crop out along the southern margin of the area minor meta sedimentary rocks are interbedded a thick section of quartzite pelitic schist and graphitic phyllite lies north of the vadito rocks this metasedimentary section can be correlated bed for bed with ortega group rocks of the nearby picuris range the vadito ortega contact appears to be conformable all rocks are isoclinally folded about south dipping axial planes and so ortega rocks are structurally below vadito rocks most previous workers have accepted this structural superposition as evidence that the vadito group is younger however abundant cross beds within ortega quartzite which rests directly against the vadito and within quartzites of the overlying rinconada formation show clearly that ortega group rocks are younger than vadito group rocks the vadito ortega contact occupies the southern limb of an overturned syncline metamorphic rocks have been deformed in two generations of tight to isoclinal folds with subparallel axes plunging to the southwest a single f1 syncline is exposed its axial plane is folded by an f2 antiform whose axial plane strikes n70 e and dips steeply to the south because the two folding events are nearly coaxial the resulting map pattern appears similar to that formed from a single period of isoclinal folding only careful analysis of structural fabrics and structural facing relationships has revealed the multiply folded nature of the rocks

microbial methane oxidation and sulfate reduction at cold seeps of the deep eastern mediterranean sea abstract the eastern mediterranean hosts a variety of active cold seep systems such as gas chimneys mud volcanoes and pockmarks in water depths of 500 to 3200 m as part of the nautinil expedition in 2003 the sediments of cold seeps on the nile deep sea fan ndsf were sampled for the first time for biogeochemical and microbiological analyses here we compare rates of the anaerobic oxidation of methane aom and sulfate reduction sr as well as the microbial community structure of a variety of cold seep systems including mud volcanoes pockmarks and brine seeps our results revealed strong differences in microbial activity among the different seep systems of the eastern central and western provinces of the ndsf as well as the olimpi field central mediterranean ridge integrated over a sediment depth of 10 cm below the seafloor sr rates ranged from 0 1 66 mmol m 2 d 1 and aom rates from 0 1 3 6 mmol m 2 d 1 sr was often considerably higher than methane oxidation indicating that electron donors other than methane were utilized in general the lowest rates were associated with pockmarks and carbonate pavements and highest rates with bacterial mats above the gassy sediments of mud volcano centers 16s rrna gene analysis and fluorescence in situ hybridization fish revealed the presence of all known groups of marine methane oxidizing archaea i e anme 1 2 3 and also of methane oxidizing bacteria i e methylobacter sp and relatives in some seep sediments presumably syntrophic sulfate reducing bacterial partners of anmes were also detected in association with the anmes several anmes formed consortia with unknown bacterial partners the microbial community structure reflected the presence of typical seep microorganisms at all sites investigated but differed to varying extents between the different types of seeps despite the high availability of methane and sulfate methanotrophic microbial activity and biomass were lower at the seeps of the eastern mediterranean compared to those of other continental margins for unknown reasons

a new stochastic model for fracture transmissivity assessment a new stochastic model is proposed for fracture counts and transmissivities in a borehole interval this new model incorporates several empirical observations including i clustering of fractures ii exponential fracture spacings iii transmissivities extending over several orders of magnitude iv power law probability tail for transmissivities at finer scales v log normal transmissivities at larger scales and vi dependence between fracture counts and transmissivities several example applications are provided using borehole data from sweden

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

genesis and solvus relations of submicroscopically intergrown paragonite and phengite in a blueschist from northern california electron microbeam techniques have been used to examine submicroscopically intergrown paragonite phengite and chlorite from the south fork mountain schist of the franciscan terrane of northern california which was subjected to blueschist facies metamorphism the sample also contains quartz albite lawsonite and rutile the subassemblage albite lawsonite rutile requires metamorphic conditions on the low temperature side of the equilibrium albite lawsonite rutile paragonite sphene quartz h2o t 200 c and p 7 4 kbars based on thermodynamic data of holland and powell 1990 the white micas appear to be optically homogeneous but back scattered electron images can distinguish two different micas by their slight difference in contrast electron microprobe analyses empa of micas show na na k ranging from 0 2 to 0 8 the two micas are resolved by transmission electron microscopy tem as packets of phengite and paragonite that range from 20 to several hundred nm in thickness the compositions determined by analytical electron microscopy aem constrain the limbs of the phengite paragonite solvus to values of na na k 0 02 and 0 97 representing less mutual solid solution than ever reported by empa the textural relations imply that the sheet silicates were derived from reactions between fluids and detrital clays and that they are in an intermediate stage of textural development we caution that microprobe analyses of apparently homogeneous sheet silicates may yield erroneous data and lead to faulty conclusions using phengite barometry and paragonite muscovite thermometry especially in fine grained rocks that formed at relatively low temperatures

