relationships between seep carbonates mud volcanism and basin geometry in the late miocene of the northern apennines of italy the montardone melange the montardone melange mm is a chaotic block in matrix unit outcropping in the montebaranzone syncline in the northern apennines the mm occurs in the uppermost part of the termina fm the middle late miocene interval of a succession deposited in a wedge top slope basin epiligurian succession the mm is closely associated with bodies of authigenic carbonates characterized by negative values of 13c from 18 22 to 39 05 pdb and chemosynthetic benthic fauna lucinid and vesicomyid bivalves in this paper we propose that the mm is a mud volcano originated by the post depositional reactivation and rising of a stratigraphically lower mud rich mass transport body canossa val tiepido sedimentary melange or olistostrome triggered by fluid overpressure we base our conclusion on 1 the mm pierces the entire termina fm and older epiligurian units and represents the direct continuation of the underlying canossa val tiepido melange 2 the geometry and facies distribution of the montebaranzone sandstone body which are compatible with a confined basin controlled by the rising of the mm 3 the systematic presence of large scale lateral extension 300 400 m seep carbonates associated with the melange suggesting a persistent gas enriched fluid vent from the ascending overpressured mud 4 blocks and clasts sourced from the mm hosted by the authigenic carbonates conveyed by ascending mud and gas enriched fluids the mm represents one of the few fossil examples of reactivation of a basin scale sedimentary melange olistostrome a three stage model showing mechanisms of mm raising is proposed

the geochemical signatures of variable gas venting at gas hydrate sites diverse evidence suggests that gas venting rates at sites of hydrate crystallization are variable in space and time but the magnitude of these variations has been difficult to quantify the hydrate crystallization model of chen and cathles j geophys res solid earth 108 2003 is used here to analyze 10 years of vent gas chemistry measurements at the bush hill hydrate mound and gas venting site green canyon 185 offshore louisiana gulf of mexico the analysis suggests that at any instant of time gas vents at variable rates in different gas channels at the same site and that the compositional differences in these vent gases are nearly as large as can be produced by hydrate crystallization almost two orders of magnitude differences in venting rate between individual gas channelways are suggested changes in the average vent gas composition over the last 10 years suggest the average venting rate varied by a factor of similar to2 or more over a few years the average c 3 c 4 composition of bush hill hydrates are leaner than could be crystallized from vent gases sampled over the last decade indicating that the venting gas flux was slower in the past by a factor of similar to2 this is compatible with geologic generalizations that venting evolves from fast mud volcano to intermediate hydrate crystallization to slow carbonate precipitation if venting organized into more discrete vents with time c 2004 elsevier ltd all rights reserved

clathrites archives of near seafloor pore fluid evolution δ44 40ca δ13c δ18o in gas hydrate environments aragonitic clathrites are methane derived precipitates that are found at sites of massive near seafloor gas hydrate clathrate accumulations at the summit of southern hydrate ridge cascadia margin these platy carbonate precipitates form inside or in proximity to gas hydrate which in our study site currently coexists with a fluid that is highly enriched in dissolved ions as salts are excluded during gas hydrate formation the clathrites record the preferential incorporation of 18o into the hydrate structure and hence the enrichment of 16o in the surrounding brine we measured 18o values as high as 2 27 relative to peedee belemnite that correspond to a fluid composition of 1 18 relative to standard mean ocean water the same trend can be observed in ca isotopes ongoing clathrite precipitation causes enrichment of the 44ca in the fluid and hence in the carbonates carbon isotopes confirm a methane source for the carbonates our triple stable isotope approach that uses the three main components of carbonates ca c o provides insight into multiple parameters influencing the isotopic composition of the pore water and hence the isotopic composition of the clathrites this approach provides a tool to monitor the geochemical processes during clathrate and clathrite formation thus recording the evolution of the geochemical environment of gas hydrate systems

miocene chemoherms of the northern apennines italy in the miocene of the northern apennines methane derived limestones from various geologic settings represent important examples of fossil chemoherms and provide a basis for more accurate interpretations of seepage systems the systematic study of fossil chemoherms has allowed the definition of new field and compositional criteria for the recognition of these deposits which were previously based almost exclusively on negative carbon isotope composition and peculiar chemosynthetic communities this has constrained the relations between seepage and sedimentary and tectonic instability processes we suggest that the peculiar brecciated structures associated with fossil chemoherms are related to diapirism of overpressured pelitic sediments due to fluid venting fluidization of sediments increases the instability of mudstones in which chemoherms are contained thus favoring gravity slumping processes and the reworking of many chemoherms

