intermediate sulfur oxidation state compounds in the euxinic surface sediments of the dvurechenskii mud volcano black sea abstract the deep black sea is known to be depleted in electron acceptors for sulfide oxidation this study on depth distributions of sulfur species s ii s 0 s n 2 s 2 o 3 2 so 3 2 so 4 2 in the dvurechenskii mud volcano a cold seep situated in the permanently anoxic eastern black sea basin sorokin trough 2060 m water depth showed remarkable concentrations of sulfide oxidation products sulfite concentrations of up to 11 mol l 1 thiosulfate concentrations of up to 22 mol l 1 zero valent sulfur concentrations of up to 150 mol l 1 and up to five polysulfide species were measured in the upper 20 cm of the sediment electron acceptors found to be available in the dvurechenskii mud volcano dmv for the oxidation of hydrogen sulfide to sulfide oxidation intermediates are iron minerals and probably also reactive manganese phases up to 60 mol g 1 of reactive iron minerals and up to 170 mol l 1 dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow thus the source for the oxidative power in the dmv are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments leading to the formation of various sulfur intermediates in comparably high concentrations another possible source of sulfide oxidation intermediates in dmv sediments could be the formation of zero valent sulfur by sulfate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero valent sulfur sulfide oxidation intermediates which are produced by these processes do not reach thermodynamic equilibrium with rhombic sulfur especially close to the active center of the dmv due to a short equilibration time thus mud volcano sediments such as in the dmv can provide oxidizing niches even in a highly reduced environment like the abyssal part of the black sea

characteristic features of pockmarks on the north sea floor and scotian shelf this paper presents the results of a comparative study of pockmarks and associated features appearing on both sides of the north atlantic on the scotian shelf off nova scotia and in the northern north sea pockmarks are formed in seabed material consisting of soft silty clay the seismic sonar and lithologic characteristics of the sediments on the scotian shelf are remarkably similar to those found in the northern north sea sediment clouds suspended in the water column immediately over the seabed have previously been observed on side scan records associated with gas charged sediments on corresponding shallow seismic records these and similar observations strongly suggest that most pockmarks are caused by gas efflux through the seafloor however the detailed mechanism of formation and the origin of the gas in the sediments is still unknown

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

pockmarks and methanogenic carbonates above the giant troll gas field in the norwegian north sea abstract acoustic imaging has revealed more than 7000 pockmarks on the seafloor above the troll east gas field in the norwegian north sea we present the first comprehensive study conducted on one of the world s largest pockmark fields complementing the acoustic data with extensive sampling geochemical and petrographical studies specifically we aimed at detecting possible active seepage still present over this vast area the pockmarks are present as isolated structures on average 35 m wide and up to 100 m in size in addition smaller satellite pockmarks surround some of the pockmarks in contrast to the muddy surroundings parts of the investigated pockmarks contain laterally extensive carbonate deposits or meter sized carbonate blocks these blocks provide shelter to abundant colonies of benthic megafauna the carbonate blocks are comprised of micritic mg calcite and calcite micritic aragonite and botryoidal aragonite framboidal pyrite is also commonly present carbon isotopic values of the carbonates are 13c depleted 13c as low as 59 7 and with 18o up to 4 5 indicating a methanogenic origin possibly linked to gas hydrate dissociation pore water extracted from shallow cores from the centre and the flanks of the pockmarks show similar cl and so4 profiles as the reference cores outside the pockmarks ruling out active methane seepage this conclusion is also supported by seafloor video observations that did not reveal any evidence of visual fluid seepage and by the absence of microbial mats and by the fact that the carbonate blocks are exposed on the seafloor and party oxidized on the surface we conclude that methane seepage formed this extensive gas field following to gas hydrate dissociation

modelling hanging wall accommodation above rigid thrust ramps abstract experimental models are used to study the role of material rheology in hanging wall accommodation above rigid flat ramp flat thrust footwalls the deformation in the hanging wall was accomplished by forwards sliding along a rigid basal staircase trajectory with a variable ramp angle ranging from 15 to 60 we model different ramp angles to examine hanging wall accommodation styles above thrust ramps of overthrust faults ranging from 15 to 30 as well as above pre existing normal faults ranging from 45 to 60 for the hanging walls we used stratified frictional sand and viscous silicone putty materials in this paper we study three types of models type 1 models represent purely frictional hanging walls where accommodation above thrust ramps was by layer parallel thickening and by generating a series of back thrusts type 2 and 3 models represent stratified frictional viscous hanging walls in these models accommodation was by a complex association of reverse and normal faults mainly controlled by the rheological anisotropy as well as by the ramp inclination angle in type 2 models the silicone covered only the lower flat while in type 3 models it also covered the rigid ramp for 30 in type 2 models and 45 in type 3 models the viscous layer inhibited the development of back thrusts in the frictional hanging wall instead the silicone thickened to develop a ductile ramp for values higher than 30 in type 2 models and 45 in type 3 models back thrusts develop in response to the bulk compression the experiments simulate many structures observed above natural thrust ramps with 30 and pre existing normal faults with 45 the models emphasise the importance of a basal ductile layer which allows the hanging wall to step up over the rigid ramp by building up its own ductile ramp the models also emphasise that foreland directed normal faulting can develop at a thrust front in the case that the vertical stress due to gravity exceeds the horizontal stress due to end loading within a thrust wedge

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

the effects of pre existing normal faults on thrust ramp development an example from the northern apennines italy the umbria marche foreland fold and thrust belt in the northern apennines of italy provides excellent evidence to test the hypothesis of synsedimentary structural control on thrust ramp development this orogenic belt consists of platform and pelagic carbonates late triassic to miocene in age whose deposition was controlled by significant synsedimentary extension normal faulting mainly active from jurassic through late cretaceous paleogene time resulted in significant lateral thickness variability within the related stratigraphic sequences by late miocene time the sedimentary cover was detached from the underlying basement and was deformed by east verging folds and west dipping thrusts two restored balanced cross sections through the southernmost part of the belt show a coincidence between the early synsedimentary normal faults and the late thrust fault ramps these evidences suggest that synsedimentary tectonic structures such as faults and the related lithological lateral changes can be regarded as mechanically important controlling factors in the process of thrust ramp development during positive tectonic inversion processes

styles of positive inversion tectonics in the central apennines and in the adriatic foreland implications for the evolution of the apennine chain italy abstract integration of new field structural and geophysical data with existing information from the apennines chain in italy and its adjacent adriatic foreland indicates that the styles of positive inversion tectonics and the modes of interaction between the extensional and the subsequent compressive structures vary starting from the cretaceous the contractional deformation induced by the mainly north directed convergence of africa adria with respect to the european plate promoted the closure of various arms of the atlantic and the neo tethys oceans which opened in different times and with distinct orientations the mosaic of continental blocks carbonate platforms rift basins and oceanic domains with several geometries and orientations with respect to the axis of the subsequent compression and the resulting heterogeneities within the shallow sedimentary cover and the overall lithosphere strongly influenced both the structural evolution of the apennine orogenic belt and the intra continental deformation within the adriatic foreland field observations reveal that the steeply e and w dipping mesozoic cenozoic normal faults are systematically decapitated by sub horizontal or gently west dipping thrusts propagating with short cut trajectories pre thrusting normal faults were commonly deformed by later thrusts but little evidence seems to support their entire reactivation as high angle reverse faults this suggests that these shallow and steeply dipping discontinuities were not suitable to be reutilized by the superficial thin skinned thrust faults propagating within the sedimentary cover in contrast presumably late paleozoic and mesozoic w dipping normal faults appear moderately reactivated in the adriatic foreland and strong positive inversion tectonics affect the deeper and buried structural levels of the apennine chain within the latter the syn rift sediments in the hangingwall blocks of the fault bounded basins were totally extruded and generated the strong uplift of the thinned adria continental crust finally the contrasting styles of interactions of the pre existing normal faults with later thrusts i e passive truncation or positive reactivation strictly result from the different evolution of the apennine chain and the combined thin and thick skinned modes of deformation of the stretched lithosphere of the adria plate