pore water geochemistry of eastern mediterranean mud volcanoes implications for fluid transport and fluid origin abstract the pore water chemistry of mud volcanoes from the olimpi mud volcano field and the anaximander mountains in the eastern mediterranean sea have been studied for three major purposes 1 modes and velocities of fluid transport were derived to assess the role of upward advection and bioirrigation for benthic fluxes 2 differences in the fluid chemistry at sites of milano mud volcano olimpi area were compiled in a map to illustrate the spatial heterogeneity reflecting differences in fluid origin and transport in discrete conduits in near proximity 3 formation water temperatures of seeping fluids were calculated from theoretical geothermometers to predict the depth of fluid origin and geochemical reactions in the deeper subsurface no indications for downward advection as required for convection cells have been found instead measured pore water profiles have been simulated successfully by accounting for upward advection and bioirrigation advective flow velocities are found to be generally moderate 3 50 cm y 1 compared to other cold seep areas depth integrated rates of bioirrigation are 1 2 orders of magnitude higher than advective flow velocities documenting the importance of bioirrigation for flux considerations in surface sediments calculated formation water temperatures from the anaximander mountains are in the range of 80 to 145 c suggesting a fluid origin from a depth zone associated with the seismic decollement it is proposed that at that depth clay mineral dehydration leads to the formation and advection of fluids reduced in salinity relative to sea water this explains the ubiquitous pore water freshening observed in surface sediments of the anaximander mountain area multiple fluid sources and formation water temperatures of 55 to 80 c were derived for expelled fluids of the olimpi area

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

active venting at the isis mud volcano offshore egypt origin and migration of hydrocarbons abstract the isis mud volcano is an active camembert like mud expulsion structure in the eastern nile deep sea fan area it has been investigated during the nautinil 2003 and mimes 2004 cruises carried out within the mediflux project active gas rich fluid venting occurs at the isis mud volcano as indicated by enhanced gas content in the sediments having a measured 7 5 mmol of methane per liter of wet sediment in the central area of the mud volcano in addition gas bubble expulsions have resulted in the formation of multiple hydrocarbon plumes in the water column with methane concentrations as high as 1550 nmol l compared to 1 nmol l for background levels in deep water in view of the stable carbon and hydrogen isotopic composition of methane 13 c 55 1 vpdb d 203 vsmow and of higher hydrocarbons 13 c of 30 3 26 1 28 4 and 25 0 vpdb for ethane propane i butane and n butane respectively their origin is mainly thermogenic these isotopic data also show that the wet compounds are co generated with oil and we suggest they predominantly originate from type ii kerogen source rocks of potentially variable maturity levels at the centre of the mud volcano the distinct kink observed in the pore water isotopic and dissolved species composition and its depth level change between subsequent cruises indicates a high frequency of fluid gas expulsion the seawater signature of the pore fluid in the upper part of the sediment column suggests that each expulsion is followed by a downward migration of overlying seawater such downward advection of bottom seawater may not only be related to the replacement of the ejected gas but also to the replacement of lower density pore fluid by bottom seawater this mechanism is thought to be a common feature at mud volcanoes and gas seepage sites in the peripheral zone pore fluid is at seawater concentration and isotopic composition down to a coring depth of 430 cmbsf we suggest that the deeper downward advection of bottom seawater is related to the less frequent fluid gas expulsion occurring at these sites compared to the centre sites in this paper we show that a combination of geochemical tools used for hydrocarbons and pore water geochemistry is a powerful approach to detect sources of ascending fluid and to reveal post eruptional fluidodynamic processes within mud volcanoes

the effects of ferromagnesian components on the paragonite muscovite solvus a semiquantitative analysis based on chemical data for natural paragonite muscovite pairs chemical data for 139 natural paragonite muscovite pg ms pairs illustrate the effects of ferromagnesian components on the p t x topology of the pg ms solvus the pairs were selected on the basis of reasonably accurate knowledge of the p t conditions of formation evidence for close approach to equilibrium at peak metamorphic conditions exclusion of pairs in which paragonite contains more than 5 mol margarite and exclusion of pairs from polymetamorphic rocks that contain more than one set of cogenetic pg ms pairs graphical analysis reveals considerable scatter in the data nevertheless it is evident that the muscovite limb of the solvus shifts markedly toward end member muscovite with increasing pressure from approximately 7 kbar to 21 kbar this shift is attributed to a pressure induced increase of the ferromagnesian content of muscovite which increases the size of the xii alkali site to the effect that k is more readily accommodated than na the data also suggest that the paragonite limb of the solvus migrates slightly toward end member paragonite with increasing pressure broadening of the pg ms solvus with increasing pressure reflects increasingly nonideal na k mixing as the phengite content of muscovite increases due to the wide scatter of data for pg phengitic ms pairs it is concluded that at the present time pg ms solvus thermometry is only viable for quasibinary pg ms pairs