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

geochemistry and origin of archaean quartz cordierite gneisses from the godthabsfjord region west greenland we report new data on the major minor and trace element compositions of metasedimentary quartzcordierite gneisses qcg an important member of the archaean malene supracrustal suite found throughout the godthabsfjord region of west greenland the analyzed qcg contain assemblages of quartz cordierite biotite garnet anthophyllite gedrite staurolite sillimanite plagioclase with abundant accessory zircon and minor rutile monazite and allanite and broadly resemble cordierite orthoamphibole rocks found in a great number of other metamorphic terrains chemically the qcg are characterized by 1 high but variable sio2 59 87 wt relative enrichments in mgo feo and al2o3 mg 0 35 0 85 and depletions in na2o k2o and especially cao 2 low concentrations of sc cr co ni and sr 3 high concentrations of y nb zr hf ta th u and ree rare earth elements with prominent negative eu anomalies in each case 5 high concentrations of ga 18 55 ppm with variable ga al ratios that are significantly higher than average crustal material low cr and ni together with enriched and fractionated ree displaying negative eu anomalies distinguish the malene qcg from published accounts of most other archaean sedimentary rocks furthermore all of the above mentioned trace element characteristics distinguish the qcg from ordinary malene clastic metasediments quartzites psammites and pelites suggesting a separate origin for the qcg these data point towards chemically evolved felsic igneous rocks being the source of the qcg consequently we propose that the malene qcg represent metamorphosed felsic volcaniclastic sediments that underwent hydrothermal alteration by heated seawater prior to metamorphism which resulted in gain of mg and fe loss of alkalis and lime and possibly eu and sr the overall trace element characteristics of the qcg elevated ga zr nb ree etc are features shared by a type granites and their volcanic equivalents such igneous rocks may represent the ultimate source material for the qcg protolith

the hakon mosby mud volcano 330 000 years of focused fluid flow activity at the sw barents sea slope studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity this paper describes the internal structure of the hakon mosby mud volcano hmmv in the southwestern barents sea and presents a conceptual model of its evolution the lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas rich fluids and free gas however the analysis of high resolution single channel seismic scs data reveals for the first time the existence of a pseudo mud chamber at the top of the 3 km deep central conduit it was once created at the seabed and is now a buried expression that acts as mud chamber the pseudo mud chamber is situated approximately 300 m below the seafloor directly above the 330 ka bear island slide bis scar reflection and below glacigenic debris flow deposits that constitute the sediment on top the sediment profiler data indicates a younger mud deposit above the debris flows which points to a reactivation of the mud volcano the reactivation was most likely triggered by the contrast in density between the gas rich mud chamber and the high density debris flow deposits three stages i e initiation sealing and reactivation and a second active period define the evolution of this young mud volcano both the morphology and size of the conduit as well as in situ temperature gradients point towards a focused and rapid fluid flow

structural and fluid evolution of a young accretionary complex the hoh rock assemblage of the western olympic peninsula washington the hoh rock assemblage of the western olympic peninsula washington was deposited in eocene to miocene time and accreted deformed uplifted and eroded by the late miocene northeast dipping fault zones within the hoh are characterized by intensely deformed mud matrix melange and they range from 200 m to 1 000 m thick kinematic indicators within the matrix indicate thrusting to the west southwest both hanging wall and footwall sections are strongly folded and faulted wall rock sections are lithostratigraphically distinct with hanging walls composed of massive coarse sandstone and conglomerate and footwall sections composed of thin to medium bedded sandstone and siltstone folds within the wall rock sections are oblique to and are truncated by the later fault zone melanges indicating that the fault zones postdate folding evidence of fluid involvement in the hoh rocks includes petroliferous outcrops carbonate and clay cement and veins of carbonate and laumontite the progressive evolution of veins and cements paragenetic sequence can be interpreted in terms of crystallization under conditions of increasing consolidation decreasing salinity and changing fluid composition suppressed carbonate luminescence may reflect crystallization under reducing conditions perhaps related to the sulfate reduction zone the presence of hydrocarbons or clay dehydration although deformational features may be associated with the earliest phase of veining most of the localized grain breakage and matrix shear zones formed after the early micritic veins and before the last phase of sparitic carbonate laumontite veins laumontite occurred syn deformationally and in equilibrium with carbonate and also post deformationally the paragenetic sequences observed in all samples from the hoh rock assemblage can be correlated suggesting that the sources and processes controlling the fluid emplacement were similar across a wide region in addition the paragenetic sequence in the hoh rocks is similar to that documented in autochthonous coeval basins of southwest washington this similarity suggests that the precipitates formed during the evolution of the hoh rocks involved fluids that originated within the matrix and did not involve exotic or far traveled fluids