ancient erosional grooves on exhumed bypass margins of carbonate platforms examples from the apennines the margins of carbonate platforms have been broadly classified into those where sediment is deposited at the margin and those where sediment bypasses the margin although modern bypass margins have been described from north of jamaica and the bahamas examples of ancient bypass margins are conspicuously absent however the recent discovery of parts of several bypass margins in the jurassic carbonates of the umbria marches apennines in italy allows a close look at the processes that create and shape these margins the bypass margins in the apennines were created on the escarpments of large normal faults which broke up a large continuous platform into a group of small isolated platform remnants the newly discovered outcrops allow us to recognize that the marginal escarpments of these platforms are characterized by a series of deep grooves that were cut into the escarpment by the subaqueous erosive action of bypassing sediment swept off the tops of the platforms and deposited in the basins erosion of the escarpments and sediment bypassing gradually diminished as the basins filled with sediments and the platforms submerged to greater depths cutting off the rapid shallow water sedimentation

anaerobic methane oxidation and a deep h2s sink generate isotopically heavy sulfides in black sea sediments the main terminal processes of organic matter mineralization in anoxic black sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2 4 m and methanogenesis below the sulfate zone the modern marine deposits comprise a ca 1 m deep layer of coccolith ooze and underlying sapropel below which sea water ions penetrate deep down into the limnic pleistocene deposits from 9000 years bp sulfate reduction rates have a subsurface maximum at the so42 ch4 transition where h2s reaches maximum concentration because of an excess of reactive iron in the deep limnic deposits most of the methane derived h2s is drawn downward to a sulfidization front where it reacts with fe iii and with fe2 diffusing up from below the h2s fe2 transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur the pore water gradients respond dynamically to environmental changes in the black sea with relatively short time constants of ca 500 yr for so42 and 10 yr for h2s whereas the fes in the black band has taken ca 3000 yr to accumulate the dual diffusion interfaces of so42 ch4 and h2s fe2 cause the trapping of isotopically heavy iron sulfide with 34s 15 to 33 at the sulfidization front a diffusion model for sulfur isotopes shows that the so42 diffusing downward into the so42 ch4 transition has an isotopic composition of 19 close to the 23 of h2s diffusing upward these isotopic compositions are however very different from the porewater so42 43 and h2s 15 at the same depth the model explains how methane driven sulfate reduction combined with a deep h2s sink leads to isotopically heavy pyrite in a sediment open to diffusion these results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth s history

progressive evolution of a fault related fold pair from growth strata geometries sant llorenc de morunys se pyrenees abstract new structural stratigraphical mapping constrains the three dimensional kinematics and mechanisms of eocene oligocene growth folding at sant llorenc de morunys ne ebro basin spain a 1 km wide sub vertical panel of syntectonic alluvial gravels passes southwards via a highly asymmetrical growth fold pair to shallowlydipping strata the axial surface of the anticline comprises either continuous or en echelon segments while that of the syncline is concave and usually continuous while converging upwards the axial surfaces do not define growth triangles principal and subsidiary growth unconformities and thickness changes occur across both axial surfaces and the common limb dips within the common limb decrease up stratigraphy and up dip mesostructures indicate that internal deformation was ongoing during folding at all stratigraphical levels and concentration of cleavage in the syncline indicates that this hinge was essentially fixed sequential restoration of three profiles shows that folds amplified principally by limb rotation but incorporated minor passive hinge migration particle movement vectors generated by section restoration are arcuate about a hinterland pinpoint a new trishear model of fault propagation folding involving non rigid limb rotation reproduces the rounded hinge forms thickening geometries and limb dip variations observed simple kink band migration models fixed axis and constant thickness theories do not replicate these features

sources and turnover of organic carbon and methane in fjord and shelf sediments off northern norway to better understand the present and past carbon cycling and transformation processes in methane influenced fjord and shelf areas of northern norway we compared two sediment cores from the hola trough and from ullsfjorden we investigated 1 the organic matter composition and sedimentological characteristics to study the sources of organic carbon corg and the factors influencing corg burial 2 pore water geochemistry to determine the contribution of organoclastic sulfate reduction and methanogenesis to total organic carbon turnover and 3 the carbon isotopic signature of hydrocarbons to identify the carbon transformation processes and gas sources high sedimentation and corg accumulation rates in ullsfjorden support the notion that fjords are important corg sinks the depth of the sulfate methane transition smt in the fjord is controlled by the supply of predominantly marine organic matter to the sediment organoclastic sulfate reduction accounts for 60 of the total depth integrated sulfate reduction in the fjord in spite of the presence of ethane propane and butane we suggest a purely microbial origin of light hydrocarbons in the sediments based on their low 13c values in the hola trough sedimentation and corg accumulation rates changed during the deglacial to post glacial transition from approximately 80 cm ka 1 to erosion at present thus corg burial in this part of the shelf is presently absent low organic matter content in the sediment and low rates of organoclastic sulfate reduction only 3 of total depth integrated sulfate reduction entail that the shallow depth of the smt is controlled mostly by ascending thermogenic methane from deeper sources this article is protected by copyright all rights reserved

multi phase reactivations and inversions of paleozoic mesozoic extensional basins during the wilson cycle case studies from the north sea uk and the northern apennines italy

multiple sulfur isotope constraints on sulfate driven anaerobic oxidation of methane evidence from authigenic pyrite in seepage areas of the south china sea abstract multiple sulfur isotope signatures and secondary ion mass spectroscopy sims sulfur isotope compositions of pyrite from two seafloor sites dh cl11 and hd109 in seepage areas of the south china sea were measured in order to study isotope effects of sulfate driven anaerobic oxidation of methane so 4 aom the multiple sulfur isotopes of pyrite reveal variable ranges for both sites 34 s between 44 1 and 2 9 for dh cl11 and between 43 8 and 1 6 for hd109 33 s between 0 02 and 0 17 for dh cl11 and between 0 03 and 0 14 for hd109 sims analysis reveals an extreme variability of 34 s values between 50 3 and 2 7 in dh cl11 between 50 1 and 52 4 in hd109 for three types of pyrite 1 framboids 2 zoned aggregates with radial overgrowth surrounding a framboidal core and 3 euhedral pyrite crystals the synchronous changes of geochemical proxies sulfate and methane concentrations 34 s sulfate and 18 o sulfate 34 s pyrite and pyrite content at the sulfate methane transition zone smtz at site dh cl11 are interpreted to be induced by so 4 aom under steady state conditions in contrast pyrite content and 34 s value fluctuations throughout core hd109 suggest that the sediment at this site was affected by multiple pyritization events during diagenesis multiple sulfur isotope signatures of early diagenetic pyrite i e with low and high 34 s values the latter above 315 cmbsf in dh cl11 above 70 cmbsf in hd109 in the upper sediment column suggest that organoclastic sulfate reduction osr and sulfur disproportionation generated the observed isotopic signatures in contrast to the early diagenetic 34 s depleted framboids the higher sims 34 s values of overgrowth and euhedral crystals suggest a late diagenetic 34 s enriched pool of dissolved sulfide derived from so 4 aom at the current and paleo smtzs interestingly pyrite resulting from so 4 aom in the smtz at site dh cl11 reveals a distinct pattern with higher 33 s values different from pyrite resulting from osr and sulfur disproportionation therefore paired 34 s and 33 s values may allow to differentiate osr and so 4 aom although a full understanding of the isotope effects associated with so 4 aom is hampered by uncertainties on the actual electron transfer mechanism in the syntrophic so 4 aom consortium