carbon isotopic thermometry and geobarometry of sillimanite isograd in thermal aureoles the depth of emplacement of upper crustal granitic bodies carbon isotope fractionation between coexisting calcite and graphite c has been studied in metamorphosed limestones from three thermal aureoles around cretaceous granitic bodies i e tanohata tono and senmaya aureoles in the kitakami mountains northeast japan c in each aureole decreases toward the granitic bodies and becomes virtually uniform near the sillimanite isograd for metapelites although calcite has variable isotopic ratios reflecting the original sedimentary compositions the relationships indicate that isotopic equilibrium has been attained in metamorphosed limestone of sillimanite grade estimated c at the sillimanite isograd is similar in the tanohata and tono aureoles but different in the senmaya aureole with smaller carbon isotopic fractionations from the temperature dependence of c and the negative dp dt of andalusite sillimanite equilibrium we conclude that the sillimanite isograd in the senmaya aureole was under higher temperature and lower pressure than in the other two localities temperatures at the sillimanite isograd are estimated by using existing calibrations of carbon isotopic exchange between calcite and graphite whereas pressures are estimated from carbon isotopic temperatures and the andalusite sillimanite equilibrium holdaway and mukhopadhyay 1993a consistency of the p t estimates is examined in the light of phase equilibria in the pelitic system the estimated pressures at the sillimanite isograd are at about 2 1 2 7 0 2 kbar for the tanohata and tono aureoles and less than 1 kbar for the senmaya aureole respectively geobarometry of sillimanite isograd in thermal aureoles indicates a marked difference in the depth of solidification of upper crustal granitoids the senmaya pluton has intruded and solidified at a very shallow level of less than 4 km whereas the tanohata and tono plutons are more deep seated ca 8 10 km the method can also be an effective tool in studying low pressure type metamorphism in which geothermobarometry using garnet is not always applicable

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

thermodynamic mixing models for muscovite paragonite solutions based on solution calorimetric and phase equilibrium data enthalpies of solution have been measured on a series of muscovite paragonite micas in 20 1 hf at 50 c under isoperibolic conditions the molar enthalpy of formation of paragonite at 298 k for which no calorimetrically measured value is currently available has been determined to be 5937 5 3 kj an inversion of all calorimetric volumetric and phase equilibrium data has been performed giving a range of mixing models compatible with most experimental data the following expressions of the mixing properties of 2m 1 micas for enthalpy h ex and volume v ex at pressures up to 10 kbar forcing excess entropy s ex to be zero and using a subregular mixing model are favoured h ex kj 10 6 4 45 1 2x ms x ms 1 x ms v ex j bar 0 452x ms 1 x ms however mixing models of higher order with asymmetric negative s ex are also possible

the nile deep sea fan preliminary results from a swath bathymetry survey we present and discuss a set of data mainly swath bathymetry backscatter images and a few seismic data that have been recently recorded over large areas of the nile deep sea fan between water depths of 1200 and 3000 m these data demonstrate the presence of at least three distinct morphostructural provinces where interacting sedimentary tectonic and salt tectonic processes control the present day morphology and the recent evolution of the major mediterranean deep sea fan the role of the ongoing collision presently occurring between the continental eratosthenes seamount and the cyprus arc may have been and still is a determining parameter for the development of the nile deep sea fan

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

structural analysis and stratigraphic problems of precambrian rocks of the picuris range new mexico precambrian metasedimentary and amphibolite rocks of the picuris range have formerly been divided into the ortega group and the overlying vadito group we present the results of a structural analysis of a small area straddling the contact between these two groups younging criteria and structural facing relationships show that the vadito group as formerly defined together with the piedra lumbre formation of the ortega group is an overturned sequence in fault contact with the remainder of the ortega group the relative ages of the two groups are unknown and their determination depends on interpretation of regional structure and structural history we define four possible structural models each of which would favor but not require reverse slip on the boundary fault suggesting that the vadito group is probably in part or entirely older than the ortega group possible models for development of the observed geometry are 1 rotational fault in major second generation folds 2 a folded and faulted angular unconformity between the two groups 3 major refolding of an earlier nappe like structure and 4 minor refolding and faulting of major first generation folds