patterns of thermal maturity as diagnostic criteria for interpretation of melanges melanges are common constituents of ancient subduction complexes interpretations of melange genesis fall into five general categories 1 gravitationally induced lateral spreading of the slope apron 2 large scale mass wasting olistostromes 3 subduction driven viscous flow within channels at the base of the accretionary wedge 4 diapiric injection and 5 tectonic deformation within shear zones interpretations are more viable when thermal maturity data are considered along with structural and stratigraphic aspects to document each distinct type of thermal maturity signature paleotemperature data must be extracted from both the matrix lithologies and the blocks of sedimentary rock within a melange as well as from surrounding formations or structural domains

water on venus new insights from tremolite decomposition abstract venus is an extremely hot and dry planet with very little water in its atmosphere and no standing water on its surface however if venus had had more water in the past as the high d h ratio implies hydrous minerals might have formed we present the first experimental study that examines the decomposition rate of hydrous minerals specifically tremolite with applications to venus we predict that tremolite can survive decomposition on venus over geologic time scales at current and at higher surface temperatures thus if future spacecraft can detect tremolite this discovery could serve as evidence of a wetter venusian history

structural evolution of shale diapirs from reactive rise to mud volcanism 3d seismic data from the baram delta offshore brunei darussalam two areas of shale diapirism in a deltaic setting were examined using 3d seismic data from offshore brunei to determine the origin evolution and geometry of shale diapirs the study areas cover parts of the egret and ampa fields within the baram delta province the ampa diapir consists of a small bulge of the mobile setap shale around which lies a zone of chaotically disrupted country rock reflections at the crest of this chaotic zone vertical cylindrical shale pipes arise that end in a wider head the diapir heads wear halos of high amplitude reflections probably due to the presence of methane gas the egret data show the same features except that the bulge of the source layer is not detected due to low reflectivity and chaotic reflections at the base of the overburden the bulging of the setap shale on the ampa data is interpreted as modified reactive diapirism in response to differential loading the initial reactive diapir shape was modified by lateral or oblique upward migration of fluidized shales into the hanging wall of the fault controlling the reactive diapir this probably occurred as a network of dykes and sills the presence of some preserved bedding is indicated by weak but coherent reflectivity from the area initially defined as chaotic shale the spreading of overpressure and the injection of shale into the overburden is thought to be a late phenomenon possibly late pliocene or early pleistocene and the mobility of the shale is attributed to overpressure increase due to gas generation within the setap shale and maybe the lower part of the overburden gas migration perhaps ahead of the diapir intrusion probably facilitated the mud injection the ampa and egret diapirs formed in two diapiric phases an early reactive diapirism and a later active diapirism but the phases have little in common they are seperated by about 9 million years of inactivity and differ in process and probably differ in degree of overpressure in overpressure generating mechanism and in properties of the diapiric mud

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

late miocene seep carbonates and fluid migration on top of the montepetra intrabasinal high northern apennines italy relations with synsedimentary folding abstract during the miocene hydrocarbon seep carbonates located atop intrabasinal highs and associated with sediment instability formed commonly at the deformation front of the northern apennine collisional orogen the parallelism between the structural trend and the distribution of seep carbonates suggests a close relationship between tectonics and gas fluid emission the montepetra intrabasinal high was formed during the closure stage of the foredeep being related to the synsedimentary growth of an anticline field geometry suggests that detachment folding was the leading mechanism of anticline growth and synsedimentary instability along the anticline flanks ten different bodies of seep carbonates occur in the tortonian early messinian sediments nine in the hinge zone and one in the southern backlimb of the anticline foraminiferal study geochemistry facies investigation and the three dimensional geometry of carbonate bodies with respect to the encasing terrigenous sediments indicate a protracted late tortonian early messinian activity of fluid migration with re mobilization and ascent of sediments from the core of the anticline stabilization of chemosynthesis related communities and in situ brecciation seepage atop the intrabasinal high was fed by different circuits one related to the compaction dewatering of shallow tortonian early messinian sediments and a deeper one related to the deformation of the anticline core and to the activity of detachment surfaces and of faults propagating through the sedimentary cover

chemosynthetic communities as fingerprints of submarine sliding linked hydrocarbon seepage miocene deep sea strata of the tuscan romagna apennines italy abstract a specialised low diversity bivalve assemblage dominated by chemosymbiotic vesicomyid bivalves calyptogena sp is associated with a large submarine landslide casaglia m della colonna slide within the turbiditic miocene marnoso arenacea formation in the northern apennines this macrofossiliferous horizon is located just at the top of the slide close to the boundary between intrabasinal deformed sediments and extrabasinal sediments there is a causal relationship between the emplacement of this large submarine slide and fluid expulsion promoting the localised and ephemeral establishment of specialised communities the occurrence of exclusively sulphur based biota and the concomitant absence of 13c depleted authigenic carbonates from the host sediment are likely an indication that hydrocarbons within subsurface fluids were consumed through sulphate reduction processes as a result high levels of shallow seated h2s were produced and then exploited by chemosymbiotic bivalves