the role of ductility contrast and basement architecture in the structural evolution of the crystal creek block mount isa inlier nw queensland australia abstract the leichhardt river fault trough of the mount isa inlier comprises fault blocks which exhibit different local deformational histories and structural orientations many structural patterns in the stratigraphically highest cover sequences do not occur in adjacent fault blocks that expose older and mechanically stronger rocks within the mount isa group sediments of the crystal creek block for example tight e trending upright folds appear to be at odds with the surrounding north south regional trends in this paper it is proposed that an inherited extensional fault geometry played a significant role in controlling the structural patterns developed during later shortening through the integration of detailed surface mapping and forward magnetic modelling an inverted half graben was identified beneath the crystal creek block exposing the underlying origin of local structural complexities structural inversion and buttressing against pre existing faults simultaneously removed extensional displacement across pre rift rocks and induced folds and faults in overlying sag phase sediments this led to the development of two structural levels characterized by different deformational styles and apparently distinct deformational histories

counter regional normal faults in shale dominated deltas origin mechanism and evolution abstract the niger and brunei deltas are two of the major prolific petroleum deltas of the world as a result large datasets of 2d and 3d seismic are available however some of the structures remain poorly understood because they are poorly imaged and a shale diapir interpretation has often prevailed these two deltas are in places driven by particular landward structures described as counter regional normal faults crnf these faults initiated on the apex of early folds as the shelf break propagated seaward during a first stage of deformation crnf started as diffuse faults rather than localised single faults later as the sediment load increased in the area affected by the crnf a major landward dipping fault developed controlling the delta front emplacement finally the fault was choked by the sedimentary system and another fault landward or seaward developed the description of the pre existing fold structures controlling the development of crnf allows a reassessment of the structural evolution of shale gravity driven tectonics it is agreed that in many cases the existence of mud diapirs and ridges may be discarded

syntectonic sedimentation in a middle triassic rift northern apennines italy abstract the anatomy of the sedimentary and volcanic fill of a middle triassic continental rift at the western margin of the tethys is illustrated by the study of a 250 m thick sequence on the tyrrhenian coasts of the northern apennines this sequence contains two cycles of sedimentation 1 a the lower cycle comprises a basal transgressive sequence from continental alluvial fans to shallow marine carbonates and an upper sequence which correspond to an increasing tectonic activity submarine syntectonic facies assemblage the lower part of the last assemblage is characterized by a thick 22 m rapidly deposited sequence of coarse carbonate breccias with minor calcareous sandy turbidites this is overlain by channelized red beds of submarine fans composed of close interstratification and juxtaposition of carbonate breccias with red clastic matrix and red sandy quartz pebble conglomerates and silty sands interbedded alkaline pillow lava record penecontemporaneous submarine eruptions the lavas are capped by thin red cherty diaspri crusts the lower cycle of sedimentation ends with a karstic surface on relatively deep marine carbonate layers this suggests a rapid emersion due to the arrest and reversal of the downsinking of the initial aborted or failed rift 2 b the upper cycle of sedimentation starts with more mature fluvial red beds and changes upward into shallow marine sands and carbonates this upper cycle represents an early stage of evolution of a new major rift this second major rift led in jurassic times to the opening of an oceanic area between europe and western italy

sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration highlights naturally enriched aom biomass was studied in high pressure continuous incubation we report the first s and o isotope fractionation values by sulfate reduction coupled to aom from culture studies there is a tight link between methane concentration and s and o isotope fractionation s and o isotope fractionation values indicate reversibility of energy limited microbial processes the wide range of environmental s and o isotope signatures can be explained abstract isotope signatures of sulfur compounds are key tools for studying sulfur cycling in the modern environment and throughout earth s history however for meaningful interpretations the isotope effects of the processes involved must be known sulfate reduction coupled to the anaerobic oxidation of methane aom sr plays a pivotal role in sedimentary sulfur cycling and is the main process responsible for the consumption of methane in marine sediments thereby efficiently limiting the escape of this potent greenhouse gas from the seabed to the overlying water column and atmosphere in contrast to classical dissimilatory sulfate reduction dsr where sulfur and oxygen isotope effects have been measured in culture studies and a wide range of isotope effects has been observed the sulfur and oxygen isotope effects by aom sr are unknown this gap in knowledge severely hampers the interpretation of sulfur cycling in methane bearing sediments especially because unlike dsr which is carried out by a single organism aom sr is presumably catalyzed by consortia of archaea and bacteria that both contribute to the reduction of sulfate to sulfide we studied sulfur and oxygen isotope effects by aom sr at various aqueous methane concentrations from 1 4 0 6 mm1 4 0 6 mm up to 58 8 10 5 mm58 8 10 5 mm in continuous incubation at steady state changes in the concentration of methane induced strong changes in sulfur isotope enrichment view the mathml sourcees34 and oxygen isotope exchange between water and sulfate relative to sulfate reduction o o as well as sulfate reduction rates srr smallest view the mathml sourcees34 21 9 1 9 21 9 1 9 and o o 0 5 0 20 5 0 2 as well as highest srr were observed for the highest methane concentration whereas highest view the mathml sourcees34 67 3 26 1 67 3 26 1 and o o 2 5 1 52 5 1 5 and lowest srr were reached at low methane concentration our results show that view the mathml sourcees34 o o and srr during aom sr are very sensitive to methane concentration and thus also correlate with energy yield in sulfate methane transition zones aom sr is likely to induce very large sulfur isotope fractionation between sulfate and sulfide i e 60 60 and will drive the oxygen isotope composition of sulfate towards the sulfate water oxygen isotope equilibrium value sulfur isotope fractionation by aom sr at gas seeps where methane fluxes are high will be much smaller i e 20 to 40

multiple sulfur isotopic evidence for the origin of elemental sulfur in an iron dominated gas hydrate bearing sedimentary environment abstract elemental sulfur is commonly regarded as the product of oxidative sulfur cycling in the sediment however reports on the occurrence of elemental sulfur in seepage areas are few and thus its origin and mechanisms controlling its distribution are insufficiently understood here we analyzed the multiple sulfur isotopic compositions for elemental sulfur and pyrite from an iron dominated gas hydrate bearing sedimentary environment of the south china sea to unravel the impact of sulfate driven anaerobic oxidation of methane so4 aom on the formation of elemental sulfur the multiple sulfur isotopes reveal variable ranges for both elemental sulfur and pyrite 34s between 15 7 and 23 3 for elemental sulfur and between 35 3 and 34 4 for pyrite 33s between 0 08 and 0 06 for elemental sulfur and between 0 03 and 0 15 for pyrite the enrichment of 34s in pyrite throughout the sediment core suggests pronounced so4 aom in paleo sulfate methane transition zones smtz in addition the occurrence of seep carbonates with very negative 13c values as low as 57 v pdb coincides with the inferred paleo smtzs and agrees with formerly locally pronounced so4 aom interestingly the multiple sulfur isotopic composition of elemental sulfur reveals a different pattern from that of pyrite derived from organoclastic sulfate reduction i e with low 34s and high 33s values for the latter in comparison to coexisting pyrite most of the elemental sulfur reveals higher 34s values as much as 28 9 which is best explained by an enrichment of 34s in the residual pool of dissolved sulfide generated by so4 aom as an intermediate sulfur phase elemental sulfur can form via sulfide oxidation coupled to iron reduction but it can only persist in the absence of free sulfide therefore the occurrence of 34s enriched elemental sulfur is likely to represent an oxidative product after hydrogen sulfide had vanished due to vertical displacement of the smtz our observations suggest that elemental sulfur may serve as a useful recorder for reconstructing the dynamics of sulfur cycling in modern and possibly ancient seepage areas