mud volcanoes and gas hydrates in the anaximander mountains eastern mediterranean sea abstract detailed multibeam sedimentological and geophysical surveys provide ample new data to confirm that the anaximander mountains eastern mediterranean are an important area for active mud volcanism and gas hydrate formation more than 3000 km of multibeam track length was acquired during two recent missions and 80 gravity and box cores were recovered morphology and backscatter data of the study area have better resolution than previous surveys and very detailed morphology maps have been made of the known targeted mud volcanoes amsterdam kazan and kula especially the amsterdam crater and the related mud breccia flows gas hydrates collected repeatedly from a large area of amsterdam mud volcano at a sub bottom depth of around 0 3 1 5 m resemble compacted snow and have a rather flaky form new gas hydrate sites were found at amsterdam mud volcano including the mud flow sloping off to the south gas hydrates sampled for the first time at kazan mud volcano are dispersed throughout the core samples deeper than 0 3 m and display a rice like appearance relative chronology and ams dating of interbedded pelagic sediments late holocene hemipelagic sapropel layer s1 and ash layers within the mud flows indicate that successive eruptions of kula mud volcano have a periodicity of about 5 10 kyrs new mud volcanoes identified on the basis of multibeam backscatter intensity were sampled documented as active and named athina and thessaloniki gas hydrates were sampled also in thessaloniki mud volcano the shallowest 1264 m among all the active mediterranean sites at the boundary of the gas hydrate stability zone biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of late cretaceous limestones paleocene siliciclastic rocks eocene biogenic limestones and miocene mudstones rough estimations of the total capacity of the anaximander mud volcanoes in methane gas are 2 56 6 40 km3

on an sn w bearing iron formation in the archaean malene supracrustals west greenland abstract in the archaean malene supracrustal rocks west greenland small horizons of iron formation occur they are rarely more than a few metres wide and can be traced with intervals for several hundreds of metres along strike the iron formation is mainly silicate and sulphide facies with high contents of trace elements such as 1 1 zn 0 18 mo 0 12 sn and 170 ppm w the iron formation is associated with stratabound scheelite mineralization and tour malinites the iron formation is suggested to be of submarine exhalative origin

criteria helpful in recognizing shear zone and diapiric melanges examples from the hoh accretionary complex olympic peninsula washington a study of the middle miocene hoh melanges exposed on the western olympic peninsula washington provides criteria for differentiating between shear zone and diapiric melanges the shear zone melange is characterized by a consistent foliation orientation throughout the outcrop intense pervasive scaly foliation uniform fold vergence directions exotic clasts predominantly phacoidal clasts and consistent clast long axis lineations the diapiric melange is characterized by radial foliation in map view well developed scaly foliation at the contacts and poorly developed scaly foliation in the center of the melange opposite fold vergence directions across the melange and rare exotic clasts additionally clasts vary in shape from phacoidal at the contacts to angular in the center in the diapiric melange large clasts are found only in the center of the melange and clast long axes vary from tightly clustered at the contacts to near random orientations in the center the systematic variation in clast size in the diapir may be due to increased shear at the margins and or clast migration to the center of the diapir caused by a velocity viscosity contrast interpretation of field data indicates that some clasts rotate continuously in the matrix yet clast long axes have a definite preferred orientation this contradiction may be resolved by theoretical models indicating that clasts rotate fastest at high angles to the shear plane thus although clasts above a critical aspect ratio asymptotically approach stability parallel to the shear plane the long axes of rotating clasts spend a proportionally greater amount of time close to the shear plane parasitic folds in the matrix indicate that clast long axes align parallel to transport direction small scale folds in the matrix clast long axis lineations and the mean foliation indicate that the hogsback section of the hoh melange was emplaced by a high angle oblique thrust directed to n10 e

the architecture of an incipient oceanic basin a tentative reconstruction of the jurassic liguria piemonte basin along the northern apennines alpine corsica transect in this paper a scenario for the early evolution of the jurassic oceanic liguria piemonte basin is sketched for this purpose four selected examples of ophiolite sequences from the northern apennines and corsica are described and analyzed in the external ligurian units northern apennines the ocean continent transition of the adria plate was characterized by a basement made up of subcontinental mantle and lower continental crust covered by extensional allochthons of upper crust both the basement rocks and the extensional allochthons are cut by basaltic dikes and covered by basalts and pelagic deposits the conjugate ocean continent transition of the corsica margin represented by the balagne nappe corsica was composed of mantle peridotites and gabbros covered by basaltic flows and minor breccias that in addition include continent derived clasts by contrast the innermost i e closest to the ocean preserved area observed in the internal ligurian northern apennines and inzecca corsica units consists of former morphological highs of mantle peridotites and gabbros bordered by small basins where the basement is covered by a volcano sedimentary complex characterized by ophiolitic breccias and cherts interlayered with basaltic flows the overall picture resulting from our reconstructions suggests an asymmetric architecture for the liguria piemonte basin with a central area bounded by two different transition zones toward the continental margins this architecture can be interpreted as the result of a rifting process whose development includes a final stage characterized by passive asymmetric extension of the lithosphere along an east dipping detachment fault system

rare earth elements in the early archaean isua iron formation west greenland abstract the rare earth element ree patterns in the 3 8 ga old isua iron formation are generally flat resembling those of some primitive basalts samples with positive negative or no europium anomaly were found it is shown that diagenesis and metamorphism did not significantly change the ree patterns the presence or absence of europium anomalies in iron formations cannot be used as an indicator of the presence or absence of oxygen in the atmosphere during the archaean and precambrian the ree contents cannot be used to distinguish algoma type from superior type iron formations there appears to be a striking similarity between the archaean submarine exhalations and modern submarine hydrothermal systems it is considered likely that archaean and early precambrian seawater had a chondritic ree pattern with a slight enrichment of light ree

small scale polygenetic melanges in the ligurian accretionary complex northern apennines italy and the role of shale diapirism in superposed melange evolution in orogenic belts abstract the argille varicolori varicolored scaly clays of the external ligurian units of the northern apennines have been widely described as a typical unmetamorphosed broken formation i e a chaotic unit without exotic blocks produced by offscraping and tectonic imbrication during the evolution of the ligurian accretionary wedge geological mapping and integrated structural and stratigraphic observations show that the argille varicolori consist of diverse types of small scale melanges non mappable at a 1 25 000 scale forming a composite chaotic unit in which the superposition of tectonic sedimentary and diapiric processes resulted in the occurrence of polygenetic chaotic bodies at different scales these melange units record the evolution of the ligurian accretionary wedge from subduction to collision and intracontinental deformation tectonically disrupted body 1 tdb1 comprises boudinage and pinch and swell structures formed by layer parallel extension contraction at the wedge front of the ligurian accretionary complex during the late cretaceous middle eocene it is interleaved with non mappable gravity driven chaotic bodies gcb developed during alternating episodes of accretion and removal of material at the wedge front the late oligocene early miocene out of sequence thrusting related to the collisional episodes in the apennines overprinted the previously formed chaotic bodies and formed a polygenetic tectonic melange tectonically disrupted body 2 tdb2 this unit is characterized by a structurally ordered block in matrix fabric and by the gradual decrease of stratal disruption away from the regional thrust overpressurized fluids concentrated along the shear surfaces and the scaly cleavage planes facilitated the diapiric upward movement of unconsolidated sediments in the early miocene this process produced non mappable shale dike injections ddb1 and mappable diapirically disrupted bodies ddb2 which show an internal zonation of deformation this deformation reworked the previously formed chaotic bodies although some of these polygenetic melanges cannot be mapped at a 1 25 000 scale their careful documentation provides a better understanding of time progressive scale independent melange forming processes

sediment instability related to fluid venting in miocene authigenic carbonate deposits of the northern apennines italy chemosynthetic carbonates identified by isotopic palaeoecological and sedimentological features are concentrated in middle late miocene satellite and foredeep deposits of the northern apennines chemoherms in the foredeep are hosted in thick pelitic intervals probably deposited in intrabasinal structural highs which are entirely or partly involved in large slumps in many cases associated with extrabasinal slides sediment textures in carbonates and in the enclosing foredeep pelitic sediments indicate a link between hydrocarbon fluid venting sediment deformation and mobilisation and tectonics the intensity and style of fluid release phases directly influenced chemoherm typology and also determined overpressure conditions in low shear strength pelitic sediments favouring sediment mobilisation and influencing slope instability which widely affected the apennine foredeep chemosynthetic carbonates are associated with sites of tectonically fractured and compressed sediments in the apennine foredeep thrust belt system thus indicating a relation with the tectonic loading of the apennine thrust sheets which favoured fluid expulsion along forerunner faults possible gas hydrate contributions to fluid expulsion processes are discussed based on sediment textures compared with modern vent areas finally sediment instability may have facilitated a large amount of fluid escape thus stopping carbonate precipitation