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

lower plate geometry controlling the development of a thrust top basin the tectonosedimentary evolution of the ofanto basin southern apennines the ofanto basin is a pliocene pleistocene thrust top basin that formed with an unusual east west orientation along the frontal part of the southern apennine allochthon during the latest stages of tectonic transport its tectonic and sedimentary evolution was studied integrating field surveys biostratigraphic analyses and the interpretation of a large seismic grid well data and seismic interpretation indicate that a large east west trending normal fault underlies the northern margin of the basin displacing the apulian carbonates that form the foreland and the footwall of the southern apennine allochthon in our reconstruction the ofanto basin formed at the rear of the bulge caused by buttressing of the southern apennine allochthon against this normal fault in a second stage of contraction the footwall of the southern apennine allochthon was involved in deformation with a different trend from the normal faulting and buttressing this caused eastward tilting of the basin and broad folding around its eastern termination good stratigraphic constraints permit the age of buttressing to be defined as early pliocene and that of the shortening in the apulian carbonates as early pleistocene this study highlights the importance of early orogenic normal faults in conditioning the evolution of the frontal parts of orogenic wedges supplementary material a 3d reconstruction of the base of the pliocene deposits of the ofanto basin based on seismic interpretation is available at www geolsoc org uk sup18559

multiple sulfur isotope constraints on the modern sulfur cycle we present 28 multiple sulfur isotope measurements of seawater sulfate 34sso4 34sso4 and 33sso4 33sso4 from the modern ocean over a range of water depths and sites along the eastern margin of the pacific ocean the average measured 34sso4 34sso4 is 21 24 0 88 2 0 88 2 with a calculated 33sso4 33sso4 of 0 050 0 050 0 014 2 0 014 2 with these values we use a box model to place constraints on the gross fraction of pyrite burial in modern sediments this model presents an improvement on previous estimates of the global pyrite burial flux because it does not rely on the assumed value of 34spyrite 34spyrite which is poorly constrained but instead uses new information about the relationship between 34s 34s and 33s 33s in global marine sulfate our calculations indicate that the pyrite burial flux from the modern ocean is between 10 and 45 of the total sulfur lost from the oceans with a more probable range between 20 and 35

methane discharge into the black sea and the global ocean via fluid flow through submarine mud volcanoes during the margasch cruise m52 1 in 2001 with rv meteor we sampled surface sediments from three stations in the crater of the dvurechenskii mud volcano dmv located in the sorokin trough of the black sea and one reference station situated 15 km to the northeast of the dmv we analysed the pore water for sulphide methane alkalinity sulphate and chloride concentrations and determined the concentrations of particulate organic carbon carbonate and sulphur in surface sediments rates of anaerobic oxidation of methane aom were determined using a radiotracer 14ch4 incubation method numerical transport reaction models were applied to derive the velocity of upward fluid flow through the quiescently dewatering dmv to calculate rates of aom in surface sediments and to determine methane fluxes into the overlying water column according to the model aom consumes 79 of the average methane flux from depth 8 9 10 6 mol a 1 such that the resulting dissolved methane emission from the volcano into the overlying bottom water can be determined as 1 9 10 6 mol a 1 if it is assumed that all submarine mud volcanoes smvs in the black sea are at an activity level like the dmv the resulting seepage represents less than 0 1 of the total methane flux into this anoxic marginal sea the new data from the dmv and previously published studies indicate that an average smv emits about 2 0 10 6 mol a 1 into the ocean via quiescent dewatering the global flux of dissolved methane from smvs into the ocean is estimated to fall into the order of 10 10 mol a 1 additional methane fluxes arise during periods of active mud expulsion and gas bubbling occurring episodically at the dmv and other smvs

pattern of extensional faulting in pelagic carbonates of the umbria marche apennines of central italy the umbria marche apennines provide a new region in which the nature passive margin extensional faulting can be studied in outcrop in these dominantly pelagic carbonate rocks of jurassic and cretaceous age horsts acted as shallow nonvolcani seamounts while tilted half grabens formed deeper basins one well exposed seamount basin transition agrees in general with the model of listric normal faulting and tilted half grabens but shows interesting and significant divergences when studied in detail a small sedimentary wedge at the faulted margin of a horst block seamount thickens unexpectedly toward the adjacent basin this wedge developed because of local convex upward curvature of the shallowest part of a fault which at depth must have concave up listric geometry the local sedimentary wedge resulted from deposition on the hanging wall as it tilted followed by differential compaction of younger limestones that lapped onto the gentle slope leading from the horst block seamount toward the basin the map pattern of listric normal faulting in the umbria marche apennines suggests that both principal strain axes were extensional in contrast to the usual pattern of listric faults crossed by transfer faults

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

are 34s enriched authigenic sulfide minerals a proxy for elevated methane flux and gas hydrates in the geologic record abstract the sulfate methane transition smt zone is a diagenetic transition within anoxic marine sediments created by the metabolic activity of a consortium of sulfate reducing bacteria and methane oxidizing archaea as interstitial dissolved sulfate is consumed by microbially mediated sulfate reduction of sedimentary organic matter som and anaerobic oxidation of methane aom large enrichments of 34 s occur in the interstitial sulfate pool these isotopic enrichments are transmitted to the dissolved sulfide pool hs and subsequently into sulfide minerals so fes fes 2 we investigate the sulfur isotopic composition of pore water sulfate and sulfide minerals at three sites underlain by gas hydrates at the blake ridge the isotopic composition of sulfate sulfur is most positive at the smt showing maximum values of 29 1 49 6 51 6 vcdt at each of the respective sites 34 s values of bulk sulfide minerals tend to be more enriched in 34 s at and below the smt ranging from 12 7 to 23 6 corresponding to enrichments of 26 7 62 4 relative to the mean value of 38 8 in the sulfate reduction zone both enhanced delivery of methane to the smt and non steady state sedimentation appear necessary to create large 34 s enrichments in sulfide minerals similar associations of aom and large 34 s enrichments 0 occur in other gas hydrate terranes cascadia margin but their exact origin is equivocal at present an analysis of 34 s data from freshwater and marine sedimentary environments reveals that 34 s enrichments within sulfide minerals occur under a range of conditions but are statistically associated with aom and systems not limited by dissolved interstitial iron in methane rich sediments methane delivery to the smt increases the role of aom in sulfate depletion that impacts the formation and isotopic composition of authigenic sulfide minerals we hypothesize that under certain diagenetic conditions large 34 s enrichments within sulfide minerals in the geologic record potentially identify 1 the former occurrence of aom 2 present day and fossil locations of the sulfate methane transition zone and 3 a diagenetic terrane today characteristic of deep water methane rich marine sediments conducive to gas hydrate formation thus 34 s enriched sulfide minerals preserved in modern and ancient continental margin sediments may allow for the identification of aom related processes that occur in methane rich sediments

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

normal faults in thrust sheets pre orogenic extension post orogenic extension or both abstract in fold and thrust belts that experienced both pre orogenic and post orogenic extension it may be difficult to establish whether observed normal faults pre dated post dated or were synchronous with thrusting geometrical structural patterns may be insufficient to constrain the relative chronology of extensional and contractional deformations the systematic use of kinematic criteria makes it possible to unequivocally define the timing relationships of reverse and normal fault development and hence to correctly unravel complex structural evolutions kinematic analysis in the southernmost umbria marche apennines of italy where both normal and thrust faults are present revealed a history of repeated tectonic inversion characterised by two distinct stages of extension separated by an episode of folding and thrusting structural overprinting relationships observed at thrust normal fault intersections were useful for i removing sequentially younger deformations and hence ii separating and quantifying the effects of orogenic contraction from those of both pre orogenic and post orogenic extension

multiple sulfur isotopes in methane seep carbonates track unsteady sulfur cycling during anaerobic methane oxidation abstract the anaerobic oxidation of methane coupled with sulfate reduction aom sr is a major microbially mediated methane consuming process in marine sediments including methane seeps the aom sr can lead to the formation of methane derived authigenic carbonates which entrap sulfide minerals pyrite and carbonate associated sulfate cas we studied the sulfur isotope compositions of the pyrite and cas in seafloor methane derived authigenic carbonate crust samples from the north sea and barents sea which reflect the time integrated metabolic activity of the aom sr community as well as the physical conditions under which those carbonates are formed in these samples pyrite exhibits 34 s values ranging from 23 4 to 14 8 and 33 s values between 0 06 and 0 16 whereas cas is characterized by 34 s values ranging from 26 2 to 61 6 and 33 s mostly between 0 05 and 0 07 such cas sulfur isotope compositions are distinctly lower in 34 s 33 s space from published porewater sulfate values from environments where the reduction of sulfate is mostly coupled to sedimentary organic matter oxidation mass balance modelling suggests that 1 aom sr appears to cause rapid carbonate precipitation under high methane flux near or at the sediment water interface and 2 that the precipitation of pyrite and carbonates are not necessarily synchronous the sulfur isotopic composition of pyrite is interpreted to reflect more variable precipitating conditions of evolving sulfide with porewater connectivity fluctuating methane fluxes and oxidative sulfur cycle taken together the multiple isotopic compositions of pyrite and sulfate in methane derived authigenic carbonates indicate protracted precipitation under conditions of non steady state methane seepage activity

triple sulfur isotope relationships during sulfate driven anaerobic oxidation of methane abstract sulfate driven anaerobic oxidation of methane sd aom plays a critical role in regulating the global methane budget determination of the diagnostic triple isotope exponent 33 ln 33 ln 34 for sd aom can help to identify and quantify microbial sulfate reduction via sd aom in the environment the history of earth s surface redox conditions can also be examined through the measurement of triple sulfur isotope compositions in sedimentary rocks due to difficulties in both culturing anaerobic methanotrophs and sampling pore water sulfate in sd aom dominated environments however the 33 values for the processes of sd aom have not been constrained we propose that a set of modern cold seep associated barite samples with low 18 o 34 s values bear a record of residual pore water sulfate during sd aom and therefore the triple sulfur isotope composition of these barites can be used to deduce 33 values we applied a 1 d diagenetic reaction transport model to fit 33 s and 34 s results from modern cold seep barites collected from five sites in the gulf of mexico based on revealed negative correlations r 2 0 77 between 33 s and 34 s values we calculated an upper limit 33 value of 0 5100 to 0 5112 0 0005 given a 1000 ln 34 value of 30 to 10 this 33 value is distinctively lower than that of organoclastic sulfate reduction osr in marine environments where the diagnostic isotope fractionation 1000 ln 34 is typically more negative than that of sd aom in addition cold seep barite data display a negative 33 s 34 s correlation whereas pore water sulfates of all osr dominated settings show a positive one therefore the diagnostic triple sulfur isotope exponent and associated negative 33 s 34 s correlation may allow for the identification of sd aom in sedimentary records

unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds implications for oceanic isotope cycles and the sedimentary record abstract sedimentary s cycling is usually conceptualized and interpreted within the context of steadily accreting 1 d transport reaction regimes unsteady processes however are common in many sedimentary systems and can result in dramatically different s reaction balances and diagenetic products than steady conditions globally important common examples include tropical deltaic topset and inner shelf muds such as those extending from the amazon river 1600 km along the guianas coast of south america these deposits are characterized by episodic reworking of the surface seabed over vertical depths of 0 1 3 m reworked surface sediments act as unsteady suboxic batch reactors unconformably overlying relict anoxic often methanic deposits and have diagenetic properties largely decoupled from net accumulation of sediment despite well oxygenated water and an abundant reactive organic matter supply physical disturbance inhibits macrofauna and benthic communities are dominated by microbial biomass across immense areas in the surficial suboxic layer molecular biological analyses tracer experiments sediment c s fe compositions and 34s 18o of pore water so 4 2 indicate close coupling of anaerobic c s and fe cycles 18o so 4 2 can increase by 2 3 during anaerobic recycling without net change in 34s so 4 2 demonstrating so 4 2 reduction coupled to complete anaerobic reoxidation to so 4 2 and a 18o so 4 2 reduction reoxidation fractionation factor 12 summed magnitudes s reoxidation must be coupled to fe oxide reduction contributing to high dissolved fe2 1 mm and fe mobilization export the reworking of amazon guianas shelf muds alone may isotopically alter 18o so 4 2 equivalent in mass to 25 of the annual riverine delivery of so 4 2 to the global ocean unsteady conditions result in preservation of unusually heavy 34s isotopic compositions of residual cr reducible s ranging from 0 to 30 in physically reworked deposits in contrast bioturbated facies adjacent to physically reworked regions accumulate isotopically light s 34s to 20 in otherwise similar decomposition regimes the isotopic patterns of both physically and biologically reworked regions can be simulated with simple diagenetic models heavy s isotopic signatures are largely a consequence of unsteady diffusion and progressive anaerobic burndown into underlying deposits whereas isotopically depleted bioturbated deposits predominantly reflect biogenic diffusive scaling and isotopic distillation diffusive pumping associated with reoxidation in burrow walls immediately adjacent to reduced zones the s isotopic transition from unsteady physically controlled regions of the amazon delta moving laterally into bioturbated facies mimics the transition of s isotopic patterns temporally in the geologic record during the rise of bioturbation no special role for s disproportionation is required to explain these differences the potential role of unsteady suboxic diagenesis and dynamic reworking of sediments has been largely ignored in models of the evolution of surficial elemental cycling and interpretations of the geologic record

bacterial sulfur disproportionation constrains timing of neoproterozoic oxygenation various geochemical records suggest that atmospheric o 2 increased in the ediacaran 635 541 ma broadly coincident with the emergence and diversification of large animals and increasing marine ecosystem complexity furthermore geochemical proxies indicate that seawater sulfate levels rose at this time too which has been hypothesized to reflect increased sulfide oxidation in marine sediments caused by sediment mixing of the newly evolved macrofauna however the exact timing of oxygenation is not yet understood and there are claims for significant oxygenation prior to the ediacaran furthermore recent evidence suggests that physical mixing of sediments did not become important until the late silurian here we report a multiple sulfur isotope record from a ca 835 630 ma succession from svalbard further supported by data from proterozoic strata in canada australia russia and the united states in order to investigate the timing of oxygenation we present isotopic evidence for onset of globally significant bacterial sulfur disproportionation and reoxidative sulfur cycling following the 635 ma marinoan glaciation widespread sulfide oxidation helps to explain the observed first order increase in seawater sulfate concentration from the earliest ediacaran to the precambrian cambrian boundary by reducing the amount of sulfur buried as pyrite expansion of reoxidative sulfur cycling to a global scale also indicates increasing environmental o 2 levels thus our data suggest that increasing atmospheric o 2 levels may have played a role in the emergence of the ediacaran macrofauna and increasing marine ecosystem complexity