methane seepages recorded in benthic foraminifera from miocene seep carbonates northern apennines italy abstract benthic foraminifera from seep carbonates and from enclosing non seep marls present within miocene formations in the northern apennines italy were investigated as proxies of methane seepage in the marine environment negative 13c values of benthic foraminifera from these seeps indicate unambiguously the local influence of co2 produced by microbial anaerobic methane oxidation on the benthic ecosystem calcareous species living within methane seeps display 13c values ranging from 9 04 to 25 74 pdb whereas in the coeval surrounding marls the same species display 13c values from 1 54 to 0 62 pdb different species cibicidoides kullenbergi c pachyderma siphonina rethiculata planulina wuellestorfi bolivina miocenica brizalina dilatata vulvulina pennatula and cibicides praecinctus in different seep carbonates indicate that benthic foraminifera independently of the taxa and of microhabitat preferences have more negative 13c values than those found in the enclosing marls therefore each species represents a potential proxy for past seafloor methane emissions in addition to the calcareous species the agglutinated species vulvulina pennatula displays 27 5 pdb in seep carbonates against 2 69 pdb in the enclosing marls this suggests that the species utilized strongly 13c depleted carbonate particles from authigenic carbonate precipitation during the mineralization of their tests

strata bound tourmaline in the archaean malene supracrustals west greenland thin tourmaline rich layers closely associated with strata bound tungsten mineralization occur in layered amphibolites and metasediments of the archaean malene supracrustals in west greenland locally tourmaline is intergrown with scheelite microprobe analyses showed that the tourmaline is of intermediate composition between schorl and dravite with small variations in composition in different layers the tourmaline is interpreted as being of submarine exhalative origin

jiulong methane reef microbial mediation of seep carbonates in the south china sea chemoherm carbonates as well as numerous other types of methane seep carbonates were discovered in 2004 along the passive margin of the northern south china sea lithologically the carbonates are micritic containing peloids clasts and clam fragments some are highly brecciated with aragonite layers of varying thicknesses lining fractures and voids dissolution and replacement is common mineralogically the carbonates are dominated by high magnesium calcites hmc and aragonite some hmcs with mgco3 contents of between 30 38 mol extreme hmc occur in association with minor amounts of dolomite all of the carbonates are strongly depleted in 13c with a range from 35 7 to 57 5 pdb and enriched in 18o 4 0 to 5 3 pdb abundant microbial rods and filaments were recognized within the carbonate matrix as well as aragonite cements likely fossils of chemosynthetic microbes involved in carbonate formation the microbial structures are intimately associated with mineral grains some carbonate mineral grains resemble microbes the isotope characteristics the fabrics the microbial structure and the mineralogies are diagnostic of carbonates derived from anaerobic oxidation of methane mediated by microbes from the succession of hmcs extreme hmc and dolomite in layered tubular carbonates combined with the presence of microbial structure and diagenetic fabric we suggest that extreme hmc may eventually transform into dolomites our results add to the worldwide record of seep carbonates and establish for the first time the exact locations and seafloor morphology where such carbonates formed in the south china sea characteristics of the complex fabric demonstrate how seep carbonates may be used as archives recording multiple fluid regimes dissolution and early transformation events

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

seafloor expression of sediment extrusion and intrusion at the el arraiche mud volcano field gulf of cadiz 1 the el arraiche mud volcano field consists of eight mud volcanoes up to 255 m high and 5 4 km wide located in the moroccan margin of the gulf of cadiz at water depths between 700 and 200 m available data include detailed swath bathymetry over the entire area dense grids of high resolution seismic data very high resolution deep tow subbottom profiles side scan sonar mosaics over the major structures selected underwater video lines and sediment samples the main morphological aspects of the mud volcanoes are from the margin toward the center a subsidence rim or moat the mud volcano slope in some cases a deep crater and a recent central mud dome at the top the slope is characterized by radial outward sediment flow deposits or by a concentric pattern of terraces and steps the sediment flow deposits can be divided into elongate outflows that accumulate at the base of the slope and short bulky outflow deposits that freeze on the steep slope the crater hosts extruded sediment ranging from fluidized sand to mud breccia with centimeter to meter sized rock clasts issued from several vents within the crater the concentric slope terraces and the central mud dome are interpreted to result from several phases of uplift caused by sediment intrusion or shallow diapirism the mud volcano growth is thus interpreted to result from a combination of extrusive and intrusive processes

anatomy of seep carbonates ancient examples from the miocene of the northern apennines italy ancient hydrocarbon seep carbonates of miocene age have been reported from marine sedimentary successions of the northern apennines in the form of irregularly shaped micritic masses containing abundant fossil remains of oligotypic assemblages they are recognized by their peculiar biological sedimentological and geochemical features and represent an excellent on land example of carbonate bodies interpreted as the remains of ancient cold seeps in the apenninic chain the abundance and the extent of the outcrops provide a rare opportunity to study the geometry facies distribution and internal structures of fossil methane derived carbonates the present study reports an integrated view of the sedimentology mineral paragenesis and geochemistry of these seep carbonates in two different tectono sedimentary settings foredeep and satellite basins the main result of this study is the recognition of 17 facies in the investigated seepcarbonates the detailed facies and microfacies analysis led to the identification of different structures which occur in welldefined parts of the carbonate masses the recurring and broadly similar stratigraphy and facies association from the two considered geological environments is diagnostic of the different stages of seep carbonate formation and evolution d 2005 elsevier b v all rights reserved

silicate facies iron formation and strata bound alteration tuffaceous exhalites derived by mixing evidence from mn garnet stilpnomelane rocks at redstone timmins ontario silicate facies iron formation composed of mn garnet stilpnomelane and ferrotschermakitic hornblende mark an exhalative sedimentary stratigraphic horizon located regionally at the break between two volcanic supercycles consisting of lowermost calc alkaline felsic pyroclastic rocks overlain by komatiitic ultramafic flows locally mn garnet stilpnomelane rock flanks and in places is footwall to a strata bound volcanic hosted nickel sulfide deposit at redstone timmins mn garnets have normal reverse and oscillatory zoning patterns with a coupled substitution of mn ca for fe mg stilpnomelane amphibole chlorite and biotite each have elevated mno contents but do not display any concentric zoning patterns the al ti and ti zr ratios of mn garnet stilpnomelane rock are similar to those of dacitic tuff at redstone however the former rock is enriched in fe mg and mn but depleted in na relative to the latter discordant alteration pipes and concordant strata bound altered rocks associated with massive base metal sulfide and archean lode au volcanic hosted deposits are predominated by fe mg mn al enriched alkali depleted rocks very similar to silicate facies iron formation at redstone mn garnet stilpnomelane rocks represent a mixture of pyroclastic material plus chemical sediment whereby all of the al ti zr v and p have a volcaniclastic origin and most of the fe mn mg ca co and rb are chemically precipitated whereas cr ni sr na nb ba and k have been leached from a volcanic precursor y is mobile perhaps due to a preferred partitioning into the mn garnet structure both silicate facies iron formation and semiconcordant alteration zones are enriched in elements commonly mobile in hydrothermal systems such as fe mg mn si relative to 100 percent tuff as well as immobile elements including al ti zr y nb rare earth elements relative to 100 percent exhalite the resultant group of aluminosilicate minerals within these altered rocks is a function of the bulk rock composition which in turn represents a mixture of exhaled chemical sediment and volcaniclastic debris strata bound fe mg mn al enriched tuffaceous exhalites typically occur in a mixed volcano sedimentary setting distal from a volcanic center but proximal to the hydrothermal vent often flanking or stratigraphically at or near a prospective gold or base metal ore horizon

petrogenesis of archaean malene supracrustal rocks nw buksefjorden region west greenland geochemical evidence for highly evolved archaean crust abstract we report new data for major minor and trace elements in forty nine samples of malene supracrustal rocks nw buksefjorden region west greenland the samples consist principally of quartz cordierite biotite garnet anthophyllite gedrite sillimanite with abundant accessory zircon and minor rutile allanite and monazite plagioclase is rare to absent while muscovite occurs in only a few cases thus the malene paragneisses closely resemble cordierite orthoamphibole rocks found in other metamorphic complexes the nw buksefjorden malene paragneisses have on average high sio2 moderate al2o3 fe2o3 t and mgo and low k2o na2o and especially cao distinctive trace element characteristics include 1 low sc co cr ni and sr 2 high y zr nb hf ta th u and ree with prominent negative eu anomalies in nearly every case and 3 high ga up to 65 ppm with ga al ratios significantly higher than average crustal material on the basis of afm assemblage type the paragneisses can be divided into distinct groups which preserve the field distinctions noted by previous workers however these groupings primarily reflect variations in mg total range from 0 26 0 89 with no meaningful distinctions appearing among trace elements except possibly cu the trace element characteristics of the nw buksefjorden malene paragneisses are identical to those of the malene quartz cordierite gneisses found throughout the greater godthabsfjord region these gneisses are different from the malene quartzite psammite pelite group of clastic metasediments the trace element data of the quartz cordierite gneisses are compatible with a protolith dominated by material derived from felsic igneous precursors an interpretation supported by immobile element discriminant plots and ternary la th sc and th co hf plots however negative eu anomalies and low sr and ca suggest that plagioclase was lost from the protolith or from the precursor lithology or both the high concentrations of ga indicate either that the source rocks for the paragneisses were unusually ga rich or that assembly of the protolith was accompanied by a major fractionation of al from ga we propose that the protolith for most of the nw buksefjorden malene paragneisses was a quartz chlorite sericite schist derived from felsic volcaniclastic sediment hydrothermally altered by seawater prior to metamorphism this alteration resulted in gain of mg and possibly fe and loss of lime and alkalis and possibly sr and eu this hypothesis contrasts with earlier proposals that the protolith included mg rich clay palygorskite that precipitated directly from seawater but it is more consistent with the new data there is a remarkably close correspondence between the element enrichments and depletions shown by the malene paragneisses and those found in a type granitic rocks and their volcanic equivalents consequently we suggest a comparable source for the paragneisses the petrogenesis of a type granites is associated typically with thickened stable continental crust this implies that the protolith for the malene paragneisses formed after or in conjunction with a major event of archaean crustal thickening