compressional and extensional tectonics in an arc system example of the southern apennines abstract adopting the southern apennines as a case example we determine the relationships between extensional and compressional structures within an arc system based on tectonic analysis in the field we show that in addition to the well known occurrence of inner extensional structures during frontal accretion two other types of extensional structures are present in the southern apennines we classify the three types of extensional structures depending on their chronologies with the accretion of the thrust unit and we characterize them in terms of palaeostresses some normal faults of the mountain chain are old extensional structures formed in a foreland basin in the matese mountains such faults with offsets ranging several hundred metres are sealed by a late neogene thrust sheet these foredeep structures were created by extension trending almost perpendicular to the axis of the present day foreland basin other normal faults located closer to the tyrrhenian sea developed simultaneously with the pliocene quaternary accretion of thrust sheets at the front of the belt in the salerne graben a tyrrhenian basin structure extension occurred perpendicular to the compression that prevailed at the front of the mountain belt a stress gradient existed between the outer part of the arc with 1 trending ene wsw and the inner part with 2 trending ene wsw in the southern apennines middle pleistocene holocene normal faults post date all compression and thrusting the corresponding recent stress field ne sw extension results from uplift of the previously subsiding adriatic lithosphere we conclude that a given thrust unit of this nw se trending mountain chain may have successively undergone ne sw extension in the foreland basin ne sw compression during the accretion nw se extension in the back arc region and ne sw extension during the recent evolution of the prism the succession of these tectonic regimes has induced complex structures as commonly observed in an arc system

oil distribution in outcropping carbonate ramp reservoirs maiella mountain central italy three dimensional models constrained by dense historical well data and laboratory measurements heavy oil and bitumens have been exploited in italy during the past in particular over the maiella mountain s northwest flank central italy where relatively undeformed hydrocarbon bearing carbonate ramp reservoirs of the bolognano formation crop out these reservoirs represent the exhumed analog of a wider petroleum system that has been investigated also in the subsurface by exploration activities both onshore and offshore central adriatic here we present for the first time a historical data set composed of 180 shallow wells drilled over the area in 1942 by a company named azienda lavorazione bitumi asfalti we digitally reconstructed this data set integrating it with field observations laboratory measurements and thin section analysis using petrel mark of schlumberger three dimensional software we modeled the reservoir and the hydrocarbon distribution also calculating volumes of hydrocarbons in place in our work we demonstrate the presence of these quite homogeneous porous carbonate reservoirs over the whole region and we identify internal reservoir geometries characterized by clinoforms likely resulting from a large scale depositional cross bedding and progradation we also infer a different function of faults in the hydrocarbon accumulations major faults were able to create independent compartments during migration whereas minor more recent elements did not control hydrocarbon accumulation likely postdating a main lower pliocene migration phase we believe that the observations derived from our work can represent a good analog for carbonate ramp reservoirs elsewhere may help in identifying appropriate modeling solutions and can be used as calibration for future renewed exploration efforts in the region both onshore and offshore

multiple episodes of fluid flow in the sw barents sea loppa high evidenced by gas flares pockmarks and gas hydrate accumulation abstract gas and gas hydrates have gained considerable attention in the last 20 yr due to their possible impact on global climate change from methane escalations our study area the sw barents sea is unique in its evolution due to the effect of glaciations which removed thick layers of sediment from the seabed unloading due to erosion and deglaciation resulted in opening of pre existing faults and creation of new ones facilitating fluid migration and eventually escape into the water from the subsurface expressions of hydrocarbon gas accumulation and fluid flow such as gas hydrates and pockmarks are widely distributed in the barents sea several gas flares some of them 200 m high in echograms occur along a segment of the ringvassoy loppa fault complex indicating open fractures and active fluid flow observation of gas flares along regional fault complexes outside pockmark regions indicates that present gas escape occurs along faults only the pockmark formation and gas flares belong to different episodes of fluid flow the pockmarks are absent outside soft sediment depocentres indicating that their existence is related to the presence of recording medium the thin sediment cover in pockmarks and their penetration down into glaciomarine sediments indicate that they formed after deposition of these sediments and that fluid escape was active to the very recent past methane hydrate stability zone mhsz modelling shows that after the last glacial maximum 18 000 20 000 14c years ago the mhsz has thinned from 600 m to zero in most parts of the sw barents sea the fluid expulsion probably happened after retreat of the glaciers causing release of methane from dissociation of methane hydrates through fluid escape processes which lasted until recently bottom simulating reflectors bsr observed are probably due to structure ii hydrates formed from gas containing higher order hydrocarbon components such as ethane propane etc along with methane the study area falls close to the new gigantic oil discoveries skrugard and havis and north of the snohvit hydrocarbon field

seismotectonic zoning in east central italy deduced from an analysis of the neogene to present deformations and related stress fields this paper concerns the space time evolution of the late miocene to present contractional and extensional deformations within east central italy with an analysis of the pattern and orientation of the related stress field an insight into the cover basement relations and a discussion of the seismotectonic implications the pattern and orientation of the deformation and stress fields have remained unchanged since late miocene time and have been always characterized by the coexistence and parallelism in contiguous areas in a given time of shortening to the east and elongation to the west with time during a multistage deformation history both the contraction and the extension fields have moved eastward basement involved tectonics with a west dipping multiple detachment system would have allowed the progressive eastward shift of crustal slices corresponding at the surface to well defined tectonic domains with consequent crustal thinning in the tuscan zone and crustal thickening beneath the apennine mountain chain by comparing macroseismic epicenters hypocenters and focal mechanisms with crustal structure and independently known active faults it appears evident that the pattern frequency and distribution of the crustal seismicity are tectonically controlled and that a contraction extension pair is active also at the present time in fact along the adriatic coastline contractional deformation prevails with involvement of pleistocene layers whereas beneath the apennine range extensional deformation prevails both t axes in the inner domain and p axes in the outer domain are oriented southwest northeast or west south west east northeast and this coaxiality reflects the situation depicted by the geologic stress field on this basis we have produced a seismotectonic zoning of east central italy with three distinct domains intramountain seismic zone isz foothills seismic zone fsz and coastal seismic zone csz a plausible explanation for the genesis of the active seismic deformations of east central italy is that the locally intense extensional upper crustal seismicity of the intramountain seismic zone is confined to the hanging wall of a major west dipping active extensional discontinuity whereas the less frequent contractional seismic activity of the coastal seismic zone is within the hanging wall of an outer major active west dipping contractional discontinuity an area of overlap between these two zones is represented by the foothills seismic zone where superposed epicentral patterns from different surfaces of weakness at different depths are the predictable result of the asymmetry of the deformation

late oligocene to pliocene extension in the maltese islands and implications for geodynamics of the pantelleria rift and pelagian platform

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

how sulfate driven anaerobic oxidation of methane affects the sulfur isotopic composition of pyrite a sims study from the south china sea abstract sulfate driven anaerobic oxidation of methane so4 aom in marine sediments commonly leads to the precipitation of pyrite it is however frequently challenging to unequivocally unravel the entire history of pyritization because of the common coexistence of so4 aom derived pyrite with pyrite resulting from organiclastic sulfate reduction osr to better understand how so4 aom affects pyritization in methane bearing sediments and how this can be identified we applied secondary ion mass spectroscopy sims to analyze the sulfur isotope composition 34s of authigenic pyrite in addition to sulfur isotope measurements of bulk sulfide and hand picked pyrite aggregates from the two seafloor sites hs148 and hs217 in the shenhu seepage area south china sea authigenic mostly tubular pyrite aggregates from these sites consist of three types of pyrite framboids zoned aggregates with radial overgrowths surrounding a framboidal core and euhedral pyrite crystals framboids with low sims 34s values as low as 41 6 at hs148 and 38 8 at hs217 are dispersed throughout the cores but are especially abundant in the shallow part of the sedimentary column i e above 483 cmbsf in hs148 above 670 cmbsf in hs217 these patterns are interpreted to reflect the dominance of osr during early diagenetic processes in the shallow sediments with increasing depth both 34s values of bulk sulfide minerals and hand picked pyrite aggregates increase sharply at 483 cmbsf in core hs148 and at 700 cmbsf in core hs217 respectively radial pyrite overgrowths and euhedral crystals become abundant at depth typified by high 34s values for hand picked pyrite moreover sims analysis reveals an extreme variability of 34s values for the three pyrite types on a small scale in these zones besides some moderately 34s enriched framboids most of the overgrowths and euhedral crystals display extremely high sims 34s values as high as 114 8 at hs148 and 74 3 at hs217 representing the heaviest stable sulfur isotope composition of pyrite ever reported to the best of our knowledge such an abrupt and extreme increase in 34spyrite values with depth is best explained by an enrichment of 34s in the pool of dissolved sulfide caused by so4 aom in the sulfate methane transition zone smtz the increase in 34s values from framboidal cores to overgrowth layers and euhedral crystals indicates continuous and finally near to complete exhaustion of dissolved sulfate at the smtz following a rayleigh distillation process so4 aom allowed for subsequent growth of later stage pyrite over the initial framboids part of which formed earlier and at shallower depth by osr the combination of a detailed petrographic study of authigenic pyrite with sims analysis of stable sulfur isotopes in organic rich strata proves to be a powerful tool for reconstructing the dynamics of sulfur cycling in modern and potentially ancient sedimentary sequences

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

fault segmentation as constraint to the occurrence of the main shocks of the 2016 central italy seismic sequence we perform the finite extent fault inversion of the three main events of the 2016 central italy seismic sequence using near source strong motion records we demonstrate that both earthquakes nucleation and rupture propagation were controlled by segmentation of the n nw s se trending quaternary normal faults the first shock of the sequence august 24th mw 6 0 ruptured at the relay zone between the laga mts lf and the cordone del vettore cvf normal faults the second shock october 26th mw 5 9 nucleated at a minor relay zone within the mt vettore mt bove fault vbf while the third and largest one october 30th mw 6 5 initiated at the relay zone between the vbf and cvf triggering the multiple rupture of the vbf cvf and probably lf we show that this latter relay zone corresponds to the deeper high angle fault zone of the sibillini mts cross structure a thrust ramp inherited from the miocene pliocene contractional phase of the apennines this structure acted as a barrier to rupture propagation of the first two events thus defining an area of large stress concentration until it acted as the initiator of the rupture originating the largest mw 6 5 event that crossed the barrier itself we suggest that the young cvf have started to cut through the barrier acting as a soft linkage between the two long lived lf and vbf the evidence that coseismic cumulative slip shows a maximum at the cvf provided by both slip inversion and original surface rupture data suggests that the cvf is growing faster than the adjacent faults

numerical modeling of carbonate crust formation at cold vent sites significance for fluid and methane budgets and chemosynthetic biological communities at many cold vent sites authigenic carbonates precipitate due to the release of carbonate alkalinity during the anaerobic oxidation of methane carbonate precipitation often induces the formation of massive crusts at the sediment surface or within surface sediments the range of physical and biogeochemical conditions allowing for the formation of carbonate crusts is largely unknown so that the significance of these widespread manifestations of fluid flow is unclear here we use numerical modeling to investigate the conditions that induce carbonate crust formation in the sediment and the effect of crust formation on sediment porosity and fluid flow rate starting with the conditions prevailing at a previously investigated reference site located on hydrate ridge off oregon several parameters are systematically varied in a number of numerical experiments these parameters include coefficients of bioturbation and bioirrigation sedimentation rate fluid flow velocity methane concentration in the ascending vent fluids and ph and saturation state at the sediment water interface the simulations show that carbonate crusts in the sediments only form if the fluids contain sufficient dissolved methane 50 mm and if bioturbation coefficients are low 50 cm ka 1 inhibit crust formation bioirrigation induces a downward displacement of the precipitation zone and accelerates the formation of a solid crust crusts only form over a rather narrow range of upward fluid flow velocities 20 60 cm a 1 which is somewhat enlarged up to 90 cm a 1 if the overlying bottom waters are supersaturated with respect to calcite at higher flow rates methane is rapidly exported into the water column so that methane oxidation and carbonate precipitation cannot proceed within the surface sediment the formation of a several centimeters thick carbonate crust in surface sediments is typically completed after a few hundred years 100 500 a crust formation reduces the supply of methane to surface sediments which imposes a strong resistance against diffusive and advective methane transport therefore rates of anaerobic methane oxidation and sulfide production are diminished and thus the density and metabolism of chemosynthetic biological communities is limited by crust formation due to the moderate flow rates and the slow diffusive transport only very little methane escapes into the bottom water overlying carbonate encrusted vent areas

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

characterization of microbial activity in pockmark fields of the sw barents sea abstract multibeam bathymetry revealed the occurrence of numerous craterlike depressions so called pockmarks on the sea floor of the hammerfest basin and the loppa high south western barents sea to investigate whether these pockmarks are related to ongoing gas seepage microbial processes associated with methane metabolism were analyzed using geochemical biogeochemical and microbiological techniques gravity cores were collected along transects crossing individual pockmarks allowing a direct comparison between different locations inside assumed activity center on the rim and outside of a pockmark reference sites concentrations of hydrocarbons in the sediment particularly methane were measured as headspace free gas and in the occluded and adsorbed gas fraction down to a depth of 2 6 m below sea floor mbsf sulfate reduction rates were quantified by radiotracer incubations concentrations of dissolved sulfate in the porewater were determined as well neither the sulfate profiles nor the gas measurements show any evidence of microbial activity or active fluid venting methane concentrations and sulfate reduction rates were extremely low or even below the detection limit the results show that the observed sediment structures are most likely paleo pockmarks their formation probably occurred during the last deglaciation

environmental evolution of the east china sea inner shelf and its constraints on pyrite sulfur contents and isotopes since the last deglaciation abstract to better understand the depositional constraints on the sulfate reduction process we present a set of sulfur isotope data for hand picked pyrites 34spyr from the coarse fraction 63 250 m of bulk sediments coupled with the contents of carbonate total organic carbon toc and nitrogen tn as well as 13c values of the toc from sediments of core ec2005 on the inner shelf of the east china sea ecs since 16 4 ka our results show that core sediments were deposited in a terrestrial environment before 13 1 ka stage i when pyrite rarely occurred during stages ii 13 1 12 3 ka and iii 12 3 12 1 ka seawater began to influence the core location forming a tidal flat environment where abundant pyrites are well preserved then the inner shelf of the ecs was fully flooded and two intervals with high stage iv 12 1 6 0 ka stage vi 5 2 1 5 ka and low sedimentation rate stage v 6 0 5 2 stage vii 1 5 ka present are identified respectively when compared with previous 34s values of chromium reducible sulfur 34scrs derived from the bulk sediments 34spyr values are usually higher indicating the macroscopic pyrites form in the later stages of sedimentary diagenesis when ongoing sulfate reduction has distilled porewater sulfate to a high degree considering the wide occurrence of biogenic shallow gas dominated by ch4 in these sediments sulfate driven anaerobic oxidation of methane so4 aom and organoclastic sulfate reduction osr are expected to be two competitive pathways for sulfate reduction we propose that the changes in sedimentation rate controls the pace of migration of the sulfate methane transition zone smtz when sedimentation rate is low the smtz may be fixed in a certain depth e g sediments deposited in stage iii and v where h2s is produced by so4 aom in contrast when sedimentation rate is very high 1 cm yr the smtz would be deep and h2s is mostly produced by osr further our results imply that sulfur diagenesis in recent since 1 5 ka ecs mud sediments might be influenced by physical reworking e g typhoon and or biological activity bioturbation resulting in partial reoxidation of pyrite crystals in fluid mud our findings therefore demonstrate that pyrite sulfur isotope compositions bulk 34scrs hand picked 34spyr are sensitive to local environmental evolution and the combined use of these two indicators can provide new insights into pathway of sulfate reduction in unsteady environments

deep below north america plate tectonics is the dominant process behind the creation and decomposition of the crust and the uppermost part of earth s mantle the lithosphere did plate tectonic processes also operate on the early earth in her perspective van der lee 1 reviews the evidence from laurentia the predecessor of the north american continent 1 http www sciencemag org cgi content full 294 5545 1297

the role of pre existing thrust faults and topography on the styles of extension in the gran sasso range central italy abstract structural analysis and field mapping together with simple geometrical and flexural elastic models document that two styles of quaternary extensional tectonics characterized the gran sasso range central apennines italy in the western part of the range extension took place on 10 15 km long range front normal faults with associated 600 1000 m high escarpments showing evidence of late glacial holocene activity this topography has been reproduced with a thin elastic plate subjected to the isostatic forces induced by the movement along high angle 55 65 planar normal faults in the eastern part of the belt extension occurred on shallow dipping normal faults 30 35 which reactivated progressively deeper pre existing thrusts in this area antithetic domino faults formed to accommodate the mechanical adjustment of the hanging wall over a variably dipping major fault surface the eastward increase in shortening due to the earlier compressional phase documented in the gran sasso belt by previous authors accounts for the more developed zones of weakness and high topographic relief in the eastern sector this setting could explain the different styles of extension and the more advanced northeastern limit of normal faulting in the eastern sector this work suggests that normal faults can originate either with low or high angle geometry in the upper crust according to the pre existing tectonic setting and that topography could be important in controlling the geometry and pattern of migrating normal faulting

bubble induced porewater mixing a 3 d model for deep porewater irrigation porewater data from vent sites of the northeastern shelf off sakhalin island sea of okhotsk exhibit bottom water concentrations down to a sediment depth of up to 300 cm below this depth solute concentrations rapidly change due to methanogenesis and anaerobic methane oxidation amo the profile shapes suggest an irrigation like process that mixes on a meter scale at these sites active gas emanation into the overlying water column and near surface gas hydrates are commonly observed we propose that methane gas bubbles rise through the soft surface sediments and cause mixing of the porewater mathematically the bubble induced irrigation can be described by eddy diffusion enhancing the diffusive transport of solutes by several orders of magnitude a 3 d numerical transport reaction model was developed to investigate the parameters defining the mixing process such as bubble rise velocity tube size tube distribution in the sediment and ebullition frequency model consistency with the field data requires eddy diffusivities 1 105 cm2 a tube densities of 4 tubes m2 equivalent to a tube spacing of 40 cm active gas seepage for more than a few weeks or months and moderate to low diagenetic reaction rates of solutes the corresponding methane gas fluxes that are predicted from the results of the model realizations range from 1 103 5 105 l m2 a due to bubble mixing solute fluxes in these sediments are increased by a factor of 3 and the maximum amo rate by a factor of 7

from extension to contraction in syn orogenic foredeep basins the contessa section umbria marche apennines italy syn orogenic deposits that occupy foredeep basins commonly experience contraction related to the migration of fold and thrust systems toward the foreland this contraction may overprint the earlier extensional deformation that is related to the initiation of the basin although predicted by models for foredeep development evidence for extension predating contraction at different scales is not extensively recorded in syn orogenic deposits mesoscopic structures from the contessa section in the umbria marche apennines italy reveal a complex history characterized by extension soon before the contractional deformation normal faults predate the folds and thrusts that are related to the miocene age orogenic event responsible for the development of the apennines extensional deformation may have resulted from flexuring of a lithospheric plate induced by the load of a stacking thrust pile the transition from extension to contraction could play an important role in the evolution of belt foredeep foreland systems as it could reflect the migration of advancing thrust fronts toward the foreland

late paleogene extensional collapse of the cordilleran foreland fold and thrust belt the cordilleran foreland fold and thrust belt collapsed and spread to the west during a middle eocene to early miocene ca 49 20 ma episode of crustal extension the sedimentary and structural record of this event is preserved in a network of half grabens that extends from southern canada to central utah extensional structures superposed on this allochthonous terrain are rooted to the physical stratigraphy structural relief and sole faults of preexisting thrust fold structures the sole faults dip 3 6 west above an undeformed precambrian crystalline basement and accommodated tectonic transport of a thick up to 20 km eastward tapering hanging wall during regimes of crustal shortening and extension the chronology of tectonism for the foreland fold and thrust belt is established here by dating latest thrusting and initial normal faulting and is best defined where thrusts and normal faults are linked by common detachment surfaces dated movement on two extensionally reactivated thrusts the lewis thrust of northwest montana and southeast british columbia and the medicine butte thrust of southwest wyoming and northeast utah suggests that the hiatus between the end of crustal shortening in the early or early middle eocene and the start of extension in the early middle eocene was brief lateral spreading and extensional basin formation in the cordilleran foreland fold and thrust belt were partly concurrent with formation of metamorphic core complexes and regional magmatism conceptually linking extensional processes that were simultaneously deforming both the hinterland and foreland of the late paleogene cordilleran orogenic wedge is accomplished by applying the extensional wedge coulomb critical taper model the rapid drop in north america pacific plate convergence rate and or steepening of the subducted oceanic slab at ca 50 ma resulted in a large reduction in east west horizontal compressive stress in the cordillera as a result the cordilleran orogenic wedge was left unsupported and it gravitationally collapsed and horizontally spread west until a new equilibrium was established at ca 20 ma subsequently crustal extension and magmatism during the basin and range event ca 17 0 ma overprinted much of this earlier phase of extension

foreland dipping normal faults in the inner edges of syn orogenic basins a case from the central apennines italy abstract extensional deformations are common within foredeep basins and generally consist of hinterland dipping normal faults located at the foredeep foreland transition zones foreland dipping normal faults at the belt foredeep boundaries by contrast are far less documented and their occurrence is not predicted by simple orogenic load models new surface data integrated with seismic reflection profiles across the central apennines of italy reveal the occurrence of foreland dipping normal faults located in the inner edges of foredeep depressions extensional deformations are systematically found within sequentially younger tortonian messinian and early pliocene foredeep basins thus suggesting that normal fault development was an intrinsic feature of the evolving belt foredeep foreland system and could have influenced the stratal architectures of the host syn orogenic deposits foreland extension is consistent with existing geodynamic models for the apennines and could represent the effects of lithospheric bending its recognition and documentation elsewhere could provide significant insights to improve our understanding of syn orogenic basin dynamics

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