extreme efficiency of mud volcanism in dewatering accretionary prisms drilling results from two mud volcanoes on the mediterranean ridge accretionary complex as well as bottom sampling and the wealth of geophysical data acquired recently have provided fundamental knowledge of the 3d geometry of mud extrusions mud volcanism is generally related to buoyancy density inversion and is triggered by the collision of the african and eurasian blocks forcing undercompacted clayey sediments to extrude along faults in the central and hinterlandward parts of the prism volumetric estimates of extruded mud in several well studied areas were based on pre stack depth migrated seismic profiles across the entire up to 150 km wide prism the resulting volumes of mud were combined with ages from mud dome drilling so that rates of mud extrusion were obtained subtracting the solid rock mass from the bulk mud volume using physical property data fluid flux as a function of mud volcanism alone has been quantified for the first time the volume of fluid extruding with the mud is found to be variable but reaches up to 15 km3 fluid per km trench length and ma along cross sections with abundant mud volcanoes such large fluid quantities in a region some 50 150 km behind the deformation front exceed estimates from those elsewhere where undoubtedly the majority of the interstitial fluid is lost due to compaction such fluids near the backstop are likely to result predominantly from mineral dehydration and diagenetic reactions at depth and consequently provide a window to understand deeper processes along the deep decollement more importantly the enormous rates with which such fluids and liquified mud escape along the out of sequence faults alter fluid budget calculations in subduction zones drastically

detecting a sequence boundary across different tectonic domains an example from the middle miocene of the northern apennines italy sequence stratigraphic concepts can provide a powerful tool for understanding the tectono sedimentary evolution of areas extending across different tectonic domains an example is provided by the upper serravallian strata of the northern apennines where a sedimentological and biostratigraphic study allows a sequence boundary to be traced across the foredeep and piggy back basin successions turbidite sedimentation of predominantly alpine and subordinate apenninic provenance occurred in the apenninic foreland basin throughout the middle miocene deep water sedimentation in the foredeep was laterally associated with deposition in shelf to slope environments in the piggy back basins in the piggy back basin succession the upper serravallian sequence boundary is a laterally extensive unconformity within homogeneous marly deposits this unconfonnity is laterally correlative with the base of lenticular turbidite bodies a stratigraphic lacuna affecting zone n14 characterizes the marginal areas where glaucony rich deposits assigned to zone n15 unconformably overlie marls displaying association of zone n13 in the depocentres where no significant stratigraphic gap has been detected the sequence boundary is narrowly constrained to lowermost zone n14 the upper serravallian unconformity of the piggy back basins succession is correlative with time equivalent features in two distinct parts inner basin and outer basin of the foredeep in the inner basin the sequence boundary separates basin margin turbidites from overlying slope hemipelagites in a more external position outer basin the sequence boundary is the base of a characteristic mega turbidite of apenninic provenance turrito layer in other sectors of the outer basin where turbidite sedimentation was entirely of alpine provenance the sequence boundary has no clear physical expression the observed facies distribution in the study area suggests that an important thrusting event affected the northern apennines in the late serravallian resulting in submarine channel incision and nondeposition in the piggy back basins compressional activity in the foredeep was responsible for the closure of the inner basin and subsequent shifting of turbidite sedimentation in the outer basin slope instability led to widespread remobilization of previously deposited turbidites triggering turbidite events of huge volume the different characteristics of the sequence boundary in the various parts of the foredeep constitute an example of differential response of a multisourced supply system to tectonic deformation

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

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities